JP6938919B2 - Manufacturing method of lithium ion secondary battery - Google Patents

Description

The present disclosure relates to a method for manufacturing a lithium ion secondary battery.

Japanese Unexamined Patent Publication No. 2016-076333 (Patent Document 1) discloses that the surface of a lithium metal is coated with lithium titanate.

Japanese Unexamined Patent Publication No. 2016-076333

There is a need to improve the energy density of lithium-ion secondary batteries (hereinafter sometimes abbreviated as "batteries"). Irreversible capacity is one of the factors that hinder the improvement of energy density. The irreversible capacity is derived from the lithium (Li) ions supplied from the positive electrode to the negative electrode at the time of the first charge, which cannot be used thereafter. For example, the higher the capacity of the negative electrode active material such as silicon (Si), the larger the irreversible capacity tends to be. The presence of irreversible capacity limits the effective charge / discharge capacity of the battery.

Prior to the completion of the battery, it has been studied to supply an amount of Li ions corresponding to the irreversible capacity to the negative electrode active material (referred to as “pre-doping”). For example, Li ions can be supplied to the negative electrode active material by leaving a Li metal (Li foil or the like) in close contact with the surface of the negative electrode. However, with this method, it is difficult to control the amount of charge. Further, the amount of charge tends to be uneven in the thickness direction of the negative electrode.

Pre-doping using an electrolytic solution is also conceivable. That is, they are immersed in the electrolytic solution in a state where the negative electrode and the Li metal are not in direct contact with each other and the negative electrode and the Li metal are short-circuited. According to this method, it is considered that Li ions can be evenly supplied to the entire negative electrode. However, in this method, the diffusion rate of Li ions is slow, and it takes a long time to charge the irreversible capacity.

An object of the present disclosure is to reduce the time required for predoping with an electrolytic solution.

Hereinafter, the technical configuration and the action and effect of the present disclosure will be described. However, the mechanism of action of the present disclosure includes estimation. The correctness of the mechanism of action should not limit the scope of this disclosure.

[1] The method for producing a lithium ion secondary battery of the present disclosure includes at least the following (A), (C), (D) and (E).
(A) A negative electrode is manufactured by arranging a negative electrode mixture layer containing a first negative electrode active material and a second negative electrode active material on the surface of the negative electrode current collector.
(C) The lithium metal is arranged at a position that is electrically connected to the negative electrode current collector and does not come into contact with the negative electrode mixture layer.
(D) The negative electrode and the lithium metal are immersed in the electrolytic solution to charge the negative electrode by a predetermined amount.
(E) A lithium ion secondary battery including a negative electrode charged by a predetermined amount is manufactured.
The second negative electrode active material is lithium titanate. The first negative electrode active material has a larger charging capacity than the second negative electrode active material per unit mass. In the negative electrode charged by a predetermined amount, the potential difference between the second negative electrode active material and the lithium metal is larger than the potential difference between the first negative electrode active material and the lithium metal.

When the negative electrode and the Li metal are electrically connected (short-circuited state), the negative electrode and the Li metal are immersed in the electrolytic solution to diffuse the Li ions so as to cancel the potential difference between the negative electrode and the Li metal. Occurs. That is, Li ions are released from the Li metal to the electrolytic solution, and Li ions are supplied from the electrolytic solution to the negative electrode. Eventually, substantially all of the Li metal elutes. This completes the predoping. It is considered that the pre-doped amount (charge amount) can be controlled by the amount of Li metal. Further, since the electrolytic solution can penetrate into the negative electrode mixture layer, it is considered that Li ions are evenly supplied to the entire negative electrode mixture layer.

In the manufacturing method of the present disclosure, the first negative electrode active material is the target of pre-doping. The first negative electrode active material has a larger charging capacity than the second negative electrode active material per unit mass. The driving force of the predope is considered to be the potential difference between the target of the predope and the Li metal. However, the potential of a general negative electrode active material drops sharply when it is charged even a little. Therefore, it is considered that the driving force of the pre-doping becomes small and the time required for the pre-doping becomes long.

Therefore, in the manufacturing method of the present disclosure, a second negative electrode active material (lithium titanate) is used. The potential difference between lithium titanate and Li metal is about 1.5V, which is relatively large. Further, lithium titanate has a very gradual decrease in potential until it is fully charged. It is considered that the coexistence of the second negative electrode active material suppresses the decrease in the driving force of the pre-doping even if the potential of the first negative electrode active material decreases. As a result, the time required for pre-doping is considered to be shortened.

[2] The first negative electrode active material is preferably at least one selected from the group consisting of graphite, amorphous carbon, silicon, silicon oxide and a silicon alloy.
When these negative electrode active materials are charged even a little, the potential drops sharply. During pre-doping, the potential difference between the negative electrode active material and the Li metal is about 0.05 to 0.3 V. Therefore, it is usually considered that the time required for pre-doping is long. However, as described above, it is considered that the time required for pre-doping is shortened by using the second negative electrode active material (lithium titanate).

[3] The surface of the second negative electrode active material is preferably coated with a lithium ion permeable film.
During the predoping, the second negative electrode active material (lithium titanate) is also charged. Upon charging, the potential of lithium titanate gradually decreases, albeit slowly. When fully charged, the potential of lithium titanate drops sharply. It is considered that the driving force of pre-doping also decreases as the potential of lithium titanate decreases. It is considered that charging of lithium titanate is suppressed by coating lithium titanate with a Li ion permeable film.

[4] The second negative electrode active material may have a mass ratio of 1% by mass or more and 5% by mass or less with respect to the total of the first negative electrode active material and the second negative electrode active material.
The higher the mass ratio of the first negative electrode active material to be pre-doped (that is, the lower the mass ratio of the second negative electrode active material), the higher the energy density is expected. On the other hand, it is considered that the lower the mass ratio of the second negative electrode active material, the longer the time required for pre-doping. Since the second negative electrode active material has a mass ratio of 1% by mass or more and 5% by mass or less, the balance between the energy density and the required time for pre-doping is good.

FIG. 1 is a flowchart showing an outline of a method for manufacturing a lithium ion secondary battery according to an embodiment of the present disclosure. FIG. 2 is a schematic plan view showing an example of the configuration of the negative electrode. FIG. 3 is a cross-sectional conceptual diagram showing an example of the configuration of the negative electrode. FIG. 4 is a schematic plan view showing an example of the configuration of the positive electrode. FIG. 5 is a schematic cross-sectional view showing an example of the configuration of the electrode group.

Hereinafter, embodiments of the present disclosure (hereinafter, also referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of the present disclosure.

<Manufacturing method of lithium-ion secondary battery>
FIG. 1 is a flowchart showing an outline of a method for manufacturing a lithium ion secondary battery according to an embodiment of the present disclosure. The manufacturing methods of the present embodiment are "(A) manufacturing of negative electrode", "(B) configuration of electrode group", "(C) arrangement of Li metal", "(D) predoping" and "(E) battery. Includes "manufacturing". That is, the manufacturing method of the present embodiment includes at least "(A) manufacturing of a negative electrode", "(C) arrangement of Li metal", "(D) pre-doping" and "(E) manufacturing of a battery". "(C) Arrangement of Li metal" may be carried out between "(A) Manufacture of negative electrode" and "(B) Composition of electrode group".

In the following, a method of manufacturing a battery including a laminated electrode group will be described as an example. However, the electrode group of this embodiment may be a winding type. Hereinafter, the manufacturing method of this embodiment will be described step by step.

<< (A) Manufacture of negative electrode >>
The manufacturing method of the present embodiment includes manufacturing a negative electrode by arranging a negative electrode mixture layer containing the first negative electrode active material and the second negative electrode active material on the surface of the negative electrode current collector.

FIG. 2 is a schematic plan view showing an example of the configuration of the negative electrode. The negative electrode 20 is a rectangular sheet. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode mixture layer 22 arranged on the surfaces (both front and back surfaces) of the negative electrode current collector 21.

The negative electrode current collector 21 may be, for example, a copper (Cu) foil. The Cu foil may be a pure Cu foil or a Cu alloy foil. The negative electrode current collector 21 may have a thickness of, for example, 5 to 30 μm. A lead tab 24 is joined to the end of the negative electrode current collector 21. The lead tab 24 is made of, for example, nickel.

The negative electrode mixture layer 22 is formed by applying the negative electrode mixture paste to the surface of the negative electrode current collector 21 and drying it. The negative electrode mixture paste is prepared by mixing a first negative electrode active material, a second negative electrode active material, a binder, a solvent, and the like. The appropriate solvent should be selected according to the binder type. The solvent may be, for example, water. For example, a die coater and a hot air drying oven are used for coating and drying.

FIG. 3 is a cross-sectional conceptual diagram showing an example of the configuration of the negative electrode. The negative electrode mixture layer 22 may be formed so as to have a thickness of, for example, 10 to 100 μm. The negative electrode mixture layer 22 contains a first negative electrode active material 1 and a second negative electrode active material 2. The negative electrode mixture layer 22 may contain, for example, a total of 80% by mass or more and 98% by mass or less of the first negative electrode active material and the second negative electrode active material.

(1st negative electrode active material)
The first negative electrode active material 1 is a target of pre-doping. The first negative electrode active material 1 mainly contributes to the charge / discharge reaction of the battery. The first negative electrode active material 1 has a larger charging capacity than the second negative electrode active material 2 per unit mass. From the viewpoint of energy density, the first negative electrode active material 1 is preferably at least one selected from the group consisting of graphite, amorphous carbon, silicon, silicon oxide and a silicon alloy. The first negative electrode active material 1 is more preferably at least one selected from the group consisting of silicon, silicon oxide and a silicon alloy.

Examples of the amorphous carbon include easily graphitizable carbon and non-graphitizable carbon. Examples of the silicon alloy include Si-Cu alloy and Si-Cu-Sn alloy. The first negative electrode active material 1 may have an average particle size of, for example, 3 to 30 μm. The average particle size indicates a cumulative 50% particle size from the fine particle side in the volume-based particle size distribution measured by the laser diffraction / scattering method.

(Second negative electrode active material)
The second negative electrode active material 2 is lithium titanate (Li ₄ Ti ₅ O ₁₂ ). In the present embodiment, in the negative electrode 20 for which pre-doping is completed (negative electrode 20 charged by a predetermined amount), the potential difference between the second negative electrode active material 2 and the Li metal 23 is the potential difference between the first negative electrode active material 1 and the Li metal 23. Greater than. That is, the potential difference between the second negative electrode active material 2 and the Li metal 23 is maintained large until the pre-doping is completed. This is considered to shorten the time required for pre-doping.

Lithium titanate can maintain a potential of about 1.5 V with respect to the Li metal during predoping. It is considered that this suppresses the decrease in the driving force of the pre-dope. The second negative electrode active material 2 may have, for example, an average particle size of 0.1 to 3 μm.

From the viewpoint of energy density, the smaller the second negative electrode active material 2, the better. From the viewpoint of the time required for pre-doping, the larger the second negative electrode active material 2, the better. The second negative electrode active material 2 may have a mass ratio of 1% by mass or more and 5% by mass or less with respect to the total of the first negative electrode active material 1 and the second negative electrode active material 2. Since the second negative electrode active material 2 has a mass ratio of 1% by mass or more and 5% by mass or less, the balance between the energy density and the required time for pre-doping is good. In this specification, if the calculation result of the mass ratio has a value after the decimal point, the first decimal place shall be rounded off.

The surface of the second negative electrode active material 2 is preferably coated with a Li ion-permeable coating film 3. It is considered that this suppresses the decrease in the potential of the second negative electrode active material 2 during pre-doping. The coating film 3 preferably covers the entire surface of the second negative electrode active material 2. However, there may be a portion of the surface of the second negative electrode active material 2 that is not covered with the coating film 3.

It is desirable that the coating film 3 is insoluble in the solvent used for the negative electrode mixture paste. When the coating film 3 is dissolved in a solvent, the surface of the second negative electrode active material 2 may be exposed and the effect of suppressing the potential decrease may be reduced. The coating film 3 may be, for example, polyvinylidene fluoride (PVdF), polyimide, or the like.

The coating film 3 may have a mass ratio of 3% by mass or more and 20% by mass or less with respect to the second negative electrode active material 2. When the coating film 3 is 3% by mass or more, it is expected that the effect of suppressing the potential decrease is enhanced. If it exceeds 20% by mass of the coating film 3, the second negative electrode active material 2 is insulated from the surroundings, so that the effect of promoting the diffusion of Li ions may be reduced.

(Other ingredients)
The negative electrode mixture layer 22 may include a conductive material, a binder, or the like (not shown). The conductive material should not be particularly limited. The conductive material may be, for example, acetylene black, thermal black, furnace black or the like. The negative electrode mixture layer 22 may contain, for example, 1 to 10% by mass of a conductive material. Binders should not be particularly limited either. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like. The negative electrode mixture layer 22 may contain, for example, 1 to 10% by mass of a binder.

<< (B) Electrode group configuration >>
The manufacturing method of the present embodiment includes forming an electrode group including a positive electrode and a negative electrode.

First, the positive electrode is manufactured. FIG. 4 is a schematic plan view showing an example of the configuration of the positive electrode. The positive electrode 10 is a rectangular sheet. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode mixture layer 12 arranged on the surface (both front and back surfaces) of the positive electrode current collector 11. The positive electrode current collector 11 may be, for example, an aluminum (Al) foil or the like. The Al foil may be a pure Al foil or an Al alloy foil. The positive electrode current collector 11 may have a thickness of, for example, 10 to 30 μm. A lead tab 14 is joined to the end of the positive electrode current collector 11. The lead tab 14 is made of, for example, Al.

The positive electrode mixture layer 12 is formed by applying the positive electrode mixture paste to the surface of the positive electrode current collector 11 and drying it. The positive electrode mixture paste is prepared by mixing a positive electrode active material, a conductive material, a binder, a solvent and the like. The appropriate solvent should be selected according to the binder type. The solvent may be, for example, N-methyl-2-pyrrolidone (NMP) or the like. For example, a die coater and a hot air drying oven are used for coating and drying.

The positive electrode mixture layer 12 may have a thickness of, for example, 10 to 100 μm. The positive electrode mixture layer 12 contains, for example, 85 to 98% by mass of positive electrode active material, 1 to 10% by mass of conductive material, and 1 to 5% by mass of binder. The positive electrode active material should not be particularly limited. The positive electrode active material is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.80 Co _0.15 Al _0.05 O _2, LiFePO _{4, and the} like. You may. One kind of positive electrode active material may be used alone, or two or more kinds of positive electrode active materials may be used in combination. The conductive material should not be particularly limited. The conductive material may be, for example, acetylene black or the like. Binders should not be particularly limited either. The binder may be, for example, PVdF, polytetrafluoroethylene (PTFE) or the like.

FIG. 5 is a schematic cross-sectional view showing an example of the configuration of the electrode group. The positive electrode 10 and the negative electrode 20 are laminated with the separator 30 interposed therebetween. As a result, the electrode group 40 is formed. In FIG. 5, two positive electrodes 10 and one negative electrode 20 are laminated. However, this is only an example, and a larger number of positive electrodes 10 and 20 may be laminated. The separator 30 is an electrically insulating porous film. The separator 30 may be made of, for example, a polyethylene (PE) porous membrane, a polypropylene (PP) porous membrane, or the like. For example, the positive electrode 10 and the negative electrode 20 may be adhered to the separator 30 by an adhesive.

<< (C) Lithium metal arrangement >>
The manufacturing method of the present embodiment includes arranging the lithium metal at a position that is electrically connected to the negative electrode current collector and does not come into contact with the negative electrode mixture layer. The Li metal 23 may be arranged before the electrode group 40 is formed, or may be arranged after the electrode group 40 is formed.

The Li metal 23 may be, for example, a Li foil. The Li metal 23 is arranged on the surface of the negative electrode current collector 21, for example. However, as shown in FIG. 2, the Li metal 23 needs to be arranged at a position where it does not come into contact with the negative electrode mixture layer 22. The Li foil can be bonded to the surface of the negative electrode current collector 21 by being pressed against the surface of the negative electrode current collector 21. The amount of the Li metal 23 may be any amount as long as it can generate Li ions exceeding the irreversible capacity of the first negative electrode active material 1.

<< (D) Pre-dope >>
The manufacturing method of the present embodiment includes charging the negative electrode by a predetermined amount by immersing the negative electrode and the lithium metal in the electrolytic solution.

The electrode group 40 is housed in a predetermined exterior body. The exterior body may be, for example, a metal container, a bag made of an Al laminated film, or the like. The electrolytic solution is injected into the exterior body. The exterior is sealed. As a result, the negative electrode 20 and the Li metal 23 are immersed in the electrolytic solution.

When the negative electrode 20 and the Li metal 23 are immersed in the electrolytic solution and are allowed to stand, Li ions are eluted from the Li metal 23 into the electrolytic solution, and Li ions are supplied from the electrolytic solution to the negative electrode 20. Will be done. In the present embodiment, since the second negative electrode active material 2 (lithium titanate) has a high potential, it is considered that the supply of Li ions is promoted. The pre-doped amount (charge amount) may be, for example, 1 to 50%, 1 to 30%, or 1 to 20% with respect to the charge capacity of the negative electrode 20. It may be 1 to 10% or 1 to 5%.

Preferably, the negative electrode 20, the Li metal 23 and the electrolytic solution are heated. It is considered that this further promotes the supply (diffusion) of Li ions. The negative electrode 20, the Li metal 23, and the electrolytic solution are preferably heated to about 45 ° C. or higher and 70 ° C. or lower, more preferably 50 ° C. or higher and 65 ° C. or lower, and even more preferably 55 ° C. or higher and 65 ° C. or lower. NS. In this embodiment, the time required for predoping can be, for example, about 27.5 to 37 days.

The electrolytic solution is a liquid electrolyte in which a Li salt is dissolved in a solvent. The solvent may be, for example, a mixed solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). The Li salt may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ] (LiFSI) or the like. The electrolytic solution may contain, for example, additives such as vinylene carbonate (VC) and lithium bis (oxalate) borate (LiBOB).

<< (E) Battery manufacturing >>
The manufacturing method of the present embodiment includes manufacturing a lithium ion secondary battery including a negative electrode (pre-doped negative electrode) charged by a predetermined amount.

After the pre-doping is completed, the first charge / discharge is performed. As a result, the positive electrode active material and the negative electrode active material are activated, and the lithium ion secondary battery is completed. In this embodiment, since pre-doping is performed, it is expected that the irreversible capacity is small and the initial charge / discharge efficiency (= initial discharge capacity ÷ initial charge capacity) is improved. That is, it is expected that the energy density of the battery will be improved.

Examples will be described below. However, the following examples do not limit the scope of this disclosure.

<Example 1>
<< (A) Manufacture of negative electrode >>
The following materials were prepared.
Second negative electrode active material: lithium titanate (average particle size: 0.5 μm)
Coating material: NMP solution of polyamic acid (solid content ratio: 10% by mass)

By planetarimixer, 60 parts by mass of lithium titanate (hereinafter sometimes abbreviated as "LTO") and 40 parts by mass of a coating material were stirred and mixed for 1 hour. This prepared the paste. A stainless steel plate was prepared. The paste obtained above was applied to the surface of the stainless steel plate. As a result, a coating film having a thickness of about 0.5 mm was formed. The coating film was dried for 20 minutes in a constant temperature bath set at 80 ° C. The coating and the stainless plate were then placed in a heating furnace. The coating was heated at 250 ° C. for 30 minutes in an argon atmosphere. As a result, the polyamic acid was imidized and a polyimide was produced.

After that, the coating film was scraped off from the stainless steel plate. The scraped coating film pieces were crushed in a mortar. A mesh with an opening of 30 μm was prepared. Coarse particles were removed by passing the crushed material through the mesh. From the above, an LTO coated with a polyimide film was obtained. Hereinafter, the LTO coated with the coating is referred to as "coated LTO".

The following materials were prepared.
First negative electrode active material: Silicon oxide (average particle size: 5 μm)
Conductive material: Acetylene black binder: CMC and SBR
Negative electrode current collector: Cu foil (thickness: 10 μm)
Solvent: Ion-exchanged water

The planetary mixer mixed 83 parts by mass of silicon oxide (SiO), 3 parts by mass of coated LTO, 4 parts by mass of CMC, 5 parts by mass of SBR, 5 parts by mass of acetylene black, and ion-exchanged water. As a result, a negative electrode mixture paste was prepared. The solid content ratio of the negative electrode mixture paste was set to 43% by mass.

The negative electrode mixture paste was applied to the surface (both front and back surfaces) of the negative electrode current collector 21 by a comma coater (registered trademark) and dried at 120 ° C. As a result, the negative electrode mixture layer 22 was formed. The mass per unit area of the negative electrode mixture layer 22 was 3.0 mg / cm ^{2 on} one side. The negative electrode mixture layer 22 was compressed by the roll press. The density of the negative electrode mixture layer 22 after compression was 1.4 g / cm ³ . The plane size of the negative electrode mixture layer 22 was 15.4 cm in the vertical dimension (corresponding to the dimension in the Y-axis direction in FIG. 2) and 10.4 cm in the horizontal dimension (corresponding to the dimension in the X-axis direction in FIG. 2). From the above, the negative electrode 20 was manufactured.

<< (B) Electrode group configuration >>
The following materials were prepared.
Positive electrode active material: LiCoO ₂ (average particle size: 10 μm)
Conductive material: Acetylene black binder: PVdF
Solvent: NMP
Positive electrode current collector: Al foil (thickness: 15 μm)

A planetary mixer mixed 90 parts by weight of LiCoO ₂ , 6 parts by weight of acetylene black, 4 parts by weight of PVdF, and NMP. As a result, a positive electrode mixture paste was prepared. The solid content ratio of the positive electrode mixture paste was 65% by mass.

The positive electrode mixture paste was applied to the surface (one side) of the positive electrode current collector 11 by a comma coater (registered trademark) and dried at 120 ° C. As a result, the positive electrode mixture layer 12 was formed. The mass per unit area of the positive electrode mixture layer 12 was 3.9 mg / cm ^{2 on} one side. The positive electrode mixture layer 12 was compressed by the roll press. The density of the positive electrode mixture layer 12 after compression was 2.7 g / cm ³ . The plane size of the positive electrode mixture layer 12 was 15 cm in the vertical dimension (corresponding to the dimension in the Y-axis direction in FIG. 4) and 10 cm in the horizontal dimension (corresponding to the dimension in the X-axis direction in FIG. 4). From the above, the positive electrode 10 was manufactured.

A separator 30 having a thickness of 25 μm was prepared. The plane size of the separator 30 was 16 cm in vertical dimension and 10.7 cm in horizontal dimension. The negative electrode 20 was sandwiched between the two positive electrodes 10. A separator 30 was arranged between the positive electrode 10 and the negative electrode 20. As a result, the laminated electrode group 40 was formed.

<< (C) Li metal arrangement >>
In an argon atmosphere, 20 mg of Li metal 23 (Li foil) was attached to the surface of the negative electrode current collector 21. The Li metal 23 was arranged at a position where it did not come into contact with the negative electrode mixture layer 22. As an exterior body, a bag made of Al laminated film was prepared. The electrode group 40 was housed in the exterior body.

<< (D) Pre-dope >>
An electrolytic solution containing the following components was prepared.
Solvent: [EC: EMC: DMC = 1: 1: 1 (volume ratio)]
Li salt: LiPF ₆ (1.1 mol / l)

4 g of electrolyte was injected into the exterior. That is, the negative electrode 20 and the Li metal 23 were immersed in the electrolytic solution. The exterior body was sealed by the vacuum sealing device. As a result, a pre-activation battery was manufactured. In the same manner, a plurality of pre-activation batteries were manufactured. A plurality of pre-activation batteries were placed in a constant temperature bath set at 60 ° C.

<< (E) Battery manufacturing >>
Each time a certain period of time elapsed, one pre-activation battery was taken out from the constant temperature bath (60 ° C.), and the first charge / discharge was performed under the following conditions.
Temperature: 25 ° C
Charging: CCCV charging (CC current = 0.1A, CV voltage = 4.1V, termination current = 5mA)
Discharge: CC discharge (CC current = 0.1A, final voltage = 2.5V)

The initial charge / discharge efficiency was calculated by dividing the initial discharge capacity by the initial charge capacity. The first elapsed time during which the initial charge / discharge efficiency did not improve by 0.5% or more was defined as the time required for predoping. The required time is shown in Table 1 below.
From the above, a lithium ion secondary battery was manufactured.

<Example 2>
The battery was manufactured by the same manufacturing method as in Example 1 except that the blending amount of the coated LTO was changed to 1 part by mass.

<Example 3>
The battery was manufactured by the same manufacturing method as in Example 1 except that the blending amount of the coated LTO was changed to 5 parts by mass.

<Example 4>
The battery is manufactured by the same manufacturing method as in Example 1 except that polycrystalline silicon (Si) having an average particle size of 6 μm is used as the first negative electrode active material instead of silicon oxide (SiO). Was done.

<Example 5>
The battery is manufactured by the same manufacturing method as in Example 1 except that the NMP solution of PVdF is used as a coating material instead of the NMP solution of polyamic acid and the coating film is heated at 370 ° C. for 30 minutes. Was done.

<Comparative example 1>
The battery was manufactured by the same manufacturing method as in Example 1 except that the negative electrode was manufactured so as not to contain a coated LTO (second negative electrode active material and coating) and no predoping was performed.

<Comparative example 2>
The battery was manufactured by the same manufacturing method as in Example 4 except that the negative electrode was manufactured so as not to contain the coated LTO and no predoping was performed.

<Comparative example 3>
The battery was manufactured by the same manufacturing method as in Example 1 except that the negative electrode was manufactured so as not to contain the coated LTO.

<Comparative example 4>
The battery was manufactured by the same manufacturing method as in Example 4 except that the negative electrode was manufactured so as not to contain the coated LTO.

<Example 6>
The battery was manufactured by the same manufacturing method as in Example 1 except that the LTO was not coated.

<Result>
As shown in Table 1 above, in the examples in which the second negative electrode active material (lithium titanate) was used, the pre-doping required as compared with Comparative Examples 3 and 4 in which the second negative electrode active material was not used. There is a tendency for the time to be short. From the results of Examples 1 and 6, it can be seen that the time required for pre-doping tends to be further shortened because the second negative electrode active material is coated with a Li ion permeable film (polyimide or the like).

It should be considered that the above embodiments and examples are exemplary in all respects and are not restrictive. The scope of the present disclosure is indicated by the scope of claims, not the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 1st negative electrode active material, 2 2nd negative electrode active material, 3 coatings, 10 positive electrodes, 11 positive electrode current collector, 12 positive electrode mixture layer, 20 negative electrode, 21 negative electrode current collector, 22 negative electrode mixture layer, 23 Li metal , 14, 24 lead tabs, 30 separators, 40 electrode groups.

Claims (5)

To manufacture a negative electrode by arranging a negative electrode mixture layer containing a first negative electrode active material and a second negative electrode active material on the surface of the negative electrode current collector.
Placing the lithium metal at a position that is electrically connected to the negative electrode current collector and does not come into contact with the negative electrode mixture layer.
By immersing the negative electrode and the lithium metal in an electrolytic solution, at least the negative electrode is charged by a predetermined amount, and a lithium ion secondary battery including the negative electrode charged by a predetermined amount is manufactured.
The second negative electrode active material is lithium titanate, and the second negative electrode active material is lithium titanate.
The first negative electrode active material has a larger charging capacity than the second negative electrode active material per unit mass.
In the negative electrode charged by a predetermined amount, the potential difference between the second negative electrode active material and the lithium metal is larger than the potential difference between the first negative electrode active material and the lithium metal.
Prior to the formation of the negative electrode mixture layer, the surface of the second negative electrode active material is coated with a lithium ion permeable coating.
Further seen including,
The coating is at least one selected from the group consisting of polyvinylidene fluoride and polyimide.
A method for manufacturing a lithium ion secondary battery. The first negative electrode active material is at least one selected from the group consisting of graphite, amorphous carbon, silicon, silicon oxide and a silicon alloy.
The method for manufacturing a lithium ion secondary battery according to claim 1. The second negative electrode active material has a mass ratio of 1% by mass or more and 5% by mass or less with respect to the total of the first negative electrode active material and the second negative electrode active material.
The method for manufacturing a lithium ion secondary battery according to claim 1 or 2. The negative electrode mixture layer is formed by applying the negative electrode mixture paste to the surface of the negative electrode current collector.
The negative electrode mixture paste is prepared by mixing the first negative electrode active material, the second negative electrode active material, a binder and a solvent.
Prior to the preparation of the negative electrode mixture paste, the second negative electrode active material is coated with the coating film.
The method for manufacturing a lithium ion secondary battery according to any one of claims 1 to 3. The coating contains a material different from that of the binder.
The method for manufacturing a lithium ion secondary battery according to claim 4.

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