Battery cell, battery device and electric device

Abstract

A battery cell, a battery device, and an electric device. The battery cell comprises a negative electrode sheet, a positive electrode sheet, and an electrolyte. 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, wherein the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a carbon-based material. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a positive electrode additive, and the positive electrode additive comprises at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. The electrolyte comprises an organic solvent, wherein the organic solvent comprises a carboxylic acid ester solvent, and the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%. The high-temperature cycle performance of the battery cell can be further improved.

Description

Battery cells, battery packs and electrical devices Technical Field

[0001] This application relates to a battery cell, a battery device, and an electrical device. Background Technology

[0002] Battery cells possess characteristics such as high capacity and long lifespan, making them widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric cars, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and power tools. Due to significant advancements in battery technology, higher performance requirements have been placed on batteries. However, the high-temperature cycling performance of battery cells needs further improvement. Summary of the Invention

[0003] This application provides a battery cell, a battery device, and an electrical device. The high-temperature cycle performance of the battery cell in this application can be further improved.

[0004] In a first aspect, embodiments of this application propose a battery cell, which includes a negative electrode, a positive electrode, and an electrolyte. The battery cell includes a negative current collector and a negative electrode film disposed on at least one side of the negative current collector. The negative electrode film includes a negative active material, which may be a carbon-based material. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive active material and a positive additive. The positive active material includes a lithium-containing phosphate, and the positive additive includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. The electrolyte includes an organic solvent, which may include a carboxylic acid ester solvent, wherein the mass content of the carboxylic acid ester solvent in the electrolyte is 3% to 70%.

[0005] Therefore, when the mass content of the carboxylic acid ester solvent in the electrolyte of this application embodiment meets the above-mentioned range, the migration rate of active ions such as lithium ions in the electrolyte is faster, which is beneficial to improving the fast charging capability of the battery cell. Adding a positive electrode additive to the positive electrode sheet allows the oxygen released by the positive electrode additive to participate in the negative electrode film formation, which can repair the solid electrolyte film and improve high-temperature cycle performance. Furthermore, the positive electrode active material of this application embodiment includes lithium phosphate, and the negative electrode active material includes carbon-based materials. The high cycle stability of both positive and negative electrode active materials is beneficial to further improving high-temperature cycle performance. Therefore, the embodiments of this application can effectively improve the high-temperature cycle performance of the battery cell.

[0006] In some embodiments, the lithium-containing iron oxide includes lithium ferrite; and / or the lithium-containing cobalt oxide includes lithium cobalt oxide. These materials can participate in film formation on the negative electrode side, improving the cycle performance of the battery cell.

[0007] In some embodiments, the lithium-containing iron oxide includes Li e FeO f , where 0 < e ≤ 5 and 0 < f ≤ 4. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0008] In some embodiments, the lithium-containing iron oxide includes at least one of Li5FeO4, Li3FeO 3.5 , and LiFeO2. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0009] In some embodiments, the lithium-containing cobalt oxide includes Li g CoO h , where 0 < g ≤ 6 and 0 < h ≤ 4. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0010] In some embodiments, the lithium-containing cobalt oxide includes one or more of Li6CoO4, Li3CoO2, and LiCoO2. The above materials can participate in film formation on the negative electrode side and improve the cycling performance of the battery cell.

[0011] In some embodiments, based on the mass of the positive electrode film layer, the mass content of the positive electrode additive is 0.5% to 3%. When using the positive electrode additive within the above mass range, it can effectively improve the stability of the positive electrode additive while also having a good oxygen release effect.

[0012] In some embodiments, a carbon coating layer is further provided on the surface of the positive electrode additive. After being coated with the carbon coating layer, the structure of the positive electrode additive is more stable, which can alleviate the side reaction between the electrolyte and the positive electrode additive, thereby further improving the cycling performance of the battery cell.

[0013] In some embodiments, the mass content of the carbon coating layer in the positive electrode additive is 1% to 5%. When the mass content of the carbon coating layer is within the above range, it can more effectively protect the positive electrode additive and is beneficial to the gradual release of oxygen.

[0014] In some embodiments, the positive electrode additive is granular. In the cross-section of the positive electrode film layer along its own thickness direction, the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle is 1.2 to 2.5. When using the positive electrode additive with the above particle size, it can effectively improve the stability of the positive electrode additive while also having a good oxygen release effect.

[0015] In some embodiments, there are multiple positive electrode additives in a cross section of the positive electrode film along its own thickness direction, and the average longest diameter of the multiple positive electrode additives is 9 μm to 13 μm. When using positive electrode additives with the above particle size, the stability of the positive electrode additives can be effectively improved, while also having a good oxygen release effect.

[0016] In some embodiments, multiple positive electrode additives are present in a cross-section along the thickness direction of the positive electrode film, and the average shortest diameter of the multiple positive electrode additives is 5 μm to 9 μm. Using positive electrode additives with the above-mentioned particle size can effectively improve the stability of the positive electrode additives while also providing a good oxygen release effect.

[0017] In some embodiments, both the lithium phosphate and the cathode additive are multiple and particulate. In a cross-section along the thickness direction of the cathode film, the average longest diameter of the multiple lithium phosphates is smaller than the average shortest diameter of the multiple cathode additives. Using cathode additives with the aforementioned particle size can effectively improve the stability of the cathode additive while also providing better oxygen release. The shorter migration path of lithium ions in the lithium phosphates reduces heat generation, decreases heat accumulation within the system, lowers the risk of electrolyte decomposition, and further improves cycle performance.

[0018] In some embodiments, the lithium-containing phosphate comprises a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than the longest diameter of the second phosphate particles. The average longest diameter of the plurality of first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the plurality of second phosphate particles is 0.1 μm to 0.5 μm. When the lithium-containing phosphate meets the above conditions, its longest diameter is relatively small, the lithium ion insertion / extraction path in the lithium-containing phosphate is shorter, and the heat generation is less. Moreover, the particle size of the lithium-containing phosphate is not too small, and agglomeration basically does not occur during the processing and preparation process, resulting in stable performance of the lithium-containing phosphate.

[0019] In some embodiments, the mass content of the second phosphate particles in the lithium phosphate is 80% to 95%. A mass content of the second phosphate particles within an appropriate range, such as 80% to 95%, can further reduce heat generation, decrease heat generation within the battery cell system, reduce the risk of electrolyte component decomposition due to heat accumulation, and improve the cycle performance of the battery cell.

[0020] In some implementations, the lithium-containing phosphate includes lithium iron phosphate, which has excellent cycle stability and can improve the cycle performance of individual battery cells.

[0021] In some embodiments, the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. The high migration rate of lithium ions in this electrolyte further reduces the internal resistance of the battery cells, thereby reducing heat generation and improving the fast-charging performance of the battery cells.

[0022] In some embodiments, the carboxylic acid ester solvent has a mass content of 5% to 30% in the electrolyte. When the mass content of the carboxylic acid ester solvent is within the above range, the conductivity of the electrolyte can be improved; and the electrolyte is compatible with the silicon-containing anode, which can effectively reduce the gas production of the battery cell and improve the fast charging capability of the battery cell.

[0023] In some embodiments, the carboxylic acid ester solvent includes cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0024] In some embodiments, the carboxylic acid ester solvent includes chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

[0025] In some embodiments, the organic solvent also includes carbonate solvents, including one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0026] Using a mixture of carbonate and carboxylic acid ester solvents can improve the stability of the electrolyte and reduce its high-temperature gas production.

[0027] In some embodiments, the electrolyte further includes a lithium salt, including lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.3 to 1.2 based on the mass of the electrolyte.

[0028] Therefore, when the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the embodiments of this application meets the above-mentioned range, on the one hand, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and the gas production at high temperature storage can be reduced; on the other hand, the organic component content of the interface film formed at the negative electrode interface is appropriate, which can also reduce the gas production at high temperature storage.

[0029] In some embodiments, the lithium bis(fluorosulfonyl)imide content is 2% to 11% by mass, based on the mass of the electrolyte. When the lithium bis(fluorosulfonyl)imide content is within the above range, the hydrofluoric acid content can be reduced, the negative electrode interface side reaction can be mitigated, the gas generation during high-temperature storage can be reduced, and the high-temperature cycle life of the battery cell can be improved.

[0030] In some embodiments, the lithium hexafluorophosphate content is between 3% and 14% by mass, depending on the mass of the electrolyte. When the lithium hexafluorophosphate content is within this range, the electrolyte conductivity is relatively high, which is beneficial for lithium-ion migration and improves the fast-charging performance of the battery cells.

[0031] In some embodiments, the electrolyte further includes one or more of fluorinated cyclic carbonates and vinylene carbonate. Fluorinated cyclic carbonates can form a lithium fluoride (LiF)-rich interfacial film on the negative electrode surface, which can alleviate the volume expansion of silicon and improve the lifespan of silicon-containing systems. The combined use of fluorinated cyclic carbonates and vinylene carbonate results in a more compact interfacial film on the negative electrode surface, which can more effectively protect the silicon-containing negative electrode, reduce the degree of side reactions at the negative electrode interface, and improve cycle performance.

[0032] In some embodiments, the fluorocyclic carbonate includes at least one of monofluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0033] In some embodiments, the mass content of the fluorocyclic carbonate is from 0.5% to 20% based on the mass of the electrolyte. When the mass content of the fluorocyclic carbonate is within the above range, an excellent interfacial film can be formed, providing excellent protection for the negative electrode.

[0034] In some embodiments, the mass content of vinylene carbonate is 0.1% to 3% based on the mass of the electrolyte. Vinylene carbonate participates in the formation of the negative electrode interface film, which can form an excellent interface film and provide excellent protection for the negative electrode.

[0035] In some embodiments, the mass content of fluorinated cyclic carbonates is 0.5% to 10% based on the mass of the electrolyte; the mass content of silicon in the silicon-based material in the negative electrode active material is 0.3% to 7.5%. When the mass content of fluorinated cyclic carbonates and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of silicon-containing systems can be improved, and the cycle performance can be improved.

[0036] In some embodiments, based on the mass of the electrolyte, the mass content of the fluorinated cyclic carbonate is greater than 10% and less than or equal to 20%; the mass content of silicon in the silicon-based material in the negative electrode active material is greater than 7.5% and less than or equal to 15%. When the mass content of the fluorinated cyclic carbonate and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of the silicon-containing system can be improved, and the cycle performance can be improved.

[0037] In some embodiments, the carbon-based material includes at least one of artificial graphite and natural graphite. The above structure exhibits excellent cycle stability, which can further improve the cycle performance of the battery cell.

[0038] Secondly, embodiments of this application also propose a battery device, including a battery cell of any embodiment of the first aspect of this application.

[0039] Thirdly, embodiments of this application also propose an electrical device, which includes a battery device as described in any of the embodiments of the second or third aspects of this application. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0041] Figure 1 is a schematic diagram of the structure of an electrical device provided in some embodiments of this application.

[0042] Figure 2 is a schematic diagram of the structure of a battery pack provided in some embodiments of this application;

[0043] Figure 3 is a schematic diagram of the structure of a battery module provided in some embodiments of this application;

[0044] Figure 4 is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0045] Figure 5 is a schematic diagram of the structure of the electrode assembly of a battery cell provided in some embodiments of this application;

[0046] Figure 6 is a schematic diagram of the structure of the negative electrode sheet of a battery cell provided in some embodiments of this application.

[0047] The accompanying drawings may not be drawn to scale.

[0048] The reference numerals in the attached drawings are explained as follows: X, thickness direction; 1, electrical device; 2, battery pack; 3, controller; 4, motor; 5, housing; 5a, first housing section; 5b, second housing section; 5c, accommodating space; 6, battery module; 7, battery cell; 10, electrode assembly; 11, positive electrode plate; 12, negative electrode plate; 121, negative electrode film; 122, negative electrode current collector; 1211, first negative electrode film; 1212, second negative electrode film; 121a, first region; 121b, second region; 121c, third region; 13, separator; 20, outer casing assembly; 21, housing; 22, end cap; 23, electrode terminal. Detailed Implementation

[0049] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0050] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all 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 stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] In this application, "multiple" means two or more (including two).

[0053] With the rapid development of the battery field, the performance requirements for battery cells are gradually increasing. For example, with the improvement of fast charging performance requirements, the conductivity of the electrolyte can be increased in related technologies. However, the increase in conductivity may lead to electrolyte decomposition at high temperatures, which will increase the amount of gas generated by the battery cell at high temperatures and may deteriorate the high-temperature cycle performance of the battery cell.

[0054] In view of the above problems, the embodiments of this application improve the high-temperature cycle performance of battery cells by synergistically regulating the positive electrode and the electrolyte. Specifically, the electrolyte of the battery cell includes carboxylic acid ester solvents. Carboxylic acid ester solvents can improve the conductivity of the electrolyte, enabling the rapid migration of active ions such as lithium ions, thereby improving the fast charging capability of the battery cell. However, excessive amounts of carboxylic acid ester solvents are prone to interfacial side reactions on the negative electrode surface, producing acidic substances and damaging the solid electrolyte interphase (SEI) film on the negative electrode surface, which may worsen the high-temperature cycle life. In the embodiments of this application, a positive electrode additive is added to the positive electrode. The oxygen element released by the positive electrode additive can participate in the formation of the negative electrode film, which can repair the SEI film and reduce the impact of carboxylic acid ester solvents on the cycle performance of the battery cell.

[0055] The battery cell described in this application is applicable to various battery devices and electrical appliances that use battery cells.

[0056] For example, the electrical device can be a mobile phone, portable device, laptop computer, electric vehicle, electric toy, power tool, vehicle, ship, and spacecraft, etc. Alternatively, for example, the electrical device can be a spacecraft, including airplanes, rockets, space shuttles, and spacecraft, etc.

[0057] Figure 1 is a schematic diagram of an example electrical device 1. This electrical device 1 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device 1, a battery pack or battery module can be used.

[0058] The electrical device 1 has a battery pack installed inside. The battery pack can be located at the bottom, head, or tail of the electrical device 1. The battery pack can be used to supply power to the electrical device 1. For example, the battery pack can be used as the operating power source for the electrical device 1, and it can also be used as the driving power source for the electrical device 1, replacing or partially replacing fuel oil or natural gas to provide driving power for the electrical device 1. The battery pack shown in Figure 1 is a battery pack 2.

[0059] Electrical device 1 may also include controller 3 and motor 4. Controller 3 is used to control the battery device to supply power to motor 4, for example, to meet the power needs of electrical device 1 during startup, navigation and driving.

[0060] A battery apparatus may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via busbars.

[0061] In some implementations, a battery cell assembly is typically formed by arranging multiple battery cells. As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form a single module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0062] As shown in Figure 2, in some embodiments, the battery device can be a battery pack 2, which includes a housing 5 and one or more battery cell assemblies housed in the housing 5.

[0063] As an example, the battery cell assembly can also be housed in the housing 5 by directly fixing multiple battery cells to the housing 5.

[0064] As an example, the housing 5 includes a first housing portion 5a and a second housing portion 5b. The housing 5 has an accommodating space 5c. The first housing portion 5a and the second housing portion 5b are fastened together to form a closed space inside the housing 5 to accommodate the battery cell assembly. Here, "closed" refers to covering or closing, which can be either sealed or unsealed. The first housing portion 5a can be a top cover or a bottom plate.

[0065] As an example, the housing 5 may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame, so that the interior of the housing 5 forms an enclosed space to accommodate the battery cell assembly.

[0066] In some implementations, the housing 5 can be part of the vehicle's chassis structure.

[0067] For example, a portion of the box body 5 may be at least a part of the vehicle floor, or a portion of the box body 5 may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0068] As an example, the battery cell assembly can be a battery module 6, which can be housed in the housing 5 by fixing the battery module 6 in the housing 5.

[0069] As shown in Figure 3, the battery module 6 includes multiple battery cells 7.

[0070] As shown in Figures 4 and 5, in some embodiments, the battery cell 7 includes an electrode assembly 10 and a housing assembly 20.

[0071] The housing assembly 20 has a receiving cavity for accommodating the electrode assembly 10 and the electrolyte.

[0072] In some embodiments, the housing assembly 20 includes a housing and electrode terminals 23 disposed on the housing.

[0073] The outer casing can be made of steel, aluminum, plastic (such as polypropylene), composite metal (such as copper-aluminum composite), or aluminum-plastic film, etc. In some embodiments, the outer casing can be a sealed structure or a non-sealed structure. As an example, when the outer casing is a non-sealed structure, it serves to protect the electrode assembly 10, and a sealing bag is included between the outer casing and the electrode assembly 10 to encapsulate the electrode assembly 10 and the electrolyte. Specifically, the sealing bag can be a bag-shaped insulating component or an aluminum-plastic film. When the outer casing is a sealed structure, it is used to encapsulate the electrode assembly 10 and electrolyte components.

[0074] As an example, the battery cell 7 can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0075] In some embodiments, the housing includes an end cap 22 and a housing 21, the housing 21 having an opening, and the end cap 22 covering the opening. The housing 21 may have one or more openings. The end cap 22 may also have one or more.

[0076] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 10. For example, if the electrode assembly 10 is a cylindrical structure, then a cylindrical housing 21 can be selected; if the electrode assembly 10 is a cuboid structure, then a cuboid housing 21 can be selected. Optionally, both the electrode assembly 10 and the housing 21 are cuboid structures.

[0077] Electrode terminal 23 can be disposed on housing 21 or on end cover 22. Electrode terminal 23 is electrically connected to the tab of electrode plate. Electrode terminal 23 can be directly connected to the tab or indirectly connected to the tab through current collector.

[0078] The electrode assembly 10 can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0079] In some embodiments, the electrode assembly 10 is a wound structure. The positive electrode 11 and the negative electrode 12 are wound into a wound structure.

[0080] In some embodiments, the electrode assembly 10 has a stacked structure.

[0081] As an example, multiple positive electrode plates 11 and multiple negative electrode plates 12 can be set, and multiple positive electrode plates 11 and multiple negative electrode plates 12 can be stacked alternately.

[0082] As an example, multiple positive electrode plates 11 can be provided, and multiple negative electrode plates 12 can be folded to form multiple stacked folded segments, with a positive electrode plate 11 sandwiched between adjacent folded segments.

[0083] As an example, both the positive electrode 11 and the negative electrode 12 are folded to form multiple stacked folded segments.

[0084] As an example, multiple separators 13 can be provided, respectively disposed between any adjacent positive electrode 11 or negative electrode 12.

[0085] As an example, the separator 13 can be continuously arranged between any adjacent positive electrode 11 or negative electrode 12 by folding or rolling.

[0086] In some embodiments, the electrode assembly 10 may be cylindrical, flat, or polygonal in shape.

[0087] In some embodiments, the electrode assembly 10 is provided with tabs that can conduct current from the electrode assembly 10. The tabs include a positive tab and a negative tab. The electrode assembly 10 can adopt a wound structure or a stacked structure, and the stacked structure is preferable to improve the energy density of the battery cell 7.

[0088] In some embodiments, the battery cell 7 includes a positive electrode 11 and an electrolyte. The positive electrode 11 includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a positive additive. The positive active material includes a lithium phosphate, and the positive additive includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. The electrolyte includes an organic solvent, which includes a carboxylic acid ester solvent. The carboxylic acid ester solvent has a mass content of 3% to 70% in the electrolyte.

[0089] The mass content of carboxylic acid ester solvent in the electrolyte is greater than or equal to 3%, which makes the migration rate of active ions such as lithium ions in the electrolyte faster, which is beneficial to improving the fast charging capability of battery cell 7.

[0090] As the mass content of carboxylic acid ester solvents increases, the migration rate of active ions increases. However, carboxylic acid ester solvents are prone to interfacial side reactions on the negative electrode surface, producing acidic substances, damaging the SEI film on the negative electrode surface, and reducing the high-temperature cycle life of the battery cell 7. In this embodiment, on the one hand, the upper limit of the addition of carboxylic acid ester solvents is limited, with the mass content of carboxylic acid ester solvents being less than or equal to 70%. On the other hand, a positive electrode additive is added to the positive electrode sheet. During charging, lithium ions from the positive electrode additive migrate to the negative electrode side through the electrolyte. Due to the migration of lithium ions, the positive electrode additive forms negatively charged groups. The negatively charged groups can release oxygen into the electrolyte. Oxygen can participate in the formation of the negative electrode film, which can repair the SEI film and improve the impact of carboxylic acid ester solvents on the high-temperature cycle life of the battery cell.

[0091] Furthermore, the positive electrode active material in the embodiments of this application includes lithium phosphate, and the negative electrode active material includes carbon-based material. The positive and negative electrode active materials have high cycle stability, which is beneficial to further improve high-temperature cycle performance.

[0092] Therefore, the embodiments of this application can effectively improve the high-temperature cycle performance of the battery cell 7 under fast charging.

[0093] Negative electrode sheet

[0094] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0095] The upper limit voltage for charging and the lower limit voltage for discharging a single battery cell vary depending on the positive electrode active material. For example, when the phosphate material includes lithium iron phosphate, the upper limit voltage for charging can be 3.65V and the lower limit voltage for discharging can be 2.0V, or the upper limit voltage for charging can be 3.8V and the lower limit voltage for discharging can be 2.0V. Another example is when the phosphate material includes lithium manganese iron phosphate, the upper limit voltage for charging can be 4.3V and the lower limit voltage for discharging can be 2.0V. Taking a charging upper limit voltage of 3.8V and a discharging lower limit voltage of 2.0V as an example, the state of a single battery cell will be described as follows: In this embodiment, the 100% state of charge (SOC) and the 0% state of charge (SOC) of a single battery cell are defined as follows...

[0096] The battery cell is charged at a constant current charging rate of 0.33C to the upper limit of the charging voltage, and then charged at a constant voltage to 0.05C, which corresponds to the 100% SOC state of the battery cell. The battery cell is then discharged at a constant current discharging rate of 0.33C to the cutoff voltage, which corresponds to the 0% SOC state of the battery cell.

[0097] In some embodiments, the compaction density of the negative electrode film layer at 0% state of charge (SOC) of the battery cell is 1.1 g / cm³. 3 Up to 1.7 g / cm 3 For example, the compaction density of the negative electrode film layer of a single battery cell at 0% charge is 1.10 g / cm³. 3 1.12 g / cm 3 1.14 g / cm 3 1.16 g / cm 3 1.18 g / cm 3 1.20g / cm 3 1.22g / cm 3 1.24 g / cm 3 1.26 g / cm 3 1.28g / cm 3 1.3g / cm 3 1.32g / cm 3 1.35g / cm 3 1.40g / cm 3 1.45g / cm 3 1.50g / cm 3 1.55g / cm 3 1.60g / cm 3 1.65g / cm 3 1.66 g / cm 3 1.68g / cm 3 1.70g / cm 3 Or a range consisting of any two of the above values.

[0098] When the compaction density of the negative electrode film is within the above range, the thickness of the negative electrode film will not be too thick, which is beneficial for the rapid charging of the battery cell; moreover, the particle packing of the negative electrode active material will not be too dense, reducing the risk of particle crushing and improving the cycle performance of the battery cell.

[0099] In some embodiments, the single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 Up to 150mg / 1540.25mm 2 For example, the single-sided coating weight of the negative electrode film is 80 mg / 1540.25 mm. 2 85mg / 1540.25mm 2 90mg / 1540.25mm 2 95mg / 1540.25mm 2 100mg / 1540.25mm 2 105mg / 1540.25mm2 110mg / 1540.25mm 2 115mg / 1540.25mm 2 120mg / 1540.25mm 2 120mg / 1540.25mm 2 122mg / 1540.25mm 2 125mg / 1540.25mm 2 128mg / 1540.25mm 2 130mg / 1540.25mm 2 132mg / 1540.25mm 2 135mg / 1540.25mm 2 137mg / 1540.25mm 2 140mg / 1540.25mm 2 145mg / 1540.25mm 2 150mg / 1540.25mm 2 155mg / 1540.25mm 2 160mg / 1540.25mm 2 165mg / 1540.25mm 2 170mg / 1540.25mm 2 175mg / 1540.25mm 2 180mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0100] When the single-sided coating weight of the negative electrode film meets the above range, its combination with an appropriate mass content of silicon element is beneficial to improving the energy density of the battery cell. The active ions migrate faster in the negative electrode film, which is beneficial to improving the fast charging capability of the battery cell.

[0101] In this embodiment, the compaction density of the negative electrode film layer at 0% State of Charge (SOC) of a battery cell is a well-known concept in the art. That is, the negative electrode sheet is disassembled from the battery cell at 0% SOC, and the compaction density of the negative electrode film layer is measured. For example, a single-sided coated negative electrode sheet (if double-sided coated, the negative electrode film layer on one side can be wiped off first) is taken, cut into small circular pieces with an area of ​​S1, weighed, and recorded as M1, and its thickness H1 is measured. Then, the negative electrode film layer of the weighed negative electrode sheet is wiped off, the weight of the negative current collector is weighed and recorded as M0, and its thickness H0 is measured. The single-sided coating weight of the negative electrode film layer = (weight of the negative electrode sheet M1 - weight of the negative current collector M0) / S1, the thickness of the negative electrode film layer = thickness of the negative electrode sheet H1 - thickness of the negative current collector H0, and the compaction density of the negative electrode film layer = single-sided coating weight of the negative electrode film layer / thickness of the negative electrode film layer.

[0102] In some embodiments, the negative electrode active material includes a silicon-based material. Optionally, the silicon-based material may include elemental silicon, silicon-carbon composites, or silicon oxide (SiO2). x At least one of (0 < x ≤ 2). The above materials can improve the capacity of the negative electrode active material, which is beneficial to reducing the coating thickness of the negative electrode film and shortening the migration path of lithium ions.

[0103] In some implementations, the specific surface area of ​​the silicon-based material is 1 m². 2 / g to 4m 2 / g, for example, 1m 2 / g, 1.2m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.8m 2 / g、2m 2 / g, 2.2m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.8m 2 / g、3m 2 / g, 3.2m 2 / g, 3.4m 2 / g, 3.5m 2 / g, 3.6m 2 / g, 3.8m 2 / g、4m 2 / g or a range consisting of any two of the above values.

[0104] When the specific surface area of ​​silicon-based materials is within the above range, it can alleviate the side reactions between silicon-based materials and electrolytes, improve cycle performance, and provide suitable insertion sites for lithium ions, thereby enhancing fast charging capability.

[0105] In the embodiments of this application, the specific surface area of ​​the material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, it can be detected according to the testing standard GB / T 19587-2017. The negative electrode sheet in the battery cell can be disassembled to obtain the relevant material as a sample, and the specific surface area can be tested using the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc.

[0106] In some embodiments, the silicon-based material is in particulate form with an average particle size of 4 μm to 12 μm, such as 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values.

[0107] When the specific surface area of ​​silicon-based materials is within the above range, it can provide suitable insertion sites for lithium ions, thereby improving fast charging capability. Under fast charging conditions, it can also alleviate side reactions between silicon-based materials and electrolytes, reduce high-temperature gas generation, and improve the cycle performance of battery cells.

[0108] In some embodiments, the negative electrode active material includes a carbon-based material, which has high cycle stability and can improve the cycle performance of the battery cell.

[0109] Optionally, the carbon-based material includes at least one of artificial graphite and natural graphite.

[0110] In some embodiments, the negative electrode active material may include, in addition to the aforementioned carbon-based materials and optionally silicon-based materials, at least one of tin-based materials and lithium titanate. Tin-based materials may include at least one of elemental tin, tin oxides, and tin alloys.

[0111] The qualitative and quantitative analysis of each substance or element in this application can be performed using suitable equipment and methods known to those skilled in the art. Relevant testing methods can be referenced from domestic and international testing standards and enterprise standards. Furthermore, those skilled in the art can adaptively modify certain testing steps / instrument parameters from the perspective of testing accuracy to obtain more accurate results. One testing method can be used for qualitative or quantitative analysis, or several testing methods can be used in combination for qualitative or quantitative determination.

[0112] For example, this application can combine JIS / K0131-1996 General Rules for X-ray Diffraction Analysis to perform X-ray powder diffraction tests and qualitative analysis on negative electrode sheets or negative electrode active materials.

[0113] Artificial graphite and natural graphite can be distinguished by SEM cross-sectional images taken by scanning electron microscope (SEM). Natural graphite has gaps between the sheet-like structures in its SEM cross-section, while artificial graphite has a dense structure with no obvious gaps. Alternatively, they can be distinguished by XRD patterns obtained by X-ray diffraction. Natural graphite has obvious 2H and 3R phases in its XRD pattern, while artificial graphite only has the 2H phase in its XRD pattern.

[0114] As shown in Figure 6, in this embodiment of the application, the negative electrode film layer 121 of the negative electrode sheet 12 includes at least one film layer, which can be a single film layer or at least two film layers. Optionally, the negative electrode film layer 121 includes at least two film layers.

[0115] When the negative electrode film layer 121 is a single layer, the negative electrode active material in the negative electrode film layer 121 includes carbon-based materials and optional silicon-based materials.

[0116] When the negative electrode film 121 employs at least two film layers, the negative electrode active material in the negative electrode film 121 includes carbon-based materials and optionally silicon-based materials. The negative electrode film 121 may include two, three, four, or even more film layers.

[0117] In some embodiments, the negative electrode film 121 includes a first negative electrode film 1211 and a second negative electrode film 1212. The first negative electrode film 1211 is disposed on the surface of the negative electrode current collector 122, and the negative electrode active material of the first negative electrode film 1211 includes a carbon-based material. The second negative electrode film 1212 is connected to the side of the first negative electrode film 1211 facing away from the negative electrode current collector 122, and the negative electrode active material of the second negative electrode film 1212 also includes a carbon-based material. The interface between the first negative electrode film 1211 and the second negative electrode film 1212 may be regular or irregular, optionally irregular; or there may be no obvious interface between the first negative electrode film 1211 and the second negative electrode film 1212.

[0118] The negative electrode film layer 121 includes at least two film layers. Layered coating is beneficial to improving both the fast charging performance and cycle life of the battery cell.

[0119] In some embodiments, at least one of the first negative electrode film 1211 and the second negative electrode film 1212 comprises a silicon-based material.

[0120] Optionally, the first negative electrode film layer 1211 may also include a silicon-based material.

[0121] Optionally, the second negative electrode film 1212 may also include a silicon-based material.

[0122] For example, the first negative electrode film 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film 1212 includes a carbon-based material and a silicon-based material. Alternatively, the first negative electrode film 1211 includes a carbon-based material and a silicon-based material, and the second negative electrode film 1212 includes a carbon-based material. Alternatively, the first negative electrode film 1211 includes a carbon-based material, and the second negative electrode film 1212 includes a carbon-based material and a silicon-based material.

[0123] When both the first negative electrode film layer 1211 and the second negative electrode film layer 1212 contain silicon-based materials, it is more beneficial to improve the energy density of the battery cell. When the first negative electrode film layer 1211 contains silicon-based materials but the second negative electrode film layer 1212 does not, the second negative electrode film layer 1212 can alleviate the volume expansion of the first negative electrode film layer 1211, reduce the side reactions between the negative electrode film layer 121 and the electrolyte, and improve cycle performance.

[0124] When the negative electrode film layer 121 uses at least two film layers, the cross-sectional shape of the negative electrode film layer 121 along the thickness direction X can be the same or similar, or of course different.

[0125] Along the thickness direction X of the negative electrode film layer 121, the negative electrode film layer 121 is divided into three regions, namely the first region 121a, the third region 121c, and the second region 121b. The first region 121a is the region of the negative electrode film layer 121 that is close to the negative electrode current collector 122 along the thickness direction X, and the thickness of the first region 121a is 1 / 3 of the thickness of the negative electrode film layer 121. The second region 121b is the region of the negative electrode film layer 121 that is away from the negative electrode current collector 122 along the thickness direction X, and the thickness of the second region 121b is 1 / 3 of the thickness of the negative electrode film layer 121.

[0126] The cross-sectional shapes of the first region 121a and the second region 121b can be the same or similar, or they can be different. The cross-sectional shapes of the first region 121a and the third region 121c can be the same or similar, or they can be different. The cross-sectional shapes of the second region 121b and the third region 121c can be the same or similar, or they can be different.

[0127] There may or may not be a clear layer interface between the first region 121a, the second region 121b, and the third region 121c. For example, the first negative electrode film layer 1211 includes the first region 121a, the second negative electrode film layer 1212 includes the second region 121b, and the third region 121c may be a part of the first negative electrode film layer 1211, or the third region 121c may be a part of the second negative electrode film layer 1212, or the third region 121c may be a part of both the first negative electrode film layer 1211 and the second negative electrode film layer 1212.

[0128] In some embodiments, in a cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the porosity of a single carbon-based material located in the first region 121a is greater than or equal to the porosity of a single carbon-based material located in the second region 121b. Optionally, the porosity of a single carbon-based material located in the first region 121a is less than the porosity of a single carbon-based material located in the second region 121b.

[0129] The carbon-based material is granular with internal voids. Along the cross-section of the negative electrode film layer 121 parallel to the thickness direction X, the percentage of void area to the total cross-sectional area of ​​the carbon-based material is the void ratio of a single carbon-based material.

[0130] During the charging process of a single battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The porosity of a single carbon-based material in the first region 121a is less than or equal to the porosity of a single carbon-based material in the second region 121b, which is more conducive to the diffusion of lithium ions in the first region 121a, improves the transmission rate, and thus facilitates the rapid charging of the battery cell.

[0131] Optionally, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b. More preferably, the average particle size of the carbon-based material in the first region 121a can be greater than the average particle size of the carbon-based material in the second region 121b, which facilitates the rapid migration of lithium ions from the second region 121b to the first region 121a, thereby improving the fast-charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be smaller than the average particle size of the carbon-based material in the second region 121b.

[0132] Optionally, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than or equal to the average particle size of the carbon-based material of the second negative electrode film layer 1212. More preferably, the average particle size of the carbon-based material of the first negative electrode film layer 1211 can be greater than the average particle size of the carbon-based material of the second negative electrode film layer 1212.

[0133] The difference in particle size between the first negative electrode film layer 1211 and the second negative electrode film layer 1212 can improve the fast charging performance of the battery cell. Specifically, during fast charging, the overpotential of the second negative electrode film layer 1212 is usually high, and the bottleneck of fast charging is mainly the second negative electrode film layer 1212. However, in the embodiment of this application, the particle size of the second negative electrode film layer 1212 is relatively small, which can shorten the solid phase transport path of lithium ions, improve the fast charging performance, and improve the problem of lithium deposition on the surface of the negative electrode sheet 12.

[0134] Optionally, the average particle size of the carbon-based material in the first region 121a is between 12 μm and 21 μm, for example, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm, or any combination of two of the above values. When the average particle size of the carbon-based material in the first region 121a is within the above range, it can improve cycle life and has virtually no adverse effect on fast charging performance.

[0135] Optionally, the average particle size of the carbon-based material in the first negative electrode film 1211 is between 12 μm and 21 μm. When the average particle size of the carbon-based material in the first negative electrode film 1211 is within the above range, it can improve cycle life and has virtually no adverse effect on fast charging performance.

[0136] Optionally, the average particle size of the carbon-based material in the second region 121b is from 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, or any combination of two of the above values. When the average particle size of the carbon-based material in the second negative electrode film layer 1212 is within the above range, it is beneficial to improve the fast charging capability of the battery cell and enhance the stability of the material.

[0137] Optionally, the average particle size of the carbon-based material in the second negative electrode film 1212 is between 9 μm and 17 μm. When the average particle size of the carbon-based material in the second negative electrode film 1212 is within the above range, the solid-phase transport path of lithium ions can be shortened, thereby improving fast charging performance and material stability.

[0138] For example, the carbon-based material of the first region 121a includes artificial graphite and natural graphite, and the carbon-based material of the second region 121b includes artificial graphite. For instance, the negative electrode active material of the first region 121a includes silicon-based material, artificial graphite and natural graphite, and the negative electrode active material of the second region 121b includes silicon-based material and artificial graphite.

[0139] For example, the carbon-based material of the first negative electrode film layer 1211 includes artificial graphite and natural graphite, and the carbon-based material of the second negative electrode film layer 1212 includes artificial graphite. For instance, the negative electrode active material of the first negative electrode film layer 1211 includes silicon-based material, artificial graphite and natural graphite, and the negative electrode active material of the second negative electrode film layer 1212 includes silicon-based material and artificial graphite.

[0140] In other embodiments, in a cross section of the negative electrode film layer 121 parallel to the thickness direction X, the void ratio of a single carbon-based material located in the first region 121a is smaller than the void ratio of a single carbon-based material located in the second region 121b.

[0141] During the charging process of a single battery cell, lithium ions diffuse from the second region 121b to the first region 121a. The second region 121b has a larger proportion of voids in the individual carbon-based material, which is conducive to the rapid transport of lithium ions from the second region 121b to the first region 121a, thus facilitating the rapid charging of the battery cell.

[0142] Optionally, the average particle size of the carbon-based material in the first region 121a can be smaller than the average particle size of the carbon-based material in the second region 121b. The relatively larger average particle size of the carbon-based material in the second region 121b results in higher pressure resistance during film preparation, which is beneficial for improving particle density. Conversely, the relatively smaller average particle size of the carbon-based material in the first region 121a enables rapid lithium-ion migration, thereby improving the fast-charging capability of the battery cell. Of course, the average particle size of the carbon-based material in the first region 121a can be greater than or equal to the average particle size of the carbon-based material in the second region 121b.

[0143] Optionally, the average particle size of the carbon-based material in the first region 121a is from 9 μm to 17 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm or any range of two of the above values.

[0144] Optionally, the carbon-based material of the first negative electrode film 1211 has an average particle size of 9 μm to 17 μm.

[0145] Optionally, the average particle size of the carbon-based material in the second region 121b is from 12 μm to 21 μm, for example, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm, 20 μm, 20.5 μm, 21 μm or any range of two of the above values.

[0146] Optionally, the carbon-based material of the second negative electrode film 1212 has an average particle size of 12 μm to 21 μm.

[0147] For example, the carbon-based material of the second region 121b includes artificial graphite and natural graphite, and the carbon-based material of the first region 121a includes artificial graphite. Optionally, the negative electrode active material also includes a silicon-based material. For example, the negative electrode active material of the second region 121b includes a silicon-based material, artificial graphite, and natural graphite, and the negative electrode active material of the first region 121a includes a silicon-based material and artificial graphite.

[0148] For example, the carbon-based material of the second negative electrode film 1212 includes artificial graphite and natural graphite, and the carbon-based material of the first negative electrode film 1211 includes artificial graphite. Optionally, the negative electrode active material further includes a silicon-based material. For example, the negative electrode active material of the second negative electrode film 1212 includes silicon-based materials, artificial graphite, and natural graphite, and the negative electrode active material of the first negative electrode film 1211 includes silicon-based materials and artificial graphite.

[0149] In the embodiments of this application, the average particle size of the active material in the first region 121a and the second region 121b can be detected by the following equipment and method: the negative electrode sheet 12 is used as a sample, and a scanning electron microscope (SEM) is used to take a cross-sectional image along the thickness direction X of the negative electrode film layer 121 to obtain an SEM cross-sectional image. The particle size of the active material in the SEM cross-section is counted, and the average particle size of the active material is calculated based on the counted number.

[0150] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an 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 weight of the negative electrode film layer.

[0151] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. In some embodiments, the mass content of the negative electrode binder is ≤5% based on the total weight of the negative electrode film layer.

[0152] In some embodiments, the negative electrode film layer may optionally include other additives. As examples, other additives may include thickeners, dispersants, etc., such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass content of other additives is ≤2% based on the total weight of the negative electrode film layer.

[0153] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil made of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material layer may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0154] The negative electrode film is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0155] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a negative electrode conductive layer 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 this application further includes a protective layer covering the surface of the negative electrode film layer.

[0156] Positive electrode sheet

[0157] In some implementations, the battery cell also includes a positive electrode.

[0158] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector and comprising a positive active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0159] In some embodiments, the dimension of the positive electrode film layer along the length of the positive electrode sheet is 200 mm to 600 mm, such as 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm, 550 mm, 600 mm or any combination of two of the above values.

[0160] When the electrode assembly has a stacked structure, the length direction of the positive electrode sheet is parallel to the length direction of the battery cell, and the dimension of the positive electrode film along the length direction can be understood as the length of the positive electrode film. The width direction of the positive electrode sheet is parallel to the width direction of the battery cell, and the dimension of the positive electrode film along the width direction can be understood as the width of the positive electrode film.

[0161] For example, the positive electrode film has a length dimension of 200 mm to 600 mm; the electrolyte includes an organic solvent, including carboxylic acid ester solvents, and the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. The length of the positive electrode film, combined with the electrolyte's conductivity, is beneficial for improving the liquid phase transport rate of lithium ions, enhancing kinetic performance, and increasing the fast-charging capability of the battery cell. Furthermore, because carboxylic acid ester solvents have low viscosity, they can uniformly wet all parts of the positive electrode film, resulting in a uniform charging degree throughout the positive electrode film. The lithium ions released from the positive electrode film are evenly distributed on the negative electrode side, reducing the risk of localized side reactions on the negative electrode side and improving high-temperature cycling performance under fast charging.

[0162] Optionally, when the positive electrode film has a length dimension of 200 mm to 600 mm, the electrolyte includes an organic solvent, including carboxylic acid ester solvents, with the carboxylic acid ester solvent having a mass content of 3% to 70%, optionally 5% to 30%. The aforementioned mass content of carboxylic acid ester solvent results in a relatively low viscosity of the electrolyte, which facilitates rapid wetting of the positive electrode film, ensuring uniform charge-discharge performance throughout the positive electrode film, reducing the risk of lithium deposition on the negative electrode side, and improving the cycle life of the battery cell.

[0163] In some embodiments, the compaction density of the positive electrode film layer at 0% state of charge (SOC) of the battery cell is 2.20 g / cm³. 3 Up to 2.85 g / cm 3 For example, at 0% state of charge (SOC), the compaction density of the positive electrode film layer in a single battery cell is 2.20 g / cm³. 3 2.25g / cm 3 2.30g / cm 3 2.32 g / cm 3 2.35g / cm 3 2.38g / cm 3 2.40 g / cm 3 2.42 g / cm 3 2.45g / cm 3 2.48 g / cm 3 2.50g / cm 3 2.52g / cm 3 2.55g / cm3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.60g / cm 3 2.62 g / cm 3 2.65g / cm 3 2.68g / cm 3 2.70 g / cm 3 2.75g / cm 3 2.80g / cm 3 2.85g / cm 3 Or a range consisting of any two of the above values.

[0164] When the compaction density of the positive electrode film is within the above range, it is beneficial to improve the energy density of the battery cell. Furthermore, since the positive active material of the positive electrode film is packed more densely, the contact resistance between particles is smaller, which can further reduce the resistance of the electrode, thereby reducing heat generation under fast charging, reducing high-temperature gas generation, and improving high-temperature cycle performance, especially the high-temperature cycle performance under fast charging system.

[0165] In some embodiments, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 Up to 300mg / 1540.25mm 2 For example, the single-sided coating weight of the positive electrode film is 250 mg / 1540.25 mm. 2 260mg / 1540.25mm 2 270mg / 1540.25mm 2 280mg / 1540.25mm 2 290mg / 1540.25mm 2 300mg / 1540.25mm 2 Or a range consisting of any two of the above values.

[0166] When the single-sided coating weight of the positive electrode film is within the above range, the heat generation per unit area of ​​the positive electrode sheet will not be too large, and it can simultaneously improve the energy density and charging rate performance of the battery cell, while preventing excessive heat accumulation within the battery cell system, reducing the risk of electrolyte decomposition at high temperatures, and improving the cycle performance of the battery cell.

[0167] In this embodiment, the compaction density of the positive electrode film layer at 0% State of Charge (SOC) of a single battery cell is a well-known concept in the art. This means disassembling the battery cell at 0% SOC to separate the positive electrode sheet and measuring the compaction density of the positive electrode film layer. For example, take a single-sided coated positive electrode sheet (if it is a double-sided coated sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, record its weight as M1, and measure its thickness H1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the positive current collector, record its weight as M0, and measure its thickness H0. The single-sided coating weight of the positive electrode film layer = (weight of the positive electrode sheet M1 - weight of the positive current collector M0) / S1, the thickness of the positive electrode film layer = thickness of the positive electrode sheet H1 - thickness of the positive current collector H0, and the compaction density of the positive electrode film layer = single-sided coating weight of the positive electrode film layer / thickness of the positive electrode film layer.

[0168] In some embodiments, the positive electrode active material includes one or more of lithium-containing transition metal oxides and lithium-containing phosphates. Optionally, the positive electrode active material includes lithium-containing phosphates. The lithium-containing phosphate can have an olivine structure, which is structurally stable during charge and discharge and can improve the cycle life of the battery cell.

[0169] Examples of lithium-containing transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0170] In some embodiments, the positive electrode film layer also includes a carbon-containing material, which is a carbon-containing conductive material. The aforementioned material can improve the conductivity of the positive electrode film layer, which is beneficial to improving the fast charging performance of the battery cell.

[0171] Optionally, the carbon content of the positive electrode film is from 0.8% to 3.5% by mass, for example, 0.8%, 0.9%, 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%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, or any range of two of the above values. Optionally, the carbon content of the positive electrode film is from 1.3% to 3.0% by mass.

[0172] For example, carbon-containing materials may include carbon nanotubes, which can act as conductive agents in the positive electrode film to improve the conductivity of the positive electrode film.

[0173] For example, the lithium phosphate with olivine structure can be an unmodified lithium phosphate such as lithium iron phosphate, or a material obtained by coating modification, such as a carbon-containing material on the surface of the lithium phosphate. The carbon-containing material can be used as a coating layer to coat the surface of the lithium phosphate, thereby improving the conductivity of the lithium phosphate, reducing the powder resistivity of the material, and facilitating the migration rate of lithium ions, improving the fast charging capability of the battery cell, and reducing the heat generation of the battery cell.

[0174] In some embodiments, lithium phosphates include those with the general formula Li x1 A y1 Me a M b P 1-c X c Y z The compound contains the following components: 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 1.3, and 0.9 ≤ x1 + y1 ≤ 1.3, 0.9 ≤ a ≤ 1.5, 0 ≤ b ≤ 0.5, and 0.9 ≤ a + b ≤ 1.5, 0 ≤ c ≤ 0.5, 3 ≤ z ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Cl, C, and N; and Y includes one or more of O and F. Lithium phosphates exhibit superior cycle stability, which is beneficial for improving the cycle performance of individual battery cells.

[0175] For example, lithium phosphates include one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. During the charging and discharging process, active ions such as Li are de-intercalated and consumed in a single battery cell, resulting in different molar contents of Li in different discharged states. In the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4, the molar contents of Li represent the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar contents of Li may change after charge-discharge cycles. In the embodiments of this application, the molar contents of oxygen (O) in the examples of positive electrode active materials such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4 are only theoretical values. Lattice oxygen release can cause changes in the molar contents of oxygen (O). In reality, the molar contents of oxygen (O) may fluctuate, and all of the above situations are within the scope of protection of this application.

[0176] In this application embodiment, the element content in the positive electrode active material has a meaning known in the art and can be detected using equipment and methods known in the art. For example, referring to EPA6010D-2014, it is tested by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model: Thermo ICAP7400). After discharging the battery cell to 0% state of charge (SOC), the positive electrode sheet is disassembled, cleaned with dimethyl carbonate (DMC), dried, and then calcined at high temperature to remove impurities. 0.4g of the positive electrode active material is weighed, and 10ml (50% concentration) of aqua regia is added. Then it is placed on a plate at 180°C for 30min. After digestion on the plate, the volume is adjusted to 100mL, and quantitative testing is performed using the standard curve method.

[0177] In some embodiments, the lithium phosphate is in the form of particles, which includes a plurality of first phosphate particles and a plurality of second phosphate particles. The longest diameter of the first phosphate particles is greater than or equal to a preset longest diameter, such as 1 μm, and the longest diameter of the second phosphate particles is less than 1 μm. It can be understood that particles with a longest diameter greater than or equal to 1 μm belong to the first phosphate particles, and particles with a longest diameter less than 1 μm belong to the second phosphate particles.

[0178] The longest diameter of the first phosphate particle is greater than that of the second phosphate particle. The average longest diameter of the first phosphate particle is 1 μm to 5 μm, and the average longest diameter of the second phosphate particle is 0.1 μm to 0.5 μm.

[0179] For example, the average longest diameter of the first phosphate particle is 1 μm to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or any range of two of the above values.

[0180] For example, the average longest diameter of the second phosphate particles is 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm or any combination of two of the above values.

[0181] When lithium phosphates meet the above conditions, their longest diameter is relatively small, the lithium ion insertion / extraction path in lithium phosphates is short, and the heat generation is low; moreover, the particle size of the above lithium phosphates is not too small, and they will not agglomerate during the processing and preparation process, which makes the performance of lithium phosphates stable; thus, it is beneficial to improve the high-temperature cycle performance of battery cells.

[0182] In some embodiments, the mass content of the second phosphate particles in the lithium phosphate is 80% to 95%, for example, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, or any combination of two of the above values. A mass content of the second phosphate particles within an appropriate range, such as 80% to 95%, can further reduce heat generation, decrease heat generation within the battery cell system, reduce the risk of electrolyte component decomposition due to heat accumulation, and improve the cycle performance of the battery cell.

[0183] In some embodiments, the positive electrode film layer includes a positive electrode additive, which includes at least one of a lithium-containing iron oxide and a lithium-containing cobalt oxide. During charging, lithium ions from the positive electrode additive migrate to the negative electrode side via the electrolyte. Due to the migration of lithium ions, the positive electrode additive forms negatively charged groups, which can release oxygen into the electrolyte. This oxygen can participate in the formation of the negative electrode film, repairing the SEI film, mitigating the impact of carboxylic acid ester solvents on the high-temperature cycle life of the battery cell, and improving the high-temperature cycle performance of the battery cell.

[0184] The positive electrode additive includes lithium, which can release lithium ions during the charging process of the battery cell to compensate for lithium loss and improve the capacity characteristics and cycle performance of the battery cell.

[0185] In some embodiments, lithium-containing iron oxides include lithium ferrite. Lithium ferrite can replenish lithium losses in the system and release oxygen to the negative electrode side to participate in the formation of the SEI film, thereby improving the cycle performance of the battery cell.

[0186] Optionally, lithium-containing iron oxides include Li e FeO f , 0 < e ≤ 5, 0 <f≤4。

[0187] For example, lithium-containing iron oxides include Li5FeO4 and Li3FeO. 3.5 At least one of LiFeO2.

[0188] In some embodiments, the lithium-containing cobalt oxide includes lithium cobalt oxide. Lithium cobalt oxide can replenish lithium losses in the system and release oxygen to the negative electrode side to participate in the formation of the SEI film, thereby improving the cycle performance of the battery cell.

[0189] Alternatively, lithium-containing cobalt oxides include Li g CoO h , 0 < g ≤ 6, 0 <h≤4。

[0190] For example, lithium-containing cobalt oxides include one or more of Li6CoO4, Li3CoO2, and LiCoO2.

[0191] In some embodiments, a carbon coating layer is further disposed on the surface of the positive electrode additive. This can be understood as the positive electrode additive having a core-shell structure, comprising a core and a carbon coating layer. The core includes at least one of lithium ferrite particles and lithium cobalt oxide particles, and the carbon coating layer is disposed on at least a portion of the surface of the core. The carbon coating layer in the positive electrode additive effectively protects the core. The structure of the positive electrode additive coated with the carbon coating layer is more stable, mitigating side reactions between the electrolyte and the positive electrode additive, thereby further improving the cycle performance of the battery cell. Furthermore, the carbon coating layer can slowly release oxygen from the core, allowing it to gradually release into the electrolyte and gradually participate in the construction and repair of the SEI film, which is more conducive to forming a high-performance SEI film and reducing SEI film impedance. For example, the core includes lithium ferrite particles, and the carbon coating layer is coated on the surface of the lithium ferrite particles.

[0192] Optionally, the carbon coating layer has a mass content of 1% to 5% in the cathode additive, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination thereof.

[0193] When the mass content of the carbon coating is within the above range, it can more effectively protect the core and facilitate the gradual release of oxygen.

[0194] In some embodiments, both the lithium phosphate and the cathode additive are granular, and each lithium phosphate and cathode additive consists of multiple particles. The average longest diameter of the multiple lithium phosphate particles is smaller than the average shortest diameter of the multiple cathode additives. When using cathode additives with the above-mentioned particle size, the stability of the cathode additive can be effectively improved, while also exhibiting a good oxygen release effect.

[0195] In some embodiments, the ratio of the longest diameter to the shortest diameter of the cathode additive in the same particle is 1.2 to 2.5, for example, 1.2, 1.4, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.5, or any combination thereof. When cathode additives with the above particle size are used, the stability of the cathode additive can be effectively improved while also exhibiting good oxygen release effect.

[0196] In some embodiments, the average longest diameter of the plurality of cathode additives is 9 μm to 13 μm, for example, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, or any combination thereof. When cathode additives with the above particle sizes are used, the stability of the cathode additives can be effectively improved while also exhibiting good oxygen release performance.

[0197] In some embodiments, the average shortest diameter of the plurality of cathode additives is 5 μm to 9 μm, for example, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or any combination thereof. When cathode additives with the above particle sizes are used, the stability of the cathode additives can be effectively improved while also exhibiting good oxygen release effect.

[0198] In this embodiment, the positive electrode sheet is cut along its thickness direction to expose the cross-section of the positive electrode film layer. This can also be understood as a cross-section of the positive electrode film layer along its own thickness direction. By performing scanning electron microscopy (SEM) testing on the cross-section of the positive electrode film layer, the longest and shortest diameters of the positive electrode additive particles, and the longest diameter of the lithium phosphate-containing particles, are determined. For example, the "longest diameter" of a particle refers to the longest straight line passing through the center point of the particle and extending to the outer periphery of the particle. The "shortest diameter" of a particle refers to the shortest straight line passing through the center point of the particle and extending to the outer periphery of the particle.

[0199] In a cross-section along the thickness direction of the positive electrode film, the longest diameter of multiple, for example, 10, positive electrode additives is counted, and their average value is calculated as the average longest diameter; the shortest diameter of multiple, for example, 10, positive electrode additives is counted, and their average value is calculated as the average shortest diameter.

[0200] In a cross-section along the thickness direction of the positive electrode film, the longest diameter of multiple, for example, 50 lithium phosphate particles is counted. Particles with a longest diameter greater than or equal to 1 μm are classified as first phosphate particles, and particles with a longest diameter less than 1 μm are classified as second phosphate particles. The average of the longest diameters of all first phosphate particles is calculated as the average longest diameter of the first phosphate particles, and the average of the longest diameters of all second phosphate particles is calculated as the average longest diameter of the second phosphate particles.

[0201] In some embodiments, the mass percentage of the positive electrode additive, based on the total mass of the positive electrode film, is 0.5% to 3%, for example, 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.5%, 3.0%, or any combination thereof. When using a positive electrode additive within the above mass range, the stability of the positive electrode additive can be effectively improved while also exhibiting good oxygen release performance.

[0202] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from 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 mass of the positive electrode film layer.

[0203] Optionally, the positive electrode conductive agent includes carbon nanotubes, and the mass content of carbon nanotubes in the positive electrode film layer is 0.1% to 2%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, or any combination thereof. Optionally, the mass content of carbon nanotubes in the positive electrode film layer is 0.15% to 1.2%.

[0204] When the mass content of carbon nanotubes is within the above range, it is beneficial to improve the conductivity of the positive electrode film and improve the fast charging performance of the battery cell.

[0205] Optionally, the specific surface area of ​​the carbon nanotubes is 500 m². 2 / g to 2500m 2 / g, for example 500m 2 / g、700m 2 / g、900m 2 / g、1100m 2 / g、1300m 2 / g, 1500m 2 / g、1700m 2 / g、1900m 2 / g、2100m 2 / g、2300m 2 / g、2500m 2 / g or a range consisting of any two of the above.

[0206] When the specific surface area of ​​carbon nanotubes is within the above range, it is beneficial to improve electron conduction ability; and when combined with an appropriate amount of carbon nanotubes, the degree of side reaction can be reduced and the cycle performance can be improved.

[0207] Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 20 nm, specifically 0.5 nm, 1.5 nm, 2.5 nm, 3.5 nm, 4.5 nm, 5.5 nm, 6.5 nm, 7.5 nm, 8.5 nm, 9.5 nm, 10.5 nm, 11.5 nm, 12.5 nm, 13.5 nm, 14.5 nm, 15.5 nm, 16.5 nm, 17.5 nm, 18.5 nm, 19.5 nm, 20 nm, or any combination of the above. Optionally, the diameter of the carbon nanotubes is from 0.5 nm to 7.5 nm.

[0208] When the diameter of carbon nanotubes is within the above range, the structure is relatively stable and has excellent electronic conductivity.

[0209] Carbon nanotubes can generally be considered as two-dimensional carbon materials rolled up. When the number of layers formed by the rolling is single, it is a single-walled carbon nanotube; when the rolling is multi-layered, it is a multi-walled carbon nanotube. The diameter of a carbon nanotube is the outer diameter of the carbon nanotube along a cross-section perpendicular to its own central axis.

[0210] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride, polytetrafluoroethylene, a terpolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a terpolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, polyacrylic acid, and fluorinated acrylate resins. In some embodiments, the mass content of the positive electrode binder is ≤5% based on the mass of the positive electrode film layer.

[0211] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include at least one foil selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material layer may include at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0212] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to it.

[0213] The positive electrode sheet does not exclude other additional functional layers besides the positive electrode film layer. For example, in some embodiments, the positive electrode sheet of this application further includes a positive conductive layer sandwiched between the positive current collector and the positive electrode film layer and disposed on the surface of the positive current collector. In other embodiments, the positive electrode sheet of this application further includes a protective layer covering the surface of the positive electrode film layer.

[0214] electrolyte

[0215] During the charging and discharging process of a single battery cell, active ions, such as lithium ions, repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor for these active ions between the positive and negative electrode plates. The electrolyte consists of organic solvents and electrolyte salts.

[0216] In some embodiments, the electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature. Exemplarily, the electrolyte conductivity at room temperature is 9 mS / cm, 9.5 mS / cm, 10 mS / cm, 10.5 mS / cm, 11 mS / cm, 11.5 mS / cm, 12 mS / cm, 12.5 mS / cm, 13 mS / cm, 13.5 mS / cm, 14 mS / cm, 14.5 mS / cm, 15 mS / cm, 15.5 mS / cm, 16 mS / cm, 16.5 mS / cm, 17 mS / cm, 17.5 mS / cm, 18 mS / cm, or any range of two of the above values.

[0217] When the conductivity of the electrolyte at room temperature, such as 25°C, is within the above range, the migration rate of lithium ions in the electrolyte is relatively high, which can further reduce the internal resistance of the battery cell, thereby reducing heat generation and reducing the amount of high-temperature gas generated due to heat accumulation, and improving the high-temperature cycle performance of the battery cell under fast charging.

[0218] In the embodiments of this application, the conductivity of the electrolyte at room temperature, such as 25°C, is the ionic conductivity, which can be detected using equipment and methods known in the art, such as by referring to industry standard HG-T 4067-2015.

[0219] In some embodiments, the organic solvent includes carboxylic acid ester solvents.

[0220] Optionally, the carboxylic acid ester solvent has a mass content of 3% to 70% in the electrolyte. Exemplarily, the mass content of the carboxylic acid ester solvent is 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, 53%, 55%, 58%, 60%, 63%, 65%, 68%, 70%, or a range of any two of the above values. Optionally, the carboxylic acid ester solvent has a mass content of 5% to 30% in the electrolyte.

[0221] When the mass content of carboxylic acid ester solvents is within the above range, the conductivity of the electrolyte can be improved; and the electrolyte and silicon-containing anode are compatible, which can effectively alleviate the side reactions on the anode side, reduce the gas production of the battery cell, and improve the fast charging capability of the battery cell.

[0222] For example, carboxylic acid ester solvents include cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. The above-mentioned materials have high electrical conductivity, which can improve the conductivity of the electrolyte.

[0223] For example, carboxylic acid ester solvents include chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate. The above materials have high conductivity, which can improve the conductivity of the electrolyte.

[0224] In some embodiments, the organic solvent includes carbonate solvents.

[0225] Using a mixture of carbonate and carboxylic acid ester solvents can improve the stability of the electrolyte, reduce its high-temperature gas production, and help improve the high-temperature cycle life of battery cells.

[0226] For example, carbonate solvents include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Optionally, carbonate solvents include one or more of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate.

[0227] In some embodiments, the electrolyte salt includes a lithium salt, which includes one or more of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate. Optionally, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0228] Lithium hexafluorophosphate may decompose to produce hydrofluoric acid (HF). The side reaction between hydrofluoric acid and the negative electrode, especially the silicon-containing negative electrode, may lead to increased gas production during high-temperature storage. The combined use of lithium hexafluorophosphate and lithium difluorosulfonylimide can reduce the hydrofluoric acid content, slow down the side reaction at the negative electrode interface, reduce the amount of gas produced during high-temperature storage, and help improve the high-temperature cycle life of the battery cells.

[0229] In some embodiments, the mass ratio of lithium difluorosulfonylimide to lithium hexafluorophosphate is 0.3 to 1.2, for example, 0.3, 0.5, 0.7, 0.9, 1.1, 1.2 or any combination of the two values ​​mentioned above, based on the mass of the electrolyte.

[0230] When the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide meets the above range, on the one hand, the content of hydrofluoric acid can be reduced, the side reaction at the negative electrode interface can be slowed down, and the amount of gas generated during high-temperature storage can be reduced; on the other hand, the organic component content of the SEI film formed at the negative electrode interface is appropriate, which can also reduce the amount of gas generated during high-temperature storage and is conducive to improving the high-temperature cycle life of the battery cell.

[0231] For example, based on the mass of the electrolyte, the mass content of lithium difluorosulfonylimide is 2% to 11%, such as 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, or any combination of two of the above values. When the mass content of lithium difluorosulfonylimide is within the above range, the hydrofluoric acid content can be reduced, the side reactions at the negative electrode interface can be mitigated, the gas generation during high-temperature storage can be reduced, and the high-temperature cycle life of the battery cell can be improved.

[0232] For example, based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate is 3% to 14%, such as 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, or any combination of two of the above values. When the mass content of lithium hexafluorophosphate is within the above range, the conductivity of the electrolyte is relatively high, which is beneficial to the migration of lithium ions and improves the fast charging performance of the battery cells.

[0233] In some embodiments, the electrolyte also contains additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0234] In some embodiments, the additive comprises cyclic carbonate additives, such as one or more of fluorocyclic carbonates and vinylene carbonates; alternatively, the additive comprises fluorocyclic carbonates and vinylene carbonates.

[0235] Fluorinated cyclic carbonates can form a lithium fluoride (LiF)-rich SEI film on the negative electrode surface, which can alleviate the volume expansion of silicon, improve the lifetime of silicon-containing systems, and improve cycle performance.

[0236] The combined use of fluorinated cyclic carbonates and vinylene carbonates results in a denser SEI film on the anode surface, which can more effectively protect the silicon-containing anode, reduce the degree of side reactions at the anode interface, and improve cycle performance.

[0237] Optionally, the fluorocyclic carbonate includes at least one of monofluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate.

[0238] Optionally, based on the mass of the electrolyte, the mass content of the fluorocyclic carbonate is from 0.5% to 20%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or any combination of two of the above values. A mass content of fluorocyclic carbonate within the above range is beneficial for improving cycle performance.

[0239] As an example, based on the mass of the electrolyte, the mass content of fluorinated cyclic carbonates is 0.5% to 10%; the mass content of silicon in the negative electrode active material of silicon-based materials is 0.3% to 7.5%.

[0240] When the mass content of silicon is relatively high, the volume expansion is relatively greater. When the mass content of fluorinated cyclic carbonates and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, which can improve the lifespan of silicon-containing systems and improve cycle performance.

[0241] As another example, based on the mass of the electrolyte, the mass content of fluorinated cyclic carbonates is greater than 10% and less than or equal to 20%, and the mass content of silicon in the negative electrode active material of silicon-based materials is greater than 7.5% and less than or equal to 15%.

[0242] When the mass content of fluorinated cyclic carbonates and the mass content of silicon meet the above conditions, the volume expansion of silicon can be more effectively mitigated, the lifespan of silicon-containing systems can be improved, and the cycle performance can be enhanced.

[0243] Optionally, based on the mass of the electrolyte, the mass content of vinylene carbonate is from 0.1% to 3%, for example, 0.1%, 0.5%, 0.6%, 1.0%, 1.1%, 1.5%, 1.6%, 2.0%, 2.1%, 2.5%, 2.6%, 3%, or any combination of two of the above values. The above-mentioned mass content of vinylene carbonate results in a more compact SEI film on the negative electrode surface, more effectively protecting the silicon-containing negative electrode, reducing the degree of side reactions at the negative electrode interface, and improving cycle performance.

[0244] The combined use of the aforementioned amounts of vinylene carbonate and fluorocyclic carbonate further optimizes the performance of the SEI film on the negative electrode surface, resulting in excellent density and low impedance. This more effectively protects the silicon-containing negative electrode, reduces the degree of side reactions at the negative electrode interface, and improves cycle performance.

[0245] In the embodiments of this application, the types and contents of inorganic components / lithium salts in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis method according to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte of a fresh battery can be used as a sample, or a battery that has been completely discharged (discharged to the lower limit cutoff voltage so that the battery's state of charge is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography analysis method.

[0246] In the embodiments of this application, the types and contents of organic components in the electrolyte are known in the art and can be detected using equipment and methods known in the art. For example, the organic components in the electrolyte can be qualitatively and quantitatively analyzed by gas chromatography using GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents".

[0247] In this embodiment, after quantitative and qualitative detection of each component in the electrolyte, the components are classified, and carboxylic acid ester solvents and carbonate solvents are included as components of organic solvents. The mass content of each component is calculated based on the mass of the electrolyte as 100%.

[0248] Fluorinated cyclic carbonates and vinylene carbonates were used as additives in the electrolyte. The mass content of each component was calculated based on the mass of the electrolyte as 100%.

[0249] Isolation component

[0250] In some embodiments, the electrode assembly further includes a spacer disposed between the positive electrode and the negative electrode.

[0251] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0252] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator.

[0253] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0254] Example

[0255] The following embodiments describe the contents disclosed in this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of the embodiments of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0256] Example 1

[0257] 1. Preparation of positive electrode sheet

[0258] The positive electrode includes a positive current collector and a positive film layer disposed on both sides of the positive current collector. The positive current collector is aluminum foil.

[0259] The positive electrode film layer comprises lithium phosphate, positive electrode additive, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black in a mass ratio of 96:1.5:1.5:1. The positive electrode film layer is formed by uniformly coating the positive electrode slurry (solvent N-methylpyrrolidone NMP) on both sides of the positive electrode current collector, followed by drying and cold pressing.

[0260] The lithium-containing phosphate comprises multiple primary phosphate particles and multiple secondary phosphate particles, wherein the secondary phosphate particles constitute 90% of the lithium-containing phosphate by mass.

[0261] In a cross-section along the thickness direction of the positive electrode film, the average longest diameter of the multiple first phosphate particles is 2 μm, the average longest diameter of the multiple second phosphate particles is 0.3 μm, and the mass content of the second phosphate particles in the lithium-containing phosphate is 90%.

[0262] The positive electrode additive consists of multiple particles, each particle including a core and a carbon coating layer disposed on the surface of the core. The core is lithium ferrite, and the carbon coating layer accounts for 2% of the mass content of the positive electrode additive. In the cross section along the thickness direction of the positive electrode film, the average longest diameter of the multiple positive electrode additives is 11 μm, and the average shortest diameter of the multiple positive electrode additives is 7 μm.

[0263] The single-sided coating weight of the positive electrode film is 280 mg / 1540.25 mm. 2 .

[0264] Lithium iron phosphate is sourced from Xiamen Tungsten Co., Ltd.

[0265] 2. Preparation of negative electrode sheet

[0266] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on both sides of the negative current collector. The negative current collector is copper foil.

[0267] The negative electrode film layer comprises carbon-based artificial graphite, conductive agent acetylene black, negative electrode binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose in a mass ratio of 96.5:1:1.5:1. The negative electrode film layer is formed by uniformly coating the negative electrode slurry (solvent is deionized water) onto the surface of the negative electrode current collector, followed by drying and cold pressing.

[0268] The single-sided coating weight of the negative electrode film is 135 mg / 1540.25 mm. 2 .

[0269] Artificial graphite originates from BTR New Materials Group Co., Ltd.

[0270] 3. Separating membrane

[0271] The separator includes a base membrane, which is a 7μm polyethylene film layer with a porosity of 35%.

[0272] The separator membrane is sourced from Shenzhen Xingyuan Material Technology Co., Ltd.

[0273] 4. Preparation of electrolyte

[0274] The electrolyte consists of organic solvents, lithium salts, and additives.

[0275] After the components of the organic solvent are mixed evenly, lithium salt and additives are added to prepare an electrolyte.

[0276] The organic solvents include 25% chain carboxylic acid ester solvents (ethyl acetate EA) and 57% carbonate solvents (27% ethylene carbonate EC, 30% dimethyl carbonate DMC). The mass content of each component in the organic solvents is calculated based on the mass of the electrolyte.

[0277] The lithium salt comprises 8% lithium hexafluorophosphate (LiPF6) and 6% lithium difluorosulfonylimide.

[0278] The additives include 2% fluorocyclic carbonate monofluoroethylene carbonate (FEC) and 2% vinylene carbonate (VC).

[0279] The conductivity of the electrolyte is 14.2 mS / cm.

[0280] 5. Preparation of battery cells

[0281] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining the electrode assembly. The electrode assembly is then placed in an outer packaging shell, dried, and injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. The compaction density of the positive electrode film layer in the battery cell at 0% SOC is 2.65 g / cm³. 3 The compaction density of the negative electrode film at 0% SOC is 1.56 g / cm³. 3 .

[0282] Comparative Example 1-1

[0283] Battery cells were prepared using a method similar to that of Example 1, except that no positive electrode additives were added to the positive electrode film layer.

[0284] Example 2

[0285] Battery cells were prepared using a method similar to that of Example 1, except that the type of positive electrode additive was adjusted.

[0286] Examples 3-1 and 3-2

[0287] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of the carbon coating layer in the cathode additive was adjusted.

[0288] Examples 4-1 and 4-2

[0289] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of the positive electrode additive was adjusted.

[0290] Examples 5-1 to 5-3

[0291] Battery cells were prepared using a method similar to that of Example 1, except that the particle size of the positive electrode additive was adjusted.

[0292] Examples 6-1 to 6-3

[0293] Battery cells were prepared using a method similar to that of Example 1, except that the particle size of the positive electrode active material was adjusted.

[0294] Examples 7-1 and 7-2

[0295] Battery cells were prepared using a method similar to that of Example 1, except that the mass content of the second phosphate particles in the positive electrode active material was adjusted.

[0296] Performance testing

[0297] 1. High-temperature cycle performance test of individual battery cells

[0298] At 45±5℃, the battery cell is charged at a constant current of 2C to 3.65V, then charged at a constant voltage to the cutoff current of 0.05C, and then discharged at a constant current of 2C to 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as the discharge capacity C1 of the battery cell in the first cycle.

[0299] Repeat the cyclic process for the same battery cell until the cycle capacity retention rate of that battery cell = Cn / C1*100% = 80%. Record the number of cycles n. For accuracy, take the average of 5 parallel samples as the test result.

[0300] The test results are shown in Table 1.

[0301] Table 1

[0302] Organic components in the electrolyte may undergo side reactions on the negative electrode side, worsening high-temperature cycling performance. Comparative Example 1-1, which did not add positive electrode additives, exhibited relatively poor high-temperature cycling performance.

[0303] In this embodiment, a positive electrode additive is added to the positive electrode film layer. The positive electrode additive can release oxygen, which can participate in the formation of the negative electrode film, repair the SEI film on the negative electrode side, reduce the side reactions on the negative electrode side, and improve the high-temperature cycling performance.

[0304] Different cathode additives, such as lithium iron phosphate and lithium cobalt oxide, can release oxygen during the charging process of a single battery cell, repair the negative electrode interface film, and improve high-temperature cycle performance.

[0305] The surface of lithium ferrite can be coated with a carbon coating layer. The carbon coating layer has a mass content of 1% to 5% in the positive electrode additive. The carbon coating layer can effectively protect lithium ferrite, alleviate the side reactions between lithium ferrite and electrolyte, enable lithium ferrite to release oxygen stably, gradually repair the SEI film, and improve the high-temperature cycle performance of the battery cell.

[0306] When the longest and shortest diameters of the cathode additive in the same particle meet an appropriate ratio, for example, when the ratio of the longest to the shortest diameter is 1.2 to 2.5, it can effectively improve the stability of the cathode additive while also having a good oxygen release effect.

[0307] The average longest diameter of lithium phosphate is smaller than the average shortest diameter of the cathode additive. When cathode additives with the above particle size are used, they have a better oxygen release effect and improve the high-temperature cycle performance of battery cells.

[0308] The lithium-containing phosphate includes multiple primary phosphate particles and multiple secondary phosphate particles. The longest diameter of the primary phosphate particles is relatively long, while the longest diameter of the secondary phosphate particles is relatively short. However, the average longest diameter of the multiple primary phosphate particles is still shorter than the average shortest diameter of the multiple cathode additives. This results in a shorter lithium ion insertion / extraction path in the lithium-containing phosphate, less heat generation, and reduced heat generation within the battery cell system. This also reduces the risk of electrolyte components decomposing due to heat accumulation and improves the cycle performance of the battery cell.

[0309] When the mass content of the second phosphate particles is within an appropriate range, such as 80% to 95%, it can further reduce heat generation, reduce heat generation within the battery cell system, reduce the risk of electrolyte components decomposing due to heat accumulation, and improve the cycle performance of the battery cell.

[0310] Comparative Example 2-1 and Comparative Example 2-2

[0311] Battery cells were prepared using a method similar to that of Example 1, except that the composition and content of the electrolyte were adjusted.

[0312] Examples 8-1 to 8-7

[0313] Battery cells were prepared using a method similar to that of Example 1, except that the composition and content of the electrolyte were adjusted.

[0314] The test results are shown in Table 2.

[0315] Table 2

[0316] In Table 3,

[0317] EA represents ethyl acetate; MA represents methyl acetate; EC represents ethylene carbonate; DMC represents dimethyl carbonate.

[0318] EMC stands for ethyl methyl carbonate; FEC stands for ethylene monofluorocarbonate.

[0319] EA:25 indicates that the mass content of EA is 25%;

[0320] EC:27 indicates that the mass content of EC is 27%.

[0321] The mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate refers to the ratio of the mass content of lithium bis(fluorosulfonyl)imide to the mass content of lithium hexafluorophosphate.

[0322] The meanings of the other examples are explained in the same way as above, and will not be repeated here.

[0323] The conductivity of the electrolyte in Example 8-1 was 9 mS / cm, and the conductivity of the electrolyte in Example 8-2 was 18 mS / cm.

[0324] In Comparative Example 2-1, the mass content of carboxylic acid ester solvent was too low, resulting in low electrolyte conductivity, high internal resistance of the battery cells, significant energy loss, and a deterioration in cycle life.

[0325] In Comparative Example 2-2, the excessively high mass content of carboxylic acid ester solvents intensified the high-temperature gas generation of carboxylic acid ester solvents on the negative electrode side, resulting in poor high-temperature cycling performance.

[0326] This application embodiment adjusts the composition of the electrolyte so that the mass content of carboxylic acid ester solvent is 3% to 70%, optionally 5% to 30%. This improves the conductivity of the electrolyte and reduces the high-temperature gas generation on the negative electrode side, thereby improving cycle performance and fast charging performance.

[0327] In this embodiment, lithium hexafluorophosphate and lithium difluorosulfonylimide are used in combination, for example, the mass content of lithium difluorosulfonylimide to the mass content of lithium hexafluorophosphate is 0.3 to 1.2, which can reduce the content of hydrofluoric acid, slow down the side reaction at the negative electrode interface, reduce the amount of gas generated during high-temperature storage, and help improve the high-temperature cycle life of the battery cell.

[0328] The fluorinated cyclic carbonate has a mass content of 0.5% to 20%. Fluorinated cyclic carbonate can form a lithium fluoride (LiF)-rich SEI film on the negative electrode surface, which can alleviate the volume expansion of silicon, improve the lifetime of silicon-containing systems, and improve cycle performance.

[0329] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the implementation of the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the implementation of the present application.

Claims

1. A single battery cell, comprising: A negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, wherein the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes a carbon-based material; A positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material and a positive electrode additive. The positive electrode active material includes a lithium-containing phosphate, and the positive electrode additive includes at least one selected from lithium-containing iron oxide and lithium-containing cobalt oxide. The electrolyte includes an organic solvent, said organic solvent including carboxylic acid ester solvents, said carboxylic acid ester solvents having a mass content of 3% to 70% in the electrolyte.

2. The battery cell according to claim 1, wherein, The lithium-containing iron oxide includes lithium ferrite; and / or The lithium-containing cobalt oxide includes lithium cobalt oxide.

3. The battery cell according to claim 1 or 2, wherein, The lithium-containing iron oxide includes Li e FeO f , 0 < e ≤ 5, 0 <f≤4。 4. The battery cell according to claim 3, wherein, The lithium-containing iron oxides include Li5FeO4 and Li3FeO. 3.5 At least one of LiFeO2.

5. The battery cell according to any one of claims 1 to 4, wherein, The lithium-containing cobalt oxide includes Li g CoO h , 0 < g ≤ 6, 0 <h≤4。 6. The battery cell according to claim 5, wherein, The lithium-containing cobalt oxide includes one or more of Li6CoO4, Li3CoO2, and LiCoO2.

7. The battery cell according to any one of claims 1 to 6, wherein, Based on the mass of the positive electrode film, the mass content of the positive electrode additive is 0.5% to 3%.

8. The battery cell according to any one of claims 1 to 7, wherein, The surface of the positive electrode additive is also provided with a carbon coating layer.

9. The battery cell according to claim 8, wherein, The carbon coating layer has a mass content of 1% to 5% in the cathode additive.

10. The battery cell according to any one of claims 1 to 9, wherein, The positive electrode additive is granular, and in a cross-section of the positive electrode film along its own thickness direction, the ratio of the longest diameter to the shortest diameter of the positive electrode additive in the same particle is 1.2 to 2.

5.

11. The battery cell according to any one of claims 1 to 10, wherein, In a cross-section of the positive electrode film along its thickness direction, there are multiple positive electrode additives, and the average longest diameter of the multiple positive electrode additives is 9 μm to 13 μm; and / or In a cross-section of the positive electrode film along its own thickness direction, there are multiple positive electrode additives, and the average shortest diameter of the multiple positive electrode additives is 5 μm to 9 μm.

12. The battery cell according to any one of claims 1 to 11, wherein, Both the lithium-containing phosphate and the positive electrode additive are multiple and granular. In the cross-section of the positive electrode film along its own thickness direction, the average longest diameter of the multiple lithium-containing phosphates is smaller than the average shortest diameter of the multiple positive electrode additives.

13. The battery cell according to any one of claims 1 to 12, wherein, The lithium-containing phosphate comprises a plurality of first phosphate particles and a plurality of second phosphate particles, wherein the longest diameter of the first phosphate particles is greater than the longest diameter of the second phosphate particles, the average longest diameter of the plurality of first phosphate particles is 1 μm to 5 μm, and the average longest diameter of the plurality of second phosphate particles is 0.1 μm to 0.5 μm.

14. The battery cell according to claim 13, wherein, The second phosphate particles have a mass content of 80% to 95% in the lithium-containing phosphate.

15. The battery cell according to any one of claims 1 to 14, wherein, The lithium-containing phosphates include lithium iron phosphate.

16. The battery cell according to any one of claims 1 to 15, wherein, The electrolyte has a conductivity of 9 mS / cm to 18 mS / cm at room temperature.

17. The battery cell according to any one of claims 1 to 16, wherein, The carboxylic acid ester solvent has a mass content of 5% to 30% in the electrolyte.

18. The battery cell according to claim 17, wherein, The carboxylic acid ester solvent includes cyclic carboxylic acid esters, which include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone; and / or The carboxylic acid ester solvent includes chain carboxylic acid esters, which include one or more of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, and butyl propionate.

19. The battery cell according to any one of claims 1 to 18, wherein, The organic solvent also includes carbonate solvents, which include one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

20. The battery cell according to any one of claims 1 to 19, wherein, The electrolyte also includes lithium salts, including lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, wherein the mass ratio of the lithium bis(fluorosulfonyl)imide to the lithium hexafluorophosphate is 0.3 to 1.2 based on the mass of the electrolyte.

21. The battery cell according to claim 20, wherein, Based on the mass of the electrolyte, the lithium bis(fluorosulfonyl)imide content is 2% to 11% by mass; and / or Based on the mass of the electrolyte, the lithium hexafluorophosphate content is 3% to 14% by mass.

22. The battery cell according to any one of claims 1 to 21, wherein, The electrolyte also includes one or more of fluorocyclic carbonates and vinylene carbonates.

23. The battery cell according to claim 22, wherein, The fluorocarbonate includes at least one of ethylene monofluorocarbonate, ethylene difluorocarbonate, and propylene trifluorocarbonate.

24. The battery cell according to claim 22 or 23, wherein, Based on the mass of the electrolyte, the mass content of the fluorocyclic carbonate is from 0.5% to 20%. and / or Based on the mass of the electrolyte, the mass content of the vinylene carbonate is from 0.1% to 3%.

25. The battery cell according to any one of claims 1 to 24, wherein, The carbon-based material includes at least one of artificial graphite and natural graphite.

26. A battery device comprising a battery cell as claimed in any one of claims 1 to 25.

27. An electrical device comprising the battery device as described in claim 26.

Images