JP4432128B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００２５】
【化８】

【００２６】
【化９】

【００２７】
【課題を解決するための手段】
本発明は、固相Ａからなる核粒子の周囲の全面または一部を、固相Ｂによって被覆した複合粒子で、前記固相Ａはケイ素、亜鉛の少なくとも一種を構成元素として含み、前記固相Ｂは固相Ａの構成元素であるケイ素、亜鉛のいずれかと、前記構成元素を除いて、周期表の２族元素、遷移元素、１２族元素、１３族元素、ならびに炭素を除く１４族元素からなる群から選ばれた少なくとも一種の元素との固溶体または金属間化合物である材料を用いることで固相Ａにより高容量、かつ固相Ｂが固相Ａの充放電でおきる膨張・収縮を抑える役割を担うことで充放電サイクル特性の優れた負極材料を用い、電解液に炭酸エチレン、炭酸ジメチル、炭酸ジエチル、炭酸エチルメチル、炭酸プロピレン、γ−ブチロラクトン、γ−バレロラクトンからなる群から選ばれた少なくとも一種の化合物を含む溶媒に支持電解質にビステトラフルオロメタンスルホン酸イミドリチウム、ビスペンタフルオロエタンスルホン酸イミドリチウム（（C₂F₅SO₂)₂NLi）、ビス（1,2-ベンゼンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,3-ナフタレンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,2'-ビフェニルジオレート（2-）−O,O'）ほう酸リチウム、ビス（5−フルオロ−2−オレート−1−ベンゼンスルホン酸−O,O’）ほう酸リチウムからなる群より選ばれる少なくとも一種の化合物を用いた場合に、高温保存時にガス発生が極めて少なく、また、くり返し充放電に際しても、負極の充放電効率が低下しないことを見出したことに基づき、広い温度範囲で使用でき、高エネルギー密度かつ電池の繰り返し使用による放電容量の低下が少なく、かつ高率充放電特性に優れた新規な非水電解質二次電池を提供することを目的とする。
【００２８】
本発明の負極材料で固相Ａは高容量のケイ素、亜鉛の少なくともいずれかを構成元素として含むことから主として充放電容量の高容量化に寄与しているものと考えられる。また固相Ａからなる核粒子の周囲の全面または一部を被覆している固相Ｂは充放電サイクル特性の改善に寄与しているものと考えている。
【００２９】
また、該複合粒子の固相Ｂにはリチウムは吸蔵されず、固相Ａにのみ吸蔵される。そのために該複合粒子で電解液と接触するのは活性なリチウムを含まない固相Ｂのみであり、したがって、この相と電解液が接触した場合にでも電解液の分解が起こりにくいものと考えている。
【００３０】
一方、本発明の電解液は溶媒、支持電解質ともに熱的安定性が高く、電解液中にわずかに含まれる水分に対しても安定であるために、高温保存時におけるガス発生が極めて少ないものとなるものと考えられる。
【００３１】
【発明の実施の形態】
本発明に用いられる正極及び負極は、リチウムイオンを電気化学的かつ可逆的に挿入・放出できる正極活物質や負極材料に導電剤、結着剤等を含む合剤層を集電体の表面に塗着して作製されたものである。
【００３２】
本発明で用いられる負極材料は、固相Ａからなる核粒子の周囲の全面または一部を、固相Ｂによって被覆した複合粒子で、前記固相Ａはケイ素、亜鉛の少なくとも一種を構成元素として含み、前記固相Ｂは固相Ａの構成元素であるケイ素、亜鉛のいずれかと、前記構成元素を除いて、周期表の２族元素、遷移元素、１２族、１３族元素、ならびに炭素を除く１４族元素からなる群から選ばれた少なくとも一種の元素との固溶体、または金属間化合物である材料（以下、"複合粒子"と呼ぶ）である。
【００３３】
本発明に用いられる複合粒子の製造方法の一つとしては、複合粒子を構成する各元素の仕込み組成分の溶融物を、乾式噴霧法、湿式噴霧法、ロール急冷法及び回転電極法などで急冷、凝固させ、その凝固物を、仕込み組成から決まる固溶体または金属間化合物の固相線温度より低い温度で熱処理するという方法がある。（要変更）溶融物の急冷凝固により、核粒子として固相Ａ粒子、そしてその固相Ａ粒子の周囲の全面または一部を被覆する固相Ｂを析出させ、その後の熱処理により、各固相Ａ、Ｂの均一性を高めることを目的にしているが、熱処理をしない場合でも、請求項１記載の複合粒子を得ることができる。また上記冷却方法以外の方法においても十分に冷却可能な方法であれば用いることができる。
【００３４】
その他の製造方法としては、固相Ａの粉末の表面に、固相Ｂを形成するのに必要な固相Ａに含まれる元素以外の元素からなる付着層を形成させ、それを、仕込み組成から決まる固溶体または金属間化合物の固相線温度より低い温度で熱処理するという方法がある。この熱処理により、固相Ａ中の成分元素が付着層に拡散して、被覆層として固相Ｂが形成される。この付着層の形成方法としては、メッキ法またはメカニカルアロイング法などによって行うことができる。その他、付着層を形成可能な方法であれば用いることができる。メカニカルアロイング法においては熱処理を必要としなくてもよい。
【００３５】
本発明の請求項１に記載の発明は、上述で得た材料を負極に、正極としてリチウム含有の遷移金属酸化物を用い、電解質として高耐酸化性有機溶媒に有機酸アニオン系リチウム塩を溶解したものを用いたことを特徴としたものである。
【００３６】
前記複合粒子は、高容量で、繰り返し充放電による放電容量の低下が少なく、かつ高率充放電特性が優れたもので、該負極とリチウムの吸蔵・放出が可能な正極と、電解質に高耐酸化性有機溶媒に有機酸アニオン系リチウム塩を溶解したものを用いることで高容量・高エネルギー密度で、かつ高い信頼性を有する電池を達成するものである。
【００３７】
本発明に用いられる非水電解質は、溶媒と、その溶媒に溶解するリチウム塩とから構成されている。非水溶媒としては、炭酸エチレン（EC）、炭酸プロピレン（PC）、ブチレンカーボネート（BC）、炭酸ビニレン（VC）などの環状カーボネート類、炭酸ジメチル（DMC）、炭酸ジエチル（DEC）、炭酸エチルメチル（EMC）、ジプロピルカーボネート（DPC）などの鎖状カーボネート類、γ−ブチロラクトン、γ−バレロラクトン等の環状カルボン酸エステル類、１，２−ジメトキシエタン（DME）、１，２−ジエトキシエタン（DEE）、エトキシメトキシエタン（EME）等の鎖状エーテル類、テトラヒドロフラン、２−メチルテトラヒドロフラン等の環状エーテル類、ジメチルスルホキシド、１，３−ジオキソラン、ホルムアミド、アセトアミド、ジメチルホルムアミド、ジオキソラン、アセトニトリル、プロピルニトリル、ニトロメタン、エチルモノグライム、リン酸トリエステル、トリメトキシメタン、ジオキソラン誘導体、スルホラン、メチルスルホラン、１，３−ジメチル−２−イミダゾリジノン、３−メチル−２−オキサゾリジノン、炭酸プロピレン誘導体、テトラヒドロフラン誘導体、エチルエーテル、１，３−プロパンサルトン、アニソール、ジメチルスルホキシド、Ｎ−メチルピロリドン、などの非プロトン性有機溶媒を挙げることができ、これらの一種または二種以上を混合して使用することができる。
【００３８】
請求項２に記載の発明は、請求項１記載の高耐酸化性有機溶媒として炭酸エチレン、炭酸ジメチル、炭酸ジエチル、炭酸エチルメチル、炭酸プロピレン、γ−ブチロラクトン、γ−バレロラクトンを含む電解液としたものである。炭酸プロピレンは従来、リチウムイオン二次電池に多く用いられている黒鉛系材料では電極との接触により、分解し、適用は困難であった。また、γ−ブチロラクトン、γ−バレロラクトンは還元分解電位が、金属リチウムあるいはリチウム合金の電極電位よりも貴であるため、これら金属を負極に用いた電池では適用が困難であった。しかしながら、本発明の複合粒子を負極に用いた場合、その電極電位はγ−ブチロラクトン、γ−バレロラクトンの還元分解電位より貴であるため、電解液が分解することなく、適用することができる。さらに、炭酸プロピレン、γ−ブチロラクトン、γ−バレロラクトンは誘電率が高く、すなわち粘度が高いため、万一、負極の複合粒子が微細化した場合でも、その粘度の高さのため、極板から脱離しにくいといった好ましい作用も生じる。
【００３９】
また、炭酸エチレン、炭酸ジメチル、炭酸ジエチル、炭酸エチルメチル、炭酸プロピレン、γ−ブチロラクトン、γ−バレロラクトンといった溶媒は金属リチウム、およびリチウム合金を負極とした系に用いた場合には、充電状態の電池を高温で保存した場合に電解液が分解し、ガスが発生したり、あるいは繰り返し充放電を行った場合には、負極の充放電反応と平行して、電解液のガス化反応がおこり、充放電効率を低下せしめ、結果としてサイクル特性が低下するといった課題があったが、本発明の複合粒子を負極に用いた場合には、これら電解液との反応性は認められない。
【００４０】
これらの溶媒に溶解するリチウム塩としては、例えばLiClO₄ 、LiBF₄ 、LiPF₆ 、LiAlCl₄、LiSbF₆、LiSCN、LiCF₃SO₃ 、LiCF₃CO₂ 、Li(CF₃SO₂)₂、LiAsF₆ 、LiB₁₀Cl₁₀、低級脂肪族カルボン酸リチウム、LiCl、LiBr、LiI、クロロボランリチウム、ビス（1,2-ベンゼンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,3-ナフタレンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,2'-ビフェニルジオレート（2-）−O,O'）ほう酸リチウム、ビス（5−フルオロ−2−オレート−1−ベンゼンスルホン酸−O,O’）ほう酸リチウム等のほう酸塩類、ビステトラフルオロメタンスルホン酸イミドリチウム（（CF₃SO₂)₂NLi）、ビスペンタフルオロエタンスルホン酸イミドリチウム（（C₂F₅SO₂)₂NLi）等のイミド塩類等を挙げることができ、これらを使用する電解液等に単独又は二種以上を組み合わせて使用することができる。また、これらのうち有機酸アニオン系リチウム塩は過塩素酸リチウム、りんふっ化リチウムに代表される無機酸アニオン系リチウム塩に比して、熱安定性にも優れており、高温使用時、あるいは高温保存時において、これら支持電解質が熱分解し、電池の特性を劣化させることはなく、より好ましく用いられる。
【００４１】
請求項３に記載の発明は請求項１記載の有機アニオン系リチウム塩をビステトラフルオロメタンスルホン酸イミドリチウム（（CF₃SO₂)₂NLi）、ビスペンタフルオロエタンスルホン酸イミドリチウム（（C₂F₅SO₂)₂NLi）、ビス（1,2-ベンゼンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,3-ナフタレンジオレート（2-）-O,O'）ほう酸リチウム、ビス（2,2'-ビフェニルジオレート（2-）−O,O'）ほう酸リチウム、ビス（5−フルオロ−2−オレート−1−ベンゼンスルホン酸−O,O’）ほう酸リチウムからなる群より選ばれる少なくとも一種の化合物としたものである。
【００４２】
ビステトラフルオロメタンスルホン酸イミドリチウム（（CF₃SO₂)₂NLi）については白金電極上での還元分解耐圧がリチウム基準極に対して0V、酸化分解耐電圧が同4.7Vであり、ビスペンタフルオロエタンスルホン酸イミドリチウム（（C₂F₅SO₂)₂NLi）については白金電極上での還元分解耐圧が同0V、酸化分解耐電圧が同4.7Vであって、また、ビス（5−フルオロ−2−オレート−1−ベンゼンスルホン酸−O,O’）ほう酸リチウムは白金電極上での還元分解耐圧が同0V、酸化分解耐電圧が同4.5Vで、またビス（2,2'-ビフェニルジオレート（2-）−O,O'）ほう酸リチウムは白金電極上での還元分解耐圧が同0V、酸化分解耐電圧が同4.1V以上である。従ってこれらの有機酸アニオンリチウム塩はコバルト酸リチウムやニッケル酸リチウム、マンガン酸リチウムといったリチウム基準極に対して4V以上の高電圧を発生する活物質に適用することは、リチウム二次電池の高エネルギー密度化の点で好ましい。
【００４３】
一方、ビス（1,2-ベンゼンジオレート（2-）-O,O'）ほう酸リチウムは白金電極上での還元分解耐圧がリチウム基準極に対して0V、酸化分解耐電圧が同3.6Vであり、ビス（2,3-ナフタレンジオレート（2-）-O,O'）ほう酸リチウムは白金電極上での還元分解耐圧が同0V、酸化分解耐電圧が同3.8Vである。これらの支持電解質を溶解した電解液をコバルト酸リチウムやニッケル酸リチウム、マンガン酸リチウムといったリチウム基準極に対して4V以上の高電圧を発生する活物質に適用することは支持電解質の分解を伴う。しかしながら、二硫化チタンリチウム（LiTiS₂）やに硫化モリブデンリチウム（LiMoS₂）といったリチウム基準極に対して3V程度の起電力である遷移金属硫化物はこの電位領域で使用可能である。
【００４４】
本発明において電解質を電池内に添加する量は、特に限定されないが、正極材料や負極材料の量や電池のサイズによって必要量を用いることができる。支持電解質の非水溶媒に対する溶解量は、特に限定されないが、０．２〜２ｍｏｌ／ｌが好ましい。特に、０．５〜１．５ｍｏｌ／ｌとすることがより好ましい。
【００４５】
本発明に用いられる負極用導電剤は、電子伝導性材料であれば何でもよい。例えば、天然黒鉛（鱗片状黒鉛など）、人造黒鉛などのグラファイト類、アセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラック等のカ−ボンブラック類、炭素繊維、金属繊維などの導電性繊維類、フッ化カーボン、銅、ニッケル等の金属粉末類およびポリフェニレン誘導体などの有機導電性材料などを単独又はこれらの混合物として含ませることができる。これらの導電剤のなかで、人造黒鉛、アセチレンブラック、炭素繊維が特に好ましい。導電剤の添加量は、特に限定されないが、１〜５０重量％が好ましく、特に１〜３０重量％が好ましい。また、本発明の負極材料はそれ自身電子伝導性を有するため、導電剤を添加しなくても電池として機能させることは可能である。
【００４６】
本発明に用いられる負極用結着剤としては、熱可塑性樹脂、熱硬化性樹脂のいずれであってもよい。本発明において好ましい結着剤は、例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン（PTFE）、ポリフッ化ビニリデン（PVDF）、スチレンブタジエンゴム、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（FEP）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（PFA）、フッ化ビニリデン−ヘキサフルオロプロピレン共重合体、フッ化ビニリデン−クロロトリフルオロエチレン共重合体、エチレン−テトラフルオロエチレン共重合体（ETFE樹脂）、ポリクロロトリフルオロエチレン（PCTFE）、フッ化ビニリデン−ペンタフルオロプロピレン共重合体、プロピレン−テトラフルオロエチレン共重合体、エチレン−クロロトリフルオロエチレン共重合体（ECTFE）、フッ化ビニリデン−ヘキサフルオロプロピレン−テトラフルオロエチレン共重合体、フッ化ビニリデン−パーフルオロメチルビニルエーテル−テトラフルオロエチレン共重合体、エチレン−アクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−アクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体を挙げる事ができ、これらの材料を単独又は混合物として用いることができる。また、これらの材料の中でより好ましい材料は、スチレンブタジエンゴム、ポリフッ化ビニリデン、エチレン−アクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−アクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体である。
【００４７】
本発明に用いられる負極用集電体としては、構成された電池において化学変化を起こさない電子伝導体であれば何でもよい。例えば、材料としてステンレス鋼、ニッケル、銅、チタン、炭素、導電性樹脂などの他に、銅やステンレス鋼の表面にカーボン、ニッケルあるいはチタンを処理させたものなどが用いられる。特に、銅あるいは銅合金が好ましい。これらの材料の表面を酸化して用いることもできる。また、表面処理により集電体表面に凹凸を付けることが望ましい。形状は、フォイルの他、フィルム、シート、ネット、パンチングされたもの、ラス体、多孔質体、発泡体、繊維群の成形体などが用いられる。厚みは、特に限定されないが、１〜５００μｍのものが用いられる。
【００４８】
本発明に用いられる正極材料には、リチウム含有の化合物を用いることができる。例えば、Li_xCoO₂ 、Li_xNiO₂、Li_xMnO₂ 、Li_xCo_yNi_1-yO₂、Li_xCo_yM_1-yO_z、Li_xNi_1-yM_yO_z、Li_xMn₂O₄ 、Li_xMn_2-yM_yO₄ (M=Na、Mg、Sc、Y、Mn、Fe、Co、Ni、Cu、Zn、Al、Cr、Pb、Sb、Bのうち少なくとも一種）、（ここで0＜x≦1.2、0≦y≦0.9、2.0≦z≦2.3）があげられる。ここで、上記のｘ値は、充放電開始前の値であり、充放電により増減する。ただし、遷移金属カルコゲン化物、バナジウム酸化物のリチウム化合物、ニオブ酸化物のリチウム化合物、有機導電性物質を用いた共役系ポリマー、シェブレル相化合物等の他の正極活物質を用いることも可能である。また、複数の異なった正極活物質を混合して用いることも可能である。正極活物質粒子の平均粒径は、特に限定はされないが、１〜３０μｍであることが好ましい。
【００４９】
本発明で使用される正極用導電剤は、用いる正極材料の充放電電位において、化学変化を起こさない電子伝導性材料であれば何でもよい。例えば、天然黒鉛（鱗片状黒鉛など）、人造黒鉛などのグラファイト類、アセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラック等のカ−ボンブラック類、炭素繊維、金属繊維などの導電性繊維類、フッ化カーボン、銅、ニッケル、アルミニウム、銀等の金属粉末類、酸化亜鉛、チタン酸カリウムなどの導電性ウィスカー類、酸化チタンなどの導電性金属酸化物あるいはポリフェニレン誘導体などの有機導電性材料などを単独又はこれらの混合物として含ませることができる。これらの導電剤のなかで、人造黒鉛、アセチレンブラック、ニッケル粉末が特に好ましい。導電剤の添加量は、特に限定されないが、１〜５０重量％が好ましく、特に１〜３０重量％が好ましい。カーボンやグラファイトでは、２〜１５重量％が特に好ましい。
【００５０】
本発明に用いられる正極用結着剤としては、熱可塑性樹脂、熱硬化性樹脂のいずれであってもよい。本発明に於いて好ましい結着剤は、例えば、ポリエチレン、ポリプロピレン、ポリテトラフルオロエチレン（PTFE）、ポリフッ化ビニリデン（PVDF）、テトラフルオロエチレン−ヘキサフルオロエチレン共重合体、テトラフルオロエチレン−ヘキサフルオロプロピレン共重合体（FEP）、テトラフルオロエチレン−パーフルオロアルキルビニルエーテル共重合体（PFA）、フッ化ビニリデン−ヘキサフルオロプロピレン共重合体、フッ化ビニリデン−クロロトリフルオロエチレン共重合体、エチレン−テトラフルオロエチレン共重合体（ETFE樹脂）、ポリクロロトリフルオロエチレン（PCTFE）、フッ化ビニリデン−ペンタフルオロプロピレン共重合体、プロピレン−テトラフルオロエチレン共重合体、エチレン−クロロトリフルオロエチレン共重合体（ECTFE）、フッ化ビニリデン−ヘキサフルオロプロピレン−テトラフルオロエチレン共重合体、フッ化ビニリデン−パーフルオロメチルビニルエーテル−テトラフルオロエチレン共重合体、エチレン−アクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−アクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体、エチレン−メタクリル酸メチル共重合体または前記材料の（Na⁺）イオン架橋体を挙げる事ができる。特に、この中で最も好ましいのはポリフッ化ビニリデン（PVDF）、ポリテトラフルオロエチレン（PTFE）である。
【００５１】
本発明に用いられる正極用集電体としては、用いる正極材料の充放電電位において化学変化を起こさない電子伝導体であれば何でもよい。例えば、材料としてステンレス鋼、アルミニウム、チタン、炭素、導電性樹脂などの他に、アルミニウムやステンレス鋼の表面にカーボン、あるいはチタンを処理させたものが用いられる。特に、アルミニウムあるいはアルミニウム合金が好ましい。これらの材料の表面を酸化して用いることもできる。また、表面処理により集電体表面に凹凸を付けることが望ましい。形状は、フォイルの他、フィルム、シート、ネット、パンチされたもの、ラス体、多孔質体、発泡体、繊維群、不織布体の成形体などが用いられる。厚みは、特に限定されないが、１〜５００μｍのものが用いられる。
【００５２】
電極合剤には、導電剤や結着剤の他、フィラー、分散剤、イオン導伝剤、圧力増強剤及びその他の各種添加剤を用いることができる。フィラーは、構成された電池において、化学変化を起こさない繊維状材料であれば何でも用いることができる。通常、ポリプロピレン、ポリエチレンなどのオレフィン系ポリマー、ガラス、炭素などの繊維が用いられる。フィラーの添加量は特に限定されないが、０〜３０重量％が好ましい。
【００５３】
本発明における負極板と正極板の構成は、少なくとも正極合剤面の対向面に負極合剤面が存在していることが好ましい。
【００５４】
さらに、放電や充放電特性を改良する目的で、他の化合物を電解質に添加することも有効である。例えば、トリエチルフォスファイト、トリエタノールアミン、環状エーテル、エチレンジアミン、ｎ−グライム、ピリジン、ヘキサリン酸トリアミド、ニトロベンゼン誘導体、クラウンエーテル類、第四級アンモニウム塩、エチレングリコールジアルキルエーテル等を挙げることができる。
【００５５】
本発明に用いられるセパレータとしては、大きなイオン透過度を持ち、所定の機械的強度を持ち、絶縁性の微多孔性薄膜が用いられる。また、一定温度以上で孔を閉塞し、抵抗をあげる機能を持つことが好ましい。耐有機溶剤性と疎水性からポリプロピレン、ポリエチレンなどの単独又は組み合わせたオレフィン系ポリマーあるいはガラス繊維などからつくられたシートや不織布または織布が用いられる。セパレータの孔径は、電極シートより脱離した正負極材料、結着剤、導電剤が透過しない範囲であることが望ましく、例えば、０．０１〜１μｍであるものが望ましい。セパレータの厚みは、一般的には、１０〜３００μｍが用いられる。また、空孔率は、電子やイオンの透過性と素材や膜圧に応じて決定されるが、一般的には３０〜８０％であることが望ましい。
【００５６】
また、ポリマー材料に、溶媒とその溶媒に溶解するリチウム塩とから構成される有機電解液を吸収保持させたものを正極合剤、負極合剤に含ませ、さらに有機電解液を吸収保持するポリマーからなる多孔性のセパレータを正極、負極と一体化した電池を構成することも可能である。このポリマー材料としては、有機電解液を吸収保持できるものであればよいが、特にフッ化ビニリデンとヘキサフルオロプロピレンの共重合体が好ましい。
【００５７】
電池の形状はコイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型、電気自動車等に用いる大型のものなどいずれにも適用できる。
【００５８】
また、本発明の非水電解質二次電池は、携帯情報端末、携帯電子機器、家庭用小型電力貯蔵装置、自動二輪車、電気自動車、ハイブリッド電気自動車等に用いることができるが、特にこれらに限定されるわけではない。
【００５９】
【実施例】
以下、実施例により本発明をさらに詳しく説明する。ただし、本発明はこれらの実施例に限定されるものではない。
【００６０】
（実施例１）
負極材料の製造方法
（表１）に本実施例で用いた負極材料（材料Ａ〜材料Ｌ）の固相Ａと固相Ｂの成分（単体元素、金属間化合物、固溶体）、仕込み時の元素比率、溶融温度、および固相線温度を示す。本実施例で以下に具体的な製造方法を示す。
【００６１】
負極材料を構成する各元素の粉体またはブロックを、表１に示す仕込み比率で溶解槽に投入し、表１に示す溶融温度で溶解し、その溶融物をロール急冷法で急冷、凝固させ、凝固物を得た。続いて、その凝固物を表１に示す仕込み組成から決まる固溶体または金属間化合物の固相線温度より１０℃〜５０℃程度低い温度で不活性雰囲気下で２０時間熱処理を行った。この熱処理品をボールミルで粉砕し、篩で分級することにより４５μｍ以下の粒子にした材料Ａ〜材料Ｌを得た。これらの材料は電子顕微鏡観察結果から固相Ａ粒子の周囲の全面または一部が固相Ｂによって被覆さていることが確認できた。
【００６２】
【表１】

【００６３】
円筒型電池の製造方法
図１に本発明における円筒型電池の縦断面図を示す。正極板５及び負極板６がセパレーター７を介して複数回渦巻状に巻回されて電池ケース１内に収納されている。そして、上記正極板５からは正極リード５ａが引き出されて封口板２に接続され、負極板６からは負極リード６ａが引き出されて電池ケース１の底部に接続されている。電池ケースやリード板は、耐有機電解液性の電子伝導性をもつ金属や合金を用いることができる。例えば、鉄、ニッケル、チタン、クロム、モリブデン、銅、アルミニウムなどの金属あるいはそれらの合金が用いられる。特に、電池ケースはステンレス鋼板、Ａｌ−Ｍｎ合金板を加工したもの、正極リードはアルミニウム、負極リードはニッケルが最も好ましい。また、電池ケースには、軽量化を図るため各種エンジニアリングプラスチックス及びこれと金属の併用したものを用いることも可能である。８は絶縁リングで極板群４の上下部にそれぞれ設けられている。そして、電解液を注入し、封口板を用いて電池缶を形成する。このとき、安全弁を封口板として用いることができる。安全弁の他、従来から知られている種々の安全素子を備えつけても良い。例えば、過電流防止素子として、ヒューズ、バイメタル、ＰＴＣ素子などが用いられる。また、安全弁のほかに電池ケースの内圧上昇の対策として、電池ケースに切込を入れる方法、ガスケット亀裂方法あるいは封口板亀裂方法あるいはリード板との切断方法を利用することができる。また、充電器に過充電や過放電対策を組み込んだ保護回路を具備させるか、あるいは、独立に接続させてもよい。また、過充電対策として、電池内圧の上昇により電流を遮断する方式を具備することができる。このとき、内圧を上げる化合物を合剤の中あるいは電解質の中に含ませることができる。内圧を上げる化合物としてはLi₂CO₃ 、LiHCO₃、Na₂CO₃ 、NaHCO₃ 、CaCO₃ 、MgCO₃ などの炭酸塩などがあげられる。キャップ、電池ケース、シート、リード板の溶接法は、公知の方法（例、直流又は交流の電気溶接、レーザー溶接、超音波溶接）を用いることができる。封口用シール剤は、アスファルトなどの従来から知られている化合物や混合物を用いることができる。
【００６４】
負極板６は、得られた前記負極材料７５重量％に対し、導電剤である炭素粉末２０重量％と結着剤のポリフッ化ビニリデン樹脂５重量％を混合し、これらを脱水Ｎ−メチルピロリジノンに分散させてスラリーを作製し、銅箔からなる負極集電体上に塗布し、乾燥後、圧延して作製した。
【００６５】
一方、正極板５は、コバルト酸リチウム粉末８５重量％に対し、導電剤の炭素粉末１０重量％と結着剤のポリフッ化ビニリデン樹脂５重量％を混合し、これらを脱水Ｎ−メチルピロリジノンに分散させてスラリーを作製し、アルミ箔からなる正極集電体上に塗布し、乾燥後、圧延して作製した。
【００６６】
また、有機電解液には、炭酸エチレンと炭酸エチルメチルの体積比１：１の混合溶媒に、ビスペンタフルオロエタンスルホン酸イミドリチウム（（C₂F₅SO₂)₂NLi）を１．５モル／リットル溶解したものを使用した。
【００６７】
以上のようにして、表２に示したように、表1の材料Ａ〜Ｌを負極に用いた電池１〜１２を作製した。尚、作製した円筒型電池は直径１８ｍｍ、高さ６５０ｍｍである。これらの電池を１００ｍＡの定電流で、まず４．１Ｖになるまで充電した後、同じく定電流１００ｍＡで２．０Ｖになるまで放電する充放電サイクルを繰り返した。尚、充放電は１００サイクルまで繰り返し行い、初期の放電容量に対する１００サイクル目の放電容量の比を容量維持率として（表２）に示した。又比較のために負極材料に黒鉛、またはAl-Li合金を用いた電池を１３、１４として作製した。
【００６８】
更に、表2には、同じ構成で１００ｍＡの定電流で、４．１Ｖになるまで充電し、一旦、２．０Ｖになるまで放電し、初期の電池容量をチェックした後、再度、同条件で４．１Ｖまで充電した電池を60℃で20日間保存した際の容量維持率として保存前の放電容量に対する保存後の放電容量の比、ならびに保存後の電池に穴を空け、流動パラフィン中で捕集したガス量を負極に黒鉛を用いた場合を１００とした比率で示した。
【００６９】
【表２】

【００７０】
（実施例２）
有機電解液を、炭酸プロピレンとし、支持電解質としてビス（5−フルオロ−2−オレート−1−ベンゼンスルホン酸−O,O’）ほう酸リチウムを１．０モル／リットル溶解したものを用いた以外は実施例１の電池の構成・試験は同様にした。その結果を、（表３）に示した。
【００７１】
【表３】

【００７２】
（実施例３）
有機電解液を、γ−ブチロラクトンとし、支持電解質としてビス（2,2'-ビフェニルジオレート（2-）−O,O'）ほう酸リチウムを１．２モル／リットル溶解したものを用いた以外は実施例１の電池の構成・試験は同様にした。その結果を、（表４）に示した。
【００７３】
【表４】

【００７４】
（実施例４）
正極集電体を0.02mmのチタン箔を用い、さらに有機電解液を、炭酸エチレン、炭酸ジメチル、炭酸ジエチルを体積比で２：３：３の混合溶媒に、支持電解質としてビステトラフルオロメタンスルホン酸イミドリチウム（（CF₃SO₂)₂NLi）を１．２モル／リットル溶解したものを用いた以外は実施例１の電池の構成・試験は同様にした。その結果を、（表５）に示した。
【００７５】
【表５】

【００７６】
（実施例５）
正極材料に二硫化チタンリチウム（LiTiS₂）を用い、さらに有機電解液を、γ−バレロラクトンとし、支持電解質としてビス（1,2-ベンゼンジオレート（2-）-O,O'）ほう酸リチウムを１．２モル／リットル溶解したものを用いた以外は実施例１の電池の構成は同様にした。ここで得られた電池を１００ｍＡの定電流で、まず２．８Ｖになるまで充電した後、同じく定電流１００ｍＡで０．５Ｖになるまで放電する充放電サイクルを繰り返した。尚、充放電は１００サイクルまで繰り返し行い、初期の放電容量に対する１００サイクル目の放電容量の比を容量維持率として（表６）に示した。更に、表６には、同じ構成で１００ｍＡの定電流で、２．８Ｖになるまで充電し、一旦、０．５Ｖになるまで放電し、初期の電池容量をチェックした後、再度、同条件で２．８Ｖまで充電した電池を60℃で20日間保存した際の容量維持率として保存前の放電容量に対する保存後の放電容量の比、ならびに保存後の電池に穴を空け、流動パラフィン中で捕集したガス量を負極に黒鉛を用いた場合を１００とした比率で示した。
【００７７】
【表６】

【００７８】
（実施例６）
正極材料に二硫化チタンリチウム（LiTiS₂）を用い、有機電解液を、炭酸エチレンと炭酸ジエチルの体積比１：２の混合溶媒に、支持電解質としてビス（2,3-ナフタレンジオレート（2-）-O,O'）ほう酸リチウムを１．０モル／リットル溶解したものを用いた以外は実施例１の電池の構成は同様にした。ここで得られた電池を１００ｍＡの定電流で、まず２．８Ｖになるまで充電した後、同じく定電流１００ｍＡで０．５Ｖになるまで放電する充放電サイクルを繰り返した。尚、充放電は１００サイクルまで繰り返し行い、初期の放電容量に対する１００サイクル目の放電容量の比を容量維持率として（表７）に示した。更に、表７には、同じ構成で１００ｍＡの定電流で、２．８Ｖになるまで充電し、一旦、０．５Ｖになるまで放電し、初期の電池容量をチェックした後、再度、同条件で２．８Ｖまで充電した電池を60℃で20日間保存した際の容量維持率として保存前の放電容量に対する保存後の放電容量の比、ならびに保存後の電池に穴を空け、流動パラフィン中で捕集したガス量を負極に黒鉛を用いた場合を１００とした比率で示した。
【００７９】
【表７】

【００８０】
なお本実施例で用いた負極材料を構成する元素は、固相ＡがSiの場合、２族元素としてMg、遷移元素としてCoおよびNi、１２族元素としてZn、１３族元素としてAl、１４族元素としてSnを用いたが、これら以外の各族の元素を用いても同様な効果が得られた。また固相ＡがZnの場合、２族元素としてMg、遷移元素としてCuおよびV、１２族元素としてCd、１３族元素としてAl、１４族元素としてGeを用いたが、これら以外の各族の元素を用いても同様な効果が得られた。
【００８１】
また負極材料構成元素の仕込み比率については、特に限定されたものではなく、相が２相になり、１相（固相Ａ）が主にSi,Znを主体とした相で、もう一つ別の相（固相Ｂ）がその周りを一部または全部を被覆するような状態になればよく、仕込み組成を特に限定するものではない。相Ｂは表１に示した固溶体,金属間化合物のみからなるだけではなく、それぞれの各固溶体,金属間化合物を構成している元素やそれ以外の元素が微量存在している場合も含まれる。
【００８２】
また、本実施例に用いた電解液の組み合わせ並びに混合比、支持電解質添加量は一意に決まるものではなく、任意の組み合わせ、混合比および添加量とすることが可能であり、また、その場合にも同様な効果が得られた。したがって電解液は、本実施例に挙げた組み合わせ、混合比、および添加量に限定されるものではない。ただし、支持電解質については、その耐酸化電圧の関係から、用いる正極材料により、その種別の選定が必要となる。
【００８３】
【発明の効果】
以上のように本発明によれば、従来の炭素材料を負極材料としたものよりも高容量で、かつサイクル特性、高率充放電特性および、高温保存特性に優れた非水電解質二次電池が得られる。
【図面の簡単な説明】
【図１】本実施例における円筒型電池の縦断面図
【符号の説明】
１ 電池ケース
２ 封口板
３ 絶縁パッキング
４ 極板群
５ 正極板
５ａ 正極リード
６ 負極板
６ａ 負極リード
７ セパレータ
８ 絶縁リング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in the electrochemical characteristics such as charge / discharge capacity and charge / discharge cycle life by improving the negative electrode material of the nonaqueous electrolyte secondary battery and applying a high oxidation resistant organic solvent as the nonaqueous electrolyte. The present invention relates to a non-aqueous electrolyte secondary battery used for a terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle powered by a motor, an electric vehicle, a hybrid electric vehicle, and the like.
[0002]
[Prior art]
In recent years, lithium secondary batteries used as a main power source for mobile communication devices and portable electronic devices have a high electromotive force and a high energy density. A lithium secondary battery using lithium metal as a negative electrode material has high energy density, but dendrite is deposited on the negative electrode during charging, and the dendrite is cut off during discharging, so that it falls off from the surface of the bulk metallic lithium negative electrode. , "Dead" lithium is generated that cannot contribute to the charge / discharge reaction. Furthermore, the dendrite grows by repeating charge and discharge, breaks through the separator, reaches the positive electrode side, and may cause an internal short circuit. In addition, the deposited dendrites have a high specific surface area and thus have high reaction activity, and react with the solvent in the electrolytic solution on the surface to form a solid electrolyte-like interface film lacking in electron conductivity. For this reason, the internal resistance of the battery is increased, or particles isolated from the electron conduction network are present, which are factors that lower the charge / discharge efficiency. For these reasons, lithium secondary batteries using lithium metal as a negative electrode material have problems in low reliability and short cycle life.
[0003]
In order to suppress such dendrites, lithium alloys typified by lithium-aluminum alloys (Li-Al alloys) and wood alloys instead of metallic lithium have been proposed as negative electrode materials. In the case of such a metal that can be alloyed with lithium and an alloy containing at least one of these metals, it can be a negative electrode material having a relatively high capacity electrochemically at the stage of an initial charge / discharge cycle. However, although the crystal structure of the original skeletal alloy is maintained by repetitive alloying with lithium and desorption of lithium by charging and discharging, phase change occurs or is different from the elemental skeleton alloy. It may change to a crystal structure. In this case, the particles of the metal or alloy that is the lithium host material that is the active material undergoes expansion and contraction, and as the charge / discharge cycle progresses, the crystal grains are stressed, resulting in cracks, As a result, shedding from the plate proceeds. The grain boundary resistance and the grain boundary contact resistance increase as the grains become finer. As a result, the resistance polarization at the time of charging / discharging increases, and at the time of voltage-controlled charging, the charging depth becomes shallow and the amount of charge electricity is small. On the other hand, during discharge, a voltage drop occurs due to resistance polarization, and the discharge end voltage is reached quickly. Therefore, both charge / discharge capacity and cycle characteristics are unlikely to be excellent.
[0004]
Currently, carbon materials capable of occluding and releasing lithium ions are used as a negative electrode material to replace lithium metal, and have been put into practical use. Usually, metallic lithium does not precipitate on the carbon material negative electrode, so there is no problem of internal short circuit due to dendrite. However, the theoretical capacity of graphite, which is one of the carbon materials, is 372 mAh / g, which is as low as 1/10 of the theoretical capacity of Li metal alone. Other compound active material materials include niobium pentoxide (Nb ₂ O ₅ ), titanium disulfide (TiS ₂ ), molybdenum dioxide (MoO ₂ ), lithium titanate (Li _4/3 Ti _5/3 O _4). ) And the like. Since these materials hold lithium in the host material in an ionized state, they are chemically stable, do not generate dendrites, and have excellent cycle characteristics compared to metallic lithium, which has high chemical activity. Improvements have been made for carbon-based materials.
[0005]
As other negative electrode materials, simple metal materials and simple non-metal materials that form a compound with lithium are known. For example, the composition formulas of the most lithium-containing compounds of silicon (Si) and zinc (Zn) are Li ₂₂ Si ₅ and LiZn, respectively, and metallic lithium does not normally precipitate in this range, so the problem of internal short circuit due to dendrite is Absent. The electrochemical capacities between these compounds and each single material are 4199 mAh / g and 410 mAh / g, respectively, both of which are larger than the theoretical capacity of graphite.
[0006]
Further, as a compound negative electrode material in addition to a single metal material and a single nonmetal material that form a compound with lithium, Japanese Patent Application Laid-Open No. 7-240201 discloses a non-ferrous metal silicide composed of a transition element. Has proposed an anode material made of an intermetallic compound containing a group 4B element and at least one of P and Sb, and having a crystal structure of any of CaF ₂ type, ZnS type, and AlLiSi type.
[0007]
On the other hand, as a solvent of an electrolytic solution used for a non-aqueous electrolyte battery, a cyclic carbonate represented by propylene carbonate (PC) and ethylene carbonate (EC), a diethyl carbonate (DEC), and a dimethyl carbonate (DMC) are representative. Chain carbonate ester, γ-butyrolactone (GBL), cyclic carboxylic acid ester represented by γ-valerolactone (GVL), chain ether such as dimethoxymethane (DMM) and 1,3-dimethoxypropane (DMP), Cyclic esters such as tetrahydrofuran (THF) or 1,3-dioxolane (DOL) are often used.
[0008]
When applied to a non-aqueous electrolyte secondary battery, a material having a high electrical conductivity is desirable. For this purpose, a solvent having a high relative dielectric constant and a low viscosity is preferably used. However, a high relative dielectric constant means that the polarity is strong, that is, the viscosity is high. Therefore, among the above-mentioned electrolytes, a high dielectric constant solvent such as propylene carbonate (dielectric constant ε = 65) and a low dielectric constant solvent typified by 1,2-dimethoxyethane (DME, ε = 7.2) are used. Often used in combination.
[0009]
As the electrolytic solution used for the nonaqueous electrolyte battery, a solution in which a supporting electrolyte of about 1 molar concentration is dissolved in the above-described solvent is used. Examples of supporting electrolytes include lithium perchlorate (LiClO ₄ ), lithium borofluoride (LiBF ₄ ), lithium phosphofluoride (LiPF ₆ ), inorganic acid anion lithium salts, and lithium trifluoromethanesulfonate (LiSO ₃ Organic acid anion lithium salts such as CF ₃ ) and lithium bistrifluoromethanesulfonate ((CF ₃ SO ₂ ) ₂ NLi) are used.
[0010]
[Problems to be solved by the invention]
However, negative electrode materials having a capacity higher than that of the carbon material as described above have the following problems.
[0011]
A single metal material and a single non-metal negative electrode material that form a compound with lithium are commonly inferior in charge / discharge cycle characteristics compared to a carbon negative electrode material. The reason is not clear, but I think as follows.
[0012]
For example, silicon contains eight silicon atoms in its crystallographic unit cell (cubic, space group Fd-3m). In terms of lattice constants a = 0.5420nm, unit cell volume is 0.1592nm ^3, the volume occupied by one silicon atom is 19.9 × 10 ^-3 nm ^3. Judging from the phase diagram of the silicon-lithium binary system, in the formation of an electrochemical compound with lithium at room temperature, two phases of silicon and the compound Li ₁₂ Si ₇ coexist at the initial stage of the reaction. Conceivable. The crystallographic unit cell of Li ₁₂ Si ₇ (orthorhombic crystal, space group Pnma) contains 56 silicon atoms. The unit cell volume is 2.4372 nm ³ in terms of the lattice constants a = 0.8610nm, b = 1.9737nm, c = 1.4341nm, and the volume per silicon atom (the unit cell volume is the silicon atom in the unit cell). The value divided by the number is 43.5 × 10 ⁻³ nm ³ . From this value, the volume of the material expands to 2.19 times when silicon is converted to the compound Li ₁₂ Si ₇ . The reaction in the two-phase coexistence state of silicon and the compound Li ₁₂ Si ₇ has a large volume difference because silicon partially changes to the compound Li ₁₂ Si ₇ , and the material is greatly distorted and easily cracked. It is considered that fine particles are likely to be formed. Further, when the compound formation reaction with electrochemical lithium proceeds, the compound Li ₂₂ Si ₅ containing the most lithium is finally produced. The crystallographic unit cell of Li ₂₂ Si ₅ (cubic, space group F23) contains 80 silicon atoms. Converted from the lattice constant a = 1.8750 nm, the unit cell volume is 6.5918 nm ³ and the volume per silicon atom (the value obtained by dividing the unit cell volume by the number of silicon atoms in the unit cell) is 82.4 × 10. ^-3 nm ^3. This value is 4.14 times that of simple silicon, and the material is greatly expanded. In the discharge reaction for the negative electrode material, a reaction in which lithium decreases from the compound occurs, and the material shrinks. Thus, since the volume difference between charging and discharging is large, it is considered that the material is greatly distorted, cracks are generated, and the particles are refined. Furthermore, it is considered that a space is generated between the fine particles, the electron conduction network is divided, the portion that cannot participate in the electrochemical reaction increases, and the charge / discharge capacity decreases.
[0013]
Zinc contains two zinc atoms in a crystallographic unit cell (hexagonal, space group P63 / mmc). Lattice constant a = 0.2665nm, in terms of c = 0.4947nm, unit cell volume is 0.030428nm ^3, the volume occupied by one zinc atom is 15.2 × 10 ^-3 nm ^3. Judging from the phase diagram of the zinc-lithium binary system, the compound LiZn containing the most lithium is finally produced through several compounds. The crystallographic unit cell of LiZn (cubic, space group Fd-3m) contains 8 zinc atoms. Converted from the lattice constant a = 0.6209 nm, the unit cell volume is 0.2394 nm ³ and the volume per one zinc atom (the value obtained by dividing the unit cell volume by the number of zinc atoms in the unit cell) is 29.9 × 10 ^-3 nm ³ . This value is 1.97 times that of simple zinc, and the material expands.
[0014]
In this way, zinc, like silicon, has a large volume change in the negative electrode material due to the charge / discharge reaction, and by repeatedly changing the state in which two phases with a large volume difference coexist, the material cracks and the particles become finer. It is thought to do. The refined material is considered to have a space between particles, an electron conduction network is cut off, a portion that cannot participate in an electrochemical reaction increases, and a charge / discharge capacity decreases.
[0015]
In other words, the large volume change common to the negative electrode material of the single metal material and the single metal non-metal material that form a compound with lithium, and the structural change caused by this, are presumed to be the reason why the charge / discharge cycle characteristics are worse than the carbon negative electrode material. ing.
[0016]
On the other hand, unlike the above-mentioned simple material, it consists of a non-ferrous metal silicide composed of transition elements and an intermetallic compound containing at least one of group 4B elements and P and Sb, and its crystal structure is CaF ₂ type, ZnS type, AlLiSi. A negative electrode material made of one of the molds has been proposed in Japanese Patent Application Laid-Open Nos. 7-240201 and 9-63651 as negative electrode materials having improved cycle life characteristics.
[0017]
A battery using a non-ferrous metal silicide negative electrode material composed of a transition element disclosed in Japanese Patent Application Laid-Open No. 7-240201 is a battery capacity at the first cycle, the 50th cycle, and the 100th cycle shown in Examples and Comparative Examples. Therefore, the charge / discharge cycle characteristics are improved as compared with the lithium metal negative electrode material, but the battery capacity is increased by only about 12% at the maximum as compared with the natural graphite negative electrode material. Therefore, although not explicitly stated in the specification, it seems that the non-ferrous metal silicide negative electrode material made of a transition element has not been significantly increased in capacity compared with the graphite negative electrode material.
[0018]
In addition, the materials disclosed in JP-A-9-63651 have improved charge / discharge cycle characteristics in the examples and comparative examples compared to the Li-Pb alloy negative electrode material, and have a higher capacity than the graphite negative electrode material. It is shown that there is. However, the discharge capacity is remarkably reduced in charge / discharge cycles up to 10 to 20 cycles, and Mg ₂ Sn, which seems to be the best, is reduced to about 70% of the initial capacity after about 20 cycles.
[0019]
Further, when metallic lithium is used as the negative electrode, the electrolytic solution in contact with the negative electrode is exposed to an extremely strong reducing atmosphere, and the electrolytic solution reacts with metallic lithium and is likely to undergo reductive decomposition. Furthermore, when an alloy mainly composed of lithium, such as a Li-Al alloy, is used for the negative electrode, the electrode potential of the negative electrode is almost equal to that of metallic lithium, and the reductive decomposition of the electrolytic solution occurs in substantially the same manner. In addition, as described above, the negative electrode active material is refined by repeated charge and discharge and falls off the electrode plate. In addition, when the alloy composition is mainly composed of a metal other than lithium, the electrode potential of the negative electrode becomes noble compared to metallic lithium or a lithium alloy, and the use of an electrolytic solution that undergoes reductive decomposition as described above can also be used. It becomes possible. However, when these alloys are alloyed with lithium, the alloys are harder and more brittle than alloys mainly composed of lithium, and the fineness of the alloys is remarkable, and detachment from the electrode plate is inevitable.
[0020]
Furthermore, when a solvent such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, or γ-valerolactone is used in a system using metallic lithium and a lithium alloy as a negative electrode, a charged battery When the electrolyte is decomposed and gas is generated when it is stored at a high temperature, or when repeated charge and discharge is performed, the gasification reaction of the electrolyte occurs in parallel with the charge and discharge reaction of the negative electrode. There is a problem that the discharge efficiency is lowered, and as a result, the cycle characteristics are lowered.
[0021]
On the other hand, when a graphite-based carbon material is used as the negative electrode material, when an electrolytic solution using propylene carbonate is applied, the decomposition of the electrolytic solution occurs at a higher potential than that on metallic lithium. It does not intercalate between layers and does not operate as a battery. Therefore, an electrolytic solution containing ethylene carbonate is frequently used in lithium secondary batteries using graphite-based negative electrode materials that are currently commercially available. However, ethylene carbonate has a melting point of 37 ° C., which is higher than room temperature. For this reason, at low temperatures, the lithium ion conductivity of the electrolytic solution is drastically lowered, and charge / discharge characteristics are lowered.
[0022]
Further, when an inorganic compound material such as titanium disulfide is used as the negative electrode material , the intercalation / deintercalation occurs at a sufficiently noble potential as compared with metallic lithium or lithium alloy. Therefore, reductive decomposition does not occur even in contact with the electrolytic solution, and lithium insertion / extraction is not hindered by decomposition of the electrolytic solution, such as propylene carbonate, which could not be applied with graphite-based materials. The range of selection of the electrolyte to be used is expanded. However, since the potential of these inorganic compound material negative electrodes is noble, the battery voltage is low, which is disadvantageous for increasing the energy density.
[0023]
As for the supporting electrolyte, lithium perchlorate, lithium borofluoride, and lithium phosphofluoride all have problems in thermal stability, and at the same time, fluorine-containing inorganic anion salts (for example, lithium phosphofluoride) In the case of (Chemical Formula 7) to (Chemical Formula 9), there is a problem that it reacts with water slightly contained in the electrolytic solution and decomposes.
[0024]
[Chemical 7]

[0025]
[Chemical 8]

[0026]
[Chemical 9]

[0027]
[Means for Solving the Problems]
The present invention is a composite particle in which the entire surface or a part of the periphery of a core particle composed of a solid phase A is coated with a solid phase B, the solid phase A containing at least one of silicon and zinc as constituent elements, B is a constituent element of the solid phase A, either silicon or zinc, and excluding the constituent element, from the group 2 element, transition element, group 12 element, group 13 element, and group 14 element excluding carbon in the periodic table Role of suppressing the expansion / contraction caused by the solid phase A and the solid phase B due to charging / discharging of the solid phase A by using a material that is a solid solution or an intermetallic compound with at least one element selected from the group The negative electrode material with excellent charge / discharge cycle characteristics is used, and the electrolyte consists of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone. In a solvent containing at least one compound selected from the group, lithium bistetrafluoromethanesulfonate imide, lithium bispentafluoroethanesulfonate ((C ₂ F ₅ SO ₂ ) ₂ NLi), bis (1, 2-Benzenediolate (2-)-O, O ') lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O') lithium borate, bis (2,2'-biphenyldiolate) (2-)-O, O ') When using at least one compound selected from the group consisting of lithium borate and bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') lithium borate In addition, it has been found that gas generation is extremely low during high-temperature storage, and that charging / discharging efficiency of the negative electrode does not decrease during repeated charging / discharging. In Less decrease in discharge capacity that, and aims to provide an excellent novel non-aqueous electrolyte secondary battery in high-rate charge and discharge characteristics.
[0028]
In the negative electrode material of the present invention, the solid phase A contains at least one of high-capacity silicon and zinc as a constituent element, which is considered to contribute mainly to an increase in charge / discharge capacity. Further, it is considered that the solid phase B covering the entire surface or a part of the periphery of the core particle composed of the solid phase A contributes to the improvement of the charge / discharge cycle characteristics.
[0029]
Further, lithium is not occluded in the solid phase B of the composite particle, but is occluded only in the solid phase A. Therefore, it is only solid phase B that does not contain active lithium that comes into contact with the electrolyte solution with the composite particles. Therefore, it is considered that the electrolyte solution is unlikely to decompose even when this phase contacts the electrolyte solution. Yes.
[0030]
On the other hand, the electrolytic solution of the present invention has high thermal stability for both the solvent and the supporting electrolyte, and is stable against moisture slightly contained in the electrolytic solution. It is considered to be.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
The positive electrode and negative electrode used in the present invention have a positive electrode active material capable of electrochemically and reversibly inserting and releasing lithium ions and a mixture layer containing a conductive agent, a binder and the like on the surface of the current collector. It was made by painting.
[0032]
The negative electrode material used in the present invention is a composite particle in which the entire surface or a part of the periphery of the core particle composed of the solid phase A is coated with the solid phase B, and the solid phase A includes at least one of silicon and zinc as constituent elements. In addition, the solid phase B excludes any of silicon and zinc, which are constituent elements of the solid phase A, and the constituent elements, excluding the group 2 element, transition element, group 12 and group 13 element of the periodic table, and carbon It is a solid solution with at least one element selected from the group consisting of group 14 elements, or a material that is an intermetallic compound (hereinafter referred to as “composite particles”).
[0033]
As one of the methods for producing composite particles used in the present invention, a melt of the charged composition of each element constituting the composite particles is rapidly cooled by a dry spray method, a wet spray method, a roll quench method, a rotating electrode method, or the like. There is a method of solidifying and heat-treating the solidified product at a temperature lower than the solidus temperature of the solid solution or intermetallic compound determined from the charged composition. (Change required) The solid phase A particles as the core particles and the solid phase B covering the entire surface or part of the solid phase A particles are precipitated by rapid solidification of the melt. Although it aims at improving the uniformity of A and B, the composite particles according to claim 1 can be obtained even when heat treatment is not performed. Also, methods other than the above cooling method can be used as long as they can be sufficiently cooled.
[0034]
As another manufacturing method, an adhesion layer made of an element other than the elements contained in the solid phase A necessary for forming the solid phase B is formed on the surface of the powder of the solid phase A, and this is obtained from the charged composition. There is a method of performing heat treatment at a temperature lower than the solidus temperature of the determined solid solution or intermetallic compound. By this heat treatment, the component elements in the solid phase A diffuse into the adhesion layer, and the solid phase B is formed as a coating layer. The adhesion layer can be formed by a plating method or a mechanical alloying method. In addition, any method that can form an adhesion layer can be used. The mechanical alloying method does not require heat treatment.
[0035]
According to the first aspect of the present invention, the material obtained above is used as a negative electrode, a lithium-containing transition metal oxide is used as a positive electrode, and an organic acid anionic lithium salt is dissolved in a highly oxidation-resistant organic solvent as an electrolyte. It is characterized by using what was done.
[0036]
The composite particles have a high capacity, little reduction in discharge capacity due to repeated charge and discharge, and excellent high rate charge / discharge characteristics. The negative electrode and a positive electrode capable of occluding and releasing lithium, and a high acid resistance to the electrolyte. A battery having a high capacity, a high energy density, and high reliability is achieved by using an organic acid anionic lithium salt dissolved in a curable organic solvent.
[0037]
The nonaqueous electrolyte used in the present invention is composed of a solvent and a lithium salt dissolved in the solvent. Non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. (EMC), chain carbonates such as dipropyl carbonate (DPC), cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propyl Nitrile, nitromethane, ethyl monogly , Phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1, Aprotic organic solvents such as 3-propane sultone, anisole, dimethyl sulfoxide, N-methylpyrrolidone, and the like can be used, and one or two or more of these can be used in combination.
[0038]
The invention according to claim 2 is an electrolyte solution containing ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone as the high oxidation resistant organic solvent according to claim 1 It is a thing. Conventionally, propylene carbonate has been decomposed by contact with an electrode in a graphite material often used in lithium ion secondary batteries, and its application has been difficult. In addition, γ-butyrolactone and γ-valerolactone have a reductive decomposition potential that is more noble than the electrode potential of lithium metal or lithium alloy, so that it was difficult to apply to batteries using these metals as the negative electrode. However, when the composite particles of the present invention are used for the negative electrode, the electrode potential is nobler than the reductive decomposition potential of γ-butyrolactone and γ-valerolactone, and therefore the electrolyte solution can be applied without being decomposed. Furthermore, since propylene carbonate, γ-butyrolactone, and γ-valerolactone have a high dielectric constant, that is, a high viscosity, even if the composite particles of the negative electrode are miniaturized, due to the high viscosity, from the electrode plate A favorable effect of being difficult to detach is also produced.
[0039]
In addition, when the solvent such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone is used in a system using metal lithium and a lithium alloy as a negative electrode, When the battery is stored at a high temperature, the electrolytic solution decomposes and gas is generated, or when repeated charging / discharging is performed, in parallel with the charging / discharging reaction of the negative electrode, the gasification reaction of the electrolytic solution occurs, Although there has been a problem that the charge / discharge efficiency is lowered and as a result the cycle characteristics are lowered, when the composite particles of the present invention are used for the negative electrode, reactivity with these electrolytes is not recognized.
[0040]
Examples of the lithium salt dissolved in these solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , lithium lower aliphatic carboxylate, LiCl, LiBr, LiI, lithium chloroborane, bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3 -Naphthalenedioleate (2-)-O, O ') lithium borate, bis (2,2'-biphenyldiolate (2-)-O, O') lithium borate, bis (5-fluoro-2-olate) Borates such as 1-benzenesulfonic acid-O, O ') lithium borate, lithium bistetrafluoromethanesulfonate imide ((CF ₃ SO ₂ ) ₂ NLi), lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂₎ can be mentioned ₂ NLi) imide salts such like, alone or in the electrolyte solution or the like to use them It can be used in combination or species. Of these, organic acid anion lithium salts are superior in thermal stability to inorganic acid anion lithium salts typified by lithium perchlorate and lithium phosphofluoride. During the high temperature storage, these supporting electrolytes are more preferably used without thermally decomposing and degrading the characteristics of the battery.
[0041]
According to a third aspect of the present invention, the organic anionic lithium salt according to the first aspect of the present invention is obtained by using lithium bistetrafluoromethanesulfonate imide lithium ((CF ₃ SO ₂ ) ₂ NLi), lithium bispentafluoroethanesulfonate imide ((C ₂ F ₅ SO ₂ ) ₂ NLi), bis (1,2-benzenediolate (2-)-O, O ′) lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O ′) From lithium borate, bis (2,2'-biphenyldiolate (2-)-O, O ') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') lithium borate And at least one compound selected from the group consisting of:
[0042]
Lithium tetrafluoromethane sulfonate imidolithium ((CF ₃ SO ₂ ) ₂ NLi) has a reduced decomposition breakdown voltage on the platinum electrode of 0V with respect to the lithium reference electrode and an oxidative decomposition breakdown voltage of 4.7V. Fluoroethanesulfonic acid imidolithium ((C ₂ F ₅ SO ₂ ) ₂ NLi) has a reduction decomposition withstand voltage of 0 V and an oxidation decomposition withstand voltage of 4.7 V on a platinum electrode, and bis (5- Fluoro-2-olate-1-benzenesulfonic acid-O, O ') Lithium borate has a reductive decomposition withstand voltage of 0 V and a oxidative decomposition withstand voltage of 4.5 V on a platinum electrode, and bis (2,2'- Biphenyldiolate (2-)-O, O ′) lithium borate has a reduction decomposition withstand voltage of 0 V on the platinum electrode and an oxidation decomposition withstand voltage of 4.1 V or more. Therefore, these organic acid anion lithium salts can be applied to active materials that generate a high voltage of 4 V or more with respect to the lithium reference electrode, such as lithium cobaltate, lithium nickelate, and lithium manganate. It is preferable in terms of densification.
[0043]
On the other hand, bis (1,2-benzenediolate (2-)-O, O ') lithium borate has a reduction decomposition pressure on the platinum electrode of 0V relative to the lithium reference electrode and an oxidation decomposition breakdown voltage of 3.6V. Yes, bis (2,3-naphthalenedioleate (2-)-O, O ') lithium borate has a reductive decomposition withstand voltage of 0 V and a oxidative decomposition withstand voltage of 3.8 V on a platinum electrode. Applying an electrolytic solution in which these supporting electrolytes are dissolved to an active material that generates a high voltage of 4 V or more with respect to a lithium reference electrode such as lithium cobalt oxide, lithium nickel oxide, or lithium manganate is accompanied by decomposition of the supporting electrolyte. However, transition metal sulfides having an electromotive force of about 3 V with respect to a lithium reference electrode such as lithium titanium disulfide (LiTiS ₂ ) and molybdenum molybdenum sulfide (LiMoS ₂ ) can be used in this potential region.
[0044]
In the present invention, the amount of the electrolyte added to the battery is not particularly limited, but a necessary amount can be used depending on the amount of the positive electrode material and the negative electrode material and the size of the battery. The amount of dissolution of the supporting electrolyte in the nonaqueous solvent is not particularly limited, but is preferably 0.2 to 2 mol / l. In particular, 0.5 to 1.5 mol / l is more preferable.
[0045]
The negative electrode conductive agent used in the present invention may be anything as long as it is an electron conductive material. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, etc. The conductive fibers, metal powders such as carbon fluoride, copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and carbon fiber are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1 to 50 weight% is preferable and especially 1 to 30 weight% is preferable. Moreover, since the negative electrode material of the present invention itself has electronic conductivity, it can function as a battery without adding a conductive agent.
[0046]
The negative electrode binder used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoro Ethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), poly Chlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexa Fluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or (Na ⁺ ) ion crosslinked product of the above materials, ethylene-methacrylic acid copolymer Polymer or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methyl methacrylate copolymer or (Na ⁺ ) of the material An ionic crosslinked body can be mentioned, and these materials can be used alone or as a mixture. Among these materials, more preferable materials are styrene butadiene rubber, polyvinylidene fluoride, ethylene-acrylic acid copolymer, (Na ⁺ ) ion-crosslinked product of the material, ethylene-methacrylic acid copolymer, or the material. (Na ⁺ ) ion crosslinked product, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion crosslinked product, ethylene-methyl methacrylate copolymer of the material, or (Na ⁺ ) ion crosslinked product of the material .
[0047]
The negative electrode current collector used in the present invention may be anything as long as it is an electronic conductor that does not cause a chemical change in the constructed battery. For example, in addition to stainless steel, nickel, copper, titanium, carbon, conductive resin, etc., materials obtained by treating the surface of copper or stainless steel with carbon, nickel, or titanium are used. In particular, copper or a copper alloy is preferable. The surface of these materials can be oxidized and used. Further, it is desirable to make the current collector surface uneven by surface treatment. As the shape, a film, a sheet, a net, a punched product, a lath body, a porous body, a foamed body, a molded body of a fiber group, and the like are used in addition to the foil. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.
[0048]
As the positive electrode material used in the present invention, a lithium-containing compound can be used. For example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O _z , Li _x Ni _{1- y My} O _z , _{Li x Mn 2 O 4, Li} x Mn 2-y M y O 4 (M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B (Here, 0 <x ≦ 1.2, 0 ≦ y ≦ 0.9, 2.0 ≦ z ≦ 2.3). Here, said x value is a value before the start of charging / discharging, and it increases / decreases by charging / discharging. However, it is also possible to use other positive electrode active materials such as transition metal chalcogenides, lithium compounds of vanadium oxide, lithium compounds of niobium oxide, conjugated polymers using organic conductive materials, and chevrel phase compounds. It is also possible to use a mixture of a plurality of different positive electrode active materials. The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 μm.
[0049]
The conductive agent for positive electrode used in the present invention may be anything as long as it is an electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, etc. Conductive fibers, metal powders such as carbon fluoride, copper, nickel, aluminum and silver, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide or polyphenylene derivatives An organic conductive material or the like can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and nickel powder are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1 to 50 weight% is preferable and especially 1 to 30 weight% is preferable. In the case of carbon or graphite, 2 to 15% by weight is particularly preferable.
[0050]
The positive electrode binder used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene. Copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene Copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or (Na ⁺⁾ ions Cross-linked product, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methyl methacrylate copolymer Or the (Na ^<+> ) ion bridge | crosslinking body of the said material can be mentioned. Particularly preferred among these are polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
[0051]
The positive electrode current collector used in the present invention may be any electronic conductor that does not cause a chemical change in the charge / discharge potential of the positive electrode material used. For example, in addition to stainless steel, aluminum, titanium, carbon, conductive resin, and the like, materials obtained by treating the surface of aluminum or stainless steel with carbon or titanium are used. In particular, aluminum or an aluminum alloy is preferable. The surface of these materials can be oxidized and used. Further, it is desirable to make the current collector surface uneven by surface treatment. As the shape, a film, a sheet, a net, a punched product, a lath body, a porous body, a foamed body, a fiber group, a non-woven body shaped body, and the like are used in addition to the foil. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.
[0052]
In addition to the conductive agent and the binder, a filler, a dispersant, an ion conducting agent, a pressure enhancer, and other various additives can be used for the electrode mixture. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable.
[0053]
In the configuration of the negative electrode plate and the positive electrode plate in the present invention, it is preferable that the negative electrode mixture surface is present at least on the opposite surface of the positive electrode mixture surface.
[0054]
Furthermore, it is also effective to add other compounds to the electrolyte for the purpose of improving discharge and charge / discharge characteristics. For example, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, pyridine, hexaphosphoric acid triamide, nitrobenzene derivatives, crown ethers, quaternary ammonium salts, ethylene glycol dialkyl ether and the like can be mentioned.
[0055]
As the separator used in the present invention, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, it is preferable to have a function of closing the hole at a certain temperature or higher and increasing the resistance. A sheet, a nonwoven fabric, or a woven fabric made of an olefin polymer such as polypropylene or polyethylene, or glass fiber, or the like, is used because of its resistance to organic solvents and hydrophobicity. The pore diameter of the separator is desirably in a range in which the positive and negative electrode materials, the binder, and the conductive agent detached from the electrode sheet do not permeate, for example, 0.01 to 1 μm is desirable. The thickness of the separator is generally 10 to 300 μm. The porosity is determined according to the permeability of the electrons and ions, the material, and the film pressure, but is generally preferably 30 to 80%.
[0056]
A polymer in which an organic electrolyte composed of a solvent and a lithium salt dissolved in the solvent is absorbed and held in a polymer material is included in the positive electrode mixture and the negative electrode mixture, and the organic electrolyte is further absorbed and held. It is also possible to constitute a battery in which a porous separator made of is integrated with a positive electrode and a negative electrode. The polymer material is not particularly limited as long as it can absorb and retain the organic electrolyte solution, but a copolymer of vinylidene fluoride and hexafluoropropylene is particularly preferable.
[0057]
The shape of the battery can be applied to any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, a large type used for an electric vehicle, and the like.
[0058]
Further, the nonaqueous electrolyte secondary battery of the present invention can be used for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, a hybrid electric vehicle, etc., but is not particularly limited thereto. I don't mean.
[0059]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0060]
Example 1
Components of solid phase A and solid phase B (single element, intermetallic compound, solid solution) of the negative electrode material (material A to material L) used in this example in the negative electrode material production method (Table 1), elements at the time of preparation The ratio, melting temperature, and solidus temperature are shown. In the present embodiment, a specific manufacturing method will be described below.
[0061]
The powder or block of each element constituting the negative electrode material is charged into the dissolution tank at the charging ratio shown in Table 1, and melted at the melting temperature shown in Table 1, and the melt is rapidly cooled and solidified by a roll quenching method. A coagulum was obtained. Subsequently, the solidified product was heat-treated in an inert atmosphere for 20 hours at a temperature lower by about 10 ° C. to 50 ° C. than the solidus temperature of the solid solution or intermetallic compound determined from the preparation composition shown in Table 1. This heat-treated product was pulverized with a ball mill and classified with a sieve to obtain materials A to L having particles of 45 μm or less. From these electron microscope observation results, it was confirmed that the entire surface or part of the periphery of the solid phase A particles was covered with the solid phase B.
[0062]
[Table 1]

[0063]
Manufacturing Method of Cylindrical Battery FIG. 1 is a longitudinal sectional view of a cylindrical battery in the present invention. The positive electrode plate 5 and the negative electrode plate 6 are wound into a spiral shape a plurality of times via a separator 7 and are stored in the battery case 1. A positive electrode lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. For the battery case and the lead plate, a metal or alloy having an organic electrolyte resistance and an electron conductivity can be used. For example, metals such as iron, nickel, titanium, chromium, molybdenum, copper, and aluminum, or alloys thereof are used. In particular, the battery case is most preferably a stainless steel plate or an Al—Mn alloy plate processed, the positive electrode lead is aluminum, and the negative electrode lead is most preferably nickel. In addition, various engineering plastics and a combination of these and a metal can be used for the battery case in order to reduce the weight. Insulating rings 8 are provided at the upper and lower portions of the electrode plate group 4, respectively. And electrolyte solution is inject | poured and a battery can is formed using a sealing board. At this time, the safety valve can be used as a sealing plate. In addition to the safety valve, various conventionally known safety elements may be provided. For example, a fuse, bimetal, PTC element, or the like is used as the overcurrent prevention element. In addition to the safety valve, as a countermeasure against the increase in the internal pressure of the battery case, a method of cutting the battery case, a method of cracking the gasket, a method of cracking the sealing plate, or a method of cutting the lead plate can be used. Further, the charger may be provided with a protection circuit incorporating a countermeasure against overcharge or overdischarge, or may be connected independently. In addition, as a measure against overcharging, a method of cutting off current by increasing the battery internal pressure can be provided. At this time, a compound for increasing the internal pressure can be contained in the mixture or the electrolyte. Examples of the compound raising the internal pressure and carbonates such as _{Li 2 CO 3, LiHCO 3,} Na 2 CO 3, NaHCO 3, CaCO 3, MgCO 3 and the like. As a welding method for the cap, the battery case, the sheet, and the lead plate, a known method (eg, direct current or alternating current electric welding, laser welding, ultrasonic welding) can be used. As the sealing agent for sealing, a conventionally known compound or mixture such as asphalt can be used.
[0064]
The negative electrode plate 6 was prepared by mixing 20% by weight of a carbon powder as a conductive agent and 5% by weight of a polyvinylidene fluoride resin as a binder with 75% by weight of the obtained negative electrode material, and mixing them with dehydrated N-methylpyrrolidinone. The slurry was dispersed to prepare a slurry, which was applied onto a negative electrode current collector made of copper foil, dried and then rolled.
[0065]
On the other hand, the positive electrode plate 5 is obtained by mixing 10% by weight of carbon powder as a conductive agent and 5% by weight of polyvinylidene fluoride resin as a binder with 85% by weight of lithium cobalt oxide powder, and dispersing these in dehydrated N-methylpyrrolidinone. Thus, a slurry was prepared, applied on a positive electrode current collector made of aluminum foil, dried, and rolled.
[0066]
For the organic electrolyte, 1.5 mol of bispentafluoroethanesulfonic acid imidolithium ((C ₂ F ₅ SO ₂ ) ₂ NLi) was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1: 1. / L dissolved material was used.
[0067]
As described above, as shown in Table 2, batteries 1 to 12 using the materials A to L in Table 1 as the negative electrode were produced. The produced cylindrical battery has a diameter of 18 mm and a height of 650 mm. These batteries were first charged with a constant current of 100 mA to 4.1 V, and then a charge / discharge cycle in which the batteries were discharged to 2.0 V with a constant current of 100 mA was repeated. Charging / discharging was repeated up to 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity is shown in Table 2 as the capacity retention rate. For comparison, batteries with graphite or Al—Li alloy as negative electrode materials were prepared as 13 and 14.
[0068]
Furthermore, Table 2 shows that the same configuration is charged with a constant current of 100 mA until 4.1 V is reached, then discharged until 2.0 V, the initial battery capacity is checked, and again under the same conditions. 4. The ratio of the discharge capacity after storage to the discharge capacity before storage as the capacity maintenance rate when the battery charged to 1 V was stored at 60 ° C. for 20 days, and the battery after storage was punctured and captured in liquid paraffin The amount of gas collected was shown as a ratio with respect to 100 when graphite was used for the negative electrode.
[0069]
[Table 2]

[0070]
(Example 2)
The organic electrolyte was propylene carbonate, and the supporting electrolyte was dissolved in 1.0 mol / liter of bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O ′) lithium borate. The configuration and test of the battery of Example 1 were the same. The results are shown in (Table 3).
[0071]
[Table 3]

[0072]
(Example 3)
The organic electrolyte was γ-butyrolactone, and the supporting electrolyte was a bis (2,2′-biphenyldiolate (2-)-O, O ′) lithium borate dissolved in 1.2 mol / liter except for that used. The configuration and test of the battery of Example 1 were the same. The results are shown in (Table 4).
[0073]
[Table 4]

[0074]
Example 4
The positive electrode current collector is made of 0.02mm titanium foil, the organic electrolyte is mixed with ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 2: 3: 3 volume ratio and bistetrafluoromethanesulfonic acid as the supporting electrolyte. The configuration and test of the battery of Example 1 were the same except that a solution in which 1.2 mol / liter of imidolithium ((CF ₃ SO ₂ ) ₂ NLi) was dissolved was used. The results are shown in (Table 5).
[0075]
[Table 5]

[0076]
(Example 5)
Lithium titanium disulfide (LiTiS ₂ ) is used as the positive electrode material, the organic electrolyte is γ-valerolactone, and bis (1,2-benzenediolate (2-)-O, O ′) lithium borate is used as the supporting electrolyte. The battery configuration of Example 1 was the same except that 1.2 mol / liter dissolved was used. The battery obtained here was charged at a constant current of 100 mA until it reached 2.8 V, and then a charge / discharge cycle was repeated until the battery was discharged at a constant current of 100 mA until it reached 0.5 V. The charging / discharging was repeated up to 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity was shown as the capacity maintenance ratio (Table 6). Furthermore, Table 6 shows that the same configuration is charged at a constant current of 100 mA until 2.8 V is reached, once discharged until 0.5 V, the initial battery capacity is checked, and again under the same conditions. 2. The ratio of the discharge capacity after storage to the discharge capacity before storage as the capacity maintenance rate when the battery charged to 2.8 V was stored at 60 ° C. for 20 days, and the battery after storage was punctured and captured in liquid paraffin The amount of gas collected was shown as a ratio with respect to 100 when graphite was used for the negative electrode.
[0077]
[Table 6]

[0078]
(Example 6)
Lithium titanium disulfide (LiTiS ₂ ) was used as the positive electrode material, the organic electrolyte was mixed with a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 2, and bis (2,3-naphthalenedioleate (2- The structure of the battery of Example 1 was the same except that a solution in which 1.0 mol / liter of lithium borate was dissolved was used. The battery obtained here was charged at a constant current of 100 mA until it reached 2.8 V, and then a charge / discharge cycle was repeated until the battery was discharged at a constant current of 100 mA until it reached 0.5 V. The charging / discharging was repeated up to 100 cycles, and the ratio of the discharge capacity at the 100th cycle to the initial discharge capacity is shown in Table 7 as the capacity retention rate. Furthermore, Table 7 shows that the same configuration is charged at a constant current of 100 mA until 2.8 V, discharged until 0.5 V, the initial battery capacity is checked, and again under the same conditions. 2. The ratio of the discharge capacity after storage to the discharge capacity before storage as the capacity maintenance rate when the battery charged to 2.8 V was stored at 60 ° C. for 20 days, and the battery after storage was punctured and captured in liquid paraffin The amount of gas collected was shown as a ratio with respect to 100 when graphite was used for the negative electrode.
[0079]
[Table 7]

[0080]
When the solid phase A is Si, the elements constituting the negative electrode material used in this example are Mg as the Group 2 element, Co and Ni as the transition element, Zn as the Group 12 element, Al as the Group 13 element, Group 14 Although Sn was used as an element, similar effects were obtained even when elements of each group other than these were used. When the solid phase A is Zn, Mg is used as the group 2 element, Cu and V are used as the transition element, Cd is used as the group 12 element, Al is used as the group 13 element, and Ge is used as the group 14 element. Similar effects were obtained even when elements were used.
[0081]
In addition, the preparation ratio of the negative electrode material constituent elements is not particularly limited. The phase is composed of two phases, and one phase (solid phase A) is mainly composed of Si and Zn. It is sufficient that the phase (solid phase B) covers a part or all of the surroundings, and the charging composition is not particularly limited. Phase B includes not only the solid solutions and intermetallic compounds shown in Table 1, but also includes cases in which trace amounts of elements constituting the respective solid solutions and intermetallic compounds and other elements are present.
[0082]
In addition, the combination and mixing ratio of the electrolyte solutions used in this example, and the amount of supporting electrolyte added are not uniquely determined, and can be arbitrarily combined, mixing ratio and amount added, and in that case The same effect was obtained. Therefore, the electrolytic solution is not limited to the combinations, mixing ratios, and addition amounts listed in this example. However, the type of the supporting electrolyte needs to be selected depending on the positive electrode material to be used because of its oxidation resistance voltage.
[0083]
【The invention's effect】
As described above, according to the present invention, there is provided a non-aqueous electrolyte secondary battery that has a higher capacity than that of a conventional carbon material as a negative electrode material and that is excellent in cycle characteristics, high rate charge / discharge characteristics, and high-temperature storage characteristics. can get.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a cylindrical battery in this embodiment.
DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode plate 5a Positive electrode lead 6 Negative electrode plate 6a Negative electrode lead 7 Separator 8 Insulation ring

Claims (2)

In a nonaqueous electrolyte secondary battery comprising a nonaqueous electrolyte, a separator, and a positive electrode and a negative electrode capable of occluding and releasing lithium, the negative electrode is formed on the entire surface or a part of the periphery of the core particles composed of the solid phase A. composite particles coated by phase B, the solid phase a is a constituent element silicon or zinc, the solid phase B is a structure based on elements of the solid phase a, with the exception of the construction elements, group 2 elements of the periodic table , A transition solution, a group 12 element, a group 13 element, and a solid solution with at least one element selected from the group consisting of group 14 elements excluding carbon, or a material that is an intermetallic compound, and has high oxidation resistance as a nonaqueous electrolyte In which an organic acid anionic lithium salt is dissolved in a basic organic solvent, and the organic acid anionic lithium salt is bispentafluoroethanesulfonic acid imidolithium ((C ₂ F ₅ SO ₂ ) ₂ NLi), bis (1, 2-benzenedio (2-)-O, O ') lithium borate, bis (2,3-naphthalenedioleate (2-)-O, O') lithium borate, bis (2,2'-biphenyldiolate (2- ) -O, O ') lithium borate, bis (5-fluoro-2-olate-1-benzenesulfonic acid-O, O') at least one compound selected from the group consisting of lithium borate Non-aqueous electrolyte secondary battery.   The high oxidation resistant organic solvent according to claim 1 contains at least one compound selected from the group consisting of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone. The nonaqueous electrolyte secondary battery according to claim 1.

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