Battery monomer, battery and electric equipment

Abstract

The invention discloses a battery monomer, a battery and electric equipment, the battery monomer comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a first positive active layer and a second positive active layer, and the charging platform voltage of the active material of the first positive active layer is smaller than the charging platform voltage of the active material of the second positive active layer; the negative pole piece comprises a first negative active layer and a second negative active layer, the first negative active layer is opposite to the first positive active layer, and the second negative active layer is opposite to the second positive active layer; cB1 of the single battery is larger than CB2, CB1 is the active capacity of the first negative electrode active layer / the active capacity of the first positive electrode active layer, and CB2 is the active capacity of the second negative electrode active layer / the active capacity of the second positive electrode active layer. Through the design, lithium precipitation caused by overcharge of the first positive electrode active layer can be improved, the loss of active lithium is improved, and the cycle life of the battery monomer is prolonged.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to battery cells, batteries and electrical equipment. Background Technology

[0002] With the development of modern technology, lithium-ion batteries are considered the preferred choice for green and environmentally friendly batteries due to their advantages such as high energy density, long cycle life, and good environmental performance. Lithium-ion batteries can be widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in electric vehicles, power tools, military equipment, and aerospace, among other fields.

[0003] When different positive electrode active materials are selected on both sides of the positive electrode in a lithium-ion battery, the performance of the two sides differs, leading to a reduction in battery cycle life. The above statements are for providing background information related to this application only and do not necessarily constitute prior art. Summary of the Invention

[0004] The main technical problem addressed by this application is to provide a battery cell, a battery, and an electrical device that can improve the cycle life of the battery cell.

[0005] To solve the above-mentioned technical problems, one technical solution adopted in this application is: providing a battery cell, the battery cell including a positive electrode sheet and a negative electrode sheet, the positive electrode sheet including a positive electrode base layer and a first positive electrode active layer and a second positive electrode active layer disposed on opposite sides of the positive electrode base layer, the first positive electrode active layer including a first positive electrode active material, the second positive electrode active layer including a second positive electrode active material, the charging platform voltage of the first positive electrode active material being less than the charging platform voltage of the second positive electrode active material; the negative electrode sheet including a negative electrode base layer and a first negative electrode active layer and a second negative electrode active layer disposed on opposite sides of the negative electrode base layer, the first negative electrode active layer being opposite to the first positive electrode active layer, the second negative electrode active layer being opposite to the second positive electrode active layer, the first active site ratio CB1 of the battery cell being greater than the second active site ratio CB2, the first active site ratio being the active capacity of the first negative electrode active layer / the active capacity of the first positive electrode active layer, and the second active site ratio being the active capacity of the second negative electrode active layer / the active capacity of the second positive electrode active layer. By setting the ratio of active sites on both sides of the electrode, making the first active site ratio CB1 greater than the second active site ratio CB2, the problem of unbalanced charging on both sides of the electrode during charging can be improved (for example, one side may be overcharged), thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery cell.

[0006] In one embodiment, the ratio of the first active site ratio CB1 to the second active site ratio CB2, CB1:CB2, is 1.009-1.201. By adjusting the ratio of active sites on both sides of the electrode, the problem of unbalanced charging on both sides of the electrode during charging can be improved (for example, the problem of overcharging on one side may occur), thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery cell.

[0007] In one embodiment, the first active site ratio CB1 is 1.12-1.30; and / or the second active site ratio CB2 is 1.08-1.12. With this configuration, the negative electrode active layer can provide sufficient active ion vacancies to receive active ions provided by the positive electrode active layer, reducing the deposition of active ions on the negative electrode side and improving the cycle life of the battery cell.

[0008] In one embodiment, the charging platform voltage of the first positive electrode active material is ≤3.5V, and the charging platform voltage of the second positive electrode active material is greater than 3.5V. This configuration improves the capacity and stability of the positive electrode sheet. By combining the first negative electrode active layer with a high-capacity first negative electrode active material, lithium plating on the first negative electrode active layer side caused by overcharging of the first positive electrode active layer in the battery cell can be mitigated, reducing the loss of active lithium and improving the cycle life of the battery cell.

[0009] In one embodiment, the first negative electrode active layer includes a first negative electrode active material, the first negative electrode active material having a capacity greater than 375 mAh / g. This design can mitigate lithium plating on the first negative electrode active layer side caused by overcharging of the first positive electrode active layer in the battery cell, reducing active lithium loss and improving the cycle life of the battery cell.

[0010] In one embodiment, the coating amount of the first negative electrode active layer is less than 0.16 g / 1540.25 mm. 2 By selecting a high-capacity negative electrode material as the active material of the first negative electrode active layer, the coating amount of active material in the first negative electrode active layer can be reduced, thereby improving the kinetics of the first negative electrode active layer, improving the side lithium deposition of the first negative electrode active layer caused by overcharging of the first positive electrode active layer in the battery cell, reducing active lithium loss, and improving the cycle life of the battery cell.

[0011] In one embodiment, the coating amount of the first negative electrode active layer is 0.12-0.15 g / 1540.25 mm. 2 By selecting a high-capacity negative electrode material as the active material of the first negative electrode active layer, the coating amount of active material in the first negative electrode active layer can be reduced, thereby improving the kinetics of the first negative electrode active layer, improving the side lithium deposition of the first negative electrode active layer caused by overcharging of the first positive electrode active layer in the battery cell, reducing active lithium loss, and improving the cycle life of the battery cell.

[0012] In one embodiment, the first negative electrode active layer includes silicon material, and the silicon material accounts for 0.01%-5.5% of the total mass of active material in the first negative electrode active layer. This configuration can improve the reduction of active lithium loss, mitigate the damage caused by the large volume expansion of the silicon negative electrode itself, improve the structural stability of the negative electrode, and ultimately increase the cycle life of the battery cell.

[0013] In one embodiment, the silicon material in the first negative electrode active layer accounts for 0.5%-3.5% of the total mass of the active material in the first negative electrode active layer. This configuration can mitigate the damage caused by the large volume expansion of the silicon negative electrode itself, improve the structural stability of the negative electrode, and ultimately increase the cycle life of the battery cell, while also reducing the loss of active lithium.

[0014] In one embodiment, the positive electrode active material of the second positive electrode active layer includes at least nickel, wherein the mass percentage of nickel in the total metal element content of the positive electrode active material of the second positive electrode active layer is 0.3-0.7%, and the mass percentage of silicon in the first negative electrode active layer is 0.5%-1.5%. This design can mitigate lithium plating caused by overcharging of the first positive electrode active layer, reduce active lithium loss, and improve the cycle life of the battery cell.

[0015] In one embodiment, the positive electrode active material of the second positive electrode active layer includes at least cobalt, wherein the mass percentage of cobalt in the total metal element content of the positive electrode active material of the second positive electrode active layer is 3%-15%. This design weakens the rate performance of the second positive electrode active layer, reduces the kinetic difference between the first and second positive electrode active layers, improves lithium deposition on the first negative electrode active layer caused by overcharging of the first positive electrode active layer in the battery cell, reduces active lithium loss, and improves the cycle life of the battery cell.

[0016] In one embodiment, the first positive electrode active layer comprises lithium iron phosphate and a first type of polyanionic material. The electronic conductivity of the first type of polyanionic material is lower than that of lithium iron phosphate, and the mass percentage of the first type of polyanionic material in the total mass of lithium iron phosphate and the first type of polyanionic material is 30%-85%. This configuration improves the conductivity of the first positive electrode active layer, reduces the internal resistance of the battery cell, enhances the kinetics of the first positive electrode active layer, mitigates lithium deposition on the first negative electrode active layer caused by overcharging of the first positive electrode active layer, reduces active lithium loss, and improves the cycle life of the battery cell.

[0017] In one embodiment, the first type of polyanionic material in the first positive electrode active layer accounts for 40%-65% of the total mass of lithium iron phosphate and the first type of polyanionic material. This configuration improves the conductivity of the first positive electrode active layer, reduces the internal resistance of the battery cell, enhances the kinetics of the first positive electrode active layer, mitigates lithium deposition on the first negative electrode active layer caused by overcharging of the first positive electrode active layer, reduces active lithium loss, and improves the cycle life of the battery cell.

[0018] In one embodiment, the first positive electrode active layer includes lithium iron phosphate and a second type of polyanionic material. The charging plateau voltage of the second type of polyanionic material is greater than that of lithium iron phosphate, and the mass percentage of the second type of polyanionic material in the total mass of lithium iron phosphate and the second type of polyanionic material is 10%-40%. This configuration reduces the voltage plateau difference between the first and second positive electrode active layers, mitigating lithium plating caused by overcharging of the first positive electrode active layer, reducing active lithium loss, and improving the cycle life of the battery cell.

[0019] In one embodiment, the first positive electrode active layer includes a first polyanionic material, which includes manganese, wherein the manganese content of the total metal elements is 0.05-0.75% by mass. This configuration improves the conductivity of the first positive electrode active layer, reduces the internal resistance of the battery cell, enhances the kinetics of the first positive electrode active layer, mitigates lithium deposition on the first negative electrode active layer caused by overcharging of the first positive electrode active layer, reduces active lithium loss, and improves the cycle life of the battery cell.

[0020] In one embodiment, the manganese element accounts for 0.15-0.65% of the total mass of the metal elements in the first polyanionic material. This configuration improves the conductivity of the first positive electrode active layer, reduces the internal resistance of the battery cell, enhances the kinetics of the first positive electrode active layer, mitigates lithium deposition on the first negative electrode active layer caused by overcharging of the first positive electrode active layer, reduces active lithium loss, and improves the cycle life of the battery cell.

[0021] In one embodiment, the first positive electrode active layer comprises Li 1+x Mn 1-y A y P 1-z E zThe compound of O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 1.000, z is any value in the range of 0.001 to 0.100, A is selected from one or more elements from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and E is selected from one or more elements from B, Si, N, S, F, Cl, and Br. This configuration promotes lithium-ion migration and improves the rate performance of the battery cell.

[0022] In one embodiment, A is one or more elements selected from Fe, Ti, V, Ni, Co, and Mg; and / or E is one element selected from B, Si, N, and S. This configuration further improves the structural stability of the positive electrode active material and the rate performance of the battery cell.

[0023] In one embodiment, the active material of the first positive electrode active layer has a core-shell structure, the shell layer of the core-shell structure includes one or more layers of pyrophosphate, phosphate, or carbon, and the core layer of the core-shell structure includes the active material Li. 1+x Mn 1- y A y P 1-z E z O4. The above settings can effectively suppress the dissolution of transition metals, reduce the content of surface impurities lithium, and reduce the corrosion of active materials by the electrolyte.

[0024] In one embodiment, the difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V is less than 25%. By controlling the difference in SOC capacity utilization between the first positive electrode active layer side and the second positive electrode active layer side above 3.9V to be within 25%, the loss of active lithium caused by overcharging on the first positive electrode active layer side can be effectively mitigated, thereby improving the cycle life of the battery cell.

[0025] To solve the above-mentioned technical problems, another technical solution adopted in this application is to provide a battery, which includes any of the above-mentioned battery cells, and the battery has at least the same advantages as the battery cells.

[0026] To solve the aforementioned technical problems, another technical solution adopted in this application is to provide an electrical device that includes the aforementioned battery. The electrical device has at least the same advantages as the battery.

[0027] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is an exploded structural diagram of a battery according to one or more embodiments;

[0030] Figure 2 This is an exploded structural diagram of a battery cell according to one or more embodiments;

[0031] Figure 3 This is a schematic diagram of the structure of an electrode assembly according to one or more embodiments;

[0032] Figure 4 This is a structural schematic diagram of a vehicle according to one or more embodiments.

[0033] In the attached image:

[0034] 1000, Vehicle; 300, Motor; 200, Controller; 100, Battery; 10, Housing; 11, First Part; 12, Second Part; 20, Battery Cell; 21, End Cap; 21a, Electrode Terminal; 22, Housing; 23, Electrode Assembly; 30, Electrode Sheet; 31, Positive Electrode Base Layer; 31a, First Positive Electrode Active Layer; 31b, Second Positive Electrode Active Layer; 32, Negative Electrode Base Layer; 32a, First Negative Electrode Active Layer; 32b, Second Negative Electrode Active Layer; 33, Separator. Detailed Implementation

[0035] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0037] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces), unless otherwise explicitly specified.

[0038] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0039] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0040] Quantities, ratios, and other numerical values ​​are presented in range format in this document. It should be understood that this range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0041] Unless otherwise specified, all steps of this application may be performed sequentially, randomly, or in parallel, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially, or steps (a) and (b) may be performed simultaneously in parallel. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0042] Lithium-ion batteries, as a new type of green rechargeable battery, are widely used in electric vehicles, energy storage systems, and renewable energy fields. With the continuous development of lithium-ion batteries in my country, they will inevitably achieve improvements in many aspects. From a technical perspective, "high efficiency," "long lifespan," and "low cost" will be the core solutions and goals pursued in the development of power battery technology during the improvement process.

[0043] This application provides a battery; please refer to... Figure 1 , Figure 1 This is an exploded structural diagram of a battery according to one or more embodiments. The battery 100 includes a housing 10 and a battery cell 20, the battery cell 20 being housed within the housing 10. The housing 10 provides a accommodating space for the battery cell 20, and the housing 10 can adopt various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, the first portion 11 and the second portion 12 overlapping each other, together defining a accommodating space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the accommodating space; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, the open side of the first portion 11 covering the open side of the second portion 12. Of course, the housing 10 formed by the first portion 11 and the second portion 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0044] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0045] Each battery cell 20 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0046] This application also provides a single battery cell; please refer to... Figure 2 , Figure 2 This is an exploded structural diagram of a battery cell according to one or more embodiments. Battery cell 20 refers to the smallest unit that makes up the battery. Figure 2 The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0047] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure and impact, giving battery cell 20 higher structural strength and improved safety performance. Functional components such as electrode terminals 21a can be provided on end cap 21. Electrode terminals 21a can be used for electrical connection with electrode assembly 23 to output or input electrical energy to battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. For example, the insulating element may be made of plastic, rubber, etc.

[0048] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0049] Electrode assembly 23 is the component in the battery cell 100 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions of the positive and negative electrode sheets without active material each constitute a tab 23a. The positive and negative tabs may be located together at one end of the main body or separately at both ends of the main body. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs 23a connect to the electrode terminals to form a current loop.

[0050] In some embodiments, the positive electrode includes a current collector and a positive active layer disposed on the current collector.

[0051] The positive electrode active layer includes a positive electrode active material, which may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0052] In one embodiment, the active layer of the positive electrode material further includes a conductive agent and a binder.

[0053] The conductive agent imparts conductivity to the electrode. The positive electrode conductive material can include any conductive material as long as it does not cause a chemical change. Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof. Optionally, the conductive agent includes one or more of conductive carbon black, conductive graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, and acetylene black.

[0054] The adhesive improves the adhesion stability of the active layer and reduces the probability of powder shedding. The adhesive can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). Optionally, the adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, acrylate, and polyurethane.

[0055] In one embodiment, the positive electrode active layer also includes other optional additives, such as thickeners and dispersants (e.g., sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0056] In some embodiments, the negative electrode includes a current collector and a negative electrode active layer disposed on the current collector.

[0057] The negative electrode active layer includes negative electrode active materials, which include, but are not limited to, carbon-based negative electrode materials, silicon-based negative electrode materials, tin-based negative electrode materials, lithium titanate negative electrode materials, and lithium metal negative electrode materials; specifically, including but not limited to graphite materials, silicon-carbon materials, graphite-silicon suboxide materials, nano-silicon materials, silicon suboxide materials, and tin-based materials; more specifically, including natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 One or more of Li-Al alloys.

[0058] In some embodiments, the negative electrode active layer may further include a binder, a conductive agent, and other optional additives. As examples, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. As examples, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). As examples, other optional additives may be thickeners and dispersants (e.g., sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0059] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0060] In one embodiment, the electrolyte includes one or more of carbonate solvents and ether solvents.

[0061] Carbonates are typically small-molecule cyclic or chain carbonates; including but not limited to one or more of ethylene carbonate, propylene carbonate, butene carbonate, vinylene carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl carbonate, diethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and fluorocarbonates; and may also be at least one ester solvent selected from γ-butyrolactone, dimethyl sulfite, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, propyl acetate, and fluorocarboxylic acid esters.

[0062] Ether solvents include, but are not limited to, one or more of dimethyl ether, diethyl ether, tetrahydrofuran, methyltetrahydrofuran, ethylene oxide, 1,3-dioxolane, fluoroethers, DME (ethylene glycol dimethyl ether), DEE (ethylene glycol diethyl ether), DEGDME (diethylene glycol dimethyl ether), TRGDME (triethylene glycol dimethyl ether), TEGDME (tetraethylene glycol dimethyl ether), dipropyl ether, and dibutyl ether.

[0063] In other embodiments, the electrolyte may further comprise any one or a mixture of several of amine solvents, sulfone solvents, and nitrile solvents. Amine solvents include at least one of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide. Sulfone solvents include at least one of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, and dipropyl sulfone. Nitrile solvents include at least one of acetonitrile, succinic anionizer, adiponitrile, and glutaronitrile. A high-voltage resistant electrolyte is preferred, as its acidity decreases under high voltage, facilitating the transport of active ions, significantly reducing side reactions on the electrode surface, and improving battery stability.

[0064] In some embodiments, the electrolyte further includes an electrolyte salt, which may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0065] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0066] In some embodiments, positive active layers can be formed on both sides of the current collector of the positive electrode sheet, meaning the positive electrode sheet has two opposing positive active layers. Similarly, negative active layers can be formed on both sides of the current collector of the negative electrode sheet, meaning the negative electrode sheet has two opposing negative active layers, corresponding to the positive electrode sheet. When positive active layers are formed on both sides of the positive electrode sheet, different positive active materials can be selected for the two positive active layers. Different types of positive and negative active materials have different advantages, and by combining different active materials, a battery cell with better overall performance can be obtained. Taking positive active materials as an example, some positive active materials have a larger capacity, which can improve the energy density of the battery cell, while others have better stability, which can extend the cycle life of the battery cell. If the two are combined, both energy density and cycle life can be improved simultaneously.

[0067] However, different positive electrode active materials generally result in performance differences on both sides of the positive electrode. For example, different positive electrode active materials have different voltage plateaus. A voltage plateau refers to the flat region on the voltage-capacity curve formed by the relationship between the voltage of the active material and the insertion or extraction of lithium ions during battery charging and discharging. The choice of active material affects the voltage plateau of the active layer, leading to different voltage plateaus on both sides of the electrode. When a battery cell is in a high state of charge (SOC), there is an imbalance in charging on both sides of the electrode. This causes the side with the lower voltage plateau of the positive electrode to be overcharged, resulting in the precipitation of active ions on the corresponding negative electrode side, leading to the loss of active ions and directly deteriorating the battery's cycle life.

[0068] Based on the above-mentioned technical problems, this application provides a battery cell, which includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode base and a first positive electrode active layer and a second positive electrode active layer disposed on opposite sides of the positive electrode base. The first positive electrode active layer includes a first positive electrode active material, and the second positive electrode active layer includes a second positive electrode active material. The charging platform voltage of the first positive electrode active material is lower than that of the second positive electrode active material. The negative electrode includes a negative electrode base and a first negative electrode active layer and a second negative electrode active layer disposed on opposite sides of the negative electrode base. The first negative electrode active layer is opposite to the first positive electrode active layer, and the second negative electrode active layer is opposite to the second positive electrode active layer. The ratio of first active sites CB1 to second active sites CB2 of the battery cell is greater than that of second active sites CB2. The first active site ratio is the active capacity of the first negative electrode active layer / the active capacity of the first positive electrode active layer, and the second active site ratio is the active capacity of the second negative electrode active layer / the active capacity of the second positive electrode active layer.

[0069] The positive and negative electrode substrates are conductive substrates that can serve as current collectors. They can be metal foils or composite materials, such as composite conductive materials formed by mixing metal materials with a polymer substrate. For example, aluminum foil or copper foil can be used as metal foils. The composite conductive material may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite conductive material can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). The substrate may be cubic in shape and have a first surface and a second surface arranged opposite to each other along its thickness direction, which are used to support the first positive electrode active layer and the second positive electrode active layer (first negative electrode active layer and second negative electrode active layer), respectively.

[0070] Please see Figure 3 , Figure 3 This is a schematic diagram of an electrode assembly according to one or more embodiments. Figure 3 In this structure, the positive electrode sheet includes a positive electrode base layer 31 and a positive electrode active layer disposed on the positive electrode base layer 31. Specifically, the positive electrode active layer includes a first positive electrode active layer 31a and a second positive electrode active layer 31b, which are respectively disposed on opposite sides of the positive electrode base layer 31. The negative electrode sheet includes a negative electrode base layer 32 and a negative electrode active layer disposed on the negative electrode base layer 32. Specifically, the negative electrode active layer includes a first negative electrode active layer 32a and a second negative electrode active layer 32b, which are respectively disposed on opposite sides of the negative electrode base layer 32. The first positive electrode active layer 31a and the first negative electrode active layer 32a correspond to each other and are separated by a separator 33; the second positive electrode active layer 31b and the second negative electrode active layer 32b correspond to each other and are separated by a separator 33.

[0071] The first positive electrode active layer includes a first type of positive electrode active material, the second positive electrode active layer includes a second type of positive electrode active material, the first negative electrode active layer includes a first type of negative electrode active material, and the second negative electrode active layer includes a second type of negative electrode active material. The properties of the positive and negative electrode active materials determine the performance of the battery cell. Among these, the energy density and cycle life of the battery cell are the most important performance characteristics. By adjusting the combination of positive and negative electrode active materials, battery cells with higher energy density and longer cycle life can be designed.

[0072] In one embodiment, the positive electrode sheet provided in this application uses active materials with different voltage platforms on both sides. Specifically, an active material with a lower voltage platform is selected as the active material of the first positive electrode active layer, and an active material with a higher voltage platform is selected as the active material of the second positive electrode active layer. That is, the charging platform voltage of the active material used in the first positive electrode active layer is lower than the charging platform voltage of the active material used in the second positive electrode active layer. Here, the charging platform voltage of the positive electrode active material refers to the charging platform voltage of a primary battery composed of such positive electrode active materials.

[0073] In one embodiment, the first positive electrode active layer includes a first positive electrode active material with a charging platform voltage ≤ 3.5V, and the second positive electrode active layer includes a second positive electrode active material with a charging platform voltage greater than 3.5V. Taking a lithium battery as an example, the first positive electrode active material can be lithium iron phosphate with a charging platform voltage of 3.4V, and the second positive electrode active material can be ternary material with a charging platform voltage of 3.75V. This arrangement, using different positive electrode active materials in the positive electrode sheet, can improve the stability and capacity of the battery cell; however, under this design, there is a difference in the voltage platform on both sides of the positive electrode sheet. Specifically, the higher the voltage platform on the positive electrode active layer side and the lower the voltage platform on the negative electrode active layer side, the higher the operating voltage of the battery cell. Because the voltage plateau on the first positive electrode active layer side is lower than that on the second positive electrode active layer side, under high SOC charging, the second positive electrode active layer side has a large capacity utilization margin in the later stages, which will cause continuous overcharging on the first positive electrode active layer side, resulting in lithium deposition on the first negative electrode active layer side and loss of active ions. In other words, under high SOC, the side with the lower voltage plateau is often forced to overcharge, causing lithium deposition on the corresponding negative electrode side, resulting in loss of active lithium and directly deteriorating the cycle life of the battery cell.

[0074] In one embodiment, the first active site ratio CB1 of the battery cell is greater than the second active site ratio CB2. The first active site ratio is the active capacity of the first negative electrode active layer / the active capacity of the first positive electrode active layer, and the second active site ratio is the active capacity of the second negative electrode active layer / the active capacity of the second positive electrode active layer.

[0075] The active site ratio of a battery cell refers to the ratio of the active capacity of the negative electrode to that of the positive electrode under the same stage and conditions; it can be called the cell balance (CB). Active capacity is the capacity of the single-sided active material coating layer per unit area in the negative or positive electrode sheet, and is measured in mAh / cm². 2The active capacity can be obtained from the specific capacity and areal density of the active material in the negative or positive electrode. Alternatively, the active site ratio is: negative electrode specific capacity * negative electrode CW * actual active material loading in the negative electrode formulation / (positive electrode specific capacity * positive electrode CW * actual active material loading in the positive electrode formulation).

[0076] In the above embodiments, the first active site ratio = (specific capacity of the first negative electrode active material * density of the first negative electrode active layer * content of the first negative electrode active material) / (specific capacity of the first positive electrode active material * density of the first positive electrode active layer * content of the first positive electrode active material), and the second active site ratio = (specific capacity of the second negative electrode active material * density of the second negative electrode active layer * content of the second negative electrode active material) / (specific capacity of the second positive electrode active material * density of the second positive electrode active layer * content of the second positive electrode active material). Here, specific capacity refers to the ratio of the electrical capacity that the active material inside the battery can release to the mass of the active material, and specific capacity is related to the type of active material. Areal density is the mass of active material per unit area of ​​the electrode sheet. Active material content refers to the proportion of active material in the active layer. The CB value can be set by considering the active sites of the ions working in the battery cell when designing the coating amount (areal density) of the positive and negative electrode active materials. Specifically, considering the amount of lithium extracted from the negative electrode (or the amount of lithium active sites) when the battery cell is working, and the amount of lithium that needs to be inserted into the negative electrode, the designed positive and negative electrode areal density ratio is more reasonable and can better utilize the capacity of the active material. In one embodiment, the ratio of the first active site to the second active site in the battery cell is both greater than 1. In this case, the active capacity of the negative electrode is larger than that of the corresponding positive electrode, which helps to reduce the situation where lithium ions are deposited on the negative electrode side of the battery cell due to the lack of a receiving source.

[0077] In one embodiment, the ratio of the first active site ratio to the second active site ratio of the battery cell is 1.009-1.201; for example, it can be 1.009, 1.030, 1.050, 1.080, 1.100, 1.150, 1.180, 1.201, etc.; or the range of any two of the above sets of values ​​can be 1.009-1.050, 1.050-1.100, 1.100-1.150, 1.150-1.201, etc.

[0078] In this embodiment, by adjusting the ratio of active sites on both sides of the electrode, the problem of unbalanced charging on both sides of the electrode during charging (for example, the problem of overcharging on one side may occur) can be balanced, thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery cell.

[0079] In this application, the CB value of the battery cell is adjusted, specifically by setting a relatively large first active site ratio, or in other words, setting the first active site ratio to be greater than the second active site ratio. With both the first and second active site ratios greater than 1, the larger first active site ratio results in a larger active capacity of the first negative electrode active layer compared to the first positive electrode active layer. This effectively reduces the deposition of active ions in the first negative electrode active layer, lowers active ion loss, and improves the battery's cycle life. The voltage plateau on the first positive electrode active layer side is lower than that on the second positive electrode active layer side. Through the design of the battery cell's active site ratio and voltage plateau, a larger active site ratio is set on the side with the lower voltage plateau to provide sufficient active ion vacancies to receive active ions from the positive electrode active layer, reducing the deposition of active ions on the negative electrode side and improving the battery cell's cycle life.

[0080] In one embodiment, the first active site ratio is 1.12-1.30; for example, it can be 1.12, 1.15, 1.20, 1.25, 1.28, 1.30, etc.; or the range of any two sets of values ​​mentioned above can be 1.12-1.14, 1.14-1.20, 1.20-1.25, 1.25-1.30, etc.

[0081] In one embodiment, the second active site ratio is 1.08-1.12; for example, it can be 1.08, 1.09, 1.10, 1.11, 1.12, etc.; or the range of any two sets of values ​​mentioned above can be 1.08-1.09, 1.09-1.10, 1.10-1.11, 1.11-1.12, etc.

[0082] At this time, the active capacity of the negative electrode is larger than that of the corresponding positive electrode. The negative electrode active layer can provide sufficient active ion vacancies to receive the active ions provided by the positive electrode active layer. This helps to reduce the situation where active ions are released from the negative electrode side of the battery cell due to lack of acceptor source, reduce active ion loss, and improve the cycle life of the battery cell.

[0083] Meanwhile, a moderate ratio of the first active site ratio to the second active site ratio can reduce the irreversible capacity loss of individual battery cells, as well as the problems of low battery capacity and reduced energy density caused by irreversible capacity loss.

[0084] According to the above formula for calculating the active site ratio, when the type and content of active materials are determined, the active site ratio on the corresponding side of the electrode can be changed by adjusting the areal density of the active layer, thereby reducing the loss of active ions and improving the cycle life of the battery.

[0085] In one embodiment, the first negative electrode active layer includes a first negative electrode active material with a capacity greater than 375 mAh / g. The battery cell is designed to pair a positive electrode active layer with a low charging platform voltage with a negative electrode active layer containing a high-capacity negative electrode material. Specifically, the first negative electrode active layer corresponding to the first positive electrode active layer uses an active material with a high capacity, such as an active material with a capacity greater than 375 mAh / g, for example, silicon particles with a capacity of 4200 mAh / g. This design can mitigate lithium plating caused by overcharging of the first positive electrode active layer, reduce active lithium loss, and improve the cycle life of the battery cell.

[0086] In one embodiment, the coating amount of the first negative electrode active layer is less than 0.16 g / 1540.25 mm. 2 Optionally, the coating amount of the first negative electrode active layer is 0.12-0.15 g / 1540.25 mm. 2 For example, it could be 0.120g / 1540.25mm. 2 0.125g / 1540.25mm 2 0.16g / 1540.25mm 2 0.130g / 1540.25mm 2 0.135g / 1540.25mm 2 0.140g / 1540.25mm 2 0.145g / 1540.25mm 2 0.150g / 1540.25mm 2 0.155g / 1540.25mm 2 0.158g / 1540.25mm 2 In this embodiment, the coating weight (CW) refers to 1540.25 mm. 2 The coating mass of single-sided active material per area (g, mg). By selecting a high-capacity negative electrode material as the active material of the first negative electrode active layer, the coating amount of active material in the first negative electrode active layer can be reduced, thereby improving the kinetics of the first negative electrode active layer, mitigating lithium plating caused by overcharging of the first positive electrode active layer, improving active lithium loss, and increasing the cycle life of the battery cell. In this embodiment, from the perspective of the capacity of the active material, matching the first positive electrode active layer with a high-capacity negative electrode can effectively increase the negative electrode capacity without increasing the CW, thereby improving the kinetics of the first negative electrode active layer and mitigating the problem of active lithium loss. Alternatively, it can significantly reduce the CW (from 0.16 to 0.14 g / 1540.25 mm) without changing the original CB design. 2 This enhances the dynamics on the negative electrode side.

[0087] In one embodiment, the type of active material for the second negative electrode active layer in the battery cell provided in this application is not limited. High-capacity materials, such as silicon, can be selected; alternatively, relatively low-capacity materials, such as graphite, can also be selected. This is because the voltage plateau on the side of the second positive electrode active layer corresponding to the second negative electrode active layer is relatively high, resulting in weak lithium plating on the side of the second negative electrode active layer. Therefore, special design from this perspective is not required, and suitable active materials can be selected from conventional perspectives such as capacity and stability.

[0088] In one embodiment, when combining different active materials, the voltage plateau of the positive electrode active layer can be controlled by adjusting the type and ratio of the positive electrode active materials, thereby reducing the difference in voltage plateau between the first and second positive electrode active layers. This improves the problem of charging imbalance on both sides of the electrode (e.g., the possibility of overcharging on one side), effectively reducing the precipitation and loss of active ions, and improving the cycle life of the battery cell.

[0089] Taking lithium batteries as an example, commonly used positive electrode active materials include polyanionic phosphate compound positive electrode active materials and ternary material positive electrode active materials.

[0090] Among them, polyanionic phosphate compound type positive electrode active materials are based on phosphate ions (PO4). 3- The main structural unit is lithium iron phosphate (LiFePO4), also known as lithium iron phosphate (LFP); lithium manganese iron phosphate (LMAP), etc. Polyanionic phosphate compounds have good thermal and structural stability, which helps to improve battery safety; they generally exhibit good cycle life, are relatively stable in charge-discharge cycles, and can maintain a long battery life; the voltage plateau is relatively low, for example, the charge-discharge plateau voltage of LFP is between 3.2-3.4V; they do not contain or contain very few toxic heavy metal elements, making them relatively environmentally friendly; the manufacturing process is relatively simple, and the raw materials are relatively inexpensive.

[0091] Ternary cathode active materials refer to compounds (NCMs) containing nickel (Ni), cobalt (Co), and manganese (Mn), or compounds containing nickel (Ni), cobalt (Co), and aluminum (Al), including lithium nickel cobalt manganese oxide (NCM) materials. Due to the combination of the advantages of different metal elements and a high voltage platform, ternary cathode active materials usually have high energy density. Different ternary materials can achieve different electrochemical performances (including voltage platform) by adjusting the ratio of nickel, cobalt, and manganese (or nickel, cobalt, and aluminum), allowing the selection of the most suitable ratio according to the specific application requirements. However, their cycle life is relatively short, and their safety performance is relatively low. Some elements in ternary cathode active materials, such as cobalt, are rare metals, making the manufacturing cost of this type of battery relatively high.

[0092] In one embodiment, the first positive electrode active layer comprises a polyanionic phosphate compound type positive electrode active material, and the second positive electrode active layer comprises a ternary material type positive electrode active material. By combining the above two materials simultaneously, the advantages of both materials can be combined to improve the energy density, cycle life, and safety of the positive electrode sheet, while reducing costs and achieving cost reduction and efficiency improvement.

[0093] The charging plateau voltage of LFP is 3.4V, and the discharging plateau voltage is 3.2V; the discharging plateau voltage of LMAP is 3.3-3.9V, which can be adjusted according to different Mn contents; the higher the Mn content, the higher the discharging plateau voltage; the discharging plateau voltage of NCM is 3.65-3.8V, which can be adjusted according to different Ni contents; the higher the Ni content, the higher the discharging plateau voltage. Therefore, the voltage plateau of the positive electrode active layer can be controlled by adjusting the type and ratio of the positive electrode active materials, thereby reducing the difference in voltage plateau between the first and second positive electrode active layers.

[0094] In one embodiment, the first positive electrode active layer comprises lithium iron phosphate and a second type of polyanionic material. The charging plateau voltage of the second type of polyanionic material is greater than that of lithium iron phosphate. The mass percentage of the second type of polyanionic material in the total mass of lithium iron phosphate and the second type of polyanionic material is 10%-40%. For example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc. Alternatively, it can be a range consisting of any two of the above sets of values, such as 10%-20%, 20%-40%, 30%-40%, etc.

[0095] Among them, the second type of polyanionic material may include lithium manganese iron phosphate, that is, the first positive electrode active layer is a mixture of lithium iron phosphate and lithium manganese iron phosphate. By incorporating lithium manganese iron phosphate with a higher voltage platform, the voltage platform on the first positive electrode active layer side can be improved as a whole, so as to reduce the difference between the voltage platforms on the first positive electrode active layer side and the second positive electrode active layer side, improve the lithium plating caused by overcharging of the first positive electrode active layer, improve the loss of active lithium, and improve the cycle life of the battery cell.

[0096] In one embodiment, the first positive electrode active layer includes lithium iron phosphate and a first type of polyanionic material. The electronic conductivity of the first type of polyanionic material is lower than that of lithium iron phosphate. The first type of polyanionic material accounts for 30%-85% of the total mass of lithium iron phosphate and the first type of polyanionic material. Optionally, the first type of polyanionic material accounts for 40%-65% of the total mass of lithium iron phosphate and the first type of polyanionic material. Specifically, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc.

[0097] LFP is a semiconductor material with an electronic conductivity of 10. -9 S / cm; LMAP is an insulating material with an electronic conductivity of 10. -13 S / cm; ternary materials (NCM) are benign conductors with an electronic conductivity of 10. -3 S / cm. When the first positive electrode active layer is selected from one or more polyanionic phosphate compounds with poor conductivity as the active material, and the second positive electrode active layer is selected from one or more ternary materials with good conductivity as the active material, due to the difference in conductivity on both sides, the second active layer with good conductivity often has a large current shunting and a large equivalent rate, resulting in overuse. This leads to accelerated use of the second active layer material, structural collapse and damage, material loss, and deterioration of the battery cell life.

[0098] The first type of polyanionic material may include lithium manganese iron phosphate, that is, the first positive electrode active layer is a mixture of lithium iron phosphate and lithium manganese iron phosphate. In this embodiment, considering the voltage plateau and internal resistance of the battery cell, the content of the first type of polyanionic material in the first positive electrode active layer is limited. The incorporation of the first type of polyanionic material can increase the charging plateau voltage on the first positive electrode active layer side and reduce the voltage plateau difference with the second positive electrode active layer side. At the same time, the first type of polyanionic material has poor conductivity. If the content is too high, it will worsen the internal resistance on the first positive electrode active layer side and the kinetic capability on the first positive electrode active layer side, thereby causing a large equivalent ratio on the second positive electrode active layer side and worsening the material loss on the second positive electrode active layer side. Therefore, considering both the charging voltage plateau and internal resistance factors, the mass ratio of the first type of polyanionic material to the total amount of lithium iron phosphate and the first type of polyanionic material is controlled to be 30%-85% to improve the loss of active lithium and improve the cycle life of the battery cell.

[0099] In one embodiment, the first positive electrode active layer includes a first polyanionic material, which includes manganese, wherein the mass percentage of manganese in the total metal element is 0.05-0.75; optionally, the mass percentage of manganese in the total metal element is 0.15-0.65. For example, it can be 0.05, 0.08, 0.10, 0.13, 0.15, 0.18, 0.20, 0.23, 0.25, 0.28, 0.30, 0.33, 0.35, 0.38, 0.40, 0.43, 0.45, 0.48, 0.50, 0.53, 0.55, 0.58, 0.60, 0.63, 0.65, 0.68, 0.70, 0.73, 0.75, etc.

[0100] By limiting the Mn content in the polyanionic material, the conductivity of the first positive electrode active layer can be effectively improved. Increasing the Mn content will reduce the conductivity of the polyanionic material to some extent, worsening the internal resistance of the electrode on the first positive electrode active layer side. Conversely, decreasing the Mn content will reduce the voltage plateau on the first positive electrode active layer side to some extent. Therefore, considering both the charging voltage plateau and internal resistance, the mass ratio of manganese in the first polyanionic material is controlled to 0.05-0.75% of the total metal elements to improve active lithium loss and enhance the cycle life of the battery cell.

[0101] In one embodiment, the first positive electrode active layer comprises Li 1+x Mn 1-y A y P 1-z E z Compounds of O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 1.000, z is any value in the range of 0.001 to 0.100, A is selected from one or more elements from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and E is selected from one or more elements from B, Si, N, S, F, Cl and Br.

[0102] With the above settings, the values ​​of x, y, and z satisfy the following condition: maintaining the chemical formula's electrical neutrality. Element A, doped at the manganese sites of lithium manganese iron phosphate (LFP), helps reduce the lattice change rate of LFP during lithium insertion / extraction, improves the structural stability of the LFP cathode material, significantly reduces manganese dissolution, and lowers oxygen activity on the particle surface. Element E, doped at the phosphorus sites, helps alter the ease of Mn-O bond length changes, thereby lowering the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance of the battery cell.

[0103] In one embodiment, A is one or more elements selected from Fe, Ti, V, Ni, Co, and Mg; and / or E is one element selected from B, Si, N, and S. This configuration further improves the structural stability of the positive electrode active material and the rate performance of the battery cell.

[0104] In one embodiment, the active material of the first positive electrode active layer has a core-shell structure, the shell layer of the core-shell structure includes one or more layers of pyrophosphate, phosphate, or carbon, and the core layer of the core-shell structure includes the active material Li. 1+x Mn 1- y A y P 1-z E z O4.

[0105] In the core-shell structure described above, the high migration barrier (>1 eV) of transition metals in pyrophosphate effectively inhibits their dissolution. Phosphate exhibits excellent lithium-ion conductivity and reduces surface impurity lithium content. The carbon layer effectively improves the conductivity and desolvation capability of LiMnPO4, and also acts as a barrier to further hinder manganese ion migration into the electrolyte and reduce electrolyte corrosion of the active material.

[0106] In one embodiment, the second positive electrode active layer includes a first ternary material, wherein the first ternary material includes at least nickel, and the mass percentage of nickel in the total metal element is ≥0.7%.

[0107] In one embodiment, the second positive electrode active layer includes a second ternary material, which includes at least nickel, wherein the nickel content accounts for 0.3-0.7% of the total mass of the metal elements.

[0108] In one embodiment, the positive electrode active material of the second positive electrode active layer includes at least cobalt, wherein the mass percentage of cobalt in the total metal elements in the positive electrode active material of the second positive electrode active layer is 3%-15%.

[0109] In one embodiment, the second positive electrode active layer includes a third ternary material, which includes at least cobalt, wherein the mass percentage of cobalt in the total metal element is 3%-15%. For example, it can be 3%, 5%, 8%, 10%, 12%, 15%, etc., or a range composed of any two of the above sets of values, such as 3%-5%, 3%-8%, 10%-12%, 12%-15%, etc.

[0110] In ternary materials, each element plays a crucial role, and the characteristics of each element also constrain battery performance. Taking nickel-cobalt-manganese ternary materials as an example: Ni exhibits high capacity but low safety; Co exhibits high cost but high stability, as Co can stabilize the layered structure of the material and improve its cycle and rate performance; Mn exhibits high safety and low cost.

[0111] Specifically, when the second positive electrode active layer is made of a ternary material with a high nickel content, the capacity caused by the overcharging of the first positive electrode active layer is greater. Furthermore, ternary materials have better kinetics. Limiting the Co content in ternary materials to a low level can relatively weaken the rate performance of the ternary materials, thus reducing the kinetic performance of the second positive electrode active layer, narrowing the kinetic difference between the active materials on both sides of the positive electrode, improving the matching degree of kinetic performance on both sides of the positive electrode, alleviating the problem of overuse of the side with better kinetic performance during the charging and discharging of the battery cell, slowing down the decay of NCM, and ultimately extending the cycle life of the battery cell.

[0112] In the above embodiments, since the second positive electrode active layer comprises a ternary material positive electrode active material, compared with the polyanionic phosphate compound positive electrode active material of the first positive electrode active layer, the second positive electrode active layer has better kinetic performance. During the charging and discharging process of the battery cell, the second positive electrode active layer is often overused. Therefore, the balance between the two sides of the electrode can be controlled by adjusting the nickel and cobalt content in the ternary material. This can be done by adjusting only one of the nickel or cobalt content, or by adjusting both the nickel and cobalt content simultaneously.

[0113] In one embodiment, the difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V is less than 25%. By controlling the difference in SOC capacity utilization between the first positive electrode active layer side and the second positive electrode active layer side above 3.9V to be within 25%, the loss of active lithium caused by overcharging on the first positive electrode active layer side can be effectively mitigated, thereby improving the cycle life of the battery cell.

[0114] In one embodiment, the first negative electrode active material includes one or more of silicon particle materials, silicon-oxygen materials, silicon-carbon materials, and lithium metal materials. That is, the first negative electrode active material with a capacity greater than 375 mAh / g includes one or more of silicon particle materials with a capacity of 4200 mAh / g, silicon-oxygen materials with a capacity of 2600 mAh / g, silicon-carbon materials with a capacity of 1800 mAh / g, and lithium metal materials with a capacity of 3860 mAh / g. In other embodiments, it may also be one or more of carbon-based negative electrodes, sulfur-containing negative electrodes, metal negative electrodes, alloy negative electrodes, and oxide negative electrodes.

[0115] In one embodiment, the first negative electrode active layer further includes a carbon material, such as graphite; that is, the first negative electrode active layer comprises a mixture of multiple materials, such as a mixture of silicon and graphite. Alternatively, the first negative electrode active layer does not use only high-capacity active materials, but is a mixture of multiple materials.

[0116] In one embodiment, the first negative electrode active layer includes silicon material, and the silicon material accounts for 0.01%-5.5% of the total mass of active material in the first negative electrode active layer. Optionally, the silicon material accounts for 0.5%-3.5% of the total mass of active material in the first negative electrode active layer. For example, the content of silicon material can be 0.01%, 0.05%, 0.10%, 0.30%, 0.50%, 0.80%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00%, 4.50%, 5.00%, 5.50%, etc. With this setting, the loss of active lithium can be reduced, the harm caused by the large volume expansion of the silicon negative electrode itself can be mitigated, the structural stability of the negative electrode can be improved, and the cycle life of the battery cell can be improved overall.

[0117] In one embodiment, the first negative electrode active layer further includes a carbon material, such as graphite; that is, the first negative electrode active layer comprises a mixture of multiple materials, such as a mixture of silicon and graphite, wherein the silicon content in the mixture is controlled to be 0.01%-5.5%. Alternatively, the first negative electrode active layer is not entirely composed of a first negative electrode active material with a capacity greater than 375 mAh / g, but may also contain active materials with relatively lower capacities, such as graphite (discharge capacity approximately 320-380 mAh / g, charge capacity approximately 350-400 mAh / g). As described above, the selection of active materials for the first and second positive electrode active layers will affect the difference between the two sides of the positive electrode sheet; therefore, different negative electrode active materials can be matched according to the selection of the active material on the positive side.

[0118] In one embodiment, the positive electrode active material of the second positive electrode active layer includes at least nickel, wherein the mass percentage of nickel in the total metal element content of the positive electrode active material of the second positive electrode active layer is ≥0.7%, and the mass percentage of silicon in the first negative electrode active layer is 1.5%-3.5% of the total active material content.

[0119] In one embodiment, the positive electrode active material of the second positive electrode active layer includes at least nickel, wherein the mass percentage of nickel in the total metal element content of the positive electrode active material of the second positive electrode active layer is 0.3-0.7%, and the mass percentage of silicon in the first negative electrode active layer is 0.5%-1.5% of the total active material content.

[0120] In ternary materials, each element plays a crucial role, and the characteristics of each element also constrain battery performance. Taking nickel-cobalt-manganese ternary materials as an example: Ni exhibits high capacity but low safety; Co exhibits high cost but high stability; Mn exhibits high safety and low cost. When the second positive electrode active layer is selected from the first ternary material with a higher nickel content, the second positive electrode active layer causes a greater overcharge capacity of the first positive electrode active layer. Consequently, the corresponding first negative electrode active layer needs to use more high-capacity active material to reduce the coating amount and improve negative electrode kinetics to mitigate active lithium loss. Conversely, when the second positive electrode active layer is selected from the second ternary material with a lower nickel content, the proportion of high-capacity negative electrode active material can be reduced accordingly.

[0121] The above embodiments address the problems of lithium plating and reduced cycle life caused by using different active materials on both sides of the positive electrode. This application provides solutions from multiple perspectives. On the one hand, from the perspective of active capacity, the problem of charging imbalance on both sides of the electrode can be improved by adjusting the ratio of active sites on both sides of the electrode. Alternatively, by combining active materials of different capacities, the design of the battery cell can be optimized to pair a positive active layer with a lower charging platform voltage with a negative active layer with a high-capacity negative electrode material, thereby improving the kinetics of the first negative active layer and mitigating the lithium plating problem caused by overcharging of the first positive active layer. On the other hand, from a kinetic perspective, the negative active material can be adjusted according to the selection of the positive active material to achieve kinetic balance on both sides of the electrode. Furthermore, based on the conductivity of the active materials, the combination of active materials can be adjusted to achieve kinetic balance on both sides of the electrode. These various embodiments can be implemented individually, meaning that any one of them can improve the problems of lithium plating and reduced cycle life caused by using different active materials on both sides of the positive electrode; or multiple embodiments can be combined, meaning that two or more conditions can be adjusted simultaneously to improve the problems of lithium plating and reduced cycle life caused by using different active materials on both sides of the positive electrode.

[0122] The battery provided in this application includes the battery cell provided in any of the above embodiments.

[0123] This application also provides an electrochemical device comprising the battery provided in this application.

[0124] In some embodiments, the application of the electrochemical device of this application is not particularly limited, and it can be used in any electronic device known in the prior art. The battery disclosed in the embodiments of this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. That is, an electrical device is provided. In some embodiments, the electrical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, ships, spacecraft, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries and lithium-ion capacitors, etc.

[0125] Electrical equipment can be equipped with individual battery cells, battery modules, or battery packs depending on its usage requirements.

[0126] Please refer to Figure 4 , Figure 4 This is a schematic diagram of a vehicle according to one or more embodiments. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power requirements of the vehicle 1000 during startup, navigation, and driving.

[0127] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0128] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0129] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0130] I. Preparation of battery cells

[0131] Example 1:

[0132] (1) Preparation of positive electrode sheet

[0133] The positive active materials of the first and second positive active layers are mixed with polyvinylidene fluoride (PVDF) and conductive carbon, respectively, and a certain amount of N-methylpyrrolidone (NMP) is added. The mass ratio of positive active material: binder: conductive agent is 96:3:1. The mixture is stirred in a drying room to form a uniform slurry with a viscosity controlled at 3000 mPa·s-10000 mPa·s. The slurry is then applied to both opposite sides of the positive electrode substrate and dried to form a positive electrode sheet. Both sides of the formed positive electrode sheet substrate have active layers, referred to as the first active layer (A side) and the second active layer (B side).

[0134] (2) Preparation of negative electrode sheet

[0135] The negative electrode active materials of the first and second negative electrode active layers are mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon, respectively. A certain amount of deionized water is added, and the mass ratio of negative electrode active material: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent is 97:1:1:1. The mixture is stirred to form a uniform slurry with a viscosity controlled at 3000 mPa·S-10000 mPa·S. The slurry is then coated on both opposite sides of a copper foil (positive electrode substrate). After drying, a negative electrode sheet is formed. Both sides of the formed negative electrode substrate have active layers, referred to as the first active layer (A side) and the second active layer (B side).

[0136] (3) Preparation of battery cells

[0137] The prepared positive electrode sheet, negative electrode sheet, and separator (polyethylene porous polymer film) are used to form battery cells. The battery cells are then hot-pressed at 90°C, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs, and the negative electrode uses copper tabs, with the tabs located on the same side of the battery cell. The battery cell with welded tabs is then fitted into a suitably sized aluminum casing for flexible connection and top cover welding. The battery cell is then vacuum-dried at 175°C for 24 hours, followed by electrolyte injection and sealing to obtain a non-charged battery cell. The non-charged battery cell then undergoes a series of processes including settling, formation, aging, venting, re-sealing, and capacity testing to obtain the lithium-ion battery product.

[0138] Examples 2-6:

[0139] Based on Example 1, the type and content of the high-capacity negative electrode active material in the first negative electrode active layer were changed, as detailed in Table 1.

[0140] Comparative Examples 1-2:

[0141] Based on Example 1, the active material used in the first negative electrode active layer was changed to only use graphite material without adding high-capacity active material. See Table 1 for details.

[0142] II. Performance Testing and Parameter Testing

[0143] (1) Cyclic life at 25℃

[0144] At 25℃, the battery was charged at a constant current of 1C to 4.2V, then switched to constant voltage charging until the charging current dropped to 0.05C. The battery was then discharged at a constant current of 1C to 2.8V. The charge-discharge cycle was repeated until the battery capacity dropped to 80% of the initial capacity. The number of cycles at this point was taken as the 25℃ cycle life of the secondary battery.

[0145] (2) Testing of elemental (nickel, cobalt, manganese, silicon) content in active materials

[0146] The results were obtained using ICP (Inductively Coupled Plasma Emission Spectrometer). The specific procedure is as follows: the powder to be tested is placed in a microwave digester (e.g., CEM-Mars6) for digestion. The digested solution is then passed into an ICP analyzer (e.g., ICAP7400). By comparing the elemental concentrations in the standard solution, the elemental content of the material is calculated. ICP can also estimate the proportion of the two materials in a mixed cathode. By dividing the ICP test result by the molar mass of the element, the corresponding proportion of each element can be deduced. Then, by determining the proportion of each material, the percentage of each element in the NCM material can be calculated.

[0147] The process involves disassembling the battery to obtain the electrodes. The coating material of the electrodes is scraped off, and organic materials such as binders and dispersants are removed using organic solvents or by calcination to obtain inorganic materials, which contain active materials. Scanning electron microscopy (SEM) or particle size analysis is used to determine the number of active materials present, thus qualitatively identifying the material type. The content of certain characteristic elements in the material is then tested, and the proportion of each material is estimated using these elemental contents. For the negative electrode, the proportion of silicon can be determined by testing the carbon and silicon content. For the positive electrode, if it is a mixture of lithium iron phosphate and lithium manganese iron phosphate, the ratio of lithium iron phosphate to lithium manganese iron phosphate can be estimated using the manganese and iron content. For ternary materials, the content of the ternary material can be estimated using the nickel content.

[0148] (3) Testing of charging platform voltage

[0149] Obtain the positive electrode active material, assemble it to form a primary cell, and perform one charge and discharge cycle on the battery. In constant current mode, discharge at a rate of 0.33C to 2.5V and let it stand for 10 minutes; charge at a rate of 0.33C to the full charge voltage +0.05V and let it stand for 10 minutes to obtain the charging capacity C1 and charging energy E1; let it stand for 10 minutes; discharge at a rate of 0.33C to 2.5V and let it stand for 10 minutes to obtain the discharge capacity C2 and charging energy E2; the charging plateau voltage = charging energy E1 / charging capacity C1, and the discharge plateau voltage = discharge energy E2 / discharge capacity C2.

[0150] (4) Gram volume test

[0151] Take a fully discharged anode electrode and wipe one side, then combine it with lithium metal to form a coin cell. Discharge it to 5mV at a rate of 0.05C in DC current mode; charge it to 50μA in DC voltage mode; let it stand for 5 minutes; then charge it to 2.0V in constant current mode. Repeat the above steps for 2 cycles, and calculate the specific capacity based on the capacity value of the second cycle.

[0152] (5) Coating weight (CW) test

[0153] Disassemble the battery, obtain the electrode sheets, weigh the electrode sheets m1, wipe off one side of the active layer, weigh the electrode sheets m2, wipe off both sides of the active layer, weigh the electrode sheets m3; the coating weight on one side is m1-m2; the coating weight on both sides is m1-m3; measure the coating area and calculate the coating amount.

[0154] (6) Capacity utilization test

[0155] The battery was left to stand at 25°C for 30 minutes, then charged at a constant current of 0.04C to 4.2V.

[0156] After standing at 25℃ for 1 hour, discharge at a constant current of 0.04C to 3V;

[0157] After standing at 25℃ for 1 hour, charge at a constant current of 0.04C to 4.2V;

[0158] Let stand at 25℃ for 1 hour, then discharge at a constant current of 1C to 3V.

[0159] After standing at 25℃ for 1 hour, charge at a constant current of 0.04C to 4.2V;

[0160] Let stand at 25℃ for 1 hour, then discharge at 3C constant current to 3V;

[0161] After standing at 25℃ for 1 hour, charge at a constant current of 0.04C to 4.2V;

[0162] Let stand at 25℃ for 1 hour, then discharge at 5C to 3V; let stand at 25℃ for 1 hour.

[0163] The process involves disassembling the battery, obtaining the positive electrode, scraping off the second positive electrode active layer, and using the positive electrode with only the first positive electrode active layer to assemble a primary battery, testing a capacity utilization value of 3.9V or higher; similarly, the battery is disassembled, the positive electrode is obtained, the first positive electrode active layer is scraped off, and using the positive electrode with only the second positive electrode active layer to assemble a primary battery, testing a capacity utilization value of 3.9V or higher (e.g., 4.2V); and calculating the difference in capacity utilization values.

[0164] (7) Electrode CB value test:

[0165] The battery cell was discharged to 2.5V at 0.1C, disassembled, and positive and negative electrodes of the same area were taken for testing. The positive electrode was divided into two samples: one sample was positive electrode plate B with the first positive active layer scraped off, leaving only the second positive active layer, and the other sample was positive electrode plate A with the second positive active layer scraped off, leaving only the first positive active layer. These were assembled into reverse coin cells with lithium metal sheets, and the discharge capacity of the corresponding electrodes was tested at a rate of 0.1C. These values ​​were recorded as positive electrode capacity Cap-A, Cap-B, and negative electrode capacity Cap-C, respectively. The ratio of the negative electrode capacity to the positive electrode capacity, Cap-C / Cap-A and Cap-C / Cap-B, is the CB value of the tested electrode.

[0166] III. Test Result Analysis

[0167] Table 1. Structure and performance of the battery cells in each embodiment and comparative example.

[0168]

[0169] Note: "Positive electrode A-side" refers to the positive electrode active material contained in the first positive electrode active layer; "Positive electrode B-side" refers to the positive electrode active material contained in the second positive electrode active layer; "Negative electrode A-side" refers to the negative electrode active material contained in the first negative electrode active layer; "Negative electrode A-side content" refers to the content of high-capacity negative electrode active material in the first negative electrode active layer, such as the silicon material content of 1.50% in Example 1; "Negative electrode A-side CW" refers to the coating amount of the active material in the first negative electrode active layer, in g / 1540.25mm. 2 LFP (3.4V) refers to lithium iron phosphate with a charging platform voltage of 3.4V; NCM; 55%; (3.75V) refers to ternary material with a nickel content of 55% and a charging platform voltage of 3.75V. The nickel content of 55% means that nickel accounts for 55% of the total mass of the metal elements in the ternary material.

[0170] The results of the above embodiments show that when the charging platform voltage of the positive electrode active material in the first positive electrode active layer is ≤3.5V and the charging platform voltage of the positive electrode active material in the second positive electrode active layer is greater than 3.5V, by incorporating high-capacity negative electrode active material into the first negative electrode active layer, the negative electrode capacity can be effectively increased without increasing the CW, or the coating amount of active material in the first negative electrode active layer can be reduced, thereby improving the kinetics of the first negative electrode active layer and thus improving the cycle life of the battery cell.

[0171] Examples 7-11:

[0172] Based on Example 1, the type of positive electrode active material in the first positive electrode active layer was changed, and a mixture of lithium iron phosphate and lithium manganese iron phosphate was selected. At the same time, the content of manganese in lithium manganese iron phosphate was adjusted, as detailed in Table 2.

[0173] Examples 12-16:

[0174] Based on Example 1, the type of positive electrode active material in the first positive electrode active layer was changed, and a mixture of lithium iron phosphate and lithium manganese iron phosphate was selected. At the same time, the content of lithium manganese iron phosphate was adjusted. See Table 2 for details.

[0175] Examples 17-21:

[0176] Based on Example 1, the type of positive electrode active material in the first positive electrode active layer was changed, and a mixture of lithium iron phosphate and lithium manganese iron phosphate was selected. At the same time, the content of cobalt in the ternary material in the second positive electrode active layer was adjusted, as detailed in Table 2.

[0177] Table 2. Structure and performance of the battery cells in each embodiment and comparative example.

[0178]

[0179] Note: "Positive A-side" refers to the positive active material contained in the first positive active layer; "Positive B-side" refers to the positive active material contained in the second positive active layer; LMAP percentage refers to the proportion of LMAP to the total mass of LFP and LMAP; LFP (3.4V) refers to lithium iron phosphate with a charging platform voltage of 3.4V; LMAP (3.44V) refers to lithium manganese iron phosphate with a charging platform voltage of 3.44V; NCM; 55%; (3.75V) refers to ternary material with a charging platform voltage of 3.75V and a nickel content of 55%, where nickel accounts for 55% of the total mass of the metal elements in the ternary material.

[0180] The results of the above embodiments show that when the charging platform voltage of the positive electrode active material in the first positive electrode active layer is ≤3.5V and the charging platform voltage of the positive electrode active material in the second positive electrode active layer is greater than 3.5V, a mixture of lithium iron phosphate and lithium manganese iron phosphate is selected in the first positive electrode active layer. The incorporation of lithium manganese iron phosphate can increase the charging platform voltage on the first positive electrode active layer side and reduce the voltage platform difference with the second positive electrode active layer side. At the same time, lithium manganese iron phosphate has poor conductivity. If the content is too high, it will worsen the internal resistance on the first positive electrode active layer side and the dynamic capability on the first positive electrode active layer side, thereby causing a large equivalent rate on the second positive electrode active layer side and worsening the material loss on the second positive electrode active layer side. Therefore, considering both the charging voltage platform and internal resistance, controlling the mass ratio of lithium manganese iron phosphate in the total amount of lithium iron phosphate and lithium manganese iron phosphate to 30%-85% can improve the cycle life of the battery cell.

[0181] Furthermore, by limiting the Mn content in lithium manganese iron phosphate, the conductivity of the first positive electrode active layer can be effectively improved. Increasing the Mn content will reduce the conductivity of lithium manganese iron phosphate to some extent, worsening the internal resistance of the electrode on the first positive electrode active layer side. Conversely, decreasing the Mn content will reduce the voltage plateau on the first positive electrode active layer side to some extent. Therefore, considering both the charging voltage plateau and internal resistance, controlling the mass ratio of manganese in the total metal elements of lithium manganese iron phosphate to 0.05-0.75 can improve the cycle life of individual battery cells.

[0182] Furthermore, ternary materials have better kinetics. By limiting the Co content in ternary materials to a low level, the rate performance of ternary materials can be relatively weakened. Therefore, it can reduce the kinetic performance of the second positive electrode active layer, reduce the kinetic difference between the active materials on both sides of the positive electrode, improve the matching degree of kinetic performance on both sides of the positive electrode, improve the problem of the side with better kinetic performance being overused during the charging and discharging of the battery cell, slow down the decay of NCM, and ultimately extend the cycle life of the battery cell.

[0183] Examples 22-28:

[0184] Based on Example 14, the ratio of the first active site and the ratio of the second active site of the battery cell, and their ratio values ​​are set, as detailed in Table 3.

[0185] Comparative Example 3:

[0186] Based on Examples 22-28, the ratio of the first active site to the second active site of the battery cell is set to be the same, as detailed in Table 3.

[0187] Table 3. Structure and performance of the battery cells in each embodiment and comparative example.

[0188]

[0189] Note: "Positive A-side" refers to the positive active material contained in the first positive active layer; "Positive B-side" refers to the positive active material contained in the second positive active layer; LMAP percentage refers to the proportion of LMAP to the total mass of LFP and LMAP; LFP (3.4V) refers to lithium iron phosphate with a charging platform voltage of 3.4V; LMAP (3.46V) refers to lithium manganese iron phosphate with a charging platform voltage of 3.46V; NCM; 55%; (3.75V) refers to ternary material with a charging platform voltage of 3.75V and a nickel content of 55%, where nickel accounts for 55% of the total mass of the metal elements in the ternary material.

[0190] The results of the above embodiments show that when the charging platform voltage of the positive electrode active material in the first positive electrode active layer is ≤3.5V and the charging platform voltage of the positive electrode active material in the second positive electrode active layer is greater than 3.5V, a relatively large first active site ratio is set, or in other words, the first active site ratio is set to be greater than the second active site ratio. With both the first and second active site ratios greater than 1, the first active site ratio is larger, therefore the active capacity of the first negative electrode active layer is greater than that of the first positive electrode active layer. This effectively reduces the deposition of active ions in the first negative electrode active layer, reduces active ion loss, and improves the cycle life of the battery.

[0191] Examples 29-31:

[0192] The difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V is set to be less than 25%, as detailed in Table 4.

[0193] Comparative Example 4:

[0194] The difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V is set to be greater than 25%, as detailed in Table 4.

[0195] Table 4. Structure and performance of the battery cells in each embodiment and comparative example.

[0196] Difference in capacity play value 25 °C cycle life Example 29 5％ 2700 cls Example 30 10％ 2550 cls Example 31 15％ 2400 cls Comparative Example 4 50％ 1550 cls

[0197] Note: The difference in capacity utilization value refers to the difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V.

[0198] The results of the above embodiments show that when the charging platform voltage of the positive active material in the first positive active layer is ≤3.5V and the charging platform voltage of the positive active material in the second positive active layer is greater than 3.5V, by controlling the difference in SOC capacity between the first positive active layer side and the second positive active layer side above 3.9V to be within 25%, the loss of active lithium caused by overcharging of the first positive active layer side can be effectively alleviated, and the cycle life of the battery cell can be improved.

[0199] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A battery cell, characterized in that, include: A positive electrode sheet includes a positive electrode base layer, a first positive electrode active layer and a second positive electrode active layer disposed on opposite sides of the positive electrode base layer, wherein the first positive electrode active layer includes a first positive electrode active material, the second positive electrode active layer includes a second positive electrode active material, and the charging platform voltage of the first positive electrode active material is lower than the charging platform voltage of the second positive electrode active material. The negative electrode sheet includes a negative electrode base layer, a first negative electrode active layer and a second negative electrode active layer disposed on opposite sides of the negative electrode base layer, the first negative electrode active layer being opposite to the first positive electrode active layer, the second negative electrode active layer being opposite to the second positive electrode active layer, the first active site ratio CB1 of the battery cell being greater than the second active site ratio CB2, the first active site ratio being the active capacity of the first negative electrode active layer / the active capacity of the first positive electrode active layer, and the second active site ratio being the active capacity of the second negative electrode active layer / the active capacity of the second positive electrode active layer.

2. The battery cell according to claim 1, characterized in that, The ratio of the first active site ratio CB1 to the second active site ratio CB2 of the battery cell is CB1:CB2, which is 1.009-1.

201.

3. The battery cell according to claim 1 or 2, characterized in that, The first active site ratio CB1 is 1.12-1.30; and / or The second active site ratio is 1.08-1.12 compared to CB2.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The charging platform voltage of the first type of positive electrode active material is ≤3.5V, and the charging platform voltage of the second type of positive electrode active material is greater than 3.5V.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The first negative electrode active layer includes a first negative electrode active material, and the capacity of the first negative electrode active material is greater than 375 mAh / g.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The coating weight of the first negative electrode active layer is less than 0.16 g / 1540.25 mm. 2 .

7. The battery cell according to claim 6, characterized in that, The coating amount of the first negative electrode active layer is 0.12-0.15 g / 1540.25 mm. 2 .

8. The battery cell according to any one of claims 1 to 7, characterized in that, The first negative electrode active layer comprises silicon material, and the silicon material accounts for 0.01%-5.5% of the total mass of the active material in the first negative electrode active layer.

9. The battery cell according to claim 8, characterized in that, The silicon material in the first negative electrode active layer accounts for 0.5%-3.5% of the total mass of the active material in the first negative electrode active layer.

10. The battery cell according to claim 8 or 9, characterized in that, The positive electrode active material of the second positive electrode active layer includes at least nickel, wherein the mass percentage of nickel in the total metal element content of the positive electrode active material of the second positive electrode active layer is 0.3-0.7%, and the mass percentage of silicon in the first negative electrode active layer is 0.5%-1.5% of the total active material content.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The positive electrode active material of the second positive electrode active layer includes at least cobalt, wherein the mass percentage of cobalt in the total metal element content of the positive electrode active material of the second positive electrode active layer is 3%-15%.

12. The battery cell according to any one of claims 1 to 11, characterized in that, The first positive electrode active layer includes lithium iron phosphate and a first type of polyanionic material. The electronic conductivity of the first type of polyanionic material is less than that of lithium iron phosphate. The first type of polyanionic material accounts for 30%-85% of the total mass of lithium iron phosphate and the first type of polyanionic material.

13. The battery cell according to claim 12, characterized in that, In the first positive electrode active layer, the first type of polyanionic material accounts for 40%-65% of the total mass of lithium iron phosphate and the first type of polyanionic material.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The first positive electrode active layer includes lithium iron phosphate and a second type of polyanionic material. The charging platform voltage of the second type of polyanionic material is greater than that of lithium iron phosphate. The mass ratio of the second type of polyanionic material to the total mass of lithium iron phosphate and the second type of polyanionic material is 15%-40%.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The first positive electrode active layer includes a first type of polyanionic material, which includes manganese, wherein the mass percentage of manganese in the total metal element is 0.05-0.

75.

16. The battery cell according to claim 15, characterized in that, In the first type of polyanionic material, the mass percentage of manganese in the total metal elements is 0.15-0.

65.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The first positive electrode active layer includes Li 1+x Mn 1-y A y P 1-z E z The active material of O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 1.000, z is any value in the range of 0.001 to 0.100, A is selected from one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and E is selected from one or more elements selected from B, Si, N, S, F, Cl and Br.

18. The battery cell according to claim 17, characterized in that, The A is selected from one or more elements chosen from Fe, Ti, V, Ni, Co, and Mg; and / or The element E is selected from B, Si, N, and S.

19. The battery cell according to claim 17 or 18, characterized in that, The active material of the first positive electrode active layer has a core-shell structure, wherein the shell layer of the core-shell structure comprises one or more layers of pyrophosphate, phosphate, or carbon, and the core layer of the core-shell structure comprises the active material Li. 1+x Mn 1-y A y P 1-z E z O4.

20. The battery cell according to any one of claims 1 to 19, characterized in that, The difference between the capacity utilization value of the first positive electrode active layer above 3.9V and the capacity utilization value of the second positive electrode active layer above 3.9V is less than 25%.

21. A battery, characterized in that, Includes the battery cell as described in any one of claims 1-20.

22. An electrical appliance, characterized in that, Includes the battery as described in claim 21.

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