JP2019160512A - Method for manufacturing lithium ion battery - Google Patents

Abstract

A lithium ion battery capable of exhibiting excellent cycle characteristics without incorporating a mechanism for applying pressure in a battery case even when an electrode having an electrode active material layer containing no binder is used. A method of manufacturing the same is provided. Preliminary charging in which a positive electrode active material layer containing positive electrode active material particles and a negative electrode active material layer containing negative electrode active material particles are charged at least once or more with respect to a laminated unit laminated via a separator. A method for manufacturing a lithium-ion battery including a step, wherein the negative electrode active material layer is a non-binding body of the negative electrode active material particles, and the preliminary charging step is performed in a range of 2.5 to A method for manufacturing a lithium ion battery, which is carried out under a load of 10 kgf/cm 2. [Selection diagram] None

Description

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

In recent years, reduction of carbon dioxide emissions has been strongly desired for environmental protection. In the automobile industry, there are high expectations for reducing carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and we are eager to develop secondary batteries for motor drives that hold the key to their practical application. Has been done. As a secondary battery, attention is focused on a lithium ion battery (also referred to as a lithium ion secondary battery) that can achieve high energy density and high output density.

As a method for manufacturing such a lithium ion battery, for example, first, a laminate in which a positive electrode active material layer containing a positive electrode active material and a negative electrode active material layer containing a negative electrode active material are arranged via a separator (also referred to as a laminate unit). And the laminated body is accommodated in the battery exterior body, and then a nonaqueous electrolytic solution is injected and sealed.

The assembled lithium ion battery first stabilizes battery characteristics by repeating charging and discharging several times (also referred to as a precharging process or aging). In the first charge, gas is generated on the surface of the negative electrode active material as the non-aqueous electrolyte is decomposed. For the purpose of discharging this gas to the outside of the container and reducing the internal resistance, a method of pressurizing the laminated body in the preliminary charging step is known.
For example, in Patent Document 1, a flat power generation element formed by laminating a positive electrode plate and a negative electrode plate with a separator interposed therebetween is applied at a pressure of 0.49 × 10 ^{−2 to} 24.5 × 10 ⁻² MPa from the outside of the exterior body. A method of performing initial charge in a pressurized state is disclosed.
Patent Document 2 discloses a method of incorporating a mechanism for applying a hydrostatic pressure to a laminate by pressurizing and sealing a fluid such as argon in a battery case.

In Patent Documents 1 and 2, the positive electrode active material layer and the negative electrode active material layer are each hardened with a binder. On the other hand, as a battery in which a defect does not occur in the active material layer even when stress is applied to the battery, Patent Document 3 discloses a positive electrode active material layer and a negative electrode active material layer, respectively, without using a binder. An electrode for a lithium ion battery in which active material particles are not bound is disclosed.

Japanese Patent Laid-Open No. 2015-069810 International Publication No. 2013/008321 JP 2017-147222 A

If a configuration in which a hydrostatic pressure is applied to the laminate as in the method described in Patent Document 2 is incorporated in the battery case, there is a problem that the energy density (capacity per battery case) of the lithium ion battery cannot be increased. It was. Further, when the method described in Patent Document 1 is applied to an electrode having an active material layer that does not contain a binder as described in Patent Document 3, the aging treatment is not performed sufficiently, and cycle characteristics and the like are not performed. There has been a problem that battery performance tends to deteriorate.

The present invention has been made in view of the above problems, and is excellent without incorporating a mechanism for applying pressure into the battery case even when an electrode having an electrode active material layer that does not contain a binder is used. It is an object of the present invention to provide a method for producing a lithium ion battery that can exhibit cycle characteristics.

The present invention relates to precharging in which a positive electrode active material layer containing positive electrode active material particles and a negative electrode active material layer containing negative electrode active material particles are subjected to a charging operation at least once for a laminate unit laminated via a separator. The negative electrode active material layer is a non-binding body of the negative electrode active material particles, and the preliminary charging step is performed with respect to the laminated unit from 2.5 to 2.5. The present invention relates to a method for manufacturing a lithium ion battery, which is performed in a state where a load of 10 kgf / cm ² is applied.

In the method for producing a lithium ion battery of the present invention, even when an electrode having an electrode active material layer that does not contain a binder is used, excellent cycle characteristics can be obtained without incorporating a mechanism for applying pressure in the battery case. A method of manufacturing a lithium ion battery that can be exhibited can be provided.

Hereafter, the manufacturing method of the lithium ion battery of this invention is demonstrated concretely.

In the method for producing a lithium ion battery of the present invention, the positive electrode active material layer containing the positive electrode active material particles and the negative electrode active material layer containing the negative electrode active material particles are 2.5 the preliminary charging process while adding a load of ~10kgf / cm ^2.
At this time, the negative electrode active material layer is a non-binding body of negative electrode active material particles.

In the negative electrode active material layer, which is a non-binding body made of negative electrode active material particles, the position of the negative electrode active material particles is not fixed in the negative electrode active material layer, and can move freely to some extent. Therefore, a part of the gas generated by the first charge is discharged while forming a discharge path accompanied by a change in the structure of the negative electrode active material layer, but a part of the gas may remain on the surface of the negative electrode active material particles. It is believed that there is.
The structural change of the negative electrode active material layer due to gas discharge may lead to the disappearance or non-uniformity of the conductive path, and the gas remaining on the surface of the negative electrode active material particles causes the uniform SEI film on the surface of the negative electrode active material particles. It is inferred that the formation is inhibited and the cycle characteristics deteriorate.

In the method for producing a lithium ion battery according to the present invention, a load of 2.5 to 10 kgf / cm ² is applied to the stack unit, so that positive electrode active material particles and negative electrode active material particles (hereinafter collectively referred to as electrode active material particles). )) Is fixed, and the movement of the electrode active material particles by the gas generated by the charging reaction can be suppressed, and the conductive path does not become non-uniform. Further, it is considered that the gas does not remain on the surface of the negative electrode active material particles, and a uniform SEI film is formed on the surface of the negative electrode active material particles.
After this SEI film is formed by the first charging operation, it is not lost even if the discharging operation is performed, and functions as a reaction field for the negative electrode reaction. Therefore, the cycle characteristics do not deteriorate even after the load is released.

In the method for manufacturing a lithium ion battery of the present invention, in the preliminary charging step, at least one charging operation is performed in a state where a load of 2.5 to 10 kgf / cm ² is applied to the stack unit.
If the load on the stacked unit in the precharging step is less than 2.5 kgf / cm ² , the effect of fixing the position of the electrode active material particles is small, and the non-uniformity of the conductive path cannot be suppressed. On the other hand, when the load on the laminated unit in the precharging step exceeds 10 kgf / cm ² , the laminated unit including the negative electrode active material layer which is a non-binding body is greatly deformed.

By performing the precharging step under the above conditions, a uniform SEI film is formed on the surface of the negative electrode active material particles as described above, and thus the cycle characteristics are not easily deteriorated. Furthermore, since the negative electrode active material layer is a non-binding body of negative electrode active material particles, there is no problem that the negative electrode active material layer is damaged or peeled off if the load is increased excessively.
Therefore, in the method for producing a lithium ion battery of the present invention, even when an electrode having an electrode active material layer not containing a binder is used, an excellent cycle can be achieved without incorporating a mechanism for applying pressure in the battery case. A lithium ion battery capable of exhibiting characteristics can be provided.

In the precharging step, a stack unit in which a positive electrode active material layer including positive electrode active material particles and a negative electrode active material layer including negative electrode active material particles are stacked via a separator is disposed between current collectors, It is performed by carrying out one or more charging operations with the above load applied.
The method of applying a load to the stack unit in the pre-charging process is not particularly limited, but with the current collector disposed on both sides in the stacking direction of the stack unit, the load is sandwiched between the current collector and a metal or rubber jig. And a method of pressurizing the laminated unit by hydrostatic pressure by immersing the laminated unit disposed between the current collectors in a nonaqueous electrolytic solution and pressurizing the nonaqueous electrolytic solution as it is.
In addition, it is not necessary to apply a load directly to the stacked unit. For example, in a state where the stacked unit is covered with a current collector or a stacked unit is accommodated in the battery outer body, A load may be applied to the stacked unit.
After the first charging operation is performed, a load on the stack unit is not necessary, and thus the load may be released as soon as the first charging operation is completed.

In the preliminary charging step, the pressure around the stack unit may be reduced.
By performing the preliminary charging step while reducing the pressure around the stack unit, the gas generated by the initial charging can be quickly discharged from the surface of the negative electrode active material particles.
Although the said pressure reduction conditions are not specifically limited, For example, 0.01-0.5 atm is preferable.

The precharging step is performed in a state in which the positive electrode active material layer, the negative electrode active material layer, and the separator constituting the laminated unit are impregnated with the nonaqueous electrolytic solution. The amount of the non-aqueous electrolyte is not particularly limited as long as it can be charged. However, it is preferable that the entire gap of the laminated unit is filled with the non-aqueous electrolyte.

As the charging operation in the preliminary filling step, it is desirable to perform a charging step of charging until the potential of the positive electrode becomes 4.2 V (vs. Li ^/ Li ⁺ ).
Further, as a discharging operation in the preliminary charging step, it is desirable to discharge until the potential of the positive electrode becomes 0.01 V (vs. Li ^/ Li ⁺ ).
The amount of current (C rate) in the charging operation is not particularly limited, but is preferably 0.01 to 1C, and more preferably 0.05 to 0.1C.

The method for producing a lithium ion battery of the present invention may further include an impregnation step of impregnating the positive electrode active material layer, the separator, and the negative electrode active material layer with a non-aqueous electrolyte before the precharging step.
The electrolyte concentration of the nonaqueous electrolytic solution is not particularly limited, but is preferably 1.2 to 4.5 mol / L.

The preliminary charging step may be performed without accommodating the stack unit in the battery outer package, or may be performed after the stack unit is stored in the battery outer package.
In the case where the preliminary charging process is performed without accommodating the stack unit in the battery outer package, the lithium ion battery can be manufactured by storing the stacked unit subjected to the precharge process in the battery outer package or the like.
In addition, when the preliminary charging step is performed in a state where the laminated unit is accommodated in the battery outer body, a lithium ion battery can be obtained by sealing the battery outer body. In addition, when the preliminary charging process is performed in a state where the battery outer package is already sealed, a lithium ion battery is obtained by completing the preliminary charging process.

In the method for producing a lithium ion battery of the present invention, the nonaqueous electrolytic solution used in the preliminary charging step may be used as the nonaqueous electrolytic solution of the lithium ion battery. May be replaced.

A description will be given of the stack unit to be charged in the preliminary charging step.
The lamination unit is formed by laminating a positive electrode active material layer containing positive electrode active material particles and a negative electrode active material layer containing negative electrode active material particles via a separator.
Furthermore, the negative electrode active material layer is a non-binding body of negative electrode active material particles.

The volume ratio of the negative electrode active material particles contained in the negative electrode active material layer is preferably 30 to 70% by volume. When the volume ratio of the negative electrode active material particles contained in the negative electrode active material layer is within this range, it is preferable because the gas generated by the initial charge can be discharged well.
The volume ratio of the negative electrode active material particles contained in the negative electrode active material layer depends on the weight of the negative electrode active material particles contained in the negative electrode active material layer relative to the volume calculated from the outer shape of the negative electrode active material layer, and the true value of the negative electrode active material particles. It can be calculated as a percentage of the volume calculated from the density.
When the negative electrode active material particles are coated negative electrode active material particles described later, the volume ratio of the negative electrode active material particles included in the negative electrode active material layer is the volume ratio of the coated negative electrode active material particles included in the negative electrode active material layer. Means.
Further, the volume ratio of the negative electrode active material particles contained in the negative electrode active material layer is the volume ratio of the negative electrode active material particles contained in the negative electrode active material layer before the load is applied to the lamination unit in the preliminary charging step. is there.

Although the thickness of the negative electrode active material layer before applying a load with respect to a lamination | stacking unit is not specifically limited, It is preferable that it is 200-750 micrometers from a viewpoint of improving an energy density.

Examples of a method for obtaining a lamination unit include a method in which a positive electrode active material layer containing positive electrode active material particles and a negative electrode active material layer containing negative electrode active material particles are separately produced and laminated via a separator, and a positive electrode active material Examples include a method of forming an active material layer as a counter electrode on a separator disposed on the material layer or the negative electrode active material layer and laminating.
Of the electrode active material layers made of electrode active material particles, those using positive electrode active material particles as electrode active material layers are positive electrode active material layers, and those using negative electrode active material particles as electrode active material layers. It is a negative electrode active material layer. Hereinafter, the positive electrode active material layer and the negative electrode active material layer will be collectively described as an electrode active material layer.

As a method for producing an electrode active material layer, a method for applying an electrode active material layer preparation composition containing electrode active material particles on a substrate, and an electrode active material layer preparation composition containing electrode active material particles A method of directly forming into a desired shape is mentioned.
The composition for preparing an electrode active material layer may be a slurry in which electrode active material particles and a dispersion medium are mixed, and is in a state of low fluidity obtained by reducing the amount of the dispersion medium as compared to the slurry (for example, funicular) A semi-solid state such as okara which is also called a state or a pendulum state). In addition to the electrode active material particles and the dispersion medium, a conductive additive may be added to the composition for preparing an electrode active material layer as necessary.

When the electrode active material is a negative electrode active material, a binder (hereinafter also referred to as a battery binder) such as polyvinylidene fluoride (PVdF) contained in a known lithium ion battery is added to the composition for preparing an electrode active material layer. do not do. Further, when the electrode active material is a positive electrode active material, the battery active material layer preparation composition may or may not contain the battery binder, but it is preferably not added.
When the electrode active material is a negative electrode active material, that is, when a binder for a battery is added to the dispersion liquid for producing the negative electrode active material layer, the negative electrode active material layer does not become a non-binding body of the negative electrode active material particles.
If the negative electrode active material layer is a binder, the gas generated during the initial charge is not sufficiently discharged, and a uniform SEI film is not formed on the surface of the negative electrode active material particles. On the other hand, since the SEI film is not formed on the surface of the positive electrode active material particles, the above-described problem of the SEI film does not occur even if the positive electrode active material layer is a binder.
However, if not only the negative electrode active material layer but also the positive electrode active material layer is a non-binder, any electrode active material layer will not be defective when the battery is deformed. It can be applied and is preferable.

The battery binder is a known solvent-drying type binder for lithium ion batteries (starch, polyvinylidene fluoride, used for binding and fixing the electrode active materials to each other and the electrode active material and the current collector). Polyvinyl alcohol, carboxymethyl cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, styrene-butadiene copolymer, etc.), and by drying and solidifying by volatilizing the solvent component, It means what firmly fixes the electrode active material and the current collector.

In the case of the method of applying the composition for preparing an electrode active material layer on a substrate, for example, as the composition for preparing an electrode active material layer, a dispersion liquid containing a dispersion medium in addition to the electrode active material particles and the conductive additive ( And a method using a slurry).
When using a dispersion, for example, water or a dispersion medium (preferably a non-aqueous electrolyte or a non-aqueous electrolyte used for a non-aqueous electrolyte so that the total concentration of the electrode active material particles and the conductive additive is 30 to 60% by weight. Solvent etc.), electrode active material particles, and a dispersion of a conductive additive are applied to a current collector with a coating device such as a bar coater, and then dried as necessary to remove water or solvent. Can be mentioned. After the drying, the electrode active material layer may be pressed with a press if necessary.

As the substrate, a current collector and other base materials (for example, paper, aramid separator, etc.) can be used. That is, the electrode active material layer preparation composition does not need to be applied directly on the current collector. For example, the electrode dispersion layer is applied to the surface of another substrate to form the electrode active material layer on the substrate. Then, a method of removing the substrate may be used.
In addition, the drying performed as necessary can be performed using a known dryer such as a forward air dryer, and the drying temperature is adjusted according to the type of the dispersion medium (water or solvent) contained in the dispersion. can do.

When the electrode active material layer is pressed after the drying, the pressure is not particularly limited, but it is preferably pressed at 1 to 200 MPa.
Especially, when producing a negative electrode active material layer, it is preferable to press with the pressure that the volume ratio of the negative electrode active material particle contained in a negative electrode active material layer will be 30-70 volume%.
The volume ratio of the negative electrode active material particles contained in the negative electrode active material layer is a volume calculated from the weight and true density of the negative electrode active material particles contained in the negative electrode active material layer with respect to the volume calculated from the outer shape of the negative electrode active material layer. As a percentage.

In addition, as a method of directly forming the composition for preparing an electrode active material layer into a desired shape, a non-aqueous electrolyte or a non-aqueous electrolyte solution is formed on the electrode active material particles as necessary. Obtained by molding a composition for preparing an electrode active material layer (which may be liquid or semi-solid like okara) obtained by adding a water solvent by a known method Can do. Examples of the molding method include compression molding, extrusion molding, and calendar molding.
However, when the electrode active material is a negative electrode active material, a battery binder is not used. If a battery binder is used when the electrode active material is a negative electrode active material, the negative electrode active materials are bound to each other by the battery binder, and a non-binding body of negative electrode active material particles cannot be obtained. is there.

When the composition for preparing an electrode active material layer is directly formed, the composition for preparing an electrode active material layer may be a dry body or a wet body, but is preferably a wet body. The wet body is obtained by adding a small amount of liquid (a nonaqueous electrolytic solution or a nonaqueous solvent constituting the nonaqueous electrolytic solution) to the dried electrode active material layer preparation composition. When the composition for preparing an electrode active material layer is a wet body, it is preferably in a pendular state or a funicular state.

The ratio of the non-aqueous electrolyte in the wet body is not particularly limited, but in order to obtain a pendular state or a funicular state, in the case of the positive electrode, the ratio of the non-aqueous electrolyte is 0.5 to 15% of the entire wet body. In the case of a negative electrode, the ratio of the non-aqueous electrolyte is preferably 0.5 to 25% by weight of the entire wet body.

Examples of a method for obtaining an electrode active material layer by compression molding include a method in which the composition for preparing an electrode active material layer is placed in a mold having an arbitrary shape and compressed using a known compression device.
The shape of the mold only needs to have a bottom surface and side surfaces, and other shapes are not particularly limited. Moreover, the type | mold which comprises a side surface, and the type | mold which comprises a bottom face may be comprised so that isolation | separation is possible.

Examples of the material constituting the mold include general materials such as metals used for molds.
Moreover, in order to reduce the friction generated between the mold and the molded body, the surface of the mold may be coated with fluorine.
The shape of the space formed in the mold (hereinafter also simply referred to as a space) may be adjusted according to the shape of the electrode active material layer desired to be obtained, and it is desirable that the shape does not change in the compression direction. A cylindrical shape, a prismatic shape, or the like is desirable.
A molded body having a substantially circular shape in plan view when a space-shaped mold is used, and a rectangular shape in plan view when a space column-shaped mold is used.

As a method for obtaining an electrode active material layer by extrusion molding, a method using a known extrusion molding machine can be mentioned.
As an extrusion molding machine, for example, a raw material cylinder to which a raw material (the electrode active material layer preparation composition) is supplied, a die (also referred to as a mold) attached to the raw material discharge side of the raw material cylinder, One having a rotating shaft-shaped screw for extruding the arranged raw material toward the die is mentioned.
A cylindrical shaped body can be obtained by charging the raw material into the raw material cylinder and extruding the raw material moved through the raw material cylinder by the rotation of the screw from the die. The shape of the molded body can be adjusted as appropriate by adjusting the shape of the die and the rotational speed of the screw.

The shape of the cylindrical molded body discharged from the die is not particularly limited, but is preferably a cylindrical shape or a quadrangular prism shape. An electrode active material layer is obtained by cutting a cylindrical molded body discharged from a die with a predetermined length.

Examples of the method for obtaining the electrode active material layer by calendering include a method using a known roll press apparatus.
The above composition for preparing an electrode active material layer is introduced from a continuous mixer such as a kneader, and the composition for preparing an electrode active material layer, which has been spread to a certain thickness on a smooth surface such as a film by a doctor blade or the like, is roll-pressed. By doing so, a sheet-like molded body can be obtained. An electrode active material layer is obtained by cutting the sheet-like molded body at a predetermined length.

In the method for directly forming the electrode active material layer preparation composition into a desired shape, the pressure applied to the electrode active material layer preparation composition is not particularly limited. It is preferable to press with the pressure from which the volume ratio of the negative electrode active material particle contained in a material layer will be 30-70 volume%.

Known positive electrode active material particles for lithium ion batteries can be used as the positive electrode active material particles.
As the positive electrode active material, a composite oxide of lithium and a transition metal (a composite oxide having one kind of transition metal (such as LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO _2, and LiMn ₂ O ₄ ), a transition metal element is used. Two kinds of complex oxides (for example, LiFeMnO ₄ , LiNi _1-x Co _x O ₂ , LiMn _1-y Co _y O ₂ , LiNi _1/3 Co _1/3 Al _1/3 O ₂ and LiNi _0.8 Co _0.15 Al _0.05 O ₂ ) and a composite oxide having three or more transition metal elements [for example, LiM _a M ′ _b M ″ _c O ₂ (M, M ′, and M ″ are different transition metals, respectively) an element, satisfy a + b + c = 1. for example _{LiNi 1/3 Mn 1/3 Co 1/3 O 2} ) , etc.] or the like}, lithium-containing transition metal phosphate (e.g. LiFePO _4, Li OPO _4, LiMnPO ₄ and LiNiPO _4), transition metal oxides (e.g., MnO ₂ and _V 2 _O 5), transition metal sulfides (e.g., MoS ₂ and TiS ₂₎ and the conductive polymer (such as polyaniline, polypyrrole, polythiophene, Polyacetylene, poly-p-phenylene, and polyvinylcarbazole), and the like may be used in combination.
The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is substituted with another transition metal.

The volume average particle diameter of the positive electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and more preferably 1 to 30 μm from the viewpoint of the electrical characteristics of the lithium ion battery. Is more preferable.

Examples of the negative electrode active material particles include known negative electrode active material particles for lithium ion batteries such as silicon-based negative electrode active material particles and carbon-based negative electrode active material particles, and preferably include silicon-based negative electrode active material particles.
When silicon-based negative electrode active material particles are included as the negative electrode active material particles, the effect of the precharging step in the method for producing a lithium ion battery of the present invention is remarkably obtained, which is preferable.

Examples of the silicon-based negative electrode active material particles include silicon and / or silicon compound particles.
Examples of the material constituting the silicon compound particles include silicon oxide (SiO _x ), silicon-carbon composite (the surface of the carbon particles covered with silicon and / or silicon carbide, the surface of the silicon particles or silicon oxide particles and carbon And / or silicon carbide and silicon alloys (silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper) Alloys, silicon-tin alloys, etc.).
Of these, silicon oxide is desirable.

Known silicon particles for secondary battery negative electrodes can be used as the silicon particles, and the silicon compound particles are KSC-1064 manufactured by Shin-Etsu Chemical Co., Ltd. Those having a diameter of 5 μm] may be used, and silicon oxide particles synthesized by a known method described in JP-A-2001-220123 and JP-A-2001-226112 may be used. .

As a material constituting the carbon-based negative electrode active material particles, carbon-based materials [for example, graphite, non-graphitizable carbon, amorphous carbon, resin fired bodies (for example, those obtained by firing and carbonizing phenol resin, furan resin, etc.), Coke (such as pitch coke, needle coke and petroleum coke), silicon carbide and carbon fiber, etc.], conductive polymer (such as polyacetylene and polypyrrole), metal (tin, silicon, aluminum, zirconium, titanium, etc.), metal Oxides (titanium oxide, lithium / titanium oxide, silicon oxide, etc.) and metal alloys (eg, lithium-tin alloy, lithium-silicon alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.) and the like Examples thereof include a mixture with a carbon-based material.
Among the above negative electrode active materials, those that do not contain lithium or lithium ions may be subjected to a pre-doping treatment in which lithium or lithium ions are included in part or all of the negative electrode active material in advance.

The volume average particle diameter of the negative electrode active material particles is preferably from 0.01 to 100 μm, more preferably from 0.1 to 40 μm, and even more preferably from 2 to 35 μm, from the viewpoint of the electrical characteristics of the lithium ion battery. .

In the present specification, the volume average particle diameter of the electrode active material particles means a particle diameter (Dv50) at an integrated value of 50% in the particle size distribution obtained by the microtrack method (laser diffraction / scattering method). The microtrack method is a method for obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light. In addition, Nikkiso Co., Ltd. microtrack etc. can be used for the measurement of a volume average particle diameter.

When the composition for preparing an electrode active material layer includes a conductive additive, the conductive additive is selected from materials having conductivity.
Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), etc. , And mixtures thereof, but are not limited thereto.
These conductive assistants may be used alone or in combination of two or more. Further, these alloys or metal oxides may be used. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and a mixture thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is more preferable. Moreover, as these conductive support agents, what coated the electroconductive material (metal thing among the above-mentioned conductive support agents) by plating etc. around the particulate ceramic material or the resin material may be used.

The volume average particle diameter of the conductive auxiliary agent is not particularly limited, but is preferably 0.01 to 10 μm and more preferably 0.02 to 5 μm from the viewpoint of the electrical characteristics of the lithium ion battery. Preferably, it is 0.03 to 1 μm.
The volume average particle diameter of the conductive assistant can be measured by a microtrack method.

The shape (form) of the conductive auxiliary agent is not limited to the particle form, and may be a form other than the particle form, or may be a form put into practical use as a so-called filler-based conductive material such as a carbon nanotube.

The conductive auxiliary agent may be a conductive fiber having a fibrous shape.
Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers obtained by uniformly dispersing highly conductive metal and graphite in synthetic fibers, and metals such as stainless steel. Examples thereof include fiberized metal fibers, conductive fibers in which the surface of organic fiber is coated with metal, and conductive fibers in which the surface of organic fiber is coated with a resin containing a conductive substance. Among these conductive fibers, carbon fibers are preferable. A polypropylene resin in which graphene is kneaded is also preferable.
When a conductive support agent is a conductive fiber, it is preferable that the average fiber diameter is 0.1-20 micrometers.

In the lithium ion battery of the present invention, the electrode active material particles may be coated electrode active material particles in which at least a part of the surface of the electrode active material particles is coated with a coating resin composition made of a coating resin.
Coated electrode active material particles using positive electrode active material particles as electrode active material particles are also referred to as coated positive electrode active material particles, and coated electrode active material particles using negative electrode active material particles as electrode active material particles are also referred to as coated negative electrode active material particles. Say.
When at least a part of the surface of the electrode active material particles is coated with the coating resin composition, it is possible to suppress the electrode from expanding due to the volume expansion of the electrode active material particles.
When the coated electrode active material particles are used, the coating resin composition containing the non-aqueous electrolyte swells and exhibits adhesiveness, so that molding can be performed under simpler conditions.
Therefore, it becomes easy to produce an electrode active material layer containing a non-aqueous electrolyte from the beginning.
The coated electrode active material when the electrode active material is a positive electrode active material is also referred to as a coated positive electrode active material, and the coated electrode active material when the electrode active material is a negative electrode active material is also referred to as a coated negative electrode active material.

The coated electrode active material particles can be coated with a coating resin composition around the electrode active material particles by a known method described in Japanese Patent Application Laid-Open No. 2017-054703 and the like. It can manufacture by mixing the resin composition for coating | cover containing the electrically conductive material to be used, and electrode active material particle. When the coating resin composition includes a conductive material, for example, the coating resin and the conductive material may be manufactured by mixing the electrode active material particles, and the coating resin and the conductive material may be mixed. After preparing the coating material, it may be produced by mixing the coating material and the electrode active material particles.
By the above method, at least a part of the surface of the electrode active material particles is coated with the coating resin composition made of the coating resin.
As the coating resin constituting the coating resin composition, the coating resins described in International Publication Nos. 2015/5117 and JP-A-2017-0547703 can be preferably used.

The resin composition for coating constituting the coated electrode active material particles may further contain a conductive material. However, the conductive additive constituting the electrode active material layer and the conductive material constituting the coating resin composition are clearly different. Since the conductive material is contained in the coating resin composition, it does not contribute to the formation of a conductive path between the electrode active material particles.
When the electrode active material layer includes a conductive additive and a conductive material, if the electrode active material layer is dispersed in a solvent in which the coating resin does not dissolve, only the conductive auxiliary agent is extracted into the solvent. The conductive material remaining in the composition and the conductive auxiliary agent can be separated.

As the conductive material, the same materials as the conductive auxiliary agent can be suitably used.

The electrode active material layer may contain an adhesive resin.
The adhesive resin means a resin having adhesiveness without solidifying even if the solvent component is volatilized and dried, and is a material different from the battery binder and is distinguished.
In addition, the coating layer constituting the coated electrode active material is fixed to the surface of the electrode active material, whereas the adhesive resin reversibly fixes the surfaces of the electrode active material. The adhesive resin can be easily separated from the surface of the electrode active material, but the coating layer cannot be easily separated. Therefore, the coating layer and the adhesive resin are different materials.

The adhesive resin includes, as an essential constituent monomer, at least one low Tg monomer selected from the group consisting of vinyl acetate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, and butyl methacrylate. The polymer whose total weight ratio is 45 weight% or more based on the total weight of a constituent monomer is mentioned.
When the adhesive resin is used, it is preferable to use 0.01 to 10% by weight of the adhesive resin with respect to the total weight of the electrode active material.

As a separator used in the method for producing a lithium ion battery of the present invention, a known separator for lithium ion battery can be used, a microporous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and porous polypropylene. Non-woven fabrics made of synthetic fibers (polyester fibers, aramid fibers, etc.) or glass fibers, and known lithium ion battery separators such as those having ceramic fine particles such as silica, alumina, titania attached to their surfaces. It is done.

The precharging step is performed by arranging a stack unit in which a positive electrode active material layer including positive electrode active material particles and a negative electrode active material layer including negative electrode active material particles are stacked via a separator between current collectors. However, as the current collector, a known current collector for lithium ion batteries can be used. For example, a known metal current collector and a resin current collector composed of a conductive material and a resin (Japanese Patent Laid-Open No. 2012-1998). Resin current collectors described in Japanese Patent No. 150905 and the like can be used.

Examples of the metal current collector include copper, aluminum, titanium, nickel, tantalum, niobium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, alloys containing one or more of these metals, and stainless steel alloys. One or more metal materials selected from These metal materials may be used in the form of a thin plate or a metal foil. Moreover, you may use what formed the said metal material by methods, such as sputtering, electrodeposition, and application | coating, on the base-material surface comprised other than the said metal material as a metal electrical power collector.

As the conductive material constituting the resin current collector, the same conductive material as that described above can be suitably used.

The resin constituting the resin current collector includes polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), polytetra Fluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin or a mixture thereof Is mentioned.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferable, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferable. (PMP).

The method for producing a lithium ion battery of the present invention may further include an impregnation step of impregnating the positive electrode active material layer, the separator and the negative electrode active material layer with a non-aqueous electrolyte before the precharging step. The electrolyte concentration of the non-aqueous electrolyte used in the process is preferably 1.2 to 4.5 mol / L. A concentration of the non-aqueous electrolyte within this range is preferable from the viewpoint of input / output characteristics and the like.

As a method of impregnating the positive electrode active material layer, the separator, and the negative electrode active material layer with a non-aqueous electrolyte,
A method of forming a laminated unit after impregnating each of a positive electrode active material layer, a separator, and a negative electrode active material layer before constituting a laminated unit with a non-aqueous electrolyte, and a positive electrode active material layer not containing a non-aqueous electrolyte There is a method in which a separator and a negative electrode active material layer are laminated to prepare a laminated unit, and the laminated unit is impregnated with a non-aqueous electrolyte.

As the non-aqueous electrolyte to be impregnated, a non-aqueous electrolyte containing an electrolyte and a non-aqueous solvent used for the production of a lithium ion battery can be used.

As the electrolyte, those used in known non-aqueous electrolytes can be used, and preferable examples thereof include lithium salts of inorganic acids such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ and LiClO _4. Electrolytes, sulfonylimide-based electrolytes having fluorine atoms such as LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ , fluorines such as LiC (CF ₃ SO ₂ ) ₃ Examples thereof include sulfonylmethide electrolytes having atoms. Among these, a sulfonylimide-based electrolyte having a fluorine atom is preferable from the viewpoint of ion conductivity at a high concentration and a thermal decomposition temperature, and LiN (FSO ₂ ) ₂ is more preferable. LiN (FSO ₂ ) ₂ may be used in combination with other electrolytes, but is more preferably used alone.

The electrolyte concentration of the non-aqueous electrolyte is not particularly limited, but is preferably 1.2 to 4.5 mol / L from the viewpoints of the handleability of the non-aqueous electrolyte and the battery capacity.

As the non-aqueous solvent, those used in known non-aqueous electrolytes can be used, for example, lactone compounds, cyclic or chain carbonates, chain carboxylates, cyclic or chain ethers, phosphate esters. , Nitrile compounds, amide compounds, sulfones and the like and mixtures thereof.

Examples of the lactone compound include a 5-membered ring (γ-butyrolactone, γ-valerolactone, etc.) and a 6-membered lactone compound (δ-valerolactone, etc.).

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate and butylene carbonate.
Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate.

Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.
Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,4-dioxane and the like.
Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trichloromethyl) phosphate, Tri (trifluoroethyl) phosphate, tri (triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphospholan-2-one, 2-trifluoroethoxy-1,3,2- Examples include dioxaphospholan-2-one and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.
Examples of the nitrile compound include acetonitrile.
Examples of the amide compound include N, N-dimethylformamide (hereinafter referred to as DMF).
Examples of the sulfone include chain sulfones such as dimethyl sulfone and diethyl sulfone, and cyclic sulfones such as sulfolane.
A non-aqueous solvent may be used individually by 1 type, and may use 2 or more types together.

Among the non-aqueous solvents, preferred are lactone compounds, cyclic carbonates, chain carbonates and phosphates from the viewpoint of battery output and charge / discharge cycle characteristics, and preferably no nitrile compounds. Further preferred are lactone compounds, cyclic carbonates and chain carbonates, and particularly preferred are cyclic carbonates and chain carbonates and a mixture of cyclic carbonates and chain carbonates. Most preferred is a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC), or a mixture of ethylene carbonate (EC) and propylene carbonate (PC). It is.

EXAMPLES Next, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples without departing from the gist of the present invention. Unless otherwise specified, “part” means “part by weight” and “%” means “% by weight”.

<Production Example 1: Production of coating resin (B1)>
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 14.3 parts of DMF and 2.9 parts of methanol and heated to 68 ° C. Next, a monomer mixture containing 41.7 parts of methacrylic acid, 16.6 parts of methyl methacrylate, 41.7 parts of 2-ethylhexyl methacrylate, 9.0 parts of DMF and 1.8 parts of methanol, and 2,2′-azobis ( 2,4-dimethylvaleronitrile) Initiator solution prepared by dissolving 0.045 parts in DMF 5.9 parts and continuously dropping over 4 hours with stirring in a dropping funnel while blowing nitrogen into a four-necked flask. Then, radical polymerization was performed. After completion of dropping, an initiator solution prepared by dissolving 0.100 part of 2,2′-azobis (2,4-dimethylvaleronitrile) in 4.5 parts of DMF was continuously added using a dropping funnel over 2 hours. Furthermore, the polymerization was continued for 4 hours at the boiling point. After removing the solvent to obtain 99.8 parts of a resin, 232.9 parts of isopropanol was added to obtain a polymer (coating resin) (B1) solution having a resin concentration of 30% by weight. When the molecular weight of the obtained coating resin (B1) was measured by GPC under the following conditions, Mw was 210,000.
<GPC measurement conditions>
Apparatus: Alliance GPCV2000 (manufactured by Waters)
Solvent: Orthodichlorobenzene Standard substance: Polystyrene Sample concentration: 3 mg / ml
Column stationary phase: PLgel 10 μm, 2 MIXED-B in series (manufactured by Polymer Laboratories)
Column temperature: 135 ° C

<Production Example 2: Production of coating resin (B2)>
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 14.3 parts of DMF and 2.9 parts of methanol and heated to 68 ° C. Next, a monomer compounding solution containing 90.0 parts of acrylic acid, 10.0 parts of methyl methacrylate, 9.0 parts of DMF and 1.8 parts of methanol, and 2,2′-azobis (2,4-dimethylvaleronitrile) The initiator solution obtained by dissolving 0.045 parts in 5.9 parts of DMF was continuously dropped with a dropping funnel over 4 hours with stirring while blowing nitrogen into a four-necked flask to perform radical polymerization. After completion of dropping, an initiator solution prepared by dissolving 0.100 part of 2,2′-azobis (2,4-dimethylvaleronitrile) in 4.5 parts of DMF was continuously added using a dropping funnel over 2 hours. Furthermore, the polymerization was continued for 4 hours at the boiling point. After removing the solvent to obtain 99.8 parts of resin, 232.9 parts of isopropanol was added to obtain a polymer (coating resin) (B2) solution having a resin concentration of 30% by weight. When the molecular weight of the obtained coating resin (B2) was measured by GPC under the same conditions as in Production Example 1, Mw was 180,000.

<Production Example 3: Preparation of Electrolytic Solution (E-1)>
LiN (FSO ₂ ) ₂ is dissolved in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (volume ratio EC: PC = 1: 1) at a rate of 1.2 mol / L, and an electrolytic solution for a lithium ion battery ( E-1) was prepared.

<Production Example 4: Preparation of electrolytic solution (E-2)>
An electrolytic solution for lithium ion battery (E-2) was prepared in the same procedure as in Production Example 3, except that the concentration of LiN (FSO ₂ ) ₂ was changed to 4.5 mol / L.

<Production Example 5: Preparation of electrolyte solution (E-3)>
An electrolyte solution for lithium ion battery (E-3) was prepared in the same procedure as in Production Example 3, except that the concentration of LiN (FSO ₂ ) ₂ was changed to 0.8 mol / L.

<Production Example 6: Production of carbon-coated silicon oxide particles>
Silicon oxide particles [manufactured by Shin-Etsu Chemical Co., Ltd., volume average particle diameter of primary particles: 5 μm] are placed in a horizontal heating furnace, and 1100 ° C./1000 Pa, average residence time of about 2 while venting methane gas into the horizontal heating furnace. A chemical vapor deposition operation for a period of time was performed to obtain carbon-coated silicon oxide particles (volume average particle diameter 6 μm) having a carbon content of 2% by weight and a surface coated with carbon.

<Production Example 7: Production of coated negative electrode active material particles (X-1)>
A coated negative electrode active material for a lithium ion battery using the coating resin (B1) solution was produced by the following method.
Non-graphitizable carbon powder [Carbotron (registered trademark) PS (F) manufactured by Kureha Battery Materials Japan Co., Ltd., volume average particle size 18 μm] 99.0 parts is mixed into a universal mixer high speed mixer FS25 [Co. ) Made by Earth Technica], and with stirring at room temperature and 720 rpm, 3.0 parts of the above coating resin (B1) solution (solid content concentration 30% by weight) was added dropwise over 2 minutes and stirred for another 5 minutes. . Then, the pressure is reduced to 0.01 MPa while maintaining the stirring, and then the temperature is raised to 140 ° C. while maintaining the stirring and the degree of vacuum, and the volatile matter is distilled off by maintaining the stirring, the pressure and the temperature for 8 hours. Then, 99.9 parts of carbon-based coated negative electrode active material particles (X-1) were obtained. The true density of the carbon-based coated negative electrode active particles (X-1) was 1.5 g / cm ³ .

<Production Example 8: Production of coated negative electrode active material particles (X-2)>
A coated negative electrode active material for a lithium ion battery using the coating resin (B2) solution was produced by the following method.
60 parts of the carbon-coated silicon oxide particles obtained in Production Example 6 were put in a universal mixer and stirred at room temperature and 150 rpm, and 67 parts of the above coating resin (B2) solution (resin solid content concentration: 30% by weight) was added to 60 parts. The mixture was mixed dropwise over a period of 30 minutes and stirred for another 30 minutes.
Next, 20 parts of acetylene black [manufactured by Denka Co., Ltd.] was mixed in three portions while stirring, and the temperature was raised to 70 ° C. while stirring for 30 minutes, and the pressure was reduced to 0.01 MPa and held for 30 minutes. By the above operation, 100 parts of coated negative electrode active material particles (X-2) were obtained. The true density of the coated negative electrode active material particles (X-2) was 1.9 g / cm ³ .

<Production Example 9: Production of coated positive electrode active material particles>
A coated positive electrode active material for a lithium ion battery using a solution of the coating resin (B1) was produced by the following method.
In a state where 96 parts of LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder was put into a universal mixer and stirred at room temperature and 150 rpm, 3.3 parts of a resin solution (resin solid content concentration of 30% by weight) was added to 60 parts. The mixture was mixed dropwise over a period of 30 minutes and stirred for another 30 minutes.
Next, 3 parts of acetylene black [manufactured by Denka Co., Ltd.] were mixed in three portions while stirring, and the temperature was raised to 70 ° C. while stirring for 30 minutes, and the pressure was reduced to 0.01 MPa and held for 30 minutes. By the above operation, 97 parts of coated positive electrode active material particles were obtained. The true density of the coated positive electrode active material particles was 4.8 g / cm ³ .

<Production Example 10: Production of positive electrode active material layer (P-1)>
98 parts of coated positive electrode active material particles obtained in Production Example 9, carbon nanofibers (described as CNF in Table 1) [VGCF (registered trademark) manufactured by Showa Denko KK, true density 2.1 g / cm ³ ] (aspect ratio: 60, electrical resistivity: 40 μΩm) 2 parts of positive electrode active material slurry obtained by mixing 120 parts of electrolyte (E-1) on an aramid separator is 60.2 mg in weight per unit area The positive electrode active material layer (P-1) was produced on the aramid separator by applying at / cm ² and absorbing liquid from the opposite side of the aramid separator.
The thickness of the positive electrode active material layer (P-1) obtained was 235 μm. The volume ratio of the coated positive electrode active material particles contained in the positive electrode active material layer (P-1) calculated from the true density of the used coated positive electrode active material particles was 52% by volume.

<Production Example 11: Production of positive electrode active material layer (P-2)>
A positive electrode active material layer (P-) was prepared in the same manner as in Production Example 10 except that the electrolytic solution (E-1) was changed to 120 parts of the electrolytic solution (E-2) and the basis weight was changed to 147.3 mg / cm ^2. 2) was produced.
The thickness of the positive electrode active material layer (P-2) obtained was 575 μm. The volume ratio of the coated positive electrode active material particles contained in the positive electrode active material layer (P-2) calculated from the true density of the used coated positive electrode active material particles was 52% by volume.

<Production Example 12: Production of positive electrode active material layer (P-3)>
A positive electrode active material layer (P-3) was produced in the same manner as in Production Example 10 except that the electrolytic solution (E-1) was changed to 120 parts of the electrolytic solution (E-3).
The thickness of the positive electrode active material layer (P-3) obtained was 235 μm. The volume ratio of the coated positive electrode active material particles contained in the positive electrode active material layer (P-3) calculated from the true density of the used coated positive electrode active material particles was 52% by volume.

<Production Example 13: Production of positive electrode active material layer (P-4)>
The positive electrode active material slurry used in Production Example 10 was applied to an aramid separator in the same manner as in Production Example 10, and suctioned gradually from the opposite side of the aramid separator until the thickness became 410 μm, the positive electrode active material layer having a thickness of 410 μm (P-4) was produced. The volume ratio of the coated positive electrode active material particles contained in the positive electrode active material layer (P-4) calculated from the true density of the used coated positive electrode active material particles was 30% by volume.

<Production Example 14: Production of negative electrode active material layer (N-1)>
The anode active material slurry obtained by mixing 98 parts of the coated anode active material particles (X-1) obtained in Production Example 7, 2 parts of carbon nanofibers, and 120 parts of the electrolyte (E-1) was used as an aramid separator. The negative electrode active material layer (N-1) was produced on the aramid separator by apply | coating with the fabric weight of 28.5 mg / cm < ² > above, and liquid-absorbing from the other side of an aramid separator.
The thickness of the obtained negative electrode active material layer (N-1) was 300 μm. The volume ratio of the coated negative electrode active material particles (X-1) contained in the negative electrode active material layer (N-1) calculated from the true density of the used coated negative electrode active material particles was 62% by volume.

<Production Example 15: Production of negative electrode active material layer (N-2)>
The negative electrode active material layer (N−) was changed in the same manner as in Production Example 14 except that the electrolytic solution (E-1) was changed to 120 parts of the electrolytic solution (E-2) and the basis weight was changed to 70.0 mg / cm ^2. 2) was produced.
The thickness of the obtained negative electrode active material layer (N-2) was 735 μm. The volume ratio of the coated negative electrode active material particles (X-1) contained in the negative electrode active material layer (N-2) calculated from the true density of the used coated negative electrode active material particles was 62% by volume.

<Production Example 16: Production of negative electrode active material layer (N-3)>
75 parts of coated negative electrode active material particles (X-1), 10 parts of coated negative electrode active material particles (X-2), 10 parts of acetylene black (Denka Co., Ltd., Denka Black, true density 1.8 g / cm ³ ), A negative electrode active material slurry obtained by mixing 5 parts of carbon nanofibers and 120 parts of electrolytic solution (E-1) was applied onto an aramid separator at a weight per unit area of 24.2 mg / cm ² and absorbed from the opposite side of the aramid separator. The negative electrode active material layer (N-3) was produced on the aramid separator by liquidating. The thickness of the obtained negative electrode active material layer (N-3) was 250 μm. The coated negative electrode active material particles (X-1) and (X) contained in the negative electrode active material layer (N-3) calculated from the true density of the used coated negative electrode active material particles (X-1) and (X-2) The total volume ratio of -2) was 53% by volume.

<Production Example 17: Production of negative electrode active material layer (N-4)>
On the aramid separator in the same manner as in Production Example 16, except that the basis weight was changed to 25.0 mg / cm ² and the liquid absorption from the opposite side of the aramid separator was performed until the thickness of the negative electrode active material layer became 430 μm. A negative electrode active material layer (N-4) was prepared. The thickness of the obtained negative electrode active material layer (N-4) was 430 μm. The coated negative electrode active material particles (X-1) and (X) contained in the negative electrode active material layer (N-4) calculated from the true density of the used coated negative electrode active material particles (X-1) and (X-2) The total volume ratio of -2) was 32% by volume.

<Production Example 18: Production of negative electrode active material layer (N-5)>
The electrolytic solution (E-1) was changed to 120 parts of the electrolytic solution (E-3), the basis weight was changed to 7.0 mg / cm ² , and the liquid absorption from the opposite side of the aramid separator was changed to the thickness of the negative electrode active material layer. A negative electrode active material layer (N-5) was produced on the aramid separator in the same manner as in Production Example 14 except that the process was performed until the thickness became 180 μm. The thickness of the obtained negative electrode active material layer (N-5) was 180 μm. The volume ratio of the coated negative electrode active material particles (X-1) contained in the negative electrode active material layer (N-5) calculated from the true density of the used coated negative electrode active material particles (X-1) was 25% by volume. It was.

<Example 1>
[Preparation of lamination unit]
The positive electrode active material layer (P-1) from which the aramid separator has been peeled off, the negative electrode active material layer (N-1) from which the aramid separator has been peeled off, and a separator [Celguard (registered trademark) 3501 PP made by Celgard] are combined and bonded together. Thus, a laminated unit was produced.
An aluminum foil having a current extraction terminal attached to the positive electrode active material layer (P-1) side of the laminated unit and a copper foil having a current extraction terminal attached to the negative electrode active material layer (N-1) side were contacted. In the state, it accommodated in the aluminum laminated film which is a battery exterior body, and produced the battery for evaluation.

[Preliminary charging process]
A battery for evaluation is sandwiched between stainless plates, a weight is applied so that a load of 2.5 kgf / cm ² is applied from above, and a current extraction terminal is a charge / discharge measuring device “Battery Analyzer 1470 type” [manufactured by Toyo Technica Co., Ltd. ] Connected.
Subsequently, using the above charge / discharge measuring apparatus, after discharging the laminated unit at a current of 0.05 C until the potential of the positive electrode becomes 0.01 V (vs. Li ⁺ / Li) and resting for 10 minutes. The lithium ion battery for evaluation according to Example 1 was obtained by performing preliminary charging by charging until the potential of the positive electrode reached 4.2 V (vs. Li ⁺ / Li).

[Durability test]
For the lithium ion battery for evaluation after the preliminary charging step, further discharge at a current of 0.05 C until the potential of the positive electrode becomes 0.01 V (vs. Li ⁺ / Li), pause for 10 minutes, 0.05 C Charging until the potential of the positive electrode becomes 4.2 V (vs. Li ⁺ / Li) by current, repeating the cycle of 10 minutes and resting 99 times, and the ratio of the 100th charge capacity to the first charge capacity (100th cycle) Capacity retention ratio) was determined, and the cycle characteristics (durability) were evaluated according to the following criteria. The results are shown in Table 1.
○: Capacity maintenance rate at 100th cycle is 80% or more, cycle characteristics are good ×: Capacity maintenance rate at 100th cycle is less than 80%, cycle characteristics are poor

[Vibration resistance test]
For the evaluation lithium ion battery after the preliminary charging step, the second charging operation was performed to measure the second charging capacity, and then the vertical / horizontal vibration combined environmental device manufactured by Espec Co., Ltd. was used. Vibration was applied. The vibration was performed for 30 minutes with a period of 1000 Hz and an amplitude of 10 mm along a direction parallel to the stacking direction of the stacking unit.
After that, the third charge test is performed, the third charge capacity is measured, the reduction rate of the charge capacity from the second charge capacity (capacity maintenance rate during vibration) is calculated, and the vibration resistance is evaluated according to the following criteria did. The results are shown in Table 1.
A: Capacity maintenance rate during vibration is 95% or more and excellent in vibration resistance B: Capacity maintenance ratio during vibration is 90% or more and less than 95%, vibration resistance is good ×: Capacity during vibration Maintenance rate is less than 90% and vibration resistance is poor

<Examples 2 to 5, Comparative Examples 1 and 2>
Other than changing the combination of the positive electrode active material layer constituting the laminated unit and the negative electrode active material layer constituting the laminated unit to the combination shown in Table 1, and changing the load in the precharging step to the weight shown in Table 1 Produced a lithium ion battery for evaluation in the same manner as in Example 1, and evaluated durability and vibration resistance in the same manner as in Example 1. The results are shown in Table 1.
In Comparative Example 2, the laminate unit was deformed during the precharging process by the load, and a lithium ion battery could not be produced. Therefore, since the durability test and the vibration resistance test could not be performed, it was described in Table 1 that it could not be performed.

From the results in Table 1, the lithium ion battery produced by the method for producing a lithium ion battery of the present invention is excellent in both durability and vibration resistance, and has cycle characteristics even when vibration is applied. It turns out that it is excellent. These are considered to be because a uniform SEI film was formed on the surface of the negative electrode active material layer by performing the charging operation in a state where a sufficient load was applied to the laminated unit in the preliminary charging step.

The lithium ion battery obtained by the method for producing a lithium ion battery of the present invention is particularly useful as a lithium ion battery used for mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims (4)

Lithium including a precharging step in which a positive electrode active material layer containing positive electrode active material particles and a negative electrode active material layer containing negative electrode active material particles are subjected to a charging operation at least once for a laminated unit laminated via a separator. A method for manufacturing an ion battery, comprising:
The negative electrode active material layer is a non-binding body of the negative electrode active material particles,
The method of manufacturing a lithium ion battery, wherein the preliminary charging step is performed in a state where a load of 2.5 to 10 kgf / cm ² is applied to the stacked unit. The method of manufacturing a lithium ion battery according to claim 1, wherein the negative electrode active material particles include silicon and / or silicon compound particles. The method further comprises an impregnation step of impregnating the positive electrode active material layer, the separator, and the negative electrode active material layer with a non-aqueous electrolyte, wherein the electrolyte concentration of the non-aqueous electrolyte is 1.2 to 4.5 mol / L. Item 3. A method for producing a lithium ion battery according to Item 1 or 2. The method for producing a lithium ion battery according to any one of claims 1 to 3, wherein the negative electrode active material layer has a thickness of 200 to 750 µm before a load is applied to the stacked unit.