JP4979049B2 - Non-aqueous secondary battery - Google Patents
Non-aqueous secondary battery Download PDFInfo
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- JP4979049B2 JP4979049B2 JP2001230197A JP2001230197A JP4979049B2 JP 4979049 B2 JP4979049 B2 JP 4979049B2 JP 2001230197 A JP2001230197 A JP 2001230197A JP 2001230197 A JP2001230197 A JP 2001230197A JP 4979049 B2 JP4979049 B2 JP 4979049B2
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- positive electrode
- active material
- electrode active
- secondary battery
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Description
【0001】
【発明の属する技術分野】
本発明は、非水二次電池に関し、更に詳しくは、充放電サイクル後及び高温貯蔵後の内部インピーダンスの増加による放電容量の低下を抑制した非水二次電池に関するものである。
【0002】
【従来の技術】
電子機器の小型化、携帯電話の普及等に伴い、それらの電源として高エネルギー密度を有する二次電池への要求がますます高まっている。現在、この要求に応える高容量二次電池としては、正極活物質としてリチウム含有複合酸化物であるLiCoO2、LiNiO2又はLiMn2O4等を用い、負極活物質として炭素系材料を用いたリチウムイオン二次電池が実用化されている。このリチウムイオン二次電池は、その平均駆動電圧が3.6Vと高く、従来のニッケル−カドミウム電池やニッケル水素電池の平均駆動電圧の約3倍である。また、負極活物質として炭素系材料を用い、充放電に関与するモビリティー(移動体)が軽金属であるリチウム(イオン)であることから、軽量化も期待できる。
【0003】
リチウムイオン二次電池は、従来のリチウム金属を負極とする非水二次電池とは異なり、前記活物質を結着剤等とともに溶液中に分散させたペーストとし、このペーストを用いて帯状の正極集電体、負極集電体の両面にそれぞれの活物質を含有する塗膜を形成して正極及び負極を作製するものである。そして、それらの帯状の正、負電極はセパレータを介して渦巻状に巻回されて電極体を形成し、電池缶に挿入されて電池が構成されている。また、前記正極には正極活物質と結着剤以外に塗膜中のインピーダンスの低減のため、炭素系材料等の導電助剤が添加されている。
【0004】
今後、携帯情報末端機器の需要拡大により、高容量且つ軽量であるリチウムイオン二次電池の電源としての重要性はますます増加するとともに、その要求特性は更に厳しくなることが予測される。この様な中で、リチウムイオン二次電池の内部インピーダンスの上昇は、負荷特性や放電容量の低下に繋がるため、内部インピーダンスの低減が技術上の重要な課題となっている。特に充放電サイクル後及び高温貯蔵後の内部インピーダンスの上昇を抑制したリチウムイオン二次電池が要求されている。
【0005】
リチウムイオン二次電池の内部インピーダンスの上昇には、様々な要因が挙げられる。例えば、正極活物質であるLiCoO2等のリチウム含有複合酸化物の表面上にはアルカリ成分が存在することが知られており、このアルカリ成分と非水電解液との反応により、非水電解液等の分解物であるガスが発生する。このガスによりイオンの移動が阻害されて内部インピーダンスが上昇することになる。
【0006】
この非水電解液の分解を抑えるため、非水電解液に6員環の環状エーテルを使用することにより、非水電解液の分解によるガス発生を抑制して、その結果電池の内部インピーダンスの上昇を防止して放電容量の低下を防ぐことが特開平9−213368号公報に提案されている。また、正極活物質の表面のアルカリ成分を中和するため、正極に有機酸や無機酸を添加することにより、塩基性の強いLiNiO2のペーストのゲル化を防止して、放電特性等の電池特性に優れた非水二次電池を提供することが特開平10−79244号公報に提案されている。
【0007】
【発明が解決しようとする課題】
しかし、前記従来の提案は、いずれも初期の内部インピーダンスの低減には効果があるが、充放電サイクル後及び高温貯蔵後の内部インピーダンスの上昇を抑制することはできないという問題があった。この原因として、充放電時において、正極活物質であるリチウム含有複合酸化物が収縮・膨張することにより、正極活物質と導電助剤との間に隙間が発生して接触面積が減少することが考えられる。また、高温貯蔵時に正極表面での非水電解液の分解の促進、あるいは結着剤の膨潤による正極活物質と導電助剤との接触面積の減少が内部インピーダンス上昇の原因となっている。
【0008】
そこで、本発明は前記従来の問題を解決するためになされたものであり、充放電サイクル後及び高温貯蔵後の内部インピーダンスの増加による放電容量の低下を抑制した非水二次電池を提供することを目的とする。
【0009】
【課題を解決するための手段】
前記目的を達成するため、本発明の非水二次電池は、正極、負極及び電解質を備えた非水二次電池であって、前記正極に芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を含有させたことを特徴とする。
【0010】
また、本発明の非水二次電池は、前記芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物が、正極活物質に対して0.01〜1質量%の割合で前記正極に含有されていることが好ましい。
【0011】
これにより、充放電サイクル後及び高温貯蔵後の内部インピーダンスの増加を抑制することができる。これは、正極に芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を含有させることにより、LiCoO2等のリチウム含有複合酸化物の表面に存在するアルカリ成分に極性基であるリン酸基又はスルホン酸基が吸着するとともに、黒鉛やカーボンブラック等の導電助剤の表面には芳香族性の置換基が吸着することにより、正極活物質と導電助剤とがより密着して存在することが可能になり、充放電サイクル後及び高温貯蔵後の内部インピーダンスが上昇することを抑えることができるものである。
【0012】
また、芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物は、正極活物質に対して0.01〜1質量%という少量を正極に含有させても効果が発揮されるという優れた特徴を有する。
【0013】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
【0014】
本発明の非水二次電池は、正極、負極及び電解質を備えた非水二次電池であって、前記正極に芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を含有させたものである。
【0015】
本発明に用いる芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物については何ら限定されることはなく、種々のものが使用できる。例えば、芳香族性の置換基を有するリン酸化合物としては、下記一般式(1)で示されるものが使用できる。
【0016】
【化1】
【0017】
式中、Xは芳香族性の置換基であり、Mは水素原子又はアルカリ金属原子である。
【0018】
また、芳香族性の置換基を有するスルホン酸化合物としては、下記一般式(2)で示されるものが使用できる。
【0019】
【化2】
【0020】
式中、X1は芳香族性の置換基であり、X2は水素原子又はアルカリ金属原子である。
【0021】
上記芳香族性の置換基は、芳香族環を有する置換基であり、フェニル基、ビフェニリル基、p−テルフェニリル基、ナフチル基、アントラセン基、インデニル基等の種々のものが該当する。中でもフェニル基は導電助剤によく吸着するため特に好ましい。即ち、正極活物質及び導電助剤に上記化合物が吸着した場合、導電助剤と正極活物質が十分に接触していることが望ましく、フェニル基を置換基とした場合にはその立体構造から導電助剤により密着するとともに、正極活物質にリン酸基又はスルホン酸基が吸着し、内部インピーダンスの低減に最も効果的である。
【0022】
芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を正極に含有させる方法は特に制限されない。例えば、正極塗料中に添加してもよいし、正極塗膜に添加してもよい。正極塗料中に添加する場合は、正極活物質を結着剤、導電助剤、有機溶媒等とともに混合、分散する時に、芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を同時に混合してもよし、また、正極塗料作製後に添加してもよい。正極塗膜に添加する場合は、正極塗膜を作製した後に、芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を含む溶液を正極塗膜上に滴下又は塗布してもよい。また、正極塗膜を芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を溶解した非水溶媒中に浸漬してもよい。非水溶媒としては、例えば、N−メチルピロリドン、ジメチルアセトアミド、ジメチルホルムアミド等を単独又は2種以上混合したものが使用できる。
【0023】
芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物は、正極活物質に対して0.01〜1質量%の割合で正極に含有されていることが好ましい。0.01質量%以上とすることにより、芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物が正極活物質の表面に存在するアルカリ成分に十分に吸着することができ、アルカリ成分と電解液との反応によるガス発生の抑制能力を十分に発揮することができ、また導電助剤にも十分に吸着でき、充放電サイクル後及び高温貯蔵後の内部インピーダンスの上昇を抑えることができる。また、1質量%以下とすることにより、正極活物質等に吸着していない芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物が存在しなくなるため、充放電サイクル時及び高温貯蔵時において未吸着分の前記化合物の分解が生じることがない。
【0024】
本発明において、正極活物質としては特に限定されることはないが、例えば、LiCoO2等のリチウムコバルト酸化物、LiMnO2等のリチウムマンガン酸化物、LiNiO2等のリチウムニッケル酸化物、二酸化マンガン、五酸化バナジウム、クロム酸化物等の金属酸化物、又はこれらを基本構造とする複合酸化物(例えば、異種金属元素での置換品)、あるいは二硫化チタン、二硫化モリブデン等の金属硫化物等が、単独で又は2種以上の混合物として、あるいはそれらの固溶体として用いられる。また、LiMO2又はLiM2O4で示され、MがCo、Ni、Mn、Fe、Cu等の金属元素を少なくとも1つ以上を含んだリチウム含有金属化合物であってもよい。中でもLiNiO2、LiCoO2、LiMn2O4等の充電時の開路電圧がLi基準で4V以上を示すリチウム含有複合酸化物を正極活物質として用いるのが、高エネルギー密度が得られる点で好ましい。
【0025】
また、正極は、例えば、前記正極活物質を含み、必要に応じて鱗片状黒鉛、カーボンブラック等の導電助剤を含み、更に結着剤を含むペーストを正極集電体上に塗布して乾燥し、正極集電体上に少なくとも正極活物質と結着剤を含有する塗膜を形成する工程を経て作製される。前記正極活物質含有ペーストの調製にあたって、結着剤はあらかじめ溶剤に溶解させた溶液として用い、前記正極活物質等の固体粒子と混合して調製することが好ましい。
【0026】
本発明において、前記正極集電体の厚さとしては、5〜60μm、特に8〜40μmが好ましく、また、前記正極活物質含有塗膜の厚さとしては、片面当たり30〜300μm、特に50〜150μmが好ましい。
【0027】
負極に用いる材料としては、リチウムイオンをドープ(吸蔵)、脱ドープ(放出)することができるものであればよく、本発明においては、そのようなリチウムイオンをドープ、脱ドープすることができる物質を負極活物質という。この負極活物質としては、特に限定されることはないが、例えば、黒鉛、熱分解炭素類、コークス類、ガラス状炭素類、有機高分子化合物の焼成体、メソカーボンマイクロビーズ、炭素繊維、活性炭等の炭素材料、アルミニウム、ケイ素、錫、インジウム等とリチウムとの合金、又はリチウムに近い低電圧で充放電できるケイ素、錫、インジウム等の酸化物等を用いることができる。
【0028】
負極活物質として炭素材料を用いる場合、その炭素材料としては下記の特性を持つものが好ましい。即ち、その結晶の(002)面の面間距離(d002)に関しては、0.350nm以下が好ましく、より好ましくは0.345nm以下、更に好ましくは0.340nm以下である。また、c軸方向の結晶子の大きさ(Lc)に関しては、3nm以上が好ましく、より好ましくは8nm以上、更に好ましくは25nm以上である。そして、前記炭素材料の平均粒径は、8〜20μm、特に10〜15μmが好ましい。また、その純度は99.9質量%以上が好ましい。
【0029】
また、負極は、例えば、前記負極活物質にポリフッ化ビニリデンやポリテトラフルオロエチレン等の結着剤を適宜添加し、更に要すれば導電助剤を適宜添加して、溶剤でペースト状にし、その負極活物質含有ペーストを銅箔等からなる負極集電体に塗布して乾燥し、負極集電体上に負極活物質含有塗膜を形成することによって作製される。なお、結着剤はあらかじめ溶剤に溶解させておいてから負極活物質等と混合してもよい。
【0030】
前記負極集電体の厚さとしては、5〜60μm、特に8〜40μmが好ましく、また、前記負極活物質含有塗膜の厚さとしては、片面当たり30〜300μm、特に50〜150μmが好ましい。
【0031】
前記正極及び負極に使用される結着剤としては,熱可塑性樹脂、ゴム弾性を有するポリマー及び多糖類を一種又はこれらの混合物として用いることができる。具体的には、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、ポリエチレン、ポリプロピレン、エチレン−プロピレン−ジエン共重合体、スチレンブタジエンゴム、ポリブタジエン、フッ素ゴム、ポリエチレンオキシド、ポリビニルピロリドン、ポリエステル樹脂、アクリル樹脂、フェノール樹脂、エポキシ樹脂、ポリビニルアルコール、ヒドロキシプロピルセルロース等のセルロース樹脂等が挙げられる。中でも正極活物質含有ペーストの結着剤としてポリフッ化ビニリデンを使用することにより、本発明の効果を最も発揮することができる。
【0032】
前記正極集電体及び負極集電体としては、例えば、アルミニウム、銅、ニッケル、ステンレス鋼、チタン等の金属の箔、エキスパンドメタル、網、フォームメタル等が用いられるが、正極集電体としては特にアルミニウム箔が好ましく、負極集電体としては特に銅箔が好ましい。
【0033】
前記正極及び負極の作製にあたって、前記正極活物質含有ペースト及び負極活物質含有ペーストを集電体に塗布する際の塗布方法としては、例えば、押出しコーター、リバースローラー、ドクターブレード等をはじめ、各種の塗布方法を採用することができる。
【0034】
本発明で用いる電解質としては、通常、液状電解質(以下、これを「電解液」という)が用いられる。そして、その電解液としては、有機溶媒に溶質を溶解させた有機溶媒系の非水電解液が用いられる。その有機溶媒系電解液の溶媒は特に限定されるものではないが、鎖状エステルを主溶媒として用いることが特に好ましい。そのような鎖状エステルとしては、例えば、ジエチルカーボネート(DEC)、ジメチルカーボネート(DMC)、エチルメチルカーボネート(EMC)、酢酸エチル(EA)、プロピオン酸メチル(MP)等の鎖状のCOO−結合を有する有機溶媒が挙げられる。この鎖状エステルが電解液の主溶媒であるということは、これらの鎖状エステルが全電解液溶媒中の50体積%より多い体積を占めることを意味しており、特に鎖状エステルが全電解液溶媒中の65体積%以上、とりわけ鎖状エステルが全電解液溶媒中の70体積%以上を占めることが好ましく、中でも鎖状エステルが全電解液溶媒中の75体積%以上を占めることが最も好ましい。
【0035】
ただし、電解液の溶媒としては、前記鎖状エステルのみで構成するよりも、電池容量の向上を図るために、前記鎖状エステルに誘電率の高いエステル(誘電率30以上のエステル)を混合して用いることが好ましい。そのような誘電率の高いエステルの全電解液溶媒中で占める量としては、10体積%以上、特に20体積%以上が好ましい。
【0036】
前記誘電率の高いエステルとしては、例えば、エチレンカーボネート(EC)、プロピレンカーボネート(PC)、ブチレンカーボネート(BC)、γ−ブチロラクトン(γ−BL)、エチレングリコールサルファイト(EGS)等が挙げられ、特にエチレンカーボネート、プロピレンカーボネート等の環状構造のものが好ましく、とりわけ環状のカーボネートが好ましく、具体的にはエチレンカーボネート(EC)が最も好ましい。
【0037】
また、前記誘電率の高いエステル以外に併用可能な溶媒としては、例えば、1,2−ジメトキシエタン(1,2−DME)、1,3−ジオキソラン(1,3−DO)、テトラヒドロフラン(THF)、2−メチル−テトラヒドロフラン(2−Me−THF)、ジエチルエーテル(DEE)等が挙げられる。そのほか、アミン系又はイミド系の有機溶媒や、含イオウ系又は含フッ素系の有機溶媒等も用いることができる。
【0038】
電解液の溶質としては、例えば、LiClO4、LiPF6、LiBF4、LiAsF6、LiSbF6、LiCF3SO3、LiC4F9SO3、LiCF3CO2、Li2C2F4(SO3)2、LiN(CF3SO2)2、LiC(CF3SO2)3、LiCnF2n+1SO3(n≧2)等が、単独で又は2種以上混合して用いられる。特に、LiPF6やLiC4F9SO3等が、充放電特性が良好なことから好ましい。電解液中における溶質の濃度は特に限定されるものではないが、0.3〜1.7mol/dm3、特に0.4〜1.5mol/dm3程度が好ましい。
【0039】
本発明において、電解質としては前記電解液以外にも固体状又はゲル状の電解質を用いることができる。このような電解質としては、無機固体電解質のほか、ポリエチレンオキサイド、ポリプロピレンオキサイド又はこれらの誘導体等を主材にした有機固体電解質等を挙げることができる。
【0040】
本発明に用いるセパレ−タとしては、例えば不織布や微孔性フィルムが用いられる。前記不織布の材質としては、ポリプロピレン、ポリエチレン、ポリエチレンテレフタレート、ポリブチレンテレフタレート等がある。微孔性フィルムの材質としては、ポリプロピレン、ポリエチレン、ポリエチレン−プロピレン共重合体等がある。
【0041】
前記セパレータは、強度が十分でしかも電解液を多く保持できるものが好ましく、そのような観点から、厚さが10〜50μmで、開孔率が30〜70%のポリプロピレン製、ポリエチレン製又はエチレン−プロピレン共重合体製の微孔性フィルムや不織布等が好ましい。
【0042】
本発明において、負極のリード体は、前記のようにして作製された負極に、抵抗溶接、超音波溶接等により負極集電体の露出部分に溶接されるが、この負極のリード体の断面積としては、大電流が流れた場合の抵抗を低減して発熱量を低減するために、0.1mm2以上で1.0mm2以下が好ましく、0.3mm2以上で0.7mm2以下がより好ましい。負極のリード体の材質としては、ニッケルが一般に用いられるが、銅、チタン、ステンレス鋼等も用いることができる。
【0043】
本発明の非水二次電池は、例えば、前記のようにして作製されたシート状の正極とシート状の負極との間にセパレータを介在させて重ね合わせ、それを渦巻状、楕円状、長円形状等に巻回して作製した巻回構造の電極体又はこれらを積層した電極体を、ニッケルメッキを施した鉄やステンレス鋼、又はアルミニウム若しくはアルミニウム合金製の電池缶、あるいは金属ラミネートフィルム内に挿入し、電解液を注入した後に封口する工程を経て作製される。また、前記電池には、通常、電池内部に発生したガスをある一定圧力まで上昇した段階で電池外部に排出して、電池の内圧上昇による破裂を防止するための防爆機構が取り付けられている。
【0044】
【実施例】
次に、実施例に基づき本発明をより具体的に説明する。ただし、本発明はこれらの実施例のみに限定されるものではない。
【0045】
(実施例1)
先ず、以下のようにして正極を作製した。正極活物質としてLiCoO2を190質量部、導電助剤としてアセチレンブラックを4質量部、結着剤としてポリフッ化ビニリデンを6質量部、芳香族性の置換基を有すリン酸化合物としてフェニルホスホン酸を正極活物質に対して0.2質量%となるように均一に混合し、更にN−メチルピロリドン60質量部を加えて混合し、ペースト状の正極塗料を調製した。このペースト状の正極塗料を70メッシュの網を通過させて大きなものを取り除いた後、厚さ15μmの帯状のアルミニウム箔からなる正極集電体の両面に均一に塗布し、乾燥して正極活物質含有塗膜を形成した。乾燥後の塗膜の厚さは215μmであり、単位面積当たりの電極質量は25.0mg/cm2であった。この帯状の電極体を乾燥後、厚み170μmに圧縮成形した。その後、所定の大きに切断し、アルミニウム製リード体を溶接して、シート状の正極を得た。
【0046】
次に、以下のようにして負極を作製した。負極活物質として黒鉛系炭素材料〔ただし、その結晶の(002)面の面間距離(d002)=0.337nm、c軸方向の結晶子の大きさ(Lc)=95nm、平均粒径10μm、純度99.9質量%以上という特性を持つ炭素材料〕180質量部を、ポリフッ化ビニリデン14質量部をN−メチルピロリドン190質量部に溶解させた溶液と混合してペースト状の負極塗料を調製した。このペースト状の負極塗料を厚さ10μmの帯状の銅箔からなる負極集電体の両面に均一に塗布し、乾燥して負極活物質含有塗膜を形成した。乾燥後の塗膜の厚さは243μmであり、単位面積当たりの電極質量は12.0mg/cm2であった。この帯状の電極体を乾燥後、厚み175μmに圧縮成形した。その後、所定の大きさに切断し、ニッケル製のリード体を溶接して、シート状の負極を得た。
【0047】
また、以下のようにして電解液を調製した。メチルエチルカーボネート(MEC)とエチレンカーボネート(EC)とを体積比2:1の割合で混合した混合溶媒に、LiPF6を1.2mol/dm3溶解させて非水電解液を得た。
【0048】
続いて、以下のようにして非水二次電池を作製した。前記正極及び負極を乾燥処理後、前記正極を厚さ25μmの微孔性ポリエチレンフィルムからなるセパレータを介して前記負極に重ね、渦巻状に巻回して渦巻状の巻回構造の電極体を形成した。これを袋状のアルミラミネートフィルム内に挿入した。次に、前記電解液を注入した後に真空封止を行ない、その状態で3時間室温で放置し、正極、負極、セパレータに電解液を十分に含浸させて本発明の非水二次電池を得た。
【0049】
(実施例2)
実施例1の正極の作製工程におけるフェニルホスホン酸を正極活物質に対して0.2質量%加えることを、p−トルエンスルホン酸を正極活物質に対して0.2質量%加えることに変更した以外は、実施例1と同様に本発明の非水二次電池を作製した。
【0050】
(実施例3)
実施例1の正極の作製工程におけるフェニルホスホン酸を正極活物質に対して0.2質量%加えることを、フェニルホスホン酸を正極活物質に対して0.005質量%加えることに変更した以外は、実施例1と同様に本発明の非水二次電池を作製した。
【0051】
(実施例4)
実施例1の正極の作製工程におけるフェニルホスホン酸を正極活物質に対して0.2質量%加えることを、フェニルホスホン酸を正極活物質に対して5質量%加えることに変更した以外は、実施例1と同様に本発明の非水二次電池を作製した。
【0052】
(比較例1)
実施例1の正極の作製工程におけるフェニルホスホン酸を添加しないこと以外は、実施例1と同様に比較例の非水二次電池を作製した。
【0053】
(比較例2)
実施例1の正極の作製工程におけるフェニルホスホン酸を添加しないこと、及び電解液としてテトラヒドロピランにLiPF6を1.2mol/dm3溶解させた非水電解液を使用したこと以外は、実施例1と同様に比較例の非水二次電池を作製した。
【0054】
(比較例3)
実施例1の正極の作製工程におけるフェニルホスホン酸を正極活物質に対して0.2質量%加えることを、トリフロロメタンホスホン酸を正極活物質に対して0.2質量%加えることに変更した以外は、実施例1と同様に本発明の非水二次電池を作製した。
【0055】
上記実施例1〜4及び比較例1〜3の各非水二次電池について充放電を繰り返した時の放電容量及び内部インピーダンスの変化を測定した。また、高温貯蔵後の放電容量及び内部インピーダンスの変化も測定した。その結果を表1に示す。
【0056】
【表1】
【0057】
放電容量の測定方法は、充電を1Cの電流制限回路を設けて4.2Vの定電圧で行ない、放電を1Cの電流で電池の電極間電圧が3Vに低下するまで行なった。そして、比較例1の電池の1サイクル目の放電容量を100%とし、その放電容量に対する相対値で他の電池の放電容量(%)を求めた。また、貯蔵特性は、60℃で1週間貯蔵した後の放電容量を測定することにより評価した。更に、内部インピーダンスは、放電容量の測定条件と同様の条件で、LCRメータにより1kHzにおける内部インピーダンスを測定し、比較例1の電池の1サイクル目の内部インピーダンスを100%とし、その内部インピーダンスに対する相対値で他の電池の内部インピーダンス(%)を求めた。
【0058】
表1から明らかなように、芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を添加した正極を用いた実施例1〜4は、比較例1と比べて1サイクル目の放電容量が高く、且つ、充放電サイクルを300サイクル繰り返した後及び高温で貯蔵した後でも放電容量の低下は少なかった。また、実施例1〜4は、比較例1に比べて1サイクル目の内部インピーダンスも低くなっており、300サイクル後及び高温貯蔵後の内部インピーダンスの上昇も抑えられていることがわかる。
【0059】
また、比較例2及び比較例3と比べても、実施例1〜4は、300サイクル後及び高温貯蔵後の放電容量は高くなっており、内部インピーダンスの上昇も抑えられていることがわかる。
【0060】
【発明の効果】
以上のように本発明によれば、非水二次電池の正極に芳香族性の置換基を有するリン酸化合物又はスルホン酸化合物を含有させることにより、充放電サイクル後及び高温貯蔵後の内部インピーダンスの増加による放電容量の低下を抑制した非水二次電池を提供することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery, and more particularly to a non-aqueous secondary battery that suppresses a decrease in discharge capacity due to an increase in internal impedance after a charge / discharge cycle and after high-temperature storage.
[0002]
[Prior art]
With the downsizing of electronic devices and the spread of mobile phones, there is an increasing demand for secondary batteries having high energy density as their power source. Currently, as a high-capacity secondary battery that meets this requirement, LiCoO which is a lithium-containing composite oxide as a positive electrode active material. 2 LiNiO 2 Or LiMn 2 O Four Etc., and a lithium ion secondary battery using a carbon-based material as a negative electrode active material has been put into practical use. This lithium ion secondary battery has a high average driving voltage of 3.6 V, which is about three times the average driving voltage of conventional nickel-cadmium batteries and nickel hydrogen batteries. Further, since a carbon-based material is used as the negative electrode active material and the mobility (moving body) involved in charge / discharge is lithium (ion) which is a light metal, weight reduction can be expected.
[0003]
Unlike conventional non-aqueous secondary batteries using lithium metal as a negative electrode, a lithium ion secondary battery is a paste in which the active material is dispersed in a solution together with a binder and the like. A positive electrode and a negative electrode are produced by forming coating films containing the respective active materials on both surfaces of the current collector and the negative electrode current collector. The belt-like positive and negative electrodes are spirally wound through a separator to form an electrode body and inserted into a battery can to constitute a battery. In addition to the positive electrode active material and the binder, a conductive auxiliary such as a carbon-based material is added to the positive electrode in order to reduce impedance in the coating film.
[0004]
In the future, as the demand for portable information terminal devices expands, the importance as a power source of a lithium ion secondary battery having a high capacity and a light weight will increase more and the required characteristics are expected to become more severe. Under such circumstances, an increase in internal impedance of a lithium ion secondary battery leads to a decrease in load characteristics and discharge capacity, and therefore, reduction of internal impedance is an important technical issue. In particular, a lithium ion secondary battery that suppresses an increase in internal impedance after a charge / discharge cycle and after high-temperature storage is required.
[0005]
There are various factors that increase the internal impedance of a lithium ion secondary battery. For example, LiCoO which is a positive electrode active material 2 It is known that there is an alkali component on the surface of lithium-containing composite oxides, etc., and the reaction between this alkali component and the non-aqueous electrolyte generates gas that is a decomposition product of the non-aqueous electrolyte etc. To do. This gas inhibits the movement of ions and increases the internal impedance.
[0006]
In order to suppress the decomposition of the non-aqueous electrolyte, the use of a 6-membered cyclic ether in the non-aqueous electrolyte suppresses gas generation due to the decomposition of the non-aqueous electrolyte, resulting in an increase in the internal impedance of the battery. Japanese Patent Laid-Open No. 9-213368 proposes preventing the discharge capacity from decreasing. In addition, in order to neutralize the alkaline component on the surface of the positive electrode active material, an organic acid or inorganic acid is added to the positive electrode to thereby form a highly basic LiNiO. 2 JP-A-10-79244 proposes to provide a non-aqueous secondary battery which prevents gelation of the paste and provides excellent battery characteristics such as discharge characteristics.
[0007]
[Problems to be solved by the invention]
However, each of the conventional proposals is effective in reducing the initial internal impedance, but there is a problem that the increase in internal impedance after the charge / discharge cycle and after high-temperature storage cannot be suppressed. As a cause of this, during charging / discharging, the lithium-containing composite oxide, which is the positive electrode active material, contracts and expands, thereby generating a gap between the positive electrode active material and the conductive additive, thereby reducing the contact area. Conceivable. In addition, acceleration of decomposition of the nonaqueous electrolyte solution on the surface of the positive electrode during high temperature storage, or a decrease in the contact area between the positive electrode active material and the conductive additive due to swelling of the binder causes an increase in internal impedance.
[0008]
Accordingly, the present invention has been made to solve the above-described conventional problems, and provides a non-aqueous secondary battery that suppresses a decrease in discharge capacity due to an increase in internal impedance after a charge / discharge cycle and after high-temperature storage. With the goal.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a non-aqueous secondary battery of the present invention is a non-aqueous secondary battery comprising a positive electrode, a negative electrode and an electrolyte, the phosphoric acid compound or sulfone having an aromatic substituent on the positive electrode. It is characterized by containing an acid compound.
[0010]
Further, in the nonaqueous secondary battery of the present invention, the phosphoric acid compound or sulfonic acid compound having an aromatic substituent is contained in the positive electrode in a proportion of 0.01 to 1% by mass with respect to the positive electrode active material. It is preferable that
[0011]
Thereby, the increase in internal impedance after a charge / discharge cycle and after high temperature storage can be suppressed. This is because LiCoO is obtained by adding a phosphoric acid compound or a sulfonic acid compound having an aromatic substituent to the positive electrode. 2 The phosphoric acid group or sulfonic acid group, which is a polar group, is adsorbed to the alkali component present on the surface of the lithium-containing composite oxide, etc., and an aromatic substituent is present on the surface of the conductive additive such as graphite or carbon black. By adsorbing, it becomes possible for the positive electrode active material and the conductive additive to be in close contact, and to suppress an increase in internal impedance after the charge / discharge cycle and after high-temperature storage. .
[0012]
Moreover, the phosphoric acid compound or sulfonic acid compound having an aromatic substituent is excellent in that the effect is exhibited even when a small amount of 0.01 to 1% by mass with respect to the positive electrode active material is contained in the positive electrode. Have
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0014]
The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode contains a phosphoric acid compound or sulfonic acid compound having an aromatic substituent. It is.
[0015]
The phosphoric acid compound or sulfonic acid compound having an aromatic substituent used in the present invention is not limited at all, and various compounds can be used. For example, what is shown by following General formula (1) can be used as a phosphoric acid compound which has an aromatic substituent.
[0016]
[Chemical 1]
[0017]
In the formula, X is an aromatic substituent, and M is a hydrogen atom or an alkali metal atom.
[0018]
Moreover, what is shown by following General formula (2) can be used as a sulfonic acid compound which has an aromatic substituent.
[0019]
[Chemical formula 2]
[0020]
Where X 1 Is an aromatic substituent and X 2 Is a hydrogen atom or an alkali metal atom.
[0021]
The aromatic substituent is a substituent having an aromatic ring, and includes various groups such as a phenyl group, a biphenylyl group, a p-terphenylyl group, a naphthyl group, an anthracene group, and an indenyl group. Among them, the phenyl group is particularly preferable because it is well adsorbed on the conductive additive. That is, when the above compound is adsorbed on the positive electrode active material and the conductive auxiliary agent, it is desirable that the conductive auxiliary agent and the positive electrode active material are in sufficient contact. While adhering with an auxiliary agent, a phosphoric acid group or a sulfonic acid group is adsorbed on the positive electrode active material, which is most effective in reducing internal impedance.
[0022]
The method for incorporating a phosphoric acid compound or a sulfonic acid compound having an aromatic substituent into the positive electrode is not particularly limited. For example, you may add in a positive electrode coating material, and may add to a positive electrode coating film. When added to the positive electrode paint, the phosphoric acid compound or sulfonic acid compound having an aromatic substituent is mixed at the same time when the positive electrode active material is mixed and dispersed together with the binder, conductive additive, organic solvent, etc. Alternatively, it may be added after preparing the positive electrode paint. When adding to a positive electrode coating film, after producing a positive electrode coating film, you may dripped or apply | coat the solution containing the phosphoric acid compound or sulfonic acid compound which has an aromatic substituent on a positive electrode coating film. Moreover, you may immerse a positive electrode coating film in the nonaqueous solvent which melt | dissolved the phosphoric acid compound or sulfonic acid compound which has an aromatic substituent. As the non-aqueous solvent, for example, N-methylpyrrolidone, dimethylacetamide, dimethylformamide or the like can be used alone or in combination of two or more.
[0023]
The phosphoric acid compound or sulfonic acid compound having an aromatic substituent is preferably contained in the positive electrode at a ratio of 0.01 to 1% by mass with respect to the positive electrode active material. By setting it as 0.01 mass% or more, the phosphoric acid compound or sulfonic acid compound which has an aromatic substituent can fully adsorb | suck to the alkaline component which exists on the surface of a positive electrode active material, an alkaline component and electrolysis The ability to suppress gas generation due to the reaction with the liquid can be sufficiently exerted, and it can be sufficiently adsorbed to the conductive assistant, and the increase in internal impedance after the charge / discharge cycle and after high temperature storage can be suppressed. Moreover, since the phosphoric acid compound or sulfonic acid compound which has an aromatic substituent which is not adsorb | sucking to positive electrode active material etc. does not exist by setting it as 1 mass% or less, in the time of a charging / discharging cycle and high temperature storage No decomposition of the unadsorbed compound occurs.
[0024]
In the present invention, the positive electrode active material is not particularly limited. For example, LiCoO 2 Lithium cobalt oxide such as LiMnO 2 Lithium manganese oxide such as LiNiO 2 Metal oxides such as lithium nickel oxide, manganese dioxide, vanadium pentoxide, chromium oxide, etc., or composite oxides having these as basic structures (for example, substitutes with different metal elements), or titanium disulfide, Metal sulfides such as molybdenum disulfide are used alone or as a mixture of two or more thereof or as a solid solution thereof. LiMO 2 Or LiM 2 O Four And M may be a lithium-containing metal compound containing at least one metal element such as Co, Ni, Mn, Fe, and Cu. Among them, LiNiO 2 LiCoO 2 , LiMn 2 O Four It is preferable to use a lithium-containing composite oxide having an open circuit voltage of 4 V or more on the basis of Li as a positive electrode active material because a high energy density is obtained.
[0025]
In addition, the positive electrode includes, for example, the positive electrode active material, and optionally includes a conductive auxiliary agent such as flaky graphite and carbon black, and further, a paste containing a binder is applied onto the positive electrode current collector and dried. Then, it is produced through a step of forming a coating film containing at least a positive electrode active material and a binder on the positive electrode current collector. In preparing the positive electrode active material-containing paste, the binder is preferably used as a solution previously dissolved in a solvent and mixed with solid particles such as the positive electrode active material.
[0026]
In the present invention, the thickness of the positive electrode current collector is preferably 5 to 60 μm, particularly preferably 8 to 40 μm, and the thickness of the positive electrode active material-containing coating film is 30 to 300 μm per side, particularly 50 to 50 μm. 150 μm is preferable.
[0027]
Any material can be used for the negative electrode as long as it can dope (occlude) and dedope (release) lithium ions, and in the present invention, a substance that can dope and dedope such lithium ions. Is referred to as a negative electrode active material. The negative electrode active material is not particularly limited. For example, graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon Carbon materials such as aluminum, silicon, tin, indium, and the like and lithium alloys, or oxides such as silicon, tin, and indium that can be charged and discharged at a low voltage close to lithium can be used.
[0028]
When a carbon material is used as the negative electrode active material, the carbon material preferably has the following characteristics. That is, the distance (d002) between the (002) planes of the crystal is preferably 0.350 nm or less, more preferably 0.345 nm or less, and further preferably 0.340 nm or less. The crystallite size (Lc) in the c-axis direction is preferably 3 nm or more, more preferably 8 nm or more, and further preferably 25 nm or more. And the average particle diameter of the said carbon material is 8-20 micrometers, Especially 10-15 micrometers is preferable. Further, the purity is preferably 99.9% by mass or more.
[0029]
Further, for example, the negative electrode is appropriately added with a binder such as polyvinylidene fluoride or polytetrafluoroethylene to the negative electrode active material, and if necessary, a conductive auxiliary agent is appropriately added, and a paste is formed with a solvent. The negative electrode active material-containing paste is applied to a negative electrode current collector made of copper foil or the like, dried, and a negative electrode active material-containing coating film is formed on the negative electrode current collector. The binder may be previously dissolved in a solvent and then mixed with the negative electrode active material or the like.
[0030]
The thickness of the negative electrode current collector is preferably 5 to 60 μm, particularly 8 to 40 μm, and the thickness of the negative electrode active material-containing coating film is preferably 30 to 300 μm, particularly 50 to 150 μm per side.
[0031]
As a binder used for the positive electrode and the negative electrode, a thermoplastic resin, a polymer having rubber elasticity, and a polysaccharide can be used as one kind or a mixture thereof. Specifically, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene-diene copolymer, styrene butadiene rubber, polybutadiene, fluoro rubber, polyethylene oxide, polyvinyl pyrrolidone, polyester resin, acrylic resin, phenol resin And cellulose resins such as epoxy resin, polyvinyl alcohol, and hydroxypropyl cellulose. In particular, the use of polyvinylidene fluoride as a binder for the positive electrode active material-containing paste can achieve the best effects of the present invention.
[0032]
Examples of the positive electrode current collector and the negative electrode current collector include metal foils such as aluminum, copper, nickel, stainless steel, and titanium, expanded metal, nets, foam metal, and the like. Aluminum foil is particularly preferable, and copper foil is particularly preferable as the negative electrode current collector.
[0033]
In the production of the positive electrode and the negative electrode, the application method when applying the positive electrode active material-containing paste and the negative electrode active material-containing paste to the current collector is, for example, an extrusion coater, reverse roller, doctor blade, A coating method can be adopted.
[0034]
As the electrolyte used in the present invention, a liquid electrolyte (hereinafter referred to as “electrolytic solution”) is usually used. As the electrolytic solution, an organic solvent-based nonaqueous electrolytic solution in which a solute is dissolved in an organic solvent is used. The solvent of the organic solvent-based electrolytic solution is not particularly limited, but it is particularly preferable to use a chain ester as the main solvent. Examples of such chain esters include chain COO-bonds such as diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethyl acetate (EA), and methyl propionate (MP). An organic solvent having The fact that this chain ester is the main solvent of the electrolytic solution means that these chain esters occupy a volume larger than 50% by volume in the total electrolytic solution solvent, and in particular, the chain ester is the total electrolytic solution. It is preferable that 65% by volume or more in the liquid solvent, in particular, the chain ester accounts for 70% by volume or more in the total electrolyte solution solvent, and most preferably, the chain ester accounts for 75% by volume or more in the total electrolyte solution solvent. preferable.
[0035]
However, as a solvent for the electrolytic solution, an ester having a high dielectric constant (an ester having a dielectric constant of 30 or more) is mixed with the chain ester in order to improve battery capacity, rather than using only the chain ester. Are preferably used. The amount of such an ester having a high dielectric constant in the total electrolyte solvent is preferably 10% by volume or more, particularly preferably 20% by volume or more.
[0036]
Examples of the high dielectric constant ester include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (γ-BL), ethylene glycol sulfite (EGS), and the like. In particular, cyclic structures such as ethylene carbonate and propylene carbonate are preferred, cyclic carbonates are particularly preferred, and ethylene carbonate (EC) is most preferred.
[0037]
Examples of the solvent that can be used together with the ester having a high dielectric constant include 1,2-dimethoxyethane (1,2-DME), 1,3-dioxolane (1,3-DO), and tetrahydrofuran (THF). , 2-methyl-tetrahydrofuran (2-Me-THF), diethyl ether (DEE) and the like. In addition, amine-based or imide-based organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can also be used.
[0038]
As the solute of the electrolytic solution, for example, LiClO Four , LiPF 6 , LiBF Four , LiAsF 6 , LiSbF 6 , LiCF Three SO Three , LiC Four F 9 SO Three , LiCF Three CO 2 , Li 2 C 2 F Four (SO Three ) 2 , LiN (CF Three SO 2 ) 2 , LiC (CF Three SO 2 ) Three , LiC n F 2n + 1 SO Three (N ≧ 2) etc. are used alone or in combination of two or more. In particular, LiPF 6 And LiC Four F 9 SO Three Etc. are preferable because of good charge / discharge characteristics. The concentration of the solute in the electrolytic solution is not particularly limited, but is 0.3 to 1.7 mol / dm. Three In particular, 0.4 to 1.5 mol / dm Three The degree is preferred.
[0039]
In the present invention, a solid or gel electrolyte can be used as the electrolyte in addition to the electrolytic solution. Examples of such an electrolyte include inorganic solid electrolytes and organic solid electrolytes mainly composed of polyethylene oxide, polypropylene oxide, or derivatives thereof.
[0040]
As a separator used for this invention, a nonwoven fabric and a microporous film are used, for example. Examples of the material for the nonwoven fabric include polypropylene, polyethylene, polyethylene terephthalate, and polybutylene terephthalate. Examples of the material for the microporous film include polypropylene, polyethylene, and a polyethylene-propylene copolymer.
[0041]
The separator preferably has sufficient strength and can hold a large amount of electrolyte. From such a viewpoint, the separator is made of polypropylene, polyethylene or ethylene having a thickness of 10 to 50 μm and a porosity of 30 to 70%. A microporous film or a nonwoven fabric made of a propylene copolymer is preferable.
[0042]
In the present invention, the negative electrode lead body is welded to the exposed negative electrode current collector by resistance welding, ultrasonic welding or the like to the negative electrode produced as described above. In order to reduce the heat generation by reducing the resistance when a large current flows, 2 1.0mm above 2 The following is preferable, 0.3 mm 2 0.7mm above 2 The following is more preferable. As a material for the negative electrode lead body, nickel is generally used, but copper, titanium, stainless steel and the like can also be used.
[0043]
The non-aqueous secondary battery of the present invention is stacked, for example, by interposing a separator between the sheet-like positive electrode and the sheet-like negative electrode produced as described above, and spirally, elliptically, or long. An electrode body with a wound structure produced by winding it in a circular shape or the like, or an electrode body obtained by laminating them is placed in a nickel-plated iron or stainless steel, aluminum or aluminum alloy battery can, or a metal laminate film. It is manufactured through a process of inserting and sealing after injecting an electrolytic solution. Further, the battery is usually provided with an explosion-proof mechanism for discharging gas generated inside the battery to the outside of the battery at a stage where the pressure is increased to a certain pressure and preventing explosion due to an increase in the internal pressure of the battery.
[0044]
【Example】
Next, based on an Example, this invention is demonstrated more concretely. However, the present invention is not limited to only these examples.
[0045]
Example 1
First, a positive electrode was produced as follows. LiCoO as positive electrode active material 2 190 parts by mass, 4 parts by mass of acetylene black as a conductive additive, 6 parts by mass of polyvinylidene fluoride as a binder, and phenylphosphonic acid as a phosphoric acid compound having an aromatic substituent with respect to the positive electrode active material Then, the mixture was uniformly mixed so as to be 0.2% by mass, and further 60 parts by mass of N-methylpyrrolidone was added and mixed to prepare a paste-like positive electrode paint. The paste-like positive electrode paint is passed through a 70-mesh net to remove a large one, and then uniformly applied to both surfaces of a positive electrode current collector made of a strip-like aluminum foil having a thickness of 15 μm, and dried to obtain a positive electrode active material A containing coating film was formed. The coating thickness after drying is 215 μm, and the electrode mass per unit area is 25.0 mg / cm. 2 Met. This strip-shaped electrode body was dried and then compression molded to a thickness of 170 μm. Then, it cut | disconnected to the predetermined magnitude | size and welded the lead body made from aluminum, and obtained the sheet-like positive electrode.
[0046]
Next, a negative electrode was produced as follows. As a negative electrode active material, a graphite-based carbon material [however, a distance (d002) between (002) planes of the crystal = 0.337 nm, a crystallite size in the c-axis direction (Lc) = 95 nm, an average particle size of 10 μm, Carbon material having a purity of 99.9% by mass or more] A paste-like negative electrode paint was prepared by mixing 180 parts by mass with a solution in which 14 parts by mass of polyvinylidene fluoride was dissolved in 190 parts by mass of N-methylpyrrolidone. . This paste-like negative electrode paint was uniformly applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 10 μm, and dried to form a negative electrode active material-containing coating film. The thickness of the coating after drying is 243 μm, and the electrode mass per unit area is 12.0 mg / cm 2 Met. This strip-shaped electrode body was dried and then compression molded to a thickness of 175 μm. Then, it cut | disconnected in the predetermined magnitude | size and welded the lead body made from nickel, and obtained the sheet-like negative electrode.
[0047]
Moreover, the electrolyte solution was prepared as follows. LiPF was mixed with a mixed solvent in which methyl ethyl carbonate (MEC) and ethylene carbonate (EC) were mixed at a volume ratio of 2: 1. 6 1.2 mol / dm Three It was dissolved to obtain a non-aqueous electrolyte.
[0048]
Subsequently, a non-aqueous secondary battery was produced as follows. After drying the positive electrode and the negative electrode, the positive electrode was stacked on the negative electrode via a separator made of a microporous polyethylene film having a thickness of 25 μm, and wound in a spiral shape to form an electrode body having a spiral winding structure. . This was inserted into a bag-like aluminum laminated film. Next, after injecting the electrolytic solution, vacuum sealing is performed, and the state is left for 3 hours at room temperature, and the positive electrode, the negative electrode, and the separator are sufficiently impregnated with the electrolytic solution to obtain the nonaqueous secondary battery of the present invention. It was.
[0049]
(Example 2)
The addition of 0.2% by mass of phenylphosphonic acid in the positive electrode production process of Example 1 to the positive electrode active material was changed to the addition of 0.2% by mass of p-toluenesulfonic acid to the positive electrode active material. A nonaqueous secondary battery of the present invention was produced in the same manner as in Example 1 except for the above.
[0050]
Example 3
Except for changing the addition of 0.2% by mass of phenylphosphonic acid to the positive electrode active material in the positive electrode production process of Example 1 to adding 0.005% by mass of phenylphosphonic acid to the positive electrode active material. The nonaqueous secondary battery of the present invention was produced in the same manner as in Example 1.
[0051]
Example 4
Except for changing the addition of 0.2% by mass of phenylphosphonic acid to the positive electrode active material in the production process of the positive electrode of Example 1 except that 5% by mass of phenylphosphonic acid was added to the positive electrode active material. A non-aqueous secondary battery of the present invention was produced in the same manner as in Example 1.
[0052]
(Comparative Example 1)
A nonaqueous secondary battery of a comparative example was produced in the same manner as in Example 1 except that phenylphosphonic acid was not added in the positive electrode production process of Example 1.
[0053]
(Comparative Example 2)
Do not add phenylphosphonic acid in the production process of the positive electrode of Example 1, and add LiPF to tetrahydropyran as the electrolyte. 6 1.2 mol / dm Three A non-aqueous secondary battery of a comparative example was produced in the same manner as in Example 1 except that the dissolved non-aqueous electrolyte was used.
[0054]
(Comparative Example 3)
The addition of 0.2% by mass of phenylphosphonic acid in the positive electrode production process of Example 1 to the positive electrode active material was changed to the addition of 0.2% by mass of trifluoromethanephosphonic acid to the positive electrode active material. A nonaqueous secondary battery of the present invention was produced in the same manner as in Example 1 except for the above.
[0055]
For each of the nonaqueous secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3, changes in discharge capacity and internal impedance when charging and discharging were repeated were measured. In addition, changes in discharge capacity and internal impedance after high-temperature storage were also measured. The results are shown in Table 1.
[0056]
[Table 1]
[0057]
The discharge capacity was measured by charging at a constant voltage of 4.2 V with a 1 C current limiting circuit and discharging until the voltage between the electrodes of the battery was reduced to 3 V with a current of 1 C. Then, the discharge capacity at the first cycle of the battery of Comparative Example 1 was set to 100%, and the discharge capacity (%) of the other battery was obtained as a relative value with respect to the discharge capacity. The storage characteristics were evaluated by measuring the discharge capacity after storage at 60 ° C. for 1 week. Furthermore, the internal impedance is the same as the measurement condition of the discharge capacity, the internal impedance at 1 kHz is measured with an LCR meter, the internal impedance at the first cycle of the battery of Comparative Example 1 is set to 100%, and the relative impedance to the internal impedance is measured. The internal impedance (%) of other batteries was obtained from the value.
[0058]
As is clear from Table 1, Examples 1-4 using the positive electrode to which the phosphoric acid compound or sulfonic acid compound having an aromatic substituent was added had a discharge capacity at the first cycle as compared with Comparative Example 1. Even after the charge / discharge cycle was repeated 300 times and stored at a high temperature, the discharge capacity decreased little. Further, in Examples 1 to 4, the internal impedance at the first cycle is lower than that of Comparative Example 1, and it is understood that the increase in internal impedance after 300 cycles and after high temperature storage is also suppressed.
[0059]
Moreover, compared with the comparative example 2 and the comparative example 3, in Examples 1-4, it turns out that the discharge capacity after 300 cycles and after high temperature storage is high, and the raise of internal impedance is also suppressed.
[0060]
【Effect of the invention】
As described above, according to the present invention, the internal impedance after the charge / discharge cycle and after the high-temperature storage is obtained by including the phosphoric acid compound or the sulfonic acid compound having an aromatic substituent in the positive electrode of the nonaqueous secondary battery. Thus, it is possible to provide a non-aqueous secondary battery that suppresses a decrease in discharge capacity due to an increase in the battery capacity.
Claims (5)
前記正極に、前記正極活物質とともに、芳香族性の置換基を有し、下記一般式(1)で表されるリン酸化合物又は下記一般式(2)で表されるスルホン酸化合物を含有させたことを特徴とする非水二次電池。
Wherein the positive electrode, the with positive electrode active material, possess an aromatic substituent, is contained phosphoric acid compound represented by the following general formula (1) or sulfonic acid compound represented by the following general formula (2) A non-aqueous secondary battery characterized by that.
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