Preparation method for positive electrode material, positive electrode material, positive electrode sheet, battery, and electric device

Abstract

The present application relates to the technical field of lithium batteries, and in particular to a preparation method for a positive electrode material, a positive electrode material, a positive electrode sheet, a battery, and an electric device. The method of the present application comprises: mixing a nitrate salt and a precursor in a solvent, and roasting to obtain a positive electrode material, wherein the precursor comprises LiFe(1-y)MyPO4, wherein M comprises one or more metal elements from Group IVB, Group VB, Group VIII, Group IIA, Group IIIA, Group IVA, and Group VA, and y is 0-0.1. The method of the present application improves the electronic conductivity of the positive electrode material, and the specific capacity and the cycle stability of the battery.

Description

Positive electrode material preparation method, positive electrode material, positive electrode sheet, battery and electrical device

[0001] This application is based on and claims priority to the Chinese patent application with application number 202311840081.1 and application date December 28, 2023. All contents of the application are hereby introduced as a whole into this application. Technical Field

[0002] The present application relates to the technical field of lithium 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

[0003] 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 stations, 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, cycle performance, and other aspects. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is 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 method of this application improves the electronic conductivity of the positive electrode material and improves the specific capacity and cycle stability of the battery.

[0005] 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:

[0006] The nitrate and the precursor are mixed in a solvent and calcined to obtain a positive electrode material; wherein the precursor includes LiFe (1-y) M y PO4, wherein the M comprises one or more metal elements of Group IVB, Group VB, Group VIII, Group IIA, Group IIIA, Group IVA and Group VA, and the y is 0-0.1.

[0007] Therefore, in the present application, the nitrate is uniformly dispersed on the surface of the precursor. During the roasting process, the oxygen generated by the thermal decomposition of the nitrate in situ oxidizes the surface of the lithium iron phosphate precursor, forming an oxide layer of uniform thickness on its surface, the main components of which are Fe2O3 and Li3Fe2(PO4)3; optionally, the metal oxide generated by the thermal decomposition of the nitrate is coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the positive electrode material and improving the specific capacity and cycle stability of the battery.

[0008] In any embodiment, the positive electrode material comprises a core and a coating layer; the core comprises LiFe (1-y) My PO4, wherein the M includes one or more metal elements of group IVB, group VB, group VIII, group IIA, group IIIA, group IVA and group VA, and the y is 0-0.1; the coating layer includes metal oxide and Li3Fe2(PO4)3, wherein the metal oxide includes Fe2O3.

[0009] In any embodiment, the metal oxide further comprises one or more of transition metal oxides other than iron, Group IIA metal oxides, and Group IIIA metal oxides.

[0010] In any embodiment, the metal oxide further comprises one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3.

[0011] As a result, the oxygen generated by the thermal decomposition of nitrate oxidizes the surface of the precursor to form an oxide layer including Li3Fe2(PO4)3 and Fe2O3, and the metal oxides generated by the thermal decomposition of nitrate are mixed with the oxide layer, thereby improving the electronic conductivity of the positive electrode material and improving the specific capacity and cycle stability of the battery.

[0012] In any embodiment, M comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or

[0013] The y is 0.001-0.1.

[0014] In any embodiment, the calcination temperature is 300° C.-600° C., optionally 350° C.-600° C.; and / or,

[0015] The calcination time is 1-10 hours; and / or,

[0016] The calcination is carried out in an inert atmosphere; and / or,

[0017] The heating rate during the calcination process is 1-15°C / min, and can be optionally 4-10°C / min.

[0018] Therefore, calcination under the above conditions is conducive to the full thermal decomposition of nitrate on the surface of the precursor to produce oxygen and metal oxides, which in turn helps to fully utilize the generated oxygen to oxidize the surface of the precursor to form an oxide layer, and mix the generated metal oxide with the oxide layer, thereby further improving the electronic conductivity of the positive electrode material and further improving the specific capacity and cycle stability of the battery.

[0019] In any embodiment, the nitrate comprises one or more of metal nitrate and ammonium nitrate.

[0020] In any embodiment, the metal nitrate comprises one or more of a transition metal nitrate, a Group IIA metal nitrate, and a Group IIIA metal nitrate; and / or,

[0021] The metal nitrate includes one or more of iron nitrate, copper nitrate, zinc nitrate, magnesium nitrate, manganese nitrate, nickel nitrate, and aluminum nitrate; and / or,

[0022] The metal nitrate may be dissolved in the solvent.

[0023] In any embodiment, the weight ratio of the nitrate to the precursor is 0.005:1-0.10:1, and can be optionally 0.01:1-0.06:1.

[0024] Therefore, the use of the above-mentioned nitrate types and ratios of nitrate to precursor is conducive to the oxidation of the precursor surface by oxygen generated by the thermal decomposition of nitrate to form an oxide layer that is conducive to the electrochemical performance. The metal oxides generated by the thermal decomposition of nitric acid work together with the oxide layer to improve the electronic conductivity and interface stability of the positive electrode material, thereby improving the specific capacity and cycle stability of the battery.

[0025] In any embodiment, the mixing is performed by ball milling.

[0026] In any embodiment, the rotation speed of the ball mill is 300-500 r / min, optionally 350-400 r / min; and / or,

[0027] The ball milling time is 1-10 hours, and can be optionally 1-4 hours.

[0028] Therefore, mixing under the above-mentioned ball milling conditions is beneficial to reducing the larger grains formed by nitrate recrystallization, improving the uniform distribution of nitrate on the surface of the precursor, and is conducive to forming a complete and uniform oxide layer, thereby ensuring that the positive electrode material has a relatively complete electronic conduction network and promoting the stable performance of its electrochemical properties.

[0029] In any embodiment, the nitrate is first dissolved in the solvent, then mixed with the precursor, and calcined.

[0030] This is beneficial to improving the uniformity of nitrate distribution on the surface of the precursor, thereby facilitating the formation of a coating layer with uniform thickness.

[0031] In any embodiment, after mixing and before calcining, the method further comprises drying the obtained mixture;

[0032] Wherein, the drying temperature is 80° C.-120° C.; and / or the drying time is 2-12 hours.

[0033] In any embodiment, the Dv50 particle size of the precursor is 0.3-5 μm, optionally 0.5-2 μm; and / or,

[0034] The precursor further comprises carbon, and the carbon content in the precursor is ≤0.1 wt %; and / or,

[0035] The solvent includes one or more of water and organic solvents, and can be selected from one or more of water, acetone, and alcohol, and can be selected from one or more of water, acetone, ethanol, isopropanol, and methanol.

[0036] The second aspect of the present application also provides a positive electrode material, including a core and a coating layer; the core includes LiFe (1-y) M y PO4, wherein the M includes one or more metal elements of group IVB, group VB, group VIII, group IIA, group IIIA, group IVA and group VA, and the y is 0-0.1; the coating layer includes metal oxide and Li3Fe2(PO4)3, wherein the metal oxide includes Fe2O3.

[0037] Therefore, in the present application, the nitrate is uniformly dispersed on the surface of the precursor. During the roasting process, the oxygen generated by the thermal decomposition of the nitrate in situ oxidizes the surface of the lithium iron phosphate precursor, forming an oxide layer of uniform thickness on its surface, the main components of which are Fe2O3 and Li3Fe2(PO4)3; optionally, the metal oxide generated by the thermal decomposition of the nitrate is coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the positive electrode material and improving the specific capacity and cycle stability of the battery.

[0038] In any embodiment, the metal oxide further comprises one or more of a transition metal oxide other than iron, a Group IIA metal oxide, and a Group IIIA metal oxide; and / or,

[0039] The metal oxide further comprises one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3; more optionally, the metal oxide further comprises CuO and ZnO; and / or,

[0040] The metal nitrates corresponding to the transition metal oxides, Group IIA metal oxides and Group IIIA metal oxides can be dissolved in a solvent.

[0041] In any embodiment, the weight ratio of the coating layer to the core is 0.005:1-0.12:1, optionally 0.0074:1-0.12:1, and more optionally 0.02:1-0.07:1.

[0042] In any embodiment, the average thickness of the coating layer is greater than 0 and less than or equal to 15 nm, optionally 0.5-15 nm or greater than 0 and less than or equal to 5 nm, more optionally 1-5 nm; and / or,

[0043] The electronic conductivity of the positive electrode material is greater than or equal to 2×10 -8 S / cm, optional 2×10 -8 -9×10 -6 S / cm; and / or,

[0044] The core further comprises carbon, and the weight content of carbon in the core is ≤0.1%.

[0045] The third aspect of the present application provides a positive electrode sheet, comprising the positive electrode active material prepared by the method of the first aspect of the present application or the positive electrode active material of the second aspect of the present application.

[0046] The fourth aspect of the present application provides a battery, comprising the positive electrode sheet of the third aspect of the present application.

[0047] The fifth aspect of the present application provides an electrical device comprising the battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0049] FIG. 2 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 1 .

[0050] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0051] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0052] FIG. 5 is an exploded view of the battery pack shown in FIG. 4 according to an embodiment of the present application.

[0053] FIG6 is a schematic diagram of an electrical device using a battery cell as a power source according to an embodiment of the present application.

[0054] FIG7 is a Raman spectrum of the surface of the positive electrode material of Example 1 of the present application (500 cm -1 below Raman shift).

[0055] FIG8 is a Raman spectrum of the surface of the positive electrode material of Example 1 of the present application (500 cm -1 above Raman shift).

[0056] FIG9 is an XRD diffraction spectrum of the surface of the positive electrode material of Example 16 of the present application.

[0057] FIG10 is a SEM photograph of the surface of the positive electrode material of Example 1 of the present application.

[0058] FIG11 is a SEM-EDS image of the surface of the positive electrode material of Example 1 of the present application.

[0059] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0060] Below, with appropriate reference to the accompanying drawings, the embodiments of the positive electrode material preparation method, positive electrode material, positive electrode sheet, negative electrode sheet, battery cell, battery module, battery pack and electric device of the present application are specifically disclosed in detail. 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 structure 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.

[0061] " 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.

[0062] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0063] 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.

[0064] 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.

[0065] Unless otherwise specified, the Dv50 particle size in this application refers to the particle size when the cumulative value of volume distribution is 50%.

[0066] [Battery Cell]

[0067] 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.

[0068] 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.

[0069] [Method for preparing positive electrode material]

[0070] One embodiment of the present application provides a method for preparing a positive electrode material, comprising:

[0071] The nitrate and the precursor are mixed in a solvent and calcined to obtain a positive electrode material; wherein the precursor includes LiFe (1-y) M y PO4, wherein the M comprises one or more metal elements of Group IVB, Group VB, Group VIII, Group IIA, Group IIIA, Group IVA and Group VA, and the y is 0-0.1, for example, 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.01, 0.012, 0.015, 0.02, 0.023, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.056, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.098, 0.1 or a range consisting of any of the above values.

[0072] Lithium iron phosphate has poor electronic conductivity, making it difficult to meet the needs of industrial applications. Although the mechanism is still unclear, the applicant unexpectedly discovered that in this application, the nitrate is evenly dispersed on the surface of the precursor. During the roasting process, the oxygen generated by the nitrate pyrolysis in situ oxidizes the surface of the lithium iron phosphate precursor, forming an oxide layer of uniform thickness on its surface, the main components of which are Fe2O3 and Li3Fe2(PO4)3. Optionally, the metal oxide generated by the nitrate pyrolysis is coated on the surface of the precursor and mixed into the oxide layer. This improves the electronic conductivity of the positive electrode material and enhances the specific capacity and cycle stability of the battery.

[0073] In some embodiments, the positive electrode material includes a core and a coating layer; the core includes LiFe (1-y) M y PO4, wherein the M comprises one or more metal elements of Group IVB, Group VB, Group VIII, Group IIA, Group IIIA, Group IVA and Group VA, and the y is 0-0.1, for example, 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.01, 0.012, 0.015, 0.02, 0.023, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.056, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.098, 0.1 or a range consisting of any of the above values; the coating layer comprises a metal oxide and Li3Fe2(PO4)3, wherein the metal oxide comprises Fe2O3.

[0074] In some embodiments, the metal oxide further comprises one or more of a transition metal oxide other than iron, a Group IIA metal oxide, and a Group IIIA metal oxide.

[0075] In some embodiments, the metal oxide further includes one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3, and may optionally further include CuO and ZnO.

[0076] As a result, the oxygen generated by the thermal decomposition of nitrate oxidizes the surface of the precursor to form an oxide layer including Li3Fe2(PO4)3 and Fe2O3, and the metal oxides generated by the thermal decomposition of nitrate are mixed with the oxide layer, thereby improving the electronic conductivity of the positive electrode material and improving the specific capacity and cycle stability of the battery.

[0077] In some embodiments, M comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or

[0078] The y is 0.001-0.1.

[0079] In some embodiments, the calcination temperature is 300°C-600°C, optionally 350°C-600°C, for example, 300°C, 310°C, 330°C, 350°C, 380°C, 400°C, 420°C, 450°C, 480°C, 500°C, 510°C, 530°C, 550°C, 570°C, 600°C or a range consisting of any of the above values; and / or,

[0080] The calcination time is 1-10 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or any range thereof; and / or,

[0081] The calcination is carried out in an inert atmosphere; and / or,

[0082] The heating rate during the calcination process is 1-15°C / min, which can be optionally 4-10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 11°C / min, 12°C / min, 13°C / min, 14°C / min, 15°C / min or a range consisting of any of the above values.

[0083] Therefore, calcination under the above conditions is conducive to the full thermal decomposition of nitrate on the surface of the precursor to produce oxygen and metal oxides, which in turn helps to fully utilize the generated oxygen to oxidize the surface of the precursor to form an oxide layer, and mix the generated metal oxide with the oxide layer, thereby further improving the electronic conductivity of the positive electrode material and further improving the specific capacity and cycle stability of the battery.

[0084] In some embodiments, the nitrate comprises one or more of metal nitrates and ammonium nitrate.

[0085] In some embodiments, the metal nitrate comprises one or more of a transition metal nitrate, a Group IIA metal nitrate, and a Group IIIA metal nitrate; and / or,

[0086] The metal nitrate includes one or more of iron nitrate, copper nitrate, zinc nitrate, magnesium nitrate, manganese nitrate, nickel nitrate, and aluminum nitrate; and / or,

[0087] The metal nitrate may be dissolved in the solvent.

[0088] In some embodiments, the weight ratio of the nitrate to the precursor is 0.005:1-0.10:1, optionally 0.01:1-0.06:1, for example, 0.005:1, 0.007:1, 0.01:1, 0.012:1, 0.015:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1 or a range consisting of any of the above values.

[0089] Therefore, the use of the above-mentioned nitrate types and ratios of nitrate to precursor is conducive to the oxidation of the precursor surface by oxygen generated by the thermal decomposition of nitrate to form an oxide layer that is conducive to the electrochemical performance. The metal oxides generated by the thermal decomposition of nitric acid work together with the oxide layer to improve the electronic conductivity and interface stability of the positive electrode material, thereby improving the specific capacity and cycle stability of the battery.

[0090] In some embodiments, mixing is performed by ball milling.

[0091] In some embodiments, the ball milling speed is 300-500 r / min, optionally 350-400 r / min, such as 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min or any range thereof; and / or,

[0092] The ball milling time is 1-10 hours, and can be optionally 1-4 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or a range consisting of any of the above values.

[0093] Therefore, mixing under the above-mentioned ball milling conditions is beneficial to reducing the larger grains formed by nitrate recrystallization, improving the uniform distribution of nitrate on the surface of the precursor, and is conducive to forming a complete and uniform oxide layer, thereby ensuring that the positive electrode material has a relatively complete electronic conduction network and promoting the stable performance of its electrochemical properties.

[0094] In some embodiments, the nitrate is first dissolved in the solvent, then mixed with the precursor, and calcined.

[0095] This is beneficial to improving the uniformity of nitrate distribution on the surface of the precursor, thereby facilitating the formation of a coating layer with uniform thickness.

[0096] In some embodiments, after mixing and before calcining, the method further comprises drying the resulting mixture;

[0097] The drying temperature is 80°C-120°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or any range thereof; and / or the drying time is 2-12h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or any range thereof.

[0098] In some embodiments, the Dv50 particle size of the precursor is 0.3-5 μm, optionally 0.5-2 μm, for example, 0.3 μm, 0.5 μm, 0.7 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 3 μm, 4 μm, 5 μm or a range consisting of any of the above values; and / or,

[0099] The precursor further comprises carbon, and the carbon content in the precursor is ≤0.1% by weight, for example, 0.001%, 0.003%, 0.005%, 0.008%, 0.1% or any range thereof; and / or,

[0100] The solvent includes one or more of water and organic solvents, and can be selected from one or more of water, acetone, and alcohol, and can be selected from one or more of water, acetone, ethanol, isopropanol, and methanol.

[0101] [Cathode material]

[0102] One embodiment of the present application provides a positive electrode material, including a core and a coating layer; the core includes LiFe (1-y) M y PO4, wherein the M comprises one or more metal elements of Group IVB, Group VB, Group VIII, Group IIA, Group IIIA, Group IVA and Group VA, and the y is 0-0.1, for example, 0, 0.001, 0.003, 0.005, 0.007, 0.008, 0.01, 0.012, 0.015, 0.02, 0.023, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.056, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, 0.095, 0.098, 0.1 or a range consisting of any of the above values; the coating layer comprises a metal oxide and Li3Fe2(PO4)3, wherein the metal oxide comprises Fe2O3.

[0103] Therefore, in the present application, the nitrate is uniformly dispersed on the surface of the precursor. During the roasting process, the oxygen generated by the thermal decomposition of the nitrate in situ oxidizes the surface of the lithium iron phosphate precursor, forming an oxide layer of uniform thickness on its surface, the main components of which are Fe2O3 and Li3Fe2(PO4)3; optionally, the metal oxide generated by the thermal decomposition of the nitrate is coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the positive electrode material and improving the specific capacity and cycle stability of the battery.

[0104] In some embodiments, the metal oxide further comprises one or more of a transition metal oxide other than iron, a Group IIA metal oxide, and a Group IIIA metal oxide; and / or,

[0105] The metal oxide further comprises one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3; more optionally, the metal oxide further comprises CuO and ZnO; and / or,

[0106] The metal nitrates corresponding to the transition metal oxides, Group IIA metal oxides and Group IIIA metal oxides can be dissolved in a solvent.

[0107] In some embodiments, the weight ratio of the coating layer to the core is 0.005:1-0.12:1, optionally 0.0074:1-0.12:1, and more optionally 0.02:1-0.07:1, for example, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.01:1, 0.013:1, 0.015:1, 0.017:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1 or a range consisting of any of the above values.

[0108] In some embodiments, the average thickness of the coating layer is greater than 0 and less than or equal to 15 nm, optionally 0.5-15 nm or greater than 0 and less than or equal to 5 nm, more optionally 1-5 nm, for example, 0.2 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm or a range consisting of any of the above values; and / or,

[0109] The electronic conductivity of the positive electrode material is greater than or equal to 2×10 -8 S / cm, optional 2×10 -8 -9×10 -6 S / cm, for example 2×10 -8 S / cm, 5×10-8 S / cm, 7×10 -8 S / cm, 8×10 -8 S / cm, 1×10 -7 S / cm, 3×10 -7 S / cm, 5×10 -7 S / cm, 7×10 -7 S / cm, 8×10 -7 S / cm, 9×10 -7 S / cm, 1×10 -6 S / cm, 3×10 -6 S / cm, 5×10 -6 S / cm, 6×10 -6 S / cm, 8×10 -6 S / cm, 9×10 -6 S / cm, 1×10 -5 S / cm, 5×10 -5 S / cm, 8×10 -5 S / cm, 1×10 -4 S / cm or any range thereof; and / or,

[0110] The core further comprises carbon, and the weight content of carbon in the core is ≤0.1%, such as 0.001%, 0.003%, 0.005%, 0.008%, 0.1% or any range thereof.

[0111] In this application, the average thickness of the coating layer is determined using conventional methods in the art; for example, a cross-section polisher is used to cut a smooth cross section through the core of the positive electrode material; then, the cross section of the positive electrode material is scanned and tested by EDS elemental analysis combined with TEM to obtain an elemental distribution map of the cross section. Because the elemental distribution of the core and the coating layer differ, the boundary between the core and the coating layer can be determined based on this, and the coating layer thickness can be measured. The coating layer thickness is measured at different locations along the cross section using the above method, and the average value is recorded as the average thickness of the coating layer.

[0112] In this application, electronic conductivity is measured using conventional methods in the art; for example, a powder resistivity tester is used to test the powder resistivity of a material under a certain pressure. The reciprocal of the powder resistivity is the electronic conductivity of the material.

[0113] [Positive electrode]

[0114] 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 positive electrode material prepared by the aforementioned method or the aforementioned positive electrode material.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.).

[0119] In some embodiments, the positive electrode material may also include other positive electrode materials for batteries that are well known in the art. As an example, the positive electrode material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode materials may also be used. These positive electrode 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 0.25O2 (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 its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, etc.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] [Negative electrode]

[0124] 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.

[0125] 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.

[0126] 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.).

[0127] 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.

[0128] 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).

[0129] 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.

[0130] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0131] 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.

[0132] [Electrolytes]

[0133] 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.

[0134] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] [Isolation film]

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0143] 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.

[0144] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 with a square structure as an example.

[0145] In some embodiments, referring to 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 be formed into 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.

[0146] 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.

[0147] FIG3 shows an example battery module 4. Referring to FIG3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0148] 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.

[0149] 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.

[0150] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] 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.

[0152] As an electrical device, a battery cell, battery module or battery pack can be selected according to its usage requirements.

[0153] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery cells, a battery pack or battery module can be used.

[0154] [Example]

[0155] 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.

[0156] Example 1

[0157] (1) Preparation of positive electrode material: Weigh 5 g of carbon-free LiFePO4 with a volume average particle size Dv50 of 1.4 μm, and weigh 0.15 g of ferric nitrate, 0.05 g of copper nitrate, and 0.05 g of zinc nitrate in a weight ratio of ferric nitrate: zinc nitrate: copper nitrate: lithium iron phosphate = 0.03:0.01:0.01:1. First, dissolve the nitrate in a mortar filled with 5 mL of alcohol (75% by weight ethanol solution). After the nitrate is completely dissolved, add the lithium iron phosphate and ball mill at 500 r / min for 1 hour to completely evaporate the alcohol. The obtained powder is evenly spread in a corundum crucible with dimensions of 6×3×2 cm. The crucible is placed in a tube furnace and Ar gas is introduced at a gas flow rate of 400 mL / min. After the gas is purged for half an hour, the temperature is raised at a heating rate of 5°C / min. After the temperature reaches 400°C, it is kept warm for 2 hours. After the insulation is completed, the positive electrode material is obtained. The conductivity of the powder obtained by the powder resistance tester is within 1.0×10 -7 -1.0×10 -6 S / cm, the untreated carbon-free lithium iron phosphate exceeds the maximum range of the instrument, which is less than 10-9 S / m.

[0158] (2) Preparation of positive electrode sheets: The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are dissolved in solvent N-methylpyrrolidone (NMP) in a weight ratio of 92:5.5:2.5, and the mixture is thoroughly stirred and 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 positive electrode sheets.

[0159] (3) Negative electrode: A metal lithium sheet is used as the negative electrode.

[0160] (4) Isolation film: Polypropylene film is used.

[0161] (5) Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, and LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0162] (6) Preparation of button battery: Assemble the above-mentioned positive electrode sheet, separator, and negative electrode sheet in a button battery box and inject electrolyte to obtain a button battery.

[0163] The secondary battery preparation methods of Examples 2-21 and Comparative Examples 1 and 3 are similar to those of Example 1, and the different parameters are detailed in Table 1.

[0164] Comparative Example 2

[0165] (1) Preparation of positive electrode materials:

[0166] Preparation of positive electrode material: Weigh 5 g of carbon-free LiFePO4 with a volume average particle size Dv50 of 1.4 μm, take nano-iron oxide, nano-zinc oxide and nano-copper oxide (weight ratio of 99:43:42), the weight ratio of the total weight of the three oxides to carbon-free LiFePO4 is 0.05:1, all the substances are mixed evenly and put into a ball mill, and alcohol is used as the ball milling medium. The speed is 500 r / min and the ball mill is used for 8 hours. The obtained sample is vacuum dried at 80°C for 12 hours to obtain the positive electrode material.

[0167] Steps (2) to (6) are the same as in Example 1.

[0168] Material testing and battery testing

[0169] (1) Testing of material chemical composition:

[0170] The surface of the positive electrode material was tested by Raman spectroscopy, SEM-EDS, and XRD to confirm the composition of the material.

[0171] Raman spectroscopy test: A LabRAM HR Evolution laser microscope Raman spectrometer was used; a solid-state laser with a wavelength of 523 nm was used as the light source, a beam diameter of 1.2 μm, and a power of 1 mW; the measurement mode was macro Raman; and a CCD detector was used.

[0172] XRD test: Bruker-D8advance X-ray diffractometer from Bruker Scientific Instruments, Germany was used; the X-ray light source was a copper target; the wavelength was K α1 =1.54056×10 -10 m, K α2 =1.54439×10 -10 m; Test conditions: voltage 40 kV, current 40 mA, anti-scattering slit 1 mm, starting angle 15°, ending angle 70°, step size 0.01671°, each step duration 0.24 s.

[0173] The SEM-EDS test was performed using a Gemini360 field emission scanning electron microscope from Carl Zeiss, Germany. The test conditions were: In-lens mode, voltage 20 KV, aperture 60 μm, and working distance 8.5 mm.

[0174] The test results show that the coating layer of the positive electrode material of Example 1 contains iron oxide and copper oxide (as shown in the Raman spectra of Figures 7-8), the SEM-EDS image shows that the coating layer of the positive electrode material of Example 1 contains zinc oxide, and the XRD diffraction spectrum shows that the coating layer of the positive electrode material of Example 1 contains Li3Fe2(PO4)3. Similarly, the XRD diffraction spectrum of the positive electrode material of Example 16 shows that its coating layer contains Li3Fe2(PO4)3 (the peak shown in the box in Figure 9).

[0175] (2) Test of the average thickness of the positive electrode material coating layer:

[0176] A flat cross-section was cut through the core of the cathode material using a cross-section polisher (JEOL, IB-09010CP Argon Ion Cross-Section Polisher). The cross-section was then scanned using EDS elemental analysis combined with TEM (X-Max EDS from Oxford Instruments, UK, combined with a Thermo Scientific Talos F200S G2 TEM from Thermo Fisher Scientific, USA) to obtain an elemental distribution map. Because the elemental distribution of the core differs from that of the coating, the boundary between the core and coating can be determined, allowing the coating thickness to be measured. The coating thickness was measured at 10 different locations along the cross-section using the above method, and the average value was recorded as the average coating thickness.

[0177] (3) Test of coating uniformity of positive electrode materials:

[0178] A Carl Zeiss Gemini360 field-emission scanning electron microscope (SEM-EDS) was used to analyze the distribution of transition metal elements on the lithium iron phosphate surface to determine whether the transition metal oxide coating was uniform. Parameter settings included: In-lens mode, voltage: 20 kV, aperture: 60 μm, and working distance: 8.5 mm.

[0179] As shown in Figures 10-11, the Cu element in the positive electrode material coating layer of Example 1 of the present application is evenly distributed.

[0180] (4) Test of electronic conductivity of positive electrode materials:

[0181] The powder resistivity of the cathode material was measured using a powder resistance tester (PRCD1100, Yuanneng Technology Co., Ltd.) at 100 MPa. The reciprocal of the powder resistivity is the electronic conductivity of the cathode material.

[0182] (5) Battery specific capacity test:

[0183] At 25°C, charge the battery at a constant current of 0.1C to 4.3V, then charge at a constant voltage of 4.3V to a current of 0.01C. Let it rest for 5 minutes, then discharge at 0.1C to 2.0V. The resulting discharge capacity is recorded as c1. Repeat the cycle once and record the resulting discharge capacity as c2. Prepare three replicates, take the average c2 of the three replicates, and divide it by the weight of the positive electrode material to obtain the battery's specific capacity.

[0184] (6) Battery cycle capacity retention test:

[0185] At 25°C, the button cell was first charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.01C, left for 5 minutes, and then discharged at 0.1C to 2.0V. This constitutes one charge-discharge cycle, and the discharge capacity is the discharge capacity of the first cycle. The button cell was cycled 50 times in this manner. The discharge capacity of the 50th cycle was measured, and the cycle capacity retention of the button cell was calculated using the following formula.

[0186] The cycle capacity retention rate (%) of the button battery after 50 cycles = 100% × discharge capacity at the 50th cycle / discharge capacity at the 1st cycle.

[0187] Table 2: Performance test results of Examples 1-21 and Comparative Examples 1-3

[0188] According to the above results, we can know that:

[0189] Compared with Comparative Example 1 where y is greater than 0.1, the positive electrode materials of Examples 1-11 and 13-21 of the present application have higher electronic conductivity, a larger specific capacity of the battery, and higher cycle performance;

[0190] Compared with the positive electrode material of Fe2O3, ZnO, and CuO coated LiFePO4 prepared by conventional method in Comparative Example 2, the batteries of Examples 1-8 and 13-21 of the present application have larger specific capacity and higher cycle performance;

[0191] Compared with the positive electrode material without a coating layer in Comparative Example 3, the positive electrode materials of Examples 1-8 and 12-21 of the present application have higher electronic conductivity, larger specific capacity of the battery, and higher cycle performance;

[0192] Compared with Example 15 using a lower weight ratio of nitrate to precursor, the positive electrode materials of Examples 1-3 of the present application have higher electronic conductivity, a larger specific capacity of the battery, and higher cycle performance; compared with Example 16 using a higher weight ratio of nitrate to precursor, the specific capacity of the battery of Examples 1-3 of the present application is greater;

[0193] Compared with Example 17 using a lower ball milling speed and Example 18 using a shorter ball milling time, the positive electrode materials of Examples 1 and 4 of the present application have higher electronic conductivity, a larger specific capacity of the battery, and higher cycle performance;

[0194] Compared with Example 19 using a higher calcination heating rate and Example 20 using a lower calcination heating rate, the positive electrode materials of Examples 1, 5-6 of the present application have higher electronic conductivity, greater specific capacity of the battery, and higher cycle performance;

[0195] Compared with the lower calcination temperature used in Example 20, the positive electrode materials of Examples 1, 7-8 of the present application have higher electronic conductivity, larger specific capacity of the battery, and higher cycle performance.

[0196] 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 cathode material, comprising: Mix nitrate with a precursor in a solvent, and then calcine to obtain a cathode material; wherein, the precursor includes LiFe (1-y) M y PO4, wherein M includes one or more metal elements from Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.

1.

2. The method according to claim 1, wherein The positive electrode material includes a core and a coating layer; the core includes LiFe (1-y) M y PO4, wherein M includes one or more metal elements from Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.1; the coating layer includes a metal oxide and Li3Fe2(PO4)3, wherein the metal oxide includes Fe2O3.

3. The method according to claim 2, wherein, The metal oxide further includes one or more of transition metal oxides other than iron, Group IIA metal oxides, and Group IIIA metal oxides.

4. The method according to claim 2 or 3, wherein The metal oxide further includes one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3.

5. The method according to any one of claims 1 to 4, wherein The M includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or, The y is from 0.001 to 0.

1.

6. The method according to any one of claims 1 to 5, wherein The temperature of the roasting is 300°C - 600°C; and / or, The time of the roasting is 1 - 10 h; and / or, The roasting is carried out in an inert atmosphere; and / or, The heating rate during the roasting process is 1 - 15°C / min.

7. The method according to any one of claims 1 to 6, wherein, The nitrate includes one or more of metal nitrates and ammonium nitrate.

8. The method according to claim 7, wherein The metal nitrate includes one or more of transition metal nitrates, Group IIA metal nitrates, and Group IIIA metal nitrates; and / or, The metal nitrate includes one or more of iron nitrate, copper nitrate, zinc nitrate, magnesium nitrate, manganese nitrate, nickel nitrate, and aluminum nitrate; and / or, The metal nitrate is soluble in the solvent.

9. The method according to any one of claims 1 to 8, wherein The weight ratio of the nitrate to the precursor is 0.005:1 - 0.10:

1.

10. The method according to any one of claims 1 to 9, wherein Mixing is carried out by ball milling.

11. The method according to claim 10, wherein, The rotation speed of the ball milling is 300 - 500 r / min; and / or, The time of the ball milling is 1 - 10 h.

12. The method according to any one of claims 1 to 11, wherein, First, dissolve the nitrate in the solvent, then mix it with the precursor and roast.

13. The method according to any one of claims 1 to 12, wherein, Before roasting after mixing, the method further includes drying the obtained mixture; Wherein, the temperature of the drying is 80°C - 120°C; and / or, the time of the drying is 2 - 12 h.

14. According to the method according to any one of claims 1 to 13, wherein, The Dv50 particle size of the precursor is 0.3 - 5 μm; and / or, The precursor further includes carbon, and the carbon content in the precursor ≤ 0.1 wt%; and / or, The solvent includes one or more of water and organic solvents.

15. A cathode material includes a core and a coating layer; the core includes LiFe (1- y) M y PO4, wherein, The M includes one or more metal elements from Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, the y is 0 - 0.1; the coating layer includes a metal oxide and Li3Fe2(PO4)3, wherein the metal oxide includes Fe2O3.

16. The cathode material according to claim 15, wherein, The metal oxide further includes one or more of transition metal oxides other than iron, Group IIA metal oxides, and Group IIIA metal oxides; and / or, The metal oxide further includes one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3; and / or, The metal nitrates corresponding to the transition metal oxides, Group IIA metal oxides, and Group IIIA metal oxides are soluble in the solvent.

17. The cathode material according to claim 15 or 16, wherein The weight ratio of the coating layer to the core is 0.005:1 - 0.12:

1.

18. The positive electrode material according to any one of claims 15 to 17, wherein, The average thickness of the coating layer is greater than 0 and less than or equal to 15 nm; and / or, The electronic conductivity of the positive electrode material is greater than or equal to 2×10 -8 S / cm; and / or, The core further includes carbon, and the weight content of carbon in the core ≤ 0.1%.

19. A positive electrode sheet, comprising a positive electrode material prepared by the method according to any one of claims 1 to 14 or a positive electrode material according to any one of claims 15 to 18.

20. A battery, comprising the positive electrode sheet according to claim 19.

21. An electrical device, comprising the battery according to claim 20.

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