JP2008071746A - Nonaqueous electrolyte secondary battery - Google Patents
Nonaqueous electrolyte secondary battery Download PDFInfo
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- JP2008071746A JP2008071746A JP2007207801A JP2007207801A JP2008071746A JP 2008071746 A JP2008071746 A JP 2008071746A JP 2007207801 A JP2007207801 A JP 2007207801A JP 2007207801 A JP2007207801 A JP 2007207801A JP 2008071746 A JP2008071746 A JP 2008071746A
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- 239000011255 nonaqueous electrolyte Substances 0.000 title claims abstract description 204
- 239000007774 positive electrode material Substances 0.000 claims abstract description 77
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 57
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 52
- 239000011230 binding agent Substances 0.000 claims abstract description 27
- 229910013063 LiBF 4 Inorganic materials 0.000 claims description 66
- 239000006258 conductive agent Substances 0.000 claims description 45
- 229910013870 LiPF 6 Inorganic materials 0.000 claims description 15
- 239000003795 chemical substances by application Substances 0.000 claims description 11
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical group O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 claims description 9
- 229910052782 aluminium Inorganic materials 0.000 claims description 8
- 229910052749 magnesium Inorganic materials 0.000 claims description 5
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 4
- 238000007580 dry-mixing Methods 0.000 claims description 4
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 claims description 2
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 claims description 2
- 229910052726 zirconium Inorganic materials 0.000 claims description 2
- 239000011777 magnesium Substances 0.000 claims 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims 1
- 239000003792 electrolyte Substances 0.000 claims 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims 1
- 238000003860 storage Methods 0.000 abstract description 33
- 229910013075 LiBF Inorganic materials 0.000 abstract description 2
- 239000004020 conductor Substances 0.000 abstract 3
- 230000000052 comparative effect Effects 0.000 description 72
- 239000000203 mixture Substances 0.000 description 19
- 239000002245 particle Substances 0.000 description 18
- -1 lithium transition metal Chemical class 0.000 description 16
- 239000011148 porous material Substances 0.000 description 14
- 239000008151 electrolyte solution Substances 0.000 description 13
- 238000004519 manufacturing process Methods 0.000 description 10
- 239000002131 composite material Substances 0.000 description 9
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- 230000003247 decreasing effect Effects 0.000 description 5
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- 239000011247 coating layer Substances 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 239000002905 metal composite material Substances 0.000 description 4
- 239000007773 negative electrode material Substances 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- 229910052723 transition metal Inorganic materials 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- CKFRRHLHAJZIIN-UHFFFAOYSA-N cobalt lithium Chemical compound [Li].[Co] CKFRRHLHAJZIIN-UHFFFAOYSA-N 0.000 description 3
- 238000000354 decomposition reaction Methods 0.000 description 3
- 229910002804 graphite Inorganic materials 0.000 description 3
- 239000010439 graphite Substances 0.000 description 3
- 229910052748 manganese Inorganic materials 0.000 description 3
- 239000011572 manganese Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000012046 mixed solvent Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 238000002360 preparation method Methods 0.000 description 3
- BJWMSGRKJIOCNR-UHFFFAOYSA-N 4-ethenyl-1,3-dioxolan-2-one Chemical compound C=CC1COC(=O)O1 BJWMSGRKJIOCNR-UHFFFAOYSA-N 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 2
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 239000003125 aqueous solvent Substances 0.000 description 2
- 150000005678 chain carbonates Chemical class 0.000 description 2
- 238000007600 charging Methods 0.000 description 2
- 150000005676 cyclic carbonates Chemical class 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000010790 dilution Methods 0.000 description 2
- 239000012895 dilution Substances 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 238000012856 packing Methods 0.000 description 2
- 230000000737 periodic effect Effects 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- ZZXUZKXVROWEIF-UHFFFAOYSA-N 1,2-butylene carbonate Chemical compound CCC1COC(=O)O1 ZZXUZKXVROWEIF-UHFFFAOYSA-N 0.000 description 1
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 239000005977 Ethylene Substances 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 239000002033 PVDF binder Substances 0.000 description 1
- KLARSDUHONHPRF-UHFFFAOYSA-N [Li].[Mn] Chemical compound [Li].[Mn] KLARSDUHONHPRF-UHFFFAOYSA-N 0.000 description 1
- SOXUFMZTHZXOGC-UHFFFAOYSA-N [Li].[Mn].[Co].[Ni] Chemical compound [Li].[Mn].[Co].[Ni] SOXUFMZTHZXOGC-UHFFFAOYSA-N 0.000 description 1
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
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- 230000000996 additive effect Effects 0.000 description 1
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- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 125000004177 diethyl group Chemical group [H]C([H])([H])C([H])([H])* 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 125000005678 ethenylene group Chemical group [H]C([*:1])=C([H])[*:2] 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000005001 laminate film Substances 0.000 description 1
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
- 229910001947 lithium 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
- 229910021437 lithium-transition metal oxide Inorganic materials 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
- 230000014759 maintenance of location Effects 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000000034 method Methods 0.000 description 1
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- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 229920001690 polydopamine Polymers 0.000 description 1
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- HNJBEVLQSNELDL-UHFFFAOYSA-N pyrrolidin-2-one Chemical compound O=C1CCCN1 HNJBEVLQSNELDL-UHFFFAOYSA-N 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 1
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- 239000000126 substance Substances 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Images
Classifications
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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
Abstract
Description
本発明は、正極活物質と導電剤とバインダーとを含む正極と、負極と、セパレータと、非水電解液とを備えた非水電解質二次電池に係り、特に、高容量で、高温条件下においても優れた保存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 non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a conductive agent, and a binder, a negative electrode, a separator, and a non-aqueous electrolyte solution. Is characterized in that excellent storage characteristics can be obtained.
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様々な機器に利用されるようになった。 A variety of non-aqueous electrolyte secondary batteries that use non-aqueous electrolyte and charge and discharge by moving lithium ions between the positive and negative electrodes as new secondary batteries with high output and high energy density It came to be used for.
そして、近年においては、携帯電話、ノートパソコン、ＰＤＡなどのモバイル機器の小型化・軽量化が著しく進行すると共に、多機能化に伴って消費電力も増加する傾向にあり、これらの駆動電源として用いる非水電解質二次電池においては、高容量且つ高性能化が強く要望されている。 In recent years, mobile devices such as mobile phones, notebook computers, and PDAs have been remarkably reduced in size and weight, and power consumption has been increasing with the increase in functionality. In non-aqueous electrolyte secondary batteries, high capacity and high performance are strongly demanded.
ここで、上記のような非水電解質二次電池を高容量化させるにあたっては、発電要素に関与しない電池缶やセパレータや電極に使用する集電体を薄くする他、正極や負極に使用する活物質の特性を向上させることが考えられる。 Here, in increasing the capacity of the non-aqueous electrolyte secondary battery as described above, the current collector used for the battery can, separator, and electrode not involved in the power generation element is thinned, and the active material used for the positive electrode and the negative electrode is used. It is conceivable to improve the properties of the substance.
そして、上記のような非水電解質二次電池においては、正極における正極活物質として、リチウム・コバルト複合酸化物やリチウム・マンガン複合酸化物等のリチウム遷移金属複合酸化物が広く利用されている。 In the non-aqueous electrolyte secondary battery as described above, lithium transition metal composite oxides such as lithium / cobalt composite oxide and lithium / manganese composite oxide are widely used as the positive electrode active material in the positive electrode.
ここで、上記のリチウム遷移金属酸化物において、リチウム・コバルト複合酸化物であるコバルト酸リチウムＬｉＣｏＯ2の理論容量は約２７３ｍＡｈ／ｇであるが、このよう
な正極活物質に用いた非水電解質二次電池においては、一般に充電終止電圧を４．２Ｖに設定して使用するようになっており、この場合、コバルト酸リチウムは１６０ｍＡｈ／ｇ程度の容量しか使用されないことになる。
Here, in the above lithium transition metal oxide, the theoretical capacity of lithium cobaltate LiCoO 2 which is a lithium-cobalt composite oxide is about 273 mAh / g, but the
このため、上記のような正極活物質に用いた上記の非水電解質二次電池における充電終止電圧を高くして、コバルト酸リチウムの使用容量を高めることが考えられ、例えば、充電終止電圧を４．４Ｖまで高めると、コバルト酸リチウムが２００ｍＡｈ／ｇ程度まで使用されるようになり、電池全体として１０％程度の高容量化を達成することができる。 For this reason, it is conceivable that the charge end voltage in the non-aqueous electrolyte secondary battery used in the positive electrode active material as described above is increased to increase the use capacity of lithium cobaltate. When the voltage is increased to 0.4 V, lithium cobaltate is used up to about 200 mAh / g, and the capacity of the battery as a whole can be increased to about 10%.
しかし、正極活物質にコバルト酸リチウム等を用いた非水電解質二次電池において、充電終止電圧を高くすると、充電された状態での正極活物質の酸化力が強くなり、正極活物質との接触により非水電解液の分解が加速されると共に、この正極活物質の結晶構造の安定性が低下し、例えば、コバルト酸リチウムの場合、リチウム参照極電位に対して４．４０Ｖ以上まで充電させると、結晶構造が崩壊しやすくなることが知られており（例えば、非特許文献１参照。）、これによりサイクル特性や保存特性が大きく劣化するという問題があった。 However, in a non-aqueous electrolyte secondary battery using lithium cobaltate or the like as the positive electrode active material, increasing the end-of-charge voltage increases the oxidizing power of the positive electrode active material in the charged state, and makes contact with the positive electrode active material. This accelerates the decomposition of the non-aqueous electrolyte and reduces the stability of the crystal structure of the positive electrode active material. For example, in the case of lithium cobaltate, when charged to 4.40 V or more with respect to the lithium reference electrode potential It has been known that the crystal structure tends to collapse (see, for example, Non-Patent Document 1), which causes a problem that cycle characteristics and storage characteristics are greatly deteriorated.
そして、近年においては、充電終止電圧を高くした場合においても正極活物質の結晶構造が崩壊するのを防止するため、Ｎｉ及びＭｎを含み層状構造を有するリチウム遷移金属複合酸化物にホウ素を含有させた正極活物質を用いるようにしたもの（例えば、特許文献２参照。）や、ＬｉとＣｏを含み層状構造を有するリチウム遷移金属複合酸化物に、Ｚｒ等の周期律表第IVＡ族元素とＭｇ等の周期律表第IIＡ族元素を含有させた正極活物質を用
いるようにしたもの（例えば、特許文献３参照。）が提案されている。
In recent years, in order to prevent the crystal structure of the positive electrode active material from collapsing even when the end-of-charge voltage is increased, boron is contained in the lithium transition metal composite oxide containing Ni and Mn and having a layered structure. A positive electrode active material (see, for example, Patent Document 2), a lithium transition metal composite oxide containing Li and Co and having a layered structure, a Group IVA element of the periodic table such as Zr, and Mg A positive electrode active material containing a Group IIA element of the periodic table such as the above is proposed (for example, see Patent Document 3).
しかし、非水電解質二次電池にこのような正極活物質を使用した場合においても、この非水電解質二次電池を上記のように充電終止電圧を高くすると共に高温環境下において使用すると、上記の正極活物質からＣｏやＭｎが溶出して負極やセパレータに析出し、これにより内部抵抗が増加すると共に容量が大きく低下するという問題があった。
本発明は、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、正極活物質と導電剤とバインダーとを含む正極と、負極と、セパレータと、非水電解液とを備えた非水電解質二次電池を改良し、高容量で且つ高温条件下においても優れた保存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 nonaqueous electrolyte secondary battery, and in particular, a positive electrode including a positive electrode active material, a conductive agent, and a binder, a negative electrode, a separator, An object of the present invention is to improve a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte so that excellent storage characteristics can be obtained even under a high capacity and high temperature condition.
本発明の非水電解質二次電池においては、上記のような課題を解決するため、正極活物質と導電剤とバインダーとを含む正極と、負極と、セパレータと、非水電解液とを備えた非水電解質二次電池において、正極活物質の表面全体が導電剤で被覆されていない正極を使用すると共に、上記のセパレータとして、その厚みをｘ（μｍ），空孔率をｙ（％）とした場合に、ｘ・ｙ≦１５００（μｍ・％）の条件を満たすものを用い、上記の非水電解液にＬｉＢＦ4が添加されたものを使用し、上記の正極をリチウム参照極電位に対して４
．４０Ｖ以上まで充電させるようにしたのである。
In order to solve the above problems, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode including a positive electrode active material, a conductive agent, and a binder, a negative electrode, a separator, and a nonaqueous electrolyte. In a non-aqueous electrolyte secondary battery, a positive electrode in which the entire surface of the positive electrode active material is not coated with a conductive agent is used, and as the separator, the thickness is x (μm) and the porosity is y (%). In this case, the one that satisfies the condition of x · y ≦ 1500 (μm ·%) is used, and the above nonaqueous electrolyte solution to which LiBF 4 is added is used. 4
. It was made to charge to 40V or more.
本発明の非水電解質二次電池においては、上記のように正極をリチウム参照極電位に対して４．４０Ｖ以上まで充電させるようにしたため、この非水電解質二次電池の容量を高めることができると共に、非水電解液にＬｉＢＦ4が添加されたものを用いるようにした
ため、非水電解液に添加されたＬｉＢＦ4によって正極活物質の表面に被膜が形成される
ようになり、正極活物質の表面全体が導電剤で被覆されていない正極を使用した場合にも、非水電解液が上記の正極活物質と直接接触するのが抑制されるようになる。
In the non-aqueous electrolyte secondary battery of the present invention, since the positive electrode is charged to 4.40 V or higher with respect to the lithium reference electrode potential as described above, the capacity of the non-aqueous electrolyte secondary battery can be increased. At the same time, since a non-aqueous electrolyte solution to which LiBF 4 is added is used, a film is formed on the surface of the positive electrode active material by LiBF 4 added to the non-aqueous electrolyte solution. Even when a positive electrode whose entire surface is not coated with a conductive agent is used, the non-aqueous electrolyte is prevented from coming into direct contact with the positive electrode active material.
この結果、本発明の非水電解質二次電池においては、上記のように正極をリチウム参照極電位に対して４．４０Ｖ以上まで充電させて、その容量を高めた場合においても、非水電解液が正極活物質と接触して分解するのが抑制されると共に、この正極活物質の結晶構造が崩壊するのも抑制され、高容量で且つ高温条件下における保存特性にも優れた非水電解質二次電池が得られるようになる。
As a result, in the non-aqueous electrolyte secondary battery of the present invention, even when the positive electrode is charged to 4.40 V or more with respect to the lithium reference electrode potential as described above and the capacity is increased, the non-aqueous electrolyte solution Is prevented from being decomposed in contact with the positive electrode active material, and the crystal structure of the positive electrode active material is also prevented from being collapsed, and the
以下、本発明に係る非水電解質二次電池の実施形態について具体的に説明する。なお、本発明の非水電解質二次電池は下記の実施形態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, embodiments of the nonaqueous electrolyte secondary battery according to the present invention will be specifically described. The nonaqueous electrolyte secondary battery of the present invention is not limited to those shown in the following embodiments, and can be implemented with appropriate modifications within a range not changing the gist thereof.
本発明の非水電解質二次電池においては、上記のように正極活物質と導電剤とバインダーとを含む正極と、負極と、セパレータと、非水電解液とを備えた非水電解質二次電池において、正極活物質の表面全体が導電剤で被覆されていない正極を使用すると共に、上記のセパレータとして、その厚みをｘ（μｍ），空孔率をｙ（％）とした場合に、ｘ・ｙ≦
１５００（μｍ・％）の条件を満たすものを用い、上記の非水電解液にＬｉＢＦ4が添加
されたものを使用し、上記の正極をリチウム参照極電位に対して４．４０Ｖ以上まで充電させるようにしている。なお、この非水電解質二次電池において、さらに容量を向上させるためには、上記の正極をリチウム参照極電位に対して４．４５Ｖ以上まで、さらには４．５０Ｖ以上まで充電させるようにすることが好ましい。
In the nonaqueous electrolyte secondary battery of the present invention, as described above, the nonaqueous electrolyte secondary battery including the positive electrode including the positive electrode active material, the conductive agent, and the binder, the negative electrode, the separator, and the nonaqueous electrolyte solution. In the above, when using a positive electrode in which the entire surface of the positive electrode active material is not coated with a conductive agent, and the thickness is x (μm) and the porosity is y (%), x · y ≦
Using a material satisfying the condition of 1500 (μm ·%), using the above nonaqueous electrolyte solution with LiBF 4 added, and charging the above positive electrode to 4.40 V or more with respect to the lithium reference electrode potential I am doing so. In order to further improve the capacity of the non-aqueous electrolyte secondary battery, the positive electrode is charged to 4.45 V or more, more preferably 4.50 V or more with respect to the lithium reference electrode potential. Is preferred.
ここで、上記のように正極活物質と導電剤とバインダーとを含む正極を作製するにあたり、正極活物質と導電剤とバインダーとを湿式混合させると、図１に示すように、隣接する正極活物質粒子１の間に導電剤とバインダーとの混合物２が点在した状態になり、正極活物質粒子１の表面全体が上記のような混合物２によって被覆されず、このように混合物２が存在しない部分においては、非水電解液が正極活物質粒子１と直接接触するようになる。
Here, in preparing the positive electrode including the positive electrode active material, the conductive agent, and the binder as described above, when the positive electrode active material, the conductive agent, and the binder are wet mixed, as shown in FIG. The
しかし、上記のようにＬｉＢＦ4が添加された非水電解液を用いると、非水電解液に添
加されたＬｉＢＦ4により、導電剤等によって被覆されていない正極活物質の表面に被膜
が形成されて、正極活物質の表面全体が被覆された状態になり、非水電解液が正極活物質と直接接触するのが抑制される。この結果、上記のように正極をリチウム参照極電位に対して４．４０Ｖ以上まで充電させ、またこの非水電解質二次電池を５０℃以上の高温条件で使用する場合においても、非水電解液が正極活物質と接触して分解するのが抑制されるようになる。
However, when a non-aqueous electrolyte to which LiBF 4 is added as described above is used, a film is formed on the surface of the positive electrode active material that is not covered with a conductive agent or the like due to LiBF 4 added to the non-aqueous electrolyte. Thus, the entire surface of the positive electrode active material is covered, and the nonaqueous electrolyte is prevented from coming into direct contact with the positive electrode active material. As a result, even when the positive electrode is charged to 4.40 V or more with respect to the lithium reference electrode potential as described above, and this non-aqueous electrolyte secondary battery is used at a high temperature of 50 ° C. or higher, the non-aqueous electrolyte solution is used. Is prevented from coming into contact with the positive electrode active material and being decomposed.
なお、ローラーミル、ボールミル、メカノフュージョン、ジェットミル等を用いた乾式混合により導電剤を正極活物質の表面に被覆処理させた後、これにバインダーを加えて湿式混合させると、図２に示すように、正極活物質粒子１の表面全体が、導電剤とバインダーとの混合物２によって被覆された状態になり、これによって非水電解液が正極活物質粒子１と直接接触するのが抑制されるようになる。但し、このように正極活物質粒子１の表面全体が導電剤とバインダーとの混合物３によって被覆された状態では、上記のようにＬｉＢＦ4が添加された非水電解液を用いた場合にも、ＬｉＢＦ4によって正極活物質粒子１の表面に被膜が形成されるということはなく、ＬｉＢＦ4による効果は得られない。
As shown in FIG. 2, when a conductive agent is coated on the surface of the positive electrode active material by dry mixing using a roller mill, ball mill, mechanofusion, jet mill, etc., and then a binder is added thereto and wet mixed. Further, the entire surface of the positive electrode
また、上記の正極活物質としては、一般に使用されているリチウム・コバルト複合酸化物、リチウム・マンガン複合酸化物、リチウム・コバルト・ニッケル・マンガン複合酸化物、リチウム・コバルト・ニッケル・アルミニウム複合酸化物、リチウム・マンガン・ニッケル・アルミニウム複合酸化物等のリチウム遷移金属複合酸化物を用いることができるが、特に高電圧化させて容量を高めることができるものを用いることが好ましく、例えば、コバルト酸リチウムのようなリチウム・コバルト複合酸化物を用いることが好ましい。 In addition, as the positive electrode active material, commonly used lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-cobalt-nickel-manganese composite oxide, lithium-cobalt-nickel-aluminum composite oxide Lithium transition metal composite oxides such as lithium, manganese, nickel, and aluminum composite oxides can be used, but it is particularly preferable to use a lithium oxide that can increase the capacity by increasing the voltage. It is preferable to use a lithium-cobalt composite oxide such as
そして、正極活物質にコバルト酸リチウムを用いた場合、前記のようにリチウム参照極電位に対して４．４０Ｖ以上まで充電させると、その結晶構造の安定性が低下するため、このコバルト酸リチウムに、少なくともＡｌ及び／又はＭｇを固溶させると共にその表面にＺｒを付着させることが好ましい。 When lithium cobaltate is used as the positive electrode active material, if the lithium reference electrode potential is charged to 4.40 V or more with respect to the lithium reference electrode potential as described above, the stability of the crystal structure decreases. It is preferable to dissolve at least Al and / or Mg and to attach Zr to the surface thereof.
ここで、上記のようにバルト酸リチウムにＡｌやＭｇを固溶させると、コバルト酸リチウムの結晶構造が安定化するようになる。なお、結晶構造を安定化させる点では、ＡｌとＭｇとの効果はほぼ同じであるが、初回充放電効率や放電作動電圧が低下するのを少なくする点からはＭｇを固溶させることが好ましい。 Here, when Al or Mg is dissolved in lithium baltate as described above, the crystal structure of lithium cobaltate is stabilized. The effect of Al and Mg is substantially the same in terms of stabilizing the crystal structure, but it is preferable to dissolve Mg in terms of reducing the initial charge / discharge efficiency and the discharge operating voltage from decreasing. .
また、ＡｌやＭｇを固溶させると、上記のように放電作動電圧が低下するおそれがあるが、上記のように表面にＺｒを付着させると、コバルト酸リチウムと非水電解液との界面の抵抗である界面電荷移動抵抗が大幅に低減され、放電作動電圧が大きく改善されるよう
になる。なお、Ｚｒ以外にＳｎ、Ｔｉ、Ｎｂ等の４価又は５価の元素を添加した場合にも、放電作動電圧が大きく改善されるが、Ｚｒ以外のＳｎ、Ｔｉ、Ｎｂ等を用いた場合、焼成時におけるコバルト酸リチウムの結晶成長が阻害され、コバルト酸リチウム自体の安全性が低下する傾向にあるため、Ｚｒを用いることが好ましい。
In addition, when Al or Mg is dissolved, the discharge operating voltage may be reduced as described above. However, when Zr is attached to the surface as described above, the interface between the lithium cobalt oxide and the nonaqueous electrolytic solution may be reduced. The interfacial charge transfer resistance, which is a resistance, is greatly reduced, and the discharge operating voltage is greatly improved. In addition, when a tetravalent or pentavalent element such as Sn, Ti, or Nb is added in addition to Zr, the discharge operating voltage is greatly improved, but when using Sn, Ti, Nb, or the like other than Zr, Since the crystal growth of lithium cobaltate during firing is inhibited and the safety of lithium cobaltate itself tends to decrease, it is preferable to use Zr.
また、上記の非水電解液としては、非水系溶媒に溶質として上記のＬｉＢＦ4を単独又
は他の溶質と一緒にして添加させたものを用いることができる。
As the above non-aqueous electrolyte, it can be used as the nonaqueous solvent as a solute was added to alone or in combination with other solute LiBF 4 above.
ここで、非水電解液に上記のＬｉＢＦ4を添加させるにあたり、このＬｉＢＦ4の添加量が少ないと、正極活物質の表面に被膜を十分に形成することが困難になる一方、ＬｉＢＦ4の添加量が多くなりすぎると、ＬｉＢＦ4による副反応によって非水電解質二次電池の放電容量や放電負荷特性が低下するため、非水電解液にＬｉＢＦ4を０．１〜５．０重量％
の範囲で添加させることが好ましい。
Here, when adding the above LiBF 4 to the non-aqueous electrolyte, if the amount of LiBF 4 added is small, it becomes difficult to form a film on the surface of the positive electrode active material, while the addition of LiBF 4 If the amount is too large, the discharge capacity and discharge load characteristics of the non-aqueous electrolyte secondary battery are reduced due to the side reaction by LiBF 4 , so that LiBF 4 is added to the non-aqueous electrolyte in an amount of 0.1 to 5.0% by weight.
It is preferable to add in the range.
また、ＬｉＢＦ4と一緒に添加させる他の溶質としては、一般に用いられている公知の
溶質を用いることができ、例えば、ＬｉＰＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＮ（ＣＦ3ＳＯ2）2、ＬｉＮ（Ｃ2Ｆ5ＳＯ2）2、ＬｉＰＦ6-x（ＣnＦ2n+1）x［但し、１＜ｘ＜６、ｎ＝１
ｏｒ ２］等を用いることができ、特に、ＬｉＰＦ6を０．６〜２．０ｍｏｌ／ｌの範囲
で含有させることが好ましい。
Further, as other solutes added together with LiBF 4 , known solutes that are generally used can be used. For example, LiPF 6 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN ( C 2 F 5 SO 2 ) 2 , LiPF 6-x (C n F 2n + 1 ) x [where 1 <x <6, n = 1
or 2] or the like, and LiPF 6 is particularly preferably contained in the range of 0.6 to 2.0 mol / l.
また、上記の非水系溶媒としては、一般に用いられている公知の非水系溶媒を用いることができ、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等の環状カーボネートや、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート等の鎖状カーボネート等を用いることができる。 Moreover, as said non-aqueous solvent, the well-known well-known non-aqueous solvent can be used, for example, cyclic carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl A chain carbonate such as carbonate can be used.
また、上記のような非水電解液に、さらに負極に被膜を形成させる被膜形成剤を含有させることが好ましい。そして、このように非水電解液に被膜形成剤を含有させると、負極の表面にこの被膜形成剤による被膜が形成され、上記のＬｉＢＦ4により負極の表面に厚
い被膜が形成されて初期容量が低下するのが防止されると共に、負極の表面でＬｉＢＦ4
が分解するのも防止されるようになる。
Moreover, it is preferable to add a film forming agent for forming a film on the negative electrode in the non-aqueous electrolyte as described above. When the non-aqueous electrolyte contains the film forming agent in this way, a film is formed from the film forming agent on the surface of the negative electrode, and a thick film is formed on the surface of the negative electrode by the above-described LiBF 4 to increase the initial capacity. It is prevented from being lowered, and LiBF 4 is formed on the surface of the negative electrode.
Is also prevented from breaking down.
ここで、上記の被膜形成剤としては、ビニレンカーボネートＶＣやビニルエチレンカーボネートＶＥＣ等を用いることができ、また上記の非水電解液にＣＯ2を溶解させるよう
にすることもできる。なお、被膜形成剤としてビニレンカーボネートＶＣやビニルエチレンカーボネートＶＥＣを含有させるにあたっては、この被膜形成剤を非水電解液中に０．１〜５．０重量％の範囲で含有させることが好ましい。
Here, as the above-mentioned film-forming agent, can be used vinylene carbonate VC and vinyl ethylene carbonate VEC, etc., can also be adapted to dissolve the CO 2 in the above non-aqueous electrolyte. In addition, when including vinylene carbonate VC and vinyl ethylene carbonate VEC as a film forming agent, it is preferable to contain this film forming agent in the range of 0.1 to 5.0 weight% in a non-aqueous electrolyte.
また、セパレータとしては、その厚みをｘ（μｍ），空孔率をｙ（％）とした場合に、ｘ・ｙで表わされる空孔体積が１５００μｍ・％以下のものを用いることが好ましく、より好ましくは８００μｍ・％以下のものを用いるようにする。 In addition, as the separator, when the thickness is x (μm) and the porosity is y (%), it is preferable to use a separator whose pore volume represented by x · y is 1500 μm ·% or less. Preferably, 800 μm ·% or less is used.
ここで、セパレータは一般に電池内部での絶縁性を確保する他に、電池を作製する際の工程に耐え得る必要がある。このため、セパレータの膜厚を低下させると、電池のエネルギー密度は向上するが、セパレータの強度が低下するため、セパレータに設ける孔の平均孔径を小さくしたり、空孔率を減少させたりすることが必要になる。これに対して、セパレータの膜厚を厚くした場合には、セパレータの強度はある程度確保できるため、セパレータに設ける孔の平均孔径や空孔率を比較的自由に選択できる一方、電池のエネルギー密度が低下する。 Here, the separator generally needs to be able to withstand the process of manufacturing the battery in addition to ensuring the insulation inside the battery. For this reason, when the film thickness of the separator is reduced, the energy density of the battery is improved, but the strength of the separator is reduced, so that the average hole diameter of the holes provided in the separator is reduced or the porosity is reduced. Is required. On the other hand, when the thickness of the separator is increased, the strength of the separator can be secured to some extent, so the average hole diameter and porosity of the holes provided in the separator can be selected relatively freely, while the energy density of the battery is descend.
このため、セパレータの膜厚をある程度の厚みにし、一般的には２０μｍ前後にして、
セパレータに設ける孔の平均孔径や空孔率を調整することが好ましい。
For this reason, the thickness of the separator is set to a certain thickness, generally around 20 μm,
It is preferable to adjust the average hole diameter and porosity of the holes provided in the separator.
そして、ｘ・ｙで表わされる上記の空孔体積が上記のようなセパレータを用いると、電池のエネルギー密度が低下するのが防止されると共に、非水電解液の分解物や正極活物質から溶出した元素等がセパレータに目詰まりしてセパレータの性能が大きく低下したり、正極活物質から溶出した元素等がセパレータを通して負極に移動したりするのが抑制されるようになる。 When the above-described pore volume represented by x · y is used, the above-described separator is used to prevent the energy density of the battery from being lowered and to elute from the decomposition product of the non-aqueous electrolyte and the positive electrode active material. Thus, the separator is clogged and the performance of the separator is greatly deteriorated, or the element eluted from the positive electrode active material is prevented from moving to the negative electrode through the separator.
また、本発明における非水電解質二次電池において、負極に用いる負極活物質としては、一般に使用されている公知の負極活物質を用いることができ、Ｌｉイオンを挿入脱離できうるものであればよく、例えば、黒鉛，グラファイト，コークス等の炭素材料、酸化スズ、金属リチウム、珪素及びそれらの混合物等を用いることができる。 In the non-aqueous electrolyte secondary battery of the present invention, as the negative electrode active material used for the negative electrode, a known negative electrode active material that is generally used can be used as long as it can insert and desorb Li ions. For example, carbon materials such as graphite, graphite, and coke, tin oxide, metallic lithium, silicon, and a mixture thereof can be used.
次に、本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、比較例を挙げ、本発明の非水電解質二次電池においては、正極をリチウム参照極電位に対して４．４０Ｖ以上まで充電させて、容量を高めた場合においても、高温での保存特性が低下するのが抑制される明らかにする。 Next, the non-aqueous electrolyte secondary battery according to the present invention will be specifically described with examples, and a comparative example will be given. In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode is set to the lithium reference electrode potential. On the other hand, even when the battery is charged to 4.40 V or more to increase the capacity, it is clarified that the storage characteristics at high temperatures are prevented from deteriorating.
（実施例１）
実施例１においては、下記の正極と負極とセパレータと非水電解液とを用いて非水電解質二次電池を作製した。
(Example 1)
In Example 1, a non-aqueous electrolyte secondary battery was manufactured using the following positive electrode, negative electrode, separator, and non-aqueous electrolyte.
［正極］
正極を作製するにあたっては、正極活物質として、コバルト酸リチウムＬｉＣｏＯ2に
ＡｌとＭｇとがそれぞれ１．０ｍｏｌ％固溶されると共にその表面にＺｒが０．０５ｍｏｌ％付与されたものを用いた。
[Positive electrode]
In producing the positive electrode, a positive electrode active material in which 1.0 mol% of Al and Mg were respectively dissolved in lithium cobaltate LiCoO 2 and 0.05 mol% of Zr was added to the surface thereof was used.
そして、この正極活物質と導電剤であるアセチレンブラックとバインダーであるポリフッ化ビニリデンとを９５：２．５：２．５の質量比になるようにし、これに希釈溶媒のＮ−メチル−２−ピロリドンを加え、これらを特殊機化工業社製のコンビミックスを用いて混練して、正極合剤スラリーを調整し、この正極合剤スラリーをアルミニウム箔からなる正極集電体の両面に塗着させ、これを乾燥させた後、これを圧延させて正極を作製した。なお、このように作製した正極の断面をＳＥＭ写真で観察した結果、前記の図１に示したように、正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態になり、正極活物質の表面全体が導電剤等によって被覆されていない状態になっていた。また、正極の充填密度は３．６０ｇ／ｃｍ3であった。 Then, the positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are made to have a mass ratio of 95: 2.5: 2.5, and the diluted solvent N-methyl-2- Add pyrrolidone, knead them using a combination machine manufactured by Tokushu Kika Kogyo Co., Ltd. to prepare a positive electrode mixture slurry, and apply this positive electrode mixture slurry to both sides of a positive electrode current collector made of aluminum foil. After drying this, this was rolled to produce a positive electrode. In addition, as a result of observing the cross section of the positive electrode thus prepared with an SEM photograph, as shown in FIG. 1, the mixture of the conductive agent and the binder was interspersed between the positive electrode active material particles. The entire surface of the active material was not covered with a conductive agent or the like. The packing density of the positive electrode was 3.60 g / cm 3 .
［負極］
負極を作製するにあたっては、負極活物質の黒鉛と、カルボキシメチルセルロースナトリウムと、スチレン・ブタジエンゴムとを９８：１：１の質量比で水溶液中において混合し、これを銅箔の両面に塗着させて乾燥させた後、これを圧延させて負極を作製した。なお、この負極における負極活物質の充填密度は１．６０ｇ／ｃｍ3であった。
[Negative electrode]
In preparing the negative electrode, graphite of negative electrode active material, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in an aqueous solution at a mass ratio of 98: 1: 1, and this was applied to both sides of the copper foil. After being dried, this was rolled to produce a negative electrode. The packing density of the negative electrode active material in this negative electrode was 1.60 g / cm 3 .
［非水電解液］
非水電解液としては、環状カーボネートのエチレンカーボネートと、鎖状カーボネートのジエチルカーボネートとを３：７の体積比で混合させた混合溶媒に、溶質としてヘキサフルオロリン酸リチウムＬｉＰＦ6を１ｍｏｌ／ｌの割合で溶解させ、これにＬｉＢＦ4を１．０重量％添加させたものを用いた。
[Non-aqueous electrolyte]
As a non-aqueous electrolyte, 1 mol / l of lithium hexafluorophosphate LiPF 6 was used as a solute in a mixed solvent obtained by mixing cyclic carbonate ethylene carbonate and chain carbonate diethyl carbonate in a volume ratio of 3: 7. A solution prepared by dissolving at a ratio and adding 1.0% by weight of LiBF 4 was used.
［セパレータ］
セパレータとしては、厚みｘが１６μｍ、空孔率ｙが４７％で、空孔体積ｘ・ｙが７５２μｍ・％になったポリプロピレン製の微多孔膜を用いた。
[Separator]
As the separator, a microporous membrane made of polypropylene having a thickness x of 16 μm, a porosity y of 47%, and a pore volume x · y of 752 μm ·% was used.
［電池の作製］
電池を作製するにあたっては、図３（Ａ），（Ｂ）に示すように、上記の正極１１と負極１２とに正極リード端子１１ａと負極リード端子１２ａとを取り付け、この正極１１と負極１２とが上記のセパレータ１３を介して対向するようにして巻回し、これをプレスして扁平電極体１０を作製した。
[Production of battery]
In manufacturing the battery, as shown in FIGS. 3A and 3B, a positive electrode lead terminal 11a and a negative
次いで、図４に示すように、上記の扁平電極体１０をアルミニウムラミネートフィルムで構成された電池容器２０内に収容させると共に、この電池容器２０内に上記の非水電解液を加え、上記の正極リード端子１１ａと負極リード端子１２ａとを外部に取り出すようにして、上記の電池容器２０の開口部を封口させて、設計容量が７８０ｍＡｈの非水電解質二次電池を作製した。
Next, as shown in FIG. 4, the
そして、この実施例１においては、上記の非水電解質二次電池を作製するにあたり、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計を行うと共に、この電位での正極容量に対する負極容量の比が１．０８になるようにした。 In Example 1, when the non-aqueous electrolyte secondary battery is manufactured, the end-of-charge voltage is 4.40 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.50 V). In addition, the ratio of the negative electrode capacity to the positive electrode capacity at this potential was set to 1.08.
（実施例２）
実施例２においては、上記の実施例１における非水電解液において、ＬｉＢＦ4を３．
０重量％添加させたものを用い、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Example 2)
In Example 2, in the nonaqueous electrolytic solution in Example 1 described above, LiBF 4 was changed to 3.
Other than that, the charge end voltage was 4.40 V (corresponding to the lithium reference electrode potential [vs. Li / Li + ] 4.50 V) in the same manner as in Example 1. A nonaqueous electrolyte secondary battery designed to be obtained was obtained.
（実施例３）
実施例３においては、上記の実施例１における非水電解液において、ＬｉＢＦ4を５．
０重量％添加させたものを用い、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Example 3)
In Example 3, in the nonaqueous electrolytic solution in Example 1 described above, LiBF 4 was changed to 5.
Other than that, the charge end voltage was 4.40 V (corresponding to the lithium reference electrode potential [vs. Li / Li + ] 4.50 V) in the same manner as in Example 1. A nonaqueous electrolyte secondary battery designed to be obtained was obtained.
（比較例１）
比較例１においては、上記の実施例１における非水電解液において、ＬｉＢＦ4を添加
させないようにし、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Comparative Example 1)
In Comparative Example 1, the end-of-charge voltage was 4.40 V (see Lithium), except that LiBF 4 was not added to the non-aqueous electrolyte in Example 1 above, and the rest was the same as in Example 1. A non-aqueous electrolyte secondary battery designed to have an electrode potential [vs. Li / Li + ] of 4.50 V) was obtained.
次に、上記のように作製した実施例１〜３及び比較例１の各非水電解質二次電池を、室温条件の下でそれぞれ７５０ｍＡの電流で充電終止電圧の４．４０Ｖまで定電流充電させた後、４．４０Ｖの定電圧で電流値が３７．５ｍＡになるまで定電圧充電させ、各非水電解質二次電池の初期の充電容量Ｑｘを求めた。そして、このように充電させた各非水電解質二次電池を１０分間休止させた後、それぞれ７５０ｍＡの電流で電池電圧が２．７５Ｖに低下するまで定電流放電させて、各非水電解質二次電池における保存前の放電容量Ｑｏを測定した。 Next, the nonaqueous electrolyte secondary batteries of Examples 1 to 3 and Comparative Example 1 manufactured as described above were charged at a constant current to a final charge voltage of 4.40 V at a current of 750 mA under room temperature conditions. Then, constant voltage charging was performed until the current value reached 37.5 mA at a constant voltage of 4.40 V, and the initial charge capacity Qx of each non-aqueous electrolyte secondary battery was determined. Then, after each non-aqueous electrolyte secondary battery charged in this manner is paused for 10 minutes, each non-aqueous electrolyte secondary battery is discharged at a constant current at a current of 750 mA until the battery voltage drops to 2.75 V. The discharge capacity Qo before storage in the battery was measured.
また、このように１回の充放電を行った各非水電解質二次電池を、上記のように室温条件の下でそれぞれ７５０ｍＡの電流で充電終止電圧の４．４０Ｖまで定電流充電させた後、４．４０Ｖの定電圧で電流値が３７．５ｍＡになるまで定電圧充電させた後、６０℃の
高温条件下で５日間放置させ、放置後の各非水電解質二次電池を室温まで冷却させ、その後、各非水電解質二次電池を、それぞれ７５０ｍＡの電流で電池電圧が２．７５Ｖに低下するまで定電流放電させて、各非水電解質二次電池における保存後の放電容量Ｑａを測定し、下記の式により各非水電解質二次電池における高温条件下での保存後の容量残存率（％）を求め、その結果を下記の表１に示した。
Further, after each non-aqueous electrolyte secondary battery that has been charged and discharged once in this way is charged at a constant current to a final charge voltage of 4.40 V at a current of 750 mA under the room temperature conditions as described above. 4. After charging at a constant voltage of 4.40 V until the current value reaches 37.5 mA, let it stand for 5 days at a high temperature of 60 ° C., then cool each non-aqueous electrolyte secondary battery to room temperature Then, each non-aqueous electrolyte secondary battery was discharged at a constant current at a current of 750 mA until the battery voltage dropped to 2.75 V, and the discharge capacity Qa after storage in each non-aqueous electrolyte secondary battery was measured. The remaining capacity (%) after storage under high temperature conditions in each nonaqueous electrolyte secondary battery was determined by the following formula, and the results are shown in Table 1 below.
保存後の容量残存率（％）＝（Ｑａ／Ｑｏ）×１００ Capacity remaining rate after storage (%) = (Qa / Qo) × 100
この結果、上記のように正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態で、正極活物質の表面全体が導電剤等によって被覆されていない正極を用いた場合において、ＬｉＢＦ4を添加させた非水電解液を用いた実施例１〜３の各非水電解質二次電
池は、ＬｉＢＦ4を添加させていない非水電解液を用いた比較例１の非水電解質二次電池
に比べて、高温条件下における保存後の容量残存率が大きく向上していた。
As a result, when the positive electrode in which the entire surface of the positive electrode active material is not coated with the conductive agent or the like in the state where the mixture of the conductive agent and the binder is interspersed between the positive electrode active material particles as described above, the LiBF is used. each of the non-aqueous electrolyte secondary batteries of examples 1 to 3 using 4 was added non-aqueous electrolyte, a non-aqueous electrolyte secondary of Comparative example 1 using the non-aqueous electrolyte that has not been added LiBF 4 Compared to the battery, the capacity remaining rate after storage under high temperature conditions was greatly improved.
また、実施例１〜３の非水電解質二次電池を比較すると、非水電解液に対するＬｉＢＦ4の添加量が多くなるに従って、さらに高温条件下における保存後の容量残存率が向上し
ていた。
Moreover, when the nonaqueous electrolyte secondary batteries of Examples 1 to 3 were compared, the capacity remaining rate after storage under high temperature conditions was further improved as the amount of LiBF 4 added to the nonaqueous electrolyte increased.
（実施例４）
実施例４においては、上記の実施例１における非水電解液において、上記の混合溶媒に、溶質としてヘキサフルオロリン酸リチウムＬｉＰＦ6を０．９ｍｏｌ／ｌの割合で溶解
させると共に、ＬｉＢＦ4を０．１ｍｏｌ／ｌの割合で溶解させたものを用い、それ以外
は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。なお、上記の非水電解液においては、非水電解液に対するＬｉＢＦ4の添加量が約１．０
重量％になっている。
Example 4
In Example 4, in the nonaqueous electrolytic solution in Example 1 above, lithium hexafluorophosphate LiPF 6 as a solute was dissolved in the above mixed solvent at a rate of 0.9 mol / l, and LiBF 4 was 0%. In the same manner as in Example 1, except that a solution dissolved at a rate of 1 mol / l was used, the end-of-charge voltage was 4.40 V (lithium reference electrode potential [vs. Li / Li + ]. A nonaqueous electrolyte secondary battery designed to be equivalent to 50 V was obtained. In the above non-aqueous electrolyte, the amount of LiBF 4 added to the non-aqueous electrolyte is about 1.0.
% By weight.
（実施例５）
実施例５においては、上記の実施例１における非水電解液において、上記の混合溶媒に、溶質としてヘキサフルオロリン酸リチウムＬｉＰＦ6を０．５ｍｏｌ／ｌの割合で溶解
させると共に、ＬｉＢＦ4を０．５ｍｏｌ／ｌの割合で溶解させたものを用い、それ以外
は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。なお、上記の非水電解液においては、非水電解液に対するＬｉＢＦ4の添加量が約５．０
重量％になっている。
(Example 5)
In Example 5, in the nonaqueous electrolytic solution in Example 1 above, lithium hexafluorophosphate LiPF 6 as a solute was dissolved in the above mixed solvent at a rate of 0.5 mol / l, and LiBF 4 was 0%. In the same manner as in Example 1, except that a material dissolved at a rate of 5 mol / l was used, the end-of-charge voltage was 4.40 V (lithium reference electrode potential [vs. Li / Li + ]. A nonaqueous electrolyte secondary battery designed to be equivalent to 50 V was obtained. In the above non-aqueous electrolyte, the amount of LiBF 4 added to the non-aqueous electrolyte is about 5.0.
% By weight.
そして、上記のようにして作製した実施例４，５の各非水電解質二次電池についても、上記の実施例１及び比較例１の非水電解質二次電池の場合と同様にして、高温条件下での保存後の容量残存率（％）を求めると共に、実施例１，４，５及び比較例１の各非水電解質二次電池について、さらに上記の初期の充電容量Ｑｘと、保存前の放電容量Ｑｏとから下記の式により各非水電解質二次電池における初期充放電効率（％）を求め、これらの結果を下記の表２に示した。 And also about each nonaqueous electrolyte secondary battery of Examples 4 and 5 produced as mentioned above, it is high temperature conditions similarly to the case of the nonaqueous electrolyte secondary battery of said Example 1 and Comparative Example 1. In addition to determining the remaining capacity rate (%) after storage below, each of the nonaqueous electrolyte secondary batteries of Examples 1, 4, 5 and Comparative Example 1 was further subjected to the above initial charge capacity Qx and before storage. The initial charge / discharge efficiency (%) in each nonaqueous electrolyte secondary battery was determined from the discharge capacity Qo by the following formula, and these results are shown in Table 2 below.
初期充放電効率（％）＝（Ｑｏ／Ｑｘ）×１００ Initial charge / discharge efficiency (%) = (Qo / Qx) × 100
この結果、上記の実施例４，５の非水電解質二次電池も、上記の実施例１〜３の非水電解質二次電池と同様に、ＬｉＢＦ4を添加させていない非水電解液を用いた比較例１の非
水電解質二次電池に比べて、高温条件下における保存後の容量残存率が大きく向上していた。
As a result, the non-aqueous electrolyte secondary batteries of Examples 4 and 5 also use the non-aqueous electrolyte solution to which LiBF 4 is not added, like the non-aqueous electrolyte secondary batteries of Examples 1 to 3. Compared with the nonaqueous electrolyte secondary battery of Comparative Example 1, the capacity remaining rate after storage under high temperature conditions was greatly improved.
また、上記の実施例４，５の非水電解質二次電池を比較した場合、上記の実施例１〜３の非水電解質二次電池の場合と同様に、ＬｉＢＦ4の添加量が多くなるに従って、高温条
件下における保存後の容量残存率が向上していた。
Further, when the nonaqueous electrolyte secondary batteries of Examples 4 and 5 are compared, as in the case of the nonaqueous electrolyte secondary batteries of Examples 1 to 3, the amount of LiBF 4 added increases. The residual capacity rate after storage under high temperature conditions was improved.
また、上記の実施例１，４，５の非水電解質二次電池を比較した場合、非水電解液中における溶質のＬｉＰＦ6とＬｉＢＦ4との合計モル濃度が１ｍｏｌ／ｌになるようにした実施例４，５のものは、ＬｉＰＦ6を１ｍｏｌ／ｌの割合で加え、さらにＬｉＢＦ4を添加させた実施例１のものに比べて、初期充放電効率が低下しており、非水電解液中におけるＬｉＰＦ6の濃度が低下するに従って、初期充放電効率がさらに低下していた。これは、非
水電解液中におけるＬｉＢＦ4が被膜形成に使用されて消費し、非水電解液中におけるリ
チウム塩の濃度が減少して、非水電解液のイオン伝導度が低下したためであると考えられる。
In addition, when the nonaqueous electrolyte secondary batteries of Examples 1, 4 and 5 were compared, the total molar concentration of solutes LiPF 6 and LiBF 4 in the nonaqueous electrolyte solution was 1 mol / l. In Examples 4 and 5, the initial charge / discharge efficiency was lower than that in Example 1 in which LiPF 6 was added at a rate of 1 mol / l, and LiBF 4 was further added. As the concentration of LiPF 6 in the medium decreased, the initial charge / discharge efficiency further decreased. This is because LiBF 4 in the non-aqueous electrolyte is used and consumed for film formation, the concentration of lithium salt in the non-aqueous electrolyte is decreased, and the ionic conductivity of the non-aqueous electrolyte is reduced. Conceivable.
（比較例２）
比較例２においては、上記の実施例１における正極の作製において、上記の正極活物質と導電剤とを９５：２．５の質量比にし、これをメカノフュージョン（ホソカワミクロン社製）により１５００回転で１０分間乾式混合させて、正極活物質の表面に導電剤を被覆処理させた後、このように導電剤を被覆処理させた正極活物質と上記のバインダーとを９
７．５：２．５の質量比にし、これに希釈溶媒のＮ−メチル−２−ピロリドンを加え、その後は上記の実施例１の場合と同様にして作製した正極を用いるようにした。なお、このように作製した正極の断面をＳＥＭ写真で観察した結果、前記の図２に示したように、正極活物質粒子の表面全体が、導電剤とバインダーとの混合物からなる被覆層によって被覆された状態になっていた。
(Comparative Example 2)
In Comparative Example 2, in the production of the positive electrode in Example 1 described above, the positive electrode active material and the conductive agent were made to have a mass ratio of 95: 2.5, and this was performed at 1500 revolutions by mechanofusion (manufactured by Hosokawa Micron). After dry mixing for 10 minutes to coat the surface of the positive electrode active material with a conductive agent, the positive electrode active material thus coated with the conductive agent and the binder described above were combined.
A mass ratio of 7.5: 2.5 was added, and N-methyl-2-pyrrolidone as a dilution solvent was added thereto. Thereafter, a positive electrode produced in the same manner as in Example 1 was used. In addition, as a result of observing the cross section of the positive electrode thus prepared with an SEM photograph, as shown in FIG. 2, the entire surface of the positive electrode active material particles was covered with a coating layer made of a mixture of a conductive agent and a binder. It was in the state that was done.
そして、この比較例２においては、上記のようにして作製した正極を用いると共に、上記の比較例１と同じＬｉＢＦ4を添加させていない非水電解液を使用し、それ以外は、上
記の実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
Then, in this comparative example 2, the use of the positive electrode prepared as described above, using a non-aqueous electrolyte that has not been added to the same LiBF 4 and Comparative Example 1 above, except that, the above-described In the same manner as in Example 1, a non-aqueous electrolyte secondary battery designed to have an end-of-charge voltage of 4.40 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.50 V) was obtained. .
（比較例３）
比較例３においては、上記の比較例２に示すようにして作製した正極を用いると共に、非水電解液として、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌの割合で溶
解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用し、それ以外は、
上記の実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Comparative Example 3)
In Comparative Example 3, a positive electrode produced as shown in Comparative Example 2 above was used, and LiPF 6 was dissolved at a rate of 1 mol / l as a non-aqueous electrolyte solution as shown in Example 2 above. Using non-aqueous electrolyte with 3.0% by weight of LiBF 4 added,
In the same manner as in Example 1, the non-aqueous electrolyte secondary battery is designed so that the end-of-charge voltage is 4.40 V (corresponding to the lithium reference electrode potential [vs. Li / Li + ] 4.50 V). Got.
（比較例４）
比較例４においては、上記の実施例１における正極の作製において、上記の正極活物質と導電剤とを９５：２．５の質量比にし、これをらいかい乳鉢を用いて３０分間乾式混合させて、正極活物質の表面に導電剤を被覆処理させた後、このように導電剤を被覆処理させた正極活物質と上記のバインダーとを９７．５：２．５の質量比にし、これに希釈溶媒のＮ−メチル−２−ピロリドンを加え、その後は上記の実施例１の場合と同様にして作製した正極を用いるようにした。なお、このように作製した正極の断面をＳＥＭ写真で観察した結果、前記の図２に示したように、正極活物質粒子の表面全体が、導電剤とバインダーとの混合物からなる被覆層によって被覆された状態になっていた。
(Comparative Example 4)
In Comparative Example 4, in the production of the positive electrode in Example 1 above, the positive electrode active material and the conductive agent were mixed at a mass ratio of 95: 2.5, and this was dry-mixed for 30 minutes using a rough mortar. Then, after coating the surface of the positive electrode active material with a conductive agent, the positive electrode active material thus coated with the conductive agent and the binder described above have a mass ratio of 97.5: 2.5. A dilution solvent N-methyl-2-pyrrolidone was added, and thereafter a positive electrode produced in the same manner as in Example 1 was used. In addition, as a result of observing the cross section of the positive electrode thus prepared with an SEM photograph, as shown in FIG. 2, the entire surface of the positive electrode active material particles was covered with a coating layer made of a mixture of a conductive agent and a binder. It was in the state that was done.
そして、この比較例４においては、上記のようにして作製した正極を用いると共に、上記の比較例１の場合と同じＬｉＢＦ4を添加させていない非水電解液を用い、それ以外は
、上記の実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
Then, in this Comparative Example 4, the use of the positive electrode prepared as described above, using a non-aqueous electrolyte that has not been added to the same LiBF 4 as in Comparative Example 1 above, except that, in the In the same manner as in Example 1, a nonaqueous electrolyte secondary battery designed to have a charge end voltage of 4.40 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.50 V) is obtained. It was.
（比較例５）
比較例５においては、上記の比較例４に示すようにして作製した正極を用いると共に、非水電解液として、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌの割合で溶
解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用し、それ以外は、
上記の実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Comparative Example 5)
In Comparative Example 5, a positive electrode produced as shown in Comparative Example 4 above was used, and LiPF 6 was dissolved at a rate of 1 mol / l as a non-aqueous electrolyte as shown in Example 2 above. Using non-aqueous electrolyte with 3.0% by weight of LiBF 4 added,
In the same manner as in Example 1, the non-aqueous electrolyte secondary battery is designed so that the end-of-charge voltage is 4.40 V (corresponding to the lithium reference electrode potential [vs. Li / Li + ] 4.50 V). Got.
そして、上記のように作製した比較例２〜５の各非水電解質二次電池についても、上記の実施例２及び比較例１の非水電解質二次電池の場合と同様にして、高温条件下における保存後の容量残存率（％）を求め、これらの結果を下記の表３に示した。 And also about each nonaqueous electrolyte secondary battery of Comparative Examples 2-5 produced as mentioned above, similarly to the case of the nonaqueous electrolyte secondary battery of said Example 2 and Comparative Example 1, it is high temperature conditions. The remaining capacity ratio (%) after storage was determined, and the results are shown in Table 3 below.
この結果、正極活物質と導電剤とを乾式混合させて、正極活物質粒子の表面全体を導電剤とバインダーとの混合物からなる被覆層によって被覆させた正極を使用した比較例２〜５の各非水電解質二次電池は、正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態になった正極を使用すると共にＬｉＢＦ4を添加させていない非水電解液を用い
た比較例１の非水電解質二次電池に比べて、高温条件下における保存後の容量残存率が大きく向上していた。
As a result, each of Comparative Examples 2 to 5 using the positive electrode in which the positive electrode active material and the conductive agent were dry-mixed and the entire surface of the positive electrode active material particles were covered with the coating layer made of the mixture of the conductive agent and the binder. A nonaqueous electrolyte secondary battery uses a positive electrode in which a mixture of a conductive agent and a binder is interspersed between positive electrode active material particles, and a comparative example using a nonaqueous electrolyte solution to which LiBF 4 is not added Compared with the nonaqueous electrolyte
しかし、上記の比較例２〜５の各非水電解質二次電池においては、ＬｉＢＦ4を３．０
重量％添加させた非水電解液を用いた実施例２の非水電解質二次電池とＬｉＢＦ4を添加
させていない非水電解液を用いた比較例１の非水電解質二次電池の場合とは異なり、ＬｉＢＦ4を３．０重量％添加させた非水電解液を用いた比較例３，５の非水電解質二次電池
が、ＬｉＢＦ4を添加させていない非水電解液を用いた比較例２，４の非水電解質二次電
池に比べて、高温条件下における保存後の容量残存率が大きく向上するということはなく、ＬｉＢＦ4を添加させた非水電解液を用いる効果は少なかった。
However, in each of the nonaqueous electrolyte secondary batteries of Comparative Examples 2 to 5, LiBF 4 is set to 3.0.
In the case of the non-aqueous electrolyte secondary battery of Example 2 using the non-aqueous electrolyte added by weight% and the non-aqueous electrolyte secondary battery of Comparative Example 1 using the non-aqueous electrolyte not added with LiBF 4 comparison is different, the non-aqueous electrolyte secondary battery of Comparative example 3 and 5 using the non-aqueous electrolytic solution obtained by adding LiBF 4 of 3.0% by weight, using a nonaqueous electrolytic solution that has not been added LiBF 4 Compared to the non-aqueous electrolyte secondary batteries of Examples 2 and 4, the capacity remaining rate after storage under high temperature conditions was not greatly improved, and the effect of using the non-aqueous electrolyte to which LiBF 4 was added was small. .
（実施例６，７）
実施例６，７においては、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌの
割合で溶解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用すると共
に、上記の実施例１における電池の作製において、電池の設計を行う充電終止電圧の値を変更させるようにした。
(Examples 6 and 7)
In Examples 6 and 7, as shown in Example 2 above, a nonaqueous electrolytic solution in which LiPF 6 is dissolved at a rate of 1 mol / l and LiBF 4 added to 3.0 wt% is used. At the same time, in the production of the battery in Example 1 described above, the value of the charge end voltage at which the battery was designed was changed.
そして、実施例６においては、充電終止電圧が４．３５Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．４５Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにし、また実施例７においては、充電終止電圧が４．３０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．４０Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにした。 In Example 6, the end-of-charge voltage is designed to be 4.35 V (corresponding to lithium reference electrode potential [vs. Li / Li + ] 4.45 V), and the negative electrode with respect to the positive electrode capacity at this potential. The capacity ratio is 1.08, and in Example 7, the end-of-charge voltage is designed to be 4.30 V (equivalent to lithium reference electrode potential [vs. Li / Li + ] 4.40 V). Thus, the ratio of the negative electrode capacity to the positive electrode capacity at this potential was set to 1.08.
（比較例６）
比較例６においても、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌの割合
で溶解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用すると共に、
上記の実施例１における電池の作製において、電池の設計を行う充電終止電圧の値を変更
させるようにした。
(Comparative Example 6)
Also in Comparative Example 6, as shown in Example 2 above, a nonaqueous electrolytic solution in which LiPF 6 was dissolved at a rate of 1 mol / l was added with 3.0% by weight of LiBF 4 ,
In the production of the battery in Example 1 above, the value of the end-of-charge voltage at which the battery was designed was changed.
そして、この比較例６においては、充電終止電圧が４．２０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．３０Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにした。 In this comparative example 6, the end-of-charge voltage is designed to be 4.20 V (corresponding to lithium reference electrode potential [vs. Li / Li + ] 4.30 V), and the positive electrode capacity at this potential is determined. The negative electrode capacity ratio was set to 1.08.
（比較例７〜９）
比較例７〜９においては、上記の比較例１の場合と同じＬｉＢＦ4を添加させていない
非水電解液を用いると共に、上記の実施例１における電池の作製において、電池の設計を行う充電終止電圧の値を変更させるようにした。
(Comparative Examples 7-9)
In Comparative Examples 7 to 9, the same non-aqueous electrolyte not added with LiBF 4 as in Comparative Example 1 above is used, and in the battery production in Example 1 above, charge termination is performed to design the battery. Changed the voltage value.
そして、比較例７においては、充電終止電圧が４．３５Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．４５Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにし、また比較例８においては、充電終止電圧が４．３０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．４０Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにし、また比較例９においては、充電終止電圧が４．２０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．３０Ｖに相当）になるように設計して、この電位での正極容量に対する負極容量の比が１．０８になるようにした。 In Comparative Example 7, the end-of-charge voltage is designed to be 4.35 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.45 V), and the negative electrode with respect to the positive electrode capacity at this potential. The capacity ratio is set to 1.08, and in Comparative Example 8, the end-of-charge voltage is designed to be 4.30 V (corresponding to lithium reference electrode potential [vs. Li / Li + ] 4.40 V). Thus, the ratio of the negative electrode capacity to the positive electrode capacity at this potential is set to 1.08. In Comparative Example 9, the end-of-charge voltage is 4.20 V (lithium reference electrode potential [vs. Li / Li + ]). 4. Corresponding to 4.30V), the ratio of the negative electrode capacity to the positive electrode capacity at this potential was 1.08.
（比較例１０）
比較例１０においては、上記の比較例２の場合と同様に、正極活物質の表面に導電剤を被覆処理させた正極を使用すると共に、上記の比較例１の場合と同じＬｉＢＦ4を添加さ
せていない非水電解液を用い、上記の実施例１における電池の作製において、充電終止電圧が４．２０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．３０Ｖに相当）になるように設計し、この電位での正極容量に対する負極容量の比が１．０８になるようにした。
(Comparative Example 10)
In Comparative Example 10, as in the case of Comparative Example 2 above, a positive electrode whose surface was coated with a conductive agent was used, and the same LiBF 4 as in Comparative Example 1 was added. In the production of the battery in Example 1 using a non-aqueous electrolyte, the end-of-charge voltage is 4.20 V (corresponding to the lithium reference electrode potential [vs. Li / Li + ] 4.30 V). The ratio of the negative electrode capacity to the positive electrode capacity at this potential was 1.08.
（比較例１１）
比較例１１においては、上記の比較例２の場合と同様に、正極活物質の表面に導電剤を被覆処理させた正極を使用すると共に、非水電解液として、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌの割合で溶解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用し、上記の実施例１における電池の作製において、充電終止電圧が４．２０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．３０Ｖに相当）になるように設計し、この電位での正極容量に対する負極容量の比が１．０８になるようにした。
(Comparative Example 11)
In Comparative Example 11, as in the case of Comparative Example 2 described above, a positive electrode in which the surface of the positive electrode active material was coated with a conductive agent was used, and as a nonaqueous electrolytic solution, as shown in Example 2 above. In addition, in the production of the battery in Example 1 described above, the end-of-charge voltage was determined by using 3.0% by weight of LiBF 4 added to a non-aqueous electrolyte solution in which LiPF 6 was dissolved at a rate of 1 mol / l. Design was made to be 4.20 V (corresponding to lithium reference electrode potential [vs. Li / Li + ] 4.30 V), and the ratio of the negative electrode capacity to the positive electrode capacity at this potential was 1.08.
そして、上記のようにして作製した実施例６，７及び比較例６〜１１の各非水電解質二次電池についても、上記の実施例２及び比較例１〜３の非水電解質二次電池の場合と同様にして、高温条件下における保存後の容量残存率（％）を求め、これらの結果を下記の表４に示した。 And also about each nonaqueous electrolyte secondary battery of Examples 6 and 7 and Comparative Examples 6-11 produced as mentioned above, the nonaqueous electrolyte secondary battery of said Example 2 and Comparative Examples 1-3 is also mentioned. Similarly to the case, the residual capacity rate (%) after storage under high temperature conditions was determined, and these results are shown in Table 4 below.
この結果、正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態になった正極を使用すると共に、充電終止電圧が４．３０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／
Ｌｉ+］４．４０Ｖに相当）以上になるように設計した実施例２，６，７の非水電解質二
次電池と比較例１，７，８の非水電解質二次電池とを、それぞれ同じ充電終止電圧で設計された非水電解質二次電池同士で比較した場合、ＬｉＢＦ4を添加させた非水電解液を用
いた実施例２，６，７の非水電解質二次電池は、ＬｉＢＦ4を添加させていない非水電解
液を用いた比較例１，７，８の非水電解質二次電池に比べて、高温条件下における保存後の容量残存率が大きく向上していた。
As a result, a positive electrode in which a mixture of a conductive agent and a binder is interspersed between positive electrode active material particles is used, and a charge end voltage is 4.30 V (lithium reference electrode potential [vs. Li /
Li + ] equivalent to 4.40 V) The non-aqueous electrolyte secondary batteries of Examples 2, 6, and 7 and the non-aqueous electrolyte secondary batteries of Comparative Examples 1, 7, and 8 designed to be equal to or higher than the above are the same. when compared with the nonaqueous electrolyte secondary battery together design charge voltage, a non-aqueous electrolyte secondary batteries of examples 2, 6, 7 using non-aqueous electrolytic solution obtained by adding LiBF 4 is, LiBF 4 Compared to the nonaqueous electrolyte secondary batteries of Comparative Examples 1, 7, and 8 using the nonaqueous electrolyte solution to which no additive was added, the capacity remaining rate after storage under high temperature conditions was greatly improved.
また、正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態になった正極を使用すると共に、充電終止電圧が４．２０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．３０Ｖに相当）になるように設計した比較例６，９の非水電解質二次電池を比較した場合、ＬｉＢＦ4を添加させた非水電解液を用いた比較例６の非水電解質二次電池と、
ＬｉＢＦ4を添加させていない非水電解液を用いた比較例９の非水電解質二次電池とでは
、保存後の容量残存率が殆ど同じであり、ＬｉＢＦ4を添加させた非水電解液を用いるこ
とによって、高温条件下における保存後の容量残存率が向上するという効果は得られなかった。
Moreover, while using the positive electrode in which the mixture of the electrically conductive agent and the binder was interspersed between the positive electrode active material particles, the charge end voltage was 4.20 V (lithium reference electrode potential [vs. Li / Li + ] 4 When the nonaqueous electrolyte secondary batteries of Comparative Examples 6 and 9 designed to be equivalent to 30 V are compared, the nonaqueous electrolyte secondary battery of Comparative Example 6 using a nonaqueous electrolyte solution to which LiBF 4 is added is compared. Battery,
In the non-aqueous electrolyte secondary battery of Comparative Example 9 using the non-aqueous electrolyte not added with LiBF 4 , the capacity remaining rate after storage was almost the same, and the non-aqueous electrolyte added with LiBF 4 was used. By using it, the effect of improving the capacity remaining rate after storage under high temperature conditions was not obtained.
また、正極活物質と導電剤とを乾式混合させて、正極活物質粒子の表面全体を導電剤とバインダーとの混合物からなる被覆層によって被覆させた正極を使用した比較例２，３，
１０，１１の各非水電解質二次電池においては、前記のようにＬｉＢＦ4を添加させた非
水電解液を用いた場合に、高温条件下における保存後の容量残存率が大きく向上するということはなかった。
In addition, Comparative Examples 2, 3 using a positive electrode in which the positive electrode active material and the conductive agent were dry-mixed and the entire surface of the positive electrode active material particles were covered with a coating layer made of a mixture of the conductive agent and the binder.
In each of the non-aqueous electrolyte
なお、正極活物質粒子間に導電剤とバインダーとの混合物が点在した状態になった正極を使用した非水電解質二次電池と、正極活物質と導電剤とを乾式混合させて正極活物質の表面に導電剤を被覆処理させた正極を使用した非水電解質二次電池の何れにおいても、設計した充電終止電圧の値が低くなるほど、保存後の容量残存率は高くなっていた。しかし、電池を設計するにあたり、このように充電終止電圧の値を低くすると、上記の正極活物質が十分に活用されず、高容量の非水電解質二次電池を得ることができなかった。 In addition, the non-aqueous electrolyte secondary battery using the positive electrode in which the mixture of the conductive agent and the binder is interspersed between the positive electrode active material particles, the positive electrode active material and the conductive agent are dry-mixed, and the positive electrode active material In any non-aqueous electrolyte secondary battery using a positive electrode whose surface was coated with a conductive agent, the capacity remaining rate after storage was higher as the designed end-of-charge voltage value was lower. However, in designing the battery, if the value of the end-of-charge voltage is lowered in this way, the positive electrode active material is not fully utilized, and a high-capacity nonaqueous electrolyte secondary battery cannot be obtained.
（実施例８）
実施例８においては、上記の実施例１における非水電解液において、実施例２と同様にＬｉＢＦ4を３．０重量％添加させると共に、負極に被膜を形成する被膜形成剤としてビ
ニレンカーボネートＶＣを１．０重量％添加させたものを用い、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Example 8)
In Example 8, 3.0% by weight of LiBF 4 was added to the nonaqueous electrolytic solution in Example 1 above, and vinylene carbonate VC was used as a film forming agent for forming a film on the negative electrode. Other than that, 1.0% by weight was added, and in the same manner as in Example 1, the end-of-charge voltage was 4.40 V (lithium reference electrode potential [vs. Li / Li + ] 4.50 V). A non-aqueous electrolyte secondary battery designed to be equivalent) was obtained.
（比較例１２）
比較例１２においては、上記の比較例１の場合と同様に、非水電解液にＬｉＢＦ4を添
加させないようにする一方、この非水電解液に、負極に被膜を形成する被膜形成剤としてビニレンカーボネートＶＣを１．０重量％添加させるようにし、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を得た。
(Comparative Example 12)
In Comparative Example 12, as in the case of Comparative Example 1 above, LiBF 4 is not added to the non-aqueous electrolyte, while vinylene is used as a film-forming agent for forming a film on the negative electrode in this non-aqueous electrolyte. Carbonate VC was added in an amount of 1.0% by weight. Otherwise, in the same manner as in Example 1, the end-of-charge voltage was 4.40 V (lithium reference electrode potential [vs. Li / Li + ] 4.50 V). A non-aqueous electrolyte secondary battery designed to be equivalent to the above was obtained.
そして、上記のようにして作製した実施例８及び比較例１２の各非水電解質二次電池についても、上記の実施例２及び比較例１の非水電解質二次電池の場合と同様にして、高温条件下での保存後の容量残存率（％）を求めると共に、実施例２，８及び比較例１，１２の各非水電解質二次電池について、さらに前記のようにして初期充放電効率（％）を求め、これらの結果を下記の表５に示した。 And also about each nonaqueous electrolyte secondary battery of Example 8 and Comparative Example 12 produced as described above, as in the case of the nonaqueous electrolyte secondary battery of Example 2 and Comparative Example 1, While calculating | requiring the capacity | capacitance residual rate (%) after the preservation | save in high temperature conditions, about each nonaqueous electrolyte secondary battery of Example 2, 8 and Comparative Example 1, 12, it was further carried out as mentioned above, and initial stage charge-and-discharge efficiency ( %) And these results are shown in Table 5 below.
この結果、ＬｉＢＦ4を３．０重量％添加させると共に負極に被膜を形成するビニレン
カーボネートＶＣを１．０重量％添加させた非水電解液を用いた実施例８の非水電解質二次電池は、負極に被膜を形成するビニレンカーボネートＶＣを添加させていない実施例２の非水電解質二次電池よりも、高温条件下での保存後の容量残存率及び初期充放電効率が
向上していた。これは、上記のビニレンカーボネートＶＣによって負極の表面に被膜が形成され、この被膜により上記のＬｉＢＦ4が負極の表面で分解するのが抑制されるように
なったためであると考えられる。
As a result, the nonaqueous electrolyte secondary battery of Example 8 using the nonaqueous electrolyte solution to which 3.0% by weight of LiBF 4 was added and 1.0% by weight of vinylene carbonate VC forming a coating film on the negative electrode was added. As compared with the nonaqueous electrolyte secondary battery of Example 2 in which vinylene carbonate VC that forms a film on the negative electrode was not added, the capacity remaining rate after storage under high temperature conditions and the initial charge / discharge efficiency were improved. This is considered to be because a film was formed on the surface of the negative electrode by the vinylene carbonate VC, and the decomposition of the LiBF 4 on the surface of the negative electrode was suppressed by this film.
なお、ＬｉＢＦ4を添加させていない非水電解液を用いた比較例１，１２の非水電解質
二次電池においては、非水電解液に負極に被膜を形成するビニレンカーボネートＶＣを添加させていない場合と添加させた場合とにおいて、高温条件下での保存後の容量残存率や初期充放電効率が殆ど変化しておらず、負極に被膜を形成するビニレンカーボネートＶＣを非水電解液に添加させた効果は得られなかった。
In the non-aqueous electrolyte secondary batteries of Comparative Examples 1 and 12 using the non-aqueous electrolyte not added with LiBF 4 , vinylene carbonate VC that forms a film on the negative electrode is not added to the non-aqueous electrolyte. In both cases, the capacity remaining rate after storage under high temperature conditions and the initial charge / discharge efficiency hardly change, and vinylene carbonate VC that forms a film on the negative electrode is added to the non-aqueous electrolyte. The effect was not obtained.
（実施例９，１０）
実施例９，１０においては、上記の実施例２に示すように、ＬｉＰＦ6を１ｍｏｌ／ｌ
の割合で溶解させた非水電解液にＬｉＢＦ4を３．０重量％添加させたものを使用すると
共に、上記の実施例１において使用したセパレータを変更し、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を作製した。
(Examples 9 and 10)
In Examples 9 and 10, as shown in Example 2 above, LiPF 6 was added at 1 mol / l.
Together to use those obtained by adding LiBF 4 in the non-aqueous electrolyte prepared by dissolving in a proportion of 3.0 wt%, and change the separator used in Example 1 above, except that, in Example 1 In the same manner as described above, a non-aqueous electrolyte secondary battery designed to have an end-of-charge voltage of 4.40 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.50 V) was produced.
そして、セパレータとして、実施例９においては厚みｘが１２μｍ、空孔率ｙが３８％で、空孔体積ｘ・ｙが４５６μｍ・％になったポリプロピレン製の微多孔膜を、実施例１０においては厚みｘが２３μｍ、空孔率ｙが４８％で、空孔体積ｘ・ｙが１１０４μｍ・％になったポリプロピレン製の微多孔膜を用いた。 As a separator, in Example 9, a microporous membrane made of polypropylene having a thickness x of 12 μm, a porosity y of 38%, and a pore volume x · y of 456 μm ·% is used in Example 10. A polypropylene microporous membrane having a thickness x of 23 μm, a porosity y of 48%, and a pore volume x · y of 1104 μm ·% was used.
（比較例１３〜１６）
比較例１３〜１６においては、上記の比較例１の場合と同様に、非水電解液にＬｉＢＦ4を添加させないようにすると共に、上記の実施例１において使用したセパレータを変更
し、それ以外は、実施例１の場合と同様にして、充電終止電圧が４．４０Ｖ（リチウム参照極電位［ｖｓ.Ｌｉ／Ｌｉ+］４．５０Ｖに相当）になるように設計した非水電解質二次電池を作製した。
(Comparative Examples 13 to 16)
In Comparative Examples 13 to 16, as in the case of Comparative Example 1 above, LiBF 4 was not added to the non-aqueous electrolyte, and the separator used in Example 1 was changed. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery designed to have a charge end voltage of 4.40 V (corresponding to a lithium reference electrode potential [vs. Li / Li + ] 4.50 V) Produced.
そして、セパレータとして、比較例１３においては厚みｘが１２μｍ、空孔率ｙが３８％で、空孔体積ｘ・ｙが４５６μｍ・％になったポリプロピレン製の微多孔膜を、比較例１４においては厚みｘが１８μｍ、空孔率ｙが４５％で、空孔体積ｘ・ｙが８１０μｍ・％になったポリプロピレン製の微多孔膜を、比較例１５においては厚みｘが２３μｍ、空孔率ｙが４８％で、空孔体積ｘ・ｙが１１０４μｍ・％になったポリプロピレン製の微多孔膜を、比較例１６においては厚みｘが２７μｍ、空孔率ｙが５２％で、空孔体積ｘ・ｙが１４０４μｍ・％になったポリプロピレン製の微多孔膜を用いた。 As a separator, a microporous membrane made of polypropylene having a thickness x of 12 μm, a porosity y of 38%, and a pore volume x · y of 456 μm ·% in Comparative Example 13 is used. A polypropylene microporous film having a thickness x of 18 μm, a porosity y of 45%, and a pore volume x · y of 810 μm ·%, in Comparative Example 15, the thickness x is 23 μm and the porosity y is A microporous membrane made of polypropylene having a pore volume x · y of 1104 μm ·% at 48%, in Comparative Example 16, has a thickness x of 27 μm, a porosity y of 52%, and a pore volume x · y A microporous membrane made of polypropylene having a thickness of 1404 μm ·% was used.
そして、上記のようにして作製した実施例９，１０及び比較例１３〜１６の各非水電解質二次電池についても、上記の実施例２及び比較例１の非水電解質二次電池の場合と同様にして、高温条件下における保存後の容量残存率（％）を求め、これらの結果を下記の表６及び図５に示した。 And about each nonaqueous electrolyte secondary battery of Examples 9 and 10 and Comparative Examples 13-16 produced as mentioned above, the case of the nonaqueous electrolyte secondary battery of said Example 2 and Comparative Example 1 and Similarly, the capacity remaining rate (%) after storage under high temperature conditions was determined, and these results are shown in Table 6 and FIG.
この結果、ＬｉＢＦ4を添加させていない非水電解液を使用した比較例１，１３〜１６
の非水電解質二次電池においては、セパレータの空孔体積ｘ・ｙが８００μｍ・％以下になると、高温条件下における保存後の容量残存率が急激に低下した。
As a result, Comparative Examples 1, 13 to 16 using a nonaqueous electrolytic solution to which LiBF 4 was not added.
In the nonaqueous electrolyte secondary battery, when the pore volume x · y of the separator was 800 μm ·% or less, the capacity remaining rate after storage under high temperature conditions rapidly decreased.
これに対して、ＬｉＢＦ4を添加させた非水電解液を使用した実施例２，９，１０の非
水電解質二次電池においては、セパレータの空孔体積ｘ・ｙが変化しても高温条件下における保存後の容量残存率の変化は少なく、セパレータの空孔体積ｘ・ｙが８００μｍ・％以下になった場合においても、高い保存後の容量残存率が得られた。
On the other hand, in the non-aqueous electrolyte secondary batteries of Examples 2, 9, and 10 using the non-aqueous electrolyte to which LiBF 4 was added, the high temperature condition was maintained even when the pore volume x · y of the separator changed. There was little change in the capacity remaining rate after storage below, and even when the pore volume x · y of the separator was 800 μm ·% or less, a high capacity remaining rate after storage was obtained.
このため、ＬｉＢＦ4を添加させた非水電解液を使用した実施例の非水電解質二次電池
においては、電池の容量密度を高めるために、セパレータの厚みを薄くした場合においても、高温条件下において高い保存後の容量残存率が得られることが分かった。
For this reason, in the non-aqueous electrolyte secondary battery of the example using the non-aqueous electrolyte to which LiBF 4 is added, in order to increase the capacity density of the battery, even when the separator is thin, It was found that a high capacity retention rate after storage was obtained.
１ 正極活物質粒子
２ 導電剤とバインダーとの混合物
１０ 扁平電極体
１１ 正極
１１ａ 正極リード端子
１２ 負極
１２ａ 負極リード端子
１３ セパレータ
２０ 電池容器
DESCRIPTION OF
Claims (10)
極電位に対して４．４０Ｖ以上まで充電させることを特徴とする非水電解質二次電池。 In a non-aqueous electrolyte secondary battery including a positive electrode including a positive electrode active material, a conductive agent, and a binder, a negative electrode, a separator, and a non-aqueous electrolyte, the entire surface of the positive electrode active material is coated with the conductive agent. In addition, a separator that satisfies the condition of x · y ≦ 1500 (μm ·%) when the thickness is x (μm) and the porosity is y (%) is used. A nonaqueous electrolyte secondary battery comprising: a nonaqueous electrolyte solution to which LiBF 4 is added; and the positive electrode is charged to 4.40 V or more with respect to a lithium reference electrode potential.
次電池。 The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein LiBF 4 is added to the nonaqueous electrolyte in a range of 0.1 to 5.0 wt%. Water electrolyte secondary battery.
る非水電解質二次電池。 The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolyte contains LiPF 6 in a range of 0.6 to 2.0 mol / l. A non-aqueous electrolyte secondary battery.
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