WO2024065213A1

WO2024065213A1 - Positive electrode active material, preparation method therefor, and positive electrode sheet, secondary battery and electric apparatus comprising same

Info

Publication number: WO2024065213A1
Application number: PCT/CN2022/121868
Authority: WO
Inventors: 袁天赐; 蒋耀; 张欣欣; 欧阳楚英; 吴凌靖; 康伟斌; 陈尚栋
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-09-27
Filing date: 2022-09-27
Publication date: 2024-04-04

Abstract

Provided in the present application are: a positive electrode active material, a preparation method therefor, and a positive electrode sheet, a secondary battery and an electric apparatus comprising same. The positive electrode active material comprises an inner core and a shell coating the inner core. The inner core comprises LimAxMn1- yByP1-zCzO4-nDn, and the shell comprises borate XaBbOc and carbon. The shell comprises one or more coating layers, each of the coating layers independently comprising one or more of the borate XaBbOc and carbon. The positive electrode active material provided by the present application enables secondary batteries to have relatively high energy density, and meanwhile can improve the rate performance, the cycle performance and/or the high-temperature stability of secondary batteries.

Description

Positive electrode active material, preparation method thereof, positive electrode sheet, secondary battery and electric device containing the same

Technical Field

The present application belongs to the field of battery technology, and specifically relates to a positive electrode active material, a preparation method thereof, a positive electrode plate containing the same, a secondary battery, and an electrical device.

Background technique

In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the application and promotion of secondary batteries, their safety performance has received more and more attention. Lithium manganese phosphate has become one of the most popular positive electrode active materials due to its advantages such as high capacity, good safety performance and abundant raw material sources. However, lithium manganese phosphate is prone to manganese ion dissolution during charging, resulting in rapid capacity decay.

Summary of the invention

The purpose of the present application is to provide a positive electrode active material, a preparation method thereof, a positive electrode plate, a secondary battery and an electrical device containing the same, wherein the positive electrode active material can enable the secondary battery to have a higher energy density while also improving the rate performance, cycle performance and/or high temperature stability of the secondary battery.

In a first aspect _, the present application provides a positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, wherein the core comprises _LimAxMn1 _- _yByP1 _- _zCzO4 _-nDn _, the A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises one or more elements selected from Group B (boron), S, Si and N. one or more elements, the D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, the m is selected from the range of 0.9 to 1.1, optionally selected from the range of 0.97 to 1.01, the x is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, the y is selected from the range of 0.001 to 0.5, optionally selected from the range of 0.25 to 0.5, the z is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005, the n is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, and the core is electrically neutral; the shell comprises a borate X _a B _b O _c and carbon, and the shell includes one or more coating layers, each coating layer independently includes one or more of borate X _a B _b O _c and carbon, wherein X includes one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, and optionally includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al, wherein a is selected from the range of 1 to 4, b is selected from the range of 1 to 7, c is selected from the range of 2 to 12, and the values of a, b and c satisfy the following condition: the borate X _a B _b O _c is kept electrically neutral.

The present invention can effectively reduce the dissolution of Mn and Mn-doped elements and promote the migration of lithium ions by doping and surface coating the compound LiMnPO ₄ with specific elements. Therefore, the positive electrode sheet and electrical devices such as secondary batteries using the positive electrode active material of the present invention can have a higher energy density, while also having improved rate performance, cycle performance and/or high temperature stability.

Furthermore, by doping specific elements in specific amounts at the Li position, Mn position, P position and O position of the compound _LiMnPO4 at the same time, improved rate performance can be obtained, and the dissolution of Mn and the doping elements at the Mn position can be further reduced, thereby obtaining improved cycle performance and/or high temperature stability, and the gram capacity and compaction density of the positive electrode active material can also be improved.

In any embodiment of the present application, the A, C and D are each independently any one element within the above respective ranges, and the B is at least two elements within the ranges.

Optionally, A is any one element selected from Mg and Nb.

Optionally, B is at least two elements selected from Fe, Ti, V, Co and Mg, and more optionally, it is Fe and one or more elements selected from Ti, V, Co and Mg.

Optionally, the C is S.

Optionally, D is F.

Thereby, the rate performance, energy density and/or high temperature stability of the battery can be further improved.

In any embodiment of the present application, (1-y):y is in the range of 1 to 4, optionally in the range of 1.5 to 3, and m:x is in the range of 9 to 1100, optionally in the range of 190-998. Thus, the energy density and cycle performance of the battery can be further improved.

In any embodiment of the present application, b:c is 1:3.

In any embodiment of the present application, the shell includes a first coating layer coating the core and a second coating layer coating the first coating layer, the first coating layer includes a borate _XaBbOc _, _and the second coating layer includes carbon. The first coating layer includes a borate, which has excellent lithium ion conductivity and electron conductivity, and can inhibit the dissolution of Mn and Mn-doped elements, thereby reducing interfacial side reactions and reducing gas production. The second coating layer is a carbon-containing layer, so it can effectively improve the electron conductivity and desolvation ability of the positive electrode active material. In addition, the "barrier" effect of the second coating layer can further hinder the dissolution and migration of Mn and Mn-doped elements into the electrolyte, and reduce the corrosion of the electrolyte to the positive electrode active material.

In any embodiment of the present application, the coating amount of the first coating layer is greater than 0 wt% and less than or equal to 6 wt%, and can be 1-6 wt%, and more preferably 2-5 wt%, based on the weight of the core. When the coating amount of the first coating layer is within the above range, the dissolution of Mn and Mn-doping elements can be further suppressed, and the transmission of lithium ions and electrons can be further promoted.

In any embodiment of the present application, the coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, and can be 1-6 wt %, and can be 2-5 wt %, based on the weight of the core. When the coating amount of the second coating layer is within the above range, the kinetic performance and safety performance of the battery can be further improved without sacrificing the gram capacity of the positive electrode active material.

In any embodiment of the present application, the lattice change rate of the positive electrode active material is 8% or less, and optionally 4% or less, thereby improving the rate performance of the battery.

In any embodiment of the present application, the Li/Mn antisite defect concentration of the positive electrode active material is 2% or less, and optionally 0.5% or less, thereby improving the gram capacity and rate performance of the positive electrode active material.

In any embodiment of the present application, the surface oxygen valence of the positive electrode active material is less than -1.82, and optionally -1.89 to -1.98. Thus, the cycle performance and high temperature stability of the battery can be improved.

In any embodiment of the present application, the compaction density of the positive electrode active material at 3T is 2.0 g/cm ³ or more, and optionally 2.2 g/cm ³ or more. Thereby, the volume energy density of the battery can be improved.

The second aspect of the present application provides a method for preparing a positive electrode active material, which comprises the following steps:

The step _{of providing a core material: the core comprises LimAxMn1-yByP1-zCzO4} _- _nDn _, _the _A _comprises _one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, S i and N, said D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, said m is selected from the range of 0.9 to 1.1, optionally selected from the range of 0.97 to 1.01, said x is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, said y is selected from the range of 0.001 to 0.5, optionally selected from the range of 0.25 to 0.5, said z is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005, said n is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, and said core is electrically neutral;

The coating step comprises providing a coating solution comprising _a borate _XaBbOc and a carbon _source respectively, adding the core material to the coating solution and mixing, and obtaining a positive electrode active material through sintering, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising the borate _XaBbOc and _carbon , and the shell comprising one or more coating layers, each coating layer independently comprising one or more of _the _{borate XaBbOc} _and _carbon , the X comprising one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, and optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al, the a being selected from the range of 1 to 4, the b being selected from the range of 1 to 7, the c being selected from the range of 2 to 12, and the values of a, b and c satisfying the following condition: the _{borate XaBbOc} _is _kept electrically neutral.

In any embodiment of the present application, the step of providing the core material includes the following steps: (1) dissolving a manganese source, a source of element B and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element B; (2) adding a lithium source, a phosphorus source, an optional source of element A, a source of element C and an optional source of element D, a solvent and the manganese salt doped with element B obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry; (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain particles; (4) sintering the particles obtained in step (3) to obtain a core.

In any embodiment of the present application, the source of element A is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate and a sulfate of element A.

In any embodiment of the present application, the source of element B is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate and a sulfate of element B.

In any embodiment of the present application, the source of element C is selected from at least one of sulfate, borate, nitrate and silicate of element C.

In any embodiment of the present application, the source of element D is selected from at least one of a simple substance of element D and an ammonium salt.

In any embodiment of the present application, the stirring in step (1) is performed at a temperature in the range of 60-120°C.

In any embodiment of the present application, the stirring in step (1) is performed at a stirring rate of 200-800 rpm.

In any embodiment of the present application, the grinding and mixing in step (2) is performed for 8-15 hours.

Therefore, by controlling the reaction temperature, stirring rate and mixing time during doping, the doping elements can be evenly distributed and the crystallinity of the material after sintering can be higher, thereby improving the gram capacity and rate performance of the positive electrode active material.

In any embodiment of the present application, the sintering in step (4) is performed at a temperature range of 600-900° C. for 6-14 hours. Thus, the high temperature stability and cycle performance of the battery can be improved.

In any embodiment of the present application, the coating step comprises:

The first coating step: providing a first coating layer coating solution containing _borate _XaBbOc , adding the core material into the first coating layer coating solution, mixing evenly, drying, and then sintering to obtain _a material coated with the first coating layer;

The second coating step comprises providing a second coating layer coating solution containing a carbon source, and then adding the material coated with the first coating layer obtained in the first coating step into the second coating layer coating solution, mixing evenly, drying, and then sintering to obtain a material coated with two coating layers, i.e., a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising _{a first coating layer coating the core and a second coating layer coating the first coating layer, the first coating layer comprising borate XaBbOc} _, _and the second coating layer comprising carbon.

In any embodiment of the present application, the first coating layer coating liquid is prepared by the following method: adding a source of element X and a boron source into a solvent, stirring the mixture evenly, and obtaining the first coating layer coating liquid.

In any embodiment of the present application, the source of element X is selected from one or more of element X's simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide.

In any embodiment of the present application, the boron source is selected from one or more of boric acid, borates, and boron oxide.

In any embodiment of the present application, the carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.

In any embodiment of the present application, the sintering in the first coating step is sintering at 300-500° C. for 2-10 hours.

In any embodiment of the present application, the sintering in the second coating step is sintering at 500-800° C. for 4-10 hours.

The third aspect of the present application provides a positive electrode plate, including 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 includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application, and the content of the positive electrode active material in the positive electrode film layer is more than 10 weight%, and can be optionally 90-99.5 weight%, based on the total weight of the positive electrode film layer.

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 method of the second aspect of the present application or the positive electrode plate of the third aspect of the present application.

A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application.

The positive electrode sheet, secondary battery, and electrical device of the present application include the positive electrode active material of the present application, and thus have at least the same advantages as the positive electrode active material.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

FIG. 2 is an exploded schematic diagram of an embodiment of a battery cell of the present application.

FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.

FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.

FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

FIG. 6 is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.

FIG. 7 shows the X-ray diffraction spectra of undoped LiMnPO ₄ and the positive electrode active material prepared in Example 2.

FIG. 8 shows an X-ray energy dispersion spectrum of the positive electrode active material prepared in Example 2.

In the drawings, the drawings may not be drawn according to the actual scale. The reference numerals are as follows: 1 battery pack, 2 upper box, 3 lower box, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover plate.

Detailed ways

Below, the embodiments of the positive electrode active material, the preparation method thereof, the positive electrode sheet, the secondary battery and the electric device containing the positive electrode active material of the present application are specifically disclosed with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected. In addition, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form a new technical solution, and such a technical solution should be deemed to be included in the disclosure of the present application.

If not otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies 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).

As used herein, the terms "plurality", "multiple", and "multi-layers" refer to two, two or more layers.

As used herein, "about" a numerical value indicates a range, which means a range of ±10% of the numerical value.

The inventors of the present application found in actual operation that the manganese ion dissolution of lithium manganese phosphate _LiMnPO4 positive electrode active material is relatively serious during the deep charge and discharge process. Although the prior art has attempted to coat lithium manganese phosphate with lithium iron phosphate to reduce the interface side reaction, this coating cannot prevent the dissolved manganese ions from migrating into the electrolyte. After the dissolved manganese ions migrate to the negative electrode, they are reduced to metallic manganese. The produced metallic manganese is equivalent to a "catalyst" that can catalyze the decomposition of the SEI film (solid electrolyte interphase) on the surface of the negative electrode. Part of the by-products produced are gases, which can easily cause the battery to swell and affect the safety performance of the battery. The other part is 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 battery to increase and affecting the kinetic performance of the battery. In addition, in order to replenish the lost SEI film, the active lithium ions inside the electrolyte and the battery are also continuously consumed, which also has an irreversible effect on the capacity retention rate of the battery.

After extensive research, the inventors of the present application found that by performing specific element doping and surface coating on the compound _LiMnPO4 , the present application can effectively reduce the dissolution of Mn and Mn-doping elements, while promoting the migration of lithium ions, thereby achieving significantly improved cycle performance and/or high temperature stability.

Positive electrode active material

Specifically, the first aspect of the present application proposes a positive electrode active material with a core-shell structure, which includes a core and a shell covering the core.

The inner core includes _LimAxMn1 _- _yByP1 _- _zCzO4 _- _nDn , wherein A includes one or more _elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, B includes one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, C includes one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, D includes one or more elements selected from Group VIA and Group VIIA, m is selected from the range of 0.9 to 1.1, x is selected from the range of 0 to 0.1, y is selected from the range of 0.001 to 0.5, z is selected from the range of 0.001 to 0.1, n is selected from the range of 0 to 0.1, and the inner core is electrically neutral.

The shell comprises _{borate XaBbOc} _and carbon, and the shell comprises one _{or more coating layers, each coating layer independently comprises one or more of borate XaBbOc} _and _carbon _, X comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, a is selected from the range of 1 to 4, b is selected from the range of 1 to 7, c is selected from the range of 2 to 12, and the values of a, b and c satisfy the following condition: _the _{borate XaBbOc} _is kept electrically neutral.

Unless otherwise specified, in the above chemical formula, when A is more than two elements, the above-mentioned limitation on the numerical range of x 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 more than two elements A1, A2...An, the stoichiometric numbers x1, x2...xn of A1, A2...An each need to fall within the numerical range of x defined in this application, and the sum of x1, x2...xn also needs to fall within the numerical range. Similarly, for the case where B, C and D are more than two elements, the limitation on the numerical range of the stoichiometric numbers of B, C and D in this application also has the above meaning.

The core of the positive active material of the present application is obtained by doping elements in the compound LiMnPO ₄ , and A, B, C and D are elements doped at the Li position, Mn position, P position and O position of the compound LiMnPO ₄ , respectively. Without wishing to be limited by theory, it is now believed that the performance improvement of lithium manganese phosphate is related to reducing the lattice change rate of lithium manganese phosphate during lithium deintercalation and reduction of surface activity. Reducing the lattice change rate can reduce the lattice constant difference between the two phases at the grain boundary, reduce the interfacial stress, and enhance the transmission capacity of Li ⁺ at the interface, thereby improving the rate performance of the positive active material. High surface activity can easily lead to serious side reactions at the interface, aggravate gas production, electrolyte consumption and damage the interface, thereby affecting the cycle performance of the battery. In the present application, the lattice change rate is reduced by doping at the Li and/or Mn positions. Mn doping can also effectively reduce the surface activity, thereby inhibiting the dissolution of manganese ions and the side reactions at the interface between the positive active material and the electrolyte. P-position doping makes the change rate of the Mn-O bond length faster, reduces the migration barrier of the small polaron of the material, and is conducive to improving the electronic conductivity. O-site doping has a good effect on reducing interface side reactions. P-site and/or O-site doping also affects the dissolution and kinetic properties of manganese ions in anti-site defects.

The inventors of the present application found that by doping the compound LiMnPO ₄ , the concentration of antisite defects in the positive electrode active material is reduced, the dissolution of Mn and Mn-site doping elements is reduced, and the kinetic performance and gram capacity of the positive electrode active material are improved; in addition, by doping the compound LiMnPO ₄ , the morphology of the particles can also be changed, thereby improving the compaction density.

The shell of the positive _electrode active material of the present application includes borate _XaBbOc and carbon. Borate has excellent lithium ion and electron conductivity, _and can reduce the surface impurity lithium content and inhibit the dissolution of Mn and Mn-doped elements, thereby reducing interface side reactions and gas production, and improving cycle performance. Carbon can effectively improve the electron conductivity and desolvation ability of the positive electrode active material.

Therefore, the present application can effectively reduce the dissolution of Mn and Mn-doping elements by performing specific element doping and surface coating on the compound _LiMnPO4 , while promoting the migration of lithium ions. As a result, the positive electrode sheets and electrical devices such as secondary batteries using the positive electrode active materials of the present application can have a higher energy density while also having improved rate performance, cycle performance and/or high temperature stability.

It should be pointed out that, by comparing the XRD spectra before and after LiMnPO ₄ doping, it is found that the positions of the main characteristic peaks of the positive electrode active material of the present application are basically consistent with those before LiMnPO ₄ doping, indicating that the doped lithium manganese phosphate positive electrode active material of the present application has no impurity phase, and the improvement in battery performance mainly comes from element doping, rather than impurity phase.

The x is selected from the range of 0 to 0.1, and the n is selected from the range of 0 to 0.1, that is, the Li position and the O position of the compound LiMnPO ₄ may be undoped or doped.

In some embodiments, optionally, the x is selected from the range of 0.001 to 0.1, that is, the element A is doped at the Li position of the compound LiMnPO ₄ .

In some embodiments, optionally, the n is selected from the range of 0.001 to 0.1, that is, the element D is doped at the O position of the compound LiMnPO ₄ .

In some embodiments, optionally, the x is selected from the range of 0.001 to 0.1, and the n is selected from the range of 0.001 to 0.1, that is, the Li position and the O position of the compound LiMnPO ₄ are doped at the same time.

The inventors of the present application unexpectedly discovered that by doping specific elements in specific amounts at the Li position, Mn position, P position and O position of the compound _LiMnPO4 at the same time, improved rate performance can be obtained, and the dissolution of Mn and the doping elements at the Mn position can be further reduced, thereby obtaining improved cycle performance and/or high temperature stability, and the gram capacity and compaction density of the positive electrode active material can also be improved.

In some embodiments, optionally, the A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W.

In some embodiments, optionally, the B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.

In some embodiments, optionally, the C includes one or more elements selected from B (boron), S, Si and N.

In some embodiments, optionally, the D includes one or more elements selected from S, F, Cl and Br.

In some embodiments, A, C and D are each independently any one element within the above respective ranges, and B is at least two elements within the above respective ranges. Thus, the composition of the positive electrode active material can be more easily and accurately controlled.

Optionally, A is any one element selected from Mg and Nb.

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

Optionally, the C is S.

Optionally, D is F.

By selecting the Li-position doping element within the above range, the lattice change rate during the delithiation process can be further reduced, thereby further improving the rate performance of the battery. By selecting the Mn-position doping element within the above range, the electronic conductivity can be further improved and the lattice change rate can be further reduced, thereby improving the rate performance and energy density of the battery. By selecting the P-position doping element within the above range, the rate performance of the battery can be further improved. By selecting the O-position doping element within the above range, the side reactions of the interface can be further reduced and the high temperature stability of the battery can be improved.

The m is selected from the range of 0.9 to 1.1, for example, 0.97, 0.977, 0.984, 0.988, 0.99, 0.991, 0.992, 0.993, 0.994, 0.995, 0.996, 0.997, 0.998, and 1.01.

In some embodiments, the m is selected from the range of 0.97 to 1.01.

The x is selected from the range of 0 to 0.1, for example, 0, 0.001, or 0.005.

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

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

The n is selected from the range of 0 to 0.1, for example, 0, 0.001, 0.005, 0.08, or 0.1.

In some embodiments, x is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005.

In some embodiments, y is selected from the range of 0.01 to 0.5, optionally selected from the range of 0.25 to 0.5.

In some embodiments, the z is selected from the range of 0.001 to 0.005.

In some embodiments, n is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005.

By selecting the x value within the above range, the kinetic performance of the positive electrode active material can be further improved. By selecting the y value within the above range, the gram capacity and rate performance of the positive electrode active material can be further improved. By selecting the z value within the above range, the rate performance of the battery can be further improved. By selecting the n value within the above range, the high temperature stability of the battery can be further improved.

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

In some embodiments, optionally, X includes one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al.

In some embodiments, b:c is 1:3.

In some embodiments _{, the shell includes multiple coating layers, and each coating layer independently includes one or more of borate XaBbOc} _and _carbon .

In some embodiments, the shell includes a first coating layer coating the core and a second coating layer coating the first coating layer, the first coating layer includes borate X _a B _b O _c , and the second coating layer includes carbon.

The first coating layer includes borate, which has excellent lithium ion conductivity and electron conductivity, and can reduce the surface impurity lithium content and inhibit the dissolution of Mn and Mn-doped elements, thereby reducing interface side reactions and reducing gas production, and improving cycle performance. The second coating layer is a carbon-containing layer, so it can effectively improve the electron conductivity and desolvation ability of the positive electrode active material. In addition, when the second coating layer is located in the outermost layer, its "barrier" effect can further hinder the dissolution and migration of Mn and Mn-doped elements into the electrolyte, and reduce the corrosion of the electrolyte on the positive electrode active material. Therefore, the positive electrode sheet and electrical devices such as secondary batteries using the positive electrode active material of the present application can have a higher energy density, while also having improved rate performance, cycle performance and/or high temperature stability.

In some embodiments, the coating amount of the first coating layer is greater than 0 wt% and less than or equal to 6 wt%, and can be optionally 1-6 wt%, and more optionally 2-5 wt%, based on the weight of the core. When the coating amount of the first coating layer is within the above range, the dissolution of Mn and Mn-doped elements can be further suppressed, and the transmission of lithium ions and electrons can be further promoted. And the following situations can be effectively avoided: if the coating amount of the first coating layer is too small, it may lead to insufficient inhibition of the dissolution of Mn and Mn-doped elements, and the improvement of lithium ion and electron transmission performance is not significant; if the coating amount of the first coating layer is too large, it may cause the coating layer to be too thick, increase the battery impedance, and affect the dynamic performance of the battery. At the same time, since the first coating layer does not contribute to the capacity, the coating amount is too large, which will reduce the gram capacity of the positive electrode active material. Therefore, when the coating amount of the first coating layer is within the above range, it can also further improve the cycle performance and storage performance of the battery without sacrificing the gram capacity of the positive electrode active material.

In some embodiments, the coating amount of the second coating layer is greater than 0 wt% and less than or equal to 6 wt%, and can be optionally 1-6 wt%, and can be more optionally 2-5 wt%, based on the weight of the kernel. As the second coating layer, the carbon-containing layer can play a "barrier" function on the one hand, preventing the positive electrode active material from directly contacting the electrolyte, thereby reducing the erosion of the electrolyte on the positive electrode active material and improving the high temperature stability of the battery. On the other hand, it has a strong electrical conductivity, which can reduce the internal resistance of the battery, thereby improving the kinetic performance of the battery. However, due to the low gram capacity of the carbon material, when the amount of the second coating layer is too large, the overall gram capacity of the positive electrode active material may be reduced. Therefore, when the coating amount of the second coating layer is within the above range, the kinetic performance and safety performance of the battery can be further improved without sacrificing the gram capacity of the positive electrode active material.

In some embodiments, the lattice change rate of the positive electrode active material is 8% or less, optionally 4% or less. By reducing the lattice change rate, lithium ion transmission can be made easier, that is, the migration ability of lithium ions in the material is stronger, which is conducive to improving the rate performance of the battery. The lattice change rate can be measured by methods known in the art, such as X-ray diffraction (XRD) method.

In some embodiments, the Li/Mn antisite defect concentration of the positive electrode active material is less than 2%, optionally less than 0.5%. The so-called Li/Mn antisite defect refers to the position of Li ⁺ and Mn2 ⁺ interchanged in the _LiMnPO4 lattice. The Li/Mn antisite defect concentration refers to the percentage of Li ⁺ interchanged with ^Mn2 + in the total amount of Li ⁺ in the positive electrode active material. The antisite defect Mn2 ⁺ will hinder the transmission of Li ⁺ . By reducing the Li/Mn antisite defect concentration, it is beneficial to improve the gram capacity and rate performance of the positive electrode active material. The Li/Mn antisite defect concentration can be measured by methods known in the art, such as XRD.

In some embodiments, the surface oxygen valence state of the positive electrode active material is less than -1.82, optionally -1.89 to -1.98. By reducing the surface oxygen valence state, the interfacial side reaction between the positive electrode active material and the electrolyte can be reduced, thereby improving the cycle performance and high temperature stability of the battery. The surface oxygen valence state can be measured by methods known in the art, such as by electron energy loss spectroscopy (EELS).

In some embodiments, the compaction density of the positive electrode active material at 3T (ton) is 2.0g/ ^cm3 or more, optionally 2.2g/ ^cm3 or more. The higher the compaction density, the greater the weight of the positive electrode active material per unit volume, so increasing the compaction density is beneficial to increasing the volume energy density of the battery. The compaction density can be measured according to GB/T 24533-2009.

Preparation

The second aspect of the present application relates to a method for preparing the positive electrode active material of the first aspect of the present application, comprising the following steps of providing a core material and a coating step.

The step _{of providing a core material: the core comprises LimAxMn1-yByP1-zCzO4} _- _nDn _, _the _A _comprises _one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, S i and N, the D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, the m is selected from the range of 0.9 to 1.1, optionally selected from the range of 0.97 to 1.01, the x is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, the y is selected from the range of 0.001 to 0.5, optionally selected from the range of 0.25 to 0.5, the z is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005, the n is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, and the core is electrically neutral.

In some embodiments, the step of providing the core material comprises the following steps: (1) dissolving a manganese source, a source of element B and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element B; (2) adding a lithium source, a phosphorus source, an optional source of element A, a source of element C and an optional source of element D, a solvent and the manganese salt doped with element B obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry; (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain particles; (4) sintering the particles obtained in step (3) to obtain a core.

In some embodiments, the manganese source may be a manganese-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the manganese source may be selected from elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

In some embodiments, the acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acid such as oxalic acid, etc., for example, oxalic acid. In some embodiments, the acid is a dilute acid with a concentration of 60 wt % or less.

In some embodiments, the lithium source may be a lithium-containing material known in the art that can be used to prepare lithium manganese phosphate. For example, the lithium source may be selected from lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, or a combination thereof.

In some embodiments, the phosphorus source may be a phosphorus-containing substance known in the art that can be used to prepare lithium manganese phosphate. For example, the phosphorus source may be selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and phosphoric acid, or a combination thereof.

In some embodiments, the source of element A is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element A.

In some embodiments, the source of element B is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate, and a sulfate of element B.

In some embodiments, the source of element C is selected from at least one of sulfates, borates, nitrates, and silicates of element C.

In some embodiments, the source of element D is selected from at least one of a simple substance of element D and an ammonium salt.

By selecting the source of each doping element, the uniformity of the distribution of the doping element can be improved, thereby improving the performance of the positive electrode active material.

The amount of each source of elements A, B, C, and D 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.

In some embodiments, the solvents in step (1) and step (2) can each independently be solvents conventionally used by those skilled in the art in the preparation of manganese salts and lithium manganese phosphate, for example, they can each independently be selected from at least one of ethanol and water (e.g., deionized water).

In some embodiments, the stirring of step (1) is performed at a temperature in the range of 60-120° C. In some embodiments, the stirring of step (1) is performed at a stirring rate of 200-800 rpm, or 300-800 rpm, or 400-800 rpm. In some embodiments, the stirring of step (1) is performed for 6-12 hours.

In some embodiments, the grinding and mixing of step (2) is performed for 8-15 hours.

By controlling the reaction temperature, stirring rate and mixing time during doping, the doping elements can be evenly distributed and the crystallinity of the material after sintering can be higher, thereby improving the gram capacity and rate performance of the positive electrode active material.

In some embodiments, the filter cake may be washed before drying the filter cake in step (1).

In some embodiments, the drying in step (1) can be performed by methods and conditions known to those skilled in the art, for example, the drying temperature can be in the range of 120-300°C. Optionally, the filter cake can be ground into particles after drying, for example, ground until the median particle size Dv ₅₀ of the particles is in the range of 50-200nm. The median particle size Dv ₅₀ refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. In the present application, the median particle size Dv ₅₀ of the material can be determined by laser diffraction particle size analysis. For example, with reference to standard GB/T 19077-2016, a laser particle size analyzer (e.g., Malvern Master Size 3000) is used for determination.

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

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

In some embodiments, the sintering in step (4) is performed under a protective atmosphere, and the protective atmosphere may be nitrogen, an inert gas, hydrogen or a mixture thereof.

In some embodiments, the coating step comprises:

In some embodiments, the first coating layer coating solution is commercially available, or alternatively, prepared by the following method: adding a source of element X and a boron source to a solvent, stirring evenly, to obtain a first coating layer coating solution. Optionally, the source of element X is selected from one or more of a simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element X. Optionally, the boron source is selected from one or more of boric acid, borate, and boron oxide.

In some embodiments, the carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid. The amount of the carbon source relative to the amount of the lithium source is generally in the range of 0.1%-5% by molar ratio.

In the above-mentioned first coating step and second coating step, the drying can be carried out at a drying temperature of 100-200°C, optionally 110-190°C, more optionally 120-180°C, even more optionally 120-170°C, and most optionally 120-160°C, and the drying time is 3-9 hours, optionally 4-8 hours, more optionally 5-7 hours, and most optionally about 6 hours.

In some embodiments, the sintering in the first coating step is sintering at 300-500° C. for 2-10 hours. Optionally, in the first coating step, the sintering can be sintered at about 300° C., about 350° C., about 400° C., about 450° C. or about 500° C. 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 sintering time can be in any range of the above-mentioned values.

In the first coating step, by controlling the sintering temperature and time within the above range, the following situations can be avoided: when the sintering temperature in the first coating step is too low and the sintering time is too short, the first coating layer will have low crystallinity and more amorphous state, and the coating effect will be poor, and the inhibition of the dissolution of Mn and Mn-doped elements will be insufficient, and the improvement of lithium ion and electron transport performance will not be significant; when the sintering temperature is too high and the sintering time is too long, the thickness of the first coating layer will increase, the battery impedance will increase, and the battery's kinetic performance and energy density will be affected.

In some embodiments, the sintering in the second coating step is sintering at 500-800° C. for 4-10 hours. Optionally, in the second coating step, the sintering can be sintered at about 500° C., about 600° C., about 700° C. or about 800° C. for 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 sintering time can be within any range of the above values.

In the second coating step, by controlling the sintering temperature and time within the above range, the following situations can be avoided: when the sintering temperature in the second coating step is too low, the degree of graphitization of the second coating layer will decrease, affecting its conductivity, thereby affecting the specific capacity of the positive electrode active material; when the sintering temperature is too high, the degree of graphitization of the second coating layer will be too high, affecting the transmission of Li ⁺ , thereby affecting the specific capacity of the positive electrode active material, etc.; when the sintering time is too short, the coating layer will be too thin, affecting its conductivity, thereby affecting the specific capacity of the positive electrode active material; when the sintering time is too long, the coating layer will be too thick, affecting the compaction density of the positive electrode active material, etc.

Positive electrode

The third aspect of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer includes the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application, and the content of the positive electrode active material in the positive electrode film layer is more than 10 weight%, and can be optionally 90-99.5 weight%, based on the total weight of the positive electrode film layer.

The positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

The positive electrode film layer does not exclude other positive electrode active materials other than the positive electrode active material of the first aspect of the present application or the positive electrode active material prepared by the method of the second aspect of the present application. For example, the positive electrode film layer may also include other positive electrode active materials other than the above-mentioned positive electrode active materials of the present application. Optionally, the other positive electrode active materials may include at least one of lithium transition metal oxides and modified compounds thereof. As an example, the other positive electrode active materials may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and their respective modified compounds.

In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode film layer may further include a positive electrode binder. The present application has no particular restrictions on the type of the positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

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

The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

Secondary battery

The fourth aspect of the present application provides a secondary battery, which includes the positive electrode plate of the third aspect of the present application.

Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can be used continuously by recharging the active materials after the battery is discharged. Generally, secondary batteries include electrode assemblies and electrolytes, and the electrode assemblies include positive electrode sheets, negative electrode sheets, and separators. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

The secondary battery mentioned in the embodiments or implementations of the present application refers to a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in the present application may include a battery cell, a battery module or a battery pack, etc. A battery cell is the smallest unit that makes up a secondary battery, which can realize the function of charging and discharging alone. The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. Figure 1 is a battery cell 5 of a square structure as an example.

In some embodiments, the battery cell includes an electrode assembly, and the single cell may further include an outer package. The electrode assembly may be made of a positive electrode sheet, a negative electrode sheet, and a separator, etc., by a winding process and/or a lamination process, and the outer package may be used to encapsulate the above-mentioned electrode assembly. The outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

In some embodiments, as shown in FIG. 2 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

In some embodiments of the present application, battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. FIG. 3 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 3, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can be further fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack. Figures 4 and 5 are schematic diagrams of a battery pack 1 as an example. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery module 4. Multiple battery modules 4 can be arranged in the battery box in any manner.

[Positive electrode]

The positive electrode plate used in the secondary battery of the present application is the positive electrode plate described in any embodiment of the third aspect of the present application.

[Negative electrode]

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

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

In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the negative electrode film layer may further include a negative electrode binder. The present application has no particular restrictions on the type of the negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

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

The negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application also includes a conductive primer layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.

[Electrolytes]

The present application has no specific limitation on the type of the electrolyte, which can be selected according to the needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (ie, an electrolyte solution).

In some embodiments, the electrolyte is an electrolyte solution including an electrolyte salt and a solvent.

The type of the electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the electrolyte salt may include at least one of lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

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

In some embodiments, the electrolyte may further include additives, for example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, additives that improve battery low temperature power performance, etc.

[Isolation film]

Secondary batteries using electrolytes and some secondary batteries using solid electrolytes also include a separator. The separator is arranged between the positive electrode plate and the negative electrode plate, and mainly plays the role of preventing the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the isolation membrane may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After vacuum packaging, standing, forming, shaping and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel or in mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

Electrical devices

The fifth aspect of the present application provides an electric device, the electric device comprising the secondary battery of the present application. The secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop 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.

The electrical device may select a specific type of secondary battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

Fig. 6 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module can be used as a power source.

As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a battery cell may be used as a power source.

Example

The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

Example 1

1) Preparation of positive electrode active materials

Preparation of doped manganese oxalate: 1.3 mol of MnSO ₄ ﹒ H ₂ O and 0.7 mol of FeSO ₄ ﹒ H ₂ O were fully mixed in a mixer for 6 hours. The mixture was transferred to a reactor, and 10 L of deionized water and 2 mol of dihydrated oxalic acid (calculated as oxalic acid) were added. The reactor was heated to 80°C and stirred at 600 rpm for 6 hours. The reaction was terminated (no 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 and then ground to obtain Fe-doped manganese oxalate particles with a median particle size Dv ₅₀ of about 100 nm.

Preparation of doped lithium manganese phosphate: 1 mol of the above manganese oxalate particles, 0.497 mol of lithium carbonate, 0.001 mol of Mo(SO ₄ ) ₃ , 0.999 mol of phosphoric acid in an 85% phosphoric acid aqueous solution, 0.001 mol of H ₄ SiO ₄ , and 0.0005 mol of NH ₄ HF ₂ are added to 20 L of deionized water. The mixture is transferred to a sand mill and fully ground and stirred for 10 hours to obtain a slurry. The slurry is transferred to a spray drying device for spray drying and granulation, the drying temperature is set to 250° C., and dried for 4 hours to obtain particles. In a nitrogen (90 volume %) + hydrogen (10 volume %) protective atmosphere, the above powder is sintered at 700° C. for 10 hours to obtain Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001 , i.e., the core. The element content can be detected by inductively coupled plasma emission spectroscopy (ICP).

Coating of the first coating layer: add 1.77 mol lithium hydroxide and 0.295 mol boron oxide into 500 mL deionized water to obtain a first coating layer coating solution, add the above core into the first coating layer coating solution, stir and mix together for 6 hours, after mixing evenly, transfer to a 150°C oven and dry for 6 hours, and then sinter at 400°C for 10 hours to obtain a material coated with the first coating layer.

Coating of the second coating layer: dissolve 74.6g of sucrose in 500ml of deionized water, then stir and fully dissolve to obtain a second coating layer coating solution, add the above-mentioned first coating layer coated material to the second coating layer coating solution, stir and mix together for 6 hours, after mixing evenly, transfer to a 150℃ oven to dry for 6 hours, and then sinter at 700℃ for 10 hours to obtain a double-layer coated material, i.e., the positive electrode active material.

2) Preparation of button cells

The positive electrode active material, polyvinylidene fluoride (PVDF) and acetylene black were added to N-methylpyrrolidone (NMP) at a weight ratio of 90:5:5, and stirred in a drying room to form a slurry. The slurry was coated on aluminum foil, dried and cold pressed to form a positive electrode sheet. The coating amount was 0.015g/ ^cm2 , and the compaction density was 2.0g/ ^cm3 .

A lithium sheet was used as the negative electrode, and a solution of 1 mol/L _LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 was used as the electrolyte. Together with the positive electrode sheet prepared above, they were assembled into a button battery (hereinafter also referred to as "button battery") in a button box.

3) Preparation of full battery

The positive electrode active material was mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 92:2.5:5.5 in an N-methylpyrrolidone solvent system, and then coated on an aluminum foil, dried, and cold pressed to obtain a positive electrode sheet. The coating amount was 0.018 g/cm ² and the compaction density was 2.4 g/cm ³ .

The negative electrode active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were mixed evenly in deionized water at a weight ratio of 90:5:2:2:1, and then coated on copper foil, dried, and cold pressed to obtain a negative electrode sheet. The coating amount was 0.0075g/ ^cm2 , and the compaction density was 1.7g/ ^cm3 .

Using a polyethylene (PE) porous polymer film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is located between the positive and negative electrodes to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer package, and the same electrolyte as that used in the above preparation of the buckle battery is injected and packaged to obtain a full battery (hereinafter also referred to as "full battery").

Examples 2 to 40 and Comparative Examples 1 to 9

The preparation of the button cell and the preparation of the full cell were the same as in Example 1 except for the preparation of the positive electrode active material.

Example 2

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of Li ₂ CO ₃ was changed to 0.4885 mol, Mo(SO ₄ ) ₃ was replaced by MgSO ₄ , the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.68 mol, 0.02 mol of Ti(SO ₄ ) ₂ was added when preparing doped manganese oxalate, and H ₄ SiO ₄ was replaced by HNO ₃ .

Example 3

1) Preparation of positive electrode active material: The process is the same as that of Example 1 except that the amount of Li ₂ CO ₃ is changed to 0.496 mol, Mo(SO ₄ ) ₃ is replaced by W(SO ₄ ) ₃ , and H ₄ SiO ₄ is replaced by H ₂ SO ₄ .

Example 4

1) Preparation of positive electrode active material: The process is the same as that of Example 1 except that the amount of Li ₂ CO ₃ is changed to 0.4985 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.0005 mol of Al ₂ (SO ₄ ) ₃ , and NH ₄ HF ₂ is replaced by NH ₄ HCl ₂ .

Example 5

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.69 mol, 0.01 mol of VCl ₂ was added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4965 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.0005 mol of Nb ₂ (SO ₄ ) ₅ , and H ₄ SiO ₄ was replaced by H ₂ SO ₄ .

Example 6

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.68 mol, 0.01 mol of VCl ₂ and 0.01 mol of MgSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4965 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.0005 mol of Nb ₂ (SO ₄ ) ₅ , and H ₄ SiO ₄ was replaced by H ₂ SO ₄ .

Example 7

1) Preparation of positive electrode active material: Except for replacing MgSO ₄ with CoSO ₄ , the rest is the same as Example 6.

Example 8

1) Preparation of positive electrode active material: Except for replacing MgSO ₄ with NiSO ₄ , the rest is the same as Example 6.

Example 9

1) Preparation of positive electrode active materials: The process was the same as in Example 1, except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.698 mol, 0.002 mol of Ti(SO ₄ ) ₂ was added when preparing the doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4955 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.0005 mol of Nb ₂ (SO ₄ ) ₅ , H ₄ SiO ₄ was replaced by H ₂ SO ₄ , and NH ₄ HF ₂ was replaced by NH ₄ HCl ₂ .

Example 10

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.68 mol, 0.01 mol of VCl ₂ and 0.01 mol of MgSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4975 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.0005 mol of Nb ₂ (SO ₄ ) ₅ , and NH ₄ HF ₂ was replaced by NH ₄ HBr ₂ .

Embodiment 11

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.69 mol, 0.01 mol of VCl ₂ was added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.499 mol, Mo(SO ₄ ) ₃ was replaced by MgSO ₄ , and NH ₄ HF ₂ was replaced by NH ₄ HBr ₂ .

Example 12

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.36 mol, the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.6 mol, 0.04 mol of VCl ₂ was added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4985 mol, Mo(SO ₄ ) ₃ was replaced by MgSO ₄ , and H ₄ SiO ₄ was replaced by HNO ₃ .

Example 13

1) Preparation of positive electrode active material: The process is the same as Example 12 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.16 mol and the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.8 mol.

Embodiment 14

1) Preparation of positive electrode active material: The process is the same as Example 12 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.3 mol and the amount of VCl ₂ is changed to 0.1 mol.

Embodiment 15

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.2 mol, 0.1 mol of VCl ₂ was added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.494 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , and H ₄ SiO ₄ was replaced by H ₂ SO ₄ .

Example 16

1) Preparation of positive electrode active material: The process was the same as in Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.2 mol, 0.1 mol of VCl ₂ was added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.467 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , 0.001 mol of H ₄ SiO ₄ was replaced by 0.005 mol of H ₂ SO ₄ and 1.175 mol of 85% phosphoric acid was replaced by 1.171 mol of 85% phosphoric acid.

Embodiment 17

1) Preparation of positive electrode active material: The process is the same as in Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.2 mol, 0.1 mol of VCl ₂ is added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ is changed to 0.492 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.005 mol of MgSO ₄ , H ₄ SiO ₄ is replaced by H ₂ SO ₄ and the amount of NH ₄ HF ₂ is changed to 0.0025 mol.

Embodiment 18

1) Preparation of positive electrode active materials: The process was the same as in Example 1 except that the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.5 mol, 0.1 mol of VCl ₂ and 0.1 mol of CoSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.492 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , H ₄ SiO ₄ was replaced by H ₂ SO ₄ and the amount of NH ₄ HF ₂ was changed to 0.0025 mol.

Embodiment 19

1) Preparation of positive electrode active material: The process is the same as that of Example 18 except that the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.4 mol and the amount of CoSO ₄ is changed to 0.2 mol.

Embodiment 20

1) Preparation of positive electrode active material: The process is the same as that of Example 18 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.5 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.1 mol, and the amount of CoSO ₄ is changed to 0.3 mol.

Embodiment 21

1) Preparation of positive electrode active material: The same as Example 18 except that 0.1 mol of CoSO ₄ was replaced by 0.1 mol of NiSO ₄ .

Embodiment 22

1) Preparation of positive electrode active material: The process is the same as that of Example 18 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.5 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.2 mol, and 0.1 mol of CoSO ₄ is replaced by 0.2 mol of NiSO ₄ .

Embodiment 23

1) Preparation of positive electrode active material: The process is the same as that of Example 18 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.4 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.3 mol, and the amount of CoSO ₄ is changed to 0.2 mol.

Embodiment 24

1) Preparation of positive electrode active materials: The process was the same as in Example 1, except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.2 mol, the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.5 mol, 0.1 mol of VCl ₂ and 0.2 mol of CoSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.497 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , H ₄ SiO ₄ was replaced by H ₂ SO ₄ , and the amount of NH ₄ HF ₂ was changed to 0.0025 mol.

Embodiment 25

1) Preparation of positive electrode active material: The process was the same as Example 18 except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.0 mol, the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.7 mol, and the amount of CoSO ₄ was changed to 0.2 mol.

Embodiment 26

1) Preparation of positive electrode active materials: The process was the same as in Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.4 mol, the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.3 mol, 0.1 mol of VCl ₂ and 0.2 mol of CoSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.4825 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , the amount of H ₄ SiO ₄ was changed to 0.1 mol, the amount of phosphoric acid was changed to 0.9 mol and the amount of NH ₄ HF ₂ was changed to 0.04 mol.

Embodiment 27

1) Preparation of positive electrode active materials: The process was the same as in Example 1, except that the amount of MnSO ₄ ﹒ H ₂ O was changed to 1.4 mol, the amount of FeSO ₄ ﹒ H ₂ O was changed to 0.3 mol, 0.1 mol of VCl ₂ and 0.2 mol of CoSO ₄ were added when preparing doped manganese oxalate, the amount of Li ₂ CO ₃ was changed to 0.485 mol, 0.001 mol of Mo(SO ₄ ) ₃ was replaced by 0.005 mol of MgSO ₄ , the amount of H ₄ SiO ₄ was changed to 0.08 mol, the amount of phosphoric acid was changed to 0.92 mol and the amount of NH ₄ HF ₂ was changed to 0.05 mol.

Embodiment 28

1) Preparation of positive electrode active material: The preparation is the same as Example 1 except that the amount of lithium hydroxide in the first coating layer coating solution is changed to 0.59 mol and the amount of boron oxide is changed to 0.098 mol.

Embodiment 29

1) Preparation of positive electrode active material: The preparation is the same as Example 1 except that the amount of lithium hydroxide in the first coating layer coating solution is changed to 1.18 mol and the amount of boron oxide is changed to 0.196 mol.

Embodiment 30

1) Preparation of positive electrode active material: The preparation is the same as Example 1 except that the amount of lithium hydroxide in the first coating layer coating solution is changed to 2.36 mol and the amount of boron oxide is changed to 0.393 mol.

Embodiment 31

1) Preparation of positive electrode active material: The preparation method is the same as that of Example 1 except that the amount of lithium hydroxide in the first coating layer coating solution is changed to 2.95 mol and the amount of boron oxide is changed to 0.492 mol.

Embodiment 32

1) Preparation of positive electrode active material: The preparation was the same as in Example 1 except that the amount of sucrose in the second coating layer coating solution was changed to 37.3 g.

Embodiment 33

1) Preparation of positive electrode active material: The preparation was the same as in Example 1 except that the amount of sucrose in the second coating layer coating solution was changed to 111.9 g.

Embodiment 34

1) Preparation of positive electrode active material: The preparation was the same as Example 1 except that the amount of sucrose in the second coating layer coating solution was changed to 149.2 g.

Embodiment 35

1) Preparation of positive electrode active material: The preparation was the same as in Example 1 except that the amount of sucrose in the second coating layer coating solution was changed to 186.5 g.

Embodiment 36

1) Preparation of positive electrode active material: The preparation is the same as Example 1 except that 1.77 mol of lithium hydroxide in the first coating layer coating solution is replaced by 0.549 mol of aluminum hydroxide and the amount of boron oxide is changed to 0.275 mol.

Embodiment 37

1) Preparation of positive electrode active material: The preparation is the same as Example 1 except that 1.77 mol of lithium hydroxide in the first coating layer coating solution is replaced by 0.750 mol of magnesium hydroxide and the amount of boron oxide is changed to 0.250 mol.

Embodiment 38

1) Preparation of positive electrode active material: The process is the same as in Example 1 except that 1.77 mol of lithium hydroxide in the first coating layer coating solution is replaced by 0.450 mol of zinc hydroxide and the amount of boron oxide is changed to 0.150 mol.

Embodiment 39

1) Preparation of positive electrode active material: The process is the same as in Example 1 except that 1.77 mol of lithium hydroxide in the first coating layer coating solution is replaced by 0.459 mol of copper hydroxide and the amount of boron oxide is changed to 0.153 mol.

Embodiment 40

1) Preparation of positive electrode active material: The process is the same as in Example 1 except that 1.77 mol of lithium hydroxide in the first coating layer coating solution is replaced by 0.480 mol of cobalt hydroxide and the amount of boron oxide is changed to 0.160 mol.

Comparative Example 1

1) Preparation of positive electrode active materials

Preparation of manganese oxalate: 1 mol of MnSO ₄ ﹒ H ₂ O is added to a reactor, and 10 L of deionized water and 1 mol of dihydrated oxalic acid (calculated as oxalic acid) are added. The reactor is heated to 80°C and stirred at 600 rpm for 6 hours. The reaction is terminated (no bubbles are generated) to obtain a manganese oxalate suspension. The suspension is then filtered, and the filter cake is dried at 120°C and then ground to obtain manganese oxalate particles with a median particle size Dv ₅₀ of 50-200 nm.

Preparation of lithium manganese phosphate: 1 mol of the above manganese oxalate particles, 0.5 mol of lithium carbonate, 85% phosphoric acid aqueous solution containing 1 mol of phosphoric acid and 7.4 g of sucrose are added to 20 L of deionized water. The mixture is transferred to a sand mill and fully ground and stirred for 10 hours to obtain a slurry. The slurry is transferred to a spray drying device for spray drying and granulation, the drying temperature is set to 250°C, and dried for 4 hours to obtain particles. In a nitrogen (90 volume %) + hydrogen (10 volume %) protective atmosphere, the above powder is sintered at 700°C for 10 hours to obtain carbon-coated LiMnPO ₄ .

Comparative Example 2

1) Preparation of positive electrode active materials

The process is the same as that of Comparative Example 1, except that 1 mol of MnSO ₄ ﹒ H ₂ O is replaced with 0.85 mol of MnSO ₄ ﹒ H ₂ O and 0.15 mol of FeSO ₄ ﹒ _{H 2} O, which are added to the mixer and mixed thoroughly for 6 hours before being added to the reactor.

Comparative Example 3

1) Preparation of positive electrode active materials

The process is the same as Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.9 mol, 0.7 mol of FeSO ₄ ﹒ H ₂ O is replaced by 0.1 mol of ZnSO ₄ , the amount of Li ₂ CO ₃ is changed to 0.495 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.005 mol of MgSO ₄ , the amount of phosphoric acid is changed to 1 mol, H ₄ SiO ₄ and NH ₄ HF ₂ are not added, and the first coating layer is not coated.

Comparative Example 4

1) Preparation of positive electrode active materials

The process is the same as Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.2 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.8 mol, the amount of Li ₂ CO ₃ is changed to 0.45 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.005 mol of Nb ₂ (SO ₄ ) ₅ , the amount of phosphoric acid is changed to 1 mol, the amount of NH ₄ HF ₂ is changed to 0.025 mol, H ₄ SiO ₄ is not added, and the first coating layer is not coated.

Comparative Example 5

1) Preparation of positive electrode active materials

The method is the same as Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.4 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.6 mol, the amount of Li ₂ CO ₃ is changed to 0.38 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.12 mol of MgSO ₄ , and the first coating layer is not coated.

Comparative Example 6

1) Preparation of positive electrode active materials

The process is the same as Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 0.8 mol, 0.7 mol of FeSO ₄ ﹒ H ₂ O is replaced by 1.2 mol of ZnSO ₄ , the amount of Li ₂ CO ₃ is changed to 0.499 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.001 mol of MgSO ₄ , and the first coating layer is not coated.

Comparative Example 7

1) Preparation of positive electrode active materials

The process is the same as Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.4 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.6 mol, the amount of Li ₂ CO ₃ is changed to 0.534 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.001 mol of MgSO ₄ , the amount of phosphoric acid is changed to 0.88 mol, the amount of H ₄ SiO ₄ is changed to 0.12 mol, the amount of NH ₄ HF ₂ is changed to 0.025 mol, and the first coating layer is not coated.

Comparative Example 8

1) Preparation of positive electrode active materials

The process is the same as that of Example 1 except that the amount of MnSO ₄ ﹒ H ₂ O is changed to 1.2 mol, the amount of FeSO ₄ ﹒ H ₂ O is changed to 0.8 mol, the amount of Li ₂ CO ₃ is changed to 0.474 mol, 0.001 mol of Mo(SO ₄ ) ₃ is replaced by 0.001 mol of MgSO ₄ , the amount of phosphoric acid is changed to 0.93 mol, the amount of H ₄ SiO ₄ is changed to 0.07 mol, the amount of NH ₄ HF ₂ is changed to 0.06 mol, and the first coating layer is not coated.

Comparative Example 9

1) Preparation of positive electrode active materials

Except that the first coating layer is not coated, the other aspects are the same as those of Example 1.

Positive electrode active materials, positive electrode sheets and battery performance test methods

1. Lattice change rate measurement method

Under a constant temperature of 25°C, the positive electrode active material samples were placed in an X-ray diffractometer (model: Bruker D8 Discover), and the samples were tested at 1°/minute. The test data were sorted and analyzed, and the lattice constants a0, b0, c0 and v0 were calculated with reference to the standard PDF card (a0, b0 and c0 represent the lengths of the unit cell in each direction, v0 represents the unit cell volume, which can be directly obtained through XRD refinement results).

The positive electrode active material sample is prepared into a buckle battery by the buckle battery preparation method in the above embodiment, and the buckle battery is charged at a small rate of 0.05C until the current is reduced to 0.01C. Then the positive electrode sheet in the buckle battery is taken out and immersed in DMC for 8 hours. Then dry, scrape the powder, and screen out the particles with a particle size of less than 500nm. Take a sample and calculate its lattice constant v1 in the same way as the above test of the fresh sample, and show (v0-v1)/v0×100% as the lattice change rate before and after complete lithium deintercalation in the table.

2. Li/Mn antisite defect concentration measurement method

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

3. Surface oxygen valence state measurement method

Take 5g of positive electrode active material sample and prepare it into buckle battery according to the buckle battery preparation method described in the above embodiment. Charge the buckle battery at a small rate of 0.05C until the current decreases to 0.01C. Then take out the positive electrode plate in the buckle battery and soak it in DMC for 8 hours. Then dry it, scrape the powder, and screen out the particles with a particle size of less than 500nm. The obtained particles are measured by electron energy loss spectroscopy (EELS, the instrument model used is Talos F200S) to obtain the energy loss near edge structure (ELNES), which reflects the state density and energy level distribution of the element. According to the state density and energy level distribution, the number of occupied electrons is calculated by integrating the valence band state density data, thereby inferring the valence state of the surface oxygen after charging.

4. Compaction density measurement method

5g of positive electrode active material sample powder was placed in a special compaction mold (American CARVER mold, model 13mm), and then the mold was placed on a compaction density instrument. A pressure of 3T (tons) was applied, and the thickness of the powder under pressure was read on the device (the thickness after pressure relief, the area of the container used for the test was ^1540.25mm2 ), and the compaction density was calculated by ρ=m/v.

5. Initial gram capacity measurement method of button cell

At a constant temperature of 25°C, charge the button battery to 4.3V at 0.1C, then charge at a constant voltage at 4.3V until the current is less than or equal to 0.05mA, let it stand for 5 minutes, and then discharge it to 2.0V at 0.1C. The discharge capacity at this time is the initial gram capacity, recorded as D0.

6.3C charging constant current ratio measurement method

At a constant temperature of 25°C, let the fresh full battery stand for 5 minutes, and discharge it to 2.5V at 1/3C. Let it stand for 5 minutes, charge it to 4.3V at 1/3C, and then charge it at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, and record the charging capacity at this time as C0. Discharge it to 2.5V at 1/3C, let it stand for 5 minutes, and then charge it to 4.3V at 3C, let it stand for 5 minutes, and record the charging capacity at this time as C1. The 3C charging constant current ratio is C1/C0×100%.

The higher the 3C charging constant current ratio, the better the battery's rate performance.

7. Full battery 45℃ cycle performance test

At a constant temperature of 45°C, charge the full battery at 1C to 4.3V, then charge at a constant voltage at 4.3V until the current is less than or equal to 0.05mA. Let it stand for 5 minutes, then discharge at 1C to 2.5V, and record the discharge capacity at this time as E0. Repeat the above charge and discharge cycle until the discharge capacity is reduced to 80% of E0. Record the number of cycles the battery has gone through at this time.

8. Measurement method of Mn (and Fe doped with Mn) dissolution after cycling

After cycling at 45°C until the capacity decays to 80%, the full battery is discharged at a rate of 0.1C to a cut-off voltage of 2.0V. Then the battery is disassembled, the negative electrode plate is taken out, and 30 discs of unit area (1540.25 ^mm2 ) are randomly selected from the negative electrode plate and tested by inductively coupled plasma emission spectroscopy (ICP) using Agilent ICP-OES730. According to the ICP results, the amount of Fe (if the Mn position of the positive electrode active material is doped with Fe) and Mn is calculated, thereby calculating the dissolution amount of Mn (and Fe doped at the Mn position) after cycling. The test standard is based on EPA-6010D-2014.

9. Full battery 60℃ inflation test

Full batteries with 100% state of charge (SOC) were stored at 60°C. The open circuit voltage (OCV) and AC internal resistance (IMP) of the battery were measured before, during and after storage to monitor the SOC, and the battery volume was measured. The full battery was taken out after every 48 hours of storage, and the open circuit voltage (OCV) and internal resistance (IMP) were tested after standing for 1 hour. The battery volume was measured by the water displacement method after cooling to room temperature. The water displacement method is to first measure the gravity F ₁ of the battery separately using a balance that automatically converts the dial data, and then completely place the battery in deionized water (density is known to be 1g/cm ³ ), and measure the gravity F ₂ of the battery at this time. The buoyancy F _buoyancy of the battery is F ₁ -F ₂ , and then according to the Archimedean principle F _buoyancy = ρ × g × V _displacement , the battery volume V = (F ₁ -F ₂ )/(ρ × g) is calculated.

From the OCV and IMP test results, the battery of the embodiment always maintained a SOC of more than 99% during the test until the end of storage.

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

10. Determination of chemical formula of positive electrode active material

The internal microstructure and surface structure of the positive electrode active material were characterized with high spatial resolution using spherical aberration electron microscopy (ACSTEM), and the chemical formula of the positive electrode active material was obtained using three-dimensional reconstruction technology.

Table 1 shows the positive electrode active material compositions of Examples 1-11 and Comparative Examples 1-9.

Table 2 shows the positive electrode active material compositions of Examples 12-27.

Table 3 shows the positive electrode active material compositions of Examples 28-40.

Table 4 shows the performance data of the positive electrode active materials, positive electrode sheets, buckle or full-charge of Examples 1-11 and Comparative Examples 1-9 measured according to the above performance test method.

Table 5 shows the performance data of the positive electrode active materials, positive electrode sheets, buckled or fully charged samples of Examples 12-27 measured according to the above performance test method.

Table 6 shows the performance data of the positive electrode active materials, positive electrode sheets, buckled or fully charged samples of Examples 28-40 measured according to the above performance test method.

Table 1

序号Serial number	内核Kernel	第一包覆层First coating layer	第二包覆层Second coating layer
对比例1Comparative Example 1	LiMnPO ₄ LiMnPO ₄	//	2％碳2% Carbon
对比例2Comparative Example 2	LiMn _0.85Fe _0.15PO ₄ LiMn _0.85 Fe _0.15 PO ₄	//	2％碳2% Carbon
对比例3Comparative Example 3	Li _0.990Mg _0.005Mn _0.95Zn _0.05PO ₄ Li _0.990 Mg _0.005 Mn _0.95 Zn _0.05 PO ₄	//	2％碳2% Carbon
对比例4Comparative Example 4	Li _0.90Nb _0.01Mn _0.6Fe _0.4PO _3.95F _0.05 Li _0.90 Nb _0.01 Mn _0.6 Fe _0.4 PO _3.95 F _0.05	//	2％碳2% Carbon
对比例5Comparative Example 5	Li _0.76Mg _0.12Mn _0.7Fe _0.3P _0.999Si _0.001O _3.999F _0.001 Li _0.76 Mg _0.12 Mn _0.7 Fe _0.3 P _0.999 Si _0.001 O _3.999 F _0.001	//	2％碳2% Carbon
对比例6Comparative Example 6	Li _0.998Mg _0.001Mn _0.4Zn _0.6P _0.999Si _0.001O _3.999F _0.001 Li _0.998 Mg _0.001 Mn _0.4 Zn _0.6 P _0.999 Si _0.001 O _3.999 F _0.001	//	2％碳2% Carbon
对比例7Comparative Example 7	Li _1.068Mg _0.001Mn _0.7Fe _0.3P _0.88Si _0.12O _3.95F _0.05 Li _1.068 Mg _0.001 Mn _0.7 Fe _0.3 P _0.88 Si _0.12 O _3.95 F _0.05	//	2％碳2% Carbon
对比例8Comparative Example 8	Li _0.948Mg _0.001Mn _0.6Fe _0.4P _0.93Si _0.07O _3.88F _0.12 Li _0.948 Mg _0.001 Mn _0.6 Fe _0.4 P _0.93 Si _0.07 O _3.88 F _0.12	//	2％碳2% Carbon
对比例9Comparative Example 9	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	//	2％碳2% Carbon
实施例1Example 1	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例2Example 2	Li _0.977Mg _0.001Mn _0.65Fe _0.34Ti _0.01P _0.999N _0.001O _3.999F _0.001 Li _0.977 Mg _0.001 Mn _0.65 Fe _0.34 Ti _0.01 P _0.999 N _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例3Example 3	Li _0.992W _0.001Mn _0.65Fe _0.35P _0.999S _0.001O _3.999F _0.001 Li _0.992 W _0.001 Mn _0.65 Fe _0.35 P _0.999 S _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例4Example 4	Li _0.997Al _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999Cl _0.001 Li _0.997 Al _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 Cl _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例5Example 5	Li _0.993Nb _0.001Mn _0.65Fe _0.345V _0.005P _0.999S _0.001O _3.999F _0.001 Li _0.993 Nb _0.001 Mn _0.65 Fe _0.345 V _0.005 P _0.999 S _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例6Example 6	Li _0.993Nb _0.001Mn _0.65Fe _0.34V _0.005Mg _0.005P _0.999S _0.001O _3.999F _0.001 Li _0.993 Nb _0.001 Mn _0.65 Fe _0.34 V _0.005 Mg _0.005 P _0.999 S _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例7Example 7	Li _0.993Nb _0.001Mn _0.65Fe _0.34V _0.005Co _0.005P _0.999S _0.001O _3.999F _0.001 Li _0.993 Nb _0.001 Mn _0.65 Fe _0.34 V _0.005 Co _0.005 P _0.999 S _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例8Example 8	Li _0.993Nb _0.001Mn _0.65Fe _0.34V _0.005Ni _0.005P _0.999S _0.001O _3.999F _0.001 Li _0.993 Nb _0.001 Mn _0.65 Fe _0.34 V _0.005 Ni _0.005 P _0.999 S _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例9Example 9	Li _0.991Nb _0.001Mn _0.65Fe _0.349Ti _0.001P _0.999S _0.001O _3.999Cl _0.001 Li _0.991 Nb _0.001 Mn _0.65 Fe _0.349 Ti _0.001 P _0.999 S _0.001 O _3.999 Cl _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例10Example 10	Li _0.995Nb _0.001Mn _0.65Fe _0.34V _0.005Mg _0.005P _0.999Si _0.001O _3.999Br _0.001 Li _0.995 Nb _0.001 Mn _0.65 Fe _0.34 V _0.005 Mg _0.005 P _0.999 Si _0.001 O _3.999 Br _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon
实施例11Embodiment 11	Li _0.998Mg _0.001Mn _0.65Fe _0.345V _0.005P _0.999Si _0.001O _3.999Br _0.001 Li _0.998 Mg _0.001 Mn _0.65 Fe _0.345 V _0.005 P _0.999 Si _0.001 O _3.999 Br _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	2％碳2% Carbon

Table 2

table 3

序号Serial number	内核Kernel	第一包覆层First coating layer	第二包覆层Second coating layer
实施例28Embodiment 28	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	1％Li ₃BO ₃ 1 _% _Li3BO3	2％碳2% Carbon
实施例29Embodiment 29	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	2％Li ₃BO ₃ 2 _% _Li3BO3	2％碳2% Carbon

实施例30Embodiment 30	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	4％Li ₃BO ₃ 4 _% _Li3BO3	2％碳2% Carbon
实施例31Embodiment 31	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	5％Li ₃BO ₃ ₅ % _Li3BO3	2％碳2% Carbon
实施例32Embodiment 32	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	1％碳1% Carbon
实施例33Embodiment 33	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	3％碳3% Carbon
实施例34Embodiment 34	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	4％碳4% Carbon
实施例35Embodiment 35	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Li ₃BO ₃ 3 _% _Li3BO3	5％碳5% Carbon
实施例36Embodiment 36	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％AlBO ₃ 3%AlBO ₃	2％碳2% Carbon
实施例37Embodiment 37	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Mg ₃(BO ₃) ₂ 3%Mg ₃ (BO ₃ ) ₂	2％碳2% Carbon
实施例38Embodiment 38	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Zn ₃(BO ₃) ₂ 3% Zn ₃ (BO ₃ ) ₂	2％碳2% Carbon
实施例39Embodiment 39	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Cu ₃(BO ₃) ₂ 3％Cu ₃ (BO ₃ ) ₂	2％碳2% Carbon

实施例40Embodiment 40	Li _0.994Mo _0.001Mn _0.65Fe _0.35P _0.999Si _0.001O _3.999F _0.001 Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001	3％Co ₃(BO ₃) ₂ 3%Co ₃ (BO ₃ ) ₂	2％碳2% Carbon

As can be seen from Tables 4 to 6 above, each positive electrode active material of the embodiments of the present application has achieved better results than the comparative example in one or all of the aspects of cycle performance, high temperature stability, gram capacity and compaction density. By doping specific elements in specific amounts at the Li position, Mn position, P position and O position of LiMnPO ₄ at the same time, improved rate performance can be obtained, while reducing the amount of Mn and Fe dissolution, and improving cycle performance and/or high temperature stability, and the gram capacity and compaction density of the positive electrode active material can also be improved. By coating the surface of the inner core with borate and carbon, the surface impurity lithium content can be reduced, and the dissolution of Mn and Mn-position doping elements can be further suppressed, thereby reducing interface side reactions and reducing gas production, thereby further improving the cycle performance and high temperature stability of the battery.

By comparing Examples 18-20 and 23-25, it can be seen that when other elements are the same, (1-y):y is in the range of 1 to 4, which can further improve the energy density and cycle performance of the battery.

FIG7 shows an X-ray diffraction spectrum (XRD) of undoped LiMnPO ₄ and the positive electrode active material prepared in Example 2. As can be seen from the figure, the position of the main characteristic peaks in the XRD diagram of the positive electrode active material of Example 2 is consistent with that of the undoped LiMnPO ₄ , indicating that the impurity phase is not introduced during the doping process, and the improvement in performance is mainly caused by element doping rather than impurity phases. FIG8 shows an X-ray energy dispersion spectrum (EDS) diagram of the positive electrode active material prepared in Example 2. The dotted elements are distributed in the figure. It can be seen from the figure that the positive electrode active material of Example 2 is uniformly doped with elements.

It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

A positive electrode active material with a core-shell structure, comprising a core and a shell covering the core, wherein:

The core comprises LimAxMn1 - yByP1 - zCzO4 - nDn , the A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, S i and N, said D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, said m is selected from the range of 0.9 to 1.1, optionally selected from the range of 0.97 to 1.01, said x is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, said y is selected from the range of 0.001 to 0.5, optionally selected from the range of 0.25 to 0.5, said z is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005, said n is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, and said core is electrically neutral;

The shell comprises borate XaBbOc and carbon, and the shell comprises one or more coating layers, each coating layer independently comprises one or more of borate XaBbOc and carbon , X comprises one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, and optionally comprises one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al, a is selected from the range of 1 to 4, b is selected from the range of 1 to 7, c is selected from the range of 2 to 12, and the values of a, b and c satisfy the following condition: the borate XaBbOc is kept electrically neutral.
The positive electrode active material according to claim 1, wherein A, C and D are each independently any one element within the above respective ranges, and B is at least two elements within the ranges;

Optionally,

The A is any one element selected from Mg and Nb, and/or,

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

Said C is S, and/or,

The D is F.
The positive electrode active material according to claim 1 or 2, wherein (1-y):y is in the range of 1 to 4, optionally in the range of 1.5 to 3, and m:x is in the range of 9 to 1100, optionally in the range of 190-998.
The positive electrode active material according to any one of claims 1 to 3, wherein b:c is 1:3.
The positive electrode active material according to any one of claims 1 to 4, wherein the shell comprises a first coating layer coating the inner core and a second coating layer coating the first coating layer, the first coating layer comprises borate XaBbOc , and the second coating layer comprises carbon.
The positive electrode active material according to claim 5, wherein

The coating amount of the first coating layer is greater than 0 wt% and less than or equal to 6 wt%, and can be 1-6 wt%, and can be 2-5 wt%, based on the weight of the core; and/or,

The coating amount of the second coating layer is greater than 0 wt % and less than or equal to 6 wt %, and can be optionally 1-6 wt %, and more optionally 2-5 wt %, based on the weight of the core.
The positive electrode active material according to any one of claims 1 to 6, wherein the positive electrode active material satisfies at least one of the following conditions (1) to (4):

(1) The lattice change rate of the positive electrode active material is 8% or less, and optionally 4% or less;

(2) the Li/Mn antisite defect concentration of the positive electrode active material is less than 2%, and optionally less than 0.5%;

(3) The surface oxygen valence state of the positive electrode active material is below -1.82, and optionally -1.89 to -1.98;

(4) The compaction density of the positive electrode active material at 3T is 2.0 g/cm 3 or more, and optionally 2.2 g/cm 3 or more.
A method for preparing a positive electrode active material comprises the following steps:

The step of providing a core material: the core comprises LimAxMn1-yByP1-zCzO4 - nDn , the A comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IIB, Group VB and Group VIB, and optionally comprises one or more elements selected from Group Zn, Al, Na, K, Mg, Nb, Mo and W, the B comprises one or more elements selected from Group IA, Group IIA, Group IIIA, Group IVA, Group VA, Group IIB, Group IVB, Group VB, Group VIB and Group VIIIB, and optionally comprises one or more elements selected from Group Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, the C comprises one or more elements selected from Group IIIA, Group IVA, Group VA and Group VIA, and optionally comprises B (boron), S, S i and N, said D comprises one or more elements selected from Group VIA and Group VIIA, optionally comprising one or more elements selected from S, F, Cl and Br, said m is selected from the range of 0.9 to 1.1, optionally selected from the range of 0.97 to 1.01, said x is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, said y is selected from the range of 0.001 to 0.5, optionally selected from the range of 0.25 to 0.5, said z is selected from the range of 0.001 to 0.1, optionally selected from the range of 0.001 to 0.005, said n is selected from the range of 0 to 0.1, optionally selected from the range of 0.001 to 0.005, and said core is electrically neutral;

The coating step comprises providing a coating solution comprising a borate XaBbOc and a carbon source respectively, adding the core material to the coating solution and mixing, and obtaining a positive electrode active material through sintering, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising the borate XaBbOc and carbon , and the shell comprising one or more coating layers, each coating layer independently comprising one or more of the borate XaBbOc and carbon , the X comprising one or more metal elements selected from transition metals, Group IA, Group IIA, Group IIIA, Group IVA, Group VA and lanthanides, and optionally comprising one or more elements selected from Li, Fe, Ni, Mg, Mn, Co, Cu, Zn, Ti, Ag, Zr, Nb, Sb and Al, the a being selected from the range of 1 to 4, the b being selected from the range of 1 to 7, the c being selected from the range of 2 to 12, and the values of a, b and c satisfying the following condition: the borate XaBbOc is kept electrically neutral.
The method according to claim 8, wherein the step of providing the core material comprises the following steps: (1) dissolving a manganese source, a source of element B and an acid in a solvent and stirring to generate a suspension of a manganese salt doped with element B, filtering the suspension and drying the filter cake to obtain a manganese salt doped with element B; (2) adding a lithium source, a phosphorus source, an optional source of element A, a source of element C and an optional source of element D, a solvent and the manganese salt doped with element B obtained in step (1) into a reaction vessel, grinding and mixing to obtain a slurry; (3) transferring the slurry obtained in step (2) to a spray drying device for spray drying and granulation to obtain particles; (4) sintering the particles obtained in step (3) to obtain a core.
The method according to claim 9, wherein

The source of element A is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate and a sulfate of element A; and/or,

The source of element B is selected from at least one of a simple substance, an oxide, a phosphate, an oxalate, a carbonate and a sulfate of element B; and/or,

The source of element C is selected from at least one of sulfate, borate, nitrate and silicate of element C; and/or,

The source of element D is selected from at least one of a simple substance of element D and an ammonium salt.
The method according to claim 9 or 10, wherein:

The stirring in step (1) is carried out at a temperature in the range of 60-120° C.; and/or,

The stirring in step (1) is performed at a stirring rate of 200-800 rpm; and/or,

The grinding and mixing of step (2) is performed for 8-15 hours; and/or,

The sintering in step (4) is carried out at a temperature range of 600-900° C. for 6-14 hours.
The method according to any one of claims 8 to 11, wherein the coating step comprises:

The first coating step: providing a first coating layer coating solution containing borate XaBbOc , adding the core material into the first coating layer coating solution, mixing evenly, drying, and then sintering to obtain a material coated with the first coating layer;

The second coating step comprises providing a second coating layer coating solution containing a carbon source, and then adding the material coated with the first coating layer obtained in the first coating step into the second coating layer coating solution, mixing evenly, drying, and then sintering to obtain a material coated with two coating layers, i.e., a positive electrode active material, wherein the positive electrode active material has a core-shell structure, comprising the core and a shell coating the core, the shell comprising a first coating layer coating the core and a second coating layer coating the first coating layer, the first coating layer comprising borate XaBbOc , and the second coating layer comprising carbon.
The method according to claim 12, wherein the first coating layer coating liquid is prepared by the following method: adding a source of element X and a boron source to a solvent, stirring evenly, to obtain a first coating layer coating liquid.
The method according to claim 13, wherein

The source of element X is selected from one or more of a simple substance, carbonate, sulfate, chloride, nitrate, organic acid salt, oxide, and hydroxide of element X; and/or,

The boron source is selected from one or more of boric acid, borate and boron oxide.
The method according to any one of claims 8 to 14, wherein the carbon source is selected from one or more of starch, sucrose, glucose, polyvinyl alcohol, polyethylene glycol, and citric acid.
The method according to any one of claims 12 to 15, wherein

The sintering in the first coating step is sintering at 300-500° C. for 2-10 hours; and/or,

The sintering in the second coating step is sintering at 500-800° C. for 4-10 hours.
A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material described in any one of claims 1 to 7 or the positive electrode active material prepared by the method described in any one of claims 8 to 16, and the content of the positive electrode active material in the positive electrode film layer is more than 10 weight%, and can be optionally 90-99.5 weight%, based on the total weight of the positive electrode film layer.
A secondary battery comprising the positive electrode active material according to any one of claims 1 to 7, or the positive electrode active material prepared by the method according to any one of claims 8 to 16, or the positive electrode sheet according to claim 17.
An electrical device comprising the secondary battery according to claim 18.