Lithium iron phosphate positive electrode material, preparation method thereof and battery

Abstract

The invention discloses a lithium iron phosphate positive electrode material, a preparation method thereof and a battery, and belongs to the technical field of battery materials. The lithium iron phosphate positive electrode material comprises an inner core and a shell coating the surface of the inner core, an inner core is lithium iron phosphate, and a shell is porous carbon doped with nano tungsten trioxide. The preparation method comprises the following steps: mixing lithium iron phosphate and porous carbon doped with nano tungsten trioxide, and sintering. The surface of the lithium iron phosphate is coated with the porous carbon doped with the nano tungsten trioxide, firstly, the porous carbon doped with the nano tungsten trioxide has more stable chemical performance, the structural stability of the porous carbon can be kept in the circulation process, a conductive coating layer which is uniformly distributed can be more easily formed on the surface of the lithium iron phosphate, and the conductivity is improved; and secondly, the direct contact between the core lithium iron phosphate and the active substance in the electrolyte can be effectively prevented, the side reaction is reduced, and the cycling stability is improved. The lithium iron phosphate positive electrode material has relatively good conductivity, capacity, first effect and cycling stability.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a lithium iron phosphate positive electrode material, a preparation method thereof, and a battery. Background Art

[0002] Lithium iron phosphate, a lithium-ion battery electrode material with the chemical formula LiFePO4 (LFP), is primarily used in various lithium-ion batteries. Its advantages include high specific capacity, low price, and environmental friendliness. However, most current lithium iron phosphates suffer from poor conductivity and are prone to surface side reactions during charge and discharge cycles.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The object of the present invention is to provide a lithium iron phosphate positive electrode material and a preparation method thereof and a battery to solve or improve the above technical problems.

[0005] The present invention can be achieved like this:

[0006] In a first aspect, the present invention provides a lithium iron phosphate positive electrode material, which includes a core and a shell coated on the surface of the core; the core is lithium iron phosphate, and the shell is porous carbon doped with nano-tungsten trioxide.

[0007] In an optional embodiment, the mass ratio of the porous carbon doped with nano-tungsten trioxide to the lithium iron phosphate is (0.05-3):100.

[0008] In an optional embodiment, the mass ratio of the porous carbon doped with nano-tungsten trioxide to the lithium iron phosphate is 0.5:100.

[0009] In an optional embodiment, the particle size of nano-tungsten trioxide is 2 nm to 50 nm.

[0010] In a second aspect, the present invention provides a method for preparing the lithium iron phosphate positive electrode material as described in the aforementioned embodiment, comprising the following steps: mixing lithium iron phosphate with porous carbon doped with nano-tungsten trioxide and sintering the mixture.

[0011] In an optional embodiment, lithium iron phosphate and porous carbon doped with nano-tungsten trioxide are mixed by grinding.

[0012] In an optional embodiment, the grinding time is 0.5 h to 2 h.

[0013] In an optional embodiment, sintering includes at least one of the following features:

[0014] Feature 1: The sintering temperature is 500°C to 700°C, preferably 650°C;

[0015] Feature 2: Sintering time is 8h to 12h, preferably 10h;

[0016] Feature 3: The sintering atmosphere is a protective gas atmosphere; preferably, the sintering atmosphere is a nitrogen atmosphere.

[0017] In an optional embodiment, the preparation of porous carbon doped with nano-tungsten trioxide includes: sintering a mixture of nano-tungsten trioxide and porous carbon.

[0018] In an optional embodiment, the mass ratio of nano-tungsten trioxide to porous carbon is (10-30):(70-90);

[0019] And / or, the nano-tungsten trioxide is mixed with the porous carbon by grinding.

[0020] In an optional embodiment, the grinding time of nano-tungsten trioxide and porous carbon is 0.5h to 2h.

[0021] In an optional embodiment, during the preparation of porous carbon doped with nano-tungsten trioxide, the sintering of the mixture includes at least one of the following features:

[0022] Feature 4: The sintering temperature of the mixture is 500°C to 700°C, preferably 600°C;

[0023] Feature 5: The sintering time of the mixture is 4 to 8 hours, preferably 6 hours;

[0024] Feature 6: The sintering atmosphere of the mixture is a protective gas atmosphere; preferably, the sintering atmosphere is a nitrogen atmosphere.

[0025] In an optional embodiment, an activator is further added during the mixing process of nano-tungsten trioxide and porous carbon.

[0026] In an optional embodiment, the mass ratio of the activator to the nano-tungsten trioxide is (0.1-0.5):1.

[0027] In an alternative embodiment, the activator is a lithium-containing compound.

[0028] In an alternative embodiment, the lithium-containing compound comprises lithium carbonate.

[0029] In an optional embodiment, the porous carbon is obtained by pre-treating a porous carbon raw material.

[0030] In an optional embodiment, the pretreatment of the porous carbon raw material includes: heating the porous carbon raw material in an aqueous hydrogen peroxide solution, and then washing the heated porous carbon raw material to neutrality.

[0031] In an optional embodiment, the ratio of the porous carbon raw material to the aqueous hydrogen peroxide solution is (50-100) g: (50-100) mL.

[0032] In an optional embodiment, the concentration of the aqueous hydrogen peroxide solution is 2 wt% to 10 wt%.

[0033] In an optional embodiment, the heating temperature is 50° C. to 65° C., and the heating time is 3 h to 4 h.

[0034] In an optional embodiment, the preparation of the porous carbon raw material includes: keeping the straw and ionized water at 235°C to 245°C for 3h to 5h, then washing, and then drying at 102°C to 108°C for 10h to 15h.

[0035] In a third aspect, the present invention provides a battery comprising the lithium iron phosphate positive electrode material of the aforementioned embodiment.

[0036] The beneficial effects of the present invention include:

[0037] The present invention coats the surface of lithium iron phosphate with porous carbon doped with nano-tungsten trioxide. Firstly, the porous carbon doped with nano-tungsten trioxide has more stable chemical properties, can maintain the structural stability of the porous carbon during the cycle, and is more likely to form a uniformly distributed conductive coating layer on the surface of the lithium iron phosphate, thereby improving the conductive performance; secondly, it can effectively prevent the inner core lithium iron phosphate from directly contacting the active material in the electrolyte, reduce side reactions, and improve cycle stability.

[0038] The preparation method of the lithium iron phosphate positive electrode material provided by the present invention is simple, easy to operate, and can be produced industrially on a large scale. In addition, the prepared lithium iron phosphate positive electrode material has excellent conductivity, capacity, first efficiency and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0040] Figure 1 This is the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1;

[0041] Figure 2 This is the SEM image of the lithium iron phosphate positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0042] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0043] The lithium iron phosphate positive electrode material, preparation method thereof, and battery provided by the present invention are described in detail below.

[0044] The present invention provides a lithium iron phosphate positive electrode material, which includes a core and a shell coated on the surface of the core; the core is lithium iron phosphate, and the shell is porous carbon doped with nano-tungsten trioxide.

[0045] By coating the surface of lithium iron phosphate with porous carbon doped with nano tungsten trioxide, firstly, the porous carbon doped with nano tungsten trioxide has more stable chemical properties, can maintain the structural stability of the porous carbon during the cycle, and is more likely to form a uniformly distributed conductive coating layer on the surface of lithium iron phosphate, thereby improving the conductivity; and, tungsten trioxide itself also has good conductivity, which can further improve the conductivity of the lithium iron phosphate positive electrode material; secondly, the coating layer can effectively prevent the core lithium iron phosphate from directly contacting the active substances in the electrolyte, reduce side reactions, and improve cycle stability, thereby helping the lithium iron phosphate positive electrode material to have better conductivity, capacity, first effect and cycle stability.

[0046] It should be emphasized that the present invention specifically dopes tungsten trioxide into porous carbon, which has better chemical properties than other oxide dopants with better conductivity (such as zirconium oxide, titanium oxide, etc.), and can significantly reduce the sintering temperature of lithium iron phosphate and reduce energy consumption, thereby achieving cost reduction and efficiency improvement.

[0047] In some optional embodiments, the mass ratio of porous carbon doped with nano tungsten trioxide to lithium iron phosphate can be (0.05-3):100, such as 0.05:100, 0.1:100, 0.2:100, 0.5:100, 0.8:100, 1:100, 1.2:100, 1.5:100, 1.8:100, 2:100, 2.5:100 or 3:100, etc., or other values ​​within the range of (0.05-3):100. If the amount of nano tungsten trioxide doped is too much, it is easy to cause the capacity of lithium iron phosphate to decrease. In some more typical embodiments, the mass ratio of porous carbon doped with nano tungsten trioxide to lithium iron phosphate is 0.5:100. Under this condition, the lithium iron phosphate positive electrode material can have better conductivity, capacity, first effect and cycle stability at the same time.

[0048] In some optional embodiments, the particle size of nano tungsten trioxide is 2nm to 50nm. Compared with nano tungsten trioxide with a particle size of 50nm or more, the present invention is more conducive to improving the uniformity and stability of doping.

[0049] Correspondingly, the present invention also provides a method for preparing the above-mentioned lithium iron phosphate positive electrode material, which may include the following steps: mixing lithium iron phosphate with porous carbon doped with nano-tungsten trioxide and sintering the mixture.

[0050] In some optional embodiments, the lithium iron phosphate and the porous carbon doped with nano-tungsten trioxide can be mixed by grinding. In addition, mechanical stirring can also be used for mixing.

[0051] In some optional embodiments, the grinding time of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 0.5h to 2h, such as 0.5h, 1h, 1.5h or 2h, or other values ​​within the range of 0.5h to 2h. In some more typical embodiments, the grinding time of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 1h.

[0052] In some optional embodiments, the sintering temperature of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 500° C. to 700° C., such as 500° C., 550° C., 600° C., 650° C., or 700° C., or other values ​​within the range of 500° C. to 700° C. In some more typical embodiments, the sintering temperature of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 650° C.

[0053] In some optional embodiments, the sintering time of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 8 hours to 12 hours, such as 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, or other values ​​within the range of 8 hours to 12 hours. In some more typical embodiments, the sintering time of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide can be 10 hours.

[0054] If the sintering temperature of lithium iron phosphate and porous carbon doped with nano tungsten trioxide is too low or the sintering time is too short, the sintering reaction will be incomplete and impurities will be produced; if the sintering temperature of lithium iron phosphate and porous carbon doped with nano tungsten trioxide is too high or the sintering time is too long, the particles will easily become larger, affecting the electrochemical properties of lithium iron phosphate and resulting in higher energy consumption.

[0055] In some optional embodiments, the sintering atmosphere is a protective gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere, etc. In some more typical embodiments, the sintering atmosphere may be a nitrogen atmosphere.

[0056] In some optional embodiments, the preparation of porous carbon doped with nano-tungsten trioxide may include: sintering a mixture of nano-tungsten trioxide and porous carbon.

[0057] The mass ratio of nano-tungsten trioxide to porous carbon can be (10-30):(70-90), such as 10:90, 15:85, 20:80, 25:75, or 30:70, or other values ​​within the range of (10-30):(70-90). If the amount of nano-tungsten trioxide is too small, the modification effect will not be achieved; if the amount of nano-tungsten trioxide is too large, the capacity of lithium iron phosphate will be reduced.

[0058] In some optional embodiments, the nano-tungsten trioxide and the porous carbon can be mixed by grinding. For example, the grinding time of the nano-tungsten trioxide and the porous carbon can be 0.5h to 2h, such as 0.5h, 1h, 1.5h or 2h. In some more typical embodiments, the grinding time of the nano-tungsten trioxide and the porous carbon can be 1h. In addition, it is not ruled out that the nano-tungsten trioxide and the porous carbon are mixed by conventional mechanical stirring.

[0059] In some optional embodiments, during the preparation of porous carbon doped with nano-tungsten trioxide, the sintering temperature of the mixture can be 500° C. to 700° C., such as 500° C., 550° C., 600° C., 650° C., or 700° C., or other values ​​within the range of 500° C. to 700° C. In some more typical embodiments, the sintering temperature of the mixture is 600° C.

[0060] In some optional embodiments, during the preparation of porous carbon doped with nano-tungsten trioxide, the mixture can be sintered for 4 to 8 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, or other values ​​within the range of 4 to 8 hours. In some more typical embodiments, the mixture can be sintered for 6 hours.

[0061] In some optional embodiments, during the preparation of porous carbon doped with nano-tungsten trioxide, the sintering atmosphere of the mixture is a protective gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere. In some more typical embodiments, the sintering atmosphere of the mixture can be a nitrogen atmosphere.

[0062] In some optional embodiments, an activator is added during the mixing process of nano-tungsten trioxide and porous carbon. The addition of the activator can reduce the reaction activation energy, promote sintering densification, and improve the structural stability of the porous carbon.

[0063] The mass ratio of the activator to the nano-tungsten trioxide can be (0.1-0.5):1, such as 0.1:1, 0.2:1, 0.3:1, 0.4:1 or 0.5:1, or other values ​​within the range of (0.1-0.5):1. If the amount of the activator is too much, side reactions may occur on the one hand, and the cost may be increased on the other hand.

[0064] The activator is illustratively a lithium-containing compound, and illustratively may include lithium carbonate.

[0065] In some optional embodiments, the porous carbon is obtained by pre-treating a porous carbon raw material.

[0066] The pretreatment of the porous carbon raw material may include: heating the porous carbon raw material in a hydrogen peroxide solution, and then washing the heated porous carbon raw material to neutrality.

[0067] The ratio of the porous carbon raw material to the aqueous hydrogen peroxide solution can be (50-100) g:(50-100) mL. The concentration of the aqueous hydrogen peroxide solution can be 2 wt% to 10 wt%, such as 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%, or other values ​​within the range of 2 wt% to 10 wt%.

[0068] In some optional embodiments, the heating temperature may be 50° C. to 65° C., such as 50° C., 52° C., 55° C., 58° C., 60° C., 62° C., or 65° C., or other values ​​within the range of 50° C. to 65° C. The heating time may be 3 h to 4 h, such as 3 h, 3.5 h, or 4 h, or other values ​​within the range of 3 h to 4 h.

[0069] As mentioned above, the porous carbon raw material is pretreated with an aqueous hydrogen peroxide solution to etch the interior of the porous carbon, which is convenient for subsequent doping modification.

[0070] In some optional embodiments, the preparation of porous carbon raw materials may include: keeping the straw and ionized water at 235°C to 245°C (such as 235°C, 240°C or 245°C, etc.) for 3h to 5h (such as 3h, 3.5h, 4h, 4.5h or 5h, etc.), then washing, and then drying at 102°C to 108°C (such as 102°C, 105°C or 108°C, etc.) for 10h to 15h (such as 10h, 12h or 15h, etc.).

[0071] The ratio of straw to ionized water can be (45g-55g):500mL. In specific operations, the straw can be soaked in ionized water according to the above ratio, mixed and sealed in a high-temperature and high-pressure reactor, and then heated to 235°C-245°C for 3-5 hours. After the insulation is completed, it is naturally cooled to room temperature and then filtered. The remaining solid after filtration is washed with anhydrous ethanol and ultrapure water to remove impurities. The washed solid is then dried at 102°C-108°C for 10-15 hours to obtain a brown-black porous carbon raw material.

[0072] Furthermore, the present invention also provides a battery cell, which includes the above-mentioned lithium iron phosphate positive electrode material.

[0073] For example, the battery cells can be used in, but are not limited to, electrical devices such as vehicles, ships, or aircraft.

[0074] The present invention also provides a battery comprising the above battery cell.

[0075] The present invention also provides an electrical device comprising the aforementioned battery cell and / or battery. For example, the electrical device may include, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. The spacecraft may include airplanes, rockets, space shuttles, and spacecraft.

[0076] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0077] Example 1

[0078] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0079] S1: Preparation of porous carbon raw materials.

[0080] Straw was immersed in deionized water at a ratio of 50g:500mL, mixed thoroughly, and sealed in a high-temperature, high-pressure reactor. The mixture was heated to 240°C and held for 4 hours. After the holding period, the mixture was naturally cooled to room temperature and filtered. The remaining solid was then washed with anhydrous ethanol and then ultrapure water, followed by drying at 105°C for 12 hours to obtain a brown-black porous carbon raw material.

[0081] S2: Pre-treating the porous carbon raw material.

[0082] 50 g of the brown-black porous carbon raw material was added to 60 mL of a 5 wt% hydrogen peroxide aqueous solution, heated to 60° C., and kept warm for 4 h. The heated porous carbon raw material was washed with deionized water until it was neutral to obtain porous carbon.

[0083] S3: Preparation of porous carbon doped with nano-tungsten trioxide.

[0084] Nano-tungsten trioxide (particle size 2nm-50nm), lithium carbonate, and the above-mentioned porous carbon were added to a mortar and ground for 1 hour to obtain a mixture. The mass ratio of nano-tungsten trioxide to porous carbon was 10:90, and the mass ratio of lithium carbonate to nano-tungsten trioxide was 0.3:1. The mixture was then placed in a graphite crucible and transferred to a nitrogen-protected box furnace for sintering. Specifically, it was heated to 600°C at a heating rate of 3°C / min and sintered at this temperature for 6 hours. After sintering, it was naturally cooled to room temperature in the furnace to obtain porous carbon doped with nano-tungsten trioxide.

[0085] S4: coating the lithium iron phosphate with porous carbon doped with nano-tungsten trioxide.

[0086] 0.3g of porous carbon doped with nano-tungsten trioxide and 60g of lithium iron phosphate (i.e., the mass ratio of porous carbon doped with nano-tungsten trioxide to lithium iron phosphate is 0.5:100) were placed in a mortar and ground for 1 hour. Then, the mixture was placed in a graphite sagger and sintered in a nitrogen-protected box furnace. Specifically, the temperature was increased to 650°C at a rate of 3°C / min and sintered at this temperature for 10 hours. After sintering, the lithium iron phosphate positive electrode material was obtained.

[0087] Example 2

[0088] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0089] S1: Preparation of porous carbon raw materials.

[0090] Straw was immersed in deionized water at a ratio of 45g:500mL, mixed thoroughly, and sealed in a high-temperature, high-pressure reactor. The mixture was heated to 235°C and held for 5 hours. After the mixture was cooled to room temperature, it was filtered and then washed with anhydrous ethanol and ultrapure water. The washed solid was then dried at 102°C for 15 hours to obtain a brown-black porous carbon raw material.

[0091] S2: Pre-treating the porous carbon raw material.

[0092] 50 g of the brown-black porous carbon raw material was added to 100 mL of a 2 wt% hydrogen peroxide aqueous solution, heated to 50° C., and kept warm for 4 h. The heated porous carbon raw material was washed with deionized water until it was neutral to obtain porous carbon.

[0093] S3: Preparation of porous carbon doped with nano-tungsten trioxide.

[0094] Nano-tungsten trioxide (particle size 2nm-50nm), lithium carbonate, and the above-mentioned porous carbon were added to a mortar and ground for 0.5h to obtain a mixture. The mass ratio of nano-tungsten trioxide to porous carbon was 20:80, and the mass ratio of lithium carbonate to nano-tungsten trioxide was 0.1:1. The mixture was then placed in a graphite crucible and transferred to a nitrogen-protected box furnace for sintering. Specifically, it was heated to 500°C at a heating rate of 3°C / min and sintered at this temperature for 8h. After sintering, it was naturally cooled to room temperature in the furnace to obtain porous carbon doped with nano-tungsten trioxide.

[0095] S4: coating the lithium iron phosphate with porous carbon doped with nano-tungsten trioxide.

[0096] 0.3g of porous carbon doped with nano-tungsten trioxide and 30g of lithium iron phosphate (i.e., the mass ratio of porous carbon doped with nano-tungsten trioxide to lithium iron phosphate is 0.1:100) are placed in a mortar and ground for 0.5h. Then, the mixture is placed in a graphite sagger and transferred to a nitrogen-protected box furnace for sintering. Specifically, the temperature is increased to 500°C at a rate of 3°C / min and sintered at this temperature for 12h. After sintering, the lithium iron phosphate positive electrode material is obtained.

[0097] Example 3

[0098] This embodiment provides a lithium iron phosphate positive electrode material, the preparation method of which includes:

[0099] S1: Preparation of porous carbon raw materials.

[0100] The straw was immersed in 500 mL of deionized water at a ratio of 55 g:500 mL. After mixing, the mixture was sealed in a high-temperature, high-pressure reactor and heated to 245°C for 3 hours. After the insulation, the mixture was naturally cooled to room temperature and filtered. The remaining solid was then washed with anhydrous ethanol and ultrapure water, respectively, and then dried at 108°C for 10 hours to obtain a brown-black porous carbon raw material.

[0101] S2: Pretreating the porous carbon raw material.

[0102] 50 g of the brown-black porous carbon raw material was added to 50 mL of a 10 wt% hydrogen peroxide aqueous solution, heated to 65° C., and kept warm for 3 h. The heated porous carbon raw material was washed with deionized water until it was neutral to obtain porous carbon.

[0103] S3: Preparation of porous carbon doped with nano-tungsten trioxide.

[0104] Nano-tungsten trioxide (particle size 2nm-50nm), lithium carbonate, and porous carbon were added to a mortar and ground for 2 hours to obtain a mixture. The mass ratio of nano-tungsten trioxide to porous carbon was 30:70, and the mass ratio of lithium carbonate to nano-tungsten trioxide was 0.5:1. The mixture was then placed in a graphite crucible and transferred to a nitrogen-protected box furnace for sintering. Specifically, it was heated to 700°C at a heating rate of 3°C / min and sintered at this temperature for 4 hours. After sintering, it was naturally cooled to room temperature in the furnace to obtain porous carbon doped with nano-tungsten trioxide.

[0105] S4: coating the lithium iron phosphate with porous carbon doped with nano-tungsten trioxide.

[0106] 0.3g of porous carbon doped with nano-tungsten trioxide and 15g of lithium iron phosphate (i.e., the mass ratio of porous carbon doped with nano-tungsten trioxide to lithium iron phosphate is 2:100) were placed in a mortar and ground for 2 hours. Then, the mixture was placed in a graphite sagger and sintered in a nitrogen-protected box furnace. Specifically, the mixture was heated to 700°C at a heating rate of 3°C / min and sintered at this temperature for 8 hours. After sintering, the lithium iron phosphate positive electrode material was obtained.

[0107] Example 4

[0108] The difference between this embodiment and embodiment 1 is that the operation S2 is not performed. That is, the porous carbon raw material is not pretreated before being mixed with the nano-tungsten trioxide and the activator.

[0109] Example 5

[0110] The difference between this embodiment and embodiment 1 is that in S3, the particle size of nano-tungsten trioxide is 100 nm to 120 nm.

[0111] Example 6

[0112] The difference between this embodiment and embodiment 1 is that in S3, the mass ratio of nano-tungsten trioxide to porous carbon is 5:95.

[0113] Example 7

[0114] The difference between this embodiment and embodiment 1 is that in S3, the mass ratio of nano-tungsten trioxide to porous carbon is 40:60.

[0115] Example 8

[0116] The difference between this embodiment and embodiment 1 is that in S3, the mass ratio of the activator to the nano-tungsten trioxide is 0.8:1.

[0117] Example 9

[0118] The difference between this embodiment and embodiment 1 is that no activator is used in S3.

[0119] Example 10

[0120] The difference between this embodiment and embodiment 1 is that in S4, the mass ratio of the porous carbon doped with nano-tungsten trioxide to the lithium iron phosphate is 5:100.

[0121] Example 11

[0122] The difference between this embodiment and embodiment 1 is that in S4, the sintering temperature of lithium iron phosphate and porous carbon doped with nano-tungsten trioxide is 800°C.

[0123] Comparative Example 1

[0124] This comparative example differs from Example 1 in that steps S2 and S3 were not performed. Instead, 0.3 g of the porous carbon raw material prepared in S1 and 60 g of lithium iron phosphate were directly placed in a mortar and ground for 1 h. The mixture was then placed in a graphite crucible and sintered in a nitrogen-protected box furnace. The sintering conditions were the same as those for S4 in Example 1.

[0125] Comparative Example 2

[0126] The difference between this comparative example and Example 1 is that an equal amount (by mass) of zirconium oxide is used instead of tungsten trioxide.

[0127] Comparative Example 3

[0128] The difference between this comparative example and Example 1 is that an equal amount (by mass) of titanium dioxide is used instead of tungsten trioxide.

[0129] Test example

[0130] (1) Taking the lithium iron phosphate cathode material prepared in Example 1 as an example, the XRD pattern of the lithium iron phosphate cathode material obtained in this example is as follows: Figure 1 As shown, the SEM image of the lithium iron phosphate positive electrode material obtained in this embodiment is as shown in Figure 2 shown.

[0131] Depend on Figure 1 It can be seen that the XRD pattern of the lithium iron phosphate positive electrode material prepared in this example is consistent with the basic standard card, and the crystal structure of the lithium iron phosphate is not changed.

[0132] Depend on Figure 2 It can be seen that the lithium iron phosphate positive electrode material prepared in this embodiment does not show agglomeration phenomenon.

[0133] (2) The powder resistivity of the lithium iron phosphate positive electrode materials prepared in Examples 1 to 11 and Comparative Examples 1 to 3 was tested according to the test method in accordance with GB / T 45324-2025 “Determination of powder resistivity of positive electrode materials for lithium ion batteries”. The results are shown in Table 1.

[0134] (3) The lithium iron phosphate positive electrode materials prepared in Examples 1 to 11 and Comparative Examples 1 to 3 were prepared into positive electrode sheets in the following manner and assembled to obtain button batteries: lithium iron phosphate, acetylene black and PVDF were dispersed in an NMP solution at a mass ratio of 90:5:5, and then coated on a positive electrode collector (aluminum foil), dried, rolled and punched to obtain a positive electrode sheet. Metal lithium was used as the negative electrode, polypropylene film as the separator, and lithium hexafluorophosphate as the electrolyte to assemble a button battery. The button battery was subjected to a constant current charge and discharge test for 100 cycles at 25°C and a voltage range of 2.0V to 3.8V. The capacity retention rate of each button battery at 0.1C discharge capacity, first efficiency and 100 cycles of 1C cycle was tested, and the results are shown in Table 1.

[0135] Table 1 Test results

[0136]

[0137]

[0138] As can be seen from Table 1:

[0139] The lithium iron phosphate positive electrode materials prepared in Examples 1 to 3 have better discharge specific capacity, first effect and capacity retention rate than those prepared in Examples 4 to 11, indicating that the preparation conditions of Examples 1 to 3 are more conducive to obtaining lithium iron phosphate positive electrode materials with better overall performance. Among them, the effect of Example 1 is the best, indicating that the preparation conditions of Example 1 are most effective in improving the above-mentioned performance of the lithium iron phosphate positive electrode material. From the comparison between Example 1 and Example 9, it can be seen that adding an activator in the process of doping nano-tungsten trioxide in porous carbon is more conducive to improving the discharge specific capacity, first effect, capacity retention rate and lower powder resistivity of the lithium iron phosphate positive electrode material.

[0140] It can be seen from Example 1, Example 4 and Comparative Example 1 that by pretreating the porous carbon raw material and doping it with nano-tungsten trioxide, the discharge specific capacity, first efficiency, and capacity retention rate of the lithium iron phosphate positive electrode material can be significantly improved and the powder resistivity of the lithium iron phosphate positive electrode material can be reduced.

[0141] It can be seen from Example 1 and Comparative Examples 2-3 that although the substances doped into the pretreated porous carbon raw materials in Comparative Examples 2-3 also have relatively high electrical conductivity, the improvement effect is relatively poor.

[0142] In summary, the present invention can obtain a lithium iron phosphate positive electrode material with better conductivity, capacity, first efficiency and cycle stability by coating the surface of lithium iron phosphate with porous carbon doped with nano-tungsten trioxide.

[0143] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate positive electrode material, characterized in that: The lithium iron phosphate positive electrode material includes a core and a shell coated on the surface of the core; the core is lithium iron phosphate, and the shell is porous carbon doped with nano-tungsten trioxide.

2. The lithium iron phosphate positive electrode material according to claim 1, characterized in that The mass ratio of the porous carbon doped with nano-tungsten trioxide to the lithium iron phosphate is (0.05-3):100; Preferably, the mass ratio of the porous carbon doped with nano-tungsten trioxide to the lithium iron phosphate is 0.5:100; Preferably, the particle size of the nano tungsten trioxide is 2nm to 50nm.

3. A method for preparing the lithium iron phosphate positive electrode material according to claim 1 or 2, characterized in that: The method comprises the following steps: mixing lithium iron phosphate with porous carbon doped with nano-tungsten trioxide and sintering the mixture; Preferably, the lithium iron phosphate and the porous carbon doped with nano-tungsten trioxide are mixed by grinding; Preferably, the grinding time is 0.5h to 2h; Preferably, sintering includes at least one of the following features: Feature 1: The sintering temperature is 500°C to 700°C, preferably 650°C; Feature 2: Sintering time is 8h to 12h, preferably 10h; Feature 3: The sintering atmosphere is a protective gas atmosphere; preferably, the sintering atmosphere is a nitrogen atmosphere.

4. The preparation method according to claim 3, characterized in that The preparation of the porous carbon doped with nano-tungsten trioxide comprises: sintering a mixture of nano-tungsten trioxide and porous carbon.

5. The preparation method according to claim 4, characterized in that The mass ratio of the nano-tungsten trioxide to the porous carbon is (10-30):(70-90); and / or, mixing the nano-tungsten trioxide and the porous carbon by grinding; Preferably, the grinding time of the nano-tungsten trioxide and the porous carbon is 0.5 h to 2 h.

6. The preparation method according to claim 4, characterized in that In the process of preparing porous carbon doped with nano-tungsten trioxide, the sintering of the mixture includes at least one of the following characteristics: Feature 4: The sintering temperature of the mixture is 500°C to 700°C, preferably 600°C; Feature 5: The sintering time of the mixture is 4 to 8 hours, preferably 6 hours; Feature 6: The sintering atmosphere of the mixture is a protective gas atmosphere; preferably, the sintering atmosphere is a nitrogen atmosphere.

7. The preparation method according to claim 4, characterized in that During the mixing process of the nano-tungsten trioxide and the porous carbon, an activator is also added; Preferably, the mass ratio of the activator to the nano tungsten trioxide is (0.1-0.5):1; Preferably, the activator is a lithium-containing compound; More preferably, the lithium-containing compound includes lithium carbonate.

8. The preparation method according to claim 4, characterized in that The porous carbon is obtained by pre-treating a porous carbon raw material; Preferably, the pretreatment of the porous carbon raw material comprises: heating the porous carbon raw material in an aqueous hydrogen peroxide solution, and then washing the heated porous carbon raw material to neutrality; Preferably, the ratio of the porous carbon raw material to the aqueous hydrogen peroxide solution is (50-100) g: (50-100) mL; Preferably, the concentration of the aqueous hydrogen peroxide solution is 2 wt% to 10 wt%; Preferably, the heating temperature is 50° C. to 65° C., and the heating time is 3 h to 4 h.

9. The preparation method according to claim 8, characterized in that The preparation of the porous carbon raw material comprises: keeping the straw and ion water at 235-245° C. for 3-5 hours, washing, and drying at 102-108° C. for 10-15 hours.

10. A battery, characterized in that: The battery comprises the lithium iron phosphate positive electrode material according to claim 1 or 2.

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