Tin-doped lithium titanium phosphate and its preparation method and application

Abstract

The present invention discloses a tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix, wherein the lithium titanium phosphate matrix is ​​doped with tin, and the doping amount of the tin element is controlled so that the molecular formula of the tin-doped lithium titanium phosphate is LiSn x Ti 2‑x (PO4)3, where x is 0.1-0.3. The present invention also provides a preparation method and application of the above-mentioned tin-doped lithium titanium phosphate. The tin-doped lithium titanium phosphate of the present invention utilizes tin to dope lithium titanium phosphate, and through optimization of the preparation method, it is beneficial to improve the capacity retention rate and cycle stability of lithium titanium phosphate.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and in particular relates to doped lithium titanium phosphate and a preparation method and application thereof. Background Art

[0002] Lithium titanium phosphate is a commonly used negative electrode material in aqueous lithium-ion batteries. Its structure is stable, and the lattice volume changes little when lithium is inserted and removed. Therefore, the material is not easy to break after repeated charge and discharge. Secondly, the material has three-dimensional ion transmission channels, and therefore has high ionic conductivity. In addition, the theoretical specific capacity of the material is 138mAh / g, which is easy to match with positive electrode materials such as lithium manganese oxide. More importantly, the lithium insertion potential of the material is within the stable voltage window of the aqueous electrolyte, making it very suitable for use as a negative electrode material for aqueous lithium-ion batteries.

[0003] Currently, researchers mostly use the sol-gel method for material synthesis, which has advantages such as low calcination temperature, short calcination time, and small product particle size. The sol-gel method uses tetrabutyl titanate as the titanium source, which is relatively expensive and easily hydrolyzed by water vapor to form amorphous titanium hydroxide precipitates, making it difficult to store. Therefore, this method faces certain resistance in industrial production. Furthermore, pure-phase lithium titanium phosphate has low conductivity, and the corresponding aqueous battery has poor cycle stability. Existing technologies have not been able to effectively address this problem with pure-phase lithium titanium phosphate.

[0004] Therefore, providing a lithium titanium phosphate that is easy to apply industrially and has a high capacity retention rate and cycle life is of great significance for the large-scale promotion and application of lithium titanium phosphate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a tin-doped lithium titanium phosphate that is easy to industrialize and has a high capacity retention rate and cycle life, as well as its preparation method and application. To solve the above technical problems, the technical solution proposed by the present invention is as follows:

[0006] A tin-doped lithium titanium phosphate comprises a lithium titanium phosphate matrix, wherein the lithium titanium phosphate matrix is ​​doped with tin, and the doping amount of the tin element is controlled so that the molecular formula of the tin-doped lithium titanium phosphate is LiSn x Ti 2-x (PO4)3, wherein x is 0.1-0.3, and the particle size of the lithium titanium phosphate matrix is ​​100-190nm.

[0007] As a general technical concept, the present invention also provides a method for preparing tin-doped lithium titanium phosphate, comprising the following steps:

[0008] (1) using titanium sulfate as a titanium source to prepare a wet-based solid phase product, titanium hydroxide;

[0009] (2) adding the wet-based solid product titanium hydroxide and the lithium source, tin source, and phosphorus source newly prepared in step (1) to anhydrous ethanol and continuously stirring to form a suspension;

[0010] (3) Drying the suspension in step (2) to obtain a powder product (white powder), calcining the powder product, and grinding to obtain the tin-doped lithium titanium phosphate.

[0011] In the above preparation method, preferably, the preparation of the wet-based solid-phase product titanium hydroxide using titanium sulfate as a titanium source includes the following steps: adding titanium sulfate to deionized water to dissolve to obtain a colorless transparent solution, stirring thoroughly, then adding ammonia water and continuously stirring to obtain a suspension, and separating the solid and liquid to obtain the wet-based solid-phase product titanium hydroxide.

[0012] In the above preparation method, preferably, the stirring time is controlled to be 12-18h when fully stirring, the molar ratio of titanium sulfate to ammonia water is controlled to be 1: (6-8), a peristaltic pump is used for feeding when adding ammonia water, and the feeding rate is controlled to be 0.1-0.3mL / min. After the feeding is completed, stirring is continued for 2-3h.

[0013] In the present invention, titanium sulfate is a commonly used raw material in the titanium dioxide industry. It has advantages such as stable chemical properties, low cost, and ease of industrialization. To facilitate the full dissolution of titanium sulfate, the stirring time when adding titanium sulfate to deionized water is preferably 12-18 hours. Ammonia water can react with titanium sulfate to produce titanium hydroxide precipitate, as shown in the following formula (1):

[0014] Ti(SO4)2+4NH3·H2O→Ti(OH)4↓+2(NH4)2SO4 formula (1);

[0015] Aqueous ammonia is highly volatile, and considering the slow feed rate of ammonia, an excess of ammonia should be used. A peristaltic pump can achieve precise control of the feed rate or feed time. A slow and uniform feed rate helps to obtain a precipitate with fine particles. If the feed rate is too fast, a lumpy precipitate may be obtained, which may encapsulate the solvent, making it impossible to obtain a fine and uniform precipitate, resulting in an uneven particle size of the final product, which in turn affects the electrochemical performance of the corresponding battery. Therefore, the feed rate should be set within the above range. When separating solid and liquid, it is preferred to use a sand core filtration device for filtration, and the filter membrane is a water-based filter membrane. If an ordinary filtration device is used, a large amount of material will be lost, and the target product cannot be obtained.

[0016] In the above preparation method, preferably, the tin source is tetrabutyltin; the lithium source is one or more of lithium carbonate, lithium hydroxide, or lithium acetate; and the phosphorus source is phosphoric acid. When phosphoric acid is used as the phosphorus source, it decomposes only into water and pyrophosphoric acid during calcination, without producing toxic gases. However, when ammonium dihydrogen phosphate is used as the phosphorus source, ammonia gas is produced during high-temperature calcination, corroding calcination equipment and polluting the environment.

[0017] In the above preparation method, preferably, when the wet-based solid phase product titanium hydroxide, lithium source, tin source and phosphorus source are mixed, the molar ratio of Li:Sn:Ti:P is controlled to be 1:x:2-x:3, wherein x is 0.1-0.3.

[0018] During the charging process, lithium ions are embedded in the lithium titanium phosphate lattice, and the titanium element is reduced from tetravalent to trivalent, and the electrochemical reaction occurs as shown in the following formula (2):

[0019] LiTi2(PO4)3+e - +Li + →Li3Ti2(PO4)3 formula (2);

[0020] Trivalent titanium ions have poor chemical stability and are easily oxidized to tetravalent titanium by oxygen and water in the system. The chemical reaction is shown in the following formula (3):

[0021] Li3Ti2(PO4)3+2H2O+0.5O2→LiTi2(PO4)3+2LiOH+H2O formula (3);

[0022] This reaction causes Li3Ti2(PO4)3 to undergo delithiation and regenerate LiTi2(PO4)3. The reaction rate of reaction (3) is relatively fast, and the potential of LiTi2(PO4)3 is higher than that of Li3Ti2(PO4)3. Therefore, the existence of this reaction will cause the battery voltage to decrease. In order to reach the charge cut-off voltage, the positive electrode may undergo excessive delithiation, thereby reducing the cycle stability of the battery. An appropriate amount of tin doping can well weaken this phenomenon. The main reason is that its chemical stability is better than that of trivalent titanium ions, and the bond energy of Sn-OP bond is stronger. Therefore, tin doping can reduce the reaction degree of formula (3), thereby improving the cycle stability of the battery. However, too high a tin content will lead to the generation of impure phases Li8SnO6 or Li3PO4. These impure phases do not have suitable lithium ion deintercalation channels, thereby reducing the battery cycle stability. Therefore, preferably, the optimal doping range x of tin element is 0.1-0.3.

[0023] In the above preparation method, preferably, in step (2), the stirring is continued at room temperature and pressure. The present invention utilizes the strong adsorption of freshly prepared titanium hydroxide and the electrostatic attraction of anions and cations in the liquid phase to prepare lithium titanium phosphate. It does not require the high temperature, high pressure, and strong convection environment required for the hydrothermal reaction, and can be carried out at room temperature and pressure, thus having the advantages of low energy consumption and high safety.

[0024] In the above preparation method, preferably, the powder product is first ground and tableted before being calcined. In the flaky sample obtained by tableting, the contact area between the components is increased, the components are closer together, and the long-range diffusion distance of the components during calcination is reduced. The pressing treatment before calcination is conducive to the synthesis of lithium titanium phosphate at a lower temperature and in a shorter time. After calcination, a product with more uniform particle size and more regular morphology can be obtained, thereby improving the battery cycle stability.

[0025] In the above preparation method, preferably, the tableting process is performed using a hydraulic press, and the pressure is controlled to be 20-30 MPa.

[0026] In the above preparation method, preferably, the calcination temperature is controlled at 750-850°C, the heating rate is 5-10°C / min, the holding time is 5-10 hours, and the calcination atmosphere is an inert atmosphere. If the calcination temperature is too low or the calcination time is too short, the raw materials will not obtain sufficient activation energy and the target material cannot be prepared. If the temperature is too high, the lithium titanium phosphate lattice may be damaged, resulting in the formation of impurities.

[0027] As a general technical concept, the present invention also provides a use of the above-mentioned tin-doped lithium titanium phosphate as a negative electrode material in an aqueous lithium-ion battery.

[0028] Our research shows that the electrical conductivity of pure phase lithium titanium phosphate is low, and the corresponding aqueous battery has poor cycle stability. Therefore, in the present invention, we doped lithium titanium phosphate with metals to improve its existing problems. Metal doping can be divided into lithium doping and titanium doping. The core of the capacity decay of lithium titanium phosphate lies in the poor chemical stability of trivalent titanium ions. Therefore, titanium doping is more conducive to improving capacity retention and cycle stability. The ionic radius of tin is similar to that of titanium ions, it occupies the titanium site in the crystal lattice, and has stable chemical properties. After doping, it can form a Sn-OP bond with stronger bond energy. Therefore, the use of tin element for doping in the present invention can improve the capacity retention and cycle stability of lithium titanium phosphate.

[0029] The preparation method of the present invention can obtain a lithium titanium phosphate negative electrode material with a particle size of 100-190nm. The present invention uses titanium sulfate as a titanium source, ammonia water as a precipitant, and adopts a peristaltic pump to feed the ammonia water to obtain a newly prepared wet-based solid-phase product titanium hydroxide with uniform particle size. The newly prepared wet-based solid-phase product titanium hydroxide and other raw materials are then placed in anhydrous ethanol and stirred. The adsorption properties of the newly prepared wet-based solid-phase product titanium hydroxide are utilized to preferentially adsorb lithium and tin metal cations in the system, and phosphate ions are adsorbed on the outer layer of the metal cations as counter ions, thereby increasing the dispersion and uniformity of each component (such as Figure 1 (As shown). Using tetrabutyltin as a tin source for doping improves the electrochemical performance of the material, enhances the unit cell structural stability of the negative electrode material, prevents overcharging of the positive electrode material, and improves the battery's cycle performance and rate capability. Tablet sintering reduces the long-range diffusion distance of various species, thereby reducing the calcination time and temperature, while also making the product particle morphology more regular and uniform. The product prepared using the method of the present invention has a high capacity retention rate and cycle life, while also being easy to industrialize, improving the shortcomings of current lithium titanium phosphate.

[0030] In addition, it should be emphasized that the reaction principle of the present invention is to synthesize tin-doped lithium titanium phosphate at room temperature and pressure through the adsorption performance of the newly prepared wet-based solid-phase product titanium hydroxide and the electrostatic attraction of anions and cations. This method has high requirements for titanium hydroxide. The newly prepared wet-based solid-phase product titanium hydroxide in step (1) has strong adsorption capacity and uniform particle size, which is conducive to subsequent synthesis reactions. Moreover, the process of synthesizing tin-doped lithium titanium phosphate using the present invention has good dispersion uniformity of elements in the final product and a relatively small product particle size, which is conducive to improving the electrochemical performance of the product. In particular, the good uniformity of the distribution of doping elements significantly improves the product performance, and the cycle stability and capacity retention rate of the product are relatively better.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] 1. The tin-doped lithium titanium phosphate of the present invention utilizes tin to dope lithium titanium phosphate, which helps improve the capacity retention and cycling stability of the lithium titanium phosphate. At a 1C rate, the initial discharge specific capacity of its aqueous battery can reach over 100 mAh / g. After 400 charge-discharge cycles, its specific capacity exceeds 80 mAh / g, the capacity retention exceeds 80%, and the average coulombic efficiency exceeds 95%. In terms of rate performance, the lithium titanium phosphate exhibits good rate specific capacity recovery after charge and discharge at different high rates.

[0033] 2. The preparation method of the present invention uses titanium sulfate as a titanium source. Titanium sulfate has low cost and is a common raw material in the titanium dioxide industry, and is easy to industrialize.

[0034] 3. The preparation method of the present invention places the newly prepared wet-based solid phase product titanium hydroxide and other raw materials in anhydrous ethanol and stirs them, utilizing the adsorption properties of titanium hydroxide, increasing the mixing uniformity of the components, and facilitating the production of products with better electrochemical properties.

[0035] 4. The preparation method of the present invention is simple in process, easy to operate, easy to realize industrial application, and has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0037] Figure 1 This is a schematic diagram of the adsorption of other raw materials using the wet solid phase product titanium hydroxide in the present invention.

[0038] Figure 2 This is the XRD pattern of LTP-1 in Example 1.

[0039] Figure 3 This is the cycling performance diagram of LTP-2 in Example 2 at 1C rate.

[0040] Figure 4 This is the first charge and discharge curve of LTP-3 in Example 3 at 1C rate.

[0041] Figure 5 This is the mapping diagram of LTP-4 in Example 4. DETAILED DESCRIPTION

[0042] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0043] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical 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.

[0044] 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.

[0045] Example 1:

[0046] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.1 Ti 1.9 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0047] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0048] (1) Weigh 4.560 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 12 h. Add 9.975 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.1 mL / min. Continue stirring for 2 h after the addition is complete to obtain suspension 1.

[0049] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.372 g of lithium carbonate, 3.458 g of phosphoric acid (concentration 85%) and 0.347 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0050] (3) The ground white powder was tableted using a hydraulic press with a pressure of 20 MPa to obtain a flake sample;

[0051] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 750 °C, a heating rate of 5 °C / min, and a constant temperature time of 5 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.1 Ti 1.9 (PO4)3; recorded as LTP-1.

[0052] The battery assembly and test conditions are as follows:

[0053] (1) The LTP-1 electrode material prepared in this example was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, and evenly coated on a 20 μm thick stainless steel foil with a thickness of 100 μm. The mixture was then vacuum-dried at 80°C for 12 h and finally pressed into a circular electrode sheet with a diameter of 12 mm using a tablet press.

[0054] (2) 100 μL of 2 mol / L Li2SO4 was used as the electrolyte. Commercial LiMn2O4 was used as the positive electrode material. Commercial LiMn2O4 was mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1, and evenly coated on a 20 μm thick stainless steel foil with a thickness of 130 μm. It was then vacuum-dried at 80°C for 12 h and finally pressed into a circular electrode sheet with a diameter of 12 mm using a tablet press. Glass fiber filter paper (GF / D) was used as the separator, and the prepared lithium titanium phosphate was used as the negative electrode material to assemble into a CR2016 button battery.

[0055] (3) At 25°C, the button cell was subjected to constant current charge and discharge tests and rate tests using the Land-CT2001A battery testing system from Wuhan Landian Company. The test voltage range was 0.6-1.8V.

[0056] Depend on Figure 2 It can be seen that the material prepared in this example corresponds well to the standard card PDF#35-0754, with sharp XRD peaks and no mixed peaks, indicating that the material has good crystallinity and no impurity phase, indicating that the Sn element is incorporated into the lattice. SEM photos show that its particle size is approximately 100-190nm. EDS surface scans show that the elements are evenly distributed throughout the sample. The assembled aqueous full battery has an initial discharge capacity of 105.3mAh / g at a 1C rate, and after 400 cycles, its discharge capacity is 85.0mAh / g.

[0057] Example 2:

[0058] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.15 Ti 1.85 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0059] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0060] (1) Weigh 4.440 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 14 h. Add 10.521 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.2 mL / min. After the addition is complete, continue stirring for 2.5 h to obtain suspension 1.

[0061] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.371 g of lithium carbonate, 3.452 g of phosphoric acid (concentration 85%) and 0.520 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0062] (3) The ground white powder was tableted using a hydraulic press with a pressure of 20 MPa to obtain a flake sample;

[0063] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 750 °C, a heating rate of 8 °C / min, and a constant temperature time of 6 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.15 Ti 1.85 (PO4)3, recorded as LTP-2.

[0064] The battery assembly and testing conditions are the same as those in Example 1.

[0065] The negative electrode material prepared in this example corresponds well to the standard card PDF#35-0754, indicating that the product is free of impurities. EDS scans show that the elements are evenly distributed throughout the sample. SEM images show that the particle size is approximately 100-190nm. At a 1C rate, its initial discharge capacity is 102.7mAh / g. After 400 charge and discharge cycles, the discharge capacity drops to 82.6mAh / g, and the capacity retention rate is 80.4%. Figure 3 .

[0066] Example 3:

[0067] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.2 Ti 1.8 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0068] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0069] (1) Weigh 4.321 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 16 h. Add 11.025 g of ammonia water (40%) using a peristaltic pump at a flow rate of 0.3 mL / min. After the addition is complete, continue stirring for 2.6 h to obtain suspension 1.

[0070] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.660 g of lithium acetate, 3.453 g of phosphoric acid (concentration 85%), and 0.694 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0071] (3) The ground white powder was tableted using a hydraulic press with a pressure of 30 MPa to obtain a flake sample;

[0072] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 800°C, a heating rate of 8°C / min, and a constant temperature time of 6 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.2 Ti 1.8 (PO4)3, recorded as LTP-3.

[0073] The battery assembly and testing conditions are the same as those in Example 1.

[0074] The negative electrode material prepared in this example corresponds well to the standard card PDF#35-0754, indicating that the product is free of impurities. SEM images show that its particle size is approximately 100-190nm. The corresponding EDS surface scanning element distribution map shows that each element has good dispersion in the sample. At a 1C rate, its initial charge and discharge specific capacity is 115.2mAh / g and 102.3mAh / g, respectively. The charge and discharge curves are shown in Figure 2. Figure 4 After 400 cycles, the charge and discharge specific capacities are 82.9 mAh / g and 82.1 mAh / g, respectively.

[0075] Example 4:

[0076] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.3 Ti 1.7 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0077] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0078] (1) Weigh 4.081 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 18 h. Add 11.902 g of ammonia water (40%) using a peristaltic pump at a flow rate of 0.3 mL / min. After the addition is complete, continue stirring for 3 h to obtain suspension 1.

[0079] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.248 g of lithium carbonate, 3.458 g of phosphoric acid (concentration 85%) and 1.041 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, and then dried at 80°C to obtain a white powder;

[0080] (3) The ground white powder was tableted using a hydraulic press with a pressure of 30 MPa to obtain a flake sample;

[0081] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 850 °C, a heating rate of 9 °C / min, and a constant temperature time of 7 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.3 Ti 1.7 (PO4)3, recorded as LTP-4.

[0082] The battery assembly and testing conditions are the same as those in Example 1.

[0083] The negative electrode material prepared in this example corresponds well to the standard card PDF#35-0754, indicating that the product has no impurity phase. Figure 5 This EDS scan shows the elemental distribution of the tin-doped lithium titanium phosphate prepared in this example. The results show that Sn, Ti, P, and O are evenly distributed throughout the sample. Electrical cycling results show that at a 1C rate, the initial discharge capacity is 103.3 mAh / g. After 400 cycles, the discharge capacity remains at 85.1 mAh / g, with a capacity retention of 82.3%.

[0084] Example 5:

[0085] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.2 Ti 1.8 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0086] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0087] (1) Weigh 4.321 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 16 h. Add 11.025 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.2 mL / min. Continue stirring for 3 h after the addition is complete to obtain suspension 1.

[0088] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.660 g of lithium acetate, 3.453 g of phosphoric acid (concentration 85%), and 0.694 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0089] (3) The ground white powder was tableted using a hydraulic press with a pressure of 30 MPa to obtain a flake sample;

[0090] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 830 °C, a heating rate of 5 °C / min, and a constant temperature time of 6 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn0.2 Ti 1.8 (PO4)3, recorded as LTP-5.

[0091] The battery assembly and testing conditions are the same as those in Example 1.

[0092] The negative electrode material prepared in this example corresponds well to standard card PDF#35-0754, indicating the absence of impurities. SEM images show particle sizes of approximately 100-190 nm. EDS surface scanning elemental distribution maps demonstrate good dispersion of all elements in the sample. At a 1C rate, the initial charge and discharge capacities were 118.7 mAh / g and 106.5 mAh / g, respectively. After 400 cycles, the charge and discharge capacities reached 89.4 mAh / g and 88.7 mAh / g, respectively.

[0093] Comparative Example 1:

[0094] A method for preparing lithium titanium phosphate (metal-free) comprises the following steps:

[0095] (1) Weigh 4.801 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 12 h. Add 9.972 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.1 mL / min. Continue stirring for 2 h after the addition is complete to obtain suspension 1.

[0096] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.375 g of lithium carbonate and 3.455 g of phosphoric acid (concentration 85%) were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0097] (3) The ground white powder was tableted using a hydraulic press with a pressure of 20 MPa to obtain a flake sample;

[0098] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 750°C, a heating rate of 5°C / min, and a constant temperature time of 5 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiTi2(PO4)3, which was recorded as D-LTP-1.

[0099] The battery assembly and testing conditions in this comparative example are the same as those in Example 1.

[0100] The product corresponds well to standard card PDF#35-0754, indicating a pure phase. The initial discharge capacity of the aqueous full battery was only 95.6 mAh / g. After 400 charge-discharge cycles at a 1C rate, the discharge capacity dropped to 68.3 mAh / g, with a capacity retention of 71.4%, lower than the corresponding data for metal-doped cells.

[0101] Comparative Example 2:

[0102] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0103] (1) Weigh 4.440 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 14 h. Add 10.521 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.2 mL / min. After the addition is complete, continue stirring for 2.5 h to obtain suspension 1.

[0104] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid product titanium hydroxide was ground with 0.371 g of lithium carbonate, 3.452 g of phosphoric acid (concentration 85%), and 0.520 g of tetrabutyltin, and then dried at 80° C. to obtain a white powder;

[0105] (3) The ground white powder was tableted using a hydraulic press with a pressure of 20 MPa to obtain a flake sample;

[0106] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 750 °C, a heating rate of 8 °C / min, and a constant temperature time of 6 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.15 Ti 1.85 (PO4)3, recorded as D-LTP-2.

[0107] The battery assembly and testing conditions in this comparative example are the same as those in Example 1.

[0108] The product corresponds well to standard card PDF#35-0754, indicating a pure phase. SEM images show an average particle size ranging from 300-500 nm, with irregular morphology and poor particle size uniformity. The initial discharge capacity of the aqueous full cell was 98.6 mAh / g. After 400 charge-discharge cycles at a 1C rate, the discharge capacity dropped to 67.3 mAh / g, with a capacity retention of only 68.2%. This suggests that solvent mixing facilitates the production of products with regular morphology and uniform particle size.

[0109] Comparative Example 3:

[0110] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0111] (1) Weigh 4.321 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 16 h. Add 11.025 g of ammonia water (40%) using a peristaltic pump at a flow rate of 0.3 mL / min. After the addition is complete, continue stirring for 2.6 h to obtain suspension 1.

[0112] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.660 g of lithium acetate, 3.453 g of phosphoric acid (concentration 85%), and 0.694 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder;

[0113] (3) The white powder was placed in a tubular heating furnace for calcination at 800°C, a heating rate of 8°C / min, and a constant temperature time of 6 hours. After cooling, the product was taken out and ground for 1 hour to obtain the final product LiSn 0.2 Ti 1.8 (PO4)3, recorded as D-LTP-3.

[0114] The battery assembly and testing conditions in this comparative example are the same as those in Example 1.

[0115] Compared to the standard card PDF#35-0754, the resulting product exhibits an impurity peak at 27-28°, corresponding to (TiO)2P2O7 (PDF#39-0207). SEM images show an average particle size range of 400-600nm. The initial discharge capacity of the aqueous full battery is only 93.2mAh / g. At a 1C rate, after 400 charge-discharge cycles, the discharge capacity drops to 42.6mAh / g, with a capacity retention rate of only 45.7%. This indicates that the non-compressed sintered product contains impurities, resulting in poor electrochemical performance of the aqueous lithium-ion battery.

[0116] Comparative Example 4:

[0117] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0118] (1) Weigh 3.612 g of titanium sulfate and place it in 100 mL of deionized water. Stir for 18 h. Add 11.902 g of ammonia water (40%) using a peristaltic pump at a flow rate of 0.3 mL / min. After the addition is complete, continue stirring for 3 h to obtain suspension 1.

[0119] (2) Suspension 1 was filtered using a suction filtration device, and then the newly prepared wet-based solid phase product titanium hydroxide was placed in anhydrous ethanol, and 0.248 g of lithium carbonate, 3.458 g of phosphoric acid (concentration 85%) and 1.735 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, and then dried at 80°C to obtain a white powder;

[0120] (3) The ground white powder was tableted using a hydraulic press with a pressure of 30 MPa to obtain a flake sample;

[0121] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 850 °C, a heating rate of 9 °C / min, and a constant temperature time of 7 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.5 Ti 1.5 (PO4)3, recorded as D-LTP-4.

[0122] The battery assembly and testing conditions in this comparative example are the same as those in Example 1.

[0123] Compared to the standard card PDF#35-0754, the resulting product exhibited significant impurity peaks of Li8SnO6 and Li3PO4. The initial discharge capacity of the aqueous full battery was only 73.5 mAh / g. At a 1C rate, after 400 charge-discharge cycles, the discharge capacity dropped to 32.6 mAh / g, with a capacity retention rate of only 44.3%. This indicates that excessive tin doping can lead to the appearance of impurities in the product, significantly reducing the initial discharge capacity and cycling stability of aqueous lithium-ion batteries.

[0124] Comparative Example 5:

[0125] A tin-doped lithium titanium phosphate, comprising a lithium titanium phosphate matrix doped with tin, the molecular formula of which is LiSn 0.2 Ti 1.8 (PO4)3, the particle size of lithium titanium phosphate matrix is ​​100-190nm.

[0126] A method for preparing tin-doped lithium titanium phosphate comprises the following steps:

[0127] (1) Weigh 6.120 g of tetrabutyl titanate and place it in 100 mL of deionized water. Stir for 16 h. Add 11.025 g of aqueous ammonia (40%) using a peristaltic pump at a flow rate of 0.2 mL / min. Continue stirring for 3 h after the addition is complete to obtain suspension 1.

[0128] (2) Suspension 1 was filtered using a suction filtration device, and the wet solid phase product titanium hydroxide was then dried in an oven at 80°C for 24 hours. The product was then placed in a beaker, and 0.660 g of lithium acetate, 3.453 g of phosphoric acid (85% concentration), and 0.694 g of tetrabutyltin were added. The suspension was stirred at room temperature and pressure for 1 hour to obtain suspension 2, which was then dried at 80°C to obtain a white powder.

[0129] (3) The ground white powder was tableted using a hydraulic press with a pressure of 30 MPa to obtain a flake sample;

[0130] (4) The flake sample was placed in a tubular heating furnace for calcination at a temperature of 800 °C, a heating rate of 5 °C / min, and a constant temperature time of 10 h. After cooling, the product was taken out and ground for 1 h to obtain the final product LiSn 0.2 Ti 1.8 (PO4)3, recorded as D-LTP-5.

[0131] The battery assembly and testing conditions are the same as those in Example 1.

[0132] The main peak of the negative electrode material prepared in this example can correspond to the standard card PDF#35-0754, but there is a miscellaneous peak at the 25° position, indicating that the product contains a certain amount of impurity phase. The SEM photo shows that its particle size is about 300-400nm. The corresponding EDS surface scanning element distribution map shows that each element has good dispersion in the sample. At a 1C rate, its initial charge and discharge specific capacity is 89.7mAh / g and 86.5mAh / g, respectively. After 400 cycles, its charge and discharge specific capacity is 64.9mAh / g and 60.1mAh / g, respectively, and the capacity decay is obvious.

Claims

1. A method for preparing tin-doped lithium titanium phosphate, characterized in that: The following steps are involved: (1) Using titanium sulfate as a titanium source to prepare wet-based solid-phase product titanium hydroxide; (2) adding the wet solid product titanium hydroxide newly prepared in step (1) and a lithium source, a tin source, and a phosphorus source into anhydrous ethanol and continuously stirring to form a suspension; the tin source is tetrabutyltin; the lithium source is one or more of lithium carbonate, lithium hydroxide, or lithium acetate; and the phosphorus source is phosphoric acid; (3) drying the suspension in step (2) to obtain a powder product, calcining the powder product, and grinding it to obtain the tin-doped lithium titanium phosphate; The method for preparing a wet-based solid-phase product of titanium hydroxide using titanium sulfate as a titanium source comprises the following steps: dissolving titanium sulfate, stirring thoroughly, adding ammonia water and continuously stirring, and performing solid-liquid separation to obtain the wet-based solid-phase product of titanium hydroxide; in the step (2), the continuous stirring is carried out at room temperature and pressure; When the wet-based solid phase product titanium hydroxide, lithium source, tin source and phosphorus source are mixed, the molar ratio of Li:Sn:Ti:P is controlled to be 1:x:2-x:3, wherein x is 0.1-0.3; The powder product is first ground and tabletted and then calcined, and the tabletting process is performed using a hydraulic press.

2. The preparation method according to claim 1, characterized in that When fully stirred, the stirring time is controlled to be 12-18 hours, the molar ratio of the titanium sulfate to the ammonia water is controlled to be 1: (6-8), and a peristaltic pump is used for feeding when adding the ammonia water, and the feeding rate is controlled to be 0.1-0.3 mL / min. After the feeding is completed, stirring is continued for 2-3 hours.

3. The preparation method according to claim 1, characterized in that During the tableting process, the pressure is controlled to be 20-30 MPa.

4. The preparation method according to claim 1 or 2, characterized in that During the calcination treatment, the calcination temperature is controlled to be 750-850° C., the heating rate is 5-10° C. / min, the constant temperature time is 5-10 hours, and the calcination atmosphere is an inert atmosphere.

5. Use of the tin-doped lithium titanium phosphate prepared by the preparation method according to any one of claims 1 to 4 as a negative electrode material in an aqueous lithium-ion battery.

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