CN115863632A - Preparation method of lithium iron phosphate carbon aerogel composite material - Google Patents
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Abstract
The invention discloses a preparation method of a lithium iron phosphate carbon aerogel composite material, which comprises the steps of mixing a phosphorus source, an iron source, a lithium source, a carbon source and an organic dispersant, mixing in a ball mill to obtain a mixed slurry A, and drying and crushing the mixed slurry A to obtain a lithium iron phosphate precursor; sintering the lithium iron phosphate precursor in an inert atmosphere to prepare a carbon-coated lithium iron phosphate material;LiFePO is prepared by adopting carbothermic method 4 Reducing ferric iron into ferrous iron to realize one-step reduction; and (3) crushing the carbon-coated lithium iron phosphate material into particles to prepare the carbon-coated lithium iron phosphate carbon aerogel composite material. According to the invention, the porous carbon aerogel and the lithium iron phosphate are compounded, a layer of porous carbon film is formed on the surface of the lithium iron phosphate, so that the electrolyte infiltration is facilitated, more lithium ion diffusion channels are provided, and the electrochemical performance of the lithium iron phosphate battery is improved.
Description
Technical Field
The invention belongs to the field of lithium ion battery materials, and particularly relates to a lithium iron phosphate carbon aerogel composite material and a preparation method thereof.
Background
Lithium iron phosphate (LiFePO) was discovered since the group of Goodenough topics in 1997 4 ) The lithium ion battery anode material has wide attention as a lithium ion battery anode material, has the specific capacity of 170mAh/g, is about 3.4V relative to the voltage of metal lithium, and is widely applied to the fields of consumer batteries, electric tools, electric bicycles, electric automobiles, communication base stations, large-scale energy storage and the like. LiFePO 4 Has the advantages of stable discharge platform, high safety performance, long cycle service life, low price, environmental protection and the like, but has low electronic conductivity (1 multiplied by 10) -9 S/cm), small lithium ion diffusion coefficient (1X 10) -14 cm 2 /s) which limits its application to high power batteries.
LiFePO 4 The mainstream synthesis methods include high temperature solid phase method, carbothermic method, microwave synthesis method, sol-gel method andhydrothermal method. Combined LiFePO 4 The problems of the material exist, and the current modification method comprises surface coating, ion doping, material particle nanocrystallization and the like. The carbon coating modification is to LiFePO 4 The method has obvious electrochemical performance, can improve the electronic conductivity of the active material on one hand, and can inhibit the particle agglomeration in the synthesis process on the other hand. The carbon-coated lithium iron phosphate composite material has the advantages that the traditional carbon source comprises an inorganic carbon source and an organic carbon source, the porosity is limited, and a transmission path for lithium ions is limited in the high-rate charge and discharge process, so that the lithium ion intercalation rate is influenced.
At present, researchers adopt a plurality of effective methods to improve the electrochemical performance of the lithium iron phosphate material in the direction of carbon-coated lithium iron phosphate. CN111211311A discloses a porous nano lithium iron phosphate composite material and a preparation method thereof, wherein a hydrothermal method is adopted to coat a hard carbon material and a nitrogen-doped element thereof on the surface of lithium iron phosphate to prepare nano porous lithium iron phosphate, but the preparation of a precursor material of the method needs a hydrothermal reaction, the operation is carried out at high temperature and high pressure, the danger coefficient is high, high-temperature sintering is still needed after the reaction is finished, and the energy consumption and the manufacturing cost are increased; CN102769134B discloses a lithium ion battery anode composite material LiFePO 4 The preparation method of the/C comprises the steps of synthesizing a compound of iron phosphate and phenolic resin by an in-situ polymerization limiting method, then grinding and uniformly mixing the compound with lithium salt, and sintering the mixture in a protective atmosphere to prepare LiFePO 4 The reaction process of the phenolic resin is difficult to control, the consistency of the product is difficult to ensure, and the method is not beneficial to commercial production.
Disclosure of Invention
The invention aims to solve the problem of LiFePO existing in the prior art 4 The material has low electronic conductivity and small lithium ion diffusion coefficient, and is coated by singly adopting glucose as a carbon source, so that the interlayer spacing is small, and Li is influenced + The de-intercalation efficiency is high, the liquid absorption and retention capacity of the material is poor under the high compaction process, and the porous LiFePO prepared by the prior art 4 The technical problems that the composite material has complex process and the consistency of the product is difficult to ensure and the like are solved, and the carbon-coated LiFePO is improved 4 Simple process, no impurity introduction, suitability forA preparation method of lithium iron phosphate carbon aerogel composite material produced in large scale. According to the method, the porous carbon aerogel and the lithium iron phosphate are compounded, a layer of porous carbon film is formed on the surface of the lithium iron phosphate, so that the method is favorable for the infiltration of electrolyte, and more lithium ion diffusion channels are provided to improve the electrochemical performance of the lithium iron phosphate battery.
In order to achieve the above object, the method for preparing a lithium iron phosphate carbon aerogel composite material according to the present invention comprises the following steps:
(1) Uniformly mixing a phosphorus source, an iron source and a lithium source according to a molar ratio to form a mixture A; mixing the mixture A with a carbon source and an organic dispersant to form a mixture B;
(2) Mixing the mixture B in a ball mill to obtain mixed slurry A, performing ball milling by adopting an intermittent wet method, and fully and uniformly mixing by controlling the ball milling rotation speed and the ball milling time;
in this step, a hydrothermal method, a sol-gel method, or a spray drying method may also be employed instead of the batch wet ball milling.
(3) Drying and crushing the mixed slurry A to obtain a lithium iron phosphate precursor, and reducing the particle agglomeration degree in the drying process by controlling the drying temperature and the drying time;
(4) Sintering the lithium iron phosphate precursor in an inert atmosphere to prepare a carbon-coated lithium iron phosphate material; preparing LiFePO by adopting carbothermic method 4 Reducing ferric iron into ferrous iron to realize one-step reduction;
(5) And (3) crushing the carbon-coated lithium iron phosphate material into particles to prepare the carbon-coated lithium iron phosphate carbon aerogel composite material.
Further, in the step (1), the phosphorus source is at least one of iron phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid, the iron source is at least one of iron phosphate, iron oxide and ferrous oxalate, and the lithium source is at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide and lithium nitrate; the carbon source is carbon aerogel or the mixture of the carbon aerogel and at least one of glucose, sucrose, phenolic resin, starch, dextrin, citric acid, oxalic acid and polyvinyl alcohol, and the carbon aerogel and the glucose are preferably compounded; the organic dispersant is at least one of ethanol, ethylene glycol, glycerol and n-propanol.
Further, in step (1), fe: p: the molar ratio of Li is 1:1: (1.01-1.08), wherein the addition amount of the carbon aerogel is 1.0-15 wt% of the total amount of the mixture B.
Further, in the step (1), the adding amount of the organic dispersant is 24 to 36 weight percent of the total amount of the mixture B.
Further, in the step (2), the rotation speed of the wet ball milling is 100-500 r/min, the ball milling time is 2-14 h, and the ball-to-material ratio of the wet ball milling is 6: (0.8-1.2).
As the optimization of the technical scheme of the invention, in the step (3), the drying is divided into two stages, the drying temperature of the first stage is 30-70 ℃, and the drying time is 2-10 h; the second stage drying temperature is 70-120 ℃, and the drying time is 4-12 h.
Preferably, in the step (4), the inert atmosphere is one of nitrogen, argon and a nitrogen-hydrogen mixed gas; the sintering is divided into two sections: in the first stage, the sintering temperature is 200-450 ℃, the heating rate is 1-10 ℃/min, and the heat preservation time is 2-7 h; the second stage sintering temperature is 400-700 ℃, the heating rate is 1-10 ℃/min, and the heat preservation time is 4-10 h; then the temperature is reduced to room temperature under inert atmosphere.
Preferably, in the step (5), the particle crushing is mechanical ball milling, the ball milling rotation speed is 100-400 r/min, and the ball milling time is 2-10 h.
As a further preferred embodiment of the present invention, in step (1), the amount of the carbon aerogel added is 6.0wt% to 15wt% of the total amount of the mixture B, and the amount of the organic dispersant added is 25% to 32% of the total amount of the mixture B, preferably 27% to 30%; in the step (4), the sintering is divided into two sections: the sintering temperature of the first stage is 350-420 ℃, the heating rate is 3-6 ℃/min, and the heat preservation time is 5-6 h; the sintering temperature of the second stage is 600-680 ℃, the heating rate is 3-6 ℃/min, and the heat preservation time is 7-8 h; then the temperature is reduced to room temperature under inert atmosphere.
Researches show that the lithium iron phosphate carbon aerogel composite material prepared by adopting the following technical parameters has the best performance: in the step (1), ferric phosphate is used as a phosphorus source and an iron source, lithium carbonate is used as a lithium source, glucose and carbon aerogel are used as carbon sources, and the molar ratio of the glucose to the carbon aerogel is (6-1): 1; in the step (2), the rotation speed of the wet ball milling is 150-300 r/min, the ball milling time is 4-8 h, and the ball-to-material ratio of the wet ball milling is 6:1; in the step (3), the drying is divided into two stages, the drying temperature of the first stage is 35-50 ℃, and the drying time is 3-6 h; the second stage drying temperature is 70-90 ℃, and the drying time is 8-11 h; in the step (4), the sintering temperature of the first stage is 380-410 ℃, the heating rate is 4-6 ℃/min, the heat preservation time is 5-6 h, the sintering temperature of the second stage is 640-670 ℃, the heating rate is 4-6 ℃/min, and the heat preservation time is 7-8 h; in the step (5), the particle crushing is mechanical ball milling, the ball milling speed is 150-300 r/min, and the ball milling time is 3-6 h.
Compared with the prior art, the preparation method of the lithium iron phosphate carbon aerogel composite material has the following beneficial effects:
(1) In the synthesis process of the lithium iron phosphate precursor, carbon aerogel is used as a partial carbon source to synthesize the porous carbon-coated lithium iron phosphate anode material. The Carbon Aerogel (CA) is a novel three-dimensional porous carbon material, has the characteristics of large specific surface area, high porosity, strong adsorption capacity, controllable nano microstructure and the like, and has higher conductivity in a wide temperature interval.
(2) The porous carbon-coated lithium iron phosphate cathode material disclosed by the invention is used for LiFePO by utilizing a carbon aerogel porous three-dimensional network structure 4 The battery system is beneficial to imbibition and storage of electrode materials, effectively improves the infiltration of lithium iron phosphate anode material electrolyte, improves the imbibition and storage capacity of the materials, and improves Li in the charging and discharging processes + The diffusion rate of (2).
(3) The carbon source in the invention uses a carbon aerogel and glucose compound carbon source, and a layer of porous carbon film is formed on the surface of the lithium iron phosphate, so that more lithium ion diffusion channels are provided.
(4) The lithium iron phosphate carbon aerogel composite material prepared by the invention can be prepared by mixing the lithium iron phosphate precursor with the carbon aerogel and performing simple high-temperature solid-phase reaction, can be directly incorporated into the industrial production of lithium iron phosphate, and does not need to adjust the existing production line.
Drawings
Fig. 1 is a raman spectrum of the carbon aerogel in example 1.
FIG. 2 is a BET test pattern of the carbon aerogel of example 1.
FIG. 3 is an SEM spectrum of a carbon aerogel in example 1.
FIG. 4 is a TEM spectrum of a carbon aerogel of example 1.
Fig. 5 is a TEM spectrum of a lithium iron phosphate carbon aerogel composite prepared in example 1.
Detailed Description
To describe the present invention, the following examples are provided to further illustrate the preparation method of lithium iron phosphate carbon aerogel composite material according to the present invention. The invention is not limited to the embodiments.
The upper and lower limit values and interval values of the raw materials and the process parameters related by the invention can realize the product of the invention, and are not listed one by one.
The technical performance of the carbon aerogel adopted in the embodiment of the invention is shown in table 1, and is a product prepared by new material technology limited company of the steel group Maanshan institute, wherein the type of the carbon aerogel adopted in the embodiments 1, 2, 3, 4, 5 and 6 is CQ-13, the type of the carbon aerogel adopted in the embodiments 7 and 8 is CQ-16, and the type of the carbon aerogel adopted in the embodiments 9 and 10 is CQ-20.
TABLE 1 Performance parameters of three types of carbon aerogels
Example 1
Example 1 iron phosphate as a phosphorus source and an iron source, lithium carbonate as a lithium source, glucose and carbon aerogel as carbon sources, and carbon aerogelThe model is CQ-13, and the organic dispersant adopts absolute ethyl alcohol; preparation of LiFePO by carbothermic method 4 and/C. The method comprises the following specific steps:
s1: according to a molar ratio of Fe: p: li =1:1: (1.01-1.08) weighing Li 2 CO 3 、FePO 4 Obtaining a lithium iron phosphate precursor mixture;
s2: the carbon source adopts a mixture of glucose and carbon aerogel, and the molar ratio is 6:1, weighing glucose and carbon aerogel, and adding the glucose and the carbon aerogel according to the proportion that the adding amount of a carbon source is 15 percent of the total mass of a phosphorus source, an iron source, a lithium source, the carbon source and an organic dispersant;
s3: carrying out ball milling and mixing on a phosphorus source, an iron source, a lithium source, a carbon source and an organic dispersant (absolute ethyl alcohol), wherein the ball-to-material ratio is 6:1, ball milling for 8 hours at the rotating speed of 200 r/min;
s4: separating the ball-milled mixed slurry, drying at 40 ℃ for 4h, and then performing vacuum drying at 80 ℃ for 10h;
s5: heating the dried mixture to 400 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 6h, then heating to 650 ℃ at the heating rate of 5 ℃/min, preserving heat for 8h, and naturally cooling to room temperature to obtain the porous hard carbon-coated lithium iron phosphate cathode material;
s6: the prepared porous hard carbon-coated lithium iron phosphate positive electrode material is subjected to particle crushing, the mechanical ball milling rotation speed is 200r/min, and the ball milling time is 4 hours;
s7: the button cell assembled by the porous hard carbon-coated lithium iron phosphate anode material is used for LiFePO 4 Electrochemical performance test is carried out on the/C sample, liFePO 4 The mass ratio of/C, SP and PVDF is 8: l: l, weighing, taking N-methyl pyrrolidone as a solvent, uniformly stirring, coating on an aluminum foil with the diameter of 15 micrometers, drying in vacuum at 120 ℃ for 12 hours, and cutting into a pole piece with the diameter of 14mm to obtain the positive pole piece. And a metal lithium sheet is taken as a negative electrode and assembled into a CR2032 type button half-cell in a glove box. And (3) carrying out charge and discharge tests on the battery by adopting a CT3001A type blue light tester.
As seen from the Raman spectrum of the carbon aerogel in example 1 shown in FIG. 1, the sample was at 1339cm -1 And 1594cm -1 NearbyAll have distinct vibration peaks corresponding to the D peak and G peak, respectively, the G band is related to the existence of graphite carbon, and the D band is corresponding to amorphous carbon with the intensity ratio I D /I G 1.14, which indicates that the carbon aerogel has higher disorder degree and conforms to the structural characteristics of hard carbon.
As can be seen from the BET test pattern of the carbon aerogel in example 1 shown in FIG. 2, the specific surface area is 1503.7m 2 ·g -1 The sample adsorption/desorption isotherms correspond to the type I curve, with P/P 0 And increasing, wherein the adsorption quantity gradually approaches to saturation, which is a micropore filling phenomenon on the micropore adsorbent, and indicates that more micropores exist in the carbon aerogel material. The existence of the carbon aerogel can effectively increase the specific surface area of the lithium iron phosphate carbon aerogel composite material, and is beneficial to increasing LiFePO 4 The contact area of the electrolyte improves the LiFePO 4 The material has the capability of absorbing and maintaining liquid, and the electron transmission rate and the ion transmission rate of the material are improved.
As shown in the SEM spectrum of the carbon aerogel in example 1 shown in figure 3, the particle size of the carbon aerogel is micron-sized, the particle size distribution is relatively uniform, the surface has rich pore structures, and the network structure is loose, so that the complete infiltration of electrolyte is facilitated, and the Li is improved + Diffusion transport rate and cycling performance under high rate conditions.
The hard carbon structural characteristics of the carbon aerogel are seen from the TEM spectrum of the carbon aerogel in example 1 shown in fig. 4.
LiFePO can be observed from a TEM spectrum of the lithium iron phosphate carbon aerogel composite material prepared in example 1 shown in FIG. 5 4 Crystal lattice stripes of the crystal and a carbon coating layer on the surface of the crystal lattice stripes.
Example 2
In the step 2), the molar ratio of 4:1 glucose and carbon aerogel were weighed and prepared, and the other steps were the same as in example 1.
Example 3
In the step S2, the molar ratio of the components is 2:1 glucose and carbon aerogel were weighed and prepared, and the rest was the same as in example 1.
Example 4
In the step S2, the molar ratio of 1:1 glucose and carbon aerogel were weighed and prepared, and the rest was the same as in example 1.
Example 5
In the step S2, the molar ratio of 1:1, weighing glucose and carbon aerogel, and preparing; s3, ball milling for 4 hours; the rest is the same as in example 1.
Example 6
In the step S2, the molar ratio of 1:1, weighing glucose and carbon aerogel, and preparing; ball milling is carried out for 6 hours in the step S3; the rest is the same as in example 1.
Example 7
The type of the adopted carbon aerogel is CQ-16; in the step S2, the adding amount of a carbon source is 9% of the total mass of the ingredients, and the carbon source is added according to a molar ratio of 2:1, weighing glucose and carbon aerogel; in the step S3, the rotating speed is 150r/min, and ball milling is carried out for 5 hours; s5, in the first stage, the sintering temperature is 380 ℃, the heating speed is 4 ℃/min, the heat preservation time is 6h, the sintering temperature in the second stage is 640 ℃, the heating speed is 4 ℃/min, and the heat preservation time is 8h; and in the step S6, the rotating speed of the mechanical ball milling is 150r/min, and the ball milling time is 6h. The rest is the same as in example 1.
Example 8
The type of the adopted carbon aerogel is CQ-16; in the step S2, the adding amount of a carbon source is 12% of the total mass of the ingredients, and the carbon source is added according to a molar ratio of 3:1, weighing glucose and carbon aerogel; in the step S3, the rotating speed is 300r/min, and ball milling is carried out for 7 hours; s5, in the first stage, the sintering temperature is 410 ℃, the temperature rising speed is 6 ℃/min, the heat preservation time is 5h, the sintering temperature in the second stage is 670 ℃, the temperature rising speed is 6 ℃/min, and the heat preservation time is 7h; and S6, in the step of mechanical ball milling, the ball milling rotation speed is 150r/min, and the ball milling time is 5h. The rest is the same as in example 1.
Example 9
The type of the adopted carbon aerogel is CQ-20; the rest is the same as in example 7.
Example 10
The type of the adopted carbon aerogel is CQ-20; the rest is the same as in example 8.
Through detection, the gram discharge capacities of the lithium iron phosphate carbon aerogel cathode materials prepared in examples 1, 2, 3, 4, 5 and 6 are shown in table 2:
TABLE 2 Performance parameters of three types of lithium iron phosphate
Research shows that carbon coating can effectively improve LiFePO 4 Electron conductivity and Li + The diffusion coefficient is properly introduced into a porous structure, so that the contact area of the active material and the electrolyte can be increased, the diffusion of electrons and ions is accelerated, and the LiFePO is improved 4 And (3) electrochemical performance of the material. But when LiFePO is used 4 When the specific surface area of the material is too large (e.g. more than 50 m) 2 And/g), particle agglomeration is easily caused in the electrode preparation and homogenization process, and the capacity exertion of the active material is influenced.
As can be seen from Table 2, when the carbon source was pure glucose, liFePO was produced 4 Specific surface area of only 8m 2 The/g, influences the performance of the product; when the carbon source is pure glucose and the carbon aerogel is mixed in the same proportion, the specific surface area is increased to 24.0-28.6 m 2 The per gram is very beneficial to improving the performance of the product; and when the carbon source is pure carbon aerogel, liFePO 4 The specific surface area is as high as 65m 2 However, the porosity (porosity) is too low, namely 48.6%, and the fine particle size can cause agglomeration, which adversely affects the performance of the product.
Table 3 shows LiFePO prepared in examples 11 to 10 4 And testing the product performance.
Table 3 LiFePO prepared in examples 1 to 10 4 Performance testing of products
As can be seen from the detection results in Table 3, the CQ-13 carbon aerogel adopted in the invention can prepare a LiFePO4/C sample with a 0.1C discharge gram capacity of more than 155mAh/g, wherein the 3C discharge gram capacity is also as high as 110.2-135.9 mAh/g; the CQ-16 carbon aerogel can be used for preparing a LiFePO4/C sample with the discharge gram capacity of 0.1C being more than 163mAh/g, wherein the discharge gram capacity of 3C is also more than 132.0mAh/g; the CQ-20 carbon aerogel can be used for preparing a LiFePO4/C sample with 0.1C discharge gram capacity of over 166mAh/g, the maximum value reaches 167.2mAh/g, the theoretical value is close to 168mAh/g, and unexpected technical effects are achieved; wherein the 3C discharge gram capacity is also larger than 138.5mAh/g.
Whereas LiFePO prepared in comparative example 1 4 The product has 0.1C discharge gram capacity of only 67.2mAh/g and 3C discharge gram capacity of only 48.3mAh/g; liFePO prepared in comparative example 2 4 The product has a 0.1C discharge gram capacity of only 96.5mAh/g and a 3C discharge gram capacity of only 76.2mAh/g. The illustration shows that the carbon source adopts pure glucose and carbon aerogel to prepare LiFePO 4 The product performance is optimal.
Claims (10)
1. The preparation method of the lithium iron phosphate carbon aerogel composite material is characterized by comprising the following steps of:
(1) Uniformly mixing a phosphorus source, an iron source and a lithium source according to a molar ratio to form a mixture A; mixing the mixture A with a carbon source and an organic dispersant to form a mixture B;
(2) Mixing the mixture B in a ball mill to obtain mixed slurry A, performing intermittent wet ball milling, and fully and uniformly mixing by controlling the ball milling rotation speed and the ball milling time;
(3) Drying and crushing the mixed slurry A to obtain a lithium iron phosphate precursor, and reducing the particle agglomeration degree in the drying process by controlling the drying temperature and the drying time;
(4) Sintering the lithium iron phosphate precursor in an inert atmosphere to prepare a carbon-coated lithium iron phosphate material; liFePO is prepared by adopting carbothermic method 4 Reducing ferric iron into ferrous iron to realize one-step reduction;
(5) And (3) crushing the carbon-coated lithium iron phosphate material into particles to prepare the carbon-coated lithium iron phosphate carbon aerogel composite material.
2. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 1, wherein: in the step (1), the phosphorus source is at least one of iron phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate and phosphoric acid, the iron source is at least one of iron phosphate, ferric oxide and ferrous oxalate, and the lithium source is at least one of lithium carbonate, lithium dihydrogen phosphate, lithium hydroxide and lithium nitrate; the carbon source is carbon aerogel or a mixture of the carbon aerogel and at least one of glucose, sucrose, phenolic resin, starch, dextrin, citric acid, oxalic acid and polyvinyl alcohol; the organic dispersant is at least one of ethanol, ethylene glycol, glycerol and n-propanol.
3. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 1, wherein: in the step (1), fe: p: the molar ratio of Li is 1:1:
(1.01-1.08), wherein the addition amount of the carbon aerogel is 1.0-15 wt% of the total amount of the mixture B.
4. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 1, wherein: in the step (1), the adding amount of the organic dispersant is 24 to 36 weight percent of the total amount of the mixture B.
5. The method of preparing a lithium iron phosphate carbon aerogel composite of claims 1, 2, 3, or 4, wherein: in the step (2), the rotation speed of the wet ball milling is 100-500 r/min, the ball milling time is 2-14 h, and the ball-to-material ratio of the wet ball milling is 6: (0.8-1.2).
6. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 5, wherein: in the step (3), the drying is divided into two stages, wherein the drying temperature of the first stage is 30-70 ℃, and the drying time is 2-10 h; the second stage drying temperature is 70-120 ℃, and the drying time is 4-12 h.
7. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 6, wherein: in the step (4), the inert atmosphere is one of nitrogen, argon and nitrogen-hydrogen mixed gas; the sintering is divided into two sections: the sintering temperature of the first stage is 200-450 ℃, the heating rate is 1-10 ℃/min, and the heat preservation time is 2-7 h; the sintering temperature of the second stage is 400-700 ℃, the heating speed is 1-10 ℃/min, and the heat preservation time is 4-10 h; then the temperature is reduced to room temperature under inert atmosphere.
8. The method for preparing a lithium iron phosphate carbon aerogel composite as claimed in claim 7, wherein: in the step (5), the particle crushing is mechanical ball milling, the ball milling speed is 100-400 r/min, and the ball milling time is 2-10 h.
9. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 4, wherein: in the step (1), the adding amount of the carbon aerogel is 6.0-15 wt% of the total amount of the mixture B, and the adding amount of the organic dispersant is 25-32% of the total amount of the mixture B; in the step (4), the sintering is divided into two sections: the sintering temperature of the first stage is 350-420 ℃, the heating rate is 3-6 ℃/min, and the heat preservation time is 5-6 h; the sintering temperature of the second stage is 600-680 ℃, the heating rate is 3-6 ℃/min, and the heat preservation time is 7-8 h; then the temperature is reduced to room temperature under inert atmosphere.
10. The method for preparing lithium iron phosphate carbon aerogel composite material according to claim 9, wherein: in the step (1), ferric phosphate is used as a phosphorus source and an iron source, lithium carbonate is used as a lithium source, glucose and carbon aerogel are used as carbon sources, and the molar ratio of the glucose to the carbon aerogel is (6-1): 1; in the step (2), the rotation speed of the wet ball milling is 150-300 r/min, the ball milling time is 4-8 h, and the ball-to-material ratio of the wet ball milling is 6:1; in the step (3), the drying is divided into two stages, the drying temperature of the first stage is 35-50 ℃, and the drying time is 3-6 h; the second stage drying temperature is 70-90 ℃, and the drying time is 8-11 h; in the step (4), the sintering temperature of the first stage is 380-410 ℃, the heating rate is 4-6 ℃/min, the heat preservation time is 5-6 h, the sintering temperature of the second stage is 640-670 ℃, the heating rate is 4-6 ℃/min, and the heat preservation time is 7-8 h; in the step (5), the particle crushing is mechanical ball milling, the ball milling speed is 150-300 r/min, and the ball milling time is 3-6 h.
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