JP3610943B2 - Nonaqueous electrolyte secondary battery - Google Patents
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- JP3610943B2 JP3610943B2 JP2001316765A JP2001316765A JP3610943B2 JP 3610943 B2 JP3610943 B2 JP 3610943B2 JP 2001316765 A JP2001316765 A JP 2001316765A JP 2001316765 A JP2001316765 A JP 2001316765A JP 3610943 B2 JP3610943 B2 JP 3610943B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Description
【０００１】
【発明の属する技術分野】
本発明は、非水電解質二次電池に関する。
【０００２】
【従来の技術】
正極と、負極と、有機溶媒や高分子固体電解質などの非水系電解質とからなり、充電により繰り返し使用が可能な非水電解質二次電池は、携帯用機器等の電源として近年広く研究されている。この非水電解質二次電池のうち、リチウムイオンが正極および負極に挿入・脱離することにより充放電を行うリチウムイオン電池は、高いエネルギー密度を有しているため、携帯電話、携帯用パソコン、ビデオカメラ等の電源として広く用いられている。このリチウムイオン電池の正極活物質としては、ＬｉＣｏＯ２が、高いエネルギー密度を有することや合成が容易であることから既に実用化されている。
【０００３】
しかし、近年のリチウムイオン電池の需要拡大に伴う更なる量産化を考えた場合、ＬｉＣｏＯ２の原料であるコバルトは埋蔵量が少ないため原料調達に支障をきたすおそれがある。また、価格が高いため材料コストの低減が困難であるという問題点もある。
【０００４】
そこで近年、ＬｉＣｏＯ２に代わってＬｉＮｉＯ２やＬｉＭｎ２Ｏ４を正極活物質とする試みがなされている。ＬｉＮｉＯ２は、原料のニッケルがコバルトと比較して安価であるのみならず、ＬｉＣｏＯ２と同様に高いエネルギー密度を有する。また、ＬｉＭｎ２Ｏ４は、原料のマンガンがニッケルと比較しても更に安価であるし、過充電時における安全性にも優れている。
【０００５】
しかし、ＬｉＮｉＯ２については、過充電時に結晶構造の変化により発熱するため、この熱により電池が分解・破裂するおそれがある等、安全面で問題がある。一方、ＬｉＭｎ２Ｏ４については、ＬｉＣｏＯ２やＬｉＮｉＯ２に比べて容量が低く、また繰り返し充放電を行った場合に結晶構造の変化に起因する容量劣化が起こるという問題点がある。
【０００６】
これらの問題点を解決するため特開平１１−３６９８号において、リチウムマンガン複合酸化物と、リチウムコバルト複合酸化物やリチウムニッケル複合酸化物を混合することにより、安価で容量や充放電サイクル特性に優れた正極活物質を得る方法が提案されている。
【０００７】
しかし、近年、携帯型機器に対する小型化要求に伴い、当該機器の電源として使用される二次電池に対しても更なる小型化が要求されている。このような状況の下では、前述の方法のように異なる種類のリチウム遷移金属複合酸化物を単に混合するだけでは正極活物質の充填密度を高めることができないため、単位容積あたりのエネルギー密度を十分に向上させることはできないという問題点があった。
【０００８】
一方、電気自動車やハイブリッド車向けの電源として用いる場合には発進・加速時に大きなパワーを要するので、当該二次電池には優れた高率放電特性が必要とされる。この点については以下のような問題点があった。すなわち、リチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径よりも大きい場合には、リチウムニッケル複合酸化物の反応性がリチウムマンガン複合酸化物と比較して相対的に低下してしまう。その結果、リチウムニッケル複合酸化物の有する優れた高率放電特性を効果的に発揮させることができないために十分な高率放電特性の非水電解質二次電池を得ることができなくなってしまうというものである。
【０００９】
【発明が解決しようとする課題】
本発明は上記事情に鑑みてなされたものであって、その目的は、安価で、高いエネルギー密度を有し、安全性に優れ、特に、優れた高率放電特性を有する非水電解質二次電池を提供することである。
【００１０】
【課題を解決するための手段】
請求項１の発明は、リチウムイオンを含む正極活物質の粒子を含有する正極と、リチウムイオン伝導性の非水電解質と、リチウムイオンを吸蔵放出可能な負極活物質を含有する負極とからなる非水電解質二次電池において、リチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを湿式混合して得たスラリーを噴霧乾燥することによって製造された正極活物質であって、前記正極活物質の粒子が各粒子内にリチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを含み、かつ前記リチウムニッケル複合酸化物の平均粒子径が前記リチウムマンガン複合酸化物の平均粒子径よりも小さいことを特徴とする。
【００１１】
請求項２の発明は、請求項１に記載の非水電解質二次電池において、前記正極活物質の各粒子に含まれる前記リチウムニッケル複合酸化物の平均粒子径が前記リチウムマンガン複合酸化物の平均粒子径の１０％以上５０％以下であることを特徴とする。
【００１２】
【発明の作用および効果】
請求項１の発明においては、次のような作用および効果が得られる。
【００１３】
まず、正極活物質の原料として高価で希少なコバルトを用いなくてすむことから、原料調達が容易になるし、また材料コストの低減が可能となる。
【００１４】
次に、正極活物質として、高いエネルギー密度を有するリチウムニッケル複合酸化物と安全性に優れたリチウムマンガン複合酸化物とを用いるので、エネルギー密度が高く、安全性に優れた非水電解質二次電池を得ることができる。
【００１５】
そして、正極活物質の粒子において、各粒子内にリチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを含有しているので、単に両者を混合した場合に比べてリチウムニッケル複合酸化物とリチウムマンガン複合酸化物の充填密度を高くすることができる。その結果、単に両者を混合した場合よりも単位容積あたりのエネルギー密度が高い非水電解質二次電池を得ることができる。
【００１６】
更に、リチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径よりも小さいために、正極活物質中におけるリチウムニッケル複合酸化物の反応性がリチウムマンガン複合酸化物と比較して相対的に高くなる。その結果、リチウムニッケル複合酸化物の有する優れた高率放電特性を効果的に発現させることができるので、当該正極活物質を使用することにより高率放電特性に優れた非水電解質二次電池を得ることができる。
【００１７】
請求項２の発明においては、請求項１の発明と同様に、安価で、高いエネルギー密度を有し、安全性に優れた非水電解質二次電池を得ることができる。これに加えて、前記リチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径の５０％以下であるために、リチウムニッケル複合酸化物の有する優れた高率放電特性を十分に発現させることができるので、請求項１の発明よりも高率放電特性に優れた非水電解質二次電池を得ることができる。また、前記リチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径の１０％以上であることから、取り扱い時の発塵が抑えられるので作業性が向上する。
【００１８】
【発明の実施の形態】
リチウムニッケル複合酸化物については、層状岩塩構造を有するＬｉＮｉＯ２を代表的に用いることができる。
【００１９】
リチウムニッケル複合酸化物は、ニッケル以外の金属を化学量論以上に添加して調製するなどによって、結晶格子中のニッケル原子の一部をこれらの金属で置換することができる。このようにニッケル原子と置換可能な金属元素としては、Ｌｉ、Ｂ、Ａｌ、Ｆｅ、Ｓｎ、Ｃｒ、Ｃｕ、Ｔｉ、Ｚｎ、Ｃｏ、Ｍｎ等の金属元素を挙げることができる。上記の金属元素の中では、Ｃｏ及び／又はＡｌによりニッケル原子を置換するのが好ましい。また、上述した金属元素の中から選ばれた複数の金属元素によりニッケル原子を置換することもできる。ただし、結晶構造を安定させることができるならば、ニッケル原子と置換される金属元素の種類はこれに限定されない。
【００２０】
ニッケル以外の金属元素により結晶格子中のニッケル原子の一部が置換されたリチウムニッケル複合酸化物は、層状岩塩構造を有する場合には通常、組成式ＬｉｘＮｉ１−ｙＭｙＯ２−ｚ（Ｍは置換した金属元素、０≦ｘ≦１．５、０＜ｙ≦１、−０．５≦ｚ≦０．５）で表すことができる。ただし、結晶構造を安定させることができるならば、リチウムニッケル複合酸化物の組成比はこれに限定されない。
【００２１】
リチウムマンガン複合酸化物については、スピネル構造を持つＬｉＭｎ２Ｏ４であってもよく、また、層状岩塩構造を持つＬｉＭｎＯ２であってもよい。
【００２２】
リチウムマンガン複合酸化物については、マンガン以外の金属を化学量論以上に添加して調製するなどによって、結晶格子中のマンガン原子の一部をこれらの金属で置換することができる。このようにマンガン原子と置換可能な金属元素としては、Ｌｉ、Ｂ、Ａｌ、Ｆｅ、Ｓｎ、Ｃｒ、Ｃｕ、Ｔｉ、Ｚｎ、Ｃｏ、Ｎｉ等を挙げることができる。上記の金属元素の中では、Ａｌ及び／又はＬｉによりマンガン原子を置換するのが好ましい。また、上述した金属元素の中から選ばれた複数の金属元素によりマンガン原子を置換することもできる。ただし、結晶構造を安定させることができるならば、マンガン原子と置換される金属元素の種類はこれに限定されない。
【００２３】
マンガン以外の金属元素により結晶格子中のマンガン原子の一部が置換されたリチウムマンガン複合酸化物は、スピネル構造を有する場合には通常、組成式ＬｉｘＭｎ２−ｙＭｙＯ４−ｚ（Ｍは置換した金属元素、０≦ｘ≦１．５、０＜ｙ≦１、−０．５≦ｚ≦０．５）で表すことができる。ただし、結晶構造を安定させることができるならば、リチウムマンガン複合酸化物の組成比はこれに限定されない。
【００２４】
本発明においては、上述したリチウムニッケル複合酸化物粒子から少なくとも１種類を選び、かつリチウムマンガン複合酸化物粒子から少なくとも１種類を選び、これらを混合した後にスラリー化し、このスラリーを乾燥することによって、リチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを各粒子内に含む正極活物質を製造できる。
【００２５】
両複合酸化物の好ましい混合比は、リチウムニッケル複合酸化物とリチウムマンガン複合酸化物との合計量に対してリチウムマンガン複合酸化物の割合が、通常１０ｍｏｌ％以上９０ｍｏｌ％以下であり、より好ましくは２０ｍｏｌ％以上８０ｍｏｌ％以下である。リチウムマンガン複合酸化物の割合が少なすぎると過充電時に電池が分解・破裂するおそれがある。一方、リチウムマンガン複合酸化物の割合が多すぎると、電池容量の不足、充放電サイクル特性の悪化という問題が生じるおそれがある。
【００２６】
リチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを混合する場合、得られたスラリーを続いて噴霧法により乾燥処理することができるので、処理手順の簡便性から湿式により混合するのが好ましい。湿式混合において通常使用する媒体としては水を用いることができるが、有機溶媒を用いることもできる。
【００２７】
上述のスラリーは、例えば５０℃〜３００℃の温度で、スプレードライヤー（噴霧乾燥機）による噴霧乾燥により乾燥される。当該乾燥工程により、リチウムマンガン複合酸化物とリチウムニッケル複合酸化物とを各粒子内に含む正極活物質を製造することができる。
【００２８】
リチウムニッケル複合酸化物の粒子、リチウムマンガン複合酸化物の粒子、正極活物質の粒子の平均粒子径については、日機装製マイクロトラックＵＰＡおよびＨＲＡを用い、レーザー回折・散乱法により測定した。
【００２９】
上記正極活物質においてリチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径よりも大きい場合には、リチウムニッケル複合酸化物の反応性がリチウムマンガン複合酸化物と比較して相対的に低くなるため、リチウムニッケル複合酸化物の有する優れた高率放電特性を十分に発現させることができなくなる。従って、リチウムニッケル複合酸化物の平均粒子径はリチウムマンガン複合酸化物の平均粒子径よりも小さいことを要する。取り扱い時の発塵などを考慮すると、好ましくは、リチウムニッケル複合酸化物の平均粒子径がリチウムマンガン複合酸化物の平均粒子径の１０％以上５０％以下である。
【００３０】
【実施例】
＜実施例１＞
平均粒子径１０μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．１μｍのＬｉＮｉＯ２１００ｇと、平均粒子径１０μｍのＬｉＭｎ２Ｏ４１００ｇを１Ｌのポリエチレン製容器に秤量し、これに純粋１００ｇを加えた後、ホモジナイザーにより湿式粉砕して平均粒子径０．２μｍとなったＬｉＭｎ２Ｏ４スラリーと、純水１００ｇとを混合し、再度ホモジナイザーにより湿式粉砕・混合を実施したスラリーをスプレードライヤーを用いて噴霧乾燥したところ、平均粒子径５μｍの、層状岩塩構造のリチウムニッケル複合酸化物とスピネル型リチウムマンガン複合酸化物との両者を含む正極活物質が得られた。
【００３１】
得られた正極活物質９１重量部に、結着剤であるポリフッ化ビニリデン６重量部と、導電剤であるアセチレンブラック３重量部とを混合した。これにＮ−メチル−ピロリドンを適宜加えてペースト状に調製した後、その合剤を厚さ２０μｍのアルミニウム箔の両面に塗布した。これを乾燥した後、加圧し、厚さが２００μｍ、幅１７５ｍｍの大きさに切り出して正極板を作成した。
【００３２】
負極ホスト物質としてのグラファイト８６部と、結着剤としてのポリフッ化ビニリデン１４部とを混合してペースト状に調製した後、その合剤を厚さ２０μｍの銅箔からなる集電体の表面に塗布した。これを乾燥した後、加圧し、１５０μｍ、幅１８０ｍｍの大きさに切り出して負極板を作成した。
【００３３】
セパレータには厚さ３５μｍ、幅２００ｍｍのポリエチレン微多孔膜を用いた。
【００３４】
これら正極板、セパレータ、負極板を順に重ね合わせ、ポリエチレンの巻芯を中心としてその周囲に長円渦状に巻いた後、電池ケースに収納した。電池ケースは直径６６ｍｍ、高さ２２０ｍｍの円筒形で、材質はステンレス３０４である。
【００３５】
電解液にはＬｉＰＦ６を１ｍｏｌ／ｌ含むエチレンカーボネート：ジエチルカーボネート＝１：１（体積比）の混合溶媒を用いた。
【００３６】
この電池を用いて、２．５ｍＡ／ｃｍ２の電流密度で充放電した際の正極層単位容積あたりの放電容量を測定したところ、１６０ｍＡｈ／ｃｍ３であった。
【００３７】
＜実施例２＞
平均粒子径１０μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．１μｍのＬｉＮｉＯ２１００ｇと、平均粒子径１５μｍのＬｉＭｎＯ４１００ｇをホモジナイザーにより湿式粉砕して得た平均粒子径０．３μｍのＬｉＭｎ２Ｏ４のスラリーとを用いた以外は実施例１と同様の手法により正極活物質を調製したところ、平均粒子径７．５μｍの正極活物質が得られた。
【００３８】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、１５０ｍＡｈ／ｃｍ３であった。
【００３９】
＜実施例３＞
平均粒子径１０μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．１μｍのＬｉＮｉＯ２１００ｇと、平均粒子径２０μｍのＬｉＭｎＯ４１００ｇをホモジナイザーにより湿式粉砕して得た平均粒子径０．４μｍのＬｉＭｎ２Ｏ４のスラリーとを用いた以外は実施例１と同様の手法により正極活物質を調製したところ、平均粒子径１０μｍの正極活物質が得られた。
【００４０】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、１４０ｍＡｈ／ｃｍ３であった。
【００４１】
＜実施例４＞
平均粒子径５μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．０５μｍのＬｉＮｉＯ２１００ｇと、平均粒子径１０μｍのＬｉＭｎＯ４１００ｇをホモジナイザーにより湿式粉砕して得た平均粒子径０．２μｍのＬｉＭｎ２Ｏ４のスラリーとを用いた以外は実施例１と同様の手法により正極活物質を調製したところ、平均粒子径３μｍの正極活物質が得られた。
【００４２】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、１５０ｍＡｈ／ｃｍ３であった。
【００４３】
＜実施例５＞
平均粒子径１０μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．１μｍのＬｉＮｉＯ２１００ｇと平均粒子径１０μｍのＬｉＭｎ２Ｏ４１００ｇとを、１Ｌポリエチレン容器に分取し、水２００ｇを加えてスラリーを調製した。このスラリーをホモジナイザー処理することなく、実施例１と同様の条件で噴霧乾燥したところ、平均粒子径１２μｍの、層状岩塩構造のリチウムニッケル複合酸化物とスピネル型リチウムマンガン複合酸化物との両者を含む正極活物質が得られた。
【００４４】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、１００ｍＡｈ／ｃｍ３であった。
【００４５】
【比較例】
＜比較例１＞
平均粒子径０．１μｍのＬｉＮｉＯ２１００ｇと平均粒子径１０μｍのＬｉＭｎ２Ｏ４１００ｇとを１Ｌポリエチレン容器に分取し、水を加えること無く密栓し、振とう機にかけて十分に乾式混合を行った。
【００４６】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、９０ｍＡｈ／ｃｍ３であった。
【００４７】
＜比較例２＞
平均粒子径２０μｍＬｉＮｉＯ２をジェットミルにより乾式粉砕して得た平均粒子径０．２μｍのＬｉＮｉＯ２１００ｇと、平均粒子径１０μｍのＬｉＭｎＯ４１００ｇをホモジナイザーにより湿式粉砕して得た平均粒子径０．２μｍのＬｉＭｎ２Ｏ４のスラリーとを用いた以外は実施例１と同様の手法により正極活物質を調製したところ、平均粒子径７．５μｍの正極活物質が得られた。
【００４８】
このようにして得られた正極活物質について実施例１と同様の方法により放電容量を測定したところ、１２０ｍＡｈ／ｃｍ３であった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
Nonaqueous electrolyte secondary batteries, which are composed of a positive electrode, a negative electrode, and a nonaqueous electrolyte such as an organic solvent or a polymer solid electrolyte, and can be repeatedly used by charging, have been widely studied in recent years as power sources for portable devices and the like. . Among these non-aqueous electrolyte secondary batteries, lithium ion batteries that charge and discharge by inserting and removing lithium ions from the positive electrode and the negative electrode have a high energy density, so that mobile phones, portable personal computers, Widely used as a power source for video cameras and the like. As a positive electrode active material of this lithium ion battery, LiCoO 2 has already been put into practical use because it has a high energy density and is easily synthesized.
[0003]
However, when considering further mass production in response to the recent increase in demand for lithium ion batteries, cobalt, which is a raw material for LiCoO 2 , has a small reserve amount, which may hinder raw material procurement. There is also a problem that it is difficult to reduce the material cost due to the high price.
[0004]
In recent years, attempts have been made to use LiNiO 2 or LiMn 2 O 4 as a positive electrode active material instead of LiCoO 2 . LiNiO 2 is not only cheaper than nickel as a raw material but also has a high energy density like LiCoO 2 . In addition, LiMn 2 O 4 is even cheaper than manganese as a raw material, and is excellent in safety during overcharge.
[0005]
However, since LiNiO 2 generates heat due to a change in crystal structure during overcharge, there is a problem in terms of safety such that the battery may be decomposed or ruptured by this heat. On the other hand, LiMn 2 O 4 has a problem that its capacity is lower than that of LiCoO 2 and LiNiO 2 , and capacity deterioration due to a change in crystal structure occurs when repeated charge / discharge is performed.
[0006]
In order to solve these problems, in Japanese Patent Laid-Open No. 11-3698, by mixing lithium manganese composite oxide, lithium cobalt composite oxide or lithium nickel composite oxide, it is inexpensive and has excellent capacity and charge / discharge cycle characteristics. A method for obtaining a positive electrode active material has been proposed.
[0007]
However, in recent years, with the demand for miniaturization of portable devices, further miniaturization is demanded for secondary batteries used as the power source of the devices. Under such circumstances, it is not possible to increase the packing density of the positive electrode active material simply by mixing different types of lithium transition metal composite oxides as in the above-described method, so that the energy density per unit volume is sufficient. However, there is a problem that it cannot be improved.
[0008]
On the other hand, when used as a power source for an electric vehicle or a hybrid vehicle, a large power is required at the time of start / acceleration. Therefore, the secondary battery is required to have excellent high rate discharge characteristics. In this regard, there were the following problems. That is, when the average particle size of the lithium nickel composite oxide is larger than the average particle size of the lithium manganese composite oxide, the reactivity of the lithium nickel composite oxide is relatively lower than that of the lithium manganese composite oxide. Resulting in. As a result, it is impossible to obtain a non-aqueous electrolyte secondary battery having sufficient high rate discharge characteristics because the excellent high rate discharge characteristics of the lithium nickel composite oxide cannot be exhibited effectively. It is.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and the object thereof is a non-aqueous electrolyte secondary battery that is inexpensive, has a high energy density, is excellent in safety, and particularly has excellent high rate discharge characteristics. Is to provide.
[0010]
[Means for Solving the Problems]
The invention of claim 1 is a non-electrode comprising a positive electrode containing particles of a positive electrode active material containing lithium ions, a lithium ion conductive non-aqueous electrolyte, and a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions. In a water electrolyte secondary battery, a positive electrode active material produced by spray drying a slurry obtained by wet mixing a lithium nickel composite oxide and a lithium manganese composite oxide, wherein the positive electrode active material particles are Each particle includes a lithium nickel composite oxide and a lithium manganese composite oxide, and an average particle size of the lithium nickel composite oxide is smaller than an average particle size of the lithium manganese composite oxide.
[0011]
The invention according to claim 2 is the nonaqueous electrolyte secondary battery according to claim 1, wherein an average particle diameter of the lithium nickel composite oxide contained in each particle of the positive electrode active material is an average of the lithium manganese composite oxide. It is characterized by being 10% or more and 50% or less of the particle diameter.
[0012]
Operation and effect of the invention
In the invention of claim 1, the following operations and effects can be obtained.
[0013]
First, since it is not necessary to use expensive and rare cobalt as a raw material for the positive electrode active material, raw material procurement becomes easy and material costs can be reduced.
[0014]
Next, since a lithium nickel composite oxide having a high energy density and a lithium manganese composite oxide excellent in safety are used as the positive electrode active material, the non-aqueous electrolyte secondary battery having high energy density and excellent safety Can be obtained.
[0015]
In addition, in the particles of the positive electrode active material, each of the particles contains a lithium nickel composite oxide and a lithium manganese composite oxide, so that the lithium nickel composite oxide and the lithium manganese composite are compared with the case where both are simply mixed. The packing density of the oxide can be increased. As a result, a nonaqueous electrolyte secondary battery having a higher energy density per unit volume than when both are simply mixed can be obtained.
[0016]
Furthermore, since the average particle size of the lithium nickel composite oxide is smaller than the average particle size of the lithium manganese composite oxide, the reactivity of the lithium nickel composite oxide in the positive electrode active material is higher than that of the lithium manganese composite oxide. Relatively high. As a result, the excellent high rate discharge characteristics possessed by the lithium nickel composite oxide can be effectively expressed. Therefore, a non-aqueous electrolyte secondary battery having excellent high rate discharge characteristics can be obtained by using the positive electrode active material. Can be obtained.
[0017]
In the invention of claim 2, as with the invention of claim 1, a non-aqueous electrolyte secondary battery that is inexpensive, has a high energy density, and is excellent in safety can be obtained. In addition, since the average particle diameter of the lithium nickel composite oxide is 50% or less of the average particle diameter of the lithium manganese composite oxide, the excellent high rate discharge characteristics of the lithium nickel composite oxide are sufficiently obtained. Since it can be expressed, a nonaqueous electrolyte secondary battery superior in high rate discharge characteristics than the invention of claim 1 can be obtained. Moreover, since the average particle diameter of the said lithium nickel complex oxide is 10% or more of the average particle diameter of a lithium manganese complex oxide, since dust generation at the time of handling is suppressed, workability | operativity improves.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
As the lithium nickel composite oxide, LiNiO 2 having a layered rock salt structure can be typically used.
[0019]
The lithium-nickel composite oxide can be prepared by adding a metal other than nickel in a stoichiometric amount or more to substitute a part of nickel atoms in the crystal lattice with these metals. Examples of metal elements that can be substituted for nickel atoms include metal elements such as Li, B, Al, Fe, Sn, Cr, Cu, Ti, Zn, Co, and Mn. Among the above metal elements, it is preferable to substitute nickel atoms with Co and / or Al. In addition, nickel atoms can be substituted with a plurality of metal elements selected from the metal elements described above. However, the kind of metal element substituted for the nickel atom is not limited to this as long as the crystal structure can be stabilized.
[0020]
A lithium nickel composite oxide in which a part of nickel atoms in the crystal lattice is substituted by a metal element other than nickel usually has a composition formula Li x Ni 1-y M y O 2-z when having a layered rock salt structure. (M is a substituted metal element, 0 ≦ x ≦ 1.5, 0 <y ≦ 1, −0.5 ≦ z ≦ 0.5). However, the composition ratio of the lithium nickel composite oxide is not limited to this as long as the crystal structure can be stabilized.
[0021]
The lithium manganese composite oxide may be LiMn 2 O 4 having a spinel structure or LiMnO 2 having a layered rock salt structure.
[0022]
The lithium manganese composite oxide can be prepared by adding a metal other than manganese in a stoichiometric amount or more. For example, a part of the manganese atom in the crystal lattice can be substituted with these metals. Examples of metal elements that can be substituted for manganese atoms include Li, B, Al, Fe, Sn, Cr, Cu, Ti, Zn, Co, and Ni. Among the above metal elements, it is preferable to substitute manganese atoms with Al and / or Li. In addition, the manganese atom can be substituted with a plurality of metal elements selected from the metal elements described above. However, the kind of metal element substituted for the manganese atom is not limited to this as long as the crystal structure can be stabilized.
[0023]
Lithium manganese composite oxide partially substituted manganese atoms in the crystal lattice of a metal element other than manganese, normally when it has a spinel structure, composition formula Li x Mn 2-y M y O 4-z ( M can be represented by a substituted metal element, 0 ≦ x ≦ 1.5, 0 <y ≦ 1, −0.5 ≦ z ≦ 0.5). However, the composition ratio of the lithium manganese composite oxide is not limited to this as long as the crystal structure can be stabilized.
[0024]
In the present invention, at least one type is selected from the above-described lithium nickel composite oxide particles, and at least one type is selected from the lithium manganese composite oxide particles. After mixing them, the slurry is formed, and the slurry is dried, A positive electrode active material containing lithium nickel composite oxide and lithium manganese composite oxide in each particle can be produced.
[0025]
A preferable mixing ratio of both composite oxides is that the ratio of the lithium manganese composite oxide to the total amount of the lithium nickel composite oxide and the lithium manganese composite oxide is usually 10 mol% or more and 90 mol% or less, more preferably It is 20 mol% or more and 80 mol% or less. If the proportion of the lithium manganese composite oxide is too small, the battery may be decomposed or ruptured during overcharge. On the other hand, if the proportion of the lithium manganese composite oxide is too large, there may be problems such as insufficient battery capacity and deterioration of charge / discharge cycle characteristics.
[0026]
When the lithium nickel composite oxide and the lithium manganese composite oxide are mixed , the obtained slurry can be subsequently subjected to a drying process by a spraying method. Therefore, it is preferable to mix by a wet process in view of the simplicity of the processing procedure. Water can be used as a medium usually used in wet mixing, but an organic solvent can also be used.
[0027]
The above-mentioned slurry is dried by spray drying with a spray dryer (spray dryer) at a temperature of 50 ° C. to 300 ° C., for example. By the drying step, a positive electrode active material containing a lithium manganese composite oxide and a lithium nickel composite oxide in each particle can be manufactured.
[0028]
The average particle size of the lithium nickel composite oxide particles, lithium manganese composite oxide particles, and positive electrode active material particles was measured by a laser diffraction / scattering method using Microtrack UPA and HRA manufactured by Nikkiso.
[0029]
In the positive electrode active material, when the average particle size of the lithium nickel composite oxide is larger than the average particle size of the lithium manganese composite oxide, the reactivity of the lithium nickel composite oxide is relative to that of the lithium manganese composite oxide. Therefore, the excellent high rate discharge characteristics possessed by the lithium nickel composite oxide cannot be sufficiently exhibited. Accordingly, the average particle size of the lithium nickel composite oxide needs to be smaller than the average particle size of the lithium manganese composite oxide. Considering dust generation during handling, the average particle diameter of the lithium nickel composite oxide is preferably 10% or more and 50% or less of the average particle diameter of the lithium manganese composite oxide.
[0030]
【Example】
<Example 1>
100 g of LiNiO 2 with an average particle size of 0.1 μm obtained by dry pulverizing an average particle size of 10 μmLiNiO 2 with a jet mill and 100 g of LiMn 2 O 4 with an average particle size of 10 μm were weighed into a 1 L polyethylene container, and pure After adding 100 g, a LiMn 2 O 4 slurry having an average particle size of 0.2 μm by wet pulverization with a homogenizer and 100 g of pure water were mixed, and the slurry that had been wet pulverized and mixed again with a homogenizer was sprayed with a spray dryer As a result, a positive electrode active material containing both a layered rock salt structure lithium nickel composite oxide and a spinel type lithium manganese composite oxide having an average particle diameter of 5 μm was obtained.
[0031]
To 91 parts by weight of the obtained positive electrode active material, 6 parts by weight of polyvinylidene fluoride as a binder and 3 parts by weight of acetylene black as a conductive agent were mixed. N-methyl-pyrrolidone was appropriately added thereto to prepare a paste, and the mixture was applied to both sides of an aluminum foil having a thickness of 20 μm. After drying this, it was pressurized and cut into a size of 200 μm thickness and 175 mm width to prepare a positive electrode plate.
[0032]
After preparing 86 parts of graphite as a negative electrode host material and 14 parts of polyvinylidene fluoride as a binder to prepare a paste, the mixture was applied to the surface of a current collector made of copper foil having a thickness of 20 μm. Applied. After drying this, it pressurized and cut out to the magnitude | size of 150 micrometers and width 180mm, and produced the negative electrode plate.
[0033]
A polyethylene microporous film having a thickness of 35 μm and a width of 200 mm was used as the separator.
[0034]
These positive electrode plate, separator, and negative electrode plate were superposed in order, wound in an oval spiral around the polyethylene core, and then housed in a battery case. The battery case has a cylindrical shape with a diameter of 66 mm and a height of 220 mm, and is made of stainless steel 304.
[0035]
As the electrolytic solution, a mixed solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) containing 1 mol / l of LiPF 6 was used.
[0036]
Using this battery, the discharge capacity per unit volume of the positive electrode layer when charged / discharged at a current density of 2.5 mA / cm 2 was measured and found to be 160 mAh / cm 3 .
[0037]
<Example 2>
An average particle size of 10 μmLiNiO 2 obtained by dry pulverization with a jet mill and 100 g of LiNiO 2 with an average particle size of 0.1 μm and LiMnO 4 100 g with an average particle size of 15 μm were obtained by wet pulverization with a homogenizer. When a positive electrode active material was prepared by the same method as in Example 1 except that the LiMn 2 O 4 slurry was used, a positive electrode active material having an average particle size of 7.5 μm was obtained.
[0038]
The discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1. As a result, it was 150 mAh / cm 3 .
[0039]
<Example 3>
An average particle size of 0.4 μm obtained by wet-pulverizing 100 g of LiNiO 2 with an average particle size of 0.1 μm and LiMnO 4 of 100 g with an average particle size of 20 μm obtained by dry pulverization of an average particle size of 10 μmLiNiO 2 with a jet mill. A positive electrode active material was prepared in the same manner as in Example 1 except that the LiMn 2 O 4 slurry was used. As a result, a positive electrode active material having an average particle diameter of 10 μm was obtained.
[0040]
The discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1. As a result, it was 140 mAh / cm 3 .
[0041]
<Example 4>
An average particle size of 0.2 μm obtained by wet-pulverizing 100 g of LiNiO 2 with an average particle size of 0.05 μm and 100 g of LiMnO 4 with an average particle size of 10 μm obtained by dry pulverization of an average particle size of 5 μmLiNiO 2 with a jet mill. A positive electrode active material was prepared in the same manner as in Example 1 except that the LiMn 2 O 4 slurry was used. As a result, a positive electrode active material having an average particle diameter of 3 μm was obtained.
[0042]
The discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1. As a result, it was 150 mAh / cm 3 .
[0043]
<Example 5>
100 g of LiNiO 2 with an average particle size of 0.1 μm and 100 g of LiMn 2 O 4 with an average particle size of 10 μm, obtained by dry pulverizing an average particle size of 10 μmLiNiO 2 with a jet mill, are dispensed into a 1 L polyethylene container, and 200 g of water is added. In addition, a slurry was prepared. When this slurry was spray-dried under the same conditions as in Example 1 without subjecting it to a homogenizer treatment, it contained both a layered rock salt structure lithium nickel composite oxide and a spinel type lithium manganese composite oxide having an average particle diameter of 12 μm. A positive electrode active material was obtained.
[0044]
When the discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1, it was 100 mAh / cm 3 .
[0045]
[Comparative example]
<Comparative Example 1>
100 g of LiNiO 2 with an average particle size of 0.1 μm and 100 g of LiMn 2 O 4 with an average particle size of 10 μm were dispensed into a 1 L polyethylene container, sealed without adding water, and thoroughly dry-mixed on a shaker. .
[0046]
The discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1. As a result, it was 90 mAh / cm 3 .
[0047]
<Comparative example 2>
An average particle diameter of 0.2 μm obtained by wet-pulverizing 100 g of LiNiO 2 with an average particle diameter of 0.2 μm and LiMnO 4 100 g with an average particle diameter of 10 μm obtained by dry pulverization of an average particle diameter of 20 μmLiNiO 2 with a jet mill. When a positive electrode active material was prepared by the same method as in Example 1 except that the LiMn 2 O 4 slurry was used, a positive electrode active material having an average particle size of 7.5 μm was obtained.
[0048]
The discharge capacity of the positive electrode active material thus obtained was measured by the same method as in Example 1. As a result, it was 120 mAh / cm 3 .
Claims (2)
リチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを湿式混合して得たスラリーを噴霧乾燥することによって製造された正極活物質であって、前記正極活物質の粒子が各粒子内にリチウムニッケル複合酸化物とリチウムマンガン複合酸化物とを含み、かつ前記リチウムニッケル複合酸化物の平均粒子径が前記リチウムマンガン複合酸化物の平均粒子径よりも小さいことを特徴とする非水電解質二次電池。In a nonaqueous electrolyte secondary battery comprising a positive electrode containing particles of a positive electrode active material containing lithium ions, a lithium ion conductive nonaqueous electrolyte, and a negative electrode containing a negative electrode active material capable of occluding and releasing lithium ions,
A positive electrode active material produced by spray drying a slurry obtained by wet mixing a lithium nickel composite oxide and a lithium manganese composite oxide, wherein the particles of the positive electrode active material are contained in each particle. A non-aqueous electrolyte secondary battery comprising an oxide and a lithium manganese composite oxide, wherein an average particle size of the lithium nickel composite oxide is smaller than an average particle size of the lithium manganese composite oxide.
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| JP2001316765A JP3610943B2 (en) | 2001-10-15 | 2001-10-15 | Nonaqueous electrolyte secondary battery |
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| JP5117730B2 (en) * | 2006-03-27 | 2013-01-16 | 日立マクセルエナジー株式会社 | Non-aqueous secondary battery and method of using the same |
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