JP4406744B2

JP4406744B2 - Cathode active material for non-aqueous secondary battery, method for producing the same, and non-aqueous secondary battery using the same

Info

Publication number: JP4406744B2
Application number: JP2000339879A
Authority: JP
Inventors: 義和尾本; 英世小山内; 正行仁科
Original assignee: Dowa Electronics Materials Co Ltd
Current assignee: Dowa Electronics Materials Co Ltd
Priority date: 2000-11-08
Filing date: 2000-11-08
Publication date: 2010-02-03
Anticipated expiration: 2020-11-08
Also published as: JP2002151071A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水系二次電池用の正極活物質とその製造方法および該正極活物質を用いた非水系二次電池に関する。
【０００２】
【従来の技術】
近年、エレクトロニクス機器の小型高性能化とコードレス化が進み、これら携帯機器用の駆動電源として二次電池に関心が集まっている。特にリチウムイオン二次電池に代表される非水系二次電池は、高電圧・高エネルギー密度を有する高性能な電池として急速にその市場を拡大している。またこのような携帯機器用途だけでなく、世界的な地球環境の保全意識の高まりとともに、電気自動車用・ロードレベリング用として、大型リチウムイオン電池の開発も加速されている。このようなリチウム二次電池はエネルギー密度が高く、非水溶液を電解液として用いているため安全性には特に配慮が必要であり、リチウム二次電池安全性評価基準ガイドライン（ＳＢＡＧ１１０１）、ＵＬ規格（ＵＬ１６４２、ＵＬ２０５４）等に安全性試験項目と基準が示されている。
【０００３】
電池の安全性を確保するためには、正極、負極、セパレータ、電解液を含めた電池全体での取り組みが必要とされ、電池設計上からの種々の対策がこれまで提案されている。
【０００４】
例えば、特開平１０−１１６６１９には、内部短絡時のジュール熱の発生を抑制するため、負極活物質として体積抵抗率が５×１０^-3Ω・ｃｍ以下である黒鉛を使用することが開示されている。また、特開平１０−１９９５７４には、導電性基体表面に、導電性基体よりも高い抵抗値を有する抵抗体層を形成することにより、内部短絡時の大電流放電を抑制することが開示されている。さらに、特開平１０−１１６６３３においては、正極に電気的に接続した金属部分と、負極に電気的に接続した金属部分を、セパレータを介して対向させ、前記金属部分のいずれか一方に導電性粉末を塗布することにより、電池の変形による内部短絡時に、金属部分間に短絡電流を導通させて発熱を抑制することが開示されている。
【０００５】
このような安全性試験項目の中でも特に重要なものは内部短絡試験（釘差し試験・圧壊試験）であるが、内部短絡の際にはＰＴＣ素子の作動やセパレータ溶融によるシャットダウンといった保護回路が機能せず、電池単体での安全性の確保、特に正極活物質の熱安定性の向上が重要である。内部短絡の場合には短絡電流による急激な局所加熱が生じ、結晶格子からリチウムがデインターカレートされて熱的に不安定な状態にある正極活物質が直接分解して活性酸素を放出し、周囲の有機電解液を燃焼させることが安全性を損なう原因とされている。
【０００６】
非水系二次電池に用いられる正極活物質としては、リチウムイオンを可逆的に挿入脱着することのできる化合物、例えばＬｉＣｏＯ₂やＬｉＮｉＯ₂などリチウムと遷移金属を主体とする複合酸化物（以下リチウム複合酸化物と記す）が代表的である。
【０００７】
このようなリチウム複合酸化物のうち、すでに実用化されているリチウム二次電池用正極活物質としてはＬｉＣｏＯ₂があるが、ＬｉＣｏＯ₂はエネルギー密度の点から性能向上の余地がなく、また、資源的に希少で高価なコバルトを用いていることから高価な材料である。そのため代替材料として、小型電池用途には高エネルギー密度を得ることが可能なＬｉＮｉＯ₂が、また大型電池用途には低容量ではあるが安価で資源的に豊富なマンガンを用いたＬｉＭｎ₂Ｏ₄等が精力的に開発されている。
【０００８】
このような正極活物質の熱安定性を改良する従来技術として、結晶格子の遷移金属サイトを酸素との結合力の高い異種元素で置換する試みが提案されている。例えば、J. Electron. Soc.、Vo1. 142、 No. 12、 December 1995、 p. 4033〜では、ＬｉＮｉＯ₂の結晶格子内のＮｉの２５％をＡｌで置換することにより、熱安定性が改善されることが報告されている。また、平成８年第３７回電池討論会で、ＮＴＴ入出力システム研究所の荒井らは、結晶格子内のＮｉの１０％をＭｎ・Ｖ・Ｔｉで置換することにより熱安定性が改善されることを報告している。しかしながらこのような異種元素置換による熱安定性の改良は、活物質としての電気化学的特性の犠牲を伴う方法であった。
【０００９】
また、正極活物質の粉体特性を規定することにより安全性の改良を図る試みも数多く提案されている。例えば、特開平１０−２５５８４３では、正極活物質として一次粒子の平均粒子径が１〜５ミクロンの複合金属活物質を用いることにより、反応表面積が減少して熱安定性が向上し、内部短絡時の電池の安全性が改良されることが開示されている。しかしながら、このような手段によっても安全性の改良は不十分であり、セパレータの突刺強度範囲を規定するという電池設計上の対策が同時に必要であるとも述べられている。
【００１０】
【発明が解決しようとする課題】
非水系二次電池の高性能化や大型電池の開発の進展に伴い、正極活物質の熱安定性、特に内部短絡時の安全性の改良が望まれている。したがって本発明の目的は、高容量でかつ内部短絡時における熱安定性が改良された正極活物質、およびそれを用いた高性能な非水系二次電池を提供することにある。
【００１１】
【課題を解決するための手段】
本発明者らは上記課題、すなわち内部短絡時における電池の安全性を向上させるために、従来提案されてきた層状結晶格子のＮｉサイトを異種元素で置換する方法や、粒度分布・比表面積という粉体物性の規定による改良以外に、安全性を向上させる手段を検討した。
充電状態の電池に内部短絡が生じた場合、短絡部に大電流が集中して流れるため、４００゜C以上の局所加熱が生じることが知られている。このような温度域は層状結晶構造を有する正極活物質、すなわちLiCoO₂やLiNiO₂、が充電状態で加熱された場合に酸素を放出して熱分解を開始する温度よりかなり高温度である。
また電池の内部短絡により破裂・発火が生じる場合は、内部短絡直後の数秒間の挙動で決まるとも言われている。従って、充電状態の正極活物質に要求される熱安定性は平衡論的な熱分解温度だけでなく速度論的な改良、すなわち急加熱された場合の熱分解速度の抑制（以下、急加熱安定性と表記）も重要と考えられる。
本発明者らは、ＬｉＮｉＯ₂系正極活物質の急加熱安定性の改良を鋭意検討した結果、ニオブ化合物を含有するＬｉＮｉＯ₂系正極活物質のＸ線回折における層状結晶構造の（００３）面の半値幅が特定の範囲を示し、該活物質が同時に特定の電気化学特性を示す場合において、急加熱安定性が著しく改良されることを発見し、本発明に到達した。
ＬｉＮｉＯ_２系の複合酸化物にニオブを含有させる公知の技術として、例えば特開平６−２８３１７４、特開平１１−４０１５３、特開平１０−３２１２２８等がある。特開平６−２８３１７４においては、ＬｉＮｉ_1-xＭ_ｘＯ_２（ただしＭはＣｕ，Ｍｎ，Ｎｂ，Ｍｏ，Ｗからなる群から選ばれる１種以上の元素）で示される複合酸化物を活物質として含むリチウム二次電池用正極であり、ニオブイオンでニッケルイオンの一部を置換することにより、充放電経過後の容量維持率を向上できることが開示されている。
また、特開平１１−４０１５３では、Ａ_ｗＰ_ｖＮｉ_ｘＭ_ｙＮ_ｚＯ_２（Ａはアルカリ金属から選ばれた少なくとも１種、ＰはＭｇ，Ｂ，Ｐ，Ｉｎから選ばれた少なくとも１種、ＭはＭｎ，Ｃｏ，Ａｌから選ばれた少なくとも１種、ＮはＳｉ，Ａｌ，Ｃａ，Ｃｕ，Ｓｎ，Ｍｏ，Ｎｂ，Ｙ，Ｂｉから選ばれた少なくとも１種）で示される複合酸化物を正極活物質とする電池が開示されている。ニオブの効果として、酸素放出能が低く、酸化物として安定に存在するので高温での安全性は改善できるが、過充電時の熱暴走反応は抑制できないと述べられている。
特開平１０−３２１２２８では、組成式：Ｌｉ_ｘＮｉ_1-yＭ_yＯ_Z（Ｍはニッケル以外の遷移金属、１４(IVＢ)族、１５(ＶＢ)族、１６(VIＢ)族、１７(VIIＢ)族から選ばれる１種以上の元素）である複合酸化物であって、その層構造中の遷移金属主体層におけるリチウム占有率が０．５％以上であるリチウム二次電池用正極活物質が開示されており、層構造中の遷移金属主体層（すなわちニッケルサイト）におけるリチウム占有率を０．５％以上とすることで高温環境下や内部短絡時の安全性が改良できるとされている。
これら公知の技術は、層状結晶構造中のニッケルサイトをニオブを含む異種元素で置換することを試みているが、熱安定性を改良するためには、ニッケルサイトを多量の異種元素で置換する必要があり、正極活物質としての電気化学的特性を著しく損なう結果となる。
本発明者らは、Ｘ線回折による層状結晶構造を有する化合物の（００３）面半値幅が特定範囲内であり、リチウムとニオブと酸素からなる少なくとも一種類以上の化合物を含有する組成物が、初回放電時に正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２Ｖから１．５Ｖの範囲において放電容量が特定の範囲内にある場合に、優れた急加熱安定性を示すことを発見し本発明に到達した。
【００１２】
すなわち本発明は、第１に、一般式：Ｌｉ_aＮｉ_1-x-y-zＣｏ_xＭ_yＮｂ_zＯ_b（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素、１≦a≦１．１、０．１≦x≦０．３、０≦y≦０．１、０．０１≦z≦０．０５、２≦b≦２．２）で示されるリチウムとニッケルとコバルトと元素Ｍとニオブと酸素からなる少なくとも一種類以上の化合物で構成される組成物からなり、初回放電時に正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２Ｖから１．５Ｖの範囲内でα［ｍＡｈ／ｇ］の放電容量を示し、そのＸ線回折における層状結晶構造の（００３）面の半値幅をβ［deg］としたとき、αおよびβがそれぞれ６０≦α≦１５０および０．１４≦β≦０．２０の条件を同時に満たすことを特徴とする非水系二次電池用正極活物質；第２に、前記αおよびβがそれぞれ８０≦α≦１５０および０．１５≦β≦０．２０である、前記第１に記載の非水系二次電池用正極活物質；第３に、一般式：Ｌｉ_aＮｉ_1-x-yＣｏ_xＭ_yＯ_b（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素、１≦a≦１．１、０．１≦x≦０．３、０≦y≦０．１、２≦b≦２．２）で示されるリチウムとニッケルとコバルトと元素Ｍと酸素からなる少なくとも一種類以上の化合物と、リチウムとニオブと酸素からなる少なくとも一種類以上の化合物とで構成される組成物からなり、初回放電時に正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２Ｖから１．５Ｖの範囲内でα［ｍＡｈ／ｇ］の放電容量を示し、そのＸ線回折における層状結晶構造の（００３）面の半値幅をβ［deg］としたとき、αおよびβがそれぞれ８０≦α≦１５０および０．１５≦β≦０．２０の条件を同時に満たすことを特徴とする非水系二次電池用正極活物質；第４に、一般式：Ｌｉ_aＮｉ_1-x-y-zＣｏ_xＭ_yＮｂ_zＯ_b（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素、１≦a≦１．１、０．１≦x≦０．３、０≦y≦０．１、０．０１≦z≦０．０５、２≦b≦２．２）で示されるリチウムとニッケルとコバルトと元素Ｍとニオブと酸素からなる少なくとも二種類以上の化合物で構成される組成を有する粒子からなり、該粒子が略球形状であってその表面近傍または内部に上記組成よりもニオブ濃度の高い少なくとも一種類以上の化合物を含有する略球殻層を有することを特徴とする非水系二次電池用正極活物質；第５に、前記略球殻層に含有される化合物がリチウムとニオブと酸素からなる少なくとも一種類以上の化合物である、前記第４記載の非水系二次電池用正極活物質；第６に、前記の第１〜５のいずれかに記載の正極活物質を正極活物質として用いたことを特徴とする非水系二次電池；第７に、Ｎｂ化合物を含有するＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）の共沈水酸化物とＬｉの化合物との混合物を酸化性雰囲気で焼成することを特徴とする、前記の第１〜５のいずれかに記載の非水系二次電池用正極活物質の製造方法；第８に、Ｎｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）およびＮｂの共沈水酸化物とＬｉの化合物との混合物を酸化性雰囲気で焼成することを特徴とする、前記の第１〜５のいずれかに記載の非水系二次電池用正極活物質の製造方法；第９に、前記焼成を６８０℃〜７８０℃で行う前記の第７または８のいずれかに記載の非水系二次電池用正極活物質の製造方法、を提供する。
【００１３】
【発明の実施の形態】
本発明の非水系二次電池用正極活物質は、Ｌｉ、Ｎｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる１種以上の元素）、Ｎｂ、酸素を主成分とし、これらの元素からなる少なくとも一種類以上の化合物で構成される組成物において、そのＸ線回折における層状結晶構造の（００３）面の半値幅と電気化学的特性とが同時にある条件を満たしていることが必要である。
【００１４】
正極活物質の一般式：Ｌｉ_aＮｉ_1-x-y-zＣｏ_xＭ_yＮｂ_zＯ_bにおいて、Ｃｏは層状構造のニッケルサイトを置換し、充放電の繰り返しによる放電容量の低下を防止するため必須であり、０．１≦x≦０．３の範囲とする。０．１＞xでは放電容量維持の効果が不足し、またｘ＞０．３では置換率が高すぎて放電容量自体が低下する。
Ｎｂの含有量は０．０１≦z≦０．０５の範囲とする。ｚ＜０．０１では急加熱安定性の改善効果が不足し、z＞０．０５では急加熱安定性の改良効果が飽和する。また層状結晶構造中のニッケルサイトを置換して平衡論的な熱安定性を改良するために、元素Ｍ（但し、ＭはＭｎ，ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）を、y≦０．１の範囲で添加しても良い。
Ｌｉの含有量は１≦ａ≦１．１の範囲とする。ａ＜１では放電容量が不足し、ａ＞１．１では本発明とは異種のＬｉ化合物が生成されやはり放電容量が低下する。酸素の含有量は２≦ｂ≦２．２の範囲とする。ｂ＜２では放電容量が不足し、ｂ＞２．２では本発明とは異種の酸化物が生成されやはり放電容量が低下する。
Ｘ線回折による層状結晶構造の（００３）面の半値幅：β［deg］は、０．１４≦β≦０．２０の範囲内である必要があり、好ましくは０．１５≦β≦０．２０である。半値幅がこの範囲内である原因については未確認であるが、β＜０．１４では層状結晶構造の結晶粒子サイズが大きすぎるため、急加熱時における結晶の熱分解速度を抑制できず、またβ＞０．２０では逆に結晶粒子サイズが小さすぎて熱分解開始温度が低下するためと推定される。尚、（００３）面の半値幅はＸ線回折粉末法でのＫα2線除去後のピークサーチデータより算出する値である。
金属リチウムを負極として用いた場合に、正極活物質は２Ｖから１．５Ｖの範囲での放電容量：α［mAh/g］は、６０≦α≦１５０を示す必要があり、好ましくは８０≦α≦１５０の範囲である。α＜６０の場合は急加熱安定性の改良効果が不足する。またα＞１５０を示す正極活物質は作成出来なかった。
層状結晶構造のＬｉ−Ｎｉ−Ｏ組成物が、正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２．０Ｖから１．５Ｖの範囲において放電容量を示すことは、“Structure and electrochemistry of Li₁ _± _yNiO₂ and a new Li₂NiO₂ phase with the Ni(OH)₂ structure"、Solid State Ionics 44(1990)87-97,J.R.Dahn によって報告されており、yＬｉ＋ＬｉＮｉＯ_２→Ｌｉ_1+yＮｉＯ_２の反応により層状結晶構造中の三価のＮｉイオンが、二価に還元されることで放電容量を示すと考えられる。従ってニッケルサイトを異種元素で置換した場合は、このような層状結晶構造中のニッケルイオンの還元反応が抑制され、正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２．０から１．５Ｖの範囲での放電容量は低下する。
以上の要件を具備する本発明の正極活物質が、優れた放電容量と急加熱安定性をしめすのは、組成物中に層状結晶構造の化合物以外に、ＬｉとＮｂと酸素の化合物（以下にLi-Nb-O化合物と略記する）が存在し、且つおそらくは層状結晶構造の化合物の結晶粒界に、均一にLi-Nb-O化合物が形成されたことよる効果と考えられ、充電状態の正極活物質が３００゜C以上に急加熱されて、層状結晶構造が熱分解されても、熱的に安定なLi-Nb-O化合物が防火壁として作用して、熱分解速度を低下させるものと推定される。
Li-Nb-O化合物は“高密度リチウム二次電池”、（株）テクノシステム、Ｐ．１６７−Ｐ．１７１に示されるように正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２．０Ｖから１．５Ｖの範囲で可逆的な充放電能を有するので、Li-Nb-O化合物が粒界層に存在しても、層状結晶構造自体の電気化学反応を阻害しない。参考として、ＬｉＮｂＯ_３の充放電曲線を図２に示す。以上のことから、高容量、高熱安定性の正極材料の結晶構造と電気化学的特性との間に前記の関係が成立したと思われる。
【００１５】
以上のことから、本発明の非水系二次電池用正極活物質は、公知の活物質の製造方法では得られない。以下に、本発明の非水系二次電池用正極活物質の製造方法を説明する。
本発明の非水系二次電池用正極活物質の製造方法は以下の通りである。Ｎｂ化合物を含有するＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）の共沈水酸化物とＬｉの化合物との混合物、あるいはＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）およびＮｂの共沈水酸化物とＬｉの化合物との混合物を酸化性雰囲気で好ましくは６８０℃〜７８０℃で５〜２０時間焼成する。また、好ましくは、Ｎｂ化合物を含有するＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）の共沈水酸化物とＬｉの化合物との混合物、あるいはＮｉ、Ｃｏ、Ｍ（但し、はＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）およびＮｂの共沈水酸化物とＬｉの化合物との混合物を酸化性雰囲気で好ましくは５００〜８００℃で５〜２０時間仮焼し、次に仮焼した焼成物を解粒分散、造粒し、仮焼温度より３０℃以上高くかつ９００℃以下の温度で１〜６時間本焼成する。
ここで、焼成を２回行う方法が好ましいのは、仮焼後に分散、造粒を行うことによって結晶をより均一化することができ、さらに造粒によって充填性を向上し細孔を制御できるからであり、その結果活物質としての電気化学的特性、粉体特性、安全性等を容易により高いレベルに改良できるからである。
さらに、Ｎｂ化合物をＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）の共沈水酸化物に含有させるのは、その後の焼成工程時にＮｂが反応・拡散するため、より均一に反応・分布させるためにはこのタイミングがもっとも適しており、その結果、Ｎｂ添加による急加熱時の安定性向上を最大限にすることができるためである。この比較はあとの実施例とともに示している。また、NbはＮｉ、Ｃｏ、Ｍ（但し、ＭはＭｎ、ＦｅおよびＡｌよりなる群から選ばれる一種以上の元素）との共沈水酸化物として調製し、添加しても効果が高い。次に焼成雰囲気を酸化性雰囲気にしているのは母材のLiNiO₂を主体とした層状化合物を安定して生成させるためと、Nbを焼成時に効率よく反応・拡散させるためである。
得られた正極活物質の電気化学特性と熱安定性は以下の方法で評価した。
【００１６】
［正極活物質の電気化学特性の評価法］
正極板の作製には、正極活物質、アセチレンブラックおよびＰＴＦＥ（ポリテトラフルオロエチレン）を使用し、これらを８７：８：５の重量比で乳鉢混合した後、ロール圧延機で混練し、シート状に成形した。負極には金属Ｌｉを、セパレータにはポリプロピレンフィルムを、電解液には炭酸エチレンと炭酸ジエチレンを体積比で１：１に混合した溶媒に電解質としてＬｉＰＦ₆を１ｍｏｌ／Ｌの濃度に溶解したものをそれぞれ用いて、図３に示すような試験電池を作製した。この試験電池では、正極５と負極４はセパレータ６を介在してステンレスケース１に収納され、封口板３とガスケット２が施されている。充放電試験では、電流密度が０．５３ｍＡ／ｃｍ²で４．２Ｖまで定電流充電した後、電流密度が０．１３ｍＡ／ｃｍ²になるまで定電圧充電を行った。その後、０．５３ｍＡ／ｃｍ²で１．５Ｖまで定電流放電を行い、活物質の重量当たりの放電容量を求めた。上記の条件で測定した４．２Ｖから２．７Ｖまでの放電容量を放電容量（Ａ）とし、２Ｖから１．５Ｖまでの間の放電容量を放電容量（Ｂ）とした。
【００１７】
［正極活物質の熱安定性の評価法］
Ａｒ雰囲気下で４．２Ｖ充電後の試験電池から正極板を取りだし、電解液を含有した状態で約５ｍｇのサンプルを各温度（２５０〜３７５℃の範囲を２５℃間隔で設定）で一定に保ったホットプレート上に各温度につき３個載せ、３サンプルとも発火しない最も高い温度を急加熱時の最大安定温度とし、これを以て熱安定性の尺度とした。
【００１８】
以下に比較例と対比しながら本発明の実施例を詳細に説明する。
【比較例１】
硝酸コバルト溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／Ｃｏ＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ^２で加圧して成形体を得た。この成形体を酸素気流中において８５０℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００１９】
【比較例２】
ニッケル、コバルトの各硝酸塩をそれぞれＮｉ：Ｃｏ＝８０：２０のモル比で混合した溶液を、液温を８０℃に調節した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この共沈水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ^２で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２０】
【比較例３】
ニッケル、コバルト、アルミニウムの各硝酸塩をそれぞれＮｉ：Ｃｏ：Ａｌ＝７１：２０：９のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２１】
【比較例４】
ニッケル、コバルト、アルミニウムの各硝酸塩をそれぞれＮｉ：Ｃｏ：Ａｌ＝６８：２０：１２のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２２】
【比較例５】
ニッケル、コバルトの各硝酸塩とＮｂ₂Ｏ₅をそれぞれＮｉ：Ｃｏ：Ｎｂ＝８５：１３：２のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において６５０℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２３】
【実施例１】
比較例５で得た成形体と同じ成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２４】
【実施例２】
比較例５で得た成形体と同じ成形体を酸素気流中において７５０℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２５】
【比較例６】
比較例５で得た成形体と同じ成形体を酸素気流中において８００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２６】
【比較例７】
ニッケル、コバルトの各硝酸塩をそれぞれＮｉ：Ｃｏ＝８７：１３のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物に、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムを、またＮｂ／（Ｎｉ＋Ｃｏ）＝０．０２となるようにＮｂ₂Ｏ₅をそれぞれ混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２７】
【比較例８】
ニッケル、コバルトの各硝酸塩をそれぞれＮｉ：Ｃｏ＝８７：１３のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物に、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３、またＮｂ／（Ｎｉ＋Ｃｏ）＝０．０２となるようにＬｉＮｂＯ_３とＬｉ塩を混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７５０℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。この粉末を活物質として用い、電気化学特性と熱安定性を求めた。
【００２８】
【比較例９】
ニッケル、コバルトの各硝酸塩をそれぞれＮｉ：Ｃｏ＝８７：１３のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるようにＬｉ塩と混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。
この焼成物とＮｂ／（Ｎｉ＋Ｃｏ）＝０．０２の量に相当するＮｂ_２Ｏ_５を、固形分濃度が５０重量％となるように、１重量％濃度の硝酸リチウム溶液中に懸濁し、湿式ビーズミルで湿式粉砕して分散スラリーを得た。このスラリーを噴霧乾燥して球状に造粒した。これを酸素気流中８００℃で２時間焼成後、球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００２９】
【比較例１０】
ニッケル、コバルトの各硝酸塩とＮｂ_２Ｏ_５をＮｉ：Ｃｏ：Ｎｂ＝８６．５：１３：０．５のモル比で混合した溶液を、液温を８０℃に制御した反応容器内に連続的に投入し、４８重量％濃度の水酸化ナトリウム溶液で中和して、ｐＨを１０．０±０．２に制御することにより共沈水酸化物の沈殿を得た。この水酸化物を、Ｌｉ／（Ｎｉ＋Ｃｏ）＝１．０３となるように水酸化リチウムと混合し、１ｔ／ｃｍ²で加圧して成形体を得た。この成形体を酸素気流中において７００℃で１０時間焼成し、臼式解碎機で解粒して層状結晶化合物の粉末を得た。
この粉末を固形分濃度が５０重量％となるように、水に懸濁し、湿式ビーズミルで湿式粉砕して分散スラリーを得た。このスラリーを噴霧乾燥して球状に造粒した。これを酸素気流中８００℃で２時間焼成後、球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００３０】
【実施例３】
ニッケル、コバルトの各硝酸塩とＮｂ_２Ｏ_５をモル比でＮｉ：Ｃｏ：Ｎｂ＝８６：１３：１とした以外は比較例１０と同じ方法で球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００３１】
【実施例４】
ニッケル、コバルトの各硝酸塩とＮｂ_２Ｏ_５をモル比でＮｉ：Ｃｏ：Ｎｂ＝８４：１３：３とした以外は比較例１０と同じ方法で球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００３２】
【実施例５】
ニッケル、コバルトの各硝酸塩とＮｂ_２Ｏ_５をモル比でＮｉ：Ｃｏ：Ｎｂ＝８３：１３：４とした以外は比較例１０と同じ方法で球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００３３】
【実施例６】
ニッケル、コバルトの硝酸塩とＮｂ_２Ｏ_５をモル比でＮｉ：Ｃｏ：Ｎｂ＝８２：１３：５とした以外は比較例１０と同じ方法で球状二次粒子を得た。これを活物質として用い、電気化学特性と熱安定性を求めた。
【００３４】
実施例および比較例の結果を表１および図４に示す。
【表１】

【００３５】
実施例５と比較例９の非水系二次電池用正極活物質について初期サイクルの放電曲線および２サイクル目の充電曲線を図１に示す。図１においては実施例５をプロットしたものを実線で示し、比較例９をプロットしたものを破線で示す。また、図２からも分かるとおり、Ｌｉ−Ｎｂ複合酸化物は、２．７Ｖから４．２Ｖまでの間に充放電容量を持っている。図１において実施例５が比較例９に比べて初期サイクルの放電末期（３．５Ｖから２．７Ｖ付近）の放電曲線の傾きが緩くなっている。また、２サイクル目の充電においても、３．５Ｖ付近の充電カーブの変曲点にも比較例９と比べてヒステリシスが認められており、実施例５の非水系二次電池用正極活物質は緩やかに電位が上昇している。このような電気化学的特性の差異はＬｉ−Ｎｂ複合酸化物の存在によるところが大きいと思われる。
実施例５と比較例９を正極活性物質として用いたモデルセルを作成し、交流インピーダンス測定を行った。複素インピーダンスプロット（Cole-Cole Plot）において連続する２つの半円が実施例５において認められ、等価回路解析によれば異なる電気化学的性質を有する二種の電極が直列回路を形成していることが確認された。すなわち実施例５においてはＬｉＮｉＯ_２系化合物の表面もしくは粒界層に異なる電気化学的性質を有する化合物層が形成されていると判断される。
この異種化合物の存在を確認するために、Ａｒスパッタリングを行いながらＥＳＣＡ分析を行ったが、深さ方向での成分元素の偏析、および実施例５と比較例９の試料間の差異は認められなかった。次にさらに微細な構造解析のため、ＦＩＢ（Focused Ion Beam）システムで厚み約０．３マイクロメートルの薄片試料を作成し、ＦＥ（Field Emission）―ＴＥＭによる観察とＥＤＸおよびＥＥＬＳ測定を行った。本方法によればナノメートルオーダーでの解析が可能である。その結果、実施例５および比較例９は粒子サイズが数十〜数百ｎｍの微粒子の集合体であった。さらに線方向元素分布を測定したところ、実施例５については粒子表面近傍もしくは粒界層に厚み１０〜３０ｎｍ程度の偏析層が認められた。比較例９においてはＮｂの偏析層は認められなかった。実施例５の測定図を図５に、比較例９の測定図を図６に示す。
この結果より交流インピーダンス測定で実施例５において認められたＬｉＮｉＯ_２系とは異種の電気化学的性質を有する化合物層は、Ｌｉ―Ｎｂ―Ｏ系化合物であると推定される。またＬｉ―Ｎｂ―Ｏ系化合物としては前述のＬｉＮｂＯ_３以外に例えばＬｉ_３ＮｂＯ_４、Ｌｉ_５Ｎｂ_２Ｏ_５等の化合物があるが、いずれの化合物も正極電位（ｖｓ．Ｌｉ／Ｌｉ＋）が２Ｖから１．５Ｖの範囲で放電容量を有している。またこれらＬｉ―Ｎｂ―Ｏ系化合物は高い熱安定性を有しており、通常の急加熱時の熱安定性評価条件においては全く発火しなかった。
【００３６】
【発明の効果】
以上説明したように、本発明によれば、高い熱安定性と大きな放電容量を有する正極活物質およびそれを用いた高性能で安全性の高い非水系二次電池が得られる。
【図面の簡単な説明】
【図１】本発明の実施例５と比較例９の充放電曲線を比較して示すグラフである。
【図２】ＬｉＮｂＯ_３の充放電曲線を示すグラフである。
【図３】本発明の実施例において使用した試験電池の構成を示す断面図である。
【図４】本発明の各実施例および比較例で測定された放電容量ＢとＸ線回折（００３）面半値幅との関係を示す散布図である。
【図５】本発明の実施例５のＦＥ―ＴＥＭ写真図およびＮｂ分布を示す図である。
【図６】比較例９のＦＥ―ＴＥＭ写真図およびＮｂ分布を示す図である。
【符号の説明】
１ステンレスケース
２ガスケット
３封口板
４負極
５正極
６セパレータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous secondary battery, a method for producing the same, and a non-aqueous secondary battery using the positive electrode active material.
[0002]
[Prior art]
In recent years, electronic devices have become smaller, higher performance, and cordless, and attention has been focused on secondary batteries as drive power sources for these portable devices. In particular, non-aqueous secondary batteries represented by lithium ion secondary batteries are rapidly expanding their market as high-performance batteries having high voltage and high energy density. In addition to such portable device applications, the development of large-sized lithium-ion batteries for electric vehicles and road leveling has been accelerated along with the growing awareness of global environmental conservation. Such a lithium secondary battery has a high energy density and uses a non-aqueous solution as an electrolytic solution, so special consideration is required for safety. Lithium secondary battery safety evaluation standard guidelines (SBA G1101), UL standard (UL1642, UL2054) etc. show safety test items and standards.
[0003]
In order to ensure the safety of the battery, it is necessary to work on the entire battery including the positive electrode, the negative electrode, the separator, and the electrolytic solution, and various countermeasures from the battery design have been proposed so far.
[0004]
For example, Japanese Patent Laid-Open No. 10-116619 discloses a volume resistivity of 5 × 10 5 as a negative electrode active material in order to suppress the generation of Joule heat during an internal short circuit.^-3It is disclosed that graphite having an Ω · cm or less is used. Japanese Patent Laid-Open No. 10-199574 discloses that a large current discharge at the time of an internal short circuit is suppressed by forming a resistor layer having a higher resistance value than the conductive substrate on the surface of the conductive substrate. Yes. Further, in Japanese Patent Laid-Open No. 10-116633, a metal part electrically connected to the positive electrode and a metal part electrically connected to the negative electrode are opposed to each other through a separator, and conductive powder is applied to one of the metal parts. It is disclosed that, when an internal short circuit due to deformation of the battery is applied, a short-circuit current is conducted between metal parts to suppress heat generation.
[0005]
Among these safety test items, the internal short circuit test (nailing test and crush test) is particularly important. However, when an internal short circuit occurs, a protection circuit such as the operation of the PTC element or shutdown due to melting of the separator must function. It is important to ensure the safety of the battery alone, and in particular to improve the thermal stability of the positive electrode active material. In the case of an internal short circuit, rapid local heating occurs due to a short circuit current, lithium is deintercalated from the crystal lattice, and the positive electrode active material in a thermally unstable state is directly decomposed to release active oxygen, Combustion of the surrounding organic electrolyte is regarded as a cause of loss of safety.
[0006]
As a positive electrode active material used for a non-aqueous secondary battery, a compound capable of reversibly inserting and desorbing lithium ions, for example, LiCoO₂And LiNiO₂A composite oxide mainly composed of lithium and a transition metal (hereinafter referred to as a lithium composite oxide) is representative.
[0007]
Among such lithium composite oxides, LiCoO is already used as a positive electrode active material for lithium secondary batteries.₂There is LiCoO₂Is an expensive material because it has no room for performance improvement in terms of energy density and uses rare and expensive cobalt in terms of resources. Therefore, as an alternative material, LiNiO capable of obtaining high energy density for small battery applications₂However, for large battery applications, LiMn is a low-capacity but inexpensive and resource-rich manganese.₂O_FourEtc. are energetically developed.
[0008]
As a conventional technique for improving the thermal stability of such a positive electrode active material, there has been proposed an attempt to replace a transition metal site of a crystal lattice with a different element having a high binding force with oxygen. For example, in J. Electron. Soc., Vo1. 142, No. 12, December 1995, p.₂It has been reported that the thermal stability is improved by substituting 25% of Ni in the crystal lattice with Al. In addition, at the 37th Battery Conference in 1996, Arai et al. Of NTT I / O System Laboratories improved thermal stability by replacing 10% of Ni in the crystal lattice with Mn, V, Ti. It is reported that. However, the improvement of the thermal stability by such substitution of different elements has been a method involving sacrifice of electrochemical characteristics as an active material.
[0009]
Many attempts have been made to improve safety by defining the powder characteristics of the positive electrode active material. For example, in JP-A-10-255843, by using a composite metal active material having an average primary particle size of 1 to 5 microns as the positive electrode active material, the reaction surface area is reduced and the thermal stability is improved. It is disclosed that the safety of the battery of the present invention is improved. However, it is also stated that the improvement of safety is not sufficient even by such means, and it is also necessary to take measures on the battery design to define the puncture strength range of the separator at the same time.
[0010]
[Problems to be solved by the invention]
As the performance of non-aqueous secondary batteries increases and the development of large batteries progresses, it is desired to improve the thermal stability of the positive electrode active material, particularly the safety during internal short circuits. Accordingly, an object of the present invention is to provide a positive electrode active material having a high capacity and improved thermal stability at the time of an internal short circuit, and a high-performance nonaqueous secondary battery using the same.
[0011]
[Means for Solving the Problems]
In order to improve the above-mentioned problem, that is, the safety of the battery at the time of an internal short circuit, the present inventors have proposed a method for replacing the Ni site of the layered crystal lattice, which has been conventionally proposed, with a different element, a particle size distribution and a specific surface area. In addition to improvements based on physical property regulations, we examined ways to improve safety.
It is known that when an internal short-circuit occurs in a charged battery, a large current flows in the short-circuited portion, causing local heating at 400 ° C. or higher. Such a temperature range is a positive electrode active material having a layered crystal structure, that is, LiCoO.₂Or LiNiO₂When heated in a charged state, the temperature is considerably higher than the temperature at which oxygen is released and thermal decomposition starts.
In addition, it is said that when a battery is ruptured or ignited due to an internal short circuit, it is determined by the behavior for a few seconds immediately after the internal short circuit. Therefore, the thermal stability required for the positive electrode active material in the charged state is not only the equilibrium thermal decomposition temperature but also the kinetic improvement, that is, the suppression of the thermal decomposition rate when rapidly heated (hereinafter, rapid heating stability). Gender and notation) are also considered important.
We have made LiNiO₂As a result of intensive investigations on improving the rapid heating stability of the cathode active material, LiNiO containing a niobium compound₂When the half-value width of the (003) plane of the layered crystal structure in the X-ray diffraction of the positive electrode active material shows a specific range and the active material simultaneously shows specific electrochemical characteristics, the rapid heating stability is remarkably improved. The present invention was reached.
LiNiO₂Examples of known techniques for incorporating niobium into a complex oxide include JP-A-6-283174, JP-A-11-40153, and JP-A-10-32228. In JP-A-6-283174, LiNi_1-xM_xO₂(Wherein M is one or more elements selected from the group consisting of Cu, Mn, Nb, Mo, and W), which is a positive electrode for a lithium secondary battery containing a composite oxide as an active material. Niobium ions are nickel ions. It is disclosed that the capacity retention rate after the lapse of charge and discharge can be improved by substituting a part of the above.
In JP-A-11-40153, A_wP_vNi_xM_yN_zO₂(A is at least one selected from alkali metals, P is at least one selected from Mg, B, P, and In, M is at least one selected from Mn, Co, and Al, and N is Si, Al , Ca, Cu, Sn, Mo, Nb, Y, and Bi) are disclosed as a positive electrode active material. The effect of niobium is described as being capable of improving safety at high temperatures because of its low oxygen releasing ability and stable presence as an oxide, but it cannot suppress thermal runaway reaction during overcharge.
In JP-A-10-32228, the composition formula: Li_xNi_1-yM_yO_Z(M is a transition metal other than nickel, one or more elements selected from 14 (IVB) group, 15 (VB) group, 16 (VIB) group, and 17 (VIIB) group), A positive electrode active material for a lithium secondary battery having a lithium occupancy of 0.5% or more in the transition metal main layer in the layer structure is disclosed, and lithium in the transition metal main layer (ie, nickel site) in the layer structure It is said that the safety at the time of high temperature environment or internal short circuit can be improved by setting the occupation ratio to 0.5% or more.
Although these known techniques attempt to replace nickel sites in the layered crystal structure with different elements including niobium, it is necessary to replace the nickel sites with a large amount of different elements in order to improve thermal stability. As a result, the electrochemical characteristics of the positive electrode active material are significantly impaired.
The inventors have a composition in which the (003) plane half-value width of a compound having a layered crystal structure by X-ray diffraction is within a specific range, and the composition contains at least one compound composed of lithium, niobium, and oxygen. It was discovered that excellent rapid heating stability was exhibited when the positive electrode potential (vs. Li / Li +) was within a specific range when the positive electrode potential (vs. Li / Li +) was in the range of 2 V to 1.5 V at the first discharge. .
[0012]
That is, the present invention firstly has the general formula: Li_aNi_1-xyzCo_xM_yNb_zO_b(Where M is one or more elements selected from the group consisting of Mn, Fe and Al, 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.05, 2 ≦ b ≦ 2.2), which is composed of at least one kind of compound composed of lithium, nickel, cobalt, element M, niobium and oxygen, and at the first discharge The positive electrode potential (vs. Li / Li +) shows a discharge capacity of α [mAh / g] within the range of 2 V to 1.5 V, and the half width of the (003) plane of the layered crystal structure in the X-ray diffraction is β [ deg], and α and β simultaneously satisfy the conditions of 60 ≦ α ≦ 150 and 0.14 ≦ β ≦ 0.20, respectively, the positive electrode active material for a non-aqueous secondary battery; The α and β are 80 ≦ α ≦ 150 and 0.15 ≦ β ≦ 0.20, respectively; First, the positive electrode active material for a non-aqueous secondary battery; Third, the general formula: Li_aNi_1-xyCo_xM_yO_b(Where M is one or more elements selected from the group consisting of Mn, Fe and Al, 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 2 ≦ b ≦ 2.2) composed of at least one compound composed of lithium, nickel, cobalt, element M, and oxygen and at least one compound composed of lithium, niobium, and oxygen. In the first discharge, the positive electrode potential (vs. Li / Li +) shows a discharge capacity of α [mAh / g] in the range of 2 V to 1.5 V, and the (003) plane half of the layered crystal structure in the X-ray diffraction A positive electrode active material for a non-aqueous secondary battery, wherein α and β simultaneously satisfy the conditions of 80 ≦ α ≦ 150 and 0.15 ≦ β ≦ 0.20, respectively, when the value range is β [deg]; Fourth, the general formula: Li_aNi_1-xyzCo_xM_yNb_zO_b(Where M is one or more elements selected from the group consisting of Mn, Fe and Al, 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0 ≦ y ≦ 0.1, 0.01 ≦ z ≦ 0.05, 2 ≦ b ≦ 2.2), comprising particles having a composition composed of at least two kinds of compounds consisting of lithium, nickel, cobalt, element M, niobium, and oxygen, A positive electrode active for a non-aqueous secondary battery, characterized in that the particles have a substantially spherical shape and have a substantially spherical shell layer containing at least one compound having a niobium concentration higher than the above composition in the vicinity or inside of the surface. Material: Fifth, The positive electrode active material for a non-aqueous secondary battery according to the fourth aspect, wherein the compound contained in the substantially spherical shell layer is at least one compound composed of lithium, niobium, and oxygen; And the positive electrode active material according to any one of the first to fifth aspects. A non-aqueous secondary battery characterized by being used as an active material; seventh, Ni, Co, M containing Nb compound (where M is one or more selected from the group consisting of Mn, Fe and Al) A mixture of a coprecipitation hydroxide of (element) and a compound of Li is fired in an oxidizing atmosphere, and the production of the positive electrode active material for a non-aqueous secondary battery according to any one of the first to fifth aspects Method: Eighth, a mixture of Ni, Co, M (where M is one or more elements selected from the group consisting of Mn, Fe and Al) and a coprecipitated hydroxide of Nb and a compound of Li is oxidized in an atmosphere. The method for producing a positive electrode active material for a non-aqueous secondary battery according to any one of 1 to 5 above, wherein the firing is performed at 680 ° C. to 780 ° C. The positive electrode active for a non-aqueous secondary battery according to any of 7th and 8th A method for producing a substance is provided.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The positive electrode active material for a non-aqueous secondary battery of the present invention is mainly composed of Li, Ni, Co, M (where M is one or more elements selected from the group consisting of Mn, Fe, and Al), Nb, and oxygen. In a composition composed of at least one kind of compound composed of these elements, the half-width of the (003) plane of the layered crystal structure in the X-ray diffraction and the electrochemical characteristics satisfy the same condition. It is necessary to be.
[0014]
General formula of positive electrode active material: Li_aNi_1-xyzCo_xM_yNb_zO_bIn this case, Co is indispensable for substituting the nickel site of the layered structure to prevent a decrease in discharge capacity due to repeated charge and discharge, and is in the range of 0.1 ≦ x ≦ 0.3. When 0.1> x, the effect of maintaining the discharge capacity is insufficient, and when x> 0.3, the replacement rate is too high and the discharge capacity itself is reduced.
The Nb content is in the range of 0.01 ≦ z ≦ 0.05. When z <0.01, the effect of improving the rapid heating stability is insufficient, and when z> 0.05, the effect of improving the rapid heating stability is saturated. In order to replace nickel sites in the layered crystal structure and improve the equilibrium thermal stability, the element M (where M is one or more elements selected from the group consisting of Mn, Fe and Al), You may add in the range of y <= 0.1.
The Li content is in the range of 1 ≦ a ≦ 1.1. When a <1, the discharge capacity is insufficient, and when a> 1.1, a Li compound different from the present invention is generated, and the discharge capacity is lowered. The oxygen content is in the range of 2 ≦ b ≦ 2.2. When b <2, the discharge capacity is insufficient, and when b> 2.2, an oxide different from that of the present invention is generated and the discharge capacity is lowered.
The half width of the (003) plane of the layered crystal structure by X-ray diffraction: β [deg] needs to be in the range of 0.14 ≦ β ≦ 0.20, preferably 0.15 ≦ β ≦ 0. 20. The reason why the half width is within this range has not been confirmed. However, when β <0.14, the crystal grain size of the layered crystal structure is too large, so the rate of thermal decomposition of crystals during rapid heating cannot be suppressed. On the other hand, if it is> 0.20, it is estimated that the crystal grain size is too small and the thermal decomposition starting temperature is lowered. The half width of the (003) plane is a value calculated from the peak search data after removing the Kα2 line by the X-ray diffraction powder method.
When metallic lithium is used as the negative electrode, the positive electrode active material must have a discharge capacity: α [mAh / g] in the range of 2 V to 1.5 V, preferably 60 ≦ α ≦ 150, preferably 80 ≦ α. ≦ 150. When α <60, the effect of improving the rapid heating stability is insufficient. Moreover, the positive electrode active material which shows (alpha)> 150 was not able to be created.
The Li—Ni—O composition having a layered crystal structure exhibits a discharge capacity in the range of 2.0 V to 1.5 V of the positive electrode potential (vs. Li / Li +).₁ _± _yNiO₂ and a new Li₂NiO₂ phase with the Ni (OH)₂ structure ", Solid State Ionics 44 (1990) 87-97, J.R.Dahn, yLi + LiNiO₂→ Li_{1 + y}NiO₂ It is considered that the trivalent Ni ions in the layered crystal structure are reduced to divalent by the above reaction to show the discharge capacity. Therefore, when the nickel site is substituted with a different element, the reduction reaction of nickel ions in such a layered crystal structure is suppressed, and the positive electrode potential (vs. Li / Li +) is in the range of 2.0 to 1.5V. The discharge capacity decreases.
The positive electrode active material of the present invention having the above requirements shows excellent discharge capacity and rapid heating stability in addition to a compound having a layered crystal structure in the composition (hereinafter referred to as a compound of Li, Nb and oxygen). Abbreviated as Li-Nb-O compound), and it is thought that this is probably due to the uniform formation of Li-Nb-O compound at the grain boundaries of the compound having a layered crystal structure. Even if the active material is rapidly heated to 300 ° C or higher and the layered crystal structure is thermally decomposed, the thermally stable Li-Nb-O compound acts as a fire barrier, reducing the rate of thermal decomposition. Presumed.
Li-Nb-O compounds are “high-density lithium secondary batteries”, Techno System, P.A. 167-P. 171 has a reversible charge / discharge capability when the positive electrode potential (vs. Li / Li +) is in the range of 2.0 V to 1.5 V, the Li—Nb—O compound is present in the grain boundary layer. Does not inhibit the electrochemical reaction of the layered crystal structure itself. For reference, LiNbO₃The charge / discharge curve is shown in FIG. From the above, it is considered that the above relationship was established between the crystal structure and electrochemical characteristics of the positive electrode material having a high capacity and high thermal stability.
[0015]
From the above, the positive electrode active material for a non-aqueous secondary battery of the present invention cannot be obtained by a known method for producing an active material. Below, the manufacturing method of the positive electrode active material for non-aqueous secondary batteries of this invention is demonstrated.
The manufacturing method of the positive electrode active material for non-aqueous secondary batteries of this invention is as follows. A mixture of a coprecipitated hydroxide of Ni, Co, and M (wherein M is one or more elements selected from the group consisting of Mn, Fe, and Al) and a compound of Li containing Nb compound, or Ni, Co, M (Wherein M is one or more elements selected from the group consisting of Mn, Fe and Al) and a mixture of a coprecipitated hydroxide of Nb and a compound of Li, preferably in a oxidizing atmosphere at 680 ° C. to 780 ° C. Bake for 20 hours. Preferably, a mixture of a coprecipitated hydroxide of Ni, Co, and M (wherein M is one or more elements selected from the group consisting of Mn, Fe, and Al) containing a Nb compound and a compound of Li, or A mixture of Ni, Co, M (wherein is one or more elements selected from the group consisting of Mn, Fe and Al) and Nb coprecipitated hydroxide and Li compound is preferably 500 to 800 ° C. in an oxidizing atmosphere. The calcined product is calcined for 5 to 20 hours and then calcined, granulated, and then calcined at a temperature of 30 ° C. or higher and 900 ° C. or lower from the calcining temperature for 1 to 6 hours.
Here, the method of performing the firing twice is preferable because the crystals can be made more uniform by performing dispersion and granulation after calcination, and further, the filling property can be improved and the pores can be controlled by granulation. As a result, the electrochemical characteristics, powder characteristics, safety and the like as the active material can be easily improved to a higher level.
Furthermore, the Nb compound is contained in the coprecipitated hydroxide of Ni, Co, M (where M is one or more elements selected from the group consisting of Mn, Fe and Al) because Nb reacts during the subsequent firing step. This is because this timing is most suitable for more uniform reaction and distribution because of diffusion, and as a result, the stability improvement during rapid heating due to the addition of Nb can be maximized. This comparison is shown along with later examples. Also, Nb is prepared as a coprecipitated hydroxide with Ni, Co, and M (where M is one or more elements selected from the group consisting of Mn, Fe, and Al), and even when added, the effect is high. Next, the firing atmosphere is the oxidizing atmosphere, which is the base material LiNiO₂This is to stably produce a layered compound mainly composed of Nb and to efficiently react and diffuse Nb during firing.
The electrochemical characteristics and thermal stability of the obtained positive electrode active material were evaluated by the following methods.
[0016]
[Method for evaluating electrochemical properties of positive electrode active material]
For the production of the positive electrode plate, a positive electrode active material, acetylene black and PTFE (polytetrafluoroethylene) were used. Molded into. Metal Li is used for the negative electrode, polypropylene film is used for the separator, and electrolyte is LiPF as an electrolyte in a solvent in which ethylene carbonate and diethylene carbonate are mixed at a volume ratio of 1: 1.₆A test battery as shown in FIG. 3 was prepared by using each of those dissolved in a concentration of 1 mol / L. In this test battery, a positive electrode 5 and a negative electrode 4 are accommodated in a stainless steel case 1 with a separator 6 interposed therebetween, and a sealing plate 3 and a gasket 2 are applied. In the charge / discharge test, the current density is 0.53 mA / cm.²After charging at a constant current of up to 4.2 V, the current density is 0.13 mA / cm.²Constant voltage charging was performed until Thereafter, 0.53 mA / cm²Then, constant current discharge was performed up to 1.5 V, and the discharge capacity per weight of the active material was determined. The discharge capacity from 4.2 V to 2.7 V measured under the above conditions was the discharge capacity (A), and the discharge capacity between 2 V and 1.5 V was the discharge capacity (B).
[0017]
[Method for evaluating thermal stability of positive electrode active material]
Remove the positive electrode plate from the test battery after charging 4.2V under Ar atmosphere, and keep about 5mg of sample at a constant temperature (250-375 ° C range set at 25 ° C intervals) while containing the electrolyte. Three samples were placed on the hot plate for each temperature, and the highest temperature at which all three samples did not ignite was defined as the maximum stable temperature during rapid heating, which was used as a measure of thermal stability.
[0018]
Examples of the present invention will be described in detail below in comparison with comparative examples.
[Comparative Example 1]
The cobalt nitrate solution is continuously charged into a reaction vessel whose liquid temperature is controlled at 80 ° C., neutralized with a 48 wt% sodium hydroxide solution, and the pH is controlled to 10.0 ± 0.2. This gave a hydroxide precipitate. This hydroxide was mixed with lithium hydroxide so that Li / Co = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 850 ° C. for 10 hours, and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0019]
[Comparative Example 2]
A solution prepared by mixing nickel and cobalt nitrates in a molar ratio of Ni: Co = 80: 20 was continuously charged into a reaction vessel whose liquid temperature was adjusted to 80 ° C., and sodium hydroxide having a concentration of 48% by weight. By neutralizing with a solution and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This coprecipitated hydroxide was mixed with lithium hydroxide so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0020]
[Comparative Example 3]
A solution prepared by mixing nickel, cobalt, and aluminum nitrates in a molar ratio of Ni: Co: Al = 71: 20: 9 was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C. By neutralizing with a sodium hydroxide solution having a concentration of% and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This hydroxide was mixed with lithium hydroxide so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0021]
[Comparative Example 4]
A solution prepared by mixing nickel, cobalt, and aluminum nitrates at a molar ratio of Ni: Co: Al = 68: 20: 12 was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C. By neutralizing with a sodium hydroxide solution having a concentration of% and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This hydroxide was mixed with lithium hydroxide so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0022]
[Comparative Example 5]
Nickel and cobalt nitrates and Nb₂O_FiveWere mixed continuously in a molar ratio of Ni: Co: Nb = 85: 13: 2 into a reaction vessel whose liquid temperature was controlled at 80 ° C., and a 48 wt% sodium hydroxide solution was used. By neutralizing and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This hydroxide was mixed with lithium hydroxide so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. The compact was fired in an oxygen stream at 650 ° C. for 10 hours, and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0023]
[Example 1]
The same molded body as that obtained in Comparative Example 5 was fired at 700 ° C. for 10 hours in an oxygen stream, and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0024]
[Example 2]
The same molded body as that obtained in Comparative Example 5 was fired in an oxygen stream at 750 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0025]
[Comparative Example 6]
The same molded body as that obtained in Comparative Example 5 was fired at 800 ° C. for 10 hours in an oxygen stream, and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0026]
[Comparative Example 7]
A solution prepared by mixing nickel and cobalt nitrates in a molar ratio of Ni: Co = 87: 13 was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C., and sodium hydroxide having a concentration of 48% by weight. By neutralizing with a solution and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. Lithium hydroxide was added to this hydroxide so that Li / (Ni + Co) = 1.03, and Nb / (Ni + Co) = 0.02.₂O_Five1t / cm²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0027]
[Comparative Example 8]
A solution prepared by mixing nickel and cobalt nitrates in a molar ratio of Ni: Co = 87: 13 was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C., and sodium hydroxide having a concentration of 48% by weight. By neutralizing with a solution and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. LiNbO was added to this hydroxide so that Li / (Ni + Co) = 1.03 and Nb / (Ni + Co) = 0.02.₃And Li salt are mixed, 1t / cm²To obtain a molded body. This molded body was fired in an oxygen stream at 750 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder. Using this powder as an active material, electrochemical characteristics and thermal stability were determined.
[0028]
[Comparative Example 9]
A solution prepared by mixing nickel and cobalt nitrates in a molar ratio of Ni: Co = 87: 13 was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C., and sodium hydroxide having a concentration of 48% by weight. By neutralizing with a solution and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This hydroxide was mixed with Li salt so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder.
Nb corresponding to the amount of this fired product and Nb / (Ni + Co) = 0.02₂O₅Was suspended in a lithium nitrate solution having a concentration of 1% by weight so that the solid content was 50% by weight, and wet-pulverized with a wet bead mill to obtain a dispersed slurry. This slurry was spray-dried and granulated into a spherical shape. After firing this at 800 ° C. for 2 hours in an oxygen stream, spherical secondary particles were obtained. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0029]
[Comparative Example 10]
Nickel and cobalt nitrates and Nb₂O₅Of Ni: Co: Nb = 86.5: 13: 0.5 in a molar ratio was continuously charged into a reaction vessel whose liquid temperature was controlled at 80 ° C., and a 48 wt% concentration of hydroxylated water was added. By neutralizing with sodium solution and controlling the pH to 10.0 ± 0.2, a coprecipitated hydroxide precipitate was obtained. This hydroxide was mixed with lithium hydroxide so that Li / (Ni + Co) = 1.03, and 1 t / cm.²To obtain a molded body. This molded body was fired in an oxygen stream at 700 ° C. for 10 hours and pulverized with a mortar-type pulverizer to obtain a layered crystal compound powder.
This powder was suspended in water so as to have a solid content concentration of 50% by weight, and wet-pulverized with a wet bead mill to obtain a dispersed slurry. This slurry was spray-dried and granulated into a spherical shape. After firing this at 800 ° C. for 2 hours in an oxygen stream, spherical secondary particles were obtained. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0030]
[Example 3]
Nickel and cobalt nitrates and Nb₂O₅Spherical secondary particles were obtained in the same manner as in Comparative Example 10 except that Ni: Co: Nb = 86: 13: 1 was used. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0031]
[Example 4]
Nickel and cobalt nitrates and Nb₂O₅Spherical secondary particles were obtained by the same method as in Comparative Example 10 except that Ni: Co: Nb = 84: 13: 3 in terms of molar ratio. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0032]
[Example 5]
Nickel and cobalt nitrates and Nb₂O₅Spherical secondary particles were obtained in the same manner as in Comparative Example 10 except that Ni: Co: Nb = 83: 13: 4 was used. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0033]
[Example 6]
Nickel, cobalt nitrate and Nb₂O₅Spherical secondary particles were obtained by the same method as Comparative Example 10 except that Ni: Co: Nb = 82: 13: 5 in terms of molar ratio. Using this as an active material, electrochemical characteristics and thermal stability were determined.
[0034]
The results of Examples and Comparative Examples are shown in Table 1 and FIG.
[Table 1]

[0035]
FIG. 1 shows the discharge curve of the initial cycle and the charge curve of the second cycle for the positive electrode active materials for non-aqueous secondary batteries of Example 5 and Comparative Example 9. In FIG. 1, the plot of Example 5 is shown by a solid line, and the plot of Comparative Example 9 is shown by a broken line. In addition, as can be seen from FIG. 2, the Li—Nb composite oxide has a charge / discharge capacity between 2.7 V and 4.2 V. In FIG. 1, the slope of the discharge curve in Example 5 in the end cycle of the initial cycle (around 3.5 V to 2.7 V) is gentler than that in Comparative Example 9. In addition, even in the second cycle charge, hysteresis was observed at the inflection point of the charge curve near 3.5 V compared to Comparative Example 9, and the positive electrode active material for the non-aqueous secondary battery of Example 5 was The potential rises slowly. Such a difference in electrochemical characteristics seems to be largely due to the presence of the Li—Nb composite oxide.
A model cell using Example 5 and Comparative Example 9 as the positive electrode active material was prepared, and AC impedance measurement was performed. Two consecutive semicircles in the complex impedance plot (Cole-Cole Plot) are observed in Example 5, and according to the equivalent circuit analysis, two kinds of electrodes having different electrochemical properties form a series circuit. Was confirmed. That is, in Example 5, LiNiO.₂It is judged that a compound layer having different electrochemical properties is formed on the surface of the system compound or the grain boundary layer.
In order to confirm the presence of this heterogeneous compound, ESCA analysis was performed while performing Ar sputtering, but no segregation of the component elements in the depth direction and no difference between the samples of Example 5 and Comparative Example 9 were observed. It was. Next, for a finer structural analysis, a thin specimen having a thickness of about 0.3 μm was prepared by a FIB (Focused Ion Beam) system, and observation by FE (Field Emission) -TEM and EDX and EELS measurements were performed. According to this method, analysis in the nanometer order is possible. As a result, Example 5 and Comparative Example 9 were aggregates of fine particles having a particle size of several tens to several hundreds of nanometers. Furthermore, when the linear element distribution was measured, in Example 5, a segregation layer having a thickness of about 10 to 30 nm was observed in the vicinity of the grain surface or in the grain boundary layer. In Comparative Example 9, no Nb segregation layer was observed. A measurement diagram of Example 5 is shown in FIG. 5, and a measurement diagram of Comparative Example 9 is shown in FIG.
From this result, the LiNiO observed in Example 5 in the AC impedance measurement.₂The compound layer having electrochemical properties different from those of the system is presumed to be a Li—Nb—O compound. Further, as the Li—Nb—O-based compound, the aforementioned LiNbO is used.₃For example, Li₃NbO₄, Li₅Nb₂O₅However, all of these compounds have a discharge capacity in the range of the positive electrode potential (vs. Li / Li +) from 2V to 1.5V. Further, these Li—Nb—O compounds have high thermal stability, and did not ignite at all under the thermal stability evaluation conditions during normal rapid heating.
[0036]
【The invention's effect】
As described above, according to the present invention, a positive electrode active material having high thermal stability and a large discharge capacity, and a high-performance and highly safe non-aqueous secondary battery using the positive electrode active material can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing a comparison of charge / discharge curves of Example 5 and Comparative Example 9 of the present invention.
FIG. 2 LiNbO₃It is a graph which shows the charging / discharging curve.
FIG. 3 is a cross-sectional view showing a configuration of a test battery used in an example of the present invention.
FIG. 4 is a scatter diagram showing the relationship between discharge capacity B and X-ray diffraction (003) plane half-value width measured in each example and comparative example of the present invention.
FIG. 5 is an FE-TEM photograph and Nb distribution of Example 5 of the present invention.
6 is an FE-TEM photograph of Comparative Example 9 and a diagram showing an Nb distribution. FIG.
[Explanation of symbols]
1 Stainless steel case
2 Gasket
3 Sealing plate
4 Negative electrode
5 Positive electrode
6 Separator

Claims

General formula: Li _a Ni _1-xz Co _x Nb _z O _b ( where 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0.01 ≦ z ≦ 0.05, 2 ≦ b ≦ 2.2), which is composed of at least one compound composed of lithium, nickel, cobalt, niobium and oxygen, and the positive electrode potential (vs. Li / Li +) is changed from 2V to 1. When the discharge capacity is α [mAh / g] within the range of 5 V and the half-value width of the (003) plane of the layered crystal structure in the X-ray diffraction is β [deg], α and β are 60 ≦ α, respectively. A positive electrode active material for a non-aqueous secondary battery, wherein the conditions of ≦ 150 and 0.14 ≦ β ≦ 0.20 are simultaneously satisfied.

The positive electrode active material for a non-aqueous secondary battery according to claim 1, wherein α and β are 80 ≦ α ≦ 150 and 0.15 ≦ β ≦ 0.20, respectively.

General _{_{formula: Li a Ni 1-x Co}} x O b ( where, 1 ≦ a ≦ 1.1,0.1 ≦ x ≦ 0.3,2 ≦ b ≦ 2.2) lithium and nickel represented by the cobalt And a composition comprising at least one compound composed of oxygen and at least one compound selected from LiNbO ₃ , Li ₃ NbO ₄ , and Li ₅ Nb ₂ O ₅ The potential (vs. Li / Li +) shows a discharge capacity of α [mAh / g] within the range of 2 V to 1.5 V, and the half-value width of the (003) plane of the layered crystal structure in the X-ray diffraction is β [deg ], The positive electrode active material for a non-aqueous secondary battery, wherein α and β simultaneously satisfy the conditions of 80 ≦ α ≦ 150 and 0.15 ≦ β ≦ 0.20, respectively.

General formula: Li _a Ni _1-xz Co _x Nb _z O _b ( where 1 ≦ a ≦ 1.1, 0.1 ≦ x ≦ 0.3, 0.01 ≦ z ≦ 0.05, 2 ≦ b ≦ 2.2) and having a composition composed of at least two kinds of compounds consisting of lithium, nickel, cobalt, niobium and oxygen, and the particles have a substantially spherical shape and are in the vicinity of the particle surface or particles. LiNbO the field layer _{_{_{3, Li 3 NbO 4, Li}}} 5 Nb 2 O the segregation layer possess by ₅ at least one or more compounds selected from one positive electrode potential at the time of initial discharge (vs.Li/Li+) from 2V When the discharge capacity of α [mAh / g] is shown in the range of 0.5 V and the half-value width of the (003) plane of the layered crystal structure in the X-ray diffraction is β [deg], α and β are 80 ≦ Same conditions as α ≦ 150 and 0.15 ≦ β ≦ 0.20 The positive electrode active material for a nonaqueous secondary battery, characterized by satisfying the.

A non-aqueous secondary battery using the positive electrode active material according to claim 1 as a positive electrode active material.

5. The non-aqueous secondary battery according to claim 1 , wherein a mixture of a Ni, Co coprecipitated hydroxide containing Nb compound and a Li compound is fired in an oxidizing atmosphere. A method for producing a positive electrode active material.

The positive electrode active material for a non-aqueous secondary battery according to any one of claims 1 to 4 , wherein a mixture of a coprecipitated hydroxide of Ni, Co and Nb and a compound of Li is fired in an oxidizing atmosphere. Manufacturing method.

The manufacturing method of the positive electrode active material for non-aqueous secondary batteries of Claim 6 or 7 which performs the said baking at 680 to 780 degreeC.