JP3897709B2 - Electrode material, method for producing the same, negative electrode for non-aqueous secondary battery, and non-aqueous secondary battery - Google Patents
Electrode material, method for producing the same, negative electrode for non-aqueous secondary battery, and non-aqueous secondary battery Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、高容量でかつサイクル特性に優れた非水二次電池を構成することのできる電極材料およびその製造方法、並びにその電極材料を用いた非水二次電池用負極および非水二次電池に関する。
【0002】
【従来の技術】
非水二次電池は高容量かつ高電圧、高エネルギー密度であることから、その発展に対して大きな期待が寄せられている。この非水二次電池では、電解液として有機溶媒にリチウム(Li)塩を溶解させた有機溶媒系の電解液が用いられ、負極活物質としてLiまたはLi合金が用いられてきた。しかし、負極活物質としてLiまたはLi合金を用いて二次電池として機能させた場合、充電時にLiのデンドライトが生成するために内部短絡を起こしやすくなり、また、析出したデンドライトは高比表面積で活性が高いため安全性に欠けるという問題があった。さらに、そのデンドライトと電解液中の溶媒とが反応して電子伝導性を欠いた被膜がデンドライトの表面上に形成されて電池の内部抵抗が高くなり、充放電効率が低下し、その結果としてサイクル耐久性が乏しくなるという問題もあった。
【0003】
現状では、LiやLi合金に代えて、Liイオンをドープ・脱ドープすることが可能なコークスやガラス状炭素などの非晶質炭素、天然または人造の黒鉛などの炭素材料を負極材料として用いることによってサイクル耐久性を改善し、二次電池として機能させている。
【0004】
また最近では、小型化および多機能化した携帯機器用二次電池の高容量化が望まれるにつれて、ケイ素(Si)や錫(Sn)などのように、より多くのLiを合金化して吸蔵可能な半金属および金属が負極材料として注目を集めており、単位体積当たりの容量を大きくするため、Siまたはその化合物を負極活物質とする試みがされている。例えば、特許文献1には、LitSi(0≦t≦5)を負極活物質として用いた非水二次電池が開示されている。
【0005】
また、本発明に関連する先行技術としては、例えば特許文献2などがある。
【0006】
【特許文献1】
特開平7−29602号公報
【0007】
【特許文献2】
特開2000−272911号公報
【0008】
【発明が解決しようとする課題】
しかし、上記Liと合金化可能な負極材料は炭素材料に比べて高容量であるが、充放電を繰り返すと、負極材料自体が膨張・収縮を繰り返して微粉末化し、負極の膨潤や電解液の不必要な吸収を引き起し、電極特性が劣化するという問題がある。その理由は以下のように考えられる。
【0009】
例えば、Siは、その結晶学的な単位格子(立方晶、空間群Fd−3m)に8個のSi原子を含んでいる。格子定数a=0.5431nmから換算して、単位格子体積は0.1602nm3であり、Si原子1個の占める体積(単位格子体積を単位格子中のSi原子数で除した値)は0.0199nm3である。ここで、Siを含む負極をLiを基準とした電位で100mV以下まで充電する(Liを挿入させる)と、Liを多く含む化合物Li15Si4やLi21Si5が生じ、容量は約4000mAh/gに相当するが、負極の体積膨張率が極めて大きくなる。例えば、Li21Si5の単位格子(立方晶、空間群F−43m)には83個のSi原子が含まれている。その格子定数a=1.8750nmから換算して、単位格子体積は6.5918nm3であり、Si原子1個あたりの体積は0.079nm3である。この値は単体Siの3.95倍であり、このように充放電時の体積差が極めて大きいため、負極粒子に大きな歪みが生じ、負極粒子が微粉化するものと考えられる。その結果、負極粒子間に空間が生じ、負極粒子間の電気的接触(電子伝導ネットワーク)が分断され、電気化学的な反応に関与できない部分が増加し、充放電容量が低下するものと考えられる。
【0010】
また、特許文献2では、Si粒子が黒鉛および非結晶質炭素中に埋設された複合体粒子を負極に用いたリチウム二次電池が開示され、充放電特性に優れたリチウム二次電池を実現している。このようにSi粒子を黒鉛および非結晶質炭素と複合化することによって、Siの膨張が緩和でき、サイクル特性は向上する。しかし、およそ1000mAh/g以上の高容量を発現するような複合体粒子では、サイクル特性は完全ではなく実用化に適するレベルに達しない。これは、上記のような高容量を発現するには、Siに多くのLiが挿入される必要があるため、Siの膨張がさらに大きくなり、複合体粒子の構造が破壊されるためと考えられる。
【0011】
本発明は、上記従来の問題を解決し、高容量でかつサイクル特性に優れた非水二次電池を構成することのできる電極材料およびその製造方法、並びにその電極材料を用いた非水二次電池用負極および非水二次電池を提供するものである。
【0012】
【課題を解決するための手段】
本発明は、リチウムと合金化可能な元素を含む材料と、導電性材料とを含む複合体粒子からなる電極材料であって、
前記リチウムと合金化可能な元素を含む材料の割合が、前記複合体粒子の全質量に対して30質量%以上80質量%以下であり、
前記複合体粒子の形状が球形で、内部に空隙を有し、
前記複合体粒子のJIS R1628に基づき測定したタップかさ密度をD1(g/cm3)、前記複合体粒子の真密度をD2(g/cm3)、前記複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下である電極材料を提供する。
【0013】
また、本発明は、上記電極材料の製造方法であって、
前記リチウムと合金化可能な元素を含む材料と、前記導電性材料と、樹脂とを混合して造粒することにより複合体粒子を形成する工程と、
前記複合体粒子を加熱して前記樹脂を燃焼または昇華させて除去することにより、前記複合体粒子内に空隙を形成する工程とを含む電極材料の製造方法を提供する。
【0014】
また、本発明は、上記電極材料の製造方法であって、
前記リチウムと合金化可能な元素を含む材料と、前記導電性材料とを溶媒中で分散させて混合物とし、前記混合物を噴霧して乾燥するスプレードライ法により造粒することにより複合体粒子を形成する工程を含む電極材料の製造方法を提供する。
【0015】
また、本発明は、上記電極材料を含む非水二次電池用負極を提供する。
【0016】
また、本発明は、上記非水二次電池用負極と、正極と、非水電解質とを備えた非水二次電池を提供する。
【0017】
【発明の実施の形態】
先ず、本発明の電極材料の実施の形態について説明する。本発明の電極材料の一形態は、リチウムと合金化可能な元素を含む材料と、導電性材料とを含む複合体粒子からなる電極材料であって、リチウムと合金化可能な元素を含む材料の割合が、複合体粒子の全質量に対して30質量%以上80質量%以下であり、その複合体粒子が内部に空隙を有し、複合体粒子のタップかさ密度をD1(g/cm3)、複合体粒子の真密度をD2(g/cm3)、複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下である。
【0018】
ここで、空隙体積占有率Vs=(1−1.35×D1/D2)×100は、複合体粒子の体積に対する複合体粒子内の空隙体積の割合を意味する。すなわち、複合体粒子を真球状であると仮定すると、その球が3次元的に最密充填する場合、面心立方格子状に充填され、その充填率(%)は、下記のとおりとなる。
【0019】
【数1】
【0020】
よって、タップかさ密度は最密充填に伴う粒子間の空隙と粒子内の空隙とを合わせた空隙量を反映した値となる。以上から、粒子内部の空隙は(0.7405・1/D1)−(1/D2)で表すことができ、空隙体積占有率はこれを粒子全体の体積(0.7405・1/D1)で除したものとなる。1/0.7405≒1.35とすると、上式は1−1.35×D1/D2となり、空隙体積占有率(%)はこれに100をかけて、Vs=(1−1.35×D1/D2)×100となる。
【0021】
複合体粒子の空隙体積占有率(Vs)が35%未満であると、充電時に複合体粒子が大きく膨張してしまう。すなわち、Liイオンの挿入(充電)に伴って、リチウムと合金化可能な元素を含む材料が膨張する際に、複合体粒子内にその膨張分を吸収する隙間が足りないため、複合体粒子が大きく膨張することが避けられない。一方、Vsが70%を超えると、複合体粒子の作製そのものが困難となり、また、複合体粒子中の隙間が多くなりすぎて、リチウムと合金化可能な元素を含む材料と導電性材料との電子伝導ネットワークが構築されにくいため、充放電されにくくなる。なお、上記複合体粒子のタップかさ密度は、所定量の複合体粒子を容器に入れ、かさ密度測定装置を用いて、JIS法に準拠したかさ密度測定方法(JIS R1628)から求める。また、真密度は、ヘリウムガスを用いたガス置換式の密度計から求める。
【0022】
また、リチウムと合金化可能な元素を含む材料の含有率は、複合体粒子の全質量に対して30〜80質量%の範囲にある必要があり、特に45〜65質量%の範囲が好ましい。30質量%未満の場合は、1000mAh/g程度の高容量を実現させるときに、リチウムと合金化可能な元素を含む材料の利用率が高くなりすぎて、複合体粒子の膨張が大きくなり、微粉化しやすくなる。また、80質量%を越えると、導電性材料との接触点が少なくなるため、電子伝導ネットワークの構築が困難となる。なお、この含有率は、蛍光X線による定性・定量分析から求めることができる。
【0023】
上記複合体粒子に含まれるリチウムと合金化可能な元素を含む材料は、化合物でも元素単体(金属、半金属または半導体元素など)でもよく、また、結晶、低結晶およびアモルファスのいずれの状態でもよい。例えば、化合物としては酸化物や窒化物などが挙げられ、金属としては他の金属との合金や固溶体などが挙げられ、他に金属間化合物でもよい。また、Si、Geなどの半導体元素にBやPをドープしてn型あるいはp型の半導体となり電気抵抗が大きく低下したものを用いてもよい。リチウムと合金化可能な元素を含む材料は、体積膨張による内部応力の集中を避けるために球形が望ましい。また、Liと合金化可能な元素としては、Ag、Au、Zn、Cd、Al、Ga、In、Tl、Ge、Pb、Si、Sn、Sb、Biなどの元素が好ましく用いられる。この中で、Siが最もLiの吸蔵量が大きく、かつ安価で環境面でも問題がないため特に好ましい。
【0024】
また、上記リチウムと合金化可能な元素を含む材料は、平均粒径が2μm以下の粒子であることが好ましい。複合体粒子が微粉化し難くなり、より効果的にサイクル耐久性を向上できるからである。
【0025】
本発明においては、複合体粒子が所定の空隙体積占有率を有することにより、その空隙を有効に活用し、充放電時のLiと合金化可能な元素を含む材料の体積膨張を吸収し、複合体粒子自体の体積膨張を抑制することができる。そのため、導電性材料としては、空隙を形成し易い繊維状またはコイル状の炭素材料および繊維状またはコイル状の銅などの金属材料から選ばれる少なくとも一つであることが好ましい。特に、繊維状炭素材料は、従来の粒子状のアセチレンブラックや人造黒鉛と比較して、柔軟性のある細い糸状であるため、接合または隣接する上記リチウムと合金化可能な元素を含む材料の膨張・収縮に効果的に追従することができ、加えて、タップかさ密度が大きいために、上記Liと合金化可能な元素を含む材料と多くの接合点を持つことができる。さらに、膨張・収縮に効果的に追従させるために、繊維状炭素材料は、塑性変形できるような弾性力を有するものがより好ましい。
【0026】
繊維状炭素材料としては、その繊維長と直径は特に制限されないが、平均繊維長は1μm以上30μm以下が好ましい。この範囲内であれば、複合体粒子内の電気的な接合が良好となり、複合体粒子内に電子伝導ネットワークを構築することができ、充放電特性が向上する。また、繊維状炭素材料の直径は2μm以下が好ましい。この範囲内であれば、繊維状炭素材料が十分な弾性を有し、リチウムと合金化可能な元素を含む材料の充放電サイクルに伴う膨張・収縮に効果的に追従できる。
【0027】
この繊維状炭素材料は強い混練や分散処理によって粉砕されやすく、繊維状の形態をとれなくなる可能性がある。よって、複合化の際には繊維状炭素材料が粉砕されにくい条件で行うのが好ましい。
【0028】
繊維状炭素材料としては、ポリアクリロニトリル(PAN)系炭素繊維、ピッチ系炭素繊維、気相成長炭素繊維などを用いることができる。繊維状炭素材料以外の導電性材料としては、高い電気伝導性と高い保液性を有し、リチウムと合金化可能な元素を含む材料が収縮しても接触を保つことができる機能を有するアセチレンブラック、ケッチェンブラックなどのカーボンブラック、人造黒鉛、易黒鉛化炭素、難黒鉛化炭素などが好適に使用できる。
【0029】
また、上記複合体粒子は、さらに炭素を含む材料によって被覆されていることが好ましい。複合体粒子の膨張を効果的に抑制し、さらに複合体粒子間の電気的接触抵抗を下げるためである。図3に炭素を含む材料によって被覆された複合体粒子の放電時と充電時の模式断面図を示す。Liと合金化可能な元素を含む材料である例えばSi粒子と、導電性材料である例えばCとを所定の空隙とともに外殻(被覆層)で覆うことにより、複合体粒子の膨張を抑制できる。
【0030】
特に、トルエンなどの炭素と水素を含む化合物からなるガス(炭化水素系ガス)を気相中で熱分解して得られる炭素、または炭素前駆体を焼成して得られる難黒鉛化炭素(ハードカーボン)系の炭素で被覆することが好ましい。これらの炭素は電子伝導性に優れているからである。また、上記2種類の炭素を組み合わせて被覆するとより効果的である。
【0031】
炭素前駆体としては石油系、石炭系のものが使用でき、例えば、合成ピッチ、タール類、フェノール樹脂、フラン樹脂、ポリアクリロニトリル、ポリ(α−ハロゲン化アクリロニトリル)などのアクリル樹脂、ポリアミドイミド樹脂、ポリアミド樹脂、ポリイミド樹脂などが使用できる。複合体粒子との混合に際して、これらの炭素前駆体を溶解する溶媒を用いてもよい。溶媒としては、例えば、テトラヒドロフラン、アセトンなどのケトン類、メタノール、エタノールなどの各種アルコール類、ジメチルホルムアミド、ジメチルアセトアミドなどのアミド類、トルエン、キシレン、ベンゼンなどの炭化水素類などが挙げられる。混合の際に溶媒を用いた場合には、焼成前に50〜150℃の温度で、好ましくは減圧下で混合物を加熱することにより、溶媒を除去する。
【0032】
また、上記熱分解や焼成は700℃以上で行うのが好ましく、800℃以上で行うのがより好ましい。処理温度が高い方が不純物の残存が少なく、かつ導電性の高い良質な炭素が得られるからである。以上の観点から、複合体粒子を炭素で被覆する場合には、リチウムと合金化可能な元素を含む材料の融点は700℃以上であることが好ましい。
【0033】
次に、本発明の電極材料の製造方法の実施の形態について説明する。本発明の複合体粒子の製造方法の一形態は、リチウムと合金化可能な元素を含む材料と導電性材料とを造粒することにより複合体粒子を作製するものである。その後、樹脂などの炭素前駆体と混合し、炭素前駆体を炭素化するか、あるいはCVD法(Chemical Vapor Deposition Method)により炭素被覆するなどの方法によって、複合体粒子を炭素で被覆することもできる。造粒方法としては、転動造粒、圧縮造粒、焼結造粒、振動造粒、混合造粒、解砕造粒、転動流動造粒、スプレードライ法による造粒などが好適に用いられる。
【0034】
スプレードライ法による造粒は、材料と溶媒とを混合したスラリーを噴霧して乾燥することにより造粒する方法である。材料粒子を2μm以下に粉砕、分散するには溶媒中で行う方が効率的であるため、スプレードライ法による造粒は2μm以下の微粒子を複合化させるのに適している。また、スプレードライ法は粒径の制御も容易であり、造粒された粒子の形状も球形であり、さらに強混練や強分散処理を行わないため、繊維状の導電性材料を用いても、繊維形状が粉砕されるおそれが少ないため、造粒方法としては特に好ましい。スプレードライ法に用いる溶媒としては、非水系溶媒(水を含まない溶媒)を用いるのが好ましい。水系溶媒(水を含む溶媒)を用いると、リチウムと合金化可能な元素を含む材料の表面が酸化される可能性が高いからである。非水系溶媒としては、特にアルコール類が取扱性や乾燥の容易性の観点から好ましい。また、スラリーの分散にはビーズミルやボールミル、湿式のジェットミルなどが好適に使用できる。分散剤を兼ねた造粒時のバインダには、ポリビニルピロリドン(PVP)やポリビニルアルコール(PVA)などが好適に使用できる。造粒後に残存した分散剤やバインダは、加熱処理により炭化することができる。また、スプレードライ法による造粒の後に、その粒子をさらに他の導電性材料とともに転動造粒や転動流動造粒などを行って2段階で造粒すると、効率的に空隙が導入でき、さらに電子伝導ネットワークも効率的に構築できるため特に好ましい。
【0035】
複合体粒子中の空隙体積占有率は、混合材料の種類、平均粒径、混合割合、造粒条件などを制御することで、35〜70%を達成できる。特に、1つの複合体粒子に含まれるリチウムと合金化可能な元素を含む材料の全表面積Ssと、導電性材料の全表面積Scの比Sc/Ssが0.5以上50以下であると35%以上の空隙体積占有率を得ることが容易となる。また、ポリエチレン(PE)やポリスチレン(PS)などの樹脂を造粒前の材料に含ませて造粒し、その後に加熱して樹脂を燃焼または昇華させて除去することにより、より効果的に複合体粒子の空隙のサイズや量をコントロールできる。
【0036】
次に、本発明の非水二次電池用負極および非水二次電池の実施の形態について説明する。本発明の非水二次電池用負極の一形態は、上記で説明した本発明の電極材料を含む負極である。
【0037】
また、上記本発明の電極材料を含む非水二次電池用負極は、非水二次電池用負極の充電開始の電位をリチウム金属に対して1.5Vとし、この充電開始時の複合体粒子の体積をV1、複合体粒子1g当たり1000mAhの電気量の充電を行った後の複合体粒子の体積をV2、さらにその充電状態から複合体粒子をリチウム金属に対して1.5Vの電位まで放電させた後の複合体粒子の体積をV3とした場合に、(V2−V1)/V1×100で求められる充電時の体積膨張率(%)を68%以下に、かつ、(V2−V3)/(V2−V1)×100で求められる放電時の体積収縮率(%)を85%以上にすることができる。
【0038】
これにより、高容量でかつサイクル特性に優れた非水二次電池を構成することができる。すなわち、充電時の体積膨張率が68%を超えた場合は、負極の厚さ方向の膨張が大きくなりすぎて、負極に歪みなどが発生したり集電体である金属箔が断裂するなどして電池構造および構成材料に対して悪影響が生じやすくなる。また、充放電サイクルに伴って、複合体粒子内部あるいは複合体粒子間の電子伝導ネットワークが断絶する可能性が高くなる。一方、放電時の体積収縮率が85%未満の場合、すなわち、充電により膨張した複合体粒子が放電時に収縮せず、充放電における粒子の膨張および収縮の可逆性に劣る場合は、リチウムと合金化可能な元素を含む材料と導電性材料との電気的接触が不十分であることが推定され、充放電サイクル特性などに問題が生じる。
【0039】
また、上記非水二次電池用負極に用いる複合体粒子は、その比表面積が50m2/g未満であることが好ましい。この範囲であれば、負極に含有されるバインダが複合体粒子の表面層に埋没しないため、複合体粒子と集電体との接着性が悪化せず、不可逆容量が増加する可能性が低い。
【0040】
また、本発明の非水二次電池の一形態は、上記で説明した本発明の非水二次電池用負極と、正極と、非水電解質とを備えた非水二次電池である。
【0041】
上記非水二次電池の充電方法は特に限定はされないが、定電流、または定電流と定電圧を組み合わせた方法で行うことが好ましい。例えば、設定電圧(E)に達するまでは、充電を一定の電流値(I)で充電する定電流充電領域と、設定電圧(E)に達した後、設定電圧(E)で定電圧充電する定電圧充電領域とを組み合わせて充電を行う方法が好ましい。これにより、効率的な充電が可能となり、最短の時間で設定した容量を引き出すことができるからである。なお、充電電流値は特に限定はされないが、10mA/cm2以下の電流密度で行うのが好ましい。これを超えると十分な容量が得られなくなる可能性があるからである。
【0042】
また、リチウムと合金化可能な元素を含む材料に吸蔵されるLi量を制限することによって非水二次電池のサイクル特性が向上する場合がある。例えば、Siは充電されてLiとの合金(LixSi)を形成するが、x≦2.625の範囲であるのが好ましく、x=2.625を越える場合(Li21Si8)には膨張率が大きくなり、サイクル特性が低下するという結果が得られている。
【0043】
本発明の複合体粒子は単体でバインダと混合して負極用合剤(負極構成材の混合物)とすることができるが、さらに負極用の導電材料を導入してもよい。負極用合剤を作製する際の負極用導電材料は、構成された非水二次電池において化学変化を起こさない電子伝導性材料であれば特に制限はないが、通常、天然黒鉛(鱗状黒鉛、鱗片状黒鉛、土状黒鉛など)、人造黒鉛、アセチレンブラック、ケッチェンブラックなどのカーボンブラック、炭素繊維や、金属粉(銅、ニッケル、アルミニウム、銀などの粉末)、金属繊維あるいはポリフェニレン誘導体などの導電性高分子材料を1種、またはこれらを混合して用いることができる。
【0044】
上記負極に用いるバインダとしては、例えば、でんぷん、ポリビニルアルコール、カルボキシメチルセルロース、ヒドロキシプロピルセルロース、再生セルロース、ジアセチルセルロース、ポリビニルクロリド、ポリビニルピロリドン、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、ポリエチレン、ポリプロピレン、エチレン−プロピレン−ジエンターポリマー(EPDM)、スルホン化EPDM、スチレンブタジエンゴム、ブタジエンゴム、ポリブタジエン、フッ素ゴム、ポリエチレンオキシドなどの多糖類、熱可塑性樹脂、ゴム弾性を有するポリマーなどやこれらの変成体などの1種、または2種以上を混合して用いることができる。
【0045】
上記正極には、正極材料、導電材料、バインダなどが含まれる。この正極材料としては特に限定されることなく各種のものを使用することができるが、特にLixCoO2、LixNiO2、LixMnO2、LixCoyNi1-yO2、LixCoyM1-yOz、LixNi1-yMyOz、LixMn2O4、LixMn2-yMyO4(Mは、Mg、Mn、Fe、Co、Ni、Cu、Zn、Al、Crのうち少なくとも1種、0≦x≦1.1、 0<y<1.0、 2.0≦z≦2.2)などのLi含有遷移金属酸化物が好適に用いられる。
【0046】
正極用の導電材料としては、用いる正極材料の充放電電位において化学変化を起こさない電子伝導性材料であれば特にその種類は制限されない。例えば、天然黒鉛、人造黒鉛などのグラファイト類、またはアセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラックなどのカーボンブラック類、または炭素繊維、金属繊維などの導電性繊維類などを単独、またはこれらを混合して使用できる。これらの導電材料の中で、人造黒鉛、アセチレンブラック、ケッチェンブラックが特に好ましい。
【0047】
正極用のバインダとしては、例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン(PTFE)、ポリフッ化ビニリデン(PVDF)、スチレンブタジエンゴム、テトラフルオロエチレン−ヘキサフルオロエチレン共重合体、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体、フッ化ビニリデン−ヘキサフルオロプロピレン共重合体、フッ化ビニリデン−クロロトリフルオロエチレン共重合体、エチレン−テトラフルオロエチレン共重合体などを使用でき、これらの材料を単独、または混合して用いることができる。また、これらの材料の中でより好ましい材料は、PVDFとPTFEである。
【0048】
本発明の非水二次電池に用いるリチウムイオン伝導性の非水電解質としては、一般に電解液と呼ばれる液状電解質、またはゲル状ポリマー電解質、または固体電解質のいずれも用いることができるが、液状電解質やゲル状ポリマー電解質などが好ましい。
【0049】
液状電解質は、有機溶媒と、その有機溶媒に溶解するLi塩とから構成されている。有機溶媒としては、プロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、γ−ブチロラクトン、1,2−ジメトキシエタン、テトラヒドロフラン、2−メチルテトラヒドロフラン、ジメチルスルフォキシド、1,3−ジオキソラン、ホルムアミド、ジメチルホルムアミド、ジオキソラン、アセトニトリル、ニトロメタン、蟻酸メチル、酢酸メチル、燐酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、3−メチル−2−オキサゾリジノン、プロピレンカーボネート誘導体、テトラヒドロフラン誘導体、ジエチルエーテル、1,3−プロパンスルトンなどの非プロトン性有機溶媒の少なくとも1種以上を混合した溶媒を用いることができる。また、その有機溶媒に溶解させるLi塩としては、例えば、LiClO4、LiBF6、LiPF6、LiCF3SO3、LiCF3CO2、LiAsF6、LiSbF6、LiB10Cl10、低級脂肪族カルボン酸Li、LiAlCl4、LiCl、LiBr、LiI、クロロボランLi、四フェニルホウ酸Liなどの1種以上を使用できる。中でも、エチレンカーボネートまたはプロピレンカーボネートと、1,2−ジメトキシエタン、ジエチルカーボネート、メチルエチルカーボネートなどとの混合溶媒に、LiClO4、LiBF6、LiPF6、LiCF3SO3などを含有させた液状電解質が好ましい。これら液状電解質を電池内に注入する量は特に限定されないが、活物質の量や電池のサイズによって必要量用いることができる。この液状電解質におけるLi塩の濃度は特に限定されないが、液状電解質1リットル当たり0.2〜3.0モルが好ましい。
【0050】
また、ゲル状ポリマー電解質は、上記液状電解質をゲル化剤でゲル化したものに相当する。そのゲル化剤としては、例えば、ポリエチレンオキシド、ポリアクリルニトリルなどの直鎖状ポリマーまたはそれらのコポリマー、あるいは紫外線や電子線などの活性光線の照射によりポリマー化する多官能モノマー、例えば、ペンタエリスリトールテトラアクリレート、ジトリメチロールプロパンテトラアクリレート、エトキシ化ペンタエリスリトールテトラアクリレート、ジペンタエリスリトールヒドロキシペンタアクリレート、ジペンタエリスリトールヘキサアクリレートなどの四官能以上のアクリレートおよび上記アクリレートと同様の四官能以上のメタクリレートなどが用いられる。ただし、上記モノマーを使用する場合でも、モノマー自体がそのままでゲル化剤になるのではなく、それらをポリマー化したポリマーがゲル化剤として作用する。
【0051】
上記のように多官能モノマーを用いて液状電解質をゲル化させる場合、必要であれば重合開始剤として、例えば、ベンゾイル類、ベンゾインアルキルエーテル類、ベンゾフェノン類、ベンゾイルフェニルフォスフィンオキシド類、アセトフェノン類、チオキサントン類、アントラキノン類などを使用することができ、さらに重合開始剤の増感剤としてアルキルアミン類、アミノエステルなども使用することができる。
【0052】
本発明の非水二次電池の形状としては、コイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型などのほか、電気自動車などに用いる大型のものなどいずれであってもよい。
【0053】
【実施例】
以下、実施例により本発明をさらに詳しく説明する。ただし、本発明はこれらの実施例に限定されるものではない。
【0054】
(実施例1)
平均粒径1μmのSi粉末と、平均繊維長5μmで直径0.2μmの繊維状炭素(CF:カーボンファイバー)と、平均粒径2μmの黒鉛とを、質量比でSi:CF:黒鉛=60:30:10の配合比で混合し、これらを撹拌式の転動造粒機を用いて造粒した。その結果、平均粒径10μmの複合体粒子が得られた。その複合体粒子の真密度(D2)は2.20g/cm3、タップかさ密度(D1)は0.8g/cm3であった。従って、この複合体粒子の空隙体積占有率Vsは、Vs=(1−1.35×D1/D2)×100の式から51%と求まった。
【0055】
次に、得られた複合体粒子90質量部に対し、負極用導電材料として炭素粉末5質量部と、バインダとしてPVDF5質量部とを混合し、これらを脱水N−メチルピロリドンに分散させてスラリーを作製し、銅箔からなる負極集電体上に塗布して、乾燥し、圧延した後、直径16mmの円板状に切り取って、これを真空で24時間乾燥させて負極とした。
【0056】
上記で得られた複合体粒子について、非水二次電池用負極の電極材料としての特性を下記の方法により試験した。
【0057】
上記負極と、対極の金属Liとを組み合わせてコイン型モデル電池を作製した。電解液には、プロピレンカーボネートとジメチルカーボネートとの混合溶媒(混合体積比1:1)に六フッ化リン酸リチウムを1mol/L溶解したものを用いた。負極の電位がリチウム金属基準で1.5Vになるまで放電した後に、一部のモデル電池を分解し、後述の方法により充電開始時の複合体粒子の体積V1を求めた。次いで、残った電池を、負極の複合体粒子を1g当たり1000mAhの電気量で充電し、この中の一部の電池から同様の方法により複合体粒子の体積V2を求めた。さらに、残りの電池を、負極の電位がリチウム金属基準で1.5Vになるまで放電させ、放電終了後に同様の方法により複合体粒子の体積V3を求めた。この結果から、充電時の体積膨張率〔(V2−V1)/V1×100〕と放電時の体積収縮率〔(V2−V3)/(V2−V1)×100〕を求めた。その結果、充電時の体積膨張率は65%であり、放電時の体積収縮率は85%であった。
【0058】
上記複合体粒子の体積は下記の方法で求めた。測定する負極をアルゴン雰囲気下でジメチルカーボネートにより洗浄した後、大気に触れることなく気密状態で走査型電子顕微鏡(SEM)まで搬送し、SEM写真から任意の粒子100個の粒径を求め、複合体粒子の形状を球状と仮定して体積を求めた。そして、100個の平均粒子体積を、求める複合体粒子の体積とした。
【0059】
一方、上記複合体粒子を用いたコイン型モデル電池のサイクル特性を調べた。電池の充放電方法は以下のように行った。充電は電流密度を0.5mA/cm2とし、定電流で充電を行い、充電電圧が120mVに達した後、1/10の電流密度になるまで定電圧で充電を行った。放電は電流密度0.5mA/cm2の定電流で行い、放電終止電圧は1.5Vとした。
【0060】
その結果、2サイクル目の放電容量は複合体粒子1g当たり1100mAhであり、50サイクル目の容量保持率〔(50サイクル目の放電容量/2サイクル目の放電容量)×100〕は70%であった。
【0061】
(実施例2)
平均粒径1μmのSi粉末と、平均繊維長5μmで直径0.2μmのCFと、平均粒径2μmの黒鉛とを、質量比でSi:CF:黒鉛=60:30:10の配合比で混合し、これらを撹拌式の転動造粒機を用いて造粒した。その結果、平均粒径10μmの複合体粒子が得られた。このようにして作製した複合体粒子のSEM写真を図1に示す。
【0062】
続いて、ベンゼンをカーボン源として、CVD法により1000℃で複合体粒子を炭素で被覆した。被覆した炭素量は被覆前後の複合体粒子の質量変化から求めた。その複合体粒子の組成は、質量比でSi:CF:黒鉛:CVD炭素=56:28:9:7であった。得られた複合体粒子の真密度は2.20g/cm3、タップかさ密度は0.85g/cm3であった。従って、この複合体粒子の空隙体積占有率Vsは、前述の計算式から48%と求まった。次に、実施例1と同様にして負極を作製したところ、実施例1と同様にして測定した充電時の体積膨張率は50%であり、放電時の体積収縮率は92%であった。
【0063】
また、実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1000mAhであり、50サイクル目の容量保持率は85%であった。
【0064】
(実施例3)
平均粒径2μmのSi粒子と、平均繊維長5μmで直径0.2μmのCFと、平均粒径2μmの黒鉛とを、質量比でSi:CF:黒鉛=60:30:10の配合比で用いた以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して56質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は0.98g/cm3であった。従って、この複合体粒子の空隙体積占有率は40%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は62%であり、放電時の体積収縮率は88%であった。
【0065】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり950mAhであり、50サイクル目の容量保持率は75%であった。
【0066】
(実施例4)
実施例1と同じ原料を用いて、配合比を質量比でSi:CF:黒鉛=40:35:25とした以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して37質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は0.81g/cm3であった。従って、この複合体粒子の空隙体積占有率は50%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は50%であり、放電時の体積収縮率は92%であった。
【0067】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり700mAhであり、50サイクル目の容量保持率は95%であった。
【0068】
(実施例5)
実施例1と同じ原料を用いて、配合比を質量比でSi:CF:黒鉛=75:15:10とした以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して70質量%であり、また、その複合体粒子の真密度は2.25g/cm3、タップかさ密度は1.0g/cm3であった。従って、この複合体粒子の空隙体積占有率は40%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は55%であり、放電時の体積収縮率は85%であった。
【0069】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1250mAhであり、50サイクル目の容量保持率は73%であった。
【0070】
(実施例6)
平均粒径1μmのSi粒子と、平均繊維長10μmで直径0.1μmのCFと、平均粒径2μmの黒鉛とを、質量比でSi:CF:黒鉛=60:30:10の配合比で用いた以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対しては56質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は0.73g/cm3であった。従って、この複合体粒子の空隙体積占有率は55%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は45%であり、放電時の体積収縮率は92%であった。
【0071】
実施例1と同様にして行ったサイクル試験の結果、2サイクル目の放電容量は複合体粒子1g当たり1050mAhであり、50サイクル目の電極の容量保持率は87%であった。
【0072】
(実施例7)
平均粒径1μmのSi粒子と、平均繊維長10μmで直径0.2μmのCFとを、質量比でSi:CF=60:40の配合比で用いた以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子をコールタールピッチでコーティングした後、1300℃で焼成して複合体粒子の表面をハードカーボンで被覆した。
【0073】
最終的に得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して52質量%であり、また、その複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.86g/cm3であった。従って、この複合体粒子の空隙体積占有率は45%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は35%であり、放電時の体積収縮率は95%であった。
【0074】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり950mAhであり、50サイクル目の電極の容量保持率は88%であった。
【0075】
(実施例8)
実施例1と同じ原料に、さらに平均粒径0.2μmのポリスチレン粒子(PS)を加え、質量比でSi:CF:黒鉛:PS=30:15:5:50の配合比で用いた以外は、実施例2と同様にして複合体粒子を作製した。用いたPSはCVD処理時に燃焼または昇華するため粒子内に新たな空隙が形成される。最終的に得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して56質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は0.73g/cm3であった。従って、この複合体粒子の空隙体積占有率は55%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は48%であり、放電時の体積収縮率は90%であった。
【0076】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり920mAhであり、50サイクル目の容量保持率は85%であった。
【0077】
(実施例9)
平均粒径0.2μmのSi粒子と、平均繊維長5μmで直径0.2μmのCFと、平均粒径0.05μmのケッチェンブラック(KB)とを、質量比でSi:CF:KB=60:30:10の配合比で用いた以外は、実施例2と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して56質量%であり、また、その複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.68g/cm3であった。従って、この複合体粒子の空隙体積占有率は56%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は50%であり、放電時の体積収縮率は95%であった。
【0078】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1000mAhであり、50サイクル目の容量保持率は87%であった。
【0079】
(実施例10)
平均粒径0.2μmのSi粉末と、平均繊維長5μmで直径0.2μmのCFと、平均粒径0.05μmのKBと、分散剤としてのポリビニルピロリドン(PVP)とを、質量比でSi:CF:KB:PVP=60:30:10:4の配合比でエタノール中にて混合した。この混合物を湿式のジェットミルで分散混合し、その後得られたスラリーをスプレードライ法にて造粒した。その結果、平均粒径10μmの造粒体が得られた。続いて、トルエンをカーボン源として、CVD法により1000℃で複合体粒子を炭素で被覆した。被覆した炭素量は被覆前後の複合体粒子の質量変化から求めた。その複合体粒子の組成は、質量比でSi:CF:KB:CVD炭素=50:25:8:17であった。得られた複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.68g/cm3であった。従って、空隙体積占有率は58%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は48%であり、放電時の体積収縮率は95%であった。
【0080】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1000mAhであり、50サイクル目の容量保持率は90%であった。
【0081】
(実施例11)
平均粒径0.2μmのSi粉末と、平均粒径0.05μmのKBと、分散剤としてのPVPとを、質量比でSi:KB:PVP=70:30:3の配合比でエタノール中にて混合した。この混合物を湿式のジェットミルで分散混合し、その後得られたスラリーをスプレードライ法にて造粒した。その結果、平均粒径3μmの造粒体が得られた。得られた造粒体(Si/KB造粒体)と、平均繊維長5μmで直径0.2μmのCFとを、質量比でSi/KB造粒体:CF=85:15の配合比で混合し、その混合体を転動流動法にて造粒した。その結果、平均粒径15μmの複合体粒子が得られた。続いて、トルエンをカーボン源として、CVD法により1000℃で複合体粒子を炭素で被覆した。被覆した炭素量は被覆前後の複合体粒子の質量変化から求めた。その複合体粒子の組成は、質量比でSi:CF:KB:CVD炭素=50:10:25:15であった。得られた複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.65g/cm3であった。従って、空隙体積占有率は60%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は47%であり、放電時の体積収縮率は95%であった。
【0082】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1000 mAhであり、50サイクル目の容量保持率は92%であった。
【0083】
(実施例12)
平均粒径1.0μmのSi粉末と、平均粒径0.05μmのKBと、分散剤のPVPとを、質量比でSi:KB:PVP=70:30:3の配合比でエタノール中にて混合した。この混合物を湿式のジェットミルで分散混合し、その後得られたスラリーをスプレードライ法にて造粒した。その結果、平均粒径5μmの造粒体が得られた。続いて、トルエンをカーボン源として、CVD法により1000℃で造粒体を炭素で被覆した。得られた複合体粒子をさらにコールタールピッチでコーティングした後、1300℃で焼成して複合体粒子の表面をハードカーボンで被覆した。
【0084】
このようにして作製した複合体粒子のSEM写真を図2に示す。最終的に得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して47質量%であり、また、その複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.78g/cm3であった。従って、この複合体粒子の空隙体積占有率は50%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は40%であり、放電時の体積収縮率は95%であった。
【0085】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり920mAhであり、50サイクル目の容量保持率は93%であった。
【0086】
(実施例13)
平均粒径1.0μmのSi粉末と、平均粒径0.05μmのKBと、分散剤のPVPとを、質量比でSi:KB:PVP=60:40:4の配合比でエタノール中にて混合した。この混合物を湿式のジェットミルで分散混合し、その後得られたスラリーをスプレードライ法にて造粒した。その結果、平均粒径5μmの造粒体が得られた。続いて、カーボン源なしに1000℃で造粒体を焼成した。最終的に得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して56質量%であり、また、その複合体粒子の真密度は2.10g/cm3、タップかさ密度は0.75g/cm3であった。従って、この複合体粒子の空隙体積占有率は52%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は55%であり、放電時の体積収縮率は85%であった。
【0087】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1050 mAhであり、50サイクル目の電極の容量保持率は80%であった。
【0088】
(実施例14)
平均粒径1.0μmのSi/Si2Ni複合体粉末と、平均粒径0.05μmのKBと、分散剤のPVPとを、質量比でSi:KB:PVP=85:15:1の配合比でエタノール中にて混合した。この混合物を湿式のジェットミルで分散混合し、その後得られたスラリーをスプレードライ法にて造粒した。その結果、平均粒径7μmの造粒体が得られた。続いて、トルエンをカーボン源として、CVD法により850℃で造粒体を炭素で被覆した。最終的に得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して40質量%であり、また、その複合体粒子の真密度は3.10g/cm3、タップかさ密度は1.15g/cm3であった。従って、この複合体粒子の空隙体積占有率は50%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は40%であり、放電時の体積収縮率は93%であった。
【0089】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり800mAhであり、50サイクル目の容量保持率は95%であった。
【0090】
(比較例1)
平均粒径1μmのSi粉末と、平均粒径2μmの黒鉛とを、質量比でSi:黒鉛=60:40の配合比で用いた以外は、実施例1と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して56質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は1.14g/cm3であった。従って、この複合体粒子の空隙体積占有率は30%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は100%であり、放電時の体積収縮率は77%であった。
【0091】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり840mAhであったが、50サイクル目の容量保持率は40%であり、大幅な容量低下が認められた。
【0092】
(比較例2)
平均粒径1μmのSi粉末と、平均粒径2μmの黒鉛とを、質量比でSi:黒鉛=90:10の配合比で用いた以外は実施例1と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して84質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は1.10g/cm3であった。従って、この複合体粒子の空隙体積占有率は32%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は110%であり、放電時の体積収縮率は70%であった。
【0093】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり1400mAhであり、50サイクル目の容量保持率は10%であった。
【0094】
(比較例3)
平均粒径1μmのSi粉末と、平均粒径2μmの黒鉛とを、質量比でSi:黒鉛=25:75の配合比で用いた以外は、実施例1と同様にして複合体粒子を作製した。得られた複合体粒子のSi含有率は、複合体粒子の全質量に対して20質量%であり、また、その複合体粒子の真密度は2.20g/cm3、タップかさ密度は1.17g/cm3であった。従って、この複合体粒子の空隙体積占有率は28%と求まった。また、実施例1と同様にして測定した充電時の体積膨張率は75%であり、放電時の体積収縮率は83%と求まった。
【0095】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり500mAhであり、50サイクル目の容量保持率は50%であった。
【0096】
(参考例1)
コールタールピッチのテトラヒドロフラン(THF)溶液にテトラメトキシシラン(TMOS)を溶解した。この溶液に平均粒径5μmの黒鉛を添加して、還流しながら攪拌・混合した。それぞれの配合比は質量比でTHF:コールタールピッチ:TMOS:黒鉛=10:1:1:3である。次いで、THFを真空乾燥して除去した。得られた粉末を窒素気流中、1000℃でコールタールピッチおよびTMOSを分解・炭素化して、珪素を含有する黒鉛および非晶質炭素からなる複合体粒子を得た。この複合体粒子のSi含有率は、複合体粒子の全質量に対して6質量%であり、その複合体粒子の空隙体積占有率は12%であった。また、実施例1と同様にして測定した充電時の体積膨張率は30%であり、放電時の体積収縮率は80%であった。
【0097】
実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり400mAhであり、50サイクル目の容量保持率は70%であった。
【0098】
(参考例2)
平均粒径2μmのSi粒子と、平均繊維長5μmで直径0.2μmのCFとを、質量比でSi:CF=60:40の配合比で乳鉢により混合して、電極材料とした。この電極材料は、SiとCFとが単に混合されているのみで、複合体は形成されなかった。この電極材料を用いて実施例1と同様にして負極を作製した。
【0099】
また、実施例1と同様にしてサイクル試験を行った結果、2サイクル目の放電容量は複合体粒子1g当たり650mAhであり、50サイクル目の放電容量はほとんど0mAh/gであった。
【0100】
以上の結果を表1に示した。
【0101】
【表1】
【0102】
表1から明らかなように、実施例1〜14の複合体粒子は、充電時における粒子の膨張が少なく、かつ放電時において可逆的に収縮できることが分かる。また、大きな放電容量を示し、充放電サイクルを繰り返しても容量低下が少なくサイクル特性にも優れていた。一方、空隙体積占有率が小さい比較例1〜3は、充電時の膨張が大きく、可逆性に劣り、充放電サイクル後の容量保持率も著しく低くなった。
【0103】
なお、参考例1は特許文献2を参考にした例であり、参考例2は複合体粒子を形成させていない例である。
【0104】
【発明の効果】
以上説明したように本発明は、電極材料の膨張を抑えることにより、高容量でかつサイクル特性に優れた非水二次電池を構成することができる。
【図面の簡単な説明】
【図1】 本発明の実施例2における複合体粒子のSEM写真である。
【図2】 本発明の実施例12における複合体粒子のSEM写真である。
【図3】 炭素を含む材料によって被覆された複合体粒子の放電時と充電時の模式断面図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode material capable of constituting a non-aqueous secondary battery having a high capacity and excellent cycle characteristics, a method for producing the same, a negative electrode for a non-aqueous secondary battery using the electrode material, and a non-aqueous secondary It relates to batteries.
[0002]
[Prior art]
Since non-aqueous secondary batteries have high capacity, high voltage, and high energy density, great expectations are placed on their development. In this non-aqueous secondary battery, an organic solvent-based electrolytic solution in which a lithium (Li) salt is dissolved in an organic solvent is used as an electrolytic solution, and Li or a Li alloy has been used as a negative electrode active material. However, when Li or Li alloy is used as a negative electrode active material to function as a secondary battery, Li dendrite is generated during charging, so internal short circuit is likely to occur, and the deposited dendrite is active with a high specific surface area. However, there was a problem that it was not safe because it was high. Furthermore, the dendrite reacts with the solvent in the electrolyte to form a film lacking electronic conductivity on the surface of the dendrite, increasing the internal resistance of the battery and reducing the charge / discharge efficiency, resulting in a cycle. There was also a problem that durability became poor.
[0003]
At present, instead of Li or Li alloy, carbon materials such as coke and glassy carbon that can be doped / undoped with Li ions, carbon materials such as natural or artificial graphite are used as negative electrode materials. Thus, the cycle durability is improved, and the battery functions as a secondary battery.
[0004]
Recently, as the capacity of secondary batteries for portable devices that have become smaller and more multifunctional is desired, more Li can be alloyed and occluded, such as silicon (Si) and tin (Sn). Such metalloids and metals are attracting attention as negative electrode materials, and in order to increase the capacity per unit volume, attempts have been made to use Si or a compound thereof as a negative electrode active material. For example, Patent Document 1 discloses Li t A non-aqueous secondary battery using Si (0 ≦ t ≦ 5) as a negative electrode active material is disclosed.
[0005]
Moreover, as a prior art relevant to this invention, there exists patent document 2, etc., for example.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-29602
[0007]
[Patent Document 2]
JP 2000-272911 A
[0008]
[Problems to be solved by the invention]
However, the negative electrode material that can be alloyed with Li described above has a higher capacity than the carbon material. However, when charging and discharging are repeated, the negative electrode material itself repeatedly expands and contracts to become a fine powder, and the negative electrode swelling and electrolyte solution There is a problem that unnecessary absorption is caused and electrode characteristics are deteriorated. The reason is considered as follows.
[0009]
For example, Si contains 8 Si atoms in its crystallographic unit cell (cubic, space group Fd-3m). Converted from the lattice constant a = 0.5431 nm, the unit lattice volume is 0.1602 nm. Three The volume occupied by one Si atom (the value obtained by dividing the unit cell volume by the number of Si atoms in the unit cell) is 0.0199 nm. Three It is. Here, when a negative electrode containing Si is charged to 100 mV or less at a potential based on Li (insertion of Li), a compound Li containing a large amount of Li 15 Si Four Or Li twenty one Si Five And the capacity corresponds to about 4000 mAh / g, but the volume expansion coefficient of the negative electrode becomes extremely large. For example, Li twenty one Si Five The unit cell (cubic crystal, space group F-43m) contains 83 Si atoms. Converted from the lattice constant a = 1.8750 nm, the unit cell volume is 6.5918 nm. Three And the volume per Si atom is 0.079 nm. Three It is. This value is 3.95 times that of simple substance Si. Since the volume difference during charge and discharge is extremely large as described above, it is considered that the negative electrode particles are greatly distorted and the negative electrode particles are pulverized. As a result, a space is created between the negative electrode particles, the electrical contact (electron conduction network) between the negative electrode particles is broken, the portion that cannot participate in the electrochemical reaction increases, and the charge / discharge capacity decreases. .
[0010]
Patent Document 2 discloses a lithium secondary battery using composite particles in which Si particles are embedded in graphite and amorphous carbon as a negative electrode, and realizes a lithium secondary battery excellent in charge and discharge characteristics. ing. Thus, by combining Si particles with graphite and amorphous carbon, the expansion of Si can be relaxed, and the cycle characteristics are improved. However, in the composite particles that express a high capacity of about 1000 mAh / g or more, the cycle characteristics are not perfect and do not reach a level suitable for practical use. This is thought to be because a large amount of Li needs to be inserted into Si in order to develop the high capacity as described above, so that the expansion of Si is further increased and the structure of the composite particle is destroyed. .
[0011]
The present invention solves the above-mentioned conventional problems, and can provide a non-aqueous secondary battery having a high capacity and excellent cycle characteristics, a method for producing the same, and a non-aqueous secondary using the electrode material A negative electrode for a battery and a non-aqueous secondary battery are provided.
[0012]
[Means for Solving the Problems]
The present invention is an electrode material comprising composite particles containing a material containing an element that can be alloyed with lithium and a conductive material,
The proportion of the material containing an element that can be alloyed with lithium is 30% by mass to 80% by mass with respect to the total mass of the composite particles,
The composite particle The shape is spherical , With voids inside,
Of the composite particles Tap tap measured according to JIS R1628 Density is D1 (g / cm Three ), The true density of the composite particles is D2 (g / cm Three ), When the void volume occupancy (%) of the composite particles is Vs = (1-1.35 × D1 / D2) × 100, an electrode material having Vs of 35% to 70% is provided.
[0013]
Further, the present invention is a method for producing the above electrode material,
Forming composite particles by mixing and granulating a material containing an element that can be alloyed with lithium, the conductive material, and a resin;
And a step of forming voids in the composite particles by heating or removing the resin by burning or sublimating the composite particles.
[0014]
Further, the present invention is a method for producing the above electrode material,
A composite particle is formed by granulating by a spray drying method in which the material containing an element that can be alloyed with lithium and the conductive material are dispersed in a solvent to form a mixture, and the mixture is sprayed and dried. The manufacturing method of the electrode material including the process to perform is provided.
[0015]
Moreover, this invention provides the negative electrode for non-aqueous secondary batteries containing the said electrode material.
[0016]
Moreover, this invention provides the nonaqueous secondary battery provided with the said negative electrode for nonaqueous secondary batteries, a positive electrode, and a nonaqueous electrolyte.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
First, an embodiment of the electrode material of the present invention will be described. One embodiment of the electrode material of the present invention is an electrode material composed of composite particles including an element that can be alloyed with lithium and a conductive material, and is a material that includes an element that can be alloyed with lithium. The ratio is 30% by mass or more and 80% by mass or less with respect to the total mass of the composite particle, the composite particle has voids inside, and the composite particle Tap cap Density is D1 (g / cm Three ), The true density of the composite particles is D2 (g / cm Three ) When the void volume occupation ratio (%) of the composite particles is Vs = (1-1.35 × D1 / D2) × 100, Vs is 35% or more and 70% or less.
[0018]
Here, the void volume occupation ratio Vs = (1-1.35 × D1 / D2) × 100 means the ratio of the void volume in the composite particle to the volume of the composite particle. That is, assuming that the composite particles are true spherical, when the spheres are three-dimensionally closely packed, they are packed in a face-centered cubic lattice, and the filling rate (%) is as follows.
[0019]
[Expression 1]
[0020]
Therefore, Tap cap The density is a value reflecting the amount of voids obtained by combining the voids between the particles and the voids in the particles accompanying the closest packing. From the above, the voids inside the particles can be represented by (0.7405 · 1 / D1) − (1 / D2), and the void volume occupancy is the total volume of the particles (0.7405 · 1 / D1). Divided by. Assuming that 1 / 0.7405≈1.35, the above equation is 1-1.35 × D1 / D2, and the void volume occupation ratio (%) is multiplied by 100 to obtain Vs = (1-1.35 × D1 / D2) × 100.
[0021]
When the void volume occupancy (Vs) of the composite particles is less than 35%, the composite particles expand greatly during charging. That is, when a material containing an element that can be alloyed with lithium expands as Li ions are inserted (charged), there are not enough gaps in the composite particle to absorb the expansion. Large expansion is inevitable. On the other hand, when Vs exceeds 70%, it becomes difficult to produce composite particles, and there are too many gaps in the composite particles, so that a material containing an element that can be alloyed with lithium and a conductive material are used. Since it is difficult to construct an electron conduction network, it is difficult to charge and discharge. In addition, the composite particles Tap cap The density is determined by putting a predetermined amount of composite particles in a container, Umbrella Compliant with JIS method using a density measuring device Umbrella Obtained from the density measurement method (JIS R1628). The true density is obtained from a gas substitution type density meter using helium gas.
[0022]
Moreover, the content rate of the material containing the element which can be alloyed with lithium needs to exist in the range of 30-80 mass% with respect to the total mass of composite particle, and the range of 45-65 mass% is especially preferable. In the case of less than 30% by mass, when realizing a high capacity of about 1000 mAh / g, the utilization factor of the material containing an element that can be alloyed with lithium becomes too high, and the expansion of the composite particles becomes large, and the fine powder It becomes easy to become. On the other hand, if it exceeds 80% by mass, the number of contact points with the conductive material is reduced, making it difficult to construct an electron conduction network. In addition, this content rate can be calculated | required from the qualitative and quantitative analysis by a fluorescent X ray.
[0023]
The material containing an element that can be alloyed with lithium contained in the composite particle may be a compound or an elemental element (metal, metalloid, semiconductor element, etc.), and may be in any state of crystal, low crystal, and amorphous. . For example, examples of the compound include oxides and nitrides, examples of the metal include alloys and solid solutions with other metals, and intermetallic compounds. Alternatively, a semiconductor element such as Si or Ge doped with B or P to become an n-type or p-type semiconductor may be used whose electric resistance is greatly reduced. The material containing an element that can be alloyed with lithium is preferably spherical in order to avoid concentration of internal stress due to volume expansion. Moreover, as an element that can be alloyed with Li, elements such as Ag, Au, Zn, Cd, Al, Ga, In, Tl, Ge, Pb, Si, Sn, Sb, and Bi are preferably used. Of these, Si is particularly preferred because it has the largest amount of Li storage, is inexpensive and has no environmental problems.
[0024]
The material containing an element that can be alloyed with lithium is preferably a particle having an average particle diameter of 2 μm or less. This is because the composite particles are hardly pulverized and the cycle durability can be improved more effectively.
[0025]
In the present invention, since the composite particles have a predetermined void volume occupation ratio, the voids are effectively utilized, and the volume expansion of the material containing an element that can be alloyed with Li at the time of charge / discharge is absorbed. Volume expansion of the body particles themselves can be suppressed. For this reason, the conductive material is preferably at least one selected from a fibrous or coiled carbon material that easily forms voids and a metallic material such as fibrous or coiled copper. In particular, the fibrous carbon material has a flexible thin thread shape as compared with the conventional particulate acetylene black and artificial graphite, and therefore, the expansion of the material containing the element that can be bonded or alloyed with the adjacent lithium.・ It can effectively follow contraction, in addition, Tap cap Because of its high density, it can have many junctions with a material containing an element that can be alloyed with Li. Furthermore, in order to effectively follow expansion / contraction, the fibrous carbon material preferably has an elastic force that can be plastically deformed.
[0026]
The fiber length and diameter of the fibrous carbon material are not particularly limited, but the average fiber length is preferably 1 μm or more and 30 μm or less. Within this range, electrical bonding within the composite particles becomes good, an electron conduction network can be built in the composite particles, and charge / discharge characteristics are improved. The diameter of the fibrous carbon material is preferably 2 μm or less. Within this range, the fibrous carbon material has sufficient elasticity and can effectively follow expansion / contraction associated with charge / discharge cycles of a material containing an element that can be alloyed with lithium.
[0027]
This fibrous carbon material is likely to be pulverized by strong kneading or dispersion treatment, and may not take a fibrous form. Therefore, it is preferable that the fiber carbon material is not easily pulverized at the time of compounding.
[0028]
As the fibrous carbon material, polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, or the like can be used. As the conductive material other than the fibrous carbon material, acetylene has a high electric conductivity and a high liquid retention property, and has a function of maintaining contact even when a material containing an element capable of alloying with lithium contracts. Carbon black such as black and ketjen black, artificial graphite, graphitizable carbon, non-graphitizable carbon and the like can be suitably used.
[0029]
Moreover, it is preferable that the said composite particle is further coat | covered with the material containing carbon. This is for effectively suppressing the expansion of the composite particles and further reducing the electrical contact resistance between the composite particles. FIG. 3 shows schematic cross-sectional views at the time of discharging and charging of the composite particles coated with the material containing carbon. By covering, for example, Si particles, which are a material containing an element that can be alloyed with Li, and C, which is a conductive material, together with a predetermined gap with an outer shell (coating layer), expansion of the composite particles can be suppressed.
[0030]
In particular, carbon obtained by pyrolyzing a gas (hydrocarbon gas) comprising a compound containing carbon and hydrogen such as toluene in a gas phase, or non-graphitizable carbon obtained by firing a carbon precursor (hard carbon) It is preferable to coat with carbon). This is because these carbons are excellent in electronic conductivity. Further, it is more effective to cover the above two kinds of carbon in combination.
[0031]
Petroleum and coal-based carbon precursors can be used, for example, synthetic pitch, tars, phenol resins, furan resins, polyacrylonitrile, acrylic resins such as poly (α-halogenated acrylonitrile), polyamideimide resins, Polyamide resin, polyimide resin, etc. can be used. When mixing with the composite particles, a solvent that dissolves these carbon precursors may be used. Examples of the solvent include ketones such as tetrahydrofuran and acetone, various alcohols such as methanol and ethanol, amides such as dimethylformamide and dimethylacetamide, and hydrocarbons such as toluene, xylene, and benzene. When a solvent is used for mixing, the solvent is removed by heating the mixture at a temperature of 50 to 150 ° C., preferably under reduced pressure, before firing.
[0032]
Moreover, it is preferable to perform the said thermal decomposition and baking at 700 degreeC or more, and it is more preferable to carry out at 800 degreeC or more. This is because the higher the processing temperature, the less residual impurities and the better conductive carbon with high conductivity. From the above viewpoint, when the composite particles are coated with carbon, the melting point of the material containing an element that can be alloyed with lithium is preferably 700 ° C. or higher.
[0033]
Next, an embodiment of the method for producing an electrode material of the present invention will be described. One form of the method for producing composite particles of the present invention is to produce composite particles by granulating a material containing an element that can be alloyed with lithium and a conductive material. Thereafter, the composite particles can be coated with carbon by mixing with a carbon precursor such as resin and carbonizing the carbon precursor, or by coating the carbon with a CVD (Chemical Vapor Deposition Method). . As the granulation method, rolling granulation, compression granulation, sintering granulation, vibration granulation, mixed granulation, pulverization granulation, rolling fluid granulation, granulation by spray drying method, etc. are preferably used. It is done.
[0034]
Granulation by the spray drying method is a method of granulating by spraying and drying a slurry in which a material and a solvent are mixed. Since it is more efficient to pulverize and disperse material particles to 2 μm or less in a solvent, granulation by spray drying is suitable for complexing fine particles of 2 μm or less. In addition, the spray-drying method is easy to control the particle size, the shape of the granulated particles is also spherical, and since no strong kneading or strong dispersion treatment is performed, even if a fibrous conductive material is used, Since there is little possibility that a fiber shape will be grind | pulverized, it is especially preferable as a granulation method. As a solvent used in the spray drying method, it is preferable to use a non-aqueous solvent (a solvent not containing water). This is because when an aqueous solvent (a solvent containing water) is used, the surface of a material containing an element that can be alloyed with lithium is likely to be oxidized. As the non-aqueous solvent, alcohols are particularly preferable from the viewpoints of handleability and ease of drying. For dispersing the slurry, a bead mill, a ball mill, a wet jet mill, or the like can be preferably used. Polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), etc. can be used suitably for the binder at the time of granulation which served as the dispersing agent. The dispersant and binder remaining after granulation can be carbonized by heat treatment. In addition, after granulation by the spray drying method, the particles are further subjected to rolling granulation or rolling fluid granulation together with other conductive materials and granulated in two stages, and voids can be efficiently introduced. Furthermore, an electron conduction network can be efficiently constructed, which is particularly preferable.
[0035]
The void volume occupation ratio in the composite particles can be 35 to 70% by controlling the kind of the mixed material, the average particle diameter, the mixing ratio, the granulation conditions, and the like. In particular, when the ratio Sc / Ss of the total surface area Ss of the material containing an element that can be alloyed with lithium contained in one composite particle and the total surface area Sc of the conductive material is 0.5 to 50, 35% It becomes easy to obtain the above void volume occupation ratio. In addition, a resin such as polyethylene (PE) or polystyrene (PS) is included in the material before granulation and granulated, and then heated to burn or sublimate and remove the resin to more effectively combine. The size and amount of voids in body particles can be controlled.
[0036]
Next, embodiments of the negative electrode for a non-aqueous secondary battery and the non-aqueous secondary battery of the present invention will be described. One form of the negative electrode for a non-aqueous secondary battery of the present invention is a negative electrode including the electrode material of the present invention described above.
[0037]
The negative electrode for a non-aqueous secondary battery containing the electrode material of the present invention has a charge starting potential of 1.5 V with respect to lithium metal for the negative electrode for the non-aqueous secondary battery. The volume of the composite particle after charging with an electric charge of 1000 mAh per 1 g of composite particles is V2, and the volume of the composite particles is discharged from the charged state to a potential of 1.5 V with respect to lithium metal. When the volume of the composite particles after being made V3 is V3, the volume expansion coefficient (%) during charging obtained by (V2-V1) / V1 × 100 is 68% or less, and (V2-V3) / (V2−V1) × 100, the volume shrinkage rate (%) during discharge can be 85% or more.
[0038]
Thereby, a non-aqueous secondary battery having a high capacity and excellent cycle characteristics can be configured. That is, when the volume expansion rate during charging exceeds 68%, the negative electrode expands too much in the thickness direction, and the negative electrode is distorted or the current collector metal foil is torn. Adversely affects the battery structure and constituent materials. In addition, with the charge / discharge cycle, there is a high possibility that the electron conduction network inside or between the composite particles is broken. On the other hand, when the volumetric shrinkage during discharge is less than 85%, that is, when the composite particles expanded by charging do not contract during discharge and are inferior in reversibility of particle expansion and contraction during charging and discharging, lithium and alloys It is presumed that the electrical contact between the material containing the element that can be converted and the conductive material is insufficient, which causes a problem in charge / discharge cycle characteristics and the like.
[0039]
The composite particles used for the negative electrode for a non-aqueous secondary battery have a specific surface area of 50 m. 2 / G is preferable. If it is this range, since the binder contained in a negative electrode is not embedded in the surface layer of composite particle | grains, the adhesiveness of composite particle | grains and an electrical power collector is not deteriorated, and possibility that an irreversible capacity | capacitance will increase is low.
[0040]
Moreover, one form of the non-aqueous secondary battery of the present invention is a non-aqueous secondary battery including the negative electrode for a non-aqueous secondary battery of the present invention described above, a positive electrode, and a non-aqueous electrolyte.
[0041]
The method for charging the non-aqueous secondary battery is not particularly limited, but it is preferably performed by a constant current or a method combining a constant current and a constant voltage. For example, until reaching the set voltage (E), a constant current charge region where charging is performed at a constant current value (I), and after reaching the set voltage (E), constant voltage charging is performed at the set voltage (E). A method of performing charging in combination with the constant voltage charging region is preferable. This is because efficient charging is possible, and the set capacity can be drawn out in the shortest time. The charging current value is not particularly limited, but is 10 mA / cm. 2 It is preferable to carry out at the following current density. This is because if it exceeds this, a sufficient capacity may not be obtained.
[0042]
In addition, the cycle characteristics of the non-aqueous secondary battery may be improved by limiting the amount of Li stored in a material containing an element that can be alloyed with lithium. For example, Si is charged and alloyed with Li (Li x Si), but preferably in the range of x ≦ 2.625, when x = 2.625 is exceeded (Li twenty one Si 8 ) Has a result that the expansion coefficient increases and the cycle characteristics deteriorate.
[0043]
The composite particles of the present invention can be mixed with a binder alone to form a negative electrode mixture (a mixture of negative electrode constituent materials), but a negative electrode conductive material may be further introduced. The conductive material for the negative electrode when producing the negative electrode mixture is not particularly limited as long as it is an electron conductive material that does not cause a chemical change in the constructed non-aqueous secondary battery, but usually natural graphite (scale-like graphite, Scale-like graphite, earth-like graphite, etc.), artificial graphite, acetylene black, carbon black such as ketjen black, carbon fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber or polyphenylene derivatives One type of conductive polymer material or a mixture thereof can be used.
[0044]
Examples of the binder used for the negative electrode include starch, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl chloride, polyvinyl pyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, and ethylene-propylene. -Diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and other polysaccharides, thermoplastic resins, rubber elastic polymers, etc. , Or a mixture of two or more.
[0045]
The positive electrode includes a positive electrode material, a conductive material, a binder, and the like. There are no particular limitations on the positive electrode material, and various materials can be used. x CoO 2 , Li x NiO 2 , Li x MnO 2 , Li x Co y Ni 1-y O 2 , Li x Co y M 1-y O z , Li x Ni 1-y M y O z , Li x Mn 2 O Four , Li x Mn 2-y M y O Four (M is at least one of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al and Cr, 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 ≦ z ≦ 2 Li-containing transition metal oxides such as .2) are preferably used.
[0046]
The type of the conductive material for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material to be used. For example, graphites such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black, or conductive fibers such as carbon fiber and metal fiber Can be used alone or in combination. Among these conductive materials, artificial graphite, acetylene black, and ketjen black are particularly preferable.
[0047]
Examples of the binder for the positive electrode include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, and tetrafluoroethylene-hexafluoropropylene. Copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, etc. are used. These materials can be used alone or in combination. Of these materials, PVDF and PTFE are more preferable materials.
[0048]
As the lithium ion conductive non-aqueous electrolyte used in the non-aqueous secondary battery of the present invention, a liquid electrolyte generally called an electrolyte solution, a gel polymer electrolyte, or a solid electrolyte can be used. A gel polymer electrolyte or the like is preferable.
[0049]
The liquid electrolyte is composed of an organic solvent and a Li salt that dissolves in the organic solvent. Examples of the organic solvent include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3 -Dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether A solvent in which at least one aprotic organic solvent such as 1,3-propane sultone is mixed. It is possible to have. Examples of the Li salt dissolved in the organic solvent include LiClO. Four , LiBF 6 , LiPF 6 , LiCF Three SO Three , LiCF Three CO 2 , LiAsF 6 , LiSbF 6 , LiB Ten Cl Ten , Lower aliphatic carboxylic acid Li, LiAlCl Four , LiCl, LiBr, LiI, chloroborane Li, tetraphenylborate Li and the like can be used. Among them, a mixed solvent of ethylene carbonate or propylene carbonate and 1,2-dimethoxyethane, diethyl carbonate, methyl ethyl carbonate, etc., LiClO Four , LiBF 6 , LiPF 6 , LiCF Three SO Three A liquid electrolyte containing these is preferred. The amount of the liquid electrolyte injected into the battery is not particularly limited, but a necessary amount can be used depending on the amount of the active material and the size of the battery. Although the density | concentration of Li salt in this liquid electrolyte is not specifically limited, 0.2-3.0 mol per liter of liquid electrolyte is preferable.
[0050]
The gel polymer electrolyte corresponds to a gel obtained by gelling the liquid electrolyte with a gelling agent. Examples of the gelling agent include linear polymers such as polyethylene oxide and polyacrylonitrile or copolymers thereof, or polyfunctional monomers that are polymerized by irradiation with actinic rays such as ultraviolet rays and electron beams, such as pentaerythritol tetra A tetrafunctional or higher acrylate such as acrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hydroxypentaacrylate, dipentaerythritol hexaacrylate, a tetrafunctional or higher methacrylate similar to the above acrylate, and the like are used. However, even when the above monomers are used, the monomers themselves do not become gelling agents as they are, but a polymer obtained by polymerizing them acts as a gelling agent.
[0051]
When gelling a liquid electrolyte using a polyfunctional monomer as described above, if necessary, as a polymerization initiator, for example, benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides, acetophenones, Thioxanthones, anthraquinones and the like can be used, and alkylamines, amino esters and the like can also be used as a sensitizer for the polymerization initiator.
[0052]
The shape of the non-aqueous secondary battery of the present invention is any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, and a large type used for an electric vehicle. Also good.
[0053]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0054]
Example 1
Si powder having an average particle diameter of 1 μm, fibrous carbon (CF: carbon fiber) having an average fiber length of 5 μm and a diameter of 0.2 μm, and graphite having an average particle diameter of 2 μm, Si: CF: graphite = 60: These were mixed at a mixing ratio of 30:10 and granulated using a stirring type rolling granulator. As a result, composite particles having an average particle size of 10 μm were obtained. The true density (D2) of the composite particles is 2.20 g / cm. Three , Tap cap Density (D1) is 0.8 g / cm Three Met. Therefore, the void volume occupation ratio Vs of the composite particles was found to be 51% from the formula of Vs = (1-1.35 × D1 / D2) × 100.
[0055]
Next, 5 parts by mass of carbon powder as a negative electrode conductive material and 5 parts by mass of PVDF as a binder are mixed with 90 parts by mass of the obtained composite particles, and these are dispersed in dehydrated N-methylpyrrolidone to obtain a slurry. It was prepared, applied on a negative electrode current collector made of copper foil, dried, rolled, cut into a disk shape having a diameter of 16 mm, and dried in vacuum for 24 hours to obtain a negative electrode.
[0056]
About the composite particle | grains obtained above, the characteristic as an electrode material of the negative electrode for non-aqueous secondary batteries was tested with the following method.
[0057]
A coin-type model battery was fabricated by combining the negative electrode and the counter electrode metal Li. As the electrolytic solution, a solution obtained by dissolving 1 mol / L of lithium hexafluorophosphate in a mixed solvent of propylene carbonate and dimethyl carbonate (mixing volume ratio 1: 1) was used. After discharging until the potential of the negative electrode became 1.5 V on the basis of lithium metal, some model batteries were disassembled, and the volume V1 of the composite particles at the start of charging was determined by the method described later. Next, the remaining battery was charged with 1000 mAh of electricity per 1 g of composite particles of the negative electrode, and the volume V2 of the composite particles was determined from some of the batteries by a similar method. Further, the remaining battery was discharged until the potential of the negative electrode became 1.5 V with respect to the lithium metal, and the volume V3 of the composite particles was determined by the same method after the discharge was completed. From this result, the volume expansion rate during charging [(V2-V1) / V1 × 100] and the volume shrinkage rate during discharging [(V2-V3) / (V2-V1) × 100] were determined. As a result, the volume expansion rate during charging was 65%, and the volume shrinkage rate during discharging was 85%.
[0058]
The volume of the composite particles was determined by the following method. After the negative electrode to be measured was washed with dimethyl carbonate in an argon atmosphere, it was transported to a scanning electron microscope (SEM) in an airtight state without being exposed to the air, and the particle size of 100 arbitrary particles was determined from the SEM photograph. The volume was determined on the assumption that the particle shape was spherical. And 100 average particle | grain volume was made into the volume of the composite particle to obtain | require.
[0059]
On the other hand, the cycle characteristics of a coin-type model battery using the composite particles were examined. The charging / discharging method of the battery was performed as follows. Charging has a current density of 0.5 mA / cm 2 Then, charging was performed at a constant current, and after the charging voltage reached 120 mV, charging was performed at a constant voltage until the current density reached 1/10. Discharge current density 0.5mA / cm 2 The discharge end voltage was 1.5V.
[0060]
As a result, the discharge capacity at the second cycle was 1100 mAh per gram of the composite particles, and the capacity retention ratio at the 50th cycle [(discharge capacity at the 50th cycle / discharge capacity at the second cycle) × 100] was 70%. It was.
[0061]
(Example 2)
Si powder with an average particle diameter of 1 μm, CF with an average fiber length of 5 μm and a diameter of 0.2 μm, and graphite with an average particle diameter of 2 μm are mixed in a mass ratio of Si: CF: graphite = 60: 30: 10. These were granulated using a stirring type rolling granulator. As a result, composite particles having an average particle size of 10 μm were obtained. An SEM photograph of the composite particles thus produced is shown in FIG.
[0062]
Subsequently, the composite particles were coated with carbon at 1000 ° C. by CVD using benzene as a carbon source. The amount of coated carbon was determined from the change in mass of the composite particles before and after coating. The composition of the composite particles was Si: CF: graphite: CVD carbon = 56: 28: 9: 7 by mass ratio. The true density of the obtained composite particles is 2.20 g / cm. Three , Tap cap Density is 0.85 g / cm Three Met. Therefore, the void volume occupation ratio Vs of the composite particles was found to be 48% from the above-described calculation formula. Next, when a negative electrode was produced in the same manner as in Example 1, the volume expansion coefficient at the time of charging measured in the same manner as in Example 1 was 50%, and the volume shrinkage ratio at the time of discharging was 92%.
[0063]
In addition, as a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1000 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 85%.
[0064]
(Example 3)
Si particles having an average particle diameter of 2 μm, CF having an average fiber length of 5 μm and a diameter of 0.2 μm, and graphite having an average particle diameter of 2 μm are used in a mass ratio of Si: CF: graphite = 60: 30: 10. Except that, composite particles were produced in the same manner as in Example 2. The Si content of the obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 0.98 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 40%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 62%, and the volume shrinkage ratio at the time of discharge was 88%.
[0065]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 950 mAh per 1 g of composite particles, and the capacity retention at the 50th cycle was 75%.
[0066]
Example 4
Composite particles were produced in the same manner as in Example 2 except that the same raw materials as in Example 1 were used, and the mixing ratio was Si: CF: graphite = 40: 35: 25 by mass ratio. The Si content of the obtained composite particles is 37% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 0.81 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 50%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 50%, and the volume shrinkage ratio at the time of discharge was 92%.
[0067]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 700 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 95%.
[0068]
(Example 5)
Composite particles were produced in the same manner as in Example 2 except that the same raw materials as in Example 1 were used and the mixing ratio was Si: CF: graphite = 75: 15: 10 in terms of mass ratio. The Si content of the obtained composite particles is 70% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.25 g / cm. Three , Tap cap Density is 1.0 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 40%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 55%, and the volume shrinkage ratio at the time of discharge was 85%.
[0069]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1250 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 73%.
[0070]
(Example 6)
Si particles having an average particle diameter of 1 μm, CF having an average fiber length of 10 μm and a diameter of 0.1 μm, and graphite having an average particle diameter of 2 μm are used in a mass ratio of Si: CF: graphite = 60: 30: 10. Except that, composite particles were produced in the same manner as in Example 2. The Si content of the obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 0.73 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was found to be 55%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 45%, and the volume shrinkage ratio at the time of discharge was 92%.
[0071]
As a result of the cycle test performed in the same manner as in Example 1, the discharge capacity at the second cycle was 1050 mAh per gram of the composite particles, and the capacity retention of the electrode at the 50th cycle was 87%.
[0072]
(Example 7)
A composite as in Example 2 except that Si particles having an average particle diameter of 1 μm and CF having an average fiber length of 10 μm and a diameter of 0.2 μm were used in a mass ratio of Si: CF = 60: 40. Body particles were prepared. The resulting composite particles were coated with coal tar pitch and then fired at 1300 ° C. to coat the surfaces of the composite particles with hard carbon.
[0073]
The Si content of the finally obtained composite particles is 52% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.10 g / cm. Three , Tap cap Density is 0.86 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was found to be 45%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 35%, and the volume shrinkage ratio at the time of discharge was 95%.
[0074]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 950 mAh per gram of the composite particles, and the capacity retention of the electrode at the 50th cycle was 88%.
[0075]
(Example 8)
Except for adding polystyrene particles (PS) having an average particle diameter of 0.2 μm to the same raw material as in Example 1, and using the mixture ratio of Si: CF: graphite: PS = 30: 15: 5: 50 by mass ratio. In the same manner as in Example 2, composite particles were produced. Since the used PS burns or sublimates during the CVD process, new voids are formed in the particles. The Si content of the finally obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 0.73 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was found to be 55%. Moreover, the volume expansion rate at the time of charge measured in the same manner as in Example 1 was 48%, and the volume shrinkage rate at the time of discharge was 90%.
[0076]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 920 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 85%.
[0077]
Example 9
Si particles having an average particle diameter of 0.2 μm, CF having an average fiber length of 5 μm and a diameter of 0.2 μm, and Ketjen black (KB) having an average particle diameter of 0.05 μm, Si: CF: KB = 60 in mass ratio. : Composite particles were produced in the same manner as in Example 2 except that the compounding ratio was 30:10. The Si content of the obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.10 g / cm. Three , Tap cap Density is 0.68 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 56%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 50%, and the volume shrinkage ratio at the time of discharge was 95%.
[0078]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1000 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 87%.
[0079]
(Example 10)
Si powder having an average particle diameter of 0.2 μm, CF having an average fiber length of 5 μm and a diameter of 0.2 μm, KB having an average particle diameter of 0.05 μm, and polyvinylpyrrolidone (PVP) as a dispersant in terms of mass ratio. : CF: KB: PVP = 60: 30: 10: 4 The mixture was mixed in ethanol. This mixture was dispersed and mixed with a wet jet mill, and then the resulting slurry was granulated by spray drying. As a result, a granulated body having an average particle size of 10 μm was obtained. Subsequently, the composite particles were coated with carbon at 1000 ° C. by a CVD method using toluene as a carbon source. The amount of coated carbon was determined from the change in mass of the composite particles before and after coating. The composition of the composite particles was Si: CF: KB: CVD carbon = 50: 25: 8: 17 by mass ratio. The true density of the obtained composite particles is 2.10 g / cm. Three , Tap cap Density is 0.68 g / cm Three Met. Therefore, the void volume occupation ratio was determined to be 58%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 48%, and the volume shrinkage ratio at the time of discharge was 95%.
[0080]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1000 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 90%.
[0081]
(Example 11)
Si powder with an average particle size of 0.2 μm, KB with an average particle size of 0.05 μm, and PVP as a dispersant in ethanol at a mixing ratio of Si: KB: PVP = 70: 30: 3 by mass ratio. And mixed. This mixture was dispersed and mixed with a wet jet mill, and then the resulting slurry was granulated by spray drying. As a result, a granulated body having an average particle size of 3 μm was obtained. The obtained granulated body (Si / KB granulated body) and CF having an average fiber length of 5 μm and a diameter of 0.2 μm were mixed at a mass ratio of Si / KB granulated body: CF = 85: 15. The mixture was granulated by a tumbling flow method. As a result, composite particles having an average particle size of 15 μm were obtained. Subsequently, the composite particles were coated with carbon at 1000 ° C. by a CVD method using toluene as a carbon source. The amount of coated carbon was determined from the change in mass of the composite particles before and after coating. The composition of the composite particles was Si: CF: KB: CVD carbon = 50: 10: 25: 15 by mass ratio. The true density of the obtained composite particles is 2.10 g / cm. Three , Tap cap Density is 0.65 g / cm Three Met. Accordingly, the void volume occupation ratio was determined to be 60%. Moreover, the volume expansion rate at the time of charge measured in the same manner as in Example 1 was 47%, and the volume shrinkage rate at the time of discharge was 95%.
[0082]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1000 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 92%.
[0083]
(Example 12)
Si powder having an average particle diameter of 1.0 μm, KB having an average particle diameter of 0.05 μm, and PVP as a dispersing agent in a mass ratio of Si: KB: PVP = 70: 30: 3 in ethanol. Mixed. This mixture was dispersed and mixed with a wet jet mill, and then the resulting slurry was granulated by spray drying. As a result, a granulated body having an average particle size of 5 μm was obtained. Subsequently, the granulated body was coated with carbon at 1000 ° C. by a CVD method using toluene as a carbon source. The obtained composite particles were further coated with coal tar pitch, and then fired at 1300 ° C. to coat the surfaces of the composite particles with hard carbon.
[0084]
An SEM photograph of the composite particles thus prepared is shown in FIG. The Si content of the composite particles finally obtained is 47% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.10 g / cm. Three , Tap cap Density is 0.78 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 50%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 40%, and the volume shrinkage ratio at the time of discharge was 95%.
[0085]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 920 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 93%.
[0086]
(Example 13)
Si powder with an average particle size of 1.0 μm, KB with an average particle size of 0.05 μm, and PVP as a dispersant in ethanol at a mixing ratio of Si: KB: PVP = 60: 40: 4 in ethanol. Mixed. This mixture was dispersed and mixed with a wet jet mill, and then the resulting slurry was granulated by spray drying. As a result, a granulated body having an average particle size of 5 μm was obtained. Subsequently, the granulated body was fired at 1000 ° C. without a carbon source. The Si content of the finally obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.10 g / cm. Three , Tap cap Density is 0.75g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 52%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 55%, and the volume shrinkage ratio at the time of discharge was 85%.
[0087]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1050 mAh per gram of the composite particles, and the capacity retention of the electrode at the 50th cycle was 80%.
[0088]
(Example 14)
Si / Si with an average particle size of 1.0 μm 2 Ni composite powder, KB having an average particle diameter of 0.05 μm, and PVP as a dispersing agent were mixed in ethanol at a mixing ratio of Si: KB: PVP = 85: 15: 1 by mass ratio. This mixture was dispersed and mixed with a wet jet mill, and then the resulting slurry was granulated by spray drying. As a result, a granulated body having an average particle size of 7 μm was obtained. Subsequently, the granulated body was coated with carbon at 850 ° C. by a CVD method using toluene as a carbon source. The Si content of the finally obtained composite particles is 40% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 3.10 g / cm 3. Three , Tap cap Density is 1.15 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 50%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 40%, and the volume shrinkage ratio at the time of discharge was 93%.
[0089]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 800 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 95%.
[0090]
(Comparative Example 1)
Composite particles were produced in the same manner as in Example 1 except that Si powder having an average particle diameter of 1 μm and graphite having an average particle diameter of 2 μm were used in a mass ratio of Si: graphite = 60: 40. . The Si content of the obtained composite particles is 56% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 1.14 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 30%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 100%, and the volume shrinkage ratio at the time of discharge was 77%.
[0091]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 840 mAh per gram of the composite particles, but the capacity retention at the 50th cycle was 40%, and the capacity was significantly reduced. Admitted.
[0092]
(Comparative Example 2)
Composite particles were produced in the same manner as in Example 1 except that Si powder having an average particle diameter of 1 μm and graphite having an average particle diameter of 2 μm were used in a mass ratio of Si: graphite = 90: 10. The Si content of the obtained composite particles is 84% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 1.10 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was determined to be 32%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 110%, and the volume shrinkage ratio at the time of discharge was 70%.
[0093]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 1400 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 10%.
[0094]
(Comparative Example 3)
Composite particles were produced in the same manner as in Example 1 except that Si powder having an average particle diameter of 1 μm and graphite having an average particle diameter of 2 μm were used in a mass ratio of Si: graphite = 25: 75. . The Si content of the obtained composite particles is 20% by mass with respect to the total mass of the composite particles, and the true density of the composite particles is 2.20 g / cm. Three , Tap cap Density is 1.17 g / cm Three Met. Therefore, the void volume occupation ratio of the composite particles was found to be 28%. Moreover, the volume expansion rate at the time of charge measured in the same manner as in Example 1 was 75%, and the volume shrinkage rate at the time of discharge was found to be 83%.
[0095]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 500 mAh per gram of the composite particles, and the capacity retention at the 50th cycle was 50%.
[0096]
(Reference Example 1)
Tetramethoxysilane (TMOS) was dissolved in a solution of coal tar pitch in tetrahydrofuran (THF). To this solution, graphite having an average particle size of 5 μm was added and stirred and mixed while refluxing. Each compounding ratio is THF: coal tar pitch: TMOS: graphite = 10: 1: 1: 3 by mass ratio. The THF was then removed by vacuum drying. The obtained powder was decomposed and carbonized with a coal tar pitch and TMOS at 1000 ° C. in a nitrogen stream to obtain composite particles composed of graphite containing silicon and amorphous carbon. The Si content of the composite particles was 6% by mass with respect to the total mass of the composite particles, and the void volume occupation ratio of the composite particles was 12%. Moreover, the volume expansion coefficient at the time of charge measured in the same manner as in Example 1 was 30%, and the volume shrinkage ratio at the time of discharge was 80%.
[0097]
As a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 400 mAh per 1 g of composite particles, and the capacity retention at the 50th cycle was 70%.
[0098]
(Reference Example 2)
Si particles having an average particle diameter of 2 μm and CF having an average fiber length of 5 μm and a diameter of 0.2 μm were mixed by a mortar at a mass ratio of Si: CF = 60: 40 to obtain an electrode material. In this electrode material, Si and CF were merely mixed, and no composite was formed. Using this electrode material, a negative electrode was produced in the same manner as in Example 1.
[0099]
In addition, as a result of performing a cycle test in the same manner as in Example 1, the discharge capacity at the second cycle was 650 mAh per 1 g of composite particles, and the discharge capacity at the 50th cycle was almost 0 mAh / g.
[0100]
The above results are shown in Table 1.
[0101]
[Table 1]
[0102]
As is clear from Table 1, it can be seen that the composite particles of Examples 1 to 14 have little particle expansion during charging and can be reversibly contracted during discharging. In addition, it showed a large discharge capacity, and even when the charge / discharge cycle was repeated, the capacity was not lowered and the cycle characteristics were excellent. On the other hand, Comparative Examples 1 to 3 having a small void volume occupancy have large expansion during charging, are inferior in reversibility, and have a significantly low capacity retention after charge / discharge cycles.
[0103]
Reference Example 1 is an example referring to Patent Document 2, and Reference Example 2 is an example in which composite particles are not formed.
[0104]
【The invention's effect】
As described above, the present invention can constitute a non-aqueous secondary battery with high capacity and excellent cycle characteristics by suppressing the expansion of the electrode material.
[Brief description of the drawings]
FIG. 1 is an SEM photograph of composite particles in Example 2 of the present invention.
FIG. 2 is a SEM photograph of composite particles in Example 12 of the present invention.
FIG. 3 is a schematic cross-sectional view of a composite particle coated with a material containing carbon at the time of discharging and charging.
Claims (14)
前記リチウムと合金化可能な元素を含む材料の割合が、前記複合体粒子の全質量に対して30質量%以上80質量%以下であり、
前記複合体粒子の形状が球形で、内部に空隙を有し、
前記複合体粒子のJIS R1628に基づき測定したタップかさ密度をD1(g/cm3)、前記複合体粒子の真密度をD2(g/cm3)、前記複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下であることを特徴とする電極材料。An electrode material composed of composite particles including a material containing an element capable of alloying with lithium and a conductive material,
The proportion of the material containing an element that can be alloyed with lithium is 30% by mass to 80% by mass with respect to the total mass of the composite particles,
The shape of the composite particles is spherical and has voids inside,
The bulk density of the composite particles measured according to JIS R1628 is D1 (g / cm 3 ), the true density of the composite particles is D2 (g / cm 3 ), and the void volume occupation rate (% ) Vs = (1-1.35 × D1 / D2) × 100, Vs is 35% or more and 70% or less.
前記リチウムと合金化可能な元素を含む材料は、平均粒径が2μm以下の粒子であり、
前記リチウムと合金化可能な元素を含む材料の割合が、前記複合体粒子の全質量に対して30質量%以上80質量%以下であり、
前記複合体粒子の形状が球形で、内部に空隙を有し、
前記複合体粒子のJIS R1628に基づき測定したタップかさ密度をD1(g/cm3)、前記複合体粒子の真密度をD2(g/cm3)、前記複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下であることを特徴とする電極材料。An electrode material composed of composite particles including a material containing an element capable of alloying with lithium and a conductive material,
The material containing an element that can be alloyed with lithium is a particle having an average particle size of 2 μm or less,
The proportion of the material containing an element that can be alloyed with lithium is 30% by mass to 80% by mass with respect to the total mass of the composite particles,
The shape of the composite particles is spherical and has voids inside,
The bulk density of the composite particles measured according to JIS R1628 is D1 (g / cm 3 ), the true density of the composite particles is D2 (g / cm 3 ), and the void volume occupation rate (% ) Vs = (1-1.35 × D1 / D2) × 100, Vs is 35% or more and 70% or less.
前記リチウムと合金化可能な元素を含む材料の割合が、前記複合体粒子の全質量に対して30質量%以上80質量%以下であり、
前記導電性材料が、繊維状またはコイル状の炭素材料および繊維状またはコイル状の金属材料から選ばれる少なくとも一つであり、
前記複合体粒子の形状が球形で、内部に空隙を有し、
前記複合体粒子のJIS R1628に基づき測定したタップかさ密度をD1(g/cm3)、前記複合体粒子の真密度をD2(g/cm3)、前記複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下であることを特徴とする電極材料。An electrode material composed of composite particles including a material containing an element capable of alloying with lithium and a conductive material,
The proportion of the material containing an element that can be alloyed with lithium is 30% by mass to 80% by mass with respect to the total mass of the composite particles,
The conductive material is at least one selected from a fibrous or coiled carbon material and a fibrous or coiled metal material;
The shape of the composite particles is spherical and has voids inside,
The bulk density of the composite particles measured according to JIS R1628 is D1 (g / cm 3 ), the true density of the composite particles is D2 (g / cm 3 ), and the void volume occupation rate (% ) Vs = (1-1.35 × D1 / D2) × 100, Vs is 35% or more and 70% or less.
前記リチウムと合金化可能な元素を含む材料の割合が、前記複合体粒子の全質量に対して30質量%以上80質量%以下であり、
前記複合体粒子が、炭素の被覆層を有し、
前記複合体粒子の形状が球形で、内部に空隙を有し、
前記複合体粒子のJIS R1628に基づき測定したタップかさ密度をD1(g/cm3)、前記複合体粒子の真密度をD2(g/cm3)、前記複合体粒子の空隙体積占有率(%)をVs=(1−1.35×D1/D2)×100とした場合、Vsが35%以上70%以下であることを特徴とする電極材料。An electrode material composed of composite particles including a material containing an element capable of alloying with lithium and a conductive material,
The proportion of the material containing an element that can be alloyed with lithium is 30% by mass to 80% by mass with respect to the total mass of the composite particles,
The composite particles have a coating layer of carbon;
The shape of the composite particles is spherical and has voids inside,
The bulk density of the composite particles measured according to JIS R1628 is D1 (g / cm 3 ), the true density of the composite particles is D2 (g / cm 3 ), and the void volume occupation rate (% ) Vs = (1-1.35 × D1 / D2) × 100, Vs is 35% or more and 70% or less.
前記リチウムと合金化可能な元素を含む材料と、前記導電性材料と、樹脂とを混合して造粒することにより複合体粒子を形成する工程と、
前記複合体粒子を加熱して前記樹脂を燃焼または昇華させて除去することにより、前記複合体粒子内に空隙を形成する工程とを含む電極材料の製造方法。It is a manufacturing method of the electrode material in any one of Claims 1-7,
Forming composite particles by mixing and granulating a material containing an element that can be alloyed with lithium, the conductive material, and a resin;
Forming the voids in the composite particles by heating the composite particles to burn or sublimate and remove the resin.
前記リチウムと合金化可能な元素を含む材料と、前記導電性材料とを溶媒中で分散させて混合物とし、前記混合物を噴霧して乾燥するスプレードライ法により造粒することにより複合体粒子を形成する工程を含む電極材料の製造方法。It is a manufacturing method of the electrode material in any one of Claims 1-7,
A composite particle is formed by granulating by a spray drying method in which the material containing an element that can be alloyed with lithium and the conductive material are dispersed in a solvent to form a mixture, and the mixture is sprayed and dried. The manufacturing method of the electrode material including the process to do.
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