JP2009252645A - Non-aqueous electrolyte secondary battery and non-aqueous electrolyte composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery capable of improving a battery property during high-temperature storage. <P>SOLUTION: The non-aqueous electrolyte second battery has positive and negative electrodes as well as a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains 1,1-carbonyldiimidazole. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte composition that can improve cycle characteristics.

  In recent years, many portable electronic devices such as a camera-integrated VTR, a digital still camera, a mobile phone, a personal digital assistant, and a notebook computer have appeared, and their size and weight have been reduced. As portable power sources for these electronic devices, research and development for improving the energy density of batteries, particularly secondary batteries, are being actively promoted. Among them, a lithium ion secondary battery that uses carbon as a negative electrode active material, a lithium-transition metal composite oxide as a positive electrode active material, and a carbonate ester mixture as an electrolyte is a lead battery that is a conventional non-aqueous electrolyte secondary battery, Since a large energy density can be obtained compared to a nickel cadmium battery, it is widely put into practical use. In particular, a laminated battery using an aluminum laminated film for the exterior has a high energy density because it is lightweight. In the laminate battery, since the deformation of the laminate battery can be suppressed by swelling the electrolyte in the polymer, the laminate polymer battery is also widely used.

In these lithium ion secondary batteries, it has been proposed to add various additives to the electrolytic solution in order to improve battery characteristics such as cycle characteristics. For example, it is considered that the acid generated by the decomposition of the lithium salt as an electrolyte decomposes the positive electrode active material as a cause of deterioration of the battery performance in a high temperature environment. However, a specific pyridine compound should be added to the electrolytic solution. Thus, a technique for trapping the acid and suppressing deterioration of the high-temperature cycle characteristics is disclosed. (For example, patent document 1).
Japanese Patent Laid-Open No. 2002-93462

  However, these pyridine compounds are considered to have insufficient oxidation resistance, and the effect of improving cycle characteristics is not sufficient.

  Accordingly, the present invention has been made in view of such problems, and an object thereof is to provide a nonaqueous electrolyte secondary battery that can improve battery characteristics during high-temperature storage.

In the present invention, it has been found that the above problem can be solved by including 1,1-carbonyldiimidazole in the electrolyte.
That is, the present invention provides the following nonaqueous electrolyte secondary battery and nonaqueous electrolyte composition.
[1] A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte together with a positive electrode and a negative electrode,
The nonaqueous electrolyte secondary battery in which the nonaqueous electrolyte contains 1,1-carbonyldiimidazole.
[2] A nonaqueous electrolyte composition containing 1,1-carbonyldiimidazole.

  According to the secondary battery of the present invention, the cycle characteristics during high-temperature storage can be improved by including 1,1-carbonyldiimidazole in the electrolyte. 1,1-carbonyldiimidazole is superior in oxidation resistance compared to nitrogen compounds containing other imidazole compounds, and has the advantage that it does not easily cause cycle deterioration due to its own decomposition.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following mode.

  FIG. 1 schematically shows a configuration of a secondary battery according to an embodiment of the present invention. This secondary battery is a so-called laminate film type, and has a wound electrode body 20 to which a positive electrode lead 21 and a negative electrode lead 22 are attached accommodated in a film-shaped exterior member 30.

  The positive electrode lead 21 and the negative electrode lead 22 are each directed from the inside of the exterior member 30 to the outside, for example, led out in the same direction. The positive electrode lead 21 and the negative electrode lead 22 are made of, for example, a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior member 30 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior member 30 is disposed, for example, so that the polyethylene film side and the wound electrode body 20 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 31 is inserted between the exterior member 30 and the positive electrode lead 21 and the negative electrode lead 22 to prevent intrusion of outside air. The adhesion film 31 is made of a material having adhesion to the positive electrode lead 21 and the negative electrode lead 22, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 30 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 2 shows a cross-sectional structure taken along line II of the spirally wound electrode body 20 shown in FIG. The wound electrode body 20 is obtained by laminating a positive electrode 23 and a negative electrode 24 via a separator 25 and an electrolyte layer 26 and winding them, and the outermost periphery is protected by a protective tape 27.

(Positive electrode)
The positive electrode 23 has a structure in which a positive electrode active material layer 23B is provided on both surfaces of a positive electrode current collector 23A. The positive electrode current collector 23A is made of, for example, a metal material such as aluminum, nickel, or stainless steel. The positive electrode active material layer 23B includes, for example, any one or a plurality of positive electrode materials capable of occluding and releasing lithium as a positive electrode active material, and a conductive agent such as a carbon material and polyvinylidene fluoride as necessary. It may contain a binder.

  Examples of the positive electrode material capable of inserting and extracting lithium include the following.

(1) Layered rock salt type (Mn type)
_{Li [Li x Mn (1-} x-y-z) Ni y M1 z] O (2-a) F b
In the formula, M1 is cobalt (Co), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), It represents at least one selected from the group consisting of zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). X, y, z, a, and b are 0 <x ≦ 0.2, 0.1 ≦ y ≦ 0.8, 0 ≦ z ≦ 0.5, and −0.1 ≦ a ≦ 0.2, respectively. , 0 ≦ b ≦ 0.1.

(2) Layered rock salt type (Ni-based)
Li _c Ni _(1-d) M2 _d O _(2-e) F _f
In the formula, M2 is cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), Represents at least one selected from the group consisting of copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). . C, d, e, and f are −0.1 ≦ c ≦ 0.1, 0.005 ≦ d ≦ 0.5, −0.1 ≦ e ≦ 0.2, and 0 ≦ f ≦ 0.1, respectively. It is a value within the range.

(3) Layered rock salt type (Co type)
Li _c Co _(1-d) M3 _d O _(2-e) F _f
In the formula, M3 is nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), Represents at least one selected from the group consisting of copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). . C, d, e, and f are −0.1 ≦ c ≦ 0.1, 0.005 ≦ d ≦ 0.5, −0.1 ≦ e ≦ 0.2, and 0 ≦ f ≦ 0.1, respectively. It is a value within the range.

(4) spinel type _{Li s Mn (2-t)} M4 t O u F v
In the formula, M4 is cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), Represents at least one selected from the group consisting of copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). . Further, s, t, u, v are values in the ranges of s ≧ 0.9, 0.005 ≦ t ≦ 0.6, 3.7 ≦ u ≦ 4.1, 0 ≦ v ≦ 0.1, respectively. is there.

(5) olivine LiM5PO ₄
In the formula, M5 is cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), Of the group consisting of niobium (Nb), copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr) and tungsten (W) At least one species is represented.

  In the nonaqueous electrolyte secondary battery of the present invention, the thickness per one side of the positive electrode active material layer 23B is 40 μm or more, preferably 80 μm or less. More preferably, it is the range of 40 micrometers or more and 60 micrometers or less. By setting the thickness of the active material layer to 40 μm or more, it is possible to increase the capacity of the battery. Moreover, the discharge capacity maintenance factor when charging / discharging is repeated can be enlarged by setting it as 80 micrometers or less.

(Negative electrode)
The negative electrode 24 has, for example, a structure in which a negative electrode active material layer 24B is provided on both surfaces of a negative electrode current collector 24A having a pair of opposed surfaces. The negative electrode current collector 24A is made of a metal material such as copper, nickel, and stainless steel, for example.

  The negative electrode active material layer 24B includes one or more negative electrode materials capable of occluding and releasing lithium as a negative electrode active material. In this secondary battery, the charge capacity of the negative electrode material capable of inserting and extracting lithium is larger than the charge capacity of the positive electrode 23 so that lithium metal does not deposit on the negative electrode 24 during the charge. It has become.

Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as non-graphitizable carbon, graphitizable carbon, and graphite. Examples of the graphite include natural graphite, graphitized carbon fiber, and artificial graphite such as graphitized mesocarbon microbeads (MCMB).
These carbon materials are preferable because the change in the crystal structure associated with insertion and extraction of lithium is very small and good cycle characteristics can be obtained and a high charge / discharge capacity can be obtained. In particular, graphite is preferable because it has a large charge / discharge capacity per mass and a low charge / discharge potential, so that high energy density can be obtained. Further, non-graphitizable carbon is preferable because the charge / discharge rate can be increased. Among these, graphitized MCMB is preferable because it has excellent lithium occlusion and release properties due to point orientation in addition to high capacity and high energy density derived from graphite.

  Further, as the negative electrode material, in addition to the carbon material shown above, a material containing an element that forms an alloy with lithium, such as silicon, tin, and a compound thereof, magnesium, aluminum, germanium, or the like may be used. Further, a material containing an element that forms a composite oxide with lithium, such as titanium, can be considered.

  In the nonaqueous electrolyte secondary battery of the present invention, the thickness per one side of the negative electrode active material layer 24B is 40 μm or more, preferably 80 μm or less. More preferably, it is the range of 40 micrometers or more and 60 micrometers or less. By setting the thickness of the active material layer to 40 μm or more, it is possible to increase the capacity of the battery. Moreover, the discharge capacity maintenance factor when charging / discharging is repeated can be enlarged by setting it as 80 micrometers or less.

(Separator)
The separator 25 separates the positive electrode 23 and the negative electrode 24 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 25 is made of, for example, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of ceramic, and a plurality of these porous films are laminated. It may be a structure. For example, the separator 25 is impregnated with an electrolytic solution that is a liquid electrolyte.

(Nonaqueous electrolyte)

The nonaqueous electrolyte (composition) in the nonaqueous electrolyte secondary battery of the present invention contains 1,1-carbonyldiimidazole represented by the following formula. Thereby, even if an acid generate | occur | produces by decomposition | disassembly of electrolyte salt, 1, 1- carbonyldiimidazole traps an acid efficiently and can maintain cycling characteristics favorably. For example, when LiPF ₆ is included as an electrolyte salt, hydrofluoric acid is considered to be generated.

  The content of 1,1-carbonyldiimidazole in the electrolyte is preferably 200 to 2000 ppm by mass, and more preferably 500 to 1000 ppm by mass. When the content is less than 200 ppm by mass, the amount of 1,1-carbonyldiimidazole is insufficient and a sufficient effect cannot be obtained, and when it exceeds 2000 ppm by mass, the solubility is insufficient, This is because a sufficient effect cannot be obtained.

  The electrolyte (electrolyte composition) in the present invention further contains a nonaqueous solvent and an electrolyte salt.

  Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used as the nonaqueous solvent, and it is preferable to use one of ethylene carbonate and propylene carbonate, in particular, a mixture of both. This is because the cycle characteristics can be improved.

  As the non-aqueous solvent, in addition to these cyclic carbonates, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and methylpropyl carbonate may be mixed and used. This is because high ionic conductivity can be obtained.

  The non-aqueous solvent preferably further contains vinylene carbonate. This is because vinylene carbonate can improve cycle characteristics.

  In addition to these, examples of the non-aqueous solvent include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl- 1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N , N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide and trimethyl phosphate.

  A compound obtained by substituting at least a part of hydrogen in these non-aqueous solvents with a halogen such as chlorine or fluorine is preferable because reversibility of the electrode reaction may be improved depending on the type of electrode to be combined. In some cases.

As the electrolyte salt, e.g., lithium hexafluorophosphate (LiPF _6), lithium tetrafluoroborate (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium hexafluoro antimonate (LiSbF ₆₎ , Inorganic lithium salts such as lithium perchlorate (LiClO ₄ ) and lithium tetrachloroaluminate (LiAlCl ₄ ), and lithium trifluoromethanesulfonate (CF ₃ SO ₃ Li), lithium bis (trifluoromethanesulfone) imide [(CF ₃ SO ₂ ) ₂ NLi], lithium bis (pentafluoroethanesulfone) imide [(C ₂ F ₅ SO ₂ ) ₂ NLi] and lithium tris (trifluoromethanesulfone) methide [(CF ₃ SO ₂ ) ₃ CLi] Of perfluoroalkanesulfonic acid derivatives Lithium salts. One electrolyte salt may be used alone, or a plurality of electrolyte salts may be mixed and used.

  The nonaqueous electrolyte may also be formed by a gel-like nonaqueous electrolyte. The gel-like non-aqueous electrolyte is formed by gelling a non-aqueous electrolyte solution obtained by dissolving an electrolyte salt, 1,1-carbonyldiimidazole or the like in a non-aqueous solvent with a matrix polymer. The gel-like nonaqueous electrolyte is configured such that a nonaqueous electrolyte is impregnated or held in a matrix polymer. By such swelling, gelation or non-fluidization of the matrix polymer, it is possible to effectively suppress leakage of the nonaqueous electrolyte in the obtained battery.

  The matrix polymer is not particularly limited as long as it is compatible with a nonaqueous electrolytic solution obtained by dissolving the electrolyte salt in the nonaqueous solvent and can be gelled. Moreover, the preferable content in the nonaqueous electrolyte of a matrix polymer is 5-20 mass%. Examples of the matrix polymer include polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride, hexafluoropropylene, and monochlorotrifluoroethylene, and vinylidene fluoride and hexafluoropropylene. Examples thereof include a copolymer with monomethylmaleic acid ester, and among them, a copolymer of vinylidene fluoride and hexafluoropropylene is preferable from the viewpoint of redox stability.

(Production method)
For example, the secondary battery can be manufactured as follows.

  The positive electrode can be produced, for example, by the following method. First, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 23A and the solvent is dried. Then, the positive electrode active material layer 23B is formed by compression molding using a roll press or the like, and the positive electrode 23 is manufactured.

  Moreover, a negative electrode can be produced by the following method, for example. First, after preparing graphite as a negative electrode active material, a conductive agent, and a binder to prepare a negative electrode mixture, the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone and pasted. A negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 24A, dried, and compression-molded to form a negative electrode active material layer 24B containing negative electrode active material particles made of the negative electrode active material described above. Get.

  Next, a precursor solution containing an electrolytic solution, a polymer compound, and a mixed solvent is applied to each of the positive electrode 23 and the negative electrode 24, and the mixed solvent is volatilized to form the electrolyte layer 26. Next, the positive electrode lead 21 is attached to the positive electrode current collector 23A, and the negative electrode lead 22 is attached to the negative electrode current collector 24A. Subsequently, the positive electrode 23 and the negative electrode 24 on which the electrolyte layer 26 is formed are laminated through a separator 25 to form a laminated body, and then the laminated body is wound in the longitudinal direction, and the protective tape 27 is attached to the outermost peripheral portion. The wound electrode body 20 is formed by bonding. After that, for example, the wound electrode body 20 is sandwiched between the exterior members 30, and the outer edge portions of the exterior members 30 are in close contact with each other by thermal fusion or the like and sealed. At that time, an adhesion film 31 is inserted between the positive electrode lead 21 and the negative electrode lead 22 and the exterior member 30. Thereby, the secondary battery shown in FIGS. 1 and 2 is completed.

  Further, this secondary battery may be manufactured as follows. First, the positive electrode 23 and the negative electrode 24 are prepared as described above, and after the positive electrode lead 21 and the negative electrode lead 22 are attached to the positive electrode 23 and the negative electrode 24, the positive electrode 23 and the negative electrode 24 are stacked and wound via the separator 25. Rotate and adhere the protective tape 27 to the outermost periphery to form a wound body that is a precursor of the wound electrode body 20. Next, the wound body is sandwiched between the exterior members 30, and the outer peripheral edge except for one side is heat-sealed to form a bag shape, and is stored inside the exterior member 30. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, and other materials such as a polymerization initiator or a polymerization inhibitor as necessary is prepared, and the interior of the exterior member 30 is prepared. After the injection, the opening of the exterior member 30 is heat-sealed and sealed. After that, if necessary, heat is applied to polymerize the monomer to form a polymer compound, thereby forming the gel electrolyte layer 26 and assembling the secondary battery shown in FIGS.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 23 and inserted in the negative electrode 24 through the electrolytic solution. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 24 and inserted into the positive electrode 24 through the electrolytic solution.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the embodiment, and various modifications can be made. For example, in the above-described embodiment and the case where the gel electrolyte in which the electrolytic solution is held in the polymer compound is used, other electrolytes may be used. Other electrolytes include, for example, an electrolyte solution, an ion conductive ceramic, an ion conductive glass, an ion conductive inorganic compound such as an ionic crystal mixed with an electrolyte solution, or another inorganic compound and an electrolyte solution. The thing mixed and the thing which mixed these inorganic compounds and gel electrolyte are mentioned.

  In the above embodiment, a battery using lithium as an electrode reactant has been described. However, another alkali metal such as sodium (Na) or potassium (K), or an alkaline earth metal such as magnesium or calcium (Ca). The present invention can also be applied to the case of using other light metals such as aluminum.

  Further, in the above embodiment, the capacity of the negative electrode is a so-called lithium ion secondary battery represented by a capacity component due to insertion and extraction of lithium, or lithium metal is used for the negative electrode active material, and the capacity of the negative electrode is Although a so-called lithium metal secondary battery represented by a capacity component due to precipitation and dissolution has been described, the present invention makes the charge capacity of the negative electrode material capable of occluding and releasing lithium smaller than the charge capacity of the positive electrode. Thus, the present invention can be similarly applied to a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof. .

  Furthermore, in the above embodiment, the laminate type secondary battery has been specifically described, but it goes without saying that the present invention is not limited to the above shape. That is, the present invention can be applied to a cylindrical battery, a square battery, and the like. Further, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

<Examples 1-1 to 1-6, Comparative Examples 1-1 to 1-4>
(Examples 1-1 to 1-6)
First, 95 parts by weight of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, ₂ parts by weight of ketjen black as a conductive material, and 3 parts by weight of polyvinylidene fluoride (PVdF) as a binder are homogeneously mixed. Then, N-methylpyrrolidone was added to obtain a positive electrode mixture coating solution. Next, the obtained positive electrode mixture coating liquid was uniformly applied to both surfaces on an aluminum foil, dried and compressed to form a positive electrode active material layer having a thickness of 50 μm per one surface. This was cut into a shape having a width of 50 mm and a length of 350 mm to produce a positive electrode.
Next, 97 parts by weight of graphitized MCMB as a negative electrode active material and 3 parts by weight of PVdF as a binder were homogeneously mixed, and N-methylpyrrolidone was added to obtain a negative electrode mixture coating solution. Next, the obtained negative electrode mixture coating liquid was uniformly applied on both surfaces of the copper foil and dried to form a negative electrode active material layer having a thickness of 50 μm per one surface. This was cut into a shape having a width of 52 mm and a length of 370 mm to prepare a negative electrode.
The nonaqueous electrolyte is prepared by dissolving 0.7 mol / kg of lithium hexafluorophosphate (LiPF ₆ ) in a nonaqueous solvent in which ethylene carbonate (EC): propylene carbonate (PC) is mixed at a mass ratio of 40:60. Further, a predetermined amount of 1,1-carbonyldiimidazole shown in Table 1 was dissolved to prepare a nonaqueous electrolytic solution. This electrolytic solution was held in a copolymer of vinylidene fluoride and hexafluoropropylene (6.9%) to obtain a gel electrolyte.

  After forming a gel electrolyte layer on the positive electrode and the negative electrode, they were laminated and wound up via a separator made of polyethylene, and placed in a bag made of an aluminum laminate film. This bag was heat-sealed to produce a laminate type secondary battery.

(High temperature cycle characteristics)
Table 1 shows the discharge capacity maintenance rate (%) when this battery was charged for 3 hours at 1C in a 45 ° C environment with 4.2V as the upper limit and then discharged at a constant current with 3V as the lower limit for 100 cycles. Show.

(High temperature storage characteristics)
Further, Table 1 shows the change in battery thickness after the battery was charged at 1 C with 4.2 V as the upper limit for 3 hours and stored at 60 ° C. for 30 days as an expansion coefficient (%). The expansion coefficient is a value calculated using the battery thickness before storage as the denominator and the thickness increased after storage as the numerator.

(Comparative Example 1-1)
A secondary battery was made in the same manner as in Example 1-1 except that the additive was not added. The results of high temperature cycle characteristics and high temperature storage characteristics are shown in Table 1.

(Comparative Example 1-2)
A secondary battery was made in the same manner as in Example 1-4 except that 2,6-di-tert-butyl-4-methylpyridine was used as an additive instead of 1,1-carbonyldiimidazole. The results of high temperature cycle characteristics and high temperature storage characteristics are shown in Table 1.

(Comparative Examples 1-3, 1-4)
Secondary as in Examples 1-3 and 1-4, except that 1,1-carbonylbis (2-methylimidazole) was used instead of 1,1-carbonyldiimidazole as an additive. A battery was created. The results of high temperature cycle characteristics and high temperature storage characteristics are shown in Table 1.

From the results shown in Table 1, all of Examples 1-1 to 1-6 containing 1,1-carbonyldiimidazole in the electrolyte had a higher temperature than Comparative Example 1-1 containing no 1,1-carbonyldiimidazole. Cycle characteristics and high temperature storage characteristics were good. Further, it was found that the content of 1,1-carbonyldiimidazole in the electrolyte is preferably 200 mass ppm or more in order to obtain a more stable and large effect. Moreover, since solubility with respect to electrolyte solution will run short if content exceeds 3000 mass ppm, it is preferable that an upper limit shall be 2000 mass ppm.
Furthermore, as shown in Comparative Examples 1-2 to 1-4, even when a compound other than 1,1-carbonyldiimidazole is added, good cycle characteristics such as 1,1-carbonyldiimidazole and high-temperature storage characteristics Could not be confirmed.

<Examples 2-1 to 2-2 and Comparative Examples 2-1 to 2-2>
(Example 2-1)
A laminate type secondary battery was produced in the same manner as in Example 1-3 except that lithium nickelate (LiNi _0.78 Co _0.19 Al _0.03 O ₂ ) was used instead of lithium cobalt oxide as the type of the positive electrode active material.

(High temperature cycle characteristics)
The discharge capacity retention rate (%) when this battery was charged for 3 hours at 1C in a 45 ° C environment with 4.2V as the upper limit and then discharged at a constant current with 2.5V as the lower limit for 100 cycles. It is shown in 2.

(High temperature storage characteristics)
In addition, Table 2 shows the change in battery thickness after the battery was charged at 1 C with 4.2 V as the upper limit for 3 hours and stored at 60 ° C. for 30 days as an expansion coefficient (%). The expansion coefficient is a value calculated using the battery thickness before storage as the denominator and the thickness increased after storage as the numerator.

(Comparative Example 2-1)
A secondary battery was made in the same manner as in Example 2-1, except that 1,1-carbonyldiimidazole was not added to the electrolytic solution. Table 2 shows the results of the high temperature cycle characteristics and the high temperature storage characteristics.

(Example 2-2)
A laminate type secondary battery was prepared in the same manner as in Example 1-3, except that the type of the positive electrode active material was changed to lithium cobalt oxide and carbon-coated lithium iron phosphate (LiFePO ₄ ) was used.

(High temperature cycle characteristics)
The discharge capacity retention rate (%) is shown when the battery is charged for 3 hours at 1C in a 45 ° C environment with 3.6 V as the upper limit and then discharged at a constant current with 2.5 V as the lower limit for 100 cycles. It is shown in 2.

(High temperature storage characteristics)
In addition, Table 2 shows the change in battery thickness after the battery was charged at 1 C with 3.6 V as the upper limit for 3 hours and stored at 60 ° C. for 30 days as an expansion coefficient (%). The expansion coefficient is a value calculated using the battery thickness before storage as the denominator and the thickness increased after storage as the numerator.

(Comparative Example 2-2)
A secondary battery was made in the same manner as in Example 2-2 except that 1,1-carbonyldiimidazole was not added to the electrolytic solution. Table 2 shows the results of the high temperature cycle characteristics and the high temperature storage characteristics.

  From the results of Table 2, it was found that lithium nickelate and lithium iron phosphate tend to be more effective than lithium cobaltate. The generation of acid due to the decomposition of the electrolyte is considered to occur not only by heat but also by the adsorbed water of battery materials, etc., but lithium nickelate and lithium iron phosphate are more hygroscopic than lithium cobaltate, It is thought that the difference of the effect was seen.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above embodiments and can be variously modified.

It is a disassembled perspective view showing the structure of the nonaqueous electrolyte secondary battery which concerns on one embodiment of this invention. It is sectional drawing showing the structure along the II line of the winding electrode body shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Winding electrode body, 23 ... Positive electrode, 23A ... Positive electrode collector, 23B ... Positive electrode active material layer, 24 ... Negative electrode, 24A ... Negative electrode collector, 24B ... Negative electrode active material layer, 25 ... Separator, 21 ... Positive electrode Lead, 22 ... negative electrode lead, 26 ... electrolyte layer, 27 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (6)

A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte together with a positive electrode and a negative electrode,
The nonaqueous electrolyte secondary battery in which the nonaqueous electrolyte contains 1,1-carbonyldiimidazole.   The nonaqueous electrolyte secondary battery according to claim 1, wherein a content of the 1,1-carbonyldiimidazole in the nonaqueous electrolyte is 200 to 2000 ppm by mass.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is artificial graphite. The nonaqueous electrolyte secondary battery according to claim 1, comprising LiPF ₆ as an electrolyte salt.   A non-aqueous electrolyte composition containing 1,1-carbonyldiimidazole.   The nonaqueous electrolyte composition according to claim 5, wherein a content of the 1,1-carbonyldiimidazole is 200 to 2000 ppm by mass.

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