Battery cell, battery apparatus and electric device

Abstract

The present invention belongs to the technical field of batteries, and provides a battery cell, a battery apparatus and an electric device. The battery cell comprises: a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, a first additive and a second additive, the positive electrode active material comprises a lithium-containing phosphate, the first additive comprises a lithium-containing iron oxide, and the second additive comprises a nickel-containing metal oxide; and a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material. The present invention is beneficial for improving the energy density and cycle performance of the battery cell.

Description

Battery cells, battery devices, electrical equipment Technical Field

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

[0002] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within the new energy industry, battery technology is a crucial factor in its development.

[0003] The development of battery technology requires consideration of various design factors, such as energy density, cycle life, lifespan, capacity, fast charging performance, and reliability. How to provide a battery cell with high energy density and long cycle life is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a battery cell with high energy density and long cycle life.

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

[0006] In a first aspect, a battery cell is provided, comprising: a positive electrode sheet, the positive electrode sheet including 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 including a positive electrode active material, a first additive and a second additive, the positive electrode active material including a lithium phosphate, the first additive including a lithium-containing iron oxide, and the second additive including a nickel-containing metal oxide; and a negative electrode sheet, the negative electrode sheet including 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, the negative electrode active material including a silicon-based material.

[0007] In this embodiment, the positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes silicon-based materials, resulting in a high energy density for the battery cell. A first additive releases lithium ions, compensating for the initial efficiency reduction caused by the silicon-based material. A second additive promotes the conversion of oxygen free radicals generated during the release of lithium ions by the first additive into oxygen, reducing the adverse effects of oxygen free radicals on the cycle performance of the battery cell. Therefore, the technical solution of this application can balance the energy density and cycle life of the battery cell.

[0008] In some embodiments, the silicon content in the silicon-based material is 0.5% to 10% by mass, optionally 3% to 8%, based on the total mass of the negative electrode film.

[0009] When the mass content of silicon in the silicon-based material is greater than or equal to 0.5% based on the total mass of the negative electrode film, the battery cell has a high energy density; when the mass content of silicon in the silicon-based material is less than or equal to 10% based on the total mass of the negative electrode film, the battery cell has a long cycle life.

[0010] When the mass content of silicon in the silicon-based material is 3% to 8% based on the total mass of the negative electrode film, the battery cell has a high energy density and a long cycle life.

[0011] In some embodiments, the mass content of the lithium-containing iron oxide is 0.5% to 5%, optionally 1% to 3%, based on the total mass of the positive electrode film.

[0012] When the mass content of lithium-containing iron oxide is greater than or equal to 0.5% based on the total mass of the positive electrode film, it is beneficial to improve the energy density of the battery cell; when the mass content of lithium-containing iron oxide is less than or equal to 5% based on the total mass of the positive electrode film, it is beneficial to balance the energy density and cycle life of the battery cell.

[0013] With a lithium-containing iron oxide content of 1.5% to 3% based on the total mass of the positive electrode film, the battery cell exhibits good energy density and cycle life.

[0014] In some embodiments, the mass content of the nickel-containing metal oxide is 0.15% to 1.5% based on the total mass of the positive electrode film.

[0015] When the mass content of nickel-containing metal oxides is greater than or equal to 0.15% based on the total mass of the positive electrode film, it is beneficial to improve the cycle performance of the battery cell; when the mass content of nickel-containing metal oxides is less than or equal to 1.5% based on the total mass of the positive electrode film, it is beneficial to improve the cycle life of the battery cell while taking into account the energy density of the battery cell.

[0016] In some embodiments, when the mass content of nickel-containing metal oxide is 0.6% to 0.9% based on the total mass of the positive electrode film, the battery cell has good energy density and cycle life.

[0017] In some embodiments, the average longest diameter of the lithium-containing iron oxide is 5 μm to 30 μm, optionally 15 μm to 20 μm, on a longitudinal section along the thickness direction of the positive electrode sheet.

[0018] When the average value of the longest diameter of the lithium-containing iron oxide is greater than or equal to 5 μm, the degree of side reactions occurring in the battery cell caused by oxygen free radicals generated by the lithium-containing iron oxide can be reduced, which is conducive to improving the cycle life of the battery cell; when the average value of the longest diameter of the lithium-containing iron oxide is less than or equal to 30 μm, it is conducive to the release of lithium ions in the lithium-containing iron oxide, which is conducive to improving the capacity and cycle life of the battery cell.

[0019] When the average value of the longest diameter of the lithium-containing iron oxide is 15 μm to 20 μm, it is conducive to further improving the cycle life of the battery cell.

[0020] In some embodiments, on the longitudinal section along the thickness direction of the positive electrode plate, the average value of the longest diameter of the nickel-containing metal oxide is 8 μm to 50 μm, and may be 8 μm to 25 μm. <X

[0021] When the average value of the longest diameter of the nickel-containing metal oxide is greater than or equal to 8 μm, it is conducive to reducing the degree of side reactions in the battery cell, which is conducive to improving the cycle life of the battery cell; when the average value of the longest diameter of the nickel-containing metal oxide is less than or equal to 50 μm, it is conducive to catalyzing the conversion of oxygen free radicals generated by the lithium-containing iron oxide into oxygen, thereby reducing the adverse effect of oxygen free radicals on the cycle performance and improving the cycle life of the battery cell.

[0022] When the average value of the longest diameter of the nickel-containing metal oxide is 8 μm to 25 μm, it is conducive to further improving the cycle life of the battery cell.

[0023] In some embodiments, the lithium-containing iron oxide includes a matrix and a coating layer located on at least part of the surface of the matrix, and the matrix includes Li

[0024] FeO b Here, 1 ≤ a ≤ 5, 1 ≤ b ≤ 5. In this way, the lithium-containing iron oxide can release lithium ions to compensate for the lithium ions consumed in forming the SEI film, which is conducive to improving the first efficiency and energy density of the battery cell. For example, in some embodiments, the matrix includes Li5FeO4. In this way, the lithium-containing iron oxide can release lithium ions to compensate for the lithium ions consumed in forming the SEI film, which is conducive to improving the first efficiency and energy density of the battery cell.

[0024] In some embodiments, the matrix includes Li5FeO4. In this way, the lithium-containing iron oxide can release lithium ions to compensate for the lithium ions consumed in forming the SEI film, which is conducive to improving the first efficiency and energy density of the battery cell.

[0025] In some embodiments, the matrix includes Li e FeO f Here, 0 ≤ e ≤ 5, 0 < f ≤ 4. During the formation process of the battery cell, the matrix decomposes, generating oxygen free radicals while generating lithium ions, and the molar contents of Li element and O element change.

[0026] In some embodiments, the matrix includes Li m FeO n , where 0 ≤ m ≤ 1 and 0 < n ≤ 2. During the formation process of the battery cell, the matrix decomposes, generating lithium ions and oxygen free radicals simultaneously, and the molar contents of Li element and O element change.

[0027] In some embodiments, the matrix includes doping elements, and the doping elements include one or more of B, P, S, Zr, and Al. The doping elements are beneficial to improving the stability of the lithium-containing iron oxide, reducing the side reaction between the lithium-containing iron oxide and the electrolyte, and thus are beneficial to improving the cycle life of the battery cell.

[0028] In some embodiments, the coating layer includes carbon element. The setting of the coating layer is beneficial to improving the stability of the lithium-containing iron oxide, and the inclusion of carbon element in the coating layer is beneficial to improving the conductivity of the lithium-containing iron oxide, and further beneficial to the performance of the capacity of the battery cell.

[0029] In some embodiments, the thickness of the coating layer is 10 nm to 100 nm. In this way, the coating layer has a suitable thickness, which is beneficial to improving the stability of the lithium-containing iron oxide and facilitating the extraction of lithium ions, and is beneficial to the performance of the capacity of the battery cell.

[0030] In some embodiments, the nickel-containing metal oxide includes N c NiO d , where N includes one or more of Li, Na, and K, 0 ≤ c ≤ 2, and 1 ≤ d ≤ 2. The above nickel-containing metal oxide can promote the conversion of oxygen free radicals generated by the lithium-containing iron oxide into oxygen, and thus can reduce the adverse effect of oxygen free radicals on the cycle performance; in addition, when the molar content of lithium element in the nickel-containing metal oxide is greater than 1, it can also play a role in supplementing lithium ions, which is beneficial to improving the cycle life of the battery cell.

[0031] In some embodiments, the nickel-containing metal oxide includes Li2NiO2. In this way, it is beneficial to improving the cycle life of the battery cell.

[0032] In some embodiments, the nickel-containing metal oxide includes Li g NiO h , where 0 ≤ g ≤ 2 and 0 < h ≤ 2. During the formation process of the battery cell, the nickel-containing metal oxide decomposes, and the molar contents of its lithium element and oxygen element will change to a certain extent.

[0033] In some embodiments, the nickel-containing metal oxide includes NiO q, where 0 < q ≤ 2. During the formation process of the battery cell, the nickel-containing metal oxide decomposes, and the molar content of oxygen element will change to a certain extent.

[0034] In some embodiments, the de-lithiation potential of the lithium-containing iron oxide is greater than that of the lithium-containing phosphate, and the de-lithiation potential of the nickel-containing metal oxide is greater than that of the lithium-containing phosphate. Thus, during the formation process, the lithium-containing iron metal oxide and the nickel-containing metal oxide can release lithium ions to provide more active lithium ions to the battery cell.

[0035] In some embodiments, in the voltage range of 2V to 4.3V, the charging specific capacity of the lithium-containing iron oxide is 300 mAh / g to 900 mAh / g, and optionally 450 mAh / g to 750 mAh / g.

[0036] The lithium-containing iron oxide has a high charging specific capacity, which is beneficial to improving the first efficiency and cycle life of the battery cell.

[0037] In some embodiments, based on the total mass of the positive electrode film layer, the mass ratio of Fe element in the lithium-containing iron oxide to Ni element in the nickel-containing metal oxide is 1 to 6, and optionally 1.5 to 4.

[0038] When the mass ratio of Fe element in the lithium-containing iron oxide to Ni element in the nickel-containing metal oxide is 1 to 6, the battery cell has good energy density and cycle performance.

[0039] When the mass ratio of Fe element in the lithium-containing iron oxide to Ni element in the nickel-containing metal oxide is 1.5 to 4, it is beneficial to further improve the cycle performance of the battery cell while having a high energy density.

[0040] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of Fe element in the lithium-containing iron oxide is 0.4% to 1.8%; the mass content of Ni element in the nickel-containing metal oxide is 0.1% to 0.85%.

[0041] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of Fe element in the lithium-containing iron oxide is 0.55% to 1%; the mass content of Ni element in the nickel-containing metal oxide is 0.2% to 0.45%.

[0042] During the decomposition process of the lithium-containing iron oxide, lithium ions and oxygen free radicals are generated. As the decomposition degree of the lithium-containing iron oxide varies, the mass content of Fe element changes. As the decomposition degree of the nickel-containing metal oxide varies, the mass content of Ni element changes.

[0043] In some embodiments, the silicon-based material includes one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. Silicon-based materials have high specific capacity, which is beneficial for improving the energy density of individual battery cells.

[0044] In some embodiments, the silicon-based material includes silicon-carbon materials.

[0045] In the structure of silicon-carbon materials, nano-silicon is deposited within a carbon framework. Silicon-carbon materials have a low specific surface area, which helps reduce side reactions between carbonate fragments generated by oxygen free radicals attacking the electrolyte and silicon, thus reducing lithium-ion consumption and improving the initial efficiency of the battery cell. With reduced side reactions between carbonate fragments and silicon, the loose organic components in the SEI film are reduced, improving the quality of the SEI film and decreasing the active lithium ions consumed during continuous SEI film repair due to damage. This results in a longer cycle life for the battery cell. Furthermore, the carbon framework provides some binding force to silicon, mitigating the problem of SEI film rupture caused by silicon expansion. This reduces the risk of continuous lithium loss due to SEI film repair, further enhancing the cycle life of the battery cell.

[0046] In some embodiments, the specific surface area of ​​the silicon-carbon material is 1.5 m². 2 / g to 3m 2 / g; and / or, the specific capacity of the silicon-carbon material is from 1500 mAh / g to 2500 mAh / g. Silicon-carbon materials have a lower specific surface area, which is beneficial for improving the initial efficiency and cycle life of battery cells; silicon-carbon materials have a higher specific capacity, which is beneficial for improving the energy density of battery cells.

[0047] In some embodiments, the negative electrode active material further includes a carbon-based material, which includes one or more of natural graphite, artificial graphite, soft carbon, and hard carbon. By combining carbon-based and silicon-based materials, the battery cell achieves a suitable energy density and cycle performance.

[0048] In some embodiments, the battery cell further includes an electrolyte comprising an electrolyte salt, which includes an imide lithium salt, specifically one or more of LiFSI and LiTFSI. Imide lithium salts facilitate the formation of an N- and S-rich SEI film, improving SEI film stability and reducing the risk of SEI film damage due to silicon-based material expansion. This, in turn, reduces the lithium ions consumed in repairing the SEI film after damage, thus improving the cycle performance of the battery cell.

[0049] In some embodiments, the electrolyte salt further includes lithium hexafluorophosphate.

[0050] In some embodiments, the imide lithium salt content is 0.3% to 5% based on the total mass of the electrolyte. This results in a suitable imide lithium salt content and good cycle performance for the battery cell.

[0051] In some embodiments, the lithium-containing phosphate comprises primary particles and secondary particles formed by the agglomeration of the primary particles. The average longest diameter of the primary particles is 100 nm to 500 nm, and the average longest diameter of the secondary particles is 1 μm to 2 μm. The lithium iron phosphate particles have a suitable size, facilitating the extraction of lithium ions and contributing to the full utilization of the battery cell's capacity.

[0052] In some embodiments, the lithium-containing phosphate includes those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y z The compounds, wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, S, Mg, Al, P, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Si, Cl, C, and N; Y includes one or more of O and F.

[0053] During the charging and discharging process of a single battery cell, the molar content of lithium, oxygen, and other elements in lithium phosphate varies within a certain range.

[0054] In some embodiments, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. These lithium-containing phosphates exhibit high structural stability, which helps to improve the cycle life of individual battery cells.

[0055] In some embodiments, at least a portion of the surface of the lithium phosphate contains carbon. This helps to improve the conductivity of the lithium phosphate, facilitating the utilization of the battery cell's capacity.

[0056] In some embodiments, the carbon content on the surface of the lithium phosphate is 1% to 2% based on the total mass of the positive electrode active material. This results in better conductivity of the positive electrode active material, facilitating the full utilization of the battery cell's capacity.

[0057] In some embodiments, the positive electrode sheet satisfies one or more of the following conditions:

[0058] The single-sided density of the positive electrode film is 0.25 g / 1540.25 mm. 2 Up to 0.45g / 1540.25mm 2 ;

[0059] The compaction density of the positive electrode sheet at 0% SOC is 2.3 g / cm³. 3 Up to 2.8 g / cm 3 .

[0060] In the above embodiments, the positive electrode film has a suitable areal density and compaction density, and the battery cell has a relatively suitable energy density and cycle performance.

[0061] In some embodiments, the negative electrode sheet satisfies one or more of the following conditions:

[0062] The single-sided density of the negative electrode film is 0.12 g / 1540.25 mm. 2 Up to 0.2g / 1540.25mm 2 ;

[0063] The compaction density of the negative electrode sheet at 0% SOC is 1.3 g / cm³. 3 Up to 1.6 g / cm 3 .

[0064] In the above embodiments, the negative electrode film layer has a suitable areal density and compaction density, and the battery cell has a relatively suitable energy density and cycle performance.

[0065] In some embodiments, when the battery cell is configured to 0% SOC, the lithium content in the positive electrode film is 4.1% to 4.3% by mass. A higher lithium content in the battery cell is beneficial for improving the energy density and cycle life of the battery cell.

[0066] In a second aspect, a battery device is provided, comprising a battery cell from the first aspect and any of the possible embodiments thereof.

[0067] Thirdly, an electrical device is provided, comprising a battery cell as described in the first aspect and any possible embodiment thereof, or a battery device as described in the second aspect, wherein the battery cell or battery device is used to store or provide electrical energy. Attached Figure Description

[0068] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0069] Figure 1 is a schematic diagram of a vehicle according to an embodiment of this application;

[0070] Figure 2 is a schematic diagram of the structure of a battery device according to an embodiment of this application;

[0071] Figure 3 is a schematic diagram of the structure of a battery cell according to an embodiment of this application;

[0072] Figure 4 is a schematic diagram of the positive electrode sheet according to an embodiment of this application;

[0073] Figure 5 is a schematic diagram of the negative electrode sheet according to an embodiment of this application.

[0074] Reference numerals: 1: Vehicle; 10: Battery unit; 30: Controller; 40: Motor; 11: Housing; 111: First housing section; 112: Second housing section; 3: Battery cell; 31: Housing; 32: End cap assembly; 33: Electrode assembly; 34: Connecting member; 331: Tab; 322: Electrode terminal; 50: Positive electrode sheet; 501: Positive current collector; 502: Positive electrode film; 60: Negative electrode sheet; 601: Negative current collector; 602: Negative electrode film.

[0075] The accompanying drawings are not drawn to scale. Detailed Implementation

[0076] Embodiments of the battery cell, battery device, and electrical appliance of this application have been described in detail with appropriate reference to the accompanying drawings; however, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] 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.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] 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.

[0081] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0082] This application aims to provide a battery cell that balances high energy density, high initial efficiency, and long cycle life. The battery cell includes: a positive electrode sheet, comprising 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, a first additive, and a second additive; the positive active material includes a lithium phosphate; the first additive includes a lithium-containing iron oxide; and the second additive includes a nickel-containing metal oxide. It also includes a negative electrode sheet, comprising 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 includes a negative active material, which is a silicon-based material.

[0083] Lithium phosphates, due to their high structural stability, are widely used in the positive electrode active materials of battery cells. To further improve the energy density of battery cells including those containing lithium phosphates, silicon-based materials are added to the negative electrode. However, due to their large specific surface area and tendency to expand, silicon-based materials require a significant amount of lithium ions to be consumed during the formation of the SEI film on the surface of the negative electrode active material, thus reducing the initial coulombic efficiency (i.e., first-time efficiency) of the battery cell. To improve the initial efficiency, lithium-containing iron oxides are added to the positive electrode to replenish active lithium ions. However, during the release of active lithium ions, lithium-containing iron oxides generate oxygen free radicals. These oxygen free radicals react with the electrolyte to produce carbonate fragments, which diffuse to the negative electrode and participate in the formation of the SEI film. This results in a more porous SEI film structure at the negative electrode, which is detrimental to the stability of the SEI film. Consequently, during the charge-discharge cycle of the battery cell, more lithium ions are consumed along with the repair of the SEI film, reducing the cycle life of the battery cell. Furthermore, due to the significant expansion of silicon-based materials, the expansion of silicon-based materials is detrimental to the stability of the SEI film, which in turn has an adverse effect on the cycle performance of the battery cells.

[0084] The second additive in this application catalyzes the oxygen free radicals generated by the first additive and promotes their conversion into oxygen, reducing the generation of carbonate fragments. This reduces the negative impact of carbonate fragments on the SEI film structure, improves the stability of the SEI film, reduces the lithium ions consumed in the continuous repair of the SEI film due to its instability, and enhances the cycle life of the battery cell. In particular, it reduces the damage to the SEI film caused by the expansion of silicon-based materials, and reduces the lithium ions consumed in repairing the SEI film due to its damage, thus improving the cycle performance of the battery cell. Therefore, the battery cell of this application can achieve both high energy density and long cycle life.

[0085] A single battery cell typically includes an electrode assembly. The electrode assembly includes a positive electrode, a negative electrode, and a separator. During the charging and discharging process of a single battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through.

[0086] In some embodiments, the positive electrode can be a positive electrode sheet, which can include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0087] In some embodiments, the negative electrode may be a negative electrode sheet, which may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0088] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0089] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0090] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride, and ceramic.

[0091] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0092] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0093] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0094] In some embodiments, the battery cell may include a housing. The housing is used to encapsulate components such as electrode assemblies and electrolytes. The housing may be made of steel, aluminum, plastic (such as polypropylene), composite metal (such as copper-aluminum composite), or aluminum-plastic film, etc. The housing includes a shell and end caps.

[0095] The battery mentioned in the embodiments of this application may be a single physical module comprising one or more battery cells to provide higher voltage and capacity. When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed via a busbar.

[0096] In some embodiments, the battery device may be a battery pack, which includes a housing and individual battery cells, with the individual battery cells or battery modules housed within the housing.

[0097] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0098] In some embodiments, the battery device may be located within an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0099] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use battery devices.

[0100] Electrical equipment can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical equipment.

[0101] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0102] For example, as shown in Figure 1, which is a structural schematic diagram of a vehicle 1 according to an embodiment of this application, vehicle 1 can be a gasoline vehicle, a natural gas vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A motor 40, a controller 30, and a battery device 10 can be installed inside vehicle 1. The controller 30 is used to control the battery device 10 to supply power to the motor 40. For example, the battery device 10 can be installed at the bottom, front, or rear of vehicle 1. The battery device 10 can be used to power vehicle 1. For example, the battery device 10 can serve as the operating power source for vehicle 1, for example, for the electrical system of vehicle 1, such as for the power requirements of vehicle 1's starting, navigation, and operation. In another embodiment of this application, the battery device 10 can not only serve as the operating power source for vehicle 1, but also as the driving power source for vehicle 1, replacing or partially replacing gasoline or natural gas to provide driving power for vehicle 1.

[0103] Figure 2 shows a partial structural schematic diagram of the battery device 10 according to an embodiment of this application. For example, as shown in Figure 2, the battery device 10 according to this application embodiment may include multiple battery cells 3 to meet different power usage requirements. The shape of the battery cell 3 according to this application embodiment can be set according to actual application. For example, the battery cell 3 can be cylindrical, or it can be cuboid or other shapes, and this application embodiment is not limited to this.

[0104] It should be understood that, as shown in FIG. 2, the battery device 10 of this embodiment may further include a housing 11, which can be used to accommodate multiple battery cells 3. The housing 11 of this embodiment has a hollow internal structure, and the multiple battery cells 3 are accommodated within the housing 11. The housing 11 may include two parts, referred to herein as a first housing portion 111 and a second housing portion 112, which are fastened together. The shapes of the first housing portion 111 and the second housing portion 112 can be determined according to the shape of the components accommodated internally, for example, according to the shape of the combination of the multiple battery cells 3 accommodated internally. At least one of the first housing portion 111 and the second housing portion 112 has an opening. For example, as shown in Figure 2, the first housing portion 111 and the second housing portion 112 can both be hollow cuboids with one open face. The openings of the first housing portion 111 and the second housing portion 112 are opposite to each other, and the first housing portion 111 and the second housing portion 112 are interlocked to form a housing 11 with a closed cavity, which can be used to accommodate multiple battery cells 3. The multiple battery cells 3 are connected in parallel, series, or mixed and placed inside the housing 11 formed by the interlocking of the first housing portion 111 and the second housing portion 112.

[0105] For example, unlike what is shown in Figure 2, only one of the first housing portion 111 and the second housing portion 112 may be a hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 112 as a hollow cuboid with one opening, and the first housing portion 111 as a plate-shaped example, then the first housing portion 111 covers the opening of the second housing portion 112 to form a housing 11 with a closed chamber, which can be used to accommodate multiple battery cells 3.

[0106] In this embodiment of the application, the battery cell can be a secondary battery, which refers to a battery cell that can be recharged to activate the active materials and continue to be used after the battery cell has been discharged.

[0107] The battery cells can be lithium-ion batteries or lithium metal batteries.

[0108] During the charging process of a single battery cell, lithium ions are released from the positive electrode active material, move and embed into the negative electrode; while during the discharging process, lithium ions are released from the negative electrode, move and embed into the positive electrode active material.

[0109] It should be understood that the “intercalation” process described in this application refers to the process by which lithium ions are intercalated in the positive electrode active material or the negative electrode due to an electrochemical reaction, and the “extraction” process described in this application refers to the process by which lithium ions are extracted from the positive electrode active material or the negative electrode due to an electrochemical reaction.

[0110] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. The following section describes the battery cell and its components provided in this application.

[0111] [Battery cell]

[0112] This application provides a battery cell including a positive electrode and a negative electrode.

[0113] Figure 3 is a schematic diagram of the structure of a battery cell according to an embodiment of this application. In one embodiment of this application, for example, referring to Figure 3, the battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33. The housing 31 has an opening for accommodating the electrode assembly 33, and the end cap assembly 32 is used to close the opening. The electrode assembly 33 may include a positive electrode, a negative electrode, and a separator located between the positive electrode and the negative electrode.

[0114] Figure 4 is a schematic diagram of a positive electrode sheet in one embodiment of this application. For example, as shown in Figure 4, the positive electrode sheet 50 includes a positive current collector 501 and a positive electrode film layer 502 disposed on at least one side of the positive current collector 501.

[0115] The positive electrode current collector 501 has two side surfaces along its own thickness direction (e.g., the z-direction in Figure 4). The positive electrode film layer 502 can be disposed on one side surface of the positive electrode current collector 501 or on both side surfaces of the positive electrode current collector 501. As an example, as shown in Figure 4, the positive electrode film layer 502 is disposed on both side surfaces of the positive electrode current collector 501.

[0116] The positive electrode film 502 includes a positive electrode active material, a first additive, and a second additive. The positive electrode active material includes a lithium phosphate, the first additive includes a lithium-containing iron oxide, and the second additive includes a nickel-containing metal oxide.

[0117] Lithium-containing phosphates can refer to lithium-containing transition metal phosphates with an olivine structure, such as lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their modified forms.

[0118] Lithium-containing iron oxides include lithium, iron, and oxygen. Within a certain voltage range, lithium-containing iron oxides can decompose to produce lithium ions, and at the same time, they also produce oxygen free radicals (also known as reactive oxygen species).

[0119] Lithium-containing iron oxides can be used as lithium replenishers; that is, lithium-containing iron oxides can generate active lithium ions to replenish the lithium ions consumed during the formation of the solid electrolyte interface (SEI) membrane.

[0120] Nickel-containing metal oxides include nickel and oxygen. In some embodiments, nickel-containing metal oxides may also include lithium.

[0121] Lithium-containing iron oxides generate oxygen free radicals along with lithium ions. These free radicals react with the electrolyte to produce carbonate fragments. These fragments diffuse to the negative electrode and participate in the formation of the SEI film, increasing the porous organic components of the SEI film. This increased porous organic content negatively impacts SEI film stability. Nickel-containing metal oxides can promote or catalyze the conversion of oxygen free radicals into oxygen, thereby reducing carbonate fragment generation. This decrease in porous organic components in the SEI film at the negative electrode leads to a more stable SEI film. With a more stable SEI film, the risk of continuously consuming lithium ions to repair or generate the SEI film is reduced, which is beneficial for improving the cycle life of individual battery cells.

[0122] Figure 5 is a schematic diagram of a negative electrode sheet in one embodiment of this application. For example, as shown in Figure 5, the negative electrode sheet 60 includes a negative current collector 601 and a negative electrode film layer 602 disposed on at least one side of the negative current collector 601.

[0123] The negative electrode current collector 601 has two side surfaces along its own thickness direction (e.g., the z-direction in FIG. 5). The negative electrode film layer 602 can be disposed on one side surface of the negative electrode current collector 601 or on both side surfaces of the negative electrode current collector 601. As an example, as shown in FIG. 5, the negative electrode film layer 602 is disposed on both side surfaces of the negative electrode current collector 601.

[0124] The negative electrode film 602 includes a negative electrode active material, which includes silicon-based materials.

[0125] Silicon-based materials include silicon, and can include elemental silicon, silicon-oxygen materials, silicon-carbon materials, etc.

[0126] Silicon-based materials have a higher specific capacity than carbon-based materials (such as graphite), which is beneficial for improving the energy density of battery cells.

[0127] By combining silicon-based materials with lithium-containing iron oxides as the first additive, the problems of high lithium-ion consumption and low initial efficiency of battery cells caused by silicon-based materials can be compensated, while also improving the energy density of battery cells.

[0128] By combining silicon-based materials, a lithium-containing iron oxide as the first additive, and a nickel-containing metal oxide as the second additive, the SEI film at the negative electrode exhibits good stability. This reduces the damage to the SEI film caused by the expansion of the silicon-based materials and minimizes the lithium-ion consumption required to repair the damaged SEI film. Consequently, the battery cell can achieve both high cycle life and high energy density.

[0129] In this embodiment, the positive electrode active material includes lithium iron phosphate, and the negative electrode active material includes silicon-based materials, resulting in a high energy density for the battery cell. A first additive releases lithium ions, improving the initial efficiency of the battery cell. A second additive promotes the conversion of oxygen free radicals generated during the release of lithium ions by the first additive into oxygen, reducing the adverse effects of oxygen free radicals on the cycle performance of the battery cell. Therefore, the technical solution of this application can balance the energy density and cycle life of the battery cell.

[0130] In some embodiments, the silicon content in the silicon-based material is 0.5% to 10% based on the total mass of the negative electrode film.

[0131] Based on the total mass of the negative electrode film, the mass content of silicon in the silicon-based material can be 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 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 a value within the range obtained by any combination of the above two values.

[0132] When the mass content of silicon in the silicon-based material is greater than or equal to 0.5% based on the total mass of the negative electrode film, the battery cell exhibits a high energy density; when the mass content of silicon in the silicon-based material is less than or equal to 10% based on the total mass of the negative electrode film, the battery cell exhibits a long cycle life. By setting the mass content of silicon in the silicon-based material to between 0.5% and 10%, the battery cell can achieve both high energy density and long cycle life.

[0133] In some embodiments, the silicon content in the silicon-based material is 3% to 8% based on the total mass of the negative electrode film.

[0134] When the mass content of silicon in the silicon-based material is 3% to 8% based on the total mass of the negative electrode film, the battery cell has a higher energy density and a longer cycle life.

[0135] In some embodiments, the mass content of lithium-containing iron oxide is 0.5% to 5% based on the total mass of the positive electrode film.

[0136] Based on the total mass of the positive electrode film, the mass content of lithium-containing iron oxide can be 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, 5%, or a value within the range obtained by any combination of the above two values.

[0137] When the mass content of lithium-containing iron oxide is greater than or equal to 0.5% based on the total mass of the positive electrode film, it is beneficial to improve the energy density of the battery cell; when the mass content of lithium-containing iron oxide is less than or equal to 5% based on the total mass of the positive electrode film, it is beneficial to balance the energy density and cycle life of the battery cell.

[0138] In some embodiments, the mass content of lithium-containing iron oxide is 1.5% to 3% based on the total mass of the positive electrode film.

[0139] With a lithium-containing iron oxide content of 1.5% to 3% based on the total mass of the positive electrode film, the battery cell exhibits good energy density and cycle life.

[0140] In some embodiments, the mass content of nickel-containing metal oxide is 0.15% to 1.5% based on the total mass of the positive electrode film.

[0141] Based on the total mass of the positive electrode film, the mass content of nickel-containing metal oxide can be 0.15%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.73%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.2%, 1.3%, 1.4%, 1.5%, or a value within the range obtained by any combination of the above two values.

[0142] When the mass content of nickel-containing metal oxides is greater than or equal to 0.05% based on the total mass of the positive electrode film, it can effectively promote the conversion of oxygen free radicals generated by lithium-containing iron oxides into oxygen, reduce the adverse effects of oxygen free radicals on the cycle performance of the battery cell, and improve the cycle performance of the battery cell. When the mass content of nickel-containing metal oxides is less than or equal to 1.5% based on the total mass of the positive electrode film, the lithium-containing iron oxides in the positive electrode film can have a more suitable content, which is beneficial to improving the cycle life of the battery cell while taking into account the energy density of the battery cell.

[0143] In some embodiments, the mass content of nickel-containing metal oxide is 0.6% to 0.9% based on the total mass of the positive electrode film.

[0144] With a total mass content of 0.6% to 0.9% nickel-containing metal oxides based on the positive electrode film, the battery cell exhibits good energy density and cycle life.

[0145] In some embodiments, when the mass content of silicon in the silicon-based material is 0.5% to 10% based on the total mass of the negative electrode film, the mass content of lithium-containing iron oxide and the mass content of nickel-containing metal oxide in the positive electrode film are set to be 0.5% to 5%, and the battery cell has a higher energy density and a longer cycle life.

[0146] In some embodiments, the average longest diameter of the lithium-containing iron oxide is 5 μm to 30 μm on a longitudinal section along the thickness direction of the positive electrode sheet.

[0147] The average longest diameter of lithium-containing iron oxides can be 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, 21 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, or a value within the range obtained by any combination of the above two values.

[0148] The longest diameter of a particle can be defined as the longest straight line that passes through the center point of the particle and extends to its outer periphery. The average longest diameter of lithium-containing iron oxide can be measured as follows: Take 30 lithium-containing iron oxide particles from a longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 particles, and then take the average value to obtain the average longest diameter of the lithium-containing iron oxide.

[0149] When the average longest diameter of lithium-containing iron oxide is greater than or equal to 5 μm, it is beneficial to reduce the oxygen free radicals generated by lithium-containing iron oxide, thereby reducing the degree of side reactions of oxygen free radicals in the battery cell and improving the cycle life of the battery cell. When the average longest diameter of lithium-containing iron oxide is less than or equal to 30 μm, it is beneficial to the extraction of lithium ions from lithium-containing iron oxide, which is beneficial to improving the capacity and cycle life of the battery cell.

[0150] In some embodiments, the thickness is 15 μm to 20 μm. This is beneficial for further improving the cycle life of the battery cells.

[0151] In some embodiments, the average longest diameter of the nickel-containing metal oxide is 8 μm to 50 μm on a longitudinal section along the thickness direction of the positive electrode sheet.

[0152] The average longest diameter of nickel-containing metal oxides can be 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, 21 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, 36 μm, 38 μm, 40 μm, 42 μm, 44 μm, 46 μm, 48 μm, 50 μm, or a value within the range obtained by any combination of the above two values.

[0153] The average length of the longest diameter of nickel-containing metal oxides can be measured as follows: Take 30 nickel-containing metal oxide particles from the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 particles, and take the average value to obtain the average length of the longest diameter of the nickel-containing metal oxides.

[0154] When the average longest diameter of nickel-containing metal oxides is greater than or equal to 8 μm, the nickel-containing metal oxides have suitable catalytic activity, which helps to reduce the risk of side reactions in the electrolyte caused by the high catalytic activity of nickel-containing metal oxides, and helps to reduce the degree of side reactions within the battery cell, thereby helping to improve the cycle life of the battery cell. When the average longest diameter of nickel-containing metal oxides is less than or equal to 50 μm, it is beneficial to catalyze the conversion of oxygen free radicals generated by lithium-containing iron oxides into oxygen, thereby reducing the adverse effects of oxygen free radicals on cycle performance and improving the cycle life of the battery cell.

[0155] In some embodiments, the diameter is 8 μm to 25 μm. This is beneficial for further improving the cycle life of the battery cells.

[0156] In some embodiments, the lithium-containing iron oxide comprises a matrix and a coating layer located on at least a portion of the surface of the matrix, the matrix comprising Li a FeO b , where 1≤a≤5, 1≤b≤5.

[0157] In Li a FeO b In the compound, a can be 1, 1.3, 1.5, 2, 2.3, 2.5, 2.8, 3, 3.5, 4, 4.5, 4.8, 5 or any of the above values; b can be 1, 1.3, 1.5, 2, 2.3, 2.5, 2.8, 3, 3.5, 4, 4.5, 4.8, 5 or any of the above values.

[0158] A lithium molar content of 1 or more in the matrix is ​​beneficial for releasing more lithium ions to replenish the active lithium consumed in the battery cell.

[0159] In the above embodiments, lithium-containing iron oxides can release lithium ions to compensate for the lithium ions consumed in forming the SEI film, which is beneficial to improving the initial efficiency and energy density of the battery cell.

[0160] In some embodiments, the substrate comprises Li5FeO4. In this way, lithium-containing iron oxides can release lithium ions to compensate for the lithium ions consumed in forming the SEI film, which is beneficial for improving the initial efficiency and energy density of the battery cell.

[0161] Li5FeO4 is the chemical formula of the matrix before delithiation. During the formation of the battery cell, Li5FeO4 decomposes to produce lithium ions and oxygen free radicals. The molar content of lithium and oxygen in the matrix will change depending on the degree of decomposition.

[0162] In some embodiments, the matrix includes Li e FeOf ,0≤e≤5,0 <f≤4。

[0163] In Li e FeO f In this context, e can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, or any of the above values, and f can be 0, 1, 1.5, 2, 2.5, 3, 3.5, 4, or any of the above values.

[0164] During the formation of a battery cell, the matrix decomposes, generating oxygen free radicals along with lithium ions, and the molar contents of Li and O elements change. For example, after decomposition, it may be an iron oxide that does not contain lithium. In the formed battery cell, the molar contents of each element in the chemical formula of the matrix of the first additive in the positive electrode film are within the above-mentioned range.

[0165] In some embodiments, the matrix includes Li m FeO n ,0≤m≤1,0 <n≤2。

[0166] In Li m FeO n In this context, m can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any of the above values, and n can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any of the above values.

[0167] During the formation of a battery cell, the matrix decomposes, generating lithium ions and oxygen free radicals, resulting in changes in the molar content of Li and O elements. In the formed battery cell, the molar content of each element in the chemical formula of the matrix of the first additive in the positive electrode film is within the aforementioned range.

[0168] In some embodiments, the matrix includes a doping element, which includes one or more of B, P, S, Zr, and Al.

[0169] Doping with elements can improve the stability of lithium-containing iron oxides and reduce side reactions between lithium-containing iron oxides and electrolytes, thereby improving the cycle life of individual battery cells.

[0170] In some embodiments, the coating layer comprises carbon.

[0171] The coating layer helps improve the stability of lithium-containing iron oxide, and the inclusion of carbon elements in the coating layer helps improve the conductivity of lithium-containing iron oxide, thereby helping to increase the capacity of the battery cell.

[0172] In some embodiments, the thickness of the coating layer is 10 nm to 100 nm.

[0173] The thickness of the coating layer can be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm or any combination of the above values.

[0174] The coating layer has a suitable thickness, which helps to improve the stability of lithium-containing iron oxide and facilitates the extraction of lithium ions, resulting in a higher capacity for the battery cell.

[0175] In some embodiments, the nickel-containing metal oxide includes N c NiO d , where N includes one or more of Li, Na, and K, 0≤c≤2, 1≤d≤2.

[0176] In N c NiO d In this context, c can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any range of the above values, and d can be 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any range of the above values.

[0177] When c is 0, the nickel-containing metal oxide can be nickel oxide; when c is greater than 0, the nickel-containing metal oxide can be a lithium-containing nickel metal oxide; when c is greater than 1, the nickel-containing metal oxide has a higher molar content of lithium, and can also provide active lithium ions to the battery cells to replenish the consumed active lithium ions.

[0178] The aforementioned nickel-containing metal oxides can promote the conversion of oxygen free radicals generated by lithium-containing iron oxides into oxygen, thereby reducing the adverse effects of oxygen free radicals on cycle performance. In addition, when the molar content of lithium in the nickel-containing metal oxides is greater than 1, it can also supplement lithium ions, which is beneficial to improving the initial efficiency and energy density of the battery cell.

[0179] In some embodiments, the nickel-containing metal oxide includes Li2NiO2. Thus, it is beneficial to improve the cycle life of the battery cell.

[0180] Before the battery cell is subjected to formation, the nickel-containing metal oxide in the positive electrode film layer of the battery cell can be Li2NiO2. During the formation process, Li2NiO2 decomposes, lithium ions are released, and the oxygen content may also change accordingly.

[0181] In some embodiments, the nickel-containing metal oxide includes Li g NiO h , where 0 ≤ g ≤ 2 and 0 < h ≤ 2.

[0182] In Li g NiO h , g can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range composed of any of the above values, and h can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or a range composed of any of the above values.

[0183] During the formation process of the battery cell, the nickel-containing metal oxide decomposes, and the molar contents of its lithium element and oxygen element will change to a certain extent. For example, the lithium in the nickel-containing metal oxide is completely released and becomes nickel oxide after decomposition. In the battery cell after formation, the molar contents of the lithium element and oxygen element of the nickel-containing metal oxide are within the above ranges.

[0184] In some embodiments, the nickel-containing metal oxide includes NiO q , where 0 < q ≤ 2. During the formation process of the battery cell, the nickel-containing metal oxide decomposes, and the molar content of the oxygen element will change to a certain extent. For example, the lithium in the nickel-containing metal oxide is completely released and becomes nickel oxide after decomposition.

[0185] It should be noted that in the reverse stage, after the battery cell is disassembled, if Li5FeO4 and Li2NiO2 are not directly detected, but by-products of Li5FeO4 (such as iron oxides) and by-products of Li2NiO2 (such as nickel oxides) can be detected, those skilled in the art can determine the presence of Li5FeO4 and Li2NiO2 in the battery cell before formation through the by-products, and then the battery cell is also within the protection scope of this application.

[0186] In some embodiments, the delithiation potential of lithium-containing iron oxides is greater than that of lithium-containing phosphates, and the delithiation potential of nickel-containing metal oxides is greater than that of lithium-containing phosphates.

[0187] The delithiation potential refers to the potential at which lithium ions are extracted from a material. For example, the upper limit of the voltage range during the formation of a battery cell is greater than the upper limit of the voltage range during the charging and discharging of the battery cell in a battery device. This facilitates the extraction of lithium from lithium-containing iron oxides and nickel-containing metal oxides, thereby increasing the number of active lithium ions in the battery cell and improving its initial efficiency.

[0188] In the above embodiments, during the formation process, lithium-containing iron metal oxides and nickel-containing metal oxides can release lithium ions to provide more active lithium ions to the battery cells.

[0189] In some embodiments, the charge capacity of the lithium-containing iron oxide is 300 mAh / g to 900 mAh / g, optionally 450 mAh / g to 750 mAh / g, in a voltage range of 2V to 4.3V.

[0190] Within a voltage range of 2V to 4.3V, the chargeable capacity of lithium-containing iron oxides can be 300mAh / g, 320mAh / g, 350mAh / g, 380mAh / g, 400mAh / g, 420mAh / g, 450mAh / g, 480mAh / g, 500mAh / g, 550mAh / g, 580mAh / g, 600mAh / g, 650mAh / g, 700mAh / g, 750mAh / g, 800mAh / g, 850mAh / g, 880mAh / g, 900mAh / g, or any value between these ranges.

[0191] Lithium-containing iron oxides have high charge capacity, which is beneficial for improving the initial efficiency and energy density of battery cells.

[0192] In some embodiments, the mass ratio of Fe in the lithium-containing iron oxide to Ni in the nickel-containing metal oxide is 1 to 6, based on the total mass of the positive electrode film.

[0193] Based on the total mass of the positive electrode film, the mass ratio of Fe in the lithium-containing iron oxide to Ni in the nickel-containing metal oxide can be 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, or any of the above values.

[0194] The mass ratio of lithium-containing iron oxide to nickel-containing metal oxide can be determined by the mass ratio of Fe in lithium-containing iron oxide to Ni in nickel-containing metal oxide.

[0195] When the mass ratio of Fe in lithium-containing iron oxide to Ni in nickel-containing metal oxide is 1 to 6, the battery cell exhibits good energy density and cycle performance.

[0196] In some embodiments, the mass ratio of Fe in the lithium-containing iron oxide to Ni in the nickel-containing metal oxide is 1.5 to 4. This is beneficial for further improving the cycle performance of the battery cell while maintaining a high energy density.

[0197] In some embodiments, based on the total mass of the positive electrode film, the mass content of Fe in the lithium-containing iron oxide is 0.4% to 1.8%; and the mass content of Ni in the nickel-containing metal oxide is 0.1% to 0.85%.

[0198] In some embodiments, based on the total mass of the positive electrode film, the mass content of Fe in the lithium-containing iron oxide is 0.55% to 1%; and the mass content of Ni in the nickel-containing metal oxide is 0.2% to 0.45%.

[0199] It should be noted that, in the reverse stage, if Li5FeO4 and Li2NiO2 are not directly detected after disassembling the battery cell, but byproducts of Li5FeO4 (such as iron oxides) and byproducts of Li2NiO2 (such as nickel oxides) are detected, those skilled in the art can determine the presence of Li5FeO4 and Li2NiO2 in the battery cell before formation by the byproducts, and the battery cell is also within the scope of protection of this application.

[0200] During the decomposition of lithium-containing iron oxides, lithium ions and oxygen free radicals are generated. The mass content of Fe varies depending on the degree of decomposition of the lithium-containing iron oxides. Similarly, the mass content of Ni varies depending on the degree of decomposition of nickel-containing metal oxides.

[0201] In some embodiments, silicon-based materials include one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. Silicon-based materials have high specific capacity, which is beneficial for improving the energy density of individual battery cells.

[0202] In some embodiments, silicon-based materials include silicon-carbon materials.

[0203] In the structure of silicon-carbon materials, nano-silicon is deposited within a carbon framework. Silicon-carbon materials have a low specific surface area, which helps reduce side reactions between carbonate fragments generated by oxygen free radicals attacking the electrolyte and silicon, thus reducing lithium-ion consumption and improving the initial efficiency of the battery cell. With reduced side reactions between carbonate fragments and silicon, the loose organic components in the SEI film are reduced, improving the quality of the SEI film and decreasing the active lithium ions consumed during continuous SEI film repair due to damage. This results in a longer cycle life for the battery cell. Furthermore, the carbon framework provides some binding force to silicon, mitigating the problem of SEI film rupture caused by silicon expansion. This reduces the risk of continuous lithium loss due to SEI film repair, further enhancing the cycle life of the battery cell.

[0204] In some embodiments, the specific surface area of ​​the silicon-carbon material is 1.5 m². 2 / g to 3m 2 / g; and / or, the specific capacity of the silicon-carbon material is from 1500mAh / g to 2500mAh / g.

[0205] The specific surface area of ​​silicon-carbon materials can be 1.5 m². 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g、2m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.6m 2 / g, 2.7m 2 / g, 2.8m 2 / g, 2.9m 2 / g、3m 2 / g or any of the above values.

[0206] Silicon-carbon materials have a low specific surface area, which is beneficial for improving the initial efficiency and cycle life of battery cells; silicon-carbon materials have a high specific capacity, which is beneficial for improving the energy density of battery cells.

[0207] In some embodiments, the negative electrode active material further includes carbon-based materials, which include one or more of natural graphite, artificial graphite, soft carbon, and hard carbon. By combining carbon-based and silicon-based materials, the battery cell achieves suitable energy density and cycle performance.

[0208] In some embodiments, the battery cell further includes an electrolyte, which includes an electrolyte salt, which includes an imide lithium salt, and the imide lithium salt includes one or more of LiFSI and LiTFSI.

[0209] Imide lithium salts help form N and S-rich SEI films, which helps improve the stability of SEI films, reduces the risk of SEI film damage caused by the expansion of silicon-based materials, and thus reduces the lithium ions consumed in repairing SEI films due to SEI film damage, which is beneficial to improving the cycle performance of battery cells.

[0210] In some embodiments, the electrolyte salt also includes lithium hexafluorophosphate.

[0211] In some embodiments, based on the total mass of the electrolyte, the mass content D of the imide lithium salt satisfies: 0.3% ≤ D ≤ 5%.

[0212] D can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any of the above values.

[0213] With a concentration of 0.3% ≤ D ≤ 5%, imide lithium salts have suitable mass content, and the battery cells exhibit good cycle performance.

[0214] In some embodiments, the electrolyte further includes a solvent. The solvent includes one or both of carbonate solvents and carboxylic acid ester solvents.

[0215] In some embodiments, the lithium phosphate includes primary particles and secondary particles formed by the aggregation of the primary particles, wherein the average longest diameter of the primary particles is 100 nm to 500 nm and the average longest diameter of the secondary particles is 1 μm to 2 μm.

[0216] In the embodiments of this application, a primary particle refers to the smallest unit of a particle within a certain observation range. A primary particle may contain defects of any form, but it is impossible to further define smaller particles within a primary particle. Primary particles may aggregate under physical forces such as van der Waals forces, but such aggregation is easily disaggregated under external forces such as ultrasound, stirring, and rolling, so that the main constituent morphology of the positive electrode active material in the film layer is still primary particles.

[0217] In the embodiments of this application, secondary particles refer to particles formed by the sequential aggregation of particles.

[0218] The average longest diameter of primary lithium iron phosphate particles is 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 480nm, 500nm or any value within the above range, and the average longest diameter of secondary particles can be 1μm, 1.5μm, 2μm or any value within the above range.

[0219] Lithium iron phosphate particles have a suitable size, which facilitates the extraction of lithium ions and helps to maximize the capacity of the battery cell.

[0220] In some embodiments, lithium phosphates include those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y z The compounds, wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, S, Mg, Al, P, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Si, Cl, C, and N; Y includes one or more of O and F.

[0221] In the general formula for lithium phosphate, x can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any of the above values; y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3 or any of the above values; a1 can be 0.9, 1, 1.2, 1.3, 1.4, 1.5 or any of the above values; b1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any of the above values; c1 can be 0, 0.1, 0.2, 0.3, 0.4, 0.5 or any of the above values; and z can be 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or any of the above values.

[0222] During the charging and discharging process of a single battery cell, the molar content of lithium, oxygen, and other elements in lithium phosphate varies within a certain range.

[0223] In some embodiments, the lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4. These lithium-containing phosphates exhibit high structural stability, which helps to improve the cycle life of battery cells.

[0224] During the charging and discharging process, lithium (Li) undergoes insertion / extraction and consumption within a single battery cell. The molar content of Li in the positive electrode active material varies depending on the discharge state of the cell. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. Similarly, the molar content of O in the examples of positive electrode active materials in this application is only an ideal value. Oxygen release from the crystal lattice causes changes in the molar content of O, resulting in fluctuations in the actual molar content of O.

[0225] In some embodiments, at least a portion of the surface of the lithium phosphate contains carbon. This helps to improve the conductivity of the lithium phosphate, facilitating the full utilization of the battery cell's capacity, resulting in a higher capacity battery cell.

[0226] As an example, at least a portion of the surface of the lithium phosphate is provided with a coating layer, which includes carbon elements. The inclusion of a carbon-containing coating layer improves the conductivity of the positive electrode active material, facilitating the full utilization of the battery cell's capacity.

[0227] In some embodiments, the carbon content of the lithium phosphate surface is 1% to 2% based on the total mass of the positive electrode active material.

[0228] Based on the total mass of the positive electrode active material, the mass content of carbon on the lithium phosphate surface can be 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any of the above values.

[0229] When the carbon content on the surface of lithium phosphate is 1% to 2% based on the total mass of the positive electrode active material, the positive electrode active material has good conductivity, which facilitates the utilization of the battery cell's capacity, resulting in a higher battery cell capacity.

[0230] In some embodiments, the positive electrode sheet satisfies one or more of the following conditions:

[0231] The single-sided density of the positive electrode film is 0.25 g / 1540.25 mm. 2 Up to 0.45g / 1540.25mm 2 ;

[0232] The compaction density of the positive electrode sheet at 0% State of Charge (SOC) is 2.3 g / cm³. 3 Up to 2.8 g / cm 3 .

[0233] The single-sided density of the positive electrode film can be 0.25 g / 1540.25 mm. 2 0.28g / 1540.25mm 2 0.3g / 1540.25mm 2 0.32g / 1540.25mm 2 0.35g / 1540.25mm 2 0.38g / 1540.25mm 2 0.4g / 1540.25mm 2 0.42g / 1540.25mm 2 0.43g / 1540.25mm 2 0.44g / 1540.25mm 2 0.45g / 1540.25mm 2 Or a range between any of the above values.

[0234] The compaction density of the positive electrode sheet at 0% SOC can be 2.3 g / cm³. 3 2.35g / cm 3 2.4g / cm 3 2.45g / cm 3 2.5g / cm 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 Or a range between any of the above values.

[0235] As an example, a battery cell with 0% SOC can be obtained by the following method. Specifically, the battery cell is first charged to 3.65V at a constant current of 0.3C, then charged to 0.05C at a constant voltage of 3.65V, and finally discharged to 2.5V to obtain a battery cell with 0% SOC. Afterwards, the battery cell is disassembled to obtain the electrode (e.g., the positive electrode), and the compaction density of the electrode is tested.

[0236] In the above embodiments, the positive electrode film has a suitable areal density and compaction density, and the battery cell has a relatively suitable energy density and cycle performance.

[0237] In some embodiments, the negative electrode sheet satisfies one or more of the following conditions:

[0238] The single-sided density of the negative electrode film is 0.12 g / 1540.25 mm. 2 Up to 0.2g / 1540.25mm 2 ;

[0239] The compaction density of the negative electrode sheet at 0% SOC is 1.3 g / cm³. 3 Up to 1.6 g / cm 3 .

[0240] The density of the negative electrode film on one side can be 0.12 g / 1540.25 mm. 2 0.13g / 1540.25mm 2 0.14g / 1540.25mm 2 0.15g / 1540.25mm 2 0.16g / 1540.25mm 2 0.17g / 1540.25mm 2 0.18g / 1540.25mm 2 0.19g / 1540.25mm 2 0.20g / 1540.25mm 2 Or a range between any of the above values.

[0241] The compaction density of the negative electrode sheet at 0% SOC can be 1.3 g / cm³. 3 1.35g / cm 3 1.4g / cm 3 1.45g / cm 3 1.5g / cm 3 1.55g / cm 3 1.6g / cm 3 Or a range between any of the above values.

[0242] In the above embodiments, the negative electrode film layer has a suitable areal density and compaction density, and the battery cell has a relatively suitable energy density and cycle performance.

[0243] In some embodiments, when the battery cell is configured to have a state of 0% SOC, the mass content of lithium in the positive electrode film is 4.1% to 4.3%.

[0244] The mass content of lithium in the positive electrode film can be 4.1%, 4.15%, 4.2%, 4.25%, 4.3%, or any of the above values.

[0245] A higher lithium content in a single battery cell is beneficial for improving the energy density and cycle life of the battery cell.

[0246] In some embodiments, the end cap assembly 32 includes electrode terminals 322, as shown in FIG3. The end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0247] The battery cell 3 also includes a connecting member 34 for connecting the tab 331 and the electrode terminal 322 of the electrode assembly 33. For example, one connecting member 34 is used to connect the tab of the positive electrode and the positive electrode terminal, and another connecting member 34 is used to connect the tab of the negative electrode and the negative electrode terminal.

[0248] [Positive electrode plate]

[0249] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0250] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0251] 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.).

[0252] In some embodiments, the positive electrode film layer further includes a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0253] In some embodiments, the positive electrode film layer further includes a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0254] In one embodiment, the positive electrode sheet can be prepared by forming a positive electrode slurry using the components described above. For example, the positive electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0255] [Negative electrode plate]

[0256] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0257] The negative electrode current collector can be a metal foil or a composite negative electrode current collector. The negative electrode current collector can be copper foil. Composite negative electrode current collectors can be formed by depositing metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0258] The negative electrode film layer may also optionally include a binder. As an example, the binder may include one or more of the following: styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0259] The negative electrode film may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0260] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., deionized water) to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained.

[0261] [Isolation Component]

[0262] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular restrictions on the type of separator; for example, any known porous membrane with good chemical and mechanical stability can be selected.

[0263] In one embodiment, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0264] This application provides a battery device, including the battery cell in any of the above embodiments.

[0265] This application provides an electrical device including a battery cell or battery device as described in any of the above embodiments, wherein the battery cell or battery device is used to store or provide electrical energy.

[0266] 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.

[0267] [Example]

[0268] Example 1

[0269] (1) Preparation of positive electrode sheet

[0270] Lithium iron phosphate (LiFePO4), the positive electrode active material, first additive, second additive, positive electrode conductive agent Super P, and positive electrode binder polyvinylidene fluoride (PVDF) were mixed in a ratio of 94.4:2.5:0.6:1:1.5. N-methylpyrrolidone (NMP) solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. The slurry-coated positive electrode current collector was then dried and cold-pressed to obtain the positive electrode sheet. The single-sided density of the positive electrode film was 0.3 g / 1540.25 mm². 2 The compaction density of the positive electrode sheet is 2.6 g / cm³. 3 .

[0271] The first additive comprises a matrix and a coating layer located on at least a portion of the surface of the matrix. The matrix comprises Li5FeO4, and the coating layer comprises carbon. The second additive comprises Li2NiO2. Based on the total mass of the positive electrode film, the mass content of the first additive is 2.5%, and the mass content of the second additive is 0.6%.

[0272] (2) Preparation of negative electrode sheet

[0273] A negative electrode active material, negative electrode conductive agent Super P, thickener sodium carboxymethyl cellulose, and negative electrode binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96:1:1.2:1.8. Deionized water was added as a solvent, and the mixture was stirred evenly under vacuum to prepare a negative electrode slurry. The negative electrode slurry was uniformly coated on both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet was obtained. The single-sided density of the negative electrode film layer was 0.15 g / 1540.25 mm². 2 The compaction density of the negative electrode sheet is 1.58 g / cm³. 3 .

[0274] The negative electrode active materials include artificial graphite and silicon carbon materials. Based on the total mass of the negative electrode film, the silicon content in the silicon carbon material is 5%.

[0275] (3) Preparation of the separating membrane

[0276] The separator consists of a 10μm PE base film.

[0277] (4) Preparation of electrolyte

[0278] The electrolyte consists of a solvent and an electrolyte salt. The solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1. The electrolyte salt is LiPF6, and the concentration of the electrolyte salt is 1 mol / L.

[0279] (5) Preparation of battery cells

[0280] The negative electrode, separator, and positive electrode are wound into an electrode assembly; the electrode assembly is placed in a housing, electrolyte is injected, and after standing and formation processes, a single battery cell is obtained.

[0281] Examples 2-7

[0282] The difference between Examples 2-7 and Example 1 is that the mass content of the first additive, the mass content of the second additive, and the mass content of silicon in the silicon-carbon material are different.

[0283] Examples 8-10

[0284] The difference between Examples 8-10 and Example 1 is that the average value of the longest diameter of the first additive and the average value of the longest diameter of the second additive are different.

[0285] Examples 11-12

[0286] The difference between Examples 11-12 and Example 1 is that the second additive is different.

[0287] Comparative Example 1

[0288] The difference between Comparative Example 1 and Example 1 is that the positive electrode film layer includes positive electrode active material but does not include the first additive and additives.

[0289] Comparative Example 2

[0290] The difference between Comparative Example 2 and Example 1 is that the positive electrode film layer includes a positive electrode active material and a first additive, but does not include an additive.

[0291] In Table 1, E1 represents the mass content of the first additive based on the total mass of the positive electrode film, E2 represents the mass content of the second additive based on the total mass of the positive electrode film, E3 represents the mass content of silicon in the silicon-based material based on the total mass of the negative electrode film, L1 represents the average value of the longest diameter of the first additive, and L2 represents the average value of the longest diameter of the second additive.

[0292] Table 1 Test results of the examples and comparative examples

[0293] In this embodiment, the capacity retention rate after 500 cycles at 25°C reflects the cycle life of a single battery cell; the higher the capacity retention rate, the longer the cycle life.

[0294] As shown in Example 1 and Comparative Examples 1-2, compared to adding only the first additive or neither the first nor the second additive, it is beneficial to improve the energy density and cycle life of the battery cell.

[0295] Referring to Examples 1-7, based on the total mass of the negative electrode film, when the mass content of silicon in the silicon-based material is 0.5% to 10%, the battery cell exhibits a longer cycle life and higher energy density. Furthermore, based on the total mass of the negative electrode film, when the mass content of silicon in the silicon-based material is 3% to 8%, it is advantageous to further balance energy density and cycle life. Based on the total mass of the positive electrode film, when the mass content of lithium-containing iron oxide is 0.5% to 5%, the battery cell exhibits a longer cycle life and higher energy density. Based on the total mass of the positive electrode film, when the mass content of lithium-containing iron oxide is 1.5% to 3%, a longer cycle life can be achieved while maintaining a higher energy density. Based on the total mass of the positive electrode film, when the mass content of nickel-containing metal oxide is 0.15% to 1.5%, the battery cell has a longer cycle life and a higher energy density. Furthermore, based on the total mass of the positive electrode film, when the mass content of nickel-containing metal oxide is 0.6% to 0.9%, a longer cycle life can be achieved while maintaining a higher energy density.

[0296] As shown in Examples 1 and 8-10, the average longest diameter of the lithium-containing iron oxide is 5 μm to 30 μm, and the average longest diameter of the nickel-containing metal oxide is 8 μm to 50 μm, which allows the battery cell to have good cycle performance and high energy density. Furthermore, the average longest diameter of the lithium-containing iron oxide is 15 μm to 20 μm, and the average longest diameter of the nickel-containing metal oxide is 8 μm to 25 μm, which also allows the battery cell to have good cycle performance.

[0297] As shown in Examples 11-12, the selection of LiNiO2 and NiO2 as the second additive is also beneficial to improving the cycle life of the battery cells.

[0298] 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.

[0299] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0300] 1. Cycle life test method

[0301] At 25℃, the battery cell was charged at a constant current rate of 0.33C to 3.65V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 5 minutes, it was discharged at a constant current rate of 1C to 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is recorded as the discharge capacity of the battery cell in the first cycle. The battery cell was subjected to 500 charge-discharge cycles using the above method, and the discharge capacity of each cycle was recorded.

[0302] The capacity retention rate of a single battery cell after 500 cycles at 25℃ and 0.33C / 1C = discharge capacity of the 500th cycle / discharge capacity of the 1st cycle × 100%.

[0303] 2. Methods for testing energy density

[0304] At 25°C, the battery cells were charged at a constant current rate of 1 / 3C to 3.65V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 5 minutes, the cells were discharged at a constant current rate of 1 / 3C to 2.5V, and the discharge energy of the battery cells was recorded.

[0305] The volume of a single battery cell is calculated by measuring its external length, width, and height. The length, width, and height represent the maximum dimensions of the casing in their respective directions.

[0306] The volumetric energy density of a single battery cell = the discharge energy of the single battery cell / the volume of the single battery cell.

[0307] 3. Test of the average value of the longest diameter

[0308] The positive electrode sheet, which includes the first additive, the second additive, and the lithium iron phosphate material, is cut along the thickness direction to expose the longitudinal section of the positive electrode film. The longest diameter of the first additive, the second additive, and the lithium iron phosphate material is determined by scanning electron microscopy (SEM) testing of the longitudinal section of the positive electrode film.

[0309] Specifically, the longest diameter of the first additive refers to the longest straight line that passes through the center point of the first additive and extends to the outer periphery of the particle; the longest diameter of the lithium iron phosphate material refers to the longest straight line that passes through the center point of the lithium iron phosphate material and extends to the outer periphery of the particle; and the longest diameter of the second additive refers to the longest straight line that passes through the center point of the second additive and extends to the outer periphery of the particle.

[0310] As an example, arbitrarily select 30 first additive particles in the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 first additive particles, and take their average value; arbitrarily select 30 lithium iron phosphate material particles in the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 lithium iron phosphate material particles, and take their average value; arbitrarily select 30 second additive particles in the longitudinal section of the positive electrode film, measure the longest diameter of each of the 30 second additive particles, and take their average value.

[0311] 4. Test method for coating thickness

[0312] Cut the positive electrode sheet along its thickness to expose the longitudinal section of the positive electrode film. By performing SEM testing on the longitudinal section of the positive electrode film, after selecting the first additive particle, it can be observed that the first additive particle has a core-shell structure. The thickness of the shell layer is the thickness of the coating layer.

[0313] 5. Testing of specific components in the positive and negative electrode films.

[0314] The positive electrode film layer of the positive electrode or the negative electrode film layer of the negative electrode can be scraped off, and the scraped material is added to aqua regia and digested under mechanical stirring for 30 minutes. The digested solution is then added to an ICAP7400 spectrometer to analyze its elemental composition. For example, for the positive electrode, the contents of Ni, Fe, and P can be measured; for the negative electrode, the contents of Si can be measured.

[0315] The mass content of the second additive (e.g., Li2NiO2) can be determined by detecting the Ni element, and the mass content of the first additive (e.g., Li5FeO4) in the positive electrode film can be determined by detecting the ratio of the P and Fe elements.

[0316] 6. Testing of the mass content of electrolyte salts

[0317] The concentration of inorganic components / lithium salts in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography, referring to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis". In the embodiments of this application, freshly prepared electrolyte can be used as a sample, the free electrolyte from a fresh battery can be used as a sample, or a fully discharged battery (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be used as a sample for detection by ion chromatography.

[0318] 7. Test methods for areal density and compacted density

[0319] The positive and negative electrode sheets are removed from the battery cell, and their thicknesses and current collector thicknesses are measured respectively. A certain area of ​​the electrode sheet is taken, its area is measured, and the mass of the film layer on the current collector after removing the current collector is measured. The electrode surface density is calculated based on this area and mass. Therefore, the compacted density of the electrode sheet PD = electrode surface density / (electrode thickness - current collector thickness).

[0320] 8. Specific surface area test

[0321] As an example, after disassembling a single battery cell, the negative electrode sheet is removed, and the negative electrode film layer is scraped off. The powder from this negative electrode film layer is then subjected to high-temperature treatment to separate the silicon-based material. Subsequently, based on the principle of gas adsorption, the specific surface area of ​​the silicon-based material is measured.

[0322] As an example, specifically, a suitable amount of sample (silicon-based material) is loaded into a special sample tube, heated and degassed under vacuum for 2 hours, and after cooling to room temperature, the total weight is weighed, and the sample mass is obtained by subtracting the mass of the sample tube; the sample tube is then placed in a workstation, and at a constant low temperature, the amount of gas adsorbed on the solid surface under different adsorption pressures is measured, and the monolayer adsorption amount of the sample is obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area per unit mass of the solid sample; wherein, the adsorbed gas is nitrogen.

[0323] 9. Gram capacity test

[0324] This section uses silicon-carbon material as an example to introduce the specific capacity testing method. Silicon-carbon material, binder, and deionized water are mixed to prepare a negative electrode slurry. This slurry is then coated onto copper foil and dried to obtain the negative electrode sheet. The negative electrode sheet is then assembled with a lithium-ion battery to form a coin cell. The battery is discharged at a constant current rate of 0.05C to 0.005V, and then charged at a constant current rate to 2.0V. The coin cell capacity is then measured. Specific capacity = coin cell capacity / mass of silicon-carbon material.

[0325] Similarly, when testing the first additive (or the second additive), the first additive, binder, and NMP are used to prepare a positive electrode slurry. This slurry is then coated onto aluminum foil and dried to obtain a positive electrode sheet. The positive electrode sheet is then assembled with a lithium-ion cell to form a coin cell. The coin cell is discharged at a constant current rate of 0.05C to 0.005V, and then charged at a constant current rate to 2.0V. The coin cell capacity is then measured. Specific capacity = coin cell capacity / mass of silicon-carbon material.

[0326] 10. Testing of delithiation potential

[0327] The delithiation potential was measured during the cell formation process. The prepared cell was first charged at a constant current of 0.1C for 10 minutes, then at a constant current of 1 / 3C to 3.65V, followed by constant voltage charging at 3.65V to 0.05C, rested for 5 minutes, and finally charged at a constant current of 0.05C to the cutoff upper limit voltage of 4.2V. The voltage (V) and capacity (Q) data obtained from the equipment were recorded, and the dQ / dV data was calculated. A dQ / dV curve was plotted with voltage V on the x-axis and the corresponding dQ / dV on the y-axis to obtain the dQ / dV curve as a function of V. The voltage value corresponding to the peak position of the curve in the 3.65V-4.2V range is the delithiation potential.

[0328] 11. Test of volume average particle size

[0329] The volumetric particle size distribution can be determined using a particle size analyzer-laser diffraction method. Specifically, refer to standard GB / T19077-2016, using a laser diffraction scattering particle size analyzer, and perform measurements according to the manufacturer's instructions. For example, take an appropriate amount of sample (first metal oxide, second metal oxide, or positive electrode active material). The sample can be obtained directly from powder (e.g., self-made or purchased) or from powder obtained through disassembly of battery products. Use a Malvern 2000 (MasterSizer 2000) laser particle size analyzer to test the average volumetric particle size of the sample material. Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009 standard.

Claims

1. A battery cell, characterized by, include: A positive electrode sheet, the positive electrode sheet comprising 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 comprising a positive electrode active material, a first additive and a second additive, the positive electrode active material comprising a lithium phosphate, the first additive comprising a lithium-containing iron oxide, and the second additive comprising a nickel-containing metal oxide. A negative electrode sheet, the negative electrode sheet comprising 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 comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material.

2. The battery cell according to claim 1, characterized in that, Based on the total mass of the negative electrode film, the silicon content in the silicon-based material is 0.5% to 10%, optionally 3% to 8%.

3. The battery cell according to claim 1 or 2, characterized in that, Based on the total mass of the positive electrode film, the mass content of the lithium-containing iron oxide is 0.5% to 5%, optionally 1.5% to 3%.

4. The battery cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the positive electrode film, the mass content of the nickel-containing metal oxide is 0.15% to 1.5%, optionally 0.6% to 0.9%.

5. The battery cell according to any one of claims 1 to 4, characterized in that, On the longitudinal section along the thickness direction of the positive electrode sheet, the average longest diameter of the lithium-containing iron oxide is 5 μm to 30 μm, and optionally 15 μm to 20 μm.

6. The battery cell according to any one of claims 1 to 5, characterized in that, On the longitudinal section along the thickness direction of the positive electrode sheet, the average longest diameter of the nickel-containing metal oxide is 8 μm to 50 μm, and can be selected as 8 μm to 25 μm.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The lithium-containing iron oxide comprises a matrix and a coating layer located on at least a portion of the surface of the matrix, the matrix comprising Li a FeO b , where 1≤a≤5, 1≤b≤5.

8. The battery cell according to any one of claims 1 to 6, characterized in that, The lithium-containing iron oxide comprises a matrix and a coating layer located on at least a portion of the surface of the matrix, the matrix comprising Li5FeO4.

9. The battery cell according to any one of claims 1 to 6, characterized in that, The lithium-containing iron oxide comprises a matrix and a coating layer located on at least a portion of the surface of the matrix, the matrix comprising Li e FeO f ,0≤e≤5,0 <f≤4。 10. The battery cell according to any one of claims 1 to 6, characterized in that, The lithium-containing iron oxide comprises a matrix and a coating layer located on at least a portion of the surface of the matrix, the matrix comprising Li m FeO n ,0≤m≤1,0 <n≤2。 11. The battery cell according to any one of claims 7 to 10, characterized in that, The matrix includes a doping element, which includes one or more of B, P, S, Zr, and Al.

12. The battery cell according to any one of claims 7 to 11, characterized in that, The coating layer includes carbon.

13. The battery cell according to any one of claims 7 to 12, characterized in that, The thickness of the coating layer is 10 nm to 100 nm.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The nickel-containing metal oxide comprises N c NiO d wherein N comprises one or more of Li, Na, K, 0≤c≤2, 1≤d≤2.

15. The battery cell according to any one of claims 1 to 13, characterized in that, The nickel-containing metal oxide includes Li2NiO2.

16. The battery cell according to any one of claims 1 to 13, characterized in that, The nickel-containing metal oxide comprises Li g NiO h 0 < g < 2, 0 < h < 2.

17. The battery cell according to any one of claims 1 to 13, characterized in that, The nickel-containing metal oxide comprises NiO q 0 < q < 2.

18. The battery cell according to any one of claims 1 to 17, characterized in that, The delithiation potential of the lithium-containing iron oxide is greater than that of the lithium-containing phosphate, and the delithiation potential of the nickel-containing metal oxide is greater than that of the lithium-containing phosphate.

19. The battery cell according to any one of claims 1 to 18, characterized in that, In a voltage range of 2V to 4.3V, the charge capacity of the lithium-containing iron oxide is 300mAh / g to 900mAh / g, optionally 450mAh / g to 750mAh / g.

20. The battery cell according to any one of claims 1 to 19, characterized in that, Based on the total mass of the positive electrode film, the mass ratio of Fe in the lithium-containing iron oxide to Ni in the nickel-containing metal oxide is 1 to 6, and can be selected as 1.5 to 4.

21. The battery cell according to any one of claims 1 to 20, characterized in that, Based on the total mass of the positive electrode film, the Fe element in the lithium-containing iron oxide has a mass content of 0.4% to 1.8%; and the Ni element in the nickel-containing metal oxide has a mass content of 0.1% to 0.85%.

22. The battery cell according to any one of claims 1 to 21, characterized in that, Based on the total mass of the positive electrode film, the Fe element in the lithium-containing iron oxide has a mass content of 0.55% to 1%; the Ni element in the nickel-containing metal oxide has a mass content of 0.2% to 0.45%.

23. The battery cell of any one of claims 1-22, wherein, The silicon-based material includes one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

24. The battery cell according to any one of claims 1 to 23, characterized in that, The silicon-based materials include silicon-carbon materials.

25. The battery cell according to claim 24, characterized in that, The silicon-carbon material has a specific surface area of 1.5 m 2 / g to 3 m 2 / g; and / or, the silicon-carbon material has a gravimetric capacity of 1500 mAh / g to 2500 mAh / g.

26. The battery cell according to any one of claims 1 to 25, characterized in that, The negative electrode active material also includes carbon-based materials, which include one or more of natural graphite, artificial graphite, soft carbon, and hard carbon.

27. The battery cell according to any one of claims 1 to 26, characterized in that, The battery cell also includes an electrolyte, which includes an electrolyte salt, which includes an imide lithium salt, and the imide lithium salt includes one or more of LiFSI and LiTFSI.

28. The battery cell according to claim 27, characterized in that, The electrolyte salt also includes lithium hexafluorophosphate.

29. The battery cell according to claim 27 or 28, characterized in that, Based on the total mass of the electrolyte, the mass content of the imide lithium salt is 0.3% to 5%.

30. The battery cell according to any one of claims 1 to 29, characterized in that, The lithium phosphate comprises primary particles and secondary particles formed by the aggregation of the primary particles. The average longest diameter of the primary particles is 100 nm to 500 nm, and the average longest diameter of the secondary particles is 1 μm to 2 μm.

31. The battery cell according to any one of claims 1 to 30, characterized in that, The lithium-containing phosphate includes those with the general formula Li x D y Me a1 M b1 P 1-c1 X c1 Y z The compounds, wherein 0.5≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, and 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z≤5; D includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, S, Mg, Al, P, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of Si, Cl, C, and N; Y includes one or more of O and F.

32. The battery cell according to any one of claims 1 to 31, characterized in that, The lithium-containing phosphate includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

33. The battery cell according to any one of claims 1 to 32, characterized in that, At least a portion of the surface of the lithium phosphate contains carbon.

34. The battery cell according to claim 33, characterized in that, Based on the total mass of the positive electrode active material, the mass content of the carbon element on the lithium phosphate surface is 1% to 2%.

35. The battery cell according to any one of claims 1 to 34, characterized in that, The positive electrode sheet satisfies one or more of the following conditions: The single-sided density of the positive electrode film is 0.25 g / 1540.25 mm. 2 Up to 0.45g / 1540.25mm 2 ; The positive electrode plate has a compact density of 2.3 g / cm 3 to 2.8 g / cm 3 .

36. The battery cell according to any one of claims 1 to 35, characterized in that, The negative electrode sheet satisfies one or more of the following conditions: The single-sided density of the negative electrode film is 0.12 g / 1540.25 mm. 2 Up to 0.2g / 1540.25mm 2 ; The compaction density of the negative electrode sheet at 0% SOC is 1.3 g / cm³. 3 Up to 1.6 g / cm 3 .

37. The battery cell according to any one of claims 1 to 36, characterized in that, When the battery cell is configured to 0% SOC, the lithium content in the positive electrode film is 4.1% to 4.3% by mass.

38. A battery device, characterized in that, Includes the battery cell according to any one of claims 1 to 37.

39. An electrical appliance, characterized in that, Includes the battery cell of any one of claims 1 to 37, or the battery device of claim 38, wherein the battery cell or battery device is used to store or provide electrical energy.

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