JP6981201B2 - Negative electrode manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a negative electrode included in a power storage device.

As an example of the power storage device, there is a lithium ion battery provided with a positive electrode and a negative electrode and capable of charging and discharging by moving lithium ions between the electrodes. Patent Document 1 discloses a method of manufacturing a negative electrode by doping an electrode (current collector) coated with a negative electrode active material with a lithium foil.

In Patent Document 1, the lithium foil attached to the resin film is superposed on the electrode, and in this state, pressure is applied from above the resin film to transfer the lithium foil to the electrode.

Japanese Unexamined Patent Publication No. 2016-105033

The resin film is peeled off from the lithium foil after the lithium foil is attached to the electrodes. However, if the lithium foil and the resin sheet are firmly attached to each other, the lithium foil may be peeled off together with the resin sheet. When the lithium foil is partially peeled off, the lithium foil on the electrode side is partially thinned or has holes.

An object of the present invention is to provide a method for manufacturing a negative electrode capable of reducing damage to a lithium foil.

A method for manufacturing a negative electrode to solve the above problems includes a layered sheet in which a base film made of stretched polytetrafluoroethylene and a lithium foil are laminated, an electrode material in which a current collector and a negative electrode active material layer are laminated, and an electrode material in which a current collector and a negative electrode active material layer are laminated. However, in the base film of the electrode composite in which the lithium foil and the negative electrode active material layer are bonded so as to face each other, a spraying step of spraying gas on the second surface opposite to the first surface in contact with the lithium foil. And a peeling step of peeling off the base film.

Stretched polytetrafluoroethylene (hereinafter referred to as "ePTFE") is a porous material having a large number of pores. According to this method, gas is sprayed from the side opposite to the lithium foil onto the base film of the electrode composite in which the layered sheet in which the base film made of ePTFE and the lithium foil are laminated and the electrode material are bonded to each other. The gas acts to float the base film from the lithium foil through the pores of the base film. As a result, the sticking between the base film and the lithium foil can be weakened. Therefore, when the base film is peeled off, the possibility that the lithium foil is peeled off from the electrode material together with the base film can be reduced, and damage to the lithium foil can be reduced.

The method for manufacturing the negative electrode is a process of arranging the layered sheet and the electrode material so that the lithium foil and the negative electrode active material layer face each other, and the layered sheet and the electrode material. The pressurizing device further comprises a pressurizing step of moving the pressurizing device relative to the layered sheet in the direction in which the fibrils of the base film extend, and the peeling step comprises the base in a direction different from the direction in which the fibrils extend. It is preferable to peel off the film.

The ePTFE obtained by uniaxially stretching polytetrafluoroethylene (hereinafter referred to as "PTFE") has a plurality of fibrils. The fibrils extend in the direction in which the PTFE is stretched, and are arranged at intervals in a direction different from the direction in which the PTFE is stretched. According to this method, in the pressurizing step, the pressurizing device and the layered sheet are relatively moved in the direction in which the fibril extends to pressurize. Further, in the peeling step, the base film is peeled off in the direction in which a plurality of fibrils are lined up at intervals from each other. Therefore, it is possible to increase the ratio of the slip state in which the peeling speed is high to the stick state in which the peeling speed is slow, and to cause a so-called stick-slip phenomenon to facilitate the peeling of the base film.

In the method for manufacturing a negative electrode, the layered sheet includes a shape memory material that deforms the base film by returning to a memorized shape when heated, and the shape memory material is the lithium foil in the base film. It is preferable that the shape memory material is blown with warm air in the spraying step, which is located at a position different from the position in contact with the shape memory material.

According to this method, in the spraying step, warm air is blown to the base film. Therefore, the shape memory material can be heated by warm air to deform the base film into the stored shape. Therefore, the base film can be more easily peeled off.

According to the present invention, damage to the lithium foil can be reduced.

The perspective view of the negative electrode of an embodiment. Side view of the layered sheet. A plan enlarged view of the base film. Top view of the base film. The manufacturing process diagram of the negative electrode. The side view which shows the arrangement process. Top view of the electrode material and the layered sheet. The side view which shows the pressurizing process. The side view which shows the spraying process. A side view showing a state in which the base film is deformed. The perspective view which shows the peeling process.

Hereinafter, an embodiment of a method for manufacturing a negative electrode will be described with reference to the drawings.
The negative electrode manufactured by the manufacturing method of the present embodiment is used for a secondary battery as a power storage device. Although not shown, the secondary battery is a square battery having a square appearance and is a lithium ion secondary battery. This secondary battery includes an electrode assembly inside the case. The electrode assembly includes a plurality of positive electrodes and a plurality of negative electrodes. The electrode assembly is configured by alternately stacking a positive electrode and a negative electrode in a state where the positive electrode and the negative electrode are insulated from each other by a separator.

As shown in FIG. 1, the negative electrode electrode 11 includes a rectangular sheet-shaped electrode material 12 and a dope layer 13 existing on both sides of the electrode material 12. The electrode material 12 is configured by laminating a rectangular sheet-shaped current collector 14 and negative electrode active material layers 15 existing on both sides of the current collector 14. The current collector 14 of the present embodiment is made of a metal foil. The dope layer 13 covers the entire surface of the negative electrode active material layer 15.

The negative electrode electrode 11 has an uncoated portion 17 in which the negative electrode active material layer 15 does not exist along one side thereof and the current collector 14 is exposed. In the negative electrode electrode 11, the negative electrode tab 18 is present in a state where the negative electrode tab 18 protrudes from a part of the uncoated portion 17. The negative electrode active material layer 15 contains an active material, a conductive material, and a binder.

Next, the layered sheet 20 used for forming the dope layer 13 on the electrode material 12 will be described. In FIG. 2, the direction in which the layer is formed in the layered sheet 20 is shown on the Z axis. The directions along the plane perpendicular to the Z axis are indicated by the X axis and the Y axis. The X-axis, Y-axis, and Z-axis are orthogonal to each other. In the following description, the direction along the X axis is also referred to as the lateral direction X, the direction along the Y axis is referred to as the longitudinal direction Y, and the direction along the Z axis is also referred to as the stacking direction Z.

As shown in FIG. 2, the layered sheet 20 includes a rectangular sheet-shaped base film 21 and a rectangular sheet-shaped lithium foil 22 laminated on one side of the base film 21. The layered sheet 20 includes a shape storage material 23 that returns to a memorized shape when heated.

The shape storage material 23 is arranged at a position different from the position in contact with the lithium foil 22 on the base film 21. The lithium foil 22 and the shape storage material 23 of the present embodiment are present on different surfaces of the base film 21. Specifically, the lithium foil 22 is in contact with the first surface 21a of the base film 21. The shape storage material 23 is in contact with the second surface 21b opposite to the first surface 21a in the base film 21. The thickness of the lithium foil 22 of the present embodiment is 5 μm, which satisfies 1 to 20 μm required as the thickness of the lithium foil 22 attached to the surface of the negative electrode active material layer 15.

As shown in FIG. 3, the base film 21 is a film made of stretched polytetrafluoroethylene (hereinafter referred to as “ePTFE”) obtained by uniaxially stretching polytetrafluoroethylene (hereinafter referred to as “PTFE”). The base film 21 has a plurality of nodes 25 which are aggregates of PTFE resin, and a plurality of fibrils 26 which connect the plurality of nodes 25. The base film 21 has a plurality of holes 27 that are gaps between the node 25 and the fibril 26.

In the present embodiment, when the ePTFE is manufactured, the stretching direction, which is the direction in which the PTFE is extended, and the longitudinal direction Y of the base film 21 coincide with each other. Therefore, the fibril 26 extends in the longitudinal direction Y. The size of the node 25 in the longitudinal direction Y is smaller than the size of the node 25 in the lateral direction X. The size of the fibril 26 in the longitudinal direction Y is larger than the size of the lateral direction X. The plurality of fibrils 26 have a distance from each other in the lateral direction X and extend substantially parallel to the longitudinal direction Y.

As shown in FIG. 4, the shape memory material 23 of the present embodiment is a flat wire mesh in which a mesh-like cylinder called a stent glass used for expanding the diameter of a blood vessel or the like in the medical field is developed. The shape storage material 23 has a plurality of through holes 23a. In the present embodiment, the mesh of the wire mesh is the through hole 23a. The second surface 21b of the base film 21 is exposed through the through hole 23a.

The shape memory material 23 is deformed when a force is applied, and returns from the deformed shape to the memorized shape when heat is applied. The shape memory material 23 is integrally formed with the base film 21 by adhesion, sticking, welding, or the like. Therefore, the shape memory material 23 deforms the base film 21 by returning to the memorized shape. The shape storage material 23 stores a rounded shape in the lateral direction X. When the flat plate-shaped shape storage material 23 is heated, the shape storage material 23 bends the base film 21 in the lateral direction X.

Next, a method of manufacturing the negative electrode electrode 11 will be described.
As shown in FIG. 5, the method for manufacturing the negative electrode electrode 11 preferably includes a forming step, a cutting step, an arranging step, a pressurizing step, a spraying step, and a peeling step.

Illustration of the forming step and the cutting step is omitted. The forming step is a step of forming the negative electrode active material layer 15 on both surfaces of the long strip-shaped current collector 14. The cutting step is a step of cutting the current collector 14 on which the negative electrode active material layer 15 is formed into the shape of the negative electrode electrode 11 to form the electrode material 12.

The arranging step, the pressurizing step, the spraying step, and the peeling step are steps of forming the dope layer 13 on the surface of the negative electrode active material layer 15 included in the electrode material 12.
As shown in FIGS. 6 and 7, the arranging step is a step of arranging the layered sheet 20 and the electrode material 12 in an overlapping manner. In the arranging step, the layered sheet 20 and the electrode material 12 are arranged so that the lithium foil 22 and the negative electrode active material layer 15 face each other.

In FIG. 7, only one layered sheet 20 is shown. The dimension of the lithium foil 22 in the longitudinal direction Y is larger than the dimension of the negative electrode active material layer 15 in the longitudinal direction Y and smaller than the dimension of the base film 21 in the longitudinal direction Y. Further, the dimension of the lithium foil 22 in the lateral direction X is larger than the dimension of the negative electrode active material layer 15 in the lateral direction X, and smaller than the dimension of the base film 21 in the lateral direction X.

As shown in FIGS. 6 and 7, in the arrangement step, the entire surface of the negative electrode active material layer 15 included in the electrode material 12 faces the lithium foil 22. In the present embodiment, two layered sheets 20 are prepared, and the electrode material 12 is arranged between the lithium foils 22 of each layered sheet 20. The lower layered sheet 20 is placed on a work table (not shown).

In the following description, one layered sheet 20, the electrode material 12 stacked on one layered sheet 20, and the other layered sheet 20 stacked on the electrode material 12 are collectively referred to as an electrode complex W. In the present embodiment, the electrode material 12 and the layered sheet 20 have the same side X, longitudinal direction Y, and stacking direction Z. The electrode complex W is composed of a set of layered sheets 20 and an electrode material 12 stacked in the stacking direction Z.

As shown in FIG. 8, the pressurizing step is a step of pressurizing the layered sheet 20 and the electrode material 12 in the stacking direction Z. The pressurizing step improves the adhesion between the surface of the negative electrode active material layer 15 of the electrode material 12 and the lithium foil 22 of the layered sheet 20. In the pressurizing step, a pressurizing device 29 for pressurizing the electrode complex W and a transport device 30 for transporting the electrode complex W are used.

The pressurizing device 29 is arranged in the stacking direction Z, and includes a pair of pressurizing rolls 29a and 29b that pressurize the layered sheet 20 and the electrode material 12. The pair of pressure rolls 29a and 29b are rotated around an axis (not shown) with the lateral direction X as the axial direction by a motor (not shown). One of the pressure rolls 29a is arranged on one side (for example, the upper side in the gravity direction) in the stacking direction Z with respect to the path through which the electrode complex W is conveyed. The other pressure roll 29b is arranged on the other side (for example, the lower side in the gravity direction) in the stacking direction Z with respect to the path through which the electrode complex W is conveyed. The pair of pressure rolls 29a and 29b rotate in opposite directions to each other. The region sandwiched by the pair of pressure rolls 29a and 29b is referred to as the pressure region P1.

The transport device 30 transports the electrode complex W in the transport direction indicated by the white arrow in FIG. The transport device 30 includes a first transport unit 31 arranged upstream of the pressurizing device 29 in the transport direction, and a second transport unit 32 arranged downstream of the pressurizing device 29 in the transport direction. The first transport unit 31 and the second transport unit 32 are, for example, belt conveyors. The transport device 30 transports the electrode complex W so that the longitudinal direction Y of the electrode complex W is along the transport direction and the stacking direction Z is along the vertical direction.

The electrode complex W is transported to the pressure region P1 by the first transport unit 31 and passes between the pair of pressure rolls 29a and 29b. That is, in the pressurizing step, the pressurizing device 29 and the layered sheet 20 move relative to each other in the longitudinal direction Y. The lithium foil 22 of the layered sheet 20 is pressed against the negative electrode active material layer 15 of the electrode material 12 by a pair of pressure rolls 29a and 29b. This improves the adhesion between the lithium foil 22 and the negative electrode active material layer 15. The load applied by the pressurizing device 29 to the electrode composite W is such that the adhesion between the lithium foil 22 and the negative electrode active material layer 15 is improved and the negative electrode active material layer 15 is not damaged (for example, 5 kN). It is set. The electrode complex W is transported to a subsequent process (spraying process) by the second transport unit 32.

As shown in FIG. 9, the spraying step is a step of blowing warm air onto the electrode complex W in which the layered sheet 20 and the electrode material 12 are bonded together. In the spraying step, a pair of blowers 35 including a heat source 34 such as a heating wire are used. The blower 35 warms a gas such as air by a heat source 34 and sends it out. The blower device 35 has a blower port (not shown) for sending gas. The blower device 35 may be provided with one blower port or may be provided with a plurality of blower ports. In FIG. 9, the gas blown out from the air outlet is shown by a alternate long and short dash line.

The pair of blowers 35 are arranged at a distance wider than the thickness of the electrode complex W in the stacking direction Z. Therefore, the electrode complex W transported by the second transport unit 32 can pass between the blower devices 35. The area between the pair of blowers 35 is referred to as a spray area P2.

The blower device 35 blows warm air onto the electrode complex W located in the blowing region P2. In other words, the blower 35 blows a gas such as air onto the second surface 21b of the base film 21. The sprayed gas passes through the through hole 23a (see FIG. 4) of the shape storage material 23 and hits the second surface 21b of the base film 21, and further passes through the hole 27 (see FIG. 3) of the base film 21. It passes through and hits the lithium foil 22. As a result, gas enters between the lithium foil 22 and the base film 21, and acts to float the base film 21 from the lithium foil 22.

As shown in FIG. 10, the shape storage material 23 sprayed with the warm gas returns to the shape stored by being heated by the gas. The shape memory material 23 is deformed in a direction in which both ends in the lateral direction X are separated from the electrode material 12.

As shown in FIG. 11, the peeling step is a step of peeling the base film 21 from the electrode material 12. In FIG. 11, one layered sheet 20 is shown, and the other layered sheet 20 is not shown. When the base film 21 of the layered sheet 20 is peeled off, the lithium foil 22 attached to the negative electrode active material layer 15 becomes a dope layer 13, and the negative electrode electrode 11 is completed. The excess portion of the lithium foil 22 that does not face the negative electrode active material layer 15 and is not attached to the negative electrode active material layer 15 is peeled off together with the base film 21.

Next, the operation when the layered sheet 20 is peeled off from the negative electrode electrode 11 will be described.
In the pressurizing step, the electrode complex W is pressurized in order from one end to the other end in the longitudinal direction Y. Therefore, the lithium foil 22 and the base film 21 are attached to each other with a stronger force in the longitudinal direction Y than in the lateral direction X. Therefore, the base film 21 is more likely to be peeled off in the lateral direction X than in the longitudinal direction Y.

In the spraying step, the base film 21 is lifted from the end of the lateral direction X. In the peeling step, the end of the base film 21 in the lateral direction X is grasped and this end is moved in the stacking direction Z so as to be separated from the electrode material 12. Then, the layered sheet 20 is gradually peeled off in the lateral direction X.

A plurality of fibrils 26 are located at intervals from each other in the lateral direction X. When the base film 21 is peeled off, the end of the portion of the base film 21 that is attached to the lithium foil 22 on the peeling side is called the peeling tip. When the base film 21 is peeled off in the lateral direction X, fibrils 26 attached to the lithium foil 22 and holes 27 not attached to the lithium foil 22 appear alternately at the peeled tip. Assuming that the base film 21 and the lithium foil 22 are stuck to each other with a certain adhesive force, when the base film 21 is peeled off, the fibril 26 causes a stick state in which the peeling speed is slow, and the hole 27 is peeled off quickly. It causes a slip condition that is faster than the stick condition. This causes a stick-slip phenomenon, and the base film 21 vibrates and easily peels off.

According to the above embodiment, the following effects can be obtained.
(1) ePTFE is a porous material having a large number of pores 27. Gas is sprayed from the side opposite to the lithium foil 22 onto the base film 21 of the electrode composite W in which the layered sheet 20 in which the base film 21 made of ePTFE and the lithium foil 22 are laminated and the electrode material 12 are laminated. .. The gas passes through the holes 27 of the base film 21 and acts to float the base film 21 from the lithium foil 22. As a result, the sticking between the base film 21 and the lithium foil 22 can be weakened. Therefore, when the base film 21 is peeled off, the possibility that the lithium foil 22 is peeled off from the electrode material 12 together with the base film 21 can be reduced, and damage to the lithium foil 22 can be reduced.

(2) The ePTFE obtained by uniaxially stretching the PTFE has a plurality of fibrils 26. The fibrils 26 extend in the direction in which the PTFE is stretched, and are arranged at intervals in a direction different from the direction in which the PTFE is stretched. In the pressurizing step, the pressurizing device 29 and the layered sheet 20 are relatively moved in the direction in which the fibril 26 extends to pressurize. Further, in the peeling step, the base film 21 is peeled off in the direction in which the plurality of fibrils 26 are arranged at intervals from each other. Therefore, it is possible to increase the ratio of the slip state in which the peeling speed is high to the stick state in which the peeling speed is slow, and cause a so-called stick-slip phenomenon to facilitate the peeling of the base film 21.

(3) In the spraying step, warm air is blown onto the base film 21. Therefore, the shape memory material 23 can be heated by warm air to deform the base film 21 into a stored shape. Therefore, the base film 21 can be more easily peeled off.

(4) The shape memory material 23 deforms the base film 21 in a direction away from the electrode material 12 and in a direction different from the direction in which the fibril 26 extends. Therefore, the base film 21 can be easily deformed as compared with the case where the base film 21 is deformed in the direction in which the fibril 26 extends.

(5) The shape storage material 23 has a through hole 23a that exposes the second surface 21b of the base film 21. The sprayed gas passes through the through hole 23a of the shape storage material 23 and hits the base film 21. Therefore, even when the shape storage material 23 is provided so as to cover the second surface 21b, the gas can be efficiently sprayed on the base film 21. By providing the shape memory material 23 so as to cover the second surface 21b, it is possible to reduce the possibility of distortion occurring when the base film 21 is deformed.

The above embodiment may be modified as follows. The above embodiment and the following modification example may be arbitrarily combined. The configurations included in the following modification examples may be arbitrarily combined.

○ The method for manufacturing the negative electrode electrode 11 does not have to include an arrangement step and a pressurization step. For example, the negative electrode electrode 11 may be manufactured by performing at least a spraying step and a peeling step on the separately prepared electrode complex W.

○ The base film 21 may contain a compound having a smaller water repellency than the ePTFE resin. That is, for example, the surfaces of the node 25 and the fibril 26 may be coated with a polymer. Examples of polymers include organic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, vinyl alcohol-tetrafluoroethylene block copolymer, and inorganic polymers obtained by solgel reaction from alkoxysilane and the like.

○ The negative electrode electrode 11 may have the negative electrode active material layer 15 and the dope layer 13 on only one side of the current collector 14.
○ The uncoated portion 17 may be composed of only the negative electrode tab 18.

○ The forming step may be performed after the cutting step. For example, the negative electrode active material layer 15 may be formed on the cut current collector 14.
○ The method for manufacturing the negative electrode electrode 11 does not have to include a forming step and a cutting step. For example, the negative electrode electrode 11 may be manufactured by attaching a lithium foil 22 to a separately prepared electrode material 12.

○ The cutting step may be performed after any one of the pressurizing step, the spraying step, and the peeling step. That is, the negative electrode electrode 11 may be manufactured by forming the dope layer 13 on the surface of the negative electrode active material layer 15 and then cutting into the shape of the negative electrode electrode 11. As a result, the positions of the dope layer 13 and the negative electrode active material layer 15 can be easily aligned.

○ The spraying step may be performed by one blower 35. The blower 35 may blow gas onto the two layered sheets 20 in order. For example, the blower 35 may blow gas onto one layered sheet 20 and then change the direction of at least one of the blower 35 and the electrode complex W to blow gas onto the other layered sheet 20. A plurality of ducts may be connected to one blower device 35, and the tip of each duct opposite to the base end connected to the blower device 35 may face the second surface 21b of different base films 21.

○ A heating device for heating the shape storage material 23 may be provided separately from the blower device 35. The method for manufacturing the negative electrode electrode 11 may include a heating step of heating the shape storage material 23 by a heating device. The heating step is preferably performed after the spraying step.

○ The spraying step and the peeling step may be performed at the same time. The base film 21 may be peeled off while blowing a gas.
○ In the pressurizing step, the pressurizing device 29 may be moved with respect to the electrode complex W. In the pressurizing step, both the electrode complex W and the pressurizing device 29 may be moved.

○ In the pressurizing step, when pressurizing the electrode complex W, at least one of the pressurizing device 29 and the electrode complex W may be moved in a direction different from the longitudinal direction Y. For example, the transport device 30 may move the electrode complex W in the lateral direction X. The pressurizing device 29 may pressurize the electrode complex W from one end to the other end in the lateral direction X.

○ The pressurizing device 29 may sandwich the electrode complex W between a pair of members having a surface larger than that of the negative electrode active material layer 15 and pressurize the electrode complex W so as to crush the entire electrode complex W. The pressurizing device 29 may pressurize the electrode composite W by sandwiching the electrode composite W with one member having a surface larger than that of the negative electrode active material layer 15 and one pressurizing roll.

○ The layered sheet 20 may include a shape storage material 23 located at a position different from the position in contact with the lithium foil 22 on the first surface 21a of the base film 21. The shape memory material 23 attached to the first surface 21a may be deformed so as to lift the base film 21 when heated.

○ The layered sheet 20 may be configured not to include the shape storage material 23.
○ The blower device 35 may be configured not to include the heat source 34. The blower 35 may send out a gas at room temperature.

○ In the spraying process, a gas other than air may be sprayed. For example, the layered sheet 20 may be sprayed with an activated gas such as nitrogen gas.
○ In the peeling step, the base film 21 may be peeled off in a direction different from the lateral direction X. For example, in the peeling step, the base film 21 may be peeled off in the longitudinal direction Y.

○ The base film 21 may be made of ePTFE obtained by biaxially stretching PTFE. The fibrils 26 included in the base film 21 may extend in different directions.
Next, the technical idea that can be grasped from the above embodiment and the modified example will be added below.

(A) A method for manufacturing a negative electrode in which the shape storage material deforms the base film in a direction away from the electrode material and in a direction different from the direction in which the fibril extends.
(B) The shape storage material is a method for manufacturing a negative electrode having a through hole for exposing the second surface of the base film.

11 ... Negative electrode electrode, 12 ... Electrode material, 14 ... Current collector, 15 ... Negative electrode active material layer, 20 ... Layered sheet, 21 ... Base film, 21a ... First surface, 21b ... Second surface, 22 ... Lithium foil, 23 ... shape memory material, 26 ... fibrils, 29 ... pressurizing device, W ... electrode composite.

Claims (3)

The layered sheet in which the base film made of stretched polytetrafluoroethylene and the lithium foil are laminated, and the electrode material in which the current collector and the negative electrode active material layer are laminated, are the lithium foil and the negative electrode active material layer. In the base film of the electrode composite in which the electrodes are bonded so as to face each other, a spraying step of spraying gas on the second surface opposite to the first surface in contact with the lithium foil.
The peeling step of peeling the base film and
A method for manufacturing a negative electrode, which comprises. An arrangement step of arranging the layered sheet and the electrode material so that the lithium foil and the negative electrode active material layer face each other.
A pressurizing step of moving the pressurizing device for pressurizing the layered sheet and the electrode material relative to the layered sheet in the direction in which the fibrils of the base film extend.
Including
The method for manufacturing a negative electrode according to claim 1, wherein the peeling step is for peeling the base film in a direction different from the direction in which the fibrils extend. The layered sheet comprises a shape memory material that deforms the base film by returning to a memorized shape when heated.
The shape memory material is located in the base film at a position different from the position in contact with the lithium foil.
The method for manufacturing a negative electrode according to claim 1 or 2, wherein the spraying step is a method of blowing warm air onto the shape storage material.

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