Battery cell and electrical apparatus

Abstract

A battery cell and an electrical apparatus. The battery cell comprises a positive electrode sheet and an electrolyte, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side of the positive electrode current collector, and the positive electrode film layer comprising a positive electrode active material. The positive electrode active material comprises a lithium-containing phosphate, the electrolyte comprises a first additive and a second additive, the first additive comprises a fluorocarbonate, and the second additive comprises at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The present application can reduce the rate of increase of internal resistance of the battery and improve the cycle performance of the battery, so that the battery cell has both cycle performance and rate performance.

Description

Battery cells and electrical devices Cross-references to related applications

[0001] This patent document claims priority and benefit to Chinese Patent Application No. 202411844922.0, filed on December 13, 2024, entitled "Battery Cell and Electrical Device". The entire contents of the aforementioned patent application are incorporated herein by reference as a part of the disclosure of this patent document. Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a battery cell and an electrical device. Background Technology

[0003] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within the new energy industry, battery technology is a crucial factor in its development.

[0004] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, capacity, rate performance, and reliability. Therefore, reducing the increase in internal resistance to improve battery performance is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell with a lower internal resistance growth rate.

[0006] To achieve the above objectives, this application provides a battery cell and an electrical device.

[0007] In a first aspect, a battery cell is provided, comprising: a positive electrode sheet and an electrolyte; the positive electrode sheet includes a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side of the positive current collector, the positive electrode film layer including a positive electrode active material; wherein, the positive electrode active material includes a lithium phosphate, and the electrolyte includes a first additive and a second additive, the first additive including a fluorocarbonate, and the second additive including at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0008] In this embodiment, the battery cell includes a positive electrode active material and an electrolyte. The positive electrode active material includes a lithium phosphate, and the electrolyte includes a first additive and a second additive. The first additive includes a fluorocarbonate, and the second additive includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. Fluorocarbonate helps form an SEI film containing inorganic LiF, resulting in stronger SEI film stability and lower impedance, which can reduce side reactions in the electrolyte during battery cycling. Lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide helps improve the thermal stability of the battery cell. Therefore, when the positive electrode active material of the battery cell includes a lithium phosphate, adding at least one of fluorocarbonate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethanesulfonyl)imide to the electrolyte of the battery cell helps form a more stable SEI film, reducing side reactions and improving the stability of the battery cell, thereby reducing the impedance of the SEI film, slowing down the rate of increase in the internal resistance of the battery cell, and improving battery cycle performance.

[0009] In one possible implementation, the fluorocarbonate includes at least one of cyclic fluorocarbonate or chain fluorocarbonate.

[0010] In this embodiment of the application, when the positive electrode active material of the battery cell includes lithium phosphate, a more stable SEI film can be formed by adding fluorinated carbonate to the electrolyte; furthermore, when the fluorinated carbonate includes at least one of cyclic fluorinated carbonate or chain fluorinated carbonate, the stability of the SEI film can be further improved.

[0011] In one possible implementation, the cyclic fluorocarbonate comprises fluoroethylene carbonate, and the chain fluorocarbonate comprises ethyltrifluoroethyl carbonate.

[0012] In the embodiments of this application, fluoroethylene carbonate and ethyl trifluoroethyl carbonate are readily available and are beneficial for widespread application in production.

[0013] In one possible implementation, the mass content w of the first additive is based on the total mass of the electrolyte. 1 Satisfy: 0.01% ≤ w 1 ≤0.2%.

[0014] In this embodiment, the first additive, which includes cyclic fluorocarbonate, helps to improve the stability of the SEI film. By making the mass ratio of the first additive in the electrolyte 0.01%-0.2%, the stability of the SEI can be guaranteed, thereby reducing the internal resistance of the battery cell and improving the rate performance.

[0015] In one possible implementation, the mass content w of the second additive is based on the total mass of the electrolyte. 2Satisfy: 1% ≤ w 2 ≤4%.

[0016] In this embodiment, the second additive, including chain-like fluorocarbonate, can enhance battery stability. By making the mass proportion of the second additive in the electrolyte 1%-4%, the stability of the battery cells can be enhanced and the side reactions of the battery cells can be reduced, thereby comprehensively improving battery performance.

[0017] In one possible implementation, the ionic conductivity σ of the electrolyte satisfies: 10 mS / cm ≤ σ ≤ 18 mS / cm.

[0018] In this embodiment of the application, by making the ionic conductivity σ of the electrolyte not less than 10 mS / cm and not greater than 18 mS / cm, the electrolyte with high conductivity can improve the lithium ion diffusion rate, reduce the diffusion resistance of lithium ions in the porous electrode, and thus improve the power performance of the battery cell.

[0019] In one possible implementation, the volume average particle size Dv50 of the positive electrode active material 1 Satisfies: 4μm≤Dv50 1 ≤11μm.

[0020] In this embodiment of the application, by making the volume average particle size of the positive electrode active material between 4μm and 11μm, the diffusion path of lithium ions can be reduced, thereby improving the power performance of the battery cell.

[0021] In one possible implementation, the specific surface area S of the positive electrode active material 1 Satisfy: 10m 2 / g≤S 1 ≤14.5m 2 / g.

[0022] In this embodiment of the application, the specific surface area of ​​the positive electrode active material is made to be 10m². 2 / g-14.5m 2 Reaching a value between / g can increase the interfacial reaction current density, which helps to further improve the power performance of individual battery cells.

[0023] In one possible implementation, the tap density TD of the positive electrode active material 1 Satisfy: TD 1 ≥0.75g / cm 3 .

[0024] In this embodiment of the application, by keeping the tap density of the positive electrode active material within the above-mentioned range, the positive electrode active material within this range helps to improve the density of the positive electrode film, making the positive electrode sheet more compact, and helps to improve the mechanical strength and conductivity of the positive electrode active material.

[0025] In one possible implementation, the lithium-containing phosphate has the general formula Li. a Fe 1-x-y Mn x M y PO4; wherein 0.6≤a≤1.1, 0≤x≤1, 0≤y≤0.1, and M is selected from at least one of the transition metal elements other than Fe and Mn, as well as non-transition metal elements.

[0026] In one possible implementation, the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their modified compounds.

[0027] In the above scheme, using at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate and their modified compounds as the positive electrode active material of the battery cell helps to improve the energy density of the battery cell.

[0028] In one possible implementation, the battery cell further includes a negative electrode sheet; the negative electrode sheet includes a negative current collector and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the negative current collector, and the negative electrode film layer comprising conductive carbon; the degree of graphitization of the conductive carbon is I. D / I G Satisfy: 0.1≤I D / I G ≤0.5.

[0029] In this embodiment, graphitized conductive carbon is added to the negative electrode film layer, and the degree of graphitization of the conductive carbon is I. D / I G Between 0.1 and 0.5, graphitized conductive carbon can form an ordered conductive network, improving conductivity and thus enhancing the power performance of the battery cell. On the other hand, graphitized conductive carbon can reduce the catalytic sites on the surface of the conductive carbon, thereby reducing side reactions at the negative electrode and further improving the stability of the battery cell.

[0030] In one possible implementation, the conductive carbon has a volume average particle size Dv50. 2 Satisfies: 10μm≤Dv50 2 ≤20μm.

[0031] In this embodiment, by ensuring that the volume average particle size of the conductive carbon is within the above-mentioned range, it can be better dispersed in the negative electrode active material to form a dense conductive network, thereby improving the overall conductivity of the negative electrode sheet. In addition, conductive carbon with a particle size within the above-mentioned range does not affect the viscosity and flowability of the negative electrode slurry, thereby helping to improve the coating uniformity of the slurry and the density of the negative electrode film.

[0032] In one possible implementation, the specific surface area S of the conductive carbon 2 Satisfy: 60m 2 / g≤S 2 ≤70m 2 / g.

[0033] In this embodiment of the application, by making the specific surface area of ​​conductive carbon within the above-mentioned range, it is helpful to improve the conductivity and material dispersion of the negative electrode film, and also to improve the electrochemical stability of the battery cell.

[0034] In one possible implementation, the conductive carbon includes at least one of conductive carbon black, Ketjen black, and acetylene black.

[0035] In this embodiment, graphitized conductive carbon is added to the negative electrode film to improve the conductivity of the negative electrode sheet and enhance the power performance of the battery cell. By including at least one of conductive carbon black, Ketjen black, and acetylene black, which are readily available and relatively inexpensive, it is beneficial for their widespread application in production.

[0036] In one possible implementation, the negative electrode film layer further includes a negative electrode active material; the volume average particle size of the negative electrode active material is Dv50. 3 Satisfies: 5.2μm≤Dv50 3 ≤8.2μm.

[0037] In this embodiment of the application, by making the volume average particle size of the negative electrode active material between 5.2 μm and 8.2 μm, the smaller particle size of the negative electrode active material can reduce the diffusion path of lithium ions and help improve the power performance of the battery cell.

[0038] In one possible implementation, the specific surface area S of the negative electrode active material 3 Meets the requirement of 1.4m 2 / g≤S 3 ≤2m 2 / g.

[0039] In this embodiment, the specific surface area of ​​the negative electrode active material affects the stability of the SEI film. By maintaining the specific surface area of ​​the negative electrode active material at 1.4 μm... 2 / g-2m 2 The ratio between / g helps to form a more stable SEI film, thereby further improving the stability of the battery cell.

[0040] In one possible implementation, the tap density TD of the negative electrode active material 2 Satisfying: 0.8g / cm 3 ≤TD 2 ≤1.2g / cm 3 .

[0041] In this embodiment of the application, by making the tap density of the negative electrode active material within the above-mentioned range, the negative electrode active material within this range helps to improve the density of the negative electrode film, making the negative electrode sheet more compact, and helping to improve the mechanical strength and conductivity of the negative electrode sheet.

[0042] In one possible implementation, the battery cell further includes a separator, the porosity of which is... satisfy:

[0043] In this embodiment, an appropriate porosity of the separator ensures that the electrolyte fully penetrates into the separator, thereby increasing the contact area between the electrolyte and the positive and negative electrode active materials and promoting lithium-ion transport. Furthermore, a separator with moderate porosity helps improve the lithium-ion conductivity, reduce the internal resistance of the battery cell, and improve the rate performance of the battery. Therefore, by maintaining the porosity of the separator within the aforementioned range, it helps to promote lithium-ion transport and improve the lithium-ion conductivity, thereby improving the performance of the battery cell.

[0044] In one possible implementation, the separator includes a substrate and a modified layer disposed on both sides of the substrate; the modified layer includes an unsaturated silane compound.

[0045] In this embodiment, lithium bis(fluorosulfonyl)imide in the second additive may generate hydrogen fluoride during the cycling process of the battery cell. By including a modified layer of unsaturated silane compound on the separator, the unsaturated silane compound can react with hydrogen fluoride to generate a stable compound, reducing the adverse effects of hydrogen fluoride on the battery cell and helping to comprehensively improve the stability of the battery cell.

[0046] In one possible implementation, the unsaturated silane compound includes at least one of vinylsilane, allylsilane, and ethynylsilane.

[0047] In the embodiments of this application, vinylsilane, allylsilane, and ethynylsilane are readily available, and using at least one of them in the separator of a battery cell can reduce the production cost of the battery cell.

[0048] In one possible implementation, the unsaturated silane compound includes at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

[0049] In this embodiment of the application, by using at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane as a modified layer material coated on the substrate of the separator, the stability of the battery cell can be improved.

[0050] In one possible implementation, the mass content w of the unsaturated silane compound is based on the total mass of the modified layer. 3 Satisfy: 1% ≤ w 3 ≤10%.

[0051] In this embodiment, unsaturated silane compounds are used as a intermediate in the product generated from lithium bis(fluorosulfonyl)imide in the second additive. By making the unsaturated silane compound account for 1%-10% of the modified layer, it helps to further improve the stability of the battery cell.

[0052] In one possible implementation, the thickness h of the separator satisfies: 5μm≤h≤18μm.

[0053] In this embodiment, the thickness of the separator affects the battery performance. By keeping the separator thickness between 5μm and 18μm, short circuits in individual battery cells can be prevented, thus improving the safety performance of the individual cells. On the other hand, while ensuring electrolyte penetration, internal resistance can be reduced, thereby improving the power performance and rate performance of the individual battery cells.

[0054] In a second aspect, an electrical device is provided, comprising a battery cell as described in the first aspect and any possible implementation thereof. Attached Figure Description

[0055] 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.

[0056] Figure 1 is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application;

[0057] Figure 2 is a conductivity test diagram of the isolation element according to an embodiment of this application;

[0058] Figure 3 is a thermogravimetric analysis diagram of the isolation component according to an embodiment of this application;

[0059] Figure 4 is a schematic diagram of a battery cell according to an embodiment of this application;

[0060] Figure 5 is a schematic diagram of a battery according to an embodiment of this application;

[0061] Figure 6 is a schematic diagram of an electrical device according to an embodiment of this application;

[0062] Figure 7 is a schematic diagram of an electrical device according to another embodiment of this application. Detailed Implementation

[0063] Embodiments of the battery cell and power supply device of this application have been described in detail with reference to the accompanying drawings, but unnecessary details 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.

[0064] 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 a 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 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 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: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" 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 "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0067] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0068] Battery systems are a crucial component of modern electric vehicle technology, playing a key role in improving the performance and efficiency of electric vehicles. With the rapid development of the electric vehicle market, consumers' increasing demands for vehicle power and driving range have driven advancements in high-power battery system technology.

[0069] The key to high-power battery systems lies in their electrochemical characteristics and design. Generally, high-power batteries need high energy density and low internal resistance to release a large amount of electricity in a short time. However, practical high-power battery systems require the use of electrolytes with high conductivity. At high temperatures, the solvent activity in high-conductivity electrolytes is high, which accelerates side reactions in the electrolyte, causing the battery's internal resistance to increase too rapidly. This negatively impacts the battery's power output, lifespan, and other related performance characteristics. Therefore, solving the problem of rapid internal resistance growth in high-power batteries is a pressing technical challenge.

[0070] In view of the above problems, this application provides a battery cell and an electrical device. The battery cell includes an electrolyte, which includes a first additive and a second additive. The first additive includes a fluorocarbonate, and the second additive includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The fluorocarbonate helps to form an inorganic-rich SEI film, enhancing SEI film stability and reducing side reactions in the electrolyte. Lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide helps to improve the stability of the battery cell, thereby reducing the rate of increase in internal resistance and improving the cycle performance of the battery.

[0071] It should be understood that during the charging process of a single battery cell, lithium ions are released from the positive electrode active material, move and embed into the negative electrode; while during the discharging process, they move and embed into the positive electrode active material.

[0072] It should be understood that the “intercalation” process described in this application refers to the process by which lithium ions are intercalated into the positive electrode active material or the negative electrode due to an electrochemical reaction, and the “extraction” and “deintercalation” processes described in this application refer to the process by which lithium ions are extracted from the positive electrode active material or the negative electrode due to an electrochemical reaction.

[0073] In this application's embodiments, a single battery cell can refer to the smallest structural unit of a battery. Multiple battery cells can first be assembled into a battery module, and then the battery module can be assembled into a battery; multiple battery cells can also be directly assembled into a battery.

[0074] [Battery cell]

[0075] This application provides a single battery cell. The single battery cell includes a positive electrode and an electrolyte.

[0076] Figure 1 is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application. For example, as shown in Figure 1, the positive electrode sheet 1 includes a positive current collector 10 and a positive electrode film layer 11 disposed on at least one side surface of the positive current collector 10. The positive electrode film layer 11 includes a positive electrode active material, which includes a lithium phosphate.

[0077] The positive electrode current collector 10 has two opposing surfaces along its thickness direction. The positive electrode film layer 11 can be disposed on one surface of the positive electrode current collector 10 or on both surfaces. As an example, as shown in FIG1, the positive electrode film layer 11 is disposed on both surfaces of the positive electrode current collector 10.

[0078] Lithium-containing phosphates possess excellent electrochemical performance, high safety, and long cycle life, and are therefore commonly used as positive electrode active materials in battery cells. Lithium-containing phosphates include, but are not limited to, lithium iron phosphate and lithium manganese phosphate.

[0079] The electrolyte includes a first additive and a second additive. The first additive includes a fluorocarbonate, and the second additive includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0080] Fluorocarbonates preferentially reduce on the negative electrode surface during the first charge-discharge cycle of a battery cell, forming a thin and uniform solid electrolyte interphase (SEI) film containing inorganic matter. This SEI film exhibits high stability during multiple charge-discharge cycles, mitigating the rate of internal resistance increase and contributing to improved power performance. Furthermore, the SEI film possesses high chemical stability and mechanical strength, effectively preventing further reactions between the electrolyte and the positive and negative electrode active materials, reducing active material loss, protecting the electrolyte, minimizing electrolyte decomposition and side reactions, and thus extending battery cell lifespan. Therefore, adding fluorocarbonates to the electrolyte can form a stable SEI film and reduce electrolyte side reactions, thereby mitigating the rate of internal resistance increase and improving cycle performance, helping to achieve a balance between rate capability and cycle performance in battery cells.

[0081] However, fluorocarbonates react with water to produce hydrogen fluoride, a byproduct that can damage the SEI film and adversely affect the performance of the battery cells. Adding lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide to the electrolyte can address this issue. Lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide possesses high thermal and chemical stability, and its decomposition products inhibit the production of hydrogen fluoride. Therefore, the hydrogen fluoride content in the battery cells can be reduced, thereby improving the cycle performance of the cells. Furthermore, lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide also contributes to the formation of an SEI film with high chemical stability and mechanical strength at high temperatures, further enhancing the stability of the SEI film.

[0082] In the above scheme, the battery cell includes a positive electrode active material and an electrolyte. The positive electrode active material includes a lithium phosphate, and the electrolyte includes a first additive and a second additive. The first additive includes a fluorocarbonate, and the second additive includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The fluorocarbonate forms an inorganic SEI film, which helps improve the stability of the SEI film, reduce side reactions in the electrolyte, and slow down the rate of internal resistance growth in the battery cell. Lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide helps improve the thermal stability of the battery cell. Therefore, by including a lithium phosphate in the positive electrode active material of the battery cell and adding fluorocarbonate and lithium bis(fluorosulfonyl)imide to the electrolyte of the battery cell, a more stable SEI film is formed, reducing side reactions and improving the stability of the battery cell, thereby mitigating the rate of internal resistance growth and improving battery performance.

[0083] In some embodiments, the fluorocarbonate includes at least one of cyclic fluorocarbonate or chain fluorocarbonate.

[0084] Cyclic fluorocarbonates are cyclic carbonates with one or more fluorine atoms in their backbone, including but not limited to fluoroethylene carbonate and difluoroethylene carbonate. Chain fluorocarbonates are linear carbonates with one or more fluorine atoms in their backbone, including but not limited to monofluoroethyl carbonate and difluoroethyl carbonate.

[0085] Compared to other types of fluorocarbons, such as branched or mixed fluorocarbons, cyclic and chain fluorocarbons are more conducive to improving battery stability.

[0086] In the above scheme, when the positive electrode active material of the battery cell contains lithium phosphate, a more stable SEI film can be formed by adding fluorinated carbonate and lithium bis(fluorosulfonyl)imide to the electrolyte; furthermore, when the fluorinated carbonate includes at least one of cyclic fluorinated carbonate or chain fluorinated carbonate, the stability of the SEI film can be further improved.

[0087] In some embodiments, cyclic fluorocarbonates include fluoroethylene carbonate, and chain fluorocarbonates include ethyltrifluoroethyl carbonate.

[0088] In the above scheme, fluoroethylene carbonate and ethyl trifluoroethyl carbonate are readily available, which is conducive to their widespread application in production.

[0089] In some embodiments, the mass content w of the first additive is determined based on the total mass of the electrolyte. 1 Satisfy: 0.01% ≤ w 1 ≤0.2%.

[0090] The w here 1 In order to be with the w below 2 To distinguish them, indicating the mass content of different substances.

[0091] When w 1 When the mass content in the electrolyte is greater than or equal to 0.01%, the first additive can improve the stability of the SEI film; when w 1 When the mass content of the first additive in the electrolyte is less than or equal to 0.2%, it will not affect the viscosity of the electrolyte and thus its fluidity.

[0092] In the above scheme, the first additive, which includes cyclic fluorocarbonate, helps to improve the stability of the SEI film. By making the mass ratio of the first additive in the electrolyte 0.01%-0.2%, the stability of the SEI can be guaranteed, thereby reducing the internal resistance of the battery cell and improving the cycle performance.

[0093] Specifically, based on the total mass of the electrolyte, the mass content of the first additive can be 0.01%, 0.05%, 0.09%, 0.16%, 0.2%, or any value within the above range.

[0094] In some embodiments, the mass content w of the second additive is based on the total mass of the electrolyte. 2 Satisfy: 1% ≤ w 2 ≤4%.

[0095] When w 2 When its mass content in the electrolyte is less than 1%, it does not significantly improve the stability of the electrolyte under high-temperature conditions; when w 2 When the mass content in the electrolyte is greater than 4%, it will also affect the fluidity of the electrolyte or increase the side reactions on the electrode materials.

[0096] In the above scheme, the second additive, including chain-like fluorocarbonate, can enhance battery stability. By making the mass proportion of the second additive in the electrolyte 1%-4%, the stability of the battery cells can be enhanced and the side reactions of the battery cells can be reduced, thereby comprehensively improving battery performance.

[0097] Specifically, based on the total mass of the electrolyte, the mass content of the second additive can be 1%, 1.5%, 2.4%, 3.9%, 4%, or any value within the above range.

[0098] In some implementations, the ionic conductivity σ of the electrolyte satisfies: 10 mS / cm ≤ σ ≤ 18 mS / cm.

[0099] Ionic conductivity refers to the current density generated by ion transport in an electrolyte under a unit electric field strength. It is used to measure the electrolyte's ability to transport ions and is an important parameter for evaluating the electrolyte's electrical conductivity. A higher ionic conductivity in the electrolyte allows more ions to participate in conduction, which can reduce the internal resistance of individual battery cells and improve the overall performance of the battery cells.

[0100] That is, by ensuring that the ionic conductivity of the electrolyte is not less than 10 mS / cm, it helps to improve the conductivity of the battery cells; by ensuring that the ionic conductivity of the electrolyte is not greater than 18 mS / cm, it helps to keep the viscosity of the electrolyte low and reduce the impact on the fluidity of the electrolyte.

[0101] In the above scheme, by making the ionic conductivity σ of the electrolyte not less than 10 mS / cm and not greater than 18 mS / cm, the electrolyte with high conductivity can improve the lithium-ion diffusion rate, reduce the diffusion resistance of lithium-ions in the porous electrode, and thus improve the power performance of the battery cell.

[0102] Specifically, the ionic conductivity of the electrolyte can be 10 mS / cm, 12 mS / cm, 14.6 mS / cm, 16.5 mS / cm, 17.2 mS / cm, 18 mS / cm or any value within the above range.

[0103] In some embodiments, the volume average particle size Dv50 of the positive electrode active material 1 Satisfies: 4μm≤Dv50 1 ≤11μm.

[0104] Dv50 can refer to the particle size at which the cumulative particle size distribution number (DV50) of a sample reaches 50%, meaning that particles smaller than DV50 account for 50% of the total particle size distribution. Here, Dv50... 1 This is to distinguish it from the Dv50 of other materials below, representing the volume average particle size of different substances.

[0105] In Dv50 1 When the particle size is greater than or equal to 4 μm, the risk of agglomeration between positive electrode active materials can be reduced, which is beneficial for a more uniform distribution of the positive electrode active material in the positive electrode film layer; in Dv50 1When the diameter is less than or equal to 11 μm, the path length for lithium ions to escape from the positive electrode is more suitable, which is conducive to the extraction of lithium ions and thus helps to improve the long-term cycle performance of the battery cell.

[0106] In the above scheme, by making the volume average particle size of the positive electrode active material between 4μm and 11μm, the diffusion path of lithium ions can be reduced, thereby improving the power performance of the battery cell.

[0107] Specifically, the volume average particle size Dv50 of the positive electrode active material 1 It can be 4μm, 6μm, 8.5μm, 9.4μm, 11μm or any value within the above range.

[0108] In some embodiments, the specific surface area S of the positive electrode active material 1 Satisfy: 10m 2 / g≤S 1 ≤14.5m 2 / g.

[0109] Specific surface area (Brunauer-Emmett-Teller, BET) refers to the total surface area per unit mass of material. Here, S... 1 This is to distinguish it from the S in the other materials below, representing the specific surface area of ​​different substances.

[0110] When the specific surface area of ​​the positive electrode active material is not less than 10m² 2 At a specific surface area of ​​1 / g, it has more active sites, providing more transport pathways for lithium ions. When the specific surface area of ​​the positive electrode active material is no greater than 14.5 m² / g... 2 At a ratio of / g, the positive electrode active material and the electrolyte have a reasonable contact area, which will not increase the interfacial resistance and affect the lithium ion transport efficiency.

[0111] In the above scheme, the specific surface area of ​​the positive electrode active material is made to be 10m². 2 / g-14.5m 2 Reaching a value between / g can increase the interfacial reaction current density, which helps to further improve the power performance of individual battery cells.

[0112] In some implementations, the tap density TD of the positive electrode active material 1 Satisfy: TD 1 ≥0.75g / cm 3 .

[0113] Tap density refers to the density of a powder material after it has been tapped under certain conditions. It is a parameter used to measure the maximum density that a powder material can achieve after being vibrated in its natural packed state.

[0114] When the tap density of the positive electrode active material is greater than or equal to 0.75 g / cm³ 3 This can increase the density of the positive electrode film and increase the content of active materials per unit volume, thereby improving the mechanical strength, conductivity and energy density of the positive electrode film.

[0115] In the above scheme, by keeping the tap density of the positive electrode active material within the above range, the positive electrode active material within this range helps to improve the density of the positive electrode film, making the positive electrode sheet more compact, and helps to improve the mechanical strength and conductivity of the positive electrode active material.

[0116] In some embodiments, the general formula for lithium phosphate is Li a Fe 1-x-y Mn x M y PO4; wherein 0.6≤a≤1.1, 0≤x≤1, 0≤y≤0.1, and M is selected from at least one of the transition metal elements other than Fe and Mn, as well as non-transition metal elements.

[0117] It should be noted that during the charging and discharging process of the battery, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li at different discharge states. In the examples of positive electrode active materials in this application, the molar contents of Li refer to 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 will change after charge-discharge cycles.

[0118] Similarly, in the examples of positive electrode active materials in the embodiments of this application, the molar content of O is only a theoretical state value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change. In the actual charging and discharging process of the battery, the molar content of O will fluctuate.

[0119] In some embodiments, the lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their modified compounds.

[0120] In the above scheme, using at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate and their modified compounds as the positive electrode active material of the battery cell helps to improve the energy density of the battery cell.

[0121] In some embodiments, the battery cell further includes a negative electrode sheet; the negative electrode sheet includes a negative current collector and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the negative current collector.

[0122] The negative electrode film layer has two opposing surfaces along its own thickness direction. The negative electrode film layer can be disposed on one surface of the negative electrode current collector, or on both surfaces of the negative electrode current collector.

[0123] The negative electrode film layer includes conductive carbon, and the graphitization degree I of the conductive carbon is... D / I G Satisfy: 0.1≤I D / I G ≤0.5.

[0124] Graphitization degree refers to the degree of order in the graphite crystal structure of a material. High graphitization degree means that the carbon atoms in the material are more ordered, forming a more ordered graphite crystal structure. Materials with higher graphitization degree have more direct electron transport paths and better electrical conductivity, which helps to improve the overall conductivity of the battery cell, reduce internal resistance, and reduce the extraction and insertion of lithium ions in the material, thereby helping to improve the power performance and rate performance of the battery cell. In addition, materials with high graphitization degree have smoother and flatter surfaces, which can reduce the number of surface defects. These surface defects are the parts where side reactions occur between the electrolyte and the material, which helps to improve the stability of the battery cell.

[0125] In the above methods for measuring graphitization degree, I D and I G These are the intensity values ​​of the material at the D peak and the G peak, respectively, in the Raman test.

[0126] When the graphitization degree of conductive carbon in the negative electrode film layer is not less than 0.1, it helps to improve the conductivity of the battery cell and reduce side reactions. When the graphitization degree of conductive carbon in the negative electrode film layer is not greater than 0.5, it can avoid the formation of a thick SEI film during the charging and discharging process of the battery cell, avoid excessive consumption of active lithium ions, and reduce the impact on the cycle life of the battery cell.

[0127] In the above scheme, graphitized conductive carbon is added to the negative electrode film layer, and the degree of graphitization of the conductive carbon is I. D / I G Between 0.1 and 0.5, graphitized conductive carbon can form an ordered conductive network, improving conductivity and thus enhancing the power performance of the battery cell. On the other hand, graphitized conductive carbon can reduce the catalytic sites on the surface of the conductive carbon, thereby reducing side reactions at the negative electrode and further improving the stability of the battery cell.

[0128] Specifically, the graphitization degree I of the carbon material in the negative electrode film layer D / I G It can be 0.1, 0.19, 0.25, 0.33, 0.48, 0.5 or any value within the above range.

[0129] In some embodiments, the volume average particle size Dv50 of the conductive carbon 2 Satisfies: 10μm≤Dv50 2 ≤20μm.

[0130] In Dv502 With a particle size greater than or equal to 0.1 μm, the risk of agglomeration between conductive carbon particles can be reduced, which is beneficial for a more uniform distribution of conductive carbon in the negative electrode film; in Dv50 2 When the carbon thickness is less than or equal to 20 μm, it can form a continuous conductive network, which is beneficial for reducing the overall conductivity of the negative electrode and improving the power performance of the battery cell.

[0131] In the above scheme, by making the volume average particle size of conductive carbon within the above range, it can be better dispersed in the negative electrode active material to form a dense conductive network and improve the overall conductivity of the negative electrode sheet. In addition, conductive carbon with a particle size within the above range does not affect the viscosity and flowability of the negative electrode slurry, thereby helping to improve the coating uniformity of the slurry and the density of the negative electrode film.

[0132] Specifically, the volume average particle size of conductive carbon is Dv50. 2 It can be 10μm, 12.2μm, 15.4μm, 16.7μm, 18.2μm, 19μm, 20μm or any value within the above range.

[0133] In some embodiments, the specific surface area S of the conductive carbon 2 Satisfy: 60m 2 / g≤S 2 ≤70m 2 / g.

[0134] When the specific surface area of ​​conductive carbon is not less than 60m² 2 At a specific surface area of ​​ / g, firstly, it has more active sites, providing more conductive paths and improving the conductivity of the negative electrode; secondly, materials with higher specific surface areas exhibit better dispersion in the negative electrode film. When the specific surface area of ​​conductive carbon is no greater than 70m², 2 At / g, the conductive carbon and the electrolyte have a reasonable contact area, which will not increase the interface resistance and affect the lithium ion transport efficiency.

[0135] In the above scheme, by keeping the specific surface area of ​​conductive carbon within the above range, it helps to improve the conductivity and material dispersion of the negative electrode film, and can also improve the electrochemical stability of the battery cell.

[0136] Specifically, the specific surface area S of conductive carbon 2 It can be 60m 2 / g、62m 2 / g, 64.5m 2 / g、66m 2 / g, 68.5m 2 / g、70m 2 / g or any value within the above range.

[0137] In some embodiments, the conductive carbon includes at least one of conductive carbon black, Ketjen black, and acetylene black.

[0138] In the above scheme, graphitized conductive carbon is added to the negative electrode film layer to improve the conductivity of the negative electrode sheet and enhance the power performance of the battery cell. By including at least one of conductive carbon black, Ketjen black, and acetylene black, which are readily available and relatively inexpensive, it is beneficial for their widespread application in production.

[0139] In some embodiments, the negative electrode film layer further includes a negative electrode active material; the volume average particle size of the negative electrode active material is Dv50. 3 Satisfies: 5.2μm≤Dv50 3 ≤8.2μm.

[0140] In the above scheme, by making the volume average particle size of the negative electrode active material between 5.2μm and 8.2μm, the smaller particle size of the negative electrode active material can reduce the diffusion path of lithium ions and help improve the power performance of the battery cell.

[0141] Specifically, the volume average particle size Dv50 of the negative electrode active material 3 It can be 5.2μm, 6.1μm, 6.5μm, 7.2μm, 7.8μm, 8.2μm or any value within the above range.

[0142] In some embodiments, the specific surface area S of the negative electrode active material 3 Meets the requirement of 1.4m 2 / g≤S 3 ≤2m 2 / g.

[0143] When the specific surface area S of the negative electrode active material 3 Greater than or equal to 1.4m 2 At a specific surface area of ​​ / g, the extraction and insertion rates of lithium ions can be increased, improving the rate performance and cycle stability of the battery; when the specific surface area S of the negative electrode active material is... 3 Less than or equal to 2m 2 When the concentration is / g, the possibility of agglomeration of the negative electrode active material can be reduced, thus avoiding affecting the uniformity and consistency of the negative electrode film.

[0144] In the above scheme, the specific surface area of ​​the negative electrode active material affects the stability of the SEI film. By maintaining the specific surface area of ​​the negative electrode active material at 1.4 m², [the stability of the SEI film is improved]. 2 / g-2m 2 The ratio between / g helps to form a more stable SEI film, thereby further improving the stability of the battery cell.

[0145] Specifically, the specific surface area S of the negative electrode active material 3It can be 1.4m 2 / g, 1.52m 2 / g, 1.65m 2 / g, 1.71m 2 / g, 1.88m 2 / g、2m 2 / g or any value within the above range.

[0146] In some implementations, the tap density TD of the negative electrode active material 2 Satisfying: 0.8g / cm 3 ≤TD 2 ≤1.2g / cm 3 .

[0147] When the tap density of the negative electrode active material is greater than or equal to 0.8 g / cm³ 3 This can increase the density of the negative electrode film and the content of active material per unit volume, thereby improving the mechanical strength, conductivity, and energy density of the battery. When the tap density of the negative electrode active material is less than or equal to 1.2 g / cm³... 3 The negative electrode film has a suitable porosity, which is conducive to the penetration of electrolyte and the contact area between electrolyte and negative electrode active material, thereby improving the lithium ion transport efficiency.

[0148] In the above scheme, by making the tap density of the negative electrode active material within the above range, the negative electrode active material within this range helps to improve the density of the negative electrode film, making the negative electrode sheet more compact, and helping to improve the mechanical strength and conductivity of the negative electrode sheet.

[0149] Specifically, the tap density of the negative electrode active material can be 0.8 g / cm³. 3 0.86 g / cm 3 0.95g / cm 3 1.08g / cm 3 1.14 g / cm 3 1.2g / cm 3 Or any value within the above range.

[0150] In some embodiments, the battery cell further includes a separator, the porosity of which is... satisfy:

[0151] A separator with appropriate porosity ensures that the electrolyte fully penetrates into it, thereby increasing the contact area between the electrolyte and the positive and negative electrode active materials and promoting lithium-ion transport. Furthermore, a separator with suitable porosity helps improve the lithium-ion conductivity, reduce the internal resistance of individual battery cells, and enhance the battery's rate performance.

[0152] In the above-mentioned scheme, by keeping the porosity of the separator within the above-mentioned range, it helps to promote the transport of lithium ions and improve the lithium ion conduction rate, thereby improving the performance of the battery cell.

[0153] Specifically, the porosity of the separator It can be 35%, 38.5%, 42%, 45%, 50%, 55%, or any value within the above range.

[0154] In some embodiments, the spacer includes a substrate and a modified layer disposed on both sides of the substrate; the modified layer includes an unsaturated silane compound.

[0155] Unsaturated silanes are a class of silane compounds containing unsaturated bonds (such as double or triple bonds). These compounds typically have one or more unsaturated carbon-carbon bonds (such as C=C or C≡C) and one or more silicon-oxygen bonds (Si-O).

[0156] The fluorinated carbonates in the first additive will generate hydrogen fluoride during the cycling of the battery cell. Unsaturated silane compounds usually contain alkoxy groups (such as methoxy or ethoxy groups), which can undergo hydrolysis in water or acidic environments to generate silanols and the corresponding alcohols (such as methanol or ethanol).

[0157] In the above scheme, by including a modified layer of unsaturated silane compound on the separator, the unsaturated silane compound can react with hydrogen fluoride to generate a stable compound, reducing the adverse effects of hydrogen fluoride on the battery cell and helping to comprehensively improve the stability of the battery cell.

[0158] In some embodiments, the unsaturated silane compound includes at least one of vinylsilane, allylsilane, and ethynylsilane.

[0159] In the above scheme, vinylsilane, allylsilane, and ethynylsilane are readily available, and using at least one of them in the separator of the battery cell can reduce the production cost of the battery cell.

[0160] In some embodiments, the unsaturated silane compound includes at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

[0161] In the above scheme, by using at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane as a modified layer material coated on the substrate of the separator, the stability of the battery cell can be improved.

[0162] In some implementations, the mass content w of the unsaturated silane compound is based on the total mass of the modified layer. 3 Satisfy: 1% ≤ w3 ≤10%.

[0163] In the above-described scheme, in the embodiments of this application, unsaturated silane compounds are used to neutralize the acidic products generated by lithium bis(fluorosulfonyl)imide in the second additive. By making the unsaturated silane compound account for 1%-10% of the mass ratio of the modified layer, it helps to further improve the stability of the battery cell.

[0164] Specifically, based on the total mass of the modified layer, the mass content w of the unsaturated silane compound is... 3 It can be 1%, 2.7%, 3.8%, 5.2%, 7.5%, 10%, or any value within the above range.

[0165] Figure 2 is a conductivity test diagram of the insulating member according to an embodiment of this application. As shown in Figure 2, when the insulating member with the modified layer is compared with the base group, the conductivity of the two is almost the same. That is to say, setting the modified layer on the insulating member substrate does not affect the conductivity of the insulating member.

[0166] Figure 3 is a thermogravimetric analysis (TGA) curve of the isolation component according to an embodiment of this application. As shown in Figure 3, when the isolation component with the modified layer is compared with the base group, the TGA curves of the two are almost the same. That is to say, setting the modified layer on the isolation component substrate does not affect the stability of the isolation component.

[0167] It should be noted that the base group in Figures 2 and 3 refers to the 16μm polypropylene spacer without the modified layer.

[0168] In some implementations, the thickness h of the spacer satisfies: 5μm≤h≤18μm.

[0169] In the above scheme, the thickness of the separator affects the battery performance. By keeping the separator thickness between 5μm and 18μm, short circuits in individual battery cells can be prevented, thus improving the safety performance of the individual cells. On the other hand, while ensuring electrolyte penetration, internal resistance can be reduced, thereby improving the power performance and rate performance of the individual battery cells.

[0170] Specifically, the thickness h of the separator can be 5μm, 8.5μm, 9.4μm, 11.5μm, 13.6μm, 15.5μm, 18μm or any value within the above range.

[0171] The embodiments of this application do not impose any particular restrictions on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape.

[0172] Figure 4 is a schematic diagram of a battery cell according to one embodiment of this application. For example, as shown in Figure 4, the battery cell 3 is a square battery cell. The battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33 disposed in the housing 31.

[0173] The electrode assembly 33 can be made from the positive electrode 1, the negative electrode and the separator by a winding process or a stacking process.

[0174] The end cap assembly 32 includes electrode terminals 322, as shown in FIG4. The end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0175] The battery cell 3 also includes a current collector 34, which is used to connect the tab 331 of the electrode assembly 33 and the electrode terminal 322. For example, in the case of a positive electrode in this embodiment, one current collector 34 is used to connect the tab of the positive electrode and the positive electrode terminal, and another current collector 34 is used to connect the tab of the negative electrode and the negative electrode terminal.

[0176] In some embodiments, the battery cell 3 includes an electrode assembly 33, which includes an electrode assembly body 330 and a tab 331 extending from the electrode assembly body 330.

[0177] In some embodiments, the battery cell 3 can be assembled into a battery module, and the number of battery cells 3 contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0178] [Positive electrode plate]

[0179] As described above, the positive electrode current collector has two opposing surfaces along its thickness direction. The positive electrode film layer can be disposed on one surface of the positive electrode current collector or on both surfaces of the positive electrode current collector.

[0180] The positive electrode current collector can be a metal foil or a composite positive electrode current collector. For example, the positive electrode current collector can be an aluminum foil.

[0181] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0182] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0183] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0184] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0186] [Negative electrode plate]

[0187] As described above, the negative electrode current collector has two opposing surfaces along its thickness direction. The negative electrode film layer can be disposed on one surface of the negative electrode current collector or on both surfaces.

[0188] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0189] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0190] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0191] As described above, in some embodiments, the negative electrode film may optionally include conductive carbon. The conductive carbon may be selected from at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0192] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0193] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive carbon, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0194] [Electrolytes]

[0195] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0196] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt, a solvent, and additives.

[0197] As described above, the additives include a first additive and a second additive, wherein the first additive includes fluorocarbonate and the second additive includes lithium fluorosulfonylimide.

[0198] Electrolyte salts may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0199] Solvents may include one or more of the following: ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0200] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and performance additives that can improve certain battery performance, such as performance additives that improve battery overcharge performance, battery high temperature or low temperature performance, etc.

[0201] [Isolation Component]

[0202] As described above, the separator includes a substrate and a modified layer.

[0203] This application does not impose any particular restrictions on the type of spacer substrate. Any well-known porous structure spacer with good chemical and mechanical stability can be selected as the spacer substrate in the embodiments of this application.

[0204] The substrate material can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The spacer substrate can be a single-layer film or a multi-layer composite film, without particular restrictions. When the spacer substrate is a multi-layer composite film, the materials of each layer can be the same or different, without particular restrictions.

[0205] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0206] [Battery]

[0207] This application provides a battery, including the battery cells described in the above embodiments. The battery cells can be battery cells after formation and aging processes. Figure 5 is a schematic diagram of a battery according to an embodiment of this application. As shown in Figure 5, the battery 5 may include multiple battery cells 3 (not shown in the figure).

[0208] Battery cells 3 can be directly assembled into battery 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into battery 5.

[0209] [Electrical appliances]

[0210] This application provides an electrical device, including the battery described in the above embodiments.

[0211] In some embodiments, the electrical device includes an energy storage device or a heavy-duty truck. Energy storage devices and heavy-duty trucks have high requirements for the lifespan and long-term cycle performance of battery cells. Applying battery cells to the aforementioned electrical devices can improve the lifespan of the electrical devices.

[0212] Electrical devices can also be lighting devices, spacecraft, etc., and the embodiments of this application include, but are not limited to, these.

[0213] Figure 6 is a schematic diagram of an electrical device according to an embodiment of this application. As shown in Figure 6, this application provides an electrical device, which is a heavy-duty truck 6. The battery in the heavy-duty truck 6 can be replaced by a battery swapping device to replace the battery with insufficient power with a fully charged battery.

[0214] Figure 7 is a schematic diagram of an electrical device according to an embodiment of this application. As shown in Figure 7, this application provides an electrical device, which is an energy storage device 7, and the energy storage device 7 may include multiple batteries 5. The energy storage device 7 can be applied to a power storage station to store and release electrical energy.

[0215] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0216] [Examples and Comparative Examples]

[0217] [Example 1]

[0218] (1) Preparation of the positive electrode sheet: Lithium iron phosphate, conductive carbon black, carbon nanotubes, polyvinylidene fluoride, and flexible dispersant were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 93.4%:3.5%:0.5%:2.3%:0.3% and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on two opposite surfaces of the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet. The Dv50 of lithium iron phosphate was... 1 It has a diameter of 8.6 μm and a specific surface area of ​​S. 1 It is 12.5m 2 / g, tap density TD 1 1.6 g / cm 3 .

[0219] (2) Preparation of the negative electrode sheet: Artificial graphite, graphitized conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) were dissolved in deionized water at a mass ratio of 94.7%:2%:1.2%:2.1%, and thoroughly mixed to prepare a negative electrode slurry. The negative electrode slurry was coated onto the negative electrode current collector copper foil, and then dried, cold-pressed, and slit to obtain the negative electrode sheet. The graphitization degree I of the conductive carbon black was... D / I G The Dv50 of graphitized conductive carbon black is 0.36. 2 The specific surface area S of conductive carbon black is 18.4 μm. 2 It is 65.7m 2 / g, Artificial Graphite Dv50 3 It has a diameter of 6.5 μm and a specific surface area S. 3 It is 1.7m 2 / g, tap density TD 2 It is 1.02 g / cm³3 .

[0220] (3) Preparation of the separator: Vinyltrimethylsilane was dissolved in an ethanol solution to obtain a modified layer solution, wherein the mass content of vinyltrimethylsilane was 1% wt. A 16 μm polyethylene (PP) separator substrate was immersed in the modified layer solution for 4 h and then removed. It was then vacuum dried in a 60 °C oven for 12 h to remove the solvent, so as to obtain a separator with a modified layer and a substrate.

[0221] (4) Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1:1. LiPF6 and the second additive LiFSI were uniformly dissolved in the above solution, and the first additive fluoroethylene carbonate (FEC) was added. In this electrolyte, the molar concentration of LiPF6 was 1 mol / L, the molar concentration of the second additive LiFSI was 0.2 mol / L, the mass content of the first additive FEC was 0.1% wt, and the ionic conductivity of the electrolyte was 14 mS / cm.

[0222] (5) Preparation of battery cell: The above positive electrode, separator and negative electrode are stacked and wound in sequence to obtain electrode assembly; the electrode assembly is placed in outer packaging, the electrolyte prepared above is added, and after encapsulation, standing, formation and aging processes, battery cell is obtained.

[0223] [Example 2]

[0224] The difference between Example 2 and Example 1 is that the first additive in Example 2 is ethyl trifluoroethyl carbonate.

[0225] [Example 3]

[0226] The difference between Example 3 and Example 1 is that the first additive in Example 3 is vinyl sulfate.

[0227] [Example 4]

[0228] The difference between Example 4 and Example 1 is that the mass content of the first additive in Example 4 is 0.4%.

[0229] [Example 5]

[0230] The difference between Example 5 and Example 1 is that the molar concentration of the second additive in Example 5 is 0.5 mol / L.

[0231] [Example 6]

[0232] The difference between Example 6 and Example 1 is that conductive carbon is not provided in the negative electrode film layer in Example 6.

[0233] [Example 7]

[0234] The difference between Example 7 and Example 1 is that the conductive carbon in the negative electrode film layer in Example 7 is normal conductive carbon black with a graphitization degree of 1.14.

[0235] [Example 8]

[0236] The difference between Example 8 and Example 1 is that the degree of graphitization I of the conductive carbon in the negative electrode film layer in Example 8 is... D / I G It is 0.05.

[0237] [Example 9]

[0238] The difference between Example 9 and Example 1 is that no modified layer is provided in the isolation component in Example 9.

[0239] [Example 10]

[0240] The difference between Example 10 and Example 1 is that the unsaturated silane compound in Example 10 is tetravinylsilane.

[0241] [Example 11]

[0242] The difference between Example 11 and Example 1 is that the second additive in Example 11 is lithium bis(trifluoromethanesulfonylimide) (LiTFSI).

[0243] [Comparative Example 1]

[0244] The difference between Comparative Example 1 and Example 9 is that the electrolyte of Comparative Example 1 does not contain the first additive and the second additive.

[0245] [Comparative Example 2]

[0246] The difference between Comparative Example 2 and Example 9 is that the electrolyte of Comparative Example 2 does not contain a second additive.

[0247] [Comparative Example 3]

[0248] The difference between Comparative Example 3 and Example 9 is that the electrolyte of Comparative Example 3 does not contain the first additive. Table 1 shows the specific parameters of Examples 1-11 and Comparative Examples 1-3.

[0249] The following is a brief description of the testing methods for the physicochemical parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0250] 1. Electrolyte composition measurement: The composition of the electrolyte can be directly measured and analyzed using an inductively coupled plasma mass spectrometer, in accordance with the HG / T4067-2015 standard.

[0251] 2. Measurement of ionic conductivity of electrolyte: The electrolyte can be measured using a conductivity meter in accordance with the HG / T4067-2015 standard.

[0252] 3. Measurement of material graphitization degree: The intensity at the D and G peaks of the material was measured using a Raman spectroscopy instrument, and I was calculated. D / I G The ratio of the graphitization value indicates the degree of graphitization of the material.

[0253] 4. Measurement of the volume average particle size Dv50 of the material: This can be determined by measuring the volume average particle size of the raw materials used in preparation. As an example, the volume average particle size Dv50 can be measured using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. Alternatively, the volume average particle size can be calculated by observing the surface of the material using a scanning electron microscope, taking a specific area, and estimating the size and number of particles observed within that area.

[0254] 5. Measurement of specific surface area of ​​materials: The specific surface area of ​​materials can be measured by gas adsorption BET method, referring to the GB / T19587-2017 standard.

[0255] 6. Measurement of material tap density: Refer to GB / T5162-2006 standard. Place a certain amount of material in a container and vibrate it using a vibrating device until the material's volume no longer decreases. Divide the material's mass by the vibrated volume to obtain the material's tap density.

[0256] 7. Measurement of the porosity of the separator: Weigh the dry separator to the mass m1. Completely immerse the separator in anhydrous ethanol for a certain period of time, then quickly remove it. Gently wipe the surface of the separator with filter paper to remove any remaining anhydrous ethanol, and then weigh the separator again to the mass m2. Calculate the porosity of the separator using ((m2-m1) / ρ) / (ρm2+(ρ-ρ0)m1)×100%. Where ρ and ρ0 are the densities of the separator and anhydrous ethanol, respectively.

[0257] The following is a brief description of the testing methods for the performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0258] 1. Measurement of the internal resistance (DCR) of a single battery cell: At 25℃, after standing for 5 minutes, charge the single battery cell at 1C constant current and constant voltage to a voltage of 3.65V, and let it stand for 1 hour; then discharge it at 0.33C constant current to 2.5V, and let it stand for 2 hours to obtain the capacity C0. Charge it at 1C constant current and constant voltage to a voltage of 3.65V, and let it stand for 1 hour; then discharge it at 1C0 constant current for 0.5 hours, and let it stand for 2 hours. Adjust it to 50% SOC, and discharge it at a current of 10C0 for 10 seconds. Record the voltage drop U0 during the process, and calculate the internal resistance R = U0 / 10C0.

[0259] For the battery cells of Examples 1-11 and Comparative Examples 1-3 above, the internal resistance values ​​before and after 200 cycles were tested respectively. The DCR growth rate of the battery cell can be calculated according to the following formula: DCR growth rate = (DCR after 200 cycles - initial DCR) / initial DCR × 100%.

[0260] 2. Cycle performance test of individual battery cells: Adjust the oven temperature to 25℃, place the individual battery cells in the oven and let them stand for 60 minutes; charge at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V with a cutoff current of 0.05C (100% SOC), and then let them stand for 10 minutes; then discharge at 1C to 2.5V, and record the discharge capacity of this step as C0, and let them stand for 10 minutes; adjust the oven temperature to 45℃ and let them stand for 60 minutes, then charge the prepared individual battery cells at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V with a cutoff current of 0.05C (100% SOC), and then let them stand for 10 minutes; then discharge at 1C to 2.5V, and record the discharge capacity of this step as Cn. This is one charge-discharge cycle. The capacity retention rate of the individual battery cell = Cn / C0 × 100%. The lithium-ion battery was charged and discharged using this method until it reached 200 cycles. The capacity retention rate at this point was recorded. Detailed test results are shown in Table 2. Table 2: Performance parameters of Examples 1-11 and Comparative Examples 1-3.

[0261] In the embodiments of this application, the DCR test can reflect the relative magnitude of the SEI film impedance, and the rate performance of the battery cell can be obtained based on the magnitude of the SEI film impedance. That is, the larger the DCR value, the larger the relative SEI film impedance, and the worse the power performance of the battery cell; the smaller the DCR value, the smaller the relative SEI film impedance, and the better the power performance of the battery cell.

[0262] As can be seen from Examples 1-11 and Comparative Examples 1-3, by adding the first additive and the second additive to the electrolyte, the magnitude of the SEI film impedance can be reduced and the growth rate of the SEI film impedance can be slowed down, and side reactions can be reduced to improve cycle performance, so that the battery cell can achieve both long cycle performance and good power performance.

[0263] As can be seen from Examples 1-3, different types of first additives can reduce the value of SEI membrane impedance and slow down the growth rate of SEI membrane impedance, reduce side reactions and improve cycle performance.

[0264] As can be seen from Examples 1 and 4, by maintaining the mass content of the first additive at 0.01%-0.2%, it is beneficial to further reduce the value of the SEI film impedance and further reduce the growth rate of the SEI film impedance, which helps to further improve the power performance of the battery.

[0265] As can be seen from Examples 1 and 5, maintaining the molar concentration of the first additive between 0.1 mol / L and 0.4 mol / L is beneficial for further reducing the value of the SEI film impedance and further reducing the growth rate of the SEI film impedance, which helps to further improve the power performance of the battery.

[0266] As can be seen from Examples 1 and 6-8, by adding conductive carbon to the negative electrode film layer, and the degree of graphitization of the conductive carbon being 0.1-0.5, the growth rate of SEI film impedance can be further reduced.

[0267] As can be seen from Examples 1 and 9, by setting a modified layer on the separator, it is beneficial to further improve the cycle performance of the battery.

[0268] As can be seen from Examples 1 and 10, different modified layer materials all contribute to improving the cycle performance of the battery.

[0269] As can be seen from Examples 1 and 11, the addition of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide as a second additive to the electrolyte can improve the stability of the battery cell, thereby reducing the rate of increase in the internal resistance of the battery cell and improving the cycle performance of the battery.

[0270] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: Positive electrode and electrolyte; The positive electrode includes a positive current collector and a positive electrode film layer, the positive electrode film layer being disposed on at least one side of the positive current collector, and the positive electrode film layer including a positive electrode active material; in, The positive electrode active material includes lithium phosphate, and the electrolyte includes a first additive and a second additive. The first additive includes fluorocarbonate, and the second additive includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

2. The battery cell according to claim 1, characterized in that, The fluorocarbonate includes at least one of cyclic fluorocarbonate or chain fluorocarbonate.

3. The battery cell according to claim 2, characterized in that, The cyclic fluorocarbonate includes fluoroethylene carbonate, and the chain fluorocarbonate includes ethyl trifluoroethyl carbonate.

4. The battery cell according to any one of claims 1-3, characterized in that, Based on the total mass of the electrolyte, the mass content of the first additive w 1 Satisfy: 0.01% ≤ w 1 ≤0.2%.

5. The battery cell according to any one of claims 1-3, characterized in that, Based on the total mass of the electrolyte, the mass content of the second additive w 2 Satisfy: 1% ≤ w 2 ≤4%.

6. The battery cell according to any one of claims 1-5, characterized in that, The ionic conductivity σ of the electrolyte satisfies: 10 mS / cm ≤ σ ≤ 18 mS / cm.

7. The battery cell according to any one of claims 1-6, characterized in that, The positive electrode active material has a volume average particle size Dv50 1 Satisfies: 4μm≤Dv50 1 ≤11μm.

8. The battery cell according to any one of claims 1-7, characterized in that, The specific surface area S of the positive electrode active material 1 Satisfy: 10m² / g ≤ S 1 ≤14.5m2 / g.

9. The battery cell according to any one of claims 1-8, characterized in that, The tap density TD of the positive electrode active material 1 Satisfy: TD 1 ≥0.75g / cm3.

10. The battery cell according to any one of claims 1-9, characterized in that, The general formula of the lithium phosphate is Li a Fe 1-x-y Mn x M y PO4; Wherein, 0.6≤a≤1.1, 0≤x≤1, 0≤y≤0.1, and M is selected from at least one of the transition metal elements other than Fe and Mn, as well as non-transition metal elements.

11. The battery cell according to any one of claims 1-10, characterized in that, The lithium-containing phosphate includes at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their modified compounds.

12. The battery cell according to any one of claims 1-11, characterized in that, The battery cell also includes a negative electrode sheet; The negative electrode sheet includes a negative current collector and a negative electrode film layer, the negative electrode film layer being disposed on at least one side of the negative current collector, and the negative electrode film layer including conductive carbon; The degree of graphitization I of the conductive carbon D / I G Satisfy: 0.1≤I D / I G ≤0.

5.

13. The battery cell according to claim 12, characterized in that, The conductive carbon has a volume average particle size Dv50 2 Satisfies: 10μm≤Dv50 2 ≤20μm.

14. The battery cell according to claim 12 or 13, characterized in that, The specific surface area S of the conductive carbon 2 Satisfy: 60m 2 / g≤S 2 ≤70m 2 / g.

15. The battery cell according to any one of claims 12-14, characterized in that, The conductive carbon includes at least one of conductive carbon black, Ketjen black, and acetylene black.

16. The battery cell according to any one of claims 12-15, characterized in that, The negative electrode film layer also includes a negative electrode active material; The negative electrode active material has a volume average particle size Dv50 3 Satisfies: 5.2μm≤Dv50 3 ≤8.2μm.

17. The battery cell according to claim 16, characterized in that, The specific surface area S of the negative electrode active material 3 Meets the requirement of 1.4m 2 / g≤S 3 ≤2m 2 / g.

18. The battery cell according to claim 16 or 17, characterized in that, The tap density TD of the negative electrode active material 2 Satisfying: 0.8g / cm 3 ≤TD 2 ≤1.2g / cm 3 .

19. The battery cell according to any one of claims 1-18, characterized in that, The battery cell also includes a separator, the porosity of which is... satisfy:

20. The battery cell according to claim 19, characterized in that, The insulating element includes a substrate and a modified layer, wherein the modified layer is disposed on both sides of the substrate; The modified layer comprises unsaturated silane compounds.

21. The battery cell according to claim 20, characterized in that, The unsaturated silane compound includes at least one of vinylsilane, allylsilane, and ethynylsilane.

22. The battery cell according to claim 20 or 21, characterized in that, The unsaturated silane compound includes at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, and vinyltrimethylsilane.

23. The battery cell according to any one of claims 20-22, characterized in that, Based on the total mass of the modified layer, the mass content w of the unsaturated silane compound is... 3 Satisfy: 1% ≤ w 3 ≤10%.

24. The battery cell according to any one of claims 20-23, characterized in that, The thickness h of the isolation element satisfies: 5μm≤h≤18μm.

25. An electrical appliance, characterized in that, include: The battery cell according to any one of claims 1-24.

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