Modified iron phosphate, modified lithium iron phosphate, and preparation method and application thereof

Abstract

The application belongs to the technical field of lithium battery recycling, and particularly relates to modified iron phosphate, modified lithium iron phosphate, and a preparation method and application thereof. A coating layer is formed on an MXene substrate, and iron phosphate is formed on the coating layer. The modified iron phosphate provided by the application not only retains the high conductivity of MXene, but also introduces a small amount of H-TiO2 to improve the lithium intercalation capacity and low-temperature stability of the material, which is conducive to reducing the impedance of charge transfer of the electrode material and improving the lithium deintercalation efficiency. The lithium iron phosphate positive electrode material prepared by using the modified iron phosphate provided by the application has more excellent rate performance and low-temperature stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery material technology, specifically relating to a modified iron phosphate, a modified lithium iron phosphate, their preparation methods and applications. Background Technology

[0002] Lithium-ion batteries, due to their high specific energy, long lifespan, and pollution-free characteristics, have experienced rapid popularization and development since their invention. Their applications have gradually shifted from traditional digital products to power supply fields, maintaining a strong growth trend. The performance of the cathode material directly affects the performance of lithium-ion batteries, and its cost directly determines the overall battery cost. Therefore, the research and development of lithium battery cathode materials is of great significance for improving lithium battery performance.

[0003] Compared to the widely used lithium cobalt oxide cathode material, lithium iron phosphate (LiFePO4) cathode material has the advantages of low cost and safety, making it one of the most promising cathode materials for lithium-ion batteries. LiFePO4 crystal has an orthorhombic olivine structure, and its electrochemical reaction product, iron phosphate (FePO4), belongs to the same pnma space group, resulting in a small difference in unit cell volume. Therefore, LiFePO4 exhibits relatively stable electrochemical cycling performance. In LiFePO4, oxygen atoms are hexagonally close-packed, phosphorus atoms are distributed in tetrahedral interstices, and iron and lithium atoms occupy octahedral interstices. Electron conduction mainly occurs through the FeO6 octahedral transition metal layer with shared vertices on the ac-plane in its crystal structure. However, the FeO6 octahedra are separated by the PO4 tetrahedra and do not form a continuous network, leading to the poor bulk electronic conductivity of LiFePO4, with an electronic conductivity of only 10⁻⁶. -9 -10 -10 The S / m value is approximately [value missing]. Furthermore, the one-dimensional lithium-ion diffusion characteristics of LiFePO4 result in a low lithium-ion diffusion coefficient. The low electronic conductivity and ion migration ability of LiFePO4 limit its large-scale application in high-power and low-temperature environments.

[0004] Therefore, there is an urgent need to improve the preparation process of lithium iron phosphate in order to enhance the electronic conductivity and ion migration ability of the material, thereby improving the rate performance and low-temperature stability of the material.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The present invention aims to provide a modified iron phosphate, a modified lithium iron phosphate, a method for preparing the same, and their applications, with the goal of improving the rate performance and / or low-temperature stability of lithium iron phosphate cathode materials.

[0007] To achieve the above-mentioned objectives of this invention, the following technical solutions can be adopted:

[0008] In a first aspect, the present invention provides a modified iron phosphate, comprising an MXene matrix, a carbon layer coated on the surface of the MXene matrix, and iron phosphate formed on the surface of the carbon layer.

[0009] In some embodiments of the present invention, the titanium portion in the MXene matrix is ​​oxidized to titanium oxide;

[0010] Preferably, the thickness of the MXene substrate is 5nm-10nm, and the lateral dimension is 100nm-300nm.

[0011] Secondly, the present invention also provides a method for preparing modified iron phosphate, comprising: reacting an MXene material having an organic coating layer with an iron salt and a phosphate to form iron phosphate on the surface of the organic coating layer, and calcining the obtained product.

[0012] In some embodiments of the present invention, MXene material with an organic coating, iron salt solution, and phosphate solution are mixed and reacted, and the resulting product is then calcined in an oxygen-containing atmosphere.

[0013] Preferably, during the reaction of the MXene material with an organic coating, the iron salt solution, and the phosphate solution, the reaction pH is controlled at 1.8-2.2, the reaction temperature at 60℃-80℃, and the reaction time at 4h-8h.

[0014] Preferably, the mass ratio of iron salt to MXene material with organic coating is controlled to be (2-10):1; by adjusting the amount of iron salt and phosphate, the molar ratio of phosphate to iron ions in iron salt is 1:(0.95-1.05).

[0015] Preferably, the iron salt is selected from at least one of ferric chloride and ferric nitrate; the phosphate is selected from at least one of ammonium hydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate; the concentration of both the iron salt solution and the phosphate solution is 0.5 mol / L-2.0 mol / L.

[0016] Preferably, after the reaction of the MXene material with the organic coating, the iron salt solution, and the phosphate solution is completed, solid-liquid separation is performed, the obtained solid material is washed and dried, and then calcined in an oxygen-containing atmosphere; more preferably, during the calcination process, the oxygen volume fraction in the oxygen-containing atmosphere is controlled to be 5%-15%, and the oxygen volume fraction in the oxygen-containing atmosphere is controlled to be 8%-12%; even more preferably, during the calcination process, the calcination temperature is controlled to be 500℃-800℃, and the calcination time is 5h-8h.

[0017] In some embodiments of the present invention, the preparation process of the MXene material with an organic coating layer includes: mixing and reacting a surfactant, an organic coating, an MXene material and water, followed by solid-liquid separation, and drying the resulting solid material.

[0018] Preferably, in the process of preparing MXene material with organic coating, the reaction temperature is controlled at 20℃-35℃ and the reaction time is controlled at 30min-60min;

[0019] Preferably, the surfactant and water are first mixed to adjust the pH to 7.5-8.5, and then the surfactant and MXene material are mixed and reacted.

[0020] Preferably, the organic coating is selected from dopamine hydrochloride;

[0021] Preferably, the mass ratio of the organic coating to the MXene material is (3-5):1;

[0022] Preferably, in the mixed system formed by surfactant, organic coating, MXene material and water, the concentration of organic coating is 0.5 g / L-1.5 g / L;

[0023] Preferably, the surfactant is selected from at least one of dodecyl dimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, and alkyl dimethyl hydroxypropyl phosphate betaine;

[0024] Preferably, the mass ratio of surfactant to MXene material is (20-30):1.

[0025] Thirdly, the present invention also provides a method for preparing modified lithium iron phosphate, comprising: mixing and calcining modified iron phosphate with a lithium source; wherein the modified iron phosphate is the modified iron phosphate in any of the above embodiments or the modified iron phosphate prepared by the preparation method in any of the above embodiments.

[0026] Preferably, the calcination is carried out in a hydrogen-containing atmosphere, with the calcination temperature controlled at 500℃-800℃ and the calcination time at 5h-15h.

[0027] Preferably, modified iron phosphate, lithium source and water are mixed to obtain a suspension, the suspension is ball-milled and dried to obtain precursor powder, and the precursor powder is ground and then calcined in a hydrogen-containing atmosphere.

[0028] Preferably, by adjusting the amount of modified iron phosphate and lithium source, the molar ratio of Li to Fe is (1-1.05):1;

[0029] Preferably, the suspension is ball-milled for 3-8 hours and then spray-dried to obtain precursor powder;

[0030] Preferably, the total mass fraction of lithium and iron in the suspension is 28%-33%;

[0031] Preferably, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

[0032] Fourthly, the present invention also provides a modified lithium iron phosphate, comprising an MXene matrix, a carbon layer coated on the surface of the MXene matrix, and lithium iron phosphate formed on the surface of the carbon layer.

[0033] In some embodiments of the present invention, the titanium portion in the MXene matrix is ​​oxidized to titanium oxide.

[0034] In some embodiments of the present invention, the thickness of the MXene substrate is 5nm-10nm and the lateral dimension is 100nm-300nm.

[0035] Fifthly, the present invention also provides a positive electrode sheet, comprising modified lithium iron phosphate prepared by the preparation method in any of the above embodiments or modified lithium iron phosphate in any of the above embodiments.

[0036] In a sixth aspect, the present invention also provides a lithium battery, including the positive electrode sheet in any of the above embodiments.

[0037] In a seventh aspect, the present invention also provides an electrical device comprising the lithium battery described in any of the above embodiments.

[0038] By forming a coating on the MXene matrix, iron phosphate is formed on the coating layer. During the formation of iron phosphate, MXene is not affected by Fe. 3+ The entire coating is oxidized to titanium dioxide. Carbonization of the coating layer exposes the MXene matrix, causing some MXene to transform into TiO2. The resulting porous structure increases the porosity of the electrode material, which is beneficial for improving Li... + The modified iron phosphate provided by this invention retains the high conductivity of MXene while introducing a small amount of TiO2 to improve the lithium insertion capacity and low-temperature stability of the material. This is beneficial for reducing the charge transfer impedance of the electrode material and improving the lithium insertion / extraction efficiency. The lithium iron phosphate cathode material prepared using the modified iron phosphate provided by this invention exhibits superior rate performance and low-temperature stability. Attached Figure Description

[0039] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A process flow diagram of the modified lithium iron phosphate preparation method provided in the embodiments of the present invention;

[0041] Figure 2 The graph shows the results of the low-temperature performance test.

[0042] Figure 3 The graph shows the results of the AC impedance spectroscopy test.

[0043] Figure 4 XPS plot for Mxene;

[0044] Figure 5 This is an XPS plot of Ti in the cathode material of Example 1;

[0045] Figure 6 The image shows the XPS plot of Ti in the cathode material of Comparative Example 1. Detailed Implementation

[0046] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0047] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0048] This invention provides a method for preparing modified lithium iron phosphate. Please refer to [link / reference]. Figure 1 This includes the following steps:

[0049] S1. Preparation of MXene materials with organic coatings

[0050] MXene material, organic coatings, surfactants, and water are mixed and reacted, followed by solid-liquid separation. The resulting solid material is then dried. The surfactants are used to better disperse the MXene material, resulting in a more uniform coating of the organic coatings on the MXene material surface.

[0051] In some embodiments, the chemical formula of MXene material is Ti3C2T. xLiFePO4 possesses advantages such as high conductivity, large specific surface area, and good mechanical properties. Introducing MXene can improve the conductivity, lithium-ion diffusion coefficient, and low-temperature stability of LiFePO4. However, during the preparation of MXene / LiFePO4 composites, MXene is easily oxidized to TiO2 by ferric iron, leading to the loss of high conductivity. In this invention, an organic coating is used to protect MXene during the formation of ferric phosphate, preventing its oxidation by ferric iron.

[0052] In some embodiments, the organic coating is dopamine hydrochloride, which is readily available and easily and uniformly coated onto the surface of the MXene material. When the organic coating is dopamine hydrochloride, the MXene material with the organic coating is designated as MXene@PDA.

[0053] In some embodiments, the surfactant is selected from at least one of dodecyl dimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, and alkyl dimethyl hydroxypropyl phosphate betaine; the surfactant can be any one or more of the above. All of the above surfactants can effectively disperse MXene materials, forming a carbon layer together with the organic coating during subsequent calcination.

[0054] In some embodiments, the mass ratio of organic coating material to MXene material is (3-5):1, and the mass ratio of surfactant to MXene material is (20-30):1. By further controlling the mass ratio of organic coating material, surfactant and MXene material, the surface of MXene material is fully coated, and the thickness of carbon layer after calcination is controlled, which is beneficial to further improve the rate performance and low temperature stability of the prepared lithium iron phosphate cathode material.

[0055] Specifically, the mass ratio of the organic coating to the MXene material can be 3:1, 4:1, 5:1, etc., and the mass ratio of the surfactant to the MXene material can be 20:1, 23:1, 25:1, 28:1, 30:1, etc.

[0056] In some embodiments, in the mixed system formed by surfactant, organic coating, MXene material, and water, the concentration of the organic coating is 0.5 g / L-1.5 g / L. By further controlling the concentration of the organic coating in the mixed system, the organic coating can be more fully coated on the surface of the MXene material, and the coating amount can be controlled appropriately. This results in a more ideal carbon content after calcination. The porous structure of the carbon layer improves the porosity of the electrode material, which is beneficial for improving the Li... + The insertion / extraction efficiency.

[0057] Specifically, in the mixed system formed by surfactant, organic coating, MXene material and water, the concentration of organic coating can be 0.5 g / L-1.5 g / L, such as 0.5 g / L, 1.0 g / L, 1.5 g / L, etc.

[0058] In some embodiments, during the preparation of MXene materials with an organic coating, a surfactant and water can be mixed first to adjust the pH to 7.5-8.5, and then the surfactant, water, organic coating, and MXene material can be mixed and reacted. The reaction temperature is controlled at 20°C-35°C, and the reaction time is 30-60 minutes. By controlling the mixing steps and optimizing the reaction conditions, the organic coating can be uniformly coated on the surface of the MXene material.

[0059] Specifically, before adding the organic coating and MXene material, the pH of the solution can be adjusted to 7.5, 7.8, 8.0, 8.2, 8.5, etc.; the reaction temperature can be controlled at 20℃, 25℃, 30℃, 35℃, etc.; and the reaction time can be 30min, 40min, 45min, 50min, 60min, etc.

[0060] S2, Iron phosphate is formed on the surface of the organic coating layer.

[0061] MXene materials with an organic coating are reacted with iron salts and phosphates to form iron phosphate on the surface of the organic coating. During the iron deposition process, MXene is less susceptible to Fe deposition because it is encapsulated by the organic coating. 3+ All of it is oxidized to titanium dioxide; at the same time, organic coatings such as polydopamine are used to react with Fe. 3+ The coordination effect of Fe makes Fe 3+ Iron phosphate with a certain thickness is enriched on the MXene surface and generated in situ.

[0062] In some embodiments, MXene material with an organic coating, an iron salt solution, and a phosphate solution are mixed and reacted. During the reaction, the pH value is controlled at 1.8-2.2, the reaction temperature at 60°C-80°C, the reaction time at 4-8 hours, and the stirring speed at 300-800 rpm. By further controlling the reaction pH value, reaction temperature, and time, a uniform deposition of iron phosphate can be formed on the surface of the organic coating.

[0063] Specifically, during the iron deposition process, the reaction pH can be controlled at 1.8, 1.9, 2.0, 2.1, 2.2, etc., the reaction temperature can be 60℃, 65℃, 70℃, 75℃, 80℃, etc., the reaction time can be 4h, 5h, 6h, 7h, 8h, etc., and the stirring speed can be 300rpm, 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, etc.

[0064] In some embodiments, the iron salt is selected from at least one of ferric chloride and ferric nitrate, and the iron salt can be any one or more of the above; the phosphate is selected from at least one of ammonium hydrogen phosphate, ammonium phosphate and ammonium dihydrogen phosphate, and the phosphate can be any one or more of the above.

[0065] In some embodiments, the mass ratio of iron salt to MXene material with organic coating is controlled at (2-10):1; by adjusting the amount of iron salt and phosphate, the molar ratio of phosphate to iron ions in the iron salt is 1:(0.95-1.05). It is preferable to control the mass ratio of iron salt, phosphate, and MXene material with organic coating within the above range to control the ratio of iron phosphate to MXene material. Excessive or insufficient MXene material dosage is detrimental to improving the rate performance and low-temperature stability of the material.

[0066] Specifically, the mass ratio of iron salt to MXene material with organic coating can be 2:1, 4:1, 6:1, 8:1, 10:1, etc. The molar ratio of phosphate to iron ions in iron salt can be 1:0.95, 1:0.98, 1:1.00, 1:1.02, 1:1.05, etc.

[0067] Furthermore, the concentrations of the iron salt solution and the phosphate solution are both 0.5 mol / L to 2.0 mol / L, such as 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, etc.

[0068] In some embodiments, after the reaction of the MXene material with the organic coating, the iron salt solution, and the phosphate solution is complete, solid-liquid separation is performed. The resulting solid material is washed and dried, and the product can be designated as MXene@PDA@FP·2H2O or MXene@PDA@FePO4·2H2O. The solid-liquid separation method is not limited and can be filtration or other solid-liquid separation methods; washing removes unreacted ions from the surface, and drying removes the washing water.

[0069] S3, calcination

[0070] The product obtained in step S2 is calcined to remove the water of crystallization of ferric phosphate and simultaneously carbonize the organic coating layer. The resulting product can be represented as MXene@C@FP. Calcination is preferably performed in an oxygen-containing atmosphere. During the carbonization of the organic coating layer (such as polydopamine), MXene is partially exposed, and the oxygen concentration is controlled to allow for the controllable partial conversion of MXene to TiO2. Furthermore, the porous structure formed after carbonization increases the porosity of the electrode material, which is beneficial for improving Li... + The insertion / extraction efficiency.

[0071] It should be noted that titanium dioxide has advantages such as high lithium intercalation capacity, low toxicity, low energy consumption, high specific capacity, and good cycle stability, without any side reactions occurring. Therefore, introducing some TiO2 into the cathode material is beneficial to improving electrochemical performance.

[0072] In some embodiments, during calcination, the oxygen volume fraction in the oxygen-containing atmosphere is controlled to be 5%-15%, preferably 8%-12%. (The last sentence appears to be incomplete and unrelated to the preceding text. It likely refers to Fe during iron deposition.) 3+ Oxidation of MXene leads to an uncontrollable ratio of MXene to TiO2 in the product. Therefore, during the subsequent high-temperature carbonization of polydopamine, MXene is partially exposed while the oxygen concentration is controlled to achieve controlled oxidation. The resulting material retains the high conductivity of MXene while introducing a small amount of TiO2 to improve the material's lithium intercalation capacity and low-temperature stability. If the volume fraction of oxygen exceeds the above range, it will affect the rate performance and low-temperature stability of the final product.

[0073] Specifically, during the calcination process, the volume fraction of oxygen in the oxygen-containing atmosphere can be controlled to be 5%, 8%, 10%, 12%, 15%, etc.

[0074] In some embodiments, during the calcination process, the calcination temperature is controlled at 500℃-800℃, and the calcination time is 5h-8h, so as to ensure that the organic coating layer is fully carbonized. Specifically, the calcination temperature can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc.

[0075] S4, roasted with lithium source

[0076] The modified iron phosphate obtained in step S3 is calcined with a lithium source to prepare a modified lithium iron phosphate cathode material. By optimizing the iron phosphate preparation process, the prepared modified lithium iron phosphate cathode material can have excellent rate performance and low-temperature stability.

[0077] In some embodiments, modified iron phosphate, a lithium source, and water are mixed to obtain a suspension. The suspension is ball-milled and dried to obtain a precursor powder. The precursor powder is then ground and calcined in a hydrogen-containing atmosphere. Ball milling and drying can make the prepared precursor powder more uniform. Calcination in a hydrogen-containing atmosphere yields MXene-HTiO@C@LFP. In the product, HTiO represents titanium oxide calcined in a hydrogen atmosphere. Treating TiO2 with hydrogen to obtain H-TiO2 can reduce the charge transfer impedance of the electrode material and improve the lithium insertion / extraction efficiency.

[0078] In some embodiments, the lithium source is selected from at least one of lithium carbonate and lithium hydroxide, and can be any one or more of the above. By adjusting the amount of modified iron phosphate and lithium source, the molar ratio of Li to Fe is made (1-1.05):1, with lithium slightly in excess, to ensure sufficient reaction of the modified iron phosphate. Specifically, the molar ratio of Li to Fe can be 1.00:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, etc.

[0079] Furthermore, by adjusting the amounts of modified iron phosphate and lithium source, the total mass fraction of lithium and iron in the suspension is made to be 28%-33%, so as to obtain a more uniform precursor by ball milling. Specifically, the total mass fraction of lithium and iron in the suspension can be 28%, 29%, 30%, 31%, 32%, 33%, etc.

[0080] In some embodiments, the suspension is ball-milled for 3-8 hours and then spray-dried to obtain precursor powder. The 3-8 hour ball milling process ensures uniform mixing of the raw materials, and the spray drying removes moisture to obtain a uniform precursor powder. Specifically, the ball milling time can be 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.

[0081] In some embodiments, calcination can be carried out in a hydrogen atmosphere, with the calcination temperature controlled at 500℃-800℃ and the calcination time at 5h-15h. After calcination, lithium iron phosphate with higher density is obtained. At the same time, TiO2 is treated with hydrogen to obtain H-TiO2, which can reduce the charge transfer impedance of the electrode material and improve the lithium insertion / extraction efficiency.

[0082] This invention provides a modified iron phosphate, comprising an MXene matrix, a carbon layer coated on the surface of the MXene matrix, and iron phosphate formed on the surface of the carbon layer. The modified iron phosphate can be prepared via steps S1-S3 of this invention. Iron phosphate is formed on the organic coating layer, and during the formation of iron phosphate, MXene is not affected by Fe. 3+ All of it is oxidized to titanium dioxide. After the coating layer is carbonized, the MXene matrix is ​​partially exposed, causing the MXene to be converted into TiO2. The carbonization forms a porous structure, which increases the porosity of the electrode material and is beneficial for improving Li... + The insertion / extraction efficiency.

[0083] In some implementations, the thickness of the MXene matrix is ​​5nm-10nm (e.g., 5nm, 8nm, 10nm, etc.), and the lateral dimension is 100nm-300nm (e.g., 100nm, 200nm, 300nm, etc.). The MXene matrix is ​​a nanosheet structure with a certain thickness, and the lateral dimension refers to the dimension of the matrix surface perpendicular to the thickness.

[0084] The present invention also provides a modified lithium iron phosphate, comprising an MXene matrix, a carbon layer coated on the surface of the MXene matrix, and lithium iron phosphate formed on the surface of the carbon layer. The modified lithium iron phosphate can be prepared by steps S1-S4 in the embodiments of the present invention.

[0085] Similarly, the titanium portion in the MXene matrix is ​​oxidized to titanium oxide. The thickness of the MXene matrix is ​​5nm-10nm (e.g., 5nm, 8nm, 10nm, etc.), and the lateral dimension is 100nm-300nm (e.g., 100nm, 200nm, 300nm, etc.).

[0086] This invention also provides a positive electrode sheet, including the above-mentioned modified lithium iron phosphate, and a positive electrode current collector, wherein the modified lithium iron phosphate is distributed on the positive electrode current collector as a positive electrode active material.

[0087] This invention also provides a lithium battery, including the aforementioned positive electrode, and may further include a negative electrode, electrolyte, separator, etc., to form a complete battery structure. The specific types of the negative electrode, electrolyte, and separator are not limited; suitable negative electrode, electrolyte, and separator can be selected based on the composition of existing lithium iron phosphate batteries.

[0088] This invention also provides an electrical device, including the aforementioned lithium battery, and may further include an electrical appliance, wherein the lithium battery supplies power to the electrical appliance.

[0089] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0090] It should be noted that the raw material used in the following examples is MXene, with the chemical formula Ti3C2T. x Its MXene consists of nanosheets with a thickness of 5nm-10nm and a lateral dimension of 100nm-300nm.

[0091] Example 1

[0092] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0093] (1) Place dodecyl dimethyl ammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.9 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T xThe mass ratio of dopamine hydrochloride to aqueous solution was 4:1, the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1 g:1 L, the stirring rate was 100 r / min at room temperature (approximately 25 °C), and the deposition time was 45 min. After the reaction was complete, the mixture was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0094] (2) Ti3C2T coated with dopamine x The material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced. The mass ratio of ferric salt to MXene@PDA was 6:1. After stirring evenly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 70°C for 6 hours at a speed of 600 rpm to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours under an oxygen atmosphere of 10% (volume fraction, the same below) to obtain anhydrous ferric phosphate.

[0095] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30wt% suspension. After ball milling for 5h, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2h, it was placed in a hydrogen atmosphere and calcined at 750℃ for 10h to obtain modified lithium iron phosphate.

[0096] Example 2

[0097] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0098] (1) Place dodecyl dimethyl ammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.9 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 4:1, the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1 g:1 L, the stirring rate was 100 r / min, and the deposition time was 45 min. After the reaction was complete, the mixture was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0099] (2) Ti3C2T coated with dopamine xThe material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced. The mass ratio of ferric salt to MXene@PDA was 6:1. After stirring thoroughly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 70°C for 6 hours at a speed of 600 rpm to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours in an atmosphere with 15% oxygen content to obtain anhydrous ferric phosphate.

[0100] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30wt% suspension. After ball milling for 5h, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2h, it was placed in a hydrogen atmosphere and calcined at 750℃ for 10h to obtain modified lithium iron phosphate.

[0101] The only difference between Example 2 and Example 1 is that the oxygen content in step (2) is higher than that in Example 1. The results show that when the oxygen content is higher, too much dopamine is consumed, too much MXene is exposed and oxidized to TiO2, and the conductivity decreases slightly due to the reduction of MXene; at the same time, the increased consumption of dopamine increases the porosity, which is beneficial to lithium ion transport.

[0102] Example 3

[0103] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0104] (1) Place dodecyl dimethyl ammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.9 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 4:1, the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1 g:1 L, the stirring rate was 100 r / min, and the deposition time was 45 min. After the reaction was complete, the mixture was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0105] (2) Ti3C2T coated with dopamine xThe material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced. The mass ratio of ferric salt to MXene@PDA was 6:1. After stirring thoroughly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 70°C for 6 hours at a speed of 600 rpm to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours under a 5% oxygen atmosphere to obtain anhydrous ferric phosphate.

[0106] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30wt% suspension. After ball milling for 5h, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2h, it was placed in a hydrogen atmosphere and calcined at 750℃ for 10h to obtain modified lithium iron phosphate.

[0107] The only difference between Example 3 and Example 1 is that the oxygen content in step (2) is lower than that in Example 1. The results show that when the oxygen content is low, the carbon layer formed by dopamine is consumed less, the resulting voids are reduced, MXene fails to be converted into TiO2, and the unconverted MXene retains its conductivity advantage.

[0108] Example 4

[0109] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0110] (1) Place dodecyl dimethyl ammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.9 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 4:1, the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1 g:1 L, the stirring rate was 100 r / min, and the deposition time was 45 min. After the reaction was complete, the mixture was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0111] (2) Ti3C2T coated with dopamine xThe material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced, with a mass ratio of ferric salt to MXene@PDA of 2:1. After stirring thoroughly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a molar ratio of phosphate to ferric ions of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 70°C for 6 hours at a speed of 600 rpm to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours in a 10% oxygen atmosphere to obtain anhydrous ferric phosphate.

[0112] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30wt% suspension. After ball milling for 5h, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2h, it was placed in a hydrogen atmosphere and calcined at 750℃ for 10h to obtain modified lithium iron phosphate.

[0113] The only difference between Example 4 and Example 1 is that step (2) uses a larger amount of MXene. The results show that using a larger amount of MXene will affect the energy density and reduce the overall capacity.

[0114] Example 5

[0115] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0116] (1) Place dodecyl dimethyl ammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.9 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 4:1, the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1 g:1 L, the stirring rate was 100 r / min, and the deposition time was 45 min. After the reaction was complete, the mixture was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0117] (2) Ti3C2T coated with dopamine x The material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced. The mass ratio of ferric salt to MXene@PDA was 10:1. After stirring evenly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 70°C for 6 hours at a speed of 600 rpm to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours in a 10% oxygen atmosphere to obtain anhydrous ferric phosphate.

[0118] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30wt% suspension. After ball milling for 5h, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2h, it was placed in a hydrogen atmosphere and calcined at 750℃ for 10h to obtain modified lithium iron phosphate.

[0119] The main difference between Example 5 and Example 1 is the amount of MXene used in step (2). The results show that the overall effect of introducing MXene in Example 2 is reduced.

[0120] Example 6

[0121] The only difference from Example 1 is that the atmosphere during calcination in step (2) is a nitrogen atmosphere.

[0122] Example 7

[0123] The only difference from Example 1 is that the atmosphere during calcination in step (2) is an air atmosphere.

[0124] The results showed that when Comparative Example 2 was calcined in an air atmosphere with excess oxygen, Mxene was largely oxidized to titanium dioxide, resulting in a significant decrease in its conductivity.

[0125] Example 8

[0126] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0127] (1) Place hexadecyltrimethylammonium bromide in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 7.5 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 3:1, and the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 0.5 g: 1 L. The stirring rate was 80 r / min at room temperature (approximately 25 °C), and the deposition time was 30 min. After the reaction was complete, the solution was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0128] (2) Ti3C2T coated with dopamine xThe material was placed in a deionized aqueous solution, and a 0.5 mol / L ferric chloride solution was introduced. The mass ratio of ferric salt to MXene@PDA was 2:1. After stirring evenly, a 0.5 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 300 rpm and 60°C for 8 hours to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 500°C for 8 hours under an oxygen atmosphere of 10% (volume fraction) to obtain anhydrous ferric phosphate.

[0129] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 28wt% suspension. After ball milling for 3 hours, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2 hours, it was placed in a hydrogen atmosphere and calcined at 500℃ for 15 hours to obtain modified lithium iron phosphate.

[0130] Example 9

[0131] This embodiment provides a method for preparing modified lithium iron phosphate. Please refer to [the provided text]. Figure 1 This includes the following steps:

[0132] (1) Place alkyl dimethyl hydroxypropyl phosphate betaine in deionized water at a mass-to-volume ratio of 4 g: 25 L, stir well, then adjust the pH to 8.5 using hydrochloric acid and NaOH, and add dopamine hydrochloride and Ti3C2T x Dopamine hydrochloride and Ti3C2T x The mass ratio of dopamine hydrochloride to aqueous solution was 5:1, and the mass-to-volume ratio of dopamine hydrochloride to aqueous solution was 1.5 g: 1 L. The stirring rate was 120 r / min at room temperature (approximately 25 °C), and the deposition time was 60 min. After the reaction was complete, the solution was filtered and dried to obtain dopamine-coated Ti3C2T. x Material.

[0133] (2) Ti3C2T coated with dopamine x The material was placed in a deionized aqueous solution, and a 1.5 mol / L ferric chloride solution was introduced, with a mass ratio of ferric salt to MXene@PDA of 10:1. After stirring evenly, a 1.5 mol / L ammonium hydrogen phosphate solution was introduced, with a molar ratio of phosphate to ferric ions of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 800 rpm and 80°C for 4 hours to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 800°C for 5 hours under an oxygen atmosphere of 10% (volume fraction) to obtain anhydrous ferric phosphate.

[0134] (3) The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1.05:1, and deionized water was added to obtain a 33wt% suspension. After ball milling for 8 hours, the lithium iron phosphate precursor powder was obtained by spray drying. After grinding for 2 hours, it was placed in a hydrogen atmosphere and calcined at 800℃ for 5 hours to obtain modified lithium iron phosphate.

[0135] Comparative Example 1

[0136] The main difference from Example 1 is that step (1) is omitted. The specific steps are as follows:

[0137] Ti3C2T x The material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced, with a ferric salt to MXene mass ratio of 4:1. After stirring thoroughly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 600 rpm and 70°C for 6 hours to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours under a 10% oxygen atmosphere to obtain anhydrous ferric phosphate.

[0138] The iron phosphate precursor and lithium carbonate were mixed in a Li:Fe ratio of 1:1, and deionized water was added to obtain a 30 wt% suspension. After ball milling for 5 h, the suspension was spray-dried to obtain lithium iron phosphate precursor powder. The powder was then ground for 2 h and calcined at 750 °C for 10 h in a hydrogen atmosphere to obtain lithium iron phosphate.

[0139] The results showed that in Comparative Example 1, without the addition of polydopamine, MXene was completely oxidized to TiO2, which had very poor conductivity and did not have a layered structure.

[0140] Comparative Example 2

[0141] The main difference from Example 1 is that: Mxene material is simply mixed, followed by the incorporation of carbon material. The specific steps are as follows:

[0142] Ti3C2T x The material was placed in a deionized aqueous solution, and a 1 mol / L ferric chloride solution was introduced, with a ferric salt to MXene mass ratio of 4:1. After stirring thoroughly, a 1 mol / L ammonium hydrogen phosphate solution was introduced, with a phosphate to ferric ion molar ratio of 1:1. The pH was controlled at 1.8-2.2, and the reaction was carried out at 600 rpm and 70°C for 6 hours to ensure complete precipitation of ferric phosphate. The obtained ferric phosphate was filtered, washed, dried, crushed, and calcined at 700°C for 6 hours under a 10% oxygen atmosphere to obtain anhydrous ferric phosphate.

[0143] Glucose, lithium carbonate, and prepared iron phosphate were mixed in a ratio of 0.05:1.05:1.0, and deionized water was added to obtain a 30 wt% suspension. After ball milling for 5 h, the suspension was spray-dried to obtain lithium iron phosphate precursor powder. The powder was then ground for 2 h and calcined at 750 °C for 10 h in a hydrogen atmosphere to obtain lithium iron phosphate.

[0144] The results showed that Comparative Example 2 could not effectively coat and protect the Mxene material. When the oxygen atmosphere was controlled, it would be oxidized to TiO2, which could not be effectively controlled, resulting in a decrease in rate performance. At the same time, the added carbon source could not be uniformly coated on the surface, nor could it form a carbon network inside.

[0145] Experimental Example 1

[0146] The electrochemical performance of the modified iron phosphate was prepared by testing the examples and comparative examples.

[0147] Test method: The binder, conductive agent, and LiFePO4 powder were mixed in a mass ratio of 1:1:8, and N-methylpyrrolidone was added to form a slurry. This slurry was then uniformly coated onto aluminum foil, vacuum dried, rolled, and punched into circular electrode sheets. Coin cells were then assembled in a glove box. Constant current charge-discharge cycle tests were performed on the coin cells, with charge-discharge voltages ranging from 2.5 to 4.2 V.

[0148] (1) Ratio Performance Test

[0149] The button cells made from the cathode materials in the above embodiments and comparative examples were tested, mainly at 1C, 3C and 10C, and the results are shown in Table 1.

[0150] Table 1. Rate performance test results of the cathode materials in the examples and comparative examples.

[0151]

[0152] It can be seen that the rate performance of the modified lithium iron phosphate cathode material prepared in the embodiments of the present invention is significantly better than that of the comparative examples. This shows that the embodiments of the present invention first use an organic coating material to coat the Mxene material and then prepare the iron phosphate, which can significantly improve the rate performance compared with the schemes of comparative examples 1-2.

[0153] Comparing Examples 1, 2-3 and 6-7, it can be seen that the oxygen content during calcination has a certain impact on performance, and it is advisable to control the oxygen content within the preferred range of the embodiments of the present invention.

[0154] Comparing Examples 1 and 4-5, it can be seen that the amount of Mxene material has a certain impact on the rate performance of the material. It is advisable to control the amount of Mxene material within the preferred range of the embodiments of the present invention.

[0155] (2) Low temperature performance test

[0156] Two cycles were performed at 0.2C at room temperature. After fully charging the battery, it was placed in a set low-temperature environment for 10 hours, and then discharged at 0.2C. For coin cell batteries, the low-temperature test was conducted at -20℃.

[0157] Test results are as follows Figure 2 As shown in the figure, the modified lithium iron phosphate prepared in the embodiments of the present invention has good low-temperature stability.

[0158] (3) AC impedance spectroscopy test

[0159] Electrochemical tests were conducted using a Shanghai Chenhua CHI660E electrochemical workstation, with a testing range of 10. -2 ~10 5 Hz, disturbance voltage of 5mV, all test environments were 25℃, and the test results are as follows. Figure 3 As shown.

[0160] from Figure 3 As can be seen, all the curves consist of a semicircle in the mid-to-high frequency range and a sloping straight line in the low-frequency range. The semicircle represents the charge transfer impedance, and the diameter of the semicircle represents the size of Rct. It can be seen that the iron phosphate material that has not been calcined in an oxygen atmosphere has a larger final charge transfer impedance, but the material that has been calcined in an oxygen atmosphere, in an environment with excessive oxygen content, has an even larger final charge impedance.

[0161] (4) XPS detection

[0162] Mxene material, dopamine-coated Ti3C2T in Example 1 x The cathode material and Ti3C2T in Comparative Example 1 x The cathode material was characterized by XPS, and the results are as follows: Figure 4 , Figure 5 and Figure 6 As shown.

[0163] XPS characterization revealed that the Ti3C2T in Comparative Example 1 without dopamine coating... x Most of them are oxidized to titanium dioxide. As the degree of oxidation increases, the layered structure of Mxene is gradually destroyed, and its electrochemical performance decreases significantly.

[0164] Industrial applicability

[0165] This invention involves first coating MXene to form iron phosphate on the coating layer, followed by calcination to obtain modified iron phosphate. Modified lithium iron phosphate is then prepared using the modified iron phosphate and a lithium source. The resulting lithium iron phosphate cathode material exhibits superior rate performance and low-temperature stability. This invention is simple to operate and has excellent industrial applicability.

Claims

1. A method for preparing modified iron phosphate, characterized in that, The modified iron phosphate comprises an MXene matrix, a carbon layer coated on the surface of the MXene matrix, and iron phosphate formed on the surface of the carbon layer; The titanium portion in the MXene matrix is ​​oxidized to titanium oxide; The preparation method includes: reacting MXene material with an organic coating layer with iron salt and phosphate to form iron phosphate on the surface of the organic coating layer, and calcining the resulting product in an oxygen-containing atmosphere; the chemical formula of the MXene material is Ti3C2T. x ; The mass ratio of iron salt to the MXene material with organic coating is controlled to be (2-10):1; During the calcination process, the oxygen volume fraction in the oxygen-containing atmosphere is controlled to be 8%-12%.

2. The method for preparing modified iron phosphate according to claim 1, characterized in that, The MXene matrix has a thickness of 5nm-10nm and a lateral dimension of 100nm-300nm.

3. The preparation method according to claim 1, characterized in that, The MXene material with the organic coating layer, iron salt solution, and phosphate solution are mixed and reacted, and the resulting product is then calcined in the oxygen-containing atmosphere.

4. The preparation method according to claim 3, characterized in that, During the reaction of the MXene material with the organic coating, the iron salt solution, and the phosphate solution, the reaction pH is controlled at 1.8-2.2, the reaction temperature at 60℃-80℃, and the reaction time at 4h-8h.

5. The preparation method according to claim 4, characterized in that, By adjusting the amounts of the iron salt and the phosphate, the molar ratio of phosphate to iron ions in the iron salt is made to be 1:(0.95-1.05).

6. The preparation method according to claim 5, characterized in that, The iron salt is selected from at least one of ferric chloride and ferric nitrate; the phosphate is selected from at least one of ammonium hydrogen phosphate, ammonium phosphate and ammonium dihydrogen phosphate; the concentration of both the iron salt solution and the phosphate solution is 0.5 mol / L-2.0 mol / L.

7. The preparation method according to claim 4, characterized in that, After the MXene material with the organic coating layer, iron salt solution, and phosphate solution have been reacted, solid-liquid separation is performed. The resulting solid material is washed and dried, and then calcined in an oxygen-containing atmosphere.

8. The preparation method according to claim 7, characterized in that, During the calcination process, the calcination temperature is controlled at 500℃-800℃, and the calcination time is 5h-8h.

9. The preparation method according to claim 1, characterized in that, The preparation process of MXene material with organic coating includes: mixing and reacting surfactant, organic coating, MXene material and water, followed by solid-liquid separation, and drying the resulting solid material.

10. The preparation method according to claim 9, characterized in that, In the process of preparing the MXene material with the organic coating, the reaction temperature is controlled at 20℃-35℃ and the reaction time is 30min-60min.

11. The preparation method according to claim 9, characterized in that, First, the surfactant and water are mixed to adjust the pH to 7.5-8.5, and then the surfactant and MXene material are mixed and reacted.

12. The preparation method according to claim 9, characterized in that, The organic coating is selected from dopamine hydrochloride.

13. The preparation method according to claim 9, characterized in that, The mass ratio of the organic coating to the MXene material is (3-5):

1.

14. The preparation method according to claim 9, characterized in that, In the mixture of the surfactant, the organic coating, the MXene material, and water, the concentration of the organic coating is 0.5 g / L to 1.5 g / L.

15. The preparation method according to claim 14, characterized in that, The surfactant is selected from at least one of dodecyl dimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, and alkyl dimethyl hydroxypropyl phosphate betaine.

16. The preparation method according to claim 15, characterized in that, The mass ratio of the surfactant to the MXene material is (20-30):

1.

17. A method for preparing modified lithium iron phosphate, characterized in that, include: The modified iron phosphate is mixed with a lithium source and calcined; wherein the modified iron phosphate is the modified iron phosphate prepared by any one of the preparation methods in claims 1-16.

18. The preparation method according to claim 17, characterized in that, The roasting is carried out in a hydrogen-containing atmosphere, with the roasting temperature controlled at 500℃-800℃ and the roasting time at 5h-15h.

19. The preparation method according to claim 17, characterized in that, The modified iron phosphate, the lithium source, and water are mixed to obtain a suspension. The suspension is ball-milled and then dried to obtain a precursor powder. The precursor powder is then ground and calcined in a hydrogen-containing atmosphere.

20. The preparation method according to claim 19, characterized in that, By adjusting the amounts of the modified iron phosphate and the lithium source, the molar ratio of Li to Fe is made to be (1-1.05):

1.

21. The preparation method according to claim 19, characterized in that, The suspension was ball-milled for 3-8 hours and then spray-dried to obtain the precursor powder.

22. The preparation method according to claim 19, characterized in that, The total mass fraction of lithium and iron in the suspension is 28%-33%.

23. The preparation method according to claim 19, characterized in that, The lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

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