JP2004095445A - Nonaqueous electrolyte secondary battery and nonaqueous electrolyte used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having excellent deep discharge characteristics and/or charge-discharge cycle characteristics. <P>SOLUTION: The nonaqueous electrolyte secondary battery comprises a positive electrode, negative electrode, separator interposed between the positive electrode and negative electrode, and nonaqueous electrolyte. At least one selected from a group of the positive electrode, negative electrode, and nonaqueous electrolyte contains alkali metal salt X and/or an oxidative decomposition product of the alkali metal salt X, and an oxygen decomposition potential of the alkali metal salt X is 3.2-4.3 V with respect to an Li potential Li<SP>+</SP>/Li. <P>COPYRIGHT: (C)2004,JPO

Description

【００１６】
（式（１）中、Ｒ^１、Ｒ^２、Ｒ^３およびＲ^４は、それぞれ独立に水素原子、水酸基、アルキル基、アルコキシル基、アリール基、スルホ基、アラルキル基またはハロゲン原子を示し、隣接する２つが結合して環構造を形成していても良い、また、Ｍは、リチウム原子、ナトリウム原子またはカリウム原子である）で表される化合物を用いることができる。
【００１７】
式（１）中のＲ^１、Ｒ^２、Ｒ^３およびＲ^４よりなる群から選ばれる少なくとも１つはアラルキル基であり、残りは水素原子であることが好ましい。
式（１）で表される化合物は、例えば、３，５−ジ−α−メチルベンジルサリチル酸リチウムおよび３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウムよりなる群から選ばれる少なくとも１種であることが好ましい。
前記アルカリ金属塩Ｘには、また、式（２）：
【００１８】
【化６】

【００１９】
（式（２）中、Ｒ^１、Ｒ^２、Ｒ^３およびＲ^４は、それぞれ独立に水素原子、水酸基、アルキル基、アルコキシル基、アリール基、スルホ基、アラルキル基またはハロゲン原子を示し、隣接する２つが結合して環構造を形成していても良い、また、Ｍは、リチウム原子、ナトリウム原子またはカリウム原子である）で表される化合物を用いることができる。
【００２０】
式（２）中のＲ^１、Ｒ^２、Ｒ^３およびＲ^４よりなる群から選ばれる少なくとも１つはアラルキル基であり、残りは水素原子であることが好ましい。
式（２）で表される化合物は、例えば、ビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウムおよびビス（３，５−ジ−α，α−ジメチルベンジルサリチル）ホウ酸リチウムよりなる群から選ばれる少なくとも１種であることが好ましい。
【００２１】
負極がアルカリ金属塩Ｘを含む場合、負極には、負極活物質１００重量部あたり、０．０１重量部〜１０重量部のアルカリ金属塩Ｘが含まれていることが好ましい。
【００２２】
本発明は、また、非水溶媒および前記非水溶媒に溶解したアルカリ金属塩Ｘからなる非水電解液に関する。
前記非水電解液におけるアルカリ金属塩Ｘの濃度は、０．００１モル／Ｌ（リットル）〜１．５モル／Ｌ、さらには０．００１モル／Ｌ〜１．２モル／Ｌであることが好ましい。
アルカリ金属塩Ｘには、非水電解液二次電池に用いる上記と同様のものを用いることができる。
【００２３】
【発明の実施の形態】
本発明の非水電解液二次電池においては、正極、負極、前記正極と負極との間に介在するセパレータおよび非水電解液からなり、正極、負極および非水電解液よりなる群から選ばれる少なくとも１つが、後述のアルカリ金属塩Ｘおよび／またはアルカリ金属塩Ｘの酸化分解生成物を含んでいる。
【００２４】
アルカリ金属塩Ｘの酸化分解電位は、一般に、Ｌｉ電位：Ｌｉ^＋／Ｌｉに対して３．２Ｖ〜４．３Ｖ、より好ましくは３．６Ｖ〜４．３Ｖである。
電池内の正極電位が対Ｌｉ電位で３．２Ｖ〜４．３Ｖの場合、アルカリ金属塩Ｘのアニオン部は、正極で酸化分解して、酸化分解生成物を生成する。酸化分解生成物は、例えば、非水電解液に対して不溶性の化合物もしくは重合体である。この酸化分解生成物は、例えば正極表面に抵抗皮膜として付着し、正極リテンションとして作用する。
【００２５】
一方、アルカリ金属塩Ｘに由来のアルカリ金属は、アニオンの分解に伴い放出された電子を用いてＬｉ^＋＋ｅ⁻→Ｌｉの反応を起こし、負極中に吸蔵されるものと考えられる。
すなわち、電池電圧０Ｖまで深放電した場合、正極側では正極リテンション量の増大で容量が減少するが、負極側ではＬｉの吸蔵反応により、負極容量が増大する。その結果、電池電圧が０Ｖに至る正極と負極とが落ち合う電位は、鉄、銅などの金属が溶解しない電位、例えば３．０Ｖ（ｖｓ　Ｌｉ^＋／Ｌｉ）を下回る電位になる。従って、負極と導通する電池ケースの腐蝕を防止できる。
【００２６】
しかも、アルカリ金属塩Ｘが電離して生成するアニオンの酸化分解は、初回の充電工程で初めて行われるため、負極に金属リチウムを貼り付けた場合のように、正極中に混在する金属が溶解し、直下の負極表面で析出して微小短絡に至ってしまうという問題も生じることはない。また、アルカリ金属塩Ｘの量を増やすと、電池電圧０Ｖ時の負極電位を、自然電位である３．２Ｖより低い側にシフトさせることができ、防蝕効果を向上させることができる。
【００２７】
本発明の効果を効率よく得るためには、アルカリ金属塩Ｘは、特に非水電解液および負極の少なくとも一方に含まれていることが好ましい。
非水電解液にアルカリ金属塩Ｘ以外の溶質（以下、溶質Ｙという。）が含まれている場合には、非水電解液中におけるアルカリ金属塩Ｘの濃度は、０．００１モル／Ｌ〜０．３０モル／Ｌであることが好ましい。
【００２８】
一方、アルカリ金属塩Ｘを非水電解液の主溶質として用いることもできる。その場合には、非水電解液中におけるアルカリ金属塩Ｘの濃度は、０．３０モル／Ｌ〜１．５モル／Ｌ、さらには０．３モル／Ｌ〜１．２モル／Ｌであることが好ましい。
【００２９】
アルカリ金属塩Ｘだけを溶質とする非水電解液を用いることも可能である。この場合、アルカリ金属塩Ｘが、通常の充電電位である４．２Ｖ以下で酸化分解してしまうと、電池特性が低下するため、アルカリ金属塩Ｘの酸化分解電位は、４．２を超えることが好ましい。アルカリ金属塩Ｘの酸化分解電位が４．２を超える場合であっても、通常の充電電位である４．２Ｖ以下で少量（例えば電解液中において０．００１モル／Ｌ相当以上）は酸化分解されるので、負極の電位を下げる効果がある。
【００３０】
負極にアルカリ金属塩Ｘが含まれている場合には、負極に含まれるアルカリ金属塩Ｘの量は、負極活物質１００重量部あたり、０．０１重量部〜１０重量部であることが好ましい。この場合、アルカリ金属塩Ｘは、非水電解液の非水溶媒に対する溶解度が０．１０モル／Ｌ以下であることが好ましい。負極にアルカリ金属塩Ｘを含ませることによっても、負極の電位を下げることができ、非水電解液にアルカリ金属塩Ｘを溶解させた場合と同様の効果を得ることができる。
アルカリ金属塩Ｘは、式（１）：
【００３１】
【化７】

【００３２】
（式（１）中、Ｒ^１、Ｒ^２、Ｒ^３およびＲ^４は、それぞれ独立に水素原子、水酸基、アルキル基、アルコキシル基、アリール基、スルホ基、アラルキル基またはハロゲン原子を示し、隣接する２つが結合して環構造を形成していても良い、また、Ｍは、リチウム原子、ナトリウム原子またはカリウム原子である）で表される化合物であることが好ましい。
特に、式（１）中のＲ^１、Ｒ^２、Ｒ^３およびＲ^４よりなる群から選ばれる少なくとも１つはアラルキル基であり、残りは水素原子であることが好ましい。
【００３３】
ここで、式（１）で表される化合物に含まれるアルキル基の炭素数は１〜８、アルコキシル基の炭素数は１〜４であることが好ましい。アルキル基としては、例えばメチル基、エチル基、プロピル基、イソプロピル基、ｔｅｒｔ−ブチル基、ｔｅｒｔ−アミル基、イソアミル基、ｎ−ヘキシル基、ｎ−オクチル基、ｔｅｒｔ−オクチル基、２−エチルヘキシル基等が好ましく、特にメチル基およびｔｅｒｔ−ブチル基が好ましい。また、アルコキシル基としては、メトキシ基、エトキシ基、プロポキシ基、イソプロポキシ基、ブトキシ基、ｔｅｒｔ−ブトキシ基等が好ましく、特にメトキシ基が好ましい。また、アリール基としては、フェニル基、トリル基、ナフチル基等が好ましく、特にフェニル基が好ましい。アラルキル基としては、ベンジル基、フェネチル基、α−メチルベンジル基、α，α−ジメチルベンジル基等が好ましく、特にα−メチルベンジル基、α，α−ジメチルベンジル基が好ましい。ハロゲン原子としてはフッ素原子、塩素原子、臭素原子が好ましい。
【００３４】
式（１）で表される化合物の具体例としては、３−メチルサリチル酸リチウム、４−メチルサリチル酸リチウム、５−メチルサリチル酸リチウム、４−ｔｅｒｔ−オクチルサリチル酸リチウム、３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウム、３，５−ジ−α−メチルベンジルサリチル酸リチウム、３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウム、３，５−ジ−メチルサリチル酸リチウム、３−クロロサリチル酸リチウム、４−クロロサリチル酸リチウム、５−フルオロサリチル酸リチウム、５−クロロサリチル酸リチウム、３，５−ジクロロサリチル酸リチウム、３，５，６−トリクロロサリチル酸リチウム、４−メトキシサリチル酸リチウム、５−ブロモサリチル酸リチウム、４−ヒドロキシ安息香酸リチウム、３−ヒドロキシ−２−ナフトエ酸リチウム、５−スルホサリチル酸リチウム等が挙げられる。これらは、単独で用いてもよく、２種以上を組み合わせて用いてもよい。
【００３５】
アルカリ金属塩Ｘを非水電解液に含ませる場合には、上記の中でも、特に、３，５−ジ−α−メチルベンジルサリチル酸リチウムおよび３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウムが特に好ましい。
また、負極にアルカリ金属塩Ｘを含ませる場合には、特に、３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウム、５−スルホサリチル酸リチウムが好ましい。
アルカリ金属塩Ｘとしては、また、式（２）：
【００３６】
【化８】

【００３７】
（式（２）中、Ｒ^１、Ｒ^２、Ｒ^３およびＲ^４は、それぞれ独立に水素原子、水酸基、アルキル基、アルコキシル基、アリール基、スルホ基、アラルキル基またはハロゲン原子を示し、隣接する２つが結合して環構造を形成していても良い、また、Ｍは、リチウム原子、ナトリウム原子またはカリウム原子である）で表される化合物を好ましく用いることができる。
特に、式（２）中のＲ^１、Ｒ^２、Ｒ^３およびＲ^４よりなる群から選ばれる少なくとも１つはアラルキル基であり、残りは水素原子であることが好ましい。
【００３８】
ここで、式（２）で表される化合物に含まれるアルキル基の炭素数は１〜８、アルコキシル基の炭素数は１〜４であることが好ましい。アルキル基としては、例えばメチル基、エチル基、プロピル基、イソプロピル基、ｔｅｒｔ−ブチル基、ｔｅｒｔ−アミル基、イソアミル基、ｎ−ヘキシル基、ｎ−オクチル基、ｔｅｒｔ−オクチル基、２−エチルヘキシル基等が好ましく、特にメチル基およびｔｅｒｔ−ブチル基が好ましい。また、アルコキシル基としては、例えばメトキシ基、エトキシ基、プロポキシ基、イソプロポキシ基、ブトキシ基、ｔｅｒｔ−ブトキシ基が好ましく、特にメトキシ基が好ましい。アリール基としては、フェニル基、トリル基、ナフチル基等が好ましく、特にフェニル基が好ましい。アラルキル基としては、ベンジル基、フェネチル基、α−メチルベンジル基、α，α−ジメチルベンジル基等が好ましく、特にα−メチルベンジル基およびα，α−ジメチルベンジル基が好ましい。ハロゲン原子としては、フッ素原子、塩素原子、臭素原子が好ましい。
【００３９】
式（２）で表される化合物の具体例としては、ビスサリチルホウ酸リチウム、ビス（３，５−ジ−ｔｅｒｔ−ブチルサリチル）ホウ酸リチウム、ビス（３，５−ジ−メチルサリチル）ホウ酸リチウム、ビス（３，５−ジクロロサリチル）ホウ酸リチウム、ビス（３−メチルサリチル）ホウ酸リチウム、ビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウム、ビス（３，５−ジ−α，α−ジメチルベンジルサリチル）ホウ酸リチウム、ビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウム等が挙げられる。これらは、単独で用いてもよく、２種以上を組み合わせて用いてもよい。
【００４０】
上記の中でも、非水電解液中に含有させるには、ビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウム、ビス（３，５−ジ−α，α−ジメチルベンジルサリチル）ホウ酸リチウムなどが好ましく、負極に含有させるには、ビス（３，５−ジクロロサリチル）ホウ酸リチウム、ビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウムなどが特に好ましい。
式（２）で表される化合物と類似の構造を有する式（３）：
【００４１】
【化９】

【００４２】
（式（３）中、Ｒ^１およびＲ^４は、それぞれ独立に水素原子、アルキル基、置換または無置換の芳香環を示し、Ｒ^２およびＲ^３は、それぞれ独立に置換または無置換の芳香環を示す、また、Ｍは、リチウム原子、ナトリウム原子またはカリウム原子である）で表される化合物についても同様の効果が期待される。なお、芳香環には、ナフチル基誘導体などの縮合環も含まれる。
【００４３】
式（３）中のＲ^１およびＲ^４で表されるアルキル基としては、メチル基、エチル基、プロピル基、ブチル基、アミル基等が挙げられ、Ｒ^１〜Ｒ^４で表される芳香環としては、ベンゼン環、ナフタレン環等が挙げられる。また、芳香環の置換基としては、アルキル基、アルコキシ基、ハロゲン原子、アリール基、アラルキル基等が挙げられる。
式（３）で表される化合物の具体例としては、例えば、ビス（１，１−ジフェニル−１−オキソ−アセチル）ホウ酸リチウムを挙げることができる。
【００４４】
非水電解液に用いる非水溶媒としては、従来から公知のものを使用することができる。例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネート、γ−ブチロラクトン、酢酸メチル、プロピオン酸メチル、メチルブチルエーテル、ビニレンカーボネート、１，２−ジメトキシエタン、１，２−ジクロロエタン、１，３−ジメトキシプロパン、４−メチル−２−ペンタノン、１，４−ジオキサン、アセトニトリル、プロピオニトリル、ブチロニトリル、バレロニトリル、ベンゾニトリル、スルホラン、３−メチル−スルホラン、テトラヒドロフラン、２−メチルテトラヒドロフラン、ジメチルホルムアミド、ジエチルホルムアミド、ジメチルスルホキシド、リン酸トリメチル、リン酸トリエチル等が挙げられる。これらの非水溶媒は２種以上を混合して用いても良い。例えば、環状カーボネートと鎖状カーボネートとを含む非水溶媒が好ましい。
【００４５】
非水電解液に含ませることができるアルカリ金属塩Ｘ以外の溶質Ｙとしては、ＬｉＰＦ_６、ＬｉＢＦ_４、　ＬｉＣｌＯ_４、ＬｉＡｓＦ_６、ＬｉＳｂＦ_６、ＬｉＳＣＮ、ＬｉＣＦ_３ＳＯ_３、ＬｉＢｒ、ＬｉＩ、ＬｉＮ（ＳＯ_２ＣＦ_３）_２、ＬｉＮ（ＳＯ_２Ｃ_２Ｆ_５）_２、ＬｉＣ（ＳＯ_２ＣＦ_３）_３、ＬｉＣ（ＳＯ_２Ｃ_２Ｆ_５）_３、Ｌｉ_２Ｂ_１０Ｃｌ_１０、低級脂肪族カルボン酸リチウム、クロロボランリチウム、四フェニルホウ酸リチウム等を挙げることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。なかでもＬｉＰＦ_６、ＬｉＢＦ_４を用いることが好ましい。溶質Ｙの非水電解液中における濃度は、０．５〜１．５モル／Ｌであることが好ましい。
【００４６】
また、近年報告されている特開平１０−２６５４７９号公報記載のリチウムビスナフタレンジオラトボレート、特表２０００−５１６９３０号公報記載のリチウムビス［２，２’−ビフェニルジオラート（２−）−Ｏ，Ｏ’］ボレート（１−）等のリチウム錯体塩、特開２００１−５５３９６号公報記載のリチウムビス［５−フルオロ−２−オラト−ベンゼンスルフォナート（２−）Ｏ，Ｏ’］−ボレート（１−）等のリチウム錯体塩等も溶質Ｙとして挙げることができる。これらは非水溶媒に対する溶解度が低いので、単独で用いることはできないが、非水電解液の溶質としてアルカリ金属塩Ｘと併用することができる。
【００４７】
非水電解液には、さらに、安定剤として、特開平１０−６４５９１号公報に開示されているアリールアルキルエーテル化合物やアリールアリールエーテル、特開平５−１５９７８７号公報に開示されている炭素−炭素三重結合を有するプロパギルアルコール等のアルコール、特開２００１−２５６９９５号公報に開示されている活性水素を持たないアルキニル基および／またはアルキニレン基を有する酸素含有脂肪族化合物を含有させることもできる。
【００４８】
正極は、例えば、普通のアルミニウム箔やラス加工もしくはエッチング処理されたアルミニウム箔からなる厚み１０μｍ〜６０μｍの正極集電体の片面または両面に、正極ペーストを塗着し、乾燥し、圧延して正極活物質層を形成することにより作製される。正極ペーストは、正極活物質と、結着剤と、導電剤と、必要に応じて増粘剤とを、分散媒に分散させて調製される。正極には活物質層を有さない無地部を設け、ここに正極リードが溶接される。
【００４９】
正極活物質としては、特に限定されるものではないが、例えば、リチウムイオンをゲストとして受け入れ得るリチウム含有遷移金属化合物が使用される。例えば、コバルト、マンガン、ニッケル、クロム、鉄およびバナジウムから選ばれる少なくとも１種の遷移金属と、リチウムとの複合金属酸化物が使用される。なかでもＬｉ_ｘＣｏＯ_２、Ｌｉ_ｘＭｎＯ_２、Ｌｉ_ｘＮｉＯ_２、ＬｉＣｒＯ_２、αＬｉＦｅＯ_２、ＬｉＶＯ_２、Ｌｉ_ｘＣｏ_ｙＮｉ_１−ｙＯ_２、Ｌｉ_ｘＣｏ_ｙＭ_１−ｙＯ_ｚ、Ｌｉ_ｘＮｉ_１−ｙＭ_ｙＯ_ｚ、Ｌｉ_ｘＭｎ_２Ｏ_４、Ｌｉ_ｘＭｎ_２−ｙＭ_ｙＯ_４　（ここで、Ｍ＝Ｎａ、Ｍｇ、Ｓｃ、Ｙ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ａｌ、Ｃｒ、Ｐｂ、ＳｂおよびＢよりなる群から選ばれる少なくとも１種、ｘ＝０〜１．２、ｙ＝０〜０．９、ｚ＝２．０〜２．３）、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物、ニオブ酸化物のリチウム化物等が好ましい。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。なお、上記のｘ値は充放電により増減する。正極活物質の平均粒径は、１μｍ〜３０μｍであることが好ましい。
【００５０】
正極ペーストに用いる結着剤、導電剤、必要に応じて添加できる増粘剤は、従来と同様のものを用いることができる。
結着剤としては、ペーストの分散媒に溶解または分散できるものであれば特に限定されるものではないが、例えば、フッ素系結着剤、アクリルゴム、変性アクリルゴム、スチレン−ブタジエンゴム（ＳＢＲ）、アクリル系重合体、ビニル系重合体等を用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。なお、フッ素系結着剤としては、例えば、ポリフッ化ビニリデン、フッ化ビニリデンと六フッ化プロピレンの共重合体、ポリテトラフルオロエチレン等が好ましく、これらはディスパージョンとして用いることができる。
【００５１】
導電剤としては、アセチレンブラック、グラファイト、炭素繊維等を用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。
増粘剤としては、エチレン−ビニルアルコール共重合体、カルボキシメチルセルロース、メチルセルロースなどが好ましい。
【００５２】
分散媒としては、結着剤が溶解可能なものが適切である。有機系結着剤を用いる場合は、Ｎ−メチル−２−ピロリドン、Ｎ，Ｎ−ジメチルホルムアミド、テトラヒドロフラン、ジメチルアセトアミド、ジメチルスルホキシド、ヘキサメチルスルホルアミド、テトラメチル尿素、アセトン、メチルエチルケトン等を単独または混合して用いることが好ましい。また、水系結着剤を用いる場合は、水や温水が好ましい。
【００５３】
正極活物質、結着剤、導電剤および必要に応じて加える増粘剤を分散媒に分散させて正極ペーストを作製する方法は、特に限定されるものではないが、例えば、プラネタリーミキサー、ホモミキサー、ピンミキサー、ニーダー、ホモジナイザー等を用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。また、正極ペーストの混練分散時に、各種分散剤、界面活性剤、安定剤等を必要に応じて添加することも可能である。
【００５４】
正極ペーストは、例えば、スリットダイコーター、リバースロールコーター、リップコーター、ブレードコーター、ナイフコーター、グラビアコーター、ディップコーター等を用いて、正極集電体へ容易に塗着することができる。正極集電体に塗着された正極ペーストは、自然乾燥に近い乾燥を行うことが好ましいが、生産性を考慮すると、７０℃〜２００℃の温度で１０分間〜５時間乾燥させるのが好ましい。
圧延は、ロールプレス機によって極板が所定の厚みになるまで、線圧１０００〜２０００ｋｇ／ｃｍで数回を行うか、線圧を変えて圧延するのが好ましい。
【００５５】
負極は、例えば、普通の銅箔やラス加工もしくはエッチング処理された銅箔からなる厚み１０μｍ〜５０μｍの負極集電体の片面または両面に、負極ペーストを塗着し、乾燥し、圧延して負極活物質層を形成することにより作製される。負極ペーストは、負極活物質と、結着剤と、必要に応じて導電剤と、増粘剤とを、分散媒に分散させて調製される。負極には活物質層を有さない無地部を設け、ここに負極リードが溶接される。
【００５６】
負極活物質としては、特に限定されるものではないが、充電・放電によりリチウムイオンを放出・吸蔵できる炭素材料を用いることが好ましい。例えば、有機高分子化合物（フェノール樹脂、ポリアクリロニトリル、セルロース等）を焼成することにより得られる炭素材料、コークスやピッチを焼成することにより得られる炭素材料、人造黒鉛、天然黒鉛、ピッチ系炭素繊維、ＰＡＮ系炭素繊維等が好ましく、その形状としては、繊維状、球状、鱗片状、塊状のものを用いることができる。
【００５７】
結着剤、必要に応じて用いられる導電剤、増粘剤には、従来と同様のものを用いることができる。例えば、正極板と同様の結着剤、導電剤、増粘剤を用いることができる。
【００５８】
セパレータとしては、ポリエチレン、ポリプロピレン、ポリフッ化ビニリデン、ポリ塩化ビニリデン、ポリアクリロニトリル、ポリアクリルアミド、ポリテトラフルオロエチレン、ポリスルホン、ポリエーテルスルホン、ポリカーボネート、ポリアミド、ポリイミド、ポリエーテル（ポリエチレンオキシドやポリプロピレンオキシド）、セルロース（カルボキシメチルセルロースやヒドロキシプロピルセルロース）、ポリ（メタ）アクリル酸、ポリ（メタ）アクリル酸エステル等の高分子からなる微多孔フィルムが好ましく用いられる。また、これらの微多孔フィルムを重ね合わせた多層フィルムも用いられる。なかでもポリエチレン、ポリプロピレン、ポリフッ化ビニリデン等からなる微多孔フィルムが好適であり、厚みは１５μｍ〜３０μｍが好ましい。
【００５９】
電池ケースの材質としては、銅、ニッケル、ステンレス鋼、ニッケルメッキ鋼などを用いることができる。これらの材料に絞り加工、ＤＩ加工等を施して電池ケースの形状にすることができる。ケースの防蝕性を高めるために、加工後の電池ケースにメッキ処理を施しても良い。
【００６０】
本発明は、例えばコイン型、ボタン型、シート型、積層型、円筒型、偏平型、角型等の電池に適用することができるが、これらに限定されるものではない。また、本発明は、電気自動車等に用いる大型の電池にも適用できる。本発明の非水電解液二次電池は、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などに用いることができるが、特にこれらの用途に限定されるものではない。
【００６１】
【実施例】
以下、本発明の詳細を実施例および比較例を挙げて説明するが、これらは本発明を何ら限定するものではない。なお、以下の実施例および比較例では、図１に縦断面図で示すような円筒型リチウム二次電池（非水電解液は図示せず）を作製した。
図１において、正極板１１と負極板１２とがセパレータ１３を介して渦巻状に捲回された極板群が、上部が開口している有底筒状の電池ケース１８に収納されている。正極板１１から引き出された正極リード１４は、上部絶縁板１６を介して、正極端子２０に導通する封口体１９の内部端子に電気的に接続されている。また、負極板１２から引き出された負極リード１５は、下部絶縁板１７を介して、電池ケース１８の底部と電気的に接続されている。電池ケース１８の開口端部は、封口体１９にかしめ加工されており、これにより電池ケース１８の内部は密閉されている。
【００６２】
まず、以下の実施例および比較例で用いるアルカリ金属塩Ｘの合成方法について、合成例１および合成例２を挙げて説明する。なお、他のアルカリ金属塩Ｘは、合成例１または合成例２と同様にして合成することができる。
【００６３】
《合成例１》
式（１）で表される化合物の一例である３，５−ジ−α−メチルベンジルサリチル酸リチウムの合成例を示す。
容積５００ｍｌの反応フラスコに３，５−ジ−α−メチルベンジルサリチル酸１５０ｇを投入し、トルエン３００ｍｌを加えてスラリー状にした。撹拌下、３，５−ジ−α−メチルベンジルサリチル酸と等モルの水酸化リチウム一水和物をフラスコ内に加えてさらに攪拌した。次いで、フラスコ内を減圧して溶媒を留去し、フラスコ内の物質を濃縮乾固した。こうして３，５−ジ−α−メチルベンジルサリチル酸リチウムの白色固体を得た。
【００６４】
《合成例２》
式（２）で表される化合物の一例であるビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウムの合成例を示す。
容積１０００ｍｌの反応フラスコに３，５−ジ−α−メチルベンジルサリチル酸１５０ｇ、炭酸リチウム８ｇ、ホウ酸１３．４ｇを投入し、トルエン７００ｍｌおよび炭酸ジメチル５０ｍｌを加えた。次いで、撹拌下、フラスコ内の混合物を加熱しながら還流脱水した。このときスラリー状態のまま理論量の水が回収できるまで還流した。理論量の水を回収後、室温まで放冷した。次いで、フラスコ内を減圧して溶媒を留去し、フラスコ内の物質を濃縮乾固した。こうしてビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウムの白色固体１５２ｇを得た。
【００６５】
《実施例１》
（ｉ）正極板の作製
正極活物質のコバルト酸リチウムを１００重量部と、導電剤のアセチレンブラックを３重量部と、結着剤のポリフッ化ビニリデン（ＰＶＤＦ）のＮ−メチル−２−ピロリドン（ＮＭＰ）溶液（ＰＶＤＦ分１２重量％）を３３重量部と、分散媒のＮＭＰを１３重量部とを混練して、正極ペーストを調製した。この正極ペーストを、厚さ２０μｍの帯状のアルミニウム箔からなる集電体の両面に塗着し、乾燥して、厚さ２９０μｍの極板を作製した。この極板を、線圧１０００Ｋｇ／ｃｍで３回圧延することにより、極板の厚さを１８０μｍにした。こうして得られた正極板の無地部に正極リードをスポット溶接で取り付けた。
【００６６】
（ｉｉ）負極板の作製
負極活物質の人造塊状黒鉛を１００重量部と、結着剤のＰＶＤＦのＮＭＰ溶液（ＰＶＤＦ分６重量％）を６７重量部と、３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムを０．０１重量部と、分散媒のＮＭＰを１３重量部とを混練して、負極ペーストを作製した。この負極ペーストを、厚さ１４μｍの帯状の銅箔からなる集電体の両面に塗着し、乾燥して、厚さ３００μｍの極板を作製した。この極板を、線圧１１０Ｋｇ／ｃｍで３回圧延することにより、極板の厚さを１９６μｍにした。こうして得られた負極板の無地部に負極リードをスポット溶接で取り付けた。
【００６７】
（ｉｉｉ）非水電解液の調製
エチレンカーボネートとエチルメチルカーボネートとの等重量比の混合溶媒中に、溶質としてヘキサフルオロリン酸リチウム（ＬｉＰＦ_６）を１．２モル／Ｌの濃度で溶解させて非水電解液を調製した。
【００６８】
（ｉｖ）電池の組み立て
得られた正極板と負極板とを、３層構造のセパレータを介して、渦巻状に捲回して、極板群を構成した。ここでは、３層構造のセパレータには、厚さ１０μｍのポリエチレン製微多孔フィルムおよびその両側に接する厚さ５μｍのポリプロピレン製微多孔フィルムからなるセパレータを用いた。極板群を上部が開口している有底の電池ケース内に収納し、正極リードの端部を封口体の内部端子に接続した。また、負極リードの端部は、電池ケースの底部に接続した。極板群の上下には、それぞれ上部絶縁板および下部絶縁板を配した。なお、電池ケースには、厚さ１．０μｍのニッケルメッキを施した厚さ０．３ｍｍの鋼板を用いた。
【００６９】
次いで、電池ケース内に非水電解液を所定量注液した後、電池ケースを封口体で封口して、ＪＩＳ　Ｃ８７１１に記載されているＩＣＲ１８６５０サイズで、電池容量が２０００ｍＡｈの電池を完成した。得られた電池は、室温で４時間放置した後、電池電圧が４．２Ｖに達するまで４００ｍＡ（０．２ＩｔＡ）の定電流定電圧充電による初回充電を行った。
【００７０】
《実施例２》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、０．２重量部に変更したこと以外は、実施例１と同様にして実施例２の非水電解液二次電池を作製した。
【００７１】
《実施例３》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、１．０重量部に変更したこと以外は、実施例１と同様にして実施例３の非水電解液二次電池を作製した。
【００７２】
《実施例４》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、１０重量部に変更したこと以外は、実施例１と同様にして実施例４の非水電解液二次電池を作製した。
【００７３】
《実施例５》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの代わりに、５−スルホサリチル酸リチウムを用い、負極に含ませるその量を、負極活物質の人造塊状黒鉛１００重量部あたり、２．０重量部にしたこと以外は、実施例１と同様にして実施例５の非水電解液二次電池を作製した。
【００７４】
《実施例６》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムと５−スルホサリチル酸リチウムとを併用し、負極に含ませるそれらの量を、負極活物質の人造塊状黒鉛１００重量部あたり、それぞれ３．０重量部と１．０重量部をとしたこと以外は、実施例１と同様にして実施例６の非水電解液二次電池を作製した。
【００７５】
《実施例７》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの代わりに、ビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウムを用い、負極に含ませるその量を、負極活物質の人造塊状黒鉛１００重量部あたり、３．０重量部にしたこと以外は、実施例１と同様にして実施例７の非水電解液二次電池を作製した。
【００７６】
《実施例８》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムとビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウムとを併用し、負極に含ませるそれらの量を、負極活物質の人造塊状黒鉛１００重量部あたり、それぞれ２．０重量部としたこと以外は、実施例１と同様にして実施例８の非水電解液二次電池を作製した。
【００７７】
《実施例９》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの代わりに、ビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウムを用い、負極に含ませるその量を、負極活物質の人造塊状黒鉛１００重量部あたり、１．５重量部とし、さらにビス（４−ｔｅｒｔ−オクチルサリチル）ホウ酸リチウム３．５重量部を併用したこと以外は、実施例１と同様にして実施例９の非水電解液二次電池を作製した。
【００７８】
《実施例１０》
３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの代わりに、式（３）で示される化合物としてビス（１，１−ジフェニル−１−オキソ−アセチル）ホウ酸リチウムを用い、負極に含ませるその量を、負極活物質の人造塊状黒鉛１００重量部あたり、２．５重量部にしたこと以外は、実施例１と同様にして実施例１０の非水電解液二次電池を作製した。
【００７９】
《実施例１１》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、２．０重量部に変更し、３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムを正極活物質１００重量部対して、１．０重量部含ませた正極板を用いたこと以外は、実施例１と同様にして実施例１１の非水電解液二次電池を作製した。
【００８０】
《比較例１》
負極板中に３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムを含有させなかったこと以外は、実施例１と同様にして比較例１の非水電解液二次電池を作製した。
【００８１】
《実施例１２》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、０．００５重量部に変更したこと以外は、実施例１と同様にして実施例１２の非水電解液二次電池を作製した。
【００８２】
《実施例１３》
負極に含ませる３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムの量を、負極活物質の人造塊状黒鉛１００重量部あたり、１５重量部に変更したこと以外は、実施例１と同様にして実施例１３の非水電解液二次電池を作製した。
【００８３】
《実施例１４》
（ｉ）正極板の作製
正極活物質のコバルト酸リチウムを１００重量部と、導電剤のアセチレンブラックを３重量部と、結着剤のポリテトラフルオロエチレン（ＰＴＦＥ）のディスパージョンをＰＴＦＥ分で４重量部と、増粘剤のカルボキシメチルセルロースを０．８重量部と、適量の水とを混練して、正極ペーストを作製した。この正極ペーストを、厚さ２０μｍの帯状のアルミニウム箔からなる集電体の両面に塗着し、乾燥して、厚さ２９０μｍの極板を作製した。この極板を、線圧１０００Ｋｇ／ｃｍで３回圧延することにより、極板の厚さを１８０μｍにした。こうして得られた正極板の無地部に正極リードをスポット溶接で取り付けた。
【００８４】
（ｉｉ）負極板の作製
負極活物質の鱗片状黒鉛１００重量部と、結着剤のスチレンブタジエンゴム（ＳＢＲ）の水溶性ディスパージョンをＳＢＲ分で４重量部と、増粘剤のカルボキシメチルセルロースを０．８重量部と、適量の水とを混練して、負極ペーストを作製した。この負極ペーストを、厚さ１４μｍの帯状の銅箔からなる集電体の両面に塗着し、乾燥して、厚さ３００μｍの極板を作製した。この極板を、線圧１１０Ｋｇ／ｃｍで３回圧延することにより、極板の厚さを１９６μｍにした。こうして得られた負極板の無地部に負極リードをスポット溶接で取り付けた。
【００８５】
（ｉｉｉ）非水電解液の調製
エチレンカーボネートと、エチルメチルカーボネートと、ジエチルカーボネートとの重量比４：５：２の混合溶媒中に、溶質として３，５−ジ−α−メチルベンジルサリチル酸リチウムを０．００１モル／Ｌ、およびヘキサフルオロリン酸リチウム（ＬｉＰＦ_６）を１．２モル／Ｌの濃度でそれぞれ溶解させて非水電解液を調製した。
【００８６】
（ｉｖ）電池の組み立て
得られた正極板と負極板とを、２層構造のセパレータを介して、渦巻状に捲回して、極板群を構成した。ここでは、２層構造のセパレータには、厚さ１０μｍのポリエチレン製微多孔フィルムおよびその片側に接する厚さ１０μｍのポリプロピレン製微多孔フィルムからなるセパレータを用いた。
この極板群を用い、上記の非水電解液を用いたこと以外は、実施例１と同様のＩＣＲ１８６５０サイズで電池容量が２０００ｍＡｈの電池を完成した。得られた電池は、室温で４時間放置した後、電池電圧が４．２Ｖに達するまで４００ｍＡ（０．２ＩｔＡ）の定電流定電圧充電による初回充電を行った。
【００８７】
《実施例１５》
非水電解液中における３，５−ジ−α−メチルベンジルサリチル酸リチウムの濃度を０．０５モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例１５の非水電解液二次電池を作製した。
【００８８】
《実施例１６》
３，５−ジ−α−メチルベンジルサリチル酸リチウムの代わりに、非水電解液中に３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウムを濃度０．２モル／Ｌで含有させたこと以外は、実施例１４と同様にして実施例１６の非水電解液二次電池を作製した。
【００８９】
《実施例１７》
非水電解液中に３，５−ジ−α−メチルベンジルサリチル酸リチウムのみを０．５モル／Ｌの濃度で含有させ、ＬｉＰＦ_６は含有させなかったこと以外は、実施例１４と同様にして実施例１７の非水電解液二次電池を作製した。
【００９０】
《実施例１８》
３，５−ジ−α−メチルベンジルサリチル酸リチウムの代わりに、非水電解液中に５−フルオロサリチル酸リチウムを０．０５モル／Ｌの濃度で含有させたこと以外は、実施例１４と同様にして実施例１８の非水電解液二次電池を作製した。
【００９１】
《実施例１９》
３，５−ジ−α−メチルベンジルサリチル酸リチウムの代わりに、非水電解液中に３，５−ジクロロサリチル酸リチウムを０．２モル／Ｌの濃度で含有させ、ＬｉＰＦ_６の濃度を０．９モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例１９の非水電解液二次電池を作製した。
【００９２】
《実施例２０》
非水電解液中における３，５−ジ−α−メチルベンジルサリチル酸リチウムの濃度を０．０４モル／Ｌに変更し、さらに５−フルオロサリチル酸リチウムを０．０１モル／Ｌの濃度で非水電解液に含有させたこと以外は、実施例１４と同様にして実施例２０の非水電解液二次電池を作製した。
【００９３】
《実施例２１》
非水電解液中における３，５−ジ−α−メチルベンジルサリチル酸リチウムの濃度を０．５モル／Ｌに変更し、さらに３，５−ジクロロサリチル酸リチウムを０．２モル／Ｌの濃度で非水電解液に含有させ、ＬｉＰＦ_６の濃度を０．３モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例２１の非水電解液二次電池を作製した。
【００９４】
《実施例２２》
３，５−ジ−α−メチルベンジルサリチル酸リチウムの代わりに、非水電解液中にビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウムのみを０．５モル／Ｌの濃度で含有させ、ＬｉＰＦ_６は含有させなかったこと以外は、実施例１４と同様にして実施例２２の非水電解液二次電池を作製した。
【００９５】
《実施例２３》
非水電解液中におけるビス（３，５−ジ−α−メチルベンジルサリチル）ホウ酸リチウムの濃度を１．２モル／Ｌに変更したこと以外は、実施例２２と同様にして実施例２３の非水電解液二次電池を作製した。
【００９６】
《実施例２４》
３，５−ジ−α−メチルベンジルサリチル酸リチウムは用いずに、非水電解液中にビス（３−ヒドロキシ−２−ナフトエ）ホウ酸リチウムを０．０１モル／Ｌ、ビスサリチルホウ酸リチウムを０．０２モル／Ｌの濃度でそれぞれ含有させ、ＬｉＰＦ_６の濃度を１．０モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例２４の非水電解液二次電池を作製した。
【００９７】
《実施例２５》
３，５−ジ−α−メチルベンジルサリチル酸リチウムは用いずに、非水電解液中にビス（３，５−ジ−α，α−ジメチルベンジルサリチル）ホウ酸リチウムを０．３モル／Ｌ、３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウムを０．３モル／Ｌの濃度でそれぞれ含有させ、ＬｉＰＦ_６の濃度を０．３モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例２５の非水電解液二次電池を作製した。
【００９８】
《実施例２６》
３，５−ジ−α−メチルベンジルサリチル酸リチウムは用いずに、非水電解液中に３，５−ジ−α，α−ジメチルベンジルサリチル酸リチウムを０．０５モル／Ｌの濃度で含有させ、ＬｉＰＦ_６の濃度を１．０モル／Ｌに変更し、負極板中に３，５−ジ−ｔｅｒｔ−ブチルサリチル酸リチウムを負極活物質１００重量部あたり０．０５重量部含有させたこと以外は、実施例１４と同様にして実施例２６の非水電解液二次電池を作製した。
【００９９】
《実施例２７》
非水電解液中における３，５−ジ−α−メチルベンジルサリチル酸リチウムの濃度を０．０００５モル／Ｌに変更したこと以外は、実施例１４と同様にして実施例２７の非水電解液二次電池を作製した。
【０１００】
《実施例２８》
非水電解液中における３，５−ジ−α−メチルベンジルサリチル酸リチウムの濃度を２．０モル／Ｌに変更し、ＬｉＰＦ_６は含有させなかったこと以外は、実施例１４と同様にして実施例２８の非水電解液二次電池を作製した。ただし、３，５−ジ−α−メチルベンジルサリチル酸リチウムは全て溶解しなかったため、実際の濃度は２．０モル／Ｌ未満である。
【０１０１】
［評価］
このようにして作製した実施例１〜実施例２８および比較例１の非水電解液二次電池を各２０個ずつ用いて、深放電状態の負極の対Ｌｉ電位、ケースの腐蝕比率、容量回復率および充放電サイクル特性を評価した。
【０１０２】
（ｉ）負極の対Ｌｉ電位
エージング終了後の電池を、電池電圧が４．２Ｖに達するまでは１４００ｍＡ（０．７ＩｔＡ）の定電流で充電し、次いで、電流値が減衰して１００ｍＡ（０．０５ＩｔＡ）になるまで定電圧で充電した。次いで、２０００ｍＡ（１．０ＩｔＡ）の定電流で、３．０Ｖの放電終止電圧まで電池を放電した後、１ＫΩの定抵抗を接続して６０℃環境下で５０日間放置した。次いで抵抗を電池から取り外し、電池ケースの底を円盤状に切り取った。そして、参照電極を電池群の巻き芯部の筒状スペースに差し込んで接液させ、それを基準に負極の対Ｌｉ電位を測定した。そして２０個の電池の負極の対Ｌｉ電位の平均値を求めた。
なお、参照電極はポリテトラフルオロエチレン製のチューブ中に白金線とリチウムホイルを挿入して作製した。
【０１０３】
（ｉｉ）ケースの腐蝕比率
上記負極の対Ｌｉ電位の測定と同様に深放電させた電池において、ケースが腐蝕しているか、目視による外観検査を行った。２０個の電池のうち腐蝕のあった電池数をｎとし、腐蝕比率はｎ／２０で表した。
【０１０４】
（ｉｉｉ）容量回復率
まず、エージング終了後の電池を、電池電圧が４．２Ｖに達するまでは１４００ｍＡ（０．７ＩｔＡ）の定電流で充電し、次いで、電流値が減衰して１００ｍＡ（０．０５ＩｔＡ）になるまで定電圧で充電した。次いで、２０００ｍＡ（１．０ＩｔＡ）の定電流で、３．０Ｖの放電終止電圧まで放電したときの初期容量を求めた。次いで、１ＫΩの定抵抗を電池に接続して６０℃環境下で５０日間放置した。
次いで、抵抗を電池から取り外し、初期容量を求めた場合と同じ充放電条件で、深放電後の容量を求めた。初期容量を１００％としたときの深放電後の容量の比率を容量回復率とした。そして２０個の電池の容量回復率の平均値を求めた。
【０１０５】
（ｉｖ）充放電サイクル特性
電池電圧が４．２Ｖに達するまでは１４００ｍＡ（０．７ＩｔＡ）の定電流充電を行い、次いで電流値が減衰して１００ｍＡ（０．０５ＩｔＡ）になるまで定電圧充電した後、２０００ｍＡ（１．０ＩｔＡ）の定電流で３．０Ｖの放電終止電圧まで放電するという充放電サイクルを行った。この充放電サイクルを、２０℃の環境下で、５００サイクル繰り返し、３サイクル目を１００％とした場合の５００サイクル目の容量の比率を、容量維持率として求めた。そして２０個の電池の容量維持率の平均値を求めた。
これらの結果を表１および表２に示す。
【０１０６】
【表１】

【０１０７】
【表２】

【０１０８】
表１〜２の内容について説明する。
実施例１〜１０および実施例１２〜１３では、アルカリ金属塩Ｘが、負極に含まれている。
実施例１１では、アルカリ金属塩Ｘが、正極と負極の両方に含まれている。
実施例１４〜２５および実施例２７〜２８では、アルカリ金属塩Ｘが非水電解液に含まれている。
実施例２６では、アルカリ金属塩Ｘが、負極と非水電解液の両方に含まれている。
一方、比較例１では、アルカリ金属塩Ｘが、正極、負極および非水電解液のいずれにも含まれていない。
【０１０９】
まず、比較例１の負極の対Ｌｉ電位に比べ、各実施例の負極の対Ｌｉ電位は低くなっている。また、ケース腐蝕比率も良好な結果が得られている。これは、実施例の電池内にはアルカリ金属塩Ｘが含まれているため、電池電圧０Ｖまで深放電した場合に正極側ではリテンション量の増大により容量が減少するが、負極側ではＬｉの吸蔵反応により容量が増大するためと考えられる。
【０１１０】
実施例１〜４および実施例１４〜１６からは、アルカリ金属塩Ｘの量を増やすことにより、電池電圧０Ｖ時の負極電位を低い側にシフトさせる効果が大きくなることがわかる。このことは、電池ケースの防蝕効果を向上させることができることを意味する。
【０１１１】
また、実施例１４〜２８からは、非水電解液の溶質として、アルカリ金属塩Ｘを単独で用いることもできるし、また、ＬｉＰＦ_６などの従来の溶質と併用することもできることがわかる。
【０１１２】
実施例１〜４および実施例１２〜１３からは、負極に含ませるアルカリ金属塩Ｘの含有量が、負極活物質１００重量部あたり０．０１重量部未満では効果が小さく、１０重量部を超えてもメリットがないことがわかる。電極中でのアルカリ金属塩Ｘの含有量が、負極活物質１００重量部あたり１０重量部を超えると、正極側の抵抗成分が大きくなり、電池反応を阻害するため、深放電後の回復性や充放電サイクル特性が低下すると考えられる。
【０１１３】
実施例１４〜１６および実施例２７〜２８からは、非水電解液中のアルカリ金属塩Ｘの濃度が、０．００１モル／Ｌ未満の場合には、効果が小さく、１．５モル／Ｌを超えてもメリットがないことがわかる。非水電解液中でのアルカリ金属塩Ｘの濃度が高くなると、正極側の抵抗成分が大きくなり、電池反応を阻害するために、深放電後の回復性や充放電サイクル特性が低下すると考えられる。
【０１１４】
【発明の効果】
以上のように、本発明の好ましい態様によれば、深放電に至っても電池ケースの腐蝕がなく、容量回復率に優れ、充放電サイクル特性にも優れた非水電解液二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例および比較例で作製した非水電解液二次電池の縦断面図である。
【符号の説明】
１１　　正極板
１２　　負極板
１３　　セパレータ
１４　　正極リード
１５　　負極リード
１６　　上部絶縁板
１７　　下部絶縁板
１８　　電池ケース
１９　　封口体
２０　　正極端子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery having excellent deep discharge characteristics and charge / discharge cycle characteristics, and a non-aqueous electrolyte used for the same.
[0002]
[Prior art]
In recent years, portable and cordless consumer electronic devices have been rapidly advancing. Accordingly, there has been an increasing demand for a small, lightweight, thin secondary battery having a high energy density which serves as a driving power supply. Among them, a secondary battery using a non-aqueous electrolyte, particularly a lithium ion secondary battery, is regarded as promising as a battery having a high voltage and a high energy density, and its development is being actively carried out.
[0003]
The negative electrodes of these nonaqueous electrolyte secondary batteries use, as main materials, those using metallic lithium itself as an active material, and metallic compounds and carbon materials capable of inserting and extracting lithium as an active material by charging and discharging. There is something. Of these, carbon materials are often used as negative electrode active materials at present.
For the positive electrode of the nonaqueous electrolyte secondary battery, various lithium-containing composite oxides capable of inserting and extracting lithium by charge and discharge are generally used as an active material.
[0004]
In a non-aqueous electrolyte secondary battery equipped with these positive and negative electrodes, when left for a long time while attached to an electronic device, deep discharge is caused by leakage current, the battery voltage is reduced to 0 V, and the negative electrode is formed. There is a problem that the case member is corroded. In the charged state of the battery (for example, a voltage of 4.2 V), the potential of the negative electrode with respect to Li is almost 0 V (Vs Li ⁺ / Li).
[0005]
By the way, when the battery is discharged to around the battery voltage of 0 V and brought into the open circuit state, 3.2 V (Vs Li ⁺ / Li). On the other hand, unlike the state before the first charge after the electrolyte injection, the state between the positive and negative electrodes is in an open circuit state. , A leakage current flows continuously. Therefore, for example, in the case where nickel plating is applied to iron having the same potential as that of the negative electrode, dissolution of iron occurs from a weak plating strength portion having a plating pinhole or a crack or chip. Then, the case may be corroded, leading to liquid leakage.
[0006]
As a countermeasure against such case corrosion at the time of deep discharge, a method of attaching metal lithium to a negative electrode has been disclosed (for example, see Patent Documents 1 and 2). In addition, a method has been proposed in which a lithium hydroxide solution is added to a battery to cause electrolysis, thereby causing occlusion of lithium on the negative electrode side and generating a decomposition gas of an anion on the positive electrode side. Reference 3).
[0007]
[Patent Document 1]
JP-A-4-192257 (pages 1-3)
[Patent Document 2]
JP-A-5-144473 (pages 1-5, FIGS. 4-6)
[Patent Document 3]
JP-A-5-242912 (pages 1-4, FIG. 2)
[0008]
However, in the method of attaching metallic lithium to the negative electrode, immediately after the injection of the electrolytic solution, the positive electrode has a sufficiently high positive electrode potential (about 3.2 V vs. Li) to dissolve metals such as iron and copper. ⁺ / Li). Therefore, in the positive electrode, dissolution of the metal mixed in the positive electrode starts immediately. Immediately after the injection of the electrolytic solution, the potential of the negative electrode sharply drops toward the potential of metallic lithium, and there is a problem that the potential of the negative electrode reaches a potential region where many metal ions are deposited. In other words, metals such as iron and copper dissolved in the positive electrode are deposited on the immediately lower negative electrode via the separator to form a micro short circuit. This is a cause of open-circuit voltage failure in recent years in which separators are becoming thinner with an increase in battery capacity. Therefore, it is difficult to adopt the method of attaching metallic lithium to the negative electrode as a countermeasure against case corrosion at the time of deep discharge from the viewpoint of forming a minute short circuit.
[0009]
In addition, in the method of adding a lithium hydroxide solution into a battery, since a decomposition gas is generated on the positive electrode side, a sealing body equipped with a special valve that opens the gas as the internal pressure of the battery rises is required. It is difficult.
[0010]
By the way, it is disclosed that the energy density of a battery is improved by adding lithium salicylate or lithium salicylaldehyde to an electrolyte of a lithium battery (for example, see Non-Patent Documents 1 and 2). However, these are evaluations of characteristics as a primary battery, and there is no description about a secondary battery.
[0011]
[Non-patent document 1]
"Abstracts of the 2nd Meeting of the Chemical Battery Research Group Meeting", 2000, p. 109
[Non-patent document 2]
"Surface", 2000, Vol. 38, No. 11, p. 42-49
[0012]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems relating to the non-aqueous electrolyte secondary battery, and for example, aims to improve the deep discharge characteristics and / or the charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery. Things.
[0013]
[Means for Solving the Problems]
The present invention comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, and at least one selected from the group consisting of a positive electrode, a negative electrode, and a non-aqueous electrolyte includes an alkali metal salt X and And / or a non-aqueous electrolyte secondary battery containing an oxidative decomposition product of an alkali metal salt X. The oxidative decomposition product is contained in the battery as, for example, a compound or polymer insoluble in the non-aqueous electrolyte.
[0014]
The alkali metal salt X has an oxidative decomposition potential of Li potential: Li ⁺ / Li with respect to 3.2 V to 4.3 V, more preferably 3.6 V to 4.3 V can be used.
The alkali metal salt X also has the formula (1):
[0015]
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[0016]
(In the formula (1), R ¹ , R ² , R ³ And R ⁴ Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and two adjacent groups may be bonded to each other to form a ring structure; Is a lithium atom, a sodium atom or a potassium atom).
[0017]
R in the formula (1) ¹ , R ² , R ³ And R ⁴ It is preferable that at least one selected from the group consisting of aralkyl groups is an aralkyl group, and the other is a hydrogen atom.
The compound represented by the formula (1) is, for example, at least one selected from the group consisting of lithium 3,5-di-α-methylbenzylsalicylate and lithium 3,5-di-α, α-dimethylbenzylsalicylate. Preferably, there is.
The alkali metal salt X also has the formula (2):
[0018]
Embedded image

[0019]
(In the formula (2), R ¹ , R ² , R ³ And R ⁴ Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and two adjacent groups may be bonded to each other to form a ring structure; Is a lithium atom, a sodium atom or a potassium atom).
[0020]
R in the formula (2) ¹ , R ² , R ³ And R ⁴ It is preferable that at least one selected from the group consisting of an aralkyl group and the rest be hydrogen atoms.
The compound represented by the formula (2) is, for example, lithium bis (3,5-di-α-methylbenzylsalicyl) borate and lithium bis (3,5-di-α, α-dimethylbenzylsalicyl) borate It is preferably at least one selected from the group consisting of:
[0021]
When the negative electrode contains the alkali metal salt X, the negative electrode preferably contains 0.01 to 10 parts by weight of the alkali metal salt X per 100 parts by weight of the negative electrode active material.
[0022]
The present invention also relates to a non-aqueous electrolyte comprising a non-aqueous solvent and an alkali metal salt X dissolved in the non-aqueous solvent.
The concentration of the alkali metal salt X in the non-aqueous electrolyte may be 0.001 mol / L (liter) to 1.5 mol / L, and more preferably 0.001 mol / L to 1.2 mol / L. preferable.
As the alkali metal salt X, the same one as described above used for the non-aqueous electrolyte secondary battery can be used.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode, the negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, selected from the group consisting of a positive electrode, a negative electrode and a non-aqueous electrolyte At least one contains an alkali metal salt X described later and / or an oxidative decomposition product of the alkali metal salt X.
[0024]
The oxidative decomposition potential of the alkali metal salt X is generally Li potential: Li ⁺ / Li relative to 3.2V to 4.3V, more preferably 3.6V to 4.3V.
When the positive electrode potential in the battery is 3.2 V to 4.3 V relative to Li potential, the anion part of the alkali metal salt X is oxidatively decomposed at the positive electrode to generate an oxidative decomposition product. The oxidative decomposition product is, for example, a compound or polymer insoluble in the non-aqueous electrolyte. This oxidative decomposition product adheres to, for example, a positive electrode surface as a resistive film and acts as positive electrode retention.
[0025]
On the other hand, the alkali metal derived from the alkali metal salt X is converted into Li by using the electrons released with the decomposition of the anion. ⁺ + E ⁻ → It is considered that a reaction of Li is caused and occluded in the negative electrode.
That is, when the battery is deeply discharged to a battery voltage of 0 V, the capacity decreases on the positive electrode side due to an increase in the positive electrode retention amount, but the negative electrode capacity increases on the negative electrode side due to the Li occlusion reaction. As a result, the potential at which the positive electrode and the negative electrode fall when the battery voltage reaches 0 V is the potential at which metals such as iron and copper do not dissolve, for example, 3.0 V (vs. Li). ⁺ / Li). Therefore, it is possible to prevent corrosion of the battery case that conducts with the negative electrode.
[0026]
In addition, the oxidative decomposition of the anion generated by ionization of the alkali metal salt X is performed for the first time in the first charging step, so that the metal mixed in the positive electrode dissolves as in the case of attaching lithium metal to the negative electrode. Also, there is no problem that a minute short circuit occurs due to deposition on the negative electrode surface immediately below. In addition, when the amount of the alkali metal salt X is increased, the negative electrode potential at a battery voltage of 0 V can be shifted to a side lower than the natural potential of 3.2 V, and the anticorrosion effect can be improved.
[0027]
In order to obtain the effects of the present invention efficiently, the alkali metal salt X is preferably contained in at least one of the nonaqueous electrolyte and the negative electrode.
When the non-aqueous electrolyte contains a solute other than the alkali metal salt X (hereinafter referred to as solute Y), the concentration of the alkali metal salt X in the non-aqueous electrolyte is 0.001 mol / L or more. It is preferably 0.30 mol / L.
[0028]
On the other hand, the alkali metal salt X can be used as the main solute of the non-aqueous electrolyte. In that case, the concentration of the alkali metal salt X in the non-aqueous electrolyte is from 0.30 mol / L to 1.5 mol / L, and more preferably from 0.3 mol / L to 1.2 mol / L. Is preferred.
[0029]
It is also possible to use a non-aqueous electrolyte containing only the alkali metal salt X as a solute. In this case, if the alkali metal salt X is oxidized and decomposed at a normal charge potential of 4.2 V or less, the battery characteristics are deteriorated. Therefore, the oxidative decomposition potential of the alkali metal salt X must exceed 4.2. Is preferred. Even when the oxidative decomposition potential of the alkali metal salt X exceeds 4.2, a small amount (e.g., equivalent to 0.001 mol / L or more in the electrolytic solution) of the normal charge potential of 4.2 V or less is used. Therefore, there is an effect of lowering the potential of the negative electrode.
[0030]
When the negative electrode contains the alkali metal salt X, the amount of the alkali metal salt X contained in the negative electrode is preferably 0.01 part by weight to 10 parts by weight per 100 parts by weight of the negative electrode active material. In this case, the solubility of the alkali metal salt X in the non-aqueous electrolyte in the non-aqueous solvent is preferably 0.10 mol / L or less. By including the alkali metal salt X in the negative electrode, the potential of the negative electrode can be lowered, and the same effect as when the alkali metal salt X is dissolved in the non-aqueous electrolyte can be obtained.
The alkali metal salt X is represented by the formula (1):
[0031]
Embedded image

[0032]
(In the formula (1), R ¹ , R ² , R ³ And R ⁴ Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and two adjacent groups may be bonded to each other to form a ring structure; Is a lithium atom, a sodium atom or a potassium atom).
In particular, R in the formula (1) ¹ , R ² , R ³ And R ⁴ It is preferable that at least one selected from the group consisting of an aralkyl group and the rest be hydrogen atoms.
[0033]
Here, the alkyl group contained in the compound represented by the formula (1) preferably has 1 to 8 carbon atoms, and the alkoxyl group preferably has 1 to 4 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a tert-butyl group, a tert-amyl group, an isoamyl group, an n-hexyl group, an n-octyl group, a tert-octyl group, and a 2-ethylhexyl group. And the like, and particularly preferably a methyl group and a tert-butyl group. As the alkoxyl group, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a tert-butoxy group, and the like are preferable, and a methoxy group is particularly preferable. Further, as the aryl group, a phenyl group, a tolyl group, a naphthyl group and the like are preferable, and a phenyl group is particularly preferable. As the aralkyl group, a benzyl group, a phenethyl group, an α-methylbenzyl group, an α, α-dimethylbenzyl group and the like are preferable, and an α-methylbenzyl group and an α, α-dimethylbenzyl group are particularly preferable. As the halogen atom, a fluorine atom, a chlorine atom and a bromine atom are preferable.
[0034]
Specific examples of the compound represented by the formula (1) include lithium 3-methylsalicylate, lithium 4-methylsalicylate, lithium 5-methylsalicylate, lithium 4-tert-octylsalicylate, 3,5-di-tert-butyl. Lithium salicylate, lithium 3,5-di-α-methylbenzylsalicylate, lithium 3,5-di-α, α-dimethylbenzylsalicylate, lithium 3,5-di-methylsalicylate, lithium 3-chlorosalicylate, 4-chloro Lithium salicylate, lithium 5-fluorosalicylate, lithium 5-chlorosalicylate, lithium 3,5-dichlorosalicylate, lithium 3,5,6-trichlorosalicylate, lithium 4-methoxysalicylate, lithium 5-bromosalicylate, 4-hydroxybenzoic acid Lithium, 3-hydride Carboxymethyl-2-lithium-naphthoic acid, lithium and 5-sulfosalicylic acid. These may be used alone or in combination of two or more.
[0035]
When the alkali metal salt X is contained in the non-aqueous electrolyte, lithium 3,5-di-α-methylbenzylsalicylate and lithium 3,5-di-α, α-dimethylbenzylsalicylate are particularly preferred among the above. Particularly preferred.
When the alkali metal salt X is contained in the negative electrode, lithium 3,5-di-tert-butylsalicylate and lithium 5-sulfosalicylate are particularly preferable.
As the alkali metal salt X, a compound represented by the formula (2):
[0036]
Embedded image

[0037]
(In the formula (2), R ¹ , R ² , R ³ And R ⁴ Each independently represents a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and two adjacent groups may be bonded to each other to form a ring structure; Is a lithium atom, a sodium atom or a potassium atom).
In particular, R in the formula (2) ¹ , R ² , R ³ And R ⁴ It is preferable that at least one selected from the group consisting of an aralkyl group and the rest be hydrogen atoms.
[0038]
Here, the alkyl group contained in the compound represented by the formula (2) preferably has 1 to 8 carbon atoms, and the alkoxyl group preferably has 1 to 4 carbon atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a tert-butyl group, a tert-amyl group, an isoamyl group, an n-hexyl group, an n-octyl group, a tert-octyl group, and a 2-ethylhexyl group. And the like, and particularly preferably a methyl group and a tert-butyl group. As the alkoxyl group, for example, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, and a tert-butoxy group are preferable, and a methoxy group is particularly preferable. As the aryl group, a phenyl group, a tolyl group, a naphthyl group and the like are preferable, and a phenyl group is particularly preferable. As the aralkyl group, a benzyl group, a phenethyl group, an α-methylbenzyl group, an α, α-dimethylbenzyl group and the like are preferable, and an α-methylbenzyl group and an α, α-dimethylbenzyl group are particularly preferable. As the halogen atom, a fluorine atom, a chlorine atom and a bromine atom are preferable.
[0039]
Specific examples of the compound represented by the formula (2) include lithium bissalicylborate, lithium bis (3,5-di-tert-butylsalicyl) borate, and bis (3,5-di-methylsalicyl) borate. Lithium, lithium bis (3,5-dichlorosalicyl) borate, lithium bis (3-methylsalicyl) borate, lithium bis (3,5-di-α-methylbenzylsalicyl) borate, bis (3,5 Lithium-di-α, α-dimethylbenzylsalicyl) borate, lithium bis (3-hydroxy-2-naphthoe) borate and the like. These may be used alone or in combination of two or more.
[0040]
Among the above, lithium (bis, 3,5-di-α-methylbenzylsalicyl) borate and bis (3,5-di-α, α-dimethylbenzylsalicyl) borate can be contained in the nonaqueous electrolyte. Lithium oxide and the like are preferable, and lithium (bis (3,5-dichlorosalicyl) borate, lithium bis (3-hydroxy-2-naphthoe) borate and the like are particularly preferable for inclusion in the negative electrode.
Formula (3) having a structure similar to that of the compound represented by Formula (2):
[0041]
Embedded image

[0042]
(In the formula (3), R ¹ And R ⁴ Each independently represents a hydrogen atom, an alkyl group, a substituted or unsubstituted aromatic ring, ² And R ³ Represents independently a substituted or unsubstituted aromatic ring, and M is a lithium atom, a sodium atom or a potassium atom), and a similar effect is expected. The aromatic ring also includes a condensed ring such as a naphthyl group derivative.
[0043]
R in the formula (3) ¹ And R ⁴ Examples of the alkyl group represented by R include a methyl group, an ethyl group, a propyl group, a butyl group, and an amyl group. ¹ ~ R ⁴ Examples of the aromatic ring represented by are a benzene ring and a naphthalene ring. Examples of the substituent of the aromatic ring include an alkyl group, an alkoxy group, a halogen atom, an aryl group, an aralkyl group, and the like.
Specific examples of the compound represented by the formula (3) include, for example, lithium bis (1,1-diphenyl-1-oxo-acetyl) borate.
[0044]
As the non-aqueous solvent used for the non-aqueous electrolyte, a conventionally known one can be used. For example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, γ-butyrolactone, methyl acetate, methyl propionate, methyl butyl ether, vinylene carbonate, 1,2- Dimethoxyethane, 1,2-dichloroethane, 1,3-dimethoxypropane, 4-methyl-2-pentanone, 1,4-dioxane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, sulfolane, 3-methyl- Sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylformamide, diethylformamide, dimethylsulfoxide, phosphorus Trimethyl, triethyl phosphate and the like. These non-aqueous solvents may be used as a mixture of two or more. For example, a non-aqueous solvent containing a cyclic carbonate and a chain carbonate is preferable.
[0045]
As a solute Y other than the alkali metal salt X that can be contained in the nonaqueous electrolyte, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiBr, LiI, LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ And lithium lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate and the like. These may be used alone or in combination of two or more. Above all, LiPF ₆ , LiBF ₄ It is preferable to use The concentration of the solute Y in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L.
[0046]
Further, recently reported lithium bisnaphthalenediolate borate described in JP-A-10-265479 and lithium bis [2,2'-biphenyldiolate (2-)-O, described in JP-T-2000-516930. Lithium complex salts such as O '] borate (1-) and lithium bis [5-fluoro-2-olato-benzenesulfonate (2-) O, O']-borate described in JP-A-2001-55396 ( Lithium complex salts such as 1-) can also be mentioned as the solute Y. Since they have low solubility in non-aqueous solvents, they cannot be used alone, but they can be used in combination with alkali metal salts X as solutes in non-aqueous electrolytes.
[0047]
Non-aqueous electrolytes further include, as stabilizers, arylalkyl ether compounds and arylaryl ethers disclosed in JP-A-10-64591, and carbon-carbon triples disclosed in JP-A-5-159787. An alcohol such as propargyl alcohol having a bond, or an oxygen-containing aliphatic compound having an alkynyl group and / or an alkynylene group having no active hydrogen and disclosed in JP-A-2001-256995 can also be contained.
[0048]
For the positive electrode, for example, a positive electrode paste is applied to one or both sides of a positive electrode current collector having a thickness of 10 μm to 60 μm made of a normal aluminum foil or a lath-processed or etched aluminum foil, dried, and rolled to form a positive electrode. It is manufactured by forming an active material layer. The positive electrode paste is prepared by dispersing a positive electrode active material, a binder, a conductive agent, and, if necessary, a thickener in a dispersion medium. The positive electrode is provided with a solid portion having no active material layer, and a positive electrode lead is welded to the uncoated portion.
[0049]
The positive electrode active material is not particularly limited. For example, a lithium-containing transition metal compound that can accept lithium ions as a guest is used. For example, a composite metal oxide of lithium and at least one transition metal selected from cobalt, manganese, nickel, chromium, iron and vanadium is used. Above all, Li _x CoO ₂ , Li _x MnO ₂ , Li _x NiO ₂ , LiCrO ₂ , ΑLiFeO ₂ , LiVO ₂ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _1-y O _z , Li _x Ni _1-y M _y O _z , Li _x Mn ₂ O ₄ , Li _x Mn _2-y M _y O ₄ (Here, M = at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B, x = 0 to 1 2, y = 0 to 0.9, z = 2.0 to 2.3), a transition metal chalcogenide, a vanadium oxide lithium, a niobium oxide lithium, and the like are preferable. These may be used alone or in combination of two or more. Note that the value x increases or decreases due to charge and discharge. The average particle size of the positive electrode active material is preferably 1 μm to 30 μm.
[0050]
As the binder, the conductive agent, and the thickener that can be added as needed, the same materials as those used in the related art can be used for the positive electrode paste.
The binder is not particularly limited as long as it can be dissolved or dispersed in the dispersion medium of the paste. For example, a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR) , An acrylic polymer, a vinyl polymer, or the like. These may be used alone or in combination of two or more. As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, polytetrafluoroethylene, and the like are preferable, and these can be used as a dispersion.
[0051]
As the conductive agent, acetylene black, graphite, carbon fiber, or the like can be used. These may be used alone or in combination of two or more.
As the thickener, ethylene-vinyl alcohol copolymer, carboxymethylcellulose, methylcellulose and the like are preferable.
[0052]
As the dispersion medium, those in which the binder can be dissolved are suitable. When an organic binder is used, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide, hexamethylsulfonamide, tetramethylurea, acetone, methylethylketone, or the like may be used alone or It is preferable to use a mixture. In the case where an aqueous binder is used, water or warm water is preferred.
[0053]
The method for preparing the positive electrode paste by dispersing the positive electrode active material, the binder, the conductive agent, and the thickener to be added as necessary in a dispersion medium is not particularly limited. For example, a planetary mixer, a homogenizer, and the like. A mixer, pin mixer, kneader, homogenizer and the like can be used. These may be used alone or in combination of two or more. Further, at the time of kneading and dispersing the positive electrode paste, various dispersants, surfactants, stabilizers and the like can be added as necessary.
[0054]
The positive electrode paste can be easily applied to the positive electrode current collector using, for example, a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, a dip coater, or the like. The positive electrode paste applied to the positive electrode current collector is preferably dried close to natural drying, but is preferably dried at a temperature of 70 ° C to 200 ° C for 10 minutes to 5 hours in consideration of productivity.
Rolling is preferably performed several times at a linear pressure of 1000 to 2000 kg / cm by a roll press until the electrode plate reaches a predetermined thickness, or rolling is performed while changing the linear pressure.
[0055]
The negative electrode is coated with a negative electrode paste on one or both sides of a negative electrode current collector having a thickness of 10 μm to 50 μm made of, for example, ordinary copper foil or lath-processed or etched copper foil, dried, and rolled to form a negative electrode. It is manufactured by forming an active material layer. The negative electrode paste is prepared by dispersing a negative electrode active material, a binder, and if necessary, a conductive agent and a thickener in a dispersion medium. The negative electrode is provided with a solid portion having no active material layer, to which a negative electrode lead is welded.
[0056]
The negative electrode active material is not particularly limited, but it is preferable to use a carbon material capable of releasing and occluding lithium ions by charging and discharging. For example, carbon materials obtained by firing organic polymer compounds (phenol resin, polyacrylonitrile, cellulose, etc.), carbon materials obtained by firing coke and pitch, artificial graphite, natural graphite, pitch-based carbon fibers, PAN-based carbon fibers and the like are preferable, and as the shape thereof, fibrous, spherical, scale-like, or lump-like ones can be used.
[0057]
As the binder, the conductive agent and the thickener used as needed, the same as those in the related art can be used. For example, the same binder, conductive agent, and thickener as used for the positive electrode plate can be used.
[0058]
Examples of separators include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyether (polyethylene oxide and polypropylene oxide), and cellulose. (Carboxymethylcellulose or hydroxypropylcellulose), microporous films composed of polymers such as poly (meth) acrylic acid and poly (meth) acrylate are preferably used. Further, a multilayer film in which these microporous films are overlapped is also used. Among them, a microporous film made of polyethylene, polypropylene, polyvinylidene fluoride or the like is preferable, and the thickness is preferably 15 μm to 30 μm.
[0059]
As the material of the battery case, copper, nickel, stainless steel, nickel-plated steel, or the like can be used. These materials can be subjected to drawing, DI processing, and the like to form a battery case. In order to enhance the corrosion resistance of the case, the processed battery case may be plated.
[0060]
The present invention can be applied to, for example, coin-type, button-type, sheet-type, stacked-type, cylindrical-type, flat-type, and square-type batteries, but is not limited thereto. Further, the present invention can be applied to a large battery used for an electric vehicle or the like. The non-aqueous electrolyte secondary battery of the present invention can be used for personal digital assistants, portable electronic devices, small home power storage devices, motorcycles, electric vehicles, hybrid electric vehicles, etc., but is particularly limited to these applications. It is not something to be done.
[0061]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but these do not limit the present invention at all. In the following Examples and Comparative Examples, a cylindrical lithium secondary battery (a non-aqueous electrolyte was not shown) as shown in the longitudinal sectional view of FIG. 1 was produced.
In FIG. 1, an electrode plate group in which a positive electrode plate 11 and a negative electrode plate 12 are spirally wound via a separator 13 is housed in a bottomed cylindrical battery case 18 having an open top. The positive electrode lead 14 pulled out from the positive electrode plate 11 is electrically connected to an internal terminal of the sealing body 19 that is electrically connected to the positive electrode terminal 20 via the upper insulating plate 16. Further, the negative electrode lead 15 pulled out from the negative electrode plate 12 is electrically connected to the bottom of the battery case 18 via the lower insulating plate 17. The open end of the battery case 18 is caulked to the sealing body 19, thereby sealing the inside of the battery case 18.
[0062]
First, a method for synthesizing an alkali metal salt X used in the following Examples and Comparative Examples will be described with reference to Synthesis Examples 1 and 2. The other alkali metal salt X can be synthesized in the same manner as in Synthesis Example 1 or Synthesis Example 2.
[0063]
<< Synthesis Example 1 >>
A synthesis example of lithium 3,5-di-α-methylbenzylsalicylate, which is an example of the compound represented by the formula (1), is shown.
A reaction flask having a volume of 500 ml was charged with 150 g of 3,5-di-α-methylbenzylsalicylic acid, and 300 ml of toluene was added to form a slurry. Under stirring, 3,5-di-α-methylbenzylsalicylic acid and an equimolar amount of lithium hydroxide monohydrate were added to the flask and further stirred. Then, the pressure in the flask was reduced to remove the solvent, and the substance in the flask was concentrated to dryness. Thus, a white solid of lithium 3,5-di-α-methylbenzylsalicylate was obtained.
[0064]
<< Synthesis Example 2 >>
A synthesis example of lithium bis (3,5-di-α-methylbenzylsalicyl) borate, which is an example of the compound represented by the formula (2), is shown.
A reaction flask having a capacity of 1000 ml was charged with 150 g of 3,5-di-α-methylbenzylsalicylic acid, 8 g of lithium carbonate and 13.4 g of boric acid, and 700 ml of toluene and 50 ml of dimethyl carbonate were added. Next, under stirring, the mixture in the flask was refluxed and dehydrated while heating. At this time, the mixture was refluxed in a slurry state until a theoretical amount of water could be recovered. After collecting the theoretical amount of water, it was allowed to cool to room temperature. Then, the pressure in the flask was reduced to remove the solvent, and the substance in the flask was concentrated to dryness. Thus, 152 g of a white solid of lithium bis (3,5-di-α-methylbenzylsalicyl) borate was obtained.
[0065]
<< Example 1 >>
(I) Production of positive electrode plate
100 parts by weight of lithium cobalt oxide as a positive electrode active material, 3 parts by weight of acetylene black as a conductive agent, and N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) as a binder (PVDF 12 33% by weight) and 13 parts by weight of NMP as a dispersion medium were kneaded to prepare a positive electrode paste. This positive electrode paste was applied to both sides of a current collector made of a 20-μm-thick strip-shaped aluminum foil, and dried to produce a 290-μm-thick electrode plate. This electrode plate was rolled three times at a linear pressure of 1000 kg / cm to make the thickness of the electrode plate 180 μm. A positive electrode lead was attached to the uncoated portion of the positive electrode plate thus obtained by spot welding.
[0066]
(Ii) Preparation of negative electrode plate
100 parts by weight of artificial negative graphite as the negative electrode active material, 67 parts by weight of an NMP solution of PVDF (PVDF content: 6% by weight) as a binder, and 0.01 part by weight of lithium 3,5-di-tert-butylsalicylate And 13 parts by weight of NMP as a dispersion medium were kneaded to prepare a negative electrode paste. This negative electrode paste was applied on both sides of a current collector made of a strip-shaped copper foil having a thickness of 14 μm, and dried to prepare an electrode plate having a thickness of 300 μm. This electrode plate was rolled three times at a linear pressure of 110 Kg / cm to reduce the thickness of the electrode plate to 196 μm. A negative electrode lead was attached to the uncoated portion of the negative electrode plate thus obtained by spot welding.
[0067]
(Iii) Preparation of non-aqueous electrolyte
Lithium hexafluorophosphate (LiPF) is used as a solute in a mixed solvent of ethylene carbonate and ethyl methyl carbonate in an equal weight ratio. ₆ ) Was dissolved at a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.
[0068]
(Iv) Battery assembly
The obtained positive electrode plate and negative electrode plate were spirally wound through a three-layered separator to form an electrode plate group. Here, as the separator having a three-layer structure, a separator composed of a 10 μm-thick polyethylene microporous film and a 5 μm-thick polypropylene microporous film in contact with both sides was used. The electrode group was housed in a bottomed battery case having an open top, and the end of the positive electrode lead was connected to the internal terminal of the sealing body. The end of the negative electrode lead was connected to the bottom of the battery case. An upper insulating plate and a lower insulating plate were arranged above and below the electrode group, respectively. In addition, a steel plate having a thickness of 0.3 mm plated with nickel having a thickness of 1.0 μm was used for the battery case.
[0069]
Next, a predetermined amount of a non-aqueous electrolytic solution was injected into the battery case, and the battery case was sealed with a sealing body to complete a battery having an ICR18650 size and a battery capacity of 2000 mAh described in JIS C8711. After the obtained battery was left at room temperature for 4 hours, the battery was initially charged by constant current and constant voltage charging of 400 mA (0.2 ItA) until the battery voltage reached 4.2 V.
[0070]
<< Example 2 >>
Except that the amount of lithium 3,5-di-tert-butylsalicylate to be contained in the negative electrode was changed to 0.2 part by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material, the same as in Example 1 was performed. A non-aqueous electrolyte secondary battery of Example 2 was produced.
[0071]
<< Example 3 >>
In the same manner as in Example 1 except that the amount of lithium 3,5-di-tert-butylsalicylate to be contained in the negative electrode was changed to 1.0 part by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material. A non-aqueous electrolyte secondary battery of Example 3 was produced.
[0072]
<< Example 4 >>
Example 1 was repeated in the same manner as in Example 1 except that the amount of lithium 3,5-di-tert-butylsalicylate contained in the negative electrode was changed to 10 parts by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material. No. 4 non-aqueous electrolyte secondary battery was produced.
[0073]
<< Example 5 >>
Instead of lithium 3,5-di-tert-butylsalicylate, lithium 5-sulfosalicylate was used, and the amount contained in the negative electrode was set to 2.0 parts by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material. Except for this, the non-aqueous electrolyte secondary battery of Example 5 was fabricated in the same manner as in Example 1.
[0074]
<< Example 6 >>
Lithium 3,5-di-tert-butylsalicylate and lithium 5-sulfosalicylate were used in combination, and the amount of each contained in the negative electrode was 3.0 parts by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material. A non-aqueous electrolyte secondary battery of Example 6 was produced in the same manner as in Example 1, except that 1.0 part by weight was used.
[0075]
<< Example 7 >>
Lithium bis (3-hydroxy-2-naphthoe) borate was used instead of lithium 3,5-di-tert-butylsalicylate, and the amount contained in the negative electrode was measured per 100 parts by weight of the artificial bulk graphite of the negative electrode active material. A non-aqueous electrolyte secondary battery of Example 7 was produced in the same manner as in Example 1, except that the amount was changed to 3.0 parts by weight.
[0076]
<< Embodiment 8 >>
Using a mixture of lithium 3,5-di-tert-butylsalicylate and lithium bis (3-hydroxy-2-naphthoe) borate, the amount contained in the negative electrode was determined per 100 parts by weight of the artificial massive graphite of the negative electrode active material. A non-aqueous electrolyte secondary battery of Example 8 was produced in the same manner as in Example 1, except that each was 2.0 parts by weight.
[0077]
<< Example 9 >>
Lithium bis (3-hydroxy-2-naphthoe) borate was used in place of lithium 3,5-di-tert-butylsalicylate, and the amount contained in the negative electrode was determined based on 100 parts by weight of the artificial bulk graphite of the negative electrode active material. , 1.5 parts by weight, and 3.5 parts by weight of lithium bis (4-tert-octylsalicyl) borate were additionally used in the same manner as in Example 1 except that the non-aqueous electrolyte secondary solution of Example 9 was used. A battery was manufactured.
[0078]
<< Example 10 >>
Lithium bis (1,1-diphenyl-1-oxo-acetyl) borate is used as the compound represented by the formula (3) in place of lithium 3,5-di-tert-butylsalicylate, and the amount to be contained in the negative electrode Was changed to 2.5 parts by weight per 100 parts by weight of the artificial negative graphite of the negative electrode active material, to produce a nonaqueous electrolyte secondary battery of Example 10 in the same manner as in Example 1.
[0079]
<< Example 11 >>
The amount of lithium 3,5-di-tert-butylsalicylate to be contained in the negative electrode was changed to 2.0 parts by weight per 100 parts by weight of the artificial bulk graphite of the negative electrode active material, and the amount of 3,5-di-tert-butylsalicylic acid was changed. A non-aqueous electrolyte secondary battery of Example 11 was produced in the same manner as in Example 1, except that a positive electrode plate containing 1.0 part by weight of lithium with respect to 100 parts by weight of the positive electrode active material was used.
[0080]
<< Comparative Example 1 >>
A non-aqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as in Example 1, except that lithium 3,5-di-tert-butylsalicylate was not contained in the negative electrode plate.
[0081]
<< Example 12 >>
Except that the amount of lithium 3,5-di-tert-butylsalicylate to be included in the negative electrode was changed to 0.005 parts by weight per 100 parts by weight of the artificial negative graphite of the negative electrode active material, the same as in Example 1 was performed. A non-aqueous electrolyte secondary battery of Example 12 was produced.
[0082]
<< Example 13 >>
Example 1 was repeated in the same manner as in Example 1 except that the amount of lithium 3,5-di-tert-butylsalicylate contained in the negative electrode was changed to 15 parts by weight per 100 parts by weight of the artificial bulk graphite as the negative electrode active material. Thirteen non-aqueous electrolyte secondary batteries were produced.
[0083]
<< Example 14 >>
(I) Production of positive electrode plate
100 parts by weight of lithium cobalt oxide as a positive electrode active material, 3 parts by weight of acetylene black as a conductive agent, 4 parts by weight of a dispersion of polytetrafluoroethylene (PTFE) as a binder, and 4 parts by weight of PTFE, and a thickener Was mixed with 0.8 part by weight of carboxymethylcellulose and an appropriate amount of water to prepare a positive electrode paste. This positive electrode paste was applied to both sides of a current collector made of a 20-μm-thick strip-shaped aluminum foil, and dried to produce a 290-μm-thick electrode plate. This electrode plate was rolled three times at a linear pressure of 1000 kg / cm to make the thickness of the electrode plate 180 μm. A positive electrode lead was attached to the uncoated portion of the positive electrode plate thus obtained by spot welding.
[0084]
(Ii) Preparation of negative electrode plate
100 parts by weight of flaky graphite as a negative electrode active material, 4 parts by weight of a water-soluble dispersion of styrene butadiene rubber (SBR) as a binder in SBR content, and 0.8 parts by weight of carboxymethyl cellulose as a thickener. An appropriate amount of water was kneaded to prepare a negative electrode paste. This negative electrode paste was applied on both sides of a current collector made of a strip-shaped copper foil having a thickness of 14 μm, and dried to prepare an electrode plate having a thickness of 300 μm. This electrode plate was rolled three times at a linear pressure of 110 Kg / cm to reduce the thickness of the electrode plate to 196 μm. A negative electrode lead was attached to the uncoated portion of the negative electrode plate thus obtained by spot welding.
[0085]
(Iii) Preparation of non-aqueous electrolyte
In a mixed solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate at a weight ratio of 4: 5: 2, 0.003 mol / L of lithium 3,5-di-α-methylbenzylsalicylate as a solute and Lithium fluorophosphate (LiPF ₆ ) Was dissolved at a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.
[0086]
(Iv) Battery assembly
The obtained positive electrode plate and negative electrode plate were spirally wound via a two-layered separator to form an electrode plate group. Here, as the separator having a two-layer structure, a separator made of a 10 μm-thick microporous polyethylene film and a 10 μm-thick microporous polypropylene film in contact with one side thereof was used.
Using this electrode plate group, a battery with an ICR18650 size and a battery capacity of 2000 mAh was completed in the same manner as in Example 1 except that the above nonaqueous electrolyte was used. After the obtained battery was left at room temperature for 4 hours, the battery was initially charged by constant current and constant voltage charging of 400 mA (0.2 ItA) until the battery voltage reached 4.2 V.
[0087]
<< Example 15 >>
Except that the concentration of lithium 3,5-di-α-methylbenzylsalicylate in the non-aqueous electrolyte was changed to 0.05 mol / L, the non-aqueous electrolyte A secondary battery was manufactured.
[0088]
<< Example 16 >>
Except that lithium 3,5-di-α, α-dimethylbenzylsalicylate is contained in the non-aqueous electrolyte at a concentration of 0.2 mol / L in place of lithium 3,5-di-α-methylbenzylsalicylate. In the same manner as in Example 14, a non-aqueous electrolyte secondary battery of Example 16 was produced.
[0089]
<< Example 17 >>
The non-aqueous electrolyte contains only lithium 3,5-di-α-methylbenzylsalicylate at a concentration of 0.5 mol / L, and LiPF ₆ A non-aqueous electrolyte secondary battery of Example 17 was made in the same manner as Example 14 except that was not contained.
[0090]
<< Example 18 >>
In the same manner as in Example 14 except that lithium 5-fluorosalicylate was contained at a concentration of 0.05 mol / L in the non-aqueous electrolyte instead of lithium 3,5-di-α-methylbenzylsalicylate. Thus, a non-aqueous electrolyte secondary battery of Example 18 was produced.
[0091]
<< Example 19 >>
Instead of lithium 3,5-di-α-methylbenzylsalicylate, lithium non-aqueous electrolyte contains lithium 3,5-dichlorosalicylate at a concentration of 0.2 mol / L, and LiPF ₆ A non-aqueous electrolyte secondary battery of Example 19 was produced in the same manner as in Example 14, except that the concentration of was changed to 0.9 mol / L.
[0092]
<< Example 20 >>
The concentration of lithium 3,5-di-α-methylbenzylsalicylate in the non-aqueous electrolyte was changed to 0.04 mol / L, and lithium 5-fluorosalicylate was further added to the non-aqueous electrolyte at a concentration of 0.01 mol / L. A non-aqueous electrolyte secondary battery of Example 20 was produced in the same manner as in Example 14, except that it was contained in the solution.
[0093]
<< Example 21 >>
The concentration of lithium 3,5-di-α-methylbenzylsalicylate in the non-aqueous electrolyte was changed to 0.5 mol / L, and lithium 3,5-dichlorosalicylate was added at a concentration of 0.2 mol / L. LiPF contained in water electrolyte ₆ A non-aqueous electrolyte secondary battery of Example 21 was produced in the same manner as in Example 14, except that the concentration of was changed to 0.3 mol / L.
[0094]
<< Example 22 >>
Instead of lithium 3,5-di-α-methylbenzyl salicylate, only lithium bis (3,5-di-α-methylbenzyl salicyl) borate is used in a non-aqueous electrolyte at a concentration of 0.5 mol / L. LiPF ₆ A non-aqueous electrolyte secondary battery of Example 22 was made in the same manner as Example 14, except that was not contained.
[0095]
<< Example 23 >>
Example 23 was repeated in the same manner as in Example 22 except that the concentration of lithium bis (3,5-di-α-methylbenzylsalicyl) borate in the nonaqueous electrolyte was changed to 1.2 mol / L. A non-aqueous electrolyte secondary battery was manufactured.
[0096]
<< Example 24 >>
Without using lithium 3,5-di-α-methylbenzyl salicylate, 0.01 mol / L of lithium bis (3-hydroxy-2-naphthoate) borate and lithium bissalicylborate in a non-aqueous electrolyte solution. At a concentration of 0.02 mol / L, respectively. ₆ A non-aqueous electrolyte secondary battery of Example 24 was produced in the same manner as in Example 14, except that the concentration of was changed to 1.0 mol / L.
[0097]
<< Example 25 >>
Lithium 3,5-di-α-methylbenzyl salicylate was not used, and lithium (bis, 3,5-di-α, α-dimethylbenzylsalicyl) borate was 0.3 mol / L in a nonaqueous electrolyte. Lithium 3,5-di-α, α-dimethylbenzylsalicylate was contained at a concentration of 0.3 mol / L, and LiPF ₆ A non-aqueous electrolyte secondary battery of Example 25 was produced in the same manner as in Example 14, except that the concentration of was changed to 0.3 mol / L.
[0098]
<< Example 26 >>
Lithium 3,5-di-α, α-dimethylbenzyl salicylate is contained in the non-aqueous electrolyte at a concentration of 0.05 mol / L without using lithium 3,5-di-α-methylbenzyl salicylate; LiPF ₆ Was changed to 1.0 mol / L, and 0.05 parts by weight of lithium 3,5-di-tert-butylsalicylate was contained in the negative electrode plate per 100 parts by weight of the negative electrode active material. A non-aqueous electrolyte secondary battery of Example 26 was produced in the same manner as in Example 14.
[0099]
<< Example 27 >>
Except that the concentration of lithium 3,5-di-α-methylbenzylsalicylate in the non-aqueous electrolyte was changed to 0.0005 mol / L, the non-aqueous electrolyte A secondary battery was manufactured.
[0100]
<< Example 28 >>
The concentration of lithium 3,5-di-α-methylbenzylsalicylate in the non-aqueous electrolyte was changed to 2.0 mol / L, and LiPF ₆ A non-aqueous electrolyte secondary battery of Example 28 was made in the same manner as Example 14, except that was not contained. However, since all the lithium 3,5-di-α-methylbenzylsalicylate did not dissolve, the actual concentration was less than 2.0 mol / L.
[0101]
[Evaluation]
Using each of the thus prepared non-aqueous electrolyte secondary batteries of Examples 1 to 28 and Comparative Example 1, 20 negative electrodes in a deep discharge state with respect to Li potential, corrosion ratio of the case, and capacity recovery Rate and charge-discharge cycle characteristics were evaluated.
[0102]
(I) Li potential relative to negative electrode
The battery after aging is charged at a constant current of 1400 mA (0.7 ItA) until the battery voltage reaches 4.2 V, and then at a constant voltage until the current value attenuates to 100 mA (0.05 ItA). Charged. Next, the battery was discharged at a constant current of 2000 mA (1.0 ItA) to a discharge end voltage of 3.0 V, and then connected to a constant resistance of 1 KΩ for 50 days in a 60 ° C. environment. Next, the resistor was removed from the battery, and the bottom of the battery case was cut into a disk shape. Then, the reference electrode was inserted into the cylindrical space of the core of the battery group and brought into contact with the liquid, and the Li potential of the negative electrode was measured based on the reference. Then, the average value of the potentials of the negative electrodes of the 20 batteries with respect to Li was determined.
The reference electrode was prepared by inserting a platinum wire and a lithium foil into a tube made of polytetrafluoroethylene.
[0103]
(Ii) Corrosion rate of case
In the battery which was deeply discharged in the same manner as in the measurement of the potential of the negative electrode with respect to Li, the appearance of the battery was visually inspected for corrosion. The number of corroded batteries among the 20 batteries was represented by n, and the corrosion ratio was represented by n / 20.
[0104]
(Iii) Capacity recovery rate
First, the battery after aging is charged with a constant current of 1400 mA (0.7 ItA) until the battery voltage reaches 4.2 V, and then the battery is charged until the current value decreases to 100 mA (0.05 ItA). Charged with voltage. Next, the initial capacity at the time of discharging at a constant current of 2000 mA (1.0 ItA) to a discharge end voltage of 3.0 V was determined. Next, a constant resistance of 1 KΩ was connected to the battery and left for 50 days in a 60 ° C. environment.
Next, the resistance was removed from the battery, and the capacity after deep discharge was obtained under the same charge and discharge conditions as when the initial capacity was obtained. The ratio of the capacity after deep discharge when the initial capacity was 100% was defined as the capacity recovery rate. Then, the average value of the capacity recovery rates of the 20 batteries was determined.
[0105]
(Iv) Charge / discharge cycle characteristics
The battery is charged at a constant current of 1400 mA (0.7 ItA) until the battery voltage reaches 4.2 V, then charged at a constant voltage until the current value attenuates to 100 mA (0.05 ItA), and then charged at 2000 mA (1.0 ItA). ), A charge / discharge cycle was performed to discharge to a discharge end voltage of 3.0 V at a constant current. This charge / discharge cycle was repeated 500 times in an environment of 20 ° C., and the ratio of the capacity at the 500th cycle when the third cycle was set to 100% was determined as the capacity retention ratio. Then, the average value of the capacity retention rates of the 20 batteries was determined.
The results are shown in Tables 1 and 2.
[0106]
[Table 1]

[0107]
[Table 2]

[0108]
The contents of Tables 1 and 2 will be described.
In Examples 1 to 10 and Examples 12 to 13, the alkali metal salt X is contained in the negative electrode.
In Example 11, the alkali metal salt X is contained in both the positive electrode and the negative electrode.
In Examples 14 to 25 and Examples 27 to 28, the alkali metal salt X is contained in the non-aqueous electrolyte.
In Example 26, the alkali metal salt X was contained in both the negative electrode and the non-aqueous electrolyte.
On the other hand, in Comparative Example 1, the alkali metal salt X was not contained in any of the positive electrode, the negative electrode, and the non-aqueous electrolyte.
[0109]
First, the negative electrode of each example has a lower Li potential than the negative electrode of Comparative Example 1. In addition, good results were obtained for the case corrosion ratio. This is because, in the battery of the example, the alkali metal salt X is contained, and when the battery is deeply discharged to a battery voltage of 0 V, the capacity decreases on the positive electrode side due to an increase in the retention amount, but the negative electrode side absorbs Li. It is considered that the capacity was increased by the reaction.
[0110]
Examples 1 to 4 and Examples 14 to 16 show that increasing the amount of the alkali metal salt X increases the effect of shifting the negative electrode potential at a battery voltage of 0 V to a lower side. This means that the corrosion prevention effect of the battery case can be improved.
[0111]
Further, from Examples 14 to 28, the alkali metal salt X can be used alone as a solute of the non-aqueous electrolyte, and LiPF ₆ It can be seen that it can be used in combination with conventional solutes such as.
[0112]
From Examples 1 to 4 and Examples 12 to 13, the effect is small when the content of the alkali metal salt X contained in the negative electrode is less than 0.01 part by weight per 100 parts by weight of the negative electrode active material, and exceeds 10 parts by weight. It turns out that there is no merit. When the content of the alkali metal salt X in the electrode exceeds 10 parts by weight per 100 parts by weight of the negative electrode active material, the resistance component on the positive electrode side becomes large and inhibits the battery reaction. It is considered that the charge / discharge cycle characteristics deteriorate.
[0113]
From Examples 14 to 16 and Examples 27 to 28, the effect was small when the concentration of the alkali metal salt X in the non-aqueous electrolyte was less than 0.001 mol / L, and 1.5 mol / L. It turns out that there is no merit even if it exceeds. When the concentration of the alkali metal salt X in the non-aqueous electrolyte is increased, the resistance component on the positive electrode side is increased, and the battery reaction is inhibited. .
[0114]
【The invention's effect】
As described above, according to the preferred embodiment of the present invention, there is provided a non-aqueous electrolyte secondary battery that does not corrode the battery case even at deep discharge, has an excellent capacity recovery rate, and has excellent charge-discharge cycle characteristics. be able to.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a non-aqueous electrolyte secondary battery manufactured in an example of the present invention and a comparative example.
[Explanation of symbols]
11 Positive electrode plate
12 Negative electrode plate
13 Separator
14 Positive electrode lead
15 Negative electrode lead
16 Upper insulating plate
17 Lower insulating plate
18 Battery case
19 Sealing body
20 Positive terminal

Claims (12)

A positive electrode, a negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode,
At least one selected from the group consisting of the positive electrode, the negative electrode, and the non-aqueous electrolyte contains an alkali metal salt X and / or an oxidative decomposition product of the alkali metal salt X,
A non-aqueous electrolyte secondary battery in which the oxidative decomposition potential of the alkali metal salt X is 3.2 V to 4.3 V with respect to Li potential: Li ⁺ / Li. A positive electrode, a negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode,
At least one selected from the group consisting of the positive electrode, the negative electrode, and the non-aqueous electrolyte contains an alkali metal salt X and / or an oxidative decomposition product of the alkali metal salt X,
The alkali metal salt X is represented by the formula (1):

(In the formula (1), R ¹ , R ² , R ^3, and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group, or a halogen atom. A non-aqueous electrolyte secondary battery which is a compound represented by the formula (I) wherein two may be bonded to each other to form a ring structure, and M is a lithium atom, a sodium atom or a potassium atom. The non-aqueous electrolyte secondary battery according to claim 2, wherein at least one selected from the group consisting of R ¹ , R ² , R ³ and R ⁴ in the formula (1) is an aralkyl group, and the remainder is a hydrogen atom. A positive electrode, a negative electrode, a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode,
At least one selected from the group consisting of the positive electrode, the negative electrode, and the non-aqueous electrolyte contains an alkali metal salt X and / or an oxidative decomposition product of the alkali metal salt X,
The alkali metal salt X is represented by the formula (2):

(In the formula (2), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and are adjacent to each other. A non-aqueous electrolyte secondary battery which is a compound represented by the formula (I) wherein two may be bonded to each other to form a ring structure, and M is a lithium atom, a sodium atom or a potassium atom. The non-aqueous electrolyte secondary battery according to claim 4, wherein at least one selected from the group consisting of R ¹ , R ² , R ³ and R ⁴ in the formula (2) is an aralkyl group, and the remainder is a hydrogen atom. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains 0.01 to 10 parts by weight of the alkali metal salt X per 100 parts by weight of the negative electrode active material. A non-aqueous solvent comprising a non-aqueous solvent and an alkali metal salt X dissolved in the non-aqueous solvent, wherein the oxidative decomposition potential of the alkali metal salt X is 3.2 V to 4.3 V with respect to Li potential: Li ⁺ / Li. Electrolyte. A non-aqueous solvent and an alkali metal salt X dissolved in the non-aqueous solvent,
The alkali metal salt X is represented by the formula (1):

(In the formula (1), R ¹ , R ² , R ^3, and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group, or a halogen atom. A non-aqueous electrolyte solution which is a compound represented by the formula (I) wherein two may be bonded to each other to form a ring structure, and M is a lithium atom, a sodium atom or a potassium atom. 9. The non-aqueous electrolyte according to claim 8, wherein at least one selected from the group consisting of R ¹ , R ² , R ³ and R ⁴ in the formula (1) is an aralkyl group, and the remainder is a hydrogen atom. A non-aqueous solvent and an alkali metal salt X dissolved in the non-aqueous solvent,
The alkali metal salt X is represented by the formula (2):

(In the formula (2), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a hydroxyl group, an alkyl group, an alkoxyl group, an aryl group, a sulfo group, an aralkyl group or a halogen atom, and are adjacent to each other. A non-aqueous electrolyte solution which is a compound represented by the formula (I) wherein two may be bonded to each other to form a ring structure, and M is a lithium atom, a sodium atom or a potassium atom. The non-aqueous electrolyte according to claim 10, wherein at least one selected from the group consisting of R ¹ , R ² , R ³ and R ⁴ in the formula (2) is an aralkyl group, and the remainder is a hydrogen atom. The non-aqueous electrolyte according to claim 7, 8 or 10, wherein the concentration of the alkali metal salt X is 0.001 mol / L to 1.5 mol / L.

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