JP2018055901A - Nonaqueous electrolyte secondary battery manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery manufacturing method including an activation step which enables the increase in capacity retention according to an initial capacity and a charge-discharge cycle in a nonaqueous electrolyte secondary battery including a Si-based negative electrode and a solid solution positive electrode.SOLUTION: A nonaqueous electrolyte secondary battery manufacturing method according to the present invention comprises an activation step of activating a nonaqueous electrolyte secondary battery by charge and discharge. The nonaqueous electrolyte secondary battery comprises a solid solution positive electrode and a Si-based negative electrode. The solid solution positive electrode includes an active material represented by the composition formula (1) below. In the activation step, a value of charge current to be applied is switched to a high charge current value more than once until a maximum voltage is reached in initial charging. The first switching of the charge current value is performed with a charge voltage of 3.75-4.52 V. In the composition formula (1), "x" satisfies 0.1≤x≤0.8, "M" represents NiCoMn, and "α", "β" and "γ" satisfy the following expressions: 0≤α≤0.5, 0≤β≤0.33, 0≤γ≤0.5, and α+β+γ=1.SELECTED DRAWING: None

Description

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

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there are high expectations for the reduction of carbon dioxide emissions through the introduction of electric vehicles and hybrid electric vehicles, and the development of electric devices such as motor drive batteries that hold the key to practical use of these devices is actively underway. Yes.

As a battery for driving a motor, a lithium ion battery having a relatively high theoretical energy is attracting attention, and is currently being developed rapidly.
Generally, in a lithium ion battery, a positive electrode obtained by applying a positive electrode active material or the like to a positive electrode current collector using a binder, and a negative electrode obtained by applying a negative electrode active material or the like to a negative electrode current collector using a binder are interposed via an electrolyte layer. Connected and housed in a battery case.

  In order for an electric vehicle equipped with such a lithium ion battery to be widely spread, it is necessary to make the lithium ion battery have high performance and make the travel distance per charge closer to the travel distance per refueling of a gasoline engine vehicle.

  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, electrochemically inactive layered Li ₂ MnO ₃ and electrochemically active layered LiMO ₂ (formula The solid solution with M being a transition metal such as Co or Ni shows a large electric capacity exceeding 200 mAh / g.

  And it is known that the battery using the said solid solution for a positive electrode will improve durability (capacity maintenance factor) by carrying out pre-charge / discharge treatment, increasing an upper limit voltage in steps.

In Patent Document 1, before performing charge / discharge pretreatment on the solid solution positive electrode, the additive in the electrolytic solution is decomposed at 3.5 V or lower, which is lower than the voltage applied in the pretreatment of the solid solution positive electrode. It is disclosed to perform an aging treatment of a negative electrode forming a SEI (Solid Electrolyte Interface) film.
Further, it is disclosed that the deterioration of the electrolytic solution and the negative electrode active material can be suppressed by the aging treatment, and the durability (capacity maintenance ratio) can be further improved.

JP 2013-243116 A

  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 capacity of the positive electrode.

  Si negative electrodes such as silicon (Si), silicon oxide (SiO), and Si alloys are known as high capacity negative electrode materials. However, since Si negative electrode materials have a large volume change during charge and discharge, they are Si-based. A battery using a negative electrode has a problem that a capacity decrease due to a charge / discharge cycle is large.

  The present invention has been made in view of such problems of the prior art, and an object thereof is to provide an initial capacity and charge / discharge in a nonaqueous electrolyte secondary battery including a Si-based negative electrode and a solid solution positive electrode. An object of the present invention is to provide a method for manufacturing a non-aqueous electrolyte secondary battery including an activation process capable of improving the capacity retention rate due to cycles.

  As a result of intensive studies to achieve the above object, the present inventor, as a result of initial charge in the activation process, the initial capacity of the Si-based negative electrode is improved when charged at a low current value, while wrinkles due to volume expansion occur. It was easy to generate, and when it was charged with a high current value, it was found that although the initial capacity is small, the generation of the wrinkles can be prevented, and the present invention has been completed.

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。 That is, the method for producing a nonaqueous electrolyte secondary battery of the present invention includes an activation process in which the nonaqueous electrolyte secondary battery is activated by charging and discharging.
The non-aqueous electrolyte secondary battery includes a solid solution positive electrode and a Si-based negative electrode,
The solid solution positive electrode includes 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 at least once before reaching the maximum voltage at the time of the first charge,
The method for producing a non-aqueous electrolyte secondary battery is characterized in that the charging current value is switched at a charging voltage of 3.75V to 4.52V.

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

  According to the present invention, during the initial charging in the activation process, charging is performed with a low current value to develop an initial capacity, and the applied charging current value is switched to a high charging current value before wrinkles are generated in the negative electrode. Therefore, it is possible to provide a method for manufacturing a non-aqueous electrolyte secondary battery that can improve the initial capacity and the capacity retention rate.

It is a graph which shows an example of the charge curve of a nonaqueous 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 a charging voltage and the expansion coefficient of a Si negative electrode. It is a graph which shows the relationship between a charging 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。 [Method for producing non-aqueous electrolyte secondary battery]
The method for producing the nonaqueous electrolyte secondary battery of the present invention will be described in detail.
The manufacturing method of the nonaqueous electrolyte secondary battery is activated by charging and discharging a nonaqueous 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. It is a manufacturing method of a nonaqueous electrolyte secondary battery including an activation process.

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

In the activation step, the initial charging is performed with a constant current, and after reaching a predetermined voltage, the charging current value to be applied is increased by switching and then reaching the maximum voltage. Switching of the charging current value in the initial charging may be performed once, but switching may be performed a plurality of times to increase the charging current value stepwise to reach the maximum voltage. And pre-processing is performed by discharging for the first time after reaching the maximum voltage.
Moreover, you may charge / discharge several times after the said first time charge / discharge.

  Hereinafter, in the present invention, charging before the first switching of the charging current value to be applied in the initial charging may be referred to as low rate charging, and 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 suppresses the generation of wrinkles in the Si-based negative electrode, while the solid solution positive electrode is activated to activate the initial capacity and capacity. The maintenance rate can be improved.

  The initial charge refers to the charge from the first charge to the discharge in the activation process in which the assembled non-aqueous electrolyte secondary battery is activated by charging and discharging, and for the first time lithium (Li) is applied to the Si-based negative electrode. This is a process in which volume expansion occurs.

  The volume expansion at this time greatly affects the presence or absence of wrinkles in the Si-based negative electrode, and by controlling the charging current value applied during the initial charge, the generation of wrinkles in the Si-based negative electrode during subsequent charging can be prevented. 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 3.75V to 4.52V. The initial capacity can be increased by switching to high-rate charging after raising the voltage at which charging reaction occurs sufficiently in low-rate charging, and it is more preferable to perform the switching at 3.90 V or higher.

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

In addition, it is possible to improve the initial capacity by charging until the charging voltage becomes sufficiently high, but if the charging voltage at low rate charging exceeds 4.52 V, Li will enter too much into the Si negative electrode and wrinkles will occur. In some cases, the distance between the electrodes becomes non-uniform, and the durability (capacity retention rate) in the charge / discharge cycle is lowered.
FIG. 3 shows the relationship between the charging voltage and the expansion rate of the Si negative electrode.

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

As shown in FIG. 1, as the charging current value is lower, a larger initial capacity is obtained at a lower charging voltage. When the charging current value exceeds 0.1 C, the increase amount of the initial capacity with respect to the charging voltage starts 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.
Note that the low rate charging may be performed if a current flows, and charging is possible if the charging current value exceeds 0 C. However, if it is too low, it takes a long time, so it is preferable to perform the charging at 0.0005 C or more.

  Further, after the first switching of the charging current value, that is, the charging current value of high rate charging is preferably more than 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 generation of wrinkles in 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, generation of wrinkles of the Si-based negative electrode can be suppressed and durability can be improved.

  During initial charging, wrinkles due to volume expansion occur during low-rate charging, and the reason why wrinkles can be prevented during high-rate charging is not clarified, but is estimated as follows.

In the low-rate charging, when the charging voltage increases, Li ⁺ also reacts with a binder such as polyimide in the Si-based negative electrode to decompose the binder, weakening the bonding between the electrode materials, and the freedom of deformation of the Si-based negative electrode is increased. To increase. On the other hand, in high rate charging, Li ⁺ does not react with a binder having a high reaction resistance, so that it is considered that deformation of the Si-based negative electrode is suppressed.

  Moreover, at the time of first charge, it is preferable that the maximum charge voltage reaches 4.55V-4.80V by high rate charge. 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 non-aqueous electrolyte secondary battery manufacturing method can be applied to non-aqueous electrolyte secondary batteries of any size. However, when applied to a large battery, an excellent effect can be obtained.
Specifically, the effect of the present invention is significant in a battery having a rated capacity of 3 Ah or more and a battery volume ratio 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 thickness of the battery including the battery outer package.

  In other words, the larger the battery and the larger the electrode area, the more uniform the dispersibility of the negative electrode active material in the Si-based negative electrode, the uneven electrode thickness due to coating unevenness, and the electrode unevenness due to pressure unevenness during electrode lamination. Deflection or the like makes it difficult to make the distance between the Si-based negative electrode and the solid solution positive electrode uniform.

  If the thickness of the Si-based negative electrode is uneven, the Si-based negative electrode is unevenly expanded and contracted, and wrinkles are likely to occur. The distance between the Si-based negative electrode and the solid solution positive electrode is not uniform. Become. Furthermore, the wrinkles of the Si-based negative electrode, the deflection of the electrode, and the like combine to increase the variation in the distance between the Si-based negative electrode and the solid solution positive electrode.

Then, at locations where the distance between the electrodes is far, the resistance increases and the amount of current decreases, making it difficult for the battery reaction to proceed.On the other hand, when the distance between the electrodes is close, the resistance decreases and the amount of current increases, and the battery reaction proceeds. It becomes easy.
Therefore, a place where the distance between the electrodes is far away does not contribute to the battery capacity, and the battery capacity is reduced. Is likely to occur, and the capacity retention rate of the battery is reduced.

[Nonaqueous electrolyte secondary battery]
Next, a nonaqueous electrolyte secondary battery that can be used in the method for producing a nonaqueous 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, which are stacked in this order. Then, one or more of the nonaqueous electrolyte secondary batteries are stacked and accommodated in the exterior body, and electric power is taken out 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 includes 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, and γ are 0 ≦ α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1 are satisfied.

The active material is a Li ₂ MnO ₃ —LiMO ₂ (M = Ni _α Co _β Mn _γ ) solid solution, and Li ₂ MnO ₃ , which has a high theoretical capacity but is inactive, and active LiMO ₂ are formed into a solid solution. The composition is made closer to the Li ₂ MnO ₃ side and a high capacity is drawn, and the highly active nature of LiMO ₂ is used. High capacity can be obtained by charging to 55 to 4.80V.

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

  Examples of the slurry application method include a screen printing method, a spray coating method, an ink jet coating method, a doctor blade coating method, and the like. Moreover, as a pressing method, a calendar roll, a flat plate press, etc. can be mentioned.

  Examples of the binder include the following materials. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile (PEN), polyacrylonitrile, polyimide, polyamide, polyamideimide, cellulose, carboxymethylcellulose (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 hydrogenated product thereof, styrene / isoprene / styrene block copolymer and Thermoplastic polymers such as hydrogenated products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene Copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene Fluororesin such as copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine Rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-teto Fluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubber (VDF-PFMVE-TFE fluororubber), vinylidene fluoride-chlorotrifluoroethylene And vinylidene fluoride-based fluororubbers such as epoxy-based fluororubbers (VDF-CTFE-based fluororubbers) and epoxy resins.

(Si negative electrode)
The Si-based negative electrode includes a silicon simple substance (Si), a silicon alloy, a silicon oxide such as SiO ₂ and SiO as an active material, a tin simple substance (Sn), a tin alloy, a tin oxide, a carbon material, etc. Other active materials may be included.

  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, the same binder as that of the solid solution positive electrode can be used.

(Nonaqueous electrolyte)
Examples of the electrolyte constituting the nonaqueous electrolyte include a liquid electrolyte and a polymer electrolyte.
The liquid electrolyte is obtained by dissolving a lithium salt (electrolyte salt) in an organic solvent, and the gel electrolyte is obtained by holding the liquid electrolyte in a matrix polymer made of an ion 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). And carbonates such as methylpropyl carbonate (MPC).

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. The compound which can be added to the active material layer of the electrode of this can be mentioned.

  Examples of the ion 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 examples of the separator (including non-woven fabric) include a microporous film made of polyolefin such as polyethylene and polypropylene, a porous flat plate, and a non-woven fabric.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to the following Example.

<Preparation of nonaqueous electrolyte secondary battery 1>
(Preparation of positive electrode active material)
To an aqueous solution (1 mol / L) in which nickel sulfate, cobalt sulfate, and manganese sulfate are dissolved, sodium hydroxide and ammonia are continuously supplied at 60 ° C. to adjust the pH to 11.3. A metal composite hydroxide comprising manganese, cobalt and solid solution in a molar ratio of 1: 1: 4 was prepared.

The metal composite hydroxide and lithium carbonate are weighed so that the ratio of the total number of moles of metal (nickel, cobalt, manganese) contained in the metal composite hydroxide and the number of moles of lithium is 2: 3. And mixed well. The temperature was raised to 900 ° C. at a temperature rising rate of 5 ° C./min, pre-baked in an air atmosphere for 2 hours, then heated to 920 ° C. at a temperature rising rate of 3 ° C./min, fired for 10 hours, and then cooled to room temperature. Thus, a 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 a binder (polyvinylidene fluoride (PIDF)), and a viscosity adjusting solvent (N- An appropriate amount of methyl-2pyrrolidone (NMP)) was mixed to adjust the 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 form a positive electrode active material layer A solid solution positive electrode having a single-side coating amount of 23.5 mg / cm ² was prepared.

(Preparation of Si-based negative electrode)
Metal powders were alloyed by a mechanical alloy method using a planetary ball mill (P-6, manufactured by Fricht, Germany). Specifically, a metal powder prepared so as to have a mass ratio of Si: Sn: Ti = 60: 10: 30 and pulverized balls made of zirconia were put into a container made of zirconia. Then, the base which fixes the container made from zirconia was rotated at 600 rpm for 12.5 hours, and metal powder was alloyed.

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

After applying the above [negative electrode active material slurry] to a current collector (copper foil, thickness 10 μm) and sufficiently drying, compression molding with a roll press machine and cutting to 3 × 4 cm to cut one side of the negative electrode active material layer [Si negative electrode] having a coating amount of 6.8 mg / cm ² was produced.

(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] having LiPF ₆ of 1.0 M.

  The solid solution positive electrode and the [Si-based negative electrode] were made to face each other, and a separator (polypropylene (PP)) was disposed therebetween to produce a solid solution positive electrode / separator / negative electrode laminate. This laminate was placed in an aluminum laminate cell, and the above [electrolytic solution] was injected into the cell and sealed to obtain a small [lithium ion secondary battery 1].

<Preparation of nonaqueous 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 formed on both surfaces of each current collector. The large-sized [lithium ion secondary battery] is the same as [Lithium ion secondary battery 1] except that the solid solution positive electrode and the Si alloy negative electrode are alternately laminated through separators to form a laminate of two positive electrodes and three negative electrodes. Battery 2] was obtained.

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

<Measurement of rated capacity>
The rated capacity was measured as follows at a temperature of 25 ° C. and a voltage range of 0 V to 4.6 V after injecting the electrolyte into the test battery and leaving it for about 10 hours.
(1) After reaching 4.6 V with a constant current charge of 0.05 C, pause for 5 minutes.
(2) After reaching 0 V with a constant current discharge of 0.05 C, rest for 5 minutes.
(3) After reaching 4.45 V with 0.1 C constant current charging, charge at a constant voltage so that the total charging time is 10 hours, and then rest for 5 minutes.
(4) After reaching 1.8 V with a constant current discharge of 0.1 C, rest for 5 minutes.
The above (3) to (4) were repeated 5 times, and the discharge capacity in the last constant current discharge was defined 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 outer package and the thickness in the projected direction.
As the projected area, the maximum projected area of the six projected areas of the front, back, right side, left side, plane, and bottom was used.
Note that it is usually the projected area of the flat or bottom surface when the battery is placed in the most stable state on the flat plate.
In addition, the thickness of the battery including the battery outer package was measured at a plurality of locations in consideration of the variation at the measurement location, and the average was taken as the thickness of the battery.

  The above-mentioned [lithium ion secondary battery 1] and [lithium ion secondary battery 2] are subjected to activation treatment by constant current charging by the method shown in Table 1 under a 25 ° C. environment and constant current discharging at 0.1 C. did.

  With respect to each activated non-aqueous electrolyte secondary battery, the battery initial capacity, the presence or absence of wrinkles of 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 charged with a constant current up to 4.45 V at a current value of 0.1 C under an environment of 25 ° C., so that the total charging time becomes 10 hours. The battery was charged at a constant voltage to obtain a fully charged state. Then, it discharged to 1.8V with the electric current value of 0.1C by the constant current system in 25 degreeC environment.
This charge / discharge cycle at 0.1 C was repeated 5 times, and the capacity at the last constant current discharge was defined as the initial capacity.

(With or without wrinkles)
The lithium ion secondary battery was disassembled and the presence or absence of wrinkles in the Si-based negative electrode was visually confirmed.
○: No wrinkle occurrence △: Minor wrinkle occurrence ×: Significant wrinkle occurrence

(Capacity maintenance rate)
Capacity maintenance rate (%) = 100th cycle discharge capacity / first cycle discharge capacity × 100
In Table 1, the initial capacity of the battery is expressed as a capacity expression rate (%) with Comparative Example 2 set to 100.

In Comparative Examples 1 and 2 charged to the maximum voltage at 0.1 C or less, the initial capacity increased, but wrinkles occurred and the capacity retention rate decreased.
In Comparative Examples 4 and 5, which were charged to the maximum voltage with a current value exceeding 0.1 C, wrinkles did not occur, but the initial capacity was small.
In the example in which the battery was initially charged at 0.05 C and the charge current value was changed to a high value before reaching the maximum voltage, both the initial capacity and the capacity maintenance ratio were compatible.

Claims (8)

A method for producing a non-aqueous electrolyte secondary battery comprising an activation step of activating by charging and discharging 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 includes 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 at least once before reaching the maximum voltage at the time of the first charge,
A method for producing a non-aqueous electrolyte secondary battery, wherein the first switching of the charging current value is performed at a charging voltage of 3.75V to 4.52V.

However, in the composition formula (1), x satisfies 0.1 ≦ x ≦ 0.8, M is Ni _α Co _β Mn _γ , and α, β, and γ are 0 ≦ α ≦ 0.5, 0 ≦ β ≦ 0.33, 0 ≦ γ ≦ 0.5, and α + β + γ = 1 are satisfied.   The method for producing 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 more.   The method for producing a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the upper limit of the charging current value until the first switching of the charging current value is 0.1 C or less.   The method for producing a nonaqueous electrolyte secondary battery according to claim 3, wherein the upper limit of the charging current value until the first switching of the charging current value is 0.05C or less.   The method for producing a nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein a charging current value after the first switching of the charging current value exceeds 0.1C.   6. The method for producing a nonaqueous electrolyte secondary battery according to claim 5, wherein the charging current value after the first switching of the charging current value is 0.3 C or more. The nonaqueous electrolyte according to any one of claims 1 to 6, wherein the maximum charging voltage reached after the first charge current value switching is 4.55V to 4.80V in the first charging. A method for manufacturing a secondary battery. 8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the rated capacity is 3 Ah or more, and the ratio of the battery volume to the rated capacity is 8 cm ³ / Ah or less. A method for producing a non-aqueous electrolyte secondary battery.
However, the battery volume is a product of the projected area and thickness of the battery including the battery outer package.

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