Cathode material composition, method of making the same, and cathode sheet, secondary battery, and power using device comprising the same

Abstract

The present application provides a positive electrode material composition, a preparation method thereof, and a positive electrode sheet, a secondary battery, and an electric device comprising the same. The positive electrode material composition comprises a positive electrode active material having a core-shell structure and an organic polysiloxane compound, wherein the positive electrode active material comprises an inner core and a shell covering the inner core, the inner core comprises Li 1+ x Mn 1‑y A y P 1‑z R z O4, and the shell comprises a first coating layer covering the inner core and a second coating layer covering the first coating layer. The positive electrode material composition of the present application can enable the secondary battery to have a higher energy density and simultaneously improve the cycle performance, safety performance, and / or rate performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode material composition, its preparation method, and a positive electrode sheet, secondary battery, and electrical device containing the same. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their safety performance has received increasing attention. Lithium manganese phosphate has become one of the most popular cathode active materials due to its advantages such as high capacity, good safety performance, and abundant raw material sources. However, lithium manganese phosphate is prone to manganese ion dissolution during charging, leading to rapid capacity decay. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode material composition, a method for preparing the same, and a positive electrode sheet, a secondary battery, and an electrical device comprising the same, which enables the secondary battery using the positive electrode material composition to have a high energy density while also improving cycle performance, safety performance, and / or rate performance.

[0004] A first aspect of this application provides a cathode material composition comprising a core-shell structured cathode active material and an organopolysiloxane compound, wherein the cathode active material includes a core and a shell covering the core, and the core comprises Li 1+x Mn 1-y A y P 1-z R z O4, x is -0.100 to 0.100, optionally -0.100 to 0.006, y is 0.001 to 0.500, optionally 0.100 to 0.450, z is 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, R is selected from one or more of B, Si, N and S; the shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and the second coating layer contains carbon.

[0005] This application, through specific elemental doping and surface coating of lithium manganese phosphate, effectively suppresses manganese ion dissolution during lithium insertion / extraction while promoting lithium ion migration. Combining the cathode active material of this application with an organopolysiloxane compound can alleviate the erosion of the cathode active material surface by the electrolyte, reduce manganese ion dissolution, and thus improve the electrochemical performance of the cathode active material. Therefore, cathode electrodes and secondary batteries using the cathode material composition of this application can achieve higher energy density while also improving cycle performance, safety performance, and / or rate performance.

[0006] In any embodiment of this application, the organopolysiloxane compound comprises at least one structural unit represented by Formula 1.

[0007]

[0008] R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate ester, carboxylic acid ester, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon, C1-C20 halogenated aliphatic hydrocarbon, C1-C20 heteroaliphatic hydrocarbon, C1-C20 halogenated heteroaliphatic hydrocarbon, C6-C20 aromatic hydrocarbon, C6-C20 halogenated aromatic hydrocarbon, C2-C20 heteroaromatic hydrocarbon, C2-C20 halogenated heteroaromatic hydrocarbon. Optionally, R1 and R2 each independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, phenyl. More preferably, R1 and R2 each independently represent H or at least one of the following functional groups: -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl.

[0009] This can further reduce manganese ion dissolution, thereby significantly improving the cycle performance and / or high-temperature stability of the secondary battery.

[0010] In any embodiment of this application, the organopolysiloxane compound includes one or more selected from linear polysiloxanes and cyclic polysiloxanes. Optionally, the organopolysiloxane compound is selected from linear polysiloxanes.

[0011] Therefore, this can further alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, reduce manganese ion dissolution, and thus significantly improve the cycle performance and storage performance of the secondary battery. Because the electrons in the ring structure of cyclic polysiloxanes have a certain degree of delocalization, compared with linear polysiloxanes, their Si-O framework has a lower affinity for electron-rich F-containing ions, resulting in a slightly lower removal rate of F-containing ions in the electrolyte, a slightly weaker effect in reducing manganese ion dissolution, and a slightly poorer improvement effect on the cycle performance of the secondary battery.

[0012] In any embodiment of this application, the linear polysiloxane further comprises end-capping groups. Optionally, the end-capping groups comprise at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxyalkyl, amino, C1-C8 aminoalkyl, carboxyl, and C1-C8 carboxyalkyl.

[0013] In any embodiment of this application, the linear polysiloxane includes one or more of the following: polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, terminal epoxy-terminated polydimethylsiloxane, terminal hydroxyl-terminated polydimethylsiloxane, terminal polyether polydimethylsiloxane, side-chain aminopropyl polysiloxane, side-chain hydroxymethyl polysiloxane, side-chain hydroxypropyl polysiloxane, side-chain polyether-grafted polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane. Optionally, the linear polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, end-group polyether polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane.

[0014] In any embodiment of this application, the cyclic polysiloxane comprises one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrosiloxane, and cyclic polymethyltrifluoropropylsiloxane. Optionally, the cyclic polysiloxane comprises one or more of 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentapolydimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, hexadecylcyclooctasiloxane, and tetradecylcycloheptasiloxane.

[0015] In any embodiment of this application, the number average molecular weight of the organopolysiloxane compound is below 300,000, and can be selected as 400 to 80,000. This enables the secondary battery to simultaneously achieve good kinetic performance and high-temperature stability.

[0016] In any embodiment of this application, the mass percentage of polar functional groups in the organopolysiloxane compound is α, where 0 ≤ α < 50%, and optionally, 5% ≤ α ≤ 30%. This can better improve the cycle performance and / or high-temperature stability of the secondary battery.

[0017] In any embodiment of this application, the content of the organopolysiloxane compound is from 0.01% to 2% by weight, optionally from 0.1% to 2% by weight, based on the total weight of the cathode material composition. This can better improve the cycle performance and / or high-temperature stability of the secondary battery.

[0018] In any embodiment of this application, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally from 4% by weight to 5.6% by weight, based on the weight of the core. This effectively utilizes the function of the first coating layer without affecting the kinetic performance of the secondary battery due to an excessively thick coating layer.

[0019] In any embodiment of this application, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally from 3% to 5% by weight, based on the weight of the core. This effectively improves the specific capacity of the positive electrode active material.

[0020] In any embodiment of this application, the interplanar spacing of the phosphate in the first coating layer is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°. This can further improve the cycle performance and rate performance of the secondary battery.

[0021] In any embodiment of this application, the interplanar spacing of the pyrophosphate in the first coating layer is 0.293 nm to 0.326 nm, and the included angle of the crystal orientation (111) is 26.41° to 32.57°. This can further improve the cycle performance and rate performance of the secondary battery.

[0022] In any embodiment of this application, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. This further improves the energy density and cycle performance of the secondary battery.

[0023] In any embodiment of this application, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. This further improves the energy density and cycle performance of the secondary battery.

[0024] In any embodiment of this application, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and can be selected as 1:3 to 1:1. This is beneficial for leveraging the synergistic effect of pyrophosphate and phosphate.

[0025] In any embodiment of this application, the crystallinity of pyrophosphate and phosphate in the first coating layer is independently 10% to 100%, optionally 50% to 100%. This is beneficial for fully utilizing the role of pyrophosphate in inhibiting the dissolution of manganese ions and phosphate in reducing the content of surface impurities and reducing interfacial side reactions.

[0026] In any embodiment of this application, A is selected from at least two of Fe, Ti, V, Ni, Co, and Mg. This further reduces surface oxygen activity and inhibits the dissolution of manganese ions.

[0027] In any embodiment of this application, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, optionally 2% or less. This improves the specific capacity and rate performance of the positive electrode active material.

[0028] In any embodiment of this application, the lattice change rate of the positive electrode active material is 8% or less, optionally 4% or less. This improves the rate performance of the secondary battery.

[0029] In any embodiment of this application, the surface oxygen valence state of the positive electrode active material is below -1.88, and can be selected as -1.98 to -1.88. This can improve the cycle performance and high-temperature storage performance of the secondary battery.

[0030] In any embodiment of this application, the compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3The above. This is beneficial for improving the volumetric energy density of secondary batteries.

[0031] In any embodiment of this application, the positive electrode material composition further comprises a conductive agent and a binder. Optionally, the binder content is 1.79% to 10% by weight, based on the total weight of the positive electrode material composition; alternatively, the conductive agent content is 0.2% to 10% by weight, based on the total weight of the positive electrode material composition.

[0032] In any embodiment of this application, the powder resistivity of the positive electrode material composition at 12 MPa is 4 ΩΩ / cm to 55 Ω / cm, optionally 4 ΩΩ / cm to 40 Ω / cm. This enables the secondary battery to have better kinetic performance.

[0033] In any embodiment of this application, the specific surface area of ​​the positive electrode material composition is 8m². 2 / g to 20m 2 / g, optional 8m 2 / g to 15m 2 / g. This allows secondary batteries to have better electrochemical performance.

[0034] A second aspect of this application provides a method for preparing a cathode material composition, comprising the following steps: providing a core material, a coating step, and a mixing step.

[0035] Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is -0.100 to 0.100, optionally -0.100 to 0.006, y is 0.001 to 0.500, optionally 0.100 to 0.450, z is 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0036] Coating step: MP2O7 powder and an XPO4 suspension containing a carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing a carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. The obtained positive electrode active material has a core-shell structure, including the core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon.

[0037] Mixing step: The obtained positive electrode active material is mixed uniformly with an organopolysiloxane compound, an optional binder and an optional conductive agent to obtain a positive electrode material composition.

[0038] In any embodiment of this application, the step of providing the core material includes the following steps: Step (1): mixing and stirring a manganese source, a source of element A, and an acid in a container to obtain manganese salt particles doped with element A; Step (2): mixing the manganese salt particles doped with element A with a lithium source, a phosphorus source, and a source of element R in a solvent to obtain a slurry, and sintering it under an inert gas atmosphere to obtain lithium manganese phosphate doped with elements A and R, wherein the lithium manganese phosphate doped with elements A and R is Li 1+x Mn 1-y A y P 1-z R z O4, x is -0.100 to 0.100, optionally -0.100 to 0.006, y is 0.001 to 0.500, optionally 0.100 to 0.450, z is 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0039] In any embodiment of this application, step (1) is performed at a temperature of 20°C to 120°C, or optionally 25°C to 80°C.

[0040] In any embodiment of this application, the stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes, or optionally 120 minutes to 360 minutes.

[0041] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be evenly distributed, and the crystallinity of the sintered material can be higher, thereby improving the specific capacity and rate performance of the positive electrode active material.

[0042] In any embodiment of this application, the source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide.

[0043] In any embodiment of this application, the source of element R is selected from one or more of the following: element R in its elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide, and inorganic acid of element R.

[0044] By selecting the sources of each dopant element within the above range, the performance of the positive electrode active material can be effectively improved.

[0045] In any embodiment of this application, the MP2O7 powder is prepared by the following method: adding the source of element M and the source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to 4 to 6, stirring and reacting fully, and then drying and sintering to obtain the powder. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.

[0046] In any embodiment of this application, during the preparation of MP2O7 powder, the drying step is to dry at 100°C to 300°C, optionally 150°C to 200°C, for 4 to 8 hours.

[0047] In any embodiment of this application, during the preparation of MP2O7 powder, the sintering step is to sinter at 500°C to 800°C, optionally 650°C to 800°C, for 4 to 10 hours in an inert gas atmosphere.

[0048] In any embodiment of this application, the sintering temperature for obtaining the positive electrode active material during the coating step is 500°C to 800°C, and the sintering time is 4 hours to 10 hours. By controlling the sintering temperature and time during coating, the specific capacity and rate performance of the positive electrode active material can be further improved.

[0049] A third aspect of this application provides a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode material composition of the first aspect of this application or a positive electrode material composition prepared by the method of the second aspect of this application, and the content of the positive electrode material composition in the positive electrode film layer is 50% by weight or more, based on the total weight of the positive electrode film layer.

[0050] In any embodiment of this application, the content of the positive electrode material composition in the positive electrode film layer is 90% to 100% by weight, based on the total weight of the positive electrode film layer.

[0051] In any embodiment of this application, the solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 90°, optionally between 3° and 60°, and further between 10° and 30°. When the contact angle is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance.

[0052] In any embodiment of this application, the porosity of the positive electrode film is 15% to 50%, optionally 15% to 30%. When the porosity is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance.

[0053] In any embodiment of this application, the resistance of the positive electrode film is greater than 0 and less than or equal to 6Ω. This enables the secondary battery to have better dynamic performance.

[0054] In any embodiment of this application, the adhesion force between the positive electrode film layer and the positive electrode current collector is greater than or equal to 0.5 MPa. This is beneficial to the performance of the secondary battery.

[0055] In any embodiment of this application, the areal density of the positive electrode film is 0.006 g / cm³. 2 Up to 0.065 g / cm 2 This is beneficial for increasing the volumetric energy density of secondary batteries.

[0056] In any embodiment of this application, the electrolyte absorption rate of the positive electrode film is from 0.0125 μg / s to 100 μg / s, and optionally from 0.5 μg / s to 40 μg / s. This is beneficial for improving the electrochemical performance of the secondary battery.

[0057] The positive electrode sheet of this application, when used in secondary batteries, can improve the energy density, cycle performance, safety performance, and / or rate performance of secondary batteries.

[0058] The fourth aspect of this application provides a secondary battery, including a positive electrode material composition of the first aspect of this application, or a positive electrode material composition prepared by the method of the second aspect of this application, or a positive electrode sheet of the third aspect of this application.

[0059] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0060] The positive electrode sheet, secondary battery, and electrical device of this application include the positive electrode material composition of this application, and therefore have at least the same advantages as the positive electrode active material composition. Attached Figure Description

[0061] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0062] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0063] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0064] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0065] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0066] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0067] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0068] Figure 7 This is a comparison diagram of the XRD pattern of the core of the positive electrode active material prepared in Example 1-1 and the standard XRD pattern of lithium manganese phosphate (00-033-0804).

[0069] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0070] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode material composition, its preparation method, and embodiments of the positive electrode sheet, secondary battery, and power device comprising the same. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0071] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0072] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0073] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0074] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0075] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0076] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0077] In this document, the median particle size Dv50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. In this application, the median particle size Dv50 of the material can be determined using laser diffraction particle size analysis. For example, it can be determined using a laser particle size analyzer (e.g., Malvem Master Size 3000) in accordance with standard GB / T19077-2016.

[0078] In this document, substituents of compounds are disclosed by groups or ranges. It is expressly anticipated that such descriptions include each individual subcombination of members of these groups and ranges. For example, it is expressly anticipated that the term “C1-C8 alkyl” individually discloses C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7, and C7-C8 alkyl groups.

[0079] In this document, the term "aliphatic hydrocarbon group" includes alkyl, alkenyl, and alkynyl groups, and the term "heteroaliphatic hydrocarbon group" refers to an aliphatic hydrocarbon group containing heteroatoms (e.g., N, O, S, etc.). The term "heteroalkyl group" refers to an alkyl group containing heteroatoms (e.g., N, O, S, etc.), such as alkoxy, alkylthio, etc.

[0080] In this document, the term "cladding layer" refers to a layer of material covering the core, which may completely or partially cover the core. The use of "cladding layer" is for ease of description only and is not intended to limit the invention. Furthermore, each cladding layer may be a complete or partial covering.

[0081] In this document, the term "source" refers to a compound that is the source of a certain element. For example, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, elements, halides, oxides, and hydroxides.

[0082] In this article, the terms "multiple" or "various" refer to two or more kinds.

[0083] In this article, “about” refers to a range of values, specifically the range of ±10% of that value.

[0084] The inventors of this application discovered in practical operation that manganese ion dissolution is severe in lithium manganese phosphate (LiMnPO4) positive electrode active materials during deep charge-discharge processes. Although existing technologies have attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce interfacial side reactions, this coating cannot prevent the dissolved manganese ions from migrating into the electrolyte. After migrating to the negative electrode, the dissolved manganese ions are reduced to metallic manganese. This generated metallic manganese acts as a "catalyst," catalyzing the decomposition of the SEI film (solid electrolyte interphase) on the negative electrode surface. Some of the byproducts are gases, which can easily cause battery expansion and affect the safety performance of the secondary battery. Others deposit on the negative electrode surface, obstructing the channels for lithium ions to enter and exit the negative electrode, increasing the impedance of the secondary battery and affecting its kinetic performance. Furthermore, to replenish the lost SEI film, the active lithium ions in the electrolyte and inside the battery are continuously consumed, thus irreversibly affecting the capacity retention rate of the secondary battery.

[0085] After extensive research, the inventors discovered that the problems of severe manganese ion dissolution and high surface reactivity in lithium manganese phosphate cathode active materials may be due to the delithiation of Mn. 3+ The Jiang-Taylor effect and Li +This is caused by changes in channel size. To address this, the inventors modified lithium manganese phosphate to obtain a positive electrode active material that significantly reduces manganese ion dissolution and lattice change rate, thereby exhibiting good cycle performance, safety performance, and / or rate performance. Furthermore, the inventors discovered that combining the positive electrode active material with an organopolysiloxane compound can mitigate the erosion of the positive electrode active material surface by the electrolyte, thus facilitating the full utilization of the electrochemical performance of the positive electrode active material.

[0086] Positive electrode material composition

[0087] Specifically, the first aspect of this application proposes a cathode material composition comprising a cathode active material having a core-shell structure and an organopolysiloxane compound.

[0088] The positive electrode active material includes a core and a shell covering the core. The core includes Li 1+ xMn 1-y A y P 1- z R z O4, x is from -0.100 to 0.100, y is from 0.001 to 0.500, z is from 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and may be selected from one or more of Fe, Ti, V, Ni, Co and Mg, R is selected from one or more of B, Si, N and S; the shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, and the second coating layer contains carbon.

[0089] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of values ​​for y applies not only to the stoichiometric coefficient of each element as A, but also to the sum of the stoichiometric coefficients of all elements as A. For example, when A consists of two or more elements A1, A2...An, the stoichiometric coefficients y1, y2...yn of each of A1, A2...An must each fall within the range of values ​​for y defined in this application, and the sum of y1, y2...yn must also fall within this range. Similarly, for the case where R consists of two or more elements, the limitation on the range of values ​​for the stoichiometric coefficients of R in this application has the same meaning.

[0090] The lithium manganese phosphate cathode active material of this application has a core-shell structure with a double-layer coating, the core including Li 1+ x Mn 1-y A y P 1-z R z O4. The element A doping at the manganese sites of lithium manganese phosphate helps reduce the lattice change rate of lithium manganese phosphate during lithium insertion / extraction, improves the structural stability of the lithium manganese phosphate cathode active material, greatly reduces the dissolution of manganese ions, and lowers the oxygen activity on the particle surface. The element R doping at the phosphorus sites helps change the ease of Mn-O bond length changes, thereby lowering the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the secondary battery.

[0091] The first coating layer of the positive electrode active material in this application includes pyrophosphate and phosphate. Since the migration barrier of transition metals in pyrophosphate is high (>1 eV), the dissolution of transition metal ions can be effectively suppressed. Meanwhile, phosphate has excellent lithium-ion conduction capabilities and can reduce the surface lithium content.

[0092] The second coating layer of the positive electrode active material in this application is a carbon-containing layer, which can effectively improve the conductivity and desolvation ability of LiMnPO4. In addition, the "barrier" effect of the second coating layer can further prevent manganese ions from migrating into the electrolyte and reduce the corrosion of the positive electrode active material by the electrolyte.

[0093] Therefore, by performing specific element doping and surface coating on lithium manganese phosphate, this application can effectively suppress the dissolution of manganese ions during the lithium insertion / extraction process, while promoting the migration of lithium ions, thereby improving the cycle performance, safety performance, and / or rate performance of secondary batteries.

[0094] The cathode material composition of this application comprises a cathode active material and an organopolysiloxane compound. The inventors of this application have discovered that using the aforementioned cathode active material in combination with the organopolysiloxane compound can alleviate the corrosion of the cathode active material surface by the electrolyte and reduce manganese ion dissolution, thereby improving the electrochemical performance of the cathode active material. A possible reason is that the Si-O framework of the organopolysiloxane compound can remove F-containing ions from the electrolyte, thereby reducing the electrolyte acidity and alleviating the corrosion of the cathode active material surface by acidic substances in the electrolyte; the organopolysiloxane compound also has a certain degree of hydrophobicity, and when it is prepared together with the cathode active material into a cathode electrode sheet, the contact angle between the resulting cathode electrode sheet and the electrolyte increases, thereby alleviating the corrosion of the cathode active material surface by the electrolyte.

[0095] Therefore, positive electrode sheets and electrical devices such as secondary batteries using the positive electrode material composition of this application can have high energy density and improve cycle performance, safety performance, and / or rate performance.

[0096] It should be noted that the core of the positive electrode active material in this application is basically consistent with the position of the main characteristic peaks before LiMnPO4 doping, indicating that the core of the doped lithium manganese phosphate positive electrode active material in this application has no impurity phase, and the improvement of the secondary battery performance mainly comes from element doping, rather than impurity phase.

[0097] In some embodiments, optionally, the coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, optionally from 4% by weight to 5.6% by weight, based on the weight of the core. When the coating amount of the first coating layer is within the above range, it can further suppress manganese ion dissolution and further promote lithium ion transport. It can also effectively avoid the following situations: if the coating amount of the first coating layer is too small, the inhibitory effect of pyrophosphate on manganese ion dissolution may be insufficient, and the improvement on lithium ion transport performance may not be significant; if the coating amount of the first coating layer is too large, the coating layer may be too thick, increasing battery impedance and affecting the kinetic performance of the secondary battery.

[0098] In some embodiments, optionally, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, optionally from 3% to 5% by weight, based on the weight of the core. The carbon-containing layer, as the second coating layer, functions as a "barrier," preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte erosion of the positive electrode active material and improving the safety performance of the secondary battery at high temperatures. On the other hand, it possesses strong conductivity, reducing the battery's internal resistance and thus improving the kinetic performance of the secondary battery. However, since carbon materials have low specific capacity, excessive amounts of the second coating layer may reduce the overall specific capacity of the positive electrode active material. Therefore, when the coating amount of the second coating layer is within the aforementioned range, the kinetic and safety performance of the secondary battery can be further improved without sacrificing the specific capacity of the positive electrode active material.

[0099] In the kernel, x is from -0.100 to 0.100, for example, x can be 0.006, 0.004, 0.003, 0.002, 0.001, 0, -0.001, -0.003, -0.004, -0.005, -0.006, -0.007, -0.008, -0.009, or -0.100. Optionally, x is from -0.100 to 0.006.

[0100] In the kernel, y is from 0.001 to 0.500, for example, y can be 0.100, 0.200, 0.250, 0.300, 0.350, 0.400, or 0.450. Optionally, y is from 0.100 to 0.450.

[0101] In the kernel, z ranges from 0.001 to 0.100, for example, z can be 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, or 0.100.

[0102] In some embodiments, optionally, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric coefficients of the Mn-doped elements. When the above conditions are met, the energy density and cycle performance of the secondary battery can be further improved.

[0103] In some embodiments, optionally, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. Here, y represents the sum of the stoichiometric coefficients of the p-site dopants. When the above conditions are met, the energy density and cycle performance of the secondary battery can be further improved.

[0104] In some embodiments, the A may optionally be selected from at least two of Fe, Ti, V, Ni, Co, and Mg.

[0105] Simultaneous doping of two or more of the aforementioned elements at the manganese sites in lithium manganese phosphate cathode active materials is beneficial to enhancing the doping effect. On the one hand, it further reduces the lattice change rate, thereby inhibiting the dissolution of manganese ions and reducing the consumption of electrolyte and active lithium ions. On the other hand, it is also beneficial to further reduce surface oxygen activity, reduce interfacial side reactions between cathode active materials and electrolyte, thereby improving the cycle performance and high-temperature storage performance of secondary batteries.

[0106] In some embodiments, optionally, the interplanar spacing of the phosphate in the first coating layer is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°.

[0107] In some embodiments, optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.293 nm to 0.326 nm, and the included angle of the crystal orientation (111) is 26.41° to 32.57°.

[0108] When the interplanar spacing and the angle between the crystal orientation (111) of the phosphate and pyrophosphate in the first coating layer are within the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the specific capacity, cycle performance and rate performance of the positive electrode active material.

[0109] In some embodiments, optionally, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, preferably 1:3 to 1:1. A suitable ratio of pyrophosphate to phosphate is beneficial for fully utilizing their synergistic effect, effectively inhibiting manganese ion dissolution and reducing surface lithium content, thus minimizing interfacial side reactions. It also effectively avoids the following situations: if there is too much pyrophosphate and too little phosphate, it may lead to increased battery impedance; if there is too much phosphate and too little pyrophosphate, the effect of inhibiting manganese ion dissolution is not significant.

[0110] In some embodiments, optionally, the crystallinity of pyrophosphate and phosphate in the first coating layer is independently 10% to 100%, optionally 50% to 100%. In the first coating layer of the lithium manganese phosphate cathode active material of this application, the pyrophosphate and phosphate with a certain degree of crystallinity are beneficial to maintaining the structural stability of the first coating layer and reducing lattice defects. This is beneficial on the one hand to fully utilize the role of pyrophosphate in inhibiting the dissolution of manganese ions, and on the other hand, it is beneficial for phosphate to reduce the content of surface impurities and lower the valence state of surface oxygen, thereby reducing interfacial side reactions between the cathode active material and the electrolyte, reducing electrolyte consumption, and improving the cycle performance and safety performance of the secondary battery.

[0111] It should be noted that, in this application, the crystallinity of pyrophosphate and phosphate can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature and sintering time. The crystallinity of pyrophosphate and phosphate can be measured by methods known in the art, such as X-ray diffraction, density method, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption method.

[0112] In some embodiments, optionally, the Li / Mn antisite defect concentration of the positive electrode active material is 4% or less, and optionally 2% or less. Li / Mn antisite defects refer to the Li... + and Mn 2+ The positions of Li and Mn are interchanged. The Li / Mn antisite defect concentration refers to the concentration of Li / Mn antisite defects in the positive electrode active material. 2+ Interchangeable Li + Zhan Li + Percentage of the total. Due to Li + The transmission channel is a one-dimensional channel, Mn 2+ In Li + It is difficult to migrate in the transmission channel, therefore, the Mn of the inversion defect is difficult to migrate. 2+ It will hinder Li +The transport of [materials / materials]. In the positive electrode active material of this application, by controlling the concentration of Li / Mn antisite defects to a low level, the specific capacity and rate performance of the positive electrode active material can be improved. In this application, the antisite defect concentration can be determined, for example, according to JIS K0131-1996.

[0113] In some embodiments, optionally, the lattice change rate of the positive electrode active material is below 8%, optionally below 6%, and more preferably below 4%. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0114] In some embodiments, optionally, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the specific discharge capacity is 140mAh / g or higher; alternatively, the average discharge voltage is 3.6V or higher, and the specific discharge capacity is 145mAh / g or higher. Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its specific discharge capacity is low, typically less than 120mAh / g, resulting in a low energy density for the secondary battery. By adjusting the lattice change rate through doping, its specific discharge capacity can be significantly increased, leading to a substantial increase in the overall energy density of the secondary battery even with a slight decrease in the average discharge voltage.

[0115] In some embodiments, optionally, the surface oxygen valence state of the positive electrode active material is below -1.88, and optionally between -1.98 and -1.88. This is because the higher the valence state of oxygen in a compound, the stronger its electron-accepting ability, i.e., the stronger its oxidizing power. In the lithium manganese phosphate positive electrode active material of this application, by controlling the surface oxygen valence state at a low level, the reactivity of the positive electrode active material surface can be reduced, the interfacial side reactions between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the secondary battery.

[0116] In some embodiments, optionally, the compaction density of the positive electrode active material at 3 tons (T) is 2.0 g / cm³. 3 The above can be selected as 2.2g / cm. 3 The higher the compaction density of the positive electrode active material, i.e., the greater the weight of the active material per unit volume, the more beneficial it is to improving the volumetric energy density of the secondary battery. In this application, the compaction density can be measured, for example, according to GB / T24533-2009.

[0117] In some embodiments, the organopolysiloxane compound comprises at least one structural unit represented by Formula 1.

[0118]

[0119] R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate ester, carboxylic acid ester, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon, C1-C20 halogenated aliphatic hydrocarbon, C1-C20 heteroaliphatic hydrocarbon, C1-C20 halogenated heteroaliphatic hydrocarbon, C6-C20 aromatic hydrocarbon, C6-C20 halogenated aromatic hydrocarbon, C2-C20 heteroaromatic hydrocarbon, C2-C20 halogenated heteroaromatic hydrocarbon. Optionally, R1 and R2 each independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, phenyl. More preferably, R1 and R2 each independently represent H or at least one of the following functional groups: -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl.

[0120] These functional groups can complex manganese ions and / or react with acidic substances in the electrolyte, thereby reducing manganese ion dissolution and further improving the cycle performance and / or high-temperature stability of the secondary battery.

[0121] When these functional groups also have electron-withdrawing properties, the Si in the Si-O framework of the organopolysiloxane compound becomes more electron-deficient, which can further enhance the affinity with F-containing ions in the electrolyte, further alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, reduce the dissolution of manganese ions, and thus significantly improve the cycle performance and / or high-temperature stability of the secondary battery.

[0122] In some embodiments, the organopolysiloxane compound includes one or more selected from linear polysiloxanes and cyclic polysiloxanes. Optionally, the organopolysiloxane compound is selected from linear polysiloxanes.

[0123] Therefore, this can further alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, reduce manganese ion dissolution, and thus significantly improve the cycle performance and storage performance of the secondary battery. Because the electrons in the ring structure of cyclic polysiloxanes have a certain degree of delocalization, compared with linear polysiloxanes, their Si-O framework has a lower affinity for electron-rich F-containing ions, resulting in a slightly lower removal rate of F-containing ions in the electrolyte, a slightly weaker effect in reducing manganese ion dissolution, and a slightly poorer improvement effect on the cycle performance of the secondary battery.

[0124] In some embodiments, the linear polysiloxane may further comprise end-capping groups. Optionally, the end-capping groups comprise at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxyalkyl, amino, C1-C8 aminoalkyl, carboxyl, and C1-C8 carboxyalkyl.

[0125] In some embodiments, the molecular formula of the cyclic polysiloxane may be as shown in Formula 2, where n represents the degree of polymerization of the structural unit shown in Formula 1. Optionally, n ≤ 12, n ≤ 11, n ≤ 10, n ≤ 9, or n ≤ 8.

[0126]

[0127] As an example, the linear polysiloxanes include, but are not limited to, one or more of the following: polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, epoxy-terminated polysiloxane, hydroxyl-terminated polydimethylsiloxane, polyether-terminated polydimethylsiloxane, side-chain aminopropylpolysiloxane, side-chain hydroxymethylpolysiloxane, side-chain hydroxypropylpolysiloxane, side-chain polyether-grafted polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane. Optionally, the linear polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, end-group polyether polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane.

[0128] As an example, the cyclic polysiloxane includes, but is not limited to, one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrosiloxane, and cyclic polymethyltrifluoropropylsiloxane. Optionally, the cyclic polysiloxane includes one or more of 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentapolydimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, hexadecylcyclooctasiloxane, and tetradecylcycloheptasiloxane.

[0129] In some embodiments, the number average molecular weight of the organopolysiloxane compound is below 300,000, for example, it can be 400 to 300,000, 400 to 200,000, 400 to 100,000, 400 to 80,000, 400 to 50,000, 400 to 20,000, 400 to 10,000, 1,000 to 100,000, 1,000 to 50,000, 1,000 to 20,000, or 1,000 to 10,000. The number average molecular weight of the organopolysiloxane compound can be determined by methods known in the art, such as gel permeation chromatography (GPC). The testing instrument can be a PL-GPC 220 high-temperature gel permeation chromatograph. In this application, "organopolysiloxane compound" can be either an oligomer or a polymer.

[0130] When the number-average molecular weight of organopolysiloxane compounds is within a suitable range, secondary batteries can simultaneously achieve good kinetic performance and high-temperature stability. This effectively avoids the following situations: if the number-average molecular weight of the organopolysiloxane compound is too low, its hydrophobicity may be poor, which may prevent the effective increase of the contact angle between the positive electrode film and the electrolyte, and consequently, may not effectively mitigate the electrolyte's erosion of the positive electrode active material surface, resulting in a potentially insignificant improvement in the cycle performance and / or high-temperature stability of the secondary battery; if the number-average molecular weight of the organopolysiloxane compound is too high, its hydrophobicity may be too strong, which may also be detrimental to slurry dispersion, thus affecting the improvement of secondary battery performance.

[0131] In some embodiments, the mass percentage of polar functional groups in the organopolysiloxane compound is α, where 0 ≤ α < 50%, and optionally, 5% ≤ α ≤ 30%.

[0132] In this application, "the mass percentage of polar functional groups in the organopolysiloxane compound" refers to the mass proportion of polar functional groups in R1, R2, and the end-capping group in the organopolysiloxane compound. In this application, polar functional groups include one or more of the following: -COOH, -OH, -SH, -CN, -SCN, amino groups (including -NH2, -NH-), phosphate ester groups, carboxylic ester groups (-COO-), amide groups (-CONH-), aldehyde groups (-CHO), sulfonyl groups (-S(=O)2-), polyether segments, halogen atoms, alkoxy groups, and epoxy groups. When the aforementioned polar functional groups are directly connected to silicon atoms, α represents the mass fraction of these polar functional groups in the organopolysiloxane compound. When the aforementioned polar functional groups are not directly connected to silicon atoms, α represents the sum of the mass fractions of the polar functional groups and the divalent to tetravalent methyl groups (e.g., -CH2, -CH-, -C-, etc.) directly connected to them in the organopolysiloxane compound. Here, "divalent to tetravalent methyl groups" refers to the carbon atom directly connected to the polar functional group and located between the polar functional group and the silicon atom, as well as other nonpolar functional groups connected to the carbon atom. Taking polymethyltrifluoropropylsiloxane as an example, α refers to the mass percentage of -CF3, excluding the ethylidene; taking polymethylchloropropylsiloxane as an example, α refers to the mass percentage of -CH2Cl, excluding the ethylidene; taking hydroxypropyl-terminated polydimethylsiloxane as an example, α refers to the mass percentage of -CH2OH. The mass percentage of polar functional groups in organopolysiloxane compounds can be determined by methods known in the art, such as titration (e.g., acid-base titration, redox titration, precipitation titration), infrared spectroscopy, and nuclear magnetic resonance spectroscopy.

[0133] When the content of polar functional groups in organopolysiloxane compounds is within a suitable range, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte is better. This can better alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, and better improve the cycle performance and / or high-temperature stability of the secondary battery. It also effectively avoids the following situation: when the content of polar functional groups in organopolysiloxane compounds is too high, their effect on reducing electrolyte acidity and removing fluoride ions from the electrolyte will not be further enhanced, but may lead to a smaller contact angle between the positive electrode film and the electrolyte, resulting in a less significant improvement in the cycle performance of the secondary battery.

[0134] In some embodiments, the content of the organopolysiloxane compound is from 0.01% to 2% by weight, optionally from 0.1% to 2% by weight, based on the total weight of the cathode material composition. When the content of the organopolysiloxane compound is within a suitable range, it is more effective in reducing electrolyte acidity and removing F-containing ions from the electrolyte, thereby better mitigating the erosion of the cathode active material surface by acidic substances in the electrolyte, and better improving the cycle performance and / or high-temperature stability of the secondary cell. It can effectively avoid the following situations: When the content of organopolysiloxane compounds is too high, it may affect the electrolyte wettability of the positive electrode film and the dynamic performance of the secondary battery. At the same time, since organopolysiloxane compounds do not provide capacity, their high content will also reduce the energy density of the secondary battery. When the content of organopolysiloxane compounds is too low, their effect of reducing electrolyte acidity and removing F-containing ions in the electrolyte is not obvious, and they cannot effectively alleviate the corrosion of the positive electrode active material surface by acidic substances in the electrolyte, thus the improvement effect on the cycle performance and / or high temperature stability of the secondary battery may not be obvious.

[0135] In some embodiments, the cathode material composition may further include a binder. The binder may be a substance known in the art that provides a bonding effect; optionally, the binder includes at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Optionally, the binder content is from 1.79% to 10% by weight, or optionally from 2% to 5% by weight, based on the total weight of the cathode material composition.

[0136] In some embodiments, the cathode material composition may further comprise a conductive agent. The conductive agent may be a substance known in the art capable of electron conduction. Optionally, the cathode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the content of the conductive agent is from 0.2% to 10% by weight, or optionally from 0.5% to 5% by weight, based on the total weight of the cathode material composition.

[0137] In some embodiments, the powder resistivity of the cathode material composition at 12 MPa is 4 Ω / cm to 55 Ω / cm, optionally 4 Ω / cm to 50 Ω / cm. Adjusting the powder resistivity of the cathode material composition within a suitable range can improve the kinetic performance of the secondary battery. The powder resistivity of the cathode material composition can be determined by methods known in the art. For example, it can be tested using a powder resistivity tester, referring to GB / T 30835-2014. An exemplary test method includes the steps of: weighing a certain amount of the sample powder to be tested and placing it in a special mold, setting the test pressure, and thus obtaining the powder resistivity at different pressures. In this application, the test pressure can be set to 12 MPa. The testing instrument can be a Suzhou Jinglü ST2722-SZ type four-probe powder resistivity tester.

[0138] In some embodiments, the specific surface area of ​​the cathode material composition is 8 m². 2 / g to 20m 2 / g, optional 8m 2 / g to 15m 2 / g. Adjusting the specific surface area of ​​the cathode material composition within a suitable range can reduce interfacial side reactions between the cathode electrode and the electrolyte, decrease the volume expansion of the secondary battery, and thus enable the secondary battery to have better electrochemical performance. The specific surface area of ​​the cathode material composition can be determined by methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0139] Preparation method

[0140] The second aspect of this application provides a method for preparing the cathode material composition of the first aspect of this application, which includes the following steps of providing a core material, a coating step, and a mixing step.

[0141] Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R zO4, wherein x is -0.100 to 0.100, optionally -0.100 to 0.006, y is 0.001 to 0.500, optionally 0.100 to 0.450, z is 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0142] Coating step: MP2O7 powder and an XPO4 suspension containing a carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing a carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. The obtained positive electrode active material has a core-shell structure, including the core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon.

[0143] Mixing step: The obtained positive electrode active material is mixed uniformly with an organopolysiloxane compound, an optional binder and an optional conductive agent to obtain a positive electrode material composition.

[0144] The preparation method of this application does not have any particular restrictions on the source of materials. Optionally, the core material in the preparation method of this application can be commercially available or prepared by the method of this application. Optionally, the core material is prepared by the method described below.

[0145] In some embodiments, optionally, the step of providing the core material includes the following steps: Step (1): mixing and stirring a manganese source, a source of element A, and an acid in a container to obtain manganese salt particles doped with element A; Step (2): mixing the manganese salt particles doped with element A with a lithium source, a phosphorus source, and a source of element R in a solvent to obtain a slurry, and sintering it under an inert gas atmosphere to obtain lithium manganese phosphate doped with elements A and R, wherein the lithium manganese phosphate doped with elements A and R is Li 1+x Mn 1-y A y P 1-z R zO4, x is -0.100 to 0.100, optionally -0.100 to 0.006, y is 0.001 to 0.500, optionally 0.100 to 0.450, z is 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more of Fe, Ti, V, Ni, Co and Mg, and R is selected from one or more of B, Si, N and S.

[0146] In some embodiments, step (1) may be performed at a temperature of 20°C to 120°C, or optionally 25°C to 80°C.

[0147] In some embodiments, the stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes, or optionally 120 minutes to 360 minutes.

[0148] By controlling the reaction temperature, stirring rate, and mixing time during doping, the doping elements can be evenly distributed, reducing lattice defects, inhibiting manganese ion dissolution, and reducing interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the specific capacity and rate performance of the positive electrode active material.

[0149] It should be noted that, in this application, the source of a certain element may include one or more of the element's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide, and the precursor is the source that enables the preparation method of this application to achieve its purpose. As an example, the source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide, or hydroxide, and element R's inorganic acid.

[0150] In some embodiments, optionally, the source of manganese in this application is one or more selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0151] In some embodiments, element A may optionally be iron, and the source of iron may optionally be one or more selected from ferrous carbonate, ferric hydroxide, and ferrous sulfate.

[0152] In some embodiments, optionally, in step (1), the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, and may be oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of less than 60% by weight.

[0153] In some embodiments, the inorganic acid of element R is optionally selected from one or more of phosphoric acid, nitric acid, boric acid, silicic acid, and orthosilicic acid.

[0154] In some embodiments, optionally, the lithium source in this application is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0155] In some embodiments, optionally, the source of phosphorus in this application is one or more selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0156] In some embodiments, optionally, the carbon source in this application is an organic carbon source, and the organic carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0157] In some embodiments, optionally, the solvent used in the preparation method described in this application is a solvent commonly used in the art. For example, the solvent in the preparation method of this application may be independently selected from at least one of ethanol and water (e.g., deionized water).

[0158] In some embodiments, optionally, the pH of the solution is controlled to be between 4 and 6 during the preparation of element A-doped manganese salt particles. It should be noted that the pH of the resulting mixture can be adjusted using methods commonly used in the art, for example, by adding an acid or a base.

[0159] In some embodiments, optionally, in step (2), the molar ratio of the manganese salt particles doped with element A to the lithium source and the phosphorus source is 1:(0.5-2.1):(0.5-2.1).

[0160] In some embodiments, optionally, in step (2), the sintering conditions are: sintering at 600°C to 800°C for 4 to 10 hours in an inert gas or a mixture of inert gas and hydrogen. This results in a higher degree of crystallinity in the sintered material, thereby improving the specific capacity and rate performance of the positive electrode active material.

[0161] In some embodiments, the inert gas and hydrogen mixture is optionally nitrogen (70 vol% to 90 vol%) + hydrogen (10 vol% to 30 vol%).

[0162] In some embodiments, the MP2O7 powder is optionally a commercially available product, or optionally, the MP2O7 powder is prepared by adding a source of element M and a source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to 4 to 6, stirring and reacting fully, and then drying and sintering to obtain the powder. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al.

[0163] In some embodiments, optionally, during the preparation of MP2O7 powder, the drying step is to dry at 100°C to 300°C, or optionally 150°C to 200°C, for 4 to 8 hours.

[0164] In some embodiments, optionally, during the preparation of MP2O7 powder, the sintering step is to sinter at 500°C to 800°C, optionally 650°C to 800°C, in an inert gas atmosphere for 4 to 10 hours.

[0165] In some embodiments, optionally, the carbon-source-containing XPO4 suspension is commercially available, or optionally, it is prepared by mixing a lithium source, an X source, a phosphorus source, and a carbon source uniformly in a solvent, and then heating the reaction mixture to 60°C to 120°C and maintaining the temperature for 2 hours to 8 hours to obtain the carbon-source-containing XPO4 suspension. Optionally, during the preparation of the carbon-source-containing XPO4 suspension, the pH of the mixture is adjusted to 4 to 6.

[0166] In some embodiments, optionally, in the coating step, the mass ratio of the A and R element-doped lithium manganese phosphate (core), MP2O7 powder, and the carbon-containing XPO4 suspension is 1:(0.001-0.05):(0.001-0.05).

[0167] In some embodiments, optionally, the sintering temperature for obtaining the positive electrode active material in the coating step is 500°C to 800°C, and the sintering time is 4 hours to 10 hours.

[0168] In some embodiments, optionally, the median particle size Dv50 of the primary particles of the double-coated lithium manganese phosphate cathode active material of this application is 50 nm to 2000 nm.

[0169] Positive electrode sheet

[0170] A third aspect of this application provides a positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer comprises a positive electrode material composition according to the first aspect of this application or a positive electrode material composition prepared by the method according to the second aspect of this application, and the content of the positive electrode material composition in the positive electrode film layer is 50% by weight or more, based on the total weight of the positive electrode film layer. The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0171] In some embodiments, the positive electrode material composition may optionally be present in the positive electrode film layer at a content of 90% to 100% by weight, based on the total weight of the positive electrode film layer.

[0172] The positive electrode film layer does not exclude components other than the positive electrode material composition of the first aspect of this application or the positive electrode material composition prepared by the method of the second aspect of this application. For example, the positive electrode film layer may also include positive electrode active materials other than the bilayer coated lithium manganese phosphate positive electrode active material of this application. Optionally, the other positive electrode active materials may include at least one of lithium transition metal oxides and their modified compounds. As an example, the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds.

[0173] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0174] In some embodiments, the solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 90°, optionally between 3° and 60°, and further between 10° and 30°. When the contact angle is within a suitable range, the secondary battery can have a high energy density while also improving cycle performance, safety performance, and / or rate performance. It can effectively avoid the following situations: if the contact angle is too small, it cannot effectively alleviate the erosion of the positive electrode active material surface by acidic substances in the electrolyte, and its effect on improving cycle performance may not be significant; if the contact angle is too large, it may cause poor electrolyte wettability of the positive electrode film, affecting the rate performance and cycle performance of the secondary battery. The solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent has a well-known meaning in the art and can be tested using methods known in the art, for example, it can be measured according to GBT30693-2014. An exemplary test method includes the following steps: at room temperature, a non-aqueous organic solvent is dropped onto the surface of the positive electrode sheet, and the contact angle is measured over 60 seconds using a contact angle measuring instrument. The testing instrument can be an LSA 200 optical contact angle measuring instrument from LAUDA Scientific, Germany. The non-aqueous organic solvent can be any non-aqueous organic solvent known in the art for use in non-aqueous electrolytes for secondary batteries; optionally, the non-aqueous organic solvent is ethylene carbonate (EC).

[0175] In some embodiments, the porosity of the positive electrode film is 15% to 50%, optionally 15% to 30%. When the porosity is within a suitable range, the secondary battery can have a high energy density while also achieving improved cycle performance, safety performance, and / or rate performance. It effectively avoids the following situations: if the porosity is too low, the electrolyte wettability of the positive electrode film may deteriorate, affecting the rate performance and cycle performance of the secondary battery; if the porosity is too high, it may affect the overall energy density of the secondary battery. The porosity of the positive electrode film has a well-known meaning in the art and can be tested using methods known in the art, such as by peeling off the positive electrode film with tape and measuring according to GB / T 24586-2009. Porosity P = [(V2-V1) / V2] × 100%. V1 (cm 3 V² (cm²) represents the true volume, which can be determined using an inert gas with a small molecular diameter (such as helium) via a displacement method, combined with Archimedes' principle and Bohr's law. 3 V represents the apparent volume, V² = S × H × A, where S (cm²) 2 ) represents the area, H (cm) represents the thickness, and A represents the number of samples.

[0176] In some embodiments, the resistance of the positive electrode film is greater than 0 and less than or equal to 6Ω. This ensures that the positive electrode has good conductivity, resulting in better dynamic performance of the secondary battery. The resistance of the positive electrode film is a well-known concept in the art and can be tested using methods known in the art, such as using an electrode resistance meter. An exemplary testing method is as follows: Take a single-sided coated and cold-pressed positive electrode (if it is a double-sided coated positive electrode, the positive electrode film on one side can be wiped off first) and place it parallel between the two conductive terminals of the electrode resistance meter. Apply a certain pressure to fix it, thus obtaining the resistance of the positive electrode film. Optionally, the diameter of the conductive terminals can be 14mm, the applied pressure can be 15MPa to 27MPa, and the sampling time range can be 10 seconds to 20 seconds. The testing instrument can be an IESTBER1000 electrode resistance meter from Yuaneng Technology Co., Ltd.

[0177] In some embodiments, the adhesion force between the positive electrode film and the positive electrode current collector is greater than or equal to 0.5 MPa. Within this range, it can prevent the occurrence of powder shedding from the positive electrode sheet, thereby benefiting the performance of the secondary battery. The adhesion force between the positive electrode film and the positive electrode current collector is a term known in the art and can be tested using methods known in the art. An exemplary test method is as follows: Cut the positive electrode sheet into a test sample 100mm long and 10mm wide; take a stainless steel plate 25mm wide, apply double-sided tape (e.g., 11mm wide), and attach the test sample to the double-sided tape on the stainless steel plate. Roll the sample back and forth three times with a 2000g roller (e.g., at a rolling speed of 300mm / min); bend the test sample 180°, manually peel the positive electrode film layer from the positive electrode current collector by 25mm, fix the test sample on a testing machine (e.g., INSTRON 336), ensuring the peeling surface is aligned with the force line of the testing machine. The testing machine continuously peels at 30mm / min. The average value of the obtained peeling force curve at a stable point is taken as the peeling force F0; the adhesion force between the positive electrode film layer and the positive electrode current collector = F0 / width of the test sample.

[0178] In some embodiments, the areal density of the positive electrode film is 0.006 g / cm³. 2 Up to 0.065 g / cm 2 This is beneficial for improving the volumetric energy density of secondary batteries. The areal density of the positive electrode film is a well-known concept in the art and can be tested using methods known in the art. An exemplary test method is as follows: Take a positive electrode sheet coated on one side and cold-pressed (if it is a positive electrode sheet coated on both sides, the positive electrode film on one side can be wiped off first) and cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1; then wipe off the positive electrode film of the above-weighed positive electrode sheet, weigh the positive current collector, and record it as M0; the areal density of the positive electrode film = (M1-M0) / S1.

[0179] In some embodiments, the electrolyte absorption rate of the positive electrode film is from 0.0125 μg / s to 100 μg / s, optionally from 0.5 μg / s to 40 μg / s. This ensures good wettability of the electrolyte within the electrode assembly, allowing it to quickly penetrate the assembly and form a new SEI film on the positive electrode surface, thereby improving the electrochemical performance of the secondary battery.

[0180] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0181] It should be noted that the parameters of each positive electrode film layer given in this application (such as contact angle, porosity, resistance, adhesion, areal density, and electrolyte absorption rate) refer to the parameters of the positive electrode film layer on one side of the positive electrode current collector. When the positive electrode film layer is disposed on both sides of the positive electrode current collector, if the parameters of the positive electrode film layer on either side meet the requirements of this application, it is considered to fall within the protection scope of this application.

[0182] In addition, the above-mentioned tests on the parameters of the positive electrode film can be conducted by sampling during the preparation of the positive electrode sheet or battery, or by sampling from the prepared battery.

[0183] When the test samples are taken from the prepared battery, as an example, the sampling can be carried out in the following steps: discharge the battery (for safety reasons, the battery is generally left fully discharged); remove the positive electrode after disassembling the battery, and soak the positive electrode in dimethyl carbonate (DMC) for a certain period of time (e.g., 2 to 10 hours); then remove the positive electrode and dry it at a certain temperature and time (e.g., 60°C for 4 hours). After drying, remove the positive electrode, and then samples can be taken from the dried positive electrode to test the parameters related to the positive electrode film layer mentioned above in this application.

[0184] Secondary batteries

[0185] A fourth aspect of this application provides a secondary battery that includes the positive electrode of the third aspect of this application.

[0186] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery consists of an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes, primarily preventing short circuits while allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, conducts the active ions.

[0187] [Positive electrode plate]

[0188] The positive electrode used in the secondary battery of this application is the positive electrode described in any embodiment of the third aspect of this application.

[0189] [Negative electrode plate]

[0190] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0191] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0192] In some embodiments, the negative electrode film may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0194] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0195] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer base material and a metal material layer formed on at least one surface of the polymer base material. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer base material may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0196] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0197] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0198] [Electrolytes]

[0199] This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0200] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0201] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0202] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0203] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0204] [Isolation membrane]

[0205] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0206] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0207] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0208] In some embodiments, the secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0209] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0210] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0211] In some implementations, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0212] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer package, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0213] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0214] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0215] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0216] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0217] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0218] Electrical appliances

[0219] The fifth aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0220] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0221] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0222] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0223] Example

[0224] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0225] The sources of raw materials involved in the embodiments of this application are as follows:

[0226]

[0227]

[0228] Example 1-1

[0229] Preparation of positive electrode active materials

[0230] (1) Preparation of co-doped lithium manganese phosphate core

[0231] Preparation of Fe, Co, and V co-doped manganese oxalate: 689.5 g of manganese carbonate (calculated as MnCO3), 455.2 g of ferrous carbonate (calculated as FeCO3), 4.6 g of cobalt sulfate (calculated as CoSO4), and 4.9 g of vanadium dichloride (calculated as VCl2) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O) were added. The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no bubbles were generated), yielding a suspension of Fe, Co, V, and S co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0232] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: 1793.4 g of manganese oxalate dihydrate particles obtained in the previous step, 369.0 g of lithium carbonate (calculated as Li₂CO₃), 1.6 g of 60% dilute sulfuric acid (calculated as 60% H₂SO₄), and 1148.9 g of ammonium dihydrogen phosphate (calculated as NH₄H₂PO₄) were added to 20 L of deionized water. The mixture was stirred for 10 hours to ensure homogeneity, resulting in a slurry. The slurry was then transferred to a spray dryer for spray drying and granulation. The drying temperature was set at 250 °C, and the drying time was 4 hours to obtain powder. Under a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, the powder was sintered at 700 °C for 4 hours to obtain 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate, i.e., the core.

[0233] (2) Preparation of lithium iron pyrophosphate and lithium iron phosphate

[0234] Preparation of lithium iron pyrophosphate powder: 4.77 g lithium carbonate, 7.47 g ferrous carbonate, 14.84 g ammonium dihydrogen phosphate, and 1.3 g oxalic acid dihydrate were dissolved in 50 mL deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 650 °C under a nitrogen atmosphere for 8 hours, and after naturally cooling to room temperature, it was ground to obtain Li₂FeP₂O₇ powder.

[0235] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.8 g ferrous carbonate, 34.5 g ammonium dihydrogen phosphate, 1.3 g oxalic acid dihydrate, and 74.6 g sucrose (in C2) were added. 12 H 22 O 11 The solution (hereinafter referred to as "the solution") was dissolved in 150 mL of deionized water to obtain a mixture, which was then stirred for 6 hours to allow the mixture to react fully. The reacted solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0236] (3) Covering

[0237] 1572.1g of the Fe, Co, V, and S co-doped lithium manganese phosphate (core) and 15.72g of the lithium iron pyrophosphate (Li2FeP2O7) powder were added to the lithium iron phosphate (LiFePO4) suspension prepared in the previous step. After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150°C for 6 hours. The resulting product was then dispersed by sand milling. After dispersion, the product was sintered at 700°C for 6 hours under a nitrogen atmosphere to obtain the target product, double-layer coated lithium manganese phosphate, i.e., the positive electrode active material.

[0238] Preparation of positive electrode sheet

[0239] A positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups -CH2NH2 and -CH2NH-, mass percentage α approximately 12%, number average molecular weight 3700) were mixed in a mixer at a weight ratio of 93.4:1.5:4.5:0.6 until the materials were uniformly mixed to obtain a positive electrode material composition. Then, the above positive electrode material composition was added to N-methylpyrrolidone (NMP) and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry was then coated with a surface density of 0.018 g / cm³. 2 The coating is evenly applied to aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0240] Preparation of negative electrode sheet

[0241] A negative electrode slurry was prepared by dissolving artificial graphite (anode active material), hard carbon, acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 90:5:2:2:1 and stirring until homogeneous. The negative electrode slurry was then coated with a solution to achieve a surface density of 0.0075 g / cm³. 2 The negative electrode sheet is obtained by uniformly coating the copper foil of the negative electrode current collector, drying, cold pressing, and slitting.

[0242] Preparation of electrolyte

[0243] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3 / 7 as an organic solvent. 12.5% ​​by weight (based on the weight of the organic solvent) of LiPF6 was added and dissolved in the organic solvent and stirred until homogeneous to obtain the electrolyte.

[0244] Preparation of the separating membrane

[0245] The material used was a commercially available PP-PE copolymer microporous film with a thickness of 20 μm and an average pore size of 80 nm (from Zogo Electronics Technology Co., Ltd., model 20).

[0246] Preparation of full cells

[0247] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, injected with the electrolyte, and sealed to obtain a full cell (hereinafter also referred to as "full cell").

[0248] Preparation of button cells

[0249] A positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups -CH2NH2 and -CH2NH-, mass percentage α approximately 12%, number average molecular weight 3700) were mixed in a mixer at a weight ratio of 89.4:5:5:0.6 until the materials were uniformly mixed to obtain a positive electrode material composition. This positive electrode material composition was then added to NMP and stirred in a drying chamber to form a slurry. The slurry was coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating surface density was 0.015 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0250] A lithium sheet is used as the negative electrode, and a solution of 1 mol / L LiPF6 in ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) in a volume ratio of 1:1:1 is used as the electrolyte. The solution is assembled with the positive electrode prepared above in a button cell to form a button cell (hereinafter also referred to as "button cell").

[0251] Examples 1-2 to 1-33

[0252] Except for the preparation of the positive electrode active material, all other processes are the same as those in Example 1-1.

[0253] Examples 1-2 to 1-6

[0254] Preparation of positive electrode adaptive materialsIn the preparation of the co-doped lithium manganese phosphate core, except that vanadium dichloride and cobalt sulfate are not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate are used, the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 are the same as those in Example 1-1. In addition, during the preparation of lithium iron pyrophosphate and lithium iron phosphate, and during the coating of the first and second coating layers, the raw materials used were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example 1-1, so that the amounts of Li2FeP2O7 / LiFePO4 in Examples 1-2 to 1-6 were 12.6g / 37.7g, 15.7g / 47.1g, 18.8g / 56.5g, 22.0g / 66.0g and 25.1g / 75.4g, respectively, and the amount of sucrose in Examples 1-2 to 1-6 was 37.3g, the other conditions were the same as in Example 1-1.

[0255] Examples 1-7 to 1-10

[0256] Preparation of positive electrode active materials Except that the amounts of sucrose used were 74.6g, 149.1g, 186.4g and 223.7g respectively, so that the corresponding coating amounts of the carbon layer as the second coating layer were 31.4g, 62.9g, 78.6g and 94.3g respectively, the conditions of Examples 1-7 to 1-10 were the same as those of Examples 1-3.

[0257] Examples 1-11 to 1-14

[0258] Preparation of positive electrode active materials Except for adjusting the amounts of various raw materials according to the coating amounts shown in Table 1 during the preparation of lithium iron pyrophosphate and lithium iron phosphate so that the amounts of Li2FeP2O7 / LiFePO4 are 23.6g / 39.3g, 31.4g / 31.4g, 39.3g / 23.6g and 47.2g / 15.7g respectively, the conditions of Examples 1-11 to 1-14 are the same as those of Examples 1-7.

[0259] Examples 1-15

[0260] Preparation of positive electrode active materials Except for the use of 492.80g of zinc carbonate instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions in Examples 1-15 were the same as those in Examples 1-14.

[0261] Examples 1-16 to 1-18

[0262] Preparation of positive electrode active materialsExcept that in Examples 1-16, 466.4 g of nickel carbonate, 5.0 g of zinc carbonate, and 7.2 g of titanium sulfate were used instead of ferrous carbonate in the preparation of the co-doped lithium manganese phosphate core; in Examples 1-17, 455.2 g of ferrous carbonate and 8.5 g of vanadium dichloride were used in the preparation of the co-doped lithium manganese phosphate core; and in Examples 1-18, 455.2 g of ferrous carbonate, 4.9 g of vanadium dichloride, and 2.5 g of magnesium carbonate were used in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-16 to 1-18 were the same as those of Examples 1-7.

[0263] Examples 1-19 to 1-20

[0264] Preparation of positive electrode active materials Except that in Examples 1-19, 369.4 g of lithium carbonate and 1.05 g of 60% dilute nitric acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, and in Examples 1-20, 369.7 g of lithium carbonate and 0.78 g of silicic acid were used instead of dilute sulfuric acid in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-19 to 1-20 were the same as those of Examples 1-18.

[0265] Examples 1-21 to 1-22

[0266] Preparation of positive electrode active materials Except for Examples 1-21, which used 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid in the preparation of the co-doped lithium manganese phosphate core, and Examples 1-22, which used 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-21 to 1-22 were the same as those of Examples 1-20.

[0267] Examples 1-23 to 1-24

[0268] Preparation of positive electrode active materials Except for Examples 1-23, which used 804.6g manganese carbonate, 231.7g ferrous carbonate, 1156.2g ammonium dihydrogen phosphate, 1.2g boric acid (99.5% by mass), and 370.8g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, and Examples 1-24, which used 862.1g manganese carbonate, 173.8g ferrous carbonate, 1155.1g ammonium dihydrogen phosphate, 1.86g boric acid (99.5% by mass), and 371.6g lithium carbonate in the preparation of the co-doped lithium manganese phosphate core, the conditions of Examples 1-23 to 1-24 were the same as those of Examples 1-22.

[0269] Examples 1-25

[0270] Preparation of positive electrode active materials Except for the use of 370.1g lithium carbonate, 1.56g silicic acid and 1147.7g ammonium dihydrogen phosphate in the preparation of co-doped lithium manganese phosphate cores in Examples 1-25, the conditions in Examples 1-25 are the same as those in Examples 1-20.

[0271] Examples 1-26

[0272] Preparation of positive electrode active materials Except for the use of 368.3g lithium carbonate, 4.9g dilute sulfuric acid with a mass fraction of 60%, 919.6g manganese carbonate, 224.8g ferrous carbonate, 3.7g vanadium dichloride, 2.5g magnesium carbonate, and 1146.8g ammonium dihydrogen phosphate in the preparation of co-doped lithium manganese phosphate cores in Examples 1-26, the conditions in Examples 1-26 are the same as those in Examples 1-20.

[0273] Examples 1-27

[0274] Preparation of positive electrode active materials Except for the use of 367.9g of lithium carbonate, 6.5g of 60% dilute sulfuric acid, and 1145.4g of ammonium dihydrogen phosphate in the preparation of the co-doped lithium manganese phosphate core in Examples 1-27, the conditions in Examples 1-27 are the same as those in Examples 1-20.

[0275] Examples 1-28 to 1-33

[0276] Preparation of positive electrode active materials Except for Examples 1-28 to 1-33, in the preparation of the co-doped lithium manganese phosphate core, 1034.5g of manganese carbonate, 108.9g of ferrous carbonate, 3.7g of vanadium dichloride, and 2.5g of magnesium carbonate were used, the amounts of lithium carbonate used were 367.6g, 367.2g, 366.8g, 366.4g, 366.0g, and 332.4g, the amounts of ammonium dihydrogen phosphate used were 1144.5g, 1143.4g, 1142.2g, 1141.1g, 1139.9g, and 1138.8g, and the amounts of 60% dilute sulfuric acid used were 8.2g, 9.8g, 11.4g, 13.1g, 14.7g, and 16.3g, the conditions in Examples 1-28 to 1-33 were the same as in Examples 1-20.

[0277] Examples 2-1 to 2-3

[0278] Except for the preparation of the positive electrode active material, all other processes are the same as those in Example 1-1.

[0279] Example 2-1

[0280] Preparation of positive electrode active materialsExcept that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step is 550°C and the sintering time is 1 hour to control the crystallinity of Li2FeP2O7 to 30%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step is 650°C and the sintering time is 2 hours to control the crystallinity of LiFePO4 to 30%, the other conditions are the same as in Examples 1-1.

[0281] Example 2-2

[0282] Preparation of positive electrode active materials Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step is 550°C and the sintering time is 2 hours to control the crystallinity of Li2FeP2O7 to 50%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step is 650°C and the sintering time is 3 hours to control the crystallinity of LiFePO4 to 50%, the other conditions are the same as in Examples 1-1.

[0283] Example 2-3

[0284] Preparation of positive electrode active materials Except that in the preparation of lithium iron pyrophosphate (Li2FeP2O7), the sintering temperature in the powder sintering step is 600℃ and the sintering time is 3 hours to control the crystallinity of Li2FeP2O7 to 70%, and in the preparation of lithium iron phosphate (LiFePO4), the sintering temperature in the coating sintering step is 650℃ and the sintering time is 4 hours to control the crystallinity of LiFePO4 to 70%, the other conditions are the same as in Examples 1-1.

[0285] Examples 3-1 to 3-5

[0286] Except for adjusting the weight percentage of aminoethylaminopropylpolydimethylsiloxane in the cathode material composition during the preparation of full cells and coin cells, the processes were the same as in Examples 1-1.

[0287] Example 3-1

[0288] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93.99:1.5:4.5:0.01 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0289] Preparation of button cellsThe positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 89.99:5:5:0.01 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0290] Example 3-2

[0291] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and alkylaminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93.9:1.5:4.5:0.1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0292] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 89.9:5:5:0.1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0293] Example 3-3

[0294] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are mixed in a mixer at a weight ratio of 93:1.5:4.5:1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0295] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (with polar functional groups -CH2NH2 and -CH2NH-, a mass percentage α of approximately 12%, and a number average molecular weight of 3700) are mixed in a mixer at a weight ratio of 89:5:5:1 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0296] Examples 3-4

[0297] Preparation of full cellsThe positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 92:1.5:4.5:2 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0298] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (with polar functional groups -CH2NH2 and -CH2NH-, a mass percentage α of approximately 12%, and a number average molecular weight of 3700) are mixed in a mixer at a weight ratio of 88:5:5:2 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0299] Examples 3-5

[0300] Preparation of full cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 89:1.5:4.5:5 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0301] Preparation of button cells The positive electrode active material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and aminoethylaminopropyl polydimethylsiloxane (polar functional groups are -CH2NH2 and -CH2NH-, mass percentage α is about 12%, number average molecular weight is 3700) are stirred in a mixer at a weight ratio of 85:5:5:5 until the materials are uniformly mixed to obtain the positive electrode material composition.

[0302] Examples 3-6 to 3-23

[0303] Except for replacing the aminoethylaminopropylpolydimethylsiloxane in the cathode material composition with the following organopolysiloxane compounds in the preparation of the full cell and the coin cell, the processes are the same as in Examples 1-1.

[0304] Examples 3-6: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 1200).

[0305] Examples 3-7: Polymethylchloropropylsiloxane (polar functional group is -CH2Cl, mass percentage α is about 30.2%, number average molecular weight is 2500).

[0306] Examples 3-8: Polymethyltrifluoropropylsiloxane (polar functional group is -CF3, mass percentage α is about 44.0%, number average molecular weight is 1400).

[0307] Examples 3-9: Mercaptopropyl polysiloxane (polar functional group is -CH2SH, mass percentage α is about 15.0%, number average molecular weight is 2000).

[0308] Examples 3-10: Hydroxyl-terminated polydimethylsiloxane (polar functional group is -OH, mass percentage α is about 3.4%, number average molecular weight is 1000).

[0309] Examples 3-11: Methoxy-terminated polydimethylsiloxane (the polar functional group is methoxy, the mass percentage α is about 3.1%, and the number average molecular weight is 2800).

[0310] Examples 3-12: Terminal polyether polydimethylsiloxane (polar functional group is polyether segment, mass percentage α is about 10.0%, number average molecular weight is 2110).

[0311] Examples 3-13: Side-chain phosphate ester grafted polydimethylsiloxane (polar functional group is phosphate ester group, mass percentage α is about 1.4%, number average molecular weight is 15600),

[0312] Examples 3-14: 1,3,5,7-octamethylcyclotetrasiloxane (mass percentage of polar functional groups α is approximately 0%, molecular weight is 280).

[0313] Examples 3-15: Cyclopentadimethylsiloxane (mass percentage of polar functional groups α is about 0%, molecular weight is 370).

[0314] Examples 3-16: Terminal polyether polydimethylsiloxane (polar functional group is polyether segment, mass percentage α is about 55.0%, number average molecular weight is 25132).

[0315] Example 3-17: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 400).

[0316] Example 3-18: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 10,000).

[0317] Example 3-19: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 50,000).

[0318] Examples 3-20: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 80,000).

[0319] Example 3-21: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 100,000).

[0320] Example 3-22: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 300,000).

[0321] Example 3-23: Polydimethylsiloxane (the mass percentage of polar functional groups α is about 0%, and the number average molecular weight is 400,000).

[0322] Comparative Examples 1 to 7

[0323] Except for the fact that the positive electrode active material was prepared according to the following method, and that no aminoethylaminopropylpolydimethylsiloxane was added to the positive electrode material composition in the preparation of the full cell and the coin cell, all other processes were the same as those in Examples 1-1.

[0324] Comparative Example 1

[0325] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to a reaction vessel, along with 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (calculated as C2H2O4·2H2O, the same below). The reaction vessel was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no more bubbles were generated), resulting in a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0326] Preparation of carbon-coated lithium manganese phosphate: Take 1789.6g of the above-obtained manganese oxalate dihydrate particles, 369.4g of lithium carbonate (calculated as Li2CO3, the same below), 1150.1g of ammonium dihydrogen phosphate (calculated as NH4H2PO4, the same below) and 31g of sucrose (calculated as C). 12 H 22 O 11 The mixture (hereinafter the same) is added to 20 liters of deionized water, and stirred for 10 hours to ensure uniform mixing, resulting in a slurry. The slurry is then transferred to a spray dryer for spray drying and granulation. The drying temperature is set at 250°C, and the mixture is dried for 4 hours to obtain a powder. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the powder is sintered at 700°C for 4 hours to obtain carbon-coated lithium manganese phosphate.

[0327] Comparative Example 2

[0328] Except for the use of 689.5g of manganese carbonate and the addition of 463.3g of ferrous carbonate, the conditions for Comparative Example 2 were the same as those for Comparative Example 1.

[0329] Comparative Example 3

[0330] Except for the use of 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 3 were the same as those of Comparative Example 1.

[0331] Comparative Example 4

[0332] Except for the use of 689.5g of manganese carbonate, 1148.9g of ammonium dihydrogen phosphate and 369.0g of lithium carbonate, and the addition of 463.3g of ferrous carbonate and 1.6g of 60% dilute sulfuric acid, the other conditions of Comparative Example 4 were the same as those of Comparative Example 1.

[0333] Comparative Example 5

[0334] Except for the additional step of preparing lithium iron pyrophosphate powder: 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate, and 32.5 g of oxalic acid dihydrate were dissolved in 50 mL of deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and then naturally cooled to room temperature before grinding. The crystallinity of Li₂FeP₂O₇ was controlled to be 5%. Except for the amount of Li₂FeP₂O₇ used when preparing the carbon-coated material, which was 62.8 g, the other conditions of Comparative Example 5 were the same as those of Comparative Example 4.

[0335] Comparative Example 6

[0336] Except for the additional step of preparing a lithium iron phosphate suspension: 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, and 50.2 g of oxalic acid dihydrate were dissolved in 500 mL of deionized water, and then stirred for 6 hours to allow the mixture to react fully. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4. In the preparation of lithium iron phosphate (LiFePO4), except for the sintering temperature of 600 °C and the sintering time of 4 hours in the coating sintering step to control the crystallinity of LiFePO4 to 8%, and the amount of LiFePO4 used in preparing the carbon-coated material being 62.8 g, the other conditions of Comparative Example 6 were the same as those of Comparative Example 4.

[0337] Comparative Example 7

[0338] Preparation of lithium iron pyrophosphate powder: 2.38 g lithium carbonate, 7.5 g ferrous carbonate, 7.4 g ammonium dihydrogen phosphate, and 8.1 g oxalic acid dihydrate were dissolved in 50 mL deionized water. The pH of the mixture was 5, and the mixture was stirred for 2 hours to allow the reaction mixture to react fully. The resulting solution was then heated to 80 °C and maintained at that temperature for 4 hours to obtain a suspension containing Li₂FeP₂O₇. The suspension was filtered, washed with deionized water, and dried at 120 °C for 4 hours to obtain powder. The powder was sintered at 500 °C under a nitrogen atmosphere for 4 hours, and after naturally cooling to room temperature, it was ground to control the crystallinity of Li₂FeP₂O₇ to 5%.

[0339] Preparation of lithium iron phosphate suspension: 11.1 g lithium carbonate, 34.7 g ferrous carbonate, 34.4 g ammonium dihydrogen phosphate, 37.7 g oxalic acid dihydrate, and 37.3 g sucrose (in C2) were added. 12 H 22 O 11 The solution (hereinafter the same) was dissolved in 1500 mL of deionized water, and then stirred for 6 hours to allow the mixture to react fully. The reacted solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0340] Coating: 15.7g of the obtained lithium iron pyrophosphate powder was added to the above-mentioned lithium iron phosphate (LiFePO4) and sucrose suspension. In the preparation process, the sintering temperature in the coating sintering step was 600℃ and the sintering time was 4 hours to control the crystallinity of LiFePO4 to 8%. The other conditions of Comparative Example 7 were the same as those of Comparative Example 4, and amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon-coated positive electrode active materials were obtained.

[0341] Comparative Example 8

[0342] Except for the absence of aminoethylaminopropylpolydimethylsiloxane in the preparation of the full cell and the coin cell, the process was the same as in Example 1-1.

[0343] Relevant parameter testing

[0344] 1. Determination of the core chemical formula and composition of different coating layers:

[0345] High spatial resolution characterization of the internal microstructure and surface structure of the positive electrode active material was performed using spherical aberration electron microscopy (ACSTEM). Combined with three-dimensional reconstruction technology, the core chemical formula and the composition of the first and second coating layers of the positive electrode active material were obtained.

[0346] 2. Initial capacity test of button cells:

[0347] The button cell obtained above is charged to 4.3V at 0.1C, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After standing for 5 minutes, it is discharged to 2.0V at 0.1C. The discharge capacity at this time is the initial specific capacity, denoted as D0.

[0348] 3. Average discharge voltage (V) test of coin cells:

[0349] The coin cells prepared above are placed in a constant temperature environment of 25°C for 5 minutes, discharged at 0.1C to 2.5V, placed in a constant temperature environment for 5 minutes, charged at 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current is less than or equal to 0.05mA. After being placed in a constant temperature environment for 5 minutes, they are discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial specific capacity, denoted as D0, and the discharge energy is the initial energy, denoted as E0. The average discharge voltage V of the coin cells is E0 / D0.

[0350] 4. Full battery gas expansion test at 60°C:

[0351] The prepared full cell was stored at 60°C at 100% state of charge (SOC). The open-circuit voltage (OCV) and internal resistance (IMP) were measured before, during, and after storage to monitor SOC, and the cell volume was also measured. After every 48 hours of storage, the full cell was removed, allowed to stand for 1 hour, and then the open-circuit voltage (OCV) and internal resistance (IMP) were measured. After cooling to room temperature, the cell volume was measured using the water displacement method. The water displacement method involves first measuring the cell's weight (F1) separately using a balance with automatic unit conversion, and then completely immersing the cell in deionized water (with a known density of 1 g / cm³). 3 In the experiment, the weight F2 of the battery at this moment is measured, and the buoyant force F on the battery is measured. 浮 That is, F1-F2, and then according to Archimedes' principle, F 浮 =ρ×g×V 排 The battery volume V is calculated to be V = (F1 - F2) / (ρ × g).

[0352] Based on the OCV and IMP test results, the batteries in all embodiments maintained a SOC of over 99% throughout the entire testing process until the end of storage.

[0353] After 30 days of storage, the battery volume was measured, and the percentage increase in battery volume after storage was calculated relative to the battery volume before storage.

[0354] 5. Cyclic performance test of the entire battery at 45°C:

[0355] Under a constant temperature environment of 45℃, the prepared full battery was charged at 1C to 4.3V, and then charged at a constant voltage of 4.3V until the current was less than or equal to 0.05mA. After resting for 5 minutes, it was discharged at 1C to 2.5V, and the discharge capacity at this point was recorded as D0. The aforementioned charge-discharge cycle was repeated until the discharge capacity decreased to 80% of D0. The number of cycles completed at this point was recorded.

[0356] 6. Transition metal dissolution test:

[0357] The full battery, after being cycled at 45°C until its capacity decayed to 80%, was discharged at a 0.1C rate until the cutoff voltage of 2.0V. Then, the battery was disassembled, the negative electrode was removed, and 30 unit areas (1540.25 mm²) were randomly selected from the negative electrode. 2 The discs were tested using an Agilent ICP-OES730 inductively coupled plasma emission spectrometry (ICP). The amounts of Fe (if the Mn site of the positive electrode active material is doped with Fe) and Mn were calculated based on the ICP results, thus determining the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0358] 7. Methods for measuring lattice change rate:

[0359] Under a constant temperature environment of 25℃, the positive electrode active material sample prepared above was placed in an XRD (model Bruker D8Discover) and tested at 1° / minute. The test data was then organized and analyzed. Referring to the standard PDF card, the lattice constants a0, b0, c0 and v0 were calculated (a0, b0 and c0 represent the length of the unit cell in each direction, and v0 represents the volume of the unit cell, which can be directly obtained from the XRD refinement results).

[0360] Using the above-described method for preparing coin cells, the positive electrode active material sample was prepared into a coin cell, and the coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. The positive electrode sheet was then removed from the coin cell and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter less than 500 nm were screened out. Samples were taken, and their cell volume v1 was calculated in the same manner as the fresh samples tested above. The lattice change rate (cell volume change rate) before and after complete lithium insertion / extraction is shown in the table.

[0361] 8. Li / Mn inverse defect concentration test:

[0362] The XRD results obtained from the "lattice change rate measurement method" are compared with the PDF (Powder Diffraction File) card of the standard crystal to determine the Li / Mn antisite defect concentration. Specifically, the XRD results obtained from the "lattice change rate measurement method" are imported into the General Structure Analysis System (GSAS) software to automatically obtain refined results, which include the occupancy of different atoms. The Li / Mn antisite defect concentration is then obtained by reading the refined results.

[0363] 9. Surface oxygen valence state test:

[0364] 5g of the positive electrode active material sample prepared above was used to prepare a coin cell according to the above method. The coin cell was charged at a low rate of 0.05C until the current decreased to 0.01C. Then, the positive electrode sheet of the coin cell was removed and immersed in dimethyl carbonate (DMC) for 8 hours. After drying, the powder was scraped off, and particles with a diameter of less than 500nm were screened out. The obtained particles were measured using electron energy loss spectroscopy (EELS, using a Talos F200S instrument) to obtain the energy loss near-edge structure (ELNES), which reflects the density of states and energy level distribution of the element. Based on the density of states and energy level distribution, the number of occupied electrons was calculated by integrating the valence band density of states data, thereby deducing the valence state of the surface oxygen after charging.

[0365] 10. Compacted density measurement:

[0366] Take 5g of the prepared positive electrode active material powder and place it in a compaction mold (CARVER mold, model 13mm, USA). Then place the mold on a compaction density instrument. Apply a pressure of 3T (tons) and read the thickness of the powder under pressure (thickness after depressurization; the area of ​​the container used for testing is 1540.25mm²) on the instrument. 2 The compaction density is calculated using p = m / v.

[0367] 11. X-ray diffraction method for testing the crystallinity of pyrophosphate and phosphate:

[0368] Take 5g of the positive electrode active material powder prepared above, and measure the total scattering intensity by X-rays. It is the sum of the scattering intensity of all matter in space. It is only related to the intensity of the primary rays, the chemical structure, and the total number of electrons participating in the diffraction, i.e., the mass, and is not related to the order state of the sample. Then, separate the crystalline scattering and non-crystalline scattering from the diffraction pattern. The crystallinity is the ratio of the scattering of the crystalline part to the total scattering intensity.

[0369] 12. Interplanar spacing and included angles:

[0370] Take 1g of each of the above-prepared positive electrode active material powders into a 50mL test tube, and inject 10mL of 75% alcohol into the test tube. Then, stir and disperse the mixture thoroughly for 30 minutes. Then, use a clean disposable plastic pipette to take an appropriate amount of the above solution and drop it onto a 300-mesh copper grid. At this time, some powder will remain on the copper grid. Transfer the copper grid along with the sample to the TEM (Talos F200s G2) sample chamber for testing and obtain the original TEM test image.

[0371] Open the original image obtained from the TEM test in DigitalMicrograph software and perform a Fourier transform (the software will automatically complete this step after clicking) to obtain the diffraction pattern. Measure the distance from the diffraction spot to the center position in the diffraction pattern to obtain the interplanar spacing. The included angle is calculated according to the Bragg equation.

[0372] 13. Powder resistivity test:

[0373] A suitable amount of the positive electrode material composition sample powder used to prepare the full battery is placed in a special mold of a powder resistivity tester. The powder resistivity under different pressures is obtained by setting the test pressure. In this application, the test pressure is 12 MPa. The testing instrument is a Suzhou Jinglü ST2722-SZ four-probe powder resistivity tester.

[0374] 14. Specific surface area test:

[0375] Five grams of the cathode material composition sample powder used to prepare the full battery were taken, and the specific surface area was measured using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA. The specific surface area was calculated using the BET (Brunauer-Emmett-Teller) method.

[0376] 15. Contact angle test:

[0377] At room temperature, ethylene carbonate (EC) droplets were dropped onto the surface of the positive electrode film, and the solid-liquid contact angle was measured over 60 seconds using an LSA 200 optical contact angle meter from LAUDA Scientific, Germany.

[0378] Table 1 shows the composition of the positive electrode active materials in Examples 1-1 to 1-33 and Comparative Examples 1 to 8.

[0379] Table 2 shows the types and contents of organopolysiloxane compounds in the cathode material compositions of Examples 1-1 to 1-33, Examples 2-1 to 2-3, and Examples 3-1 to 3-23.

[0380] Table 3 shows the performance data of the positive electrode active materials, positive electrode material compositions, positive electrode sheets, coin cells, or all-electric cells of Examples 1-1 to 1-33 and Comparative Examples 1 to 8, measured according to the above performance test methods.

[0381] Table 4 shows the performance data of the positive electrode active material, positive electrode material composition, positive electrode sheet, button cell or all-electric cell of Examples 2-1 to 2-3, measured according to the above performance test methods.

[0382] Table 5 shows the performance data of the positive electrode material compositions, positive electrode sheets, coin cells or full cells of Examples 3-1 to 3-23, measured according to the above performance test methods.

[0383] Table 1

[0384]

[0385]

[0386] Table 2

[0387]

[0388]

[0389]

[0390]

[0391]

[0392] Based on Examples 1-1 to 1-33 and Comparative Examples 1 to 8, the presence of the first coating layer helps reduce the Li / Mn antisite defect concentration and the amount of Fe and Mn dissolved after cycling, thereby increasing the specific capacity of the battery and improving its safety and cycle performance. When other elements are doped at the Mn and phosphorus sites, the lattice change rate, antisite defect concentration, and the amount of Fe and Mn dissolved can be significantly reduced, increasing the specific capacity of the battery and improving its safety and cycle performance. Combining the positive electrode active materials of Examples 1-1 to 1-33 with organopolysiloxane compounds can further alleviate the erosion of the positive electrode active material surface by the electrolyte and reduce the amount of Fe and Mn dissolved, thereby further improving the battery's cycle performance.

[0393] As can be seen from Examples 1-2 to 1-6, as the amount of the first coating layer increases from 3.2% to 64%, the concentration of Li / Mn antisite defects in the resulting material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases. This leads to improved battery safety and cycling performance at 45°C, although the specific capacity decreases slightly. Optionally, the battery exhibits optimal overall performance when the total amount of the first coating layer is between 4% and 5.6% by weight.

[0394] Based on Examples 1-3 and Examples 1-7 to 1-10, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the leaching of Fe and Mn after cycling gradually decreases, resulting in improved battery safety and cycle performance at 45°C, although the specific capacity decreases slightly. Optionally, the battery exhibits optimal overall performance when the total amount of the second coating layer is between 3% and 5% by weight.

[0395] Based on Examples 1-11 to 1-15 and Comparative Examples 5 to 6, it can be seen that when Li2FeP2O7 and LiFePO4 are present in the first coating layer, especially when the weight ratio of Li2FeP2O7 and LiFePO4 is 1:3 to 3:1, and especially when it is 1:3 to 1:1, the improvement in battery performance is more significant.

[0396] Figure 7 This is a comparison diagram of the XRD pattern of the positive electrode active material core prepared in Example 1-1 and the standard XRD pattern (00-033-0804) of lithium manganese phosphate. Figure 7 As shown, the core of the positive electrode active material in this application is basically consistent with the position of the main characteristic peaks before lithium manganese phosphate doping, indicating that the core of the positive electrode active material in this application has no impurity phase, and the improvement of the secondary battery performance mainly comes from element doping, rather than impurity phase.

[0397] As shown in Table 4, as the crystallinity of pyrophosphate and phosphate in the first coating layer gradually increases, the lattice change rate, Li / Mn antisite defect concentration and Fe and Mn dissolution of the corresponding material gradually decrease, the specific capacity of the battery gradually increases, and the safety performance and cycle performance gradually improve.

[0398] As can be seen from Table 5, when the positive electrode active material is the same, selecting an organopolysiloxane compound that meets one or more of the following criteria—content of polar functional groups, number-average molecular weight, and amount added—to be used in combination with the positive electrode active material can further improve the cycle performance of the battery without affecting the energy density and kinetic performance.

[0399] As can be seen from Examples 1-1, 3-1 to 3-5, the powder resistance of the positive electrode active material composition first decreases and then increases with the increase of the amount of organopolysiloxane compound added. The possible reason is that when the amount of organopolysiloxane compound added is within a certain range, its hydrophobicity reduces the interaction between conductive agents and alleviates their aggregation, thereby forming a better conductive network.

[0400] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode material composition comprising a positive electrode active material having a core-shell structure and an organopolysiloxane compound, wherein, The positive electrode active material includes a core and a shell covering the core. The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, x is from -0.100 to 0.100, y is from 0.001 to 0.500, z is from 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S; The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, wherein M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. The second coating layer contains carbon.

2. The cathode material composition according to claim 1, wherein, The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, x ranges from -0.100 to 0.006, and y ranges from 0.100 to 0.

450.

3. The cathode material composition according to claim 1, wherein, The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, where A is selected from one or more of Fe, Ti, V, Ni, Co, and Mg.

4. The cathode material composition according to claim 1, wherein, The organopolysiloxane compound comprises at least one structural unit represented by Formula 1. R1 and R2 independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, -CN, -SCN, amino, phosphate ester, carboxylic acid ester, amide, aldehyde, sulfonyl, polyether segment, C1-C20 aliphatic hydrocarbon, C1-C20 halogenated aliphatic hydrocarbon, C1-C20 heteroaliphatic hydrocarbon, C1-C20 halogenated heteroaliphatic hydrocarbon, C6-C20 aromatic hydrocarbon, C6-C20 halogenated aromatic hydrocarbon, C2-C20 heteroaromatic hydrocarbon, C2-C20 halogenated heteroaromatic hydrocarbon.

5. The cathode material composition according to claim 1, wherein, R1 and R2 each independently represent H or at least one of the following functional groups: -COOH, -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, phenyl.

6. The cathode material composition according to claim 1, wherein, R1 and R2 each independently represent H or at least one of the following functional groups: -OH, -SH, amino, phosphate ester, polyether segment, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl.

7. The cathode material composition according to any one of claims 1-6, wherein, The organopolysiloxane compound includes one or more selected from linear polysiloxanes and cyclic polysiloxanes.

8. The cathode material composition according to any one of claims 1-6, wherein, The organopolysiloxane compound is selected from linear polysiloxanes.

9. The cathode material composition according to claim 7, wherein, The linear polysiloxane further comprises end-capping groups, which include at least one of the following functional groups: polyether, C1-C8 alkyl, C1-C8 haloalkyl, C1-C8 heteroalkyl, C1-C8 haloheteroalkyl, C2-C8 alkenyl, C2-C8 haloalkenyl, C6-C20 aromatic hydrocarbon, C1-C8 alkoxy, C2-C8 epoxy, hydroxyl, C1-C8 hydroxyalkyl, amino, C1-C8 aminoalkyl, carboxyl, and C1-C8 carboxylalkyl.

10. The cathode material composition according to claim 7, wherein, The linear polysiloxanes include one or more of the following: polydimethylsiloxane, polydiethylsiloxane, polymethylethylsiloxane, polymethylvinylsiloxane, polyphenylmethylsiloxane, polymethylhydrosiloxane, carboxyl-functionalized polysiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, perfluorooctylmethylpolysiloxane, mercaptopropylpolysiloxane, aminoethylaminopropylpolydimethylsiloxane, methoxy-terminated polydimethylsiloxane, hydroxypropyl-terminated polydimethylsiloxane, aminopropyl-terminated polydimethylsiloxane, epoxy-terminated polysiloxane, hydroxyl-terminated polydimethylsiloxane, terminal polyether polydimethylsiloxane, side-chain aminopropylpolysiloxane, side-chain hydroxymethylpolysiloxane, side-chain hydroxypropylpolysiloxane, side-chain polyether-grafted polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane; and / or... The cyclic polysiloxane includes one or more of cyclic polydimethylsiloxane, cyclic polymethylvinylsiloxane, cyclic polymethylhydrosiloxane, and cyclic polymethyltrifluoropropylsiloxane.

11. The cathode material composition according to claim 7, wherein, The linear polysiloxane includes one or more of polydimethylsiloxane, polymethylchloropropylsiloxane, polymethyltrifluoropropylsiloxane, mercaptopropyl polysiloxane, aminoethylaminopropyl polydimethylsiloxane, hydroxyl-terminated polydimethylsiloxane, terminal polyether polydimethylsiloxane, and side-chain phosphate-grafted polydimethylsiloxane; and / or The cyclic polysiloxanes include one or more of the following: 1,3,5,7-octamethylcyclotetrasiloxane, 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasiloxane, cyclopentadimethylsiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, hexadecylcyclooctasiloxane, and tetradecylcycloheptasiloxane.

12. The cathode material composition according to any one of claims 1-6, wherein, The number average molecular weight of the organopolysiloxane compound is below 300,000.

13. The cathode material composition according to any one of claims 1-6, wherein, The number average molecular weight of the organopolysiloxane compound is between 400 and 80,000.

14. The cathode material composition according to any one of claims 1-6, wherein, The mass percentage of polar functional groups in the organopolysiloxane compound is α, where 0 ≤ α < 50%.

15. The cathode material composition according to any one of claims 1-6, wherein, The mass percentage of polar functional groups in the organopolysiloxane compound is α, where 5% ≤ α ≤ 30%.

16. The cathode material composition according to any one of claims 1-6, wherein, The content of the organopolysiloxane compound is from 0.01% to 2% by weight, based on the total weight of the cathode material composition.

17. The cathode material composition according to any one of claims 1-6, wherein, The content of the organopolysiloxane compound is from 0.1% to 2% by weight, based on the total weight of the cathode material composition.

18. The cathode material composition according to any one of claims 1-6, wherein, The coating amount of the first coating layer is greater than 0% by weight and less than or equal to 7% by weight, based on the weight of the core; And / or, The second coating layer has a coating amount greater than 0% by weight and less than or equal to 6% by weight, based on the weight of the core.

19. The cathode material composition according to any one of claims 1-6, wherein, The first coating layer has a coating amount of 4% to 5.6% by weight, based on the weight of the core; And / or, The second coating layer has a coating amount of 3% to 5% by weight, based on the weight of the core.

20. The cathode material composition according to any one of claims 1-6, wherein, The interplanar spacing of the phosphate in the first coating layer is 0.345 nm to 0.358 nm, and the included angle of the crystal orientation (111) is 24.25° to 26.45°; and / or, The interplanar spacing of the pyrophosphate in the first coating layer is 0.293 nm to 0.326 nm, and the included angle of the crystal orientation (111) is 26.41° to 32.57°.

21. The cathode material composition according to any one of claims 1-6, wherein, In the kernel, the ratio of y to 1-y is 1:10 to 10:1; and / or, In the kernel, the ratio of z to 1-z is 1:9 to 1:

999.

22. The cathode material composition according to any one of claims 1-6, wherein, In the kernel, the ratio of y to 1-y is 1:4 to 1:1; and / or, In the kernel, the ratio of z to 1-z is between 1:499 and 1:

249.

23. The cathode material composition according to any one of claims 1-6, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1; and / or, The crystallinity of pyrophosphate and phosphate in the first coating layer is independently between 10% and 100%.

24. The cathode material composition according to any one of claims 1-6, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 1:1; and / or, The crystallinity of pyrophosphate and phosphate in the first coating layer is independently 50% to 100%.

25. The cathode material composition according to any one of claims 1-6, wherein, The A is selected from at least two of Fe, Ti, V, Ni, Co and Mg.

26. The cathode material composition according to any one of claims 1-6, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) The concentration of Li / Mn antisite defects in the positive electrode active material is less than 4%; (2) The lattice change rate of the positive electrode active material is less than 8%; (3) The surface oxygen valence state of the positive electrode active material is below -1.88; (4) The compaction density of the positive electrode active material at 3 tons is 2.0 g / cm³. 3 above.

27. The cathode material composition according to any one of claims 1-6, wherein, The positive electrode active material satisfies at least one of the following conditions (1) to (4): (1) The concentration of Li / Mn antisite defects in the positive electrode active material is less than 2%; (2) The lattice change rate of the positive electrode active material is less than 4%; (3) The surface oxygen valence state of the positive electrode active material is -1.98 to -1.88; (4) The compaction density of the positive electrode active material at 3 tons is 2.2 g / cm³. 3 above.

28. The cathode material composition according to any one of claims 1-6, wherein, It also contains conductive agents and binders.

29. The cathode material composition according to claim 28, wherein, The binder content is from 1.79% to 10% by weight, based on the total weight of the cathode material composition.

30. The cathode material composition according to claim 28, wherein, The conductive agent content is from 0.2% to 10% by weight, based on the total weight of the positive electrode material composition.

31. The cathode material composition according to any one of claims 1-6, wherein, The positive electrode material composition has a powder resistivity of 4 Ω / cm to 55 Ω / cm at 12 MPa; and / or, The specific surface area of ​​the cathode material composition is 8m². 2 / g to 20m 2 / g.

32. The cathode material composition according to any one of claims 1-6, wherein, The positive electrode material composition has a powder resistivity of 4 Ω / cm to 40 Ω / cm at 12 MPa; and / or, The specific surface area of ​​the cathode material composition is 8m². 2 / g to 15m 2 / g.

33. A method for preparing a positive electrode material composition, comprising the following steps: Steps for providing kernel material: The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is from -0.100 to 0.100, y is from 0.001 to 0.500, z is from 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S; Coating step: MP2O7 powder and an XPO4 suspension containing a carbon source are provided. The core material and MP2O7 powder are added to the XPO4 suspension containing a carbon source and mixed. The positive electrode active material is obtained by sintering. M and X are each independently selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al. The obtained positive electrode active material has a core-shell structure, including the core and a shell covering the core. The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer. The first coating layer includes pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon. Mixing step: The obtained positive electrode active material is mixed evenly with an organopolysiloxane compound to obtain a positive electrode material composition.

34. The method according to claim 33, wherein, The kernel includes Li 1+x Mn 1-y A y P 1-z R z O4, x is -0.100 to 0.006, y is 0.100 to 0.450; and / or, the kernel comprises Li 1+x Mn 1-y A y P 1-z R z O4, where A is selected from one or more of Fe, Ti, V, Ni, Co, and Mg.

35. The method according to claim 33, wherein, Mixing step: The obtained positive electrode active material is mixed evenly with organopolysiloxane compound, binder and conductive agent to obtain positive electrode material composition.

36. The method according to any one of claims 33 to 35, wherein, The step of providing kernel materials includes the following steps: Step (1): Mix and stir the source of manganese, the source of element A and acid in a container to obtain manganese salt particles doped with element A; Step (2): The manganese salt particles doped with element A are mixed with lithium sources, phosphorus sources, and element R sources in a solvent to obtain a slurry. After sintering under an inert gas atmosphere, lithium manganese phosphate doped with elements A and R is obtained, wherein the lithium manganese phosphate doped with elements A and R is Li. 1+x Mn 1-y A y P 1-z R z O4, x is from -0.100 to 0.100, y is from 0.001 to 0.500, z is from 0.001 to 0.100, A is selected from one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R is selected from one or more of B, Si, N and S.

37. The method of claim 36, wherein, Step (1) is performed at a temperature between 20°C and 120°C; and / or, The stirring in step (1) is carried out at 500 rpm to 700 rpm for 60 minutes to 420 minutes.

38. The method according to claim 36, wherein, Step (1) is performed at a temperature between 25°C and 80°C; and / or, The stirring in step (1) is carried out at 500 rpm to 700 rpm for 120 minutes to 360 minutes.

39. The method according to claim 36, wherein, The source of element A is selected from one or more of element A's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide; and / or, the source of element R is selected from one or more of element R's elemental form, sulfate, halide, nitrate, organic acid salt, oxide or hydroxide, and inorganic acid of element R.

40. The method according to any one of claims 33 to 35, wherein, The MP2O7 powder is prepared by adding the source of element M and the source of phosphorus to a solvent to obtain a mixture, adjusting the pH of the mixture to 4 to 6, stirring and reacting fully, and then drying and sintering. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.

41. The method according to claim 40, wherein, The drying step involves drying at 100°C to 300°C for 4 to 8 hours; and / or, The sintering step involves sintering at 500°C to 800°C in an inert gas atmosphere for 4 to 10 hours; and / or, The sintering temperature for obtaining the positive electrode active material in the coating step is 500°C to 800°C, and the sintering time is 4 hours to 10 hours.

42. The method according to claim 40, wherein, The drying step involves drying at 150°C to 200°C for 4 to 8 hours; and / or, The sintering step involves sintering at 650°C to 800°C in an inert gas atmosphere for 4 to 10 hours.

43. A positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode material composition according to any one of claims 1-32 or a positive electrode material composition prepared by any one of claims 33-42, and the positive electrode material composition having a content of 50% by weight or more in the positive electrode film layer based on the total weight of the positive electrode film layer.

44. The positive electrode sheet according to claim 43, wherein, The content of the positive electrode material composition in the positive electrode film is 90% to 100% by weight, based on the total weight of the positive electrode film.

45. The positive electrode sheet according to claim 43 or 44, wherein, The positive electrode plate satisfies at least one of the following conditions (1) to (6): (1) The solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 90°; (2) The porosity of the positive electrode film is 15% to 50%; (3) The resistance of the positive electrode film is greater than 0 and less than or equal to 6Ω; (4) The adhesion force between the positive electrode film layer and the positive electrode current collector is greater than or equal to 0.5 MPa; (5) The areal density of the positive electrode film is 0.006 g / cm³. 2 Up to 0.065 g / cm 2 ; (6) The positive electrode film has an electrolyte absorption rate of 0.0125 μg / s to 100 μg / s.

46. ​​The positive electrode sheet according to claim 43 or 44, wherein, The positive electrode plate satisfies at least one of the following conditions (1) to (3): (1) The solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 3° and 60°; (2) The porosity of the positive electrode film is 15% to 30%; (3) The positive electrode film has an electrolyte absorption rate of 0.5 μg / s to 40 μg / s.

47. The positive electrode sheet according to claim 43 or 44, wherein, The solid-liquid contact angle between the positive electrode film and the non-aqueous organic solvent is between 10° and 30°.

48. A secondary battery comprising a positive electrode material composition according to any one of claims 1-32, or a positive electrode material composition prepared by any one of claims 33-42, or a positive electrode sheet according to any one of claims 43-46.

49. An electrical device comprising the secondary battery of claim 48.

Images