Positive electrode active material, method for preparing the same, and positive electrode sheet, secondary battery, and electric device comprising the same

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet containing the positive electrode active material, a secondary battery and an electric device, the positive electrode active material has a core-shell structure, comprising an inner core and a shell covering the inner core, wherein the chemical formula of the inner core is Li a A x Mn 1‑y B y P 1‑z C z O 4‑n D n The shell comprises a first coating layer covering the inner core and a second coating layer covering the first coating layer, the first coating layer comprises pyrophosphate MP2O7 and phosphate XPO4, and the second coating layer contains carbon. The positive electrode active material can make the secondary battery and the electric device have high energy density and good cycle performance, rate performance and safety performance.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode active material, its preparation method, and a positive electrode sheet containing the same, a secondary battery, and an electrical device. 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. Therefore, it is necessary to provide a cathode active material with excellent overall performance. Summary of the Invention

[0003] The purpose of this application is to provide a positive electrode active material, a method for preparing the same, and a positive electrode sheet, a secondary battery, and an electrical device containing the same, so that the secondary battery and electrical device using the positive electrode active material have high energy density and good cycle performance, rate performance, and safety performance.

[0004] The first aspect of this application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, wherein...

[0005] The chemical formula of the core is Li a A x Mn 1-y B y P 1-z C z O 4-n D n The A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from B (boron), S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br; the a is selected from the range of 0.9 to 1.1; the x is selected from the range of 0.001 to 0.1; the y is selected from the range of 0.001 to 0.5; the z is selected from the range of 0.001 to 0.1; the n is selected from the range of 0.001 to 0.1; and the core is electrically neutral.

[0006] The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, wherein 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; and the second coating layer contains carbon.

[0007] This application improves the cycle performance, rate performance, and safety performance of lithium manganese phosphate by simultaneously doping specific elements at the Li, Mn, P, and O sites in specific amounts and coating the surface of the lithium manganese phosphate with a coating layer.

[0008] In any embodiment of this application, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal direction (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal direction (111) is 26.41°-32.57°. When the interplanar spacing and the included angle of the crystal direction (111) of the phosphate and pyrophosphate in the first coating layer are within the above ranges, 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.

[0009] 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 optionally 1:3 to 1:1. A suitable ratio of pyrophosphate to phosphate is beneficial for fully leveraging their synergistic effect, effectively inhibiting manganese ion dissolution and reducing surface lithium content, thereby reducing interfacial side reactions and improving the battery's cycle performance, rate performance, and safety performance.

[0010] In any embodiment of this application, the crystallinity of the pyrophosphate and the phosphate is independently 10% to 100%, optionally 50% to 100%. This helps to maintain the structural stability of the first coating layer and reduce lattice defects.

[0011] In any embodiment of this application, x is selected from the range of 0.001 to 0.005. This can further improve the kinetic performance of the positive electrode active material.

[0012] In any embodiment of this application, y is selected from the range of 0.01 to 0.5, and optionally from the range of 0.25 to 0.5. This can further improve the specific capacity and rate performance of the positive electrode active material.

[0013] In any embodiment of this application, z is selected from the range of 0.001 to 0.005. This can further improve the rate performance of the battery.

[0014] In any embodiment of this application, n is selected from the range of 0.001 to 0.005. This can further improve the high-temperature stability of the battery.

[0015] In any embodiment of this application, (1-y):y is in the range of 1 to 4, optionally in the range of 1.5 to 3, and a:x is in the range of 9 to 1100, optionally in the range of 190-998. This further improves the energy density and cycle performance of the battery.

[0016] 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 4-5.6% by weight, based on the weight of the core. This further suppresses manganese ion dissolution while further promoting lithium ion transport.

[0017] 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 3-5% by weight, based on the weight of the core. This effectively increases the specific capacity of the positive electrode active material. Consequently, the kinetic and safety performance of the battery can be further improved without sacrificing the specific capacity of the positive electrode active material.

[0018] In any embodiment of this application, A, C and D are each independently any one of the elements within their respective ranges, and B is at least two elements within its range;

[0019] Optionally,

[0020] A is an element selected from Mg and Nb, and / or,

[0021] The element B is selected from at least two elements chosen from Fe, Ti, V, Co, and Mg, and optionally from Fe and one or more elements chosen from Ti, V, Co, and Mg, and / or,

[0022] The C is S, and / or,

[0023] The D is F.

[0024] This can further improve the rate performance, energy density, and / or high-temperature stability of the battery.

[0025] 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.

[0026] In any embodiment of this application, the lattice change rate of the positive electrode active material is 8% or less, optionally 6% or less. This is beneficial for enhancing the Li... + This improves the battery's rate performance by enhancing its transmission capabilities.

[0027] In any embodiment of this application, the surface oxygen valence state of the positive electrode active material is below -1.88, optionally from -1.99 to -1.88. This reduces the reactivity of the positive electrode active material surface, decreases interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.

[0028] 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 is an option, specifically 2.2 g / cm³. 3 The above. This is beneficial for improving the volumetric energy density of batteries.

[0029] A second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps:

[0030] Steps for providing kernel material: The kernel includes Li a A x Mn 1-y B y P 1-z C z O 4-n D n The core is wherein A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from B (boron), S, Si, and N; D comprises one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; x is selected from the range of 0.001 to 0.1; y is selected from the range of 0.001 to 0.5; z is selected from the range of 0.001 to 0.1; n is selected from the range of 0.001 to 0.1; and the core is electrically neutral.

[0031] 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.

[0032] The positive electrode active material has a core-shell structure, which includes a 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.

[0033] In any embodiment of this application, the step of providing kernel material includes the following steps:

[0034] Step (1): Dissolve and stir the manganese source, element B source and acid in a solvent to generate a suspension of manganese salt doped with element B. Filter the suspension and dry the filter cake to obtain manganese salt doped with element B.

[0035] Step (2): Add the lithium source, phosphorus source, source of element A, source of element C and source of element D, solvent and manganese salt doped with element B obtained in step (1) into the reaction vessel, grind and mix to obtain a slurry;

[0036] Step (3): Transfer the slurry obtained in step (2) to a spray drying equipment for spray drying and granulation to obtain granules;

[0037] Step (4): Sinter the particles obtained in step (3) to obtain the core Li. a A x Mn 1-y B y P 1-z C z O 4-n D n .

[0038] In any embodiment of this application, the source of element A is selected from at least one of element A's elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; the source of element B is selected from at least one of element B's elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; the source of element C is selected from at least one of element C's sulfate, borate, nitrate, and silicate; and the source of element D is selected from at least one of element D's elemental form and ammonium salt.

[0039] In any embodiment of this application, the stirring in step (1) is carried out at a temperature in the range of 60-120°C.

[0040] In any embodiment of this application, the stirring in step (1) is carried out at a stirring rate of 200-800 rpm.

[0041] In any embodiment of this application, the grinding and mixing in step (2) is carried out for 8-15 hours.

[0042] 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.

[0043] In any embodiment of this application, the sintering in step (4) is carried out at a temperature range of 600-900°C for 6-14 hours. This allows for control of the crystallinity of the positive electrode active material, reduces the dissolution of Mn and Mn-site doped elements after cycling, and thereby improves the high-temperature stability and cycle performance of the battery.

[0044] 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 4-6, 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.

[0045] In any embodiment of this application, during the preparation of MP2O7 powder, the drying step is to dry at 100-300°C, optionally 150-200°C, for 4-8 hours.

[0046] In any embodiment of this application, during the preparation of MP2O7 powder, the sintering step is to sinter at 500-800°C, optionally 650-800°C, for 4-10 hours in an inert gas atmosphere.

[0047] In any embodiment of this application, the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10 hours. Therefore, 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.

[0048] 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 the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application, and the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

[0049] In any embodiment of this application, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer. When the content of the positive electrode active material is within the above range, it is beneficial to fully utilize the advantages of the positive electrode active material of this application.

[0050] The fourth aspect of this application provides a secondary battery, including the positive electrode active material of the first aspect of this application, or the positive electrode active material prepared by the method of the second aspect of this application, or the positive electrode sheet of the third aspect of this application.

[0051] The fifth aspect of this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0052] The positive electrode sheet, secondary battery, and electrical device of this application include the positive electrode active material of this application, and therefore have at least the same advantages as the positive electrode active material. Attached Figure Description

[0053] 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.

[0054] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0055] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0056] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0057] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0058] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0059] 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.

[0060] Figure 7 The X-ray diffraction (XRD) patterns of undoped LiMnPO4 and the cathode active material core prepared in Example 2 are shown.

[0061] Figure 8 The X-ray energy dispersive spectroscopy (EDS) spectrum of the core of the positive electrode active material prepared in Example 2 is shown.

[0062] 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

[0063] The following detailed description, with appropriate reference to the accompanying drawings, discloses the positive electrode active material, its preparation method, and embodiments of the positive electrode sheet, secondary battery, and power-consuming 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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).

[0070] In this paper, the median particle size Dv 50 This refers to the particle size corresponding to a cumulative volumetric distribution percentage of 50% for the material. In this application, the median particle size Dv of the material... 50 Particle size can be determined using laser diffraction particle size analysis. For example, referring to standard GB / T19077-2016, a laser particle size analyzer (e.g., Malvern Master Size 3000) can be used for determination.

[0071] 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.

[0072] 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.

[0073] In this application, "about" for a certain value represents a range, specifically a range of ±10% of that value.

[0074] The inventors of this application discovered in practical operation that manganese ion dissolution is severe in lithium manganese phosphate cathode 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 migration of dissolved manganese ions 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 battery safety performance; others deposit on the negative electrode surface, obstructing the channels for lithium ions to enter and exit the negative electrode, increasing battery impedance and affecting battery kinetic performance. Furthermore, to replenish the lost SEI film, the electrolyte and active lithium ions inside the battery are continuously consumed, irreversibly affecting the battery's capacity retention rate.

[0075] 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 excellent cycle performance, rate performance, and safety performance.

[0076] Positive electrode active material

[0077] The first aspect of this application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, wherein...

[0078] The chemical formula of the core is Li a A x Mn 1-y B y P 1-z C z O 4-n D nThe A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from B (boron), S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br; the a is selected from the range of 0.9 to 1.1; the x is selected from the range of 0.001 to 0.1; the y is selected from the range of 0.001 to 0.5; the z is selected from the range of 0.001 to 0.1; the n is selected from the range of 0.001 to 0.1; and the core is electrically neutral.

[0079] The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer, wherein 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; and the second coating layer contains carbon.

[0080] Unless otherwise stated, in the above chemical formulas, when A consists of two or more elements, the limitation on the range of x values ​​described above 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 x1, x2...xn of each of A1, A2...An must each fall within the range of x values ​​defined in this application, and the sum of x1, x2...xn must also fall within this range. Similarly, for the case where B, C, and D consist of two or more elements, the limitation on the range of stoichiometric coefficients of B, C, and D in this application also has the above meaning.

[0081] The core of the positive electrode active material in this application is obtained by elemental doping of the compound LiMnPO4, where A, B, C, and D are the elements doped at the Li, Mn, P, and O sites of LiMnPO4, respectively. Not wanting to be confined to theory, it is now believed that the performance improvement of lithium manganese phosphate is related to reducing the lattice change rate of lithium manganese phosphate during lithium insertion / extraction and reducing surface activity. Reducing the lattice change rate can reduce the difference in lattice constants between the two phases at the grain boundary, reduce interfacial stress, and enhance Li... +The ability to transport substances at the interface improves the rate performance of the positive electrode active material. However, high surface activity can easily lead to severe interfacial side reactions, exacerbating gas generation, electrolyte consumption, and interface damage, thus affecting the battery's cycle performance. In this application, lattice change rate is reduced through Li and Mn doping. Mn doping also effectively reduces surface activity, thereby suppressing manganese ion dissolution and interfacial side reactions between the positive electrode active material and the electrolyte. P-site doping accelerates the change rate of the Mn-O bond length, lowering the small polaron migration barrier of the positive electrode active material, which is beneficial to electronic conductivity. O-site doping has a good effect on reducing interfacial side reactions. P-site and O-site doping also affect the manganese ion dissolution and kinetics of antisite defects.

[0082] The inventors of this application unexpectedly discovered that by simultaneously doping specific elements in specific amounts at the Li, Mn, P, and O sites of the compound LiMnPO4, improved rate performance can be obtained, while reducing the dissolution of Mn and the dopant elements at the Mn sites, resulting in improved cycle performance and / or high-temperature stability. Furthermore, the specific capacity and compaction density of the positive electrode active material can also be increased. Optionally, A is one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B is one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C is one or more elements selected from B (boron), S, Si, and N; and D is one or more elements selected from S, F, Cl, and Br.

[0083] 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.

[0084] 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.

[0085] Therefore, this application effectively suppresses the dissolution of manganese ions during the lithium insertion / extraction process and promotes the migration of lithium ions by simultaneously doping specific elements at specific amounts at the Li, Mn, P and O sites of lithium manganese phosphate and coating the surface with a coating layer, thereby improving the cycle performance, rate performance and safety performance of the battery.

[0086] 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 has no impurity phase, and the improvement in battery performance mainly comes from element doping, rather than impurity phase.

[0087] In some embodiments, A, C, and D are each independently any one element within their respective ranges, and B is at least two elements within that range. This allows for easier and more accurate control of the composition of the positive electrode active material core.

[0088] Optionally, A is any element selected from Mg and Nb.

[0089] Optionally, B is at least two elements selected from Fe, Ti, V, Co and Mg, or alternatively, Fe and one or more elements selected from Ti, V, Co and Mg.

[0090] Optionally, C is S.

[0091] Optionally, D is F.

[0092] By selecting doping elements at the Li sites within the aforementioned range, the lattice change rate during the lithium removal process can be further reduced, thereby improving the rate performance of the battery. Similarly, selecting doping elements at the Mn sites within the aforementioned range can further increase electronic conductivity and reduce the lattice change rate, thus enhancing the rate performance and capacity of the battery. Selecting doping elements at the P sites within the aforementioned range can further improve the rate performance of the battery. Finally, selecting doping elements at the O sites within the aforementioned range can further mitigate interfacial side reactions and improve the high-temperature stability of the battery.

[0093] The value 'a' is selected from the range of 0.9 to 1.1, for example, 0.97, 0.977, 0.984, 0.988, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, 1.01.

[0094] The x is selected from the range of 0.001 to 0.1, for example, 0.001 or 0.005.

[0095] The value of y is selected from the range of 0.001 to 0.5, for example, 0.001, 0.005, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.34, 0.345, 0.349, 0.35, 0.4.

[0096] The z is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, 0.1.

[0097] The n is selected from the range of 0.001 to 0.1, for example, 0.001, 0.005, 0.08, 0.1.

[0098] In some implementations, x is selected from the range of 0.001 to 0.005.

[0099] In some implementations, y is selected from the range of 0.01 to 0.5, and optionally from the range of 0.25 to 0.5.

[0100] In some implementations, z is selected from the range of 0.001 to 0.005.

[0101] In some implementations, n is selected from the range of 0.001 to 0.005.

[0102] By selecting the x-value within the above range, the kinetic performance of the cathode active material can be further improved. By selecting the y-value within the above range, the specific capacity and rate performance of the cathode active material can be further improved. By selecting the z-value within the above range, the rate performance of the battery can be further improved. By selecting the n-value within the above range, the high-temperature stability of the battery can be further improved.

[0103] In some embodiments, the core of the positive electrode active material satisfies (1-y): y is in the range of 1 to 4, optionally in the range of 1.5 to 3, and a:x is in the range of 9 to 1100, optionally in the range of 190-998. Here, y represents the sum of the stoichiometric coefficients of the Mn-site doping elements. When the above conditions are met, the energy density and cycle performance of the battery can be further improved.

[0104] In some embodiments, optionally, the interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°.

[0105] In some embodiments, optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

[0106] 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.

[0107] In some embodiments, optionally, the weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:1, and optionally 1:3 to 1:1.

[0108] A suitable ratio of pyrophosphate and phosphate is beneficial for fully leveraging their synergistic effect. It effectively inhibits manganese ion dissolution and reduces surface lithium content, minimizing interfacial side reactions, thereby improving battery cycle performance, rate performance, and safety performance. 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.

[0109] In some embodiments, optionally, the crystallinity of the pyrophosphate and the phosphate is each independently 10% to 100%, optionally 50% to 100%.

[0110] In the first coating layer of the lithium manganese phosphate cathode active material of this application, the presence of pyrophosphate and phosphate with a certain degree of crystallinity helps maintain the structural stability of the first coating layer and reduces lattice defects. This is beneficial in two ways: firstly, it allows the pyrophosphate to fully inhibit the dissolution of manganese ions; secondly, it helps the 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 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 implementations, 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 4-5.6% by weight, based on the weight of the core.

[0113] When the coating amount of the first coating layer is within the above-mentioned range, it can further suppress the dissolution of manganese ions and further promote the transport of lithium ions. 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 the dissolution of manganese ions 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 battery's kinetic performance.

[0114] In some implementations, the second coating layer may optionally have a coating amount greater than 0% by weight and less than or equal to 6% by weight, optionally 3-5% by weight, based on the weight of the core.

[0115] 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 battery safety at high temperatures. On the other hand, its strong conductivity reduces internal resistance, thus improving battery kinetic performance. However, due to the low specific capacity of carbon materials, excessive use 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, it can further improve the battery's kinetic and safety performance without sacrificing the specific capacity of the positive electrode active material.

[0116] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is optionally below 4%, and optionally below 2%.

[0117] Li / Mn antisite defects refer to the defects in the LiMnPO4 lattice where 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 K 0131-1996.

[0118] In some embodiments, the lattice change rate of the positive electrode active material is optionally less than 8%, and optionally less than 6%.

[0119] The lithium insertion / extraction process in LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the rate of lattice change; the smaller the rate of lattice change, 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 battery's rate performance by enhancing its transmission capabilities.

[0120] In some embodiments, optionally, the average discharge voltage of the positive electrode active material is 3.5V or higher, and the discharge specific capacity is 140mAh / g or higher; optionally, the average discharge voltage is 3.6V or higher, and the discharge specific capacity is 145mAh / g or higher.

[0121] Although the average discharge voltage of undoped LiMnPO4 is above 4.0V, its discharge specific capacity is low, usually less than 120mAh / g, resulting in a low energy density. By adjusting the lattice change rate through doping, its discharge specific capacity can be significantly increased, and the overall energy density of the battery can be significantly increased with a slight decrease in the average discharge voltage.

[0122] In some embodiments, the surface oxygen valence state of the positive electrode active material is optionally below -1.88, and optionally from -1.99 to -1.88.

[0123] This is because the higher the valence state of oxygen in a compound, the stronger its ability to gain electrons, i.e., the stronger its oxidizing power. In the lithium manganese phosphate cathode active material of this application, by controlling the surface valence state of oxygen at a low level, the reactivity of the cathode active material surface can be reduced, the interfacial side reactions between the cathode active material and the electrolyte can be reduced, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0124] 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 is an option, specifically 2.2 g / cm³. 3 above.

[0125] A higher compaction density of the positive electrode active material, i.e., a greater weight of active material per unit volume, is more conducive to improving the volumetric energy density of the battery. In this application, the compaction density can be measured, for example, according to GB / T 24533-2009.

[0126] Preparation method

[0127] The second aspect of this application provides a method for preparing the positive electrode active material of the first aspect of this application, which includes the following steps:

[0128] Steps for providing kernel material: The kernel includes Li a A x Mn 1-y B y P 1-z C z O 4-n D nThe core is wherein A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from B (boron), S, Si, and N; D comprises one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; x is selected from the range of 0.001 to 0.1; y is selected from the range of 0.001 to 0.5; z is selected from the range of 0.001 to 0.1; n is selected from the range of 0.001 to 0.1; and the core is electrically neutral.

[0129] 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.

[0130] The positive electrode active material has a core-shell structure, which includes a 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.

[0131] In some implementations, the step of providing the core material may optionally include the following steps:

[0132] Step (1): Dissolve and stir the manganese source, element B source and acid in a solvent to generate a suspension of manganese salt doped with element B. Filter the suspension and dry the filter cake to obtain manganese salt doped with element B.

[0133] Step (2): Add the lithium source, phosphorus source, source of element A, source of element C and source of element D, solvent and manganese salt doped with element B obtained in step (1) into the reaction vessel, grind and mix to obtain a slurry;

[0134] Step (3): Transfer the slurry obtained in step (2) to a spray drying equipment for spray drying and granulation to obtain granules;

[0135] Step (4): Sinter the particles obtained in step (3) to obtain the core Li. a A x Mn 1-y B y P 1-z C z O4-n D n .

[0136] In some embodiments, the source of element A is selected from at least one of elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; the source of element B is selected from at least one of elemental form, oxide, phosphate, oxalate, carbonate, and sulfate; the source of element C is selected from at least one of sulfate, borate, nitrate, and silicate of element C; and the source of element D is selected from at least one of elemental form and ammonium salt of element D. By selecting the source of each dopant element, the uniformity of the dopant element distribution can be improved, thereby improving the performance of the positive electrode active material.

[0137] In some embodiments, the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of 60% by weight or less.

[0138] In some embodiments, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate, such as elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

[0139] In some embodiments, the lithium source may be a lithium-containing material known in the art that can be used to prepare lithium manganese phosphate, such as lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, or a combination thereof.

[0140] In some embodiments, the phosphorus source may be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate, such as one or a combination of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0141] The amount of source added for each of elements A, B, C, and D depends on the target doping amount, and the ratio of the amount of lithium source, manganese source, and phosphorus source used conforms to the stoichiometric ratio.

[0142] In some embodiments, the solvents described in steps (1) and (2) may each be a solvent commonly used by those skilled in the art in the preparation of manganese salts and lithium manganese phosphate, for example, each may be independently selected from at least one of ethanol, water (e.g., deionized water).

[0143] In some embodiments, the stirring in step (1) is carried out at a temperature in the range of 60-120°C. In some embodiments, the stirring in step (1) is carried out at a stirring rate of 200-800 rpm, 300-800 rpm, or 400-800 rpm. In some embodiments, the stirring in step (1) is carried out for 6-12 hours. In some embodiments, the grinding and mixing in step (2) is carried out for 8-15 hours.

[0144] 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.

[0145] In some implementations, the filter cake may be washed before drying in step (1).

[0146] In some embodiments, the drying in step (1) can be carried out in a manner and under conditions known to those skilled in the art, for example, the drying temperature can be in the range of 120-300°C. Optionally, the filter cake can be ground into particles after drying, for example, ground to a median particle size Dv. 50 Within the 50-200nm range.

[0147] In some embodiments, the temperature and time of spray drying in step (3) can be the temperature and time conventional for spray drying in the art, for example, 1-6 hours at 100-300°C.

[0148] In some embodiments, sintering in step (4) is carried out at a temperature range of 600-900°C for 6-14 hours. By controlling the sintering temperature and time, the crystallinity of the positive electrode active material can be controlled, and the amount of Mn and Mn-site doped elements dissolved after cycling can be reduced, thereby improving the high-temperature stability and cycle performance of the battery.

[0149] In some embodiments, sintering in step (4) is carried out under a protective atmosphere, which may be nitrogen, an inert gas, hydrogen, or a mixture thereof.

[0150] 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 4-6, stirring and reacting fully, and then drying and sintering to obtain the final product, wherein M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.

[0151] In some embodiments, optionally, during the preparation of MP2O7 powder, the drying step is to dry at 100-300°C, optionally 150-200°C, for 4-8 hours.

[0152] In some embodiments, optionally, during the preparation of MP2O7 powder, the sintering step involves sintering at 500-800°C, optionally 650-800°C, in an inert gas atmosphere for 4-10 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.

[0153] In some embodiments, optionally, the XPO4 suspension containing the carbon source 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 60-120°C and maintaining the temperature for 2-8 hours to obtain the XPO4 suspension containing the carbon source. Optionally, during the preparation of the XPO4 suspension containing the carbon source, the pH of the mixture is adjusted to 4-6.

[0154] In some embodiments, optionally, during the coating step, the mass ratio of the core, MP2O7 powder, and XPO4 suspension containing a carbon source is 1:(0.001-0.05):(0.001-0.05).

[0155] In some embodiments, optionally, the sintering temperature in the coating step is 500-800°C and the sintering time is 4-10 hours.

[0156] 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 50-2000 nm.

[0157] Positive electrode sheet

[0158] 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 the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application, and the content of the positive electrode active material in the positive electrode film layer is more than 10% by weight, based on the total weight of the positive electrode film layer.

[0159] 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.

[0160] In some embodiments, the content of the positive electrode active material in the positive electrode film layer is 90-99.5% by weight, based on the total weight of the positive electrode film layer. When the content of the positive electrode active material is within the above range, it is beneficial to fully utilize the advantages of the positive electrode active material of this application.

[0161] The positive electrode film layer does not exclude other positive electrode active materials besides the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the method of the second aspect of this application. For example, the positive electrode film layer may also 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 modified compounds.

[0162] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0163] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0164] 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.

[0165] 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.

[0166] Secondary batteries

[0167] The fourth aspect of this application provides a secondary battery that includes the positive electrode sheet of the third aspect of this application.

[0168] 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.

[0169] [Positive electrode plate]

[0170] 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.

[0171] [Negative electrode plate]

[0172] 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.

[0173] 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.

[0174] 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.

[0175] 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).

[0176] 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.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] [Electrolytes]

[0181] 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).

[0182] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0183] 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).

[0184] 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).

[0185] 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.

[0186] [Isolation membrane]

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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).

[0192] 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.

[0193] 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 forming 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 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0198] 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.

[0199] 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.

[0200] Electrical appliances

[0201] 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.

[0202] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0203] 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.

[0204] 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.

[0205] Example

[0206] 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.

[0207] Example 1

[0208] (1) Preparation of positive electrode active material

[0209] S1: Preparation of doped manganese oxalate

[0210] 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0211] S2: Preparation of co-doped lithium manganese phosphate cores

[0212] 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, and 0.0005 mol of NH4HF2 were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying and granulation. The drying temperature was set at 250°C, and the powder was dried for 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the powder was sintered at 700°C for 10 hours to obtain Li. 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999Si 0.001 O 3.999 F 0.001 That is, a co-doped lithium manganese phosphate core.

[0213] S3: Preparation of lithium iron pyrophosphate powder

[0214] 4.77 g of lithium carbonate, 7.47 g of ferrous carbonate, 14.84 g of ammonium dihydrogen phosphate, and 1.3 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 completely. 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 a 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.

[0215] S4: Preparation of lithium iron phosphate suspension

[0216] 11.1g lithium carbonate, 34.8g ferrous carbonate, 34.5g ammonium dihydrogen phosphate, 1.3g oxalic acid dihydrate, and 37.3g sucrose (in C...) 12 H 22 O 11 The solution (hereinafter the same) 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 sucrose and LiFePO4.

[0217] S5: Encapsulation

[0218] 10 mol (approximately 1570 g) of the co-doped lithium manganese phosphate core obtained according to step S2 and 15.7 g of Li2FeP2O7 powder obtained in step S3 were added to the LiFePO4 suspension obtained in step S4 (containing 37.3 g sucrose and 47.2 g LiFePO4). 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 positive electrode active material.

[0219] (2) Preparation of positive electrode sheet

[0220] The above-mentioned positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 92:2.5:5.5 and stirred until homogeneous to obtain the positive electrode slurry. Then, the positive electrode slurry was prepared at a ratio of 0.280 g / 1540.25 mm. 2The material is evenly coated onto aluminum foil, then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0221] (3) Preparation of negative electrode sheet

[0222] 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 prepared at a concentration of 0.117 g / 1540.25 mm. 2 The negative electrode sheet is obtained by uniformly coating the copper foil of the negative electrode current collector, drying, cold pressing, and slitting.

[0223] (4) Preparation of electrolyte

[0224] 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.

[0225] (5) Separating membrane

[0226] The PP-PE copolymer microporous film with a thickness of 20μm and an average pore size of 80nm (from Zogo Electronics Technology Co., Ltd., model 20) was used.

[0227] (6) Preparation of full cells

[0228] 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").

[0229] (7) Preparation of button cells

[0230] The three-layer coated lithium manganese phosphate positive electrode active material, PVDF, and acetylene black prepared above were added to NMP in a weight ratio of 90:5:5, and stirred in a drying chamber to form a slurry. The slurry was then coated onto aluminum foil, dried, and cold-pressed to form a positive electrode sheet. The coating amount was 0.2 g / cm³. 2 The compacted density is 2.0 g / cm³. 3 .

[0231] 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. Together with the positive electrode sheet prepared above, they are assembled into a coin cell (hereinafter also referred to as "coin cell") in a coin cell box.

[0232] Example 2

[0233] Except for changing the amount of FeSO4·H2O to 0.68 mol, the amount of Li2CO3 to 0.4885 mol, Mo(SO4)3 to MgSO4, H4SiO4 to HNO3, and adding 0.02 mol of Ti(SO4)2 when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0234] Example 3

[0235] Except for changing the amount of Li2CO3 to 0.496 mol, replacing Mo(SO4)3 with W(SO4)3, and replacing H4SiO4 with H2SO4 in steps S1 and S2, the other conditions are the same as in Example 1.

[0236] Example 4

[0237] Except for steps S1 and S2, where the amount of Li2CO3 is changed to 0.4985 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.0005 mol of Al2(SO4)3, and NH4HF2 is replaced with NH4HCl2, the other conditions are the same as in Example 1.

[0238] Example 5

[0239] Except for steps S1 and S2, where the amount of FeSO4·H2O is changed to 0.69 mol, the amount of Li2CO3 is changed to 0.4965 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.0005 mol of Nb2(SO4)5, H4SiO4 is replaced with H2SO4, and 0.01 mol of VCl2 is added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0240] Example 6

[0241] Except for steps S1 and S2, where the amount of FeSO4·H2O is changed to 0.68 mol, the amount of Li2CO3 is changed to 0.4965 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.0005 mol of Nb2(SO4)5, H4SiO4 is replaced with H2SO4, and 0.01 mol of VCl2 and 0.01 mol of MgSO4 are added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0242] Example 7

[0243] Except for replacing MgSO4 with CoSO4 in steps S1 and S2, the other conditions are the same as in Example 6.

[0244] Example 8

[0245] Except for replacing MgSO4 with NiSO4 in steps S1 and S2, the other conditions are the same as in Example 6.

[0246] Example 9

[0247] Except for steps S1 and S2, where the amount of FeSO4·H2O is changed to 0.698 mol, the amount of Li2CO3 is changed to 0.4955 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.0005 mol of Nb2(SO4)5, H4SiO4 is replaced with H2SO4, NH4HF2 is replaced with NH4HCl2, and 0.002 mol of Ti(SO4)2 is added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0248] Example 10

[0249] Except for steps S1 and S2, where the amount of FeSO4·H2O is changed to 0.68 mol, the amount of Li2CO3 is changed to 0.4975 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.0005 mol of Nb2(SO4)5, NH4HF2 is replaced with NH4HBr2, and 0.01 mol of VCl2 and 0.01 mol of MgSO4 are added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0250] Example 11

[0251] Except for changing the amount of FeSO4·H2O to 0.69 mol, the amount of Li2CO3 to 0.499 mol, Mo(SO4)3 to MgSO4, NH4HF2 to NH4HBr2, and adding 0.01 mol of VCl2 when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0252] Example 12

[0253] Except for steps S1 and S2, where the amount of MnSO4·H2O is changed to 1.36 mol, the amount of FeSO4·H2O is changed to 0.6 mol, the amount of Li2CO3 is changed to 0.4985 mol, Mo(SO4)3 is replaced with MgSO4, H4SiO4 is replaced with HNO3, and 0.04 mol of VCl2 is added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0254] Example 13

[0255] Except for changing the amount of MnSO4·H2O to 1.16 mol and the amount of FeSO4·H2O to 0.8 mol in steps S1 and S2, the other conditions are the same as in Example 12.

[0256] Example 14

[0257] Except for changing the amount of MnSO4·H2O to 1.3 mol and the amount of VCl2 to 0.1 mol in steps S1 and S2, the other conditions are the same as in Example 12.

[0258] Example 15

[0259] Except for steps S1 and S2, where the amount of MnSO4·H2O is changed to 1.2 mol, the amount of Li2CO3 is changed to 0.494 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.005 mol of MgSO4, H4SiO4 is replaced with H2SO4, and 0.1 mol of VCl2 is added when preparing the doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0260] Example 16

[0261] Except for steps S1 and S2, where the amount of MnSO4·H2O is changed to 1.2 mol, the amount of Li2CO3 is changed to 0.467 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.005 mol of MgSO4, 0.001 mol of H4SiO4 is replaced with 0.005 mol of H2SO4, 1.175 mol of 85% phosphoric acid is replaced with 1.171 mol of 85% phosphoric acid, and 0.1 mol of VCl2 is added when preparing the doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0262] Example 17

[0263] Except for steps S1 and S2, where the amount of MnSO4·H2O is changed to 1.2 mol, the amount of Li2CO3 is changed to 0.492 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.005 mol of MgSO4, H4SiO4 is replaced with H2SO4, the amount of OH4HF2 is changed to 0.0025 mol, and 0.1 mol of VCl2 is added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0264] Example 18

[0265] Except for steps S1 and S2, where the amount of FeSO4·H2O is changed to 0.5 mol, the amount of Li2CO3 is changed to 0.492 mol, 0.001 mol of Mo(SO4)3 is replaced with 0.005 mol of MgSO4, H4SiO4 is replaced with H2SO4, the amount of NH4HF2 is changed to 0.0025 mol, and 0.1 mol of VCl2 and 0.1 mol of CoSO4 are added when preparing doped manganese oxalate in step S1, the other conditions are the same as in Example 1.

[0266] Example 19

[0267] Except for changing the amount of FeSO4·H2O to 0.4 mol and the amount of CoSO4 to 0.2 mol in steps S1 and S2, the other conditions are the same as in Example 18.

[0268] Example 20

[0269] Except for changing the amount of MnSO4·H2O to 1.5 mol, the amount of FeSO4·H2O to 0.1 mol, and the amount of CoSO4 to 0.3 mol in steps S1 and S2, the other conditions are the same as in Example 18.

[0270] Example 21

[0271] Except for replacing CoSO4 with NiSO4 in steps S1 and S2, the other conditions are the same as in Example 18.

[0272] Example 22

[0273] Except for steps S1 and S2, where the amount of MnSO4·H2O is changed to 1.5 mol, the amount of FeSO4·H2O is changed to 0.2 mol, and 0.1 mol of CoSO4 is replaced with 0.2 mol of NiSO4, the other conditions are the same as in Example 18.

[0274] Example 23

[0275] Except for changing the amount of MnSO4·H2O to 1.4 mol, the amount of FeSO4·H2O to 0.3 mol, and the amount of CoSO4 to 0.2 mol in steps S1 and S2, the other conditions are the same as in Example 18.

[0276] Example 24

[0277] Except for changing the amount of MnSO4·H2O to 1.2 mol, the amount of FeSO4·H2O to 0.5 mol, and the amount of CoSO4 to 0.2 mol in steps S1 and S2, the other conditions are the same as in Example 18.

[0278] Example 25

[0279] Except for changing the amount of MnSO4·H2O to 1.0 mol, the amount of FeSO4·H2O to 0.7 mol, and the amount of CoSO4 to 0.2 mol in steps S1 and S2, the other conditions are the same as in Example 18.

[0280] Example 26

[0281] Except for steps S1 and S2, where the amounts of MnSO4·H2O are changed to 1.4 mol, FeSO4·H2O to 0.3 mol, Li2CO3 to 0.4825 mol, 0.001 mol Mo(SO4)3 to 0.005 mol MgSO4, H4SiO4 to 0.1 mol, phosphoric acid to 0.9 mol, NH4HF2 to 0.04 mol, and 0.1 mol VCl2 and 0.2 mol CoSO4 are added during the preparation of doped manganese oxalate in step S1, all other conditions are the same as in Example 1.

[0282] Example 27

[0283] Except for steps S1 and S2, where the amounts of MnSO4·H2O are changed to 1.4 mol, FeSO4·H2O to 0.3 mol, Li2CO3 to 0.485 mol, 0.001 mol Mo(SO4)3 to 0.005 mol MgSO4, H4SiO4 to 0.08 mol, phosphoric acid to 0.92 mol, NH4HF2 to 0.05 mol, and 0.1 mol VCl2 and 0.2 mol CoSO4 are added during the preparation of doped manganese oxalate in step S1, all other conditions are the same as in Example 1.

[0284] Examples 28 to 32

[0285] Except for steps S3 and S4, in which the amounts of various raw materials used are adjusted according to the coating amounts shown in Table 5 so that the amounts of Li2FeP2O7 / LiFePO4 in Examples 28 to 32 are 12.6g / 37.7g, 14.1g / 42.4g, 18.8g / 56.5g, 22.0g / 66.0g, and 25.1g / 75.4g, respectively, the other conditions are the same as in Example 1.

[0286] Examples 33 to 36

[0287] Except in step S4, where the amount of sucrose is adjusted to 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 are 31.4g, 62.9g, 78.6g and 94.3g respectively, the other conditions are the same as in Example 1.

[0288] Examples 37 to 40

[0289] Except for steps S3 and S4, in which the amounts of various raw materials used are adjusted according to the coating amounts shown in Table 5 so that the amounts of Li2FeP2O7 / LiFePO4 in Examples 37 to 40 are 23.6g / 39.3g, 31.4g / 31.4g, 39.3g / 23.6g, and 47.2g / 15.7g, respectively, the other conditions are the same as in Example 1.

[0290] Example 41

[0291] Except for adjusting the sintering temperature to 550°C and the sintering time to 1 hour in step S4 to control the crystallinity of Li2FeP2O7 to 30%, and adjusting the coating sintering temperature to 650°C and the sintering time to 2 hours in step S5 to control the crystallinity of LiFePO4 to 30%, the other conditions are the same as in Example 1.

[0292] Example 42

[0293] Except for adjusting the sintering temperature to 550°C and the sintering time to 2 hours in step S4 to control the crystallinity of Li2FeP2O7 to 50%, and adjusting the coating sintering temperature to 650°C and the sintering time to 3 hours in step S5 to control the crystallinity of LiFePO4 to 50%, the other conditions are the same as in Example 1.

[0294] Example 43

[0295] Except for adjusting the sintering temperature to 600°C and the sintering time to 3 hours in step S4 to control the crystallinity of Li2FeP2O7 to 70%, and adjusting the coating sintering temperature to 650°C and the sintering time to 4 hours in step S5 to control the crystallinity of LiFePO4 to 70%, the other conditions are the same as in Example 1.

[0296] Examples 44 to 57

[0297] Except for changing the stirring speed and heating temperature when preparing doped manganese oxalate in step S1, and the grinding and stirring time, sintering temperature and sintering time in the sand mill when preparing co-doped lithium manganese phosphate core in step S2, the other conditions are the same as in Example 1, as shown in Table 8 below.

[0298] Examples 58 to 61

[0299] Except for adjusting the drying temperature / drying time in step S3 for preparing lithium iron pyrophosphate powder to 100℃ / 4h, 150℃ / 6h, 200℃ / 6h and 200℃ / 6h respectively, and adjusting the sintering temperature and sintering time to 700℃ / 6h, 700℃ / 6h, 700℃ / 6h and 600℃ / 6h respectively, all other conditions are the same as in Example 1.

[0300] Examples 62 to 64

[0301] Except for adjusting the drying temperature / drying time during step S5 to 150℃ / 6h, 150℃ / 6h and 150℃ / 6h respectively, and adjusting the sintering temperature and sintering time to 680℃ / 4h, 750℃ / 6h and 800℃ / 8h respectively, the other conditions are the same as in Example 38.

[0302] Comparative Example 1

[0303] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0304] Preparation of manganese oxalate:1 mol of MnSO4·H2O was added to a reaction vessel, along with 10 L of deionized water and 1 mol of oxalic acid dihydrate (calculated as oxalic acid). 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), yielding a manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and subsequently ground to obtain a median particle size Dv. 50 Manganese oxalate particles with a diameter of 50-200 nm.

[0305] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.5 mol of lithium carbonate, an 85% phosphoric acid aqueous solution containing 1 mol of phosphoric acid, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C, and the granules were dried for 4 hours to obtain particles. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated LiMnPO4.

[0306] Comparative Example 2

[0307] Except that in Comparative Example 1, 1 mol of MnSO4·H2O was replaced with 0.85 mol of MnSO4·H2O and 0.15 mol of FeSO4·H2O, and the mixture was added to a mixer and thoroughly mixed for 6 hours before being added to the reactor, the other conditions were the same as in Comparative Example 1.

[0308] Comparative Example 3

[0309] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0310] Preparation of doped manganese oxalate: 1.9 mol of MnSO4·H2O and 0.1 mol of ZnSO4 were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding an Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0311] Preparation of positive electrode active materials:1 mol of the above-mentioned manganese oxalate particles, 0.495 mol of lithium carbonate, 0.005 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 1 mol of phosphoric acid, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.990 Mg 0.005 Mn 0.95 Zn 0.05 PO4.

[0312] Comparative Example 4

[0313] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0314] Preparation of doped manganese oxalate: 1.2 mol of MnSO4·H2O and 0.8 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0315] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.45 mol of lithium carbonate, 0.005 mol of Nb₂(SO₄)₅, an 85% phosphoric acid aqueous solution containing 1 mol of phosphoric acid, 0.025 mol of NH₄HF₂, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250 °C, and the granules were dried for 4 hours to obtain particles. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700 °C for 10 hours to obtain carbon-coated Li₂. 0.90 Nb 0.01 Mn 0.6 Fe 0.4 PO 3.95 F 0.05 .

[0316] Comparative Example 5

[0317] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0318] Preparation of doped manganese oxalate: 1.4 mol of MnSO4·H2O and 0.6 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0319] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.38 mol of lithium carbonate, 0.12 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.76 Mg 0.12 Mn 0.7 Fe 0.3 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0320] Comparative Example 6

[0321] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0322] Preparation of doped manganese oxalate: 0.8 mol MnSO4·H2O and 1.2 mol ZnSO4 were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding an Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0323] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.499 mol of lithium carbonate, 0.001 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.998 Mg 0.001 Mn 0.4 Zn 0.6 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0324] Comparative Example 7

[0325] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0326] Preparation of doped manganese oxalate: 1.4 mol of MnSO4·H2O and 0.6 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0327] Preparation of positive electrode active materials:1 mol of the above-mentioned manganese oxalate particles, 0.534 mol of lithium carbonate, 0.001 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 0.88 mol of phosphoric acid, 0.12 mol of H4SiO4, 0.025 mol of NH4HF2, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 1.068 Mg 0.001 Mn 0.7 Fe 0.3 P 0.88 Si 0.12 O 3.95 F 0.05 .

[0328] Comparative Example 8

[0329] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0330] Preparation of doped manganese oxalate: 1.2 mol of MnSO4·H2O and 0.8 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0331] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.474 mol of lithium carbonate, 0.001 mol of MgSO4, an 85% phosphoric acid aqueous solution containing 0.93 mol of phosphoric acid, 0.07 mol of H4SiO4, 0.06 mol of NH4HF2, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C, and the granules were dried for 4 hours to obtain particles. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.948 Mg 0.001 Mn0.6 Fe 0.4 P 0.93 Si 0.07 O 3.88 F 0.12 .

[0332] Comparative Example 9

[0333] Except for changing the preparation steps of the positive electrode active material, the other conditions are the same as in Example 1.

[0334] Preparation of doped manganese oxalate: 1.3 mol of MnSO4·H2O and 0.7 mol of FeSO4·H2O were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction vessel, and 10 L of deionized water and 2 mol of oxalic acid dihydrate (calculated as oxalic acid) were added. 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), yielding a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120 °C and then ground to obtain a median particle size Dv. 50 The particles are Fe-doped manganese oxalate particles with a diameter of approximately 100 nm.

[0335] Preparation of positive electrode active materials: 1 mol of the above-mentioned manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO4)3, an 85% phosphoric acid aqueous solution containing 0.999 mol of phosphoric acid, 0.001 mol of H4SiO4, 0.0005 mol of NH4HF2, and 0.01 mol of sucrose were added to 20 L of deionized water. The mixture was transferred to a sand mill and thoroughly ground and stirred for 10 hours to obtain a slurry. The slurry was then transferred to a spray drying equipment for spray drying granulation. The drying temperature was set at 250°C and the drying time was 4 hours to obtain granules. Under a protective atmosphere of nitrogen (90 vol%) + hydrogen (10 vol%), the above powder was sintered at 700°C for 10 hours to obtain carbon-coated Li. 0.994 Mo 0.001 Mn 0.65 Fe 0.35 P 0.999 Si 0.001 O 3.999 F 0.001 .

[0336] Comparative Example 10

[0337] Except for changing steps S3 and S5 and not performing step S4, the other conditions are the same as in Example 1.

[0338] S3: Preparation of lithium iron pyrophosphate powder

[0339] 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 completely. 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 a 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%.

[0340] S5: Encapsulation

[0341] 10 mol (approximately 1570 g) of the co-doped lithium manganese phosphate core obtained according to step S2, 62.8 g of Li2FeP2O7 powder obtained in step S3, and 37.3 g of sucrose were mixed evenly in 500 mL of deionized water and then dried in a vacuum oven 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 amorphous lithium iron pyrophosphate, carbon-coated positive electrode active material.

[0342] Comparative Example 11

[0343] Except for changing steps S4 and S5 and not performing step S3, the other conditions are the same as in Example 1.

[0344] S4: Preparation of lithium iron phosphate suspension

[0345] 14.7 g of lithium carbonate, 46.1 g of ferrous carbonate, 45.8 g of ammonium dihydrogen phosphate, 50.2 g of oxalic acid dihydrate, and 37.3 g of sucrose were dissolved in 500 mL of deionized water to obtain a mixture. The mixture was then stirred for 6 hours to allow it to react completely. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0346] S5: Encapsulation

[0347] 10 mol (approximately 1570 g) of the co-doped lithium manganese phosphate core obtained according to step S2 was added to the LiFePO4 suspension obtained in step S4 (containing 37.3 g sucrose and 62.8 g LiFePO4). After stirring and mixing evenly, the mixture was transferred to a vacuum oven and dried at 150 °C for 6 hours. The product was then dispersed by sand milling. After dispersion, the product was sintered at 600 °C for 4 hours under a nitrogen atmosphere to obtain amorphous lithium iron phosphate, carbon-coated cathode active material.

[0348] Comparative Example 12

[0349] Except for changing steps S3 to S5, the other conditions are the same as in Example 1.

[0350] S3: Preparation of lithium iron pyrophosphate powder

[0351] 2.38 g of lithium carbonate, 7.5 g of ferrous carbonate, 7.4 g of ammonium dihydrogen phosphate, and 8.1 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 completely. 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 a 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%.

[0352] S4: Preparation of lithium iron phosphate suspension

[0353] 11.1 g of lithium carbonate, 34.8 g of ferrous carbonate, 34.5 g of ammonium dihydrogen phosphate, 37.7 g of oxalic acid dihydrate, and 37.3 g of sucrose were dissolved in 1500 mL of deionized water to obtain a mixture. The mixture was then stirred for 6 hours to allow it to react completely. The resulting solution was then heated to 120 °C and maintained at that temperature for 6 hours to obtain a suspension containing LiFePO4.

[0354] S5: Encapsulation

[0355] 10 mol (approximately 1570 g) of the co-doped lithium manganese phosphate core obtained according to step S2 and 15.7 g of Li2FeP2O7 powder obtained in step S3 were added to the LiFePO4 suspension obtained in step S4 (containing 37.3 g sucrose and 47.2 g LiFePO4). 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 600 °C for 4 hours under a nitrogen atmosphere to control the crystallinity of LiFePO4 to 8%, yielding amorphous lithium iron pyrophosphate, amorphous lithium iron phosphate, and carbon-coated cathode active materials.

[0356] Relevant parameter testing

[0357] 1. Determination of the core chemical formula and composition of different coating layers:

[0358] 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.

[0359] 2. Initial capacity test of button cells:

[0360] 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.

[0361] 3. Average discharge voltage (V) test of coin cells:

[0362] 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.

[0363] 4. Full battery gas expansion test at 60°C:

[0364] 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. Every 48 hours of storage, the full cell was removed, allowed to stand for 1 hour, and then the OCV and 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).

[0365] 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.

[0366] 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.

[0367] 5. Cyclic performance test of the entire battery at 45°C:

[0368] 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.

[0369] 6. Methods for measuring lattice change rate:

[0370] 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).

[0371] 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.

[0372] 7. Li / Mn inverse defect concentration test:

[0373] 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.

[0374] 8. Transition metal dissolution test:

[0375] 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. 2The discs were subjected to inductively coupled plasma emission spectroscopy (ICP) using an Agilent ICP-OES 730. 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, thereby calculating the amount of Mn (and Mn-doped Fe) dissolved after cycling. The testing standard was based on EPA-6010D-2014.

[0376] 9. Surface oxygen valence state test:

[0377] 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.

[0378] 10. Compacted density measurement:

[0379] 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 ρ = m / v.

[0380] 11. X-ray diffraction method for testing the crystallinity of pyrophosphate and phosphate:

[0381] 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.

[0382] 12. Interplanar spacing and included angles:

[0383] 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 sample chamber of a TEM (Talos F200sG2) for testing and obtain the original TEM test image.

[0384] 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.

[0385] Table 1 shows the composition of the positive electrode active materials in Examples 1 to 11 and Comparative Examples 1 to 12.

[0386] Table 2 shows the performance data of the positive electrode active materials, positive electrode sheets, coin cells or all-electric cells of Examples 1 to 11 and Comparative Examples 1 to 12, measured according to the above performance test methods.

[0387] Table 1

[0388]

[0389]

[0390] Table 2

[0391]

[0392] As shown in Table 2, this application modifies lithium manganese phosphate by simultaneously doping specific elements at specific amounts at the Li, Mn, P, and O sites, and by multi-layer coating the lithium manganese phosphate. The resulting positive electrode active material achieves a smaller lattice change rate, a smaller Li / Mn antisite defect concentration, a larger compaction density, a surface oxygen valence state closer to -2, and less Fe and Mn dissolution after cycling. As a result, the battery of this application has better performance, such as higher capacity, better high-temperature storage performance, and better high-temperature cycling performance.

[0393] Figure 7 The X-ray diffraction (XRD) patterns of undoped LiMnPO4 and the cathode active material core prepared in Example 2 are shown. As can be seen from the figure, the main characteristic peak positions in the XRD pattern of the cathode active material core of Example 2 are consistent with those of undoped LiMnPO4, indicating that the doping process did not introduce impurity phases, and the performance improvement mainly comes from elemental doping rather than impurity phases. Figure 8The X-ray energy dispersive spectroscopy (EDS) spectrum of the cathode active material core prepared in Example 2 is shown. The dots in the spectrum represent the doping elements. The spectrum shows that the elemental doping in the cathode active material core prepared in Example 2 is uniform.

[0394] Table 3 shows the composition of the positive electrode active materials in Examples 12 to 27.

[0395] Table 4 shows the performance data of the positive electrode active material, positive electrode sheet, button cell or all-electric cell of Examples 12 to 27, measured according to the above performance test methods.

[0396] Table 3

[0397]

[0398] Table 4

[0399]

[0400] As shown in Table 4, with other elements being equal, when (1-y):y is in the range of 1 to 4 and a:x is in the range of 9 to 1100, and optionally when (1-y):y is in the range of 1.5 to 3 and a:x is in the range of 190 to 998, the energy density and cycle performance of the battery can be further improved.

[0401] Table 5 shows the composition of the positive electrode active materials in Examples 28 to 40.

[0402] Table 6 shows the performance data of the positive electrode active material, positive electrode sheet, button cell or all-electric cell of Examples 28 to 40, measured according to the above performance test methods.

[0403] Table 5

[0404] Serial Number kernel First coating layer Second coating layer Example 28 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[0.8%Li2FeP2O7 / 2.4%LiFePO4]]> 1% carbon Example 29 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[0.9%Li2FeP2O7 / 2.7%LiFePO4]]> 1% carbon Example 30 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1.2%Li2FeP2O7 / 3.6%LiFePO4]]> 1% carbon Example 31 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1.4%Li2FeP2O7 / 4.2%LiFePO4]]> 1% carbon Example 32 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1.6%Li2FeP2O7 / 4.8%LiFePO4]]> 1% carbon Example 33 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1%Li2FeP2O7 / 3%LiFePO4]]> 2% carbon Example 34 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1%Li2FeP2O7 / 3%LiFePO4]]> 4% carbon Example 35 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1%Li2FeP2O7 / 3%LiFePO4]]> 5% carbon Example 36 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1%Li2FeP2O7 / 3%LiFePO4]]> 6% carbon Example 37 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[1.5%Li2FeP2O7 / 2.5%LiFePO4]]> 1% carbon

[0405] Example 38 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[2%Li2FeP2O7 / 2%LiFePO4]]> 1% carbon Example 39 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[2.5%Li2FeP2O7 / 1.5%LiFePO4]]> 1% carbon Example 40 <![CDATA[Li 0.994 Know 0.001 Mn 0.65 Want 0.35 P 0.999 To 0.001 SHE 3.999 F 0.001 ]]> <![CDATA[3%Li2FeP2O7 / 1%LiFePO4]]> 1% carbon

[0406] Table 6

[0407]

[0408] Based on Examples 1 and 28-32, it can be seen that as the amount of the first coating layer increases from 3.2% to 6.4%, the concentration of Li / Mn antisite defects in the resulting positive electrode active material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases, thus improving the safety and cycle performance of the battery, although the specific capacity decreases slightly. Optionally, when the total amount of the first coating layer is 4-5.6% by weight, the overall performance of the battery is optimal.

[0409] As can be seen from Examples 1 and 33 to 36, as the amount of the second coating layer increases from 1% to 6%, the concentration of Li / Mn antisite defects in the resulting positive electrode active material gradually decreases, and the dissolution of Fe and Mn after cycling gradually decreases, thus improving the safety and cycle performance of the battery, but slightly reducing the specific capacity. Optionally, when the total amount of the second coating layer is 3-5% by weight, the overall performance of the battery is optimal.

[0410] As can be seen from Examples 1 and 37 to 40, 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.

[0411] Table 7 shows the performance data of the positive electrode active material, positive electrode sheet, button cell or all-electric cell of Examples 1, 41 to 43, measured according to the above performance test methods.

[0412] Table 7

[0413]

[0414] As shown in Table 7, as the crystallinity of pyrophosphate and phosphate in the first coating layer gradually increases, the lattice change rate of the corresponding positive electrode active material, the concentration of Li / Mn antisite defects, and the amount of Fe and Mn dissolved after cycling gradually decrease, the battery capacity gradually increases, and the safety performance and cycle performance gradually improve.

[0415] Examples 44 to 57 are identical to Example 1 except for changes to the stirring speed and heating temperature during step S1 (preparing the doped manganese oxalate) and the grinding and stirring time, sintering temperature, and sintering time in the sand mill during step S2 (preparing the co-doped lithium manganese phosphate core). Details are shown in Table 8 below. Table 9 shows the performance data of the positive electrode active material, positive electrode sheet, coin cell, or all-electric cell of Examples 44 to 57, measured according to the above performance testing methods.

[0416] Table 8

[0417]

[0418] Table 9

[0419]

[0420] As can be seen from Table 9, by adjusting the stirring speed and heating temperature during the preparation of doped manganese oxalate in step S1, and the grinding and stirring time, sintering temperature and sintering time in the sand mill during the preparation of co-doped lithium manganese phosphate core in step S2, the performance of the positive electrode active material and the battery can be further improved.

[0421] Examples 58 to 61 are identical to Example 1 except for changes in the drying temperature, drying time, sintering temperature, and sintering time during step S3 for preparing lithium iron pyrophosphate powder, as detailed in Table 10 below. Table 11 shows the performance data of the positive electrode active material, positive electrode sheet, coin cell, or all-cell battery of Examples 58 to 61, measured according to the above performance testing methods.

[0422] Examples 62 to 64 are identical to Example 38 except for changes in the drying temperature, drying time, sintering temperature, and sintering time during the coating process in step S5, as detailed in Table 12 below. Table 13 shows the performance data of the positive electrode active material, positive electrode sheet, coin cell, or all-electric cell of Examples 62 to 64, measured according to the above performance testing methods.

[0423] Table 10

[0424]

[0425] Table 11

[0426]

[0427] Table 12

[0428]

[0429] Table 13

[0430]

[0431] As shown in Tables 11 and 13, by adjusting parameters such as drying temperature, drying time, sintering temperature, and sintering time in steps S3 to S5, the performance of the positive electrode active material and the battery can be further improved.

[0432] 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 active material with a core-shell structure, comprising a core and a shell covering the core, wherein, The chemical formula of the core is Li a A x Mn 1-y B y P 1-z C z O 4-n D n The A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; the B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; the C comprises one or more elements selected from boron, S, Si, and N; the D comprises one or more elements selected from S, F, Cl, and Br; the a is selected from the range of 0.9 to 1.1; the x is selected from the range of 0.001 to 0.1; the y is selected from the range of 0.001 to 0.5; the z is selected from the range of 0.001 to 0.1; the n is selected from the range of 0.001 to 0.1; and the core is electrically neutral. The shell includes a first covering layer covering the core and a second covering layer covering the first covering layer, wherein, The first coating layer comprises 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, and the crystallinity of the pyrophosphate and phosphate is each independently from 10% to 100%. The second coating layer contains carbon.

2. The positive electrode active material according to claim 1, wherein, The interplanar spacing of the phosphate in the first coating layer is 0.345-0.358 nm, and the included angle of the crystal orientation (111) is 24.25°-26.45°; the interplanar spacing of the pyrophosphate in the first coating layer is 0.293-0.326 nm, and the included angle of the crystal orientation (111) is 26.41°-32.57°.

3. The positive electrode active material according to claim 1, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 3:

1.

4. The positive electrode active material according to claim 3, wherein, The weight ratio of pyrophosphate to phosphate in the first coating layer is 1:3 to 1:

1.

5. The positive electrode active material according to claim 1, wherein, The crystallinity of the pyrophosphate and phosphate is independently between 50% and 100%.

6. The positive electrode active material according to claim 1, wherein, The x is selected from the range of 0.001 to 0.005; and / or the y is selected from the range of 0.01 to 0.5; and / or the z is selected from the range of 0.001 to 0.005; and / or the n is selected from the range of 0.001 to 0.

005.

7. The positive electrode active material according to claim 5, wherein, The value of y is selected from the range of 0.25 to 0.

5.

8. The positive electrode active material according to claim 1, wherein, (1-y): y is in the range of 1 to 4, and a:x is in the range of 9 to 1100.

9. The positive electrode active material according to claim 8, wherein, (1-y): y is in the range of 1.5 to 3.

10. The positive electrode active material according to claim 8, wherein, a:x is in the range of 190-998.

11. The positive electrode active material according to claim 1, 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.

12. The positive electrode active material according to claim 11, wherein, The first coating layer has a coating weight of 4-5.6% by weight, based on the weight of the core; and / or, The second coating layer has a coating amount of 3-5% by weight, based on the weight of the core.

13. The positive electrode active material according to claim 1, wherein, A, C, and D are any one of their respective ranges, and B is at least two of its ranges.

14. The positive electrode active material according to claim 13, wherein, A is an element selected from Mg and Nb, and / or, The element B is selected from at least two elements chosen from Fe, Ti, V, Co, and Mg, and / or, The C is S, and / or, The D is F.

15. The positive electrode active material according to claim 14, wherein, The B is Fe and one or more elements selected from Ti, V, Co and Mg.

16. The positive electrode active material according to any one of claims 1-15, 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 below 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.

17. The positive electrode active material according to claim 16, 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 below 2%; (2) The lattice change rate of the positive electrode active material is less than 6%; (3) The surface oxygen valence state of the positive electrode active material is -1.99 to -1.88; (4) The compaction density of the positive electrode active material at 3 tons is 2.2 g / cm³. 3 above.

18. A method for preparing a positive electrode active material, comprising the following steps: Steps for providing kernel material: The kernel includes Li a A x Mn 1-y B y P 1-z C z O 4-n D n The core is wherein A comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C comprises one or more elements selected from boron, S, Si, and N; D comprises one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1; x is selected from the range of 0.001 to 0.1; y is selected from the range of 0.001 to 0.5; z is selected from the range of 0.001 to 0.1; n is selected from the range of 0.001 to 0.1; and the core is electrically neutral. 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 positive electrode active material has a core-shell structure, which includes a 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. The crystallinity of the pyrophosphate and phosphate is independently 10% to 100%. The second coating layer contains carbon.

19. The method according to claim 18, wherein, The step of providing kernel materials includes the following steps: Step (1): Dissolve and stir the manganese source, element B source and acid in a solvent to generate a suspension of manganese salt doped with element B. Filter the suspension and dry the filter cake to obtain manganese salt doped with element B. Step (2): Add the lithium source, phosphorus source, source of element A, source of element C and source of element D, solvent and manganese salt doped with element B obtained in step (1) into the reaction vessel, grind and mix to obtain a slurry; Step (3): Transfer the slurry obtained in step (2) to a spray drying equipment for spray drying and granulation to obtain granules; Step (4): Sinter the particles obtained in step (3) to obtain the core Li. a A x Mn 1-y B y P 1-z C z O 4-n D n .

20. The method according to claim 19, wherein, The source of element A is selected from at least one of the simple substance, oxide, phosphate, oxalate, carbonate and sulfate of element A; the source of element B is selected from at least one of the simple substance, oxide, phosphate, oxalate, carbonate and sulfate of element B; the source of element C is selected from at least one of the sulfate, borate, nitrate and silicate of element C; and the source of element D is selected from at least one of the simple substance and ammonium salt of element D.

21. The method according to claim 19, wherein, The stirring in step (1) is carried out at a temperature in the range of 60-120°C; and / or, The stirring in step (1) is carried out at a stirring rate of 200-800 rpm; and / or, The grinding and mixing in step (2) shall be carried out for 8-15 hours; and / or, The sintering in step (4) is carried out at a temperature range of 600-900℃ for 6-14 hours.

22. The method according to claim 18, 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. The pH of the mixture is adjusted to 4-6, stirred and fully reacted, and then dried and sintered. M is selected from one or more of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al.

23. The method according to claim 22, wherein, Drying is performed at 100-300℃ for 4-8 hours; and / or, Sintering is carried out at 500-800℃ in an inert gas atmosphere for 4-10 hours.

24. The method according to claim 23, wherein, Drying is performed at 150-200℃ for 4-8 hours; and / or, Sintering is carried out at 650-800℃ for 4-10 hours in an inert gas atmosphere.

25. The method according to claim 18, wherein, The sintering temperature in the coating step is 500-800℃, and the sintering time is 4-10 hours.

26. 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, wherein, The positive electrode film layer comprises the positive electrode active material according to any one of claims 1-17 or the positive electrode active material prepared by any one of claims 18-25, and the content of the positive electrode active material in the positive electrode film layer is 10% by weight or more, based on the total weight of the positive electrode film layer.

27. The positive electrode sheet according to claim 26, wherein, The content of the positive electrode active material in the positive electrode film is 90-99.5% by weight, based on the total weight of the positive electrode film.

28. A secondary battery, comprising a positive electrode active material according to any one of claims 1-17, or a positive electrode active material prepared by any one of claims 18-25, or a positive electrode sheet according to any one of claims 26-27.

29. An electrical device comprising the secondary battery of claim 28.

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