JP7434218B2 - Manufacturing method of non-aqueous secondary battery - Google Patents

Description

The present invention relates to a method for manufacturing a non-aqueous secondary battery.

Electric vehicles and hybrid vehicles use non-aqueous secondary batteries as their power source. In the field of lithium ion secondary batteries, which are an example of non-aqueous secondary batteries, there is a known technology in which the negative electrode active material is dispersed in the negative electrode solvent by coating the particle surface of the negative electrode active material with a negative electrode dispersant. (For example, Patent Document 1). Specifically, graphite, which is an example of a negative electrode active material, has hydrophobicity. The negative electrode dispersant is a polymeric material that includes a hydrophilic group and a hydrophobic group. The negative electrode dispersant is adsorbed onto the graphite surface by its hydrophobic groups, and forms an interface with water, which is a negative electrode solvent, by its hydrophilic groups.

Japanese Patent Application Publication No. 2011-198710

General graphite has functional groups such as carboxy groups and hydroxy groups on the surface of its particles. In the vicinity of the functional groups on the surface of the graphite particle, the hydrophobicity decreases, making it difficult for the negative electrode dispersant to adsorb onto the surface of the graphite particle. On the surface of the graphite particles, a portion where an interface with the negative electrode solvent is not formed deteriorates the dispersibility of the graphite particles in the negative electrode solvent. As a result, dilatancy occurs in the negative electrode mixture paste, which deteriorates the coatability of the negative electrode mixture paste onto the negative electrode base material.

A method for manufacturing a non-aqueous secondary battery to solve the above problems includes a step of producing a negative electrode mixture paste using a negative electrode active material, a negative electrode dispersant, a negative electrode solvent, and a negative electrode binder, and A method for manufacturing a non-aqueous secondary battery, comprising: forming a negative electrode mixture layer by coating a negative electrode mixture paste on a negative electrode base material; After kneading the negative electrode active material, which is graphite that has been subjected to a surface treatment for removal, and the negative electrode dispersant, which has adsorption properties to the surface of the graphite from which the surface functional groups have been removed, a first step of adding the negative electrode binder to the kneaded material produced in the first step, and producing the negative electrode from the kneaded material to which the negative electrode binder has been added; and a second step of producing a mixture paste.

According to the above manufacturing method, by using graphite that has been surface-treated to remove surface functional groups as the negative electrode active material, the negative electrode dispersant can be easily adsorbed onto the entire surface of the graphite particles. Thereby, the dispersibility of the graphite particles in the negative electrode solvent can be improved, and as a result, it is possible to suppress deterioration in the coatability of the negative electrode mixture paste onto the negative electrode base material. Moreover, by coating the entire surface of the graphite particles with the negative electrode dispersant, the entire particle surface of the negative electrode active material has uniform polarity. As a result, in the second step, segregation of the negative electrode binder to the part of the surface of the graphite particle that is not coated with the negative electrode dispersant is suppressed, and the negative electrode binder spreads the negative electrode dispersant over the entire surface of the graphite particle. It is evenly adsorbed through the medium. As a result, it is possible to suppress a decrease in the binding force between graphite particles due to segregation of the negative electrode binder.

In the above method for manufacturing a non-aqueous secondary battery, the negative electrode dispersant contained in the negative electrode mixture paste has a viscosity of a first amount of the negative electrode dispersant adsorbed to the negative electrode active material and a viscosity of the negative electrode mixture paste. a second amount of the negative electrode dispersant for adjustment; in the first step, the negative electrode solvent is added after kneading the first amount of the negative electrode dispersant and the negative electrode active material; In the second step, it is preferable that the second amount of the negative electrode dispersant is further added to the kneaded material to which the negative electrode binder has been added.

The negative electrode dispersant kneaded in the first step coats the graphite surface and contributes to the dispersion of graphite particles, but becomes liberated when the negative electrode dispersant covering the graphite surface becomes saturated. The liberated negative electrode dispersant has the function of increasing the viscosity of the negative electrode mixture paste, while adsorbing the added negative electrode binder and reducing the amount of negative electrode binder that contributes to binding between graphite particles. let Therefore, by adding the negative electrode dispersant separately in the first step and after the negative electrode binder is added in the second step, the negative electrode dispersant necessary for coating the graphite surface in the first step, The amount of the free negative electrode dispersant when adding the negative electrode binder can be reduced compared to the case where the negative electrode dispersant necessary for adjusting the viscosity of the negative electrode mixture paste is added at once. Therefore, when adding the negative electrode binder, the amount of the negative electrode binder added can be reduced by the amount of the negative electrode dispersant in a free state. As a result, it is possible to increase battery capacity and reduce internal resistance.

In the method for manufacturing a non-aqueous secondary battery, the negative electrode dispersant is preferably carboxymethyl cellulose.
Since carboxymethyl cellulose has a hydrophilic group and a hydrophobic group, it can be adsorbed to the surface of graphite particles by the hydrophobic group, and can form an interface with the negative electrode solvent by the hydrophilic group. Further, carboxymethylcellulose in a free state without being adsorbed on the particle surface of the negative electrode active material has a function of increasing the viscosity of the negative electrode mixture paste. Therefore, by using carboxymethyl cellulose as a negative electrode dispersant, it is possible not only to improve the dispersibility of graphite particles in the negative electrode solvent, but also to adjust the viscosity of the negative electrode mixture paste.

In the method for manufacturing a non-aqueous secondary battery, the first amount is preferably 0.18% or more and 0.42% or less based on the mass of the negative electrode active material.
According to the above manufacturing method, in the first step, the first amount of carboxymethylcellulose, which is a negative electrode dispersant, is 0.18% or more and 0.42% or less based on the mass of graphite, which is a negative electrode active material. By doing so, the entire surface of the graphite particles can be covered with the negative electrode dispersant, and the amount of free negative electrode dispersant present when the negative electrode binder is added in the second step can be reduced.

In the method for manufacturing a non-aqueous secondary battery, the negative electrode binder is preferably styrene-butadiene rubber.
According to the above manufacturing method, by using styrene-butadiene rubber as the negative electrode binder, the styrene-butadiene rubber is adsorbed to the surface of the graphite particles via the negative electrode dispersant, thereby increasing the binding force between the graphite particles. I can do it.

In the method for manufacturing a nonaqueous secondary battery, the mass of the negative electrode binder added in the second step is preferably 1.2 times or more and 1.6 times or less relative to the first amount. .
According to the above manufacturing method, the mass of styrene-butadiene rubber, which is a negative electrode binder added in the second step, is 1.2 times or more relative to the first amount, which is the mass of carboxymethyl cellulose, which is a negative electrode dispersant. By being 6 times or less, it is possible to sufficiently secure the binding force of the graphite particles in the negative electrode mixture paste, and to prevent a decrease in battery capacity and an increase in internal resistance due to excessive addition of negative electrode binder. can be suppressed.

In the above method for manufacturing a non-aqueous secondary battery, it is preferable that the negative electrode active material has a ratio of an amount of oxygen element to an amount of carbon element of less than 1%.
According to the above manufacturing method, in the negative electrode active material, the ratio of the amount of oxygen element to the amount of carbon element is less than 1%, so that the portion of the entire surface of the graphite particle whose hydrophobicity is reduced due to the presence of the functional group. is in a sufficiently small state, the entire surface of the graphite particles can be more suitably coated with the negative electrode dispersant. Thereby, the dispersibility of the graphite particles in the negative electrode solvent can be further improved.

According to the present invention, by improving the dispersibility of graphite particles contained in the negative electrode mixture paste into the negative electrode solvent, deterioration in the coatability of the negative electrode mixture paste can be suppressed.

FIG. 1 is a perspective view of a cell battery of a lithium ion secondary battery according to the present embodiment. FIG. 2 is an exploded view of a part of the electrode body of the present embodiment. FIG. 2 is a schematic diagram showing a state in which a negative electrode active material and a negative electrode dispersant are kneaded in a first step of a conventional negative electrode mixture paste manufacturing process. FIG. 4 is a schematic diagram continuing from FIG. 3 and showing a state in which a negative electrode binder is added in the second step. FIG. 2 is a schematic diagram showing a state in which a negative electrode active material and a negative electrode dispersant are kneaded in the first step of the manufacturing process of the negative electrode mixture paste of the present embodiment. FIG. 6 is a schematic diagram continuing from FIG. 5 and showing a state in which a negative electrode binder is added in the second step. FIG. 7 is a schematic diagram continuing from FIG. 6 and showing a state in which a negative electrode dispersant is further added in the second step.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.
[Lithium ion secondary battery]
As shown in FIG. 1, a lithium ion secondary battery 10, which is an example of a nonaqueous secondary battery, is configured as a cell battery. After a plurality of lithium ion secondary batteries 10 are stacked and sealed in a resin case or the like, a control device, a measuring device, etc. are attached to the battery pack, and the battery pack is used as a vehicle battery pack. A battery pack including the lithium ion secondary battery 10 is used in a hybrid vehicle or an electric vehicle.

The lithium ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of metal such as aluminum alloy. The lithium ion secondary battery 10 is configured as a sealed battery case by attaching a lid 12 to a battery case 11.

The lid body 12 is provided with two external terminals 13A and 13B. External terminals 13A and 13B are used for charging and discharging power. The electrode body 20 is housed inside the battery case 11 . The positive electrode side current collecting portion 20A, which is the positive electrode side end of the electrode body 20, is electrically connected to the positive electrode external terminal 13A via the positive electrode side current collecting member 14A. The negative electrode side current collecting part 20B, which is the negative electrode side end of the electrode body 20, is electrically connected to the negative electrode external terminal 13B via the negative electrode side current collecting member 14B. Further, a non-aqueous electrolyte is injected into the battery case 11 from an injection hole (not shown).

As shown in FIG. 2, the electrode body 20 is a flat wound body obtained by winding a laminate in which a long positive electrode plate 21 and a negative electrode plate 24 are laminated with a separator 27 in between. In the laminate before winding, the positive electrode plate 21, the separator 27, the negative electrode plate 24, and the separator 27 are laminated in this order so that the longitudinal directions of the positive electrode plate 21 and the negative electrode plate 24 coincide.

[Positive plate]
The positive electrode plate 21 includes a sheet-like positive electrode base material 22 formed in an elongated shape, and positive electrode mixture layers 23 provided on both sides of the positive electrode base material 22. The positive electrode plate 21 is manufactured by kneading the materials constituting the positive electrode mixture layer 23 to prepare a positive electrode mixture paste, and then applying the positive electrode mixture paste to the positive electrode base material 22 and drying it. The positive electrode base material 22 functions as a current collector in the positive electrode. As the positive electrode base material 22, a thin film made of aluminum or an alloy containing aluminum as a main component is used.

At one end of the positive electrode plate 21 in the transverse direction, a connecting portion 22A is provided where the positive electrode base material 22 is exposed without the positive electrode mixture layer 23 formed thereon. In the state of the wound body, the connecting portion 22A has opposing surfaces pressed against each other to constitute the positive electrode side current collecting portion 20A.

The positive electrode mixture paste, which is the material of the positive electrode mixture layer 23, includes a positive electrode active material, a positive electrode conductive material, a positive electrode solvent, and a positive electrode binder. The positive electrode active material is a material that can insert and release lithium ions, and for example, lithium cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickel oxide (LiNiO ₂ ), etc. can be used. . Alternatively, a material in which LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ are mixed in an arbitrary ratio may be used.

As the positive electrode conductive material, for example, carbon black such as acetylene black and Ketjen black, and graphite are used. As the positive electrode solvent, for example, NMP (N-methyl-2-pyrrolidone) solution is used. As the positive electrode binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, or carboxymethyl cellulose (CMC) is used.

[Negative electrode plate]
The negative electrode plate 24 includes a sheet-like negative electrode base material 25 formed in an elongated shape, and negative electrode mixture layers 26 provided on both surfaces of the negative electrode base material 25. The negative electrode plate 24 is manufactured by kneading the materials constituting the negative electrode mixture layer 26 to prepare a negative electrode mixture paste, and then applying the negative electrode mixture paste to the negative electrode base material 25 and drying it. The negative electrode base material 25 functions as a current collector in the negative electrode. As the negative electrode base material 25, a thin film made of copper or an alloy containing copper as a main component can be used.

A connecting portion 25A in which the negative electrode base material 25 is exposed without forming the negative electrode mixture layer 26 is provided at one end of the negative electrode plate 24 in the lateral direction. In the state of the wound body, the connecting portion 25A has opposing surfaces pressed against each other to constitute the negative electrode side current collecting portion 20B.

The negative electrode mixture layer 26 is provided on the surface of the negative electrode base material 25. The negative electrode mixture paste, which is the material of the negative electrode mixture layer 26, includes a negative electrode active material, a negative electrode dispersant, a negative electrode solvent, a negative electrode binder, and the like. In this embodiment, water is used as the negative electrode solvent.

The negative electrode active material is a material capable of inserting and releasing lithium ions, and is, for example, graphite such as natural graphite or artificial graphite. In this embodiment, powdered graphite is used as the negative electrode active material. General graphite has hydrophilic groups such as carboxy groups and hydroxy groups as functional groups present on its particle surface. In the vicinity of the functional groups on the graphite particle surface, the hydrophobicity decreases, so that the adsorption of the negative electrode dispersant onto the graphite particle surface decreases. In this embodiment, graphite whose surface functional groups have been removed by surface treatment is used as the negative electrode active material in order to enhance adsorption of the negative electrode dispersant onto the surface of graphite particles. Specifically, the graphite used in this embodiment is heat-treated in a high-temperature environment of an inert gas atmosphere such as argon to remove functional groups present on the surface of graphite particles.

According to the inventors' investigation, the ratio O _C [%] of the amount of oxygen element to the amount of carbon element was 4.5% in graphite without surface treatment to remove surface functional groups. . Further, the ratio O _C [%] of the amount of oxygen element to the amount of carbon element in a state where the surface functional groups of the graphite particles were completely removed by the surface treatment was 0.5%. Therefore, it is thought that about 0.5% of oxygen in a form other than the surface functional group exists in the graphite particles, like the oxygen contained inside the graphite particles. Note that the amount of oxygen element relative to the amount of carbon element in graphite can be determined by a known analytical method, for example, X-ray photoelectron spectroscopy (XPS).

In this embodiment, graphite as the negative electrode active material has a ratio O _C [%] of the amount of oxygen element to the amount of carbon element of 3% or less, preferably less than 1%, more preferably 0.7% or less, and most preferably It is 0.5% or less. If the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is 3% or less, the negative electrode dispersant can be easily adsorbed on the surface of the graphite particles. In particular, if the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is less than 1%, the portion of the entire surface of the graphite particle whose hydrophobicity is reduced due to the presence of the functional group is sufficiently small. Therefore, the entire surface of the graphite particles can be more suitably coated with the negative electrode dispersant.

The negative electrode dispersant coats the surface of the negative electrode active material to form an interface with the negative electrode solvent, thereby increasing the dispersibility of the negative electrode active material in the negative electrode solvent. The negative electrode dispersant is a water-soluble polymeric material that has adsorption properties to graphite, which is a negative electrode active material. The negative electrode dispersant is, for example, carboxymethyl cellulose (CMC). Since CMC has a hydrophilic group and a hydrophobic group as its functional groups, it has an adsorption property for graphite, which is a negative electrode active material, and an affinity for water, which is a negative electrode solvent.

The negative electrode binder increases the binding force between particles of the negative electrode active material. The negative electrode binder is a water-soluble polymer material, such as styrene-butadiene rubber (SBR). SBR is a non-polar polymer material.

[Separator]
The separator 27 prevents contact between the positive electrode plate 21 and the negative electrode plate 24 and holds the nonaqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the ends of the separator 27 toward the center.

The separator 27 is a nonwoven fabric made of polypropylene or the like. As the separator 27, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, a porous polyvinyl chloride membrane, an ion conductive polymer electrolyte membrane, etc. can be used.

[Nonaqueous electrolyte]
A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. can be used. Supporting salts include LiPF ₆ , LiBF ₄ , LiClO _{4 , LiAsF 6 ,} LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiC(CF ₃ SO ₂ ) ₃ , LiI One or more kinds of lithium compounds (lithium salts) selected from the following can be used.

In this embodiment, ethylene carbonate is employed as the nonaqueous solvent. Lithium bisoxalate borate (LiBOB) as a lithium salt as an additive is added to the non-aqueous electrolyte. For example, LiBOB is added to the nonaqueous electrolyte so that the concentration of LiBOB in the nonaqueous electrolyte is 0.001 to 0.1 [mol/L].

[Operation of embodiment]
First, with reference to FIGS. 3 and 4, a conventional manufacturing process for negative electrode mixture paste will be described.
As shown in FIG. 3, in the conventional negative electrode mixture paste manufacturing process, first, a negative electrode active material 31 and a negative electrode dispersant 32 are kneaded, and then water (not shown) as a negative electrode solvent is added. A first step of producing one kneaded material 30A is performed.

The negative electrode active material 31 is, for example, graphite particles. The negative electrode active material 31 has a surface functional group 31A such as a hydroxy group or a carboxy group on its surface. In the vicinity of the surface functional group 31A on the surface of the negative electrode active material 31, hydrophobicity is reduced due to the presence of the surface functional group 31A.

The negative electrode dispersant 32 is, for example, CMC. The negative electrode dispersant 32 exists in two states: a coated body 32A that coats the particle surface of the negative electrode active material 31, and a free form 32B that is liberated in the negative electrode solvent.

The coating 32A adsorbs onto the particle surface of the negative electrode active material 31 with its hydrophobic groups, and forms an interface with water, which is a negative electrode solvent, with its hydrophilic groups. In the vicinity of the surface functional group 31A of the negative electrode active material 31, although the surface of the negative electrode active material 31 itself is hydrophobic, the presence of the surface functional group 31A reduces its hydrophobicity. Since the negative electrode dispersant 32 has larger particles than the surface functional group 31A, its adsorption to the negative electrode active material 31 decreases as the hydrophobicity decreases due to the surface functional group 31A. Therefore, when the surface functional group 31A exists in the negative electrode active material 31, it is difficult to uniformly cover the entire surface of the negative electrode active material 31 with the negative electrode dispersant 32, and the surface of the negative electrode active material 31 is not covered with the negative electrode dispersant 32. There are many parts. In this case, the dispersibility of the negative electrode active material 31 in water, which is the negative electrode solvent, deteriorates, causing dilatancy in the negative electrode mixture paste, which deteriorates the applicability of the negative electrode mixture paste to the negative electrode base material.

The free body 32B is the surplus negative electrode dispersant 32 in a state in which the negative electrode dispersant 32 present as the covering body 32A is saturated. The free body 32B has a function of increasing the viscosity of the negative electrode mixture paste. In the conventional kneading process of negative electrode mixture paste, the negative electrode dispersant 32 is mixed in an amount necessary to coat the particle surface of the negative electrode active material 31 and an amount necessary to adjust the viscosity of the negative electrode mixture paste. are kneaded at once.

As shown in FIG. 4, after the first step, a second step is performed in which a negative electrode binder 33 is added to the first kneaded material 30A produced in the first step to produce a second kneaded material 30B. be exposed. The negative electrode binder 33 contributes to binding of particles of the negative electrode active material 31 to each other. The negative electrode binder 33 is a non-polar polymeric material, and an example is SBR.

The negative electrode binder 33 added to the first kneaded material 30A is adsorbed on the particle surface of the negative electrode active material 31 via the negative electrode dispersant 32, and is also adsorbed on the particle surface of the negative electrode active material 31. It is also adsorbed to areas not covered by the agent 32. The part of the particle surface of the negative electrode active material 31 covered with the negative electrode dispersant 32 has high polarity due to the hydrophilic groups that the negative electrode dispersant 32 has. On the other hand, the part of the particle surface of the negative electrode active material 31 that is not covered with the negative electrode dispersant 32 has polarity due to the presence of the surface functional group 31A, but has lower polarity than the part covered with the negative electrode dispersant 32. In addition, since the negative electrode binder 33 has smaller particles and lower polarity than the negative electrode dispersant 32, even if the surface functional group 31A is present, it is adsorbed on the surface of the negative electrode active material 31 itself. easy to be Therefore, the negative electrode binder 33 is likely to segregate on the part of the particle surface of the negative electrode active material 31 that is not covered with the negative electrode dispersant 32, which is a part with relatively low polarity. In this case, on the particle surface of the negative electrode active material 31, there is a part where the negative electrode binder 33 is insufficient due to the segregation of the negative electrode binder 33, so the binding force between the particles of the negative electrode active material 31 is reduced in that part. state.

Further, the negative electrode binder 33 added to the first kneaded material 30A is adsorbed not only on the particle surface of the negative electrode active material 31 but also on the educts 32B. The negative electrode binder 33 adsorbed on the free body 32B does not contribute to binding of the particles of the negative electrode active material 31 to each other. In other words, the free body 32B adsorbs a part of the negative electrode binder 33 added in the second step, reducing the amount of the negative electrode binder 33 that contributes to binding between particles of the negative electrode active material 31. let

Therefore, in the conventional negative electrode mixture paste manufacturing process, in order to ensure sufficient binding force between the particles of the negative electrode active material 31, a portion of the added negative electrode binder 33 is adsorbed to the free substances 32B. Therefore, it was necessary to increase the amount of negative electrode binder 33 added. On the other hand, since the negative electrode binder 33 is a resistor without conductivity, the internal resistance of the lithium ion secondary battery 10 is increased by the amount of the negative electrode binder 33 in the negative electrode mixture paste.

In addition, in the manufacturing process of the conventional lithium ion secondary battery 10, the second kneaded material 30B generated in the second step is applied to the negative electrode base material 25 as a negative electrode mixture paste. Thereafter, the negative electrode mixture paste coated on the negative electrode base material 25 is dried and press-molded, thereby forming the negative electrode mixture layer 26. Then, the negative electrode plate 24 is manufactured by cutting the negative electrode base material 25 into an arbitrary size.

Next, the manufacturing process of the negative electrode mixture paste of this embodiment will be described with reference to FIGS. 5 to 7.
As shown in FIG. 5, in the manufacturing process of the negative electrode mixture paste of this embodiment, first, the negative electrode active material 41 and the negative electrode dispersant 42 are kneaded, and then water (not shown) as a negative electrode solvent is added. A first step of producing the first kneaded material 40A is performed.

The negative electrode active material 41 used in this embodiment is graphite particles whose surface functional groups have been removed by surface treatment. Specifically, the negative electrode active material 41 used is one in which the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is 3.0% or less. In addition, in the negative electrode active material 41, the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is preferably less than 1%, more preferably 0.7% or less, and more preferably 0.5% or less. More preferred.

The negative electrode dispersant 42 is a water-soluble polymeric material that has adsorption properties to graphite, and in this embodiment, CMC is used. The negative electrode dispersant 42 exists as a coating 42A that coats the particle surface of the negative electrode active material 41. The coating 42A adsorbs onto the particle surface of the negative electrode active material 41 with its hydrophobic groups, and forms an interface with water, which is a negative electrode solvent, with its hydrophilic groups.

In this embodiment, since graphite particles from which functional groups on the particle surface have been removed are used as the negative electrode active material 41, a decrease in hydrophobicity on the surface of the negative electrode active material 41 is suppressed. Therefore, the entire particle surface of the negative electrode active material 41 can be uniformly coated with the negative electrode dispersant 42. As a result, by improving the dispersibility of the negative electrode active material 41 in the negative electrode solvent, deterioration in the coating properties of the negative electrode mixture paste can be suppressed.

In this embodiment, the negative electrode dispersant 42 is added in two steps: a first step and a second step, which will be described later. In the first step, a first amount W _CMC of the negative electrode dispersant 42 is added to the negative electrode dispersant 42 in an amount that can be adsorbed onto the particle surface of the negative electrode active material 41 . In other words, the first amount W _CMC is such an amount that the entire particle surface of the negative electrode active material 41 can be sufficiently covered and the negative electrode dispersant 42 in a free state in the negative electrode solvent is not present as much as possible.

The first amount W _CMC is, for example, 0.18% or more and 0.42% or less in mass ratio with respect to the added amount W _C of the negative electrode active material 41. By adding the negative electrode dispersant 42 in the above range as the first amount W _CMC , the negative electrode dispersant 42 can cover the entire particle surface of the negative electrode active material 41 and is released without being adsorbed to the particle surface of the negative electrode active material 41. 42 can be reduced. Specifically, for the first quantity W _CMC , a value calculated using the following equations (1) and (2) can be used.

Each parameter in equations (1) and (2) will be explained below. S _C represents the specific surface area of the negative electrode active material 41. The specific surface area _SC of the negative electrode active material 41 can be determined by a known measurement method, for example, a gas adsorption method. The specific surface area _SC of the negative electrode active material 41 used in this embodiment is, for example, 6.3 m ² /g or more and 7.6 m ² /g or less.

_WC represents the amount of negative electrode active material 41 added. The amount W _C of the negative electrode active material 41 added is arbitrarily determined depending on the required amount of the negative electrode mixture paste. _MCMC represents a representative value of the molecular weight of CMC. The molecular weight M _CMC [g/mol] of CMC used in this embodiment is, for example, 300,000 or more and 600,000 or less, preferably 500,000.

S _CMC represents the area per molecule of CMC. The area S _CMC per molecule of CMC can be calculated using, for example, molecular model simulation. The area S _CMC per molecule of CMC uses, for example, any value from 1.0×10 ⁻¹⁵ m ² to 2.0×10 ⁻¹⁵ m ² .

X _O is a correction coefficient according to the ratio O _C [%] of the amount of oxygen element to the amount of carbon element. When the surface functional groups remain on the negative electrode active material 41, the amount of the negative electrode dispersant 42 adsorbed onto the surface of the negative electrode active material 41 decreases due to the presence of the surface functional groups. Therefore, by increasing the amount of negative electrode dispersant 42 added according to the ratio O _C [%] of the amount of oxygen element to the amount of carbon element using the correction coefficient X _O , the amount of negative electrode dispersant 42 adsorbed on the negative electrode active material 41 Correction is performed to increase the amount of and improve the dispersibility of the negative electrode active material 41. The correction coefficient X _O is calculated from the above equation (2). Note that the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is assumed to be 0.5% or more and 4.5% or less.

X _CMC is a correction coefficient for correcting variations in the molecular weight of CMC actually added. The correction coefficient X _CMC is set, for example, to a value of 0.6 or more and 1.4 or less. In addition, when the average molecular weight of CMC actually added can be calculated in advance, it is not necessary to substitute the average molecular weight of CMC as the molecular weight M _CMC of CMC and perform correction using the correction coefficient X _CMC .

As shown in FIG. 6, in the second step performed after the first step, a negative electrode binder 43 is added to the first kneaded material 40A produced in the first step to produce a second kneaded material 40B. be done. The negative electrode binder 43 contributes to binding of particles of the negative electrode active material 41 to each other. The negative electrode binder 43 is a water-soluble, non-polar polymer material, and an example is SBR.

The negative electrode binder 43 added to the first kneaded material 40A is adsorbed onto the particle surface of the negative electrode active material 41 via the negative electrode dispersant 42. The particle surface of the negative electrode active material 41 is in a state where the entire surface is coated with the negative electrode dispersant 42 in the first step, that is, a state where the particle surface has uniform polarity as a whole. Therefore, segregation of the negative electrode binder 43 on the particle surface of the negative electrode active material 41 is suppressed, and the negative electrode binder 43 is uniformly dispersed over the entire particle surface of the negative electrode active material 41 via the negative electrode dispersant 42. Thereby, it is possible to suppress a decrease in the binding force between particles of the negative electrode active material 41 due to segregation of the negative electrode binder 43.

Further, in the first step of the present embodiment, the amount of the negative electrode dispersant 42 added is adjusted so that the negative electrode dispersant 42 in a free state does not exist in the negative electrode solvent as much as possible. Therefore, compared to the conventional manufacturing process, the amount of negative electrode binder 43 added can be reduced by the amount of negative electrode binder 43 that is adsorbed to negative electrode dispersant 42 in a free state. As a result, the battery capacity of the lithium ion secondary battery 10 can be increased and the internal resistance can be reduced.

Specifically, the amount of the negative electrode binder 43 added in the second step is 1.2 times the first amount W _CMC of the negative electrode dispersant 42 kneaded in the first step in terms of mass ratio. It is 1.6 times or less, more preferably 1.3 times or more and 1.5 times or less. By adding the negative electrode binder 43 in the above range, it is possible to sufficiently secure the binding force between the particles of the negative electrode active material 41 in the negative electrode mixture paste, and prevent the negative electrode binder 43 from being added in excess. The accompanying decrease in battery capacity of the lithium ion secondary battery 10 and increase in internal resistance can be suppressed. The amount of the negative electrode binder 43 added is, for example, 0.22% or more and 0.67% or less in mass ratio with respect to the amount W _C of the negative electrode active material 41 added.

As shown in FIG. 7, in the second step of the present embodiment, after the negative electrode binder 43 is added to the first kneaded material 40A, a negative electrode dispersant is added to the second kneaded material 40B. Add 42. In the second step, the negative electrode dispersant 42 added to the second kneaded material 40B exists as a liberated substance 42B in the negative electrode solvent. The free body 42B has a function of increasing the viscosity of the negative electrode mixture paste. In this embodiment, the second kneaded material 40B produced by the above procedure is used as a negative electrode mixture paste.

In the second step, a second amount of the negative electrode dispersant 42 is added, which is an amount necessary to adjust the negative electrode mixture paste to a desired viscosity. The second amount is selected as an arbitrary amount depending on the viscosity of the target negative electrode mixture paste. The second addition amount is, for example, 0.08% or more and 0.32% or less in mass ratio with respect to the addition amount _WC of the negative electrode active material 41.

In this embodiment, the negative electrode dispersant 42 necessary for coating the particle surface of the negative electrode active material 41 is added in the first step, and the negative electrode mixture is added after the negative electrode binder 43 is added in the second step. A negative electrode dispersant 42 necessary for adjusting the viscosity of the paste is added. Thereby, the amount of the free negative electrode dispersant 42 present when adding the negative electrode binder 43 can be reduced compared to the conventional manufacturing process while imparting the necessary viscosity to the negative electrode mixture paste.

Further, the negative electrode mixture paste produced in the above process is applied to the negative electrode base material 25. Thereafter, the negative electrode mixture paste coated on the negative electrode base material 25 is dried and press-molded, thereby forming the negative electrode mixture layer 26. Then, the negative electrode plate 24 is manufactured by cutting the negative electrode base material 25 into an arbitrary size.

[Effects of embodiment]
According to the above embodiment, the effects listed below can be obtained.
(1) By using graphite particles whose surface functional groups have been removed by surface treatment as the negative electrode active material 41, the negative electrode dispersant 42 can be easily adsorbed onto the entire surface of the negative electrode active material 41. As a result, the dispersibility of the negative electrode active material 41 in the negative electrode solvent can be improved, so that deterioration in the applicability of the negative electrode mixture paste to the negative electrode base material due to the occurrence of dilatancy in the negative electrode mixture paste can be suppressed.

(2) By covering the entire surface of the negative electrode active material 41 with the negative electrode dispersant 42, segregation of the negative electrode binder 43 onto the surface of the negative electrode active material 41 is suppressed. Thereby, the negative electrode binder 43 is uniformly adsorbed onto the entire surface of the negative electrode active material 41 via the negative electrode dispersant 42. As a result, a decrease in the binding force between particles of the negative electrode active material 41 due to segregation of the negative electrode binder 43 can be suppressed.

(3) In this embodiment, the negative electrode dispersant 42 necessary for coating the particle surface of the negative electrode active material 41 is added in the first step, and the negative electrode binder 43 is further added in the second step. A negative electrode dispersant 42 necessary for adjusting the viscosity of the negative electrode mixture paste is added. By adding the negative electrode dispersant 42 separately in the first step and the second step, the negative electrode binder 43 is added in the second step more than when adding the negative electrode dispersant 42 at once in the first step. At the same time, the amount of the negative electrode dispersant 42 that becomes free can be reduced. The amount of negative electrode binder 43 added can be reduced by the amount of negative electrode dispersant 42 in a free state. As a result, the battery capacity of the lithium ion secondary battery 10 can be increased and the internal resistance can be reduced.

(4) The first amount W _CMC , which is the amount added of the negative electrode dispersant 42 in the first step, is 0.18% or more and 0.42% or less in mass ratio with respect to the added amount W _C of the negative electrode active material 41. be. As a result, the entire surface of the negative electrode active material 41 can be covered with the negative electrode dispersant 42, and the amount of free negative electrode dispersant 42 that is present when the negative electrode binder 43 is added in the second step is reduced. can.

(5) The amount of the negative electrode binder 43 added in the second step is 1.2 times or more in mass ratio to the first amount W _CMC of the negative electrode dispersant 42 kneaded in the first step. It is less than twice that. As a result, it is possible to sufficiently secure the binding force between the particles of the negative electrode active material 41 in the negative electrode mixture paste, and to reduce the battery capacity of the lithium ion secondary battery 10 due to excessive addition of the negative electrode binder 43. It is possible to suppress the decrease in internal resistance and the increase in internal resistance.

(6) In the negative electrode active material 41, if the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is 3.0% or less, the hydrophobicity of the entire surface of the graphite particles is low due to the presence of surface functional groups. The part that has been removed will be sufficiently small. Therefore, in the first step, the entire surface of the graphite particles as the negative electrode active material 41 can be more suitably coated with the negative electrode dispersant 42. Thereby, the graphite particles can be suitably dispersed in the negative electrode solvent. Note that if the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is less than 1%, more preferably 0.7% or less, and still more preferably 0.5% or less, the above effect can be further enhanced. can.

[Example]
An embodiment of the present invention will be described below. Note that the examples do not limit the present invention.

First, in the first step, graphite as the negative electrode active material 41 and CMC as the negative electrode dispersant 42 were kneaded. The surface functional groups of the graphite were removed by surface treatment, and the ratio O _C [%] of the amount of oxygen element to the amount of carbon element was 3% or less. Further, the graphite had a specific surface area S _C of 6.3 m ² /g. CMC had an average molecular weight of about 500,000 [g/mol]. The first amount W _CMC , which is the amount of CMC added in the first step, was 0.3% by mass relative to the amount of graphite added. Thereafter, water was added as a negative electrode solvent to obtain a target solid content to prepare a first kneaded product 40A.

Next, in the second step, SBR as a negative electrode binder 43 was added to the first kneaded product 40A to produce a second kneaded product 40B. The amount of SBR added was 0.4% by mass relative to the amount of graphite added. Furthermore, CMC was added to the second kneaded material 40B to prepare a negative electrode mixture paste. The second amount, which is the amount of CMC added in the second step, was 0.1% by mass relative to the amount of graphite added. Thereafter, the produced negative electrode mixture paste was applied to the negative electrode base material 25, and after drying, it was pressed to produce the negative electrode plate 24.

In this example, the amount of SBR used could be reduced by 4% to 68% compared to the conventional negative electrode mixture paste manufacturing method. Furthermore, when peel strength measurements were performed on the produced negative electrode plate 24, it was confirmed that it had the same peel strength as the negative electrode plate 24 using a negative electrode mixture paste produced by a conventional manufacturing method. Ta.

Note that the above embodiment can be modified and implemented as follows.
- Graphite as the negative electrode active material 41 is not limited to one in which the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is 3.0% or less. For example, since the ratio O _C [%] of the amount of oxygen element to the amount of carbon element in graphite without surface treatment is 4.5%, the ratio O _C [%] of the amount of oxygen element to the amount of carbon element is If it is smaller than 4.5%, the above effects (1) and (2) can be obtained.

- The amount of the negative electrode binder 43 added in the second step is 1.2 times or more and 1.6 times or less in mass ratio with respect to the first amount W _CMC of the negative electrode dispersant 42 kneaded in the first step. Not limited to range. For example, in order to further increase the binding force between the particles of the negative electrode active material 41 in the negative electrode mixture paste, the amount of the negative electrode binder 43 added may be changed to the amount of the negative electrode dispersant 42 kneaded in the first step. The mass ratio may be more than 1.6 times the amount W _CMC .

- The first amount W _CMC , which is the amount added of the negative electrode dispersant 42 in the first step, is in the range of 0.18% or more and 0.42% or less in terms of mass ratio with respect to the added amount W _C of the negative electrode active material 41. Not limited. In the case of adding the negative electrode dispersant 42 separately in the first step and the second step, for example, the first amount W _CMC is 0.42 in mass ratio to the added amount W _C of the negative electrode active material 41. It may be more than %. Even in this case, when adding the negative electrode binder 43, the amount of the released negative electrode dispersant 42 can be reduced by the amount of the negative electrode dispersant 42 added in the second step. In other words, the first amount W _CMC is larger than the amount necessary to cover the negative electrode active material 41, and the amount necessary to cover the negative electrode active material 41 and the amount necessary for adjusting the viscosity of the negative electrode mixture paste. If the amount is less than the sum of the above amounts, the effect of (3) above can be obtained.

- An example has been described in which the values calculated by equations (1) and (2) are used as the first quantity W _CMC . Not limited to this, for example, from the viewpoint of more reliably covering the negative electrode active material 41 with the negative electrode dispersant 42, the negative electrode dispersant in the first step is Correction may be made to increase the amount of 42 added.

- In the first step, the negative electrode dispersant 42 may be added at once in an amount necessary to coat the negative electrode active material 41 and in an amount necessary to adjust the viscosity of the negative electrode mixture paste. In this case, the negative electrode dispersant 42 is not added in the step after adding and stirring the negative electrode binder 43 in the second step. Even in this case, since graphite that has been surface-treated to remove surface functional groups is used as the negative electrode active material 41, the effects (1) and (2) above can be obtained.

- The electrode body 20 is an example of a wound body in which a laminate in which a positive electrode plate 21 and a negative electrode plate 24 are laminated with a separator 27 interposed therebetween is wound. It may be a laminate in which the laminates are alternately laminated with the laminates interposed therebetween.

- The lithium ion secondary battery 10 may be installed in an automatic transport machine, a special vehicle for cargo handling, an electric vehicle, a hybrid vehicle, etc., as well as a computer or other electronic equipment, and may be used in other systems. It may be configured. For example, it may be installed in a moving body such as a ship or an aircraft, and is a power supply system that supplies power from a power plant to a building, home, etc. where a secondary battery is installed via a substation, etc. Good too.

DESCRIPTION OF SYMBOLS 10... Lithium ion secondary battery 11... Battery case 12... Lid body 13A, 13B... External terminal 20... Electrode body 21... Positive electrode plate 22... Positive electrode base material 23... Positive electrode mixture layer 24... Negative electrode plate 25... Negative electrode base material 26 ...Negative electrode mixture layer 27...Separator 30A, 40A...First kneaded product 30B, 40B...Second kneaded product 31, 41...Negative electrode active material 31A...Surface functional group 32, 42...Negative electrode dispersant 32A, 42A...Coating Body 32B, 42B... Free body 33, 43... Negative electrode binder

Claims (6)

A step of generating a negative electrode mixture paste using a negative electrode active material, a negative electrode dispersant, a negative electrode solvent, and a negative electrode binder, and forming a negative electrode mixture layer by applying the negative electrode mixture paste to a negative electrode base material. A method for manufacturing a non-aqueous secondary battery, the method comprising:
The step of generating the negative electrode mixture paste includes:
After kneading the negative electrode active material, which is graphite that has been surface-treated to remove surface functional groups, and the negative electrode dispersant, which has adsorption properties to the surface of the graphite from which the surface functional groups have been removed. , a first step of adding the negative electrode solvent to produce a kneaded product;
a second step of adding the negative electrode binder to the kneaded material produced in the first step and producing the negative electrode mixture paste from the kneaded material to which the negative electrode binder has been added. ,
The negative electrode dispersant contained in the negative electrode mixture paste includes a first amount of the negative electrode dispersant adsorbed to the negative electrode active material, and a second amount of the negative electrode dispersant for adjusting the viscosity of the negative electrode mixture paste. an agent;
In the first step, the first amount of the negative electrode dispersant and the negative electrode active material are kneaded, and then the negative electrode solvent is added;
In the second step, the second amount of the negative electrode dispersant is further added to the kneaded material to which the negative electrode binder has been added.
A method for manufacturing a non-aqueous secondary battery, characterized by: The method for manufacturing a non-aqueous secondary battery according to claim 1 , wherein the negative electrode dispersant is carboxymethyl cellulose. The method for manufacturing a non-aqueous secondary battery according to claim 2 , wherein the first amount is 0.18% or more and 0.42% or less based on the mass of the negative electrode active material. The method for manufacturing a non-aqueous secondary battery according to claim 3 , wherein the negative electrode binder is styrene-butadiene rubber. The nonaqueous binder according to claim 4 , wherein the mass of the negative electrode binder added in the second step is 1.2 times or more and 1.6 times or less relative to the first amount. Method of manufacturing next battery. The method for manufacturing a nonaqueous secondary battery according to any one of claims 1 to 5 , wherein the negative electrode active material has a ratio of an amount of oxygen element to an amount of carbon element of less than 1%.

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