JP3805053B2 - Lithium secondary battery - Google Patents
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- JP3805053B2 JP3805053B2 JP02663797A JP2663797A JP3805053B2 JP 3805053 B2 JP3805053 B2 JP 3805053B2 JP 02663797 A JP02663797 A JP 02663797A JP 2663797 A JP2663797 A JP 2663797A JP 3805053 B2 JP3805053 B2 JP 3805053B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Description
【0001】
【発明の属する技術分野】
本発明は、リチウムを吸蔵、放出する活物質を有する正極、負極、及びリチウムイオン移動媒体を有する二次電池に関するものである。
【0002】
【従来の技術】
近年、電子機器の小型化、軽量化は目覚ましく、それに伴い電源となる電池に対しても小型、軽量かつ高エネルギー密度である事が望まれている。一次電池の分野では既にリチウム電池等の小型軽量電池が実用化されているが、これらは一次電池であるが故に繰り返し使用できず、その用途分野は限られたものであった。一方、二次電池の分野では従来より鉛電池、ニッケル−カドミウム電池が用いられてきたが、両者とも小型軽量化という点で大きな問題点を有している。かかる観点から、非水電解液二次電池が注目され、リチウムを負極に用いた非水電解液二次電池の研究開発が盛んに行われている。この電池は高エネルギー密度を有し、自己放電も少なく、軽量という優れた特徴を有するものである。しかし、この非水電解液二次電池では、充放電サイクルの進行に伴い、充放電時にリチウムがデンドライト状に結晶成長し、正極に到達して内部短絡に至る可能性が高くなる欠点が有り、実用化への大きな障害となっている。
【0003】
そこで、リチウムをインターカレート又はドーピングする炭素材料を負極活物質(以下、炭素負極という)に用いた種々の非水電解液二次電池が提案された。炭素材料については、インターカレーションを利用したものとして、黒鉛層間化合物を負極として用いることが、例えば特開昭59−143280号公報に記載されている。また、ドーピング現象を利用した負極材料として、樹脂焼成体やコークス等の炭素質材料を用いることが、特開昭58−35881号公報、特開昭58−209864号公報、特開昭59−173979号公報、特開昭62−90863号公報、特開昭63−13282号公報、特開平2−66856号公報などに記載されている。実際に、黒鉛や難黒鉛化炭素を負極活物質に用いた二次電池が実用化されている。
【0004】
また、Al,Ge,Si,Sn,Zn,Pbなどの金属又は半金属は、リチウムと合金化する事が公知化されており、これらの合金化された負極活物質(以下、合金負極という)に用いた二次電池が検討されている。このような二次電池は、高容量かつ高エネルギー密度であり、炭素負極よりも多くのリチウムイオンを吸蔵、放出できるため、炭素負極を用いた場合に比べると、高容量かつ高エネルギー密度な二次電池を得ることができるが、サイクル特性が悪いため実用化に至っていない。
【0005】
最近では、炭素負極よりも高容量、かつサイクル寿命が長い二次電池の開発が試みられており、負極材料として鉄珪化物、ニッケル珪化物、マンガン珪化物を用いたものが開示されている(特開平5−159780号公報、特開平8−153517号公報、特開平8−153538号公報)。また、Mg2GeやNiSi2などのCaF2型構造金属間化合物が負極材料として高容量である事が、第36回電池討論会にて公知化されている。
【0006】
【発明が解決しようとする課題】
しかしながら、携帯型電子機器の高性能化や小型化は今後も続くと考えられ、二次電池の更なる高容量化、高エネルギー密度化が望まれている。
そこで本発明の目的は、従来知られているリチウム、或いはリチウムと合金化する金属又は半金属を負極活物質に用いた二次電池と同等の容量及びエネルギー密度を有し、かつ従来の炭素材料を負極活物質に用いた二次電池と同等のサイクル特性を有する優れた二次電池を提供するものである。
【0007】
【課題を解決するための手段】
本発明は前記課題を解決するためになされたものである。
即ち、本発明の一は、リチウムを吸蔵、放出することのできる活物質を用いた正極、負極、及びリチウムイオン移動媒体を有する二次電池において、正極活物質として、化学組成式Li x M y N z O 2 (Mはコバルト、ニッケル、マンガン及びその他の遷移金属から選ばれる少なくとも1種を表し、Nは非遷移金属の少なくとも一種を表わし、x,y,zは各々0.05<x<1.10、0.85≦y≦1.00、0≦z<0.10)またはLi (1+x) Mn (2−x) O 4 (0≦X≦1)で表わされるリチウム含有金属酸化物を用い、負極活物質として、Ge,Si,Sn,Znの元素群から選ばれる少なくとも1種類以上の元素と上記元素群以外の金属ないしは半金属との金属間化合物(ただしプラズマ溶射ないし減圧プラズマ溶射やパルスプラズマ蒸着方式で被覆層を設ける場合を除く)であって、CuKα線を用いたX線回折法で最も強度の強いピークの半値幅が2θ値で0.6°以上である低結晶性の金属間化合物、またはCuKα線を用いたX線回折法で2θ値で20°から40°に頂点を有するブロードな散乱帯を有する非晶質の金属間化合物を用いる事を特徴とする二次電池を提案するものである。
また、本発明の二は、Ge,Si,Sn,Znの元素群から選ばれる少なくとも1種類以上の元素と上記元素群以外の金属ないしは半金属との結晶性の金属間化合物をボールミルで機械的破壊を行う、または各純元素からの機械的合金化によって、CuKα線を用いたX線回折法で最も強度の強いピークの半値幅が2θ値で0.6°以上である低結晶性の金属間化合物からなる負極活物質を作製する工程を含む本発明の一の二次電池の製造方法を提案するものである。
また、本発明の三は、Ge,Si,Sn,Znの元素群から選ばれる少なくとも1種類以上の元素と上記元素群以外の金属ないしは半金属との結晶性の金属間化合物を溶融させ液体ロール急冷法によって、CuKα線を用いたX線回折法で2θ値で20°から40°に頂点を有するブロードな散乱帯を有する非晶質の金属間化合物からなる負極活物質を作製する工程を含む本発明の一の二次電池の製造方法を提案するものである。
【0008】
本発明の二次電池は、従来の合金負極を用いた二次電池よりもサイクル特性が遥かに優れ、また炭素負極よりも容量、エネルギー密度に優れており、これら両者の長所を有しているのである。
この理由としては、合金負極では繰り返して充放電した時に活物質の微結晶化、微粉化がみられるが、本発明の二次電池では、Ge,Si,Sn,Znなどリチウムと合金化する元素の周りにリチウムと合金化しにくい他の元素が存在する事で、上記のような微結晶化、微粉化が抑制されている事によると推察している。リチウムと合金化しにくい元素としては、B,Co,Cr,Cu,Fe,Mn,Mo,Ni,Ti,V,Wなどが挙げられる。
【0009】
また、本発明に用いる金属間化合物は低結晶性ないしは非晶質である。低結晶性とは、CuKα線を用いたX線回折法で、最も強度の強いピークの半値幅が、2θ値で0.6°以上である事を言う。また、ここで言う非晶質とは、CuKα線を用いたX線回折法で、2θ値で20°から40°に頂点を有するブロードな散乱帯を有するものであり、結晶性のピークを有してもよい。低結晶性又は非晶質である金属間化合物を用いる事で、繰り返し充放電に伴う活物質の微結晶化及び、又は微粉化がほとんど起きないため、サイクル特性をさらに向上させることができる。
【0010】
本発明の二次電池の基本構成要素としては、リチウムを吸蔵、放出できる活物質からなる負極と正極、及びリチウムイオン移動媒体が挙げられる。
本発明の二次電池に用いる負極活物質である金属間化合物を具体的に例示するが、特に限定はされない。
【0011】
Geを含有するものとしては、As3GeLi5,CoFeGe,CoGeMn,FeGe2,Fe1.7Ge,FeGeMn,FeGeNi,GeLi5P3,GeMg2,GeMnNi,GeMo3,β’−Ge2Mo,GeNb3,GeNi1.70,GeNi3,Ge3Pu,Ge3U,GeV3などが挙げられる。
Siを含有するものとしては、As3Li5Si,BeSiZr,CoSi2,β−Cr3Si,Cu3Mg2Si,Fe3Si,Li5P3Si,Mg2Si,MoSi2,Nb3Si,NiSi2,θ−Ni2Si,β−Ni3Si,ReSi2,α−RuSi,SiTa2,Si2Th,Si2U,β−Si2U,Si3U,SiV3,Si2W,SiZr2などが挙げられる。
【0012】
Snを含有するものとしては、AsSn,AuSn,CaSn3,CeSn3,CoCu2Sn,Co2MnSn,CoNiSn,CoSn2,Co3Sn2,CrCu2Sn,(Cr,Ni)Cu2Sn,Cu2FeSn,CuMgSn,Cu2MnSn,Cu4MnSn,(Cu,Ni)3Sn,Cu2NiSn,CuSn,FeSn2,IrSn,IrSn2,LaSn3,MgNi2Sn,Mg2Sn,MnNi2Sn,MnSn2,Mn2Sn,Mo3Sn,Nb3Sn,NdSn3,NiSn,Ni3Sn2,PdSn,Pd3Sn,Pd3Sn2,PrSn3,PtSn,PtSn2,Pt3Sn,PuSn3,RhSn,Rh3Sn2,RuSn2,SbSn,SnTi2,Sn3U,SnV3などが挙げられる。
【0013】
Znを含有するものとしては、AgAsZn,β−AgZn,AsLiZn,AsNaZn,β−AuZn,CeZn,β’−CuZn,EuZn,LaZn,LiPZn,MgNiZn,MgZn2,PrZn,Pt3Zn,PuZn2,Th2Zn,TiZn2,TiZn3,Zn2Zrなどが挙げられる。
本発明の二次電池に用いる金属間化合物の組成は、金属間化合物を粉末のまま蛍光X線分析する、又は濃塩酸、熱濃硫酸、濃硝酸、王水などで粉末を溶解した水溶液をICP分析や原子吸光分析する事などにより同定できる。また、上記金属間化合物の組成にはないBやCoなどの他元素、又は他の化合物を10wt%未満であれば含有していてもよい。
【0014】
結晶性の金属間化合物は、各純元素を所定量秤量し混合した粉末又は粒状物を、アルゴンや窒素などの不活性ガス雰囲気下で、電気炉又は高周波誘導加熱装置又はアーク熔解炉などで、融点以上沸点以下の温度まで加熱し溶解させ、その後固化させる事により得られる。その他に、還元拡散法を用いる事で、各酸化物から得ることもできる。また、低結晶性又は非晶質にしたい場合は、前記のように作製した結晶性の金属間化合物を高周波誘導加熱装置やプラズマジェット装置、赤外集中加熱装置などで溶融させ、公知の超急冷法を用いる。超急冷法としては、セラミックスプロセッシング(技報堂出版 1987)218−219頁記載のgun法、Hammer−Anvil法、slap法、ガスアトマイズ法、水アトマイズ法、ディスク式アトマイズ法、プラズマスプレー法、遠心急冷法、片ロール法、双ロール法、melt drag法などがある。特に片ロール法や双ロール法のような液体ロール急冷法では105〜106K/sec、ガスアトマイズ法では104〜105K/secの冷却速度が得られ、本発明の非晶質金属間化合物を容易に得ることができる。スパッタ法により薄膜状の非晶質金属間化合物を得ることも可能である。また、結晶性の金属間化合物をボールミルなどで機械的破壊を行う、または各純元素からの機械的合金化によっても低結晶性又は非晶質な金属間化合物の作製が可能である。
【0015】
以上のような方法で得られた、板状インゴット又は球状、フレーク状の粉末又はリボン状などの形態を有する金属間化合物を、公知の粉砕、分級、混合方法を用いる事により、微粉末状にし粒度分布を調整する。平均粒径としては、1μm以上、50μm以下である事が好ましい。
本発明の二次電池に用いる電極は、電極集電体上に電極合剤層が形成されたものを用いる。このような電極は、前記金属間化合物と結着剤、必要に応じて導電フィラーを混合した電極合剤を溶剤に分散させることにより得られた電極合剤スラリーを電極集電体に塗工し、その後乾燥して得る。また必要に応じて、ローラープレスを行う。
【0016】
本発明の負極に用いる集電体としては特に限定されないが、Cu、Ni、ステンレススチールなどの10−100μ程度の厚みの金属製箔又は網などを用いる。結着剤としてはポリテトラフルオロエチレン、ポリトリフルオロエチレン、ポリエチレン、ニトリルゴム、ポリブタジエンゴム、ブチルゴム、ポリスチレン、スチレンブタジエンゴム、スチレンブタジエンラテックス、多硫化ゴム、ニトロセルロース、アクリロニトリルブタジエンゴム、ポリフッ化ビニル、ポリフッ化ビニリデンやフッ素ゴムなどが望ましいが、特に制限されない。
【0017】
また、活物質の電気抵抗が高い時は、導電性を上げるために導電フィラーを添加する事がある。導電フィラーとしては、黒鉛やカーボンブラックなどの炭素材料や、Cu,Fe,Tiなどの金属粉末を用いる。
本発明の負極と組み合わされる正極の活物質としては、化学組成式LixMyNzO2(Mはコバルト、ニッケル、マンガン及びその他の遷移金属から選ばれる少なくとも1種を表し、Nは非遷移金属の少なくとも一種を表わし、x,y,zは各々0.05<x<1.10、0.85≦y≦1.00、0≦z<0.10)で表わされるリチウム含有金属酸化物を用いることができる。これらは電位が高く、電池として高電圧が得られ、またサイクル性が良好である。上記のMとしては、Co、Ni、Mnの単独、及びCo/Ni、Mn/Cr、Mn/Feの複合が特に好ましい。上記のNとしては、非遷移金属であれば特に制限はないが、Al、In、Snが好ましい。また、Li(1+x)Mn(2−x)O4(0≦X≦1)で表わされるリチウム含有金属酸化物も用いる事ができる。
【0018】
正極の集電体としては、Al、Cu、Ni、ステンレススチールなどの10〜100μm程度の厚みの金属製箔又は網などを用いる事ができるが、リチウム含有遷移金属酸化物のような4V級の電位を有する活物質を用いる場合には、Al製の金属製箔又は網を用いる事が好ましい。
本発明に用いられるリチウムイオン媒体としては、例えばリチウム塩を非プロトン性有機溶媒に溶解した溶液や、リチウム塩を高分子マトリックスに分散させた固体、或いはリチウム塩を非プロトン性有機溶媒に溶解した溶液と高分子マトリックスの混合物などが用いられる。前記有機溶媒は、エチレンカーボネートと、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネートなどの直鎖カーボネートが必須成分として含有している事が望ましい。その他エーテル類、ケトン類、ラクトン類、ニトリル類、アミン類、アミド類、スルホン系化合物、カーボネート類、エステル類などを含有していてもよい。これらの代表例としては、プロピレンカーボネート、1,2−ジメトキシエタン、1,2−ジエトキシエタン、γ−ブチルラクトン、テトラヒドロフラン、1,3−ジオキソラン、4−メチル−1,3−ジオキソラン、ジエチルエーテル、スルホラン、メチルスルホラン、アセトニトリル、プロピオニトリルなどが挙げられるが、必ずしもこれらに限定されるものではない。前記リチウム塩としては、LiBF4、LiPF6、LiClO4、LiAsF6、CF3SO3Li、CH3SO3Li、LiI、LiP、LiCl、LiBr、(CF3SO2)2NLiなどがあげられる。また、前記高分子マトリックスとしては、例えばポリエチレンオキシド、ポリプロピレンオキシド、ポリテトラメチレンオキシド、ポリビニルアルコール、ポリビニルブチラールなどの脂肪族ポリエーテル、ポリエチレンスルフィド、ポリプロピレンスルフィドなどの脂肪族ポリチオエーテル、ポリエチレンサクシネート、ポリブチレンアジペート、ポリカプロラクトンなどの脂肪族ポリエステル、ポリエチレンイミン、ポリイミド、ポリフッ化ビニリデン、及びその前駆体などを用いることができる。
【0019】
また、正極と負極の間に、短絡防止のためのセパレータを設ける事ができる。セパレータとしては、ポリエチレン、ポリプロピレンなどのポリオレフィンの単独の微多孔膜、或はそれらを貼り合わせた膜や、ポリオレフィン、ポリエステル、ポリアミド、セルロースなどの不織布も単独で、或は上記微多孔膜と貼り合わせた膜を使用できる。
【0020】
本発明の二次電池のその他構成要素として、端子、絶縁板、金属缶等の部品が用いられる事がある。また、本発明を図1に示すような電池缶として使用する場合には、材質としてステンレススチール、ニッケル鍍金スチール、鉄、アルミニウムなどを用いる。
電池の構造としては、特に限定されないが、正極、負極とセパレータを単層又は復層としたペーパー型電池、積層型電池、又は正極、負極とセパレータをロール状に巻いた、図1に示す円筒状や、角形状電池などの形態が挙げられる。
【0021】
【発明の実施の形態】
以下、実施例、比較例により本発明をさらに詳しく説明するが、本発明の範囲はこれに限定されるものではない。
【0022】
【実施例】
比較例1−F〜1−N
負極活物質として、高結晶性のGeMg 2 ,GeNi3,Mg2Si,NiSi2,SiV3,Mg2Sn,Cu2NiSn,MgZn2,TiZn2(以下、各々活物質F〜Nとする)を用いた例を示す。
【0023】
高結晶性金属間化合物の作製
活物質F〜Nの各純元素を量論比どうりに秤量し混合した粉末を、アルゴン雰囲気下にて電気炉で、表1に示す各温度で約2時間熱処理して後、ゆっくり冷却、固化させて、板状の金属間化合物を得た。この板状物をハンマーで砕いた粗粉を、サンプルミルにて粉末状にし、これを400メッシュで篩って平均粒径約9μmの微粉末を得た。
【0024】
X線回折
代表例として活物質Fについて、CuKα線を用いたX線回折の測定結果を図2に示す。このように高結晶性の金属間化合物であり、24.2°付近に回折強度の一番強いピークが存在し、そのピークの半値幅は0.16°であった。他の活物質についても同様に高結晶性である事を確認した。
【0025】
組成分析
前記の金属間化合物を王水にて溶解させた水溶液をICP分析により組成分析を行ったところ、各活物質が上記組成どうりである事を確認した。
負極の作製
前記のように作製した金属間化合物42wt%、導電フィラーとして鱗片状黒鉛(ロンザ(株)社製KS6)4wt%、アセチレンブラック(電気化学工業(株)社製デンカブラック)2wt%、結着剤としてポリフッ化ビニリデン溶液(呉羽化学工業(株)社製クレハKFポリマー#9130をN−メチル−2−ピロリドンに固形分率13wt%で溶解した液、以下PVdF溶液)を36wt%、N−メチル−2−ピロリドン(以下、NMP)を16wt%を各々添加したものをスリーワンモーターにて混合、攪拌して電極合剤スラリーを得た。そして、このスラリーを集電体である12μm厚の銅箔上に塗工、乾燥した後、150℃にてローラープレスを行なって、負極集電体と負極合剤層からなる膜厚約30μmの負極を得た。
【0026】
正極の作製
平均粒径3μmのLiCoO2100重量部に対し、導電剤としてグラファイト5重量部、結着剤としてポリフッ化ビニリデンを溶解したジメチルホルムアミド溶液(5重量%)100重量部を加え、混合、攪拌してスラリーを得た。そして、このスラリーを集電体である15μm厚のAl箔上に塗工、乾燥後、プレス成形する事で、集電体と正極合剤層からなる正極を作製した。
【0027】
充放電評価
負極単独の性能をみるため、以下のように負極電位をコントロールしてサイクル評価を行った。上記のように得た正極と負極について、各々2.00cm2と2.05cm2に打ち抜き、集電体を溶接した各電極をポリエチレン製微多孔膜を介して向かい合うようにし、ガラス板及びクリップにて挟み込んだ。そして、正極及び負極の集電体を短絡しないようにガラス製試験セルの鰐口クリップにはさんだ後、負極近傍にくるように参照極であるリチウム金属をセットした。一方、このガラス製試験セルの内部を減圧して十分水分を除去した後、エチレンカ−ボネ−トとメチルエチルカーボネートを体積割合で1:2の混合溶媒に1モル/リットルで電解質LiPF6を溶解させた後、モレキュラーシーブスで脱水して電解液を液を、十分水分を除去した前記ガラス製試験セルに極低湿度下で滴下し、十分含浸させた。
【0028】
このようにして得た試験セルの充放電試験は、参照極からみた負極の電位をコントロールする事により行う。ここでいう充電とは負極がリチウムイオンを吸蔵する方向であり、逆に放電とはリチウムイオンを放出する方向である。なお、正極活物質は、負極のリチウムイオン吸蔵量をまかなえるだけ十分な量を塗布してある。充電は電流密度1mA/cm2、10mV、24時間定電圧充電を行い、放電は電流密度1mA/cm2の1.2V定電流カットオフ放電を行った。この結果及び使用した負極の合剤層体積から、1サイクル目の負極合剤層の単位体積当たりの放電量(以下、放電容量)、及び1サイクル目の放電容量を100%とした時の100サイクル目の放電容量の維持率(以下、容量維持率)を求めた。
【0029】
比較例1−Q〜1−T
金属負極として、Ge,Si,Sn,Znを用いた例を示す。各金属ないし半金属としては、高純度化学研究所社製の粉末を購入し、400メッシュで篩って得た微粉末を使用した。それ以外は、比較例1−F〜1−Nと同じ方法で実験、評価を行った。
【0030】
比較例1−U,V
炭素負極として、鱗片状黒鉛((株)中越黒鉛工業所社製CX3000、以下黒鉛)及びニードルコークス(興和石油(株)社製、以下コークス)を用いた例を示す。各炭素材料47wt%、PVdF溶液36wt%、NMP17wt%を添加したものを混合、攪拌して得た電極合剤スラリーから負極を作製した事以外は、比較例1−F〜1−Nと同じ方法で実験、評価を行った。
【0031】
以上の結果を表1に示す。
【0032】
【表1】
【0033】
実施例2−F’,H’,K’,M’
負極活物質として、低結晶性のGeMg 2 ,Mg2Si,Mg2Sn,MgZn2(以下、各々活物質F’,H’,K’,M’とする)を用いた例を示す。
【0034】
低結晶性金属間化合物の作製
低結晶性金属間化合物を得るために、機械的合金化(MA法)という製造法を用いた。MA法について具体的に説明すると、活物質F’,H’,K’,M’の各構成元素を量論比どおりに秤量し混合した粉末5gを、直径25mmのステンレスボール8個とともに内容積500cm3のステンレスポットミルにアルゴン雰囲気下にて入れ、回転ボールミルを2週間行った。ボールミル後に得られた粉末を400メッシュで篩い、平均粒径約9μmの微粉末を得た。代表例として活物質F’について、CuKα線を用いたX線回折の測定結果を図3に示す。このように低結晶性の金属間化合物であり、24.1°付近に回折強度の一番強いピークが存在し、そのピークの半値幅は0.66°であった。他の活物質についても同様に低結晶性である事を確認した。その後の実験及び評価は比較例1−F〜1−Nと同じ方法で行った。
【0035】
実施例3−G’,I’,J’,L’,N’
負極活物質として、非晶質のGeNi 3 ,NiSi2,SiV3,Cu2NiSn,TiZn2(以下、各々活物質G’,I’,J’,L’,N’とする)を用いた例を示す。
非晶質金属間化合物の作製
非晶質金属間化合物を得るために、高周波誘導加熱−片ロール型超急冷装置を用いた(以下、RS法)。高周波電源はトランジスターインバーター方式で、出力3KW、周波数200KHzである。片ロールは銅製で、寸法は直径200mm、幅20mmであり、またロール駆動方式はマグネットカップリングで、回転数3000rpmで運転を行った。比較例1−F〜1−Nで示したのと同じ製法で作製した各高結晶性金属間化合物10gを上記RS法にてアルゴン雰囲気下で超急冷凝固させ、リボン状の物質を得た。これをサンプルミルにて粉末状にし、さらに400メッシュで篩って平均粒径約9μmの活物質G’,I’,J’,L’,N’を得た。CuKα線を用いたX線回折の測定を行い、非晶質である事を確認した。その後の実験及び評価は比較例1−F〜1−Nと同じ方法で行った。以上の結果を表1に示す。
【0036】
実施例2、3のGe,Si,Sn,Znを含有する低結晶性又は非晶質な金属間化合物を負極活物質に用いた方が、比較例1の高結晶性金属間化合物を用いたものよりも容量維持率が高く、サイクル特性が優れていて、より望ましい事がわかる。
【0037】
【発明の効果】
Ge,Si,Sn,Znを含有する金属間化合物を活物質に用いた負極は、炭素負極に比べ放電容量が遥かに高く、また合金負極に比べるとサイクル特性が優れている。また、低結晶性又は非晶質な金属間化合物を負極活物質に用いる事でより良好なサイクル特性を得る事ができる。従って、本発明の二次電池は、炭素負極を用いた現状の二次電池よりも遥かに高容量、高エネルギー密度であり、かつ合金負極を用いた二次電池よりも良好なサイクル特性を有している。
【図面の簡単な説明】
【図1】 本発明の非水電解液二次電池の一例を示す概略図である。
【図2】 高結晶性金属間化合物GeMg2のX線回折の結果である。
【図3】 低結晶性金属間化合物GeMg2のX線回折の結果である。
【符号の説明】
1・・・負極
2・・・セパレータ
3・・・正極
4・・・正極端子
5・・・電池容器(負極端子)[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode having an active material that occludes and releases lithium, a negative electrode, and a secondary battery having a lithium ion transfer medium.
[0002]
[Prior art]
In recent years, electronic devices have been remarkably reduced in size and weight, and accordingly, a battery serving as a power source is desired to be small in size, light in weight, and high in energy density. In the field of primary batteries, small and lightweight batteries such as lithium batteries have already been put into practical use. However, since these are primary batteries, they cannot be used repeatedly, and their application fields are limited. On the other hand, lead batteries and nickel-cadmium batteries have been used in the field of secondary batteries, but both have major problems in terms of size and weight reduction. From this point of view, non-aqueous electrolyte secondary batteries have attracted attention, and research and development of non-aqueous electrolyte secondary batteries using lithium as a negative electrode have been actively conducted. This battery has excellent characteristics such as high energy density, low self-discharge, and light weight. However, in this non-aqueous electrolyte secondary battery, as the charge / discharge cycle progresses, lithium has a dendrite-like crystal growth at the time of charge / discharge, and there is a disadvantage that the possibility of reaching the positive electrode and causing an internal short circuit increases. This is a major obstacle to commercialization.
[0003]
Accordingly, various nonaqueous electrolyte secondary batteries using a carbon material intercalating or doping lithium as a negative electrode active material (hereinafter referred to as a carbon negative electrode) have been proposed. As for the carbon material, it is described in, for example, Japanese Patent Application Laid-Open No. 59-143280 that a graphite intercalation compound is used as a negative electrode using intercalation. Further, as a negative electrode material utilizing the doping phenomenon, it is possible to use a carbonaceous material such as a resin fired body or coke as disclosed in JP-A-58-35881, JP-A-58-209864, JP-A-59-173979. No. 6, JP-A 62-90863, JP-A 63-13282, JP-A 2-66856 and the like. Actually, secondary batteries using graphite or non-graphitizable carbon as a negative electrode active material have been put into practical use.
[0004]
Further, it is publicly known that metals or semimetals such as Al, Ge, Si, Sn, Zn, and Pb are alloyed with lithium, and these alloyed negative electrode active materials (hereinafter referred to as alloy negative electrodes). The secondary battery used for this is being studied. Such a secondary battery has a high capacity and a high energy density, and can occlude and release more lithium ions than a carbon negative electrode. Therefore, the secondary battery has a higher capacity and a higher energy density than when a carbon negative electrode is used. Although a secondary battery can be obtained, it has not been put into practical use because of poor cycle characteristics.
[0005]
Recently, the development of secondary batteries with higher capacity and longer cycle life than carbon anodes has been attempted, and those using iron silicide, nickel silicide, manganese silicide as the anode material are disclosed ( JP-A-5-159780, JP-A-8-153517, JP-A-8-153538). Mg2Ge or NiSi2CaF2The fact that the type structure intermetallic compound has a high capacity as a negative electrode material has been publicized at the 36th Battery Conference.
[0006]
[Problems to be solved by the invention]
However, high performance and miniaturization of portable electronic devices are considered to continue in the future, and further increase in capacity and energy density of secondary batteries are desired.
Accordingly, an object of the present invention is to provide a conventional carbon material having a capacity and energy density equivalent to those of a conventionally known lithium, or a secondary battery using a metal or metalloid alloyed with lithium as a negative electrode active material The present invention provides an excellent secondary battery having cycle characteristics equivalent to those of a secondary battery using as a negative electrode active material.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve the above problems.
That is, the present inventionOneIs a secondary battery having a positive electrode, a negative electrode, and a lithium ion transfer medium using an active material capable of inserting and extracting lithium.As the positive electrode active material, the chemical composition formula Li x M y N z O 2 (M represents at least one selected from cobalt, nickel, manganese, and other transition metals, N represents at least one non-transition metal, and x, y, and z are each 0.05 <x <1.10. 0.85 ≦ y ≦ 1.00, 0 ≦ z <0.10) or Li (1 + x) Mn (2-x) O 4 Using a lithium-containing metal oxide represented by (0 ≦ X ≦ 1),As a negative electrode active material,Ge, Si, Sn, ZnAn intermetallic compound of at least one element selected from the group of elements and a metal or metalloid other than the above element group(However, the case where a coating layer is provided by plasma spraying or low-pressure plasma spraying or pulse plasma deposition method) and the half-width of the strongest peak in the X-ray diffraction method using CuKα ray is 0.2. Low crystalline intermetallic compound of 6 ° or more, or amorphous intermetallic compound having a broad scattering band having an apex from 20 ° to 40 ° in 2θ value by X-ray diffraction using CuKα rayThe present invention proposes a secondary battery characterized by using
In the second aspect of the present invention, a crystalline intermetallic compound of at least one element selected from the element group of Ge, Si, Sn, and Zn and a metal or semimetal other than the above element group is mechanically processed by a ball mill. Low crystalline metal whose half-width of the strongest peak in the X-ray diffraction method using CuKα rays is 0.6 ° or more in terms of 2θ value by performing destruction or mechanical alloying from each pure element The manufacturing method of the secondary battery of this invention including the process of producing the negative electrode active material which consists of intermetallic compounds is proposed.
In the third aspect of the present invention, a liquid roll is prepared by melting a crystalline intermetallic compound of at least one element selected from the element group of Ge, Si, Sn, and Zn and a metal or semimetal other than the element group. Including a step of producing a negative electrode active material made of an amorphous intermetallic compound having a broad scattering band having an apex from 20 ° to 40 ° with a 2θ value by an X-ray diffraction method using CuKα rays by a rapid cooling method. The manufacturing method of the secondary battery of this invention is proposed.
[0008]
The secondary battery of the present invention has far better cycle characteristics than a secondary battery using a conventional alloy negative electrode, and has a capacity and energy density superior to those of a carbon negative electrode, and has the advantages of both of them. It is.
The reason for this is that when the alloy negative electrode is repeatedly charged and discharged, the active material is microcrystallized and pulverized, but in the secondary battery of the present invention,Ge, Si, Sn, ZnIt is presumed that the microcrystallization and pulverization as described above are suppressed by the presence of other elements that are difficult to alloy with lithium around the element that is alloyed with lithium. Examples of elements that are difficult to alloy with lithium include B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Ti, V, and W.
[0009]
The intermetallic compound used in the present invention is low crystalline or amorphous.is there.Low crystallinity means that the half-width of the strongest peak is 0.6 ° or more in terms of 2θ value in the X-ray diffraction method using CuKα rays. The term “amorphous” as used herein refers to an X-ray diffraction method using CuKα rays, which has a broad scattering band having an apex from 20 ° to 40 ° as a 2θ value, and has a crystallinity peak. May be. By using an intermetallic compound having low crystallinity or amorphousness, the active material is hardly crystallized and / or finely powdered due to repeated charge / discharge, so that the cycle characteristics can be further improved.
[0010]
Examples of basic components of the secondary battery of the present invention include a negative electrode and a positive electrode made of an active material capable of inserting and extracting lithium, and a lithium ion transfer medium.
Although the intermetallic compound which is a negative electrode active material used for the secondary battery of this invention is illustrated concretely, especially limitation isNot.
[0011]
As for containing Ge, As3GeLi5, CoFeGe, CoGeMn, FeGe2, Fe1.7Ge, FeGeMn, FeGeNi, GeLi5P3, GeMg2, GeMnNi, GeMo3, Β'-Ge2Mo, GeNb3, GeNi1.70, GeNi3, Ge3Pu, Ge3U, GeV3etcCan be mentioned.
As containing Si, As3Li5Si, BeSiZr, CoSi2, Β-Cr3Si, Cu3Mg2Si, Fe3Si, Li5P3Si, Mg2Si, MoSi2, Nb3Si, NiSi2, Θ-Ni2Si, β-Ni3Si, ReSi2, Α-RuSi, SiTa2, Si2Th, Si2U, β-Si2U, Si3U, SiV3, Si2W, SiZr2Etc.
[0012]
Examples of Sn-containing materials include AsSn, AuSn, and CaSn.3, CeSn3, CoCu2Sn, Co2MnSn, CoNiSn, CoSn2, Co3Sn2, CrCu2Sn, (Cr, Ni) Cu2Sn, Cu2FeSn, CuMgSn, Cu2MnSn, Cu4MnSn, (Cu, Ni)3Sn, Cu2NiSn, CuSn, FeSn2, IrSn, IrSn2, LaSn3, MgNi2Sn, Mg2Sn, MnNi2Sn, MnSn2, Mn2Sn, Mo3Sn, Nb3Sn, NdSn3, NiSn, Ni3Sn2, PdSn, Pd3Sn, Pd3Sn2, PrSn3, PtSn, PtSn2, Pt3Sn, PuSn3, RhSn, Rh3Sn2, RuSn2, SbSn, SnTi2, Sn3U, SnV3Etc.
[0013]
Examples of Zn-containing materials include AgAsZn, β-AgZn, AsLiZn, AsNaZn, β-AuZn, CeZn, β'-CuZn, EuZn, LaZn, LiPZn, MgNiZn, and MgZn.2, PrZn, Pt3Zn, PuZn2, Th2Zn, TiZn2, TiZn3, Zn2Zr etc. are mentioned.
The composition of the intermetallic compound used in the secondary battery of the present invention is an ICP solution in which the intermetallic compound is subjected to fluorescent X-ray analysis while being powdered, or an aqueous solution in which the powder is dissolved with concentrated hydrochloric acid, hot concentrated sulfuric acid, concentrated nitric acid, aqua regia, etc. It can be identified by analysis or atomic absorption analysis. Further, other elements such as B and Co that are not included in the composition of the intermetallic compound, or other compounds may be contained as long as they are less than 10 wt%.
[0014]
CrystallineIntermetallic compounds are powders or granular materials in which a predetermined amount of each pure element is weighed and mixed in an electric furnace, a high-frequency induction heating device, or an arc melting furnace in an inert gas atmosphere such as argon or nitrogen. It is obtained by heating to the following temperature and dissolving, followed by solidification. In addition, it can also be obtained from each oxide by using a reduction diffusion method. When it is desired to make it low crystalline or amorphous, the crystalline intermetallic compound produced as described above is melted by a high frequency induction heating device, a plasma jet device, an infrared intensive heating device, etc. Use the law. Examples of the ultra-quenching method include the gun method, Hammer-Anvil method, slap method, gas atomization method, water atomization method, disk atomization method, plasma spray method, centrifugal quenching method, ceramic processing (Gihodo Publishing 1987), pages 218-219, There are a single roll method, a twin roll method, a melt drag method, and the like. Especially in the liquid roll quenching method such as the single roll method and the twin roll method, 105-106K / sec, 10 for gas atomization method4-105A cooling rate of K / sec can be obtained, and the amorphous intermetallic compound of the present invention can be easily obtained. It is also possible to obtain a thin amorphous intermetallic compound by sputtering. Further, it is possible to produce a low crystalline or amorphous intermetallic compound by mechanically destroying a crystalline intermetallic compound with a ball mill or the like, or by mechanical alloying from each pure element.
[0015]
The intermetallic compound having a form such as a plate-like ingot or spherical, flaky powder or ribbon obtained by the above method is made into a fine powder by using a known pulverization, classification and mixing method. Adjust the particle size distribution. The average particle size is preferably 1 μm or more and 50 μm or less.
The electrode used for the secondary battery of the present invention is one in which an electrode mixture layer is formed on an electrode current collector. In such an electrode, an electrode mixture slurry obtained by dispersing an electrode mixture in which the intermetallic compound, a binder, and, if necessary, a conductive filler are mixed in a solvent is applied to an electrode current collector. Then get dry. If necessary, a roller press is performed.
[0016]
Although it does not specifically limit as a collector used for the negative electrode of this invention, Metal foil or a net | network of about 10-100 micrometers thickness, such as Cu, Ni, stainless steel, etc. are used. Binders include polytetrafluoroethylene, polytrifluoroethylene, polyethylene, nitrile rubber, polybutadiene rubber, butyl rubber, polystyrene, styrene butadiene rubber, styrene butadiene latex, polysulfide rubber, nitrocellulose, acrylonitrile butadiene rubber, polyvinyl fluoride, Polyvinylidene fluoride and fluororubber are desirable, but are not particularly limited.
[0017]
Further, when the electrical resistance of the active material is high, a conductive filler may be added to increase conductivity. As the conductive filler, a carbon material such as graphite or carbon black, or a metal powder such as Cu, Fe, or Ti is used.
As the active material of the positive electrode combined with the negative electrode of the present invention, the chemical composition formula LixMyNzO2(M represents at least one selected from cobalt, nickel, manganese, and other transition metals, N represents at least one non-transition metal, and x, y, and z are each 0.05 <x <1.10. A lithium-containing metal oxide represented by 0.85 ≦ y ≦ 1.00 and 0 ≦ z <0.10) can be used. These have a high potential, a high voltage can be obtained as a battery, and the cycleability is good. As M, Co, Ni, Mn alone and a composite of Co / Ni, Mn / Cr, Mn / Fe are particularly preferable. N is not particularly limited as long as it is a non-transition metal, but Al, In, and Sn are preferable. Li(1 + x)Mn(2-x)O4It is also possible to use a lithium-containing metal oxide represented by (0 ≦ X ≦ 1)it can.
[0018]
As the current collector of the positive electrode, a metal foil or net having a thickness of about 10 to 100 μm such as Al, Cu, Ni, stainless steel, etc. can be used. When using an active material having a potential, it is preferable to use a metal foil or net made of Al.
Examples of the lithium ion medium used in the present invention include a solution in which a lithium salt is dissolved in an aprotic organic solvent, a solid in which a lithium salt is dispersed in a polymer matrix, or a lithium salt dissolved in an aprotic organic solvent. A mixture of a solution and a polymer matrix is used. The organic solvent preferably contains ethylene carbonate and linear carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate as essential components. In addition, ethers, ketones, lactones, nitriles, amines, amides, sulfone compounds, carbonates, esters and the like may be contained. Typical examples of these include propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyllactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether , Sulfolane, methylsulfolane, acetonitrile, propionitrile and the like, but are not necessarily limited thereto. As the lithium salt, LiBF4, LiPF6LiClO4, LiAsF6, CF3SO3Li, CH3SO3Li, LiI, LiP, LiCl, LiBr, (CF3SO2)2NLi etc. are mention | raise | lifted. Examples of the polymer matrix include aliphatic polyethers such as polyethylene oxide, polypropylene oxide, polytetramethylene oxide, polyvinyl alcohol and polyvinyl butyral, aliphatic polythioethers such as polyethylene sulfide and polypropylene sulfide, polyethylene succinate, poly Aliphatic polyesters such as butylene adipate and polycaprolactone, polyethyleneimine, polyimide, polyvinylidene fluoride, and precursors thereof can be used.
[0019]
Further, a separator for preventing a short circuit can be provided between the positive electrode and the negative electrode. As the separator, a single microporous film of polyolefin such as polyethylene or polypropylene, or a film obtained by bonding them together, or a non-woven fabric such as polyolefin, polyester, polyamide or cellulose, or a single film bonded to the microporous film. Can be used.
[0020]
As other components of the secondary battery of the present invention, parts such as a terminal, an insulating plate, and a metal can may be used. Moreover, when using this invention as a battery can as shown in FIG. 1, stainless steel, nickel-plated steel, iron, aluminum, etc. are used as a material.
The structure of the battery is not particularly limited, but is a paper-type battery, a laminated battery, or a cylinder shown in FIG. 1 in which the positive electrode, the negative electrode, and the separator are wound in a roll shape. And forms such as a square battery.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, the scope of the present invention is not limited to this.
[0022]
【Example】
Comparative Examples 1-F to 1-N
As a negative electrode active material, highly crystallineGeMg 2 ,GeNi3, Mg2Si, NiSi2, SiV3, Mg2Sn, Cu2NiSn, MgZn2, TiZn2(Hereafter, each active materialFNAn example using
[0023]
Preparation of highly crystalline intermetallic compounds
Active materialFNEach of the pure elements was weighed and mixed in a stoichiometric ratio, and the powder was heat-treated at each temperature shown in Table 1 for about 2 hours in an electric furnace in an argon atmosphere, and then slowly cooled and solidified. A shaped intermetallic compound was obtained. The coarse powder obtained by pulverizing the plate-like material with a hammer was powdered with a sample mill, and sieved with 400 mesh to obtain a fine powder having an average particle diameter of about 9 μm.
[0024]
X-ray diffraction
As a representative example, the measurement result of the X-ray diffraction using the CuKα ray is shown in FIG. Thus, it is a highly crystalline intermetallic compound, the peak with the strongest diffraction intensity exists in the vicinity of 24.2 °, and the half width of the peak is 0.16 °. The other active materials were confirmed to be highly crystalline as well.
[0025]
Composition analysis
Composition analysis of an aqueous solution in which the intermetallic compound was dissolved in aqua regia was conducted by ICP analysis, and it was confirmed that each active material had the above composition.
Production of negative electrode
42 wt% of intermetallic compound produced as described above, scaly graphite (KS6 manufactured by Lonza Co., Ltd.) 4 wt%, acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) 2 wt%, binder A polyvinylidene fluoride solution (Kureha KF Co., Ltd. Kureha KF Polymer # 9130 dissolved in N-methyl-2-pyrrolidone at a solid content of 13 wt%, hereinafter referred to as a PVdF solution) is 36 wt%, N-methyl- What added each 16 wt% 2-pyrrolidone (henceforth, NMP) was mixed and stirred with the three one motor, and the electrode mixture slurry was obtained. And after apply | coating this slurry on the 12-micrometer-thick copper foil which is a collector, and drying, roller press is performed at 150 degreeC, and the film thickness of about 30 micrometers consisting of a negative electrode collector and a negative mix layer is carried out. A negative electrode was obtained.
[0026]
Fabrication of positive electrode
LiCoO with an average particle size of 3 μm2To 100 parts by weight, 5 parts by weight of graphite as a conductive agent and 100 parts by weight of a dimethylformamide solution (5% by weight) in which polyvinylidene fluoride was dissolved as a binder were added, mixed and stirred to obtain a slurry. The slurry was coated on a 15 μm-thick Al foil as a current collector, dried, and press-molded to produce a positive electrode composed of the current collector and a positive electrode mixture layer.
[0027]
Charge / discharge evaluation
In order to see the performance of the negative electrode alone, cycle evaluation was performed while controlling the negative electrode potential as follows. Each of the positive electrode and the negative electrode obtained as described above was 2.00 cm.2And 2.05cm2Each electrode welded with a current collector was made to face each other through a polyethylene microporous membrane and sandwiched between a glass plate and a clip. Then, a lithium metal as a reference electrode was set so as to be near the negative electrode after being sandwiched between the mouth clip of the glass test cell so as not to short-circuit the positive and negative electrode current collectors. On the other hand, after the inside of this glass test cell was depressurized to sufficiently remove water, the electrolyte LiPF was mixed with ethylene carbonate and methyl ethyl carbonate in a 1: 2 solvent mixture at a volume ratio of 1 mol / liter.6Then, the electrolyte solution was dehydrated with molecular sieves and the electrolyte was dropped into the glass test cell from which water had been sufficiently removed, under extremely low humidity, and sufficiently impregnated.
[0028]
The charge / discharge test of the test cell thus obtained is performed by controlling the potential of the negative electrode viewed from the reference electrode. Here, charging is a direction in which the negative electrode occludes lithium ions, and conversely, discharging is a direction in which lithium ions are released. The positive electrode active material is applied in an amount sufficient to cover the lithium ion occlusion amount of the negative electrode. Charge current density 1mA / cm210 mV, 24 hours constant voltage charge, discharge is 1 mA / cm current density2The 1.2V constant current cut-off discharge was performed. From this result and the mixture layer volume of the negative electrode used, the discharge amount per unit volume of the negative electrode mixture layer in the first cycle (hereinafter, discharge capacity) and 100 when the discharge capacity in the first cycle is 100% The discharge capacity retention rate at the cycle (hereinafter, capacity retention rate) was determined.
[0029]
Comparative example1-Q~ 1-T
As a metal negative electrode,Ge, Si, Sn, ZnAn example using is shown. As each metal or metalloid, a powder obtained by purchasing high-purity chemical research company powder and sieving with 400 mesh was used. Other than that,Comparative Examples 1-F to 1-NExperiments and evaluations were carried out in the same manner.
[0030]
Comparative Example 1-U, V
An example in which scaly graphite (CX3000 manufactured by Chuetsu Graphite Industries Co., Ltd., hereinafter referred to as graphite) and needle coke (manufactured by Kowa Oil Co., Ltd., hereinafter referred to as coke) is shown as the carbon negative electrode. Except for preparing a negative electrode from an electrode mixture slurry obtained by mixing and stirring each carbon material 47 wt%, PVdF solution 36 wt%, NMP 17 wt% added,Comparative Examples 1-F to 1-NExperiments and evaluations were carried out in the same manner.
[0031]
The results are shown in Table 1.
[0032]
[Table 1]
[0033]
Example 2-F ′, H ′, K ′, M ′
As a negative electrode active material, low crystallineGeMg 2 ,Mg2Si, Mg2Sn, MgZn2(Less than,Each active material F ′, H ′, K ′, M ′An example using
[0034]
Preparation of low crystalline intermetallic compounds
In order to obtain a low crystalline intermetallic compound, a manufacturing method called mechanical alloying (MA method) was used. The MA method will be explained in detail.Active material F ′, H ′, K ′, M ′5 g of powder obtained by weighing and mixing each of the constituent elements according to the stoichiometric ratio together with 8 stainless steel balls with a diameter of 25 mm and an internal volume of 500 cm3Was placed in a stainless steel pot mill under an argon atmosphere, and a rotating ball mill was performed for 2 weeks. The powder obtained after ball milling was sieved with 400 mesh to obtain a fine powder having an average particle size of about 9 μm. As a representative example, the measurement result of the X-ray diffraction using CuKα rays for the active material F ′ is shown in FIG. Thus, it is a low crystalline intermetallic compound, and the peak with the strongest diffraction intensity exists in the vicinity of 24.1 °, and the half width of the peak is 0.66 °. The other active materials were confirmed to have low crystallinity as well. Subsequent experiments and evaluationsComparative Examples 1-F to 1-NWas done in the same way.
[0035]
Example 3-G ′, I ′, J ′, L ′, N ′
As a negative electrode active material, amorphousGeNi 3 ,NiSi2, SiV3, Cu2NiSn, TiZn2(Hereafter, eachActive material G ′, I ′, J ′, L ′, N ′An example using
Preparation of amorphous intermetallic compounds
In order to obtain an amorphous intermetallic compound, a high-frequency induction heating-single roll type ultra rapid cooling apparatus was used (hereinafter referred to as RS method). The high-frequency power source is a transistor inverter type, with an output of 3 KW and a frequency of 200 KHz. The single roll was made of copper and had a diameter of 200 mm and a width of 20 mm. The roll drive system was a magnetic coupling, and the operation was performed at a rotational speed of 3000 rpm.Comparative Examples 1-F to 1-N10 g of each highly crystalline intermetallic compound produced by the same production method as described above was rapidly solidified in the above-mentioned RS method under an argon atmosphere to obtain a ribbon-like substance. This is powdered with a sample mill, and further sieved with 400 mesh, and the average particle size is about 9 μm.Active material G ′, I ′, J ′, L ′, N ′Got. X-ray diffraction was measured using CuKα rays, and it was confirmed to be amorphous. Subsequent experiments and evaluationsComparative Examples 1-F to 1-NWas done in the same way. The results are shown in Table 1.
[0036]
Examples 2 and 3Ge, Si, Sn, ZnIt is better to use a low crystalline or amorphous intermetallic compound containingComparative Example 1It can be seen that the capacity retention rate is higher than that using the highly crystalline intermetallic compound, and the cycle characteristics are excellent, which is more desirable.
[0037]
【The invention's effect】
Ge, Si, Sn, ZnThe negative electrode using an intermetallic compound containing as an active material has a discharge capacity much higher than that of a carbon negative electrode, and has excellent cycle characteristics as compared with an alloy negative electrode. Further, by using a low crystalline or amorphous intermetallic compound as the negative electrode active material, better cycle characteristics can be obtained. Therefore, the secondary battery of the present invention has much higher capacity and higher energy density than the current secondary battery using a carbon negative electrode, and has better cycle characteristics than a secondary battery using an alloy negative electrode. is doing.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a non-aqueous electrolyte secondary battery of the present invention.
FIG. 2 Highly crystalline intermetallic compound GeMg2This is a result of X-ray diffraction.
FIG. 3 Low crystalline intermetallic compound GeMg2This is a result of X-ray diffraction.
[Explanation of symbols]
1 ... Negative electrode
2 ... Separator
3 ... Positive electrode
4 ... Positive terminal
5 ... Battery container (negative electrode terminal)
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