Carbon-coated lithium iron phosphate and preparation method thereof, and lithium battery

Abstract

The application discloses carbon-coated lithium iron phosphate and a preparation method and lithium battery thereof, and the preparation method of the carbon-coated lithium iron phosphate comprises the following steps: (1) mixing an iron phosphate precursor and a fullerene solution, and then drying to obtain a fullerene-coated iron phosphate precursor; wherein the solvent of the fullerene solution is a non-aqueous solvent; (2) mixing the fullerene-coated iron phosphate precursor, a lithium source, a metal ion dopant and a carbon source, and then performing ball milling to obtain a mixture, and drying the mixture; the metal ion dopant comprises a metal doping element; (3) sintering the dried mixture in a protective atmosphere to obtain the carbon-coated lithium iron phosphate. The method can improve the conductivity of the carbon-coated lithium iron phosphate material, reduce the powder resistance of the material, and improve the energy efficiency of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular, the present application relates to a carbon-coated lithium iron phosphate and a preparation method thereof, and a lithium battery. BACKGROUND

[0002] At present, the powder resistance of lithium iron phosphate material is high, the conductivity is poor, the discharge energy efficiency of the prepared battery is low, which cannot meet the design requirements of the battery cell, resulting in an increase in the defective rate of the battery cell.

[0003] During the synthesis of lithium iron phosphate, carbon coating by adding a carbon source can reduce the powder resistance of the material and improve the discharge energy efficiency of the battery. However, in the current carbon-coated lithium iron phosphate technology, the carbon source is usually a combination of organic and inorganic carbon sources, and the graphitization degree of the carbon source is low, and the conductivity is poor. SUMMARY

[0004] The present application is based on the discovery and understanding of the inventors that the powder resistance of lithium iron phosphate material is high, the conductivity is poor, and the discharge energy efficiency of the battery is low. In the current carbon-coated lithium iron phosphate, the graphitization degree of the carbon source is low, and the conductivity is poor.

[0005] The present application aims to at least solve one of the technical problems in the related art. To this end, the embodiments of the present application propose a carbon-coated lithium iron phosphate and a preparation method thereof, and a lithium battery, which can improve the conductivity of the carbon-coated lithium iron phosphate material, reduce the powder resistance of the material, and improve the energy efficiency of the battery.

[0006] The present application provides a preparation method of carbon-coated lithium iron phosphate, comprising the following steps:

[0007] (1) mixing a lithium iron phosphate precursor and a fullerene solution, and then drying to obtain a fullerene-coated lithium iron phosphate precursor; wherein the solvent of the fullerene solution is a non-aqueous solvent;

[0008] (2) mixing the fullerene-coated lithium iron phosphate precursor, a lithium source, a metal ion dopant, and a carbon source, and then ball milling to obtain a mixture, and drying the mixture; the metal ion dopant comprises a metal doping element;

[0009] (3) sintering the dried mixture in a protective atmosphere to obtain carbon-coated lithium iron phosphate.

[0010] The preparation method of the carbon-coated lithium iron phosphate of the embodiment of the present application has the advantages and technical effects that the carbon-coated lithium iron phosphate can effectively improve the electrical conductivity of the lithium iron phosphate material, reduce the powder resistance of the material, and thus improve the energy efficiency of the battery. Compared with the related art of improving the electrical conductivity by adding a conductive agent, the method of the present application does not increase the powder resistance of the material and has a smaller influence on the performance of the battery. The synthesis method of the present application is simple, the raw materials are low in price, the carbon-coated lithium iron phosphate material has uniform particle size and good crystallinity, is suitable for large-scale production, and is more practical and economical.

[0011] In the embodiment of the present application, the fullerene-coated iron phosphate precursor is prepared by mixing the iron phosphate precursor and the fullerene solution, the solvent of the fullerene solution is a non-aqueous solvent, the fullerene is uniformly coated on the iron phosphate precursor at a molecular level by using the solubility of the fullerene, and the SP 2 The electrical conductivity of the track hybrid improves the electrical conductivity of the lithium iron phosphate material, reduces the powder resistance of the material, and improves the energy efficiency of the battery. If the iron phosphate precursor and the fullerene are only physically mixed, it is difficult to uniformly coat; if water is used as the solvent of the fullerene solution, the physical and chemical properties of the fullerene and water are completely different, and the affinity between them is very weak. Excessive water molecules can reduce the hydrophobicity and affect the properties of the fullerene, thereby causing performance degradation, and therefore, the fullerene aqueous solution is not suitable for mixing with the iron phosphate precursor.

[0012] In the embodiment of the present application, the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, and the carbon source are mixed and ball milled, the lithium source, the metal ion dopant, and the carbon source are uniformly coated on the precursor, and after high-temperature sintering, the metal-doped elements are doped into the structure of the lithium iron phosphate, the metal-doped elements in the lithium iron phosphate can replace the iron sites, form lattice distortion and other lattice defects, and thus improve the ionic conductivity and electronic conductivity of the carbon-coated lithium iron phosphate. The present application additionally adds other carbon sources as reducing agents to participate in chemical reactions and simultaneously coat the lithium iron phosphate, thereby enhancing the electrical conductivity.

[0013] In some embodiments, in the step (1), the solvent of the fullerene solution comprises at least one of dimethylbenzene, toluene, or chlorobenzene.

[0014] In some embodiments, in the step (1), the particle size of the iron phosphate precursor is 100-500 nm;

[0015] And / or, the mass ratio of the iron phosphate precursor to the fullerene is 97-100:0.01-3;

[0016] And / or, the mixing is performed under heating; the temperature of the mixing is 40-80℃; and the time of the mixing is 2-3h.

[0017] In some embodiments, in the step (2), the molar ratio of lithium element in the lithium source, iron element in the fullerene-coated iron phosphate precursor, and metal doping element in the metal ion dopant is 1.0-1.08:0.95-0.99:0-0.05;

[0018] And / or, in the mixture of the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, and the carbon source, the mass percentage of the carbon source is 3%-10%;

[0019] And / or, the ball milling time is 3-7h.

[0020] In some embodiments, in the step (2), the lithium source includes at least one of lithium hydroxide and lithium carbonate;

[0021] And / or, the carbon source includes at least one of glucose, phenolic resin, sucrose, citric acid, polyethylene glycol, and conductive carbon black.

[0022] In some embodiments, in the step (2), the metal doping element includes at least one of aluminum, titanium, magnesium, and vanadium;

[0023] And / or, the metal ion dopant includes at least one of an oxide, a hydroxide, and a salt of the metal doping element.

[0024] In some embodiments, in the step (3), the sintering temperature is 500-800℃;

[0025] And / or, the sintering time is 8-36h;

[0026] And / or, the particle size of the carbon-coated lithium iron phosphate is 0.3-2.0μm.

[0027] In some embodiments, in the step (3), the dried mixture is first pre-sintered under a protective atmosphere, cooled, ground, and then sintered under a protective atmosphere; the pre-sintering temperature is 500-600℃; the pre-sintering time is 12-24h; the sintering temperature is 600-800℃; and the sintering time is 8-12h.

[0028] The embodiment of the present application provides a carbon-coated lithium iron phosphate prepared by the preparation method.

[0029] The lithium battery provided by the embodiment of the present application comprises a positive electrode material, and the positive electrode material comprises the carbon-coated lithium iron phosphate provided by the embodiment of the present application. In the embodiment of the present application, the carbon-coated lithium iron phosphate has high electrical conductivity and low powder resistance, and can improve the energy efficiency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a Raman test diagram of the carbon-coated lithium iron phosphate provided by the embodiment 2 of the present application.

[0031] Figure 2 is a galvanostatic impedance test diagram of the lithium battery provided by the embodiment of the present application and the comparative example.

[0032] Figure 3 is a charge-discharge curve diagram of the lithium battery provided by the embodiment of the present application and the comparative example.

[0033] Figure 4 is a comparison diagram of the energy efficiency of the lithium battery provided by the embodiment of the present application and the comparative example.

[0034] Figure 5 is a comparison diagram of the capacity retention rate of the lithium battery provided by the embodiment of the present application and the comparative example.

[0035] Figure 6 is a comparison diagram of the average discharge voltage of the lithium battery provided by the embodiment of the present application and the comparative example.DETAILED DESCRIPTION

[0036] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below by referring to the accompanying drawings are exemplary, and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0037] The preparation method of the carbon-coated lithium iron phosphate provided by the embodiment of the present application comprises the following steps:

[0038] (1) mixing an iron phosphate precursor and a fullerene solution, and then drying to obtain a fullerene-coated iron phosphate precursor; wherein the solvent of the fullerene solution is a non-aqueous solvent;

[0039] (2) mixing the fullerene-coated iron phosphate precursor, a lithium source, a metal ion dopant and a carbon source to perform ball milling, to obtain a mixture, and drying the mixture; the metal ion dopant comprises a metal doping element;

[0040] (3) sintering the dried mixture in a protective atmosphere to obtain the carbon-coated lithium iron phosphate.

[0041] The preparation method of the carbon-coated lithium iron phosphate of the embodiment of the present application can effectively improve the electrical conductivity of the lithium iron phosphate material, and reduce the powder resistance of the material, thereby improving the energy efficiency of the battery. Compared with the related art of improving the electrical conductivity by adding a conductive agent, the method of the present application does not increase the powder resistance of the material, and has a smaller influence on the performance of the battery. The synthesis method of the present application is simple, and the raw materials are low in price. The carbon-coated lithium iron phosphate material has uniform particle size and good crystallinity, is suitable for large-scale production, and is more practical and economical.

[0042] In the embodiment of the present application, the fullerene-coated iron phosphate precursor is prepared by mixing the iron phosphate precursor and the fullerene solution. The solvent of the fullerene solution is a non-aqueous solvent. The fullerene is uniformly coated on the iron phosphate precursor at a molecular level by using the solubility of the fullerene, and the SP 2 conductivity of the orbital hybridization, the electrical conductivity of the lithium iron phosphate material is improved, the powder resistance of the material is reduced, and the energy efficiency of the battery is improved. If the iron phosphate precursor and the fullerene are only physically mixed, it is difficult to uniformly coat them. If water is used as the solvent of the fullerene solution, the physical and chemical properties of the fullerene and water are completely different, and the affinity between them is very weak. Too many water molecules will reduce the hydrophobicity, affect the properties of the fullerene, and thus cause performance degradation. Therefore, the fullerene aqueous solution is not suitable for mixing with the iron phosphate precursor.

[0043] In the embodiment of the present application, the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, and the carbon source are mixed and ball milled. The lithium source, the metal ion dopant, and the carbon source are uniformly coated on the precursor. After high-temperature sintering, the metal-doped elements are doped into the structure of the lithium iron phosphate. The metal-doped elements in the lithium iron phosphate can replace the iron sites, form lattice distortion and other lattice defects, thereby improving the ionic conductivity and electronic conductivity of the carbon-coated lithium iron phosphate.

[0044] In some embodiments, the step (1) uses a fullerene solution; optionally, the solvent of the fullerene solution includes at least one of xylene, toluene, or chlorobenzene, and the xylene includes at least one of o-xylene, m-xylene, or p-xylene; optionally, the concentration of the fullerene solution is greater than 5 g / L, and specifically, for example, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, or 10 g / L. In the embodiment of the present application, the fullerene solution using xylene, toluene, or chlorobenzene as the solvent can uniformly coat the fullerene on the iron phosphate precursor at a molecular level, and fully exert the SP 2 conductivity of the orbital hybridization, the electrical conductivity of the lithium iron phosphate material is improved, the powder resistance of the material is reduced, and the energy efficiency of the battery is improved.

[0045] In some embodiments, in the step (1), the fullerene comprises fullerene C 60 , the fullerene C 60 is a closed fullerene.

[0046] In some embodiments, in the step (1), the mass ratio of the iron phosphate precursor and the fullerene is 97-100:0.01-3, specifically, 97-100 (e.g., 97, 98, 99, 100):0.01-3 (0.01, 0.1, 0.5, 1, 2, 2.5, 3). In the embodiments of the present application, the mass ratio of the iron phosphate precursor and the fullerene is 97-100:0.01-3, which is beneficial to reduce the resistivity. When the content of the fullerene is too low or no fullerene is contained, the effect of reducing the resistivity is not good; when the content of the fullerene is too high, the carbon coating effect is affected.

[0047] In some embodiments, in the step (1), the iron phosphate precursor is used;

[0048] Optionally, the particle size of the iron phosphate precursor is 100-500 nm, specifically, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm;

[0049] The present application does not have special restrictions on the preparation method of the iron phosphate precursor. Non-limiting examples include, for example, using a hydrothermal method to synthesize the iron phosphate precursor; optionally, reacting an iron source and a phosphorus source to obtain the iron phosphate precursor; the iron source comprises at least one of ferric chloride, iron oxide, iron powder, ferrous oxalate, ferrous sulfate, and ferric nitrate; the phosphorus source comprises at least one of phosphoric acid, ammonium dihydrogen phosphate, and monobasic ammonium phosphate; optionally, the iron source and the phosphorus source are used in an equimolar ratio; optionally, the reaction temperature is 60-100°C;

[0050] In specific embodiments, an equimolar ratio of ferrous sulfate heptahydrate and ammonium dihydrogen phosphate solution is weighed and added to a reaction kettle for mixing and stirring, and the reaction obtains the iron phosphate precursor.

[0051] In some embodiments, in the step (1), the iron phosphate precursor and the fullerene solution are mixed;

[0052] Optionally, the mixing time is 2-3 h;

[0053] Optionally, the mixing is carried out under stirring;

[0054] Optionally, the mixing is carried out under heating; the mixing temperature is 40-80°C, specifically, for example, 40°C, 50°C, 60°C, 70°C, 80°C; the heating is carried out by water bath heating;

[0055] Optionally, the iron phosphate precursor is added to the fullerene solution;

[0056] Optionally, after mixing, filtering and washing are performed, and then drying is performed to obtain the fullerene-coated iron phosphate precursor; optionally, after drying, sieving is performed.

[0057] In the embodiment of the present application, the iron phosphate precursor and the fullerene solution are mixed under heating conditions, which is beneficial to improving the mixing uniformity.

[0058] In some embodiments, in the step (2), the molar ratio of lithium elements in the lithium source, iron elements in the fullerene-coated iron phosphate precursor, and metal doping elements in the metal ion dopant is 1.0-1.08:0.95-0.99:0-0.05; specifically, 1.0-1.08 (for example, 1.00, 1.02, 1.05, 1.08):0.95-0.99 (for example, 0.95, 0.96, 0.97, 0.98, 0.99):0-0.05 (for example, 0, 0.01, 0.02, 0.03, 0.04, 0.05), and optionally, 1.05:0.98:0.02. In the embodiment of the present application, the molar ratio of lithium elements, iron elements, and doping elements is 1.0-1.08:0.95-0.99:0-0.05, which is beneficial to the complete lattice of the lithium iron phosphate grown and the appropriate grain size.

[0059] In some embodiments, in the step (2), in the mixture of the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, and the carbon source, the mass percentage of the carbon source is 3%-10%, and specifically, for example, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. In the embodiment of the present application, the addition of the traditional carbon source is beneficial to enhancing the electronic conductivity.

[0060] In some embodiments, in the step (2), the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, the carbon source, and the dispersant are mixed for ball milling; optionally, the dispersant includes water, and preferably, deionized water; the mass of the dispersant is 2-3 times the mass of the solid raw materials, and the solid raw materials include the fullerene-coated iron phosphate precursor, the lithium source, the metal ion dopant, and the carbon source.

[0061] In some embodiments, in the step (2), the ball milling time is 3-7 h, and specifically, for example, 3 h, 4 h, 5 h, 6 h, or 7 h.

[0062] In some embodiments, in the step (2), the lithium source includes at least one of lithium hydroxide and lithium carbonate.

[0063] In some embodiments, in the step (2), the carbon source comprises at least one of glucose, phenolic resin, sucrose, citric acid, polyethylene glycol (PEG), and conductive carbon black.

[0064] In some embodiments, in the step (2), the carbon-coated lithium iron phosphate comprises a metal-doped element; the metal-doped element comprises at least one of aluminum, titanium, magnesium, and vanadium; optionally, the metal ion dopant comprises at least one of an oxide, a hydroxide, and a salt of the metal-doped element; optionally, the salt is selected from a chloride, an isopropyl alcohol salt, or an ammonium salt of the metal-doped element. In the embodiments of the present application, the metal-doped element comprises aluminum, titanium, magnesium, and vanadium, wherein titanium, vanadium, and iron are in the same period and have similar atomic radii, and are easy to occupy iron sites in the crystal lattice; the oxide of aluminum has stable performance and can protect the material to reduce side reactions; magnesium doping occupies lithium sites to improve the ionic conductivity of the material. When isopropyl alcohol salt is used as a metal ion dopant for doping, a hydrolysis reaction will occur during the ball milling process, and the product is uniformly coated on the precursor.

[0065] In some embodiments, in the step (2), the drying temperature is 60-100°C; and the drying is performed by drying.

[0066] In some embodiments, in the step (3), the sintering temperature is 500-800°C, and specifically, for example, 500°C, 600°C, 700°C, or 800°C; and the sintering time is 8-36h, and specifically, for example, 8h, 10h, 12h, 18h, 24h, 30h, or 36h.

[0067] Optionally, the protective atmosphere comprises nitrogen; and the sintering is performed in a nitrogen-protected furnace.

[0068] Optionally, the mixture after drying is first pre-sintered in a protective atmosphere, ground after cooling, and then sintered in a protective atmosphere; the pre-sintering temperature is 500-600°C, and specifically, for example, 500°C, 550°C, or 600°C; the pre-sintering time is 12-24h, and specifically, for example, 12h, 18h, or 24h; the grinding is performed by sand grinding using a sand grinder; the grinding time is 2-3h; the sintering temperature is 600-800°C, and specifically, for example, 600°C, 700°C, or 800°C; the sintering time is 8-12h, and specifically, for example, 8h, 10h, or 12h; and the sintering temperature is higher than the pre-sintering temperature.

[0069] Optionally, the sintered product is cooled to room temperature in the furnace; or the sintered product is cooled to room temperature in the furnace, crushed, and then the carbon-coated lithium iron phosphate is obtained; and the crushing is performed by gas crushing.

[0070] In the embodiment of the present application, pre-sintering is performed first, and then sintering is performed, and the temperature of sintering is higher than that of pre-sintering, the reaction is performed in steps, pre-sintering makes the doping ions and carbon first coated on the surface of the precursor, and then high-temperature sintering is beneficial to the growth of lithium iron phosphate crystal grains.

[0071] The carbon-coated lithium iron phosphate in the embodiment of the present application is prepared by the preparation method described in the embodiment of the present application. In the embodiment of the present application, the carbon-coated lithium iron phosphate has high electrical conductivity and low powder resistance, and can improve the energy efficiency of the battery.

[0072] In some embodiments, the particle size of the carbon-coated lithium iron phosphate is 0.3-2.0 μm, and specifically, for example, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.5 μm, or 2.0 μm.

[0073] In some embodiments, the mass percentage of carbon in the carbon-coated lithium iron phosphate is 0.5-2%, and specifically, for example, 0.5%, 1%, 1.3%, 1.5%, or 2%; the mass percentage of fullerene in the carbon-coated lithium iron phosphate is 0.5-2%, and specifically, for example, 0.5%, 1%, 1.3%, 1.5%, or 2%; the mass percentage of metal doping elements in the carbon-coated lithium iron phosphate is 0-0.5%, and specifically, for example, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%; the mass percentage of lithium elements in the carbon-coated lithium iron phosphate is 4-5%, and specifically, for example, 4%, 4.5%, or 5%; the mass percentage of iron elements in the carbon-coated lithium iron phosphate is 30-38%, and specifically, for example, 30%, 32%, 34.5%, 36%, or 38%; and the molar ratio of lithium elements, iron elements, and metal doping elements is 1.0-1.08:0.95-0.99:0-0.05; specifically, 1.0-1.08 (for example, 1.00, 1.02, 1.05, or 1.08):0.95-0.99 (for example, 0.95, 0.96, 0.97, 0.98, or 0.99):0-0.05 (for example, 0, 0.01, 0.02, 0.03, 0.04, or 0.05), and optionally, 1.05:0.98:0.02.

[0074] The lithium battery in the embodiment of the present application includes a positive electrode material, and the positive electrode material includes the carbon-coated lithium iron phosphate described in the embodiment of the present application. In the embodiment of the present application, the carbon-coated lithium iron phosphate has high electrical conductivity and low powder resistance, and can improve the energy efficiency of the battery.

[0075] The present application is described below with reference to specific embodiments, and it should be noted that these embodiments are merely descriptive and do not limit the present application in any way.

[0076] Example 1

[0077] A preparation method of carbon-coated lithium iron phosphate, comprising the following steps:

[0078] (1) 9.0 g of fullerene C 60 was dissolved in 1.8 L of o-xylene to obtain a fullerene solution, 739.02 g of iron phosphate precursor (particle size of 100-500 nm) was mixed with the fullerene solution, and the mixture was heated in a water bath at a temperature of 60 DEG C and stirred uniformly at a speed of 200 r / min for 3 hours; the mixed slurry was filtered, washed, dried, and sieved to obtain a fullerene-coated iron phosphate precursor;

[0079] (2) The fullerene-coated iron phosphate precursor was mixed with 7.99 g of titanium dioxide, 369.45 g of lithium carbonate, 18.0 g of glucose, 18.0 g of PEG, and 17.0 g of conductive carbon black in deionized water, and ball-milled for 5 hours to obtain a mixture, and the mixture was dried at a temperature of 80 DEG C;

[0080] (3) The dried mixture was placed in a nitrogen protection furnace and pre-fired at 600 DEG C for 12 hours, and then ground and crushed after cooling, and sintered at a temperature of 780 DEG C for 12 hours, and then cooled to room temperature in the furnace, and then crushed to obtain a carbon-coated lithium iron phosphate positive electrode material.

[0081] The powder resistivity of the carbon-coated lithium iron phosphate positive electrode material was 23.05 Ω·cm, and the 2C soft package discharge capacity was 2.75 Ah and the discharge gram capacity was 133.49 mAh / g at 25 DEG C.

[0082] Example 2

[0083] The preparation method was the same as that of Example 1, except that in step (1), the amount of fullerene was 18.0 g; and in step (2), the amount of conductive carbon black was 8.0 g.

[0084] Example 3

[0085] The preparation method was the same as that of Example 1, except that in step (2), 7.99 g of titanium dioxide was replaced by 20.4 g of aluminum isopropoxide.

[0086] Example 4

[0087] The preparation method was the same as that of Example 1, except that in step (2), 7.99 g of titanium dioxide was replaced by 4.0 g of magnesium oxide.

[0088] Example 5

[0089] The preparation method was the same as that of Example 1, except that in step (2), 7.99 g of titanium dioxide was replaced by 11.6 g of ammonium metavanadate.

[0090] Comparative Example 1

[0091] The preparation method is the same as that of Example 1, except that step (1) is omitted, and in step (2), 739.02 g of iron phosphate precursor, 7.99 g of titanium dioxide, 369.45 g of lithium carbonate, 18.0 g of glucose, 18.0 g of PEG, and 26.0 g of conductive carbon black are mixed in deionized water, and ball-milled for 5 hours to obtain a mixture, which is dried at a temperature of 80°C.

[0092] Comparative Example 2

[0093] The preparation method is the same as that of Example 1, except that in step (1), deionized water is used instead of o-xylene.

[0094] Comparative Example 3

[0095] The preparation method is the same as that of Example 1, except that the mixing step in step (1) is omitted, and in step (2), 739.02 g of iron phosphate precursor, 9.0 g of fullerene C 60 is directly mixed with 7.99 g of titanium dioxide, 369.45 g of lithium carbonate, 18.0 g of glucose, 18.0 g of PEG, and 17.0 g of conductive carbon black in deionized water.

[0096] Comparative Example 4

[0097] The preparation method is the same as that of Example 1, except that in step (1), fullerene C 60 is replaced by graphene.

[0098] Comparative Example 5

[0099] The preparation method is the same as that of Example 1, except that in step (2), titanium dioxide is omitted.

[0100] Table 1

[0101]

[0102] As can be seen from Table 1, the carbon-coated lithium iron phosphate material powders prepared in Examples 1-5 using the preparation method of the present application have lower powder resistivity and better discharge gram capacity.

[0103] In Comparative Example 1, conductive carbon black is used instead of closed fullerene C 60 , and compared with Example 1, the carbon-coated lithium iron phosphate material in Comparative Example 1 has higher powder resistance and relatively lower discharge gram capacity.

[0104] The powder resistance of the fullerene solution in Comparative Example 2 is increased and the discharge capacity is decreased because the fullerene solution uses water as a solvent. The physical and chemical properties of fullerene and water are completely different, and the affinity between them is very weak. Excessive water molecules can reduce the hydrophobicity, affect its own properties, and thus lead to performance degradation, which is not conducive to the coating of the fullerene on the iron phosphate precursor, resulting in an increase in powder resistance and a decrease in discharge capacity.

[0105] In Comparative Example 3, the step of coating the iron phosphate precursor with fullerene is omitted, and fullerene is directly mixed. The coating effect of fullerene is poor, the powder resistance is increased, and the discharge capacity is decreased.

[0106] In Comparative Example 4, graphene is used instead of closed fullerene C 60 , and compared with Example 1, the powder resistance of the carbon-coated lithium iron phosphate material in Comparative Example 4 is higher, and the discharge capacity is relatively lower.

[0107] In Comparative Example 5, the carbon-coated lithium iron phosphate material does not contain metal-doped elements. At this time, compared with Example 1, the powder resistance of the material is higher, and the discharge capacity is relatively lower. This is because the metal-doped elements in the carbon-coated lithium iron phosphate material can replace the iron site, form lattice distortion and other lattice defects, and thus improve the ionic conductivity and electronic conductivity of the carbon-coated lithium iron phosphate.

[0108] From Figure 1 it can be seen that the sp 60 hybrid orbital ratio of the carbon-coated lithium iron phosphate material doped with fullerene C 2 in Example 2 is good, the fullerene is uniformly coated at the molecular level, and the SP 2 hybrid conductivity of the fullerene can be fully utilized to improve the conductivity of the carbon-coated lithium iron phosphate material, reduce the powder resistance of the material, and improve the energy efficiency of the battery.

[0109] From Figure 2 it can be seen that the battery resistance of the battery made of the carbon-coated lithium iron phosphate material doped with fullerene C 60 in Example 1 and Example 2 is smaller.

[0110] From Figure 3 it can be seen that the polarization of the battery made of the carbon-coated lithium iron phosphate material doped with fullerene C 60 in Example 1 and Example 2 is smaller under large rate discharge.

[0111] From Figure 4 it can be seen that the energy efficiency of the battery made of the carbon-coated lithium iron phosphate material doped with fullerene C 60 in Example 1 and Example 2 is higher.

[0112] From Figure 5It can be seen that the fullerenes C 60 The battery made of the doped carbon-coated lithium iron phosphate material has good cycle performance.

[0113] From Figure 6 It can be seen that the fullerenes C 60 The battery made of the doped carbon-coated lithium iron phosphate material has high discharge voltage platform.

[0114] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the different embodiments or examples described in the present specification and the features of the different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0115] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and the changes, modifications, replacements and variations of the above embodiments made by those skilled in the art are within the protection scope of the present application.

Claims

1. A method for preparing carbon-coated lithium iron phosphate, characterized in that, Includes the following steps: (1) The iron phosphate precursor and the fullerene solution are mixed and then dried to obtain the fullerene-coated iron phosphate precursor; wherein the solvent of the fullerene solution is a non-aqueous solvent; and the particle size of the iron phosphate precursor is 100-500 nm. (2) The fullerene-coated iron phosphate precursor, lithium source, metal ion dopant and carbon source are mixed and ball-milled to obtain a mixture, and the mixture is dried; the metal ion dopant includes a metal doping element; the metal doping element includes at least one of aluminum, titanium, magnesium and vanadium; (3) The dried mixture is sintered under a protective atmosphere to obtain carbon-coated lithium iron phosphate.

2. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (1), the solvent of the fullerene solution includes at least one of xylene, toluene, or chlorobenzene.

3. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (1), the mass ratio of the iron phosphate precursor to the fullerene is 97-100:0.01-3; And / or, the mixing is carried out under heating conditions; the mixing temperature is 40-80°C; the mixing time is 2-3 hours.

4. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (2), the molar ratio of lithium in the lithium source, iron in the fullerene-coated iron phosphate precursor, and metal dopant in the metal ion dopant is 1.0-1.08:0.95-0.99:0-0.

05. And / or, in the mixture of the fullerene-coated iron phosphate precursor, lithium source, metal ion dopant and carbon source, the mass percentage of the carbon source is 3%-10%; And / or, the ball milling time is 3 to 7 hours.

5. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (2), the lithium source includes at least one of lithium hydroxide and lithium carbonate; And / or, the carbon source includes at least one of glucose, phenolic resin, sucrose, citric acid, polyethylene glycol, and conductive carbon black.

6. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (2), the metal ion dopant includes at least one of the oxides, hydroxides, and salts of the metal dopant element.

7. The method for preparing carbon-coated lithium iron phosphate according to claim 1, characterized in that, In step (3), the sintering temperature is 500~800℃; And / or, the sintering time is 8-36 hours; And / or, the particle size of the carbon-coated lithium iron phosphate is 0.3-2.0 μm.

8. The method for preparing carbon-coated lithium iron phosphate according to claim 7, characterized in that, In step (3), the dried mixture is first pre-fired under a protective atmosphere, then ground after cooling, and then sintered under a protective atmosphere; the pre-fired temperature is 500~600℃; the pre-fired time is 12~24h; the sintering temperature is 600~800℃; and the sintering time is 8~12h.

9. A carbon-coated lithium iron phosphate, characterized in that, It is prepared by any one of the preparation methods according to claims 1-8.

10. A lithium battery, characterized in that, It includes a cathode material, wherein the cathode material includes the carbon-coated lithium iron phosphate as described in claim 9.

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