An alkaline earth metal ion-doped titanium-based phosphate composite material, a preparation method thereof, and an application thereof

Abstract

The present invention relates to an alkaline earth metal ion-doped titanium-based phosphate composite material, a preparation method and an application thereof, belonging to the technical field of sodium ion batteries. The chemical formula of the alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention is K x M y TiOPO4 / C, M is selected from one or more of beryllium, magnesium, calcium, strontium and barium, 0.8 ≤ x ≤ 0.95, 0.001 ≤ y ≤ 0.1, and the values of x and y satisfy the charge balance of the chemical formula. By doping with alkaline earth metal ions, the lattice structure is effectively stabilized, and the exchange of K-Na ions is avoided, thereby significantly improving the cycle stability and service life of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and particularly relates to an alkaline earth metal ion-doped titanium-based phosphate composite material, a preparation method thereof, and an application thereof. Background Art

[0002] As a sodium ion electrode material, sodium titanium phosphate has excellent structural and thermal stability. However, its extremely low electronic conductivity and relatively narrow ion diffusion channels severely limit its application in sodium ion batteries. Among various titanium-based phosphate materials, KTiOPO4 has a larger cross cavity, and the potential of KTiOPO4 is the lowest, at 1.23 V, which has great potential in achieving faster ion kinetics and lower cycling strain in sodium ion batteries. However, when KTiOPO4 is used as a sodium ion negative electrode material, potassium ions will be replaced by sodium ions through ion exchange during the charge-discharge cycle, and this ion exchange will cause changes in the material composition and structure, thereby affecting the battery life and reversible capacity.

[0003] Therefore, it is still necessary to develop a titanium-based phosphate material with a long service life and a high reversible capacity. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides an alkaline earth metal ion-doped titanium-based phosphate composite material, a preparation method thereof, and an application thereof. Through the strategy of alkaline earth metal ion doping, the electrochemical performance of the titanium-based phosphate material in secondary sodium ion batteries is improved from multiple angles and dimensions. By optimizing the type and doping amount of alkaline earth metal ions, as well as process parameters, the lattice structure of the titanium-based phosphate material is stabilized, the K-Na ion exchange is effectively avoided, and the performance of the sodium ion battery is significantly improved.

[0005] The first object of the present invention is to provide an alkaline earth metal ion-doped titanium-based phosphate composite material, and the chemical formula of the alkaline earth metal ion-doped titanium-based phosphate composite material is K x M y TiOPO4 / C, where M is selected from one or more of beryllium, magnesium, calcium, strontium, and barium, 0.8 ≤ x ≤ 0.95, 0.001 ≤ y ≤ 0.1, and the values of x and y satisfy the charge balance of the chemical formula.

[0006] In one embodiment of the present invention, the M is selected from magnesium and / or calcium.

[0007] In one embodiment of the present invention, the chemical formula of the alkaline earth metal ion-doped titanium-based phosphate composite material is K 0.9 Ca 0.05 TiOPO4 and / or K 0.9 Mg 0.05 TiOPO4.

[0008] In one embodiment of the present invention, the K x M y The mass ratio of TiOPO4 to C is (0.7 - 0.99):(0.01 - 0.3).

[0009] The second object of the present invention is to provide a method for preparing the alkaline earth metal ion-doped titanium-based phosphate composite material, comprising the following steps: mixing a K source, an M source, a Ti source, a P source, and a carbon source uniformly by wet ball milling, and obtaining the alkaline earth metal ion-doped titanium-based phosphate composite material through drying, sintering, cooling, and pulverizing.

[0010] In one embodiment of the present invention, the K source is selected from one or more of potassium hydroxide, potassium carbonate, potassium sulfate, potassium dihydrogen phosphate, and potassium acetate;

[0011] and / or, the M source is selected from one or more of beryllium source, magnesium source, calcium source, strontium source, and barium source;

[0012] and / or, the Ti source is selected from one or more of titanium oxysulfate, titanium dioxide, tetrabutyl titanate, and titanium tetrachloride;

[0013] and / or, the P source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus pentoxide, and potassium dihydrogen phosphate;

[0014] and / or, the carbon source is selected from one or more of acetylene black, graphite, conductive carbon black, sucrose, and glucose.

[0015] In one embodiment of the present invention, the manner of uniform mixing is selected from one or more of dry ball milling, wet ball milling, and high-speed dispersion.

[0016] In one embodiment of the present invention, the particle size D90 of the material after wet ball milling is less than 1 μm;

[0017] and / or, the drying manner is selected from one or more of fluidized bed drying, spray drying, and tray drying.

[0018] In one embodiment of the present invention, the sintering is carried out under a protective atmosphere, heating at a heating rate of 1 °C / min - 5 °C / min to 700 °C - 850 °C, and holding for 4 h - 24 h.

[0019] In one embodiment of the present invention, the protective atmosphere is selected from nitrogen atmosphere and / or argon atmosphere.

[0020] In one embodiment of the present invention, the cooling manner is selected from active cooling and / or natural cooling.

[0021] In one embodiment of the present invention, the pulverization method is selected from one or more of mechanical pulverization, jet mill pulverization, and disk pulverization.

[0022] The third object of the present invention is to provide an application of the alkaline earth metal ion-doped titanium-based phosphate composite material or the alkaline earth metal ion-doped titanium-based phosphate composite material prepared by the method in a sodium-ion battery.

[0023] The technical solution of the present invention has the following advantages compared with the prior art:

[0024] In the alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention, through the doping of alkaline earth metal ions, the lattice structure is effectively stabilized, and the exchange of K-Na ions is avoided, thereby significantly improving the cycle stability and service life of the battery. Compared with potassium ions, alkaline earth metal ions have a slightly larger electronegativity, and their attraction to anionic groups is stronger. When forming chemical bonds, the covalent characteristics of alkaline earth metal ions are more obvious. This strong bonding effect can stabilize the chemical bond network in the material, enhance the overall stability of the material, and reduce the structural damage and performance degradation caused by the breaking of chemical bonds during charge and discharge.

[0025] The preparation method of the present invention realizes the effective doping of alkaline earth metal ions through the type and doping amount of alkaline earth metal ions, as well as the optimization of process parameters. It can effectively reduce the Fermi level, improve the electronic conductivity and ionic conductivity of titanium-based phosphate materials, thereby greatly improving the life and reversible capacity of sodium-ion batteries, making the energy transmission during charge and discharge of the battery more efficient, reducing the internal resistance, and improving the power performance of the battery. In addition, the outermost electron configuration of alkaline earth metal ions is ns², with two units of positive charge. Compared with alkali metal ions, their charge density is larger. In the material, the larger charge density enables alkaline earth metal ions to attract surrounding electrons more strongly, thus having a more significant impact on the electronic structure of the material. It can effectively adjust the Fermi level of the material, change the energy band structure, and further optimize the electrical properties of the material, such as improving the conductivity and carrier mobility of the material.

[0026] The preparation method of the present invention has the characteristics of strong operability and easy mass production, which is conducive to reducing production costs and promoting the large-scale commercial application of sodium-ion batteries. Description of the Drawings

[0027] In order to make the content of the present invention easier to be clearly understood, the following further describes the present invention in detail according to specific embodiments of the present invention and in combination with the drawings, where:

[0028] Figure 1 It is the XRD spectrum of the alkaline earth metal ion-doped titanium-based phosphate composite materials of Example 1 and Comparative Example 1 in Test Example 1 of the present invention;

[0029] Figure 2 The charge-discharge curve of the battery made of the alkaline earth metal ion-doped titanium-based phosphate composite material in Example 1 of Test Example 2 of the present invention at a rate of 1C. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the exemplified embodiments do not limit the present invention.

[0031] In the present invention, unless otherwise specified, the technical and scientific terms used in the present invention have the same meanings as those generally understood by those skilled in the technical field to which the present invention belongs.

[0032] In the present invention, unless otherwise specified, the term "and / or" includes any and all combinations of one or more of the related listed items.

[0033] In the present invention, unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial channels without special instructions. Example 1

[0034] The alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention and its preparation method specifically include the following steps:

[0035] S1. Using potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.9 Ca 0.05 TiOPO4 / C (the mass ratio of K 0.9 Ca 0.05 TiOPO4 and C is 0.95:0.05), then add deionized water and ball mill evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.9 μm;

[0036] S2. Spray-dry the mixture to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0037] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it to 750 °C at a heating rate of 2.5 °C / min and hold for 10 h. Mechanically crush the material after natural cooling to obtain the alkaline earth metal ion-doped titanium-based phosphate composite material. Example 2

[0038] The alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention and its preparation method specifically include the following steps:

[0039] S1. Using potassium dihydrogen phosphate as the K source and P source, barium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.9 Ba 0.05 TiOPO4 / C (the mass ratio of K 0.9 Ba 0.05 TiOPO4 to C is 0.9:0.1), then add deionized water and ball mill evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.85 μm;

[0040] S2. Perform spray drying on the mixture to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0041] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it up to 750 °C at a heating rate of 5 °C / min and keep it warm for 10 h. Mechanically crush the naturally cooled material to obtain the alkaline earth metal ion-doped titanium-based phosphate composite material. Example 3

[0042] The alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention and its preparation method specifically include the following steps:

[0043] S1. Using potassium dihydrogen phosphate as the K source and P source, magnesium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.9 Mg 0.05 TiOPO4 / C (the mass ratio of K 0.9 Mg 0.05 TiOPO4 to C is 0.98:0.02), then add deionized water and ball mill evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.95 μm;

[0044] S2. Perform spray drying on the mixture to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0045] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it up to 750 °C at a heating rate of 2 °C / min and keep it warm for 10 h. Mechanically crush the naturally cooled material to obtain the alkaline earth metal ion-doped titanium-based phosphate composite material. Example 4

[0046] The alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention and its preparation method specifically include the following steps:

[0047] S1. Using potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.99 Ca 0.005 TiOPO4 / C (the mass ratio of K 0.99 Ca 0.005 TiOPO4 and C is 0.93:0.07), then add deionized water and ball mill evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.94 μm;

[0048] S2. Perform spray drying on the mixture to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0049] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it to 750 °C at a heating rate of 3 °C / min and hold for 10 h. Mechanically crush the naturally cooled material to obtain the alkaline earth metal ion-doped titanium-based phosphate composite material. Example 5

[0050] The alkaline earth metal ion-doped titanium-based phosphate composite material of the present invention and its preparation method specifically include the following steps:

[0051] S1. Using potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.8 Ca 0.1 TiOPO4 / C (the mass ratio of K 0.8 Ca 0.1 TiOPO4 and C is 0.8:0.2), then add deionized water and ball mill evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.87 μm;

[0052] S2. Perform spray drying on the mixture to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0053] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it to 750 °C at a heating rate of 4 °C / min and hold for 10 h. Mechanically crush the naturally cooled material to obtain the alkaline earth metal ion-doped titanium-based phosphate composite material. Comparative Example 1

[0054] Basically the same as Example 1, the difference is that no calcium doping is carried out, and it specifically includes the following steps:

[0055] S1. Using potassium dihydrogen phosphate as the K source and P source, titanium dioxide as the Ti source, and acetylene black as the carbon source material, these raw materials are mixed according to KTiOPO4 / C (the mass ratio of KTiOPO4 to C is 0.7:0.3), and then deionized water is added and ball-milled evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.9 μm;

[0056] S2. The mixture is spray-dried to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0057] S3. The precursor powder is sintered in a sintering furnace under a nitrogen atmosphere, heated to 750 °C at a heating rate of 3 °C / min, and held for 10 h. The material after natural cooling is mechanically pulverized to obtain an alkaline earth metal ion-doped titanium-based phosphate composite material. Comparative Example 2

[0058] Basically the same as Example 1, the difference lies in the amounts of potassium dihydrogen phosphate and calcium carbonate, and the specific steps are as follows:

[0059] S1. Using potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material, these raw materials are mixed according to K 0.6 Ca 0.2 TiOPO4 / C (K 0.6 Ca 0.2 The mass ratio of TiOPO4 to C is 0.8:0.2), and then deionized water is added and ball-milled evenly with a solid content of 40 wt% to obtain a mixture with a particle size D90 of about 0.92 μm;

[0060] S2. The mixture is spray-dried to obtain a precursor powder with a particle size D50 of about 6.8 μm;

[0061] S3. The precursor powder is sintered in a sintering furnace under a nitrogen atmosphere, heated to 750 °C at a heating rate of 3 °C / min, and held for 10 h. The material after natural cooling is mechanically pulverized to obtain an alkaline earth metal ion-doped titanium-based phosphate composite material. Comparative Example 3

[0062] Basically the same as Example 1, the difference is that calcium carbonate is replaced with manganese carbonate, and the specific steps are as follows:

[0063] S1. Using potassium dihydrogen phosphate as the K source and P source, manganese carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material, these raw materials are mixed according to K 0.9 Mn 0.05 TiOPO4 / C (K 0.9 Mn0.05 Mix (the mass ratio of TiOPO4 to C is 0.95:0.05), then add deionized water and ball-mill evenly with a solid content of 40 wt% to obtain a mixture with a D90 particle size of about 0.9 μm;

[0064] S2. Spray-dry the mixture to obtain a precursor powder with a D50 particle size of about 6.8 μm;

[0065] S3. Sinter the precursor powder in a sintering furnace under a nitrogen atmosphere, heat it to 750 °C at a heating rate of 2.5 °C / min, hold for 10 h, and mechanically crush the naturally cooled material to obtain an alkaline earth metal ion-doped titanium-based phosphate composite material. Comparative Example 4

[0066] Basically the same as Example 1, except for the particle size after ball milling, which specifically includes the following steps:

[0067] S1. Use potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.9 Ca 0.05 TiOPO4 / C (K 0.9 Ca 0.05 Mix (the mass ratio of TiOPO4 to C is 0.95:0.05), then add deionized water and ball-mill evenly with a solid content of 40 wt% to obtain a mixture with a D90 particle size of about 2 μm;

[0068] S2. Spray-dry the mixture to obtain a precursor powder with a D50 particle size of about 6.8 μm;

[0069] S3. Sinter the precursor powder in a sintering furnace under a nitrogen atmosphere, heat it to 750 °C at a heating rate of 2.5 °C / min, hold for 10 h, and mechanically crush the naturally cooled material to obtain an alkaline earth metal ion-doped titanium-based phosphate composite material. Comparative Example 5

[0070] Basically the same as Example 1, except for the particle size after ball milling, which specifically includes the following steps:

[0071] S1. Use potassium dihydrogen phosphate as the K source and P source, calcium carbonate as the doped alkaline earth metal source, titanium dioxide as the Ti source, and acetylene black as the carbon source material. Mix these raw materials according to K 0.9 Ca 0.05 TiOPO4 / C (K 0.9 Ca 0.05Mix (with the mass ratio of TiOPO4 to C being 0.95:0.05), then add deionized water and ball mill evenly. The solid content is 40 wt%, obtaining a mixture with a D90 particle size of approximately 0.9 μm.

[0072] S2. Spray-dry the mixture to obtain a precursor powder with a D50 particle size of approximately 6.8 μm.

[0073] S3. Place the precursor powder in a sintering furnace under a nitrogen atmosphere for sintering. Heat it to 750 °C at a heating rate of 8 °C / min and hold for 10 h. Mechanically crush the naturally cooled material to obtain an alkaline earth metal ion-doped titanium-based phosphate composite material.

[0074] Test Example 1

[0075] Perform XRD characterization on the alkaline earth metal ion-doped titanium-based phosphate composite materials of Example 1 and Comparative Example 1. The results are as Figure 1 shown. It can be seen from Figure 1 that the XRD diffraction peaks of the two are consistent, indicating that within a certain doping range, the lattice structure of the material does not change.

[0076] Test Example 2

[0077] (1) Test the powder resistivity R (Ω·cm) of the titanium-based phosphate composite materials of Examples 1-5 and Comparative Examples 1-5: Use an ST2742C type automated powder resistivity tester to measure the powder resistivity of the titanium-based phosphate composite materials. Under the condition of the same carbon content, it can intuitively reflect the electronic conductivity of the titanium-based phosphate composite materials. Record the curve between the pressure (MPa) and the resistivity (Ω·cm), and use the resistivity at a pressure of 60 MPa as the comparison between different samples.

[0078] (2) Fabricate batteries based on the titanium-based phosphate composite materials of Examples 1-5 and Comparative Examples 1-5 and test their performance:

[0079] Battery assembly:

[0080] Negative electrode sheet: The titanium-based phosphate composite material, the conductive agent is acetylene black, the binder is polyvinylidene fluoride (PVDF), and the negative electrode current collector is 6 μm aluminum foil; after mixing the titanium-based phosphate composite material, the conductive agent and the binder according to the mass ratio of 8:1:1, add N-methylpyrrolidone and stir into a uniform and stable negative electrode slurry, then evenly coat the negative electrode slurry on the surface of the negative electrode current collector, perform 200 μm blade coating, and obtain a negative electrode sheet after drying and cold pressing. The mass loading of the titanium-based phosphate composite material is about 2.5 mg / cm 2 .

[0081] Counter electrode: A sodium metal sheet.

[0082] Separator membrane: The base membrane of the separator membrane is a polyethylene membrane with a thickness of 9 μm.

[0083] Electrolyte: Sodium hexafluorophosphate is dissolved in polycarbonate to prepare an electrolyte with a concentration of 1 mol / L.

[0084] Assembly of sodium-ion battery: The negative electrode sheet, separator membrane, counter electrode, and separator membrane are arranged in sequence, and the winding method is selected for the assembly method.

[0085] Performance test: The assembled sodium-ion battery is tested for specific capacity, cycle stability, etc.:

[0086] (1) Specific capacity (mAh / g) test: The specific capacity of the titanium-based phosphate composite material is tested in the voltage range of 0 - 3V.

[0087] (2) Cycle stability (%) test: The sodium-ion battery is tested on a battery cycle test device. The discharge voltage range is set to 0.5V - 3V. At room temperature, the sodium-ion battery is cycled at 5C charge and 5C discharge, and the number of cycles when the capacity tends to be stable is recorded; at the same time, the initial capacity Qinitial and the capacity Q8000th cycle after the 8000th cycle are recorded, and the capacity retention rate after 8000 cycles of each battery is calculated = (Q8000th cycle / Qinitial) × 100%.

[0088] Table 1 and Figure 2 The following shows the relevant performance parameters finally measured:

[0089] Table 1

[0090]

[0091] From Table 1 and Figure 2 it can be seen that with the types and doping amounts of alkaline earth metal ions and the optimization of process parameters, the specific capacity and cycle stability of the titanium-based phosphate composite material have been improved to varying degrees.

[0092] It can be seen from Examples 1-3 and Comparative Example 1 that the specific capacity, powder resistivity and cycle stability of the titanium-based phosphate composite material obtained by doping with different alkaline earth metals (at a certain doping content) are not much different. This is because the electron cloud structures of different alkaline earth metal ions are similar, and they can enter the lattice after doping. When the alkaline earth metal ions with strong electronegativity form ligands with oxygen ions and phosphate ions, their electron cloud structures enable them to form strong chemical bonds with the ligands. This strong bonding can stabilize the chemical bond network in the material, enhance the overall stability of the material, and reduce the structural damage and performance degradation caused by chemical bond breakage during the charge and discharge process. Adjusting the crystal structure of the titanium-based phosphate composite material can increase the phase stability and ensure the long-term cycle stability of the titanium-based phosphate composite material. At the same time, alkaline earth metal doping can effectively adjust the Fermi level of the material, change the band structure, increase the mobility of oxygen ions and the conductivity of grain boundary oxygen ions, and thus improve the overall conductivity of the material.

[0093] It can be seen from Examples 1, 4-5 and Comparative Examples 1-2 that when the doping amount is between 0.001-0.1, the specific capacity increases slightly with the increase of the doping content. This is because as the doping amount of alkaline earth metal ions increases, the attraction to anion groups such as oxygen ions and phosphate ions increases, and the energy band gap of the material decreases slightly, causing an increase in specific capacity. At the same time, the lattice structure is more stable and the capacity retention rate is also improved. However, when the alkaline earth metal doping amount is less than 0.001 (Comparative Example 1), although the specific capacity of the material does not decrease much, due to the lack of strong coupling of alkaline earth ions, the powder conductivity and cycle stability are greatly increased and decreased respectively. When the alkaline earth metal doping amount is higher than 0.1 (Comparative Example 2), because the amount of alkaline earth metal doped is too much, the lattice distortion is caused, thereby changing the ion diffusion channel of the original material, resulting in a sharp decrease in the specific capacity and cycle stability of the material.

[0094] It can be seen from Example 1 and Comparative Example 3 that when manganese ions are used for doping, the specific capacity of the obtained material is very low. This is mainly because the electronic configuration of manganese ions is relatively complex, the d orbital has a specific extension direction and shape in space, and its electron cloud distribution is in a complex shape such as a petal shape, which makes the manganese ions have strong directionality and spatial selectivity when forming chemical bonds, and cannot be well combined with anion groups such as oxygen ions and phosphate ions, making it difficult to generate materials with the desired crystal structure.

[0095] It can be seen from Example 1 and Comparative Example 4 that when the particle size D90 of the slurry obtained by wet ball milling is greater than 1 μm, due to the relatively large particle size of the raw material, the distance of the material transmission process during the sintering process increases, resulting in an increase in the primary particle size of the material and the easy generation of impurities. The appearance of excessive particle size and impurities is not conducive to the conduction of ions inside the material and the stability of the lattice structure. During the charge and discharge process, it will hinder the normal deintercalation of ions, thereby reducing the specific capacity of the obtained titanium-based phosphate composite material, and also seriously affecting the cyclic stability of the material, causing the material to rapidly decay after multiple charge and discharge.

[0096] It can be seen from Example 1 and Comparative Example 5 that when the heating rate is too fast during the sintering process, the phosphorus source does not have time to decompose. As a key component in the formation of titanium-based phosphate composite materials, insufficient decomposition of the phosphorus source will lead to an imbalance in the proportion of the material components and an inability to form an ideal crystal structure. The incompletely decomposed phosphorus source may exist in the material in the form of an impurity phase, affecting the purity of the material. This will not only interfere with the transmission channel of ions inside the material, making it difficult for ions to migrate in the lattice and reducing the specific capacity of the material, but will also destroy the stability of the lattice, causing the lattice to be more susceptible to irreversible deformation during the charge and discharge process, seriously damaging the cyclic stability of the material.

[0097] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries, characterized in that: The chemical formula of the alkaline earth metal ion-doped titanium-based phosphate composite material is K x M y TiOPO4 / C, M is selected from one or more of beryllium, magnesium, calcium, strontium and barium, 0.8≤x≤0.95, 0.001≤y≤0.1, and the values ​​of x and y satisfy the charge balance of the chemical formula; the K x M y The mass ratio of TiOPO4 and C is (0.7-0.99): (0.01-0.3); The preparation method of the alkaline earth metal ion-doped titanium-based phosphate composite material comprises the following steps: uniformly mixing a K source, an M source, a Ti source, a P source and a carbon source by wet ball milling, and obtaining the alkaline earth metal ion-doped titanium-based phosphate composite material by drying, sintering, cooling and crushing; The particle size D90 of the material after wet ball milling is less than 1 μm; The sintering is carried out under a protective atmosphere, with the temperature being raised to 700° C.-850° C. at a heating rate of 1° C. / min-5° C. / min, and the temperature being kept for 4h-24h.

2. The alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries according to claim 1, characterized in that: The M is selected from magnesium and / or calcium.

3. The alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries according to claim 1, characterized in that: The chemical formula of the alkaline earth metal ion-doped titanium-based phosphate composite material is K 0.9 Ca 0.05 TiOPO4 and / or K 0.9 Mg 0.05 TiOPO4.

4. The alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries according to claim 1, characterized in that: The K source is selected from one or more of potassium hydroxide, potassium carbonate, potassium sulfate, potassium dihydrogen phosphate and potassium acetate; And / or, the M source is selected from one or more of a beryllium source, a magnesium source, a calcium source, a strontium source and a barium source; and / or, the Ti source is selected from one or more of titanyl sulfate, titanium dioxide, tetrabutyl titanate and titanium tetrachloride; And / or, the P source is selected from one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphorus pentoxide and potassium dihydrogen phosphate; And / or, the carbon source is selected from one or more of acetylene black, graphite, conductive carbon black, sucrose and glucose.

5. The alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries according to claim 1, characterized in that: The drying method is selected from one or more of fluidized bed drying, spray drying and tray drying.

6. The alkaline earth metal ion-doped titanium-based phosphate composite material for sodium ion batteries according to claim 1, characterized in that: The protective atmosphere is selected from nitrogen atmosphere and / or argon atmosphere.

7. Use of the alkaline earth metal ion-doped titanium-based phosphate composite material according to any one of claims 1 to 6 in a sodium ion battery.

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