Lithium iron phosphate composite material, preparation method and use thereof

Abstract

This disclosure provides a lithium iron phosphate composite material, its preparation method, and its applications. The preparation method involves mixing porous inorganic nanofiber aerogel, a lithium source, an iron source, a phosphorus source, and a carbon source to obtain a dispersion. This dispersion is then spray-dried to obtain a precursor, which is subsequently sintered to obtain the lithium iron phosphate composite material. This disclosure utilizes porous inorganic nanofiber aerogel to form a composite material in situ during the synthesis of lithium iron phosphate. The presence of porous nanofibers results in a more uniform distribution of lithium iron phosphate particles, preventing agglomeration. The combined effect of porous nanofibers and aerogel effectively shortens the lithium iron phosphate synthesis time. + The transmission path effectively improves the rate performance of the obtained material; at the same time, it can also play a supporting role, avoid damage caused by processing such as pressing, and alleviate the volume change of the obtained material during charging and discharging, avoid cracking and other problems, and improve the stability of the material.

Description

Technical Field

[0001] This disclosure pertains to the field of batteries and relates to a cathode material, particularly a lithium iron phosphate composite material and its preparation method and applications. Background Technology

[0002] Secondary lithium-ion batteries (LIBs) have attracted much attention and have been commercialized in many fields due to their advantages such as high operating voltage and energy density, especially the low toxicity and environmental friendliness of electrode materials. They are the mainstream technology in the field of electrochemical energy storage.

[0003] Among them, lithium iron phosphate (LiFePO4, LFP) batteries have advantages over other cathode materials, including high safety, strong stability, low cost, abundant resources, and long cycle life. However, due to its own crystal structure, its poor conductivity and slow ion migration rate greatly limit the improvement of its electrochemical performance, especially causing low rate performance, thus affecting its further commercial development in the future.

[0004] Low rate performance typically indicates slow lithium-ion migration. To address this issue, researchers have been controlling the microstructure and size of lithium ions (LFPs) to shorten the Li-ion migration time. + While the diffusion path of lithium iron phosphate (LFP) is important, the small crystallite size of LFP increases the polaron phenomenon in the structure, leading to reduced conductivity and thus negatively impacting the rate performance of LFP. Another effective approach is to develop porous lithium iron phosphate materials. These materials utilize porous channels to provide rapid transport pathways for electrons and ions, and the increased specific surface area and nanoscale pore wall thickness can promote charge transfer and improve the lithium-ion diffusion rate. For example, CN115986065A discloses a microwave-assisted hydrothermal method for preparing lithium iron phosphate cathode materials. This method uses microwave-assisted hydrothermal processing to prepare a porous lithium iron phosphate precursor, which is then sintered into carbon-coated porous lithium iron phosphate.

[0005] However, when lithium iron phosphate is manufactured into porous lithium iron phosphate, it is easy for it to crack and break during the rolling process of the electrode sheet, causing the coating layer to fall off and come into direct contact with the electrolyte, which accelerates the loss of positive electrode active material, reduces battery stability, reduces capacity, and accelerates cycle performance degradation.

[0006] Therefore, new strategies are needed to improve the overall structural stability of cathode materials while maintaining the porous structure. This can not only accelerate the lithium-ion migration rate and improve rate performance, but also avoid cracking during the pressing of the electrode sheet. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] In view of the problems existing in the prior art, the purpose of this disclosure is to provide a lithium iron phosphate composite material, its preparation method and uses. The preparation method involves mixing porous inorganic nanofiber aerogel, a lithium source, an iron source and a phosphorus source to obtain a dispersion, which is then spray-dried to obtain a precursor, followed by sintering to obtain the lithium iron phosphate composite material. This disclosure utilizes porous inorganic nanofiber aerogel to form an in-situ coating on lithium iron phosphate during synthesis. The presence of porous nanofibers makes the lithium iron phosphate particles more uniformly distributed and prevents agglomeration. The combined effect of porous nanofibers and aerogel can effectively shorten the LiFePO4 synthesis time. + The transmission path effectively improves the rate performance of the obtained material; at the same time, it can also play a supporting role, avoid damage caused by processing such as pressing, and alleviate the volume change of the obtained material during charging and discharging, avoid cracking and other problems, and improve the stability of the material.

[0009] To achieve this objective, the present disclosure adopts the following technical solution:

[0010] In a first aspect, this disclosure provides a method for preparing a lithium iron phosphate composite material, the method comprising:

[0011] A dispersion was obtained by mixing porous inorganic nanofiber aerogel, lithium source, iron source, phosphorus source and carbon source, which was then spray-dried to obtain a precursor, and then sintered to obtain a lithium iron phosphate composite material.

[0012] This disclosure involves mixing inorganic nanofiber aerogel into the raw materials for synthesizing lithium iron phosphate (LFP) cathode materials to obtain a uniformly mixed precursor. This allows porous inorganic nanofibers to be positioned between and on the surface of LFP particles during the formation of the LFP composite material, forming a coating layer. Overall, the LFP particles adhere to the porous framework constructed by the inorganic nanofibers. These nanofibers, with their specific aspect ratio, provide support and buffering during the pressing process, preventing cracking. Furthermore, this preparation method effectively increases the specific surface area of ​​the cathode material without affecting its structure, enhancing contact with the electrolyte and providing more electrochemical reaction sites. The presence of porous nanofibers results in a more uniform particle distribution and prevents agglomeration. The combined effect of porous nanofibers and aerogel effectively shortens the Li-P-T ratio. + The transmission path.

[0013] The ultralight and highly elastic properties of aerogel can buffer the volume changes caused by the charging and discharging of lithium batteries, and the nanofibers act as a support inside the lithium iron phosphate, preventing cracking during electrode pressing. The structure of porous titanium dioxide nanofibers can be controlled by combining different percentages of pore-forming agents and electrospinning parameters, providing more options for subsequent composite cathode materials.

[0014] The following are optional technical solutions of this disclosure, but are not intended to limit the technical solutions provided by this disclosure. The technical objectives and beneficial effects of this disclosure can be better achieved through the following technical solutions.

[0015] As an optional technical solution of this disclosure, the method for preparing the porous inorganic nanofiber aerogel includes:

[0016] Porous inorganic fibers are mixed with a gelling agent and dried to form porous inorganic nanofiber aerogels.

[0017] The mixing of porous inorganic fibers and gelling agents described in this disclosure can be carried out in solvents such as water and / or ethanol to achieve sufficient and stable dispersion of the porous inorganic fibers before drying.

[0018] In one embodiment, the mass ratio of the porous inorganic nanofibers to the gelling agent is 1:(3-7), such as 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0019] In one embodiment, the porous inorganic nanofibers and the gelling agent are mixed in water, and the amount of water is 6 to 12 times the total mass of the other raw materials, such as 6, 7, 8, 9, 10, 11 or 12 times, but not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0020] In one embodiment, the porous inorganic nanofibers comprise any one or a combination of at least two of titanium dioxide, silicon dioxide, or boron nitride, with typical but non-limiting examples including combinations of titanium dioxide and silicon dioxide, combinations of titanium dioxide and boron nitride, or combinations of silicon dioxide and boron nitride, and further optionally, porous silicon dioxide nanofibers.

[0021] In one embodiment, the gelling agent comprises silica sol.

[0022] This disclosure may use carbon dioxide sol as a gelling agent. The sol has good hydrophilicity, can be diluted to any concentration, and its stability will not be reduced.

[0023] In one embodiment, the gelling agent further includes a coagulating agent.

[0024] In one embodiment, the coagulant includes esters and / or alcohols; the esters include at least one of dibutyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl orthosilicate, ethyl orthosilicate, triethyl phosphate, or tetraethyl orthosilicate, and ethyl orthosilicate is further optional; the alcohols include at least one of methanol, ethanol, or polyethylene glycol.

[0025] In one embodiment, the porous inorganic nanofiber aerogel also contains carbon materials.

[0026] This disclosure further describes the doping of carbon materials into porous inorganic nanofiber aerogels, which can improve the conductivity of the cathode material.

[0027] For example, a method for preparing carbon-doped porous titanium dioxide nanofiber aerogel includes: mixing porous titanium dioxide nanofibers, carbon materials and a gelling agent, and drying to obtain carbon-doped porous titanium dioxide nanofiber aerogel.

[0028] In one embodiment, the carbon material includes graphene.

[0029] This disclosure introduces carbon materials, particularly graphene, into an aerogel for doping, and utilizes the carbon materials and inorganic nanofibers to form a composite material for lithium iron phosphate. In the preparation of lithium iron phosphate cathode materials, carbon materials can not only improve the conductivity but also replace a portion of the carbon source used in the synthesis of lithium iron phosphate, thereby reducing manufacturing costs. In the formed aerogel, the carbon materials and titanium dioxide nanofibers are uniformly dispersed and mixed. Besides graphene, other carbon materials, such as carbon nanotubes, can also be used. Graphene is further selected because, among all carbon materials, it has better conductivity, and its two-dimensional planar structure provides a larger contact area with titanium dioxide, resulting in the best optimization effect.

[0030] In one embodiment, the carbon material accounts for 0.01% to 5% of the total mass of the porous inorganic nanofiber aerogel, for example, 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, 3.3%, 3.5%, 3.8%, 4%, 4.3%, 4.5%, 4.8%, or 5%, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0031] In one embodiment, the drying method includes any one or a combination of at least two of freeze drying, supercritical drying, vacuum drying, or microwave drying. Typical but non-limiting examples of such combinations include combinations of freeze drying and supercritical drying, freeze drying and vacuum drying, freeze drying and microwave drying, supercritical drying and vacuum drying, or microwave drying and vacuum drying.

[0032] As an optional technical solution of this disclosure, the method for preparing the porous titanium dioxide nanofibers includes:

[0033] A precursor solution is obtained by mixing a titanium source, a pore-forming agent, and a solvent. This solution is then electrospun to obtain a spun fabric, which is subsequently calcined to obtain porous titanium dioxide nanofibers.

[0034] In one embodiment, the pore-forming agent comprises camphene.

[0035] This disclosure further selects camphene as a pore-forming agent, which can coexist stably with the titanium source without reacting with each other. Camphene can be pyrolyzed and volatilized above 160°C, and its volatilization temperature is relatively low. It can be directly sublimated from the solid phase, thus achieving the pore-forming function at a relatively low temperature.

[0036] In one embodiment, the amount of the pore-forming agent is 0.1% to 20% of the mass of the titanium source, for example, 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0037] In one embodiment, the solid-liquid ratio of the titanium source to the solvent is 1g:(2-5)mL, for example, 1g:2mL, 1g:2.3mL, 1g:2.6mL, 1g:2.9mL, 1g:3.2mL, 1g:3.5mL, 1g:3.8mL, 1g:4.1mL, 1g:4.4mL, 1g:4.7mL, or 1g:5mL, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0038] In one embodiment, the solvent includes ethanol and / or acetic acid.

[0039] In one embodiment, the solvent is ethanol and acetic acid in a volume ratio of (2-5):1, such as 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.7:1, 4:1, 4.2:1, 4.5:1, 4.8:1, or 5:1, but is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0040] In one embodiment, the obtained spun fabric is first dried at 160–180°C, for example, 160°C, 162°C, 164°C, 166°C, 168°C, 170°C, 172°C, 174°C, 176°C, 178°C, or 180°C, for a drying time of 10–24 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, and then calcined. However, the calcination is not limited to the listed values; other unlisted values ​​within the above range are also applicable.

[0041] The present invention first dries the obtained spun fabric at 160-180°C, which allows camphene, the pore-forming agent, to fully exert its pore-forming effect and to volatilize and remove all pore-forming agents as much as possible.

[0042] As an optional technical solution of this disclosure, the applied voltage for electrospinning is 6 to 10 kV, such as 6 kV, 6.5 kV, 7 kV, 7.5 kV, 8 kV, 8.5 kV, 9 kV, 9.5 kV, or 10 kV, etc., and the rotation speed is 30 to 80 rpm, such as 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm, or 80 rpm, etc., and the distance between the collecting plate and the needle is 8 to 25 cm, such as 8 cm, 10 cm, 12 cm, 14 cm, 16 cm, 18 cm, 20 cm, 23 cm, or 25 cm, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0043] As an optional technical solution of this disclosure, the calcination is carried out in an oxygen-containing atmosphere, and the calcination temperature is 300-650℃, such as 300℃, 330℃, 360℃, 390℃, 420℃, 450℃, 480℃, 510℃, 540℃, 570℃, 600℃, 630℃ or 650℃, etc., and the time is 2-5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, etc., but is not limited to the listed values, and other unlisted values ​​within the above range are also applicable.

[0044] In one embodiment, the process of preparing the porous titanium dioxide nanofibers is carried out in an environment with a humidity of 20% to 80%.

[0045] As an optional technical solution of this disclosure, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium acetate. Typical but non-limiting examples of such combinations include combinations of lithium carbonate and lithium hydroxide, combinations of lithium carbonate and lithium acetate, or combinations of lithium hydroxide and lithium acetate.

[0046] In one embodiment, the phosphorus source comprises ammonium dihydrogen phosphate.

[0047] In one embodiment, the iron source includes any one or a combination of at least two of ferric phosphate tetrahydrate, iron oxide, iron sulfate, or iron(II,III) oxide. Typical but non-limiting examples of such combinations include combinations of ferric phosphate tetrahydrate and iron oxide, combinations of iron(II,III) oxide and iron sulfate, combinations of iron(II,III) oxide and ferric phosphate tetrahydrate, combinations of iron(II,III) oxide and iron oxide, combinations of ferric phosphate tetrahydrate and iron sulfate, or combinations of iron oxide and iron sulfate.

[0048] In one embodiment, the carbon source includes any one or a combination of at least two of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose, or vitamins. Typical but non-limiting examples of such combinations include combinations of glucose and sucrose, glucose and starch, glucose and phenolic resin, glucose and dextrin, glucose and citric acid, glucose and oxalic acid, glucose and cellulose, glucose and vitamins, sucrose and starch, phenolic resin and dextrin, citric acid and oxalic acid, or cellulose and vitamins.

[0049] In one embodiment, the temperature of the spray-drying gas is between 160 and 300°C, such as 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, or 300°C, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0050] In one embodiment, the gas includes air and / or an inert gas, such as nitrogen, and may further be hot air.

[0051] The advantage of using spray drying in this disclosure is that it can achieve granulation while drying, ensuring the effect of instantaneous drying, and can also adjust parameters to control the size of the particles.

[0052] In one embodiment, the sintering temperature is 400–700°C, such as 400°C, 430°C, 450°C, 480°C, 500°C, 520°C, 550°C, 570°C, 600°C, 620°C, 660°C, 680°C, or 700°C, and the time is 6–18 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, or 18 hours, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0053] In one implementation, the amount of iron source and phosphorus source is controlled according to a molar ratio of iron to phosphate of 1:1.

[0054] In one embodiment, the amount of porous inorganic nanofiber aerogel is controlled according to a molar ratio of porous inorganic nanofibers to iron of (0.03 to 0.08):1, for example, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1 or 0.08:1, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0055] In one embodiment, the amount of lithium source is controlled according to a molar ratio of lithium to iron of (1 to 1.03):1, such as 1:1, 1.01:1, 1.015:1, 1.02:1, 1.025:1 or 1.03:1, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0056] In one embodiment, the amount of carbon source is controlled according to a molar ratio of carbon to iron of (0.05 to 0.12):1, such as 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.10:1, 0.11:1, or 0.12:1, but is not limited to the listed values. Other unlisted values ​​within the above range are also applicable.

[0057] As an optional technical solution of this disclosure, the preparation method includes:

[0058] A titanium source, a pore-forming agent, and a solvent are mixed; the solid-liquid ratio of the titanium source to the solvent is controlled at 1 g:(2-5) mL; the pore-forming agent includes camphene, and the amount of the pore-forming agent accounts for 0.1% to 20% of the mass of the titanium source; the solvent is ethanol and acetic acid in a volume ratio of (2-5):1, to obtain a precursor solution; the applied voltage is set to 6-10 kV, the rotation speed is 30-80 rpm, and the distance between the collecting plate and the needle is 8-25 cm, and the obtained precursor solution is electrospun to obtain a spun fabric; the obtained spun fabric is first dried at 160-180℃ for 10-24 h, and then calcined at 300-650℃ for 2-5 h in an oxygen-containing atmosphere to obtain porous titanium dioxide nanofibers;

[0059] Porous titanium dioxide nanofibers, carbon materials, and a gelling agent are mixed in water; the mass ratio of the porous inorganic nanofibers to the gelling agent is 1:(3-7); the carbon material includes graphene, and the amount of the carbon material accounts for 0.01% to 5% of the mass of the porous titanium dioxide nanofiber aerogel; the gelling agent includes silica sol and / or coagulation accelerators; the amount of water is 6 to 12 times the total mass of the other raw materials; after drying, carbon-doped porous titanium dioxide nanofiber aerogel is obtained.

[0060] The raw materials are mixed according to the following ratio: (0.03-0.08):(1-1.03):1:1:(0.05-0.12). The lithium source includes any one or at least two combinations of lithium carbonate, lithium hydroxide, or lithium acetate. The phosphorus source includes ammonium dihydrogen phosphate. The iron source includes any one or at least two combinations of ferric phosphate tetrahydrate, iron oxide, ferric sulfate, or iron(III) oxide. The carbon source includes any one or at least two combinations of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose, or vitamins. The resulting dispersion is spray-dried using hot air at 160-300°C to obtain a precursor, which is then sintered at 400-700°C for 6-18 hours to obtain a lithium iron phosphate composite material.

[0061] In a second aspect, this disclosure provides a lithium iron phosphate composite material, obtained according to the preparation method described in the first aspect.

[0062] Thirdly, this disclosure provides a battery comprising the lithium iron phosphate composite material described in the second aspect.

[0063] Compared with existing technical solutions, this disclosure has at least the following beneficial effects:

[0064] This disclosure employs porous inorganic nanofiber aerogel to composite lithium iron phosphate cathode material precursors, thereby obtaining lithium iron phosphate composite materials. The preparation method effectively increases the specific surface area of ​​the cathode material without affecting its structure, which is beneficial for enhancing contact with the electrolyte and providing more electrochemical reaction active sites. The presence of nanofibers makes the cathode material particles more uniformly distributed and prevents agglomeration. The combined effect of porous fibers and aerogel can effectively shorten the Li-P ... + The transmission path;

[0065] The ultralight and highly elastic properties of aerogel can buffer the volume changes caused by the charging and discharging of lithium batteries, and the nanofibers act as a support inside the lithium iron phosphate, preventing cracking during electrode pressing. The structure of porous inorganic nanofibers can be controlled by combining different percentages of pore-forming agents and electrospinning parameters, providing more options for subsequent composite cathode materials.

[0066] This disclosure introduces carbon materials, especially graphene, into aerogel for doping. The carbon materials and inorganic nanofibers are used to form a composite coating of lithium iron phosphate. In the preparation of lithium iron phosphate cathode materials, the carbon materials can not only improve the conductivity, but also replace part of the carbon source used to synthesize lithium iron phosphate, thereby reducing the manufacturing cost.

[0067] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0068] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0069] Figure 1 This is a SEM image of the lithium iron phosphate composite material obtained in Example 4. Detailed Implementation

[0070] The technical solution of this disclosure will be further illustrated below through specific implementation methods.

[0071] Those skilled in the art will understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0072] Example 1

[0073] This embodiment provides a method for preparing lithium iron phosphate composite materials, the preparation method comprising:

[0074] (1) Tetrabutyl titanate, glacial acetic acid and anhydrous ethanol are mixed evenly in a ratio of 1:1:3. Camphene with a mass ratio of 9% is added with a tetrabutyl titanate content of 100%. The mixture is stirred overnight to form a transparent light yellow liquid.

[0075] (2) Using electrospinning, the solution of (1) above was subjected to an applied voltage of 8kV and the rotation speed was kept at 40rpm to prepare titanium dioxide nanofiber spuns. First, the polymer was removed by drying at 160℃ for 15h, and then the porous titanium dioxide nanofibers were formed by calcination and annealing at 400℃ for 3h.

[0076] (3) The prepared porous titanium dioxide nanofibers and graphene with a mass fraction of 1% were added to deionized water and ultrasonically dispersed. Then, a gelling agent was added and mixed. The gelling agent included silica sol and dibutyl carbonate. The mass ratio of porous titanium dioxide nanofibers:deionized water:gelling agent was controlled to be 1:90:5. The graphene-doped porous titanium dioxide nanofiber aerogel was obtained by freeze drying.

[0077] (4) The above graphene-doped porous titanium dioxide nanofiber aerogel and the raw materials of positive electrode material, lithium carbonate, iron phosphate and carbon source glucose, are made into a dispersion. The mixture is uniformly dispersed in water according to the molar ratio of titanium, lithium, iron and carbon elements of 0.05:1.01:1:0.08. The spray drying temperature is set to 210℃ and spray drying is carried out to obtain the precursor.

[0078] (5) The mixture from step (4) is sintered at 650°C for 8 hours to obtain a lithium iron phosphate material coated with graphene-doped porous titanium dioxide nanofiber aerogel.

[0079] Example 2

[0080] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 6% to 9%. Except for the above, the other conditions are exactly the same as in Example 1.

[0081] Example 3

[0082] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 6% to 9%, in step (3) the amount of graphene is adjusted from 1% to 3%, and in step (5) the sintering time is adjusted from 8h to 10h. Except for the above, the other conditions are exactly the same as in Example 1.

[0083] Example 4

[0084] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 6% to 12%, in step (3) the amount of graphene is adjusted from 1% to 3%, and in step (5) the sintering time is adjusted from 8h to 10h. Except for the above, the other conditions are exactly the same as in Example 1.

[0085] Example 5

[0086] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 6% to 12%, in step (2) the calcination temperature is adjusted from 400℃ to 500℃, in step (3) the amount of graphene is adjusted from 1% to 3%, and in step (5) the sintering time is adjusted from 8h to 10h. Except for the above, the other conditions are exactly the same as in Example 1.

[0087] Example 6

[0088] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (3), graphene is not used in the preparation method. Except for the above, the other conditions are exactly the same as those in Example 4.

[0089] Example 7

[0090] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (3), carbon nanotubes are used instead of graphene. Except for the above, the other conditions are exactly the same as in Example 4.

[0091] Example 8

[0092] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 12% to 1%. Except for the above, the other conditions are exactly the same as in Example 4.

[0093] Example 9

[0094] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 12% to 3%. Except for the above, the other conditions are exactly the same as in Example 4.

[0095] Example 10

[0096] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 12% to 20%. Except for the above, the other conditions are exactly the same as in Example 4.

[0097] Example 11

[0098] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (1), the amount of camphene is adjusted from 12% to 23%. Except for the above, the other conditions are exactly the same as in Example 4.

[0099] Example 12

[0100] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (3), the amount of graphene is adjusted from 3% to 0.5%, and in step (5), the sintering time is adjusted from 8h to 10h. Except for the above, the other conditions are exactly the same as in Example 1.

[0101] Example 13

[0102] This embodiment provides a method for preparing lithium iron phosphate composite material. In step (3), the amount of graphene is adjusted from 3% to 5.5%, and in step (5), the sintering time is adjusted from 8h to 10h. Except for the above, the other conditions are exactly the same as in Example 1.

[0103] Comparative Example 1

[0104] This comparative example provides a method for preparing lithium iron phosphate composite materials, wherein the preparation method does not use porous titanium dioxide nanofiber aerogel, and the preparation method is as follows:

[0105] The lithium source, phosphorus source, iron source and carbon source in step (4) of Example 4 were made into a dispersion, spray dried and sintered at 650°C for 10 hours to obtain lithium iron phosphate composite material.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing a lithium iron phosphate composite material. In step (1), camphene is not used in the preparation method, and the other conditions are exactly the same as those in Example 4.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing lithium iron phosphate composite material. In step (3), no gelling agent is used. Instead, porous titanium dioxide nanofibers and graphene are mixed and freeze-dried. The resulting sample is then applied to step (4). Except for the above, the other conditions are exactly the same as in Example 4.

[0110] Control group 1

[0111] A method for preparing lithium iron phosphate cathode material disclosed in CN115986065A includes:

[0112] (1) Mix lithium acetate dihydrate, ferrous sulfate heptahydrate, and phosphoric acid in a molar ratio of 1:1:1 and place them in lithium acetate dihydrate and pure water (1:25) and mix evenly.

[0113] (2) Add 0.004 times the mass of polyethylene glycol and 0.02 times the mass of glucose to the precursor solution, place it in a microwave reactor, microwave power 60W, microwave frequency 1000MHz, temperature controlled at 180℃ for 40min.

[0114] (3) After cooling to room temperature, centrifuge to separate the solid, wash with pure water 3 to 5 times, and dry at 90°C for 6 hours to obtain a porous lithium iron phosphate precursor.

[0115] (4) The porous lithium iron phosphate precursor was sintered at 600°C for 7 hours in a nitrogen atmosphere to produce carbon-coated porous lithium iron phosphate.

[0116] The materials or composite materials obtained from the above examples, comparative examples, and control groups were used as cathode materials to prepare coin cells for lithium-ion battery electrochemical performance testing. The specific steps are as follows:

[0117] The positive electrode material, conductive agent acetylene black, and adhesive polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone at a ratio of 8:1:1, and then coated onto aluminum foil and dried in a vacuum drying oven at 120°C for 12 hours. After drying, the battery was assembled in an argon glove box and pressed into a 1 cm diameter circular positive electrode sheet under 30 MPa. The negative electrode was a lithium metal sheet, the electrolyte was 1 M LiPF6-EC:DMC (volume ratio 1:1), and a polypropylene porous membrane was used as the separator.

[0118] Table 1 shows the rate performance test results of the battery samples, with charge / discharge cutoff voltages ranging from 2.7 to 4.3V, and 5 charge / discharge cycles performed at current densities of 0.2C, 1C, 3C, 5C, and 8C. Table 2 shows the cycle performance test results of the sample batteries, with charge / discharge cutoff voltages ranging from 2.7 to 4.3V and a current density of 1C = 160 mA / g.

[0119] Table 1

[0120]

[0121]

[0122] Table 2

[0123]

[0124]

[0125] As can be seen from Tables 1 and 2:

[0126] Table 1 shows the discharge capacity of different embodiments at different rates (0.2C, 1C, 3C, 5C, 8C). As can be seen from the table, the discharge capacity of Example 4 at different rates is 154.2 mAh / g, 146.5 mAh / g, 139.8 mAh / g, 130.2 mAh / g, and 119.9 mAh / g, respectively, which is the best among all embodiments. This is attributed to the introduction of porous titanium dioxide nanofiber aerogel into the cathode material preparation, forming a nanoporous lithium iron phosphate structure. This shortens the lithium-ion transport path, resulting in superior reversibility of lithium-ion extraction and insertion during charge and discharge, enabling lithium-ion insertion even at high rates. Furthermore, its cycle performance is also excellent compared to other embodiments and comparative examples, maintaining a cycle retention rate of 96.1% after 100 cycles at 1C discharge. Figure 1 The image shows a SEM image of the lithium-ion battery composite cathode material prepared in Example 4. After magnification of 5000 times, it can be seen that the primary lithium iron phosphate particles with uniform size and the secondary particles formed by agglomeration are visible. The structure and morphology are good and the dispersion is uniform, with only a small amount of agglomeration effect.

[0127] By comparing Examples 1-4 and Examples 8-11, the amount of camphene was adjusted. It was found that when the amount of camphene decreased, the battery discharge capacity also decreased at 0.2C and other rates. This may be because too little camphene cannot create enough pores to shorten the lithium-ion diffusion channels and achieve efficient lithium-ion transport. When the amount of camphene was too high or exceeded the limit, the cycle retention rates of Examples 10 and 11 after 100 cycles were 93.8% and 93.4%, respectively, which were relatively low. This may be because the presence of too much pore-forming agent damaged the structure of the nanofibers, rendering them unsupporting and prone to cracking during electrode pressing. During repeated charge and discharge, lithium ions continuously extract and insert into the positive electrode, causing the material volume to expand and contract, increasing the possibility of material cracking and leading to a decrease in cycle performance.

[0128] The amount of graphene was adjusted by comparing Examples 1, 3-4 and Examples 12-13. It was found that when the amount of graphene was too small, the battery discharge capacity was low. This may be because too little graphene resulted in too low conductivity of the cathode material, affecting its electrical performance. As the amount of graphene increased, the discharge capacity also increased. However, the presence of too much graphene may cause it to agglomerate together, hindering the transport of lithium ions.

[0129] Compared to Comparative Examples 1-3, Example 4, which prepared lithium iron phosphate in the normal manner without using titanium dioxide aerogel, showed lower rate performance and cycle performance than Example 4, demonstrating the merits of this disclosure. Comparative Example 2, which prepared nanofiber aerogel composite lithium iron phosphate without introducing camphene for pore formation, showed slightly lower performance than Example 4 but better performance than Comparative Example 1, demonstrating that introducing aerogel improves the electrical performance of lithium iron phosphate.

Claims

1. A method for preparing a lithium iron phosphate composite material, characterized in that, The preparation method includes: A titanium source, a pore-forming agent, and a solvent are mixed; the solid-liquid ratio of the titanium source to the solvent is controlled at 1 g:(2~5) mL; the pore-forming agent includes camphene, and the amount of the pore-forming agent accounts for 0.1%~20% of the mass of the titanium source; the solvent is ethanol and acetic acid with a volume ratio of (2~5):1, to obtain a precursor solution; the applied voltage is set to 6~10 kV, the rotation speed is 30~80 rpm, and the distance between the collecting plate and the needle is 8~25 cm, and the obtained precursor solution is electrospun to obtain a spun fabric; the obtained spun fabric is first dried at 160~180℃ for 10~24 h, and then calcined at 300~650℃ for 2~5 h in an oxygen-containing atmosphere to obtain porous titanium dioxide nanofibers; Porous titanium dioxide nanofibers, carbon materials, and a gelling agent are mixed in water; the mass ratio of the porous titanium dioxide nanofibers to the gelling agent is 1:(3~7); the gelling agent includes silica sol and / or a coagulating agent; the amount of water is 6~12 times the total mass of other raw materials; after drying, a carbon-doped porous titanium dioxide nanofiber aerogel is obtained; the carbon material includes graphene, and the amount of carbon material accounts for 0.01%~5% of the mass of the porous titanium dioxide nanofiber aerogel. All raw materials are mixed according to the following ratios: the molar amount of Ti in the carbon-doped porous titanium dioxide nanofiber aerogel, the molar amount of Li in the lithium source, the molar amount of Fe in the iron source, the molar amount of phosphate in the phosphorus source, and the ratio of the carbon source to the total molar amount of carbon atoms in all raw materials is (0.03~0.08):(1~1.03):1:1:(0.05~0.12). The lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide, or lithium acetate. The phosphorus source includes ammonium dihydrogen phosphate. The iron source includes any one or a combination of at least two of ferric phosphate tetrahydrate, iron oxide, ferric sulfate, or iron(II,III) oxide; the carbon source includes any one or a combination of at least two of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose, or vitamins. The above substances are dispersed in a solvent to obtain a dispersion, which is then spray-dried using hot air at 160-300°C to obtain a precursor, which is then sintered at 400-700°C for 6-18 hours to obtain a lithium iron phosphate composite material.

2. The preparation method according to claim 1, characterized in that, The coagulating substances include esters and / or alcohols.

3. A lithium iron phosphate composite material, characterized in that, The preparation method according to claim 1 or 2 is used.

4. A battery, characterized in that, The lithium iron phosphate composite material as described in claim 3.

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