Lithium iron phosphate composite material, and preparation method therefor and use thereof

Abstract

A lithium iron phosphate composite material, and a preparation method therefor and the use thereof. The preparation method comprises: mixing a porous inorganic nanofiber aerogel, a lithium source, an iron source, a phosphorus source and a carbon source to obtain a dispersion, carrying out spray drying to obtain a precursor, and then sintering same to obtain a lithium iron phosphate composite material. The porous inorganic nanofiber aerogel is used for in-situ compounding of lithium iron phosphate, and the lithium iron phosphate is synthesized; the presence of the porous nanofiber makes lithium iron phosphate particles be more uniformly distributed and do not agglomerate; and the dual effect of combining the porous nanofiber with the aerogel can effectively shorten the transport path of Li+, thereby effectively improving the rate capacity of an obtained material. In addition, a supporting effect can further be achieved, thereby avoiding damage caused by pressing and other machining processes, and volume change during charging and discharging of the obtained material can be alleviated, thereby avoiding the problem of cracking, etc., and improving the stability of the material.

Description

A lithium iron phosphate composite material and its preparation method and use Technical Field

[0001] The present disclosure belongs to the field of batteries and relates to a positive electrode material, and in particular to a lithium iron phosphate composite material and a preparation method and use thereof. Background Art

[0002] Secondary lithium-ion batteries (LIBs) have attracted much attention and have been commercially applied 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 current electrochemical energy storage field.

[0003] Compared to other cathode materials, lithium iron phosphate batteries (LiFePO4, LFP) offer advantages such as high safety, strong stability, low cost, abundant resources, and long cycle life. However, due to limitations in their crystal structure, shortcomings such as poor conductivity and slow ion migration significantly limit their electrochemical performance, particularly the tendency to suffer from poor rate performance, thus hindering their future commercialization.

[0004] Usually, low rate performance indicates slow lithium ion migration. To solve this problem, researchers shortened the Li + However, if the LFP crystallite size is too small, the polaron phenomenon of the structure will increase, causing a decrease in conductivity, which is detrimental to the rate performance of LFP. In this regard, another effective way is to develop porous lithium iron phosphate materials, using porous channels to provide channels for rapid transmission of electrons and ions, and the increased specific surface area and nanoscale pore wall thickness can promote charge transfer and increase the diffusion rate of lithium ions. For example, CN115986065A discloses a method for preparing lithium iron phosphate positive electrode materials by microwave-assisted hydrothermal method, which uses microwave-assisted hydrothermal method to prepare porous lithium iron phosphate precursor, and then sinter it into carbon-coated porous lithium iron phosphate.

[0005] However, when lithium iron phosphate is manufactured into porous lithium iron phosphate, it is easy to cause it to crack and break during the rolling process of the electrode sheet, causing the coating layer to fall off, and directly contact with the electrolyte, accelerating the loss of positive electrode active materials, reducing battery stability, capacity, and accelerating cycle performance degradation.

[0006] Therefore, new strategies are needed to improve the overall structural stability of the positive electrode material while maintaining the porous structure. This will not only accelerate the lithium ion migration rate and improve the rate performance, but also avoid cracking problems during the electrode pressing process.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] In view of the problems existing in the prior art, the purpose of the present disclosure is to provide a lithium iron phosphate composite material and its preparation method and use. The preparation method comprises mixing porous inorganic nanofiber aerogel, lithium source, iron source and phosphorus source to obtain a dispersion, spray drying to obtain a precursor, and then sintering to obtain a lithium iron phosphate composite material. The present disclosure uses porous inorganic nanofiber aerogel to form an in-situ coating on lithium iron phosphate while synthesizing it. The presence of porous nanofibers makes the lithium iron phosphate particles more evenly distributed and no longer agglomerates. The dual effect of porous nanofibers and aerogel can effectively shorten the Li + The transmission path can effectively improve the rate performance of the obtained material; at the same time, it can play a supporting role, avoid damage caused by processing such as pressing, and can alleviate the volume change of the obtained material during charging and discharging, avoid cracking and other problems, and improve the stability of the material.

[0010] To achieve this goal, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing a lithium iron phosphate composite material, the preparation method comprising:

[0012] Porous inorganic nanofiber aerogel, lithium source, iron source, phosphorus source and carbon source are mixed to obtain a dispersion, which is spray-dried to obtain a precursor, and then sintered to obtain a lithium iron phosphate composite material.

[0013] The present invention mixes inorganic nanofiber aerogel with the raw materials for synthesizing lithium iron phosphate positive electrode materials to obtain a uniformly mixed precursor, and then in the process of forming the lithium iron phosphate composite material, the porous inorganic nanofibers can be placed between and on the surface of the lithium iron phosphate particles and form a certain coating layer. From the overall perspective, the lithium iron phosphate particles are attached to the porous skeleton built by the porous inorganic nanofibers, and supported by these nanofibers with a certain aspect ratio, so that the lithium iron phosphate composite material still has support and buffering after the lithium iron phosphate is subjected to force during the pressing process, thereby avoiding the cracking problem during the pressing process. Moreover, the preparation method effectively increases the specific surface area of ​​the positive electrode material without affecting the structure of the positive electrode material, which is beneficial to enhance the contact with the electrolyte and provide more active sites for electrochemical reactions. The presence of porous nanofibers makes the positive electrode material particles more evenly distributed and no longer agglomerated. The dual effects of porous nanofibers superimposed on aerogel can effectively shorten the Li + transmission path.

[0014] The ultra-light and highly elastic properties of aerogels can mitigate the volume changes associated with lithium-ion battery charging and discharging. The nanofibers provide support within the lithium iron phosphate, preventing cracking during electrode pressing. By combining varying mass percentages of pore-forming agents and electrospinning parameters, the structure of porous titanium dioxide nanofibers can be manipulated, providing more options for subsequent composite cathode materials.

[0015] The following are optional technical solutions of the present disclosure, but are not intended to limit the technical solutions provided by the present disclosure. Through the following technical solutions, the technical objectives and beneficial effects of the present disclosure can be better achieved and realized.

[0016] As an optional technical solution of the present disclosure, a method for preparing the porous inorganic nanofiber aerogel includes:

[0017] The porous inorganic fibers are mixed with a gelling agent, and after drying, a porous inorganic nanofiber aerogel is obtained.

[0018] The mixing of the porous inorganic fibers and the gelling agent disclosed herein can be carried out in a solvent such as water and / or ethanol to achieve sufficient and stable dispersion of the porous inorganic fibers, and then dried.

[0019] In one embodiment, the mass ratio of the porous inorganic nanofibers to the gelling agent is 1:(3-7), for example, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5 or 1:7, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0020] In one embodiment, the porous inorganic nanofibers are mixed with the gelling agent in water, and the amount of water used is 6 to 12 times the total mass of the other raw materials, for example, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times or 12 times, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0021] In one embodiment, the porous inorganic nanofibers include any one or a combination of at least two of titanium dioxide, silicon dioxide or boron nitride, typical but non-limiting examples of the combination include a combination of titanium dioxide and silicon dioxide, a combination of titanium dioxide and boron nitride, or a combination of silicon dioxide and boron nitride, and can further be porous silicon dioxide nanofibers.

[0022] In one embodiment, the gelling agent comprises silica sol.

[0023] The present disclosure can use dioxide sol as a gelling agent. The sol has relatively good hydrophilicity and can be diluted to any concentration without reducing stability.

[0024] In one embodiment, the gelling agent further comprises a coagulant.

[0025] In one embodiment, the coagulant substance includes an ester substance and / or an alcohol substance; the ester substance includes at least one of dibutyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, methyl orthosilicate, ethyl orthosilicate, triethyl phosphate or tetraethyl orthosilicate, and ethyl orthosilicate can be further selected; the alcohol substance includes at least one of methanol, ethanol or polyethylene glycol.

[0026] In one embodiment, the porous inorganic nanofiber aerogel further contains carbon material.

[0027] The present disclosure further dopes carbon materials into the porous inorganic nanofiber aerogel to improve the conductivity of the positive electrode material.

[0028] Illustratively, the method for preparing the carbon material-doped porous titanium dioxide nanofiber aerogel includes: mixing porous titanium dioxide nanofibers, carbon material and a gelling agent, and drying to obtain the carbon material-doped porous titanium dioxide nanofiber aerogel.

[0029] In one embodiment, the carbon material comprises graphene.

[0030] The present invention introduces carbon materials, particularly graphene, into aerogels for doping, and utilizes the carbon materials and inorganic nanofibers to form a composite material with lithium iron phosphate. The carbon materials not only improve the conductivity of lithium iron phosphate cathode materials but also replace a portion of the carbon source used to synthesize lithium iron phosphate, thereby reducing manufacturing costs. In the resulting aerogel, the carbon materials and titanium dioxide nanofibers are uniformly dispersed and mixed. In addition to graphene, other carbon materials are also suitable, such as carbon nanotubes. Graphene is further selected because it has the best conductivity of all carbon materials, and its two-dimensional planar structure allows for a larger area of ​​mixed contact with titanium dioxide, resulting in the best optimization effect.

[0031] 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%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0032] In one embodiment, the drying method comprises any one of freeze drying, supercritical drying, vacuum drying or microwave drying, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of freeze drying and supercritical drying, a combination of freeze drying and vacuum drying, a combination of freeze drying and microwave drying, a combination of supercritical drying and vacuum drying, or a combination of microwave drying and vacuum drying.

[0033] As an optional technical solution of the present disclosure, a method for preparing the porous titanium dioxide nanofibers includes:

[0034] A titanium source, a pore-forming agent and a solvent are mixed to obtain a precursor solution, which is electrospun to obtain a spun material, which is then calcined to obtain porous titanium dioxide nanofibers.

[0035] In one embodiment, the pore former comprises camphene.

[0036] The present disclosure further allows camphene to be selected 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. The volatilization temperature is relatively low and it can be directly sublimated from the solid phase, thus achieving the pore-forming function at a relatively low temperature.

[0037] 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%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0038] 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, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0039] In one embodiment, the solvent comprises ethanol and / or acetic acid.

[0040] In one embodiment, the solvent is ethanol and acetic acid in a volume ratio of (2 to 5):1, for example, 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, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0041] 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, and the drying time is 10-24h, for example, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, and then calcined, but it is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0042] The present invention firstly dries the obtained spun fabric at 160-180° C., so that the pore-forming agent camphene can fully exert its pore-forming effect and volatilize and remove all the pore-forming agent as much as possible.

[0043] As an optional technical solution disclosed in the present invention, the applied voltage of the electrospinning is 6 to 10 kV, for example, 6 kV, 6.5 V, 7 kV, 7.5 kV, 8 kV, 8.5 kV, 9 kV, 9.5 kV or 10 kV, etc., the rotation speed is 30 to 80 rpm, for example, 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, for example, 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 values ​​not listed within the above numerical range are also applicable.

[0044] As an optional technical solution of the present disclosure, the calcination is carried out in an oxygen-containing atmosphere, and the calcination temperature is 300-650°C, for example, 300°C, 330°C, 360°C, 390°C, 420°C, 450°C, 480°C, 510°C, 540°C, 570°C, 600°C, 630°C or 650°C, and the calcination time is 2-5h, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0045] In one embodiment, the process of preparing the porous titanium dioxide nanofibers is performed in an environment with a humidity of 20% to 80%.

[0046] As an optional technical solution of the present disclosure, the lithium source includes any one of lithium carbonate, lithium hydroxide or lithium acetate, or a combination of at least two of them. Typical but non-limiting examples of the combination include a combination of lithium carbonate and lithium hydroxide, a combination of lithium carbonate and lithium acetate, or a combination of lithium hydroxide and lithium acetate.

[0047] In one embodiment, the phosphorus source comprises ammonium dihydrogen phosphate.

[0048] In one embodiment, the iron source comprises any one of ferric phosphate tetrahydrate, ferric oxide, ferric sulfate or ferroferric oxide, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of ferric phosphate tetrahydrate and ferric oxide, a combination of ferroferric oxide and ferric sulfate, a combination of ferroferric oxide and ferric phosphate tetrahydrate, a combination of ferroferric oxide and ferric oxide, a combination of ferric phosphate tetrahydrate and ferric sulfate, or a combination of ferric oxide and ferric sulfate.

[0049] In one embodiment, the carbon source comprises any one of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose or vitamins, or a combination of at least two thereof. Typical but non-limiting examples of the combination include a combination of glucose and sucrose, a combination of glucose and starch, a combination of glucose and phenolic resin, a combination of glucose and dextrin, a combination of glucose and citric acid, a combination of glucose and oxalic acid, a combination of glucose and cellulose, a combination of glucose and vitamins, a combination of sucrose and starch, a combination of phenolic resin and dextrin, a combination of citric acid and oxalic acid, or a combination of cellulose and vitamins.

[0050] In one embodiment, the gas temperature of the spray drying is between 160 and 300°C, for example, 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 values ​​not listed within the above numerical range are also applicable.

[0051] In one embodiment, the gas comprises air and / or an inert gas, such as nitrogen, and may further be hot air.

[0052] The advantage of using spray drying in the present disclosure is that the granulation function can be achieved while drying, ensuring the effect of instantaneous drying, and the parameters can be adjusted to control the size of the particles.

[0053] In one embodiment, the sintering temperature is 400-700°C, for example, 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 sintering time is 6-18h, for example, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h or 18h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0054] In one embodiment, the amounts of the iron source and the phosphorus source are controlled so that the molar ratio of the iron element to the phosphate radical is 1:1.

[0055] In one embodiment, the amount of porous inorganic nanofiber aerogel is controlled according to the molar ratio of porous inorganic nanofiber to iron element of (0.03-0.08):1, for example, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1 or 0.08:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0056] In one embodiment, the amount of lithium source is controlled according to the molar ratio of lithium to iron (1 to 1.03):1, for example, 1:1, 1.01:1, 1.015:1, 1.02:1, 1.025:1 or 1.03:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0057] In one embodiment, the amount of the carbon source is controlled according to the molar ratio of carbon to iron (0.05-0.12):1, for example, 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, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0058] As an optional technical solution of the present disclosure, the preparation method includes:

[0059] 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 to be 1 g:(2-5) mL; the pore-forming agent comprises camphene, the amount of the pore-forming agent accounts for 0.1% to 20% of the mass of the titanium source, and 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 set to 30-80 rpm, the distance between the collecting plate and the needle is set to 8-25 cm, and the obtained precursor solution is subjected to electrostatic spinning to obtain a spun material; the obtained spun material is first dried at 160-180° C. for 10-24 h, and then calcined at 300-650° C. for 2-5 h in an oxygen-containing atmosphere to obtain porous titanium dioxide nanofibers;

[0060] Mixing porous titanium dioxide nanofibers, a carbon material, and a gelling agent in water; the mass ratio of the porous inorganic nanofibers to the gelling agent is 1:(3-7); the carbon material includes graphene, 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 a coagulant, the amount of water is 6 to 12 times the total mass of the other raw materials, and after drying, a porous titanium dioxide nanofiber aerogel doped with the carbon material is obtained;

[0061] According to the ratio of the molar amount of Ti element in carbon-doped porous titanium dioxide nanofiber aerogel, the molar amount of Li element in lithium source, the molar amount of Fe element in iron source, the molar amount of phosphate in phosphorus source and the total molar amount of carbon atoms in all raw materials (0.03-0.08): (1-1.03): 1: 1: (0.05-0.12), all raw materials are mixed; the lithium source includes any one of lithium carbonate, lithium hydroxide or lithium acetate or a combination of at least two; the phosphorus source includes ammonium dihydrogen phosphate; the iron source includes any one of tetrahydrated iron phosphate, iron oxide, iron sulfate or ferroferric oxide or a combination of at least two; the carbon source includes any one of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose or vitamins or a combination of at least two, to obtain a dispersion, which is spray-dried using hot air at 160-300°C to obtain a precursor, which is then sintered at 400-700°C for 6-18h to obtain a lithium iron phosphate composite material.

[0062] In a second aspect, the present disclosure provides a lithium iron phosphate composite material obtained according to the preparation method described in the first aspect.

[0063] In a third aspect, the present disclosure provides a battery comprising the lithium iron phosphate composite material described in the second aspect.

[0064] Compared with the existing technical solutions, the present disclosure has at least the following beneficial effects:

[0065] The present invention uses porous inorganic nanofiber aerogel to compound lithium iron phosphate cathode material precursor, thereby obtaining lithium iron phosphate composite material. The preparation method effectively increases the specific surface area of ​​the cathode material without affecting the structure of the cathode material, which is conducive to enhancing the contact with the electrolyte and providing more electrochemical reaction active sites. The presence of nanofibers makes the cathode material particles more evenly distributed and no longer agglomerated. The dual effects of porous fibers and aerogel can effectively shorten the Li + transmission path;

[0066] The ultra-light and highly elastic properties of aerogels can mitigate the volume changes associated with charging and discharging in lithium-ion batteries. Furthermore, the nanofibers provide support within the lithium iron phosphate, preventing cracking during electrode pressing. By combining varying mass percentages of pore-forming agents and electrospinning parameters, the structure of porous inorganic nanofibers can be manipulated, providing more options for subsequent composite cathode materials.

[0067] The present invention introduces carbon materials, especially graphene, into aerogel for doping, and uses carbon materials and inorganic nanofibers to form a composite coating on lithium iron phosphate. The carbon materials can not only improve the conductivity of lithium iron phosphate positive electrode materials in the preparation of lithium iron phosphate positive electrode materials, but also replace part of the carbon source used to synthesize lithium iron phosphate, thereby reducing manufacturing costs.

[0068] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation to the technical solution of this article.

[0070] FIG1 is a SEM image of the lithium iron phosphate composite material obtained in Example 4. DETAILED DESCRIPTION

[0071] The technical solution of the present disclosure is further illustrated below through specific implementation methods.

[0072] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present disclosure and should not be considered as specific limitations of the present disclosure.

[0073] Example 1

[0074] This embodiment provides a method for preparing a lithium iron phosphate composite material, the preparation method comprising:

[0075] (1) Tetrabutyl titanate, glacial acetic acid and anhydrous ethanol are mixed in a ratio of 1:1:3, and amphene is added in a percentage by mass ratio of 9% with a tetrabutyl titanate content of 100%, and the mixture is mixed together to form a transparent light yellow liquid, and stirred overnight;

[0076] (2) Using the electrospinning method, the solution of (1) was subjected to an applied voltage of 8 kV and a rotation speed of 40 rpm to prepare a titanium dioxide nanofiber spinning material, which was first dried at 160°C for 15 h to remove the polymer, and then calcined and annealed at 400°C for 3 h to form porous titanium dioxide nanofibers;

[0077] (3) adding the prepared porous titanium dioxide nanofibers and graphene with a mass fraction ratio of 1% to deionized water for ultrasonic dispersion, and then adding a gelling agent for mixing, wherein the gelling agent includes silica sol and dibutyl carbonate, and the mass ratio of porous titanium dioxide nanofibers: deionized water: gelling agent is controlled to be 1:90:5, and freeze-drying is performed to obtain graphene-doped porous titanium dioxide nanofiber aerogel;

[0078] (4) preparing a dispersion of the graphene-doped porous titanium dioxide nanofiber aerogel and the raw materials of the positive electrode material, lithium carbonate, iron phosphate, and carbon source glucose, and uniformly dispersing the mixture in water according to a molar ratio of titanium, lithium, iron, and carbon of 0.05:1.01:1:0.08, setting the spray drying temperature to 210° C. and spray drying to obtain a precursor;

[0079] (5) The mixed material of step (4) was sintered at a high temperature of 650° C. for 8 h to obtain a graphene-doped porous titanium dioxide nanofiber aerogel composite-coated lithium iron phosphate material.

[0080] Example 2

[0081] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, in step (1), the amount of camphene is adjusted from 6% to 9%. Except for the above, other conditions are exactly the same as those in Example 1.

[0082] Example 3

[0083] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, 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, other conditions are exactly the same as those in Example 1.

[0084] Example 4

[0085] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, the amount of camphene is adjusted from 6% to 12% in step (1), the amount of graphene is adjusted from 1% to 3% in step (3), and the sintering time is adjusted from 8 h to 10 h in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0086] Example 5

[0087] This embodiment provides a preparation method of a lithium iron phosphate composite material. In the preparation method, the amount of camphene is adjusted from 6% to 12% in step (1), the calcination temperature is adjusted from 400°C to 500°C in step (2), the amount of graphene is adjusted from 1% to 3% in step (3), and the sintering time is adjusted from 8h to 10h in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0088] Example 6

[0089] This embodiment provides a method for preparing a lithium iron phosphate composite material. The preparation method does not use graphene in step (3). Except for the above, other conditions are exactly the same as those in Example 4.

[0090] Example 7

[0091] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, carbon nanotubes are used instead of graphene in step (3). Except for the above, other conditions are exactly the same as those in Example 4.

[0092] Example 8

[0093] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, in step (1), the amount of camphene is adjusted from 12% to 1%. Except for the above, other conditions are exactly the same as those in Example 4.

[0094] Example 9

[0095] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, in step (1), the amount of camphene is adjusted from 12% to 3%. Except for the above, other conditions are exactly the same as those in Example 4.

[0096] Example 10

[0097] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, in step (1), the amount of camphene is adjusted from 12% to 20%. Except for the above, other conditions are exactly the same as those in Example 4.

[0098] Example 11

[0099] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, in step (1), the amount of camphene is adjusted from 12% to 23%. Except for the above, other conditions are exactly the same as those in Example 4.

[0100] Example 12

[0101] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, the amount of graphene is adjusted from 3% to 0.5% in step (3), and the sintering time is adjusted from 8 hours to 10 hours in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0102] Example 13

[0103] This embodiment provides a method for preparing a lithium iron phosphate composite material. In the preparation method, the amount of graphene is adjusted from 3% to 5.5% in step (3), and the sintering time is adjusted from 8 hours to 10 hours in step (5). Except for the above, other conditions are exactly the same as those in Example 1.

[0104] Comparative Example 1

[0105] This comparative example provides a preparation method of a lithium iron phosphate composite material, which does not use porous titanium dioxide nanofiber aerogel. The preparation method is:

[0106] The lithium source, phosphorus source, iron source and carbon source in step (4) of Example 4 were prepared into a dispersion, spray-dried, and sintered at 650° C. for 10 h to obtain a lithium iron phosphate composite material.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing a lithium iron phosphate composite material. In the preparation method, camphene is not used in step (1). Except for the above, other conditions are exactly the same as those in Example 4.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing a lithium iron phosphate composite material. In the preparation method, no gelling agent is used in step (3). Only porous titanium dioxide nanofibers and graphene are mixed and freeze-dried, and the obtained sample is applied to step (4). Except for the above, other conditions are exactly the same as those in Example 4.

[0111] Control group 1

[0112] A method for preparing a lithium iron phosphate positive electrode material disclosed in CN115986065A is used, comprising:

[0113] (1) lithium acetate dihydrate, ferrous sulfate heptahydrate, and phosphoric acid were mixed in a molar ratio of 1:1:1 and placed in lithium acetate dihydrate and pure water (1:25) and mixed evenly;

[0114] (2) 0.004 times the mass of the precursor solution of polyethylene glycol and 0.02 times the mass of the precursor solution of glucose were added to the precursor solution, and the mixture was placed in a microwave reactor with a microwave power of 60 W, a microwave frequency of 1000 MHz, and a temperature controlled at 180°C for 40 min;

[0115] (3) cooling to room temperature, centrifuging and collecting the solid, washing it with pure water for 3 to 5 times, and drying it at 90° C. for 6 h to obtain a porous lithium iron phosphate precursor;

[0116] (4) The porous lithium iron phosphate precursor was sintered at 600° C. for 7 h in a nitrogen atmosphere to prepare carbon-coated porous lithium iron phosphate.

[0117] The materials or composite materials obtained in the above examples, comparative examples and control groups were used as positive electrode materials to prepare button batteries for lithium-ion battery electrochemical performance testing. The specific steps are as follows:

[0118] The positive electrode material, conductive agent acetylene black and adhesive polyvinylidene fluoride were uniformly mixed in N-methylpyrrolidone in a ratio of (8:1:1), then coated on 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 punched into a 1cm diameter circular positive electrode sheet at 30MPa. The negative electrode was a metal lithium sheet, the electrolyte was 1M LiPF6-EC:DMC (volume ratio 1:1), and a polypropylene porous membrane was used as a separator.

[0119] Table 1 shows the rate performance test of the battery sample, with a charge and discharge cut-off voltage of 2.7 to 4.3V and a current density of 0.2C, 1C, 3C, 5C, and 8C for 5 cycles. Table 2 shows the cycling performance test of the sample battery, with a charge and discharge cut-off voltage of 2.7 to 4.3V and a current density of 1C = 160mA / g.

[0120] Table 1

[0121] Table 2

[0122] It can be seen from Table 1 and Table 2 that:

[0123] Table 1 shows the discharge capacity of different embodiments at different rates (0.2C, 1C, 3C, 5C, 8C). It can be seen from the table that the discharge capacity of Example 4 at different rates is 154.2mAh / g, 146.5mAh / g, 139.8mAh / g, 130.2mAh / g and 119.9mAh / g, respectively. It is the one with the best discharge capacity performance among all the embodiments. This is due to the introduction of porous titanium dioxide nanofiber aerogel for compounding in the preparation of the positive electrode material to form a nanoporous structure of lithium iron phosphate, which shortens the lithium ion transmission path and makes the material have excellent reversibility for lithium ion extraction and embedding during the charge and discharge process. Even at high rates, lithium ion embedding can be achieved. At the same time, the cycle performance is also excellent compared with other embodiments and comparative examples. After 100 cycles of 1C discharge, the cycle retention rate is 96.1%. FIG1 is an SEM image of the lithium-ion battery composite positive electrode material prepared in Example 4. After magnification 5000 times, uniform lithium iron phosphate primary particles and agglomerated secondary particles can be seen. The structure and morphology are well dispersed and uniform, with only a small amount of agglomeration effect.

[0124] By embodiment 1-4 and embodiment 8-11 contrast, the consumption of amphene has been adjusted, find that when amphene consumption reduces, under 0.2C and other multiplying rates, battery discharge capacity also presents the phenomenon of minimization, this may be due to too little amphene and there is no way to make enough porous, does not shorten lithium ion diffusion channel and realizes efficient lithium ion transmission.When amphene consumption is too high or exceeds limit value, embodiment 10 and embodiment 11 circulate 100 back cycle retention rates are 93.8% and 93.4%, which is on the low side, this may be because the existence of too much pore former destroys the structure of nanofiber, no longer has supporting effect, cracking occurs easily when pole piece is pressed, and when positive electrode lithium ion constantly deviates from embedding in repeated charge and discharge process, material volume expansion shrinks, and material cracking possibility increases, causes cycle performance to decline.

[0125] By comparing Examples 1, 3-4 and 12-13, the amount of graphene was adjusted. It was found that when the amount of graphene was too little, the battery discharge capacity was low. This may be because too little graphene leads to too low conductivity of the positive electrode material, affecting its electrical properties. As the amount of graphene increases, the discharge capacity also increases. However, the presence of too much graphene may cause itself to agglomerate together, hindering the transmission of lithium ions.

[0126] Compared with Comparative Examples 1-3, Example 4, which does not use titanium dioxide aerogel to prepare lithium iron phosphate in a normal manner, has lower rate performance and cycle performance than Example 4, demonstrating the advantages of the present disclosure. Comparative Example 2, which does not introduce camphene for pore formation and simply prepares nanofiber aerogel composite lithium iron phosphate, has slightly lower performance than Example 4, but better performance than Comparative Example 1, demonstrating that the introduction of aerogel can improve the electrical properties of lithium iron phosphate.

Claims

1. A method for preparing a lithium iron phosphate composite material, the preparation method comprising: Porous inorganic nanofiber aerogel, lithium source, iron source, phosphorus source and carbon source are mixed to obtain a dispersion, which is spray-dried to obtain a precursor, and then sintered to obtain a lithium iron phosphate composite material.

2. The preparation method according to claim 1, wherein The method for preparing the porous inorganic nanofiber aerogel comprises: The porous inorganic nanofibers are mixed with a gelling agent, and after drying, a porous inorganic nanofiber aerogel is obtained.

3. The preparation method according to claim 2, wherein The gelling agent includes silica sol.

4. The preparation method according to claim 2 or 3, wherein The gelling agent also includes a coagulant.

5. The preparation method according to claim 4, wherein The coagulant-accelerating substance includes ester substances and / or alcohol substances.

6. The preparation method according to claim 1 or 2, wherein: The porous inorganic nanofiber aerogel also contains carbon material.

7. The preparation method according to claim 6, wherein: The carbon material includes graphene.

8. The preparation method according to claim 6 or 7, wherein: The carbon material accounts for 0.01% to 5% of the total mass of the porous inorganic nanofiber aerogel.

9. The preparation method according to any one of claims 1 to 8, wherein: The porous inorganic nanofibers include porous titanium dioxide nanofibers.

10. The preparation method according to claim 9, wherein: The method for preparing the porous titanium dioxide nanofibers comprises: A titanium source, a pore-forming agent and a solvent are mixed to obtain a precursor solution, electrostatic spinning is performed to obtain a spun product, and then calcination is performed to obtain porous titanium dioxide nanofibers.

11. The preparation method according to claim 10, wherein: The pore former includes camphene.

12. The preparation method according to claim 10 or 11, wherein: The amount of the pore-forming agent used accounts for 0.1% to 20% of the mass of the titanium source.

13. The preparation method according to claim 11 or 12, wherein: The obtained spun material is first dried at 160-180°C for 10-24 hours and then calcined.

14. The preparation method according to claim 13, wherein: The calcination is performed in an oxygen-containing atmosphere, and the calcination temperature is 300 to 650°C.

15. The preparation method according to any one of claims 1 to 14, wherein: The preparation method comprises: 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 to be 1 g: (2-5) mL; the pore-forming agent comprises 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 set to 30-80 rpm, the distance between the collecting plate and the needle is set to 8-25 cm, and the obtained precursor solution is subjected to electrostatic spinning to obtain a spun material; the obtained spun material is first dried at 160-180° C. for 10-24 h, and then calcined at 300-650° C. for 2-5 h in an oxygen-containing atmosphere to obtain a porous titanium dioxide nanofiber; Mixing porous titanium dioxide nanofibers, carbon materials and gelling agents 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 a coagulant, and the amount of water is 6 to 12 times the total mass of other raw materials, and after drying, a porous titanium dioxide nanofiber aerogel doped with a carbon material is obtained; Mix all the raw materials according to the ratio of the molar amount of Ti element in the carbon-doped porous titanium dioxide nanofiber aerogel, the molar amount of Li element in the lithium source, the molar amount of Fe element in the iron source, the molar amount of phosphate in the phosphorus source and the total molar amount of carbon atoms in all the raw materials of (0.03-0.08):(1-1.03):1:1:(0.05-0.12); The lithium source includes any one of lithium carbonate, lithium hydroxide or lithium acetate, or a combination of at least two of them; the phosphorus source includes ammonium dihydrogen phosphate; the iron source includes any one of tetrahydrated iron phosphate, iron oxide, iron sulfate or ferroferric oxide, or a combination of at least two of them; the carbon source includes any one of glucose, sucrose, starch, phenolic resin, dextrin, citric acid, oxalic acid, cellulose or vitamins, or a combination of at least two of them. The above substances are dispersed in a solvent to obtain a dispersion, which is then spray-dried using hot air at 160 to 300° C. to obtain a precursor, which is then sintered at 400 to 700° C. for 6 to 18 hours to obtain a lithium iron phosphate composite material.

16. A lithium iron phosphate composite material obtained according to the preparation method according to any one of claims 1 to 15.

17. A battery comprising the lithium iron phosphate composite material according to claim 16.

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