Positive electrode material preparation method, positive electrode material, positive plate, battery and electric device

Abstract

The invention belongs to the technical field of lithium batteries, and particularly relates to a preparation method of 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 nitrate and a precursor in a solvent, and roasting to obtain the positive electrode material, wherein the precursor comprises LiFe (1-y) MyPO4, M comprises one or more metal elements in IVB family, VB family, VIII family, IIA family, IIIA family, IVA family and VA family, and y is 0-0.1. According to the method, the electronic conductivity of the positive electrode material is improved, and the specific capacity and cycling stability of the battery are improved.

Description

Technical Field

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

[0002] In recent years, with the increasingly wide application range of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are also put forward for their energy density, cycle performance, etc. Summary of the Invention

[0003] The present application is made in view of the above problems, and its purpose is to provide a method for preparing a cathode material, the cathode material, a cathode electrode sheet, a battery, and an electrical device. The method of the present application improves the electronic conductivity of the cathode material and increases the specific capacity and cycle stability of the battery.

[0004] To achieve the above object, a first aspect of the present application provides a method for preparing a cathode material, including:

[0005] Mixing a nitrate with a precursor in a solvent, and roasting to obtain the cathode material; wherein, the precursor includes LiFe (1-y) M y PO4, wherein, M includes one or more metal elements in Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.1.

[0006] Thus, 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 precursor lithium iron phosphate, forming an oxide layer with a uniform thickness on its surface, and the main components 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 cathode material and increasing the specific capacity and cycle stability of the battery.

[0007] In any embodiment, the cathode 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 in 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.

[0008] 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.

[0009] In any embodiment, the metal oxide further comprises one or more of CuO, ZnO, MgO, MnO₂, NiO, and Al₂O₃.

[0010] Thereby, the oxygen generated by the thermal decomposition of the nitrate forms an oxide layer including Li₃Fe₂(PO₄)₃ and Fe₂O₃ on the surface of the precursor by oxidation. The metal oxide generated by the thermal decomposition of the nitrate is mixed with the oxide layer, thereby enhancing the electronic conductivity of the cathode material and improving the specific capacity and cycling stability of the battery.

[0011] In any embodiment, M comprises one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or,

[0012] y is 0.001 - 0.1.

[0013] In any embodiment, the temperature of the calcination is 300°C - 600°C, and optionally 350°C - 600°C; and / or,

[0014] The time of the calcination is 1 - 10 h; and / or,

[0015] The calcination is carried out in an inert atmosphere; and / or,

[0016] The heating rate during the calcination is 1 - 15°C / min, and optionally 4 - 10°C / min.

[0017] Thereby, calcining under the above conditions is conducive to the full thermal decomposition of the nitrate on the surface of the precursor to generate oxygen and metal oxide, which further helps to fully utilize the generated oxygen to oxidize the surface of the precursor to form an oxide layer, and to mix the generated metal oxide with the oxide layer, thereby further enhancing the electronic conductivity of the cathode material and further improving the specific capacity and cycling stability of the battery.

[0018] In any embodiment, the nitrate comprises one or more of metal nitrates and ammonium nitrate.

[0019] In any embodiment, the metal nitrate comprises one or more of transition metal nitrates, Group IIA metal nitrates, and Group IIIA metal nitrates; and / or,

[0020] The metal nitrate comprises one or more of iron nitrate, copper nitrate, zinc nitrate, magnesium nitrate, manganese nitrate, nickel nitrate, and aluminum nitrate; and / or,

[0021] The metal nitrate can be dissolved in the solvent.

[0022] 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.

[0023] Thus, by using the above types of nitrates and the ratio of nitrate to precursor, it is beneficial for the oxygen generated by the thermal decomposition of nitrate to oxidize the surface of the precursor to form an oxide layer that is conducive to the electrochemical performance. The metal oxide generated by the thermal decomposition of nitric acid and the oxide layer act together to improve the electronic conductivity and interfacial stability of the cathode material, thereby improving the specific capacity and cycle stability of the battery.

[0024] In any embodiment, mixing is carried out by ball milling.

[0025] In any embodiment, the rotation speed of the ball milling is 300 - 500 r / min, and can be optionally 350 - 400 r / min; and / or,

[0026] The time of the ball milling is 1 - 10 h, and can be optionally 1 - 4 h.

[0027] Thus, mixing under the above ball milling conditions is beneficial for reducing the larger grains formed by the recrystallization of nitrate, improving the uniform distribution of nitrate on the surface of the precursor, and facilitating the formation of a complete and uniform oxide layer, thereby ensuring that the cathode material has a relatively complete electron conduction network and promoting the stable performance of its electrochemical properties.

[0028] In any embodiment, first dissolve the nitrate in the solvent, and then mix it with the precursor and calcine.

[0029] Thus, it is beneficial to improve the uniformity of the distribution of nitrate on the surface of the precursor, and thus is beneficial for the formation of a coating layer with uniform thickness.

[0030] In any embodiment, after mixing and before calcining, the method further includes drying the obtained mixture;

[0031] Among them, the temperature of the drying is 80°C - 120°C; and / or, the time of the drying is 2 - 12 h.

[0032] In any embodiment, the Dv50 particle size of the precursor is 0.3 - 5 μm, and can be optionally 0.5 - 2 μm; and / or,

[0033] The precursor further includes carbon, and the carbon content in the precursor ≤ 0.1 wt%. And / or,

[0034] The solvent includes one or more of water and organic solvents, optionally including one or more of water, acetone, and alcohol, and more optionally including one or more of water, acetone, ethanol, isopropanol, and methanol.

[0035] The second aspect of the present application also provides a cathode material, including a core and a coating layer; the core includes LiFe (1-y) M y PO4, where M includes one or more metal elements in Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.1; the coating layer includes metal oxide and Li3Fe2(PO4)3, where the metal oxide includes Fe2O3.

[0036] Thus, in the present application, nitrate is uniformly dispersed on the surface of the precursor. During the calcination process, the oxygen generated by the thermal decomposition of nitrate in-situ oxidizes the surface of the precursor lithium iron phosphate, forming an oxide layer with a uniform thickness on its surface, mainly composed of Fe2O3 and Li3Fe2(PO4)3; optionally, the metal oxide generated by the thermal decomposition of nitrate is coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the cathode material and enhancing the specific capacity and cycle stability of the battery.

[0037] In any embodiment, 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,

[0038] the metal oxide further includes one or more of CuO, ZnO, MgO, MnO2, NiO, and Al2O3; more optionally, the metal oxide further includes CuO and ZnO; and / or,

[0039] The metal nitrates corresponding to the transition metal oxides, Group IIA metal oxides, and Group IIIA metal oxides are soluble in the solvent.

[0040] 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.

[0041] 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, and more optionally 1 - 5 nm; and / or,

[0042] The electronic conductivity of the cathode material is greater than or equal to 2×10 -8 S / cm, optionally 2×10 -8-9×10 -6 S / cm; and / or,

[0043] The core further includes carbon, and the weight content of carbon in the core ≤ 0.1%.

[0044] The third aspect of the present application provides a positive electrode plate, including 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.

[0045] The fourth aspect of the present application provides a battery, including the positive electrode plate of the third aspect of the present application.

[0046] The fifth aspect of the present application provides an electrical device, including the battery of the fourth aspect of the present application. Description of the Drawings

[0047] Figure 1 is a schematic diagram of a battery cell of an embodiment of the present application.

[0048] Figure 2 is Figure 1 the exploded view of the battery cell of an embodiment of the present application shown.

[0049] Figure 3 is a schematic diagram of a battery module of an embodiment of the present application.

[0050] Figure 4 is a schematic diagram of a battery pack of an embodiment of the present application.

[0051] Figure 5 is Figure 4 the exploded view of the battery pack of an embodiment of the present application shown.

[0052] Figure 6 is a schematic diagram of an electrical device using the battery cell of an embodiment of the present application as a power source.

[0053] Figure 7 is the Raman spectrum of the surface of the positive electrode material in Example 1 of the present application (500 cm -1 Raman shift below).

[0054] Figure 8 is the Raman spectrum of the surface of the positive electrode material in Example 1 of the present application (500 cm -1 Raman shift above).

[0055] Figure 9 is the XRD diffraction spectrum of the surface of the positive electrode material in Example 16 of the present application.

[0056] Figure 10 is the SEM photograph of the surface of the positive electrode material in Example 1 of the present application.

[0057] Figure 11 It is the SEM-EDS image of the surface of the cathode material in Embodiment 1 of the present application.

[0058] Explanation of the reference numerals:

[0059] 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed implementation manners

[0060] Hereinafter, the implementation manners of the cathode material preparation method, cathode material, cathode electrode sheet, anode electrode sheet, battery cell, battery module, battery pack, and electrical device of the present application specifically disclosed will be 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 identical structures are omitted. This is to avoid the following descriptions from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0061] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] If there is no special instruction, all the implementation manners and optional implementation manners of the present application can be combined with each other to form a new technical solution.

[0063] If there is no special instruction, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0064] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) carried out sequentially, or may also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may also 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 volume distribution value is 50%.

[0066] [Battery cell]

[0067] A battery cell, also known as a rechargeable battery or a storage battery, refers to a battery that can activate the active material through charging after discharging and can be used continuously.

[0068] Generally, a battery cell includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode plate and the negative electrode plate. The separator is arranged between the positive electrode plate and the negative electrode plate, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing active ions to pass through. The electrolyte is between the positive electrode plate and the negative electrode plate, mainly playing a role in conducting active ions.

[0069] [Method for preparing a positive electrode material]

[0070] One embodiment of this application provides a method for preparing a positive electrode material, including:

[0071] Mixing a nitrate and a precursor in a solvent and then calcining to obtain the positive electrode 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, such as 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 composed of any of the above values.

[0072] Lithium iron phosphate has poor electronic conductivity and is difficult to meet the requirements of industrial applications. Although the mechanism is not yet clear, the applicant unexpectedly found that: in this application, nitrates are uniformly dispersed on the surface of the precursor. During the calcination process, the oxygen generated by the pyrolysis of nitrates in-situ oxidizes the surface of the precursor lithium iron phosphate, forming an oxide layer with a uniform thickness on its surface, mainly composed of Fe2O3 and Li3Fe2(PO4)3; optionally, the metal oxides generated by the pyrolysis of nitrates are coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the cathode material and enhancing the specific capacity and cycle stability of the battery.

[0073] In some embodiments, the cathode material includes a core and a coating layer; the core includes LiFe (1-y) M y PO4, where M includes one or more metal elements from Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.1, such as 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 composed of any of the above values; the coating layer includes metal oxides and Li3Fe2(PO4)3, where the metal oxides include Fe2O3.

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

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

[0076] Thus, the oxygen generated by the pyrolysis of nitrates oxidizes the surface of the precursor to form an oxide layer including Li3Fe2(PO4)3 and Fe2O3, and the metal oxides generated by the pyrolysis of nitrates are mixed with the oxide layer, thereby improving the electronic conductivity of the cathode material and enhancing the specific capacity and cycle stability of the battery.

[0077] In some embodiments, M includes one or more elements such as Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; and / or,

[0078] y is 0.001 - 0.1.

[0079] In some embodiments, the temperature of the calcination is 300°C - 600°C, optionally 350°C - 600°C, such as 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 composed of any of the above values; and / or,

[0080] the time of the calcination is 1 - 10 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or a range composed of any of the above values; and / or,

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

[0082] the heating rate during the calcination is 1 - 15°C / min, optionally 4 - 10°C / min, such as 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 composed of any of the above values.

[0083] Thus, calcining under the above conditions is beneficial to the sufficient thermal decomposition of nitrate on the surface of the precursor to generate oxygen and metal oxides, which further helps to fully utilize the generated oxygen to oxidize the surface of the precursor to form an oxide layer, and mix the generated metal oxides with the oxide layer, thereby further improving the electronic conductivity of the cathode material and further improving the specific capacity and cycle stability of the battery.

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

[0085] In some embodiments, the metal nitrate includes one or more of transition metal nitrates, Group IIA metal nitrates, and Group IIIA metal nitrates; 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 is soluble 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, such as 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 any range composed of the above values.

[0089] Therefore, by using the above types of nitrates and the ratio of nitrate to precursor, it is beneficial for the oxygen generated by the thermal decomposition of nitrate to oxidize the surface of the precursor to form an oxide layer that is conducive to the electrochemical performance. The metal oxide generated by the thermal decomposition of nitric acid and the oxide layer act together to improve the electronic conductivity and interfacial stability of the cathode material, thereby improving the specific capacity and cycle stability of the battery.

[0090] In some embodiments, the mixing is carried out by ball milling.

[0091] In some embodiments, the rotation speed of the ball milling 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 composed of the above values; and / or,

[0092] The time of the ball milling is 1 - 10 h, optionally 1 - 4 h, such as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h or any range composed of the above values.

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

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

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

[0096] In some embodiments, after mixing and before calcination, the method further includes drying the obtained mixture;

[0097] Among them, the drying temperature is 80°C - 120°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C or a range composed of any of the above values; and / or, the drying time is 2 - 12 h, such as 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or a range composed of any of the above values.

[0098] In some embodiments, the Dv50 particle size of the precursor is 0.3 - 5 μm, optionally 0.5 - 2 μm, such as 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 composed of any of the above values; and / or,

[0099] The precursor further includes carbon, and the carbon content in the precursor is ≤ 0.1 wt%, such as 0.001%, 0.003%, 0.005%, 0.008%, 0.1% or a range composed of any of the above values; and / or,

[0100] The solvent includes one or more of water and organic solvents, optionally including one or more of water, acetone, and alcohol, and more optionally including one or more of water, acetone, ethanol, isopropanol, and methanol.

[0101] [Cathode material]

[0102] An embodiment of the present application provides a cathode material, including a core and a coating layer; the core includes LiFe (1-y) M y PO4, where M includes one or more metal elements from Group IVB, VB, VIII, IIA, IIIA, IVA, and VA, and y is 0 - 0.1, such as 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 composed of any of the above values; the coating layer includes a metal oxide and Li3Fe2(PO4)3, where the metal oxide includes Fe2O3.

[0103] Thus, in the present application, nitrates are uniformly dispersed on the surface of the precursor. During the calcination process, the oxygen generated by the pyrolysis of nitrates in-situ oxidizes the surface of the precursor lithium iron phosphate, forming an oxide layer with a uniform thickness on its surface, mainly composed of Fe2O3 and Li3Fe2(PO4)3. Optionally, the metal oxides generated by the pyrolysis of nitrates are coated on the surface of the precursor and mixed into the oxide layer; thereby improving the electronic conductivity of the cathode material and enhancing the specific capacity and cycle stability of the battery.

[0104] In some embodiments, 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,

[0105] the metal oxide further includes one or more of CuO, ZnO, MgO, MnO2, NiO, and A12O3; more optionally, the metal oxide further includes CuO and ZnO; and / or,

[0106] The metal nitrates corresponding to the transition metal oxides, Group IIA metal oxides, and Group IIIA metal oxides are soluble in the 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, more optionally 0.02∶1 - 0.07∶1, such as 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 any range composed of the above arbitrary 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, such as 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 any range composed of the above arbitrary values; and / or,

[0109] The electronic conductivity of the cathode material is greater than or equal to 2×10 -8 S / cm, optionally 2×10 -8 -9×10 -6 S / cm, such as 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 a range composed of any of the above values; and / or,

[0110] The core further includes carbon, and the weight content of carbon in the core ≤ 0.1%, such as 0.001%, 0.003%, 0.005%, 0.008%, 0.1% or a range composed of any of the above values.

[0111] In this application, the average thickness of the coating layer is measured by a conventional method in the art; for example, a flat cross-section is cut out from the core of the cathode material by a cross-section polishing instrument; then the cross-section of the cathode material is scanned and tested by EDS elemental analysis combined with TEM to obtain the elemental distribution map of the cross-section. Since there are differences in the elemental distribution between the core and the coating layer, the boundary between the core and the coating layer can be determined accordingly, and then the thickness of the coating layer can be measured. The thickness of the coating layer is measured at different positions on the cross-section according to the above method, and the average value is recorded as the average thickness of the coating layer.

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

[0113] [Cathode electrode sheet]

[0114] The cathode electrode sheet generally includes a cathode current collector and a cathode film layer provided on at least one surface of the cathode current collector, and the cathode film layer includes the cathode material prepared by the foregoing method or the foregoing cathode material.

[0115] During the charge and discharge process of the battery, the insertion and extraction of Li and its consumption will occur, and the molar content of Li is different when the battery is discharged to different states. In the list of cathode materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li will change.

[0116] In the list of cathode materials in this application, the molar content of O is only the theoretical state value, and the release of oxygen from the lattice 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 own thickness direction, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0118] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as 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 cathode material may further include other cathode materials known in the art for batteries. As an example, the cathode material may include at least one of the following materials: lithium phosphate with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery cathode materials can also be used. These cathode materials can be used alone or in combination of two or more. Among them, 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 LiNi1 / 3Co1 / 3Mn1 / 3O2 (which can also be abbreviated as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2(which can also be abbreviated as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2(which can also be abbreviated as NCM 211 )、LiNi0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated 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. Examples of olivine-structured lithium-containing phosphates may include but are not limited to lithium manganese phosphate (such as LiMnPO4), composites of lithium manganese phosphate and carbon, etc.

[0120] In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0121] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an 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 plate can be prepared by the following method: dispersing the above-mentioned components for preparing the positive electrode plate, such as positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0123] [Negative electrode plate]

[0124] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and 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 own thickness direction, and the negative electrode film layer is provided 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, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper 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.).

[0127] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries 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, etc. The silicon-based materials may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials 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 conventional materials that can be used as the negative electrode active material of the battery 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 also optionally include a binder. As an 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 also optionally include a conductive agent. As an 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 also optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0131] In some embodiments, the negative electrode plate can be prepared by the following method: dispersing the above components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode plate can be obtained.

[0132] [Electrolyte]

[0133] The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

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

[0135] In some embodiments, the electrolyte salt can 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[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, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0137] In some embodiments, the electrolyte solution may optionally further include additives. By way of example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performance, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature or low-temperature performance of the battery, etc.

[0138] [Separator film]

[0139] In some embodiments, the battery cell further includes a separator film. There is no particular limitation on the type of separator film in this application, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film 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 plate, the negative electrode plate, and the separator film can be made into an electrode assembly by a winding process or a stacking process.

[0142] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0143] In some embodiments, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate can be listed, etc.

[0144] This application does not particularly limit the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0145] In some embodiments, referring to Figure 2 , the outer packaging can include a housing 51 and a cover plate 53. Among them, the housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can be formed into an electrode assembly 52 through a winding process or a stacking 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 included 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, the battery cells can be assembled into a battery module. The number of battery cells included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0147] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple battery cells 5 can be fixed by fasteners.

[0148] Optionally, the battery module 4 can further include a housing with a receiving space, and multiple battery cells 5 are accommodated in the receiving space.

[0149] In some embodiments, the above battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0150] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[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 by the present application. The battery cells, battery modules, or battery packs can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can include mobile devices (such as mobile phones, laptop computers, 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, satellites, energy storage systems, etc., but is not limited thereto.

[0152] As the electrical device, the battery cells, battery modules, or battery packs can be selected according to its usage requirements.

[0153] Figure 6 is an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for the high power and high energy density of the battery cells, a battery pack or a battery module can be adopted.

[0154] [Embodiment]

[0155] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial procurement.

[0156] Embodiment 1

[0157] (1) Preparation of positive electrode material: Weigh 5g of carbon-free LiFePO4 with a volume average particle size Dv50 of 1.4μm, and weigh 0.15g of iron nitrate, 0.05g of copper nitrate, and 0.05g of zinc nitrate respectively according to the weight ratio of iron nitrate: zinc nitrate: copper nitrate: lithium iron phosphate = 0.03:0.01:0.01:1. First, dissolve the nitrate in a mortar filled with 5mL of alcohol (75% by weight ethanol solution). After the nitrate is completely dissolved, add the lithium iron phosphate and ball mill at a speed of 500r / min for 1h to completely evaporate the alcohol. The obtained powder is evenly spread in a corundum crucible with a size of 6×3×2cm, and the crucible is placed in a tubular furnace and Ar gas is introduced at a gas flow rate of 400mL / min. After the gas is purged for half an hour, the temperature begins to rise at a heating rate of 5℃ / min. After the temperature rises to 400℃, it is kept warm for 2h. After the insulation is completed, the positive electrode material is obtained. The conductivity of the powder obtained by the powder resistance tester is 1.0×10 -7 -1.0×10 -6 S / cm, 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 a solvent N-methylpyrrolidone (NMP) at a weight ratio of 92:5.5:2.5, and the mixture is stirred thoroughly 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 at a volume ratio of 1:1:1, and then 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 cell: Assemble the above-mentioned positive electrode sheet, separator, and negative electrode sheet in a button cell box and inject electrolyte to obtain a button cell.

[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 the 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 99∶43∶42), and the total weight of the three oxides and the weight of the carbon-free LiFePO4 have a ratio of 0.05∶1. Mix all substances evenly and load them into a ball milling tank. Use alcohol as the ball milling medium and ball mill at a speed of 500 r / min for 8 h. Vacuum dry the obtained sample at 80 °C for 12 h to obtain the positive electrode material.

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

[0168]

[0169]

[0170] Material testing and battery testing

[0171] (1) Testing of the chemical composition of the material:

[0172] Test the surface of the positive electrode material by Raman spectroscopy, SEM-EDS, and XRD to confirm the components in the material.

[0173] Raman spectroscopy test: Use a LabRAM HR Evolution type laser micro-Raman spectrometer; use a solid laser with a wavelength of 523 nm as the light source, the beam diameter is 1.2 μm, and the power is 1 mW; the measurement mode is macro-Raman; use a CCD detector.

[0174] XRD test: Use a Bruker-D8advance X-ray diffractometer from Bruker Scientific Instruments GmbH, Germany; the X-Ray light source is a copper target; the wavelength is K α1 = 1.54056×10 -10 m, K a2 = 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°, and the duration of each step is 0.24 s.

[0175] Use a Gemini360 type field emission scanning electron microscope from Carl Zeiss AG, Germany, and perform SEM-EDS testing. Test conditions: mode In-lens, voltage 20 KV, aperture 60 μm, working distance 8.5 mm.

[0176] The test results show that the coating layer of the positive electrode material in Example 1 contains iron oxide and copper oxide (such as Figures 7 - 8as shown in the Raman spectrum), the SEM-EDS image shows that the coating layer of the cathode material in Example 1 contains zinc oxide, and the XRD diffraction spectrum shows that the coating layer of the cathode material in Example 1 contains Li3Fe2(PO4)3. Approximately, the XRD diffraction spectrum of the cathode material in Example 16 shows that its coating layer contains Li3Fe2(PO4)3( Figure 9 the peaks shown in the box).

[0177] (2) Test of the average thickness of the coating layer of the cathode material:

[0178] Use a cross-section polishing instrument [IB-09010CP type argon ion cross-section polishing instrument of JEOL Ltd., Japan], cut out a flat cross-section through the core of the cathode material; then scan and test the cross-section of the cathode material by EDS elemental analysis combined with TEM (X-Max type EDS of Oxford Instruments Group, UK combined with Thermo Scientific-Talos F200S G2 type TEM of Thermo Fisher Scientific Inc., USA) to obtain the elemental distribution map of the cross-section. Since there are differences in the elemental distribution between the core and the coating layer, the boundary between the core and the coating layer can be determined accordingly, and then the thickness of the coating layer can be measured. Measure the thickness of the coating layer at 10 different positions on the cross-section according to the above method, and take the average value as the average thickness of the coating layer.

[0179] (3) Test of the coating uniformity of the cathode material:

[0180] Use a Gemini360 type field emission scanning electron microscope of Carl Zeiss AG, Germany, and analyze the distribution of transition metal elements on the surface of lithium iron phosphate through the SEM-EDS mode to judge whether the transition metal oxide is uniformly coated. Parameter settings: Mode: In-lens, Voltage: 20KV, Aperture: 60μm, Working distance: 8.5mm.

[0181] As Figures 10 - 11 shown, the Cu element in the coating layer of the cathode material in Example 1 of this application is uniformly distributed.

[0182] (4) Test of the electronic conductivity of the cathode material:

[0183] Use a powder resistance tester (PRCDl100 model of Yuanneng Technology Co., Ltd.) to test the powder resistivity of the cathode material under 100 MPa. Take the reciprocal of the powder resistivity as the electronic conductivity of the cathode material.

[0184] (5) Test of the specific capacity of the battery:

[0185] At 25 °C, the battery is charged at a constant current of 0.1C to 4.3V, then charged at a constant voltage of 4.3V until the current reaches 0.01C, left standing for 5 min, and then discharged at 0.1C to 2.0V. The obtained discharge capacity is denoted as c1, and the discharge capacity obtained by repeating the cycle once is denoted as c2. Prepare three parallel samples, take the average value of c2 of the three parallel samples, and then divide by the weight of the positive electrode material to obtain the specific capacity of the battery.

[0186] (6) Test for cycle capacity retention rate of the battery:

[0187] At 25 °C, first charge the button cell at a constant current of 0.1C to 4.3V, then charge it at a constant voltage of 4.3V until the current reaches 0.01C, leave it standing for 5 min, and then discharge it at 0.1C to 2.0V. This is one charge-discharge cycle, and the discharge capacity this time is the discharge capacity of the 1st week cycle. The button cell is charged and discharged in 50-week cycles in the above manner, the discharge capacity of the 50th week cycle is detected, and the cycle capacity retention rate of the button cell is calculated by the following formula.

[0188] Cycle capacity retention rate (%) of the button cell for 50-week cycles = 100% × Discharge capacity of the 50th week cycle / Discharge capacity of the 1st week cycle.

[0189] Table 2: Performance test results of Examples 1-21 and Comparative Examples 1-3

[0190]

[0191]

[0192]

[0193] It can be seen from the above results that:

[0194] Compared with the y of Comparative Example 1 being greater than 0.1, the electronic conductivity of the positive electrode materials of Examples 1-11, 13-21 of the present application is higher, the specific capacity of the battery is larger, and the cycle performance is higher;

[0195] Compared with the positive electrode materials of Fe2O3, ZnO, CuO-coated LiFePO4 prepared by the conventional method in Comparative Example 2, the specific capacity of the batteries of Examples 1-8, 13.21 of the present application is larger, and the cycle performance is higher;

[0196] Compared with the positive electrode material without a coating layer in Comparative Example 3, the electronic conductivity of the positive electrode materials of Examples 1-8, 12-21 of the present application is higher, the specific capacity of the battery is larger, and the cycle performance is higher;

[0197] Compared with Example 15 which uses a lower nitrate-to-precursor weight ratio, the positive electrode materials of Examples 1-3 of the present application have higher electronic conductivity, greater specific capacity of the battery, and better cycling performance; compared with Example 16 which uses a higher nitrate-to-precursor weight ratio, the specific capacity of the batteries of Examples 1-3 of the present application is greater;

[0198] Compared with Example 17 which uses a lower ball milling speed and Example 18 which uses a shorter ball milling time, the positive electrode materials of Examples 1 and 4 of the present application have higher electronic conductivity, greater specific capacity of the battery, and better cycling performance;

[0199] Compared with Example 19 which uses a higher calcination heating rate and Example 20 which uses a lower calcination heating rate, the positive electrode materials of Examples 1 and 5-6 of the present application have higher electronic conductivity, greater specific capacity of the battery, and better cycling performance;

[0200] Compared with Example 20 which uses a lower calcination temperature, the positive electrode materials of Examples 1 and 7-8 of the present application have higher electronic conductivity, greater specific capacity of the battery, and better cycling performance.

[0201] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same composition and the same effect as the technical idea within the technical solution scope of the present application are all included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a cathode material, comprising: Mix nitrate and 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, where M includes one or more metal elements in 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, where 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 0.001 - 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 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 of 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 is ≤ 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 positive electrode 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 is ≤ 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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