JP3613869B2

JP3613869B2 - Non-aqueous electrolyte battery

Info

Publication number: JP3613869B2
Application number: JP00706496A
Authority: JP
Inventors: 定幸浅岡; 庄一郎渡邊; 茂雄小林
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1996-01-19
Filing date: 1996-01-19
Publication date: 2005-01-26
Anticipated expiration: 2016-01-19
Also published as: JPH09199127A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水電解液二次電池の、特にその正極活物質の結晶構造に関するものである。
【０００２】
【従来の技術】
近年、民生用電子機器のポータブル化、コードレス化が急速に進んでいる。現在、これら電子機器の駆動用電源としての役割をニッケル−カドミウム電池あるいは密閉型小型鉛蓄電池が担っているが、ポータブル化、コードレス化が進展し定着するに従い、駆動用電源となる二次電池の高エネルギー密度化、小型軽量化の要望が強くなっている。
【０００３】
このような状況から、例えば特開昭６３−５９５０７号公報に示されているように、高い作動電圧を示すリチウム複合遷移金属酸化物例えばＬｉＣｏＯ_２を正極活物質に用い、リチウムイオンの挿入・離脱を利用した非水電解液二次電池が提案されている。
【０００４】
【発明が解決しようとする課題】
リチウムコバルト複合酸化物は作動電圧は高いものの資源的に稀少でコストの面で割高となり、また放電容量も小さい。これに対してリチウムニッケル複合酸化物は資源的には豊富であるが放電容量は十分であるとはいえず、充放電サイクルを繰り返し行うことにより容量が徐々に低下するサイクル劣化の問題がある。
【０００５】
これらの問題を解決するために、粉末Ｘ線回折法によりリチウムニッケル複合酸化物の結晶状態と放電容量との相関について様々な検討がなされている。線源にＣｕＫαを用いた粉末Ｘ線回折における２θ＝１８°〜２０°付近の（００３）面の回折ピーク及び２θ＝４４°〜４６°付近の（１０４）面の回折ピークの強度比（特開平６−６０８８７号公報、特開平５−２９０８４５号公報、特開平６−２１５７７３号公報）や半価幅（特開平６−２６７５３９号公報）と放電容量との間に一定の相関があることが報告されている。
【０００６】
またＬｉ_ｘＮｉＯ_２は電池の充放電に伴い結晶相が変化することが報告されており（Ｗ．Ｌｉ，Ｊ．Ｎ．ＲｅｉｍｅｒｓａｎｄＪ．Ｒ．Ｄａｈｎ，ＳｏｌｉｄＳｔａｔｅＩｏｎｉｃｓ，１２３−１３０，６７（１９９３））、特に充電終止電圧に対応する０．１８≦ｘ≦０．３２の領域では、いずれもＲ−３ｍに帰属されるＣ軸長の異なる２種類の結晶相が混在することが知られている。
【０００７】
結晶中に上述の様な２種類の結晶相が存在することにより結晶に歪みが生じ、充放電サイクルを繰り返すうちに構造破壊が生じ一部が可逆性を失って充放電容量が低下するものと考えられる。
【０００８】
一方、米国特許第４，９８０，０８０号、特開平５−３２５９６６号公報に示されているように、リチウムニッケル複合酸化物のニッケルの一部をコバルトで置換したＬｉ_ｘＮｉ_{（１−ｙ）}Ｃｏ_ｙＯ_２が合成され、サイクル特性の改善が報告されている。
【０００９】
本発明の目的は上記正極活物質に関する問題点の解決を図るものであり、充電終了時において正極活物質中に２種類の結晶相が混在することにより結晶構造が破壊されることを防止して、充放電サイクル特性の優れた非水電解液二次電池を提供するものである。
【００１０】
【課題を解決するための手段】
本発明は一般式Ｌｉ_xＮｉ_(1-y)Ｍ_yＯ₂（０≦ｘ≦１．２，０＜ｙ≦０．５，ＭはＴｉ，Ｖ，Ｃｒ，Ｍｎ，Ｆｅ，Ｃｏ，Ｃｕ，Ｚｎ，Ａｌ，Ｂの金属元素のうち一種類以上）で表されるリチウムニッケル複合酸化物（ただし、下記の一般式（Ｉ）
Ｌｉ_xＮｉ_1-yＭｅ_yＯ₂ （Ｉ）
（式中、ＭｅはＮｉ以外の遷移金属元素、０＜ｘ＜１．１、０≦ｙ＜０．６を表す）で表されるリチウム複合酸化物において、Ｘ線回折によるリートベルト解析法による３ａサイトに占めるリチウム含有率が９０％以上で、かつ六方晶の層状化合物（空間群Ｒ−３ｍ）に属する上記リチウム複合酸化物の純度が９０％以上であることを特徴とするリチウム複合酸化物を除く）、
を主材とする正極と、リチウム、リチウム合金またはリチウムイオンを吸蔵・放出する化合物を主材とする負極とを備えたリチウム電池に関するものであって、前記リチウムニッケル複合酸化物が、充電終了時において単一の結晶相のみから成り、Ｒ−３ｍに帰属される結晶相となることを特徴とする。
【００１１】
ここで、充電終了時とは、充電時の電池の開回路電圧がリチウムに対して３．９〜４．３Ｖで、かつ正極活物質のＸの値が０．１≦Ｘ≦０．５である場合である。
【００１２】
【発明の実施の形態】
具体的には、リチウムニッケル複合酸化物のニッケルの一部を異種元素で置換すると共に、その置換元素の添加方法は、ニッケル水酸化物と置換元素水酸化物を濃度を限定すると共に同時に析出させる共沈法により生成したＮｉ_{（１−ｙ）}Ｍ_ｙ（ＯＨ）_２を原料とし、リチウム化合物と共に焼成することによるものである。
【００１３】
前記の方法で合成したＬｉ_ｘＮｉ_{（１−ｙ）}Ｍ_ｙＯ_２は、充電終了時の正極板のＣｕＫα線を使用したＸ線回折において、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが単一ピークであることを特徴とする。
【００１４】
なお、正極板そのもののＸ線回折の測定は、正極板の平面をＸ線装置の試料台に平行に設置して行った。
【００１５】
Ｌｉ_ｘＮｉＯ_２には充電終止電圧に対応する０．１８≦ｘ≦０．３２の領域では、いずれもＲ−３ｍに帰属されるＣ軸長の異なる２種類の結晶相が混在することが知られている。
【００１６】
このため充放電サイクルを繰り返すたびに結晶に歪みが生じ、構造破壊により一部が可逆性を失って充放電容量が低下するものと考えられる。
【００１７】
本発明のＬｉ_ｘＮｉ_{（１−ｙ）}Ｍ_ｙＯ_２で表されるリチウムニッケル複合酸化物のうち、充電終了時の正極板のＣｕＫα線を使用したＸ線回折において、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークがともに単一ピークとなるものは、Ｒ−３ｍまたはＣ２／ｍに帰属される単一の結晶相のみを有するため、充電終止電圧付近における結晶格子の歪みが小さく構造破壊を防止でき、電池の充放電サイクル特性を向上させることができる。
【００１８】
なお、このような特性は単にニッケルの一部を異種元素で置換するだけでは得られないものである。
【００１９】
【実施例】
以下、本発明の実施例を図面を参照しながら説明する。
【００２０】
なお、試作電池の充電は４．２Ｖまで定電流５００ｍＡで行った後、さらに４．２Ｖの定電圧でトータル２時間行い、放電は３．０Ｖまで定電流７５０ｍＡで行った。
【００２１】
充電状態の正極板のＸ線回折の測定は、５サイクル目の充電状態の電池を分解して正極板を取り出し、正極板の平面をＸ線装置の試料台に平行に設置し、ＣｕＫα線を使用して行った。本発明の実施例および比較例の電池の充電終了時における正極板のＸ線回折図を図１（ａ）〜（ｃ）に示す。また比較として充電前の電池の正極板のＸ線回折図を図１（ｄ）に示す。
【００２２】
（実施例１）
図２に本実施例で用いた円筒形電池の縦断面図を示す。図２において１は耐有機電解液性のステンレス鋼板を加工した電池ケース、２は安全弁を設けた封口板、３は絶縁パッキングを示す。４は極板群であり、正極板５及び負極板６がセパレーター７を介して複数回渦巻状に巻回されてケース内に収納されている。そして上記正極板５からは正極アルミリード５ａが引き出されて封口板２に接続され、負極板６からは負極ニッケルリード６ａが引き出されて電池ケース１の底部に接続されている。８は絶縁リングで極板群４の上下部にそれぞれ設けられている。
【００２３】
負極合剤は、コークスを加熱処理した炭素粉１００重量部に、スチレンブタジエンゴム３．５重量部を混合し、カルボキシメチルセルロース水溶液に懸濁させたペースト状ものを用いた。このペーストを厚さ０．０１５ｍｍの銅箔の両面に塗着し、乾燥後０．２ｍｍに圧延し、幅３９ｍｍ、長さ４２５ｍｍの大きさに切り出して負極板６とした。
【００２４】
正極活物質の合成には共沈法により合成した水酸化ニッケルを用いた。すなわち、硫酸ニッケル（ＮｉＳＯ_４）水溶液と硫酸コバルト（ＣｏＳＯ_４）水溶液を混合し、温度及びｐＨを制御して沈殿を析出させ、ニッケルの一部をＣｏで置換した一般式Ｎｉ_{（１−ｙ）}Ｃｏ_ｙ（ＯＨ）_２で表される水酸化ニッケルのうち、ｙ＝０．１０、０．１５、０．２０、０．３０および０．５０のものを合成した。但し、他のコバルト塩（例えばＣｏ（ＮＯ_３）_２）を用いた場合にも同様の合成が可能であった。
【００２５】
水酸化リチウム−水和物（ＬｉＯＨ・Ｈ_２Ｏ）と上記水酸化ニッケル（Ｎｉ_{（１−ｙ）}Ｃｏ_ｙ（ＯＨ）_２）とのＬｉ：Ｎｉ＋Ｃｏ原子比１：１混合物を空気雰囲気下、７００℃で５時間熱処理してリチウムニッケル複合酸化物粉末ＬｉＮｉ_{（１−ｙ）}Ｃｏ_ｙＯ_２を得た。
【００２６】
正極合剤は、前記正極活物質粉末１００重量部に、アセチレンブラック５重量部、ポリフッ化ビニリデン（ＰＶＤＦ）５重量部を混合し、Ｎ−メチルピロリジノンに懸濁させたペースト状のものを用いた。このペーストを厚さ０．０２０ｍｍのアルミニウム（Ａｌ）箔の両面に塗着し、乾燥後０．１３ｍｍに圧延し、幅３７ｍｍ、長さ３８０ｍｍの大きさに切り出して正極板５とした。
【００２７】
炭酸エチレン（ＥＣ）と炭酸ジエチル（ＤＥＣ）の等容積混合溶媒に、六フッ化リン酸リチウム（ＬｉＰＦ_６）を１．５ｍｏｌ／ｌの割合で溶解させ電解液とした。
【００２８】
正極板５と負極板６をセパレーター７を介して渦巻状に巻回し、直径１６．３ｍｍ、高さ５０．７ｍｍの電池ケースに収納した。電解液を極板群４に注入した後、電池を密封口し、試験電池とした。
【００２９】
この様にして作製した電池のうち、ｙ＝０．１０のものを電池Ａ、ｙ＝０．１５のものを電池Ｂ、ｙ＝０．２０のものを電池Ｃ、ｙ＝０．３０のものを電池Ｄ、ｙ＝０．５０のものを電池Ｅとした。
【００３０】
電池Ａ，Ｂ，Ｃ，Ｄ，Ｅの充電終了時の正極板のＸ線回折図はいずれも図１（ａ）と同様の特徴を有していた。すなわち、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが共に単一ピークであった。このＸ線回折図により、Ｒ−３ｍに帰属される単一の結晶相のみを有する。
【００３１】
（実施例２）
ニッケルの一部をＭｎで置換した一般式Ｎｉ_{（１−ｙ）}Ｍｎ_ｙ（ＯＨ）_２で表される水酸化ニッケルのうち、ｙ＝０．１１および０．１６のものを共沈法により合成した。水酸化リチウム−水和物（ＬｉＯＨ・Ｈ_２Ｏ）と前記水酸化ニッケル（Ｎｉ_{（１−ｙ）}Ｍｎ_ｙ（ＯＨ）_２）とのＬｉ：Ｎｉ＋Ｍｎ原子比１：１混合物を空気雰囲気下、８００℃で２４時間熱処理してリチウムニッケル複合酸化物粉末ＬｉＮｉ_{（１−ｙ）}Ｍｎ_ｙＯ_２を得た。
【００３２】
ｙ＝０．１１のものを電池Ｆ、ｙ＝０．１６のものを電池Ｇとした。
電池ＦおよびＧの充電終了時の正極板のＸ線回折図はいずれも図１（ａ）と同様の特徴を有していた。すなわち、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが共に単一ピークであった。このＸ線回折図により、Ｒ−３ｍに帰属される単一の結晶相のみを有する。
【００３３】
（実施例３）
ニッケルの一部をＡｌで置換した一般式Ｎｉ_{（１−ｙ）}Ａｌ_ｙ（ＯＨ）_２で表される水酸化ニッケルのうち、ｙ＝０．１０のものを共沈法により合成した。水酸化リチウム−水和物（ＬｉＯＨ・Ｈ_２Ｏ）と前記水酸化ニッケル（Ｎｉ_{（１−ｙ）}Ａｌ_ｙ（ＯＨ）_２）とのＬｉ：Ｎｉ＋Ａｌ原子比１：１混合物を空気雰囲気下、７００℃で５時間熱処理してリチウムニッケル複合酸化物粉末ＬｉＮｉ_{（１−ｙ）}Ａｌ_ｙＯ_２を得た。
【００３４】
前記正極活物質粉末を用いた他は（実施例１）と同様に電池を作製し、この電池を電池Ｈとした。
【００３５】
電池Ｈの充電終了時の正極板のＸ線回折図はいずれも図１（ａ）と同様の特徴を有していた。すなわち、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが共に単一ピークであった。このＸ線回折図により、Ｒ−３ｍに帰属される単一の結晶相のみを有する。
【００３６】
（比較例１）
水酸化リチウム−水和物（ＬｉＯＨ・Ｈ_２Ｏ）と水酸化ニッケル（Ｎｉ（ＯＨ）_２）とのＬｉ：Ｎｉ原子比１：１混合物を酸素雰囲気下、７００℃で１３時間熱処理してリチウムニッケル複合酸化物粉末ＬｉＮｉＯ_２を得た。
【００３７】
前記正極活物質粉末を用いた他は（実施例１）と同様に電池を作製し、この電池を電池Ｉとした。
【００３８】
電池Ｉの充電状態の正極板のＸ線回折図は図１（ｂ）に示すように２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが共に分裂している。このＸ線回折図により、いずれもＲ−３ｍに帰属されるＣ軸長の異なる２種類の結晶相が混在することが分かる。
【００３９】
（比較例２）
水酸化ニッケル（Ｎｉ（ＯＨ）_２）と酸化コバルト（Ｃｏ_３Ｏ_４）のＮｉ／Ｃｏ比０．９５／０．０５、０．９０／０．１０、０．８５／０．１５、０．８０／０．２０および０．５０／０．５０混合物に、それぞれ水酸化リチウム−水和物（ＬｉＯＨ・Ｈ_２Ｏ）をＬｉ：Ｎｉ＋Ｃｏ原子比１：１で混合し、酸素雰囲気下、７００℃で５時間熱処理してリチウムニッケル複合酸化物粉末ＬｉＮｉ_{（１−ｙ）}Ｃｏ_ｙＯ_２（ｙ＝０．０５，０．１０，０．１５，０．２０，０．５０）を得た。
【００４０】
前記正極活物質粉末を用いた他は（実施例１）と同様に電池を作製し、このうち、ｙ＝０．０５のものを電池Ｊ、ｙ＝０．１０のものを電池Ｋ、ｙ＝０．１５のものを電池Ｌ、ｙ＝０．２０のものを電池Ｍ、ｙ＝０．５０のものを電池Ｎとした。
【００４１】
電池Ｊ，Ｋ，Ｌ，Ｍ，Ｎの充電状態の正極板のＸ線回折図はいずれも図１（ｃ）と同様の特徴を有していた。すなわち、２θ＝１８°〜２０°付近の回折ピークの低角側にわずかに分裂ピークが見られ、回折ピーク自体が広幅化している。このＸ線回折図により、わずかに複数の結晶相が混在し結晶相が乱れていることが分かる。
【００４２】
本発明の実施例および比較例の電池のサイクル試験結果を（表１）に示す。なお、電池Ａ〜Ｎはそれぞれ３０個組み立てて試験を行い、（表１）には平均値を示した。
【００４３】
【表１】

【００４４】
この試験結果から以下のことが分かる。
ＬｉＮｉＯ_２を正極活物質として用いた電池Ｉでは、Ｘ線回折図により、活物質中にいずれもＲ−３ｍに帰属されるＣ軸長の異なる２種類の結晶相が混在することが分かる。結晶中にこの様な２種類の結晶相が存在することにより結晶に歪みが生じ、充放電サイクルを繰り返すうちに構造破壊が生じ一部が可逆性を失って充放電容量が低下するため、電池Ｉはサイクル特性が極端に悪いことが分かる。
【００４５】
ＬｉＯＨ・Ｈ_２Ｏ、Ｎｉ（ＯＨ）_２およびＣｏ_３Ｏ_４から成る混合物を熱処理することによって得られたＬｉＮｉ_{（１−ｙ）}Ｃｏ_ｙＯ_２を正極活物質として用いた電池Ｊ，Ｋ，Ｌ，Ｍ，Ｎでは、Ｘ線回折図により、わずかに複数の結晶相が混在し結晶相が乱れていることが分かる。これらの電池の場合にも結晶の歪みにより構造破壊が生じるため、電池Ｊ，Ｋ，Ｌ，Ｍ，Ｎはサイクル特性が悪いことが分かる。
【００４６】
共沈法により生成したＮｉ_{（１−ｙ）}Ｃｏ_ｙ（ＯＨ）_２（０＜ｙ≦０．５）から合成したリチウムニッケル複合酸化物ＬｉＮｉ_{（１−ｙ）}Ｃｏ_ｙＯ_２を正極活物質として用いた電池Ａ，Ｂ，Ｃ，Ｄ，Ｅでは、Ｘ線回折図により、活物質中にＲ−３ｍに帰属される単一の結晶相のみを有する。この様なリチウムニッケル複合酸化物では充電終止電圧付近における結晶格子の歪みが小さく構造破壊を生じないため、電池Ａ，Ｂ，Ｃ，Ｄ，Ｅは良好なサイクル特性を示す。
【００４７】
但し、電池Ａの充電状態の正極板のＸ線回折図は、２θ＝１８°〜２０°付近の回折ピークおよび２θ＝４４°〜４６°付近の回折ピークが共にわずかに非対称であり、わずかに結晶相が乱れている。このため電池Ｂ，Ｃは電池Ａに比べサイクル特性が優れており、Ｃｏによる置換量はｙ＞０．１０が好ましい。
【００４８】
また、ｙ＝０．５の電池Ｅは初期容量が低く好ましくない。従って、Ｃｏによる置換量は０．１０＜ｙ≦０．３０が好ましい。
【００４９】
共沈法により生成したＭ＝Ｍｎ，ＡｌであるＮｉ_{（１−ｙ）}Ｍ_ｙ（ＯＨ）_２（０＜ｙ≦０．３）から合成したリチウムニッケル複合酸化物ＬｉＮｉ_{（１−ｙ）}Ｍ_ｙＯ_２を正極活物質として用いた電池Ｆ，Ｇ，Ｈの充電状態の正極板のＸ線回折図もまた図１（ａ）に類似したものとなり、初期放電容量は上記のＭ＝Ｃｏである電池Ａ，Ｂ，Ｃに比べて低いものの、良好なサイクル特性を示す。
【００５０】
その他の置換元素（Ｍ＝Ｔｉ，Ｖ，Ｃｒ，Ｆｅ，Ｃｕ，Ｚｎ，Ｂ等）についても同様の効果が得られた。また、上記実施例においては水酸化リチウムを用いて正極活物質を合成したが、炭酸リチウムや硝酸リチウム等のリチウム塩を用いても同様の効果が得られた。
【００５１】
上記実施例においては円筒形の電池を用いて評価を行ったが、角形など電池形状が異なっても同様の効果が得られる。
【００５２】
さらに、上記実施例において負極には炭素材料を用いたが、本発明における効果は正極板において作用するため、リチウムイオンを吸蔵・放出可能な物質であれば特に制限なく用いることができる。例えばリチウムやリチウム合金、Ｆｅ_２Ｏ_３、ＷＯ_２等の酸化物、ＴｉＳ_２等の硫化物など、他の負極材料を用いても同様の効果が得られる。
【００５３】
また、上記実施例において電解液として六フッ化リン酸リチウム（ＬｉＰＦ_６）を使用したが、他のリチウム含有塩、例えば過塩素酸リチウム（ＬｉＣｉＯ_４）、トリフルオロメチルスルホン酸リチウム（ＣＦ_３ＳＯ_３Ｌｉ）、六フッ化砒酸リチウム（ＬｉＡｓＦ_６）等でも同様の効果が得られた。
【００５４】
さらに、上記実施例では炭酸エチレン（ＥＣ）と炭酸ジエチル（ＤＥＣ）の混合溶媒を用いたが、他の非水溶媒、例えば炭酸プロピレン（ＰＣ）等の環状エステル、テトラヒドロフラン（ＴＨＦ）等の環状エーテル、ジメトキシエタン（ＤＭＥ）等の鎖状エーテル、プロピオン酸メチル（ＭＰ）等の鎖状エステルなどの非水溶媒や、これらの多元系混合溶媒を用いても同様の効果が得られた。
【００５５】
【発明の効果】
以上の説明から明らかなように、本発明は充電終了時にＲ−３ｍに帰属される単一の結晶相のみを有するリチウムニッケル複合酸化物を正極活物質に用いることにより、充電終止電圧付近における結晶格子の歪みが小さく構造破壊を防止でき、電池の充放電サイクル特性を向上させることができる。
【００５６】
充放電サイクル特性の優れた非水電解液二次電池を提供することができる。
【図面の簡単な説明】
【図１】（ａ）充電後の電池Ａ〜Ｈの正極板のＸ線回折図
（ｂ）充電後の電池Ｉの正極板のＸ線回折図
（ｃ）充電後の電池Ｊ〜Ｎの正極板のＸ線回折図
（ｄ）充電前の電池Ａ〜Ｅの正極板のＸ線回折図
【図２】円筒形電池の縦断面図
【符号の説明】
１電池ケース
２封口板
３絶縁パッキング
４極板群
５正極板
５ａ正極リード
６負極板
６ｂ負極リード
７セパレーター
８絶縁リング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystal structure of a non-aqueous electrolyte secondary battery, particularly a positive electrode active material thereof.
[0002]
[Prior art]
In recent years, consumer electronic devices have become increasingly portable and cordless. Currently, nickel-cadmium batteries or sealed small lead-acid batteries play a role as power sources for driving these electronic devices. However, as portable and cordless devices become more established and established, secondary batteries that serve as power sources for drive The demand for higher energy density and smaller and lighter weight is increasing.
[0003]
Under such circumstances, for example, as disclosed in Japanese Patent Laid-Open No. 63-59507, lithium composite transition metal oxide showing a high operating voltage, for example, LiCoO ₂ is used as a positive electrode active material, and lithium ion insertion / extraction is performed. A non-aqueous electrolyte secondary battery using the above has been proposed.
[0004]
[Problems to be solved by the invention]
Although the lithium cobalt composite oxide has a high operating voltage, it is rare in terms of resources, is expensive in terms of cost, and has a small discharge capacity. On the other hand, lithium nickel composite oxide is abundant in terms of resources, but it cannot be said that the discharge capacity is sufficient, and there is a problem of cycle deterioration in which the capacity gradually decreases by repeatedly performing the charge / discharge cycle.
[0005]
In order to solve these problems, various studies have been made on the correlation between the crystalline state of the lithium nickel composite oxide and the discharge capacity by powder X-ray diffraction. Intensity ratio of diffraction peak of (003) plane near 2θ = 18 ° to 20 ° and diffraction peak of (104) plane near 2θ = 44 ° to 46 ° in powder X-ray diffraction using CuKα as a radiation source (special There is a certain correlation between the discharge capacity and the half-value width (Japanese Patent Laid-Open No. 6-267539) and the half-width (Japanese Patent Laid-Open No. 6-267539), and It has been reported.
[0006]
Li _x NiO ₂ has also been reported to change in crystal phase as the battery is charged and discharged (W. Li, JN Reimers and JR Dahn, Solid State Ionics, 123-130, 67 ( 1993)), in particular, in the region of 0.18 ≦ x ≦ 0.32 corresponding to the end-of-charge voltage, it is known that two types of crystal phases with different C-axis lengths belonging to R-3m are mixed. ing.
[0007]
Due to the presence of the two types of crystal phases as described above in the crystal, the crystal is distorted, the structure is destroyed while repeating the charge / discharge cycle, and part of it loses reversibility and the charge / discharge capacity decreases. Conceivable.
[0008]
On the other hand, as shown in US Pat. No. 4,980,080 and JP-A-5-325966, Li _x Ni _{(1-y) in} which a part of nickel in the lithium nickel composite oxide is substituted with cobalt. Co _y O ₂ has been synthesized and improved cycle characteristics have been reported.
[0009]
The object of the present invention is to solve the above-mentioned problems related to the positive electrode active material, and prevents the crystal structure from being destroyed by the mixture of two types of crystal phases in the positive electrode active material at the end of charging. The present invention provides a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics.
[0010]
[Means for Solving the Problems]
The present invention has the general formula _{_{Li x Ni (1-y)}} M y O 2 (0 ≦ x ≦ 1.2,0 <y ≦ 0.5, M is Ti, V, Cr, Mn, Fe, Co, Cu, Lithium nickel composite oxide represented by one or more metal elements of Zn, Al, and B (however, the following general formula (I)
Li _x Ni _1-y Me _y O ₂ (I)
(In the formula, Me represents a transition metal element other than Ni, 0 <x <1.1, 0 ≦ y <0.6). According to the Rietveld analysis method by X-ray diffraction, Lithium composite oxide characterized in that the lithium content in the 3a site is 90% or more and the purity of the lithium composite oxide belonging to the hexagonal layered compound (space group R-3m) is 90% or more except for),
And a lithium battery comprising a negative electrode mainly composed of lithium, a lithium alloy or a compound that absorbs and releases lithium ions, wherein the lithium nickel composite oxide is at the end of charging. It comprises only a single crystal phase in, characterized in that the crystalline phase to be assigned to R-3 m.
[0011]
Here, at the end of charging, the open circuit voltage of the battery at the time of charging is 3.9 to 4.3 V with respect to lithium, and the value of X of the positive electrode active material is 0.1 ≦ X ≦ 0.5. This is the case.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Specifically, a part of nickel in the lithium nickel composite oxide is replaced with a different element, and the addition method of the replacement element is to simultaneously deposit nickel hydroxide and the replacement element hydroxide while limiting the concentration. This is because Ni _(1-y) M _y (OH) ₂ produced by the coprecipitation method is used as a raw material and calcined with a lithium compound.
[0013]
Li _x Ni _(1-y) M _y O ₂ synthesized by the above method has a diffraction peak around 2θ = 18 ° to 20 ° and 2θ in X-ray diffraction using CuKα rays of the positive electrode plate at the end of charging. A diffraction peak near 44 ° to 46 ° is a single peak.
[0014]
The X-ray diffraction measurement of the positive electrode plate itself was performed with the plane of the positive electrode plate placed parallel to the sample stage of the X-ray apparatus.
[0015]
It is known that Li _x NiO ₂ contains two types of crystal phases having different C-axis lengths belonging to R-3m in the region of 0.18 ≦ x ≦ 0.32 corresponding to the end-of-charge voltage. It has been.
[0016]
For this reason, it is considered that each time the charge / discharge cycle is repeated, the crystal is distorted, and part of the crystal loses reversibility due to structural destruction, resulting in a decrease in charge / discharge capacity.
[0017]
Among the lithium nickel composite oxides represented by Li _x Ni _(1-y) M _y O ₂ of the present invention, in X-ray diffraction using CuKα rays of the positive electrode plate at the end of charging, 2θ = 18 ° to 20 ° When the diffraction peak in the vicinity of ° C and the diffraction peak in the vicinity of 2θ = 44 ° to 46 ° both have a single peak have only a single crystal phase attributed to R-3m or C2 / m, the charging is terminated. The distortion of the crystal lattice in the vicinity of the voltage is small, structural breakdown can be prevented, and the charge / discharge cycle characteristics of the battery can be improved.
[0018]
Such characteristics cannot be obtained simply by replacing a part of nickel with a different element.
[0019]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
The prototype battery was charged at a constant current of 500 mA up to 4.2 V, then further charged at a constant voltage of 4.2 V for a total of 2 hours, and discharged at a constant current of 750 mA up to 3.0 V.
[0021]
The X-ray diffraction measurement of the charged positive electrode plate is performed by disassembling the charged battery in the fifth cycle, taking out the positive electrode plate, placing the plane of the positive electrode plate parallel to the sample stage of the X-ray apparatus, and Done using. 1A to 1C show X-ray diffraction patterns of the positive electrode plate at the end of charging of the batteries of the examples and comparative examples of the present invention. For comparison, an X-ray diffraction diagram of the positive electrode plate of the battery before charging is shown in FIG.
[0022]
(Example 1)
FIG. 2 shows a longitudinal sectional view of the cylindrical battery used in this example. In FIG. 2, 1 is a battery case obtained by processing an organic electrolyte resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which a positive electrode plate 5 and a negative electrode plate 6 are wound in a spiral shape through a separator 7 and accommodated in a case. A positive electrode aluminum lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode nickel lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. Insulating rings 8 are provided at the upper and lower portions of the electrode plate group 4, respectively.
[0023]
As the negative electrode mixture, a paste was used in which 3.5 parts by weight of styrene butadiene rubber was mixed with 100 parts by weight of carbon powder obtained by heat-treating coke and suspended in an aqueous carboxymethyl cellulose solution. This paste was applied to both sides of a 0.015 mm thick copper foil, dried and rolled to 0.2 mm, and cut into a size of 39 mm width and 425 mm length to obtain a negative electrode plate 6.
[0024]
Nickel hydroxide synthesized by a coprecipitation method was used for the synthesis of the positive electrode active material. That is, nickel sulfate (NiSO ₄₎ aqueous cobalt sulfate (CoSO ₄₎ aqueous solution were mixed to precipitate precipitated by controlling the temperature and pH, generally a portion of the nickel has been replaced by Co formula _{Ni (1-y)} Among nickel hydroxides represented by Co _y (OH) ₂ , those having y = 0.10, 0.15, 0.20, 0.30 and 0.50 were synthesized. However, the same synthesis was possible when other cobalt salts (for example, Co (NO ₃ ) ₂ ) were used.
[0025]
A Li: Ni + Co atomic ratio 1: 1 mixture of lithium hydroxide-hydrate (LiOH.H ₂ O) and the above nickel hydroxide (Ni _(1-y) Co _y (OH) ₂ ) was added in an air atmosphere to 700 ° C. 5 hours heat treatment to at obtain a lithium nickel composite oxide powder _{_{LiNi (1-y) Co y}} O 2.
[0026]
The positive electrode mixture used was a paste in which 100 parts by weight of the positive electrode active material powder was mixed with 5 parts by weight of acetylene black and 5 parts by weight of polyvinylidene fluoride (PVDF) and suspended in N-methylpyrrolidinone. . This paste was applied to both surfaces of an aluminum (Al) foil having a thickness of 0.020 mm, dried and rolled to 0.13 mm, cut into a size of 37 mm in width and 380 mm in length to obtain a positive electrode plate 5.
[0027]
Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an equal volume mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a rate of 1.5 mol / l to obtain an electrolytic solution.
[0028]
The positive electrode plate 5 and the negative electrode plate 6 were spirally wound through a separator 7 and stored in a battery case having a diameter of 16.3 mm and a height of 50.7 mm. After injecting the electrolyte solution into the electrode plate group 4, the battery was sealed and used as a test battery.
[0029]
Of the batteries thus produced, those with y = 0.10 are batteries A, those with y = 0.15 are batteries B, those with y = 0.20 are batteries C, and those with y = 0.30. Was designated as battery D, and battery E was designated as y = 0.50.
[0030]
All of the X-ray diffraction patterns of the positive electrode plate at the end of charging of the batteries A, B, C, D, and E had the same characteristics as in FIG. That is, the diffraction peak around 2θ = 18 ° to 20 ° and the diffraction peak around 2θ = 44 ° to 46 ° were both single peaks. According to this X-ray diffraction pattern, it has only a single crystal phase attributed to R-3m.
[0031]
(Example 2)
Of the nickel hydroxide represented by the general formula _{_{Ni (1-y) Mn y}} (OH) 2 to a portion of the nickel has been replaced by Mn, synthesized by coprecipitation those y = 0.11 and 0.16 did. Lithium hydroxide - Li of a hydrate (LiOH · _H 2 O) and the nickel hydroxide _{_{(Ni (1-y) Mn}} y (OH) 2): Ni + Mn atomic ratio of 1: 1 mixture under an air atmosphere, 800 ℃ in and heat-treated for 24 hours to obtain a lithium nickel composite oxide powder _{_{LiNi (1-y) Mn y}} O 2.
[0032]
The battery with y = 0.11 was designated as battery F, and the battery with y = 0.16 was designated as battery G.
The X-ray diffraction pattern of the positive electrode plate at the end of the charging of the batteries F and G had the same characteristics as in FIG. That is, the diffraction peak around 2θ = 18 ° to 20 ° and the diffraction peak around 2θ = 44 ° to 46 ° were both single peaks. According to this X-ray diffraction pattern, it has only a single crystal phase attributed to R-3m.
[0033]
(Example 3)
Among nickel hydroxides represented by the general formula Ni _(1-y) Al _y (OH) _{2 in} which a part of nickel was substituted with Al, those having y = 0.10 were synthesized by a coprecipitation method. A Li: Ni + Al atomic ratio 1: 1 mixture of lithium hydroxide-hydrate (LiOH.H ₂ O) and the nickel hydroxide (Ni _(1-y) Al _y (OH) ₂ ) was added in an air atmosphere to 700 ° C. 5 hours heat treatment to at obtain a lithium nickel composite oxide powder _{_{LiNi (1-y) Al y}} O 2.
[0034]
A battery was produced in the same manner as in Example 1 except that the positive electrode active material powder was used.
[0035]
The X-ray diffraction pattern of the positive electrode plate at the end of charging of the battery H had the same characteristics as in FIG. That is, the diffraction peak around 2θ = 18 ° to 20 ° and the diffraction peak around 2θ = 44 ° to 46 ° were both single peaks. According to this X-ray diffraction pattern, it has only a single crystal phase attributed to R-3m.
[0036]
(Comparative Example 1)
Lithium hydroxide-hydrate (LiOH.H ₂ O) and nickel hydroxide (Ni (OH) ₂ ) in a Li: Ni atomic ratio 1: 1 mixture were heat-treated at 700 ° C. for 13 hours in an oxygen atmosphere. Nickel composite oxide powder LiNiO ₂ was obtained.
[0037]
A battery was produced in the same manner as in Example 1 except that the positive electrode active material powder was used, and this battery was designated as Battery I.
[0038]
As shown in FIG. 1B, the X-ray diffraction diagram of the positive electrode plate in the charged state of the battery I shows that both the diffraction peak around 2θ = 18 ° to 20 ° and the diffraction peak around 2θ = 44 ° to 46 ° are split. ing. It can be seen from this X-ray diffraction diagram that two types of crystal phases having different C-axis lengths belonging to R-3m are mixed.
[0039]
(Comparative Example 2)
Ni / Co ratio of nickel hydroxide (Ni (OH) ₂ ) to cobalt oxide (Co ₃ O ₄ ) 0.95 / 0.05, 0.90 / 0.10, 0.85 / 0.15,. Lithium hydroxide-hydrate (LiOH.H ₂ O) was mixed with the 80 / 0.20 and 0.50 / 0.50 mixtures at a Li: Ni + Co atomic ratio of 1: 1, respectively, and 700 ° C. in an oxygen atmosphere. Then, a lithium nickel composite oxide powder LiNi _(1-y) Co _y O ₂ (y = 0.05, 0.10, 0.15, 0.20, 0.50) was obtained.
[0040]
Batteries were prepared in the same manner as in Example 1 except that the positive electrode active material powder was used. Among them, batteries with y = 0.05 were batteries J, batteries with y = 0.10 were batteries K, and y = The battery with 0.15 was designated as battery L, the battery with y = 0.20 was designated as battery M, and the battery with y = 0.50 was designated as battery N.
[0041]
The X-ray diffraction patterns of the positive plates of the batteries J, K, L, M, and N in the charged state all had the same characteristics as in FIG. That is, a split peak is slightly seen on the low angle side of the diffraction peak near 2θ = 18 ° to 20 °, and the diffraction peak itself is broadened. From this X-ray diffraction diagram, it can be seen that a plurality of crystal phases are slightly mixed and the crystal phases are disordered.
[0042]
Table 1 shows the cycle test results of the batteries of Examples and Comparative Examples of the present invention. Each of the batteries A to N was assembled and tested, and (Table 1) shows an average value.
[0043]
[Table 1]

[0044]
From the test results, the following can be understood.
In the battery I using LiNiO ₂ as the positive electrode active material, it can be seen from the X-ray diffraction diagram that two types of crystal phases having different C-axis lengths belonging to R-3m are mixed in the active material. The presence of these two types of crystal phases in the crystal causes distortion in the crystal, which causes structural destruction during repeated charge / discharge cycles, and partly loses reversibility, thus reducing the charge / discharge capacity. It can be seen that I has extremely poor cycle characteristics.
[0045]
Batteries J, K, and L using LiNi _(1-y) Co _y O ₂ obtained by heat-treating a mixture of LiOH.H ₂ O, Ni (OH) ₂ and Co ₃ O ₄ as a positive electrode active material , M, and N, it can be seen from the X-ray diffraction diagram that a plurality of crystal phases are slightly mixed and the crystal phases are disordered. In these batteries as well, structural breakdown occurs due to crystal distortion, so that it can be seen that batteries J, K, L, M, and N have poor cycle characteristics.
[0046]
Lithium nickel composite oxide LiNi _(1-y) Co _y O ₂ synthesized from Ni _(1-y) Co _y (OH) ₂ (0 <y ≦ 0.5) produced by the coprecipitation method is used as the positive electrode active material. The batteries A, B, C, D, and E used have only a single crystal phase belonging to R-3m in the active material according to an X-ray diffraction diagram. In such a lithium nickel composite oxide, since the distortion of the crystal lattice near the end-of-charge voltage is small and structural breakdown does not occur, the batteries A, B, C, D, and E exhibit good cycle characteristics.
[0047]
However, the X-ray diffraction diagram of the positive electrode plate in the charged state of the battery A shows that the diffraction peak around 2θ = 18 ° to 20 ° and the diffraction peak around 2θ = 44 ° to 46 ° are both slightly asymmetric, The crystal phase is disordered. Therefore, the batteries B and C have better cycle characteristics than the battery A, and the substitution amount by Co is preferably y> 0.10.
[0048]
Further, the battery E with y = 0.5 is not preferable because of its low initial capacity. Therefore, the substitution amount by Co is preferably 0.10 <y ≦ 0.30.
[0049]
Li-nickel composite oxide LiNi _(1-y) M _y synthesized from Ni _(1-y) M _y (OH) ₂ (0 <y ≦ 0.3) where M = Mn, Al produced by the coprecipitation method The X-ray diffraction pattern of the positive electrode plates in the charged state of the batteries F, G, and H using O ₂ as the positive electrode active material is also similar to FIG. 1A, and the initial discharge capacity is M = Co described above. Although it is lower than batteries A, B and C, it shows good cycle characteristics.
[0050]
Similar effects were obtained with other substitution elements (M = Ti, V, Cr, Fe, Cu, Zn, B, etc.). In the above examples, the positive electrode active material was synthesized using lithium hydroxide, but the same effect was obtained even when lithium salts such as lithium carbonate and lithium nitrate were used.
[0051]
In the above examples, evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape is different, such as a square.
[0052]
Furthermore, although a carbon material is used for the negative electrode in the above-described examples, the effect of the present invention is that the positive electrode plate acts, so that any material that can occlude / release lithium ions can be used without particular limitation. For example, the same effect can be obtained by using other negative electrode materials such as lithium, lithium alloy, oxides such as Fe ₂ O ₃ and WO ₂ , and sulfides such as TiS ₂ .
[0053]
Moreover, although lithium hexafluorophosphate (LiPF ₆ ) was used as the electrolytic solution in the above examples, other lithium-containing salts such as lithium perchlorate (LiCiO ₄ ), lithium trifluoromethylsulfonate (CF ₃ SO) ₃ Li), lithium hexafluoroarsenate (LiAsF ₆ ), and the like, the same effect was obtained.
[0054]
Further, in the above examples, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was used, but other non-aqueous solvents, for example, cyclic esters such as propylene carbonate (PC), cyclic ethers such as tetrahydrofuran (THF), etc. The same effect was obtained even when a non-aqueous solvent such as a chain ether such as dimethoxyethane (DME) or a chain ester such as methyl propionate (MP), or a multicomponent mixed solvent thereof was used.
[0055]
【The invention's effect】
As apparent from the above description, the present invention is by using the lithium nickel composite oxide having only a single crystal phase to be assigned to R-3 m at the end of charge in the positive electrode active material, in the vicinity of the charge end voltage The distortion of the crystal lattice is small and structural breakdown can be prevented, and the charge / discharge cycle characteristics of the battery can be improved.
[0056]
A nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics can be provided.
[Brief description of the drawings]
FIG. 1 (a) X-ray diffraction pattern of positive plates of batteries A to H after charging (b) X-ray diffraction pattern of positive plates of battery I after charging (c) Positive electrodes of batteries J to N after charging X-ray diffraction pattern of the plate (d) X-ray diffraction pattern of the positive electrode plates of the batteries A to E before charging [FIG. 2] Longitudinal sectional view of the cylindrical battery [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6b Negative electrode lead 7 Separator 8 Insulation ring

Claims

In a non-aqueous electrolyte battery comprising a negative electrode made of lithium, a lithium alloy or a compound that occludes / releases lithium ions, a positive electrode, and an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent,
The positive active material is the formula _{_{Li x Ni (1-y)}} M y O 2 (0 ≦ x ≦ 1.2,0 <y ≦ 0.5, M is Ti, V, Cr, Mn, Fe, Co, A lithium composite oxide represented by one or more of Cu, Zn, Al, and B metal elements,
The lithium composite oxide consists only a single crystal phase at the time of charge termination, a nonaqueous electrolyte battery characterized by comprising a crystal phase which is attributable to R-3 m (provided that the positive electrode active material is below General formula (I)
Li _x Ni _1-y Me _y O ₂ (I)
(Wherein, Me represents a transition metal element other than Ni, 0 <x <1.1, 0 ≦ y <0.6), in a lithium composite oxide represented by a Rietveld analysis method by X-ray diffraction Lithium composite oxide, characterized in that the lithium content in the 3a site is 90% or more and the purity of the lithium composite oxide belonging to the hexagonal layered compound (space group R-3m) is 90% or more Except when).

The non-aqueous electrolyte battery according to claim 1, wherein an open circuit voltage at the end of charging of the battery is 3.9 to 4.3 V with respect to lithium.

The nonaqueous electrolyte battery according to claim 1, wherein an x value of the positive electrode active material at the end of charging is 0.1 ≦ x ≦ 0.5.

In the X-ray diffraction diagram using CuKα rays of the positive electrode plate at the end of charging of the battery using the positive electrode active material, a diffraction peak around 2θ = 18 ° to 20 ° and a diffraction peak around 2θ = 44 ° to 46 ° The nonaqueous electrolyte battery according to claim 1, wherein is a single peak.

The non-aqueous electrolyte battery according to claim 1, wherein the positive electrode active material is a lithium composite oxide synthesized from Ni _(1-y) M _y (OH) ₂ and a Li compound produced by a coprecipitation method. .