JP7276957B2 - lithium ion secondary battery - Google Patents

Description

The present invention relates to lithium ion secondary batteries.

In recent years, lithium-ion secondary batteries have been widely used as power sources for electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage. In recent years, in particular, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be installed in hybrid vehicles and electric vehicles. It is known that the reactivity of the lithium ion secondary battery greatly varies depending on the electrolyte solution containing the organic solvent used, which affects the battery characteristics. Therefore, in Patent Document 1, vinylene carbonate (hereinafter referred to as VC) and lithium bis[oxalato]borate (hereinafter referred to as LiBOB) are added as additives to a mixed organic solvent as an electrolytic solution. We are working to improve the cycle characteristics and safety of secondary batteries.

JP 2017-139087 A

However, as a result of intensive studies by the inventors, it was found that in a battery in which the above additive was added to the mixed organic solvent, the characteristics of the battery were greatly affected by the aging treatment conditions during the initial charge. It was found that the combination of , further affects the characteristics of the battery.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium ion secondary battery capable of sufficiently drawing out the performance of an additive in an electrolytic solution.

In the lithium ion secondary battery of the present invention, the non-aqueous electrolyte contains lithium hexafluorophosphate (hereinafter, LiPF ₆ ) as an electrolyte, and VC, LiBOB, and difluoro[oxolato-O,O' as additives. ] Lithium borate (hereinafter referred to as LiDFOB) is contained, and as the initial charging step of the lithium ion secondary battery, the state of charge (hereinafter, SOC: State Of Charge) of the lithium ion secondary battery is reduced to 30% or less. An initial charging step of charging to a first SOC and storing for a predetermined time, and a subsequent charging step of charging to an SOC higher than the first SOC and storing for a predetermined time are provided.

INDUSTRIAL APPLICABILITY The lithium-ion secondary battery of the present invention suppresses an increase in direct current resistance and a decrease in discharge capacity when the battery is used repeatedly, so that the battery performance can be improved.

1 is a cross-sectional view of a lithium ion secondary battery according to an embodiment of the invention; FIG. FIG. 4 is a diagram showing direct-current resistance DCIR before and after storage; FIG. 3 is a diagram showing post-storage increase rates of DC resistance DCIR before and after storage (DCIR after storage/DCIR before storage). FIG. 4 is a diagram showing discharge capacity values before and after storage; It is a figure showing the discharge capacity maintenance rate before and after storage (discharge capacity before storage/discharge capacity after storage). It is a figure showing direct-current resistance DCIR before and behind a cycle test. FIG. 4 is a diagram showing DCIR increase rates before and after a cycle test (DCIR after cycle test/DCIR before cycle test). It is a figure showing discharge capacity before and after a cycle test. It is a figure showing the discharge capacity maintenance rate before and behind a cycle test (discharge capacity before a cycle test/discharge capacity after a cycle test).

Preferred embodiments of the present invention are described below. INDUSTRIAL APPLICABILITY The present invention can be widely applied to various lithium ion secondary batteries comprising a negative electrode in which a negative electrode mixture layer is applied to at least one side 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 provided with this electrolytic solution, but the scope of application of the present invention is not intended to be limited to such an electrolytic solution or battery.
[Overall configuration of lithium ion secondary battery]
First, the overall configuration of a lithium ion secondary battery according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to one embodiment of the invention. Such a lithium ion secondary battery is called a laminated lithium ion secondary battery. Although FIG. 1 shows the configuration of a laminated cell, 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 a configuration in which a battery element 10 to which a positive electrode lead 21 and a negative electrode lead 22 are attached is enclosed in an exterior body 30 formed of a laminate film. have. In this embodiment, the positive electrode lead 21 and the negative electrode lead 22 are led out in opposite directions from the interior of the exterior body 30 toward the exterior. In addition, although not shown, the positive electrode lead and the negative electrode lead may be led out in the same direction from the inside of the package toward the outside. Moreover, 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, by, for example, 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. It has a configuration in which a plurality of negative electrodes 12 each having a negative electrode mixture layer 12B formed on its surface are laminated. At this time, positive electrode mixture layer 11B formed on one main surface of positive electrode current collector 11A of one positive electrode 11 and one main surface of negative electrode current collector 12A of negative electrode 12 adjacent to the one positive electrode 11 The negative electrode mixture layer 12</b>B formed thereon faces each other with the separator 13 interposed therebetween. In this manner, a plurality of positive electrodes, separators, and negative electrodes are laminated in this order.

By injecting an electrolytic solution containing the complex compound according to the embodiment into this, the adjacent positive electrode mixture layer 11B, separator 13 and negative electrode mixture layer 12B constitute one cell layer 14 . Therefore, the lithium-ion secondary battery 1 of the present embodiment has a structure in which a plurality of cell layers 14 are stacked and electrically connected in parallel. The positive electrode and the negative electrode may each have an active material layer formed on one side of each current collector. The complex compound will be described later.
[Negative electrode for lithium ion secondary battery]
The negative electrode 12 has a structure in which a negative electrode mixture layer 12B is provided on one side of a negative electrode current collector 12A. Here, the negative electrode mixture layer 12B contains a negative electrode active material, a conductive aid, and a water-dispersible binder. These substances in the negative electrode mixture layer 12B are in contact with the electrolytic solution containing the complex compound injected into the battery.

The negative electrode mixture layer 12B in this embodiment is formed in a film shape with a predetermined thickness on the surface of the negative electrode current collector 12A. Although various materials can be used for the negative electrode current collector 12A, metals and alloys are usually used. Specifically, conductive base materials for positive electrodes include aluminum, nickel, SUS, and the like, and conductive base materials for negative electrodes include copper, nickel, SUS, and the like. Among them, aluminum and copper are preferable from the viewpoint of balance between high conductivity and cost. Aluminum means aluminum and aluminum alloys, and copper means pure copper and copper alloys. In this embodiment, the aluminum foil can be used on the secondary battery positive electrode side and the secondary battery negative electrode side, and the copper foil can be used on the secondary battery negative electrode side. Although the aluminum foil is not particularly limited, various foils such as pure aluminum A1085 material and A3003 material can be used. The same applies to the copper foil, and although there is no particular limitation, a rolled copper foil or an electrolytic copper foil is preferably used.

The thickness of the negative electrode mixture layer of the present embodiment is, for example, preferably 5 μm or more, and more preferably 10 μm or more. Also, it is preferably 200 μm or less, more preferably 100 μm or less, and still more preferably 75 μm or less. When the thickness of the negative electrode mixture layer is within the above range, it is easy to obtain a sufficient lithium intercalation/deintercalation function for charge/discharge at a high charge/discharge rate. The negative electrode active material, the conductive aid, and the water-dispersible binder that constitute the negative electrode mixture layer 12B will be described in order below.
(Negative electrode active material)
As negative electrode active materials, metal lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped/dedoped with lithium ions, and transition metals that can be doped/dedoped with lithium ions. Nitrides and at least one selected from the group consisting of carbon materials capable of doping and dedoping lithium ions (may be used alone, or a mixture containing two or more of these may be used) can be used. Among these, a carbon material capable of doping/dedoping lithium ions is 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 fibrous, spherical, potato-like, or flake-like.

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. When graphite carbon particles are used, the particle size of the graphite carbon particles is not particularly limited, but it is usually about 5 to 50 μm, preferably about 20 to 30 μm. is less than 0.337 nm, the R value (the ratio of the peak intensity at 1360 cm ^-1 to the peak intensity at 1580 cm ^-1 ) in Raman spectroscopy is 0.12 or more and 0.8 or less, and the BET specific surface area is 0 It is preferably between 0.1 m ² /g and 2.0 m ² /g. Graphitized MCMB, graphitized MCF, and the like are used as artificial graphite. As the graphite material, one containing boron can also be used. As the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those in which amorphous carbon and graphite are mixed can be used.
These carbon materials may be used singly or in combination of two or more.

(Conductive auxiliary material)
The negative electrode mixture layer preferably contains a conductive aid. As the conductive aid used in the present invention, a known conductive aid can be used. The known conductive aid is not particularly limited as long as it is a carbon material having conductivity, and includes graphite, carbon black, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon fiber), fullerene, and the like. It can be used alone or in combination of two or more. Examples of commercially available carbon black include Toka Black (registered trademark) #4300, #4400, #4500, #5500 (manufactured by Tokai Carbon Co., Ltd., Furnace Black), Printex L (registered trademark), etc. (manufactured by Degussa, Furnace Black), Raven7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205, etc. (manufactured by Columbian, Furnace Black), #2350, #2400B, # 2600B, #30050B , #3030B, #3230B, #3350B, #3400B, #5400B, etc. (manufactured by Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LITX-50, LITX-200, etc. (manufactured by Cabot Corporation , Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketjenblack (registered trademark) EC-300J, EC-600JD (manufactured by Akzo), Denka Black (registered trademark), Denka Black HS -100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black), etc. Examples of graphite include artificial graphite, flaky graphite, massive graphite, and natural graphite such as earthy graphite, but are limited to these. not a thing

(Water-dispersible binder)
1 selected from styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, carboxymethylcellulose (CMC), and hydroxypropylmethylcellulose, polyvinyl alcohol, hydroxypropylcellulose, and diacetylcellulose as the water-dispersible binder; A species or a combination of two or more species can be used. In particular, it is desirable to use a suitable mixture of styrene-butadiene rubber and carboxymethylcellulose as the negative electrode binder.

It is desirable to use 0.1 to 4% by weight of the water-dispersible binder with respect to the negative electrode mixture layer in order to achieve compatibility between the physical properties of the negative electrode mixture layer (electrolytic solution permeability and peel strength) and the battery performance. . If it is less than 0.1 wt %, the adhesive strength of the active material will be weak, which may cause detachment of the active material during the charge/discharge process. If it exceeds 4 wt %, the amount of active material is reduced, which is undesirable in terms of battery capacity.

(other ingredients)
The negative electrode mixture layer according to the present embodiment may contain other suitable components in addition to the components described above. For example, when the negative electrode mixture layer is formed from mixture slurry, the negative electrode mixture layer may contain various compounding components derived from the mixture slurry. Examples of various ingredients derived from such mixture slurry include thickeners and other additives such as surfactants, dispersants, wetting agents, and antifoaming agents.
(Method for forming negative electrode mixture layer)
The mixture layer provided in the negative electrode for a lithium ion secondary battery of the present embodiment is obtained by applying a negative electrode mixture slurry containing the above-described negative electrode active material, conductive aid, and water-dispersible binder to the surface of the current collector and drying it. It can be manufactured by 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 coating properties on the current collector. . Liquid media compatible with water include alcohols, glycols, cellosolves, aminoalcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphate esters. , ethers, nitriles, etc., and may be used as long as they are compatible with water.

There are no particular limitations on the coating/drying method for coating and drying the mixture slurry on the current collector. Examples include methods such as slot die coating, slide coating, curtain coating, and gravure coating. Drying methods include drying with hot air, hot air, low humidity air, vacuum drying, and (far) infrared rays. The drying time and 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.
In the method for producing the mixture layer, after applying the mixture slurry on the current collector and drying it, a step of applying pressure using a mold press or a roll press to reduce the porosity of the active material layer is included. is preferred.

(Positive electrode active material)
The positive electrode active material is not particularly limited as long as it is a material capable of intercalating and deintercalating lithium, and may be a positive electrode active material commonly used in lithium ion secondary batteries. Specifically, in addition to oxides containing lithium (Li) and nickel (Ni) as constituent metal elements, at least one other metal element other than lithium and nickel (i.e., transition metal elements other than Li and Ni and and/or typical metal elements) as constituent metal elements in a proportion equal to or lower than that of nickel in terms of the number of atoms. Metal elements other than Li and Ni include, for example, 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 singly or in combination.

In a preferred embodiment, the positive electrode active material has, for example, general formula (1): Li _t Ni _1-xy Co _x Al _y O ₂ (where 0.95≦t≦1.15, satisfies 0≦x≦0.3, 0.1≦y≦0.2, and x+y<0.5). 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 has, for _example , general formula (2): _{LiNiaCobMncO2 (} where 0<a<1, 0<b<1, 0<c< 1 and satisfies a+b+c=1). NCM has high energy density per volume and excellent 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. Moreover, it is usually 99.9 wt% or less, preferably 99 wt% or less.

Examples of binders that may be used for the positive electrode active material layer include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles. Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride-hexafluoropropylene copolymer, and the like. Examples of 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. A binder can be used individually by 1 type, and can be used in combination of 2 or more types as needed.

[Separator]
Examples of separators include microporous membranes and porous flat plates made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide, as well as non-woven fabrics. A preferred example is a single-layer or multi-layer porous resin sheet mainly composed of one or more polyolefin resins. The thickness of the separator can be, for example, 15 μm to 30 μm. In a preferred embodiment, the separator has a shutdown function and has 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 clogs the pores, thereby interrupting current.

[Electrolyte]
The electrolytic solution is preferably, for example, one commonly used in lithium ion secondary batteries, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and lithium hexafluoroarsenate (LiAsF ₆ ). , lithium hexafluorotantalate (LiTaF ₆ ), lithium tetrachloride aluminum oxide (LiAlCl ₄ ), inorganic acid anion salts such as lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ), lithium trifluoromethanesulfonate ( LiCF ₃ SO ₃ ), lithium bis(trifluoromethanesulfonyl)imide (Li(CF ₃ SO ₂ ) ₂ N), lithium bis(pentafluoroethanesulfonyl) imide (Li(C ₂ F ₅ SO ₂ ) ₂ N), etc. At least one kind of lithium salt selected from organic acid anion salts can be mentioned. Among them, lithium hexafluorophosphate (LiPF ₆ ) is preferable.

Examples of organic solvents 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. , 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). Further, examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC). Further, chain carbonates include, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC) can be mentioned. Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Furthermore, γ-lactones include, for example, γ-butyrolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane. Furthermore, chain ethers include, for example, 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 can be used singly or in combination of two or more.

This solvent preferably contains one or more of non-aqueous solvents such as other organic solvents. Examples of the nonaqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 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 trimethyl acetate, ethyl trimethyl acetate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate and the like. 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 in particular, high viscosity (high dielectric constant) solvents such as ethylene carbonate or propylene carbonate (for example, relative 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 of the electrolyte salt and the mobility of ions are improved.

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

Examples of vinylene carbonate compounds include vinylene carbonate (1,3-dioxol-2-one), methylvinylene carbonate (4-methyl-1,3-dioxol-2-one), ethylvinylene carbonate (4-ethyl- 1,3-dioxol-2-one), 4,5-dimethyl-1,3-dioxol-2-one, 4,5-diethyl-1,3-dioxol-2-one, 4-fluoro-1,3 -dioxol-2-one or 4-trifluoromethyl-1,3-dioxol-2-one.

Examples of vinylethylene carbonate compounds include vinylethylene 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-dioxolan-2 -one, 4,4-divinyl-1,3-dioxolan-2-one and 4,5-divinyl-1,3-dioxolan-2-one.

Examples of methylene ethylene carbonate compounds include 4-methylene-1,3-dioxolan-2-one, 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one or 4,4-diethyl-5- methylene-1,3-dioxolane-2-one and the like.

These may be used alone or in combination of multiple types. Among them, vinylene carbonate is preferred. This is because a high effect can be obtained.

Moreover, the solvent may contain sultone (cyclic sulfonic acid ester) and acid anhydride. This is because the chemical stability of the electrolytic solution is further improved. Examples of sultone include propane sultone and propene sultone. These may be used alone or in combination of multiple types. Among them, propene sultone is preferred. Also, 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. Acid anhydrides include, for example, carboxylic anhydrides such as succinic anhydride, glutaric anhydride and maleic anhydride; disulfonic anhydrides such as ethanedisulfonic anhydride and propanedisulfonic anhydride; sulfobenzoic anhydride; Anhydrides of a carboxylic acid such as sulfopropionic acid or sulfobutyric anhydride and a sulfonic acid are included. These may be used alone or in combination of multiple types. Among them, sulfobenzoic anhydride is preferred. Moreover, 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 of the electrolyte salt and the mobility of ions are improved. For the same reason, the intrinsic viscosity of the electrolyte salt dissolved in the solvent (so-called intrinsic viscosity of the electrolytic solution) is also preferably 10.0 mPa·s or less at 25°C.

<Additive>
The electrolytic solution of the present embodiment includes vinylene carbonate (hereinafter referred to as VC), lithium bis[oxalato]borate (hereinafter referred to as LiBOB), and lithium difluoro[oxolato-O,O']borate. (hereinafter referred to as LiDFOB). These additives are added mainly for the purpose of surface protection and resistance reduction of the negative electrode and positive electrode.

Negative electrode production 1. Slurry preparation A 5 L planetary disper was used for slurry preparation.
450 g of 1% CMC (CMC dissolved in pure water) was added to 960 g of natural graphite, 10 g of Super-P (conductive carbon, BET specific surface area of 62 m ² /g), and mixed for 30 minutes. Next, 300 g of a 1%-CMC aqueous solution was added and kneaded for 30 minutes, and then 250 g of 1%-CMC was added and kneaded for 30 minutes. After that, 50 g of SBR (40% emulsion) as a binder was added and mixed for 30 minutes, followed by vacuum defoaming for 30 minutes. Thus, a slurry having a solid concentration of 45% was prepared.

2. Coating/Drying A die coater was used for slurry coating. The slurry was applied to one side of a copper foil (thickness: 10 μm) and dried so that the coating weight after drying was 12.2 mg/cm ² . Next, the slurry was applied to the opposite side (uncoated side) of the copper foil so that the coating weight was 12.2 mg/cm ² and dried. The thus obtained negative electrode roll coated on both sides (24.4 mg/cm ² ) 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 (clearance) between the upper and lower rolls was adjusted, and the negative electrode was compressed to a press density of 1.45±0.05 g/cm ³ .

4. The electrode was slit so as to obtain a slit electrode coating area (front surface: 58 mm×358 mm, back surface: 58 mm×363 mm) and a margin for tab welding to obtain negative electrode A-1.

Preparation of positive electrode 1. Slurry preparation A 5 L planetary disper was used for slurry preparation. NCM523 (composition formula: LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) 920 g, Super-P (conductive carbon) 20 g, KS-6 (flaky graphite) 20 g were mixed for 10 minutes, and then N- 100 g of methylpyrrolidone (NMP) was added and mixed for an additional 20 minutes.

Next, 150 g of 8%-binder solution was added and kneaded for 30 minutes, and then 150 g of 8%-binder solution was added and kneaded for 30 minutes. After that, 200 g of 8%-binder solution was added and kneaded for 30 minutes. Then, 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 defoaming for 30 minutes. Thus, a slurry having a solid concentration of 60% was prepared.

2. Coating/Drying A die coater was used for slurry coating. The slurry was applied to one side of an aluminum foil (thickness: 20 μm, width: 200 mm) and dried so that the coating weight after drying was 22.0 mg/cm ² . Next, the slurry was applied to an aluminum foil on the opposite side (uncoated side) so that the coating weight was 22.0 mg/cm ² and dried.
The thus obtained positive electrode roll coated on both sides (44.0 mg/cm ² ) was dried in a vacuum drying oven at 130° C. for 12 hours.

3. Press A 35-ton press was used. The gap (clearance) between the upper and lower rolls was adjusted, and the positive electrode was compressed to a press density of 3.2±0.05 g/cm ³ .

4. Slit The electrode was slit so as to obtain a slit electrode coating area (surface: 56 mm × 320 mm, back: 56 mm × 320 mm) and a tab welding margin to obtain a positive electrode C-1.

Battery production Wound type battery (design capacity 1 Ah)
1. A porous PE separator (60.5 mm×750 mm) was used as the wound separator.
Negative electrode A-1 (front surface/back surface), a separator, positive electrode C-1 (back surface/front surface), and a separator were laminated and wound, and then press-molded. Next, an aluminum tab was bonded to the margin of the positive electrode C-1 by an ultrasonic bonding machine, and a nickel tab was bonded to the margin of the negative electrode A-1 by an ultrasonic bonding machine. This was sandwiched between laminate sheets, and three sides were heat-sealed.

Ethylene carbonate (hereinafter referred to as EC), dimethyl carbonate (hereinafter referred to as DMC) and methyl ethyl carbonate (EMC) as non-aqueous solvents for electrolyte preparation EC:DMC:EMC = 30:40:30 (mass ratio) They were mixed to prepare a mixed solvent. In preparing the electrolytic solution, LiPF ₆ contained in the electrolytic solution was dissolved so that the concentration of the electrolytic solution in the non-aqueous electrolytic solution was 1.15 mol/liter. Various additives were added to this mixed solvent. Table (1) below shows composition examples showing combinations of amounts of each additive added. The amount of each additive added is represented by wt %.

The batteries of Examples 1-4 and the batteries of Examples 5-8 used the electrolytic solutions of Composition Examples 1-4. The battery of Comparative Example 1 uses the electrolyte of Composition Example 5, the battery of Comparative Example 2 uses the electrolyte of Composition Example 6, and the battery of Comparative Example 3 uses the battery of Composition Example 7. In the battery of Comparative Example 4, the electrolytic solution of Composition Example 1 was used.

尚、組成例８～２２で加えた添加剤は、下記の名称で表される。
ＬｉＦＳＩ：リチウムビス（フルオロスルホニル）イミド
ＬｉＰＦ_２Ｏ_２：ジフルオロリン酸リチウム
ＬｉＳＯ_３ＣＦ_３：トリフルオロメタンスルホン酸リチウム
ＬｉＳＯ_３Ｆ：フルオロスルホン酸リチウム
Ｓ化合物：４, ４'-ビス(２-オキソ-１, ３, ２-ジオキサチオラン) Composition examples obtained by adding various additives to Composition Example 1 are shown in Table (2) below. The batteries of Examples 9-23 used the electrolytic solutions of Composition Examples 8-22.

The additives added in Composition Examples 8 to 22 are represented by the following names.
LiFSI: Lithium bis(fluorosulfonyl)imide LiPF ₂ O ₂ : Lithium difluorophosphate LiSO ₃ CF ₃ : Lithium trifluoromethanesulfonate LiSO ₃ F: Lithium fluorosulfonate S compound: 4,4′-bis(2-oxo- 1,3,2-dioxathiolane)

2. Injection of Electrolyte Before injecting the electrolyte into each composition example, the above was dried at 70° C. for 12 hours under reduced pressure in a vacuum dryer. After pouring 4.7±0.1 g of electrolytic solution, it was heat-sealed while being vacuumed.

3. Aging treatment [First aging condition (for Examples 1 to 4, Comparative Examples 1 to 3 and Examples 9 to 23)]
As aging treatment at the time of initial charging, after CC charging (SOC 8%) for 24 minutes at an ambient temperature of 25° C. and a charging rate of 0.2 C, the state was maintained for 12 hours (corresponding to the initial charging step). Next, after CC charging (SOC 48%) for 48 minutes at an ambient temperature of 25° C. and a charging rate of 0.5 C, the battery was held in a constant temperature bath at an ambient temperature of 60° C. for 12 hours (corresponding to the next charging step). Next, the ambient temperature was returned to 25° C., and degassing was performed for final sealing. Note that CC discharging means charging with a constant current, and SOC means the state of charge of the battery.

[Second aging conditions (for Examples 5 to 8)]
As aging treatment at the time of initial charging, after CC charging (SOC 8%) for 24 minutes at an ambient temperature of 25° C. and a charging rate of 0.2 C, the state was maintained for 12 hours (corresponding to the initial charging step). Next, after CC charging (SOC 48%) for 48 minutes at an ambient temperature of 25° C. and a charging rate of 0.5 C, the battery was held in a constant temperature bath with an ambient temperature of 60° C. for 12 hours (corresponding to the first step of the next charging step). . Next, after CC charging (SOC 100%) for 44 minutes at an ambient temperature of 25° C. and a charging rate of 0.5 C, the battery was held in a thermostat at an ambient temperature of 60° C. for 60 hours (corresponding to the second step of the next charging step). . Next, the ambient temperature was returned to 25° C., and degassing was performed for final sealing.
[Initial capacity confirmation]
After CCCV (termination condition: 4.2 V, cutoff 1/20 C) charging was performed at a charging rate of 0.5 C, the battery was rested for 30 minutes. Next, CC (termination condition: 2.5 V) discharge was performed at a discharge rate of 1 C, and then rested for 30 minutes. Furthermore, CC (termination condition: 2.5 V) additional discharge was performed at a discharge rate of 1/3 C, and then rested for 30 minutes. Note that CCCV charging means charging with a constant current-constant voltage.

[Third aging condition (for Comparative Example 4)]
After CC (terminating condition: 4.2 V, cutoff 1/20C) charging (SOC 100%) at an ambient temperature of 25°C and a charging rate of 0.2C, then an ambient temperature of 25°C and a charging rate of 0.2C. was discharged to 2.5 V (SOC 0%). After performing this cycle twice, degassing and main sealing was performed.

Batteries of Examples 1 to 4, Comparative Examples 1 to 3 and Examples 9 to 19 were produced by subjecting the uncharged batteries of Composition Examples 1 to 4 and 8 to 18 to the first aging treatment. Similarly, the batteries of Examples 5 to 8 were produced by subjecting the uncharged batteries of Composition Examples 1 to 4 to the second aging treatment. Similarly, the uncharged battery of Composition Example 1 was subjected to the third aging treatment to prepare a battery of Comparative Example 1.

[Battery resistance]
Next, the direct current resistance DCIR of each battery was measured before and after storage.
(DC resistance DCIR)
In the measurement of the direct current resistance DCIR, the initial battery resistance was measured at an atmospheric temperature of 25° C. after charging and discharging by the following method. First, constant current low voltage charge (0.5C-CCCV) to 3.7V at a discharge rate of 0.5C, after resting for 10 minutes, CC10s discharge at a discharge rate of 1.0C to adjust the SOC (State of Charge) bottom.
Next, CC10s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 2C.
Next, CC20s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 3C.
Next, CC30s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 4C.
Next, CC40s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 5C.
Next, CC50s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 6C.
Next, CC60s charging was performed at a charging rate of 1C, and after resting for 10 minutes, CC10s discharging was performed at a discharging rate of 7C.
Next, CC70s charging was performed at a charging rate of 1C. In addition, CC10s discharge means discharging for 10 seconds with a constant current (Constant Current).
The direct current resistance was obtained from each charge/discharge rest current and each charge/discharge rest voltage, and the obtained direct current resistance was used as the initial battery resistance of the battery.

(Test conditions for storage test)
After the battery was stored at an ambient temperature of 60° C. for 2 weeks, the battery resistance after storage was obtained by the above method, and the DC resistance before and after storage was shown in a graph.

(Test conditions for cycle test)
Also, the battery was stored at an ambient temperature of 45° C., charged at a charge rate of 0.5 C CCCV (terminating condition: 4.2 V, cutoff 1/20 C), and then rested for 30 minutes. Next, CC (termination condition: 2.5 V) discharge was performed at a discharge rate of 1 C, and then rested for 30 minutes. This charge/discharge cycle was performed 100 times.
After completion of 100 charge-discharge cycles, the battery was stored at an ambient temperature of 25° C., charged with CCCV (termination condition: 4.2 V, cutoff 1/20 C) at a charge rate of 0.5 C, and rested for 30 minutes. Next, CC (termination condition: 2.5 V) discharge was performed at a discharge rate of 1 C, and then rested for 30 minutes. Furthermore, CC (termination condition: 2.5 V) additional discharge was performed at a discharge rate of 1/3 C, and then rested for 30 minutes.

Test results based on the above conditions are shown in FIGS. 2 to 9. FIG. 2 to 9, Examples 1 to 23 and Comparative Examples 1 to 4 are arranged in order on the horizontal axis, and test data corresponding to each example are shown on the vertical axis.

[Regarding DC resistance DCIR before and after storage]
FIG. 2 is a diagram showing the DC resistance DCIR before and after storage, and FIG. 3 is a diagram showing the post-storage increase rate of the DC resistance DCIR before and after storage (DCIR after storage/DCIR before storage). ● in FIG. 2 represents the DC resistance DCIR before the storage test, and ◯ represents the DC resistance DCIR after the storage test.

(Analysis based on Figure 2)
As shown in FIG. 2, comparing Example 4, Comparative Example 1, and Comparative Example 2, in which the amount of LiBOB added is the same, the DC resistance DCIR after storage in Example 4 is lower than the DC resistance after storage in Comparative Examples 1 and 2. smaller than the resistor DCIR. Therefore, by adding a combination of VC and LiDFOB to LiBOB, it is possible to effectively suppress an increase in DC resistance DCIR after storage compared to the case where only VC is added to LiBOB.
Moreover, Example 4, in which the first aging treatment was performed, has a lower DC resistance DCIR after storage than Comparative Example 4, in which the third aging treatment is performed. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can suppress an increase in the DC resistance DCIR after storage.
Further, when comparing Examples 1 to 4 in which VC and LiDFOB were added to LiBOB and the first aging treatment was performed with Comparative Example 3, the DC resistance DCIR after storage in Examples 1 to 4 was the comparative example. It is smaller than the direct current resistance DCIR after storage in 3. Here, as shown in "Table 1", the wt.% ratio obtained by dividing the wt.% of LiBOB by the wt.% of VC (hereinafter referred to as the weight ratio to VC) and the wt.% of LiBOB wt.% ratio divided by wt. ). All of Examples 1 to 4 and Comparative Example 3 have a weight ratio to VC of 1.67 or more. On the other hand, the weight ratio to LiDFOB of Examples 1 to 4 is 1 or less, while the weight ratio to LiDFOB of Comparative Example 3 is greater than 1 (1.63). Also, while the LiDFOB molar ratios of Examples 1 to 4 are 0.5 or more, the molar ratio to LiDFOB of Comparative Example 3 is less than 0.5 (0.46). From this, the relationship between the amounts of LiBOB, VC, and LiDFOB added is that the weight ratio to VC is 1.67 or more, the weight ratio to LiDFOB is 1.0 or less, and the molar ratio to LiDFOB is 0.5. It is preferable that it is above. Further, the total amount of LiBOB, VC and LiDFOB added is preferably 0.5 wt.% or more and 5.0 wt.% or less.
Further, the DC resistances DCIR after storage of Examples 1 to 4 subjected to the first aging treatment and the DC resistances DCIR of Examples 5 to 8 after storage subjected to the second aging treatment were compared with each other in Example 1 and Example 5. , Example 2 and Example 6, Example 3 and Example 7, and Example 4 and Example 8, respectively, the second aging treatment is more effective than the first aging treatment. Resistance DCIR is low. Therefore, the three-stage aging process can further suppress the post-storage DC resistance DCIR than the two-stage aging process.
Further, the DC resistances DCIR after storage in Examples 9-23 are lower than the DC resistances DCIR after storage in Comparative Examples 1-4. Therefore, even if other additives are added in addition to VC, LiBOB and LiDFOB, the effects of these other additives are not inhibited.

(Analysis based on Figure 3)
As shown in FIG. 3, Example 4, in which the first aging treatment is performed, has a lower rate of increase in DC resistance DCIR than Comparative Example 4, in which the third aging treatment is performed. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can further suppress the DC resistance DCIR increase rate before and after storage.
Further, when comparing Example 4 and Comparative Example 1, in which the amounts of VC and LiBOB added are the same, the DC resistance DCIR increase rate in Example 4 is smaller than that in Comparative Example 1. Therefore, by adding LiDFOB, it is possible to effectively suppress an increase in the DC resistance DCIR increase rate compared to the case where only VC is added.
In addition, the DC resistance DCIR increase rate before and after storage of Examples 1 to 4 subjected to the first aging treatment and the DC resistance DCIR increase rate of Examples 5 to 8 subjected to the second aging treatment are compared with those of Example 1 and Example. 5. When comparing Examples 2 and 6, Examples 3 and 7, and Examples 4 and 8, the second aging treatment is better than the first aging treatment. DC resistance DCIR rise rate is low. Therefore, the three-stage aging process can further suppress the DC resistance DCIR increase rate before and after storage than the two-stage aging process.
Further, the rate of increase in DC resistance DCIR after storage in Examples 9-23 is lower than the rate of increase in DC resistance DCIR after storage in Comparative Examples 1-4. Therefore, even if other additives are added in addition to LiBOB, VC and LiDFOB, the effects of these other additives are not inhibited.

[Discharge capacity before and after storage]
FIG. 4 is a diagram showing discharge capacity values before and after storage, and FIG. 5 is a diagram showing discharge capacity retention rates (discharge capacity before storage/discharge capacity after storage) before and after storage. ● in FIG. 4 represents the discharge capacity before the storage test, and ◯ represents the discharge capacity after the storage test.

(Analysis based on Figure 4)
As shown in FIG. 4, when comparing Example 4 and Comparative Example 4, in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 with the first aging treatment is compared with Comparative Example 4 with the third aging treatment. Compared to , the discharge capacity after storage is large. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can suppress the decrease in discharge capacity after storage.
Further, the discharge capacities after storage in Examples 9-23 are not lower than the discharge capacities after storage in Comparative Examples 1-4. Therefore, even if other additives are added in addition to LiBOB, VC, and LiDFOB, the effects of these other additives are not inhibited, and the discharge capacity is not lowered by the other additives. .

(Analysis based on Figure 5)
As shown in FIG. 5, when comparing Example 4 and Comparative Example 4, in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 with the first aging treatment is compared with Comparative Example 4 with the third aging treatment. It is the same discharge capacity maintenance rate as. Therefore, the aging treatment in two stages does not adversely affect the discharge capacity retention rate.

[Regarding the DC resistance DCIR before and after the cycle test]
FIG. 6 is a diagram showing the DC resistance DCIR before and after the cycle test, and FIG. 7 is a diagram showing the rate of DCIR increase before and after the cycle test (DCIR after the cycle test/DCIR before the cycle test). ● in FIG. 6 represents the DC resistance DCIR before the cycle test, and ◯ represents the DC resistance DCIR after the cycle test.

(Analysis based on Figure 6)
As shown in FIG. 6, comparing Example 4, Comparative Example 1, and Comparative Example 2 in which the amount of LiBOB added is the same, the DC resistance DCIR after the cycle test in Example 4 is is less than the DC resistance DCIR of Therefore, by adding a combination of VC and LiDFOB to LiBOB, it is possible to effectively suppress an increase in the DC resistance DCIR after the cycle test, as compared with the case where only VC is added to LiBOB.
Further, when comparing Example 4 and Comparative Example 4, in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 in which the first aging treatment was performed has a higher cycle time than Comparative Example 4 in which the third aging treatment was performed. The DC resistance DCIR after the test is remarkably low. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can suppress an increase in the DC resistance DCIR after the cycle test.
Further, the DC resistance DCIR after the cycle test of Examples 1 to 4 subjected to the first aging treatment and the DC resistance DCIR after the cycle test of Examples 5 to 8 subjected to the second aging treatment were compared with Example 1. When comparing Example 5, Example 2 and Example 6, Example 3 and Example 7, and Example 4 and Example 8, respectively, the second aging treatment is better than the first aging treatment. DC resistance DCIR after cycle test is also low. Therefore, the three-stage aging process can further suppress the DC resistance DCIR after the cycle test than the two-stage aging process.
Further, the DC resistance DCIR after the cycle test in Examples 9-23 is lower than the DC resistance DCIR after the cycle test in Comparative Examples 1-4. Therefore, even if other additives are added in addition to LiBOB, VC, and LiDFOB, the effects of these other additives are not inhibited, and the other additives increase the DC resistance DCIR after the cycle test. nor increase.

(Analysis based on Figure 7)
As shown in FIG. 7, when comparing Example 4 and Comparative Example 4, in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 with the first aging treatment is compared with Comparative Example 4 with the third aging treatment. , the rate of DCIR increase before and after the cycle test of the DC resistance DCIR is remarkably low. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, two-step aging treatment can further suppress the DC resistance DCIR increase rate before and after the cycle test.
Further, when comparing Example 4 and Comparative Example 1 in which the amounts of LiBOB and VC added are the same, the rate of increase in DC resistance DCIR before and after the cycle test in Example 4 is the same as the rate of increase in DC resistance DCIR before and after the cycle test in Comparative Example 1. less than the rate. Therefore, by combining LiBOB with VC and LiDFOB, it is possible to effectively suppress an increase in the DC resistance DCIR increase rate before and after the cycle test, as compared with the case where only VC is added to LiBOB.
In addition, when comparing Examples 1 to 4 in which VC and LiDFOB were added to LiBOB and the first aging treatment was performed with Comparative Example 3, the DC resistance DCIR before and after the cycle test in Examples 1 to 4 was It is smaller than the DC resistance DCIR before and after the cycle test in Comparative Example 3. All of Examples 1 to 4 and Comparative Example 3 have a weight ratio to VC of 1.67 or more. On the other hand, the weight ratio to LiDFOB of Examples 1 to 4 is 1 or less, while the weight ratio to LiDFOB of Comparative Example 3 is greater than 1 (1.63). In addition, while the molar ratio to LiDFOB in Examples 1 to 4 is 0.5 or more, the molar ratio to LiDFOB in Comparative Example 3 is less than 0.5 (0.46). From this, the relationship between the amounts of LiBOB, VC, and LiDFOB added is that the weight ratio to VC is 1.67 or more, the weight ratio to LiDFOB is 1.0 or less, and the molar ratio to LiDFOB is 0.5. It is preferable that it is above. Further, the total amount of LiBOB, VC and LiDFOB added is preferably 0.5 wt.% or more and 5.0 wt.% or less.
Further, the rate of increase in DC resistance DCIR before and after the cycle test in Examples 9-23 does not increase much more than the rate of increase in DC resistance DCIR before and after the cycle test in Comparative Examples 1-4. Therefore, even if other additives are added in addition to LiBOB, VC, and LiDFOB, the effects of these other additives are not inhibited, and the other additives increase the DC resistance DCIR before and after the cycle test. rate will not increase.

[Discharge capacity before and after cycle test]
8 is a diagram showing the discharge capacity before and after the cycle test, and FIG. 9 is a diagram showing the discharge capacity retention rate before and after the cycle test (discharge capacity before cycle test/discharge capacity after cycle test). ● in FIG. 8 represents the discharge capacity before the cycle test, and ◯ represents the discharge capacity after the cycle test.

(Analysis based on Figure 8)
As shown in FIG. 8, when comparing Example 4 and Comparative Example 4 in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 in which the first aging treatment was performed was compared with Comparative Example 4 in which the third aging treatment was performed. Compared to , the discharge capacity after the cycle test is large. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can suppress the decrease in discharge capacity after the cycle test.
Further, comparing Example 4 and Comparative Example 1, in which the amounts of LiBOB and VC added are the same, the discharge capacity after the cycle test in Example 4 is larger than the discharge capacity after the cycle test in Comparative Example 1. Therefore, by adding a combination of VC and LiDFOB to LiBOB, the decrease in discharge capacity after the cycle test can be effectively suppressed as compared with the case where only VC is added to LiBOB.
In addition, the discharge capacity after the cycle test of Examples 1 to 4 subjected to the first aging treatment and the discharge capacity after the cycle test of Examples 5 to 8 subjected to the second aging treatment were compared with each other. , Example 2 and Example 6, Example 3 and Example 7, and Example 4 and Example 8, respectively, the second aging treatment is more effective than the first aging treatment. Large capacity. Therefore, the three-step aging treatment can further suppress the decrease in the discharge capacity after the cycle test than the two-step aging treatment.
In addition, the discharge capacities before and after the cycle test in Examples 9-23 do not decrease significantly from the discharge capacities before and after the cycle test in Comparative Examples 1-4. Therefore, even if other additives are added in addition to LiBOB, VC, and LiDFOB, the effects of these other additives are not inhibited, and the discharge capacity is not lowered by the other additives. .

(Analysis based on Figure 9)
As shown in FIG. 9, when comparing Example 4 and Comparative Example 4 in which the amounts of LiBOB, VC, and LiDFOB added are the same, Example 4 in which the first aging treatment was performed was compared with Comparative Example 4 in which the third aging treatment was performed. Compared to , the discharge capacity retention rate after the cycle test is high. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can suppress the decrease in the discharge capacity retention rate after the cycle test.
Further, when comparing Example 4 and Comparative Example 1 in which the amounts of LiBOB and VC added are the same, the discharge capacity retention rate after the cycle test in Example 4 is higher than the discharge capacity retention rate after the cycle test in Comparative Example 1. . Therefore, by adding a combination of VC and LiDFOB to LiBOB, it is possible to effectively suppress a decrease in the discharge capacity retention rate after the cycle test, as compared with the case where only VC is added to LiBOB.
In addition, the discharge capacity retention rate after the cycle test of Examples 1 to 4 with the first aging treatment and the discharge capacity retention rate after the cycle test of Examples 5 to 8 with the second aging treatment were compared with Example 1. and Example 5, Example 2 and Example 6, Example 3 and Example 7, Example 4 and Example 8, respectively, the second aging treatment is better than the first aging treatment The discharge capacity retention rate is higher than that of Therefore, the three-step aging treatment can further suppress the decrease in the discharge capacity retention rate after the cycle test, rather than the two-step aging treatment.
Further, the discharge capacity retention ratios before and after the cycle test in Examples 9 to 23 are not much lower than the discharge capacity retention ratios before and after the cycle test in Comparative Examples 1 to 4. Therefore, even if other additives are added in addition to LiBOB, VC, and LiDFOB, the effects of these other additives are not inhibited, and the discharge capacity retention rate is not lowered by the other additives. Nor.

As described above, the two-stage aging treatment during the initial charging performed for the examples can effectively form a SEI (Solid Electrolyte Interphase) layer on the negative electrode surface. Further, by increasing the number of stages from the two-stage aging treatment to perform the three-stage aging treatment, the SEI can be formed more effectively. As a result, it is believed that the decomposition of the compound in the electrolyte solution on the surface of the negative electrode is suppressed, and the co-insertion of the compound in the electrolyte solution and the subsequent exfoliation of graphite are effectively inhibited. It was also found that the addition of LiDFOB to the electrolyte containing LiBOB and VC can effectively improve the DC resistance DCIR, the DC resistance DCIR increase rate, the discharge capacity, and the discharge capacity retention rate.

Reference Signs List 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 method for manufacturing a lithium ion secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium ions, a separator, and a non-aqueous electrolyte for a lithium ion secondary battery,
The non-aqueous electrolytic solution contains lithium hexafluorophosphate (hereinafter, LiPF ₆ ) as an electrolyte, and vinylene carbonate (hereinafter, VC), lithium bis[oxalato]borate (hereinafter, LiBOB), and difluoro[ Oxolato-O,O'] containing lithium borate (hereinafter, LiDFOB),
The non-aqueous electrolytic solution contains 0.9 mol/l to 1.3 mol/l of LiPF ₆ as an electrolyte with respect to the non-aqueous solvent,
The total amount of VC, LiBOB and LiDFOB added to the non-aqueous electrolyte was 0.5 wt. % or more 5.0 wt. % or less,
The wt.% ratio obtained by dividing the wt.% of LiBOB by the wt.% of VC is 1.67 or more, and the wt.% ratio obtained by dividing the wt.% of LiBOB by the wt.% of LiDFOB is 1.0 or less. and the molar ratio obtained by dividing the number of moles of LiBOB by the number of moles of LiDFOB is 0.5 or more,
As the initial charging process,
an initial charging step of charging the state of charge (hereinafter referred to as SOC) of the lithium ion secondary battery to a first SOC of 30% or less and storing the battery for a predetermined time;
a subsequent charging step of charging the SOC to an SOC higher than the first SOC and storing the battery for a predetermined time;
has
In the initial charging step, after charging at a C rate of 0.1 C to 0.3 C and at a first SOC of 5% to 15%, the ambient temperature is maintained at 25° C. to 45° C. for 6 hours to 72 hours. can be,
In the next charging step, after charging at a C rate of 0.1 C to 0.5 C and an SOC higher than the first SOC of 40% to 60%, the ambient temperature is set to 45 ° C. to 60 ° C. and held for 6 hours to 600 hours. A method for manufacturing a lithium ion secondary battery, characterized by comprising a step of A method for manufacturing a lithium ion secondary battery comprising a positive electrode and a negative electrode capable of absorbing and releasing lithium ions, a separator, and a non-aqueous electrolyte for a lithium ion secondary battery,
The non-aqueous electrolytic solution contains lithium hexafluorophosphate (hereinafter, LiPF ₆ ) as an electrolyte, and vinylene carbonate (hereinafter, VC), lithium bis[oxalato]borate (hereinafter, LiBOB), and difluoro[ Oxolato-O,O'] containing lithium borate (hereinafter, LiDFOB),
The non-aqueous electrolytic solution contains 0.9 mol/l to 1.3 mol/l of LiPF ₆ as an electrolyte with respect to the non-aqueous solvent,
The total amount of VC, LiBOB and LiDFOB added to the non-aqueous electrolyte was 0.5 wt. % or more 5.0 wt. % or less,
The wt.% ratio obtained by dividing the wt.% of LiBOB by the wt.% of VC is 1.67 or more, and the wt.% ratio obtained by dividing the wt.% of LiBOB by the wt.% of LiDFOB is 1.0 or less. and the molar ratio obtained by dividing the number of moles of LiBOB by the number of moles of LiDFOB is 0.5 or more,
As the initial charging process,
an initial charging step of charging the state of charge (hereinafter referred to as SOC) of the lithium ion secondary battery to a first SOC of 30% or less and storing the battery for a predetermined time;
a subsequent charging step of charging the SOC to an SOC higher than the first SOC and storing the battery for a predetermined time;
has
The initial charging step includes
After charging at 0.1 C to 0.3 C as the C rate and 5% to 15% as the first SOC, the ambient temperature is maintained at 25 ° C. to 45 ° C. for 6 hours to 72 hours,
In the next charging step, after charging to 40% to 60% as SOC higher than the first SOC at a C rate of 0.1 C to 0.5 C, the ambient temperature is set to 45 ° C. to 60 ° C. and held for 6 hours to 300 hours. a first step of
After the first step, after charging to 80% to 100% as an SOC higher than the first SOC at a C rate of 0.1 C to 0.5 C, the ambient temperature is set to 45 ° C. to 60 ° C. for 6 hours to 600 hours. a second step of holding;
A method for manufacturing a lithium ion secondary battery , comprising : In the method for manufacturing a lithium ion secondary battery according to claim 1 or 2 ,
LitNi1-xyCoxAlyOz (in the formula, 0.95 ≤ t ≤ 1.15, 0 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.2, x + y < 0.5, z satisfies the number of oxygen atoms in the element in the formula) or LiNiaCobMncOz (where 0.5 ≤ a ≤ 0.95, 0 < b < 0.5, 0 < c <0.5 and a+
It satisfies b+c=1. z satisfies the oxygen number of the elements in the formula. ) having a lithium-containing composite oxide,
The negative electrode, as a negative electrode active material, has an interplanar spacing of (002) plane of less than 0.337 nm by wide- ^angle X-ray diffraction, and an R value in Raman spectroscopy (peak intensity of 1360 cm with respect to peak intensity of 1580 cm ^-1 ratio) of 0.12 or more and 0.8 or less and a BET specific surface area of 0.1 ^m 2 /g to 2.0 m ² /g. A method for manufacturing a secondary battery.

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