JP5079951B2

JP5079951B2 - Non-aqueous electrolyte secondary battery positive electrode active material, its manufacturing method, non-aqueous electrolyte secondary battery, and positive electrode manufacturing method

Info

Publication number: JP5079951B2
Application number: JP2001195157A
Authority: JP
Inventors: 哲藤原; 茂小野; 忠俊室田
Original assignee: Santoku Corp
Current assignee: Santoku Corp
Priority date: 2001-06-27
Filing date: 2001-06-27
Publication date: 2012-11-21
Anticipated expiration: 2021-06-27
Also published as: CN1311574C; KR100934612B1; KR20040015266A; CN1520621A; WO2003003489A1; JP2003017050A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水溶液を電解質とした二次電池における、負荷特性を有効に改善し、高容量化が可能な非水電解液２次電池用正極活物質、その製造方法、該正極活物質を用いた非水電解液２次電池、並びに該非水電解液２次電池用正極の製造方法に関する。
【０００２】
【従来の技術】
近年、ビデオカメラ、携帯型ＣＤ、携帯電話、ＰＤＡやノートパソコン等の携帯用電子機器の小型化、軽量化、高性能化が進んでいる。これらの携帯用電子機器の電源には、高容量かつ重負荷特性に優れた安全性の高い二次電池が必要とされている。このような目的に合致した二次電池としては、シール鉛蓄電池やニッケル・カドミウム蓄電池が使用されてきたが、よりエネルギー密度の高い電池としてニッケル水素蓄電池や非水電解液二次電池としてリチウムイオン二次電池が実用化に至っている。
リチウムイオン二次電池は、正極活物質として、Ｌｉと、Ｃｏ、Ｎｉ、Ｍｎ等の遷移金属との複合酸化物を用い、負極活物質にリチウムイオンを挿入・脱挿入できる炭素等の炭素質材料を用いた二次電池であり、ニッケル水素蓄電池等に比べて容量が大きく、また電圧が高いという特徴を持っている。しかし、最近の一層の高容量化や大電流化の要求に対して正極活物質の充填密度を上げることや、正極活物質と混合する導電助剤の量を減らすことにより正極活物質量を増加させるなどの対策が必要となっている。
【０００３】
このような要望に答えるべく様々な研究がなされているが、その中に正極活物質を球形にして充填効率を高め、充填効率の向上により活物質どうしの接触面積を増やすことによって導電性を向上させ、正極中の導電助剤を低減して、実質的に活物質量を増加する試みがなされている。
例えば、特開平１０−７４５１６号公報には、正極活物質を中空球形にして充填効率を向上させると共に比表面積を増加し、電解液との接触面積を増やして重負荷時の反応性を高めるという技術が開示されている。しかし、この方法では、活物質が中空球形であるため、球形による充填効率の向上を見込めるとしても、単位体積当たりに充填できる活物質の量は低下してしまい、高容量は望めない。
また、特開平１１−２７３６７８号公報には、コバルト酸リチウム正極活物質のコバルト源として、球形又は楕円球形のオキシ水酸化コバルトを用い、オキシ水酸化コバルトとリチウム化合物とを混合、焼成して球形の正極活物質を製造する技術が開示されている。更に、特開平１１−２８８７１６号公報には、１次粒子が放射状に集まった球形又は楕円球形の水酸化ニッケルコバルトとリチウム化合物とを混合、焼成して球形の正極活物質を製造する技術が開示されている。
しかし、これらの方法では、正極活物質を生成する反応が起きる際にリチウム化合物の分解反応や遷移金属化合物の分解反応が同時に起こる。これらの分解反応は水蒸気や炭酸ガス等の気体の生成を伴うため、生成した活物質は球形を保っているものの非常に空隙の多いものとなり、単位体積当たりに充填できる活物質の量は低下してしまい、高容量は望めない。
【０００４】
【発明が解決しようとする課題】
従って、本発明の目的は、非水電解液２次電池における負荷特性を有効に改善し、高容量化が可能な、充填効率が高く、充填密度の大きな非水電解液２次電池用正極活物質及びその製造方法を提供することにある。
本発明の別の目的は、優れた放電容量が得られる非水電解液２次電池及び該非水電解液２次電池用正極の製造方法を提供することにある。
【０００５】
【課題を解決するための手段】
本発明によれば、Ｌｉと、Ｃｏ及びＦｅからなる群より選択される少なくとも一種の遷移元素とを含む複合酸化物粒子からなり、前記複合酸化物粒子が、最長径をD１、最短径をD２とした際のD１／D２が１．０〜２．０の範囲にある球状及び／又は楕円球状の粒子を９０％以上含み、該複合酸化物粒子のタップ密度が、３．１ｇ／ｃｍ³以上であることを特徴とする非水電解液２次電池用正極活物質が提供される。
また本発明によれば、Ｃｏ及びＦｅからなる群より選択される少なくとも一種の遷移元素の化合物粒子と、リチウム化合物とを含む原材料を混合し、得られた混合物を、仮焼工程として該リチウム化合物の融点以上の温度で保持した後、本焼成工程として該リチウム化合物の分解温度以上で保持することを特徴とする非水電解液２次電池用正極活物質の製造方法が提供される。
更に本発明によれば、正極活物質粉末を有する正極と、負極と、電解液とを備え、該正極活物質粉末が上記非水電解液２次電池用正極活物質を含むことを特徴とする非水電解液２次電池が提供される。
更にまた本発明によれば、複合酸化物粒子を含む正極活物質を成形加工する、上記非水電解液２次電池に用いる正極の製造方法であって、平均粒径が１０％以上異なる少なくとも２種の複合酸化物粒子を混合して正極活物質に用いる前記複合酸化物粒子を得ることを特徴とし、該複合酸化物粒子が、主として粒径２〜１００μｍの粒子からなり、且つ平均粒径が５〜８０μmであり、Ｌｉと、Ｃｏ及びＦｅからなる群より選択される少なくとも一種の遷移元素とを含み、最長径をD１、最短径をD２とした際のD１／D２が１．０〜２．０の範囲にある球状及び／又は楕円球状の粒子を９０％以上含み、該複合酸化物粒子のタップ密度が、３．１ｇ／ｃｍ³以上である、非水電解液２次電池用正極の製造方法が提供される。
【０００６】
【発明の実施の形態】
以下、本発明を更に詳細に説明する。
本発明の非水電解液２次電池用正極活物質（以下、本発明の正極活物質という）は、Ｌｉと、Ｃｏ及びＦｅからなる群より選択される少なくとも一種の遷移元素とを含む特定の複合酸化物粒子からなる。
【０００７】
前記複合酸化物としては、例えば、ＬｉＣｏＯ₂ 、ＬｉＦｅＯ ₂ で表される酸化物等が挙げられる。
本発明の正極活物質は、上記組成に加えて、アルカリ金属、アルカリ土類金属、Ｔｉ、Ｚｒ、Ｈｆ、Ｙ、Ｓｃ及び希土類金属等からなる群より選択される少なくとも一種が含まれていても良い。これらの金属元素は、本発明の正極活物質の格子間隔を広げて容量を増加させたり、充放電効率を高めたり、正極活物質の焼結性を向上して密度を上げる等の作用を有する。
これら添加元素の添加量は、全体の１質量％以下が好ましく、特に、０．５質量％以下、更には０．３質量％以下が望ましい。１質量％を超えて添加しても密度向上が望めず、かえって本発明の正極活物質の容量が低下する恐れがあるので好ましくない。
【０００８】
本発明の正極活物質としての複合酸化物粒子の形状は、主に球状又は楕円球状である。針状や紡錘状、板状、不定形のものでは、充填効率を上げることができないため好ましくなく、楕円球状であってもアスペクト比が大きく、紡錘状に近くなると充填効率が下がるため好ましくない。
従って、前記複合酸化物粒子は、最長径をD１、最短径をD２とした際のD１／D２(アスペクト比)が１．０〜２．０、好ましくは１．０〜１．５の範囲にある球状及び／又は楕円球状の粒子を９０％以上含む。
【０００９】
本発明の正極活物質のタップ密度は高い方がよい。タップ密度が低いと正極活物質の充填効率が悪くなるため、限られた極板の体積内に多くの活物質を充填することができず、容量が低下してしまう。本発明の正極活物質においてタップ密度は３．１ｇ／ｃｍ³以上である。
【００１０】
上記タップ密度の向上には、粒子の粒度分布と平均粒径が重要な役割をもつ。粘度分布がブロード過ぎたり、シャープすぎたりすると粒子の充填効率が悪くなり、平均粒径が小さすぎると粒子の表面エネルギーが大きくなるため、このような場合も充填効率の低下を招く。平均粒径が大きすぎると、電極を作成する際に集電体上に活物質を均一に塗布することが困難になる。
従って、本発明の正極活物質を構成する複合酸化物粒子の粒径は、主として２〜１００μｍ、特に１０〜１００μmの範囲にあることが好ましく、特に、その８０％以上、更にはその８５％以上、更にまた９０％以上が上記範囲にあることが望ましい。また、平均粒径は５〜８０μｍ、特に３０〜８０μm、更に３０〜６０μｍであることが好ましい。平均粒径が５μｍ未満であったり、８０μmより大きかったりすると、たとえ粒径の範囲が上述の好ましい範囲にあったとしても粒度分布がシャープになりすぎて充填効率が低下するため好ましくない。
前記複合酸化物の比表面積は、好ましくは０．０５〜０．２４ｍ²／ｇ、特に好ましくは０．１〜０．２ｍ²／ｇである。比表面積が０．０５ｍ²／ｇ未満では、得られる正極の内部抵抗が大きくなり、高率放電特性が低下するので好ましくなく、一方、０．２４ｍ²／ｇを超える場合には、電解液等との反応性が高くなり、得られる正極の熱安定性が低下するので好ましくない。
また、本発明の正極活物質を構成する複合酸化物粒子を用いて実際に正極を製造する際には、正極活物質の充填効率を高くするために、上記平均粒径が異なる少なくとも２種の上記複合酸化物粒子の混合物を用いることが好ましい。この際、混合する複合酸化物粒子は、平均粒径が１０％以上異なることが好ましい。
【００１１】
本発明の正極活物質を製造する方法は、本発明の正極活物質が得られれば特に限定されない。例えば、リチウム源となるリチウム化合物と遷移金属源となる遷移元素の化合物とを混合し、適当な条件を設定して焼成する方法等により得ることができる。好ましい方法としては、以下に示す本発明の製造方法等が挙げられる。
本発明の製造方法は、特定の遷移金属源となる遷移元素の化合物粒子と、リチウム源となるリチウム化合物とを含む原材料を混合し、得られた混合物を、特定の仮焼工程及び本焼成工程を行うことを特徴とする。
【００１２】
上記リチウム源となるリチウム化合物は、融点が８００℃以下で、熱分解温度が１１００℃以下であるものが好ましく、例えば、水酸化リチウム、塩化リチウム、硝酸リチウム、炭酸リチウム、硫酸リチウム等の無機塩；蟻酸リチウム、酢酸リチウム、蓚酸リチウム等の有機塩等が挙げられる。
上記遷移金属源となる遷移元素の化合物粒子は、Ｃｏ及びＦｅからなる群より選択される少なくとも一種の遷移元素の化合物粒子であって、熱分解温度が１１００℃以下であるものが好ましく、例えば、水酸化物や炭酸塩等が挙げられるが、タップ密度を向上させる目的を考慮すると、熱分解しない遷移金属の酸化物粒子が望ましい。
【００１３】
上記遷移金属源の粒子形状は、球状及び／又は楕円球状の球形粒子であることが好ましい。このような粒子を得る方法としては、例えば、不定形の一次粒子を造粒によって球形にする方法や、液状又はスラリー状の化合物を噴霧乾燥又は噴霧焼成法によって球形にする方法、均一沈殿法等により球形の粒子を直接得る方法等が挙げられる。球形の酸化物粒子とする場合は、これらの球形粒子を焼成して得ることができるが、この際の焼成温度が低いとタップ密度も低くなってしまうため、５００℃以上の温度で焼成することが好ましい。
球状及び／又は楕円球状の遷移金属源は、この段階である程度のタップ密度を有することが好ましい。この段階におけるタップ密度が低いと、得られる正極活物質のタップ密度も低くなってしまう。このような球状及び／又は楕円球状の遷移金属源のタップ密度は、好ましくは２．０ｇ／ｃｍ³以上、より好ましくは２．２ｇ／ｃｍ³以上、更に好ましくは２．４ｇ／ｃｍ³以上である。
【００１４】
本発明の製造方法において、上述のリチウム源と遷移金属源とを含む原材料には、必要に応じて、上述の添加元素、すなわち、アルカリ金属、アルカリ土類金属、Ｔｉ、Ｚｒ、Ｈｆ、Ｙ、Ｓｃ及び希土類金属等からなる群より選択される少なくとも一種の金属化合物を含んでいても良い。これら原材料の混合は公知の方法で行なうことができる。
【００１５】
本発明の製造方法では、得られる本発明の正極活物質のタップ密度を向上させる目的で、上記原材料の混合物の焼成を、特定な仮焼工程及び特定の本焼成工程の２段階で行う。
特定の仮焼工程は、原材料に用いたリチウム化合物の融点以上の温度に保持する。この仮焼工程では、原材料である遷移元素の化合物粒子中にリチウム化合物を含浸させることを目的とする。従って、保持温度の上限は、リチウム化合物の分解温度未満であることが好ましく、且つ３００〜９５０℃、特に５００〜８００℃が望ましい。保持時間は１０〜３００分間が好ましい。
特定の本焼成工程は、仮焼工程を経た、例えば、リチウム化合物を含浸した遷移元素の化合物を、原材料に用いたリチウム化合物の分解温度以上に保持する。この本焼成工程では、リチウム化合物と遷移元素の化合物とを反応させ、目的とする本発明の正極活物質を生成させることを目的とする。この際の温度は、リチウム化合物の分解温度以上であればよいが、リチウム化合物の分解温度が低い場合には遷移元素の化合物粒子との反応に時間を要する場合があるため、好ましくは７００〜１１００℃、より好ましくは８００〜１１００℃である。保持時間は、短かすぎると反応が完結せず、長すぎると固相反応が進行しすぎて粒子同士が付着してしまうことがあるため、好ましくは１０〜１８００分間、より好ましくは１０〜９００分間である。
【００１６】
本発明の製造方法では、上記工程により本発明の正極活物質を得ることができるが、必要に応じて、他の工程を含んでいても良い。
【００１７】
本発明の非水電解液２次電池は、正極活物質粉末を有する正極と、負極と、電解液とを備え、前記正極活物質として本発明の正極活物質を含むものであれば良く、他の構成、並びに他の追加の構成等は公知のもの等から適宜選択することができる。
また、上記非水電解液２次電池に用いる正極を製造するには、上述の複合酸化物粒子として、平均粒径が１０％以上異なる少なくとも２種の複合酸化物粒子を混合した混合物を用いることが望ましい。
【００１８】
【実施例】
以下、実施例により本発明を更に詳細に説明するが、本発明はこれに限定されるものではない。
実施例１
純度９９．８％のコバルトメタル１００ｇを硝酸に溶解した後、純水で希釈し、１６５０ｍｌとした。続いて、４Nの水酸化ナトリウム溶液８２０ｍｌを加え撹拌した後にろ過し、球状又は楕円球状の粒子で構成される水酸化物のケーキを得た。そのケーキを８５０℃で４時間焼成し、１３７ｇの球状又は楕円球状の粒子である複合酸化物粒子を得た。得られた複合酸化物粒子１３７ｇと炭酸リチウム６５ｇとを均一に混合した後、得られた混合物を７００℃で２４０分間仮焼成を行い、更に、８５０℃で３００分間本焼成を行って、球状又は楕円球状の粒子を得た。
得られた粒子をＩＣＰ発光分光分析装置、Ｘ線回折装置、電子顕微鏡、タップデンサー装置(セイシン企業製、ＸＹＴ−２０００)を用いて調査した結果、一次粒子が０．２〜１０μmであり、二次粒子が１０〜１００μmの複合粒子で、アスペクト比１〜１．５で、タップ密度２．９ｇ／ｃｍ³以上である形状を有するＬｉＣｏＯ₂の粒子であることが判った。また、粒子の比表面積が、０．１５ｍ²／ｇであることが判った。
なお、タップ密度の測定は、得られた粒子を２０ｍｌシリンダーヘ１０．０ｇ採取し、タップ高さ２ｃｍ、タップ回数２００回にて測定した。また、比表面積の測定は、得られた粒子を１ｇ採取し、２００℃で２０分間脱気後、カンタクロム社製の商品名「NOVA2000」を用いてＮ₂吸着ＢＥＴ法により行った。これらの結果を表１に示す。
また得られた正極活物質としての粒子の１０００倍率のＳＥＭ写真を図１に、５０００倍率のＳＥＭ写真を図２にそれぞれ示す。
【００１９】
更に、得られた粒子と、導電助剤としてのアセチレンブラックと、結着剤としてのＰＴＦＥとを重量比で５０：４０：１０の割合で混合し正極合剤を調製し、ステンレス鋼鈑を集電体とした正極を作製した。また、ステンレス鋼鈑を集電体としたリチウム金属の負極を作製した。更にエチレンカーボネートとジメチルカーボネートとを体積比１：１の割合で混合した溶液に過塩素酸リチウムを１ｍｏｌ／ｌの割合で溶解して電解液を調製した。得られた正極、負極、電解液を用いリチウムイオン２次電池を作製した。
得られた電池を充電電流密度３ｍＡ／ｃｍ²になる条件で充電上限電圧４．３Ｖ、放電下限電圧を３Ｖとして初期放電容量を測定した。また、得られた粒子と、導電助剤としてのグラファイトと、結着剤としてＰＶＤＦとを質量比で９０：５：５の割合で混合しドクターブレード法により厚さ２０μmのＡｌ集電体に塗布し、圧力３ｔ／ｃｍ²でプレスして電極を作製した。得られた電極の体積及び質量を測定し、Ａｌ集電体の体積及び質量を差し引き、電極密度を算出した。これらの結果を表１に示す。
【００２０】
実施例２及び３
実施例１のケーキ焼成温度を、７００℃又は９００℃、仮焼成時間を４８０分間又は６４０分間、本焼成温度を８５０℃又は９５０℃、本焼成時間を１２００分間又は１００時間とそれぞれし、炭酸リチウムの代わりに、硝酸リチウム３５ｇ又は硫酸リチウム４４ｇとそれぞれした以外は実施例１と同様の操作により球状又は楕円球状粒子を作製し、各測定及び評価を行った。結果を表１に示す。
【００２２】
比較例１及び２
球状又は楕円球状粒子である水酸化物の代わりに、針状又は不定形である水酸化物を用いた以外は実施例１と同様の操作により針状又は不定形の複合酸化物を作製し、測定及び評価を行った。結果を表１に示す。
【００２３】
【表１】

【００２４】
実施例１２〜１４
実施例１で調製した粒子を分級して、平均粒径１０μｍの小粒子群と、平均粒径７０μｍの大粒子群とに分け、それぞれを質量比で１：１(実施例１２)、３：７(実施例１３)又は１：９(実施例１４)で混合して正極活物質を得、更に、実施例１と同様に電極を作製して各測定及び評価を行なった。結果を表２に示す。
【００２５】
【表２】

【００２６】
【発明の効果】
本発明の非水電解液二次電池用正極活物質は、球状及び／又は楕円球状粒子の複合酸化物であり、該粒子のアスペクト比が１．０〜２．０の範囲にあり、タップ密度が２．９ｇ／ｃｍ³以上であるので、これを用いて電極を作成した場合、電極密度を３．４〜３．７ｇ／ｃｍ³程度にすることができ、非水電解液二次電池における体積あたりの放電容量や、負荷特性を有効に改善することができる。また本発明の製造方法では、このような正極活物質を容易に得ることができる。更に、本発明の非水電解液２次電池は、本発明の正極活物質を用いるので、放電容量及び負荷特性を向上させることができる。
【図面の簡単な説明】
【図１】実施例１で調製した正極活物質としての粒子の１０００倍率のＳＥＭ写真である。
【図２】実施例１で調製した正極活物質としての粒子の５０００倍率のＳＥＭ写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery capable of effectively improving load characteristics and increasing capacity in a secondary battery using a non-aqueous solution as an electrolyte, a manufacturing method thereof, and the positive electrode active material. The present invention relates to the used non-aqueous electrolyte secondary battery and a method for producing the positive electrode for the non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, portable electronic devices such as video cameras, portable CDs, cellular phones, PDAs, and notebook personal computers have been reduced in size, weight, and performance. A power source for these portable electronic devices requires a high-capacity secondary battery with high safety and excellent heavy load characteristics. Sealed lead-acid batteries and nickel-cadmium batteries have been used as secondary batteries that meet these objectives. However, nickel-metal hydride batteries and non-aqueous electrolyte secondary batteries are used as lithium-ion batteries as higher energy density batteries. Secondary batteries have come into practical use.
The lithium ion secondary battery uses a composite oxide of Li and a transition metal such as Co, Ni, Mn, etc., as a positive electrode active material, and a carbonaceous material such as carbon that can insert / deinsert lithium ions into the negative electrode active material The battery has a feature that it has a larger capacity and a higher voltage than a nickel metal hydride storage battery. However, the amount of positive electrode active material is increased by increasing the packing density of the positive electrode active material in response to the recent demand for higher capacity and higher current, and by reducing the amount of conductive additive mixed with the positive electrode active material. It is necessary to take measures such as
[0003]
Various studies have been made to answer such demands, and the positive electrode active material is made spherical to increase the filling efficiency, and the conductivity is improved by increasing the contact area between the active materials by improving the filling efficiency. Attempts have been made to substantially increase the amount of active material by reducing the conductive additive in the positive electrode.
For example, Japanese Patent Laid-Open No. 10-74516 discloses that the positive electrode active material is made into a hollow sphere to improve the filling efficiency and increase the specific surface area, and increase the contact area with the electrolyte to increase the reactivity under heavy load. Technology is disclosed. However, in this method, since the active material is a hollow sphere, the amount of active material that can be filled per unit volume is reduced even if an improvement in filling efficiency due to the sphere can be expected, and a high capacity cannot be expected.
JP-A-11-273678 discloses using spherical or elliptical spherical cobalt oxyhydroxide as a cobalt source of a lithium cobaltate positive electrode active material, mixing cobalt oxyhydroxide and a lithium compound, firing, and spherical. A technique for producing a positive electrode active material is disclosed. Furthermore, Japanese Patent Application Laid-Open No. 11-288716 discloses a technique for producing a spherical positive electrode active material by mixing and firing a spherical or elliptical spherical nickel cobalt hydroxide in which primary particles are gathered radially and a lithium compound. Has been.
However, in these methods, when the reaction for generating the positive electrode active material occurs, the decomposition reaction of the lithium compound and the decomposition reaction of the transition metal compound occur simultaneously. Since these decomposition reactions involve the generation of gas such as water vapor and carbon dioxide gas, the generated active material has a spherical shape although it maintains a spherical shape, and the amount of active material that can be filled per unit volume decreases. Therefore, high capacity cannot be expected.
[0004]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to effectively improve the load characteristics in a non-aqueous electrolyte secondary battery, increase the capacity, have high filling efficiency, and have a high packing density. It is to provide a substance and a manufacturing method thereof.
Another object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of obtaining an excellent discharge capacity and a method for producing the positive electrode for the non-aqueous electrolyte secondary battery.
[0005]
[Means for Solving the Problems]
According to the present invention, a Li, made from the composite oxide particles including at least one transition element selected from the group consisting of Co 及 beauty Fe, the composite oxide particles, the maximum diameter D1, the shortest diameter 90% or more of spherical and / or ellipsoidal particles having D1 / D2 in the range of 1.0 to 2.0 when D2 is set, and the composite oxide particles have a tap density of 3.1 g / cm ³ The positive electrode active material for a non-aqueous electrolyte secondary battery is provided as described above.
According to the present invention, the lithium compound particles of at least one transition element selected from the group consisting of Co 及 beauty Fe, mixing raw materials containing lithium compound, the resulting mixture, a calcining step After being held at a temperature equal to or higher than the melting point of the compound, a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery is provided, which is maintained as a decomposition temperature of the lithium compound as a main firing step.
Furthermore, according to the present invention, a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolytic solution are provided, and the positive electrode active material powder includes the positive electrode active material for a non-aqueous electrolyte secondary battery. A non-aqueous electrolyte secondary battery is provided.
Furthermore, according to the present invention, there is provided a method for producing a positive electrode for use in the non-aqueous electrolyte secondary battery, wherein the positive electrode active material containing composite oxide particles is molded, wherein the average particle size differs by at least 10%. The composite oxide particles used for the positive electrode active material are obtained by mixing seed composite oxide particles, and the composite oxide particles are mainly composed of particles having a particle size of 2 to 100 μm and have an average particle size of a 5 to 80 m, wherein the Li, and at least one transition element selected from the group consisting of Co 及 beauty Fe, a maximum diameter D1, the D1 / D2 at the time of the shortest diameter and D2 1.0 to A positive electrode for a non-aqueous electrolyte secondary battery, comprising 90% or more of spherical and / or ellipsoidal particles in the range of 2.0, wherein the composite oxide particles have a tap density of 3.1 g / cm ³ or more. A manufacturing method is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, referred to as the positive electrode active material of the present invention), a particular including where the Li, a transition element of at least one selected from the group consisting of Co 及 beauty Fe The composite oxide particles.
[0007]
As the composite oxide, for example, oxides represented by LiCoO _{_2,} Li Fe O ₂ and the like.
In addition to the above composition, the positive electrode active material of the present invention may contain at least one selected from the group consisting of alkali metals, alkaline earth metals, Ti, Zr, Hf, Y, Sc, and rare earth metals. good. These metal elements have actions such as increasing the capacity of the positive electrode active material of the present invention by increasing the lattice spacing, increasing the charge / discharge efficiency, improving the sinterability of the positive electrode active material, and increasing the density. .
The addition amount of these additive elements is preferably 1% by mass or less, particularly 0.5% by mass or less, more preferably 0.3% by mass or less. Even if added in excess of 1% by mass, the density cannot be improved, and the capacity of the positive electrode active material of the present invention may be reduced.
[0008]
The shape of the composite oxide particles as the positive electrode active material of the present invention is mainly spherical or elliptical. Needle-shaped, spindle-shaped, plate-shaped, and irregular shapes are not preferable because the filling efficiency cannot be increased. Even an elliptical sphere is not preferable because the aspect ratio is large, and the efficiency close to the spindle shape decreases.
Therefore, the composite oxide particles have a D1 / D2 (aspect ratio) of 1.0 to 2.0, preferably 1.0 to 1.5 when the longest diameter is D1 and the shortest diameter is D2. 90% or more of certain spherical and / or elliptical particles are included.
[0009]
The tap density of the positive electrode active material of the present invention is preferably higher. When the tap density is low, the filling efficiency of the positive electrode active material is deteriorated, so that a large amount of the active material cannot be filled in the limited volume of the electrode plate, and the capacity is reduced. Power strips density Te positive electrode active material odor of the present invention is 3.1 g / cm ³ or more.
[0010]
In improving the tap density, the particle size distribution and the average particle size play important roles. If the viscosity distribution is too broad or too sharp, the packing efficiency of the particles deteriorates, and if the average particle size is too small, the surface energy of the particles increases, and in this case also, the packing efficiency decreases. When the average particle size is too large, it becomes difficult to uniformly apply the active material on the current collector when the electrode is formed.
Therefore, the particle size of the composite oxide particles constituting the positive electrode active material of the present invention is preferably mainly in the range of 2 to 100 μm, particularly 10 to 100 μm, particularly 80% or more, more preferably 85% or more. Furthermore, it is desirable that 90% or more be in the above range. The average particle size is preferably 5 to 80 μm, more preferably 30 to 80 μm, and further preferably 30 to 60 μm. If the average particle size is less than 5 μm or larger than 80 μm, even if the particle size range is in the above-mentioned preferable range, the particle size distribution becomes too sharp and the filling efficiency is lowered, which is not preferable.
The specific surface area of the composite oxide is preferably 0.05 to 0.24 m ² / g, particularly preferably 0.1 to 0.2 m ² / g. The specific than surface area of 0.05 m ² / g, the positive electrode internal resistance of the increases obtained, it is not preferable because the high-rate discharge characteristics are lowered, whereas, if it exceeds 0.24 m ² / g, the electrolyte solution or the like And the thermal stability of the resulting positive electrode is lowered, which is not preferable.
Further, when the positive electrode is actually produced using the composite oxide particles constituting the positive electrode active material of the present invention, at least two kinds of different average particle diameters are used in order to increase the filling efficiency of the positive electrode active material. It is preferable to use a mixture of the composite oxide particles. At this time, the mixed oxide particles to be mixed preferably have an average particle size different by 10% or more.
[0011]
The method for producing the positive electrode active material of the present invention is not particularly limited as long as the positive electrode active material of the present invention is obtained. For example, it can be obtained by a method in which a lithium compound as a lithium source and a transition element compound as a transition metal source are mixed and fired under appropriate conditions. Preferred methods include the production methods of the present invention shown below.
The production method of the present invention comprises mixing a raw material containing transition element compound particles serving as a specific transition metal source and a lithium compound serving as a lithium source, and subjecting the resulting mixture to a specific calcining step and a main firing step. It is characterized by performing.
[0012]
The lithium compound serving as the lithium source preferably has a melting point of 800 ° C. or lower and a thermal decomposition temperature of 1100 ° C. or lower. For example, inorganic salts such as lithium hydroxide, lithium chloride, lithium nitrate, lithium carbonate, and lithium sulfate An organic salt such as lithium formate, lithium acetate, lithium oxalate and the like.
Compound particles of the transition element which serves as the transition metal source is a compound particles of the transition at least one element selected from the group consisting of Co 及 beauty Fe, preferably has a thermal decomposition temperature of 1100 ° C. or less, for example, , Hydroxides, carbonates, and the like are mentioned, but considering the purpose of improving the tap density, transition metal oxide particles that are not thermally decomposed are desirable.
[0013]
The particle shape of the transition metal source is preferably spherical and / or elliptical spherical particles. As a method for obtaining such particles, for example, a method of making amorphous primary particles spherical by granulation, a method of making a liquid or slurry compound spherical by spray drying or spray firing, a uniform precipitation method, etc. And a method for directly obtaining spherical particles. In the case of spherical oxide particles, these spherical particles can be obtained by firing, but if the firing temperature at this time is low, the tap density will be low, so firing at a temperature of 500 ° C. or higher. Is preferred.
The spherical and / or elliptical transition metal source preferably has some tap density at this stage. If the tap density at this stage is low, the tap density of the resulting positive electrode active material will also be low. The tap density of such a spherical and / or elliptical transition metal source is preferably 2.0 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and even more preferably 2.4 g / cm ³ or more. is there.
[0014]
In the production method of the present invention, the raw material containing the lithium source and the transition metal source described above may contain the above-described additive elements, that is, alkali metal, alkaline earth metal, Ti, Zr, Hf, Y, It may contain at least one metal compound selected from the group consisting of Sc and rare earth metals. These raw materials can be mixed by a known method.
[0015]
In the production method of the present invention, for the purpose of improving the tap density of the obtained positive electrode active material of the present invention, the mixture of the raw materials is fired in two stages, a specific calcining step and a specific main baking step.
The specific calcining step is held at a temperature equal to or higher than the melting point of the lithium compound used as the raw material. The purpose of this calcining step is to impregnate a lithium compound into transition element compound particles that are raw materials. Accordingly, the upper limit of the holding temperature is preferably lower than the decomposition temperature of the lithium compound, and is preferably 300 to 950 ° C, particularly 500 to 800 ° C. The holding time is preferably 10 to 300 minutes.
In the specific main firing step, for example, the transition element compound impregnated with the lithium compound is maintained at a temperature equal to or higher than the decomposition temperature of the lithium compound used as a raw material. The purpose of this firing step is to react a lithium compound with a transition element compound to produce the intended positive electrode active material of the present invention. The temperature at this time may be equal to or higher than the decomposition temperature of the lithium compound. However, when the decomposition temperature of the lithium compound is low, the reaction with the transition element compound particles may take time, and is preferably 700 to 1100. ° C, more preferably 800-1100 ° C. If the retention time is too short, the reaction will not be completed, and if it is too long, the solid-phase reaction may proceed too much and the particles may adhere to each other. Therefore, the retention time is preferably 10 to 1800 minutes, more preferably 10 to 900. For minutes.
[0016]
In the production method of the present invention, the positive electrode active material of the present invention can be obtained by the above-described steps, but other steps may be included as necessary.
[0017]
The non-aqueous electrolyte secondary battery of the present invention only needs to include a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolyte, and include the positive electrode active material of the present invention as the positive electrode active material. The other configurations and the like can be appropriately selected from known configurations.
Moreover, in order to manufacture the positive electrode used for the non-aqueous electrolyte secondary battery, a mixture obtained by mixing at least two kinds of composite oxide particles having an average particle diameter of 10% or more different as the composite oxide particles is used. Is desirable.
[0018]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
Example 1
100 g of cobalt metal having a purity of 99.8% was dissolved in nitric acid and then diluted with pure water to make 1650 ml. Subsequently, 820 ml of 4N sodium hydroxide solution was added and stirred, followed by filtration to obtain a hydroxide cake composed of spherical or oval spherical particles. The cake was baked at 850 ° C. for 4 hours to obtain 137 g of composite oxide particles which are spherical or oval spherical particles. After uniformly mixing 137 g of the obtained composite oxide particles and 65 g of lithium carbonate, the obtained mixture was temporarily baked at 700 ° C. for 240 minutes, and further subjected to main baking at 850 ° C. for 300 minutes to obtain spherical or Oval spherical particles were obtained.
As a result of investigating the obtained particles using an ICP emission spectroscopic analyzer, an X-ray diffractometer, an electron microscope, and a tap denser device (XYT-2000, manufactured by Seishin Enterprise), the primary particles were 0.2 to 10 μm. It was found that the secondary particles were composite particles of 10 to 100 μm, LiCoO ₂ particles having a shape with an aspect ratio of 1 to 1.5 and a tap density of 2.9 g / cm ³ or more. Moreover, it turned out that the specific surface area of particle | grains is 0.15 m < ² > / g.
The tap density was measured by collecting 10.0 g of the obtained particles into a 20 ml cylinder and measuring the tap height of 2 cm and the number of taps of 200 times. The specific surface area was measured by collecting 1 g of the obtained particles, degassing at 200 ° C. for 20 minutes, and then performing the N ₂ adsorption BET method using a trade name “NOVA2000” manufactured by Cantachrome. These results are shown in Table 1.
Further, an SEM photograph at 1000 magnifications of the obtained particles as the positive electrode active material is shown in FIG. 1, and an SEM photograph at 5000 magnifications is shown in FIG.
[0019]
Furthermore, the obtained particles, acetylene black as a conductive additive, and PTFE as a binder were mixed at a weight ratio of 50:40:10 to prepare a positive electrode mixture, and a stainless steel plate was collected. A positive electrode was prepared as an electric body. Also, a lithium metal negative electrode using a stainless steel plate as a current collector was prepared. Furthermore, an electrolytic solution was prepared by dissolving lithium perchlorate at a ratio of 1 mol / l in a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1. A lithium ion secondary battery was fabricated using the obtained positive electrode, negative electrode, and electrolytic solution.
The initial discharge capacity of the obtained battery was measured under the condition that the charge current density was 3 mA / cm ² and the charge upper limit voltage was 4.3 V and the discharge lower limit voltage was 3 V. Further, the obtained particles, graphite as a conductive aid, and PVDF as a binder were mixed at a mass ratio of 90: 5: 5 and applied to an Al current collector having a thickness of 20 μm by the doctor blade method. Then, an electrode was manufactured by pressing at a pressure of 3 t / cm ² . The volume and mass of the obtained electrode were measured, and the volume and mass of the Al current collector were subtracted to calculate the electrode density. These results are shown in Table 1.
[0020]
Examples 2 and 3
The baking temperature of Example 1 is 700 ° C or 900 ° C, the temporary baking time is 480 minutes or 640 minutes , the main baking temperature is 850 ° C or 950 ° C , and the main baking time is 1200 minutes or 100 hours , respectively. Instead of 35 g of lithium nitrate or 44 g of lithium sulfate, spherical or oval spherical particles were prepared in the same manner as in Example 1, and each measurement and evaluation were performed. The results are shown in Table 1.
[0022]
Comparative Examples 1 and 2
In place of the hydroxide that is spherical or oval spherical particles, a needle-like or amorphous composite oxide is produced by the same operation as in Example 1 except that a hydroxide that is needle-like or amorphous is used. Measurement and evaluation were performed. The results are shown in Table 1.
[0023]
[Table 1]

[0024]
Examples 12-14
The particles prepared in Example 1 are classified into a small particle group having an average particle diameter of 10 μm and a large particle group having an average particle diameter of 70 μm, and each has a mass ratio of 1: 1 (Example 12), 3: 7 (Example 13) or 1: 9 (Example 14) was mixed to obtain a positive electrode active material. Further, an electrode was prepared in the same manner as in Example 1, and each measurement and evaluation was performed. The results are shown in Table 2.
[0025]
[Table 2]

[0026]
【Effect of the invention】
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a composite oxide of spherical and / or elliptical spherical particles, the aspect ratio of the particles is in the range of 1.0 to 2.0, and the tap density Is 2.9 g / cm ³ or more, and when an electrode is produced using this, the electrode density can be about 3.4 to 3.7 g / cm ³ . The discharge capacity per volume and load characteristics can be improved effectively. Moreover, in the manufacturing method of this invention, such a positive electrode active material can be obtained easily. Furthermore, since the non-aqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention, the discharge capacity and load characteristics can be improved.
[Brief description of the drawings]
1 is an SEM photograph at 1000 magnifications of particles as a positive electrode active material prepared in Example 1. FIG.
2 is a SEM photograph at 5000 magnifications of particles as a positive electrode active material prepared in Example 1. FIG.

Claims

And Li, made from the composite oxide particles including at least one transition element selected from the group consisting of Co 及 beauty Fe, the composite oxide particles, the maximum diameter D1, D1 at the time of the shortest diameter and D2 90% or more of spherical and / or ellipsoidal particles having a / D2 in the range of 1.0 to 2.0, and the tap density of the composite oxide particles is 3.1 g / cm ³ or more A positive electrode active material for a non-aqueous electrolyte secondary battery.

2. The positive electrode active material according to claim 1, wherein the composite oxide particles include at least one selected from the group consisting of alkali metals, alkaline earth metals, Ti, Zr, Hf, Y, Sc, and rare earth metals. .

3. The positive electrode active material according to claim 1, wherein the composite oxide particles are mainly composed of particles having a particle diameter of 2 to 100 μm and an average particle diameter of 5 to 80 μm.

4. The positive electrode active material according to claim 1, wherein the composite oxide particles have a specific surface area of 0.05 to 0.24 m ² / g.

And compound particles of at least one transition element selected from the group consisting of Co 及 beauty Fe, mixing raw materials containing lithium compound, the resulting mixture at a temperature above the melting point of the lithium compound as a calcination step 2. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein after the holding, the main calcination step is carried out at or above the decomposition temperature of the lithium compound.

The transition element compound particles are transition metal oxide particles having a spherical shape and / or an elliptical spherical shape, and a tap density of 2.0 g / cm ³ or more. Item 6. The production method according to Item 5.

The temperature in the calcining step is 300 to 950 ° C., the holding time is 10 to 300 minutes, the temperature in the main baking step is 700 to 1100 ° C., and the holding time is 10 to 1800 minutes. The manufacturing method of Claim 5 or 6.

A positive electrode having a positive electrode active material powder, a negative electrode, and an electrolyte solution, wherein the positive electrode active material powder contains the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4. A non-aqueous electrolyte secondary battery characterized by the above.

9. The method for producing a positive electrode for use in a non-aqueous electrolyte secondary battery according to claim 8, wherein the positive electrode active material containing the composite oxide particles is molded, wherein at least two kinds of composite oxidations having an average particle size different by 10% or more. The composite oxide particles used for the positive electrode active material are obtained by mixing product particles. The composite oxide particles are mainly composed of particles having a particle size of 2 to 100 μm, and an average particle size of 5 to 80 μm. There, Li and, and at least one transition element selected from the group consisting of Co 及 beauty Fe, a maximum diameter D1, D1 / D2 at the time of the shortest diameter and D2 is 1.0 to 2.0 A method for producing a positive electrode for a nonaqueous electrolyte secondary battery, comprising 90% or more of spherical and / or ellipsoidal particles in a range, wherein the composite oxide particles have a tap density of 3.1 g / cm ³ or more.