Battery cell, battery and electric device

Abstract

A battery cell, a battery and an electric device. The battery cell comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein a positive electrode film layer in the positive electrode sheet 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 arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprising a carbon-containing material of a layered structure; the thickness of an organic base film in the separator is greater than 13 μm, but less than 20 μm; and the electrolyte comprises a lithium salt, which comprises a first lithium salt and a second lithium salt, the mass content of fluorine atoms in molecules of the first lithium salt being greater than or equal to 38%, the reduction potential of the second lithium salt relative to Li / Li+ being greater than or equal to 1.2 V, the reduction potential of the second lithium salt relative to Li / Li+ being greater than the reduction potential of the first lithium salt relative to Li / Li+, the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt being (2-4):1, and the mass content of the first lithium salt being 6% to 8.5%. The DCR increase during cycling at a high temperature can be reduced, and the energy storage efficiency can be improved.

Description

Battery cells, batteries and electrical devices

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410268449.X, 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 DC impedance of a battery cell increases significantly during a cycle, especially under high temperature conditions.

[0006] Summary of the Invention

[0007] The present application provides a battery cell, a battery, and an electrical device, which can reduce the DCR growth under high-temperature cycles and improve energy storage efficiency.

[0008] In the first aspect, the embodiment of the present application proposes a battery cell, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein 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, wherein the positive electrode film layer includes a lithium-containing material with an olivine structure; 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, wherein the negative electrode film layer includes a carbon-containing material with a layered structure; the thickness of the separator is greater than 13 μm and less than 20 μm; the electrolyte includes a lithium salt, wherein the lithium salt includes a first lithium salt and a second lithium salt, wherein the mass content of fluorine atoms in the first lithium salt molecule is ≥38%; and the second lithium salt has a relative Li / Li ratio of 1:1 to 1:1. + The reduction potential of the second lithium salt is ≥1.2V relative to Li / Li + The reduction potential of the first lithium salt is greater than that of the first lithium salt relative to Li / Li + The reduction potential of the first lithium salt is 0.0447 W / m, wherein the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4):1, and the mass content of the first lithium salt is 6% to 8.5%.

[0009] Therefore, the mass content of fluorine atoms in the first lithium salt molecule in the embodiment of the present application is relatively high (greater than or equal to 38%), which helps to optimize the SEI film components on the surface of the negative electrode active material, forming a SEI film rich in lithium fluoride LiF on the surface of the negative electrode active material, so that the thermal stability and electrochemical stability of the SEI film are improved, and it can play a good protective role for the negative electrode active material. However, due to the high hardness of lithium fluoride, the flexibility of the film is poor, and the SEI film may be damaged during the cycle charge and discharge process of the battery cell. The second lithium salt has a higher reduction potential than the first lithium salt, and its relative to Li / Li + The reduction potential is ≥1.2V, which can be better than the first lithium salt in forming a film on the surface of the negative electrode active material, can effectively alleviate the problem that the SEI film is hard and easy to break due to the high fluorine content, effectively improve the stability of the SEI film, further enhance the protection of the negative electrode active material, reduce the side reaction between the negative electrode active material and the electrolyte, reduce the DCR growth of high temperature cycle, and improve the energy storage efficiency; the embodiment of the present application further regulates the mass content of the first lithium salt to be 6% to 8.5%, and the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4):1, which can effectively regulate the components of the SEI film, enhance the stability of the SEI film, and enhance the protection effect of the SEI film on the negative electrode active material, reduce the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, can reduce the DCR growth under high temperature cycle, and improve the energy storage efficiency.

[0010] In some embodiments, the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2.5 to 4): 1. When the above range is met, the stability of the SEI film can be further improved, and the protection effect of the SEI film on the negative electrode active material can be enhanced.

[0011] In some embodiments, the mass content of the first lithium salt relative to the total mass of the electrolyte is 6% to 8%. When the mass content of the first lithium salt falls within the above range, it can effectively reduce the generation of hydrofluoric acid, thereby improving cycle performance. Furthermore, when the mass content of the first lithium salt falls within the above range, it is beneficial for the first lithium salt to form a lithium fluoride-rich SEI film on the surface of the negative electrode active material, further improving the thermal and electrochemical stability of the SEI film, providing good protection for the negative electrode active material, and extending the cycle life of the negative electrode active material.

[0012] In some embodiments, the mass content of the second lithium salt relative to the total mass of the electrolyte is 0.5% to 3.00%, optionally 1% to 3%, or optionally 2% to 3%. When the mass content of the second lithium salt is within the above range, the second lithium salt and the first lithium salt are combined to improve the stability of the SEI film during cycling.

[0013] In some embodiments, the first lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (AsF6Li), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). The relatively high fluorine content in the first lithium salt can increase the content of lithium fluoride formed in the SEI film, further improving the thermal and electrochemical stability of the SEI film.

[0014] In some embodiments, the mass content of fluorine atoms in the molecular formula of the first lithium salt is ≥70%.

[0015] In some embodiments, the first lithium salt includes lithium hexafluorophosphate (LiPF 6 ).

[0016] In some embodiments, the second lithium salt has a relative ratio of Li / Li + The reduction potential of the second lithium salt is 1.2 V to 1.9 V. The reduction potential of the second lithium salt is higher, and it can preferentially form a film on the surface of the negative electrode active material.

[0017] In some embodiments, the second lithium salt includes at least one of lithium difluorooxalatoborate LiDFOB, lithium bis(oxalatodifluorophosphate) LiDFOP, lithium tetrafluorooxalatophosphate LiTFOP, and lithium bis(oxalatoborate) LiBOB.

[0018] In some embodiments, the second lithium salt includes at least one of lithium difluorooxalatoborate (LiDFOB) and lithium bisoxalatoborate (LiBOB).

[0019] In some embodiments, the electrolyte further includes a first additive including lithium difluorophosphate. Lithium difluorophosphate can promote rapid film formation of the first lithium salt, optimize film composition, and reduce film impedance.

[0020] In some embodiments, based on the total mass of the electrolyte, the ratio of the mass content of lithium difluorophosphate to the mass content of the first lithium salt is (0.05 to 0.5):1. When the mass content ratio of lithium difluorophosphate to the first lithium salt is within the above range, lithium difluorophosphate significantly promotes film formation of the first lithium salt and can cooperate with the second lithium salt to form a film layer with high stability and low impedance. Moreover, the viscosity of the electrolyte system is not too high, the formed film layer is not too thick, and the impedance is low.

[0021] In some embodiments, the total mass content of lithium difluorophosphate and the second lithium salt is ≤ 6% based on the total mass of the electrolyte. In the embodiments of the present application, when the total mass content of lithium difluorophosphate and the second lithium salt is within the above range, lithium difluorophosphate can effectively reduce the initial DCR of the battery system, and the second lithium salt can improve the increase in DCR of the battery system.

[0022] In some embodiments, based on the total mass of the electrolyte, the mass content of lithium difluorophosphate is 0.5% to 3.5%; optionally 1% to 2%; optionally 1.2% to 1.6%.

[0023] In some embodiments, the lithium-containing material includes an M element, where M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce. The lithium-containing material contains the M element in the aforementioned amount, and the M element can at least form a localized fast ion conductor phase within the lithium-containing material, thereby accelerating the transport of lithium ions within the material and improving the cycling performance under operating conditions.

[0024] In some embodiments, M includes at least one of Mg, Al, Ti, V, and Zn, and the mass content of the M element relative to the total mass of the lithium-containing material is 100 ppm to 2000 ppm.

[0025] In some embodiments, the lithium-containing material includes a core portion and a carbon coating layer, the core portion includes lithium-containing 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 Pa·s.

[0026] Therefore, in the embodiment of the present application, the lithium-containing material is coated and modified by the carbon coating layer, which can improve the conductivity of the lithium-containing material and improve the cycle performance under the working state; however, due to the dense coating of the carbon coating layer, the electrolyte may not penetrate the core of the lithium-containing material well, worsening the DCR growth under high-temperature cycling; 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-containing material and reduce the DCR growth under high-temperature cycling.

[0027] In some embodiments, the first solvent includes at least one of dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethyl acetate EA, ethylene glycol monopropyl ether EP, methyl acrylate MA, and propyl propionate PP.

[0028] In some embodiments, the organic solvent further includes a second solvent, and the organic solvent further includes at least one of ethylene carbonate EC and propylene carbonate PC.

[0029] 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-containing 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 cycle performance of the battery cell under operating conditions and the increase in DCR under high-temperature cycling can be achieved.

[0030] In some embodiments, the electrolyte includes an organic solvent comprising dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). The weight percentage of dimethyl carbonate (DMC) relative to the electrolyte is 39% to 45%; the weight percentage of ethyl methyl carbonate (EMC) relative to the electrolyte is 16% to 20%; the weight percentage of ethylene carbonate (EC) relative to the electrolyte is 16% to 21%; and the weight percentage of propylene carbonate (PC) relative to the electrolyte is 4% to 8%. This solvent system, combined with the aforementioned lithium salt system, can further reduce the increase in DCR during high-temperature cycling and improve energy storage efficiency.

[0031] In some embodiments, the lithium-containing material includes first particles and second particles, wherein the particle size of the first particles is greater than a predetermined particle size, and the particle size of the second particles is less than or equal to the predetermined particle size. Optionally, the first particles and the second particles each independently include at least one of a single particle and an agglomerated particle formed by agglomeration of multiple single particles. Optionally, the predetermined particle size is the average particle size of the lithium-containing material. Optionally, the predetermined particle size is any value between 0.7 μm and 1 μm; for example, the predetermined particle size is 1 μm. The lithium-containing material is obtained by mixing large and small particles, and the contact area between the particles is large, which can form a good electron and ion path between the particles, which is beneficial to improving the cycle performance of the battery cell under the working state.

[0032] In some embodiments, the volume distribution particle size D of the carbonaceous material is v 99 is 25μm to 50μm; optionally 30μm to 45μm. The carbon-containing material meeting the above range has a relatively large particle size, a small specific surface area, and a relatively small area in contact with the electrolyte, which can reduce side reactions and improve the cycle life under working conditions.

[0033] In some embodiments, the electrolyte further includes a second additive, the second additive including at least one of fluoroethylene carbonate FEC and vinylene carbonate VC; adding the second additive to the electrolyte and combining the second additive with large-particle artificial graphite are beneficial to both improving cycle life and increasing DCR during high-temperature cycling.

[0034] In some embodiments, the mass content of the second additive is 0.5% to 2.5% based on the total mass of the electrolyte.

[0035] In some embodiments, the compaction density of the positive electrode film layer on one side is 2.1 g / cm 3 Up to 2.4g / cm 3When the compaction density of the positive electrode film layer meets the above range, it can take into account the porosity and thickness of the positive electrode film layer while meeting the appropriate gram capacity of the positive electrode electrode, thereby taking into account the migration rate and migration path of lithium ions in the positive electrode film layer, and improving the fast charging performance of the battery cell.

[0036] In some embodiments, 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 the appropriate gram capacity of the negative electrode plate, thereby taking into account the migration rate and migration path of lithium ions in the negative electrode film layer, thereby improving the fast charging performance of the battery cell.

[0037] In some embodiments, 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 When the surface density of the positive electrode film layer meets the above range, it can take into account the porosity and thickness of the positive electrode film layer while meeting the appropriate gram capacity of the positive electrode electrode, thereby taking into account the migration rate and migration path of lithium ions in the positive electrode film layer, and improving the fast charging performance of the battery cell.

[0038] 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 the appropriate gram capacity of the negative electrode plate, 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.

[0039] In some embodiments, the thickness H1 of the positive electrode film layer on one side and the thickness H2 of the negative electrode film layer on one side satisfy the following conditions: 0.9 ≤ H1 / H2 ≤ 1.3, and 70 μm ≤ H1 ≤ 85 μm, or 70 μm ≤ H2 ≤ 90 μm. When the thickness of the above film layers meets the above ranges, the electrode sheet is thickly coated, and the negative and positive electrode film layers cooperate, allowing 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.

[0040] In some embodiments, the thickness of the organic base film in the isolation membrane is greater than or equal to 13.5 μm and less than or equal to 19.5 μm; optionally, the thickness of the organic base film in the isolation membrane is greater than or equal to 15 μm and less than or equal to 18 μm. When the thickness of the organic base film in the isolation membrane is within the above range, the isolation membrane is not too thick, the transmission path of lithium ions in the liquid phase is relatively short, and the transmission of lithium ions is relatively less hindered, resulting in smoother transmission, faster transmission rate, and better rapid charging performance of the battery cell. Furthermore, the isolation membrane is not too thin, which can improve the heat resistance and cycle stability of the isolation membrane.

[0041] In some embodiments, the isolation membrane is an organic-based membrane, which has low ion transport resistance and is conducive to improving the fast charging performance of the battery cell.

[0042] 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.

[0043] 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

[0044] 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.

[0045] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0046] FIG. 2 is an exploded schematic diagram of an embodiment of the battery cell of FIG. 1 .

[0047] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0048] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0049] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0050] FIG6 is a schematic diagram of an embodiment of an electric device including the battery cell of the present application as a power source.

[0051] The drawings are not necessarily drawn to scale.

[0052] The following are the descriptions of the reference numerals:

[0053] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0054] 5. Battery cell; 51. Housing; 52. Electrode assembly;

[0055] 53. Cover plate;

[0056] 6. Electrical equipment. DETAILED DESCRIPTION

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

[0058] " Range " disclosed in this application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" are listed herein, and "0 to 5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

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

[0060] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

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

[0062] Home energy storage products can store electricity locally for subsequent use; they primarily utilize rechargeable batteries (cells) for charge and discharge cycles. Compared to automotive batteries, users have higher usage requirements for home energy storage products, and therefore require higher energy storage efficiency from energy storage batteries. However, in high-temperature regions with abundant solar energy resources, such as Africa, applicants have discovered that the energy storage efficiency of cell batteries is low in high-temperature environments. This not only reduces battery storage efficiency but also fails to meet customer needs.

[0063] In view of the above problems, the embodiments of the present application propose a battery cell, which uses an olivine-structured lithium-containing material as the positive electrode active material and a layered carbon-containing material as the negative electrode active material, and uses an electrolyte with a specific composition. This can significantly reduce the cycle DCR growth of the battery at high temperature and improve the energy storage efficiency.

[0064] Next, the technical solutions of the implementation methods of this application are described in detail.

[0065] battery cells

[0066] A first aspect of the embodiments of the present application provides a battery cell.

[0067] The battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte 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. The positive electrode film layer includes a lithium-containing material with an olivine structure. 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. The negative electrode film layer includes a carbon-containing material with a layered structure. The electrolyte includes a lithium salt. The lithium salt includes a first lithium salt and a second lithium salt. The mass content of fluorine atoms in the first lithium salt molecule is ≥38%; the second lithium salt has a relative Li / Li ratio of 1:1. + The reduction potential of the second lithium salt is ≥1.2V relative to Li / Li + The reduction potential of the first lithium salt is greater than that of the first lithium salt relative to Li / Li + The reduction potential of the first lithium salt is 0.0447 W / m, wherein the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4):1, and the mass content of the first lithium salt is 6% to 8.5%.

[0068] The battery cell of the embodiment of the present application is preferably an energy storage battery cell, and the positive electrode active material is a lithium-containing material with an olivine structure. The lattice stability of the lithium-containing material with an olivine structure is good, and the insertion and extraction of lithium ions have little effect on the lattice of the lithium-containing material, so that the lithium-containing material has good reversibility, so the cycle stability of the positive electrode active material is good. However, compared with the positive electrode active material, the insertion and extraction of lithium ions have a more significant effect on the carbon-containing material with a layered structure, such as the sheet phase structure of artificial graphite. In particular, during the cycle of more than 10,000 times, the multiple shrinkage and / or expansion makes the SEI film on the graphite surface more likely to rupture, and the electrolyte and artificial graphite are in direct contact to produce side reactions. Especially under the conditions of high temperature cycling, the high temperature will aggravate the dissolution of the SEI film into the electrolyte, causing further damage to the SEI film structure, aggravating the generation of side reactions, aggravating the growth of the cycle DCR, and reducing the energy storage efficiency of the battery cell. The battery of the present application uses an electrolyte including a first lithium salt and a second lithium salt so that the relative contents of the first lithium salt and the second lithium salt meet a reasonable range, which can significantly improve the performance of the SEI film, provide good protection for the negative electrode active material, reduce the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, reduce the DCR growth during high-temperature cycling, and improve energy storage efficiency.

[0069] The mechanism of action is speculated to be as follows: the mass content of fluorine atoms in the first lithium salt molecule is relatively high (greater than or equal to 38%), which helps to optimize the SEI film components on the surface of the negative electrode active material, forming a SEI film rich in lithium fluoride LiF on the surface of the negative electrode active material, thereby improving the thermal stability and electrochemical stability of the SEI film, and providing good protection for the negative electrode active material. However, due to the high hardness of lithium fluoride, the flexibility of the film is poor, and the SEI film may be damaged during the cycle charge and discharge of the battery cell. The second lithium salt has a higher reduction potential than the first lithium salt, and its relative to Li / Li + The reduction potential is ≥1.2V, which is better than the first lithium salt in forming a film on the surface of the negative electrode active material. It can effectively alleviate the problem that the SEI film is hard and easy to break due to the high fluorine content, effectively improve the stability of the SEI film, further enhance the protection of the negative electrode active material, reduce the side reaction between the negative electrode active material and the electrolyte, reduce the DCR growth of high temperature cycle, and improve the energy storage efficiency.

[0070] Research has found that when the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is less than 2:1, the content of the first lithium salt participating in the film formation is low, which is not conducive to the formation of a SEI film with a high fluorine content, so that the thermal stability and electrochemical stability of the SEI film cannot be effectively improved. Therefore, even if the content of the second lithium salt is high at this time, the risk of SEI dissolution and damage at high temperatures cannot be avoided. When the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is greater than 4:1, the fluorine content of the SEI film formed by the electrolyte is too high, the SEI film hardness is too high, and the repeated contraction and / or expansion of the negative electrode active material makes the SEI film prone to cracking. In addition, the low content of the second lithium salt at this time cannot improve the problem of high SEI film hardness. The SEI film still has the risk of damage, which is not conducive to improving the stability of the SEI film.

[0071] Therefore, the embodiment of the present application regulates the mass content of the first lithium salt to be 6% to 8.5%, and the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4): 1, which can effectively regulate the components of the SEI film, improve the stability of the SEI film, and improve the protection effect of the SEI film on the negative electrode active material, reduce the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, and can reduce the DCR growth under high temperature cycling and improve energy storage efficiency.

[0072] The battery cell also includes an isolation membrane, in which the thickness of the organic base film is greater than 13μm and less than 20μm. The above-mentioned isolation membrane is combined with the first lithium salt and the second lithium salt in a specific range to effectively reduce the DCR growth under high-temperature cycling and improve energy storage efficiency.

[0073] Optionally, the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4): 1; optionally (2.5 to 4): 1. When the above range is met, the stability of the SEI film can be further improved, and the protective effect of the SEI film on the negative electrode active material can be enhanced.

[0074] Illustratively, the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4.0:1 or a range consisting of any two of the above values.

[0075] The embodiment of the present application can further improve the stability of the SEI film and enhance the protective effect of the SEI film on the negative electrode active material by further selecting the content of at least one of the first lithium salt and the second lithium salt.

[0076] In some embodiments, the mass content of the first lithium salt relative to the total mass of the electrolyte is 6% to 8.5%, optionally 6% to 8%. Due to the relatively high fluorine content in the first lithium salt molecule, hydrofluoric acid (HF) is easily formed during the cycle, and hydrofluoric acid may cause the dissolution of transition metal elements in the lithium-containing material with an olivine structure, which is not conducive to improving the cycle performance. However, in the embodiments of the present application, the mass content of the first lithium salt meets the above range, which can effectively reduce the generation of hydrofluoric acid and help improve the cycle performance. Moreover, when the mass content of the first lithium salt is within the above range, it is conducive to the formation of a lithium fluoride-rich SEI film on the surface of the negative electrode active material by the first lithium salt, which can further improve the thermal stability and electrochemical stability of the SEI film, and is conducive to providing good protection for the negative electrode active material, thereby improving the cycle life of the negative electrode active material.

[0077] Illustratively, the mass content of the first lithium salt relative to the total mass of the electrolyte can be 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, or a range consisting of any two of the above values.

[0078] In some embodiments, the mass content of the second lithium salt relative to the total mass of the electrolyte is 0.5% to 3.00%, optionally 1% to 3%, or optionally 2% to 3%. When the mass content of the second lithium salt is within the above range, the second lithium salt and the first lithium salt are combined to improve the stability of the SEI film during cycling.

[0079] Illustratively, the mass content of the second lithium salt relative to the total mass of the electrolyte is 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% or a range consisting of any two of the above values.

[0080] The mass content of fluorine atoms in the first lithium salt molecular formula is ≥38% and <100%, which is conducive to the formation of a lithium fluoride-rich SEI film on the surface of the negative electrode active material. The mass content of fluorine atoms in the first lithium salt molecular formula refers to the mass content of fluorine atoms calculated based on the total mass of the first lithium salt molecular formula.

[0081] For example, the first lithium salt may include at least one of lithium hexafluorophosphate LiPF 6 , lithium tetrafluoroborate LiBF 4 , lithium hexafluoroarsenate AsF 6 Li , and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

[0082] Optionally, the mass content of lithium hexafluorophosphate LiPF6 in the first lithium salt may be greater than the mass content of other lithium salts.

[0083] Optionally, the mass content of fluorine atoms in the molecular formula of the first lithium salt is ≥70%. This relatively high fluorine content in the first lithium salt can increase the content of lithium fluoride formed in the SEI film, further improving the thermal and electrochemical stability of the SEI film. For example, the first lithium salt can include at least one of lithium hexafluorophosphate (LiPF6) and lithium tetrafluoroborate (LiBF4); further optionally, the first lithium salt can include lithium hexafluorophosphate (LiPF6).

[0084] For example, the mass content of fluorine atoms in the first lithium salt molecular formula may be 38%, 38.5%, 39.7%, 40%, 40.5%, 41%, 41.5%, 42%, 42.5%, 43%, 43.5%, 44%, 44.5%, 45%, 45.5%, 46%, 46.5%, 47%, 47.5%, 48%, 48.5%, 49%, 49.5%, 50%, 50.5%, 51%, 51.5%, 52%, 52.5%, 53%. , 53.5%, 54%, 54.5%, 55%, 56%, 57%, 57.5%, 58%, 58.5%, 59%, 59.5%, 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% or a range consisting of any two of the above values.

[0085] The second lithium salt relative to Li / Li + The reduction potential of the second lithium salt is ≥1.2V, and optionally, the second lithium salt is + The reduction potential of the second lithium salt is 1.2V to 1.9V; optionally 1.2V to 1.8V; optionally 1.5V to 1.8V; the reduction potential of the second lithium salt is higher, and it can preferentially form a film on the surface of the negative electrode active material.

[0086] Optionally, the second lithium salt includes at least one of lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatodifluorophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP), and lithium bis(oxalatoborate) (LiBOB). Further, optionally, the second lithium salt includes at least one of lithium difluorooxalatoborate (LiDFOB) and lithium bis(oxalatoborate) (LiBOB). The boron-containing second lithium salt preferentially forms a boron-containing SEI film on the surface of the negative electrode active material. The boron and fluorine elements interact to form a boron-fluorine complex on the surface of the negative electrode active material, which facilitates the rapid formation of a film of the first lithium salt on the surface of the negative electrode active material. Furthermore, the formed film is denser and more stable, further enhancing the protective effect on the negative electrode active material and reducing side reactions between the negative electrode active material and the electrolyte, thereby reducing the DCR during high-temperature cycling.

[0087] In the embodiment of the present application, the reduction potential of the second lithium salt is a well-known meaning in the art and can be detected by using well-known equipment and methods in the art. For example, lithium difluorooxalatoborate LiDFOB is used to detect its reduction potential relative to Li / Li + The reduction potential of

[0088] Step (1) Preparation of electrolyte: Prepare the electrolyte in a nitrogen-filled glove box, controlling the moisture and oxygen levels below 5 ppm. Mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7, and then add LiPF6 to form a base electrolyte. Add LiDFOB to the base electrolyte to obtain an electrolyte for the experiment, wherein the mass content of LiPF6 is 12.5% ​​and the mass content of LiDFOB is 1%. If other lithium salts are to be tested, replace LiDFOB with other lithium salts.

[0089] Step (2) Preparation of button cells: In a glove box filled with nitrogen atmosphere, place the positive electrode sheet in the center of the positive electrode shell, add the electrolyte (Base electrolyte or experimental electrolyte) prepared in step (1), and the positive electrode sheet can be prepared using the positive electrode sheet in Example 1; stick the isolation film PP from one side of the positive electrode sheet to the other side, and make the isolation film completely soaked with the electrolyte, with basically no bubbles; put the lithium sheet and the negative electrode shell upside down on the positive electrode shell, press tightly, and then seal the battery with a sealing film to prepare a CR2025 button cell.

[0090] Step (3) Reduction potential test: Test using a charge-discharge meter in a constant temperature room at 25°C. Discharge from 3.0V to 0V at a sweep rate of 0.05C / s. Create a Dq / Dv curve for the data and compare it with the Base group to observe the presence and location of new peaks. The voltage corresponding to the highest peak in the new peak is the reduction potential.

[0091] In some embodiments, the electrolyte further includes a first additive, the first additive including lithium difluorophosphate; based on the total mass of the electrolyte, the ratio of the mass content of lithium difluorophosphate to the mass content of the first lithium salt is (0.05 to 0.5):1; optionally (0.1 to 0.25):1.

[0092] Lithium difluorophosphate can promote rapid film formation of the first lithium salt, optimize film composition, and reduce film impedance. In particular, when the mass ratio of lithium difluorophosphate to the first lithium salt is within the aforementioned range, lithium difluorophosphate significantly promotes film formation of the first lithium salt and can cooperate with the second lithium salt to form a film with high stability and low impedance. Furthermore, the viscosity of the electrolyte system is not too high, so the formed film is not too thick and has low impedance.

[0093] For example, the ratio of the mass content of lithium difluorophosphate to the mass content of the first lithium salt can be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or a range consisting of any two of the above values.

[0094] In some embodiments, based on the total mass of the electrolyte, the total mass content of lithium difluorophosphate and the second lithium salt is ≤6%; can be greater than 0 and less than or equal to 4.5%; can be 2.4% to 4.2%.

[0095] In the embodiment of the present application, when the total mass content of lithium difluorophosphate and the second lithium salt is within the above range, lithium difluorophosphate can effectively reduce the initial DCR in the battery system, and the second lithium salt can improve the growth of DCR in the battery system. Therefore, the coordinated effect of lithium difluorophosphate and the second lithium salt maintains the overall DCR of the battery at a low level, ensuring that the DCR of the battery throughout its life cycle will not be too high; and because the viscosity of the electrolyte system is not high, the SEI film layer formed will not be too thick, and the impedance is relatively small.

[0096] For example, the total mass content of lithium difluorophosphate and the second lithium salt can be 0.05%, 1%, 1.5%, 2%, 2.4%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 5%, 5.5%, 6%, or a range consisting of any two of the above values.

[0097] In some embodiments, based on the total mass of the electrolyte, the mass content of lithium difluorophosphate is 0.5% to 3.5%, and optionally 0.5% to 1.5%.

[0098] Illustratively, the mass content of lithium difluorophosphate may be 0.5% to 3.5%; optionally 1% to 2%; optionally 1.2% to 1.6%.

[0099] For example, the mass content of lithium difluorophosphate is 0.5%, 0.8%, 1.0%, 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%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5% or a range consisting of any two of the above values.

[0100] In some embodiments, the electrolyte further includes a second additive, comprising at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Optionally, the second additive comprises both fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Fluoroethylene carbonate (FEC) can significantly reduce high-temperature cycling DCR, but has little effect on improving cycle life. Vinylene carbonate (VC) can significantly improve cycle life, but may increase high-temperature cycling DCR. When both additives are added to the electrolyte, they can both improve the cycle life of the battery cell and reduce impedance.

[0101] Optionally, based on the total mass of the electrolyte, the mass content of the second additive is 0.5% to 2.5%. When the mass content of the second additive is within the above range, the cycle life of the battery cell can be effectively improved and the cycle impedance can be reduced.

[0102] Illustratively, the mass content of the second 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.

[0103] In some embodiments, the electrolyte further comprises an organic solvent, and the viscosity of the organic solvent does not exceed 0.8 Pa·s. The first solvent has a relatively low viscosity, which is beneficial for reducing the viscosity of the electrolyte.

[0104] Illustratively, the viscosity of the organic solvent is less than or equal to 0.8 Pa·s, for example, 0.1 Pa·s, 0.2 Pa·s, 0.3 Pa·s, 0.4 Pa·s, 0.5 Pa·s, 0.6 Pa·s, 0.7 Pa·s, 0.8 Pa·s, or a range consisting of any two of the above values.

[0105] In some embodiments, the mass content of the organic solvent is 30% to 60% based on the total mass of the electrolyte. When the mass content of the organic solvent is within the above range, the viscosity of the electrolyte system will not be too high.

[0106] Illustratively, 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%, or a range consisting of any two of the above values.

[0107] In some embodiments, the organic solvent may include at least one of dimethyl carbonate DMC, ethyl acetate EA, ethylene glycol monopropyl ether EP, methyl acrylate MA, and propyl propionate PP.

[0108] In some embodiments, the electrolyte includes an organic solvent comprising dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). The weight percentage of dimethyl carbonate (DMC) relative to the electrolyte is 39% to 45%; the weight percentage of ethyl methyl carbonate (EMC) relative to the electrolyte is 16% to 20%; the weight percentage of ethylene carbonate (EC) relative to the electrolyte is 16% to 21%; and the weight percentage of propylene carbonate (PC) relative to the electrolyte is 4% to 8%. This solvent system, combined with the aforementioned lithium salt system, can further reduce the increase in DCR during high-temperature cycling and improve energy storage efficiency.

[0109] 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.

[0110] In the embodiments of the present application, the types and contents of the inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, the inorganic components / lithium salt concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method with reference to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower limit cut-off voltage so that the battery's state of charge is approximately 0% SOC) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using an ion chromatography analysis method.

[0111] In the embodiments of the present application, the types and contents of the organic components in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" for qualitative and quantitative analysis of the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using an ion chromatography analysis method.

[0112] 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.

[0113] To identify and quantify individual species, the following settings were used with respect to flip angle and scanning time.

[0114] Fluorine spectrum test pulse sequence: 2gfhigqn.2;

[0115] Delay time: 1 second;

[0116] Number of scans: 16 times.

[0117] 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:

[0118] PF6 - Relative content = (I PF6 - ×M PF6 - / 6) / (I CF3ph ×M CF3ph / 3), where I is the corresponding NMR peak area, and M is the corresponding relative molecular mass. The content of lithium hexafluorophosphate in the electrolyte is then calculated based on the molar ratio of hexafluorophosphate to lithium ions.

[0119] 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:

[0120] PO2F2 - Relative content = (I PO2F2- ×M PO2F2- / 2) / (I CF3ph ×M CF3ph / 3), where I is the corresponding NMR peak area, and M is the corresponding relative molecular mass. The content of lithium difluorophosphate in the electrolyte is then calculated based on the molar ratio of difluorophosphate to lithium ions.

[0121] 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.

[0122] In some embodiments, the electrolyte has a retention coefficient of 4.0 g / Ah to 5.0 g / Ah.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] [Positive electrode]

[0127] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0128] 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 achieve a suitable 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.

[0129] 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 3When 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 the appropriate 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.

[0130] 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.

[0131] 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 the appropriate 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.

[0132] 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 2When 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 the appropriate 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.

[0133] 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.

[0134] The "average" here can be the average value after 5 parallel tests.

[0135] In some embodiments, the thickness H1 of the single-sided positive electrode film layer and the thickness H2 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. The above-mentioned electrode is a thick-coated electrode. Due to the 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.

[0136] In some embodiments, the thickness H1 of the single-sided positive electrode film layer satisfies: 70 μm≤H1≤85 μm, for example, 70 μm, 72 μm, 75 μm, 78 μm, 80 μm, 82 μm, 85 μm, or a range consisting of any two of the above values.

[0137] The positive electrode film layer includes a positive electrode active material, which can be a positive electrode active material for batteries known in the art. As an example, the positive electrode active material can include a lithium-containing material with an olivine structure.

[0138] In some embodiments, the olivine-structured lithium-containing material may include at least one of a lithium iron phosphate material, a lithium manganese phosphate material, and a lithium nickel phosphate material. Alternatively, the olivine-structured lithium-containing material may include a lithium iron phosphate material, which has better lattice stability and better cycle stability.

[0139] In some embodiments, the lithium-containing material with an olivine structure may include an M element; M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes at least one of S, Si, Cl, B, C, and N; the above materials are relatively stable and can effectively improve the cycle life of the battery system. The M element can be disposed on the surface of the lithium-containing material to act as a coating to improve the structural stability of the lithium-containing material; or it can be located in the crystal phase of the lithium-containing material to stabilize the lattice structure; it can also be located on the surface of the lithium-containing material and in the crystal phase of the lithium-containing material. When the lithium-containing material is tested, the M element can be detected, which means that the lithium-containing material is considered to include the M element. For example, the lithium-containing material with an olivine structure can be a lithium iron phosphate material, which includes the above-mentioned M element.

[0140] In some embodiments, M comprises at least one of Mg, Al, Ti, V, and Zn, and may be Al. The mass content of M relative to the total mass of the lithium-containing material is 100 ppm to 2000 ppm, and may be 300 ppm to 500 ppm. The lithium-containing material contains the aforementioned amount of M, which can at least form a localized fast ion conductor phase within the lithium-containing material, accelerating lithium ion transport within the material and improving cycling performance under operating conditions.

[0141] Exemplarily, the M element 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-containing material to play a coating role and improve the structural stability of the lithium-containing material; or be located in the crystal phase of the lithium-containing material to stabilize the lattice structure; or may be located on the surface of the lithium-containing material and in the crystal phase of the lithium-containing material at the same time.

[0142] 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.

[0143] In some embodiments, the lithium-containing material includes a core portion and a carbon coating layer, wherein the core portion includes lithium-containing particles, and the carbon coating layer is disposed on at least a portion of the outer surface of the core portion. In this embodiment, the electrolyte includes a first solvent having a viscosity not exceeding 0.8 Pa·s. Exemplarily, the lithium-containing particles may be lithium iron phosphate particles.

[0144] The olivine-structured lithium-containing material is modified by coating with a carbon coating layer, which can improve the conductivity of the olivine-structured lithium-containing material 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 olivine-structured lithium-containing material well, worsening the DCR growth under high-temperature cycling; and the embodiment of the present application is combined with a low-viscosity organic solvent system to improve the electrolyte wetting performance of the olivine-structured lithium-containing material and reduce the DCR growth under high-temperature cycling.

[0145] Illustratively, the first solvent includes at least one of dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethyl acetate EA, ethylene glycol monopropyl ether EP, methyl acrylate MA, and propyl propionate PP.

[0146] In some embodiments, the organic solvent further includes a second solvent, and the organic solvent further includes at least one of ethylene carbonate EC and propylene carbonate PC.

[0147] In some embodiments, the mass content of the carbon coating layer is 1.0% to 1.5% based on the total mass of the olivine-structured lithium-containing 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 increase in the DCR under high-temperature cycling can be achieved. When the organic solvent includes a first solvent and a second solvent, the mass content of the organic solvent is the total mass content of the first and second solvents. For example, the organic solvent includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0148] 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.

[0149] 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.

[0150] 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 1 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, and the lithium-containing material with an olivine structure is used as a sample. The SEM spectrum is observed using a scanning electron microscope SEM. 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 categories of large and small particles by adopting the concept of the 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.

[0151] Lithium iron phosphate materials include large-particle lithium iron phosphate and small-particle lithium iron phosphate. The particle size distribution of lithium iron phosphate materials is relatively wide. The mixture of large and small particles makes the contact area between particles larger, and better 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.

[0152] In some embodiments, based on the total number of first particles and second particles, the ratio of the first particles to the second particles is 0.5:1 to 2:1, such as 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.3:1, 1.5:1, 1.6:1, 1.8:1, 2:1, or a range consisting of any two of the foregoing values. When the ratio of the large and small particles is within the foregoing range, the contact area between the particles is large, and good electron and ion pathways can be formed between the particles, which is beneficial for improving the cycling performance of the battery cell under operating conditions.

[0153] 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.

[0154] 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.

[0155] In the embodiment of the present application, the content of the elements in the positive electrode active material has a meaning well known in the art and can be detected by equipment and methods well known in the art. For example, with reference to EPA6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry and measured by plasma atomic emission (ICP-OES, instrument model: Thermo ICAP7400). First, 0.4g of the positive electrode active material is weighed and 10ml (50% concentration) of aqua regia is added thereto. Then it is placed on a 180°C plate for 30min. After digestion on the plate, the volume is fixed to 100mL and the standard curve method is used for quantitative testing.

[0156] In some embodiments, the mass content of the olivine-structured lithium-containing 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 olivine-structured lithium-containing 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.

[0157] 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.

[0158] 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%.

[0159] 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, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0160] 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).

[0161] [Negative electrode]

[0162] The battery cell also includes a negative electrode plate.

[0163] 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 the thickness direction of the negative electrode current collector, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0164] In some embodiments, the compaction density of a single negative electrode film layer may be 1.0 g / cm 3to 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 the appropriate 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.

[0165] 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 the appropriate 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.

[0166] In some embodiments, the thickness H2 of the single-sided negative electrode film layer satisfies: 70 μm≤H2≤90 μm, for example, 70 μm, 72 μm, 75 μm, 78 μm, 80 μm, 85 μm, 90 μm, or a range consisting of any two of the above values.

[0167] In some embodiments, the negative electrode film layer comprises a layered carbonaceous material. Optionally, the carbonaceous material comprises at least one of artificial graphite and natural graphite, and artificial graphite can be selected, as artificial graphite has relatively high structural stability.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] In some embodiments, the volume distribution particle size D of the artificial graphite is v 99 is 25μm to 50μm, and can be optionally 30μm to 45μm. Artificial graphite that meets the above range has a relatively large particle size, a small specific surface area, and a relatively small area in contact with the electrolyte, which can reduce side reactions and improve the cycle life under working conditions.

[0172] For example, the volume distribution particle size D of the artificial graphite is v 99 is 25μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 50μm or a range consisting of any two of the above values.

[0173] In the embodiment of the present application, the volume distribution particle size D v 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) and then the negative electrode sheet is disassembled. After washing the electrolyte and drying, the negative electrode sheet is calcined to remove components such as the binder. The powder is scraped and sieved to obtain the negative electrode active material particles. The obtained negative electrode active material particles are tested for the volume distribution particle size D of the particles using a Mastersizer 2000E laser particle size analyzer according to the test standard GB / T19077-2016. 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.

[0174] In some embodiments, the volume distribution particle size D of the artificial graphite is v 99 is 30μm to 45μm; the electrolyte also includes a second additive, the second additive includes at least one of fluoroethylene carbonate FEC and vinylene carbonate VC; optionally, based on the total mass of the electrolyte, the mass content of the second additive is 0.5% to 2.5%.

[0175] Adding a second additive to the electrolyte and combining it with large-particle artificial graphite can help to improve both cycle life and DCR growth in high-temperature cycles.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] [Isolation film]

[0183] The battery cell includes a separator.

[0184] In some embodiments, the isolation membrane may include an organic base membrane and a coating disposed on at least one side of the organic base membrane. The organic base membrane may be understood as a porous polymer membrane. Optionally, the coating may include inorganic particles and / or organic particles, and the coating may be provided to improve the heat resistance of the isolation membrane. The inorganic particles include at least one of boehmite, aluminum oxide, barium sulfate, magnesium oxide, silicon oxide, titanium oxide, zinc oxide, cerium oxide, and barium titanate. Optionally, the organic particles include at least one of polystyrene particles and polyacrylic wax particles.

[0185] In other embodiments, the isolation membrane may be an organic-based membrane, which may be understood as a porous polymer membrane. In this case, the isolation membrane may not be provided with a coating.

[0186] In some embodiments, the thickness H3 of the organic base film in the isolation membrane satisfies the following conditions: 13 μm < H3 < 20 μm; optionally, 13.5 μm ≤ H3 ≤ 19.5 μm. Alternatively, 15 μm ≤ H3 ≤ 18 μm. When the thickness of the organic base film in the isolation membrane is within the above range, the isolation membrane 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, faster transmission rate, and improved fast charging performance of the battery cell. Furthermore, the isolation membrane is not too thin, which can improve the heat resistance and cycle stability of the isolation membrane.

[0187] For example, the thickness H3 of the organic base film in 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, 15 μm, 15.1 μm, 15.2 μm, 15.3 μm, 15.4 μm, 15.5 μm, 15.6 μm, 15.7 μm, 15.8 μm, 15.9 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm, m, 15.7μm, 15.8μm, 15.9μm, 16.0μm, 16.1μm, 16.2μm, 16.3μm, 16.4μm, 16.5μm, 16.6μm, 16.7μm, 16.8μm, 16.9μm, 17.0μm , 17.1μm, 17.2μm, 17.3μm, 17.4μm, 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] In the embodiments of the present application, porosity refers to the percentage of the pore volume of the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells".

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] Figure 3 is a schematic diagram of an exemplary battery module 4. 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 together using fasteners.

[0198] 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.

[0199] 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.

[0200] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. 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 comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0201] Electrical devices

[0202] 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.

[0203] The electrical device can select battery cells, battery modules or battery packs according to its usage requirements.

[0204] FIG6 is a schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0205] 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.

[0206] Example

[0207] 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.

[0208] Example 1

[0209] 1. Preparation of positive electrode sheet

[0210] The positive electrode sheet includes a positive electrode collector aluminum foil and a positive electrode film layer arranged on both sides of the positive electrode collector. 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 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.

[0211] The positive electrode active material includes a lithium iron phosphate material, which also includes aluminum (Al) at a content of 400 ppm. The lithium iron phosphate material also includes a carbon coating layer, which accounts for 1.2% by weight of the lithium iron phosphate material. The lithium iron phosphate material includes first particles and second particles. The first particles have an average particle size of 1.2 μm, and the second particles have an average particle size of 0.9 μm. The first particles have a ratio of 1:1 to the second particles.

[0212] The compaction density of the single-sided positive electrode film layer is 2.2g / cm 3 The surface density of the single-side positive electrode film layer is 0.27g / 1540.25mm 2 The thickness H1 of the single-sided positive electrode film layer is 70 μm.

[0213] 2. Preparation of negative electrode sheet

[0214] The negative electrode sheet includes a negative electrode current collector copper foil and a negative electrode film layer arranged on both sides of the negative electrode current collector. The negative electrode film layer includes a film layer formed by evenly coating the negative electrode slurry (the solvent is deionized water) on the surface of the negative electrode current collector copper foil, drying, and cold pressing. The negative electrode 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.

[0215] The negative electrode active material includes artificial graphite, and its volume distribution particle size D v99 is 35μm.

[0216] The compaction density of the single-sided negative electrode film is 1.1g / cm 3 The surface density of the single-side positive electrode film layer is 0.13g / 1540.25mm 2 The thickness H2 of the single-side negative electrode film layer is 70μm, and H1 / H2 is 1.

[0217] 3. Isolation film

[0218] The separator is a 16 μm porous polypropylene film with a porosity of 35%.

[0219] 4. Preparation of electrolyte

[0220] The electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent (86.66%) includes a first solvent and a second solvent, the first solvent includes dimethyl carbonate DMC (43.33%) and ethyl methyl carbonate EMC (18.20%), and the second solvent includes ethylene carbonate EC (18.20%) and propylene carbonate PC (6.93%).

[0221] The lithium salt includes a first lithium salt lithium hexafluorophosphate LiPF6 (8%) and a second lithium salt, and the second lithium salt includes lithium difluorooxalatoborate LiDFOB (1.2%) and lithium bisoxalatoborate LiBOB (1.2%).

[0222] The additives include a first additive, lithium difluorophosphate LiPO2F2 (1.44%), and a second additive, fluoroethylene carbonate FEC (1.5%).

[0223] 5. Preparation of batteries

[0224] 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.

[0225] Example 1-1

[0226] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the electrolyte did not include the first additive and the second additive.

[0227] Example 2-1 to Example 2-3

[0228] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that in Example 2-1 and Example 2-2, at least the mass content of the first lithium salt was adjusted.

[0229] Example 3-1 to Example 3-3

[0230] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that at least one of the type and mass content of the first lithium salt was adjusted in Examples 3-1 to 3-3.

[0231] Comparative Example 1

[0232] A lithium-ion battery was prepared by a method similar to that of Example 1. The difference from Example 1 was that the type of lithium salt was changed in Comparative Example 1. The lithium salt included lithium perchlorate (2.4%), and the reduction potential of lithium perchlorate was less than 1.2V.

[0233] Comparative Example 2 and Comparative Example 3

[0234] A lithium-ion battery was prepared using a method similar to that of Example 1. Unlike Example 1, in Comparative Examples 2 and 3, the mass ratio of the first lithium salt to the second lithium salt was adjusted.

[0235] Comparative Example 4

[0236] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that in Comparative Example 4, at least the mass content of the first lithium salt was adjusted.

[0237] Example 4-1 to Example 4-5

[0238] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that at least one of the type and content of the second lithium salt was adjusted in Examples 4-1 and 4-5.

[0239] Performance Testing

[0240] 1. Cycle performance test of lithium-ion batteries:

[0241] At 45° C., the lithium-ion batteries prepared in the examples and comparative examples were charged to 3.6 V at a 1C rate and discharged to 2.5 V at a 1C rate, and cycled until the lithium-ion batteries were cycled 600 times, and the capacity retention rate of the lithium-ion batteries was recorded.

[0242] 2. DCR growth rate test of static storage of lithium-ion batteries:

[0243] The initial DC internal resistance DCR0 of the lithium-ion batteries prepared in the examples and comparative examples was tested. After storage at 60° C. for 90 days, the DCR1 of the lithium-ion batteries was tested, and the growth rate of DCR was [(DCR1-DCR0) / DCR0]*100%.

[0244] The test conditions for DCR are as follows:

[0245] 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.

[0246] Test results

[0247] The test results of Examples 1 to 4-5 and Comparative Examples 1-4 are shown in Table 1.

[0248] Table 1

[0249] The mass content of each component of the electrolyte in Table 1 is calculated based on the total mass of the electrolyte. In Table 1, the reduction potential of the second lithium salt is as follows:

[0250] The reduction potential of lithium difluorooxalatoborate LiDFOB is 1.6 V;

[0251] The reduction potential of lithium bis(oxalatoborate) LiBOB is 1.5V;

[0252] The reduction potential of lithium difluorobis(oxaloyl)phosphate LiDFOP is 1.8V;

[0253] The reduction potential of lithium tetrafluorooxalophosphate LiTFOP is 1.7V.

[0254] In Table 1, when LiDFOB is used as the second lithium salt, LiBF4 may also be detected in the electrolyte. For example, when 1% to 1.2% LiDFOB is present in the electrolyte, a certain amount of LiBF4 is also present. This is because the production of LiDFOB may produce LiBF4 as a byproduct, resulting in trace amounts of LiBF4 in the product. However, the introduction of LiDFOB has little effect on the content of the first lithium salt.

[0255] As can be seen from Table 1,

[0256] In Comparative Example 1, the reduction potential of the perchlorate in the lithium salt is relatively small, and lithium hexafluorophosphate cannot be preferentially involved in film formation, which makes the risk of rupture of the formed SEI film higher. The amount of lithium salt added in Comparative Example 4 is relatively high, which makes the DCR increase too much and deteriorates the battery performance. Compared with Comparative Examples 2 and 3, the ratio of the mass content of the first lithium salt and the second lithium salt in the embodiment is (2 to 4):1, especially when it is (2.5 to 4):1, the first lithium salt and the second lithium salt can work together to play an excellent protective role on the negative electrode active material, reduce the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, and can reduce the DCR growth under high temperature cycles, thereby improving energy storage efficiency and cycle performance.

[0257] In the embodiment of the present application, a first lithium salt with a relatively high fluorine atomic mass content (for example, ≥38%) and a second lithium salt with a relatively high reduction potential are added to the electrolyte. The first lithium salt can form a SEI film rich in lithium fluoride LiF on the surface of the negative electrode active material. However, due to the high hardness and poor flexibility of lithium fluoride, the SEI film may be damaged during the cyclic charge and discharge process of the battery cell. The second lithium salt has a higher reduction potential than the first lithium salt, and its relative to Li / Li + The reduction potential is ≥1.2V, which can form a film on the surface of the negative electrode active material better than the first lithium salt. It can effectively alleviate the problem that the SEI film is hard and easy to break due to the high fluorine content, effectively improve the stability of the SEI film, and further enhance the protection of the negative electrode active material. It reduces the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, can reduce the DCR growth under high-temperature cycling, and improve energy storage efficiency and cycle performance.

[0258] The second lithium salt added in Example 1, Example 4-1 to Example 4-5 has a relatively high reduction potential and can form a film preferentially over the first lithium salt, which is beneficial to alleviating the problem of high hardness and easy breakage of the SEI film due to the high fluorine content, effectively improving the stability of the SEI film, further enhancing the good protection of the negative electrode active material, reducing the risk of impedance deterioration caused by side reactions between the negative electrode active material and the electrolyte, and can reduce the DCR growth under high-temperature cycling, thereby improving energy storage efficiency and cycle performance.

[0259] Example 5-1 and Example 5-2

[0260] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the mass content of the first additive was adjusted in Examples 5-1 and 5-2.

[0261] Example 6-1 to Example 6-4

[0262] A lithium-ion battery was prepared using a method similar to that of Example 1. Unlike Example 1, the mass content of Dv99 of the artificial graphite and the second additive was adjusted in Examples 6-1 to 6-4.

[0263] Example 7

[0264] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that in Example 7, at least the type of organic solvent was adjusted, wherein the organic solvent included dimethyl carbonate (61.53%) and ethyl methyl carbonate (EMC) (25.13%).

[0265] Test results

[0266] Examples 6-1 to 7 were tested using the same test method as in Table 1, and the test results are shown in Table 2.

[0267] Table 2

[0268] In Table 2, the total mass content A of the first lithium salt is 8%, the total mass content B of the second lithium salt is 2.4%, and A / B is 3.3.

[0269] As shown in Table 2, by regulating the mass content of lithium difluorophosphate in Examples 5-1 and 5-2, the rapid film formation of the first lithium salt can be effectively promoted, the film composition can be optimized, and the film impedance can be reduced. By regulating the mass content of the second additive in Examples 6-1 and 6-4, the cycle life of the battery cells can be effectively improved and the static storage impedance can be improved. The combination of the second additive and large-particle artificial graphite is beneficial for balancing the improvement of cycle life and the increase of DCR under static storage. In Example 7, by adding a low-viscosity organic solvent, the viscosity of the electrolyte is reduced, which facilitates the migration of lithium ions.

[0270] Example 8-1 to Example 8-7

[0271] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the content or type of the M element in the lithium iron phosphate material was adjusted in Examples 8-1 to 8-7.

[0272] Example 9-1 to Example 9-3

[0273] A lithium-ion battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the content of the carbon coating layer in the lithium iron phosphate material was adjusted in Examples 9-1 to 9-3, and the viscosity of the organic solvent was adjusted simultaneously.

[0274] Example 10-1 to Example 10-3

[0275] A lithium-ion battery was prepared using a method similar to that of Example 1. Unlike Example 1, Examples 10-1 to 10-3 adjusted the particle size of the particles in the lithium iron phosphate material; Examples 10-1 and 10-2 adjusted the particle size of the large and small particles; and the particle size distribution of the lithium iron phosphate material in Example 10-3 was narrower, for example, smaller than the particle size distribution in Example 10-1, with an average particle size of 1.2 μm.

[0276] Test results

[0277] Examples 8-1 to 10-3 were tested using the same test method as in Table 1, and the test results are shown in Table 3.

[0278] Table 3

[0279] As shown in Table 3, Examples 8-1 to 8-4 regulate the aluminum content in the lithium iron phosphate material. The Al element can form a localized fast ion conductor phase within the lithium iron phosphate material, accelerating the transport of lithium ions within the material and improving the cycling performance under operating conditions. Examples 1, 8-5, and 8-7 regulate the type of M element in the lithium iron phosphate material, which can regulate the DCR growth rate and cycling performance of the lithium-ion battery. When the M element is Al, the improvement effect is particularly excellent.

[0280] In Examples 9-1 to 9-3, the lithium iron phosphate materials are modified by coating with a carbon coating layer, which can enhance the conductivity of the lithium iron phosphate materials and improve the cycle performance under working conditions; and the above-mentioned materials are combined with the above-mentioned low-viscosity organic solvent system to improve the wetting performance of the electrolyte on the lithium iron phosphate materials and reduce the DCR growth under high-temperature cycling.

[0281] Compared with Example 10-3, Example 1, Example 10-1 and Example 10-2 are obtained by mixing large particles and small particles. The contact area between the particles is larger, and better electron and ion paths can be formed between the particles, which is beneficial to improving the cycle performance of the battery cell under working conditions.

[0282] Example 11-1 to Example 11-3

[0283] A lithium-ion battery was prepared using a method similar to that of Example 1. Unlike Example 1, Examples 11-1 to 11-3 adjusted the coating parameters of the positive electrode film layer and / or the negative electrode film layer (such as compaction density, surface density, thickness, etc.).

[0284] Test results

[0285] Examples 11-1 to 11-3 were tested using the same test method as in Table 1, and the test results are shown in Table 4.

[0286] Table 4

[0287] As can be seen from Table 4, Example 1 and Example 11-1 to Example 11-3 can further improve the DCR growth rate and cycle performance of the lithium-ion battery by regulating the coating parameters of the positive electrode film layer and / or the negative electrode film layer (such as compaction density, surface density, thickness and other parameters).

[0288] Example 12-1 to Example 12-4

[0289] A lithium ion battery was prepared using a method similar to that of Example 1, except that:

[0290] The isolation membrane of Example 12-1 includes a porous polymer film (organic base film) and a ceramic coating arranged on both sides of the organic film layer. The ceramic coating includes aluminum oxide ceramics. The thickness of the organic film layer is 13.5 μm, and the thickness of the single-side ceramic coating is 2 μm.

[0291] The isolation membranes of Examples 12-2 to 12-4 are porous polymer membranes without a coating layer; however, the thickness and / or porosity of the isolation membranes are adjusted.

[0292] Test results

[0293] Examples 12-1 to 12-4 were tested using the same test method as in Table 1, and the test results are shown in Table 5.

[0294] Table 5

[0295] As shown in Table 5, Example 1 and Example 12-1 to Example 12-4 can further improve the DCR growth rate and cycle performance of the lithium-ion battery by regulating the parameters of the isolation membrane.

[0296] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A battery cell, comprising: A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer 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 disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises a carbonaceous material with a layered structure; An isolation film, wherein the thickness of the organic base film in the isolation film is greater than 13 μm and less than 20 μm; as well as An electrolyte comprising a lithium salt, wherein the lithium salt comprises: A first lithium salt, wherein the mass content of fluorine atoms in the first lithium salt molecule is ≥38%; and The second lithium salt, relative to Li / Li + The reduction potential of the second lithium salt is ≥1.2V, and the second lithium salt is + The reduction potential of the first lithium salt relative to Li / Li + The reduction potential of Wherein, based on the total mass of the electrolyte, the ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2 to 4):1, and the mass content of the first lithium salt is 6% to 8.5%.

2. The battery cell according to claim 1, wherein: The ratio of the mass content of the first lithium salt to the mass content of the second lithium salt is (2.5 to 4):

1.

3. The battery cell according to claim 1 or 2, wherein: The mass content of the first lithium salt relative to the total mass of the electrolyte is 6% to 8%; or The mass content of the second lithium salt relative to the total mass of the electrolyte is 0.5% to 3%.

4. The battery cell according to any one of claims 1 to 3, wherein: The first lithium salt includes at least one of lithium hexafluorophosphate LiPF6, lithium tetrafluoroborate LiBF4, lithium hexafluoroarsenate AsF6Li, and lithium bis(trifluoromethanesulfonyl)imide LiTFSI.

5. The battery cell according to any one of claims 1 to 4, wherein: The mass content of fluorine atoms in the first lithium salt molecular formula is ≥70%.

6. The battery cell according to any one of claims 1 to 5, wherein: The first lithium salt includes lithium hexafluorophosphate LiPF6.

7. The battery cell according to any one of claims 1 to 6, wherein: The second lithium salt has a relative ratio of Li / Li + The reduction potential is 1.2V to 1.9V.

8. The battery cell according to any one of claims 1 to 7, wherein: The second lithium salt includes at least one of lithium difluorooxalatoborate LiDFOB, lithium bis(oxalatodifluorophosphate) LiDFOP, lithium tetrafluorooxalatophosphate LiTFOP, and lithium bis(oxalatoborate) LiBOB.

9. The battery cell according to any one of claims 1 to 8, wherein: The second lithium salt includes at least one of lithium difluorooxalatoborate LiDFOB and lithium bisoxalatoborate LiBOB.

10. The battery cell according to any one of claims 1 to 9, wherein: The electrolyte further includes a first additive, wherein the first additive includes lithium difluorophosphate; Based on the total mass of the electrolyte, the ratio of the mass content of the lithium difluorophosphate to the mass content of the first lithium salt is (0.05 to 0.5):

1.

11. The battery cell according to claim 10, wherein: Based on the total mass of the electrolyte, the total mass content of the lithium difluorophosphate and the second lithium salt is ≤6%.

12. The battery cell according to claim 10 or 11, wherein: Based on the total mass of the electrolyte, the mass content of the lithium difluorophosphate is 0.5% to 3.5%.

13. The battery cell according to any one of claims 1 to 12, wherein: The lithium-containing material includes M elements, and M includes at least one of B, Mg, Al, Ti, V, Si, P, S, Ca, Sc, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce.

14. The battery cell according to claim 13, wherein: M includes at least one of Mg, Al, Ti, V and Zn, and the mass content of the M element relative to the total mass of the lithium-containing material is 100 ppm to 2000 ppm.

15. The battery cell according to any one of claims 1 to 14, wherein: The lithium-containing material comprises a core portion and a carbon coating layer, wherein the core portion comprises lithium-containing 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, wherein the organic solvent includes a first solvent, and the viscosity of the first solvent does not exceed 0.8 Pa·s.

16. The battery cell according to claim 15, wherein: The first solvent includes at least one of dimethyl carbonate DMC, ethyl methyl carbonate EMC, ethyl acetate EA, ethylene glycol monopropyl ether EP, methyl acrylate MA and propyl propionate PP.

17. The battery cell according to claim 15 or 16, wherein: The organic solvent further includes a second solvent, and the organic solvent further includes at least one of ethylene carbonate EC and propylene carbonate PC.

18. The battery cell according to any one of claims 15 to 17, wherein: Based on the total mass of the lithium-containing material, the mass content of the carbon coating layer is 1.0% to 1.5%; Based on the total mass of the electrolyte, the mass content of the organic solvent is ≥45%.

19. The battery cell according to any one of claims 1 to 18, wherein: The electrolyte includes an organic solvent, and the organic solvent includes: Dimethyl carbonate DMC, whose mass content relative to the electrolyte is 39% to 45%; Ethyl methyl carbonate (EMC), whose mass content relative to the electrolyte is 16% to 20%; Ethylene carbonate EC, whose mass content relative to the electrolyte is 16% to 21%; and Propylene carbonate PC, with a mass content of 4% to 8% relative to the mass of the electrolyte.

20. The battery cell according to any one of claims 1 to 19, wherein: The lithium-containing material includes first particles and second particles, the particle size of the first particles is larger than a preset particle size, and the particle size of the second particles is smaller than or equal to the preset particle size; The first particles and the second particles each independently include at least one of a single particle and / or an agglomerated particle formed by agglomeration of a plurality of single particles.

21. The battery cell according to claim 20, wherein: The preset particle size is any value between 0.7 μm and 1 μm.

22. The battery cell according to any one of claims 1 to 21, wherein: The volume distribution particle size D of the carbonaceous material v 99 is 30μm to 45μm.

23. The battery cell according to claim 22, wherein: The electrolyte further includes a second additive, wherein the second additive includes at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

24. The battery cell according to claim 23, wherein: Based on the total mass of the electrolyte, the mass content of the second additive is 0.5% to 2.5%.

25. The battery cell according to any one of claims 1 to 24, wherein: The compaction density of the positive electrode film layer on one side is 2.1g / cm 3 Up to 2.4g / cm 3 and / or The compaction density of the negative electrode film layer on one side can be 1.0 g / cm 3 to 1.3g / cm 3 .

26. The battery cell according to any one of claims 1 to 25, wherein: 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 and / or 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 .

27. The battery cell according to any one of claims 1 to 26, wherein: The thickness H1 of the positive electrode film layer on one side and the thickness H2 of the negative electrode film layer on one side satisfy: 0.9≤H1 / H2≤1.3, And 70μm≤H1≤85μm, or 70μm≤H2≤90μm.

28. The battery cell according to any one of claims 1 to 27, wherein: The thickness of the organic base film in the isolation film is greater than or equal to 13.5 μm and less than or equal to 19.5 μm.

29. The battery cell according to any one of claims 1 to 28, wherein: The thickness of the organic base film in the isolation film is greater than or equal to 15 μm and less than or equal to 18 μm.

30. The battery cell according to any one of claims 1 to 29, wherein: The isolation film is an organic base film.

31. A battery comprising the battery cell according to any one of claims 1 to 30.

32. An electrical device comprising the battery according to claim 31.

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