A high-diffusion-coefficient sodium-ion battery negative electrode material, a preparation method thereof and an application thereof

Abstract

The application discloses a kind of high diffusion coefficient sodium ion battery negative material and preparation method and application, belong to battery material preparation technical field.K 1‑2x TiO 1‑ x The preparation of PO4@C includes the following steps: mixing a phosphorus source, a potassium source and a titanium source, then mixing with a carbon source to obtain a slurry, and drying to obtain a precursor; the precursor is subjected to three-stage treatment: (1) heat treatment under an inert gas atmosphere to a first set temperature; (2) heat treatment of the product of the first stage under a hydrogen atmosphere to 400-600°C; (3) cooling the product of the second stage to a second set temperature at a rate of 10-20°C / min under a hydrogen atmosphere to obtain a sodium ion battery negative material. The preparation method of the application overcomes the defects that the ion channels in the KTOP crystal are limited by the crystal structure and the ion transmission is not smooth, optimizes the crystal structure and ion channels through post-hydrogen annealing and process parameter optimization, improves the diffusion coefficient of the material and improves the battery performance.

Description

TECHNICAL FIELD

[0001] The application relates to a high-diffusion-coefficient sodium ion battery negative electrode material and a preparation method and application thereof, and belongs to the technical field of batteries. BACKGROUND

[0002] In the field of energy storage today, sodium ion batteries are attracting attention due to their abundant sodium resources and relatively low cost. However, the performance of sodium ion batteries still needs to be improved, especially in terms of negative electrode materials.

[0003] Among the negative electrode materials of sodium ion batteries, KTiOPO4 (KTOP) has larger cross cavities, and the potential of KTiOPO4 is the lowest, being 1.23 V, which has great potential in realizing faster ion kinetics and lower cycle strain of sodium ion batteries. However, the diffusion coefficient of this material is low, which seriously limits the charge and discharge rate and cycle life of the battery. Traditional material preparation methods can regulate the electronic structure through doping engineering, embedding layer engineering and other methods, which can change the valence state of metal ions, the atomic coordination environment, the charge density distribution and the energy band structure, and then optimize the electrochemical performance and improve the ion conductivity. However, these measures have little effect on KTOP materials, and how to introduce defects into KTOP through a simple and effective preparation method to improve the ion diffusion rate is a subject worthy of study. SUMMARY

[0004] To solve the above problems, the application introduces a certain content of oxygen defects through post-hydrogen annealing, and does not have adverse effects on the crystal structure of the material, thereby obtaining a high-diffusion-coefficient sodium ion battery negative electrode material.

[0005] The first object of the application is to provide a preparation method of a sodium ion battery negative electrode material, comprising the following steps:

[0006] S1, mixing a phosphorus source, a potassium source and a titanium source according to the stoichiometric ratio of K 1-2x TiO 1-x PO4, and then mixing the mixture with a carbon source to obtain a slurry; wherein x=0.001-0.1;

[0007] S2, drying the slurry of S1 to obtain a precursor;

[0008] S3, performing three-stage treatment on the precursor of S2 to obtain a sodium ion battery negative electrode material with a chemical formula of K 1-2x TiO 1-x PO4@C;

[0009] The three-stage treatment comprises:

[0010] The first stage is to heat to a first set temperature for heat treatment in an inert gas atmosphere;

[0011] Second stage: heat treatment of the product of the first stage under a hydrogen atmosphere at a temperature of 400-600 DEG C;

[0012] Third stage: cooling the product of the second stage to a second set temperature at a rate of 10-20 DEG C / min under a hydrogen atmosphere.

[0013] In the prior art, the sodium ion battery negative electrode material potassium titanyl phosphate (KTOP) has many problems such as low diffusion coefficient, poor electrical conductivity, complex preparation process and high cost, which is related to the fact that the ion channels in the KTOP crystal are limited by the crystal structure, resulting in poor ion transmission. The ion channel is a path in the crystal structure that allows ions to pass through. The KTOP crystal has a complex three-dimensional framework structure, which contains many small channels and voids. If these channels are not smooth, the diffusion path of ions in the crystal will become complex, and the transmission speed of ions will be significantly reduced. Therefore, how to improve the diffusion coefficient of the material by optimizing the crystal structure and ion channels to improve the battery performance is the main research focus of the present application.

[0014] In the preparation process of the crystal material, high-temperature hydrogen annealing treatment is used to "artificially" create oxygen defects, so as to improve the electrical conductivity of the material. Therefore, the present application proposes a new preparation method of a high-diffusion-coefficient sodium ion battery negative electrode material. The carbon-coated KTOP precursor is sintered in stages in the present application. The first stage is mainly related to the formation of the structure of KTOP. In the second stage, the temperature is kept at 400-600 DEG C and the protective atmosphere is changed to hydrogen. Combined with the rapid cooling method in the third stage, a certain amount of oxygen defects can be formed and "fixed". This unique sintering method and atmosphere control greatly optimize the crystal structure of the material, thereby significantly improving the diffusion coefficient of sodium ions in the material. In particular, although there are many ways to form oxygen defects, we found through research that different introduction methods have different effects on the KTOP lattice structure. The formation of some oxygen defects will cause the lattice to expand or shrink, which will adversely affect the capacity of the material: oxygen defects introduced by doping metal or non-metal ions will also introduce additional defect levels, affecting the electronic structure and electrical properties of the material; oxygen defects introduced by chemical reaction method will form new active sites on the surface of the material, which may cause some undesirable electrochemical reactions to occur, affecting the stability of the material surface. Therefore, these methods are abandoned in the pre-experiment. Only when hydrogen annealing is assisted by certain cooling conditions, the oxygen defects not only increase the ion migration sites in the material, but also can adjust the electronic structure of the material and reduce the charge transfer resistance, significantly improve the diffusion coefficient of ions, and the specific capacity of the material does not decrease but increases, and the diffusion coefficient is improved by at least one order of magnitude, which has the greatest improvement on the performance of the battery.

[0015] Preferably, the temperature of the second stage of heat treatment is 400-600℃, such as 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 595℃, 599℃, and the like, including but not limited to the values listed above. More preferably, it is 500℃.

[0016] Preferably, the cooling rate of the third stage is 10-20℃ / min, such as 10.5℃ / min, 11℃ / min, 11.5℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 14.5℃ / min, 15.5℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 19.5℃ / min, and the like, including but not limited to the values listed above. More preferably, it is 15℃ / min.

[0017] Further, in step S1, at least one of the following is included:

[0018] (1) the potassium source includes one or more of potassium carbonate, potassium hydroxide, potassium sulfate, and potassium dihydrogen phosphate, preferably potassium dihydrogen phosphate;

[0019] (2) the titanium source includes one or more of titanium dioxide, metatitanic acid, titanic acid, and titanium tetrachloride, preferably titanium dioxide;

[0020] (3) the phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and phosphorus pentoxide;

[0021] (4) the carbon source includes one or more of graphite, activated carbon, hard carbon, graphene, and carbon black.

[0022] Further, in step S1, at least one of the following is included:

[0023] (1) in the sodium-ion battery negative electrode material, the mass percentage of the carbon source is 1-5wt%;

[0024] (2) the mixing method includes wet ball milling;

[0025] (3) the mixing includes the following steps: first, mixing the phosphorus source, the potassium source, and the titanium source to obtain slurry A, and then mixing slurry A with the carbon source to obtain slurry B;

[0026] (4) the slurry contains a solvent; the solvent includes water or a mixed solvent of water and ethanol (the content of ethanol in the mixed solvent is 0.1-10wt%).

[0027] Preferably, the mass percentage of the carbon source is 1-5wt%, such as 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 4.8wt%, 4.9wt%, etc., including but not limited to the values listed above. More preferably, it is 2wt%.

[0028] Further, in step S2, the drying at least comprises one of the following:

[0029] The drying mode comprises centrifugal spray drying;

[0030] Preferably, the inlet air temperature of the centrifugal spray drying is 100-240℃;

[0031] Preferably, the outlet air temperature of the centrifugal spray drying is 80-110℃;

[0032] Preferably, the centrifugal speed of the centrifugal spray drying is 10000-20000rpm.

[0033] Further, in the first stage of step S3, at least one of the following is included:

[0034] (1) The inert gas comprises argon and / or hydrogen;

[0035] (2) The first set temperature is 600-800℃;

[0036] (3) The heating rate is 1-10℃ / min;

[0037] (4) The heat treatment time is 10-20h;

[0038] (5) The flow rate of the inert gas is 5-15L / min.

[0039] Preferably, the first set temperature is 600-800℃, such as 610℃, 630℃, 650℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 795℃, etc., including but not limited to the values listed above. More preferably, it is 700℃.

[0040] Preferably, the heating rate is 1-10℃ / min, such as 1.5℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 9.5℃ / min, etc., including but not limited to the values listed above. More preferably, it is 3℃ / min.

[0041] Preferably, the time of the heat treatment is 10-20h, such as 10.5h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 19.5h, etc., including but not limited to the values listed above. More preferably, it is 12h.

[0042] Preferably, the flow rate of the inert gas is 5-15L / min, such as 6L / min, 7L / min, 8L / min, 9L / min, 10L / min, 11L / min, 12L / min, 13L / min, 14L / min, 14.5L / min, etc., including but not limited to the values listed above. More preferably, it is 8L / min.

[0043] Further, in the second stage of step S3, at least one of the following is included:

[0044] (1) the time of the heat treatment is 2-10h;

[0045] (2) the rate of the cooling is 1-10℃ / min;

[0046] (3) the flow rate of the hydrogen is 10-20L / min.

[0047] Preferably, the time of the heat treatment is 2-10h, such as 2.5h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 9.5h, etc., including but not limited to the values listed above. More preferably, it is 5h.

[0048] Preferably, the rate of the cooling is 1-10℃ / min, such as 1.5℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 9.5℃ / min, etc., including but not limited to the values listed above. More preferably, it is 5℃ / min.

[0049] Preferably, the flow rate of the hydrogen is 10-20L / min, such as 11L / min, 12L / min, 13L / min, 14L / min, 15L / min, 16L / min, 17L / min, 18L / min, 19L / min, etc., including but not limited to the values listed above. More preferably, it is 12L / min.

[0050] Further, at least one of the following is included:

[0051] (1) when the time of the heat treatment is 2h, the flow rate of the hydrogen is greater than 10L / min;

[0052] (2) when the flow rate of the hydrogen is 10L / min, the time of the heat treatment is greater than 2h;

[0053] (3) when the time of the heat treatment is 10h, the flow rate of the hydrogen gas is less than or equal to 20L / min;

[0054] (4) when the flow rate of the hydrogen gas is 20L / min, the time of the heat treatment is less than or equal to 10h.

[0055] Further, in the third stage of step S3, at least one of the following is included:

[0056] (1) the second set temperature is 20-30℃ (room temperature);

[0057] (2) the flow rate of the hydrogen gas is 10-20L / min;

[0058] (3) the cooling method includes liquid cooling or air cooling.

[0059] Preferably, the flow rate of the hydrogen gas is 10-20L / min, such as 11L / min, 12L / min, 13L / min, 14L / min, 15L / min, 16L / min, 17L / min, 18L / min, 19L / min, etc., including but not limited to the above-mentioned listed values. More preferably, 15L / min.

[0060] The present application configures slurry A according to the stoichiometric ratio, then adds a specific content of carbon source for wet ball milling to obtain slurry B, where the selection range of the carbon source is wide and the content is accurately controlled at 1-5wt%, effectively improving the electrical conductivity and structural stability of the material. Then, the slurry is made into spherical precursor mixed powder by using the centrifugal spray drying method, and the inlet air temperature, outlet air temperature and centrifugal speed are controlled to make the precursor have good morphology and particle size distribution. Then, through a staged sintering process and a change of atmosphere, especially hydrogen annealing to produce oxygen defects, a sodium ion battery negative electrode material with high diffusion coefficient is prepared.

[0061] The second object of the present application is to provide a sodium ion battery negative electrode material prepared by the above preparation method, and the chemical formula of the sodium ion battery negative electrode material is K 1-2x TiO 1-x PO4@C, wherein x=0.001-0.1, a certain content of oxygen defects is produced by hydrogen annealing.

[0062] Preferably, x=0.001-0.1, such as 0.002, 0.005, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.02, 0.05, 0.07, 0.09, 0.1, etc., including but not limited to the above-mentioned listed values. More preferably, 0.01-0.02.

[0063] A third object of the present application is to provide a negative electrode sheet comprising a current collector and a negative active layer disposed on at least one side of the current collector along the thickness direction, the negative active layer containing the sodium-ion battery negative electrode material.

[0064] Further, the negative active layer comprises the following components in mass percentage: 75-95% of negative electrode material, 5-15% of conductive agent and 5-15% of binder.

[0065] Further, the current collector is an aluminum foil, and can also be other materials that can be used as a current collector.

[0066] Further, the conductive agent used in the present application is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes and graphene.

[0067] Further, the binder is a binder known to those skilled in the art, i.e. there is no special limitation, such as one or more of chitosan, xanthan gum, gellan gum, gum arabic, polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, polymethylacryl, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyacrylamide, butadiene rubber, sodium alginate, polyethylene glycol, guar gum, guar gum polymer and guar gum copolymer. PVDF (polyvinylidene fluoride) is selected in the embodiment of the present application.

[0068] A fourth object of the present application is to provide a sodium-ion battery containing the negative electrode sheet.

[0069] Further, the sodium-ion battery also contains an electrolyte, and the electrolyte contains a sodium salt electrolyte.

[0070] Further, the electrolyte is an electrolyte known to those skilled in the art, i.e. there is no special limitation, the solvent is at least one of methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate and diethylene glycol dimethyl ether; the electrolyte salt is at least one of sodium perchlorate, sodium bis(oxalate)borate and sodium hexafluorophosphate.

[0071] The beneficial effects of the present application are:

[0072] Due to the advancement of the present technical solution, it can be widely applied in the fields of sodium-ion battery material preparation technology, material surface treatment technology and hydrogen annealing technology:

[0073] Firstly, in the technical field of sodium-ion battery material preparation, the present application provides a method for manufacturing oxygen defects and metal ion defects by post-hydrogen annealing to improve the diffusion coefficient of powder materials. This method can effectively solve the problem of low diffusion coefficient of KTiOPO4 as a negative electrode material of sodium-ion battery, thereby improving the performance of sodium-ion battery. With the wide application of sodium-ion battery, the demand for high-performance positive and negative electrode materials is increasing, and the present application provides an effective solution with broad market prospects.

[0074] Secondly, in the field of material surface treatment, the present application processes KTiOPO4 by post-hydrogen annealing to improve the diffusion coefficient of the material and thus improve its performance. This method can be applied to other material surface treatment fields, such as lithium-ion battery materials and supercapacitor materials, to improve the dispersibility and conductivity of these materials and improve their performance.

[0075] In summary, the present application has significant technical advantages and broad application prospects in improving the performance of sodium-ion battery, improving the surface performance of materials and optimizing the hydrogen annealing process. With the continuous progress of technology and the growth of market demand, the present application is expected to play an important role in related fields and promote the development and application of related technologies. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 Charge-discharge curve of the material prepared in Example 1. DETAILED DESCRIPTION

[0077] The present application will be further described below in conjunction with the drawings and specific examples, so that those skilled in the art can better understand the present application and implement it, but the examples are not limiting the present application.

[0078] The preparation method involved in the present application is as follows:

[0079] 1) A slurry A is prepared with stoichiometric proportions of phosphorus source, potassium source and titanium source; then a carbon source is added, and a slurry B is prepared by wet ball milling; the carbon source is one or more of graphite, activated carbon, hard carbon, graphene and carbon black; the content of the carbon source is 1-5wt%.

[0080] 2) The slurry B is obtained by centrifugal spray drying to obtain spherical carbon-coated potassium titanium phosphate compound precursor mixed powder;

[0081] 3) sintering the precursor mixed powder to obtain carbon-coated potassium titanyl phosphate compound powder; the sintering is performed in three stages: the first stage is sintering under a protective atmosphere at 600-800°C for 10-20 hours, the protective atmosphere being nitrogen, argon or other inert gas; the second stage is after the first stage, the temperature is 400-600°C, the holding time is 2-10 hours, and the protective atmosphere is hydrogen. The third stage is a cooling stage, which is cooled to room temperature at a certain cooling rate, and the cooling method is liquid cooling or air cooling.

[0082] Preferably, the inlet air temperature of the centrifugal spray drying is 100-240°C, the outlet air temperature is controlled at 80-110°C, and the centrifugal speed is set at 10000-20000 rpm. More preferably, the inlet air temperature can be controlled at 200-240°C, the outlet air temperature is controlled at 100-110°C, and the centrifugal speed is set at 12000-15000 rpm to obtain spherical carbon-coated potassium titanyl phosphate compound precursor mixed powder.

[0083] Preferably, in the first stage, the temperature is raised to 600-800°C at a rate of 1-10°C / min, and the gas flow is 5-15 L / min.

[0084] Preferably, in the second stage, the temperature is lowered to 400-600°C at a rate of 1-10°C / min, and the gas flow is 10-20 L / min.

[0085] Preferably, in the third stage, the temperature is lowered to 20-30°C at a rate of 10-20°C / min, and the gas flow is 10-20 L / min.

[0086] Example 1

[0087] 1) A slurry A is prepared with stoichiometric ratio of 1:1:1 of phosphorus source, potassium source and titanium source; then a carbon source is added, and a slurry B is prepared by wet ball milling; the solvent for wet ball milling is water. Specifically, KH2PO4 is used as K source and P source, TiO2 is used as Ti source, deionized water is added and mixed uniformly, 2wt% acetylene black is added as carbon source, the solid content is 50%, and a vertical ball mill is used for ball milling for 4h.

[0088] 2) The slurry B is dried by centrifugal spray drying to obtain spherical carbon-coated potassium titanyl phosphate compound precursor mixed powder; the inlet air temperature is controlled at 220°C, the outlet air temperature is controlled at 110°C, and the centrifugal speed is set at 13000 rpm.

[0089] 3) The precursor mixed powder is sintered, and the sintering is performed in three stages:

[0090] First, the temperature is raised to 750°C at a rate of 3°C / min under a nitrogen atmosphere and held for 12h, and the gas flow is 8 L / min;

[0091] Then the protective atmosphere was changed to hydrogen gas with a flow rate of 12 L / min, and the temperature was decreased to 500°C at a rate of 5°C / min, and the holding time was 5 h;

[0092] Finally, the temperature was decreased to room temperature at a rate of 15°C / min, and the protective atmosphere was still hydrogen gas. The carbon-coated potassium titanyl phosphate compound powder was obtained.

[0093] Example 2

[0094] The holding temperature of the second stage in step 3) was changed from 500°C to 400°C, and the rest was the same as in Example 1.

[0095] Example 3

[0096] The holding temperature of the second stage in step 3) was changed from 500°C to 600°C, and the rest was the same as in Example 1.

[0097] Example 4

[0098] The cooling rate of the third stage in step 3) was changed from 15°C / min to 10°C / min, and the rest was the same as in Example 1.

[0099] Example 5

[0100] The cooling rate of the third stage in step 3) was changed from 15°C / min to 20°C / min, and the rest was the same as in Example 1.

[0101] Example 6

[0102] (1) The gas flow rate of the second stage in step 3) was changed from 12 L / min to 10 L / min, and the holding time was changed from 5 h to 10 h, and the rest was the same as in Example 1.

[0103] (2) The gas flow rate of the second stage in step 3) was changed from 12 L / min to 20 L / min, and the holding time was changed from 5 h to 2 h, and the rest was the same as in Example 1.

[0104] (3) The gas flow rate of the second stage in step 3) was changed from 12 L / min to 10 L / min, and the holding time was changed from 5 h to 2 h, and the rest was the same as in Example 1.

[0105] Example 7

[0106] (1) The holding temperature of the first stage in step 3) was changed from 750°C to 600°C, and the holding time was changed from 12 h to 10 h, and the rest was the same as in Example 1.

[0107] (2) The holding temperature of the first stage in step 3) was adjusted from 750°C to 800°C, and the holding time was adjusted from 12 h to 20 h, and the rest was the same as in Example 1.

[0108] (3) The temperature increasing rate of the first stage in step 3) was adjusted from 3°C / min to 10°C / min, and the gas flow was adjusted from 8 L / min to 15 L / min, and the rest was the same as in Example 1.

[0109] (4) The temperature increasing rate of the first stage in step 3) was adjusted from 3°C / min to 1°C / min, and the gas flow was adjusted from 8 L / min to 5 L / min, and the rest was the same as in Example 1.

[0110] Example 8

[0111] (1) The temperature decreasing rate of the second stage in step 3) was adjusted from 5°C / min to 10°C / min, and the gas flow was adjusted from 8 L / min to 10 L / min, and the rest was the same as in Example 1.

[0112] (2) The temperature decreasing rate of the second stage in step 3) was adjusted from 5°C / min to 1°C / min, and the gas flow was adjusted from 8 L / min to 20 L / min, and the rest was the same as in Example 1.

[0113] Comparative Example 1

[0114] The holding temperature of the second stage in step 3) was adjusted from 500°C to 300°C, and the rest was the same as in Example 1.

[0115] Comparative Example 2

[0116] The holding temperature of the second stage in step 3) was adjusted from 500°C to 800°C, and the rest was the same as in Example 1.

[0117] Comparative Example 3

[0118] The temperature decreasing rate of the third stage in step 3) was adjusted from 15°C / min to 5°C / min, and the rest was the same as in Example 1.

[0119] Comparative Example 4

[0120] Step 3) was replaced by the following step, and the rest was the same as in Example 1:

[0121] The precursor mixed powder was heated to 750°C at a rate of 3°C / min under a nitrogen atmosphere and held for 12 h, and the gas flow was 8 L / min, to obtain a carbon-coated titanyl phosphate potassium compound powder.

[0122] Comparative Example 5

[0123] In addition to hydrogen annealing, high-temperature sintering can also be used to form oxygen defects. When high-temperature sintering is used to prepare electrode materials, oxygen atoms can obtain enough energy to escape from the lattice and leave the surface of the material due to the high temperature, thereby leaving vacancies in the lattice and forming oxygen defects. As mentioned earlier, the bulk and surface of the sample after high-temperature sintering both show oxygen loss, forming oxygen defects.

[0124] Therefore, we studied whether high-temperature sintering is suitable for forming ideal KTOP materials with oxygen defects: replace step 3) with the following steps, and the rest are the same as example 1:

[0125] The precursor mixed powder was heated to 950°C at a rate of 3°C / min under a nitrogen atmosphere and held for 12 h, with a gas flow of 8 L / min, to obtain a carbon-coated potassium titanyl phosphate compound powder.

[0126] Test example

[0127] The negative electrode materials prepared in the above examples and comparative examples were used to construct sodium ion batteries, and the electrical properties of each battery were tested.

[0128] Chemical formula determination: The prepared material was heated in air at 500-600°C to remove the carbon coating, and then the elemental content was determined by ICP to determine the chemical formula of the material.

[0129] Specific capacity test: The obtained negative electrode material, superP, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, NMP was added and stirred to obtain an active slurry. The positive electrode active slurry was uniformly coated on the surface of an aluminum foil current collector, and a 200 um doctor blade coating was prepared. After drying and cold pressing, the electrode sheet was obtained, and the mass loading of the active material was about 2.5 mg cm -2 The negative electrode was a metal sodium sheet. PE was selected as the separator, with a thickness of 10 μm. Cell assembly: the positive electrode sheet, separator, negative electrode sheet, and separator were arranged in order, and the winding method was selected. Electrolyte preparation: sodium hexafluorophosphate was dissolved in ethylene carbonate to a concentration of 1 mol / L. The above assembled coin cell was subjected to conventional 0.1C charge-discharge characterization, and the charge-discharge voltage range was 0-3V.

[0130] Sodium ion diffusion coefficient test: the ion diffusion coefficient of the material was tested by the constant current intermittent titration method GITT.

[0131] The results are as follows:

[0132] Table 1 test results

[0133]

[0134] From the comparison of Examples 1-3 and Comparative Examples 1-2, it can be seen that the hydrogen annealing temperature has an effect on the product: when the annealing temperature is between 400-600℃, the content of oxygen defects in the material is about 1%, and as the temperature rises, the oxygen defect content and specific capacity increase slightly, and the diffusion coefficient is in the order of 10-9. When the annealing temperature is less than 400℃, the hydrogen is not capable of capturing oxygen atoms due to the low annealing temperature, and oxygen defects cannot be formed, at which time the specific capacity decreases by about 20%, and the diffusion coefficient decreases to the order of 10-10. When the temperature is higher than 600℃, there are too many oxygen defects, which causes the lattice to collapse, resulting in a sharp decrease in the specific capacity and diffusion coefficient of the material.

[0135] From the comparison of Examples 4-5 and Comparative Example 3, it can be seen that the third-stage cooling rate has an effect on the product: as the cooling rate increases, the oxygen defects generated in the second stage can be well maintained, and when the cooling rate drops below 10℃ / min, the oxygen defects generated in the second stage will be offset during the cooling process through cation segregation, and cannot be well maintained. We speculate that when the cooling rate is increased to more than 20℃ / min, more oxygen defects can be formed, but since the powder sintering generally uses a push plate kiln or a roller kiln, it is difficult to achieve such a fast cooling rate.

[0136] From Example 6, it can be seen that when the second-stage holding temperature and the third-stage cooling rate are determined, the second-stage gas flow rate and holding time are mutually influenced: when the gas flow rate is relatively small, the holding time needs to be appropriately extended, and vice versa. However, when both the flow rate and the time are at the lower limit, the effect of hydrogen reduction on the formation of oxygen defects is basically none.

[0137] From Example 7, it can be seen that the first-stage sintering temperature, time, heating rate, and gas flow rate have no obvious effect on the formation of oxygen defects in the product, and the material can maintain a certain amount of oxygen defects, thereby stabilizing the specific capacity of the material at 125mAh / g. This also suggests that although the conditions required in the first stage are more stringent, as long as the second and third stages of sintering are controlled, relatively stable oxygen defect materials can be obtained, laying a foundation for the industrial large-scale preparation of the material, and the product consistency is good.

[0138] From Example 8, it can be seen that the second-stage cooling rate also has no obvious effect on the formation of oxygen defects in the product, and the oxygen defect content remains at about 1%, and the specific capacity is 123-124mAh / g.

[0139] From the comparison of Comparative Example 4 and Example 1, it can be seen that when there is no second-stage hydrogen annealing and third-stage rapid cooling stage, oxygen defects will not be "generated" and "fixed" in the material.

[0140] As can be seen from the comparison between Comparative Example 5 and Example 1, by the way of forming oxygen defects through high-temperature sintering, not only oxygen defects are formed, but also phosphate ions are destroyed, thus causing the collapse of the crystal structure, resulting in the loss of the ability of the material to deintercalate sodium ions, and the calculated specific capacity is only 15 mAh / g.

[0141] Obviously, the above examples are merely illustrative examples for the sake of clarity, and are not limiting on the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. It is not necessary or possible to exhaust all the embodiments here. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for preparing a sodium-ion battery anode material, characterized in that, Includes the following steps: S1, Press K 1-2x TiO 1-x The stoichiometric ratio of PO4 is obtained by mixing phosphorus, potassium, and titanium sources, and then mixing them with a carbon source to obtain a slurry; where x = 0.001-0.

1. S2. Dry the slurry from S1 to obtain the precursor; S3. The precursor of S2 is subjected to a three-stage process to obtain the chemical formula K. 1-2x TiO 1-x PO4@C sodium-ion battery anode material; The three-stage processing includes: First stage: Heat treatment is carried out by heating to the first set temperature in an inert gas atmosphere; Second stage: The product from the first stage is cooled to 400-600℃ in a hydrogen atmosphere for heat treatment; The third stage: The product from the second stage is cooled to a second set temperature at a rate of 10-20℃ / min under a hydrogen atmosphere; wherein, In the first stage, the first set temperature is 600-800℃, and the heat treatment time is 10-20h; In the second stage, the hydrogen flow rate is 10-20 L / min, the heat treatment time is 2-10 h, and any of the following conditions are met: (1) When the heat treatment time is 2 hours, the hydrogen flow rate is greater than 10 L / min; (2) When the flow rate of the hydrogen is 10 L / min, the heat treatment time is greater than 2 h; (3) When the heat treatment time is 10h, the hydrogen flow rate is less than or equal to 20L / min; (4) When the flow rate of the hydrogen is 20 L / min, the heat treatment time is less than or equal to 10 h.

2. The preparation method according to claim 1, characterized in that, Step S1 includes at least one of the following features: (1) The potassium source includes one or more of potassium carbonate, potassium hydroxide, potassium sulfate and potassium dihydrogen phosphate; (2) The titanium source includes one or more of titanium dioxide, metatitanic acid, titanic acid and titanium tetrachloride; (3) The phosphorus source includes one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, and phosphorus pentoxide; (4) The carbon source includes one or more of graphite, activated carbon, hard carbon, graphene and carbon black.

3. The preparation method according to claim 1, characterized in that, Step S1 includes at least one of the following features: (1) In the sodium-ion battery anode material, the mass percentage of carbon source is 1-5 wt%; (2) The mixing method includes wet ball milling; (3) The mixing includes the following steps: first, mixing phosphorus source, potassium source and titanium source to obtain slurry A, and then mixing slurry A with carbon source to obtain slurry B; (4) The slurry contains a solvent; the solvent includes water or a mixture of water and ethanol.

4. The preparation method according to claim 1, characterized in that, In step S2, the drying method is centrifugal spray drying.

5. The preparation method according to claim 1, characterized in that, In the first stage of step S3, at least one of the following features is included: (1) The inert gas includes argon and / or hydrogen; (2) The heating rate is 1-10℃ / min; (3) The flow rate of the inert gas is 5-15 L / min.

6. The preparation method according to claim 1, characterized in that, In the second stage of step S3, the cooling rate is 1-10℃ / min.

7. The preparation method according to claim 1, characterized in that, In the third stage of step S3, at least one of the following features is included: (1) The second set temperature is 20-30℃; (2) The flow rate of the hydrogen gas is 10-20 L / min; (3) The cooling methods include liquid cooling or air cooling.

8. A sodium-ion battery anode material prepared by the preparation method according to any one of claims 1-7.

9. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active layer disposed on at least one side of the current collector along the thickness direction, wherein the negative electrode active layer contains the sodium-ion battery negative electrode material of claim 8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery contains the negative electrode sheet as described in claim 9.

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