JP3960691B2

JP3960691B2 - Anode active material for non-aqueous carbon-coated lithium secondary battery

Info

Publication number: JP3960691B2
Application number: JP25656298A
Authority: JP
Inventors: 秀治佐藤; 享布施; 正司石原
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 1998-09-10
Filing date: 1998-09-10
Publication date: 2007-08-15
Anticipated expiration: 2018-09-10
Also published as: JP2000090916A

Description

【０００１】
【発明の属する技術分野】
本発明は、小型、軽量の電気機器や電気自動車の電源として好適な、非水系リチウム二次電池、特に該二次電池用の負極活物質に関する。
【０００２】
【従来の技術】
近年、電子機器の小型化に伴い、高容量の二次電池が求められている。そのためニッケル・カドミウム電池、ニッケル・水素電池に比べ、よりエネルギー密度の高い非水系リチウム二次電池が注目されている。
【０００３】
負極材料としては、最初リチウム金属を用いることが試みられたが、充放電を繰り返すうちにデンドライト状のリチウムが析出し、セパレータを貫通して正極にまで達し、短絡して発火事故を起こす可能性があることが判明した。
【０００４】
また、特開昭５７−２０８０７９には、リチウムを負極活物質とし、電極板として結晶化度が高い黒鉛を使用することが提案された。しかしながら、黒鉛は充放電の原理にリチウムイオンの黒鉛結晶中へのインターカレーションを利用するため、常温、常圧下では、最大リチウム導入化合物のＬｉＣ₆から算出される黒鉛の理論容量である３７２mAh/gを超える放電容量が得られないとい問題があった。しかも、黒鉛材料の電解液との濡れ性の低さは、充放電初期のリチウム脱ドープ容量が、本来黒鉛材料が発現できるはずの３５０mAh/g以上の容量よりも低くなるという問題があった。
【０００５】
そこで、黒鉛性炭素質物の表面を炭素化可能な有機物で被覆、焼成した炭素質物を用いることが知られているが、この材料は充放電時の電位が黒鉛のそれと同様リチウム金属の酸化還元電位に近く、しかも黒鉛性炭素質物より高容量が得られるという利点があるが、やはり黒鉛の理論容量である３７２mAh/gを超える容量は得られていない。
【０００６】
更に、高容量を発現できる負極材料として、Ａｌ、Ｓｉなどリチウムのドープ、脱ドープが可能な金属を用いることが知られているが、この材料は電極表面での電解液の分解や、充放電サイクルに対する容量の低下に問題がある。
【０００７】
これらの問題を解決するために、特開平１−２９８６４５、特開平１−２５５１６５などには、炭素質物で金属粉末を被覆した負極材料を用いたリチウム二次電池が開示されている。炭素質物で金属材料を被覆することにより、充放電に伴う金属部分の構造的劣化を抑制できる作用があるものと考えられる。また、特開平１０−３９２０には、炭素質物に混合する金属の粒子の粒径を５００nm以下とすることが開示されている。炭素質物中の金属粒子の粒径を小さくすることで、充放電時に生じる金属部分の大きな体積変化が抑制され、サイクル効率の向上に寄与することが考えられるが、炭素質物に金属の微粒子を混合した後焼成しているため、金属の融解、凝集が起こり易く、制御が難しい。更に特開平８−２４１７１５には、金属酸化物などを炭素化又は黒鉛化可能な有機物を非酸化性雰囲気中で焼成した、炭素質物／金属複合負極材料が開示されているが、このときの焼成後の炭素質物に対する金属の割合は、４０重量％以下に限られており、具体的に製造されたものは約２０重量％以下のものである。
【０００８】
【発明が解決しようとする課題】
本発明の目的は、リチウムの充放電を行った場合に、従来の黒鉛系電極材料よりも高容量を発現でき、かつ負極材料の全重量に対する金属質物の含有量が多いにも関わらず、従来の炭素質物／金属質物複合負極材料よりサイクル劣化が小さい非水系リチウム二次電池用の負極活物質を提供することにある。
【０００９】
【課題を解決するための手段】
本発明は、熱処理後には電気化学的にリチウムイオンを吸蔵及び放出することができるようになる物質ａと炭素質物前駆体ｂとを混合、熱処理して、前記物質ａ由来の金属質物粒子が炭素質物で被覆された非水系リチウム二次電池用負極活物質であって、
（イ）上記物質ａが、元素周期表Ｉａ族、IIａ族、チタン、バナジウム、タンタル、VIａ族、マンガン、VIII族、Ｉｂ族、IIｂ族、IIIｂ族、IVｂ族、ヒ素、アンチモン及びビスマスから選ばれる元素の酸化物、硫化物、窒化物、セレン化物、テルル化物、硝酸塩、硫酸塩、あるいは該化合物を主成分とする複合化合物、及びこれら化合物の混合物から選ばれるものであり、
（ロ）かつ前記物質ａの二次粒子の平均粒径が１０μm以下か、又は一次粒子の平均粒径が５００nm以下であり、
（ハ）前記炭素質物前駆体ｂを熱処理した炭素質物の、学振法によって規定されたＸ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）が３．３８Å以上、及びｃ軸方向の結晶子の大きさ（Ｌｃ）が１００Å以下であり、かつ
（ニ）前記物質ａと物質ｂを熱処理した後の負極活物質中の金属質物の割合が５〜８５重量％である、負極活物質である。
【００１０】
【発明の実施の形態】
次に本発明の詳細を述べる。
【００１１】
「金属質物」
本発明の金属質物は、元素周期表Ｉａ族、IIａ族、チタン、バナジウム、タンタル、VIａ族、マンガン、VIII族、Ｉｂ族、IIｂ族、IIIｂ族、IVｂ族、ヒ素、アンチモン及びビスマスから選ばれる元素の酸化物、硫化物、窒化物、セレン化物、テルル化物、硝酸塩、硫酸塩、該化合物を主成分とする複合化合物、あるいはこれら化合物の混合物であり、該化合物粒子の二次粒子の平均粒径が１０μm以下か、又は一次粒子の平均粒径が５００nm以下のものを選択する。
【００１２】
上記化合物としては、上記の要件を満たす限り限定なく用いることができるが、具体的にはＡｇ₂Ｏ、Ａｌ₂Ｏ₃、Ｂｉ₂Ｏ₃、ＣｄＯ、ＣｒＯ₂、Ｃｒ₂Ｏ₃、Ｃｕ₂Ｏ、Ｆｅ₂Ｏ₃、Ｉｎ₂Ｏ₃、ＩｒＯ₂、ＭｇＯ、ＭｎＯ₂、Ｍｎ₂Ｏ₃、ＯｓＯ₂、ＯｓＯ₄、ＰｂＯ、Ｐｂ₃Ｏ₄、ＰｂＯ₂、ＰｄＯ、ＰｔＯ、ＲｕＯ₂、ＳｎＯ、ＳｎＯ₂，ＳｉＯ、ＳｉＯ₂、ＴａＯ₂、ＴｉＯ、Ｔｉ₂Ｏ₃、ＴｉＯ₂、Ｖ₂Ｏ₃、Ｖ₂Ｏ₄、Ｖ₂Ｏ₅、ＶＯ₂、Ｖ₂Ｏ₃、ＷＯ、ＷＯ₂、ＷＯ₃、ＺｎＯ等の金属酸化物；Ｂｉ₂Ｓ₃、ＣｄＳ、Ｉｎ₂Ｓ₃、ＰｂＳ、ＰｔＳ、ＳｎＳ、ＳｎＳ₂、ＴａＳ₂、ＴｉＳ₂、Ｖ₂Ｓ₃、Ｖ₂Ｓ₂、ＷＳ₂、ＺｎＳ等の金属硫化物；Ｂｉ₂Ｔｅ₃、ＳｎＴｅ、ＳｎＴｅ₂、ＷＴｅ₂、ＺｎＴｅ等の金属テルル化物；Ｓｉ₃Ｎ₄、ＴａＳｉ₂、ＴｉＳｉ₂、Ｖ₃Ｓｉ、Ｖ₂Ｓｉ、ＷＳｉ₂等の金属ケイ化物；ＡｌＮ、ＴａＮ、Ｗ₂Ｎ、ＷＮ等の金属窒化物；これら前述の金属化合物から選択されるものの複合金属化合物；又はこれらとアルカリ金属の複合酸化物；アルカリ土類金属との複合酸化物；前述のいずれかの金属化合物と同士の複合金属化合物；更には、これらのものから選択された化合物同士の混合物を用いることができる。錫酸、錫酸塩、一酸化錫、二酸化錫、錫酸アルカリ金属塩、錫酸アルカリ土類金属塩、錫酸アンモニウム、錫酸アンチモン、酸化アンチモン、一酸化ケイ素、酸化銀、酸化亜鉛、酸化アルミ及び二酸化ケイ素が挙げられる。
【００１３】
物質ａの平均粒径が上記範囲より大きいと、熱処理後においても完全に金属質物まで還元されにくい、あるいは粒径が大きい物を全量還元できるような温度まで熱処理温度を引き上げる、あるいは熱処理時間を長くする等の工程を行うと、絶縁性の炭素質物が多量に形成され、負極容量の低下につながる等の問題が生じてくる化合物もある。また、前述したような金属化合物の代わりに金属質物そのものを炭素質物前駆体と混合し熱処理すると、金属の融点が炭素化が始まる温度以下にあることが多いため、金属質物同士の融着がおこり、熱処理後に炭素質物と分離したり、たとえ炭素質物中に取り込まれても大きく粒成長してしまい、負極としたときサイクルの維持率が悪くなる。
【００１４】
本発明では、炭素化が始まる温度以下では構造が安定で、融解、凝集を起こしにくい前述の物質ａを使用することで、熱処理後に炭素質物中に、前記物質ａ由来の金属質物の粒子を、より細かいまま保持することができる。更に、使用する物質ａの粒子径が小さく、一般的に金属質物よりも表面積が大きいため、炭素質物前駆体ｂとの混合段階において、分散性及び／又は相溶性に優れ、熱処理後にもより均質な材料を作成できる。
【００１５】
本発明に使用される前記物質ａは、その粒子の二次粒子の平均粒径が１０〜０．０１μm、好ましくは７〜０．０５μm、更に好ましくは５〜０．１μmのもの、又は一次粒子の平均粒径が５００〜１nm、好ましくは４００〜３nmのものである。具体的には、例えば粒径１０nmのシリカ超微粒子、アルミノシリカの超微粒子、酸化錫又は酸化錫と酸化アンチモンの複合金属酸化物の一次粒子の平均粒径５nmの超微粒子が特に好ましい。また、これらの粒子を溶媒に分散させたゲル、酸化錫の表面を有機物で被覆した一次粒子の平均粒径１０nmの酸化錫ゾル、これを溶媒に分散させたゲル等は特に好ましい。
【００１６】
「炭素質物前駆体ｂ」
本発明で述べる「炭素質物前駆体」とは、後述する、熱処理後には電気化学的にリチウムイオンを吸蔵及び放出することができるようになる物質ａとともに熱処理された後は、リチウムイオンを吸蔵及び放出可能な性質を有する有機化合物である。
【００１７】
具体的には、炭素化可能な有機物として、液相で炭素化が進行する軟ピッチから硬ピッチまでのコールタールピッチや、乾留液化油などの石炭系重質油や、常圧残油、減圧残油等の直流系重質油、原油、ナフサなどの熱分解時に副生するエチレンタール等分解系重質油等の石油系重質油、あるいは以上のものを炭素化が進む以下の温度で蒸留、溶媒抽出等の手段を経て固化したものが挙げられる。更にアセナフチレン、デカシクレン、アントラセンなどの芳香族炭化水素；フェナジンやアクリジンなどの窒素含有環状化合物；チオフェンなどの硫黄含有環状化合物；３０MPa以上の加圧が必要となるがアダマンタンなどの脂環が挙げられる。炭素化可能な熱可塑性高分子としては、炭素化に至る過程で液相を経るビフェニルやテルフェニルなどのポリフェニレン；ポリ塩化ビニル、ポリ酢酸ビニル、ポリビニルブチラールなどのポリビニルエステル類；ポリビニルアルコールが挙げられる。また、以上に列挙した有機物、高分子に適量のリン酸、ホウ酸、塩酸等の酸類、水酸化ナトリウム等のアルカリ類を添加したものでもよい。更にこれらのものを１００〜６００℃、好ましくは２００〜４００℃で、酸素、硫黄、窒素又はホウ素から選ばれる元素により、適度に架橋処理したものでもよい。適度な架橋構造を炭素質物又は炭素質物前駆体中に形成することにより、後述する金属質物を安定に系内に保持することができ、更に熱処理中に起こる金属質物の凝集を妨げる効果も生じる。
【００１８】
これらの炭素質物前駆体を熱処理した後の炭素質物の性質は、学振法によって規定されたＸ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）が３．３８Å以上、及びｃ軸方向の結晶子の大きさ（Ｌｃ）が１００Å以下のものを選択するとよい。
【００１９】
物質ａと炭素質物前駆体ｂの混合方法としては、従来の方法を限定なく用いることが可能であるが、それぞれの原料の状態に合わせ、「マイクロス」^R分散機、アキシャルミキサー、ホモジェナイザー、ホモディスパーザー、ペイントシェーカー、加熱式二軸混練機、加熱式ブレードニーダー、メカノヒュージョン、ボールミル、ジェットミル、ハイブリダイゼーションマシン、あるいはＶブレンダー等を用いると、より均一に前駆体同士が混合されるので好ましい。これらの混合方法は適宜組み合わせて用いてもよい。これらの混合方法には、混合と同時に解砕や粉砕を行えるものもあり、それらを用いた場合には、混合前の物質ａの一次又は二次粒子の平均粒径が、上記の範囲外にあっても、混合、解砕、あるいは粉砕が行われることで、最終的に上記の平均粒径の範囲内に収まればよい。
上記の混合後、６００〜２，０００℃、より好ましくは７００〜１，５００℃、更に好ましくは８００〜１，３００℃で、好ましくは還元的雰囲気下で熱処理し、その後、解砕、あるいは粉砕し、１〜１００μm、好ましくは５〜５０μmの平均粒径をもつ電極活物質として使用する。
【００２０】
熱処理、解砕、粉砕等の工程を経て最終調製された電極材料粉体において、粉体全体を１００重量％としたとき、金属質物は５〜８５重量％で、炭素質物前駆体の熱処理物の含量は１５〜９５重量％である。金属質物は１５〜８０重量％、更には３５〜７０重量％、特に４０〜６５重量％であることが好ましい。なお、上記範囲は原料仕込み比ではなく、最終的な調製段階での含有量である。そのため、仕込み時には、最終段階での組成比を考慮して原料の配合量を決定する必要がある。これより金属質物の含有量が少ないと、リチウム電池を組立てたときに、実際上大きな放電容量の増加が見込めず、またこれ以上の含有量であると、金属質物を炭素質物が被覆することができず、また、熱処理段階で金属質物同士が融解、凝集するなどして粒子径が大きく成長してしまうため、電池のサイクルの維持が難しくなる。
【００２１】
本発明の負極活物質の製造方法は、上記物質ａと物質ｂを使用する限り限定なく、従来公知の方法が採用可能である。例えば、有機化合物と金属化合物を加熱手段がある混合機で、最終組成が上記範囲内となる仕込み比で混合し、脱気・脱揮処理を行い、６００〜２，０００℃で０．１〜１２時間、好ましくは７００〜１，５００℃、特に好ましくは８００〜１，３００℃で０．５〜５時間焼成し、この熱処理物を、好ましくは１〜１００μm、更に好ましくは５〜５０μmの範囲に解砕又は粉砕して、該負極活物質粉体を得る。
【００２２】
次に、本発明の負極活物質を用いて、電池を製造する方法について説明する。上記負極活物質粉体に結着剤、溶媒等を加えてスラリー状とし、銅箔等の金属製の集電体の基板に、このスラリーを塗布・乾燥して電極とする。また、該負極活物質をそのままロール成形、圧縮成形等の方法で電極の形状に成形することもできる。
【００２３】
上記の目的で使用できる結着剤としては、溶媒に対して安定な、ポリエチレン、ポリプロピレン、ポリエチレンテレフタレート、芳香族ポリアミド、セルロース等の樹脂系高分子；スチレン・ブタジエンゴム、イソプレンゴム、ブタジエンゴム、エチレン・プロピレンゴム等のゴム状高分子；スチレン・ブタジエン・スチレンブロック共重合体、その水素添加物、スチレン・エチレン・ブタジエン・スチレン共重合体、スチレン・イソプレン・スチレンブロック共重合体、その水素添加物等の熱可塑性エラストマー状高分子；シンジオタクチック１，２−ポリブタジエン、エチレン・酢酸ビニル共重合体、プロピレン・α−オレフィン（炭素数２〜１２）共重合体等の軟質樹脂状高分子；ポリフッ化ビニリデン、ポリテトラフルオロエチレン、エチレン共重合体等のフッ素系高分子；アルカリ金属イオン、特にリチウムイオンのイオン伝導性を有する高分子組成物が挙げられる。
【００２４】
上記のイオン伝導性を有する高分子としては、ポリエチレンオキシド、ポリプロピレンオキシド等のポリエーテル系高分子化合物；ポリエーテル化合物の架橋体高分子；ポリエピクロルヒドリン、ポリホスファゼン、ポリシロキサン、ポリビニルピロリドン、ポリビニリデンカーボネート、ポリアクリロニトリル等の高分子化合物に、リチウム塩、又はリチウムを主体とするアルカリ金属塩を複合させた系、あるいはこれにプロピレンカーボネート、エチレンカーボネート、γ−ブチロラクトン等の高い誘電率を有する有機化合物を配合した系を用いることができる。
【００２５】
負極活物質粉体と上記の結着剤との混合形態としては、各種の形態をとることができる。即ち、両者の粒子が混合した形態、繊維状の結着剤が該電極粒子に絡み合う形で混合した形態、又は結着剤の層が電極粒子表面に付着した形態などが挙げられる。該電極粉体と上記結着剤との混合割合は、電極粉体に対し、好ましくは０．１〜３０重量％、より好ましくは０．３〜２０重量％、特に好ましくは０．５〜１０重量％である。これ以上の量の結着剤を添加すると、電極の内部抵抗が大きくなり、好ましくなく、これ以下の量では集電体と電極粉体の結着性に劣る。
【００２６】
こうして作製した負極板と、以下に説明する電解液及び正極板を、その他の電池構成要素であるセパレータ、ガスケット、集電体、封口板、セルケース等と組み合わせて二次電池を構成する。作成可能な電池は、筒型、角型、コイン型等特に限定されるものではないが、基本的にはセル床板上に集電体と負極板を乗せ、その上に電解液とセパレータを、更に負極と対向するように正極を乗せ、ガスケット、封口板と共にかしめて二次電池とする。
【００２７】
電解液用に使用できる非水溶媒としては、プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、エチルメチルカーボネート、１，２−ジメトキシエタン、γ−ブチロラクトン、テトラヒドロフラン、テトラヒドロフラン、２−メチルテトラヒドロフラン、スルホラン、１，３−ジオキソラン等の公知の有機溶媒の単独、又は二種類以上を混合したものを用いることができる。
【００２８】
これらの溶媒に、０．５〜２．０M程度のＬｉＣｌＯ₄、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＡｓＦ₆、ＬｉＣｌ、ＬｉＢｒ等の公知の電解質を溶解して電解液とする。
【００２９】
また、リチウムイオン等のアルカリ金属カチオンの導電体である高分子固体電解質を用いることもできる。
【００３０】
正極材料は特に限定されないが、リチウムイオンなどのアルカリ金属カチオンを充放電時に吸蔵、放出できる金属カルコゲン化合物からなることが好ましい。そのような金属カルコゲン化合物としては、バナジウム酸化物、バナジウム硫化物、モリブデン酸化物、モリブデン硫化物、マンガン酸化物、クロム酸化物、チタン酸化物、チタン硫化物及びこれらの複合酸化物、複合硫化物等が挙げられる。好ましくはＣｒ₃Ｏ₈、Ｖ₂Ｏ₅、Ｖ₅Ｏ₁₃、ＶＯ₂、Ｃｒ₂Ｏ₅、ＭｎＯ₂、ＴｉＯ₂、ＭｏＶ₂Ｏ₈、ＴｉＳ₂Ｖ₂Ｓ₅ＭｏＳ₂、ＭｏＳ₃ＶＳ₂、Ｃｒ_0.25Ｖ_0.75Ｓ₂、Ｃｒ_0.5Ｖ_0.5Ｓ₂等である。またＬｉＭＹ₂（Ｍは、Ｃｏ、Ｎｉ，Ｆｅ等の遷移金属、ＹはＯ、Ｓ等のカルコゲン化合物）、ＬｉＭ₂Ｙ₄（ＭはＭｎ、ＹはＯ）、あるいはこれらの酸化物の不定比化合物、ＷＯ₃等の酸化物、ＣｕＳ、Ｆｅ_0.25Ｖ_0.75Ｓ₂、Ｎａ_0.1ＣｒＳ₂等の硫化物、ＮｉＰＳ₃、ＦｅＰＳ₃等のリン、硫黄化合物、ＶＳｅ₂、ＮｂＳｅ₃等のセレン化合物等を用いることもできる。これらを負極体と同様、結着剤と混合して集電体の上に塗布して正極体とする。
【００３１】
電解液を保持するセパレーターは、一般的に保液性に優れた材料であり、例えばポリオレフィン系樹脂の不織布や多孔性フィルム等を使用して、上記電解液を含浸させる。
【００３２】
【実施例】
次に実施例により本発明を更に詳細に説明するが、本発明はこれらの例によってなんら限定されるものではない。
【００３３】
電極材料の評価方法
評価は以下のように行った。結着剤を用いてペレット状に成形した上記の負極体を、セパレーター、電解液と共に、対極をリチウム金属とした半電池とし、２０１６コインセル中に組み立て、充放電試験機で充放電容量を評価したが、正極体とともに組んだ全電池でも同様な効果が期待できる。
【００３４】
（実施例１）
二次粒子の平均粒径０．６μm（一次粒子の平均粒径４００nm）の酸化錫（IV）（ＳｎＯ₂；福井新素材（株）製）微粒子粉と、コールタールピッチを熱処理して得た揮発分（以下、ＶＭと称す）が２２．１％で、ガンマレジン量が２５．０％で、かつ原子比Ｏ／Ｃが０．００９である原料（以下、ピッチＡと称す）を、空気の存在下で機械的エネルギーを付与しながら２８０℃で１時間処理して得られた固体を粉末化した。得られた粉体を、回分式加熱炉で不活性雰囲気下にて、９００℃に保ち、１時間熱処理した。不活性雰囲気下で放冷後、得られた粉体を解砕し、１０〜２５μmに整え、サンプル粉体とした。該粒子の炭素質部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）は３．４７Å、及びｃ軸方向の結晶子の大きさ（Ｌｃ）が２３Åであった。また、元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、４７重量％であった。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
なお、揮発分（ＶＭ）は、ＪＩＳ−Ｍ８８１２に従って、ガンマレジン量は、ＪＩＳ−Ｋ２４２５に従ってトルエン不溶分量を測定して、それぞれ求めた。
また、酸素含有量（原子比Ｏ／Ｃ）は、炭素及び酸素の重量含有率からそれぞれの原子量を用いて計算した。炭素の含有量は、全自動元素分析装置（パーキンエルマー社製「ＣＨＮ計２４０Ｃ」）で測定した。酸素含有量は、酸素窒素分析装置（ＬＥＣＯ社製「ＴＣ４３６」）を用い、試料１０mgをニッケルカプセルに封入し、ヘリウム気流下において３００Wで３００秒、続いて５，５００Wで１００秒加熱し、発生ガス中の二酸化炭素を赤外吸収より定量して求めた。
この電極材料サンプル２ｇに対し、ポリフッ化ビニリデン（ＰＶｄＦ）のジメチルアセトアミド溶液を固形分換算で１０重量％加えたものを撹拌し、スラリーを得た。このスラリーを銅箔上に塗布し、８０℃で予備乾燥した。更に圧着したのち、直径１２．５mmの円盤状に打ち抜き、１１０℃で減圧乾燥して電極とした。
得られた電極に対し、電解液を含浸させたポリプロピレン製セパレーターをはさみ、リチウム金属電極に対向させたコイン型セルを作製し、充放電試験を行った。電解液には、エチレンカーボネートとジエチルカーボネートを容量比１：１の比率で混合した溶媒に、過塩素酸リチウムを１．０mol/Lの割合で溶解させたものを用いた。
基準充放電試験は、電流密度０．１６mA/cm²で極間電位差が０Ｖになるまでドープを行い、電流密度０．３３mA/cm²で極間電位差が１．５Ｖになるまで脱ドープを行った。
容量値は、コイン型セル３個について各々充放電試験を行い、第１回目の充放電時サイクルのドープ容量、脱ドープ容量の平均、及び第４回目の放電容量を初回の放電容量で割った値の１００分率（容量維持率％）で評価した。炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００３５】
【表１】

【００３６】
（実施例２）
実施例１において、二次粒子の平均粒径０．６μm（一次粒子の平均粒径４００nm）の酸化錫（IV）（ＳｎＯ₂；福井新素材（株）製）微粒子粉のピッチＡに対する混合量を多くし、熱処理後の元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、６５重量％である以外は、実施例１と同様の操作を行った。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００３７】
（実施例３）
実施例１における金属質物部分が、一次粒子の粒径５０〜２００nmにある酸化アンチモン（Ｓｂ₂Ｏ₃；高純度化学試薬）と、実施例１で用いた酸化錫（IV）の混合物であり、熱処理後のアンチモンと錫の重量比がＳｎ：Ｓｂ＝９：１となるように調整し、熱処理後の元素分析から算出された炭素質物／金属質物複合粉体内の金属質物の含有量が、粉体全体を１００重量％としたとき、５７重量％である以外は、実施例１と同様の操作を行った。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫・アンチモン合金微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００３８】
（実施例４）
実施例１で用いた二次粒子の粒径０．６μmの酸化錫（IV）（ＳｎＯ₂；和光純薬試薬）粉を、石油系ピッチであるエチレンヘビーエンド（三菱化学製）とともに、室温で「マイクロス」^R分散機により撹拌、均一混合した。得られたスラリー状の混合物を、回分式加熱炉で窒素／酸素混合雰囲気下にて、３５０℃で１時間熱処理し、その後９００℃に保ち、更に１時間熱処理した。不活性雰囲気下で放冷後、得られた粉体を粉砕し、１０〜２５μmに整えてサンプル粉体とした。該元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、４０重量％であった。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００３９】
（実施例５）
二次粒子の平均粒径２μmの酸化錫（IV）（ＳｎＯ₂；和光純薬試薬）粉と、石油系ピッチであるエチレンヘビーエンド（三菱化学製）を、常温で「マイクロス」^R分散機により撹拌、均一混合した以外は、実施例１と同様の操作を行った。元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５７重量％であった。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４０】
（実施例６）
実施例５の二次粒子の平均粒径２μmの酸化錫（IV）（ＳｎＯ₂；和光純薬試薬）を用い、石油系ピッチであるエチレンヘビーエンド（三菱化学製）に対する混合量を多くした以外は、実施例５と同様の操作を行った。熱処理後の元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、７４重量％であった。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４１】
（実施例７）
酸化錫（IV）微粒子の表面を有機物で被覆した一次粒子の平均粒径５nmのものを、石油系ピッチであるエチレンヘビーエンド（三菱化学製）に添加し、室温で「マイクロス」^R分散機により均一混合した。得られた粉体を、回分式加熱炉で不活性雰囲気下にて９００℃に保ち、１時間熱処理した。撹拌し、均一混合した以外は、実施例１と同様の操作を行った。熱処理後の元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５６重量％であった。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４２】
（実施例８）
実施例１における金属質物部分が、酸化錫（IV）・酸化アンチモン分子混合酸化物微粒子の表面を有機物で被覆した一次粒子の平均粒径５nmのものであり、熱処理後のアンチモンと錫の重量比がＳｎ：Ｓｂ＝９：１となるように調整し、熱処理後の元素分析から算出された炭素質物／金属質物複合粉体内の金属質物の含有量が、粉体全体を１００重量％としたとき、５２重量％である以外は、実施例１と同様の操作を行った。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫・アンチモン合金微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌc）とともに、結果を表１に示す。
【００４３】
（実施例９）
一次粒子の平均粒径５nmの酸化錫（IV）・酸化アンチモンの分子状混合酸化物の微粒子を、アンモニア性水溶液（pH１０．８）に分散させたのものを、水溶性フェノール樹脂エマルジョン（群栄化学製）に添加し、ホモディスパーザーにより室温で撹拌した。得られたスラリー状の物を不活性ガス雰囲気下、１００℃で３時間熱処理し固化させた。これを軽く解砕し、得られた粉体を回分式加熱炉で不活性雰囲気下にて９００℃に保ち、１時間熱処理した。熱処理後のアンチモンと錫の重量比がＳｎ：Ｓｂ＝９３：７となるように調整した。熱処理後の元素分析から算出された炭素質物／金属質物複合粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５７重量％であった。電極製造方法、評価方法は、実施例１と同様の操作を行った。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫・アンチモン合金微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４４】
（実施例１０）
実施例９における金属質物部分が、一次粒子の平均粒径５nmの酸化錫（IV）（pH１０．７）であり、熱処理後の元素分析から算出された炭素質物／金属質物複合粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５６重量％である以外は、実施例１と同様の操作を行った。
この粉体を走査型顕微鏡で観察したところ、炭素質物マトリックス中に被覆された錫金属微粒子が高分散しているのが見られた。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４５】
（比較例１）
二次粒子の平均粒径２μmの酸化錫（IV）（ＳｎＯ₂；Aldrich製）粉と、石油系ピッチであるエチレンヘビーエンド（三菱化学製）を、大気中で撹拌、均一混合した。得られたスラリーを回分式加熱炉で不活性雰囲気下にて９００℃に保ち、１時間熱処理した。不活性雰囲気下で放冷後、得られた粉体を解砕しようとしたところ、錫粒子の大きな成長（最大６μm程度）がみられ、電極には成形できなかった。また、元素分析から算出された該粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、９５重量％であった。
【００４６】
（比較例２）
金属質物部分が、二次粒子の平均粒径２０μmの酸化錫（IV）であり、元素分析から算出された熱処理後の炭素質物／金属質物複合粉体内の金属質物の含有量が、粉体全体を１００重量％としたとき、６５重量％である以外は、実施例１と同様の操作を行った。
炭素質物部分の粉末Ｘ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）、及びｃ軸方向の結晶子の大きさ（Ｌｃ）とともに、結果を表１に示す。
【００４７】
（比較例３）
金属質物部分が、二次粒子の平均粒径１０μmの錫金属である以外は、比較例１と同様の操作を行った。得られた粉体を解砕しようとしたところ、錫粒子の大きな成長（最大５００μm程度）がみられ、電極には成形できなかった。元素分析から算出された熱処理後の炭素質物／金属質物複合粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５０重量％であった。
【００４８】
（比較例４
実施例１で、炭素質物前駆体を熱処理した、炭素質物の水素／炭素の原子比が０．０２、学振法によって規定されたＸ線広角回折法による（００２）面の面間隔（ｄ₀₀₂）が３．４１Å、及びｃ軸方向の結晶子の大きさ（Ｌｃ）が２８０Åであり、元素分析から算出された熱処理後の炭素質物／金属質物複合粉体内の金属質物の含有量は、粉体全体を１００重量％としたとき、５１重量％である以外は、実施例１と同様の操作を行った。得られた粉体を解砕しようとしたところ、錫粒子の大きな成長（最大２００μm程度）がみられ、電極には成形できなかった。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous lithium secondary battery, particularly a negative electrode active material for the secondary battery, which is suitable as a power source for small and lightweight electric devices and electric vehicles.
[0002]
[Prior art]
In recent years, with the miniaturization of electronic equipment, a high-capacity secondary battery is required. Therefore, non-aqueous lithium secondary batteries with higher energy density are attracting attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
[0003]
Attempts were made to use lithium metal as the negative electrode material, but dendritic lithium precipitated during repeated charging and discharging, could reach the positive electrode through the separator, and could cause a fire accident due to a short circuit. Turned out to be.
[0004]
Japanese Patent Laid-Open No. 57-208079 proposed using lithium as a negative electrode active material and graphite having a high crystallinity as an electrode plate. However, since graphite uses intercalation of lithium ions into graphite crystals for charge / discharge principle, at a normal temperature and normal pressure, the theoretical capacity of graphite calculated from the maximum lithium-introduced compound LiC ₆ is 372 mAh / There was a problem that a discharge capacity exceeding g could not be obtained. Moreover, the low wettability of the graphite material with the electrolytic solution has a problem that the lithium dedoping capacity at the initial stage of charge and discharge is lower than the capacity of 350 mAh / g or more that should originally be able to express the graphite material.
[0005]
Therefore, it is known to use a carbonaceous material obtained by coating the surface of a graphitic carbonaceous material with an organic material that can be carbonized and calcining, but this material has a redox potential of lithium metal similar to that of graphite. However, a capacity exceeding 372 mAh / g, which is the theoretical capacity of graphite, has not been obtained.
[0006]
Furthermore, it is known to use a metal capable of doping and undoping lithium, such as Al and Si, as a negative electrode material capable of developing a high capacity. There is a problem in capacity reduction with respect to the cycle.
[0007]
In order to solve these problems, JP-A-1-298645, JP-A-1-255165, and the like disclose lithium secondary batteries using a negative electrode material in which a metal powder is coated with a carbonaceous material. By covering the metal material with a carbonaceous material, it is considered that there is an action capable of suppressing the structural deterioration of the metal part due to charge / discharge. Japanese Patent Application Laid-Open No. 10-3920 discloses that the particle size of the metal particles mixed with the carbonaceous material is 500 nm or less. By reducing the particle size of the metal particles in the carbonaceous material, it is conceivable that the large volume change of the metal part that occurs during charging and discharging is suppressed, contributing to the improvement of cycle efficiency. After firing, the metal is easily melted and aggregated and is difficult to control. Further, JP-A-8-241715 discloses a carbonaceous material / metal composite negative electrode material obtained by firing an organic substance capable of carbonizing or graphitizing a metal oxide or the like in a non-oxidizing atmosphere. The ratio of the metal to the subsequent carbonaceous material is limited to 40% by weight or less, and specifically produced is about 20% by weight or less.
[0008]
[Problems to be solved by the invention]
The object of the present invention is that when lithium charge / discharge is performed, a higher capacity than that of a conventional graphite-based electrode material can be expressed, and the content of the metal material relative to the total weight of the negative electrode material is high. An object of the present invention is to provide a negative electrode active material for a non-aqueous lithium secondary battery that has less cycle degradation than the carbonaceous / metal composite composite negative electrode material.
[0009]
[Means for Solving the Problems]
In the present invention, after the heat treatment, the substance a and the carbonaceous material precursor b capable of electrochemically inserting and extracting lithium ions are mixed and heat-treated, and the metal material particles derived from the substance a are carbonized. A negative electrode active material for a non-aqueous lithium secondary battery coated with a material,
(A) The substance a is selected from Group Ia, Group IIa, Titanium, Vanadium, Tantalum, Group VIa, Manganese, Group VIII, Group Ib, Group IIb, Group IIIb, Group IVb, Arsenic, Antimony, and Bismuth Selected from oxides, sulfides, nitrides, selenides, tellurides, nitrates, sulfates, or complex compounds based on these compounds, and mixtures of these compounds,
(B) and the average particle size of secondary particles of the substance a is 10 μm or less, or the average particle size of primary particles is 500 nm or less,
(C) The carbonaceous material obtained by heat-treating the carbonaceous material precursor b has a (002) plane spacing (d ₀₀₂ ) of 3.38 mm or more by the X-ray wide angle diffraction method defined by the Gakushin method, and the c-axis direction. And (d) the proportion of the metal material in the negative electrode active material after heat-treating the substance a and the substance b is 5 to 85% by weight. It is a substance.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, details of the present invention will be described.
[0011]
"Metallic material"
The metallic substance of the present invention is selected from Group Ia, Group IIa, Titanium, Vanadium, Tantalum, Group VIa, Manganese, Group VIII, Group Ib, Group IIb, Group IIIb, Group IVb, Arsenic, Antimony, and Bismuth. Elemental oxides, sulfides, nitrides, selenides, tellurides, nitrates, sulfates, complex compounds based on these compounds, or mixtures of these compounds, the average particle size of secondary particles of the compound particles A particle having a diameter of 10 μm or less or a primary particle having an average particle diameter of 500 nm or less is selected.
[0012]
The compound can be used without limitation as long as the above requirements are satisfied. Specifically, Ag ₂ O, Al ₂ O ₃ , Bi ₂ O ₃ , CdO, CrO ₂ , Cr ₂ O ₃ , Cu ₂ O can be used. Fe ₂ O ₃ , In ₂ O ₃ , IrO ₂ , MgO, MnO ₂ , Mn ₂ O ₃ , OsO ₂ , OsO ₄ , PbO, Pb ₃ O ₄ , PbO ₂ , PdO, PtO, RuO ₂ , SnO, SnO _{_{2, SiO, SiO 2, TaO}} 2, TiO, Ti 2 O 3, TiO 2, V 2 O 3, V 2 O 4, V 2 O 5, VO 2, V 2 O 3, WO, WO 2, WO 3 Metal oxides such as ZnO; Bi ₂ S ₃ , CdS, In ₂ S ₃ , PbS, PtS, SnS, SnS ₂ , TaS ₂ , TiS ₂ , V ₂ S ₃ , V ₂ S ₂ , WS ₂ , ZnS, etc. metal _{_{sulfides; Bi 2 Te 3, SnTe,}} SnTe 2, WTe 2, ZnTe and the like of the metal ether _{_{_{Iodide; Si 3 N 4, TaSi 2}}} , TiSi 2, V 3 Si, V 2 Si, a metal silicide such as _{WSi 2; AlN, TaN, W} 2 N, metal nitrides such as WN; these aforementioned metal compounds A composite metal compound of a selected one; or a composite oxide of these and an alkali metal; a composite oxide of an alkaline earth metal; a composite metal compound of any of the aforementioned metal compounds; A mixture of the obtained compounds can be used. Stannic acid, stannate, tin monoxide, tin dioxide, alkali metal stannate, alkaline earth metal stannate, ammonium stannate, antimony stannate, antimony oxide, silicon monoxide, silver oxide, zinc oxide, oxidation Aluminum and silicon dioxide are mentioned.
[0013]
If the average particle size of the substance a is larger than the above range, the heat treatment temperature is raised to a temperature at which it is difficult to completely reduce the metallic material even after the heat treatment, or the entire material having a large particle size can be reduced, or the heat treatment time is lengthened. When a process such as this is performed, there is a compound in which a large amount of insulating carbonaceous material is formed, resulting in a problem that the negative electrode capacity is reduced. In addition, when the metal material itself is mixed with the carbonaceous material precursor and heat-treated instead of the metal compound as described above, the melting point of the metal is often below the temperature at which carbonization starts, so that the metal materials are fused to each other. When it is separated from the carbonaceous material after heat treatment, or even if it is taken into the carbonaceous material, it grows large grains, and when it is used as a negative electrode, the cycle maintenance rate is deteriorated.
[0014]
In the present invention, by using the above-mentioned substance a, which has a stable structure below the temperature at which carbonization begins and is less likely to melt and aggregate, particles of the metal substance derived from the substance a in the carbonaceous substance after heat treatment, It can be kept finer. Further, since the substance a used has a small particle size and generally has a larger surface area than the metal material, it is excellent in dispersibility and / or compatibility in the mixing stage with the carbonaceous material precursor b, and is more homogeneous after heat treatment. You can make the right material.
[0015]
The substance a used in the present invention has an average secondary particle size of 10 to 0.01 μm, preferably 7 to 0.05 μm, more preferably 5 to 0.1 μm, or primary particles. Have an average particle diameter of 500 to 1 nm, preferably 400 to 3 nm. Specifically, ultrafine particles having an average particle diameter of 5 nm, for example, ultrafine particles of silica having a particle diameter of 10 nm, ultrafine particles of aluminosilica, or primary particles of tin oxide or a composite metal oxide of tin oxide and antimony oxide are particularly preferable. Further, a gel in which these particles are dispersed in a solvent, a tin oxide sol having an average particle diameter of 10 nm in which the surface of tin oxide is coated with an organic substance, a gel in which these are dispersed in a solvent, and the like are particularly preferable.
[0016]
“Carbonaceous precursor b”
The “carbonaceous material precursor” described in the present invention refers to a lithium ion that is stored and absorbed after the heat treatment with a substance a that can electrochemically store and release lithium ions after heat treatment, which will be described later. Organic compounds with releasable properties.
[0017]
Specifically, as carbonizable organic substances, coal-tar heavy pitches from soft pitch to hard pitch, where carbonization proceeds in the liquid phase, heavy coal oils such as dry distillation liquefied oil, atmospheric residual oil, reduced pressure DC heavy oil such as residual oil, petroleum heavy oil such as ethylene tar cracked heavy oil produced as a by-product during thermal cracking of crude oil, naphtha, etc. A solidified product by means of distillation, solvent extraction or the like. Furthermore, aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; nitrogen-containing cyclic compounds such as phenazine and acridine; sulfur-containing cyclic compounds such as thiophene; and an alicyclic ring such as adamantane although pressure of 30 MPa or more is required. Examples of the carbonizable thermoplastic polymer include polyphenylenes such as biphenyl and terphenyl that undergo a liquid phase in the process of carbonization; polyvinyl esters such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral; and polyvinyl alcohol. . Further, organic materials and polymers listed above may be those obtained by adding an appropriate amount of acids such as phosphoric acid, boric acid and hydrochloric acid, and alkalis such as sodium hydroxide. Further, these may be appropriately crosslinked at 100 to 600 ° C., preferably 200 to 400 ° C., with an element selected from oxygen, sulfur, nitrogen or boron. By forming an appropriate cross-linked structure in the carbonaceous material or the carbonaceous material precursor, the metallic material described later can be stably held in the system, and further, an effect of preventing the aggregation of the metallic material that occurs during the heat treatment also occurs.
[0018]
The properties of the carbonaceous material after heat-treating these carbonaceous material precursors are such that the (002) plane spacing (d ₀₀₂ ) is 3.38 mm or more by the X-ray wide angle diffraction method defined by the Gakushin method, and the c-axis It is preferable to select a crystallite size (Lc) in the direction of 100 mm or less.
[0019]
As a mixing method of the substance a and the carbonaceous material precursor b, a conventional method can be used without limitation, but according to the state of each raw material, “Micros” ^R disperser, axial mixer, homogenizer , Homodispersers, paint shakers, heated biaxial kneaders, heated blade kneaders, mechano-fusions, ball mills, jet mills, hybridization machines, or V blenders can be used to mix precursors more uniformly. Therefore, it is preferable. These mixing methods may be used in appropriate combination. Some of these mixing methods can be pulverized or pulverized simultaneously with mixing. When these are used, the average particle size of the primary or secondary particles of the substance a before mixing is out of the above range. Even if it exists, it should just be settled in the range of said average particle diameter by mixing, crushing, or grinding | pulverization finally.
After the above mixing, heat treatment is performed at 600 to 2,000 ° C., more preferably 700 to 1,500 ° C., further preferably 800 to 1,300 ° C., preferably in a reducing atmosphere, and then pulverized or pulverized. And used as an electrode active material having an average particle diameter of 1 to 100 μm, preferably 5 to 50 μm.
[0020]
In the electrode material powder finally prepared through processes such as heat treatment, pulverization, and pulverization, when the total powder is 100% by weight, the metal material is 5 to 85% by weight, and the heat treatment product of the carbonaceous material precursor is The content is 15 to 95% by weight. The metallic substance is preferably 15 to 80% by weight, more preferably 35 to 70% by weight, and particularly preferably 40 to 65% by weight. The above range is not the raw material charge ratio but the content at the final preparation stage. Therefore, at the time of preparation, it is necessary to determine the blending amount of the raw material in consideration of the composition ratio in the final stage. If the content of the metallic material is less than this, when the lithium battery is assembled, a practically large increase in discharge capacity cannot be expected, and if the content is more than this, the carbonaceous material may cover the metallic material. In addition, it is difficult to maintain the cycle of the battery because the particle size grows large by melting and agglomerating metal materials in the heat treatment stage.
[0021]
The method for producing the negative electrode active material of the present invention is not limited as long as the material a and the material b are used, and a conventionally known method can be adopted. For example, an organic compound and a metal compound are mixed in a mixer having a heating means at a charging ratio in which the final composition is within the above range, and degassing / devolatilization treatment is performed. It is calcined for 12 hours, preferably 700 to 1,500 ° C., particularly preferably 800 to 1,300 ° C. for 0.5 to 5 hours, and this heat-treated product is preferably in the range of 1 to 100 μm, more preferably 5 to 50 μm. The negative electrode active material powder is obtained by crushing or pulverizing.
[0022]
Next, a method for producing a battery using the negative electrode active material of the present invention will be described. A binder, a solvent or the like is added to the negative electrode active material powder to form a slurry, and this slurry is applied to a substrate of a metal current collector such as a copper foil and dried to form an electrode. Further, the negative electrode active material can be directly formed into the shape of an electrode by a method such as roll molding or compression molding.
[0023]
Binders that can be used for the above-mentioned purposes include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, and cellulose that are stable to solvents; styrene-butadiene rubber, isoprene rubber, butadiene rubber, and ethylene.・ Rubber polymers such as propylene rubber; styrene / butadiene / styrene block copolymer, hydrogenated product thereof, styrene / ethylene / butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer, hydrogenated product thereof Thermoplastic elastomeric polymers such as syndiotactic 1,2-polybutadiene, soft resinous polymers such as ethylene / vinyl acetate copolymer, propylene / α-olefin (carbon number 2 to 12) copolymer; Vinylidene fluoride, polytetrafluoroethylene Fluorine polymers such as ethylene copolymers; alkali metal ions, the polymer composition may be mentioned in particular has an ionic conductivity of lithium ions.
[0024]
Examples of the polymer having ion conductivity include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether compounds; polyepichlorohydrin, polyphosphazene, polysiloxane, polyvinyl pyrrolidone, polyvinylidene carbonate, A compound in which a polymer compound such as polyacrylonitrile is combined with a lithium salt or an alkali metal salt mainly composed of lithium, or an organic compound having a high dielectric constant such as propylene carbonate, ethylene carbonate, or γ-butyrolactone is blended with this. System can be used.
[0025]
As a mixed form of the negative electrode active material powder and the above-mentioned binder, various forms can be taken. That is, a form in which both particles are mixed, a form in which a fibrous binder is entangled with the electrode particles, or a form in which a binder layer is attached to the surface of the electrode particles. The mixing ratio of the electrode powder and the binder is preferably from 0.1 to 30% by weight, more preferably from 0.3 to 20% by weight, particularly preferably from 0.5 to 10%, based on the electrode powder. % By weight. Addition of a binder in an amount larger than this increases the internal resistance of the electrode, which is not preferred. If the amount is less than this, the binding property between the current collector and the electrode powder is poor.
[0026]
A secondary battery is configured by combining the negative electrode plate thus prepared, the electrolyte solution described below, and the positive electrode plate with other battery components such as a separator, a gasket, a current collector, a sealing plate, and a cell case. The battery that can be created is not particularly limited, such as a cylindrical shape, a square shape, a coin shape, etc., but basically a current collector and a negative electrode plate are placed on a cell floor plate, and an electrolyte and a separator are placed thereon. Further, a positive electrode is placed so as to face the negative electrode, and caulked together with a gasket and a sealing plate to obtain a secondary battery.
[0027]
Non-aqueous solvents that can be used for the electrolyte include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, A known organic solvent such as 1,3-dioxolane or a mixture of two or more of them can be used.
[0028]
A known electrolyte such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr or the like is dissolved in these solvents to obtain an electrolytic solution.
[0029]
A polymer solid electrolyte that is a conductor of an alkali metal cation such as lithium ion can also be used.
[0030]
The positive electrode material is not particularly limited, but is preferably made of a metal chalcogen compound that can occlude and release alkali metal cations such as lithium ions during charge and discharge. Examples of such metal chalcogen compounds include vanadium oxide, vanadium sulfide, molybdenum oxide, molybdenum sulfide, manganese oxide, chromium oxide, titanium oxide, titanium sulfide, and composite oxides and composite sulfides thereof. Etc. Preferably _{_{_{Cr 3 O 8, V 2 O}}} 5, V 5 O 13, VO 2, Cr 2 O 5, MnO 2, TiO 2, MoV 2 O 8, TiS 2 V 2 S 5 MoS 2, MoS 3 VS 2, Cr _0.25 V _0.75 S ₂ , Cr _0.5 V _0.5 S _2, etc. LiMY ₂ (M is a transition metal such as Co, Ni, Fe, etc., Y is a chalcogen compound such as O, S, etc.), LiM ₂ Y ₄ (M is Mn, Y is O), or non-stoichiometry of these oxides Compounds, oxides such as WO ₃ , sulfides such as CuS, Fe _0.25 V _0.75 S ₂ and Na _0.1 CrS ₂ , phosphorus such as NiPS ₃ and FePS ₃ , sulfur compounds, selenium compounds such as VSe ₂ and NbSe _3, etc. It can also be used. As with the negative electrode body, these are mixed with a binder and applied onto the current collector to form a positive electrode body.
[0031]
The separator for holding the electrolytic solution is generally a material having excellent liquid retaining properties, and is impregnated with the electrolytic solution using, for example, a polyolefin resin nonwoven fabric or a porous film.
[0032]
【Example】
EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
[0033]
The evaluation method of the electrode material was evaluated as follows. The negative electrode body formed into a pellet using a binder was made into a half battery with a separator and an electrolyte solution and a counter electrode made of lithium metal, assembled into a 2016 coin cell, and the charge / discharge capacity was evaluated with a charge / discharge tester. However, the same effect can be expected with all batteries assembled together with the positive electrode body.
[0034]
Example 1
Obtained by heat-treating tin (IV) oxide (SnO ₂ ; manufactured by Fukui Shin Material Co., Ltd.) fine particle powder having an average secondary particle diameter of 0.6 μm (average primary particle diameter of 400 nm) and coal tar pitch. A raw material (hereinafter referred to as pitch A) having a volatile content (hereinafter referred to as VM) of 22.1%, a gamma resin amount of 25.0%, and an atomic ratio O / C of 0.009 is used. The solid obtained by processing at 280 ° C. for 1 hour while applying mechanical energy in the presence was pulverized. The obtained powder was heat-treated in a batch heating furnace at 900 ° C. in an inert atmosphere for 1 hour. After cooling in an inert atmosphere, the obtained powder was crushed and adjusted to 10 to 25 μm to obtain a sample powder. The interplanar spacing (d ₀₀₂ ) of the (002) plane of the carbonaceous part of the particles by a powder X-ray wide angle diffraction method was 3.47 mm, and the crystallite size (Lc) in the c-axis direction was 23 mm. The content of the metallic substance in the powder calculated from elemental analysis was 47% by weight when the entire powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The volatile content (VM) was determined according to JIS-M8812, and the amount of gamma resin was determined by measuring the amount of insoluble toluene according to JIS-K2425.
The oxygen content (atomic ratio O / C) was calculated from the weight content of carbon and oxygen using the respective atomic weights. The carbon content was measured with a fully automatic elemental analyzer ("CHN meter 240C" manufactured by PerkinElmer). Oxygen content is generated by using an oxygen-nitrogen analyzer (“TC436” manufactured by LECO), enclosing 10 mg of a sample in a nickel capsule, heating in a helium stream for 300 seconds at 300 W, and subsequently heating at 5,500 W for 100 seconds. Carbon dioxide in the gas was quantified by infrared absorption.
To 2 g of this electrode material sample, 10% by weight of a dimethylacetamide solution of polyvinylidene fluoride (PVdF) added in terms of solid content was stirred to obtain a slurry. This slurry was applied onto a copper foil and pre-dried at 80 ° C. After further pressure bonding, it was punched into a disk shape having a diameter of 12.5 mm and dried under reduced pressure at 110 ° C. to obtain an electrode.
The obtained electrode was sandwiched with a polypropylene separator impregnated with an electrolytic solution to produce a coin cell facing the lithium metal electrode, and a charge / discharge test was performed. As the electrolytic solution, a solution in which lithium perchlorate was dissolved at a rate of 1.0 mol / L in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used.
Reference charge and discharge test was performed to dope at a current density of 0.16 mA / cm ² until the interelectrode potential difference becomes to 0V, and subjected to undoping at a current density of 0.33 mA / cm ² until the interelectrode potential difference becomes 1.5V It was.
The capacity value was obtained by performing a charge / discharge test on each of the three coin-type cells, and dividing the doping capacity in the first charging / discharging cycle, the average of the dedoping capacity, and the fourth discharging capacity by the initial discharging capacity. The value was evaluated at 100 minutes (capacity maintenance rate%). The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0035]
[Table 1]

[0036]
(Example 2)
In Example 1, the amount of tin (IV) oxide (SnO ₂ ; manufactured by Fukui Shin Material Co., Ltd.) fine particles with an average secondary particle size of 0.6 μm (average primary particle size of 400 nm) mixed with pitch A The content of the metallic substance in the powder calculated from the elemental analysis after the heat treatment was the same as in Example 1 except that the content was 65% by weight when the whole powder was 100% by weight. Went.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0037]
(Example 3)
The metal part in Example 1 is a mixture of antimony oxide (Sb ₂ O ₃ ; high-purity chemical reagent) having a primary particle size of 50 to 200 nm and tin (IV) oxide used in Example 1, The weight ratio of antimony and tin after heat treatment was adjusted to be Sn: Sb = 9: 1, and the content of the metal material in the carbonaceous material / metal material composite powder calculated from the elemental analysis after the heat treatment was The same operation as in Example 1 was carried out except that the total body was 100% by weight and that it was 57% by weight.
When this powder was observed with a scanning microscope, it was found that the tin / antimony alloy fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0038]
Example 4
The tin (IV) oxide (SnO ₂ ; Wako Pure Chemical Reagent) powder with a secondary particle size of 0.6 μm used in Example 1 was mixed with petroleum heavy pitch ethylene heavy end (Mitsubishi Chemical) at room temperature. “Micros” The mixture was stirred and uniformly mixed with an ^R disperser. The obtained slurry mixture was heat-treated at 350 ° C. for 1 hour in a batch heating furnace in a nitrogen / oxygen mixed atmosphere, then kept at 900 ° C. and further heat-treated for 1 hour. After cooling in an inert atmosphere, the obtained powder was pulverized and adjusted to 10 to 25 μm to obtain a sample powder. The content of the metallic substance in the powder calculated from the elemental analysis was 40% by weight when the entire powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0039]
(Example 5)
"Micros" ^R disperser at room temperature with tin (IV) oxide (SnO ₂ ; Wako Pure Chemical Reagents) powder with an average secondary particle size of 2 μm and petroleum heavy pitch ethylene heavy end (Mitsubishi Chemical) The same operation as in Example 1 was performed except that stirring and uniform mixing were performed. The content of the metallic substance in the powder calculated from elemental analysis was 57% by weight when the entire powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0040]
(Example 6)
Except for using tin (IV) oxide (SnO ₂ ; Wako Pure Chemical Reagent) with an average particle size of 2 μm as secondary particles of Example 5 and increasing the amount of mixing with ethylene heavy end (Mitsubishi Chemical), which is a petroleum pitch. The same operation as in Example 5 was performed. The content of the metallic substance in the powder calculated from elemental analysis after the heat treatment was 74% by weight when the entire powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0041]
(Example 7)
"Micros" ^R disperser is added at room temperature to the particles of tin oxide (IV), whose primary particles are coated with organic matter and have an average particle size of 5nm, and are added to ethylene heavy end (Mitsubishi Chemical), which is a petroleum pitch. To mix evenly. The obtained powder was heat-treated for 1 hour at 900 ° C. in an inert atmosphere in a batch heating furnace. The same operation as in Example 1 was performed except that stirring and uniform mixing were performed. The content of the metallic substance in the powder calculated from elemental analysis after the heat treatment was 56% by weight when the whole powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0042]
(Example 8)
The metal part in Example 1 is an average particle diameter of 5 nm of primary particles obtained by coating the surface of tin oxide (IV) / antimony oxide molecule mixed oxide fine particles with an organic substance, and the weight ratio of antimony and tin after heat treatment Is adjusted so that Sn: Sb = 9: 1, and the content of the metallic substance in the carbonaceous substance / metallic substance composite powder calculated from the elemental analysis after the heat treatment is 100% by weight of the whole powder The same operation as in Example 1 was performed except that the content was 52% by weight.
When this powder was observed with a scanning microscope, it was found that the tin / antimony alloy fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0043]
Example 9
A water-soluble phenol resin emulsion (Gunei Chemical Co., Ltd.) obtained by dispersing fine particles of molecular mixed oxide of tin oxide (IV) and antimony oxide with an average primary particle size of 5 nm in an aqueous ammoniacal solution (pH 10.8). And stirred at room temperature with a homodisperser. The obtained slurry was heat-treated at 100 ° C. for 3 hours in an inert gas atmosphere and solidified. This was lightly crushed, and the obtained powder was heat-treated for 1 hour in a batch heating furnace at 900 ° C. in an inert atmosphere. The weight ratio of antimony and tin after heat treatment was adjusted to be Sn: Sb = 93: 7. The content of the metallic material in the carbonaceous material / metallic composite powder calculated from the elemental analysis after the heat treatment was 57% by weight when the entire powder was 100% by weight. The electrode manufacturing method and the evaluation method were the same as in Example 1.
When this powder was observed with a scanning microscope, it was found that the tin / antimony alloy fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0044]
(Example 10)
The metal substance part in Example 9 is tin (IV) oxide (pH 10.7) having an average primary particle diameter of 5 nm, and the metal substance in the carbonaceous substance / metal substance composite powder calculated from the elemental analysis after the heat treatment. The content of was the same as that of Example 1 except that it was 56% by weight when the whole powder was 100% by weight.
When this powder was observed with a scanning microscope, it was found that tin metal fine particles coated in the carbonaceous material matrix were highly dispersed.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0045]
(Comparative Example 1)
Tin (IV) oxide (SnO ₂ ; manufactured by Aldrich) powder having an average particle size of 2 μm and secondary heavy ethylene ethylene end (manufactured by Mitsubishi Chemical) were stirred and uniformly mixed in the atmosphere. The resulting slurry was heat treated for 1 hour in a batch heating furnace at 900 ° C. in an inert atmosphere. When the obtained powder was allowed to cool after being allowed to cool in an inert atmosphere, large growth of tin particles (about 6 μm at maximum) was observed, and the electrode could not be molded. Further, the content of the metallic substance in the powder calculated from elemental analysis was 95% by weight when the whole powder was 100% by weight.
[0046]
(Comparative Example 2)
The metallic substance part is tin oxide (IV) having an average particle diameter of 20 μm of secondary particles, and the content of the metallic substance in the carbonaceous substance / metallic substance composite powder after heat treatment calculated from elemental analysis is the whole powder. Was 100% by weight, and the same operation as in Example 1 was performed except that the amount was 65% by weight.
The results are shown in Table 1 together with the (002) plane spacing (d ₀₀₂ ) and the crystallite size (Lc) in the c-axis direction by powder X-ray wide angle diffraction of the carbonaceous material part.
[0047]
(Comparative Example 3)
The same operation as in Comparative Example 1 was performed except that the metallic material part was tin metal having an average particle size of 10 μm of secondary particles. When the obtained powder was crushed, a large growth of tin particles (about 500 μm at the maximum) was observed, and the electrode could not be molded. The content of the metal material in the carbonaceous material / metal material composite powder after the heat treatment calculated from elemental analysis was 50% by weight when the entire powder was 100% by weight.
[0048]
(Comparative Example 4
In Example 1, the carbonaceous material precursor was heat-treated, and the hydrogen / carbon atomic ratio of the carbonaceous material was 0.02, and the (002) plane spacing (d ₀₀₂ ) by the X-ray wide angle diffraction method defined by the Gakushin method ) Is 3.41 mm, and the crystallite size (Lc) in the c-axis direction is 280 mm, and the content of the metal material in the carbonaceous material / metal material composite powder after heat treatment calculated from elemental analysis is The same operation as in Example 1 was performed except that the total body was 100% by weight and that the amount was 51% by weight. When the obtained powder was crushed, a large growth of tin particles (up to about 200 μm) was observed, and the electrode could not be molded.

Claims

After the heat treatment, the material a and the carbonaceous material precursor b capable of electrochemically inserting and extracting lithium ions are mixed and heat-treated, and the metal material particles derived from the material a are coated with the carbonaceous material. A negative active material for a non-aqueous lithium secondary battery,
(A) The substance a is one or more selected from the group consisting of tin monoxide, tin dioxide, silicon monoxide, silicon dioxide and antimony oxide,
(B) The average particle size of secondary particles of the substance a is 10 μm or less, or the average particle size of primary particles is 500 nm or less,
(C) The carbonaceous material obtained by heat-treating the substance b has a (002) plane spacing (d ₀₀₂ ) of 3.38 mm or more by the X-ray wide angle diffraction method defined by the Gakushin method, and a crystallite in the c-axis direction And (d) the proportion of the metallic material in the negative electrode active material after heat-treating the substance a and the substance b is 35 to 85% by weight.
Negative electrode active material.

The negative electrode active material according to claim 1, wherein the heat treatment is performed in a temperature range of 600 to 2,000 ° C.

The negative electrode active material according to claim 2, wherein the heat treatment is performed in a temperature range of 700 to 1,500 ° C. 4.

The negative electrode active material according to claim 1, wherein the substance a is tin dioxide.

The negative electrode active material according to any one of claims 1 to 4, wherein the substance a is an oxide particle whose particle surface is coated with an organic substance, or a dispersion of the particle in a solvent.

The interplanar spacing (d ₀₀₂ ) of the (002) plane according to the X-ray wide angle diffraction method defined by the Gakushin method of the carbonaceous material obtained by heat-treating the substance b is 3.38 to 3.65 mm. The negative electrode active material according to any one of 5.

The negative electrode active material according to claim 1, wherein the substance b has a structure in which molecules of an organic compound are molecularly cross-linked with oxygen, sulfur, nitrogen, and / or boron atoms.

The negative electrode active material according to claim 7, wherein the crosslinked structure is formed by firing at 100 to 600 ° C.

(D) The negative electrode active material of any one of Claims 1-8 whose ratio of the metal substance in the negative electrode active material after heat-processing the said substance a and the said substance b is 35 to 70 weight%.

A non-aqueous lithium secondary battery comprising a negative electrode comprising the negative electrode active material according to claim 1, a positive electrode, and an electrolytic solution.

A method for producing a negative electrode active material for a non-aqueous lithium secondary battery in which metal particles derived from the substance a capable of electrochemically inserting and extracting lithium ions after heat treatment are coated with a carbonaceous material. ,
(1) (I) It is at least one selected from the group consisting of tin monoxide, tin dioxide, silicon monoxide, silicon dioxide and antimony oxide, and (b) the average particle size of the secondary particles is 10 μm or less, Or a step of preparing a substance a in which the average particle size of primary particles is 500 nm or less;
(2) preparing a carbonaceous material precursor b;
(3) mixing the substance a and the substance b;
(4) A step of firing the mixed mixture to reduce the substance a to obtain a negative electrode active material in which the metal particles derived from the substance a are coated with a carbonaceous material;
Including
The negative electrode active material
(C) The carbonaceous material obtained by heat-treating the substance b has a (002) plane spacing (d ₀₀₂ ) of 3.38 mm or more by the X-ray wide angle diffraction method specified by the Gakushin method, and a crystallite in the c-axis direction. The size (Lc) is 100 mm or less, and (d) the ratio of the metallic material in the negative electrode active material after the heat treatment of the material a and the material b is 35 to 85% by weight.
A method characterized by that.

The manufacturing method of the negative electrode active material of Claim 11 which bakes by the temperature range of 700-1500 degreeC at a process (4).

The method for producing a negative electrode active material according to claim 11 or 12, wherein the substance a is tin dioxide.

The method for producing a negative electrode active material according to any one of claims 11 to 13, wherein the substance a is an oxide particle whose particle surface is coated with an organic substance, or a dispersion of the particle in a solvent.

A method for producing a non-aqueous lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, wherein the negative electrode active material is produced by the method according to claim 11.