JP2004296412A

JP2004296412A - Method of manufacturing negative electrode active material for non-aqueous electrolyte secondary battery

Info

Publication number: JP2004296412A
Application number: JP2003105798A
Authority: JP
Inventors: Yoshiki Sakaguchi; 善樹坂口; Tomoyoshi Matsushima; 智善松島; Kiyotaka Yasuda; 清隆安田; Kazuko Taniguchi; 和子谷口; Makoto Dobashi; 誠土橋
Original assignee: Mitsui Mining and Smelting Co Ltd
Current assignee: Mitsui Mining and Smelting Co Ltd
Priority date: 2003-02-07
Filing date: 2003-04-09
Publication date: 2004-10-21

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an active material used for a negative electrode for a non-aqueous electrolyte secondary battery, prevented in exfoliation of the active material from a collector, assuring collecting property of the active material even if repeating charge/discharge, having a high charge/discharge efficiency, and improving the cycle life. <P>SOLUTION: Particles of silicon, tin or these compounds and ultra-fine particles of a metal with a D<SB>50</SB>value of less than 100 μm are mixed and pulverized simultaneously to obtain their mixed particles. The metal is more than one or more kinds of elements selected from the group consisting of Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (excluding for the case where the other particle of the mixed particle is of tin or its compound), Si (excluding for the case where the other particle of the mixed particle is of silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd and Nd. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、非水電解液二次電池用負極活物質の製造方法に関する。本製造方法によって得られた活物質を用いた非水電解液二次電池は、エネルギー密度が高く、リチウムを多量に吸蔵、脱蔵することができ、またサイクル寿命の向上したものとなる。
【０００２】
現在、携帯電話やパーソナルコンピュータの二次電池には、リチウムイオン二次電池が主に使用されている。この理由は、同電池が他の二次電池と比較して高いエネルギー密度を有しているからである。近年の携帯電話やパーソナルコンピュータの多機能化に伴いこれらの消費電力が著しく増加しており、大容量の二次電池がますます必要となっている。しかし、現状の電極活物質を用いている限り、近い将来そのニーズに応えるのは困難となると予想される。
【０００３】
リチウムイオン二次電池の負極活物質には、一般にグラファイトが使用されている。現在では、グラファイトの５〜１０倍の容量ポテンシャルを有しているＳｎ系合金やＳｉ系合金の開発が活発になされている。例えば、Ｓｎ−Ｃｕ系合金のフレークをメカニカルアロイング法、ロール鋳造法及びガスアトマイズ法を用いて製造することが提案されている（非特許文献１参照）。またＮｉ−Ｓｉ系合金、Ｃｏ−Ｓｉ系合金をガスアトマイズ法などで製造することも提案されている（特許文献１参照）。しかしながら、これらの合金は、容量は大きいものの不可逆容量が大きく、またサイクル寿命が短いという問題があり、未だ実用化には至っていない。
【０００４】
集電体として用いられている銅箔にスズを電解めっきして、負極用の電極に用いる試みもなされている（特許文献２参照）。しかしながら、スズよりも容量ポテンシャルの大きいシリコンについては、シリコンが電解めっきできない元素であることから、これを含有したリチウムイオン二次電池用のめっき銅箔の開発は報告されていない。
【０００５】
【特許文献１】
特開２００１−２９７７５７号公報
【特許文献２】
特開２００１−６８０９４号公報
【非特許文献１】
Ｊ．Ｅｌｅｃｔｒｏｃｈｅｍ．Ｓｏｃ．，１４８（５），Ａ４７１−Ａ４８１（２００１）
【０００６】
従って、本発明は、活物質の集電体からの剥離が防止され、充放電を繰り返しても活物質の集電性が確保され、充放電効率が高く、またサイクル寿命が向上した非水電解液二次電池用負極に用いられる活物質の製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、シリコン若しくはスズ又はこれらの化合物と金属との混合粒子からなり、該金属がＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素である非水電解液二次電池用負極活物質の製造方法であって、
シリコン若しくはスズ又はこれらの化合物の粒子とＤ_５０値が１００μｍ以下の前記金属の超微粒子との混合及び粉砕を同時に行い両者の混合粒子を得ることを特徴とする非水電解液二次電池用負極活物質の製造方法を提供することにより前記目的を達成したものである。
【０００８】
また本発明は、シリコン化合物又はスズ化合物の粒子からなり、該粒子がシリコン又はスズとＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素を含む非水電解液二次電池用負極活物質の製造方法であって、
シリコン又はスズと前記元素とを高周波溶解によって溶解させて溶湯となし、該溶湯を冷却された鋳型に流し込んで冷却固化させて前記化合物を得、該化合物を粉砕して粒子となすことを特徴とする非水電解液二次電池用負極活物質の製造方法を提供するものである。
【０００９】
また本発明は、シリコン化合物又はスズ化合物の粒子からなり、該粒子がシリコン又はスズとＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素を含む非水電解液二次電池用負極活物質の製造方法であって、
シリコン又はスズと前記元素とを高周波溶解によって溶解させて溶湯となし、該溶湯を回転する銅製のロールに射出して前記化合物からなる薄帯を得、該薄帯を粉砕して粒子となすことを特徴とする非水電解液二次電池用負極活物質の製造方法を提供するものである。
【００１０】
また本発明は、シリコン化合物又はスズ化合物の粒子からなり、該粒子がシリコン又はスズとＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素を含む非水電解液二次電池用負極活物質の製造方法であって、
シリコン又はスズと前記元素とを高周波溶解によって溶解させて溶湯となし、該溶湯をノズルから射出して、そこに５〜１００ａｔｍの不活性ガスを吹き付けて前記化合物からなる粒子を得、該粒子を更に粉砕することを特徴とする非水電解液二次電池用負極活物質の製造方法を提供するものである。
【００１１】
また本発明は、シリコン又はスズの粒子の表面を金属が被覆した粒子からなり、該金属がＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素からなる非水電解液二次電池用負極活物質の製造方法であって、
前記金属を含むめっき浴中にシリコン又はスズの粒子を懸濁させて無電解めっきを行い、該粒子の表面を該金属で被覆することを特徴とする非水電解液二次電池用負極活物質の製造方法を提供するものである。
【００１２】
また本発明は、少なくともシリコン若しくはスズ又はこれらの化合物と炭素との混合粒子からなる非水電解液二次電池用負極活物質の製造方法であって、
シリコン若しくはスズ又はこれらの化合物の粒子とＤ_５０値が１００μｍ以下の炭素の超微粒子との混合及び粉砕を同時に行いこれらの混合粒子を得ることを特徴とする非水電解液二次電池用負極活物質の製造方法を提供するものである。
【００１３】
【発明の実施の形態】
以下、本発明をその好ましい実施形態に基づき説明する。本発明の製造方法に従い製造される負極活物質は粒子状のものである。この負極活物質を用いた非水電解液二次電池用負極は、集電体の片面又は両面上に、負極活物質の粒子からなる活物質の層、及び該層上に位置する表面被覆層を含む活物質構造体が形成されてなるものである。
【００１４】
本発明の製造方法に従って製造される負極活物質には、
１）シリコン若しくはスズ又はこれらの化合物と金属との混合粒子からなり、該金属がＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｆｅ、Ｃｒ、Ｚｎ、Ｂ、Ａｌ、Ｇｅ、Ｓｎ（但し、混合粒子の他方がスズ又はその化合物である場合を除く）、Ｓｉ（但し、混合粒子の他方がシリコン又はその化合物である場合を除く）、Ｉｎ、Ｖ、Ｔｉ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される１種類以上の元素（以下、これらの金属を総称して添加金属という）であるもの（以下、負極活物質Ａという）、
２）シリコン化合物又はスズ化合物の粒子からなり、該粒子がシリコン又はスズと１種類以上の前記添加金属を含むもの（以下、負極活物質Ｂという）、
３）シリコン又はスズの粒子の表面を前記添加金属が被覆した粒子からなるもの（以下、負極活物質Ｃという）、
４）少なくともシリコン若しくはスズ又はこれらの化合物と炭素との混合粒子（以下、負極活物質Ｄという）が包含される。
【００１５】
本発明の製造方法に従って製造される負極活物質は、その平均粒径が好ましくは４０μｍ以下であり、更に好ましくは２０μｍ以下である。また負極活物質の粒径をＤ_５０値で表すと０．１〜８μｍ、特に０．５〜５μｍであることが好ましい。負極活物質の粒径が４０μｍ超であると、前述した被覆層からの負極活物質の脱落が起こりやすくなり、電極の寿命が短くなる場合がある。負極活物質の平均粒径の下限値に特に制限はなく小さいほど好ましい。以下に説明する負極活物質の製造方法に鑑みると、下限値は０．０１μｍ程度である。平均粒径は、粒度分布測定装置（例えば日機装製のマイクロトラック（商品名））や、電子顕微鏡観察（ＳＥＭ観察）によって測定される。
【００１６】
先ず負極活物質Ａの製造方法について説明する。本製造方法においては、シリコン若しくはスズ又はこれらの化合物の粒子とＤ_５０値が１００μｍ以下の添加金属の超微粒子との混合及び粉砕を同時に行い両者の混合粒子を得る。ここで、シリコン又はスズの化合物とは、シリコン又はスズと添加金属との合金を含み、１）シリコン又はスズと添加金属との固溶体、２）シリコン又はスズと添加金属との金属間化合物、或いは３）シリコン又はスズ単相、添加金属単相、シリコン又はスズと添加金属との固溶体、シリコン又はスズと添加金属との金属間化合物のうちの二相以上の相からなる複合体の何れかである。
【００１７】
混合粉砕前のシリコン若しくはスズ又はこれらの化合物の粒子はその平均粒径が２０〜５００μｍ、特に２０〜３００μｍであることが、粉砕効率を向上させ得る点から好ましい。一方、混合粉砕前の添加金属はそのＤ_５０値が１００μｍ以下であり、好ましくは２０μｍ以下、更に好ましくは５μｍ以下の超微粒子である。平均粒径で表すと、５μｍ以下であり、特に２μｍ以下であることが好ましい。添加金属がこのような超微粒子であることによって、シリコン若しくはスズ又はこれらの化合物の粒子との接触面積や、集電体との接触面積を大きくすることができ、電子伝導性が確保される。添加金属の超微粒子の平均粒径の下限値に特に制限はなく、小さければ小さいほど好ましい。例えばＤ_５０値の下限を０．０１μｍとすることができる。
【００１８】
粉砕機によって、前述の平均粒径を有するシリコン若しくはスズ又はこれらの化合物の粒子と添加金属の超微粒子との混合及び粉砕を同時に行う。粉砕機としてはアトライター、ジェットミル、サイクロンミル、ペイントシェイカ、ファインミルなどを用いることができる。粉砕機による混合及び粉砕によって、シリコン若しくはスズ又はこれらの化合物と添加金属とが均一に混ざり合った混合粒子からなる負極活物質Ａが得られる。
【００１９】
このようにして得られた負極活物質Ａにおいては、シリコン又はスズの量が３０〜９９．９重量％、特に５０〜９５重量％、とりわけ７０〜９０重量％であることが好ましい。一方、添加金属の量は０．１〜７０重量％、特に５〜５０重量％、とりわけ１０〜３０重量％であることが好ましい。組成がこの範囲内であれば、電池の高容量化及び負極の長寿命化を図ることができる。添加金属としてはＡｇ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｅが好ましく、特に電子伝導性に優れ且つリチウム化合物の形成能の低さの点から、Ａｇ、Ｃｕを用いることが望ましい。
【００２０】
次に負極活物質Ｂの製造方法について説明する。本製造方法は急冷法と呼ばれるものである。この方法によれば、合金の結晶子が微細なサイズとなり且つ均質分散されることにより、微粉化が抑制され、電子伝導性が保持される。本製造方法は、鋳造法、ロール鋳造法、ガスアトマイズ法の３つに大別される。何れの方法を用いる場合にも、先ずシリコン又はスズと添加金属とを含む原料の溶湯を準備する。原料は高周波溶解によって溶湯となす。溶湯の温度はシリコン系の場合１２００〜１５００℃、特に１３００〜１４５０℃とすることが急冷条件との関係で好ましい。同様の理由により、スズ系の場合５００〜１５００℃、特に７００〜１３００℃とすることが好ましい。
【００２１】
鋳造法を用いる場合には、冷却された鋳型に溶湯を流し込む。鋳型の温度は０〜４０℃、特に５〜３０℃であることが好ましい。溶湯の流し込みによって鋳型の温度は上昇するが、溶湯の冷却速度が１０^２Ｋ／ｓｅｃ以上、特に１０^３Ｋ／ｓｅｃ以上となるように鋳型を低温に保つことが好ましい。溶湯の固化によって得られたシリコン化合物又はスズ化合物は粉砕され篩い分けされて所定の平均粒径を有する粒子となされる。粉砕には例えばアトライター、ファインミル、ジェットミルなどが用いられる。鋳型は、溶湯の固化によって得られたシリコン化合物又はスズ化合物の粉砕が容易な形状とすることが好ましい。この観点から例えば扁平な形状の鋳型を用いることが好ましい。
【００２２】
ロール鋳造法を用いる場合には、溶湯を高速回転する銅製のロールにおける周面に対して射出する。ロールの回転速度は、溶湯を急冷させる観点から回転数５００〜４０００ｒｐｍ、特に１０００〜２０００ｒｐｍとすることが好ましい。ロールの回転速度を周速で表す場合には、８〜７０ｍ／ｓｅｃ、特に１５〜３０ｍ／ｓｅｃであることが好ましい。前述の範囲の温度の溶湯を、前述範囲の速度で回転するロールを用いて急冷することで、冷却速度は１０^２Ｋ／ｓｅｃ以上、特に１０^３Ｋ／ｓｅｃ以上という高速になる。射出された溶湯はロールにおいて急冷されて薄帯となる。この薄帯を粉砕、篩い分けして所定の平均粒径を有する粒子を得る。粉砕には、先に述べた鋳造法に用いられるものと同様のものを用いることができる。
【００２３】
ガスアトマイズ法を用いる場合には、溶湯をノズルから射出して、そこにアルゴンなどの不活性ガスを５〜１００ａｔｍ、好ましくは５〜５０ａｔｍの圧力で吹き付けて粒子化及び急冷をする。そして得られた粒子を更に粉砕し、篩い分けして所定の平均粒径を有する粒子を得る。
【００２４】
これらの方法によって得られた負極活物質Ｂの組成は、負極活物質Ａと同様にシリコン又はスズの量が３０〜９９．９重量％で、添加金属の量が０．１〜７０重量％であることが好ましい。更に好ましい組成は、シリコン又はスズの量が４０〜９０重量％で、添加金属の量が１０〜６０重量％である。負極活物質Ｂが、シリコン又はスズと添加金属とを含む三元系以上の合金である場合には、シリコン又はスズ及び添加金属に加えて、Ｂ、Ａｌ、Ｎｉ、Ｃｏ、Ｓｎ、Ｆｅ、Ｃｒ、Ｚｎ、Ｉｎ、Ｖ、Ｙ、Ｚｒ、Ｎｂ、Ｔａ、Ｗ、Ｌａ、Ｃｅ、Ｐｒ、Ｐｄ及びＮｄからなる群から選択される元素が少量含まれていてもよい。これによって、微粉化が抑制されるという付加的な効果が奏される。この効果を一層高めるため、これらの元素は、シリコン又はスズと添加金属との合金中に０．０１〜１０重量％、特に０．０５〜１．０重量％含まれていることが好ましい。
【００２５】
次に負極活物質Ｃの製造方法について説明する。本製造方法においては、先ずシリコン又はスズ粒子が懸濁されており且つ添加金属を含むめっき浴を用意する。シリコン又はスズ粒子の平均粒径は４０μｍ以下であることが好ましい。このめっき浴中において、シリコン又はスズ粒子を無電解めっきして該シリコン又はスズ粒子の表面に添加金属を被覆させる。めっき浴中におけるシリコン又はスズ粒子の濃度は４００〜６００ｇ／ｌ程度とすることが好ましい。添加金属として銅を無電解めっきする場合には、めっき浴中に硫酸銅、ロシェル塩等を含有させておくことが好ましい。この場合硫酸銅の濃度は６〜９ｇ／ｌ、ロシェル塩の濃度は７０〜９０ｇ／ｌであることが、めっき速度のコントロールの点から好ましい。同様の理由からめっき浴のｐＨは１２〜１３、浴温は２０〜３０℃であることが好ましい。めっき浴中に含まれる還元剤としては、例えばホルムアルデヒド等が用いられ、その濃度は１５〜３０ｃｃ／ｌ程度とすることができる。
【００２６】
このようにして得られた負極活物質Ｃにおいては、シリコン又はスズの量は７０〜９９．９重量％、特に８０〜９９重量％、とりわけ８５〜９５であることが好ましい。一方、添加金属の量は０．１〜３０重量％、特に１〜２０重量％、とりわけ５〜１５重量％であることが好ましい。
【００２７】
次に負極活物質Ｄの製造方法について説明する。本製造方法は先に説明した負極活物質Ａの製造方法と類似している。従って、本製造方法に関して特に説明しない点については負極活物質Ａの製造方法の説明が適宜適用される。本製造方法においては、シリコン若しくはスズ又はこれらの化合物の粒子とＤ_５０値が１００μｍ以下の炭素の超微粒子との混合及び粉砕を同時に行いこれらの混合粒子を得る。混合及び粉砕にはメカニカルミリングが好適に用いられる。メカニカルミルングによって、シリコン若しくはスズ又はこれらの化合物と炭素とが均一に混ざり合った混合粒子からなる負極活物質Ｄが得られる。炭素としてはグラファイトが好適に用いられる。
【００２８】
負極活物質Ｄを用いると、特にサイクル寿命が向上すると共に負極容量が増加する。この理由は次の通りである。炭素、特に非水電解液二次電池用負極に用いられているグラファイトは、リチウムの吸脱蔵に寄与し、３００ｍＡｈ／ｇ程度の負極容量を有し、しかもリチウム吸蔵時の体積膨張が非常に小さいという特徴を持つ。一方、シリコンは、グラファイトの１０倍以上である４２００ｍＡｈ／ｇ程度の負極容量を有するという特徴を持つ。反面シリコンは、リチウム吸蔵時の体積膨張がグラファイトの約４倍に達する。そこで、シリコンとグラファイトのような炭素とを所定の比率でメカニカルミリング法などを用い混合・粉砕して粉末とすると、リチウム吸蔵時のシリコンの体積膨張がグラファイトによって緩和されて、サイクル寿命が向上し、また１０００〜３０００ｍＡｈ／ｇ程度の負極容量が得られる。シリコンと炭素との混合比率は、シリコンの量が１０〜９０重量％、特に３０〜７０重量％、とりわけ３０〜５０重量％であることが好ましい。一方、炭素の量は９０〜１０重量％、特に７０〜３０重量％、とりわけ７０〜５０重量％であることが好ましい。組成がこの範囲内であれば、電池の高容量化及び負極の長寿命化を図ることができる。なお、この混合粒子においては、シリコンカーバイドなどの化合物は形成されていない。
【００２９】
負極活物質Ｄは、シリコン若しくはスズ又はこれらの化合物及び炭素に加えて他の金属元素を含む、３種以上の混合粒子であってもよい。金属元素としては先に述べた添加金属のうちの１種又は２種以上を用いることができる。
【００３０】
本発明の製造方法に従って製造された各種負極活物質を用いた負極は、冒頭で述べた通り集電体の片面又は両面上に、負極活物質の粒子からなる活物質の層、及び該層上に位置する表面被覆層を含む活物質構造体が形成されてなるものである。負極活物質の粒子からなる活物質層は表面被覆層によって完全に被覆されている必要はなく、その一部が露出していてもよい。しかし、リチウムの吸脱蔵に起因する負極活物質の微粉化によって該負極活物質が脱落することを防止する観点からは、活物質層は表面被覆層によって完全に被覆されていることが好ましい。活物質層が表面被覆層に完全に被覆されていたとしても、後述する負極の製造方法によれば、プレス加工時に表面被覆層に微細な破断部が発生し、そこから電解液及びリチウムが表面被覆層内部にまで浸透して負極活物質と反応することができる。負極活物質がが表面被覆層によって完全に被覆されている状態の負極の一例を図１及び図２に示す。図１及び図２においては、銅からなる集電体１上に、シリコン−銅合金粒子からなる活物質層３が形成されており、活物質層３上には銅からなる表面被覆層２が位置している。活物質層３は表面被覆層２によって完全に被覆されている。表面被覆層２には、その厚み方向に延びる微細な破断部が観察される。更に、活物質層３中の合金粒子間には空隙が観察される。図１においては、表面被覆層２の一部が活物質層３に入り込んでおり、合金粒子の表面が銅で被覆されていることが判る。一方、図２においては、表面被覆層２は活物質層３中にそれほど入り込んでおらず、両層２，３は比較的明瞭に分かれている。図１及び図２におけるこのような形態の相違は、負極の製造方法に起因している。
【００３１】
負極を構成する集電体は非水電解液二次電池の集電体となり得る金属から構成されている。特にリチウム二次電池の集電体となり得る金属から構成されていることが好ましい。そのような金属としては例えば銅、鉄、コバルト、ニッケル、亜鉛若しくは銀又はこれらの金属の合金などが挙げられる。これらの金属のうち銅又は銅合金を用いることが特に好適である。銅を用いる場合、集電体は銅箔の状態で用いられる。この銅箔は例えば銅含有溶液を用いた電解析出により得られ、その厚みは２〜１００μｍ、特に１０〜３０μｍが望ましい。特に特開２０００−９０９３７号公報に記載の方法より得られた銅箔は、厚みが１２μｍ以下と極めて薄いことから好ましく用いられる。
【００３２】
集電体の表面に形成されている表面被覆層は、該被覆層の酸化及び脱落の防止の点から、リチウム化合物の形成能の低い導電性材料からなる。そのような導電性材料としては例えば銅、銀、ニッケル、コバルト、クロム、インジウム及びこれらの金属の合金（例えば銅とスズとの合金）などが挙げられる。これらの金属のうち、リチウム化合物の形成能が特に低い金属である銅、銀、ニッケル、クロム、コバルト及びこれらの金属を含む合金を用いることが好ましい。また前記導電性材料として、導電性プラスチックや導電性ペーストなどを用いることもできる。「リチウム化合物の形成能が低い」とは、リチウムと金属間化合物若しくは固溶体を形成しないか、又は形成したとしてもリチウムが微量であるか若しくは非常に不安定であることを意味する。
【００３３】
活物質層が表面被覆層によって被覆されていることにより、本発明の負極を用いた二次電池はその単位体積当たり及び単位重量当たりのエネルギー密度が従来のものに比べて非常に大きくなる。また負極活物質が表面被覆層によって閉じこめられているので、リチウムの吸脱蔵に起因する負極活物質の脱落が効果的に防止される。また電気的に孤立した負極活物質が生成することが効果的に防止され、集電機能が保たれる。その結果、負極としての機能低下が抑えられる。更に負極の長寿命化も図られる。特に、表面被覆層の一部が活物質層に入り込んでいると、集電機能が一層効果的に保たれる。活物質であるシリコンやシリコン合金をそのままの状態で集電体上に形成すると、リチウムの吸脱蔵に起因してこれらが微粉化して集電体から電気的に孤立化してしまう。その結果、負極としての機能が低下し、不可逆容量の増大、充放電効率の低下、短寿命化などの問題が生じてしまう。
【００３４】
活物質層及び表面被覆層を含む活物質構造体中における負極活物質の量は５〜８０重量％であり、好ましくは１０〜５０重量％、更に好ましくは２０〜５０重量％である。負極活物質の量が５重量％未満では、電池のエネルギー密度を十分に向上させることが困難である。一方、８０重量％超では負極活物質の脱落が起こりやすくなり、不可逆容量の増大、充放電効率の低下、短寿命化などの問題が生じてしまう。
【００３５】
活物質層中には前述した負極活物質に加えて導電性炭素材料の粒子が含まれていることが好ましい。これによって活物質構造体に電子伝導性が一層付与される。この観点から活物質層中に含まれる導電性炭素材料の量は０．１〜２０重量％、特に１〜１０重量％であることが好ましい。導電性炭素材料の粒子の粒径は４０μｍ以下、特に２０μｍ以下であることが、電子伝導性の一層付与の点から好ましい。該粒子の粒径の下限値に特に制限はなく小さいほど好ましい。該粒子の製造方法に鑑みると、その下限値は０．０１μｍ程度となる。導電性炭素材料としては、例えばアセチレンブラック、グラファイトなどが挙げられる。
【００３６】
表面被覆層の厚みは０．３〜５０μｍ、特に０．３〜１０μｍ、とりわけ１〜１０μｍであることが、負極活物質の脱落防止及び集電機能の維持の点から好ましい。具体的には、厚みが０．３μｍ以上であれば活物質の膨張収縮に起因する脱落を効果的に防止でき、また５０μｍ以下であれば充放電が阻害されない。活物質層の厚みは１〜１００μｍ、特に３〜４０μｍであることが、負極容量の十分な確保の点から好ましい。表面被覆層及び活物質層を含む活物質構造体の厚みは２〜１００μｍ、特に２〜５０μｍ程度であることが好ましい。
【００３７】
次に、負極の好ましい製造方法について説明する。本製造方法においては、先ず集電体の表面に塗工するスラリーを準備する。スラリーは、本発明の製造方法に従い製造された負極活物質の粒子、導電性炭素材料の粒子、結着剤及び希釈溶媒を含んでいる。これらの成分のうち、負極活物質の粒子及び導電性炭素材料の粒子については先に説明した通りである。結着剤としてはポリビニリデンフルオライド（ＰＶＤＦ）、ポリエチレン（ＰＥ）、エチレンプロピレンジエンモノマー（ＥＰＤＭ）などが用いられる。希釈溶媒としてはＮ−メチルピロリドン、シクロヘキサンなどが用いられる。
【００３８】
スラリー中における負極活物質の粒子の量は１４〜４０重量％程度とすることが好ましい。導電性炭素材料の粒子の量は０．４〜４重量％程度とすることが好ましい。結着剤の量は０．４〜４重量％程度とすることが好ましい。また希釈溶媒の量は６０〜８５重量％程度とすることが好ましい。
【００３９】
このスラリーを集電体の表面に塗工して活物質層を形成する。集電体は予め製造しておいてもよく、或いは本発明の負極の製造工程における一工程としてインラインで製造されてもよい。集電体がインラインで製造される場合、電解析出によって製造されることが好ましい。集電体へのスラリーの塗工量は、乾燥後の活物質層の膜厚が、最終的に得られる活物質構造体の厚みの１〜３倍程度となるような量とすることが好ましい。スラリーの塗膜が乾燥して活物質層が形成された後、該活物質層が形成された集電体を、リチウム化合物の形成能の低い導電性材料を含むめっき浴中に浸漬し、その状態下に活物質層上に該導電性材料による電解めっきを行い表面被覆層を形成する。電解めっきの条件としては、例えば導電性材料として金属である銅を用いる場合、硫酸銅系溶液を用いるときには、銅の濃度を３０〜１００ｇ／ｌ、硫酸の濃度を５０〜２００ｇ／ｌ、塩素の濃度を３０ｐｐｍ以下とし、液温を３０〜８０℃、電流密度を１〜１００Ａ／ｄｍ^２とすればよい。この場合には先に説明した図１に示す形態の負極が得られる。ピロ燐酸銅系溶液を用いる場合には、銅の濃度２〜５０ｇ／ｌ、ピロ燐酸カリウムの濃度１００〜７００ｇ／ｌとし、液温を３０〜６０℃、ｐＨを８〜１２、電流密度を１〜１０Ａ／ｄｍ^２とすればよい。この場合には先に説明した図２に示す形態の負極が得られる。
【００４０】
このようにして活物質層上に表面被覆層が形成された後、活物質層を表面被覆層ごとプレス加工する。これによって活物質層を圧密化する。圧密化によって、負極活物質の粒子及び導電性炭素材料の粒子の間の空隙を、表面被覆層を構成する導電性材料が埋め、負極活物質の粒子及び導電性炭素材料の粒子が分散された状態となる。またこれらの粒子と表面被覆層とが密着して、電子伝導性が付与される。十分な電子伝導性を得る観点から、プレス加工による圧密化は、プレス加工後の活物質層と表面被覆層との厚みの総和が、プレス加工前の９０％以下、好ましくは８０％以下となるように行うことが好ましい。プレス加工には、例えばロールプレス機を用いることができる。プレス加工後の活物質層には、５〜３０体積％の空隙が存在していることが好ましい。この空隙の存在によって、充電時にリチウムを吸蔵して体積が膨張する場合に、その体積膨張に起因する応力が緩和される。このような空隙はプレス加工の条件を前述のようにコントロールすればよい。この空隙の値は、電子顕微鏡マッピングによって求めることができる。
【００４１】
本製造方法においては、活物質層上に電解めっきを行うに先立ち、該活物質層をプレス加工することが好ましい（このプレス加工を、先に述べたプレス加工と区別する意味で前プレス加工と呼ぶ）。前プレス加工を行うことで、活物質層と集電体との剥離が防止され、また負極活物質の粒子が表面被覆層の表面に露出することが防止される。その結果、負極活物質の粒子の脱落に起因する電池のサイクル寿命の劣化を防ぐことができる。前プレス加工の条件としては、前プレス加工後の活物質層の厚みが、前プレス加工前の活物質層の厚みの９５％以下、特に９０％以下となるような条件であることが好ましい。
【００４２】
このようにして得られた負極は、公知の正極、セパレータ、非水系電解液と共に用いられて非水電解液二次電池となされる。正極は、正極活物質並びに必要により導電剤及び結着剤を適当な溶媒に懸濁し、正極合剤を作製し、これを集電体に塗布、乾燥した後、ロール圧延、プレスし、さらに裁断、打ち抜きすることにより得られる。正極活物質としては、リチウムニッケル複合酸化物、リチウムマンガン複合酸化物、リチウムコバルト複合酸化物等の従来公知の正極活物質が用いられる。セパレーターとしては、合成樹脂製不織布、ポリエチレン又はポリプロピレン多孔質フイルム等が好ましく用いられる。非水電解液は、リチウム二次電池の場合、支持電解質であるリチウム塩を有機溶媒に溶解した溶液からなる。リチウム塩としては、例えば、ＬｉＣ１Ｏ_４、ＬｉＡ１Ｃｌ_４、ＬｉＰＦ_６、ＬｉＡｓＦ_６、ＬｉＳｂＦ_６、ＬｉＳＣＮ、ＬｉＣ１、ＬｉＢｒ、ＬｉＩ、ＬｉＣＦ_３ＳＯ_３、ＬｉＣ_４Ｆ_９ＳＯ_３等が例示される。
【００４３】
【実施例】
以下、実施例により本発明を更に詳細に説明する。しかしながら本発明の範囲はかかる実施例に制限されるものではない。以下の例中、特に断らない限り「％」は「重量％」を意味する。
【００４４】
〔実施例１〕
（１）負極活物質の製造
シリコン及び銅を高周波溶解によって溶湯となした。溶湯の温度は１４００℃であった。この溶湯を５℃に冷却された鋳型に流し込んだ。鋳型の形状は扁平であった。溶湯の冷却速度は１０^２Ｋ／ｓｅｃ以上であった。固化によって得られたシリコン−銅合金をアトライターを用いて粉砕し更に篩い分けして、表１に示すＤ_５０値を有する負極活物質の粒子を得た。負極活物質の組成は同表に示す通りであった。
（２）スラリーの調製
以下の組成のスラリーを調製した。
・シリコン−銅合金粒子１６％
・アセチレンブラック（粒径０．１μｍ）２％
・結着剤（ポリビニリデンフルオライド）２％
・希釈溶媒（Ｎ−メチルピロリドン）８０％
【００４５】
（２）活物質層の形成
調製されたスラリーを、厚さ３０μｍの銅箔上に塗工し乾燥させた。乾燥後の活物質層の厚みは６０μｍであった。
【００４６】
（３）表面被覆層の形成
活物質層が形成された銅箔を、以下の組成を有するめっき浴中に浸漬し、活物質層上に電解めっきを行った。
・銅５０ｇ／ｌ
・硫酸６０ｇ／ｌ
・浴温４０℃
表面被覆層の形成後、銅箔をめっき浴から引き上げ、次いで活物質層を表面被覆層ごとロールプレス加工し圧密化した。このようにして得られた表面被覆層の厚みは、電子顕微鏡観察の結果２０μｍであった。また化学分析の結果、活物質構造体におけるシリコン−銅合金粒子の量は４５％、アセチレンブラックの量は５％であった。
【００４７】
〔実施例２〜１２〕
鋳造により表１に示す組成のシリコン系合金からなる負極活物質の粒子を製造し、該粒子を用いる以外は実施例１と同様にして負極を得た。
【００４８】
〔実施例１３〕
シリコン及び銅を高周波溶解によって溶湯となした。溶湯の温度は１４００℃であった。この溶湯を、高速回転する銅製のロールにおける周面に対して射出した。ロールの回転速度は１０００ｒｐｍであった。射出された溶湯はロールにおいて急冷されてシリコン−銅合金の薄帯となった。このときの冷却速度は１０^３Ｋ／ｓｅｃ以上であったこの薄帯をアトライターを用いて粉砕し更に篩い分けして、表１に示すＤ_５０値を有する負極活物質の粒子を得た。負極活物質の組成は同表に示す通りであった。これ以外は実施例１と同様にして負極を得た。
【００４９】
〔実施例１４〕
表１に示す組成及び粒径の負極活物質の粒子を製造し、該粒子を用いる以外は実施例１３と同様にして負極を得た。
【００５０】
〔実施例１５〕
シリコン及び銅を高周波溶解によって溶湯となした。溶湯の温度は１４００℃であった。この溶湯をノズルから射出して、そこに３０ａｔｍのアルゴンガスを吹き付けた。溶湯は急冷されてシリコン−銅合金の粒子となった。この粒子をアトライターを用いて粉砕し更に篩い分けして、表１に示すＤ_５０値を有する負極活物質の粒子を得た。負極活物質の組成は同表に示す通りであった。これ以外は実施例１と同様にして負極を得た。
【００５１】
〔実施例１６〕
表１に示す組成及び粒径の負極活物質の粒子を製造し、該粒子を用いる以外は実施例１５と同様にして負極を得た。
【００５２】
〔実施例１７〕
粒径０．２〜８μｍのシリコン粒子が懸濁されており且つ硫酸銅及びロシェル塩を含むめっき浴中において、該シリコン粒子を無電解めっきして該シリコン粒子の表面に銅を被覆させて銅被覆シリコン粒子を得た。めっき浴中におけるシリコン粒子の濃度は５００ｇ／ｌ、硫酸銅の濃度は７．５ｇ／ｌ、ロシェル塩の濃度は８５ｇ／ｌであった。めっき浴のｐＨは１２．５、浴温は２５℃であった。還元剤としてはホルムアルデヒドを用い、その濃度は２２ｃｃ／ｌであった。得られた粒子のＤ_５０値は表１に示す通りであった。また粒子の組成は同表に示す通りであった。これ以外は実施例１と同様にして負極を得た。
【００５３】
〔実施例１８〜２１〕
表１に示す組成及び粒径の負極活物質の粒子を製造し、該粒子を用いる以外は実施例１７と同様にして負極を得た。
【００５４】
〔実施例２２〕
シリコン粒子（Ｄ_５０値８０μｍ）９５％及び銅粒子（Ｄ_５０値１μｍ）５％を混合し、アトライターによってこれらの粒子の混合及び粉砕を同時に行った。これによってシリコンと銅とが均一に混ざり合った粒径０．１〜１０μｍ（Ｄ_５０値２μｍ）の混合粒子を得た。この混合粒子を用いる以外は実施例１と同様にして負極を得た。
【００５５】
〔実施例２３〜３０〕
表２に示す組成及び粒径の負極活物質の粒子を製造し、該粒子を用いる以外は実施例２２と同様にして負極を得た。なお、添加金属粒子のＤ_５０値は何れも１μｍであった。
【００５６】
〔実施例３１及び３２〕
シリコン及び銅を高周波溶解によって溶湯となした。溶湯の温度は１４００℃であった。この溶湯を５℃に冷却された鋳型に流し込んだ。鋳型の形状は扁平であった。溶湯の冷却速度は１０^２Ｋ／ｓｅｃ以上であった。固化によって得られたシリコン−銅合金をアトライターを用いて粉砕し更に篩い分けした。シリコン−銅合金の組成は表２に示す通りであった。実施例２２において用いたシリコン粒子に代えてこのシリコン−銅合金粒子を用い、且つシリコン−銅合金粒子と銅粒子との割合を表２に示す値とする以外は実施例２２と同様にして負極を得た。
【００５７】
〔実施例３３及び３４〕
実施例３１及び３２において銅粒子に代えて銀粒子を用いる以外は実施例３１及び３２と同様にして負極を得た。なお、銀粒子のＤ_５０値は１μｍであった。
【００５８】
〔実施例３５〜４６〕
鋳造により表３に示す組成のスズ系合金からなる負極活物質の粒子を製造し、該粒子を用いる以外は実施例１と同様にして負極を得た。
【００５９】
〔実施例４７及び４８〕
ロール鋳造により表３に示す組成のスズ系合金からなる負極活物質の粒子を製造し、該粒子を用いる以外は実施例１３と同様にして負極を得た。
【００６０】
〔実施例４９及び５０〕
ガスアトマイズにより表３に示す組成のスズ系合金からなる負極活物質の粒子を製造し、該粒子を用いる以外は実施例１５と同様にして負極を得た。
【００６１】
〔実施例５１〜５５〕
無電解めっきにより表３に示す組成の負極活物質の粒子を製造し、該粒子を用いる以外は実施例１７と同様にして負極を得た。
【００６２】
〔実施例５６〜６８〕
表４に示す組成の負極活物質の混合粒子を製造し、該混合粒子を用いる以外は実施例２２と同様にして負極を得た。なお、添加金属粒子のＤ_５０値は何れも１μｍであった。
【００６３】
〔実施例６９〕
シリコン粒子（粒径１００μｍ）２０％及びグラファイト粒子（Ｄ_５０値２０μｍ）８０％を混合し、メカニカルミリングによってこれらの粒子の混合及び粉砕を同時に行った。これによってシリコンとグラファイトとが均一に混ざり合った粒径０．５μｍ（Ｄ_５０値）の混合粒子を得た。この混合粒子を用い且つ表面被覆層をニッケルから形成する以外は実施例２２と同様にして負極を得た。
【００６４】
〔実施例７０〜７３〕
混合粒子の組成を表４に示す値とする以外は実施例６９と同様にして負極を得た。
【００６５】
〔性能評価〕
実施例及び比較例で得られた負極を用いて以下の通り非水電解液二次電池を作製した。以下の方法で不可逆容量、充電時体積容量密度、１０サイクル時の充放電効率及び５０サイクル容量維持率を測定した。これらの結果を以下の表１〜表４に示す。
【００６６】
〔非水電解液二次電池の作製〕
対極として金属リチウムを用い、また作用極として前記で得られた負極を用い、両極をセパレーターを介して対向させた。更に非水電解液としてＬｉＰＦ_６／エチレンカーボネートとジエチルカーボネートの混合溶液（１：１容量比）を用いて通常の方法によって非水電解液二次電池を作製した。
【００６７】
〔不可逆容量〕
不可逆容量（％）＝（１−初回放電容量／初回充電容量）×１００
すなわち、充電したが放電できず、活物質に残存した容量を示す。
【００６８】
〔容量密度〕
初回の放電容量を示す。単位はｍＡｈ／ｇである。
【００６９】
〔１０サイクル時の充放電効率〕
１０サイクル時の充放電効率（％）＝１０サイクル目の放電容量／１０サイクル目の充電容量×１００
【００７０】
〔５０サイクル容量維持率〕
５０サイクル容量維持率（％）＝２０サイクル目の放電容量／最大放電容量×１００
【００７１】
【表１】

【００７２】
【表２】

【００７３】
【表３】

【００７４】
【表４】

【００７５】
表１〜表４に示す結果から明らかなように、各実施例で得られた負極活物質用いた二次電池は、従来の二次電池と同程度の不可逆容量、充放電効率及び容量維持率を示し、更に容量密度が従来の二次電池よりも極めて高いことが判る。
【００７６】
【発明の効果】
以上詳述した通り、本発明の製造方法に従って得られた負極活物質を用いた非水電解液二次電池用負極によれば、従来の負極よりもエネルギー密度の高い二次電池を得ることができる。また本発明の製造方法に従って得られた負極活物質を用いた非水電解液二次電池用負極によれば、活物質の集電体からの剥離が防止され、充放電を繰り返しても活物質の集電性が確保される。またこの負極を用いた二次電池は充放電を繰り返しても劣化率が低く寿命が大幅に長くなり、充放電効率も高くなる。
【図面の簡単な説明】
【図１】本発明の製造方法に従って得られた負極活物質を用いた負極の一例を示す走査型電子顕微鏡像である。
【図２】本発明の製造方法に従って得られた負極活物質を用いた負極の他の例を示す走査型電子顕微鏡像である。
【符号の説明】
１集電体
２被覆層
３活物質層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery using the active material obtained by the present manufacturing method has a high energy density, can occlude and desorb a large amount of lithium, and has an improved cycle life.
[0002]
At present, lithium ion secondary batteries are mainly used as secondary batteries for mobile phones and personal computers. This is because the battery has a higher energy density than other secondary batteries. The power consumption of mobile phones and personal computers has been increasing remarkably with the recent multifunctionalization of mobile phones and personal computers, and large-capacity secondary batteries are increasingly required. However, as long as the current electrode active material is used, it is expected that it will be difficult to meet the needs in the near future.
[0003]
Generally, graphite is used as a negative electrode active material of a lithium ion secondary battery. At present, the development of Sn-based alloys and Si-based alloys having a capacitance potential 5 to 10 times that of graphite has been actively conducted. For example, it has been proposed to manufacture flakes of an Sn-Cu alloy using a mechanical alloying method, a roll casting method, and a gas atomizing method (see Non-Patent Document 1). It has also been proposed to produce a Ni-Si alloy or a Co-Si alloy by a gas atomizing method or the like (see Patent Document 1). However, these alloys have a large capacity but a large irreversible capacity and a short cycle life, and have not yet been put to practical use.
[0004]
Attempts have also been made to electroplate tin on a copper foil used as a current collector and use it as an electrode for a negative electrode (see Patent Document 2). However, with respect to silicon having a larger capacity potential than tin, since silicon is an element that cannot be electroplated, development of a plated copper foil for lithium ion secondary batteries containing the same has not been reported.
[0005]
[Patent Document 1]
JP 2001-297775 A
[Patent Document 2]
JP 2001-68094 A
[Non-patent document 1]
J. Electrochem. Soc. , 148 (5), A471-A481 (2001)
[0006]
Therefore, the present invention provides a non-aqueous electrolysis system in which the active material is prevented from peeling from the current collector, the current collecting property of the active material is secured even after repeated charging and discharging, the charging and discharging efficiency is high, and the cycle life is improved. An object of the present invention is to provide a method for producing an active material used for a negative electrode for a liquid secondary battery.
[0007]
[Means for Solving the Problems]
The present invention consists of mixed particles of silicon or tin or a compound thereof and a metal, wherein the metal is Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (however, Except when the other is tin or its compound), Si (except when the other of the mixed particles is silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La , Ce, Pr, Pd and a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which is one or more elements selected from the group consisting of Nd,
Particles of silicon or tin or their compounds and D ₅₀ The object of the present invention is to provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises simultaneously mixing and grinding with ultrafine particles of the metal having a value of 100 μm or less to obtain a mixed particle of both. Is achieved.
[0008]
Further, the present invention comprises particles of a silicon compound or a tin compound, wherein the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (however, the other of mixed particles). Is a tin or a compound thereof), Si (except that the other of the mixed particles is a silicon or a compound thereof), In, V, Ti, Y, Zr, Nb, Ta, W, La, A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Ce, Pr, Pd, and Nd,
Dissolving silicon or tin and the element by high-frequency melting to form a molten metal, casting the molten metal into a cooled mold, cooling and solidifying to obtain the compound, and pulverizing the compound into particles. To provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery.
[0009]
Further, the present invention comprises particles of a silicon compound or a tin compound, wherein the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (however, the other of mixed particles). Is a tin or a compound thereof), Si (except that the other of the mixed particles is a silicon or a compound thereof), In, V, Ti, Y, Zr, Nb, Ta, W, La, A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Ce, Pr, Pd, and Nd,
Dissolving silicon or tin and the element by high-frequency melting to form a molten metal, injecting the molten metal into a rotating copper roll to obtain a ribbon comprising the compound, and pulverizing the ribbon into particles. It is intended to provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery characterized by the following.
[0010]
Further, the present invention comprises particles of a silicon compound or a tin compound, wherein the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (however, the other of mixed particles). Is a tin or a compound thereof), Si (except that the other of the mixed particles is a silicon or a compound thereof), In, V, Ti, Y, Zr, Nb, Ta, W, La, A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Ce, Pr, Pd, and Nd,
Silicon or tin and the element are melted by high frequency melting to form a molten metal, the molten metal is injected from a nozzle, and an inert gas of 5 to 100 atm is sprayed thereon to obtain particles made of the compound. Another object of the present invention is to provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which is characterized by further pulverization.
[0011]
Further, the present invention comprises particles in which the surface of silicon or tin particles is coated with a metal, and the metal is made of Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (where mixed particles are used). , Si (except when the other of the mixed particles is silicon or a compound thereof), In, V, Ti, Y, Zr, Nb, Ta, W, A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising one or more elements selected from the group consisting of La, Ce, Pr, Pd, and Nd,
A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising suspending silicon or tin particles in a plating bath containing the metal, performing electroless plating, and coating the surface of the particles with the metal. Is provided.
[0012]
Further, the present invention is a method for producing a negative electrode active material for a nonaqueous electrolyte secondary battery comprising at least silicon or tin or a mixed particle of these compounds and carbon,
Particles of silicon or tin or their compounds and D ₅₀ It is intended to provide a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which comprises simultaneously mixing and grinding carbon ultrafine particles having a value of 100 μm or less to obtain these mixed particles.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on preferred embodiments. The negative electrode active material produced according to the production method of the present invention is in the form of particles. A negative electrode for a non-aqueous electrolyte secondary battery using this negative electrode active material has a layer of an active material composed of particles of a negative electrode active material on one or both surfaces of a current collector, and a surface coating layer located on the layer. An active material structure containing is formed.
[0014]
The negative electrode active material produced according to the production method of the present invention,
1) Consisting of mixed particles of silicon or tin or a compound of these and a metal, wherein the metal is Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, Sn (however, the other of the mixed particles is Excluding tin or its compound), Si (except that the other of the mixed particles is silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce , One or more elements selected from the group consisting of Pr, Pd, and Nd (hereinafter, these metals are collectively referred to as additive metals) (hereinafter, referred to as negative electrode active material A),
2) particles of silicon compound or tin compound, wherein the particles contain silicon or tin and one or more kinds of the additional metals (hereinafter, referred to as negative electrode active material B);
3) Particles comprising particles of silicon or tin coated on the surface of the additive metal (hereinafter referred to as negative electrode active material C);
4) At least mixed particles of silicon or tin or a compound thereof and carbon (hereinafter, referred to as negative electrode active material D) are included.
[0015]
The average particle size of the negative electrode active material produced according to the production method of the present invention is preferably 40 μm or less, more preferably 20 μm or less. The particle size of the negative electrode active material is D ₅₀ When expressed in terms of a value, it is preferably from 0.1 to 8 μm, particularly preferably from 0.5 to 5 μm. If the particle size of the negative electrode active material is more than 40 μm, the negative electrode active material tends to fall off from the above-mentioned coating layer, and the life of the electrode may be shortened. There is no particular limitation on the lower limit of the average particle size of the negative electrode active material, and the smaller the better, the better. In view of the method for manufacturing a negative electrode active material described below, the lower limit is about 0.01 μm. The average particle size is measured by a particle size distribution measuring device (for example, Microtrack (trade name) manufactured by Nikkiso Co., Ltd.) or by electron microscope observation (SEM observation).
[0016]
First, a method for producing the negative electrode active material A will be described. In the present production method, particles of silicon or tin or a compound thereof and D ₅₀ Mixing with the ultrafine particles of the added metal having a value of 100 μm or less and pulverization are simultaneously performed to obtain a mixed particle of both. Here, the compound of silicon or tin includes an alloy of silicon or tin and an additional metal, 1) a solid solution of silicon or tin and an additional metal, 2) an intermetallic compound of silicon or tin and an additional metal, or 3) Any one of a single phase of silicon or tin, a single phase of an additional metal, a solid solution of silicon or tin and an additional metal, or a composite of two or more phases of an intermetallic compound of silicon or tin and an additional metal. is there.
[0017]
The particles of silicon, tin or a compound thereof before mixing and pulverization preferably have an average particle diameter of 20 to 500 μm, particularly preferably 20 to 300 μm, from the viewpoint of improving the pulverization efficiency. On the other hand, the added metal before mixing and pulverization is the D ₅₀ Ultrafine particles having a value of 100 μm or less, preferably 20 μm or less, more preferably 5 μm or less. The average particle diameter is 5 μm or less, and particularly preferably 2 μm or less. When the additive metal is such ultrafine particles, the contact area with the particles of silicon or tin or a compound of these or the contact area with the current collector can be increased, and the electron conductivity is secured. There is no particular limitation on the lower limit of the average particle size of the ultrafine particles of the added metal, and the smaller the smaller, the better. For example, D ₅₀ The lower limit of the value can be 0.01 μm.
[0018]
The pulverizer simultaneously mixes and pulverizes particles of silicon or tin or a compound thereof having the above-mentioned average particle diameter with ultrafine particles of the added metal. As a pulverizer, an attritor, a jet mill, a cyclone mill, a paint shaker, a fine mill, or the like can be used. By mixing and pulverizing with a pulverizer, a negative electrode active material A composed of mixed particles in which silicon or tin or a compound thereof and an additional metal are uniformly mixed is obtained.
[0019]
In the negative electrode active material A thus obtained, the amount of silicon or tin is preferably 30 to 99.9% by weight, particularly preferably 50 to 95% by weight, particularly preferably 70 to 90% by weight. On the other hand, the amount of the added metal is preferably 0.1 to 70% by weight, particularly preferably 5 to 50% by weight, particularly preferably 10 to 30% by weight. When the composition is within this range, it is possible to increase the capacity of the battery and extend the life of the negative electrode. Ag, Cu, Ni, Co, and Ce are preferable as the added metal, and particularly, Ag and Cu are desirably used from the viewpoint of excellent electron conductivity and low ability to form a lithium compound.
[0020]
Next, a method for producing the negative electrode active material B will be described. This manufacturing method is called a quenching method. According to this method, since the crystallites of the alloy have a fine size and are homogeneously dispersed, pulverization is suppressed, and electron conductivity is maintained. This manufacturing method is roughly classified into three methods: a casting method, a roll casting method, and a gas atomizing method. Regardless of which method is used, first, a raw material melt containing silicon or tin and an additional metal is prepared. The raw material is melted by high frequency melting. In the case of silicon, the temperature of the molten metal is preferably 1200 to 1500 ° C., particularly preferably 1300 to 1450 ° C. in view of the rapid cooling condition. For the same reason, the temperature is preferably 500 to 1500 ° C., particularly preferably 700 to 1300 ° C. in the case of tin.
[0021]
When using a casting method, a molten metal is poured into a cooled mold. The temperature of the mold is preferably 0 to 40C, particularly preferably 5 to 30C. Although the temperature of the mold rises due to the casting of the molten metal, the cooling rate of the molten metal is reduced by 10%. ² K / sec or more, especially 10 ³ It is preferable to keep the mold at a low temperature so as to be K / sec or more. The silicon compound or tin compound obtained by solidification of the molten metal is pulverized and sieved to obtain particles having a predetermined average particle size. For the pulverization, for example, an attritor, a fine mill, a jet mill or the like is used. It is preferable that the mold has a shape in which the silicon compound or tin compound obtained by solidification of the molten metal is easily crushed. From this viewpoint, it is preferable to use, for example, a mold having a flat shape.
[0022]
When the roll casting method is used, the molten metal is injected onto a peripheral surface of a copper roll rotating at a high speed. The rotation speed of the roll is preferably from 500 to 4000 rpm, particularly from 1000 to 2000 rpm, from the viewpoint of rapidly cooling the molten metal. When the rotation speed of the roll is represented by a peripheral speed, it is preferably from 8 to 70 m / sec, particularly preferably from 15 to 30 m / sec. By quenching the molten metal of the temperature in the above-mentioned range using a roll rotating at the speed in the above-mentioned range, the cooling rate becomes 10 ² K / sec or more, especially 10 ³ The speed becomes higher than K / sec. The injected molten metal is quenched in a roll to form a ribbon. The ribbon is pulverized and sieved to obtain particles having a predetermined average particle size. For the pulverization, those similar to those used in the casting method described above can be used.
[0023]
In the case of using the gas atomizing method, a molten metal is injected from a nozzle, and an inert gas such as argon is sprayed onto the molten metal at a pressure of 5 to 100 atm, preferably 5 to 50 atm to form particles and quench. The obtained particles are further pulverized and sieved to obtain particles having a predetermined average particle size.
[0024]
The composition of the negative electrode active material B obtained by these methods is similar to that of the negative electrode active material A in that the amount of silicon or tin is 30 to 99.9% by weight, and the amount of the added metal is 0.1 to 70% by weight. Preferably, there is. More preferably, the amount of silicon or tin is 40 to 90% by weight, and the amount of added metal is 10 to 60% by weight. When the negative electrode active material B is a ternary or higher alloy containing silicon or tin and an additive metal, B, Al, Ni, Co, Sn, Fe, Cr, in addition to silicon or tin and the additive metal. , Zn, In, V, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd and Nd. Thereby, an additional effect that pulverization is suppressed is exerted. In order to further enhance this effect, it is preferable that these elements are contained in an alloy of silicon or tin and the additional metal in an amount of 0.01 to 10% by weight, particularly 0.05 to 1.0% by weight.
[0025]
Next, a method for producing the negative electrode active material C will be described. In the present manufacturing method, first, a plating bath containing silicon or tin particles suspended therein and containing an additional metal is prepared. The average particle size of the silicon or tin particles is preferably 40 μm or less. In this plating bath, the silicon or tin particles are electrolessly plated to coat the surface of the silicon or tin particles with the additional metal. The concentration of silicon or tin particles in the plating bath is preferably about 400 to 600 g / l. When copper is electrolessly plated as an additional metal, it is preferable that copper sulfate, Rochelle salt, or the like be contained in the plating bath. In this case, the concentration of copper sulfate is preferably 6 to 9 g / l, and the concentration of Rochelle salt is preferably 70 to 90 g / l from the viewpoint of controlling the plating rate. For the same reason, the pH of the plating bath is preferably 12 to 13, and the bath temperature is preferably 20 to 30C. As the reducing agent contained in the plating bath, for example, formaldehyde or the like is used, and its concentration can be about 15 to 30 cc / l.
[0026]
In the negative electrode active material C thus obtained, the amount of silicon or tin is preferably 70 to 99.9% by weight, particularly preferably 80 to 99% by weight, particularly preferably 85 to 95%. On the other hand, the amount of the added metal is preferably 0.1 to 30% by weight, particularly preferably 1 to 20% by weight, particularly preferably 5 to 15% by weight.
[0027]
Next, a method for producing the negative electrode active material D will be described. This manufacturing method is similar to the method for manufacturing the negative electrode active material A described above. Therefore, the description of the manufacturing method of the negative electrode active material A is appropriately applied to the points which are not particularly described in the present manufacturing method. In the present production method, particles of silicon or tin or a compound thereof and D ₅₀ Mixing and pulverization with ultrafine particles of carbon having a value of 100 μm or less are performed simultaneously to obtain these mixed particles. For mixing and pulverization, mechanical milling is preferably used. By the mechanical milling, a negative electrode active material D composed of mixed particles in which silicon or tin or a compound thereof and carbon are uniformly mixed is obtained. Graphite is preferably used as carbon.
[0028]
When the negative electrode active material D is used, the cycle life is particularly improved and the negative electrode capacity is increased. The reason is as follows. Carbon, particularly graphite used for a negative electrode for a non-aqueous electrolyte secondary battery, contributes to the absorption and desorption of lithium, has a negative electrode capacity of about 300 mAh / g, and has a very large volume expansion when lithium is absorbed. It has the characteristic of being small. On the other hand, silicon has a feature that it has a negative electrode capacity of about 4200 mAh / g, which is 10 times or more that of graphite. On the other hand, silicon has a volume expansion of about four times that of graphite when absorbing lithium. Therefore, if silicon and carbon such as graphite are mixed and pulverized at a predetermined ratio using a mechanical milling method or the like to form a powder, the volume expansion of silicon during lithium occlusion is reduced by the graphite, and the cycle life is improved. Also, a negative electrode capacity of about 1000 to 3000 mAh / g can be obtained. The mixing ratio of silicon and carbon is preferably such that the amount of silicon is 10 to 90% by weight, particularly 30 to 70% by weight, particularly 30 to 50% by weight. On the other hand, the amount of carbon is preferably 90 to 10% by weight, particularly 70 to 30% by weight, particularly preferably 70 to 50% by weight. When the composition is within this range, it is possible to increase the capacity of the battery and extend the life of the negative electrode. In this mixed particle, a compound such as silicon carbide is not formed.
[0029]
The negative electrode active material D may be a mixture of three or more kinds of particles containing silicon or tin, or a compound of these or carbon and another metal element in addition to carbon. As the metal element, one or more of the above-described additive metals can be used.
[0030]
The negative electrode using the various negative electrode active materials manufactured according to the manufacturing method of the present invention, as described at the beginning, on one or both surfaces of the current collector, an active material layer composed of particles of the negative electrode active material, and on the layer The active material structure including the surface coating layer located in the above is formed. The active material layer composed of the negative electrode active material particles does not need to be completely covered with the surface coating layer, and may be partially exposed. However, from the viewpoint of preventing the negative electrode active material from falling off due to pulverization of the negative electrode active material due to absorption and desorption of lithium, it is preferable that the active material layer is completely covered by the surface coating layer. Even if the active material layer is completely covered by the surface coating layer, according to the method for manufacturing a negative electrode described below, a fine break occurs in the surface coating layer during press working, and the electrolyte and lithium are removed from the surface. It can penetrate into the inside of the coating layer and react with the negative electrode active material. FIGS. 1 and 2 show an example of a negative electrode in a state where the negative electrode active material is completely covered by the surface coating layer. In FIGS. 1 and 2, an active material layer 3 made of silicon-copper alloy particles is formed on a current collector 1 made of copper, and a surface coating layer 2 made of copper is formed on the active material layer 3. positioned. The active material layer 3 is completely covered by the surface coating layer 2. In the surface coating layer 2, fine breaks extending in the thickness direction are observed. Further, voids are observed between the alloy particles in the active material layer 3. In FIG. 1, it can be seen that a part of the surface coating layer 2 has entered the active material layer 3 and the surface of the alloy particles is coated with copper. On the other hand, in FIG. 2, the surface coating layer 2 does not enter the active material layer 3 so much, and the two

layers

2 and 3 are relatively clearly separated. Such a difference between the forms in FIGS. 1 and 2 is caused by the method for manufacturing the negative electrode.
[0031]
The current collector constituting the negative electrode is made of a metal that can be a current collector of the nonaqueous electrolyte secondary battery. In particular, it is preferably made of a metal that can be a current collector of a lithium secondary battery. Examples of such a metal include copper, iron, cobalt, nickel, zinc or silver, and alloys of these metals. It is particularly preferable to use copper or a copper alloy among these metals. When copper is used, the current collector is used in a copper foil state. This copper foil is obtained by, for example, electrolytic deposition using a copper-containing solution, and its thickness is preferably 2 to 100 μm, particularly preferably 10 to 30 μm. In particular, a copper foil obtained by the method described in JP-A-2000-90937 is preferably used because it has a very small thickness of 12 μm or less.
[0032]
The surface coating layer formed on the surface of the current collector is made of a conductive material having a low ability to form a lithium compound from the viewpoint of preventing the coating layer from oxidizing and falling off. Examples of such conductive materials include copper, silver, nickel, cobalt, chromium, indium, and alloys of these metals (eg, alloys of copper and tin). Among these metals, it is preferable to use copper, silver, nickel, chromium, cobalt, and alloys containing these metals, which are metals having a particularly low ability to form a lithium compound. In addition, a conductive plastic, a conductive paste, or the like can be used as the conductive material. "Low ability to form a lithium compound" means that no intermetallic compound or solid solution is formed with lithium, or even if formed, the amount of lithium is very small or very unstable.
[0033]
Since the active material layer is covered with the surface coating layer, the energy density per unit volume and unit weight of the secondary battery using the negative electrode of the present invention is much higher than that of the conventional battery. Further, since the negative electrode active material is confined by the surface coating layer, the falling of the negative electrode active material due to the absorption and desorption of lithium is effectively prevented. Further, generation of an electrically isolated negative electrode active material is effectively prevented, and the current collecting function is maintained. As a result, a decrease in the function as the negative electrode is suppressed. Further, the life of the negative electrode can be prolonged. In particular, when a part of the surface coating layer enters the active material layer, the current collecting function is more effectively maintained. When silicon or a silicon alloy, which is an active material, is formed on a current collector as it is, these particles are finely divided due to absorption and desorption of lithium, and are electrically isolated from the current collector. As a result, the function as the negative electrode decreases, and problems such as an increase in irreversible capacity, a decrease in charge / discharge efficiency, and a shortened life occur.
[0034]
The amount of the negative electrode active material in the active material structure including the active material layer and the surface coating layer is 5 to 80% by weight, preferably 10 to 50% by weight, and more preferably 20 to 50% by weight. If the amount of the negative electrode active material is less than 5% by weight, it is difficult to sufficiently improve the energy density of the battery. On the other hand, if it exceeds 80% by weight, the negative electrode active material tends to fall off, which causes problems such as an increase in irreversible capacity, a decrease in charge / discharge efficiency, and a shortened life.
[0035]
The active material layer preferably contains particles of a conductive carbon material in addition to the above-described negative electrode active material. Thereby, the electron conductivity is further imparted to the active material structure. From this viewpoint, the amount of the conductive carbon material contained in the active material layer is preferably 0.1 to 20% by weight, particularly preferably 1 to 10% by weight. The particle size of the conductive carbon material particles is preferably 40 μm or less, particularly preferably 20 μm or less, from the viewpoint of further imparting electron conductivity. There is no particular limitation on the lower limit of the particle size of the particles, and the smaller the value, the better. In view of the method for producing the particles, the lower limit is about 0.01 μm. Examples of the conductive carbon material include acetylene black, graphite, and the like.
[0036]
The thickness of the surface coating layer is preferably from 0.3 to 50 μm, particularly from 0.3 to 10 μm, particularly preferably from 1 to 10 μm, from the viewpoint of preventing the negative electrode active material from falling off and maintaining the current collecting function. Specifically, when the thickness is 0.3 μm or more, falling off due to expansion and contraction of the active material can be effectively prevented, and when the thickness is 50 μm or less, charge and discharge are not hindered. The thickness of the active material layer is preferably from 1 to 100 μm, particularly preferably from 3 to 40 μm, from the viewpoint of ensuring sufficient negative electrode capacity. The thickness of the active material structure including the surface coating layer and the active material layer is preferably 2 to 100 μm, particularly preferably about 2 to 50 μm.
[0037]
Next, a preferred method for producing the negative electrode will be described. In the present manufacturing method, first, a slurry to be applied to the surface of the current collector is prepared. The slurry contains particles of the negative electrode active material, particles of the conductive carbon material, a binder, and a diluting solvent produced according to the production method of the present invention. Among these components, the particles of the negative electrode active material and the particles of the conductive carbon material are as described above. As the binder, polyvinylidene fluoride (PVDF), polyethylene (PE), ethylene propylene diene monomer (EPDM), or the like is used. As a diluting solvent, N-methylpyrrolidone, cyclohexane or the like is used.
[0038]
The amount of the negative electrode active material particles in the slurry is preferably about 14 to 40% by weight. The amount of the conductive carbon material particles is preferably about 0.4 to 4% by weight. The amount of the binder is preferably about 0.4 to 4% by weight. The amount of the diluting solvent is preferably about 60 to 85% by weight.
[0039]
This slurry is applied to the surface of the current collector to form an active material layer. The current collector may be manufactured in advance, or may be manufactured in-line as one step in the manufacturing process of the negative electrode of the present invention. When the current collector is manufactured in-line, it is preferably manufactured by electrolytic deposition. The amount of the slurry applied to the current collector is preferably such that the thickness of the active material layer after drying is about 1 to 3 times the thickness of the finally obtained active material structure. . After the slurry coating is dried to form the active material layer, the current collector on which the active material layer is formed is immersed in a plating bath containing a conductive material having a low ability to form a lithium compound. Under this condition, the surface of the active material layer is electroplated with the conductive material to form a surface coating layer. Electroplating conditions include, for example, when copper, which is a metal, is used as the conductive material, and when a copper sulfate-based solution is used, the concentration of copper is 30 to 100 g / l, the concentration of sulfuric acid is 50 to 200 g / l, and the concentration of chlorine is The concentration is 30 ppm or less, the liquid temperature is 30 to 80 ° C., and the current density is 1 to 100 A / dm. ² And it is sufficient. In this case, the above-described negative electrode having the form shown in FIG. 1 is obtained. When a copper pyrophosphate-based solution is used, the concentration of copper is 2 to 50 g / l, the concentration of potassium pyrophosphate is 100 to 700 g / l, the liquid temperature is 30 to 60 ° C., the pH is 8 to 12, and the current density is 1 -10A / dm ² And it is sufficient. In this case, the above-described negative electrode having the form shown in FIG. 2 is obtained.
[0040]
After the surface coating layer is thus formed on the active material layer, the active material layer is pressed together with the surface coating layer. Thereby, the active material layer is compacted. Due to the compaction, the gap between the negative electrode active material particles and the conductive carbon material particles was filled with the conductive material forming the surface coating layer, and the negative electrode active material particles and the conductive carbon material particles were dispersed. State. In addition, these particles and the surface coating layer adhere to each other to provide electron conductivity. From the viewpoint of obtaining sufficient electron conductivity, in the consolidation by pressing, the sum of the thicknesses of the active material layer and the surface coating layer after pressing is 90% or less, preferably 80% or less before pressing. It is preferable to carry out as follows. For the press working, for example, a roll press machine can be used. It is preferable that the active material layer after the press working has a void of 5 to 30% by volume. Due to the presence of this void, when lithium is absorbed during charging and the volume expands, the stress caused by the volume expansion is reduced. Such a gap may be controlled by controlling the press working conditions as described above. The value of this gap can be determined by electron microscope mapping.
[0041]
In the present manufacturing method, it is preferable to press the active material layer before performing electroplating on the active material layer (this pressing is referred to as pre-pressing in the sense of being distinguished from the pressing described above). Call). By performing the pre-pressing, separation of the active material layer from the current collector is prevented, and particles of the negative electrode active material are prevented from being exposed on the surface of the surface coating layer. As a result, it is possible to prevent the cycle life of the battery from deteriorating due to the falling off of the particles of the negative electrode active material. The conditions for the pre-pressing are preferably such that the thickness of the active material layer after the pre-pressing is 95% or less, particularly 90% or less, of the thickness of the active material layer before the pre-pressing.
[0042]
The negative electrode thus obtained is used together with a known positive electrode, a separator, and a non-aqueous electrolyte to form a non-aqueous electrolyte secondary battery. The positive electrode is prepared by suspending a positive electrode active material and, if necessary, a conductive agent and a binder in an appropriate solvent to prepare a positive electrode mixture, applying the mixture to a current collector, drying the roll, rolling, pressing, and further cutting. , By punching. As the positive electrode active material, a conventionally known positive electrode active material such as a lithium nickel composite oxide, a lithium manganese composite oxide, and a lithium cobalt composite oxide is used. As the separator, a synthetic resin nonwoven fabric, a polyethylene or polypropylene porous film, or the like is preferably used. In the case of a lithium secondary battery, the nonaqueous electrolyte is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. As the lithium salt, for example, LiC1O ₄ , LiA1Cl ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiSCN, LiCl, LiBr, LiI, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ Etc. are exemplified.
[0043]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such an embodiment. In the following examples, “%” means “% by weight” unless otherwise specified.
[0044]
[Example 1]
(1) Production of negative electrode active material
Silicon and copper were melted by high frequency melting. The temperature of the molten metal was 1400 ° C. This molten metal was poured into a mold cooled to 5 ° C. The shape of the mold was flat. The cooling rate of the molten metal is 10 ² It was K / sec or more. The silicon-copper alloy obtained by solidification was pulverized using an attritor and further sieved to obtain a D shown in Table 1. ₅₀ A negative electrode active material particle having a value was obtained. The composition of the negative electrode active material was as shown in the same table.
(2) Preparation of slurry
A slurry having the following composition was prepared.
-Silicon-copper alloy particles 16%
・ Acetylene black (particle size 0.1μm) 2%
・ Binder (polyvinylidene fluoride) 2%
-Diluent solvent (N-methylpyrrolidone) 80%
[0045]
(2) Formation of active material layer
The prepared slurry was applied on a copper foil having a thickness of 30 μm and dried. The thickness of the active material layer after drying was 60 μm.
[0046]
(3) Formation of surface coating layer
The copper foil on which the active material layer was formed was immersed in a plating bath having the following composition, and electrolytic plating was performed on the active material layer.
・ Copper 50g / l
・ Sulfuric acid 60g / l
・ Bath temperature 40 ℃
After the formation of the surface coating layer, the copper foil was pulled out of the plating bath, and then the active material layer was roll-pressed together with the surface coating layer to be consolidated. The thickness of the surface coating layer thus obtained was 20 μm as observed by an electron microscope. As a result of chemical analysis, the amount of silicon-copper alloy particles in the active material structure was 45%, and the amount of acetylene black was 5%.
[0047]
[Examples 2 to 12]
A negative electrode active material particle composed of a silicon-based alloy having the composition shown in Table 1 was produced by casting, and a negative electrode was obtained in the same manner as in Example 1 except for using the particle.
[0048]
[Example 13]
Silicon and copper were melted by high frequency melting. The temperature of the molten metal was 1400 ° C. This molten metal was injected onto a peripheral surface of a copper roll rotating at high speed. The rotation speed of the roll was 1000 rpm. The injected molten metal was quenched in a roll to form a silicon-copper alloy ribbon. The cooling rate at this time is 10 ³ This ribbon, which had a K / sec or more, was pulverized using an attritor and further sieved. ₅₀ A negative electrode active material particle having a value was obtained. The composition of the negative electrode active material was as shown in the same table. Except for this, the negative electrode was obtained in the same manner as in Example 1.
[0049]
[Example 14]
Negative electrode active material particles having the composition and particle size shown in Table 1 were produced, and a negative electrode was obtained in the same manner as in Example 13 except for using the particles.
[0050]
[Example 15]
Silicon and copper were melted by high frequency melting. The temperature of the molten metal was 1400 ° C. This molten metal was injected from a nozzle, and 30 atm of argon gas was blown there. The molten metal was quenched into silicon-copper alloy particles. The particles were pulverized using an attritor and further sieved to obtain D as shown in Table 1. ₅₀ A negative electrode active material particle having a value was obtained. The composition of the negative electrode active material was as shown in the same table. Except for this, the negative electrode was obtained in the same manner as in Example 1.
[0051]
[Example 16]
Negative electrode active material particles having the composition and particle size shown in Table 1 were produced, and a negative electrode was obtained in the same manner as in Example 15 except for using the particles.
[0052]
[Example 17]
In a plating bath containing suspended silicon particles having a particle size of 0.2 to 8 μm and containing copper sulfate and Rochelle salt, the silicon particles are subjected to electroless plating to coat the surface of the silicon particles with copper. Coated silicon particles were obtained. The concentration of silicon particles in the plating bath was 500 g / l, the concentration of copper sulfate was 7.5 g / l, and the concentration of Rochelle salt was 85 g / l. The pH of the plating bath was 12.5, and the bath temperature was 25 ° C. Formaldehyde was used as the reducing agent, and its concentration was 22 cc / l. D of the obtained particles ₅₀ The values were as shown in Table 1. The composition of the particles was as shown in the table. Except for this, the negative electrode was obtained in the same manner as in Example 1.
[0053]
[Examples 18 to 21]
Negative electrode active material particles having the composition and particle size shown in Table 1 were produced, and a negative electrode was obtained in the same manner as in Example 17 except for using the particles.
[0054]
[Example 22]
Silicon particles (D ₅₀ 95%) and copper particles (D ₅₀ 5% (value 1 μm) were mixed and these particles were simultaneously mixed and ground by an attritor. As a result, a particle diameter of 0.1 to 10 μm (D ₅₀ 2 μm) were obtained. A negative electrode was obtained in the same manner as in Example 1 except that the mixed particles were used.
[0055]
[Examples 23 to 30]
A negative electrode was obtained in the same manner as in Example 22 except that particles of the negative electrode active material having the composition and particle diameter shown in Table 2 were produced, and the particles were used. In addition, D of the added metal particles ₅₀ Each value was 1 μm.
[0056]
[Examples 31 and 32]
Silicon and copper were melted by high frequency melting. The temperature of the molten metal was 1400 ° C. This molten metal was poured into a mold cooled to 5 ° C. The shape of the mold was flat. The cooling rate of the molten metal is 10 ² It was K / sec or more. The silicon-copper alloy obtained by solidification was pulverized using an attritor and further sieved. The composition of the silicon-copper alloy was as shown in Table 2. A negative electrode was prepared in the same manner as in Example 22 except that the silicon-copper alloy particles were used in place of the silicon particles used in Example 22, and the ratio between the silicon-copper alloy particles and the copper particles was set to a value shown in Table 2. Got.
[0057]
[Examples 33 and 34]
A negative electrode was obtained in the same manner as in Examples 31 and 32 except that silver particles were used instead of copper particles in Examples 31 and 32. In addition, D of silver particles ₅₀ The value was 1 μm.
[0058]
[Examples 35 to 46]
Negative electrode active material particles composed of a tin-based alloy having the composition shown in Table 3 were produced by casting, and a negative electrode was obtained in the same manner as in Example 1 except that the particles were used.
[0059]
[Examples 47 and 48]
A negative electrode was obtained in the same manner as in Example 13 except that particles of a negative electrode active material composed of a tin-based alloy having the composition shown in Table 3 were produced by roll casting, and the particles were used.
[0060]
[Examples 49 and 50]
Negative electrodes were obtained in the same manner as in Example 15 except that particles of a negative electrode active material composed of a tin-based alloy having the composition shown in Table 3 were produced by gas atomization, and the particles were used.
[0061]
[Examples 51 to 55]
Negative electrode active material particles having the composition shown in Table 3 were produced by electroless plating, and a negative electrode was obtained in the same manner as in Example 17 except for using the particles.
[0062]
[Examples 56 to 68]
Mixed particles of the negative electrode active material having the composition shown in Table 4 were produced, and a negative electrode was obtained in the same manner as in Example 22 except that the mixed particles were used. In addition, D of the added metal particles ₅₀ Each value was 1 μm.
[0063]
(Example 69)
Silicon particles (particle diameter 100 μm) 20% and graphite particles (D ₅₀ 80%), and these particles were simultaneously mixed and pulverized by mechanical milling. As a result, a particle size of 0.5 μm (D ₅₀ Value). A negative electrode was obtained in the same manner as in Example 22, except that the mixed particles were used and the surface coating layer was formed from nickel.
[0064]
[Examples 70 to 73]
A negative electrode was obtained in the same manner as in Example 69 except that the composition of the mixed particles was changed to the values shown in Table 4.
[0065]
(Performance evaluation)
Using the negative electrodes obtained in Examples and Comparative Examples, nonaqueous electrolyte secondary batteries were produced as follows. The irreversible capacity, the volume capacity density during charge, the charge / discharge efficiency during 10 cycles, and the capacity retention rate at 50 cycles were measured by the following methods. The results are shown in Tables 1 to 4 below.
[0066]
(Preparation of non-aqueous electrolyte secondary battery)
Metal lithium was used as a counter electrode, the negative electrode obtained above was used as a working electrode, and both electrodes were opposed to each other via a separator. Further, as a non-aqueous electrolyte, LiPF ₆ / A non-aqueous electrolyte secondary battery was prepared by a usual method using a mixed solution of ethylene carbonate and diethyl carbonate (1: 1 volume ratio).
[0067]
(Irreversible capacity)
Irreversible capacity (%) = (1−first discharge capacity / first charge capacity) × 100
That is, it indicates the capacity that was charged but could not be discharged and remained in the active material.
[0068]
[Capacity density]
This shows the initial discharge capacity. The unit is mAh / g.
[0069]
[Charge / discharge efficiency during 10 cycles]
Charge / discharge efficiency at 10 cycles (%) = discharge capacity at 10th cycle / charge capacity at 10th cycle × 100
[0070]
[50 cycle capacity maintenance rate]
50 cycle capacity retention rate (%) = discharge capacity at 20th cycle / maximum discharge capacity × 100
[0071]
[Table 1]

[0072]
[Table 2]

[0073]
[Table 3]

[0074]
[Table 4]

[0075]
As is clear from the results shown in Tables 1 to 4, the secondary batteries using the negative electrode active material obtained in each of the examples have the same irreversible capacity, charge / discharge efficiency, and capacity retention ratio as the conventional secondary batteries. Further, it can be seen that the capacity density is much higher than that of the conventional secondary battery.
[0076]
【The invention's effect】
As described in detail above, according to the negative electrode for a non-aqueous electrolyte secondary battery using the negative electrode active material obtained according to the production method of the present invention, it is possible to obtain a secondary battery having a higher energy density than a conventional negative electrode. it can. Further, according to the negative electrode for a non-aqueous electrolyte secondary battery using the negative electrode active material obtained according to the production method of the present invention, the active material is prevented from peeling off from the current collector, and the active material is repeatedly charged and discharged. Current collecting performance is secured. In addition, a secondary battery using this negative electrode has a low deterioration rate even when charge and discharge are repeated, greatly increases the life, and increases the charge and discharge efficiency.
[Brief description of the drawings]
FIG. 1 is a scanning electron microscope image showing an example of a negative electrode using a negative electrode active material obtained according to the production method of the present invention.
FIG. 2 is a scanning electron microscope image showing another example of the negative electrode using the negative electrode active material obtained according to the production method of the present invention.
[Explanation of symbols]
1 current collector
2 Coating layer
3 Active material layer

Claims

It is composed of mixed particles of silicon or tin or a compound thereof and a metal, wherein the metal is Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, or Sn (however, the other of the mixed particles is tin or (Except when the compound is the compound), Si (except when the other of the mixed particles is silicon or the compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which is at least one element selected from the group consisting of Pd and Nd,
Silicon or tin or particles and D ₅₀ value is 100μm or less of the metal ultrafine particles and the mixing and simultaneously performs nonaqueous electrolyte negative electrode for a secondary battery, characterized by obtaining mixed particles of both the grinding of these compounds Active material manufacturing method.

The process according to claim 1, wherein ₅₀ value D of the ultrafine particles of the metal is 20μm or less.

It is composed of particles of a silicon compound or a tin compound, and the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, or Sn (where the other of the mixed particles is tin or a compound thereof). ), Si (except when the other of the mixed particles is silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd. And a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Nd,
Dissolving silicon or tin and the element by high-frequency melting to form a molten metal, casting the molten metal into a cooled mold, cooling and solidifying to obtain the compound, and pulverizing the compound into particles. Of producing a negative electrode active material for a non-aqueous electrolyte secondary battery.

It is composed of particles of a silicon compound or a tin compound, and the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, or Sn (where the other of the mixed particles is tin or a compound thereof). ), Si (except when the other of the mixed particles is silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd. And a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Nd,
Dissolving silicon or tin and the element by high-frequency melting to form a molten metal, injecting the molten metal into a rotating copper roll to obtain a ribbon made of the compound, and crushing the ribbon into particles; A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, comprising the steps of:

It is composed of particles of a silicon compound or a tin compound, and the particles are composed of silicon or tin and Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, or Sn (where the other of the mixed particles is tin or a compound thereof). ), Si (except when the other of the mixed particles is silicon or its compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr, Pd. And a method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery including one or more elements selected from the group consisting of Nd,
Silicon or tin and the element are melted by high frequency melting to form a molten metal, the molten metal is injected from a nozzle, and an inert gas of 5 to 100 atm is sprayed thereon to obtain particles made of the compound. A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery, which is further pulverized.

The surface of silicon or tin particles is made of particles coated with a metal, and the metal is made of Ag, Cu, Ni, Co, Fe, Cr, Zn, B, Al, Ge, or Sn (provided that the other of the mixed particles is tin or tin). (Except when the compound is the compound), Si (except when the other of the mixed particles is silicon or the compound), In, V, Ti, Y, Zr, Nb, Ta, W, La, Ce, Pr. , A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising one or more elements selected from the group consisting of Pd and Nd,
A negative electrode active material for a non-aqueous electrolyte secondary battery, comprising suspending silicon or tin particles in a plating bath containing the metal, performing electroless plating, and coating the surface of the particles with the metal. Manufacturing method.

A method for producing a negative electrode active material for a non-aqueous electrolyte secondary battery comprising at least silicon or tin or a mixed particle of these compounds and carbon,
Silicon or tin or particles and D ₅₀ value is less mixing and simultaneously performs negative active for a non-aqueous electrolyte secondary battery, characterized by obtaining a mixture of these particles milled with ultrafine particles of carbon 100μm of these compounds The method of manufacturing the substance.