JP4133116B2 - Negative electrode active material for lithium ion secondary battery, method for producing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents
Negative electrode active material for lithium ion secondary battery, method for producing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery Download PDFInfo
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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・放出可能なリチウムイオン二次電池用負極活物質、その製造法、該活物質を有する負極及びそれを用いたリチウムイオン二次電池に関し、更に詳しくは初期充放電効率、放電容量が大きく、サイクル特性に優れ、且つ工業生産性に優れたリチウムイオン二次電池用負極活物質、その製造法、電極及びそれを用いたリチウムイオン二次電池に関する。
【０００２】
【従来の技術】
リチウムイオン二次電池は、理論エネルギー密度が他の二次電池と比較して格段に高いため、携帯電話・電子機器に用いられる高性能電池のみならず、最近では電気自動車の新型電池として強い関心が寄せられている。現在、実用化されているリチウムイオン二次電池の負極活物質としてリチウムイオンをインターカレートさせた黒鉛系炭素材料等が使用されている。しかしながら黒鉛系炭素材料は、炭素6原子に対してリチウム1原子をインターカレートさせるのが限界であり、炭素材料の理論的な電気容量は372mAh/gが限界である。従って、今後の二次電池に必要な高容量特性を充足するために新たな負極材料の開発が望まれている。
このような状況のもと、Si、Sn等は1原子あたり最大4.4個のLiを吸蔵できるため非常に魅力的な材料である。しかし、Si及びSnは、Liの吸蔵時、3倍以上の非常に大きな体積膨張を引き起こす。その結果、微粉化が生じ、電極からの脱離等が引き起こされ、十分な導通が保てなくなり、数サイクル程度で初期放電容量の1/5以下まで容量が低下してしまう。
近年、サイクル劣化を抑制する電極材料としてSnM(M=O,O2)等が提案され、精力的に研究開発されている。これらSnMは、Liに対して活性であるため、初回充電時にSnM+xLi→Sn+LixMという反応により実際に充放電反応に寄与するSnとLi2O相を生成し、Li2O相がSnの体積変化を抑制する緩衝相となり、金属Snと比較してサイクル特性が向上すると言われている。しかし、これらSnMの負極は、第1回目のLi挿入時に生ずる不可逆的なLi2O相の生成のため、1回目と2回目以降のサイクルで大きく容量が異なる。この不可逆容量の存在が、その実用化への大きな障害の1つとなっている。
【０００３】
【発明が解決しようとする課題】
本発明の目的は、初期充放電効率に優れ、充放電に伴うサイクル劣化を抑制し、黒鉛系炭素材料の理論容量である372mAh/gを大きく超える放電容量を実現し、SnM(M=O,O2)と比較して初期充放電効率及びサイクル劣化ともに優れたリチウムイオン二次電池用負極、該負極に用いる活物質、その製造法及び該負極を備えたリチウムイオン二次電池を提供することにある。
【０００４】
【課題を解決するための手段】
発明者らは、上記課題を解決するために、金属Snの体積変化を抑制する緩衝相として、Liに対して不活性な物質を中心に検討を進めてきた結果、希土類酸化物がサイクル寿命及び初期充放電効率を向上しうることを知見し、本発明を完成するに至った。希土類金属酸化物と金属Snとの存在によりサイクル寿命及び初期充放電効率の向上が見られる要因の1つとして、これらがナノスケールで微分散させた構造を有していることが推測される。
【０００５】
すなわち、本発明によれば、平均粒径0.01〜75μmの粉末であって、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物と、金属Snとを含み、表面のX線回折測定により、前記希土類金属の酸化物ピークと前記金属Snピークとが観察され、希土類-Snの金属間化合物ピークが観察されず、且つ酸素含有割合が0.7〜6質量％であり、リチウムの吸収放出能を有することを特徴とするリチウムイオン二次電池用負極活物質が提供される。
また本発明によれば、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物と、金属Snとを含む粉末であり、R-Snで示される金属間化合物及び／又はR-Sn-(M1)で示される金属間化合物(Rは希土類元素、M1は、Li、B、C、N、Mg、Al、Si、P、S、Ca、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Zr、Nb、Mo、In、Sb、Pb、Hf、Ag、Ta及びBiからなる群より選択される1種又は2種以上を示す)を粉末内部に含み、且つ酸素含有割合が0.7〜6質量％であり、リチウムの吸収放出能を有することを特徴とするリチウムイオン二次電池用負極活物質が提供される。
更にまた本発明によれば、希土類元素及びSnを含む金属間化合物を有する合金を、酸素濃度3at％以上の雰囲気下において5〜1000℃で反応させる工程(a)を含むことを特徴とする前記負極活物質の製造法が提供される。
また本発明によれば、負極活物質を含む負極材料を集電体に塗布・乾燥して得たリチウムイオン二次電池用負極であって、該負極表面をX線回折法により測定することによって、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物ピークと、金属Snピークと、集電体金属のピークとが観察され、希土類-Snの金属間化合物ピークが観察されず、且つ負極活物質の酸素含有割合が0.7〜6質量％であることを特徴とするリチウムイオン二次電池用負極が提供される。
更に本発明によれば、前記負極活物質を含む負極材料と集電体とを備えたリチウムイオン二次電池用負極が提供される。
更に本発明によれば、前記負極を備えたことを特徴とするリチウムイオン二次電池が提供される。
【０００６】
【発明の実施の形態】
以下、本発明を更に詳細に説明する。
本発明の負極活物質は、リチウムイオン二次電池負極に利用した際に従来の炭素材やSnM(M=O,O2)と比較し、初期充放電効率、サイクル特性に優れた特性を示すことが可能であり、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物と、金属Snとを含み、且つ酸素を特定含有割合で含む。
【０００７】
本発明の負極活物質は、好ましくは、表面のX線回折測定により、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物ピークと、金属Snピークとが観察され、希土類-Snの金属間化合物ピークが観察されない。
【０００８】
本発明の負極活物質において、表面層に観察される金属Snは、Liと容易に合金化し、1原子あたり最大4.4個のLiと合金化する。一方、表面層に観察される希土類酸化物は、Snの大きな体積膨張(3倍以上)を抑制する緩衝相になると共に、Liに対して不活性な物質であるため、SnM(M=O,O2)と比較して、初回充電時の不可逆容量の原因とされるLi2O相の生成が抑制され、初期充放電効率の低下を招かない。希土類酸化物の中でもCeO2は最も安定な部類に属し、高い初期充放電効率を達成できるため、本発明の負極活物質において表面層に観察される希土類酸化物は、CeO2単独、もしくはCeO2と90mol％未満、特に70mol％未満、更に50mol％未満のCeO2以外の希土類酸化物とから構成されることが好ましい。また、表面層にSnM(M=O,O2)のピークが観察されないことが好ましい。
本発明の負極活物質においては、表面層に希土類-Snの金属間化合物ピークが観察されないが、内部においては、希土類-Sn金属間化合物を有することが好ましい。金属間化合物相は、嵩密度が希土類酸化物より大きく、活物質中に適度に存在したほうが体積あたりのエネルギー密度を向上させる。また、希土類-Sn金属間化合物は、Liの充放電に伴う合金相の体積膨張により微粉化し易いため、緩衝相としての希土類酸化物が表面層に存在し、該希土類-Sn金属間化合物は内部に存在することが望ましい。これにより、集電体からの脱離が抑制され、高いサイクル寿命が達成できる。従って、本発明の負極活物質において、希土類-Sn金属間化合物相の存在割合は、2〜99質量％の範囲が好ましく、更には10〜80質量％の範囲が好ましい。
【０００９】
上記金属間化合物相は、R-Snで示される金属間化合物及び／又はR-Sn-(M1)で示される金属間化合物が好ましい。ここで、Rは希土類元素、M1は、Li、B、C、N、Mg、Al、Si、P、S、Ca、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Zr、Nb、Mo、In、Sb、Pb、Hf、Ag、Ta及びBiからなる群より選択される1種又は2種以上を示す。更に、R-SnXで示される金属間化合物及び／又はR-SnX-(M1)yで示される金属間化合物が特に好ましい。ここで、Xは2〜3の有理数、yは、0＜y≦10の有理数を示す。
RSn3相は、希土類-Sn系金属間化合物の中で最も多くのSnを含有している相である。換言すれば、最も充放電容量が大きい相であり、充分な放電容量が得られる。従って、RSn3相の存在割合は、活物質中の金属間化合物中で50質量％以上が好ましく、更には80質量％以上が好ましい。
【００１０】
本発明の負極活物質においては、Li、B、C、Mg、Al、Si、P、S、Ca、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Ge、Zr、Nb、Mo、Ｗ、Ag、In、Sb、Pb、Hf、Ta及びBiからなる群より選択される1種又は2種以上を含んでいても良い。B、C、P又はSは、格子間に侵入し、Li、Mg、Al、Si、Ca、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn、Ga、Zr、Nb、Mo、Ｗ、In、Sb、Pb、Hf、Ag、Bi又はTaは、原子半径がCe、もしくはSnより小さいため、格子にひずみを与え、格子欠陥を発生させる。この欠陥、もしくはひずみ場によりLiの充放電に伴う体積膨張・収縮を緩和し、サイクル寿命の向上が期待される。
上記置換元素は、元素単体でも体積変化を緩和するし、希土類元素、Snとの金属間化合物として存在しても良い。また、Sn、希土類元素中に固溶していても良く、酸化物であっても良い。
【００１１】
本発明の負極活物質においては、酸素を特定割合含有する。本発明の負極活物質において酸素は、主として希土類酸化物として含有され、大部分が粒子表面に存在する。これら酸化物皮膜は、Liの充放電に伴う体積膨張を緩和する緩衝相としての役割がある。従って、これら酸化物皮膜の存在量が少なすぎるとサイクル劣化が激しくなり、また、多すぎるとリチウムイオンの合金中への拡散を阻害する。従って、本発明の負極活物質中の酸素含有割合は、0.7〜6質量％、好ましくは0.8〜4質量％ある。酸素含有割合が0.7質量％未満、若しくは6質量％を超える場合には、リチウムイオン二次電池に用いた際に、初期放電容量が低下し、且つサイクル特性も低下するので好ましくない。
【００１２】
本発明の負極活物質は、好ましくは平均粒径0.01〜75μmの粉末が好ましく、サイクル劣化を抑制するために38μm以下、更には15μm以下が望ましい。平均粒径が0.01μm未満では著しく取り扱いが困難となるため好ましくない。
【００１３】
本発明の負極活物質は、希土類元素及びSnを含む金属間化合物を有する合金を、酸素濃度3at％以上の雰囲気下において5〜1000℃で反応させて得た、希土類酸化物及び金属Snを含み、且つ酸素含有割合が0.7〜6重量％、平均粒径が0.01〜75μmであり、リチウムの吸収放出能を有する粉末であっても良い。この点については、後述する本発明の負極活物質の製造法において更に詳細に説明する。また、酸素含有割合及び平均粒径については前述の好ましい範囲が同様に挙げられ、任意成分についても前述のものが好ましく挙げられる。
【００１４】
本発明の負極活物質の製造法は、前記活物質が得られれば特に限定されないが、以下の本発明の製造法が好ましい。
本発明の製造法は、希土類元素及びSnを含む金属間化合物を有する合金(以下、原料合金という)を、特定酸素濃度雰囲気下において、特定温度で反応させる工程(A)を含む。
工程(A)に用いる原料合金は、例えば、原料となる金属を混合した後、加熱溶解し、金型等に鋳込んで固化させる等の公知の方法で得ることができる。原料合金の原料は、所望の組成を構成する金属単体の混合物でも良いし、予め合金化した母合金を用いても良い。本発明の製造法においては、できるだけ均一な組織を有する金属間化合物を用いる方が好ましいため、加熱溶解には撹拌効果の大きな溶解法が好ましく、特に高周波溶解が好ましい。加熱溶解における雰囲気は、アルゴンガス等の不活性ガス雰囲気が好ましい。
溶湯の冷却は、例えば、金型冷却法、アトマイズ法、ロール冷却法、回転電極法等の公知の冷却法を用いることができる。溶湯を冷却する際の雰囲気は、不活性ガス雰囲気が好ましい。また、R-Snの金属間化合物を調製した後、上述の式R-Snx-(M1)yで示される組成中の(M1)、例えば、金属Li等をR-Snの金属間化合物とメカニカルアロイ法により合金化し、原料合金を調製することもできる。
【００１５】
前記工程(A)に用いる原料合金は、前記冷却等により得ることができるが、組織を均質化し結晶の大きさをそろえる目的で更に熱処理を施しても良い。該熱処理は、例えば、0.07〜10MPaの不活性ガス雰囲気下で行なうことができる。
熱処理の条件は、100〜1150℃の温度範囲で100時間以下保持する条件が好ましい。熱処理温度が100℃未満では、各合金相、単体元素の拡散が極めて起こり難く、熱処理の効果が得られない。一方、1150℃を超えると合金自体が再溶融するため、冷却固化した合金同士の溶着等が生じ、所望の目的が達成できない。熱処理時間は、熱処理する合金の組織、量、形状、使用する熱処理装置等によって上記範囲から適時選択できるが、好ましくは30分〜48時間である。熱処理時間が100時間を超えると経済性を損なう。
【００１６】
工程(A)においては、前記原料合金を、特定の酸素濃度雰囲気下に5〜1000℃の温度で反応させる。酸素との反応は、酸素ガスを含む混合ガスと反応させる方法や、処理温度域において前記原料合金を酸化する化合物と混合して処理する方法等が挙げられる。混合ガスで処理する際の混合ガス中の酸素濃度は3at％以上が望ましく、15at％以上が更に好ましく、上限濃度は限定されない。この際、酸化反応を円滑に行う目的で、原料合金を予め粉砕しておいてもよい。酸化反応は電池を作製するまでの間ならいつ行なっても良いが、結着材等と混合後、集電体に塗布した後に酸化反応を行なうことは合金粒子表面に緻密な希土類酸化物層を形成するためには特に有効である。
【００１７】
工程(A)により、合金中の金属間化合物の表面に希土類酸化物層が形成され、Liの吸放出に伴う体積膨張を緩和する優れた緩衝相となる。ここで、希土類酸化物層の厚さは0.001〜10μmが好ましく、0.01〜4μmが更に好ましい。また工程(A)により、合金中の金属間化合物の表面に金属Snも生成される。該金属Snも希土類酸化物の緩衝作用、相互作用により微粉化・電極からの脱離が抑制される。
工程(A)においては、合金中の金属間化合物の表面にSnの酸化物が生成される場合がある。Sn酸化物はLiに対して活性であり、Li2Oを容易に生成し、初期不可逆容量の原因となるが、一部、希土類酸化物中に存在することによりLiの充放電を促進する。従って、その存在割合は負極活物質中の全酸化物の10質量％以下が望ましい。
本発明の製造法では、前記工程(A)の他に、本発明の所望の効果を損なわない範囲で他の工程を含んでいても良い。
【００１８】
本発明のリチウム二次電池用負極は、前記本発明の負極活物質を含む負極材料と集電体とを備えたものである。
例えば、前記負極活物質を含む負極材料を集電体に塗布・乾燥して得たリチウムイオン二次電池用負極であって、該負極表面をX線回折法により測定することによって、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物ピークと、金属Snピークと、集電体金属のピークとが観察され、希土類-Snの金属間化合物ピークが観察されず、且つ負極活物質の酸素含有割合が0.7〜6質量％であることを特徴とする。
前記負極表面のX線回折法により、更に集電体金属−Snの金属間化合物ピークが観察されても良い。
【００１９】
本発明の負極は、前記本発明の負極活物質を用いて、公知の方法等により製造できる。例えば、本発明の負極活物質粉末に、適当なバインダを混合し、必要に応じて導電性向上のために適当な導電粉を混合する。この混合物に、バインダが溶解する溶媒を加え、必要であればホモジナイザー等で充分に撹拌してスラリー状にする。該スラリーを圧延銅箔、電解銅箔等の電極基板(集電体)に、ドクターブレード等を用いて塗布し、乾燥した後、ロール圧延等で電極活物質を圧密化させることで負極を製造することができる。
【００２０】
前記バインダとしては、例えば、PVDF(ポリフッ化ビニリデン)、PMMA(ポリメチルメタクリレート)、PTFE(ポリテトラフルオロエチレン)等の非水溶性の樹脂、ならびにCMC(カルボキシメチルセルロース)、PVA(ポリビニルアルコール)等の水溶性樹脂が挙げられる。
前記溶媒としては、例えば、NMP(N-メチルピロリドン)、DMF(ジメチルホルムアミド)等の有機溶媒、又は水が挙げられる。
前記導電粉としては、例えば、アセチレンブラック、ケッチェンブラック、黒鉛等の炭素材や、Ni等の金属のいずれも使用できるが、好ましいのは炭素材である。炭素材は、その層間にLiを吸蔵できるので、導電性に加えて負極の充放電容量にも寄与できる。
【００２１】
本発明の負極においては、電池を作製後に生じるLiの不可逆容量の存在を補償するために、予め負極の負極活物質に添加元素Liを適当量含有させることができる。このような添加元素Liを含有させるには、金属Li、LiH(水素化リチウム)、Li3N(窒化リチウム)等のリチウム供給源と共存させて電極を作製しても、その初回充放電時の不可逆分のLiは補償できる。しかし、これら金属Li、LiH、Li3Nの負極活物質中での存在量が多くなりすぎると取り扱いが困難となる。また、金属Li、LiH、LiNは密度が小さいため、負極活物質中の存在割合が多くなりすぎると電池のエネルギー密度を低下させてしまう。以上より、金属Li、LiH、LiNの存在量は、合金組成の初期充放電効率から考慮して、適宜選択することができ0〜50質量％が好ましく、更に0〜20質量％が好ましい。
【００２２】
本発明のリチウムイオン二次電池は、前記本発明の負極を備えておれば良く、基本構造として、負極、正極、セパレータ、非水系の電解質を備えている。電解質としてポリマー電解質を用いても良い。負極以外の電池構成材料は公知のものを適当に組み合わせて使用することができる。
電池の形状は特に制限されず、例えば、円筒形、角型、コイン型、シール型等が挙げられる。
【００２３】
【実施例】
以下、本発明を実施例及び比較例により更に詳細に説明するが本発明はこれらに限定されない。
実施例 1 〜 4 及び比較例 1 〜 4
＜リチウムイオン二次電池負極用合金の作製＞
本実施例及び比較例において合金作成に使用した原材料は99.5％以上の材料を使用した。Mmは質量比でLa：Ce：Nd：Pr：Smが28：51：16：4：1の(株)三徳製の希土類合金を使用した。
実施例1〜4及び比較例1においては、表1に示す原料組成を構成する金属混合物を溶融した後、得られた溶湯を、銅鋳型を用い金型鋳造法で合金サンプル(希土類元素−Sn金属間化合物)を得た。実施例3及び4においては、得られた合金サンプルをアルゴンガス雰囲気下において表1に示す適当な条件で保持する熱処理を施した。次いで、各サンプルをアルゴンガス雰囲気下において機械的粉砕法により粉体化を行い、ふるいを用いて25μm以下に分級した。
更に、実施例1〜4のサンプル粉体については、表1に示す任意の酸素ガスを含む混合ガス中で任意の熱処理温度・熱処理時間で熱処理することにより、酸化処理を行った。
一方、比較例2〜4については、ふるいを用いて25μm以下に分級した、表1に示す原料組成の粉体を用いた。尚、比較例2では、CeO2：Sn＝1：3（質量比）の混合物を用いた。
次いで、以下の方法により各粉体を用いてリチウムイオン二次電池用負極を作製し、充放電容量、容量維持率及び充放電効率を評価した。
【００２４】
＜リチウムイオン二次電池用負極の作製及び充放電試験方法＞
上記で調製した各粉末と、導電助剤のケッチェンブラックと、結着剤のポリフッ化ビニリデン(PVDF)とを質量比で85：5：10に混合し、適量のN-メチルピロリドン(NMP)を加えて混錬した後、18μmの厚さを有する電解銅箔に塗布し、60℃の乾燥機において仮乾燥した後、ローラープレスにより圧密化した。それを直径1.0cmの大きさに打ち抜き、130℃で真空乾燥することにより試験電極を作製した。得られた試験電極の表面の構成相を粉末X線回折(XRD)により測定した。この結果を表1の表層の主な析出相の欄に示す。また、実施例1、比較例1及び2のX線回折の結果を示すグラフを図1に示す。
また、試験電極表面層の活物質の酸素含有割合をにより測定した。結果を表1に示す。
次いで、得られた試験電極上に、セパレータにポリプロピレン多孔質フィルムを、対極に金属リチウムを用い電解液にエチレンカーボネート(EC)：ジメチルカーボネート(DMC)=1：2(体積比)の混合溶媒にLiPF6を1mol濃度で溶解させた溶液を用いて2極式セルを作製した。このセルを温度25℃において電流密度が0.2mA/cm2で0〜1.0Vvs.Li/Li+の電位範囲で定電流充放電試験を行った。尚、評価セルの組み立てと充放電試験は、アルゴンガス雰囲気下のグローブボックス内で行った。結果を表1に示す。
表1に示す容量維持率とは、最大放電容量を50サイクル目にどれだけ維持したかを示す指標を容量維持率(S)とし、以下の式により算出して評価した。
(S)=50サイクル目の放電容量/最大放電容量×100(％)
表1に示す初期充放電効率とは、初回充電容量に対して初回放電容量の割合を示す指標を初期充放電効率(Z)とし、以下の式により算出して評価した。
(Z)=初回放電容量/初回充電容量×100(％)
【００２５】
【表１】
表1より、実施例1〜4は活物質の表層に希土類酸化物層が存在し、50サイクル時の容量維持率が高い。一方、比較例1は実施例1及び3と原料組成が同一でありながら表層に希土類酸化物が存在しない。その結果、50サイクル時の容量維持率が極端に低い。比較例2はCeO2粉末、金属Sn粉末を所定量、混合した活物質であるが、初期放電容量も小さく、サイクル特性も良好とはいえない。これは実施例1〜4と比較して、CeO2、Snがナノスケールで微分散していないこと、並びに酸素含有割合が高いこと等が原因と推測される。また、比較例3及び4はSn系酸化物であり、これらSn系酸化物はLiに対して活性であるため初回の充電でLi2Oが生成され、初期充放電効率が低いことが判る。
【００２７】
実施例 5 〜 8 及び比較例 5
表2に示す原料組成及び各条件とした以外は、実施例1〜4及び比較例1〜4と同様に、リチウムイオン二次電池負極用合金を作製し、更に、リチウムイオン二次電池用負極の作製及び充放電試験を行った。但し、実施例8においては、原料合金を、CeSn3の金属間化合物を調製した後、得られた金属間化合物と金属Liとをメカニカルアロイ法により合金化し、原料組成CeSn3Li5の原料合金を調製した後、負極の作製及び各試験を行なった。結果を表2に示す。
【００２８】
【表２】
表2において、実施例5〜8では放電特性を向上させる元素であるB、Si、Liを添加したときの放電特性が良好であることが判るが、比較例4では添加元素としてAuを用い、且つ活物質中の酸素含有割合を本発明の範囲外としたために放電特性が実施例5〜8の結果より劣ることが判る。
【００３０】
【発明の効果】
本発明のリチウムイオン二次電池用負極は、初期充放電効率に優れ、充放電に伴うサイクル劣化が抑制される。また、本発明の負極活物質は、このような負極の製造に有用である。従って、本発明の負極活物質及び負極は、SnO2、SnO等の酸化物系負極より、初期放電効率、サイクル寿命に優れ、かつ、現在、実用化されている炭素材料負極を用いたリチウムイオン二次電池よりも高容量化・コンパクト化が可能となり、産業上の利用価値が極めて高い。
【図面の簡単な説明】
【図１】実施例1、比較例1及び2において調製した試験電極の表面の構成相を粉末X線回折(XRD)により測定した結果を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode active material for lithium ion secondary batteries capable of inserting and extracting lithium, a method for producing the same, a negative electrode having the active material, and a lithium ion secondary battery using the negative electrode active material. The present invention relates to a negative electrode active material for a lithium ion secondary battery having a large discharge capacity, excellent cycle characteristics, and excellent industrial productivity, a production method thereof, an electrode, and a lithium ion secondary battery using the same.
[0002]
[Prior art]
Lithium ion secondary batteries have a much higher theoretical energy density than other secondary batteries, so not only high-performance batteries used in mobile phones and electronic devices, but recently as a new battery for electric vehicles. Has been sent. At present, a graphite-based carbon material in which lithium ions are intercalated is used as a negative electrode active material of a lithium ion secondary battery in practical use. However, graphite-based carbon materials are limited to intercalate 1 lithium atom to 6 carbon atoms, and the theoretical electric capacity of carbon material is limited to 372 mAh / g. Therefore, development of a new negative electrode material is desired in order to satisfy the high capacity characteristics required for future secondary batteries.
Under such circumstances, Si, Sn, etc. are very attractive materials because they can occlude up to 4.4 Li atoms per atom. However, Si and Sn cause a very large volume expansion of 3 times or more when Li is occluded. As a result, pulverization occurs, causing detachment from the electrode, etc., and sufficient continuity cannot be maintained, and the capacity decreases to 1/5 or less of the initial discharge capacity in several cycles.
In recent years, SnM (M = O, O 2 ) and the like have been proposed as electrode materials for suppressing cycle deterioration, and have been vigorously researched and developed. Since these SnMs are active against Li, Sn and Li 2 O phases that actually contribute to the charge / discharge reaction are generated by the reaction of SnM + xLi → Sn + LixM during the initial charge, and the Li 2 O phase is Sn It is said that it becomes a buffer phase that suppresses the volume change of the metal, and the cycle characteristics are improved as compared with metal Sn. However, these SnM negative electrodes have different capacities in the first and second and subsequent cycles because of the generation of irreversible Li 2 O phase that occurs during the first Li insertion. The existence of this irreversible capacity is one of the major obstacles to its practical use.
[0003]
[Problems to be solved by the invention]
The object of the present invention is excellent in initial charge / discharge efficiency, suppresses cycle deterioration due to charge / discharge, realizes a discharge capacity greatly exceeding the theoretical capacity of graphite-based carbon material, 372 mAh / g, SnM (M = O, Provided is a negative electrode for a lithium ion secondary battery that is superior in both initial charge / discharge efficiency and cycle deterioration compared to O 2 ), an active material used for the negative electrode, a production method thereof, and a lithium ion secondary battery including the negative electrode. It is in.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have studied mainly a substance inert to Li as a buffer phase for suppressing volume change of metallic Sn. The inventors have found that the initial charge / discharge efficiency can be improved and have completed the present invention. As one of the factors that the cycle life and the initial charge / discharge efficiency are improved due to the presence of the rare earth metal oxide and the metal Sn, it is presumed that these have a finely dispersed structure on the nanoscale.
[0005]
That is, according to the present invention, it is a powder having an average particle diameter of 0.01 to 75 μm, and is composed of one or more rare earth metals selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc. The oxide peak of the rare earth metal and the metal Sn peak are observed by surface X-ray diffraction measurement, the rare earth-Sn intermetallic compound peak is not observed, and oxygen A negative electrode active material for a lithium ion secondary battery having a content ratio of 0.7 to 6% by mass and having an ability to absorb and release lithium is provided.
Further, according to the present invention, Y, a lanthanoid series containing Sc, a powder containing one or more rare earth metal oxides selected from the group consisting of elements from La to Lu, and metal Sn, Intermetallic compound represented by R-Sn and / or intermetallic compound represented by R-Sn- (M 1 ) (R is a rare earth element, M 1 is Li, B, C, N, Mg, Al, Si, Selected from the group consisting of P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sb, Pb, Hf, Ag, Ta, and Bi Negative electrode active for a lithium ion secondary battery, characterized in that it has an oxygen content ratio of 0.7 to 6% by mass and has an ability to absorb and release lithium. Substance is provided.
Furthermore , according to the present invention, the method includes the step (a) of reacting an alloy having an intermetallic compound containing a rare earth element and Sn at 5 to 1000 ° C. in an atmosphere having an oxygen concentration of 3 at% or more. A method for producing a negative electrode active material is provided.
According to the present invention, there is also provided a negative electrode for a lithium ion secondary battery obtained by applying and drying a negative electrode material containing a negative electrode active material on a current collector, wherein the negative electrode surface is measured by an X-ray diffraction method. Observation of one or more rare earth metal oxide peaks, metal Sn peaks, and current collector metal peaks selected from the group consisting of elements from lanthanoid series La to Lu, including Y, Y, and Sc Thus, there is provided a negative electrode for a lithium ion secondary battery in which no rare earth-Sn intermetallic compound peak is observed and the oxygen content of the negative electrode active material is 0.7 to 6% by mass.
Furthermore, according to this invention, the negative electrode for lithium ion secondary batteries provided with the negative electrode material containing the said negative electrode active material and a collector is provided.
Furthermore, according to this invention, the lithium ion secondary battery provided with the said negative electrode is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The negative electrode active material of the present invention exhibits excellent initial charge / discharge efficiency and cycle characteristics when compared to conventional carbon materials and SnM (M = O, O 2 ) when used in a negative electrode for a lithium ion secondary battery. Lanthanoid series containing Y and Sc, one or more rare earth metal oxides selected from the group consisting of elements from La to Lu, metal Sn, and specifying oxygen Including by content.
[0007]
The negative electrode active material of the present invention is preferably an oxidation of one or more rare earth metals selected from the group consisting of elements from lanthanoid series La to Lu containing Y and Sc by X-ray diffraction measurement of the surface. An object peak and a metal Sn peak are observed, and a rare earth-Sn intermetallic compound peak is not observed.
[0008]
In the negative electrode active material of the present invention, the metal Sn observed in the surface layer is easily alloyed with Li and alloyed with a maximum of 4.4 Li per atom. On the other hand, the rare earth oxide observed in the surface layer is a buffer phase that suppresses the large volume expansion (three times or more) of Sn and is an inert substance to Li, so SnM (M = O, Compared with O 2 ), the generation of the Li 2 O phase, which is the cause of irreversible capacity at the first charge, is suppressed, and the initial charge / discharge efficiency is not lowered. Among rare earth oxides, CeO 2 belongs to the most stable class and can achieve high initial charge / discharge efficiency. Therefore, the rare earth oxide observed in the surface layer in the negative electrode active material of the present invention is CeO 2 alone or CeO 2 And rare earth oxides other than CeO 2 of less than 90 mol%, particularly less than 70 mol%, and even less than 50 mol%. Further, it is preferable that no SnM (M = O, O 2 ) peak is observed in the surface layer.
In the negative electrode active material of the present invention, a rare earth-Sn intermetallic compound peak is not observed in the surface layer, but preferably contains a rare earth-Sn intermetallic compound inside. The intermetallic compound phase has a bulk density higher than that of the rare earth oxide, and the energy density per volume is improved when it is appropriately present in the active material. In addition, the rare earth-Sn intermetallic compound is easily pulverized due to the volume expansion of the alloy phase accompanying the charge / discharge of Li, so that the rare earth oxide as a buffer phase exists in the surface layer, It is desirable to exist. Thereby, desorption from the current collector is suppressed, and a high cycle life can be achieved. Therefore, in the negative electrode active material of the present invention, the abundance ratio of the rare earth-Sn intermetallic compound phase is preferably in the range of 2 to 99% by mass, and more preferably in the range of 10 to 80% by mass.
[0009]
The intermetallic compound phase is preferably an intermetallic compound represented by R-Sn and / or an intermetallic compound represented by R-Sn- (M 1 ). Here, R is a rare earth element, M 1 is Li, B, C, N, Mg, Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, 1 type or 2 types or more selected from the group which consists of Ga, Zr, Nb, Mo, In, Sb, Pb, Hf, Ag, Ta, and Bi are shown. Furthermore, R-Sn X in shown by the intermetallic compound and / or R-Sn X - (M 1 ) intermetallic compound represented by y are especially preferred. Here, X is a rational number of 2 to 3, and y is a rational number of 0 < y ≦ 10.
The RSn 3 phase is the phase containing the most Sn among rare earth-Sn intermetallic compounds. In other words, it is a phase with the largest charge / discharge capacity, and a sufficient discharge capacity can be obtained. Therefore, the proportion of the RSn 3 phase present is preferably 50% by mass or more, more preferably 80% by mass or more in the intermetallic compound in the active material.
[0010]
In the negative electrode active material of the present invention, Li, B, C, Mg, Al, Si, P, S, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr Nb, Mo, W, Ag, In, Sb, Pb, Hf, Ta, and Bi may be included in one or more selected from the group consisting of Bi. B, C, P or S penetrates between the lattices, Li, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo , W, In, Sb, Pb, Hf, Ag, Bi or Ta have an atomic radius smaller than Ce or Sn, so that the lattice is distorted and lattice defects are generated. This defect or strain field is expected to reduce volume expansion / contraction associated with charging / discharging of Li and improve cycle life.
The above-described substitutional element may relieve the volume change even with a single element, and may exist as an intermetallic compound with a rare earth element and Sn. In addition, Sn or a rare earth element may be dissolved, or an oxide may be used.
[0011]
The negative electrode active material of the present invention contains a specific ratio of oxygen. In the negative electrode active material of the present invention, oxygen is mainly contained as a rare earth oxide, and most is present on the particle surface. These oxide films have a role as a buffer phase that relaxes volume expansion associated with charging and discharging of Li. Accordingly, if the amount of these oxide films is too small, cycle deterioration becomes severe, and if too large, diffusion of lithium ions into the alloy is inhibited. Therefore, the oxygen content in the negative electrode active material of the present invention is 0.7 to 6% by mass, preferably 0.8 to 4% by mass. When the oxygen content is less than 0.7% by mass or more than 6% by mass, it is not preferable because the initial discharge capacity is reduced and the cycle characteristics are also reduced when used in a lithium ion secondary battery.
[0012]
The negative electrode active material of the present invention is preferably a powder having an average particle size of 0.01 to 75 μm, and is preferably 38 μm or less, and more preferably 15 μm or less in order to suppress cycle deterioration. An average particle size of less than 0.01 μm is not preferable because handling becomes extremely difficult.
[0013]
The negative electrode active material of the present invention includes a rare earth oxide and metal Sn obtained by reacting an alloy having an intermetallic compound containing a rare earth element and Sn at 5 to 1000 ° C. in an atmosphere having an oxygen concentration of 3 at% or more. Further, it may be a powder having an oxygen content ratio of 0.7 to 6% by weight and an average particle diameter of 0.01 to 75 μm and capable of absorbing and releasing lithium. This will be described in more detail in the method for producing a negative electrode active material of the present invention described later. Moreover, the above-mentioned preferable range is mentioned similarly about an oxygen content rate and an average particle diameter, The above-mentioned thing is mentioned preferably also about an arbitrary component.
[0014]
Although the manufacturing method of the negative electrode active material of this invention will not be specifically limited if the said active material is obtained, The following manufacturing methods of this invention are preferable.
The production method of the present invention includes a step (A) of reacting an alloy having an intermetallic compound containing a rare earth element and Sn (hereinafter referred to as a raw material alloy) at a specific temperature in a specific oxygen concentration atmosphere.
The raw material alloy used in the step (A) can be obtained by a known method such as, for example, mixing a metal as a raw material, melting by heating, casting into a mold or the like, and solidifying. The raw material of the raw material alloy may be a mixture of simple metals constituting a desired composition, or a pre-alloyed mother alloy may be used. In the production method of the present invention, it is preferable to use an intermetallic compound having a uniform structure as much as possible. Therefore, a dissolution method having a large stirring effect is preferable for dissolution by heating, and high-frequency dissolution is particularly preferable. The atmosphere in heating and melting is preferably an inert gas atmosphere such as argon gas.
For the cooling of the molten metal, for example, a known cooling method such as a mold cooling method, an atomizing method, a roll cooling method, or a rotating electrode method can be used. The atmosphere for cooling the molten metal is preferably an inert gas atmosphere. Also, after the preparation of an intermetallic compound of R-Sn, wherein R-Sn x above - (M 1) in the composition represented by y (M 1), for example, between the metal of the metal Li or the like R-Sn A raw material alloy can also be prepared by alloying with a compound by a mechanical alloy method.
[0015]
The raw material alloy used in the step (A) can be obtained by the cooling or the like, but may be further subjected to heat treatment for the purpose of homogenizing the structure and aligning the crystal size. The heat treatment can be performed, for example, in an inert gas atmosphere of 0.07 to 10 MPa.
The heat treatment is preferably performed under a temperature range of 100 to 1150 ° C. for 100 hours or less. When the heat treatment temperature is less than 100 ° C., the diffusion of each alloy phase and single element hardly occurs, and the heat treatment effect cannot be obtained. On the other hand, when the temperature exceeds 1150 ° C., the alloy itself is remelted, so that the cooled and solidified alloys are welded to each other, and the desired purpose cannot be achieved. The heat treatment time can be appropriately selected from the above range depending on the structure, amount and shape of the alloy to be heat treated, the heat treatment apparatus used, etc., but is preferably 30 minutes to 48 hours. If the heat treatment time exceeds 100 hours, the economy is impaired.
[0016]
In step (A), the raw material alloy is reacted at a temperature of 5 to 1000 ° C. in a specific oxygen concentration atmosphere. Examples of the reaction with oxygen include a method of reacting with a mixed gas containing oxygen gas, and a method of mixing and processing the raw material alloy with a compound that oxidizes in the processing temperature range. The oxygen concentration in the mixed gas during treatment with the mixed gas is preferably 3 at% or more, more preferably 15 at% or more, and the upper limit concentration is not limited. At this time, the raw material alloy may be pulverized in advance for the purpose of smoothly performing the oxidation reaction. The oxidation reaction may be carried out at any time until the battery is manufactured. However, after mixing with the binder, etc., and applying to the current collector, the oxidation reaction is performed to form a dense rare earth oxide layer on the surface of the alloy particles. It is particularly effective for forming.
[0017]
By the step (A), a rare earth oxide layer is formed on the surface of the intermetallic compound in the alloy, and an excellent buffer phase that relaxes the volume expansion accompanying the absorption and release of Li is obtained. Here, the thickness of the rare earth oxide layer is preferably 0.001 to 10 μm, and more preferably 0.01 to 4 μm. Further, in the step (A), metal Sn is also generated on the surface of the intermetallic compound in the alloy. The metal Sn is also prevented from being pulverized and desorbed from the electrode by the buffering action and interaction of the rare earth oxide.
In the step (A), an oxide of Sn may be generated on the surface of the intermetallic compound in the alloy. Sn oxide is active with respect to Li and easily generates Li 2 O and causes initial irreversible capacity. However, the presence of a part in the rare earth oxide promotes charge and discharge of Li. Therefore, the abundance ratio is desirably 10% by mass or less of the total oxide in the negative electrode active material.
In the production method of the present invention, in addition to the step (A), other steps may be included as long as the desired effects of the present invention are not impaired.
[0018]
The negative electrode for lithium secondary batteries of the present invention comprises a negative electrode material containing the negative electrode active material of the present invention and a current collector.
For example, a negative electrode for a lithium ion secondary battery obtained by applying and drying a negative electrode material containing the negative electrode active material on a current collector, and measuring the surface of the negative electrode by X-ray diffractometry, Y, Sc One or two or more rare earth metal oxide peaks selected from the group consisting of elements from La to Lu containing lanthanoid series, a metal Sn peak, and a current collector metal peak are observed. No Sn intermetallic compound peak is observed, and the oxygen content of the negative electrode active material is 0.7 to 6 mass%.
A current collector metal-Sn intermetallic compound peak may be further observed by X-ray diffraction of the negative electrode surface.
[0019]
The negative electrode of the present invention can be produced by a known method using the negative electrode active material of the present invention. For example, an appropriate binder is mixed with the negative electrode active material powder of the present invention, and an appropriate conductive powder is mixed as necessary to improve conductivity. A solvent in which the binder is dissolved is added to this mixture, and if necessary, it is sufficiently stirred with a homogenizer or the like to form a slurry. The slurry is applied to an electrode substrate (current collector) such as rolled copper foil or electrolytic copper foil using a doctor blade or the like, dried, and then the negative electrode is produced by compacting the electrode active material by roll rolling or the like. can do.
[0020]
Examples of the binder include water-insoluble resins such as PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), and PTFE (polytetrafluoroethylene), as well as CMC (carboxymethyl cellulose) and PVA (polyvinyl alcohol). Water-soluble resin is mentioned.
Examples of the solvent include organic solvents such as NMP (N-methylpyrrolidone) and DMF (dimethylformamide), and water.
As the conductive powder, for example, any of carbon materials such as acetylene black, ketjen black and graphite, and metals such as Ni can be used, and carbon materials are preferred. Since the carbon material can occlude Li between the layers, it can contribute to the charge / discharge capacity of the negative electrode in addition to the conductivity.
[0021]
In the negative electrode of the present invention, an appropriate amount of the additive element Li can be previously contained in the negative electrode active material of the negative electrode in order to compensate for the presence of the irreversible capacity of Li generated after the battery is produced. In order to contain such an additive element Li, even if an electrode is produced in the presence of a lithium supply source such as metal Li, LiH (lithium hydride), Li 3 N (lithium nitride), etc. The irreversible amount of Li can be compensated. However, if the abundance of these metals Li, LiH, and Li 3 N in the negative electrode active material becomes too large, handling becomes difficult. In addition, since the density of metals Li, LiH, and LiN is small, the energy density of the battery is lowered when the proportion of the presence in the negative electrode active material is excessive. From the above, the abundances of the metal Li, LiH, and LiN can be appropriately selected in consideration of the initial charge / discharge efficiency of the alloy composition, preferably 0 to 50% by mass, and more preferably 0 to 20% by mass.
[0022]
The lithium ion secondary battery of this invention should just be equipped with the said negative electrode of this invention, and is equipped with the negative electrode, the positive electrode, the separator, and the nonaqueous electrolyte as a basic structure. A polymer electrolyte may be used as the electrolyte. Battery constituent materials other than the negative electrode can be used in appropriate combination of known materials.
The shape of the battery is not particularly limited, and examples thereof include a cylindrical shape, a square shape, a coin shape, and a seal shape.
[0023]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these.
Examples 1 to 4 and Comparative Examples 1 to 4
<Preparation of lithium ion secondary battery anode alloy>
In this example and the comparative example, the raw material used for producing the alloy was 99.5% or more. Mm used a rare earth alloy manufactured by Santoku Co., Ltd. having a mass ratio of La: Ce: Nd: Pr: Sm of 28: 51: 16: 4: 1.
In Examples 1 to 4 and Comparative Example 1, after melting the metal mixture constituting the raw material composition shown in Table 1, the obtained molten metal was alloy sample (rare earth element-Sn by a copper casting mold). Intermetallic compound) was obtained. In Examples 3 and 4, the obtained alloy samples were subjected to heat treatment that was held under appropriate conditions shown in Table 1 in an argon gas atmosphere. Next, each sample was pulverized by a mechanical pulverization method in an argon gas atmosphere, and classified to 25 μm or less using a sieve.
Furthermore, the sample powders of Examples 1 to 4 were subjected to an oxidation treatment by heat treatment at any heat treatment temperature and heat treatment time in a mixed gas containing any oxygen gas shown in Table 1.
On the other hand, for Comparative Examples 2 to 4, powders having the raw material compositions shown in Table 1 classified using a sieve to 25 μm or less were used. In Comparative Example 2, a mixture of CeO2: Sn = 1: 3 (mass ratio) was used.
Subsequently, the negative electrode for lithium ion secondary batteries was produced using each powder with the following method, and charge / discharge capacity, a capacity maintenance rate, and charge / discharge efficiency were evaluated.
[0024]
<Production of negative electrode for lithium ion secondary battery and charge / discharge test method>
Each powder prepared above, Ketjen Black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 85: 5: 10, and an appropriate amount of N-methylpyrrolidone (NMP) is mixed. The mixture was kneaded, applied to an electrolytic copper foil having a thickness of 18 μm, temporarily dried in a dryer at 60 ° C., and then consolidated by a roller press. This was punched out to a size of 1.0 cm in diameter and vacuum-dried at 130 ° C. to prepare a test electrode. The constituent phase on the surface of the obtained test electrode was measured by powder X-ray diffraction (XRD). The results are shown in the main precipitated phase column of the surface layer in Table 1. A graph showing the results of X-ray diffraction of Example 1 and Comparative Examples 1 and 2 is shown in FIG.
Moreover, the oxygen content ratio of the active material of the test electrode surface layer was measured. The results are shown in Table 1.
Next, on the obtained test electrode, a polypropylene porous film is used as a separator, and metal lithium is used as a counter electrode, and an electrolytic solution is a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1: 2 (volume ratio). A bipolar cell was fabricated using a solution in which LiPF 6 was dissolved at a concentration of 1 mol. This cell was subjected to a constant current charge / discharge test at a temperature of 25 ° C. and a current density of 0.2 mA / cm 2 in a potential range of 0 to 1.0 V vs. Li / Li + . The assembly of the evaluation cell and the charge / discharge test were performed in a glove box under an argon gas atmosphere. The results are shown in Table 1.
The capacity maintenance rate shown in Table 1 was evaluated by calculating the following formula using the capacity maintenance rate (S) as an index indicating how much the maximum discharge capacity was maintained at the 50th cycle.
(S) = 50th cycle discharge capacity / maximum discharge capacity x 100 (%)
The initial charge / discharge efficiency shown in Table 1 was evaluated by calculating the following formula using the following formula as the initial charge / discharge efficiency (Z) as an index indicating the ratio of the initial discharge capacity to the initial charge capacity.
(Z) = Initial discharge capacity / Initial charge capacity x 100 (%)
[0025]
[Table 1]
From Table 1, Examples 1 to 4 have a rare earth oxide layer in the surface layer of the active material, and have a high capacity retention rate at 50 cycles. On the other hand, Comparative Example 1 has the same raw material composition as Examples 1 and 3, but has no rare earth oxide in the surface layer. As a result, the capacity retention rate at 50 cycles is extremely low. Comparative Example 2 is an active material in which a predetermined amount of CeO 2 powder and metal Sn powder are mixed, but the initial discharge capacity is small and the cycle characteristics are not good. This is presumed to be caused by the fact that CeO 2 and Sn are not finely dispersed on the nanoscale and the oxygen content is high compared to Examples 1 to 4. Further, Comparative Examples 3 and 4 are Sn-based oxides, and since these Sn-based oxides are active with respect to Li, it can be seen that Li 2 O is generated by the first charge and the initial charge / discharge efficiency is low.
[0027]
Examples 5 to 8 and Comparative Example 5
A lithium ion secondary battery negative electrode alloy was produced in the same manner as in Examples 1 to 4 and Comparative Examples 1 to 4 except that the raw material composition and each condition shown in Table 2 were used, and further, a negative electrode for a lithium ion secondary battery. And a charge / discharge test were performed. However, in Example 8, after preparing an intermetallic compound of CeSn 3 as a raw material alloy, the obtained intermetallic compound and metal Li were alloyed by a mechanical alloy method, and a raw material alloy of a raw material composition CeSn 3 Li 5 After the preparation, the negative electrode was prepared and tested. The results are shown in Table 2.
[0028]
[Table 2]
In Table 2, in Examples 5-8, it can be seen that the discharge characteristics when B, Si, and Li, which are elements that improve the discharge characteristics, are good, but in Comparative Example 4, Au is used as the additive element, And since the oxygen content rate in an active material was made outside the range of the present invention, it turns out that discharge characteristics are inferior to the result of Examples 5-8.
[0030]
【The invention's effect】
The negative electrode for a lithium ion secondary battery of the present invention is excellent in initial charge / discharge efficiency, and cycle deterioration associated with charge / discharge is suppressed. Moreover, the negative electrode active material of the present invention is useful for the production of such a negative electrode. Therefore, the negative electrode active material and the negative electrode of the present invention are superior in initial discharge efficiency and cycle life than oxide-based negative electrodes such as SnO 2 and SnO, and lithium ions using a carbon material negative electrode that is currently in practical use. Higher capacity and compactness than secondary batteries are possible, and the industrial utility value is extremely high.
[Brief description of the drawings]
FIG. 1 is a graph showing the results of measuring the constituent phases of the surfaces of test electrodes prepared in Example 1 and Comparative Examples 1 and 2 by powder X-ray diffraction (XRD).
Claims (11)
該負極表面をX線回折法により測定することによって、Y、Scを含むランタノイド系列LaからLuまでの元素からなる群より選択される1種又は2種以上の希土類金属の酸化物ピークと、金属Snピークと、集電体金属のピークとが観察され、希土類-Snの金属間化合物ピークが観察されず、且つ負極活物質の酸素含有割合が0.7〜6質量％であることを特徴とするリチウムイオン二次電池用負極。A negative electrode for a lithium ion secondary battery obtained by applying and drying a negative electrode material containing a negative electrode active material on a current collector,
By measuring the surface of the negative electrode by an X-ray diffraction method, an oxide peak of one or more rare earth metals selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc, a metal A lithium peak in which a Sn peak and a current collector metal peak are observed, a rare earth-Sn intermetallic compound peak is not observed, and the oxygen content of the negative electrode active material is 0.7 to 6% by mass Negative electrode for ion secondary battery.
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| JP5354091B2 (en) * | 2010-03-25 | 2013-11-27 | トヨタ自動車株式会社 | Battery active material and battery |
| WO2011117992A1 (en) * | 2010-03-25 | 2011-09-29 | トヨタ自動車株式会社 | Active material for battery, and battery |
| JP5810587B2 (en) * | 2011-03-31 | 2015-11-11 | Tdk株式会社 | Active material for lithium ion secondary battery, electrode for lithium ion secondary battery, lithium ion secondary battery |
| CN103094562B (en) * | 2012-11-06 | 2015-03-04 | 西北工业大学 | Preparation method of stannic sulfide/rare-earth metal negative pole material for lithium ion battery |
| WO2014099517A1 (en) | 2012-12-19 | 2014-06-26 | Imra America, Inc. | Negative electrode active material for energy storage |
| ES2718917T3 (en) * | 2013-05-16 | 2019-07-05 | Albemarle Germany Gmbh | Active lithium tank for lithium-ion batteries |
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