JP2011258564A - Nonaqueous electrolyte secondary battery - Google Patents
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Abstract
Description
本発明は、コバルト酸リチウムを正極活物質として含む非水電解質二次電池に関するものである。
The present invention relates to a non-aqueous electrolyte secondary battery containing lithium cobalt oxide as a positive electrode active material.
近年、金属リチウムまたはリチウムイオンを吸蔵・放出し得る合金、もしくは炭素材料などを負極活物質とし、化学式：ＬｉＭＯ２（ＭＯは遷移金属）で表されるリチウム遷移金属複合酸化物を正極材料とする非水電解質二次電池が、高エネルギー密度を有する電池として注目されている。
In recent years, metallic lithium or an alloy capable of inserting and extracting lithium ions, or a carbon material is used as a negative electrode active material, and a lithium transition metal composite oxide represented by a chemical formula: LiMO 2 (MO is a transition metal) is used as a positive electrode material. Nonaqueous electrolyte secondary batteries are attracting attention as batteries having a high energy density.
上記リチウム遷移金属複合酸化物の例としては、コバルト酸リチウム（ＬｉＣｏＯ２）が代表的なものとして挙げられ、既に非水電解質二次電池の正極活物質として実用化されている。コバルト酸リチウムなどのリチウム遷移金属複合酸化物を正極活物質として用い、黒鉛などの炭素材料を負極活物質として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４．１〜４．２Ｖとしている。この場合、正極活物質は、その理論容量に対して５０〜６０％しか利用されていない。従って、充電終止電圧をより高くすれば、正極の容量（利用率）を向上させることができ、容量及びエネルギー密度を高めることができる。
A typical example of the lithium transition metal composite oxide is lithium cobaltate (LiCoO 2 ), which has already been put into practical use as a positive electrode active material for non-aqueous electrolyte secondary batteries. In a non-aqueous electrolyte secondary battery using a lithium transition metal composite oxide such as lithium cobaltate as a positive electrode active material and a carbon material such as graphite as a negative electrode active material, generally the end-of-charge voltage is 4.1 to 4. .2V. In this case, only 50 to 60% of the positive electrode active material is used with respect to its theoretical capacity. Therefore, if the charge end voltage is further increased, the capacity (utilization rate) of the positive electrode can be improved, and the capacity and energy density can be increased.
しかしながら、電池の充電終止電圧を高めると、ＬｉＣｏＯ２の構造劣化及び正極表面における電解液の分解等が生じ易くなる。特に、充電状態において高温下に保存した場合、正極と電解液との反応により生じるガスに起因する電池厚みの増加や、反応生成物による抵抗の増加、または正極材料の崩壊などにより、充放電特性の劣化が生じるという問題があった。
However, when the end-of-charge voltage of the battery is increased, the structural deterioration of LiCoO 2 and the decomposition of the electrolytic solution on the positive electrode surface tend to occur. In particular, when stored under high temperature in the charged state, the charge / discharge characteristics are increased due to the increase in battery thickness due to the gas generated by the reaction between the positive electrode and the electrolyte, the increase in resistance due to the reaction product, or the collapse of the positive electrode material. There was a problem that deterioration of the product occurred.
正極活物質としてコバルト酸リチウムを用い、負極活物質として黒鉛材料を用いた非水電解質二次電池において、特許文献１では、充電状態における高温保存特性を改善するため、電解液中にアルキルエステル等のエステル基を有する化合物を含有させることが提案されている。
In a non-aqueous electrolyte secondary battery using lithium cobaltate as a positive electrode active material and a graphite material as a negative electrode active material, Patent Document 1 discloses an alkyl ester or the like in an electrolytic solution in order to improve high-temperature storage characteristics in a charged state. It has been proposed to include a compound having an ester group.
しかしながら、電池の充電電圧を従来の４．２Ｖよりも高くした場合（すなわち正極の充電電位をリチウム基準で４．３Ｖ（以下、４．３Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）と記載する）より高くした場合）、電解液にエステル基を有する化合物を添加しても、充電状態での高温保存による電池の膨化や電池性能の低下が大きくなり、十分な改善は得られなかった。
However, when the charging voltage of the battery is higher than the conventional 4.2V (that is, the charging potential of the positive electrode is higher than 4.3V (hereinafter referred to as 4.3V (vs. Li / Li + ) on the basis of lithium)). In this case, even when a compound having an ester group was added to the electrolytic solution, the battery expanded due to high-temperature storage in a charged state and the battery performance decreased, and sufficient improvement could not be obtained.
本発明の目的は、コバルト酸リチウムを正極活物質として含み、正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電される非水電解質二次電池において、充電保存特性に優れた非水電解質二次電池を提供することにある。
An object of the present invention is to provide a non-aqueous electrolyte secondary battery that includes lithium cobaltate as a positive electrode active material and is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ). The object is to provide a non-aqueous electrolyte secondary battery having excellent storage characteristics.
本発明は、正極活物質を含む正極と、金属リチウム以外の負極活物質を含む負極と、非水電解質とを備える非水電解質二次電池において、
前記正極活物質の主剤としてコバルト酸リチウムを含み、前記非水電解質に、前記正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ ＋ ）に達するまで充電した際に分解されるエーテル基を有する化合物が０．１〜１０体積％含有されており、前記正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電した際の前記正極に対する負極の充電容量比が１．０〜１．２となるように前記正極活物質及び前記負極活物質が含まれていることを特徴としている。
The present invention provides a nonaqueous electrolyte secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material other than metallic lithium, and a nonaqueous electrolyte.
Ether containing lithium cobaltate as a main component of the positive electrode active material, and decomposed when the nonaqueous electrolyte is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ). 0.1 to 10% by volume of a compound having a group, and charging of the negative electrode with respect to the positive electrode when charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ) The positive electrode active material and the negative electrode active material are contained so that a capacity ratio is 1.0 to 1.2.
コバルト酸リチウムを正極活物質として含む非水電解質二次電池において、充電状態で高温保存した際に、電池の厚み増加や容量の低下が生じるのは、充電により酸化状態が高くなった活物質中のコバルトの触媒作用により、電解液の分解や、セパレータの目詰まり、負極上への副生成物の堆積による放電性の低下が生じるためであると考えられる。
In a non-aqueous electrolyte secondary battery containing lithium cobalt oxide as a positive electrode active material, when it is stored at a high temperature in a charged state, the thickness of the battery increases or the capacity decreases. This is considered to be because the catalytic action of cobalt causes degradation of the electrolytic solution, clogging of the separator, and deterioration of dischargeability due to deposition of by-products on the negative electrode.
正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電される非水電解質二次電池において、本発明に従い、エーテル基を有する化合物を非水電解質中に所定量含有させておくことにより、上記のような高温保存した際の電池の厚み増加や、容量低下を抑制することができる。本発明に従い、エーテル基を有する化合物を非水電解質に含有させておくことにより、このような効果が得られる理由の詳細については明らかではないが、従来よりも高い充電電圧で初回の充電がなされる際に、非水電解質中に含有されるエーテル基を有する化合物が分解し、正極活物質の表面に炭素及び酸素を有する被膜が形成され、正極と非水電解質との副反応が抑制されるためであると推測される。このような効果は、同じ炭素及び酸素を含む化合物であっても、エステル基を有するような化合物では得ることができない。
In a non-aqueous electrolyte secondary battery that is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ), according to the present invention, a predetermined amount of a compound having an ether group is contained in the non-aqueous electrolyte. By containing, it is possible to suppress an increase in battery thickness and a decrease in capacity when stored at a high temperature as described above. According to the present invention, the details of the reason why such an effect can be obtained by adding a compound having an ether group to the non-aqueous electrolyte is not clear, but the first charge is performed at a higher charging voltage than before. In this case, the compound having an ether group contained in the non-aqueous electrolyte is decomposed to form a film containing carbon and oxygen on the surface of the positive electrode active material, and side reactions between the positive electrode and the non-aqueous electrolyte are suppressed. This is presumed. Such an effect cannot be obtained with a compound having an ester group even if the compound contains the same carbon and oxygen.
また、エーテル基を有する化合物は、現在溶媒として使用されているカーボネート化合物に比較して、蒸気圧が高く、また酸化分解電位が低く、アノード酸化を受け易いため、コバルト酸リチウム等の高い電池反応電位を有する材料を正極活物質として使用する二次電池では、溶媒として用いることは不適切であるとされている。しかしながら、本発明のように、正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電される非水電解質二次電池においては、本発明に従い、エーテル基を有する化合物を非水電解質に所定量含有させておくことにより、充電保存特性を改善することができる。
In addition, a compound having an ether group has a higher vapor pressure, a lower oxidative decomposition potential, and is more susceptible to anodic oxidation than a carbonate compound currently used as a solvent. In a secondary battery that uses a material having a potential as a positive electrode active material, it is considered inappropriate to use it as a solvent. However, as in the present invention, a nonaqueous electrolyte secondary battery that is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ) has an ether group according to the present invention. By storing the compound in a predetermined amount in the non-aqueous electrolyte, the charge storage characteristics can be improved.
本発明において、コバルト酸リチウムは、正極活物質の主剤として含有されており、正極活物質として６０重量％以上含まれていることが好ましい。また、本発明におけるコバルト酸リチウムには、ジルコニウム及びマグネシウムが含まれていることが好ましい。コバルト酸リチウム中に含まれるジルコニウムの量は、遷移金属中０．０１〜２．０モル％の範囲であることが好ましい。また、マグネシウムの含有量は、０．１〜２．０モル％の範囲であることが好ましい。これらの元素の量が少な過ぎると、容量低下を抑制する効果が十分に得られない場合がある。また、これらの元素が多過ぎると、正極の放電特性に悪影響を及ぼす場合がある。
In this invention, lithium cobaltate is contained as a main ingredient of a positive electrode active material, and it is preferable that 60 weight% or more is contained as a positive electrode active material. Moreover, it is preferable that the zirconium cobaltate in this invention contains zirconium and magnesium. The amount of zirconium contained in lithium cobaltate is preferably in the range of 0.01 to 2.0 mol% in the transition metal. Moreover, it is preferable that content of magnesium is the range of 0.1-2.0 mol%. If the amount of these elements is too small, the effect of suppressing the decrease in capacity may not be sufficiently obtained. Moreover, when there are too many of these elements, it may have a bad influence on the discharge characteristic of a positive electrode.
また、ジルコニウム（Ｚｒ）は、コバルト酸リチウムの表面に粒子の状態で焼結して付着していることが好ましい。Ｚｒ含有化合物が、コバルト酸リチウムの表面に付着することにより、充放電時のコバルト酸リチウムの表面でのリチウムイオン及び電子の授受を容易にし、電解液の酸化分解を抑制することができるものと考えられる。
Zirconium (Zr) is preferably adhered to the surface of lithium cobaltate by sintering in the form of particles. The Zr-containing compound adheres to the surface of the lithium cobalt oxide, thereby facilitating the transfer of lithium ions and electrons on the surface of the lithium cobalt oxide during charging and discharging, and suppressing the oxidative decomposition of the electrolyte. Conceivable.
また、マグネシウム（Ｍｇ）は、コバルト酸リチウムの表面のＺｒ含有化合物と、コバルト酸リチウム内の両方に存在していることが確認されており、これらの両方にＭｇが拡散することにより、Ｚｒ含有化合物とコバルト酸リチウムとが強固に焼結されることが確認されている。従って、Ｍｇを添加することにより、Ｚｒ含有化合物とコバルト酸リチウムの接合状態が強くなり、電解液の分解を抑制する効果が大幅に向上するものと考えられる。
Further, it has been confirmed that magnesium (Mg) exists in both the Zr-containing compound on the surface of lithium cobaltate and the lithium cobaltate, and Mg diffuses in both of these so It has been confirmed that the compound and lithium cobaltate are strongly sintered. Therefore, it is considered that by adding Mg, the bonding state between the Zr-containing compound and lithium cobalt oxide becomes strong, and the effect of suppressing the decomposition of the electrolytic solution is greatly improved.
本発明において用いるコバルト酸リチウムは、化学式ＬｉａＣｏ１−ｘ−ｙ−ｚＺｒｘＭｇｙＭｚＯ２（ＭはＡｌ、Ｔｉ、及びＳｎから選ばれる少なくとも１つの元素、０≦ａ≦１．１、ｘ＞０、ｙ＞０、ｚ≧０、０＜ｚ＋ｙ＋ｚ≦０．０３を満たす。）で表されるものであることが好ましい。
The lithium cobalt oxide used in the present invention has a chemical formula Li a Co 1-xyz Zr x Mg y M z O 2 (M is at least one element selected from Al, Ti, and Sn, 0 ≦ a ≦ 1 0.1, x> 0, y> 0, z ≧ 0, 0 <z + y + z ≦ 0.03).
本発明において非水電解質に含有されるエーテル基を含む化合物としては、ジエチルエーテルやテトラヒドロフラン等が挙げられる。これらのエーテル基を含む化合物は、低沸点（ジエチルエーテルの沸点：３４．５℃、テトラヒドロフランの沸点：６６℃）であるにもかかわらず、エーテル基を含む化合物を含有しない電池と比較して高温保存時における電池膨化が抑制されている。従って、上述のように、非水電解質中に添加したエーテル基を含む化合物は、保存前すなわち初回の充電時にそのほとんどが分解されているものと考えられる。
In the present invention, examples of the compound containing an ether group contained in the nonaqueous electrolyte include diethyl ether and tetrahydrofuran. Although these compounds containing ether groups have a low boiling point (boiling point of diethyl ether: 34.5 ° C., boiling point of tetrahydrofuran: 66 ° C.), they are higher in temperature than batteries not containing compounds containing ether groups. The expansion of the battery during storage is suppressed. Therefore, as described above, it is considered that most of the compound containing an ether group added to the nonaqueous electrolyte is decomposed before storage, that is, at the first charge.
エーテル基を有する化合物の非水電解質中の含有量は０．１〜１０体積％である。より好ましい含有量は、エーテル基を有する化合物の種類によって異なる。例えば、ジエチルエーテルの場合、１〜１０体積％であることが好ましく、テトラヒドロフランの場合、０．１〜１体積％であることが好ましい。エーテル基を有する化合物の含有量が少な過ぎると、電池膨化及び容量低下を抑制する効果が十分に得られず、また含有量が多過ぎると、正極表面上に形成される被膜が多くなり過ぎ、電池性能に悪影響を及ぼす場合がある。
The content of the compound having an ether group in the nonaqueous electrolyte is 0.1 to 10% by volume. The more preferable content varies depending on the type of the compound having an ether group. For example, in the case of diethyl ether, it is preferably 1 to 10% by volume, and in the case of tetrahydrofuran, it is preferably 0.1 to 1% by volume. When the content of the compound having an ether group is too small, the effect of suppressing battery expansion and capacity reduction cannot be sufficiently obtained, and when the content is too large, the film formed on the surface of the positive electrode is too much, Battery performance may be adversely affected.
本発明において用いるエーテル基を有する化合物としては、炭化水素鎖を有する化合物が好ましく、例えば、ジエチルエーテル、エチルメチルエーテル、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、トリエチレングリコールジメチルエーテル、テトラエチレングリコールジメチルエーテル、エチレングリコールジエチルエーテル、１，４−ジオキサン、テトラヒドロフラン、２−メチルテトラヒドロフラン、１２−クラウン−４−エーテル、及び１５−クラウン−５−エーテルなどが挙げられる。これらの中でも、特に、ジエチルエーテル、２−メチルテトラヒドロフラン、テトラヒドロフラン、ジエチレングリコールジメチルエーテル、１、４−ジオキサン、１２−クラウン−４−エーテル、及び１５−クラウン−５−エーテルからなるグループより選ばれる少なくとも１種であることが好ましい。
The compound having an ether group used in the present invention is preferably a compound having a hydrocarbon chain, for example, diethyl ether, ethyl methyl ether, dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether. 1,4-dioxane , tetrahydrofuran, 2-methyltetrahydrofuran, 12-crown-4-ether, 15-crown-5-ether and the like. Among these, in particular, at least one selected from the group consisting of diethyl ether, 2-methyltetrahydrofuran, tetrahydrofuran, diethylene glycol dimethyl ether, 1,4-dioxane, 12-crown-4-ether, and 15-crown-5-ether. It is preferable that
本発明においては、非水電解質中に、さらにビニレンカーボネートが０．５〜４重量％含有されていることが好ましい。ビニレンカーボネートが分解して負極表面上に被膜を形成することにより、充電状態での高温保存時における負極と電解液との反応を抑制することができるからである。また、同様の理由により、非水電解質に用いる溶媒として、エチレンカーボネートが含まれていることが好ましい。
In the present invention, it is preferable that 0.5 to 4% by weight of vinylene carbonate is further contained in the nonaqueous electrolyte. This is because vinylene carbonate is decomposed to form a film on the surface of the negative electrode, whereby the reaction between the negative electrode and the electrolytic solution during high-temperature storage in a charged state can be suppressed. For the same reason, it is preferable that ethylene carbonate is contained as a solvent used for the non-aqueous electrolyte.
本発明において用いる非水電解質の溶媒としては、エチレンカーボネート、プロピレンカーボネートなどの環状カーボネートと、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の混合溶媒が一般的に用いられる。特に、本発明においては、鎖状カーボネートとしてジエチルカーボネートが含有されていることが好ましい。ジエチルカーボネートを含有させることにより、高充電状態及び高温下における電解液の酸化分解の反応をより抑制することができる。ジエチルカーボネートの含有量としては、１０〜７０体積％の範囲内であることが好ましい。
As the nonaqueous electrolyte solvent used in the present invention, a mixed solvent of a cyclic carbonate such as ethylene carbonate or propylene carbonate and a chain carbonate such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate is generally used. In particular, in the present invention, it is preferable that diethyl carbonate is contained as the chain carbonate. By containing diethyl carbonate, it is possible to further suppress the oxidative decomposition reaction of the electrolytic solution in a highly charged state and at a high temperature. The content of diethyl carbonate is preferably in the range of 10 to 70% by volume.
本発明における負極活物質としては、黒鉛材料が好ましく用いられる。上記のビニレンカーボネートは、このような黒鉛材料の表面に良好な被膜を形成させることができる。
As the negative electrode active material in the present invention, a graphite material is preferably used. The above-mentioned vinylene carbonate can form a good film on the surface of such a graphite material.
本発明において用いる非水電解質の溶質としては、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ２ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＮ（Ｃ２Ｆ５ＳＯ２）２、ＬｉＮ（ＣＦ３ＳＯ２）（Ｃ４Ｆ９ＳＯ２）、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣ（Ｃ２Ｆ５ＳＯ２）３、ＬｉＡｓＦ６、ＬｉＣｌＯ４、Ｌｉ２Ｂ１０Ｃｌ１０、Ｌｉ２Ｂ１２Ｃｌ１２など及びそれらの混合物が例示される。これらの中でも、ＬｉＰＦ６（ヘキサフルオロリン酸リチウム）が好ましく用いられる。
As the solute of the non-aqueous electrolyte used in the present invention, LiPF 6 , LiBF 4 , LiCF 2 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 and the like A mixture thereof is exemplified. Among these, LiPF 6 (lithium hexafluorophosphate) is preferably used.
本発明においては、上述のように、正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電した際の正極に対する負極の充電容量比（負極充電容量／正極充電容量）が１．０〜１．２となるように正極活物質及び負極活物質が含まれる。この充電容量比は、正極と負極の対向する部分での充電容量比である。このように正極と負極の充電容量比を１．０以上に設定しておくことにより、負極表面に金属リチウムが析出するのを防止することができる。また、１．２以下に設定しておくことにより、過剰量の負極活物質により、エネルギー密度が低下しないようにすることができる。負極活物質として黒鉛材料を用いた場合には、充電終止電圧は４．３〜４．４Ｖとなるように設定される。充電終止電圧が４．４Ｖより高くなると、電解液の分解や正極の崩壊の抑制効果が十分でなくなるため、充電終止電圧は４．４Ｖ以下であることが好ましい。
In the present invention, as described above, the charge capacity ratio of the negative electrode to the positive electrode (negative electrode charge capacity / positive electrode charge) when charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ). The positive electrode active material and the negative electrode active material are included so that (capacity) is 1.0 to 1.2. This charge capacity ratio is a charge capacity ratio at a portion where the positive electrode and the negative electrode face each other. Thus, by setting the charge capacity ratio of the positive electrode and the negative electrode to 1.0 or more, it is possible to prevent metallic lithium from being deposited on the negative electrode surface. Moreover, by setting it to 1.2 or less, it is possible to prevent the energy density from being lowered by an excessive amount of the negative electrode active material. When a graphite material is used as the negative electrode active material, the end-of-charge voltage is set to be 4.3 to 4.4V. When the end-of-charge voltage is higher than 4.4V, the effect of suppressing the decomposition of the electrolyte and the collapse of the positive electrode is not sufficient, so the end-of-charge voltage is preferably 4.4V or less.
本発明によれば、コバルト酸リチウムを正極活物質として含み、正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電される非水電解質二次電池において、充電保存特性を大幅に改善することができる。
According to the present invention, in a non-aqueous electrolyte secondary battery that includes lithium cobalt oxide as a positive electrode active material and is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ), Storage characteristics can be greatly improved.
以下、本発明を実施例に基づき、さらに詳細に説明するが、本発明は以下の実施例に何ら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することが可能なものである。
Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. Is.
（実施例１）
〔正極活物質の作製〕
Ｌｉ２ＣＯ３とＣｏ３Ｏ４とＺｒＯ２とＭｇＯを、Ｌｉ：Ｃｏ：Ｚｒ：Ｍｇのモル比が１：０．９９３：０．００２：０．００５となるようにして石川式らいかい乳鉢にて混合した後、空気雰囲気中にて８５０℃で２０時間熱処理後に粉砕することにより、平均粒子径が約６．４μｍのコバルト酸リチウムを得た。ＢＥＴ比表面積は０．４２ｍ２／ｇであった。
Example 1
[Preparation of positive electrode active material]
Li 2 CO 3 , Co 3 O 4 , ZrO 2 and MgO with a molar ratio of Li: Co: Zr: Mg of 1: 0.993: 0.002: 0.005 Then, the mixture was pulverized after heat treatment at 850 ° C. for 20 hours in an air atmosphere to obtain lithium cobalt oxide having an average particle size of about 6.4 μm. The BET specific surface area was 0.42 m 2 / g.
〔正極の作製〕
以上のようにして得た正極活物質に、導電剤としての炭素と、結着剤としてのポリフッ化ビニリデンと、分散媒としてのＮ−メチル−２−ピロリドンを、活物質と導電剤と結着剤の重量比が９０：５：５の比率になるようにして加えた後に混練して、正極スラリーを作製した。作製したスラリーを集電体としてのアルミニウム箔上に塗布した後、乾燥し、その後圧延ローラーを用いて圧延し、集電タブを取り付けることで、正極を作製した。
[Production of positive electrode]
To the positive electrode active material obtained as described above, carbon as a conductive agent, polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone as a dispersion medium are bound to the active material and the conductive agent. After adding the agent so that the weight ratio of the agent was 90: 5: 5, the mixture was kneaded to prepare a positive electrode slurry. After apply | coating the produced slurry on the aluminum foil as a collector, it dried, it rolled using the rolling roller after that, and the positive electrode was produced by attaching a current collection tab.
〔負極の作製〕
増粘剤であるカルボキシメチルセルロースを水に溶かした水溶液中に、負極活物質として人造黒鉛と、結着剤としてのスチレン−ブタジエンゴムとを、活物質と結着剤と増粘剤の重量比が９５：３：２の比率になるようにして加えた後に混練して、負極スラリーを作製した。作製したスラリーを集電体としての銅箔上に塗布した後、乾燥し、その後圧延ローラーを用いて圧延し、集電タブを取り付けることで、負極を作製した。
(Production of negative electrode)
In an aqueous solution in which carboxymethyl cellulose, a thickener, is dissolved in water, artificial graphite as a negative electrode active material and styrene-butadiene rubber as a binder, the weight ratio of the active material, the binder, and the thickener is The mixture was added in a ratio of 95: 3: 2, and then kneaded to prepare a negative electrode slurry. After apply | coating the produced slurry on the copper foil as a collector, it dried and then rolled using the rolling roller, and the negative electrode was produced by attaching a current collection tab.
〔電解液の作製〕
エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）とを体積比３：７で混合した溶媒に対し、ヘキサフルオロリン酸リチウム（ＬｉＰＦ６）を、濃度が１モル／リットルとなるように溶解し、さらにビニレンカーボネート（ＶＣ）を電解液に対し、２．０重量％、ジエチルエーテルを１．０体積％となるように添加して、電解液を作製した。
(Preparation of electrolyte)
In a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7, lithium hexafluorophosphate (LiPF 6 ) is dissolved so as to have a concentration of 1 mol / liter, and Vinylene carbonate (VC) was added to the electrolytic solution so as to be 2.0% by weight and diethyl ether to 1.0% by volume to prepare an electrolytic solution.
〔電池の作製〕
以上のようにして得た正極及び負極を、充電電圧を４．４Ｖとしたとき（正極の電位を４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）としたとき）の負極充電容量／正極充電容量比が１．０となるようにセパレータを介して対向するように巻取って巻取り体を作製し、Ａｒ雰囲気下のグローブボックス中にて、巻取り体を電解液とともにアルミニウムラミネートに封入することにより、電池規格サイズとして、厚み３．６ｍｍ×幅３．５ｃｍ×長さ６．２ｃｍの非水電解質二次電池Ａ１を得た。
[Production of battery]
Negative electrode charge capacity / positive electrode charge capacity ratio of the positive electrode and the negative electrode obtained as described above when the charging voltage is 4.4 V (when the positive electrode potential is 4.5 V (vs. Li / Li + )). Is wound so as to face each other through a separator so as to be 1.0, and the wound body is enclosed in an aluminum laminate together with an electrolytic solution in a glove box under an Ar atmosphere. As a battery standard size, a nonaqueous electrolyte secondary battery A1 having a thickness of 3.6 mm, a width of 3.5 cm, and a length of 6.2 cm was obtained.
〔充電保存特性の評価〕
作製した非水電解質二次電池を、６５０ｍＡの定電流で、電圧が４．４Ｖに達するまで充電し、さらに４．４Ｖの定電圧で電流値が３２ｍＡになるまで充電した後、６５０ｍＡの定電流で、電圧が２．７５Ｖに達するまで放電することにより、電池の保存前放電容量（ｍＡｈ）を測定した。
[Evaluation of charge storage characteristics]
The produced nonaqueous electrolyte secondary battery was charged at a constant current of 650 mA until the voltage reached 4.4 V, and further charged at a constant voltage of 4.4 V until the current value reached 32 mA, and then a constant current of 650 mA. Then, the discharge capacity before storage (mAh) of the battery was measured by discharging until the voltage reached 2.75V.
さらに、当該電池を上記の方法で４．４Ｖまで充電し、保存前電池厚みを測定した。
Furthermore, the said battery was charged to 4.4V by said method, and the battery thickness before a preservation | save was measured.
６０℃に昇温した恒温槽中で５日間保存した後取り出し、十分に冷却した後の電池厚みを測定した。充電保存後の電池厚みと充電保存前の電池厚みの差を、充電保存前の電池厚みで割って得た値を電池膨化率とした。
After storing for 5 days in a thermostatic chamber heated to 60 ° C., the battery thickness after taking out and sufficiently cooling was measured. The value obtained by dividing the difference between the battery thickness after storage by charge and the battery thickness before storage by charge by the battery thickness before storage by charge was defined as the battery expansion rate.
冷却後の電池を、６５０ｍＡの定電流で、電圧が２．７５Ｖに低下するまで放電することにより、電池の保存後放電容量（ｍＡｈ）を評価した。充電保存後に放電した放電容量を残存容量とし、保存前の放電容量で割った得た値を容量残存率とした。
The discharged battery (mAh) after storage was evaluated by discharging the cooled battery at a constant current of 650 mA until the voltage dropped to 2.75V. The discharge capacity discharged after storage was defined as the remaining capacity, and the value obtained by dividing by the discharge capacity before storage was defined as the capacity remaining rate.
表１に上記電池膨化率と容量残存率を示す。
Table 1 shows the battery expansion rate and capacity remaining rate.
（実施例２）
電解液の作製において、ジエチルエーテルを電解液に対し２．０体積％添加したこと以外は実施例１と同様にして、電解液を作製した。
(Example 2)
In the production of the electrolytic solution, an electrolytic solution was produced in the same manner as in Example 1 except that 2.0% by volume of diethyl ether was added to the electrolytic solution.
実施例１と同様にして非水電解質二次電池Ａ２を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A2 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例３）
電解液の作製において、添加化合物ジエチルエーテルの添加量を５．０体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 3)
In the preparation of the electrolytic solution, an electrolytic solution was prepared in the same manner as in Example 1 except that the addition amount of the additive compound diethyl ether was 5.0% by volume.
実施例１と同様にして非水電解質二次電池Ａ３を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A3 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例４）
電解液の作製において、添加化合物ジエチルエーテルの添加量を１０．０体積％としたこと以外は実施例１と同様にして、電解液を作製した。
Example 4
In the preparation of the electrolytic solution, an electrolytic solution was prepared in the same manner as in Example 1 except that the addition amount of the additive compound diethyl ether was 10.0% by volume.
実施例１と同様にして非水電解質二次電池Ａ４を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A4 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例５）
電解液の作製において、添加化合物をジエチルエーテルの代わりに２−メチル−テトラヒドロフラン（２Ｍｅ−ＴＨＦ）０．１体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 5)
An electrolyte solution was prepared in the same manner as in Example 1 except that the additive compound was changed to 0.1% by volume of 2-methyl-tetrahydrofuran (2Me-THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ５を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A5 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例６）
電解液の作製において、添加化合物をジエチルエーテルの代わりに２−メチル−テトラヒドロフラン（２Ｍｅ−ＴＨＦ）０．５体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 6)
An electrolyte solution was prepared in the same manner as in Example 1 except that the additive compound was changed to 0.5% by volume of 2-methyl-tetrahydrofuran (2Me-THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ６を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A6 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例７）
電解液の作製において、添加化合物をジエチルエーテルの代わりに２−メチル−テトラヒドロフラン（２Ｍｅ−ＴＨＦ）１．０体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 7)
An electrolyte solution was prepared in the same manner as in Example 1 except that the additive compound was 1.0% by volume of 2-methyl-tetrahydrofuran (2Me-THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ７を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A7 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例８）
電解液の作製において、添加化合物をジエチルエーテルの代わりにテトラヒドロフラン（ＴＨＦ）０．１体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 8)
In preparing the electrolytic solution, an electrolytic solution was prepared in the same manner as in Example 1 except that the additive compound was changed to 0.1% by volume of tetrahydrofuran (THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ８を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A8 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例９）
電解液の作製において、添加化合物をジエチルエーテルの代わりにテトラヒドロフラン（ＴＨＦ）０．５体積％としたこと以外は実施例１と同様にして、電解液を作製した。
Example 9
In the preparation of the electrolytic solution, an electrolytic solution was prepared in the same manner as in Example 1 except that the additive compound was 0.5% by volume of tetrahydrofuran (THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ９を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A9 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例１０）
電解液の作製において、添加化合物をジエチルエーテルの代わりにテトラヒドロフラン（ＴＨＦ）１．０体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 10)
An electrolyte solution was prepared in the same manner as in Example 1 except that the additive compound was 1.0% by volume of tetrahydrofuran (THF) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ１０を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A10 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例１１）
電解液の作製において、添加化合物をジエチルエーテルの代わりに１，４−ジオキサン（１，４−ＤＯ）１．０体積％としたこと以外は実施例１と同様にして、電解液を作製した。
(Example 11)
In preparing the electrolytic solution, an electrolytic solution was prepared in the same manner as in Example 1 except that the additive compound was 1.0% by volume of 1,4-dioxane (1,4-DO) instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ１１を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A11 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例１２）
電解液の作製において、ジエチルエーテルの代わりに、ジエチレングリコールジメチルエーテル（ＤＤＥ）を電解液に対し、１．０体積％添加したこと以外は実施例１と同様にして、電解液を作製した。
(Example 12)
In the production of the electrolytic solution, an electrolytic solution was produced in the same manner as in Example 1 except that 1.0% by volume of diethylene glycol dimethyl ether (DDE) was added to the electrolytic solution instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ１２を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A12 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例１３）
電解液の作製において、ジエチルエーテルの代わりに、１２−クラウン−４−エーテルを電解液に対し、１．０体積％添加したこと以外は実施例１と同様にして、電解液を作製した。
(Example 13)
In the production of the electrolytic solution, an electrolytic solution was produced in the same manner as in Example 1 except that 12 vol% of 12-crown-4-ether was added to the electrolytic solution instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ１３を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A13 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（実施例１４）
電解液の作製において、ジエチルエーテルの代わりに、１５−クラウン−５−エーテルを電解液に対し、１．０体積％添加したこと以外は実施例１と同様にして、電解液を作製した。
(Example 14)
In the production of the electrolytic solution, an electrolytic solution was produced in the same manner as in Example 1, except that 15-crown-5-ether was added in an amount of 1.0% by volume to the electrolytic solution instead of diethyl ether.
実施例１と同様にして非水電解質二次電池Ａ１４を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery A14 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（比較例１）
電解液の作製において、添加化合物をビニレンカーボネート（ＶＣ）２重量％のみとしたこと以外は実施例１と同様にして、電解液を作製した。
(Comparative Example 1)
An electrolyte solution was prepared in the same manner as in Example 1 except that the additive compound was only 2% by weight of vinylene carbonate (VC).
実施例１と同様にして非水電解質二次電池Ｘ１を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery X1 was produced in the same manner as in Example 1, and the charge storage characteristics were evaluated.
（比較例２）
電解液の作製において、添加化合物をビニレンカーボネート（ＶＣ）２重量％、酢酸メチル１体積％としたこと以外は比較例１と同様にして、電解液を作製した。
(Comparative Example 2)
An electrolytic solution was prepared in the same manner as in Comparative Example 1 except that the additive compound was 2% by weight of vinylene carbonate (VC) and 1% by volume of methyl acetate.
比較例１と同様にして非水電解質二次電池Ｘ２を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery X2 was produced in the same manner as in Comparative Example 1, and the charge storage characteristics were evaluated.
（比較例３）
電解液の作製において、添加化合物をビニレンカーボネート（ＶＣ）２重量％、プロピオン酸エチル１体積％としたこと以外は比較例１と同様にして、電解液を作製した。
(Comparative Example 3)
In the preparation of the electrolytic solution, an electrolytic solution was prepared in the same manner as in Comparative Example 1 except that the additive compound was 2% by weight of vinylene carbonate (VC) and 1% by volume of ethyl propionate.
比較例１と同様にして非水電解質二次電池Ｘ３を作製し、充電保存特性を評価した。
A nonaqueous electrolyte secondary battery X3 was produced in the same manner as in Comparative Example 1, and the charge storage characteristics were evaluated.
上記のようにして作製した実施例１〜１４の非水電解質二次電池Ａ１〜Ａ１４、及び比較例１〜３の非水電解質二次電池Ｘ１〜Ｘ３の充電保存特性の評価結果を表１に示す。
Table 1 shows the evaluation results of the charge storage characteristics of the nonaqueous electrolyte secondary batteries A1 to A14 of Examples 1 to 14 and the nonaqueous electrolyte secondary batteries X1 to X3 of Comparative Examples 1 to 3 manufactured as described above. Show.
なお、電池膨化率及び容量残存率の値はパーセント表示とした。
In addition, the values of the battery expansion rate and the capacity remaining rate are expressed in percentage.
表１に示す結果から明らかなように、本発明に従う実施例１〜１４の電池Ａ１〜Ａ１４は、比較例１〜３の電池Ｘ１〜Ｘ３に比べ、電池膨化率が減少すると共に、優れた容量残存率を示すことがわかる。比較例２及び３においては、エステル基を有する化合物を添加しているが、エステル基を有する化合物を添加しても、本発明の効果が得られないことがわかる。
As is clear from the results shown in Table 1, the batteries A1 to A14 of Examples 1 to 14 according to the present invention have a reduced battery expansion rate and an excellent capacity compared to the batteries X1 to X3 of Comparative Examples 1 to 3. It can be seen that the residual rate is shown. In Comparative Examples 2 and 3, a compound having an ester group is added, but it is understood that the effects of the present invention cannot be obtained even if a compound having an ester group is added.
また、本発明に従う実施例１〜１４においては、電池膨化率が、比較例１〜３に比べ、小さくなっており、低沸点成分であるエーテル基を有する化合物が、初回の充電時において分解されていることが推測される。
Further, in Examples 1 to 14 according to the present invention, the battery expansion rate is smaller than those of Comparative Examples 1 to 3, and the compound having an ether group which is a low boiling point component is decomposed at the first charge. I guess that.
〔参考実験〕
（参考例１）
正極及び負極を、充電電圧を４．２Ｖとしたときの負極充電容量／正極充電容量比が１．１となるように作製し、セパレータを介して対向するように巻取ったこと以外は、実施例４と同様にして非水電解質二次電池Ｂ１を得た。
[Reference experiment]
(Reference Example 1)
Implementation was performed except that the positive electrode and the negative electrode were prepared so that the negative electrode charge capacity / positive electrode charge capacity ratio was 1.1 when the charge voltage was 4.2 V, and were wound so as to face each other via a separator. In the same manner as in Example 4, a nonaqueous electrolyte secondary battery B1 was obtained.
（参考例２）
正極及び負極を、充電電圧を４．２Ｖとしたときの負極充電容量／正極充電容量比が１．１となるように作製し、セパレータを介して対向するように巻取ったこと以外は、比較例１と同様にして非水電解質二次電池Ｙ１を得た。
(Reference Example 2)
Comparison was made except that the positive electrode and the negative electrode were manufactured so that the negative electrode charge capacity / positive electrode charge capacity ratio was 1.1 when the charge voltage was 4.2 V, and were wound so as to face each other through the separator. In the same manner as in Example 1, a nonaqueous electrolyte secondary battery Y1 was obtained.
上記のようにして作製した参考例１の非水電解質二次電池Ｂ１、及び参考例２の非水電解質二次電池Ｙ１の充電保存特性の評価結果を表２に示す。
Table 2 shows the evaluation results of the charge storage characteristics of the non-aqueous electrolyte secondary battery B1 of Reference Example 1 and the non-aqueous electrolyte secondary battery Y1 of Reference Example 2 produced as described above.
なお、電池膨化率及び容量残存率の値はパーセント表示とした。
In addition, the values of the battery expansion rate and the capacity remaining rate are expressed in percentage.
表２に示す結果から明らかなように、従来一般的な充電電圧である４．２Ｖの充電条件すなわち正極の電位が４．３Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）となるように充電した場合には、エーテル基を有する化合物を非水電解質中に含有させても、電池膨化を抑制することができず、また容量残存率の低下し、本発明の効果が得られないことがわかる。これは、４．２Ｖの充電電圧で充電した場合、添加したエーテル基を有する化合物が初回充電時に十分に分解せずに電解液中に残留し、この残留分が高温保存時に気化あるいは正極と反応してガス発生などを引き起こすと共に、劣化を促進させたものと考えられる。
As is apparent from the results shown in Table 2, when charging is performed so that the charge condition of 4.2 V, which is a conventional charge voltage, that is, the positive electrode potential is 4.3 V (vs. Li / Li + ). It can be seen that even when a compound having an ether group is contained in the non-aqueous electrolyte, the expansion of the battery cannot be suppressed, the capacity remaining rate is lowered, and the effect of the present invention cannot be obtained. This is because, when charged at a charging voltage of 4.2 V, the added ether group-containing compound remains in the electrolyte without being sufficiently decomposed during the first charge, and this residue is vaporized or reacted with the positive electrode during high-temperature storage. It is thought that this caused gas generation and promoted deterioration.
以上のことから、電解液にエーテル基を有する化合物を添加することによる本発明の効果は、充電電圧が従来の４．２Ｖよりも高い電池系において得られる効果であることがわかる。
From the above, it can be seen that the effect of the present invention by adding the compound having an ether group to the electrolytic solution is an effect obtained in a battery system having a charging voltage higher than the conventional 4.2V.
Claims (7)
正極活物質を含む正極と、金属リチウム以外の負極活物質を含む負極と、非水電解質とを備える非水電解質二次電池において、
前記正極活物質の主剤としてコバルト酸リチウムを含み、前記非水電解質に、前記正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ ＋ ）に達するまで充電した際に分解されるエーテル基を有する化合物が０．１〜１０体積％含有されており、前記正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／Ｌｉ＋）に達するまで充電した際の前記正極に対する負極の充電容量比が１．０〜１．２となるように前記正極活物質及び前記負極活物質が含まれてい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 comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material other than metallic lithium, and a non-aqueous electrolyte,
Ether containing lithium cobaltate as a main component of the positive electrode active material, and decomposed when the nonaqueous electrolyte is charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ). 0.1 to 10% by volume of a compound having a group, and charging of the negative electrode with respect to the positive electrode when charged until the potential of the positive electrode reaches 4.4 to 4.5 V (vs. Li / Li + ) A non-aqueous electrolyte secondary battery comprising the positive electrode active material and the negative electrode active material so that a capacity ratio is 1.0 to 1.2.
前記コバルト酸リチウムが、化学式Ｌｉ ａ Ｃｏ １−ｘ−ｙ−ｚ Ｚｒ ｘ Ｍｇ ｙ Ｍ ｚ Ｏ ２ （ＭはＡｌ、Ｔｉ、及びＳｎから選ばれる少なくとも１つの元素、０≦ａ≦１．１、ｘ＞０、ｙ＞０、ｚ≧０、０＜ｚ＋ｙ＋ｚ≦０．０３を満たす。）で表されることを特徴とする請求項１または請求項２に記載の非水電解質二次電池。
The lithium cobalt oxide has the chemical formula Li a Co 1-xyz Zr x Mg y M z O 2 (M is at least one element selected from Al, Ti, and Sn, 0 ≦ a ≦ 1.1, The nonaqueous electrolyte secondary battery according to claim 1, wherein x> 0, y> 0, z ≧ 0, and 0 <z + y + z ≦ 0.03 are satisfied.
前記コバルト酸リチウムが、その表面に粒子の状態で焼結して付着したＺｒ含有化合物を有することを特徴とする請求項３に記載の非水電解質二次電池。The non-aqueous electrolyte secondary battery according to claim 3, wherein the lithium cobalt oxide has a Zr-containing compound that is sintered and attached to the surface in the form of particles.
前記負極活物質が黒鉛材料であり、前記正極の電位が４．４〜４．５Ｖ（ｖｓ．Ｌｉ／ＬｉThe negative electrode active material is a graphite material, and the potential of the positive electrode is 4.4 to 4.5 V (vs. Li / Li ＋+ ）となったときの電池電圧が４．３〜４．４Ｖであることを特徴とする請求項１〜４のいずれか１項に記載の非水電解質二次電池。The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the battery voltage is 4.3 to 4.4V.
前記非水電解質に、溶媒としてジエチルカーボネートが含まれていることを特徴とする請求項１〜５のいずれか１項に記載の非水電解質二次電池。
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the nonaqueous electrolyte contains diethyl carbonate as a solvent.
前記非水電解質に、さらにビニレンカーボネートが０．５〜４重量％含有されていることを特徴とする請求項１〜６のいずれか１項に記載の非水電解質二次電池。The nonaqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the nonaqueous electrolyte further contains 0.5 to 4% by weight of vinylene carbonate.
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