JP2020077575A - Lithium ion secondary battery - Google Patents

Abstract

To improve battery performance furthermore, by improving the state of the positive electrode surface, in addition to the negative electrode surface.SOLUTION: In a lithium ion secondary battery of the present invention having a positive electrode and a negative electrode capable of occluding and ejecting lithium ions, a separator, electrolyte, and a case for receiving a group of these battery elements, lithium hexafluorophosphate and methane disulfonyl difluoride exist in the electrolyte before reception in the case, addition amount of the methane disulfonyl difluoride to the electrolyte before reception is 0.5 wt% or more, and the value of resistance at 10 Hz of the AC resistance of the lithium ion secondary battery, after receiving the group of battery elements in the case and storing it for a prescribed period, is lower by 15% or more, compared with the case where the methane disulfonyl difluoride is not added.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium ion secondary battery.

  2. Description of the Related Art In recent years, lithium ion secondary batteries have been widely used as electronic devices such as mobile phones and notebook computers, electric vehicles, and power sources for power storage. In particular, recently, a demand for a battery having a high capacity, a high output and a high energy density, which can be mounted on a hybrid vehicle or an electric vehicle, is rapidly expanding. It is known that this lithium-ion secondary battery has a great difference in reactivity depending on the electrolytic solution containing an organic solvent used, and affects battery characteristics. Therefore, in Patent Document 1, methanedisulfonyldifluoride (hereinafter referred to as a sulfone compound) is added as an additive to a mixed organic solvent as an electrolytic solution to improve cycle characteristics and storage characteristics of a secondary battery. ing.

Japanese Patent No. 4538753

  However, as a result of diligent studies by the inventor, it was found that further improvement in battery performance can be expected by paying attention to the decrease in the resistance value of the positive electrode when the additive is added to the mixed organic solvent. In particular, in recent years, not only the cycle characteristics but also the demands for higher output and larger capacity are expanding, and from that point as well, it is extremely important to reduce the resistance of the battery.

  It is an object of the present invention to further improve the battery performance by adding not only the state of the negative electrode surface but also the state of the positive electrode surface when the sulfone compound is added to the electrolytic solution.

  The lithium ion secondary battery of the present invention is a lithium ion secondary battery having a positive electrode and a negative electrode capable of inserting and extracting lithium ions, a separator, an electrolytic solution, and a case accommodating these battery element groups. A lithium hexafluorophosphate and a sulfone compound are contained in the electrolytic solution before being housed in the case, the addition amount of the sulfone compound to the electrolytic solution before being housed is 0.5 wt% or more, and the battery element is provided in the case. The lithium ion secondary battery after accommodating the group and storing it for a predetermined period has a resistance value of 10% or less in the AC resistance at 10 Hz as compared with the case where no sulfone compound is added.

  INDUSTRIAL APPLICABILITY The lithium-ion secondary battery of the present invention can improve the battery performance by reducing the internal resistance of the battery and particularly suppressing the positive electrode resistance.

1 is a sectional view of a lithium ion secondary battery according to an embodiment of the present invention. 9 is a table in which the DC resistance DCIR before and after storage of the batteries 01, 1 to 3 is standardized with the battery 01 as a reference. 9 is a table in which AC resistances EIS-Z "before and after storage of batteries 01, 02, 1 to 3 are standardized with battery 0 as a reference. It is a graph showing EIS-Z "(10 Hz) after storage of batteries 01, 02, and 1-3.

Hereinafter, preferred embodiments of the present invention will be described. INDUSTRIAL APPLICABILITY The present invention can be widely applied to various lithium ion secondary batteries including a negative electrode in which a negative electrode mixture layer is applied to at least one surface of a negative electrode current collector, a positive electrode, a separator, lithium ions, and an electrolytic solution. .. Hereinafter, the present invention will be described in more detail mainly with reference to an electrolytic solution and a lithium ion secondary battery including the electrolytic solution, but the present invention is not intended to be limited to the electrolytic solution or the battery.
[Overall configuration of lithium-ion secondary battery]
First, the overall configuration of a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a lithium ion secondary battery according to an embodiment of the present invention. Such a lithium ion secondary battery is called a stacked lithium ion secondary battery. Although the structure of the laminated cell is shown in FIG. 1, the lithium-ion secondary battery of the present invention may be a wound type in which a positive electrode, a negative electrode, and a separator are stacked and wound in layers.

  As shown in FIG. 1, the lithium-ion secondary battery 1 of the present embodiment has an inside of an outer casing 30 (corresponding to a case) in which a battery element 10 to which a positive electrode lead 21 and a negative electrode lead 22 are attached is formed of a laminate film. It has a structure enclosed in. Then, in the present embodiment, the positive electrode lead 21 and the negative electrode lead 22 are led out in the opposite directions from the inside of the exterior body 30 to the outside. Although not shown, the positive electrode lead and the negative electrode lead may be led out in the same direction from the inside to the outside of the outer package. Further, such a positive electrode lead and a negative electrode lead can be attached to a positive electrode current collector and a negative electrode current collector which will be described later, for example, by ultrasonic welding or resistance welding.

  As shown in FIG. 1, the battery element 10 includes a positive electrode 11 in which a positive electrode mixture layer 11B is formed on both main surfaces of a positive electrode current collector 11A, a separator 13, and a negative electrode current collector 12A. A plurality of negative electrodes 12 each having a negative electrode active material layer 12B formed on the surface thereof are laminated. At this time, the positive electrode mixture layer 11B formed on one main surface of the positive electrode current collector 11A of the one positive electrode 11 and one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the one positive electrode 11 The negative electrode active material layer 12B formed thereabove faces through the separator 13. In this way, a plurality of positive electrodes, separators and negative electrodes are laminated in this order.

By pouring the electrolyte solution into this, the adjacent positive electrode mixture layer 11B, the separator 13 and the negative electrode active material layer 12B form one unit cell layer 14. Therefore, the lithium ion secondary battery 1 of the present embodiment has a configuration in which a plurality of unit cell layers 14 are stacked and electrically connected in parallel. The positive electrode and the negative electrode may be those in which each active material layer is formed on one surface of each current collector.
[Negative electrode for lithium-ion secondary battery]
The negative electrode 12 has a configuration in which a negative electrode mixture layer 12B is provided on one surface of a negative electrode current collector 12A. Here, the negative electrode mixture layer 12B contains a negative electrode active material, a conductive auxiliary material, and a water-dispersible binder. These substances in the negative electrode mixture layer 12B are in contact with the electrolytic solution injected into the battery.

  The negative electrode mixture layer 12B in the present embodiment is formed in a film shape with a predetermined thickness on the surface of the negative electrode current collector 12A. As the negative electrode current collector 12A, various types can be used, but usually a metal or an alloy is used. Specifically, examples of the conductive base material for the positive electrode include aluminum, nickel, and SUS, and examples of the conductive base material for the negative electrode include copper, nickel, and SUS. Among them, aluminum and copper are preferable from the viewpoint of high conductivity and cost balance. In addition, aluminum means aluminum and an aluminum alloy, and copper means pure copper and a copper alloy. In this embodiment, the aluminum foil can be used on the secondary battery positive electrode side, the secondary battery negative electrode side, and the copper foil can be used on the secondary battery negative electrode side. The aluminum foil is not particularly limited, but various materials such as A1085 material and A3003 material which are pure aluminum can be used. The same applies to the copper foil, and although not particularly limited, rolled copper foil or electrolytic copper foil is preferably used.

The thickness of the negative electrode mixture layer of the present embodiment is preferably, for example, 5 μm or more, more preferably 10 μm or more. The thickness is preferably 200 μm or less, more preferably 100 μm or less, still more preferably 75 μm or less. When the thickness of the negative electrode mixture layer is in the above range, it is easy to obtain a sufficient lithium occlusion / release function for charge / discharge at a high charge / discharge rate. Hereinafter, the negative electrode active material, the conductive auxiliary material, and the water-dispersible binder constituting the negative electrode mixture layer 12B will be described in order.
(Negative electrode active material)
As the negative electrode active material, metallic lithium, a lithium-containing alloy, a metal or an alloy capable of alloying with lithium, an oxide capable of doping / dedoping lithium ions, a transition metal capable of doping / dedoping lithium ions At least one selected from the group consisting of nitrides and carbon materials capable of doping / dedoping lithium ions (may be used alone, or may be used as a mixture containing two or more thereof). Can be used. Among these, carbon materials capable of doping / dedoping lithium ions are preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The form of the carbon material may be any of fibrous, spherical, potato-like and flake-like forms. The particle size is not particularly limited, but is usually 5 to 50 μm, preferably about 20 to 30 μm.

  Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or lower, and mesophase pitch carbon fiber (MCF).

Examples of the graphite material include natural graphite and artificial graphite. As the artificial graphite, graphitized MCMB, graphitized MCF or the like is used. Further, as the graphite material, a material containing boron can be used. Further, as the graphite material, a material coated with a metal such as gold, platinum, silver, copper, tin, a material coated with amorphous carbon, or a material mixed with amorphous carbon and graphite can be used.
These carbon materials may be used alone or in combination of two or more.

(Conduction aid)
The negative electrode mixture layer preferably contains a conductive auxiliary material. As the conductive auxiliary material used in the present invention, a known conductive auxiliary material can be used. The known conductive aid is not particularly limited as long as it is a carbon material having conductivity, but graphite, carbon black, conductive carbon fibers (carbon nanotube, carbon nanofiber, carbon fiber), fullerene, etc. They can be used alone or in combination of two or more. Examples of commercially available carbon blacks include Toka Black # 4300, # 4400, # 4500 and # 5500 (manufactured by Tokai Carbon Co., furnace black), Printex L, etc. (manufactured by Degussa, furnace black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conducttex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK 100, 115, 205 etc. (Columbyan company, furnace black), # 2350, # 2400B, # 2600B, # 30050B, # 3030 #, 3030B, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3030 #, # 3050 #. 3350B, # 3400B, # 5400B, etc. (Mitsubishi Chemical Co., furnace black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LITX-50, LITX-200, etc. (Cabot Co., furnace black), Ensaco250G, Ensaco260G. , Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketjenblack EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denki Kagaku Kogyo, acetylene black). Examples of graphite include, but are not limited to, natural graphite such as artificial graphite, flake graphite, massive graphite, and earth graphite.

(Water dispersible binder)
The water-dispersible binder is selected from styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, carboxymethyl cellulose (CMC), and hydroxypropyl methyl cellulose, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose 1 One kind or a combination of two or more kinds can be used. In particular, it is desirable to use a mixture of styrene butadiene rubber and carboxymethyl cellulose as the negative electrode binder.

  The above water-dispersible binder is preferably used in an amount of 0.1 to 4 wt% with respect to the negative electrode mixture layer in order to achieve both physical properties (electrolyte permeability and peel strength) of the negative electrode mixture layer and battery performance. .. If it is less than 0.1 wt%, the adhesive force of the active material is weakened, which may cause desorption of the active material during the charging / discharging process. If it exceeds 4% by weight, the amount of the active material decreases, which is not desirable in terms of battery capacity.

(Other ingredients)
The negative electrode mixture layer according to the present embodiment may contain other appropriate components in addition to the above components. For example, when the negative electrode mixture layer is formed from the mixture slurry, the negative electrode mixture layer may contain various compounding components derived from the mixture slurry. Examples of various compounding ingredients derived from such a mixture slurry include a thickener and other additives such as a surfactant, a dispersant, a wetting agent, and a defoaming agent.
(Method of forming negative electrode mixture layer)
The composite material layer included in the negative electrode for the lithium-ion secondary battery of the present embodiment is applied to the surface of the current collector with the negative electrode active material, the conductive auxiliary material, and the negative electrode composite material slurry containing the water-dispersible binder, and dried. Can be manufactured. It is preferable to use water as the solvent contained in the mixture slurry, but if necessary, for example, a liquid medium compatible with water may be used in order to improve coatability on the current collector. .. The liquid medium compatible with water includes alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters. Examples thereof include ethers, ethers, nitriles, etc., and may be used in a range compatible with water.

There is no particular limitation on the coating / drying method for coating / drying the mixture slurry on the current collector. Examples include methods such as slot / die coating, slide coating, curtain coating, or gravure coating. Examples of the drying method include drying with warm air, hot air, low humidity air, vacuum drying, and (far) infrared rays. The drying time and the drying temperature are not particularly limited, but the drying time is usually 1 minute to 30 minutes and the drying temperature is usually 40 ° C to 80 ° C.
The method for producing the composite material layer has a step of lowering the porosity of the active material layer by applying a pressure treatment after applying and drying the mixture slurry on the current collector, using a die press or a roll press. Is preferred.

(Cathode active material)
The positive electrode active material is not particularly limited as long as it is a material capable of inserting and extracting lithium, and may be a positive electrode active material commonly used in lithium ion secondary batteries. Specifically, in addition to an oxide containing lithium (Li) and nickel (Ni) as constituent metal elements, at least one metal element other than lithium and nickel (that is, a transition metal element other than Li and Ni, and / Or a typical metal element) is also meant to include an oxide containing as a constituent metal element in the same or smaller proportion as nickel in terms of the number of atoms. Examples of metal elements other than Li and Ni include Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, It may be one or more metal elements selected from the group consisting of La and Ce. These positive electrode active materials may be used alone or in combination of two or more.

In a preferred embodiment, the positive electrode active material, for example, the general formula _{(1): Li t Ni 1} -x-y Co x Al y O 2 ( where, in the formula, 0.95 ≦ t ≦ 1.15, A lithium nickel cobalt aluminum oxide (NCA) represented by 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.2, and x + y <0.5 is satisfied. A specific example of NCA is LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

In another preferred embodiment, the positive electrode active material may be, for example, a compound represented by the general formula (2): LiNi _a Co _b Mn _c O ₂ (wherein 0 <a <1, 0 <b <1, 0 <c < 1 and satisfying a + b + c = 1) is a lithium nickel cobalt manganese oxide (NCM). NCM has a high energy density per volume and is excellent in thermal stability.
The content of the positive electrode active material in the electrode mixture layer is usually 10 wt% or more, preferably 30 wt% or more, more preferably 50 wt% or more, and particularly preferably 70 wt% or more. Further, it is usually 99.9 wt% or less, preferably 99 wt% or less.

  The binder that may be used in the positive electrode active material layer includes, for example, polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride-hexafluoropropylene copolymer, and the like. Examples of the rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, a binder containing fluorine is preferable in consideration of improving the oxidation resistance of the positive electrode active material layer. The binder may be used alone or in combination of two or more as required.

[Separator]
Examples of the separator include a microporous film made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose and polyamide, a porous flat plate, and a non-woven fabric. A preferred example is a porous resin sheet having a single-layer or multi-layer structure mainly composed of one or more kinds of polyolefin resins. The thickness of the separator can be, for example, 15 μm to 30 μm. In a preferred embodiment, the separator has a shut-down function and includes a porous resin layer made of a thermoplastic resin such as polyethylene. According to this aspect, when the temperature of the separator reaches the softening point of the thermoplastic resin, the resin melts and the pores are clogged, so that the current can be cut off.

[Electrolyte]
The electrolytic solution is preferably, for example, one that is usually used in a lithium ion secondary battery, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Here, as the lithium salt, for example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ). Lithium hexafluorotantalate (LiTaF ₆ ), lithium tetrachloroaluminate (LiAlCl ₄ ), lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ), and other inorganic acid anion salts, lithium trifluoromethanesulfonate ( LiCF ₃ SO _3), lithium bis (trifluoromethanesulfonyl) imide _{(Li (CF 3 SO 2)} 2 N), lithium bis (pentafluoroethane sulfonyl) imide _{(Li (C 2 F 5 SO} 2) 2 N) , such as At least one kind of lithium salt selected from organic acid anion salts and the like can be mentioned. Among them, lithium hexafluorophosphate (LiPF ₆ ) is preferable.

  Examples of the organic solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, and γ-lactone. It is possible to use at least one organic solvent selected from the group consisting of compounds, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, and fluorine-containing chain ethers.

  Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate (BC). In addition, examples of the fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC). Furthermore, as the chain carbonates, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), dipropyl carbonate (DPC). Can be mentioned. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Furthermore, examples of γ-lactones include γ-butyrolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane. Furthermore, examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. .. Other examples include nitriles such as acetonitrile and amides such as dimethylformamide. These may be used alone or in combination of two or more.

(Methanedisulfonyldifluoride)
Here, in the embodiment, the electrolytic solution contains methanedisulfonyldifluoride (hereinafter referred to as a sulfone compound) as an additive. The content of the sulfone compound can be set arbitrarily, but is preferably 0.01% by weight or more and 10% by weight or less. This is because high chemical stability can be obtained in the electrolytic solution. More specifically, if it is less than 0.01% by weight, the chemical stability of the electrolytic solution may not be sufficiently and stably obtained, and if it is more than 10% by weight, the main electrical conductivity of the electrochemical device may be insufficient. This is because there is a possibility that sufficient performance (for example, capacity characteristics of a battery) cannot be obtained.

  The solvent used together with the sulfone compound preferably contains one or more non-aqueous solvents such as other organic solvents. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, and the like. 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, Methyl butyrate, methyl isobutyrate, methyl trimethylacetate, ethyl trimethylacetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, Examples thereof include N, N′-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphoric acid. Among them, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate is preferable, and particularly, a high viscosity (high dielectric constant) solvent such as ethylene carbonate or propylene carbonate (for example, a ratio of A combination of a dielectric constant ε ≧ 30) and a low-viscosity solvent such as dimethyl carbonate, ethylmethyl carbonate or diethyl carbonate (for example, viscosity ≦ 1 mPa · s) is more preferable. This is because the dissociation property of the electrolyte salt and the ion mobility are improved.

  Further, the solvent may contain a cyclic carbonic acid ester having an unsaturated bond. This is because the chemical stability of the electrolytic solution is further improved. Examples of the cyclic carbonic acid ester having an unsaturated bond include vinylene carbonate-based compounds, vinyl ethylene carbonate-based compounds, and methylene ethylene carbonate-based compounds.

  Examples of the vinylene carbonate-based compound include vinylene carbonate (1,3-dioxole-2-one), methylvinylene carbonate (4-methyl-1,3-dioxole-2-one), ethylvinylene carbonate (4-ethyl- 1,3-dioxole-2-one), 4,5-dimethyl-1,3-dioxole-2-one, 4,5-diethyl-1,3-dioxole-2-one, 4-fluoro-1,3 -Dioxole-2-one, 4-trifluoromethyl-1,3-dioxole-2-one and the like can be mentioned.

  Examples of vinyl ethylene carbonate compounds include vinyl ethylene carbonate (4-vinyl-1,3-dioxolan-2-one), 4-methyl-4-vinyl-1,3-dioxolan-2-one, 4-ethyl. -4-Vinyl-1,3-dioxolan-2-one, 4-n-propyl-4-vinyl-1,3-dioxolan-2-one, 5-methyl-4-vinyl-1,3-dioxolane-2 -One, 4,5-divinyl-1,3-dioxolan-2-one, 4,5-divinyl-1,3-dioxolan-2-one and the like.

  Examples of the methylene ethylene carbonate compound include 4-methylene-1,3-dioxolan-2-one, 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one and 4,4-diethyl-5-one. Examples thereof include methylene-1,3-dioxolan-2-one.

  These may be used alone or as a mixture of a plurality of types. Of these, vinylene carbonate is preferable. This is because a high effect can be obtained.

  Further, the solvent may contain sultone (cyclic sulfonic acid ester) or acid anhydride. This is because the chemical stability of the electrolytic solution is further improved.

  Examples of the sultone include propane sultone and propene sultone. These may be used alone or as a mixture of a plurality of types. Of these, propene sultone is preferable. The content of sultone in the solvent is preferably 0.5% by weight or more and 3% by weight or less. This is because a high effect can be obtained in any case.

  Examples of the acid anhydrides include succinic anhydride, carboxylic acid anhydrides such as glutaric anhydride and maleic anhydride, and disulfonic anhydrides such as ethanedisulfonic acid and propanedisulfonic anhydride, and sulfobenzoic anhydride and anhydride. Examples thereof include anhydrides of carboxylic acids such as sulfopropionic acid or sulfobutyric anhydride, and sulfonic acids. These may be used alone or as a mixture of a plurality of types. Of these, sulfobenzoic anhydride is preferable. Further, the content of the acid anhydride in the solvent is preferably 0.5% by weight or more and 3% by weight or less. This is because a high effect can be obtained in any case.

  The intrinsic viscosity of the solvent is preferably 10.0 mPa · s or less at 25 ° C. This is because the dissociation property of the electrolyte salt and the ion mobility are improved. The intrinsic viscosity in a state where the electrolyte salt is dissolved in the solvent (so-called intrinsic viscosity of the electrolytic solution) is preferably 10.0 mPa · s or less at 25 ° C for the same reason.

[Example]
Preparation of negative electrode 1. Slurry preparation For the slurry preparation, a 5 L planetary dispa was used.
To 960 g of natural graphite and 10 g of Super-P (conductive carbon, BET specific surface area 62 m ² / g), 450 g of 1% CMC (CMC dissolved in pure water) was added and mixed for 30 minutes. Next, after adding 300 g of 1% -CMC aqueous solution and kneading for 30 minutes, 250 g of 1% -CMC was further added and kneading for 30 minutes. Thereafter, 50 g of SBR (40% emulsion) serving as a binder was added and mixed for 30 minutes, and then vacuum degassing was performed for 30 minutes. Thus, a slurry having a solid content concentration of 45% was prepared.

2. Coating / drying A die coater was used for slurry coating. The above slurry was applied to one side of a copper foil (thickness 10 μm) and dried so that the applied weight after drying was 11.0 mg / cm ² . Next, on the opposite surface (uncoated surface), the above slurry was applied to a copper foil and dried so that the applied weight was 11.0 mg / cm ² . The thus obtained double-sided coated (22.0 mg / cm ² ) negative electrode roll was dried in a vacuum drying oven at 120 ° C. for 12 hours to obtain an electrode.

3. Press A small press was used. The gap between the upper and lower rolls was adjusted, and the negative electrode was compressed so that the press density was 1.45 ± 0.05 g / cm ³ .

4. Slit The electrode was slit so that the electrode application area (front surface: 58 mm × 372 mm, back surface: 58 mm × 431 mm) and tab welding margin were obtained, and the negative electrode A-1 was obtained.

Preparation of positive electrode 1. Slurry preparation For the slurry preparation, a 5 L planetary dispa was used. 920 g of NCM523 (compositional formula LiNi _0.5 Co _0.2 Mn _0.3 O ₂ manufactured by Umicore), Super-P (conductive carbon manufactured by TIMCAL) 20 g, KS-6 (scaly graphite manufactured by TIMREX). After mixing 20 g for 10 minutes, 100 g of N-methylpyrrolidone (NMP) was added and further mixed for 20 minutes.

  Next, after adding 150 g of 8% -binder solution and kneading for 30 minutes, 150 g of 8% -binder solution was further added and kneading for 30 minutes. Then, 200 g of 8% -binder solution was added and kneaded for 30 minutes. Next, 80 g of a solution dissolved in NMP was added and kneaded for 30 minutes. After that, 27 g of NMP was added for viscosity adjustment and mixed for 30 minutes, followed by vacuum degassing for 30 minutes. Thus, a slurry having a solid content concentration of 60% was prepared.

2. Coating / drying A die coater was used for slurry coating. The above slurry was applied to one side of an aluminum foil (thickness 20 μm, width 200 mm) and dried so that the applied weight after drying was 19.0 mg / cm ² . Then, on the opposite surface (uncoated surface), the above-mentioned slurry was applied onto an aluminum foil so that the applied weight was 19.0 mg / cm ² , and dried.
The double-sided coated positive electrode roll (38.0 mg / cm ² ) thus obtained was dried in a vacuum drying oven at 130 ° C. for 12 hours.

3. Press A 35 ton press was used. The gap between the upper and lower rolls was adjusted and the positive electrode was compressed so that the press density was 2.9 ± 0.05 g / cm ³ .

4. Slit The electrode was slit so that the electrode application area (front surface: 56 mm × 334 mm, back: 56 mm × 408 mm) and the tab welding margin were obtained to obtain a positive electrode C-1.

Battery fabrication Wound type battery (design capacity 1Ah)
1. The separator with the porous heat-resistant layer (60.5 mm × 450 mm) was used as the wound separator.
Negative electrode A-1 (front surface / back surface), separator (arranged so that the porous insulating layer is in contact with positive electrode C-1), positive electrode C-1 (back surface / front surface), separator (porous insulating layer is positive electrode C-1) They were arranged so as to come into contact with each other, and were wound and press-molded. Next, an aluminum tab was joined to the margin of the positive electrode C-1 with an ultrasonic bonding machine, and a nickel tab was joined to the margin of the negative electrode A-1 with an ultrasonic bonding machine. This was sandwiched between laminate sheets and heat-sealed on three sides.

Preparation of Electrolyte Solution Ethylene carbonate (hereinafter, EC), dimethyl carbonate (hereinafter, DMC), and methyl ethyl carbonate (EMC) were mixed as a non-aqueous solvent to prepare a mixed solvent. In producing the electrolytic solution, LiPF ₆ contained in the electrolytic solution was dissolved so that the electrolyte concentration in the finally obtained non-aqueous electrolytic solution was 1 mol / liter. An electrolyte solution containing no additive was prepared as the electrolyte solution of Comparative Example 1. Further, a sulfone compound was added to the above mixed solvent to prepare nonaqueous electrolytic solutions of Comparative Example 2 and Example. An electrolyte solution of Sample 0 was prepared in which the addition amount of the sulfone compound (that is, the content relative to the total amount of the final nonaqueous electrolyte solution) was 0.25% by mass. Further, as the addition amount of the sulfone compound, Sample 1 having 0.5% by mass, Sample 2 having 1.0% by mass, and Sample 3 having 1.5% by mass were prepared. Samples 1 to 3 are the electrolytic solutions of the examples. Further, in the final non-aqueous electrolyte, the mass ratio of EC, DMC and EMC was adjusted to be EC: DMC: EMC = 30: 35: 35 (mass ratio). As the battery of Comparative Example 1, a battery made of an additive-free electrolyte was designated as Battery 01, as the battery of Comparative Example 2 the battery made of Sample 0 was designated as Battery 02, and as the battery of Example, batteries made of Samples 1 to 3 were designated. Are batteries 1 to 3.

2. Electrolytic solution injection Before the electrolytic solution injection, the above was dried under reduced pressure at 70 ° C. for 12 hours in a vacuum dryer. After injecting 4.7 ± 0.1 g of an electrolytic solution (1 mol-LiPF6, EC / DEC = 3/7 (vol. Ratio), additive VC 1.0% by mass), heat sealing was performed while drawing a vacuum.
3. Aging treatment The batteries 01, 02, 1 to 3 after injection of the electrolytic solution were held for 12 hours at an ambient temperature of 40 ° C. Then, at 40 ° C. atmosphere temperature, constant current charging is performed at 0.05 C to 3.0 V, constant current charging at 0.1 C to 3.4 V, constant current charging at 0.24 C to 3.7 V, and 40 ° C. atmosphere. It rested for 24 h under temperature. After that, constant current constant voltage charging (0.5C-CCCV) was performed at 0.5C to 4.2V under an atmosphere temperature of 40 ° C, and after 30 minutes of rest, constant current discharging (0.5V) to 0.5V at 0.5C. 5C-CC). Furthermore, it was charged to 4.2V with 0.5C-CCCV, and was discharged to 3.7V with 0.5C-CC, and was charged to 3.7V. And it preserve | saved at 40 degreeC atmospheric temperature for 7 days. Thus, batteries 01, 02, 1 to 3 were obtained.

[Battery resistance]
Next, the DC resistance DCIR and the AC resistance EIS-Z "of the batteries 01, 02, 1-3 before and after storage were measured. A standardized table, FIG. 3, is a table in which the alternating current resistance EIS-Z ″ before and after storage of the batteries 01, 02, 1 to 3 is standardized with the battery 01. In addition, the normalization indicates a relative value when the value of each battery is divided by the value of the battery 01 and the battery 01 is set to 100.
(DC resistance DCIR)
In the measurement of DC resistance, after charging / discharging by the following method, the initial battery resistance was measured at 25 ° C.
First, CC (s) were discharged from SOC (State of Charge) 50% at a discharge rate of 0.2C, and CC-CVs were charged at a charge rate of 0.2C.
Next, CC10s discharge was performed at a discharge rate of 1C, and CC-CV10s charge was performed at a discharge rate of 2C.
Next, CC10s discharge was performed at a discharge rate of 2C, and CC-CV10s charge was performed at a charge rate of 2C.
Next, CC10s discharge was performed at a discharge rate of 5C, and CC-CV10s charge was performed at a charge rate of 5C. Thus, batteries 01, 02, 1 to 3 were obtained.
In addition, CC10s discharge means discharging with a constant current (Constant Current) for 10 seconds. CC-CV10s charging means charging with a constant current constant voltage (Constant Current-Constant Voltage) for 10 seconds.
DC resistance was determined from each charge / discharge rest current and each charge / discharge rest voltage, and the obtained DC resistance was used as the initial battery resistance of the battery. After the battery was stored at 60 ° C. for 1 week, the battery resistance after storage was determined by the above method, and the DC resistance before and after storage is shown in the DCIR column in FIG. The value of each battery is standardized with the battery 01.

(AC resistance EIS-Z ")
In measuring the AC resistance, the AC impedance of the batteries 01, 02, 1 to 3 was measured by the following method. The SOC of the battery was adjusted to 50%, and the Bode-Plot at 25 ° C was measured (BioLogic, VSP-300).
The frequency was changed from 0.1 Hz to 6 MHz, and Bode-Plot was obtained from the resistance value of the imaginary part and the response frequency. Furthermore, the resistance value at 10 Hz was extracted by Bode-Plot. After storing the battery at 60 ° C for 1 week, the EIS after storage was obtained by the above method, and the AC resistance before and after storage is shown in the EIS-Z "(10Hz) column of Fig. 3. Value of each battery Is standardized with Battery 01. EIS-Z "(10 Hz) is represented mainly as a resistance value derived from the positive electrode.

  As shown in the table of FIG. 2, the DC resistances DCIR of the batteries 1 to 3 before and after storage are lower than those of the battery 01 before the addition of the sulfone compound. Therefore, it can be seen that the resistance of the entire battery is lowered. In addition, as shown in FIG. 3, in the battery 02 with the sulfo compound addition amount of 0.25 wt%, the EIS-Z "(10 Hz) before and after storage is almost the same as that of the battery 01 before the sulf compound addition. On the other hand, EIS-Z "(10 Hz) before and after storage in batteries 1 to 3 has a lower value than that of battery 01 before addition of the sulfone compound. Therefore, it can be seen that the resistance derived from the positive electrode is remarkably reduced. From this, it is understood that when the addition amount of the sulfone compound is small, the sulfone compound can act on the negative electrode, but cannot act on the positive electrode and the resistance derived from the positive electrode cannot be reduced. On the other hand, in the batteries 1 to 3, the battery 3 containing 1.5% by mass of the sulfone compound had a larger decrease in both DC resistance and AC resistance than the battery 1 containing 0.5% by mass. It can be said that the effect of the addition of is remarkable.

  Fig. 4 is a graph showing EIS-Z "(10 Hz) after storage of batteries 01, 02, 1-3. From this graph, the resistance value of battery 02 in which the amount of sulfone compound added is less than 0.5 wt% is shown. It can be seen that there is almost no decrease with respect to the resistance value of Battery 01. In addition, when the amount of the sulfone compound added is in the range of 0.5 wt% to 1.0 wt%, the value of the battery 0 (0 wt%) after storage in the positive electrode The resistance value has dropped by 15% or more. Although there is no significant change between Battery 1 (0.5 wt%) and Battery 2 (1.0 wt%), Battery 2 (1.0 wt%) and Battery 3 ( It can be seen that the resistance value at the positive electrode is significantly reduced between the values of 1.5 wt%) and 40% or more with respect to the battery 01.

  Therefore, in order to reduce the resistance value derived from the positive electrode, the added amount of the sulfone compound is preferably 0.5 wt% or more, more preferably 1.5 wt% or more.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 10 Battery element 11 Positive electrode 12 Negative electrode 13 Separator 21 Positive electrode lead 22 Negative electrode lead

Claims (3)

A lithium-ion secondary battery having a positive electrode and a negative electrode capable of inserting and extracting lithium ions, a separator, an electrolytic solution, and a case housing these battery element groups,
Having lithium hexafluorophosphate and methanedisulfonyldifluoride (hereinafter, sulfone compound) in the electrolytic solution before being stored in the case,
Of the AC resistance of the lithium ion secondary battery after the addition of the sulfone compound to the pre-housing electrolyte solution is 0.5 wt% or more, and the battery element group is housed in the case and stored for a predetermined period. A lithium-ion secondary battery having a resistance value at 10 Hz that is 15% or more lower than that when the sulfone compound is not added. The lithium ion secondary battery according to claim 1,
The amount of the sulfone compound added to the pre-storage electrolyte is 1.5 wt% or more, and the resistance value at 10 Hz of the AC resistance of the lithium-ion secondary battery after storage for the predetermined period is equal to that of the sulfone compound. A lithium ion secondary battery characterized by being 40% or more lower than when not added. The lithium ion secondary battery according to claim 1 or 2,
The positive electrode active material of the positive electrode is LiNiaCobMncO2 (wherein 0 <a <1, 0 <b <1, 0 <c <1, and satisfies a + b + c = 1). Next battery.

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