JP4097127B2

JP4097127B2 - Negative electrode material for lithium ion secondary battery, method for producing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Info

Publication number: JP4097127B2
Application number: JP2002150675A
Authority: JP
Inventors: 孝之大月; 哲男境
Original assignee: National Institute of Advanced Industrial Science and Technology AIST; Santoku Corp
Current assignee: National Institute of Advanced Industrial Science and Technology AIST; Santoku Corp
Priority date: 2002-05-24
Filing date: 2002-05-24
Publication date: 2008-06-11
Anticipated expiration: 2022-05-24
Also published as: JP2003346793A

Description

【０００１】
【発明の属する技術分野】
本発明は、Li、希土類元素、Snを主成分とした合金等からなるリチウムイオン二次電池用負極材料、その製造法、該負極材料を用いた負極及び該負極を備えたリチウムイオン二次電池に関し、更に詳しくは、初期充放電効率が高く、放電容量が大きく、サイクル特性に優れ、且つ工業的な生産性に優れたリチウムイオン二次電池用負極、その原材料となる負極材料、その製造法及び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(密度：2.33g/cm³)とSn(密度：7.3g/cm³)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。
そのような背景のもと現在、体積膨張率の異なる(Liと合金化し難い)元素とSi又はSnとをナノレベルで複合化、もしくは合金化することで微粉化を抑制し、サイクル寿命を延ばす試みが精力的に行われている。例えば、リチウムイオン二次電池の負極活物質として、Si系ではFeSi₂、NiSi₂、CoSi₂、VSi₂、MnSi₂、またSn系ではNi₃Sn₂、Ni₃Sn、Ni₃Sn₄、FeSn₂、FeSn、CoSn₂等の金属間化合物の使用可能性が検討されている。しかし、上記体積膨張率の異なる元素と合金化している金属間化合物も、現状においては電池設計時に非常に重要なファクターである初期充放電効率(初回充電容量に対する初回放電容量の割合)が低く、放電容量も小さく、更にサイクル特性も良好とは言えない。
【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たリチウム二次電池用負極、該負極に用いる負極材料、その製造法及び該負極を備えたリチウム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、強い極性を有し、微粉化し難いRSn₃相(R=希土類元素等)に着目し、更に初回の充放電により合金中に残留するLiを予め、吸蔵(充電)させたRSn₃-Lix(0≦x≦13)を基本骨格とした合金を高周波溶解法により作製した。その結果、高い放電容量及び優れたサイクル特性を達成した。次いでLiの充放電容量を増加する添加元素とサイクル寿命を向上させる添加元素について鋭意検討を行った結果、特定の元素を適正量添加することにより、更に放電特性が向上しうることを知見し、本発明を完成するに至った。
【０００５】
すなわち、本発明によれば、式(1)で表される組成を有する合金を含み、且つ該合金が酸素を0.05〜5質量％及び／又は窒素を0.0005〜2質量％含むリチウムイオン二次電池用負極材料が提供される。
(Li)x(R)y(Sn)z(Ma)w(Mb)v・・・(1)
(式中、Rは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、MaはB、C、Si、P、Al、Zn、V、Mn、Cu、Ag、In、Sb、Pb及びBiからなる群より選択される1種又は2種以上、MbはTi、V、Cr、Fe、Co、Ni、Cu、B、Mg、Zr、Hf、Nb、Ta及びMoからなる群より選択される1種又は2種以上でMa≠Mb。x、y、zはそれぞれモル比で、0≦x≦13、0.70≦y≦1.10、2.20≦z≦3.50、0≦w≦0.70、0≦v≦0.70、0≦w+v≦0.70である。)
また本発明によれば、式(1)で表される組成を有する合金を含むリチウムイオン二次電池用負極材料が提供される。
(Li)x(R)y(Sn)z(Ma)w(Mb)v・・・(1)
(式中、Rは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、MaはB、C、Si、P、Al、Zn、V、Mn、Cu、Ag、In、Sb、Pb及びBiからなる群より選択される1種又は2種以上、MbはTi、V、Cr、Fe、Co、Ni、Cu、B、Mg、Zr、Hf、Nb、Ta及びMoからなる群より選択される1種又は2種以上でMa≠Mb。x、y、zはそれぞれモル比で、0≦x≦13、0.70≦y≦1.10、2.20≦z≦3.50、0＜w≦0.70、0≦v≦0.70、0＜w+v≦0.70である。)
更に本発明によれば、式(1)で表される組成を有する合金を含むリチウムイオン二次電池用負極材料が提供される。
(Li)x(R)y(Sn)z(Ma)w(Mb)v・・・(1)
(式中、Rは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、MaはB、C、Si、P、Al、Zn、V、Mn、Cu、Ag、In、Sb、Pb及びBiからなる群より選択される1種又は2種以上、MbはTi、V、Cr、Fe、Co、Ni、Cu、B、Mg、Zr、Hf、Nb、Ta及びMoからなる群より選択される1種又は2種以上でMa≠Mb。x、y、zはそれぞれモル比で、0≦x≦13、0.70≦y≦1.10、2.20≦z≦3.50、0≦w≦0.70、0＜v≦0.70、0＜w+v≦0.70である。)
更にまた本発明によれば、式(1)で表される組成を有する合金溶湯を製造する工程(a)、
(Li)x(R)y(Sn)z(Ma)w(Mb)v・・・(1)
(式中、Rは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、MaはB、C、Si、P、Al、Zn、V、Mn、Cu、Ag、In、Sb、Pb及びBiからなる群より選択される1種又は2種以上、MbはTi、V、Cr、Fe、Co、Ni、Cu、B、Mg、Zr、Hf、Nb、Ta及びMoからなる群より選択される1種又は2種以上でMa≠Mb。x、y、zはそれぞれモル比で、0≦x≦13、0.70≦y≦1.10、2.20≦z≦3.50、0≦w≦0.70、0≦v≦0.70、0≦w+v≦0.70である。)
製造した合金溶湯を冷却固化する工程(b)、及び冷却固化した合金を、0.07〜10MPaの希ガス及び／又は水素ガス中において100〜1150℃の温度範囲で１分〜100時間保持する工程(c)を含む上記リチウムイオン二次電池用負極材料の製造法が提供される。
また本発明によれば、上記負極材料を活物質として含む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、上記負極を備え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】
本発明の負極材料は、リチウムイオン二次電池負極とした際に従来の炭素材の理論容量より、はるかに高い放電容量、同等以上の初期充放電効率を示し、またサイクル特性も従来の合金系負極材よりはるかに優れたサイクル特性を示すことが可能であり、前記式(1)で表される組成を有する合金を含む。
【０００７】
式(1)中、Rは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(以下、希土類(R)と略す)である。該希土類(R)は、Snとの組み合わせにおいて電気陰性度の差が大きく、強い極性を有してイオン結合的にSnと合金化するためサイクル寿命の向上が望める。
希土類(R)の中でもCeは、Snとの組合わせにおいて最も電気陰性度の差が大きな部類に属し、非常に微粉化し難い合金系の達成を可能にする。またCeは、4価までの酸化数を有するのでLiの配位能が大きく、種々ある希土類(R)の中で最も充放電容量が大きい合金系の製造を可能にする元素に属する。
従って、希土類(R)は、Ce単独であるか、もしくはCeと、90mol％未満、特に50mol％未満のCe以外の希土類(R)とからなる構成が好ましい。希土類(R)は、Snと金属間化合物を主に形成するが、希土類(R)自体で存在してもLiの吸蔵・放出に伴う体積膨張を緩和することができる。希土類(R)の量が多すぎると充放電容量の低下を招き、少なすぎると微粉化を抑制できなくなるため、式(1)において希土類(R)の量を示すyの範囲は、0.70≦y≦1.10、好ましくは0.90≦y≦1.05である。
【０００８】
式(1)においてLiは、所望の合金組成の初期充放電効率を考慮して、その含有割合を適宜選択することができ、後述する負極の構成によっては必ずしも含有されてい無くても良い。Liの含有割合が多すぎると取り扱いが困難になると共に、充放電容量の低下を招く恐れがある。従って、式(1)においてLiの量を示すxの範囲は、0≦x≦13、好ましくは4.0≦x≦8.0である。
【０００９】
式(1)においてSnは、Liを吸蔵する金属である。Snの含有割合は少なすぎると充放電容量が小さくなる。また多すぎると容量は増加するが他の元素と合金化できない残留金属Snの割合が増加し、微粉化が促進され、サイクル寿命が低下する恐れが生じる。従って、式(1)においてSnの量を示すzの範囲は2.20≦z≦3.50、好ましくは2.70≦z≦3.10である。
本発明の式(1)で表される組成を有する合金において許容できる残留金属Snの割合は、粉末Ｘ線回折におけるSnの(2 0 0)面のピーク強度が、RSn₃相(Rは式(1)中のRと同様である)に由来するピーク中で最強ピーク強度の30％以下、好ましくは15％以下、更に好ましくは5％以下となる割合である。
【００１０】
式(1)において置換元素Maは、B、C、Si、P、Al、Zn、V、Mn、Cu、Ag、In、Sb、Pb及びBiからなる群より選択される1種又は2種以上である。該置換元素Maの使用によりLi吸蔵量及び放出量を増加させることができ、結果として充放電容量を増加させうる。その理由は、置換元素MaのうちのB、Cは格子間に侵入でき、またSi、P、Al、Zn、V、Mn、Cu、Ag、In、Sb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とができ、この欠陥又はひずみ場にLiが吸蔵されうるためと推測される。また置換元素MaのうちAl、Zn、V、Cu、Ag、Inは、CeもしくはSnより導電率が大きいので、合金自体の導電率を向上させることができ、その結果、充放電容量が増加すると考えられる。
式(1)において置換元素Mbは、Ti、V、Cr、Fe、Co、Ni、Cu、B、Mg、Zr、Hf、Nb、Ta及びMoからなる群より選択される1種類又は2種類以上であり、且つMa≠Mbである。該置換元素Mbの使用によりサイクル寿命を延ばすことができる。
【００１１】
前記置換元素(Ma、Mb)は、その置換元素単体、もしくは置換元素(Ma、Mb)と、希土類(R)及び／又はSnとの金属間化合物を形成し、それらが複合的に合金中に分散し、Liの充放電に伴うSnの体積膨張を緩和していると推定される。これら置換元素(Ma、Mb)の含有割合を適正値に調整することにより、放電特性のバランスを制御することができる。Maの含有割合が多いとLi吸蔵量は増加するが、サイクル寿命が低下する傾向がある。またMbの含有割合が多いとサイクル寿命は向上するが、Li吸蔵量が低下し、放電容量も低下する傾向がある。従って、式(1)においてMa又はMbの量を示すw又はvの範囲は、それぞれ0≦w≦0.70、0≦v≦0.70、0≦w+v≦0.70である。
【００１２】
本発明において、式(1)で表される合金の組織は、主にCu₃Au構造を有するRSn₃相であることが好ましい。RSn₃相はR-Sn系二元系合金では最もSn結合数が多い相である。言い換えるなら最も放電容量が大きい相である。式(1)で表される合金の組織は、サイクル寿命の向上、並びに適度の活性度を得る目的で他の相を含んでいても良い。但し、Sn単相を含む場合は特性の劣化が著しいので好ましくない。RSn₃相以外の相の含有割合は、合金の組織観察を行った場合の面積率で0.5〜30％、特に2〜5％が好ましい。RSn₃相以外の相としては、Maと希土類(R)との金属間化合物相、Mbと希土類(R)との金属間化合物相、MaとSnとの金属間化合物相、MbとSnとの金属間化合物相、希土類(R)とSnとの金属間化合物相等が挙げられる。また置換元素Mb、Maは、元素単体で存在していても良い。これら金属間化合物もしくは置換元素単体は、複合的に合金中に分散し、Liの吸蔵・放出に伴う合金の体積膨張を緩和する効果がある。前記金属間化合物相は、１種又は２種以上存在していても良い。
【００１３】
前記Mbと希土類(R)との金属間化合物相としては、例えば、Ce₂Fe₁₇、Ce₂Fe₂、Nd₂Fe₁₇、Pr₂Fe₁₇、PrFe₂、Sm₂Fe₁₇、SmFe₃、SmFe₂、Ce₂₄Co₁₁、CeCo₂、CeCo₃、Ce₂Co₇、Ce₅Co₁₉、Ce₂Co₁₇、CeCo₅、LaCo₁₃、LaCo₅、La₅Co₁₉、α-La₂Co₇、β-La₂Co₇、La₂Co₃、La₂Co_1.7、LaCo、Nd₂Co₁₇、NdCo₅、Nd₅Co₁₉、Nd₂Co₇、NdCo₃、NdCo₂、α-Nd₂Co₃、β-Nd₂Co₃、Nd₂Co_1.7、Nd₇Co₃、Nd₃Co、Pr₂Co₁₇、PrCo₅、Pr₅Co₁₉、PrCo₃、Pr₂Co₇、PrCo₂、Pr₂Co_1.7、Pr₅Co₂、Pr₃Co、α-Sm₂Co₁₇、β-Sm₂Co₁₇、SmCo₃、SmCo₂、Sm₉Co₄、Sm₃Co、Ce₇Ni₃、CeNi、CeNi₂、CeNi₃、Ce₂Ni₇、CeNi₅、La₃Ni、La₇Ni₃、LaNi、La₂Ni₃、La₇Ni₁₆、LaNi₃、α-La₂Ni₇、β-La₂Ni₇、LaNi₅、Nd₃Ni、Nd₇Ni₃、NdNi、NdNi₂、NdNi₃、Nd₂Ni₇、NdNi₅、Nd₂Ni₁₇、Pr₃Ni、Pr₇Ni₃、PrNi、PrNi₂、PrNi₃、Pr₂Ni₇、PrNi₅、Sm₃Ni、SmNi、SmNi₂、SmNi₃、Sm₂Ni₇、Sm₅Ni₁₉、SmNi₅、Sm₂Ni₁₇、CeCu₆、CeCu₄、CeCu₂、CeCu、LaCu₆、LaCu、NdCu₆、NdCu₅、NdCu₄、Nd₂Cu₇、NdCu₂、NdCu、PrCu₆、PrCu₄、PrCu₅、PrCu₂、PrCu、SmCu₆、SmCu₄、SmCu₅、Sm₂Cu₇、SmCu₂、SmCu、CeB₄、CeB₆、LaB₄、LaB₆、LaB₉、Nd₂B₅、NdB₄、NdB₆、NdB₆₆、Sm₂B₅、SmB₄、SmB₆、SmB₆₆、CeMg₁₂、Ce₅Mg₄₁、CeMg₃、CeMg₂、CeMg、CeMg_10.3、LaMg₁₂、La₂Mg₁₇、LaMg₃、LaMg₂、LaMg等が挙げられる。
【００１４】
前記MbとSnとの金属間化合物相としては、例えば、Ti₃Sn、Ti₂Sn、Ti₅Sn₃、α-Ti₆Sn₅、β-Ti₆Sn₅、V₃Sn、V₂Sn₃、Fe₅Sn₃、Fe₃Sn₂、FeSn、FeSn₂、α-Co₃Sn₂、β-Co₃Sn₂、CoSn、CoSn₂、Ni₃Sn、Ni₃Sn₂、Ni₃Sn₄、Cu₆Sn₅、Cu₃Sn、Mg₂Sn、Zr₄Sn、Zr₅Sn₃、ZrSn₃、Hf₅Sn₃、Hf₅Sn₄、HfSn、HfSn₂、Nb₃Sn、Nb₆Sn₅、NbSn₂、Mo₃Sn、MoSn₂等が挙げられる。
【００１５】
前記Maと希土類(R)との金属間化合物相としては、例えば、CeB₄、CeB₆、LaB₄、LaB₆、LaB₉、Nd₂B₅、NdB₄、NdB₆、NdB₆₆、PrB₄、PrB₆、Sm₂B₅、SmB₄、SmB₆、SmB₆₆、Ce₂C₃、α-CeC₂、β-CeC₂、La₂C₃、α-LaC₂、β-LaC₂、Pr₂C₃、α-PrC₂、β-PrC₂、Ce₅Si₃、Ce₃Si₂、Ce₅Si₄、CeSi、Ce₃Si₅、CeSi₂、Nd₅Si₃、Nd₅Si₄、NdSi、Nd₃Si₄、α-Nd₂Si₃、β-Nd₂Si₃、α-Pr₅Si₃、β-Pr₅Si₃、Pr₅Si₄、PrSi、Pr₃Si₄、α-PrSi₂、β-PrSi₂、Sm₅Si₃、Sm₅Si₄、SmSi、Sm₃Si₅、α-SmSi₂、β-SmSi₂、PrP、PrP₂、PrP₅、PrP₇、α-Al₁₁Ce₃、β-Al₁₁Ce₃、Al₃Ce、Al₂Ce、AlCe、α-AlCe₃、β-AlCe₃、α-Al₁₁La₃、β-Al₁₁La₃、Al₃La、Al₂La、AlLa、AlLa₃、α-Al₁₁Nd₃、β-Al₁₁Nd₃、Al₃Nd、Al₂Nd、AlNd、AlNd₃、α-Al₁₁Pr₃、β-Al₁₁Pr₃、Al₃Pr、Al₂Pr、α-AlPr、β-AlPr、AlPr₂、α-AlPr₃、β-AlPr₃、Al₃Sm、Al₂Sm、AlSm、AlSm₂、CeZn、CeZn₂、CeZn₃、Ce₃Zn₁₁、Ce₁₃Zn₅₈、CeZn₅、Ce₃Zn₂₂、Ce₂Zn₁₇、CeZn₁₁、LaZn、LaZn₂、LaZn₄、LaZn₈、LaZn₁₃、NdZn、NdZn₂、NdZn₃、Nd₃Zn₁₁、Nd₁₃Zn₅₈、Nd₃Zn₂₂、NdZn₁₁、NdZn₁₂、Nd₂Zn₁₇、PrZn、α-PrZn₂、β-PrZn₂、PrZn₃、Pr₃Zn₁₁、Pr₁₃Zn₅₈、Pr₃Zn₂₂、α-Pr₂Zn₁₇、β-Pr₂Zn₁₇、PrZn₁₁、SmZn、α-SmZn₂、β-SmZn₂、SmZn₃、Sm₃Zn₁₁、Sm₁₃Zn₅₈、Sm₃Zn₂₂、Sm₂Zn₁₇、Nd₆Mn₂₃、NdMn₂、Mn₂₃Pr₆、Mn₂₃Sm₆、Mn₂Sm、Cu₆Ce、Cu₅Ce、Cu₄Ce、Cu₂Ce、CuCe、α-Cu₆La、β-Cu₆La、Cu₅La、Cu₄La、Cu₂La、CuLa、Cu₆Nd、Cu₅Nd、Cu₄Nd、Cu₇Nd₂、Cu₂Nd、CuNd、Cu₆Pr、Cu₄Pr、Cu₂Pr、CuPr、Cu₆Sm、Cu₅Sm、Cu₄Sm、Cu₇Sm₂、Cu₂Sm、CuSm、Ag₄Ce、Ag₅₁Ce₁₄、α-Ag₂Ce、β-Ag₂Ce、γ-Ag₂Ce、α-AgCe、β-AgCe、α-Ag₅La、β-Ag₅La、Ag₅₁La₁₄、Ag₂La、AgLa、Ag₅₁Nd₁₄、α-Ag₂Nd、β-Ag₂Nd、AgNd、Ag₅Pr、Ag₅₁Pr₁₄、α-Ag₂Pr、β-Ag₂Pr、AgPr、Ag₅₁Sm₁₄、α-Ag₂Sm、β-Ag₂Sm、AgSm、Ce₃In、Ce₂In、Ce₃In₅、CeIn₂、CeIn₃、In₃La、In₂La、In₅La₃、InLa、InLa₂、InLa₃、Nd₃In、Nd₂In、NdIn、Nd₃In₅、NdIn₃、Pr₃In、Pr₂In、Pr₃In₅、PrIn₃、Sm₃In、Sm₂In、SmIn、Sm₃In₅、SmIn₃、Ce₂Sb、Ce₅Sb₃、Ce₄Sn₃、CeSb、CeSn₂、La₂Sb、La₃Sn₂、LaSb、LaSb₂、Nd₂Sb、Nd₅Sb₃、Nd₄Sn₃、NdSb、NdSb₂、Pr₂Sb、Pr₅Sn₃、Pr₄Sb₃、α-PrSb、β-PrSb、Sb₂Sm、SbSm、Sb₃Sm₄、α-Sb₃Sm₅、β-Sb₃Sm₅、La₅Pb₃、La₄Pb₃、La₅Pb₄、α-La₃Pb₄、β-La₃Pb₄、LaPb₂、LaPb₃、Ce₂Pb、CePb、CePb₃、Pb₃Pr、Pb₂Pr、Pb₄Pr₃、Pb₁₀Pr₁₁、Pb₄Pr₅、Pb₃Pr₅、PbPr₃、Pb₃Sm、Pb₂Sm、Pb₁₀Sm₁₁、Pb₄Sm₅、Pb₃Sm₅、PbSm₃、La₂Bi、La₅Bi₃、La₄Bi₃、LaBi、LaBi₂、Ce₂Bi、Ce₅Bi₃、Ce₄Bi₃、CeBi、CeBi₂、Bi₂Pr、BiPr、Bi₃Pr₅、BiPr₂、Nd₂Bi、Nd₅Bi₃、Nd₄Bi₃、NdBi、NdBi₂等が挙げられる。
【００１６】
前記MaとSnとの金属間化合物相としては、例えば、Sn₄P₃、Sn₃P₄、SnP₃、V₃Sn、V₂Sn₃、Mn₃Sn、Mn₂Sn、MnSn₂、Cu₆Sn₅、Cu₃Sn、Ag₃Sn、Ag₄Sn等が挙げられる。
【００１７】
前記希土類(R)とSnの金属間化合物相としては、RSn_3-X(X=有理数、0＜X＜3)の条件を満たす相が挙げられ、例えば、Ce₃Sn、α-Ce₅Sn₃、β-Ce₅Sn₃、Ce₅Sn₄、Ce₁₁Sn₁₀、Ce₃Sn₅、Ce₃Sn₇、Ce₂Sn₅、α-La₅Sn₃、β-La₅Sn₃、La₅Sn₄、La₁₁Sn₁₀、LaSn、La₂Sn₃、La₃Sn₅、PrSn₃、α-Pr₅Sn₃、β-Pr₅Sn₃、Pr₅Sn₄、PrSn、α-Pr₃Sn₅、β-Pr₃Sn₅、Nd₅Sn₃、Nd₅Sn₄、Nd₁₁Sn₁₀、NdSn、Nd₃Sn₅、NdSn₂、Nd₂Sn₇、Nd₂Sn₅、Sm₅Sn₃、Sm₄Sn₃、Sm₁₁Sn₁₀、Sm₅Sn₄、Sm₂Sn₃、SmSn₂、SmSn₃が挙げられる。該RSn_3-X相は、RSn₃相と比較してSn含有量が少ない相である。言い換えればSnの吸蔵量が小さい相であり、RSn₃相と比較してLiの吸蔵・放出に伴う体積膨張が小さい。この相は合金中での割合が大きくなると充放電容量の低下を引き起こすが、ある程度合金中に存在するとLiの吸蔵・放出に伴う体積膨張を緩和する効果がある。
【００１８】
式(1)で表される合金を負極材料の活物質として使用するには、通常、粉末の形態で使用でき、該粉末の微粉化を抑制するため、その平均粒径は0.1〜25μmであることが好ましい。該粉末状の合金に含まれる結晶の平均粒径は、サイクル劣化を抑制するために15μm以下が好ましく、特に10μm以下が望ましい。該結晶の平均粒径が0.1μm未満では、合金粉末の微粉化は抑制されるものの表面積が増大し、酸素値が極端に増加するため、充放電効率の低下、充放電容量の低下を招いてしまうので好ましくない。
【００１９】
式(1)で表される合金には、式(1)の組成以外に、その製造工程等に起因して酸素及び／又は窒素等が含まれることがある。該酸素は、主として希土類(R)又はSnとの酸化物として合金粒子表面に存在し、酸化物皮膜を形成してLiの充放電に伴う合金の体積膨張を緩和する作用を示す。このような酸化物の存在割合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Liイオンの合金中への拡散を阻害し、充放電容量が低下すると共に吸蔵したLiを酸化し、充放電効率の低下を招いてしまう。従って、合金中に含有する酸素元素の含有割合は、0.05〜5質量％が好ましく、更には0.10〜3質量％が特に好ましい。
同様に合金に含まれる窒素も、適性量の含有によりサイクル寿命を向上させることができる。従って、合金中に含有する窒素元素の含有割合は、0.0005〜2質量％が好ましく、更には0.0005〜0.5質量％が特に好ましい。
【００２０】
本発明の上記負極材料の製造は、例えば、式(1)で表される組成を有する合金溶湯を製造する工程(a)と、該合金溶湯を冷却固化する工程(b)と、冷却固化した合金を特定条件で加熱処理する工程(c)とを含む本発明の製造法等により得ることができる他、前記工程(a)及び(b)を含み、工程(c)を含まない方法等によっても得ることができる。
【００２１】
前記工程(a)において、合金溶湯の原料は、式(1)で表される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。合金溶湯の製造は公知の方法が採用できるが、高周波溶解法が好ましく、アーク溶解法やメカニカルアロイング法は、得られる合金の残留金属Snが多くなる傾向にあるので好ましくない。合金溶湯を製造する際の雰囲気は、溶湯の酸化を防ぐため不活性ガス雰囲気が望ましい。また、原料の歩留まりを向上させるために個々の原料を投入する時期をずらして溶融しても良い。
【００２２】
工程(b)において、合金溶湯の冷却は、例えば、金型鋳造法、アトマイズ法、ロール冷却法、回転電極法等の公知の冷却方法を用いることができる。合金溶湯を冷却する際の雰囲気は、得られる合金の酸化を防ぐため不活性ガス雰囲気が望ましい。
工程(b)により得られる冷却固化した合金の組織は、Sn単相を含まないことが望ましいが、次工程等によりSn単相を削減することができるので、工程(b)の段階ではSn単相を含んでいても良い。従って、工程(b)においてSn単相の含有割合が少ない場合等には、必ずしも工程(c)を行う必要はない。
【００２３】
工程(c)は、工程(b)で得られる冷却固化した合金の組織の均質化、結晶性の向上、残留金属Snの低減等を目的とする熱処理工程である。工程(c)は、前記冷却固化した合金の酸化を防止するために、また、活性度を向上させる目的で、0.07〜10MPaの希ガス及び／又は水素ガス雰囲気において行うことができる。希ガス及び水素ガスの混合ガスを用いる場合には、水素ガス5容量％以上を含む混合ガスが好ましい。前記雰囲気ガスの圧力が、0.07MPa未満の高い減圧下の場合、合金中のSnが熱処理により表面に析出する傾向があり、そのような材料で電池を作製して評価した場合、サイクル寿命を低下させてしまう傾向がある。
工程(c)では、前記雰囲気において、工程(b)で冷却した合金を100〜1150℃の温度範囲で１分〜100時間保持する。熱処理温度が100℃未満では、残留金属Sn、Li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、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宜選択できる。1分未満では熱処理の効果が現れず、100時間を超えると経済性を損なう。好ましくは30分〜48時間である。
【００２４】
工程(b)により得られる合金が、サイクル特性に悪影響を及ぼす残留Sn単相を含む場合、上記工程(c)により低減できるが、更に残留Sn単相を削減するために、工程(c)で得られた合金を、粉砕後、篩分する工程(d)を行うこともできる。
工程(d)において粉砕は、機械粉砕等で行うことができる。粉砕した合金からSn単相を篩分により除去することができるのは、金属Snの延性が合金中の金属間化合物より大きいため、金属間化合物の方が優先的に粉砕され、Sn単相の粒径が大きくなるためである。篩分する際の粒径の目安は25〜200μｍが好ましく、特に50〜100μｍが望ましい。
【００２５】
本発明のリチウムイオン二次電池用負極は、上記本発明の負極材料を活物質として含み、周知の任意の電極製造法にしたがって得ることができる。例えば、本発明の負極材料の粉末に、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。得られた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方法等により製造することができる。
【００２６】
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；Ni等の金属が挙げられる。特に炭素材は、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好ましい。
【００２７】
本発明の負極を製造するにあたり、活物質として用いる本発明の負極材料は、活物質中に通常50〜100質量％、特に80〜100質量％含有させることが好ましい。特に、本発明の負極材料において、式(1)で表される組成を有する合金が、Liを含有しないか、もしくは、所望の組成合金で必要な初期不可逆分に満たないLiしか含有していない合金である場合には、活物質として本発明の負極材料に加えて、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を含ませることができる。
このようなリチウム供給源を用いることにより、初回充放電時の不可逆分のLiが補償されるが、負極活物質中におけるリチウム供給源の含有割合が多くなりすぎると、取扱い性に問題が生じる恐れがある。また、前記リチウム供給源は、密度が小さいため、負極活物質中の含有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。従って、リチウム供給源を用いる場合の活物質中における含有割合は、合金組成の初期充放電効率を考慮して、50質量％未満、特に、20質量％未満が好ましい。
【００２８】
本発明のリチウムイオン二次電池は、上記本発明の負極を備えておれば良く、通常、基本構造として、本発明の負極、正極、セパレータ及び非水系の電解質、例えばポリマー電解質を含む。これら電池構成材料は、負極を除いて公知のものを適当に組合わせて構成させることができる。二次電池の形状は特に制限されず、円筒形、角型、コイン型、シール型等のいずれでも良い。
【００２９】
【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。尚、例中に使用した原材料は99.5％以上の材料を使用した。また、ミッシュメタル(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1〜11及び比較例1〜2
リチウムイオン二次電池用負極材料合金の作製
表1に示す組成を構成する金属混合物を高周波溶融した後、得られた溶湯を銅鋳型を用いた金型鋳造法(金型法)もしくは、回転ロールにタンデッシュを介して溶湯を注湯するストリップキャスト法(SC法)でフレーク状の合金片を得た。次いで、表1に示す条件で熱処理を施した。熱処理を施していない各合金片及び熱処理を施した各合金片を、アルゴンガス雰囲気下において機械的粉砕法により粉砕体し、篩を用いて25μm以下に分級し負極材料合金を製造した。尚、合金溶湯の製造及び合金溶湯の冷却はそれぞれアルゴンガス雰囲気中で行った。
次に、得られた各粉体合金の組成を元素分析法により測定し、表1に示す組成であることを確認した。また、各粉体合金の構成相を粉末X線回折(XRD)により測定し、構成相中の残留金属Snの析出割合を(W)とし、以下の式により算出して評価した。結果を表1に示す。
(W)=(金属Sn(2 0 0)面のピーク強度／RSn₃に由来するピーク中で最強ピーク強度)×100
【００３０】
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
負極活物質としての上記調製した合金粉末と、導電助剤としてのケッチェンブラックと、結着剤としてのPVDFとを質量比で85：5：10に混合し、適量のNMPを加えて混練した後、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。
得られた試験電極と、セパレータとしてのポリプロピレン多孔質フィルムと、対極としての金属リチウムと、電解液としての、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とを用いて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0.2mA/cm²で0〜1.0V vs. Li/Li⁺の電位範囲において定電流充放電試験を行った。また、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としての容量維持率(S)を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(％)
更に、初回充電容量に対する初回放電容量の割合を示す指標としての初期充放電効率(Z)を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(％)
以上の結果を表１に示す。尚、セルの組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。
【００３１】
比較例 3
試験電極として人造黒鉛を用いた以外は、実施例1と同様に充放電試験を行った。結果を表1に示す。
【００３２】
【表１】

【００３３】
表1より実施例1〜11 は、初期放電容量及び初期充放電効率が優れている。特に熱処理を施すことによりサイクル寿命が向上することが判る。希土類元素を含有しない組成の比較例1及び2では、放電容量、サイクル特性ともに低いことが判る。また実施例1〜11の重量あたりの放電容量は、比較例3の黒鉛より1.5倍以上高い値となり、また初期充放電効率も黒鉛とほぼ同等の値となり、本実施例の負極が優れた放電特性を示すことが判る。
【００３４】
実施例12 〜 23及び比較例4〜5
合金組成を表2に示す組成に代え、合金片の熱処理条件を表2に示す条件に代えた以外は実施例1と同様に、残留金属Snの析出割合(W)の測定、セルの作製及び充放電試験(初期放電容量及び初期充放電効率)を行った。結果を表2に示す。
【００３５】
【表２】

【００３６】
表2より、実施例12 〜 23は、置換元素(Ma)の割合が本発明の範囲外である比較例4及び5に比して明らかに初期放電容量が増加していることが判る。
【００３７】
実施例24 〜 45及び比較例6
合金組成を表3に示す組成に代え、合金片の熱処理条件を表3に示す条件に代えた以外は実施例1と同様に、残留金属Snの析出割合(W)の測定、セルの作製及び充放電試験(初期充放電効率及び50サイクル目の容量維持率)を行った。結果を表3に示す。
【００３８】
【表３】

【００３９】
表3より本発明における置換元素(Mb)以外の置換元素を有する比較例6では、置換元素(Mb)を有する実施例24 〜 45に比して明らかに容量維持率が劣ることが判る。また、熱処理を施した合金を用いたサイクル寿命が向上している実施例では、XRD測定により、置換元素(Mb)と希土類(R)との金属間化合物相、置換元素(Mb)とSnとの金属間化合物相、RSn₃相(R＜0)、置換元素(Mb)単体が複合的に析出していることが確認された。
【００４０】
実施例46 〜 59及び比較例7〜8
合金組成を表4に示す組成に代え、合金片の熱処理条件を表4に示す条件に代えた以外は実施例1と同様に、残留金属Snの析出割合(W)の測定、セルの作製及び充放電試験を行った。結果を表4に示す。
【００４１】
【表４】

【００４２】
置換元素(Ma、Mb)を含む実施例46 〜 59では、Snの含有割合が本発明の範囲より低く、かつ置換元素(Ma、Mb)の含有割合が本発明の範囲よりも高い比較例7及び8に比して、高い初期放電容量を示すことが判る。
【００４６】
実施例60 〜 61
表5に示す酸素量及び窒素量を含む合金片を実施例1と同様に調製し、残留金属Snの析出割合(W)の測定、セルの作製及び充放電試験を行った。結果を表5に示す。
【００４７】
【表５】

【００４８】
【発明の効果】
本発明のリチウムイオン二次電池用負極は、特定組成の合金を含む本発明の負極材料を活物質とするので、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、特に優れた放電容量が達成される。また、本発明の負極材料は、このような負極の製造に有用である。従って、本発明の負極材料及び負極は、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をより高容量化・コンパクト化させることが可能となり、産業上の利用価値が極めて高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a negative electrode material for a lithium ion secondary battery made of an alloy containing Li, rare earth elements, Sn as a main component, a manufacturing method thereof, a negative electrode using the negative electrode material, and a lithium ion secondary battery including the negative electrode More specifically, the negative electrode for a lithium ion secondary battery having a high initial charge / discharge efficiency, a large discharge capacity, excellent cycle characteristics, and excellent industrial productivity, a negative electrode material as a raw material thereof, and a production method thereof And a lithium ion secondary battery.
[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 (density: 2.33 g / cm^Three) And Sn (density: 7.3 g / cm^Three) 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.
Under such circumstances, by combining or alloying elements with different volume expansion rates (difficult to alloy with Li) and Si or Sn at the nano level, pulverization is suppressed and cycle life is extended. Attempts are being made vigorously. For example, as a negative electrode active material of a lithium ion secondary battery, SiSi₂, NiSi₂, CoSi₂, VSi₂, MnSi₂In addition, Ni in the Sn system_ThreeSn₂, Ni_ThreeSn, Ni_ThreeSn_Four, FeSn₂, FeSn, CoSn₂The possibility of using intermetallic compounds such as However, intermetallic compounds alloyed with elements having different volume expansion coefficients also have a low initial charge / discharge efficiency (ratio of initial discharge capacity to initial charge capacity), which is a very important factor at the time of battery design, The discharge capacity is small and the cycle characteristics are not good.
[0003]
[Problems to be solved by the invention]
An object of the present invention is an anode for a lithium secondary battery that has excellent initial charge / discharge efficiency, suppresses cycle deterioration associated with charge / discharge, and realizes a discharge capacity greatly exceeding the theoretical capacity of a graphite-based carbon material, which is 372 mAh / g, An object of the present invention is to provide a negative electrode material used for the negative electrode, a manufacturing method thereof, and a lithium secondary battery including the negative electrode.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have a strong polarity and RSn that is difficult to micronize._ThreeFocusing on the phase (R = rare earth element, etc.), and RSn in which Li remaining in the alloy was occluded (charged) in advance by first charge / discharge_ThreeAn alloy having -Lix (0 ≦ x ≦ 13) as a basic skeleton was prepared by a high frequency melting method. As a result, a high discharge capacity and excellent cycle characteristics were achieved. Then, as a result of earnestly examining the additive element that increases the charge / discharge capacity of Li and the additive element that improves the cycle life, it was found that the discharge characteristics can be further improved by adding an appropriate amount of a specific element, The present invention has been completed.
[0005]
  That is, according to the present invention, an alloy having a composition represented by the formula (1) is included, and the alloy contains 0.05 to 5 oxygen.mass%And / or nitrogen 0.0005-2mass%A negative electrode material for a lithium ion secondary battery is provided.
  (Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu including Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50, 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 ≦ w + v ≦ 0.70.)
  According to the present invention, there is also provided a negative electrode material for a lithium ion secondary battery comprising an alloy having a composition represented by formula (1).
  (Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu including Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50, 0 <w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 <w + v ≦ 0.70.)
  Furthermore, according to the present invention, there is provided a negative electrode material for a lithium ion secondary battery comprising an alloy having a composition represented by the formula (1).
  (Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu including Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ (3.50, 0 ≦ w ≦ 0.70, 0 <v ≦ 0.70, 0 <w + v ≦ 0.70)
  Furthermore, according to the present invention, the step (a) of producing a molten alloy having the composition represented by the formula (1),
  (Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu including Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50, 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 ≦ w + v ≦ 0.70.)
  A step (b) of cooling and solidifying the produced molten alloy, and a step of holding the cooled and solidified alloy in a temperature range of 100 to 1150 ° C. for 1 minute to 100 hours in a rare gas and / or hydrogen gas of 0.07 to 10 MPa ( A method for producing the above-described negative electrode material for a lithium ion secondary battery comprising c) is provided.
  Moreover, according to this invention, the negative electrode for lithium ion secondary batteries which contains the said negative electrode material as an active material is provided.
  Furthermore, according to this invention, a lithium ion secondary battery provided with the said negative electrode is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
When the negative electrode material of the present invention is used as a negative electrode for a lithium ion secondary battery, it shows a discharge capacity much higher than the theoretical capacity of a conventional carbon material, and an initial charge / discharge efficiency equal to or higher than that of a conventional carbon material. It can exhibit cycle characteristics far superior to those of the negative electrode material, and includes an alloy having a composition represented by the formula (1).
[0007]
In the formula (1), R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc (hereinafter abbreviated as rare earth (R)). The rare earth (R) has a large difference in electronegativity in combination with Sn, and has a strong polarity and is alloyed with Sn in an ionic bond, so that an improvement in cycle life can be expected.
Among rare earths (R), Ce belongs to a class having the largest difference in electronegativity in combination with Sn, and makes it possible to achieve an alloy system that is very difficult to pulverize. Further, Ce has an oxidation number of up to tetravalent, and therefore has a high coordination capacity of Li, and belongs to an element that makes it possible to produce an alloy system having the largest charge / discharge capacity among various rare earths (R).
Accordingly, the rare earth (R) is preferably composed of Ce alone or composed of Ce and rare earth (R) other than Ce of less than 90 mol%, particularly less than 50 mol%. Rare earth (R) mainly forms an intermetallic compound with Sn, but even if it exists in the rare earth (R) itself, the volume expansion associated with insertion and extraction of Li can be reduced. If the amount of the rare earth (R) is too large, the charge / discharge capacity decreases, and if it is too small, the pulverization cannot be suppressed.Therefore, the range of y indicating the amount of the rare earth (R) in the formula (1) is 0.70 ≦ y ≦ 1.10, preferably 0.90 ≦ y ≦ 1.05.
[0008]
In the formula (1), Li can be appropriately selected in consideration of the initial charge / discharge efficiency of the desired alloy composition, and may not necessarily be contained depending on the configuration of the negative electrode described later. If the Li content is too high, handling becomes difficult and the charge / discharge capacity may be reduced. Therefore, the range of x indicating the amount of Li in the formula (1) is 0 ≦ x ≦ 13, preferably 4.0 ≦ x ≦ 8.0.
[0009]
In the formula (1), Sn is a metal that occludes Li. If the Sn content is too small, the charge / discharge capacity decreases. On the other hand, if the amount is too large, the capacity increases, but the proportion of residual metal Sn that cannot be alloyed with other elements increases, so that pulverization is promoted and the cycle life may be reduced. Therefore, the range of z indicating the amount of Sn in the formula (1) is 2.20 ≦ z ≦ 3.50, preferably 2.70 ≦ z ≦ 3.10.
In the alloy having the composition represented by the formula (1) of the present invention, the allowable ratio of residual metal Sn is such that the peak intensity of Sn (2 0 0) plane in powder X-ray diffraction is RSn._ThreeIn the peak derived from the phase (R is the same as R in the formula (1)), it is a ratio of 30% or less, preferably 15% or less, more preferably 5% or less of the strongest peak intensity.
[0010]
In the formula (1), the substitution element Ma is one or more selected from the group consisting of B, C, Si, P, Al, Zn, V, Mn, Cu, Ag, In, Sb, Pb and Bi. It is. By using the substitution element Ma, it is possible to increase the amount of occlusion and release of Li and consequently increase the charge / discharge capacity. The reason is that B and C among the substitution elements Ma can penetrate between the lattices, and Si, P, Al, Zn, V, Mn, Cu, Ag, In, and Sb have an atomic radius smaller than Ce or Sn. It is presumed that the lattice can be strained to generate lattice defects, and Li can be occluded in this defect or strain field. In addition, Al, Zn, V, Cu, Ag, In of the substitution element Ma has higher conductivity than Ce or Sn, so that the conductivity of the alloy itself can be improved, and as a result, the charge / discharge capacity increases. Conceivable.
In the formula (1), the substitution element Mb is one or more selected from the group consisting of Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, Nb, Ta and Mo. And Ma ≠ Mb. The cycle life can be extended by using the substitution element Mb.
[0011]
The substitution element (Ma, Mb) forms an intermetallic compound of the substitution element alone or substitution element (Ma, Mb) and rare earth (R) and / or Sn, and these are combined in the alloy. It is presumed that the volume expansion of Sn accompanying dispersion and relaxation of Li is alleviated. The balance of the discharge characteristics can be controlled by adjusting the content ratio of these substitution elements (Ma, Mb) to an appropriate value. When the content ratio of Ma is large, the amount of Li storage increases, but the cycle life tends to decrease. If the Mb content is high, the cycle life is improved, but the Li storage amount tends to decrease and the discharge capacity tends to decrease. Therefore, the ranges of w or v indicating the amount of Ma or Mb in the formula (1) are 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, and 0 ≦ w + v ≦ 0.70, respectively.
[0012]
In the present invention, the structure of the alloy represented by the formula (1) is mainly Cu._ThreeRSn with Au structure_ThreeA phase is preferred. RSn_ThreeThe phase is the phase with the largest number of Sn bonds in the R-Sn binary alloy. In other words, it is the phase with the largest discharge capacity. The structure of the alloy represented by the formula (1) may contain other phases for the purpose of improving the cycle life and obtaining an appropriate degree of activity. However, when the Sn single phase is included, the characteristics are remarkably deteriorated. RSn_ThreeThe content ratio of phases other than the phase is preferably 0.5 to 30%, particularly preferably 2 to 5% in terms of the area ratio when the structure of the alloy is observed. RSn_ThreeThe phases other than the phases include an intermetallic compound phase of Ma and rare earth (R), an intermetallic compound phase of Mb and rare earth (R), an intermetallic compound phase of Ma and Sn, and an intermetallic phase of Mb and Sn. Examples thereof include a compound phase and an intermetallic compound phase of rare earth (R) and Sn. Further, the substitution elements Mb and Ma may exist as a single element. These intermetallic compounds or simple substitution elements are dispersed in the alloy in a complex manner, and have the effect of relaxing the volume expansion of the alloy accompanying the insertion and extraction of Li. One or more intermetallic compound phases may be present.
[0013]
Examples of the intermetallic compound phase of Mb and rare earth (R) include, for example, Ce₂Fe₁₇, Ce₂Fe₂, Nd₂Fe₁₇, Pr₂Fe₁₇, PrFe₂, Sm₂Fe₁₇, SmFe_Three, SmFe₂, Ce_{twenty four}Co₁₁, CeCo₂, CeCo_Three, Ce₂Co₇, Ce_FiveCo₁₉, Ce₂Co₁₇, CeCo_Five, LaCo₁₃, LaCo_Five, La_FiveCo₁₉, Α-La₂Co₇, Β-La₂Co₇, La₂Co_Three, La₂Co_1.7, LaCo, Nd₂Co₁₇, NdCo_Five, Nd_FiveCo₁₉, Nd₂Co₇, NdCo_Three, NdCo₂, Α-Nd₂Co_Three, Β-Nd₂Co_Three, Nd₂Co_1.7, Nd₇Co_Three, Nd_ThreeCo, Pr₂Co₁₇, PrCo_Five, Pr_FiveCo₁₉, PrCo_Three, Pr₂Co₇, PrCo₂, Pr₂Co_1.7, Pr_FiveCo₂, Pr_ThreeCo, α-Sm₂Co₁₇, Β-Sm₂Co₁₇, SmCo_Three, SmCo₂, Sm₉Co_Four, Sm_ThreeCo, Ce₇Ni_Three, CeNi, CeNi₂, CeNi_Three, Ce₂Ni₇, CeNi_Five, La_ThreeNi, La₇Ni_Three, LaNi, La₂Ni_Three, La₇Ni₁₆, LaNi_Three, Α-La₂Ni₇, Β-La₂Ni₇, LaNi_Five, Nd_ThreeNi, Nd₇Ni_Three, NdNi, NdNi₂, NdNi_Three, Nd₂Ni₇, NdNi_Five, Nd₂Ni₁₇, Pr_ThreeNi, Pr₇Ni_Three, PrNi, PrNi₂, PrNi_Three, Pr₂Ni₇, PrNi_Five, Sm_ThreeNi, SmNi, SmNi₂, SmNi_Three, Sm₂Ni₇, Sm_FiveNi₁₉, SmNi_Five, Sm₂Ni₁₇, CeCu₆, CeCu_Four, CeCu₂, CeCu, LaCu₆, LaCu, NdCu₆, NdCu_Five, NdCu_Four, Nd₂Cu₇, NdCu₂, NdCu, PrCu₆, PrCu_Four, PrCu_Five, PrCu₂, PrCu, SmCu₆, SmCu_Four, SmCu_Five, Sm₂Cu₇, SmCu₂, SmCu, CeB_Four, CeB₆, LaB_Four, LaB₆, LaB₉, Nd₂B_Five, NdB_Four, NdB₆, NdB₆₆, Sm₂B_Five, SmB_Four, SmB₆, SmB₆₆, CeMg₁₂, Ce_FiveMg₄₁, CeMg_Three, CeMg₂, CeMg, CeMg_10.3, LaMg₁₂, La₂Mg₁₇, LaMg_Three, LaMg₂, LaMg and the like.
[0014]
As the intermetallic compound phase of Mb and Sn, for example, Ti_ThreeSn, Ti₂Sn, Ti_FiveSn_Three, Α-Ti₆Sn_Five, Β-Ti₆Sn_Five, V_ThreeSn, V₂Sn_Three, Fe_FiveSn_Three, Fe_ThreeSn₂, FeSn, FeSn₂, Α-Co_ThreeSn₂, Β-Co_ThreeSn₂, CoSn, CoSn₂, Ni_ThreeSn, Ni_ThreeSn₂, Ni_ThreeSn_Four, Cu₆Sn_Five, Cu_ThreeSn, Mg₂Sn, Zr_FourSn, Zr_FiveSn_Three, ZrSn_Three, Hf_FiveSn_Three, Hf_FiveSn_Four, HfSn, HfSn₂, Nb_ThreeSn, Nb₆Sn_Five, NbSn₂, Mo_ThreeSn, MoSn₂Etc.
[0015]
Examples of the intermetallic compound phase of Ma and rare earth (R) include CeB_Four, CeB₆, LaB_Four, LaB₆, LaB₉, Nd₂B_Five, NdB_Four, NdB₆, NdB₆₆, PrB_Four, PrB₆, Sm₂B_Five, SmB_Four, SmB₆, SmB₆₆, Ce₂C_Three, Α-CeC₂, Β-CeC₂, La₂C_Three, Α-LaC₂, Β-LaC₂, Pr₂C_Three, Α-PrC₂, Β-PrC₂, Ce_FiveSi_Three, Ce_ThreeSi₂, Ce_FiveSi_Four, CeSi, Ce_ThreeSi_Five, CeSi₂, Nd_FiveSi_Three, Nd_FiveSi_Four, NdSi, Nd_ThreeSi_Four, Α-Nd₂Si_Three, Β-Nd₂Si_Three, Α-Pr_FiveSi_Three, Β-Pr_FiveSi_Three, Pr_FiveSi_Four, PrSi, Pr_ThreeSi_Four, Α-PrSi₂, Β-PrSi₂, Sm_FiveSi_Three, Sm_FiveSi_Four, SmSi, Sm_ThreeSi_Five, Α-SmSi₂, Β-SmSi₂, PrP, PrP₂, PrP_Five, PrP₇, Α-Al₁₁Ce_Three, Β-Al₁₁Ce_Three, Al_ThreeCe, Al₂Ce, AlCe, α-AlCe_Three, Β-AlCe_Three, Α-Al₁₁La_Three, Β-Al₁₁La_Three, Al_ThreeLa, Al₂La, AlLa, AlLa_Three, Α-Al₁₁Nd_Three, Β-Al₁₁Nd_Three, Al_ThreeNd, Al₂Nd, AlNd, AlNd_Three, Α-Al₁₁Pr_Three, Β-Al₁₁Pr_Three, Al_ThreePr, Al₂Pr, α-AlPr, β-AlPr, AlPr₂, Α-AlPr_Three, Β-AlPr_Three, Al_ThreeSm, Al₂Sm, AlSm, AlSm₂, CeZn, CeZn₂, CeZn_Three, Ce_ThreeZn₁₁, Ce₁₃Zn₅₈, CeZn_Five, Ce_ThreeZn_{twenty two}, Ce₂Zn₁₇, CeZn₁₁, LaZn, LaZn₂, LaZn_Four, LaZn₈, LaZn₁₃, NdZn, NdZn₂, NdZn_Three, Nd_ThreeZn₁₁, Nd₁₃Zn₅₈, Nd_ThreeZn_{twenty two}, NdZn₁₁, NdZn₁₂, Nd₂Zn₁₇, PrZn, α-PrZn₂, Β-PrZn₂, PrZn_Three, Pr_ThreeZn₁₁, Pr₁₃Zn₅₈, Pr_ThreeZn_{twenty two}, Α-Pr₂Zn₁₇, Β-Pr₂Zn₁₇, PrZn₁₁, SmZn, α-SmZn₂, Β-SmZn₂, SmZn_Three, Sm_ThreeZn₁₁, Sm₁₃Zn₅₈, Sm_ThreeZn_{twenty two}, Sm₂Zn₁₇, Nd₆Mn_{twenty three}, NdMn₂, Mn_{twenty three}Pr₆, Mn_{twenty three}Sm₆, Mn₂Sm, Cu₆Ce, Cu_FiveCe, Cu_FourCe, Cu₂Ce, CuCe, α-Cu₆La, β-Cu₆La, Cu_FiveLa, Cu_FourLa, Cu₂La, CuLa, Cu₆Nd, Cu_FiveNd, Cu_FourNd, Cu₇Nd₂, Cu₂Nd, CuNd, Cu₆Pr, Cu_FourPr, Cu₂Pr, CuPr, Cu₆Sm, Cu_FiveSm, Cu_FourSm, Cu₇Sm₂, Cu₂Sm, CuSm, Ag_FourCe, Ag₅₁Ce₁₄, Α-Ag₂Ce, β-Ag₂Ce, γ-Ag₂Ce, α-AgCe, β-AgCe, α-Ag_FiveLa, β-Ag_FiveLa, Ag₅₁La₁₄, Ag₂La, AgLa, Ag₅₁Nd₁₄, Α-Ag₂Nd, β-Ag₂Nd, AgNd, Ag_FivePr, Ag₅₁Pr₁₄, Α-Ag₂Pr, β-Ag₂Pr, AgPr, Ag₅₁Sm₁₄, Α-Ag₂Sm, β-Ag₂Sm, AgSm, Ce_ThreeIn, Ce₂In, Ce_ThreeIn_Five, CeIn₂, CeIn_Three, In_ThreeLa, In₂La, In_FiveLa_Three, InLa, InLa₂, InLa_Three, Nd_ThreeIn, Nd₂In, NdIn, Nd_ThreeIn_Five, NdIn_Three, Pr_ThreeIn, Pr₂In, Pr_ThreeIn_Five, PrIn_Three, Sm_ThreeIn, Sm₂In, SmIn, Sm_ThreeIn_Five, SmIn_Three, Ce₂Sb, Ce_FiveSb_Three, Ce_FourSn_Three, CeSb, CeSn₂, La₂Sb, La_ThreeSn₂, LaSb, LaSb₂, Nd₂Sb, Nd_FiveSb_Three, Nd_FourSn_Three, NdSb, NdSb₂, Pr₂Sb, Pr_FiveSn_Three, Pr_FourSb_Three, Α-PrSb, β-PrSb, Sb₂Sm, SbSm, Sb_ThreeSm_Four, Α-Sb_ThreeSm_Five, Β-Sb_ThreeSm_Five, La_FivePb_Three, La_FourPb_Three, La_FivePb_Four, Α-La_ThreePb_Four, Β-La_ThreePb_Four, LaPb₂, LaPb_Three, Ce₂Pb, CePb, CePb_Three, Pb_ThreePr, Pb₂Pr, Pb_FourPr_Three, Pb_TenPr₁₁, Pb_FourPr_Five, Pb_ThreePr_Five, PbPr_Three, Pb_ThreeSm, Pb₂Sm, Pb_TenSm₁₁, Pb_FourSm_Five, Pb_ThreeSm_Five, PbSm_Three, La₂Bi, La_FiveBi_Three, La_FourBi_Three, LaBi, LaBi₂, Ce₂Bi, Ce_FiveBi_Three, Ce_FourBi_Three, CeBi, CeBi₂, Bi₂Pr, BiPr, Bi_ThreePr_Five, BiPr₂, Nd₂Bi, Nd_FiveBi_Three, Nd_FourBi_Three, NdBi, NdBi₂Etc.
[0016]
Examples of the intermetallic compound phase of Ma and Sn include Sn_FourP_Three, Sn_ThreeP_Four, SnP_Three, V_ThreeSn, V₂Sn_Three, Mn_ThreeSn, Mn₂Sn, MnSn₂, Cu₆Sn_Five, Cu_ThreeSn, Ag_ThreeSn, Ag_FourSn etc. are mentioned.
[0017]
As the rare earth (R) and Sn intermetallic compound phase, RSn_3-X(X = rational number, 0 <X <3)_ThreeSn, α-Ce_FiveSn_Three, Β-Ce_FiveSn_Three, Ce_FiveSn_Four, Ce₁₁Sn_Ten, Ce_ThreeSn_Five, Ce_ThreeSn₇, Ce₂Sn_Five, Α-La_FiveSn_Three, Β-La_FiveSn_Three, La_FiveSn_Four, La₁₁Sn_Ten, LaSn, La₂Sn_Three, La_ThreeSn_Five, PrSn_Three, Α-Pr_FiveSn_Three, Β-Pr_FiveSn_Three, Pr_FiveSn_Four, PrSn, α-Pr_ThreeSn_Five, Β-Pr_ThreeSn_Five, Nd_FiveSn_Three, Nd_FiveSn_Four, Nd₁₁Sn_Ten, NdSn, Nd_ThreeSn_Five, NdSn₂, Nd₂Sn₇, Nd₂Sn_Five, Sm_FiveSn_Three, Sm_FourSn_Three, Sm₁₁Sn_Ten, Sm_FiveSn_Four, Sm₂Sn_Three, SmSn₂, SmSn_ThreeIs mentioned. RSn_3-XPhase is RSn_ThreeIt is a phase with less Sn content compared to the phase. In other words, it is a phase with a small amount of Sn storage, RSn_ThreeCompared with the phase, the volume expansion associated with the insertion and release of Li is small. This phase causes a decrease in charge / discharge capacity when the ratio in the alloy increases, but if present in the alloy to some extent, it has the effect of relaxing the volume expansion associated with the insertion and extraction of Li.
[0018]
In order to use the alloy represented by the formula (1) as the active material of the negative electrode material, it can be usually used in the form of a powder, and its average particle size is 0.1 to 25 μm in order to suppress the pulverization of the powder. It is preferable. The average particle size of crystals contained in the powdered alloy is preferably 15 μm or less, particularly preferably 10 μm or less, in order to suppress cycle deterioration. If the average grain size of the crystal is less than 0.1 μm, the alloy powder is suppressed from being pulverized, but the surface area is increased and the oxygen value is extremely increased, leading to a decrease in charge / discharge efficiency and a decrease in charge / discharge capacity. This is not preferable.
[0019]
  In addition to the composition of formula (1), the alloy represented by formula (1) may contain oxygen and / or nitrogen or the like due to its production process. The oxygen is present mainly on the surface of the alloy particles as an oxide with rare earth (R) or Sn, and forms an oxide film to exhibit a function of relaxing the volume expansion of the alloy accompanying Li charge / discharge. If the ratio of such an oxide is too small, the cycle deterioration becomes severe, and if it is too large, the diffusion of Li ions into the alloy is hindered, the charge / discharge capacity is lowered and the stored Li is oxidized and charged. The discharge efficiency will be reduced. Therefore, the content ratio of the oxygen element contained in the alloy is 0.05 to 5mass%Is preferable, and further 0.10 to 3mass%Is particularly preferred.
  Similarly, the nitrogen contained in the alloy can also improve the cycle life by containing an appropriate amount. Therefore, the content ratio of nitrogen element contained in the alloy is 0.0005-2.mass%Is preferable, and further 0.0005 to 0.5mass%Is particularly preferred.
[0020]
Production of the negative electrode material of the present invention includes, for example, a process (a) for producing a molten alloy having a composition represented by the formula (1), a process (b) for cooling and solidifying the molten alloy, and a cooling and solidification process. In addition to being obtained by the production method of the present invention including the step (c) of heat-treating the alloy under specific conditions, the method includes the steps (a) and (b) and does not include the step (c). Can also be obtained.
[0021]
In the step (a), the raw material of the molten alloy may be a mixture of simple metals constituting the composition represented by the formula (1), or a mother alloy prealloyed may be used. A known method can be used to manufacture the molten alloy, but the high frequency melting method is preferable, and the arc melting method and the mechanical alloying method are not preferable because residual metal Sn tends to increase in the obtained alloy. The atmosphere for producing the molten alloy is preferably an inert gas atmosphere to prevent oxidation of the molten metal. Further, in order to improve the yield of the raw material, it may be melted by shifting the timing of introducing the individual raw materials.
[0022]
In the step (b), for cooling the molten alloy, a known cooling method such as a die casting method, an atomizing method, a roll cooling method, a rotating electrode method, or the like can be used. The atmosphere for cooling the molten alloy is preferably an inert gas atmosphere in order to prevent oxidation of the resulting alloy.
Although it is desirable that the structure of the cooled and solidified alloy obtained in the step (b) does not contain a Sn single phase, it is possible to reduce the Sn single phase in the next step or the like. It may contain a phase. Therefore, when the content ratio of the Sn single phase is small in the step (b), the step (c) is not necessarily performed.
[0023]
Step (c) is a heat treatment step aimed at homogenizing the structure of the cooled and solidified alloy obtained in step (b), improving crystallinity, reducing residual metal Sn, and the like. Step (c) can be performed in a rare gas and / or hydrogen gas atmosphere of 0.07 to 10 MPa in order to prevent oxidation of the cooled and solidified alloy and to improve the activity. When a mixed gas of a rare gas and hydrogen gas is used, a mixed gas containing 5% by volume or more of hydrogen gas is preferable. When the pressure of the atmospheric gas is high under a reduced pressure of less than 0.07 MPa, Sn in the alloy tends to precipitate on the surface by heat treatment, and when a battery is produced and evaluated with such a material, the cycle life is reduced. There is a tendency to let you.
In the step (c), the alloy cooled in the step (b) is held in the temperature range of 100 to 1150 ° C. for 1 minute to 100 hours in the atmosphere. When the heat treatment temperature is less than 100 ° C., the diffusion of residual metals Sn and Li 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 treated, the heat treatment apparatus used and the like. If it is less than 1 minute, the effect of heat treatment does not appear, and if it exceeds 100 hours, the economy is impaired. Preferably, it is 30 minutes to 48 hours.
[0024]
When the alloy obtained by step (b) contains a residual Sn single phase that adversely affects cycle characteristics, it can be reduced by the above step (c), but in order to further reduce the residual Sn single phase, in step (c) A step (d) of sieving the obtained alloy after pulverization can also be performed.
In the step (d), the pulverization can be performed by mechanical pulverization or the like. The reason why the Sn single phase can be removed from the pulverized alloy by sieving is that the ductility of the metal Sn is larger than the intermetallic compound in the alloy, so the intermetallic compound is preferentially pulverized, and the Sn single phase This is because the particle size becomes large. The standard of the particle size when sieving is preferably 25 to 200 μm, and particularly preferably 50 to 100 μm.
[0025]
The negative electrode for lithium ion secondary batteries of the present invention contains the negative electrode material of the present invention as an active material, and can be obtained according to any known electrode manufacturing method. For example, a suitable binder is mixed with the powder of the negative electrode material of the present invention, and a suitable 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 obtained slurry is applied to an electrode substrate (current collector) such as a rolled copper foil or electrolytic copper foil using a doctor blade or the like, dried, and then consolidated by a method such as roll rolling to consolidate the electrode active material. Can be manufactured.
[0026]
Examples of the binder include water-insoluble resins such as PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), and PTFE (polytetrafluoroethylene), and 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.
Examples of the conductive powder include carbon materials such as acetylene black, ketjen black, and graphite; and metals such as Ni. In particular, a carbon material is preferable because it can occlude Li between the layers, and thus contributes to the charge / discharge capacity of the negative electrode in addition to conductivity.
[0027]
  In producing the negative electrode of the present invention, the negative electrode material of the present invention used as an active material is usually 50 to 100 in the active material.mass%, Especially 80-100mass%It is preferable to contain. In particular, in the negative electrode material of the present invention, the alloy having the composition represented by the formula (1) does not contain Li or contains only Li that is less than the initial irreversible necessary for the desired composition alloy. In the case of an alloy, in addition to the negative electrode material of the present invention as an active material, metal Li, LiH (lithium hydride), Li_ThreeA lithium source such as N (lithium nitride) can be included.
  By using such a lithium supply source, the irreversible amount of Li at the time of initial charge / discharge is compensated, but if the content of the lithium supply source in the negative electrode active material is too large, there is a risk of handling problems. There is. Further, since the lithium supply source has a low density, if the content ratio in the negative electrode active material is excessively increased, the energy density of the battery is lowered. Therefore, the content ratio in the active material when using a lithium source is 50% considering the initial charge / discharge efficiency of the alloy composition.mass%Less than 20mass%Less than is preferable.
[0028]
The lithium ion secondary battery of the present invention only needs to include the negative electrode of the present invention, and usually includes the negative electrode of the present invention, a positive electrode, a separator, and a nonaqueous electrolyte such as a polymer electrolyte as a basic structure. These battery constituent materials can be configured by appropriately combining known materials except for the negative electrode. The shape of the secondary battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a coin shape, a seal shape, and the like.
[0029]
【Example】
  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these. The raw materials used in the examples were 99.5% or more. Misch metal (Mm)Mass ratioThen, a rare earth alloy manufactured by Santoku Co., Ltd. having La: Ce: Nd: Pr: Sm of 28: 51: 16: 4: 1 was used.
  Examples 1-11 and Comparative Examples 1-2
Preparation of anode material alloy for lithium ion secondary battery
  After high-frequency melting of the metal mixture constituting the composition shown in Table 1, the resulting molten metal is cast by a mold casting method using a copper mold (mold method), or a molten metal is poured through a tundish into a rotating roll. Flaked alloy pieces were obtained by the casting method (SC method). Next, heat treatment was performed under the conditions shown in Table 1. Each alloy piece not subjected to heat treatment and each alloy piece subjected to heat treatment were pulverized by a mechanical pulverization method in an argon gas atmosphere, and classified to 25 μm or less using a sieve to produce an anode material alloy. The production of the molten alloy and the cooling of the molten alloy were each performed in an argon gas atmosphere.
  Next, the composition of each obtained powder alloy was measured by elemental analysis, and the composition shown in Table 1 was confirmed. The constituent phase of each powder alloy was measured by powder X-ray diffraction (XRD), and the precipitation ratio of residual metal Sn in the constituent phase was defined as (W), and was calculated and evaluated by the following formula. The results are shown in Table 1.
(W) = (peak intensity of metal Sn (2 0 0) plane / RSn_ThreeThe strongest peak intensity among the peaks derived from
[0030]
Preparation of negative electrode for lithium ion secondary battery and charge / discharge test method
  The above-prepared alloy powder as a negative electrode active material, ketjen black as a conductive additive, and PVDF as a binder.Mass ratioAfter mixing with 85: 5: 10 and kneading with an appropriate amount of NMP, it was 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 obtained test electrode, a polypropylene porous film as a separator, metallic lithium as a counter electrode, and a mixed solvent of ethylene carbonate (EC): dimethyl carbonate (DMC) = 1: 2 (volume ratio) as an electrolytic solution LiPF₆A bipolar cell was prepared using a solution in which was dissolved at a concentration of 1 mol. This cell has a current density of 0.2mA / cm at a temperature of 25 ° C.²0 ~ 1.0V vs. Li / Li⁺The constant current charge / discharge test was conducted in the potential range. Further, the capacity retention rate (S) as an index indicating how much the maximum discharge capacity was maintained at the 50th cycle was calculated and evaluated by the following formula.
(S) = 50th cycle discharge capacity / maximum discharge capacity x 100 (%)
  Furthermore, the initial charge / discharge efficiency (Z) as an index indicating the ratio of the initial discharge capacity to the initial charge capacity was calculated and evaluated by the following equation.
  (Z) = Initial discharge capacity / Initial charge capacity x 100 (%)
  The results are shown in Table 1. The cell assembly and charge / discharge test were performed in a glove box under an argon gas atmosphere.
[0031]
Comparative example Three
A charge / discharge test was conducted in the same manner as in Example 1 except that artificial graphite was used as the test electrode. The results are shown in Table 1.
[0032]
[Table 1]

[0033]
  Example 1 to Table 111 Is the firstExcellent initial discharge capacity and initial charge / discharge efficiency.Especially heatIt can be seen that the treatment improves the cycle life. It can be seen that Comparative Examples 1 and 2 having compositions containing no rare earth element have low discharge capacity and cycle characteristics. Examples 1 to11The discharge capacity per weight is 1.5 times higher than that of the graphite of Comparative Example 3, and the initial charge / discharge efficiency is almost the same value as that of graphite, indicating that the negative electrode of this example exhibits excellent discharge characteristics. .
[0034]
  Example12 ~ twenty threeAnd Comparative Examples 4-5
  The alloy composition was changed to the composition shown in Table 2, and the heat treatment conditions of the alloy pieces were changed to the conditions shown in Table 2, in the same manner as in Example 1, measurement of the precipitation ratio (W) of the residual metal Sn, production of the cell, and A charge / discharge test (initial discharge capacity and initial charge / discharge efficiency) was conducted. The results are shown in Table 2.
[0035]
[Table 2]

[0036]
  From Table 2, Examples12 ~ twenty threeIt can be seen that the initial discharge capacity is clearly increased as compared with Comparative Examples 4 and 5 in which the ratio of the substitution element (Ma) is outside the scope of the present invention.
[0037]
  Exampletwenty four ~ 45And Comparative Example 6
  The alloy composition was changed to the composition shown in Table 3, and the heat treatment conditions of the alloy pieces were changed to the conditions shown in Table 3, in the same manner as in Example 1, measurement of the precipitation ratio (W) of the residual metal Sn, the production of the cell and A charge / discharge test (initial charge / discharge efficiency and capacity retention rate at the 50th cycle) was conducted. The results are shown in Table 3.
[0038]
[Table 3]

[0039]
  From Table 3, in Comparative Example 6 having a substitution element other than the substitution element (Mb) in the present invention, an example having a substitution element (Mb)twenty four ~ 45It can be seen that the capacity retention rate is clearly inferior to that. Further, in the examples in which the cycle life using the heat-treated alloy is improved, the XRD measurement shows that the intermetallic compound phase of the substitution element (Mb) and the rare earth (R), the substitution element (Mb) and Sn The intermetallic phase of RSn_ThreeIt was confirmed that the phase (R <0) and the substitution element (Mb) alone were precipitated in a complex manner.
[0040]
  Example46 ~ 59And Comparative Examples 7-8
  The alloy composition was changed to the composition shown in Table 4, and the heat treatment conditions of the alloy pieces were changed to the conditions shown in Table 4, as in Example 1, measurement of the precipitation ratio (W) of the residual metal Sn, the production of the cell, and A charge / discharge test was conducted. The results are shown in Table 4.
[0041]
[Table 4]

[0042]
  Examples containing substitutional elements (Ma, Mb)46 ~ 59Therefore, compared with Comparative Examples 7 and 8 in which the content ratio of Sn is lower than the range of the present invention and the content ratio of substitutional elements (Ma, Mb) is higher than the range of the present invention, it shows a high initial discharge capacity. I understand.
[0046]
  Example60 ~ 61
  tableFiveAn alloy piece containing the oxygen content and the nitrogen content shown in Table 1 was prepared in the same manner as in Example 1, and the measurement of the precipitation ratio (W) of the residual metal Sn, the production of the cell, and the charge / discharge test were performed. Table resultsFiveShown in
[0047]
[Table 5]

[0048]
【The invention's effect】
Since the negative electrode material for lithium ion secondary batteries of the present invention uses the negative electrode material of the present invention containing an alloy having a specific composition as an active material, it is excellent in initial charge / discharge efficiency, cycle deterioration associated with charge / discharge is suppressed, and particularly excellent Discharge capacity is achieved. Moreover, the negative electrode material of the present invention is useful for the production of such a negative electrode. Therefore, the negative electrode material and the negative electrode of the present invention can make a lithium ion secondary battery using a carbon material negative electrode, which is currently in practical use, higher in capacity and more compact, and has an industrial utility value. high.

Claims

Includes an alloy having a composition represented by the formula (1), and a negative electrode material for a lithium ion secondary battery alloy contains 0.0005 wt% to 0.05 to 5% by weight and / or nitrogen oxygen.
(Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50, 0 ≦ w ≦ 0.70, 0 ≦ v ≦ 0.70, 0 ≦ w + v ≦ 0.70.)

A negative electrode material for a lithium ion secondary battery comprising an alloy having a composition represented by formula (1).
(Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(In the formula, R is one or more selected from the group consisting of elements from the lanthanoid series La to Lu containing Y and Sc, Ma is B, C, Si, P, Al, Zn, V, Mn One or more selected from the group consisting of Cu, Ag, In, Sb, Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, One or two or more selected from the group consisting of Nb, Ta and Mo and Ma ≠ Mb, where x, y and z are molar ratios, respectively 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50, 0 < w ≦ 0.70 , 0 ≦ v ≦ 0.70, 0 < w + v ≦ 0.70 .)

formula (1) The negative electrode material for lithium ion secondary batteries containing the alloy which has a composition represented by these.
(Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
( Where R Is Y , Sc Lanthanoid series including La From Lu Selected from the group consisting of up to 1 Seed or 2 More than species, Ma Is B , C , Si , P , Al , Zn , V , Mn , Cu , Ag , In , Sb , Pb as well as Bi Selected from the group consisting of 1 Seed or 2 More than species, Mb Is Ti , V , Cr , Fe , Co , Ni , Cu , B , Mg , Zr , Hf , Nb , Ta as well as Mo Selected from the group consisting of 1 Seed or 2 More than seeds Ma ≠ Mb . x , y , z Is the molar ratio, 0 ≦ x ≦ 13 , 0.70 ≦ y ≦ 1.10 , 2.20 ≦ z ≦ 3.50 , 0 ≦ w ≦ 0.70 , 0 < v ≦ 0.70 , 0 < w + v ≦ 0.70 It is. )

R in formula (1) according to any one of claims 1 to 3 is Ce alone or from a group consisting of elements of elements from La to Lu containing Y and Sc other than Ce and less than 90 mol% of Ce. The negative electrode material according to any one of claims 1 to 3, wherein the negative electrode material comprises one or more selected.

The peak intensity of Sn (2 0 0) plane in powder X-ray diffraction of the alloy represented by formula (1) according to any one of claims 1 to 3 is RSn ₃ phase (R is formula (1) The negative electrode material according to any one of claims 1 to 4, which is 30% or less of the strongest peak intensity among the peaks derived from (same as R in the middle).

The alloy represented by the formula (1) according to any one of claims 1 to 3, wherein an intermetallic compound phase of Ma and rare earth (R), an intermetallic compound phase of Mb and rare earth (R), Ma claim 1-5 having intermetallic compound phase with Sn, intermetallic phase between Mb and Sn, at least one intermetallic phase of intermetallic phases of Sn and rare earth (R) The negative electrode material according to 1.

The intermetallic compound phase of rare earth (R) and Sn is RSn _3-X (R is the same as R in formula (1)), X = rational number, 0 <X <3) The negative electrode material according to claim 6 .

The negative electrode material according to any one of claims 1 to 7 , wherein the alloy represented by the formula (1) according to any one of claims 1 to 3 is a powder having an average particle size of 0.1 to 25 µm.

Step (a) of producing a molten alloy having a composition represented by formula (1),
(Li) x (R) y (Sn) z (Ma) w (Mb) v ... (1)
(Wherein, R Y, 1 or more kinds of lanthanoid series La containing Sc is selected from the group consisting of elements up to Lu, Ma is B, C, Si, P, Al, Zn, V, Mn , Cu, Ag, in, Sb , 1 or two or more selected from the group consisting of Pb and Bi, Mb is Ti, V, Cr, Fe, Co, Ni, Cu, B, Mg, Zr, Hf, nb, 1 kind or Ma ≠ Mb of two or more selected from the group consisting of Ta, and Mo. x, y, z are each a molar ratio, 0 ≦ x ≦ 13, 0.70 ≦ y ≦ 1.10, 2.20 ≦ z ≦ 3.50 , 0 ≦ w ≦ 0.70 , 0 ≦ v ≦ 0.70 , 0 ≦ w + v ≦ 0.70 . )
A step (b) of cooling and solidifying the produced molten alloy, and a step of holding the cooled and solidified alloy in a temperature range of 100 to 1150 ° C. for 1 minute to 100 hours in a rare gas and / or hydrogen gas of 0.07 to 10 MPa ( The manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claims 1-8 containing c).

The production method according to claim 9, wherein the production of the molten alloy in the step (a) is performed by a high frequency melting method.

The method according to claim 9 or 10, further comprising a step (d) of pulverizing the alloy produced in the step (c) and then sieving to remove the Sn single phase part.

The negative electrode for lithium ion secondary batteries which contains the negative electrode material of any one of Claims 1-8 as an active material.

The negative electrode according to claim 12, wherein the active material further contains one or more selected from the group consisting of metals Li, LiH, and Li ₃ N.

The negative electrode according to claim 12 or 13, wherein the content of the negative electrode material according to any one of claims 1 to 8 in the active material is 50% by weight or more.

A lithium ion secondary battery provided with the negative electrode of any one of Claims 12-14.