Battery cell, battery apparatus and electrical device

Abstract

A battery cell, a battery apparatus and an electrical device. The battery cell comprises: a positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material which comprises a lithium-containing phosphate, and the mass content of lithium in the positive electrode film layer of the battery cell at 0% SOC is 3.9% to 4.3%; and a negative electrode sheet, comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector. In a first direction of the negative electrode sheet, the edge of the negative electrode film layer extends beyond the edge of the positive electrode film layer; the negative electrode film layer comprises a middle region and an edge region; in the first direction, the edge region is located on at least one side of the middle region; the middle region comprises a first negative electrode active material, and the edge region comprises a second negative electrode active material, the specific capacity of the second negative electrode active material being greater than the specific capacity of the first negative electrode active material. Thus, the present application can reduce the risk of lithium plating in the edge region while balancing the cycle performance and energy density of the battery cell.

Description

Battery cells, battery devices, electrical equipment Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery cell, a battery device, and an electrical appliance. Background Technology

[0002] 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.

[0003] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, lifespan, capacity, fast charging performance, and reliability. How to reduce the risk of lithium plating on the negative electrode in a single battery cell and improve the cycle performance of the battery cell while maintaining energy density is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell with a lower risk of lithium plating and better cycle performance and energy density.

[0005] To achieve the above objectives, this application provides a battery cell, a battery device, and an electrical appliance.

[0006] In a first aspect, a battery cell is provided, comprising: a positive electrode and a negative electrode; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, the negative electrode includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector, the edge of the negative electrode film layer extending beyond the edge of the positive electrode film layer along a first direction of the negative electrode, wherein the positive electrode film layer includes a positive active material, the positive active material includes a lithium phosphate, and the lithium content in the positive electrode film layer at 0% SOC of the battery cell is 3.9% to 4.3% by mass; the negative electrode film layer includes a middle region and an edge region, the edge region being located on at least one side of the middle region along the first direction, the middle region including a first negative active material, the edge region including a second negative active material, and the specific capacity of the second negative active material being greater than the specific capacity of the first negative active material.

[0007] In this embodiment, the edge of the negative electrode film extends beyond the edge of the positive electrode film, which helps reduce the risk of lithium plating in the negative electrode film. The positive electrode active material includes lithium iron phosphate, and the mass content of lithium in the positive electrode film at 0% SOC of the battery cell is 3.9% to 4.3%, which helps improve the cycle performance of the battery cell while maintaining a high energy density. The negative electrode film includes a middle region and an edge region. Along the first direction, the edge region is located on at least one side of the middle region. The middle region includes a first negative electrode active material, and the edge region includes a second negative electrode active material. The specific capacity of the second negative electrode active material is greater than that of the first negative electrode active material. Thus, the edge region can accommodate more lithium ions than the middle region, which can compensate for the increased risk of lithium plating in the edge region due to the excessively high mass content of lithium in the positive electrode film. This helps reduce the risk of lithium plating in the edge region and thus helps improve the cycle performance of the battery cell.

[0008] In some embodiments, the specific capacity of the first negative electrode active material is 330 mAh / g to 350 mAh / g. When the specific capacity of the first negative electrode active material is greater than or equal to 330 mAh / g, the middle region of the negative electrode film has a suitable capacity and can store a suitable number of lithium ions, which is compatible with the mass content of lithium in the positive electrode film. This helps to reduce the risk of lithium plating in the middle region, thereby improving the cycle performance of the battery cell. When the specific capacity of the first negative electrode active material is less than or equal to 350 mAh / g, it can be compatible with the mass content of lithium in the positive electrode film, reducing the waste of capacity in the middle region.

[0009] In some embodiments, the specific capacity of the first negative electrode active material is 340 mAh / g to 350 mAh / g. This is beneficial for improving the cycle performance of the battery cell.

[0010] In some embodiments, the specific capacity of the second negative electrode active material is between 340 mAh / g and 400 mAh / g. When the specific capacity of the second negative electrode active material is greater than or equal to 340 mAh / g, it is beneficial to reduce the risk of lithium plating in the edge region, thereby improving the cycle performance of the battery cell; when the specific capacity of the second negative electrode active material is less than or equal to 400 mAh / g, it is possible to reduce the waste of capacity in the edge region while reducing the risk of lithium plating.

[0011] In some embodiments, the specific capacity of the second negative electrode active material is between 350 mAh / g and 370 mAh / g. This is beneficial for improving the cycle performance of the battery cell.

[0012] In some embodiments, the size of the intermediate region along the first direction is 100 mm to 300 mm. This provides a suitable size for the intermediate region to be adapted to the capacity, energy density, etc., of the individual battery cells.

[0013] In some embodiments, the total size of the edge region along the first direction is 1.5 mm to 5 mm. When the total size of the edge region is greater than or equal to 1.5 mm, the edge region of the negative electrode film extends beyond the positive electrode film by a certain distance, which helps to reduce the risk of lithium plating in the edge region and improve the cycle performance of the battery cell. When the total size of the edge region is less than or equal to 5 mm, it helps to reduce the space occupied by the edge region and improve the energy density of the battery cell.

[0014] In some embodiments, the total size of the edge region is 2 mm to 3 mm. This results in better cycle performance and higher energy density for the battery cell.

[0015] In some embodiments, the first negative electrode active material comprises graphite, and the second negative electrode active material comprises graphite. Graphite thus exhibits lower expansion, which is beneficial for improving the cycle performance of the battery cell.

[0016] In some embodiments, the powder resistance of graphite in the first negative electrode active material is greater than that of graphite in the second negative electrode active material. Thus, the graphite in the second negative electrode active material has a lower resistance than the graphite in the first negative electrode active material, and the edge region is more conducive to lithium-ion transport and intercalation than the middle region, which helps reduce the risk of lithium plating in the edge region, thereby improving the cycle performance of the battery cell.

[0017] In some embodiments, under a pressure of 3T, the powder resistivity of graphite in the first negative electrode active material is 4Ω / cm to 10Ω / cm. Thus, the graphite in the first negative electrode active material has a suitable powder resistivity, the intermediate region facilitates lithium-ion transport, and the battery cell exhibits good kinetic performance.

[0018] In some embodiments, under a pressure of 3T, the powder resistivity of the graphite in the second negative electrode active material is 0.5 Ω / cm to 3.5 Ω / cm. Thus, the graphite in the second negative electrode active material has a suitable powder resistivity, the edge region facilitates lithium-ion transport, which helps reduce the risk of lithium plating at the edge region and improves the cycle performance of the battery cell.

[0019] In some embodiments, the first negative electrode active material includes graphite, and the second negative electrode active material includes graphite and silicon-based materials.

[0020] Silicon-based materials have a higher specific capacity than graphite, and can hold more lithium ions. By setting the first negative electrode active material to include graphite and the second negative electrode active material to include both graphite and silicon-based materials, the edge region can hold more lithium ions than the middle region, which helps reduce the risk of lithium plating in the edge region and improves the cycle performance of the battery cell.

[0021] In some embodiments, based on the total mass of the second negative electrode active material, the ratio of silicon mass content to carbon mass content is 0.5% to 30%. When the ratio of silicon mass content to carbon mass content is greater than or equal to 0.5% based on the total mass of the second negative electrode active material, it is beneficial to increase the capacity of the second negative electrode active material, thereby increasing the number of lithium ions that can be accommodated in the edge region, reducing the risk of lithium plating in the edge region, and thus improving the cycle performance of the battery cell. When the ratio of silicon mass content to carbon mass content is less than or equal to 30% based on the total mass of the second negative electrode active material, the silicon-based material and graphite in the edge region have a suitable mass ratio, which is beneficial to reduce the expansion of the edge region, thereby improving the cycle performance of the battery cell.

[0022] In some embodiments, the ratio of silicon content to carbon content based on the total mass of the second negative electrode active material is 1.5% to 10%. This is beneficial for improving the cycle performance of the battery cell.

[0023] In some embodiments, the ratio of the coating weight per unit area of ​​the intermediate region to the coating weight per unit area of ​​the edge region is 1.1 to 1.5. This results in a lower coating weight per unit area in the edge region, which helps to shorten the lithium-ion transport path in the edge region and reduces the risk of lithium plating in the edge region.

[0024] In some embodiments, the negative electrode sheet includes a negative electrode tab that extends beyond the negative electrode film layer along the width direction of the negative electrode sheet; the edge regions are located on both sides of the central region along the width direction of the negative electrode sheet. Thus, the edge regions on both sides extend beyond the positive electrode film layer, which helps reduce the risk of lithium plating on the negative electrode sheet.

[0025] In some embodiments, along the width direction of the negative electrode sheet, the edge region away from the negative electrode tab includes a first sub-region and a second sub-region, the first sub-region being farther away from the middle region relative to the second sub-region, and the thickness of the first sub-region being less than the thickness of the second sub-region.

[0026] In the preparation of the negative electrode sheet, a negative electrode slurry is typically first coated onto the negative electrode current collector. Then, along the width direction of the negative electrode sheet, the negative electrode current collector is cut at its midpoint (e.g., a single sheet is cut into two). During coating, the thickness is greater near the midpoint of the negative electrode current collector compared to the midpoint further away. After cutting, the midpoint before cutting corresponds to the edge region further away from the negative electrode tab. Along the width direction of the negative electrode sheet, this edge region includes a first sub-region and a second sub-region. The first sub-region is further away from the midpoint and has a smaller thickness than the second sub-region. This reduces the risk of the edge region of the negative electrode film detaching from the negative electrode current collector during cold pressing, thus mitigating the risk of lithium plating at the edge region.

[0027] In some embodiments, the thickness difference between the second sub-region and the first sub-region is 3 μm to 5 μm. This appropriate thickness difference between the second and first sub-regions helps reduce the risk of the negative electrode film layer in the edge region detaching from the negative electrode current collector, thereby reducing the risk of lithium plating in the edge region due to the negative electrode film layer detaching from the negative electrode current collector.

[0028] In some embodiments, the difference between the thickness of the intermediate region and the thickness of the edge region away from the negative electrode tab along the width direction of the negative electrode sheet is 3 μm to 10 μm. This appropriate difference in thickness between the intermediate region and the edge region away from the negative electrode tab along the width direction of the negative electrode sheet helps reduce the risk of the negative electrode film layer in the edge region detaching from the negative electrode current collector, thereby reducing the risk of lithium plating in the edge region due to the negative electrode film layer detaching from the negative electrode current collector.

[0029] In some embodiments, the positive electrode film layer includes a lithium replenishing agent, wherein the molar content of lithium in the lithium replenishing agent is greater than the molar content of lithium in the positive electrode active material. The inclusion of a lithium replenishing agent helps increase the molar content of lithium in the positive electrode film layer, thereby improving the energy density of the battery cell.

[0030] In some embodiments, the positive electrode sheet includes a positive electrode tab, which extends out of the positive electrode film layer along the width direction of the positive electrode sheet; the positive electrode film layer includes a main region and a thinned region, which is located away from the positive electrode tab relative to the main region along the width direction of the positive electrode sheet, and the thickness of the thinned region is less than the thickness of the main region.

[0031] By incorporating a thinning region in the positive electrode film, which has a lower lithium content compared to the main body, the lithium concentration at the edges of the positive electrode film is reduced. Consequently, less lithium diffuses and embeds into the corresponding thinning region of the negative electrode, reducing the risk of lithium plating at this location and thus improving the cycle performance of the battery cell. Furthermore, the thinning region also helps reduce the risk of the positive electrode film detaching from the positive current collector.

[0032] In some embodiments, the ratio of the thickness of the thinned region to the thickness of the main region is 0.87 to 0.99, optionally 0.90 to 0.97. This provides a suitable range for the thicknesses of the main region and the thinned region, which helps to reduce the lithium content in the thinned region and the risk of lithium deposition at the edge of the negative electrode film, while maintaining a relatively high lithium content in the positive electrode film. This balances the energy density and cycle performance of the battery cell.

[0033] In some embodiments, both the thinned region and the main body region include the lithium-containing phosphate, and the main body region further includes at least one of a lithium-containing transition metal oxide and a lithium replenishing agent, wherein the molar content of lithium in the lithium replenishing agent is greater than the molar content of lithium in the lithium-containing transition metal oxide and the molar content of lithium in the lithium-containing phosphate. Thus, the main body region of the positive electrode film has a higher lithium content than the thinned region, which helps reduce the risk of lithium deposition at the edge of the negative electrode film, resulting in better cycle performance of the battery cell; and the higher lithium content in the positive electrode film leads to a higher energy density of the battery cell.

[0034] In some embodiments, the lithium replenishing agent includes at least one selected from lithium metal oxides, lithium carbonates, lithium silicates, lithium oxalates, lithium sulfides, lithium nitrides, and lithium oxides. The higher molar content of lithium in the above-mentioned lithium replenishing agents is beneficial for providing more lithium ions to the battery cells.

[0035] In some embodiments, the lithium-containing metal oxide includes at least one of Li6CoO4, Li5FeO4, Li2CuO2, and Li2NiO2; the lithium-containing oxalate includes at least one of Li2C2O4, Li2C4O4, and Li6C6O6; the lithium-containing oxide includes at least one of Li2O and Li2O2; the lithium-containing silicate includes at least one of lithium silicate and lithium metasilicate; the lithium-containing carbonate includes Li2CO3; the lithium-containing nitride includes Li3N; and the lithium-containing sulfide includes Li2S.

[0036] The above lithium supplement has a relatively high molar content of lithium element, which is beneficial to providing more lithium ions to the battery cell; moreover, the above lithium supplement can be well adapted to the electrolyte, the positive electrode active material, and the negative electrode active material in the battery cell.

[0037] In some embodiments, the lithium supplement includes: Li a MO b , where 1 ≤ a ≤ 5, 1 ≤ b ≤ 5, and M includes at least one of Fe, Cu, Co, Mn, Ni, and Al. The above lithium supplement is beneficial to increasing the mass content of lithium element in the positive electrode film layer, so that the battery cell has a relatively high energy density.

[0038] In some embodiments, the lithium supplement includes Li5FeO4. The above lithium supplement is beneficial to increasing the mass content of lithium element in the positive electrode film layer, so that the battery cell has a relatively high energy density.

[0039] In some embodiments, the lithium supplement includes Li e FeO f , 0 ≤ e ≤ 5, 0 < f ≤ 4. During the formation process of the battery cell, the lithium supplement decomposes to generate lithium ions, and at the same time, the molar contents of the O element and the Li element in the lithium supplement change.

[0040] In some embodiments, the lithium supplement includes Li m FeO n , 0 ≤ m ≤ 1, 0 < n ≤ 2. During the formation process of the battery cell, the lithium supplement decomposes to generate lithium ions, and at the same time, the molar contents of the O element and the Li element in the lithium supplement change.

[0041] In some embodiments, the average value of the longest diameter of the lithium supplement is 3 μm to 30 μm.

[0042] When the average value of the longest diameter of the lithium supplement is greater than or equal to 3 μm, the degree of side reactions occurring in the battery cell caused by the lithium deintercalation products of the lithium supplement can be reduced, which is beneficial to improving the cycle life of the battery cell; when the average value of the longest diameter of the lithium supplement is less than or equal to 30 μm, it is beneficial for lithium ions to escape from the lithium supplement, facilitating the transmission and diffusion of lithium ions, so that the capacity of the battery cell can be exerted, and the battery cell has a relatively high energy density.

[0043] In some embodiments, the average value of the longest diameter of the lithium supplement is 5 μm to 20 μm. In this way, it is beneficial to improve the energy density and cycle performance of the battery cell.

[0044] In some embodiments, the lithium replenishing agent includes a matrix and a coating layer disposed on at least a portion of the surface of the matrix, the coating layer comprising carbon. The coating layer improves the stability of the lithium replenishing agent, and the inclusion of carbon in the coating layer enhances the conductivity of the lithium replenishing agent, thereby improving the energy density of the battery cell.

[0045] In some embodiments, the thickness of the coating layer is 10 nm to 100 nm. This coating layer has a suitable thickness, which is beneficial for improving the stability of the lithium replenishment agent and facilitating the extraction of lithium ions, resulting in a higher energy density for the battery cell.

[0046] In some embodiments, the mass content of the lithium replenishing agent is 0.05% to 5% based on the total mass of the positive electrode film.

[0047] When the mass content of the lithium replenisher is greater than or equal to 0.05% based on the total mass of the positive electrode film, it is beneficial to increase the mass content of lithium in the positive electrode film, resulting in a higher energy density for the battery cell. Conversely, when the mass content of the lithium replenisher is less than or equal to 5% based on the total mass of the positive electrode film, it helps to reduce the adverse effects of excessive lithium replenisher-induced delithiation byproducts on the cycle performance of the battery cell. Therefore, when the mass content of the lithium replenisher is between 0.05% and 5% based on the total mass of the positive electrode film, the battery cell exhibits higher energy density and better cycle performance.

[0048] In some embodiments, the mass content of the lithium replenishing agent is 0.1% to 3% based on the total mass of the positive electrode film. This results in a battery cell with high energy density and good cycle performance.

[0049] In some embodiments, the lithium-containing phosphate comprises primary particles and secondary particles formed by the agglomeration of the primary particles. The average longest diameter of the primary particles is 100 nm to 500 nm, and the average longest diameter of the secondary particles is 1 μm to 4 μm. The lithium iron phosphate particles have a suitable size, facilitating the extraction of lithium ions and contributing to the full utilization of the battery cell's capacity, resulting in a higher energy density for the battery cell.

[0050] In some embodiments, the lithium-containing phosphate includes those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y zThe compounds, wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D 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 Si, Cl, C, and N; Y includes one or more of O and F.

[0051] During the charging and discharging process of a single battery cell, the molar content of lithium, oxygen, and other elements in lithium phosphate varies within a certain range.

[0052] In some embodiments, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. These lithium-containing phosphates exhibit high structural stability, which helps to improve the cycle life of individual battery cells.

[0053] In some embodiments, at least a portion of the surface of the lithium phosphate contains carbon. This helps to improve the conductivity of the lithium phosphate, facilitating the utilization of the battery cell's capacity and resulting in a battery cell with higher energy density.

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

[0055] Thirdly, an electrical device is provided, comprising a battery cell as described in the first aspect and any possible embodiment thereof, or a battery device as described in the second aspect, wherein the battery cell or battery device is used to store or provide electrical energy. Attached Figure Description

[0056] 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.

[0057] Figure 1 is a structural schematic diagram of a vehicle according to an embodiment of this application;

[0058] Figure 2 is a schematic diagram of the structure of a battery device according to an embodiment of this application;

[0059] Figure 3 is a schematic diagram of the structure of a battery cell according to an embodiment of this application;

[0060] Figure 4 is a schematic diagram of the positive and negative electrode plates in combination according to an embodiment of this application;

[0061] Figure 5 is a schematic diagram of the positive electrode sheet according to an embodiment of this application;

[0062] Figure 6 is a cross-sectional view of the positive electrode plate in Figure 5 along the BB direction;

[0063] Figure 7 is a schematic diagram of the negative electrode sheet according to an embodiment of this application;

[0064] Figure 8 is a cross-sectional view of the positive electrode in Figure 7 along the AA direction.

[0065] Reference numerals: 1: Vehicle; 10: Battery unit; 30: Controller; 40: Motor; 11: Housing; 111: First housing section; 112: Second housing section; 3: Battery cell; 31: Housing; 32: End cap assembly; 33: Electrode assembly; 330: Electrode assembly main body; 331: Tab; 34: Connecting member; 322: Electrode terminal; 6: Negative electrode sheet; 601: Negative current collector; 61: Negative electrode film; 602: Negative electrode tab; 611: Intermediate region; 612: Edge region; 6121: First sub-region; 6122: Second sub-region; 5: Positive electrode sheet; 501: Positive current collector; 51: Positive electrode film; 502: Positive electrode tab; 511: Main body region; 512: Thinned region. Detailed Implementation

[0066] Embodiments of the battery cell, battery device, and electrical appliance of this application have been described in detail with appropriate reference to the accompanying drawings; however, 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.

[0067] 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.

[0068] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0069] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0070] 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.

[0071] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0072] This application aims to develop a battery cell with low lithium plating risk, long cycle life, and high energy density. The battery cell includes a positive electrode and a negative electrode; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector, and the negative electrode includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector. Along a first direction of the negative electrode, the edge of the negative electrode film layer extends beyond the edge of the positive electrode film layer. The positive electrode film layer includes a positive active material, which includes a lithium phosphate. The lithium content in the positive electrode film layer at 0% SOC is 3.9% to 4.3% by mass. The negative electrode film layer includes a central region and an edge region. Along the first direction, the edge region is located on at least one side of the central region. The central region includes a first negative active material, and the edge region includes a second negative active material. The specific capacity of the second negative active material is greater than that of the first negative active material.

[0073] In a single battery cell, the negative electrode film layer of the negative electrode sheet includes a central region and an edge region. The edge of the edge region of the negative electrode film layer typically extends beyond the edge of the positive electrode film layer of the positive electrode sheet to reduce the risk of lithium plating in the negative electrode film layer. However, even in this case, a certain amount of lithium will still be embedded in the edge region of the negative electrode film layer. This is because, during the charging process of the battery cell, lithium ions do not migrate linearly from the positive active material of the positive electrode film layer to the negative active material of the negative electrode film layer. Instead, they first enter the electrolyte and then migrate to the negative electrode film layer under the influence of the lithium ion concentration gradient and the electric field. Since the edge of the negative electrode film layer is in contact with the electrolyte, lithium ions will also be embedded at the edge of the negative electrode film layer under the influence of the lithium ion concentration gradient and the electric field. During the discharge process of the battery cell, lithium in the edge region of the negative electrode film layer and lithium in the central region of the negative electrode film layer opposite to the edge of the positive electrode film layer both migrate to the edge of the positive electrode film layer, resulting in an increase in the lithium content at the edge of the positive electrode. During subsequent charging, the lithium content at the edge of the positive electrode film increases, leading to an increase in the lithium content migrating to the edge region of the negative electrode film. Correspondingly, during subsequent discharging, the lithium content at the edge of the positive electrode film also increases. Thus, after multiple charge-discharge cycles, the lithium content at the edge region of the negative electrode film increases, increasing the risk of lithium plating at the edge region of the negative electrode film.

[0074] Furthermore, when the lithium content in the positive electrode film at 0% SOC is 3.9% to 4.3%, the lithium content in the positive electrode film increases, which exacerbates the risk of lithium plating at the edge of the negative electrode film, leading to a sharp drop in the cycle life of the battery cell and hindering the improvement of the cycle performance of the battery cell.

[0075] This application improves the lithium storage capacity of the edge region of the negative electrode film by setting the specific capacity of the second negative electrode active material to be greater than that of the middle region. Thus, when the lithium content in the positive electrode film is high, resulting in a high lithium content in the edge region of the negative electrode film, lithium in the edge region can be intercalated into the second negative electrode active material. This reduces the risk of lithium ions failing to intercalate into the second negative electrode active material due to weak lithium storage capacity in the edge region, thereby reducing the risk of lithium plating in the edge region and the risk of a significant drop in cycle life caused by lithium plating.

[0076] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. 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 electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0077] In some embodiments, the positive electrode can be a positive electrode sheet, which can include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0078] In some embodiments, the negative electrode may be a negative electrode sheet, which may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0079] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0080] 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.

[0081] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride, and ceramic.

[0082] 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.

[0083] In some embodiments, the battery cell also includes an electrolyte, which 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. The electrolyte can be liquid, gel, or solid.

[0084] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0085] In some embodiments, the battery cell may include a housing. The housing is used to encapsulate components such as electrode assemblies and electrolytes. The housing may be made of steel, aluminum, plastic (such as polypropylene), composite metal (such as copper-aluminum composite), or aluminum-plastic film, etc. The housing includes a shell and end caps.

[0086] The battery mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed via a busbar.

[0087] In some embodiments, the battery device may be a battery pack, which includes a housing and individual battery cells, with the individual battery cells or battery modules housed within the housing.

[0088] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0089] In some embodiments, the battery device may be located within an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0090] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0091] For example, as shown in Figure 1, which is a structural schematic diagram of a vehicle 1 according to an embodiment of this application, vehicle 1 can be a gasoline vehicle, a natural gas vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A motor 40, a controller 30, and a battery device 10 can be installed inside vehicle 1. The controller 30 is used to control the battery device 10 to supply power to the motor 40. For example, the battery device 10 can be installed at the bottom, front, or rear of vehicle 1. The battery device 10 can be used to power vehicle 1. For example, the battery device 10 can serve as the operating power source for vehicle 1, for example, for the electrical system of vehicle 1, such as for the power requirements of vehicle 1's starting, navigation, and operation. In another embodiment of this application, the battery device 10 can not only serve as the operating power source for vehicle 1, but also as the driving power source for vehicle 1, replacing or partially replacing gasoline or natural gas to provide driving power for vehicle 1.

[0092] Figure 2 shows a partial structural schematic diagram of the battery device 10 according to an embodiment of this application. For example, as shown in Figure 2, the battery device 10 according to this application embodiment may include multiple battery cells 3 to meet different power usage requirements. The shape of the battery cell 3 according to this application embodiment can be set according to actual application. For example, the battery cell 3 can be cylindrical, or it can be cuboid or other shapes, and this application embodiment is not limited to this.

[0093] It should be understood that, as shown in FIG. 2, the battery device 10 of this embodiment may further include a housing 11, which can be used to accommodate multiple battery cells 3. The housing 11 of this embodiment has a hollow internal structure, and the multiple battery cells 3 are accommodated within the housing 11. The housing 11 may include two parts, referred to herein as a first housing portion 111 and a second housing portion 112, which are fastened together. The shapes of the first housing portion 111 and the second housing portion 112 can be determined according to the shape of the components accommodated internally, for example, according to the shape of the combination of the multiple battery cells 3 accommodated internally. At least one of the first housing portion 111 and the second housing portion 112 has an opening. For example, as shown in Figure 2, the first housing portion 111 and the second housing portion 112 can both be hollow cuboids with one open face. The openings of the first housing portion 111 and the second housing portion 112 are opposite to each other, and the first housing portion 111 and the second housing portion 112 are interlocked to form a housing 11 with a closed cavity, which can be used to accommodate multiple battery cells 3. The multiple battery cells 3 are connected in parallel, series, or mixed and placed inside the housing 11 formed by the interlocking of the first housing portion 111 and the second housing portion 112.

[0094] For example, unlike what is shown in Figure 2, only one of the first housing portion 111 and the second housing portion 112 may be a hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 112 as a hollow cuboid with one opening, and the first housing portion 111 as a plate-shaped example, then the first housing portion 111 covers the opening of the second housing portion 112 to form a housing 11 with a closed chamber, which can be used to accommodate multiple battery cells 3.

[0095] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0096] The battery cells can be lithium-ion batteries or lithium metal batteries.

[0097] 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, lithium ions are released from the negative electrode, move and embed into the positive electrode active material.

[0098] It should be understood that the “intercalation” process described in this application refers to the process by which lithium ions are intercalated in the positive electrode active material or the negative electrode due to an electrochemical reaction, and the “extraction” process described in this application refers to the process by which lithium ions are extracted from the positive electrode active material or the negative electrode due to an electrochemical reaction.

[0099] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. The following section describes the battery cell and its components provided in this application.

[0100] [Battery cell]

[0101] Figure 3 is a structural schematic diagram of a battery cell according to an embodiment of the present application. Figure 4 is a schematic diagram of the positive electrode and negative electrode in combination according to an embodiment of the present application. Figure 5 is a schematic diagram of the positive electrode according to an embodiment of the present application. Figure 6 is a schematic diagram of the positive electrode in Figure 5 along the BB direction. Figure 7 is a schematic diagram of the negative electrode according to an embodiment of the present application. Figure 8 is a schematic diagram of the negative electrode in Figure 7 along the AA direction.

[0102] In one embodiment of this application, for example, referring to Figures 3 to 8, the battery cell 3 includes a positive electrode 5 and a negative electrode 6; the positive electrode 5 includes a positive current collector 501 and a positive electrode film layer 51 located on at least one surface of the positive current collector 501, and the negative electrode 6 includes a negative current collector 601 and a negative electrode film layer 61 located on at least one surface of the negative current collector 601. Along the first direction of the negative electrode, the edge of the negative electrode film layer extends beyond the edge of the positive electrode film layer.

[0103] The positive electrode current collector 501 has two opposing surfaces along its own thickness direction, and the negative electrode current collector 601 has two opposing surfaces along its own thickness direction. The positive electrode film layer 51 can be located on one or both surfaces of the positive electrode current collector 501; the negative electrode film layer 61 can be located on one or both surfaces of the negative electrode current collector 601.

[0104] The first direction of the negative electrode sheet can be the width direction of the negative electrode sheet (e.g., the y direction in Figure 4) or the length direction of the negative electrode sheet (e.g., the x direction in Figure 4). The width direction of the negative electrode sheet is the direction in which the negative electrode tab protrudes from the negative electrode film layer 61, and the length direction of the negative electrode sheet is perpendicular to the width direction of the negative electrode sheet and parallel to the surface on which the negative electrode sheet is located.

[0105] As an example, along the width direction of the negative electrode sheet, the edge of the negative electrode film extends beyond the edge of the positive electrode film. In this case, the positive electrode sheet 5 and the negative electrode sheet 6 can be formed into an electrode assembly 33 by winding.

[0106] As an example, along the length of the negative electrode sheet, the edge of the negative electrode film extends beyond the edge of the positive electrode film.

[0107] As an example, the edges of the negative electrode film extend beyond the edges of the positive electrode film along both the length and width directions of the negative electrode sheet. In this case, the positive electrode sheet 5 and the negative electrode sheet 6 can be stacked to form the electrode assembly 33.

[0108] The fact that the edge of the negative electrode film extends beyond the edge of the positive electrode film can mean that the projection of the negative electrode film 61 onto the xoy plane covers the projection of the positive electrode film 51 onto the xoy plane.

[0109] The positive electrode film 51 includes a positive electrode active material, which includes lithium phosphate. The mass content of lithium in the positive electrode film 51 of the battery cell at 0% SOC is 3.9% to 4.3%.

[0110] Lithium-containing phosphates can refer to lithium-containing transition metal phosphates with an olivine structure, such as lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their modified forms.

[0111] 0% SOC means that the state of charge of a single battery cell is 0%.

[0112] As an example, a battery cell with 0% SOC can be obtained by the following method. Specifically, the battery cell is first charged to 3.65V at a constant current of 0.33C, then charged to 0.05C at a constant voltage of 3.65V, and finally discharged to 2.5V to obtain a battery cell with 0% SOC.

[0113] The mass content of lithium in the positive electrode film layer 51 of the battery cell at 0% SOC can be 3.9%, 3.95%, 4.0%, 4.1%, 4.2%, 4.25%, 4.3% or any value within the above range.

[0114] As an example, the mass content of lithium in the positive electrode film can be brought to the range mentioned above by adding a lithium supplement (e.g., Li5FeO4) to the positive electrode film.

[0115] As another example, by adding lithium sheets (e.g., adding lithium metal) to the negative electrode, the mass content of lithium in the negative electrode is increased, thereby increasing the mass content of lithium in the positive electrode film layer, so that the mass content of lithium in the positive electrode film layer reaches the aforementioned range.

[0116] As another example, the mass content of lithium in the positive electrode film can be brought to the above range by adding lithium iron phosphate positive electrode active material and positive electrode active material with a specific capacity higher than that of lithium iron phosphate (e.g., lithium-containing nickel cobalt manganese metal oxide).

[0117] As another example, the concentration of electrolyte salts in the electrolyte can be increased to bring the mass content of lithium in the positive electrode film to the range mentioned above.

[0118] The lithium content in the positive electrode film 51 of the battery cell at 0% SOC is 3.9% to 4.3% by mass. The high lithium content in the positive electrode film is beneficial for providing more active lithium ions, which helps to improve the cycle life of the battery cell while also ensuring a high energy density.

[0119] The negative electrode film layer 61 includes a middle region 611 and an edge region 612. Along the first direction, the edge region 612 is located on at least one side of the middle region 611. The middle region 611 includes a first negative electrode active material, and the edge region 612 includes a second negative electrode active material. The specific capacity of the second negative electrode active material is greater than that of the first negative electrode active material.

[0120] As an example, along the first direction, the edge region 612 is located on one side of the middle region 611.

[0121] As another example, as shown in Figure 8, the edge region 612 is located on both sides of the middle region 611 along the first direction.

[0122] The larger the specific capacity of the negative electrode active material, the more lithium ions it can hold. By setting the specific capacity of the second negative electrode active material to be greater than that of the first negative electrode active material, the edge region 612 of the second negative electrode active material can hold more lithium ions, and the risk of lithium plating in the edge region 612 is lower. In addition, the fact that the second negative electrode active material in the edge region 612 has a larger specific capacity than the first negative electrode active material also helps to compensate for the problem of increased lithium content in the edge region 612 of the negative electrode film due to the excessively high lithium content in the positive electrode film, which further helps to reduce the risk of lithium plating in the edge region 612.

[0123] In this embodiment, the edge of the negative electrode film 61 extends beyond the edge of the positive electrode film 51, which helps reduce the risk of lithium plating in the negative electrode film 61. The positive electrode active material includes lithium iron phosphate, and the mass content of lithium in the positive electrode film 51 at 0% SOC of the battery cell is 3.9% to 4.3%. The negative electrode film 61 includes a middle region 611 and an edge region 612. Along the first direction, the edge region 612 is located on at least one side of the middle region 611. The middle region 611 includes a first negative electrode active material, and the edge region 612 includes a second negative electrode active material. The specific capacity of the second negative electrode active material is greater than that of the first negative electrode active material. In this way, the edge region 612 can accommodate more lithium ions than the middle region 611, which can compensate for the increased risk of lithium plating in the edge region 612 due to the excessively high mass content of lithium in the positive electrode film. This helps reduce the risk of lithium plating in the edge region 612, thereby improving the cycle performance of the battery cell.

[0124] In some embodiments, the specific capacity of the first negative electrode active material is from 330 mAh / g to 350 mAh / g.

[0125] The specific capacity of the first negative electrode active material can be 330mAh / g, 332mAh / g, 335mAh / g, 338mAh / g, 340mAh / g, 342mAh / g, 345mAh / g, 348mAh / g, 350mAh / g, or any value within the above range.

[0126] When the specific capacity of the first negative electrode active material is greater than or equal to 330 mAh / g, the intermediate region 611 of the negative electrode film layer 61 has a suitable capacity and can store a suitable number of lithium ions, which is compatible with the mass content of lithium in the positive electrode film layer 51. This helps to reduce the risk of lithium plating in the intermediate region 611, thereby improving the cycle performance of the battery cell. When the specific capacity of the first negative electrode active material is less than or equal to 350 mAh / g, it can be compatible with the mass content of lithium in the positive electrode film layer, reducing the waste of capacity in the intermediate region.

[0127] In this embodiment, by setting the specific capacity of the first negative electrode active material to 330 mAh / g to 350 mAh / g, the battery cell has good cycle performance.

[0128] In some embodiments, the specific capacity of the first negative electrode active material is 340 mAh / g to 350 mAh / g. This is beneficial for improving the cycle performance of the battery cell.

[0129] In some embodiments, the specific capacity of the second negative electrode active material is from 340 mAh / g to 400 mAh / g.

[0130] The specific capacity of the second negative electrode active material can be 340mAh / g, 345mAh / g, 350mAh / g, 355mAh / g, 360mAh / g, 365mAh / g, 370mAh / g, 375mAh / g, 380mAh / g, 385mAh / g, 390mAh / g, 395mAh / g, 400mAh / g, or any value within the above range.

[0131] When the specific capacity of the second negative electrode active material is greater than or equal to 340 mAh / g, the edge region 612 can accommodate more lithium ions, which helps to reduce the risk of lithium plating in the edge region 612, thereby improving the cycle performance of the battery cell; when the specific capacity of the second negative electrode active material is less than or equal to 400 mAh / g, the waste of capacity in the edge region can be reduced while reducing the risk of lithium plating.

[0132] In some embodiments, the specific capacity of the second negative electrode active material is between 350 mAh / g and 370 mAh / g. This is beneficial for improving the cycle performance of the battery cell.

[0133] In some embodiments, the size of the intermediate region 611 is 100 mm to 300 mm along the first direction.

[0134] As an example, as shown in Figure 8, the dimensions of the intermediate region 611 along the width direction (y direction) of the negative electrode sheet can be as shown by L1 in Figure 8.

[0135] Along the first direction, the size of the intermediate area 611 can be 100mm, 110mm, 130mm, 150mm, 180mm, 200mm, 220mm, 250mm, 280mm, 300mm or any value within the above range.

[0136] The intermediate region 611 can have different dimensions for battery cells of different sizes or capacities. For example, the larger the size of the intermediate region 611, the larger the size and capacity of the battery cell.

[0137] In this embodiment, the size of the intermediate region 611 along the first direction is 100mm to 300mm. This gives the intermediate region 611 a suitable size, making it compatible with the capacity, energy density, and other properties of the battery cell.

[0138] In some embodiments, the total dimension of the edge region 612 along the first direction is 1.5 mm to 5 mm.

[0139] Along the first direction, the total size of the edge region 612 can be 1.5mm, 1.8mm, 2mm, 2.5mm, 2.8mm, 3mm, 3.2mm, 3.5mm, 3.8mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm or any value within the above range.

[0140] When the edge region 612 is located on both sides of the middle region 611 along the first direction, the total size of the edge region 612 is the sum of the sizes of the two edge regions 612 along the first direction. For example, as shown in FIG8, the total size of the edge region 612 along the first direction is the sum of L21 and L22.

[0141] When the edge region 612 is located on one side of the middle region 611 along the first direction, the total size of the edge region 612 is the size of the edge region 612 along the first direction.

[0142] When the total size of the edge region 612 is greater than or equal to 1.5 mm, the edge region 612 of the negative electrode film layer 61 extends beyond the positive electrode film layer 51 by a certain distance, which helps to reduce the risk of lithium plating in the edge region 612 and improve the cycle performance of the battery cell; when the total size of the edge region 612 is less than or equal to 5 mm, it helps to reduce the space occupied by the edge region 612 and improve the energy density of the battery cell.

[0143] In some embodiments, the total size of the edge region 612 is 2 mm to 3 mm. This results in better cycle performance and higher energy density for the battery cell.

[0144] In some embodiments, the first negative electrode active material comprises graphite, and the second negative electrode active material comprises graphite. Thus, graphite exhibits lower expansion, which is beneficial for improving the cycle performance of the battery cell.

[0145] In some embodiments, the powder resistance of graphite in the first negative electrode active material is greater than that of graphite in the second negative electrode active material.

[0146] The powder resistance of graphite in the first negative electrode active material and the powder resistance of graphite in the second negative electrode active material are the powder resistances under the same pressure.

[0147] The lower the resistivity of graphite powder, the better it is for the transport and diffusion of lithium ions, and the lower the risk of lithium plating.

[0148] In this embodiment, the graphite in the second negative electrode active material has a lower resistance than the graphite in the first negative electrode active material, and the edge region 612 is more conducive to the transport and insertion of lithium ions than the middle region 611, which helps to reduce the risk of lithium plating in the edge region 612, thereby improving the cycle performance of the battery cell.

[0149] In some embodiments, under a pressure of 3T, the powder resistance of graphite in the first negative electrode active material is 4Ω / cm to 10Ω / cm.

[0150] Under 3T pressure, the powder resistance of graphite in the first negative electrode active material can be 4Ω / cm, 5Ω / cm, 6Ω / cm, 7Ω / cm, 7.5Ω / cm, 8Ω / cm, 8.2Ω / cm, 9Ω / cm, 10Ω / cm or any value within the above range.

[0151] In this embodiment, the graphite in the first negative electrode active material has a suitable powder resistance, the intermediate region 611 facilitates the transport of lithium ions, and the battery cell has good kinetic performance.

[0152] In some embodiments, under a pressure of 3T, the powder resistivity of graphite in the second negative electrode active material is 0.5Ω / cm to 3.5Ω / cm.

[0153] Under 3T pressure, the powder resistance of graphite in the second negative electrode active material can be 0.5Ω / cm, 0.8Ω / cm, 1Ω / cm, 1.2Ω / cm, 1.5Ω / cm, 1.8Ω / cm, 1.9Ω / cm, 2Ω / cm, 3Ω / cm, 3.5Ω / cm or any value within the above range.

[0154] In this embodiment, the graphite in the second negative electrode active material has a suitable powder resistance, and the edge region 612 facilitates the transport of lithium ions, which helps to reduce the risk of lithium plating in the edge region 612 and improves the cycle performance of the battery cell.

[0155] In some embodiments, the first negative electrode active material includes graphite, and the second negative electrode active material includes graphite and silicon-based materials.

[0156] Silicon-based materials have a higher specific capacity than graphite, and can hold more lithium ions than graphite.

[0157] By setting the first negative electrode active material to include graphite and the second negative electrode active material to include graphite and silicon-based materials, the edge region 612 can accommodate more lithium ions than the middle region 611, which helps to reduce the risk of lithium plating in the edge region 612 and improves the cycle performance of the battery cell.

[0158] In some embodiments, the silicon-based material may be at least one of silicon-carbon material, silicon-oxygen material, and elemental silicon.

[0159] In some embodiments, the ratio of the mass content of silicon to the mass content of carbon, based on the total mass of the second negative electrode active material, is 0.5% to 30%.

[0160] Based on the total mass of the second negative electrode active material, the ratio of the mass content of silicon to the mass content of carbon can be 0.5%, 1%, 1.5%, 2%, 3%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or any value within the above range.

[0161] When the ratio of silicon content to carbon content is greater than or equal to 0.5% based on the total mass of the second negative electrode active material, it is beneficial to increase the capacity of the second negative electrode active material, which in turn is beneficial to increase the number of lithium ions that the edge region 612 can accommodate, reduce the risk of lithium plating in the edge region 612, and thus improve the cycle performance of the battery cell. When B is less than or equal to 30%, the silicon-based material and graphite in the edge region 612 have a suitable mass ratio, which is beneficial to reduce the expansion of the edge region 612, and thus improve the cycle performance of the battery cell.

[0162] In some embodiments, the ratio of silicon content to carbon content based on the total mass of the second negative electrode active material is 1.5% to 10%. This is beneficial for improving the cycle performance of the battery cell.

[0163] In some embodiments, the ratio of the coating weight per unit area of ​​the intermediate region 611 to the coating weight per unit area of ​​the edge region 612 is 1.1 to 1.5.

[0164] The ratio of the coating weight per unit area of ​​the intermediate region 611 to the coating weight per unit area of ​​the edge region 612 can be 1.1, 1.2, 1.3, 1.4, 1.5 or any value within the above range.

[0165] The ratio of the coating weight per unit area of ​​the intermediate region 611 to the coating weight per unit area of ​​the edge region 612 is 1.1 to 1.5, which helps to reduce the transport and insertion of lithium ions in the edge region 612 and reduces the risk of lithium plating in the edge region 612.

[0166] In some embodiments, the negative electrode 6 includes a negative electrode tab 602, which extends out of the negative electrode film layer 61 along the width direction of the negative electrode 6; and edge regions 612 are located on both sides of the middle region 611 along the width direction of the negative electrode 6. In this way, the edge regions on both sides extend beyond the positive electrode film layer along the width direction of the negative electrode 6, which helps to reduce the risk of lithium plating on the negative electrode.

[0167] In some embodiments, along the width direction of the negative electrode sheet, the edge region 612 away from the negative electrode tab 602 includes a first sub-region 6121 and a second sub-region 6122. The first sub-region 6121 is away from the middle region 611 relative to the second sub-region 6122, and the thickness of the first sub-region 6121 is less than the thickness of the second sub-region 6122.

[0168] The thickness of the first sub-region 6121 can vary gradually along the width direction of the negative electrode sheet. For example, along the width direction of the negative electrode sheet and in the direction from the middle region 611 to the first sub-region 6121, the thickness of the first sub-region 6121 gradually decreases.

[0169] The thickness of the second sub-region 6122 can vary gradually along the width direction of the negative electrode sheet. For example, along the width direction of the negative electrode sheet and in the direction from the middle region 611 to the second sub-region 6122, the thickness of the second sub-region 6122 gradually decreases.

[0170] The thickness of the first sub-region 6121 is less than the thickness of the second sub-region 6122, which can mean that the average thickness of the first sub-region 6121 is less than the average thickness of the second sub-region 6122. The average thickness of the first sub-region 6121 can be the average of the maximum thickness and the minimum thickness of the first sub-region 6121, and the average thickness of the second sub-region 6122 can be the average of the maximum thickness and the minimum thickness of the second sub-region 6122.

[0171] In the process of preparing the negative electrode sheet 6, a negative electrode slurry is typically first coated onto the negative electrode current collector. Then, along the width direction of the negative electrode sheet 6, the negative electrode current collector is cut at its midpoint (for example, a single negative electrode current collector is cut into two). During the coating process, the thickness is greater near the midpoint of the negative electrode current collector compared to the midpoint further away from it, along the width direction of the negative electrode sheet 6. After cutting the negative electrode current collector, the midpoint near the midpoint before cutting corresponds to the edge region 612 away from the negative electrode tab 602 after cutting. Before the negative electrode current collector is cut, the thickness of the negative electrode film layer is thicker closer to the middle of the negative electrode current collector. In order to make the thickness of the negative electrode film layer more uniform at each position and reduce the risk of the negative electrode film layer falling off in the edge region of the negative electrode tab 602 after cutting, the negative electrode film layer in the edge region of the negative electrode tab 602 after cutting is subjected to gradient thinning treatment to obtain the first sub-region 6121 and the second sub-region 6122 with different thicknesses.

[0172] Along the width direction of the negative electrode sheet 6, the edge region 612 away from the negative electrode tab 602 includes a first sub-region 6121 and a second sub-region 6122. The first sub-region 6121 is farther away from the middle region 611 than the second sub-region 6122, and the first sub-region 6121 has a smaller thickness than the second sub-region 6122. This helps reduce the risk of the edge region 612 of the negative electrode film layer 61 detaching from the negative electrode current collector during the cold pressing process of the negative electrode sheet 6, thereby reducing the risk of lithium plating in the edge region 612 due to the detachment of the negative electrode film layer 61 from the negative electrode current collector. In addition, the arrangement of the first sub-region 6121 and the second sub-region 6122 also facilitates the subsequent fabrication of battery cells and reduces the complexity of battery cell fabrication.

[0173] In some embodiments, the difference between the thickness of the second sub-region 6122 and the thickness of the first sub-region 6121 is 3 μm to 5 μm.

[0174] The difference between the thickness of the second sub-region 6122 and the thickness of the first sub-region 6121 can be the difference between the maximum thickness of the second sub-region 6122 and the minimum thickness of the first sub-region 6121.

[0175] As an example, along the width direction of the negative electrode sheet, the second sub-region 6122 has the maximum thickness at the end closer to the middle region 611, and the first sub-region 6121 has the minimum thickness at the end farther from the middle region 611.

[0176] The difference between the thickness of the second sub-region 6122 and the thickness of the first sub-region 6121 can be 3μm, 3.2μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm or any value within the above range.

[0177] In this embodiment, the thickness of the second sub-region 6122 and the first sub-region 6121 has a suitable difference, which helps to reduce the risk of the negative electrode film layer 61 of the edge region 612 detaching from the negative electrode current collector, thereby helping to reduce the risk of lithium plating in the edge region 612 caused by the negative electrode film layer 61 of the edge region 612 detaching from the negative electrode current collector.

[0178] In some embodiments, the thickness of the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet is less than the thickness of the middle region 611.

[0179] In some embodiments, the difference between the thickness of the intermediate region 611 and the thickness of the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet is 3 μm to 10 μm.

[0180] The difference between the thickness of the intermediate region 611 and the thickness of the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet can be 3μm, 3.2μm, 3.5μm, 3.8μm, 4μm, 4.2μm, 4.5μm, 4.8μm, 5μm, 6μm, 6.5μm, 7μm, 8μm, 9μm, 9.5μm, 10μm or any value within the above range.

[0181] The thickness of the intermediate region 611 is relatively uniform. For example, along the width direction of the negative electrode sheet, the thickness of the intermediate region 611 is basically the same at various locations. The thickness of the edge region 612, which is away from the negative electrode tab 602, varies in a gradient along the width direction of the negative electrode sheet.

[0182] The difference between the thickness of the intermediate region 611 and the thickness of the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet can be the difference between the average thickness of the intermediate region 611 and the minimum thickness of the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet.

[0183] In this embodiment, the thickness of the middle region 611 and the edge region 612 away from the negative electrode tab 602 along the width direction of the negative electrode sheet 6 have a suitable difference, which helps to reduce the risk of the negative electrode film layer 61 of the edge region 612 detaching from the negative electrode current collector, thereby helping to reduce the risk of lithium plating in the edge region 612 caused by the negative electrode film layer 61 of the edge region 612 detaching from the negative electrode current collector.

[0184] In some embodiments, the thickness of the edge region 612 near the negative electrode tab 602 along the width direction of the negative electrode sheet is the same as the thickness of the middle region 611.

[0185] For example, along the width direction of the negative electrode sheet, the thickness at various locations near the edge region 612 of the negative electrode tab 602 is basically the same.

[0186] In some embodiments, the positive electrode film layer 51 includes a lithium replenishing agent, wherein the molar content of lithium in the lithium replenishing agent is greater than the molar content of lithium in the positive electrode active material.

[0187] Lithium replenishers are used to replenish active lithium ions. During the charging process of a single battery cell, lithium ions are irreversibly released from the lithium replenisher.

[0188] As an example, during the formation process, lithium replenishment agents release lithium ions to provide lithium ions to the battery cells.

[0189] The lithium content in the lithium replenisher is greater than that in the positive electrode active material, allowing the lithium replenisher to release more lithium ions compared to the positive electrode active material. The addition of the lithium replenisher helps increase the molar lithium content in the positive electrode film layer 51, thereby improving the cycle life of the battery cell.

[0190] In some embodiments, the positive electrode 5 includes a positive electrode tab 502, and a positive electrode film 51 extends from the positive electrode tab 502 along the width direction of the positive electrode 5. The positive electrode film 51 includes a main region 511 and a thinned region 512. Along the width direction of the positive electrode 5, the thinned region 512 is away from the positive electrode tab 502 relative to the main region 511, and the thickness of the thinned region 512 is less than the thickness of the main region 511.

[0191] In the preparation of the positive electrode sheet, a positive electrode slurry is typically first coated onto the positive current collector. Then, along the width direction of the positive electrode sheet, the current collector is cut at its midpoint (e.g., a single sheet is cut into two). During coating, the thickness is greater near the midpoint of the current collector compared to the midpoint further away. After cutting, the midpoint before cutting corresponds to the thinned region 512 of the diced positive electrode sheet. Before cutting, the positive electrode film is thicker closer to the midpoint. To make the thickness of the positive electrode film more uniform across different locations and reduce the risk of film detachment from the edge region far from the positive electrode tab after cutting, a gradient thinning process is performed on the edge region far from the positive electrode tab to obtain the thinned region 512.

[0192] By setting the thinning region 512, which has a lower lithium content per unit area compared to the main region 511, the lithium concentration at the edge of the positive electrode film 51 is reduced. This results in less lithium diffusing and embedding into the corresponding thinning region 512 of the negative electrode. This compensates for the increased risk of lithium plating at the corresponding thinning region 512 of the negative electrode, caused by the longer migration path of lithium ions between the thinning region 512 and the negative electrode compared to the distance between the main region 511 and the negative electrode. This helps reduce the risk of lithium plating at the corresponding thinning region 512 of the negative electrode, thus improving the cycle performance of the battery cell. Furthermore, the thinning region 512 also helps reduce the risk of the positive electrode film detaching from the positive current collector.

[0193] In some embodiments, the projection of the edge region 612 away from the negative electrode tab along the width direction of the negative electrode sheet onto the xoy plane at least partially covers the projection of the thinned region 512 onto the xoy plane.

[0194] During the drying process after coating the negative electrode slurry, the binder in the slurry will float to the surface. Thus, along the thickness direction of the negative electrode sheet, the mass content of the binder at locations farther from the negative electrode current collector is greater than the mass content at locations closer to the negative electrode current collector.

[0195] The thickness of the edge region 612 away from the negative electrode tab along the width direction of the negative electrode sheet is smaller than that of other locations in the negative electrode film layer (e.g., the middle region 611). The mass content of the binder on the surface of the edge region 612 away from the negative electrode tab along the width direction of the negative electrode sheet is higher, which affects the intercalation of lithium ions and increases the risk of lithium plating in the edge region 612 away from the negative electrode tab along the width direction of the negative electrode sheet.

[0196] By setting the specific capacity of the second negative electrode active material in the edge region 612 to be greater than that of the first negative electrode active material in the middle region 611, the problem of increased lithium plating risk in the edge region 612 away from the negative electrode tab in the width direction of the negative electrode sheet due to the difference in thickness between the middle region 611 and the edge region 612 away from the negative electrode tab in the width direction of the negative electrode sheet can be compensated. This helps to reduce the risk of lithium plating in the edge region 612 away from the negative electrode tab in the width direction of the negative electrode sheet. In addition, by setting the thinning region 512 of the positive electrode film, the risk of lithium plating in the edge region 612 away from the negative electrode tab in the width direction of the negative electrode sheet can be further reduced.

[0197] In some embodiments, the ratio of the thickness of the thinned region 512 to the thickness of the body region 511 is 0.87 to 0.99.

[0198] The ratio of the thickness of the thinned region 512 to the thickness of the main body region 511 can be 0.87, 0.88, 0.9, 0.92, 0.95, 0.96, 0.98, 0.99 or any value within the above range.

[0199] The thickness of the main body region 511 can be the average thickness of the main body region 511. For example, along the width direction of the positive electrode sheet, the thickness of the main body region 511 is basically the same at various locations. The average thickness of the main body region 511 can be the average of the thicknesses of the main body region 511 at multiple locations.

[0200] The thickness of the thinning region 512 can gradually change along the width direction of the positive electrode sheet. The thickness of the thinning region is the minimum thickness of the thinning region.

[0201] In this embodiment, the thickness of the main body region 511 and the thickness of the thinned region 512 are within a suitable range, which is beneficial to reduce the mass content of lithium in the thinned region 512 and reduce the risk of lithium deposition in the edge region 612 of the negative electrode film layer 61. At the same time, the positive electrode film layer 51 also has a high mass content of lithium, which is beneficial to balance the energy density and cycle performance of the battery cell.

[0202] In some embodiments, the ratio of the thickness of the thinned region 512 to the thickness of the main region 511 is 0.90 to 0.97. This is beneficial for balancing the lithium content in the positive electrode film layer 51 and the lithium content in the thinned region 512, resulting in a battery cell with higher energy density and better cycle performance.

[0203] In some embodiments, both the thinning region 512 and the body region 511 include lithium phosphate, and the body region 511 further includes at least one of lithium transition metal oxide and lithium replenishing agent, wherein the molar content of lithium in the lithium replenishing agent is greater than the molar content of lithium in the lithium transition metal oxide and the molar content of lithium in the lithium phosphate.

[0204] In lithium-containing transition metal oxides, lithium ions can be reversibly extracted. Lithium-containing transition metal oxides may include 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, and their modified compounds.

[0205] As an example, the thinning region 512 includes lithium phosphate, and the body region 511 includes lithium phosphate and a lithium replenishing agent.

[0206] As an example, the thinning region 512 includes lithium-containing phosphate, and the body region 511 includes lithium-containing phosphate and lithium-containing transition metal oxide.

[0207] As an example, the thinning region 512 includes lithium-containing phosphate, and the body region 511 includes lithium-containing phosphate, lithium-containing transition metal oxide, and lithium replenishing agent.

[0208] In this embodiment, the main region 511 of the positive electrode film layer 51 has a higher lithium content than the thinned region 512, which helps to reduce the risk of lithium plating in the edge region 612 of the negative electrode film layer 61, and the battery cell has better cycle performance; and the positive electrode film layer 51 has a higher lithium content, and the battery cell has a higher energy density.

[0209] In some embodiments, the lithium replenishing agent includes at least one of the following: lithium metal oxide, lithium carbonate, lithium silicate, lithium oxalate, lithium sulfide, lithium nitride, and lithium oxide. The higher molar content of lithium in the above-mentioned lithium replenishing agents is beneficial for providing more lithium ions to the battery cells.

[0210] In some embodiments, lithium-containing metal oxides include at least one of Li6CoO4, Li5FeO4, Li2CuO2, and Li2NiO2; lithium-containing oxalates include at least one of Li2C2O4, Li2C4O4, and Li6C6O6; lithium-containing oxides include at least one of Li2O and Li2O2; lithium-containing silicates include at least one of lithium silicate and lithium metasilicate; lithium-containing carbonates include Li2CO3; lithium-containing nitrides include Li3N; and lithium-containing sulfides include Li2S.

[0211] The lithium replenishing agent has a high molar content of lithium, which is beneficial for providing more lithium ions to the battery cells; and the lithium replenishing agent can be well matched with the electrolyte, positive electrode active material and negative electrode active material in the battery cells.

[0212] In some embodiments, the lithium supplement includes: Li a MO b Where 1≤a≤5, 1≤b≤5, and M includes at least one of Fe, Cu, Co, Mn, Ni, and Al.

[0213] In Li a MO b In the compound, a can be 1, 1.3, 1.5, 2, 2.3, 2.5, 2.8, 3, 3.5, 4, 4.5, 4.8, 5 or any of the above values; b can be 1, 1.3, 1.5, 2, 2.3, 2.5, 2.8, 3, 3.5, 4, 4.5, 4.8, 5 or any of the above values.

[0214] The lithium element molar content in the lithium replenisher is greater than or equal to 1, which is conducive to the release of more lithium ions to replenish the active lithium consumed in the battery cell.

[0215] The aforementioned lithium supplement is beneficial to increasing the mass content of lithium in the positive electrode film layer 51, thereby giving the battery cell a higher energy density.

[0216] In some embodiments, the lithium replenishing agent includes Li5FeO4. This lithium replenishing agent helps to increase the mass content of lithium in the positive electrode film layer 51, thereby giving the battery cell a higher energy density.

[0217] In some embodiments, lithium supplements include Li e FeO f,0≤e≤5,0 <f≤4。

[0218] In Li e FeO f In this context, e can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, or any of the above values, and f can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any of the above values.

[0219] During the formation of a battery cell, the lithium replenisher decomposes to generate lithium ions, and at the same time, the molar content of O and Li elements in the lithium replenisher changes.

[0220] In some embodiments, lithium supplements include Li m FeO n ,0≤m≤1,0 <n≤2。

[0221] In Li m FeO n In this context, m can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any of the above values, and n can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any of the above values.

[0222] During the formation of a battery cell, the lithium replenisher decomposes to generate lithium ions, and at the same time, the molar content of O and Li elements in the lithium replenisher changes.

[0223] It should be noted that, in the reverse stage, if lithium replenishing agent (e.g., Li5FeO4) is not directly detected after disassembling the battery cell, but byproducts of Li5FeO4 (e.g., iron oxides) are detected, those skilled in the art can determine the presence of Li5FeO4 in the battery cell before formation by the byproducts, and the battery cell is also within the scope of protection of this application.

[0224] In some embodiments, the average longest diameter of the lithium supplement is 3 μm to 30 μm.

[0225] The average longest diameter of the lithium replenishing agent can be 3μm, 4μm, 5μm, 6μm, 8μm, 10μm, 12μm, 13μm, 15μm, 16μm, 18μm, 20μm, 21μm, 22μm, 24μm, 26μm, 28μm, 30μm or any value within the above range.

[0226] When the average longest diameter of the lithium replenishing agent is greater than or equal to 3 μm, the degree of side reactions occurring in the battery cell due to the delithiation products of the lithium replenishing agent can be reduced, which is beneficial to improving the cycle life of the battery cell. When the average longest diameter of the lithium replenishing agent is less than or equal to 30 μm, it is beneficial for lithium ions to be extracted from the lithium replenishing agent, which facilitates the transport and diffusion of lithium ions, thereby benefiting the capacity of the battery cell and giving the battery cell a higher energy density.

[0227] In some embodiments, the average longest diameter of the lithium replenishing agent is 5 μm to 20 μm. This is beneficial for improving the energy density and cycle performance of the battery cells.

[0228] In some embodiments, the lithium replenishing agent includes a matrix and a coating layer disposed on at least a portion of the surface of the matrix, the coating layer comprising carbon.

[0229] The coating layer helps improve the stability of the lithium replenisher, and the inclusion of carbon elements in the coating layer helps improve the conductivity of the lithium replenisher, which in turn helps improve the energy density of the battery cell.

[0230] In some embodiments, the matrix can be a lithium-containing iron oxide. For example, the chemical formula of the matrix satisfies Li e FeO f ,0≤e≤5,0 <f≤4。

[0231] In some embodiments, the thickness of the coating layer is 10 nm to 100 nm.

[0232] The thickness of the coating layer can be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm or any value within the above range.

[0233] With a coating thickness of 10nm to 100nm, the coating has a suitable thickness, which is beneficial to improving the stability of the lithium replenishment agent and facilitating the extraction of lithium ions, resulting in a higher energy density for the battery cell.

[0234] In some embodiments, the mass content of the lithium replenishing agent is 0.05% to 5% based on the total mass of the positive electrode film.

[0235] Based on the total mass of the positive electrode film, the mass content of the lithium replenishing agent can be 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 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%, 2.1%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, 5%, or any value within the above range.

[0236] When the mass content of the lithium replenisher is greater than or equal to 0.05% based on the total mass of the positive electrode film 51, it is beneficial to increase the mass content of lithium in the positive electrode film 51, resulting in a higher energy density for the battery cell. Conversely, when the mass content of the lithium replenisher is less than or equal to 5% based on the total mass of the positive electrode film 51, it helps to reduce the adverse effects of excessive lithium replenisher delithiation byproducts on the cycle performance of the battery cell. Therefore, when the mass content of the lithium replenisher is between 0.05% and 5% based on the total mass of the positive electrode film 51, the battery cell exhibits both high energy density and good cycle performance.

[0237] In some embodiments, the mass content of the lithium replenisher is 0.1% to 3% based on the total mass of the positive electrode film 51. This results in a single battery cell with high energy density and good cycle performance.

[0238] In some embodiments, the lithium phosphate includes primary particles and secondary particles formed by the aggregation of primary particles, wherein the average longest diameter of the primary particles is 100 nm to 500 nm and the average longest diameter of the secondary particles is 1 μm to 4 μm.

[0239] In the embodiments of this application, a primary particle refers to the smallest unit of a particle within a certain observation range. A primary particle may contain defects of any form, but it is impossible to further define smaller particles within a primary particle. Primary particles may aggregate under physical forces such as van der Waals forces, but such aggregation is easily disaggregated under external forces such as ultrasound, stirring, and rolling, so that the main constituent morphology of the positive electrode active material in the film layer is still primary particles.

[0240] In the embodiments of this application, secondary particles refer to particles formed by the sequential aggregation of particles.

[0241] The average longest diameter of primary lithium iron phosphate particles is 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 480nm, 500nm or any value within the above range, and the average longest diameter of secondary particles can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm or any value within the above range.

[0242] Lithium iron phosphate particles have a suitable size, which facilitates the extraction of lithium ions and helps to maximize the capacity of the battery cell, resulting in a high energy density for the battery cell.

[0243] In some embodiments, lithium phosphates include those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y z The compounds, wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D 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 Si, Cl, C, and N; Y includes one or more of O and F.

[0244] In the general formula for lithium phosphate, x can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any of the above values; y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any of the above values; a1 can be 0.9, 1, 1.2, 1.3, 1.4, 1.5 or any of the above values; b1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any of the above values; c1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any of the above values; and z can be 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or any of the above values.

[0245] During the charging and discharging process of a single battery cell, the molar content of lithium, oxygen, and other elements in lithium phosphate varies within a certain range.

[0246] In some embodiments, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. These lithium-containing phosphates exhibit high structural stability, which helps to improve the cycle life of battery cells.

[0247] During the charging and discharging process, lithium (Li) undergoes insertion / extraction and consumption within a single battery cell. The molar content of Li in the positive electrode active material varies depending on the discharge state of the cell. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. Similarly, the molar content of O in the examples of positive electrode active materials in this application is only an ideal value. Oxygen release from the crystal lattice causes changes in the molar content of O, resulting in fluctuations in the actual molar content of O.

[0248] In some embodiments, at least a portion of the surface of the lithium phosphate contains carbon. This helps to improve the conductivity of the lithium phosphate, facilitating the full utilization of the battery cell's capacity and resulting in a battery cell with higher energy density.

[0249] As an example, at least a portion of the surface of the lithium phosphate is provided with a coating layer, which includes carbon elements. The inclusion of a carbon-containing coating layer improves the conductivity of the positive electrode active material, facilitating the full utilization of the battery cell's capacity.

[0250] In some embodiments, the carbon content of the lithium phosphate surface is 1% to 2% based on the total mass of the positive electrode active material.

[0251] Based on the total mass of the positive electrode active material, the mass content of carbon on the lithium phosphate surface can be 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any of the above values.

[0252] When the carbon content on the surface of lithium phosphate is 1% to 2% based on the total mass of the positive electrode active material, the positive electrode active material has good conductivity, which facilitates the utilization of the battery cell's capacity, resulting in a higher battery cell capacity.

[0253] In some embodiments, the battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33. The housing 31 has an opening for receiving the electrode assembly 33, and the end cap assembly 32 is used to close the opening.

[0254] In some embodiments, the end cap assembly 32 includes electrode terminals 322, as shown in FIG3. 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.

[0255] In some embodiments, the electrode assembly 33 includes an electrode assembly body portion 330 and a tab portion 331 extending from the electrode assembly body portion 330. The tab portion 331 may be formed by integrating multiple tabs.

[0256] The battery cell 3 also includes a connecting member 34 for connecting the tab 331 of the electrode assembly 33 and the electrode terminal 322. For example, one connecting member 34 is used to connect the tab of the positive electrode and the positive electrode terminal, and another connecting member 34 is used to connect the tab of the negative electrode and the negative electrode terminal.

[0257] [Positive electrode plate]

[0258] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0259] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0260] 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.).

[0261] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0262] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0263] In one embodiment, the positive electrode sheet can be prepared by forming a positive electrode slurry using the components described above. For example, the positive electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0264] [Negative electrode plate]

[0265] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0266] The negative electrode current collector can be a metal foil or a composite negative electrode current collector. The negative electrode current collector can be copper foil. Composite negative electrode current collectors can be formed by depositing metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0267] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include one or more 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 one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more 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.

[0268] The negative electrode film layer may also optionally include a binder. As an example, the binder may include one or more of the following: styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0269] The negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0270] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., deionized water) to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained.

[0271] [Isolation Component]

[0272] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular restrictions on the type of separator; for example, any known porous membrane with good chemical and mechanical stability can be selected.

[0273] In one embodiment, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0274] This application provides a battery device, including the battery cell in any of the above embodiments.

[0275] This application provides an electrical device including a battery cell or battery device as described in any of the above embodiments, wherein the battery cell or battery device is used to store or provide electrical energy.

[0276] 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.

[0277] [Example]

[0278] Example 1

[0279] (1) Preparation of positive electrode sheet

[0280] Lithium iron phosphate (LiFePO4), lithium supplementer Li5FeO4, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:0.6:1.4. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred under vacuum until it became homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil. The positive electrode current collector coated with slurry was then coated, thinned, dried, and cold-pressed to obtain the positive electrode sheet.

[0281] Of these, based on the total mass of the positive electrode film, the mass content of the positive electrode active material is 96%, and the mass content of the lithium supplement is 2%. Along the width direction of the positive electrode sheet, the positive electrode film includes a main region and a thinned region. The single-sided thickness of the main region is 78.5 μm, and the single-sided thickness of the thinned region is 76 μm.

[0282] (2) Preparation of negative electrode sheet

[0283] The first negative electrode active material, artificial graphite, the negative electrode conductive agent Super P, the thickener sodium carboxymethyl cellulose, and the negative electrode binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 97:0.5:1.2:1.3. Deionized water was added as a solvent, and the mixture was stirred evenly under the action of a vacuum mixer to prepare a negative electrode slurry containing the first negative electrode active material.

[0284] The second negative electrode active material, artificial graphite, the negative electrode conductive agent Super P, the thickener sodium carboxymethyl cellulose, and the negative electrode binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 97:0.5:1.2:1.3. Deionized water is added as a solvent, and the mixture is stirred evenly under the action of a vacuum mixer to prepare a negative electrode slurry containing the second negative electrode active material.

[0285] A negative electrode slurry containing a first negative electrode active material and a negative electrode slurry containing a second negative electrode active material are respectively coated on the corresponding middle and edge regions of the negative electrode current collector. After coating, thinning, drying and cold pressing, a negative electrode sheet is obtained.

[0286] The first negative electrode active material has a specific capacity of 345.8 mAh / g and a powder resistivity of 5.86 Ω / cm; the second negative electrode active material has a specific capacity of 360.2 mAh / g and a powder resistivity of 2.12 Ω / cm. Along the width of the negative electrode sheet, the central region has a dimension of 180 mm, the edge region has a total dimension of 3 mm, the thickness of the negative electrode sheet corresponding to the central region is 170 μm, and the minimum thickness of the negative electrode sheet corresponding to the edge region furthest from the negative electrode tab is 163 μm; the coating weight per unit area of ​​the central region is 165 mg / 1540 mm². 2 The coating weight per unit area in the edge region is 127 mg / 1540 mm². 2 The ratio of the coating weight per unit area in the middle zone to the coating weight per unit area in the edge zone is 1.3.

[0287] (3) Preparation of the separating membrane

[0288] The separator consists of a 7μm polyethylene (PE) film.

[0289] (4) Preparation of electrolyte

[0290] The electrolyte consists of a solvent and an electrolyte salt. The solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1. The electrolyte salt is LiPF6, and the concentration of the electrolyte salt is 1 mol / L.

[0291] (5) Preparation of battery cells

[0292] The negative electrode, separator, and positive electrode are wound into an electrode assembly; the electrode assembly is placed in a housing, electrolyte is injected, and after standing and formation processes, a single battery cell is obtained.

[0293] Example 2-3

[0294] The difference between Examples 2-3 and Example 1 is that the mass content of lithium in the positive electrode film is different.

[0295] Specifically, the change in the mass content of lithium in the positive electrode film is achieved by setting different mass contents of lithium supplementing agent.

[0296] Examples 4-5

[0297] The difference between Examples 4-5 and Example 1 lies in the specific capacity of the first and second negative electrode active materials. In Example 4, the powder resistivity of the first negative electrode active material is 6.1 Ω / cm, and the powder resistivity of the second negative electrode active material is 2.12 Ω / cm; in Example 5, the powder resistivity of the first negative electrode active material is 5.86 Ω / cm, and the powder resistivity of the second negative electrode active material is 3.5 Ω / cm.

[0298] Example 6

[0299] The difference between Example 6 and Example 1 is that the total size of the edge region is different along the width direction of the negative electrode sheet.

[0300] Examples 7-8

[0301] The difference between Examples 7-8 and Example 1 is that the coating weight per unit area in the middle region of the negative electrode sheet is different from the coating weight per unit area in the edge region.

[0302] In Example 7, the coating weight per unit area of ​​the intermediate region was 165 mg / 1540 mm². 2 The coating weight per unit area in the edge zone is 150 mg / 1540 mm². 2 The ratio of the coating weight per unit area in the middle zone to the coating weight per unit area in the edge zone is 1.1.

[0303] In Example 8, the coating weight per unit area of ​​the intermediate region was 165 mg / 1540 mm. 2The coating weight per unit area of ​​the edge zone is 110 mg / 1540 mm. 2 The ratio of the coating weight per unit area in the middle zone to the coating weight per unit area in the edge zone is 1.5.

[0304] Examples 9-10

[0305] The difference between Examples 9-10 and Example 1 is that the ratio of the thickness of the thinned region to the thickness of the main body region is different in the positive electrode sheet.

[0306] Examples 11-13

[0307] The difference between Examples 11-13 and Example 1 is that the second negative electrode active material also includes a silicon-based material, which is a silicon-carbon material.

[0308] In Example 11, based on the total mass of the second negative electrode active material, the mass ratio of silicon to carbon is 1.5%.

[0309] In Example 12, based on the total mass of the second negative electrode active material, the mass ratio of silicon to carbon is 10%.

[0310] In Example 13, based on the total mass of the second negative electrode active material, the mass ratio of silicon to carbon is 20%.

[0311] Comparative Example 1

[0312] The difference between Comparative Example 1 and Example 1 is that the negative electrode active materials in the middle and edge regions of the negative electrode film are the same, and the specific capacity of the negative electrode active materials is 345.8 mAh / g.

[0313] Comparative Example 2

[0314] The difference between Comparative Example 2 and Example 1 is that the specific capacity of the first negative electrode active material is greater than that of the second negative electrode active material, wherein the specific capacity of the first negative electrode active material is 345.8 mAh / g and the specific capacity of the second negative electrode active material is 340 mAh / g.

[0315] Comparative Example 3

[0316] The difference between Comparative Example 3 and Example 1 is that the mass content of lithium in the positive electrode film layer of the battery cell at 0% SOC is less than 3.9%, specifically 3.5%.

[0317] Comparative Example 4

[0318] The difference between Comparative Example 4 and Example 1 is that the mass content of lithium in the positive electrode film layer of the battery cell at 0% SOC is greater than 4.3%, specifically 4.5%.

[0319] In Table 1, A represents the mass content of lithium in the positive electrode film at 0% SOC of the battery cell, B represents the mass content of lithium replenishment agent based on the total mass of the positive electrode film, Q1 represents the specific capacity of the first negative electrode active material in the middle region, Q2 represents the specific capacity of the second negative electrode active material in the edge region, C represents the ratio of the coating weight per unit area in the middle region to the coating weight per unit area in the edge region, L2 represents the total size of the edge region of the negative electrode sheet, and D2 / D1 represents the ratio of the thickness of the thinned area to the thickness of the main body area of ​​the positive electrode sheet.

[0320] Table 1. Test results of Examples 1-10 and Comparative Examples 1-4

[0321] In Table 1 above, the volumetric energy density of Example 1 is 450 Wh / L, and the volumetric energy density of Comparative Example 4 is 420 Wh / L.

[0322] Table 2 Test results of Examples 11-13

[0323] As shown in Examples 1-10 and Comparative Examples 1-2, by setting the edge region of the negative electrode film layer to include the second negative electrode active material and the middle region of the negative electrode film layer to include the first negative electrode active material, and the specific capacity of the second negative electrode active material is greater than that of the first negative electrode active material, it is beneficial to reduce the risk of lithium plating in the edge region and to improve the cycle life of the battery cell.

[0324] In conjunction with Examples 1-10 and Comparative Example 3, setting the lithium content in the positive electrode film layer of the battery cell to be less than 3.9% at 0% SOC is beneficial to improving the cycle life of the battery cell.

[0325] In conjunction with Examples 1-10 and Comparative Example 4, when the lithium content in the positive electrode film layer of a single battery cell is set to be greater than 4.3% at 0% SOC, the cycle life of the battery cell is improved, but the energy density of the battery cell is low.

[0326] As shown in Examples 1-3, by setting the lithium content in the positive electrode film layer of the battery cell to 3.9% to 4.3% at 0% SOC, and by combining the first negative electrode active material in the middle region and the second negative electrode active material in the edge region, the battery cell has a high cycle life.

[0327] As shown in Examples 1-4, the specific capacity of the first negative electrode active material is greater than or equal to 330 mAh / g, the capacity of the middle region of the negative electrode film matches the mass content of lithium in the positive electrode film, and the battery cell has a high cycle life.

[0328] Combined with Examples 1-3 and 5, the specific capacity of the second negative electrode active material is greater than or equal to 340 mAh / g, the risk of lithium deposition at the edge of the negative electrode film is low, and the battery cell has a high cycle life.

[0329] As shown in Examples 1 and 6, setting the total size of the edge region along the width direction of the negative electrode sheet to be greater than or equal to 1.5 mm reduces the risk of lithium plating on the negative electrode sheet and results in a higher cycle life for the battery cell. Setting the total size of the edge region along the width direction of the negative electrode sheet to be less than or equal to 5 mm helps to reduce the space occupied by the edge region and improve the energy density of the battery cell.

[0330] In conjunction with Examples 1 and 7-8, the ratio of coating weight per unit area in the middle region to coating weight per unit area in the edge region is 1.1 to 1.5, resulting in a longer cycle life for the battery cell.

[0331] In conjunction with Examples 1 and 9-10, the ratio of the thickness of the thinned region to the thickness of the main region of the positive electrode film is set to 0.87 to 0.99. The risk of lithium plating at the edge region of the negative electrode film is low, and the battery cell has a high cycle life.

[0332] As shown in Examples 11-13, adding silicon-based materials to the edge region helps reduce the risk of lithium plating in the edge region; in the second negative electrode active material in the edge region, the mass ratio of silicon to carbon is 1.5% to 20%, and the battery cell has a long cycle life and high energy density.

[0333] 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.

[0334] The following is a brief description of the testing methods for the physicochemical and 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.

[0335] 1. Cycle life test method

[0336] At 25℃, the battery cell was charged at a constant current rate of 1 / 3C to 3.65V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 1C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as the discharge capacity of the battery cell in the first cycle. The battery cell was subjected to 1000 charge-discharge cycles using the above method, and the discharge capacity of each cycle was recorded.

[0337] The capacity retention rate of a single lithium-ion battery cell after 1000 cycles at 25°C and 1 / 3C / 1C = discharge capacity of the 1000th cycle / discharge capacity of the 1st cycle × 100%.

[0338] 2. Test method for lithium plating

[0339] The battery cells were disassembled to observe whether lithium plating appeared at the edge of the negative electrode.

[0340] As an example, if white lithium metal is observed in the edge region, it is considered that lithium plating has occurred in the edge region.

[0341] As another example, the following method can be used to further assist in determining whether lithium plating has occurred: Specifically, ethanol is titrated onto the surface of the negative electrode; if bubbles are produced, it indicates that lithium plating has occurred.

[0342] 3. Test method for specific capacity of negative electrode active materials

[0343] A slurry is prepared by combining a negative electrode active material (e.g., a first negative electrode active material or a second negative electrode active material) with a conductive agent and a binder. This slurry is then coated onto a negative electrode current collector to form a coin cell. A lithium sheet is used as the positive electrode. A charge-discharge test of 0.05C / 1C is performed within a voltage range of 0.005V to 2V, and the first charge capacity of the coin cell is recorded.

[0344] The specific capacity of the negative electrode active material = the capacity of the first charge / the mass of the negative electrode active material.

[0345] 4. Testing of lithium content in the positive electrode sheet

[0346] Discharge the battery cell to 0% SOC at 25℃ and 1 / 3C rate, disassemble the battery cell, and remove the positive electrode plate.

[0347] The positive electrode film layer of the positive electrode sheet was scraped off and added to aqua regia. The material was then digested under mechanical stirring and high temperature and pressure for 30 minutes. The digested solution was then added to an ICAP7400 spectrometer (EPA 6010D-2018) to analyze the lithium content. The lithium mass content was calculated as: mass of lithium / mass of all elements in the positive electrode film layer.

[0348] 5. Test of the average value of the longest diameter

[0349] The positive electrode sheet, which includes lithium replenishing particles and lithium iron phosphate material, is cut along the thickness direction to expose the longitudinal section of the positive electrode film. The longest diameter of the lithium replenishing agent and lithium iron phosphate material is determined by scanning electron microscopy (SEM) of the longitudinal section of the positive electrode film.

[0350] Specifically, the longest diameter of a lithium replenishing agent refers to the longest straight line that passes through the center point of the lithium replenishing agent and extends to the outer periphery of the particle, while the longest diameter of a lithium iron phosphate material refers to the longest straight line that passes through the center point of the lithium iron phosphate material and extends to the outer periphery of the particle.

[0351] As an example, arbitrarily select 30 lithium replenishing agent particles in the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 lithium replenishing agent particles, and take their average value; arbitrarily select 30 lithium iron phosphate material particles in the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 lithium iron phosphate material particles, and take their average value.

[0352] 6. Test method for coating thickness

[0353] Cut the positive electrode sheet along its thickness to expose the longitudinal section of the positive electrode film. By performing SEM testing on the longitudinal section of the positive electrode film, and selecting the lithium replenishing particles, it can be observed that the lithium replenishing particles have a core-shell structure. The thickness of the shell layer is the thickness of the coating layer.

[0354] 7. Test method for powder resistance

[0355] Weigh an appropriate amount of powder, and then use a powder resistivity tester (ST2722 digital four-probe instrument, manufactured by Suzhou Jingge Electronics Co., Ltd.) to determine the powder resistivity of the sample according to GB / T 30835-2014. The test pressure is 3 tons.

[0356] 8. Test of the mass ratio of silicon to carbon elements

[0357] The battery cell was disassembled to obtain the negative electrode sheet. Then, the edge region of the negative electrode sheet was cut off, and the negative electrode film layer in the edge region was scraped off to separate the second negative electrode active material. Next, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the mass content of silicon and carbon in the second negative electrode active material, and the mass ratio of silicon to carbon was then calculated.

[0358] 9. Test of coating weight per unit area

[0359] The battery cell is disassembled to obtain the electrode sheets, and the thickness of the electrode sheets and the thickness of the current collector are measured separately. A certain area of ​​the electrode sheet is taken, its area is measured, and the mass of the film layer on the current collector after removing the current collector is weighed. The coating weight per unit area of ​​the electrode sheet is calculated based on this area and mass.

[0360] 10. Testing of the mass content of lithium supplement

[0361] The battery cell is disassembled to obtain the positive electrode sheet, and the mass content of phosphorus (P) and iron (Fe) elements in the positive electrode film layer is measured. By detecting the ratio of P to Fe content, the mass content of lithium supplementer (e.g., Li5FeO4) in the positive electrode film layer can be determined.

[0362] 11. Measurement of volumetric energy density

[0363] At 25°C, the battery cells were charged at a constant current rate of 1 / 3C to 3.65V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 5 minutes, the cells were discharged at a constant current rate of 1 / 3C to 2.5V, and the discharge energy of the battery cells was recorded.

[0364] The volume of a single battery cell is calculated by measuring the length, width, and height of its outer casing.

[0365] The volumetric energy density of a single battery cell = the discharge energy of the single battery cell / the volume of the single battery cell.

Claims

1. A battery cell, characterized in that, Including positive electrode plates and negative electrode plates; The positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector; the negative electrode includes a negative current collector and a negative electrode film layer located on at least one surface of the negative current collector; along a first direction of the negative electrode, the edge of the negative electrode film layer extends beyond the edge of the positive electrode film layer, wherein... The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate, and the mass content of lithium in the positive electrode film layer of the battery cell at 0% SOC is 3.9% to 4.3%. The negative electrode film layer includes a middle region and an edge region. Along the first direction, the edge region is located on at least one side of the middle region. The middle region includes a first negative electrode active material, and the edge region includes a second negative electrode active material. The specific capacity of the second negative electrode active material is greater than that of the first negative electrode active material.

2. The battery cell according to claim 1, characterized in that, The specific capacity of the first negative electrode active material is 330 mAh / g to 350 mAh / g; optionally, it is 340 mAh / g to 350 mAh / g.

3. The battery cell according to claim 2, characterized in that, The specific capacity of the second negative electrode active material is from 340 mAh / g to 400 mAh / g; optionally, it is from 350 mAh / g to 370 mAh / g.

4. The battery cell according to any one of claims 1 to 3, characterized in that, Along the first direction, the size of the intermediate region is 100mm to 300mm.

5. The battery cell according to any one of claims 1 to 4, characterized in that, Along the first direction, the total size of the edge region is 1.5 mm to 5 mm; optionally, it is 2 mm to 3 mm.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The first negative electrode active material includes graphite, and the second negative electrode active material includes graphite.

7. The battery cell according to claim 6, characterized in that, The powder resistance of graphite in the first negative electrode active material is greater than that of graphite in the second negative electrode active material.

8. The battery cell according to claim 7, characterized in that, Under 3T pressure, the powder resistance of graphite in the first negative electrode active material is 4Ω / cm to 10Ω / cm.

9. The battery cell according to claim 7 or 8, characterized in that, Under 3T pressure, the powder resistivity of graphite in the second negative electrode active material is 0.5Ω / cm to 3.5Ω / cm.

10. The battery cell according to any one of claims 1 to 5, characterized in that, The first negative electrode active material includes graphite, and the second negative electrode active material includes graphite and silicon-based materials.

11. The battery cell according to claim 10, characterized in that, Based on the total mass of the second negative electrode active material, the ratio of silicon content to carbon content is 0.5% to 30%; optionally, it is 1.5% to 10%.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The ratio of the coating weight per unit area of ​​the intermediate zone to the coating weight per unit area of ​​the edge zone is 1.1 to 1.

5.

13. The battery cell according to any one of claims 1 to 12, characterized in that, The negative electrode sheet includes a negative electrode tab, and the negative electrode tab extends out of the negative electrode film layer along the width direction of the negative electrode sheet; Along the width direction of the negative electrode sheet, the edge region is located on both sides of the middle region.

14. The battery cell according to claim 13, characterized in that, Along the width direction of the negative electrode sheet, the edge region away from the negative electrode tab includes a first sub-region and a second sub-region. The first sub-region is farther away from the middle region relative to the second sub-region, and the thickness of the first sub-region is less than the thickness of the second sub-region.

15. The battery cell according to claim 14, characterized in that, The difference between the thickness of the second sub-region and the thickness of the first sub-region is 3 μm to 5 μm.

16. The battery cell according to claim 14 or 15, characterized in that, The difference between the thickness of the intermediate region and the thickness of the edge region away from the negative electrode tab along the width direction of the negative electrode sheet is 3 μm to 10 μm.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The positive electrode film layer includes a lithium replenishing agent, wherein the molar content of lithium in the lithium replenishing agent is greater than the molar content of lithium in the positive electrode active material.

18. The battery cell according to any one of claims 1 to 17, characterized in that, The positive electrode sheet includes a positive electrode tab, and the positive electrode tab extends out of the positive electrode film layer along the width direction of the positive electrode sheet; The positive electrode film layer includes a main region and a thinned region. Along the width direction of the positive electrode sheet, the thinned region is farther away from the positive electrode tab relative to the main region, and the thickness of the thinned region is less than the thickness of the main region.

19. The battery cell according to claim 18, characterized in that, The ratio of the thickness of the thinned area to the thickness of the main body area is 0.87 to 0.99, and can be selected as 0.90 to 0.

97.

20. The battery cell according to claim 18 or 19, characterized in that, Both the thinning region and the main body region include the lithium-containing phosphate, and the main body region also includes at least one of lithium-containing transition metal oxide and lithium replenishing agent, wherein the molar content of lithium element in the lithium replenishing agent is greater than the molar content of lithium element in the lithium-containing transition metal oxide and the molar content of lithium element in the lithium-containing phosphate.

21. The battery cell according to any one of claims 17 to 20, characterized in that, The lithium supplement includes at least one of the following: lithium metal oxide, lithium carbonate, lithium silicate, lithium oxalate, lithium sulfide, lithium nitride, and lithium oxide.

22. The battery cell according to claim 21, characterized in that, The lithium-containing metal oxide includes at least one of Li6CoO4, Li5FeO4, Li2CuO2, and Li2NiO2; The lithium oxalate includes at least one of Li2C2O4, Li2C4O4, and Li6C6O6; The lithium-containing oxide includes at least one of Li2O and Li2O2; The lithium-containing silicate includes at least one of lithium silicate and lithium metasilicate; The lithium-containing carbonate includes Li2CO3; The lithium-containing nitride includes Li3N; The lithium-containing sulfide includes Li2S.

23. The battery cell according to any one of claims 17 to 21, characterized in that, The lithium supplement includes: Li a MO b , where 1≤a≤5, 1≤b≤5, and M includes at least one of Fe, Cu, Co, Mn, Ni, and Al.

24. The battery cell according to any one of claims 17 to 21, characterized in that, The lithium supplement includes Li5FeO4.

25. The battery cell according to any one of claims 17 to 21, characterized in that, The lithium supplement includes Li e FeO f ,0≤e≤5,0 <f≤4。 26. The battery cell according to any one of claims 17 to 21, characterized in that, The lithium supplement includes Li m FeO n ,0≤m≤1,0 <n≤2。 27. The battery cell according to any one of claims 17 to 26, characterized in that, The average longest diameter of the lithium replenishing agent is 3 μm to 30 μm; optionally, the average longest diameter of the lithium replenishing agent is 5 μm to 20 μm.

28. The battery cell according to any one of claims 17 to 27, characterized in that, The lithium replenishing agent includes a matrix and a coating layer disposed on at least a portion of the surface of the matrix, the coating layer comprising carbon.

29. The battery cell according to claim 28, characterized in that, The thickness of the coating layer is 10 nm to 100 nm.

30. The battery cell according to any one of claims 17 to 29, characterized in that, Based on the total mass of the positive electrode film, the mass content of the lithium replenishing agent is 0.05% to 5%; optionally, it is 0.1% to 3%.

31. The battery cell according to any one of claims 1 to 30, characterized in that, The lithium phosphate comprises primary particles and secondary particles formed by the aggregation of the primary particles. The average longest diameter of the primary particles is 100 nm to 500 nm, and the average longest diameter of the secondary particles is 1 μm to 4 μm.

32. The battery cell according to any one of claims 1 to 31, characterized in that, The lithium-containing phosphate includes those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y z Compounds wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D 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; Y includes one or more of O and F.

33. The battery cell according to any one of claims 1 to 32, characterized in that, The lithium-containing phosphate includes at least one of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

34. The battery cell according to any one of claims 1 to 33, characterized in that, At least a portion of the surface of the lithium phosphate contains carbon.

35. A battery device, characterized in that, include: Multiple battery cells according to any one of claims 1 to 34.

36. An electrical appliance, characterized in that, include: A plurality of battery cells according to any one of claims 1 to 34, or a battery device according to claim 35, wherein the battery cells or battery devices are used to store or provide electrical energy.

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