JP2004047449A - Manufacturing method for surface modified lithium nickel composite oxide, positive electrode active material using surface modified lithium nickel composite oxide, positive electrode material, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress increase in impedance caused by high temperature storage or the like of a lithium secondary battery. <P>SOLUTION: Surface modified lithium nickel composite oxide is manufactured by placing an element having an atomic weight of 28 or more of group 4A-6A elements of the periodic table on the surface of a lithium nickel composite oxide, and then baking them. By using the surface modified lithium nickel composite oxide as the positive electrode active material of the lithium secondary battery, the high temperature stability of the lithium secondary battery is tremendously enhanced. <P>COPYRIGHT: (C)2004,JPO

Description

【０１０５】
［正極剤２の製造］
正極剤１の製造において、リチウムニッケル複合酸化物として、一次粒径が１μｍであるＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２及びＬｉＮｉ_０．７Ｃｏ_０．２Ｍｎ_０．１Ｏ_２をそれぞれ用いたこと、及びＳｂ_２Ｏ_３の仕込量をリチウムニッケル複合酸化物に対して１ｍｏｌ％とした以外は、正極剤１と同様にして正極剤２を製造した。
【０１０６】
このようにして得られた正極剤２のうち、リチウムニッケル複合酸化物としてＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２を用いたものを正極剤２ａとし、ＬｉＮｉ_０．７Ｃｏ_０．２Ｍｎ_０．１Ｏ_２を用いたものを正極剤２ｂとした。
［正極剤３の製造］
正極剤１の製造において、Ｓｂ化合物としてトリフェニルアンチモンを用いたこと、及びトリフェニルアンチモンの仕込量をリチウムニッケル複合酸化物に対して０．５ｍｏｌ％とした以外は、正極剤１と同様にして正極剤３を製造した。［正極剤４の製造］
正極剤１の製造において、一次粒子平均粒径が０．０２μｍのＳｂ_２Ｏ_３（日本精鉱（株）製ＰＡＴＯＸ−Ｕ）、一次粒子平均粒径が０．５μｍのＳｂ_２Ｏ_３（日本精鉱（株）製ＰＡＴＯＸ−Ｍ）、一次粒子平均粒径が１μｍのＳｂ_２Ｏ_３（日本精鉱（株）製ＰＡＴＯＸ−Ｃ）、一次粒子平均粒径が３μｍのＳｂ_２Ｏ_３（日本精鉱（株）製ＰＡＴＯＸ−Ｐ）、一次粒子平均粒径が８μｍのＳｂ_２Ｏ_３（日本精鉱（株）製ＰＡＴＯＸ−Ｌ）をそれぞれ必要に応じて粉砕して、一次粒径がそれぞれ０．００４μｍ、０．００８μｍ、０．０２μｍ、０．５μｍ、１．６μｍ、３．２μｍ、５μｍ、８μｍであるＳｂ_２Ｏ_３をＳｂ化合物としたこと、及びＳｂ_２Ｏ_３の仕込量をリチウムニッケル複合酸化物に対して１ｍｏｌ％とした以外は、正極剤１と同様にして正極剤４を製造した。
【０１０７】
このようにして得た正極剤４のうち、一次粒径の異なるＳｂ_２Ｏ_３を用いた正極剤を表−２のように呼ぶ。
【０１０８】
【表２】

【０１０９】
［正極剤５の製造］
正極剤１の製造において、Ｓｂ化合物をトリフェニルアンチモンとしたこと、トリフェニルアンチモンの仕込量をリチウムニッケル複合酸化物に対して０．５ｍｏｌとしたこと、及び粉末状のリチウムニッケル複合酸化物を入れた焼成皿と粉末状のトリフェニルアンチモンを入れた焼成皿とをそれぞれ同じ炉内に置き、酸素気流中で加熱してトリフェニルアンチモンを気化させてリチウムニッケル複合酸化物と反応させたこと以外は、正極剤１の製造と同様にして正極５を製造した。
［正極剤６の製造］
正極剤１の製造において、Ｓｂ_２Ｏ_３の仕込量をリチウムニッケル複合酸化物に対して１．０ｍｏｌ％としたこと、及び焼成を６００℃と７００℃でそれぞれ行ったこと以外は、正極剤１の製造と同様にして正極剤６を製造した。
【０１１０】
このようにして得た正極剤６のうち、焼成温度を６００℃としたものを正極剤６ａ、焼成温度を７００℃としたものを正極剤６ｂとした。
［正極剤１’、正極剤２ａ’、正極剤２ｂ’］
正極剤１の製造で用いた、一次粒径が０．６〜０．８μｍであるリチウムニッケル複合酸化物：ＬｉＮｉ_０．８２Ｃｏ_０．１５Ａｌ_０．０３Ｏ_２を正極剤１’とする。
【０１１１】
正極剤２の製造で用いた、一次粒径が０．５〜１μｍであるＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２及びＬｉＮｉ_０．７Ｃｏ_０．２Ｍｎ_０．１Ｏ_２をそれぞれ正極剤２ａ’、正極剤２ｂ’とする。
つまり、正極剤１’、２ａ’、及び２ｂ’は、Ｓｂ化合物で処理していない未処理のリチウムニッケル複合酸化物となっている。
（２）正極の製造
［正極１の製造］
上記のようにして得られた正極剤１〜６及び正極剤１’、２ａ’、２ｂ’を用いて、正極１を製造した。その方法を以下に示す。
【０１１２】
まず、以下の組成をプラネタリーミキサータイプの混練機により２時間混練し正極塗料を製造した。
【０１１３】
【表３】
Ｓｂ表面修飾リチウムニッケル複合酸化物又は未処理のリチウムニッケル複
合酸化物　　　　　　　　　　　　　　　　　　　　　　　　　　　８５重量部
アセチレンブラック　　　　　　　　　　　　　　　　　　　　１０重量部
ポリフッ化ビリニデン　　　　　　　　　　　　　　　　　　５重量部
Ｎ−メチル−２−ピロリドン　　　　　　　　　　　　８０重量部
次に上記の正極塗料を１５μｍ厚のアルミニウム集電体基材上に、エクストルージョン型のダイコーティングによって塗布、乾燥し、活物質がバインダーによって集電体上に結着された正極材料層を製造した。ついで、ロールプレス（カレンダー）をもちいて圧密することによって電極シートを製造した。この後、電極シートから電極を切り出し、正極１とした。
［正極２の製造］
上記のようにして得られた正極剤１〜６及び正極剤１’、２ａ’、２ｂ’を用いて、正極２を製造した。その方法を以下に示す。
【０１１４】
まず、以下の組成をプラネタリーミキサータイプの混練機により２時間混練し正極塗料を製造した。
【０１１５】
【表４】
Ｓｂ表面修飾リチウムニッケル複合酸化物又は未処理のリチウムニッケル複
合酸化物　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　４５重量部
リチウムコバルト複合酸化物（ＬｉＣｏＯ_２）　　　　４５重量部
アセチレンブラック　　　　　　　　　　　　　　　　　　　　　　　　　　　５重量部
ポリフッ化ビニリデン　　　　　　　　　　　　　　　　　　　　　　　　　５重量部
Ｎ−メチル−２−ピロリドン　　　　　　　　　　　　　　　　　　　８０重量部
次に上記の正極塗料１を１５μｍ厚のアルミニウム集電体基材上に、エクストルージョン型のダイコーティングによって塗布、乾燥し、活物質がバインダーによって集電体上に結着された正極材料層を製造した。ついで、ロールプレス（カレンダー）をもちいて圧密することによって電極シートを製造した。この後、電極シートから電極を切り出し、正極２とした。
（３）負極の製造
［負極の製造］
最初に以下の組成を、プラネタリーミキサータイプの混練機により２時間混練し負極塗料とした。
【０１１６】
【表５】
グラファイト（粒径１５μｍ）　　　　　　　　　　　　　　　　　９０部
ポリフッ化ビニリデン　　　　　　　　　　　　　　　　　　　　　　　　　１０部
Ｎ−メチル−２−ピロリドン　　　　　　　　　　　　　　　　　１００部
次に上記の負極塗料を２０μｍ厚の銅集電体基材上にエクストルージョン型のダイコーティングによって塗布、乾燥し、活物質がバインダーによって集電体上に結着された負極材料層を製造した。ついで、ロールプレス（カレンダー）を用い圧密することによって電極シートを作製した。この後、電極シートから電極を切り出し、負極とした。
［正極・負極材料層の比］
上記の正極１、正極２、及び負極の製造においては、（正極の充電容量）／（負極の充電容量）＝０．９３となるように、正極材料層及び負極材料層の膜厚を調整した。ここで、負極の充電容量は、対極Ｌｉを用い１．５Ｖ〜３ｍＶまで充電したときの負極単位体積あたりの容量（ｍＡｈ／ｇ）を基準とした。
（４）電解質の製造
［電解質層形成用の塗料１の製造］
電解質にポリマーを含有するリチウム二次電池を作製する場合には、下記組成を混合・攪拌して、電解質層形成用の塗料１を製造した。
【０１１７】
【表６】
１Ｍ濃度のＬｉＰＦ_６をリチウム塩として含有するエチレンカーボネート及
びプロピレンカーボネートの混合液（体積比率；エチレンカーボネート：プ
ロピレンカーボネート＝１：１）　　　　　　　　　　　　　　　　　９２５部
テトラエチレングルコールジアクリレート　　　　　　　　　　　　　　４４部
ポリエチレンオキシドトリアクリレート　　　　　　　　　　　　　　　　２２部
重合開始剤　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　２部
添加剤（無水コハク酸）　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　９部
［電解液１の製造］
１Ｍ濃度のＬｉＰＦ_６をリチウム塩として溶解したエチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、及びエチルメチルカーボネート（ＥＭＣ）の混合液（体積比ＥＣ：ＤＭＣ：ＥＭＣ＝３０：３５：３５）を電解液１とした。
［電解液２の製造］
１Ｍ濃度のＬｉＰＦ_６をリチウム塩として溶解したエチレンカーボネート（ＥＣ）及びジエチルカーボネート（ＤＥＣ）の混合液（体積比ＥＣ：ＤＥＣ＝５０：５０）を電解液２とした。
（５）リチウム二次電池の製造
［液系リチウム二次電池１、２の製造］
上記のようにして準備した正極１と負極とを高分子多孔質フィルム製セパレーターを介して積層し、さらに正極及び負極それぞれの電極端子部に電流を取り出すリード線を接続して、電池積層体を製造した。
【０１１８】
こうして得られた電池積層体を、アルミニウム膜の両面を樹脂層で被覆したラミネートフィルムを対向成形した袋状ケースに収容後、電解液１又は２を注入し、電解液を正極、負極、及びセパレーターに含浸させた。
２枚のポリエチレン製テープで電極端子部を挟み（端子部の短絡防止のため）、減圧シールで封口後、リード線を取り出した辺をを除くシール部を電池外装材側面に沿うように折曲した。折曲されたシール部は外装材被包部側面に市販のエポキシ系接着剤で接着した。このうにして、製造した平板状の液系リチウム二次電池のうち、電解液１を用いたリチウム二次電池を液系リチウム二次電池１、電解液２を用いたリチウム二次電池を液系リチウム二次電池２とした。
［ポリマー系リチウム二次電池１の製造］
上記のようにして準備した正極２、負極に、上記のようにして準備した電解質層形成用の塗料１を塗布し、別途電解質層形成用の塗料１に浸した高分子多孔質フィルム（スペーサー）を用意し、このフィルムを正極２と負極との間に挟んだ後、９０℃で１０分加熱することにより、電解質層形成用の塗料中のテトラエチレングルコールジアクリレート及びポリエチレンオキシドトリアクリレートを重合させた。これによって、活物質とバインダーを含み集電体上に形成された正極、負極を有し、該正極と負極との間に非流動化された電解質層を有する平板状の単位電池要素を作製した。このようにして得たポリマーを含有する電解質をポリマー電解質１という
次に、この単位電池要素の正極及び負極それぞれの電極端子部に電流を取り出すリード線を接続した後、これをアルミニウム膜の両面を樹脂層で被覆したラミネートフィルムを対向成形した袋状ケースに収容した。その後、２枚のポリエチレン製テープで電極端子部を挟み（端子部の短絡防止のため）、ラミネートフィルムを真空シールで封入後、リード線を取り出した辺を除くシール部を電池外装材側面に沿うように折曲した。折曲されたシール部は外装材被包部側面に市販のエポキシ系接着剤で接着して平板状のポリマー系リチウム二次電池１を製造した。
（６）ＸＰＳ分析
Ｓｂで表面を修飾した、Ｓｂ表面修飾リチウムニッケル複合酸化物である正極剤１ｃ及び１ｅについては、その表面のＳｂ濃度を測定するために、それぞれの正極剤のＸＰＳ分析を行った。測定方法を以下に示す。
【０１１９】
金属板に両面テープを貼付け、その上に粉末状態の正極剤１ｃ又は１ｅをテープが見えない厚みにふりかけ、表面が平滑になるよう圧着したものをホルダーに固定し、測定に供した。
ＸＰＳ測定装置として、Ｐｈｙｓｉｃａｌ　Ｅｌｅｃｔｒｏｎｉｃｓ社製のＥＳＣＡ−５５００ＭＣを用いた。そして、測定のための光源には単色化Ａｌ−Ｋα線（１４ｋＶ、１５０Ｗ）を用いて、Ｎｉ２ｐ，Ｃｏ２ｐ，Ａｌ２ｓ，Ｓｂ３ｄ３／２の各元素について下記条件にて測定を行った。尚、測定の際、帯電補正のために電子中和銃を用いた。
【０１２０】
ＰａｓｓＥｎｅｒｇｙ：２９．３５ｅＶ
データ取込間隔：０．１２５ｅＶ／ｓｔｅｐ
測定面積：０．８ｍｍ径
取出角：４５度
得られた各測定元素の測定ピークにつき、それぞれ始点と終点とを決めて、シャーリー法で始点と終点とを結んだ。そして、始点と終点とを結んだ線とピークとに囲まれる面積を、各測定元素ごとに求め、これを各測定元素のピーク面積とした。Ｓｂ３ｄ３／２の測定例を図１に示す。図１において、始点１は、Ｓｂ３ｄ３／２ピークにおける結合エネルギーの低エネルギー側の裾が完全に平坦になった部分に取り、終点２は、高エネルギー側のピークの裾が完全に平坦になった部分に取った。このようにして決めた始点と終点とをシャーリー法を用いてベースライン３で結んで、ベースラインとピークとに囲まれる面積を、Ｓｂ３ｄ３／２のピーク面積とした。このようにして求めた、正極剤１ｃ及び１ｅの各測定元素のピーク面積を表−３に示す。
【０１２１】
次に、測定元素各々に決められた相対感度補正係数を用い、前記各々の測定元素のピーク面積をそれそれの元素の相対感度補正係で除して、各測定元素の補正後ピーク面積を求めた。このようにして得られた、正極剤１ｃ及び１ｅの各測定元素の補正後ピーク面積を表−３に示す。尚、測定に用いたＸＰＳ測定装置（Ｐｈｙｓｉｃａｌ　Ｅｌｅｃｔｒｏｎｉｃｓ社製のＥＳＣＡ−５５００ＭＣ）における、各測定元素の相対感度補正係数は、以下の通りである。
【０１２２】
【表７】
Ｎｉ２ｐ　　　　　　　　　　　　　　：　３．６５３
Ｃｏ２ｐ　　　　　　　　　　　　　　：　３．２５５
Ａｌ２ｓ　　　　　　　　　　　　　　：　０．２８８
Ｓｂ３ｄ３／２　　　　　　　　：　３．０６６
上記のようにして求められる、Ｓｂ３ｄ３／２補正後ピーク面積、Ｎｉ２ｐ補正後ピーク面積、Ｃｏ２ｐ補正後ピーク面積、及びＡｌ２ｓ補正後ピーク面積の値から、下記一般式（２）で表されるメタル濃度に対するＳｂ濃度を算出した。このようにして得た正極剤１ｃ及び１ｅのＳｂ濃度は、Ｓｂ_２Ｏ_３の仕込量が０．１ｍｏｌ％の正極剤１ｃが、４．５％、１ｍｏｌ％の正極剤１ｅが１８．３％であった。
【０１２３】
【数４】
Ｓｂ濃度＝［（Ｓｂ３ｄ３／２補正後ピーク面積）／｛（Ｓｂ３ｄ３／２補正後
ピーク面積）＋（Ｎｉ２ｐ補正後ピーク面積）＋（Ｃｏ２ｐ補正後ピーク面積）
＋（Ａｌ２ｓ補正後ピーク面積）｝］×１００・・・（２）
【０１２４】
【表８】

【０１２５】
（７）リチウム二次電池の評価
［電池容量測定］
正極剤１’を使用して製造した正極１を用いた液系リチウム二次電池１の正極活物質である、ＬｉＮｉ_０．８２Ｃｏ_０．１５Ａｌ_０．０３Ｏ_２の単位重量当たりの容量が１８５ｍＡｈ／ｇであったので、正極活物質１ｇ当たりの１Ｃ’を１８５ｍＡとし、各リチウム二次電池の放電容量を以下のように測定して、各リチウム二次電池の「本来の」１Ｃの値を求めた。すなわち、２５℃のもと、０．５Ｃ’×（正極活物質重量）の定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。その後、０．２Ｃ’×（正極活物質重量）の定電流にて２．７Ｖまで放電を行った際の容量を測定し、これをリチウム二次電池の放電容量αとした。そして、このようにして得られた放電容量α（ｍＡｈ）のα（ｍＡ）を各々のリチウム二次電池の１Ｃとした。
【０１２６】
各リチウム二次電池の電池容量は、２５℃のもと、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。その後、０．２ＣｍＡで２．７Ｖまで定電流放電を行った際の容量を測定し、これを各々のリチウム二次電池の電池容量とした。
［レート特性測定］
各リチウム二次電池を、２５℃のもと、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。
【０１２７】
その後、液系リチウム二次電池１、２については、６Ｃ放電レートで２．７Ｖまで定電流放電を行い、得られた放電容量と、上記［電池容量測定］で得られた０．２Ｃ放電レート容量との割合をレート特性とした。
一方、ポリマー系リチウム二次電池１については、２Ｃ放電レートで２．７Ｖまで定電流放電を行い、得られた放電容量と、上記［電池容量測定］で得られた０．２Ｃ放電レート容量との割合をレート特性とした。
［インピーダンス測定］
ｓｏｌａｒｔｒｏｎ　ｉｎｓｔｒｕｍｅｎｔｓ社製のＳＩ　１２８７　Ｅｌｅｃｔｒｏｃｈｅｍｉｃａｌ　Ｉｎｔｅｒｆａｃｅと同社製ＳＩ１２６０　Ｉｍｐｅｄａｎｃｅ／Ｇａｉｎ−Ｐｈａｓｅ　Ａｎａｌｙｚｅｒ　とを組み合わせた装置を用いて　、２５℃のもと、４．２Ｖ又は３．７Ｖまで充電した各リチウム二次電池のインピーダンスを２５℃、周波数１００ＫＨｚ〜０．０１Ｈｚの領域で測定した。
［サイクル容量維持試験］
液系リチウム二次電池１を、２５℃のもと、２Ｃで４．２Ｖまで定電流充電した後４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行って充電をした後、２Ｃで３．０Ｖまで定電流放電を行って放電を行った。この充放電を１サイクルとして４００サイクルの充放電を行った。
【０１２８】
サイクル容量維持率は、各液系リチウム二次電池１における、１サイクル目の２Ｃ放電の容量に対する４００サイクル後の２Ｃ放電における容量を計算することにより求めた。
［高温サイクル容量維持率試験］
ポリマー系リチウム二次電池１を、６０℃のもと、４．２Ｖまで１．０Ｃで定電流充電した後４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行って充電をした後、１Ｃで３．０Ｖまで定電流放電を行って放電を行った。
【０１２９】
高温サイクル容量維持率は、各ポリマー系リチウム二次電池における、１サイクル目の１Ｃ放電の容量に対する４００サイクル後の１Ｃ放電における容量を計算することにより求めた。
また、高温サイクル容量維持率試験前の電池のインピーダンスを上記［インピーダンス測定］に記した方法で２５℃のもと、３．７Ｖまで充電した状態で測定した。更に、高温サイクル容量維持率試験後、２５℃のもと、３．７Ｖまで充電した状態でインピーダンスを測定した。そして、得られた試験前後のインピーダンス値をそれぞれ用いて、（試験後のインピーダンス）／（試験前のインピーダンス）をインピーダンス変化として算出した。
［高温保存試験］
各リチウム二次電池を、２５℃のもと、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。そしてこの充電状態におけるインピーダンスを測定した後、電池を６０℃又は９０℃の恒温槽中に入れ、所定時間放置した後に恒温槽より取り出した。そして、インピーダンス変化、残存容量測定、再充電後の電池容量測定、再充電後のレート特性測定を以下に記す方法で行った。
・インピーダンス変化
高温保存試験前の各リチウム二次電池のインピーダンスを上記［インピーダンス測定］に示した方法で行った。更に、高温保存試験後、恒温槽より取り出した状態におけるリチウム二次電池のインピーダンスを再度測定した。さらに、一旦前記リチウム二次電池を０．２ＣｍＡにて２．７Ｖまで放電した後、再度、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行って充電状態とし、この状態でリチウム二次電池のインピーダンスを測定した。
【０１３０】
高温保存試験前後のそれぞれインピーダンス値の比、すなわち、（試験後のインピーダンス）／（試験前のインピーダンス）をインピーダンス変化とした。また、高温保存試験前のインピーダンス値と高温保存試験後の再充電後のインピーダンス値との比、すなわち、（試験後再充電後のインピーダンス）／（試験前のインピーダンス）を再充電後のインピーダンス変化とした。
【０１３１】
尚、上記インピーダンス変化については、インピーダンス変化が１よりも若干小さい値に近ければ近いほど、インピーダンス変化が小さいことになる。また、上記再充電後のインピーダンス変化については、再充電後にインピーダンス変化が１に近ければ近いほど、インピーダンス変化が小さいことになる。その理由を以下に示す。
【０１３２】
すなわち、４．２Ｖ充電でリチウム二次電池を高温保存すると、自己放電による電圧低下が発生する。この電圧低下は、電解質がポリマーを含有するか又電解液のみから構成されるかといった電解質の種類の違いや、高温保存条件（保存時間、保存温度）に影響される。この自己放電による電圧低下は、液系リチウム二次電池を６０℃×２４ｈｒｓ保存した場合は、通常０．５Ｖ程度であり、ポリマー系リチウム二次電池を９０℃×４ｈｒｓ保存した場合は、通常０．１Ｖ程度である。
【０１３３】
一方、リチウム二次電池の充電電圧に対するインピーダンス値の変化は次の通りである。すなわち、充電電圧が２．７Ｖから徐々に高くなるにつれインピーダンス値は徐々に低下していき、充電電圧が４Ｖ付近でインピーダンス値は最低値をとる。その後更に４．２Ｖまで充電電圧が上がるにつれ再度インピーダンスが上昇する。
【０１３４】
従って、高温保存試験におけるリチウム二次電池のインピーダンス変化が全くない場合には、高温保存後は、自己放電に伴う電圧低下によりインピーダンス値の低下が発生するため、高温保存直後のインピーダンス値は、高温保存試験前のインピーダンス値よりも若干小さい値となる。このため、上記インピーダンス変化については、インピーダンス変化が１よりも若干小さい値に近ければ近いほど、インピーダンス変化が小さいことを意味するのである。
【０１３５】
これに対し、リチウム二次電池を再度充電すれば、インピーダンス値は充電電圧が４．２Ｖの時の値に復帰する。よって、高温保存試験におけるリチウム二次電池のインピーダンス変化が全くない場合には、再充電後のインピーダンス変化は１になるはずである。このため、再充電後のインピーダンス値は、１に近ければ近いほど、インピーダンス変化が小さいことになるのである。
・残存容量測定
高温保存試験後に恒温槽より取り出した各リチウム二次電池を、０．２ＣｍＡで３Ｖまで放電し、その放電容量を残存容量とした。そして、高温保存試験前の電池容量に対する残存容量（（残存容量／高温保存試験前の電池容量）×１００）を残存容量率とした。
・再充電後の電池容量測定（容量回復率の測定）
上記残存容量測定後、０．２ＣｍＡにて２．７Ｖまで放電した後、再度、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。その後、０．２ＣｍＡで２．７Ｖまで定電流放電を行った際の容量を測定して、これを再充電後の電池容量とした。そして、高温保存試験前の電池容量に対する、前記再充電後の電池容量を容量回復率とした。
・再充電後の低温特性
液系リチウム二次電池については、容量回復率を測定した後、２５℃のもと、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。その後、２５℃および−３０℃で２．７Ｖまで１ＣｍＡ放電を行った。その際の２５℃での放電容量に対する−３０℃での放電容量の割合（（−３０℃での放電容量／２５℃での放電容量）×１００）を再充電後の低温特性とした。
［低温特性試験］
液系リチウム二次電池については、２５℃のもと、０．５ＣｍＡ定電流にて４．２Ｖまで充電した後、４．２Ｖにて電流値が２５ｍＡに減衰するまで定電圧充電を行った。その後、２５℃および−３０℃で２．７Ｖまで１ＣｍＡ放電を行った。その際の２５℃での放電容量に対する−３０℃での放電容量の割合（（−３０℃での放電容量／２５℃での放電容量）×１００）を低温特性とした。
［実施例１〜８、比較例１〜４］
表−４に示す電池構成を有するリチウム二次電池を製造した。
【０１３６】
【表９】

【０１３７】
実施例１及び比較例１の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−５に示す。さらに、実施例１及び比較例１の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性をそれぞれ測定した。測定結果を表−５に示す。
【０１３８】
【表１０】

【０１３９】
表−５から、未処理のリチウムニッケル複合酸化物（比較例１）と比較して、Ｓｂ_２Ｏ_３でリチウムニッケル複合酸化物表面を修飾することにより、インピーダンス変化、再充電のインピーダンス変化、及び高温保存試験後の再充電後の低温特性が改善されることがわかる。特に、Ｓｂ_２Ｏ_３の仕込量が増加するにつれ、インピーダンス変化及び再充電後のインピーダンス変化が良好になっていくことがわかる。一方、電池容量、レート特性、及びサイクル容量維持率は、Ｓｂ_２Ｏ_３の仕込量が増えるにつれ、徐々に低下していくことがわかる。これは、求められるリチウム二次電池の性能に合わせて、自由にリチウム二次電池を設計できることを意味する。すなわち、電池容量等をより重視するようなリチウム二次電池においては、Ｓｂ_２Ｏ_３の仕込量を少なくすればよい。一方、高温環境下で使用されることが多く、高温保存時等のインピーダンス変化を小さくすることをより重視するようなリチウム二次電池においては、Ｓｂ_２Ｏ_３の仕込み量を多くすればいいのである。
【０１４０】
実施例２及び比較例２の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−６に示す。さらに、実施例２及び比較例２の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、及び容量回復率をそれぞれ測定した。測定結果を表−６に示す。
【０１４１】
【表１１】

【０１４２】
表−６から、リチウムニッケル複合酸化物をＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２及びＬｉＮｉ_０．７Ｃｏ_０．２Ｍｎ_０．１Ｏ_２とし、その表面をそれぞれＳｂ_２Ｏ_３で表面修飾した場合、高温保存試験における残存容量率及び容量回復率を損なうことなく、インピーダンス変化及び再充電後のインピーダンス変化を大幅に抑制することができることがわかる。一方、Ｓｂ_２Ｏ_３での処理により、電池容量は低下するが、サイクル特性は損なわれず、レート特性及び低温特性はむしろ改善されていることがわかる。
【０１４３】
実施例３及び比較例１の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−７に示す。さらに、実施例３及び比較例１の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、及び容量回復率をそれぞれ測定した。測定結果を表−７に示す。
【０１４４】
【表１２】

【０１４５】
表−７から、リチウムニッケル複合酸化物をトリフェニルアンチモンで表面修飾した場合、高温保存試験における残存容量率及び容量回復率を損なうことなく、インピーダンス変化及び再充電後のインピーダンス変化を大幅に抑制することができることがわかる。一方、トリフェニルアンチモンでの処理により、電池容量は低下するが、サイクル特性及びレート特性はほどんど損なわれず、低温特性はむしろ改善されていることがわかる。
【０１４６】
実施例４及び比較例３の各リチウム二次電池について、電池容量、及びレート特性を、それぞれ上記［電池容量測定］及び［レート特性測定］に従って測定した。測定結果を表−８に示す。次に、実施例４及び比較例３の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度９０℃・放置時間４時間の保存試験条件及び恒温漕内放置温度６０℃・放置時間１週間でそれぞれ高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、及び容量回復率をそれぞれ測定した。測定結果を表−８に示す。さらに、実施例４及び比較例３の各リチウム二次電池について、高温サイクル試験を上記［高温サイクル容量維持率試験］に従って、高温サイクル容量維持率及びインピーダンス変化を測定した。測定結果を表−８に示す。
【０１４７】
【表１３】

【０１４８】
表−８から、ポリマー系リチウム二次電池においても、リチウムニッケル複合酸化物の表面をＳｂ_２Ｏ_３で修飾することにより、高温保存試験における、インピーダンス変化、再充電後のインピーダンス変化、残存容量率及び容量回復率が大幅に改善されることがわかる。特にＳｂ_２Ｏ_３の修飾量が増えるに従って、上記高温保存試験における各種特性がさらに改良されていくことがわかる。また、高温サイクル容量維持率試験における、高温サイクル容量維持率及びインピーダンス変化もＳｂ_２Ｏ_３の表面修飾量が増えるに従って、良好になっていくことがわかる。一方、電池容量及びレート特性は、Ｓｂ_２Ｏ_３の仕込量が増えるにつれ、徐々に低下していくことがわかる。これは、求められるリチウム二次電池の性能に合わせて、自由にリチウム二次電池を設計できることを意味する。
【０１４９】
実施例５の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−９に示す。さらに、実施例５の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、及び容量回復率をそれぞれ測定した。測定結果を表−９に示す。
【０１５０】
【表１４】

【０１５１】
表−９から、実施例５の電池構成においては、リチウムニッケル複合酸化物の一次粒径に対するＳｂ化合物の一次粒径が０．０１〜４の範囲に、電池容量、サイクル特性、及び低温特性、並びに高温保存試験後のインピーダンス変化、再充電後のインピーダンス変化、残存容量、及び容量回復率の各種性能を最適にするような一次粒径比が存在することがわかる。
【０１５２】
実施例６及び比較例１の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−１０に示す。さらに、実施例６及び比較例１の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性をそれぞれ測定した。測定結果を表−１０に示す。
【０１５３】
【表１５】

【０１５４】
表−１０から、トリフェニルアンチモンを気相法によりリチウムニッケル複合酸化物の表面に修飾することにより、サイクル容量維持率、低温特性、並びに高温保存試験におけるインピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性の各種特性が改良されることがわかる。一方、トリフェニルアンチモンを気相法によりリチウムニッケル複合酸化物の表面に修飾することにより、電池容量は若干低下するが、レート特性はほぼ同等であるため、電池性能のバランスが非常に良好なリチウム二次電池を得ることができるといえる。
【０１５５】
実施例７の各リチウム二次電池について、電池容量、レート特性、サイクル特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、［サイクル容量維持試験］、及び［低温特性試験］に従って測定した。測定結果を表−１１に示す。さらに、実施例７の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性をそれぞれ測定した。測定結果を表−１１に示す。
【０１５６】
【表１６】

【０１５７】
表−１１から、実施例７の電池構成においては、Ｓｂ_２Ｏ_３の融点６５６℃以下の温度（６００℃）で焼成を行うと、前記融点以上の温度（７００℃）で焼成した場合と比較して、低温特性、並びに高温保存試験におけるインピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性の各種特性が十分でないことが分かる。これは、焼成温度がＳｂ化合物の融点よりも低い場合には、リチウムニッケル複合酸化物表面をＳｂ化合物で修飾することによる効果が十分に発揮されない場合があることを意味する。しかしながら、焼成温度６００℃のリチウム二次電池においては、電池容量やサイクル容量維持率はかえって良好となるため、求められるリチウム二次電池の性能に合わせて焼成温度を変化させてやれば、リチウム二次電池の性能を自由に設計できることを意味する。
【０１５８】
実施例８及び比較例４の各リチウム二次電池について、電池容量、レート特性、及び低温出力特性を、それぞれ上記［電池容量測定］、［レート特性測定］、及び［低温特性試験］に従って測定した。測定結果を表−１２に示す。さらに、実施例８及び比較例４の各リチウム二次電池について、上記［高温保存試験］に従って、恒温槽内放置温度６０℃・放置時間２４時間の保存試験条件で高温保存試験を行い、インピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性をそれぞれ測定した。測定結果を表−１２に示す。
【０１５９】
【表１７】

【０１６０】
表−１２から、ＥＣとＤＥＣとの混合溶媒を用いた電解液において、リチウムニッケル複合酸化物の表面をＳｂ_２Ｏ_３で修飾すると、レート特性を損なうことなく、低温特性並びに高温保存試験におけるインピーダンス変化、再充電後のインピーダンス変化、残存容量率、容量回復率、及び再充電後の低温特性の各種特性が改良されることがわかる。
［実施例９］
ＬｉＮｉ_０．８２Ｃｏ_０．１５Ａｌ_０．０３Ｏ_２で表される、平均二次粒子径１１μｍ（平均一次粒子径１μｍ）の正極活物質粉末に対し、平均一次粒子径０．５μｍのＳｂ_２Ｏ_３粉末（日本精鉱（株）製　ＰＡＴＯＸ−Ｍ）を、０．７５ｍｏｌ％相当となる様に添加し、密閉した容器中で十分に振とう混合した後、酸素気流中、６８０℃にて２Ｈｒ焼成を行った（サンプル名称：「０．７５ｍｏｌ％処理Ｓｂサンプル」）。また、同じ正極活物質粉末と、Ｓｂ_２Ｏ_３粉末を、Ｓｂ_２Ｏ_３粉末の添加量を２．０ｍｏｌ％となる様にした点を除いては、前述のものと同様に混合、焼成したサンプルを得た（サンプル名称：「２．０ｍｏｌ％処理Ｓｂサンプル」）。
得られた、０．７５ｍｏｌ％処理Ｓｂサンプル及び２．０ｍｏｌ％処理Ｓｂサンプルに加え、Ｓｂ_２Ｏ_３の添加及び焼成を施していない正極活物質粉末（サンプル名称：「未処理サンプル」）に関し、以下記載の方法で、ＴＰＤ−ＭＳ分析を実施した。
・ＴＰＤ−ＭＳ分析法
粉末状の、未処理サンプル、０．７５ｍｏｌ％処理Ｓｂサンプル、及び２ｍｏｌ％処理Ｓｂサンプル約５０ｍｇをそれぞれ精秤後以下の処理を行った。
粉末状のサンプルをパイロライザーに充填し、Ｈｅガス（８０ｍｌ／ｍｉｎ．）中で４００℃３０分加熱し、塩基点上に吸着しているガスを除去する。
その後、１００℃に降温し、系内を約１０^−２ｔｏｒｒまで真空排気した後、約７０ｔｏｒｒのＣＯ_２を導入し、サンプル表面の塩基点にＣＯ_２を１５分間飽和吸着させる。飽和吸着させるために時間は１５分必要である。
次に、１００℃で約１０^−２ｔｏｒｒまで真空排気し、雰囲気中に残留するＣＯ_２、や物理吸着しているＣＯ_２を除去した後に、Ｈｅフロー（２００ｍｌ／ｍｉｎ．）処理後、室温に戻す。
室温から９００℃まで１０℃／ｍｉｎ．で昇温し、昇温時に発生するＣＯ_２量の温度プロファイルを測定する。これによって、塩基点に吸着したＣＯ_２の吸着状態すなわち塩基性を評価した。
そして、得られたＣＯ_２量の温度プロファイルにおいて、１００〜３６０℃付近に観測されたピークトップの温度を求めた。測定結果を図２に示す。図２からわかるように、未処理サンプル、０．７５ｍｏｌ％処理Ｓｂサンプル、及び２ｍｏｌ％処理ＳｂサンプルのＣＯ_２脱離ピークトップ温度は、未処理サンプルが２７０℃、０．７５ｍｏｌ％処理Ｓｂサンプル及び２ｍｏｌ％処理Ｓｂサンプルが２３０℃であった。
以上の結果から、Ｓｂの複合酸化物で修飾した正極剤は、未処理に比べて、塩基性が低下することがわかる。
【０１６１】
【発明の効果】
本発明によれば、各種の電池特性が非常に高いレベルで満足されるリチウム二次電池を提供する表面修飾リチウムニッケル複合酸化物及びその製造方法を得ることができる。
特に、高温保存した際又は高温環境下で充放電を繰り返した際のインピーダンス変化が良好に抑制されるリチウム二次電池を提供する表面修飾リチウムニッケル複合酸化物及びその製造方法を得ることができる。
また、本発明によれば、高温保存後の残存容量率、容量回復率、及び再充電後の低温特性に優れ、高温サイクル試験における容量維持率の高いリチウム二次電池を提供する表面修飾リチウムニッケル複合酸化物及びその製造方法を得ることができる。
さらに、本発明によれば、電池容量、レート特性、サイクル容量維持率、及び低温特性に優れるリチウム二次電池を提供する表面修飾リチウムニッケル複合酸化物及びその製造方法を得ることができる。そして、本発明によれば、リチウム二次電池がポリマー系リチウム二次電池である場合には、高温保存によるガス発生も大幅に抑制することができるリチウム二次電池を提供する表面修飾リチウムニッケル複合酸化物及びその製造方法を得ることができる。
【図面の簡単な説明】
【図１】Ｓｂ３ｄ３／２のＸＰＳ測定結果及びそのピーク面積の求め方を示す図である。
【図２】表面修飾リチウムニッケル複合酸化物のＴＰＤ−ＭＳ測定結果を示す図である。
【符号の説明】
１　　始点
２　　終点
３　　ベースライン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a lithium nickel composite oxide whose surface is modified with a predetermined compound, and a positive electrode active material for a lithium secondary battery, a positive electrode material, and a lithium secondary battery using the same.
[0002]
[Prior art]
As a positive electrode active material used for a lithium secondary battery (in this specification, it may be simply referred to as a battery), a lithium transition metal composite oxide is expected to be promising. Among these lithium transition metal composite oxides, a lithium nickel composite oxide using nickel as a transition metal has attracted attention as a useful positive electrode active material because of its large battery capacity per unit weight. Actually, a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material can ensure a high capacity by setting the charging voltage to 4 V or more.
[0003]
Lithium secondary batteries are being adopted as power supplies for electric devices such as personal digital assistants (PDAs), portable personal computers, and mobile phones. However, in recent years, the power consumption of these electric devices tends to increase due to, for example, the establishment of technology for high-speed wired or wireless communication of large volumes of data such as moving images between the portable information terminals or mobile phones. is there. For this reason, it is desired to further increase the battery capacity of a lithium secondary battery used as a power supply.
[0004]
Further, adoption of a lithium secondary battery as a power source for an electric vehicle is also being studied. When used as a power source for automobiles, it is necessary to start an engine or accelerate suddenly, so that a lithium secondary battery is required to be able to take out a large current instantaneously.
As described above, by using the lithium nickel composite oxide, the energy density of the lithium secondary battery can be increased. Therefore, it is not only considered to adopt a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material as a power source for consumer devices such as portable information terminals, portable personal computers, and mobile phones, but also for automobiles. It is also being considered to adopt it as a power source for the system.
[0005]
[Problems to be solved by the invention]
However, a lithium secondary battery using a lithium nickel composite oxide has a higher thermal conductivity than a lithium secondary battery using another lithium transition metal composite oxide (eg, lithium cobalt composite oxide, lithium manganese composite oxide). There is a problem that stability is poor. Specifically, when a lithium secondary battery using a lithium nickel composite oxide is stored in a fully charged state at a high temperature (for example, 60 ° C./24 hours), or is repeatedly charged and discharged at a high temperature (for example, 60 ° C.), the positive electrode There is a problem that the impedance of the device increases. This increase in the impedance of the positive electrode causes deterioration of the battery characteristics such as deterioration of the rate characteristics of the lithium secondary battery, reduction of the low-temperature output, and reduction of the battery capacity. Therefore, it is very important to suppress an increase in the impedance of the positive electrode due to high-temperature storage and repeated charging and discharging at high temperatures.
[0006]
Actually, when a lithium secondary battery is used as a power source of a portable personal computer, the temperature of the personal computer is raised by heat generated by an electronic circuit in the portable personal computer. May be exposed to the environment. When a lithium secondary battery is used as a power source of an automobile, the ambient temperature of the lithium secondary battery is always around 60 ° C. since the lithium secondary battery is usually installed in an engine room. Therefore, in order to make a lithium secondary battery using a lithium nickel composite oxide practically usable, it is very important to suppress an increase in impedance due to high-temperature storage or repeated charge / discharge at a high temperature. is there.
[0007]
[Means for Solving the Problems]
In view of the above circumstances, the present inventors have found that in a lithium secondary battery using a lithium nickel composite oxide as a positive electrode active material, while maintaining the high capacity that is an advantage of the lithium nickel composite oxide, (In the present specification, this may be referred to as “high-temperature cycle operation”). In order to suppress an increase in the impedance of the lithium secondary battery, intensive studies have been made. As a result, it has been found that a lithium secondary battery having no impedance rise even at high temperature storage and high temperature cycle operation can be obtained if at least a composite oxide of a predetermined element is present on the surface of the lithium nickel composite oxide. Completed the invention.
[0008]
That is, the first gist of the present invention is characterized in that after a compound of an element belonging to the 4A to 6A group and having an atomic weight of 28 or more is present on the surface of the lithium nickel composite oxide, the compound is fired. The present invention relates to a method for producing a surface-modified lithium nickel composite oxide. In the present invention, firing means that the above-mentioned compound is reacted by heat treatment at room temperature (25 ° C.) or higher.
A second gist of the present invention is a surface-modified lithium nickel composite oxide used as a positive electrode active material of a lithium secondary battery, wherein the surface of the lithium nickel composite oxide includes a Group 4A to 6A element of the periodic table. And a surface modified lithium-nickel composite oxide characterized by the presence of a composite oxide of an element having an atomic weight of 28 or more.
[0009]
Further, a third gist of the present invention resides in a positive electrode material for a lithium secondary battery, which contains the surface-modified lithium nickel composite oxide.
[0010]
Furthermore, a fourth gist of the present invention resides in a lithium secondary battery using the surface-modified lithium nickel composite oxide as a positive electrode active material.
The present inventors have found that when a lithium secondary battery using a lithium nickel composite oxide is stored at a high temperature, or when the charge and discharge are repeated at a high temperature, an increase in the impedance of the lithium secondary battery is caused by the lithium nickel composite oxide. It was attributed to the reactivity on the surface of the object. That is, compared to other lithium transition metal composite oxides, the lithium nickel composite oxide has a higher basicity and, therefore, has higher reactivity. It was presumed that a film was formed by oxidative decomposition on the oxide surface, and this film was a factor that caused an increase in impedance. Based on the above assumption, the present inventors have proposed that if the surface of a lithium nickel composite oxide is coated with some material or reacted with some material to suppress the activity of the surface, the lithium nickel composite oxide It is considered that the impedance rise can be suppressed even when the secondary battery is stored at a high temperature or when charge and discharge are repeatedly performed at a high temperature. Furthermore, since lithium nickel composite oxides generally have high basicity, if the basicity can be reduced by surface modification, improvement in battery performance is expected. From such a viewpoint, the present inventors considered that a substance which stably exists on the surface of the lithium nickel composite oxide is preferable as the above-mentioned material. However, the coating material or the reaction material may be stored at a high temperature without impairing battery characteristics such as impedance, battery capacity, rate characteristics, and low temperature characteristics in a normal state of a lithium secondary battery using a lithium nickel composite oxide. The material must be capable of suppressing an increase in impedance at the time of operation and during high-temperature cycle operation. The present inventors have conducted intensive studies on such a material, and as a result, as the material, an oxide or a composite oxide of an element in the periodic table 4A to 6A and having an atomic weight of 28 or more is preferable, and It has been found that among these compounds, oxides or composite oxides of Sb are particularly suitable.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail. First, a method for producing a surface-modified lithium nickel composite oxide will be described. Next, the surface-modified lithium nickel composite oxide will be described. Then, a lithium secondary battery using a surface-modified lithium nickel composite oxide as a positive electrode active material will be described.
(A) Method for producing surface-modified lithium nickel composite oxide
The surface-modified lithium-nickel composite oxide of the present invention is produced by allowing a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more to exist on the surface of the lithium-nickel composite oxide, followed by firing. You. In the present invention, the “surface-modified lithium-nickel composite oxide” includes a case where the existing compound is reacted on the surface of the lithium-nickel composite oxide by firing. In the present invention, when a surface-modified lithium nickel composite oxide is produced using an Sb compound as a predetermined compound, this surface-modified lithium nickel composite oxide may be particularly referred to as an Sb surface-modified lithium nickel composite oxide. is there.
In the present invention, the periodic table of elements in 1983 is used. That is, group 4A elements are C, Si, Ge, Sn, and Pb, group 5A elements are N, P, As, Sb, and Bi, and group 6A elements are O, S, Se, and Te. , And Po.
Hereinafter, the production method of the present invention will be described in more detail.
[0012]
(A-1) Lithium nickel composite oxide
The lithium nickel composite oxide used in the present invention is an oxide containing at least lithium and nickel. Examples of the lithium nickel composite oxide include α-NaFeO₂LiNiO having a layered structure such as a structure₂And a lithium nickel composite oxide such as As a specific composition, for example, LiNiO₂, LiNi₂O₄And the like. In this case, the lithium nickel composite oxide may be one obtained by substituting a part of the site occupied by Ni with an element other than Ni. By substituting a part of the Ni site with another element, the stability of the crystal structure can be improved, and a decrease in capacity that occurs when a part of the Ni element moves to the Li site when repeatedly charged and discharged is reduced. As a result, the cycle characteristics are also improved. Further, by substituting a part of the Ni site with an element other than Ni, the heat generation start temperature of DSC (Differential Scanning Calorimetry) shifts to a higher temperature side. The thermal runaway reaction of the nickel composite oxide is also suppressed, and as a result, safety during high-temperature storage is improved.
[0013]
When a part of the site occupied by Ni is replaced with an element other than Ni, the element (hereinafter referred to as a substitution element) includes, for example, Al, Ti, V, Mn, Co, Li, Cu, Zn, Mg, Ga, Zr, and the like. Of course, the Ni site may be replaced by two or more other elements. Preferably, Al, Ti, Co, Li, Mg, Ga, and Mn are used, and Al, Ti, Co, and Mn are more preferable. By partially replacing the Ni element with Al, Ti, Co, and Mn, the effect of improving cycle characteristics and safety is enhanced.
[0014]
When the Ni site is substituted by the substitution element, the proportion is usually 2.5 mol% or more, preferably 5 mol% or more of the Ni element, and usually 50 mol% or less, preferably 30 mol% or less of the Ni element. . If the substitution ratio is too small, the effect of improving the cycle characteristics and the like may not be sufficient, and if it is too large, the capacity of the battery may decrease.
[0015]
Incidentally, the above composition may have a non-stoichiometric property such as a small amount of oxygen deficiency. Further, a part of the oxygen site may be substituted with sulfur or a halogen element.
In the present invention, the lithium nickel composite oxide is preferably a compound represented by the following general formula (1), which is unsubstituted or whose Ni site is substituted by Co and a predetermined element.
[0016]
Embedded image
Li_αNi_XCo_YM_ZO_{2- β}F_β(1)
In the general formula (1), α is a number that changes depending on the state of charge and discharge in the battery, and α is usually 0 or more, preferably 0.3 or more, more preferably 0.95 or more. , Usually 1.1 or less, preferably 1.08 or less. Within this range, high charge / discharge characteristics (sometimes referred to as cycle characteristics in this specification) are improved while maintaining high capacity. In particular, when α is set to 0.95 or more, the balance between the capacity and the cycle characteristics is better maintained.
[0017]
X is 0.1 or more, preferably 0.5 or more, more preferably 0.7 or more, while X is 1 or less, preferably 0.9 or less. Within this range, the cycle characteristics will be good while keeping the capacity high. From the viewpoint of capacity, it is preferable that X is close to 1, but it is particularly preferable that X be 0.7 or more and 0.9 or less in consideration of cycle characteristics.
[0018]
Y is 0 or more, preferably 0.05 or more, more preferably 0.1 or more, while 0.9 is 0.9 or less, preferably 0.4 or less, more preferably 0.3 or less. Within this range, safety as a lithium secondary battery can be secured while maintaining good cycle characteristics.
Z is 0 or more, preferably 0.01 or more, more preferably 0.05 or more, while Z is 0.8 or less, preferably 0.2 or less, more preferably 0.1 or less. Within this range, the safety as a lithium secondary battery can be ensured without reducing the battery capacity.
[0019]
Note that the above X, Y, and Z satisfy the relationship of 0.9 ≦ X + Y + Z ≦ 1.1, but are usually 1.0.
β is 0 or more, preferably 0.01 or more, while β is 0.5 or less, preferably 0.1 or less. Within this range, the lithium secondary battery is taken into the crystals of the lithium-nickel composite oxide, so that the safety as a lithium secondary battery can be enhanced.
[0020]
M is at least one selected from the group consisting of Li, Mg, Ca, Sr, Cu, Zn, Al, Ga, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, and Fe. . When M is at least one of the above elements, the safety as a lithium secondary battery can be improved. Preferably, M is at least one selected from the group consisting of Li, Mg, Al, Ga, Ti, Nb, Cr, Mo, Mn, and Fe. These elements have an advantage that they have an ionic radius close to that of Ni and are easily replaced with Ni, and are also easily available industrially. More preferably, M is at least one of Mn, Mg, Al, and Ga. This is because these elements are particularly easily available industrially. It is particularly preferable that M is Al or Mn. Al and Mn have the advantage of low cost.
[0021]
The specific surface area of the lithium nickel composite oxide used in the present invention is usually 0.01 m²/ G or more, preferably 0.1 m²/ G or more, more preferably 0.3 m²/ G or more and usually 10 m²/ G or less, preferably 1 m²/ G or less, more preferably 0.7 m²/ G or less. When the specific surface area is within this range, the charge / discharge characteristics at a large current deteriorate due to the reduction of sites where lithium ions are intercalated and deintercalated while effectively suppressing gas generation during high-temperature storage. No more. The measurement of the specific surface area follows the BET method.
[0022]
The average secondary particle size of the lithium-nickel composite oxide used in the present invention is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more, most preferably 0.5 μm or more, and usually 300 μm or more. Or less, preferably 100 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. When the average secondary particle size is in the above range, high safety as a lithium secondary battery can be maintained while suppressing cycle deterioration of the battery. Further, since the internal resistance value of the battery can be reduced, the battery output can be increased.
[0023]
(A-2) A compound of an element belonging to Groups 4A to 6A and having an atomic weight of 28 or more
In the present invention, in order to suppress the reactivity of the surface of the lithium nickel composite oxide at a high temperature, the surface is coated or modified with a compound of a 4A to 6A group element having an atomic weight of 28 or more. In addition, it is necessary to make the active sites on the surface of the lithium nickel composite oxide inactive.
It is speculated that the decrease in stability at high temperatures of lithium secondary batteries using lithium nickel composite oxide as a positive electrode active material occurs because unreacted residual NiO reacts with the electrolyte during the synthesis of lithium nickel composite oxide. Is done. For this reason, it is preferable that the compound that coats or modifies the surface of the lithium nickel composite oxide is a compound that reacts with NiO to form a composite oxide during firing. From such a viewpoint, it is preferable to use, as the compound, a compound of an element belonging to Groups 4A to 6A and having an atomic weight of 28 or more. Among the 4A to 6A group elements, carbon and nitrogen are difficult to obtain a stable compound, and oxygen is originally contained in the lithium nickel composite oxide, so that the atomic weight among the 4A to 6A group elements is 28 or more. Element must be used.
Examples of such compounds include Si compounds, Ge compounds, Sn compounds, Pb compounds, P compounds, As compounds, Sb compounds, Bi compounds, S compounds, Se compounds, Te compounds, and Po compounds.
From the viewpoint that the composite oxide produced by reacting with NiO does not have combustion promoting properties, P compounds, Sb compounds, Bi compounds, and Te compounds are preferable, and Sb compounds or Bi compounds are more preferable. It is particularly preferable to use an Sb compound.
The Bi compound is not particularly limited, but is preferably a compound that finally exists as a bismuth composite oxide on the surface of the lithium nickel composite oxide as described above. Examples of such a compound include triphenylbismuth.
[0024]
Although the Sb compound used in the present invention is not particularly limited, antimony oxide, antimony halide, antimony sulfide, antimony selenide, antimony telluride, antimony acetate, antimony oxychloride, trimethoxyantimony, triethoxyantimony, tripropoxyantimony , Tributoxyantimony, triphenylantimony, and triphenylantimony dichloride. By using these Sb compounds, an increase in impedance of a lithium secondary battery using a lithium nickel composite oxide during high-temperature storage or the like can be favorably suppressed.
[0025]
Among the above compounds, examples of antimony oxide include Sb₂O₃, Sb₂O₄, Sb₂O₅And Sb₂O₅These antimony oxides are solid at room temperature and normal humidity. Examples of the antimony halide include antimony fluoride, antimony chloride, antimony bromide, and antimony iodide. These antimony halides are solid at room temperature. The properties of antimony sulfide, antimony selenide, and antimony telluride are powdery solids at room temperature and normal humidity, respectively. Antimony acetate, antimony oxychloride, and trimethoxyantimony are solid at room temperature and humidity. The properties of triethoxyantimony, tripropoxyantimony, and tributoxyantimony are liquid at normal temperature and normal humidity. The properties of triphenylantimony and triphenylantimony dichloride are solid at room temperature and normal humidity, respectively. In addition, in this specification, normal temperature means 25 degreeC, and normal humidity means 50% RH.
[0026]
Among these Sb compounds, more preferred is Sb₂O₃, Sb₂O₄, Sb₂O₅And Sb₂O₅Antimony oxide, antimony halide, antimony acetate, and triphenylantimony. By using these Sb compounds, the effects of the present invention can be more remarkably exhibited.
Of these Sb compounds, particularly preferred is Sb₂O₃, Antimony iodide, antimony acetate, and triphenylantimony. Sb₂O₃Since has a low melting point of 656 ° C., a uniform reaction can be completed by a reaction between a solid and a liquid at a decomposition temperature of the lithium nickel composite oxide (generally 780 to 800 ° C.) or lower. Further Sb₂O₃Is advantageous in that it is industrially produced in large quantities and is inexpensive. Antimony iodide has the advantage of being easily reacted as a gas. Further, even if the reaction is carried out as a gas, the generated gas is iodine, so that the safety is high and the adverse effect on the reactor material is small. Triphenylantimony not only has the advantage of being easily reacted as a gas, but also has the advantage that no dangerous gas is generated when reacted as a gas.
[0027]
(A-3) Method for Existing Compounds of Elements of Groups 4A to 6A and Having an Atomic Weight of 28 or More
In the method for producing a surface-modified lithium-nickel composite oxide of the present invention, a compound of an element belonging to the 4A to 6A group and having an atomic weight of 28 or more is present on the surface of the lithium-nickel composite oxide.
(1) Mixing ratio of a compound of a group 4A to 6A element having an atomic weight of 28 or more with a lithium nickel composite oxide
When a compound of a 4A to 6A element having an atomic weight of 28 or more is present on the surface of the lithium nickel composite oxide, a lithium nickel composite oxidation of a compound of a 4A to 6A element having an atomic weight of 28 or more is performed. The mixing ratio to the product is usually 0.001 mol% or more, preferably 0.01 mol% or more, more preferably 0.05 mol% or more, while it is usually 10 mol% or less, preferably 7 mol% or less, more preferably 5 mol%. Or less, particularly preferably 3 mol% or less, most preferably 2 mol% or less.
In particular, when an Sb compound is used as a compound of a 4A to 6A group element having an atomic weight of 28 or more, if the Sb compound is 0.05 mol% or more and 3 mol% or less with respect to the lithium nickel composite oxide, It is possible to obtain a battery capacity, a rate characteristic, and a low-temperature output characteristic substantially equal to those of an untreated lithium nickel composite oxide, while effectively suppressing an increase in impedance due to high-temperature storage or the like. When the amount of the Sb compound is set to 0.1 mol% or more and 2 mol% or less with respect to the lithium nickel composite oxide, it is possible to effectively suppress an increase in impedance due to high-temperature storage and the like, and at the same time to an untreated lithium nickel composite oxide. Battery capacity, rate characteristics, and low-temperature output characteristics.
[0028]
In the production of the surface-modified lithium nickel composite oxide, it is preferable that a compound of a 4A to 6A group element having an atomic weight of 28 or more is uniformly present on the surface of the particles of the lithium nickel composite oxide.
For example, when the compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is a powdery particle at room temperature, the element of the group 4A to 6A having an atomic weight greater than the primary particle diameter of the lithium nickel composite oxide is used. It is very preferable that the primary particle diameter of the compound of the element having a value of 28 or more is small. When the primary particle diameter of a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is too large with respect to the primary particle diameter of the lithium nickel composite oxide, the compound partially covers the lithium nickel composite oxide surface. May not be able to be uniformly modified.
From such a viewpoint, the primary particle size ratio of the compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element to the lithium nickel composite oxide is usually 0.005 or more, preferably 0.01 or more, more preferably Is 0.015 or more, while it is usually 5 or less, preferably 4 or less, more preferably 2 or less, and particularly preferably 1 or less.
In particular, when an Sb compound is used as a compound of a 4A to 6A group element having an atomic weight of 28 or more, if the primary particle size ratio of the Sb compound to the lithium nickel composite oxide is 0.01 or more, the Sb compound becomes a solid. When the powder is in the form of a powder, the Sb compound can be easily handled and the cost can be reduced. Further, when the primary particle size ratio is 0.015 or more, there is an advantage that a commercially available Sb compound can be used as it is. On the other hand, when the primary particle size ratio between the lithium nickel composite oxide and the Sb compound is 2 or less, the battery capacity, the rate characteristics, and the low-temperature output characteristics are each untreated while the impedance rise during high-temperature storage and the like is particularly effectively suppressed. There is an advantage that the performance can be equivalent to that of the case. Further, when the primary particle size ratio is 1 or less, there is an advantage that a commercially available Sb compound can be used as it is.
[0029]
(2) A method of presenting a compound of a 4A to 6A group element having an atomic weight of 28 or more
The method for causing a compound of an element having a group 4A to 6A element and an atomic weight of 28 or more to be present on the particle surface of the lithium nickel composite oxide is not particularly limited, but a wet method, a dry method, or a gas phase method is used. Is preferred.
(2-1) Wet method
The wet method is a method of dissolving or dispersing a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element in a solvent and dispersing a lithium nickel composite oxide in the solvent, thereby forming a group 4A to 6A element having an atomic weight of A method in which a compound of 28 or more elements is brought into contact with a lithium-nickel composite oxide in a solvent so that the compound is present on the surface of the lithium-nickel composite oxide.
In particular, when an Sb compound is used as a compound of a group 4A to 6A element having an atomic weight of 28 or more, the Sb compound is contacted with the lithium nickel composite oxide in a solvent to form the lithium nickel composite oxide. A method in which the Sb compound is present on the surface of a product can be exemplified.
[0030]
Here, as a solvent for dissolving or dispersing a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element, for example, acetone, methanol, ethanol, hexane, cyclohexane, toluene, and water are mentioned. Can be.
As a device for dispersing a compound of a group 4A to 6A element having an atomic weight of 28 or more in a solvent, any device capable of kneading and stirring while applying heat may be used. It is more preferable that the dispersing device has a function that can be added. As such an apparatus, a rotary evaporator can be mentioned in a laboratory. In addition, when a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is dispersed in a solvent, a uniform slurry can be obtained by using a dispersing agent. It becomes easy to make the compounds of the above elements uniformly adhere to the surface of the lithium nickel composite oxide. Examples of the dispersant include a surfactant.
[0031]
As an apparatus for allowing a compound of an element having a group 4A to 6A element and having an atomic weight of 28 or more to be present on the surface of the lithium nickel composite oxide, for example, a group of elements belonging to the group 4A to 6A while moving particles of the lithium nickel composite oxide is used. A device capable of adhering a compound of an element having an atomic weight of 28 or more. Industrially, a dispersion solution (for example, a slurry) containing a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is sprayed while spraying a lithium nickel composite oxide powder using a spray or the like. For example, a pan coating machine, a spray dryer and the like can be used.
[0032]
(2-2) Dry method
The dry method refers to a method in which a solid compound of an element having an atomic weight of 28 or more and a lithium nickel composite oxide particle (solid) is brought into contact with a solid 4A to 6A element without a solvent, and the solid 4A is mixed. By mixing a lithium nickel composite oxide particle with a compound of an element having an atomic weight of 28 to 6A that is a Group 4A to 6A element and having an atomic weight of 28 or more on the particle surface of the lithium nickel composite oxide. Is a method in which a compound of the element is present.
In particular, the dry process is preferably performed by bringing a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more into contact with the lithium-nickel composite oxide in a powder state, respectively. A compound of an element having an atomic weight of 28 or more, which is a group 4A to 6A element, is present on the surface. For example, when the compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is an Sb compound, the Sb compound is brought into contact with the lithium-nickel composite oxide in a powder state to convert the Sb compound into a lithium-nickel composite. What is necessary is just to exist on an oxide surface.
[0033]
(2-3) Gas phase method
Further, the vapor phase method is a method of contacting a group 4A to 6A element by bringing a compound of a gaseous group 4A to 6A element having an atomic weight of 28 or more into contact with solid lithium nickel composite oxide particles. Means that a compound of an element having an atomic weight of 28 or more is present on the surface of the lithium nickel composite oxide particles. The vapor phase method has an advantage that a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more can be easily uniformly present on the surface of the lithium nickel composite oxide.
In particular, as the vapor phase method, a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more is converted into a gaseous state, and the compound is brought into contact with the lithium nickel composite oxide to thereby form the lithium nickel composite oxide. This is a method in which a compound of an element belonging to the group 4A to 6A and having an atomic weight of 28 or more is present on the surface of the oxide.
For example, when an Sb compound is used as a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element, the Sb compound is made into a gaseous state and brought into contact with a lithium nickel composite oxide to form a lithium nickel composite oxide. What is necessary is just to make the Sb compound exist on the surface of the object. As a specific method, a method in which lithium nickel composite oxide particles are put in a furnace and gaseous Sb compound (for example, triphenylantimony) vapor is blown into the particles, or a solid lithium nickel composite oxide and A method in which both Sb compounds are placed in a furnace, the furnace is heated to vaporize the Sb compounds, and adhere to the surface of the lithium-nickel composite oxide.
[0034]
(A-4) Firing method
In the method for producing a surface-modified lithium-nickel composite oxide of the present invention, a compound of an element having a group of 4A to 6A and an atomic weight of 28 or more is present on the surface of the lithium-nickel composite oxide, and then calcined. . When calcination is performed, a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element becomes a composite oxide, and thus is firmly attached to the surface of the lithium nickel composite oxide.
(1) Firing temperature
First, the firing temperature is not particularly limited. Preferably, the calcination is carried out at a temperature equal to or higher than the melting point of a compound of an element belonging to the group 4A to 6A and having an atomic weight of 28 or more. In the case where a compound of an element having an atomic weight of 28 or more which is a group 4A to 6A element is present in a solid state on the surface of the lithium nickel composite oxide particles, the compound can be fired at a temperature not lower than the melting point of the compound. Is melted and the melt covers the lithium nickel composite oxide, and the reaction can be completed uniformly by a solid-liquid reaction. On the other hand, when calcined at a temperature equal to or lower than the melting point, a reaction between a solid compound of a group 4A to 6A element having an atomic weight of 28 or more and a solid lithium nickel composite oxide, that is, a solid-solid Because of the reaction, the reaction between the compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element and the lithium nickel composite oxide is slow. It is difficult to make the compounds of the above elements uniformly exist on the surface of the lithium nickel composite oxide.
On the other hand, the firing temperature is preferably equal to or lower than the decomposition temperature of the lithium nickel composite oxide. If the firing temperature is higher than the decomposition temperature, the lithium-nickel composite oxide itself is decomposed, so that a compound of a 4A to 6A group element having an atomic weight of 28 or more is deposited on the surface of the lithium-nickel composite oxide. It may be difficult to firmly adhere. Here, the decomposition temperature of the lithium nickel composite oxide varies depending on its composition. That is, for example, when a part of the Ni site is replaced with Co or Al, the decomposition temperature of the lithium nickel composite oxide increases as the replacement amount increases. Further, the lithium nickel composite oxide is Li [Li_0.2Ni_0.4Mn_0.4] O₂In the case of the composition, the synthesis of the lithium-nickel composite oxide is performed at 900 ° C., and the baking with a compound of an element having an atomic weight of 28 or more which is a 4A to 6A element is preferably performed at 900 ° C. or less. . The composition (for example, LiNi_0.82Co_0.15Al_0.03O₂, LiNi_0.8Co_0.2O₂And LiNi_0.7Co_0.2Mn_0.1O₂) Is considered to be the decomposition temperature around 780 ° C. (at least the temperature at which the battery performance starts to decrease). Therefore, at 780 ° C. or less, a compound of an element belonging to Group 4A to 6A and having an atomic weight of 28 or more (Sb compound) ) And firing. For example, in the examples, Sb is used as the Sb compound.₂O₃When is used, its melting point is 656 ° C., and 656 to 780 ° C. is the optimum temperature range for firing. However, it is considered that the reaction proceeds to some extent even if it takes time even at 656 ° C. or lower.
[0035]
From the above, since the firing temperature depends on the type and properties of the compound (Sb compound in the example) of the group 4A to 6A element having an atomic weight of 28 or more, the composition of the lithium nickel composite oxide, etc. Although it is difficult to define the temperature range uniquely, it is generally 400 ° C. or higher, preferably 500 ° C. or higher, more preferably 656 ° C. or higher, while generally 850 ° C. or lower, preferably 780 ° C. ° C or lower, more preferably 750 ° C or lower. Within this temperature range, a temperature range that is equal to or higher than the melting point of a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more and equal to or lower than the decomposition temperature of the lithium nickel composite oxide is easily secured.
[0036]
(2) Atmosphere during firing
The atmosphere for sintering the lithium-nickel composite oxide with a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element may be performed in the air, but is preferably performed in an oxygen atmosphere. That is. On the other hand, when a large amount of carbon dioxide gas or moisture is mixed in the firing atmosphere, the lithium nickel composite oxide itself may be deteriorated during firing, so that the carbon dioxide gas or moisture in the firing atmosphere is minimized. Is preferred.
[0037]
(3) Firing time
The firing time for firing the lithium nickel composite oxide with a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element depends on the firing temperature. That is, at the time of firing, it is a matter of the reaction rate whether or not the compound of the element of the periodic table 4A to 6A and having an atomic weight of 28 or more and the lithium nickel composite oxide sufficiently reacts. When the firing temperature is high, the firing time is short, while when the firing temperature is low, the firing time needs to be long.
[0038]
In addition, the firing time when firing a compound of an element having an atomic weight of 28 or more which is a group 4A to 6A element and a lithium nickel composite oxide depends on the scale at which firing is performed. In other words, it takes about 1 hour at the laboratory level such as 100 g scale, and about 2 hours at 1 kg scale. In the case of industrial production, the temperature of the furnace for firing and the temperature of the compound of the element of the periodic table 4A to 6A and having an atomic weight of 28 or more and the temperature of the lithium nickel composite oxide are substantially the same. Since some time is required before the firing, when determining the firing time, sufficient attention must be paid to the scale for firing.
[0039]
Further, the sintering time when sintering a lithium nickel composite oxide with a compound of an element having an atomic weight of 28 or more, which is a group 4A to 6A element, is based on an element having an atomic weight of 28 or more which is a group 4A to 6A element to be used. Depends on the type of compound. For example, Sb among Sb compounds as a compound of an element having an atomic weight of 28 or more which is a group 4A to 6A element₂O₃When is used, it is usually 1 minute or more, preferably 30 minutes or more, more preferably 1 hour or more, while it is usually 72 hours or less, preferably 12 hours or less, more preferably 6 hours or less.
[0040]
In particular, when the Sb compound is used as the compound of an element having an atomic weight of 28 or more which is a group 4A to 6A element, the firing time does not exceed a short time in consideration of productivity. Whether or not the reaction between the and the Sb compound is completed may vary depending on the mixed state. Therefore, the upper limit of the calcination time is determined by the productivity and the calcination temperature of the Sb surface-modified lithium nickel composite oxide. For example, when the calcination temperature is set to 700 ° C., setting the calcination time to 24 hours is considered to be sufficient. .
[0041]
(B) Surface-modified lithium nickel composite oxide
The surface-modified lithium-nickel composite oxide of the present invention is a surface-modified lithium-nickel composite oxide used as a positive electrode active material of a lithium secondary battery. It is necessary to have at least a compound oxide of an element having an atomic weight of 28 or more.
(B-1) A complex oxide of an element belonging to Groups 4A to 6A of the periodic table and having an atomic weight of 28 or more
The term “composite oxide of an element in the periodic table 4A to 6A having an atomic weight of 28 or more” includes an element of the group 4A to 6A in the periodic table having an atomic weight of 28 or more, oxygen, and other elements. Refers to a compound.
Examples of complex oxides of elements of the Periodic Tables 4A to 6A and having an atomic weight of 28 or more include, for example, Si, Ge, Sn, Pb, P, As, Sb, Bi, S, Se, Te, and Po. A composite oxide of the selected element can be given.
It is considered that NiO remaining without reacting at the time of synthesizing the lithium nickel composite oxide is a cause of promoting a decrease in stability at high temperature of the lithium secondary battery using the lithium nickel composite oxide as the positive electrode active material. In other words, in a high-temperature environment, the NiO and the electrolytic solution react on the surface of the lithium-nickel composite oxide to form a film or the like, and the stability of the lithium secondary battery at high temperatures is considered to be reduced. . Accordingly, if a compound of a group 4A to 6A element having an atomic weight of 28 or more reacts with NiO to form a composite oxide and reduce the amount of NiO present on the surface of the lithium nickel composite oxide, lithium It is presumed that the stability of the secondary battery at high temperatures can be improved.
From such a viewpoint, an element selected from P, Sb, Bi, and Te that is a group 4A to 6A element of the periodic table and that has an atomic weight of 28 or more is preferable, and more preferable is Sb or Bi. Yes, particularly preferred is Sb.
Preferred as a composite oxide of elements of the periodic table 4A to 6A and having an atomic weight of 28 or more include at least one of Li and Ni and an element of the periodic table 4A to 6A and an element having an atomic weight of 28 or more. And a composite oxide of oxygen, and particularly preferred are Ni, a composite oxide of oxygen and an element having an atomic weight of 28 or more, which is a Group 4A to 6A element, or Ni and Li, It is a composite oxide of oxygen with an element having an atomic weight of 28 or more which is a group 4A to 6A element in the periodic table.
For example, when Sb is used as an element in the periodic table 4A to 6A and having an atomic weight of 28 or more, it is preferable to use Ni or a composite oxide containing Ni and Li in addition to Sb and oxygen. It is preferable to contain Ni, or Ni and Li, because it is possible to reduce the amount of NiO, and in the firing step, the modifying material and the lithium nickel composite oxide containing Ni and Li This is because there is a high possibility of reaction.
As such a composite oxide, specifically, LiSbO₂, NiSbO₆, Li₃SbO₄, LiSbO₃, Li₃NiSb₂O₉And the like. From the viewpoint of the stability of the compound, it is preferable to use a composite oxide of Sb, oxygen, and Ni or Ni and Li. As such a composite oxide, specifically, NiSbO₆, Li₃NiSb₂O₉Can be mentioned.
On the surface of the lithium-nickel composite oxide, although there may be substances other than the composite oxide of elements in the periodic table 4A to 6A and having an atomic weight of 28 or more, a predetermined amount of the element in the periodic table 4A to 6A is used. If the composite oxide of an element having an atomic weight of 28 or more exists, the effect of the present invention is sufficiently exhibited. In order to sufficiently exhibit the effects of the present invention, the mixing ratio of the compound of an element having an atomic weight of 28 or more, which is a group 4A to 6A element in the periodic table with respect to the lithium nickel composite oxide, is adjusted to the above (A-3) It is preferable to set the range as described above.
(B-2) Lithium nickel composite oxide
As the lithium-nickel composite oxide used in the Sb surface-modified lithium-nickel composite oxide of the present invention, those similar to those described in the above (A-1) may be used. Further, as described in the above (A-1), a compound represented by the following general formula (1) is preferable as the lithium nickel composite oxide.
[0042]
Embedded image
Li_αNi_XCo_YM_ZO_{2- β}F_β(1)
(In the general formula (1), α, X, Y, Z, and β are 0 <α ≦ 1.1, 0.1 ≦ X ≦ 1, 0 ≦ Y ≦ 0.9, and 0 ≦ Z ≦ 0, respectively. 0.8, 0.9 ≦ X + Y + Z ≦ 1.1, 0 ≦ β ≦ 0.5 M is Li, Mg, Ca, Sr, Cu, Zn, Al, Ga, Ti, Zr, V , Nb, Ta, Cr, Mo, W, Mn, and Fe.)
Here, preferable ranges of α, X, Y, Z, β, and M are the same as described in the above (A-1).
(B-3) Preferred embodiment of surface-modified lithium nickel composite oxide
(1) Regulation by X-ray photoelectron spectroscopy
When the surface-modified lithium-nickel composite oxide of the present invention is an Sb-surface-modified lithium-nickel composite oxide, it is preferable that M in the above general formula (1) be Al and X-ray photoelectron spectroscopy under the following measurement conditions. When measured by the method (X-ray @ photo-electron @ spectroscopy), the Sb concentration represented by the following formula (2) is 1% or more and 95% or less.
[0043]
(Equation 2)
Sb concentration = [(peak area after Sb3d3 / 2 correction) / ｛(after Sb3d3 / 2 correction)
Peak area) + (peak area after Ni2p correction) + (peak area after Co2p correction)
+ (Peak area after Al2s correction)}] × 100 (2)
(Measurement conditions for X-ray photoelectron spectroscopy)
1. Measurement of surface modified lithium nickel composite oxide
A double-sided tape is attached to a metal plate, and a surface-modified lithium-nickel composite oxide in a powder state is sprinkled on the metal plate so that the tape cannot be seen.
[0044]
The measurement is performed under the following conditions using a monochromatic Al-Kα ray (14 kV, 150 W) as a light source for the measurement. At the time of the measurement, an electron neutralizing gun is used for charge correction.
PassEnergy: 29.35 eV
Data acquisition interval: 0.125 eV / step
Measurement area: 0.8mm diameter
Extraction angle: 45 degrees
The measurement elements are Ni2p, Co2p, Al2s, and Sb3d3 / 2.
2. Measurement of Sb concentration
The start point and the end point of each peak of each measurement element are determined, and the start point and the end point are connected by the Shirley method. Then, the area surrounded by the line connecting the start point and the end point and the peak is determined for each measurement element, and this is defined as the peak area of each measurement element.
[0045]
Next, using the relative sensitivity correction coefficient determined for each of the measurement elements, the peak area of each of the measurement elements is divided by the relative sensitivity correction coefficient of each element. The peak area thus divided by the relative sensitivity correction coefficient is referred to as “post-correction peak area”.
In the Sb surface-modified lithium nickel composite oxide of the present invention, it is necessary that Sb on the surface of the lithium nickel composite oxide be present in a predetermined amount or more in order to react the Sb compound with the surface of the lithium nickel composite oxide to obtain the compound. is there. In the present invention, in order to confirm whether or not such an Sb surface-modified lithium nickel composite oxide is obtained, X-ray photovoltaic spectroscopy, which is an effective means for detecting information on the outermost surface of a substance, is used. .
[0046]
X-ray photoelectron spectroscopy is a technique in which a sample surface is irradiated with characteristic X-rays (Al Kα, Mg Kα, etc.) as a primary light source, and photoelectrons emitted from the excited sample surface are detected by an energy spectrometer. is there. The escape depth of photoelectrons is about 5 nm, which is an effective means for detecting information on the outermost surface of the measurement sample. The difference between the energy of the incident X-ray and the kinetic energy of the photoelectrons emitted from the excited sample surface represents the binding energy of the photoelectrons, and this binding energy is specific to the type of element. Further, the value of the binding energy is slightly shifted depending on the type of an adjacent element or the type of a chemical bond. By using the X-ray photoelectron spectroscopy, information on elemental qualification and chemical state can be obtained by utilizing the above phenomenon. Further, by comparing the peak areas derived from the respective constituent elements, the relative element composition can be known. In the present invention, the Sb concentration was estimated by determining the relative ratio of a predetermined element on the surface of the lithium nickel composite oxide.
[0047]
The XPS measurement of the surface-modified lithium nickel composite oxide in the present invention is specifically performed as follows.
First, a double-sided tape is attached to a metal plate, and a surface-modified lithium nickel composite oxide in a powder state is sufficiently sprinkled on the double-sided tape until the tape becomes invisible, and then the surface is smoothed. Thereafter, the double-sided tape to which the surface-modified lithium nickel composite oxide has been attached is fixed to a holder together with the metal plate, and is subjected to measurement.
[0048]
A monochromatic Al-Kα ray (14 kV, 150 W) is used as a light source for measurement. The measurement is carried out under the following conditions. At the time of the measurement, an electron neutralizing gun is used to correct the charge. Here, the reason that the charge correction by the electron neutralizing gun is necessary for the measurement is that the surface-modified lithium nickel composite oxide is not a completely conductive sample but is charged.
PassEnergy: 29.35 eV
Data acquisition interval: 0.125 eV / step
Measurement area: 0.8mm diameter
Extraction angle: 45 degrees
The XPS measurement is performed in the above measurement conditions, and the measurement elements are Ni2p, Co2p, Al2s, and Sb3d3 / 2.
[0049]
After the XPS measurement, the starting point and the ending point of each peak of the measured element in the obtained raw data are determined, and the starting point and the ending point are connected by the Shirley method. Here, the starting point and the ending point of the peak are set to a portion where the skirt of the peak becomes completely flat. This is because if the starting point and the ending point are determined in the middle of the tail of the peak, an accurate peak area may not be obtained. A specific example of how to determine the start point and the end point will be described with reference to FIG. FIG. 1 is an example of XPS measurement of the measurement element Sb3d3 / 2, in which the horizontal axis represents binding energy (BINDING @ ENERGY: eV) and the vertical axis represents signal intensity (N (E) / E: counts / s). In FIG. 1, the starting point 1 is located at a portion where the bottom of the binding energy in the Sb3d3 / 2 peak on the low energy side is completely flat. On the other hand, the end point 2 is located at a portion where the tail of the peak on the high energy side is completely flat. The start point and the end point determined in this way are connected by the baseline 3 using the Shirley method. Then, the area surrounded by the baseline and the peak is determined for each measurement element, and this is defined as the peak area of each measurement element. In FIG. 1, the peak area refers to the area of a hatched portion surrounded by a baseline and a peak.
[0050]
Next, using the relative sensitivity correction coefficient determined for each measurement element, the peak area of each measurement element is divided by the relative sensitivity correction coefficient of each element. Here, the reason why the peak area of each measurement element is divided by the relative sensitivity correction coefficient of each element is that it is necessary to consider the difference in the generation efficiency of each photoelectron. That is, the photoelectron generation efficiencies are not all the same. For example, when the elements A, B, and C exist at the same element ratio, the photoelectron A1s of the element A has a signal intensity of 100 while the photoelectron B1s of the element B has This is because the signal intensity is 80 (the generation efficiency is low), and the photoelectron C1s of the element C has the signal intensity 120 (the generation efficiency is high). Since the relative sensitivity ratio slightly differs depending on the measurement conditions and the measurement model, the device maker provides a value unique to each device as a correction coefficient. Therefore, even if the data of the peak area obtained from the raw data of the XPS measurement is used as it is, this data does not reflect the actual element ratio. For this reason, in the present invention, the relative sensitivity correction coefficient determined for each device as described above is used.
[0051]
The peak area thus divided by the relative sensitivity correction coefficient is referred to as “post-correction peak area”. That is, for example, the “peak area after Sb3d3 / 2 correction” is a value obtained by dividing the peak area indicated by oblique lines in FIG. 1 by the relative sensitivity correction coefficient of Sb3d3 / 2.
In the examples described later, 3.653 for Ni2p, 3.255 for Co2p, 0.288 for Al2s, and 3.066 for Sb3d3 / 2 were used as relative sensitivity correction coefficients. The relative sensitivity correction coefficient is a value determined by the X-ray photoelectron spectrometer used. In the examples described below, the X-ray photoelectron spectrometer uses ESCA-5500MC manufactured by Physical @ Electronics.
[0052]
From the values of the peak area after Sb3d3 / 2 correction, the peak area after Ni2p correction, the peak area after Co2p correction, and the peak area after Al2s correction determined as described above, the metal concentration represented by the following general formula (2) Is calculated with respect to.
[0053]
(Equation 3)
Sb concentration = [(Sb3d3 / 2 corrected peak area) / {(Sb3d3 / 2 corrected peak area) + (Ni2p corrected peak area) + (Co2p corrected peak area) + (Al2s corrected peak area)}] × 100 ・ ・ ・ (2)
In the present invention, the Sb concentration represented by the general formula (2) is 1% or more, preferably 2% or more, more preferably 5% or more, while 95% or less, preferably 70% or less. It is preferably at most 50%, particularly preferably at most 30%, most preferably at most 25%. Within the above range, it is possible to effectively suppress an increase in impedance at the time of high-temperature storage or the like.
(2) Heated thermal desorption / pyrolysis-spectrometry by mass spectrometry
Another preferred embodiment of the Sb surface-modified lithium nickel composite oxide of the present invention is a temperature-programmed thermal desorption / pyrolysis-mass spectrometry (Temperature \ Programmed \ Decomposition / Decomposition-Mass \ Spectroscopy: hereinafter simply referred to as TPD-MS) under the following measurement conditions. It may be described.) When measured, CO is in the range of 150 to 250 ° C.₂Has a peak due to elimination of
(Measurement conditions of thermal desorption / pyrolysis-mass spectrometry at elevated temperature)
(A) A surface-modified lithium nickel composite oxide in a powder state is heated to about 400 ° C. in He gas, and then cooled to about 100 ° C.
Specifically, 50 mg of a powdery surface-modified lithium nickel composite oxide was precisely weighed, filled into a pyrolyzer, heated at 400 ° C. for 30 minutes in He gas (80 ml / min.), And then surface-modified lithium nickel The gas adsorbed on the composite oxide surface is removed, and the CO₂The reproducibility of the adsorption state can be improved. (B) CO₂To introduce CO into the surface of the surface-modified lithium nickel composite oxide₂Is adsorbed.
Specifically, the temperature is lowered to 100 ° C.^-2evacuate to about 70 torr and reduce CO2 to about 70 torr.₂Into the surface of the surface-modified lithium nickel composite oxide (especially at the base point).₂For 15 minutes. In order to perform the saturated adsorption, at least about 15 minutes are required.
(C) Thereafter, CO remaining in the atmosphere or the like₂And then lower the temperature to around room temperature.
Specifically, at 100 ° C., about 10^-2Evacuate to torr and remove CO remaining in the atmosphere₂Adsorbed CO on the surface of surface-modified lithium nickel composite oxide₂, And then returned to room temperature after He flow (200 ml / min.) Treatment.
(D) The temperature is raised to around 900 ° C., and CO generated when the temperature is raised₂Measure the temperature profile of the volume.
Specifically, 10 ° C./min. And the CO generated at the time of temperature rise₂Measure the temperature profile of the volume.
The TPD-MS is a technique of continuously introducing a gas generated when the temperature of a sample is continuously increased into a mass spectrometer and measuring a temperature profile of the generated gas. This method is an effective method for examining the state of chemical adsorption and the type of functional group because the process of decomposing and desorbing a sample can be measured. Specifically, it is possible to identify the adsorbed species and adsorption active sites by the number of peaks in the temperature profile, to compare the binding state from the desorption temperature, and to compare the number of surface active points or the amount of adsorption and the amount of functional groups from the amount of desorption. . Further, since a relatively large amount of sample can be analyzed, it is possible to analyze a very small amount of generated gas.
In the present invention, the reason why it is effective to use TPD-MS as an analysis method of the surface-modified lithium nickel composite oxide is as follows. That is, CO₂CO after adsorption₂By measuring the temperature profile of desorption, it is possible to examine the amount and distribution of base points present on the solid surface. In the lithium-nickel composite oxide, the base point present on the solid surface is considered to be a reaction point at a high temperature (a cause of deteriorating the characteristics of the lithium secondary battery at a high temperature). What is necessary is just to analyze the quantity and distribution of the base point with the surface modified lithium nickel composite oxide surface. Specifically, CO adsorbed saturated at the base site₂The temperature distribution of thermal desorption of CO was examined, and CO in the surface-modified lithium nickel composite oxide was investigated.₂If the desorption peak is shifted to a lower temperature side compared to the untreated lithium nickel composite oxide, the basicity of the surface-modified lithium nickel composite oxide is reduced (the high temperature characteristics of the lithium secondary battery). Has been improved).
Here, in the TPD-MS measurement, CO 2₂To measure the adsorption and desorption of₂Is considered to specifically adsorb to the base site.
As described above, CO in the surface-modified lithium nickel composite oxide₂The desorption peak may be shifted to a lower temperature side as compared with the untreated lithium nickel composite oxide, but the specific temperature range is as follows. That is, when TPD-MS is measured at 0 to 900 ° C., since the desorption temperature reflects the bonding state, CO 2 up to 300 ° C.₂The profile is CO which is saturated at base point.₂Desorption of CO₂Profile is Li₂CO₃Generated by decomposition of CO₂it is conceivable that.
Then, in the present invention, "CO in the range of 150 to 250 ° C.₂The peak due to the desorption of "is a mass of 44 (CO 2) in TPD-MS measurement.₂) Means that a peak (apex) is observed in a temperature region of 150 to 250 ° C. when the temperature dependence of the desorption amount is measured.
FIG. 2 shows TPD- of a lithium-nickel composite oxide surface-modified and an untreated lithium-nickel composite oxide obtained by performing a surface modification using an Sb compound as a compound of an element having an atomic weight of 28 or more, which is an element in the periodic table 4A to 6A. This is an MS measurement result (measured from 25 to 900 ° C.) (for details, see Examples described later). As can be seen from FIG. 2, the lithium-nickel composite oxide treated with the Sb compound at 0.75 mol% or 2 mol% has CO 2 around 220 to 230 ° C.₂The peak due to desorption of is observed. On the other hand, the lithium-nickel composite oxide not treated with the Sb compound (untreated) gradually becomes CO2 around 220 ° C.₂Is observed, but no peak (apex) exists in the temperature region of 150 to 250 ° C.
[0054]
(C) Lithium secondary battery
The Sb surface-modified lithium nickel composite oxide of the present invention is used as a positive electrode active material of a lithium secondary battery. A lithium secondary battery generally has a battery element having a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte, and a case for housing the battery element.
(C-1) Positive electrode, positive electrode active material, and positive electrode material
The positive electrode usually has a positive electrode material layer formed on a current collector, and the positive electrode material layer is composed of a positive electrode material. The positive electrode material contains a positive electrode active material capable of inserting and extracting Li, a binder and a conductive material described below.
In the present invention, an Sb surface-modified lithium nickel composite oxide is used as the positive electrode active material. Lithium-nickel composite oxide has the advantage of increasing the current capacity per unit weight, but has poor thermal stability and has the problem that the impedance of the lithium secondary battery increases during high-temperature storage or high-temperature cycle operation. . In the present invention, the increase in the impedance can be suppressed by modifying the surface of the lithium nickel composite oxide with the Sb compound.
[0055]
The positive electrode material for a lithium secondary battery of the present invention and the Sb surface-modified lithium nickel composite oxide used for the lithium secondary battery are as described in (B) above.
As the positive electrode active material, the Sb surface-modified lithium nickel composite oxide may be used alone, or may be used in combination with another lithium transition metal composite oxide. As such a lithium transition metal composite oxide, a lithium cobalt composite oxide can be given. The lithium-cobalt composite oxide is an oxide containing at least lithium and cobalt. Lithium-cobalt composite oxide is a useful cathode material having a flat discharge curve and excellent rate characteristics. Examples of the lithium-cobalt composite oxide include LiCoO having a layered structure.₂And the like. The lithium-cobalt composite oxide may be one obtained by substituting some of the sites occupied by Co with an element other than Co. Replacing the Co site with another element may improve the cycle characteristics and rate characteristics of the battery. When a part of the site occupied by Co is replaced with an element other than Co, examples of the replacement element include Ti, Al, Ti, V, Mn, Li, Ni, Cu, Zn, Mg, Ga, Sb, and Ge. And preferably Ti, Al, Li, Ni, Mg, Ga, Sb, and Ge, and more preferably Ti, Al, and Mg. Note that the Co site may be substituted with two or more kinds of other elements.
[0056]
When the Co site is substituted by a substitution element, the proportion is usually 0.03 mol% or more of the Co element, preferably 0.05 mol% or more, and usually 30 mol% or less of the Co element, preferably 20 mol% or less. It is. If the substitution ratio is too small, the stability of the crystal structure may not be sufficiently improved. If the substitution ratio is too large, the capacity of the battery may decrease.
[0057]
Lithium-cobalt composite oxide usually has LiCoOO as a basic composition before charging.₂However, as described above, a part of the Co site may be replaced with another element. In the above composition formula, a small amount of oxygen deficiency or indefiniteness may be present, and a part of oxygen sites may be substituted with sulfur or a halogen element. Further, in the above composition formula, the amount of lithium can be excessive or insufficient.
[0058]
The specific surface area of the lithium cobalt composite oxide is usually 0.01 m²/ G or more, preferably 0.1 m²/ G or more, more preferably 0.4 m²/ G or more and usually 10 m²/ G or less, preferably 5.0 m²/ G or less, more preferably 2.0 m²/ G or less. If the specific surface area is too small, the rate characteristics and the capacity will be reduced. If the specific surface area is too large, undesired reactions with the electrolyte and the like will be caused, and the cycle characteristics may be reduced. The measurement of the specific surface area follows the BET method.
[0059]
The average secondary particle size of the lithium-cobalt composite oxide is usually 0.1 μm or more, preferably 0.2 μm or more, more preferably 0.3 μm or more, most preferably 0.5 μm or more, and usually 300 μm or less, preferably It is 100 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. If the average secondary particle size is too small, the cycle deterioration of the battery may increase, or a problem may occur in safety. If the average secondary particle size is too large, the internal resistance of the battery may increase, making it difficult to output.
[0060]
Examples of the positive electrode active material that can be used in combination with the lithium nickel composite oxide in addition to the lithium cobalt composite oxide include transition metal oxides, various lithium transition metal composite oxides other than the above lithium cobalt composite oxide, and various transition metal sulfides. Inorganic compounds can be mentioned. Here, Fe, Mn, or the like is used as the transition metal. Specifically, MnO, V₂O₅, V₆O₁₃, TiO₂Transition metal oxide powder such as, composite oxide powder of lithium and transition metal such as lithium manganese composite oxide, TiS₂, FeS, MoS₂And transition metal sulfide powders such as. These compounds may be partially substituted with elements in order to improve their properties. Organic compounds such as polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, and N-fluoropyridinium salts can also be used in combination. Naturally, these inorganic compounds and organic compounds may be mixed and used in combination. The particle size of the active material of these positive electrodes is usually 1 to 30 μm, preferably 1 to 10 μm. If the particle size is too large or too small, battery characteristics such as rate characteristics and cycle characteristics tend to decrease.
[0061]
(C-2) Negative electrode, negative electrode active material
The negative electrode used in the lithium secondary battery of the present invention is usually formed by forming a negative electrode material layer on a current collector, and in the negative electrode material layer, a negative electrode active material capable of inserting and extracting Li is usually used. contains.
Examples of the negative electrode active material include a carbon-based active material. Examples of the carbon-based active material include graphite and coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke, and phenolic resin. And carbonized materials such as crystalline cellulose, and carbon materials partially graphitized thereof, furnace black, acetylene black, pitch-based carbon fibers, and the like. These carbon-based active materials can also be used in the form of a mixture with a metal, a salt thereof, or an oxide, or a coating. In addition to the carbon-based active material, examples of the negative electrode active material include oxides such as silicon, tin, zinc, manganese, iron, and nickel, and sulfates, and lithium metal, Li-Al, Li-Bi-Cd, and Li. A metal such as a lithium alloy such as —Sn—Cd, a lithium transition metal nitride, silicon, and tin can also be used. The particle size of these negative electrode active materials is usually 1 to 50 μm, preferably 5 to 30 μm. If it is too large or too small, the battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics tend to decrease. Of course, two or more negative electrode active materials selected from the above may be used in combination.
[0062]
(C-3) Common items of positive electrode and negative electrode
The positive electrode material layer and the negative electrode material layer may contain a binder in addition to the positive electrode active material and the negative electrode active material. In the case of a binder based on 100 parts by weight of the active material, it is usually at least 0.01 part by weight, preferably at least 0.1 part by weight, more preferably at least 1 part by weight, usually at most 50 parts by weight, preferably at most 30 parts by weight, furthermore Preferably it is 15 parts by weight or less. If the amount of the binder is too small, it is difficult to form a strong positive electrode. If the amount of the binder is too large, the energy density and the cycle characteristics may decrease.
[0063]
Examples of the binder include alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone. Polymers having a ring such as; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, polyacrylamide and other acrylic derivative-based polymers; Fluorinated resins such as polyvinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl acetate, polyvinyl alcohol Polyvinyl chloride, halogen-containing polymers such as polyvinylidene chloride; various resins such as a conductive polymer such as polyaniline can be used polyvinyl alcohol-based polymer. In addition, a mixture of the above-mentioned polymers and the like, a modified substance, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer and the like can also be used. Also, inorganic compounds such as silicate and glass can be used. In the present invention, it is preferable to use a fluorine-based resin such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene.
[0064]
The weight average molecular weight of the binder is usually at least 1,000, preferably at least 10,000, more preferably at least 20,000, usually at most 5,000,000, preferably at most 1,000,000, more preferably at most 300,000. If it is too low, the strength of the coating film decreases, which is not preferable. If it is too high, the viscosity becomes high and it becomes difficult to form an active material layer.
[0065]
In addition, the positive electrode material layer and the negative electrode material layer may contain additives that exhibit various functions such as a conductive material and a reinforcing material, a powder, a filler, and the like, as necessary. The conductive material is not particularly limited as long as it is capable of imparting conductivity by being mixed in an appropriate amount with the above-mentioned active material, but usually, acetylene black, carbon black, carbon powder such as graphite, various metal fibers, foil and the like Is mentioned. As the reinforcing material, various inorganic and organic spherical or fibrous fillers can be used.
[0066]
In the present invention, the positive electrode material layer preferably contains an organic acid or a lithium salt of an organic acid. By including an organic acid or a lithium salt of an organic acid in the positive electrode material layer, the thermal stability of the lithium nickel composite oxide is further improved.
The organic acid is not particularly limited, for example, acetic acid, propionic acid, stearic acid, glyoxylic acid, pyruvic acid, acetoacetic acid, levulinic acid, phenylacetic acid, benzoylpropionic acid, benzoic acid, oxalic acid, malonic acid Succinic acid, glutaric acid, adipic acid, maleic acid, phthalic acid, trimellitic acid, polyacrylic acid, polymethacrylic acid, tricarballylic acid, benzenetricarboxylic acid, and the like. Further, the lithium salt of the organic acid is not particularly limited, and examples thereof include the lithium salt of the organic acid.
[0067]
The organic acid is particularly preferably a divalent or higher valent organic acid. When the valence is two or more, the stability at the time of high-temperature storage is further improved. Examples of the divalent or higher valent organic acid include a divalent organic acid and a trivalent organic acid. Examples of the divalent organic acid include an aliphatic saturated dicarboxylic acid, an aliphatic unsaturated dicarboxylic acid, an aromatic dicarboxylic acid, and the like. Specific examples of the aliphatic saturated dicarboxylic acid include oxalic acid, malonic acid, succinic acid, and glutaric acid. Specific examples of the aliphatic unsaturated dicarboxylic acid include maleic acid. Specific compounds of the aromatic dicarboxylic acid include, for example, phthalic acid and the like. Examples of the trivalent organic acid include tricarballylic acid and benzenetricarboxylic acid.
[0068]
The lithium salt of an organic acid is also preferably a lithium salt of a divalent or higher valent organic acid, and examples thereof include the lithium salts of the above divalent and trivalent organic acids.
As the organic acid, oxalic acid and succinic acid are particularly preferably used, and oxalic acid is most preferably used. These organic acids have a small molecular size and a great effect of improving the stability at high temperatures. As the lithium salt of an organic acid, it is preferable to use a lithium salt of oxalic acid or succinic acid, and it is more preferable to use a lithium salt of oxalic acid for the same reason as the above organic acid. By using the organic acid and / or the lithium salt of the organic acid and further modifying the surface of the lithium-nickel composite oxide with an Sb compound, the thermal stability of the lithium secondary battery of the present invention in a high-temperature environment is dramatically increased. To improve.
[0069]
The organic acid and / or lithium salt of the organic acid is usually 0.1 part by weight or more, preferably 0.2 part by weight or more, more preferably 0.3 part by weight or more based on 100 parts by weight of the positive electrode material layer. On the other hand, it is usually at most 1.0 part by weight, preferably at most 0.8 part by weight, more preferably at most 0.6 part by weight. When the amount of addition is in this range, the charge / discharge characteristics of the lithium secondary battery can be kept good while improving the thermal stability when stored in a high-temperature environment.
[0070]
As a material of the current collector used for the positive electrode and the negative electrode, usually, metals such as aluminum, copper, nickel, tin, and stainless steel, alloys of these metals, and the like can be used. In this case, the current collector of the positive electrode is usually aluminum, and the current collector of the negative electrode is usually copper. The shape of the current collector is not particularly limited, and examples thereof include a plate shape and a mesh shape. The thickness of the current collector is usually 1 to 50 μm, preferably 1 to 30 μm. If the thickness is too small, the mechanical strength will be weak, but if it is too thick, the battery will be large, occupying a large space in the battery, and the energy density of the battery will be small.
[0071]
The thickness of each of the positive electrode and the negative electrode is usually 1 μm or more, preferably 10 μm or more, and usually 500 μm or less, preferably 200 μm or less. Battery performance such as capacity and rate characteristics tends to decrease even if it is too thick or too thin.
The method for producing the positive electrode and the negative electrode is not particularly limited. For example, a slurry in which a solvent contains a positive electrode material for a lithium secondary battery including an active material and a binder and a conductive material used as needed is used as a current collector. And dried. Further, for example, it can also be manufactured by kneading an active material and a positive electrode material for a lithium secondary battery such as a binder and a conductive material used as needed without using a solvent, and then pressing the mixture on a current collector.
[0072]
(C-4) Electrolyte
The electrolyte used in the lithium secondary battery of the present invention generally contains a solute and a non-aqueous solvent (in this specification, the solute and the non-aqueous solvent may be collectively referred to as an electrolyte or a non-aqueous electrolyte. is there.). Further, the electrolyte may contain a solute, a non-aqueous solvent and a polymer. By containing the polymer, the electrolyte becomes non-fluidized, the liquid retention is improved, and liquid leakage can be prevented, so that the safety during high-temperature storage can be improved.
[0073]
As the solute, any of conventionally known lithium salts can be used. For example, LiClO₄, LiAsF₆, LiPF₆, LiBF₄, LiB (C₆H₅)₄, CH₃SO₃Li, CF₃SO₃Li, LiN (SO₂CF₃)₂, LiN (SO₂C₂F₅)₂, LiC (SO₂CF₃)₃, LiSbF₆And LiSCN, and at least one of these can be used. Among these, from the point that the effect of the present invention becomes remarkable, LiClO₄, LiPF₆Is particularly preferred. The content of these solutes in the nonaqueous electrolyte is usually 0.5 to 2.5 mol / l.
[0074]
Examples of the non-aqueous solvent include, for example, cyclic carbonates such as ethylene carbonate, propylene carbonate and vinylene carbonate, non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, and dimethoxy. One or a mixture of two or more of ethers such as ethane, lactones such as γ-butyl lactone, and nitriles such as acetonitrile can be mentioned. Among these, one or a mixed solution of two or more selected from cyclic carbonates, acyclic carbonates, and lactones is preferable.
[0075]
From the viewpoint of ensuring the stability of the electrolyte during high-temperature storage, in the present invention, it is more preferable that the non-aqueous solvent contains a high-boiling solvent having a boiling point of 150 ° C. or more at 20 ° C./1 atm. The high-boiling solvent generally refers to a solvent having a boiling point in the range of 150 ° C to 300 ° C, preferably a boiling point of 180 ° C to 270 ° C, more preferably a boiling point in the range of 200 ° C to 250 ° C. A certain solvent. By using a solvent having a boiling point in the above range, the thermal stability of the battery during high-temperature storage can be more reliably improved. Examples of such a solvent include ethylene carbonate (boiling point: 243 ° C.), propylene carbonate (boiling point: 240 ° C.), γ-butyrolactone (boiling point: 204 ° C.), and the like. These high-boiling solvents may be used alone or in combination of two or more, and further used in combination with a low-boiling solvent (in the present invention, a solvent having a boiling point of 150 ° C. or lower). May be. Here, "the boiling point at 20 ° C./1 atm. Is not lower than X ° C." means that the vapor pressure does not exceed 1 atm even when heating from 20 ° C. to X ° C. under 1 atm.
[0076]
The non-aqueous electrolyte may further contain an additive for ensuring safety and battery characteristics (for example, cycle characteristics), in addition to the solute and the non-aqueous solvent.
The polymer contained in the electrolyte is not particularly limited as long as it can secure the liquid retaining property of the electrolyte to some extent, and examples thereof include an acrylic polymer such as polymethyl methacrylate and an alkylene oxide having an alkylene oxide unit. And a fluorine-based polymer such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymer. Among these polymers, from the viewpoint of sufficiently securing the liquid retaining property of the electrolyte, the polymer has a bond (cross-linking) formed so as to bridge between any two atoms of molecules consisting of chain-bonded atoms. It is preferable to use a polymer (this is referred to as “crosslinkable polymer” in the present specification).
[0077]
Examples of the material serving as the basic skeleton of the crosslinkable polymer include, for example, those produced by polycondensation of polyester, polyamide, polycarbonate, and polyimide; those produced by polyaddition such as polyurethane and polyurea; and polymethyl methacrylate. And those produced by addition polymerization such as acrylic polymers and polyvinyl polymers such as polyvinyl acetate and polyvinyl chloride.
[0078]
In the present invention, since it is preferable to polymerize after impregnating the spacers (details will be described later), it is preferable to use a polymer produced by addition polymerization, which can easily control the polymerization and does not generate by-products during the polymerization. Is desirable. Examples of such a polymer include an acrylic polymer. Acrylic polymers are preferable materials in terms of battery characteristics such as battery capacity, rate characteristics, and mechanical strength.
[0079]
As the acrylic polymer, a polymer obtained by polymerizing a monomer having an acryloyl group is particularly preferable. Examples of the monomer having an acryloyl group include, for example, methyl acrylate, ethyl acrylate, butyl acrylate, acrylamide, 2-ethoxyethyl acrylate, diethylene glycol ethyl ether acrylate, polyethylene glycol alkyl ether acrylate, polypropylene glycol alkyl ether acrylate, and 2-cyanoethyl. Monoacrylates such as acrylates; alkanes such as 1,2-butanediol diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, neopentanediol diacrylate, and 1,6-hexanediol diacrylate Diol diacrylates; ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene Polyethylene glycol diacrylates such as recol diacrylate and tetraethylene glycol diacrylate; polypropylene glycol diacrylates such as propylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, and tetrapropylene glycol diacrylate; bisphenol F ethoxy Rate diacrylate, bisphenol F ethoxylate dimethacrylate, bisphenol A ethoxylate diacrylate, trimethylolpropane triacrylate, trimethylolpropane ethoxylate triacrylate, trimethylolpropane propoxylate triacrylate, isocyanuric acid ethoxylate triacrylate, glycerol eth Shi triacrylate, glycerol propoxylate triacrylate, pentaerythritol ethoxylate tetraacrylate, ditrimethylolpropane ethoxylate tung tetraacrylate, and di pentaerythritol ethoxylate hexaacrylate.
[0080]
Among these, a polyacrylate polymer having an ethylene glycol unit is particularly preferable from the viewpoint of lithium ion conductivity.
In the present invention, a copolymer of the above monomer component and another monomer component can be used as the acrylic polymer. That is, polymerization may be carried out in the presence of a monomer having another structure in addition to the above-mentioned monomer as a monomer component. In particular, when a monomer having a group having an unsaturated double bond such as a methacryloyl group, a vinyl group, or an allyl group coexists, the strength and liquid retention of the electrolyte may be improved. As such a monomer, compounds such as methyl methacrylate, methacrylamide, butadiene, acrylonitrile, styrene, vinyl acetate, and vinyl chloride can be used.
[0081]
When the acrylic polymer is used, the abundance of the monomer having an acryloyl group with respect to all the monomers is not particularly limited, but is usually 50% by weight or more, preferably 70% by weight or more, and particularly preferably 80% by weight or more. A higher abundance is advantageous in that the polymerization rate is higher and the productivity of the electrolyte can be increased.
The crosslinkable polymer has a crosslink. The cross-linking can be produced by causing a cross-linking reaction between polymers with a cross-linking agent. Further, the polymer can be produced by using a monomer having a plurality of reaction points (hereinafter, sometimes referred to as a “polyfunctional monomer”) as a raw material of the polymer. The latter method is preferred.
[0082]
In the case of producing a crosslinkable polymer by the latter method, a monomer having one reaction point (hereinafter, sometimes referred to as a “monofunctional monomer”) can be used as a raw material in addition to the polyfunctional monomer. When a polyfunctional monomer and a monofunctional monomer are used in combination, the equivalent ratio of the functional groups of the polyfunctional monomer is usually at least 10%, preferably at least 15%, more preferably at least 20%.
[0083]
The most preferred method for producing a crosslinkable polymer is a method in which a polyfunctional monomer having a plurality of acryloyl groups is polymerized, if necessary, with a monofunctional monomer having one acryloyl group.
The content of the polymer contained in the electrolyte is usually 80% by weight or less, preferably 50% by weight or less, more preferably 20% by weight or less based on the total weight of the electrolyte. If the polymer content is too large, the ionic conductivity tends to decrease due to a decrease in the concentration of the non-aqueous electrolyte, and battery characteristics such as rate characteristics tend to decrease. On the other hand, if the proportion of the polymer is too small, gel formation becomes difficult, the retention of the non-aqueous solvent is reduced, and not only flow and liquid leakage may occur, but also the safety of the battery may not be ensured. Therefore, the content of the polymer with respect to the electrolyte is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 2% by weight or more, and most preferably 5% by weight or more.
[0084]
The ratio of the polymer to the non-aqueous solvent is appropriately selected according to the molecular weight of the polymer, but is usually 0.1% by weight or more, preferably 1% by weight or more, usually 50% by weight or less, preferably 30% by weight or less. . If the proportion of the polymer is too small, it is difficult to form a gel, the retention of the non-aqueous electrolyte is reduced, and problems of flow and liquid leakage tend to occur. When the proportion of the polymer is too large, the viscosity becomes too high to make handling difficult, and the ionic conductivity tends to decrease due to the decrease in the concentration of the non-aqueous electrolyte, and battery characteristics such as rate characteristics tend to deteriorate.
[0085]
In the present invention, it is preferable to use a method of forming a polymer by filling a gap of a spacer (details will be described later) with the electrolyte containing a monomer that is a raw material of the polymer, and then polymerizing the monomer. .
As a method of polymerizing these monomers, for example, a method using heat, ultraviolet rays, an electron beam and the like can be mentioned, but in the present invention, the monomers may be polymerized by heating or irradiation with ultraviolet rays from the ease of production. preferable. In the case of heat polymerization, a heat-initiated polymerization initiator can be added to the electrolyte to be impregnated in order to make the reaction proceed effectively. Usable thermal polymerization initiators include azo compounds such as azobisisobutyronitrile and dimethyl 2,2'-azobisinbutyrate, benzoyl peroxide, cumene hydroperoxide, t-butylperoxy-2-ethylhexano. Peroxides such as ate can be used, and those which are preferable in terms of reactivity, polarity, safety and the like may be used alone or in combination. In order to obtain a polymer, usually at least 30% of all functional groups of the monomer are reacted, preferably at least 40%, more preferably at least 50%.
[0086]
(C-5) Spacer
The electrolyte is preferably impregnated in a positive electrode, a negative electrode, and a spacer that may be disposed between the positive electrode and the negative electrode, in order to improve ion conductivity by lithium ions.
The spacer is usually used to prevent a short circuit between the positive electrode and the negative electrode. The spacer usually consists of a porous membrane. Examples of the material used as the spacer include, for example, polyolefins such as polyethylene and polypropylene, and polyolefins in which some or all of these hydrogen atoms have been replaced with fluorine atoms, polyacrylonitrile, and a porous film of a resin such as polyaramid. No. From the viewpoint of chemical stability with respect to the electrolyte and stability with respect to the applied voltage, preferably, polyolefin or fluorine-substituted polyolefin, specifically, polyethylene or polypropylene, a part of these hydrogen atoms Or those in which all are substituted by fluorine atoms can be mentioned. Among these, particularly preferred are polyolefins such as polyethylene and polypropylene, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride, and most preferred are polyolefins such as polyethylene and polypropylene. Of course, these copolymers and mixtures can also be used.
[0087]
The number average molecular weight of the resin used as a raw material for the spacer is usually 10,000 or more, preferably 100,000 or more, and is usually 10,000,000 or less, preferably 3,000,000 or less. If the molecular weight is too small, the mechanical strength becomes insufficient, and the short circuit of the electrode tends to occur. On the other hand, if the molecular weight is too large, it tends to be difficult to impregnate the electrolyte into the pores of the porous membrane, which tends to reduce the production efficiency of the battery and the battery performance such as rate characteristics. Further, when the molecular weight is too large, it may be difficult to form a film by a method of mixing a plasticizer described below and then stretching.
[0088]
As mentioned above, usually, the spacer is a porous membrane. Examples of the porous film include a porous stretched film and a nonwoven fabric, and in the present invention, a stretched film produced by stretching is more preferable. The porous stretched film has a more uniform resistance in the film than the nonwoven fabric, so that local deposition of lithium, that is, precipitation of dendrite that causes a short circuit between electrodes can be suppressed.
[0089]
The stretching of the porous stretched film may be either uniaxial or biaxial stretching, but it is preferable to use biaxial stretching. When the film is biaxially stretched, the film has a good balance of mechanical strength in the vertical and horizontal directions, so that handling in battery production becomes easy.
The porosity of the spacer is usually at least 30%, preferably at least 35%, usually at most 80%, preferably at most 75%, more preferably at most 72%. If the porosity is too small, the film resistance increases and the rate characteristics deteriorate. In particular, the capacity when used at a high rate is reduced. On the other hand, if the porosity is too large, the mechanical strength of the film is reduced, so that a short circuit is likely to occur when the shape of the battery element changes. In the present invention, the larger the porosity, the greater the effect of using the crosslinkable polymer to retain the electrolyte, and thus the higher the safety and stability during high-temperature storage.
[0090]
The average pore diameter of the pores present in the spacer is usually 1.0 μm or less, preferably 0.2 μm or less, more preferably 0.18 μm or less, most preferably 0.15 μm or less, and usually 0.01 μm or more, preferably Is 0.07 μm or more. If the pore size is too large, a short circuit is likely to occur, while if the pore size is too small, the membrane resistance tends to increase and the battery performance such as rate characteristics tends to decrease. In the present invention, the larger the average pore diameter, the greater the effect of the electrolyte in retaining the liquid by the use of the crosslinkable polymer, and thus the higher the safety and stability during high-temperature storage.
[0091]
The thickness of the spacer is usually 5 μm or more, preferably 7 μm or more, usually 50 μm or less, preferably 28 μm or less, more preferably 25 μm or less, and most preferably 20 μm or less. If the film thickness is too small, self-discharge easily occurs due to the mild short phenomenon. If the film thickness is too large, not only battery characteristics such as rate characteristics become insufficient, but also volume energy density tends to decrease. In the present invention, when a crosslinkable polymer is used when the thickness of the spacer is small, self-discharge is effectively prevented.
[0092]
The spacer can be manufactured, for example, as follows. A resin having a number average molecular weight of about 100,000 to 10,000,000, preferably 100,000 to 3,000,000 is mixed with a plasticizer as a heterogeneous dispersion medium, kneaded, and then formed into a sheet. Further, a desired spacer can be obtained by passing through a step of extracting a plasticizer with a solvent and a step of stretching in a longitudinal or transverse direction at a predetermined magnification or both.
[0093]
(C-6) Unit battery element, battery element, and case
The lithium secondary battery of the present invention usually has a battery element housed in a case. The battery element is usually formed on the basis of a unit battery element composed of a positive electrode and a negative electrode mainly composed of an active material, and an electrolyte. It is formed by laminating a plurality of the unit battery elements formed in a flat shape. That is, as the form of the battery element, for example, a flat plate stacked type in which a plurality of flat unit battery elements are stacked, a flat wound type in which a long unit battery element is wound into a flat shape, Further, a cylindrical wound type in which a long unit battery element is wound in a cylindrical shape can be used. In the present invention, the form of the battery element is preferably a flat wound type or a flat plate laminated type from the viewpoint that productivity and miniaturization are possible.
[0094]
In the lithium secondary battery of the present invention, examples of the case for housing the battery element include a metal case made of SUS (stainless steel) or the like and a case having shape changeability. The metal case has the advantage of being able to sufficiently secure the safety of the lithium secondary battery due to its high rigidity, but has the disadvantage that it is not suitable for batteries of portable electric devices due to its heavy weight. There is a point. On the other hand, a case having a variable shape made of a laminated film or the like has an advantage that the case can be reduced in weight because the thickness of the case is thin, but has a disadvantage that the rigidity is low and the impact resistance of the lithium secondary battery is inferior. There is a point. That is, the type of the above case may be selected depending on the use in which the lithium secondary battery is used.
[0095]
As described above, when a lithium secondary battery is used as a power source of a portable electric device, a case having shape variability is preferably used. As the material of the shape-variable case, metals such as aluminum, nickel-plated iron and copper, and synthetic resins can be used. Preferably, it is a laminate film provided with a gas barrier layer and a resin layer, particularly a laminate film in which resin layers are provided on both surfaces of the gas barrier layer. Such a laminated film has high gas barrier properties, high shape variability, and thinness. As a result, the thickness and weight of the exterior material can be reduced, and the capacity of the battery as a whole can be improved.
[0096]
As the material of the gas barrier layer used for the laminate film, use metals such as aluminum, iron, copper, nickel, titanium, molybdenum, and gold, alloys such as stainless steel and Hastelloy, and metal oxides such as silicon oxide and aluminum oxide. Can be. Preferably, aluminum is lightweight and excellent in workability.
As the resin used for the resin layer, various synthetic resins such as thermoplastics, thermoplastic elastomers, thermosetting resins, and plastic alloys can be used. These resins include those in which a filler such as a filler is mixed.
[0097]
The thickness of the shape-variable case is generally 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.05 μm or more, and usually 1 mm or less, preferably 0.5 mm or less, more preferably 0.3 mm or less. , More preferably 0.2 mm or less, most preferably 0.15 mm or less. The thinner the battery, the smaller and lighter the battery can be.However, if the battery is too thin, not only does the risk of rupture of the case due to gas generation during high-temperature storage increase, but it also becomes impossible to provide sufficient rigidity or the sealing performance decreases. There is a possibility.
[0098]
The total thickness of the lithium secondary battery in which the battery element is housed in the case is usually 5 mm or less, preferably 4.5 mm or less, and more preferably 4 mm or less. The effect of the present invention is particularly great for such a thin lithium secondary battery. However, an extremely thin battery usually has a capacity of 0.5 mm or more, preferably 1 mm or more, and more preferably 2 mm or more, because the capacity is too small or the production is difficult.
[0099]
In addition, for convenience such as mounting the battery to the device, the battery element is sealed in a variable shape case and molded into a preferable shape, and then, if necessary, the plurality of lithium secondary batteries are formed into an outer case having more rigidity. It is also possible to store.
(C-7) Applications of lithium secondary batteries
Examples of the electric device in which the lithium secondary battery of the present invention is used as a power supply include, for example, a portable personal computer (in the present specification, the personal computer may be simply referred to as a personal computer), a pen input personal computer, a mobile personal computer, E-book player, mobile phone, cordless phone handset, pager, handy terminal, mobile fax, mobile copy, mobile printer, headphone stereo, video movie, LCD TV, handy cleaner, portable CD, minidisc, electric shaver, transceiver, electronic Notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting fixtures, toys, game machines, road conditioners, clocks, strobes, cameras, medical equipment (pacemakers) Car, hearing aids, massaging machines, etc.), and the like. Further, the lithium secondary battery of the present invention can be used as a power source for an electric vehicle.
[0100]
As described above, the present invention has been described in detail, but the present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.
[0101]
【Example】
Hereinafter, examples using the surface-modified lithium nickel composite oxide of the present invention for a lithium secondary battery will be described. However, these are merely examples, and it is needless to say that the present invention is not limited to these examples.
(1) Production of positive electrode agent
[Production of positive electrode agent 1]
LiNi composite oxide having a primary particle size of 1 μm: LiNi_0.82Co_0.15Al_0.03O₂Was used to react an Sb compound with this material to produce an Sb surface-modified lithium nickel composite oxide.
[0102]
Specifically, the Sb compound was weighed into a 300 ml beaker, and about 50 ml of acetone was added and stirred to disperse. Then, the acetone was evaporated while adding and stirring the lithium nickel composite oxide. Finally, it was heated in an oven at 120 ° C. to completely dry it. Since the mixture of the dried Sb compound and the lithium-nickel composite oxide was agglomerated, the mixture was lightly broken with a spoon to make a powder. The obtained mixed powder was placed in an alumina baking dish and calcined in an oxygen stream at 700 ° C. for 4 hours to obtain an Sb surface-modified lithium nickel composite oxide.
[0103]
The Sb compound used in the production of the positive electrode material 1 was Sb having an average primary particle size of 0.02 μm.₂O₃(PATOX-U manufactured by Nippon Seiko Co., Ltd.), and the Sb compound was added to the lithium-nickel composite oxide in an amount of 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 3. 5 and 7 mol% were added, respectively.
The Sb thus obtained₂O₃Are called as shown in Table-1.
[0104]
[Table 1]

[0105]
[Production of positive electrode agent 2]
In the production of the positive electrode material 1, LiNi having a primary particle size of 1 μm is used as the lithium nickel composite oxide._0.8Co_0.2O₂And LiNi_0.7Co_0.2Mn_0.1O₂And Sb₂O₃Positive electrode material 2 was produced in the same manner as positive electrode material 1 except that the amount of was charged to 1 mol% based on the lithium nickel composite oxide.
[0106]
Of the positive electrode agent 2 thus obtained, LiNi was used as a lithium nickel composite oxide._0.8Co_0.2O₂Is used as the positive electrode agent 2a, and LiNi_0.7Co_0.2Mn_0.1O₂Was used as positive electrode agent 2b.
[Production of positive electrode agent 3]
In the production of the positive electrode material 1, the same procedure as in the positive electrode material 1 was carried out except that triphenylantimony was used as the Sb compound and the amount of triphenylantimony was 0.5 mol% based on the lithium nickel composite oxide. A positive electrode agent 3 was produced. [Production of positive electrode agent 4]
In the production of the positive electrode agent 1, Sb having an average primary particle size of 0.02 μm₂O₃(Nippon Seiko Co., Ltd., PATOX-U), Sb having an average primary particle size of 0.5 μm₂O₃(Nippon Seiko Co., Ltd., PATOX-M), Sb having an average primary particle diameter of 1 μm₂O₃(PATOX-C manufactured by Nippon Seiko Co., Ltd.), Sb having an average primary particle size of 3 μm₂O₃(PATOX-P manufactured by Nippon Seiko Co., Ltd.), Sb having an average primary particle size of 8 μm₂O₃(PATOX-L manufactured by Nippon Seimitsu Co., Ltd.) was pulverized as necessary, and the primary particle diameters were 0.004 μm, 0.008 μm, 0.02 μm, 0.5 μm, 1.6 μm, and 3.2 μm, respectively. Sb of 5 μm and 8 μm₂O₃Is an Sb compound, and Sb₂O₃Positive electrode material 4 was produced in the same manner as positive electrode material 1 except that the amount of was charged to 1 mol% with respect to the lithium nickel composite oxide.
[0107]
Among the positive electrode agents 4 thus obtained, Sb with different primary particle diameters₂O₃Are referred to as shown in Table-2.
[0108]
[Table 2]

[0109]
[Production of positive electrode agent 5]
In the production of the positive electrode agent 1, the Sb compound was triphenylantimony, the amount of triphenylantimony charged was 0.5 mol based on the lithium nickel composite oxide, and the powdery lithium nickel composite oxide was charged. Except that the fired dish and the fired dish containing powdered triphenylantimony were each placed in the same furnace and heated in an oxygen stream to vaporize the triphenylantimony and react with the lithium nickel composite oxide. The positive electrode 5 was produced in the same manner as in the production of the positive electrode agent 1.
[Production of positive electrode agent 6]
In the production of the positive electrode agent 1, Sb₂O₃The positive electrode material 6 was produced in the same manner as the production of the positive electrode material 1 except that the charged amount of lithium was 1.0 mol% with respect to the lithium-nickel composite oxide, and that firing was performed at 600 ° C. and 700 ° C., respectively. did.
[0110]
Of the positive electrode agents 6 thus obtained, those having a firing temperature of 600 ° C. were referred to as positive electrode agents 6a, and those having a firing temperature of 700 ° C. were referred to as positive electrode agents 6b.
[Positive electrode agent 1 ', positive electrode agent 2a', positive electrode agent 2b ']
LiNi composite oxide having a primary particle size of 0.6 to 0.8 μm used in the production of the positive electrode agent 1: LiNi_0.82Co_0.15Al_0.03O₂Is referred to as positive electrode agent 1 '.
[0111]
LiNi having a primary particle size of 0.5 to 1 μm used in the production of the positive electrode agent 2_0.8Co_0.2O₂And LiNi_0.7Co_0.2Mn_0.1O₂Are referred to as positive electrode agent 2a 'and positive electrode agent 2b', respectively.
That is, the positive electrode agents 1 ', 2a', and 2b 'are untreated lithium nickel composite oxides that have not been treated with the Sb compound.
(2) Manufacture of positive electrode
[Manufacture of positive electrode 1]
Positive electrode 1 was manufactured using positive electrode agents 1 to 6 and positive electrode agents 1 ', 2a', and 2b 'obtained as described above. The method is described below.
[0112]
First, the following composition was kneaded with a planetary mixer type kneader for 2 hours to produce a positive electrode paint.
[0113]
[Table 3]
Sb surface modified lithium nickel composite oxide or untreated lithium nickel composite
Compound oxide 85 parts by weight
Acetylene black 10 parts by weight
5 parts by weight of polyvinylidene fluoride
N-methyl-2-pyrrolidone 80 parts by weight
Next, the above-mentioned positive electrode paint is applied on an aluminum current collector base material having a thickness of 15 μm by extrusion die coating and dried to produce a positive electrode material layer in which the active material is bound on the current collector by a binder. did. Next, an electrode sheet was manufactured by compacting using a roll press (calender). Thereafter, an electrode was cut out from the electrode sheet to obtain a positive electrode 1.
[Production of positive electrode 2]
Positive electrode 2 was manufactured using positive electrode agents 1 to 6 and positive electrode agents 1 ', 2a', and 2b 'obtained as described above. The method is described below.
[0114]
First, the following composition was kneaded with a planetary mixer type kneader for 2 hours to produce a positive electrode paint.
[0115]
[Table 4]
Sb surface modified lithium nickel composite oxide or untreated lithium nickel composite
Composite oxide 45 parts by weight
Lithium cobalt composite oxide (LiCoO₂) 45 parts by weight
Acetylene black 5 parts by weight
Polyvinylidene fluoride 5 parts by weight
N-methyl-2-pyrrolidone 80 parts by weight
Next, the above-mentioned positive electrode paint 1 is applied on an aluminum current collector base material having a thickness of 15 μm by extrusion die coating, and dried, to form a positive electrode material layer in which an active material is bound on the current collector by a binder. Manufactured. Next, an electrode sheet was manufactured by compacting using a roll press (calender). Thereafter, an electrode was cut out from the electrode sheet to obtain a positive electrode 2.
(3) Production of negative electrode
[Production of negative electrode]
First, the following composition was kneaded for 2 hours with a planetary mixer type kneader to obtain a negative electrode paint.
[0116]
[Table 5]
Graphite (particle size 15μm) 90 parts
Polyvinylidene fluoride 10 parts
N-methyl-2-pyrrolidone 100 parts
Next, the negative electrode paint was applied on a 20 μm-thick copper current collector substrate by extrusion die coating, and dried to produce a negative electrode material layer in which the active material was bound on the current collector by a binder. . Subsequently, the electrode sheet was produced by compacting using a roll press (calender). Thereafter, the electrode was cut out from the electrode sheet to obtain a negative electrode.
[Positive electrode / negative electrode material ratio]
In the manufacture of the positive electrode 1, the positive electrode 2, and the negative electrode, the thicknesses of the positive electrode material layer and the negative electrode material layer were adjusted such that (charge capacity of the positive electrode) / (charge capacity of the negative electrode) = 0.93. . Here, the charge capacity of the negative electrode was based on the capacity per unit volume of the negative electrode (mAh / g) when charged to 1.5 V to 3 mV using the counter electrode Li.
(4) Production of electrolyte
[Manufacture of paint 1 for forming electrolyte layer]
In the case of producing a lithium secondary battery containing a polymer in the electrolyte, the following composition was mixed and stirred to produce a paint 1 for forming an electrolyte layer.
[0117]
[Table 6]
1M concentration of LiPF₆Ethylene carbonate containing lithium as a lithium salt and
And propylene carbonate mixed solution (volume ratio; ethylene carbonate:
Ropylene carbonate = 1: 1) 925 parts
Tetraethylene glycol diacrylate 44 parts
Polyethylene oxide triacrylate 22 parts
Polymerization initiator 2 parts
Additive (succinic anhydride) 9 parts
[Production of electrolyte solution 1]
1M concentration of LiPF₆Was dissolved as a lithium salt, and a mixed solution (volume ratio EC: DMC: EMC = 30: 35: 35) of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) was used as electrolyte 1.
[Production of electrolyte solution 2]
1M concentration of LiPF₆Was dissolved as a lithium salt, and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC: DEC = 50: 50) was used as an electrolytic solution 2.
(5) Production of lithium secondary battery
[Manufacture of liquid lithium secondary batteries 1 and 2]
The positive electrode 1 and the negative electrode prepared as described above are laminated via a polymer porous film separator, and a lead wire for extracting current is connected to each of the electrode terminals of the positive electrode and the negative electrode. Manufactured.
[0118]
After the thus obtained battery laminate is housed in a bag-shaped case in which a laminate film in which both surfaces of an aluminum film are covered with a resin layer is molded oppositely, electrolyte solution 1 or 2 is injected, and the electrolyte solution is used as a positive electrode, a negative electrode, and a separator. Was impregnated.
The electrode terminals are sandwiched between two polyethylene tapes (to prevent short-circuiting of the terminals), sealed with a reduced-pressure seal, and the seal excluding the side from which the lead wire is taken out is bent along the side of the battery exterior material did. The bent seal portion was adhered to the side surface of the outer package member with a commercially available epoxy adhesive. In this way, of the flat liquid lithium secondary batteries manufactured in this manner, the lithium secondary battery using the electrolytic solution 1 was used as the liquid lithium secondary battery 1 and the lithium secondary battery using the electrolytic solution 2 was used as the liquid. The lithium secondary battery 2 was used.
[Manufacture of polymer lithium secondary battery 1]
The coating material 1 for forming the electrolyte layer prepared as described above is applied to the positive electrode 2 and the negative electrode prepared as described above, and separately immersed in the coating material 1 for forming the electrolyte layer (spacer). Is prepared and sandwiched between the positive electrode 2 and the negative electrode, and then heated at 90 ° C. for 10 minutes to polymerize the tetraethylene glycol diacrylate and the polyethylene oxide triacrylate in the paint for forming the electrolyte layer. I let it. This produced a flat unit battery element having a positive electrode, a negative electrode formed on a current collector containing an active material and a binder, and having a non-fluidized electrolyte layer between the positive electrode and the negative electrode. . The electrolyte containing the polymer thus obtained is referred to as polymer electrolyte 1.
Next, after connecting a lead wire for extracting current to each of the electrode terminals of the positive electrode and the negative electrode of the unit battery element, this is housed in a bag-shaped case in which a laminate film in which both surfaces of an aluminum film are covered with a resin layer is opposedly formed. did. Thereafter, the electrode terminal portion is sandwiched between two polyethylene tapes (to prevent short-circuiting of the terminal portion), the laminated film is sealed with a vacuum seal, and the seal portion excluding the side from which the lead wire is taken out is along the side of the battery exterior material. Folded. The folded seal portion was adhered to the side surface of the outer packaging material enclosing portion with a commercially available epoxy adhesive to produce a flat polymer lithium secondary battery 1.
(6) XPS analysis
For the positive electrode agents 1c and 1e, which are Sb surface-modified lithium nickel composite oxides whose surfaces were modified with Sb, XPS analysis was performed on each of the positive electrode agents in order to measure the Sb concentration on the surface. The measuring method is described below.
[0119]
A double-sided tape was attached to a metal plate, and the positive electrode agent 1c or 1e in a powder state was sprinkled on the metal plate so that the tape could not be seen.
As an XPS measuring apparatus, ESCA-5500MC manufactured by Physical @ Electronics was used. Using a monochromatic Al-Kα ray (14 kV, 150 W) as a light source for measurement, measurement was performed on each element of Ni2p, Co2p, Al2s, and Sb3d3 / 2 under the following conditions. At the time of measurement, an electron neutralizing gun was used for charge correction.
[0120]
PassEnergy: 29.35 eV
Data acquisition interval: 0.125 eV / step
Measurement area: 0.8mm diameter
Extraction angle: 45 degrees
With respect to the obtained measurement peaks of the respective measurement elements, a start point and an end point were determined, and the start point and the end point were connected by the Shirley method. Then, the area surrounded by the line connecting the start point and the end point and the peak was determined for each measurement element, and this was defined as the peak area of each measurement element. FIG. 1 shows a measurement example of Sb3d3 / 2. In FIG. 1, the starting point 1 is located at a portion where the low energy side of the binding energy in the Sb3d3 / 2 peak is completely flat, and the ending point 2 is where the high energy side peak is completely flat. Taken in pieces. The starting point and the ending point thus determined were connected by the baseline 3 using the Shirley method, and the area surrounded by the baseline and the peak was defined as the peak area of Sb3d3 / 2. Table 3 shows the peak areas of the respective measurement elements of the positive electrode agents 1c and 1e thus determined.
[0121]
Next, using the relative sensitivity correction coefficient determined for each of the measurement elements, the peak area of each of the measurement elements is divided by the relative sensitivity correction factor of each of the elements to determine the corrected peak area of each of the measurement elements. Was. Table 3 shows the corrected peak areas of the respective measurement elements of the positive electrode agents 1c and 1e thus obtained. In addition, the relative sensitivity correction coefficient of each measurement element in the XPS measuring apparatus (ESCA-5500MC manufactured by Physical @ Electronics) used for the measurement is as follows.
[0122]
[Table 7]
Ni2p: 3.653
Co2p: 3.255
Al2s: 0.288
Sb3d3 / 2: 3.066
From the values of the peak area after Sb3d3 / 2 correction, the peak area after Ni2p correction, the peak area after Co2p correction, and the peak area after Al2s correction determined as described above, the metal concentration represented by the following general formula (2) The Sb concentration with respect to was calculated. The Sb concentration of the positive electrode agents 1c and 1e thus obtained was Sb₂O₃Of the positive electrode agent 1c having a charged amount of 0.1 mol% was 4.5%, and 18.3% of the positive electrode agent 1e was 1 mol%.
[0123]
(Equation 4)
Sb concentration = [(peak area after Sb3d3 / 2 correction) / ｛(after Sb3d3 / 2 correction)
Peak area) + (peak area after Ni2p correction) + (peak area after Co2p correction)
+ (Peak area after Al2s correction)}] × 100 (2)
[0124]
[Table 8]

[0125]
(7) Evaluation of lithium secondary battery
[Battery capacity measurement]
LiNi, which is a positive electrode active material of a liquid lithium secondary battery 1 using the positive electrode 1 manufactured using the positive electrode agent 1 ',_0.82Co_0.15Al_0.03O₂Was 185 mAh / g, so 1 C 'per gram of the positive electrode active material was set to 185 mA, and the discharge capacity of each lithium secondary battery was measured as follows. The "original" 1C value was determined. That is, at 25 ° C., the battery was charged to 4.2 V with a constant current of 0.5 C ′ × (weight of the positive electrode active material), and then charged at 4.2 V until the current value attenuated to 25 mA. Was. Thereafter, the capacity at the time of discharging to 2.7 V at a constant current of 0.2 C ′ × (weight of the positive electrode active material) was measured, and this was defined as the discharge capacity α of the lithium secondary battery. Then, α (mA) of the discharge capacity α (mAh) thus obtained was defined as 1C of each lithium secondary battery.
[0126]
The battery capacity of each lithium secondary battery was charged to 4.2 V at a constant current of 0.5 CmA at 25 ° C., and then constant voltage charging was performed at 4.2 V until the current value attenuated to 25 mA. . Thereafter, the capacity when constant current discharging was performed to 2.7 V at 0.2 CmA was measured, and this was defined as the battery capacity of each lithium secondary battery.
[Rate characteristic measurement]
Each lithium secondary battery was charged to 4.2 V at a constant current of 0.5 CmA at 25 ° C., and then charged at 4.2 V at a constant voltage until the current value attenuated to 25 mA.
[0127]
Thereafter, with respect to the liquid lithium secondary batteries 1 and 2, a constant current discharge was performed up to 2.7 V at a 6 C discharge rate, and the obtained discharge capacity was compared with the 0.2 C discharge rate obtained in the above [Battery capacity measurement]. The ratio with the capacity was defined as the rate characteristic.
On the other hand, with respect to the polymer lithium secondary battery 1, a constant current discharge was performed up to 2.7 V at a 2C discharge rate, and the obtained discharge capacity was compared with the 0.2C discharge rate capacity obtained in the above [Battery capacity measurement]. Is defined as the rate characteristic.
[Impedance measurement]
Each lithium secondary battery was charged to 4.2 V or 3.7 V at 25 ° C. by using a device combining SI @ 1287 Electrochemical Interface manufactured by solartron instruments and SI1260 Impedance / Gain-Phase Analyzer manufactured by the company. The impedance was measured at 25 ° C. in a frequency range of 100 KHz to 0.01 Hz.
[Cycle capacity maintenance test]
The liquid lithium secondary battery 1 was charged at a constant current of 2 C at 4.2 ° C. to 4.2 V at 25 ° C., and then charged at a constant voltage of 4.2 V until the current value attenuated to 25 mA. Discharge was performed by discharging at a constant current up to 3.0 V at 2C. With this charge / discharge as one cycle, charge / discharge of 400 cycles was performed.
[0128]
The cycle capacity retention rate was determined by calculating the capacity in the 2C discharge after 400 cycles with respect to the capacity in the first cycle of the 2C discharge in each liquid lithium secondary battery 1.
[High temperature cycle capacity retention test]
The polymer-based lithium secondary battery 1 was charged at a constant current of 1.0 C up to 4.2 V at 60 ° C., and then charged at a constant voltage of 4.2 V until the current value attenuated to 25 mA. Thereafter, the battery was discharged by discharging at a constant current of 1 C to 3.0 V.
[0129]
The high-temperature cycle capacity retention rate was obtained by calculating the capacity at 1C discharge after 400 cycles with respect to the capacity at 1C discharge at the first cycle in each polymer-based lithium secondary battery.
Further, the impedance of the battery before the high-temperature cycle capacity retention test was measured by the method described in [Impedance Measurement] above at 25 ° C. and charged to 3.7 V. Further, after the high-temperature cycle capacity retention rate test, the impedance was measured while being charged to 3.7 V at 25 ° C. Then, using the obtained impedance values before and after the test, (impedance after the test) / (impedance before the test) was calculated as an impedance change.
[High temperature storage test]
Each lithium secondary battery was charged to 4.2 V at a constant current of 0.5 CmA at 25 ° C., and then charged at 4.2 V at a constant voltage until the current value attenuated to 25 mA. After measuring the impedance in this charged state, the battery was placed in a thermostat at 60 ° C. or 90 ° C., left for a predetermined time, and then taken out of the thermostat. Then, impedance change, remaining capacity measurement, battery capacity measurement after recharging, and rate characteristic measurement after recharging were performed by the following methods.
・ Impedance change
The impedance of each lithium secondary battery before the high-temperature storage test was measured by the method described in the above [Impedance measurement]. Furthermore, after the high-temperature storage test, the impedance of the lithium secondary battery in a state where it was taken out of the thermostat was measured again. Further, once the lithium secondary battery was discharged to 2.7 V at 0.2 CmA, it was charged again to 4.2 V at a constant current of 0.5 CmA, and the current value attenuated to 25 mA at 4.2 V. The battery was charged at a constant voltage until charging, and the impedance of the lithium secondary battery was measured in this state.
[0130]
The ratio of the impedance values before and after the high-temperature storage test, that is, (impedance after test) / (impedance before test) was defined as the impedance change. Also, the ratio of the impedance value before the high-temperature storage test to the impedance value after the recharge after the high-temperature storage test, that is, (impedance after the recharge after the test) / (impedance before the test) is the impedance change after the recharge. And
[0131]
As for the impedance change, the closer the impedance change is to a value slightly smaller than 1, the smaller the impedance change is. Regarding the impedance change after the recharge, the closer the impedance change to 1 after the recharge, the smaller the impedance change. The reason is shown below.
[0132]
That is, when the lithium secondary battery is stored at 4.2 V charge at a high temperature, a voltage drop occurs due to self-discharge. This voltage drop is affected by differences in the type of electrolyte, such as whether the electrolyte contains a polymer or is composed solely of an electrolytic solution, and high-temperature storage conditions (storage time, storage temperature). The voltage drop due to the self-discharge is usually about 0.5 V when the liquid lithium secondary battery is stored at 60 ° C. × 24 hrs, and usually 0 V when the polymer lithium secondary battery is stored at 90 ° C. × 4 hrs. It is about 1V.
[0133]
On the other hand, the change of the impedance value with respect to the charging voltage of the lithium secondary battery is as follows. That is, as the charging voltage gradually increases from 2.7 V, the impedance value gradually decreases. When the charging voltage is around 4 V, the impedance value has the lowest value. Thereafter, the impedance increases again as the charging voltage further increases to 4.2 V.
[0134]
Therefore, if there is no change in the impedance of the lithium secondary battery in the high-temperature storage test, the impedance value after self-discharge after the high-temperature storage decreases because of the decrease in the impedance value. The value is slightly smaller than the impedance value before the storage test. For this reason, as for the impedance change, the closer the impedance change is to a value slightly smaller than 1, the smaller the impedance change is.
[0135]
On the other hand, when the lithium secondary battery is charged again, the impedance value returns to the value when the charging voltage is 4.2V. Therefore, if there is no change in impedance of the lithium secondary battery in the high-temperature storage test, the change in impedance after recharging should be 1. Therefore, the closer the impedance value after recharging is to 1, the smaller the impedance change.
・ Remaining capacity measurement
Each lithium secondary battery taken out of the thermostat after the high-temperature storage test was discharged to 3 V at 0.2 CmA, and the discharge capacity was defined as the remaining capacity. The remaining capacity relative to the battery capacity before the high-temperature storage test ((remaining capacity / battery capacity before the high-temperature storage test) × 100) was defined as the remaining capacity ratio.
・ Battery capacity measurement after recharge (measurement of capacity recovery rate)
After the measurement of the remaining capacity, the battery was discharged to 2.7 V at 0.2 CmA, charged again to 4.2 V at a constant current of 0.5 CmA, and kept constant at 4.2 V until the current value attenuated to 25 mA. Voltage charging was performed. Thereafter, the capacity at the time of constant current discharging to 2.7 V at 0.2 CmA was measured, and this was defined as the battery capacity after recharging. The battery capacity after the recharge with respect to the battery capacity before the high-temperature storage test was defined as a capacity recovery rate.
・ Low temperature characteristics after recharging
After measuring the capacity recovery rate of the liquid lithium secondary battery, the battery was charged to 4.2 V at a constant current of 0.5 CmA at 25 ° C., and the current value attenuated to 25 mA at 4.2 V. Charged to constant voltage until Thereafter, 1 CmA discharge was performed at 25 ° C. and −30 ° C. to 2.7 V. The ratio of the discharge capacity at −30 ° C. to the discharge capacity at 25 ° C. ((discharge capacity at −30 ° C./discharge capacity at 25 ° C.) × 100) at that time was defined as low-temperature characteristics after recharging.
[Low temperature property test]
The liquid lithium secondary battery was charged at 25 C at a constant current of 0.5 CmA to 4.2 V, and then charged at 4.2 V at a constant voltage until the current value attenuated to 25 mA. Thereafter, 1 CmA discharge was performed at 25 ° C. and −30 ° C. to 2.7 V. The ratio of the discharge capacity at −30 ° C. to the discharge capacity at 25 ° C. at that time ((discharge capacity at −30 ° C./discharge capacity at 25 ° C.) × 100) was defined as low-temperature characteristics.
[Examples 1 to 8, Comparative Examples 1 to 4]
A lithium secondary battery having the battery configuration shown in Table 4 was manufactured.
[0136]
[Table 9]

[0137]
For each lithium secondary battery of Example 1 and Comparative Example 1, the battery capacity, rate characteristic, cycle characteristic, and low-temperature output characteristic were measured by the above [battery capacity measurement], [rate characteristic measurement], and [cycle capacity maintenance test], respectively. , And [low temperature property test]. Table 5 shows the measurement results. Further, with respect to each of the lithium secondary batteries of Example 1 and Comparative Example 1, a high-temperature storage test was performed according to the above-mentioned [high-temperature storage test] under the storage test conditions of a standing temperature of 60 ° C. and a standing time of 24 hours, and impedance change , The change in impedance after recharging, the remaining capacity ratio, the capacity recovery ratio, and the low-temperature characteristics after recharging were measured. Table 5 shows the measurement results.
[0138]
[Table 10]

[0139]
From Table-5, it was found that Sb was higher than that of the untreated lithium nickel composite oxide (Comparative Example 1).₂O₃It can be seen that, by modifying the surface of the lithium nickel composite oxide with, the change in impedance, the change in impedance in recharging, and the low-temperature characteristics after recharging after a high-temperature storage test are improved. In particular, Sb₂O₃It can be understood that the impedance change and the impedance change after recharging become better as the charge amount of the battery increases. On the other hand, the battery capacity, rate characteristics, and cycle capacity₂O₃It can be seen that the amount gradually decreases as the charged amount of increases. This means that the lithium secondary battery can be freely designed according to the required performance of the lithium secondary battery. That is, in a lithium secondary battery that places more importance on battery capacity and the like, Sb₂O₃May be reduced. On the other hand, a lithium secondary battery that is often used in a high-temperature environment and places more emphasis on reducing impedance changes during storage at a high temperature, etc.₂O₃What is necessary is just to increase the preparation amount.
[0140]
For the lithium secondary batteries of Example 2 and Comparative Example 2, the battery capacity, rate characteristics, cycle characteristics, and low-temperature output characteristics were measured by the above [battery capacity measurement], [rate characteristic measurement], and [cycle capacity maintenance test], respectively. , And [low temperature property test]. Table 6 shows the measurement results. Further, with respect to each of the lithium secondary batteries of Example 2 and Comparative Example 2, a high-temperature storage test was performed according to the above-mentioned [high-temperature storage test] under a storage test condition of a standing temperature of 60 ° C. and a standing time of 24 hours to change impedance. , The change in impedance after recharging, the remaining capacity ratio, and the capacity recovery ratio were measured. Table 6 shows the measurement results.
[0141]
[Table 11]

[0142]
Table 6 shows that the lithium nickel composite oxide was LiNi_0.8Co_0.2O₂And LiNi_0.7Co_0.2Mn_0.1O₂And the surface is Sb₂O₃It can be seen that, when the surface is modified with, the impedance change and the impedance change after recharging can be significantly suppressed without impairing the residual capacity ratio and the capacity recovery ratio in the high-temperature storage test. On the other hand, Sb₂O₃It can be seen that the battery processing decreases the battery capacity but does not impair the cycle characteristics, but rather improves the rate characteristics and low-temperature characteristics.
[0143]
For the lithium secondary batteries of Example 3 and Comparative Example 1, the battery capacity, rate characteristics, cycle characteristics, and low-temperature output characteristics were measured by the above [battery capacity measurement], [rate characteristic measurement], and [cycle capacity maintenance test], respectively. , And [low temperature property test]. Table 7 shows the measurement results. Further, with respect to each of the lithium secondary batteries of Example 3 and Comparative Example 1, a high-temperature storage test was performed according to the above-mentioned [high-temperature storage test] under the storage test conditions of a standing temperature of 60 ° C. and a standing time of 24 hours, and impedance change was performed. , The change in impedance after recharging, the remaining capacity ratio, and the capacity recovery ratio were measured. Table 7 shows the measurement results.
[0144]
[Table 12]

[0145]
From Table 7, when the surface of the lithium nickel composite oxide is modified with triphenylantimony, the impedance change and the impedance change after recharging are largely suppressed without impairing the residual capacity ratio and the capacity recovery ratio in the high-temperature storage test. We can see that we can do it. On the other hand, although the battery capacity is reduced by the treatment with triphenylantimony, the cycle characteristics and the rate characteristics are hardly impaired, and the low-temperature characteristics are rather improved.
[0146]
For each of the lithium secondary batteries of Example 4 and Comparative Example 3, the battery capacity and the rate characteristic were measured in accordance with the above [battery capacity measurement] and [rate characteristic measurement], respectively. Table 8 shows the measurement results. Next, for each of the lithium secondary batteries of Example 4 and Comparative Example 3, according to the above-mentioned [high-temperature storage test], storage test conditions of a temperature of 90 ° C in a thermostat and a storage time of 4 hours, and a temperature of 60 ° C in a thermostat. A high-temperature storage test was performed for each one-week standing time, and the impedance change, the impedance change after recharging, the remaining capacity ratio, and the capacity recovery ratio were measured. Table 8 shows the measurement results. Further, with respect to each of the lithium secondary batteries of Example 4 and Comparative Example 3, a high-temperature cycle test was performed to measure a high-temperature cycle capacity retention rate and an impedance change in accordance with the above-mentioned [high-temperature cycle capacity retention rate test]. Table 8 shows the measurement results.
[0147]
[Table 13]

[0148]
Table 8 shows that the surface of the lithium nickel composite oxide was Sb in the polymer lithium secondary battery as well.₂O₃It can be seen that the modification with significantly improves the impedance change, the impedance change after recharging, the residual capacity ratio and the capacity recovery ratio in the high-temperature storage test. Especially Sb₂O₃It can be seen that as the amount of modification increases, various characteristics in the above-mentioned high-temperature storage test are further improved. In the high-temperature cycle capacity retention test, the high-temperature cycle capacity retention and the impedance change were also Sb.₂O₃It can be seen that as the amount of surface modification increases, it becomes better. On the other hand, the battery capacity and rate characteristics are Sb₂O₃It can be seen that the amount gradually decreases as the charged amount of increases. This means that the lithium secondary battery can be freely designed according to the required performance of the lithium secondary battery.
[0149]
For each of the lithium secondary batteries of Example 5, the battery capacity, rate characteristics, cycle characteristics, and low-temperature output characteristics were measured using the above [battery capacity measurement], [rate characteristic measurement], [cycle capacity maintenance test], and [low temperature], respectively. Characteristic test]. Table 9 shows the measurement results. Further, with respect to each lithium secondary battery of Example 5, a high-temperature storage test was performed under the storage test conditions of a constant temperature bath of 60 ° C. and a storage time of 24 hours according to the above [high-temperature storage test]. Was measured for the change in impedance, the remaining capacity ratio, and the capacity recovery ratio. Table 9 shows the measurement results.
[0150]
[Table 14]

[0151]
From Table-9, in the battery configuration of Example 5, the primary particle size of the Sb compound with respect to the primary particle size of the lithium nickel composite oxide was in the range of 0.01 to 4, and the battery capacity, cycle characteristics, and low-temperature characteristics were as follows. Further, it can be seen that there is a primary particle size ratio that optimizes various performances of the impedance change after the high-temperature storage test, the impedance change after the recharge, the remaining capacity, and the capacity recovery rate.
[0152]
For the lithium secondary batteries of Example 6 and Comparative Example 1, the battery capacity, rate characteristics, cycle characteristics, and low-temperature output characteristics were measured by the above [battery capacity measurement], [rate characteristic measurement], and [cycle capacity maintenance test], respectively. , And [low temperature property test]. Table 10 shows the measurement results. Further, the lithium secondary batteries of Example 6 and Comparative Example 1 were subjected to a high-temperature storage test according to the above-mentioned [high-temperature storage test] under a storage test condition of a standing temperature of 60 ° C. and a standing time of 24 hours to change impedance. , The change in impedance after recharging, the remaining capacity ratio, the capacity recovery ratio, and the low-temperature characteristics after recharging were measured. Table 10 shows the measurement results.
[0153]
[Table 15]

[0154]
From Table-10, by modifying the surface of the lithium-nickel composite oxide by the vapor phase method with triphenylantimony, the cycle capacity retention, low-temperature characteristics, impedance change in high-temperature storage test, impedance change after recharging, and residual It is understood that various characteristics such as the capacity ratio, the capacity recovery ratio, and the low-temperature characteristics after recharging are improved. On the other hand, by modifying triphenylantimony on the surface of the lithium-nickel composite oxide by the gas phase method, the battery capacity is slightly reduced, but the rate characteristics are almost the same. It can be said that a secondary battery can be obtained.
[0155]
For each lithium secondary battery of Example 7, the battery capacity, rate characteristics, cycle characteristics, and low-temperature output characteristics were measured using the above-mentioned [battery capacity measurement], [rate characteristic measurement], [cycle capacity maintenance test], and [low temperature], respectively. Characteristic test]. Table 11 shows the measurement results. Further, a high-temperature storage test was performed on each lithium secondary battery of Example 7 in accordance with the above-mentioned [high-temperature storage test] under a storage test condition of a standing temperature of 60 ° C. and a standing time of 24 hours. Was measured for its impedance change, residual capacity ratio, capacity recovery ratio, and low-temperature characteristics after recharging. Table 11 shows the measurement results.
[0156]
[Table 16]

[0157]
From Table 11, it can be seen that in the battery configuration of Example 7, Sb₂O₃Baking at a temperature (600 ° C.) having a melting point of 656 ° C. or lower as compared with baking at a temperature (700 ° C.) or higher at the melting point, a change in impedance in a high-temperature storage test, a change in impedance after recharging, It can be seen that various characteristics such as impedance change, remaining capacity ratio, capacity recovery ratio, and low-temperature characteristics after recharging are not sufficient. This means that if the firing temperature is lower than the melting point of the Sb compound, the effect of modifying the surface of the lithium nickel composite oxide with the Sb compound may not be sufficiently exerted. However, in the case of a lithium secondary battery having a firing temperature of 600 ° C., the battery capacity and the cycle capacity retention ratio are rather good. Therefore, if the firing temperature is changed in accordance with the required performance of the lithium secondary battery, the lithium secondary battery can be recharged. This means that the performance of the secondary battery can be freely designed.
[0158]
For each of the lithium secondary batteries of Example 8 and Comparative Example 4, the battery capacity, rate characteristics, and low-temperature output characteristics were measured according to the above [battery capacity measurement], [rate characteristic measurement], and [low-temperature characteristic test], respectively. . Table 12 shows the measurement results. Further, the lithium secondary batteries of Example 8 and Comparative Example 4 were subjected to a high-temperature storage test according to the above-mentioned [high-temperature storage test] under a storage test condition of a temperature of 60 ° C. and a storage time of 24 hours in a constant temperature bath, and impedance change was performed. , The change in impedance after recharging, the remaining capacity ratio, the capacity recovery ratio, and the low-temperature characteristics after recharging were measured. Table 12 shows the measurement results.
[0159]
[Table 17]

[0160]
Table 12 shows that the surface of the lithium nickel composite oxide was treated with Sb in the electrolytic solution using the mixed solvent of EC and DEC.₂O₃When modified with, various characteristics such as low-temperature characteristics and impedance change in high-temperature storage test, impedance change after recharging, remaining capacity ratio, capacity recovery rate, and low-temperature characteristics after recharging are improved without impairing rate characteristics. You can see that.
[Example 9]
LiNi_0.82Co_0.15Al_0.03O₂Sb having an average primary particle diameter of 0.5 μm with respect to the positive electrode active material powder having an average secondary particle diameter of 11 μm (average primary particle diameter of 1 μm)₂O₃A powder (Nippon Seiko Co., Ltd., PATOX-M) was added in an amount equivalent to 0.75 mol%, and the mixture was sufficiently shaken and mixed in a closed container, and then calcined at 680 ° C. for 2 hours in an oxygen stream. (Sample name: “0.75 mol% treated Sb sample”). Further, the same positive electrode active material powder and Sb₂O₃Powder, Sb₂O₃A sample mixed and fired in the same manner as described above, except that the amount of the powder added was 2.0 mol%, was obtained (sample name: "2.0 mol% treated Sb sample").
In addition to the obtained 0.75 mol% treated Sb sample and 2.0 mol% treated Sb sample,₂O₃TPD-MS analysis was performed on the positive electrode active material powder (sample name: “unprocessed sample”) that had not been subjected to the addition and calcination by the method described below.
・ TPD-MS analysis
Approximately 50 mg of the powdery, untreated sample, 0.75 mol% treated Sb sample, and 2 mol% treated Sb sample were precisely weighed and then subjected to the following treatment.
A powdery sample is filled in a pyrolyzer, and heated at 400 ° C. for 30 minutes in He gas (80 ml / min.) To remove a gas adsorbed on a base point.
Thereafter, the temperature is lowered to 100 ° C.^-2After evacuation to about torr, about 70 torr of CO₂And introduce CO to the base point on the sample surface.₂For 15 minutes. It takes 15 minutes for saturation adsorption.
Next, at 100 ° C. for about 10^-2Evacuate to torr and remove CO remaining in the atmosphere₂CO that is physically adsorbed₂, And then returned to room temperature after He flow (200 ml / min.) Treatment.
10 ° C / min. From room temperature to 900 ° C. And the CO generated at the time of temperature rise₂Measure the temperature profile of the volume. As a result, CO adsorbed at the base site₂Was evaluated for its adsorption state, that is, basicity.
And the obtained CO₂In the temperature profile of the amount, the peak top temperature observed around 100 to 360 ° C. was determined. FIG. 2 shows the measurement results. As can be seen from FIG. 2, the CO of the untreated sample, the 0.75 mol% treated Sb sample, and the 2 mol% treated Sb sample₂The desorption peak top temperature was 270 ° C. for the untreated sample, and 230 ° C. for the 0.75 mol% treated Sb sample and the 2 mol% treated Sb sample.
From the above results, it can be understood that the positive electrode agent modified with the composite oxide of Sb has a lower basicity than the untreated one.
[0161]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the surface modification lithium nickel composite oxide which provides the lithium secondary battery which satisfies various battery characteristics at a very high level, and its manufacturing method can be obtained.
In particular, it is possible to obtain a surface-modified lithium-nickel composite oxide that provides a lithium secondary battery in which a change in impedance when stored at a high temperature or when charge and discharge are repeated in a high-temperature environment is suppressed well, and a method for producing the same.
Further, according to the present invention, a surface-modified lithium nickel which provides a lithium secondary battery excellent in the remaining capacity ratio after high-temperature storage, the capacity recovery ratio, and the low-temperature characteristics after recharging, and having a high capacity retention ratio in a high-temperature cycle test A composite oxide and a method for producing the same can be obtained.
Further, according to the present invention, it is possible to obtain a surface-modified lithium nickel composite oxide which provides a lithium secondary battery having excellent battery capacity, rate characteristics, cycle capacity retention, and low-temperature characteristics, and a method for producing the same. According to the present invention, when the lithium secondary battery is a polymer-based lithium secondary battery, a surface-modified lithium-nickel composite that provides a lithium secondary battery that can significantly suppress gas generation due to high-temperature storage An oxide and a method for producing the oxide can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing an XPS measurement result of Sb3d3 / 2 and a method of obtaining a peak area thereof.
FIG. 2 is a diagram showing a TPD-MS measurement result of a surface-modified lithium nickel composite oxide.
[Explanation of symbols]
1 Starting point
2 End point
3 Baseline

Claims (19)

A method for producing a surface-modified lithium-nickel composite oxide, characterized in that a compound of an element belonging to the group 4A to 6A and having an atomic weight of 28 or more is present on the surface of the lithium-nickel composite oxide and then calcined. The method for producing a surface-modified lithium nickel composite oxide according to claim 1, wherein the lithium nickel composite oxide is represented by the following general formula (1).

(In the general formula (1), α, X, Y, Z, β are respectively 0 <α ≦ 1.1, 0.1 ≦ X ≦ 1, 0 ≦ Y ≦ 0.9, 0 ≦ Z ≦ 0 0.8, 0.9 ≦ X + Y + Z ≦ 1.1, 0 ≦ β ≦ 0.5 M is Li, Mg, Ca, Sr, Cu, Zn, Al, Ga, Ti, Zr, V , Nb, Ta, Cr, Mo, W, Mn, and Fe.) The method for producing a surface-modified lithium nickel composite oxide according to claim 1 or 2, wherein the compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element is an Sb (antimony) compound. The Sb compound, antimony oxide, antimony halide, antimony sulfide, antimony selenide, antimony telluride, antimony acetate, antimony oxychloride, trimethoxyantimony, triethoxyantimony, tripropoxyantimony, tributoxyantimony, triphenylantimony, 4. The method for producing a surface-modified lithium nickel composite oxide according to claim 3, wherein the method is at least one selected from the group consisting of: and triphenylantimony dichloride. The method for producing a surface-modified lithium nickel composite oxide according to claim 4, wherein the Sb compound is any one of antimony oxide, antimony halide, antimony acetate, and triphenylantimony. When a compound of a group 4A to 6A element having an atomic weight of 28 or more is present on the surface of the lithium-nickel composite oxide, the group 4A to 6A element having an atomic weight of The method for producing a surface-modified lithium nickel composite oxide according to any one of claims 1 to 5, wherein a compound of 28 or more elements is used in an amount of 0.001 mol% or more and 10 mol% or less. The ratio of the primary particle diameter of a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element that is solid at 25 ° C. to the primary particle diameter of the lithium nickel composite oxide is 0.005 or more and 5 or less. A method for producing the surface-modified lithium nickel composite oxide according to any one of claims 1 to 6. By bringing a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element into contact with the lithium nickel composite oxide in a solvent, the surface of the lithium nickel composite oxide is coated with the group 4A to 6A element. The method for producing a surface-modified lithium nickel composite oxide according to any one of claims 1 to 7, wherein a compound of an element having an atomic weight of 28 or more is present. By bringing a compound of an element having an atomic weight of 28 or more that is a group 4A to 6A element into contact with the lithium nickel composite oxide in a powder state, the surface of the lithium nickel composite oxide is treated with the group 4A to 6A. The method for producing a surface-modified lithium nickel composite oxide according to any one of claims 1 to 7, wherein a compound of an element having an atomic weight of 28 or more is present. The compound of the 4A to 6A group element having an atomic weight of 28 or more is made into a gaseous state, and is brought into contact with the lithium nickel composite oxide, whereby the surface of the lithium nickel composite oxide becomes 4A to 6A. The method for producing a surface-modified lithium-nickel composite oxide according to any one of claims 1 to 7, wherein a compound of an element belonging to the group III and having an atomic weight of 28 or more is present. The method for producing a surface-modified lithium nickel composite oxide according to any one of claims 1 to 10, wherein the calcination is performed at a temperature equal to or higher than the melting point of a compound of an element having a group of 4A to 6A and having an atomic weight of 28 or more. A surface-modified lithium nickel composite oxide used as a positive electrode active material of a lithium secondary battery,
A surface-modified lithium-nickel composite oxide, characterized in that a composite oxide of an element belonging to Groups 4A to 6A of the periodic table and having an atomic weight of 28 or more is present on the surface of the lithium-nickel composite oxide. The composite oxide of an element having an atomic weight of 28 or more that is an element in the Periodic Tables 4A to 6A includes at least one of Li and Ni, an element having an atomic weight of 28 or more that is an element in the Groups 4A to 6A of the periodic table, and oxygen. The surface-modified lithium nickel composite oxide according to claim 12, which is a composite oxide with: The surface-modified lithium-nickel composite oxide according to claim 12 or 13, wherein the element having an atomic weight of 28 or more which is a group 4A to 6A element of the periodic table is Sb (antimony). The surface-modified lithium nickel composite oxide according to any one of claims 12 to 14, wherein the lithium nickel composite oxide is represented by the following general formula (1).

(In the general formula (1), α, X, Y, Z, β are respectively 0 <α ≦ 1.1, 0.1 ≦ X ≦ 1, 0 ≦ Y ≦ 0.9, 0 ≦ Z ≦ 0 0.8, 0.9 ≦ X + Y + Z ≦ 1.1, 0 ≦ β ≦ 0.5 M is Li, Mg, Ca, Sr, Cu, Zn, Al, Ga, Ti, Zr, V , Nb, Ta, Cr, Mo, W, Mn, and Fe.) The surface-modified lithium nickel composite oxide according to any one of claims 12 to 15, which is measured by temperature-programmed thermal desorption / pyrolysis-mass spectrometry under the following measurement conditions. A surface-modified lithium nickel composite oxide having a peak in the range of 150 to 250 ° C. due to elimination of CO ₂ .
(Measurement conditions of thermal desorption / pyrolysis-mass spectrometry at elevated temperature)
(1) The surface-modified lithium nickel composite oxide in a powder state is heated to about 400 ° C. in He gas, and then cooled to about 100 ° C.
(2) CO ₂ is introduced to adsorb CO ₂ on the surface of the surface-modified lithium nickel composite oxide.
(3) After that, the CO ₂ remaining in the atmosphere or the like is exhausted, and the temperature is lowered to around room temperature.
(4) The temperature is raised to around 900 ° C., and the temperature profile of the amount of CO ₂ generated at the time of the temperature rise is measured. M in the general formula (1) is Al, and when measured by X-ray photo-electron spectroscopy (X-ray photoelectron spectroscopy) under the following measurement conditions, the Sb concentration represented by the following formula (2) is 1 The surface-modified lithium nickel composite oxide according to claim 15, which is not less than 95% and not more than 95%.

(Measurement conditions for X-ray photoelectron spectroscopy)
1. Measurement of surface-modified lithium-nickel composite oxide A double-sided tape was attached to a metal plate, and a powdery surface-modified lithium-nickel composite oxide was sprinkled on the metal plate so that the tape could not be seen. Fix to and provide for measurement.
The measurement is performed under the following conditions using a monochromatic Al-Kα ray (14 kV, 150 W) as a light source for the measurement. At the time of the measurement, an electron neutralizing gun is used for charging correction.
PassEnergy: 29.35 eV
Data acquisition interval: 0.125 eV / step
Measurement area: 0.8 mm Diameter take-out angle: 45 degrees The measurement elements are Ni2p, Co2p, Al2s, and Sb3d3 / 2.
2. Measurement of Sb concentration The starting point and the ending point of each peak of the measuring element are determined, and the starting point and the ending point are connected by the Shirley method. Then, the area surrounded by the line connecting the start point and the end point and the peak is determined for each measurement element, and this is defined as the peak area of each measurement element.
Next, using the relative sensitivity correction coefficient determined for each of the measurement elements, the peak area of each of the measurement elements is divided by the relative sensitivity correction coefficient of each element. The peak area thus divided by the relative sensitivity correction coefficient is referred to as “post-correction peak area”. A positive electrode material for a lithium secondary battery, comprising the surface-modified lithium nickel composite oxide according to any one of claims 12 to 17. A lithium secondary battery comprising the surface-modified lithium nickel composite oxide according to any one of claims 12 to 17 as a positive electrode active material.

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