JP7024480B2 - Manufacturing method of negative electrode for lithium ion battery - Google Patents

Description

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

Japanese Unexamined Patent Publication No. 2017-228398 (Patent Document 1) discloses that a negative electrode is manufactured by passing a wet powder through a gap between a pair of rotating rolls.

Japanese Unexamined Patent Publication No. 2017-228398

Generally, a negative electrode for a lithium ion battery (hereinafter, may be abbreviated as "negative electrode") is manufactured by applying a suspension. That is, the negative electrode is manufactured by applying the suspension to the surface of the base material and drying it. For example, a suspension is formed by dispersing the negative electrode active material (particles) in an aqueous solution of carboxymethyl cellulose (CMC). In the art, the suspension is also referred to as "slurry", "paste" or the like.

CMC is a water-soluble polymer. In the suspension, CMC is dissolved in water. Therefore, it is considered that a thin and uniform CMC film is formed on the surface of the negative electrode active material in the negative electrode manufactured by the suspension. The CMC coating is considered to suppress excessive contact between the negative electrode active material and the electrolytic solution. It is considered that a predetermined cycle durability can be obtained by this. However, the suspension contains a large amount of water. When a negative electrode is manufactured from a suspension, the drying cost tends to increase. In order to reduce the drying cost, it is conceivable to use a wet powder instead of the suspension.

Wet powder contains a small amount of water. Water is dispersed in the wet powder as droplets. Since the amount of water in the wet powder is small, a part of CMC may not be dissolved in water and may exist as a solid (powder). CMC wet with water tends to aggregate. Since CMC tends to aggregate, it is considered difficult to form a thin and uniform CMC film on the surface of the negative electrode active material in the negative electrode manufactured by the wet powder. Therefore, it is considered difficult to maintain a predetermined cycle durability.

An object of the present disclosure is to produce a negative electrode having excellent cycle durability by using a wet powder.

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

The method for manufacturing a negative electrode for a lithium ion battery of the present disclosure includes at least the following (a) to (e).
(A) Prepare a wet powder.
(B) The negative electrode mixture layer is formed by passing the wet powder through the gap between the pair of rotating rolls.
(C) An aqueous solution of carboxymethyl cellulose is applied to the surface of the negative electrode mixture layer.
(D) An inorganic filler layer is formed on the surface of the negative electrode mixture layer.
(E) After forming the inorganic filler layer, the negative electrode mixture layer is dried to manufacture a negative electrode.
The aqueous solution of carboxymethyl cellulose has a viscosity of 1200 mPa · s or less.
The wet powder contains x% by weight of the negative electrode active material and y by weight of carboxymethyl cellulose. The aqueous solution of carboxymethyl cellulose contains z mass% of carboxymethyl cellulose.
x, y and z satisfy the relationship of x + y + z = 100 and z ≧ 0.2.

In the negative electrode manufacturing method of the present disclosure, after the negative electrode mixture layer is formed by the wet powder, the CMC aqueous solution is applied to the surface of the negative electrode mixture layer. As a result, it is expected that a thin and uniform CMC film will be formed on the surface of the negative electrode active material. Therefore, improvement in cycle durability is expected.

In the negative electrode manufacturing method of the present disclosure, an inorganic filler layer is formed on the surface of the negative electrode active material layer. The inorganic filler layer is also formed by applying the suspension. When the negative electrode mixture layer is formed by a suspension, it is difficult to apply the second suspension (inorganic filler layer) until the first suspension (negative electrode mixture layer) has been dried. be. Therefore, the drying operation is required at least twice.

Since the negative electrode mixture layer formed of the wet powder has a low water content, it is possible to apply the suspension on the negative electrode mixture layer in the state before drying. Therefore, according to the method for manufacturing a negative electrode of the present disclosure, it is considered that the drying operation is reduced at least once.

FIG. 1 is a flowchart showing an outline of a method for manufacturing a negative electrode for a lithium ion battery according to the present embodiment. FIG. 2 is a conceptual diagram showing an example of a method for forming a negative electrode mixture layer according to the present embodiment.

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

<Manufacturing method of negative electrode for lithium ion battery>
FIG. 1 is a flowchart showing an outline of a method for manufacturing a negative electrode for a lithium ion battery according to the present embodiment. The method for producing the negative electrode of the present embodiment is "(a) preparation of wet powder", "(b) formation of negative electrode mixture layer", "(c) application of CMC aqueous solution", and "(d) inorganic filler layer". Includes at least "formation" and "(e) drying".

<< (a) Preparation of wet powder >>
The method for producing a negative electrode of the present embodiment includes preparing a wet powder.

The wet powder can be prepared, for example, by a stirring granulation method. Wet powder can be prepared by mixing the negative electrode active material, CMC and water with, for example, a stirring granulator. The solid content ratio of the wet powder may be, for example, 60% by mass or more and 90% by mass or less. The solid content ratio indicates the mass ratio of components other than water. The negative electrode active material may be, for example, graphite, graphitizable carbon, non-graphitizable carbon, lithium titanate, or the like. One kind of negative electrode active material may be used alone. Two or more kinds of negative electrode active materials may be used in combination.

The wet powder is prepared to contain x% by weight of the negative electrode active material and y by weight of CMC. “X mass%” and “y mass%” indicate the mass ratio to the total of the negative electrode active material and CMC contained in the final product (negative electrode), respectively. x can be, for example, a value of 98-99. y can be, for example, a value of 0.4 to 0.8.

<< (b) Formation of negative electrode mixture layer >>
The method for manufacturing a negative electrode of the present embodiment includes forming a negative electrode mixture layer by passing a wet powder through a gap between a pair of rotating rolls.

FIG. 2 is a conceptual diagram showing an example of a method for forming a negative electrode mixture layer according to the present embodiment.
The roll coater 10 includes a first rotary roll 11, a second rotary roll 12, and a third rotary roll 13. The first rotating roll 11, the second rotating roll 12, and the third rotating roll 13 are arranged so that their axes of rotation are parallel to each other. The arrows drawn on each roll indicate the direction of rotation of each roll.

The hopper 14 supplies the wet powder 1 between the first rotating roll 11 and the second rotating roll 12. The wet powder 1 is formed into a layer in the gap between the first rotating roll 11 and the second rotating roll 12. That is, the negative electrode mixture layer 102 is formed by passing the wet powder 1 through the gap between the pair of rotating rolls. The third rotating roll 13 conveys the base material 101. The negative electrode mixture layer 102 is transferred to the surface of the base material 101. The base material 101 may be, for example, a copper (Cu) foil or the like.

<< (c) Application of CMC aqueous solution >>
The method for manufacturing a negative electrode of the present embodiment includes applying a CMC aqueous solution to the surface of the negative electrode mixture layer.

It is expected that a thin and uniform CMC film will be formed on the surface of the negative electrode active material by applying the CMC aqueous solution. The application method should not be particularly limited. The CMC aqueous solution can be applied by, for example, a slot die method, a gravure method, or the like.

Aqueous CMC solution can be prepared by dissolving CMC in water. The CMC aqueous solution is prepared to contain z mass% CMC. In this embodiment, x, y and z satisfy the relationship of x + y + z = 100 and z ≧ 0.2. z can be, for example, a value of 0.2 to 0.6.

The CMC aqueous solution has a viscosity of 1200 mPa · s or less. If the viscosity of the CMC aqueous solution exceeds 1200 mPa · s, the cycle durability may decrease. It is considered that when the viscosity of the CMC aqueous solution becomes high, it becomes difficult for the CMC aqueous solution to permeate into the negative electrode mixture layer, and the ratio of the negative electrode active material having no CMC coating becomes high. The viscosity of the CMC aqueous solution is measured by a general rotary rheometer. The measurement temperature is 20 ° C ± 5 ° C. The shear rate is 2s ^-1 . Viscosity is measured at least 3 times. At least three arithmetic means are adopted.

The viscosity of the CMC aqueous solution can be adjusted, for example, by the concentration of CMC, the shear rate at which CMC is dissolved in water, and the like. The CMC aqueous solution may have a viscosity of, for example, 1180 mPa · s or less. The CMC aqueous solution may have a viscosity of, for example, 950 mPa · s or less. The CMC aqueous solution may have a viscosity of, for example, 820 mPa · s or less. The CMC aqueous solution may have a viscosity of, for example, 460 mPa · s or more.

<< (d) Formation of inorganic filler layer >>
The method for manufacturing a negative electrode of the present embodiment includes forming an inorganic filler layer on the surface of the negative electrode mixture layer.

The inorganic filler layer is porous. The inorganic filler layer can be formed by coating the suspension. The inorganic filler layer contains an inorganic filler and a binder. Inorganic fillers should not be particularly limited. The inorganic filler may be, for example, alumina, boehmite, magnesia, titania, zirconia or the like. One kind of inorganic filler may be used alone. Two or more kinds of inorganic fillers may be used in combination. The binder may be, for example, an acrylic polymer or the like.

<< (e) Drying >>
The method for manufacturing a negative electrode of the present embodiment includes manufacturing a negative electrode by drying a negative electrode mixture layer after forming an inorganic filler layer.

For example, the negative electrode mixture layer is dried by hot air. The hot air temperature may be, for example, about 50 to 120 ° C. The time from the application of the CMC aqueous solution to the completion of drying (hereinafter, also referred to as “drying time”) is, for example, 10 seconds or more. The drying time may be 12 seconds or longer. When the drying time is 12 seconds or more, it is expected that the cycle durability will be improved. The drying time may be, for example, 14 seconds or less.

Hereinafter, examples of the present disclosure will be described. However, the following explanation does not limit the scope of claims.

<Manufacturing of negative electrodes for lithium-ion batteries>
<Example 1>
<< (a) Preparation of wet powder >>
Natural graphite was prepared as the negative electrode active material. Wet powder was prepared by mixing the negative electrode active material, CMC and water.

<< (b) Formation of negative electrode mixture layer >>
The negative electrode mixture layer 102 was formed by the roll coater 10 of FIG. 2. That is, the negative electrode mixture layer 102 was formed by passing the wet powder 1 through the gap between the pair of rotating rolls. The negative electrode mixture layer 102 was transferred to the surface of the base material 101 (Cu foil).

<< (c) Application of CMC aqueous solution >>
A 0.3 mass% CMC aqueous solution was prepared. The CMC aqueous solution has a viscosity of 1200 mPa · s. A CMC aqueous solution was applied to the surface of the negative electrode mixture layer.

<< (d) Formation of inorganic filler layer >>
An inorganic filler layer was formed on the surface of the negative electrode mixture layer.

<< (e) Drying >>
After the formation of the inorganic filler layer, the negative electrode mixture layer was dried. From the above, the negative electrode was manufactured. The time (drying time) from the application of the CMC aqueous solution to the completion of drying is 10 seconds.

<Examples 2 and 3>
As shown in Table 1 below, the negative electrode was manufactured in the same manner as in Example 1 except that the drying time was changed.

<Examples 4 to 7>
As shown in Table 1 below, a negative electrode was manufactured in the same manner as in Example 1 except that the viscosities of the y, z, and CMC aqueous solutions were changed.

<Comparative Example 1>
A negative electrode was manufactured in the same manner as in Example 1 except that the CMC aqueous solution was not applied.

<Comparative Examples 2 and 3>
As shown in Table 1 below, a negative electrode was manufactured in the same manner as in Example 1 except that the viscosity of the CMC aqueous solution was changed.

<Comparative Example 4>
As shown in Table 1 below, a negative electrode was manufactured in the same manner as in Example 1 except that the viscosities of the y, z, and CMC aqueous solutions were changed.

<Reference example>
By applying the suspension (paste), a negative electrode having the same composition as that of the negative electrode of Example 1 was produced.

<Evaluation>
A lithium ion battery containing each negative electrode obtained above was manufactured. The positive electrode active material is nickel cobalt lithium aluminate (also referred to as "NCA"). The composition of the positive electrode is "NCA: acetylene black: polyvinylidene fluoride = 94.4: 4.1: 1.5 (mass ratio)". The separator is a porous film made of polyethylene. The separator has a thickness of 15 μm.

The charge / discharge cycle was repeated 500 cycles. The capacity retention rate after 500 cycles was calculated. The results are shown in Table 1 below. It is considered that the higher the capacity retention rate, the better the cycle durability of the negative electrode.

As shown in Table 1 above, the examples in which the CMC aqueous solution has a viscosity of 1200 mPa · s or less and x, y and z satisfy the relationship of “x + y + z = 100 and z ≧ 0.2” satisfy such conditions. Cycle durability is improved as compared with the unsatisfied comparative example. It is considered that the coating of the CMC aqueous solution forms a thin and uniform CMC film on the surface of the negative electrode active material.

The embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The technical scope defined by the description of the scope of claims includes all changes within the meaning and scope equivalent to the scope of claims.

1 Wet powder, 10 roll coater, 11 1st rotation roll, 12 2nd rotation roll, 13 3rd rotation roll, 14 hopper, 101 base material, 102 negative electrode mixture layer.

Claims (1)

Preparing wet powder,
Forming a negative electrode mixture layer by passing the wet powder through a gap between a pair of rotating rolls.
Applying an aqueous solution of carboxymethyl cellulose to the surface of the negative electrode mixture layer,
Forming an inorganic filler layer on the surface of the negative electrode mixture layer,
And, after forming the inorganic filler layer, the negative electrode is manufactured by drying the negative electrode mixture layer.
Including at least
The aqueous solution of carboxymethyl cellulose has a viscosity of 1200 mPa · s or less and has a viscosity of 1200 mPa · s or less.
The wet powder contains x% by mass of the negative electrode active material and y% by mass of carboxymethyl cellulose, and the aqueous solution of carboxymethyl cellulose contains z by mass of carboxymethyl cellulose.
x, y and z satisfy the relationship of x + y + z = 100 , 0.4 ≦ y ≦ 0.8 and 0.2 ≦ z ≦ 0.6 .
A method for manufacturing a negative electrode for a lithium ion battery.

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