Positive electrode active material and preparation method thereof, positive electrode, battery and electronic equipment

Abstract

The invention provides a positive electrode active material and a preparation method thereof, a positive electrode, a battery and electronic equipment. The positive electrode active material comprises an inner core, a first coating layer and a second coating layer, the surface of the inner core is coated with the first coating layer, and at least part of the surface of the first coating layer is coated with the second coating layer; the inner core comprises lithium iron phosphate, the first coating layer comprises a carbon-based material, the second coating layer comprises a metal simple substance, and the metal simple substance comprises at least one of a palladium simple substance, a platinum simple substance, a tin simple substance and a molybdenum simple substance. As the metal elementary substance has high conductivity, after the metal elementary substance coats at least part of the surface of the carbon-coated lithium iron phosphate material through adsorption bonding, the obtained positive electrode active material has high conductivity, and the low-temperature performance of the battery can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a positive electrode active material, in particular to a positive electrode active material and a preparation method thereof, a positive electrode, a battery, and an electronic device. Background Art

[0002] Lithium iron phosphate positive electrode material has the advantages of good high temperature resistance, high cycle performance, and does not contain rare metals such as cobalt. However, due to the low electronic conductivity and ionic conductivity of lithium iron phosphate itself, its electron and ion conduction speed is slower at low temperatures, resulting in poor low-temperature discharge performance of lithium iron phosphate batteries.

[0003] To improve the electronic conductivity of lithium iron phosphate cathode materials, they are typically coated. Commonly used coating materials for lithium iron phosphate are carbon-based materials, such as graphene, carbon nanotubes, and microcrystalline cellulose. However, the electron conduction speed of carbon-coated lithium iron phosphate materials at low temperatures still needs to be further improved.

[0004] Therefore, there is an urgent need to further improve the electrical conductivity of lithium iron phosphate materials and increase their electron conduction speed at low temperatures. Summary of the Invention

[0005] The present invention provides a positive electrode active material having high electrical conductivity and good performance under low temperature conditions.

[0006] The present invention also provides a method for preparing the above-mentioned positive electrode active material. The positive electrode active material prepared by this preparation method can effectively improve its electrical conductivity and enhance its conductive performance, thereby improving the low-temperature performance of the battery; and the preparation method is simple and can be stably carried out at room temperature.

[0007] The present invention also provides a positive electrode, comprising the positive electrode active material or the positive electrode active material prepared by the above preparation method, so that the positive electrode has the properties of high electrical conductivity and high discharge specific capacity at low temperature.

[0008] The present invention also provides a battery comprising the positive electrode, so the battery also has good low-temperature performance.

[0009] The present invention also provides an electronic device comprising the battery, so that the electronic device has the characteristic of continuous and stable operation at low temperatures.

[0010] A first aspect of the present invention provides a positive electrode active material, which includes a core, a first coating layer and a second coating layer, wherein the first coating layer is coated on the surface of the core, and the second coating layer is coated on at least part of the surface of the first coating layer; the core includes lithium iron phosphate, the first coating layer includes a carbon-based material, and the second coating layer includes a metal element, and the metal element includes at least one of palladium element, platinum element, tin element, and molybdenum element.

[0011] The positive electrode active material as described above, wherein the mass content of the second coating layer in the positive electrode active material is 4000-10000 ppm.

[0012] The positive electrode active material as described above, wherein the thickness of the first coating layer in the positive electrode active material is 3-6 nm.

[0013] The positive electrode active material as described above, wherein the average particle size of the positive electrode active material is 80-100 nm.

[0014] The positive electrode active material as described above, wherein the particle size of the metal element is 2-10 nm.

[0015] The positive electrode active material as described above, wherein the electrical conductivity of the positive electrode active material is not less than 0.1987 S / cm.

[0016] A second aspect of the present invention provides a method for preparing the positive electrode active material of the first aspect, comprising:

[0017] Grinding, granulating, and calcining raw materials including a phosphorus source, an iron source, a lithium source, and a carbon source to obtain a first product;

[0018] The first product, a metal precursor and a solvent are mixed to obtain a first mixed system; a reducing agent is mixed with the first mixed system to obtain a second mixed system; the second mixed system reacts to obtain the positive electrode active material; wherein the metal precursor includes at least one of a salt containing palladium element, a salt containing platinum element, a salt containing tin element, and a salt containing molybdenum element.

[0019] The preparation method as described above, wherein the calcination temperature is 670-720° C. and the calcination time is 8-12 hours.

[0020] In the preparation method as described above, the reaction temperature of the second mixed system is 20-35° C., and the reaction time is 6-10 h.

[0021] The preparation method as described above, wherein the salt containing palladium element includes at least one of [Pd(NH3)4](NO3)2, Pd(OAc)2, and Pd(NO3)2; and / or, the salt containing platinum element includes at least one of H2PtCl6, [Pt(NH3)4](NO3)2, PtSO4, and Pt(OAc)2; and / or, the salt containing tin element includes at least one of SnCl4, SnSO4, and Na2SnO3; and / or, the salt containing molybdenum element includes at least one of (NH4)2MoO4 and Na2MoO4.

[0022] The preparation method as described above, wherein the reducing agent includes at least one of NaBH4, KBH4 or NaBH(OAc)3.

[0023] The preparation method as described above, wherein the molar ratio of the reducing agent to the metal precursor is (1-4):1;

[0024] And / or, the mass of the metal element in the metal precursor accounts for 0.1%-1.5% of the first product.

[0025] For the positive electrode active material as described above, the stirring speed when the reducing agent is mixed with the first mixed system is 300-700 rpm.

[0026] A third aspect of the present invention provides a positive electrode, comprising the positive electrode active material described in the first aspect, or the positive electrode active material prepared by the preparation method described in the second aspect.

[0027] A fourth aspect of the present invention provides a battery comprising the positive electrode described in the third aspect.

[0028] A fifth aspect of the present invention provides an electronic device comprising the battery described in the fourth aspect.

[0029] The positive electrode active material provided by the present invention has a first coating layer (including a carbon-based material) coated on the surface of lithium iron phosphate, and the carbon-based material coating improves the electronic conductivity of the lithium iron phosphate; at the same time, a second coating layer (including at least one of the metal elements palladium, platinum, tin, and molybdenum) is coated on at least part of the surface of the first coating layer, and the metal element is coated by adsorption bonding. Since the electrical conductivity of the metal element is relatively high, the electronic conduction speed of the material can be further improved after the metal element is coated. Therefore, the positive electrode active material has a relatively high electrical conductivity and can effectively improve the low-temperature performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0031] Figure 1 TEM image of the positive electrode active material in Example 3 of the present invention;

[0032] Figure 2 This is the EDS spectrum of the positive electrode active material in Example 3 of the present invention;

[0033] Figure 3 1 is the XRD diagram of the positive electrode active material in Examples 1 to 4 of the present invention.

[0034] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0036] In existing technology, lithium iron phosphate is often coated with carbon-based materials to improve its electronic conductivity, thereby increasing the discharge capacity of the lithium iron phosphate cathode material at high rates. However, the improvement in conductivity of lithium iron phosphate after carbon-based coating is insufficient.

[0037] After analysis, the inventors discovered that the likely cause is that the carbon-based material-coated lithium iron phosphate has insufficient electrical conductivity. This conductivity further decreases at low temperatures, leading to poor low-temperature performance. Therefore, to improve the battery's low-temperature performance, significantly increasing the conductivity of the lithium iron phosphate material is an effective measure.

[0038] Based on the above analysis, the inventors attempted to introduce metals into carbon-coated lithium iron phosphate materials. Metals have stronger electrical conductivity than carbon materials, especially in low-temperature environments. This can significantly increase the electron conduction speed of lithium iron phosphate, resulting in better discharge performance of the battery at low temperatures. Currently, there are two main methods for introducing metals into lithium iron phosphate materials: metal doping and metal coating. Metal doping requires the metal element to be doped into the crystal lattice of the lithium iron phosphate material, which has drawbacks such as harsh reaction conditions and complex doping processes, resulting in less than ideal doping results. Metal coating, on the other hand, improves the material's electrical conductivity even more than metal doping.

[0039] Furthermore, through research, the inventors have creatively discovered that certain specific metals (elemental palladium, elemental platinum, elemental tin, and elemental molybdenum) can be adsorbed and bonded to the first coating layer while exhibiting high electrical conductivity. The strong interaction between the metals and the carbon-based material improves the material's electrical conductivity while maintaining excellent stability and preventing the loss of metal elements in the electrolyte. Furthermore, these metals exhibit good compatibility with lithium ions, further facilitating the insertion and removal of lithium ions. Coating at least a portion of the surface of the carbon-coated lithium iron phosphate material with these specific metals can enhance the material's electrical conductivity, thereby improving its performance at low temperatures.

[0040] Based on this, the first aspect of the present invention provides a positive electrode active material, which includes a core, a first coating layer and a second coating layer, the first coating layer is coated on the surface of the core, and the second coating layer is coated on at least part of the surface of the first coating layer; the core includes lithium iron phosphate, the first coating layer includes a carbon-based material, and the second coating layer includes a metal element, and the metal element includes at least one of palladium element, platinum element, tin element, and molybdenum element.

[0041] It should be explained that the positive electrode active material in the present invention is composed of a core, a first coating layer and a second coating layer from the inside to the outside; the first coating layer is coated on the surface of the core, and the second coating layer is coated on part or all of the surface of the first coating layer.

[0042] The first coating layer in the present invention includes a carbon-based material. The present invention does not specifically limit the type of the carbon-based material, and conventional materials in the art can be used.

[0043] The present invention does not impose any specific limitation on the thickness of the first coating layer, which can be adjusted according to actual conditions.

[0044] The present invention does not impose any specific limitation on the coating amount of the second coating layer, that is, the mass content of the second coating layer in the positive electrode active material, and can be adjusted according to actual conditions.

[0045] It should be noted that when the metal element includes multiple (two or more) metal elements mentioned above, the present invention does not impose any specific limitation on the ratio of each metal element.

[0046] The positive electrode active material in the present invention includes a core (lithium iron phosphate), a first coating layer (including a carbon-based material) coated on the surface of the core, and a second coating layer (including the above-mentioned metal element) coated on at least part of the surface of the first coating layer. Among them, the first coating layer can optimize the conductive network and ion transmission path on the surface of lithium iron phosphate, effectively improve the electronic conductivity of lithium iron phosphate and enhance its ion diffusion capacity, improve the rate performance and rapid charge and discharge capacity of the battery, but the lithium iron phosphate coated only with the first coating layer has a low discharge capacity at low temperatures. Therefore, on this basis, the second coating layer is further coated, and the metal element in the second coating layer has higher conductivity and good compatibility with lithium ions, which can further optimize the conductive network and ion diffusion path on the surface of lithium iron phosphate, promote electron transmission and rapid diffusion of ions, and effectively improve the discharge capacity of lithium iron phosphate at low temperatures; at the same time, the aforementioned metal element can be adsorbed and bonded on the carbon-based material, ensuring that the metal element is stably coated on the surface of the carbon-based material. Therefore, the positive electrode active material in the present invention can effectively improve the low temperature performance of the battery.

[0047] Furthermore, in order to improve the conductivity of the positive electrode active material, the mass content of the second coating layer and the thickness of the first coating layer may also be controlled.

[0048] In a specific embodiment, the mass content of the second coating layer in the positive electrode active material is 4000-10000 ppm. The charge and discharge process of lithium iron phosphate requires the insertion and extraction of lithium ions. Within this range, the conductivity of the positive electrode active material is further improved.

[0049] Illustratively, the mass content is 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm, 8500 ppm, 9000 ppm, 9500 ppm or 10000 ppm, or a range consisting of any two of these values.

[0050] The mass content of the second coating layer in the positive electrode active material of the present invention can be obtained by ICP testing.

[0051] In a specific embodiment, the thickness of the first coating layer in the positive electrode active material is 3-6 nm. The thickness of the first coating layer within this range is conducive to the insertion and extraction of lithium ions.

[0052] Illustratively, the thickness is 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm or 6 nm, or a range consisting of any two of these values.

[0053] The thickness of the first coating layer in the positive electrode active material of the present invention can be measured by transmission electron microscopy (TEM).

[0054] Furthermore, in order to increase the specific capacity of the positive electrode active material, the particle size of the positive electrode active material can also be controlled.

[0055] In a specific embodiment, the average particle size of the positive electrode active material is 80-100 nm. Within this particle size range, the specific capacity of the positive electrode active material is relatively large.

[0056] Illustratively, the average particle size is 80 nm, 82 nm, 84 nm, 86 nm, 88 nm, 90 nm, 92 nm, 94 nm, 96 nm, 98 nm or 100 nm, or a range consisting of any two of these values.

[0057] The average particle size of the positive electrode active material in the present invention refers to the average particle size of primary particles.

[0058] The particle size of the positive electrode active material in the present invention can be obtained by SEM testing or TEM testing.

[0059] In one embodiment, the particle size of the metal element is 2-10 nm. A smaller particle size within this range is more conducive to the insertion and extraction of lithium ions, further improving the low-temperature performance of the battery.

[0060] Illustratively, the particle size is 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm, 8 nm, 8.5 nm, 9 nm, 9.5 nm or 10 nm, or a range consisting of any two of these values.

[0061] In one embodiment, the conductivity of the positive electrode active material is not less than 0.1987 S / cm. Specifically, the conductivity of the positive electrode active material can be adjusted to be within the aforementioned range by controlling the particle size of the positive electrode active material, thereby improving the conductivity of the positive electrode active material.

[0062] Illustratively, the conductivity is 0.1987 S / cm, 0.1988 S / cm, 0.1999 S / cm, 0.2001 S / cm, 0.2002 S / cm, 0.2100 S / cm, 0.2118 S / cm, 0.2119 S / cm, 0.2198 S / cm, 0.2203 S / cm, 0.2218 S / cm, 0.2219 S / cm, 0.2220 S / cm, 0.2221 S / cm, 0.2222 S / cm, 0.2225 S / cm or 0.2279 S / cm, or a range consisting of any two of these values.

[0063] A second aspect of the present invention provides a method for preparing a positive electrode active material, comprising:

[0064] Grinding, granulating, and calcining raw materials including a phosphorus source, an iron source, a lithium source, and a carbon source to obtain a first product;

[0065] The first product, the metal precursor and the solvent are mixed to obtain a first mixed system; the reducing agent is mixed with the first mixed system to obtain a second mixed system; the second mixed system reacts to obtain a positive electrode active material; wherein the metal precursor includes at least one of a salt containing palladium element, a salt containing platinum element, a salt containing tin element, and a salt containing molybdenum element.

[0066] Specifically, raw materials including a phosphorus source, an iron source, a lithium source and a carbon source are first ground to obtain an abrasive; the abrasive is granulated, and the product obtained after the granulation is sintered to obtain a first product; then, the first product, a metal precursor and a solvent are uniformly mixed to prepare a first mixed system; then, a reducing agent is uniformly mixed with the first mixed system to prepare a second mixed system; finally, the second mixed system is reacted to obtain a positive electrode active material.

[0067] When the metal precursor is two or more of the above-mentioned specific compounds, the present invention does not impose any specific limitation on the ratio between the specific compounds.

[0068] The phosphorus source refers to a raw material that provides the phosphorus element, the iron source refers to a raw material that provides the iron element, the lithium source refers to a raw material that provides the lithium element, and the carbon source refers to a raw material that provides the carbon element.

[0069] The present invention does not specifically limit the types of phosphorus source, iron source, lithium source, and carbon source, and they can be conventional materials in the art. For example, the phosphorus source includes at least one of ferric phosphate, phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the iron source includes at least one of ferric phosphate, ferrous sulfate, and ferrous oxalate. The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate. The carbon source includes at least one of glucose and polyethylene glycol (PEG); preferably, the carbon source includes glucose and polyethylene glycol; using a mixture of glucose and polyethylene glycol as the carbon source can better control the particle size of the first product, so that a positive electrode active material with a target average particle size (80-100 nm) can be obtained subsequently. Preferably, the mass ratio of glucose to polyethylene glycol is 4:1.

[0070] The present invention does not impose any specific restrictions on the ratio of the phosphorus source, iron source, lithium source, and carbon source, and the ratios can be adjusted according to actual conditions.

[0071] The present invention does not impose any specific limitation on the type of reducing agent, as long as it can reduce the metal precursor to the corresponding metal element, and conventional materials in the art can be used.

[0072] The present invention does not impose any specific restrictions on the type of solvent used in preparing the first mixed system; it only needs to be able to uniformly mix the first product and the metal precursor. Preferably, the solvent comprises at least one of an alcohol and water. More preferably, the solvent is an alcohol having a total carbon number of C1-C4, specifically at least one of methanol, ethanol, propanol, isopropanol, n-butanol, and isobutanol. Using such solvents can improve the dispersion of the first product and the metal precursor.

[0073] When the above-mentioned solvent is a mixture of the aforementioned specific compounds, the present invention does not specifically limit the ratio of each specific compound in the mixture.

[0074] The present invention does not specifically limit the sources of the solvent, metal precursor, and reducing agent; any commercially available product or a product prepared by a conventional preparation method known to those skilled in the art may be used.

[0075] The present invention does not specifically limit the grinding method. In one embodiment, sand milling can be used for grinding. Preferably, the particle size after sand milling is 280-320 nm. Within this range, it is beneficial to obtain a positive electrode active material with a particle size of 80-100 nm.

[0076] Illustratively, the particle size after sand grinding is 280 nm, 282 nm, 284 nm, 286 nm, 288 nm, 290 nm, 292 nm, 294 nm, 296 nm, 298 nm, 300 nm, 305 nm, 310 nm, 315 nm or 320 nm, or a range consisting of any two of these values.

[0077] The present invention does not specifically limit the granulation method. In one embodiment, the granulation can be performed by spray drying. Preferably, the inlet temperature is 230°C and the outlet temperature is 105±5°C.

[0078] The present invention does not impose any specific limitation on the mixing method, and it is sufficient that the materials in the first mixing system and the second mixing system are mixed uniformly. In one embodiment, the mixing can be performed by stirring.

[0079] The present invention does not impose any specific limitation on the heating rate during calcination. Preferably, the heating rate is 5-8°C / min.

[0080] Illustratively, the heating rate is 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min or 8°C / min, or a range consisting of any two of these values.

[0081] The present invention does not impose any specific limitation on the mass ratio of the first product to the metal precursor in the first mixed system, and the mass ratio can be adjusted as needed.

[0082] The present invention does not impose any specific limitation on the ratio of the amount of the reducing agent to the amount of the metal precursor in the second mixed system, and the ratio can be adjusted as needed.

[0083] Furthermore, after the reaction is completed, the reaction system can be subjected to solid-liquid separation, washing, and drying in sequence to obtain the positive electrode active material.

[0084] The present invention does not impose any specific restrictions on the method of solid-liquid separation, as long as the solid phase (positive electrode active material) in the reaction system can be separated. In one embodiment, separation can be performed by filtration.

[0085] The present invention does not specifically limit the washing method, and it is sufficient to clean the separated solid phase. For example, it can be washed with ethanol 3-5 times and then washed with deionized water 2-3 times.

[0086] The present invention does not impose any specific restrictions on the drying temperature, as long as the solvent and water in the washed solid phase can be removed. Preferably, the drying temperature is 60-80°C and the drying time is 12-15 hours.

[0087] For example, the drying temperature is 60° C., 65° C., 70° C., 75° C., or 80° C., or a range consisting of any two values ​​thereof, and the drying time is 12 h, 13 h, 14 h, or 15 h, or a range consisting of any two values ​​thereof.

[0088] Furthermore, in order to better disperse the first product and the metal precursor in the first mixed system, the first product can be added to the solvent and stirred for a first time, and then the metal precursor is added and stirred for a second time to obtain the first mixed system.

[0089] The first stirring speed is preferably 400-600 rpm, and the stirring time is preferably 0.5-1 h; the second stirring speed is preferably 400-600 rpm, and the stirring time is preferably 2-3 h.

[0090] Illustratively, the first stirring speed is 400 rpm, 450 rpm, 500 rpm, 550 rpm or 600 rpm, or a range consisting of any two values ​​therein.

[0091] Illustratively, the first stirring time is 0.5 h, 0.75 h or 1 h, or a range consisting of any two values ​​therein.

[0092] Illustratively, the second stirring speed is 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, or a range consisting of any two values ​​therein.

[0093] Exemplarily, the second stirring time is 2 h, 2.5 h, 3 h, or a range consisting of any two values ​​therein.

[0094] Furthermore, since the reducing agent used in the present invention has a strong reducing property and a fast reaction speed, in order to control the reaction speed and make the reaction more complete, the form of adding the reducing agent can also be adjusted to make the reaction speed moderate and the reaction more complete.

[0095] In one embodiment, when adding the reducing agent to the first mixed system, the reducing agent can be first prepared as a solution (e.g., an aqueous solution of the reducing agent), and then the reducing agent solution can be added dropwise to the first mixed system to form the second mixed system. By preparing the reducing agent as a solution, the reaction rate can be controlled to achieve a gradual reduction effect, thereby avoiding excessive reduction of the metal precursor, which would cause uneven coating of the metal element, affect the overall conductivity and ion diffusion of the positive electrode active material, and thus affect the low-temperature performance of the battery.

[0096] The present invention does not impose any specific restrictions on the concentration of the reducing agent solution and can be adjusted according to actual conditions. In one embodiment, the concentration of the reducing agent solution is 0.8-1.2 M. Within this concentration range, the reaction rate can be well controlled and the reduction effect of the metal precursor can be enhanced.

[0097] Illustratively, the concentration of the reducing agent solution is 0.8 M, 0.85 M, 0.9 M, 0.95 M, 1.0 M or 1.2 M, or a range consisting of any two of these values.

[0098] In one embodiment, the reducing agent solution is added at a rate of 50-60 s / mL. Exemplarily, the rate of addition is 50 s / mL, 52 s / mL, 54 s / mL, 56 s / mL, 58 s / mL, or 60 s / mL, or a range consisting of any two of these values. Within this rate range, the reduction reaction is further fully carried out, and the metal coating is more uniform.

[0099] The present invention is to obtain carbon-coated lithium iron phosphate (first product) by roasting the raw materials including phosphorus source, iron source, lithium source and carbon source. The carbon coating can improve the electronic conductivity of lithium iron phosphate and improve its ion diffusion capacity, which can improve the rate performance and rapid charge and discharge capacity of the battery at room temperature; However, the discharge capacity of carbon-coated lithium iron phosphate at low temperature is still poor; Therefore, the raw materials including carbon-coated lithium iron phosphate, metal precursor and reducing agent are further reacted under specific conditions, and the metal precursor can be reduced to the corresponding metal element. The metal element after reduction can be immediately adsorbed and bonded on the surface of the carbon-coated lithium iron phosphate material, and a positive active material with good low temperature performance can be prepared. This is mainly because the metal element has higher conductivity than the carbon-based material, and it also has better compatibility with lithium ions, which is conducive to the embedding and embedding of lithium ions, thereby improving the transmission performance of electrons and the diffusion capacity of ions. Therefore, the positive active material obtained by the above preparation method can effectively improve the discharge performance of the battery at low temperatures.

[0100] In a specific embodiment, the calcination temperature is 670-720° C. and the calcination time is 8-12 hours. Within the calcination temperature and time range, the carbon coating layer can be better coated on the surface of the lithium iron phosphate.

[0101] Illustratively, the calcination temperature is 670°C, 680°C, 690°C, 700°C, 710°C or 720°C, or a range consisting of any two of these values; the calcination time is 8h, 9h, 10h, 11h or 12h, or a range consisting of any two of these values.

[0102] In one embodiment, the reaction temperature of the second mixed system is 20-35°C and the reaction time is 6-10 hours. Within this reaction time and reaction temperature range, the reduction reaction proceeds more fully; the reaction time is calculated from the start of adding the reducing agent.

[0103] Illustratively, the reaction temperature of the second mixed system is 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C or 35°C, or a range consisting of any two of the values ​​therein; the reaction time of the second mixed system is 6h, 7h, 8h, 9h or 10h, or a range consisting of any two of the values ​​therein.

[0104] Furthermore, the type of metal precursor can be limited so that the reduced metal element has higher electrical conductivity and can be better adsorbed and bonded to the surface of the carbon-coated lithium iron phosphate.

[0105] In a specific embodiment, the salt containing palladium element includes at least one of [Pd(NH3)4](NO3)2, Pd(OAc)2, and Pd(NO3)2; and / or, the salt containing platinum element includes at least one of H2PtCl6, [Pt(NH3)4](NO3)2, PtSO4, and Pt(OAc)2; and / or, the salt containing tin element includes at least one of SnCl4, SnSO4, and Na2SnO3; and / or, the salt containing molybdenum element includes at least one of (NH4)2MoO4 and Na2MoO4.

[0106] When the metal precursor includes the aforementioned multiple compounds at the same time, the present invention does not impose any specific limitation on the ratio between the various compounds.

[0107] Furthermore, the type of reducing agent can be controlled so that the reducing agent can better reduce the metal precursor, which is beneficial to the reduction reaction and deposition.

[0108] In a specific embodiment, the reducing agent includes at least one of NaBH4, KBH4 or NaBH(OAc)3. The above reducing agents have strong reducing properties and can effectively reduce the metal precursor to the corresponding metal element.

[0109] When the reducing agent is a mixture of the aforementioned specific compounds, the present invention does not specifically limit the ratio of each specific compound in the mixture.

[0110] Furthermore, the mass ratio of the first product to the metal precursor, and the molar ratio of the reducing agent to the metal precursor can also be controlled.

[0111] In one embodiment, the ratio of the amount of the reducing agent to the amount of the metal precursor is (1-4): 1. Within this range, the reducing agent can better reduce the metal element.

[0112] Illustratively, the ratio of the amounts of substances is 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, or a range consisting of any two values ​​therein.

[0113] In a specific embodiment, the mass of the metal element in the metal precursor accounts for 0.1%-1.5% of the first product. Within this range, it is helpful to better coat the surface of the first product with the metal element generated by reduction.

[0114] Illustratively, the mass of the metal element in the metal precursor accounts for 0.1%, 0.4%, 0.7%, 1.1%, 1.3% or 1.5% of the first product, or a range consisting of any two of these values.

[0115] In one embodiment, the stirring speed when the reducing agent is mixed with the first mixed system is 300-700 rpm.

[0116] Illustratively, the stirring speed when the reducing agent is mixed with the first mixed system is 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm or 700 rpm, or a range consisting of any two of these values.

[0117] Illustratively, the stirring time when the reducing agent is mixed with the first mixed system is 2 h, 2.5 h or 3 h, or a range consisting of any two values ​​therein.

[0118] A third aspect of the present invention provides a positive electrode, comprising the positive electrode active material of the first aspect, or the positive electrode active material prepared by the preparation method of the second aspect.

[0119] Since the positive electrode active material included in the positive electrode has an effect of good electrical conductivity at low temperatures, the positive electrode including the positive electrode active material has good low-temperature performance.

[0120] The present invention does not specifically limit the structure of the positive electrode. In one embodiment, the positive electrode includes a positive electrode current collector and a positive electrode active layer disposed on at least a portion of the surface of the positive electrode current collector. The positive electrode active layer includes the above-mentioned positive electrode active material, a conductive agent and a binder.

[0121] The present invention does not specifically limit the material of the positive electrode current collector, and it can be any conventional material in the art. For example, the material of the positive electrode current collector can be any one of aluminum foil and nickel foil.

[0122] The present invention does not specifically limit the type of the conductive agent, and it can be any conventional material in the art. For example, the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber.

[0123] The present invention does not specifically limit the type of binder, and it can be any conventional material in the art. For example, the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane.

[0124] The present invention does not specifically limit the preparation method of the positive electrode sheet. In one embodiment, the positive electrode can be prepared by a method comprising the following steps:

[0125] The positive electrode active material of the present invention, the conductive agent and the binder are dispersed in N-methylpyrrolidone (NMP) solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector, and the positive electrode sheet is obtained after drying, rolling and slitting.

[0126] The present invention does not impose any specific restrictions on the amounts of the positive electrode active material, the conductive agent, and the binder, which can be adjusted according to actual conditions.

[0127] A fourth aspect of the present invention provides a battery comprising the positive electrode of the third aspect.

[0128] Since the positive electrode included in the battery has good electrical conductivity at low temperatures, the battery including the positive electrode has the properties of high electrical conductivity and high discharge specific capacity at low temperatures.

[0129] The battery in the present invention can be a single cell or a battery pack.

[0130] It should be noted that the battery cells constituting the battery pack may be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a combination of these connection methods, and there is no particular limitation thereto.

[0131] The battery of the present invention includes, in addition to the positive electrode, a negative electrode, an electrolyte, and a separator.

[0132] The present invention does not specifically limit the structure of the negative electrode. In one embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least a portion of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a binder, and a conductive agent.

[0133] The present invention does not specifically limit the material of the negative electrode current collector, and it can be any conventional material in the art. For example, the negative electrode current collector can be any one of copper foil, nickel foam, and copper foam.

[0134] The present invention does not specifically limit the type of negative electrode active material, and can be any negative electrode active material commonly used in batteries. For example, the negative electrode active material can be selected from at least one of graphite, hard carbon, soft carbon, mesocarbon microbeads, silicon-based negative electrode materials (primarily including silicon monoxide and silicon-carbon negative electrodes), and tin-based negative electrode materials (primarily including tin and tin alloys).

[0135] The present invention does not specifically limit the type of binder, and the binder may be any binder commonly used in current battery negative electrodes. For example, the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0136] The present invention does not specifically limit the type of conductive agent, and can be any conductive agent commonly used in battery negative electrodes. For example, the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene.

[0137] The present invention does not specifically limit the preparation method of the negative electrode. In one embodiment, the negative electrode can be prepared by a method comprising the following steps:

[0138] The negative electrode active material, conductive agent and binder are dispersed in deionized water and fully stirred to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode collector, and the negative electrode sheet is obtained after drying, rolling and cutting.

[0139] The present invention does not impose any specific restrictions on the amounts of the negative electrode active material, the conductive agent, and the binder, which can be adjusted according to actual conditions.

[0140] The present invention does not specifically limit the composition of the electrolyte, and may include one or more solvents commonly used in current battery electrolytes, as well as electrolyte lithium salts commonly used in current battery electrolytes. For example, the solvent may include at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, and γ-butyrolactone; and the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0141] The present invention does not impose any specific restrictions on the material of the separator, and can be any separator material commonly used in current batteries. For example, the separator can be selected from any of polypropylene separators (PP), polyethylene separators (PE), polypropylene / polyethylene two-layer composite films (PP / PE), polyimide electrospun separators (PI), polypropylene / polyethylene / polypropylene three-layer composite films (PP / PE / PP), cellulose non-woven separators, and separators with ceramic coatings.

[0142] The present invention does not specifically limit the preparation method of the battery. In one embodiment, the battery can be prepared by a method comprising the following steps:

[0143] The positive electrode sheet, separator, and negative electrode sheet are wound or stacked to form a bare cell, which is then encapsulated in a pre-stamped aluminum-plastic film bag. After the encapsulated cells are dried to remove moisture, the electrolyte is injected into the dried cells. After the cells are stored, formed, and resealed, the lithium-ion battery is completed.

[0144] A fifth aspect of the present invention provides an electronic device comprising the battery according to the fourth aspect, so that the electronic device has the characteristic of continuous and stable operation at low temperatures.

[0145] The present invention does not specifically limit the electrical equipment. For example, it can be an electric car, a mobile phone, a tablet computer, a laptop computer, a wearable device (watch, bracelet), a digital camera, etc.

[0146] Hereinafter, the positive electrode active material provided by the present invention and the positive electrode and battery including the positive electrode active material will be described in detail through specific examples.

[0147] Example 1

[0148] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting pale yellow powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0149] Step 2: In this example, the metal precursor used was [Pd(NH3)4](NO3)2. 30g of LFP-C was dispersed in an ethanol solution, and [Pd(NH3)4](NO3)2 was added, with the metal element in [Pd(NH3)4](NO3)2 accounting for 0.6% of the LFP-C mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (the molar ratio of NaBH4 to [Pd(NH3)4](NO3)2 was 3:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours, filtered, washed, and the resulting black solid was dried in an oven at 60°C overnight to obtain the cathode active material, designated LFP-C-Pd.

[0150] Example 2

[0151] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0152] Step 2: In this example, the metal precursor used was HPtCl. 30g of LFP-C was dispersed in an ethanol solution and HPtCl was added, with the metal element in the HPtCl constituting 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH solution (the molar ratio of NaBH to HPtCl was 3:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Pt powder.

[0153] Example 3

[0154] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0155] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0156] Example 4

[0157] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0158] Step 2: In this example, the metal precursor used was (NH4)2MoO4. 30g of LFP-C was dispersed in an ethanol solution. (NH4)2MoO4 was added, with the metal element in the (NH4)2MoO4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (the molar ratio of NaBH4 to (NH4)2MoO4 was 3:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Mo powder.

[0159] Example 5

[0160] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0161] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 1:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0162] Example 6

[0163] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0164] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.4% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0165] Example 7

[0166] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0167] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.8% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0168] Example 8

[0169] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0170] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 1% of the LFP-C. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0171] Example 9

[0172] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0173] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.2% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0174] Example 10

[0175] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 3, except that:

[0176] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0177] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0178] Example 11

[0179] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0180] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0181] Example 12

[0182] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 380 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0183] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0184] Example 13

[0185] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 230 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0186] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0187] Example 14

[0188] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0189] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 200 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 200 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0190] Example 15

[0191] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0192] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 100 rpm for 2 hours, a 1M NaBH4 solution (the molar ratio of NaBH4 to SnCl4 was 3:1) was added dropwise. The solution was stirred at 100 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0193] Example 16

[0194] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0195] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 800 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to SnCl4) was added dropwise. The solution was stirred at 800 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0196] Example 17

[0197] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0198] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a molar ratio of NaBH4 to SnCl4 of 6:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0199] Example 18

[0200] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0201] Step 2: In this example, the metal precursor used was SnCl4. 30g of LFP-C was dispersed in an ethanol solution. SnCl4 was added, with the metal element in the SnCl4 accounting for 0.6% of the LFP-C by mass. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (the molar ratio of NaBH4 to SnCl4 was 0.5:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Sn powder.

[0202] Comparative Example 1

[0203] In this comparative example, no metal precursor was used to coat LFP-C.

[0204] The specific method involves mixing iron phosphate, lithium carbonate, PEG, and glucose, sand-grinding them to a particle size of 280-320 nm, and then spraying them to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose is 1:1:0.004:0.2. The resulting powder is then calcined at 680°C for 8 hours in a tube furnace under nitrogen protection at a constant temperature to obtain a black powder. This black powder is carbon-coated lithium iron phosphate powder, designated LFP-C.

[0205] Comparative Example 2

[0206] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace at 680°C for 8 hours under a nitrogen atmosphere. This black powder, carbon-coated lithium iron phosphate powder, was designated LFP-C.

[0207] Step 2: In this example, the metal precursor used was Mn(NO₃)₂. 30g of LFP-C was dispersed in an ethanol solution. Mn(NO₃)₂ was added, with the metal element in the Mn(NO₃)₂ accounting for 0.6% of the LFP-C mass. After stirring at 500 rpm for 2 hours, a 1M NaBH₄ solution (with a 3:1 molar ratio of NaBH₄ to Mn(NO₃)₂) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Mn powder.

[0208] Comparative Example 3

[0209] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace at 680°C for 8 hours under a nitrogen atmosphere. This black powder, carbon-coated lithium iron phosphate powder, was designated LFP-C.

[0210] Step 2: In this example, the metal precursor used was Bi(NO₃)₃. 30g of LFP-C was dispersed in an ethanol solution. Bi(NO₃)₃ was added, with the metal element in Bi(NO₃)₃ constituting 0.6% of the LFP-C by weight. After stirring at 500 rpm for 2 hours, a 1M NaBH₄ solution (the molar ratio of NaBH₄ to Bi(NO₃)₃ was 3:1) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Bi powder.

[0211] Comparative Example 4

[0212] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace at 680°C for 8 hours under a nitrogen atmosphere. This black powder, carbon-coated lithium iron phosphate powder, was designated LFP-C.

[0213] Step 2: In this example, NiCl2 was used as the metal precursor. 30g of LFP-C was dispersed in an ethanol solution. NiCl2 was added, with the metal element in the NiCl2 accounting for 0.6% of the LFP-C. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to NiCl2) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Ni powder.

[0214] Comparative Example 5

[0215] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace at 680°C for 8 hours under a nitrogen atmosphere. This black powder, carbon-coated lithium iron phosphate powder, was designated LFP-C.

[0216] Step 2: In this example, the metal precursor used was CrCl₄. 30g of LFP-C was dispersed in an ethanol solution and CrCl₄ was added, with the metal element in the CrCl₄ accounting for 0.6% of the LFP-C. After stirring at 500 rpm for 2 hours, a 1M NaBH₄ solution (with a 3:1 molar ratio of NaBH₄ to CrCl₄) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Cr powder.

[0217] Comparative Example 6

[0218] Step 1: Iron phosphate, lithium carbonate, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, PEG, and glucose was 1:1:0.004:0.2. The resulting powder was calcined in a tube furnace at 680°C for 8 hours under a nitrogen atmosphere. This black powder, carbon-coated lithium iron phosphate powder, was designated LFP-C.

[0219] Step 2: In this example, the metal precursor used was CoCl2. 30g of LFP-C was dispersed in an ethanol solution. CoCl2 was added, with the metal element in the CoCl2 accounting for 0.6% of the LFP-C. After stirring at 500 rpm for 2 hours, a 1M NaBH4 solution (with a 3:1 molar ratio of NaBH4 to CoCl2) was added dropwise. The solution was stirred at 500 rpm for 6 hours. The resulting black solid was filtered and washed, and then dried in an oven at 60°C overnight to obtain LFP-C-Co powder.

[0220] Comparative Example 7

[0221] Iron phosphate, lithium carbonate, tin chloride, PEG, and glucose were mixed and sand-milled to a particle size of 280-320 nm. The mixture was then sprayed to obtain a uniform pale yellow powder. The molar ratio of iron phosphate, lithium carbonate, tin chloride, PEG, and glucose was 1:1:0.035:0.004:0.2. The resulting powder was calcined in a tube furnace under nitrogen at 680°C for 8 hours to obtain a black powder, lithium iron phosphate powder, designated LFP-Sn.

[0222] Test example

[0223] 1. TEM and EDS tests were performed on the above Example 3, and XRD tests were performed on Examples 1-4.

[0224] like Figure 1 As shown, Figure 1 TEM image of the positive electrode active material in Example 3 of the present invention, Figure 1 In the figure, the black round particles in the carbon layer are metallic element tin, and their particle size is relatively small at around 1 nm.

[0225] like Figure 2 As shown, Figure 2 This is the EDS spectrum of the positive electrode active material in Example 3 of the present invention, where red represents iron and blue represents the metallic element tin in the second coating layer. The metallic element tin is more concentratedly coated on the surface of the carbon layer.

[0226] like Figure 3 As shown, Figure 3 is the XRD pattern of the positive electrode active material in Examples 1 to 4 of the present invention, Figure 3 LFP-Sn, LFP-Mo, LFP-Pd and LFP-Pt only have XRD diffraction peaks of lithium iron phosphate, and no diffraction peaks of Sn, Mo, Pd and Pt metal elements, indicating that the metal element particles have not agglomerated and the particle size is small, which is consistent with the TEM results. Figure 3 Here, LFP-Sn represents LFP-C-Sn prepared in Example 3, LFP-Mo represents LFP-C-Mo prepared in Example 4, LFP-Pd represents LFP-C-Pd prepared in Example 1, and LFP-Pt represents LFP-C-Pt prepared in Example 2.

[0227] 2. The physical and chemical properties of the positive electrode active materials prepared in the above examples and comparative examples were tested. The test results are shown in Table 1.

[0228] 1) Test method for mass content of the second coating layer

[0229] ICP test method is based on GBT30902-2014.

[0230] The instrument used was Thermo Fisher Scientific.

[0231] 2) Test method for particle size of positive electrode active material

[0232] The SEM test method adopts GB / T 23414-2009.

[0233] The SEM instrument used was JIB-PS500i.

[0234] 3) Conductivity test method

[0235] The powder conductivity is measured using a four-probe method (RTS-8 digital four-probe tester). Pressure is applied to a powder-filled mold while a resistance tester transmits an electrical signal through the probes to obtain the conductivity of different powder materials. The test conditions are: the four probes are equally spaced (1 mm), the probe material is tungsten steel, the current is 1 mA, and the voltage is 1 V.

[0236] Table 1

[0237]

[0238] As can be seen from Table 1, when the second coating layer metal is Sn, the first coating layer thickness is 4.3nm, the metal content is 6000ppm, the metal element particle size is 3.4nm, and the positive electrode active material is 84nm, the material conductivity is the highest and has the best conductivity.

[0239] 3. The positive electrode active materials prepared in the above examples and comparative examples were assembled into CR2025 button-type half-cells for electrochemical testing, which specifically included the following steps:

[0240] The battery slurry was prepared using N-methylpyrrolidone as a solvent, PVDF as a binder, and acetylene black as a conductive agent. The mass ratio of the positive electrode active material, binder, and conductive agent in the battery slurry was 90:5:5. The battery slurry was evenly coated on aluminum foil and vacuum dried. In a glove box, the positive electrode sheet was obtained after cutting and pressing. The compaction density of the sheet was 2.10g / cm 3 , with a surface density of 15g / cm 2 The positive electrode sheet was assembled with a lithium negative electrode sheet, a polyethylene separator for lithium batteries, an electrolyte, and a spring gasket to form a CR2025 button cell. The electrolyte comprised lithium hexafluorophosphate, ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate, wherein the mass ratio of lithium hexafluorophosphate, ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate was 13.26:37.17:24.78:24.78.

[0241] The electrochemical test of button cells was performed using the Xinwei button cell test channel. The test conditions used in the capacity test were:

[0242] 1) Room temperature charge and discharge capacity

[0243] The test temperature is 25°C, the test window is 2.5~4.3V, the charging current is 0.1C, and the battery is charged at a constant voltage of 3.8V to a cutoff current of 0.02C, and then discharged at 0.1C to obtain the room temperature charge specific capacity and room temperature discharge specific capacity.

[0244] 2) Normal temperature 0.5C charge specific capacity and low temperature 1C discharge specific capacity

[0245] The test temperature was 25°C, the test window was 2.5-4.3V, and two cycles of charge and discharge were performed at 0.1C; then the battery was charged to 3.8V at 0.5C, and the 0.5C charge specific capacity was recorded; then the battery was placed at -20°C until the temperature of the battery body was consistent with the ambient temperature, and then discharged to 2.0V at a constant current of 1C, and the 1C discharge specific capacity at a low temperature of -20°C was obtained.

[0246] The test results are shown in Table 2.

[0247] Table 2

[0248]

[0249]

[0250]

[0251] As shown in Table 2, the positive electrode active material produced by metal coating using the metal precursor selected in the present invention as a raw material has high electrical conductivity, which can effectively improve the low-temperature performance of the battery. In particular, using Sn as the second coating layer can maximize the conductivity of the lithium iron phosphate positive electrode material, further improving the low-temperature performance of the material.

[0252] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and illustrated in the accompanying drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A positive electrode active material, characterized in that The positive electrode active material includes a core, a first coating layer and a second coating layer, the first coating layer is coated on the surface of the core, and the second coating layer is coated on at least part of the surface of the first coating layer; the core includes lithium iron phosphate, the first coating layer includes a carbon-based material, and the second coating layer includes a metal element, and the metal element includes at least one of palladium element, platinum element, tin element, and molybdenum element.

2. The positive electrode active material according to claim 1, characterized in that The mass content of the second coating layer in the positive electrode active material is 4000-10000 ppm.

3. The positive electrode active material according to claim 1 or 2, characterized in that The thickness of the first coating layer in the positive electrode active material is 3-6 nm.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The average particle size of the positive electrode active material is 80-100 nm.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The particle size of the metal element is 2-10 nm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The electrical conductivity of the positive electrode active material is not less than 0.1987 S / cm.

7. A method for preparing the positive electrode active material according to any one of claims 1 to 6, characterized in that: include: Grinding, granulating, and calcining raw materials including a phosphorus source, an iron source, a lithium source, and a carbon source to obtain a first product; The first product, a metal precursor and a solvent are mixed to obtain a first mixed system; a reducing agent is mixed with the first mixed system to obtain a second mixed system; the second mixed system reacts to obtain the positive electrode active material; wherein the metal precursor includes at least one of a salt containing palladium element, a salt containing platinum element, a salt containing tin element, and a salt containing molybdenum element.

8. The preparation method according to claim 7, characterized in that The calcination temperature is 670-720° C. and the calcination time is 8-12 hours.

9. The preparation method according to claim 7 or 8, characterized in that The reaction temperature of the second mixed system is 20-35° C., and the reaction time is 6-10 h.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The salt containing palladium element includes at least one of [Pd(NH3)4](NO3)2, Pd(OAc)2, and Pd(NO3)2; and / or, the salt containing platinum element includes at least one of H2PtCl6, [Pt(NH3)4](NO3)2, PtSO4, and Pt(OAc)2; and / or, the salt containing tin element includes at least one of SnCl4, SnSO4, and Na2SnO3; and / or, the salt containing molybdenum element includes at least one of (NH4)2MoO4 and Na2MoO4.

11. The preparation method according to any one of claims 7 to 10, characterized in that: The reducing agent includes at least one of NaBH4, KBH4 or NaBH(OAc)3.

12. The preparation method according to any one of claims 7 to 11, characterized in that: The molar ratio of the reducing agent to the metal precursor is (1-4):1; And / or, the mass of the metal element in the metal precursor accounts for 0.1%-1.5% of the first product.

13. The preparation method according to any one of claims 7 to 12, characterized in that: The stirring speed when the reducing agent is mixed with the first mixed system is 300-700 rpm.

14. A positive electrode, characterized in that The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 6, or the positive electrode active material prepared by the preparation method according to any one of claims 7 to 13.

15. A battery, characterized in that: Comprising the positive electrode according to claim 14.

16. An electronic device, characterized in that: Including the battery according to claim 15.

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