Method for preparing positive electrode material, positive electrode material, positive electrode plate, battery and electric device

Abstract

The invention provides a method for preparing a positive electrode material, the positive electrode material, a positive electrode plate, a battery and an electric device. The method comprises the following steps: mixing, drying and sintering a precursor and a phosphorus source in a solvent to obtain an intermediate product; wherein the precursor comprises lithium manganese iron phosphate containing or not containing doping elements, and the doping elements comprise one or more of IIA group elements, IIIA group elements, IVA group elements and transition metal elements; and mixing the intermediate product and a carbon source in a solvent, drying and sintering to obtain the positive electrode material. The structural stability and the conductivity of the positive electrode material are improved, and the specific capacity, the storage performance and the cycle performance of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a method for preparing a positive electrode material, a positive electrode material, a positive electrode sheet, a battery, and an electrical device. Background Art

[0002] In recent years, the application of secondary batteries has become increasingly widespread. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As secondary batteries have achieved great development, higher requirements have been placed on their energy density, storage performance, and cycle performance. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems and aims to provide a method for preparing a positive electrode material, a positive electrode material, a positive electrode sheet, a battery, and an electrical device. The structural stability and conductivity of the positive electrode material of this application are improved, thereby improving the specific capacity, storage performance, and cycle performance of the battery.

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0005] A precursor and a phosphorus source are mixed in a solvent, dried, and sintered to obtain an intermediate product; wherein the precursor comprises lithium manganese iron phosphate with or without a doping element, and the doping element comprises one or more of a Group IIA element, a Group IIIA element, a Group IVA element, and a transition metal element;

[0006] The intermediate product is mixed with a carbon source in a solvent, dried, and sintered to obtain a positive electrode material.

[0007] Therefore, the present application adopts a precursor containing lithium manganese iron phosphate, a phosphorus source and a carbon source to prepare the positive electrode material through a two-step coating method, which can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of cracking of the positive electrode material and shedding of the coating layer, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0008] The second aspect of the present application also provides a method for preparing a positive electrode material, comprising the following steps:

[0009] A precursor, a phosphorus source, and a carbon source are mixed in a solvent, dried, and sintered to obtain a positive electrode material; wherein the precursor includes lithium manganese iron phosphate with or without doping elements, and the doping elements include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

[0010] Therefore, the present application adopts a precursor containing lithium manganese iron phosphate, a phosphorus source and a carbon source to prepare the positive electrode material through a one-step coating method, which can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of cracking of the positive electrode material and shedding of the coating layer, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0011] In any embodiment of the first aspect, in the step of preparing the intermediate product, a precursor, a phosphorus source and a source of a doping element are mixed in a solvent, dried and sintered to obtain an intermediate product; wherein the doping element independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements and transition metal elements.

[0012] In any embodiment of the second aspect, the precursor, phosphorus source, carbon source and source of the doping element are mixed in a solvent, dried and sintered to obtain a positive electrode material; wherein the doping element independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements and transition metal elements.

[0013] Therefore, introducing doping elements when preparing the coating layer can improve the conductivity of the positive electrode material and improve the specific capacity, storage performance and cycle performance of the battery.

[0014] In any embodiment of the first or second aspect, the positive electrode material comprises a core and a coating layer covering the core; the core comprises LiFe x1 Mn y1 M 1-x1-y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2 PO4 and carbon; wherein, 0<x1<1, 0<y1<1, 0≤1-x1-y1<1, 0≤z≤1.5, 0≤x2≤1, 0≤y2≤1, 0≤1-x2-y2≤1; the M elements in the core and the coating layer independently include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

[0015] In any embodiment of the first or second aspect, the molar ratio of the lithium manganese iron phosphate containing or not containing a doping element in the precursor to the phosphorus element in the phosphorus source is 1:0.2-1:0.00001; and / or,

[0016] The weight ratio of lithium manganese iron phosphate containing or not containing doping elements to the carbon source in the precursor is 1:1.2-1:0.0005; and / or,

[0017] The molar ratio of the lithium manganese iron phosphate containing or not containing the doping element in the precursor to the doping element in the source of the doping element is 1:0.3-1:0.00001.

[0018] Therefore, the use of the above-mentioned raw material ratio is conducive to preparing a positive electrode material with stable structure and high conductivity, so as to improve the specific capacity, storage performance and cycle performance of the battery.

[0019] In any embodiment of the first or second aspect, the mixing temperature is independently 10° C. to 60° C.; and / or,

[0020] The mixing time is independently 5 min to 30 hours; and / or,

[0021] The mixing is performed by grinding; and / or,

[0022] The sintering temperature is independently 150°C-1000°C; and / or,

[0023] The sintering time is independently 3-20 hours; and / or,

[0024] The sintering is independently carried out in an inert atmosphere; and / or,

[0025] The drying temperature is independently 150°C to 550°C; and / or,

[0026] The drying is performed by oven drying or spray drying.

[0027] The above-mentioned mixing conditions are conducive to improving the performance of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0028] The above-mentioned sintering conditions are conducive to making the coating layer firmly coated on the surface of the core, improving the structural stability of the positive electrode material and also improving the conductivity of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0029] In any embodiment of the first or second aspect, in the step of preparing the positive electrode material, before drying, the obtained mixture is passed through a 350-450 mesh sieve, and the sieved portion is collected; and / or,

[0030] In the step of preparing the positive electrode material, after sintering, the sintered product is crushed; and / or,

[0031] The phosphorus source includes one or more of phosphoric acid, phosphate, monohydrogen phosphate, and dihydrogen phosphate; and / or,

[0032] The carbon source includes one or more of an organic carbon source and an inorganic carbon source; and / or,

[0033] The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

[0034] Therefore, in the step of preparing the positive electrode material, controlling the particle size of the insoluble matter in the mixture by screening is beneficial to improving the particle uniformity and structural stability of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0035] In any embodiment of the first or second aspect, the precursor is prepared by the following steps:

[0036] reacting a lithium source, a manganese source, an iron source and a phosphorus source in a solvent, separating the solid and the liquid, and collecting a solid phase;

[0037] The solid phase is dried and sintered to obtain a precursor.

[0038] In any embodiment of the first or second aspect, in the step of preparing the solid phase, a lithium source, a manganese source, an iron source, a phosphorus source and a source of a doping element are reacted in a solvent, the solid-liquid is separated, and the solid phase is collected; wherein the doping element includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0039] Therefore, introducing doping elements into the precursor is beneficial to further improve the conductivity and structural stability of the positive electrode material, thereby improving the battery's specific capacity, storage performance and cycle performance.

[0040] In any embodiment of the first or second aspect, the precursor comprises LiFe x3 Mn y3 M 1-x3-y3 PO4, wherein 0<x3<1, 0<y3<1, 0≤1-x3-y3<1, and the M element includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0041] In any embodiment of the first or second aspect, the doping elements independently include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or,

[0042] The M elements in the core, the coating layer and the precursor independently include one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni and B.

[0043] In any embodiment of the first or second aspect, in the step of preparing the precursor,

[0044] The molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, the phosphorus element in the phosphorus source and the doping element in the source of the doping element is 1:y3:x3:1:(1-x3-y3); and / or,

[0045] The reaction temperature is 20°C-50°C; and / or,

[0046] The reaction time is 1 minute to 8 hours; and / or,

[0047] The drying temperature is 50°C-200°C; and / or,

[0048] The drying time is 10 minutes to 5 hours; and / or,

[0049] The sintering temperature is 150°C-800°C; and / or,

[0050] The sintering time is 1-12 hours; and / or,

[0051] The sintering is performed in an inert atmosphere.

[0052] The above reaction conditions are conducive to improving the material properties of the precursor, and then improving the performance of the positive electrode material, thereby enhancing the specific capacity, storage performance and cycle performance of the battery.

[0053] The above-mentioned sintering conditions are conducive to improving the material properties of the precursor, and then improving the performance of the positive electrode material, thereby enhancing the specific capacity, storage performance and cycle performance of the battery.

[0054] In any embodiment of the first or second aspect, in the step of preparing the precursor,

[0055] The solid-liquid separation is performed by filtration or centrifugation; and / or,

[0056] Before drying, washing the solid phase; and / or,

[0057] crushing the dried material before sintering; and / or,

[0058] The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt and organic acid salt; and / or,

[0059] The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of manganese; and / or,

[0060] The iron source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of iron; and / or,

[0061] The phosphorus source includes one or more of phosphoric acid, phosphate, hydrogen phosphate, and dihydrogen phosphate; and / or,

[0062] The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

[0063] The third aspect of the present application also provides a positive electrode material, comprising a core and a coating layer covering the core; the core comprises LiFe x1 Mn y1 M 1-x1-y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2 PO4 and carbon; wherein, 0<x1<1, 0<y1<1, 0≤1-x1-y1<1, 0≤z≤1.5, 0≤x2≤1, 0≤y2≤1, 0≤1-x2-y2≤1; the M elements in the core and the coating layer independently include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

[0064] Therefore, the present application can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of positive electrode material cracking and coating layer shedding, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0065] In any embodiment, the M element in the core and the coating layer independently includes one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or,

[0066] The average diameter of the core is 0.04-8.5 μm; and / or,

[0067] The average thickness of the coating layer is 0.5-700 nm; and / or,

[0068] In the coating layer, the Li z Fe x2 Mn y2 M 1-x2-y2 The weight ratio of PO4 to the carbon is 1:10 6 -1:0.002; and / or,

[0069] The powder resistivity of the positive electrode material is ≤403Ω·cm; and / or,

[0070] The Dv50 particle size of the positive electrode material is 0.1-10 μm.

[0071] The fourth aspect of the present application provides a positive electrode plate, comprising the positive electrode material prepared by the method of the first or second aspect of the present application or the positive electrode material described in the third aspect of the present application.

[0072] The fifth aspect of the present application provides a battery, comprising a positive electrode material prepared by the method of the first or second aspect of the present application, the positive electrode material described in the third aspect of the present application, or the positive electrode sheet described in the fourth aspect of the present application.

[0073] The sixth aspect of the present application provides an electrical device comprising the battery described in the fifth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 Schematic diagram of a battery cell according to one embodiment of the present application.

[0075] Figure 2 yes Figure 1 FIG. 1 is an exploded view of a battery cell according to an embodiment of the present application.

[0076] Figure 3 Schematic diagram of a battery module according to one embodiment of the present application.

[0077] Figure 4 Schematic diagram of a battery pack according to one embodiment of the present application.

[0078] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0079] Figure 6 FIG2 is a schematic diagram of an electrical device using a battery cell according to an embodiment of the present application as a power source.

[0080] Description of reference numerals:

[0081] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0082] Below, the embodiments of the negative electrode active material and its manufacturing method, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be 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 description 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.

[0083] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0084] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0085] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0086] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0087] Unless otherwise specified, the Dv50 particle size in this application refers to the particle size when the cumulative value of volume distribution is 50%.

[0088] [Battery Cell]

[0089] A battery cell, also known as a rechargeable battery or storage battery, refers to a battery that can be recharged to activate the active material after discharge and continue to be used.

[0090] Typically, a battery cell consists of a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process of the battery, active ions (such as lithium ions) are embedded and released back and forth between the positive and negative electrode sheets. The separator is set between the positive and negative electrode sheets, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte between the positive and negative electrode sheets mainly plays the role of conducting active ions.

[0091] [Method for preparing positive electrode material]

[0092] One embodiment of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0093] A precursor and a phosphorus source are mixed in a solvent, dried, and sintered to obtain an intermediate product; wherein the precursor comprises lithium manganese iron phosphate with or without a doping element, and the doping element comprises one or more of a Group IIA element, a Group IIIA element, a Group IVA element, and a transition metal element;

[0094] The intermediate product is mixed with a carbon source in a solvent, dried, and sintered to obtain a positive electrode material.

[0095] Compared with other positive electrode materials, the conductivity of lithium manganese iron phosphate positive electrode material is poor, mainly because its structure contains an insulator with a spin exchange band gap of 0.2eV and a semiconductor with a crystal field band gap of 0.3eV. The commonly used coating method cannot solve this problem, and it is easy to cause problems such as material cracking and coating layer falling off, resulting in poor electrical performance of the battery.

[0096] Although the mechanism is still unclear, the applicant unexpectedly discovered that the present application uses a precursor containing lithium manganese iron phosphate, a phosphorus source and a carbon source to prepare the positive electrode material through a two-step method, which can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of cracking of the positive electrode material and the shedding of the coating layer, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0097] In some embodiments, in the step of preparing the intermediate product, a precursor, a phosphorus source, and a source of a doping element are mixed in a solvent, dried, and sintered to obtain an intermediate product; wherein the doping element independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0098] Therefore, introducing doping elements when preparing the coating layer can improve the conductivity of the positive electrode material and improve the specific capacity, storage performance and cycle performance of the battery.

[0099] Another embodiment of the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0100] A precursor, a phosphorus source, and a carbon source are mixed in a solvent, dried, and sintered to obtain a positive electrode material; wherein the precursor includes lithium manganese iron phosphate with or without doping elements, and the doping elements include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

[0101] Although the mechanism is still unclear, the applicant unexpectedly discovered that the present application uses a precursor containing lithium manganese iron phosphate, a phosphorus source and a carbon source to prepare the positive electrode material through a one-step method, which can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of cracking of the positive electrode material and the shedding of the coating layer, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0102] In some embodiments, a precursor, a phosphorus source, a carbon source, and a source of a doping element are mixed in a solvent, dried, and sintered to obtain a positive electrode material; wherein the doping element independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0103] Therefore, introducing doping elements when preparing the coating layer can improve the conductivity of the positive electrode material and improve the specific capacity, storage performance and cycle performance of the battery.

[0104] In some embodiments, the positive electrode material includes a core and a coating layer covering the core; the core includes LiFe x1 Mn y1 M 1-x1-y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2PO4 and carbon; wherein, 0<x1<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0<y1<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0≤1-x1-y1<1 (for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0≤z≤1.5 (for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1. 3, 1.4, 1.5 or any range consisting of the above values), 0≤x2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values), 0≤y2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values), 0≤1-x2-y2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values); the M element in the core and the coating layer independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0105] In some embodiments, the molar ratio of the lithium manganese iron phosphate with or without doping elements in the precursor to the phosphorus element in the phosphorus source is 1:0.2-1:0.00001, for example, 1:0.2, 1:0.1, 1:0.05, 1:0.01, 1:0.005, 1:0.001, 1:0.0005, 1:0.0001, 1:0.00005, 1:0.00001 or a range consisting of any of the above values; and / or,

[0106] The weight ratio of the lithium manganese iron phosphate containing or not containing doping elements to the carbon source in the precursor is 1:1.2-1:0.0005, and can be 1:1.2-1:0.005, for example, 1:1.2, 1:1.1, 1:1, 1:0.5, 1:0.1, 1:0.05, 1:0.01, 1:0.005, 1:0.001, 1:0.0005 or a range consisting of any of the above values; and / or,

[0107] The molar ratio of the lithium manganese iron phosphate containing or not containing the doping element in the precursor to the doping element in the source of the doping element is 1:0.3-1:0.00001, which can be optionally 1:0.08-1:0.04, for example, 1:0.3, 1:0.1, 1:0.08, 1:0.06, 1:0.04, 1:0.02, 1:0.01, 1:0.005, 1:0.001, 1:0.0001, 1:0.00001 or a range consisting of any of the above values.

[0108] Therefore, the use of the above-mentioned raw material ratio is conducive to preparing a positive electrode material with stable structure and high conductivity, so as to improve the specific capacity, storage performance and cycle performance of the battery.

[0109] In some embodiments, the mixing temperature is independently 10°C-60°C, such as 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or any range thereof; and / or,

[0110] The mixing time is independently 5 min to 30 hours, optionally 5 min to 20 hours, more optionally 0.5 hour to 12 hours, for example 5 min, 10 min, 0.5 hour, 1 hour, 2 hours, 3 hours, 5 hours, 7 hours, 8 hours, 10 hours, 12 hours, 14 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours, 25 hours, 26 hours, 28 hours, 30 hours or a range consisting of any of the above values; and / or,

[0111] The mixing is performed by grinding; and / or,

[0112] The sintering temperature is independently 150°C-1000°C, optionally 200°C-900°C, more optionally 400°C-900°C, for example 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C or any range thereof; and / or,

[0113] The sintering time is independently 3-20 hours, for example, 3, 4, 5, 7, 9, 10, 12, 14, 15, 16, 18, 19, 20 hours or any range thereof; and / or,

[0114] The sintering is independently carried out in an inert atmosphere; and / or,

[0115] The drying temperature is independently 150°C to 550°C, such as 150°C, 200°C, 300°C, 400°C, 500°C, 550°C or any range thereof; and / or,

[0116] The drying is performed by oven drying or spray drying.

[0117] The above-mentioned mixing conditions are conducive to improving the performance of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0118] The above-mentioned sintering conditions are conducive to making the coating layer firmly coated on the surface of the core, improving the structural stability of the positive electrode material and also improving the conductivity of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0119] In some embodiments, in the step of preparing the positive electrode material, before drying, the obtained mixture is passed through a 350-450 mesh sieve, for example, 350 mesh, 400 mesh, 450 mesh, or a range consisting of any of the above values, and the sieved portion is collected; and / or,

[0120] In the step of preparing the positive electrode material, after sintering, the sintered product is crushed and optionally sieved; and / or,

[0121] The phosphorus source includes one or more of phosphoric acid, phosphates, monohydrogen phosphates, and dihydrogen phosphates, and can be selected from one or more of phosphoric acid, ferric phosphate, ferrous phosphate, ferrous ammonium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate; and / or,

[0122] The carbon source includes one or more of an organic carbon source and an inorganic carbon source, and can be selected from one or more of citric acid, glucose, sucrose, polyvinyl alcohol, polypyrrole, polyethylene glycol, asphalt, anthracene, and aniline; and / or,

[0123] The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

[0124] Therefore, in the step of preparing the positive electrode material, controlling the particle size of the insoluble matter in the mixture by screening is beneficial to improving the particle uniformity and structural stability of the positive electrode material, thereby improving the specific capacity, storage performance and cycle performance of the battery.

[0125] In some embodiments, the precursor is prepared by the following steps:

[0126] reacting a lithium source, a manganese source, an iron source and a phosphorus source in a solvent, separating the solid and the liquid, and collecting a solid phase;

[0127] The solid phase is dried and sintered to obtain a precursor.

[0128] In some embodiments, in the step of preparing the solid phase, a lithium source, a manganese source, an iron source, a phosphorus source and a source of a doping element are reacted in a solvent, the solid and liquid are separated, and the solid phase is collected; wherein the doping element includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0129] Therefore, introducing doping elements into the precursor is beneficial to further improve the conductivity and structural stability of the positive electrode material, thereby improving the battery's specific capacity, storage performance and cycle performance.

[0130] In some embodiments, the precursor includes LiFe x3 Mn y3 M 1-x3-y3 PO4, wherein 0<x3<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or a range consisting of any of the above values), 0<y3<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or a range consisting of any of the above values), 0≤1-x3-y3<1 (for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or a range consisting of any of the above values), and the M element includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0131] In some embodiments, the doping elements independently include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or,

[0132] The M elements in the core, the coating layer and the precursor independently include one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni and B.

[0133] In some embodiments, in the step of preparing the precursor,

[0134] The molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, the phosphorus element in the phosphorus source and the doping element in the source of the doping element is 1:y3:x3:1:(1-x3-y3); and / or,

[0135] The reaction temperature is 20°C-50°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C or any range thereof; and / or,

[0136] The reaction time is 1 minute to 8 hours, optionally 10 minutes to 6 hours, for example 1 minute, 5 minutes, 10 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or a range consisting of any of the above values; and / or,

[0137] The drying temperature is 50°C-200°C, such as 50°C, 100°C, 150°C, 200°C or any range thereof; and / or,

[0138] The drying time is 10 minutes to 5 hours, for example, 10 minutes, 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or any range thereof; and / or,

[0139] The sintering temperature is 150°C-800°C, optionally 200°C-700°C, for example, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 600°C, 650°C, 700°C, 750°C, 800°C or any range thereof; and / or,

[0140] The sintering time is 1-12 hours, for example, 1, 2, 3, 5, 7, 8, 9, 10, 11, 12 hours or any range thereof; and / or,

[0141] The sintering is performed in an inert atmosphere.

[0142] The above reaction conditions are conducive to improving the material properties of the precursor, and then improving the performance of the positive electrode material, thereby enhancing the specific capacity, storage performance and cycle performance of the battery.

[0143] The above-mentioned sintering conditions are conducive to improving the material properties of the precursor, and then improving the performance of the positive electrode material, thereby enhancing the specific capacity, storage performance and cycle performance of the battery.

[0144] In some embodiments, in the step of preparing the precursor,

[0145] The solid-liquid separation is performed by filtration or centrifugation; and / or,

[0146] Before drying, washing the solid phase; and / or,

[0147] crushing the dried material before sintering; and / or,

[0148] The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt, and organic acid salt, and can be selected from one or more of lithium hydroxide, lithium oxide, lithium carbonate, lithium acetate, lithium oxalate, lithium phosphate, and lithium chloride; and / or,

[0149] The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of manganese; and / or,

[0150] The iron source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of iron; and / or,

[0151] The phosphorus source includes one or more of phosphoric acid, phosphates, hydrogen phosphates, and dihydrogen phosphates, and can be selected from one or more of phosphoric acid, ferric phosphate, ferrous phosphate, ferrous ammonium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and lithium phosphate; and / or,

[0152] The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

[0153] [Cathode material]

[0154] One embodiment of the present application provides a positive electrode material, comprising a core and a coating layer covering the core; the core comprises LiFe x1 Mn y1 M 1-x1-y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2PO4 and carbon; wherein, 0<x1<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0<y1<1 (for example, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0≤1-x1-y1<1 (for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range thereof), 0≤z≤1.5 (for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1. 3, 1.4, 1.5 or any range consisting of the above values), 0≤x2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values), 0≤y2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values), 0≤1-x2-y2≤1 (for example, 0, 0.01, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range consisting of the above values); the M element in the core and the coating layer independently includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

[0155] Therefore, the present application can effectively reduce the stress of the positive electrode material during the expansion and contraction process, reduce the occurrence of positive electrode material cracking and coating layer shedding, improve the structural stability and conductivity of the positive electrode material, and improve the battery's specific capacity, storage performance and cycle performance.

[0156] In some embodiments, the M elements in the core and the coating layer independently include one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or,

[0157] The average diameter of the core is 0.04-8.5 μm, for example, 0.04 μm, 0.08 μm, 0.1 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 2 μm, 2.1 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 8.5 μm or a range consisting of any of the above values; and / or,

[0158] The average thickness of the coating layer is 0.5-700 nm, optionally 1-500 nm, for example, 0.5 nm, 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 70 nm, 100 nm, 150 nm, 200 nm, 240 nm, 260 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 700 nm or a range consisting of any of the above values; and / or,

[0159] In the coating layer, the Li z Fe x2 Mn y2 M 1-x2-y2 The weight ratio of PO4 to the carbon is 1:10 6 -1:0.002, for example 1:10 6 , 1:5, 1:4.5, 1:4.2, 1:4, 1:3, 1:2.5, 1:2.1, 1:1.98, 1:1.96, 1:1.91, 1:1.5, 1:1, 1:0.53, 1:0.4, 1:0.3, 1:0.1, 1:0.05, 1:0.021, 1:0.01, 1:0.005, 1:0.002 or a range consisting of any of the above values; and / or,

[0160] The powder resistivity of the positive electrode material is ≤403Ω·cm, optionally ≤300Ω·cm, and more optionally ≤250Ω·cm; and / or,

[0161] The Dv50 particle size of the positive electrode material is 0.1-10 μm, which can be selected from 1-3 μm, such as 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 2.9 μm, 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range consisting of any of the above values.

[0162] The average diameter of the core and the average thickness of the coating layer are tested by conventional methods in the field; for example, the positive electrode material particles are scanned by a TEM-EDS combination to determine the boundary line between the core and the shell, and the distance from the core to the boundary line and the distance from the core to the outermost edge of the shell are measured in the projection electron microscope image. The random orientation measurement is repeated 50 times, and then a total of 50 positive electrode material particles are taken to repeat the above test. Twice the average value of the distance from the core to the boundary line is the average diameter of the core, and the average value of the difference between the distance from the core to the outermost edge of the shell and the distance from the core to the boundary line is the average thickness of the shell.

[0163] The Dv50 particle size is measured using conventional methods in the art; for example, a sample is taken, the sample is completely dispersed, and the Dv50 particle size is measured using a laser particle size analyzer.

[0164] The powder resistivity is tested using conventional methods in the art; for example, a sample is placed in a four-probe resistivity tester, and the forward resistivity and reverse resistivity of the sample are tested respectively, and the average of the two is taken as the powder resistivity of the sample; optionally, the test pressure is adjusted to 7.85 MPa.

[0165] [Positive electrode]

[0166] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned method.

[0167] The battery's charge and discharge processes involve the intercalation and deintercalation of lithium, leading to different molar Li contents at different discharge states. The molar Li contents listed in this application for cathode materials refer to the initial state of the material, i.e., the state before addition of the materials. When the cathode material is used in a battery system, the molar Li content will change after charge and discharge cycles.

[0168] In the list of positive electrode materials in this application, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0169] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0170] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0171] In some embodiments, the positive electrode active material may also include at least one of the following materials: lithium transition metal oxides and modified compounds thereof. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include but are not limited to lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and at least one of its modified compounds, etc.

[0172] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0173] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0174] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0175] [Negative electrode]

[0176] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0177] As an 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 either or both of the two opposite surfaces of the negative electrode current collector.

[0178] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0179] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0180] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0181] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0183] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0184] [Electrolytes]

[0185] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0186] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0187] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0188] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0189] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0190] [Isolation film]

[0191] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0192] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0193] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0194] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0195] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0196] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The battery cell 5 is a square structure as an example.

[0197] In some embodiments, reference Figure 2 , the outer packaging 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 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0198] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain one or more battery cells. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0199] Figure 3 4 is an example of a battery module. Figure 3In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of battery cells 5 may further be fixed by fasteners.

[0200] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0201] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0202] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0203] In addition, the present application also provides an electrical device, which includes at least one of the battery cells, battery modules, or battery packs provided in the present application. The battery cells, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0204] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0205] Figure 6 This is an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells in this device, a battery pack or battery module can be used.

[0206] [Example]

[0207] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0208] Example 1

[0209] (1) Preparation of precursor:

[0210] 766g LiOH, 3325g NH4H2PO4, 1499g MnSO4, and 1945g FeSO4 were put into 14kg pure water, and then 191.2g NiO, 834.6g MnO2, and 128.0g Fe2O3 were added. The mixture was stirred and reacted at 25°C for 60 minutes, and the precipitate was collected by filtration. The precipitate was washed with pure water, filtered, dried at 100°C for 120 minutes, and crushed to obtain a dry powder. The dry powder was then placed in a nitrogen atmosphere sintering furnace and sintered at a constant temperature of 500°C for 3 hours to obtain a precursor.

[0211] (2) Preparation of positive electrode materials:

[0212] ① Put all the precursors and 241g of iron phosphate into 14kg of deionized water, grind them with a sand mill at 25℃ for 2 hours to obtain a slurry, filter, collect the precipitate, and dry it at 500℃ for 3h to obtain a dry powder; place the dry powder in a nitrogen atmosphere furnace at 500℃ and sinter it for 3 hours, then cool it down and take it out.

[0213] ② The prepared powder and 1 kg of glucose were added to 14 kg of deionized water and ground at 25°C using a sand mill for 2 hours to obtain a slurry; part of the slurry that passed through a 400-mesh sieve was collected and spray-dried at 300°C to obtain a dry powder; the dry powder was placed in a nitrogen atmosphere furnace at 800°C and sintered for 6 hours, then cooled and taken out, and crushed until it could completely pass through an 800-mesh sieve to obtain the positive electrode material.

[0214] (3) Preparation of positive electrode sheet:

[0215] The positive electrode material, polyvinylidene fluoride, conductive carbon black and N-methylpyrrolidone are dissolved in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 95:2.5:2.5:100, and the mixture is thoroughly stirred and evenly mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed and cut to obtain the positive electrode sheet.

[0216] (4) Preparation of negative electrode sheet:

[0217] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in deionized water in a weight ratio of 95.5:1.5:1.8:1.2, and the mixture is fully stirred and mixed to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain the negative electrode sheet.

[0218] (5) Isolation film: Polypropylene film is used.

[0219] (6) Preparation of electrolyte:

[0220] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1 mol / L.

[0221] (7) Preparation of button cells:

[0222] The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the above-prepared electrolyte is added. After packaging, standing, formation, aging and other processes, a secondary battery is obtained.

[0223] The secondary battery preparation methods of Example 2-43 and Comparative Example 1-2 are similar to those of Example 1, and the different product parameters are detailed in Table 1-2.

[0224] Comparative Example 1

[0225] (1) Preparation of precursor: same as step (1) in Example 1.

[0226] (2) Preparation of positive electrode materials:

[0227] All the precursors were put into 14 kg of deionized water and ground with a sand mill at 25°C for 2 hours to obtain a slurry. The precipitate was collected by filtration and dried at 500°C for 3 hours to obtain a dry powder. The dry powder was placed in a nitrogen atmosphere furnace at 500°C and sintered for 3 hours, then cooled and taken out.

[0228] The prepared powder and 1 kg of glucose were added to 14 kg of deionized water and ground at 25°C with a sand mill for 2 hours to obtain a slurry; part of the slurry that passed through a 400-mesh sieve was collected and spray-dried at 300°C to obtain a dry powder; the dry powder was placed in a nitrogen atmosphere furnace at 800°C and sintered for 6 hours, then cooled and taken out, and crushed into a size that could completely pass through an 800-mesh sieve to obtain the positive electrode material.

[0229] The rest is the same as in Example 1.

[0230] Comparative Example 2

[0231] (1) Preparation of precursor: same as step (1) in Example 1.

[0232] (2) Preparation of positive electrode materials:

[0233] All the precursors and 1 kg of glucose were put into 14 kg of deionized water and ground with a sand mill at 25°C for 2 hours to obtain a slurry; part of the slurry that passed through a 400-mesh sieve was collected and spray-dried at 300°C to obtain a dry powder; the dry powder was placed in a nitrogen atmosphere furnace at 800°C and sintered for 6 hours, then cooled and taken out, and crushed into a size that could completely pass through an 800-mesh sieve to obtain the positive electrode material.

[0234] The rest is the same as in Example 1.

[0235]

[0236]

[0237]

[0238]

[0239]

[0240]

[0241]

[0242] Materials and battery testing

[0243] (1) Testing of the chemical formula of the precursor, the coating composition of the cathode material, and the element ratio:

[0244] Weigh 0.2 g of the precursor or cathode material into a 100 mL beaker, add 10 mL of 10% w / w nitric acid solution, heat and digest at 120°C for 0.5 hours, and then dilute to volume with a 100 mL volumetric flask; then use a pipette to transfer 1 mL to a 100 mL volumetric flask and dilute to volume to obtain the test solution.

[0245] An inductively coupled plasma optical emission spectrometer (ICP-OES, instrument brand: Agilent 5800) is used to determine the mass fractions of lithium, manganese, iron, phosphorus, and doping elements in the test solution; the molar fraction of each element in the precursor is calculated based on the mass fraction of each element in the test solution of the precursor, thereby determining the chemical formula and element molar ratio of the precursor; the molar fraction of each element in the positive electrode material is calculated based on the mass fraction of each element in the test solution of the positive electrode material, and the molar fraction of each element in the precursor is deducted to obtain the elemental composition of the coating layer, thereby calculating the element molar ratio;

[0246] Weigh 0.1g of positive electrode material, add 1.5g of flux metal tungsten particles and mix, put it into a high-frequency infrared carbon-sulfur analyzer for sintering and test the mass ratio of carbon in the positive electrode material.

[0247] (2) Test of the average diameter of the core and the average thickness of the coating:

[0248] The positive electrode material particles (with a particle size of Dv50 ± 0.1 μm) were scanned by a TEM-EDS combination instrument to determine the boundary line between the core and the shell. The distance from the core to the boundary line and the distance from the core to the outermost edge of the shell were measured in the projection electron microscope image. The random orientation measurement was repeated 50 times. Then, a total of 50 positive electrode material particles were taken to repeat the above test. Twice the average value of the distance from the core to the boundary line was the average diameter of the core, and the average value of the difference between the distance from the core to the outermost edge of the shell and the distance from the core to the boundary line was the average thickness of the shell.

[0249] (3) Dv50 particle size test of positive electrode material:

[0250] Take an appropriate amount of sample, add 20 mL of deionized water, and ultrasonically treat for 5 minutes (53 KHz, 120 W) to completely disperse the sample. Use a laser particle size analyzer (MasterSizer 2000) to measure the Dv50 particle size of the material.

[0251] (4) Test of powder resistivity of positive electrode material:

[0252] Weigh 1g of sample and place it in a mold. Then place the mold in a four-probe resistivity tester and adjust the pressure to 7.85MPa. After the mold height and pressure are stable, test the forward resistivity and reverse resistivity of the sample respectively, and take the average of the two as the powder resistivity of the sample.

[0253] (5) Battery charging capacity and discharge capacity test:

[0254] Shenzhen Xinweier battery testing system was used to cycle the button batteries at a charge and discharge rate of 0.1C. The test temperature was 25.0℃, and the charge and discharge voltage was 2.0V-4.3V. The charge capacity in grams was obtained by dividing the charge capacity in the first cycle by the mass of the positive electrode material, and the discharge capacity in grams was obtained by dividing the discharge capacity in the first cycle by the mass of the positive electrode material.

[0255] (6) Test of battery cycle capacity retention at 25°C:

[0256] Shenzhen Xinweier battery testing system was used to cycle the button batteries at a charge and discharge rate of 1C for 2000 times. The test temperature was 25.0℃ and the charge and discharge voltage was 2.0V-4.3V. The capacity retention rate was obtained by dividing the discharge capacity of the last cycle by the discharge capacity of the first cycle.

[0257] (7) Battery storage performance test at 60°C:

[0258] Using the Shenzhen Xinweier battery testing system, button-type batteries were initially charged and discharged at a 1C charge / discharge rate, with a charge / discharge voltage ranging from 2.0V to 4.3V. After charging, the batteries were placed in a 60°C constant-temperature oven. Every seven days, the batteries were removed and tested at a 1C charge / discharge rate. After charging, they were placed in the 60°C constant-temperature oven again, repeating this cycle for 420 days. The capacity retention rate was calculated by dividing the final measured discharge capacity by the discharge capacity of the first cycle.

[0259] Table 3: Test results of positive electrode materials and battery performance of Examples 1-43 and Comparative Examples 1-2

[0260]

[0261]

[0262] According to the above results, we can know that:

[0263] Compared with the positive electrode material prepared in Comparative Example 1 without adding a phosphorus source, the batteries made from the positive electrode materials of Examples 1-20, 23-27, and 30-43 of the present application have higher charge and discharge specific capacity, higher cycle capacity retention rate, and better storage performance.

[0264] Compared with Comparative Example 2 in which no phosphorus source is added and the positive electrode material is prepared in one step, the batteries made from the positive electrode materials of Examples 1-20, 23-27, and 30-43 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0265] Compared with Example 31 which uses a higher sintering temperature in the first step and Example 32 which uses a lower sintering temperature in the second step, the batteries made with the positive electrode materials of Examples 1 and 6-7 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0266] Compared with Example 33 which uses a higher second-step sintering temperature and Example 34 which uses a lower second-step sintering temperature, the batteries made with the positive electrode materials of Examples 1 and 8-9 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0267] Compared with the shorter mixing time in step 1 of Example 35 and the longer mixing time in step 1 of Example 36, the batteries made from the positive electrode materials of Examples 1 and 10-11 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0268] Compared with the shorter mixing time in step 2 of Example 37 and the longer mixing time in step 2 of Example 38, the batteries made from the positive electrode materials of Examples 1 and 12-13 of the present application have higher charging capacity in grams, higher cycle capacity retention rate, and better storage performance.

[0269] Compared with the use of a longer reaction time when preparing the precursor in Example 39 and the use of a shorter reaction time when preparing the precursor in Example 40, the batteries made from the positive electrode materials of Examples 1 and 16-17 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0270] Compared with the lower sintering temperature used in preparing the precursor in Example 41 and the higher sintering temperature used in preparing the precursor in Example 42, the batteries made from the positive electrode materials of Examples 1 and 18-19 of the present application have higher charge and discharge gram capacity, higher cycle capacity retention rate, and better storage performance.

[0271] Compared with the higher weight ratio of precursor compound to carbon source used in Example 43, the batteries made with the positive electrode materials of Examples 1, 4-5, and 27 of the present application have higher charge and discharge capacity, higher cycle capacity retention rate, and better storage performance.

[0272] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a positive electrode material, comprising the following steps: The precursor and the phosphorus source are mixed in a solvent, dried, and sintered to obtain an intermediate product; wherein, The precursor includes lithium manganese iron phosphate with or without doping elements, wherein the doping elements include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements; The intermediate product is mixed with a carbon source in a solvent, dried, and sintered to obtain a positive electrode material.

2. A method for preparing a positive electrode material, comprising the following steps: The precursor, phosphorus source and carbon source are mixed in a solvent, dried and sintered to obtain a positive electrode material; wherein, The precursor includes lithium manganese iron phosphate with or without doping elements, and the doping elements include one or more of group II A elements, group III A elements, group IVA elements, and transition metal elements.

3. The method according to claim 1, wherein In the step of preparing the intermediate product, a precursor, a phosphorus source and a source of a doping element are mixed in a solvent, dried and sintered to obtain an intermediate product; wherein the doping element independently includes one or more of group IIA elements, group IIIA elements, group IVA elements and transition metal elements.

4. The method according to claim 2, wherein: The precursor, phosphorus source, carbon source and source of doping element are mixed in a solvent, dried and sintered to obtain a positive electrode material; wherein the doping element independently includes one or more of group IIA elements, group IIIA elements, group IVA elements and transition metal elements.

5. The method according to any one of claims 1 to 4, wherein The positive electrode material includes a core and a coating layer covering the core; the core includes LiFe x1 Mn y1 M 1-x1-y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2 PO4 and carbon; wherein, 0<x1<1, 0<y1<1, 0≤1-x1-y1<1, 0≤z≤1.5, 0≤x2≤1, 0≤y2≤1, 0≤1-x2-y2≤1; the M elements in the core and the coating layer independently include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

6. The method according to any one of claims 1 to 5, wherein The molar ratio of the lithium manganese iron phosphate containing or not containing a doping element in the precursor to the phosphorus element in the phosphorus source is 1:0.2-1:0.00001; and / or, The weight ratio of lithium manganese iron phosphate containing or not containing doping elements to the carbon source in the precursor is 1:1.2-1:0.0005; and / or, The molar ratio of the lithium manganese iron phosphate containing or not containing the doping element in the precursor to the doping element in the source of the doping element is 1:0.3-1:0.00001.

7. The method according to any one of claims 1 to 6, wherein The mixing temperature is independently 10°C to 60°C; and / or, The mixing time is independently 5 min to 30 hours; and / or, The mixing is performed by grinding; and / or, The sintering temperature is independently 150°C-1000°C; and / or, The sintering time is independently 3-20 hours; and / or, The sintering is independently carried out in an inert atmosphere; and / or, The drying temperature is independently 150°C to 550°C; and / or, The drying is performed by oven drying or spray drying.

8. The method according to any one of claims 1 to 7, wherein In the step of preparing the positive electrode material, before drying, the obtained mixture is passed through a 350-450 mesh sieve, and the sieved portion is collected; and / or, In the step of preparing the positive electrode material, after sintering, the sintered product is crushed; and / or, The phosphorus source includes one or more of phosphoric acid, phosphate, monohydrogen phosphate, and dihydrogen phosphate; and / or, The carbon source includes one or more of an organic carbon source and an inorganic carbon source; and / or, The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

9. The method according to any one of claims 1 to 8, wherein The precursor is prepared by the following steps: reacting a lithium source, a manganese source, an iron source and a phosphorus source in a solvent, separating the solid and the liquid, and collecting a solid phase; The solid phase is dried and sintered to obtain a precursor.

10. The method according to claim 9, wherein: In the step of preparing the solid phase, a lithium source, a manganese source, an iron source, a phosphorus source and a source of a doping element are reacted in a solvent, the solid and liquid are separated, and the solid phase is collected; wherein the doping element includes one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

11. The method according to any one of claims 1 to 10, wherein The precursor includes LiFe x3 Mn y3 M 1-x3- y3 PO4, wherein 0<x3<1, 0<y3<1, 0≤1-x3-y3<1, and the M element includes one or more of Group IIA elements, Group IIIA elements, Group IVA elements, and transition metal elements.

12. The method according to any one of claims 1 to 11, wherein The doping elements independently include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or The M elements in the core, the coating layer and the precursor independently include one or more elements of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni and B.

13. The method according to any one of claims 9 to 12, wherein: In the steps of preparing the precursor: The molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, the phosphorus element in the phosphorus source and the doping element in the source of the doping element is 1:y3:x3:1:(1-x3-y3); and / or, The reaction temperature is 20°C-50°C; and / or, The reaction time is 1 minute to 8 hours; and / or, The drying temperature is 50°C-200°C; and / or, The drying time is 10 minutes to 5 hours; and / or, The sintering temperature is 150°C-800°C; and / or, The sintering time is 1-12 hours; and / or, The sintering is performed in an inert atmosphere.

14. The method according to any one of claims 9 to 13, wherein In the step of preparing the precursor, The solid-liquid separation is performed by filtration or centrifugation; and / or, Before drying, washing the solid phase; and / or, crushing the dried material before sintering; and / or, The lithium source includes one or more of lithium hydroxide, oxide, inorganic acid salt and organic acid salt; and / or, The manganese source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of manganese; and / or, The iron source includes one or more of organic acid salts, inorganic acid salts, oxides, and hydroxides of iron; and / or, The phosphorus source includes one or more of phosphoric acid, phosphate, hydrogen phosphate, and dihydrogen phosphate; and / or, The source of the doping element includes one or more of hydroxides, oxides, acids, and salts of the doping element.

15. A positive electrode material comprising a core and a coating layer covering the core; the core comprising LiFe x1 Mn y1 M 1-x1- y1 PO4, the coating layer includes Li z Fe x2 Mn y2 M 1-x2-y2 PO4 and carbon; among them, 0<x1<1, 0<y1<1, 0≤1-x1-y1<1, 0≤z≤1.5, 0≤x2≤1, 0≤y2≤1, 0≤1-x2-y2≤1; the M elements in the core and the coating layer independently include one or more of group IIA elements, group IIIA elements, group IVA elements, and transition metal elements.

16. The positive electrode material according to claim 15, wherein The M elements in the core and the coating layer independently include one or more elements selected from the group consisting of Mg, Ti, V, Si, Cr, Mn, Fe, Co, Ni, and B; and / or The average diameter of the core is 0.04-8.5 μm; and / or, The average thickness of the coating layer is 0.5-700 nm; and / or, In the coating layer, the Li z Fe x2 Mn y2 M 1-x2-y2 The weight ratio of PO4 to the carbon is 1:10 6 -1:0.002; and / or, The powder resistivity of the positive electrode material is ≤403Ω·cm; and / or, The Dv50 particle size of the positive electrode material is 0.1-10 μm.

17. A positive electrode sheet comprising the positive electrode material prepared by the method according to any one of claims 1 to 14 or the positive electrode material according to claim 15 or 16.

18. A battery comprising the positive electrode material prepared by the method according to any one of claims 1 to 14, the positive electrode material according to claim 15 or 16, or the positive electrode sheet according to claim 17.

19. An electrical device comprising the battery according to claim 18.

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