The active material may be, for example, spherical, lumpy, flake-shaped, or columnar. The active material can have any size. The active material may have, for example, a D50 of 1 μm to 30 μm or a D50 of 5 μm to 20 μm.

The active material may be, for example, a positive electrode active material. The positive electrode active material can store and release lithium (Li) ions at a higher potential than that of a negative electrode active material. The positive electrode active material can include any component. The positive electrode active material may include, for example, at least one selected from the group consisting of LiCoO₂, LiNiO₂, LiMnO₂, LiMn₂O₄, Li(NiCoMn)O₂, Li(NiCoAl)O₂, and LiFePO₄. For example, “(NiCoMn)” in “Li(NiCoMn)O₂” indicates that the total composition ratio in parentheses is 1. The amount of individual components is freely selected as long as the total is 1. Li(NiCoMn)O₂may include, for example, Li(Ni_1/3Co_1/3Mn_1/3)O₂, Li(Ni_0.5Co_0.2Mn_0.3)O₂, Li(Ni_0.8Co_0.1Mn_0.1)O₂.

The negative electrode active material can store and release Li ions at a lower potential than that of the positive electrode active material. The negative electrode active material can include any component. The negative electrode active material may include, for example, at least one selected from the group consisting of graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, and Li₄Ti₅O₁₂.

The binder may be soluble or insoluble in the liquid material. The blending amount of the binder may be, for example, 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the active material. The binder can include any component. The binder may include, for example, at least one selected from the group consisting of PVdF, PTFE, PVdF-HFP, SBR, CMC, and PAA.

The blending amount of the conductive material may be, for example, 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the active material. The conductive material can include any component. The conductive material may include, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fibers, carbon nanotubes, and graphene flakes. The carbon black may include, for example, at least one selected from the group consisting of acetylene black, furnace black, channel black, and thermal black.

(a2) Roll Forming

The present manufacturing method may include processing the wet powder into an active material layer by roll forming.

FIG. 5 is a schematic view illustrating an example of a film forming apparatus. A film forming apparatus 300 can process a wet powder 2 into an active material layer 20. The film forming apparatus 300 includes a first roll 301, a second roll 302, and a third roll 303. Each roll rotates in the direction of the arrow. Rotation axes of the rolls are parallel to each other. When the rotation speed of the first roll 301 is ω1, the rotation speed of the second roll 302 is ω2, and the rotation speed of the third roll 303 is ω3, for example, the relationship of “ω1<ω2<ω3” may be satisfied.

A gap AB is formed between the first roll 301 and the second roll 302. The wet powder 2 is supplied to the gap AB. In the gap AB, the wet powder 2 is compacted and spread to form the active material layer 20 (sheet). The active material layer 20 may have a thickness of, for example, 10 μm to 500 μm, or may have a thickness of 50 μm to 200 μm.

(a3) Transfer

The present manufacturing method may include placing the active material layer 20 on the surface of the electrode current collector 10. For example, the film forming apparatus 300 may transfer the active material layer 20 to the electrode current collector 10. A gap BC is formed between the second roll 302 and the third roll 303. The second roll 302 conveys the active material layer 20 to the gap BC. The third roll 303 conveys the electrode current collector 10 to the gap BC.

In the gap BC, the active material layer 20 is rubbed against the surface of the electrode current collector 10. As a result, the active material layer 20 adheres to the surface of the electrode current collector 10. That is, the active material layer 20 is arranged on the surface of the electrode current collector 10.

FIG. 6 is an image illustrating an example of the end portion shape. FIG. 6 illustrates a portion corresponding to the region VI of FIG. 5. In the method of forming the active material layer 20 with the wet powder, the shape of the end portion in a width direction (X-axis direction) tends to be disordered.

FIG. 7 is a second schematic cross-sectional view illustrating an electrode manufacturing process. The active material layer 20 is formed so as to include a first portion 20a and a second portion 20b. The second portion 20b is adjacent to the first portion 20a. The first portion 20a covers the adhesive layer 12 (first region 11a). The second portion 20b covers the second region 11b. The active material layer 20 may be formed so as to cover the entire surface of the electrode current collector 10, for example.

(b) Formation of Groove Portion

FIG. 8 is a third schematic cross-sectional view illustrating an electrode manufacturing process. The present manufacturing method includes forming a groove portion 21 on the surface of the active material layer 20. The groove portion 21 can be formed, for example, by embossing. That is, the groove portion 21 (recess portion) may be formed by pressing a convex shape against the surface of the active material layer 20. For example, an embossed roll may be used.

After forming the groove portion 21, the active material layer 20 may be dried. The active material layer 20 can be dried by any method. For example, a hot air drying oven may be used.

The groove portion 21 can function as, for example, a flow path for the electrolytic solution. It is expected that the formation of the groove portion 21 will improve the battery performance (for example, cycle characteristics). The cross-sectional shape of the groove portion 21 is freely selected. The cross-sectional shape of the groove portion 21 may be rectangular, U-shaped, or V-shaped. The groove portion 21 may have a depth of, for example, 10 μm to 150 μm. The ratio of the depth of the groove portion 21 to the thickness of the active material layer 20 may be, for example, 0.1 to 0.9 or 0.3 to 0.7.

The groove portion 21 can be formed in each of the first portion 20a and the second portion