JP6119641B2 - Cylindrical non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a cylindrical non-aqueous electrolyte secondary battery, and more particularly to a cylindrical non-aqueous electrolyte secondary battery with high energy density that improves discharge characteristics in a low-temperature environment and has excellent cycle characteristics.

  In recent years, there is a demand for a power source that has a high energy density and can be used in a low-temperature environment of −30 ° C. or lower and that has a longer life as a power source for a power source of an electric vehicle or a hybrid electric vehicle.

  Conventionally, aqueous secondary batteries such as lead storage batteries and nickel metal hydride batteries have been mainstream as secondary batteries for in-vehicle power. These batteries are excellent in output characteristics and cycle characteristics, but are not satisfactory in terms of battery weight and energy density per volume.

  In recent years, research and development of non-aqueous electrolyte secondary batteries using a positive electrode and a negative electrode that can release or occlude lithium ions have been actively conducted as secondary batteries for in-vehicle power. Non-aqueous electrolyte secondary batteries have excellent characteristics such as light weight, high energy density, and low self-discharge.

  In a nonaqueous electrolyte secondary battery, an organic solvent is generally used for the electrolyte in order to achieve a high operating voltage. Since this electrolyte solution requires a high dielectric constant for dissolving the non-aqueous electrolyte and a low viscosity for increasing the mobility of the dissolved ions, a high dielectric constant solvent such as ethylene carbonate (EC) or propylene carbonate (PC) is generally used. And an organic electrolytic solution in which a low viscosity solvent such as dimethyl carbonate or ethyl methyl carbonate is mixed.

  However, such an organic electrolyte generally has a lower electrical conductivity than an aqueous electrolyte, and thus low temperature output characteristics and cycle characteristics are insufficient for vehicle-mounted power.

  Patent Document 1 describes that by making the composition ratio of the organic mixed solvent suitable, it can be used in a wide temperature range, and the cycle characteristics can be improved by improving the electrochemical stability of the electrolytic solution. Has been.

  According to Patent Document 2, it is possible to improve the cycle characteristics without depending on the composition of the organic electrolytic solution by optimizing the amount of the electrolytic solution per battery discharge capacity and holding a sufficient amount of the electrolytic solution in the electrode. It is stated that it can be done.

JP-A-7-45304 JP 2001-229980 A

In the organic electrolytic solution described in Patent Document 1, the freezing point of the organic electrolytic solution is set to less than −20 ° C. by reducing the mixing ratio of dimethyl carbonate. However, when the mixing ratio of dimethyl carbonate, which is a low-viscosity solvent, is decreased, the viscosity of the organic electrolyte is increased and the conductivity is decreased. Therefore, in a non-aqueous electrolyte secondary battery having a high energy density exceeding 550 Wh / L. However, there is a problem that the cycle characteristics are deteriorated mainly due to the influence of the diffusion of the electrolyte during charging and discharging.

On the other hand, the optimization of the amount of electrolyte described in Patent Document 2 is intended to retain a sufficient amount of electrolyte in the electrode. However, the general formula LiMO ₂ (where M is at least one of Co and Ni). In a non-aqueous electrolyte secondary battery having an energy density of more than 550 Wh / L using a lithium transition metal composite oxide represented by Species) or an intercalation compound containing lithium, an electrolyte solution that does not contribute to the energy amount of the battery It is not possible to secure a sufficient space for holding the film, and it cannot be a means for solving the above problems.

The present invention can be also be used under -30 ° C. The following low-temperature environment, and to provide a non-aqueous electrolyte secondary battery excellent as cycle characteristics.

The non-aqueous electrolyte secondary battery of the present invention is a positive electrode and a negative electrode, a separator and a cylindrical non-aqueous electrolyte secondary battery having an electrolyte solution containing a lithium transition metal composite oxide, the electrolyte The mass is 55% or less with respect to the mass of the lithium transition metal composite oxide, the electrolytic solution contains dimethyl carbonate, and the volume ratio of dimethyl carbonate is 20% or more and 55% or less with respect to the total amount of the nonaqueous solvent, lithium transition metal composite oxide has the general _{formula: Li x Ni 1- (p +} q + r) Co p Al q M r O 2 + y ( at least one element M is selected from the group consisting of tungsten, titanium and zirconium, 0. 9 ≦ x ≦ 1.2, −1.0 ≦ y ≦ 0.1, 0.0001 ≦ r ≦ 0.01, 0 <p + q + r ≦ 0.4).

  In the present invention, by reducing the volume ratio of dimethyl carbonate in the electrolytic solution to 55% or less with respect to the total amount of the non-aqueous solvent, the freezing point of the electrolytic solution becomes −30 ° C. or lower, and the discharge characteristics in a low temperature environment are improved. To do.

  Furthermore, by using a lithium transition metal composite oxide to which at least one element selected from the group consisting of tungsten, titanium, and zirconium is added as the positive electrode active material, the reaction uniformity of the lithium transition metal composite oxide can be improved. improves. Thereby, the uniformity of the concentration distribution of the electrolytic solution in the electrode plate is improved, the deposition of lithium metal on the negative electrode due to the liquid withering of the electrolytic solution is suppressed, and the cycle characteristics are improved.

  As a result, in a high energy density non-aqueous electrolyte secondary battery in which the mass of the electrolyte is 55% or less with respect to the mass of the lithium transition metal composite oxide, By suppressing the deposition of lithium metal on the negative electrode due to the liquid withering of the electrolyte, both low temperature discharge characteristics and cycle characteristics can be achieved.

  The present invention provides a non-aqueous electrolyte secondary battery having high low temperature characteristics, excellent long life characteristics, and high energy density.

It is a longitudinal cross-sectional view of the nonaqueous electrolyte secondary battery in one Embodiment of this invention.

  The objects, features, and advantages of the present invention will become more apparent by referring to the following detailed description and accompanying drawings.

  First, a preferred embodiment of the non-aqueous electrolyte secondary battery according to the present invention will be described.

  A nonaqueous electrolyte secondary battery 1 shown in FIG. 1 includes a battery case 2 made of stainless steel and an electrode group accommodated in the battery case 2. The electrode group includes a positive electrode 5, a negative electrode 6, and a polyethylene separator 7, and the positive electrode 5 and the negative electrode 6 are wound around the separator 7 in a spiral shape. An upper insulating plate 8a and a lower insulating plate 8b are disposed above and below the electrode group. The battery case 2 is sealed by caulking the sealing plate 3 to the opening end of the battery case 2 via the gasket 4. One end of an aluminum positive electrode lead 5a is attached to the positive electrode 5, and the other end of the positive electrode lead 5a is connected to a sealing plate 3 that also serves as a positive electrode terminal. One end of a nickel negative electrode lead 6 a is attached to the negative electrode 6, and the other end of the negative electrode lead 6 a is connected to the battery case 2 that also serves as a negative electrode terminal.

The positive electrode 5 has the general formula as a positive electrode active _{material: Li x Ni 1- (p +} q + r) Co p Al q M r O 2 + y ( at least one element M is selected from the group consisting of tungsten, titanium and zirconium, 0.9 ≦ x ≦ 1.2, −1.0 ≦ y ≦ 0.1, 0.0001 ≦ r ≦ 0.01, 0 <p + q + r ≦ 0.4).

  In the lithium transition metal composite oxide used in the present embodiment, p, q, and r indicate the content ratios of cobalt (Co), aluminum (Al), and element M in this order. The sum of p, q, and r (p + q + r) indicates the amount of substitution of Co, Al, and element M as different elements with respect to nickel (Ni) in the lithium-containing nickel oxide. The range of (p + q + r) is preferably 0 <(p + q + r) ≦ 0.4, and more preferably 0.03 ≦ (p + q + r) ≦ 0.3. If (p + q + r) is too small, that is, if the amount of Ni in the lithium-containing nickel oxide is replaced by Co, Al and element M is too small, the cycle life and thermal stability as the positive electrode active material tend to decrease. is there. Conversely, if (p + q + r) is too large, that is, if the amount of substitution by Co, Al and element M is too large, the capacity of the positive electrode active material tends to decrease.

  The range of p indicating the Co content ratio is preferably 0 ≦ p ≦ 0.4, more preferably 0 <p <0.4, and particularly preferably 0.01 ≦ p ≦ 0.3. The range of q indicating the Al content ratio is preferably 0 ≦ q ≦ 0.3, more preferably 0 <q <0.3, and particularly preferably 0.01 ≦ q ≦ 0.2. The range of r indicating the content ratio of the element M is preferably 0.0001 ≦ r ≦ 0.01.

  The element M includes at least one element selected from the group consisting of tungsten, titanium, and zirconium. By selecting these elements as the element M, the reaction uniformity in the secondary particles of the lithium transition metal composite oxide synthesized by firing can be improved. In addition, the cycle characteristics and reliability of the nonaqueous electrolyte secondary battery can be improved.

  The range of 1- (p + q + r) indicating the Ni content ratio is 0.6 ≦ [1- (p + q + r)] <1, preferably 0.6 <[1- (p + q + r)] ≦ 0.97. is there.

  In the lithium transition metal composite oxide represented by the above general formula, y represents an oxygen excess amount or an oxygen deficiency amount, and the range is preferably -0.1 to 0.1. If y is out of the above range, the amount of excess oxygen or oxygen deficiency tends to increase and the crystal structure tends to be distorted, which may reduce the reversibility during charge / discharge.

As a binder contained in a positive electrode mixture, the binder used for the positive electrode of a nonaqueous electrolyte secondary battery can be mentioned without particular limitation. Specifically, fluorine-containing polymers such as polytetrafluoroethylene, polyvinylidene fluoride (PVDF), modified PVDF, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer; styrene -Rubber such as butadiene rubber; and polyolefin resins such as polyethylene and polypropylene. These can be used individually by 1 type and can also be used in combination of 2 or more type.

  Examples of the conductive agent include graphites; carbon blacks such as acetylene black, ketjen black, furnace black, lamp black, and thermal black; carbon fibers and metal fibers.

  The negative electrode 6 includes a negative electrode active material capable of inserting and extracting lithium without any particular limitation. Specific examples include carbon materials such as graphite and amorphous carbon, silicon and its oxide, tin and its oxide.

  A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  As a binder, the thing similar to what was illustrated as a binder used for formation of the positive electrode 5 is mentioned.

  The negative electrode mixture can further contain an additive such as a conductive agent. Examples of the conductive agent include those exemplified as the conductive agent used for forming the positive electrode 5.

  The separator 7 is interposed between the positive electrode 5 and the negative electrode 6 and separates the positive electrode 5 and the negative electrode 6. Examples of the separator 7 include a microporous thin film, a woven fabric, and a nonwoven fabric having an insulating property that have a high ion permeability and sufficient mechanical strength.

  The material of the separator is preferably a polyolefin such as polypropylene or polyethylene from the viewpoint that it has excellent durability and can exhibit a shutdown function during overheating.

  The thickness of the separator is generally 10 to 300 μm, preferably 40 μm or less, more preferably 5 to 30 μm, and still more preferably 10 to 25 μm.

  Furthermore, the separator may be a single layer film made of one material, or a composite film or a multilayer film made of two or more materials. The porosity of the separator is preferably 30 to 70%, and more preferably 35 to 60%. The porosity indicates the ratio of the volume of the hole portion to the total volume of the separator.

The electrode group is accommodated in the battery case 2 together with a non-aqueous electrolyte solution (not shown).
The nonaqueous electrolytic solution includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, dimethyl carbonate (DMC) occupies 20% to 55% of the entire solvent volume, and ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, fluoroethylene carbonate (FEC), or γ -It contains at least one non-aqueous solvent selected from the group consisting of cyclic esters such as butyrolactone (GBL). Non-aqueous solvents other than these can be mixed without any particular limitation. Specifically, chain carbonates such as ethyl methyl carbonate (EMC) and diethyl carbonate (DEC); tetrahydrofuran, 1,4-dioxane, 1, A cyclic ether such as 3-dioxolane; a chain ether such as 1,2-dimethoxyethane and 1,2-diethoxyethane; and a chain ester such as methyl acetate can be used in combination.

Examples of the lithium salt include various lithium salts used as a solute in the non-aqueous electrolyte solution of the non-aqueous electrolyte secondary battery. _{Specifically, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiSO 3 CF 3, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) ( SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) _{3 and the} like. These can be used individually by 1 type and can also be used in combination of 2 or more type. The concentration of the lithium salt is preferably 0.5 to 2 mol / L.

  The nonaqueous electrolytic solution preferably further contains a cyclic carbonate having at least one carbon-carbon unsaturated bond. Such a cyclic carbonate decomposes on the negative electrode to form a film having high lithium ion conductivity. This coating contributes to the improvement of charge / discharge efficiency. Examples of the cyclic carbonate having at least one carbon-carbon unsaturated bond include vinylene carbonate, 3-methyl vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, and the like. In the cyclic carbonate, a part of hydrogen atoms may be substituted with fluorine atoms. The dissolved amount of the cyclic carbonate in the non-aqueous solvent is preferably 0.1 to 10% by mass with respect to the total amount of the non-aqueous solvent.

  The nonaqueous electrolytic solution may further contain a benzene derivative. The benzene derivative decomposes during overcharge and forms a film on the electrode, thereby inactivating the battery. As the benzene derivative, those having a phenyl group and a cyclic compound group adjacent to the phenyl group are preferable. Specific examples include cyclohexyl benzene, biphenyl, diphenyl ether and the like. The content of the benzene derivative is preferably 10% by volume or less of the whole non-aqueous solvent.

  Hereinafter, the present invention will be described more specifically with reference to examples. The scope of the present invention is not limited to the examples.

(Experimental example 1)
(1) Preparation of positive electrode active material Lithium carbonate (Li ₂ CO ₃ ) and a coprecipitated hydroxide represented by Ni _0.7495 Co _0.2 Al _0.05 W _0.0005 (OH) ₂ were _mixed with carbonic acid. The mixture obtained was mixed so that the ratio of the number of moles of Li in lithium to the number of moles of Ni, Co and Al in the coprecipitated hydroxide (Ni + Co + Al) was 1.03: 1. Baking was performed at 700 ° C. for 20 hours in an atmosphere. After firing, the fired product was crushed and classified to obtain lithium transition metal composite oxide A having an average particle size of 10 μm. The composition of the obtained lithium transition metal composite oxide A was LiNi _0.7495 Co _0.2 Al _0.05 W _0.005 O ₂ , and the Li content ratio x was 1.00.

(2) Production of positive electrode 90 parts by mass of positive electrode active material A, N-methyl-2-pyrrolidone (NMP) solution of PVDF containing 5 parts by mass of polyvinylidene fluoride (PVDF), 5 parts by mass of acetylene black ( A positive electrode mixture slurry was obtained by mixing AB). A positive electrode active material layer was formed by applying and drying a positive electrode mixture slurry on both surfaces of an aluminum foil having a thickness of 20 μm as a positive electrode current collector. The thus obtained laminate including the positive electrode active material layers on both sides of the positive electrode current collector was pressed and rolled with a pair of rollers to obtain a positive electrode 5 having a total thickness of 120 μm. In addition, the exposed part of the positive electrode current collector in which the positive electrode active material layer was not formed was provided on one side in the short direction of the positive electrode current collector.

(3) Production of negative electrode A negative electrode mixture slurry was obtained by mixing 95 parts by mass of artificial graphite powder and an NMP solution of PVDF containing 5 parts by mass of PVDF. A negative electrode active material layer was formed by applying and drying a negative electrode mixture slurry on both surfaces of a 10 μm thick copper foil as a negative electrode current collector. The thus obtained laminate including the negative electrode active material layers on both sides of the negative electrode current collector was pressed and rolled with a pair of rollers to obtain a negative electrode 6 having a total thickness of 180 μm. In addition, the exposed part of the negative electrode collector in which the negative electrode active material layer was not formed was provided in the short side of the negative electrode collector.

(4) Preparation of non-aqueous electrolyte Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:55:25. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution A was obtained.

(5) Production of Cylindrical Battery The positive electrode 5 and the negative electrode 6 are placed between the positive electrode and the negative electrode with a microporous separator 7 (composite film of polyethylene and polypropylene, product number “2300” manufactured by Celgard Co., Ltd.) An electrode group was obtained by winding in a spiral shape with a thickness of 25 μm. A positive electrode lead 5a made of aluminum was welded to the exposed portion of the positive electrode current collector of the positive electrode 5, and a negative electrode lead 6a made of nickel was welded to the exposed portion of the negative electrode current collector. The electrode group thus obtained was inserted into a battery case 2 having a substantially cylindrical shape with a bottom having a diameter of 18 mm and a height of 65 mm. Next, 55% of the non-aqueous electrolyte A is injected into the battery case with respect to the total mass of the lithium transition metal composite oxide, and the battery case 2 is covered with the sealing plate 3 via the gasket 4 at the open end. The battery was completed by crimping. Then, the open circuit voltage was stabilized by leaving the obtained battery at room temperature for about 24 hours.

(Experimental example 2)
Lithium carbonate (Li ₂ CO ₃ ) and a coprecipitated hydroxide represented by Ni _0.7495 Co _0.2 Al _0.05 Ti _0.0005 (OH) ₂ , the number of moles of Li in the lithium carbonate, The coprecipitation hydroxide was mixed so that the ratio of the total number of Ni, Co, and Al (Ni + Co + Al) to the number of moles was 1.03: 1, and the resulting mixture was heated at 700 ° C. under an oxygen atmosphere at 20 ° C. Baked for hours. After firing, the fired product was crushed and classified to obtain lithium transition metal composite oxide B having an average particle size of 10 μm. The composition of the obtained lithium transition metal composite oxide B was LiNi _0.7495 Co _0.2 Al _0.05 Ti _0.005 O ₂ , and the Li content ratio x was 1.00. A battery was fabricated in the same manner as in Experimental Example 1, except that the lithium transition metal composite oxide A was used in place of the lithium transition metal composite oxide B.

(Experimental example 3)
Lithium carbonate (Li ₂ CO ₃ ) and a coprecipitated hydroxide represented by Ni _0.7495 Co _0.2 Al _0.05 Zr _0.0005 (OH) ₂ , the number of moles of Li in the lithium carbonate, The coprecipitation hydroxide was mixed so that the ratio of the total number of Ni, Co, and Al (Ni + Co + Al) to the number of moles was 1.03: 1, and the resulting mixture was heated at 700 ° C. in an oxygen atmosphere. Baked for 20 hours. After firing, the fired product was crushed and classified to obtain lithium transition metal composite oxide C having an average particle size of 10 μm. The composition of the obtained lithium transition metal composite oxide C was LiNi _0.7495 Co _0.2 Al _0.05 Zr _0.005 O ₂ , and the Li content ratio x was 1.00. A battery was fabricated in the same manner as in Experimental Example 1, except that the lithium transition metal composite oxide A was used instead of the lithium transition metal composite oxide C.

(Experimental example 4)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:20:60. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution B was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution B was used in place of the nonaqueous electrolytic solution A.

(Experimental example 5)
Propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:55:25. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution C was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution C was used instead of the nonaqueous electrolytic solution A.

(Experimental example 6)
γ-Butyrolactone, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:55:25. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A non-aqueous electrolyte D was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution D was used in place of the nonaqueous electrolytic solution A.

(Experimental example 7)
Fluoroethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:55:25. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. Nonaqueous electrolyte E was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution E was used instead of the nonaqueous electrolytic solution A.

(Experimental example 8)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 30:55:15. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution F was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution F was used instead of the nonaqueous electrolytic solution A.

(Experimental example 9)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 25:20:55. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution G was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution G was used instead of the nonaqueous electrolytic solution A.

(Experimental example 10)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 35:55:10. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution H was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution H was used instead of the nonaqueous electrolytic solution A.

(Experimental example 11)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:60:20. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution I was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution I was used in place of the nonaqueous electrolytic solution A.

(Experimental example 12)
Ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 20:15:65. A nonaqueous electrolytic solution was prepared by dissolving vinylene carbonate and LiPF ₆ in the thus obtained nonaqueous solvent. By adjusting the content of vinylene carbonate to 1% by mass with respect to the total amount of the non-aqueous solvent, the concentration of LiPF ₆ in the non-aqueous electrolyte is adjusted to 1.0 mol / L. A nonaqueous electrolytic solution J was obtained. A battery was fabricated in the same manner as in Experimental Example 1, except that the nonaqueous electrolytic solution J was used in place of the nonaqueous electrolytic solution A.

(Experimental example 13)
Lithium carbonate (Li ₂ CO ₃ ) and a coprecipitated hydroxide represented by Ni _0.75 Co _0.2 Al _0.05 (OH) ₂ , the number of moles of Li in lithium carbonate, and the above-mentioned coprecipitated hydroxide The mixture was mixed so that the ratio of the total number of Ni, Co, and Al (Ni + Co + Al) in the product was 1.03: 1, and the resulting mixture was calcined at 700 ° C. for 20 hours in an oxygen atmosphere. . After firing, the fired product was crushed and classified to obtain lithium transition metal composite oxide D having an average particle size of 10 μm. The composition of the obtained lithium transition metal composite oxide D was LiNi _0.7495 Co _0.2 Al _0.05 O ₂ , and the Li content ratio x was 1.00. A battery was fabricated in the same manner as in Experimental Example 1, except that the lithium transition metal composite oxide A was used instead of the lithium transition metal composite oxide D.

(Experimental example 14)
A battery was fabricated in the same manner as in Experimental Example 1, except that the lithium transition metal composite oxide A was replaced with the lithium transition metal composite oxide D, and the nonaqueous electrolyte A was replaced with the nonaqueous electrolyte I. .

(Experimental example 15)
The positive electrode and the negative electrode were prepared so that the mass of the positive electrode active material layer and the mass of the negative electrode active material layer were 45% by mass of Experimental Example 1, respectively, and the nonaqueous electrolyte A was replaced with the nonaqueous electrolyte I. Produced a battery in the same manner as in Experimental Example 1.

(Experimental example 16)
A positive electrode and a negative electrode were prepared so that the mass of the positive electrode active material layer and the mass of the negative electrode active material layer were 45% by mass of Experimental Example 1, respectively, and the non-aqueous electrolyte A was replaced with the non-aqueous electrolyte I. A battery was fabricated in the same manner as in Experimental Example 1, except that 60% of the non-aqueous electrolyte I was injected into the total mass of the lithium transition metal composite oxide.

(Experimental example 17)
A battery was fabricated in the same manner as in Experimental Example 1, except that the positive electrode and the negative electrode were fabricated so that the mass of the positive electrode active material layer and the mass of the negative electrode active material layer were 45% by mass of Experimental Example 1, respectively.

(Experiment 18)
The positive electrode and the negative electrode were prepared so that the mass of the positive electrode active material layer and the mass of the negative electrode active material layer were 45% by mass of Experimental Example 1, respectively, and the total mass of the lithium transition metal composite oxide in the battery case A battery was fabricated in the same manner as in Experimental Example 1, except that 60% of the non-aqueous electrolyte A was injected.

  Table 1 shows the measurement results of the energy density, low temperature discharge characteristics, and cycle characteristics of the batteries obtained in Experimental Examples 1 to 10 and Experimental Examples 11 to 18.

  The energy density was measured by the following procedure. First, the battery was charged to 4.2 V at a constant current of 10 hours in an atmosphere of 25 ° C. Then, it was discharged to 2.5 V at a constant current of 10 hours. The discharge capacity (Wh) at this time was measured and used as the initial discharge capacity Q. Energy density E (Wh / L) was determined by dividing initial discharge capacity Q thus determined by battery volume V (0.0165 L).

  The low temperature discharge characteristics were measured by the following procedure. First, the battery was charged to 4.2 V at a constant current of 10 hours in an atmosphere of 25 ° C. Next, after storing in an atmosphere of −30 ° C. for 6 hours, the battery was discharged to 3 V at a constant current of 1 hour in an atmosphere of −30 ° C. The discharge capacity (Wh) at this time was measured to obtain a low temperature discharge capacity.

  The cycle characteristics were measured by the following procedure. The battery was charged at an upper limit voltage of 4.2 V in an atmosphere of 25 ° C., charged at a constant current and constant voltage for 4 hours at a maximum current value of 2 hours, and then 2.5 V at a constant current of 1 hour. The charge / discharge cycle was repeated until the battery was discharged.

  The ratio (Q2 / Q1) between the discharge capacity (Q1) at the first cycle of this charge / discharge cycle and the discharge capacity (Q2) after the elapse of 500 cycles was defined as the battery capacity retention rate.

As shown in Table 1, in the batteries of Experimental Examples 1 to 4, the low temperature discharge capacity is improved as compared with the characteristics of the batteries of Experimental Example 11 and Experimental Examples 14 to 16. This is presumably because the freezing point of the electrolytic solution could be set to −30 ° C. or lower by setting the volume ratio of dimethyl carbonate in the electrolytic solution solvent to 55% or less.

  Furthermore, in the batteries of Experimental Examples 1 to 4, the cycle characteristics are improved as compared with the characteristics of the battery of Experimental Example 13. When at least one element selected from the group consisting of tungsten, titanium and zirconium is added to the lithium transition metal composite oxide, a high resistance layer (NiO) formed on the surface of the lithium transition metal composite oxide during charge / discharge Layer) becomes thinner. As a result, the reaction uniformity of the lithium transition metal composite oxide has been improved, the uniformity of the concentration distribution of the electrolyte in the electrode plate during the cycle has been improved, and the deposition of lithium metal on the negative electrode due to liquid drainage has been suppressed. Conceivable.

  In addition, since the volume ratio of dimethyl carbonate in the electrolyte was reduced to 55% or less, liquid dying due to oxidative decomposition of dimethyl carbonate in the cycle and generation of a high resistance layer formed on the material surface due to oxidative decomposition were suppressed. It can be considered that this is also synergistically contributing to the improvement of cycle characteristics.

  Furthermore, the batteries of Experimental Examples 1 to 4 were able to improve the energy density as compared with the battery of Experimental Example 18. This is because the cycle characteristics can be secured even if the amount of the electrolyte injected into the battery is decreased and the amount of the positive and negative electrode active materials is increased due to the effect of improving the cycle characteristics described above. On the other hand, the cycle characteristics of the battery of Experimental Example 12 are not improved as the batteries of Experimental Example 1 or Experimental Example 4. This is presumably because when the volume ratio of dimethyl carbonate is too low, the viscosity of the electrolyte solution is excessively increased and the conductivity is excessively decreased, thereby eliminating the effect of improving the cycle characteristics described above. Therefore, it can be seen that the volume ratio of dimethyl carbonate is preferably 20% or more and 55% or less with respect to the total amount of the non-aqueous solvent.

  In addition, the batteries of Experimental Examples 5 to 7 have improved cycle characteristics as compared with the battery of Experimental Example 13 as in Experimental Example 1. Even if any one of ethylene carbonate, propylene carbonate, γ-butyrolactone, and fluoroethylene carbonate is used alone or in combination with the cyclic ester used in the non-aqueous solvent, the effect of improving the cycle characteristics similar to Experimental Example 1 is exhibited. It shows that

  On the other hand, in the battery of Experimental Example 9, the effect of improving the cycle characteristics is reduced as compared with the batteries of Experimental Example 1, Experimental Example 4, and Experimental Example 8. The reason for this is not clear, but when the volume ratio of the cyclic ester in the electrolytic solution exceeds the volume ratio of dimethyl carbonate, the effect of improving the cycle characteristics is not exhibited like the battery of Experimental Example 1. It is thought that there is. Therefore, it can be seen that the volume ratio of the cyclic ester in the electrolytic solution is preferably not more than the volume ratio of dimethyl carbonate.

  In addition, the battery of Experimental Example 10 is less effective in improving cycle characteristics than the batteries of Experimental Example 1, Experimental Example 4, and Experimental Example 8. This is considered to be because when the volume ratio of the cyclic ester in the non-aqueous solvent exceeds 30%, the viscosity of the electrolytic solution is excessively increased and the electrical conductivity is excessively decreased, thereby reducing the effect of improving the cycle characteristics. Therefore, it can be seen that the volume ratio of the cyclic ester is preferably 30% or less with respect to the total amount of the non-aqueous solvent.

  The non-aqueous electrolyte secondary battery of the present invention has high low-temperature characteristics, excellent long-life characteristics, and high energy density. For example, electric vehicles, hybrid cars, electric assist bicycles, electric tools, emergency power supplies, loads It is suitable as a power source such as a leveling power source.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Battery case 3 Sealing plate 4 Gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate

Claims (3)

A cylindrical non-aqueous electrolyte secondary battery having a positive electrode including a lithium transition metal composite oxide, a negative electrode, a separator, and an electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent ,
The electrolyte solution has a mass of 55% or less based on the mass of the lithium transition metal composite oxide,
The electrolyte contains dimethyl carbonate;
The volume ratio of the dimethyl carbonate is 20% or more and 55% or less with respect to the total amount of the non-aqueous solvent,
The lithium transition metal composite oxide has the general _{formula: Li x Ni 1- (p +} q + r) Co p Al q M r O 2 + y ( at least one element M is selected from the group consisting of tungsten, titanium and zirconium, 0 .9 ≦ x ≦ 1.2, −1.0 ≦ y ≦ 0.1, 0.0001 ≦ r ≦ 0.01, 0 <p + q + r ≦ 0.4) battery. The electrolytic solution contains at least one cyclic ester selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone, and fluoroethylene carbonate,
The cylindrical non-aqueous electrolyte secondary battery according to claim 1, wherein a volume ratio of the cyclic ester is equal to or less than a volume ratio of the dimethyl carbonate. The cylindrical nonaqueous electrolyte secondary battery according to claim 2, wherein a volume ratio of the cyclic ester is 30% or less with respect to a total amount of the nonaqueous solvent.

Images