JP3769344B2 - Positive electrode composition for lithium secondary battery and lithium secondary battery - Google Patents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description
【０００１】
【発明の属する技術分野】
本発明は、リチウム二次電池用正極活物質として安定なリチウム遷移金属複合酸化物を含有する正極剤組成物及びこれを用いたリチウム二次電池に関する。
【０００２】
【従来の技術】
近年、民生用電子機器のポ−タブル化、コ−ドレス化が急速に進むに従い、小型電子機器の電源としてリチウム二次電池が実用化されている。このリチウム二次電池については、１９８０年に水島等によりコバルト酸リチウムがリチウム二次電池の正極活物質として有用であるとの報告（「マテリアル リサ−チブレティン」vol15,P783-789(1980)）がなされて以来、コバルト酸リチウムを始めとしてリチウム遷移金属酸化物系正極活物質に関する研究開発が活発に進められており、これまで数多くの提案がなされている。
【０００３】
中でもいち早く実用化されたコバルト酸リチウムとしては、例えばコバルト酸リチウムの組成をＬｉｘＣｏＯ2(但し、１０５≦ｘ≦１３）とすることによりリチウムリッチにしたもの（特開平３−127454号公報）、逆にＬｉｘＣｏＯ2(但し０＜ｘ≦１）とすることによってコバルトリッチにしたもの（特開平３−134969号公報）、Ｍｎ、Ｗ、Ｎｉ、Ｌａ及びＺｒなどの金属イオンをド−プさせたもの（特開平３−201368号公報、特開平４−328277号公報、特開平４−319259号公報、特開平４−319260号公報）等などが提案されている。
【０００４】
その他のリチウム遷移金属酸化物としては、例えば、Ｌｉ1-a ＮｉＯ2(但し、０≦ａ≦１）（米国特許第４３０２５１８号明細書）、Ｌｉb Ｎｉ2-b Ｏ2 及びＬｉＮｉ1-d Ｃｏd Ｏ2(但し、０．８４≦ｂ≦１．２２、０．０９≦ｄ≦０．５）（特開平２−４０８６１号公報）、Ｌｉn Ｎｉm Ｃｏ1-m Ｏ2(但し、０＜ｍ≦０．７５、ｎ≦１）（特開昭６３−２９９０５６号公報）などのリチウムと遷移金属を主体とする複合酸化物が提案されている。
【０００５】
かかる正極活物質で材料中のアルカリを問題としているものとして、コバルト酸リチウム中の残留Ｌｉ2 ＣＯ3 が１０重量％以下とするもの（特開平４−56064 号公報、特開平４−328278号公報）、正極表面に炭酸リチウムが被覆されているもの（特開平４−329268号）、Ｌｉx ＭＯ2(但し、０．３≦ｘ≦１．２、Ｍは遷移金属を示す）中のＮａ及びＫの総含有量が１０００ppm 以下としたもの（特開平５−343006号公報）、Ｌｉ及びＣｏを主成分とする複合金属酸化物中の残存アルカリ量が０．１５重量％以下としたもの（特開平５−74455 号公報）等が挙げられる。これらは、いずれも正極活物質としてのリチウム遷移金属酸化物中のアルカリ量をそれぞれ特定したものであるが、それらは放電容量の向上と電池内圧の上昇に応じて作動する電流遮断手段、また正極集電体の腐食防止、高温下でのサイクル特性、保存特性及び安全性等の向上を図ることを目的としている。
【０００６】
かかるリチウム遷移金属酸化物を使用してリチウム二次電池の正極を作製する場合、これを構成する物質の物理学的特性が電池特性に著しく影響を及ぼす。例えば、ロ−ル圧延方式により、アルミ箔等へ正極剤ぺ−ストを塗布し作製されたシ−ト状電極は、写真フィルム及び製版材料などに比べると塗布膜が著しく厚く、正極剤ペ−ストの物性によっては正極剤組成が変動し、放電容量の変動（バラツキ）を大きくする。したがって、サイクル特性の向上したシ−ト状正極板を作製することができないことがある。これらの原因は未だ不明な点も多いが、多くの場合、正極活物質のリチウム複合酸化物の化学的、物理的特性によるものと考えられる。
【０００７】
【発明が解決しようとする課題】
従って、本発明の目的は、安定した正極剤組成物及び優れた放電容量及びサイクル特性を示すリチウム二次電池を提供することにある。
【０００８】
【課題を解決するための手段】
かかる実情において、本発明者は、鋭意検討を行った結果、リチウム二次電池の正極を作製するにあたり、正極活物質であるリチウム遷移金属複合酸化物中の実質存在する水酸化リチウムとこれを含有する正極剤組成物の一定条件下での粘度が相互に関連して正極剤の安定性に大きく影響を与えること及びこれらを一定レベル以下に制御すれば、バラツキのない安定な正極材が得られること及びこれを用いた二次電池は優れた放電容量及びサイクル特性を示すことを見い出し、本発明を完成するに至った。
【０００９】
すなわち、本発明は、正極活物質、導電剤、ポリビニリデンフルオライド及び溶剤を含有してなるリチウム二次電池用正極剤組成物（有機酸化合物を含有しない。）において、正極活物質を構成するリチウム遷移金属複合酸化物中の実質残存水酸化リチウム含有量が中和滴定法による測定値で０．４重量％以下及び前記正極剤組成物における粘度比Ｘが
Ｘ＝Ｂ／Ａ≦１．３
（式中、Ａは２０℃における均質化３０分放置後の粘度（ｃＰ）を示し、Ｂは２０℃における均質化２時間放置後の粘度（ｃＰ）を示す。）であるリチウム二次電池用正極剤組成物を提供するものである。
【００１０】
また、本発明は、上記正極剤組成物で構成されるリチウム二次電池を提供するものである。
【００１１】
【発明の実施の形態】
本発明において、正極活物質を構成するリチウム遷移金属複合酸化物は、式（１）；
ＬｉｘＡｙＯｚ （１）
（式中、ＡはＣｏ、Ｎｉ及びＭｎより選ばれる少なくとも１種以上の遷移金属原子を示し、０．０５≦ｘ≦１．１、０≦ｙ≦２．０、２≦ｚを示す。）で表わされる。該リチウム遷移金属複合酸化物は、（１）式を満足するものであれば、特に制限されないが、コバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウムから選ばれる１種又は２種以上が挙げられ、具体的には、例えばＬｉＣｏＯ2 、ＬｉＮｉＯ2 、ＬｉＣｏ0.8 Ｎｉ0.2 Ｏ2 、ＬｉＣｏ0.8 Ｍｎ0.2 Ｏ2 、ＬｉＭｎ2 Ｏ4 等が使用できる。
【００１２】
本発明において、上記リチウム遷移金属複合酸化物は、該複合酸化物中、実質残存水酸化リチウム含有量が中和滴定法による測定値で０．４重量％（以下「％」という）以下であることが必要である。通常、リチウム遷移金属複合酸化物中に含まれる不純物は、原料で使用される炭酸リチウムや酸化コバルト、水酸化ニッケル、酸化ニッケル等の未反応物質である。特に、炭酸リチウムは反応中又は反応終了後、空気中の水分と反応して水酸化リチウムとなり易い。かかる不純物中の水酸化リチウム量がリチウム遷移金属酸化物中に０． ４％を超える量で存在すると、正極剤組成物を作製したときに、時間の経過と共に粘性を高くさせる作用があり、また初期容量等の放電特性が低下してしまい好ましくない。したがって、０．４％以下のリチウム複合金属酸化物を得るには、原料の選定及び反応の制御等を適確に行い、かつ分析試験により選別等を行えばよい。
【００１３】
また、上記中和滴定法は、Ｗａｒｄｅｒ法やＷｉｎｋｌｅｒ法とも呼ばれ水酸化リチウムと炭酸リチウムとの混合物の定量分析法としては公知な分析方法（例えば、分析化学、培風館、阿部著、昭和２５年発行、223 〜224 頁）である。この滴定は、始めにフェノ−ルフタレインを指示薬として滴定し、全水酸化リチウムと炭酸リチウムの半分が中和され、残りの炭酸塩はフェノ−ルフタレイン終点からメチルオレンジ指示薬による終点までに中和されるものである。すなわち、
次式（２）〜（４）；
ＬｉＯＨ＋ＨＣ１→ＬｉＣ１＋Ｈ2 Ｏ （２）
Ｌｉ2 ＣＯ3 ＋ＨＣ１→ＬｉＣ１＋ＬｉＨＣＯ3 （３）
ＬｉＨＣＯ3 ＋ＨＣ１→ＬｉＣ１＋ＣＯ2 ＋Ｈ2 Ｏ （４）
において、式（２）及び式（３）の合計滴定量をａml、式（４）の滴定量をｂmlとすると、次の関係が成り立つ。
【００１４】
ａ（ｍｌ）＝全ＬｉＯＨ＋１／２Ｌｉ２ＣＯ３に当量であるＨＣｌの容積
ｂ（ｍｌ）＝１／２Ｌｉ２ＣＯ３に当量であるＨＣｌの容積
（ａ−ｂ）（ｍｌ）＝全ＬｉＯＨに当量であるＨＣｌの容積
すなわち、第２回目の滴定に要したＨＣｌの量ｂ（ｍｌ）の２倍が炭酸リチウムの全量に相当し、第１回目の滴定に要したＨＣｌの量ａ（ｍｌ）から、第２回目の滴定に要したＨＣｌの量ｂ（ｍｌ）を差し引いた（ａ−ｂ）（ｍｌ）が水酸化リチウムの全量になる。
【００１５】
上記リチウム遷移金属酸化物の他の物性値は、特に制限されないが、ＢＥＴ比表面積が０．１〜１．０m2／ｇ、平均粒子径５〜２０μｍの範囲の粉体とすることが好ましい。また、その他の物性、例えば、粒子形状及び表面電荷状態あるいは各種物性を与える製造時の焼成雰囲気、焼成速度及び最高設定温度等のセラミックス化の条件等により、同じ物性の範囲であっても後述する正極剤組成物の粘度比が異なる場合がある。
【００１６】
本発明において、リチウム二次電池の正極材は、前記リチウム遷移金属複合酸化物の粉体を主剤として、導電剤、結合剤及び溶剤等の正極材料より主として構成されるものである。上記導電剤としては、化学変化を起こさない電子導電性材料であれば特に制限されないが、通常、鱗状黒鉛、及び鱗片状黒鉛などの天然黒鉛、人口黒鉛、カ−ボンブラック、アセチレンブラック、ケッチェンブラック、炭素繊維、金属粉、金属繊維及びポリフェニレン誘導体などが挙げられ、これらの１種または２種の混合物が使用できる。
【００１７】
上記結合剤としては、多糖類、熱可燃性樹脂及びゴム弾性を有するポリマ−を使用でき、具体的には、例えばポリビニリデンフルオライド（ＰＶＤＦ）、ポリフッ化エチレン（ＰＴＦＥ）などが挙げられる。結合剤は溶媒に溶けていてもよいし、分散または懸濁などのように析出していてもよい。また、結合剤は１種又は２種以上の混合物として使用してもよい。
【００１８】
上記溶媒としては、特に制限されないが、例えば、Ｎ−メチルピロリドン、キシレン、トルエン、アセトン、メチルエチルケトン、メチルイソブチルケトン、シクロヘキサン、エタノ−ル、メタノ−ル、酢酸メチル、酢酸エチル、メチレンクロライド及びエチレンクロライドなどが挙げられる。また、溶媒は、これを１種又は２種以上の混合物として使用してもよい。
【００１９】
該正極剤組成物を構成する正極活物質、導電剤、結合剤及び溶媒の配合割合としては、特に制限されないが、正極活物質１００重量部に対し、導電剤を１〜５０重量部、好ましくは１〜３０重量部、結合剤を０．１１〜５０重量部、好ましくは０．１１〜３０重量部及び溶媒３０〜６００重量部、好ましくは３０〜１００重量部の範囲とすることが、十分な放電容量及び放電サイクル特性を示す点から好ましい。
【００２０】
本発明のリチウム二次電池用正極剤組成物は、上記材料の組成物より構成され、かかる正極剤組成物の粘度比Ｘが、
Ｘ＝Ｂ／Ａ≦１．３
（式中、Ａは２０℃における均質化３０分放置後の粘度（ｃＰ）を示し、Ｂは２０℃における均質化２時間放置後の粘度（ｃＰ）を示す。）であることが必要である。
【００２１】
また、該正極剤組成物の上記粘度比は、２０℃における均質化の後、３０分放置後及び２時間放置後の粘度を測定することにより求められるものであり、均質化とは、リチウム遷移金属複合酸化物５ｇ、導電剤、結合剤及び溶媒をそれぞれ上記配合割合の範囲とし、これを容量４５mlのボ−ルミルに充填し、２０℃にて５分間、２５００r.p.m に混練したものを言う。また、該正極剤組成物の上記粘度比１．３以下に特定した理由は、１．３を超えるとゲル化して塗料化できず、正極材が作製できなくなる他、ゲル化に至らなくても、正極のバラツキが生じ、品質保証上、電池の評価をした場合、初期容量が多くの場合低く、仮に高くとも、すぐに劣化して放電容量が小さくなるなどの問題を生じるからである。
【００２２】
また、本発明のリチウム二次電池の正極剤組成物を用いて正極材を作製する方法としては、公知の方法で行えばよく、例えば、正極活物質として上記リチウム遷移金属複合酸化物、導電剤、結合剤及び溶媒を、例えばボ−ルミルにて、十分混練し、混練後のペ−ストをアルミ箔等の導電性基板に塗布し、その後乾燥してプレス等にて適宜の形状に打ち抜き正極材とする方法が挙げられる。
【００２３】
また、本発明におけるリチウム二次電池は、上記正極材を用いて、リチウム二次電池を構成する各部材を積層してリチウム二次電池を作製すればよい。
【００２４】
該二次電池は、例えばポ−タブル電子機器の電源、各種メモリ−やソ−ラ−バッテリ−のバックアップ電源、電気自動車、電力貯蔵用バッテリ−などの広い用途に使用できる。
【００２５】
【実施例】
次に、実施例を挙げて、本発明をさらに具体的に説明するが、これは、単に例示であって、本発明を制限するものではない。
【００２６】
実施例１〜１０、比較例１〜５
公知の反応により、数種のＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４を得た。次いで、該物質中の水酸化リチウム含有量を下記方法により求めた。結果を全アルカリ量とともに表１に示す。また、該物質を用い、下記方法により正極材組成物を作製し、粘度比Ｘを求めた。結果を表１に示す。表中、リチウム遷移金属酸化物Ｎｏ．１はＬｉＣｏＯ２、Ｎｏ．２はＬｉＮｉＯ２、Ｎｏ．３はＬｉＭｎ ２ Ｏ ４ を示す。
【００２７】
（リチウム遷移金属酸化物中に含まれる水酸化リチウムの定量分析）
ＬｉＣｏＯ2 、ＬｉＮｉＯ2 又は、ＬｉＭｎ2 Ｏ4 の試料を３０ｇビ−カ−に計り取り、マグネチックスタラ−を用いて純水１００ｇ中で３０分間分散させる。分散させた後、ろ過を行いろ液を回収する。ろ液にフェノ−ルフタレインを加え、１Ｎ−ＨＣ１で滴定し、ａmlを得る（第１終点）。次いでＢＰＢ（ブロモフェノ−ルブル−）を加え１Ｎ−ＨＣ１で滴定し、ｂmlを得る。（第２終点）。（ａ−ｂ）mlを残存水酸化リチウム（ＬｉＯＨ）量とした。
【００２８】
（正極剤組成物の作製及び粘度測定）
リチウム遷移金属複合酸化物５ｇ、グラファイト１．０ｇ、ＰＶＤＦ０．３ｇ、Ｎ−メチル−２−ピロリドン４mlを４５mlの容量をもつボ−ルミルに入れ、２５００rpm にて、２０℃、５分間混練した。混練終了後、得られた混合スラリ−（正極剤組成物）を３０分及び２時間放置後、２０℃の温度下、Ｂ型粘度計でロ−タ回転速度１．５r.p.m.、測定時間２０秒の条件でそれぞれ測定を行う。
【００２９】
【表１】
（リチウム二次電池の作製）
次に、上記方法で作成された混練後の正極剤組成物をアルミ箔に塗布した後乾燥し、２ｔ／cm2 の圧力によりプレスして２cm角に打ち抜いて正極材を得た。また、リチウム二次電池は、電解液にエチレンカ−ボネ−ト（ＥＣ）／ジエチルカ−ボネ−ト（ＤＥＣ）の混合溶媒にＩＭのＬｉＣｌＯ4 を溶解させたものを使用し、負極にはリチウム金属を用いて作製した。
【００３１】
（電池性能の評価）
作製したリチウム二次電池を作動させ、初期放電容量を測定して電池性能を評価した。その結果を表１に示した。
（初期放電容量の測定）
初期放電容量は正極に対して０．５mA／cm2 で４．２Ｖまで充電した後、２．７Ｖまで放電させる充放電を繰り返すことにより測定した。
【００３２】
【発明の効果】
本発明は、数多くの実験に基づき、電池性能のパラメ−タとして、リチウム遷移金属複合酸化物中の特定アルカリ度及び正極剤組成物の特定粘度を設定することにより、安定な正極剤組成物を得ることができ、これにより優れた放電容量及びサイクル特性を示す信頼性の高い電池を得ることができた。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode composition containing a stable lithium transition metal composite oxide as a positive electrode active material for a lithium secondary battery, and a lithium secondary battery using the same.
[0002]
[Prior art]
In recent years, as portable electronic devices have become increasingly portable and cordless, lithium secondary batteries have been put to practical use as power sources for small electronic devices. Regarding this lithium secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium secondary batteries ("Material Research Bulletin" vol15, P783-789 (1980)). Since then, research and development on lithium transition metal oxide-based positive electrode active materials including lithium cobalt oxide have been actively carried out, and many proposals have been made so far.
[0003]
Among them, as lithium cobaltate that has been put into practical use at an early stage, for example, lithium cobalt oxide having a lithium cobalt oxide composition of LixCoO 2 (105 ≦ x ≦ 13) (Japanese Patent Laid-Open No. 3-127454), LixCoO 2 (where 0 <x ≦ 1) to make it cobalt rich (Japanese Patent Laid-Open No. 3-134969), doped with metal ions such as Mn, W, Ni, La and Zr (JP-A-3-201368, JP-A-4-328277, JP-A-4-319259, JP-A-4-319260) and the like have been proposed.
[0004]
Other lithium transition metal oxides include, for example, Li 1-a NiO 2 (where 0 ≦ a ≦ 1) (US Pat. No. 4,302,518), Li b Ni 2-b O 2 and LiNi 1-d. Co d O 2 (where, 0.84 ≦ b ≦ 1.22,0.09 ≦ d ≦ 0.5) ( JP-A 2-40861 discloses), Li n Ni m Co 1 -m O 2 ( where, There have been proposed composite oxides mainly composed of lithium and a transition metal, such as 0 <m ≦ 0.75, n ≦ 1) (Japanese Patent Laid-Open No. 63-299056).
[0005]
In the positive electrode active material, the alkali in the material is a problem, and the residual Li 2 CO 3 in the lithium cobaltate is 10% by weight or less (Japanese Patent Laid-Open Nos. 4-56064 and 4-328278). ), Lithium in which the surface of the positive electrode is coated with lithium carbonate (Japanese Patent Laid-Open No. 4-329268), Li x MO 2 (where 0.3 ≦ x ≦ 1.2, M represents a transition metal) and Na A total K content of 1000 ppm or less (JP-A-5-343006), a residual alkali amount in a composite metal oxide containing Li and Co as main components and 0.15% by weight or less (special No. 5-74455). Each of these specifies the amount of alkali in the lithium transition metal oxide as the positive electrode active material, but these are current interrupting means that operate in response to an increase in discharge capacity and an increase in the internal pressure of the battery. The purpose is to prevent current collector corrosion, improve cycle characteristics at high temperature, storage characteristics and safety.
[0006]
When a positive electrode of a lithium secondary battery is produced using such a lithium transition metal oxide, the physical characteristics of the material constituting the lithium secondary battery significantly affect the battery characteristics. For example, a sheet-like electrode produced by applying a positive electrode paste to an aluminum foil or the like by a roll rolling method has a coating film that is significantly thicker than a photographic film or a plate making material. Depending on the physical properties of the strike, the composition of the positive electrode agent varies, and the variation (variation) in discharge capacity increases. Therefore, it may not be possible to produce a sheet-like positive electrode plate with improved cycle characteristics. These causes are still unclear, but in many cases, it is considered to be due to the chemical and physical characteristics of the lithium composite oxide of the positive electrode active material.
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a stable positive electrode composition and a lithium secondary battery exhibiting excellent discharge capacity and cycle characteristics.
[0008]
[Means for Solving the Problems]
In such a situation, the present inventors have conducted intensive studies, and as a result, in producing a positive electrode of a lithium secondary battery, the lithium transition metal composite oxide, which is a positive electrode active material, contains lithium hydroxide substantially present therein. The stability of the positive electrode composition under certain conditions greatly affects the stability of the positive electrode agent in relation to each other, and if these are controlled to a certain level or less, a stable positive electrode material without variations can be obtained. And a secondary battery using the same has been found to exhibit excellent discharge capacity and cycle characteristics, and the present invention has been completed.
[0009]
That is, this invention comprises a positive electrode active material in the positive electrode composition for lithium secondary batteries (it does not contain an organic acid compound) containing a positive electrode active material, a electrically conductive agent, polyvinylidene fluoride, and a solvent . The residual lithium hydroxide content in the lithium transition metal composite oxide is 0.4 % by weight or less as measured by a neutralization titration method, and the viscosity ratio X in the positive electrode composition is X = B / A ≦ 1.3
(In the formula, A represents the viscosity ( cP ) after 30 minutes of homogenization at 20 ° C., and B represents the viscosity ( cP ) after 2 hours of homogenization at 20 ° C.). A positive electrode composition is provided.
[0010]
Moreover, this invention provides the lithium secondary battery comprised with the said positive electrode agent composition.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the lithium transition metal composite oxide constituting the positive electrode active material has the formula (1);
LixAyOz (1)
(In the formula, A represents at least one transition metal atom selected from Co, Ni, and Mn, and represents 0.05 ≦ x ≦ 1.1, 0 ≦ y ≦ 2.0, and 2 ≦ z.) It is represented by The lithium transition metal composite oxide is not particularly limited as long as it satisfies the formula (1), but one or more selected from lithium cobaltate, lithium nickelate, and lithium manganate may be mentioned, Specifically, for example LiCoO 2, LiNiO 2, LiCo 0 . 8 Ni 0. 2 O 2, LiCo 0. 8 Mn 0. 2 O 2, LiMn 2 O 4 or the like can be used.
[0012]
In the present invention, the lithium transition metal composite oxide has a residual lithium hydroxide content of 0.4 wt% (hereinafter referred to as “%”) or less as measured by a neutralization titration method. It is necessary. Usually, impurities contained in the lithium transition metal composite oxide are unreacted substances such as lithium carbonate, cobalt oxide, nickel hydroxide, and nickel oxide used as raw materials. In particular, lithium carbonate tends to react with moisture in the air during the reaction or after the reaction to become lithium hydroxide. The amount of lithium hydroxide in the impurities is 0. 0 in the lithium transition metal oxide. If it is present in an amount exceeding 4%, it has an effect of increasing the viscosity with the passage of time when producing the positive electrode composition, and the discharge characteristics such as the initial capacity are deteriorated, which is not preferable. Accordingly, in order to obtain a lithium composite metal oxide of 0.4% or less, the selection of raw materials and the control of the reaction, etc. are performed appropriately, and the selection is performed by an analytical test.
[0013]
The neutralization titration method is also called the Warder method or the Winkler method, and is known as a quantitative analysis method for a mixture of lithium hydroxide and lithium carbonate (for example, Analytical Chemistry, Baifukan, Abe, 1950) Issue, pages 223-224). In this titration, first, phenolphthalein is used as an indicator, half of the total lithium hydroxide and lithium carbonate are neutralized, and the remaining carbonate is neutralized from the phenolphthalein endpoint to the endpoint with methyl orange indicator. Is. That is,
The following formulas (2) to (4);
LiOH + HC1 → LiC1 + H 2 O (2)
Li 2 CO 3 + HC1 → LiC1 + LiHCO 3 (3)
LiHCO 3 + HC1 → LiC1 + CO 2 + H 2 O (4)
Where the total titer of formula (2) and formula (3) is aml and the titer of formula (4) is bml, the following relationship holds:
[0014]
a (ml) = volume of HCl equivalent to total LiOH + 1/2 Li 2 CO 3 b (ml) = volume of HCl equivalent to 1/2 Li 2 CO 3 (ab) (ml) = equivalent to total LiOH HCl volume ie is, twice the amount of HCl required for the second round of the titration b (ml) corresponds to a total amount of lithium carbonate acid, amount of HCl required for the first round of the titration a (ml) (Ab) (ml) obtained by subtracting the amount of HCl b (ml) required for the second titration is the total amount of lithium hydroxide.
[0015]
Other physical property values of the lithium transition metal oxide are not particularly limited, but are preferably powders having a BET specific surface area of 0.1 to 1.0 m 2 / g and an average particle diameter of 5 to 20 μm. In addition, other physical properties such as particle shape and surface charge state or various physical properties will be described later even in the same physical property range depending on the conditions of ceramization such as firing atmosphere during production, firing speed and maximum set temperature. The viscosity ratio of the positive electrode composition may be different.
[0016]
In the present invention, the positive electrode material of the lithium secondary battery is mainly composed of a positive electrode material such as a conductive agent, a binder, and a solvent with the powder of the lithium transition metal composite oxide as a main ingredient. The conductive agent is not particularly limited as long as it is an electronic conductive material that does not cause a chemical change. Usually, natural graphite such as scaly graphite and scaly graphite, artificial graphite, carbon black, acetylene black, ketjen Examples thereof include black, carbon fiber, metal powder, metal fiber, and polyphenylene derivative, and one or a mixture of these can be used.
[0017]
Examples of the binder include polysaccharides, heat flammable resins, and polymers having rubber elasticity. Specific examples include polyvinylidene fluoride (PVDF) and polyfluorinated ethylene (PTFE). The binder may be dissolved in a solvent, or may be precipitated as dispersed or suspended. Moreover, you may use a binder as a 1 type, or 2 or more types of mixture.
[0018]
The solvent is not particularly limited, and examples thereof include N-methylpyrrolidone, xylene, toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexane, ethanol, methanol, methyl acetate, ethyl acetate, methylene chloride and ethylene chloride. Etc. Moreover, you may use this as a 1 type, or 2 or more types of mixture.
[0019]
The mixing ratio of the positive electrode active material, the conductive agent, the binder, and the solvent constituting the positive electrode composition is not particularly limited, but the conductive agent is 1 to 50 parts by weight, preferably 100 parts by weight of the positive electrode active material. 1 to 30 parts by weight, 0.11 to 50 parts by weight of binder, preferably 0.11 to 30 parts by weight and solvent 30 to 600 parts by weight, preferably 30 to 100 parts by weight are sufficient. This is preferable from the viewpoint of the discharge capacity and the discharge cycle characteristics.
[0020]
The positive electrode composition for a lithium secondary battery of the present invention is composed of the composition of the above materials, and the viscosity ratio X of the positive electrode composition is
X = B / A ≦ 1.3
(In the formula, A indicates the viscosity ( cP ) after 30 minutes of homogenization at 20 ° C., and B indicates the viscosity ( cP ) after 2 hours of homogenization at 20 ° C.). .
[0021]
The viscosity ratio of the positive electrode composition is determined by measuring the viscosity after standing for 30 minutes and after standing for 2 hours after homogenization at 20 ° C. The metal composite oxide 5g, the conductive agent, the binder and the solvent are each in the above blending ratio range, filled in a 45 ml capacity ball mill, and kneaded at 2500 rpm for 5 minutes at 20 ° C. . The reason why the viscosity ratio of the positive electrode composition is specified to be 1.3 or less is that if it exceeds 1.3, it cannot be gelled and formed into a paint, and a positive electrode material cannot be produced. This is because, when the battery is evaluated for quality assurance, the initial capacity is low in many cases, and even if it is high, there is a problem that the discharge capacity is reduced and the discharge capacity is reduced.
[0022]
Moreover, as a method of producing a positive electrode material using the positive electrode composition of the lithium secondary battery of the present invention, a known method may be used. For example, the above lithium transition metal composite oxide, conductive agent as a positive electrode active material The binder and solvent are sufficiently kneaded, for example, in a ball mill, the paste after kneading is applied to a conductive substrate such as aluminum foil, and then dried and punched into an appropriate shape with a press or the like. Examples of the method include making a material.
[0023]
Moreover, the lithium secondary battery in this invention should just produce a lithium secondary battery by laminating | stacking each member which comprises a lithium secondary battery using the said positive electrode material.
[0024]
The secondary battery can be used in a wide range of applications such as a power source for portable electronic devices, a backup power source for various memories and solar batteries, an electric vehicle, and a battery for storing power.
[0025]
【Example】
EXAMPLES Next, the present invention will be described more specifically with reference to examples. However, this is merely an example and does not limit the present invention.
[0026]
Examples 1-10, Comparative Examples 1-5
Several types of LiCoO 2 , LiNiO 2 and LiMn 2 O 4 were obtained by a known reaction. Next, the lithium hydroxide content in the substance was determined by the following method. The results are shown in Table 1 together with the total alkali amount. Moreover, the positive electrode material composition was produced by the following method using the substance, and the viscosity ratio X was determined. The results are shown in Table 1. In the table, lithium transition metal oxide No. 1 is LiCoO 2 , No. 1 2 is LiNiO 2 , No. 2 ; 3 represents LiMn 2 O 4 .
[0027]
(Quantitative analysis of lithium hydroxide contained in lithium transition metal oxide)
A sample of LiCoO 2 , LiNiO 2 or LiMn 2 O 4 is weighed into a 30 g beaker and dispersed in 100 g of pure water using a magnetic stirrer for 30 minutes. After the dispersion, filtration is performed to collect the filtrate. Add phenolphthalein to the filtrate and titrate with 1N-HC1 to obtain aml (first endpoint). BPB (bromophenol blue) is then added and titrated with 1N-HCl to obtain bml. (Second end point). (Ab) ml was defined as the amount of residual lithium hydroxide (LiOH).
[0028]
(Preparation of positive electrode composition and viscosity measurement)
5 g of lithium transition metal composite oxide, 1.0 g of graphite, 0.3 g of PVDF, and 4 ml of N-methyl-2-pyrrolidone were placed in a ball mill having a capacity of 45 ml and kneaded at 2500 rpm for 5 minutes at 20 ° C. After completion of the kneading, the obtained mixed slurry (positive electrode composition) was allowed to stand for 30 minutes and 2 hours, and then at a temperature of 20 ° C. with a B-type viscometer, a rotor rotation speed of 1.5 rpm and a measurement time of 20 Measure each under the second condition.
[0029]
[Table 1]
(Production of lithium secondary battery)
Next, the kneaded positive electrode composition prepared by the above method was applied to an aluminum foil, dried, pressed at a pressure of 2 t / cm 2 , and punched into a 2 cm square to obtain a positive electrode material. Further, the lithium secondary battery uses an electrolyte in which IM LiClO 4 is dissolved in a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC), and lithium metal is used for the negative electrode. It was produced using.
[0031]
(Evaluation of battery performance)
The produced lithium secondary battery was operated and the initial discharge capacity was measured to evaluate the battery performance. The results are shown in Table 1.
(Measurement of initial discharge capacity)
The initial discharge capacity was measured by charging / discharging the positive electrode to 4.2 V at 0.5 mA / cm 2 and then discharging / discharging to 2.7 V.
[0032]
【The invention's effect】
Based on numerous experiments, the present invention provides a stable positive electrode composition by setting a specific alkalinity in the lithium transition metal composite oxide and a specific viscosity of the positive electrode composition as parameters of battery performance. As a result, a highly reliable battery exhibiting excellent discharge capacity and cycle characteristics could be obtained.
Claims (3)
Ｘ＝Ｂ／Ａ≦１．３
（式中、Ａは２０℃における均質化３０分放置後の粘度（ｃＰ）を示し、Ｂは２０℃における均質化２時間放置後の粘度（ｃＰ）を示す。）であることを特徴とするリチウム二次電池用正極剤組成物。Lithium transition metal composite oxide constituting a positive electrode active material in a positive electrode composition for a lithium secondary battery (containing no organic acid compound) comprising a positive electrode active material, a conductive agent, polyvinylidene fluoride, and a solvent The content of residual lithium hydroxide in the solution is 0.4 wt% or less as measured by neutralization titration method, and the viscosity ratio X in the positive electrode composition is X = B / A ≦ 1.3
(In the formula, A represents the viscosity ( cP ) after 30 minutes of homogenization at 20 ° C., and B represents the viscosity ( cP ) after 2 hours of homogenization at 20 ° C.). A positive electrode composition for a lithium secondary battery.
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| JP02214297A JP3769344B2 (en) | 1997-01-21 | 1997-01-21 | Positive electrode composition for lithium secondary battery and lithium secondary battery |
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| JP02214297A JP3769344B2 (en) | 1997-01-21 | 1997-01-21 | Positive electrode composition for lithium secondary battery and lithium secondary battery |
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| JPH10208728A JPH10208728A (en) | 1998-08-07 |
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| US10020503B2 (en) | 2013-03-25 | 2018-07-10 | Kabushiki Kaisha Toshiba | Active material for battery, nonaqueous electrolyte battery, and battery pack |
| US10217995B2 (en) | 2013-09-18 | 2019-02-26 | Kabushiki Kaisha Toshiba | Active material for battery, nonaqueous electrolyte battery, and battery pack |
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| JP2010177030A (en) * | 2009-01-29 | 2010-08-12 | Nippon Chem Ind Co Ltd | Surface treating agent of lithium based composite oxide, surface treating liquid of lithium based composite oxide, electrolyte for lithium-ion secondary battery, positive electrode active material for surface-treated lithium-ion secondary battery and method of manufacturing the same, negative electrode active material for surface-treated lithium-ion secondary battery and method of manufacturing the same, and lithium-ion secondary battery and method of manufacturing the same |
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| JP5709231B1 (en) * | 2014-02-20 | 2015-04-30 | Ｎｅｃエナジーデバイス株式会社 | Positive electrode for lithium ion secondary battery and lithium ion secondary battery using the same |
| KR102278999B1 (en) | 2018-01-19 | 2021-07-20 | 주식회사 엘지에너지솔루션 | Positive electrode, and secondary battery comprising the positive electrode |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3231813B2 (en) * | 1991-09-13 | 2001-11-26 | 旭化成株式会社 | Organic electrolyte battery |
| JP2750077B2 (en) * | 1993-12-08 | 1998-05-13 | 富士電気化学株式会社 | Method for producing electrode slurry for lithium battery |
| FR2752091B1 (en) * | 1996-08-02 | 1998-09-04 | Accumulateurs Fixes | COMPOSITION FOR POSITIVE ELECTRODE, METHOD OF PREPARATION |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10020503B2 (en) | 2013-03-25 | 2018-07-10 | Kabushiki Kaisha Toshiba | Active material for battery, nonaqueous electrolyte battery, and battery pack |
| US10217995B2 (en) | 2013-09-18 | 2019-02-26 | Kabushiki Kaisha Toshiba | Active material for battery, nonaqueous electrolyte battery, and battery pack |
| US20210036319A1 (en) * | 2019-08-02 | 2021-02-04 | Samsung Sdi Co., Ltd. | Positive active material for rechargeable lithium battery, method of preparing the same, positive electrode for rechargeable lithium battery including the same and rechargeable lithium battery including the same |
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| JPH10208728A (en) | 1998-08-07 |
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