JP6805682B2 - Manufacturing method of non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a method for producing a non-aqueous electrolyte secondary battery, and more particularly, a non-aqueous electrolyte secondary battery including a solid solution positive electrode and a Si-based negative electrode includes an activation step of charging / discharging and activating the non-aqueous electrolyte secondary battery. The present invention relates to a method for manufacturing a water electrolyte secondary battery.

In recent years, there is an urgent need to reduce the amount of carbon dioxide in order to cope with global warming. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles and hybrid electric vehicles, and the development of electric devices such as motor drive batteries, which hold the key to their practical application, is being actively carried out. There is.

Lithium-ion batteries, which have relatively high theoretical energy, are attracting attention as motor drive batteries, and are currently being rapidly developed.
In a lithium ion battery, generally, a positive electrode in which a positive electrode active material or the like is applied to a positive electrode current collector using a binder and a negative electrode in which a negative electrode active material or the like is applied to a negative electrode current collector using a binder are formed via an electrolyte layer. It is connected and stored in a battery case.

In order for electric vehicles equipped with such lithium-ion batteries to become widespread, it is necessary to improve the performance of lithium-ion batteries so that the mileage per charge is close to the mileage per refueling of gasoline engine vehicles.

Therefore, it is desired to improve the energy density of the lithium ion battery, and it is necessary to increase the electric capacity per unit mass of the positive electrode and the negative electrode.

As the positive electrode material capable of increasing the electric capacity, a so-called solid solution positive electrode material is known, and in particular, an electrochemically inactive and layered Li ₂ MnO ₃ and an electrochemically active layered Li MO ₂ (formula). The solid solution with (M in, transition metal such as Co, Ni) shows a large electric capacity exceeding 200 mAh / g.

It is known that a battery using the solid solution as a positive electrode has improved durability (capacity retention rate) by pretreatment with charge / discharge while increasing the upper limit voltage stepwise.

According to Patent Document 1, before the charge / discharge pretreatment of the solid solution positive electrode is performed, the additive in the electrolytic solution is decomposed at 3.5 v or less, which is lower than the voltage applied in the pretreatment of the solid solution positive electrode. It is disclosed that an aging treatment of a negative electrode forming a SEI (Solid Electrolyte Interface) film is performed.
It is disclosed that the aging treatment can suppress the deterioration of the electrolytic solution and the negative electrode active material, and further improve the durability (capacity retention rate).

Japanese Unexamined Patent Publication No. 2013-243116

However, the one described in Patent Document 1 uses a carbon-based material such as graphite as the negative electrode material, and it is difficult to increase the capacity of the negative electrode in accordance with the increase in the capacity of the positive electrode.

As a high-capacity negative electrode material, a Si-based negative electrode such as silicon (Si), silicon oxide (SiO), or a Si alloy is known. However, the Si-based negative electrode material has a large volume change during charge and discharge, and therefore is a Si-based negative electrode material. A battery using a negative electrode has a problem that the capacity is greatly reduced due to a charge / discharge cycle.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide an initial capacity and charge / discharge in a non-aqueous electrolyte secondary battery including a Si-based negative electrode and a solid solution positive electrode. It is an object of the present invention to provide a method for manufacturing a non-aqueous electrolyte secondary battery, which includes an activation step capable of improving the capacity retention rate by a cycle.

As a result of diligent studies to achieve the above object, the present inventor has improved the initial capacity of the Si-based negative electrode when it is charged with a low current value at the time of initial charging in the activation step, while wrinkles due to volume expansion occur. We have found that the above-mentioned wrinkles can be prevented although the initial capacity becomes smaller when the battery is charged with a high current value because it is likely to occur, and the present invention has been completed.

That is, the method for producing a non-aqueous electrolyte secondary battery of the present invention includes an activation step of charging / discharging the non-aqueous electrolyte secondary battery to activate it.
The non-aqueous electrolyte secondary battery includes a solid solution positive electrode and a Si-based negative electrode.
The solid solution positive electrode contains an active material represented by the following composition formula (1).
The activation step is a process of switching the applied charging current value to a high charging current value one or more times before reaching the maximum voltage at the time of initial charging.
The first-time switching of the charging current value, that the charging voltage have 4.52V line below or 3.75V, the maximum charging voltage reached after the charging current value switching one time is 4.55V~4.80V This is a method for manufacturing a non-aqueous electrolyte secondary battery.

[Li _1.5 ] [Li _{{0.5 (1-x)}} Mn _1-x M _1.5x ] O ₃ ... Composition formula (1)

However, in the composition formula (1), x satisfies 0.1 ≦ x ≦ 0.8, M is Ni _α Co _β Mn _γ , and α, β, γ are 0 ≦ α ≦ 0.5, 0 ≦. It satisfies β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1.

According to the present invention, at the time of initial charging in the activation step, the battery is charged with a low current value to develop the initial capacity, and the applied charging current value is switched to a high charging current value before wrinkles occur on the negative electrode. Since the occurrence of wrinkles is prevented, it is possible to provide a method for manufacturing a non-aqueous electrolyte secondary battery capable of improving the initial capacity and the capacity retention rate.

It is a graph which shows an example of the charge curve of the non-aqueous electrolyte secondary battery. It is a dQ / dV curve based on the charge curve of FIG. It is a graph which shows the relationship between the charge voltage and the expansion coefficient of a Si negative electrode. It is a graph which shows the relationship between the charge current value, a wrinkle area ratio and durability.

但し、組成式（１）中、ｘは０．１≦ｘ≦ ０．８を満たし、ＭはＮｉ_αＣｏ_βＭｎ_γ であり、α、β、γは０≦α≦０．５、０≦β≦０．３３、０≦γ≦０．５、かつα＋β＋γ＝１を満たす。 [Manufacturing method of non-aqueous electrolyte secondary battery]
The method for manufacturing the non-aqueous electrolyte secondary battery of the present invention will be described in detail.
The method for producing a non-aqueous electrolyte secondary battery activates a non-aqueous electrolyte secondary battery including a solid solution positive electrode containing an active material represented by the following composition formula (1) and a Si-based negative electrode by charging / discharging. This is a method for manufacturing a non-aqueous electrolyte secondary battery including an activation step.

However, in the composition formula (1), x satisfies 0.1 ≦ x ≦ 0.8, M is Ni _α Co _β Mn _γ , and α, β, γ are 0 ≦ α ≦ 0.5, 0 ≦. It satisfies β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1.

The activation step is performed by charging the initial charge with a constant current, reaching a predetermined voltage, switching the applied charging current value to increase it, and then reaching the maximum voltage. The switching of the charging current value in the initial charging may be performed once, but it may be switched a plurality of times to gradually increase the charging current value to reach the maximum voltage. Then, the pretreatment is performed by first discharging the voltage after reaching the maximum voltage.
Further, after the initial charge / discharge, the charge / discharge may be performed a plurality of times.

Hereinafter, in the present invention, the charging before the first switching of the charging current value applied in the initial charging may be referred to as low-rate charging, and the charging after switching may be referred to as high-rate charging.

In the present invention, the low-rate charging activates the Si-based negative electrode to increase the initial capacity, and the high-rate charging activates the solid solution positive electrode while suppressing the occurrence of wrinkles in the Si-based negative electrode to activate the initial capacity and capacity. The maintenance rate and can be improved.

The above-mentioned initial charging refers to charging from the first charging to discharging in the activation step of charging / discharging and activating the assembled non-aqueous electrolyte secondary battery, and lithium (Li) is applied to the Si-based negative electrode for the first time. This is the process of invading and causing volume expansion.

The volume expansion at this time greatly affects the presence or absence of wrinkles on the Si-based negative electrode, and by controlling the charging current value applied during the initial charging, it is possible to prevent the occurrence of wrinkles on the Si-based negative electrode during subsequent charging. At the same time, the initial capacity of the Si-based negative electrode can be improved.

The first switching is performed when the charging voltage is 3.75 V or more and 4.52 V or less. The initial capacity can be increased by switching to high-rate charging after raising the voltage to a voltage at which the charging reaction sufficiently occurs in low-rate charging, and the above switching is more preferably performed at 3.90 V or higher.

FIG. 1 shows a charging curve, and FIG. 2 shows a dQ / dV curve for analyzing the charging curve of FIG. 1 in detail. It can be seen from FIGS. 1 and 2 that there are inflection points at 3.75 V and 3.90 V, and that the voltage change occurs due to the phase transition accompanying the change in the Li content of the Si-based negative electrode.

In addition, the initial capacity can be improved by charging until the charging voltage becomes sufficiently high, but if the charging voltage in low-rate charging exceeds 4.52V, too much Li enters the Si-based negative electrode and wrinkles occur. , The distance between the electrodes may become non-uniform and the durability (capacity retention rate) in the charge / discharge cycle may decrease.
FIG. 3 shows the relationship between the charging voltage and the expansion coefficient of the Si negative electrode.

Before the first charge current value switching in the initial charge, that is, low rate charging is preferably performed at 0.1 C or less, and more preferably at 0.05 C or less.

As shown in FIG. 1, the lower the charging current value is, the larger the initial capacity is obtained at a lower charging voltage, and when it exceeds 0.1 C, the amount of increase in the initial capacity with respect to the charging voltage begins to decrease. By performing low-rate charging at 0.1 C or less, the initial capacity of the Si-based negative electrode can be increased.
It should be noted that the low-rate charging can be performed as long as a current flows and the charging current value exceeds 0C, but if it is too low, it takes a long time, so it is preferably performed at 0.0005C or more.

Further, after the first switching of the charging current value, that is, the charging current value of high-rate charging preferably exceeds 0.1C, and more preferably 0.3C or more and 10.0C or less.

The high-rate charging activates the solid solution positive electrode while suppressing the occurrence of wrinkles on the Si-based negative electrode. FIG. 4 shows the relationship between the charging current value, the wrinkle area ratio, and the durability.
As shown in FIG. 4, when the charging current value exceeds 0.1 C, the occurrence of wrinkles on the Si-based negative electrode can be suppressed and the durability can be improved.

At the time of initial charging, wrinkles due to volume expansion occur during low-rate charging, and the reason why wrinkles can be prevented during high-rate charging has not been clarified, but it is presumed as follows.

In the low-rate charging, when the charging voltage becomes high, Li ⁺ reacts with a binder such as polyimide in the Si-based negative electrode, the binder is decomposed, the bond between the electrode materials is weakened, and the degree of freedom of deformation of the Si-based negative electrode is increased. To increase. On the other hand, in high-rate charging, it is considered that the deformation of the Si-based negative electrode is suppressed because Li ⁺ does not react with the binder having a high reaction resistance.

Further, at the time of initial charging, it is preferable that the maximum charging voltage reaches 4.55V to 4.80V by high rate charging. When the charging voltage reaches the above range, the solid solution positive electrode can be sufficiently activated and the initial capacity can be improved.

The above-mentioned method for manufacturing a non-aqueous electrolyte secondary battery can be applied to a non-aqueous electrolyte secondary battery of any size, but when applied to a large-sized battery, an excellent effect is obtained.
Specifically, the effect of the present invention is large in a battery having a rated capacity of 3 Ah or more and a ratio of the battery volume to the rated capacity of 8 cm ³ / Ah or less, particularly a large battery having a rated capacity of 5 Ah or more.
In the present invention, the battery volume refers to the product of the projected area and the thickness of the battery including the battery exterior.

That is, as the size of the battery increases and the electrode area increases, the uniform dispersibility of the negative electrode active material in the Si-based negative electrode, the thickness unevenness of the electrode due to uneven coating, and the uneven pressurization during electrode lamination cause the electrode. Due to deflection and the like, it becomes difficult to make the distance between the electrodes of the Si-based negative electrode and the solid solution positive electrode uniform.

If the thickness is uneven in the plane of the Si-based negative electrode, the expansion and contraction of the Si-based negative electrode is also uneven and wrinkles are likely to occur, and the distance between the electrodes of the Si-based negative electrode and the solid solution positive electrode becomes non-uniform. Become. Further, the wrinkles of the Si-based negative electrode and the deflection of the electrode are combined to increase the variation in the distance between the electrodes between the Si-based negative electrode and the solid solution positive electrode.

Then, in the place where the distance between the poles is long, the resistance becomes large and the amount of current becomes small, which makes it difficult for the battery reaction to proceed. It will be easier.
Therefore, the location where the distance between the poles is long does not contribute to the battery capacity and the battery capacity decreases, and the battery reaction selectively occurs at the location where the distance between the poles is short, and a side reaction with the electrolytic solution, deterioration of the active material, etc. Is likely to occur, so that the capacity retention rate of the battery is lowered.

[Non-aqueous electrolyte secondary battery]
Next, a non-aqueous electrolyte secondary battery that can use the method for producing a non-aqueous electrolyte secondary battery of the present invention will be described.
The non-aqueous electrolyte secondary battery includes a solid solution positive electrode, a non-aqueous electrolyte, and a Si-based negative electrode, and these are laminated in this order. Then, one or two or more of the non-aqueous electrolyte secondary batteries are stacked and housed in the exterior body, and electric power is taken out to the outside through the positive electrode current collector plate and the negative electrode current collector plate.

但し、組成式（１）中、ｘは０．１≦ｘ≦ ０．８を満たし、ＭはＮｉ_αＣｏ_βＭｎ_γ であり、α、β、γは０≦α≦０．５、０≦β≦０．３３、０≦γ≦０．５、かつα＋β＋γ＝１を満たす。 (Solid solution positive electrode)
The solid solution positive electrode contains an active material represented by the following composition formula (1).

However, in the composition formula (1), x satisfies 0.1 ≦ x ≦ 0.8, M is Ni _α Co _β Mn _γ , and α, β, γ are 0 ≦ α ≦ 0.5, 0 ≦. It satisfies β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1.

The active material is _{Li 2 MnO} 3 -LiMO 2 system _{(M = Ni α Co β Mn} γ) solid solution, and _Li 2 MnO ₃ theoretical capacity is high, but inactive, and active LiMO ₂ and solid solution, The composition is closer to the Li ₂ MnO ₃ side to draw out a high capacity, and the highly active properties of LiMO ₂ are utilized. With respect to the solid solution positive electrode containing the above active material, 4. High capacity can be obtained by charging to 55-4.80V.

The solid solution positive electrode can be formed by applying a slurry containing an active material and a binder to a current collector or the like, drying the slurry, and then pressing the slurry.

Examples of the slurry coating method include a screen printing method, a spray coating method, an inkjet coating method, and a doctor blade coating method. In addition, examples of the pressing method include a calendar roll and a flat plate press.

Examples of the binder include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethyl cellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene / butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and its hydrogen additive, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as the hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether co-weight. Fluororesin such as coalescence (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), etc. Vinylidene Fluoride-Hexafluoropropylene Fluororesin (VDF-HFP Fluororesin), Vinylidene Fluoride-Hexafluoropropylene-Tetrafluoroethylene Fluororesin (VDF-HFP-TFE Fluororesin), Vinylidene Fluoride-Pentafluoro Propylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene Examples thereof include vinylidene fluoride-based fluororubbers such as vinylidene fluoride-chlorotrifluoroethylene-based fluororubbers (VDF-CTFE-based fluororubbers) and epoxy resins. ..

(Si-based negative electrode)
The Si-based negative electrode contains silicon oxide such as silicon simple substance (Si), silicon alloy, SiO ₂ , SiO as an active material, and is composed of tin simple substance (Sn), tin alloy, tin oxide, carbon material, etc. It may contain other active materials.

The Si-based negative electrode can be formed by applying a slurry containing the active material and a binder to a current collector or the like. As the binder, a binder similar to that of the solid solution positive electrode can be used.

(Non-aqueous electrolyte)
Examples of the electrolyte constituting the non-aqueous electrolyte include a liquid electrolyte and a polymer electrolyte.
The liquid electrolyte is a solution of a lithium salt (electrolyte salt) in an organic solvent, and the gel electrolyte is a liquid electrolyte held in a matrix polymer made of an ionic conductive polymer.

Examples of the organic solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). , Methylpropyl carbonate (MPC) and other carbonates.

Furthermore, as the lithium _{salt, Li (CF 3 SO 2)} 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 SO 3 , etc. Examples of compounds that can be added to the active material layer of the electrode of.

Examples of the ionic conductive polymer used as the polymer electrolyte matrix polymer include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

A separator may be used for the non-aqueous electrolyte. Specific forms of the separator (including non-woven fabric) include, for example, a microporous membrane made of polyolefin such as polyethylene or polypropylene, a porous flat plate, and a non-woven fabric.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following Examples.

<Manufacturing of non-aqueous electrolyte secondary battery 1>
(Preparation of positive electrode active material)
Sodium hydroxide and ammonia were continuously supplied at 60 ° C. to an aqueous solution (1 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved to adjust the pH to 11.3, and nickel was prepared by the coprecipitation method. And manganese and cobalt were dissolved at a molar ratio of 1: 1: 4 to prepare a metal composite hydroxide.

The metal composite hydroxide and lithium carbonate are weighed so that the ratio of the total number of moles of metals (nickel, cobalt, manganese) contained in the metal composite hydroxide to the number of moles of lithium is 2: 3. And mixed well. The temperature is raised to 900 ° C. at a heating rate of 5 ° C./min, temporarily fired in an air atmosphere for 2 hours, then raised to 920 ° C. at a heating rate of 3 ° C./min, fired for 10 hours, and then cooled to room temperature. As a result, the positive electrode active material Li _1.5 [Ni _0.20 Co _0.20 Mn _0.80 [Li] _0.30 O ₃ was obtained.

(Preparation of solid solution positive electrode)
94.5% by mass of the positive electrode active material, 3% by mass of a conductive additive (Ketjen black, average particle size: 300 nm), 2.5% by mass of binder (polyvinylidene fluoride (PIDF)), and a viscosity adjusting solvent (N-). An appropriate amount of methyl-2pyrrolidone (NMP) was mixed to prepare a positive electrode active material slurry.

This positive electrode active material slurry is applied to a current collector (aluminum foil, thickness 20 μm), dried at 120 ° C. for 3 minutes, compression-molded with a roll press, and cut into 3 × 4 cm to obtain a positive electrode active material layer. A solid solution positive electrode having a single-sided coating amount of 23.5 mg / cm ² was prepared.

(Manufacturing of Si-based negative electrode)
The metal powder was alloyed by the mechanical alloy method using a planetary ball mill (P-6 manufactured by Frichchu, Germany). Specifically, the metal powder prepared so that the mass ratio of Si: Sn: Ti = 60: 10: 30 and the zirconia crushed balls were put into a zirconia container. Then, the pedestal for fixing the zirconia container was rotated at 600 rpm for 12.5 hours to alloy the metal powder.

80% by mass of the Si alloy powder, 5% by mass of a conductive auxiliary agent (Ketchen black, average particle size: 300 nm), and 15% by mass of polyimide (PI) were added to N-methylpyrrolidone and mixed [negative electrode]. Active material slurry] was prepared.

The above [negative electrode active material slurry] is applied to a current collector (copper foil, thickness 10 μm), dried sufficiently, compression-molded with a roll press, and cut into 3 × 4 cm to cut one side of the negative electrode active material layer. A [Si-based negative electrode] having a coating amount of 6.8 mg / cm ² was prepared.

(Preparation of electrolyte)
LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DEC) in a ratio of 3: 7 (volume ratio) to prepare an [electrolyte solution] having a LiPF ₆ of 1.0 M.

The solid solution positive electrode and the [Si-based negative electrode] were opposed to each other, and a separator (polypropylene (PP)) was placed between them to prepare a laminated body of the solid solution positive electrode, the separator, and the negative electrode. This laminate was placed in an aluminum laminate cell, and the above [electrolyte solution] was injected into the cell to seal the laminate to obtain a small [lithium ion secondary battery 1].

<Manufacturing of non-aqueous electrolyte secondary battery 2>
The current collectors of the positive electrode and the negative electrode were changed to 120 × 210 cm, and active material layers were coated and molded on both sides of each current collector. Similar to [Lithium Ion Secondary Battery 1], a large [Lithium Ion Secondary Battery 1] is formed by alternately laminating a solid solution positive electrode and a Si alloy negative electrode via a separator to form a laminate of two positive electrodes and three negative electrodes. Battery 2] was obtained.

The rated capacity of the above [lithium ion secondary battery 1] and [lithium ion secondary battery 2] and the ratio of the battery volume to the rated capacity (battery volume / rated capacity) were measured by the following method.

<Measurement of rated capacity>
The rated capacity was measured as follows in a voltage range of 0 V to 4.6 V at a temperature of 25 ° C. after injecting the electrolytic solution into the test battery and leaving it to stand for about 10 hours.
(1) After reaching 4.6V with a constant current charge of 0.05C, rest for 5 minutes.
(2) After reaching 0V with a constant current discharge of 0.05C, it is paused for 5 minutes.
(3) After reaching 4.45 V with a constant current charge of 0.1 C, the battery is charged with a constant voltage so that the total charging time is 10 hours, and then pauses for 5 minutes.
(4) After reaching 1.8V with a constant current discharge of 0.1C, rest for 5 minutes.
The above (3) to (4) were repeated 5 times, and the discharge capacity at the final constant current discharge was set as the rated capacity.

<Measurement of battery volume>
The battery volume was determined by the product of the projected area of the battery including the battery exterior and the thickness in the projection direction.
As the projected area, the selling maximum projected area of the six projected areas of front, back, right side, left side, plane, and bottom was used.
Usually, it is the projected area of the flat surface or the bottom surface when the battery is placed on the flat plate in the most stable state.
The thickness of the battery including the battery exterior was measured at a plurality of locations in consideration of the variation in the thickness at the time of full charge, and the average was taken as the thickness of the battery.

The above [lithium ion secondary battery 1] and [lithium ion secondary battery 2] are charged at a constant current by the method shown in Table 1 in an environment of 25 ° C., and discharged at a constant current at 0.1 C for activation treatment. did.

For each activated non-aqueous electrolyte secondary battery, the initial capacity of the battery, the presence or absence of wrinkles on the Si-based negative electrode, and the capacity retention rate were measured by the following methods. The evaluation results are shown in Table 1.

(Measurement of initial capacity)
The charging current is a constant current-constant voltage method, and each evaluation battery is constantly charged to 4.45 V with a current value of 0.1 C in an environment of 25 ° C, so that the total charging time is 10 hours. The battery was fully charged by constant voltage charging. Then, it was discharged to 1.8 V at a current value of 0.1 C by a constant current method in an environment of 25 ° C.
This charge / discharge cycle at 0.1 C was repeated 5 times, and the capacity at the time of the final constant current discharge was set as the initial capacity.

(Presence or absence of wrinkles)
The lithium ion secondary battery was disassembled and the presence or absence of wrinkles on the Si-based negative electrode was visually confirmed.
○: No wrinkles △: Minor wrinkles occur ×: Significant wrinkles occur

(Capacity maintenance rate)
Capacity retention rate (%) = 100th cycle discharge capacity / 1st cycle discharge capacity x 100
In Table 1, the initial battery capacity is represented by the capacity expression rate (%) with Comparative Example 2 as 100.

In Comparative Examples 1 and 2 charged to the maximum voltage at 0.1 C or less, the initial capacity was large, but wrinkles were generated and the capacity retention rate was lowered.
In Comparative Examples 4 and 5 charged to the maximum voltage with a current value exceeding 0.1 C, wrinkles did not occur, but the initial capacitance became small.
In the example in which the battery was initially charged at 0.05 C and the charging current value was switched to increase before reaching the maximum voltage, both the initial capacity and the capacity retention rate could be achieved.

Claims (7)

A method for manufacturing a non-aqueous electrolyte secondary battery, which comprises an activation step of charging / discharging and activating the non-aqueous electrolyte secondary battery.
The non-aqueous electrolyte secondary battery includes a solid solution positive electrode and a Si-based negative electrode.
The solid solution positive electrode contains an active material represented by the following composition formula (1).
The activation step is a process of switching the applied charging current value to a high charging current value one or more times before reaching the maximum voltage at the time of initial charging.
The first switching of the charging current value is performed when the charging voltage is 3.75V or more and 4.52V or less, and the maximum charging voltage reached after the first switching of the charging current value is 4.55V to 4.80V. method of manufacturing a nonaqueous electrolyte secondary battery you characterized.

[Li _1.5 ] [Li _{{0.5 (1-x)}} Mn _1-x M _1.5x ] O ₃ ... Composition formula (1)

However, in the composition formula (1), x satisfies 0.1 ≦ x ≦ 0.8, M is Ni _α Co _β Mn _γ , and α, β, γ are 0 ≦ α ≦ 0.5, 0 ≦. It satisfies β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, wherein the first switching of the charging current value is performed at 3.90 V or higher. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the upper limit of the charging current value until the first charging current value switching is 0.1 C or less. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 3, wherein the upper limit of the charging current value until the first charging current value switching is 0.05 C or less. The method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the charging current value after the first switching of the charging current value exceeds 0.1 C. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 5, wherein the charging current value after the first charging current value switching is 0.3 C or more. The item according to any one of claims 1 to 6, wherein the non-aqueous electrolyte secondary battery has a rated capacity of 3 Ah or more and a ratio of the battery volume to the rated capacity of 8 cm ³ / Ah or less. A method for manufacturing a non-aqueous electrolyte secondary battery.
However, the battery volume is the product of the projected area and the thickness of the battery including the battery exterior.

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