JP7276956B2 - 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 difluoro[oxolato-O,O'] lithium borate (hereinafter referred to as LiDFOB) are added as additives to a mixed organic solvent as an electrolytic solution. ) is added to improve the cycle characteristics and storage characteristics of the secondary battery.

Japanese Patent No. 4423888

However, as a result of intensive studies, the inventors have found that the characteristics of a battery in which the additive is added to the mixed organic solvent are greatly affected by the aging treatment conditions during the initial charge.

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 further contains VC and LiDFOB as additives. as the initial charging step, the state of charge (hereinafter referred to as SOC) of the lithium ion secondary battery is charged to a first SOC of 30% or less, and then stored for a predetermined time; and a next charging step of storing for a predetermined time.

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). It is an image figure showing SEI (Solid Electrolyte Interphase) in a negative electrode.

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 inside 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 single 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 positive electrode side of the secondary battery and the negative electrode side of the secondary battery, and the copper foil can be used on the negative electrode side of the secondary battery. Although the aluminum foil is not particularly limited, various foils such as pure aluminum A1085 material and A3003 material can be used. The copper foil is the same and is not particularly limited, but 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 carboxymethyl cellulose 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.
The method for producing the mixture layer includes a step of applying pressure to the active material layer using a mold press or a roll press after coating and drying the mixture slurry on the current collector to reduce the porosity of the active material layer. 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 contains vinylene carbonate (hereinafter referred to as VC) 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８～１８で加えた添加剤は、下記の名称で表される。
ＴＭＳＰ：トリス（トリメチルシリル）ホスフェート
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
ＣＨ_３ＳＦＯ_２：メタンスルホニルフルオリド
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 9-19 used the electrolytic solutions of Composition Examples 8-18.

The additives added in Composition Examples 8 to 18 are represented by the following names.
TMSP: tris(trimethylsilyl) _phosphate LiFSI: lithium bis(fluorosulfonyl ₎ imide _LiPF2O2 : lithium difluorophosphate _CH3SFO2 : methanesulfonyl fluoride
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 19)]
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 direct current resistance, 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 19 and Comparative Examples 1 to 4 are arranged in order on the horizontal axis, and the test data corresponding to each example are listed 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, Example 1, 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, comparing Example 1 with Comparative Examples 1 and 2, the DC resistance DCIR after storage in Example 1 is smaller than the DC resistance DCIR after storage in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, it is possible to effectively suppress an increase in DC resistance DCIR after storage compared to the case where only one of the additives is added.
Further, the DC resistances DCIR after storage in Examples 9-19 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 and LiDFOB, the effects of these other additives are not inhibited.

(Analysis based on Figure 3)
As shown in FIG. 3, Example 1, 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 1 and Comparative Example 2, the rate of increase in DC resistance DCIR in Example 1 is smaller than the rate of increase in DC resistance DCIR in Comparative Example 2. FIG. Therefore, by combining VC and LiDFOB, it is possible to effectively suppress an increase in the direct current resistance DCIR increase rate compared to the case where only LiDFOB 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 DC resistances DCIR after storage in Examples 9-19 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 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, Example 1, in which the first aging treatment is performed, has a larger discharge capacity 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 the decrease in discharge capacity after storage.
Further, comparing Example 1 with Comparative Examples 1 and 2, the discharge capacity after storage in Example 1 is larger than the discharge capacity after storage in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, the decrease in discharge capacity after storage can be effectively suppressed as compared with the case where only one of the additives is added.
Further, the discharge capacities after storage in Examples 9-19 are larger than the discharge capacities after storage in Comparative Examples 1-4. Therefore, even if other additives are added in addition to VC and LiDFOB, the effects of these other additives are not inhibited.

(Analysis based on Figure 5)
As shown in FIG. 5, Example 1, in which the first aging treatment was performed, has a higher discharge capacity retention rate after storage than Comparative Example 4, in which the third aging treatment was performed. Therefore, rather than repeating charging and discharging until the SOC reaches 100%, aging treatment in two stages can further improve the discharge capacity retention rate before and after storage.
Further, when comparing Example 1 with Comparative Examples 1 and 2, the discharge capacity retention rate in Example 1 is higher than the discharge capacity retention rate in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, the discharge capacity retention rate can be effectively improved compared to the case where only one of the additives is added.
In addition, the discharge capacity retention rates before and after storage of Examples 1 to 4 subjected to the first aging treatment and the discharge capacity retention rates of Examples 5 to 8 subjected to the second aging treatment were compared with each other. When comparing Example 2 and Example 6, Example 3 and Example 7, and Example 4 and Example 8, respectively, the second aging treatment showed a higher discharge capacity than the first aging treatment. High retention rate. Therefore, the three-stage aging treatment can further improve the discharge capacity retention rate than the two-stage aging treatment.
Further, the discharge capacity retention ratios after storage in Examples 9 to 19 are higher than those in Comparative Examples 1, 2 and 4. Therefore, even if other additives are added in addition to VC and LiDFOB, the effects of these other additives are not inhibited.

[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, Example 1, in which the first aging treatment is performed, has a lower DC resistance DCIR after the cycle test 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 the cycle test.
Further, comparing Example 1 with Comparative Examples 1 and 2, the DC resistance DCIR after the cycle test in Example 1 is smaller than the DC resistance DCIR after the cycle test in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, it is possible to effectively suppress the increase in DC resistance DCIR after the cycle test, as compared with the case where only one of the additives is added.
Further, the DC resistance DCIR after the cycle test in Examples 9-19 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 VC and LiDFOB, the effects of these other additives are not inhibited.

(Analysis based on Figure 7)
As shown in FIG. 7, in Example 1 in which the first aging treatment was performed, the DCIR increase rate after the cycle test of the DC resistance DCIR was lower than in Comparative Example 4 in which the third aging treatment was performed. 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, comparing Example 1 with Comparative Examples 1 and 2, the rate of increase in DC resistance DCIR after the cycle test in Example 1 is smaller than the rate of increase in DC resistance DCIR after the cycle test in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, it is possible to effectively suppress an increase in the DC resistance DCIR increase rate after the cycle test compared to the case where only one of the additives is added.
Further, the rate of increase in DC resistance DCIR before and after the cycle test of Examples 1 to 4 subjected to the first aging treatment and the rate of increase in DC resistance DCIR after the cycle test of Examples 5 to 8 subjected to the second aging treatment are shown in Examples. 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 rate of increase in DC resistance DCIR after the cycle test is lower than when Therefore, the three-stage aging process can further suppress the DC resistance DCIR increase rate before and after the cycle test than the two-stage aging process.
Further, the DC resistances DCIR after storage in Examples 9-19 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 and LiDFOB, the effects of these other additives are not inhibited.

[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, Example 1, which was subjected to the first aging treatment, has a larger discharge capacity after the cycle test than Comparative Example 4, which was subjected to the third aging treatment. 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, when comparing Example 1 with Comparative Examples 1 and 2, the discharge capacity after storage in Example 1 is larger than the discharge capacity after the cycle test in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, it is possible to effectively suppress the decrease in discharge capacity after the cycle test compared to the case where only one of the additives is added.
Further, the discharge capacities after storage in Examples 9-19 are larger than the discharge capacities after the cycle test in Comparative Examples 1-4. Therefore, even if other additives are added in addition to VC and LiDFOB, the effects of these other additives are not inhibited.

(Analysis based on Figure 9)
As shown in FIG. 9, Example 1, in which the first aging treatment was performed, has a higher discharge capacity retention rate after the cycle test than Comparative Example 4, in which the third aging treatment was performed. Therefore, the two-stage aging treatment can further improve the discharge capacity retention rate before and after the cycle test, rather than repeating charging and discharging until the SOC reaches 100%.
Further, when comparing Example 1 with Comparative Examples 1 and 2, the discharge capacity retention rate in Example 1 is higher than the discharge capacity retention rate in Comparative Examples 1 and 2. Therefore, by combining VC and LiDFOB, the discharge capacity retention rate can be effectively improved compared to the case where only one of the additives is added.
In addition, the discharge capacity retention rates before and after storage of Examples 1 to 4 subjected to the first aging treatment and the discharge capacity retention rates of Examples 5 to 8 subjected to the second aging treatment were compared with each other. When comparing between 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 in the cycle test. The subsequent discharge capacity retention rate is high. Therefore, the three-stage aging treatment can further improve the discharge capacity retention rate after the cycle test, rather than the two-stage aging treatment.
Further, the discharge capacity retention ratios after the cycle test in Examples 9-19 are higher than those in Comparative Examples 1-4. Therefore, even if other additives are added in addition to VC and LiDFOB, the effects of these other additives are not inhibited.

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.

Moreover, in Examples 2 to 4, the amount of TMSP added was changed. Specifically, the amount of TMSP added in Example 3 was changed to 5 times the amount of TMSP added in Example 2, and the amount of TMSP added in Example 4 was changed to 10 times the amount of TMSP added in Example 2. However, the accompanying change in DC resistance DCIR and change in discharge capacity are slight. From this, the combination of VC and LiDFOB as additives and the aging treatment conditions have a strong causal relationship, and when VC and LiDFOB are used as additives, two-step aging treatment at the time of initial charging should be performed. Therefore, the characteristics of the battery can be effectively improved. As in Comparative Example 3, when the molar ratio of TMSP to LiDFOB (LiDFOB/TMSP) is 10 or less, the direct current resistance DCIR increases and the discharge capacity retention rate decreases, especially in the cycle test. As for the amount to be added, it is preferable that the molar ratio of LiDFOB/TMSP is 20 or more.

Although the detailed mechanism of SEI layer formation in this embodiment is not clear, as shown in the SEI image diagram of FIG. 10, LiDFOB forms a two-dimensional pseudo-oligomerized layer, It is believed that LiDFOB and VC and EC form a three-dimensional layer. Moreover, when TMSP participates in this reaction, it is thought that it becomes a nucleus during SEI formation, further promoting three-dimensionalization.

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) and difluoro[oxolato-O,O′]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 and LiDFOB added to the non-aqueous electrolytic solution is 0.5 wt% or more and 5.0 wt% or less, and the wt% ratio obtained by dividing the wt% of LiDFOB by the wt% of VC is 1.67 or more. and the molar ratio obtained by dividing the number of moles of LiDFOB by the number of moles of VC is 1 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) and difluoro[oxolato-O,O′]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 and LiDFOB added to the non-aqueous electrolytic solution is 0.5 wt% or more and 5.0 wt% or less, and the wt% ratio obtained by dividing the wt% of LiDFOB by the wt% of VC is 1.67 or more. and the molar ratio obtained by dividing the number of moles of LiDFOB by the number of moles of VC is 1 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,
The next charging step includes:
a first step of charging the battery at a C rate of 0.1 C to 0.5 C and to an SOC higher than the first SOC of 40% to 60%, and then holding the ambient temperature at 45° C. to 60° C. for 6 hours to 300 hours; ,
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 satisfies a + b + c = 1. z satisfies the number of oxygen atoms of the elements in the formula.
The negative electrode has a (002) plane spacing of 0.3 according to a wide-angle X-ray diffraction method as a negative electrode active material.
less than 37 nm, an R value (ratio of peak intensity at 1360 cm ⁻¹ to peak intensity at 1580 cm ⁻¹ ) in Raman spectroscopy of 0.12 or more and 0.8 or less, and a BET specific surface area of 0.1 m ² A method for producing a lithium-ion secondary battery, comprising graphitic carbon particles having a particle size of 2.0 m ² /g to 2.0 m 2 /g.

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