JP2011124118A - Nonaqueous electrolyte secondary battery - Google Patents
Nonaqueous electrolyte secondary battery Download PDFInfo
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- JP2011124118A JP2011124118A JP2009281324A JP2009281324A JP2011124118A JP 2011124118 A JP2011124118 A JP 2011124118A JP 2009281324 A JP2009281324 A JP 2009281324A JP 2009281324 A JP2009281324 A JP 2009281324A JP 2011124118 A JP2011124118 A JP 2011124118A
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- secondary battery
- electrolyte secondary
- negative electrode
- tungsten
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- 239000011255 nonaqueous electrolyte Substances 0.000 title claims abstract description 74
- DZKDPOPGYFUOGI-UHFFFAOYSA-N tungsten(iv) oxide Chemical compound O=[W]=O DZKDPOPGYFUOGI-UHFFFAOYSA-N 0.000 claims abstract description 123
- 229910052751 metal Inorganic materials 0.000 claims abstract description 43
- 239000002184 metal Substances 0.000 claims abstract description 43
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 claims abstract description 42
- 229910052721 tungsten Inorganic materials 0.000 claims abstract description 39
- 239000010937 tungsten Substances 0.000 claims abstract description 39
- 239000011149 active material Substances 0.000 claims abstract description 31
- 239000011164 primary particle Substances 0.000 claims abstract description 14
- 239000000203 mixture Substances 0.000 claims description 20
- 239000011230 binding agent Substances 0.000 claims description 6
- 239000007774 positive electrode material Substances 0.000 claims description 5
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 4
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical group O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 claims description 4
- 229910001930 tungsten oxide Inorganic materials 0.000 claims description 4
- 239000003792 electrolyte Substances 0.000 claims 1
- 150000003839 salts Chemical class 0.000 claims 1
- CMPGARWFYBADJI-UHFFFAOYSA-L tungstic acid Chemical compound O[W](O)(=O)=O CMPGARWFYBADJI-UHFFFAOYSA-L 0.000 claims 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims 1
- 230000006866 deterioration Effects 0.000 abstract description 3
- 239000007773 negative electrode material Substances 0.000 description 28
- 239000002245 particle Substances 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 16
- 239000006258 conductive agent Substances 0.000 description 14
- 239000003575 carbonaceous material Substances 0.000 description 9
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 8
- 229910021383 artificial graphite Inorganic materials 0.000 description 8
- 239000002904 solvent Substances 0.000 description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 6
- 229910001416 lithium ion Inorganic materials 0.000 description 6
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten trioxide Chemical compound O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 description 6
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 5
- 239000002033 PVDF binder Substances 0.000 description 5
- 229910052744 lithium Inorganic materials 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- 239000000843 powder Substances 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- -1 LiCF 3 SO 3 Inorganic materials 0.000 description 3
- 239000003125 aqueous solvent Substances 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 238000000465 moulding Methods 0.000 description 3
- 239000010450 olivine Substances 0.000 description 3
- 229910052609 olivine Inorganic materials 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- PBYZMCDFOULPGH-UHFFFAOYSA-N tungstate Chemical class [O-][W]([O-])(=O)=O PBYZMCDFOULPGH-UHFFFAOYSA-N 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- SBZXBUIDTXKZTM-UHFFFAOYSA-N diglyme Chemical compound COCCOCCOC SBZXBUIDTXKZTM-UHFFFAOYSA-N 0.000 description 2
- 239000000835 fiber Substances 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 238000012423 maintenance Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000012856 packing Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 150000003657 tungsten Chemical class 0.000 description 2
- ZZXUZKXVROWEIF-UHFFFAOYSA-N 1,2-butylene carbonate Chemical compound CCC1COC(=O)O1 ZZXUZKXVROWEIF-UHFFFAOYSA-N 0.000 description 1
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 description 1
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 229910015015 LiAsF 6 Inorganic materials 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- 229910013684 LiClO 4 Inorganic materials 0.000 description 1
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 239000004734 Polyphenylene sulfide Substances 0.000 description 1
- 239000004743 Polypropylene Substances 0.000 description 1
- KFDQGLPGKXUTMZ-UHFFFAOYSA-N [Mn].[Co].[Ni] Chemical compound [Mn].[Co].[Ni] KFDQGLPGKXUTMZ-UHFFFAOYSA-N 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000006183 anode active material Substances 0.000 description 1
- 150000005678 chain carbonates Chemical class 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 150000005676 cyclic carbonates Chemical class 0.000 description 1
- XAYGUHUYDMLJJV-UHFFFAOYSA-Z decaazanium;dioxido(dioxo)tungsten;hydron;trioxotungsten Chemical compound [H+].[H+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].[NH4+].O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.O=[W](=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O.[O-][W]([O-])(=O)=O XAYGUHUYDMLJJV-UHFFFAOYSA-Z 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 239000004210 ether based solvent Substances 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- ACFSQHQYDZIPRL-UHFFFAOYSA-N lithium;bis(1,1,2,2,2-pentafluoroethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)C(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)C(F)(F)F ACFSQHQYDZIPRL-UHFFFAOYSA-N 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical group [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- 239000002905 metal composite material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 229920001690 polydopamine Polymers 0.000 description 1
- 229920000069 polyphenylene sulfide Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 229910052723 transition metal Inorganic materials 0.000 description 1
- 150000003624 transition metals Chemical class 0.000 description 1
Classifications
-
- 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
Abstract
Description
本発明は、正極と負極と非水電解質とを備え、負極又は正極の活物質に二酸化タングステンを用いた非水電解質二次電池に関するものである。特に、負極の活物質に二酸化タングステンを用いた非水電解質二次電池において、充放電によって二酸化タングステンを用いた負極における導電性等が低下するのを防止し、優れた充放電サイクル特性が得られるようにした点に特徴を有するものである。 The present invention relates to a nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, and using tungsten dioxide as an active material of the negative electrode or the positive electrode. In particular, in a non-aqueous electrolyte secondary battery using tungsten dioxide as the active material for the negative electrode, it is possible to prevent deterioration in conductivity and the like in the negative electrode using tungsten dioxide due to charge / discharge, and to obtain excellent charge / discharge cycle characteristics. It has the feature in the point made like this.
近年、携帯電話、ノートパソコン、ＰＤＡなどの移動情報端末の小型・軽量化が急速に進展しており、その電源として用いる電池の高容量化が要求されている。 In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and there is a demand for higher capacity batteries used as power sources.
そして、このような要求に対応するため、近年においては、高出力，高エネルギー密度の新型二次電池として、非水電解液を用い、リチウムイオンを正極と負極との間で移動させて充放電を行うようにした非水電解質二次電池が広く利用されるようになった。 In order to meet such demands, in recent years, as a new secondary battery with high output and high energy density, a non-aqueous electrolyte is used, and lithium ions are moved between the positive electrode and the negative electrode to charge and discharge. Non-aqueous electrolyte secondary batteries designed to perform the above have come to be widely used.
ここで、上記のような非水電解質二次電池においては、その正極や負極における活物質に様々なものが用いられている。そして、例えば、高容量で、半導体の駆動電圧と同程度の適当な作動電圧を示すメモリーバックアップ用電源として用いる非水電解質二次電池として、その負極における活物質に二酸化タングステンを用いたものが知られている。 Here, in the nonaqueous electrolyte secondary battery as described above, various materials are used as active materials in the positive electrode and the negative electrode. For example, as a non-aqueous electrolyte secondary battery that is used as a memory backup power source that has a high capacity and an appropriate operating voltage comparable to that of a semiconductor, a non-aqueous electrolyte secondary battery using tungsten dioxide as an active material in its negative electrode is known. It has been.
しかし、負極における活物質に二酸化タングステンを用いた場合、特許文献１に指摘されているように、二酸化タングステンにインターカレーションされるリチウムイオンの量が多くなると構造変化が生じ、有効充放電容量が大きく低下するという問題があった。 However, when tungsten dioxide is used as the active material in the negative electrode, as pointed out in Patent Document 1, when the amount of lithium ions intercalated in tungsten dioxide increases, the structural change occurs, and the effective charge / discharge capacity increases. There was a problem of a significant drop.
そして、この特許文献１においては、負極活物質として、二酸化タングステンを非酸化雰囲気中で熱処理させた生成物を用い、非水電解質二次電池における有効充放電容量が大きく低下するのを抑制するようにしたものが提案されている。 And in this patent document 1, as a negative electrode active material, the product which heat-processed tungsten dioxide in the non-oxidizing atmosphere is used, and it suppresses that the effective charging / discharging capacity | capacitance in a nonaqueous electrolyte secondary battery falls significantly. What has been proposed is proposed.
しかし、上記のように負極活物質に二酸化タングステンを用いた非水電解質二次電池の場合、二酸化タングステンだけでは負極における導電性が悪く、適切な充放電が行えないという問題があった。 However, in the case of a non-aqueous electrolyte secondary battery using tungsten dioxide as the negative electrode active material as described above, there is a problem that tungsten dioxide alone has poor conductivity in the negative electrode and cannot be appropriately charged and discharged.
このため、二酸化タングステンを用いた負極に、人造黒鉛等の炭素材料や、銅，ニッケル等の金属粉末や金属繊維からなる導電剤を加えて、負極における導電性を高めることが行われている。 For this reason, a conductive material made of a carbon material such as artificial graphite, a metal powder such as copper or nickel, or a metal fiber is added to the negative electrode using tungsten dioxide to increase the conductivity of the negative electrode.
しかし、二酸化タングステンを用いた負極に人造黒鉛等の炭素材料からなる導電剤を加えた非水電解質二次電池の場合、二酸化タングステンにおいてリチウムイオンを吸蔵・放出させる作動電位が約１.０〜０．５Ｖ（ｖｓ.Ｌｉ／Ｌｉ+）と低いため、二酸化タングステンにリチウムイオンを吸蔵させる際に、上記の炭素材料の表面で非水電解液が反応して分解したり、また上記の炭素材料にリチウムイオンが吸蔵されて、負極における導電性が低下し、適切な充放電が行えなくなるという問題があった。 However, in the case of a nonaqueous electrolyte secondary battery in which a conductive agent made of a carbon material such as artificial graphite is added to a negative electrode using tungsten dioxide, the operating potential for inserting and extracting lithium ions in tungsten dioxide is about 1.0 to 0. .5V (vs. Li / Li + ) is low, so when lithium ions are occluded in tungsten dioxide, the non-aqueous electrolyte reacts and decomposes on the surface of the carbon material, or the carbon material There is a problem that lithium ions are occluded, the conductivity of the negative electrode is lowered, and appropriate charge / discharge cannot be performed.
また、銅，ニッケル等の金属粉末や金属繊維からなる導電剤を加えた非水電解質二次電池の場合、充放電による二酸化タングステンの体積変化により上記の導電剤と適切に接触されなくなり、負極における導電性が低下して、適切な充放電が行えなくなるという問題があった。 In addition, in the case of a nonaqueous electrolyte secondary battery to which a conductive agent made of metal powder such as copper or nickel or a metal fiber is added, it is not properly contacted with the above conductive agent due to the volume change of tungsten dioxide due to charge and discharge, and in the negative electrode There was a problem that the electrical conductivity was lowered and proper charge / discharge could not be performed.
本発明は、正極と負極と非水電解質とを備えた非水電解質二次電池における上記のような問題を解決することを課題とするものであり、特に、負極の活物質に二酸化タングステンを用いた非水電解質二次電池において、充放電によって二酸化タングステンを用いた負極における導電性等が低下するのを防止し、優れた充放電サイクル特性が得られるようにすることを課題とするものである。 An object of the present invention is to solve the above-described problems in a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. In particular, tungsten dioxide is used as the active material of the negative electrode. It is an object of the present invention to prevent deterioration in conductivity and the like in a negative electrode using tungsten dioxide due to charge / discharge and to obtain excellent charge / discharge cycle characteristics in a non-aqueous electrolyte secondary battery. .
本発明においては、上記のような課題を解決するため、正極と負極と非水電解質とを備えた非水電解質二次電池において、上記の負極又は正極に、二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を用いるようにした。 In the present invention, in order to solve the above-described problems, in a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, tungsten is formed on the surface of primary particles of tungsten dioxide on the negative electrode or the positive electrode. An active material formed with a metal was used.
ここで、二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を負極に用いる場合、正極の活物質としては、非水電解質二次電池の正極に一般に使用されているコバルト酸リチウム、ニッケル酸リチウム、スピネル型マンガン酸リチウム、リチウム含有コバルト・ニッケル・マンガン複合酸化物、オリビン構造を有するリン酸鉄リチウムなどのリチウム含有遷移金属複合酸化物を用いることができる。特に、正極の活物質にオリビン構造を有するリン酸鉄リチウムを用いた場合、約３．０〜２．０Ｖの作動電圧を有し、電位平坦性にも優れた非水電解質二次電池が得られ、約３．０〜２．０Ｖの電圧範囲で動作する多くの半導体部品のバックアップ用電池等として好適に利用できるようになる。 Here, when an active material in which tungsten metal is formed on the surface of primary particles of tungsten dioxide is used for the negative electrode, the active material for the positive electrode is lithium cobalt oxide generally used for the positive electrode of the nonaqueous electrolyte secondary battery. Lithium-containing transition metal composite oxides such as lithium nickelate, spinel-type lithium manganate, lithium-containing cobalt-nickel-manganese composite oxide, and lithium iron phosphate having an olivine structure can be used. In particular, when lithium iron phosphate having an olivine structure is used as the positive electrode active material, a non-aqueous electrolyte secondary battery having an operating voltage of about 3.0 to 2.0 V and excellent potential flatness is obtained. Therefore, it can be suitably used as a backup battery for many semiconductor components operating in a voltage range of about 3.0 to 2.0V.
一方、二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を正極に用いる場合、負極の活物質としては、例えば、黒鉛等の炭素材料、アルミニウム，シリコン等のリチウムと合金化する金属などを用いることができ、これらの負極の活物質を用いた場合には、１．０〜０．５Ｖ程度の作動電圧を有する非水電解質二次電池が得られるようになる。 On the other hand, when an active material in which tungsten metal is formed on the surface of primary particles of tungsten dioxide is used for the positive electrode, examples of the negative electrode active material include alloying with carbon materials such as graphite and lithium such as aluminum and silicon. A metal etc. can be used, and when these negative electrode active materials are used, a non-aqueous electrolyte secondary battery having an operating voltage of about 1.0 to 0.5 V can be obtained.
ここで、上記のように二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を負極や正極に用いた場合、この非水電解質二次電池を充放電させても、二酸化タングステンの一次粒子の表面に形成されたタングステン金属によって十分な導電性が確保されるようになり、負極や正極における導電性が低下するのが防止されるようになる。特に、二酸化タングステンの一次粒子相互がその表面に形成されたタングステン金属によって結合されていると、このタングステン金属によって二酸化タングステンの粒子間における導電性がさらに高まり、負極や正極における導電性が低下するのが一層防止されるようになる。 Here, when an active material in which tungsten metal is formed on the surface of primary particles of tungsten dioxide as described above is used for a negative electrode or a positive electrode, even if this nonaqueous electrolyte secondary battery is charged and discharged, Sufficient conductivity is secured by the tungsten metal formed on the surface of the primary particles, and a decrease in conductivity in the negative electrode and the positive electrode is prevented. In particular, when the primary particles of tungsten dioxide are bonded to each other by tungsten metal formed on the surface, the conductivity between the tungsten dioxide particles is further increased by this tungsten metal, and the conductivity at the negative electrode and the positive electrode is decreased. Is further prevented.
また、上記の活物質において、二酸化タングステンに対するタングステン金属の割合が少なくなりすぎると、十分な導電性を確保することが困難になる一方、タングステン金属の割合が多くなりすぎると、充放電に関与する二酸化タングステンの割合が低下し、十分な充放電容量を得ることができなくなる。このため、上記の活物質中における二酸化タングステンとタングステン金属とのモル比が８０：２０〜２５：７５の範囲であることが好ましい。なお、二酸化タングステンとタングステン金属とのモル比が８０：２０の場合には、活物質中にタングステン金属が１５体積％程度存在することになり、十分な導電性を確保することが可能になる。また、上記のタングステン金属は二酸化タングステンに比べて密度が非常に高いため、二酸化タングステンとタングステン金属とのモル比を２５：７５にしても、活物質中に十分な量の二酸化タングステンが存在し、十分な充放電容量を得ることができるようになる。 In the above active material, if the ratio of tungsten metal to tungsten dioxide is too small, it becomes difficult to ensure sufficient conductivity, while if the ratio of tungsten metal is too large, it is involved in charge / discharge. The proportion of tungsten dioxide decreases, and sufficient charge / discharge capacity cannot be obtained. For this reason, it is preferable that the molar ratio of tungsten dioxide and tungsten metal in the active material is in the range of 80:20 to 25:75. When the molar ratio of tungsten dioxide to tungsten metal is 80:20, about 15 volume% of tungsten metal is present in the active material, and sufficient conductivity can be ensured. Moreover, since the above tungsten metal has a very high density compared to tungsten dioxide, even if the molar ratio of tungsten dioxide to tungsten metal is 25:75, there is a sufficient amount of tungsten dioxide in the active material, Sufficient charge / discharge capacity can be obtained.
また、上記のような活物質を得るにあたっては、三酸化タングステン等のタングステン酸化物やパラタングステン酸アンモニウム等のタングステン酸塩を還元雰囲気中において焼成する方法や、タングステン金属を酸化させる方法がある。 In order to obtain the active material as described above, there are a method of baking tungsten oxide such as tungsten trioxide and a tungstate salt such as ammonium paratungstate in a reducing atmosphere, and a method of oxidizing tungsten metal.
ここで、タングステン金属を酸化させる方法の場合、タングステン金属が粒子の中心部に存在し、粒子の外部に二酸化タングステンが存在する粒子構造となり、タングステン金属によって導電性を十分に確保することが困難になるおそれがある。一方、タングステン酸化物やタングステン酸塩を還元雰囲気中において焼成する方法の場合、タングステン酸化物やタングステン酸塩が還元された二酸化タングステン粒子の表面にタングステン金属が存在する構造となり、タングステン金属によって導電性を十分に確保することができるようになるため好ましい。なお、上記のようにして二酸化タングステン粒子の表面にタングステン金属を存在させるにあたり、二酸化タングステン粒子の表面を被覆するタングステン金属が多くなりすぎると、十分な充放電ができなくなるため、タングステン金属の割合を少なくし、二酸化タングステンとタングステン金属とのモル比を８０：２０〜３５：６５の範囲にすることがより好ましい。 Here, in the case of the method of oxidizing tungsten metal, the tungsten metal is present in the center of the particle, and the particle structure is such that tungsten dioxide exists outside the particle, making it difficult to sufficiently secure the conductivity by the tungsten metal. There is a risk. On the other hand, in the method of firing tungsten oxide or tungstate in a reducing atmosphere, tungsten metal is present on the surface of the tungsten dioxide particles from which tungsten oxide or tungstate has been reduced. Is preferable because it can be sufficiently secured. When tungsten metal is present on the surface of the tungsten dioxide particles as described above, if too much tungsten metal covers the surface of the tungsten dioxide particles, sufficient charge / discharge cannot be performed. More preferably, the molar ratio of tungsten dioxide to tungsten metal is in the range of 80:20 to 35:65.
また、上記のように二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を用いて負極や正極を作製する場合、炭素材料等の導電剤を別個に加えなくても、この活物質の表面におけるタングステン金属によって導電性が確保されるため、炭素材料等の導電剤を加える量を少なくし、また全く加えないようにすることができ、上記の活物質と結着剤とで構成された合剤を負極や正極の集電体に付与させて負極や正極を作製することができる。そして、このように炭素材料等の導電剤を加えないようにすると、炭素材料等の導電剤を加えた場合における前記のような問題の発生も防止される。 In addition, when a negative electrode or a positive electrode is manufactured using an active material in which tungsten metal is formed on the surface of primary particles of tungsten dioxide as described above, the active material can be obtained without adding a conductive agent such as a carbon material separately. Conductivity is ensured by the tungsten metal on the surface of the material, so the amount of conductive material such as carbon material added can be reduced and not added at all, and it consists of the above active material and binder The negative electrode or the positive electrode can be produced by applying the prepared mixture to the current collector of the negative electrode or the positive electrode. If the conductive agent such as the carbon material is not added as described above, the occurrence of the above problems when the conductive agent such as the carbon material is added can be prevented.
また、本発明の非水電解質二次電池における上記の非水電解質としては、非水系溶媒に溶質を溶解させた公知の非水電解液を用いることができる。 Moreover, as said nonaqueous electrolyte in the nonaqueous electrolyte secondary battery of this invention, the well-known nonaqueous electrolyte solution which melt | dissolved the solute in the nonaqueous solvent can be used.
そして、この非水電解液における非水系溶媒としては、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、ビニレンカーボネートなどの環状カーボネート系溶媒や、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネートなどの鎖状カーボネート系溶媒や、１，２−ジメトキシエタン、ジエチレングリコールジメチルエーテルなど鎖状エーテル系溶媒などを用いることができる。 Examples of the non-aqueous solvent in the non-aqueous electrolyte include cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, and chain carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Solvents and chain ether solvents such as 1,2-dimethoxyethane and diethylene glycol dimethyl ether can be used.
また、この非水系溶媒に溶解させる溶質としても、非水電解質二次電池において一般に使用されているリチウム塩を用いることができ、例えば、ＬｉＰＦ6，ＬｉＢＦ4，ＬｉＣＦ3ＳＯ3，ＬｉＮ（ＣＦ3ＳＯ2）2，ＬｉＮ（Ｃ2Ｆ5ＳＯ2）2，ＬｉＮ（ＣＦ3ＳＯ2）（Ｃ4Ｆ9ＳＯ2），ＬｉＣ（ＣＦ3ＳＯ2）3，ＬｉＣ（Ｃ2Ｆ5ＳＯ2）3，ＬｉＡｓＦ6，ＬｉＣｌＯ4，Ｌｉ2Ｂ10Ｃｌ10，Ｌｉ2Ｂ12Ｃｌ12や、これらの混合物等を用いることができる。 Further, as a solute dissolved in the non-aqueous solvent, a lithium salt generally used in a non-aqueous electrolyte secondary battery can be used. For example, LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN (CF 3 SO 2) 2, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) (C 4 F 9 SO 2), LiC (CF 3 SO 2) 3, LiC (C 2 F 5 SO 2) 3 , LiAsF 6 , LiClO 4 , Li 2 B 10 Cl 10 , Li 2 B 12 Cl 12 , a mixture thereof, or the like can be used.
本発明の非水電解質二次電池においては、二酸化タングステンの一次粒子の表面にタングステン金属が形成されてなる活物質を負極や正極に用いるようにしたため、この非水電解質二次電池を充放電させても、二酸化タングステンの一次粒子の表面に形成されたタングステン金属によって十分な導電性が確保されるようになり、負極や正極における導電性が低下するのが防止されるようになる。 In the nonaqueous electrolyte secondary battery of the present invention, an active material in which tungsten metal is formed on the surface of the primary particles of tungsten dioxide is used for the negative electrode and the positive electrode. Therefore, the nonaqueous electrolyte secondary battery is charged and discharged. However, sufficient conductivity is ensured by the tungsten metal formed on the surface of the primary particles of tungsten dioxide, so that the conductivity of the negative electrode and the positive electrode is prevented from being lowered.
この結果、本発明の非水電解質二次電池においては、充放電によって二酸化タングステンを用いた負極や正極における導電性等が低下して充放電特性が低下するのが防止され、優れた充放電サイクル特性が得られるようになる。特に、上記の活物質を負極に用いると、適当な正極の活物質と組み合わせて使用することにより、高容量で適切な作動電圧を示す非水電解質二次電池が得られるようになる。 As a result, in the nonaqueous electrolyte secondary battery of the present invention, it is possible to prevent the charge and discharge characteristics from being deteriorated due to the decrease in conductivity and the like in the negative electrode and the positive electrode using tungsten dioxide due to charge and discharge, and an excellent charge and discharge cycle. Characteristics can be obtained. In particular, when the above active material is used for a negative electrode, a non-aqueous electrolyte secondary battery having a high capacity and an appropriate operating voltage can be obtained by using it in combination with an appropriate positive electrode active material.
以下、この発明に係る非水電解質二次電池について、実施例を挙げて具体的に説明すると共に、この実施例に係る非水電解質二次電池においては、充放電サイクル特性が向上されることを、比較例を挙げて明らかにする。なお、本発明の非水電解質二次電池は下記の実施例に示したものに限定されるものではなく、その要旨を変更しない範囲において適宜変更して実施できるものである。 Hereinafter, the nonaqueous electrolyte secondary battery according to the present invention will be specifically described with reference to examples, and in the nonaqueous electrolyte secondary battery according to this example, the charge / discharge cycle characteristics are improved. It is clarified by giving a comparative example. The nonaqueous electrolyte secondary battery of the present invention is not limited to those shown in the following examples, and can be implemented with appropriate modifications within the scope not changing the gist thereof.
（実施例１）
実施例１においては、下記のようにして作製した負極と正極と非水電解液とを用い、図１に示すような扁平なコイン型の非水電解質二次電池を作製した。
Example 1
In Example 1, a flat coin-type non-aqueous electrolyte secondary battery as shown in FIG. 1 was manufactured using the negative electrode, the positive electrode, and the non-aqueous electrolyte prepared as described below.
［負極の作製］
負極活物質として、粒径が５０〜１００μｍ程度になった三酸化タングステンの粉末を７００℃の水素気流中で所要時間焼成し、負極活物質中における酸素量が７．５質量％になったものを用いた。
[Production of negative electrode]
As a negative electrode active material, a powder of tungsten trioxide having a particle size of about 50 to 100 μm is fired for a required time in a hydrogen stream at 700 ° C., and the amount of oxygen in the negative electrode active material becomes 7.5% by mass Was used.
ここで、このように作製した負極活物質をＳＥＭにより観察した結果を図２に示すと共に、図３に模式的にこの負極活物質の断面状態を示した。この結果、この負極活物質においては、図３に示すように、二酸化タングステン粒子１の表面にタングステン金属２が焼結により形成されると共に、このタングステン金属２によって二酸化タングステン粒子１相互が結合された状態になっていた。また、このようにして得た負極活物質をＸＲＤ（ＲＩＧＡＫＵ Ｃｏ． ＲＩＮＴ−ＴＴＲII）で調べたところ、二酸化タングステンとタングステン金属からなり、酸素分析装置（ＬＥＣＯ Ｃｏ． ＲＯ６００）で求めた酸素濃度から負極活物質の組成を算出した結果、二酸化タングステンとタングステン金属とのモル比が５０：５０になっていた。 Here, the result of observing the thus prepared negative electrode active material by SEM is shown in FIG. 2, and the cross-sectional state of this negative electrode active material is schematically shown in FIG. As a result, in this negative electrode active material, as shown in FIG. 3, tungsten metal 2 was formed on the surface of tungsten dioxide particles 1 by sintering, and tungsten dioxide particles 1 were bonded to each other by this tungsten metal 2. It was in a state. Further, when the negative electrode active material thus obtained was examined by XRD (RIGAKU Co. RINT-TTRII), it was composed of tungsten dioxide and tungsten metal, and the negative electrode was determined from the oxygen concentration determined by an oxygen analyzer (LECO Co. RO600). As a result of calculating the composition of the active material, the molar ratio of tungsten dioxide to tungsten metal was 50:50.
そして、上記のように作製した負極活物質と結着剤のポリフッ化ビニリデンとを９７．５：２．５の質量比になるようにして、Ｎ−メチル−２−ピロリドン溶剤中において混合し、これを乾燥させた後、粉砕させて負極合剤を得た。次いで、この負極合剤を直径４．１６ｍｍの成型冶具に入れて、８００ｋｇ・ｆの圧力で加圧成型し、円板状になった負極を作製した。 Then, the negative electrode active material produced as described above and the polyvinylidene fluoride binder were mixed in an N-methyl-2-pyrrolidone solvent so as to have a mass ratio of 97.5: 2.5, This was dried and then pulverized to obtain a negative electrode mixture. Next, this negative electrode mixture was put in a molding jig having a diameter of 4.16 mm, and pressure-molded with a pressure of 800 kg · f to produce a disc-shaped negative electrode.
［正極の作製］
正極活物質にオリビン構造を有するリン酸鉄リチウムＬｉＦｅＰＯ４を用い、この正極活物質と、結着剤のポリフッ化ビニリデンと、導電剤の人造黒鉛を９２．５：５：２．５の質量比になるようにして、Ｎ−メチル−２−ピロリドン溶剤中において混合し、これを乾燥させた後、粉砕させて正極合剤を得た。次いで、この正極合剤を直径４．１６ｍｍの成型冶具に入れて、８００ｋｇ・ｆの圧力で加圧成型し、円板状になった正極を作製した。
[Production of positive electrode]
Lithium iron phosphate LiFePO 4 having an olivine structure is used as the positive electrode active material, and the positive electrode active material, the polyvinylidene fluoride as the binder, and the artificial graphite as the conductive agent in a mass ratio of 92.5: 5: 2.5 The mixture was mixed in an N-methyl-2-pyrrolidone solvent, dried, and pulverized to obtain a positive electrode mixture. Next, this positive electrode mixture was put into a molding jig having a diameter of 4.16 mm and subjected to pressure molding at a pressure of 800 kg · f to produce a disc-shaped positive electrode.
［非水電解液の作製］
ジエチレングリコールジメチルエーテルからなる非水系溶媒に、溶質としてリチウムビストリフルオロメタンスルホニルイミドＬｉＮ（ＣＦ３ＳＯ２）２を１．０ｍｏｌ／ｌの濃度になるように溶解させて、非水電解液を作製した。
[Preparation of non-aqueous electrolyte]
Lithium bistrifluoromethanesulfonylimide LiN (CF 3 SO 2 ) 2 was dissolved as a solute in a non-aqueous solvent composed of diethylene glycol dimethyl ether to a concentration of 1.0 mol / l to prepare a non-aqueous electrolyte.
［電池の作製］
電池を作製するにあたっては、図１に示すように、上記のようにして作製した正極１１と負極１２との間に、ポリフェニレンサルファイドの不織布からなるセパレータ１３を介在させ、これらに上記の非水電解液を含浸させて、正極缶１４ａと負極缶１４ｂとで形成される電池ケース１４内に収容させるようにした。そして、上記の正極１１を炭素の導電性ペーストを用いた正極集電体１５を介して正極缶１４ａに接続させる一方、上記の負極１２を炭素の導電性ペーストを用いた負極集電体１６を介して負極缶１４ｂに接続させ、この正極缶１４ａと負極缶１４ｂとをポリプロピレン製の絶縁パッキン１７によって電気的に絶縁させて、直径が６ｍｍ、厚さが１．４ｍｍになった扁平なコイン型の非水電解質二次電池を作製した。
[Production of battery]
In producing the battery, as shown in FIG. 1, a separator 13 made of a polyphenylene sulfide non-woven fabric is interposed between the positive electrode 11 and the negative electrode 12 produced as described above, and the non-aqueous electrolysis described above is interposed therebetween. The liquid was impregnated and contained in the battery case 14 formed of the positive electrode can 14a and the negative electrode can 14b. The positive electrode 11 is connected to the positive electrode can 14a through the positive electrode current collector 15 using a carbon conductive paste, while the negative electrode 12 is connected to the negative electrode current collector 16 using a carbon conductive paste. A flat coin type having a diameter of 6 mm and a thickness of 1.4 mm, wherein the positive electrode can 14a and the negative electrode can 14b are electrically insulated by an insulating packing 17 made of polypropylene. A non-aqueous electrolyte secondary battery was prepared.
（比較例１）
比較例１においては、実施例１における負極の作製において、負極活物質を得るにあたり、上記の粒径が５０〜１５０μｍ程度になった三酸化タングステンの粉末を７００℃の水素気流中で焼成させる時間を短くし、負極活物質中における酸素量が１４．８質量％になったものを用いた。
(Comparative Example 1)
In Comparative Example 1, in preparing the negative electrode in Example 1, when obtaining the negative electrode active material, the time for firing the tungsten trioxide powder having a particle size of about 50 to 150 μm in a hydrogen stream at 700 ° C. The oxygen content in the negative electrode active material was 14.8% by mass.
ここで、このように作製した負極活物質をＳＥＭにより観察した結果を図４に示した。また、このようにして得た負極活物質の組成を前記実施例１と同様の方法で調べた結果、二酸化タングステン粒子だけで構成されていた。 Here, the result of observing the thus prepared negative electrode active material by SEM is shown in FIG. Moreover, as a result of examining the composition of the negative electrode active material thus obtained by the same method as in Example 1, it was composed only of tungsten dioxide particles.
そして、上記の二酸化タングステン粒子からなる負極活物質を用いる以外は、上記の実施例１と同様にして非水電解質二次電池を作製した。 And the nonaqueous electrolyte secondary battery was produced like said Example 1 except using the negative electrode active material which consists of said tungsten dioxide particle.
（比較例２）
比較例２においては、実施例１における負極の作製において、負極活物質として、上記の比較例１と同じ二酸化タングステン粒子からなる負極活物質を用いると共に導電剤として人造黒鉛を用い、この負極活物質と結着剤のポリフッ化ビニリデンと導電剤の人造黒鉛とを９２．５：２．５：５の質量比になるようにして、Ｎ−メチル−２−ピロリドン溶剤中において混合し、これを乾燥させた後、粉砕させて負極合剤を得た。
(Comparative Example 2)
In Comparative Example 2, in the production of the negative electrode in Example 1, the negative electrode active material composed of the same tungsten dioxide particles as in Comparative Example 1 was used as the negative electrode active material, and artificial graphite was used as the conductive agent. And polyvinylidene fluoride as a binder and artificial graphite as a conductive agent are mixed in an N-methyl-2-pyrrolidone solvent at a mass ratio of 92.5: 2.5: 5 and dried. Then, the mixture was pulverized to obtain a negative electrode mixture.
そして、このようにして得た負極合剤を用いる以外は、上記の実施例１と同様にして非水電解質二次電池を作製した。 And the nonaqueous electrolyte secondary battery was produced like the said Example 1 except using the negative mix obtained in this way.
（比較例３）
比較例３においては、実施例１における負極の作製において、負極活物質として、上記の比較例１と同じ二酸化タングステン粒子からなる負極活物質を用いると共に導電剤として粒径が６００ｎｍ程度になったタングステン粉末を用い、この負極活物質と結着剤のポリフッ化ビニリデンと導電剤のタングステン粉末とを９２．５：２．５：５の質量比になるようにして、Ｎ−メチル−２−ピロリドン溶剤中において混合し、これを乾燥させた後、粉砕させて負極合剤を得た。
(Comparative Example 3)
In Comparative Example 3, in the production of the negative electrode in Example 1, the negative electrode active material composed of the same tungsten dioxide particles as in Comparative Example 1 was used as the negative electrode active material, and tungsten having a particle size of about 600 nm as the conductive agent. N-methyl-2-pyrrolidone solvent using a powder so that the negative electrode active material, polyvinylidene fluoride as a binder, and tungsten powder as a conductive agent are in a mass ratio of 92.5: 2.5: 5 The mixture was mixed in, dried, and then pulverized to obtain a negative electrode mixture.
そして、このようにして得た負極合剤を用いる以外は、上記の実施例１と同様にして非水電解質二次電池を作製した。 And the nonaqueous electrolyte secondary battery was produced like the said Example 1 except using the negative mix obtained in this way.
次に、上記のようにして作製した実施例１及び比較例１〜３の各非水電解質二次電池を、それぞれ室温環境下において、１００μＡの定電流で電池電圧が３．２Ｖになるまで充電させて１０秒間休止させた後、１００μＡの定電流で電池電圧が０．０１Ｖになるまで放電させて１０秒間休止させ、これに１サイクルとして１０サイクルの充放電を繰り返した。 Next, the nonaqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 to 3 manufactured as described above were charged at a constant current of 100 μA and a battery voltage of 3.2 V under a room temperature environment. After 10 seconds of rest, the battery was discharged at a constant current of 100 μA until the battery voltage reached 0.01 V, rested for 10 seconds, and 10 cycles of charge / discharge were repeated as one cycle.
そして、上記の各非水電解質二次電池について、それぞれ１サイクル目の放電容量Ｑ１と１０サイクル目の放電容量Ｑ１０とを測定し、下記の式により、１０サイクル後の容量維持率を求め、その結果を下記の表１に示した。なお、表中の負極合剤の組成に関しては、結着剤のポリフッ化ビニリデンをＰＶｄＦとして示した。
１０サイクル後の容量維持率（％）＝（Ｑ１０／Ｑ１）×１００
And about each said nonaqueous electrolyte secondary battery, discharge capacity Q1 of the 1st cycle and discharge capacity Q10 of the 10th cycle are measured, respectively, and the capacity maintenance rate after 10 cycles is calculated by the following formula, The results are shown in Table 1 below. In addition, regarding the composition of the negative electrode mixture in the table, the binder polyvinylidene fluoride was shown as PVdF.
Capacity maintenance rate after 10 cycles (%) = (Q10 / Q1) × 100
この結果、二酸化タングステン粒子の表面にタングステン金属が形成された負極活物質を用いた実施例１の非水電解質二次電池は、上記の比較例１〜３の各非水電解質二次電池に比べて、１０サイクル後の容量維持率が大きく向上しており、充放電サイクル特性が大きく改善されることが分かった。 As a result, the nonaqueous electrolyte secondary battery of Example 1 using the negative electrode active material in which tungsten metal was formed on the surface of the tungsten dioxide particles was compared with the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 3 described above. Thus, it was found that the capacity retention rate after 10 cycles was greatly improved, and the charge / discharge cycle characteristics were greatly improved.
これは、上記のような負極活物質を用いた実施例１の非水電解質二次電池の場合、二酸化タングステン粒子からなる負極活物質を用いた比較例１の非水電解質二次電池に比べて、前記のように二酸化タングステンの一次粒子の表面に形成されたタングステン金属によって負極における導電性が大きく向上されたためであると考えられる。 This is because the non-aqueous electrolyte secondary battery of Example 1 using the negative electrode active material as described above is compared with the non-aqueous electrolyte secondary battery of Comparative Example 1 using the negative electrode active material made of tungsten dioxide particles. This is probably because the conductivity of the negative electrode was greatly improved by the tungsten metal formed on the surface of the primary particles of tungsten dioxide as described above.
また、比較例２の非水電解質二次電池のように、二酸化タングステン粒子からなる負極活物質の他に導電剤の人造黒鉛を添加させた負極合剤を用いた場合、前記のように導電剤として添加した人造黒鉛の表面で非水電解液が反応して分解したり、また人造黒鉛にリチウムイオンが吸蔵されて、負極における導電性が低下したため、実施例１の非水電解質二次電池に比べて、１０サイクル後の容量維持率が低下したものと考えられる。 Further, as in the case of the non-aqueous electrolyte secondary battery of Comparative Example 2, when a negative electrode mixture in which artificial graphite as a conductive agent is added in addition to the negative electrode active material composed of tungsten dioxide particles, the conductive agent is used as described above. As the non-aqueous electrolyte reacts and decomposes on the surface of the artificial graphite added as above, or the lithium ions are occluded in the artificial graphite and the conductivity in the negative electrode is lowered, the non-aqueous electrolyte secondary battery of Example 1 is obtained. In comparison, it is considered that the capacity retention rate after 10 cycles was lowered.
また、比較例３の非水電解質二次電池のように、二酸化タングステン粒子からなる負極活物質の他に導電剤のタングステン粉末を添加させた負極合剤を用いた場合、タングステン粉末の粒径が大きくて、二酸化タングステン粒子とタングステン粉末との密着性が悪くなり、また充放電による二酸化タングステン粒子の体積変化によって、二酸化タングステン粒子がタングステン粉末から離れて、負極における導電性が大きく低下したため、実施例１の非水電解質二次電池に比べて、１０サイクル後の容量維持率が大きく低下したものと考えられる。 Further, when a negative electrode mixture in which tungsten powder of a conductive agent is added in addition to a negative electrode active material composed of tungsten dioxide particles as in the non-aqueous electrolyte secondary battery of Comparative Example 3, the particle size of the tungsten powder is Since the adhesion between the tungsten dioxide particles and the tungsten powder is poor and the tungsten dioxide particles are separated from the tungsten powder due to the volume change of the tungsten dioxide particles due to charge and discharge, the conductivity in the negative electrode is greatly reduced. It is considered that the capacity retention rate after 10 cycles was greatly reduced as compared with the nonaqueous electrolyte secondary battery of No. 1.
１ 二酸化タングステン粒子
２ タングステン金属
１１ 正極
１２ 負極
１３ セパレータ
１４ 電池ケース
１４ａ 正極缶
１４ｂ 負極缶
１５ 正極集電体
１６ 負極集電体
１７ 絶縁パッキン
DESCRIPTION OF SYMBOLS 1 Tungsten dioxide particle 2 Tungsten metal 11 Positive electrode 12 Negative electrode 13 Separator 14 Battery case 14a Positive electrode can 14b Negative electrode can 15 Positive electrode collector 16 Negative electrode collector 17 Insulation packing
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