Sodium-ion battery negative electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention relates to a sodium-ion battery negative electrode material, a preparation method thereof and a sodium-ion battery, and belongs to the technical field of sodium-ion batteries. The chemical formula of the sodium ion battery negative electrode material is MTiOPO4, wherein M is selected from one or more of Na, Li and K. The preparation method comprises the following steps: S1, carrying out ball milling and spray drying on MH2PO4 and TiO2 to obtain a precursor; and S2, sintering and grinding the precursor to obtain the sodium ion battery negative electrode material. The sodium ion battery negative electrode material MTiOPO4 provided by the invention has a larger cross cavity, and has huge potential in the aspect of realizing faster ion kinetics and lower cyclic strain of the sodium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium ion battery negative electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] Negative electrode materials for sodium-ion batteries play a key role in improving battery performance. At present, the mainstream negative electrode materials are carbon-based materials, alloy materials and transition metal oxides. Carbon-based materials such as hard carbon and soft carbon can provide reversible insertion and extraction sites for sodium ions due to their stable structure and good conductivity. Among them, hard carbon has attracted much attention due to its high sodium storage capacity. In some systems, the reversible capacity exceeds 300mAh / g, but the hard carbon material has SEI film. The rupture and re-growth of SEI film during the cycle process leads to the consumption of sodium ions. The cycle life of such battery systems is not long. Alloy materials such as Sn and Sb have extremely high theoretical sodium storage capacity, which can reach 800mAh / g-1000mAh / g, but the huge volume change during the charge and discharge process can easily cause material pulverization and electrode structure damage, limiting their application. Transition metal oxides such as titanium-based oxides can be used for sodium ion storage due to their stable crystal structure and unique redox active centers. However, the most mature of the existing titanium-based oxides is sodium titanium phosphate, but its electrochemical potential as a negative electrode material for sodium ion batteries is relatively high, about 2.1V (relative to the metallic sodium electrode).

[0003] Therefore, it is still necessary to develop a titanium-based oxide with low electrochemical potential and that can be mass-produced on an industrial scale. Summary of the invention

[0004] To this end, the technical problem to be solved by the present invention is to overcome the problems of low specific energy and low rate performance of the negative electrode materials of sodium ion batteries in the prior art.

[0005] In order to solve the above technical problems, the present invention provides a sodium ion battery negative electrode material and a preparation method thereof and a sodium ion battery.

[0006] The first object of the present invention is to provide a negative electrode material for a sodium ion battery, wherein the chemical formula of the negative electrode material for a sodium ion battery is MTiOPO4, where M is selected from one or more of Na, Li and K.

[0007] In one embodiment of the present invention, the chemical formula of the negative electrode material of the sodium ion battery is K 1-x Na x TiOPO4 and / or Li 1-y Na y TiOPO4, 0≤x<1, 0≤y<1.

[0008] In one embodiment of the present invention, the chemical formula of the negative electrode material of the sodium ion battery is K 0.15 Na 0.85 TiOPO4, K 0.9 Na 0.1 TiOPO4, K 0.8 Na 0.2 TiOPO4 and K 0.7 Na 0.3 One or more of TiOPO4.

[0009] The second object of the present invention is to provide a method for preparing the negative electrode material of a sodium ion battery, comprising the following steps:

[0010] S1, ball milling and spray drying MH2PO4 and TiO2 to obtain a precursor;

[0011] S2. Sintering and grinding the precursor described in S1 to obtain the negative electrode material for the sodium ion battery.

[0012] In one embodiment of the present invention, in S1, the MH2PO4 is selected from one or more of KH2PO4, NaH2PO4 and LiH2PO4;

[0013] And / or, the TiO2 is anatase phase titanium dioxide.

[0014] In one embodiment of the present invention, in S1, the ball milling speed is 300rpm-800rpm, the time is 2h-24h, the temperature is 60℃-90℃, the material-ball ratio is 2:(1-2), and the solid content is 30%-60%; the particle size D50 of the material after ball milling does not exceed 1μm.

[0015] Further, the speed of the ball mill is 300rpm, 350rpm, 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm, 800rpm, or any speed between any two values; the time is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, or any time between any two values. Any time; the temperature is 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, or any temperature between any two values; the ball ratio is (2:1), (2:1.1), (2:1.2), (2:1.3), (2:1.4), (2:1.5), (2:1.6), (2:1.7), (2:1.8), (2:1.9), (2:2), or any ratio between any two values; the solid content is 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any solid content between any two values.

[0016] In one embodiment of the present invention, in S1, the inlet air temperature of the spray drying is 150°C-250°C, the rotation speed is 12000rpm-18000rpm; the particle size D50 of the material after spray drying is 5μm-30μm.

[0017] Further, the inlet air temperature of the spray drying is 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, 250°C, or any temperature between any two values; the rotation speed is 12000rpm, 13000rpm, 14000rpm, 15000rpm, 16000rpm, 17000rpm, 18000rpm, or any rotation speed between any two values.

[0018] In one embodiment of the present invention, in S2, the sintering is carried out under a protective atmosphere, with the temperature being increased to 700°C-850°C at a heating rate of 2°C / min-5°C / min, and the temperature being kept for 2h-6h.

[0019] Furthermore, the sintering heating rate is 2°C / min, 3°C / min, 4°C / min, 5°C / min, or any rate between any two values; the temperature is 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any temperature between any two values; the insulation time is 2h, 3h, 4h, 5h, 6h, or any time between any two values.

[0020] In one embodiment of the present invention, the reaction mode of the preparation method is: MH2PO4+TiO2=MTiOPO4+H2O.

[0021] The third object of the present invention is to provide a sodium ion battery, wherein the negative electrode material of the sodium ion battery is the negative electrode material of the sodium ion battery, and the positive electrode material is selected from a polyanion positive electrode material and / or a Prussian blue positive electrode material.

[0022] The technical solution of the present invention has the following advantages over the prior art:

[0023] (1) The sodium ion battery negative electrode material MTiOPO4 described in the present invention has a larger cross-cavity and has great potential in achieving faster ion dynamics and lower cycle strain in sodium ion batteries.

[0024] (2) The sodium ion battery negative electrode material MTiOPO4 described in the present invention can obtain active materials with different specific capacities by regulating the ratio of different metal ions.

[0025] (3) The preparation method described in the present invention uses anatase phase titanium dioxide as a titanium source. The crystal structure of anatase phase titanium dioxide is relatively open. This structure enables anatase to have a higher specific surface area and more surface active sites. It can react with potassium dihydrogen phosphate and sodium dihydrogen phosphate under heating conditions to form stable compounds.

[0026] (4) The preparation method described in the present invention adopts a conventional solid-phase synthesis method. By controlling the process parameters of ball milling (such as the temperature of ball milling), the synthetic purity of the material is guaranteed, the specific capacity of the material is fully utilized, and it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 XRD spectra of the negative electrode materials of the sodium ion battery of Example 7 and Comparative Example 1 in Test Example 1 of the present invention;

[0029] Figure 2 XRD spectra of the negative electrode materials of the sodium ion battery of Example 1 and Comparative Example 2 in Test Example 1 of the present invention;

[0030] Figure 3 A charge and discharge curve diagram of a battery made of the sodium ion battery negative electrode material of Example 1 in Test Example 2 of the present invention at a 1C rate;

[0031] Figure 4 The charge and discharge curve of the battery made of the sodium ion battery negative electrode material of Example 4 in Test Example 2 of the present invention at a rate of 1C;

[0032] Figure 5 The charge and discharge curve of the battery made of the sodium ion battery negative electrode material of Example 6 in Test Example 2 of the present invention at a rate of 1C;

[0033] Figure 6 The charge and discharge curve and ion diffusion rate calculation diagram of the battery made of the sodium ion battery negative electrode material of Example 1 in Test Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The present invention is 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 implement it. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0035] In the present invention, unless otherwise explained, technical and scientific terms used in the present invention have the same meanings as commonly understood by those skilled in the art to which the present invention belongs.

[0036] In the present invention, unless otherwise stated, the term "and / or" used in the present invention includes any and all combinations of one or more of the associated listed items.

[0037] In the present invention, unless otherwise stated, the experimental methods used in the embodiments of the present invention are conventional methods unless otherwise stated, and the materials, reagents, etc. used are all commercially available unless otherwise stated.

[0038] In the present invention, unless otherwise specified, the reaction mode involved in the preparation of the negative electrode material for sodium ion batteries in the embodiments of the present invention is MH2PO4+TiO2=MTiOPO4+H2O.

[0039] Example 1

[0040] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:.

[0041] S1. Weigh the corresponding mass of potassium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 2:1, the solid content is 50%, ball milling is carried out at 400 rpm and 80 ° C for 5 hours, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.5 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 200 ° C, and the rotation speed is 15000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0042] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 700°C at a heating rate of 2°C / min and kept at this temperature for 5 hours. After naturally cooling to room temperature, the precursor was ground to obtain KTiOPO4, a negative electrode material for sodium ion batteries.

[0043] Example 2

[0044] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0045] S1. Weigh the corresponding mass of potassium dihydrogen phosphate, sodium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 2:1, the solid content is 50%, ball milling is carried out at 400 rpm and 80 ° C for 5 hours, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.8 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 200 ° C, and the rotation speed is 15000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0046] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 750°C at a heating rate of 4°C / min and kept at this temperature for 5 hours. After naturally cooling to room temperature, the precursor was ground to obtain the sodium ion battery negative electrode material K. 0.8 Na 0.2 TiOPO4.

[0047] Example 3

[0048] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0049] S1. Weigh the corresponding mass of potassium dihydrogen phosphate, sodium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 1:1, the solid content is 40%, ball milling is carried out at 400 rpm and 80°C for 5 h, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 180°C, and the rotation speed is 12000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0050] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 800°C at a heating rate of 2°C / min and kept at this temperature for 2 hours. After naturally cooling to room temperature, the precursor was ground to obtain the sodium ion battery negative electrode material K. 0.7 Na 0.3 TiOPO4.

[0051] Example 4

[0052] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0053] S1. Weigh the corresponding mass of sodium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 2:1.5, the solid content is 45%, ball milling is carried out at 400 rpm and 80 ° C for 5 h, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 210 ° C, and the rotation speed is 15000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0054] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 780°C at a heating rate of 5°C / min and kept warm for 3 hours. After naturally cooling to room temperature, the precursor was ground to obtain NaTiOPO4, a negative electrode material for sodium ion batteries.

[0055] Example 5

[0056] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0057] S1. Weigh the corresponding mass of lithium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 2:1, the solid content is 55%, ball milling is carried out at 400 rpm and 80°C for 5 hours, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 200°C, and the rotation speed is 18000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0058] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 780°C at a heating rate of 5°C / min and kept warm for 3 hours. After naturally cooling to room temperature, the precursor was ground to obtain LiTiOPO4, a negative electrode material for sodium ion batteries.

[0059] Example 6

[0060] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0061] S1. According to the stoichiometric ratio, lithium dihydrogen phosphate, sodium dihydrogen phosphate and anatase phase titanium dioxide of corresponding mass are weighed, deionized water is added, and the mixture is put into a planetary ball mill, zirconium oxide beads are used as grinding media, the material-ball ratio is 1:1, the solid content is 50%, and the mixture is ball milled at 400 rpm and 80°C for 5 h. The particle size of the slurry is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; the slurry is then spray-dried by a centrifugal spray dryer, the inlet air temperature is 240°C, and the rotation speed is 17000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0062] S2, the precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 780°C at a heating rate of 5°C / min and kept warm for 3h, and then ground after naturally cooling to room temperature to obtain the sodium ion battery negative electrode material Li 0.5 Na 0.5 TiOPO4.

[0063] Example 7

[0064] The sodium ion battery negative electrode material and the preparation method thereof of this embodiment specifically include the following steps:

[0065] S1. Weigh the corresponding mass of potassium dihydrogen phosphate, sodium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 1:1, the solid content is 40%, ball milling is carried out at 400 rpm and 80°C for 5 h, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 180°C, and the rotation speed is 12000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0066] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 800°C at a heating rate of 2°C / min and kept at this temperature for 2 hours. After naturally cooling to room temperature, the precursor was ground to obtain the sodium ion battery negative electrode material K. 0.15 Na 0.85 TiOPO4.

[0067] Comparative Example 1

[0068] The method is basically the same as Example 7, except that the anatase phase titanium dioxide is replaced with rutile phase titanium dioxide, and specifically comprises the following steps:

[0069] S1. Weigh the corresponding mass of potassium dihydrogen phosphate, sodium dihydrogen phosphate and rutile phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 1:1, the solid content is 40%, ball milling is carried out at 400 rpm and 80°C for 5 hours, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.3 μm; then spray dry the slurry with a centrifugal spray dryer, the inlet air temperature is 180°C, and the rotation speed is 12000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0070] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 800°C at a heating rate of 2°C / min and kept at this temperature for 2 hours. After naturally cooling to room temperature, the precursor was ground to obtain the sodium ion battery negative electrode material K. 0.15 Na 0.85 TiOPO4.

[0071] Comparative Example 2

[0072] The method is basically the same as Example 1, except that the ball milling temperature is changed to 20° C., and specifically comprises the following steps:

[0073] S1. Weigh the corresponding mass of potassium dihydrogen phosphate and anatase phase titanium dioxide according to the stoichiometric ratio, add deionized water, put into a planetary ball mill, use zirconium oxide beads as grinding media, the material-ball ratio is 2:1, the solid content is 50%, ball milling is carried out at 400 rpm and 20°C for 5 hours, and the slurry particle size is tested by a laser particle size analyzer until the particle size D50 of the slurry is less than 0.5 μm; then use a centrifugal spray dryer to spray dry the slurry, the inlet air temperature is 200°C, and the rotation speed is 15000 rpm, to obtain a precursor with a particle size D50 of about 10 μm;

[0074] S2. The precursor was transferred to a tubular furnace in a nitrogen atmosphere, heated to 700°C at a heating rate of 2°C / min and kept at this temperature for 5 hours. After naturally cooling to room temperature, the precursor was ground to obtain KTiOPO4, a negative electrode material for sodium ion batteries.

[0075] Test Example 1

[0076] XRD characterization was performed on the negative electrode materials of sodium ion batteries of Examples 1 and 7 and Comparative Examples 1-2. The results are as follows: Figure 1-Figure 2 shown.

[0077] from Figure 1 It can be seen that only anatase-type titanium dioxide can be sintered to produce the required titanium-phosphorus oxide, indicating that the crystal phase selection of titanium dioxide is very important for the synthesis of materials. This is because when Example 7 uses anatase-phase titanium dioxide as a titanium source, since the oxygen ions are cubically packed, the Ti atoms are located in the octahedral voids, and can react with potassium dihydrogen phosphate and sodium dihydrogen phosphate under heating conditions to form stable compounds. However, when Comparative Example 1 uses rutile-phase titanium dioxide as a titanium source, since the rutile-phase titanium dioxide structure is more stable, it is difficult to react with other compounds, so it is still a rutile titanium dioxide phase after sintering.

[0078] from Figure 2It can be seen that in the XRD of the sodium ion battery negative electrode material of Comparative Example 2, there is a heterogeneous phase of potassium dihydrogen phosphate (the five-pointed star in the figure is the diffraction peak of potassium dihydrogen phosphate), which shows that the ball milling temperature has a certain influence on the purity of the synthetic material. This is because of the solubility of potassium dihydrogen phosphate, sodium dihydrogen phosphate, and lithium dihydrogen phosphate. At 20°C, the solubility of potassium dihydrogen phosphate is 22.6g / L, the solubility of sodium dihydrogen phosphate is 86.9g / L, and the solubility of lithium dihydrogen phosphate is 30.5g / L; in order to obtain a uniformly mixed slurry, it is necessary to completely dissolve all the solid phase titanium dioxide in water during ball milling, and use anatase phase titanium dioxide as a template during sintering to react chemically and generate the required phase. Otherwise, a heterogeneous phase will appear during sintering, and the main components of the heterogeneous phase are raw materials such as potassium dihydrogen phosphate, sodium dihydrogen phosphate, and lithium dihydrogen phosphate that have not reacted completely, which leads to a decrease in specific capacity. Therefore, when comparative example 2 was ball-milled at room temperature, the reaction was incomplete due to the insufficient solubility of potassium dihydrogen phosphate, and there was an impurity phase of potassium dihydrogen phosphate.

[0079] Test Example 2

[0080] Battery Assembly:

[0081] Negative electrode sheet: Sodium ion battery negative electrode material, conductive agent is conductive carbon black (super P), adhesive is polyvinylidene fluoride (PVDF), negative electrode current collector is 6μm aluminum foil; sodium ion battery negative electrode material, conductive agent and adhesive are mixed according to the mass ratio of 8:1:1, N-methylpyrrolidone is added and stirred into a uniform and stable negative electrode slurry, and then the negative electrode slurry is evenly coated on the surface of the negative electrode current collector, and 200μm scraper coating is performed, and the negative electrode sheet is obtained after drying and cold pressing. The mass loading of the sodium ion battery negative electrode material is about 2.5mg / cm 2 .

[0082] Counter electrode: Sodium metal sheet.

[0083] Isolation film: The base film of the isolation film is a polyethylene film with a thickness of 9μm.

[0084] Electrolyte: Sodium hexafluorophosphate was dissolved in ethylene carbonate to prepare an electrolyte with a concentration of 1 mol / L.

[0085] Assembly of sodium ion battery: Arrange the negative electrode sheet, separator, counter electrode and separator in sequence, and use winding as the assembly method.

[0086] Performance Test:

[0087] The assembled sodium ion battery is tested for charge / discharge, sodium ion diffusion coefficient, etc.:

[0088] (1) Charge / discharge test: The sodium ion battery is charged / discharged at a rate of 1C in the voltage range of 0-3V;

[0089] (2) Sodium ion diffusion coefficient test: the ion diffusion coefficient of the material is tested by the constant current intermittent titration method (GITT);

[0090] Table 1 and Figure 3-6 The following are the relevant performance parameters finally measured:

[0091] Table 1

[0092]

[0093] From Table 1 and Figure 3-5 It can be seen that the sodium ion battery negative electrode material KTiOPO4 of Example 1 has the highest actual specific capacity (116mAh / g) and the lowest electrochemical potential (1.23V (relative to sodium electrode)). As the proportion of potassium ions in the material decreases, the difference between its actual capacity and theoretical specific capacity becomes larger and larger. This is mainly because potassium ions have a larger ionic radius and can provide a larger ion diffusion channel for the insertion of sodium ions, thereby having a higher electrochemical capacity; as the proportion of potassium ions decreases, the potassium ions that serve as framework support during the charge and discharge process become fewer and fewer, and the deintercalation of sodium ions tends to be difficult, which is manifested as a decrease in specific capacity and a decrease in the sodium ion diffusion coefficient. When the negative electrode material of the sodium ion battery is LiTiOPO4, the theoretical specific capacity of this material is the highest, reaching 161mAh / g, but the actual specific capacity is only 35mAh / g. This is because the radius of lithium ions is small and they cannot serve as lattice structure support. The deintercalation of sodium ions is very difficult. When some sodium ions are "doped" (Li 0.5 Na 0.5 TiOPO4), its capacity is improved, this is because the addition of sodium ions can support a large enough space to meet the sodium ion in the electrolyte. The electrochemical potential of the sodium ion battery negative electrode material in each embodiment does not change much, mainly because the potential is determined by Ti 3+ ions to Ti 4+ Theoretically, it is a fixed value, but due to the changes in the crystal field around the titanium ions caused by different cations and their contents, the electrochemical potential produces slight deviations.

[0094] From Table 1 and Figure 6 It can be seen that Figure 6 The left side is the voltage during charge and discharge (marked as B in the figure), and the right side is the sodium ion diffusion coefficient calculated at different charge and discharge voltages (marked as C in the figure). Example 1 has the highest actual specific capacity (116 mAh / g) and the largest sodium ion diffusion coefficient (3*10 -9 cm 2 s -1This is because the larger ionic radius of potassium ions can provide a larger ion diffusion channel for the insertion of sodium ions, thereby having a higher electrochemical capacity and ion diffusion coefficient; the average sodium ion diffusion coefficient of the samples in other embodiments is less than 10 -9 cm 2 s -1 , a high sodium ion diffusion coefficient is beneficial to the high rate performance and cycle stability of the battery.

[0095] 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. A sodium ion battery negative electrode material, characterized in that: The chemical formula of the sodium ion battery negative electrode material is MTiOPO4, where M is selected from one or more of Na, Li and K.

2. The sodium ion battery negative electrode material according to claim 1, characterized in that The chemical formula of the negative electrode material of the sodium ion battery is K 1-x Na x TiOPO4 and / or Li 1-y Na y TiOPO4, 0≤x<1, 0≤y<1.

3. The sodium ion battery negative electrode material according to claim 1, characterized in that The chemical formula of the negative electrode material of the sodium ion battery is K 0.15 Na 0.85 TiOPO4, K 0.9 Na 0.1 TiOPO4, K 0.8 Na 0.2 TiOPO4 and K 0.7 Na 0.3 One or more of TiOPO4.

4. The method for preparing a negative electrode material for a sodium ion battery according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, ball milling and spray drying MH2PO4 and TiO2 to obtain a precursor; S2. Sintering and grinding the precursor described in S1 to obtain the negative electrode material for the sodium ion battery.

5. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: In S1, the MH2PO4 is selected from one or more of KH2PO4, NaH2PO4 and LiH2PO4; And / or, the TiO2 is anatase phase titanium dioxide.

6. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: In S1, the ball milling speed is 300rpm-800rpm, the time is 2h-24h, the temperature is 60℃-90℃, the material-ball ratio is 2:(1-2), and the solid content is 30%-60%; the particle size D50 of the material after ball milling does not exceed 1μm.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: In S1, the inlet air temperature of the spray drying is 150°C-250°C, and the rotation speed is 12000rpm-18000rpm; the particle size D50 of the material after spray drying is 5μm-30μm.

8. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: In S2, the sintering is carried out under a protective atmosphere, with the temperature being increased to 700°C-850°C at a heating rate of 2°C / min-5°C / min, and the temperature being kept for 2h-6h.

9. The method for preparing a negative electrode material for a sodium ion battery according to claim 4, characterized in that: The reaction mode of the preparation method is: MH2PO4+TiO2=MTiOPO4+H2O.

10. A sodium ion battery, characterized in that: The negative electrode material of the sodium ion battery is the negative electrode material of the sodium ion battery according to any one of claims 1 to 3, and the positive electrode material is selected from a polyanion positive electrode material and / or a Prussian blue positive electrode material.

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