Post-treatment method for improving reversible specific capacity of P2 type layered oxide of sodium ion battery

Abstract

The invention relates to the technical field of sodium ion battery positive electrode material preparation, in particular to a post-treatment method for improving the reversible specific capacity of a P2 type layered oxide of a sodium ion battery. According to the method, the P2-type layered oxide of the sodium-ion battery is washed in the mixed solution of the alcohol and the water and then is annealed, so that the residual alkali on the surface of the material can be effectively reduced, the crystallinity of the material is enhanced, the microstructure of the positive electrode material is improved, the reversible specific capacity per gram of the material is improved, and the method is low in cost and simple in operation mode.

Description

Technical Field

[0001] The present application relates to the technical field of preparation of positive electrode materials for sodium ion batteries, and in particular to a post-treatment method for improving the reversible specific capacity of P2-type layered oxides for sodium ion batteries. Background Art

[0002] Sodium-ion batteries are considered to be a promising alternative to lithium-ion batteries because of their good high and low temperature performance, environmental friendliness, and similar intercalation compound structure and similar charge and discharge mechanism as lithium-ion batteries. However, the lower energy density and shorter cycle life of sodium ions have severely restricted the development of sodium-ion batteries. Sodium-ion batteries are composed of positive electrodes, negative electrodes, separators, and electrolytes. Among them, the positive and negative electrodes are the main factors affecting the energy density, cycle life, and rate performance of sodium-ion batteries. The positive electrode material has become the main bottleneck of sodium-ion battery technology because its specific capacity is much lower than the specific energy of the negative electrode material. Therefore, the development of stable and efficient positive electrode materials is the key to promoting sodium-ion battery technology.

[0003] Among them, the P2-type layered oxide positive electrode material is considered to be one of the promising positive electrode materials because of its good cycle stability and high energy density. However, the insufficient air stability of the material seriously affects the transportation and storage of the material. At present, there are a large number of literatures proving that water in the air will react with the sodium on the surface of the material to increase the residual alkali on the surface, and even water will enter the lattice along the crystal plane to cause the material to collapse and crack on the surface, thereby affecting the electrochemical properties of the material. However, there are also literature reports that humid air is not just harmful to positive electrode materials. At present, there are a large number of means to improve the air stability and discharge capacity of materials. For example, CN202410349931.6 discloses a method of reducing the interlayer spacing of the sodium layer by doping the rare earth metal yttrium into the sodium layer, thereby improving the air stability and reversible specific capacity of the lattice. CN202410305269.4 discloses a method for improving the air stability of a material by coating Na5YSi4O12 on NaNi0.4Fe0.2Mn0.4O2. The prepared material has excellent reversible specific capacity, circulation and air stability, and the method properly solves the problem of residual alkali on the surface of the positive electrode material. CN202410063503.7 discloses a method for preparing a copper uniformly distributed high-tap precursor material. By optimizing the process of the coprecipitation method, the copper is uniformly distributed in the material, thereby obtaining a material with high tap density and good air stability.

[0004] The above three methods all solve the problem of water absorption of materials by doping and coating, which increases the cost of material preparation. Therefore, how to efficiently solve the problem of water absorption of materials and improve the reversible specific capacity of materials are issues that need to be solved. Summary of the invention

[0005] In order to solve the above-mentioned technical problems existing in the prior art, the present application provides a post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries, which is specifically achieved through the following technical solutions.

[0006] A post-treatment method for improving the reversible specific capacity of a P2-type layered oxide of a sodium ion battery comprises the following steps:

[0007] (1) weighing deionized water and dissolving it in an organic solution to obtain a mixed solution;

[0008] (2) weighing a sodium ion battery P2 type positive electrode material and adding it to the mixed solution obtained in step (1), stirring for 2 to 3 hours, and then removing the solution by suction filtration to obtain a positive electrode material solid;

[0009] (3) The positive electrode material solid obtained in step (2) is subjected to high temperature sintering, and then the sintered product is taken out after the furnace temperature drops to room temperature, and the sintered product is ground into powder and passed through a 100-200 mesh sieve to obtain a post-processed P2 type positive electrode material.

[0010] Furthermore, the organic solution in step (1) is any one of methanol, ethanol and glycerol.

[0011] Furthermore, in the step (1), the volume ratio of water to organic solvent is (2-5): (300-500).

[0012] Furthermore, in the step (2), the ratio of the added sodium ion battery P2 type positive electrode material to the mixed solution is (30-200 g): 300 ml.

[0013] Furthermore, the stirring in step (2) is carried out in a magnetic stirrer for 2 to 3 hours.

[0014] Furthermore, the stirring speed of the magnetic stirrer in step (2) is 200 to 500 rpm.

[0015] Furthermore, the high temperature sintering in step (3) is to transfer the obtained positive electrode material solid to a tubular furnace for high temperature sintering.

[0016] Furthermore, the high temperature sintering in step (3) has a heating rate of 2 to 5°C / min, a sintering temperature of 700 to 800°C, and a sintering time of 6 to 10 hours.

[0017] Furthermore, the furnace temperature is lowered to room temperature.

[0018] Compared with the prior art, the technical effects created by this application are embodied in:

[0019] (1) The present invention washes the sodium ion battery P2 type layered oxide in a mixed solution of alcohol and water, and then anneals it to effectively reduce the surface residual alkali of the material, enhance the crystallinity of the material, improve the micromorphology of the positive electrode material, and increase the reversible gram-specific capacity of the material. The method is low in cost and simple in operation.

[0020] (2) After the material is post-treated using the present invention, the crystallinity of the material is significantly improved; the sodium content on the surface of the material is significantly reduced, and the residual alkali amount on the surface of the material can be significantly reduced; and the discharge curve of the treated material has an obvious discharge platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 XRD images of O2 cathode materials at different post-treatment stages.

[0022] Figure 2 It is P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 SEM and EDS spectra of O2 positive electrode materials before and after post-treatment.

[0023] Figure 3 It is P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 Rate discharge images of O2 cathode material before and after post-treatment. DETAILED DESCRIPTION

[0024] The technical solution of the present application is further limited below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0025] Example 1

[0026] A post-treatment method for improving the reversible specific capacity of P2-type layered oxides for sodium ion batteries:

[0027] (1) Weigh 3 ml of deionized water and dissolve it in 300 ml of ethanol solution to obtain a mixed solution;

[0028] (2) Weigh 100g of sodium ion battery P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 The O2 positive electrode material is added to the mixed solution obtained in step (1), placed in a magnetic stirrer and stirred at 300 rpm for 2 h, and then the solution is removed by suction filtration to obtain the washed P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material solid;

[0029] (3) The positive electrode material solid obtained in step (2) was transferred to a tube furnace and heated to 750°C at a heating rate of 3°C / min, and kept warm for 8 hours. After the furnace temperature dropped to room temperature, the sintered product was taken out and ground into powder and passed through a 200-mesh sieve to obtain a post-treated P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material.

[0030] Example 2

[0031] A post-treatment method for improving the reversible specific capacity of P2-type layered oxides for sodium ion batteries:

[0032] (1) Weigh 2 ml of deionized water and dissolve it in 500 ml of ethanol solution to obtain a mixed solution;

[0033] (2) Weigh 200g of sodium ion battery P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 The O2 positive electrode material is added to the mixed solution obtained in step (1), placed in a magnetic stirrer and stirred at 200 rpm for 3 h, and then the solution is removed by suction filtration to obtain the washed P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material solid;

[0034] (3) The positive electrode material solid obtained in step (2) was transferred to a tube furnace and heated to 700°C at a heating rate of 2°C / min, and kept warm for 10 hours. After the furnace temperature dropped to room temperature, the sintered product was taken out and ground into powder and passed through a 200-mesh sieve to obtain a post-treated P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material.

[0035] Example 1

[0036] A post-treatment method for improving the reversible specific capacity of P2-type layered oxides for sodium ion batteries:

[0037] (1) Weigh 5 ml of deionized water and dissolve it in 300 ml of ethanol solution to obtain a mixed solution;

[0038] (2) Weigh 50g of sodium ion battery P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 The O2 positive electrode material is added to the mixed solution obtained in step (1), placed in a magnetic stirrer and stirred at 500 rpm for 2 h, and then the solution is removed by suction filtration to obtain the washed P2-Na0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material solid;

[0039] (3) The positive electrode material solid obtained in step (2) was transferred to a tube furnace and heated to 800°C at a heating rate of 5°C / min, and kept warm for 6 hours. After the furnace temperature dropped to room temperature, the sintered product was taken out and ground into powder and passed through a 200-mesh sieve to obtain a post-treated P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 O2 positive electrode material.

[0040] Taking Example 1 as an example, Example 1 is post-treated to obtain P2-Na 0.67 Fe 1 / 2 Mn 1 / 2 The O2 positive electrode materials were subjected to XRD analysis, SEM analysis, and electrochemical performance tests.

[0041] Depend on Figure 1 From the XRD image, it can be seen that after the positive electrode material is washed with the mixed solution, the main diffraction peak of the material is split into two, and more miscellaneous peaks appear, which indicates that water has entered the interior of the crystal. The diffraction peak intensity of the material after annealing at 700°C is enhanced, especially the diffraction intensity of the main diffraction peak is significantly improved, which indicates that the crystallinity of the material is significantly improved after the material is post-treated using the present invention.

[0042] Depend on Figure 2 From the SEM image, we can see that the primary particle size of the material is smaller after treatment. This may be because water enters the lattice and causes the crystal to collapse. The subsequent annealing treatment causes the material to recrystallize, which significantly reduces the primary particle size. The smaller particle size is more conducive to the diffusion of sodium ions and can significantly improve the rate performance of the material. Figure 2 It can be seen from the EDS image that the sodium content on the surface of the material after washing and annealing is significantly reduced, which indicates that the treatment method used in the present invention can significantly reduce the amount of residual alkali on the surface of the material.

[0043] Depend on Figure 3 It can be seen that the material before treatment has a discharge capacity of only 122mAh / g at a discharge rate of 0.1C, and can only be charged and discharged at a rate of 2C or below. The material after treatment has a discharge capacity of nearly 140mAh / g at a discharge rate of 0.1C, and even has a discharge capacity of nearly 45mAh / g at a charge and discharge rate of 8C. The discharge curve of the treated material has an obvious discharge platform, which is consistent with the conclusion of the SEM spectrum analysis.

[0044] Finally, it should be pointed out that the above embodiments are only representative examples of the present application. Obviously, the technical solution of the present application is not limited to the above embodiments, and there may be many variations. All variations that can be directly derived or associated with the contents disclosed in the present application by a person of ordinary skill in the art should be considered as the protection scope of the present application.

Claims

1. A post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries, characterized in that: The following steps are involved: (1) weighing deionized water and dissolving it in an organic solution to obtain a mixed solution; (2) weighing a sodium ion battery P2 type positive electrode material and adding it to the mixed solution obtained in step (1), stirring for 2 to 3 hours, and then removing the solution by suction filtration to obtain a positive electrode material solid; (3) The positive electrode material solid obtained in step (2) is subjected to high temperature sintering, and then the sintered product is taken out after the furnace temperature drops to room temperature, and the sintered product is ground into powder and passed through a 100-200 mesh sieve to obtain a post-processed P2 type positive electrode material.

2. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The organic solution in step (1) is any one of methanol, ethanol and glycerol.

3. The post-treatment method for improving the reversible specific capacity of P2-type layered oxide of sodium ion battery according to claim 1, characterized in that: The volume ratio of water to organic solvent in the step (1) is (2-5): (300-500).

4. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: In the step (2), the ratio of the added sodium ion battery P2 type positive electrode material to the mixed solution is (30-200 g): 300 ml.

5. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The stirring in step (2) is carried out in a magnetic stirrer for 2 to 3 hours.

6. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The stirring speed of the magnetic stirrer in step (2) is 200 to 500 rpm.

7. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The high temperature sintering in step (3) is to transfer the obtained positive electrode material solid to a tubular furnace for high temperature sintering.

8. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The high temperature sintering in step (3) has a heating rate of 2 to 5°C / min, a sintering temperature of 700 to 800°C, and a sintering time of 6 to 10 hours.

9. The post-treatment method for improving the reversible specific capacity of P2-type layered oxides of sodium ion batteries according to claim 1, characterized in that: The furnace temperature was lowered to room temperature.

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