JP2004192896A

JP2004192896A - Cathode active substance, its manufacturing method and nonaqueous electrolyte secondary battery

Info

Publication number: JP2004192896A
Application number: JP2002357887A
Authority: JP
Inventors: Takashi Okawa; 剛史大川; Mashio Shibuya; 真志生渋谷; Gen Fukushima; 弦福嶋
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 2002-12-10
Filing date: 2002-12-10
Publication date: 2004-07-08
Anticipated expiration: 2022-12-10
Also published as: JP4193481B2

Abstract

<P>PROBLEM TO BE SOLVED: To realize good battery characteristics and prevention of swelling due to gas generation at the same time. <P>SOLUTION: An average particle size and a specific surface area of a composite oxide of lithium as a cathode active substance and transition metal are to be in an appropriate range, and a fluorine treatment is applied on it. The average particle size of the composite oxide is 3 μm to 24 μm, and the specific surface area 0.10m<SP>2</SP>/g to 0.92m<SP>2</SP>/g. Further, as a result of the fluorine treatment, 0.2 to 3.5 weight percent of fluorine atoms against the composite oxide exist on the surface of the complex oxide as an active substance material. The fluorine treatment is made by having fluorine treatment gas contacted with a fluorine gas partial pressure of ≥5%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、リチウムのドープ、脱ドープにより起電力を得る非水電解質二次電池に用いられる正極活物質及びその製造方法に関するものであり、さらには、この正極活物質を用いた非水電解質二次電池に関するものである。特に、高温保存時のガス発生が少なく、形状安定性に優れた非水電解質二次電池を提供するための正極活物質の改良に関する。
【０００２】
【従来の技術】
近年、携帯電話、携帯オーディオプレイヤー、ＰＤＡ等のポータブル電子機器が数多く登場し、その小型軽量化が図られている。そして、これらの電子機器のポータブル電源として、大きなエネルギー密度を持つ非水電解質二次電池（いわゆるリチウムイオン二次電池）が広く使用されている。
【０００３】
ところで、リチウムイオン二次電池には、非水溶媒を含む非水電解液が用いられており、液漏れを防止するために、通常は外装として金属製容器が用いられている。しかしながら、外装にこのような金属製容器を用いた場合には、例えば薄型大面積のシート型電池、薄型小面積のカード型電池、あるいは柔軟で自由度の高い形状を有する電池等を作製することが大変困難である。
【０００４】
そこで、その有効な解決手段として、無機・有機の完全固体電解質や、高分子ゲルからなる半固体電解質を用いて電池を作製することが検討されている。具体的には、高分子と電解質とからなる高分子固体電解質や、マトリックス高分子に非水電解液を可塑剤として加えてなるゲル状の電解質を用いた、いわゆる固体電解質電池が提案されている。
【０００５】
固体電解質電池は、電解質が固体又はゲル状であるために、液漏れの心配がなく、電解質が固定化され、電解質の厚みを固定することができる。また、電解質と電極との接着性もよく、電解質と電極との接触を良好な状態に保持することができる。このため、固体電解質電池は、金属製容器により電解液を閉じ込めたり、電池素子に圧力をかける必要がなく、成型自由度の高いフィルム状の外装を使用することができ、多様化するポータブル電子機器に合わせた電池設計が可能である。
【０００６】
特に、外装に高分子フィルムと金属箔とからなり熱融着が可能な防湿性ラミネートフィルム用いることで、ホットシール等により容易に密閉構造が実現できる。また、防湿性ラミネートフィルムは、フィルム自体の強度が強く、気密性に優れており、金属容器に比べて軽量で薄く、安価である等の利点も有している。
【０００７】
【発明が解決しようとする課題】
しかしながら、フィルム状の外装は材料自身が柔らかいため、電池内圧の変化に敏感に反応してしまうという欠点がある。すなわち、電極表面での電解質の酸化・分解の結果発生したガス等により電池が膨れてしまい、形状異常を起こすという問題がある。特に、満充電の電池を夏期の車中等に長期間放置した場合に悪影響を及ぼすことが懸念される。
【０００８】
そこで本発明は、このような従来の実情に鑑みて提案されたものであり、充電状態で高温に長期間放置した場合にもガス発生が少なく、フィルム状の外装を使用しても形状安定性に優れた非水電解質二次電池を実現することが可能な正極活物質を提供することを目的とし、その製造方法を提供することを目的とする。さらに、充電状態で高温に長期間保存した場合にもガス発生が少なく、フィルム状の外装を使用しても形状安定性に優れた非水電解質二次電池を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明者らは、上記の問題を解決するために長期に亘り鋭意研究を重ねてきた。その結果、リチウムと遷移金属との複合酸化物を正極活物質として用いる場合、その比表面積を適正な範囲に設定すること、及びフッ素化処理を施すことが、負荷特性の確保と高温保存時のガス発生による膨れの抑制につながり、これらを併用したときにはじめて良好な電池特性及びガス発生による膨れ防止を同時に実現し得ることを見出すに至った。
【００１０】
本発明は、このような知見に基づいて完成されたものであり、本発明の正極活物質は、リチウムと遷移金属との複合酸化物を含み、前記複合酸化物は、平均粒子径が３μｍ〜２４μｍ、比表面積が０．１０ｍ^２／ｇ〜０．９２ｍ^２／ｇであり、フッ素処理が施されていることを特徴とするものである。また、本発明の非水電解質二次電池は、リチウムと遷移金属との複合酸化物を正極活物質として含有する正極と、リチウム金属、リチウム合金又はリチウムをドープ、脱ドープすることが可能な材料を含有する負極と、非水電解質と、これらを収容する外装容器とを備え、前記複合酸化物は、平均粒子径が３μｍ〜２４μｍ、比表面積が０．１０ｍ^２／ｇ〜０．９２ｍ^２／ｇであり、フッ素処理が施されていることを特徴とするものである。
【００１１】
正極活物質であるリチウムと遷移金属との複合酸化物の平均粒子径、比表面積を適正な範囲とし、さらにフッ素処理を施すことで、高温保存時のガス発生が抑えられ、例えば外装容器に防湿性ラミネートフィルムを用いた場合にも膨れが抑えられる。ここで、フッ素化処理によって負荷特性が低下する傾向にあるが、複合酸化物の平均粒子径や比表面積を前記範囲内に設定することで、負荷特性を維持することができ、満足し得る電池性能が得られる。
【００１２】
また、本発明の正極活物質の製造方法は、平均粒子径が３μｍ〜２４μｍ、比表面積が０．１０ｍ^２／ｇ〜０．９２ｍ^２／ｇであるリチウムと遷移金属との複合酸化物に対して、フッ素ガス分圧が５％以上のフッ素処理用ガスを接触させてフッ素処理を行うことを特徴とする。
【００１３】
フッ素化処理に際しては、フッ素ガスの分圧を調整することによりフッ素化の程度を調整することが可能であるが、フッ素ガスの分圧が低すぎると効果が不足する。フッ素ガス分圧を５％以上とすることで、十分なフッ素化が実現され、高温保存時のガス発生による膨れが抑制される。
【００１４】
【発明の実施の形態】
以下、本発明を適用した正極活物質、その製造方法、非水電解質二次電池について詳細に説明する。
【００１５】
本発明の正極活物質は、リチウムと遷移金属との複合酸化物を活物質材料として含むものである。ここで、前記複合酸化物は、例えば、一般式ＬｉｘＭｙＮｚＯ２（ＭはＣｏ又はＮｉであり、ＮはＣｏ，Ｍｎ，Ｎｉ，Ｃｒ，Ｆｅ，Ｖ，Ａｌ，Ｂ，Ｍｇから選ばれる少なくとも１種である。また、０．０５≦ｘ≦１．１０，０＜ｙ，０．８０≦ｙ＋ｚ≦１．００である。）で表される化合物である。
【００１６】
上記複合酸化物においては、その平均粒子径と比表面積が重要であり、これらを適正な範囲に設定することで、高温保存時のガス発生による膨れを抑えながら、良好な電池性能を得ることができる。具体的には、平均粒子径は３μｍ〜２４μｍ、比表面積は０．１０ｍ^２／ｇ〜０．９２ｍ^２／ｇとする。
【００１７】
前記平均粒子径が３μｍ未満である場合には、非水電解質二次電池の正極活物質として用いたときに初期容量が低下する。また、逆に、前記平均粒子径が２４μｍを越えて大きい場合には、電池特性が低下する。一方、前記比表面積については、比表面積が０．１０ｍ^２／ｇ未満のものを用いると、非水電解質二次電池の負荷特性が低下し、逆に０．９２ｍ^２／ｇを越えて大きなものを用いると、高温保存時にガス発生による膨れが発生する。
【００１８】
前記複合酸化物は、平均粒子径と比表面積を前記適正な範囲に設定することに加えて、フッ素化処理が施されていることが必要である。この場合、フッ素化処理の結果、活物質材料である複合酸化物の表面に当該複合酸化物に対して０．２〜３．５重量％のフッ素原子が存在することが好ましい。複合酸化物に対するフッ素原子の割合が０．２重量％未満の場合には、高温保存時にガス発生による膨れが発生する。逆に３．５重量％より多い場合には初期容量が低下し、負荷特性も低下する。
【００１９】
フッ素化処理としては、例えばＦ_２ガス／不活性ガスの混合ガスと直接反応させる方法がある。例えば、処理すべき正極活物質、すなわち前記複合酸化物を前記混合ガス中で一定時間放置する。その結果、目的とする表面にフッ素原子が存在する複合酸化物（活物質材料）が得られる。このとき、Ｆ_２ガス分圧を変更することにより複合酸化物のフッ素化の程度を調整することが可能であるが、Ｆ_２ガス分圧が３％未満である場合には効果が小さいため、フッ素ガス分圧は３％より大きい分圧であることが好ましい。
【００２０】
また、前記複合酸化物に不純物として炭酸リチウムが含まれる場合、上記フッ素化処理により炭酸リチウムもフッ素化されて安定なフッ化リチウムとなる。生成したフッ化リチウムは、活物質上での電極反応を阻害し、負荷特性が低下する。そのため、前記複合酸化物が不純物としてｘ重量％の炭酸リチウムを含むとすると、これをフッ素化処理して正極活物質に用いる場合、ｘ≦４であることが好ましい。この場合、目的とする効果を得るためには、フッ素化処理後の表面に存在するフッ素原子の量のうち前記炭酸リチウムのフッ素化により消費された量を差し引いた量、すなわちフッ素化処理後の表面に存在するフッ素量−ｘ／２（重量％）が、複合酸化物（活物質材料）に対して０．２〜３．５重量％であることが好ましい。
【００２１】
以上が本発明の正極活物質及びその製造方法であるが、かかる正極活物質は、非水電解質二次電池（いわゆるリチウムイオン二次電池）の正極活物質材料として用いることができる。ここで、非水電解質二次電池の構成としては、前記正極活物質を用いた正極の他、負極、非水電解質、及び外装容器を挙げることができる。
【００２２】
ここで、負極に用いる負極活物質としては特に限定されないが、例えばリチウム金属、リチウムと合金を形成可能な金属及びその合金、リチウムをドープ脱ドープする材料等を挙げることができる。リチウムをドープ脱ドープする材料としては、例示するならば難黒鉛化性炭素、人造黒鉛、天然黒鉛、熱分解炭素類、コークス類（ピッチコークス、ニードルコークス、石油コークス等）、グラファイト類、ガラス状炭素類、有機高分子化合物焼成体（フェノール樹脂、フラン樹脂等を適当な温度で焼成し炭素化したもの）、炭素繊維、活性炭、カーボンブラック類等の炭素質材料を挙げることができる。また、酸化鉄、酸化ルテニウム、酸化モリブデン、酸化タングステン、酸化チタン、酸化スズ等の比較的電位が卑な電位でリチウムをドープ脱ドープする酸化物やその他窒化物なども同様に使用可能である。
【００２３】
電解質としては、電解質塩を含有させた固体電解質、マトリクス高分子に非水溶媒と電解質塩を含浸させたゲル状電解質のいずれも用いることができる。また、固体電解質やゲル状電解質では、正極、負極それぞれに成分が異なる電解質を使用することもできるが、１種類の電解質を使用する場合は、非水溶媒に電解質塩を溶解させた非水電解液も使用可能である。
【００２４】
前記ゲル状電解質に用いる非水電解液や電解液として用いる非水電解液は、有機溶媒と電解質とを適宜組み合わせて調製されるが、これら有機溶媒はこの種の電池に用いられるものであればいずれも使用可能である。例示するならば、プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、１，２−ジメトキシエタン、１，２−ジエトキシエタン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１，３−ジオキソラン、４メチル１，３ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリル、酢酸エステル、酪酸エステル、プロピオン酸エステル等である。これらは、単独で使用しても、複数種混合して用いてもよい。特に、高温での安定性の点から、高沸点溶媒を含有させることが好ましい。
【００２５】
固体電解質としては、リチウムイオン導電性を有する材料であれば無機固体電解質、高分子固体電解質のいずれも用いることができる。無機固体電解質として、窒化リチウム、よう化リチウムが挙げられる。高分子固体電解質は、電解質塩とそれを溶解する高分子化合物からなり、高分子化合物はポリ（エチレンオキサイド）や同架橋体などのエーテル系高分子、ポリ（メタクリレート）エステル系、アクリレート系等を単独あるいは分子中に共重合、または混合して用いることができる。
【００２６】
ゲル状電解質のマトリックス高分子としては、上記非水電解液を吸収してゲル化するものであれば種々の高分子が利用できる。具体的には、例えば、ポリビニリデンフルオロライドやポリビニリデンフルオロライド−ｃｏ−ヘキサフルオロプロピレン等のフッ素系高分子、ポリエチレンオキサイドや同架橋体等のエーテル系高分子、ポリアクリロニトリル等を使用できる。特に、酸化還元安定性の観点からは、フッ素系高分子を用いることが望ましい。ゲル状電解質では、これらマトリックス高分子に電解質塩を含有させることにより、イオン導電性を賦与する。
【００２７】
上記非水電解質に用いられる電解質塩は、この種の電池に用いられるものであればいずれも使用可能である。例示するならば、ＬｉＣｌＯ_４、ＬｉＡｓＦ_６、ＬｉＰＦ_６、ＬｉＢＦ_４、ＬｉＢ（Ｃ_６Ｈ_５）_４、ＣＨ_３ＳＯ_３Ｌｉ、ＣＦ_３ＳＯ_３Ｌｉ、ＬｉＣｌ、ＬｉＢｒ、ＬｉＮ（ＣＦ_３ＳＯ_２）_２等である。
【００２８】
本発明の非水電解質二次電池は、電池形状については特に限定されることはなく、円筒型、角型、コイン型、ボタン型、ラミネートシート型等、任意の形状にすることができるが、特に、ラミネートフィルムを外装材に用いた非水電解質二次電池において効果的である。
【００２９】
また、本発明の非水電解質二次電池において、電極（負極及び正極）の作製方法は問わない。例えば、活物質材料に公知の結着剤等を添加し溶剤を加えて塗布する方法、結物質材料に公知の結着剤等を添加し加熱して塗布する方法、活物質材料単独、あるいは導電性材料、さらには結着材と混合して成型等の処理を施して成型体電極を作成する方法等を採ることができる。具体的には、活物質を結着材、有機溶剤等と混合してスラリー状とした後、集電体上に塗布、乾燥することにより前記負極や正極を作製することができる。あるいは、結着材の有無にかかわらず、活物質に熱を加えたまま加圧成型することにより強度を有した電極を作製することも可能である。勿論、電極に作製方法は、これらに限定されるものではない。
【００３０】
さらに、前記負極及び正極の組み合わせからなる発電要素の作製方法としては、正負極間にセパレーターを介して巻芯の周囲に捲回する作成方法、電極とセパレーターを順次積層する積層方式等が挙げられる。薄形電池や角型電池を作製する場合にも、例えば前記捲回する方式を採用することができる。
【００３１】
【実施例】
以下、本発明の具体的な実施例について、実験結果に基づいて説明する。
【００３２】
実施例１
先ず、以下のようにして正極電極を作製した。
平均粒子径３μｍ、比表面積０．９２ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することによりフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を比色法により測定したところ、１．２重量％であった。なお、ＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末の平均粒子径は湿式レーザー粒度分布計で、比表面積はマックソーブにより測定した。
【００３３】
次いで、このフッ素化処理が施されたＬｉＮｉＯ_２９１重量％と、導電剤である黒鉛６重量％と、結着剤であるポリビニリデンフルオライド３重量％とを混合して正極合剤を作製した。次に、これをＮ−メチル−２−ピロリドンに分散させてスラリー状とした。さらに、これを正極集電体となる厚さ２０μｍの帯状のアルミニウム箔の片面に均一に塗布した後に乾燥させた。そして、ロールプレス機で圧縮成型することによって正極活物質層を作製した。
【００３４】
次に、負極電極を以下のようにして作製した。
先ず、粉砕した黒鉛粉末９０重量％と、結着剤であるポリビニリデンフルオライド１０重量％とを混合し、負極合剤を作製した。この負極合剤をＮ−メチル−２−ピロリドンに分散させてスラリー状とした。これを負極集電体となる厚さ２０μｍの帯状の銅箔の片面に均一に塗布した後に乾燥させた。そして、ロールプレス機で圧縮成型することによって負極活物質層を作製した。
【００３５】
また、ゲル状電解質を次のようにして作製した。先ず、炭酸エチレン（ＥＣ）１１．５重量％と、炭酸プロピレン（ＰＣ）１１．５重量％と、電解質塩であるＬｉＰＦ_６４重量％とを混合して可塑剤を調整した。これに対して分子量が６０００００であるブロック共重合ポリビニリデンフルオライド−ｃｏ−ヘキサフルオロプロピレン１０重量％と、炭酸ジエチル６０重量％とを混合して溶解させた。次に、これを負極活物質層及び正極活物質層の片面に均一に塗布して含浸させた。そして、常温で８時間放置することによって炭酸ジエチルを気化させて除去し、ゲル状電解質を作製した。
【００３６】
最後に、上述したようにゲル状電解質が塗布された正極活物質層と負極活物質層とを、ゲル状電解質が塗布された面同士を対向させて圧着し、発電素子を作製した。この発電素子を、厚さ１８０μｍの防湿性アルミラミネートフィルム外装中に真空封止して、寸法がおよそ２．５ｃｍ×４．０ｃｍ×０．４６ｍｍである平板型ゲル状電解質電池を作製した。
【００３７】
図１及び図２に作製した平板型ゲル状電解質電池の構成を示す。ゲル状電解質電池１は、正極活物質層２と、負極活物質層３とが、ゲル状電解質４を介して形成された発電素子５が、外装フィルム６の内部に収容されてなる。正極活物質層２は正極リード７と接続されており、負極活物質層３は負極リード８と接続されている。正極リード７及び負極リード８は、樹脂フィルム９を介して外装フィルム６に接着されることにより密閉性が確保されており、その先端部が外装フィルム６の外部に臨み、外部端子としての機能を果たしている。なお、図１では、ゲル状電解質１と正極活物質層３、負極活物質層４の図示を省略する。また、図２では、正極リード７と負極リード８、樹脂フィルム９の図示を省略する。
【００３８】
実施例２
平均粒子径３μｍ、比表面積０．９２ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、１．８重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００３９】
実施例３
平均粒子径３μｍ、比表面積０．９２ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．６重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４０】
実施例４
平均粒子径３μｍ、比表面積０．９２ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、４．４重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４１】
実施例５
平均粒子径１５μｍ、比表面積０．５５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４２】
実施例６
平均粒子径１５μｍ、比表面積０．５５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．２重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４３】
実施例７
平均粒子径１５μｍ、比表面積０．５５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、１．６重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４４】
実施例８
平均粒子径１５μｍ、比表面積０．５５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．４重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４５】
実施例９
平均粒子径１５μｍ、比表面積０．５５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．８重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４６】
実施例１０
平均粒子径２２μｍ、比表面積０．３４ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４７】
実施例１１
平均粒子径２２μｍ、比表面積０．３４ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．３重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４８】
実施例１２
平均粒子径２２μｍ、比表面積０．３４ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、２．０重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００４９】
実施例１３
平均粒子径２２μｍ、比表面積０．３４ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．７重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５０】
実施例１４
平均粒子径５μｍ、比表面積０．４７ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、３．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５１】
実施例１５
平均粒子径５μｍ、比表面積０．４７ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、４．０重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５２】
実施例１６
平均粒子径１２μｍ、比表面積０．３０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧３％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、０．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５３】
実施例１７
平均粒子径１２μｍ、比表面積０．３０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、０．５重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５４】
実施例１８
平均粒子径１２μｍ、比表面積０．３０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、３．３重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５５】
実施例１９
平均粒子径１２μｍ、比表面積０．３０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、３．７重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５６】
実施例２０
平均粒子径２０μｍ、比表面積０．１０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、０．２重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５７】
実施例２１
平均粒子径２０μｍ、比表面積０．１０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、１．７重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５８】
実施例２２
平均粒子径２０μｍ、比表面積０．１０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、３．２重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００５９】
実施例２３
平均粒子径２０μｍ、比表面積０．１０ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、３．７重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６０】
比較例１
平均粒子径２μｍ、比表面積０．９５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．５重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６１】
比較例２
平均粒子径２μｍ、比表面積０．９５ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．５重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６２】
比較例３
平均粒子径２６μｍ、比表面積０．３１ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧３％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６３】
比較例４
平均粒子径２６μｍ、比表面積０．３１ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、０．４重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６４】
比較例５
平均粒子径２６μｍ、比表面積０．３１ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、１．７重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６５】
比較例６
平均粒子径２６μｍ、比表面積０．３１ｍ^２／ｇのＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粉末を、８０℃、Ｆ_２分圧５０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＮｉ_０．８Ｃｏ_０．２Ｏ_２粒子中に含まれるフッ素量を測定したところ、３．３重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６６】
比較例７
平均粒子径２μｍ、比表面積０．６３ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、１．６重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６７】
比較例８
平均粒子径２５μｍ、比表面積０．０８ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧３％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、０．１重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６８】
比較例９
平均粒子径２５μｍ、比表面積０．０８ｍ^２／ｇのＬｉＣｏＯ_２粉末を、８０℃、Ｆ_２分圧２０％のＦ_２／Ａｒ混合ガス中で１０時間放置することでフッ素化処理を施した。フッ素化処理後のＬｉＣｏＯ_２粒子中に含まれるフッ素量を測定したところ、１．５重量％であった。これを正極活物質として用いた以外は実施例１と同様にして電池を作製した。
【００６９】
上記実施例１〜実施例２３、及び比較例１〜比較例９で作製された平板型ゲル状電解質電池について、以下に示す方法によって初回充電容量、負荷特性、及び高温保存特性を評価した。
【００７０】
＜初回充電容量＞
未処理の活物質に対するフッ素化処理後の活物質の電池容量変化率を求めた。先ず、作製直後の各電池（実施例１〜２３，比較例１〜９）を２３℃で、未処理の活物質理論容量の２時間率充電（０．５Ｃ）（定電流定電圧充電）を４．２Ｖまで１０時間行った。このときの各電池の充電容量を求め、未処理の電池の充電容量に対する処理後の電池（実施例１〜２３，比較例１〜９）の容量の減少率を１００分率として計算した。
【００７１】
＜負荷特性＞
理論容量の１／２時間率放電（２Ｃ）を行い、次のように評価した。先ず、各電池に対して、２３℃で定電流定電圧充電を上限４．２Ｖまで１０時間行った。次に、５時間率放電（０．２Ｃ）を終止電圧３．０Ｖまで行った。このときの放電容量を０．２Ｃ放電容量として求めた。その後、再び定電流定電圧充電を上限４．２Ｖまで１０時間行い、次いで１／２時間率放電（２Ｃ）を終止電圧３．０Ｖまで行った。このときの放電容量を２Ｃ放電容量として求めた。０．２Ｃ放電容量に対する２Ｃ放電容量を１００分率として計算した。
【００７２】
＜高温保存特性＞
充電状態の電池を高温保存した際の電池寸法の変化を評価した。先ず、各電池に対して、２３℃で定電流定電圧充電を上限４．３Ｖまで１０時間行った。この時の各電池の厚さを測定し、初期厚さとした。その後、各電池を８０℃恒温槽中にて１５日間保存した後、恒温槽から取り出した直後の電池厚さを測定した。この時の厚さから初期厚さを減じた分（変化量）を初期厚さに対する１００分率として算出し、それを未処理の電池の変化率から差し引いたものをセル膨れ低減率として計算した。
【００７３】
上述した実施例１〜実施例２３、及び比較例１〜比較例９について、初回充電容量減少率、セル膨れ低減率、負荷特性を測定した結果を、表１に示す。
【００７４】
【表１】

表１から、フッ素化処理によって高温保存時のセル膨れが抑制されることが判明した。ただし、平均粒子径が２μｍの複合酸化物や平均粒子径が２５μｍ以上の複合酸化物にフッ素化処理をした場合には、比較例２，６，７のように初回充電容量減少率が大きくなるか、比較例１，３のように効果が小さいことがわかった。また、フッ素化処理によって全体的に負荷特性が低下する傾向が確認されたが、元来負荷特性が低めである平均粒子径２５μｍ以上の活物質にフッ素化処理を施すと、比較例４，５，６，８，９のようにさらに負荷特性が低下し、電池としての性能が低下してしまうことがわかった。
【００７５】
これに対して、適正な平均粒子径、比表面積を有する複合酸化物にフッ素化処理を施した各実施例の場合、初回充電容量減少率が小さく、セル厚さ増加率も抑制され、且つ負荷特性も優れていると判明した。すなわち、３μｍ〜２４μｍの平均粒子径を有する活物質（リチウムと遷移金属の複合酸化物）にフッ素化処理を施すことにより、高温保存時の膨れを抑制でき、且つその他の電池特性も満足するものが得られることが判明した。特に、フッ素処理後のフッ素量が０．２重量％〜３．５重量％である実施例１〜３，実施例６〜８，実施例１１，１２，実施例１７，１８，実施例２０〜２２は、セル膨れ低減率が大きく、且つその他の特性も高いことから、より好適であると言える。
【００７６】
【発明の効果】
以上の説明からも明らかなように、平均粒子径が３μｍから２４μｍ、比表面積が０．１０ｍ^２／ｇ〜０．９２ｍ^２／ｇである複合酸化物にフッ素化処理を施したものを正極活物質として用いることによって、高温保存時のガス膨れが少なくフィルム状の外装を用いても信頼性の高い非水電解質二次電池を得ることが可能である。特に、フッ素化の処理量が活物質である複合酸化物に対して０．２〜３．５重量％である時に、セル膨れ低減率が大きく、充電容量や負荷特性等の電池特性に優れた非水電解質二次電池を実現することが可能である。
【図面の簡単な説明】
【図１】ゲル状電解質電池の概略平面図である。
【図２】ゲル状電解質電池の概略断面図である。
【符号の説明】
１ゲル状電解質電池
２正極活物質層
３負極活物質層
４ゲル状電解質
５発電要素
６外装フィルム[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material used for a non-aqueous electrolyte secondary battery that obtains an electromotive force by doping and de-doping of lithium, and a method for producing the same. Further, the present invention relates to a non-aqueous electrolyte It relates to the next battery. In particular, the present invention relates to an improvement of a positive electrode active material for providing a nonaqueous electrolyte secondary battery that generates less gas during high-temperature storage and has excellent shape stability.
[0002]
[Prior art]
In recent years, many portable electronic devices such as a mobile phone, a portable audio player, and a PDA have appeared, and their size and weight have been reduced. A non-aqueous electrolyte secondary battery having a large energy density (so-called lithium ion secondary battery) is widely used as a portable power supply for these electronic devices.
[0003]
By the way, a non-aqueous electrolyte containing a non-aqueous solvent is used for a lithium ion secondary battery, and a metal container is usually used as an exterior to prevent liquid leakage. However, when such a metal container is used for the exterior, for example, a thin large-area sheet-type battery, a thin small-area card-type battery, or a battery having a flexible and highly flexible shape is manufactured. Is very difficult.
[0004]
Therefore, as an effective solution, it has been studied to manufacture a battery using an inorganic / organic completely solid electrolyte or a semi-solid electrolyte made of a polymer gel. Specifically, a so-called solid electrolyte battery using a polymer solid electrolyte composed of a polymer and an electrolyte or a gel electrolyte obtained by adding a nonaqueous electrolyte to a matrix polymer as a plasticizer has been proposed. .
[0005]
In a solid electrolyte battery, since the electrolyte is in a solid or gel state, there is no risk of liquid leakage, the electrolyte is fixed, and the thickness of the electrolyte can be fixed. Further, the adhesiveness between the electrolyte and the electrode is good, and the contact between the electrolyte and the electrode can be maintained in a good state. For this reason, the solid electrolyte battery does not need to confine the electrolyte in a metal container or apply pressure to the battery element, and can use a film-like exterior having a high degree of freedom in molding, thereby diversifying portable electronic devices. It is possible to design the battery according to.
[0006]
In particular, by using a moisture-proof laminated film made of a polymer film and a metal foil for the exterior and capable of being heat-sealed, a sealed structure can be easily realized by hot sealing or the like. Further, the moisture-proof laminated film has advantages such as high strength of the film itself, excellent airtightness, light weight, thinness, and low cost as compared with metal containers.
[0007]
[Problems to be solved by the invention]
However, the film-shaped exterior has a drawback that the material itself is soft, and thus reacts sensitively to a change in battery internal pressure. That is, there is a problem in that the battery swells due to a gas or the like generated as a result of oxidation and decomposition of the electrolyte on the electrode surface, causing an abnormal shape. In particular, when a fully charged battery is left in a car in summer or the like for a long period of time, there is a concern that adverse effects may occur.
[0008]
Therefore, the present invention has been proposed in view of such a conventional situation. Even when the battery is left at a high temperature for a long time in a charged state, the gas generation is small, and the shape stability is obtained even when a film-like exterior is used. It is an object of the present invention to provide a positive electrode active material capable of realizing a nonaqueous electrolyte secondary battery having excellent performance, and to provide a method for producing the same. It is still another object of the present invention to provide a nonaqueous electrolyte secondary battery that generates less gas even when stored at a high temperature for a long time in a charged state and has excellent shape stability even when a film-like package is used.
[0009]
[Means for Solving the Problems]
The present inventors have intensively studied for a long time to solve the above problems. As a result, when using a composite oxide of lithium and a transition metal as the positive electrode active material, setting the specific surface area to an appropriate range, and performing fluorination treatment ensure load characteristics and ensure high-temperature storage. It has been found that swelling due to gas generation is suppressed, and that when these are used in combination, good battery characteristics and prevention of swelling due to gas generation can be realized at the same time.
[0010]
The present invention has been completed based on such findings, and the positive electrode active material of the present invention includes a composite oxide of lithium and a transition metal, and the composite oxide has an average particle diameter of 3 μm or more. 24 μm, specific surface area 0.10 m²/G~0.92m²/ G, and is characterized by being subjected to a fluorine treatment. Further, the non-aqueous electrolyte secondary battery of the present invention has a positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material, and a material capable of doping and undoping lithium metal, a lithium alloy or lithium. , A non-aqueous electrolyte, and an outer container containing the same, wherein the composite oxide has an average particle diameter of 3 μm to 24 μm, and a specific surface area of 0.10 m.²/G~0.92m²/ G, and is characterized by being subjected to a fluorine treatment.
[0011]
The average particle diameter and specific surface area of the composite oxide of lithium and the transition metal, which are the positive electrode active materials, are set to appropriate ranges, and by performing a fluorine treatment, gas generation during high-temperature storage can be suppressed. In the case where a water-soluble laminate film is used, swelling can be suppressed. Here, the load characteristics tend to decrease due to the fluorination treatment, but by setting the average particle diameter and the specific surface area of the composite oxide within the above ranges, the load characteristics can be maintained and the battery can be satisfied. Performance is obtained.
[0012]
The method for producing a positive electrode active material of the present invention has an average particle diameter of 3 μm to 24 μm and a specific surface area of 0.10 m.²/G~0.92m²/ G of a composite oxide of lithium and a transition metal is contacted with a fluorine treatment gas having a fluorine gas partial pressure of 5% or more to carry out fluorine treatment.
[0013]
In the fluorination treatment, the degree of fluorination can be adjusted by adjusting the partial pressure of the fluorine gas, but the effect is insufficient if the partial pressure of the fluorine gas is too low. By setting the fluorine gas partial pressure to 5% or more, sufficient fluorination is realized, and swelling due to gas generation during high-temperature storage is suppressed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a positive electrode active material to which the present invention is applied, a method for producing the same, and a nonaqueous electrolyte secondary battery will be described in detail.
[0015]
The positive electrode active material of the present invention contains a composite oxide of lithium and a transition metal as an active material. Here, the composite oxide is, for example, LixMyNzO2 (where M is Co or Ni, and N is at least one selected from Co, Mn, Ni, Cr, Fe, V, Al, B, and Mg). 0.05 ≦ x ≦ 1.10, 0 <y, 0.80 ≦ y + z ≦ 1.00.)
[0016]
In the composite oxide, its average particle size and specific surface area are important, and by setting these in an appropriate range, it is possible to obtain good battery performance while suppressing swelling due to gas generation during high-temperature storage. it can. Specifically, the average particle diameter is 3 μm to 24 μm, and the specific surface area is 0.10 m²/G~0.92m²/ G.
[0017]
When the average particle diameter is less than 3 μm, the initial capacity decreases when used as a positive electrode active material of a nonaqueous electrolyte secondary battery. On the other hand, when the average particle diameter is larger than 24 μm, the battery characteristics deteriorate. On the other hand, the specific surface area is 0.10 m²/ G, the load characteristics of the non-aqueous electrolyte secondary battery deteriorate,²If a material larger than / g is used, swelling due to gas generation occurs during high-temperature storage.
[0018]
The composite oxide needs to have been subjected to a fluorination treatment in addition to setting the average particle diameter and the specific surface area in the appropriate ranges. In this case, as a result of the fluorination treatment, it is preferable that 0.2 to 3.5% by weight of fluorine atoms be present on the surface of the composite oxide as the active material. When the ratio of fluorine atoms to the composite oxide is less than 0.2% by weight, swelling due to gas generation occurs during high-temperature storage. Conversely, if the content is more than 3.5% by weight, the initial capacity is reduced, and the load characteristics are also reduced.
[0019]
As the fluorination treatment, for example, F₂There is a method of directly reacting with a gas / inert gas mixture. For example, the positive electrode active material to be treated, that is, the composite oxide is left in the mixed gas for a certain period of time. As a result, a composite oxide (active material) in which fluorine atoms are present on the target surface is obtained. At this time, F₂The degree of fluorination of the composite oxide can be adjusted by changing the gas partial pressure.₂Since the effect is small when the gas partial pressure is less than 3%, the fluorine gas partial pressure is preferably a partial pressure larger than 3%.
[0020]
Further, when lithium carbonate is contained as an impurity in the composite oxide, lithium carbonate is also fluorinated by the above-mentioned fluorination treatment to be stable lithium fluoride. The generated lithium fluoride inhibits the electrode reaction on the active material, and the load characteristics are reduced. Therefore, assuming that the composite oxide contains x weight% of lithium carbonate as an impurity, it is preferable that x ≦ 4 when this is fluorinated and used as a positive electrode active material. In this case, in order to obtain the desired effect, the amount obtained by subtracting the amount consumed by the fluorination of the lithium carbonate from the amount of the fluorine atoms present on the surface after the fluorination treatment, that is, the amount after the fluorination treatment It is preferable that the amount of fluorine existing on the surface-x / 2 (% by weight) is 0.2 to 3.5% by weight based on the composite oxide (active material).
[0021]
The positive electrode active material of the present invention and the method for producing the same have been described above. Such a positive electrode active material can be used as a positive electrode active material for a non-aqueous electrolyte secondary battery (a so-called lithium ion secondary battery). Here, examples of the configuration of the nonaqueous electrolyte secondary battery include a negative electrode, a nonaqueous electrolyte, and an outer container, in addition to the positive electrode using the positive electrode active material.
[0022]
Here, the negative electrode active material used for the negative electrode is not particularly limited, and examples thereof include lithium metal, a metal capable of forming an alloy with lithium and its alloy, and a material for doping and undoping lithium. Examples of the material for doping and undoping lithium include non-graphitizable carbon, artificial graphite, natural graphite, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, and glassy materials. Examples thereof include carbons, organic polymer compound fired bodies (phenol resins, furan resins and the like fired at an appropriate temperature and carbonized), and carbonaceous materials such as carbon fibers, activated carbon, and carbon blacks. In addition, oxides and other nitrides that dope and dedope lithium at a relatively low potential such as iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, and tin oxide can also be used.
[0023]
As the electrolyte, any of a solid electrolyte containing an electrolyte salt and a gel electrolyte obtained by impregnating a matrix polymer with a nonaqueous solvent and an electrolyte salt can be used. In the case of a solid electrolyte or a gel electrolyte, an electrolyte having different components can be used for each of the positive electrode and the negative electrode. However, when one type of electrolyte is used, a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent is used. Liquids can also be used.
[0024]
The non-aqueous electrolyte used for the gel electrolyte or the non-aqueous electrolyte used as the electrolyte is prepared by appropriately combining an organic solvent and an electrolyte.If these organic solvents are used for this type of battery, Both can be used. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-methyl1,3 Dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, acetate, butyrate, propionate and the like. These may be used alone or as a mixture of two or more. In particular, it is preferable to contain a high boiling point solvent from the viewpoint of stability at high temperatures.
[0025]
As the solid electrolyte, any of an inorganic solid electrolyte and a polymer solid electrolyte can be used as long as the material has lithium ion conductivity. Examples of the inorganic solid electrolyte include lithium nitride and lithium iodide. The polymer solid electrolyte is composed of an electrolyte salt and a polymer compound that dissolves the electrolyte salt. The polymer compound may be an ether polymer such as poly (ethylene oxide) or the same crosslinked product, a poly (methacrylate) ester, an acrylate, or the like. They can be used singly, or copolymerized or mixed in the molecule.
[0026]
As the matrix polymer of the gel electrolyte, various polymers can be used as long as they absorb the non-aqueous electrolyte and gel. Specifically, for example, a fluorine-based polymer such as polyvinylidenefluoride or polyvinylidenefluoride-co-hexafluoropropylene, an ether-based polymer such as polyethylene oxide or the same crosslinked product, and polyacrylonitrile can be used. In particular, from the viewpoint of oxidation-reduction stability, it is desirable to use a fluoropolymer. In a gel electrolyte, ionic conductivity is imparted by adding an electrolyte salt to these matrix polymers.
[0027]
As the electrolyte salt used for the non-aqueous electrolyte, any electrolyte salt can be used as long as it is used for this type of battery. For example, LiClO₄, LiAsF₆, LiPF₆, LiBF₄, LiB (C₆H₅)₄, CH₃SO₃Li, CF₃SO₃Li, LiCl, LiBr, LiN (CF₃SO₂)₂And so on.
[0028]
Non-aqueous electrolyte secondary battery of the present invention, the battery shape is not particularly limited, cylindrical, square, coin-shaped, button-shaped, laminate sheet type, etc., can be any shape, In particular, it is effective in a non-aqueous electrolyte secondary battery using a laminate film as an exterior material.
[0029]
In addition, in the nonaqueous electrolyte secondary battery of the present invention, a method for forming electrodes (negative electrode and positive electrode) is not limited. For example, a method of adding a known binder and the like to an active material and applying a solvent thereto, a method of adding a known binder and the like to a binder material and applying by heating, an active material alone or a conductive material For example, a method of mixing with a conductive material and further a binder and performing a process such as molding to form a molded electrode can be employed. Specifically, the negative electrode and the positive electrode can be manufactured by mixing the active material with a binder, an organic solvent, and the like to form a slurry, applying the slurry on a current collector, and drying the slurry. Alternatively, regardless of the presence or absence of the binder, it is also possible to produce a strong electrode by performing pressure molding while applying heat to the active material. Of course, the manufacturing method of the electrode is not limited to these.
[0030]
Further, as a method for producing a power generating element composed of a combination of the negative electrode and the positive electrode, a method of winding around a winding core with a separator between positive and negative electrodes, a lamination method of sequentially laminating electrodes and separators, and the like are mentioned. . In the case of producing a thin battery or a prismatic battery, for example, the above-mentioned winding method can be adopted.
[0031]
【Example】
Hereinafter, specific examples of the present invention will be described based on experimental results.
[0032]
Example 1
First, a positive electrode was manufactured as follows.
Average particle diameter 3μm, specific surface area 0.92m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a / Ar mixed gas. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured by a colorimetric method, it was 1.2% by weight. In addition, LiNi_0.8Co_0.2O₂The average particle size of the powder was measured with a wet laser particle size distribution meter, and the specific surface area was measured with a Maxsorb.
[0033]
Next, the fluorinated LiNiO₂A positive electrode mixture was prepared by mixing 91% by weight, 6% by weight of graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride as a binder. Next, this was dispersed in N-methyl-2-pyrrolidone to form a slurry. Further, this was uniformly applied to one side of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector, and then dried. And the positive electrode active material layer was produced by compression-molding with a roll press machine.
[0034]
Next, a negative electrode was produced as follows.
First, 90% by weight of ground graphite powder and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. This was uniformly applied to one surface of a 20 μm-thick strip-shaped copper foil serving as a negative electrode current collector, and then dried. And the negative electrode active material layer was produced by compression-molding with the roll press machine.
[0035]
Further, a gel electrolyte was prepared as follows. First, 11.5% by weight of ethylene carbonate (EC), 11.5% by weight of propylene carbonate (PC), and LiPF as an electrolyte salt₆4% by weight to prepare a plasticizer. On the other hand, 10% by weight of a block copolymerized polyvinylidene fluoride-co-hexafluoropropylene having a molecular weight of 600,000 and 60% by weight of diethyl carbonate were mixed and dissolved. Next, this was uniformly applied and impregnated on one surface of the negative electrode active material layer and the positive electrode active material layer. Then, the mixture was allowed to stand at room temperature for 8 hours to vaporize and remove diethyl carbonate, thereby producing a gel electrolyte.
[0036]
Finally, the positive electrode active material layer coated with the gel electrolyte and the negative electrode active material layer were press-bonded with the surfaces coated with the gel electrolyte facing each other to produce a power generating element. This power generation element was vacuum-sealed in a moisture-proof aluminum laminated film package having a thickness of 180 μm to produce a flat gel electrolyte battery having dimensions of about 2.5 cm × 4.0 cm × 0.46 mm.
[0037]
FIG. 1 and FIG. 2 show the configuration of the manufactured flat gel electrolyte battery. The gel electrolyte battery 1 is configured such that a power generation element 5 in which a positive electrode active material layer 2 and a negative electrode active material layer 3 are formed via a gel electrolyte 4 is accommodated in an exterior film 6. The positive electrode active material layer 2 is connected to a positive electrode lead 7, and the negative electrode active material layer 3 is connected to a negative electrode lead 8. The positive electrode lead 7 and the negative electrode lead 8 are hermetically sealed by being adhered to the exterior film 6 via the resin film 9, and their tips face the exterior of the exterior film 6, and function as external terminals. Play. 1, illustration of the gel electrolyte 1, the positive electrode active material layer 3, and the negative electrode active material layer 4 is omitted. 2, the illustration of the positive electrode lead 7, the negative electrode lead 8, and the resin film 9 is omitted.
[0038]
Example 2
Average particle diameter 3μm, specific surface area 0.92m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 1.8% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0039]
Example 3
Average particle diameter 3μm, specific surface area 0.92m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.6% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0040]
Example 4
Average particle diameter 3μm, specific surface area 0.92m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 4.4% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0041]
Example 5
Average particle size 15μm, specific surface area 0.55m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 3% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0042]
Example 6
Average particle size 15μm, specific surface area 0.55m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.2% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0043]
Example 7
Average particle size 15μm, specific surface area 0.55m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 1.6% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0044]
Example 8
Average particle size 15μm, specific surface area 0.55m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.4% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0045]
Example 9
Average particle size 15μm, specific surface area 0.55m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.8% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0046]
Example 10
Average particle size 22μm, specific surface area 0.34m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 3% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0047]
Example 11
Average particle size 22μm, specific surface area 0.34m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.3% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0048]
Example 12
Average particle size 22μm, specific surface area 0.34m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 2.0% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0049]
Example 13
Average particle size 22μm, specific surface area 0.34m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.7% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0050]
Example 14
Average particle diameter 5μm, specific surface area 0.47m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 3.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0051]
Example 15
Average particle diameter 5μm, specific surface area 0.47m²/ G LiCoO₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 4.0% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0052]
Example 16
Average particle diameter 12 μm, specific surface area 0.30 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 3% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 0.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0053]
Example 17
Average particle diameter 12 μm, specific surface area 0.30 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 0.5% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0054]
Example 18
Average particle diameter 12 μm, specific surface area 0.30 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 3.3% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0055]
Example 19
Average particle diameter 12 μm, specific surface area 0.30 m²/ G LiCoO₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 3.7% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0056]
Example 20
Average particle diameter 20 μm, specific surface area 0.10 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 0.2% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0057]
Example 21
Average particle diameter 20 μm, specific surface area 0.10 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 1.7% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0058]
Example 22
Average particle diameter 20 μm, specific surface area 0.10 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 3.2% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0059]
Example 23
Average particle diameter 20 μm, specific surface area 0.10 m²/ G LiCoO₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 3.7% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0060]
Comparative Example 1
Average particle diameter 2μm, specific surface area 0.95m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.5% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0061]
Comparative Example 2
Average particle diameter 2μm, specific surface area 0.95m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 30% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.5% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0062]
Comparative Example 3
Average particle size 26μm, specific surface area 0.31m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 3% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0063]
Comparative Example 4
Average particle size 26μm, specific surface area 0.31m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 5% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 0.4% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0064]
Comparative Example 5
Average particle size 26μm, specific surface area 0.31m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 1.7% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0065]
Comparative Example 6
Average particle size 26μm, specific surface area 0.31m²/ G LiNi_0.8Co_0.2O₂Powder at 80 ° C, F₂50% partial pressure F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiNi after fluorination treatment_0.8Co_0.2O₂When the amount of fluorine contained in the particles was measured, it was 3.3% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0066]
Comparative Example 7
Average particle diameter 2μm, specific surface area 0.63m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 1.6% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0067]
Comparative Example 8
Average particle diameter 25 μm, specific surface area 0.08 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 3% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 0.1% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0068]
Comparative Example 9
Average particle diameter 25 μm, specific surface area 0.08 m²/ G LiCoO₂Powder at 80 ° C, F₂Partial pressure 20% F₂A fluorination treatment was performed by allowing the mixture to stand for 10 hours in a mixed gas of / Ar. LiCoO after fluorination treatment₂When the amount of fluorine contained in the particles was measured, it was 1.5% by weight. A battery was fabricated in the same manner as in Example 1, except that this was used as a positive electrode active material.
[0069]
The initial charge capacity, load characteristics, and high-temperature storage characteristics of the flat gel electrolyte batteries manufactured in Examples 1 to 23 and Comparative Examples 1 to 9 were evaluated by the following methods.
[0070]
<First charge capacity>
The rate of change in battery capacity of the active material after the fluorination treatment relative to the untreated active material was determined. First, each of the batteries (Examples 1 to 23 and Comparative Examples 1 to 9) immediately after fabrication was charged at 23 ° C. at a 2-hour rate (0.5 C) (constant current and constant voltage charging) of the untreated active material theoretical capacity. It went to 4.2V for 10 hours. At this time, the charge capacity of each battery was obtained, and the reduction rate of the capacity of the treated batteries (Examples 1 to 23 and Comparative Examples 1 to 9) with respect to the charge capacity of the untreated battery was calculated as a percentage.
[0071]
<Load characteristics>
A half-hour rate discharge (2C) of the theoretical capacity was performed and evaluated as follows. First, constant current and constant voltage charging was performed on each battery at 23 ° C. to an upper limit of 4.2 V for 10 hours. Next, a 5-hour rate discharge (0.2 C) was performed to a final voltage of 3.0 V. The discharge capacity at this time was determined as a 0.2 C discharge capacity. Thereafter, constant-current and constant-voltage charging was performed again to the upper limit of 4.2 V for 10 hours, and then 1/2 hour rate discharge (2C) was performed to the final voltage of 3.0 V. The discharge capacity at this time was determined as a 2C discharge capacity. The calculation was performed with a 2C discharge capacity relative to a 0.2C discharge capacity as a percentage.
[0072]
<High temperature storage characteristics>
The change in battery dimensions when the charged battery was stored at high temperature was evaluated. First, constant current and constant voltage charging was performed on each battery at 23 ° C. to an upper limit of 4.3 V for 10 hours. At this time, the thickness of each battery was measured and set as the initial thickness. After that, each battery was stored in a thermostat at 80 ° C. for 15 days, and the thickness of the battery immediately after being taken out of the thermostat was measured. The amount obtained by subtracting the initial thickness from the thickness at this time (the amount of change) was calculated as a percentage of the initial thickness, and the result of subtracting it from the change ratio of the untreated battery was calculated as the cell swelling reduction ratio. .
[0073]
Table 1 shows the results of measuring the initial charge capacity reduction rate, the cell swelling reduction rate, and the load characteristics of Examples 1 to 23 and Comparative Examples 1 to 9 described above.
[0074]
[Table 1]

Table 1 shows that the fluorination treatment suppresses cell swelling during high-temperature storage. However, when the fluorination treatment is performed on a composite oxide having an average particle diameter of 2 μm or a composite oxide having an average particle diameter of 25 μm or more, the initial charge capacity reduction rate increases as in Comparative Examples 2, 6, and 7. Or it turned out that the effect is small like Comparative Examples 1 and 3. In addition, it was confirmed that the load characteristics generally tended to be reduced by the fluorination treatment. However, when the fluorination treatment was applied to the active material having an average particle diameter of 25 μm or more, which originally had a low load characteristic, Comparative Examples 4 and 5 , 6, 8, and 9, the load characteristics further decreased, and the performance as a battery was found to decrease.
[0075]
In contrast, in each of the examples in which the fluorination treatment was performed on the composite oxide having an appropriate average particle size and specific surface area, the initial charge capacity reduction rate was small, the cell thickness increase rate was suppressed, and the load was reduced. The properties were also found to be excellent. That is, by subjecting an active material (composite oxide of lithium and transition metal) having an average particle diameter of 3 μm to 24 μm to fluorination treatment, swelling during high-temperature storage can be suppressed, and other battery characteristics are also satisfied. Was found to be obtained. In particular, Examples 1 to 3, Examples 6 to 8, Examples 11, 12, Examples 17, 18, and Examples 20 to 20 in which the amount of fluorine after the fluorine treatment is 0.2% to 3.5% by weight. 22 can be said to be more suitable since the cell swelling reduction rate is high and other characteristics are high.
[0076]
【The invention's effect】
As is clear from the above description, the average particle diameter is 3 μm to 24 μm, and the specific surface area is 0.10 m.²/G~0.92m²/ G composite oxide that has been subjected to fluorination treatment is used as the positive electrode active material, so that non-aqueous electrolyte secondary batteries with little gas swelling during high-temperature storage and high reliability even when using a film-like package It is possible to obtain In particular, when the fluorination treatment amount is 0.2 to 3.5% by weight with respect to the composite oxide as the active material, the cell swelling reduction rate is large, and the battery characteristics such as charge capacity and load characteristics are excellent. It is possible to realize a non-aqueous electrolyte secondary battery.
[Brief description of the drawings]
FIG. 1 is a schematic plan view of a gel electrolyte battery.
FIG. 2 is a schematic sectional view of a gel electrolyte battery.
[Explanation of symbols]
1 Gel electrolyte battery
2 Positive electrode active material layer
3 Negative electrode active material layer
4 Gel electrolyte
5 Power generation elements
6 Exterior film

Claims

Including a composite oxide of lithium and a transition metal,
The composite oxide has an average particle diameter of 3Myuemu～24myuemu, specific surface area of 0.10m ^² /g~0.92m ² / g, the positive electrode active material, wherein the fluorine treatment is performed.

The positive electrode active material according to claim 1, wherein 0.2 to 3.5% by weight of fluorine atoms are present on the surface of the composite oxide by the fluorination treatment.

Average particle diameter of 3Myuemu～24myuemu, specific surface area 0.10m ^² /g~0.92m ² / the composite oxide of g in which lithium and a transition metal, the fluorine gas partial pressure is 5% or more of the fluorine treatment A method for producing a positive electrode active material, comprising performing a fluorine treatment by contacting a working gas.

A positive electrode containing a composite oxide of lithium and a transition metal as a positive electrode active material,
Lithium metal, lithium alloy or lithium doped, a negative electrode containing a material that can be undoped,
A non-aqueous electrolyte,
With an outer container for accommodating these,
The composite oxide has an average particle diameter of 3Myuemu～24myuemu, specific surface area of 0.10m ^² /g~0.92m ² / g, a non-aqueous electrolyte secondary characterized in that the fluorine treatment is performed battery.

The non-aqueous electrolyte secondary battery according to claim 4, wherein 0.2 to 3.5% by weight of fluorine atoms are present on the surface of the composite oxide by the fluorination treatment.

The composite oxide is a general formula LixMyNzO2 (M is Co or Ni, and N is at least one selected from Co, Mn, Ni, Cr, Fe, V, Al, B, and Mg. 5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the compound is represented by the following formula: 0.5 ≦ x ≦ 1.10, 0 <y, 0.80 ≦ y + z ≦ 1.00.

The non-aqueous electrolyte secondary battery according to claim 4, wherein the non-aqueous electrolyte includes a gelled matrix polymer.

The non-aqueous electrolyte secondary battery according to claim 4, wherein the outer container is made of a moisture-proof laminated film composed of a polymer film and a metal foil.