JP4893003B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

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

  Along with the rapid miniaturization and diversification of consumer mobile phones, portable devices and personal digital assistants, etc., the battery that is the power source is small, lightweight, high energy density, and repeatedly charged and discharged for a long time. There is a strong demand for the development of secondary batteries that can be realized. 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 nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode active material includes lithium disulfide, vanadium pentoxide and molybdenum trioxide, lithium cobalt composite oxide, lithium nickel. Various compounds represented by a general formula Li _x MO ₂ (wherein M is one or more transition metals) such as composite oxides and spinel-type manganese oxides have been studied. Among these, lithium cobalt composite oxide, lithium nickel composite oxide, spinel-type lithium manganese composite oxide, and the like can be charged and discharged at an extremely high (noble) potential of 4 V (vs Li / Li ⁺ ) or higher. Therefore, a battery having a high discharge voltage can be realized by using it as the positive electrode.

  Various materials such as metallic lithium, lithium alloys, and carbon materials capable of occluding and releasing lithium have been studied as negative electrode active materials for non-aqueous electrolyte secondary batteries. A battery having excellent discharge cycle performance is obtained, and there is an advantage that safety is high.

For the electrolyte of a non-aqueous electrolyte secondary battery, a supporting salt such as LiPF ₆ or LiBF ₄ is generally mixed with a mixed solvent of a high dielectric constant solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate or diethyl carbonate. A dissolved electrolyte is used.

  In order to improve the charge / discharge cycle performance of non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries that require high energy density, positive electrode materials, negative electrode materials, and non-aqueous electrolytes are being developed. In recent years, a method for adding a small amount of an additive to a water electrolyte has been actively studied. For example, Patent Document 1 exemplifies that a high discharge capacity can be obtained even when a charge / discharge cycle test is performed by increasing the initial discharge capacity by reducing the initial irreversible capacity of the negative electrode using a phosphate additive. . Patent Document 2 exemplifies that charge / discharge cycle performance and high-temperature storage characteristics are improved by adding a silyl ester compound and tetrafluoroborate to a non-aqueous electrolyte.

  In recent years, demand for non-aqueous electrolyte secondary batteries as power sources for mobile vehicles such as hybrid cars has been increasing, and in addition to high energy density, which has been regarded as important in the past, it supports rapid charging and discharging. For this reason, it has been demanded that performance capable of charging and discharging with a large current, that is, high input / output performance lasts for a long time. Maintaining a high discharge capacity over a long period of time does not necessarily match maintaining a high input / output characteristic over a long period of time. This is mainly because the decrease in the discharge capacity of non-aqueous electrolyte secondary batteries used at low loads is due to the change in the balance between the charge levels of the positive and negative electrodes due to the decomposition reaction of the non-aqueous electrolyte on the electrodes. On the other hand, the decrease in input / output characteristics, that is, the increase in resistance is mainly caused by an increase in internal resistance such as current collection resistance, electrolyte resistance, and charge transfer resistance between the positive and negative electrodes and the electrolyte. It is. Therefore, in applications that require high input / output, a method for suppressing an increase in internal resistance is important. Patent Document 3 discloses pulse discharge before conducting a long-term pulse cycle test by using nitrite, nitrate, carbonate, dicarbonate, phosphonate, phosphate, sulfate, and fluorocarbon or a mixture thereof in the electrolyte. Although it is said that the voltage delay at the time, that is, the increase in polarization can be suppressed, there is only an example of dibenzyl carbonate as an example, and there is only an example of silver vanadium oxide as a positive electrode active material, and it is specified as a nonaqueous electrolyte. There is no description that the internal resistance can be greatly reduced by combining the positive electrode active material having a specific crystal structure and a specific composition range. This also applies to Patent Documents 1 and 2.

  Regarding the method for suppressing the increase of the internal resistance of the non-aqueous electrolyte secondary battery over a long period of use, there is not yet sufficient, active material, current collecting structure, separator, improvement of non-aqueous electrolyte, and electrolyte additive Further improvement of the charge / discharge cycle performance is required, for example, by the addition of and the improvement of the mixing method.

  Therefore, prior to the present invention, for the purpose of obtaining a non-aqueous electrolyte secondary battery with a small increase in internal resistance over a long period of use, the present inventors have described "a positive electrode that occludes and releases lithium and an occlusion / release of lithium A non-aqueous electrolyte secondary battery comprising a negative electrode to be discharged and a non-aqueous electrolyte, wherein the non-aqueous electrolyte contains a 0.02 to 0.2 M sulfate ester compound, and 0.005 to 0.00. A nonaqueous electrolyte secondary battery containing 04M phosphoric acid silyl ester compound has been proposed (Patent Document 4). Furthermore, the present inventors have proposed a preferable component ratio and composition ratio of the positive electrode material in the non-aqueous electrolyte secondary battery in order to enhance the effect of suppressing the increase in internal resistance by the sulfate ester compound and the phosphoric acid silyl ester compound. (Patent Document 5).

  Patent Document 6 describes that by adding unsaturated sultone to an electrolyte, resistance increase, gas generation, and self-discharge due to high-temperature storage can be suppressed. However, it is not clear what the resistance change is when the charge / discharge cycle of the nonaqueous electrolyte secondary battery to which the unsaturated sultone is added is repeated, and it has not been predicted at all. That is, the change during storage at high temperature is a change when the battery voltage is stored in a substantially maintained state, whereas the change due to repeated charge / discharge cycles is caused by the electrode material generated by the lithium insertion / release reaction. Since this is a change in the environment accompanied by a change caused by expansion and contraction and a change caused by the interface reaction between the electrode and the electrolyte caused by the battery taking various voltage states, both conditions and environment are completely different. The new surface is always in contact with the electrolyte due to expansion and contraction associated with charge / discharge, so it is considered that when unsaturated sultone is added, the resistance increases with charge / discharge cycles due to polymerization of the double bond portion. Therefore, it does not necessarily agree with the result of preservation. Furthermore, in non-aqueous electrolyte secondary batteries to which unsaturated sultone is added, it is disclosed in Patent Document 6 how the resistance change associated with repetition of charge / discharge cycles occurs when the type and composition ratio of the positive electrode material are changed. It was not clear and could not be predicted at all.

JP 2000-331710 A JP 2004-342607 A JP 2000-164251 A Japanese Patent Application No. 2005-293127 Japanese Patent Application No. 2005-370855 JP 2002-329528 A

An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a small increase in resistance even after repeated charge / discharge cycles and having excellent charge / discharge cycle performance.
In detail, it is an object to provide a non-aqueous electrolyte secondary battery with improved charge / discharge cycle performance. In a non-aqueous electrolyte secondary battery using unsaturated sultone as an electrolytic solution additive, Patent Document 6 reveals. The present invention has been completed as a result of intensive studies on “component ratios and composition ratios in materials” in a positive electrode active material by lithium transition metal oxides containing transition elements such as Mn, Ni, and Co that are not present. .

The invention according to claim 1 is a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the nonaqueous electrolyte includes at least one type of unsaturated sultone represented by the following chemical formula, The positive electrode active material contained is a composite oxide Li _x Mna _a Ni _b Co _c O _d having a layered α-NaFeO ₂ type crystal structure (0 <x <1.3, a + b + c = 1, 1.7 ≦ d ≦ 2.3), and | a−b | <0.03, and 0.33 ≦ c <1.

(Here, R _{1 to} R ₄ are each a hydrogen atom or the same or different alkyl group, alkoxy group, halogen, halogen-containing alkyl group, and aryl group, and n is 1 or 2.)

  The invention according to claim 2 is characterized in that, in claim 1, the unsaturated sultone is 1,3-propene sultone.

  According to a third aspect of the present invention, in the first or second aspect, the negative electrode is made of a carbon material capable of inserting and extracting lithium.

  According to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having a small increase in resistance even after repeated charge / discharge cycles and having excellent charge / discharge cycle performance.

The present invention provides a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte includes at least one kind of unsaturated sultone, and the positive electrode active material contained in the positive electrode includes a layered α composite oxide having -NaFeO ₂ type crystal structure _{Li x Mn a Ni b Co c} O d (0 <x <1.3, a + b + c = 1,1.7 ≦ d ≦ 2.3) a, | a −b | <0.03 and 0.33 ≦ c <1.

The unsaturated sultone used in the present invention has the following structure.

(Here, R _{1 to} R ₄ are each a hydrogen atom or the same or different alkyl group, alkoxy group, halogen, halogen-containing alkyl group, and aryl group, and n is 1 or 2.)

Of these, unsaturated sultone in which n = 1 and R _{1 to} R ₄ are both hydrogen atoms, that is, 1,3-propene sultone is preferable.

In the nonaqueous electrolyte battery including the positive electrode, the negative electrode, and the nonaqueous electrolyte, the effect that the unsaturated sultone suppresses the increase in resistance due to repeated charge / discharge cycles is added when the unsaturated sultone is added to the nonaqueous electrolyte as an additive. The positive electrode active material contained in the positive electrode is a composite oxide Li _x Mn _a Ni _b Co _c O _d (0 <x <1.3, a + b + c = 1, 1.7) having a layered α-NaFeO ₂ type crystal structure. ≦ d ≦ 2.3) where | a−b | <0.03 and 0.33 ≦ c <1.

  In the present invention, as the nonaqueous electrolyte, at least one kind of unsaturated sultone is contained, and either an electrolytic solution or a solid electrolyte can be used. Substances other than unsaturated sultone can also be used. In the case of using an electrolytic solution, as an electrolytic solution solvent, ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, sulfolane, 1,2-dimethoxyethane, 1,2-di- Ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, halogenated dioxolane, trifluoroethyl methyl ether, ethylene glycol diacetate, propylene glycol diacetate, ethylene glycol dipropionate, propylene glycol dipropio , Methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl fluoroacetate, full Ethyl oloacetate, propyl fluoroacetate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate, diisopropyl carbonate, dibutyl carbonate, acetonitrile, fluoroacetonitrile, ethoxy Alkoxy and halogen-substituted cyclic phosphazenes such as pentafluorocyclotriphosphazene, diethoxytetrafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene and phosphorus such as chain phosphazenes, triethyl phosphate, trimethyl phosphate, trioctyl phosphate Acid alkyl esters, triethyl borate, Boric acid esters such as c acid tributyl, N- methyl oxazolidinone, a non-aqueous solvent such as N- ethyl-oxazolidinones, or in itself can be used a mixture of these solvents.

  The unsaturated sultone represented by Chemical Formula 1 is desirably contained in the non-aqueous electrolyte in the range of 0.01 to 5.0% by mass at the time of manufacturing the battery. Good. By making the content of the unsaturated sultone contained in the nonaqueous electrolyte used in the production of the battery 0.01% by mass or more, the effect of suppressing the increase in resistance associated with the charge / discharge cycle can be made sufficient. Moreover, the possibility that the internal resistance of the battery becomes too large can be reduced by setting the content of unsaturated sultone to 5.0 mass% or less. Especially, it is preferable to set it as the range of 0.2-2.0 mass%.

The non-aqueous electrolyte varies depending on the non-aqueous electrolyte and the supporting salt used, but usually the supporting salt is dissolved in 0.5 to 1.5 mol / L in these non-aqueous 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 salts such as LiPF ₃ (CF ₂ CF ₃ ) ₃ or mixtures thereof can be used.

  In addition to the unsaturated sultone, 0.01 to 2% by mass of the additive is usually added to the nonaqueous electrolyte based on the weight of the nonaqueous electrolyte in order to improve battery characteristics. It may be mixed in the electrolyte, sulfate ester compound or phosphate ester compound, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, phenyl vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, dimethyl vinylene carbonate, diethyl Carbonates such as vinylene carbonate and fluoroethylene carbonate, vinyl esters such as vinyl acetate and vinyl propionate, diallyl sulfide, allyl phenyl sulfide, allyl vinyl sulfide, allyl ethyls Sulfides such as fido, propyl sulfide, diallyl disulfide, allyl ethyl disulfide, allyl propyl disulfide, allyl phenyl disulfide, etc., cyclic sulfones such as 1,3-propane sultone, 1,4-butane sultone, 1,3-prop-2-ene sultone, etc. Acid esters, methyl methanesulfonate, ethyl methanesulfonate, propyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, propyl ethanesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, propyl benzenesulfonate, methane Phenyl sulfonate, phenyl ethane sulfonate, phenyl propane sulfonate, methyl benzyl sulfonate, ethyl benzyl sulfonate, propyl benzyl sulfonate, methane sulfonate Chain sulfonates such as benzyl, ethane sulfonate, benzyl propane sulfonate, dimethyl sulfite, diethyl sulfite, ethyl methyl sulfite, methyl propyl sulfite, ethyl propyl sulfite, diphenyl sulfite, methyl phenyl Sulphite, ethyl methyl sulfite, ethylene sulfite, vinyl ethylene sulfite, divinyl ethylene sulfite, propylene sulfite, vinyl propylene sulfite, butylene sulfite, vinyl butylene sulfite, vinylene sulfite, phenyl ethylene sulfite, etc. Sulfites, benzene, toluene, xylene, biphenyl, cyclohexylbenzene, 2-fluorobiphenyl, 4-fluorobiphenyl , Diphenyl ether, tert-butylbenzene, orthoterphenyl, metaterphenyl, naphthalene, fluoronaphthalene, cumene, fluorobenzene, aromatic compounds such as 2,4-difluoroanisole, halogen-substituted alkanes such as perfluorooctane, boric acid You may add suitably according to the objective, such as trimethylsilyl and a triethylsilyl borate.

  When a solid electrolyte is used, a porous polymer solid electrolyte membrane is preferably used as the polymer solid electrolyte, and the polymer solid electrolyte may further contain an electrolytic solution. Moreover, when using a gel-like polymer solid electrolyte, the electrolyte solution which comprises gel and the electrolyte solution contained in the pore etc. may differ. When such a polymer solid electrolyte is used, unsaturated sultone may be contained in the electrolytic solution. However, when high output is required, such as for HEV applications, it is more preferable to use a non-aqueous electrolyte alone as the electrolyte than to use a solid electrolyte or a polymer solid electrolyte.

As a compound as a positive electrode material, as an active material, Li _x Mn _a Ni _b Co _c O _d (0 <x <1.3, a + b + c = 1, | a−b | <0.03, 0.33 ≦ c < 1. A compound represented by 1.7 ≦ d ≦ 2.3) is contained.
In addition to the active material, other positive electrode active materials may be mixed and used. Examples of other positive electrode active materials include group I metals such as CuO, Cu ₂ O, Ag ₂ O, CuS, and CuSO _4. Compounds, group IV metal compounds such as TiS ₂ , SiO ₂ , SnO, group V compounds such as V ₂ O ₅ , V ₆ O ₁₂ , VO _x , Nb ₂ O ₅ , Bi ₂ O ₈ , Sb ₂ O ₃ , CrO Group VI metal compounds such as ₈ , Cr ₂ O ₈ , MoO ₈ , MoS ₂ , WO ₃ , SeO ₂ , Group VII metal compounds such as MnO ₂ , Mn ₂ O ₈ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, and other group VIII metal compounds, for example, metal oxides such as lithium-cobalt based composite oxides and lithium-manganese based composite oxides, and disulfides , Polypyrrole, polyaniline Emissions, polyparaphenylene, polyacetylene, conductive polymer compounds such as polyacene-based material, but pseudo-graphite structure carbonaceous materials, and the like, but is not limited thereto.

For the positive electrode, the lithium-containing transition metal oxide is kneaded with a dielectric agent and a binder, and further, if necessary, with a filler to form a positive electrode mixture, and then the positive electrode mixture is used as a current collector foil, lath plate, etc. It is manufactured by applying or press-bonding to a heat treatment at a temperature of about 50 ° C. to 250 ° C. for about 2 hours. In the positive electrode, in addition to the main constituent components, a conductive agent, a binder, a thickener, a filler, and the like may be contained as other constituent components.
By using the positive electrode active material characterized by the present invention described above, the effect of the unsaturated sultone additive represented by Chemical Formula 1 is specifically recognized, and the increase in resistance associated with repeated charge / discharge cycles is significantly suppressed, Charge / discharge cycle performance can be dramatically improved.

  In the positive electrode active material, by setting | a−b | <0.03, the positive electrode active material has high discharge efficiency and high discharge capacity (see WO03 / 081698). Specifically, the discharge capacity decreases when Mn with ab> 0.03 is large, and the discharge capacity is good when Ni with ab <−0.03 is large. Safety is insufficient. That is, in the positive electrode active material outside the range of | a−b | <0.03, the high rate discharge performance and the total balance of discharge capacity and safety are inferior to those of the claimed positive electrode active material.

  Further, by taking a value in the range of 0.33 ≦ c <1, preferably 0.34 <c <1, the initial resistance value of the nonaqueous electrolyte secondary battery before use can be lowered. This effect is particularly noticeable at low temperatures.

  The compound as the negative electrode material contains a carbon material capable of occluding and releasing lithium, and includes amorphous materials such as non-graphitizable carbon and graphitizable carbon, and crystalline carbon materials such as graphite. Used. It is particularly preferable to use an amorphous material. Further, in addition to the carbon material, the modification can be performed using a metal oxide such as tin oxide or silicon oxide, phosphorus, boron, fluorine, or the like. In particular, by modifying the surface of the carbon material by the above method, it is possible to suppress the decomposition of the electrolyte and improve the battery characteristics, which is desirable.

  Furthermore, lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal-containing alloys such as wood alloys are used for the negative electrode, or in combination, It is also possible to use a carbon material in which lithium is inserted by electrochemical reduction in advance.

  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 in particular, a synthetic resin microporous membrane can be preferably used. Among them, polyolefin microporous membranes such as polyethylene and polypropylene microporous membranes, polyethylene and polypropylene microporous membranes combined with aramid and polyimide, or microporous membranes composited with these, thickness, membrane strength, membrane resistance, etc. It is suitably used in terms of

  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. However, in this case, since the battery output is reduced, it is preferable that the amount of the solid polymer electrolyte is kept to a minimum.

  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.

  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 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 50 mm, and a thickness of 5.0 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 7 via a positive electrode lead 10. It is connected.

The positive electrode plate is composed of 6% by mass of polyvinylidene fluoride as a binder, 6% by mass of acetylene black as a conductive agent, and a positive electrode active material LiMn _0.09 Ni _0.08 Co as a lithium-manganese-nickel-cobalt composite oxide. N-methylpyrrolidone is added to a positive electrode mixture obtained by mixing _0.83 O ₂ 88% by mass to prepare a paste, which is then applied to both sides of a 20 μm thick aluminum foil current collector and dried. It was prepared by.

  The negative electrode plate was prepared by adding 90% by mass of non-graphitizable carbon and 10% by mass of polyvinylidene fluoride to N-methylpyrrolidone to prepare a paste, which was then applied to both sides of a 10 μm thick copper foil current collector and dried. Made by doing.

A polyethylene microporous membrane is used as a separator, and a mixed solvent of ethyl carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 3: 2: 5 (volume ratio) is used as an electrolyte. Furthermore, LiPF ₆ was dissolved to 1 mol / L after adjustment, and 1,3-propene sultone was added to 1.0% by mass with respect to the total amount of the electrolytic solution.

  Three cells of the nonaqueous electrolyte secondary battery of Example 1 were produced by the above-described configuration and procedure.

[Examples 2 to 5 and Comparative Examples 1 to 7]
For the batteries of Examples 2 to 5 and Comparative Examples 1 to 7, as shown in Table 1, the nonaqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the composition of the positive electrode active material was changed. Three cells each were produced. However, in Comparative Example 5, lithium manganese oxide LiMn ₂ O ₄ having a spinel crystal structure was used as the positive electrode active material, and in Comparative Example 1, lithium cobalt oxide LiCoO ₂ was used as the positive electrode active material. Further, each of the nonaqueous electrolyte secondary batteries was changed in the same manner as in Example 4 and Comparative Example 1 except that the nonaqueous electrolyte used in the production of the battery was not added with unsaturated sultone. Three cells were prepared, and Comparative Example 6 and Comparative Example 7 were used.

About the square nonaqueous electrolyte secondary battery of Examples 1-5 and Comparative Examples 1-7 produced as described above, initial charge / discharge of 4 cycles was performed at 25 ° C. However, the charging conditions in the first cycle are a charging current of 45 mA, a charging voltage of 4.28 V, and a constant current and constant voltage charging with a charging time of 15 hours. The charging conditions after the second cycle are a charging current of 90 mA and a charging voltage of 4.28 V. The constant current and constant voltage charging was performed for 6 hours. The discharge conditions were constant current discharge with a discharge current of 90 mA and a final voltage of 2.50 V in all four cycles. The discharge capacity at the fourth cycle was defined as “initial discharge capacity X _a ”. The discharge capacity was 25 ° C. After charging for 6 hours with a constant current-constant voltage charge with a charge current of 90 mA and a charge voltage of 4.28 V, that is, with a current value of 90 mA, the voltage reached 4.28 V. Thereafter, constant voltage charging was performed at 4.28 V, charging was performed for a total of 6 hours, and then constant current discharging was performed under conditions of a discharge current of 90 mA and a final voltage of 2.50 V.

The resistance value before and after the charge / discharge cycle test was measured under a severe condition of -20 ° C. where the influence of the resistance increase becomes significant. The initial resistance value was measured by setting the battery charge depth (SOC) to 50% by charging for 3 hours with a current value of charge current of 1 ItmA, a constant current of a charge voltage of 3.78 V and a constant voltage charge, and −20 ° C. After 4 hours of cooling, the voltage when discharged for 10 seconds at 0.2 ItmA, the voltage when discharged for 10 seconds at 0.5 ItmA, and the voltage when discharged for 10 seconds at 1 ItmA were measured, and the discharge current (I ) Was measured by measuring the slope (R _a = E / I) of the voltage drop (E) with respect to), and this value (R _a ) was defined as “initial resistance value (Ω)”. For each battery, X _a (mA) was defined as 1 ItmA based on the value of the initial discharge capacity X _a (mAh).

The cycle test was conducted by the following method. After measuring the initial resistance R _a (initial resistance value), a charge end voltage was 4.10 V and a discharge end voltage was 3.03 V at a current value of 1 ItmA, and 300 cycles were performed at 45 ° C. After cooling to 25 ° C., the discharge capacity X _b is confirmed by the same method as the condition for confirming the initial discharge capacity, and then the DC resistance R _b after the charge / discharge cycle test is measured at −20 ° C. in the same manner as described above. did.

Increase rate of DC resistance was calculated using the formula (1) below from the DC resistance R _b after DC resistance R _a and the cycle test before the cycle test.

Resistance increase rate (%) = (R _b / R _a −1) × 100 (1)
Table 1 shows the resistance increase rate.

Capacity retention rate was calculated using the following equation (2) from the discharge capacity X _b confirming after the initial discharge capacity X _a and cycle tests confirmed before the cycle test.

Capacity maintenance rate (%) = X _b / X _a × 100 (2)

[Effect of additive]
From Example 4 and Comparative Example 6, and Comparative Example 1 and Comparative Example 7 in which the composition of the positive electrode active material is the same, it is clear that the resistance increase rate is large and the capacity retention rate is low when unsaturated sultone is not added. It was. That is, it was revealed that by adding unsaturated sultone, a battery having high input / output characteristics and excellent charge / discharge cycle performance was obtained.

[Effect of positive electrode active material composition]
Comparing the example with a comparative example having a positive electrode active material having a value of c outside the range of 0.33 ≦ c <1, in the example, the rate of increase in resistance after repeated charge / discharge cycles is low and the capacity is maintained. It is clear from Table 1 that the rate is high. Even if the value of c satisfies 0.33 ≦ c <1, if the value of c is outside the range of | a−b | <0.03, the value of c is in the range of 0.33 ≦ c <1. It turns out that it may be equivalent to the case where it is outside, or it may worsen conversely. That is, it is clear that the nonaqueous electrolyte secondary battery of the example is a battery having a small increase in resistance and excellent charge / discharge cycle performance even when the charge / discharge cycle is repeated.

  It is clear from Table 1 that the effects of the additive and the positive electrode active material are synergistically achieved. That is, for example, regarding the rate of increase in resistance associated with repeated charge / discharge cycles, when the value of c is outside the range of 0.33 ≦ c <1, it is clear when comparing Comparative Example 7 and Comparative Example 1. The addition of unsaturated sultone is only suppressed to 1/3 to 1/4, but surprisingly, when the value of c satisfies 0.33 ≦ c <1, As is clear from comparison between Example 6 and Example 4, it can be seen that a remarkable effect of being suppressed to about 1/10 is achieved.

That is, in the present invention, the composition of the positive electrode active material is Li _x Mn _a Ni _b Co _c O _d (0 <x <1.3, a + b + c = 1, 1.7 ≦ d ≦ 2.3). Unsaturated sultone is added to the electrolyte solution in the electrolyte secondary battery, and the composition is | a−b | <0.03 and 0.33 ≦ c <1, so that the charge / discharge cycle performance is excellent. It became clear that it became a battery.

In addition, since a part of unsaturated sultone is consumed on an electrode when a battery is prepared and charged and discharged, the amount of the nonaqueous electrolyte contained in the battery is smaller than the amount normally added.
When the amount of 1,3-propene sultone added in the nonaqueous electrolyte used in the production of the battery was variously changed and the experiment was performed in the same manner as in the above example, the amount of 1,3-propene sultone added was 0.00. It was confirmed that the same effect was exhibited when the content was 01 to 5.0% by mass. In addition, when the battery of Example 1 was produced separately and the initial charge / discharge was performed, and the nonaqueous electrolyte was collected and analyzed, 10 ppm of 1,3-propene sultone was detected.

  According to the present invention, even when charging and discharging are repeatedly used, an increase in the internal resistance of the nonaqueous electrolyte secondary battery can be suppressed, and the capacity retention rate does not decrease. Therefore, the nonaqueous solution has excellent input characteristics and output characteristics. An electrolyte secondary battery can be provided.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Square type nonaqueous electrolyte secondary battery 2 Winding type electrode group 3 Positive electrode 4 Negative electrode 5 Separator 6 Battery case 7 Battery cover 8 Safety valve 9 Negative electrode terminal 10 Positive electrode lead 11 Negative electrode lead

Claims (3)

In a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, the non-aqueous electrolyte includes at least one kind of unsaturated sultone represented by the following chemical formula, and the positive electrode active material contained in the positive electrode is layered A composite oxide Li _x Mn _a Ni _b Co _c O _d (0 <x <1.3, a + b + c = 1, 1.7 ≦ d ≦ 2.3) having an α-NaFeO ₂ type crystal structure, A nonaqueous electrolyte secondary battery in which | a−b | <0.03 and 0.33 ≦ c <1.

(Here, R _{1 to} R ₄ are each a hydrogen atom or the same or different alkyl group, alkoxy group, halogen, halogen-containing alkyl group, and aryl group, and n is 1 or 2.)   The non-aqueous electrolyte secondary battery according to claim 1, wherein the unsaturated sultone is 1,3-propene sultone. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is made of a carbon material capable of inserting and extracting lithium.

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