Battery cell, battery, and electric device

Abstract

A battery cell, a battery, and an electric device. The battery cell comprises an electrode assembly and an electrolyte; the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator; the positive electrode sheet comprises a positive electrode current collector, and a positive electrode film layer which is arranged on at least one side of the positive electrode current collector and contains a positive electrode active material; the positive electrode active material comprises a lithium-containing material of an olivine structure; the negative electrode sheet comprises a negative electrode current collector, and a negative electrode film layer which is arranged on at least one side of the negative electrode current collector and contains a negative electrode active material; the negative electrode active material comprises a carbon material; the separator is arranged between the positive electrode sheet and the negative electrode sheet; the thickness of the positive electrode film layer on a single side of the positive electrode sheet is H1, and the unit thereof is μm; the thickness of the negative electrode film layer on a single side of the negative electrode sheet is H2, and the unit thereof is μm; the thickness of the separator is H3, and the unit thereof is μm; and the battery cell satisfies: 65 μm ≤ H1 ≤ 90 μm, 138 μm ≤ H1+H2+H3 ≤ 190 μm, and 7 ≤ (H1+H2) / H3 ≤ 12.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410268465.9, 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 fast charging performance of current battery cells is poor.

[0006] Summary of the Invention

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

[0008] In a first aspect, an embodiment of the present application proposes a battery cell, which includes an electrode assembly and an electrolyte, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator, the positive electrode sheet including a positive electrode collector and a positive electrode film layer provided on at least one side of the positive electrode collector and containing a positive electrode active material, the positive electrode active material including an olivine-structured lithium-containing material; the negative electrode sheet including a negative electrode collector and a negative electrode film layer provided on at least one side of the negative electrode collector and containing a negative electrode active material, the negative electrode active material including a carbon material; the separator is provided between the positive electrode sheet and the negative electrode sheet, wherein the thickness of the single-side positive electrode film layer in the positive electrode sheet is H1, and its unit is μm; the thickness of the single-side negative electrode film layer in the negative electrode sheet is H2, and its unit is μm; the thickness of the separator is H3, and its unit is μm; the battery cell satisfies: 65μm≤H1≤90μm, 138μm≤H1+H2+H3≤190μm, and 7≤(H1+H2) / H3≤12.

[0009] Therefore, the embodiment of the present application includes the above-mentioned positive electrode active material and negative electrode active material. In the above system, by adjusting 138μm≤H1+H2+H3≤190μm, and 7≤(H1+H2) / H3≤12, it is beneficial to shorten the transmission path of lithium ions, especially the solid-phase transmission path of lithium ions, which can effectively improve the fast charging performance of the battery cell.

[0010] In some embodiments, 7.5≤(H1+H2) / H3≤11.50. When the embodiments of the present application meet the above range, it is beneficial to further shorten the lithium ion transmission path, especially the solid phase transmission path of lithium ions, and can effectively improve the fast charging performance of the battery cell.

[0011] In some embodiments, the separator is a porous polymer membrane that satisfies the following conditions: 13 μm < H3 < 20 μm; alternatively, 13.5 μm ≤ H3 ≤ 19.5 μm. When the separator thickness is within the above range, the separator is not excessively thick, the lithium ion transport path in the liquid phase is relatively short, and the transport barrier is relatively small, resulting in smoother transport and faster transport rates, which is beneficial for improving the fast charging performance of the battery cell. Furthermore, the separator thickness is not excessively thin, which improves the separator's heat resistance and cycling stability.

[0012] In some embodiments, the porous polymer membrane comprises at least one of a polypropylene membrane and a polyethylene membrane. Optionally, the porous polymer membrane is a polypropylene membrane or a polyethylene membrane. These materials have excellent heat resistance and are less susceptible to burn-through during the battery's charge-discharge cycle, thereby improving the battery's cycling stability. Furthermore, since the porous polymer membrane lacks a ceramic coating, the transport barriers to lithium ions within the membrane are further reduced, further improving the migration rate and facilitating rapid charging of the battery.

[0013] In some embodiments, the porosity of the separator is 35% to 45%. When the porosity of the separator is within the above range, the porosity is relatively high, which can further reduce the transmission barrier of lithium ions, increase the migration rate of lithium ions, and further improve the fast charging performance of the battery cell.

[0014] In some embodiments, the compaction density of a single-sided positive electrode film layer is 2.1 g / cm 3 Up to 2.4g / cm 3 The compaction density of the single-side negative electrode film is 1.0g / cm 3 to 1.3g / cm 3 The cooperation between the negative electrode film layer and the positive electrode film layer enables the lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0015] In some embodiments, the surface density of the single-sided positive electrode film layer is 0.26g / 1540.25mm 2 Up to 0.29g / 1540.25mm 2 The surface density of the negative electrode film layer on one side is 0.12g / 1540.25mm 2 Up to 0.14g / 1540.25mm 2 The cooperation between the negative electrode film layer and the positive electrode film layer enables the lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0016] In some embodiments, 0.9≤H1 / H2≤1.3; and 60μm≤H2≤80μm. In the embodiments of the present application, when the thickness of the negative electrode film layer and the thickness of the positive electrode film layer are regulated to meet the above ranges, lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0017] In some embodiments, the electrolyte has a liquid retention coefficient of 4.0 g / Ah to 5.0 g / Ah. When the liquid retention coefficient of the battery cell is within the above range, the electrolyte can effectively wet the positive and negative electrode plates and increase the migration rate of lithium ions in the liquid phase, which is beneficial for improving the fast charging capability of the battery cell.

[0018] In some embodiments, the electrolyte includes a lithium salt, the lithium salt includes a first lithium salt and a second lithium salt, the first lithium salt includes at least one of lithium hexafluorophosphate LiPF6 and lithium bis(trifluoromethylsulfonyl)imide LiTFSI, and can be lithium hexafluorophosphate LiPF6, and the mass percentage of the first lithium salt relative to the total mass of the electrolyte is ≤10%, and can be selected from 5% to 10%; the second lithium salt includes at least one of lithium tetrafluoroborate LiBF4 and lithium difluorophosphate LiPO2F2, and the mass percentage of the second lithium salt relative to the total mass of the electrolyte is ≥1%.

[0019] Therefore, in the embodiment of the present application, the viscosity of the first lithium salt is relatively high, which is not conducive to the rapid migration of lithium ions; the viscosity of the second lithium salt is relatively low, and the second lithium salt can form an SEI film rich in boron and / or fluorine elements on the surface of the negative electrode active material, which can effectively repair the SEI film interface, reduce the impedance of the cycle process, and improve the cycle performance; the second lithium salt can also alleviate the decomposition of lithium hexafluorophosphate into hydrofluoric acid to a certain extent, and can further alleviate the side reaction between hydrofluoric acid and the active material, and can take into account the improvement of the fast charging performance and cycle performance of the battery cell.

[0020] In some embodiments, the second lithium salt includes lithium tetrafluoroborate LiBF4 and lithium difluorophosphate LiPO2F2; optionally, the mass percentage of lithium tetrafluoroborate LiBF4 relative to the total mass of the electrolyte is 0.3% to 1.0%, and the mass percentage of lithium difluorophosphate LiPO2F2 relative to the total mass of the electrolyte is 0.3% to 3.5%; further optionally, the mass percentage of lithium tetrafluoroborate LiBF4 relative to the total mass of the electrolyte is 0.5% to 0.8%, and the mass percentage of lithium difluorophosphate LiPO2F2 relative to the total mass of the electrolyte is 0.3% to 1.5%.

[0021] In some embodiments, the lithium salt further includes a third lithium salt, comprising at least one of a fluorine-containing lithium borate salt and a fluorine-containing lithium phosphate salt, wherein the third lithium salt comprises 0.1% to 2.5% by weight relative to the total mass of the electrolyte. Adding the third lithium salt in this amount can reduce the viscosity of the electrolyte system, facilitate rapid migration of lithium ions in the liquid phase, and enhance the fast charging performance of the battery cell.

[0022] In some embodiments, the fluorine-containing lithium borate salt includes at least one of lithium difluorooxalatoborate LiDFOB and lithium bisoxalatoborate LiBOB; and / or the fluorine-containing lithium phosphate salt includes at least one of lithium difluorobisoxalatophosphate LiDFOP and lithium tetrafluorooxalatophosphate LiTFOP.

[0023] In some embodiments, the electrolyte further includes an organic solvent; the organic solvent content, by weight, relative to the total mass of the electrolyte, is ≥ 45%; optionally ranging from 60% to 95%; and / or the organic solvent comprises at least one of ethylene carbonate (EC) and propylene carbonate (PC). Adding this organic solvent reduces the viscosity of the electrolyte system, facilitates rapid migration of lithium ions in the liquid phase, and enhances the fast-charging performance of the battery cells.

[0024] In some embodiments, the electrolyte further includes an additive, including at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Optionally, the additive comprises 0.5% to 2.5% by weight of the total weight of the electrolyte. When the additive is within this range, the cycle life of the battery cell and the static storage impedance can be effectively improved.

[0025] In some embodiments, the olivine-structured lithium-containing material includes an olivine-structured lithium iron phosphate material, and the carbon material includes graphite. The aforementioned positive and negative active materials, along with an electrode assembly of appropriate thickness, can further enhance the rapid charging performance of the battery cell.

[0026] In some embodiments, the olivine-structured lithium-containing material comprises a general formula of Li x Ay Me a M b P 1-c X c Q z A compound, wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, and N; and Q includes at least one of O and F.

[0027] 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.

[0028] In a third aspect, the present application further proposes an electrical device comprising a battery according to any embodiment of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0031] FIG. 2 is an exploded schematic diagram of an embodiment of the battery cell of FIG. 1 .

[0032] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0033] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0034] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0035] FIG6 is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0036] The drawings are not necessarily drawn to scale.

[0037] The following are the descriptions of the reference numerals:

[0038] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0039] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0040] 53. Cover plate;

[0041] 6. Electrical equipment. DETAILED DESCRIPTION

[0042] Below, the battery cells, batteries, and electrical devices of the present application are described in detail, with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of substantially identical structures may be omitted. This is to avoid unnecessary length in the following description and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0043] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and a 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 a particular range. The range limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a 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, 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 the 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 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] 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.

[0046] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, a method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0047] Home energy storage products can store electricity locally for later use. They primarily utilize rechargeable batteries (cells) for charge and discharge cycles. Consumers are increasingly demanding the performance of home energy storage products, particularly fast-charging performance.

[0048] In view of the above problems, the implementation scheme of the present application proposes a battery cell, which is beneficial to shorten the transmission path of lithium ions, especially the solid-phase transmission path of lithium ions, by adjusting 100μm≤H1+H2+H3≤150μm and 5≤(H1+H2) / H3≤8, and can effectively improve the fast charging performance of the battery cell.

[0049] Next, the technical solutions of the implementation methods of this application are described in detail.

[0050] battery cells

[0051] A first aspect of the embodiments of the present application provides a battery cell.

[0052] The 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 positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and containing a positive electrode active material. The positive electrode active material includes an olivine-structured lithium-containing material. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and containing a negative electrode active material. The negative electrode active material includes a carbon material. The separator is provided between the positive electrode sheet and the negative electrode sheet.

[0053] in,

[0054] The thickness of the positive electrode film layer on one side of the positive electrode sheet is H1, and its unit is μm;

[0055] The thickness of the negative electrode film layer on one side of the negative electrode sheet is H2, and its unit is μm;

[0056] The thickness of the isolation film is H3, and its unit is μm;

[0057] The battery cell meets the following requirements: 138 μm ≤ H1 + H2 + H3 ≤ 190 μm, and 7 ≤ (H1 + H2) / H3 ≤ 12.

[0058] During the charging process of a battery cell, lithium ions in the positive electrode film layer are released from the positive electrode active material and migrate through the electrolyte to the negative electrode active material in the negative electrode film layer. Lithium ions are mainly transported in the solid phase between the positive and negative electrode film layers, and in the electrolyte, lithium ions are transported in the liquid phase. During the transport in the liquid phase, they can migrate to the negative electrode film layer through the separator. During the discharge process of a battery cell, lithium ions in the negative electrode film layer are released from the negative electrode active material and migrate through the electrolyte to the positive electrode active material in the positive electrode film layer. Lithium ions are mainly transported in the solid phase between the positive and negative electrode film layers, and in the electrolyte, lithium ions are transported in the liquid phase. During the transport in the liquid phase, they can migrate to the positive electrode film layer through the separator.

[0059] The total thickness H1+H2+H3 of the positive electrode film layer, separator film, and negative electrode film layer is related to the length of the lithium ion transmission path. As the total thickness of the positive electrode film layer, separator film, and negative electrode film layer increases, the lithium ion transmission path increases. Studies have found that when H1+H2+H3>190μm, the lithium ion transmission path is too long, and fast charging of the battery cell cannot be achieved. When H1+H2+H3≤190μm, the lithium ion transmission path will not be too long, and lithium ions can quickly migrate from the positive electrode film layer to the negative electrode film layer, which is conducive to fast charging of the battery cell. However, as the total thickness of the positive electrode film layer, separator film, and negative electrode film layer decreases, the positive and negative electrode film layers may not meet the capacity requirements. Therefore, it is necessary to regulate H1+H2+H3≥138μm.

[0060] However, the rapid migration of lithium ions is also affected by the thickness distribution system in the positive electrode film layer, the negative electrode film layer and the isolation membrane, and it is necessary to comprehensively consider the thickness of the positive electrode film layer, the thickness of the negative electrode film layer and the thickness of the isolation membrane; considering that the solid phase transmission process of lithium ions mainly occurs in the positive electrode film layer and the negative electrode film layer, and the liquid phase transmission process mainly occurs in the isolation membrane, the total thickness of the positive electrode film layer and the negative electrode film layer has a greater influence on the transmission path of lithium ions, and the resistance of solid phase transmission is usually large. Therefore, the embodiment of the present application can make lithium ions migrate rapidly between the positive electrode film layer and the negative electrode film layer by regulating the ratio of the total thickness H1+H2 of the positive electrode film layer and the negative electrode film layer to the isolation membrane H3 to (7 to 12), which is beneficial to improving the fast charging performance of the battery cell.

[0061] In summary, the embodiments of the present application, by adjusting 138μm≤H1+H2+H3≤190μm and 7≤(H1+H2) / H3≤12, can help shorten the lithium ion transmission path, especially the solid-phase transmission path of lithium ions, and can effectively improve the fast charging performance of battery cells. In particular, in thick-coated pole pieces, by adjusting 138μm≤H1+H2+H3≤190μm and 7≤(H1+H2) / H3≤12, it can help shorten the lithium ion transmission path, especially the solid-phase transmission path of lithium ions, and can effectively improve the fast charging performance of battery cells.

[0062] Exemplarily, H1+H2+H3 can be 138μm, 139μm, 140μm, 141μm, 142μm, 143μm, 144μm, 145μm, 146μm, 147μm, 148μm, 149μm, 150μm, 155μm, 160μm, 165μm, 170μm, 175μm, 180μm, 185μm, 190μm or a range consisting of any two of the above values.

[0063] 7≤(H1+H2) / H3≤12, optionally, 7.5≤(H1+H2) / H3≤11.50.

[0064] Illustratively, (H1+H2) / H3 can be 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.2, 8.5, 8.8, 9.0, 9.2, 9.5, 9.8, 10.0, 10.2, 10.5, 10.8, 11.0, 11.2, 11.30, 11.5, 11.8, 12.0, or a range consisting of any two of the above values.

[0065] In the embodiments of the present application, the thickness of the positive electrode film layer or the negative electrode film layer is the thickness on a single side. Taking the positive electrode film layer as an example, if the positive electrode film layer is provided on both sides of the positive electrode current collector, the thickness of the positive electrode film layer on one side of the positive electrode current collector is the thickness of the positive electrode film layer on a single side; or if the positive electrode film layer is provided on one side of the two sides of the positive electrode current collector, the thickness of the positive electrode film layer on that side is the thickness of the positive electrode film layer on a single side. Taking the negative electrode film layer as an example, if the negative electrode film layer is provided on both sides of the negative electrode current collector, the thickness of the negative electrode film layer on one side of the negative electrode current collector is the thickness of the negative electrode film layer on a single side; or if the negative electrode film layer is provided on one side of the two sides of the negative electrode current collector, the thickness of the negative electrode film layer on that side is the thickness of the negative electrode film layer on a single side.

[0066] The thickness of the positive electrode film layer is well known in the art and can be detected using equipment and methods well known in the art. 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. For example, according to GB / T 17359-2012 "Quantitative Analysis by Microbeam Energy Spectrometry", the thickness of the positive electrode film layer can be obtained by performing ion polishing cross-section elemental analysis on a positive electrode sheet that does not contain electrolyte as a sample. For another example, using a micrometer to measure multiple times and obtain an average value: Take a positive electrode sheet without electrolyte (a positive electrode sheet coated on both sides with a positive electrode film layer), first use a micrometer to measure the thickness of the positive electrode sheet at any five locations, and obtain the average value H1. After wiping the positive electrode film layer clean, measure the thickness of the remaining current collector at any five locations, and obtain the average value H2. The thickness of the single-layer positive electrode film layer is (H2-H1) / 2. The testing process of the negative electrode film layer is similar to that of the positive electrode film layer and will not be repeated here.

[0067] In the embodiments of this application, the term "isolator" is a term commonly known in the art and can be tested using equipment and methods commonly known in the art. Ten isolators are taken as test samples, and their thicknesses are measured using a micrometer. The average thickness of the ten isolators is calculated as the thickness of the isolator. In the embodiments of this application, a newly prepared isolator can be used as a sample, or a fully discharged battery (discharged to the lower cutoff voltage, resulting in a battery state of charge of approximately 0%) can be disassembled, the isolator removed from the battery, and the dried isolator used as a sample.

[0068] [Isolation film]

[0069] The battery cell includes a separator, which may include a porous polymer film.

[0070] In some embodiments, the thickness H3 of the separator satisfies the following conditions: 13 μm < H3 < 20 μm; alternatively, 13.5 μm ≤ H3 ≤ 19.5 μm. Alternatively, 15 μm ≤ H3 ≤ 18 μm. When the separator thickness is within the above range, the separator is not too thick, the lithium ion transmission path in the liquid phase is relatively short, and the lithium ion transmission barrier is relatively small, resulting in smoother transmission and faster transmission rate, which is beneficial for improving the fast charging performance of the battery cell. Furthermore, the separator thickness is not too thin, which can improve the heat resistance and cycling stability of the separator.

[0071] For example, the thickness H3 of the isolation film may be 13.1 μm, 13.2 μm, 13.3 μm, 13.4 μm, 13.5 μm, 13.6 μm, 13.7 μm, 13.8 μm, 13.9 μm, 14 μm, 14.1 μm, 14.2 μm, 14.3 μm, 14.4 μm, 14.5 μm, 14.6 μm, 14.7 μm, 14.8 μm, 14.9 μm, 14.10 μm, 14.20 μm, 14.30 μm, 14.40 μm, 14.50 μm, 14.60 μm, 14.70 μm, 14.80 μm, 14.90 μm, 14.110 μm, 14.120 μm, 14.130 μm, 14.140 μm, 14.150 μm, 14.160 μm, 14.170 μm, 14.180 μm, 14.190 μm, 14.20 μm, 14.210 μm, 14.220 μm, 14.230 μm, 14.240 μm, 14.25 4.7μm, 14.8μm, 14.9μm, 15μm, 15.1μm, 15.2μm, 15.3μm, 15.4μm, 15.5μm, 15.6 μm, 15.7μm, 15.8μm, 15.9μm, 16.0μm, 16.1μm, 16.2μm, 16.3μm, 16.4μm, 16.5μm m, 16.6μm, 16.7μm, 16.8μm, 16.9μm, 17.0μm, 17.1μm, 17.2μm, 17.3μm, 17.4μm m, 17.5μm, 17.6μm, 17.7μm, 17.8μm, 17.9μm, 18.0μm, 18.1μm, 18.2μm, 18.3μm , 18.4μm, 18.5μm, 18.6μm, 18.7μm, 18.8μm, 18.9μm, 19.0μm, 19.1μm, 19.2μm, 19.3μm, 19.4μm, 19.5μm, 19.6μm, 19.7μm, 19.8μm, 19.9μm or a range consisting of any two of the above values.

[0072] Specifically, the isolation membrane can be a porous polymer membrane, which can be a single-layer membrane or a multi-layer membrane. When the porous polymer membrane is a multi-layer membrane, the multi-layer membrane can be two layers, three layers, four layers or even more layers, and the materials in the multi-layer membrane can be the same or different.

[0073] In some embodiments, the porous polymer film may include at least one of a polypropylene film and a polyethylene film; when the porous polymer film is a multilayer film, the porous polymer film may be a polypropylene film and a polyethylene film stacked along the thickness direction of the porous polymer film; the porous polymer film may be made of the same material, such as a multilayer polypropylene film stacked together, or a multilayer polyethylene film stacked together. The above materials have excellent heat resistance and are not easily burned through during the battery cell charge and discharge cycle, which can improve the cycle stability of the battery cell. Moreover, since the surface of the porous polymer film is not provided with a ceramic coating, the transmission barrier of lithium ions in the porous polymer film can be further reduced, the migration rate is further improved, and it is more conducive to the rapid charging of the battery cell.

[0074] In some embodiments, the porous polymer film is a polypropylene film or a polyethylene film, and both the polypropylene film and the polyethylene film are "bare films". "Bare film" means that the isolation membrane is composed of an organic base membrane, and there is no coating on the surface of the organic base membrane. Compared with the isolation membranes with organic / inorganic coatings commonly used on the market, this bare membrane has less obstruction to the transmission of lithium ions, and the same material and the transmission medium of lithium ions in the isolation membrane are the same, the conduction of lithium ions is smoother, and the rate is accelerated. Furthermore, since the "bare film" does not include a heat-resistant layer, the thickness of the "bare film" is set to be not less than 13μm and not more than 20μm. The above thickness range makes the mechanical strength and hardness of the bare film higher, and it is not easy for the "bare film" to be damaged or even burned through due to heat generation during the cycle of the battery cell; and the thickness will not be too thick, which can improve the transmission rate of lithium ions in the "bare film".

[0075] In some embodiments, the porosity of the separator is 35% to 45%. When the porosity of the separator is within the above range, the porosity is relatively high, which can further reduce the transmission barrier of lithium ions, increase the migration rate of lithium ions, and further improve the fast charging performance of the battery cell.

[0076] Exemplarily, the porosity of the isolation membrane can be 35%, 35.5%, 36%, 36.5%, 37%, 37.5%, 38%, 38.5%, 39%, 39.5%, 40%, 40.5%, 41%, 41.5%, 42%, 42.5%, 43%, 43.5%, 44%, 44.5% or a range consisting of any two of the above values.

[0077] In the embodiments of this application, porosity refers to the percentage of the pore volume within the separator to the total volume of the separator. Porosity can be tested in accordance with the standard GB / T 36363-2018, "Polyolefin Separators for Battery Cells." It should be noted that the actual testing process may vary slightly from the standard to obtain a more accurate test value, depending on instrument differences, test errors, and to minimize the impact of porosity on the test.

[0078] In the embodiments of the present application, the porosity of the isolation membrane can be adjusted by selecting the material of the isolation membrane and the preparation process of the isolation membrane.

[0079] [Positive electrode]

[0080] The battery cell includes a positive electrode plate.

[0081] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0082] In some embodiments, the compaction density of a single-sided positive electrode film layer is 2.1 g / cm 3 Up to 2.4g / cm 3 , for example, 2.10 g / cm 3 , 2.15g / cm 3 , 2.20g / cm 3 , 2.25g / cm 3 , 2.30g / cm 3 , 2.35g / cm 3 , 2.4g / cm 3 or a range consisting of any two of the above values. When the compaction density of the positive electrode film layer meets the above range, it can meet a certain gram capacity of the positive electrode sheet while taking into account the porosity and thickness of the positive electrode film layer, thereby taking into account the migration rate and migration path of lithium ions in the positive electrode film layer, thereby improving the fast charging performance of the battery cell.

[0083] In combination with the compaction density of the positive electrode film layer, the compaction density of the negative electrode film layer on one side can be 1.0 g / cm 3 to 1.3g / cm 3 When the compaction density of the negative electrode film layer meets the above range, it can take into account the porosity and thickness of the negative electrode film layer while meeting a certain gram capacity of the negative electrode electrode sheet, thereby taking into account the migration rate and migration path of lithium ions in the negative electrode film layer; and the negative electrode film layer and the positive electrode film layer cooperate, so that the lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0084] In the embodiment of the present application, the compaction density of the single-sided positive electrode film layer has a meaning well known in the art and can be tested by methods known in the art. For example, 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 film layer of the above-mentioned weighed positive electrode sheet, weigh the weight of the positive electrode collector, and record it as M0. The surface density of the positive electrode film layer = (the weight of the positive electrode sheet M1-the weight of the positive electrode collector M0) / S1, and the compaction density of the positive electrode film layer = the surface density of the positive electrode film layer / the thickness of the positive electrode film layer. The compaction density test process of the single-sided negative electrode film layer is the same as the compaction density test process of the single-sided positive electrode film layer, and will not be repeated here.

[0085] In some embodiments, the surface density of the single-sided positive electrode film layer is 0.26g / 1540.25mm 2 Up to 0.29g / 1540.25mm 2 , for example, 0.260g / 1540.25mm 2 、0.265g / 1540.25mm 2, 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 Or a range consisting of any two of the above values. When the areal density of the positive electrode film layer meets the above range, it can meet a certain gram capacity of the positive electrode sheet while taking into account the porosity and thickness of the positive electrode film layer, thereby taking into account the migration rate and migration path of lithium ions in the positive electrode film layer, thereby improving the fast charging performance of the battery cell.

[0086] Matching the surface density of the positive electrode film layer, the surface density of the negative electrode film layer on one side is 0.12g / 1540.25mm 2 Up to 0.14g / 1540.25mm 2 When the surface density of the negative electrode film layer meets the above range, it can take into account the porosity and thickness of the negative electrode film layer while meeting a certain gram capacity of the negative electrode electrode sheet, thereby taking into account the migration rate and migration path of lithium ions in the negative electrode film layer; and the negative electrode film layer and the positive electrode film layer cooperate, so that the lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0087] In the embodiments of the present application, the areal density of a single-sided positive electrode film layer is well known in the art and can be measured using methods known in the art. Areal density = weight of a single-sided positive electrode film layer / area of ​​a single-sided positive electrode film layer. Since both sides of the positive electrode current collector may have a positive electrode film layer, the weight of a single-sided positive electrode film layer = (average weight of the electrode sheet - average weight of the current collector) / 2. Compacted density = areal density / average thickness of the positive electrode film layer. Since both sides of the positive electrode current collector have a positive electrode film layer, the average thickness of the positive electrode film layer = (average thickness of the electrode sheet - average thickness of the current collector) / 2.

[0088] The "average" here can be the average value after 5 parallel tests.

[0089] In some embodiments, the thickness of the single-sided positive electrode film layer and the thickness of the single-sided negative electrode film layer satisfy: 0.9≤H1 / H2≤1.3, for example, H1 / H2 can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 1, 1.05, 1.10, 1.15, 1.20, 1.25, 1.3 or a range consisting of any two of the above values. Since there is a difference in the migration rate of lithium ions between the negative electrode active material in the negative electrode film layer and the positive electrode active material in the positive electrode film layer, when the thickness of the negative electrode film layer and the thickness of the positive electrode film layer are controlled in the embodiments of the present application to meet the above range, the lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0090] In some embodiments, the thickness H1 of the single-sided positive electrode film layer satisfies: 65μm≤H1≤90μm, for example, 65μm, 68μm, 70μm, 72μm, 75μm, 78μm, 80μm, 82μm, 85μm, 88μm, 90μm or a range consisting of any two of the above values.

[0091] The positive electrode film layer is a thick coating layer. The thickness of the single-sided film layer is coordinated with the surface density of the film layer, which can further enable lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell. The thickness of the single-sided film layer is coordinated with the compaction density of the film layer, which can further enable lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0092] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing material with an olivine structure.

[0093] The kinetic performance of lithium-containing materials with olivine structure is relatively poor. By combining it with the thickness parameters of the electrode assembly (138μm≤H1+H2+H3≤190μm, and 7≤(H1+H2) / H3≤12), lithium ions can migrate rapidly in the electrode assembly, improving the kinetic performance and thus improving the fast charging capability.

[0094] In some embodiments, the olivine-structured lithium-containing material comprises a general formula of Li x A y Me a M b P 1-c X c Q zA compound, wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, and N; and Q includes at least one of O and F.

[0095] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0096] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0097] The olivine-structured lithium-containing material may include at least one of a lithium iron phosphate material, a lithium manganese phosphate material, a lithium nickel phosphate material, and a lithium cobalt phosphate material. Alternatively, the olivine-structured lithium-containing material may include an olivine-structured lithium iron phosphate material. Lithium iron phosphate materials have excellent lattice stability and cycle stability.

[0098] In some embodiments, the lithium iron phosphate material includes an M element. This material is 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, improving the structural stability of the lithium iron phosphate material; or located within the crystalline 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 within the crystalline phase of the lithium iron phosphate material. If the M element can be detected during testing of the lithium iron phosphate material, it is considered that the lithium iron phosphate material includes the M element.

[0099] During the charge and discharge process, battery cells are accompanied by the deintercalation and deintercalation of active ions, such as Li, and their molar content varies when the battery cells are discharged to different states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the material's initial state, i.e., the state before the materials are added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0100] 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 cycling performance during operation.

[0101] 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.

[0102] 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.

[0103] In some embodiments, the lithium iron phosphate material includes a core portion and a carbon coating layer, the core portion includes lithium iron phosphate particles, and the carbon coating layer is disposed on at least a portion of the outer surface of the core portion; the electrolyte further includes an organic solvent, the organic solvent includes a first solvent, and the viscosity of the first solvent does not exceed 0.8 mPa·s.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] In some embodiments, the olivine-structured lithium-containing material includes first particles and second particles, wherein the first particles have a particle size greater than a predetermined particle size, and the second particles have a particle size less than or equal to the predetermined particle size. For example, the lithium iron phosphate material includes the first particles and the second particles.

[0108] Alternatively, the preset particle size can be the average particle size of the lithium-containing material with an olivine structure, and the preset particle size is a fixed value, such as any value between 0.7 μm and 1 μm, such as 0.7 μm; the average particle size has a meaning well known in the art and can be detected using equipment and methods well known in the art. For example, a freshly prepared positive electrode sheet can be taken, or a battery that has been discharged (discharged to the lower limit cut-off voltage so that the battery is charged to about 0% SOC) can be reversely disassembled, and the positive electrode sheet can be obtained from the battery for drying; then the positive electrode film layer in the positive electrode sheet is scraped off from the positive electrode current collector as a test sample. The lithium-containing material with an olivine structure is observed using a scanning electron microscope (SEM) to observe the SEM spectrum. For example, 100 particles are randomly selected from the SEM image, and the particle size of each of the 100 particles is measured. The longest diameter of the particle can be used as the particle size, and then the average value of the longest diameter is calculated as the preset particle size. In the embodiment of the present application, the particles are divided into two types of particles, large and small, by adopting the concept of a preset particle size. Large particles exceeding the preset particle size are used as first particles, and small particles less than or equal to the preset particle size are used as second particles.

[0109] Lithium iron phosphate materials are obtained by mixing large particles and small particles. The particle size distribution is wide, the contact area between particles is large, and good electron and ion pathways can be formed between the particles, which is beneficial to improving the cycle performance of the battery cell under working conditions.

[0110] In some embodiments, the first particles include at least one of a single particle and an agglomerated particle formed by agglomerating multiple single particles. A single particle refers to an independent particle, while an agglomerated particle refers to a particle formed by the agglomeration of two or more independent particles. The mixed use of single particles and agglomerated particles can also increase the contact area between particles, forming a better electron and ion pathway between particles, further improving the cycling performance of the battery cell under operating conditions.

[0111] In some embodiments, the second particles each independently include at least one of a single particle and an agglomerated particle formed by agglomeration of a plurality of single particles.

[0112] 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 EPA 6010D-2014, by inductively coupled plasma atomic emission spectrometry, using plasma atomic emission (ICP-OES, instrument model: Thermo ICAP7400) for determination. First, 0.4g of the positive electrode active material was weighed and 10ml (50% concentration) of aqua regia was added thereto. Then it was placed on a 180°C plate for 30min. After digestion on the plate, the volume was fixed to 100mL, and the standard curve method was used for quantitative testing.

[0113] 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 film 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.

[0114] In some embodiments, the positive electrode film 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 content of the positive electrode conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0115] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0116] 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).

[0117] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. 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 can be, but is not limited to, N-methylpyrrolidone (NMP).

[0118] [Negative electrode]

[0119] The battery cell also includes a negative electrode plate.

[0120] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film 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 film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0121] In some embodiments, the compaction density of a single negative electrode film layer may be 1.0 g / cm 3 to 1.3g / cm 3 When the compaction density of the negative electrode film layer meets the above range, it can take into account the porosity and thickness of the negative electrode film layer while meeting a certain gram capacity of the negative electrode electrode sheet, thereby taking into account the migration rate and migration path of lithium ions in the negative electrode film layer; and the negative electrode film layer and the positive electrode film layer cooperate, so that the lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0122] In some embodiments, the surface density of the negative electrode film layer on one side is 0.12g / 1540.25mm 2 Up to 0.14g / 1540.25mm 2 When the surface density of the negative electrode film layer meets the above range, it can take into account the porosity and thickness of the negative electrode film layer while meeting a certain gram capacity of the negative electrode electrode sheet, thereby taking into account the migration rate and migration path of lithium ions in the negative electrode film layer; and the negative electrode film layer and the positive electrode film layer cooperate, so that the lithium ions released from the positive electrode film layer can be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0123] In some embodiments, the thickness H2 of the single-sided negative electrode film layer satisfies: 60 μm≤H2≤80 μm, for example, 60 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 78 μm, 80 μm or a range consisting of any two of the above values.

[0124] The negative electrode film layer is a thick coating layer. The thickness of the single-sided film layer is coordinated with the surface density of the film layer, which can further enable lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell. The thickness of the single-sided film layer is coordinated with the compaction density of the film layer, which can further enable lithium ions released from the positive electrode film layer to be quickly embedded in the negative electrode film layer, further improving the fast charging performance of the battery cell.

[0125] In some embodiments, the negative electrode film layer includes a carbon-containing material with a layered structure. Optionally, the carbon-containing material includes graphite, for example, at least one of artificial graphite and natural graphite, and artificial graphite can be selected, and the structural stability of artificial graphite is relatively high. The lithium-containing material with an olivine structure is used as the positive electrode active material system, and the carbon material (graphite system) is used as the negative electrode active material system. By being used in conjunction with the thickness parameters of the electrode assembly (138μm≤H1+H2+H3≤190μm, and 7≤(H1+H2) / H3≤12), lithium ions can be rapidly migrated in the electrode assembly, thereby improving the kinetic performance and thus improving the fast charging capability.

[0126] 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.

[0127] 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.

[0128] In some embodiments, the weight content of the artificial graphite is greater than or equal to 85% and less than 100% based on the total weight of the negative electrode film 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.

[0129] In some embodiments, the volume distribution particle size D of the artificial graphite is v 99 is 30μm to 45μm. The particle size of artificial graphite meeting the above range is relatively large, the specific surface area is small, and the area in contact with the electrolyte is relatively small, which can reduce side reactions and improve the cycle life under working conditions.

[0130] For example, the volume distribution particle size D of the artificial graphite is v 99 is 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm or a range consisting of any two of the above values.

[0131] In the embodiment of the present application, the volume distribution particle size Dv 99 is a well-known meaning in the art, and the volume distribution particle size D of the particles is v 99 refers to the particle size corresponding to 99% in the volume distribution, which can be tested using equipment and methods known in the art. For example, a freshly prepared negative electrode active material is taken as a sample for testing, or a fresh battery cell is fully discharged to 0% state of charge (SOC), the negative electrode pole piece is disassembled, the negative electrode current collector is removed, and the negative electrode film layer is retained. The negative electrode film layer is immersed in N-methylpyrrolidone (NMP) to wash out the binder in the negative electrode film layer, retaining the negative electrode active material. After the negative electrode active material is dried, the volume distribution particle size D of the particles is measured using a Mastersizer 2000E laser particle size analyzer in accordance with the test standard GB / T 19077-2016. v In the embodiment of the present application, a fresh battery cell may be a battery cell that has just been shipped from the factory (not subjected to charge and discharge cycles after formation), or a battery cell that is mounted on an electrical device and has been cycled less than 10 times.

[0132] Volume distribution particle size D of artificial graphite v 99 is 30μm to 45μm; the electrolyte also includes at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC); optionally, the combined weight content of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) is 0.5% to 2.5% based on the total weight of the electrolyte. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) combined with large-particle artificial graphite can achieve both improved cycle life and increased DCR during static storage.

[0133] In some embodiments, the negative electrode film 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 mass content of the negative electrode conductive agent is ≤5% based on the total mass of the negative electrode film layer.

[0134] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The embodiments of the present application do not particularly limit the type of the negative electrode binder. As an 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 content of the negative electrode binder is ≤5% based on the total mass of the negative electrode film layer.

[0135] In some embodiments, the negative electrode film layer may optionally include other additives. For example, these additives may include thickeners, such as sodium carboxymethylcellulose (CMC-Na), PTC thermistor materials, and the like. In some embodiments, the weight content of these additives is ≤ 2% based on the total weight of the negative electrode film layer.

[0136] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Copper foil may be used as an example of a metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For 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. For example, the polymer base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, and polyethylene.

[0137] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. 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.

[0138] The negative electrode sheet does not exclude other additional functional layers in addition to the negative electrode film 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 film 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 film layer.

[0139] [Electrolyte]

[0140] In some embodiments, the electrolyte has a retention coefficient of 4.0 g / Ah to 5.0 g / Ah.

[0141] The liquid retention coefficient of a battery cell can reflect the liquid retention capacity of the electrolyte. When the liquid retention coefficient of a battery cell is within the above range, the electrolyte can better wet the positive and negative electrode plates, and can increase the migration rate of lithium ions in the liquid phase, which is beneficial to improving the fast charging capability of the battery cell.

[0142] Illustratively, the battery's liquid retention coefficient can be 4.0 g / Ah, 4.1 g / Ah, 4.2 g / Ah, 4.3 g / Ah, 4.4 g / Ah, 4.5 g / Ah, 4.6 g / Ah, 4.7 g / Ah, 4.8 g / Ah, 4.9 g / Ah, 5.0 g / Ah, or a range consisting of any two of the above values.

[0143] In the embodiments of the present application, the liquid retention coefficient of a battery cell is a well-known term in the art and can be tested using well-known equipment and methods in the art. For example, according to GB / T 31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles," at 25°C, the battery cell is charged at 1C to 3.6V and then discharged at 1C to 2.5V, with the discharged capacity C used as the denominator. The battery cell is weighed as M0, and then the positive electrode sheet, negative electrode sheet, separator, and electrolyte are disassembled, with free electrolyte remaining in the housing / bag. All of the above solid components (including but not limited to the positive electrode sheet, negative electrode sheet, separator, and other mechanical parts of the disassembled battery cell that contribute to M0) are placed in a 60°C oven and baked for at least 4 hours. All components of the battery cell are then weighed as M1, with the weight difference between M0 and M1 used as the numerator. The liquid retention coefficient is equal to the capacity C divided by the weight difference between M0 and M1.

[0144] In the embodiment of the present application, the viscosity of the electrolyte and the performance of the solid electrolyte interphase (SEI) film can be adjusted by adjusting at least one of the specific type and content of the components in the electrolyte.

[0145] [Lithium salt]

[0146] In some embodiments, the electrolyte includes a lithium salt, the lithium salt includes a first lithium salt and a second lithium salt, the first lithium salt includes at least one of lithium hexafluorophosphate LiPF6 and lithium bis(trifluoromethylsulfonyl)imide LiTFSI, and can be lithium hexafluorophosphate LiPF6, and the mass percentage of the first lithium salt relative to the total mass of the electrolyte is ≤10%, and can be selected from 5% to 10%; the second lithium salt includes at least one of lithium tetrafluoroborate LiBF4 and lithium difluorophosphate LiPO2F2, and the mass percentage of the second lithium salt relative to the total mass of the electrolyte is ≥1%.

[0147] Lithium salts can provide active lithium ions for the battery system. The viscosity of the first lithium salt is relatively high, which is not conducive to the rapid migration of lithium ions. The viscosity of the second lithium salt is relatively low, and the second lithium salt can form an SEI film rich in boron and / or fluorine elements on the surface of the negative electrode active material, which can effectively repair the SEI film interface, reduce the impedance of the cycle process, and improve the cycle performance. The second lithium salt can also alleviate the decomposition of lithium hexafluorophosphate into hydrofluoric acid to a certain extent, and can further alleviate the side reaction between hydrofluoric acid and active materials, and can take into account the improvement of the fast charging performance and cycle performance of the battery cell.

[0148] For example, the mass percentage of the first lithium salt is greater than 0% and less than or equal to 10%, for example, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.9% or more. 1, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5%, 3.6%, 3.8%, 4.0%, 4.2%, 4.5%, 4.6%, 4.8%, 5.0%, 5.2%, 5.5%, 5.6%, 5.8%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, 7.2%, 7.5%, 7.8%, 8.0%, 8.2%, 8.5%, 8.8%, 9.0%, 9.2%, 9.5%, 9.8%, 10%, or a range consisting of any two of the above values.

[0149] For example, the mass percentage of the second lithium salt is greater than 0% and less than or equal to 5%, for example, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.91, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5%, 3.6%, 3.8%, 4.0%, 4.2%, 4.5%, 4.6%, 4.8%, 5.0% or a range consisting of any two of the above values.

[0150] In some embodiments, the second lithium salt includes lithium tetrafluoroborate (LiBF4) and lithium difluorophosphate (LiPO2F2). The combination of these two lithium salts can form a boron- and fluorine-rich SEI film on the surface of the negative electrode active material, effectively repairing the SEI film interface, reducing cycling impedance, and improving cycling performance.

[0151] In some embodiments, the mass percentage of lithium tetrafluoroborate (LiBF4) relative to the total mass of the electrolyte is 0.3% to 1.0%, and the mass percentage of lithium difluorophosphate (LiPO2F2) relative to the total mass of the electrolyte is 0.3% to 3.5%. The combination of these two lithium salts in these amounts forms a boron- and fluorine-rich SEI film on the surface of the negative electrode active material, effectively repairing the SEI film interface, reducing cycling impedance, and improving cycling performance. Furthermore, the increased inorganic content and porous structure of the formed SEI film facilitate rapid lithium ion migration or release from the negative electrode active material, further enhancing the rapid charging performance of the battery cell.

[0152] It should be noted that when the solubility of lithium difluorophosphate in the electrolyte is high, its content can be ≥3%.

[0153] In order to further reduce the impedance of the cycle process and improve the fast charging performance, optionally, the mass percentage of lithium tetrafluoroborate LiBF4 relative to the total mass of the electrolyte is 0.5% to 0.8%, and the mass percentage of lithium difluorophosphate LiPO2F2 relative to the total mass of the electrolyte is 0.3% to 1.5%.

[0154] For example, the mass percentage of lithium tetrafluoroborate LiBF4 can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1% or a range consisting of any two of the above values.

[0155] Exemplarily, the mass percentage of lithium difluorophosphate LiPO2F2 can be 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%, 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.95%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.2%, 3.5% or a range consisting of any two of the above values.

[0156] In some embodiments, the lithium salt further includes a third lithium salt, the third lithium salt including at least one of a fluorine-containing lithium borate salt and a fluorine-containing lithium phosphate salt, wherein the mass percentage of the third lithium salt relative to the total mass of the electrolyte is 0.1% to 2.5%.

[0157] The fluorine-containing lithium borate salt in the third lithium salt is a different type from the lithium tetrafluoroborate (LiBF4) in the second lithium salt, and the fluorine-containing lithium phosphate salt in the third lithium salt is a different type from the lithium difluorophosphate (LiPO2F2) in the second lithium salt. Adding the third lithium salt in this amount reduces the viscosity of the electrolyte system, facilitates the rapid migration of lithium ions in the liquid phase, and enhances the fast-charging performance of the battery cells.

[0158] For example, the mass percentage of the third lithium salt can be 0.1%, 0.15%, 0.18%, 0.2%, 0.22%, 0.25%, 0.28%, 0.3%, 0.32%, 0.35%, 0.38%, 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 0.95%. , 0.98%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 1.95%, 2.0%, 2.05%, 2.1%, 2.15%, 2.2%, 2.25%, 2.3%, 2.35%, 2.4%, 2.45%, 2.5% or a range consisting of any two of the above values.

[0159] In some embodiments, the fluorine-containing lithium borate salt may include at least one of lithium difluorooxalatoborate (LiDFOB) and lithium bis(oxalatoborate) (LiBOB). Alternatively, the fluorine-containing lithium borate salt may include lithium difluorooxalatoborate (LiDFOB) and lithium bis(oxalatoborate) (LiBOB). These fluorine-containing lithium borates may also contribute to the formation of a boron-containing SEI film, which may improve cycling performance.

[0160] In some embodiments, the fluorine-containing lithium phosphate salt may include at least one of lithium difluorobis(oxalatophosphate) LiDFOP and lithium tetrafluorobis(oxalatophosphate) LiTFOP. Alternatively, the fluorine-containing lithium phosphate salt may include lithium difluorobis(oxalatophosphate) LiDFOP and lithium tetrafluorobis(oxalatophosphate) LiTFOP. The above-mentioned fluorine-containing lithium phosphate salts may also participate in the formation of a fluorine-containing SEI film, which is beneficial for improving cycle performance.

[0161] [Organic solvents]

[0162] In some embodiments, the electrolyte further includes an organic solvent, with the organic solvent comprising ≥45% by weight of the total electrolyte, optionally ranging from 60% to 91%. The addition of this organic solvent reduces the viscosity of the electrolyte system, facilitates rapid migration of lithium ions in the liquid phase, and enhances the rapid charging performance of the battery cells.

[0163] Illustratively, the mass percentage of the organic solvent can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91% or a range consisting of any two of the above values.

[0164] In some embodiments, the organic solvent may include at least one of ethylene carbonate (EC) and propylene carbonate (PC). Alternatively, the organic solvent may include ethylene carbonate (EC) and propylene carbonate (PC).

[0165] [additive]

[0166] In some embodiments, the electrolyte further includes an additive, which may include at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Alternatively, the additive may include both fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Fluoroethylene carbonate (FEC) can significantly reduce static storage impedance, while vinylene carbonate (VC) can significantly improve cycle life. When both are added to the electrolyte, they can both improve the cycle life of the battery cell and improve the static storage impedance.

[0167] Optionally, based on the total mass of the electrolyte, the mass percentage of the additive is 0.5% to 2.5%. When the mass percentage of the additive is within the above range, the cycle life of the battery cell can be effectively improved and the static storage impedance can be improved.

[0168] Illustratively, the mass percentage of the additive can be 0.5%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or a range consisting of any two of the above values.

[0169] 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.

[0170] 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 methods with reference to the 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 (with a charged state of 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.

[0171] 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 a charged state of 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.

[0172] 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 (C7H5F3). This premixed NMR reagent solution is pre-dried with 4A molecular sieves (15g of freshly opened 4A molecular sieves per 100ml of premixed NMR reagent solution is dried at room temperature (20-25°C) in a nitrogen glove box for over 30 days). 19F NMR measurements are performed using a Bruker Avance 400HD NMR instrument.

[0173] To identify and quantify individual species, the following settings were used with respect to flip angle and scanning time.

[0174] Fluorine spectrum test pulse sequence: 2gfhigqn.2;

[0175] Delay time: 1 second;

[0176] Number of scans: 16 times.

[0177] 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:

[0178] 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.

[0179] 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:

[0180] 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.

[0181] 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.

[0182] 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.

[0183] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0184] 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).

[0185] The present invention has no particular restrictions on the shape of the battery cell, which can be cylindrical, square, or any other shape. FIG1 shows a battery cell 5 with a square structure as an example.

[0186] In some embodiments, as shown in FIG2 , 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.

[0187] 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.

[0188] 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.

[0189] Figure 3 is a schematic diagram of one embodiment of a battery module 4 of the present application. As shown in Figure 3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple battery cells 5 may be secured using fasteners.

[0190] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0191] 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.

[0192] Figure 4 is a schematic diagram of one embodiment of a battery pack 1 of the present application, and Figure 5 is an exploded schematic diagram of the embodiment of the battery pack 1 shown in Figure 4 . As shown in Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0193] Electrical devices

[0194] 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.

[0195] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0196] Figure 6 is a schematic diagram of an embodiment of an electric device 6 that includes a battery cell of the present application as a power source. The electric device 6 can be 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 can be used.

[0197] 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.

[0198] Example

[0199] 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.

[0200] Example 1

[0201] 1. Preparation of positive electrode sheet

[0202] The positive electrode sheet includes a positive electrode current collector aluminum foil and a positive electrode film layer. The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode current collector aluminum foil, and a film layer formed after drying and cold pressing. The positive electrode film 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.

[0203] The positive electrode active material includes a lithium iron phosphate material, which also contains aluminum (Al) at a content of 400 ppm. The lithium iron phosphate material also includes a carbon coating layer, with the carbon coating layer comprising 1.2% by weight relative to the lithium iron phosphate material. The lithium iron phosphate material includes first particles and second particles. The first particles have a particle size greater than 1 μm, and the second particles have a particle size less than or equal to 1 μm.

[0204] The compaction density of the single-sided positive electrode film layer is 2.2g / cm 3 , the surface density is 0.28g / 1540.25mm 2 .

[0205] 2. Preparation of negative electrode sheet

[0206] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode film layer. The negative electrode film layer includes a negative electrode slurry (the solvent is deionized water) uniformly coated on the surface of the negative electrode current collector copper foil, and a film layer formed after drying and cold pressing. The negative electrode film 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.

[0207] The negative electrode active material includes artificial graphite, and its volume distribution particle size D v 99 is 35μm.

[0208] The compaction density of the single-sided negative electrode film is 1.2g / cm 3 , the surface density is 0.13g / 1540.25mm 2 .

[0209] 3. Isolation film

[0210] The isolation film is a porous polypropylene PP film.

[0211] 4. Preparation of electrolyte

[0212] The electrolyte includes an organic solvent, lithium salt and additives.

[0213] The lithium salt includes a first lithium salt, lithium hexafluorophosphate (LiPF6) (7%), a second lithium salt, and a third lithium salt. The second lithium salt includes lithium tetrafluoroborate (LiBF4) (0.7%) and lithium difluorophosphate (LiPO2F2) (1%), and the third lithium salt includes lithium difluorooxalatoborate (LiDFOB) (2%). The mass content of each component in the lithium salt is calculated based on the total mass of the electrolyte.

[0214] The additive includes fluoroethylene carbonate FEC (1%), and the mass content of the additive is calculated based on the total mass of the electrolyte.

[0215] The organic solvent includes dimethyl carbonate DMC (40%), ethyl methyl carbonate EMC (20%), ethylene carbonate EC (30%) and propylene carbonate PC (10%). The mass content of each component in the organic solvent is calculated based on the total mass of the organic solvent. The mass content of the organic solvent relative to the total mass of the electrolyte is 88.3%.

[0216] The electrolyte retention coefficient is 4.5g / Ah.

[0217] 5. Preparation of batteries

[0218] 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.

[0219] Comparative Examples 1 and 2: Lithium-ion batteries were prepared using a method similar to that of Example 1. Unlike Example 1, the total thickness of the positive electrode film layer, the negative electrode film layer, and the separator was adjusted in Comparative Examples 1 and 2.

[0220] Comparative Examples 3 and 4: Lithium-ion batteries were prepared using a method similar to that of Example 1. Unlike Example 1, the thickness of at least one of the positive electrode film layer, the negative electrode film layer, and the separator was adjusted in Comparative Examples 3 and 4.

[0221] Comparative Example 5: A lithium-ion battery was prepared using a method similar to that of Example 1. Unlike Example 1, Comparative Example 5 adjusted the structure of the isolation membrane. The isolation membrane used a porous PP film layer and an alumina ceramic coating provided on both sides of the porous PP film layer. The thickness of the porous PP film layer was 20 μm, the thickness of the single-sided alumina ceramic coating was 2.5 μm, and the total thickness of the isolation membrane was 25 μm.

[0222] Example 2-1 to Example 2-6: A lithium-ion battery is prepared using a method similar to Example 1. Unlike Example 1, Examples 2-1 to Example 2-6 at least adjust the total thickness H1+H2+H3 of the positive electrode film layer, the negative electrode film layer and the isolation film.

[0223] Examples 3-1 and 3-3: Lithium-ion batteries were prepared using a method similar to Example 1. Unlike Example 1, Examples 3-1 and 3-3 adjusted at least one of the material and porosity of the separator. In Example 3-1, the separator was made of polyethylene (PE) film. In Examples 3-2 and 3-3, the separator porosity was adjusted.

[0224] Example 4-1 and Example 4-2: Lithium-ion batteries were prepared using a method similar to Example 1. The difference from Example 1 was that the compaction density of the positive electrode film layer was adjusted in Examples 4-1 and 4-2.

[0225] Performance Testing

[0226] 1. Cycle performance test of lithium-ion batteries:

[0227] At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were charged to 3.6V at a 3C rate and discharged to 2.5V at a 1C rate. Cycling tests were performed until the lithium-ion batteries were cycled 600 times, and the capacity retention rate of the lithium-ion batteries was recorded.

[0228] 2. DCR growth rate test of static storage of lithium-ion batteries:

[0229] The initial DC internal resistance DCR0 of the lithium-ion batteries prepared in the examples and comparative examples was tested. The DCR1 of the lithium-ion batteries was tested after storage at 60° C. for 300 days. The growth rate of DCR was [(DCR1-DCR0) / DCR0]*100%.

[0230] The test conditions for DCR are as follows:

[0231] At 25°C, charge the lithium-ion battery to 3.6V at a rate of 0.33C, then discharge it to 2.5V at a rate of 0.33C. Charge it again at a rate of 0.5C for 30 minutes, recording the voltage at this time as U1. Discharge it at a rate of 4C for 30 seconds, recording the voltage at this time as U2. The DCR of a lithium-ion battery is (U1-U2) / I.

[0232] DCR affects charging performance, which is reflected by the DCR growth rate. The larger the DCR growth rate, the worse the charging performance; the smaller the DCR growth rate, the better the charging performance.

[0233] Test results

[0234] The test results of Comparative Examples 1 to 5 and Examples 1 to 4-2 are shown in Table 1.

[0235] Table 1

[0236] In Comparative Example 2, the combined thickness of the positive electrode film, separator, and negative electrode film is relatively small, and the positive and negative electrode films may not meet the required capacity. In Comparative Examples 1 and 5, the combined thickness of the positive electrode film, separator, and negative electrode film is too large, resulting in an excessively long lithium ion transport path and preventing rapid charging of the battery cells. Furthermore, as can be seen in Comparative Examples 3 and 4, excessive combined thickness of the positive and negative electrode film increases the solid-phase transport path for lithium ions, while excessive thickness of the separator increases the liquid-phase transport path for lithium ions, both of which are detrimental to rapid lithium ion transport.

[0237] Compared to Comparative Examples 1, 2 and 5, the embodiments of the present application can improve the cycle performance of the battery cell by adjusting the total thickness of the positive electrode film layer, the separator and the negative electrode film layer, and can adjust the solid-liquid phase transmission path of lithium ions, which is beneficial to shorten the transmission path of lithium ions, especially the solid phase transmission path of lithium ions, on the basis of meeting the capacity requirements of the lithium-ion battery, and can effectively improve the fast charging performance of the battery cell. By adjusting at least one of the thickness and porosity of the separator within a reasonable range, the rate of lithium ion transmission in the liquid phase can be adjusted, and the fast charging performance of the battery cell can be improved. By adjusting the thickness, compaction density, etc. of at least one of the positive electrode film layer and the negative electrode film layer within a reasonable range, the rate of lithium ion transmission in the solid phase can be effectively adjusted, and the fast charging performance of the battery cell can be improved.

[0238] Example 5-1 to Example 5-3:

[0239] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass percentage of the first lithium salt was adjusted in Examples 5-1 to 5-3.

[0240] Example 6-1 to Example 6-4:

[0241] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass percentage of the second lithium salt was adjusted in Examples 6-1 to 6-4.

[0242] Example 7-1 and Example 7-2:

[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 of the third lithium salt was adjusted in Examples 7-1 and 7-2.

[0244] Example 8:

[0245] 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 mass percentage of the additives were adjusted in Example 8.

[0246] Example 9-1 and Example 9-2:

[0247] Lithium-ion batteries were prepared using a method similar to that of Example 1. Unlike Example 1, the electrolyte retention coefficient of Examples 9-1 and 9-2 was adjusted.

[0248] Test results

[0249] The test results of Example 1 and Example 5-1 to Example 9-2 are shown in Table 2.

[0250] Table 2

[0251] The mass content of each component of the electrolyte in Table 2 is calculated based on the total mass of the electrolyte.

[0252] In Examples 5-1 to 6-4, by using the first lithium salt and the second lithium salt in combination, a SEI film rich in boron and / or fluorine elements can be formed on the surface of the negative electrode active material, and the SEI film interface can be effectively repaired, thereby reducing the impedance of the cycle process and improving the cycle performance; the second lithium salt 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 can take into account the improvement of the rapid charging performance and cycle performance of the battery cell. In Examples 7-1 and 7-2, by further adding the third lithium salt, the viscosity of the electrolyte system can be reduced, which is conducive to the rapid migration of lithium ions in the liquid phase and improves the rapid charging performance of the battery cell. Example 8 contains two additives, FEC and VC, which can reduce the static storage impedance. Examples 9-1 and 9-2 can further improve the performance of lithium-ion batteries by further regulating the liquid retention coefficient of the electrolyte.

[0253] 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 an electrode assembly and an electrolyte, wherein the electrode assembly comprises: A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and containing a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing material with an olivine structure; A negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector and containing a negative electrode active material, wherein the negative electrode active material comprises a carbon material; and A separator is provided between the positive electrode sheet and the negative electrode sheet. in, The thickness of the positive electrode film layer on one side of the positive electrode sheet is H1, and its unit is μm; The thickness of the negative electrode film layer on one side of the negative electrode sheet is H2, in μm; The thickness of the isolation film is H3, and its unit is μm; The battery cell satisfies the following requirements: 65 μm≤H1≤90 μm, 138 μm≤H1+H2+H3≤190 μm, and 7≤(H1+H2) / H3≤12.

2. The battery cell according to claim 1, wherein: 7.5≤(H1+H2) / H3≤11.

50.

3. The battery cell according to claim 1 or 2, wherein: The isolation membrane is a porous polymer membrane, and the porous polymer membrane satisfies: 13 μm<H3<20 μm.

4. The battery cell according to claim 3, wherein: The porous polymer film satisfies: 13.5 μm≤H3≤19.5 μm.

5. The battery cell according to claim 3 or 4, wherein: The porous polymer film includes at least one of a polypropylene film and a polyethylene film. The battery cell according to claim 5 , wherein: The porous polymer film is a polypropylene film; or the porous polymer film is a polyethylene film.

7. The battery cell according to any one of claims 1 to 6, wherein: The porosity of the isolation film is 35% to 45%.

8. The battery cell according to any one of claims 1 to 7, wherein: The compaction density of the positive electrode film layer on one side is 2.1g / cm 3 Up to 2.4g / cm 3 The compaction density of the negative electrode film layer on one side is 1.0 g / cm 3 to 1.3g / cm 3 and / or The surface density of the positive electrode film layer on one side is 0.26g / 1540.25mm 2 Up to 0.29g / 1540.25mm 2 The surface density of the negative electrode film layer on one side is 0.12g / 1540.25mm 2 Up to 0.14g / 1540.25mm 2 .

9. The battery cell according to claim 8, wherein: 0.9≤H1 / H2≤1.3; and 60μm≤H2≤80μm.

10. The battery cell according to any one of claims 1 to 9, wherein: The electrolyte has a liquid retention coefficient of 4.0 g / Ah to 5.0 g / Ah.

11. The battery cell according to any one of claims 1 to 10, wherein: The electrolyte includes a lithium salt, and the lithium salt includes: A first lithium salt comprises at least one of lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), wherein the mass percentage of the first lithium salt relative to the total mass of the electrolyte is ≤10%; and The second lithium salt includes at least one of lithium tetrafluoroborate LiBF4 and lithium difluorophosphate LiPO2F2, and the mass percentage of the second lithium salt relative to the total mass of the electrolyte is ≥1%.

12. The battery cell according to claim 11, wherein: The first lithium salt is lithium hexafluorophosphate LiPF6.

13. The battery cell according to claim 11 or 12, wherein: The mass percentage of the first lithium salt relative to the total mass of the electrolyte is 5% to 10%.

14. The battery cell according to any one of claims 11 to 13, wherein: The second lithium salt includes lithium tetrafluoroborate LiBF4 and lithium difluorophosphate LiPO2F2.

15. The battery cell according to claim 14, wherein: The mass percentage of the lithium tetrafluoroborate LiBF4 relative to the total mass of the electrolyte is 0.3% to 1.0%; the mass percentage of the lithium difluorophosphate LiPO2F2 relative to the total mass of the electrolyte is 0.3% to 3.5%.

16. The battery cell according to claim 15, wherein: The mass percentage of the lithium tetrafluoroborate LiBF4 relative to the total mass of the electrolyte is 0.5% to 0.8%; the mass percentage of the lithium difluorophosphate LiPO2F2 relative to the total mass of the electrolyte is 0.3% to 1.5%.

17. The battery cell according to any one of claims 11 to 16, wherein: The lithium salt further includes a third lithium salt, which includes at least one of a fluorine-containing lithium borate salt and a fluorine-containing lithium phosphate salt. The mass percentage of the third lithium salt relative to the total mass of the electrolyte is 0.1% to 2.5%.

18. The battery cell according to claim 17, wherein: The fluorine-containing lithium borate salt includes at least one of lithium difluorooxalatoborate LiDFOB and lithium bisoxalatoborate LiBOB; and / or The fluorine-containing lithium phosphate salt includes at least one of lithium difluorodioxalatophosphate LiDFOP and lithium tetrafluorooxalatophosphate LiTFOP.

19. The battery cell according to any one of claims 1 to 18, wherein: The electrolyte further includes an organic solvent; The mass percentage of the organic solvent relative to the total mass of the electrolyte is ≥45%; and / or The organic solvent includes at least one of ethylene carbonate (EC) and propylene carbonate (PC).

20. The battery cell according to any one of claims 1 to 19, wherein: The electrolyte further includes an additive, wherein the additive includes at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

21. The battery cell according to claim 20, wherein: Based on the total mass of the electrolyte, the mass percentage of the additive is 0.5% to 2.5%.

22. The battery cell according to any one of claims 1 to 21, wherein: The lithium-containing material with an olivine structure includes a lithium iron phosphate material with an olivine structure, and the carbon material includes graphite.

23. The battery cell according to any one of claims 1 to 22, wherein: The lithium-containing material of the olivine structure includes a general formula of Li x A y Me a M b P 1-c X c Q z A compound, wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes at least one of Na, K, and Mg; Me includes at least one of Mn, Fe, Co, and Ni; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, and N; and Q includes at least one of O and F.

24. A battery comprising the battery cell according to any one of claims 1 to 23.

25. An electrical device comprising the battery according to claim 24.

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