Lithium vanadium phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a lithium vanadium phosphate positive electrode material and a preparation method and application thereof, the lithium vanadium phosphate positive electrode material is an erbium-doped Li3V2 (PO4) 3 / C material, the structural formula of the lithium vanadium phosphate positive electrode material is Li3V2-xErx (PO4) 3 / C, and x is more than 0 and less than or equal to 0.12. The preparation method of the lithium vanadium phosphate positive electrode material comprises the following steps: (1) mixing lithium dihydrogen phosphate, a vanadium source, an erbium source and a carbon source to obtain a mixture; (2) carrying out ball milling on the mixture, and then carrying out drying treatment to obtain a dried material; and (3) sintering the dried material to obtain the lithium vanadium phosphate positive electrode material. According to the invention, the Li3V2 (PO4) 3 / C material is used as a basis and is doped with the erbium element to obtain the Li3V2-xErx (PO4) 3 / C material, and the erbium-doped Li3V2 (PO4) 3 / C material does not influence the crystal structure, the morphology, the particle size and the like, and can effectively improve the electronic conductivity, the specific discharge capacity and the cycling stability of the Li3V2 (PO4) 3 / C material, so that the Li3V2 (PO4) 3 / C material has better electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium vanadium phosphate cathode material, its preparation method, and its application. Background Technology

[0002] The quality of the positive and negative electrode materials for lithium-ion batteries is a crucial factor in evaluating their performance. The capacity, cycle performance, and safety of the positive electrode material all constrain the development of lithium-ion batteries. Li3V2(PO4)3 / C, as a novel positive electrode material, possesses a high theoretical specific capacity (197 mAh / g) and voltage plateau (3.0-4.8V), along with low raw material costs. Furthermore, Li3V2(PO4)3 / C exhibits a three-dimensional lithium-ion diffusion channel, a large lithium-ion diffusion coefficient, excellent high-rate discharge performance, good high-current charge-discharge performance, high specific energy density, and good low-temperature performance. Moreover, within the 3.0-4.8V voltage range, all three lithium ions can undergo reversible insertion and extraction within Li3V2(PO4)3 / C, achieving a theoretical capacity of 197 mAh / g, making it a highly promising positive electrode material for lithium-ion batteries. However, Li3V2(PO4)3 / C materials have the disadvantages of poor electronic conductivity and cycling performance. Therefore, how to improve the electronic conductivity and cycling performance of Li3V2(PO4)3 / C materials is an urgent problem to be solved. Summary of the Invention

[0003] In view of this, the present invention provides a lithium vanadium phosphate cathode material, its preparation method and application, to solve the problem of poor electronic conductivity and cycle performance of existing Li3V2(PO4)3 / C materials.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] On one hand, the present invention provides a lithium vanadium phosphate cathode material, wherein the cathode material is an erbium-doped Li3V2(PO4)3 / C material, and its structural formula is Li3V 2-x Er x (PO4)3 / C, where 0 < x ≤ 0.12.

[0006] Preferably, the value of x is 0.05≤x≤0.08.

[0007] On the other hand, the present invention provides a method for preparing the above-mentioned lithium vanadium phosphate cathode material, comprising the following steps:

[0008] (1) Lithium dihydrogen phosphate, vanadium source, erbium source and carbon source are mixed to obtain a mixture;

[0009] (2) The mixture is ball-milled and then dried to obtain dried material;

[0010] (3) The dried material is sintered to obtain lithium vanadium phosphate cathode material.

[0011] Preferably, the molar ratio of lithium, vanadium, erbium, phosphorus and carbon in the mixture is 3.15:(2.0-x):x:3.0:(2.0-3.5), where 0 < x ≤ 0.12.

[0012] Preferably, the vanadium source includes at least one of vanadium pentoxide and ammonium metavanadate.

[0013] Preferably, the erbium source includes at least one of erbium trioxide, erbium sulfate trihydrate, erbium carbonate, and erbium oxalate.

[0014] Preferably, the carbon source includes at least one of glucose, sucrose, and citric acid.

[0015] Preferably, the ball mill rotates at a speed of 400-600 r / min for 6-8 h, with a ball-to-material mass ratio of 20-25:1-2, and uses ethanol and / or water as a dispersant.

[0016] Preferably, the drying process is carried out at a temperature of 60-80°C for 10-14 hours.

[0017] Preferably, the sintering includes a first sintering and a second sintering performed sequentially; wherein the first sintering involves heating from room temperature to 300-400℃ at a rate of 4-5℃ / min, and sintering at 300-400℃ for 4-5 hours; the second sintering involves heating from 300-400℃ to 800-900℃ at a rate of 2-3℃ / min, and sintering at 800-900℃ for 8-10 hours.

[0018] Preferably, the sintering process further includes the following steps: cooling the sintered material, grinding it, and sieving it to obtain the positive electrode material.

[0019] Preferably, the sieving process involves passing the material through a 200-400 mesh sieve and collecting the material that passes through the sieve.

[0020] Furthermore, the present invention also provides an application of the lithium vanadium phosphate cathode material described in any one of the above claims or the lithium vanadium phosphate cathode material prepared by the method described in any one of the above claims in a lithium-ion battery.

[0021] This invention provides a lithium vanadium phosphate cathode material, its preparation method, and its application. Compared with the prior art, its advantages are as follows:

[0022] This invention is based on Li3V2(PO4)3 / C material and dops it with erbium to obtain Li3V 2-x Er xErbium-doped Li3V2(PO4)3 / C materials not only do not affect the crystal structure, morphology, and particle size, but also effectively improve the electronic conductivity, discharge specific capacity, and cycle stability of Li3V2(PO4)3 / C materials, giving them better electrochemical performance.

[0023] Furthermore, this invention prepares Li3V using a carbothermal reduction method. 2-x Er x The (PO4)3 / C material is simple to implement and easy to achieve. It uses lithium dihydrogen phosphate as both the lithium and phosphorus source, which reduces ammonia emissions compared to the traditional method of using ammonium dihydrogen phosphate as the phosphorus source. It is green, environmentally friendly, and suitable for industrial production. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 The images show the XRD patterns of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1.

[0026] Figure 2 SEM images of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1;

[0027] Figure 3 The particle size distribution diagrams are for the lithium vanadium phosphate cathode materials of Example 1 and Comparative Example 1.

[0028] Figure 4 Raman spectra of lithium vanadium phosphate cathode materials in Example 1 and Comparative Example 1;

[0029] Figure 5 XPS images of lithium vanadium phosphate cathode materials from Example 1 and Comparative Example 1;

[0030] Figure 6 This is a schematic diagram showing the constant current charge-discharge test results of the lithium vanadium phosphate cathode material in Examples 1-5 and Comparative Example 1;

[0031] Figure 7 The graph shows the cycling performance of lithium vanadium phosphate cathode materials in Examples 1-5 and Comparative Example 1 at a 2C rate.

[0032] Figure 8 Cyclic voltammetry diagrams of lithium vanadium phosphate cathode materials in Examples 1-5 and Comparative Example 1 are shown.

[0033] Figure 9Nyquist plots of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1;

[0034] Figure 10 The first charge-discharge cycle of the lithium vanadium phosphate cathode material in Example 1 and Comparative Example 1 is shown. Detailed Implementation

[0035] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments below are merely illustrative and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the later embodiments, conditions and methods known in the art can be used for processing.

[0036] In one aspect, the present invention provides a lithium vanadium phosphate cathode material, wherein the cathode material is an erbium-doped Li3V2(PO4)3 / C material with the structural formula Li3V 2-x Er x (PO4)3 / C, where 0 < x ≤ 0.12, preferably 0.05 ≤ x ≤ 0.08, and specifically can be 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 and 0.12, etc.

[0037] This invention improves the electronic conductivity and cycle stability of Li3V2(PO4)3 / C materials by doping them with erbium, thus giving them better electrochemical performance.

[0038] In another aspect, the present invention provides a method for preparing the above-mentioned lithium vanadium phosphate cathode material, comprising the following steps:

[0039] (1) Lithium dihydrogen phosphate, vanadium source, erbium source and carbon source are mixed to obtain a mixture;

[0040] (2) The mixture is ball-milled and then dried to obtain dried material;

[0041] (3) The dried material is sintered to obtain lithium vanadium phosphate cathode material.

[0042] In this invention, lithium dihydrogen phosphate, vanadium source, erbium source and carbon source are first mixed to obtain a mixture.

[0043] In some embodiments of the present invention, the molar ratio of lithium, vanadium, erbium, phosphorus and carbon in the mixture is 3.15:(2.0-x):x:3.0:(2.0-3.5), where 0 < x ≤ 0.12. Therefore, the molar ratio of lithium, vanadium, erbium, phosphorus and carbon can be 3.15:1.97:0.03:3.0:3.5, 3.15:1.95:0.05:3.0:3.0, 3.15:1.92:0.08:3.0:3.5, 3.15:1.9:0.10:3.0:2.0 and 3.15:1.88:0.12:3.0:3.5, etc.

[0044] Erbium (Er₂O₃) is abundant in nature, relatively inexpensive compared to rare earth elements, and Er₂O₃... 3+ Ionic radius and V 3+ Li + When the erbium is close to or appropriately replaced, it can suppress lattice distortion and volume change during the charging and discharging process, improve structural reversibility, and significantly extend cycle life. Therefore, the present invention uses erbium-doped lithium vanadium phosphate, which has the advantages of process compatibility and low cost.

[0045] In some embodiments of the present invention, the vanadium source includes at least one of vanadium pentoxide and ammonium metavanadate, the erbium source includes at least one of erbium trioxide, erbium sulfate trihydrate, erbium carbonate and erbium oxalate, and the carbon source includes at least one of glucose, sucrose and citric acid.

[0046] In some embodiments of the present invention, the ball milling speed is 400-600 r / min, specifically 400 r / min, 500 r / min and 600 r / min, etc.; the ball milling time is 6-8 h, specifically 6 h, 7 h and 8 h, etc.; the dispersant used in the ball milling process is ethanol and / or water, that is, the dispersant is ethanol, water or a mixed solution of ethanol and water.

[0047] In some embodiments of the present invention, the ball-to-material mass ratio is 20-25:1-2, for example, 25:1, 20:1, 25:3, 20:2, 23:1, etc. Preferably, the balls consist of large balls, medium balls, and small balls in a mass ratio of 7:2:1, wherein the diameter of the large balls is 8-10 mm, the diameter of the medium balls is 5-6 mm, and the diameter of the small balls is 2-3 mm. Grinding with balls of different diameters allows for more thorough grinding of the material.

[0048] In some embodiments of the present invention, the drying temperature is 60-80°C, specifically 60°C, 70°C, and 80°C, and the drying time is 10-14 hours, specifically 12 hours, 13 hours, and 14 hours.

[0049] In some embodiments of the present invention, the sintering includes a first sintering and a second sintering performed sequentially. The first sintering involves heating from room temperature to 300-400°C at a rate of 4-5°C / min, and then sintering at 300-400°C for 4-5 hours. Specifically, the heating rate can be 4°C / min or 5°C / min, the temperature of the first sintering can be 300°C, 350°C, or 400°C, and the time can be 4 hours or 5 hours. The second sintering involves heating from 300-400°C to 800-900°C at a rate of 2-3°C / min, and then sintering at 800-900°C for 8-10 hours. Specifically, the heating rate can be 2°C / min or 3°C / min, the temperature of the second sintering can be 800°C, 850°C, or 900°C, and the time can be 8 hours, 9 hours, or 10 hours. Segmented sintering can optimize the crystal structure, improve particle uniformity, and reduce defects, thereby improving the crystal structure quality and electrochemical performance of lithium vanadium phosphate. At the same time, the slower heating rate in the second stage is conducive to slow crystal growth and better crystallinity.

[0050] In some embodiments of the present invention, the sintering is carried out in a tube furnace. Before sintering, argon gas is introduced into the tube furnace to replace the air in the tube furnace, so as to prevent oxygen in the air from affecting the synthesis of the cathode material. The argon gas introduction time can be, for example, 1 hour. The specific argon gas introduction time can be adjusted according to the actual situation and is not specifically limited.

[0051] In some embodiments of the present invention, the sintering process further includes the following steps: cooling the sintered material, grinding it, and sieving it to obtain the cathode material. The sieving process involves passing the material through a 200-400 mesh sieve and collecting the undersize material; specifically, it can be passing through a 400 mesh, 300 mesh, or 200 mesh sieve, etc.

[0052] In another aspect, the present invention provides an application of the lithium vanadium phosphate cathode material described in any one of the above claims or the lithium vanadium phosphate cathode material prepared by the method described in any one of the above claims in a lithium-ion battery.

[0053] The technical solutions of this invention will be clearly and completely described below with reference to specific embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0054] Example 1

[0055] This embodiment provides a method for preparing lithium vanadium phosphate cathode material, specifically including the following steps:

[0056] (1) Weigh lithium dihydrogen phosphate, vanadium pentoxide, erbium trioxide and glucose according to the elemental molar ratio Li:V:Er:P:C=3.15:1.95:0.05:3.0:3.5 and mix them to obtain a mixture;

[0057] (2) The mixture was put into a planetary ball mill for ball milling to obtain a slurry. Ethanol was used as the dispersant during the ball milling process. The rotation speed was 400 r / min, the ball milling time was 8 h, and the ball-to-material mass ratio was 20:1. The ball-milled slurry was dried at 80℃ for 12 h to obtain the dried material.

[0058] (3) Introduce argon gas into the tube furnace for 1 hour, then place the dried material in the tube furnace and raise the temperature from room temperature to 400°C at a rate of 5°C / min, and sinter at 400°C for 4 hours. Continue to raise the temperature from 400°C to 800°C at a rate of 5°C / min, and sinter at 800°C for 8 hours. After sintering, allow it to cool naturally to room temperature.

[0059] (4) Grind the cooled material, then pass it through a 400-mesh sieve and collect the sieve residue to obtain lithium vanadium phosphate cathode material, denoted as Li3V. 1.95 Er 0.05 (PO4)3 / C material (i.e., x = 0.05).

[0060] Example 2

[0061] This embodiment is basically the same as Embodiment 1, except that: lithium dihydrogen phosphate, vanadium pentoxide, erbium trioxide and glucose are weighed and mixed according to the elemental molar ratio Li:V:Er:P:C=3.15:1.92:0.08:3.0:3.5 to obtain a mixture.

[0062] The lithium vanadium phosphate cathode material finally obtained in this embodiment is denoted as Li3V. 1.92 Er 0.08 (PO4)3 / C material (i.e., x = 0.08).

[0063] Example 3

[0064] This embodiment is basically the same as Embodiment 1, except that: lithium dihydrogen phosphate, vanadium pentoxide, erbium trioxide and glucose are weighed and mixed according to the elemental molar ratio Li:V:Er:P:C=3.15:1.97:0.03:3.0:3.5 to obtain a mixture.

[0065] The lithium vanadium phosphate cathode material finally obtained in this embodiment is denoted as Li3V. 1.97 Er 0.03 (PO4)3 / C material (i.e., x = 0.03).

[0066] Example 4

[0067] This embodiment is basically the same as Embodiment 1, except that: lithium dihydrogen phosphate, vanadium pentoxide, erbium trioxide and glucose are weighed and mixed according to the elemental molar ratio Li:V:Er:P:C=3.15:1.9:0.1:3.0:3.5 to obtain a mixture.

[0068] The lithium vanadium phosphate cathode material finally obtained in this embodiment is denoted as Li3V. 1.9 Er 0.1 (PO4)3 / C material (i.e., x = 0.1).

[0069] Example 5

[0070] This embodiment is basically the same as Embodiment 1, except that: lithium dihydrogen phosphate, vanadium pentoxide, erbium trioxide and glucose are weighed and mixed according to the elemental molar ratio Li:V:Er:P:C=3.15:1.88:0.12:3.0:3.5 to obtain a mixture.

[0071] The lithium vanadium phosphate cathode material finally obtained in this embodiment is denoted as Li3V. 1.88 Er 0.12 (PO4)3 / C material (i.e., x = 0.12).

[0072] Comparative Example 1

[0073] This comparative example is basically the same as Example 1, except that lithium dihydrogen phosphate, vanadium pentoxide and glucose are weighed and mixed according to the elemental molar ratio Li:V:P:C = 3.15:2.0:3.0:3.5 to obtain a mixture.

[0074] The lithium vanadium phosphate cathode material finally obtained in this comparative example is denoted as Li3V2(PO4)3 / C material (i.e., x=0).

[0075] The physical properties of the lithium vanadium phosphate cathode materials of Examples 1-5 and Comparative Example 1 were tested in this invention.

[0076] Specifically, such as Figure 1 The figure shows the XRD patterns of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1. It can be seen from the figures that the erbium-doped Li3V… 2-x Er x The characteristic peaks of the XRD pattern of the (PO4)3 / C material are consistent with those of the standard PDF card, and it still has a monoclinic crystal structure, indicating that doping erbium into the Li3V2(PO4)3 / C material does not affect the crystal structure of the material.

[0077] like Figure 2The image shows SEM images of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1. As can be seen from the images, erbium doping did not significantly affect the morphology of the Li3V2(PO4)3 / C material.

[0078] like Figure 3 The figure shows the particle size distribution of lithium vanadium phosphate cathode materials in Example 1 and Comparative Example 1. It can be seen from the figure that the average particle size of the two materials is similar, indicating that erbium doping does not significantly change the particle size of Li3V2(PO4)3 / C material, and therefore does not affect its electrochemical performance.

[0079] like Figure 4 The figure shows the Raman spectra of lithium vanadium phosphate cathode materials of Example 1(b) and Comparative Example 1(a). It can be seen from the figure that the Raman spectra of lithium vanadium phosphate cathode materials in the 1200-1450 cm⁻¹ range are as follows: -1 The range of D-band and 1500-1650cm -1 The G-band within the range corresponds to sp 3 Disorder vibrations and sp of hybrid carbon 2 Ordered vibrations of hybrid carbon, peak area ratio (I G / I D ) is usually used to characterize the electronic conductivity of materials, because sp 2 Hybridized carbon compared to sp 3 Hybridized carbon has an extra free electron, therefore its electronic conductivity is higher than that of sp. 3 It has good electronic conductivity, that is, the peak area of ​​the G band (I G ) and the peak area of ​​the D band (I D The higher the ratio of Ip(PO4)3 to Ip(PO4)3 / C, the better the conductivity of the material. Fitting analysis of the peak areas of the Raman spectra of the two materials showed that the Ip(PO4)3 of the Li3V2(PO4)3 / C material... G / I D The value is 0.385, Li3V 1.95 Er 0.05 (PO4)3 / C material I G / I D The value is 0.417, Li3V 1.95 Er 0.05 (PO4)3 / C material I G / I D The value compared to the I of undoped Li3V2(PO4)3 / C material G / I D The value increases significantly, indicating that erbium doping can significantly improve the electronic conductivity of Li3V2(PO4)3 / C materials.

[0080] like Figure 5 The image shows XPS images of lithium vanadium phosphate cathode materials from Example 1 and Comparative Example 1. Figure 5 (a) shows the full spectrum of the two materials. It can be seen from the figure that the Li3V2(PO4)3 / C material and the Li3V... 1.95 Er 0.05 (PO4)3 / C materials all have spectral peaks of O1s, V2p, C1s and P2p. The spectral peaks of Li1s and Er4d were not detected in XPS tests. This is because the response factor of Li is small and the Li1s spectral peak cannot be detected. At the same time, the doping amount of erbium is small and it is not easy to be detected. Figure 5 (b) shows the V2p orbitals of the two materials. From the figure, it can be seen that the Li3V2(PO4)3 / C material and the Li3V... 1.95 Er 0.05 In the (PO4)3 / C material, the peaks of the V2p electron binding energy are all between 516-519 eV, and within this range, the corresponding valence state of vanadium is +3, indicating that erbium doping does not affect the change of vanadium valence in the Li3V2(PO4)3 / C material.

[0081] The present invention uses the lithium vanadium phosphate cathode materials of Examples 1-5 and Comparative Example 1 to assemble coin cells, and tests the electrochemical performance of the assembled coin cells.

[0082] The assembly method of the button cell is as follows: Lithium vanadium phosphate positive electrode material, acetylene black and polytetrafluoroethylene are mixed in a mass ratio of 8:1:1 and N-methylpyrrolidone is added to adjust the viscosity. The mixture is stirred for 10 hours to obtain a paste. The paste is evenly coated on the surface of aluminum foil and vacuum dried at 120°C for 12 hours. Then, the dried aluminum foil is cut into electrode sheets with a diameter of 14 mm using a slicing machine. The electrode sheet is used as the positive electrode sheet, lithium metal sheet is used as the negative electrode sheet, and LiPF6 / EC+DEC+DMC system is used as the electrolyte. The assembly is carried out in a glove box filled with argon gas and the water and oxygen contents are both less than 0.01 ppm to obtain the button cell.

[0083] 1. Ratio Performance Test

[0084] The rate performance test process is as follows: First, the coin cell battery is placed for 5 minutes, then activated with a current density of 0.1C. It is first charged with constant current, then charged with constant voltage, and then discharged with constant current at a rate of 0.1C, and the cycle is repeated 5 times. Then, it is charged and discharged sequentially at the set rates of 0.2C, 0.5C, 1C, 2C, 5C, 10C and 20C.

[0085] like Figure 6The figure shows the constant current charge-discharge test results of lithium vanadium phosphate cathode materials in Examples 1-5 and Comparative Example 1. As can be seen from the figure, at low charge-discharge rates of 0.1C, 0.2C, 0.5C, and 1C, the discharge specific capacity of the lithium vanadium phosphate cathode material is relatively high when the erbium doping amount is 0.05%, with a discharge specific capacity of 119 mAh / g at 0.1C. Furthermore, at medium-high discharge rates of 2C, 5C, 10C, and 20C, the discharge specific capacity of the erbium-doped lithium vanadium phosphate cathode material is higher than that of the Li3V2(PO4)3 / C material, indicating that erbium doping can significantly improve the discharge performance of Li3V2(PO4)3 / C material at medium-high rates. Specifically, at low charge-discharge rates of 0.1C, 0.2C, 0.5C, and 1C, the discharge specific capacity of Li3V2(PO4)3 / C material is higher than that of the Li3V2(PO4)3 / C material. 1.95 Er 0.05 The discharge specific capacities of the (PO4)3 / C material are 119 mAh / g, 116 mAh / g, 110 mAh / g, and 105 mAh / g, respectively. The discharge specific capacities of the undoped Li3V2(PO4)3 / C material are 111 mAh / g, 109 mAh / g, 104 mAh / g, and 100 mAh / g, respectively. This means that at low discharge rates, the Li3V2(PO4)3 / C material exhibits high specific capacities. 1.95 Er 0.05 The discharge specific capacity of (PO4)3 / C material is higher than that of Li3V2(PO4)3 / C material. At medium-to-high discharge rates of 2C, 5C, 10C, and 20C, Li3V2... 1.95 Er 0.05 The discharge specific capacities of the (PO4)3 / C material were 100 mAh / g, 80 mAh / g, 55 mAh / g and 30 mAh / g, respectively, while the discharge specific capacities of the undoped Li3V2(PO4)3 / C material were 90 mAh / g, 70 mAh / g, 30 mAh / g and 2 mAh / g, respectively. This means that erbium doping can significantly improve the electrochemical performance of Li3V2(PO4)3 / C material at medium and high rates.

[0086] 2. Cyclic performance test

[0087] The cycle performance test process is as follows: First, the button cell battery is placed for 5 minutes, then activated at a rate of 0.1C, first constant current charging, then constant voltage charging, and finally constant current discharging; 500 charge-discharge cycles are performed at a rate of 2C.

[0088] like Figure 7 The figure shows the cycling performance of lithium vanadium phosphate cathode materials in Examples 1-5 and Comparative Example 1 at a 2C rate. It can be seen from the figure that Li3V... 1.95 Er 0.05 (PO4)3 / C materials and Li3V 1.92 Er 0.08The discharge specific capacity of (PO4)3 / C material is consistently higher than that of Li3V2(PO4)3 / C material, and even after 500 charge-discharge cycles, Li3V2... 1.95 Er 0.05 The capacity retention rate of (PO4)3 / C material is 86.1%, while that of Li3V2(PO4)3 / C material is 79.5%, indicating that erbium doping can effectively improve the cycling performance of Li3V2(PO4)3 / C material.

[0089] 3. Cyclic Voltmeter-Ammeter Test

[0090] like Figure 8 The figure shows the cyclic voltammograms of lithium vanadium phosphate cathode materials from Examples 1-5 and Comparative Example 1, with test conditions of voltage 3.0-4.3V and scan rate 0.1mV / s. As can be seen from the figure, the cyclic voltammograms of each lithium vanadium phosphate cathode material exhibit three pairs of reversible redox peaks, with Li3V... 1.95 Er 0.05( The reduction and oxidation peaks of the (PO4)3 / C material are sharper, with the potential differences of the three corresponding redox peaks being 0.133V, 0.131V, and 0.161V, respectively. In contrast, the potential differences of the three corresponding redox peaks in the Li3V2(PO4)3 / C material are 0.155V, 0.145V, and 0.177V, respectively. 1.95 Er 0.05( Compared to Li3V2(PO4)3 / C, the oxidation peak of the erbium-doped Li3V2(PO4)3 / C material shifts negatively, while the reduction peak shifts positively. This results in a smaller redox potential difference, increased reversibility, and improved electrochemical performance. This indicates that erbium doping can enhance the electrochemical reversibility of Li3V2(PO4)3 / C materials, thereby improving their electrochemical performance to some extent.

[0091] 4. AC impedance test

[0092] To investigate the effect of erbium doping on the electrode process kinetics of Li3V2(PO4)3 / C material, electrochemical impedance spectroscopy (EIS) measurements were performed on the lithium vanadium phosphate cathode materials of Examples 1-5 and Comparative Example 1. The frequency range of the measurements was 10 mHz-100 kHz. Figure 9 The figure shows the Nyquist plots of the lithium vanadium phosphate cathode materials of Examples 1-5 and Comparative Example 1. It can be seen from the figure that when the erbium doping amount is 0.05, 0.08 and 0.10, the charge transfer resistance of the cathode material is less than that of the Li3V2(PO4)3 / C material, indicating that an appropriate amount of erbium doping is beneficial to reducing the impedance of the Li3V2(PO4)3 / C material.

[0093] 5. Charge and discharge performance test

[0094] like Figure 10 The figure shows the first charge-discharge curves of the lithium vanadium phosphate cathode materials of Example 1 and Comparative Example 1. The tests were conducted at a voltage of 3.0-4.3V and a rate of 0.1C. The figure shows that the Li3V2(PO4)3 / C material and the Li3V... 1.95 Er 0.05 Both (PO4)3 / C materials exhibit three plateaus during charging: 3.60V, 3.70V, and 4.10V. Both have three pairs of relatively symmetrical charge / discharge plateaus, and Li3V... 1.95 Er 0.05 The first-cycle discharge specific capacity of (PO4)3 / C material is 120 mAh / g, while that of Li3V2(PO4)3 / C material is 111 mAh / g, indicating that erbium-doped Li3V2(PO4)3 / C material has better charge and discharge performance.

[0095] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A lithium vanadium phosphate cathode material, characterized in that, The cathode material is erbium-doped Li3V2(PO4)3 / C material, with the structural formula Li3V 2-x Er x (PO4)3 / C, where 0 < x ≤ 0.

12.

2. The lithium vanadium phosphate cathode material according to claim 1, characterized in that, The value of x is 0.05≤x≤0.

08.

3. A method for preparing the lithium vanadium phosphate cathode material according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Lithium dihydrogen phosphate, vanadium source, erbium source and carbon source are mixed to obtain a mixture; (2) The mixture is ball-milled and then dried to obtain dried material; (3) The dried material is sintered to obtain lithium vanadium phosphate cathode material.

4. The method for preparing lithium vanadium phosphate cathode material according to claim 3, characterized in that, The molar ratio of lithium, vanadium, erbium, phosphorus and carbon in the mixture is 3.15:(2.0-x):x:3.0:(2.0-3.5), where 0 < x ≤ 0.

12.

5. The method for preparing lithium vanadium phosphate cathode material according to claim 3, characterized in that, The vanadium source includes at least one of vanadium pentoxide and ammonium metavanadate. The erbium source includes at least one of erbium trioxide, erbium sulfate trihydrate, erbium carbonate, and erbium oxalate; The carbon source includes at least one of glucose, sucrose, and citric acid.

6. The method for preparing lithium vanadium phosphate cathode material according to claim 3, characterized in that, The ball mill operates at a speed of 400-600 r / min for 6-8 h, with a ball-to-material mass ratio of 20-25:1-2. Ethanol and / or water are used as dispersants in the ball mill.

7. The method for preparing lithium vanadium phosphate cathode material according to claim 3, characterized in that, The drying process is carried out at a temperature of 60-80℃ for 10-14 hours.

8. The method for preparing lithium vanadium phosphate cathode material according to claim 3, characterized in that, The sintering includes a first sintering and a second sintering performed sequentially. The first sintering involves heating from room temperature to 300-400℃ at a rate of 4-5℃ / min, and then sintering at 300-400℃ for 4-5 hours. The second sintering involves heating from 300-400℃ to 800-900℃ at a rate of 2-3℃ / min, and then sintering at 800-900℃ for 8-10 hours.

9. The method for preparing lithium vanadium phosphate cathode material according to any one of claims 3-8, characterized in that, The sintering process further includes the following steps: cooling the sintered material, grinding it, and sieving it to obtain the cathode material. The sieving process involves passing the material through a 200-400 mesh sieve and collecting the material that passes through the sieve.

10. The application of the lithium vanadium phosphate cathode material according to any one of claims 1-2 or the lithium vanadium phosphate cathode material prepared by the method according to any one of claims 3-9 in a lithium-ion battery.

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