Battery cell, battery device, and energy storage device

Abstract

A battery cell, a battery device, and an energy storage device. The battery cell comprises an electrode assembly and an electrolyte, the electrode assembly comprises a positive electrode sheet, a separator, and a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material and a lithium-rich compound; the areal density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm2; the electrolyte comprises dimethyl carbonate, and based on the total mass of the electrolyte, the mass percentage of dimethyl carbonate is 15%-50%.

Description

Battery cells, battery devices and energy storage devices

[0001] Cross-referencing

[0002] This application incorporates, in its entirety, patent application No. PCT / CN2025 / 085927, filed on March 28, 2025, entitled “Lithium-ion secondary battery, battery device, power device, preparation of positive electrode active material”, and PCT patent application No. PCT / CN2025 / 140521, filed on December 5, 2025, entitled “Battery cell, battery device and energy storage device”. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a battery cell, battery device and energy storage device. Background Technology

[0004] Energy conservation and emission reduction are key to sustainable social development. Rechargeable batteries, with their ability to store or release energy as needed, are widely used in various energy storage systems and are an important component in promoting energy transition and sustainable development. For the new energy industry, battery technology is a crucial factor in its development.

[0005] With increasing market demands for higher energy storage capacity, longer lifespan, and higher energy conversion efficiency in energy storage batteries, the requirements for battery capacity, cycle performance, and energy conversion efficiency are becoming more stringent. However, existing technologies struggle to simultaneously improve these performance characteristics, making the challenge of achieving a balance between these performance metrics a pressing technical problem in this field. Summary of the Invention

[0006] This application aims to at least address one of the technical problems existing in the background art. Therefore, one objective of this application is to provide a battery cell with high capacity, good cycle performance, and high energy conversion efficiency.

[0007] This application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium-rich compound. The density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm². 2 The electrolyte includes dimethyl carbonate, and the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0008] Adding lithium-rich compounds to battery cells helps improve their cycle performance; increasing the density of any side of the positive electrode film helps increase the capacity of the battery cell. However, the applicant found that increasing the density of any side of the positive electrode film to greater than or equal to 0.3 g / 1540.25 mm... 2 Subsequently, lithium-rich compounds in the positive electrode film layer tend to agglomerate, leading to uneven lithium-ion insertion / extraction in the positive electrode sheet. On the one hand, this phenomenon easily induces concentration polarization, increasing the internal resistance of the battery cell and reducing its energy conversion efficiency (RTE). On the other hand, uneven reaction in the positive electrode film layer can easily lead to excessive local delithiation or insertion of lithium in the positive electrode film layer and the corresponding negative electrode film layer, and can also easily lead to uneven formation of the SEI and CEI films, thus affecting the battery cycle performance. In the embodiments of this application, dimethyl carbonate is further added to the electrolyte, and its mass percentage is controlled within the range of 15%-50%. This helps to reduce the electrolyte viscosity, increase the lithium-ion migration rate, and thereby improve the uniformity of lithium ions in the battery by improving liquid phase diffusion. This enhances the effect of the lithium replenishment agent on improving the cycle life of the battery cell and improves the energy conversion efficiency of the battery cell.

[0009] In any embodiment, the mass percentage of dimethyl carbonate is 30%-50% based on the total mass of the electrolyte.

[0010] The mass percentage of dimethyl carbonate is further within the above range, which helps to further reduce the electrolyte viscosity, improve the uniformity of lithium ion insertion / extraction, and thus further improve the cycle performance and energy conversion efficiency of the battery cell.

[0011] In any embodiment, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.45g / 1540.25mm 2 .

[0012] In any embodiment, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.4g / 1540.25mm 2 .

[0013] Having a density on any side of the positive electrode film within the above range helps to reduce the thickness of the positive electrode film, suppress the aggregation of lithium-rich compounds, improve the uniformity of lithium ion insertion / extraction in the positive electrode film, and thus further improve the cycle performance and energy conversion efficiency of the battery cell.

[0014] In any embodiment, the capacity of the battery cell is 400Ah-3000Ah.

[0015] When the capacity of a single battery cell is within the aforementioned range, it generates a high amount of heat and has difficulty dissipating it. The accumulated heat raises the internal temperature of the battery, exacerbating the side reactions at the sites of excessive lithium insertion and delithiation caused by the aggregation of lithium-rich compounds, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the positive electrode film layer comprises a lithium-rich compound; the density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm². 2 Based on the total mass of the electrolyte, dimethyl carbonate accounts for 15%-50% of the mass, and still has good cycle performance and energy conversion efficiency when the capacity of the battery cell is in the range of 400Ah-3000Ah.

[0016] In any embodiment, the capacity of the battery cell is 400Ah-1500Ah.

[0017] In any embodiment, the capacity of the battery cell is 400Ah-1100Ah.

[0018] A battery cell capacity within the aforementioned range helps reduce the internal temperature of the battery cell, further improving its cycle performance and energy conversion efficiency.

[0019] In any embodiment, the lithium-rich compound accounts for 3%-20% of the total mass of the positive electrode film.

[0020] An increase in the mass percentage of lithium-rich compounds is accompanied by a decrease in the mass percentage of positive electrode active materials. When the mass percentage of lithium-rich compounds is within the above range, it helps to balance the capacity, cycle performance, and energy conversion efficiency of the battery cell.

[0021] In any embodiment, the lithium-rich compound accounts for 5%-15% of the total mass of the positive electrode active material and the lithium-rich compound.

[0022] When the mass percentage of lithium-rich compounds is within the above range, the battery cell achieves excellent capacity, cycle performance, and energy conversion efficiency, which helps to improve the overall performance of the battery cell.

[0023] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 .

[0024] The compaction density of the positive electrode film is within the above range, which helps to reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0025] In any embodiment, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm3 .

[0026] In any embodiment, the positive electrode active material comprises lithium transition metal phosphate particles with at least a portion of their surface disposed of carbon material.

[0027] Lithium-containing transition metal phosphates, as positive electrode active materials, have the advantage of good structural stability, which helps to further improve the cycle performance of battery cells.

[0028] In any embodiment, based on the total area of ​​lithium transition metal phosphate particles in the cross section along the thickness direction of the positive electrode film, the area ratio of lithium transition metal phosphate particles with particle size R1 satisfying 1500nm≤R1≤5000nm is 8.0%-20.0%, and can be optionally 10.0%-20.0%.

[0029] If the area ratio of lithium-containing transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is within the above range, it indicates that there are more large-sized particles in the positive electrode film layer. This helps to increase the compaction density of the positive electrode film layer, thereby reducing the thickness of the positive electrode film layer, improving the uniformity of the distribution of lithium-rich compound particles in the positive electrode film layer, and further improving the energy conversion efficiency and cycle performance of the battery cell.

[0030] In any embodiment, based on the total area of ​​lithium transition metal phosphate particles in the cross section along the thickness direction of the positive electrode film, the area ratio of lithium transition metal phosphate particles with particle size R1 satisfying 1500nm≤R1≤5000nm is 10.0%-20.0%.

[0031] In any embodiment, based on the total area of ​​lithium transition metal phosphate particles in the cross section along the thickness direction of the positive electrode film, the area ratio of lithium transition metal phosphate particles with particle size R2 satisfying 1000nm≤R2<200nm is 15.0%-25.0%.

[0032] Lithium-containing transition metal phosphate particles with a particle size R2 satisfying 1000nm≤R2<200nm represent smaller positive electrode active materials in the positive electrode film. Their area proportion is within the above range, which helps to further improve the compaction density of the positive electrode film through particle gradation, reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0033] In any embodiment, based on the total area of ​​lithium transition metal phosphate particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of lithium transition metal phosphate particles with particle size R2 satisfying 1000nm≤R2<200nm is 16%-20%.

[0034] In any embodiment, in the cross-section of the positive electrode film along the electrode thickness direction, the median L of the spheroidity in the cumulative distribution curve of the spheroidity area of ​​the lithium transition metal phosphate particles is... A50 It ranges from 0.6 to 0.85.

[0035] The median sphericity of lithium transition metal phosphate particles within the above range indicates that they have high roundness, which helps to improve the slippage of particles in the positive electrode film, reduce the "bridging" phenomenon between particles, further improve the compaction density of the positive electrode film, reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0036] In any embodiment, in the cross-section of the positive electrode film along the electrode thickness direction, the median L of the spheroidity in the cumulative distribution curve of the spheroidity area of ​​the lithium transition metal phosphate particles is... A50 It is 0.65-0.8.

[0037] In any embodiment, the electrolyte comprises a linear carbonate solvent, the linear carbonate solvent comprising dimethyl carbonate, and the linear carbonate solvent further comprising one or more of diethyl carbonate and ethyl methyl carbonate.

[0038] Linear carbonates have low viscosity, and dimethyl carbonate has even lower viscosity than other linear carbonates. The presence of dimethyl carbonate and other types of linear carbonates in the electrolyte helps to further reduce its viscosity, increase the lithium-ion diffusion rate, and improve the uneven lithium-ion insertion / extraction phenomenon in the positive electrode film caused by the aggregation of lithium-rich compounds, thereby further improving the energy conversion efficiency and cycle performance of the battery cell.

[0039] In any embodiment, the linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate is 10%-50% based on the total mass of the electrolyte.

[0040] In any embodiment, the electrolyte comprises a cyclic carbonate solvent, which includes one or more of ethylene carbonate and propylene carbonate.

[0041] Cyclic carbonates have a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the conductivity of the electrolyte, further improving the uneven lithium ion insertion / extraction phenomenon in the positive electrode film, and improving the energy conversion efficiency and cycle performance of the battery cell.

[0042] In any embodiment, the cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate is 10%-40% based on the total mass of the electrolyte.

[0043] In any embodiment, the cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate is 0.5%-10% based on the total mass of the electrolyte.

[0044] Propylene carbonate has a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the electrolyte conductivity and reducing the internal resistance of the battery cell. However, propylene carbonate is prone to co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the mass percentage of propylene carbonate is within the above-mentioned range, which helps to balance the energy conversion efficiency and cycle performance of the battery cell.

[0045] In any embodiment, the cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate is 2.5%-10% based on the total mass of the electrolyte.

[0046] In any embodiment, the electrolyte includes an additive, which includes one or more of fluoroethylene carbonate and vinylene carbonate.

[0047] Uneven distribution of lithium-rich compounds can easily lead to uneven lithium-ion insertion / extraction, resulting in uneven stress during cycling. Excessive local stress can damage the SEI film, accelerating its rupture and repair process, thus affecting the cycle performance and energy conversion efficiency of the battery cell. Including the aforementioned additives in the electrolyte helps form a dense and stable SEI film on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0048] In any embodiment, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 0.05%-5% of the total mass of the electrolyte.

[0049] In any embodiment, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 2%-3% of the total mass of the electrolyte.

[0050] When the mass percentage of fluoroethylene carbonate is within the above range, it helps to form an SEI film of suitable thickness, taking into account both the stability and interfacial impedance of the SEI film, thereby balancing the cycle performance and energy conversion efficiency of the battery cell and further improving the overall performance of the battery cell.

[0051] In any embodiment, the additive includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte.

[0052] In any embodiment, the additive includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.5%-8% based on the total mass of the electrolyte.

[0053] In any embodiment, the linear carbonate solvent includes ethyl methyl carbonate, and the additive includes fluoroethylene carbonate.

[0054] The applicant discovered that the combined use of ethyl methyl carbonate and fluoroethylene carbonate helps improve the cycle performance of battery cells.

[0055] In any embodiment, the cyclic carbonate solvent includes propylene carbonate, and the additive includes vinylene carbonate.

[0056] Propylene carbonate readily undergoes a co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. The applicant discovered that using propylene carbonate in combination with ethylene carbonate can effectively suppress the co-intercalation reaction of propylene carbonate, further improving the cycle performance of the battery cell.

[0057] In any embodiment, the electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0058] In any embodiment, the electrolyte solution comprises lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 1%-7% based on the total mass of the electrolyte solution.

[0059] Lithium difluorosulfonylimide helps to form a dense and stable SEI film on the negative electrode side, thereby helping to improve the phenomenon of excessive local stress damaging the SEI film during cycling caused by uneven distribution of lithium-rich compounds, and further improving the cycle performance and energy conversion efficiency of the battery cell.

[0060] In any embodiment, the electrolyte solution comprises lithium bisfluorosulfonylimide, and the mass percentage of lithium bisfluorosulfonylimide is 2%-7% based on the total mass of the electrolyte solution.

[0061] In any embodiment, the electrolyte comprises lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate is 2%-15% based on the total mass of the electrolyte.

[0062] In any embodiment, the electrolyte comprises lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate is 4%-8% based on the total mass of the electrolyte.

[0063] In any embodiment, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.5-5.5.

[0064] As the content of lithium difluorosulfonylimide increases, the SEI film becomes thicker. When the mass ratio of lithium hexafluorophosphate and lithium difluorosulfonylimide is within the above range, the electrolyte has a suitable active lithium concentration and the SEI film has a suitable thickness, thus balancing the conductivity of the electrolyte and the interfacial impedance on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0065] In any embodiment, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 2-4.

[0066] In any embodiment, the positive electrode film layer comprises carbon nanotubes.

[0067] The aggregation of lithium-rich compounds in the cathode film layer leads to uneven lithium-ion insertion and extraction. Higher electron transport capacity is required in the region of high-concentration lithium-ion insertion and extraction. The cathode film layer includes carbon nanotubes, which helps to form a good electron transport network within the cathode film layer, thereby helping to improve the uniformity of lithium-ion insertion and extraction in the cathode film layer, and further improving the cycle performance and energy conversion efficiency of the battery cell.

[0068] In any embodiment, the carbon nanotubes account for 0.1%-3% of the total mass of the positive electrode film.

[0069] In any embodiment, the carbon nanotubes account for 0.5%-1% of the total mass of the positive electrode film.

[0070] In any embodiment, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

[0071] In any embodiment, the positive electrode active material comprises the components shown in Formula I:

[0072] Li m Fe x P y O j Q q Formula I,

[0073] Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0074] In any embodiment, the lithium-rich compound includes one or more of lithium iron ferrite, lithium nickel ferrite, lithium manganese ferrite, lithium cobalt ferrite, lithium sulfide, lithium nitride, lithium hydroxide, lithium fluoride, lithium oxalate, lithium oxide, and lithium peroxide.

[0075] In any embodiment, the lithium-rich lithium iron ore comprises the components shown in general formula II:

[0076] Li 5+a1 Fe 1+b1 O 4+c1 Formula II

[0077] Where -5≤a1≤0.5, -0.1≤b1≤0.5, and -0.4≤c1≤0.4.

[0078] In any implementation, -5≤a1≤0.

[0079] In any implementation, -5≤a1≤0, b1=1, c1=4.

[0080] In any embodiment, the lithium-rich nickel oxide comprises the components shown in Formula III:

[0081] Li 2+a2 Ni 1+b2 O 2+c2 Formula III

[0082] Where -2≤a2≤0.2, -0.1≤b2≤0.1, and -0.2≤c2≤0.2.

[0083] In any implementation, -2≤a2≤0.

[0084] In any implementation, -2≤a2≤0, b2=1, c2=2.

[0085] In any embodiment, the D of the lithium-rich compound particles is calculated based on the total area of ​​the lithium-rich compound particles in a cross-section along the thickness direction of the positive electrode film. A 50 represents 1μm-50μm.

[0086] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0087] The total coating area of ​​the positive electrode film layer in a single battery cell is within the aforementioned range, which helps to increase the capacity to ≥400Ah. However, high-capacity battery cells generate a lot of heat and have difficulty dissipating it. Heat accumulation leads to an increase in the internal temperature of the battery, exacerbating the side reactions at the sites of excessive lithium insertion and extraction caused by the agglomeration of lithium-rich compounds, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the positive electrode film layer includes lithium-rich compounds; the density of any side of the positive electrode film layer is greater than or equal to 0.3g / 1540.25mm². 2 Based on the total mass of the electrolyte, dimethyl carbonate accounts for 15%-50% of the mass, and still has good cycle performance and energy conversion efficiency when the capacity of the battery cell is in the range of 400Ah-3000Ah.

[0088] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 19.4 m². 2 -120m 2 .

[0089] In any embodiment, the total coating area of ​​the positive electrode film layer contained in the battery cell is 20m². 2 -120m 2 .

[0090] In any embodiment, the battery cell further includes a housing and a top cover assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the top cover assembly covers the housing opening. The top cover assembly includes a positive electrode terminal. The positive current collector includes a positive current collector portion and a positive electrode tab disposed on at least one side of the positive current collector portion. The positive electrode tab extends from the positive current collector portion along a first direction, and the positive electrode tab is directly connected to the positive electrode terminal. The first direction is parallel to the thickness direction of the top cover assembly.

[0091] The direct connection between the positive electrode tab and the positive electrode terminal helps reduce the number of connections required to electrically connect the tab to the positive terminal, thereby reducing the ohmic resistance of the battery cell, reducing heat generation in the battery cell, and further improving the energy conversion efficiency of the battery cell.

[0092] In any embodiment, the positive electrode tab is welded to the positive electrode terminal.

[0093] A second aspect of this application provides a battery device, which includes the battery cell provided in the first aspect.

[0094] A third aspect of this application provides an energy storage device, which includes the battery device provided in the second aspect, the battery device being used to store electrical energy.

[0095] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0096] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0097] Figure 1 is a schematic diagram of a battery cell provided in some embodiments of this application;

[0098] Figure 2 is an exploded view of a single battery cell provided in some embodiments of this application;

[0099] Figure 3 is a schematic diagram of a battery module provided in some embodiments of this application;

[0100] Figure 4 is a schematic diagram of a battery pack provided in some embodiments of this application;

[0101] Figure 5 is an exploded view of a battery pack provided in some embodiments of this application;

[0102] Figure 6 is a schematic diagram of a positive current collector provided in some embodiments of this application.

[0103] Explanation of reference numerals in the attached figures:

[0104] The reference numerals in the attached drawings are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Positive current collector; 61. Positive current collector; 62. Positive electrode tab; X, First direction. Detailed Implementation

[0105] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the battery cell, battery device, and energy storage device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0106] 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.

[0107] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0108] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0109] 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.

[0110] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0111] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0112] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0113] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0114] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0115] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0116] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited to this. Figure 1 shows a cuboid battery cell 5 as an example.

[0117] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0118] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0119] In some embodiments, individual battery cells can be assembled into a battery module. The number of battery cells in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0120] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0121] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0122] Figures 3 and 4 are schematic diagrams of a battery pack 1 as an example. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 and forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0123] The battery provided in this application embodiment may include a lithium-ion battery.

[0124] A single battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0125] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0126] In some embodiments, as shown in FIG5, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0127] Electrode assemblies typically include positive and negative electrodes. The negative electrode is the electrode that absorbs or lithiates lithium ions during battery charging and releases or delithiates lithium during discharge. The positive electrode is the electrode that releases or delithiates lithium ions during battery charging and absorbs or lithiates lithium during discharge.

[0128] Adding lithium-rich compounds to the positive electrode film of a battery cell helps improve its cycle performance; increasing the areal density of the positive electrode film helps increase the battery cell's capacity. However, the applicant has found that adding lithium-rich compounds to battery cells with high positive electrode film are not as effective in improving cycle performance as adding them to cells with low positive electrode film areal density, and significantly reduce the cell's energy conversion efficiency. Therefore, how to balance battery cell capacity, cycle performance, and energy conversion efficiency has become a technical problem that urgently needs to be solved by those skilled in the art.

[0129] Therefore, a first aspect of this application provides a battery cell, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium-rich compound. The density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm². 2 The electrolyte includes dimethyl carbonate, and the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

[0130] Adding lithium-rich compounds to battery cells helps improve their cycle performance; increasing the density of any side of the positive electrode film helps increase the capacity of the battery cell. However, the applicant found that increasing the density of any side of the positive electrode film to greater than or equal to 0.3 g / 1540.25 mm... 2 Subsequently, lithium-rich compounds in the positive electrode film layer tend to agglomerate, leading to uneven lithium-ion insertion / extraction in the positive electrode sheet. On the one hand, this phenomenon easily induces concentration polarization, increasing the internal resistance of the battery cell and reducing its energy conversion efficiency (RTE). On the other hand, uneven reaction in the positive electrode film layer can easily lead to excessive local delithiation or insertion of lithium in the positive electrode film layer and the corresponding negative electrode film layer, and can also easily lead to uneven formation of the SEI and CEI films, thus affecting the battery cycle performance. In the embodiments of this application, dimethyl carbonate is further added to the electrolyte, and its mass percentage is controlled within the range of 15%-50%. This helps to reduce the electrolyte viscosity, increase the lithium-ion migration rate, and thereby improve the uniformity of lithium ions in the battery by improving liquid phase diffusion. This enhances the effect of the lithium replenishment agent on improving the cycle life of the battery cell and improves the energy conversion efficiency of the battery cell.

[0131] In this application, "lithium-rich compound" has the meaning known in the art, referring to a compound rich in lithium that can play a lithium replenishment role in battery cells. Specifically, it refers to a lithium-containing material disposed in a battery cell to provide an active lithium source that can participate in lithium intercalation / deintercalation reactions during formation or cycling, compensating for lithium consumed during electrolyte decomposition, side reactions, and interfacial film formation, thereby maintaining the reversible lithium inventory of the battery cell, improving capacity retention, and cycle performance. It is understood that lithium ions in lithium-rich compounds are gradually consumed during the cycling process of the battery cell. Therefore, when the positive electrode film is obtained from the dismantling of a battery cell, the lithium ion content in the lithium-rich compound may be partially or completely consumed by the reaction, or even undetectable. Battery cells in which lithium-rich compounds are added to the positive electrode film during preparation are all within the scope of protection of this application.

[0132] This application does not limit the types of lithium-rich compounds; any type known in the art may be used.

[0133] In some embodiments, the lithium-rich compound includes one or more of inorganic lithium salts, metal oxides, and organic compounds.

[0134] In some embodiments, the lithium-rich compound includes inorganic lithium salt compounds, which include one or more of lithium halides, lithium nitrides, lithium sulfides, lithium carbonate, lithium nitrates, lithium sulfates, lithium phosphates, lithium silicates, lithium aluminates, lithium borates, and lithium germanates.

[0135] In some embodiments, the lithium-rich compound comprises a metal oxide. Optionally, the metal oxide further comprises a second metal element including one or more of iron, nickel, manganese, copper, zinc, cobalt, chromium, zirconium, antimony, titanium, vanadium, molybdenum, and tin. In some embodiments, the metal oxide comprises one or more of lithium-rich lithium iron ferrite, lithium-rich lithium nickel ferrite, lithium-rich lithium manganese ferrite, lithium-rich lithium cobalt ferrite, lithium oxide, lithium peroxide, and lithium hydroxide.

[0136] In some embodiments, the lithium-rich compound includes an organic compound, which includes one or more of carboxylic acid organolithium salts, aromatic organolithium salts, polymeric organolithium salts, and organic coordination lithium salts.

[0137] In this application, the types and contents of the positive electrode active material and lithium-rich compounds can be tested using methods and instruments known in the art. For example, they can be detected by coupling X-ray diffraction (XRD) with energy-dispersive X-ray spectroscopy (EDS) or inductively coupled plasma mass spectrometry (ICP-MS). As an example, XRD and EDS can be used together for testing. Specifically, using an X-ray diffractometer (e.g., a Bruker D8 Discover), the key parameters are set as follows: scan range 2θ = 15°-70° (the range can be appropriately expanded as needed, such as 5°-90°), scan step size or scan speed is set to 1° / min, to obtain diffraction data of the positive electrode film; then, the obtained diffraction data is imported into phase analysis or refinement software (e.g., GSAS-II) and compared with standard diffraction data of the corresponding crystal phase in a crystal structure database (e.g., crystal structure information stored in .cif file format). Specifically, CIF files of various crystalline phases (e.g., lithium-containing transition metal oxide phases, lithium-containing phosphate phases, etc.) that may exist in the lithium-rich compound and cathode active material can be imported into the software. Each phase is then fitted or compared with the measured XRD patterns. When the fitting results of one or more crystalline phases are basically consistent with the diffraction peak positions and shapes of the test patterns, the types of phases contained in the lithium-rich compound and cathode active material in the cathode film can be determined. Based on this, EDS analysis of the elements contained in the cross-section along the thickness direction of the cathode film can further determine the types of lithium-rich compound and cathode active material. After XRD refinement, the phase fraction of the lithium-rich compound can be obtained in the Phases, which is the mass percentage of the lithium-rich compound based on the total mass of the cathode active material and the lithium-rich compound.

[0138] The positive electrode film in this application can be either a freshly prepared positive electrode film or a positive electrode film obtained from disassembly of a battery.

[0139] In this application, the density of any side of the positive electrode film layer refers to the areal density of a single-sided positive electrode film layer disposed on any side of the positive electrode current collector, which can be tested using methods and instruments known in the art. As an example, take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the current collector, and record it as M0. The density of any side of the positive electrode film layer = (M1-M0) / S1, in g / 1540mm². 2 To ensure the accuracy of the test results, multiple groups (e.g., 10 groups) of samples can be tested, and the average value can be calculated as the test result.

[0140] In some embodiments, the density of any side of the positive electrode film can be 0.30 g / 1540 mm. 2 0.31g / 1540mm 2 0.32g / 1540mm 2 0.33g / 1540mm 2 0.34g / 1540mm 2 0.35g / 1540mm 2 0.36g / 1540mm 2 0.37g / 1540mm 2 0.38g / 1540mm 2 0.39g / 1540mm 2 0.40g / 1540mm 2 0.41g / 1540mm 2 0.42g / 1540mm 2 0.43g / 1540mm 2 0.44g / 1540mm 2 0.45g / 1540mm 2 Or the range of values ​​between any two.

[0141] In this application, the types and mass percentages of each component in the electrolyte can be obtained by detecting the electrolyte using any method known to those skilled in the art. For example, the composition and content of the electrolyte can be characterized using one or more of the following methods: gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectrometry (GC-MS). For example, referring to GB / T-9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" and / or GB / T6041-2002 "General Rules for Mass Spectrometry Analysis Methods", gas chromatography and mass spectrometry are coupled. After gas chromatography separates the components in the sample, the components are broken into ion fragments in mass spectrometry and separated according to mass-to-charge ratio (m / z) to form specific mass spectra, obtaining qualitative analysis of each organic component in the electrolyte. Then, the organic components in the electrolyte are separated in the chromatographic column, and detection signal spectra of each component are generated. Component qualitative analysis is performed using retention time, and quantitative analysis is performed by standardizing and correcting peak area, obtaining quantitative analysis of the organic components in the electrolyte. Referring to JY / T-020, the types of anions of electrolyte salts in the electrolyte are detected by ion chromatography and quantitatively analyzed. Referring to JY / T0578-2020, nuclear magnetic resonance spectroscopy (NMR) is used to obtain qualitative and quantitative analysis of the components in the electrolyte.

[0142] The electrolyte referred to in this article can be either fresh electrolyte or electrolyte obtained from the disassembly of a battery cell. The electrolyte obtained from the disassembly of a battery cell can be either the free electrolyte in the battery casing or the electrolyte obtained by centrifugation from the electrodes.

[0143] In some embodiments, based on the total mass of the electrolyte, the mass percentage of dimethyl carbonate can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range between the two.

[0144] In some embodiments, the dimethyl carbonate accounts for 30%-50% of the total mass of the electrolyte.

[0145] The mass percentage of dimethyl carbonate is further within the above range, which helps to further reduce the electrolyte viscosity, improve the uniformity of lithium ion insertion / extraction, and thus further improve the cycle performance and energy conversion efficiency of the battery cell.

[0146] In some embodiments, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.45g / 1540.25mm 2 .

[0147] In some embodiments, the density of any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.4g / 1540.25mm 2 .

[0148] Having a density on any side of the positive electrode film within the above range helps to reduce the thickness of the positive electrode film, suppress the aggregation of lithium-rich compounds, improve the uniformity of lithium ion insertion / extraction in the positive electrode film, and thus further improve the cycle performance and energy conversion efficiency of the battery cell.

[0149] In some embodiments, the capacity of the battery cell is 400Ah-3000Ah.

[0150] In this application, the capacity of a single battery cell can be tested using methods and instruments known in the art. As an example, at 25°C, the battery cell is discharged at a constant power of 0.25P until its voltage reaches 2.5V, and then allowed to stand for 30 minutes. The battery cell is then subjected to a charge-discharge cycle test at a constant power of 0.25P: First charge-discharge cycle: The battery cell is charged at a constant power of 0.25P to 3.65V, allowed to stand for 30 minutes, and then discharged at a constant power of 0.25P to 2.5V. The discharge capacity Q1 is recorded, and Q1 is the capacity of the battery cell, in Ah.

[0151] In some implementations, the capacity of a single battery cell can be 400Ah, 450Ah, 500Ah, 550Ah, 600Ah, 650Ah, 700Ah, 750Ah, 800Ah, 850Ah, 900Ah, 950Ah, 1000Ah, 1050Ah, 1100Ah, 1150Ah, 1200Ah, 1250Ah, 1300Ah, 1350Ah, 1400Ah, 1450Ah, 1500Ah, 1550Ah, 1600Ah, 1650Ah, or 1700Ah. h, 1750Ah, 1800Ah, 1850Ah, 1900Ah, 1950Ah, 2000Ah, 2050Ah, 2100Ah, 2150Ah, 2200Ah, 2250Ah, 2300Ah, 2350Ah, 2400Ah, 2450Ah, 2500Ah, 2550Ah, 2600Ah, 2650Ah, 2700Ah, 2750Ah, 2800Ah, 2850Ah, 2900Ah, 2950Ah, 3000Ah, or any range of two.

[0152] When the capacity of a single battery cell is within the aforementioned range, it generates a high amount of heat and has difficulty dissipating it. The accumulated heat raises the internal temperature of the battery, exacerbating the side reactions at the sites of excessive lithium insertion and delithiation caused by the aggregation of lithium-rich compounds, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the positive electrode film layer comprises a lithium-rich compound; the density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm². 2 Based on the total mass of the electrolyte, dimethyl carbonate accounts for 15%-50% of the mass, and still has good cycle performance and energy conversion efficiency when the capacity of the battery cell is in the range of 400Ah-3000Ah.

[0153] In some embodiments, the capacity of the battery cell is 400Ah-1500Ah.

[0154] In some embodiments, the capacity of the battery cell is 400Ah-1100Ah.

[0155] A battery cell capacity within the aforementioned range helps reduce the internal temperature of the battery cell, further improving its cycle performance and energy conversion efficiency.

[0156] In some embodiments, the lithium-rich compound accounts for 3%-20% of the total mass of the positive electrode film.

[0157] In this application, the mass percentage of the lithium-rich compound, based on the total mass of the positive electrode active material and the lithium-rich compound, can be tested according to the aforementioned test methods for the types and contents of the positive electrode active material and the lithium-rich compound.

[0158] In some embodiments, based on the total mass of the positive electrode active material and the lithium-rich compound, the mass percentage of the lithium-rich compound can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or any value between the two.

[0159] An increase in the mass percentage of lithium-rich compounds is accompanied by a decrease in the mass percentage of positive electrode active materials. When the mass percentage of lithium-rich compounds is within the above range, it helps to balance the capacity, cycle performance, and energy conversion efficiency of the battery cell.

[0160] In some embodiments, the lithium-rich compound accounts for 5%-15% of the total mass of the positive electrode active material and the lithium-rich compound.

[0161] When the mass percentage of lithium-rich compounds is within the above range, the battery cell achieves excellent capacity, cycle performance, and energy conversion efficiency, which helps to improve the overall performance of the battery cell.

[0162] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 .

[0163] In this application, the compaction density of the positive electrode sheet can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven and left to stand for 2 hours. Once the battery temperature is maintained at 25°C, the individual battery cells are discharged at a constant power of 0.25P until the voltage of the individual cells reaches 2.5V, and then left to stand for 30 minutes. The battery is then disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S, obtaining a mass of W1. The thickness T1 of the positive electrode sheet is measured using a micrometer. Then, the positive electrode film layer of the weighed electrode sheet is wiped off, and the mass of the current collector is weighed and recorded as W2. The thickness T2 of the current collector is measured using a micrometer. The compaction density of the positive electrode sheet is then calculated as PD = (W1 - W2) / [(T1 - T2) × S], in g / cm³. 3 .

[0164] In some embodiments, the compaction density of the positive electrode film can be 2.5 g / cm³. 3 2.52g / cm 3 2.54 g / cm 3 2.56 g / cm 3 2.58g / cm 3 2.6g / cm 3 2.62 g / cm 3 2.64 g / cm 3 2.66 g / cm 3 2.68g / cm 3 2.7g / cm 3 2.72 g / cm 3 2.74 g / cm 3 2.76 g / cm 3 2.78g / cm 3 2.8g / cm 3 2.82 g / cm 3 2.84 g / cm 3 2.86 g / cm 3 2.88g / cm 3 2.9g / cm 3 2.92g / cm 3 2.94 g / cm 3 2.96 g / cm 3 2.98g / cm 3 3g / cm 3 Or the range of values ​​between any two.

[0165] The compaction density of the positive electrode film is within the above range, which helps to reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0166] In some embodiments, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -2.8g / cm 3 .

[0167] In some embodiments, the positive electrode active material comprises lithium transition metal phosphate particles with at least a portion of their surface disposed of carbon material.

[0168] In this application, the carbon-coated material disposed on at least a portion of the surface of a lithium-containing transition metal phosphate can be detected by any method known in the art. As an example, the carbon-coated material disposed on at least a portion of the surface of the lithium-containing transition metal phosphate can be observed by characterizing the phosphate using a transmission electron microscope coupled with energy dispersive spectroscopy. It should be noted that the elements in the carbon-coated material are not limited to carbon, but may also include other non-carbon elements. The carbon coating layer containing the carbon-coated material is not limited to a film, but also includes island-shaped, irregular, or discontinuous coating layers.

[0169] Lithium-containing transition metal phosphates, as positive electrode active materials, have the advantage of good structural stability, which helps to further improve the cycle performance of battery cells.

[0170] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of lithium transition metal phosphate particles with particle size R1 satisfying 1500nm≤R1≤5000nm is 8.0%-20.0%.

[0171] In this application, the term "particle" refers to a particle in the positive electrode film layer that has a recognizable complete boundary in the field of view at a certain magnification, such as 10,000x. Defects and scratches may exist inside the particle, but a complete boundary sufficient to divide the particle cannot be identified inside the particle.

[0172] In this application, the particle identification method is as follows: The positive electrode film layer is cut along the thickness direction of the electrode sheet using an argon ion beam (for example, a Leica EMTIC3XCP device can be used, operating voltage: 6kV, operating time: 6h). After exposing the cut surface, a scanning electron microscope (for example, a Hitachi SU8230 device can be used, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) is used to observe the cut surface of the positive electrode film layer along the thickness direction of the electrode sheet. Images are acquired using a field emission scanning electron microscope at a non-edge location in the cut surface of the positive electrode film layer (after observing the electrode edge under the scanning electron microscope, the field of view is adjusted to the center of the sample) in secondary electron mode. Electron micrographs are taken at 10kx magnification, and the particles in the electron micrographs are analyzed using ImageJ software (1.46r, win64 version). The specific steps for using ImageJ software are as follows: Load the scanning electron microscope (SEM) image to be analyzed; use the Cellpose plugin to identify particles, and then perform manual corrections; use ImageJ to read and analyze data. The specific method for using the Cellpose plugin to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmentation module) to 15 pixels, click "runcyto3" to identify particles; manually mark particles in the image that were not identified by the software, were not fully identified, or were identified incorrectly. Particles that were not identified by the software, were not fully identified, or were identified incorrectly mainly include the following: 1. Particles that are too large or have scratches on their surface, making them unidentifiable or incompletely identifiable; 2. During argon ion beam cutting, scratches may be generated on the particle surface, and the software may misinterpret these scratches as particle boundaries, leading to identification errors; 3. Particles that are too small and were not successfully identified; 4. Particles located at the edge of the SEM field of view, with the interior penetrated by the edge, preventing a complete view of the morphology, resulting in identification errors due to partial identification replacing the whole.For the unidentified or misidentified particles mentioned above, manual calibration is performed. The specific process is as follows: 1. Delete large particles located around the edges of the scanning electron microscope that are not fully displayed. 2. Determine if any unidentified or misidentified particles have internal cracks or scratches. If no cracks or scratches are found, classify it as a single particle and manually mark it based on the observed particle boundary. 3. If cracks or scratches are found inside the particle, determine if they penetrate the particle. If not, classify it as a single particle and manually mark it. 4. If cracks or scratches penetrate the particle, determine if they are linear or irregular. 5. If the cracks or scratches are irregular, classify them as the boundary between particles and divide the particles along this boundary. 6. If the cracks or scratches are linear, perform contrast comparison. 7. If the contrast is not obvious and there is no crack-like appearance, classify it as a scratch and mark it as a single particle. 8. If the contrast is strong and there is a crack-like appearance, classify it as the boundary between particles and mark it as two particles. After manual marking, delete information irrelevant to the particles from the automatic image processing, thus completing the particle identification and marking in the image.

[0173] In existing technologies, laser particle size analyzers are typically used to statistically analyze the particle size of positive electrode active materials using Malvern laser diffraction. However, the applicant's research indicates that because lithium-containing transition metal phosphate particles are prone to agglomeration, the test results obtained by Malvern laser diffraction based on the principle of laser scattering often only reflect the particle size of the agglomerates, and cannot accurately reflect the particle size of the positive electrode active material, let alone its dispersion state in the film layer. This is because the dispersion of the positive electrode active material in the film layer increases during slurry preparation and film forming rolling. The test results obtained by Malvern laser diffraction are affected by the particle size, specific surface area, and degree of agglomeration of the positive electrode active material. Compared to the actual dispersion in the electrode sheet, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by Malvern laser diffraction cannot be equated with or analogized to the particle size statistically obtained in the embodiments of this application.

[0174] In this application, the method for testing the area ratio of lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm, based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode film along the electrode thickness direction, is as follows: According to the above-described testing method for the types of positive electrode active materials and lithium-rich compounds in the positive electrode film, the distinguishing elements between lithium-rich compounds and positive electrode active materials are identified, and the types of particles in the SEM-EDS images are determined and labeled based on these distinguishing elements. The images after particle identification and labeling are imported into ImageJ software for analysis. The scale is set according to the scanning electron microscope image, and the particle size, area, sphericity, and roughness of the lithium transition metal phosphate particles in the cross-section of the positive electrode film along the electrode thickness direction are statistically analyzed using the "Feret," "Area," "Round," and "Solidity" analysis functions. According to the software manual (ImageJUserGuideIJ1.46r), the obtained "Feret" parameter represents the maximum spacing between all parallel lines in the two-dimensional projection of the particle, thus characterizing the particle size; the obtained "Area" parameter represents the pixel area of ​​the particle. Since particles with a diameter less than 50nm have a large error in the statistical process and are difficult to accurately identify, and the particle size of conductive agents is generally less than 50nm, which will also introduce a large error into the statistical results, particles with a diameter less than 50nm are not counted in the particle size statistics process of this application, and the statistical data of particles whose AR, Round, or Solidity is displayed as "NaN" are deleted. The sum of the "Area" parameters of lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm and the sum of the "Area" parameters of all lithium transition metal phosphate particles are calculated, and these are respectively used as the area of ​​lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm and the total area of ​​the statistically counted lithium transition metal phosphate particles. The area ratio of lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is calculated by dividing the sum of the areas of the lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm by the total area of ​​the statistically analyzed particles.

[0175] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode film along the electrode thickness direction, the area percentage of lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm ≤ R1 ≤ 5000nm can be 8.0%, 8.2%, 8.4%, 8.6%, 8.8%, 9.0%, 9.2%, 9.4%, 9.6%, 9.8%, 10.0%, 10.2%, 10.4%, 10.6%, 10.8%, 11.0%, 11.2%, 11.4%, 11.6%, 11.8%, 12.0%, 12.2%, 12.4%, 12.6%, 12.8%, etc. 13.0%, 13.2%, 13.4%, 13.6%, 13.8%, 14.0%, 14.2%, 14.4%, 14.6%, 14.8%, 15.0%, 15.2%, 15.4%, 15.6%, 15.8%, 16.0%, 16.2%, 16.4%, 16.6%, 16.8%, 17.0%, 17.2%, 17.4%, 17.6%, 17.8%, 18.0%, 18.2%, 18.4%, 18.6%, 18.8%, 19.0%, 19.2%, 19.4%, 19.6%, 19.8%, 20.0%, or any range between two of these values.

[0176] If the area ratio of lithium-containing transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm is within the above range, it indicates that there are more large-sized particles in the positive electrode film layer. This helps to increase the compaction density of the positive electrode film layer, thereby reducing the thickness of the positive electrode film layer, improving the uniformity of the distribution of lithium-rich compound particles in the positive electrode film layer, and further improving the energy conversion efficiency and cycle performance of the battery cell.

[0177] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of lithium transition metal phosphate particles with particle size R1 satisfying 1500nm≤R1≤5000nm is 10.0%-20.0%.

[0178] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode film along the thickness direction of the electrode, the area ratio of lithium transition metal phosphate particles with particle size R2 satisfying 1000nm≤R2<200nm is 15.0%-25.0%.

[0179] In this application, the area ratio of lithium transition metal phosphate particles with a particle size R2 satisfying 1000nm≤R2<200nm can be tested by referring to the test method described above, which is based on the total area of ​​lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm≤R1≤5000nm in the cross-section of the positive electrode film along the thickness direction of the electrode.

[0180] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode film along the electrode thickness direction, the area percentage of lithium transition metal phosphate particles with a particle size R2 satisfying 1000nm≤R2<200nm can be 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5%, 20.0%, 20.5%, 21.0%, 21.5%, 22.0%, 22.5%, 23.0%, 23.5%, 24.0%, 24.5%, 25.0%, or any value range between the two.

[0181] Lithium-containing transition metal phosphate particles with a particle size R2 satisfying 1000nm≤R2<200nm represent smaller positive electrode active materials in the positive electrode film. Their area proportion is within the above range, which helps to further improve the compaction density of the positive electrode film through particle gradation, reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0182] In some embodiments, based on the total area of ​​lithium transition metal phosphate particles in the cross section of the positive electrode film along the electrode thickness direction, the area ratio of lithium transition metal phosphate particles with particle size R2 satisfying 1000nm≤R2<200nm is 16%-20%.

[0183] In some embodiments, in the cumulative distribution curve of the spheroidal area of ​​lithium transition metal phosphate particles in a cross-section along the electrode thickness direction of the positive electrode film, the median L of the spheroidal degree is... A50 It ranges from 0.6 to 0.85.

[0184] In this application, the median test method for the sphericity of lithium transition metal phosphate particles in the cumulative distribution curve of sphericity area along the thickness direction of the positive electrode film is as follows: Referring to the "Test Method for the Area Ratio of Lithium Transition Metal Phosphate Particles with Particle Size R1 Satisfying 1500nm≤R1≤5000nm Based on the Total Area of ​​Lithium Transition Metal Phosphate Particles in the Cross-Section of the Positive Electrode Film Along the Thickness Direction of the Electrode Film" above in this application, the "Round" parameter of the lithium transition metal phosphate particles is analyzed and obtained. The "Round" parameter represents the ratio of the pixel area of ​​the particle to the area of ​​a circle with the fitted major axis as its diameter, and can be used to characterize the sphericity of the particle. The closer the particle is to a sphere, the closer the ratio of the pixel area to the area of ​​the circle with the fitted major axis as its diameter is to 1. Therefore, the "Round" parameter of the particle obtained by analysis is used to characterize the sphericity of the particle. The sphericity of at least 1000 lithium transition metal phosphate particles was arranged in ascending order. A cumulative distribution curve of the sphericity area of ​​the lithium transition metal phosphate particles was obtained, with sphericity as the horizontal axis and cumulative area percentage as the vertical axis. The median sphericity L... A50 This is the sphericity value corresponding to a cumulative area ratio of 50% on the vertical axis in the cumulative distribution curve of the sphericity area of ​​particles.

[0185] Those skilled in the art can control the sphericity of particles using any known process. For example, the sphericity of particles can be adjusted through processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, and adding surfactants, as well as by adjusting the parameters of each process.

[0186] In some embodiments, in the cumulative distribution curve of the spheroidal area of ​​lithium transition metal phosphate particles in a cross-section along the electrode thickness direction of the positive electrode film, the median L of the spheroidal degree is... A50 It can be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, or any value range between the two.

[0187] The median sphericity of lithium transition metal phosphate particles within the above range indicates that they have high roundness, which helps to improve the slippage of particles in the positive electrode film, reduce the "bridging" phenomenon between particles, further improve the compaction density of the positive electrode film, reduce the thickness of the positive electrode film, improve the uniformity of the distribution of lithium-rich compound particles in the positive electrode film, and further improve the energy conversion efficiency and cycle performance of the battery cell.

[0188] In some embodiments, in the cumulative distribution curve of the spheroidal area of ​​lithium transition metal phosphate particles in a cross-section along the electrode thickness direction of the positive electrode film, the median L of the spheroidal degree is... A50 It is 0.65-0.8.

[0189] In some embodiments, the electrolyte comprises a linear carbonate solvent, which includes dimethyl carbonate, and further comprises one or more of diethyl carbonate and ethyl methyl carbonate.

[0190] Linear carbonates have low viscosity, and dimethyl carbonate has even lower viscosity than other linear carbonates. The presence of dimethyl carbonate and other types of linear carbonates in the electrolyte helps to further reduce its viscosity, increase the lithium-ion diffusion rate, and improve the uneven lithium-ion insertion / extraction phenomenon in the positive electrode film caused by the aggregation of lithium-rich compounds, thereby further improving the energy conversion efficiency and cycle performance of the battery cell.

[0191] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the ethyl methyl carbonate accounts for 10%-50% of the total mass of the electrolyte.

[0192] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate based on the total mass of the electrolyte can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, or any value between the two.

[0193] In some embodiments, the electrolyte comprises a cyclic carbonate solvent, which includes one or more of ethylene carbonate and propylene carbonate.

[0194] Cyclic carbonates have a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the conductivity of the electrolyte, further improving the uneven lithium ion insertion / extraction phenomenon in the positive electrode film, and improving the energy conversion efficiency and cycle performance of the battery cell.

[0195] In some embodiments, the cyclic carbonate solvent includes ethylene carbonate, and the ethylene carbonate accounts for 10%-40% of the total mass of the electrolyte.

[0196] In some embodiments, the cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate based on the total mass of the electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any range between the two.

[0197] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the propylene carbonate accounts for 0.5%-10% of the total mass of the electrolyte.

[0198] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate based on the total mass of the electrolyte can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any value between the two.

[0199] Propylene carbonate has a high dielectric constant, which helps to increase the concentration of active lithium ions in the electrolyte, thereby improving the electrolyte conductivity and reducing the internal resistance of the battery cell. However, propylene carbonate is prone to co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the mass percentage of propylene carbonate is within the above-mentioned range, which helps to balance the energy conversion efficiency and cycle performance of the battery cell.

[0200] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the propylene carbonate accounts for 2.5%-10% of the total mass of the electrolyte.

[0201] In some embodiments, the electrolyte includes an additive, which includes one or more of fluoroethylene carbonate and vinylene carbonate.

[0202] Uneven distribution of lithium-rich compounds can easily lead to uneven lithium-ion insertion / extraction, resulting in uneven stress during cycling. Excessive local stress can damage the SEI film, accelerating its rupture and repair process, thus affecting the cycle performance and energy conversion efficiency of the battery cell. Including the aforementioned additives in the electrolyte helps form a dense and stable SEI film on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0203] In some embodiments, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 0.05%-5% of the total mass of the electrolyte.

[0204] In some embodiments, the additive includes fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate based on the total mass of the electrolyte can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 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%, or 1.8%. %, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, or any range of two.

[0205] In some embodiments, the additive includes fluoroethylene carbonate, and the fluoroethylene carbonate accounts for 2%-3% of the total mass of the electrolyte.

[0206] When the mass percentage of fluoroethylene carbonate is within the above range, it helps to form an SEI film of suitable thickness, taking into account both the stability and interfacial impedance of the SEI film, thereby balancing the cycle performance and energy conversion efficiency of the battery cell and further improving the overall performance of the battery cell.

[0207] In some embodiments, the additive includes vinylene carbonate, which accounts for 0.1% to 8% of the total mass of the electrolyte.

[0208] In some embodiments, the additive includes vinylene carbonate, and the mass percentage of vinylene carbonate, based on the total mass of the electrolyte, can be 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, 5.1%, 5.3%, 5.5%, 5.7%, 5.9%, 6.1%, 6.3%, 6.5%, 6.7%, 6.9%, 7.1%, 7.3%, 7.5%, 7.7%, 7.9%, 8%, or any range between the two.

[0209] In some embodiments, the additive includes vinylene carbonate, which accounts for 0.5%-8% of the total mass of the electrolyte.

[0210] In some embodiments, the linear carbonate solvent includes ethyl methyl carbonate, and the additive includes fluoroethylene carbonate.

[0211] The applicant discovered that the combined use of ethyl methyl carbonate and fluoroethylene carbonate helps improve the cycle performance of battery cells.

[0212] In some embodiments, the cyclic carbonate solvent includes propylene carbonate, and the additive includes vinylene carbonate.

[0213] Propylene carbonate readily undergoes a co-intercalation reaction at the negative electrode, thus affecting the cycle performance of the battery cell. The applicant discovered that using propylene carbonate in combination with ethylene carbonate can effectively suppress the co-intercalation reaction of propylene carbonate, further improving the cycle performance of the battery cell.

[0214] In some embodiments, the electrolyte comprises an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

[0215] In some embodiments, the electrolyte solution comprises lithium bisfluorosulfonylimide, wherein the lithium bisfluorosulfonylimide accounts for 1%-7% of the total mass of the electrolyte solution.

[0216] In some embodiments, the electrolyte solution comprises lithium difluorosulfonylimide, and the mass percentage of lithium difluorosulfonylimide based on the total mass of the electrolyte can be 1%, 1.1%, 1.3%, 1.5%, 1.7%, 1.9%, 2.1%, 2.3%, 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, 4.7%, 4.9%, 5.1%, 5.3%, 5.5%, 5.7%, 5.9%, 6.1%, 6.3%, 6.5%, 6.7%, 6.9%, 7%, or any value range between the two.

[0217] Lithium difluorosulfonylimide helps to form a dense and stable SEI film on the negative electrode side, thereby helping to improve the phenomenon of excessive local stress damaging the SEI film during cycling caused by uneven distribution of lithium-rich compounds, and further improving the cycle performance and energy conversion efficiency of the battery cell.

[0218] In some embodiments, the electrolyte solution comprises lithium bisfluorosulfonylimide, wherein the lithium bisfluorosulfonylimide accounts for 2%-7% of the total mass of the electrolyte solution.

[0219] In some embodiments, the electrolyte comprises lithium hexafluorophosphate, wherein the mass percentage of lithium hexafluorophosphate is 2%-15% based on the total mass of the electrolyte.

[0220] In some embodiments, the electrolyte comprises lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate based on the total mass of the electrolyte can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, or any value between the two.

[0221] In some embodiments, the electrolyte comprises lithium hexafluorophosphate, wherein the mass percentage of lithium hexafluorophosphate is 4%-8% based on the total mass of the electrolyte.

[0222] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonyl imide in the electrolyte is 0.5-5.5.

[0223] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte can be 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, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, or any range between the two.

[0224] As the content of lithium difluorosulfonylimide increases, the SEI film becomes thicker. When the mass ratio of lithium hexafluorophosphate and lithium difluorosulfonylimide is within the above range, the electrolyte has a suitable active lithium concentration and the SEI film has a suitable thickness, thus balancing the conductivity of the electrolyte and the interfacial impedance on the negative electrode side, further improving the cycle performance and energy conversion efficiency of the battery cell.

[0225] In some embodiments, the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 2-4.

[0226] In some embodiments, the positive electrode film layer comprises carbon nanotubes.

[0227] The aggregation of lithium-rich compounds in the cathode film layer leads to uneven lithium-ion insertion and extraction. Higher electron transport capacity is required in the region of high-concentration lithium-ion insertion and extraction. The cathode film layer includes carbon nanotubes, which helps to form a good electron transport network within the cathode film layer, thereby helping to improve the uniformity of lithium-ion insertion and extraction in the cathode film layer, and further improving the cycle performance and energy conversion efficiency of the battery cell.

[0228] In some embodiments, the carbon nanotubes account for 0.1%-3% of the total mass of the positive electrode film.

[0229] In some embodiments, based on the total mass of the positive electrode film, the mass percentage of the carbon nanotubes can be 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%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or any value between the two.

[0230] In some embodiments, the carbon nanotubes account for 0.5%-1% of the total mass of the positive electrode film.

[0231] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

[0232] In some embodiments, the positive electrode active material comprises the components shown in Formula I:

[0233] Li m Fe x P y O j Q q Formula I,

[0234] Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0235] In some implementations, m can be selected as 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any value range between two of these; x can be selected as 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value range between two of these. y can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or any value between two of these; j can be 3.5, 3.6, 3.7, 3.8, 3.9, 4 or any value between two of these; q can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any value between two of these.

[0236] In some embodiments, the lithium-rich compound includes one or more of lithium iron ferrite, lithium nickel ferrite, lithium manganese ferrite, lithium cobalt ferrite, lithium sulfide, lithium nitride, lithium hydroxide, lithium fluoride, lithium oxalate, lithium oxide, and lithium peroxide.

[0237] In some embodiments, the lithium-rich lithium iron ore comprises the components shown in general formula II:

[0238] Li 5+a1 Fe 1+b1 O 4+c1 Formula II

[0239] Where -5≤a1≤0.5, -0.1≤b1≤0.5, and -0.4≤c1≤0.4.

[0240] In some implementations, -5 ≤ a1 ≤ 0.

[0241] In some implementations, -5≤a1≤0, b1=1, c1=4.

[0242] In some implementations, a1 can be -5, -4.99, -4.95, -4.9, -4.8, -4.6, -4.4, -4.2, -4, -3.8, -3.6, -3.4, -3.2, -3, -2.8, -2.6, -2.4, -2.2, -2, -1.8, -1.6, -1.4, -1.2, -1, -0.8, -0.6, -0.4, or -0. 2, 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any value between two of these; b1 can be -0.1, -0.08, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, or any value between two of these; c1 can be -0.4, -0.38, -0.36, -0.34, -0.32, -0.3, -0.28, -0.26, -0.24, -0.22, -0.2, -0.18, -0.16, -0.14, -0.12, -0.1, -0.08, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, or any value range between two of these.

[0243] In some embodiments, the lithium-rich nickel oxide comprises the components shown in Formula III:

[0244] Li 2+a2 Ni 1+b2 O 2+c2 Formula III

[0245] Where -2≤a2≤0.2, -0.1≤b2≤0.1, and -0.2≤c2≤0.2.

[0246] In some implementations, -2≤a2≤0.

[0247] In some implementations, -2≤a2≤0, b2=1, c2=2.

[0248] In some implementations, a2 can be -2, 99, 1.95, -1.9, -1.85, -1.8, -1.75, -1.7, -1.65, -1.6, -1.55, -1.5, -1.45, -1.4, -1.35, -1.3, -1.25, -1.2, -1.15, -1.1, -1.05, -1, -0.95, -0.9, -0.85, -0.8, -0.75, -0.7, -0.65, -0.6, -0.55, -0.5, -0.45, -0.4, -0.35, -0.3, -0.25, -0.2, -0.15, -0.1, -0.05, 0, 0.05, 0.1, 0.15, 0.2, or any value between two of these; b2 can be -0.1, -0.0 8, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48 0.5 or any value between the two; c2 can be -0.2, -0.18, -0.16, -0.14, -0.12, -0.1, -0.08, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2 or any value between the two.

[0249] In some embodiments, the D of the lithium-rich compound particles is calculated based on the total area of ​​the lithium-rich compound particles in a cross-section along the thickness direction of the positive electrode film. A 50 represents 1μm-50μm.

[0250] In this application, based on the total area of ​​lithium-rich compound particles in the cross-section of the positive electrode film along the electrode thickness direction, the D of the lithium-rich compound particles is... A 50 can be tested using the method described above, which measures the total area of ​​lithium transition metal phosphate particles in the cross-section along the electrode thickness direction of the positive electrode film. The test method determines the area ratio of lithium transition metal phosphate particles with a particle size R1 satisfying 1500nm ≤ R1 ≤ 5000nm. Specifically, at least 50 lithium-rich compound particles are obtained using the above method, arranged in ascending order of their "Feret" (particle size) parameters. A cumulative area distribution curve of the lithium-rich compound particles is obtained with particle size as the horizontal axis and cumulative area ratio as the vertical axis. The D of the lithium-rich compound particles...A In the cumulative area distribution curve of particle size for particles with a diameter of 50, the particle size corresponding to the cumulative area ratio of the vertical axis is 50%.

[0251] In some embodiments, the D of the lithium-rich compound particles is calculated based on the total area of ​​the lithium-rich compound particles in a cross-section along the thickness direction of the positive electrode film. A 50 can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, etc. μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, 39μm, 4 0μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm or any numerical range between the two.

[0252] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 11m². 2 -150m 2 .

[0253] In this application, the total coating area of ​​the positive electrode film layer contained in the battery cell refers to the sum of the areas of all positive current collectors in the battery cell covered by the positive electrode film layer; wherein, for a double-sided coated positive electrode sheet, its coating area is the sum of the areas of both sides of the positive current collector covered by the positive electrode film layer; for a battery cell including multiple electrode components, the total coating area of ​​the positive film layer is the sum of the areas of all positive current collectors in the multiple electrode components covered by the positive electrode film layer.

[0254] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell can be 11m². 2 12m 2 13m 2 14m 2 15m 2 16m 2 17m 2 18m 2 19m 2 19.4m 2 20m 2 21m 2 22m 2 23m 2 24m 2 25m 2 26m2 27m 2 28m 2 29m 2 30m 2 32m 2 34m 2 36m 2 38m 2 40m 2 42m 2 44m 2 46m 2 48m 2 50m 2 55m 2 60m 2 65m 2 70m 2 75m 2 80m 2 85m 2 90m 2 95m 2 100m 2 105m 2 110m 2 115m 2 120m 2 125m 2 130m 2 135m 2 140m 2 145m 2 150m 2 Or a range of values ​​between any two.

[0255] The total coating area of ​​the positive electrode film layer in a single battery cell is within the aforementioned range, which helps to increase the capacity to ≥400Ah. However, high-capacity battery cells generate a lot of heat and have difficulty dissipating it. Heat accumulation leads to an increase in the internal temperature of the battery, exacerbating the side reactions at the sites of excessive lithium insertion and extraction caused by the agglomeration of lithium-rich compounds, thus affecting the cycle performance of the battery cell. In the embodiments of this application, the positive electrode film layer includes lithium-rich compounds; the density of any side of the positive electrode film layer is greater than or equal to 0.3g / 1540.25mm². 2 Based on the total mass of the electrolyte, dimethyl carbonate accounts for 15%-50% of the mass, and still has good cycle performance and energy conversion efficiency when the capacity of the battery cell is in the range of 400Ah-3000Ah.

[0256] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 19.4 m². 2 -120m 2.

[0257] In some embodiments, the total coating area of ​​the positive electrode film layer contained in the battery cell is 20m². 2 -120m 2 .

[0258] In some embodiments, the battery cell further includes a housing and a top cover assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the top cover assembly covers the housing opening. The top cover assembly includes a positive electrode terminal. As shown in FIG6, the positive current collector 6 includes a positive current collector portion 61 and a positive electrode tab 62 disposed on at least one side of the positive current collector portion 61. The positive electrode tab 62 extends from the positive current collector portion 61 along a first direction X, and the positive electrode tab 62 is directly connected to the positive electrode terminal. The first direction X is parallel to the thickness direction of the top cover assembly.

[0259] The direct connection between the positive electrode tab and the positive electrode terminal helps reduce the number of connections required to electrically connect the tab to the positive terminal, thereby reducing the ohmic resistance of the battery cell, reducing heat generation in the battery cell, and further improving the energy conversion efficiency of the battery cell.

[0260] In some embodiments, the positive electrode tab is welded to the positive electrode terminal.

[0261] 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.).

[0262] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0263] In some embodiments, the positive electrode active material layer can be prepared by dispersing the components used to prepare the positive electrode active material layer, such as positive electrode active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and after drying, cold pressing and other processes, a positive electrode active material layer can be obtained.

[0264] [Negative electrode plate]

[0265] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0266] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0267] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0268] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0269] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0270] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0271] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0272] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0273] [Isolation membrane]

[0274] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0275] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0276] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0277] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0278] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0279] A second aspect of this application provides a battery device, including the battery cell provided in the first aspect of this application.

[0280] The battery device disclosed in this application can be used in various energy storage systems that use the battery device as an energy storage element. Besides vehicles, the battery device can also be used in, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0281] The third aspect of this application provides an energy storage device that uses a battery device as a power source. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system.

[0282] Example

[0283] 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.

[0284] I. Preparation Method

[0285] 1. Preparation of Example 1

[0286] (1) Positive electrode plate

[0287] ① Preparation of positive electrode active materials

[0288] Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, and titanium dioxide were mixed evenly in methanol and ground to obtain a mixed raw material. The ratio of lithium dihydrogen phosphate to ferrous oxalate resulted in a lithium to iron molar ratio of 1.03:1.0. The ferrous oxalate had particle sizes Dv10 of 6.1 μm, Dv50 of 60.5 μm, and Dv90 of 105.5 μm. The ferrous oxalate contained 30.9% Fe by mass and 0.03% ferric iron by mass.

[0289] The mixed raw materials were ball-milled multiple times and demagnetized in a ball mill to obtain a mixed slurry. The number of grinding cycles and time were controlled, and the particle size Dv50 of the ground mixed slurry was 3.0 μm.

[0290] The spray-dried slurry yields a dried precursor powder, which is light yellow in appearance and uniform in color.

[0291] The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere and held at that temperature for 3 hours. Then, the temperature was increased to a second temperature of 770°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process, the temperature was lowered and cooled.

[0292] The obtained material was crushed using an airflow pulverization method with a staged frequency of 22Hz and a pulverizing airflow of 0.55MPa to obtain carbon-coated lithium iron phosphate cathode active material.

[0293] The carbon content of the positive electrode active material is 1.2% by mass.

[0294] The Dv10, Dv50, and Dv90 mentioned above refer to data obtained through the Malvern laser scattering method.

[0295] ② Preparation of the positive electrode film

[0296] The prepared positive electrode active material, lithium-rich compound Li5FeO4, conductive agent carbon nanotubes, and binder polyvinylidene fluoride were mixed in a solvent N-methylpyrrolidone. The mixture was thoroughly mixed, stirred, and dispersed in a stirring tank to form a positive electrode slurry. Based on the total mass of the positive electrode film, the conductive agent accounted for 1% of the mass, and the binder accounted for 2% of the mass. After the stirring process, the positive electrode slurry was transferred and coated onto a current collector aluminum foil, dried, subjected to ultimate compaction, slitting, and sheet preparation to obtain the positive electrode sheet. The density of any side of the positive electrode film was 340 mg / 1540 cm³. 2 .

[0297] (2) Negative electrode plate

[0298] Artificial graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed evenly in deionized water at a mass ratio of 97:0.5:2:0.5 to prepare a negative electrode slurry. The negative electrode slurry was then coated onto a copper foil current collector, dried, compacted, slit, and sheeted to obtain the negative electrode sheet. The one-sided density of the negative electrode film was 169 mg / 1540.25 cm³. 2 .

[0299] (3) Separating membrane

[0300] A polyethylene film with a thickness of 7 μm was used as the separator.

[0301] (4) Electrolyte

[0302] Based on the total mass of the electrolyte, the electrolyte comprises 30% dimethyl carbonate (DMC), 20% ethyl methyl carbonate (EMC), 20% ethylene carbonate (EC), 10% propylene carbonate (PC), 2% lithium bis(fluorosulfonyl)imide (LiFSI), 8% lithium hexafluorophosphate (LiPF6), 3% fluoroethylene carbonate (FEC), and 7% vinylene carbonate (VC).

[0303] (5) Battery cell

[0304] The positive electrode, separator, and negative electrode are stacked in sequence. The separator must be able to isolate the anode and cathode. The bare cell is obtained by winding. The bare cell is placed in the casing, the top cover assembly is closed, electrolyte is injected, and the battery cell undergoes processes such as encapsulation, formation, and venting to obtain a single battery cell. The positive electrode tab is directly welded to the positive electrode terminal in the top cover assembly.

[0305] Among them, based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode layer along the electrode thickness direction, the area proportion of lithium transition metal phosphate particles with particle size R1 satisfying 1500nm≤R1≤5000nm is 14.59%; based on the total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode layer along the electrode thickness direction, the area proportion of lithium transition metal phosphate particles with particle size R2 satisfying 1000nm≤R2<1500nm is 19.81%; in the cumulative distribution curve of the sphericity area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode layer along the electrode thickness direction, the median L of sphericity is... A50 The value is 0.716; based on the total area of ​​lithium-rich compound particles in the cross-section of the positive electrode film along the electrode thickness direction, the D of the lithium-rich compound particles is... A 50 represents 20μm.

[0306] When a single battery cell is discharged to 0% SOC, the compaction density of the positive electrode film is 2.56 g / cm³. 3 The compaction density of the negative electrode film is 1.4 g / cm³. 3 The process of discharging a single battery cell to 0% SOC involves placing the battery in a 25°C oven for 2 hours, allowing the battery temperature to remain at 25°C, and then discharging the single battery cell at a constant power of 0.25P until the voltage of the single battery cell reaches 2.5V.

[0307] The battery cell includes four electrode components, each of which includes one positive electrode sheet. The positive electrode sheet is coated on both sides, and the length of the single-sided positive electrode film layer on a single positive current collector is 15,000 mm and the width is 198 mm.

[0308] 2. Preparation of other embodiments

[0309] Examples 2-5 and Comparative Example 1 were prepared using methods that were basically the same as those in Example 1, except that the mass ratio of lithium-rich compounds was adjusted, as detailed in Table 2.

[0310] Examples 6-9 and Comparative Example 2 are prepared in basically the same way as Example 1, except that the areal density of any side of the positive electrode film layer is adjusted, and the density of any side of the negative electrode film layer is adjusted accordingly under the condition that the ratio of the density of any side of the positive electrode film layer to the density of any side of the negative electrode film layer is equal to that in Example 1; wherein, the density of any side of the positive electrode film layer in each example is detailed in Table 2.

[0311] Examples 10-17 and Comparative Examples 2-3 are prepared in basically the same way as Example 1, except that the mass ratio of some components in the electrolyte is adjusted, as detailed in Table 1.

[0312] Table 1

[0313] The preparation methods of Examples 17-18 are basically the same as those of Example 1. The difference is that the length of the positive current collector and the length of the positive electrode film are adjusted, so that the total coating area of ​​the positive electrode film contained in the battery cell is different and the capacity of the battery cell is different. See Table 5 for details.

[0314] The preparation methods of Example 19 are basically the same as those of Example 1, except that the positive electrode tab and the positive electrode terminal in the top cover assembly are connected by an adapter piece.

[0315] The preparation methods of Example 20 and Example 1 are basically the same, except that the sintering temperature of the precursor powder and the compaction density of the positive electrode sheet are adjusted in the preparation of the positive electrode active material.

[0316] The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere, and held at that temperature for 3 hours. Then, the temperature was increased to a second temperature of 755°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process, the material was cooled. The compacted density of the positive electrode sheet is detailed in Table 7.

[0317] Example 21 is basically the same as the preparation method of Example 1, except that the particle size Dv50 of the mixed slurry after grinding and the compaction density of the positive electrode sheet were adjusted in the preparation of the positive electrode active material.

[0318] The mixed raw materials were ball-milled multiple times and demagnetized in a ball mill to obtain a mixed slurry. The number of grinding cycles and time were controlled, and the particle size Dv50 of the ground mixed slurry was 4.0 μm. The compaction density of the positive electrode sheet is detailed in Table 7.

[0319] Example 22 is basically the same as Example 1, except that the sintering temperature of the precursor powder and the compaction density of the positive electrode sheet were adjusted in the preparation of the positive electrode active material.

[0320] The precursor powder was placed in a sintering furnace and heated from 25°C to 350°C at a rate of 2°C / min under a nitrogen atmosphere, and held at that temperature for 3 hours. Then, the temperature was increased to a second temperature of 790°C at a rate of 5°C / min and held at that temperature for 10 hours. After the process, the temperature was lowered and cooled. The compacted density of the positive electrode sheet is detailed in Table 7.

[0321] II. Testing Methods

[0322] 1. Cyclic performance test

[0323] At 45℃, the battery cells were discharged at a constant power of 0.25P until the voltage of the battery cell reached 2.5V, and then allowed to rest for 30 minutes. Next, the battery cells were subjected to a charge-discharge cycle test at a constant power of 0.25P: First charge-discharge cycle: The battery cell was charged at a constant power of 0.25P to 3.65V, allowed to rest for 30 minutes, and then discharged at a constant power of 0.25P to 2.5V, recording the discharge capacity Q1; subsequently, after allowing the battery to rest for 30 minutes, the first charge-discharge cycle was repeated; this cycle was repeated 1000 times, and the discharge capacity Qn was recorded. The capacity retention rate of the battery cell is calculated as Qn / Q1 × 100%.

[0324] 2. Real-Time Efficiency (RTE) Test

[0325] At 25℃, the battery cells were discharged at a constant power of 0.25P until the voltage of the battery cells reached 2.5V, and then allowed to stand for 30 minutes. Next, the battery cells were subjected to a charge-discharge test at a constant power of 0.25P: the battery cells were charged at a constant power of 0.25P to 3.65V, and the charging voltage-charging capacity curve was recorded; after standing for 30 minutes, the cells were discharged at a constant power of 0.25P to 2.5V, and the discharging voltage-discharging capacity curve was recorded.

[0326] In the charging voltage-charging capacity curve, the charging energy W1 is obtained by integrating the charging voltage relative to the charging capacity in the range of 2.5V to 3.6V; in the discharging voltage-discharging capacity curve, the discharging energy W2 is obtained by integrating the discharging voltage relative to the discharging capacity in the range of 2.5V to 3.6V; RTE = W2 / W1 × 100%.

[0327] III. Test Results and Analysis

[0328] The test results of the above embodiments and comparative examples are detailed in Tables 2-7.

[0329] As shown in Tables 2-7, the battery cell provided in this application includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium-rich compound. The density of any side of the positive electrode film layer is greater than or equal to 0.3 g / 1540.25 mm². 2 The electrolyte includes dimethyl carbonate, which accounts for 15%-50% of the total mass of the electrolyte, and has high capacity, good cycle performance and energy conversion efficiency.

[0330] Table 2

[0331] As can be seen from the comparison between Examples 1-5 and Comparative Example 1, the inclusion of lithium-rich compounds in the positive electrode film layer helps improve the cycle performance of the battery cell. As can be seen from the comparison between Examples 6-8 and Comparative Example 2, the increased areal density on any side of the positive electrode film layer helps improve the capacity of the battery cell.

[0332] Based on the total mass of the positive electrode active material and lithium-rich compounds, the mass ratio of lithium-rich compounds is in the range of 5%-15%, and the battery cell takes into account excellent capacity, cycle performance and energy conversion efficiency.

[0333] The density on any side of the positive electrode film is 0.3 g / 1540.25 mm. 2 -0.4g / 1540.25mm 2 Within this range, it helps to further improve the cycle performance and energy conversion efficiency of individual battery cells.

[0334] Table 3

[0335] As shown in Table 3, based on the total mass of the electrolyte, dimethyl carbonate accounts for 15%-50% of the total mass, which helps to significantly improve the performance of the positive electrode film containing lithium-rich compounds and with a density greater than or equal to 0.3 g / 1540.25 mm on any side of the positive electrode film. 2 The cycle performance and energy conversion efficiency of the battery cells.

[0336] Based on the total mass of the electrolyte, the mass ratio of dimethyl carbonate is in the range of 30%-50%, which helps to further improve the cycle performance and energy conversion efficiency of the battery cells.

[0337] Table 4

[0338] As shown in Table 4, the addition of propylene carbonate to the electrolyte helps to further improve the energy conversion efficiency of the battery cells. The addition of vinylene carbonate to the electrolyte helps to improve the cycle performance of the battery cells. With both propylene carbonate and ethylene carbonate in the electrolyte, the battery cells exhibit excellent cycle performance and energy conversion efficiency.

[0339] Table 5

[0340] As shown in Table 5, increasing the total coating area of ​​the positive electrode film in a single battery cell helps to improve the capacity of the battery cell. The positive electrode film provided in this application contains lithium-rich compounds, and the density on any side of the positive electrode is greater than or equal to 0.3 g / 1540.25 mm². 2 Furthermore, the battery cells with capacities ranging from 400Ah to 3000Ah possess both excellent cycle performance and energy conversion efficiency.

[0341] Table 6

[0342] As shown in Table 6, directly connecting the positive electrode tab to the positive electrode terminal helps to further improve the energy conversion efficiency of the battery cell.

[0343] Table 7

[0344] As shown in Table 7, the compaction density of the positive electrode film is 2.5 g / cm³. 3 -3g / cm 3 The battery cells exhibit good cycle performance and energy conversion efficiency. Increasing the compaction density of the positive electrode film helps improve the cycle performance and energy conversion efficiency of the battery cells.

[0345] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized by, The device includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The negative electrode includes a negative current collector and a negative electrode film layer disposed on at least one side of the negative current collector. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive active material and a lithium-rich compound. The positive electrode film layer has a density of 0.3 g / 15 40.25 mm or more on either side thereof 2 ; The electrolyte includes dimethyl carbonate, and the mass percentage of dimethyl carbonate is 15%-50% based on the total mass of the electrolyte.

2. The battery cell of claim 1, wherein, Based on the total mass of the electrolyte, the mass percentage of dimethyl carbonate is 30%-50%.

3. The battery cell according to claim 1 or 2, characterized in that, 0.3 g / 15 40.25 mm 2 -0.45 g / 15 40.25 mm 2 0.3 g / 15 40.25 mm 2 -0.4 g / 15 40.25 mm 2 .

4. The battery cell of any one of claims 1-3, wherein, The capacity of the battery cell is 400Ah-3000Ah, optionally 400Ah-1500Ah, and further optionally 400Ah-1100Ah.

5. The battery cell of any one of claims 1-4, wherein, Based on the total mass of the positive electrode active material and the lithium-rich compound, the mass percentage of the lithium-rich compound is 3%-20%, optionally 5%-15%.

6. The battery cell of any one of claims 1-5, wherein, The compacted density of the positive electrode film layer is 2.5 g / cm 3 - 3 g / cm 3 .

7. The battery cell of any one of claims 1-6, wherein, The positive electrode active material includes lithium transition metal phosphate particles with carbon material disposed on at least part of their surface.

8. The battery cell of claim 7, wherein, The total area of ​​lithium transition metal phosphate particles in the cross-section of the positive electrode film along the thickness direction of the electrode sheet is 8.0%-20.0%, and can be optionally 10.0%-20.0%.

9. The battery cell according to claim 7 or 8, characterized in that, Based on the total area of ​​lithium transition metal phosphate particles in the cross-section along the thickness direction of the positive electrode film, the area ratio of lithium transition metal phosphate particles with particle size R2 satisfying 200nm≤R2<1000nm is 15.0%-25.0%, and can be selected as 16%-20%.

10. The battery cell of any one of claims 7-10, wherein, In a section of the positive electrode film layer along the thickness direction of the electrode tab, in a cumulative distribution curve of sphericity of the lithium-containing transition metal phosphate particles in the section, a median value L of the sphericity is A50 0.6-0.85, and optionally 0.65-0.

8.

11. The battery cell of any one of claims 1-11, wherein, The electrolyte includes a linear carbonate solvent, which includes dimethyl carbonate and further includes one or more of diethyl carbonate and ethyl methyl carbonate.

12. The battery cell of claim 11, wherein, The linear carbonate solvent includes ethyl methyl carbonate, and the mass percentage of ethyl methyl carbonate is 10%-50% based on the total mass of the electrolyte.

13. The battery cell of any one of claims 1-12, wherein, The electrolyte includes cyclic carbonate solvents, which include one or more of ethylene carbonate and propylene carbonate.

14. The battery cell of claim 13, wherein, The cyclic carbonate solvent satisfies at least one of the following conditions: (1) The cyclic carbonate solvent includes ethylene carbonate, and the mass percentage of ethylene carbonate is 10%-40% based on the total mass of the electrolyte; (2) The cyclic carbonate solvent includes propylene carbonate, and the mass percentage of propylene carbonate is 0.5%-10% based on the total mass of the electrolyte, optionally 2.5%-10%.

15. The battery cell of any one of claims 1-14, wherein, The electrolyte includes additives, which include one or more of fluoroethylene carbonate and vinylene carbonate.

16. The battery cell of claim 15, wherein, The additive satisfies at least one of the following conditions: (1) The additive includes fluoroethylene carbonate, and the mass percentage of the fluoroethylene carbonate is 0.05%-5% based on the total mass of the electrolyte, and can be 2%-3%; (2) The additive includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.1%-8% based on the total mass of the electrolyte, optionally 0.5%-8%.

17. The battery cell of any one of claims 1-16, wherein, The electrolyte comprises ethyl methyl carbonate and fluoroethylene carbonate.

18. The battery cell of any one of claims 1-17, wherein, The electrolyte includes propylene carbonate and vinylene carbonate.

19. The battery cell of any one of claims 1-18, wherein, The electrolyte includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate and lithium difluorosulfonylimide.

20. The battery cell of claim 19, wherein, The electrolyte solution comprises lithium bis(fluorosulfonyl)imide, and the mass percentage of lithium bis(fluorosulfonyl)imide based on the total mass of the electrolyte solution is 1%-7%, optionally 2%-7%; and / or, The electrolyte includes lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate is 2%-15% based on the total mass of the electrolyte, optionally 4%-8%.

21. The battery cell of claim 19 or 20, wherein, The electrolyte salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide, and the mass ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.5-5.5, optionally 2-4.

22. The battery cell of claim 21, wherein, The positive electrode film layer includes carbon nanotubes.

23. The battery cell of claim 22, wherein, Based on the total mass of the positive electrode film, the mass percentage of the carbon nanotubes is 0.1%-3%, optionally 0.5%-1%.

24. The battery cell of any one of claims 1-23, wherein, The positive electrode active material includes one or more of lithium iron phosphate, lithium iron phosphate doped and modified materials, and lithium iron phosphate coated and modified materials.

25. The battery cell of any one of claims 1-24, wherein, The positive electrode active material comprises the components shown in general formula I: Li m Fe x P y O j Q q Formula I, Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

26. The battery cell of any one of claims 1-25, wherein, The lithium-rich compounds include one or more of inorganic lithium salts, metal oxides, and organic compounds.

27. The battery cell of any one of claims 1-26, wherein, The lithium-rich compounds include one or more of lithium iron ferrite, lithium nickel ferrite, lithium manganese ferrite, lithium cobalt ferrite, lithium sulfide, lithium nitride, lithium hydroxide, lithium fluoride, lithium oxalate, lithium oxide, and lithium peroxide.

28. The battery cell of claim 27, wherein, The lithium-rich compound satisfies at least one of the following conditions: (1) The lithium iron ferrite rich in lithium comprises the components shown in general formula II: Li 5+a1 Fe 1+b1 O 4+c1 Formula II Wherein, -5≤a1≤0.5, -0.1≤b1≤0.5, -0.4≤c1≤0.4; optionally, -5≤a1≤0, and further optionally, -5≤a1≤0, b1=1, c1=4; (2) The lithium-rich nickel oxide comprises the components shown in general formula III: Li 2+a2 Ni 1+b2 O 2+c2 Formula III Wherein, -2≤a2≤0.2, -0.1≤b2≤0.1, -0.2≤c2≤0.2; optionally, -2≤a2≤0; further optionally, -2≤a2≤0, b2=1, c2=2.

29. The battery cell of any one of claims 1-28, wherein, The D50 of the lithium-rich compound particles is 1-50 pm based on the total area of the lithium-rich compound particles in the section of the positive electrode film layer along the thickness direction of the electrode tab. A 50 is 1-50 pm.

30. The battery cell of any one of claims 1-29, wherein, The total coated area of the positive electrode film layer included in the battery cell is 11m 2 -150m 2 , optionally 19.4m 2 -120m 2 , further optionally 20m 2 -120m 2 .

31. The battery cell of any one of claims 1-30, wherein, The battery cell further includes a housing and a top cover assembly. The housing has a housing opening, the electrode assembly is housed within the housing, and the top cover assembly covers the housing opening. The top cover assembly includes a positive electrode terminal. The positive current collector includes a positive current collector portion and a positive electrode tab disposed on at least one side of the positive current collector portion. The positive electrode tab extends from the positive current collector portion along a first direction and is directly connected to the positive electrode terminal. The first direction is parallel to the thickness direction of the top cover assembly. Optionally, the positive electrode tab is welded to the positive electrode terminal.

32. A battery device, characterized by Includes the battery cell according to any one of claims 1-31.

33. An energy storage device, comprising: Includes the battery device of claim 32, the battery device being used for storing electrical energy.

Images