Method for preparing lithium titanium phosphate by taking doped titanium pyrophosphate as precursor

Abstract

The invention discloses a method for preparing lithium titanium phosphate by taking doped titanium pyrophosphate as a precursor, which comprises the following steps of: firstly, preparing a compound titanium hydrogen phosphate by liquid-phase mixing of a phosphorus source and a titanium source, then doping ions M, preparing doped titanium pyrophosphate by liquid-phase reaction, and then carrying out liquid-phase coating on the doped titanium pyrophosphate to obtain the lithium titanium phosphate. And carrying out further heat treatment to form a doped titanium pyrophosphate precursor with uniformly distributed elements and tightly combined coating layers, further mixing the doped titanium pyrophosphate precursor with a lithium source, and carrying out heat treatment to obtain the lithium titanium phosphate. According to the preparation process disclosed by the invention, the number of reactants in a solid-phase reaction is reduced, the uniformity of the reaction is improved, and the mass transfer process of reaction particles in the reaction process is improved, so that a multi-element doped lithium titanium phosphate product with high purity, controllable particle size and morphology and high sphericity is successfully prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a method for preparing lithium titanium phosphate by using doped titanium pyrophosphate as a precursor. Background Art

[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 being used more and more widely in the field of lithium-ion batteries, including diaphragm coating, positive electrode blending, negative electrode blending, positive electrode coating, organic-inorganic composite, positive electrode surface coating and other applications. Oxide solid electrolyte products prepared by traditional solid-state methods have problems such as sticking during the preparation process, impure product phases, uneven primary particle size and low sphericity. They can no longer meet the needs of downstream customers for controllable solid electrolyte particle size and morphology, high product purity, and large-scale stable supply, and solutions are urgently needed. Summary of the invention

[0003] In order to overcome the problems in the prior art, the present 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, and the diffusion and chemical reaction capabilities during the solid phase reaction are enhanced. Then, the doped titanium pyrophosphate is mixed with a lithium source and subjected to heat treatment to obtain lithium titanium phosphate, thereby reducing the number of reactants in the solid phase reaction, improving the uniformity of the reaction, and improving the mass transfer process of the reaction particles during the reaction, thereby successfully preparing a high-purity multi-doped lithium titanium phosphate product with controllable particle size and morphology and high sphericity.

[0004] In order to solve the above technical problems, the technical solution proposed by the present invention is: The present invention provides a method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor, comprising the following steps: S1. Mixing a phosphorus source and a titanium source by a liquid phase method, the reaction temperature is 25-180° C., the pH of the reaction system is 0-2, and after the reaction is completed, a compound of titanium hydrogen phosphate is obtained and washed.

[0005] S2, adding a doping compound to the compound titanium hydrogen phosphate washed in step S1 to carry out a liquid phase ion exchange reaction, adding a titanium source to carry out liquid phase coating after the reaction is completed, and treating after the coating is completed to obtain a doped titanium pyrophosphate precursor coated with a titanium compound.

[0006] S3, treating the doped titanium pyrophosphate precursor coated with the titanium-containing compound obtained in step S2, mixing it evenly with a lithium source, and then performing a high-temperature heat treatment to obtain lithium titanium phosphate.

[0007] In the present invention, a phosphorus source and a titanium source are first mixed in liquid phase, and a liquid phase crystallization reaction occurs under an acidic pH of 0-2. The liquid phase reaction system is controlled at 25-180° C. The titanium source is hydrolyzed under a strong acidic condition to generate titanium ions and a phosphorus source to generate titanium hydrogen phosphate and a hydrate thereof. The product has a layered structure and can undergo proton exchange with alkaline earth metal ions to achieve metal ion doping. The product is dried and fully washed, and then mixed with a doping compound, i.e., M ions, in liquid phase to undergo a liquid phase reaction. The M ions undergo ion exchange with H ions, and the M ions are doped into the layered structure of titanium hydrogen phosphate and a hydrate thereof. At the same time, a titanium source is added to the liquid phase reaction system for surface coating. Since the titanium ions and the compounds are relatively inert in the system, only a coating layer is formed on the surface and no metal ions enter the surface. Lattice, so lattice doping and liquid phase coating can be carried out simultaneously; the liquid phase coating product is heat treated to form a tightly bound solid solution compound, namely, a doped titanium pyrophosphate precursor, which has high reactivity, and finally the doped titanium pyrophosphate is mixed with a lithium source for a two-phase reaction, and a lithium titanium phosphate solid electrolyte is obtained after heat treatment. 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 number of reactants in the solid phase reaction is reduced, the uniformity of the reaction is improved, and the mass transfer process of the reaction particles during the reaction is improved, thereby successfully preparing a high-purity, multi-doped lithium titanium phosphate product with controllable particle size and morphology and high sphericity.

[0008] As an optional embodiment, in the method provided by the present invention, in step S1, the pH of the reaction system is 0-1.

[0009] As an optional embodiment, 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.

[0010] Furthermore, the preferred pH is 5-7.

[0011] As an optional embodiment, in the method provided by the present invention, in step S2, the temperature of the liquid phase ion exchange reaction is 45-180° C., and the stirring speed during the reaction is ≥800 rpm / min.

[0012] Further, 60-120°C is preferred.

[0013] In the present invention, a certain stirring speed is ensured to improve the uniformity of the surface coating layer of the liquid phase coating, and to increase the ion doping speed, and to control the temperature of the liquid phase ion exchange reaction. If the temperature is too low, a solid solution cannot be formed, and the temperature affects the ion doping amount.

[0014] As an optional embodiment, in the method provided by the present invention, in step S2, after coating, washing, drying and heat treatment are performed, and the heat treatment temperature is 450-800°C.

[0015] Further, 500-700°C is preferred.

[0016] In the present invention, the product after liquid phase coating is washed, dried and then heat treated, the purpose of which is to generate doped titanium pyrophosphate crystals on the one hand, and to form a compact solid solution with uniform element distribution between the coated product and the doped titanium pyrophosphate, that is, the doped titanium pyrophosphate precursor coated with the titanium-containing compound in the present invention. The solid solution compound has higher reaction activity in the solid phase reaction than the original compound, and is more conducive to the subsequent solid phase reaction.

[0017] As an optional embodiment, in the method provided by the present invention, in step S3, the temperature of the high-temperature heat treatment of the doped titanium pyrophosphate precursor and the lithium source is 600-900°C.

[0018] Further, 700-800°C is preferred.

[0019] In the present invention, controlling the solid phase reaction temperature of the doped titanium pyrophosphate precursor and the lithium source can transform the titanium pyrophosphate into lithium titanium phosphate, which is beneficial to the transformation of the crystal form. If the temperature is too low, the crystal form cannot be changed, and if the temperature is higher than this, the uniformity and morphology of the particle size cannot be controlled.

[0020] As an optional embodiment, in the method provided by the present invention, the particle size of the doped titanium pyrophosphate precursor is 0.1-1 μm.

[0021] As an optional embodiment, 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 high-energy ball milling reaction, high-temperature and high-pressure hydrothermal reaction, coprecipitation reaction, condensation reflux reaction or aging reaction.

[0022] As an optional embodiment, in the method provided by the present invention, the molar ratio of phosphorus to titanium in the phosphorus source and the titanium source is ≥1.5, the molar ratio of M in the compound containing the doped ion M to the titanium in the compound titanium hydrogen phosphate is 0.5-10:1; the molar ratio of lithium in the lithium source to titanium in the doped titanium pyrophosphate is 0.5-1.5:1.

[0023] As an optional embodiment, 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.

[0024] As an optional embodiment, 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.

[0025] As an optional embodiment, 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.

[0026] As an optional embodiment, in the method provided by the present invention, the molecular formula of the doped titanium pyrophosphate precursor coated with the titanium-containing compound is M x Ti 1-x P2O7, where 0≤X≤0.7, M is Mg 2+ 、Al 3+ Sn 4+ 、Zr 4+ , Y 3+ and Hf 4+ One or more of .

[0027] As an optional embodiment, in the method provided by the present invention, the doping ion M of the doping compound is selected from Mg 2+ 、Al 3+ Sn 4+ 、Zr 4+ , Y 3+ and Hf 4+ One or more of .

[0028] As an optional embodiment, in the method provided by the present invention, the mixing method of the doped titanium pyrophosphate precursor coated with the titanium compound and the lithium source is selected from one of a high-speed mixer, a spiral ribbon mixer, an air flow mixer, a high-energy ball mill or a sand mill.

[0029] Further, high energy ball milling or sand milling is preferred.

[0030] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention adopts a liquid phase method for preparation, which avoids the problem of potting sticking in the traditional solid phase method and solves the problem of large-scale production.

[0031] (2) In the present invention, doped titanium pyrophosphate is prepared by liquid phase reaction, and liquid phase coating is performed on it. After further heat treatment, a solid solution (doped titanium pyrophosphate precursor coated with a titanium compound) with uniform element distribution and tight coating layer bonding is formed, which reduces the reaction activation energy, ensures the uniformity of the reactants, and improves the phase purity of the solid electrolyte product.

[0032] (3) The present invention first prepares a doped titanium pyrophosphate precursor coated with a titanium compound, and heat treats it to form a stable solid solution. The precursor is used to prepare lithium titanium phosphate, and no further titanium source needs to be added in the solid phase reaction to achieve lithium titanium phosphate Li 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.

[0033] (4) The present invention prepares lithium titanium phosphate through a precursor, thereby reducing the number of reaction components in the sintering process, especially the number of components in the sintering process of preparing a multi-doped lithium titanium phosphate solid electrolyte, and reducing 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 obtained lithium titanium phosphate product has high sphericity and good uniformity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 This is a physical picture of the lithium titanium phosphate product prepared in Example 3 of the present invention; Figure 2 This is a physical picture of the lithium titanium phosphate product prepared in Comparative Example 1 of the present invention; Figure 3 This is a SEM image of the doped titanium pyrophosphate prepared in Example 1 of the present invention; Figure 4 This is a SEM image of the doped titanium pyrophosphate prepared in Example 2 of the present invention; Figure 5 This is a SEM image of the doped titanium pyrophosphate prepared in Example 3 of the present invention; Figure 6 This is a SEM image of lithium titanium phosphate prepared in Example 1 of the present invention; Figure 7 This is a SEM image of lithium titanium phosphate prepared in Example 2 of the present invention; Figure 8 This is a SEM image of lithium titanium phosphate prepared in Example 3 of the present invention; Fig. 9 This is a SEM image of lithium titanium phosphate prepared in Example 4 of the present invention; Fig.10 This is a SEM image of lithium titanium phosphate prepared in Example 5 of the present invention; Fig.11 This is a SEM image of lithium titanium phosphate prepared in Example 6 of the present invention; Fig.12 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 1 of the present invention; Fig.13 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 2 of the present invention; Fig.14 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 3 of the present invention; Fig.15 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 4 of the present invention; Fig.16 This is a SEM image of lithium titanium phosphate prepared in Comparative Example 5 of the present invention; Fig.17 The XRD diagram of the doped titanium pyrophosphate prepared in Example 1, Example 2 and Example 3 of the present invention; Fig.18 XRD diagram of lithium titanium phosphate prepared in Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 of the present invention; Fig.19 This is the XRD diagram of the lithium titanium phosphate prepared in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0038] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0039] Example 1 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 80 g of 15% H3PO4 aqueous solution and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to <1.

[0040] (2) The phosphoric acid aqueous solution with pH < 1 was placed in a stirred solution at 60°C at a stirring speed of 800 rpm / min, and 10 g of TiOSO4 was slowly added into the liquid phase for reaction for 3 h. The pH change during the reaction was monitored to ensure that the pH of the system was ≤ 2. After the reaction was completed, Ti(HPO4)2·H2O was prepared by filtering.

[0041] (3) Add deionized water to prepare a Ti(HPO4)2·H2O aqueous solution in a ratio of 10:1, and wash repeatedly until the pH is ≥5.

[0042] (4) Add 5 g of fully dried Ti(HPO4)2·H2O and 35 g of 0.2 mol / L Al(NO3)3·9H2O aqueous solution respectively, react at 60°C for 3 h, and stir at 1200 rpm / min.

[0043] (5) After the above reaction for 3 h, add 0.2 g of TiO2 (primary particle size ≤ 60 nm) and continue the reaction for 3 h at a stirring speed of 1200 rpm / min.

[0044] (6) The reactants were filtered, washed, and dried at 120° C. for 10 h. The dried products were heat treated at 450° C. for 4 h to obtain a doped titanium pyrophosphate precursor.

[0045] (7) Add 5.2 g of doped titanium pyrophosphate precursor and 0.85 g of LiOH respectively, transfer to high-energy ball mill, ball-to-material ratio 4:1, ball mill speed 800 rpm / min, time for 4 h, rest time 60 s. After the ball milling is completed, transfer to heat treatment at 600 ° C for 4 h to obtain lithium titanium phosphate product.

[0046] Example 2 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 16.21 g TiO2 and 41.29 g H3PO4 (85 wt%) respectively, and the pH of the reaction system is less than 1.

[0047] (2) The weighed raw materials were transferred into a high-energy ball mill and mixed evenly. The mixture was ball milled at normal pressure and 25°C with a ball-to-material ratio of 4:1 and a ball milling speed of 800 rpm / min for 36 hours with an interval of 60 seconds. After the reaction was completed, the mixture was filtered.

[0048] (3) Deionized water was added to prepare an aqueous solution with a ratio of 10:1, and the deionized water was repeatedly washed until the pH value was 5, and then dried to obtain Ti(HPO4)2·H2O.

[0049] (4) Add 5 g of fully dried Ti(HPO4)2·H2O and 35 g of 0.2 mol / L Al(NO3)3·9H2O aqueous solution respectively, react at 60°C for 3 h, and stir at 1200 rpm / min.

[0050] (5) After the above reaction for 3 h, add 0.2 g of TiO2 (primary particle size ≤ 60 nm) and continue the reaction for 3 h at a stirring speed of 1200 rpm / min.

[0051] (6) The reactants were filtered, washed, and dried at 120°C for 10 h. The dried products were heat treated at 600°C for 4 h to obtain a doped titanium pyrophosphate precursor.

[0052] (7) 5.2 g of doped titanium pyrophosphate precursor and 1.3 g of Li2CO3 were added respectively, and the mixture was transferred to a high-speed mixer for mixing. After the mixing was completed, the mixture was heat treated at 700°C for 4 h to obtain a lithium titanium phosphate product.

[0053] Example 3 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 140 g of 10% NH4H2PO4 aqueous solution and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0054] (2) The above-mentioned phosphoric acid aqueous solution with pH = 0.8 was placed in a stirred state at 160°C at a stirring speed of 1600 rpm / min, and 10 g of TiOSO4 was slowly added. The pH change during the reaction was monitored to ensure that the pH of the system was ≤ 2. The liquid phase reaction was performed for 3 hours and then filtered.

[0055] (3) Deionized water was added to prepare an aqueous solution with a ratio of 10:1, and the deionized water was repeatedly washed until the pH value was 5, and then dried to obtain Ti(HPO4)2·H2O.

[0056] (4) Add 5 g of fully dried Ti(HPO4)2·H2O and 35 g of 0.2 mol / L Al(NO3)3·9H2O aqueous solution respectively, react at 120°C for 3 h, and stir at 1600 rpm / min.

[0057] (5) After the above reaction for 3 h, add 0.2 g of TiO2 (primary particle size ≤ 60 nm) and continue the reaction for 3 h at a stirring speed of 2400 rpm / min.

[0058] (6) The reactants were filtered, washed, and dried at 120°C for 10 h. The dried products were heat treated at 600°C for 4 h to obtain a doped titanium pyrophosphate precursor.

[0059] (7) 5.2 g of doped titanium pyrophosphate precursor and 1.3 g of Li2CO3 were added respectively, and the mixture was mixed in a high-speed mixer. After mixing, the mixture was heat treated at 800 °C for 4 h to obtain a lithium titanium phosphate product.

[0060] Example 4 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 140 g of 10% NH4H2PO4 aqueous solution and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0061] (2) The above-mentioned phosphoric acid aqueous solution with pH = 0.8 was placed in a stirred state at 160°C at a stirring speed of 1600 rpm / min, and 10 g of TiOSO4 was slowly added. The pH change during the reaction was monitored to ensure that the pH of the system was ≤ 2. The liquid phase reaction was performed for 3 hours and then filtered.

[0062] (3) Deionized water was added to prepare an aqueous solution with a ratio of 10:1, and the deionized water was repeatedly washed until the pH value was 5, and then dried to obtain Ti(HPO4)2·H2O.

[0063] (4) Add 5 g of fully dried Ti(HPO4)2·H2O and 5.6 g of 1 mol / L Sn(SO4)2 aqueous solution respectively, react at 120°C for 3 h, and stir at 1600 rpm / min.

[0064] (5) After the above reaction for 3 h, 0.25 g of TiO(OH)2 was added and the reaction was continued for 3 h with a stirring speed of 2400 rpm / min.

[0065] (6) The reactants were filtered, washed, and dried at 120°C for 10 h. The dried products were heat treated at 600°C for 4 h to obtain a doped titanium pyrophosphate precursor.

[0066] (7) 5.2 g of doped titanium pyrophosphate precursor and 0.85 g of LiOH were added respectively, and the mixture was mixed in a high-speed mixer. After mixing, the mixture was heat treated at 800 °C for 4 h to obtain a lithium titanium phosphate product.

[0067] Example 5 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 140 g of 10% NH4H2PO4 aqueous solution and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to 0.8.

[0068] (2) Place the above-mentioned phosphoric acid aqueous solution with pH = 0.8 at 160°C and stir at a stirring speed of 1600 rpm / min, slowly add 10 g of TiOSO4, monitor the pH change during the reaction to ensure that the pH of the system is ≤ 2, and filter after the liquid phase reaction for 3 hours.

[0069] (3) Deionized water was added to prepare an aqueous solution with a ratio of 10:1, and the deionized water was repeatedly washed until the pH value was 5, and then dried to obtain Ti(HPO4)2·H2O.

[0070] (4) Add 5 g of fully dried Ti(HPO4)2·H2O, 17.5 g of 0.2 mol / L Al(NO3)3·9H2O aqueous solution, and 6 g of 0.5 mol / L MgCl2 aqueous solution, respectively, and react at 120°C for 3 h with a stirring speed of 1600 rpm / min.

[0071] (5) After the above reaction for 3 h, 0.25 g of TiO(OH)2 was added and the reaction was continued for 3 h with a stirring speed of 2400 rpm / min.

[0072] (6) The reactants were filtered, washed, and dried at 120°C for 10 h. The dried products were heat treated at 600°C for 4 h to obtain a doped titanium pyrophosphate precursor.

[0073] (7) 5.2 g of doped titanium pyrophosphate precursor and 0.85 g of LiOH were added respectively and mixed in a high-speed mixer. After mixing, the mixture was heat treated at 800 °C for 4 h to obtain a lithium titanium phosphate product.

[0074] Example 6 A method for preparing lithium titanium phosphate using a doped titanium pyrophosphate precursor comprises the following steps: (1) Weigh 80 g of 15% H3PO4 aqueous solution and add an appropriate amount of concentrated sulfuric acid aqueous solution to adjust the pH of the phosphoric acid aqueous solution to <1.

[0075] (2) The phosphoric acid aqueous solution with a pH value less than 1 was placed in a stirred state at 60°C at a stirring speed of 800 rpm / min, and 10 g of TiOSO4 was slowly added. The pH change during the reaction was monitored to ensure that the pH value of the system was ≤ 2. The liquid phase reaction was carried out for 3 h. After the reaction was completed, Ti(HPO4)2·H2O was prepared by filtering.

[0076] (3) Add deionized water to prepare a Ti(HPO4)2·H2O aqueous solution in a ratio of 10:1, and wash repeatedly until the pH is ≥5.

[0077] (4) Add 5 g of fully dried Ti(HPO4)2·H2O and 35 g of 0.2 mol / L Al(NO3)3·9H2O aqueous solution respectively, react at 60°C for 3 h, and stir at 1200 rpm / min.

[0078] (5) After the above reaction was continued for 3 h, 0.68 g of Ti(OCH(CH3)2)4 was added and the reaction was continued for 3 h with a stirring speed of 1200 rpm / min.

[0079] (6) The reactants were filtered, washed, and dried at 120°C for 10 h. The dried products were heat treated at 600°C for 4 h to obtain a doped titanium pyrophosphate precursor.

[0080] (7) Add 5.2 g of doped titanium pyrophosphate precursor and 1.3 g of Li2CO3 respectively, transfer to high-energy ball mill, ball-to-material ratio 4:1, ball milling speed 800 rpm / min, time 4 h, rest time 60 s. After the ball milling is completed, transfer to heat treatment at 900 °C for 4 h to obtain lithium titanium phosphate product.

[0081] Comparative Example 1 A method for preparing a lithium titanium phosphate product by a solid phase method comprises the following steps: (1) Weigh 33.67 g Li2CO3, 10.71 g Al2O3, 94.85 g TiO2, 242.2 g NH3H2PO4, and 1525.72 g C3H8O respectively.

[0082] (2) The weighed raw materials are transferred into a high-energy ball mill for mixing at a ball milling speed of 800 rpm / min for 6 hours with an interval of 60 seconds.

[0083] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120°C for 10 h to prepare precursor 1.

[0084] (4) The precursor 1 is transferred into a sintering furnace and heat treated at 900°C for 4 hours to obtain a lithium titanium phosphate product.

[0085] Comparative Example 2 A method for preparing lithium titanium phosphate using titanium pyrophosphate as a raw material comprises the following steps: (1) Weigh 10.56 g Li2CO3, 3.36 g Al2O3, 3.32 g TiO2, 73.20 g TiP2O7, and 20 g C3H8O respectively.

[0086] (2) The weighed raw materials are transferred into a high-energy ball mill for mixing. The ball milling speed is 800 rpm / min, and the ball-to-material ratio is 4:1. The mixing time is 6 hours, and the interval time is 60 seconds.

[0087] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120 °C for 10 h to prepare precursor 1.

[0088] (4) The precursor 1 is transferred into a sintering furnace and heat treated at 700°C for 4 hours to obtain a lithium titanium phosphate product.

[0089] Comparative Example 3 A method for preparing lithium titanium phosphate using titanium pyrophosphate as a raw material comprises the following steps: (1) Weigh 10.56 g Li2CO3, 3.36 g Al2O3, 3.32 g TiO2, 73.20 g TiP2O7, and 20 g C3H8O respectively.

[0090] (2) The weighed raw materials are transferred into a high-energy ball mill for mixing. The ball milling speed is 800 rpm / min, and the ball-to-material ratio is 4:1. The milling time is 6 hours, and the interval time is 60 seconds.

[0091] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120 °C for 10 h to prepare precursor 1.

[0092] (4) The precursor 1 is transferred into a sintering furnace and heat treated at 900°C for 4 hours to obtain a lithium titanium phosphate product.

[0093] Comparative Example 4 A method for preparing lithium titanium phosphate using titanium pyrophosphate as a raw material comprises the following steps: (1) Weigh 10.56 g Li2CO3, 1.68 g Al2O3, 1.57 g MgCl2, 3.32 g TiO2, 73.20 g TiP2O7, and 20 g C3H8O respectively.

[0094] (2) The weighed raw materials are transferred into a high-energy ball mill for mixing. The ball milling speed is 800 rpm / min, and the ball-to-material ratio is 4:1. The mixing time is 6 hours, and the interval time is 60 seconds.

[0095] (3) The high-energy ball milling product was transferred into a vacuum drying oven and dried at 120 °C for 10 h to prepare precursor 1.

[0096] (4) The precursor 1 is transferred into a sintering furnace and heat treated at 900°C for 4 hours to obtain a lithium titanium phosphate product.

[0097] Comparative Example 5 A method for preparing lithium titanium phosphate using titanium pyrophosphate as a raw material comprises the following steps: The difference from Example 6 is that the heat treatment temperature in step (7) is 1000° C., and the remaining steps are the same as in Example 6.

[0098] The lithium titanium phosphate prepared in the embodiment and the comparative example was tested. Figure 1 and Figure 2 It can be seen that compared with the traditional solid-phase synthesis process of lithium titanium phosphate, the process of preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor proposed in the present invention does not produce agglomeration in the product, and no product-sagger reaction occurs, thus solving the problem of sagger sticking in the synthesis of lithium titanium phosphate solid electrolyte. Figure 3 , Figure 4 , Figure 5 According to the electron microscopy observation results shown, Example 1, Example 2, and Example 3 respectively prepared nanoscale and submicron-scale doped titanium pyrophosphate precursors based on different liquid phase reaction conditions, with a particle size of 0.1-1 μm, achieving precise control of the doped titanium pyrophosphate precursor; further, based on the above-mentioned precursors of different particle sizes and controlling the temperature in the preferred range of 450°C-800°C, a Figure 6 , Figure 7 , Figure 8 The lithium titanium phosphate solid electrolytes with uniform particles and high sphericity of different sizes are compared with the solid electrolytes prepared by the process methods of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. Fig.12 , Fig.13 , Fig.14 , Fig.15 The blocky and non-uniformly sized lithium titanium phosphate solid electrolyte products displayed have been significantly improved, and the precursor particle size and heat treatment reaction temperature can be adjusted based on the different particle size requirements of different application scenarios to achieve customized production of lithium titanium phosphate solid electrolytes from nanoscale to micrometer scale. Fig.11 and Fig.16The SEM characterization results show that when the heat treatment temperature is further increased to 900°C, obvious connections begin to appear between the primary particles. When the heat treatment temperature is increased to 1000°C, the product prepared by the preparation method of the present invention begins to agglomerate. It is analyzed that when the heat treatment temperature is ≥900°C, the temperature has a major influence on the solid phase reaction process. The particle size of the primary particles continues to grow and connect into blocks at high temperatures. Therefore, only by controlling the heat treatment temperature at a lower temperature can the particle size and morphology of the product be accurately controlled. Example 3, Example 4, and Example 5 are based on the same doped titanium pyrophosphate preparation process and heat treatment conditions to prepare Al 3+ Sn 4+ 、Al 3+ With Mg 2+ Co-doped lithium titanium phosphate solid electrolyte, according to Figure 8 , Fig. 9 , Fig.10 The three products have no significant difference in primary morphology and particle size, indicating that the preparation method according to the present invention can not only achieve the reaction of different M (M is Mg 2+ 、Al 3+ Sn 4+ 、Zr 4+ , Y 3+ and Hf 4+ The particle size of lithium titanium phosphate solid electrolyte doped with one of the metal elements can be precisely controlled, and the particle size of lithium titanium phosphate solid electrolyte doped with multiple metal elements can also be precisely controlled. Fig.18 It can be seen that the lithium titanium phosphate solid electrolytes obtained by the methods described in the embodiments of the present invention are all high-purity and free of other impurities. In the preparation method described in Comparative Example 5, obvious original lithium titanium phosphate impurities appear. Analysis shows that this may be related to the volatilization of P element or Li element during the high-temperature solid phase reaction. The experimental results further show that the lithium titanium phosphate solid electrolyte prepared by the preparation method of the present invention should be controlled to be carried out at a lower heat treatment temperature; Fig.18 and Fig.19 The main difference between the sintered product phases of Example 2 and Comparative Example 2 is that Example 2 prepares lithium aluminum titanium phosphate based on the doped titanium pyrophosphate described in the present invention, while Comparative Example 2 prepares lithium titanium phosphate based on titanium pyrophosphate that is not specifically coated and doped. The above differences further determine the number of reactants in the solid phase heat treatment process and the size and uniformity of the reactant particle size. Combining the preparation process and product phase results described in Example 5 and Comparative Example 3, under the same 700°C heat treatment conditions, Example 2 and Example 5 successfully prepared high-purity, impurity-free lithium titanium phosphate solid electrolyte and Mg 2+ 、Al 3+The synergistically doped titanium lithium phosphate solid electrolyte, while the products in Comparative Examples 2 and 3 have significant titanium dioxide and lithium phosphate impurities, which is a manifestation of uniform reaction process and no additional components. The heat treatment temperature is further increased to 900 ° C. Although the impurity strength is improved, it still exists. Analysis shows that the reason for the difference in the above results is mainly due to the obtained doped titanium pyrophosphate precursor with solid solution properties. On the one hand, the particle size of the precursor product is effectively controlled, the specific surface area is increased, and the diffusion and chemical reaction capacity during the solid phase reaction are enhanced. On the other hand, the number of reactants in the solid phase reaction is reduced, the uniformity of the reaction is improved, and the mass transfer process of the reaction particles during the reaction is improved, thereby ensuring uniform phase formation under low temperature conditions, which not only ensures the high purity of the product, but also achieves precise control of the particle size and morphology of the product.

[0099] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling 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: The following steps are involved: S1, mixing a phosphorus source and a titanium source by a liquid phase method, the reaction temperature is 25-180°C, the pH of the reaction system is 0-2, and after the reaction is completed, a compound titanium hydrogen phosphate is obtained and washed; S2, adding a doping compound to the compound titanium hydrogen phosphate washed in step S1 to carry out a liquid phase ion exchange reaction, adding a titanium source after the reaction is completed to carry out liquid phase coating, and after the coating is completed, treating to obtain a doped titanium pyrophosphate precursor coated with a titanium compound; S3, uniformly mixing the doped titanium pyrophosphate precursor obtained in step S2 with a lithium source, and then performing a high-temperature heat treatment to obtain lithium titanium phosphate.

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° C., and the stirring speed during the reaction is ≥800 rpm / min.

5. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that: In step S2, after coating, the coating is washed, dried and heat treated at a temperature of 450-800°C.

6. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that: In step S3, the temperature of high temperature heat treatment of the doped titanium pyrophosphate precursor and the lithium source is 600-900°C.

7. 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.

8. 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 of the phosphorus source and the titanium source is selected from one of high-energy ball milling reaction, high-temperature and high-pressure hydrothermal reaction, coprecipitation reaction, condensation reflux reaction or aging reaction.

9. 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 M in the compound containing doped ions M to titanium in the compound titanium hydrogen phosphate is 0.5-10:1; the molar ratio of lithium in the lithium source to titanium in the doped titanium pyrophosphate is 0.5-1.5:

1.

10. The method for preparing lithium titanium phosphate using doped titanium pyrophosphate as a precursor according to claim 1, characterized in that: The doping ion M of the doping compound is selected from Mg 2+ 、Al 3+ Sn 4+ 、Zr 4+ , Y 3+ and Hf 4+ One or more of; 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, C 16 H 36 O4Ti and Ti(OCH(CH3)2)4 or more; the lithium source is selected from one or more of LiOH, Li3PO4, Li2CO3, LiCl, CH3COOLi, LiH2PO4.

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