JP4893038B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, with the rapid miniaturization and diversification of consumer mobile phones, portable devices and personal digital assistants, etc., the batteries used as the power source are compact, lightweight, high energy density, and repeatedly charged for a long time. There is a strong demand for the development of secondary batteries capable of discharging. Among them, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are the most promising and active as secondary batteries that satisfy these needs compared to lead batteries and nickel cadmium batteries that use aqueous electrolytes. Research has been conducted.

The positive electrode active material of the nonaqueous electrolyte secondary battery includes general formula Li _x such as titanium disulfide, vanadium pentoxide and molybdenum trioxide, lithium cobalt composite oxide, lithium nickel composite oxide and spinel type manganese oxide. Various compounds represented by MO ₂ (where M is one or more transition metals) have been studied.

Especially, lithium cobalt composite oxide, lithium nickel composite oxide, spinel type lithium manganese composite oxide, etc. can be charged and discharged at an extremely noble potential of 4 V (vsLi / Li ⁺ ) or more, so that they can be used as positive electrodes. By using it, a battery having a high discharge voltage can be realized.

  Various negative electrode active materials for non-aqueous electrolyte secondary batteries, such as metallic lithium, lithium alloys, and carbon materials capable of occluding / releasing lithium, have been studied. There is an advantage that a battery having a long life can be obtained and safety is high.

  However, the non-aqueous electrolyte secondary battery has a high energy density and uses a flammable organic solvent, which causes internal short circuit or overcharge due to abnormal use. In some cases, the battery temperature may rise rapidly due to the decomposition of the battery member, and the safety valve may open, and an organic solvent or other decomposition gas may be ejected or smoke may be generated.

  Therefore, a technique for improving the safety of the battery without impairing the battery performance has been sought. For example, in order to ensure the safety of the battery at an internal short circuit or high temperature, the hole is closed by melting at a high temperature. Techniques such as attaching a shutdown separator or a PTC element whose resistance increases with increasing temperature are employed.

  Until now, in order to improve the performance of a battery, adding various compounds to a nonaqueous electrolyte has been examined. For example, in Patent Document 1, as an overcharge protection means of a lithium ion battery, a polymerizable aromatic additive such as biphenyl or 3-chloro-thiophene is added to a liquid electrolyte, and the voltage is polymerized at a voltage higher than the maximum operating voltage of the battery. A method for protecting a battery from overcharging has been proposed.

  In Patent Document 2, in order to improve the safety of a non-aqueous secondary battery and improve charge / discharge cycle characteristics, at least one of a negative electrode material, a positive electrode material, and an electrolyte includes polyoxyethylene, polyglycerin fatty acid ester, and the like. A technique for incorporating a nonionic surfactant is disclosed.

  Patent Document 3 discloses a technique in which a saccharide such as monose or diose is included in the electrolytic solution in order to improve the charge / discharge cycle characteristics and storage characteristics at high temperatures of the non-aqueous electrolyte secondary battery.

Furthermore, in Patent Document 4, a non-aqueous secondary battery contains a fatty acid ester of sugar or reducing sugar in the electrolyte solution in order to form a stable film with easy movement of lithium ions and low electrical resistance on the negative electrode surface. Techniques for making them disclosed are disclosed. However, in Patent Document 4, lithium metal or a lithium alloy is used for the negative electrode, and the concentration of the fatty acid ester of reducing sugar in the electrolytic solution is extremely small such as 10 ⁻⁷ to 10 ⁻² mol / liter.

Patent Document 5 discloses a compound represented by the chemical formula R ⁰ (OCOR) _n in an electrolyte solution (where n is 2 or more and 6 or less) in order to suppress decomposition of the nonaqueous electrolyte solution in a nonaqueous battery. R represents an integer, and each R independently represents an alkyl group having 1 to 10 carbon atoms substituted with at least one halogen atom, and R ⁰ represents an n-valent hydrocarbon group which may be substituted. A technique for containing the present invention is disclosed.
Japanese Patent No. 3061756 JP 08-298135 A Japanese Patent Laid-Open No. 2000-021443 JP 2000-090969 A JP 2005-268094 A

  In order to ensure the safety of non-aqueous electrolyte secondary batteries, various methods such as shutdown separators, PTC elements, and addition of additives to the electrolyte are used in combination. Improvements in battery structure, material type, material composition, etc. are still being made vigorously.

  In particular, the addition of additives to non-aqueous electrolytes may be simple, and there has been a strong demand for ensuring safety by a new technique, particularly for overcharging. Furthermore, it has also been required not to adversely affect the battery life characteristics.

  However, attempts to improve the safety of non-aqueous batteries by adding additives to the electrolyte disclosed in Patent Documents 1 to 5 are still insufficient, although a certain improvement effect has been obtained. It was necessary to combine with PTC elements.

  Therefore, an object of the present invention is to provide a highly safe non-aqueous electrolyte secondary battery by adding an additive to the electrolyte of the non-aqueous electrolyte secondary battery, in particular, high safety during overcharge. The object is to provide a non-aqueous electrolyte secondary battery.

  The invention of claim 1 is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the electrolyte contains a fatty acid ester compound of a sugar alcohol in an amount of 1 wt% or more and a saturation solubility or less. .

  According to a second aspect of the present invention, in the nonaqueous electrolyte secondary battery, the nonaqueous electrolyte is composed of a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester containing a halogen, and a sulfur compound having a carbon-carbon unsaturated bond. It contains at least one selected from the group.

  According to the present invention, the fatty acid ester compound of sugar alcohol is contained in the electrolyte of the nonaqueous electrolyte secondary battery in an amount of 1 wt% or more and a saturation solubility or less, thereby improving safety when the battery is overcharged. .

  In the non-aqueous electrolyte secondary battery, the electrolyte is at least one selected from the group consisting of a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester containing halogen, and a sulfur compound having a carbon-carbon unsaturated bond. By containing the nonaqueous electrolyte secondary battery, the safety is high when the battery is overcharged, the initial capacity is large, and the life is long.

  The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte. When the electrolyte contains a fatty acid ester compound of a sugar alcohol in an amount of 1 wt% or more and a saturation solubility or less, the battery is overcharged. Safety in the event of an accident.

  The reason why the safety of a battery when it is overcharged by including a fatty alcohol ester compound of a sugar alcohol in the non-aqueous electrolyte is not clear at this time, but these compounds react with a negative electrode with a low potential. When the battery is overcharged, it reacts with the fresh surface of the lithium metal deposited on the negative electrode and dissolves it, so that the lithium metal and nonaqueous electrolyte when the battery becomes hot during overcharge It is conceivable to suppress the reaction.

  The fatty acid ester compound of sugar alcohol used in the present invention is represented by the following general formula (1).

（ここで、Ａは−ＣＨ_２Ｏ（Ｃ＝Ｏ）Ｒ、またはＡ同士が互いに連結した環状構造であり、Ｒは水素または炭化水素基である。また、ｎは１以上の整数であり、環状構造の場合は３以上の整数である。）
また、糖アルコールの脂肪酸エステル化合物の炭化水素基は、過充電時に電池が高温になった際の負極活物質と非水電解質の反応を適度に抑制する効果があるものと考えられる。ただし、糖アルコールの脂肪酸エステル化合物の非水電解質への添加量が１ｗｔ％以下の場合は、このような効果が十分ではないために、電池が過充電された場合の安全性向上に寄与できなかったものと考えられる。

(Here, A is —CH ₂ O (C═O) R, or a cyclic structure in which A are connected to each other, R is hydrogen or a hydrocarbon group, and n is an integer of 1 or more, In the case of a cyclic structure, it is an integer of 3 or more.)
In addition, the hydrocarbon group of the fatty acid ester compound of sugar alcohol is considered to have an effect of moderately suppressing the reaction between the negative electrode active material and the non-aqueous electrolyte when the battery becomes high temperature during overcharge. However, when the addition amount of the fatty acid ester compound of sugar alcohol to the non-aqueous electrolyte is 1 wt% or less, such an effect is not sufficient, so it cannot contribute to the safety improvement when the battery is overcharged. It is thought that.

  The amount of sugar alcohol fatty acid ester compound added to the non-aqueous electrolyte is the sugar alcohol fatty acid ester for all components (electrolyte solvent, electrolyte salt, sugar alcohol fatty acid ester compound, and other additives) constituting the electrolyte. It shall be represented by the concentration (wt%) of the compound.

  Moreover, in the nonaqueous electrolyte secondary battery of the present invention, the nonaqueous electrolyte further includes a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester containing a halogen, and a sulfur compound having a carbon-carbon unsaturated bond. By containing at least one selected, a non-aqueous electrolyte secondary battery having high safety when the battery is overcharged, large initial capacity, and long life can be obtained.

  By the way, since the fatty acid ester compound of sugar alcohol has high reactivity with the negative electrode, it gradually reacts with the negative electrode during a normal charge / discharge cycle, and the life performance tends to decrease. A small amount of a cyclic ester having a carbon unsaturated bond, a cyclic ester containing halogen, or a sulfur compound having a carbon-carbon unsaturated bond is added as an additive, and a stable film is formed on the negative electrode in advance. It is considered that the fatty acid ester compound was prevented from excessively decomposing at the initial charge and gradually degrading at the negative electrode during the life test, thereby suppressing the decrease in the life performance. In this way, it is considered that both high safety and life characteristics can be achieved.

  Such a small amount of the additive is contained in the nonaqueous electrolyte when the nonaqueous electrolyte is produced, and after the liquid is injected into the nonaqueous electrolyte secondary battery, the effect is exhibited by charging the battery.

  R in the fatty acid ester compound of the sugar alcohol represented by the general formula (1) is hydrogen or a hydrocarbon group, but when R is hydrogen, the deterioration during charge / discharge cycles tends to be large and is a hydrocarbon group. It is more preferable.

  When R is a hydrocarbon, the hydrocarbon group includes a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, etc., and may be linear, branched or cyclic It may be a phenyl group or a benzyl group.

  However, if the carbon number of R becomes too large, the effect of improving the safety when the battery is overcharged is reduced, and the solubility in the nonaqueous electrolyte is reduced, so the carbon number of R is 1 to 3. 1 is more preferable. n is preferably 1 to 4 in that the effect of improving safety when the battery is overcharged and the solubility in the nonaqueous electrolyte are ensured. In the case of a cyclic structure in which A and A are connected to each other, n is 3 or more, and preferably 6.

  Here, when a halogen element is included as a substituent in R, although a decrease in life performance can be suppressed, a safety improvement effect when the battery is overcharged cannot be obtained sufficiently, which is not preferable.

  Specific examples of the fatty acid ester compound of the sugar alcohol represented by the general formula (1) include glycerol triacetate, glycerol tripropanoate, glycerol tributanoate, erythritol tetraacetate, erythritol tetrapropanoate, erythritol tetrabutanoate, Examples include, but are not limited to, xylitol pentaacetate, xylitol pentapropanoate, xylitol pentabutanoate, sorbitol hexaacetate, sorbitol hexapropanoate, sorbitol hexabutanoate, inositol hexaacetate and their stereoisomers. It is not a thing.

  Examples of the cyclic ester having a carbon-carbon unsaturated bond include vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, vinyl vinylene carbonate, divinyl vinylene carbonate, vinylene carbonate derivatives such as fluoro vinylene carbonate and difluoro vinylene carbonate, and vinyl ethylene carbonate. And vinylethylene carbonate derivatives such as divinylethylene carbonate, and vinylene carbonate is particularly preferable.

  Examples of the cyclic ester containing halogen include ethylene carbonate derivatives such as fluoroethylene carbonate, fluoropropylene carbonate, and fluorobutylene carbonate, and more preferred is fluoroethylene carbonate.

  Examples of sulfur compounds having a carbon-carbon unsaturated bond include sultone such as 1,3-propene sultone and 1,4-butene sultone, divinyl sulfone, diallyl sulfone, bis (vinylsulfonyl) methane, bis (allylsulfonyl) methane, etc. And sulfones such as diallyl sulfide and diallyl disulfide, and more preferably 1,3-propene sultone.

  Compounds such as a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester containing halogen, and a sulfur compound having a carbon-carbon unsaturated bond may be added singly or in combination of two or more. May be. The concentration of these additives in the non-aqueous electrolyte is preferably 0.01 wt% or more, more preferably 0.1 wt% or more, and particularly preferably 0.5 wt% or more. Further, the upper limit is preferably 10 wt% or less, more preferably 5 wt% or less, and particularly preferably 2 wt% or less.

  Here, if the lower limit is not reached, the effect of improving the life performance due to the film formation is not sufficiently obtained, and if the upper limit is exceeded, an excessively high resistance film is formed and the discharge capacity is reduced. You may be invited.

  As the non-aqueous electrolyte, either an electrolytic solution or a solid electrolyte can be used. When using an electrolytic solution, as an electrolytic solution solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate Chain carbonates such as ethyl butyl carbonate, dipropyl carbonate, propyl butyl carbonate and dibutyl carbonate and their halides, lactones such as γ-butyrolactone and γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2 -Ethers such as methyltetrahydrofuran, 1,3-dioxolane, 3-methyl-1,3-dioxolane and their halides, methyl acetate, Fatty acids such as ethyl acetate, butyl acetate, propyl acetate, butyl acetate, pentyl acetate, hexyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, hexyl propionate Esters and halides thereof, nitriles such as acetonitrile and propanenitrile and halides thereof, hexafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, diethoxytetrafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, Phosphazenes such as hexachlorocyclotriphosphazene, phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, and triphenyl phosphate Le acids and their halides, such as halides of polyhydric alcohols can be used.

  Preferably, ethylene carbonate, propylene carbonate, and butylene carbonate are used alone or mixed as the cyclic carbonate and contained in an amount of 10 to 60% by volume based on the total amount of the nonaqueous solvent, and more preferably 20 to 40%.

The nonaqueous electrolyte is used by dissolving the supporting salt in these nonaqueous solvents. Examples of the supporting salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ CO ₂ , LiCF ₃ SO ₃ , LiCF ₃ CF ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN (SO ₂ CF ₃ ). ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (COCF ₃ ) ₂ , LiN (COCF ₂ CF ₃ ) ₂ LiBF ₂ C ₂ O ₄ , LiBC ₄ O ₈ , LiPF ₂ (C ₂ O ₄ ) ₂ and A salt such as LiPF ₃ (CF ₂ CF ₃ ) ₃ or a mixture thereof can be used. More preferably, LiPF ₆ is used alone from the viewpoint of battery discharge characteristics and cost, or LiPF ₆ is mainly used. It is preferable to mix a small amount of the electrolyte.

  In order to improve battery characteristics, chain sulfates such as dimethyl sulfate, diethyl sulfate and dipropyl sulfate and their halides, ditrimethylsilyl sulfate, ethylene glycol sulfate, propylene glycol sulfate, trimethylene glycol sulfate, etc. Cyclic sulfates and their halides, chain sulfites such as dimethyl sulfite, diethyl sulfite and dipropyl sulfite and their halides, cyclic sulfites such as ethylene sulfite and trimethylene sulfite and their halides, dimethyl sulfone Chain sulfones such as diethyl sulfone and halides thereof, chain sulfides such as dimethyl sulfide, diethyl sulfide, diphenyl sulfide and diphenyl disulfide and halides thereof, Silyl esters of acids such as tristrimethylsilyl acid, tristrimethylsilyl borate, bistrimethylsilyl sulfate, tetrakistrimethylsilyl titanate, carbodiimides such as N, N′-dicyclohexylcarbodiimide, N, N′-diisopropylcarbodiimide, 1,1,1 , 3,3,3-hexamethyldisilazane, silazanes such as 1,1,3,3,5,5-hexamethylcyclotrisilazane, succinic anhydride, maleic anhydride, sulfobenzoic anhydride, etc. A small amount of an acid anhydride can also be added, and the addition amount is more preferably 2 wt% or less and 1 wt% or less with respect to the whole nonaqueous electrolyte.

  Similarly, small amounts of aromatic compounds can be added as overcharge inhibitors, examples of which are benzene, toluene, orthoxylene, paraxylene, metaxylene, cumene, cyclohexylbenzene, cyclopentylbenzene, fluorobenzene, difluorobenzene. , Trifluorobenzene, naphthalene, methylnaphthalene, fluoronaphthalene, difluoronaphthalene, trimethylsilylbenzene, bistrimethylsilylbenzene, tristrimethylsilylbenzene, t-amylbenzene, biphenyl, fluorobiphenyl, difluorobiphenyl, methylbiphenyl, cyclohexylbiphenyl, terphenyl, dibenzofuran , Diphenyl ether, ethoxybenzene, methoxybenzene, 2,4-difluoroanisole, 2,3-diph Such Oroanisoru the like, when used in admixture with fatty acid esters of sugar alcohol of the present invention is more effective.

  When a solid electrolyte is used, a porous polymer solid electrolyte membrane is used as the polymer solid electrolyte, and the polymer solid electrolyte is further added with a non-aqueous electrolyte containing a fatty acid ester of sugar alcohol shown in Chemical Formula 1. good.

As the positive electrode active material, a composite oxidation represented by a composition formula Li _x MO ₂ , Li _y M ₂ O ₄ (where M is one or more transition metals, 0 ≦ x ≦ 1.0 ≦ y ≦ 2). Metal chalcogenides or metal oxides having a structure, a tunnel structure or a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , LiCo _a Ni _b Mn _1-ab O ₂ (where a + b ≦ 1), LiMn ₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , LiFePO ₄ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS _{2 and the} like can be mentioned. Zr, Mg, Al, etc. may be dissolved or surface coated with these oxides.

  Examples of the organic compound include conductive polymers such as polyaniline. Furthermore, the above various active materials may be mixed and used regardless of whether they are inorganic compounds or organic compounds.

  Further, as the negative electrode material, carbonaceous materials such as graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like are suitable, and together with these carbon materials, Al, Si, Sn In view of safety and life performance, it is particularly preferable to mainly use guaphite, non-graphitizable carbon, and graphitizable carbon. When Li is present as a simple Li metal in the negative electrode, it easily reacts with the sugar alcohol fatty acid ester of the present invention at the time of deposition during charge and discharge, which is not preferable from the viewpoint of life performance.

  Moreover, as a separator of the nonaqueous electrolyte battery according to the present invention, a woven fabric, a non-woven fabric, a synthetic resin microporous membrane, or the like can be used, and a synthetic resin microporous membrane can be particularly preferably used. Among these, polyolefin microporous membranes such as polyethylene and polypropylene microporous membranes, heat-resistant resins processed from polyimide and aramid, or microporous membranes composed of these are suitable in terms of thickness, membrane strength, membrane resistance, etc. Used.

  Furthermore, a separator can also be used by using a solid electrolyte such as a polymer solid electrolyte. Further, a synthetic resin microporous membrane and a polymer solid electrolyte may be used in combination. In this case, a porous polymer solid electrolyte membrane may be used as the polymer solid electrolyte, and the polymer solid electrolyte may further contain an electrolytic solution.

  In addition, the shape of the battery is not particularly limited, and can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a rectangular shape, a long cylindrical shape, a coin shape, a button shape, a sheet shape, and a cylindrical battery. The effects of the present invention can be obtained more significantly in the easily deformable square, long cylindrical, coin, button, and sheet types.

  Hereinafter, specific embodiments to which the present invention is applied will be described. However, the present invention is not limited to the embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. .

[Example 1]
FIG. 1 is a schematic cross-sectional view of a prismatic nonaqueous electrolyte secondary battery of the present example. In this rectangular nonaqueous electrolyte secondary battery 1, a positive electrode 3 formed by applying a positive electrode mixture to an aluminum current collector and a negative electrode 4 formed by applying a negative electrode mixture to a copper current collector are interposed via a separator 5. The wound flat flat electrode group 2 and the non-aqueous electrolyte are housed in a battery case 6 and have a width of 34 mm, a height of 42 mm, and a thickness of 5 mm.

  A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, a negative electrode terminal 9 is connected to the negative electrode 4 via a negative electrode lead 11, and a positive electrode 3 is connected to the battery lid via a positive electrode lead 10. Has been.

  The positive electrode plate is made of a positive electrode mixture obtained by mixing 3% by weight of polyvinylidene fluoride as a binder, 2% by weight of acetylene black as a conductive agent, and 95% by weight of lithium cobaltate as a positive electrode active material. Methylpyrrolidone was added to prepare a paste, which was then applied to both sides of a 15 μm thick aluminum foil current collector and dried.

  A negative electrode plate was prepared by adding 96% by weight of graphite, 2% by weight of carboxymethyl cellulose and 2% by weight of styrene butadiene rubber to water to prepare a paste, and then applying and drying the paste on both sides of a 10 μm thick copper foil current collector. Produced by

A polyethylene microporous membrane is used for the separator, and the electrolyte solution is a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 25: 75 (volume ratio) and LiPF ₆ is added at 0.8 mol / liter. In addition, glycerol triacetate (GTA) as a fatty acid ester compound of the sugar alcohol represented by the general formula (1) is added to the total weight of the electrolyte (total weight of EC, EMC, LiPF _6, and GTA). On the other hand, a nonaqueous electrolytic solution dissolved so as to be 1.0 wt% was used.

  Five cells of the non-aqueous electrolyte secondary battery of Example 1 were produced by the above configuration / procedure. In the following Examples 2 to 13 and Comparative Examples 1 to 4, the number of cells produced was 5 cells.

[Example 2]
A nonaqueous electrolyte secondary battery of Example 2 was fabricated in the same manner as Example 1 except that the amount of GTA added was 5 wt% with respect to the total weight of the electrolyte.

[Example 3]
A nonaqueous electrolyte secondary battery of Example 3 was fabricated in exactly the same manner as Example 1 except that the amount of GTA added was 10 wt% with respect to the total weight of the electrolyte.

[Example 4]
A nonaqueous electrolyte secondary battery of Example 4 was produced in the same manner as Example 1 except that the amount of GTA added was 20 wt% with respect to the total weight of the electrolyte.

[Example 5]
Example 1 Except that the amount of GTA added was 5 wt% with respect to the total weight of the electrolyte, and further 5 wt% was added with respect to the total weight of the electrolyte of glycerol tripropionate (GTP). 5 non-aqueous electrolyte secondary batteries were produced.

[Example 6]
Glycerol tripropionate (GTP) was added instead of GTA, and the non-aqueous electrolyte secondary of Example 6 was exactly the same as Example 1 except that the addition amount was 10 wt% with respect to the total electrolyte weight. A battery was produced.

[Example 7]
The nonaqueous electrolyte secondary of Example 7 was exactly the same as Example 1 except that glycerol tributyrate (GTB) was added instead of GTA, and the addition amount was 10 wt% with respect to the total weight of the electrolyte. A battery was prepared.

[Example 8]
The nonaqueous electrolyte secondary battery of Example 8 is the same as Example 1 except that erythritol tetraacetate (ETA) is added instead of GTA, and the addition amount is 10 wt% with respect to the total weight of the electrolyte. Was made.

[Example 9]
The nonaqueous electrolyte secondary battery of Example 9 is the same as Example 1 except that sorbitol hexaacetate (SHA) is added instead of GTA, and the addition amount is 10 wt% with respect to the total weight of the electrolyte. Was made.

[Example 10]
The nonaqueous electrolyte secondary of Example 10 was exactly the same as Example 1 except that sorbitol hexaacetate (SHA) was added instead of GTA, and the addition amount was 20 wt% with respect to the total weight of the electrolyte. A battery was produced.

[Example 11]
Implemented except that sorbitol hexaacetate (SHA) was added instead of GTA, the addition amount was 10 wt% with respect to the total electrolyte weight, and vinylene carbonate (VC) was added with 1 wt% with respect to the total electrolyte weight. A nonaqueous electrolyte secondary battery of Example 11 was produced in exactly the same manner as Example 1.

[Example 12]
Instead of GTA, sorbitol hexaacetate (SHA) is added, the amount added is 10 wt% with respect to the total electrolyte weight, and propene sultone (1,3-propene-sultone, PRS) is added to the total electrolyte weight. On the other hand, a nonaqueous electrolyte secondary battery of Example 12 was produced in the same manner as Example 1 except that 1 wt% was added.

[Example 13]
Except that sorbitol hexaacetate (SHA) was added instead of GTA, the addition amount was 10 wt% with respect to the total electrolyte weight, and 2 wt% of fluoroethylene carbonate (FEC) was added with respect to the total electrolyte weight. A nonaqueous electrolyte secondary battery of Example 13 was produced in exactly the same manner as Example 1.

[Comparative Example 1]
A nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as Example 1 except that GTA was not added.

[Comparative Example 2]
A nonaqueous electrolyte secondary battery of Comparative Example 2 was fabricated in exactly the same manner as in Example 1 except that the amount of GTA added was 0.5 wt% with respect to the total weight of the electrolytic solution.

[Comparative Example 3]
A nonaqueous electrolyte secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that vinylene carbonate (VC) was added in an amount of 1 wt% based on the total weight of the electrolyte instead of GTA.

[Comparative Example 4]
The nonaqueous electrolyte of Comparative Example 4 was the same as Example 1 except that 1 wt% of propene sultone (1,3-propene-sultone, PRS) was added to GTA instead of GTA. A secondary battery was produced.

[Comparative Example 5]
A nonaqueous electrolyte secondary battery of Comparative Example 5 was produced in the same manner as in Example 1 except that fluoroethylene carbonate (FEC) was added in an amount of 2 wt% based on the total weight of the electrolyte instead of GTA.

  Table 1 shows the types and amounts of additives in the batteries of Examples 1 to 13 and Comparative Examples 1 to 5. However, in Example 10, SHA was not completely dissolved, and a residue was observed, reaching saturation solubility at room temperature. However, from the amount of residue, it was estimated that about 15 wt% was dissolved.

  The initial discharge capacity was confirmed about the square nonaqueous electrolyte secondary battery of Examples 1-13 and Comparative Examples 1-5 produced as mentioned above. The discharge capacity is determined by performing a constant current discharge at 25 ° C. for 3 hours with a constant current-constant voltage charge with a charge current of 350 mA and a charge voltage of 4.03 V, and then with a discharge current of 700 mA and a final voltage of 2.5 V. It was measured.

  The overcharge test was performed by overcharging the battery after the initial capacity confirmation test with a charging current of 500 mA, switching to constant voltage charging when the voltage reached 12 V, and further performing constant voltage charging for 1 hour. . The result was determined based on the presence or absence of smoke. The smoke was detected when smoke was generated, the valve was opened when the safety valve was opened, and no abnormality was determined when there was no abnormality. Similarly, the case where the current during overcharging was 700 mA and 900 mA was also carried out.

  As a life test, a 45 ° C. charge / discharge cycle test was performed. The high temperature charge / discharge cycle test at 45 ° C. is the same as the initial discharge capacity check test after 50 cycles in a 45 ° C. constant temperature bath under the charge / discharge conditions during the initial discharge capacity check test and after cooling at 25 ° C. for 5 hours. The charge / discharge test was performed under the conditions, and the ratio of the capacity after 50 cycles with respect to the initial capacity in 100 minutes was calculated as the capacity retention rate.

  Table 2 shows the test results of the batteries of Examples 1 to 13 and Comparative Examples 1 to 5. In Table 2, “Initial capacity” indicates the average value of the initial discharge capacity of each battery. The “overcharge test result” indicates the determination result when an overcharge test is performed for each cell at each current value, and the retention rate is the capacity after 50 cycles of 45 ° C. charge / discharge cycles for 2 cells each. The average retention rate is shown.

  As a result, when the initial discharge capacities of Examples 1 to 5 and Comparative Examples 1 and 2 were compared, in Examples 1 to 5 in which the amount of GTA added was 1.0 wt% or more, Comparative Example 1 in which GTA was not added In addition, the initial capacity tended to decrease as compared with Comparative Example 2 in which 0.5 wt% of GTA was added, and the decrease tended to increase as the amount of GTA added increased.

  Moreover, also in Examples 6 to 10 in which the type of fatty acid ester compound of sugar alcohol was changed, the initial capacity was lower than those of Comparative Examples 1 and 2.

  However, as in Examples 11 to 13, by coexisting with a fatty acid ester compound of sugar alcohol and VC, PRS or FEC, the initial capacity is larger than that of Comparative Example 1 in which no GTA was added, and only VC was used. It was found that this was equivalent to Comparative Example 3 of No. 1, Comparative Example 4 of PRS only, and Comparative Example 5 of FEC only.

  Regarding the overcharge test result, when the amount of GTA, which is a fatty acid ester compound of sugar alcohol, is 0.5%, the result is equivalent to that of Comparative Example 1, and the effect could not be confirmed. In the case of 1 wt%, when the current value was 500 mA, smoke was not seen just by opening the safety valve, and safety during overcharging was improved.

  In addition, when the amount of GTA added is 5 wt%, there is no abnormality in the battery when overcharged at 500 mA and 700 mA, and the safety valve only opens when overcharged at 900 mA. Greatly improved. When the amount of GTA mixed was 10 wt% or more, there was no abnormality at any current value, and the safety was further greatly improved.

  As for other sugar alcohol fatty acid esters, there was no abnormality even when overcharged at 900 mA in Examples 6 to 10 in which the addition amount was 10 wt% or in Example 5 in which the total addition amount was 10 wt% by mixing 5 wt%. The addition of a sugar alcohol fatty acid ester compound to the non-aqueous electrolyte improves the safety when the battery is overcharged, and the effect is large when the addition amount is 5% or more. It was found that the effect is particularly great in the above cases.

  Further, in Example 10, since a large effect was obtained even when SHA was almost saturated, the safety at the time of overcharge can be secured even when the amount of addition is larger even with other compounds. it can.

  In Example 11 with addition of VC and SHA, Example 12 with addition of PRS and SHA, and Example 13 with addition of FEC and SHA, the safety at 900 mA overcharge is high, and the fatty acid ester compound of sugar alcohol is carbon. -Nonaqueous electrolyte secondary battery with high safety when the battery is overcharged even when a carbonic ester having a carbon unsaturated bond, a cyclic ester having a halogen, or a sulfur compound having a carbon-carbon unsaturated bond is further added Was found to be obtained.

  In the case of Comparative Example 1 in which GTA was not added until Example 1 to Example 10 in which the safety of the battery during overcharge was improved when comparing the retention rate after 50 cycles during the 45 ° C. charge / discharge cycle test. However, in Example 11 to which VC was added, Example 12 to which PRS was added, and Example 13 to which FEC was added, all showed a better capacity retention than Comparative Example 1, and VC , PRS, and FEC were added independently, respectively, and the same retention ratio as Comparative Example 3, Comparative Example 4, and Comparative Example 5 was obtained.

  From this, by adding a fatty alcohol ester compound of a sugar alcohol and either a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester having a halogen, or a sulfur compound having a carbon-carbon unsaturated bond. It was found that a non-aqueous electrolyte secondary battery having a large initial capacity, high safety during overcharge, and a long life can be obtained.

  In the examples and comparative examples, the case where the electrolyte solvent is EC: EMC is described. However, when PC or BC is used as the cyclic carbonate in addition to EC, or when DMC or DEC is used instead of EMC. It has been confirmed that the same result can be obtained, and it is confirmed that the same result can be obtained even when the mixing ratio of the cyclic carbonate and the chain carbonate is changed. Furthermore, although the concentration of the electrolyte is changed by adding a fatty alcohol ester compound of a sugar alcohol, it is also confirmed that the electrolyte concentration does not greatly affect the results of this test.

  Furthermore, the same results were obtained when using lithium manganese double oxide, lithium nickel double oxide, lithium-cobalt-nickel-manganese double oxide or a mixed system thereof as the positive electrode active material. Similar results were obtained even when non-graphitizable carbon, coke, or an alloy was used as part of the negative electrode.

The figure which shows the cross-section of the square battery of the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Square nonaqueous electrolyte secondary battery 2 Winding type electrode group 3 Positive electrode 4 Negative electrode 5 Separator 6 Battery case 7 Battery cover

Claims (2)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the electrolyte contains a fatty acid ester compound of a sugar alcohol in an amount of 1 wt% or more and a saturation solubility or less. The non-aqueous electrolyte contains at least one selected from the group consisting of a cyclic ester having a carbon-carbon unsaturated bond, a cyclic ester containing halogen, and a sulfur compound having a carbon-carbon unsaturated bond. Item 2. The nonaqueous electrolyte secondary battery according to Item 1.

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