Secondary battery and preparation method thereof, negative pole piece and preparation method thereof, and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a secondary battery and a preparation method thereof, a negative pole piece and a preparation method thereof, and an electric device. The secondary battery comprises a positive pole piece, a negative pole piece and a diaphragm; the negative pole piece comprises a negative current collector and a buffer layer arranged on at least one surface of the negative current collector, and the buffer layer is arranged on at least partial area of one surface of the negative current collector. The buffer layer can provide pressure for the negative electrode piece in the secondary battery, metal deposition on the negative electrode side in the cycle process of the secondary battery is compact, the buffer layer can provide deposition space for the deposition layer in the metal deposition process, and the cycle performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery, a preparation method thereof, a negative electrode sheet and a preparation method thereof, and an electric device. BACKGROUND

[0002] As an indispensable energy storage and conversion device in modern life, batteries play an important role.

[0003] If the pressure inside the battery cell is insufficient during the battery cycle process, the battery cycle performance will decrease. SUMMARY

[0004] The main purpose of the present application is to provide a secondary battery, which aims to improve the cycle performance of the secondary battery.

[0005] To achieve the above-mentioned purpose, the present application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator.

[0006] The negative electrode sheet comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, and the buffer layer is arranged on at least part of the area of one surface of the negative electrode current collector.

[0007] The negative electrode sheet of the present application comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, and the buffer layer is arranged on at least part of the area of one surface of the negative electrode current collector, which helps to densify the metal deposition on the negative side during the cycle process of the secondary battery, and the buffer layer can provide deposition space for the deposition layer during the metal deposition process, thereby providing expansion space for the expansion of the negative electrode, and improving the cycle performance of the battery.

[0008] It can be understood that the arrangement of the buffer layer causes the negative electrode sheet inside the battery cell to be subjected to a certain pressure during the cycle process of the secondary battery, which helps to densify the metal deposition on the negative side. For example, in a lithium metal battery, the dense deposition of lithium on the negative side will reduce the specific surface area of the overall lithium deposition layer, which helps to reduce the side reaction between the lithium deposition layer and the electrolyte, reduce the consumption of the electrolyte, and the scalability of the buffer layer also helps to provide space for the deposition of metal on the negative electrode and provide expansion space for the expansion of the negative electrode. At the same time, during the discharge process, the negative electrode sheet is subjected to a certain pressure, which can reduce the interfacial impedance, help the uniform dissolution of lithium, reduce the concentration polarization of lithium ions, reduce the polarization of the battery, reduce the capacity attenuation of the battery, and thus improve the cycle performance of the battery.

[0009] Optionally, the buffer layer comprises at least two spaced buffer bodies, and the two buffer bodies are located on both sides of the center point of one surface of the negative electrode current collector.

[0010] The buffer layer comprises at least two buffer bodies arranged at intervals, and the two buffer bodies are located on both sides of the center point of one surface of the negative current collector, which helps to improve the stability of the buffer layer in supporting the negative electrode sheet, and is conducive to improving the uniformity of the stress distribution of the negative electrode sheet, and further helps to improve the uniformity of metal deposition.

[0011] Optionally, the two buffer bodies are symmetrically distributed along the center point of one surface of the negative current collector.

[0012] The two buffer bodies are symmetrically distributed along the center point of one surface of the negative current collector, which helps to improve the stability of the buffer layer in supporting the negative electrode sheet, and is conducive to improving the uniformity of the stress distribution of the negative electrode sheet, and further helps to improve the uniformity of metal deposition.

[0013] Optionally, the two buffer bodies have the same area.

[0014] The two buffer bodies have the same area, which helps to improve the stability of the buffer layer in supporting the negative electrode sheet, and helps to evenly distribute the stress of the buffer layer compression and rebound, reduces stress concentration, and makes the metal deposition uniform.

[0015] Optionally, the two buffer bodies are located on opposite sides of one surface of the negative current collector, respectively.

[0016] The two buffer bodies are located on opposite sides of one surface of the negative current collector, respectively, which helps to evenly distribute the stress of the buffer layer compression and rebound, reduces stress concentration, and makes the metal deposition uniform.

[0017] In addition, the two buffer bodies are located on opposite sides of one surface of the negative current collector, respectively, which helps to make the metal deposition near the middle of the negative current collector, and the buffer bodies on both sides help to limit the deposited metal, limit the drift of pulverized lithium, confine the pulverized lithium between the two sides of the buffer body, reduce the overlap of the pulverized lithium to the tab, and reduce the risk of battery short circuit.

[0018] Optionally, the length of the two buffer bodies is the same as the length of the negative current collector.

[0019] It can be understood that in the structure of the negative current collector having long edges and short edges, the buffer bodies can be located on the opposite two long edges or on the opposite two short edges. When located on the opposite two long edges, the length of the buffer body is the same as the length of the long edge of the negative current collector, and when located on the opposite two short edges, the length of the buffer body is the same as the length of the short edge of the negative current collector. In this way, the deposited metal can be limited, the drift of the pulverized lithium can be limited, the pulverized lithium can be confined between the two sides of the buffer body, the overlap of the pulverized lithium to the tab can be reduced, and the risk of battery short circuit can be reduced.

[0020] Optionally, the width of the two buffer bodies accounts for 3%-50% of the width of the negative current collector.

[0021] When the two buffer bodies are located on opposite sides of the negative current collector, the percentage of the width of the two buffer bodies to the width of the negative current collector is 3%-50%, which meets the above range, and helps the buffer layer to provide scalable elasticity, that is, the buffer layer provides compression and rebound support between the electrode sheets, provides pressure to the battery during the cycle process, improves the uniformity of metal deposition and dissolution, and further improves the cycle performance of the battery.

[0022] Optionally, the elastic stress of the buffer layer is 2MPa-6.5MPa.

[0023] The elastic stress of the buffer layer is 2MPa-6.5MPa, which means that the buffer layer always has the ability to resist elastic deformation under the condition of internal pressure of the battery, that is, the elastic stress of the buffer layer meets the above range, which helps to maintain the stable compression and rebound ability of the buffer layer and reduces the problem of elastic expansion failure of the buffer layer.

[0024] Optionally, the percentage of the area of the buffer layer on one surface of the negative current collector to the area of the one surface of the negative current collector is 3%-50%.

[0025] In the scheme of arranging the buffer layer on part of the area of at least one surface of the negative current collector, metal can be deposited in the area of the surface which is not arranged with the buffer layer, at this time, the percentage of the area of the buffer layer to the area of one surface of the negative current collector is 3%-50%, which can be understood as meeting the above range, which helps the buffer layer to provide scalable elasticity, that is, the buffer layer provides compression and rebound support between the electrode sheets, provides pressure to the battery during the cycle process, improves the uniformity of metal deposition and dissolution, and further improves the cycle performance of the battery; of course, meeting the upper limit of the above range helps to reduce the volume of the battery and reduce the risk of reducing the volume energy density of the battery. It can be understood that it is difficult to further improve the cycle performance of the battery by continuously increasing the coverage area of the buffer layer on the negative current collector, and continuously increasing the area will also increase the size of the battery and reduce the volume energy density. Therefore, meeting the above range helps to improve the cycle performance and volume energy density of the battery.

[0026] Optionally, the material of the buffer layer includes at least one of polypropylene, polyethylene, and polyimide.

[0027] And / or, the buffer layer includes a porous structure.

[0028] In an embodiment, the material of the buffer layer includes at least one of polypropylene, polyethylene, and polyimide. In another embodiment, the buffer layer includes a porous structure, which helps the buffer layer to absorb electrolyte, and the electrolyte absorbed by the buffer layer is released during the charging and discharging process, so that the electrolyte infiltration during the cycle process of the battery is improved.

[0029] Optionally, the positive electrode tab comprises a positive current collector and a positive active layer arranged on at least one surface of the positive current collector.

[0030] The same surface of the negative current collector comprises a buffer area and an active material area, the buffer layer is located in the buffer area, and the projection of the positive active layer is located in the active material area.

[0031] The positive electrode tab comprises a positive current collector and a positive active layer arranged on at least one surface of the positive current collector; the same surface of the negative current collector comprises a buffer area and an active material area, the buffer layer is located in the buffer area, and the projection of the positive active layer is located in the active material area, so as to facilitate the effective deposition of active ions on the positive side to the active material area on the negative side.

[0032] And the projection of the positive active layer is located in the active material area of the negative electrode, which reduces the deposition of active ions on the positive side to the buffer layer, so that when the buffer layer is located on both sides of the negative current collector, the buffer layer can limit the deposition of metal in the middle of the negative current collector to a certain extent, which can limit the drift of pulverized lithium and reduce the risk of short circuit; it can be understood that the lithium deposited on the negative current collector is dead lithium / pulverized lithium that loses electrical connection with the negative current collector, and the pulverized lithium is in a free state inside the battery cell, which can cause short circuit when the positive and negative tabs are connected. The projection of the positive active layer in the active material area can help reduce the risk of battery short circuit.

[0033] Optionally, the positive current collector is provided with an insulating layer corresponding to the region of the buffer layer.

[0034] The insulating layer is arranged opposite to the buffer layer, which can improve the support of the insulating layer to the buffer layer in the battery, and facilitate the elastic deformation of the buffer layer.

[0035] Optionally, the at least one surface of the negative current collector is provided with an active material supplement layer.

[0036] The active material supplement layer is used to supplement the lost active material, for example, in a lithium metal battery, the active material supplement layer is a lithium supplement layer, which can supplement the lithium consumption of each cycle, because lithium metal will form SEI (Solid Electrolyte Interphase) during deposition and dissolution, and the lithium supplement layer can supplement the consumption of lithium during the formation of SEI, thereby improving the cycle performance of the battery.

[0037] Optionally, the same surface of the negative current collector comprises a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material supplement layer is located in the active material area.

[0038] The same surface of the negative current collector includes a buffer area and an active material area, a buffer layer is located in the buffer area, and an active material supplement layer is located in the active material area. For example, in a lithium metal battery, the active material supplement layer is a lithium supplement layer, which helps the metal to be deposited on the surface of the lithium supplement layer.

[0039] Optionally, the thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

[0040] The thickness L of the buffer layer refers to the thickness in its natural state, that is, the thickness when it is not extruded. When the battery is assembled, the buffer layer is compressed to the same thickness as the active material supplement layer, so that the buffer layer has an expansion rebound force and extrudes the negative electrode plate. When the thickness L of the buffer layer is greater than the thickness T of the active material supplement layer, after the buffer layer is compressed to the same thickness as the active material supplement layer, the buffer layer has an expansion rebound force and extrudes the negative electrode plate.

[0041] For example, in a lithium metal battery, when the battery is assembled, the buffer layer is compressed to the same thickness as the lithium supplement layer, the lithium metal layer on the negative side becomes thicker during the deposition process, the buffer layer expands and rebounds to provide space for the deposition of lithium metal; after the lithium metal deposition layer disappears, the thickness of the buffer layer is compressed again, so the buffer layer is repeatedly compressed and is always in a compressed state, which always extrudes the negative electrode plate, so that the lithium metal battery always has a certain pressure during charging and discharging, and keeps the lithium on the negative side to be deposited densely.

[0042] Optionally, the thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the relationship: 1.5T≤L≤1.64T.

[0043] The thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the above relationship, which helps the buffer layer to be in a compressed state, and the buffer layer provides pressure for the negative electrode plate during the charging and discharging of the battery, which helps the metal to be deposited uniformly.

[0044] Optionally, the thickness of the active material supplement layer is 2-100 μm.

[0045] And / or, the thickness of the buffer layer is 10-200 μm.

[0046] The thickness of the active material supplement layer satisfies the above range, which can supplement the consumption of the active material during the battery cycle. It can be understood that the active material will gradually be consumed as the battery is cycled, and in order to improve the cycle performance of the battery, the active material supplement layer is added in excess in the present scheme, that is, there is always an active material supplement layer during the entire cycle of the battery. Therefore, when the buffer layer is arranged on the opposite sides of the negative current collector, the active material supplement layer is arranged in the middle of the negative current collector, and the active material supplement layer has a certain thickness. During the expansion and contraction of the buffer layer, the active material supplement layer can support between the electrode sheets, reducing the problem of uneven stress of the negative electrode sheet.

[0047] The thickness of the buffer layer is in the above range, which helps the buffer layer to provide a certain amount of compression and expansion, so as to provide pressure for the negative electrode sheet during the battery cycle. For example, when the battery is assembled, the initial state of the buffer layer in the battery is a compressed state. As the metal on the negative side is deposited, the thickness of the metal layer on the negative side increases, and the initially compressed buffer layer expands. As the metal on the negative side is dissolved out, the thickness of the metal layer on the negative side decreases, and the expanded buffer layer is compressed again. In this way, the buffer layer provides pressure for the negative electrode sheet during the battery cycle.

[0048] Optionally, the negative current collector is connected with a negative tab, and the buffer layer is close to the negative tab.

[0049] The negative current collector is connected with a negative tab, and the buffer layer is close to the negative tab, which can reduce the contact between the negative tab and the negative metal layer and reduce the risk of short circuit of the battery.

[0050] Optionally, the separator includes a base film and a coating layer arranged on the surface of the base film, and the coating layer includes a binder and / or ceramic particles.

[0051] The secondary battery includes a jelly-roll battery, a square battery, a cylindrical battery, and a soft-pack battery.

[0052] In order to maintain good contact between the buffer layer and the separator during the elastic expansion and contraction of the buffer layer, and to provide the separator with the ability to resist elastic force, the separator includes a base film and a coating layer arranged on the surface of the base film, and the coating layer includes a binder and / or ceramic particles. The adhesive can provide better adhesion between the separator and the buffer layer, reducing the displacement of the buffer layer during expansion and contraction. The ceramic particles can improve the mechanical strength of the separator, so that the separator has better strength to resist the elastic stress of the buffer layer.

[0053] The secondary battery of the present application includes a jelly-roll battery, a square battery, a cylindrical battery, and a soft-pack battery.

[0054] Optionally, the application further provides a negative electrode tab, comprising a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, wherein at least part of the surface of the negative electrode current collector is provided with the buffer layer.

[0055] Optionally, the buffer layer comprises at least two spaced buffer bodies, and the two buffer bodies are distributed symmetrically along the center point of one surface of the negative electrode current collector.

[0056] Optionally, the width of the two buffer bodies accounts for 3% to 50% of the width of the negative electrode current collector.

[0057] Optionally, the elastic stress of the buffer layer is 2 MPa to 6.5 MPa.

[0058] Optionally, at least one surface of the negative electrode current collector is provided with an active material supplement layer.

[0059] Optionally, the same surface of the negative electrode current collector comprises a buffer area and an active material area, the buffer layer is arranged in the buffer area, and the active material supplement layer is arranged in the active material area.

[0060] The thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

[0061] Optionally, the thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the relationship: 1.5T≤L≤1.64T.

[0062] Optionally, the thickness of the active material supplement layer is 2 μm to 100 μm.

[0063] And / or, the thickness of the buffer layer is 10 μm to 200 μm.

[0064] Optionally, the negative electrode current collector is connected with a negative electrode tab, and the buffer layer is close to the negative electrode tab.

[0065] Optionally, the application further provides a preparation method of a secondary battery, comprising:

[0066] preparing a positive electrode tab, a negative electrode tab and a separator, wherein the negative electrode tab comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector;

[0067] alternately stacking or winding the positive electrode tab, the separator and the negative electrode tab, and winding the outermost side with the separator to obtain an electric core;

[0068] arranging a clamp outside the electric core to compress the electric core, wherein the compression amount of the buffer layer is 38% to 80% to obtain a secondary battery.

[0069] In the preparation process of the secondary battery, after obtaining the battery cell, a clamp is arranged outside the battery cell, so that the battery cell is compressed, and the compression amount of the buffer layer is 38% to 80%. In this way, the buffer layer is always in a compressed state in the battery, the buffer layer in the compressed state in the battery has a rebound force to extrude the negative electrode plate, and the compression amount of the buffer layer is 38% to 80%, so that after the metal is deposited on the negative electrode side, the buffer layer rebounds to a certain extent, and the rebounded buffer layer is still in a compressed state and still extrudes the negative electrode plate to a certain extent, which is helpful for the buffer layer to extrude the negative electrode plate during the battery cycle process, and is helpful for the dense deposition of the metal and improves the cycle performance of the battery.

[0070] Optionally, the same surface of the negative current collector includes a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material area is provided with an active material supplement layer.

[0071] In the step of arranging the clamp outside the battery cell to compress the battery cell, the buffer layer is compressed to the same thickness as the active material supplement layer.

[0072] After the buffer layer and the active material supplement layer are arranged on the same surface of the negative current collector, the buffer layer is compressed to the same thickness as the active material supplement layer when the battery cell is compressed, which is helpful for the rebound of the buffer layer after the metal is deposited on the negative electrode side, and the rebounded buffer layer is still in a compressed state.

[0073] Optionally, the compression amount of the buffer layer is 50%-64%.

[0074] The compression amount of the buffer layer meets the above range, which is helpful for the buffer layer to be in a compressed state during the battery cycle process, and also reduces the problem of buffer layer overflow to the metal deposition area when the compression amount of the buffer layer is too large.

[0075] Optionally, the application also provides a preparation method of a negative electrode plate, comprising:

[0076] The buffer body is arranged on the opposite sides of at least one surface of the foil, and the buffer body on at least one side is arranged intermittently to form a negative electrode tab in the intermittent area.

[0077] According to the preset size of the negative current collector, the negative current collector is cut out on the negative current collector foil, the opposite sides of one surface of the negative current collector are provided with a buffer body, and the negative current collector is connected with the negative electrode tab.

[0078] In order to simultaneously prepare the negative tab during the preparation of the negative electrode sheet, the negative tab is close to the buffer layer, the buffer layer is arranged on the opposite sides of at least one surface of the foil, the buffer layer on at least one side is discontinuously arranged, the negative tab is formed in the discontinuous area, the negative current collector is cut out on the foil according to the preset size of the negative current collector, the buffer layer is arranged on the opposite sides of the negative current collector, and the negative tab is connected to the negative current collector.

[0079] Optionally, the step of arranging the buffer layer on the opposite sides of at least one surface of the foil comprises:

[0080] The active material supplement layer and the two spaced buffer layers are arranged on at least one surface of the foil, the two buffer layers are located on the opposite sides of the active material supplement layer, the thickness of the buffer layer is 10-200 μm, and the thickness of the active material supplement layer is 5-100 μm.

[0081] The active material supplement layer is arranged between the two buffer layers, which helps to limit the pulverized lithium by the two buffer layers during the battery cycle, so that the pulverized lithium is limited between the two sides of the buffer layer, the pulverized lithium is reduced to be connected to the tab, and the risk of battery short circuit is reduced.

[0082] In order to compress the buffer layer, the thickness of the buffer layer is greater than the thickness of the active material supplement layer, the thickness of the buffer layer is 10-200 μm, and the thickness of the active material supplement layer is 5-100 μm. During the preparation of the battery, the buffer layer is compressed to the same thickness as the active material supplement layer, which helps the buffer layer to be compressed all the time, to extrude the negative electrode sheet, so that the lithium metal battery has a certain pressure all the time during the charging and discharging process, and the lithium deposition on the negative side is kept dense.

[0083] Optionally, the application also provides a power utilization device comprising the secondary battery.

[0084] The negative electrode sheet of the application comprises a negative current collector and a buffer layer arranged on at least one surface of the negative current collector. The buffer layer is arranged on at least part of the area of one surface of the negative current collector. The buffer layer can provide pressure for the negative electrode sheet inside the secondary battery, which helps to make the metal deposition on the negative side dense during the cycle of the secondary battery. During the metal deposition process, the buffer layer can provide deposition space for the deposition layer, and improve the cycle performance of the battery.

[0085] It can be understood that the setting of the buffer layer makes the negative pole sheet inside the battery cell receive certain pressure during the secondary battery cycle process, which helps the metal deposition on the negative side to be dense. Taking the lithium metal battery as an example, the dense deposition of lithium on the negative side can reduce the specific surface area of the overall lithium deposition layer, which helps to reduce the side reaction of the lithium deposition layer and the electrolyte, reduces the consumption of the electrolyte, and the scalability of the buffer layer also helps to provide space for the deposition of metal on the negative pole; at the same time, during the discharging process, the negative pole sheet receives certain pressure, which can reduce the interface impedance, help the uniform dissolution of lithium, reduce the concentration polarization of lithium ions, reduce the polarization of the battery, reduce the capacity attenuation of the battery, and further improve the cycle performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0086] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to the structures shown in the drawings without creative labor for those skilled in the art.

[0087] FIG. 1 The structure schematic diagram of the negative pole sheet of an embodiment of the present application is shown in FIG. 1.

[0088] FIG. 2 The structure schematic diagram of the negative pole sheet of another embodiment of the present application is shown in FIG. 2.

[0089] FIG. 3 The structure schematic diagram of the negative pole current collector of an embodiment of the present application is shown in FIG. 3.

[0090] FIG. 4 The structure schematic diagram of the positive pole sheet and the negative pole sheet of an embodiment of the present application is shown in FIG. 4.

[0091] FIG. 5 The structure schematic diagram of the positive pole sheet and the negative pole sheet of another embodiment of the present application is shown in FIG. 5.

[0092] FIG. 6 The structure schematic diagram of the negative pole sheet of another embodiment of the present application is shown in FIG. 6.

[0093] FIG. 7 The structure schematic diagram of the foil in the preparation process of the negative pole sheet of the present application is shown in FIG. 7.

[0094] FIG. 8 The schematic diagram of the battery cell of an embodiment of the present application is shown in FIG. 8.

[0095] FIG. 9 The schematic diagram of the battery cell of an embodiment of the present application is shown in FIG. 9. FIG. 8 The exploded view of the battery cell of an embodiment of the present application is shown in FIG. 10.

[0096] FIG. 10is a schematic view of a battery module according to an embodiment of the present application;

[0097] FIG. 11 is a schematic view of a battery pack according to an embodiment of the present application;

[0098] FIG. 12 is FIG. 11 is an exploded view of a battery pack according to an embodiment of the present application;

[0099] FIG. 13 is a schematic view of an electric device using a battery cell as a power source according to an embodiment of the present application.

[0100] BRIEF DESCRIPTION OF DRAWINGS

[0101] Reference Numeral Name Reference Numeral Name 1 Battery pack 5 Battery cell 2 Upper case 51 Housing 3 Lower case 52 Electrode assembly 4 Battery module 53 Cover plate 10 Negative current collector 20 Buffer layer 201 Buffer body 30 Center point of negative current collector 40 Positive current collector 50 Positive active layer 60 Insulating layer 70 Active material supplement layer 80 Negative tab

[0102] The implementation, functional features and advantages of the present application will be further described with reference to the accompanying drawings in conjunction with embodiments. DETAILED DESCRIPTION

[0103] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0104] Hereinafter, the secondary battery and the method of manufacturing the same, the negative electrode sheet and the method of manufacturing the same, and the electric device are specifically disclosed, with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, redundant descriptions of structures that are substantially the same are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0105] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0106] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0107] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0108] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0109] During the battery cycle, the pressure inside the battery cell is insufficient, which will lead to a decrease in battery cycle performance.

[0110] For example, taking lithium metal batteries as an example, a certain pressure is required inside the battery cell during the charging and discharging process of lithium metal batteries. If the pressure is insufficient, the lithium metal will be deposited loosely, resulting in a large specific surface area of ​​lithium metal deposition and many side reactions, which will affect the battery's cycle performance.

[0111] To solve the above problems, the application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and a separator; the negative electrode sheet comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, and at least part of the area of one surface of the negative electrode current collector is provided with the buffer layer.

[0112] The buffer layer has the properties of compressibility and elasticity.

[0113] The test method of the percentage W of the area of the buffer layer on one surface of the negative electrode current collector to the area of one surface of the negative electrode current collector is as follows: the battery is disassembled to obtain the negative electrode sheet, the area S of one surface of the negative electrode current collector is measured, the area s of the buffer layer on the surface is measured, and then W = s / S*100%.

[0114] At least part of the area of one surface of the negative electrode current collector is provided with the buffer layer, which means that the buffer layer can be arranged on part of the area of one surface of the negative electrode current collector or on the whole area of one surface of the negative electrode current collector.

[0115] The negative electrode sheet of the application comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, at least part of the area of one surface of the negative electrode current collector is provided with the buffer layer, the buffer layer can provide pressure for the negative electrode sheet inside the secondary battery, which helps the dense deposition of metal on the negative electrode side during the cycle process of the secondary battery, and the buffer layer can provide deposition space for the deposition layer during the deposition process, thereby providing expansion space for the expansion of the negative electrode, and improving the cycle performance of the battery.

[0116] It can be understood that the arrangement of the buffer layer makes the negative electrode sheet inside the battery cell receive certain pressure during the cycle process of the secondary battery, which helps the dense deposition of metal on the negative electrode side. Taking a lithium metal battery as an example, the dense deposition of lithium on the negative electrode side can reduce the specific surface area of the overall lithium deposition layer, which helps to reduce the side reaction between the lithium deposition layer and the electrolyte, reduces the consumption of the electrolyte, and the elasticity of the buffer layer also helps to provide space for the deposition of metal on the negative electrode and provide expansion space for the expansion of the negative electrode. At the same time, during the discharge process, the negative electrode sheet receives certain pressure, which can reduce the interface impedance, help the uniform dissolution of lithium, reduce the concentration polarization of lithium ions, reduce the polarization of the battery, reduce the capacity attenuation of the battery, and thus improve the cycle performance of the battery.

[0117] Further, generally, the volume expansion caused by lithium deposition-stripping during the cycle process usually needs to rely on external buffer structures such as elastic washers, springs and the like to provide expansion space and expansion pressure. On the one hand, these additional devices increase the complexity of the system application, limiting the application range. At the same time, the energy density of the system is reduced, which weakens the advantage of high energy density of the lithium metal cell itself.

[0118] By adopting the scheme of the present application, the buffer layer is directly arranged on the negative pole piece, the use of the buffer structure outside the battery cell in the battery can be reduced, the arrangement of these additional devices is reduced, and the energy density of the battery is improved.

[0119] It can be understood that at least part of the area of one surface of the negative pole current collector is provided with the buffer layer, that is, the entire surface of at least one surface of the negative pole current collector can be provided with the buffer layer, at this time, the percentage of the area of the buffer layer on the at least one surface of the negative pole current collector to the area of one surface of the negative pole current collector is 100%, such as shown in FIG. 1. FIG. 1 As shown in FIG. 2, the surface of the negative pole current collector 10 is provided with the buffer layer 20. Taking a lithium metal battery as an example, during lithium metal deposition, lithium metal can be deposited on the surface of the buffer layer 20.

[0120] Of course, the buffer layer can be partially arranged on at least one surface of the negative pole current collector, at this time, the percentage of the area of the buffer layer on the at least one surface of the negative pole current collector to the area of one surface of the negative pole current collector is greater than or equal to 3% and less than 100%, such as shown in FIG. 3. FIG. 2 As shown in FIG. 4, the surface of the negative pole current collector 10 is partially provided with the buffer layer 20. Taking a lithium metal battery as an example, during lithium metal deposition, lithium metal can be deposited on the surface of the buffer layer 20 or on the part of the negative pole current collector where the buffer layer is not arranged.

[0121] In an embodiment, the buffer layer at least includes two buffer bodies arranged at intervals, and the two buffer bodies are located on both sides of the center point of one surface of the negative pole current collector.

[0122] The center point of one surface of the negative pole current collector refers to the geometric center point of one surface of the negative pole current collector, such as shown in FIG. 5. FIG. 3 As shown in FIG. 6, in the negative pole current collector 10, the intersection of the two diagonal lines is the center point 30 of the negative pole current collector.

[0123] The buffer layer at least includes two buffer bodies arranged at intervals, and the two buffer bodies are located on both sides of the center point of one surface of the negative pole current collector, which helps to improve the stability of the support of the buffer layer to the pole piece, is beneficial to improve the uniformity of the stress distribution of the negative pole piece, and further helps to improve the uniformity of metal deposition. Such as shown in FIG. 7. FIG. 2 As shown in FIG. 8, the surface of the negative pole current collector 10 is provided with two buffer bodies 201 on both sides of the center point.

[0124] In an embodiment, the two buffer bodies are symmetrically distributed along the center point of one surface of the negative pole current collector.

[0125] The two buffer bodies are symmetrically distributed along the center point of one surface of the negative pole current collector, which helps to improve the stability of the support of the buffer layer to the pole piece, is beneficial to improve the uniformity of the stress distribution of the negative pole piece, and further helps to improve the uniformity of metal deposition.

[0126] In an embodiment, the two buffer bodies have the same area.

[0127] The two buffer bodies have the same area, which helps to improve the stability of the buffer layer in supporting the pole piece, helps to evenly distribute the stress distribution of the buffer layer compression and rebound, reduces stress concentration, and makes the metal deposition uniform.

[0128] In an embodiment, the two buffer bodies are located on opposite sides of one surface of the negative current collector.

[0129] The two buffer bodies are located on opposite sides of one surface of the negative current collector, which helps to evenly distribute the stress distribution of the buffer layer compression and rebound, reduces stress concentration, and makes the metal deposition uniform.

[0130] In addition, the two buffer bodies are located on opposite sides of one surface of the negative current collector, which helps to make the metal deposition near the middle of the negative current collector, and the buffer bodies on both sides help to limit the deposited metal, limit the drift of the pulverized lithium, confine the pulverized lithium between the two sides of the buffer body, reduce the overlap of the pulverized lithium to the tab, and reduce the risk of battery short circuit.

[0131] In an embodiment, the length of the two buffer bodies is the same as the length of the negative current collector.

[0132] It can be understood that in the structure of the negative current collector having long edges and short edges, the buffer bodies can be located on opposite two long edges or opposite two short edges. When located on opposite two long edges, the length of the buffer body is the same as the length of the long edge of the negative current collector, and when located on opposite two short edges, the length of the buffer body is the same as the length of the short edge of the negative current collector. In this way, it helps to limit the deposited metal, limit the drift of the pulverized lithium, confine the pulverized lithium between the two sides of the buffer body, reduce the overlap of the pulverized lithium to the tab, and reduce the risk of battery short circuit.

[0133] In an embodiment, the width of the two buffer bodies accounts for 3%-50% of the width of the negative current collector.

[0134] When the two buffer bodies are located on opposite sides of the negative current collector, the width of the two buffer bodies accounts for 3%-50% of the width of the negative current collector, which meets the above range, helps the buffer layer to provide elastic elasticity, that is, the buffer layer provides compression and rebound support between the pole pieces, provides pressure to the battery during the cycle process, improves the uniformity of metal deposition and dissolution, and further improves the cycle performance of the battery.

[0135] In the above 3%-50%, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to point values in the embodiments and 3%, 5%, 10%, 25%, 50%, etc., and range values between any two point values.

[0136] In an embodiment, the elastic stress of the buffer layer is 2-6.5 MPa.

[0137] Elastic stress refers to the internal stress generated by the material when subjected to external force.

[0138] The test procedure of the elastic stress of the buffer layer is as follows: prepare the buffer layer, and measure the stress of the buffer layer by extruding the buffer layer. For example, the static method is to determine the elastic stress by applying a known static force on the material sample and then measuring the deformation generated thereby. A universal testing machine is used to compress the sample, and the stress data of the buffer layer is recorded.

[0139] The elastic stress of the buffer layer is 2-6.5 MPa, which means that the buffer layer has the ability to resist elastic deformation under the condition of extrusion stress inside the battery, that is, the elastic stress of the buffer layer meets the above range, which helps to maintain the stable compression resilience of the buffer layer and reduce the problem of elastic expansion failure of the buffer layer.

[0140] In the above 2-6.5 MPa, the values include the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 6.5 MPa, etc., as well as the range values between any two point values.

[0141] In an embodiment, the percentage of the area of the buffer layer on one surface of the negative current collector to the area of the one surface of the negative current collector is 3%-50%.

[0142] In the scheme of arranging the buffer layer on part of the area of at least one surface of the negative current collector, the metal can be deposited on the other area of the surface which is not arranged with the buffer layer. At this time, the percentage of the area of the buffer layer to the area of one surface of the negative current collector is 3%-50%. It can be understood that meeting the above range helps the buffer layer to provide elastic expansion, that is, the buffer layer provides compression and resilience support between the pole pieces, provides pressure for the battery during the cycle process, improves the uniformity of metal deposition and dissolution, and further improves the cycle performance of the battery. Of course, meeting the upper limit of the above range helps to reduce the size of the battery and reduce the risk of reducing the volumetric energy density of the battery. It can be understood that it is difficult to further improve the cycle performance of the battery by continuing to increase the coverage area of the buffer layer on the negative current collector, and continuing to increase the area will also increase the size of the battery and reduce the volumetric energy density. Therefore, meeting the above range helps to improve the cycle performance and volumetric energy density of the battery.

[0143] For example, as shown in FIG. 1, the buffer layer 2 is arranged on the surface of the negative current collector 1, and the metal is deposited on the surface of the negative current collector 1 which is not arranged with the buffer layer 2. FIG. 2As shown, taking a lithium metal battery as an example, during lithium metal deposition, lithium metal can be deposited at the part between the two buffer bodies 201.

[0144] It can be understood that, under the arrangement of the cell external buffer structure, the direct contact and extrusion between the internal pole pieces are prone to increase the local non-uniformity of stress in the case of uneven thickness of the pole piece surface, leading to increased polarization and accelerated capacity decay of the cell. In the present application, the metal can be deposited on the surface of the current collector other than the region where the buffer layer is arranged. The buffer layer mainly serves to extrude the adjacent pole piece, and the thickness consistency of the buffer layer during the extrusion process is good, and it is difficult to appear the case of uneven thickness of the buffer layer. Arranging the buffer layer on the negative pole piece can reduce the problem of uneven distribution of stress caused by direct contact and extrusion of the negative pole piece, reduce the increase of polarization, and reduce the capacity decay of the cell.

[0145] Of the above 3%-50%, the values include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Specific examples include, but are not limited to, the point values in the embodiments and 3%, 5%, 10%, 25%, 50%, etc., as well as the range values between any two point values.

[0146] In an embodiment, the material of the buffer layer includes at least one of polypropylene, polyethylene, and polyimide.

[0147] In an embodiment, the buffer layer includes a porous structure.

[0148] In an embodiment, the material of the buffer layer includes at least one of polypropylene, polyethylene, and polyimide. In another embodiment, the buffer layer includes a porous structure, which helps the buffer layer to absorb electrolyte, and the electrolyte absorbed by the buffer layer is released during the charging and discharging process, so that the electrolyte infiltration in the battery cycle process is improved.

[0149] In an embodiment, the positive pole piece includes a positive current collector and a positive active layer arranged on at least one surface of the positive current collector; and the same surface of the negative current collector includes a buffer region and an active material region, the buffer layer is located in the buffer region, and the projection of the positive active layer is located in the active material region.

[0150] The positive pole piece includes a positive current collector and a positive active layer arranged on at least one surface of the positive current collector; and the same surface of the negative current collector includes a buffer region and an active material region, the buffer layer is located in the buffer region, and the projection of the positive active layer is located in the active material region. In this way, it is helpful for the active ions on the positive side to be effectively deposited to the active material region on the negative side.

[0151] And the projection of the positive active layer is located in the active material area of the negative electrode, reducing the deposition of active ions on the buffer layer on the positive side, so that when the buffer layer is located on both sides of the negative current collector, it helps the buffer layer to limit the deposition of metal in the middle of the negative current collector, to a certain extent, it can limit the drift of pulverized lithium, so that the pulverized lithium is limited between the two sides of the buffer layer, reducing the risk of short circuit; it can be understood that the lithium deposited on the negative current collector is dead lithium / pulverized lithium that loses electrical connection with the negative current collector, and the pulverized lithium is in a free state inside the battery cell, which can cause short circuit when the positive and negative tabs are connected. The projection of the positive active layer in the active material area helps to reduce the risk of battery short circuit.

[0152] As shown in FIG. 4 When the buffer body 201 is located on the opposite sides of the negative current collector 10, the active material area is located between the two buffer bodies 201 of the negative current collector 10, and the positive active layer 50 is provided on the positive current collector 40, and the projection of the positive active layer 50 is located in the active material area of the negative current collector 10.

[0153] In an embodiment, the region of the positive current collector corresponding to the buffer layer is provided with an insulating layer.

[0154] The insulating layer is arranged opposite to the buffer layer, which can improve the support of the insulating layer to the buffer layer in the battery, and help the buffer layer to elastically deform.

[0155] As shown in FIG. 5 When the buffer body 201 is located on the opposite sides of the negative current collector 10, the region of the positive current collector corresponding to the buffer body 201 is provided with an insulating layer 60.

[0156] In an embodiment, at least one surface of the negative current collector is provided with an active material supplement layer.

[0157] The active material supplement layer is used to supplement the lost active material, for example, in a lithium metal battery, the active material supplement layer is a lithium supplement layer, which can supplement the lithium consumption of each cycle, because lithium metal will form SEI (Solid Electrolyte Interphase) during deposition and dissolution, the lithium supplement layer can supplement the lithium consumption during the formation of SEI, and improve the cycle performance of the battery.

[0158] In an embodiment, the same surface of the negative current collector includes a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material supplement layer is located in the active material area.

[0159] The same surface of the negative current collector includes a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material supplement layer is located in the active material area. For example, in a lithium metal battery, the active material supplement layer is a lithium supplement layer, which helps the metal to deposit on the surface of the lithium supplement layer.

[0160] As shown in FIG. 5 FIG. 1, when the buffer body 201 is located on the opposite sides of the negative current collector 10, the active material area is located between the two buffer bodies 201 of the negative current collector 10, and at this time, the active material supplement layer 70 is located between the two buffer bodies 201 of the negative current collector 10.

[0161] In an embodiment, the thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

[0162] The thickness L of the buffer layer refers to the thickness in the natural state, that is, the thickness when not subjected to extrusion. During battery assembly, the buffer layer is compressed to the same thickness as the active material supplement layer, so that the buffer layer has an expansion resilience and extrusion to the negative electrode plate. When the thickness L of the buffer layer is greater than the thickness T of the active material supplement layer, after the buffer layer is compressed to the same thickness as the active material supplement layer, the buffer layer has an expansion resilience and extrusion to the negative electrode plate.

[0163] The buffer layer in the battery is initially in a compressed state, providing pressure to the inside of the cell. During the cycle process, the deposition layer thickens during the metal deposition process, the thickness of the buffer layer is released, providing space for the expansion of the negative electrode. After the deposition layer of the lithium metal disappears, the thickness of the buffer layer is compressed again.

[0164] For example, taking a lithium metal battery as an example, during battery assembly, the buffer layer is compressed to the same thickness as the lithium supplement layer, and the lithium metal layer on the negative side thickens during the deposition process. The buffer layer expands and rebounds, providing space for the deposition of lithium metal. After the deposition layer of lithium metal disappears, the thickness of the buffer layer is compressed again. The buffer layer is repeatedly compressed and is always in a compressed state, always extruding the negative electrode plate, so that the lithium metal battery always has a certain pressure during the charging and discharging process, and the lithium on the negative side is densely deposited.

[0165] In an embodiment, the thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the relationship: 1.5T≤L≤1.64T.

[0166] The measurement steps of the thickness L of the buffer layer and the thickness T of the active material supplement layer: during the preparation of the negative electrode plate, the thickness of the buffer layer and the thickness of the active material supplement layer can be tested by using a micrometer. In the battery, the battery can be disassembled, and the thickness of the buffer layer and the thickness of the active material supplement layer can be tested by using a micrometer.

[0167] The thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the above relationship, which helps the buffer layer to be in a compressed state, and the buffer layer provides pressure to the negative electrode plate during the charging and discharging process of the battery, which helps the metal to be uniformly deposited.

[0168] In the above 1.5T≤L≤1.64T, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values, specific examples include but are not limited to the point values in the embodiments and L=1.5T, L=1.51T, L=1.55T, L=1.57T, L=1.6T, L=1.61T, L=1.64T, etc., and the range values between any two point values.

[0169] In an embodiment, the thickness of the active material supplement layer is 2-100 μm.

[0170] In an embodiment, the thickness of the buffer layer is 10-200 μm.

[0171] The thickness of the active material supplement layer meets the above range, which can supplement the consumption of active material during battery cycling. It can be understood that the active material will gradually be consumed as the battery cycles, and in order to improve the cycle performance of the battery, the active material supplement layer is added in excess in the present scheme, that is, there is always an active material supplement layer during the entire cycle of the battery. When the buffer layer is arranged on the opposite sides of the negative current collector, the active material supplement layer is arranged in the middle of the negative current collector, and the active material supplement layer has a certain thickness, which can support the active material supplement layer between the pole pieces during the expansion and contraction of the buffer layer, reducing the problem of uneven stress of the negative pole piece.

[0172] The thickness of the buffer layer is in the above range, which helps the buffer layer to provide a certain amount of compression and expansion, so as to provide pressure for the negative pole piece during the battery cycle. For example, when the battery is assembled, the initial state of the buffer layer in the battery is a compressed state, and as the metal on the negative side is deposited, the thickness of the metal layer on the negative side increases, and the initially compressed buffer layer expands. As the metal on the negative side is dissolved out, the thickness of the metal layer on the negative side decreases, and the expanded buffer layer is compressed again, so as to provide pressure for the negative pole piece during the battery cycle.

[0173] In the above 2-100 μm, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values, specific examples include but are not limited to the point values in the embodiments and 2 μm, 3 μm, 5 μm, 10 μm, 20 μm, 50 μm, 80 μm, 100 μm, etc., and the range values between any two point values.

[0174] In the range of 1-200 μm, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values, specific examples include but are not limited to the point values in the embodiments and 10 μm, 12 μm, 13 μm, 15 μm, 20 μm, 40 μm, 80 μm, 100 μm, 150 μm, 180 μm, 200 μm, etc., and the range values between any two point values.

[0175] In an embodiment, the negative current collector is connected with a negative tab, and the buffer layer is close to the negative tab.

[0176] The negative current collector is connected with a negative tab, and the buffer layer is close to the negative tab, as shown in FIG. 8, the negative tab 80 is connected to the negative current collector 10 close to the buffer body 201, which can reduce the contact between the negative tab and the negative metal layer and reduce the risk of short circuit of the battery. FIG. 8

[0177] In an embodiment, the separator includes a base film and a coating layer provided on the surface of the base film, and the coating layer includes a binder and / or ceramic particles.

[0178] In an embodiment, the secondary battery includes a stacked battery, a square battery, a cylindrical battery, and a soft package battery.

[0179] In order to maintain good contact between the buffer layer and the separator during elastic expansion and to provide the separator with resistance to elastic force, the separator includes a base film and a coating layer provided on the surface of the base film, and the coating layer includes a binder and / or ceramic particles. The binder can provide better adhesion between the separator and the buffer layer and reduce displacement of the buffer layer during expansion. The ceramic particles can improve the mechanical strength of the separator and provide the separator with better strength to resist the elastic stress of the buffer layer.

[0180] The secondary battery of the present application includes a stacked battery, a square battery, a cylindrical battery, and a soft package battery.

[0181] With the scheme of the present application, the buffer layer provided on the negative tab provides extrusion force to the negative tab during compression and expansion, which simplifies external facilities and improves the energy density of the system. It can be understood that, in general, in order to provide pressure to the negative tab, external buffer materials such as elastic pads and springs are needed to provide pressure, which increases the application complexity of the battery system, limits the application range, and reduces the energy density of the battery system. The scheme of the present application provides a buffer layer on the negative tab, which can simplify the battery structure and improve the energy density of the battery. In the scheme of providing buffer layers on opposite sides of the negative tab, the stress distribution of the buffer layer during compression and expansion is uniform, stress concentration is reduced, and the buffer layer can provide part of the pressure and expansion space required for metal deposition during charging and discharging, which improves the cycle performance of the battery. ​

[0182] In an embodiment, the application also provides a negative electrode tab, which comprises a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector, and the buffer layer is arranged on at least part of the surface of the negative electrode current collector.

[0183] In an embodiment, the buffer layer comprises at least two buffer bodies arranged at intervals, and the two buffer bodies are located on both sides of the center point of the surface of the negative electrode current collector.

[0184] In an embodiment, the two buffer bodies are symmetrically distributed along the center point of the surface of the negative electrode current collector.

[0185] In an embodiment, the two buffer bodies have the same area.

[0186] In an embodiment, the two buffer bodies are located on opposite sides of the surface of the negative electrode current collector, respectively.

[0187] In an embodiment, the length of the two buffer bodies is the same as the length of the negative electrode current collector.

[0188] In an embodiment, the width of the two buffer bodies accounts for 3%-50% of the width of the negative electrode current collector.

[0189] In an embodiment, the elastic stress of the buffer layer is 2-6.5 MPa.

[0190] In an embodiment, the material of the buffer layer comprises at least one of polypropylene, polyethylene, and polyimide.

[0191] In an embodiment, the buffer layer comprises a porous structure.

[0192] In an embodiment, the at least one surface of the negative electrode current collector is provided with an active material supplement layer.

[0193] In an embodiment, the same surface of the negative electrode current collector comprises a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material supplement layer is located in the active material area.

[0194] In an embodiment, the thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

[0195] In an embodiment, the thickness L of the buffer layer and the thickness T of the active material supplement layer satisfy the relationship: 1.5T≤L≤1.64T.

[0196] In an embodiment, the thickness of the active material supplement layer is 2-100 μm.

[0197] In an embodiment, the thickness of the buffer layer is 10-200 μm.

[0198] In an embodiment, the negative electrode current collector is connected with a negative electrode tab, and the buffer layer is close to the negative electrode tab.

[0199] In an embodiment, the application further provides a preparation method of a secondary battery, comprising: preparing a positive electrode tab, a negative electrode tab and a separator, the negative electrode tab comprising a negative electrode current collector and a buffer layer arranged on at least one surface of the negative electrode current collector; alternately stacking or winding the positive electrode tab, the separator and the negative electrode tab, and winding the outermost side with the separator to obtain a battery cell; arranging a clamp outside the battery cell to compress the battery cell, and the compression amount of the buffer layer is 38% to 80% to obtain the secondary battery.

[0200] In the preparation process of the secondary battery, after obtaining the battery cell, a clamp is arranged outside the battery cell to compress the battery cell, and the compression amount of the buffer layer is 38% to 80%. In this way, the buffer layer is always in a compressed state in the battery, the buffer layer in the compressed state in the battery has a rebound force to extrude the negative electrode tab, and the compression amount of the buffer layer is 38% to 80%, so that the buffer layer rebounds after the metal is deposited on the negative electrode side, and the rebounded buffer layer is still in a compressed state and still extrudes the negative electrode tab, which helps the buffer layer to extrude the negative electrode tab during the cycle of the battery, and helps the dense deposition of the metal and improves the cycle performance of the battery.

[0201] The compression amount of the buffer layer refers to (the thickness before compression-the thickness after compression) / the thickness before compression*100%.

[0202] In the above 38% to 80%, the values include the minimum value and the maximum value in the range, and every value between the minimum value and the maximum value, and specific examples include but are not limited to the point values in the embodiments and 38%, 40%, 50%, 60%, 70%, 80%, etc., and the range values between any two point values.

[0203] In an embodiment, the same surface of the negative electrode current collector comprises a buffer area and an active material area, the buffer layer is located in the buffer area, and the active material area is provided with an active material supplement layer; in the step of arranging a clamp outside the battery cell to compress the battery cell, the buffer layer is compressed to the same thickness as the active material supplement layer.

[0204] After the buffer layer and the active material supplement layer are arranged on the same surface of the negative electrode current collector, the buffer layer is compressed to the same thickness as the active material supplement layer when the battery cell is compressed, which helps the buffer layer to be in a compressed state after rebounding after the metal is deposited on the negative electrode side.

[0205] The compression amount of the buffer layer is tested by testing the thickness D1 of the buffer layer without stress and the thickness D2 of the active material supplement layer, and the compression amount of the buffer layer is (D1-D2) / D1*100%.

[0206] In one embodiment, the compression amount of the buffer layer is 50%-64%.

[0207] The compression amount of the buffer layer satisfies the above range, which helps the buffer layer to be in a compressed state during the battery cycle, and also reduces the problem of the buffer layer overflowing into the metal deposition area when the compression amount of the buffer layer is too large.

[0208] In the above 38% to 64%, the values ​​include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Specific examples include but are not limited to the point values ​​in the embodiments and 38%, 40%, 50%, 60%, 64%, etc., as well as the range values ​​between any two of the above point values.

[0209] In one embodiment, the present application also provides a method for preparing a negative electrode sheet, comprising: providing a buffer body on opposite sides of at least one surface of a foil, the buffer body on at least one side being provided intermittently, and forming a negative electrode tab in the intermittent area; cutting out a negative electrode collector on the negative electrode collector foil according to a preset size of the negative electrode collector (for example, laser cutting or die punching), providing a buffer body on opposite sides of the negative electrode collector, and connecting a negative electrode tab to the negative electrode collector.

[0210] In order to prepare the negative electrode tab at the same time as preparing the negative electrode sheet, the negative electrode tab is close to the buffer layer, and a buffer body is arranged on opposite sides of at least one surface of the foil, wherein the buffer body on one side is arranged continuously and the buffer body on the other side is arranged intermittently, and the negative electrode tab is formed in the intermittent area. The negative electrode collector is cut out on the foil according to the preset size of the negative electrode collector, and the buffer body is provided on opposite sides of the negative electrode collector, and the negative electrode tab is connected to the negative electrode collector.

[0211] In one embodiment, buffer bodies are provided on opposite sides of one surface of a foil, wherein the buffer body on one side is provided continuously and the buffer body on the other side is provided intermittently. A negative electrode collector is cut out from the foil according to a preset size of the negative electrode collector, and a negative electrode tab is provided on the negative electrode collector.

[0212] In another embodiment, buffer bodies are provided on opposite sides of one surface of the foil, and the buffer bodies on both sides are provided intermittently. The negative electrode collector is cut out from the foil according to the preset size of the negative electrode collector, and two negative electrode tabs are provided on the negative electrode collector.

[0213] like FIG. 9 As shown, on the two opposite sides of the foil, one side is provided with a continuous buffer body 201, and the other side is provided with a spaced buffer body 201, and the foil is exposed at the spaced portion. The foil at the spaced portion is used as a negative electrode tab 80, and the negative electrode collector is cut on the foil according to the preset size of the negative electrode collector, so that the negative electrode tab is provided on the negative electrode collector, and the negative electrode tab is close to the buffer layer.

[0214] In an embodiment, the step of disposing the buffer layer on the opposite sides of the at least one surface of the foil includes: disposing an active material supplement layer and two spaced buffer bodies on the at least one surface of the foil, the two buffer bodies being located on opposite sides of the active material supplement layer, the thickness of the buffer body being 10 μm to 200 μm, and the thickness of the active material supplement layer being 5 μm to 100 μm.

[0215] The active material supplement layer is disposed between the two buffer bodies, which helps to limit the pulverized lithium between the two buffer bodies during the battery cycle, so that the pulverized lithium is limited between the two sides of the buffer body, reducing the risk of short circuit of the battery.

[0216] In order to compress the buffer layer, the thickness of the buffer body is greater than the thickness of the active material supplement layer, the thickness of the buffer body is 10 μm to 200 μm, and the thickness of the active material supplement layer is 5 μm to 100 μm. During the preparation of the battery, the buffer body is compressed to the same thickness as the active material supplement layer, which helps the buffer layer to be in a compressed state all the time, and to always extrude the negative electrode plate, so that the lithium metal battery always has a certain pressure during the charging and discharging process, and keeps the lithium dense deposition on the negative side.

[0217] In an embodiment, the application also provides a kind of electric device, and the electric device includes the secondary battery as described above.

[0218] In addition, the battery (battery cell, battery module, battery pack) and the electric device of the application are described below with reference to the accompanying drawings.

[0219] In one embodiment of the application, a battery cell is provided.

[0220] Generally, the battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The separator is the improved separator described above.

[0221] The positive electrode plate includes a positive electrode current collector and a positive electrode coating layer disposed on at least one surface of the positive electrode current collector.

[0222] As an example, the positive electrode current collector has two opposite surfaces in its own thickness direction, and the positive electrode coating layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0223] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0224] In some embodiments, when the secondary battery is a lithium ion battery, the positive electrode active material can employ a positive electrode active material for a lithium ion battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate with an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0225] The battery will be accompanied by Li de-intercalation and consumption during charging and discharging, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode material in the present application, the molar content of Li is the initial state of the material, i.e., the state before feeding. When the positive electrode material is applied to a battery system, the molar content of Li will change after charging and discharging cycles.

[0226] In the enumeration of the positive electrode material in the present application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0227] In some embodiments, the positive electrode coating can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene-fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0228] In some embodiments, the positive electrode coating can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0229] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode sheet can be obtained.

[0230] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have specific limitations on the type of electrolyte, which can be selected as needed.

[0231] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0232] In some embodiments, the electrolyte can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain performance of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, and the like.

[0233] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0234] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0235] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, and the like can be listed.

[0236] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, FIG. 8 is a square structure battery cell 5 as an example.

[0237] In some embodiments, referring to FIG. 9 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0238] In some embodiments, the battery cell pool can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0239] FIG. 10 is a battery module 4 as an example. Referring to FIG. 10 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0240] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 can be accommodated in the accommodation space.

[0241] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0242] FIG. 11 and FIG. 12 is a battery pack 1 as an example. Referring to FIG. 11 and FIG. 12 In the battery pack 1, a battery box and a plurality of battery modules 4 disposed in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0243] In addition, the present application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0244] As the power utilization device, the battery cell, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0245] FIG. 13 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the battery cell for the power utilization device, the battery pack or the battery module can be used.

[0246] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power supply.

[0247] Embodiments

[0248] Embodiment 1

[0249] Preparation of the negative electrode sheet

[0250] The negative current collector (copper foil, 12 pm) is attached with a buffer layer (polypropylene material) on both sides, that is, the buffer layer is located on the opposite sides of the copper foil, one side is a continuous buffer body, and the other side is an intermittent buffer body. The long edge of the pole piece is provided with a buffer layer by means of die cutting, and the intermittent part is cut as a negative electrode tab.

[0251] The length of the negative current collector is 203 pm, the length of the buffer layer is 203 pm, and the width of the negative current collector is the sum of the width of the metal deposition layer 141 pm and the width of the two buffer bodies.

[0252] Preparation of the positive pole piece: mix lithium nickel cobalt manganese oxide, conductive agent acetylene black and binder PVDF in a mass ratio of 98:1:1, add solvent NMP and stir until the system is uniform to obtain a positive electrode slurry; uniformly coat the positive electrode slurry on both sides of the positive current collector aluminum foil, dry at room temperature, then transfer to an oven for further drying, and then cut into a rectangle of 207 mm*138 mm as a positive electrode pole piece, and the positive electrode surface capacity is 3.5 mAh / cm 2 .

[0253] The separator: the base film uses a polyethylene porous film, the surface coating includes a binder and ceramic particles, and the width of the separator is 147 mm.

[0254] Preparation of the electrolyte: take 1.51 g of lithium hexafluorophosphate salt, add 3 g of solvent EC and 7 g of EMC, and fully stir to form a colorless transparent electrolyte with a concentration of 1 M.

[0255] Battery assembly: stack the positive pole piece, the separator and the negative pole piece layer by layer, wherein the negative pole piece is 11 layers, the positive pole piece is 10 layers, and the outermost layer is wound with an additional layer of the separator to complete the stacking. The dry battery prepared in this way is compressed by a clamp outside the dry battery and wrapped in an aluminum plastic film bag to form a stacked dry battery. Inject 41.4 g of the electrolyte prepared above, vacuum heat seal the aluminum plastic film bag, and stand still at room temperature for at least 6 hours before starting the cycle test. The rated capacity of the stacked battery prepared in this way is 23 Ah.

[0256] Example 2

[0257] On the basis of Example 1, the negative current collector (copper foil, 12 pm) is attached with a buffer layer on both sides after lithium supplementation, that is, the buffer layer is located on the opposite sides of the copper foil, the lithium supplementation layer is located between the two buffer layers, one side is a continuous buffer body, and the other side is an intermittent buffer body. The long edge of the pole piece is provided with a buffer layer by means of die cutting, and the intermittent part is cut as a negative electrode tab.

[0258] The length of the negative current collector is 203 pm, the length of the buffer layer is 203 pm, the thickness of the lithium supplementation layer is 50 pm, and the width of the negative current collector is the sum of the width of the lithium supplementation layer 141 pm and the width of the two buffer layers.

[0259] Example 3

[0260] On the basis of Example 1, a buffer layer is provided on the entire side surface of the negative current collector.

[0261] Examples 4 to 10

[0262] On the basis of Example 2, the area percentage of the buffer layer on one side of the negative current collector, the thickness of the lithium supplement layer, and the thickness of the buffer layer are adjusted, as shown in Table 1 below.

[0263] Comparative Example 1

[0264] On the basis of Example 1, no buffer layer is provided.

[0265] Comparative Example 2

[0266] On the basis of Comparative Example 1, no buffer layer is provided, and a lithium supplement layer is provided, as shown in Table 1 below.

[0267] Performance test

[0268] First week full charge lithium deposition thickness: At the end of the first week full charge of the battery, the residual electrolyte on the surface of the negative electrode sheet is cleaned with DMC (dimethyl carbonate). Ion beam interface polishing treatment is performed on the negative electrode sheet to expose the cross section, and a scanning electron microscope SME is used to observe the deposition morphology and thickness of the negative electrode sheet.

[0269] Battery cycle performance: The initial pre-tightening force during battery cycling is determined by compressing the buffer layer to the thickness of the lithium supplement layer, the environmental temperature is set to 25°C, and the battery is charged and discharged at a rate of 0.2C-1C (i.e. 4.6A-23A). The cut-off voltage of charging and discharging is set to 4.3V and 2.8V, respectively. When the discharge capacity decays to 80% of the first cycle discharge capacity, the battery life is considered to be cut off. Specifically, charge at a current of 0.5C to a voltage of 4.3V, and charge at a constant voltage of 4.3V to 0.05C, and stand for 10 min; discharge at a current of 0.5C to a voltage of 2.8V, and stand for 10 min; repeat the above for less than 100 cycles, and record the capacity retention rate while disassembling the battery to observe the distribution of powdered lithium.

[0270] Table 1 Experimental data list

[0271]

[0272] As can be seen from Table 1 above, compared with Comparative Example 1, Examples 1 and 3 have a buffer layer, and the lithium deposition thickness of Examples 1 and 3 is less than that of Comparative Example 1, indicating that the buffer layer can provide pressure for the negative electrode sheet inside the secondary battery, which helps to densify the metal deposition on the negative side during the cycle process of the secondary battery.

[0273] Compared with Comparative Example 2, the buffer layer and the lithium supplement layer are provided in Example 2, the buffer layer is not provided in Comparative Example 2, and the lithium supplement layer is provided, and the lithium deposition thickness of Example 2 is less than that of Comparative Example 2. Moreover, the buffer layer is not provided on the side edge of the negative current collector in Comparative Example 2, and the overflow of the pulverized lithium generated by the negative electrode to the edge of the negative electrode is obvious; in Example 2, the two buffer bodies are respectively located on the opposite sides of one surface of the negative current collector, which helps to make the metal deposition on the position close to the middle of the negative current collector, and the buffer bodies on the two sides help to limit the deposited metal, limit the drift of the pulverized lithium, confine the pulverized lithium between the two buffer bodies, reduce the lap joint of the pulverized lithium to the tab, and reduce the risk of short circuit of the battery.

[0274] Examples 4 to 10 are all provided with the buffer layer and the lithium supplement layer, and when the compression amount of the buffer layer under the pre-tightening force is 38% to 80%, the lithium deposition thickness in Examples 4 to 10 is less than that of the comparative examples, and further, when the compression amount of the buffer layer under the pre-tightening force is 50% to 64%, the deposition of lithium is more dense and the thickness is smaller.

[0275] In Examples 9 and 10, the compression amount of the buffer layer is large, and the buffer layer overflows to the metal deposition area, which is not conducive to the deposition of lithium. When the compression amount of the buffer layer under the pre-tightening force is 50% to 64%, it helps to keep the buffer layer in a compressed state during the battery cycle, and also reduces the problem of buffer layer overflow to the metal deposition area when the compression amount of the buffer layer is too large.

[0276] The buffer layer can provide pressure for the negative electrode sheet inside the secondary battery, which helps to make the metal deposition on the negative electrode side dense during the cycle of the secondary battery, and the buffer layer can provide deposition space for the deposition layer during the metal deposition process, thereby improving the cycle performance of the battery.

[0277] Moreover, the buffer layer is provided on the side edge of the negative current collector, which helps to limit the pulverized lithium.

[0278] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made under the inventive concept of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet and a separator; The negative electrode plate includes a negative electrode current collector and a buffer layer provided on at least one surface of the negative electrode current collector. The buffer layer is provided on at least a partial area of ​​one surface of the negative electrode current collector.

2. The secondary battery according to claim 1, wherein The buffer layer includes at least two buffer bodies that are spaced apart from each other. The two buffer bodies are located on both sides of a center point of one surface of the negative electrode current collector.

3. The secondary battery according to claim 2, wherein The two buffer bodies are symmetrically distributed along the center point of one surface of the negative electrode current collector.

4. The secondary battery according to claim 2 or 3, wherein: The two buffer bodies have the same area.

5. The secondary battery according to any one of claims 2 to 4, wherein The two buffer bodies are respectively located on two opposite sides of one surface of the negative electrode current collector.

6. The secondary battery according to claim 5, wherein The lengths of the two buffer bodies are the same as that of the negative electrode current collector.

7. The secondary battery according to claim 5 or 6, wherein: The width of the two buffer bodies accounts for 3%-50% of the width of the negative electrode current collector.

8. The secondary battery according to any one of claims 1 to 7, wherein The elastic stress of the buffer layer is 2MPa-6.5MPa.

9. The secondary battery according to any one of claims 1 to 8, wherein The area of ​​the buffer layer on one surface of the negative electrode current collector accounts for 3% to 50% of the area of ​​the one surface of the negative electrode current collector.

10. The secondary battery according to any one of claims 1 to 9, wherein The material of the buffer layer includes at least one of polypropylene, polyethylene, and polyimide; And / or, the buffer layer includes a porous structure.

11. The secondary battery according to any one of claims 1 to 10, wherein The positive electrode plate includes a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector; The negative electrode current collector includes a buffer zone and an active material zone on the same surface. The buffer layer is located in the buffer zone, and the projection of the positive electrode active layer is located in the active material zone.

12. The secondary battery according to claim 11, wherein An insulating layer is provided in the region of the positive electrode current collector corresponding to the buffer layer.

13. The secondary battery according to any one of claims 1 to 12, wherein An active material supplement layer is provided on at least one surface of the negative electrode current collector.

14. The secondary battery according to claim 13, wherein The negative electrode current collector includes a buffer zone and an active material zone on the same surface. The buffer layer is located in the buffer zone, and the active material supplement layer is located in the active material zone.

15. The secondary battery according to claim 14, wherein The thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

16. The secondary battery according to claim 15, wherein The relationship between the thickness L of the buffer layer and the thickness T of the active material supplement layer is: 1.5T≤L≤1.64T.

17. The secondary battery according to any one of claims 14 to 16, wherein: The thickness of the active substance supplement layer is 2 μm-100 μm; And / or, the buffer layer has a thickness of 10 μm-200 μm.

18. The secondary battery according to any one of claims 1 to 17, wherein The negative electrode current collector is connected to a negative electrode tab, and the buffer layer is close to the negative electrode tab.

19. The secondary battery according to any one of claims 1 to 18, wherein The diaphragm includes a base film and a coating provided on the surface of the base film, wherein the coating includes a binder and / or ceramic particles; And / or, the secondary battery includes a laminated battery, a square battery, a cylindrical battery, or a soft-pack battery.

20. A negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode current collector and a buffer layer provided on at least one surface of the negative electrode current collector. The buffer layer is provided on at least a partial area of ​​one surface of the negative electrode current collector.

21. The negative electrode sheet according to claim 20, wherein: The buffer layer includes at least two buffer bodies that are spaced apart from each other. The two buffer bodies are respectively located on two opposite sides of one surface of the negative electrode current collector.

22. The negative electrode sheet according to claim 21, wherein: The width of the two buffer bodies accounts for 3%-50% of the width of the negative electrode current collector.

23. The negative electrode sheet according to any one of claims 20 to 22, wherein: The elastic stress of the buffer layer is 2MPa-6.5MPa.

24. The negative electrode sheet according to any one of claims 20 to 23, wherein: An active material supplement layer is provided on at least one surface of the negative electrode current collector.

25. The negative electrode sheet according to claim 24, wherein: The negative electrode current collector includes a buffer zone and an active material zone on the same surface, the buffer layer is located in the buffer zone, and the active material supplement layer is located in the active material zone; The thickness L of the buffer layer is greater than the thickness T of the active material supplement layer.

26. The negative electrode sheet according to claim 25, wherein: The relationship between the thickness L of the buffer layer and the thickness T of the active material supplement layer is: 1.5T≤L≤1.64T.

27. The negative electrode sheet according to claim 25 or 26, characterized in that: The thickness of the active substance supplement layer is 2 μm-100 μm; And / or, the buffer layer has a thickness of 10 μm-200 μm.

28. A method for preparing a secondary battery, characterized in that: include: Prepare a positive electrode sheet, a negative electrode sheet and a separator, wherein the negative electrode sheet includes a negative electrode current collector and a buffer layer provided on at least one surface of the negative electrode current collector; Alternately stacking or winding the positive electrode sheet, the separator, and the negative electrode sheet, and wrapping the separator on the outermost side to obtain a battery cell; A clamp is arranged outside the battery core to compress the battery core, and the compression amount of the buffer layer is 38% to 80%, thereby obtaining a secondary battery.

29. The method for preparing a secondary battery according to claim 28, wherein: The negative electrode current collector includes a buffer zone and an active material zone on the same surface, the buffer layer is located in the buffer zone, and the active material zone is provided with an active material supplement layer; The step of arranging a clamp outside the battery cell to compress the battery cell includes compressing the buffer layer to the same thickness as the active material supplement layer.

30. The method for preparing a secondary battery according to claim 28 or 29, wherein: The compression amount of the buffer layer is 50%-64%.

31. A method for preparing a negative electrode sheet, characterized in that: include: Buffer bodies are provided on opposite sides of at least one surface of the foil, wherein the buffer bodies on at least one side are provided discontinuously, and negative electrode tabs are formed in the discontinuous areas; The negative electrode current collector is cut out from the foil according to a preset size of the negative electrode current collector. Buffer bodies are provided on opposite sides of one surface of the negative electrode current collector. The negative electrode tab is connected to the negative electrode current collector.

32. The method for preparing a negative electrode sheet according to claim 31, wherein: The step of providing a buffer layer on two opposite sides of at least one surface of the foil material comprises: An active material supplement layer and two buffer bodies are arranged at intervals on at least one surface of the foil. The two buffer bodies are located on opposite sides of the active material supplement layer. The thickness of the buffer body is 10μm to 200μm, and the thickness of the active material supplement layer is 5μm-100μm.

33. An electrical device, characterized in that: The electric device includes the secondary battery according to any one of claims 1 to 19.

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