Battery cell, battery and electric device

Abstract

Disclosed in the present application are a battery cell, a battery and an electric device. The battery cell comprises a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet comprises a first positive electrode active layer and a second positive electrode active layer, and a charging plateau voltage of an active material of the first positive electrode active layer is less than a charging plateau voltage of an active material of the second positive electrode active layer; the negative electrode sheet comprises a first negative electrode active layer and a second negative electrode active layer, 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; and CB1 of the battery cell is greater 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. By means of such a design, lithium plating caused by the overcharging of the first positive electrode active layer can be mitigated, thereby reducing the loss of active lithium, and prolonging the cycle life of the battery cell.

Description

Battery cell, battery and electric device

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411095115.3, filed on August 9, 2024, entitled “Battery cell, battery and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the field of new energy technology, in particular to a battery cell, a battery and an electric device. BACKGROUND

[0004] With the development of modern science and technology, lithium ion batteries are considered to be the first choice of green and environmentally friendly batteries due to their high energy density, long cycle life and good environmental protection. Lithium ion batteries can be widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric vehicles, electric tools, military equipment and aerospace.

[0005] When different positive active materials are selected on both sides of the positive electrode sheet in the lithium ion battery, the performance of both sides is different, which will cause the cycle life of the battery to decrease. The above statement is only used to provide background technical information related to the present application, and does not necessarily constitute the prior art. SUMMARY

[0006] The technical problem solved by the present application is to provide a battery cell, a battery and an electric device, which can improve the cycle life of the battery cell.

[0007] To solve the above technical problems, one technical solution adopted by the present application is to provide a battery monomer, which comprises a positive electrode sheet and a negative electrode sheet. The positive electrode sheet comprises a positive electrode base layer and a first positive electrode active layer and a second positive electrode active layer arranged on the opposite sides of the positive electrode base layer. The first positive electrode active layer comprises a first positive electrode active material, and the second positive electrode active layer comprises a second positive electrode active material. The charging platform voltage of the first positive electrode active material is less than that of the second positive electrode active material. The negative electrode sheet comprises a negative electrode base layer and a first negative electrode active layer and a second negative electrode active layer arranged on the opposite sides of the negative electrode base layer. 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 first active site ratio CB1 of the battery monomer 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. By arranging the active site ratio on both sides of the sheet, the first active site ratio CB1 is greater than the second active site ratio CB2, which can improve the charging imbalance problem (for example, overcharging on one side may occur) on both sides of the sheet during charging, thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery monomer.

[0008] In an embodiment, the ratio CB1:CB2 of the first active site ratio CB1 and the second active site ratio CB2 is 1.009-1.201. By adjusting the active site ratio on both sides of the sheet, the charging imbalance problem (for example, overcharging on one side may occur) on both sides of the sheet during charging can be improved, thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery monomer.

[0009] In an 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. By such arrangement, the negative electrode active layer can provide sufficient active ion vacancies to receive the active ions provided by the positive electrode active layer, reduce the precipitation of active ions on the side of the negative electrode sheet, and improve the cycle life of the battery monomer.

[0010] In an 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. By such arrangement, the capacity and stability of the positive electrode sheet can be improved. In the case of the first negative electrode active layer matched with the first negative electrode active material with high capacity, the lithium precipitation on the side of the first negative electrode active layer caused by overcharging of the first positive electrode active layer can be improved, the loss of active lithium is reduced, and the cycle life of the battery monomer is improved.

[0011] In an embodiment, the first negative active layer comprises a first negative active material, and the capacity of the first negative active material is greater than 375 mAh / g. Through this design, the lithium precipitation on the side of the first negative active layer caused by overcharging of the first positive active layer in the battery cell can be improved, the loss of active lithium can be reduced, and the cycle life of the battery cell can be improved.

[0012] In an embodiment, the coating amount of the first negative active layer is less than 0.16 g / 1540.25 mm 2 . By selecting a high-capacity negative material as the active material of the first negative active layer, the coating amount of the active material in the first negative active layer can be reduced, thereby improving the kinetics of the first negative active layer, improving the lithium precipitation on the side of the first negative active layer caused by overcharging of the first positive active layer in the battery cell, reducing the loss of active lithium, and improving the cycle life of the battery cell.

[0013] In an embodiment, the coating amount of the first negative active layer is 0.12-0.15 g / 1540.25 mm 2 . By selecting a high-capacity negative material as the active material of the first negative active layer, the coating amount of the active material in the first negative active layer can be reduced, thereby improving the kinetics of the first negative active layer, improving the lithium precipitation on the side of the first negative active layer caused by overcharging of the first positive active layer in the battery cell, reducing the loss of active lithium, and improving the cycle life of the battery cell.

[0014] In an embodiment, the first negative active layer comprises a silicon material, and the mass fraction of the silicon material in the total amount of active materials in the first negative active layer is 0.01%-5.5%. Through this setting, the harm caused by the large volume expansion of the silicon negative electrode can be reduced on the basis of improving the loss of active lithium, the stability of the negative electrode structure can be improved, and the overall cycle life of the battery cell can be improved.

[0015] In an embodiment, the mass fraction of the silicon material in the total amount of active materials in the first negative active layer is 0.5%-3.5%. Through this setting, the harm caused by the large volume expansion of the silicon negative electrode can be reduced on the basis of improving the loss of active lithium, the stability of the negative electrode structure can be improved, and the overall cycle life of the battery cell can be improved.

[0016] In an embodiment, the positive active material of the second positive active layer comprises at least nickel element, and the mass fraction of the nickel element in the total amount of metal elements in the positive active material of the second positive active layer is 0.3-0.7, and the mass fraction of the silicon material in the total amount of active materials in the first negative active layer is 0.5%-1.5%. Through this design, the lithium precipitation caused by overcharging of the first positive active layer can be improved, the loss of active lithium can be improved, and the cycle life of the battery cell can be improved.

[0017] In an embodiment, the positive active material of the second positive active layer comprises at least cobalt element, and the mass percentage of cobalt element in the total amount of metal elements in the positive active material of the second positive active layer is 3-15%. Through this design, the rate capability of the second positive active layer can be weakened, the kinetic difference between the first positive active layer and the second positive active layer can be reduced, the lithium side precipitation of the first negative active layer caused by overcharge of the first positive active layer in the battery cell can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0018] In an embodiment, the first positive active layer comprises lithium iron phosphate and a first type of polyanion material, the electronic conductivity of the first type of polyanion material is less than that of lithium iron phosphate, and the mass percentage of the first type of polyanion material in the total amount of lithium iron phosphate and the first type of polyanion material is 30-85%. Through this setting, the electronic conductivity of the first positive active layer side can be improved, the battery cell internal resistance can be reduced, the kinetic capability of the first positive active layer side can be improved, the lithium side precipitation of the first negative active layer caused by overcharge of the first positive active layer in the battery cell can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0019] In an embodiment, the mass percentage of the first type of polyanion material in the total amount of lithium iron phosphate and the first type of polyanion material in the first positive active layer is 40-65%. Through this setting, the electronic conductivity of the first positive active layer side can be improved, the battery cell internal resistance can be reduced, the kinetic capability of the first positive active layer side can be improved, the lithium side precipitation of the first negative active layer caused by overcharge of the first positive active layer in the battery cell can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0020] In an embodiment, the first positive active layer comprises lithium iron phosphate and a second type of polyanion material, the charge platform voltage of the second type of polyanion material is greater than that of lithium iron phosphate, and the mass percentage of the second type of polyanion material in the total amount of lithium iron phosphate and the second type of polyanion material is 10-40%. Through this setting, the difference between the voltage platforms of the first positive active layer side and the second positive active layer side can be reduced, the lithium precipitation caused by overcharge of the first positive active layer can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0021] In an embodiment, the first positive active layer comprises a first type of polyanion material, and the first type of polyanion material comprises manganese element, and the mass percentage of manganese element in the total amount of metal elements is 0.05-0.75. Through this setting, the electronic conductivity of the first positive active layer side can be improved, the battery cell internal resistance can be reduced, the kinetic capability of the first positive active layer side can be improved, the lithium side precipitation of the first negative active layer caused by overcharge of the first positive active layer in the battery cell can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0022] In an embodiment, the mass fraction of manganese in the total amount of metal elements in the first polyanion material is 0.15-0.65. Through this setting, the conductive capacity of the first positive electrode active layer side can be improved, the internal resistance of the battery cell can be reduced, the kinetic capacity of the first positive electrode active layer side can be improved, the lithium extraction of the first negative electrode active layer side caused by overcharging of the first positive electrode active layer in the battery cell can be improved, the active lithium loss can be reduced, and the cycle life of the battery cell can be improved.

[0023] In an embodiment, the first positive electrode active layer comprises a compound of Li 1+x Mn 1-y A y P 1-z E z O4, wherein x is any value in the range of -0.100-0.100, y is any value in the range of 0.001-1.000, z is any value in the range of 0.001-0.100, A is selected from one or more elements of 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 of B, Si, N, S, F, Cl and Br. Through the above setting, lithium ion migration can be promoted, and the rate performance of the battery cell can be improved.

[0024] In an embodiment, A is selected from one or more elements of Fe, Ti, V, Ni, Co and Mg; and / or E is selected from one element of B, Si, N and S. Through the above setting, the structural stability of the positive electrode active material and the rate performance of the battery cell can be further improved.

[0025] In an embodiment, the active material of the first positive electrode active layer has a core-shell structure, the coating shell layer of the core-shell structure comprises one or more layers of pyrophosphate, phosphate and 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. Through the above setting, the dissolution of transition metals can be effectively inhibited, the surface lithium content can be reduced, and the corrosion of the electrolyte to the active material can be reduced.

[0026] In an embodiment, the difference between the capacity release value of the first positive electrode active layer above 3.9V and the capacity release value of the second positive electrode active layer above 3.9V is less than 25%. By controlling the difference between the SOC capacity release of the first positive electrode active layer side and the second positive electrode active layer side above 3.9V to be within 25%, the active lithium loss caused by overcharging of the first positive electrode active layer side can be effectively alleviated, and the cycle life of the battery cell can be improved.

[0027] To solve the above technical problems, another technical solution adopted by the present application is to provide a battery, which comprises the battery monomer of any one of the above, and the battery has at least the same advantages as the battery monomer.

[0028] To solve the above technical problems, another technical solution adopted by the present application is to provide a battery, which comprises the battery monomer of any one of the above, and the battery has at least the same advantages as the battery monomer.

[0029] The above description is only a summary of the technical solutions of the present application. In order to enable one skilled in the art to better understand the technical means of the present application and to implement the same according to the contents of the description, and in order to enable the above and other purposes, features and advantages of the present application to be more apparent and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0031] Fig. 1 is an exploded structural schematic diagram of a battery according to one or more embodiments;

[0032] Fig. 2 is an exploded structural schematic diagram of a battery monomer according to one or more embodiments;

[0033] Fig. 3 is a structural schematic diagram of an electrode assembly according to one or more embodiments;

[0034] Fig. 4 is a structural schematic diagram of a vehicle according to one or more embodiments.

[0035] In the drawings: 1000, vehicle; 300, motor; 200, controller; 100, battery; 10, box body; 11, first part; 12, second part; 20, battery monomer; 21, end cover; 21a, electrode terminal; 22, shell; 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 film. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and effects of the present application clearer and more apparent, the embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot be used to limit the protection scope of the present application.

[0037] 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 belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," "having" and "with" and any variations thereof herein are intended to cover both the inclusive and exclusive cases.

[0038] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces), unless otherwise explicitly specified.

[0039] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0040] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0041] Quantities, ratios, and other numerical values are presented herein in a range format. It is to be understood that such range format is used merely for the convenience of the reader and is not intended to limit the actual scope of such values to the particular values represented in such a range. It is therefore to be understood that for the described numerical properties following each numerical value, the text "and above" is to be interpreted in the context of the specific range from which the value is derived.

[0042] If not specified, all steps of the present application can be carried out in sequence, randomly, or in parallel, preferably in sequence. For example, the method comprises steps (a) and (b), indicating that the method can comprise steps (a) and (b) in sequence, steps (b) and (a) in sequence, or steps (a) and (b) in parallel. For example, the method can also comprise step (c), indicating that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] Lithium-ion batteries, as a new type of green secondary battery, are widely used in electric vehicles, energy storage systems and renewable energy fields. With the new development of lithium-ion batteries in China, lithium-ion batteries will achieve improvement in many aspects. From the technical aspect, in the improvement process, "high efficiency", "high long life" and "low cost" will be the core scheme and pursuit target of the development of power battery technology.

[0044] The present application provides a battery, please refer to Figure 1, Figure 1 is an exploded structural schematic diagram of the battery according to one or more embodiments. The battery 100 includes a box 10 and a battery cell 20, the battery cell 20 is contained in the box 10. Among them, the box 10 is used to provide accommodation space for the battery cell 20, the box 10 can adopt a variety of structures. In some embodiments, the box 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are covered with each other, the first part 11 and the second part 12 together define an accommodation space for containing the battery cell 20. The second part 12 can be a hollow structure with one end open, the first part 11 can be a plate structure, the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 together define the accommodation space; the first part 11 and the second part 12 can also be hollow structures with one side open, the open side of the first part 11 covers the open side of the second part 12. Of course, the box 10 formed by the first part 11 and the second part 12 can be a variety of shapes, such as cylinder, cuboid, etc.

[0045] In the battery 100, the battery cells 20 can be multiple, and the multiple battery cells 20 can be connected in series, in parallel, or in a mixed manner. The mixed manner means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and the whole of the multiple battery cells 20 is accommodated in the case 10. Of course, the battery 100 can also be in a form that the multiple battery cells 20 are connected in series, in parallel, or in a mixed manner to form a battery module, and the multiple battery modules are connected in series, in parallel, or in a mixed manner to form a whole, and the whole is accommodated in the case 10. The battery 100 can also include other structures. For example, the battery 100 can also include a current collecting member for electrically connecting the multiple battery cells 20.

[0046] Each of the battery cells 20 can be a secondary battery or a primary battery, and can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 can be in a shape of a cylinder, a flat body, a cuboid, or other shapes.

[0047] The application also provides a battery cell. Please refer to FIG. 2, which is an exploded structural schematic diagram of a battery cell according to one or more embodiments. The battery cell 20 refers to the smallest unit of a battery. As shown in FIG. 2, the battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23, and other functional components.

[0048] The end cover 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. Without limitation, the shape of the end cover 21 can be adapted to the shape of the shell 22 to fit the shell 22. Optionally, the end cover 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that the end cover 21 is not easy to deform when subjected to extrusion and collision, so that the battery cell 20 can have higher structural strength, and the safety performance can also be improved. The end cover 21 can be provided with functional components such as an electrode terminal 21a. The electrode terminal 21a can be used to electrically connect with the electrode assembly 23 for outputting or inputting the electric energy of the battery cell 20. In some embodiments, the end cover 21 can also be provided with a pressure relief mechanism for relieving the internal pressure when the internal pressure or temperature of the battery cell 20 reaches a threshold value. The material of the end cover 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the application do not make special limitations thereon. In some embodiments, an insulating piece can also be provided on the inner side of the end cover 21, which can be used to isolate the electrical connection components in the shell 22 from the end cover 21 to reduce the risk of short circuit. Exemplarily, the insulating piece can be plastic, rubber, etc.

[0049] The shell 22 is a component used in cooperation with the end cover 21 to form an internal environment of the battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, electrolyte, and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be provided on the shell 22, and the end cover 21 is used to cover the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the shell 22 can also be integrated, specifically, the end cover 21 and the shell 22 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the internal environment of the shell 22, the end cover 21 is used to cover the shell 22. The shell 22 can be of various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations thereto.

[0050] The electrode assembly 23 is a component in which electrochemical reactions occur in the battery cell 100. One or more electrode assemblies 23 can be contained in the shell 22. The electrode assembly 23 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is usually provided between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet have a portion with active material constituting a main body of the electrode assembly, and a portion without active material of the positive electrode sheet and the negative electrode sheet respectively constituting a tab 23a. The positive electrode tab and the negative electrode tab can be located together at one end of the main body or respectively at both ends of the main body. In the charging and discharging process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a connects the electrode terminal to form a current loop.

[0051] In some embodiments, the positive electrode sheet includes a current collector and a positive active layer disposed on the current collector.

[0052] The positive active layer includes a positive active material, which can include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and a modified compound of each of them. However, the present application is not limited to these materials, and other conventional materials that can be used as positive active materials for batteries can also be used. These positive active materials can be used alone or in combination with two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2), and modified compounds thereof. Examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0053] In an embodiment, the active layer of the cathode material further includes a conductive agent and a binder.

[0054] The conductive agent imparts electrical conductivity to the electrode. The cathode conductive material can include any electrically conductive material, so long as it does not cause chemical changes. Non-limiting examples of cathode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, 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 fibers, carbon nanotubes, graphene, ketjen black, and acetylene black.

[0055] The binder improves the adhesion stability of the active layer, reducing the probability of powder falling. The binder 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 binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, acrylate, polyurethane.

[0056] In an embodiment, the positive active layer further comprises other optional additives, which can be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials.

[0057] In some embodiments, the negative electrode tab comprises a current collector and a negative active layer disposed on the current collector.

[0058] The negative active layer comprises a negative active material, which includes but is not limited to carbon-based negative materials, silicon-based negative materials, tin-based negative materials, lithium titanate negative materials, metal lithium negative materials, etc.; specifically includes but is not limited to graphite materials, silicon-carbon materials, graphite-silicon monoxide materials, nano-silicon materials, silicon monoxide materials, and tin-based materials; more specifically includes natural graphite, artificial graphite, mesophase carbon microbeads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel-structured Li4Ti5O12, and Li-Al alloys. 12

[0059] In some embodiments, the negative active layer can further comprise a binder, a conductive agent, and other optional additives. As an example, the conductive agent can be one or more of super conductive carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P (SP), graphene, and carbon nanofibers. As an example, the binder 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). As an example, the other optional additives can be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials.

[0060] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, without particular limitation.

[0061] In an embodiment, the electrolyte comprises one or more of carbonate solvents and ether solvents.

[0062] ​The carbonate is typically a small molecule cyclic or chain carbonate; including but not limited to one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, one or more of fluoro-carbonate; can also be at least one ester solvent of gamma-butyrolactone, dimethyl sulfite, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, propyl acetate, fluoro-carboxylate.

[0063] The ether solvent includes but is not limited to one or more of dimethyl ether, diethyl ether, tetrahydrofuran, methyl tetrahydrofuran, oxirane, 1,3-dioxolane, fluoro-ether, 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.

[0064] In other embodiments, the electrolyte can also include any one or mixture of several of an amine solvent, a sulfone solvent, and a nitrile solvent. The amine solvent includes at least one of N-methylacetamide, N-methylformamide, dimethylformamide, diethylformamide. The sulfone solvent includes at least one of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, chlorosulfoxide, dipropyl sulfone. The nitrile solvent includes at least one of acetonitrile, butanedinitrile, hexanedinitrile, pentanedinitrile. The electrolyte is preferably a high-voltage electrolyte with reduced acidity at high voltage, which can facilitate the transport of active ions, significantly reduce the side reactions on the electrode surface, and improve the stability of the battery.

[0065] In some embodiments, the electrolyte further includes an electrolyte salt, which can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0066] In some embodiments, the electrolyte can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that can improve certain performance of the battery, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature or low-temperature performance of the battery, etc.

[0067] In some embodiments, the current collector of the positive electrode tab can be provided with positive active layers on both sides, i.e., the positive electrode tab has two positive active layers facing away from each other, and similarly, the current collector of the negative electrode tab can be provided with negative active layers on both sides, i.e., the negative electrode tab has two negative active layers facing away from each other, to correspond to the positive electrode tab. When the positive electrode tab has positive active layers on both sides, the positive active layers on both sides can be selected to be different positive active materials. Different types of positive active materials and negative active materials have different advantages, and the battery cell can have better comprehensive performance by matching different active materials. Taking the positive active material as an example, some positive active materials have large capacity and can improve the energy density of the battery cell, and some positive active materials have good stability and can prolong the cycle life of the battery cell; if the two are combined, the energy density and cycle life can be improved at the same time.

[0068] However, different positive active materials generally cause performance differences between the two sides of the positive electrode tab. For example, different positive active materials have different voltage platforms. The voltage platform refers to the flat region on the voltage-capacity curve formed by the relationship between the voltage of the active material and the lithium ion insertion or extraction during the charging and discharging process of the battery. The type of active material affects the voltage platform of the active layer, resulting in different voltage platforms on both sides of the tab. At a high state of charge (SOC), the battery cell has a charging imbalance problem between the two sides of the tab, which causes the side with a low voltage platform of the positive electrode tab to be forced to overcharge, causing the active ions on the corresponding side of the negative electrode tab to be precipitated, resulting in the loss of active ions and directly deteriorating the cycle life of the battery.

[0069] Based on the above technical problems, the present application provides a battery cell, which includes a positive electrode tab and a negative electrode tab. The positive electrode tab includes a positive electrode base layer and first and second positive active layers arranged on opposite sides of the positive electrode base layer. The first positive active layer includes a first positive active material, and the second positive active layer includes a second positive active material. The charging platform voltage of the first positive active material is less than that of the second positive active material. The negative electrode tab includes a negative electrode base layer and first and second negative active layers arranged on opposite sides of the negative electrode base 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. 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 active layer / the active capacity of the first positive active layer, and the second active site ratio is the active capacity of the second negative active layer / the active capacity of the second positive active layer.

[0070] The positive electrode base layer and the negative electrode base layer are conductive base layers that can serve as current collectors. The conductive base layers can be metal foils or composite materials. For example, the conductive base layers can be metal foils such as aluminum foils or copper foils. The composite conductive materials can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite conductive materials can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.). The base layer can be a cuboid shape having a first surface and a second surface arranged opposite to each other along the thickness direction of the base layer, and the first surface and the second surface are respectively configured to carry the first positive electrode active layer and the second positive electrode active layer (the first negative electrode active layer and the second negative electrode active layer).

[0071] Referring to FIG. 3, FIG. 3 is a structural schematic diagram of an electrode assembly according to one or more embodiments. In FIG. 3, the positive electrode tab includes a positive electrode base layer 31 and a positive electrode active layer disposed on the positive electrode base layer 31, and specifically, the positive electrode active layer includes a first positive electrode active layer 31a and a second positive electrode active layer 31b disposed on opposite sides of the positive electrode base layer 31; the negative electrode tab includes a negative electrode base layer 32 and a negative electrode active layer disposed on the negative electrode base layer 32, and specifically, the negative electrode active layer includes a first negative electrode active layer 32a and a second negative electrode active layer 32b disposed on opposite sides of the negative electrode base layer 32. The first positive electrode active layer 31a corresponds to the first negative electrode active layer 32a and is separated by a separator 33; the second positive electrode active layer 31b corresponds to the second negative electrode active layer 32b and is separated by the separator 33.

[0072] 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, the first negative electrode active layer includes a first negative electrode active material, and the second negative electrode active layer includes a second negative electrode active material. The properties of the positive electrode active material and the negative electrode active material determine the performance of the battery cell. Among them, the energy density and the cycle life of the battery cell are the performances that are concerned. By adjusting the collocation of the positive electrode active material and the negative electrode active material, a battery cell with higher energy density and longer cycle life can be designed.

[0073] In an embodiment, the positive electrode tab provided by the present application uses active materials with different voltage platforms on both sides, wherein the active material with a lower voltage platform is selected as the active material of the first positive electrode active layer, and the 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 on the side of the first positive electrode active layer is less than the charging platform voltage of the active material used on the side of the second positive electrode active layer. The charging platform voltage of the positive electrode active material refers to the charging platform voltage of the primary cell composed of the positive electrode active material.

[0074] In an embodiment, the first positive electrode active layer comprises a first positive electrode active material, and the charging platform voltage of the first positive electrode active material is ≤3.5V; the second positive electrode active layer comprises a second positive electrode active material, and the charging platform voltage of the second positive electrode active material is >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. By using different positive electrode active materials in the positive electrode tab, the stability and capacity of the battery monomer can be improved; however, under this design, the voltage platforms on both sides of the positive electrode tab are different. The higher the voltage platform on the side of the positive electrode active layer, the lower the voltage platform on the side of the negative electrode active layer, and the higher the working voltage of the battery monomer. Since the voltage platform on the side of the first positive electrode active layer is lower than that on the side of the second positive electrode active layer, the second positive electrode active layer has a large capacity at a high SOC, which will cause continuous overcharging on the side of the first positive electrode active layer, resulting in lithium precipitation on the side of the first negative electrode active layer and loss of active ions. That is, at a high SOC, the side with a low voltage platform is forced to overcharge, causing lithium precipitation on the corresponding negative side and loss of active lithium, which directly deteriorates the cycle life of the battery monomer.

[0075] In an embodiment, the first active site ratio CB1 of the battery monomer is greater than the second active site ratio CB2, and 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.

[0076] The active site ratio of the battery monomer refers to the ratio of the active capacity of the opposite side of the negative electrode and the positive electrode under the same conditions at the same stage, which can be referred to as CB value (cell balance). The active capacity is the capacity of the single-sided active material coating layer in the unit area of the negative electrode tab or the positive electrode tab, and the unit is mAh / cm 2The active capacity can be obtained by the gram capacity of the active material in the negative electrode or the positive electrode, the surface density of the active material. Or, the active site ratio is the negative gram capacity * negative CW * actual active material loading in the negative formula / (positive gram capacity * positive CW * actual active material loading in the positive formula).

[0077] In the above embodiment, the first active site ratio = (first negative active material gram capacity * first negative active layer surface density * first negative active material content) / (first positive active material gram capacity * first positive active layer surface density * first positive active material content), and the second active site ratio = (second negative active material gram capacity * second negative active layer surface density * second negative active material content) / (second positive active material gram capacity * second positive active layer surface density * second positive active material content). The gram capacity refers to the ratio of the electric capacity that can be released by the active material inside the battery to the mass of the active material, and the gram capacity is related to the type of active material. The surface density is the mass of the active material in a unit area of the electrode sheet. The active material content refers to the proportion of the active material in the active layer. The CB value can be designed by considering the active site of the ion in the battery cell during operation to design the coating amount (surface density) of the positive and negative active materials. Specifically, considering the amount of lithium (or the amount of lithium active site) that the negative electrode releases during the operation of the battery cell, and the amount of lithium that the negative electrode needs to embed, the designed positive and negative electrode surface density ratio is more reasonable and can fully utilize the capacity of the active material. In an embodiment, the first active site ratio and the second active site ratio of the battery cell are both greater than 1. At this time, the negative active capacity is greater than the corresponding positive active capacity, which is beneficial to reduce the situation that lithium ions are precipitated without being accepted on the negative side of the battery cell.

[0078] In an 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 a range formed by any two of the above values, which can be 1.009-1.050, 1.050-1.100, 1.100-1.150, 1.150-1.201, etc.

[0079] In this embodiment, by adjusting the active site ratio on both sides of the electrode sheet, the problem of charging imbalance on both sides of the electrode sheet during charging (for example, overcharging on one side) 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.

[0080] In the application, the CB value of the battery monomer is adjusted, specifically, a relatively large first active site ratio is set, or the first active site ratio is set to be larger than the second active site ratio. On the basis that both the first active site ratio and the second active site ratio are greater than 1, the first active site ratio is larger, so the active capacity of the first negative active layer is larger than the active capacity of the first positive active layer, thereby effectively reducing the precipitation of active ions of the first negative active layer, reducing the loss of active ions, and improving the cycle life of the battery. The voltage platform on the side of the first positive active layer is lower than the voltage platform on the side of the second positive active layer. Through the matching design of the active site ratio and the voltage platform of the battery monomer, a larger active site ratio is set on the side of the lower voltage platform to provide sufficient active ion vacancies to receive the active ions provided by the positive active layer, reduce the precipitation of active ions on the side of the negative electrode sheet, and improve the cycle life of the battery monomer.

[0081] In an 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 a range formed by any two of the above values, which can be 1.12-1.14, 1.14-1.20, 1.20-1.25, 1.25-1.30, etc.

[0082] In an 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 a range formed by any two of the above values, which can be 1.08-1.09, 1.09-1.10, 1.10-1.11, 1.11-1.12, etc.

[0083] At this time, the negative active capacity ratio is larger than the active capacity of the corresponding positive electrode, and the negative active layer can provide sufficient active ion vacancies to receive the active ions provided by the positive active layer, which is beneficial to reduce the precipitation of active ions on the negative side of the battery monomer without receiving source, reduce the loss of active ions, and improve the cycle life of the battery monomer.

[0084] At the same time, the values of the first active site ratio and the second active site ratio are moderate, which can reduce the irreversible capacity loss of the battery monomer, and the problems of low battery capacity and reduced energy density caused by the irreversible capacity loss.

[0085] According to the calculation formula of the active site ratio, under the condition that the types and contents of the active materials are determined, the active site ratio on the corresponding side of the electrode sheet can be changed by adjusting the area density of the active layer, so as to reduce the loss of active ions and improve the cycle life of the battery.

[0086] In an embodiment, the first negative active layer comprises a first negative active material, and the capacity of the first negative active material is greater than 375 mAh / g. The battery cell is designed such that the positive active layer with a lower charging platform voltage is matched with the negative active layer with a high-capacity negative active material, i.e., the first negative active layer corresponding to the first positive active layer is selected to use an active material with a higher capacity, and specifically, an active material with a capacity greater than 375 mAh / g can be selected, for example, a silicon particle material with a capacity of 4200 mAh / g is selected as the active material of the first negative active layer. Through this design, the lithium precipitation caused by overcharging of the first positive active layer can be improved, the loss of active lithium can be improved, and the cycle life of the battery cell can be improved.

[0087] In an embodiment, the coating amount of the first negative active layer is less than 0.16 g / 1540.25 mm 2 . Alternatively, the coating amount of the first negative active layer is 0.12-0.15 g / 1540.25 mm 2 . For example, it can be 0.120 g / 1540.25 mm 2 , 0.125 g / 1540.25 mm 2 , 0.16 g / 1540.25 mm 2 , 0.130 g / 1540.25 mm 2 , 0.135 g / 1540.25 mm 2 , 0.140 g / 1540.25 mm 2 , 0.145 g / 1540.25 mm 2 , 0.150 g / 1540.25 mm 2 , 0.155 g / 1540.25 mm 2 , 0.158 g / 1540.25 mm 2 , etc. In this embodiment, the coating amount (CW) refers to the single-sided active material coating mass (grams, milligrams) under the area of 1540.25 mm 2 . By selecting a high-capacity negative active material as the active material of the first negative active layer, the coating amount of the active material in the first negative active layer can be reduced, thereby improving the kinetics of the first negative active layer, improving the lithium precipitation caused by overcharging of the first positive active layer, improving the loss of active lithium, and improving the cycle life of the battery cell. In this embodiment, from the capacity of the active material, the first positive active layer is matched with a high-capacity negative electrode, which can effectively improve the negative electrode capacity without increasing the CW, thereby improving the kinetics of the first negative active layer and improving the problem of loss of active lithium. In other words, without changing the original CB design, the CW can be greatly reduced (from 0.16 to 0.14, unit g / 1540.25 mm 2 ), and the kinetics of the negative electrode side is improved.

[0088] In an embodiment, the active material type of the second negative active layer in the battery cell provided by the present application is not limited, and a high-capacity material such as a silicon material can be selected; or a relatively low-capacity material such as a graphite material can be selected. This is because the voltage plateau on the side of the second positive active layer corresponding to the second negative active layer is relatively high, so that the lithium precipitation phenomenon on the side of the second negative active layer is weak, and no special design is required from this perspective, and the appropriate active material can be selected from the perspective of conventional capacity, stability, etc.

[0089] In an embodiment, when different active materials are used, the type and proportion of the positive active material can be adjusted to control the voltage plateau of the positive active layer, so as to reduce the difference between the voltage plateaus on the sides of the first positive active layer and the second positive active layer. In turn, the problem of charge imbalance on both sides of the electrode sheet (for example, overcharging on one side) is improved, thereby effectively reducing the precipitation of active ions, reducing the loss of active ions, and improving the cycle life of the battery cell.

[0090] Taking a lithium battery as an example, the commonly used positive active materials include polyanion phosphate compound type positive active materials and ternary material type positive active materials.

[0091] The polyanion phosphate compound type positive active material takes phosphate ion (PO4 3- ) as the main structural unit, and includes lithium iron phosphate LiFePO4, also known as lithium iron phosphate (LFP); lithium manganese iron phosphate (LMAP), etc. The polyanion phosphate compound has good thermal stability and structural stability, which helps to improve the safety of the battery; generally exhibits good cycle life, is relatively stable in charge and discharge cycles, and can maintain a relatively long battery life; has a relatively low voltage plateau, for example, the charge and discharge plateau voltage of LFP is between 3.2-3.4V; contains no or relatively few toxic heavy metal elements, and is relatively environmentally friendly; the preparation process is relatively simple, and the raw materials are relatively inexpensive.

[0092] The ternary material type positive active material refers to a compound containing nickel (Ni), cobalt (Co), and manganese (Mn) (NCM), or a compound containing nickel (Ni), cobalt (Co), and aluminum (Al), including lithium nickel cobalt manganese oxide material (NCM), etc. Due to the advantages of combining different metal elements and the relatively high voltage plateau, the ternary material type positive active material generally has a relatively high energy density; different ternary materials can achieve different electrochemical properties (including voltage plateau) by adjusting the proportion of nickel, cobalt, and manganese (or nickel, cobalt, and aluminum), and the most suitable proportion can be selected according to the specific application requirements; the cycle life is relatively short, and the safety performance is relatively low; some elements of the ternary material type positive active material, such as cobalt, are rare metals, which makes the manufacturing cost of this type of battery relatively high.

[0093] In an embodiment, the first positive electrode active layer comprises a polyanion phosphate compound type positive electrode active material, and the second positive electrode active layer comprises a ternary material type positive electrode active material. By simultaneously matching the above two materials, the advantages of the two 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.

[0094] The charge platform voltage of LFP is 3.4V, and the discharge platform voltage is 3.2V; the discharge platform voltage of LMAP is 3.3-3.9V, which can be adjusted according to different Mn content, and the more the Mn content, the higher the discharge platform voltage; the discharge platform voltage of NCM is 3.65-3.8V, which can be adjusted according to different Ni content, and the more the Ni content, the higher the discharge platform voltage. Therefore, the type and matching ratio of the positive electrode active material can be adjusted to regulate the voltage platform of the positive electrode active layer, so as to reduce the difference between the voltage platforms of the first positive electrode active layer side and the second positive electrode active layer side.

[0095] In an embodiment, the first positive electrode active layer comprises lithium iron phosphate and a second type of polyanion material, the charge platform voltage of the second type of polyanion material is greater than that of lithium iron phosphate, and the mass ratio of the second type of polyanion material to the total amount of lithium iron phosphate and the second type of polyanion material is 10%-40%. For example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc. Or a range composed of any two of the above numerical values, such as 10%-20%, 20%-40%, 30%-40%, etc.

[0096] The second type of polyanion material can include lithium manganese iron phosphate, that is, the first positive electrode active layer selects a mixed material of lithium iron phosphate and lithium manganese iron phosphate; by adding lithium manganese iron phosphate with a higher voltage platform, the voltage platform of the first positive electrode active layer side can be improved as a whole, so as to reduce the difference between the voltage platforms of the first positive electrode active layer side and the second positive electrode active layer side, improve lithium precipitation caused by overcharging of the first positive electrode active layer, improve active lithium loss, and improve the cycle life of the battery cell.

[0097] In an embodiment, the first positive electrode active layer comprises lithium iron phosphate and a first type of polyanion material, the electronic conductivity of the first type of polyanion material is less than that of lithium iron phosphate, and the mass ratio of the first type of polyanion material to the total amount of lithium iron phosphate and the first type of polyanion material is 30%-85%. Alternatively, the mass ratio of the first type of polyanion material to the total amount of lithium iron phosphate and the first type of polyanion material is 40%-65%. Specifically, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc.

[0098] wherein LFP is a semiconductor material, the electronic conductivity is in the range of 10 -9 S / cm; LMAP belongs to an insulator material, the electronic conductivity is in the range of 10 -13 S / cm; and the ternary material (NCM) is a good conductor material, the electronic conductivity is in the range of 10 -3 S / cm. When the first positive active layer selects one or more polyanionic phosphate compounds with poor conductivity as the active material, and the second positive active layer selects one or more ternary materials with good conductivity as the active material; due to the difference in conductivity, the second active layer with good conductivity often has large current shunt and large equivalent rate, causing excessive use, leading to accelerated use of the second active layer material, structural collapse and damage, material loss, and deterioration of the battery life.

[0099] The first type of polyanionic material can include lithium iron manganese phosphate, that is, the first positive active layer selects a mixed material of lithium iron phosphate and lithium manganese iron phosphate. In this embodiment, considering the battery voltage platform and internal resistance, the content of the first type of polyanionic material in the first positive active layer is limited. The incorporation of the first type of polyanionic material can increase the charging platform voltage on the side of the first positive active layer and reduce the voltage platform difference on the side of the second positive active layer. 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 side of the first positive active layer and worsen the kinetic ability on the side of the first positive active layer, thereby causing large equivalent rate on the side of the second positive active layer and worsening the material loss on the side of the second positive active layer. Therefore, considering the charging voltage platform and internal resistance, 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 adjusted to 30%-85% to improve the loss of active lithium and improve the cycle life of the battery.

[0100] In an embodiment, the first positive active layer includes a first type of polyanionic material, and the first type of polyanionic material includes manganese elements, wherein the mass ratio of manganese elements to the total amount of metal elements is 0.05-0.75; optionally, the mass ratio of manganese elements to the total amount of metal elements 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.

[0101] The content of Mn in the polyanion material is limited, which can effectively improve the conductivity of the first positive active layer side. The increase of the content of Mn will reduce the conductivity of the polyanion material to some extent, and will worsen the internal resistance of the first positive active layer side. The decrease of the content of Mn will reduce the voltage platform of the first positive active layer side to some extent. Therefore, considering the charging voltage platform and internal resistance, the mass fraction of manganese in the first polyanion material is controlled to be 0.05-0.75 of the total amount of metal elements, so as to improve the loss of active lithium and improve the cycle life of the battery cell.

[0102] In an embodiment, the first positive active layer includes a compound of Li 1+x Mn 1-y A y P 1-z E z O4, wherein x is any value in the range of -0.100-0.100, y is any value in the range of 0.001-1.000, z is any value in the range of 0.001-0.100, A is selected from one or more elements of 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 of B, Si, N, S, F, Cl and Br.

[0103] Through the above setting, the values of x, y and z satisfy the following conditions: to keep the chemical formula electrically neutral. The element A doped at the manganese site of lithium manganese iron phosphate helps to reduce the lattice change rate of lithium manganese iron phosphate during lithium extraction, improve the structural stability of lithium manganese iron phosphate positive electrode material, greatly reduce the dissolution of manganese and reduce the oxygen activity on the particle surface. The element E doped at the phosphorus site helps to change the difficulty of Mn-O bond length change, thereby reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the battery cell.

[0104] In an embodiment, A is selected from one or more elements of Fe, Ti, V, Ni, Co and Mg; and / or E is selected from one element of B, Si, N and S. Through the above setting, the structural stability of the positive electrode active material and the rate performance of the battery cell can be further improved.

[0105] In an embodiment, the active material of the first positive active layer has a core-shell structure, and the coating shell layer of the core-shell structure includes one or more layers of pyrophosphate, phosphate and carbon. 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.

[0106] In the above core-shell structure, the migration barrier of transition metal in pyrophosphate is high (>1eV), which can effectively inhibit the dissolution of transition metal. The phosphate has excellent lithium ion conductivity and can reduce the content of surface lithium. The carbon layer can effectively improve the conductivity and desolvation ability of LiMnPO4, and also can play a "barrier" role to further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the electrolyte to the active material.

[0107] In an embodiment, the second positive electrode active layer comprises a first ternary material, and the first ternary material comprises at least nickel element, wherein the mass percentage of the nickel element in the total amount of metal elements is greater than or equal to 0.7.

[0108] In an embodiment, the second positive electrode active layer comprises a second ternary material, and the second ternary material comprises at least nickel element, wherein the mass percentage of the nickel element in the total amount of metal elements is 0.3-0.7.

[0109] In an embodiment, the second positive electrode active layer comprises a third ternary material, and the third ternary material comprises at least cobalt element, wherein the mass percentage of the cobalt element in the total amount of metal elements is 3%-15%.

[0110] In an embodiment, the second positive electrode active layer comprises a third ternary material, and the third ternary material comprises at least cobalt element, wherein the mass percentage of the cobalt element in the total amount of metal elements is 3%-15%. For example, it can be 3%, 5%, 8%, 10%, 12%, 15%, or a range formed by any two of the above values, such as 3%-5%, 3%-8%, 10%-12%, 12%-15%, etc.

[0111] Each element in the ternary material plays an important role, and the characteristics of each element also restrict the battery performance. Taking nickel-cobalt-manganese ternary material as an example: Ni shows high capacity and low safety; Co shows high cost and high stability, Co can stabilize the layered structure of the material and improve the cycle and rate performance of the material; Mn shows high safety and low cost.

[0112] When the second positive electrode active layer selects a ternary material with high nickel content, the capacity of the second positive electrode active layer causing overcharging of the first positive electrode active layer is greater. Further, the kinetics of the ternary material is better, and limiting the Co content in the ternary material to a lower level can relatively weaken the rate performance of the ternary material, thereby reducing the kinetics performance of the second positive electrode active layer, narrowing the difference in kinetics performance between the two sides of the positive electrode sheet, improving the matching degree of the kinetics performance of the two sides of the positive electrode sheet, improving the problem that the side with better kinetics performance is overused during the charging and discharging process of the battery monomer, slowing down the decay of NCM, and ultimately prolonging the cycle life of the battery monomer.

[0113] In the above embodiment, since the second positive electrode active layer includes a ternary material type positive electrode active material, the kinetic performance of the second positive electrode active layer is better than that of the polyanion type phosphate compound type positive electrode active material of the first positive electrode active layer. In the charging and discharging process of the battery cell, the second positive electrode active layer side is often overused. Therefore, the balance of the two sides of the electrode tab can be adjusted by adjusting the nickel content and the cobalt content in the ternary material. It can be single adjustment of one of the nickel content and the cobalt content, or it can be simultaneous adjustment of the nickel content and the cobalt content.

[0114] In an embodiment, the difference between the capacity release value of the first positive electrode active layer above 3.9V and the capacity release value of the second positive electrode active layer above 3.9V is less than 25%. By controlling the difference between the SOC capacity release of the first positive electrode active layer side and the second positive electrode active layer side above 3.9V within 25%, the loss of active lithium caused by overcharging of the first positive electrode active layer side can be effectively alleviated, and the cycle life of the battery cell is improved.

[0115] In an embodiment, the first negative electrode active material includes one or more of a silicon particle material, a silicon-oxygen material, a silicon-carbon material, and a lithium metal material. That is, the first negative electrode active material with a capacity greater than 375mAh / g includes one or more of a silicon particle material with a capacity release of 4200mAh / g, a silicon-oxygen material with a capacity release of 2600mAh / g, a silicon-carbon material with a capacity release of 1800mAh / g, and a lithium metal material with a capacity release of 3860mAh / g. In other embodiments, it can also be one or more of a carbon-based negative electrode, a sulfur-containing negative electrode, a metal negative electrode, an alloy negative electrode, and an oxide negative electrode.

[0116] In an embodiment, the first negative electrode active layer further includes a carbon material, such as a graphite material. That is, the first negative electrode active layer includes a mixture of multiple materials, such as a mixture of silicon material and graphite material. Alternatively, the first negative electrode active layer does not completely use high-capacity active materials, but is a mixture of multiple materials.

[0117] In an embodiment, the first negative electrode active layer includes a silicon material, and the mass fraction of the silicon material in the total amount of active materials in the first negative electrode active layer is 0.01%-5.5%. Optionally, the mass fraction of the silicon material in the total amount of active materials in the first negative electrode active layer is 0.5%-3.5%. For example, the content of the 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. Through such a setting, the harm caused by the large volume expansion of the silicon negative electrode can be reduced on the basis of improving the loss of active lithium, the stability of the negative electrode structure is improved, and the cycle life of the battery cell is improved as a whole.

[0118] In an embodiment, the first negative active layer further comprises a carbon material, such as a graphite material; that is, the first negative active layer comprises a mixture of multiple materials, such as a mixture of silicon material and graphite material, and the content of silicon material in the mixed material is controlled to be 0.01%-5.5%. Alternatively, the first negative active layer is not entirely composed of the first negative active material with a capacity greater than 375 mAh / g, but can also contain a relatively low-capacity active material, such as a graphite material (discharge capacity of about 320-380 mAh / g, and charge capacity of about 350-400 mAh / g). As known from the foregoing, the selection of active materials of the first and second positive active layers will affect the difference between the two sides of the positive electrode sheet, and therefore, different negative active materials can be matched according to the selection of active materials on the positive side.

[0119] In an embodiment, the positive active material of the second positive active layer at least comprises nickel element, and the mass fraction of nickel element in the total amount of metal elements in the positive active material of the second positive active layer is ≥0.7, and the mass fraction of silicon material in the total amount of active materials in the first negative active layer is 1.5%-3.5%.

[0120] In an embodiment, the positive active material of the second positive active layer at least comprises nickel element, and the mass fraction of nickel element in the total amount of metal elements in the positive active material of the second positive active layer is 0.3-0.7, and the mass fraction of silicon material in the total amount of active materials in the first negative active layer is 0.5%-1.5%.

[0121] In an embodiment, the positive active material of the second positive active layer at least comprises nickel element, and the mass fraction of nickel element in the total amount of metal elements in the positive active material of the second positive active layer is ≥0.7, and the mass fraction of silicon material in the total amount of active materials in the first negative active layer is 1.5%-3.5%.

[0122] In the above embodiments, the selection of different active materials on both sides of the positive electrode sheet causes problems such as lithium precipitation and cycle life. The present application provides solutions from multiple perspectives. On the one hand, from the perspective of active capacity, the ratio of active sites on both sides of the electrode sheet can be adjusted to improve the charging imbalance on both sides of the electrode sheet. By matching active materials with different capacities, the positive active layer with a lower charging platform voltage can be matched with a negative active layer with a high-capacity negative electrode material in the battery cell to improve the kinetics on the side of the first negative active layer and to improve the problem of lithium precipitation caused by overcharging of the first positive active layer. On the other hand, from the perspective of kinetics, 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 sheet. In addition, from the perspective of the conductivity of the active material, the matching of the active material can be adjusted to achieve kinetic balance on both sides of the electrode sheet. The above multiple embodiments can be implemented individually, i.e., any one of the above solutions can be used to improve the problems caused by the selection of different active materials on both sides of the positive electrode sheet, such as lithium precipitation and cycle life. Alternatively, multiple embodiments can be combined, i.e., two or more conditions can be adjusted simultaneously to improve the problems caused by the selection of different active materials on both sides of the positive electrode sheet, such as lithium precipitation and cycle life.

[0123] The battery provided by the present application includes the battery cell provided by any of the above embodiments.

[0124] The present application also provides an electrochemical device comprising the battery provided by the present application.

[0125] In some embodiments, the use of the electrochemical device of the present application is not particularly limited and can be used in any electronic device known in the art. The battery disclosed in the embodiments of the present application can be used in a power consumption device using a battery as a power source or a variety of energy storage systems using a battery as an energy storage element. That is, a power consumption device is provided. In some embodiments, the power consumption device of the present application can be used in, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a ship, a spacecraft, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0126] The power consumption device can select a battery cell, a battery module, or a battery pack according to its use requirements.

[0127] Please refer to FIG. 4, which is a structural schematic diagram of a vehicle according to one or more embodiments. The vehicle 1000 can be a fuel automobile, a gas automobile, or a new energy automobile, which can be a pure electric vehicle, a hybrid vehicle, or a range extended vehicle, etc. The vehicle 1000 is internally provided with a battery 100, which can be arranged at the bottom, head, or tail of the vehicle 1000. The battery 100 can be used for power supply of the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further include a controller 200 and a motor 300, the controller 200 being used to control the battery 100 to supply power to the motor 300, for example, for the working power demand of the vehicle 1000 during starting, navigation, and driving.

[0128] In some embodiments of the present application, the battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, instead of or partially instead of fuel or natural gas to provide driving power for the vehicle 1000.

[0129] The beneficial effects of the present application will be further described below in combination with embodiments.

[0130] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application more clear, the following will be further described in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0131] I. Preparation of battery monomer

[0132] Embodiment 1:

[0133] (1) Preparation of positive electrode sheet

[0134] The positive electrode active materials of the first positive electrode active layer and the second positive electrode active layer are respectively mixed with polyvinylidene fluoride (PVDF) and conductive carbon, and a certain amount of N-methyl pyrrolidone (NMP) is added, and the mass ratio of the positive electrode active material, the binder, and the conductive agent is 96:3:1. The mixture is stirred in a drying room to form a uniform slurry, the viscosity is controlled to be 3000 mPa·S-10000 mPa·S, and the slurry is coated on the two opposite surfaces of the positive electrode substrate, respectively. After drying treatment, the positive electrode sheet is prepared, and the two surfaces of the positive electrode sheet substrate are provided with active layers, which are respectively referred to as the first active layer (A surface) and the second active layer (B surface).

[0135] (2) Preparation of negative electrode sheet

[0136] The negative active material of the first negative active layer and the second negative active layer is mixed with sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and conductive carbon, and then added into a certain amount of deionized water, and the mass ratio of the negative active material: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive agent is 97: 1: 1: 1, and then stirred to form a uniform slurry, and the viscosity is controlled at 3000 mPa·S-10000 mPa·S. The slurry is coated on the two opposite sides of the copper foil (positive electrode substrate) respectively, and then dried to form a negative electrode sheet. The two sides of the negative electrode sheet substrate have active layers, which are referred to as the first active layer (A side) and the second active layer (B side).

[0137] (3) Preparation of battery monomer

[0138] The prepared positive electrode sheet, negative electrode sheet and separator (polyethylene porous polymer film) are used to prepare a battery monomer. The battery monomer is hot-pressed at 90°C, and then the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses an aluminum tab, and the negative electrode uses a copper tab. The positive and negative electrode tabs are located on the same side of the battery monomer. The battery monomer after welding of the tabs is placed in an aluminum shell of appropriate size for soft linking and top cover welding. The battery monomer is vacuum dried at 175°C for 24 hours, and then electrolyte is injected and sealed to obtain a non-charged battery monomer. The non-charged battery monomer is sequentially subjected to processes such as standing, formation, aging, exhaust, two-sealing, capacity testing, etc. to obtain a lithium ion battery product.

[0139] Examples 2-6:

[0140] On the basis of Example 1, the type and content of high-capacity negative active material in the first negative active layer are changed, and the details are shown in Table 1.

[0141] Comparative Examples 1-2:

[0142] On the basis of Example 1, the active material used in the first negative active layer is changed, and only graphite material is used without adding high-capacity active material. The details are shown in Table 1.

[0143] II. Performance test and parameter test

[0144] (1) 25°C cycle life

[0145] At 25°C, when the constant current charging is carried out at 1C rate current to 4.2V, the constant voltage charging is carried out, and when the charging current decreases to 0.05C rate current, the charging is stopped. When the constant current discharging is carried out at 1C rate current to 2.8V, the discharging is stopped. The charging and discharging cycle is repeated until the battery capacity decreases to 80% of the initial capacity, and the cycle number at this time is taken as the 25°C cycle life of the secondary battery.

[0146] (2) Element (nickel, cobalt, manganese, silicon) content test in active material

[0147] The ICP (Inductive Coupled Plasma Emission Spectrometer) test is used. The specific operation is as follows: the powder to be tested is placed in a microwave digestion instrument (for example, CEM-Mars6) for digestion, and the solution after digestion is introduced into an ICP tester (for example, ICAP7400) for testing. By comparing the element concentration in the standard solution, the element content in the material can be calculated. ICP can also calculate the proportion of two materials in the mixed positive electrode. By dividing the ICP test result by the element molar mass, the corresponding proportion of each element can be calculated, and then the proportion of each material can be determined. Then the proportion of each element in the NCM material can be calculated.

[0148] Among them, the battery is disassembled to obtain the pole piece, the coated layer material of the pole piece is scraped, and the binder, dispersant and other organic materials in the material are removed by using an organic solvent or using a burning method to obtain inorganic materials containing active materials. Scanning electron microscopy or particle size analysis is used to determine that the material contains several active materials and qualitatively determine the material type. Then the content of some characteristic elements in the material is tested, and the proportion of each material is calculated by using the element content. For the negative pole piece, the proportion of the silicon negative electrode can be obtained by testing the content of carbon and silicon elements. For the positive pole piece, if it is a mixed positive electrode of lithium iron phosphate and lithium manganese iron phosphate, the proportion of lithium iron phosphate and lithium manganese iron phosphate can be calculated by the content of manganese and iron. For ternary materials, the content of ternary materials can be calculated by the content of nickel element.

[0149] (3) Test of charging platform voltage

[0150] The positive active material is obtained, and a primary cell is assembled. The battery is charged and discharged once, discharged at a rate of 0.33C to 2.5V in constant current mode, and then rested for 10 min. Charged at a rate of 0.33C to the full charge voltage +0.05V, and then rested for 10 min. The charging capacity C1 and the charging energy E1 are obtained. Rest for 10 min. Discharge at a rate of 0.33C to 2.5V, and then rest for 10 min. The discharge capacity C2 and the discharge energy E2 are obtained. The charging platform voltage = the charging energy E1 / the charging capacity C1, and the discharge platform voltage = the discharge energy E2 / the discharge capacity C2.

[0151] (4) Test of gram capacity

[0152] Take the anode electrode piece in full and rub one side, and lithium metal to form a button cell. Discharge to 5 mV at 0.05C rate in DC current mode; charge to 50 μA in DC voltage mode; stand for 5 min; charge to 2.0V in constant current mode again; the above steps are cycled for 2 times, and the capacity value of the second cycle is taken to calculate the gram capacity.

[0153] (5) Test of coating weight (CW)

[0154] Disassemble the battery, obtain the electrode piece, weigh m1, wipe off the active layer on one side, weigh m2, wipe off the active layer on both sides, weigh 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 weight.

[0155] (6) Capacity release test

[0156] Place the battery at 25℃ for 30 min, and charge to 4.2V at 0.04C constant current;

[0157] Stand for 1 hour at 25℃, and discharge to 3V at 0.04C constant current;

[0158] Stand for 1 hour at 25℃, and charge to 4.2V at 0.04C constant current;

[0159] Stand for 1 hour at 25℃, and discharge to 3V at 1C constant current;

[0160] Stand for 1 hour at 25℃, and charge to 4.2V at 0.04C constant current;

[0161] Stand for 1 hour at 25℃, and discharge to 3V at 3C constant current;

[0162] Stand for 1 hour at 25℃, and charge to 4.2V at 0.04C constant current;

[0163] Stand for 1 hour at 25℃, and discharge to 3V at 5C; stand for 1 hour at 25℃.

[0164] Among them, disassemble the battery, obtain the positive electrode piece, scrape off the second positive active layer, and use the positive electrode piece with only the first positive active layer to form a primary battery, and test the capacity release value above 3.9V; similarly, disassemble the battery, obtain the positive electrode piece, scrape off the first positive active layer, and use the positive electrode piece with only the second positive active layer to form a primary battery, and test the capacity release value above 3.9V (for example, 4.2V); calculate the difference of the capacity release values.

[0165] (7) Test of CB value of electrode piece:

[0166] Discharge the battery monomer at 0.1C to 2.5V, disassemble, take the same area size of the positive and negative electrodes to be tested, wherein the positive electrode is divided into two samples, one sample is the positive electrode tab B scraped off the first positive active layer and only the second positive active layer is reserved, and one sample is the positive electrode tab A scraped off the second positive active layer and only the first positive active layer is reserved, respectively assembled with lithium metal pieces into reverse type batteries, and the discharge capacity of the corresponding tab is tested at 0.1C rate, and is respectively recorded as the positive electrode tab capacity Cap-A, Cap-B, and the negative electrode tab capacity Cap-C. Then the tab capacity ratio of the negative electrode to the positive electrode Cap-C / Cap-A, Cap-C / Cap-B is the CB value of the test tab.

[0167] III. Test result analysis

[0168] Table 1 Structure and performance of battery monomers of each example and comparative example

[0169] Note: "Positive A surface" refers to the positive active material contained in the first positive active layer; "positive B surface" refers to the positive active material contained in the second positive active layer; "negative A surface" refers to the negative active material contained in the first negative active layer; "negative A surface content" refers to the content of high-capacity negative active material in the first negative active layer, such as the content of silicon material in Example 1 is 1.50%; negative A surface CW refers to the coating amount of the active material in the first negative active layer, unit is 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 a ternary material with a charging platform voltage of 3.75V and a nickel content of 55%, and the nickel content of 55% refers to that the nickel accounts for 55% of the total mass of metal elements in the ternary material.

[0170] From the above example results, it can be seen 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 adding high-capacity negative active material in the first negative active layer, the negative electrode capacity can be effectively improved without increasing the CW, or in other words, the coating amount of the active material in the first negative active layer can be reduced, thereby improving the kinetics of the first negative active layer and improving the cycle life of the battery monomer.

[0171] Examples 7-11:

[0172] On the basis of Example 1, the type of positive active material in the first positive active layer is changed, and lithium iron phosphate and manganese lithium iron phosphate are selected for mixing, and the content of manganese element in the manganese lithium iron phosphate is regulated, which is specifically shown in Table 2.

[0173] Examples 12-16:

[0174] On the basis of Example 1, the type of positive electrode active material in the first positive electrode active layer is changed, and lithium iron phosphate and lithium manganese iron phosphate are selected for mixing, while the content of lithium manganese iron phosphate is regulated. For details, see Table 2.

[0175] Examples 17-21:

[0176] On the basis of Example 1, the type of positive electrode active material in the first positive electrode active layer is changed, and lithium iron phosphate and lithium manganese iron phosphate are selected for mixing, while the content of cobalt element in the ternary material in the second positive electrode active layer is regulated. For details, see Table 2.

[0177] Table 2: Structure and performance of battery cells of each example and comparative example

[0178] 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; LMAP ratio refers to the proportion of LMAP in 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 nickel content of 55% and a charging platform voltage of 3.75V, and the nickel content of 55% refers to the total mass of nickel accounting for 55% of the total mass of metal elements in the ternary material.

[0179] As can be seen from the above example results, 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, the mixed material of lithium iron phosphate and lithium manganese iron phosphate is selected for the first positive electrode active layer, and the incorporation of lithium manganese iron phosphate can increase the charging platform voltage on the side of the first positive electrode active layer and reduce the voltage platform difference with the side of the second positive electrode active layer. At the same time, the conductivity of lithium manganese iron phosphate is poor, and if the content is too high, it will worsen the internal resistance of the side of the first positive electrode active layer and worsen the kinetic ability of the side of the first positive electrode active layer, thereby causing the equivalent rate of the side of the second positive electrode active layer to be large and the material loss of the side of the second positive electrode active layer to be worsened. Therefore, considering the charging voltage platform and internal resistance factors, regulating the mass ratio of lithium manganese iron phosphate in the total amount of lithium iron phosphate and lithium manganese iron phosphate to be 30%-85% can improve the cycle life of the battery cell.

[0180] Further, by limiting the Mn content in lithium manganese iron phosphate, the conductive capacity of the first positive electrode active layer side can be effectively improved. An increase in Mn content will reduce the conductivity of acid manganese iron lithium to some extent, which will worsen the internal resistance of the first positive electrode active layer side. A decrease in Mn content will reduce the voltage platform of the first positive electrode active layer side to some extent. Therefore, considering the charging voltage platform and internal resistance, regulating the mass ratio of manganese to the total amount of metal elements in lithium manganese iron phosphate to 0.05-0.75 can improve the cycle life of the battery monomer.

[0181] Furthermore, the kinetics of the ternary material is good. Limiting the Co content in the ternary material to a lower level can relatively weaken the rate performance of the ternary material, thus reducing the kinetics performance of the second positive electrode active layer, narrowing the difference in kinetics performance between the two sides of the positive electrode sheet, improving the matching degree of the kinetics performance of the two sides of the positive electrode sheet, improving the problem that the side with better kinetics performance is overused during the charging and discharging process of the battery monomer, slowing down the decay of NCM, and ultimately prolonging the cycle life of the battery monomer.

[0182] Examples 22-28:

[0183] On the basis of Example 14, the first active site ratio, the second active site ratio, and the ratio of the battery monomer were set, and the details are shown in Table 3.

[0184] Comparative Example 3:

[0185] On the basis of Examples 22-28, the first active site ratio and the second active site ratio of the battery monomer were set to be the same, and the details are shown in Table 3.

[0186] Table 3: Structure and performance of battery monomer of each example and comparative example

[0187] Note: "Positive A surface" refers to the positive electrode active material contained in the first positive electrode active layer; "positive B surface" refers to the positive electrode active material contained in the second positive electrode active layer; LMAP ratio refers to the proportion of LMAP in 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 a ternary material with a nickel content of 55% and a charging platform voltage of 3.75V, and the nickel content of 55% refers to the total mass of nickel accounting for 55% of the total mass of metal elements in the ternary material.

[0188] The above example results can show that when the charge platform voltage of the positive active material in the first positive active layer is ≤3.5V, and the charge platform voltage of the positive active material in the second positive active layer is greater than 3.5V, a relatively large first active site ratio is set, or the first active site ratio is greater than the second active site ratio. On the basis that the first active site ratio and the second active site ratio are both greater than 1, the first active site ratio is greater, so the active capacity of the first negative active layer is greater than the active capacity of the first positive active layer, thereby effectively reducing the active ion precipitation of the first negative active layer, reducing the loss of active ions, and improving the cycle life of the battery.

[0189] Examples 29-31:

[0190] The difference between the capacity release value of the first positive active layer above 3.9V and the capacity release value of the second positive active layer above 3.9V is less than 25%, as shown in Table 4.

[0191] Comparative Example 4:

[0192] The difference between the capacity release value of the first positive active layer above 3.9V and the capacity release value of the second positive active layer above 3.9V is greater than 25%, as shown in Table 4.

[0193] Table 4: Structure and performance of battery cells of each example and comparative example

[0194] Note: The difference in capacity release value refers to the difference between the capacity release value of the first positive active layer above 3.9V and the capacity release value of the second positive active layer above 3.9V.

[0195] The above example results can show that when the charge platform voltage of the positive active material in the first positive active layer is ≤3.5V, and the charge 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 release above 3.9V between the first positive active layer side and the second positive active layer side 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 is improved.

[0196] The above is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A battery cell, wherein, The battery cell comprises: a positive electrode tab, comprising a positive electrode base layer, a first positive electrode active layer and a second positive electrode active layer arranged on opposite sides of the positive electrode base layer, the first positive electrode active layer comprising a first positive electrode active material, and the second positive electrode active layer comprising 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; a negative electrode tab, comprising a negative electrode base layer, a first negative electrode active layer and a second negative electrode active layer arranged on opposite sides of the negative electrode base layer, the first negative electrode active layer being opposite to the first positive electrode active layer, and 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, wherein the ratio CB1:CB2 of the first active site ratio CB1 and the second active site ratio CB2 of the battery cell is 1.009-1.

201.

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

12.

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

5. The battery cell according to any one of claims 1 to 4, wherein the first negative electrode active layer comprises 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, wherein The coating amount of the first negative electrode active layer is less than 0.16 g / 15 40.25 mm 2 .

7. The battery cell according to claim 6, wherein 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, wherein the first negative electrode active layer comprises a silicon material, and the mass fraction of the silicon material in the total amount of active materials in the first negative electrode active layer is 0.01%-5.5%.

9. The battery cell according to claim 8, wherein the mass fraction of the silicon material in the total amount of active materials in the first negative electrode active layer is 0.5%-3.5%.

10. The battery cell according to claim 8 or 9, wherein the second positive electrode active layer comprises at least a nickel element, and the mass fraction of the nickel element in the total amount of metal elements in the positive electrode active material of the second positive electrode active layer is 0.3-0.7, and the mass fraction of the silicon material in the total amount of active materials in the first negative electrode active layer is 0.5%-1.5%.

11. The battery cell according to any one of claims 1 to 10, wherein The positive active material of the second positive active layer comprises at least cobalt element, and the mass percentage of cobalt element in the total amount of metal elements in the positive active material of the second positive active layer is 3%-15%.

12. The battery cell according to any one of claims 1 to 11, wherein The first positive active layer comprises lithium iron phosphate and a first polyanion-type material, the electronic conductivity of the first polyanion-type material is less than that of lithium iron phosphate, and the mass percentage of the first polyanion-type material in the total amount of lithium iron phosphate and the first polyanion-type material is 30%-85%.

13. The battery cell according to claim 12, wherein The mass percentage of the first polyanion-type material in the total amount of lithium iron phosphate and the first polyanion-type material in the first positive active layer is 40%-65%.

14. The battery cell according to any one of claims 1 to 13, wherein The first positive active layer comprises lithium iron phosphate and a second polyanion-type material, the charge platform voltage of the second polyanion-type material is greater than that of lithium iron phosphate, and the mass percentage of the second polyanion-type material in the total amount of lithium iron phosphate and the second polyanion-type material is 15%-40%.

15. The battery cell according to any one of claims 1 to 14, wherein The first polyanion-type material comprises manganese element, and the mass percentage of manganese element in the total amount of metal elements is 0.05-0.

75.

16. The battery cell according to claim 15, wherein The mass percentage of manganese element in the total amount of metal elements in the first polyanion-type material is 0.15-0.

65.

17. The battery cell according to any one of claims 1 to 16, wherein The first positive electrode active layer includes an active material of the chemical formula Li 1+x Mn 1-y A y P 1-z E z 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 of 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 of B, Si, N, S, F, Cl, and Br.

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

19. The battery cell according to claim 17 or 18, wherein The active material of the first positive electrode active layer has a core-shell structure, the cladding shell layer of the core-shell structure includes one or more layers of pyrophosphate, phosphate, carbon, the core layer of the core-shell structure includes 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, wherein The difference between the capacity release value of the first positive active layer above 3.9 V and the capacity release value of the second positive active layer above 3.9 V is less than 25%.

21. A battery, wherein, A battery comprising the battery cell according to any one of claims 1 to 20.

22. An electrical device, comprising: A battery comprising the battery according to claim 21.

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