Battery cell and terminal device

Abstract

The invention discloses a battery cell and a terminal device. The battery cell comprises an electrode assembly, and the electrode assembly comprises a first pole piece, a diaphragm and a second pole piece which are wound. The electrode assembly comprises a first straight section, a first bent section, a second straight section and a second bent section which are sequentially connected, the first straight section and the second straight section are oppositely arranged in the first direction, and the first bent section and the second bent section are oppositely arranged in the second direction. The first pole piece comprises a first current collector and a first active material layer, and the first active material layer is arranged on one side of the first current collector in the thickness direction of the first current collector. A plurality of first grooves are formed in the surface, deviating from the first current collector, of the first active material layer; observed in the second direction, the first reference line penetrates through the first bending sections in the third direction, first intersection points exist between the multiple first grooves of at least one layer of first bending sections and the first reference line, the number of the first intersection points is N1, and N1 / W1 is larger than or equal to 60 and smaller than or equal to 1000. The battery cell is beneficial to reducing the risk of lithium precipitation.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a battery cell and a terminal device. Background Art

[0002] In existing wound cells, the corners of the cells correspond to the bent sections of the electrode assembly. During the cycle of the cells, due to the expansion of the electrode sheets and other reasons, the electrode sheets located in the bent sections will squeeze the electrolyte out of the corners of the cells, resulting in less electrolyte at the corners of the cells, causing lithium deposition at the corners of the cells. Summary of the invention

[0003] In view of the above situation, the present application provides a battery cell, which is helpful to reduce the risk of lithium plating.

[0004] An embodiment of the present application provides a battery cell, which includes an electrode assembly. The thickness direction of the electrode assembly is a first direction. The electrode assembly includes a first pole piece, a diaphragm, and a second pole piece that are wound. The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section that are connected in sequence, the first straight section and the second straight section are arranged opposite to each other along the first direction, and the first bent section and the second bent section are arranged opposite to each other along the second direction. The first pole piece includes a first current collector and a first active material layer, and the first active material layer is arranged on one side of the first current collector along the thickness direction of the first current collector. A plurality of first grooves are provided on the surface of the first active material layer away from the first current collector, and the first grooves extend from one side of the first active material layer in the third direction to the other side of the first active material layer in the third direction, and the first direction, the second direction, and the third direction are perpendicular to each other. The length of the first active material layer along the third direction is W1, and the unit of W1 is mm. Observing along the second direction, the first reference line passes through the first bending segment along the third direction, and the multiple first grooves of at least one layer of the first bending segment have first intersections with the first reference line. The number of first intersections is N1, 60≤N1 / W1≤1000.

[0005] In the above-mentioned battery cell, the number of first intersections is the number of first grooves of a corresponding layer of the first bending section. N1 / W1 refers to the number of first intersections of a corresponding layer of the first bending section at a unit distance along the third direction. When N1 / W1 is small (less than 60), the number of first grooves located at the first corner of the battery cell will be small, which cannot meet the supply of electrolyte at the first corner of the battery cell, and lithium deposition will occur at the first corner of the battery cell. When N1 / W1 is large (greater than 1000), the number of first grooves located at the first corner of the battery cell will be excessive, the arrangement of the first grooves will be too dense, and a redundant design with no additional benefits will be formed, which will lose the energy density of the electrode. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the first corner of the battery cell can be reduced, and it is beneficial to improve the energy density of the battery cell.

[0006] In some embodiments of the present application, 100≤N1 / W1≤800, which further takes into account the wetting effect of the electrolyte and the reduction of the impact of the groove on the energy density of the battery cell.

[0007] In some embodiments of the present application, 300≤N1 / W1≤500.

[0008] In some embodiments of the present application, when observed along the second direction, the second reference line passes through the second bending section along the third direction, and the multiple first grooves of at least one layer of the second bending section have a second intersection with the second reference line, and the number of the second intersections is N2, 60≤N2 / W1≤1000. The number of second intersections is the number of first grooves of the corresponding layer of the second bending section. N2 / W1 refers to the number of second intersections of the corresponding layer of the second bending section at a unit distance along the third direction Y. When N2 / W1 is small (less than 60), the number of first grooves located at the second corner of the battery cell will be small, which cannot meet the supply of electrolyte at the second corner of the battery cell, thereby causing lithium deposition at the second corner of the battery cell. When N2 / W1 is large (greater than 1000), the number of first grooves located at the second corner of the battery cell will be excessive, the arrangement of the first grooves will be too dense, and a redundant design with no additional benefits will be formed, which will lose the energy density of the pole piece. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the second corner of the battery cell can be reduced, and the energy density of the battery cell can be improved.

[0009] In some embodiments of the present application, 100≤N2 / W1≤800, which further takes into account the wetting effect of the electrolyte and the reduction of the impact of the groove on the energy density of the battery cell.

[0010] In some embodiments of the present application, 300≤N2 / W1≤500.

[0011] In some embodiments of the present application, along the length direction of the first pole piece after it is unfolded, the spacing between two adjacent first grooves is W2, 0.01mm≤W2≤0.16mm, so as to reduce the risk of interference of the first grooves during the etching process and reduce the risk of lithium deposition in the battery cell. The inclination angle of the extension direction of the first groove relative to the length direction of the first pole piece after it is unfolded is θ, 0<θ<180° and θ≠90°, so as to meet the production tolerance requirements.

[0012] In some embodiments of the present application, as observed along the second direction, the distance between two adjacent first intersection points is D1, 0mm<D1≤2mm, so as to reduce the risk of insufficient electrolyte supply in the local area between the two first intersection points at the first corner of the battery cell, thereby reducing the risk of lithium deposition at the first corner of the battery cell.

[0013] In some embodiments of the present application, along the third direction, the smaller one of the distances between the first intersection point and the two edges of the first active material layer is D3, D3 / sinθ < K×W1 / 2, 1 < K < 2, and the unit of D3 is mm. By defining D3 / sinθ < K×W1 / 2, the required distance for the electrolyte to be transported from one end of the first groove to the first intersection point is less than the longest transport distance, so as to reduce the risk of insufficient electrolyte supply, and further reduce the risk of lithium deposition at the first corner of the battery cell.

[0014] In some embodiments of the present application, when observed along the second direction, the distance between two adjacent second intersection points is D2, 0mm < D2 ≤ 2mm, so as to reduce the risk of insufficient electrolyte supply in the local area where the second corner of the battery cell is located between the two second intersection points, and further reduce the risk of lithium deposition at the second corner of the battery cell.

[0015] In some embodiments of the present application, along the third direction, the smaller one of the distances between the second intersection point and the two edges of the first active material layer is D4, D4 / sinθ < K×W1 / 2, 1 < K < 2, and the unit of D4 is mm. By defining D3 / sinθ < K×W1 / 2, the required distance for the electrolyte to be transported from one end of the first groove to the first intersection point is less than the longest transport distance, so as to reduce the risk of insufficient electrolyte supply, and further reduce the risk of lithium deposition at the second corner of the battery cell.

[0016] In some embodiments of the present application, along the thickness direction of the first electrode, the thickness of the first active material layer is H1, and the depth of the first groove is H2, 1 / 6 ≤ H2 / H1 ≤ 3 / 4. When H2 / H1 is relatively small (less than 1 / 6), the area of the first active material layer 22 wetted by the electrolyte is small, and it is not conducive to forming an electrolyte transport channel. When H2 / H1 is relatively large (greater than 3 / 4), the energy density of the electrode is lost. By defining 1 / 6 ≤ H2 / H1 ≤ 3 / 4, the area of the first active material layer wetted by the electrolyte can be increased, and it is conducive to forming an electrolyte transport channel and reducing the loss of the energy density of the electrode.

[0017] In some embodiments of the present application, when observed along the extending direction of the first groove, the first groove includes a bottom wall and two side walls connected to both sides of the bottom wall. Each side wall is inclined relative to the bottom wall, and the two side walls form an opening at the end far from the bottom wall. The length of the bottom wall is less than the length of the opening, which is conducive to increasing the area of the first active material layer wetted by the electrolyte and enabling the first active material layer to be in full contact with the electrolyte.

[0018] In some embodiments of the present application, the first pole piece further includes a second active material layer, and along the thickness direction of the first current collector, the second active material layer is arranged on the side of the first current collector away from the first active material layer; a plurality of second grooves are arranged on the surface of the second active material layer away from the first current collector, and the second grooves extend from one side of the second active material layer in the third direction to the other side of the second active material layer in the third direction. The second grooves can further increase the area of ​​the second active material layer infiltrated by the electrolyte, so that the second active material layer is in full contact with the electrolyte.

[0019] An embodiment of the present application further provides a terminal device, which includes the battery cell in the above embodiment.

[0020] In the above-mentioned battery cell and terminal device, the number of first intersections is the number of first grooves of the corresponding first bending section. N1 / W1 refers to the number of first intersections of the corresponding first bending section at a unit distance along the third direction. When N1 / W1 is small (less than 60), the number of first grooves located at the first corner of the battery cell will be small, which cannot meet the supply of electrolyte at the first corner of the battery cell, and lithium deposition will occur at the first corner of the battery cell. When N1 / W1 is large (greater than 1000), the number of first grooves located at the first corner of the battery cell will be excessive, the arrangement of the first grooves will be too dense, and a redundant design with no additional benefits will be formed, which will lose the energy density of the electrode. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the first corner of the battery cell can be reduced, and it is beneficial to improve the energy density of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of a battery cell in one embodiment of the present application.

[0022] Figure 2 It is a schematic diagram of the winding structure of a battery cell in one embodiment of the present application.

[0023] Figure 3 It is a schematic diagram of the structure of the first active material layer of the electrode in one embodiment of the present application.

[0024] Figure 4 It is a schematic diagram of the arrangement structure of the first groove on the pole piece in an embodiment of the present application.

[0025] Figure 5 It is a schematic diagram of the structure of the second active material layer of the electrode in one embodiment of the present application.

[0026] Figure 6 It is a schematic diagram of the structure of a terminal device in an embodiment of the present application.

[0027] Main component symbols

[0028] Battery Cell 100

[0029] Terminal device 200

[0030] Electrode assembly 10

[0031] The first straight section 10A

[0032] The first bending section 10B

[0033] The second straight section 10C

[0034] The second bending section 10D

[0035] First pole piece 20

[0036] First current collector 21

[0037] First active material layer 22

[0038] First groove 22A

[0039] Bottom wall 221

[0040] Side wall 222

[0041] Opening 223

[0042] First reference line E

[0043] First intersection 22B

[0044] Second reference line F

[0045] Second intersection 22C

[0046] Second active material layer 23

[0047] Second groove 23A

[0048] Diaphragm 30

[0049] The second pole piece 40

[0050] First direction Z

[0051] Second direction X

[0052] The third direction Y

[0053] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0055] It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a centrally disposed element at the same time. When an element is considered to be "disposed" on another element, it may be directly disposed on the other element or there may be a centrally disposed element at the same time.

[0056] When a quantity value is considered to be "equal" to another quantity value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two quantity values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be approximately equal. When a quantity value is considered to be in a ratio of "1:1" to another quantity value, it means that the two are equal within a set deviation, and the set deviation range is within 5%. In other words, when at least one of the two quantity values ​​fluctuates within the set deviation range, even if their values ​​are not equal, they are still judged to be equal in ratio.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more related listed items. The term "overlap" used herein refers to the overlap of the projections of two parts or the overlap of the projections of two parts.

[0058] An embodiment of the present application provides a battery cell, which includes an electrode assembly. The thickness direction of the electrode assembly is a first direction, the width direction of the electrode assembly is a second direction, and the length direction of the electrode assembly is a third direction, and the first direction, the second direction and the third direction are perpendicular to each other. The electrode assembly includes a first pole piece, a diaphragm and a second pole piece that are wound. The electrode assembly includes a first straight section, a first bent section, a second straight section and a second bent section that are connected in sequence, the first straight section and the second straight section are arranged oppositely along the first direction, and the first bent section and the second bent section are arranged oppositely along the second direction. The first pole piece includes a first current collector and a first active material layer, and the first active material layer is arranged on one side of the first current collector along the thickness direction of the first current collector. A plurality of first grooves are provided on the surface of the first active material layer away from the first current collector, and the first grooves extend from one side of the first active material layer in the third direction to the other side of the first active material layer in the third direction. The length of the first active material layer along the third direction is W1, and the unit of W1 is mm. Observing along the second direction, the first reference line passes through the first bending segment along the third direction, and the multiple first grooves of at least one layer of the first bending segment have first intersections with the first reference line. The number of first intersections is N1, 60≤N1 / W1≤1000.

[0059] In the above-mentioned battery cell, the number of first intersections is the number of first grooves of a corresponding layer of the first bending section. N1 / W1 refers to the number of first intersections of a corresponding layer of the first bending section at a unit distance along the third direction. When N1 / W1 is small (less than 60), the number of first grooves located at the first corner of the battery cell will be small, which cannot meet the supply of electrolyte at the first corner of the battery cell, and lithium deposition will occur at the first corner of the battery cell. When N1 / W1 is large (greater than 1000), the number of first grooves located at the first corner of the battery cell will be excessive, the arrangement of the first grooves will be too dense, and a redundant design with no additional benefits will be formed, which will lose the energy density of the electrode. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the first corner of the battery cell can be reduced, and it is beneficial to improve the energy density of the battery cell.

[0060] The embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0061] Please also read Figure 1 and Figure 2 An embodiment of the present application provides a battery cell 100, which is applied to a secondary battery. A secondary battery refers to a battery that can be continuously used by activating active materials by charging after the battery is discharged.

[0062] The battery cell 100 includes an electrode assembly 10, which is used to convert chemical energy into electrical energy. The thickness direction of the electrode assembly 10 is a first direction Z. Observed along the first direction Z, the width direction of the electrode assembly 10 is a second direction X, and the length direction of the electrode assembly 10 is a third direction Y. The first direction Z, the second direction X, and the third direction Y are perpendicular to each other.

[0063] The electrode assembly 10 is a wound structure. The electrode assembly 10 includes a first electrode sheet 20, a separator 30, and a second electrode sheet 40 that are wound. The polarity of the first electrode sheet 20 is opposite to the polarity of the second electrode sheet 40. Optionally, the first electrode sheet 20 has a negative polarity and the second electrode sheet 40 has a positive polarity; or the first electrode sheet 20 has a positive polarity and the second electrode sheet 40 has a negative polarity.

[0064] The electrode assembly 10 includes a first straight section 10A, a first bent section 10B, a second straight section 10C, and a second bent section 10D connected in sequence. The first straight section 10A and the second straight section 10C are arranged opposite to each other along a first direction Z. The first bent section 10B and the second bent section 10D are arranged opposite to each other along a second direction X. The first bent section 10B corresponds to the first corner of the battery cell 100, and the second bent section 10D corresponds to the second corner of the battery cell 100.

[0065] The first pole piece 20 includes a first current collector 21 and a first active material layer 22. The first active material layer 22 is used to generate current and collect the current on the first current collector 21. Optionally, the first active material layer 22 is coated on the surface of the first current collector 21 by extrusion coating, transfer coating, spray coating, etc.

[0066] Please also read Figure 3 , along the thickness direction of the first current collector 21, the first active material layer 22 is arranged on one side of the first current collector 21. A plurality of first grooves 22A are provided on the surface of the first active material layer 22 away from the first current collector 21, and the first grooves 22A extend from one side of the first active material layer 22 in the third direction Y to the other side of the first active material layer 22 in the third direction Y. The first grooves 22A can increase the area of ​​the first active material layer 22 infiltrated by the electrolyte, so that the first active material layer 22 is in full contact with the electrolyte. Optionally, the first grooves 22A are formed by laser etching on the surface of the first active material layer 22 away from the first current collector 21.

[0067] Please also read Figure 4 The first groove 22A located in the first bending section 10B can store electrolyte on the one hand, and can form a transmission channel for electrolyte on the other hand, so as to supply electrolyte to the first corner of the battery cell 100, thereby reducing the risk of lithium deposition caused by less electrolyte at the first corner of the battery cell 100. Observing along the second direction X, the first reference line E passes through the first bending section 10B along the third direction Y, and the first grooves 22A of at least one layer of the first bending section 10B have a first intersection 22B with the first reference line E, and the number of the first intersections 22B is the number of the first grooves 22A of the corresponding layer of the first bending section 10B.

[0068] The length of the first active material layer 22 along the third direction Y is W1, and the unit of W1 is mm. The number of first intersections 22B is N1, 60≤N1 / W1≤1000. N1 / W1 refers to the number of first intersections 22B of a corresponding layer of the first bending segment 10B at a unit distance along the third direction Y. When N1 / W1 is small (less than 60), the number of first grooves 22A located at the first corner of the battery cell 100 will be small, and the supply of electrolyte at the first corner of the battery cell 100 cannot be met, thereby causing lithium deposition at the first corner of the battery cell 100. When N1 / W1 is large (greater than 1000), the number of first grooves 22A located at the first corner of the battery cell 100 will be excessive, the arrangement of the first grooves 22A will be too dense, and a redundant design with no additional benefits will be formed, which will lose energy density. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the first corner of the battery cell 100 can be reduced, and the energy density of the battery cell 100 can be improved.

[0069] Optionally, the value of N1 / W1 is 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, and any other value in the range of 60≤N1 / W1≤1000.

[0077] Furthermore, in some embodiments, the outermost first bending segment 10B satisfies 60≤N1 / W1≤1000, so as to facilitate contact with the electrolyte at the first corner of the battery cell 100, further reducing the risk of lithium deposition at the first corner of the battery cell 100, and helping to improve the energy density of the battery cell 100.

[0078] It can be understood that, in some embodiments, each layer of the first pole piece 20 located in the first bending section 10B satisfies 60≤N1 / W1≤1000, so as to further reduce the risk of lithium deposition at the first corner of the battery cell 100 and help improve the energy density of the battery cell 100.

[0079] Please also read Figure 2 and Figure 4 In some embodiments, the first groove 22A located in the second bending section 10D can store electrolyte on the one hand, and can form a transmission channel for electrolyte on the other hand, so as to supply electrolyte to the second corner of the battery cell 100, thereby reducing the risk of lithium deposition caused by less electrolyte at the second corner of the battery cell 100. Observing along the second direction X, the second reference line F passes through the second bending section 10D along the third direction Y, and the multiple first grooves 22A of at least one layer of the second bending section 10D have a second intersection 22C with the second reference line F, and the number of the second intersections 22C is the number of the first grooves 22A of the corresponding layer of the second bending section 10D.

[0080] The number of second intersections 22C is N2, 60≤N2 / W1≤1000. N2 / W1 refers to the number of second intersections 22C of a corresponding layer of second bending segments 10D at a unit distance along the third direction Y. When N2 / W1 is small (less than 60), the number of first grooves 22A located at the second corner of the battery cell 100 is small, which cannot meet the supply of electrolyte at the second corner of the battery cell 100, thereby causing lithium deposition at the second corner of the battery cell 100. When N2 / W1 is large (greater than 1000), the number of first grooves 22A located at the second corner of the battery cell 100 is excessive, the arrangement of the first grooves 22A is too dense, and a redundant design with no additional benefits is formed, which will lose energy density. By limiting 60≤N2 / W1≤1000, the risk of lithium deposition at the second corner of the battery cell 100 can be reduced, and it is beneficial to improve the energy density of the battery cell 100.

[0081] Optionally, the value of N2 / W1 is 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, and any other value in the range of 60≤N2 / W1≤1000.

[0089] Furthermore, in some embodiments, the outermost second bending segment 10D satisfies 60≤N2 / W1≤1000, so as to facilitate contact with the electrolyte at the second corner of the battery cell 100, further reducing the risk of lithium deposition at the second corner of the battery cell 100, and helping to improve the energy density of the battery cell 100.

[0090] It can be understood that, in some embodiments, each layer of the first pole piece 20 located in the second bending section 10D satisfies 60≤N2 / W1≤1000, so as to further reduce the risk of lithium deposition at the first corner of the battery cell 100 and help improve the energy density of the battery cell 100.

[0091] In some embodiments, each layer of the first pole piece 20 located in the first straight section 10A and the second straight section 10C is not provided with the first groove 22A, so as to improve the energy density of the battery cell 100 .

[0092] In some embodiments, each layer of the first pole piece 20 located in the first straight section 10A and the second straight section 10C is also provided with a first groove 22A to improve the overall electrolyte infiltration efficiency of the battery cell 100 .

[0093] Please also read Figure 3 and Figure 4 In some embodiments, along the length direction of the first pole piece 20 after unfolding, the spacing between two adjacent first grooves 22A is W2, 0.01mm≤W2≤0.16mm. When W2 is small (less than 0.01mm), the two adjacent first grooves 22A are prone to interference during the etching process; when W2 is large (greater than 0.16mm), the number of first grooves 22A is small, which cannot meet the electrolyte replenishment of the battery cell 100, thereby causing lithium deposition in the battery cell 100. By limiting 0.01mm≤W2≤0.16mm, the risk of interference between the first grooves 22A during the etching process is reduced, and the risk of lithium deposition in the battery cell 100 is reduced. It should be noted that the spacing between two adjacent first grooves 22A can be measured using an optical measuring machine (OMM), and the distance between the first edge of one first groove 22A and the first edge of another adjacent first groove 22A is measured using the OMM as W2. If two adjacent first grooves 22A are not parallel, the maximum spacing and the minimum spacing between the two adjacent first grooves 22A are measured by OMM, and then the average spacing between the two adjacent first grooves 22A is calculated by (maximum spacing + minimum spacing) / 2 as W2. Optionally, the value of W2 is 0.01mm, 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.1mm, 0.11mm, 0.12mm, 0.13mm, 0.14mm, 0.15mm, 0.16mm and any other value within the range of 0.01mm≤W2≤0.16mm.

[0094] It should be noted that the length direction of the first pole piece 20 after unfolding is consistent with the coating direction of the first active material layer 22 during the processing of the first pole piece 20.

[0095] In some embodiments, the inclination angle of the extending direction of the first groove 22A relative to the length direction of the first pole piece 20 after unfolding is θ, where 0 < θ < 180° and θ ≠ 90°, so as to meet the requirements of production tolerances.

[0096] Optionally, after the first pole piece 20 is unfolded, the θ values of the multiple first grooves 22A are equal or unequal.

[0097] Please continue to refer to Figure 4 , in some embodiments, when observing along the second direction X, the distance between two adjacent first intersections 22B is D1, where 0 mm < D1 ≤ 2 mm, so as to reduce the risk of insufficient electrolyte supply in the local area where the first corner of the battery cell 100 is located between the two first intersections 22B, and further reduce the risk of lithium deposition at the first corner of the battery cell 100.

[0098] In some embodiments, along the third direction Y, the smaller of the distances between the first intersection 22B and the two edges of the first active material layer 22 is D3, and D3 / sinθ < K × W1 / 2, where 1 < K < 2, and the unit of D3 is mm.

[0099] Optionally, the value of K is one of 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and any other value within the range of 1 < K < 2.

[0100] The specific derivation process is as follows:

[0101] During the cycling of the battery cell 100, along the third direction Y, the middle position of the first pole piece 20 is most likely to lack electrolyte. In the extreme case where θ = 90°, the extending direction of the first groove 22A is the same as the third direction Y. The maximum value of the longest transmission distance of the electrolyte is limited by the flow rate of the electrolyte. The flow rate of the electrolyte is related to the viscosity of the electrolyte, the coating weight of the first active material layer, and the compaction density of the first active material layer. Considering the influence of these three variables, the parameter K is defined, and 1 < K < 2. When the viscosity of the electrolyte is greater, and / or, the coating weight of the first active material layer is greater, and / or, the compaction density of the first active material layer is greater, the value of K is smaller. The maximum value of the longest transmission distance of the electrolyte satisfies the following relationship: K × W1 / 2.

[0102] The required distance for the electrolyte to be transported from one end of the first groove 22A to the first intersection point 22B is D3 / sinθ. Only when the required distance is less than the longest transport distance can the supply amount of the electrolyte at the corresponding first intersection point 22B be sufficient, that is, D3 / sinθ < K×W1 / 2, so as to reduce the risk of insufficient supply of the electrolyte and further reduce the risk of lithium deposition at the first corner of the battery cell 100.

[0103] Please continue to refer to Figure 4 , when observing along the second direction X, the distance between two adjacent second intersection points 22C is D2, and 0mm < D2 ≤ 2mm, so as to reduce the risk of insufficient supply of the electrolyte in the local area where the second corner of the battery cell 100 is located between the two second intersection points 22C, and further reduce the risk of lithium deposition at the second corner of the battery cell 100.

[0104] Along the third direction Y, the smaller of the distances between the second intersection point 22C and the two edges of the first active material layer 22 is D4, D4 / sinθ < K×W1 / 2, 1 < K < 2, and the unit of D4 is mm.

[0105] The specific derivation process is as follows:

[0106] During the cycling process of the battery cell 100, along the third direction Y, the middle position of the first electrode sheet 20 is most likely to lack electrolyte. In the extreme case where θ = 90°, the extending direction of the first groove 22A is the same as the third direction Y. The maximum value of the longest transport distance of the electrolyte is limited by the flow velocity of the electrolyte. The flow velocity of the electrolyte is related to the viscosity of the electrolyte, the coating weight of the first active material layer, and the compaction density of the first active material layer. Considering the influence of the above three variables, the parameter K is defined, and 1 < K < 2. When the viscosity of the electrolyte is greater, and / or the coating weight of the first active material layer is greater, and / or the compaction density of the first active material layer is greater, the value of K is smaller. The maximum value of the longest transport distance of the electrolyte satisfies the following relationship: K×W1 / 2.

[0107] The required distance for the electrolyte to be transported from one end of the first groove 22A to the second intersection point 22C is D4 / sinθ. Only when the required distance is less than the longest transport distance can the supply amount of the electrolyte at the corresponding second intersection point 22C be sufficient, that is, D4 / sinθ < K×W1 / 2, so as to reduce the risk of insufficient supply of the electrolyte and further reduce the risk of lithium deposition at the second corner of the battery cell 100.

[0108] Please refer to again Figure 3In some embodiments, along the first direction Z, the thickness H1 of the first active material layer 22 and the depth H2 of the first groove 22A satisfy the following relationship: 1 / 6≤H2 / H1≤3 / 4. When H2 / H1 is small (less than 1 / 6), the area of ​​the first active material layer 22 wetted by the electrolyte will be small, and it will be unfavorable to form a transmission channel for the electrolyte. When H2 / H1 is large (greater than 3 / 4), energy density will be lost. By limiting 1 / 6≤H2 / H1≤3 / 4, the area of ​​the first active material layer 22 wetted by the electrolyte can be increased, which is conducive to forming a transmission channel for the electrolyte and reducing the loss of energy density.

[0109] Optionally, the value of H2 / H1 is 1 / 6, 1 / 3, 5 / 12, 1 / 2, 7 / 12, 2 / 3, 3 / 4 and any other value in the range of 1 / 6≤H2 / H1≤3 / 4.

[0110] Please continue reading Figure 3 In some embodiments, when viewed along the extension direction of the first groove 22A, the first groove 22A includes a bottom wall 221 and two side walls 222 connected to both sides of the bottom wall 221. Each side wall 222 is arranged obliquely relative to the bottom wall 221, and an opening 223 is formed at one end of the two side walls 222 away from the bottom wall 221. Along the first direction Z, the projection of the bottom wall 221 is located within the projection of the opening 223 to form a groove structure that is wide at the top and narrow at the bottom, which facilitates the electrolyte to enter the first groove 22A from the opening 223, and reduces the first active material layer 22 etched at the bottom wall 221, thereby reducing the loss of energy density. In addition, each side wall 222 is arranged obliquely relative to the bottom wall 221, which is conducive to increasing the area of ​​the first active material layer 22 infiltrated by the electrolyte, so that the first active material layer 22 is in full contact with the electrolyte.

[0111] It is understandable that in other embodiments, at least one side wall 222 is configured to be a curved surface, so as to reduce the first active material layer 22 etched at the side wall 222 and reduce the loss of energy density.

[0112] In some embodiments, along the first direction Z, the thickness H3 of the first current collector 21 satisfies: 3μm≤H3≤15μm, so as to meet the structural strength requirements of the first current collector 21 and reduce the space waste caused by the large thickness of the first current collector 21, which is beneficial to improve the energy density of the first pole piece 20.

[0113] Optionally, the value of H3 is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm and any other value in the range of 3μm≤H3≤15μm.

[0114] Optionally, the first current collector 21 is a metal current collector or a composite current collector.

[0115] See also Figure 5 In some embodiments, the first pole piece 20 further includes a second active material layer 23. The second active material layer 23 is disposed on one side of the first current collector 21 along the thickness direction of the first current collector 21. A plurality of second grooves 23A are disposed on the surface of the second active material layer 23 away from the first current collector 21, and the second grooves 23A extend from one side of the second active material layer 23 in the third direction Y to the other side of the second active material layer 23 in the third direction Y. The second grooves 23A can further increase the area of ​​the second active material layer 23 infiltrated by the electrolyte, so that the second active material layer 23 is in full contact with the electrolyte.

[0116] In some embodiments, along the first direction Z, a projection of each first groove 22A of one first active material layer 22 is parallel to a projection of a first groove 22A of another first active material layer 22 to facilitate processing.

[0117] Optionally, along the first direction Z, a projection of each first groove 22A of one first active material layer 22 overlaps with a projection of a first groove 22A of another first active material layer 22 .

[0118] In some embodiments, along the first direction Z, a projection of each first groove 22A of one first active material layer 22 intersects a projection of a first groove 22A of another first active material layer 22 .

[0119] See also Figure 6 One embodiment of the present application further provides a terminal device 200, which includes the battery cell 100 in any of the above embodiments. Optionally, the terminal device 200 may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, etc.

[0120] The specific implementation of the battery cell 100 in the embodiment and the comparative example is described below.

[0121] Embodiment 1:

[0122] The battery cell is 200 and the capacity is 4Ah. The assembly process is as follows:

[0123] (1) Preparation of negative electrode sheet: The negative electrode active materials artificial graphite, conductive carbon black (Super P), styrene-butadiene rubber (SBR), and CMC (sodium carboxymethyl cellulose) are mixed in a weight ratio of 97:0.5:1.3:1.2 (the addition ratio can be adjusted), and deionized water is added as a solvent to prepare a slurry with a weight percentage of 50wt%, and stirred evenly. The slurry is evenly coated on one surface of a copper foil (negative electrode current collector, Cu with a thickness of 6μm), and then dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. When preparing a double-sided coated negative electrode sheet, the above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then the coated sheet is cold pressed to a thickness of 105μm, and a first groove is formed on the surface of the negative electrode active material layer away from the negative electrode current collector by laser etching, and then a negative electrode tab is welded on the copper foil. The material of the negative electrode tab is nickel or copper-plated nickel.

[0124] (2) Preparation of positive electrode sheet: The positive electrode active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), CNT (carbon nanotube), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:0.5:0.5:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly. The slurry is evenly coated on one surface of the aluminum foil (positive electrode collector), and then dried at 90°C to obtain a positive electrode sheet coated with positive electrode active materials on one side. When preparing a double-sided coated positive electrode sheet, repeat the above coating steps on the other surface of the aluminum foil. The coated electrode sheet is then cold pressed to a thickness of 95μm, and the positive electrode tab is welded on the aluminum foil. The material of the positive electrode tab is aluminum.

[0125] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0126] (4) Preparation of isolation membrane: A 7 μm thick polyethylene porous polymer film was used as the isolation membrane.

[0127] (5) Preparation of electrode assembly: The positive electrode sheet, the separator and the negative electrode sheet are wound together.

[0128] (6) Assembly of the electrode assembly: Place the aluminum-plastic film with the holes punched and formed in an assembly fixture, with the holes facing upward, place the electrode assembly in the holes, and apply external force to press it. Then, cover the electrode assembly with another aluminum-plastic film with the holes punched and formed, with the holes facing downward, and heat-seal the four sides of the two aluminum-plastic films by hot pressing to obtain an assembled electrode assembly.

[0129] (7) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and after vacuum packaging, static standing, hot pressing, shaping and other processes, a secondary battery is produced.

[0130] Cycle performance test pass rate:

[0131] 20 cells were taken from each group of samples for 25°C cycle test. Those that could meet the capacity retention rate of 800 cycles (the discharge capacity of the cell after 800 cycles divided by the discharge capacity of the cell in the first cycle)>80% were considered passed.

[0132] 25℃ cycle test process:

[0133] A battery performance tester (brand: Xinweier; model: CT-4008W-5V6A-80CH) was used to charge the battery to a full charge voltage of 4.5V with a current of 4A (charging rate of 1C), and then charged at a constant voltage to a cut-off current of 200mA (0.05C), followed by standing for 10 minutes, and then discharged with a current of 2A (0.5C) to a voltage of 3V, and then stood for 10 minutes. This process was recorded as 1 cycle, and at this time there would be a discharge capacity of 1 cycle; then the charge and discharge were repeated;

[0134] Volume energy density test method:

[0135] Volume energy density = rated capacity × platform voltage / (length × width × thickness)

[0136] Test method for rated capacity and platform voltage:

[0137] (1) Charge at 0.2C constant current to full charge voltage, and charge at constant voltage to 0.05C; let stand for 5 minutes;

[0138] (2) 0.2C discharge to full discharge voltage.

[0139] The above charge-discharge cycle is carried out three times, and the third discharge capacity is taken as the rated capacity;

[0140] The average voltage of the third discharge cycle is recorded as the plateau voltage.

[0141] Method for measuring the length, width and thickness of the battery cell: Use a vernier caliper to measure.

[0142] Table 1

[0143]

[0144]

[0145] Note: 1. “ / ” in Table 1 means there is no experimental data for this item;

[0146] 2. The data n / 20 in the column “Number of cells passing the cycle performance test” in Table 1 means that n out of the 20 cells tested passed the test.

[0147] Among them, the first pole piece in comparative example 1 is not provided with a groove; the other parameters of comparative examples 1 to 5 and embodiments 2 to 6 except the parameters involved in Table 1 are the same as those of embodiment 1.

[0148] From the comparison between Comparative Example 1 and Comparative Examples 2 to 3 and Examples 1 to 6, it can be seen that by limiting 60≤N1 / W1≤1000, the risk of lithium plating at the first corner of the battery cell 100 can be reduced and the pass rate of the cycle performance test can be improved.

[0149] In order to take into account both the wetting effect of the electrolyte and the reduction of the influence of the grooves on the volume energy density, it is preferably 100≤N1 / W1≤800, and more preferably 300≤N1 / W1≤500.

[0150] From the comparison between Example 4 and Example 7 to Example 14, it can be seen that, on the basis of setting the first groove in the first bending section, setting the second groove in the second bending section can further improve the electrolyte infiltration effect and improve the pass rate of the cycle test performance. By limiting 60≤N2 / W1≤1000, the risk of lithium deposition at the second corner of the battery cell 100 can be reduced, and the pass rate of the cycle performance test can be improved.

[0151] In order to take into account both the wetting effect of the electrolyte and the reduction of the influence of the grooves on the volume energy density, it is preferably 100≤N2 / W1≤800, and more preferably 300≤N2 / W1≤500.

[0152] In summary, in the above-mentioned battery cell 100 and terminal device 200, the multiple first grooves 22A of at least one layer of the first bending section 10B have a first intersection 22B with the first reference line E, and the number of the first intersections 22B is the number of the first grooves 22A of the corresponding layer of the first bending section 10B. The number of first intersections 22B is N1, 60≤N1 / W1≤1000. N1 / W1 refers to the number of first intersections 22B of the corresponding layer of the first bending section 10B per unit distance along the third direction Y. When N1 / W1 is small (less than 60), the number of the first grooves 22A located at the first corner of the battery cell 100 will be small, which cannot meet the supply of the electrolyte at the first corner of the battery cell 100, thereby causing lithium deposition at the first corner of the battery cell 100. When N1 / W1 is large (greater than 1000), the number of first grooves 22A located at the first corner of the battery cell 100 will be excessive, the first grooves 22A will be arranged too densely and form a redundant design with no additional benefits, which will lose energy density. By limiting 60≤N1 / W1≤1000, the risk of lithium deposition at the first corner of the battery cell 100 can be reduced, and the energy density of the battery cell 100 can be improved.

[0153] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the disclosure scope of the present application.

Claims

1. A battery cell, characterized in that: The battery cell includes an electrode assembly. The thickness direction of the electrode assembly is the first direction. The electrode assembly includes a first pole piece, a separator, and a second pole piece that are wound. The electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section that are connected in sequence. The first straight section and the second straight section are disposed opposite to each other along the first direction. The first bent section and the second bent section are disposed opposite to each other along the second direction; The first pole piece includes a first current collector and a first active material layer. Along the thickness direction of the first current collector, the first active material layer is disposed on one side of the first current collector. A plurality of first grooves are provided on the surface of the first active material layer facing away from the first current collector. The first grooves extend from one side of the first active material layer in the third direction to the other side of the first active material layer in the third direction. The first direction, the second direction, and the third direction are perpendicular to each other pairwise. The length of the first active material layer along the third direction is W1, and the unit of W1 is mm; When observed along the second direction, a first reference line passes through the first bent section along the third direction. A plurality of the first grooves of at least one layer of the first bent section have first intersections with the first reference line. The number of the first intersections is N1, and 60≤N1 / W1≤1000.

2. The battery cell according to claim 1, characterized in that: 100≤N1 / W1≤800.

3. The battery cell according to claim 2, characterized in that: 300≤N1 / W1≤500.

4. The battery cell according to claim 1, characterized in that: When observed along the second direction, a second reference line passes through the second bent section along the third direction. A plurality of the first grooves of at least one layer of the second bent section have second intersections with the second reference line. The number of the second intersections is N2, and 60≤N2 / W1≤1000.

5. The battery cell according to claim 4, characterized in that: 100≤N2 / W1≤800.

6. The battery cell according to claim 5, characterized in that: 300≤N2 / W1≤500.

7. The battery cell according to any one of claims 1 to 6, characterized in that: Along the length direction of the first pole piece after unfolding, the distance between two adjacent first grooves is W2, and 0.01mm≤W2≤0.16mm; The inclination angle of the extending direction of the first grooves relative to the length direction of the first pole piece after unfolding is θ, 0<θ<180° and θ≠90°.

8. The battery cell according to claim 1, characterized in that: When observed along the second direction, the distance between two adjacent first intersections is D1, and 0mm<D1≤2mm.

9. The battery cell according to claim 1, characterized in that: Along the third direction, the smaller one of the distances between the first intersection and the two edges of the first active material layer is D3, D3 / sinθ<K×W1 / 2, 1<K<2, and the unit of D3 is mm.

10. The battery cell according to claim 4, characterized in that: When observed along the second direction, the distance between two adjacent second intersections is D2, and 0mm<D2≤2mm.

11. The battery cell according to claim 4, characterized in that: Along the third direction, the smaller one of the distances between the second intersection and the two edges of the first active material layer is D4, D4 / sinθ<K×W1 / 2, 1<K<2, and the unit of D4 is mm.

12. The battery cell according to claim 1, characterized in that: Along the thickness direction of the first pole piece, the thickness of the first active material layer is H2, and the depth of the first grooves is H1, and 1 / 6≤H2 / H1≤3 / 4.

13. The battery cell according to claim 1, characterized in that: Observing along the extension direction of the first groove, the first groove includes a bottom wall and two side walls connected to the two sides of the bottom wall, each of the side walls is inclined relative to the bottom wall, and an opening is formed at one end of the two side walls away from the bottom wall, and the length of the bottom wall is less than the length of the opening.

14. The battery cell according to claim 1, characterized in that: The first pole piece also includes a second active material layer, which is arranged on the side of the first current collector away from the first active material layer along the thickness direction of the first current collector; a plurality of second grooves are provided on the surface of the second active material layer away from the first current collector, and the second grooves extend from one side of the second active material layer in the third direction to the other side of the second active material layer in the third direction.

15. A terminal device, characterized in that: The terminal device comprises the battery cell according to any one of claims 1 to 14.

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