A method for preparing lithium titanium phosphate by using doped titanium pyrophosphate as a precursor

Abstract

The application discloses a method for preparing lithium titanium phosphate by using doped titanium pyrophosphate as a precursor. First, a titanium hydrogen phosphate compound is prepared by mixing a phosphorus source and a titanium source in liquid phase, then ions M are doped, doped titanium pyrophosphate is prepared through liquid phase reaction, and then liquid phase coating is performed on the doped titanium pyrophosphate. After further heat treatment, a doped titanium pyrophosphate precursor with uniform element distribution and a tightly combined coating layer is formed. Further mixing with a lithium source and heat treatment are performed to obtain lithium titanium phosphate. The preparation process of the application reduces the number of reactants in solid phase reaction, improves the uniformity of the reaction, and improves the mass transfer process of the reaction particles in the reaction process, thereby successfully preparing a high-purity, particle size and morphology controllable, high-sphericity and multi-doped lithium titanium phosphate product.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor. Background Technology

[0002] With the continuous development of solid-state battery technology, oxide solid electrolytes such as lithium titanium aluminum phosphate and lithium lanthanum zirconium oxide are increasingly widely used in the field of lithium-ion batteries, including applications such as separator coating, positive electrode blending, negative electrode blending, positive electrode coating, organic-inorganic composite, and positive electrode surface coating. However, oxide solid electrolyte products prepared by traditional solid-state methods have problems such as pot sticking during preparation, impure phases in the product, uneven primary particle size, and low sphericity. These problems can no longer meet the needs of downstream customers for controllable particle size and morphology of solid electrolytes, high product purity, and stable large-scale supply, and solutions are urgently needed. Summary of the Invention

[0003] To overcome the problems in the prior art, this invention provides a method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor. By preparing doped titanium pyrophosphate, the particle size of the precursor doped titanium pyrophosphate is effectively controlled, enhancing the diffusion and chemical reaction capabilities during the solid-state reaction. Then, the doped titanium pyrophosphate is mixed with a lithium source and heat-treated to obtain lithium titanium phosphate. This reduces the amount of reactants in the solid-state reaction, improves the uniformity of the reaction, and enhances the mass transfer process of the reactant particles during the reaction. Thus, a high-purity, multi-component doped lithium titanium phosphate product with controllable particle size and morphology and high sphericity is successfully prepared.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0005] This invention provides a method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor, comprising the following steps:

[0006] S1. Phosphorus source and titanium source are mixed and reacted using a liquid phase method at a reaction temperature of 25-180℃ and a pH of 0-2. After the reaction is completed, titanium hydrogen phosphate is obtained and washed.

[0007] S2. Add a doped compound to the washed titanium hydrogen phosphate compound from step S1 and carry out a liquid-phase ion exchange reaction. After the reaction is completed, add a titanium source for liquid-phase coating. After coating, process to obtain a doped titanium pyrophosphate precursor coated with titanium compound.

[0008] S3. The titanium-containing compound-coated doped titanium pyrophosphate precursor obtained in step S2 is processed and mixed evenly with a lithium source, and then subjected to high-temperature heat treatment to obtain lithium titanium phosphate.

[0009] In this invention, a phosphorus source and a titanium source are first mixed in liquid phase, and a liquid-phase crystallization reaction occurs under acidic conditions (pH 0-2). The liquid-phase reaction system is controlled at 25-180℃. Under strongly acidic conditions, the titanium source hydrolyzes to release titanium ions, which react with the phosphorus source to form titanium hydrogen phosphate and its hydrate. This product has a layered structure and can undergo proton exchange with alkaline earth metal ions, thereby achieving metal ion doping. After drying and thorough washing, this product is mixed with a dopant compound, namely M ions, in liquid phase for a liquid-phase reaction. M ions undergo ion exchange with H ions, and M ions are incorporated into the layered structure of titanium hydrogen phosphate and its hydrate. Simultaneously, a titanium source is added to the liquid-phase reaction system for surface coating. Because titanium ions and compounds are relatively inert in this system, they only form a coating layer on the surface and do not penetrate into the liquid phase. Since the crystal lattice is used, lattice doping and liquid-phase coating can be carried out simultaneously. The liquid-phase coating product is heat-treated to form a tightly bonded solid solution compound, namely the doped titanium pyrophosphate precursor. This precursor has high reactivity. Finally, the doped titanium pyrophosphate is mixed with a lithium source to carry out a two-phase reaction. After heat treatment, lithium titanium phosphate solid electrolyte is obtained. Based on this method, on the one hand, the particle size of the precursor doped titanium pyrophosphate is effectively controlled, the specific surface area is increased, and the diffusion and chemical reaction capabilities during the solid-phase reaction are enhanced. On the other hand, the amount of reactants in the solid-phase reaction is reduced, the uniformity of the reaction is improved, and the mass transfer process of the reactant particles during the reaction is improved. Thus, a high-purity, multi-component doped lithium titanium phosphate product with controllable particle size and morphology and high sphericity is successfully prepared.

[0010] As an optional implementation, in the method provided by the present invention, in step S1, the pH of the reaction system is 0-1.

[0011] As an optional implementation, in the method provided by the present invention, in step S1, the obtained compound is washed with deionized water, and the pH of the washed product is 4-7.

[0012] Furthermore, a pH of 5-7 is preferred.

[0013] As an optional implementation, in the method provided by the present invention, in step S2, the temperature of the liquid phase ion exchange reaction is 45-180℃, and the stirring speed during the reaction process is ≥800rpm / min.

[0014] Furthermore, 60-120℃ is preferred.

[0015] In this invention, a certain stirring speed is maintained to improve the uniformity of the surface coating layer of the liquid phase coating and to increase the ion doping rate. The temperature of the liquid phase ion exchange reaction is controlled. If the temperature is too low, a solid solution cannot be formed, and the temperature affects the amount of ion doping.

[0016] As an optional implementation, in the method provided by the present invention, in step S2, after the coating is completed, the product is washed, dried and heat-treated, and the heat treatment temperature is 450-800℃.

[0017] Furthermore, 500-700℃ is preferred.

[0018] In this invention, the product coated with liquid phase is washed, dried, and then subjected to heat treatment. The purpose is twofold: firstly, to generate doped titanium pyrophosphate crystals; and secondly, to form a dense, uniformly distributed solid solution between the coated product and the doped titanium pyrophosphate, i.e., the titanium-containing compound-coated doped titanium pyrophosphate precursor in this invention. The solid solution compound has higher reactivity in solid-phase reactions than the original compound, which is more conducive to subsequent solid-phase reactions.

[0019] As an optional implementation, in the method provided by the present invention, in step S3, the temperature at which the doped titanium pyrophosphate precursor and the lithium source are subjected to high-temperature heat treatment is 600-900°C.

[0020] Furthermore, 700-800℃ is preferred.

[0021] In this invention, controlling the solid-state reaction temperature between the doped titanium pyrophosphate precursor and the lithium source can transform titanium pyrophosphate into lithium titanium phosphate, which is beneficial for the transformation of crystal form. If the temperature is too low, the crystal form cannot be changed, and if the temperature is too high, the uniformity of particle size and morphology cannot be controlled.

[0022] As an optional implementation, in the method provided by the present invention, the particle size of the doped titanium pyrophosphate precursor is 0.1-1 μm.

[0023] As an optional implementation, in the method provided by the present invention, in step S1, the reaction method of the phosphorus source and the titanium source is selected from one of the following: high-energy ball milling reaction, high-temperature and high-pressure hydrothermal reaction, co-precipitation reaction, condensation reflux reaction, or aging reaction.

[0024] As an optional implementation, in the method provided by the present invention, the molar ratio of phosphorus to titanium in the phosphorus source and titanium source is ≥1.5, the molar ratio of element M in the compound containing doped ion M to element titanium in the compound titanium hydrogen phosphate is 0.5-10:1, and the molar ratio of lithium in the lithium source to element titanium in the doped titanium pyrophosphate is 0.5-1.5:1.

[0025] As an optional implementation, in the method provided by the present invention, the phosphorus source is selected from one or more of P2O5, H3PO4, NH4H2PO4, (NH4)2HPO4 and H4P2O7.

[0026] As an optional implementation, in the method provided by the present invention, the titanium source is selected from TiO2, H2TiO3, Ti(SO4)2, TiCl4, TiOSO4, TiO(OH)2, C 16 H 36 One or more of O4Ti and Ti(OCH(CH3)2)4.

[0027] As an optional implementation, in the method provided by the present invention, the lithium source is selected from one or more of LiOH, Li3PO4, Li2CO3, LiCl, CH3COOLi, and LiH2PO4.

[0028] As an optional implementation, in the method provided by this invention, the molecular formula of the titanium compound-coated doped titanium pyrophosphate precursor is M. x Ti 1-x P₂O₇, where 0 ≤ X ≤ 0.7, and M is Mg. 2+ Al 3+ Sn 4+ Zr 4+ Y 3+ and Hf 4+ One or more of them.

[0029] As an optional implementation, in the method provided by the present invention, the dopant ion M of the doped compound is selected from Mg. 2+ Al 3+ Sn 4+ Zr 4+ Y 3+ and Hf 4+ One or more of them.

[0030] As an optional implementation, in the method provided by the present invention, the mixing method of the titanium compound-coated doped titanium pyrophosphate precursor and the lithium source is selected from one of the following: high-speed mixer, ribbon mixer, air-flow mixer, high-energy ball mill, or sand mill.

[0031] Furthermore, high-energy ball milling or sand milling is preferred.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] (1) The present invention uses a liquid phase method to prepare the product, which avoids the problem of sticking in the pot that occurs in the traditional solid phase method and solves the problem of large-scale production.

[0034] (2) In this invention, doped titanium pyrophosphate is prepared by liquid phase reaction and then coated with liquid phase. After further heat treatment, a solid solution with uniform element distribution and tight coating layer is formed (doped titanium pyrophosphate precursor coated with titanium compound), which reduces the reaction activation energy, ensures the uniformity of reactants, and improves the phase purity of solid electrolyte products.

[0035] (3) In this invention, a titanium-containing compound-coated doped titanium pyrophosphate precursor is first prepared, and then heat-treated to make it a stable solid solution. Using this precursor to prepare lithium titanium phosphate, no further addition of titanium source is required in the solid-phase reaction, thus achieving lithium titanium phosphate (LiTi). 1+x M x Ti 2-x (PO4)3 (0≤X≤0.7, M is Mg) 2+ Al 3+ Sn 4+ Zr 4+ Y 3+ and Hf 4+ Preparation of one or more solid electrolytes.

[0036] (4) The present invention prepares lithium titanium phosphate through precursor, which reduces the number of reaction components in the sintering process, especially the number of components in the sintering process of multi-doped lithium titanium phosphate solid electrolyte, and lowers the phase formation temperature of the product. On the one hand, it reduces energy consumption, and on the other hand, it is more conducive to controlling the particle size and morphology of the product. The resulting lithium titanium phosphate product has high sphericity and good uniformity. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a photograph of the lithium titanium phosphate product prepared in Example 3 of this invention.

[0039] Figure 2 This is a physical image of the lithium titanium phosphate product prepared in Comparative Example 1 of this invention;

[0040] Figure 3 This is a SEM image of the doped titanium pyrophosphate prepared in Example 1 of this invention;

[0041] Figure 4 This is a SEM image of the doped titanium pyrophosphate prepared in Example 2 of this invention;

[0042] Figure 5 This is a SEM image of the doped titanium pyrophosphate prepared in Example 3 of this invention;

[0043] Figure 6 This is a SEM image of lithium titanium phosphate prepared in Example 1 of this invention;

[0044] Figure 7 This is a SEM image of lithium titanium phosphate prepared in Example 2 of this invention;

[0045] Figure 8 This is a SEM image of lithium titanium phosphate prepared in Example 3 of this invention;

[0046] Figure 9 This is a SEM image of lithium titanium phosphate prepared in Example 4 of this invention;

[0047] Figure 10 This is a SEM image of lithium titanium phosphate prepared in Example 5 of this invention;

[0048] Figure 11 This is a SEM image of lithium titanium phosphate prepared in Example 6 of this invention;

[0049] Figure 12 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 1 of this invention;

[0050] Figure 13 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 2 of this invention;

[0051] Figure 14 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 3 of this invention;

[0052] Figure 15 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 4 of this invention;

[0053] Figure 16 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 5 of this invention;

[0054] Figure 17 The images show the XRD patterns of the doped titanium pyrophosphate prepared in Examples 1, 2, and 3 of this invention.

[0055] Figure 18 The images show the XRD patterns of lithium titanium phosphate prepared in Examples 1, 2, 3, 4, 5, and 6 of this invention.

[0056] Figure 19 The images show the XRD patterns of lithium titanium phosphate prepared in Comparative Examples 1, 2, 3, 4, 5, and 6 of this invention. Detailed Implementation

[0057] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0058] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0059] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0060] Example 1

[0061] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0062] (1) Weigh 80g of H3PO4 aqueous solution with a mass fraction of 15%, and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to <1.

[0063] (2) Place the above-mentioned phosphoric acid aqueous solution with pH < 1 at 60°C and stir at a stirring speed of 800 rpm / min. Slowly add 10g of TiOSO4 to react in the liquid phase for 3h. Monitor the pH change during the reaction process to ensure that the pH of the system is ≤ 2. After the reaction is completed, filter and prepare Ti(HPO4)2·H2O.

[0064] (3) Add deionized water to prepare a Ti(HPO4)2·H2O aqueous solution with a ratio of 10:1, and wash repeatedly until pH≥5.

[0065] (4) Add 5g of fully dried Ti(HPO4)2·H2O and 35g of 0.2mol / L Al(NO3)3·9H2O aqueous solution respectively, and react at 60℃ for 3h with a stirring speed of 1200rpm / min.

[0066] (5) After the above reaction for 3 hours, add 0.2 g of TiO2 (the primary particle size is ≤60 nm) and continue the reaction for 3 hours. The stirring speed is 1200 rpm / min.

[0067] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 450°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0068] (7) Add 5.2g of doped titanium pyrophosphate precursor and 0.85g of LiOH respectively, and transfer to high-energy ball mill with a ball-to-material ratio of 4:1, a ball milling speed of 800rpm / min, a duration of 4h, and an interval of 60s. After ball milling, transfer to heat treatment at 600℃ for 4h to obtain lithium titanium phosphate product.

[0069] Example 2

[0070] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0071] (1) Weigh out 16.21g TiO2 and 41.29g H3PO4 (85wt%) respectively. The pH of the reaction system is <1.

[0072] (2) Transfer the weighed raw materials into a high-energy ball mill jar and mix them evenly. Ball mill at atmospheric pressure and 25°C with a ball-to-material ratio of 4:1, a ball milling speed of 800 rpm / min, a time of 36 h, and an interval of 60 s. After the reaction is complete, filter the mixture.

[0073] (3) Add deionized water to prepare an aqueous solution with a ratio of 10:1. Wash repeatedly with deionized water until pH=5, and then dry to obtain Ti(HPO4)2·H2O.

[0074] (4) Add 5g of fully dried Ti(HPO4)2·H2O and 35g of 0.2mol / L Al(NO3)3·9H2O aqueous solution respectively, and react at 60℃ for 3h with a stirring speed of 1200rpm / min.

[0075] (5) After the above reaction for 3 hours, add 0.2 g of TiO2 (the primary particle size is ≤60 nm) and continue the reaction for 3 hours. The stirring speed is 1200 rpm / min.

[0076] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 600°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0077] (7) Add 5.2g of doped titanium pyrophosphate precursor and 1.3g of Li2CO3 respectively, and mix them in a high-speed mixer. After mixing, heat treat at 700℃ for 4h to obtain lithium titanium phosphate product.

[0078] Example 3

[0079] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0080] (1) Weigh 140g of NH4H2PO4 aqueous solution with a mass fraction of 10%, and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0081] (2) Place the above-mentioned phosphoric acid aqueous solution with pH=0.8 at 160℃ and stir at a stirring speed of 1600rpm / min. Slowly add 10g TiOSO4, monitor the pH change during the reaction process, and ensure that the pH of the system is ≤2. Filter after 3h of liquid phase reaction.

[0082] (3) Add deionized water to prepare an aqueous solution with a ratio of 10:1. Wash repeatedly with deionized water until pH=5, and then dry to obtain Ti(HPO4)2·H2O.

[0083] (4) Add 5g of fully dried Ti(HPO4)2·H2O and 35g of 0.2mol / L Al(NO3)3·9H2O aqueous solution respectively, and react at 120℃ for 3h with a stirring speed of 1600 rpm / min.

[0084] (5) After the above reaction for 3 hours, add 0.2 g of TiO2 (the primary particle size is ≤60 nm) and continue the reaction for 3 hours. The stirring speed is 2400 rpm / min.

[0085] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 600°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0086] (7) Add 5.2g of doped titanium pyrophosphate precursor and 1.3g of Li2CO3 respectively, and mix them in a high-speed mixer. After mixing, heat treat at 800℃ for 4h to obtain lithium titanium phosphate product.

[0087] Example 4

[0088] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0089] (1) Weigh 140g of NH4H2PO4 aqueous solution with a mass fraction of 10%, and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0090] (2) Place the above-mentioned phosphoric acid aqueous solution with pH=0.8 at 160℃ and stir at a stirring speed of 1600rpm / min. Slowly add 10g TiOSO4, monitor the pH change during the reaction process, and ensure that the pH of the system is ≤2. Filter after 3h of liquid phase reaction.

[0091] (3) Add deionized water to prepare an aqueous solution with a ratio of 10:1. Wash repeatedly with deionized water until pH=5, and then dry to obtain Ti(HPO4)2·H2O.

[0092] (4) Add 5g of fully dried Ti(HPO4)2·H2O and 5.6g of 1mol / L Sn(SO4)2 aqueous solution respectively, and react at 120℃ for 3h with a stirring speed of 1600 rpm / min.

[0093] (5) After the above reaction for 3 hours, add 0.25 g of TiO(OH)2 and continue the reaction for 3 hours with a stirring speed of 2400 rpm / min.

[0094] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 600°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0095] (7) Add 5.2g of doped titanium pyrophosphate precursor and 0.85g of LiOH respectively, and transfer them to a high-speed mixer for mixing. After mixing, heat treatment at 800℃ for 4h is carried out to obtain lithium titanium phosphate product.

[0096] Example 5

[0097] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0098] (1) Weigh 140g of NH4H2PO4 aqueous solution with a mass fraction of 10%, and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0099] (2) Place the above-mentioned phosphoric acid aqueous solution with pH=0.8 at 160℃ and stir at a stirring speed of 1600rpm / min. Slowly add 10g TiOSO4, monitor the pH change during the reaction process, and ensure that the pH of the system is ≤2. Filter after the liquid phase reaction for 3h.

[0100] (3) Add deionized water to prepare an aqueous solution with a ratio of 10:1. Wash repeatedly with deionized water until pH=5, and then dry to obtain Ti(HPO4)2·H2O.

[0101] (4) Add 5g of fully dried Ti(HPO4)2·H2O, 17.5g of 0.2mol / L Al(NO3)3·9H2O aqueous solution, and 6g of 0.5mol / L MgCl2 aqueous solution respectively, and react at 120℃ for 3h with a stirring speed of 1600 rpm / min.

[0102] (5) After the above reaction for 3 hours, add 0.25 g of TiO(OH)2 and continue the reaction for 3 hours with a stirring speed of 2400 rpm / min.

[0103] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 600°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0104] (7) Add 5.2g of doped titanium pyrophosphate precursor and 0.85g of LiOH respectively, and transfer them to a high-speed mixer for mixing. After mixing, heat treatment at 800℃ for 4h is carried out to obtain lithium titanium phosphate product.

[0105] Example 6

[0106] A method for preparing lithium titanium phosphate from a doped titanium pyrophosphate precursor includes the following steps:

[0107] (1) Weigh 80g of H3PO4 aqueous solution with a mass fraction of 15%, and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to <1.

[0108] (2) Place the above-mentioned phosphoric acid aqueous solution with pH < 1 at 60°C and stir at a stirring speed of 800 rpm / min. Slowly add 10g TiOSO4, monitor the pH change during the reaction process, and ensure that the pH of the system is ≤ 2. The liquid phase reaction is carried out for 3 hours. After the reaction is completed, filter and prepare Ti(HPO4)2·H2O.

[0109] (3) Add deionized water to prepare a Ti(HPO4)2·H2O aqueous solution with a ratio of 10:1, and wash repeatedly until pH≥5.

[0110] (4) Add 5g of fully dried Ti(HPO4)2·H2O and 35g of 0.2mol / L Al(NO3)3·9H2O aqueous solution respectively, and react at 60℃ for 3h with a stirring speed of 1200 rpm / min.

[0111] (5) After the above reaction for 3 hours, add 0.68 g of Ti(OCH(CH3)2)4 and continue the reaction for 3 hours with a stirring speed of 1200 rpm / min.

[0112] (6) The above reactants were filtered, washed, and dried at 120°C for 10 hours. The dried product was then heat-treated at 600°C for 4 hours to obtain the doped titanium pyrophosphate precursor.

[0113] (7) Add 5.2g of doped titanium pyrophosphate precursor and 1.3g of Li2CO3 respectively, and transfer to high-energy ball mill with a ball-to-material ratio of 4:1, a ball milling speed of 800 rpm / min, a duration of 4h, and an interval of 60s. After ball milling, transfer to heat treatment at 900℃ for 4h to obtain lithium titanium phosphate product.

[0114] Comparative Example 1

[0115] A method for preparing lithium titanium phosphate products via solid-state process includes the following steps:

[0116] (1) Weigh out 33.67g Li2CO3, 10.71g Al2O3, 94.85g TiO2, 242.2g NH3H2PO4, and 1525.72g C3H8O respectively.

[0117] (2) Transfer the weighed raw materials into a high-energy ball mill jar for high-energy ball milling and mixing. The ball milling speed is 800 rpm / min, the time is 6 hours, and the interval is 60 seconds.

[0118] (3) The high-energy ball milling product was transferred to a vacuum drying oven and dried at 120°C for 10 hours to prepare precursor 1.

[0119] (4) The precursor 1 was transferred into a sintering furnace and heat-treated at 900°C for 4 hours to obtain lithium titanium phosphate product.

[0120] Comparative Example 2

[0121] A method for preparing lithium titanium phosphate from titanium pyrophosphate as a raw material includes the following steps:

[0122] (1) Weigh out 10.56g Li2CO3, 3.36g Al2O3, 3.32g TiO2, 73.20g TiP2O7 and 20g C3H8O respectively.

[0123] (2) Transfer the weighed raw materials into a high-energy ball mill jar for high-energy ball milling and mixing. The ball milling speed is 800 rpm / min, the ball-to-material ratio is 4:1, the duration is 6 hours, and the interval is 60 seconds.

[0124] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120°C for 10 hours to prepare precursor 1.

[0125] (4) The precursor 1 was transferred into a sintering furnace and heat-treated at 700°C for 4 hours to obtain lithium titanium phosphate product.

[0126] Comparative Example 3

[0127] A method for preparing lithium titanium phosphate from titanium pyrophosphate as a raw material includes the following steps:

[0128] (1) Weigh out 10.56g Li2CO3, 3.36g Al2O3, 3.32g TiO2, 73.20g TiP2O7 and 20g C3H8O respectively.

[0129] (2) Transfer the weighed raw materials into a high-energy ball mill jar for high-energy ball milling and mixing. The ball milling speed is 800 rpm / min, the ball-to-material ratio is 4:1, the duration is 6 hours, and the interval is 60 seconds.

[0130] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120°C for 10 hours to prepare precursor 1.

[0131] (4) The precursor 1 was transferred into a sintering furnace and heat-treated at 900°C for 4 hours to obtain lithium titanium phosphate product.

[0132] Comparative Example 4

[0133] A method for preparing lithium titanium phosphate from titanium pyrophosphate as a raw material includes the following steps:

[0134] (1) Weigh out 10.56g Li2CO3, 1.68g Al2O3, 1.57g MgCl2, 3.32g TiO2, 73.20g TiP2O7 and 20g C3H8O respectively.

[0135] (2) Transfer the weighed raw materials into a high-energy ball mill jar for high-energy ball milling and mixing. The ball milling speed is 800 rpm / min, the ball-to-material ratio is 4:1, the duration is 6 hours, and the interval is 60 seconds.

[0136] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120°C for 10 hours to prepare precursor 1.

[0137] (4) The precursor 1 was transferred into a sintering furnace and heat-treated at 900°C for 4 hours to obtain lithium titanium phosphate product.

[0138] Comparative Example 5

[0139] A method for preparing lithium titanium phosphate from titanium pyrophosphate as a raw material includes the following steps:

[0140] The difference from Example 6 is that the heat treatment temperature in step (7) is 1000°C, and the other steps are the same as in Example 6.

[0141] The lithium titanium phosphate prepared in the examples and comparative examples was tested, and... Figure 1 and Figure 2It can be seen that, compared with the traditional solid-state synthesis of lithium titanium phosphate, the process for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor proposed in this invention does not exhibit agglomeration and does not result in product reaction with the crucible, thus solving the crucible sticking problem in the synthesis of lithium titanium phosphate solid electrolyte. According to Figure 3 , Figure 4 , Figure 5 The electron microscopy observations shown in Examples 1, 2, and 3 demonstrate the preparation of nanoscale and submicron-scale doped titanium pyrophosphate precursors under different liquid-phase reaction conditions, with particle sizes ranging from 0.1 to 1 μm, achieving precise control over the doped titanium pyrophosphate precursor. Furthermore, based on the aforementioned precursors of different particle sizes and with the temperature controlled within the preferred range of 450℃-800℃, [the following was successfully prepared]. Figure 6 , Figure 7 , Figure 8 The exhibited lithium titanium phosphate solid electrolytes of different sizes with uniform particle size and high sphericity are significantly superior to those prepared using the processes described in Comparative Examples 1, 2, 3, and 4. Figure 12 , Figure 13 , Figure 14 , Figure 15 The blocky and unevenly sized lithium titanium phosphate solid electrolyte products exhibited show significant improvement, and the precursor particle size and heat treatment reaction temperature can be adjusted to achieve customized production of lithium titanium phosphate solid electrolytes from the nanoscale to the microscale based on different particle size requirements of different application scenarios. Figure 11 and Figure 16 SEM characterization results showed that further increasing the heat treatment temperature to 900℃ led to the widespread and obvious connections between primary particles. When the heat treatment temperature was increased to 1000℃, the product prepared by the method described in this invention began to agglomerate. Analysis suggests that when the heat treatment temperature is ≥900℃, temperature plays a major role in the solid-state reaction process. The primary particle size continuously grows and aggregates at high temperatures. Therefore, only by controlling the heat treatment temperature at a lower level can precise control of the product particle size and morphology be achieved. Examples 3, 4, and 5 prepared Al0.05 based on the same doped titanium pyrophosphate preparation process and heat treatment conditions. 3+ Sn 4+ Al 3+ With Mg 2+ Co-doped lithium titanium phosphate solid electrolyte, according to Figure 8 , Figure 9 , Figure 10 The observed results show no significant difference in the primary morphology and particle size of the three products, indicating that the preparation method described in this invention can achieve the preparation of different M (M is Mg) particles. 2+ Al 3+ Sn 4+ Zr4+ Y 3+ and Hf 4+ The particle size of lithium titanium phosphate solid electrolyte (one type) doped with one of the following can be precisely controlled, and the particle size of lithium titanium phosphate solid electrolyte (multi-metal element co-doped) can also be precisely controlled. According to Figure 18 It can be seen that the methods described in the embodiments of the present invention all yield high-purity lithium titanium phosphate solid electrolytes free of other impurities. In contrast, the preparation method described in Comparative Example 5 showed obvious original lithium titanium phosphate impurities, which is believed to be related to the volatilization of P or Li elements during the high-temperature solid-phase reaction. This experimental result further indicates that the preparation of lithium titanium phosphate solid electrolytes based on the methods described in the present invention should be carried out at a relatively low heat treatment temperature. Figure 18 and Figure 19 The main difference between the sintered product phases of Example 2 and Comparative Example 2 is that Example 2 uses doped titanium pyrophosphate to prepare lithium titanium aluminum phosphate, while Comparative Example 2 uses uncoated and undoped titanium pyrophosphate to prepare lithium titanium phosphate. This difference further determines the quantity and particle size and uniformity of the reactants in the solid-state heat treatment process. Combining the analysis of the preparation process and product phase results described in Example 5 and Comparative Example 3, under the same 700℃ heat treatment conditions, Examples 2 and 5 successfully prepared high-purity, impurity-free lithium titanium phosphate solid electrolyte and Mg... 2+ Al 3+ The co-doped lithium titanium phosphate solid electrolyte was compared to that in Comparative Examples 2 and 3, significant titanium dioxide and lithium phosphate impurities were observed in the products. This indicates a uniform reaction process without the presence of additional impurities. Further increasing the heat treatment temperature to 900℃ improved the impurity intensity, but these impurities still remained. Analysis suggests that the difference in results is primarily due to the acquisition of a doped titanium pyrophosphate precursor with solid solution properties. This effectively controlled the particle size of the precursor product, increased the specific surface area, and enhanced diffusion and chemical reactivity during the solid-phase reaction. Furthermore, it reduced the amount of reactants in the solid-phase reaction, improved the reaction uniformity, and enhanced the mass transfer process of the reactant particles. This ensured uniform phase formation at low temperatures, guaranteeing both high product purity and precise control over particle size and morphology.

[0142] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor, characterized in that, Includes the following steps: S1. Phosphorus source and titanium source are mixed and reacted using a liquid phase method. The reaction temperature is 25-180℃ and the pH of the reaction system is 0-2. After the reaction is completed, titanium hydrogen phosphate is obtained and washed. S2. Add a doped compound to the washed titanium hydrogen phosphate compound in step S1 to carry out a liquid-phase ion exchange reaction. After the reaction is completed, add a titanium source for liquid-phase coating. After coating, wash, dry and heat-treat to obtain a doped titanium pyrophosphate precursor coated with titanium compound. The heat treatment temperature is 450-800℃. S3. Mix the doped titanium pyrophosphate precursor obtained in step S2 with a lithium source until homogeneous, and then perform high-temperature heat treatment to obtain lithium titanium phosphate; the high-temperature heat treatment temperature of the doped titanium pyrophosphate precursor and the lithium source is 600-900℃.

2. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, In step S1, the pH of the reaction system is 0-1.

3. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, In step S1, the obtained compound is washed with deionized water, and the pH of the washed product is 4-7.

4. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, In step S2, the temperature of the liquid-phase ion exchange reaction is 45-180℃, and the stirring speed during the reaction is ≥800 rpm.

5. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, The particle size of the doped titanium pyrophosphate precursor is 0.1-1 μm.

6. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, In step S1, the reaction method for the phosphorus source and the titanium source is selected from one of the following: high-energy ball milling reaction, high-temperature and high-pressure hydrothermal reaction, co-precipitation reaction, condensation and reflux reaction, or aging reaction.

7. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, The molar ratio of phosphorus to titanium in the phosphorus source and titanium source is ≥1.5; the molar ratio of dopant element M in the doped compound to titanium in the compound titanium hydrogen phosphate is 0.5-10:1; and the molar ratio of lithium in the lithium source to titanium in the doped titanium pyrophosphate is 0.5-1.5:

1.

8. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that, The dopant ion M of the doped compound is selected from Mg. 2+ Al 3+ Sn 4+ Zr 4+ Y 3+ and Hf 4+ One or more of the following; the phosphorus source is selected from one or more of P2O5, H3PO4, NH4H2PO4, (NH4)2HPO4, and H4P2O7, and the titanium source is selected from TiO2, H2TiO3, Ti(SO4)2, TiCl4, TiOSO4, TiO(OH)2, and C. 16 H 36 One or more of O4Ti and Ti(OCH(CH3)2)4; the lithium source is selected from one or more of LiOH, Li3PO4, Li2CO3, LiCl, CH3COOLi, and LiH2PO4.

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