Pole piece and lithium ion battery

Abstract

The utility model belongs to the technical field of lithium ion batteries, and particularly relates to a pole piece and a lithium ion battery, the pole piece is sequentially divided into a main body area, a thinned area and a tab area along the width direction of the pole piece, the pole piece comprises a current collector, the current collector is provided with a first end close to the main body area and a second end close to the tab area, and the lower bottom surface of the current collector is positioned on the same horizontal plane; the thickness of the current collector is sequentially increased from the first end to the second end, the upper surface and the lower surface close to the first end are close to each other, and the upper surface and the lower surface close to the second end are parallel to each other; and the active material coating is arranged on at least one surface of the current collector along the thickness direction, and is arranged on the main body region and the thinned region. According to the utility model, the uniformity of current distribution in the width direction of the current collector can be realized, overlarge local temperature rise caused by current density concentration is avoided, and the battery rate capability of the battery is ensured; and under the same overcurrent capability, less inactive current collectors are introduced, and the energy density of the battery can be considered.

Description

Technical Field

[0001] This utility model belongs to the field of lithium-ion battery technology, and in particular relates to an electrode and a lithium-ion battery. Background Technology

[0002] With the continuous expansion of the new energy vehicle market and the gradual upgrading of consumer demands, shortening battery fast charging time and improving battery energy density have become the main research directions for solving consumers' range anxiety. Among them, improving battery rate performance is one of the main directions for shortening battery fast charging time. The existing method uses copper-aluminum foil of uniform thickness as current collector, and the tabs are cut out of the edge of the foil by die-cutting to lead / receive electron current to the external circuit. Increasing the thickness of the current collector to increase the current flow area can effectively improve the battery rate performance.

[0003] However, the current collector itself, as a carrier of electrons, does not possess electrochemical activity and does not participate in electrochemical reactions. Increasing the thickness of the current collector inevitably leads to a decrease in the mass / volume ratio of active materials inside the cell; that is, increasing the thickness of the current collector inevitably comes at the cost of energy density. On the other hand, if the current collector thickness is too low, it will cause a high temperature rise, or even cause the battery temperature to exceed the normal operating range, thereby leading to a loss of energy efficiency in the cell and limiting the battery's rate performance. Utility Model Content

[0004] In view of the shortcomings of the prior art described above, the purpose of this utility model is to provide an electrode and a lithium-ion battery to solve the technical problem that improving the rate performance of the battery will affect the energy density of the battery.

[0005] To achieve the above and other related objectives, the technical solution of this utility model is as follows:

[0006] An electrode sheet, wherein the electrode sheet is divided into a main body region, a thinning region, and an electrode tab region along its width direction, the electrode sheet comprising:

[0007] The current collector has a first end near the main body region and a second end near the tab region. The bottom surface of the current collector is located on the same horizontal plane. The thickness of the current collector increases sequentially from the first end to the second end. The upper and lower surfaces near the first end are close to each other, and the upper and lower surfaces near the second end are parallel to each other.

[0008] An active material coating is disposed on at least one surface of the current collector along the thickness direction, and the active material coating is disposed on the main body region and the thinned region.

[0009] Optionally, the thickness of the current collector in the main body region and the thinned region gradually linearly increases in the direction close to the tab region, and the slope of the linear increase of the thickness of the current collector in the thinned region is different from the slope of the linear increase of the thickness of the current collector in the main body region, and the thickness of the current collector in the tab region remains consistent from one end close to the thinned region to one end away from the thinned region.

[0010] Optionally, the slope of the linear increase of the thickness of the current collector in the thinned region is smaller than the slope of the linear increase of the thickness of the current collector in the main body region, and the current collector is smoothly transitioned at the junction of the main body region and the thinned region.

[0011] Optionally, the thickness of the current collector in the tab region is the same as the thickness of the thinned region.

[0012] Optionally, the thickness of the active material coating gradually decreases from the main body region to the thinned region.

[0013] Optionally, the thickness of the active material coating in the main body region is greater than or equal to the thickness of the current collector in the main body region.

[0014] Optionally, the side of the active material coating in the main body region away from the current collector is a horizontal surface.

[0015] Optionally, the side of the active material coating close to the current collector in the thinned region is a bevel surface, and the side of the active material coating away from the current collector in the thinned region is a curved surface.

[0016] Optionally, the active material coating is arranged on the front and back surfaces of the current collector, respectively, and is symmetrically distributed with respect to the current collector.

[0017] Based on the same concept, the utility model also provides a lithium electronic battery, including the pole piece and diaphragm as described above, the pole piece is positive pole piece and / or negative pole piece, the positive pole piece and negative pole piece are laminated and are arranged, and the diaphragm is arranged between adjacent positive pole piece and negative pole piece.

[0018] As described above, the utility model of a pole piece and lithium electronic battery has the following beneficial effects:

[0019] By the partitioned thickness gradient structure of the current collector arranged in the main body area, the thinning area and the tab area, uniformity of the current distribution in the width direction of the current collector is achieved, the excessive local temperature rise caused by the current density concentration is avoided, the safety use of the battery is affected, the battery rate performance is ensured, under the same overcurrent capacity, less inactive current collectors are introduced, the energy density of the battery can be considered, the current collector has a thicker thickness at the tab area, on the one hand, the overcurrent capacity of the tab is ensured, on the other hand, the thin tab is prevented from being folded during the process of die cutting or winding over the roller due to the fact that the tab is too thin to support the main body, the tab is folded, and the internal short circuit of the battery cell is caused, and the safety risk is caused. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a current diagram during charging and discharging;

[0021] Figure 2 is a structure diagram of the current collector and the active material coating of the embodiment of the utility model;

[0022] Figure 3 is a structure diagram of the battery cell of the embodiment of the utility model;

[0023] Figure 4 is Figure 3 a structure diagram of the middle part.

[0024] BRIEF DESCRIPTION OF DRAWINGS

[0025] 10a-current collector; 20a-active material coating; 30a-electron flow;

[0026] 10-current collector; 11-main body area; 12-thinning area; 13-tab area; 101-first end; 102-second end;

[0027] 20-active material coating; 21-positive electrode coating; 22-negative electrode coating;

[0028] 100-positive electrode sheet; 200-negative electrode sheet; 300-separator. DETAILED DESCRIPTION

[0029] The implementation of the utility model will be described by specific embodiments, and those skilled in the art can easily understand other advantages and effects of the utility model from the content disclosed in the specification. The utility model can also be implemented or applied by different specific embodiments, and each detail in the specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the utility model.

[0030] It is to be noted that the diagrams provided in the present embodiment only schematically illustrate the basic concept of the present application, and thus only the components related to the present application are shown in the diagrams, rather than being drawn according to the number, shape and size of the components in actual implementation. The shape, number and proportion of the components in actual implementation can be changed at will, and the layout of the components can be more complex. It is understood that the structure, proportion, size, etc. shown in the diagrams attached to the present specification are only used to cooperate with the content disclosed in the specification, so as to be understood and read by those skilled in the art, and do not limit the implementation conditions of the present application, and therefore do not have substantial technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" in the present specification are only for the convenience of clear description, and do not limit the scope of the present application, and the change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the scope of the present application.

[0031] In the discharging process of the lithium ion battery, the reduction reaction loses electrons at the positive electrode / electrolyte interface, and the electron flow 30a enters the current collector 10a along the conductive network inside the pole piece, and then converges to the tab through the current collector 10a; the electron flow 30a received by the negative electrode is transmitted from the tab to the current collector 10a to the inside of the active material coating 20a, and participates in the oxidation reaction at the negative electrode / electrolyte interface. The charging process is opposite to this. Referring to Figure 1 Obviously, in the process of transmitting electrons, the current size at each part of the current collector 10a is not consistent, and the current density is higher near the tab. The common way is to increase the thickness of the current collector to increase the flow area, which can effectively improve the rate performance of the battery, and increasing the thickness of the current collector must sacrifice the energy density.

[0032] Based on this, the present application provides a pole piece and a lithium electronic battery, wherein the thickness of the current collector adopts a gradient structure to bear the current transmission pressure at different positions. In order to describe the present application in detail, the following specific description is made:

[0033] Please refer to Figure 2As shown, the utility model provides a kind of pole piece, the pole piece is sequentially divided into main body area 11, thinning area 12 and tab area 13 along the width direction of itself, the pole piece includes: current collector 10 and active material coating 20 being arranged on the surface of current collector 10, wherein, the current collector 10 has first end 101 close to the main body area 11 and second end 102 close to the tab area 13, the lower bottom surface of the current collector is located in the same horizontal plane, the thickness of the current collector increases sequentially from the direction of the first end 101 to the second end 102, the upper surface close to the first end 101 and the lower surface are close to each other, the upper surface close to the second end 102 and the lower surface are parallel to each other;Active material coating 20 is arranged on at least one surface of the current collector 10 along the thickness direction, and the active material coating 20 is arranged on the main body area 11 and the thinning area 12.

[0034] Specifically, from main body area 11 to thinning area 12 and then to tab area 13, the thickness of current collector 10 gradually increases. Current collector 10 can be used for welding tab or as tab and external circuit connection in tab area 13. This design helps to optimize current distribution, reduce resistance and improve the performance of battery while maintaining the stability of the overall structure of the battery;Through the design of the current collector 10 with gradually changing thickness, the uniformity of the current distribution in the width direction of the current collector 10 is facilitated, and the excessive local temperature rise caused by the concentration of current density is avoided, which affects the safe use of the battery and ensures the battery rate performance of the battery;Under the same overcurrent capacity, less inactive current collector 10 is introduced, and the energy density of the battery can be considered. The upper surface and the lower surface of the current collector 10 close to the first end 101 are close to each other, which may help to increase the contact area of the active material coating 20 and the current collector 10, thereby improving the capacity and energy density of the battery;The upper surface and the lower surface of the current collector 10 close to the second end 102 are parallel to each other, which ensures the stability of the tab area 13 and the uniformity of current transmission, and is beneficial to the long-term stable operation of the battery. The design of thicker thickness of current collector 10 in tab area 13 ensures the overcurrent capacity of tab on the one hand, and avoids the folding of thin tab during processing, such as die cutting or winding through roller, due to the difficulty of supporting the body caused by the too thin tab, thereby causing internal short circuit of battery cell and safety risk.

[0035] In some embodiments, the thickness of the current collector 10 in the main body region 11 and the thinning region 12 each gradually linearly increases in a direction close to the tab region 13, and the slope of the linear increase of the thickness of the current collector 10 in the thinning region 12 is different from the slope of the linear increase of the thickness of the current collector 10 in the main body region 11, and the thickness of the current collector 10 in the tab region 13 remains consistent from one end close to the thinning region 12 to one end away from the thinning region 12. Specifically, the thickness of the current collector 10 in the main body region 11 gradually and linearly increases in a direction towards the tab region 13 from the first end 101 (i.e., the end away from the tab region 13), which can provide a uniform current distribution path for the main body region 11, while ensuring that the current collector 10 in the main body region 11 can bear sufficient mechanical stress and electrochemical activity during the charging and discharging of the battery, thereby maintaining the overall stability and performance of the battery structure.

[0036] The thickness of the current collector 10 in the main body region 11 linearly increases with a coefficient k1: h1=k1x+h0, where h1 is the thickness of the current collector 10 in the main body region 11, x is the distance from the coordinate origin position, h0 is the initial thickness of the current collector 10 at the coordinate origin (i.e., the minimum thickness of the current collector 10), and k1 is the thickness increase coefficient of the current collector 10 in the main body region 11. The value of k1 ranges from 0.04 to 0.15 um / mm, and the higher the overcurrent capacity requirement of the battery, the larger the value of k1 selected.

[0037] The thinning region 12 is adjacent to the main body region 11, and the thickness of the current collector 10 in the thinning region 12 also linearly increases from one end away from the tab region 13 to one end close to the tab region 13, but it is worth noting that the slope of the linear increase of the thickness of the current collector 10 in the thinning region 12 is different from the slope of the linear increase of the thickness of the current collector 10 in the main body region 11. This differentiated design aims to optimize the current transmission path in the tab by adjusting the thickness variation rate of the current collector 10 in the thinning region 12, reduce unnecessary resistance loss, and at the same time, provide a smoother transition area for the connection of the current collector 10 in the tab region 13, thereby enhancing the overall conductivity and mechanical strength of the tab.

[0038] The thickness of the current collector 10 in the tab region 13 remains constant from one end close to the thinning region 12 to one end away from the thinning region 12, and the thickness of the current collector 10 in the tab region 13 is thicker than the thickness of the current collector 10 in the thinning region 12, which ensures that the current collector 10 in the tab region 13 has sufficient mechanical strength and conductivity, can stably and reliably carry large current, and reduces resistance fluctuations caused by thickness changes, thereby improving the safety and reliability of the battery.

[0039] In the above embodiment, the slope of the linear increase of the thickness of the current collector 10 in the thinning area 12 is smaller than the slope of the linear increase of the thickness of the current collector 10 in the main body area 11, and the current collector 10 is smoothly transitioned at the junction of the main body area 11 and the thinning area 12. Specifically, when the thickness of the current collector 10 in the thinning area 12 linearly increases in the direction towards the tab area 13, the slope of the current collector 10 in the thinning area 12 is smaller than the thickness of the current collector 10 in the main body area 11. The design of the differentiated slope aims to: first, provide a smoother transition for the transmission of the current from the main body area 11 to the tab area 13 by gradually reducing the rate of thickness change, thereby reducing the resistance change and uneven current distribution caused by the sudden change in thickness; second, enhance the mechanical strength and electrical conductivity of the tab in the tab area 13 by gradually increasing the thickness of the current collector 10 in the thinning area 12, while reducing the stress concentration problem that may be caused by a too large difference in thickness. The junction of the current collector 10 in the main body area 11 and the thinning area 12 is designed to be smoothly transitioned, i.e., there is no obvious thickness mutation or step between the current collector 10 in the main body area 11 and the thinning area 12. This smooth transition design is crucial for ensuring the continuous transmission of the current in the tab, as it avoids the concentration of current density and the increase of resistance caused by the sudden change in thickness, thereby reducing the energy loss and heat generation of the battery during the charging and discharging process. In addition, the smoothly transitioned junction also helps to improve the overall mechanical strength and durability of the tab, reducing the risk of structural damage caused by stress concentration.

[0040] The thickness of the current collector 10 at the starting end of the thinning area 12 is the same as the thickness at the end of the main body area 11. The thickness of the current collector 10 in the thinning area 12 linearly increases with a coefficient k2: h2 = h1' + k2 x (x - x1), where h2 is the thickness of the current collector 10 in the thinning area 12, h1' is the thickness of the current collector 10 at the end of the main body area 11, x is the distance coordinate from the origin, x1 is the width of the main body area 11, k2 is the thickness increase coefficient of the current collector 10 in the thinning area 12, and the thickness increase coefficient k2 < k1, the value range of k2 is 0.02-0.13 um / mm. According to the overcurrent requirement of the battery and the thinning ratio of the current collector 10 in the thinning area 12, the higher the overcurrent requirement, the larger the value of k2, and the smaller the thinning ratio, the larger the value of k2.

[0041] In some embodiments, the thickness of the current collector 10 at the tab area 13 is the same as the thickness at the end of the thinned area 12. Specifically, by ensuring that the thickness of the current collector 10 at the tab area 13 is the same as the thickness at the end of the thinned area 12, a seamless transition of the current from the thinned area 12 to the tab area 13 is achieved, avoiding uneven current distribution and increased resistance due to sudden thickness changes, thereby ensuring continuous and stable transmission of current during the charging and discharging process of the battery. The consistency of the thickness helps to form a more solid mechanical connection between the tab area 13 and the thinned area 12 of the current collector 10, enhancing the overall structural strength of the tab, which is crucial for improving the durability and stability of the battery in complex working environments. The consistency of the thickness also helps to optimize the overall performance of the battery by reducing unnecessary resistance loss and energy waste, improving the energy storage efficiency and discharge capacity of the battery.

[0042] It can be understood that the active material coating 20 is respectively arranged on the front and back surfaces of the current collector 10, and is symmetrically distributed with respect to the current collector 10. Specifically, the active material coating 20 corresponds to the main body area 11 and the thinned area 12 through a coating correction mechanism, and the tab area 13 that meets the product design is cut through die cutting. Through the symmetrically distributed active material coating 20, the surface area of the current collector 10 can be maximized, thereby increasing the load of active material, which is beneficial to improve the energy density and storage capacity of the battery, so that the battery can store more energy under the same volume or weight, prolonging the use time of the battery. Moreover, during the charging and discharging process, the battery will generate heat, and the symmetrically distributed active material coating 20 helps to evenly dissipate heat, avoiding the problem of local overheating caused by heat concentration, reducing the risk of thermal runaway of the battery.

[0043] In the above embodiments, the thickness of the active material coating 20 gradually decreases from the main body area 11 to the thinned area 12. Specifically, the gradual decrease in the thickness of the active material coating 20 makes the distribution of current in the tab more uniform. In the main body area 11, the thicker active material coating 20 can carry more current, and as the coating thickness gradually decreases to the thinned area 12, the current density also decreases accordingly, thereby avoiding heat accumulation and performance degradation caused by excessive current density. In the main body area 11, sufficient active material ensures high capacity and long cycle life of the battery; while in the thinned area 12, the thinner coating reduces unnecessary resistance and weight, which helps to improve the energy density and power density of the battery. The thicker active material coating 20 in the main body area 11 can provide better heat conduction and heat dissipation capacity, while the thinner active material coating 20 in the thinned area 12 reduces heat accumulation, thereby reducing the risk of overheating of the battery.

[0044] In some embodiments, the thickness of the active material coating 20 in the main body area 11 is greater than or equal to the thickness of the current collector 10 in the main body area 11. Specifically, the thickened active material coating 20 can accommodate more active material particles, thereby increasing the capacity and energy density of the battery. This means that the battery can store more energy under the same volume or weight, thereby prolonging the use time of the battery. The thicker active material coating 20 can make more efficient use of the surface area of the current collector 10, and the thickened coating also helps to improve the utilization of active materials, so that more active materials can participate in the charging and discharging process of the battery.

[0045] In the above embodiments, the thickness of the active material coating 20 in the main body area 11 gradually linearly decreases in the direction close to the tab area 13, and the side of the active material coating 20 away from the current collector 10 in the main body area 11 is a horizontal plane. Specifically, the active material is coated on the surface of the current collector 10 by coating, and the leveling property of the slurry is used to ensure that the side of the active material coating 20 away from the current collector 10 in the main body area 11 is a horizontal plane. The thickness of the active material coating 20 in the main body area 11 gradually linearly decreases, which helps to achieve more uniform current distribution during the charging and discharging process of the battery. By optimizing the thickness distribution of the coating, the surface area of the current collector 10 can be maximized while ensuring the performance of the battery, thereby improving the energy density of the battery. The gradual decrease in the thickness of the coating helps to form a more uniform temperature distribution inside the battery, avoiding the occurrence of local overheating.

[0046] It should be noted that the side of the active material coating 20 close to the current collector 10 at the thinned area 12 is a bevel, and the side of the active material coating 20 away from the current collector 10 at the thinned area 12 is a curved surface. Specifically, the thickness of the active material coating 20 at the thinned area 12 is lower than the thickness of the active material coating 20 in the main body area 11, and the thinner active material coating 20 at the thinned area 12 can reduce the concentration of current at the thinned area 12, avoiding local overheating and performance degradation. The bevel of the lower surface of the active material coating 20 at the thinned area 12 has a more uniform contact area with the current collector 10, thereby optimizing the distribution of current in the battery, which helps to reduce current concentration and local overheating, and improves the performance and safety of the battery. To ensure that the edge of the coated pole piece does not appear thick after rolling and demolding, the edge is thinned during the active material coating process, so that the side of the active material coating 20 away from the current collector 10 at the thinned area 12 is a curved surface.

[0047] In addition, the active material coating 20 includes a positive electrode coating 21 and a negative electrode coating 22, the positive electrode coating 21 adopts a positive electrode active material, such as a transition metal oxide (such as manganese lithium iron phosphate, lithium nickel manganese cobalt phosphate, etc.) or a phosphate compound; the negative electrode coating 22 adopts a negative electrode active material, such as graphite or silicon.

[0048] Based on the same concept, the utility model also provides a lithium electronic battery, refer to Figure 3 and Figure 4 , including the pole piece and diaphragm 300 as described above, the pole piece is positive pole piece 100 and / or negative pole piece 200, the positive pole piece 100 and negative pole piece 200 are stacked, and the diaphragm 300 is arranged between adjacent positive pole piece 100 and negative pole piece 200. Specifically, for the positive pole piece 100, the positive electrode coating 21 is coated on the current collector 10 thereof; for the negative pole piece 200, the negative electrode coating 22 is coated on the current collector 10 thereof; the positive pole piece 100 and the negative pole piece 200 are staggered respectively, and the lug area of the positive pole piece 100 and the lug area of the negative pole piece 200 are arranged on the opposite sides; the positive pole piece 100, the negative pole piece 200 and the diaphragm 300 form a bare cell structure as shown in Figure 3 by winding or laminating, and the electrons are led out from the lug area 13 of each current collector 10, connected to the external circuit, forming an electron loop.

[0049] In summary, the utility model provides a pole piece and lithium electronic battery, the current collector 10 is arranged in the zoned thickness gradually changing structure of main body area 11, thinning area 12 and lug area 13, realizes the uniformity of current distribution in the width direction of current collector 10, avoids that the current density concentration leads to local temperature rise too much, influences the safe use of battery, guarantees the battery rate performance of battery;Under the same overcurrent capacity, introduce less inactive current collector 10, can give consideration to the energy density of battery;The current collector 10 adopts thicker thickness at the lug area 13, on the one hand ensures the overcurrent capacity of lug, on the other hand avoids that the thin lug is folded in the process, and seriously leads to internal short circuit of cell, causes safety risk when passing through die cutting or winding over roll.

[0050] The above embodiments are only illustrative of the principles and effects of the utility model, and are not used to limit the utility model. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the utility model. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the utility model should be covered by the claims of the utility model.

Claims

1. An electrode sheet, characterized in that, The electrode sheet is divided into a main body region, a thinning region, and an electrode tab region along its width direction. The electrode sheet includes: The current collector has a first end near the main body region and a second end near the tab region. The bottom surface of the current collector is located on the same horizontal plane. The thickness of the current collector increases sequentially from the first end to the second end. The upper and lower surfaces near the first end are close to each other, and the upper and lower surfaces near the second end are parallel to each other. An active material coating is disposed on at least one surface of the current collector along the thickness direction, and the active material coating is disposed on the main body region and the thinned region.

2. The electrode sheet according to claim 1, characterized in that, The thickness of the current collector in the main body region and the thinning region gradually increases linearly along the direction close to the tab region, and the slope of the linear increase of the thickness of the current collector in the thinning region is different from the slope of the linear increase of the thickness in the main body region. The thickness of the current collector in the tab region remains consistent from the end close to the thinning region to the end far from the thinning region.

3. The electrode sheet according to claim 2, characterized in that, The slope of the linear increase in thickness of the current collector in the thinned region is less than the slope of the linear increase in thickness in the main body region, and the current collector smoothly transitions at the junction of the main body region and the thinned region.

4. An electrode sheet according to claim 2, characterized in that, The thickness of the current collector in the tab region is the same as the thickness at the end of the thinning region.

5. An electrode sheet according to claim 1, characterized in that, The thickness of the active material coating gradually decreases from the main area to the thinned area.

6. An electrode sheet according to claim 5, characterized in that, The thickness of the active material coating in the main body area is greater than or equal to the thickness of the current collector in the main body area.

7. An electrode sheet according to claim 5, characterized in that, The active material coating is on a horizontal surface on the side of the main body area away from the current collector.

8. An electrode sheet according to claim 5, characterized in that, The active material coating has a sloping surface on the side of the thinned area near the current collector, and an arc surface on the side of the active material coating away from the current collector in the thinned area.

9. An electrode sheet according to claim 1, characterized in that, The active material coating is respectively disposed on the front and back surfaces of the current collector, and is symmetrically distributed with respect to the current collector.

10. A lithium-ion battery, characterized in that, The invention includes an electrode sheet and a separator as described in any one of claims 1-9, wherein the electrode sheet is a positive electrode sheet and / or a negative electrode sheet, the positive electrode sheet and the negative electrode sheet are stacked, and the separator is disposed between adjacent positive electrode sheets and negative electrode sheets.

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