JP3661183B2

JP3661183B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery

Info

Publication number: JP3661183B2
Application number: JP2000009056A
Authority: JP
Inventors: 竜一葛尾; 正典相馬; 哲松本
Original assignee: Sumitomo Metal Mining Co Ltd
Current assignee: Sumitomo Metal Mining Co Ltd
Priority date: 2000-01-18
Filing date: 2000-01-18
Publication date: 2005-06-15
Anticipated expiration: 2020-01-18
Also published as: JP2001202959A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水系電解質二次電池用正極活物質の製造方法に関するものであり、より詳しくは高いサイクル特性を損なうことなく電極としての成形性や充填密度を向上させ、さらに電池として高い初期容量を具備させることが可能となる非水系電解質二次電池用の正極活物質およびその製造方法に関するものである。
【０００２】
【従来の技術】
近年、携帯電話やノート型パソコンなどの携帯機器の普及に伴い、高いエネルギー密度を有するとともに、小型、軽量な二次電池の要求が高まっている。このようなものとして非水系電解液タイプのリチウムイオン二次電池があり、研究開発が盛んに行われ実用化されてきている。
このリチウムイオン二次電池は、リチウム含有複合酸化物を活物質とする正極と、リチウム、リチウム合金、金属酸化物あるいはカーボンのようなリチウムを吸蔵・放出することが可能な材料を活物質とする負極と、非水系電解液を含むセパレータまたは固体電解質を主要構成要素としている。これら構成要素のうち、正極活物質として検討されているものにはリチウムコバルト複合酸化物（ＬｉＣｏＯ_２）、リチウムニッケル複合酸化物（ＬｉＮｉＯ_２）、リチウムマンガン複合酸化物（ＬｉＭｎ_２Ｏ_４）などが挙げられる。特にリチウムコバルト複合酸化物を正極に用いた二次電池では、優れた初期容量特性やサイクル特性を得るための開発がこれまで数多く行われ、すでに様々な成果が得られて実用化に至っている。
【０００３】
しかしリチウムコバルト複合酸化物は、原料に希産で高価なコバルトを用いるため正極活物質、さらには製品としての二次電池のコストアップの大きな原因となっている。一方コバルトよりも安価なニッケルを用いたリチウムニッケル複合酸化物は、コスト的にも容量的にも有利であり、リチウムコバルト複合酸化物の有力な代替材料として開発が進められているが、このリチウムニッケル複合酸化物を正極活物質に用いた二次電池は、充電状態での正極活物質の不安定性から、高温に保持すると分解、発熱、発火などの危険性を有しており、安全性に関して解決しなければならない問題が数多く残っている。
これに対してリチウムマンガン複合酸化物は、リチウムコバルト複合酸化物やリチウムニッケル複合酸化物に比べて容量がやや小さいものの、コバルトやニッケルよりも安価で資源的にも豊富なマンガンを用いているためにコスト的に有利であり、かつ充電状態での安全性にも優れているため、次世代の正極材料として期待されている。
【０００４】
さてリチウムイオン二次電池においては、初期の放電容量（初期容量）が高く、かつ充放電サイクルの繰り返しによる容量の劣化（サイクル特性）が少ないものが求められており、さらに容量に関しては、冒頭に述べた小型化の観点から、単位体積当たりの放電容量が大きいものが求められている。
しかし前記リチウムマンガン複合酸化物は、純粋にマンガンのみで合成した材料を正極活物質としてリチウムイオン二次電池を作製した場合には、サイクル特性が悪く、高温環境下で使用されたり保存された場合に比較的電池性能を損ない易いという欠点を有していた。
【０００５】
このような欠点を解決するためにマンガンの一部をクロムやニッケル、コバルトなどの金属元素に置き換える方法が提案され、これにより結晶構造の安定性が向上し、サイクル特性や高温保持特性が改善されることが判明した。
そして一般にこれらの金属元素を添加する際には反応性を向上させ、また反応をより均一に進行させるために、原料の金属元素の化合物やマンガン化合物、リチウム化合物とを十分に粉砕して混合してから合成する必要がある。しかしながらこのような方法で得られたリチウムマンガン複合酸化物はその工程上、粒子が非常に細かくなるために、正極を形成する際の成形性が悪化する上、電極としての充填密度が上げられず単位体積当たりの電池としての容量が低いものとなってしまう。
【０００６】
したがって反応性を高め、反応をより均一に進めるための方法として、添加する金属元素の化合物とマンガン化合物、リチウム化合物を溶媒に溶かして混合し、スプレードライなどで噴霧して乾燥し、同時に反応を進行させる方法なども提案されているが、この方法で得られたリチウムマンガン複合酸化物は細かい一次粒子が凝集した二次粒子の形態をもっているものの、二次粒子内部が中空で十分な密度と強度を有するものが得られず、結果的に電極としての充填密度が上げられないという問題点を有していた。
【０００７】
【発明が解決しようとする課題】
このようにリチウムマンガン複合酸化物を正極活物質とした従来の非水系電解質二次電池においては、高いサイクル特性を維持したまま、電極としての成形性、充填密度を向上させ、電池として高い初期容量を具備させることが困難であるという問題点を有していた。
【０００８】
本発明はこのような問題点に着目してなされたもので、その目的とするところは、他の元素添加によって高いサイクル特性を維持したまま正極としての成形性、充填密度を損なわずに初期容量の向上を図れる二次電池を組立てることができる非水系電解質二次電池用正極活物質の製造方法を提供することにある。
【０００９】
【課題を解決するための手段】
上記問題を解決するため本発明者らは鋭意研究を重ねた結果、マンガンの一部がクロム、ニッケル、コバルト、アルミニウム、マグネシウム、鉄などの金属元素で置換されたリチウムマンガン複合酸化物を正極活物質に適用するに際し、細かい一次粒子が凝集して比較的密に詰まった球状または楕円球状の二次粒子を構成した粉体特性をもつマンガン化合物原料の形状を崩さないように金属元素の化合物を添加し、これをリチウム化合物と混合して熱処理することにより得られたリチウムマンガン複合酸化物を用いることによって、上述した問題の発生を防止でき、かつ成形性、充填性に優れ、高いサイクル特性を維持したまま単位体積当たりの放電容量が大きい二次電池を構成できることを見出し、本発明を完成するに至った。
【００１０】
すなわち、本発明の第１の実施態様に係る非水系電解質二次電池用正極活物質の製造方法は、Ｌｉ_１＋ｘＭｎ_２−ｙＭ_ｙＯ_４（式中、ＭはＣｒ、Ｎｉ、Ｃｏ、Ａｌ、ＭｇおよびＦｅからなる群から選ばれた少なくとも１種の金属元素）で表されるリチウムマンガン複合酸化物からなる非水系電解質二次電池用正極活物質の製造方法であって、Ｃｒ、Ｎｉ、Ｃｏ、Ａｌ、ＭｇおよびＦｅからなる群から選ばれた少なくとも１種の金属元素Ｍの化合物を、マンガンと金属元素Ｍのモル比が２−ｙ：ｙ（式中、ｙは０＜ｙ≦０．３３である）となるように、予め二次粒子の形状が球状または楕円球状であるマンガン化合物に添加する工程、前記工程で得られた金属元素Ｍの化合物が添加されたマンガン化合物と、リチウム化合物とを、０≦ｘ≦０．１０となるように混合する工程、次に、該混合物を熱処理する工程、を有することを特徴とするものである。
そして前記金属元素Ｍの化合物をＭの硝酸塩または酢酸塩とし、該Ｍの硝酸塩または酢酸塩を加熱融解するか、もしくは溶媒に溶解する工程、得られた溶液中にマンガン化合物を加えて、加熱攪拌して、該マンガン化合物に該Ｍの硝酸塩または酢酸塩を含浸させた粉末を得る工程、得られた粉末とリチウム化合物と混合する工程を有することを特徴とする。
また前記金属元素Ｍの化合物をＭの水酸化物とし、前記金属元素Ｍの硝酸塩を溶媒に溶解する工程、得られた金属元素Ｍの塩溶液にマンガン化合物を投入しマンガン化合物に金属元素Ｍの塩を含浸させる工程、次に得られたＭ塩含浸マンガン化合物溶液にアルカリ溶液を加え、金属元素Ｍの塩と中和反応させてＭの水酸化物を生成させる工程、得られた金属元素Ｍの水酸化物が分散含浸されたマンガン化合物と、リチウム化合物とを混合する工程を有することを特徴とする。
【００１１】
前記第２の実施態様に係る製造方法では前記混合物の熱処理温度は６００℃以上で９５０℃未満とし、４時間以上実施するものである。
【００１２】
【発明の実施の形態】
以下本発明の実施の形態について詳細に説明する。
本発明はマンガンの一部をサイクル特性向上のためにクロム、ニッケル、コバルト、アルミニウム、マグネシウム、鉄などで置換したリチウムマンガン複合酸化物からなる活物質の製造方法に関するものである。
リチウムマンガン複合酸化物は二次電池の正極活物質として考えた場合、結晶構造からリチウムがイオンとして脱離・挿入することによって充放電が行われる。金属元素などで置換しない純粋なリチウムマンガン複合酸化物は、充放電サイクルを繰り返した場合、初期に比べて容量が劣化するという問題がある。これはリチウムイオンが結晶構造から脱離・挿入を繰り返す際に母体の構造が徐々に破壊され、リチウムイオンが戻るべき場所が結晶構造内から失われていくためであると考えられる。この構造破壊を防ぐためにマンガンの一部を他の元素に置換する方法が提案され、この方法により充放電サイクルが改善されることが報告されている。
【００１３】
一般にはマンガンの一部を他の元素に置換すると、正極材料の容量を決定するＭｎ^３＋の量が減少するため初期容量は減少してしまうが、Ｌｉ_１＋ｘＭｎ_２−ｙＭ_ｙＯ_４（式中、ＭはＣｒ、Ｎｉ、Ｃｏ、Ａｌ、Ｍｇ、Ｆｅからなる群から選ばれた少なくとも１種の金属元素）で表されるリチウムマンガン複合酸化物においては、０≦ｘ≦０．１０で、かつ０＜ｙ≦０．３３なる条件を満たすことにより、実用的に許容範囲内の容量低下に抑えることができることが本発明者らの種々の研究により判明した。
しかしながら一般に他の元素に置換するためには、合成の際にマンガン原料化合物と置換金属原料化合物をリチウム原料化合物と粉砕しながら十分に混合する必要がある。粉末固体を反応物質として用いる固相反応は、固相相互の接触部分で反応が開始し、それら界面に反応生成物が生成することにより反応が進行していくため粒子が微細であればあるほど接触部分は増大し、均一な組成が得られるためである。
【００１４】
このようにしてできるだけ均一な組成になるように細かく粉砕混合する方法で合成された元素置換型リチウムマンガン複合酸化物は、その物質自体の特性としてサイクル特性が改善されている。しかしこれを正極材料としての観点から見ると、細かい粒子が多数存在するため電極としての充填性に直接影響するタップ密度が低く、電極としての成形性が悪い上、導電助剤として添加するカーボンや、成形性を向上させるための結着剤の量を多くしなければならないため、成形された正極の単位体積中に含まれる活物質の量は少なくなり、結果として二次電池としての初期容量が低下してしまう。
【００１５】
一方マンガン原料と金属原料を両方溶媒に溶かして混合し、その後溶媒を蒸発させて原子レベルの混合を実現する方法も提案されているが、例えばスプレードライのような方法では二次粒子内部が中空な球状粒子となってしまい、その強度やタップ密度が十分なものとはならない。また共沈法のようにマンガン原料と金属原料を原子レベルで共沈殿させる方法は、組成の均一性という観点からは最も理想的な方法であるが、得られる粉末の粒径の制御が難しいという問題点をもつ。
したがって粉体ができるだけ大きなタップ密度（充填密度）をもつようにするためには、幾何学的には粉体の粒子が球状で、ある程度の幅を持った粒度分布をもつことが重要であるが、現実の正極活物質としての粉末を考えると粒子の形状は球体に近く、できるだけ粒度分布がシャープで、その中心粒径が数μｍ〜数十μｍ程度であり、かつ電極としての成形性を考慮すると粒径１μｍ以下の微粉はできるだけ少ない方が好ましい。このような粉体性状をもつマンガン化合物は実際に調製可能であり市販もされている。
【００１６】
本発明者らはこのような粉体性状をもつマンガン化合物を原料として、その粉体特性を維持するような金属元素の添加方法を用いて合成を行なえば、結果的に得られるリチウムマンガン複合酸化物もマンガン原料と同様な粉体特性を持ち、上記のような問題点を回避することができることを見出した。
【００１７】
すなわち本発明に係る非水系電解質二次電池用正極活物質の製造方法は、Ｌｉ_１＋ｘＭｎ_２−ｙＭ_ｙＯ_４（式中、ＭはＣｒ、Ｎｉ、Ｃｏ、Ａｌ、ＭｇおよびＦｅからなる群から選ばれた少なくとも１種の金属元素）で表されるリチウムマンガン複合酸化物からなる非水系電解質二次電池用正極活物質の製造方法であって、Ｃｒ、Ｎｉ、Ｃｏ、Ａｌ、ＭｇおよびＦｅからなる群から選ばれた少なくとも１種の金属元素Ｍの化合物を、マンガンと金属元素Ｍのモル比が２−ｙ：ｙ（式中、ｙは０＜ｙ≦０．３３である）となるように、予め二次粒子の形状が球状または楕円球状であるマンガン化合物に添加する工程、前記工程で得られた金属元素Ｍの化合物が添加されたマンガン化合物と、リチウム化合物とを、０≦ｘ≦０．１０となるように混合する工程、次に、該混合物を熱処理する工程、を有することを特徴とするものである。
このような粉体特性をもつリチウムマンガン複合酸化物は、二次粒子の形状が球状または楕円球状であるマンガン化合物の粉体特性が損なわれるような粉砕混合工程を経ずに、前記金属元素Ｍの化合物を、例えば該金属元素Ｍの化合物のみを微粉砕してマンガン化合物と混合したり、金属元素Ｍの化合物のみを溶媒に溶解してマンガン化合物に分散させるなどの方法によって、マンガンと金属元素Ｍのモル比が２−ｙ：ｙ（式中、ｙは０＜ｙ≦０．３３である）となるように予め添加したマンガン化合物をリチウム化合物と混合し、この混合物を熱処理することで得ることができる。
すなわち、マンガンと金属元素Ｍのモル比が、０＜ｙ≦０．３３の範囲において２−ｙ：ｙとなるように予め添加したマンガン化合物を用いることにより、実用的に許容範囲内の容量低下に抑えることが可能となり、この条件を外れると初期容量が著しく低下してしまう。
【００１８】
そして本発明で用いるリチウム化合物としては炭酸リチウムや水酸化リチウム、水酸化リチウム一水和物、硝酸リチウム、過酸化リチウムなどが挙げられる。またマンガン化合物としては酸化マンガン、水酸化マンガン、塩化マンガン、炭酸マンガン、硝酸マンガン、硫酸マンガン、酢酸マンガンなどが挙げられ、二次粒子の形状が球状または楕円球状であるような粉体特性をもつものであれば好適に用いることが可能である。
さらに金属元素Ｍの化合物としては酸化物、水酸化物、塩化物、炭酸塩、硝酸塩、硫酸塩、酢酸塩など、マンガン化合物との固相反応が十分進むような微粉砕粉、あるいは溶媒に溶解させマンガン化合物に均一に分散、付着、反応させられるものであれば用いることが可能である。中でも金属元素Ｍの硝酸塩や酢酸塩はいずれも溶媒（例えば水）に溶解可能であり、マンガン化合物への添加、分散が容易である。
【００１９】
そしてこれら金属元素Ｍの化合物を用いてリチウムマンガン複合酸化物を得る方法としては以下の２つの方法がある。
(1)金属元素Ｍの化合物をＭの硝酸塩または酢酸塩とする場合には、マンガンの化合物に添加する際に、Ｍの硝酸塩または酢酸塩を加熱融解するか、もしくは溶媒に溶解し、その中にマンガン化合物を投入して、加熱攪拌して、該マンガン化合物に該Ｍの硝酸塩または酢酸塩を含浸させ、均一に分散、添加させた粉末をリチウム化合物と混合し、熱処理することで組成的に均一で、かつマンガン化合物原料の粉体特性を損なわずにリチウムマンガン複合酸化物を得ることができる。
【００２０】
(2)金属元素Ｍの化合物をＭの水酸化物とする場合には、マンガンの化合物に添加する際に、Ｍの硝酸塩を溶媒に溶解し、得られた金属元素Ｍの塩溶液にマンガン化合物を投入してマンガン化合物に金属元素Ｍの塩を含浸させ、得られたＭ塩含浸マンガン化合物溶液にアルカリ溶液を加え、金属元素Ｍの塩と中和反応させてＭの水酸化物を生成させ、得られた金属元素Ｍの水酸化物が分散含浸されたマンガン化合物と、リチウム化合物と混合し、熱処理することで組成的に均一で、かつマンガン化合物原料の粉体特性を損なわずにリチウムマンガン複合酸化物を得ることができる。
【００２１】
ついでマンガン化合物とリチウム化合物の混合物を熱処理する際、その温度を６００℃以上で９５０℃未満とすることにより、添加した金属元素Ｍの化合物などの異相を生じさせることなく、金属元素Ｍを完全に固溶させることができ、結晶構造の高い完全性を実現できる。好ましくは熱処理温度を７００℃以上で８５０℃以下とすることでより高い初期容量を実現できる。
なお熱処理温度が６００℃未満であると反応が不十分なため結晶性が悪くなり、一方９５０℃以上となると結晶構造が立方晶から構造相転移を起こして正方晶となり好ましくない。また前記熱処理は４時間以上実施することが好ましく、４時間未満の熱処理では反応が不十分となり結晶性の低下や異相の出現を招いてしまう。
本発明によるマンガンの一部をクロム、ニッケル、コバルト、アルミニウム、マグネシウム、鉄などで置換し、二次粒子の形状が球状または楕円球状のリチウムマンガン複合酸化物からなる正極活物質を用いた場合、金属元素の置換によって高いサイクル特性を維持したまま、成形性や充填密度を向上させ、高い初期容量を具備する二次電池を組立てることができる。
【００２２】
【実施例】
以下本発明の実施例を比較例とともに詳述する。
［実施例１］
マンガンの一部をクロムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸クロム九水和物を準備した。球状の二酸化マンガンと硝酸クロム九水和物を、マンガンとクロムのモル比が(1)１．６７：０．３３、(2)１．８３：０．１７、(3)１．８９：０．１１、(4)１．９４：０．０６となるようにそれぞれ秤量した後、硝酸クロム九水和物が完全に溶解する量の純水中に硝酸クロム九水和物を溶解した。
その後その溶液中に球状の二酸化マンガンのみを入れて加熱しながら撹拌して水分を揮発させ、乾燥粉末を調製した。この乾燥粉末と水酸化リチウム一水和物を、リチウムとマンガン＋クロムのモル比が１：２となるように秤量し、球状の二次粒子の形骸が維持される程度の強度で十分に混合した。
この混合粉末を酸素気流中で４７５℃で２時間仮焼した後、８００℃で２０時間焼成し、室温まで炉冷した。
【００２３】
得られた焼成物を、ＣｕのＫα線を用いた粉末Ｘ線回折で分析したところ、スピネル構造を有する所望の正極活物質のみが単相で確認できた。また粉末Ｘ線回折図形のリートベルト解析から、格子定数を求めたところ、試料(1)〜(4)に対してクロムの添加量が増大するにつれて直線的に格子定数が減少していくことが確認でき、クロムの固溶が確認された。
そして得られた正極活物質のタップ密度を測定し、前記した格子定数とともに下記する表１に示す。
また得られた正極活物質を用いて以下のように電池を作製し、充放電容量により電池特性を測定した。活物質粉末９０重量％にアセチレンブラック５重量％およびＰＶＤＦ（ポリ沸化ビニリデン）５重量％を混合し、ＮＭＰ（ｎ−メチルピロリドン）を加えてペースト化した。これを２０μｍ厚のアルミニウム箔に乾燥後の活物質重量が０．０５ｇ／ｃｍ^２になるように塗布し、１２０℃で真空乾燥を行い、１ｃｍφのディスク状に打ち抜いて正極とした。
【００２４】
そして図１に示すように得られた正極１と、負極３としてリチウム金属を、また電解液には１ＭのＬｉＣｌＯ_４を支持塩とするエチレンカーボネート（ＥＣ）とジメチルカーボネート（ＤＭＣ）の等量混合溶液を用い、ポリエチレンからなるセパレータ２に前記電解液を染み込ませ、露点が−８０℃に管理されたＡｒ雰囲気のグローブボックス中で、２０３２型のコイン電池を組立てた。
なお図１において、４はガスケット、５は正極缶、６は負極缶である。
このようにして組立てられたコイン電池を組立後２４時間程度放置し、開回路電圧（ＯＣＶ）が安定した後、正極に対する電流密度を０．５ｍＡ／ｃｍ^２とし、カットオフ電圧４．３〜３．０Ｖで充放電試験を行って電池特性を評価した。
得られた１サイクル目の放電容量（初期容量）、５０サイクル目の放電容量および初期容量に対する５０サイクル目の放電容量の比（容量維持率）を下記する表２に示す。
【００２５】
［実施例２］
マンガンの一部をニッケルに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸ニッケル六水和物を準備し、球状の二酸化マンガンと硝酸ニッケル六水和物を、マンガンとニッケルのモル比が(1)１．８３：０．１７、(2)１．８９：０．１１、(3)１．９４：０．０６、(4)１．９７：０．０３となるようにそれぞれ秤量した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン二次電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００２６】
［実施例３］
マンガンの一部をコバルトに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸コバルト六水和物を準備した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン二次電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００２７】
［実施例４］
マンガンの一部をアルミニウムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸アルミニウム六水和物を準備し、球状の二酸化マンガンと硝酸アルミニウム六水和物を、マンガンとアルミニウムのモル比が(1)１．８３：０．１７、(2)１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン二次電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００２８】
［実施例５］
マンガンの一部をマグネシウムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸マグネシウム六水和物を準備し、球状の二酸化マンガンと硝酸マグネシウム六水和物を、マンガンとマグネシウムのモル比が(1)１．８３：０．１７、(2)１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン二次電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００２９】
［実施例６］
マンガンの一部を鉄に置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸鉄六水和物を準備し、球状の二酸化マンガンと硝酸鉄六水和物を、マンガンと鉄のモル比が1.）１．８３：０．１７、2.）１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン二次電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３０】
［実施例７］
マンガンの一部をクロムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸クロム九水和物を準備した。球状の二酸化マンガンと硝酸クロム九水和物を、マンガンとクロムのモル比が(1)１．６７：０．３３、(2)１．８３：０．１７、(3)１．８９：０．１１となるようにそれぞれ秤量した後、硝酸クロム九水和物が完全に溶解する量の純水中に硝酸クロム九水和物を溶解した。その溶液中に球状の二酸化マンガンのみを入れて撹拌しつつ、中和するのに必要な量の水酸化ナトリウム溶液を滴下して十分に反応させた。その後濾過によって上澄み液を除去し洗浄後、加熱乾燥によって乾燥粉末を調製した。
この乾燥粉末と水酸化リチウム一水和物をリチウムとマンガン＋クロムのモル比が１：２となるように秤量し、球状の二次粒子の形骸が維持される程度の強度で十分に混合した。この混合粉末を、酸素気流中で４７５℃で２時間仮焼した後、８００℃で２０時間焼成し、室温まで炉冷した。
得られた焼成物の格子定数と正極活物資のタップ密度とを実施例１と同様にして測定して下記する表１に併せて示す。
【００３１】
また得られた活物質を用いて以下のように電池を作製し、充放電容量により電池特性を測定した。すなわち活物質粉末８７重量％にアセチレンブラック５重量％およびＰＶＤＦ（ポリ沸化ビニリデン）８重量％を混合し、ＮＭＰ（ｎ−メチルピロリドン）を加えペースト化した。このペーストを用いて実施例１と同様な手順で正極を調製し、ついで実施例１と同様にして図１に示したような２０３２型のコイン電池を組立てた。
このようにして組立てられたコイン電池について実施例１と同様にして電池特性を評価し、得られた１サイクル目の放電容量（初期容量）と５０サイクル目の放電容量、および初期容量に対する５０サイクル目の放電容量の比（容量維持率）を下記する表２に併せて示す。
【００３２】
［実施例８］
マンガンの一部をニッケルに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸ニッケル六水和物を準備した以外は、実施例７と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３３】
［実施例９］
マンガンの一部をコバルトに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸コバルト六水和物を準備した以外は、実施例７と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３４】
［実施例１０］
マンガンの一部をアルミニウムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸アルミニウム六水和物を準備し、球状の二酸化マンガンと硝酸アルミニウム六水和物を、マンガンとアルミニウムのモル比が(1)１．８３：０．１７、(2)１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例７と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３５】
［実施例１１］
マンガンの一部をマグネシウムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸マグネシウム六水和物を準備し、球状の二酸化マンガンと硝酸マグネシウム六水和物を、マンガンとマグネシウムのモル比が(1)１．８３：０．１７、(2)１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例７と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価して結果を下記する表１と表２に併せて示す。
【００３６】
［実施例１２］
マンガンの一部を鉄に置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、硝酸鉄六水和物を準備し、球状二酸化マンガンと硝酸鉄六水和物を、マンガンと鉄のモル比が(1)１．８３：０．１７、(2)１．８９：０．１１となるようにそれぞれ秤量した以外は、実施例７と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３７】
［比較例１］
マンガンの一部を元素で置換しない純粋な正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガンを、リチウムとマンガンのモル比が１：２となるように秤量した以外は、実施例１と同様な手順で正極活物質を合成し、さらにリチウムコイン電池を組立て、実施例１と同様に格子定数とタップ密度を測定し、また実施例１と同様に電池特性を評価してその結果を下記する表１と表２に併せて示す。
【００３８】
［比較例２］
マンガンの一部をクロムに置換した正極活物質を合成するために、市販の水酸化リチウム一水和物、球状の二酸化マンガン、酸化クロムを準備した。水酸化リチウム一水和物と球状の二酸化マンガンと酸化クロムを、リチウムとマンガンとクロムのモル比が(1)１：１．６７：０．３３、(2)１：１．８３：０．１７、(3)１：１．８９：０．１１となるようにそれぞれ秤量した後、これらをエタノールを媒体に用いてボールミルで１５時間十分に粉砕して湿式混合した。得られたスラリー状の混合物を８５℃で大気中で３時間乾燥し、混合乾燥粉末を調製した。
この混合乾燥粉末を、酸素気流中で４７５℃で２時間仮焼した後、８００℃で２０時間焼成し、室温まで炉冷して、得られた焼成物の格子定数およびタップ密度を実施例１と同様に測定し、また実施例１と同様にして組立てた電池の電池特性を実施例１と同様に評価して、得られた結果を下記する表１と表２に併せて示す。
【００３９】
【表１】

【００４０】
【表２】

【００４１】
前記表１と表２から分かる通り、実施例１〜１２の電池は、純粋にマンガンのみで合成した比較例１の電池と比較していずれも高いタップ密度を維持しながら、８０％以上の高い容量維持率を示していた。またマンガンやリチウム化合物および金属元素の化合物を十分に粉砕して混合してなる比較例２と比較していずれも８０％以上の高い容量維持率を保ちながら、高いタップ密度を実現し、充填性が向上していた。
【００４２】
【発明の効果】
以上述べた通り本発明の非水系電解質二次電池用正極活物質の製造方法により得られた非水系電解質二次電池用正極活物質は、非水系二次電池の正極活物質として用いることにより、高いサイクル特性を維持したまま、正極としての成形性、充填密度の向上を図ることが可能であり、また単位体積当たりの初期容量の大きな二次電池を提供することができるという効果がある。
【図面の簡単な説明】
【図１】正極活物質を用いたコイン電池の概略縦断面図である。
【符号の説明】
１正極
２セパレータ
３負極
４ガスケット
５正極缶
６負極缶[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.QualityIt relates to a manufacturing method, and more specifically, for a non-aqueous electrolyte secondary battery that can improve the moldability and packing density as an electrode without impairing high cycle characteristics, and can have a high initial capacity as a battery. The positive electrode active material and the manufacturing method thereof.
[0002]
[Prior art]
  In recent years, with the widespread use of mobile devices such as mobile phones and laptop computers, there is an increasing demand for secondary batteries that have a high energy density and are small and light. There is a non-aqueous electrolyte type lithium ion secondary battery as such, and research and development have been actively conducted and put into practical use.
  This lithium ion secondary battery uses a positive electrode having a lithium-containing composite oxide as an active material and a material capable of inserting and extracting lithium, such as lithium, a lithium alloy, a metal oxide, or carbon, as an active material. The main component is a negative electrode and a separator or solid electrolyte containing a non-aqueous electrolyte. Among these components, lithium cobalt complex oxide (LiCoO) is considered as a positive electrode active material.₂), Lithium nickel composite oxide (LiNiO)₂), Lithium manganese composite oxide (LiMn)₂O₄) And the like. In particular, secondary batteries using a lithium cobalt composite oxide as a positive electrode have been developed to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained and put into practical use.
[0003]
  However, since lithium cobalt complex oxide uses rare and expensive cobalt as a raw material, it is a major cause of the cost increase of the positive electrode active material and the secondary battery as a product. On the other hand, lithium-nickel composite oxides using nickel, which is cheaper than cobalt, are advantageous in terms of cost and capacity, and are being developed as potential alternative materials for lithium-cobalt composite oxides. Secondary batteries using nickel composite oxide as the positive electrode active material have the risk of decomposition, heat generation, ignition, etc. if kept at high temperatures due to the instability of the positive electrode active material in the charged state. There remain many problems that need to be solved.
  On the other hand, although lithium manganese composite oxide has slightly smaller capacity than lithium cobalt composite oxide and lithium nickel composite oxide, it uses cheaper and more abundant resources than cobalt and nickel. Therefore, it is expected to be a next-generation positive electrode material because it is advantageous in terms of cost and is excellent in safety in a charged state.
[0004]
  A lithium ion secondary battery is required to have a high initial discharge capacity (initial capacity) and little capacity deterioration (cycle characteristics) due to repeated charge / discharge cycles. From the viewpoint of miniaturization as described above, a battery having a large discharge capacity per unit volume is required.
  However, the lithium-manganese composite oxide has poor cycle characteristics when a lithium ion secondary battery is manufactured using a material synthesized purely of manganese alone as a positive electrode active material, and is used or stored in a high-temperature environment. However, the battery performance is relatively easily lost.
[0005]
  In order to solve these drawbacks, a method of replacing a part of manganese with a metal element such as chromium, nickel, cobalt, etc. has been proposed, which improves the stability of the crystal structure and improves the cycle characteristics and high temperature holding characteristics. Turned out to be.
  In general, when these metal elements are added, the raw metal element compound, manganese compound, and lithium compound are sufficiently pulverized and mixed in order to improve the reactivity and to promote the reaction more uniformly. It is necessary to synthesize after that. However, since the lithium manganese composite oxide obtained by such a method has very fine particles in the process, the formability at the time of forming the positive electrode is deteriorated and the packing density as an electrode cannot be increased. The battery capacity per unit volume will be low.
[0006]
  Therefore, as a method to increase the reactivity and make the reaction proceed more uniformly, dissolve the metal element compound, manganese compound, and lithium compound to be added in a solvent, mix them, and spray and dry them by spray drying. Although a method of proceeding has been proposed, the lithium manganese composite oxide obtained by this method has the form of secondary particles in which fine primary particles are aggregated, but the inside of the secondary particles is hollow and sufficient density and strength As a result, the packing density as an electrode cannot be increased.
[0007]
[Problems to be solved by the invention]
  As described above, in the conventional non-aqueous electrolyte secondary battery using lithium manganese composite oxide as the positive electrode active material, while maintaining high cycle characteristics, the moldability and filling density as an electrode are improved, and the battery has a high initial capacity. It was difficult to provide
[0008]
  The present invention has been made paying attention to such problems, and its purpose is to maintain initial cycle capacity without impairing formability and packing density as a positive electrode while maintaining high cycle characteristics by adding other elements. Cathode active material for non-aqueous electrolyte secondary battery capable of assembling a secondary battery capable of improvingQualityIt is to provide a manufacturing method.
[0009]
[Means for Solving the Problems]
  In order to solve the above problems, the present inventors have conducted extensive research. As a result, a lithium manganese composite oxide in which a part of manganese is substituted with a metal element such as chromium, nickel, cobalt, aluminum, magnesium, iron or the like is activated. When applying to a substance, a compound of a metal element is used so that the shape of the raw material of the manganese compound having powder characteristics that constitutes spherical or oval spherical secondary particles in which fine primary particles aggregate and are relatively densely packed By using the lithium manganese composite oxide obtained by adding, mixing this with a lithium compound and heat-treating, it is possible to prevent the above-mentioned problems from occurring, and it has excellent moldability and filling properties, and high cycle characteristics. The present inventors have found that a secondary battery having a large discharge capacity per unit volume can be configured while maintaining it, and have completed the present invention.
0010]
  That is,The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the first embodiment of the present invention includes Li_{1 + x}Mn_2-yM_yO₄Where M is at least one metal element selected from the group consisting of Cr, Ni, Co, Al, Mg and Fe.A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-manganese composite oxide, comprising at least one metal selected from the group consisting of Cr, Ni, Co, Al, Mg and Fe In the compound of the element M, the shape of the secondary particles is spherical in advance so that the molar ratio of manganese to the metal element M is 2-y: y (where y is 0 <y ≦ 0.33). A step of adding to the ellipsoidal manganese compound, a step of mixing the manganese compound to which the compound of the metal element M obtained in the step is added, and the lithium compound so that 0 ≦ x ≦ 0.10, Next, the method includes a step of heat-treating the mixture.Is.
  And the compound of the metal element M is M nitrate or acetate,TheMelt nitrate or acetate of M or dissolve in solventIn the resulting solutionManganese compoundsIs added to the manganese compound, and the M nitrate or acetate is added to the manganese compound.ImpregnatedThe step of obtaining a powder, the obtained powder andMix with lithium compoundsHave stepsIt is characterized by that.
  In addition, the metal element M compound is M hydroxide., A step of dissolving the nitrate of the metal element M in a solvent, a step of introducing a manganese compound into the obtained salt solution of the metal element M and impregnating the manganese compound with the salt of the metal element M, and then impregnating the M salt obtained A step of adding an alkaline solution to the manganese compound solution and neutralizing with a salt of the metal element M to form a hydroxide of M, a manganese compound in which the obtained hydroxide of the metal element M is dispersed and impregnated, and lithium Having a step of mixing with the compoundIt is characterized by that.
[0011]
  In the manufacturing method according to the second embodiment, the heat treatment temperature of the mixture is 600 ° C. or more and less than 950 ° C., and is carried out for 4 hours or more.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described in detail.
  The present invention relates to an active material comprising a lithium manganese composite oxide in which a part of manganese is replaced with chromium, nickel, cobalt, aluminum, magnesium, iron, etc. in order to improve cycle characteristics.Manufacturing methodIt is about.
  When the lithium manganese composite oxide is considered as a positive electrode active material of a secondary battery, charging / discharging is performed by desorption / insertion of lithium as ions from the crystal structure. A pure lithium manganese composite oxide that is not substituted with a metal element or the like has a problem that the capacity deteriorates compared to the initial stage when the charge / discharge cycle is repeated. This is considered to be because when the lithium ions are repeatedly desorbed and inserted from the crystal structure, the base structure is gradually destroyed, and the place where the lithium ions should return is lost from within the crystal structure. In order to prevent this structural breakdown, a method of substituting a part of manganese with another element has been proposed, and it has been reported that this method improves the charge / discharge cycle.
[0013]
  In general, when a part of manganese is replaced with another element, Mn determines the capacity of the positive electrode material.³⁺The initial capacity decreases because the amount of_{1 + x}Mn_2-yM_yO₄In the lithium manganese composite oxide represented by (wherein M is at least one metal element selected from the group consisting of Cr, Ni, Co, Al, Mg, and Fe), 0 ≦ x ≦ 0.10 In addition, it has been found by various studies by the present inventors that it is possible to suppress the capacity drop to a practically allowable range by satisfying the condition of 0 <y ≦ 0.33.
  However, in general, in order to substitute with another element, it is necessary to sufficiently mix the manganese raw material compound and the substituted metal raw material compound with the lithium raw material compound during the synthesis. The solid phase reaction using a powdered solid as a reactant is initiated at the contact portion between the solid phases, and the reaction proceeds as a reaction product is generated at the interface. This is because the contact area increases and a uniform composition is obtained.
[0014]
  In this way, the element-substituted lithium manganese composite oxide synthesized by the method of finely pulverizing and mixing so that the composition is as uniform as possible has improved cycle characteristics as the characteristics of the substance itself. However, from the viewpoint of the positive electrode material, there are a large number of fine particles, so the tap density that directly affects the fillability as an electrode is low, the moldability as an electrode is poor, and carbon added as a conductive additive Since the amount of the binder for improving the moldability has to be increased, the amount of the active material contained in the unit volume of the molded positive electrode is reduced, resulting in an initial capacity as a secondary battery. It will decline.
[0015]
  On the other hand, a method has been proposed in which both manganese raw material and metal raw material are dissolved in a solvent and then mixed, and then the solvent is evaporated to achieve atomic level mixing. Spherical particles, and the strength and tap density are not sufficient. In addition, the method of coprecipitation of manganese raw material and metal raw material at the atomic level as in the coprecipitation method is the most ideal method from the viewpoint of the uniformity of the composition, but it is difficult to control the particle size of the resulting powder. Has a problem.
  Therefore, in order to make the powder have as large a tap density (packing density) as possible, it is important that the powder particles are spherical in shape and have a particle size distribution with a certain width. Considering the powder as the actual positive electrode active material, the particle shape is close to a sphere, the particle size distribution is as sharp as possible, the center particle size is about several μm to several tens μm, and the moldability as an electrode is considered Then, it is preferable that the amount of fine powder having a particle size of 1 μm or less is as small as possible. Manganese compounds having such powder properties can be actually prepared and are also commercially available.
[0016]
  When the present inventors use a manganese compound having such powder properties as a raw material and synthesize it using a metal element addition method that maintains its powder characteristics, the resulting lithium manganese composite oxidation It has been found that the product has the same powder characteristics as the manganese raw material and can avoid the above problems.
[0017]
  That is, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention comprises:_{1 + x}Mn_2-yM_yO₄Where M is at least one metal element selected from the group consisting of Cr, Ni, Co, Al, Mg and Fe.A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-manganese composite oxide, comprising at least one metal selected from the group consisting of Cr, Ni, Co, Al, Mg and Fe In the compound of the element M, the shape of the secondary particles is spherical in advance so that the molar ratio of manganese to the metal element M is 2-y: y (where y is 0 <y ≦ 0.33). A step of adding to the ellipsoidal manganese compound, a step of mixing the manganese compound to which the compound of the metal element M obtained in the step is added, and the lithium compound so that 0 ≦ x ≦ 0.10, Next, a step of heat-treating the mixture It is characterized byIs.
  The lithium manganese composite oxide having such powder characteristics can be obtained by performing the above-mentioned metal element M without going through a pulverization and mixing step that impairs the powder characteristics of the manganese compound whose secondary particles are spherical or elliptical. For example, by compounding the compound of the metal element M with a manganese compound by pulverizing only the compound of the metal element M, or by dissolving only the compound of the metal element M in a solvent and dispersing it in the manganese compound, A manganese compound previously added so that the molar ratio of M is 2-y: y (where y is 0 <y ≦ 0.33) is mixed with a lithium compound, and the mixture is heat-treated. be able to.
  That is, by using a manganese compound added in advance so that the molar ratio of manganese to the metal element M is 2-y: y in the range of 0 <y ≦ 0.33, the capacity is reduced within a practically acceptable range. If this condition is not met, the initial capacity will be significantly reduced.
[0018]
  Examples of the lithium compound used in the present invention include lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium nitrate, and lithium peroxide. Examples of manganese compounds include manganese oxide, manganese hydroxide, manganese chloride, manganese carbonate, manganese nitrate, manganese sulfate, and manganese acetate. Any material can be suitably used.
  Further, the metal element M compound is dissolved in finely pulverized powder or a solvent that sufficiently promotes solid phase reaction with manganese compounds such as oxide, hydroxide, chloride, carbonate, nitrate, sulfate, acetate, etc. It can be used as long as it can be uniformly dispersed, adhered and reacted with the manganese compound. Above all, the nitrate and acetate of the metal element M can be dissolved in a solvent (for example, water) and can be easily added to and dispersed in the manganese compound.
[0019]
  And there are the following two methods as a method for obtaining a lithium manganese composite oxide using a compound of these metal elements M.
  (1) When the metal element M compound is M nitrate or acetate, when it is added to the manganese compound, the M nitrate or acetate is heated and melted or dissolved in a solvent. Put manganese compound into, Heat and stirTo manganese compoundsThe M nitrate or acetateImpregnated, uniformly dispersed and addedPowderIs mixed with a lithium compound and heat-treated to obtain a lithium manganese composite oxide that is compositionally uniform and does not impair the powder characteristics of the manganese compound raw material.
[0020]
  (2) When the metal element M compound is a hydroxide of M, the M nitrate is dissolved in a solvent when added to the manganese compound.In the salt solution of the obtained metal element MPut manganese compound into manganese compoundSalt of metal element MImpregnate,To the obtained M salt-impregnated manganese compound solutionAlkaline solutionThe salt of metal element M andNeutralization reactionA manganese compound in which a hydroxide of metal element M obtained is dispersed and impregnated,By mixing and heat-treating with a lithium compound, a lithium manganese composite oxide can be obtained which is compositionally uniform and does not impair the powder characteristics of the manganese compound raw material.
[0021]
  Next, when the mixture of the manganese compound and the lithium compound is heat-treated, the temperature is set to 600 ° C. or higher and lower than 950 ° C., so that the metal element M can be completely removed without causing a heterogeneous phase such as a compound of the added metal element M. It can be dissolved and high crystal structure completeness can be realized. Preferably, a higher initial capacity can be realized by setting the heat treatment temperature to 700 ° C. or higher and 850 ° C. or lower.
  When the heat treatment temperature is less than 600 ° C., the crystallinity is deteriorated due to insufficient reaction. On the other hand, when the heat treatment temperature is 950 ° C. or more, the crystal structure undergoes a structural phase transition from cubic to tetragonal, which is not preferable. The heat treatment is preferably carried out for 4 hours or longer. If the heat treatment is less than 4 hours, the reaction becomes insufficient, leading to a decrease in crystallinity and appearance of a different phase.
  When a part of manganese according to the present invention is replaced with chromium, nickel, cobalt, aluminum, magnesium, iron, etc., and a positive electrode active material made of lithium manganese composite oxide having a secondary or spherical spherical shape is used, By replacing the metal element, it is possible to assemble a secondary battery having a high initial capacity by improving formability and packing density while maintaining high cycle characteristics.
[0022]
【Example】
  Examples of the present invention will be described in detail below together with comparative examples.
  [Example 1]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and chromium nitrate nonahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was replaced with chromium. Spherical manganese dioxide and chromium nitrate nonahydrate with a molar ratio of manganese to chromium of (1) 1.67: 0.33, (2) 1.83: 0.17, (3) 1.89: 0 .11, (4) 1.94: 0.06, each was weighed, and then chromium nitrate nonahydrate was dissolved in pure water in such an amount that chromium nitrate nonahydrate was completely dissolved.
  Thereafter, only spherical manganese dioxide was put into the solution and stirred while heating to volatilize water, thereby preparing a dry powder. This dry powder and lithium hydroxide monohydrate are weighed so that the molar ratio of lithium to manganese + chromium is 1: 2, and mixed sufficiently with sufficient strength to maintain the shape of spherical secondary particles. did.
  This mixed powder was calcined at 475 ° C. for 2 hours in an oxygen stream, then calcined at 800 ° C. for 20 hours, and cooled to room temperature.
[0023]
  When the obtained fired product was analyzed by powder X-ray diffraction using Cu Kα rays, only a desired positive electrode active material having a spinel structure could be confirmed in a single phase. Moreover, when the lattice constant was obtained from the Rietveld analysis of the powder X-ray diffraction pattern, the lattice constant decreased linearly as the amount of chromium added to the samples (1) to (4) increased. It was confirmed that solid solution of chromium was confirmed.
  And the tap density of the obtained positive electrode active material was measured, and it shows in following Table 1 with the above-mentioned lattice constant.
  Moreover, the battery was produced as follows using the obtained positive electrode active material, and the battery characteristic was measured by charge / discharge capacity. 90% by weight of the active material powder was mixed with 5% by weight of acetylene black and 5% by weight of PVDF (polyvinylidene fluoride), and NMP (n-methylpyrrolidone) was added to form a paste. The active material weight after drying the aluminum foil of 20 μm thickness is 0.05 g / cm²Then, it was vacuum-dried at 120 ° C. and punched out into a 1 cmφ disk shape to obtain a positive electrode.
[0024]
  Then, as shown in FIG. 1, the positive electrode 1 and the negative electrode 3 were made of lithium metal, and the electrolyte was 1M LiClO.₄Using a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in an equal amount as a supporting salt, the electrolyte solution is infiltrated into the separator 2 made of polyethylene, and a glove in an Ar atmosphere in which the dew point is controlled at −80 ° C. A 2032 type coin battery was assembled in the box.
  In FIG. 1, 4 is a gasket, 5 is a positive electrode can, and 6 is a negative electrode can.
  The assembled coin battery is left for about 24 hours after assembly, and after the open circuit voltage (OCV) is stabilized, the current density with respect to the positive electrode is 0.5 mA / cm.²The battery characteristics were evaluated by conducting a charge / discharge test at a cut-off voltage of 4.3 to 3.0V.
  Table 2 below shows the obtained discharge capacity (initial capacity) of the first cycle, the discharge capacity of the 50th cycle, and the ratio of the discharge capacity of the 50th cycle to the initial capacity (capacity maintenance ratio).
[0025]
  [Example 2]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, nickel nitrate hexahydrate were prepared to synthesize positive electrode active material in which a part of manganese was replaced by nickel, and spherical manganese dioxide and nickel nitrate were prepared. The hexahydrate has a molar ratio of manganese to nickel of (1) 1.83: 0.17, (2) 1.89: 0.11, (3) 1.94: 0.06, (4) 1 .97: A positive electrode active material was synthesized by the same procedure as in Example 1 except that each was weighed to 0.03, and a lithium coin secondary battery was assembled. The density was measured, and the battery characteristics were evaluated in the same manner as in Example 1. The results are also shown in Tables 1 and 2 below.
[0026]
  [Example 3]
  Except that a commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and cobalt nitrate hexahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was substituted with cobalt, the same as in Example 1 The positive electrode active material was synthesized by a simple procedure, a lithium coin secondary battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 and the results were The results are shown in Table 1 and Table 2 below.
[0027]
  [Example 4]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and aluminum nitrate hexahydrate were prepared to synthesize positive electrode active material in which a part of manganese was replaced with aluminum, and spherical manganese dioxide and aluminum nitrate were prepared. Hexahydrate was the same as Example 1 except that the molar ratio of manganese to aluminum was (1) 1.83: 0.17 and (2) 1.89: 0.11, respectively. The positive electrode active material was synthesized by the procedure, a lithium coin secondary battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, the battery characteristics were evaluated in the same manner as in Example 1, and the results were as follows. Table 1 and Table 2 are shown together.
[0028]
  [Example 5]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and magnesium nitrate hexahydrate were prepared to synthesize positive electrode active materials in which a part of manganese was replaced with magnesium, and spherical manganese dioxide and magnesium nitrate were prepared. Hexahydrate was the same as Example 1 except that the molar ratio of manganese to magnesium was (1) 1.83: 0.17 and (2) 1.89: 0.11, respectively. The positive electrode active material was synthesized by the procedure, a lithium coin secondary battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, the battery characteristics were evaluated in the same manner as in Example 1, and the results were as follows. Table 1 and Table 2 are shown together.
[0029]
  [Example 6]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and iron nitrate hexahydrate were prepared to synthesize positive electrode active materials in which a part of manganese was replaced with iron, and spherical manganese dioxide and iron nitrate were prepared. Hexahydrate was the same as Example 1 except that the molar ratio of manganese to iron was 1.) 1.83: 0.17 and 2.) 1.89: 0.11, respectively. The positive electrode active material was synthesized by the procedure, a lithium coin secondary battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, the battery characteristics were evaluated in the same manner as in Example 1, and the results were as follows Table 1 and Table 2 are shown together.
[0030]
  [Example 7]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and chromium nitrate nonahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was replaced with chromium. Spherical manganese dioxide and chromium nitrate nonahydrate with a molar ratio of manganese to chromium of (1) 1.67: 0.33, (2) 1.83: 0.17, (3) 1.89: 0 After weighing each so as to be .11, chromium nitrate nonahydrate was dissolved in pure water in such an amount that chromium nitrate nonahydrate was completely dissolved. While only spherical manganese dioxide was put into the solution and stirred, an amount of sodium hydroxide solution required for neutralization was added dropwise to allow sufficient reaction. Thereafter, the supernatant was removed by filtration, washed, and then dried by heating to prepare a dry powder.
  The dry powder and lithium hydroxide monohydrate were weighed so that the molar ratio of lithium to manganese + chromium was 1: 2, and mixed sufficiently with sufficient strength to maintain the shape of spherical secondary particles. . This mixed powder was calcined at 475 ° C. for 2 hours in an oxygen stream, then calcined at 800 ° C. for 20 hours, and cooled in the furnace to room temperature.
  The lattice constant of the obtained fired product and the tap density of the positive electrode active material were measured in the same manner as in Example 1, and are also shown in Table 1 below.
[0031]
  Moreover, the battery was produced as follows using the obtained active material, and the battery characteristic was measured by the charge / discharge capacity. That is, 87% by weight of the active material powder was mixed with 5% by weight of acetylene black and 8% by weight of PVDF (polyvinylidene fluoride), and NMP (n-methylpyrrolidone) was added to form a paste. Using this paste, a positive electrode was prepared in the same procedure as in Example 1, and then a 2032 type coin battery as shown in FIG. 1 was assembled in the same manner as in Example 1.
  The battery characteristics of the coin battery thus assembled were evaluated in the same manner as in Example 1, and the obtained first cycle discharge capacity (initial capacity), 50th cycle discharge capacity, and 50 cycles relative to the initial capacity. The discharge capacity ratio (capacity maintenance ratio) of the eyes is also shown in Table 2 below.
[0032]
  [Example 8]
  Except that a commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and nickel nitrate hexahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was replaced with nickel, the same as in Example 7 The positive electrode active material was synthesized by a simple procedure, a lithium coin battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 and the results are described below. It shows together in Table 1 and Table 2.
[0033]
  [Example 9]
  Except that a commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and cobalt nitrate hexahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was substituted with cobalt, the same as in Example 7 The positive electrode active material was synthesized by a simple procedure, a lithium coin battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 and the results are described below. It shows together in Table 1 and Table 2.
[0034]
  [Example 10]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and aluminum nitrate hexahydrate were prepared to synthesize positive electrode active material in which a part of manganese was replaced with aluminum, and spherical manganese dioxide and aluminum nitrate were prepared. Hexahydrate was the same as Example 7 except that the molar ratio of manganese to aluminum was (1) 1.83: 0.17 and (2) 1.89: 0.11, respectively. The positive electrode active material was synthesized by the procedure, a lithium coin battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, the battery characteristics were evaluated in the same manner as in Example 1, and the results are shown in the table below. 1 and Table 2 are shown together.
[0035]
  [Example 11]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and magnesium nitrate hexahydrate were prepared to synthesize positive electrode active materials in which a part of manganese was replaced with magnesium, and spherical manganese dioxide and magnesium nitrate were prepared. Hexahydrate was the same as Example 7 except that the molar ratio of manganese to magnesium was (1) 1.83: 0.17 and (2) 1.89: 0.11, respectively. The cathode active material was synthesized by the procedure, a lithium coin battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1 and the results are shown in Table 1 below. And are shown together in Table 2.
[0036]
  [Example 12]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and iron nitrate hexahydrate were prepared in order to synthesize a positive electrode active material in which a part of manganese was replaced with iron, and spherical manganese dioxide and iron nitrate hexahydrate were prepared. The same procedure as in Example 7 except that the hydrate was weighed so that the molar ratio of manganese to iron was (1) 1.83: 0.17 and (2) 1.89: 0.11, respectively. Then, a positive electrode active material was synthesized, a lithium coin battery was assembled, the lattice constant and the tap density were measured in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1. And are shown together in Table 2.
[0037]
  [Comparative Example 1]
  In order to synthesize a pure positive electrode active material in which a part of manganese is not replaced by an element, a commercially available lithium hydroxide monohydrate, spherical manganese dioxide is used so that the molar ratio of lithium to manganese is 1: 2. Except for weighing, a positive electrode active material was synthesized in the same procedure as in Example 1, a lithium coin battery was assembled, the lattice constant and tap density were measured in the same way as in Example 1, and the battery in the same way as in Example 1. The characteristics are evaluated and the results are shown in Tables 1 and 2 below.
[0038]
  [Comparative Example 2]
  Commercially available lithium hydroxide monohydrate, spherical manganese dioxide, and chromium oxide were prepared in order to synthesize a positive electrode active material in which a part of manganese was replaced with chromium. Lithium hydroxide monohydrate, spherical manganese dioxide and chromium oxide, and the molar ratio of lithium, manganese and chromium are (1) 1: 1.67: 0.33, (2) 1: 1.83: 0. 17, (3) 1: 1.89: 0.11 and then weighed sufficiently with a ball mill for 15 hours using ethanol as a medium and wet mixed. The obtained slurry-like mixture was dried in the air at 85 ° C. for 3 hours to prepare a mixed dry powder.
  The mixed dry powder was calcined at 475 ° C. for 2 hours in an oxygen stream, then calcined at 800 ° C. for 20 hours, and cooled to room temperature. The lattice constant and tap density of the obtained calcined product were determined in Example 1. The battery characteristics of the battery assembled in the same manner as in Example 1 were evaluated in the same manner as in Example 1, and the results obtained are shown in Tables 1 and 2 below.
[0039]
[Table 1]

[0040]
[Table 2]

[0041]
  As can be seen from Table 1 and Table 2, the batteries of Examples 1 to 12 were higher than 80% while maintaining a high tap density as compared with the battery of Comparative Example 1 purely synthesized with manganese alone. The capacity maintenance rate was shown. In addition, compared with Comparative Example 2 in which manganese, a lithium compound, and a compound of a metal element are sufficiently pulverized and mixed, each of them achieves a high tap density while maintaining a high capacity retention rate of 80% or more, and fillability Had improved.
[0042]
【The invention's effect】
  As described above, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present inventionThe positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the production method ofBy using it as a positive electrode active material for a non-aqueous secondary battery, it is possible to improve the moldability and packing density as a positive electrode while maintaining high cycle characteristics, and it has a large initial capacity per unit volume. The secondary battery can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic longitudinal sectional view of a coin battery using a positive electrode active material.
[Explanation of symbols]
  1 Positive electrode
  2 Separator
  3 Negative electrode
  4 Gasket
  5 Positive electrode can
  6 Negative electrode can

Claims

Li ₁ + _{x Mn} (wherein, M represents Cr, Ni, Co, Al, at least one metal element selected from the group consisting of Mg and _{_{Fe) 2-y M y O}} 4 lithium-manganese composite oxide represented by A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising: a compound of at least one metal element M selected from the group consisting of Cr, Ni, Co, Al, Mg, and Fe; Added in advance to the manganese compound in which the shape of the secondary particles is spherical or elliptical so that the molar ratio of the metal element M is 2-y: y (where y is 0 <y ≦ 0.33) The step of mixing, the step of mixing the manganese compound to which the compound of the metal element M obtained in the step is added and the lithium compound so that 0 ≦ x ≦ 0.10, and then heat-treating the mixture Process, The positive electrode active method for producing a material for a non-aqueous electrolyte secondary battery according to.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that a compound of the metal element M with nitrates or acetates of M.

The compound of the metal element M is M nitrate or acetate, and the M nitrate or acetate is heated and melted or dissolved in a solvent. A manganese compound is added to the obtained solution, and the mixture is heated and stirred. The non-aqueous electrolyte secondary according to claim 2 , further comprising a step of obtaining a powder obtained by impregnating the manganese compound with the nitrate or acetate of M, and a step of mixing the obtained powder with a lithium compound. A method for producing a positive electrode active material for a battery.

The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, characterized in that a compound of the metal element M and a hydroxide of M.

A step of dissolving the nitrate of the metal element M in a solvent, a step of introducing a manganese compound into the obtained salt solution of the metal element M and impregnating the manganese compound with a salt of the metal element M, and then the obtained M salt-impregnated manganese A step of adding an alkali solution to the compound solution and neutralizing with a salt of the metal element M to form a hydroxide of M, a manganese compound in which the obtained hydroxide of the metal element M is dispersed and impregnated, and a lithium compound 5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, further comprising a step of mixing

6. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the heat treatment temperature of the mixture is 600 ° C. or higher and lower than 950 ° C. for 4 hours or more.