Battery cell, battery, and electric device

Abstract

A battery cell, a battery, and an electric device. The battery cell comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet comprises a positive electrode active material layer; the positive electrode active material layer comprises a lithium-containing material of an olivine structure; the negative electrode sheet comprises a negative electrode active material layer; the size of the positive electrode active material layer in the length direction of the positive electrode sheet is L1 mm, the size of the positive electrode active material layer in the width direction of the positive electrode sheet is W1 mm, the size of the negative electrode active material layer in the length direction is L2 mm, the size of the negative electrode active material layer in the width direction is W2 mm, 1<(L2-L1) / (W2-W1)≤4, L2 / L1>1, and 500≤L1≤600; the electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and based on the total mass of the electrolyte, the ratio of the mass content of the lithium hexafluorophosphate to the mass content of the lithium bis(fluorosulfonyl)imide is greater than 1. The usage reliability of the battery cell can be improved.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410268476.7, filed on March 8, 2024, entitled “Battery Cell, Battery and Electrical Device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to a battery cell, a battery and an electrical device. Background Art

[0004] Battery cells, with their high capacity and long lifespan, are widely used in electronic devices such as mobile phones, laptops, electric bicycles, electric cars, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes, and power tools. As the battery industry has made significant progress, higher performance requirements have been placed on battery cells.

[0005] However, the current reliability of battery cells is poor and still needs to be further improved.

[0006] Summary of the Invention

[0007] The present application provides a battery cell, a battery, and an electrical device, which can improve the reliability of the battery cell.

[0008] In a first aspect, an embodiment of the present application proposes a battery cell, the battery cell comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the positive electrode sheet comprising a positive electrode collector and a positive electrode active material layer disposed on at least one side of the positive electrode collector, the positive electrode active material layer comprising an olivine-structured lithium-containing material, the negative electrode sheet comprising a negative electrode collector and a negative electrode active material layer disposed on at least one side of the negative electrode collector, the dimension of the positive electrode active material layer along the length direction of the positive electrode sheet being L1 mm, the dimension of the positive electrode active material layer along the width direction of the positive electrode sheet being W1 mm, the dimension of the negative electrode active material layer along the length direction being L2 mm, and the dimension of the negative electrode active material layer along the width direction being W2 mm, wherein 1<(L2-L1) / (W2-W1)≤4, and L2 / L1>1, 500≤L1≤600; the electrolyte comprising lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the ratio of the mass content of lithium hexafluorophosphate to the mass content of lithium bisfluorosulfonyl imide based on the total mass of the electrolyte being greater than 1.

[0009] Therefore, the embodiment of the present application further designs the protruding area so that the protruding area size of the negative electrode plate in the length direction is larger than the protruding area size in the width direction, and the ability of the negative electrode active material layer to receive active ions in the length direction is stronger than the ability to receive active ions in the width direction. In particular, the ability of the negative electrode active material layer to receive active ions in the area close to the electrode ear can be improved, thereby improving the overall ability of the negative electrode active material layer to receive active ions, reducing the risk of active ions precipitating into metal, and improving the reliability of the battery cell.

[0010] In some embodiments, 1.25≤(L2-L1) / (W2-W1)≤4, and optionally 1.5≤(L2-L1) / (W2-W1)≤2.5. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0011] In some embodiments, 3≤L2-L1≤10, which may be 5≤L2-L1≤10. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0012] In some embodiments, 2≤W2-W1≤6. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0013] In some embodiments, 500≤L2≤600; optionally, 540≤L2≤560. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0014] In some embodiments, 500≤L1≤600; optionally, 540≤L1≤560. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0015] In some embodiments, 100≤W2≤155. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0016] In some embodiments, 100≤W1≤155. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0017] In some embodiments, the battery cell further includes a separator disposed between the positive and negative electrode sheets. The separator has a length dimension of L3 mm, 2 ≤ L3 - L2 ≤ 10, optionally 2 ≤ L3 - L2 ≤ 8, and further optionally 2 ≤ L3 - L2 ≤ 5. The separator is longer than the negative electrode sheet, further reducing the risk of short circuits between the positive and negative electrode sheets.

[0018] In some embodiments, the battery cell further includes a separator disposed between the positive and negative electrode sheets, with a width dimension of W3 mm, where 2 ≤ W3 - W2 ≤ 5. The separator's width is greater than that of the negative electrode sheet, further reducing the risk of short circuits between the positive and negative electrode sheets.

[0019] In some embodiments, 500≤L3≤600. The length of the separator is relatively long, which can further reduce the risk of short circuit between the positive electrode sheet and the negative electrode sheet.

[0020] In some embodiments, 100≤W3≤160. The width of the separator is relatively long, which can further reduce the risk of short circuit between the positive electrode sheet and the negative electrode sheet.

[0021] In some embodiments, the battery cell further includes an electrolyte, the electrolyte including lithium hexafluorophosphate LiPF6 and lithium bisfluorosulfonyl imide LiFSI, and based on the total mass of the electrolyte, the ratio of the mass content of lithium hexafluorophosphate LiPF6 to the mass content of lithium bisfluorosulfonyl imide LiFSI is greater than 1; it can be optionally 1.05 to 1.4, and the total mass content of lithium hexafluorophosphate LiPF6 and lithium bisfluorosulfonyl imide LiFSI is 10% to 16%; it can be optionally 12% to 16%.

[0022] Therefore, in the embodiment of the present application, lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSI work together to improve the conductivity of the electrolyte. On the one hand, the improvement of conductivity can reduce the internal resistance of the battery cell, reduce the temperature rise at the connection between the current collector and the tab, and make the temperature rise of the current collector and the tab more balanced; on the other hand, the improvement of electrolyte conductivity is conducive to the active ions near the tab being more embedded in the negative electrode active material, reducing the amount of metal precipitation on the negative electrode plate per unit time, which is beneficial to improving the reliability of the battery cell.

[0023] In some embodiments, the mass content of lithium hexafluorophosphate (LiPF6) is 6.5% to 9%. When the mass content of lithium hexafluorophosphate (LiPF6) is within the above range, the viscosity of the electrolyte can be improved, which is beneficial to improving the conductivity of the electrolyte.

[0024] In some embodiments, the total mass content of lithium bis(fluorosulfonyl)imide (LiFSI) is 6% to 8%. When the mass content of lithium bis(fluorosulfonyl)imide (LiFSI) is within the above range, it can effectively repair the SEI film interface, reduce the impedance of the cycling process, facilitate the rapid migration of active ions, enable the active ions to be quickly embedded in the negative electrode active material, and reduce the risk of active ions precipitating as metal on the surface of the negative electrode. Lithium bis(fluorosulfonyl)imide (LiFSI) can also, to a certain extent, alleviate the decomposition of lithium hexafluorophosphate into hydrofluoric acid, further alleviate the side reaction between hydrofluoric acid and active materials, and improve the cycling performance of the battery cell.

[0025] In some embodiments, the electrolyte further includes an additive, the additive including at least one of lithium difluorophosphate and lithium fluorosulfonate; optionally, based on the total mass of the electrolyte, the mass content of lithium difluorophosphate is 0.05% to 0.2%; optionally, based on the total mass of the electrolyte, the mass content of lithium fluorosulfonate is 0.01% to 0.1%.

[0026] Therefore, the combination of lithium difluorophosphate and lithium fluorosulfonate in the embodiment of the present application can form a low-impedance SEI film on the surface of the negative electrode plate, improve the transmission capacity of active ions in the negative electrode active material layer, and reduce the risk of metal precipitation near the tab of the negative electrode plate; lithium difluorophosphate and lithium fluorosulfonate can consume a large amount of electrons in the process of participating in the formation of the SEI film, which can reduce the density of electrons at the tab, and thus reduce the risk of active ions being reduced to metal by electrons, and further improve the reliability of the battery cell.

[0027] In some embodiments, the electrolyte further comprises an organic solvent, the organic solvent comprising a first solvent and a second solvent, the first solvent comprising at least one of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, ethylene glycol monopropyl ether, methyl acrylate, and propyl propionate; and the second solvent comprising at least one of ethylene carbonate and propylene carbonate. Optionally, the total mass content of the first solvent is 55% to 70% based on the total mass of the electrolyte; and optionally, the total mass content of the second solvent is 20% to 35% based on the total mass of the electrolyte. The combination of the two solvents can effectively reduce the overall viscosity of the electrolyte, which is conducive to improving the migration rate of active ions in the electrolyte.

[0028] In some embodiments, the olivine-structured lithium-containing material includes a lithium iron phosphate material. Optionally, the lithium iron phosphate material includes an M element, where M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce. These materials have high cycling stability and can effectively improve the cycling performance of battery cells.

[0029] In some embodiments, M comprises at least one of Mg, Al, Ti, V, and Zn, and the mass percentage of M relative to the total mass of the lithium iron phosphate material is 100 ppm to 1000 ppm, and optionally 300 ppm to 500 ppm. M can at least form a localized fast ion conductor phase within the lithium iron phosphate material, accelerating lithium ion transport within the material and improving the kinetic performance of the battery cell.

[0030] In some embodiments, the ratio of the surface density of the single-sided positive electrode active material layer to the surface density of the single-sided negative electrode active material layer is 2.0 to 2.5; alternatively, the surface density of the single-sided positive electrode active material layer is 0.27 g / 1540.25 mm 2 Up to 0.33g / 1540.25mm 2 ; Optionally, the surface density of the single-side negative electrode active material layer is 0.11g / 1540.25mm 2 Up to 0.16g / 1540.25mm 2 The negative electrode active material layer and the positive electrode active material layer cooperate so that the lithium ions released from the positive electrode active material layer can be quickly embedded in the negative electrode active material layer, reducing the risk of lithium plating at the negative electrode.

[0031] In some embodiments, the negative active material layer includes at least one of artificial graphite and natural graphite.

[0032] In some embodiments, the positive electrode sheet further includes a positive electrode tab disposed on at least one side of the positive electrode current collector along its length. Active ions released from the positive electrode tab are substantially absorbed by the negative electrode sheet, reducing the risk of active ion precipitation as metal and improving the reliability of the battery cell.

[0033] In some embodiments, the negative electrode plate further includes a negative electrode tab, which is disposed on at least one side of the negative electrode current collector along the length direction. The lengthwise overhang of the negative electrode plate is larger than the widthwise overhang, which can enhance the ability of the negative electrode active material layer near the tab to receive active ions, thereby enhancing the overall ability of the negative electrode active material layer to receive active ions, reducing the risk of active ions precipitating into metal, and improving the reliability of the battery cell.

[0034] In some embodiments, the positive electrode tab is positioned on one side of the positive electrode current collector along the length direction, and the negative electrode tab is positioned on one side of the negative electrode current collector along the length direction. The positive and negative electrode tabs work together to facilitate the embedding of active ions into the negative electrode sheet, improving the reliability of the battery cell.

[0035] In some embodiments, the negative electrode tab protrudes from the negative electrode current collector in the direction from the positive electrode current collector toward the positive electrode tab. Active ions released from the positive electrode tab can be largely absorbed by the negative electrode tab, reducing the risk of active ions precipitating into metal and improving the reliability of the battery cell.

[0036] In some embodiments, the negative electrode tab protrudes from the negative electrode current collector in the direction from the positive electrode tab to the positive electrode current collector.

[0037] In some embodiments, the positive electrode tabs are disposed on both sides of the positive electrode current collector along the length direction, which can enhance the overall current flow capacity of the positive electrode tabs and improve the reliability of the battery cell.

[0038] In some embodiments, the negative electrode tabs are disposed on both sides of the negative electrode current collector along the length direction, which can enhance the overall current capacity of the negative electrode tabs and improve the reliability of the battery cell.

[0039] In a second aspect, the present application further proposes a battery, which includes a battery cell according to any embodiment of the first aspect of the present application.

[0040] In a third aspect, the present application further proposes an electrical device comprising a battery as in any embodiment of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0042] FIG1 is a schematic top view of an embodiment of an electrode assembly in a battery cell of the present application.

[0043] FIG. 2 is a schematic structural diagram of the electrode assembly shown in FIG. 1 at another angle.

[0044] FIG3 is a schematic structural diagram of the electrode assembly shown in FIG1 at another angle.

[0045] FIG4 is a schematic structural diagram of an embodiment of a positive electrode plate in a battery cell of the present application.

[0046] FIG5 is a schematic structural diagram of an embodiment of a negative electrode plate in a battery cell of the present application.

[0047] FIG6 is a schematic structural diagram of another embodiment of the positive electrode sheet in the battery cell of the present application.

[0048] FIG7 is a schematic structural diagram of another embodiment of the negative electrode plate in the battery cell of the present application.

[0049] FIG8 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0050] FIG. 9 is an exploded schematic diagram of the embodiment of the battery cell of FIG. 8 .

[0051] FIG10 is a schematic diagram of an embodiment of a battery module of the present application.

[0052] FIG11 is a schematic diagram of an embodiment of a battery pack of the present application.

[0053] FIG. 12 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 11 .

[0054] FIG13 is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0055] The drawings are not necessarily drawn to scale.

[0056] The reference numerals in the accompanying drawings are as follows: X, width direction; Y, length direction; Z, thickness direction; 1, battery pack; 2, upper case; 3, lower case; 4, battery module; 5, battery cell; 51, shell; 52, electrode assembly; 7, positive electrode sheet; 71, positive electrode current collector; 72, positive electrode active material layer; 73, positive electrode tab; 8, negative electrode sheet; 81, negative electrode current collector; 82, negative electrode active material layer; 83, negative electrode tab; 9, separator; 53, cover plate; 6, electrical device. DETAILED DESCRIPTION

[0057] Below, the embodiments of the battery cell, battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0058] " Range " disclosed in this 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 inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. 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.

[0059] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0060] 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.

[0061] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates 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.

[0062] A battery cell includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is positioned between the positive and negative electrode sheets to separate them while allowing active ions to pass through. During the battery cell charging process, active ions escape from the positive active material layer in the positive electrode sheet and migrate to the negative active material in the negative electrode sheet. During this process, edge lithium deposition may occur on the negative electrode sheet.

[0063] In order to reduce the risk of lithium deposition at the edge of the negative electrode plate, the relevant technology usually sets the area of ​​the negative electrode plate to be larger than that of the positive electrode plate, so that the negative electrode plate can basically receive the active ions from the positive electrode plate, reducing the risk of active ions precipitating into metal at the edge of the negative electrode plate.

[0064] The area where the negative electrode active material layer in the negative electrode sheet exceeds the positive electrode active material layer in the positive electrode sheet is called the excess area. As the excess area increases, the amount of active ions that can be received increases. However, if the excess area is too large, it may cause the negative electrode sheet to be over-sized, resulting in space waste and reducing the energy density of the battery cell; as the excess area decreases, the risk of active ions precipitating into metals increases; therefore, how to set the excess area is related to the balanced improvement of the battery cell's reliability and energy density.

[0065] In view of the above problems, the embodiment of the present application proposes a battery cell, which includes a positive electrode sheet and a negative electrode sheet. The length of the positive electrode sheet is smaller than the length of the negative electrode sheet, the width of the positive electrode sheet is smaller than the width of the negative electrode sheet, and the excess area of ​​the negative electrode sheet in the length direction is designed to be larger than the excess area in the width direction, so that the active ions can basically be embedded in the negative electrode active material layer of the negative electrode sheet, thereby improving the reliability of the battery cell.

[0066] Next, the technical solutions of the implementation methods of this application are described in detail.

[0067] battery cells

[0068] In a first aspect, embodiments of the present application provide a battery cell.

[0069] As shown in Figures 1 to 5, the battery cell includes an electrode assembly 52, which includes a positive electrode sheet 7, a negative electrode sheet 8, and an electrolyte. The positive electrode sheet 7 includes a positive electrode current collector 71 and a positive electrode active material layer 72 disposed on at least one side of the positive electrode current collector 71. The positive electrode active material layer 72 includes an olivine-structured lithium-containing material. The negative electrode sheet 8 includes a negative electrode current collector 81 and a negative electrode active material layer 82 disposed on at least one side of the negative electrode current collector 81.

[0070] The size of the positive electrode active material layer 72 along the length direction Y of the positive electrode sheet 7 is L1 mm, the size of the positive electrode active material layer 72 along the width direction X of the positive electrode sheet 7 is W1 mm, the size of the negative electrode active material layer 82 along the length direction Y is L2 mm, and the size of the negative electrode active material layer 82 along the width direction X is W2 mm.

[0071] Where, 1<(L2-L1) / (W2-W1)≤4, and L2 / L1>1;

[0072] The electrolyte includes lithium hexafluorophosphate and lithium bisfluorosulfonyl imide. Based on the total mass of the electrolyte, the ratio of the mass content of the lithium hexafluorophosphate to the mass content of the lithium bisfluorosulfonyl imide is greater than 1.

[0073] At least one side of the negative electrode sheet 8 in the longitudinal direction Y extends beyond the positive electrode sheet 7; for example, the negative electrode sheet 8 extends beyond the positive electrode sheet 7 on one side in the longitudinal direction Y, while the other side may not extend beyond the positive electrode sheet 7. Alternatively, for example, the negative electrode sheet 8 extends beyond the positive electrode sheet 7 on both sides in the longitudinal direction Y.

[0074] At least one side of the negative electrode sheet 8 in the width direction X exceeds the positive electrode sheet 7; for example, the negative electrode sheet 8 exceeds the positive electrode sheet 7 on one side in the width direction X, and may not exceed the positive electrode sheet 7 on the other side. Alternatively, for example, the negative electrode sheet 8 exceeds the positive electrode sheet 7 on both sides in the width direction X.

[0075] The exceeding area shown in FIG1 is the area where the negative electrode active material layer 82 in the negative electrode plate 8 exceeds the positive electrode active material layer 72 in the positive electrode plate 7. This area is a rectangular annular area (the negative electrode plate 8 exceeds the positive electrode plate 7 on both sides in the length direction Y, and the negative electrode plate 8 exceeds the positive electrode plate 7 on both sides in the width direction X). The size of this area in the length direction Y is L2-L1, and the size of this area in the width direction X is W2-W1.

[0076] When the battery cell meets the above range, the size of the positive electrode sheet 7 in the length direction Y is smaller than the size of the negative electrode sheet 8 in the length direction Y, the size of the positive electrode sheet 7 in the width direction X is smaller than the size of the negative electrode sheet 8 in the width direction X, and the excess area of ​​the negative electrode sheet 8 in the length direction Y is designed to be larger than the excess area in the width direction X, so that the active ions can basically be embedded in the negative active material layer 82 of the negative electrode sheet 8, thereby improving the reliability of the battery cell; and the excess size will not be wasted, which can effectively improve the energy density of the battery cell.

[0077] The electrode assembly 52 may be a wound structure or a laminated structure, and may be a laminated structure, wherein the laminated structure includes a plurality of positive electrode sheets 7 and a plurality of negative electrode sheets 8 .

[0078] The pole piece in a battery cell is a sheet-like structure with a relatively thin thickness. The surface perpendicular to the thickness direction can be considered the front of the pole piece, which is usually a quadrilateral. To improve the space utilization of the battery cell when assembled into a battery, the battery cell can be configured as a long cell, and the pole piece can be configured as a rectangular sheet structure, that is, its front is rectangular, with the long side of the rectangle being longer than the short side. The long side is the length, and the short side is the width. The long side of the rectangle can be considered parallel to the length direction Y of the pole piece, and the short side can be considered parallel to the width direction X of the pole piece.

[0079] The positive electrode sheet 7 and the negative electrode sheet 8 are stacked, with the length direction Y of the positive electrode sheet 7 being parallel to the length direction Y of the negative electrode sheet 8, and the width direction X of the positive electrode sheet 7 being parallel to the width direction X of the negative electrode sheet 8. FIG2 shows a schematic diagram of the stacking of the electrode assembly 52, in which the positive electrode sheet 7, the separator 9, and the negative electrode sheet 8 are stacked in sequence along the thickness direction Z of the electrode assembly 52.

[0080] The pole piece includes a current collector and a tab. The tab is provided on at least one side of the current collector. To further improve the energy density of the battery cell, for example, the tab is provided on at least one side of the current collector along the length direction Y, or the tab is provided on at least one side of the current collector along the width direction X. Optionally, the tab can be further provided on at least one side of the current collector along the length direction Y, for example, both sides.

[0081] An active material layer is provided on the current collector, which is used to extract or embed active ions such as lithium ions, sodium ions, etc., to realize the migration of active ions; no active material layer is provided on the tab, which is used to electrically connect the current collector and other components of the battery cell, such as electrode terminals, to realize the conduction of the external circuit.

[0082] For example, the positive electrode sheet 7 includes a positive electrode current collector 71 and a positive electrode tab 73 disposed on at least one side of the positive electrode current collector 71 along the length direction Y. The positive electrode active material layer 72 is disposed on the positive electrode current collector 71, and the positive electrode tab 73 is not disposed on the positive electrode active material layer 72. The positive electrode tab 73 can be disposed on one side of the positive electrode current collector 71 along the length direction Y, or the positive electrode tab 73 can be disposed on both sides of the positive electrode current collector 71 along the length direction Y.

[0083] For example, the negative electrode sheet 8 includes a negative electrode current collector 81 and a negative electrode tab 83 disposed on at least one side of the negative electrode current collector 81 along the length direction Y. The negative electrode current collector 81 is provided with a negative electrode active material layer 82, and the negative electrode tab 83 is not provided with a negative electrode active material layer 82. The negative electrode tab 83 can be disposed on one side of the negative electrode current collector 81 along the length direction Y, or the negative electrode tab 83 can be disposed on both sides of the negative electrode current collector 81 along the length direction Y.

[0084] In some embodiments, the positive electrode tab 73 is disposed on one side of the positive electrode current collector 71 along the longitudinal direction Y, and the negative electrode tab 83 can be disposed on one side of the negative electrode current collector 81 along the longitudinal direction Y. Figures 3 and 4 show that the positive electrode tab 73 is disposed on one side of the positive electrode current collector 71 along the longitudinal direction Y, and Figures 3 and 5 show that the negative electrode tab 83 can be disposed on one side of the negative electrode current collector 81 along the longitudinal direction Y.

[0085] For example, the positive electrode tab 73 and the negative electrode tab 83 can be located on the same side of the electrode assembly 52. ​​Specifically, the negative electrode tab 83 protrudes from the negative electrode current collector 81 in the direction from the positive electrode current collector 71 to the positive electrode tab 73. FIG3 shows that the positive electrode tab 73 and the negative electrode tab 83 are located on the same side of the electrode assembly 52.

[0086] For another example, the positive electrode tab 73 and the negative electrode tab 83 can be respectively located on both sides of the electrode assembly 52, for example, the positive electrode tab 73 and the negative electrode tab 83 are arranged opposite to each other along the length direction; specifically, in the direction from the positive electrode tab 73 to the positive electrode collector 71, the negative electrode tab 83 protrudes from the negative electrode collector 81.

[0087] As shown in FIG6 and FIG7 , in other embodiments, the positive electrode tabs 73 may be disposed on both sides of the positive electrode collector 71 along the length direction Y, and the negative electrode tabs 83 may be disposed on both sides of the negative electrode collector 81 along the length direction Y.

[0088] In the related art, although the negative electrode plate is provided with a protruding area; however, compared with the current collector, the area of ​​the tab is relatively small, the current density at the connection between the current collector and the tab is large, the temperature rise is high, and the number of active ions released from the positive electrode active material layer 72 near the tab is large, which may not be fully embedded in the negative electrode active material layer 82, resulting in metal precipitation in the area of ​​the negative electrode active material layer 82 near the tab.

[0089] The embodiment of the present application further designs the excess area so that the excess area size of the negative electrode plate 8 in the length direction Y is larger than the excess area size in the width direction X. The ability of the negative electrode active material layer 82 to receive active ions in the length direction Y is stronger than the ability to receive active ions in the width direction X. In particular, the ability of the negative electrode active material layer 82 to receive active ions in the area close to the tab is improved, thereby improving the overall ability of the negative electrode active material layer 82 to receive active ions, reducing the risk of active ions precipitating into metal, and improving the reliability of the battery cell.

[0090] Specifically, the dimension of the positive electrode active material layer 72 along the length direction Y can be considered as the length of the positive electrode active material layer 72, and the dimension of the positive electrode active material layer 72 along the width direction X can be considered as the width of the positive electrode active material layer 72. The dimension of the negative electrode active material layer 82 along the length direction Y can be considered as the length of the negative electrode active material layer 82, and the dimension of the negative electrode active material layer 82 along the width direction X can be considered as the width of the negative electrode active material layer 82.

[0091] The length of the negative active material layer 82 (L2 mm) minus the length of the positive active material layer 72 (L1 mm) is the length of the excess area of ​​the negative active material layer 82. The width of the negative active material layer 82 (W2 mm) minus the width of the positive active material layer 72 (W1 mm) is the width of the excess area of ​​the negative active material layer 82. When the excess area length is greater than the excess area width, i.e., 1 < (L2 - L1) / (W2 - W1), the negative active material layer 82 has a stronger ability to receive active ions in the length direction Y. It can effectively receive active ions from near the tabs, allowing nearly all active ions released from the positive active material to be embedded in the negative active material layer 82, reducing the risk of active ion precipitation as metal, thereby improving the reliability of the battery cell. As the excess area length increases, the amount of active ions that can be received increases. However, if the excess area length is too large, it may result in waste of the negative electrode plate 8, which is not conducive to improving the energy density of the battery cell. Therefore, the embodiments of the present application further control (L2-L1) / (W2-W1)≤4, which can improve the reliability of the battery cell while also improving the energy density of the battery cell. In particular, when the positive electrode active material layer 72 includes an olivine-structured lithium-containing material and the electrolyte includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the embodiments of the present application control 1<(L2-L1) / (W2-W1)≤4, which can improve the reliability of the battery cell while also improving the energy density of the battery cell.

[0092] The implementation manner of the present application further regulates 1.25≤(L2-L1) / (W2-W1)≤4, optionally, 1.5≤(L2-L1) / (W2-W1)≤2.5, which can further improve the reliability and energy density of the battery cell.

[0093] Illustratively, (L2-L1) / (W2-W1) can be 1.01, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95, 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 3, 3.2, 3.5, 3.6, 3.8, 4.0, or a range consisting of any two of the above values.

[0094] In the embodiment of the present application, the dimensions of the negative electrode active material layer 82 and the positive electrode active material layer 72 are further adjusted to further improve the reliability and energy density of the battery cell.

[0095] In some embodiments, 3 ≤ L2 - L1 ≤ 10, optionally 5 ≤ L2 - L1 ≤ 10. For example, L2 - L1 can be 3, 3.5, 4, 4.5, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 10, or a range consisting of any two of the foregoing values. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0096] In some embodiments, the length L2mm of the negative electrode active material layer 82 may be between 500mm and 600mm, optionally satisfying the condition 540≤L2≤560. For example, the length L2mm of the negative electrode active material layer 82 may be 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, or 600mm, or a range consisting of any two of the foregoing values. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0097] In some embodiments, the length L1mm of the positive electrode active material layer 72 may be between 500mm and 600mm, optionally satisfying the condition 540≤L1≤560. For example, the length L1mm of the positive electrode active material layer 72 may be 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, 595mm, or 600mm, or a range consisting of any two of the foregoing values. When a battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0098] In some embodiments, 2 ≤ W2 - W1 ≤ 6. For example, W2 - W1 can be 2, 2.2, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.6, 4.8, 5, 5.2, 5.5, 5.8, 6, or a range consisting of any two of the above values. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0099] In some embodiments, the width W2mm of the negative electrode active material layer 82 can be 100mm to 155mm, and can be optionally 140mm to 155mm, for example, 100mm, 105mm, 110mm, 115mm, 120mm, 125mm, 130mm, 135mm, 140mm, 145mm, 148mm, 150mm, 155mm, or a range consisting of any two of the above values.

[0100] In some embodiments, the width W1 mm ​​of the positive electrode active material layer 72 may be 100 mm to 155 mm, and may optionally be 140 mm to 155 mm, for example, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 148 mm, 150 mm, 155 mm, or a range consisting of any two of the foregoing values. When the battery cell meets the above range, the reliability and energy density of the battery cell can be further improved.

[0101] The electrode assembly 52 further includes a separator 9, which is disposed between the positive electrode sheet 7 and the negative electrode sheet 8 to separate the positive electrode sheet 7 and the negative electrode sheet 8, thereby reducing the risk of short circuit between the positive electrode sheet 7 and the negative electrode sheet 8. The area of ​​the separator 9 can be larger than the area of ​​the negative electrode sheet 8, thereby further reducing the risk of short circuit between the positive electrode sheet 7 and the negative electrode sheet 8.

[0102] In some embodiments, the separator 9 has a dimension L3 mm along the length direction Y, 2≤L3-L2≤10, optionally, 2≤L3-L2≤8, and further optionally, 2≤L3-L2≤5. For example, L3-L2 can be 2, 2.2, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.6, 4.8, 5, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or a range consisting of any two of the above values. The separator has a relatively long length, which can further reduce the risk of short circuiting between the positive and negative electrode sheets.

[0103] In some embodiments, the separator 9 has a length L3 mm along the length direction Y. That is, the length L3 mm of the separator 9 can be 500 mm to 600 mm, or optionally 550 mm to 560 mm; for example, 500 mm, 510 mm, 520 mm, 530 mm, 540 mm, 550 mm, 560 mm, 570 mm, 580 mm, 590 mm, 595 mm, 600 mm, or a range consisting of any two of the foregoing values. The relatively long length of the separator can further reduce the risk of short circuiting between the positive and negative electrode sheets.

[0104] In some embodiments, the separator 9 has a dimension W3 mm along the width direction X, where 2 ≤ W3 - W2 ≤ 5. For example, W3 - W2 can be 2, 2.2, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.6, 4.8, 5, or a range consisting of any two of the above values. The separator's relatively long width can further reduce the risk of short circuits between the positive and negative electrode sheets.

[0105] In some embodiments, the separator 9 has a dimension W3 mm along the width direction X. That is, the width W3 mm of the separator 9 can be 100 mm to 160 mm, and optionally 150 mm to 160 mm; for example, 100 mm, 105 mm, 110 mm, 115 mm, 120 mm, 125 mm, 130 mm, 135 mm, 140 mm, 145 mm, 148 mm, 150 mm, 155 mm, 160 mm, or a range consisting of any two of the foregoing values. The relatively long width of the separator can further reduce the risk of short circuiting between the positive and negative electrode sheets.

[0106] In the embodiments of the present application, the length and width of the positive electrode active material layer in the positive electrode sheet, the length and width of the negative electrode active material layer in the negative electrode sheet, and the length and width of the separator are all well-known in the art and can be measured using equipment and methods well-known in the art. Taking the positive electrode sheet as an example, the positive electrode sheet is taken as a sample and a micrometer is used to measure the length and width of the positive electrode active material layer in the positive electrode sheet. Taking the negative electrode sheet as an example, the negative electrode sheet is taken as a sample and a micrometer is used to measure the length and width of the negative electrode active material layer in the negative electrode sheet. Taking the separator as an example, the separator is taken as a sample and a micrometer is used to measure the length and width of the separator.

[0107] The embodiments of the present application can further improve the performance of the battery cell, such as the reliability and energy density, by further improving the materials and structural types of the positive electrode sheet, the negative electrode sheet and the separator.

[0108] [Positive electrode]

[0109] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two surfaces that oppose each other in its thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0110] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a layered positive electrode active material (such as lithium nickel cobalt manganese oxide, lithium nickel oxide / sodium, lithium cobalt oxide / sodium, lithium manganese oxide / sodium, lithium-rich / sodium layered and rock salt phase layered materials), an olivine structured lithium-containing material (such as lithium iron phosphate materials, lithium manganese phosphate materials, etc.), a spinel structured positive electrode active material (such as spinel lithium manganese oxide, spinel lithium nickel manganese oxide, lithium-rich spinel lithium manganese oxide, and lithium nickel manganese oxide, etc.).

[0111] In some embodiments, the lithium iron phosphate material includes an M element; M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; the above materials are relatively stable and can effectively improve the cycle life of the battery system. The M element can be disposed on the surface of the lithium iron phosphate material to act as a coating, thereby improving the structural stability of the lithium iron phosphate material; or it can be located in the crystal phase of the lithium iron phosphate material to stabilize the lattice structure; or it can be located both on the surface of the lithium iron phosphate material and in the crystal phase of the lithium iron phosphate material. When the lithium iron phosphate material is tested, if the M element can be detected, it is considered that the lithium iron phosphate material includes the M element.

[0112] In some embodiments, M comprises at least one of Mg, Al, Ti, V, and Zn, optionally including Al. The mass content of M relative to the total mass of the lithium iron phosphate material is between 100 ppm and 2000 ppm, and optionally between 300 ppm and 500 ppm. The lithium iron phosphate material contains the aforementioned amount of M, which can at least form a localized fast ion conductor phase within the lithium iron phosphate material, accelerating lithium ion transport within the material and improving the kinetic performance of the battery cell.

[0113] Exemplarily, the lithium iron phosphate material may include at least one of Mg, Al, Ti, V and Zn. The above-mentioned M element may be arranged on the surface of the lithium iron phosphate material to play a coating role and improve the structural stability of the lithium iron phosphate material; or be located in the crystal phase of the lithium iron phosphate material to stabilize the lattice structure; or may be located on the surface of the lithium iron phosphate material and in the crystal phase of the lithium iron phosphate material at the same time.

[0114] Illustratively, the mass content of element M can be 100 ppm, 200 ppm, 300 ppm, 400 ppm, 450 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or a range consisting of any two of the above values.

[0115] In some embodiments, the lithium iron phosphate material includes a core and a carbon coating layer, the core includes lithium iron phosphate particles, and the carbon coating layer is disposed on at least a portion of the outer surface of the core; the electrolyte also includes an organic solvent, the organic solvent includes a first solvent, and the viscosity of the first solvent does not exceed 0.8 Pa·s.

[0116] Lithium iron phosphate materials are modified by coating with a carbon coating layer, which can improve the conductivity of the lithium iron phosphate materials and improve the cycle performance under working conditions; however, due to the dense coating of the carbon coating layer, the electrolyte may not penetrate the core of the lithium iron phosphate material well, worsening the DCR growth under static storage conditions; and the embodiment of the present application is combined with a low-viscosity organic solvent system to improve the wetting performance of the electrolyte on the lithium iron phosphate material and reduce the DCR growth under static storage conditions.

[0117] In some embodiments, the mass content of the carbon coating layer is 1.0% to 1.5% based on the total mass of the lithium iron phosphate material; the mass content of the organic solvent is ≥ 45% based on the total mass of the electrolyte, and can optionally be 60% to 91%. When the mass content of the carbon coating layer and the mass content of the organic solvent are within the above ranges, both the cycling performance of the battery cell under operating conditions and the DCR increase under static storage conditions can be improved.

[0118] Exemplarily, the mass content of the carbon coating layer can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a range consisting of any two of the above values; the mass content of the organic solvent can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 36.4%, 37%, 38%, 39%, 40%, 40.4%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 50.4%, 51%, 52%, 52.5%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91% or a range consisting of any two of the above values.

[0119] In the embodiment of the present application, the content of the elements in the positive electrode active material has a meaning well known in the art and can be detected by equipment and methods well known in the art. For example, with reference to EPA6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry and measured by plasma atomic emission (ICP-OES, instrument model: Thermo ICAP7400). First, 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added thereto. Then it is placed on a 180°C plate for 30min. After digestion on the plate, the volume is fixed to 100mL and the standard curve method is used for quantitative testing.

[0120] In some embodiments, the mass content of the lithium iron phosphate material is greater than or equal to 85% and less than 100% based on the total mass of the positive electrode active material layer. For example, the mass content of the lithium iron phosphate material can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range consisting of any two of the foregoing values.

[0121] In some embodiments, the positive electrode active material layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent based on the total mass of the positive electrode active material layer is ≤5%.

[0122] In some embodiments, the positive electrode active material layer may further optionally include a positive electrode binder. The present application embodiment has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylic resins. In some embodiments, based on the total mass of the positive electrode active material layer, the mass percentage of the positive electrode binder is ≤5%.

[0123] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0124] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0125] In some embodiments, the surface density of the single-sided positive electrode active material layer is 0.27 g / 1540.25 mm 2Up to 0.33g / 1540.25mm 2 , for example, 0.270g / 1540.25mm 2 , 0.275g / 1540.25mm 2 、0.280g / 1540.25mm 2 , 0.285g / 1540.25mm 2 、0.290g / 1540.25mm 2 、0.30g / 1540.25mm 2 、0.31g / 1540.25mm 2 、 0.32g / 1540.25mm 2 、0.33g / 1540.25mm 2 or a range consisting of any two of the above values. When the areal density of the positive electrode active material layer falls within the above range, it is possible to balance the porosity and thickness of the positive electrode active material layer while maintaining a certain gram capacity of the positive electrode sheet. This, in turn, balances the migration rate and migration path of lithium ions in the positive electrode active material layer, thereby improving the rapid charging performance of the battery cell.

[0126] Matching the surface density of the positive electrode active material layer, the surface density of the negative electrode active material layer on one side is 0.11g / 1540.25mm 2 Up to 0.15g / 1540.25mm 2 , for example 0.11g / 1540.25mm 2 , 0.12g / 1540.25mm 2 、0.13g / 1540.25mm 2 、0.14g / 1540.25mm 2 、0.15g / 1540.25mm 2 or a range consisting of any two of the above values. When the areal density of the negative electrode active material layer falls within the above range, it is possible to balance the porosity and thickness of the negative electrode active material layer while meeting a certain gram capacity of the negative electrode sheet, thereby balancing the migration rate and migration path of lithium ions in the negative electrode active material layer. Furthermore, the negative electrode active material layer and the positive electrode active material layer cooperate to enable lithium ions released from the positive electrode active material layer to be rapidly embedded in the negative electrode active material layer, reducing the risk of lithium plating in the negative electrode sheet.

[0127] In the embodiment of the present application, the surface density of the single-sided positive electrode active material layer has a meaning well known in the art and can be tested using methods known in the art. Surface density = weight of single-sided positive electrode active material layer / area of ​​single-sided positive electrode active material layer, wherein since the positive electrode current collector may have a positive electrode active material layer on both sides, the weight of single-sided positive electrode active material layer = (average weight of the electrode sheet - average weight of the current collector) / 2. The specific testing process is: take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, and record it as M1. Then wipe off the positive electrode active material layer of the weighed positive electrode sheet, weigh the weight of the positive electrode current collector, and record it as M0. The surface density of the positive electrode active material layer = (weight of the positive electrode sheet M1 - weight of the positive electrode current collector M0) / S1. The process of testing the area density of the single-sided negative electrode active material layer is similar to the process of testing the area density of the single-sided positive electrode active material layer, and will not be repeated here.

[0128] The "average" here can be the average value after 5 parallel tests.

[0129] [Negative electrode]

[0130] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0131] The negative electrode active material can be any negative electrode active material known in the art for use in battery cells. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include at least one of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide, and tin alloys.

[0132] In some embodiments, the negative electrode active material in the negative electrode active material layer includes at least one of artificial graphite and natural graphite; optionally, the negative electrode active material includes artificial graphite, which has relatively high structural stability.

[0133] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0134] For example, the graphite material in the present application can be subjected to X-ray powder diffraction testing and qualitative analysis on the negative electrode sheet or negative electrode active material in combination with JIS / K0131-1996 General Rules for X-ray Diffraction Analysis.

[0135] In some embodiments, the total weight content of the artificial graphite and the natural graphite is greater than or equal to 85% and less than 100% based on the total weight of the negative electrode active material layer. For example, the weight content of the artificial graphite can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or a range consisting of any two of the foregoing values.

[0136] In some embodiments, the negative electrode active material layer may further optionally include a negative electrode conductive agent. The present embodiments do not particularly limit the type of negative electrode conductive agent. For example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the weight percentage of the negative electrode conductive agent is ≤5% based on the total weight of the negative electrode active material layer.

[0137] In some embodiments, the negative electrode active material layer may further optionally include a negative electrode binder. The present application embodiment does not particularly limit the type of negative electrode binder. For example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5% based on the total weight of the negative electrode active material layer.

[0138] In some embodiments, the negative electrode active material layer may optionally include other additives. For example, these additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, the weight percentage of these additives is ≤ 2% based on the total weight of the negative electrode active material layer.

[0139] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0140] The negative electrode active material layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0141] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode active material layer. For example, in some embodiments, the negative electrode sheet of the embodiments of the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode active material layer.

[0142] [Isolation film]

[0143] The embodiments of the present application have no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0144] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0145] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0146] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0147] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0148] [Electrolyte]

[0149] In some embodiments, the battery cell further includes an electrolyte. During the charge and discharge process of the battery cell, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet, and the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0150] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt may include at least one of lithium hexafluorophosphate LiPF6 and lithium bisfluorosulfonyl imide LiFSI. Optionally, the lithium salt may include lithium hexafluorophosphate LiPF6 and lithium bisfluorosulfonyl imide LiFSI. Based on the total mass of the electrolyte, the ratio of the mass content of lithium hexafluorophosphate LiPF6 to the mass content of lithium bisfluorosulfonyl imide LiFSI is greater than 1, and the total mass content of lithium hexafluorophosphate LiPF6 and lithium bisfluorosulfonyl imide LiFSI is 10% to 16%.

[0151] Lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) work together to improve the conductivity of the electrolyte. This improved conductivity reduces the internal resistance of the battery cell, lowering the temperature rise at the junction of the current collector and the tab, resulting in a more balanced temperature rise between the current collector and the tab. Furthermore, the increased electrolyte conductivity allows more active ions near the tab to be embedded in the negative electrode active material, reducing the amount of metal precipitated on the negative electrode plate per unit time and improving the reliability of the battery cell. The present embodiment further regulates the ratio of the mass content of lithium hexafluorophosphate (LiPF6) to the mass content of lithium bis(fluorosulfonyl)imide (LiFSI) to a value between 1.05 and 1.4, further improving the reliability of the battery cell.

[0152] For example, the ratio of the mass content of lithium hexafluorophosphate LiPF6 to the mass content of lithium bis(fluorosulfonyl)imide LiFSI can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.12, 1.13, 1.15, 1.16, 1.18, 1.19, 1.2, 1.22, 1.24, 1.25, 1.28, 1.30, 1.32, 1.33, 1.35, 1.38, 1.40, or a range consisting of any two of the above values.

[0153] Illustratively, the mass content of lithium hexafluorophosphate (LiPF6) is 6.5% to 9%, such as 6.5%, 6.6%, 6.8%, 7%, 7.2%, 7.4%, 7.5%, 7.6%, 7.8%, 7.9%, 8.0%, 8.2%, 8.5%, 8.8%, 9%, or a range consisting of any two of the foregoing values. When the mass content of lithium hexafluorophosphate (LiPF6) is within the foregoing range, the viscosity of the electrolyte can be improved, thereby improving the conductivity of the electrolyte.

[0154] Exemplarily, the mass content of lithium bis(fluorosulfonyl)imide LiFSI is 6% to 8%, such as 6%, 6.5%, 6.6%, 6.8%, 7%, 7.2%, 7.4%, 7.5%, 7.6%, 7.8%, 7.9%, 8.0% or a range consisting of any two of the above values. When the mass content of lithium bis(fluorosulfonyl)imide LiFSI is within the above range, lithium bis(fluorosulfonyl)imide LiFSI can form a fluorine-rich solid electrolyte interface (Solid Electrolyte Interphase, SEI) film on the surface of the negative electrode active material, effectively repair the SEI film interface, reduce the impedance of the cycle process, facilitate the rapid migration of active ions, enable the active ions to be quickly embedded in the negative electrode active material, and reduce the risk of active ions precipitating as metal on the surface of the negative electrode sheet; lithium bis(fluorosulfonyl)imide LiFSI can also alleviate the decomposition of lithium hexafluorophosphate into hydrofluoric acid to a certain extent, further alleviate the side reaction between hydrofluoric acid and the active material, and take into account the improvement of the cycle performance of the battery cell.

[0155] In some embodiments, the electrolyte further includes an additive, and the additive includes at least one of lithium difluorophosphate and lithium fluorosulfonate. Optionally, the additive includes lithium difluorophosphate and lithium fluorosulfonate.

[0156] On the one hand, the combination of lithium difluorophosphate and lithium fluorosulfonate can form a low-impedance SEI film on the surface of the negative electrode, improve the transmission capacity of active ions in the negative electrode active material layer, and reduce the risk of metal precipitation near the tab of the negative electrode; on the other hand, lithium difluorophosphate and lithium fluorosulfonate can consume a large amount of electrons in the process of participating in the formation of the SEI film, which can reduce the density of electrons at the tab, thereby reducing the risk of active ions being reduced to metal by electrons, and further improving the reliability of the battery cell.

[0157] Illustratively, based on the total mass of the electrolyte, the mass content of lithium difluorophosphate is 0.05% to 0.2%, for example, 0.05%, 0.06%, 0.08%, 0.10%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2% or a range consisting of any two of the above values.

[0158] Illustratively, based on the total mass of the electrolyte, the mass content of lithium fluorosulfonate is 0.01% to 0.1%, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.10%, 0.11% or a range consisting of any two of the above values.

[0159] In some embodiments, the electrolyte further comprises an organic solvent, comprising a first solvent and a second solvent, wherein the viscosity of the first solvent is less than that of the second solvent. The combination of the two solvents can effectively reduce the overall viscosity of the electrolyte, thereby increasing the migration rate of active ions in the electrolyte. Optionally, the viscosity of the first solvent does not exceed 0.8 Pa·s.

[0160] In some embodiments, the first solvent may include at least one of dimethyl carbonate DMC and ethyl methyl carbonate EMC, ethyl acetate, ethylene glycol monopropyl ether EP, methyl acrylate MA and propyl propionate PP; the second solvent may include at least one of ethylene carbonate EC and propylene carbonate PC. The viscosity of the above-mentioned first solvent is relatively small, which can reduce the overall viscosity of the electrolyte; the above-mentioned second solvent has a relatively strong ability to dissociate lithium salts, which is beneficial to improving the migration rate of lithium ions. By adopting the above-mentioned solvent system, the embodiment of the present application has a relatively low viscosity of the electrolyte, and active ions such as lithium ions are more easily balanced inside the battery cell, which can reduce the risk of lithium ions being excessively dense in the local area of ​​the battery cell and causing lithium precipitation; and the above-mentioned solvent system and the above-mentioned lithium salt are used in combination, and the conductivity of the electrolyte is relatively high, which is beneficial to improving the migration rate of lithium ions, thereby improving the dynamic performance of the battery cell.

[0161] In some embodiments, the total mass content of the first solvent is 55% to 70% based on the total mass of the electrolyte, for example, 55%, 56%, 57%, 58%, 59%, 60%, 62%, 63%, 65%, 68%, 70%, or a range consisting of any two of the foregoing values. When the total mass content of the first solvent is within the foregoing range, the overall viscosity of the electrolyte can be reduced, the uniformity of lithium ion transfer can be improved, the risk of lithium plating can be reduced, and the reliability of the battery cell can be improved.

[0162] In some embodiments, the total mass content of the second solvent is 20% to 35% based on the total mass of the electrolyte, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range consisting of any two of the foregoing values. When the total mass content of the second solvent is within the foregoing range, the dissociation ability of the lithium salt can be enhanced, which facilitates the rapid migration of lithium ions and further improves the kinetic performance of the battery cell.

[0163] The qualitative and quantitative properties of each substance or element in this application can be detected using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international detection standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0164] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, the inorganic components / lithium salt concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method with reference to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery's state of charge is approximately 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using an ion chromatography analysis method.

[0165] In the embodiments of the present application, the types and contents of the organic components in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" for qualitative and quantitative analysis of the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using an ion chromatography analysis method.

[0166] For example, using liquid-phase nuclear magnetic resonance (NMR) chromatography to test the composition of an electrolyte additive, for example, lithium difluorophosphate and lithium hexafluorophosphate, a 7ml glass bottle is prepared in a nitrogen glove box. 5ml of a premixed NMR reagent solution is added to the bottle and allowed to stand in the nitrogen glove box at room temperature (20-25°C) for 24 hours to allow the electrolyte in the electrode and separator to diffuse into the premixed NMR solution, thus obtaining the NMR test sample. The premixed NMR solution consists of 100ml of deuterated acetonitrile and 3ml of trifluoromethylbenzene. This premixed NMR reagent solution is pre-dried with molecular sieve 4A (100ml of the premixed NMR reagent solution is added with 15g of freshly opened 4A molecular sieves and dried in a nitrogen glove box at room temperature (20-25°C) for more than 30 days). 19F NMR measurements are performed using a Bruker Avance 400HD NMR system.

[0167] To identify and quantify individual species, the following settings were used with respect to flip angle and scanning time.

[0168] Fluorine spectrum test pulse sequence: 2gfhigqn.2;

[0169] Delay time: 1 second;

[0170] Number of scans: 16 times.

[0171] The relative contents of trifluoromethylbenzene and LiPF6 were calculated based on the integrated intensity of the signal peaks of the two substances in F-NMR. The calculation method is:

[0172] PF6 - Relative content = (I PF6 - ×M PF6 - / 6) / (I CF3ph ×M CF3ph / 3), where I is the corresponding NMR peak area, M is the corresponding relative molecular mass, and then the content of lithium hexafluorophosphate in the electrolyte is calculated based on the molar ratio of hexafluorophosphate to lithium ions.

[0173] Based on the F-NMR of trifluoromethylbenzene and PO2F2 - The relative content of the two substances is calculated based on the integrated intensity of the signal peaks. The calculation method is:

[0174] PO2F2 - Relative content = (I PO2F2- ×M PO2F2- / 2) / (I CF3ph ×M CF3ph / 3), where I is the corresponding NMR peak area, M is the corresponding relative molecular mass, and then the content of lithium difluorophosphate in the electrolyte is calculated based on the molar ratio of difluorophosphate to lithium ions.

[0175] In some embodiments, the various solutes or solvents in the electrolyte mentioned in this application include substances actively added when preparing the electrolyte, and also include substances derived from certain substances already existing in the electrolyte during the preparation of the electrolyte or in the process of preparing a battery from the electrolyte, or during the storage or use of a battery containing the electrolyte.

[0176] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0177] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0178] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft shell, such as a bag-type soft shell. The soft shell can be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0179] The present invention has no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape. FIG8 shows a battery cell 5 with a square structure as an example.

[0180] In some embodiments, as shown in FIG9 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may 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 connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator may be formed into an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated 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 may be one or more, which can be adjusted according to demand.

[0181] The preparation methods of the battery cells of the embodiments of the present application are well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be wound and / or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging, dried, and then injected with electrolyte. The battery cell is then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell.

[0182] In some embodiments of the present application, the battery cells according to the present application can be assembled into a battery module. The battery module can contain multiple battery cells, and the specific number can be adjusted according to the application and capacity of the battery module.

[0183] Figure 10 is a schematic diagram of an example battery module 4. As shown in Figure 10, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be secured using fasteners. Optionally, the battery module 4 may also include a housing having a storage space, and the multiple battery cells 5 are accommodated in the storage space.

[0184] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0185] Figures 11 and 12 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 11 and 12, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the battery box.

[0186] Electrical devices

[0187] A second aspect of the embodiments of the present application provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs of the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop 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, a satellite, an energy storage system, etc.

[0188] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0189] FIG13 is a schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0190] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0191] Example

[0192] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0193] Example 1

[0194] 1. Preparation of positive electrode sheet

[0195] The positive electrode sheet includes a positive electrode collector aluminum foil and a positive electrode active material layer. The positive electrode active material layer includes a film layer formed by uniformly coating the positive electrode slurry (the solvent is N-methylpyrrolidone NMP) on the surface of the positive electrode collector aluminum foil, drying, and cold pressing. The positive electrode active material layer includes a positive electrode active material, a conductive agent carbon black, and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.4:1.1.

[0196] The positive electrode active material includes lithium iron phosphate materials. The surface density of the positive electrode active material layer is 0.3g / 1540.25mm 2 .

[0197] 2. Preparation of negative electrode sheet

[0198] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode active material layer. The negative electrode active material layer includes a film layer formed by uniformly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector copper foil, drying, and cold pressing. The negative electrode active material layer includes a negative electrode active material, a binder styrene-butadiene rubber (SBR), a thickener sodium carboxymethyl cellulose (CMC-Na), and a conductive agent carbon black (Super P) in a weight ratio of 96.2:1.8:1.2:0.8.

[0199] The negative electrode active material includes artificial graphite. The surface density of the negative electrode active material layer is 0.15g / 1540.25mm 2 The ratio of the area density of the single-sided positive electrode active material layer to the area density of the single-sided negative electrode active material layer is 2:1.

[0200] 3. Isolation film

[0201] The isolation membrane is a porous polypropylene membrane.

[0202] 4. Preparation of electrolyte

[0203] The electrolyte includes an organic solvent, lithium salt and additives.

[0204] 5. Preparation of batteries

[0205] The lithium-ion battery includes an outer packaging shell, an electrode assembly and an electrolyte. The electrode assembly and the electrolyte are arranged in the outer packaging shell. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The electrode assembly is a wound electrode assembly, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0206] Comparative Example 1 and Comparative Example 2

[0207] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the length of the positive electrode active material layer in the positive electrode sheet was adjusted.

[0208] Example 2-1 to Example 2-5

[0209] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that at least one of the width and length of the negative electrode active material layer in the negative electrode sheet was adjusted.

[0210] Example 3-1 and Example 3-2

[0211] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that at least one of the width and length of the separator was adjusted.

[0212] Example 4-1 and Example 4-2

[0213] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the surface density of the negative electrode active material layer was adjusted.

[0214] The surface density of the negative electrode active material layer in Example 4-1 is 0.13 g / 1540.25 mm 2 The ratio of the surface density of the single-sided positive electrode active material layer to the surface density of the single-sided negative electrode active material layer is 2.3:1.

[0215] The surface density of the negative electrode active material layer in Example 4-2 is 0.16 g / 1540.25 mm 2 The ratio of the surface density of the single-sided positive electrode active material layer to the surface density of the single-sided negative electrode active material layer is 1.875:1.

[0216] Example 5

[0217] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the material of the positive electrode active material was adjusted. The positive electrode active material included a lithium iron phosphate material, which included aluminum. The content of the aluminum was 400 ppm.

[0218] The relevant parameters of Examples 1 to 5, Comparative Examples 1 and 2 are shown in Table 1.

[0219] The electrolyte compositions of the above embodiments and comparative examples are the same as that of Example 1, as shown in Table 2.

[0220] Performance Testing

[0221] 1. Lithium plating test of lithium-ion batteries

[0222] At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were fully charged to 3.6V at 4C and fully discharged to 2.0V at 1C. This was repeated 10 times, and then the lithium-ion batteries were fully charged at 4C again. The negative electrode sheets were then disassembled and the lithium deposition on the surface of the negative electrode sheets was observed.

[0223] Test results

[0224] The test results are shown in Table 1.

[0225] Table 1

[0226] After testing,

[0227] If the lithium deposition area on the negative electrode surface is less than 5%, it is considered to be slight lithium deposition.

[0228] The area of ​​lithium deposition on the negative electrode surface is 5% to 40%, which is considered to be moderate lithium deposition.

[0229] When the area of ​​lithium plating on the negative electrode surface is greater than 40%, it is considered to be severe lithium plating.

[0230] The area of ​​lithium deposition on the surface of the negative electrode of Comparative Example 1 is 49%, which is severe lithium deposition.

[0231] In Table 1, taking Comparative Example 1 as a benchmark, its lithium deposition situation is defined as 100%, and the percentage of the lithium deposition area of ​​other embodiments and comparative examples to the lithium deposition area of ​​Comparative Example 1 is calculated. When the lithium deposition situation is 10% to 82%, it is moderate lithium deposition; when the lithium deposition situation is less than 10%, it is slight lithium deposition; when the lithium deposition situation is greater than 82%, it is severe lithium deposition.

[0232] In Comparative Example 1, the overhanging area is relatively small, posing a risk of lithium deposition. Compared to Comparative Example 1, in the embodiment, the overhanging area is adjusted to a larger lengthwise overhanging area than the widthwise overhanging area of ​​the negative electrode sheet. This allows the active ions to be largely embedded in the negative electrode active material layer of the negative electrode sheet, reducing the degree of lithium deposition and improving the reliability of the battery cell. However, further increasing the overhanging area may lead to a decrease in energy density. For example, in Comparative Example 2, the overhanging area in the lengthwise direction is too large, potentially resulting in a decrease in energy density.

[0233] From Examples 1 to 2-5, it can be seen that when 1<(L2-L1) / (W2-W1)≤4, especially when 1.5≤(L2-L1) / (W2-W1)≤2.5, the degree of lithium plating of the battery is low, and the reliability of the battery is further improved.

[0234] By adjusting the size of the isolation membrane, Example 3-1 and Example 3-2 can further adjust the degree of lithium plating of the battery, thereby further improving the reliability of the battery.

[0235] In Examples 4-1 and 4-2, by adjusting the surface density of the negative electrode active material layer, the negative electrode active material layer's ability to receive active ions can be further adjusted, thereby adjusting the degree of lithium deposition in the battery and further improving the battery's reliability. In Example 5, by adding aluminum to the positive electrode active material, battery performance can be further improved.

[0236] Example 6-1 to Example 6-5

[0237] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the content of at least one of lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSI in the electrolyte was adjusted.

[0238] Example 7-1 to Example 7-5

[0239] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the content of at least one of lithium difluorophosphate and lithium fluorosulfonate in the electrolyte was adjusted.

[0240] Example 8-1 and Example 8-2

[0241] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the content of the organic solvent in the electrolyte was adjusted.

[0242] Comparative Example 3

[0243] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type and content of the lithium salt in the electrolyte were adjusted.

[0244] Table 2

[0245] In Table 2,

[0246] The first solvent includes dimethyl carbonate DMC and ethyl methyl carbonate EMC in a mass ratio of 1:1.

[0247] The second solvent includes ethylene carbonate (EC) and propylene carbonate (PC) in a mass ratio of 1:1. The mass content of the second solvent is 100% of the total mass of the electrolyte minus the total mass content of (lithium salt + additive + first solvent). For example, the mass content of the second solvent in Example 1 is 29.85%, the mass content of the second solvent in Example 8-1 is 24.85%, and the mass content of the second solvent in Example 8-2 is 34.85%.

[0248] As shown in Table 2, in Comparative Example 3, only lithium hexafluorophosphate LiPF6 is added to the electrolyte as a lithium salt, and its mass content is 15.00%. The viscosity in the system is relatively high, which is not conducive to the migration of lithium ions and may increase the risk of lithium precipitation.

[0249] Lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide LiFSI are added to the electrolyte, especially in Example 1 and Example 6-1 to Example 6-5, the ratio of the mass content of lithium hexafluorophosphate LiPF6 to the mass content of lithium bis(fluorosulfonyl)imide LiFSI is 1.05 to 1.4. The combined action of lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSI can improve the conductivity of the electrolyte, reduce the internal resistance of the battery cell, and facilitate the embedding of more active ions near the tab into the negative electrode active material, thereby reducing the amount of metal precipitation on the negative electrode sheet per unit time, which is beneficial to improving the reliability of the battery cell.

[0250] In Example 7-1 and Example 7-2, by regulating the mass content of lithium difluorophosphate and lithium fluorosulfonate, the mass content of lithium difluorophosphate is 0.05% to 0.2%, and / or the mass content of lithium fluorosulfonate is 0.01% to 0.1%, which can improve the transmission capacity of active ions in the negative electrode active material layer and reduce the risk of metal precipitation near the tab of the negative electrode.

[0251] In Example 8-1 and Example 8-2, by adjusting the mass content of the low-viscosity solvent, the migration rate of active ions in the electrolyte can be increased, and the degree of lithium deposition in the battery cell can be improved.

[0252] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A battery cell comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte; the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, the positive electrode active material layer comprising an olivine-structured lithium-containing material; and the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The size of the positive electrode active material layer along the length direction of the positive electrode sheet is L1 mm, the size of the positive electrode active material layer along the width direction of the positive electrode sheet is W1 mm, the size of the negative electrode active material layer along the length direction is L2 mm, and the size of the negative electrode active material layer along the width direction is W2 mm. in, 1<(L2-L1) / (W2-W1)≤4, and L2 / L1>1, 500≤L1≤600; The electrolyte includes lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSI. Based on the total mass of the electrolyte, the ratio of the mass content of the lithium hexafluorophosphate LiPF6 to the mass content of the lithium bis(fluorosulfonyl)imide LiFSI is greater than 1.

2. The battery cell according to claim 1, wherein: 1.25≤(L2-L1) / (W2-W1)≤4.

3. The battery cell according to claim 2, wherein: 1.5≤(L2-L1) / (W2-W1)≤2.

5.

4. The battery cell according to any one of claims 1 to 3, wherein: 3≤L2-L1≤10; or 2≤W2-W1≤6.

5. The battery cell according to claim 4, wherein: 5≤L2-L1≤10.

6. The battery cell according to any one of claims 1 to 5, wherein: 500≤L2≤600。 7. The battery cell according to any one of claims 1 to 6, wherein: 100≤W2≤155; or 100≤W1≤155.

8. The battery cell according to any one of claims 1 to 7, wherein: The battery cell further includes a separator, which is disposed between the positive electrode sheet and the negative electrode sheet. The separator has a dimension of L3 mm along the length direction and a dimension of W3 mm along the width direction, and 2≤L3-L2≤10; and / or 2≤W3-W2≤5.

9. The battery cell according to claim 8, wherein: 2≤L3-L2≤8.

10. The battery cell according to claim 9, wherein: 2≤L3-L2≤5.

11. The battery cell according to any one of claims 1 to 10, wherein: 500≤L3≤600; and / or 100≤W3≤160.

12. The battery cell according to any one of claims 1 to 11, wherein: The total mass content of the lithium hexafluorophosphate LiPF6 and lithium bis(fluorosulfonyl)imide LiFSI is 10% to 16%.

13. The battery cell according to claim 12, wherein: Based on the total mass of the electrolyte, the ratio of the mass content of the lithium hexafluorophosphate LiPF6 to the mass content of the lithium bis(fluorosulfonyl)imide LiFSI is 1.05 to 1.

4.

14. The battery cell according to claim 13, wherein: Based on the total mass of the electrolyte, the mass content of the lithium hexafluorophosphate LiPF6 is 6.5% to 9%; or Based on the total mass of the electrolyte, the total mass content of the lithium bis(fluorosulfonyl)imide LiFSI is 6% to 8%.

15. The battery cell according to any one of claims 1 to 14, wherein: The electrolyte further includes an additive, wherein the additive includes at least one of lithium difluorophosphate and lithium fluorosulfonate.

16. The battery cell according to claim 15, wherein: Based on the total mass of the electrolyte, the mass content of the lithium difluorophosphate is 0.05% to 0.2%; and / or Based on the total mass of the electrolyte, the mass content of the lithium fluorosulfonate is 0.01% to 0.1%.

17. The battery cell according to any one of claims 1 to 16, wherein: The electrolyte further includes an organic solvent, and the organic solvent includes: a first solvent comprising at least one of dimethyl carbonate and ethyl methyl carbonate, ethyl acetate, ethylene glycol monopropyl ether, methyl acrylate, and propyl propionate; and The second solvent includes at least one of ethylene carbonate and propylene carbonate.

18. The battery cell according to claim 17, wherein: Based on the total mass of the electrolyte, the total mass content of the first solvent is 55% to 70%; and / or Based on the total mass of the electrolyte, the total mass content of the second solvent is 20% to 35%.

19. The battery cell according to any one of claims 1 to 18, wherein: The lithium-containing material with an olivine structure includes a lithium iron phosphate material.

20. The battery cell according to claim 19, wherein The lithium iron phosphate material includes M elements, and M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce.

21. The battery cell according to claim 20, wherein: M includes at least one of Mg, Al, Ti, V and Zn, and the mass percentage of the M element relative to the total mass of the lithium iron phosphate material is 100 ppm to 1000 ppm.

22. The battery cell according to any one of claims 1 to 21, wherein: The ratio of the area density of the positive electrode active material layer on one side to the area density of the negative electrode active material layer on one side is 2.0 to 2.

5.

23. The battery cell according to claim 22, wherein: The surface density of the positive electrode active material layer on one side is 0.27g / 1540.25mm 2 Up to 0.33g / 1540.25mm 2 and / or The surface density of the negative electrode active material layer on one side is 0.11 g / 1540.25 mm 2 Up to 0.16g / 1540.25mm 2 .

24. The battery cell according to any one of claims 1 to 23, wherein: The negative electrode active material layer includes at least one of artificial graphite and natural graphite.

25. The battery cell according to any one of claims 1 to 24, wherein: The positive electrode sheet further includes a positive electrode tab, and the positive electrode tab is arranged on at least one side of the positive electrode collector along the length direction; and / or The negative electrode sheet further includes a negative electrode tab, which is disposed on at least one side of the negative electrode collector along the length direction.

26. The battery cell according to claim 25, wherein: The positive electrode tab is arranged on one side of the positive electrode collector along the length direction, and the negative electrode tab is arranged on one side of the negative electrode collector along the length direction; In the direction from the positive electrode current collector to the positive electrode tab, the negative electrode tab protrudes from the negative electrode current collector; or The negative electrode tab protrudes from the negative electrode collector in a direction from the positive electrode tab to the positive electrode collector.

27. The battery cell according to claim 25, wherein: The positive electrode tabs are arranged on both sides of the positive electrode current collector along the length direction; and / or The negative electrode tabs are arranged on both sides of the negative electrode current collector along the length direction.

28. A battery comprising the battery cell according to any one of claims 1 to 27.

29. An electrical device comprising the battery according to claim 28.

Images