Positive electrode active material, method for manufacturing the same, positive electrode sheet, secondary battery, battery module, battery pack, and power tool

Abstract

The application provides a positive electrode active material, a preparation method thereof, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. The positive electrode active material comprises a core containing Li 1+x Mn 1‑y A y P 1‑z R z O4, a first coating layer containing crystalline pyrophosphate M a P2O7 and crystalline oxide M' b O c and a second coating layer containing carbon which coats the first coating layer. The positive electrode active material can reduce the generation of Li / Mn antisite defects, reduce manganese elution and reduce the lattice change rate, improve the capacity of the secondary battery, and improve the cycle performance, high-temperature storage performance and safety performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a positive electrode active material, a preparation method of the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] In recent years, with the increasingly wide application of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their energy density, cycle performance and safety performance. As the existing positive electrode active material of secondary batteries, lithium manganese phosphate is prone to produce Li / Mn anti-site defects during charging and discharging, and manganese leaching is serious, which affects the specific capacity of the secondary battery and leads to poor safety performance and cycle performance of the secondary battery. SUMMARY

[0003] The present application is carried out in view of the above-mentioned problems, and aims to provide a positive electrode active material, a preparation method of the positive electrode active material, a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device, so as to solve the problems of the existing lithium manganese phosphate positive electrode active material being prone to produce Li / Mn anti-site defects during charging and discharging, and manganese leaching being serious, thereby solving the problems of low capacity, poor safety performance and cycle performance of the secondary battery, etc.

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a positive electrode active material with a core-shell structure, which comprises a core and a shell covering the core,

[0005] The core comprises Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Zn, Fe, Ti, V, Ni, Co and Mg, and R is one or more elements selected from B, Si, N and S;

[0006] The shell comprises a first coating layer covering the core and a second coating layer covering the first coating layer;

[0007] The first coating layer comprises a crystalline pyrophosphate M a P2O7and a crystalline oxide M' b O c wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally one or more elements selected from Li, Fe and Zr, M' is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IIIA elements, Group IVA elements, lanthanide series elements and Sb, optionally one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, more optionally one or more elements selected from Mg, Al, Si, Zn, Zr and Sn;

[0008] The second coating layer comprises carbon.

[0009] The present inventor has found in practical operation that the lithium manganese phosphate positive electrode active material is prone to Li / Mn anti-site defects and serious manganese dissolution during deep charge and discharge. The dissolved manganese is reduced to metallic manganese after migrating to the negative electrode. The generated metallic manganese acts as a "catalyst" to catalyze the decomposition of the SEI film on the surface of the negative electrode, and the byproducts generated are partly gas, which can easily cause the battery to swell and affect the safety performance of the secondary battery, and partly deposited on the surface of the negative electrode, which hinders the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase and affecting the kinetic performance and cycle performance of the battery. In addition, to make up for the loss of the SEI film, the electrolyte and active lithium inside the battery are continuously consumed, which has an irreversible impact on the capacity retention rate of the secondary battery.

[0010] Therefore, the present inventor has unexpectedly found that by doping specific elements in specific amounts at the Mn and P sites of the compound LiMnPO4, coating the first coating layer containing pyrophosphate and oxide on the surface of the compound, and coating the second coating layer containing carbon on the surface of the first coating layer to obtain a positive electrode active material, the generation of Li / Mn anti-site defects, manganese dissolution and lattice change rate can be greatly reduced, the capacity of the secondary battery can be improved, and the cycle performance, high-temperature storage performance and safety performance of the secondary battery can be improved.

[0011] Unless otherwise specified, the chemical formula Li 1+x Mn1-y A y P 1-z R z In Formula O4, when A is two or more elements, the above-mentioned limitation on the value range of y is not only a limitation on the stoichiometric number of each element as A, but also a limitation on the sum of the stoichiometric numbers of each element as A. For example, when A is two or more elements A1, A2, …, An, the stoichiometric numbers y1, y2, …, yn of A1, A2, …, An, respectively, each need to fall within the value range of y limited in the present application, and the sum of y1, y2, …, yn also needs to fall within the value range. Similarly, for the case where R is two or more elements, the limitation on the value range of the stoichiometric number of R in the present application also has the above-mentioned meaning.

[0012] Unless otherwise specified, the chemical formula M a In Formula P2O7, when M is two or more elements, the above-mentioned limitation on the value range of a is not only a limitation on the stoichiometric number of each element as M, but also a limitation on the sum of the stoichiometric numbers of each element as M. For example, when M is two or more elements M1, M2, …, Mn, the stoichiometric numbers a1, a2, …, an of M1, M2, …, Mn, respectively, each need to fall within the value range of a limited in the present application, and the sum of a1, a2, …, an also needs to fall within the value range. Similarly, for the case where M' is two or more elements in Formula O b O c In Formula O, when M' is two or more elements, the limitation on the value range of the stoichiometric number b of M' in the present application also has the above-mentioned meaning.

[0013] In any embodiment of the first aspect, 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°;

[0014] Optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm; and / or,

[0015] Optionally, the included angle of the crystal direction (111) of the pyrophosphate in the first coating layer is 29.00°-30.00°.

[0016] When the interplanar spacing of the pyrophosphate and the included angle of the crystal direction (111) in the first coating layer are within the above-mentioned ranges, impurity phases in the coating layer can be effectively avoided, thereby improving the gravimetric capacity of the material and the cycle performance and rate performance of the secondary battery.

[0017] In any embodiment of the first aspect, the ratio of y to 1-y in the core is 1:10 to 10:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric numbers of the Mn-site doping elements. When the above condition is met, the energy density and cycle performance of the secondary battery produced using the positive electrode active material can be further improved.

[0018] In any embodiment of the first aspect, the ratio of z to 1-z in the core is 1:9 to 1:999, optionally 1:499 to 1:249. Here, z represents the sum of the stoichiometric numbers of the P-site doping elements. When the above condition is met, the energy density and cycle performance of the secondary battery produced using the positive electrode active material can be further improved.

[0019] In any embodiment of the first aspect, the amount of the first coating layer is greater than 0 wt% and less than or equal to 7 wt%, optionally 4-5.6 wt%, based on the weight of the core.

[0020] When the amount of the first coating layer is within the above range, manganese elution can be further inhibited, while the transport of lithium ions is further promoted, maintaining a low impedance of the secondary battery and improving the kinetic performance of the secondary battery.

[0021] In any embodiment of the first aspect, the weight ratio of the pyrophosphate salt to the oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.

[0022] A suitable ratio of the pyrophosphate salt to the oxide is conducive to fully exerting the synergistic effect of both, further inhibiting manganese elution while maintaining a low impedance of the secondary battery.

[0023] In any embodiment of the first aspect, the crystallinity of the pyrophosphate salt in the first coating layer is 10% to 100%, optionally 50% to 100%.

[0024] In the first coating layer of the lithium manganese phosphate positive electrode active material of the present application, the pyrophosphate salt with a certain crystallinity is conducive to maintaining the structural stability of the first coating layer and reducing lattice defects. This is conducive to fully exerting the role of the pyrophosphate salt in hindering manganese elution, and on the other hand, it is also conducive to reducing the content of surface impurity lithium and the valence state of surface oxygen, thereby reducing the interfacial side reaction of the positive electrode material with the electrolyte, reducing the consumption of the electrolyte, and improving the cycle performance and safety performance of the secondary battery.

[0025] In any embodiment of the first aspect, the amount of the second coating layer is greater than 0 wt% and less than or equal to 6 wt%, optionally 3-5 wt%, based on the weight of the core.

[0026] The carbon-containing layer, serving as the second coating layer, acts as a barrier, preventing direct contact between the positive electrode active material and the electrolyte, thereby reducing electrolyte corrosion and improving battery safety at high temperatures. Furthermore, its strong conductivity reduces internal resistance, thus improving the kinetic performance of the secondary battery. When the coating amount of the second layer is within the aforementioned range, it can further improve the kinetic and safety performance of the secondary battery while maintaining a high specific capacity of the positive electrode active material.

[0027] In any embodiment of the first aspect, in the positive electrode active material, A is selected from at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. By selecting doping elements within the above range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce surface oxygen activity, reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0028] In any embodiment of the first aspect, the Li / Mn antisite defect concentration of the positive electrode active material is 5.1% or less, optionally 4% or less, and more preferably 2% or less. In the positive electrode active material of this application, the Li / Mn antisite defect refers to the Li... + and Mn 2+ The positions of Li have been interchanged. + 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 + Transport efficiency. By controlling the concentration of Li / Mn antisite defects at low levels, the specific capacity and rate performance of LiMnPO4 can be improved.

[0029] In any embodiment of the first aspect, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is 7.5% or less, optionally 6% or less, and more preferably 4% or less. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of secondary batteries.

[0030] In any embodiment of the first aspect, the surface oxygen valence state of the positive electrode active material is -1.83 or less, optionally -1.88 or less, more optionally -1.98 to -1.88. This is because the higher the valence state of oxygen in the compound, the stronger the electron-accepting ability, i.e. the stronger the oxidizing property. In the positive electrode active material of the present application, by controlling the surface valence state of oxygen at a lower level, the reactivity of the surface of the positive electrode material can be reduced, the interface side reaction between the positive electrode material and the electrolyte can be reduced, and thus the cycle performance and high-temperature storage performance of the secondary battery can be improved.

[0031] In any embodiment of the first aspect, the compaction density of the positive electrode active material under 3 tons (T) is 2.0 g / cm 3 or more, optionally 2.2 g / cm 3 or more. The higher the compaction density of the positive electrode active material, i.e. the greater the weight of active material per unit volume, the more beneficial it is to improve the volumetric energy density of the secondary battery.

[0032] The second aspect of the present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0033] The step of providing a core material: the core material comprises Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any numerical value in the range of -0.100 to 0.100, y is any numerical value in the range of 0.001 to 0.500, z is any numerical value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Zn, Fe, Ti, V, Ni, Co and Mg, and R is one or more elements selected from B, Si, N and S;

[0034] The coating step: providing a powder comprising pyrophosphate M a P2O7and a suspension liquid comprising a carbon source and an oxide M' b O c The core material, the powder comprising pyrophosphate M a P2O7and the suspension liquid comprising a carbon source and an oxide M' b O csintering to obtain the positive electrode active material, wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally one or more elements selected from Li, Fe and Zr, M' is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IVA elements, lanthanide series elements and Sb, optionally one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, more optionally one or more elements selected from Mg, Al, Si, Zn, Zr and Sn;

[0035] wherein the positive electrode active material has a core-shell structure comprising a core and a shell covering the core, the core comprising Li 1+ x Mn 1-y A y P 1-z R z O4, the shell comprising a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer comprising crystalline pyrophosphate M a P2O7and crystalline oxide M' b O c , the second coating layer comprising carbon; wherein A, R, M, M', x, y, z, a, b, c are as defined above.

[0036] Thus, the present applicant surprisingly found that by doping specific elements in specific amounts at Mn sites and P sites of the compound LiMnPO4, coating the surface of the compound with a first coating layer containing pyrophosphate and oxide and coating the surface of the first coating layer with a second coating layer containing carbon to obtain the positive electrode active material, the generation of Li / Mn antisite defects can be greatly reduced, manganese elution can be reduced and the lattice change rate can be lowered, the capacity of the secondary battery can be improved, and the cycle performance, high-temperature storage performance and safety performance of the secondary battery can be improved.

[0037] In any embodiment of the second aspect of the present application, the step of providing the core material comprises the following steps:

[0038] Step (1): mixing a manganese source, a source of element A and an acid to obtain a mixture;

[0039] Step (2): mixing the mixture with a source of lithium, a source of phosphorus, a source of element R and optionally a solvent, and sintering under inert gas protection to obtain a core material comprising Li 1+x Mn 1-y A y P 1-z R z O4.

[0040] In any embodiment of the second aspect of the present application, step (1) is performed at 20-120°C, optionally at 25-80°C; and / or, in step (1), the mixing is performed by stirring at 500-700 rpm for 60-420 minutes.

[0041] In any embodiment of the second aspect of the present application, the source of element A is selected from one or more of elemental A, sulfate, halide, nitrate, organic acid salt, oxide and hydroxide; and / or, the source of element R is selected from one or more of elemental R, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide and inorganic acid.

[0042] In any embodiment of the second aspect of the present application, the powder comprising pyrophosphate M a P2O7is prepared by the following steps:

[0043] Mixing the source of element M, the source of phosphorus and optionally a solvent to obtain a mixture, adjusting the pH of the mixture to 4-6, and continuing to mix, and then drying and sintering.

[0044] In any embodiment of the second aspect of the present application, in the step of preparing the powder comprising pyrophosphate M a P2O7, the drying is drying at 100-300°C for 4-8h, optionally at 150-200°C; and / or, the sintering is sintering at 500-800°C and under inert gas protection for 4-10h, optionally sintering at 650-800°C.

[0045] In any embodiment of the second aspect of the present application, the sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10h.

[0046] The third aspect of the present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the preparation method of the second aspect of the present application; optionally, the content of the positive electrode active material in the positive electrode film layer is 10 wt% or more, based on the total weight of the positive electrode film layer.

[0047] In any embodiment of the third aspect of the present 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. The secondary battery has high capacity and good cycle performance, high-temperature storage performance and safety performance.

[0048] The fourth aspect of the present application provides a secondary battery comprising the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the preparation method of the second aspect of the present application or the positive electrode sheet of the third aspect of the present application.

[0049] The fifth aspect of the present application provides a battery module comprising the secondary battery of the fourth aspect of the present application.

[0050] The sixth aspect of the present application provides a battery pack comprising the battery module of the fifth aspect of the present application.

[0051] The seventh aspect of the present application provides a power utilization device comprising at least one selected from the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application and the battery pack of the sixth aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is a schematic diagram of the positive electrode active material with a core-shell structure according to an embodiment of the present application.

[0053] Figure 2 is a schematic diagram of the secondary battery according to an embodiment of the present application.

[0054] Figure 3 is a schematic diagram of the secondary battery according to an embodiment of the present application. Figure 2 is an exploded view of the secondary battery according to an embodiment of the present application.

[0055] Figure 4 is a schematic diagram of the battery module according to an embodiment of the present application.

[0056] Figure 5 is a schematic diagram of the battery pack according to an embodiment of the present application.

[0057] Figure 6 is a schematic diagram of the battery pack according to an embodiment of the present application. Figure 5 is an exploded view of the battery pack according to an embodiment of the present application.

[0058] Figure 7 is a schematic diagram of the power utilization device using the secondary battery according to an embodiment of the present application as a power source.

[0059] BRIEF DESCRIPTION OF DRAWINGS

[0060] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 11 inner core; 12 first coating layer; 13 second coating layer. Detailed Implementation

[0061] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, the method for preparing the positive electrode active material, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the power supply device of this application. 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 for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0062] 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.

[0063] In this application, the terms "below a certain value" and "above a certain value" refer to the range defined by a certain value as the upper or lower limit.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0066] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, a method further comprising step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0067] If not specified otherwise, the terms "comprising" and "including" as used in the present application mean both open and closed inclusive. For example, "comprising" and "including" can mean that other components not listed can also be included or can mean that only the listed components are included.

[0068] If not specified otherwise, the term "or" in the present application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following satisfy the condition "A or B": 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).

[0069] If not specified otherwise, in the present application, the median particle size Dv 50 The term "median particle size Dv 50 The median particle size Dv

[0070] If not specified otherwise, in the present application, the term "coating layer" refers to a layer of a substance coated on a core, and the layer of the substance can completely or partially coat the core. The term "coating layer" is used only for the convenience of description and is not intended to limit the present application. Similarly, the term "thickness of the coating layer" refers to the thickness of the layer of the substance coated on the core in the radial direction of the core.

[0071] If not specified otherwise, in the present application, the term "source" refers to a compound that serves as a source of an element. As examples, the types of "sources" include, but are not limited to, carbonates, sulfates, nitrates, simple substances, halides, oxides, and hydroxides, etc.

[0072] [Secondary battery]

[0073] A secondary battery, also called a rechargeable battery or a storage battery, refers to a battery that can be used continuously after activation of active materials by charging after discharging of the battery.

[0074] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During charging and discharging of the battery, active ions (e.g., lithium ions) are inserted into and extracted from between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to prevent short circuiting of the positive and negative electrodes, while allowing the active ions to pass therethrough. The electrolyte is disposed between the positive electrode sheet and the negative electrode sheet, and mainly functions to conduct the active ions.

[0075] [Positive active material]

[0076] The present application provides a positive active material having a core-shell structure, which includes a core and a shell covering the core,

[0077] The core contains Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, optionally one or more elements selected from Zn, Fe, Ti, V, Ni, Co, and Mg, and R is one or more elements selected from B, Si, N, and S.

[0078] The shell includes a first coating layer covering the core and a second coating layer covering the first coating layer.

[0079] The first coating layer contains a crystalline pyrophosphate M a P2O7 and a crystalline oxide M' b O cwherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, optionally one or more elements selected from the group consisting of Li, Fe, and Zr, M' is one or more elements selected from the group consisting of alkali metals, alkaline earth metals, transition metals, Group IVA elements, lanthanide series elements, and Sb, optionally one or more elements selected from the group consisting of Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La, and Ce, more optionally one or more elements selected from the group consisting of Mg, Al, Si, Zn, Zr, and Sn;

[0080] The second coating layer comprises carbon.

[0081] As shown in Figure 1 The positive electrode active material with a core-shell structure of the present application includes an inner core 11, a first coating layer 12 coating the inner core 11, and a second coating layer 13 coating the first coating layer 12. The inner core 11 includes Li 1+x Mn 1-y A y P 1- z R zO4; the element A doped in the manganese site of the lithium manganese phosphate helps to reduce the lattice change rate of the lithium manganese phosphate during the lithium deintercalation process, improve the structural stability of the lithium manganese phosphate positive electrode material, greatly reduce the dissolution of manganese and reduce the oxygen activity on the particle surface; the element R doped in the phosphorus site helps to change the difficulty of the Mn-O bond length change, thereby reducing the lithium ion migration barrier, promoting the lithium ion migration and improving the rate performance of the secondary battery. The first coating layer 12 includes a crystalline pyrophosphate and a crystalline oxide; since the transition metal has a high migration barrier in the pyrophosphate (>1eV), the dissolution of the transition metal can be effectively inhibited; the crystalline oxide has high structural stability and low surface activity, and therefore, the interface side reaction can be effectively reduced by the coating of the crystalline oxide, thereby improving the high-temperature cycle and high-temperature storage performance of the battery. In addition, since the second coating layer 13 is a carbon-containing layer, the conductivity and desolvation capacity of LiMnPO4 can be effectively improved. In addition, the "barrier" effect of the second coating layer 13 can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the electrolyte to the active material. Therefore, the positive electrode active material of the present application can reduce the generation of Li / Mn anti-site defects, effectively inhibit the Mn dissolution during the lithium deintercalation process, and promote the migration of lithium ions, thereby improving the rate performance of the battery cell, improving the cycle performance, high-temperature performance and safety performance of the secondary battery. It should be pointed out that the main characteristic peaks of the positive electrode active material of the present application are basically the same as those before doping LiMnPO4, which indicates that the doped lithium manganese phosphate positive electrode active material has no impurity phase, and the improvement of the performance of the secondary battery is mainly due to the element doping, rather than the impurity phase.

[0082] In some embodiments, Li 1+x Mn 1-y A y P 1-z R z O4 remains electrically neutral.

[0083] Unless otherwise specified, the chemical formula Li 1+x Mn 1-y A y P 1-z R z O4, when A is two or more elements, the above-mentioned limitation on the value range of y is not only a limitation on the stoichiometric number of each element as A, but also a limitation on the sum of the stoichiometric numbers of each element as A. For example, when A is two or more elements A1, A2……An, the stoichiometric numbers y1, y2……yn of A1, A2……An respectively each need to fall within the value range of y limited by the present application, and the sum of y1, y2……yn also needs to fall within the value range. Similarly, for the case where R is two or more elements, the limitation on the value range of the stoichiometric number of R in the present application also has the above-mentioned meaning.

[0084] Unless otherwise specified, the chemical formula M a In P2O7, when M is two or more elements, the above-mentioned limitation on the value range of a is not only a limitation on the stoichiometric number of each element as M, but also a limitation on the sum of the stoichiometric numbers of each element as M. For example, when M is two or more elements M1, M2, …, Mn, the stoichiometric numbers a1, a2, …, an of M1, M2, …, Mn, respectively, each need to fall within the value range of a limited by the present application, and the sum of a1, a2, …, an also needs to fall within the value range. Similarly, for the chemical formula M' b O c In the case where M' is two or more elements in the chemical formula M'

[0085] In some embodiments, when A is one, two, three, or four elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, A y Q n1 D n2 E n3 K n4 , n1+n2+n3+n4=y, and n1, n2, n3, n4 are positive numbers and not zero at the same time, Q, D, E, K are each independently one selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and optionally, at least one of Q, D, E, K is Fe. Optionally, one of n1, n2, n3, n4 is zero, and the rest are not zero; more optionally, two of n1, n2, n3, n4 are zero, and the rest are not zero; further optionally, three of n1, n2, n3, n4 are zero, and the rest are not zero. Core Li 1+x Mn 1-y A y P 1-z R z O4, it is advantageous to dope one, two, three, or four of the above-mentioned A elements at the manganese site, and optionally, one, two, or three of the above-mentioned A elements; in addition, it is advantageous to dope one or two R elements at the phosphorus site, which is advantageous for uniform distribution of the doping elements.

[0086] In some embodiments, the values of x, y, and z satisfy the following conditions: to maintain the entire core electrically neutral.

[0087] Core Li 1+x Mn 1-y A y P 1-z Rz In O4, the value of x is influenced by the valence states of A and R, as well as the values ​​of y and z, to ensure the overall system remains electrically neutral. If the value of x is too small, the lithium content of the entire core system will decrease, affecting the specific capacity of the material. The value of y limits the total amount of all dopants. If y is too small, the doping amount is too low, and the dopants will not play a role. If y exceeds 0.5, the Mn content in the system will be low, affecting the voltage plateau of the material. R is doped at the P site. Since the PO tetrahedron is relatively stable, and a large z value would affect the stability of the material, the z value is limited to 0.001-0.100.

[0088] Furthermore, maintaining the electrical neutrality of the entire core system ensures that defects and impurities in the cathode active material are minimized. If an excess of transition metal (such as manganese) exists in the cathode active material, due to the relatively stable structure of the material system itself, the excess transition metal is likely to precipitate as elemental form or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. In addition, ensuring the electrical neutrality of the system can, in some cases, generate lithium vacancies in the material, thereby improving the material's kinetic performance.

[0089] By controlling the process (e.g., thoroughly mixing and grinding materials from various sources), it is possible to ensure that each element is uniformly distributed in the crystal lattice and that no aggregation occurs. The main characteristic peak positions in the XRD pattern of lithium manganese phosphate doped with elements A and R are consistent with those of undoped LiMnPO4, indicating that no impurity phase was introduced during the doping process. Therefore, the improvement in core performance mainly comes from elemental doping, rather than impurity phases. After preparing the positive electrode active material, the inventors of this application used focused ion beam (FIB) to cut the middle region of the prepared positive electrode active material particles. Tests conducted using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) revealed that the elements were uniformly distributed and no aggregation occurred.

[0090] In some implementations, the values ​​of a, b, and c satisfy the following condition: making M a P2O7 and M′ b O c Maintain electrical neutrality.

[0091] In some embodiments, 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°;

[0092] Optionally, the interplanar spacing of the pyrophosphate in the first coating layer is 0.300-0.310 nm (e.g., 0.303 nm); and / or,

[0093] Optionally, the included angle of the crystal direction (111) of the pyrophosphate in the first coating layer is 29.00°-30.00° (for example, 29.496°).

[0094] When the interplanar spacing of the crystal face of the pyrophosphate in the first coating layer and the included angle of the crystal direction (111) are in the above range, impurity phases in the coating layer can be effectively avoided, thereby improving the gravimetric capacity of the material and the cycle performance and rate performance of the secondary battery.

[0095] In some embodiments, in the core, the ratio of y to 1-y is 1:10 to 10:1, optionally 1:4 to 1:1. Here, y represents the sum of the stoichiometric numbers of the Mn-site doping elements. When the above condition is met, the energy density and cycle performance of the secondary battery prepared from the positive electrode active material can be further improved.

[0096] In some embodiments, in the core, the ratio of z to 1-z is 1:9 to 1:999, optionally 1:499 to 1:249. Here, z represents the sum of the stoichiometric numbers of the P-site doping elements. When the above condition is met, the energy density and cycle performance of the secondary battery prepared from the positive electrode active material can be further improved.

[0097] In some embodiments, 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.

[0098] When the coating amount of the first coating layer is in the above range, manganese elution can be further inhibited, while further promoting the transport of lithium ions, maintaining low impedance of the secondary battery, and improving the kinetic performance of the secondary battery.

[0099] In some embodiments, the weight ratio of the pyrophosphate to the oxide in the first coating layer is 1:3 to 3:1, optionally 1:3 to 1:1.

[0100] The suitable ratio of the pyrophosphate to the oxide is conducive to fully exerting the synergistic effect of both, can further inhibit manganese elution, while maintaining a lower impedance of the secondary battery.

[0101] In some embodiments, the thickness of the first coating layer is 1-100 nm. In this way, the migration barrier of the transition metal in the first coating layer is high, and the elution of the transition metal can be effectively reduced. The oxide has high stability, which can effectively reduce the interface side reaction, thereby improving the high-temperature stability of the material.

[0102] In some embodiments, the thickness of the second coating layer is 1-100 nm.

[0103] In some embodiments, the crystallinity of the pyrophosphate in the first coating layer is 10% to 100%, optionally 50% to 100%.

[0104] In the first coating layer of the lithium manganese phosphate cathode active material of the present application, the pyrophosphate with a certain degree of crystallinity is conducive to maintaining the structural stability of the first coating layer and reducing lattice defects. On the one hand, this is conducive to fully exerting the role of pyrophosphate in hindering the dissolution of manganese, and on the other hand, it is conducive to reducing the content of surface impurity lithium and the valence state of surface oxygen, thereby reducing the interface side reaction of the cathode material with the electrolyte, reducing the consumption of the electrolyte, and improving the cycle performance and safety performance of the secondary battery.

[0105] In some embodiments, the crystallinity of the pyrophosphate in the first coating layer of the cathode active material can be tested by conventional technical means in the art, for example, by density method, infrared spectroscopy method, differential scanning calorimetry method and nuclear magnetic resonance absorption method, and can also be tested by, for example, X-ray diffraction method.

[0106] The specific method for testing the crystallinity of the pyrophosphate in the first coating layer of the cathode active material by X-ray diffraction method can include the following steps:

[0107] A certain amount of cathode active material powder is taken, and the total scattering intensity is measured by X-ray, which is the sum of the scattering intensities of the entire space matter, and only related to the intensity of the primary ray, the chemical structure of the cathode active material powder, and the total number of electrons participating in diffraction, i.e. the mass, and is not related to the order state of the sample; then the crystalline scattering and the non-crystalline scattering are separated from the diffraction pattern, and the crystallinity is the ratio of the crystalline scattering to the total scattering intensity.

[0108] It should be noted that in some embodiments, the crystallinity of the pyrophosphate in the coating layer can be adjusted by adjusting the process conditions of the sintering process, such as sintering temperature, sintering time, etc.

[0109] In some embodiments, the coating amount of the second coating layer is greater than 0% by weight and less than or equal to 6% by weight, which can be 3-5% by weight, based on the weight of the core.

[0110] The carbon-containing layer as the second coating layer can play a "barrier" function on the one hand, avoiding direct contact between the cathode active material and the electrolyte, thereby reducing the corrosion of the electrolyte on the active material and improving the safety performance of the battery at high temperature. On the other hand, it has strong conductivity, which can reduce the internal resistance of the battery and thus improve the kinetic performance of the secondary battery. When the coating amount of the second coating layer is in the above range, the kinetic performance and safety performance of the secondary battery can be further improved on the premise of maintaining a high specific capacity of the cathode active material.

[0111] In some embodiments, in the positive electrode active material, A is selected from at least one element chosen from Zn, Fe, Ti, V, Ni, Co, and Mg. Optionally, A is selected from at least two elements chosen from Fe, Ti, V, Ni, Co, and Mg. By selecting doping elements within the above range, it is beneficial to enhance the doping effect. On the one hand, it further reduces the lattice change rate, thereby suppressing the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it also helps to further reduce surface oxygen activity, reduce interfacial side reactions between the positive electrode active material and the electrolyte, thereby improving the cycle performance and high-temperature storage performance of the battery.

[0112] In some embodiments, the Li / Mn antisite defect concentration of the positive electrode active material is 5.1% or less, optionally 4% or less, and more preferably 2% or less. In the positive electrode active material of this application, the Li / Mn antisite defect refers to the Li... + and Mn 2+ The positions of Li have been interchanged. + 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 Li / Mn antisite defects can be improved by controlling the concentration of Li / Mn antisite defects at a low level. In this application, the antisite defect concentration can be determined, for example, according to JIS K 0131-1996.

[0113] In some embodiments, the lattice change rate of the positive electrode active material before and after complete lithium insertion / extraction is less than 7.5%, optionally less than 6%, and more preferably less than 4%. The lithium insertion / extraction process of LiMnPO4 is a two-phase reaction. The interfacial stress between the two phases is determined by the magnitude of the lattice change rate; the smaller the lattice change rate, the smaller the interfacial stress. + The easier the transmission, the better. Therefore, reducing the lattice change rate of the core will be beneficial for enhancing Li. + This improves the transmission capacity, thereby enhancing the rate performance of the secondary battery. The lattice change rate can be measured using methods known in the art, such as X-ray diffraction (XRD).

[0114] In some embodiments, the surface oxygen valence state of the positive electrode active material is less than -1.83, optionally less than -1.88, and more optionally between -1.98 and -1.88. The higher the valence state of oxygen in the compound, the stronger the electron-accepting ability, i.e. the stronger the oxidizing property. By controlling the surface valence state of oxygen to a lower level, the reactivity of the surface of the positive electrode material is reduced, the interface side reaction between the positive electrode material and the electrolyte is reduced, and the cycle performance and high-temperature storage performance of the secondary battery are improved. The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

[0115] In some embodiments, the compaction density of the positive electrode active material is 2.0 g / cm3or more at 3 tons (T). 3 In some embodiments, the compaction density of the positive electrode active material is 2.0 g / cm3or more at 3 tons (T). 3 The higher the compaction density of the positive electrode active material, i.e. the greater the weight of active material per unit volume, the more beneficial it is to improve the volumetric energy density of the secondary battery. In the present application, the compaction density can be determined, for example, according to GB / T 24533-2009.

[0116] In some embodiments, the average discharge voltage of the positive electrode active material is 3.5 V or more, and the discharge gram capacity is 135 mAh / g or more; optionally, the average discharge voltage is 3.6 V or more, and the discharge gram capacity is 145 mAh / g or more.

[0117] Although the average discharge voltage of undoped LiMnPO4 is 4.0 V or more, its discharge gram capacity is low, typically less than 130 mAh / g, and thus the energy density is low. By adjusting the lattice change rate through doping, the discharge gram capacity can be greatly improved, and the overall energy density is significantly increased with a slight decrease in the average discharge voltage.

[0118] In some embodiments, x is selected from any value in the range of -0.100 to 0.006, such as -0.01, -0.005, -0.001, 0, 0.001, 0.002, 0.004, 0.005. By selecting the value of x in this range, the generation of Li / Mn anti-site defects, manganese dissolution and lattice change rate can be further reduced, the capacity of the secondary battery is further improved, and the cycle performance, high-temperature storage performance and safety performance of the secondary battery are improved.

[0119] In some embodiments, y is selected from any value in the range of 0.1 to 0.4, such as 0.2, 0.3, 0.4. By selecting the value of y in this range, the generation of Li / Mn anti-site defects, manganese dissolution and lattice change rate can be further reduced, the capacity of the secondary battery is further improved, and the cycle performance, high-temperature storage performance and safety performance of the secondary battery are improved.

[0120] In some embodiments, a is any number in the range of 1-4, for example a is 1, 2, 3, 4.

[0121] In some embodiments, b is any number in the range of 1-2, for example b is 1, 2.

[0122] In some embodiments, c is any number in the range of 1-5, optionally in the range of 1-3, for example c is 1, 2, 3, 4, 5.

[0123] [Method for preparing positive electrode active material]

[0124] The present application provides a method for preparing a positive electrode active material, comprising the following steps:

[0125] The step of providing a core material: the core material comprises Li 1+x Mn 1-y A y P 1-z R z O4, wherein x is any number in the range of -0.100-0.100, y is any number in the range of 0.001-0.500, z is any number in the range of 0.001-0.100, A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, optionally one or more elements selected from Zn, Fe, Ti, V, Ni, Co and Mg, and R is one or more elements selected from B, Si, N and S;

[0126] The step of coating: providing a powder comprising pyrophosphate M a P2O7 and a suspension comprising a carbon source and oxide M' b O c The core material, the powder comprising pyrophosphate M a P2O7 and the suspension comprising a carbon source and oxide M' b O csintering to obtain the positive electrode active material, wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb and Al, optionally one or more elements selected from Li, Fe and Zr, M' is one or more elements selected from alkali metals, alkaline earth metals, transition metals, Group IVA elements, lanthanide series elements and Sb, optionally one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La and Ce, more optionally one or more elements selected from Mg, Al, Si, Zn, Zr and Sn;

[0127] wherein the positive electrode active material has a core-shell structure comprising a core and a shell covering the core, the core comprising Li 1+ x Mn 1-y A y P 1-z R z O4, the shell comprising a first coating layer covering the core and a second coating layer covering the first coating layer, the first coating layer comprising a crystalline pyrophosphate M a P2O7and a crystalline oxide M' b O c , the second coating layer comprising carbon; wherein A, R, M, M', x, y, z, a, b, c are as defined above.

[0128] Thus, the present applicant surprisingly found that by doping specific elements in specific amounts at Mn sites and P sites of the compound LiMnPO4, coating the surface of the compound with a first coating layer containing pyrophosphate and oxide and coating the surface of the first coating layer with a second coating layer containing carbon to obtain a positive electrode active material, the generation of Li / Mn antisite defects can be greatly reduced, manganese elution can be reduced and the lattice change rate can be lowered, the capacity of the secondary battery can be improved, and the cycle performance, high-temperature storage performance and safety performance of the secondary battery can be improved.

[0129] In some embodiments, the step of providing the core material comprises the following steps:

[0130] Step (1): mixing a manganese source, a source of element A and an acid to obtain a mixture;

[0131] Step (2): mixing the mixture with a source of lithium, a source of phosphorus, a source of element R and optionally a solvent, sintering under inert gas protection to obtain a core material containing Li 1+x Mn 1-y A y P 1-z R z O4. The definitions of A and R are as described above.

[0132] In some embodiments, step (1) is carried out at 20-120°C, optionally at 40-120°C (e.g. about 25°C, about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C); and / or, in step (1), the mixing is carried out by stirring at a speed of 500-700 rpm for 60-420 minutes (more optionally 120-360 minutes, e.g. about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours).

[0133] In some embodiments, in step (2), the mixing is carried out at a temperature of 20-120°C, optionally 40-120°C (e.g. about 30°C, about 50°C, about 60°C, about 70°C, about 80°C, about 90°C, about 100°C, about 110°C or about 120°C) for 1-10 hours (e.g. about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours, about 10 hours, about 11 hours or about 12 hours).

[0134] When the temperature and time during the preparation of the core particles are within the above ranges, the lattice defects of the core particles obtained and the positive electrode active material prepared therefrom are less, which is beneficial to inhibit the dissolution of manganese, reduce the interface side reaction of the positive electrode active material with the electrolyte, and thus improve the cycle performance and safety performance of the secondary battery.

[0135] In some embodiments, in step (2), the mixing is carried out at a pH of 3.5-6, optionally at a pH of 4-6, more optionally at a pH of 4-5. It should be noted that the pH can be adjusted by methods commonly used in the art in the present application, for example, by adding an acid or a base.

[0136] In some alternative embodiments, the mixture obtained in step (1) is filtered, dried and ground to obtain manganese salt particles doped with element A with a particle size Dv50 of 50-200 nm, and the manganese salt particles doped with element A are used in step (2) to mix with a source of lithium, a source of phosphorus, a source of element R and optionally a solvent.

[0137] In some embodiments, in step (2), the molar ratio of the mixture or the element A doped manganese salt particles to the lithium source, the phosphorus source is 1:0.5-2.1:0.5-2.1, optionally about 1:1:1.

[0138] In some embodiments, in step (2), the sintering is performed at 600-950℃ for 4-10 hours under an inert gas or a mixture of inert gas and hydrogen; optionally, the protective atmosphere is a mixture of 70-90% by volume of nitrogen and 10-30% by volume of hydrogen; optionally, the sintering is performed at about 650℃, about 700℃, about 750℃, about 800℃, about 850℃ or about 900℃ for about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, about 7 hours, about 8 hours, about 9 hours or about 10 hours; optionally, the sintering temperature and the sintering time can be in any range of any of the above values, which can improve the crystallinity of the inner core, reduce the generation of impurities, and maintain the particle size of the inner core, thereby improving the gravimetric capacity and the tap density of the positive active material and the overall performance of the secondary battery including the rate capability.

[0139] In some alternative embodiments, the mixture after step (2) is dried to obtain a powder, and then the powder is sintered to obtain the inner core material containing Li 1+x Mn 1-y A y P 1-z R z O4.

[0140] In some embodiments, the powder containing pyrophosphate M a P2O7is prepared by the following steps:

[0141] The source of element M, the phosphorus source and the optional solvent are mixed to obtain a mixture, the pH of the mixture is adjusted to 4-6, and the mixture is continuously mixed, and then dried and sintered.

[0142] In some embodiments, in the step of preparing the powder containing pyrophosphate M a P2O7, the drying is performed at 100℃-300℃ for 4-8h, optionally at 150℃-200℃; and / or the sintering is performed at 500℃-800℃ under the protection of inert gas for 4-10h, optionally at 650℃-800℃.

[0143] In some embodiments, the sintering temperature in the coating step is 500-800℃ and the sintering time is 4-10h.

[0144] The source of the material is not particularly limited in the preparation method of the present application, and the source of a certain element can include one or more of the element in its elemental form, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide, provided that the source can achieve the purpose of the preparation method of the present application.

[0145] In some embodiments, the source of element A is selected from one or more of the elemental form, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide of element A; and / or, the source of element R is selected from one or more of the elemental form, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid of element R.

[0146] In some embodiments, the source of element M is selected from one or more of the elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide of element M.

[0147] In some embodiments, the source of element M' is selected from one or more of the elemental form, carbonate, sulfate, halide, nitrate, organic acid salt, oxide, and hydroxide of element M'.

[0148] The amount of each source of elements A, R, M, M' added 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.

[0149] In the present application, the manganese source can be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the manganese source can be selected from one or more of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, and manganese carbonate.

[0150] In the present application, the acid can be selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, silicic acid, and organic acids such as oxalic acid. In some embodiments, the acid is a dilute organic acid with a concentration of 60% by weight or less.

[0151] In the present application, the lithium source can be a lithium-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate.

[0152] In the present application, the phosphorus source can be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. As an example, the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0153] In the present application, as an example, the carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

[0154] [Positive electrode sheet]

[0155] The present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer including the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned preparation method, and the content of the positive electrode active material in the positive electrode film layer being 10% by weight or more based on the total weight of the positive electrode film layer.

[0156] 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. This ensures that the secondary battery has high capacity and good cycle performance, high-temperature storage performance, and safety performance.

[0157] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0158] In some embodiments, the positive electrode film layer can further include other positive electrode active materials for batteries known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphates of olivine structure and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries can also be used. These positive electrode active materials can be used alone or in combination with two or more. Among them, examples of lithium-containing phosphates of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP for short)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0159] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0160] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0161] [Anode electrode sheet]

[0162] The anode electrode sheet includes an anode current collector and an anode film layer disposed on at least one surface of the anode current collector, the anode film layer including an anode active material.

[0163] As an example, the anode current collector has two surfaces opposite in the thickness direction thereof, and the anode film layer is disposed on either one or both of the two surfaces of the anode current collector.

[0164] In some embodiments, the anode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0165] In some embodiments, the anode active material can employ an anode active material for a battery known in the art. As an example, the anode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as an anode active material for a battery can also be used. These anode active materials can be used alone or in combination of two or more.

[0166] In some embodiments, the anode film layer can further optionally include a binder. As an example, the binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0167] In some embodiments, the anode film layer can further optionally include a conductive agent. As an example, the conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0168] In some embodiments, the anode film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0169] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and then drying, cold-pressing, or the like to obtain the negative electrode sheet.

[0170] [Electrolyte]

[0171] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application, and can be selected as needed. For example, the electrolyte can be liquid, gel, or solid.

[0172] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0173] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0174] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0175] In some embodiments, the electrolyte solution can optionally further include an additive. As an example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0176] [Separator]

[0177] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0178] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0179] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0180] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0181] 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0182] 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. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0183] In some implementations, refer to Figure 3 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 can be placed over 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 within 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 selected by those skilled in the art according to specific practical needs.

[0184] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0185] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 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.

[0186] Optionally, the battery module 4 can further include a case having an accommodation space, and the plurality of secondary batteries 5 can be accommodated in the accommodation space.

[0187] In some embodiments, the above-described battery module can be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0188] Figure 5 and Figure 6 is a battery pack 1 as an example. Referring to Figure 5 and Figure 6 In the battery pack 1, a battery box and a plurality of battery modules 4 disposed in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0189] In addition, the present application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0190] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0191] Figure 7 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0192] [Embodiment]

[0193] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the manufacturer of the reagent or instrument is not indicated, it is a conventional product that can be obtained by market purchase. In the embodiments of the present application, the content of each component is calculated by mass without crystallization water if not specifically stated.

[0194] The raw materials used in the preparation examples and examples of the present application are as follows:

[0195]

[0196]

[0197] Example 1-1

[0198] (1) Preparation of a lithium manganese phosphate core co-doped with phosphorus

[0199] Preparation of Fe, Co, and V co-doped manganese oxalate: 689.5 g of manganese carbonate (as MnCO3, same below), 455.2 g of ferrous carbonate (as FeCO3, same below), 4.6 g of cobalt sulfate (as CoSO4, same below), and 4.9 g of vanadium dichloride (as VCl2, same below) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C, and stirred at a rotation speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a suspension of Fe, Co, and V co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain Fe, Co, and V co-doped manganese oxalate dihydrate particles having a median particle size Dv50 of 100 nm.

[0200] Preparation of Fe, Co, V, and S co-doped lithium manganese phosphate: The manganese oxalate dihydrate particles obtained in the previous step (1793.4 g), 369.0 g of lithium carbonate (as Li2CO3, same below), 1.6 g of dilute sulfuric acid having a concentration of 60% (as 60% H2SO4, same below), and 1148.9 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 liters of deionized water, and the mixture was stirred for 10 hours to make it uniform, to obtain a slurry. The slurry was transferred to a spray drying device to perform spray drying granulation, and the drying temperature was set to 250°C, and the drying was performed for 4 hours, to obtain a powder. The above powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%) + hydrogen (10 vol%) protective atmosphere, to obtain 1572.1 g of Fe, Co, V, and S co-doped lithium manganese phosphate.

[0201] (2) Preparation of lithium iron pyrophosphate and a suspension containing aluminum trioxide and sucrose

[0202] Preparation of lithium iron pyrophosphate powder: 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 reaction mixture was allowed to react sufficiently by stirring for 2 hours. Then, the reacted solution was warmed to 80°C and maintained at this 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 for 8 hours in a nitrogen atmosphere, and ground after naturally cooling to room temperature, to obtain a Li2FeP2O7 powder.

[0203] Preparation of a suspension containing aluminum trioxide and sucrose: 47.1 g of nano-Al2O3 (particle size of about 20 nm) and 74.6 g of sucrose (C 12 H 22 O 11 The above mixture was allowed to mix sufficiently by stirring for 6 hours. Then, the resulting solution was warmed to 120°C and maintained at this temperature for 6 hours, to obtain a suspension containing aluminum trioxide and sucrose.

[0204] (3) Coating

[0205] The 1572.1 g of the above Fe, Co, V, and S co-doped lithium manganese phosphate and 15.72 g of the above lithium iron pyrophosphate (Li2FeP2O7) powder were added to the suspension containing aluminum trioxide and sucrose prepared in the above step, and the mixture was stirred until uniform. The resulting product was then dried in a vacuum oven at 150°C for 6 hours. The resulting product was then dispersed by sand milling. After dispersion, the resulting product was sintered at 700°C for 6 hours in a nitrogen atmosphere, to obtain a target product, double-coated lithium manganese phosphate.

[0206] Examples 1-2 to 1-6

[0207] In the preparation of the co-doped lithium manganese phosphate core, the preparation conditions of the lithium manganese phosphate core in Examples 1-2 to 1-6 were the same as in Example 1-1, except that vanadium dichloride and cobalt sulfate were not used, and 463.4 g of ferrous carbonate, 1.6 g of 60% concentrated dilute sulfuric acid, 1148.9 g of ammonium dihydrogen phosphate, and 369.0 g of lithium carbonate were used.

[0208] Further, in the preparation of the lithium iron pyrophosphate and the suspension containing the aluminum trioxide and the sucrose, and in the process of coating the first and second coating layers, the amounts of the raw materials used were adjusted in accordance with the ratios of the coating amounts shown in Table 1 to the coating amounts corresponding to Example 1-1, so that the amounts of Li2FeP2O7 / Al2O3 in Examples 1-2 to 1-6 were 12.6 g / 37.68 g, 15.7 g / 47.1 g, 18.8 g / 56.52 g, 22.0 g / 65.94 g, and 25.1 g / 75.36 g, respectively, and the amount of sucrose in Examples 1-2 to 1-6 was 37.3 g, except that the other conditions were the same as in Example 1-1.

[0209] Examples 1-7 to 1-10

[0210] Examples 1-7 to 1-10

[0211] Examples 1-11 to 1-14

[0212] Examples 1-11 to 1-14

[0213] Example 1-15

[0214] Example 1-15

[0215] Examples 1-16 to 1-18

[0216] Examples 1-16 to 1-18

[0217] Examples 1-19 to 1-20

[0218] The conditions of Examples 1-19 to 1-20 are the same as those of Example 1-18 except that in the preparation of the co-doped lithium manganese phosphate core, Example 1-19 uses 369.4 g of lithium carbonate and 1.05 g of 60% concentration of dilute nitric acid instead of dilute sulfuric acid, and Example 1-20 uses 369.7 g of lithium carbonate and 0.78 g of silicic acid instead of dilute sulfuric acid.

[0219] Examples 1-21 to 1-22

[0220] The conditions of Examples 1-21 to 1-22 are the same as those of Example 1-20 except that in the preparation of the co-doped lithium manganese phosphate core, Example 1-21 uses 632.0 g of manganese carbonate, 463.30 g of ferrous carbonate, 30.5 g of vanadium dichloride, 21.0 g of magnesium carbonate, and 0.78 g of silicic acid, and Example 1-22 uses 746.9 g of manganese carbonate, 289.6 g of ferrous carbonate, 60.9 g of vanadium dichloride, 42.1 g of magnesium carbonate, and 0.78 g of silicic acid.

[0221] Examples 1-23 to 1-24

[0222] The conditions of Examples 1-23 to 1-24 are the same as those of Example 1-22 except that in the preparation of the co-doped lithium manganese phosphate core, Example 1-23 uses 804.6 g of manganese carbonate, 231.7 g of ferrous carbonate, 1156.2 g of ammonium dihydrogen phosphate, 1.2 g of boric acid (mass fraction 99.5%), and 370.8 g of lithium carbonate, and Example 1-24 uses 862.1 g of manganese carbonate, 173.8 g of ferrous carbonate, 1155.1 g of ammonium dihydrogen phosphate, 1.86 g of boric acid (mass fraction 99.5%), and 371.6 g of lithium carbonate.

[0223] Example 1-25

[0224] The conditions of Example 1-25 are the same as those of Example 1-20 except that in the preparation of the co-doped lithium manganese phosphate core, Example 1-25 uses 370.1 g of lithium carbonate, 1.56 g of silicic acid, and 1147.7 g of ammonium dihydrogen phosphate.

[0225] Example 1-26

[0226] The conditions of Examples 1-26 are the same as those of Example 1-20, except that 368.3 g of lithium carbonate, 4.9 g of dilute sulfuric acid with a mass fraction of 60%, 919.6 g of manganese carbonate, 224.8 g of ferrous carbonate, 3.7 g of vanadium dichloride, 2.5 g of magnesium carbonate, and 1146.8 g of ammonium dihydrogen phosphate are used in the preparation of the co-doped lithium manganese phosphate core in Example 1-26.

[0227] Example 1-27

[0228] The conditions of Example 1-27 are the same as those of Example 1-20, except that 367.9 g of lithium carbonate, 6.5 g of dilute sulfuric acid with a concentration of 60%, and 1145.4 g of ammonium dihydrogen phosphate are used in the preparation of the co-doped lithium manganese phosphate core in Example 1-27.

[0229] Examples 1-28 to 1-33

[0230] The conditions of Examples 1-28 to 1-33 are the same as those of Example 1-20, except that 1034.5 g of manganese carbonate, 108.9 g of ferrous carbonate, 3.7 g of vanadium dichloride, and 2.5 g of magnesium carbonate are used in the preparation of the co-doped lithium manganese phosphate core, the amount of lithium carbonate used is 367.6 g, 367.2 g, 366.8 g, 366.4 g, 366.0 g, and 332.4 g, respectively, the amount of ammonium dihydrogen phosphate used is 1144.5 g, 1143.4 g, 1142.2 g, 1141.1 g, 1139.9 g, and 1138.8 g, respectively, the amount of dilute sulfuric acid with a concentration of 60% used is 8.2 g, 9.8 g, 11.4 g, 13.1 g, 14.7 g, and 16.3 g, respectively, in Examples 1-28 to 1-33.

[0231] Examples 1-34 to Example 1-38, Example 1-43

[0232] The raw materials used in the preparation of lithium iron pyrophosphate and the suspension containing the oxide and sucrose, and the processes of coating the first and second coating layers were adjusted according to the ratio of the coating amount shown in Table 1 to the coating amount corresponding to Example 1-1, so that the amount of Li2FeP2O7 / MgO used in Example 1-34 was 15.72 g / 47.1 g, the amount of Li2FeP2O7 / ZrO2 used in Example 1-35 was 15.72 g / 47.1 g, the amount of Li2FeP2O7 / ZnO used in Example 1-36 was 15.72 g / 47.1 g, the amount of Li2FeP2O7 / SnO2 used in Example 1-37 was 15.72 g / 47.1 g, the amount of Li2FeP2O7 / SiO2 used in Example 1-38 was 15.72 g / 47.1 g, and the amount of Li2FeP2O7 / V2O5 used in Example 1-43 was 15.72 g / 47.1 g, and the other conditions were the same as those of Example 1-1.

[0233] Examples 1-39 to 1-41

[0234] 1) In Example 1-39, the preparation of the core Li 1.1 Mn 0.6 Fe 0.393 Mg 0.007 P 0.9 Si 0.1 O4.

[0235] Preparation of Fe and Mg co-doped manganese oxalate: 689.5 g of manganese carbonate (as MnCO3, the same below), 455.2 g of ferrous carbonate (as FeCO3, the same below), and 5.90 g of magnesium carbonate (as MgCO3, the same below) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, the same below) were added. The reaction kettle was heated to 80°C, and stirred at a speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a suspension of Fe and Mg co-doped manganese oxalate. The suspension was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain Fe and Mg co-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0236] Preparation of Fe, Mg and Si co-doped lithium manganese phosphate: The MnMn2(C2O4)2.2H2O particles (1791.3 g) obtained in the previous step, 406.3 g of lithium carbonate (as Li2CO3, same below), 7.8 g of silicic acid (as H2SiO3, same below) and 1035.0 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 L of deionized water, and the mixture was stirred for 10 hours to make it uniform, to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, and the drying temperature was set to 250°C, and dried for 4 hours to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%)+hydrogen (10 vol%) protective atmosphere to obtain 1574.0 g of Fe, Mg and Si co-doped lithium manganese phosphate.

[0237] 2) In Example 1-40, the core is LiMn 0.999 Fe 0.001 P 0.995 N 0.005 O4.

[0238] Preparation of Fe-doped manganese oxalate: 1148.0 g of manganese carbonate (as MnCO3, same below) and 11.58 g of ferrous carbonate (as FeCO3, same below) were thoroughly mixed in a mixer for 6 hours. The mixture was transferred to a reaction kettle, and 5 L of deionized water and 1260.6 g of dihydroxy oxalic acid (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C, and stirred at a speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a Fe-doped manganese oxalate suspension. The suspension was then filtered, and the filter cake was dried at 120°C, followed by grinding, to obtain Fe-doped MnMn2(C2O4)2.2H2O particles with a median particle size Dv50 of 100 nm.

[0239] Preparation of Fe and N co-doped lithium manganese phosphate: The MnMn2(C2O4)2.2H2O particles (1789.9 g) obtained in the previous step, 369.4 g of lithium carbonate (as Li2CO3, same below), 5.25 g of dilute nitric acid (as 60% HNO3, same below) and 1144.3 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 L of deionized water, and the mixture was stirred for 10 hours to make it uniform, to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, and the drying temperature was set to 250°C, and dried for 4 hours to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol%)+hydrogen (10 vol%) protective atmosphere to obtain 1567.7 g of Fe and N co-doped lithium manganese phosphate.

[0240] 3) In Example 1-41, the core is LiMn 0.50 Fe 0.50 P 0.995 N0.005 Preparation of O4.

[0241] Preparation of Fe-doped manganese oxalate: 574.7 g of manganese carbonate (as MnCO3, same below) and 579.27 g of ferrous carbonate (as FeCO3, same below) were thoroughly mixed in a blender for 6 hours. The mixture was transferred to a reaction kettle and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (as C2H2O4.2H2O, same below) were added. The reaction kettle was heated to 80°C and stirred at 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), obtaining a Fe-doped manganese oxalate suspension. The suspension was then filtered and the filter cake was dried at 120°C, followed by grinding, obtaining Fe-doped manganese oxalate dihydrate particles with a median particle size Dv50 of 100 nm.

[0242] Preparation of Fe and N co-doped lithium manganese phosphate: the manganese oxalate dihydrate particles obtained in the previous step (1794.4 g), 369.4 g of lithium carbonate (as Li2CO3, same below), 5.25 g of dilute nitric acid (as 60% HNO3, same below) and 1144.3 g of ammonium dihydrogen phosphate (as NH4H2PO4, same below) were added to 20 liters of deionized water and the mixture was stirred for 10 hours to homogenize it, obtaining a slurry. The slurry was transferred to a spray-drying apparatus and spray-dried granulation was performed, setting the drying temperature at 250°C and drying for 4 hours, obtaining a powder. The above powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, obtaining 1572.2 g of Fe and N co-doped lithium manganese phosphate.

[0243] The other conditions of Examples 1-39 to 1-41 refer to Example 1-1.

[0244] Example 1-42

[0245] In the preparation of zirconium pyrophosphate, 123.2 g of zirconium dioxide (as ZrO2, same below) and 230.6 g of phosphoric acid (as 85% H3PO4, same below) were thoroughly mixed. It was heated to 350°C while continuously stirring for 2 hours to allow the reaction mixture to react fully. The reacted solution was then kept at 350°C for 4 hours, obtaining a viscous paste containing ZrP2O7, which eventually became a solid, and was washed with deionized water. The resulting product was ground in a ball mill with ethanol for 4 h and the resulting product was dried under an infrared lamp, obtaining ZrP2O7 powder.

[0246] Example 1-44

[0247] In the preparation of silver pyrophosphate, 463.4 g of silver oxide (Ag2O, hereinafter the same) and 230.6 g of phosphoric acid (85% H3PO4, hereinafter the same) were mixed well. The reaction mixture was heated to 450°C while being stirred for 2 hours to allow the reaction to proceed sufficiently. Then, the reacted solution was maintained at 450°C for 4 hours to obtain a viscous paste containing Ag4P2O7, which was finally changed into a solid, and washed with deionized water. The obtained product was ground in a ball mill with ethanol for 4 hours, and the obtained product was dried under an infrared lamp to obtain Ag4P2O7 powder.

[0248] Example 1-45

[0249] Except that 1044.6 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 369.4 g of lithium carbonate were used in the preparation of the core, and 105.4 g of ferrous carbonate and 10.5 g of dilute nitric acid (60% HNO3, hereinafter the same) were additionally added, it was the same as in Example 1-1.

[0250] Example 1-46

[0251] Except that 104.5 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 371.3 g of lithium carbonate were used in the preparation of the core, and 1052.8 g of ferrous carbonate and 5.25 g of dilute nitric acid (60% HNO3, hereinafter the same) were additionally added, it was the same as in Example 1-1.

[0252] Example 1-47

[0253] Except that the amounts of the various raw materials were adjusted to correspond to the coating amounts shown in Table 1 so that the amounts of Li2FeP2O7 / Al2O3 were 62.9 g / 47.1 g, respectively, in the preparation of lithium iron pyrophosphate and the suspension containing aluminum trioxide and sucrose, the other conditions of Example 1-47 were the same as in Example 1-1.

[0254] Example 1-48

[0255] Except that the amount of sucrose was 111.9 g so that the corresponding coating amount of the carbon layer as the second coating layer was 47.1 g, the remaining operations were the same as in Example 1-1.

[0256] Example 1-49

[0257] Except that 1034.3 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 371.3 g of lithium carbonate were used in the preparation of the core, and 115.8 g of ferrous carbonate and 5.25 g of dilute nitric acid (60% HNO3, hereinafter the same) were additionally added, it was the same as in Example 1-1.

[0258] Example 1-50

[0259] Except for using 1091.8 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 371.3 g of lithium carbonate in the preparation of the core, and additionally adding 57.9 g of ferrous carbonate, 5.25 g of dilute nitric acid (60% HNO3, same below), other conditions are the same as Example 1-1.

[0260] Example 1-51

[0261] Except for using 804.5 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 371.3 g of lithium carbonate in the preparation of the core, and additionally adding 347.4 g of ferrous carbonate, 5.25 g of dilute nitric acid (60% HNO3, same below), the amount of sucrose is 111.9 g, and the corresponding carbon coating amount is 47.1 g, other conditions are the same as Example 1-1.

[0262] Example 1-52

[0263] Except for using 747.0 g of manganese carbonate, 1138.5 g of ammonium dihydrogen phosphate, and 371.3 g of lithium carbonate, and additionally adding 405.3 g of ferrous carbonate, 5.25 g of dilute nitric acid (60% HNO3, same below), the amount of sucrose is 111.9 g, and the corresponding carbon coating amount is 47.1 g, other conditions are the same as Example 1-1.

[0264] Example 2-1

[0265] Except for controlling the crystallinity of Li2FeP2O7 to be 30% by setting the sintering temperature to 550°C and the sintering time to 1 h in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP2O7), and controlling the crystallinity of Al2O3 to be 100% by setting the sintering temperature to 650°C and the sintering time to 2 h in the coating sintering step in the preparation of Al2O3, other conditions are the same as Example 1-1.

[0266] Example 2-2

[0267] Except for controlling the crystallinity of Li2FeP2O7 to be 50% by setting the sintering temperature to 550°C and the sintering time to 2 h in the powder sintering step in the preparation of lithium iron pyrophosphate (Li2FeP2O7), and controlling the crystallinity of Al2O3 to be 100% by setting the sintering temperature to 650°C and the sintering time to 3 h in the coating sintering step in the preparation of Al2O3, other conditions are the same as Example 1-1.

[0268] Example 2-3

[0269] ​​​​​​​​​​​​​​​​​​​​​Example 1-1

[0270] Example 2-4

[0271] Example 1-1

[0272] Examples 3-1 to 3-12

[0273] Examples 3-1 to 3-12

[0274] Examples 4-1 to 4-4:

[0275] Example 1-7 except that the drying temperature / drying time in the drying step in the coating process was 150°C / 6h, 150°C / 6h, 150°C / 6h, 150°C / 6h, 150°C / 6h, 150°C / 6h, and 150°C / 6h, respectively; and the sintering temperature and sintering time in the sintering step in the coating process was 600°C / 4h, 600°C / 6h, 600°C / 6h, 600°C / 6h, 600°C / 6h, 600°C / 6h, and 800°C / 8h, respectively.

[0276] Examples 4-5 to 4-7:

[0277] Example 1-12 except that the drying temperature / drying time in the drying step in the coating process was 150°C / 6h, 150°C / 6h, and 150°C / 6h, respectively; and the sintering temperature and sintering time in the sintering step in the coating process was 600°C / 4h, 600°C / 6h, and 800°C / 8h, respectively.

[0278] Comparative Example 1

[0279] Preparation of manganese oxalate: 1149.3 g of manganese carbonate was added to a reaction kettle, and 5 liters of deionized water and 1260.6 g of oxalic acid dihydrate (C2H2O4·2H2O) were added. The reaction kettle was heated to 80°C, and stirred at a rotation speed of 600 rpm for 6 hours until the reaction was terminated (no gas bubbles were generated), to obtain a manganese oxalate suspension, which was then filtered. The filter cake was dried at 120°C, and then ground, to obtain manganese oxalate dihydrate particles having a median particle size Dv50 of 100 nm.

[0280] Preparation of carbon-coated lithium manganese phosphate: 1789.6 g of the above-obtained manganese oxalate dihydrate particles, 369.4 g of lithium carbonate (Li2CO3), 1150.1 g of ammonium dihydrogen phosphate (NH4H2PO4), and 31 g of sucrose (C12H22O11) were added to 20 liters of deionized water, and the mixture was stirred for 10 hours to obtain a slurry. The slurry was transferred to a spray drying device for spray drying granulation, and the drying temperature was set to 250°C, and the drying was performed for 4 hours, to obtain a powder. The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, to obtain carbon-coated lithium manganese phosphate. 12 H 22 O 11 The powder was sintered at 700°C for 4 hours in a nitrogen (90 vol.%) + hydrogen (10 vol.%) protective atmosphere, to obtain carbon-coated lithium manganese phosphate.

[0281] Comparative Example 2

[0282] Example 1-12 except that 689.5 g of manganese carbonate was used, and 463.3 g of ferrous carbonate was additionally added.

[0283] Comparative Example 3

[0284] Example 1 was repeated except that 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate were used, and 1.6 g of dilute sulfuric acid having a concentration of 60% was additionally added.

[0285] Comparative Example 4

[0286] Example 1 was repeated except that 689.5 g of manganese carbonate, 1148.9 g of ammonium dihydrogen phosphate and 369.0 g of lithium carbonate were used, and 463.3 g of ferrous carbonate and 1.6 g of dilute sulfuric acid having a concentration of 60% were additionally added.

[0287] Comparative Example 5

[0288] Example 4 was repeated except that the following step was additionally added: when preparing the lithium iron pyrophosphate powder, 9.52 g of lithium carbonate, 29.9 g of ferrous carbonate, 29.6 g of ammonium dihydrogen phosphate and 32.5 g of oxalic acid dihydrate were dissolved in 50 ml of deionized water. The pH of the mixture was 5, and the reaction mixture was allowed to react for 2 hours with stirring. Then, the reacted solution was warmed to 80°C and maintained at this 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 for 4 hours in a nitrogen atmosphere, and ground after naturally cooling to room temperature, to control the crystallinity of Li2FeP2O7 to be 5%. Except that the amount of Li2FeP2O7 used was 62.8 g when preparing the carbon-coated material, Example 5 was the same as Comparative Example 4.

[0289] Comparative Example 6

[0290] Example 4 was repeated except that the following step was additionally added: 62.92 g of nano-Al2O3 (having a particle size of about 20 nm) and 37.4 g of sucrose (C 12 H 22 O 11 12O3) were dissolved in 1500 ml of deionized water, and then the mixture was allowed to react for 6 hours with stirring. Then, the reacted solution was warmed to 120°C and maintained at this temperature for 6 hours, to obtain a suspension containing aluminum trioxide and sucrose. Except that the other conditions were the same as those of Comparative Example 4, Comparative Example 6 was the same as Example 4.

[0291] Comparative Example 7

[0292] Preparation of amorphous lithium iron pyrophosphate powder: 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 reaction mixture was allowed to react fully by stirring for 2 hours. The reacted solution was then warmed to 80°C and maintained at this 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 natural cooling to room temperature, it was ground to control the crystallinity of Li2FeP2O7 to 5%.

[0293] Preparation of a suspension containing aluminum trioxide and sucrose: 47.19 g of nano-Al2O3 (particle size of about 20 nm) and 37.4 g of sucrose (C 12 H 22 O 11 The reacted solution was then warmed to 120°C and maintained at this temperature for 6 hours to obtain a suspension containing aluminum trioxide and sucrose.

[0294] To the above suspension, 1573.0 g of the core and 15.73 g of lithium iron pyrophosphate powder were added, and the sintering temperature in the coating and sintering step during the preparation process was 600°C, and the sintering time was 4 hours to control the crystallinity of LiFePO4 to 8% or less, and the other conditions were the same as those of Comparative Example 4 to obtain an amorphous lithium iron pyrophosphate, amorphous aluminum oxide, and carbon-coated positive electrode active material.

[0295] Comparative Examples 8 to 11

[0296] In the preparation of lithium iron pyrophosphate (Li2FeP2O7), the drying temperature / drying time in the drying step were 80°C / 3h, 80°C / 3h, 80°C / 3h, and 80°C / 3h, respectively, in Comparative Examples 8 to 10, and the sintering temperature and sintering time in the sintering step during the coating process were 400°C / 3h, 400°C / 3h, and 350°C / 2h, respectively, in Comparative Examples 8 to 10, and the drying temperature / drying time in the drying step during the coating process was 80°C / 3h in Comparative Example 11, and the weight ratio of Li2FeP2O7 / Al2O3 was 1:3 and 1:1, respectively, in Comparative Examples 8 and 9, and only Li2FeP2O7 was used in Comparative Example 10, and only Al2O3 was used in Comparative Example 11, and the other conditions were the same as those of Examples 1 to 7.

[0297] Preparation of positive electrode tab

[0298] The double-coated lithium manganese phosphate cathode active material prepared above, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are added to N-methyl pyrrolidone (NMP) in a weight ratio of 92:2.5:5.5, stirred and mixed uniformly to obtain a cathode slurry. Then the cathode slurry is coated uniformly on an aluminum foil, dried, cold-pressed, and cut to obtain a cathode electrode sheet. 2 The double-coated lithium manganese phosphate cathode active material prepared above, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are added to N-methyl pyrrolidone (NMP) in a weight ratio of 92:2.5:5.5, stirred and mixed uniformly to obtain a cathode slurry. Then the cathode slurry is coated uniformly on an aluminum foil, dried, cold-pressed, and cut to obtain a cathode electrode sheet.

[0299] Preparation of negative electrode tab

[0300] The negative electrode active material artificial graphite, conductive agent Super-P, binder styrene-butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water in a mass ratio of 95%:1.5%:1.8%:1.7%, stirred and mixed uniformly to obtain a negative electrode slurry with a viscosity of 3000 mPa.s and a solid content of 52%; the negative electrode slurry is coated on a 6 μm negative electrode current collector copper foil, then baked at 100°C for 4 hours to dry, and rolled to obtain a negative electrode electrode sheet with a compacted density of 1.75 g / cm 3 .

[0301] Separator film

[0302] A polypropylene film is used.

[0303] Preparation of electrolyte

[0304] Ethylene carbonate, dimethyl carbonate, and 1,2-propylene carbonate are mixed in a volume ratio of 1:1:1, and then LiPF6 is uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 is 1 mol / L.

[0305] Preparation of full cell

[0306] The above-obtained positive electrode electrode sheet, separator, and negative electrode electrode sheet are stacked in order with the separator between the positive and negative electrodes to play a separating role, and are wound to obtain a bare battery cell. The bare battery cell is placed in an outer package, the above electrolyte is injected and packaged to obtain a full battery (hereinafter also referred to as "full").

[0307] Preparation of button cell

[0308] The above-prepared positive electrode active material, PVDF, and acetylene black are added to NMP in a weight ratio of 90:5:5, stirred in a dry room to prepare a slurry. The above slurry is coated on an aluminum foil, dried, cold-pressed to obtain a positive electrode electrode sheet. The coating amount is 0.2 g / cm 2 , and the compacted density is 2.0 g / cm 3 .

[0309] The 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) with a volume ratio of 1:1:1 is used as the electrolyte. The positive electrode sheet prepared above is assembled into a button cell (hereinafter also referred to as "button") in a button cell box.

[0310] Property test of positive active material

[0311] 1. Determination of the core chemical formula and the composition of different coating layers:

[0312] The interior microstructure and surface structure of the positive electrode active material are characterized by a spherical aberration scanning electron microscope (ACSTEM) at high spatial resolution, and the core chemical formula and the composition of the first and second coating layers of the positive electrode active material are obtained by three-dimensional reconstruction technology.

[0313] 2. Initial gram capacity test of button cell:

[0314] The button cell prepared above is charged at 0.1C to 4.3V under 2.5-4.3V, then charged at 4.3V to a current less than or equal to 0.05mA, and left for 5min, then discharged at 0.1C to 2.0V. The discharge capacity at this time is the initial gram capacity, denoted as D0.

[0315] 3. Average discharge voltage (V) test of button:

[0316] The button cell prepared above is left for 5min at 25℃ constant temperature environment, discharged at 0.1C to 2.5V, left for 5min, charged at 0.1C to 4.3V, then charged at 4.3V to a current less than or equal to 0.05mA, left for 5min, then discharged at 0.1C to 2.5V. The discharge capacity at this time is the initial gram capacity, denoted as D0, the discharge energy is the initial energy, denoted as E0, and the average discharge voltage V of the button is E0 / D0.

[0317] 4. Full cell 60℃ gas expansion test:

[0318] The full cell prepared above in 100% charged state (SOC) is stored at 60℃. The open circuit voltage (OCV) and the impedance (IMP) of the cell are measured before and after storage to monitor the SOC, and the volume of the cell is measured. After every 48h of storage, the full cell is taken out, left for 1h, and then the open circuit voltage (OCV) and the impedance (IMP) are tested, and the volume of the cell is measured by the drainage method after cooling to room temperature. The drainage method is to first measure the gravity F1 of the cell by a balance alone with a dial data automatic unit conversion, then completely place the cell in deionized water (the density is known to be 1g / cm 3), the gravity F2 of the battery cell at this time is measured, and the buoyancy F 浮 , i.e. F1-F2, and then according to the Archimedes principle F 浮 = p x g x V 排 , the volume V of the battery cell is calculated as (F1-F2) / (p x g).

[0319] From the OCV and IMP test results, the batteries of all examples maintained a SOC of more than 99% throughout the experiment until the end of storage.

[0320] After 30 days of storage, the volume of the battery cell was measured, and the percentage increase in the volume of the battery cell after storage relative to the volume of the battery cell before storage was calculated.

[0321] In addition, the residual capacity of the battery cell was measured. The full battery was charged to 4.3V at 1C under 2.5-4.3V, and then charged to a current less than or equal to 0.05mA at 4.3V. After 5 minutes of standing, the charge capacity at this time was recorded as the residual capacity of the battery cell.

[0322] 5. Full battery cycle performance test at 45°C:

[0323] In a constant temperature environment of 45°C, the full battery prepared above was charged to 4.3V at 1C under 2.5-4.3V, and then charged to a current less than or equal to 0.05mA at 4.3V. After 5 minutes of standing, it was discharged to 2.5V at 1C, and the discharge capacity at this time was recorded as D0. The aforementioned charge and discharge cycle was repeated until the discharge capacity was reduced to 80% of D0. The number of cycles the battery had undergone was recorded.

[0324] 6. Lattice change rate test:

[0325] In a constant temperature environment of 25°C, the positive active material sample prepared above was placed in an XRD (model: Bruker D8 Discover), and the sample was tested at 1° / min. The test data were analyzed and arranged, and the lattice constants a0, b0, c0 and v0 (a0, b0 and c0 represent the length of each aspect of the unit cell, and v0 represents the volume of the unit cell, which can be directly obtained through XRD refinement results) at this time were calculated by referring to the standard PDF card.

[0326] The positive active material sample was prepared into a coin cell using the above coin cell preparation method, and the coin cell was charged at a small rate of 0.05C until the current decreased to 0.01C. Then the positive electrode sheet in the coin cell was taken out and soaked in dimethyl carbonate (DMC) for 8 hours. Then it was dried, scraped and sieved to obtain particles with a particle size less than 500 nm. The sample was taken and the unit cell volume v1 was calculated in the same way as the fresh sample above. The lattice change rate (unit cell volume change rate) before and after the complete deintercalation of lithium was calculated as (v0-v1) / v0x100% and shown in the table.

[0327] 7. Li / Mn anti-site defect concentration test:

[0328] The XRD results tested in the "lattice change rate measurement method" were compared with the standard crystal PDF (Powder Diffraction File) card to obtain the Li / Mn anti-site defect concentration. Specifically, the XRD results tested in the "lattice change rate measurement method" were imported into the general structure analysis system (GSAS) software to automatically obtain the refinement results, which included the occupancy of different atoms. The Li / Mn anti-site defect concentration was obtained by reading the refinement results.

[0329] 8. Transition metal elution test:

[0330] The full cell cycled at 45°C to a capacity attenuation of 80% was discharged at a rate of 0.1C to a cut-off voltage of 2.0V. Then the battery was disassembled and the negative electrode sheet was taken out. 30 circular pieces of unit area (1540.25mm 2 ) were randomly taken on the negative electrode sheet, and the inductively coupled plasma emission spectrum (ICP) was tested by Agilent ICP-OES730. According to the ICP results, the amount of Fe (if the Mn site of the positive active material is doped with Fe) and Mn was calculated, and the elution amount of Mn (and Fe doped in the Mn site) after cycling was calculated. The test standard is based on EPA-6010D-2014.

[0331] 9. Surface oxygen valence state test:

[0332] 5 g of the positive electrode active material sample prepared above was prepared into a button cell according to the button cell preparation method described above. The button cell was charged at a small rate of 0.05 C until the current decreased to 0.01 C. Then the positive electrode plate in the button cell was taken out and soaked in dimethyl carbonate (DMC) for 8 hours. Then it was dried, scraped and sieved to obtain particles with a particle size less than 500 nm. The obtained particles were measured by electron energy loss spectroscopy (EELS, the instrument used was Talos F200S) to obtain energy loss near-edge structure (ELNES), which reflects the state density and energy level distribution of elements. According to the state density and energy level distribution, the number of occupied electrons was calculated by integrating the valence band state density data, so as to calculate the valence state of surface oxygen after charging.

[0333] 10. Compacted density measurement:

[0334] 5 g of the positive electrode active material powder prepared above was placed in a compaction special mold (CARVER mold, model 13 mm), and then the mold was placed on a compaction density instrument. A pressure of 3 T was applied, and the thickness of the powder under pressure was read on the device (the thickness after unloading, the area of the container for testing was 1540.25 mm 2 ). The compacted density was calculated by p = m / v.

[0335] 11. X-ray diffraction method for testing crystallinity of pyrophosphate and phosphate

[0336] 5 g of the positive electrode active material powder prepared above was measured by X-ray to obtain the total scattering intensity, which is the sum of the scattering intensity of the entire space matter, only related to the intensity of the primary ray, the chemical structure, the total number of electrons participating in diffraction, and the mass, and has nothing to do with the order state of the sample; then the crystalline scattering and the non-crystalline scattering were separated from the diffraction pattern, and the crystallinity was the ratio of the crystalline scattering to the total scattering intensity.

[0337] 12. Crystal plane spacing and angle

[0338] 1 g of each of the positive electrode active material powders prepared above was taken in a 50 mL test tube, 10 mL of alcohol with a mass fraction of 75% was injected into the test tube, and then it was fully stirred and dispersed for 30 minutes, then an appropriate amount of the above solution was taken with a clean disposable plastic pipette and dropped on a 300 mesh copper mesh, at this time, part of the powder will be left on the copper mesh, the copper mesh with the sample was transferred to the TEM (Talos F200s G2) sample chamber for testing, and the TEM test original picture was obtained, and the original picture format (xx.dm3) was saved.

[0339] The original picture obtained by the TEM test is opened in Digital Micrograph software, and a diffraction pattern is obtained by Fourier transform (automatically completed by the software after clicking operation). The distance from the diffraction spot in the diffraction pattern to the center position is measured, and the interplanar spacing is obtained. The included angle is calculated according to the Bragg equation.

[0340] 13. Coating thickness test:

[0341] The thickness of the coating is mainly tested by FIB to cut a thin slice of about 100 nm thickness from the middle of the single particle of the positive active material prepared above, and then the thin slice is subjected to TEM test to obtain a TEM test original picture, and the original picture format (xx.dm3) is saved.

[0342] The original picture obtained by the TEM test is opened in Digital Micrograph software, and a diffraction pattern is obtained by Fourier transform (automatically completed by the software after clicking operation). The distance from the diffraction spot in the diffraction pattern to the center position is measured, and the interplanar spacing is obtained. The included angle is calculated according to the Bragg equation.

[0343] The thickness of the coating is mainly tested by FIB to cut a thin slice of about 100 nm thickness from the middle of the single particle of the positive active material prepared above, and then the thin slice is subjected to TEM test to obtain a TEM test original picture, and the original picture format (xx.dm3) is saved.

[0344] The above results are shown in Tables 1-4.

[0345]

[0346]

[0347]

[0348] It can be seen from Examples 1-1 to 1-52 and Comparative Example 1-4 that the presence of the first coating layer is beneficial to reduce the Li / Mn antisite defect concentration and the Fe and Mn elution amount of the obtained material after cycling, improve the discharge capacity and the tap density of the battery, and improve the safety performance and the cycle performance of the battery. When other elements are doped at the Mn site and the phosphorus site respectively, the lattice change rate, the antisite defect concentration and the Fe and Mn elution amount of the obtained material can be significantly reduced, the capacity and the tap density of the battery are improved, and the safety performance and the cycle performance of the battery are improved.

[0349] It can be seen from Examples 1-2 to 1-6 that as the amount of the first coating layer increases from 3.2% to 6.4%, the Li / Mn antisite defect concentration of the obtained material gradually decreases, the Fe and Mn elution amount after cycling gradually decreases, and the safety performance and the cycle performance of the corresponding battery at 45°C are also improved, but the discharge capacity slightly decreases. Alternatively, when the total amount of the first coating layer is 4-5.6% by weight, the comprehensive performance of the corresponding battery is best.

[0350] From Examples 1-3 and 1-7 to 1-10, it can be seen that as the amount of the second coating layer increases from 1% to 6%, the Fe and Mn elution amounts of the resulting material gradually decrease after cycling, the safety performance and the cycling performance at 45°C of the corresponding battery are also improved, but the discharge capacity slightly decreases. Alternatively, when the total amount of the second coating layer is 3-5 wt%, the comprehensive performance of the corresponding battery is optimal.

[0351] From Examples 1-11 to 1-15 and Comparative Examples 5-6, it can be seen that when Li2FeP2O7 and Al2O3 are both present in the first coating layer, and particularly when the weight ratio of Li2FeP2O7 and Al2O3 is 1:3 to 3:1, and especially 1:3 to 1:1, the improvement in battery performance is more obvious.

[0352]

[0353]

[0354]

[0355]

[0356] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other modes constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material having a core-shell structure, comprising an inner core and a shell covering the inner core, The inner core comprises Li 1+x Mn 1-y A y P 1-z R z O4, wherein, the x is any value in the range of -0.100 to 0.100, the y is any value in the range of 0.001 to 0.500, the z is any value in the range of 0.001 to 0.100, the A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and the R is one or more elements selected from B, Si, N and S; the shell comprises a first coating layer covering the inner core and a second coating layer covering the first coating layer; wherein the first coating layer comprises a crystalline pyrophosphate M a P2O7and a crystalline oxide M' b O c wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and M' is one or more elements selected from Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La, and Ce. the second coating layer contains carbon.

2. The positive electrode active material according to claim 1, wherein the A is one or more elements selected from Zn, Fe, Ti, V, Ni, Co and Mg.

3. The positive electrode active material according to claim 1, wherein the M is one or more elements selected from Li, Fe and Zr.

4. The positive electrode active material according to claim 1, wherein the M' is one or more elements selected from Mg, Al, Si, Zn, Zr and Sn.

5. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of y to 1-y is 1:10 to 10:

1.

6. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of y to 1-y is 1:4 to 1:

1.

7. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of z to 1-z is 1:9 to 1:

999.

8. The positive electrode active material according to claim 1, wherein in the inner core, the ratio of z to 1-z is 1:499 to 1:

249.

9. 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 inner core.

10. The positive electrode active material according to claim 1, wherein the coating amount of the first coating layer is 4 to 5.6% by weight based on the weight of the inner core.

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

1.

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

1.

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

14. The positive electrode active material according to claim 1, wherein the interplanar spacing of pyrophosphate in the first coating layer is 0.300 to 0.310 nm; and / or the included angle of crystal orientation (111) of pyrophosphate in the first coating layer is 29.00° to 30.00°.

15. The positive electrode active material according to claim 1, wherein the crystallinity of pyrophosphate in the first coating layer is 10% to 100%.

16. The positive electrode active material according to claim 1, wherein the crystallinity of pyrophosphate in the first coating layer is 50% to 100%.

17. The positive electrode active material according to claim 1, wherein The second coating layer has a coating amount of greater than 0% by weight and less than or equal to 6% by weight based on the weight of the core.

18. The positive electrode active material according to claim 1, wherein, The second coating layer has a coating amount of 3-5% by weight based on the weight of the core.

19. The positive electrode active material according to claim 1, wherein, The A is at least two elements selected from the group consisting of Fe, Ti, V, Ni, Co and Mg.

20. The positive electrode active material according to claim 1, wherein, The Li / Mn antisite defect concentration of the positive electrode active material is 5.1% or less.

21. The positive electrode active material according to claim 1, wherein, The Li / Mn antisite defect concentration of the positive electrode active material is 4% or less.

22. The positive electrode active material according to claim 1, wherein, The Li / Mn antisite defect concentration of the positive electrode active material is 2% or less.

23. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 7.5% or less.

24. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 6% or less.

25. The positive electrode active material according to claim 1, wherein, The lattice change rate of the positive electrode active material before and after complete deintercalation of lithium is 4% or less.

26. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.83 or less.

27. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.88 or less.

28. The positive electrode active material according to claim 1, wherein, The surface oxygen valence state of the positive electrode active material is -1.98 to -1.

88.

29. The positive electrode active material according to any one of claims 1-28, wherein, The positive electrode active material has a compaction density of 2.0 g / cm 3 The above.

30. The positive electrode active material according to any one of claims 1-28, wherein, The positive electrode active material has a compaction density of 2.2 g / cm 3 The above.

31. A method for producing a positive electrode active material, comprising the steps of: The step of providing a core material comprising Li 1+x Mn 1-y A y P 1-z R z O4, wherein the x is any value in the range of -0.100 to 0.100, the y is any value in the range of 0.001 to 0.500, the z is any value in the range of 0.001 to 0.100, the A is one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and the R is one or more elements selected from B, Si, N, and S. Coating step: providing a powder comprising pyrophosphate M a P2O7, and a suspension comprising a carbon source and an oxide M' b O c Mixing the core material, the powder comprising pyrophosphate M a P2O7, and the suspension comprising a carbon source and an oxide M' b O c sintering, to obtain a positive electrode active material, wherein a is greater than 0 and less than or equal to 4, b is greater than 0 and less than or equal to 2, c is greater than 0 and less than or equal to 5, M is one or more elements selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al, and M' is one or more elements selected from the group consisting of Li, Be, B, Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, W, La, and Ce. wherein the positive electrode active material has a core-shell structure comprising an inner core and a shell coating the inner core, the inner core comprising Li 1+x Mn 1-y A y P 1-z R z O4, the shell comprising a first coating layer coating the inner core and a second coating layer coating the first coating layer, the first coating layer comprising a crystalline pyrophosphate M a P2O7and a crystalline oxide M' b O c and the second coating layer comprising carbon.

32. The method of manufacturing according to claim 31, wherein, The A is one or more elements selected from the group consisting of Zn, Fe, Ti, V, Ni, Co and Mg.

33. The method of manufacturing according to claim 31, wherein, The M is one or more elements selected from the group consisting of Li, Fe and Zr.

34. The method of manufacturing according to claim 31, wherein, The M' is one or more elements selected from the group consisting of Mg, Al, Si, Zn, Zr and Sn.

35. The production method according to claim 31, wherein the step of providing a core material comprises the steps of: Step (1): mixing a manganese source, a source of element A and an acid to obtain a mixture; Step (2): mixing the mixture with a source of lithium, a source of phosphorus and a source of element R or mixing the mixture with a source of lithium, a source of phosphorus, a source of element R and a solvent, and sintering under inert gas protection to obtain a core material containing Li 1+x Mn 1-y A y P 1-z R z O4.

36. The method of manufacturing according to claim 35, wherein, The step (1) is performed at 20°C-120°C; and / or, in the step (1), the mixing is performed by stirring at 500-700 rpm for 60-420 minutes.

37. The method of manufacturing according to claim 35, wherein, The step (1) is performed at 25°C-80°C.

38. The method of manufacturing according to claim 35, wherein, The source of element A is selected from one or more of the group consisting of an elemental substance of element A, a sulfate, a halide, a nitrate, an organic acid salt, an oxide and a hydroxide; and / or, The source of the element R is selected from one or more of the group consisting of the element R in its elemental form, sulfate, halide, nitrate, organic acid salt, oxide, hydroxide, and inorganic acid.

39. The preparation method of claim 31, wherein, The powder comprising pyrophosphate M a The powder comprising P2O7 is prepared by the following steps: The source of the element M is mixed with the source of phosphorus or the source of the element M, the source of phosphorus and the solvent are mixed to obtain a mixture, the pH of the mixture is adjusted to 4-6, and the mixture is continuously mixed, and then dried and sintered.

40. The method of manufacturing according to claim 39, wherein, The drying is at 100-300°C for 4-8h; and / or, the sintering is at 500-800°C under inert gas protection for 4-10h.

41. The method of manufacturing according to claim 40, wherein, The drying is at 150-200°C; and / or, the sintering is at 650-800°C.

42. The preparation method of claim 31, wherein, The sintering temperature in the coating step is 500-800°C, and the sintering time is 4-10h.

43. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising the positive electrode active material of any one of claims 1-30 or the positive electrode active material prepared by the preparation method of any one of claims 31-42.

44. The cathode sheet of Claim 43, wherein, 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.

45. The cathode sheet of Claim 43, wherein, 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.

46. A secondary battery comprising the positive electrode active material of any one of claims 1-30 or the positive electrode active material prepared by the preparation method of any one of claims 31-42 or the positive electrode sheet of any one of claims 43-45.

47. A battery module comprising: The secondary battery of claim 46 is included.

48. A battery pack, characterized by The battery module of claim 47 is included.

49. An electrical device, comprising: At least one of the secondary battery of claim 46, the battery module of claim 47, and the battery pack of claim 48 is included.

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