Quaternary sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses a quaternary sodium battery positive electrode material and a preparation method thereof, and belongs to the technical field of sodium ion battery positive electrode material production. A carbonate coprecipitation method is adopted, a four-metal-element metal salt solution and a carbonate precipitant solution are controlled to react in an alkaline aqueous solution, a precursor is prepared, and the positive electrode material with the structural formula of NaMnxFeyNizCOrO2 is obtained through material mixing and calcination. According to the method, a more stable crystal structure is provided for the material, and the cycling stability of the material is improved, so that the performance of the positive electrode material is obviously improved, and the energy density and the practicability are further improved.

Description

Technical Field

[0001] The present invention relates to a positive electrode material for a sodium ion battery, and specifically to a positive electrode material for a quaternary sodium ion battery. and a preparation method thereof. Background Art

[0002] Ternary sodium positive electrode materials have good performance, high capacity, excellent cycle performance and coulomb rate, low cost and good safety, so they have received widespread attention.

[0003] At present, the preparation technology of ternary sodium cathode materials is becoming more and more mature, and has been widely used in sodium ion energy storage batteries. However, there are also some problems. Although ternary cathode materials have higher discharge specific energy, such materials are prone to structural collapse and crystal distortion during the cycle process. The crystal structure is destroyed, the embedding and migration of sodium ions are affected, and the side reactions will also be aggravated, resulting in reduced charge and discharge performance, which seriously hinders its development and application. Summary of the invention

[0004] In order to improve the stability of ternary sodium positive electrode materials and improve the problem of crystal structure collapse during the cycle process, the present invention proposes a quaternary sodium ion battery positive electrode material.

[0005] The structural formula of the quaternary sodium ion battery positive electrode material of the present invention is: NaMn x Fe y Ni z CO r O2, where x+y+z+r=1.

[0006] The cobalt-containing quaternary sodium positive electrode material precursor particle morphology of the present invention has a discharge capacity of about 145mAh / g compared with the conventional nickel-iron-manganese ternary positive electrode material, and the first charge and discharge efficiency is about 90%. Compared with the general ternary sodium positive electrode material, its capacity is increased by about 10mAh / g, but after 100 cycles, its capacity retention rate can reach about 95%, which has a significant improvement in cycle stability.

[0007] Another object of the present invention is to provide a method for preparing the above positive electrode material.

[0008] The specific steps are: 1) Dissolve nickel salt, manganese salt, cobalt salt and iron salt in deionized water to obtain a mixed metal salt aqueous solution; dissolve sodium carbonate in deionized water, and then add a certain amount of ammonia water to obtain a precipitant solution with a pH value of 7.5-10.5; 2) first adding the base liquid into the reaction container, then adding the mixed metal salt aqueous solution and the precipitant solution into the reaction container to carry out a co-precipitation reaction under the protection of nitrogen; After the reaction is completed, the precipitate and the supernatant are separated, and the precipitate is washed, filtered, dried, and ground to obtain a precursor; 3) The precursor and the sodium salt are uniformly mixed and then calcined. During the calcination, the temperature is first raised to 400-500° C., kept warm for 3 hours, then raised to 700-900° C., kept warm for 8-24 hours, and finally cooled to room temperature to obtain a ternary sodium cathode material.

[0009] In the preparation method of the present invention, sodium carbonate is used as the main precipitant and ammonia water is used as the complexing agent to synthesize the ternary sodium positive electrode material by reacting in the bottom liquid. The surface of the prepared precursor particles is smoother and the specific surface area is increased, which is conducive to the formation of a ternary sodium positive electrode material with a relatively stable crystal structure, which is beneficial to Li + Compared with the ternary sodium positive electrode material prepared by the general method, the material prepared by the present invention is not easy to collapse when compacted, thus significantly improving the performance of the positive electrode material.

[0010] The process flow of the present invention is relatively simple and easy to operate. The first discharge capacity of the assembled battery test at 0.1C is about 145mAh / g, and the first charge and discharge efficiency is about 90%. Compared with the general ternary sodium positive electrode material, its capacity has been effectively improved. After 100 cycles, the capacity retention rate can reach about 95%, which has been significantly improved. The ternary sodium positive electrode material has a smooth surface, an increased specific surface area, good crystallinity, is not easy to collapse when compacted, has a higher tap density, and thus has better cycle performance.

[0011] Furthermore, the total concentration of the metal salts in the mixed metal salt aqueous solution of the present invention is 0.5-2.2 mol / L. If the metal salt concentration is too low, the complexation reaction is incomplete; if the concentration is too high, the secondary particles formed are too large. When the concentration of the transition metal salt solution is within the range of 0.5-2.2 mol / L, the complexation reaction of metal ions and ammonia can be promoted, which is more beneficial for synthesizing precursors with spherical morphology and narrow particle size.

[0012] The molar ratio of the nickel salt, manganese salt, cobalt salt and iron salt is based on the molecular formula NaMn x Fe y Ni z CO r O 2， Wherein 0.3<X≤0.7, 0.01≤y≤0.3, 0.01≤z≤0.35, 0<1-xyzr≤1. Under this ratio condition, a complete crystalline layered oxide structure can be formed.

[0013] The concentration of the transition metal salt solution has a very important influence on the average particle size and particle size distribution of the secondary particles of the ternary sodium positive electrode material precursor.

[0014] The nickel salt is nickel sulfate, nickel nitrate or nickel acetate; The manganese salt is manganese sulfate, manganese nitrate or manganese acetate; the cobalt salt is cobalt sulfate, cobalt nitrate or cobalt acetate.

[0015] Transition metals of sulfates, nitrates, and acetates are easily soluble in water at room temperature, and the solutions are relatively stable at room temperature. In the co-precipitation reaction, the elemental composition of each part is relatively uniform.

[0016] The concentration of sodium carbonate is 1 / 2 of the concentration of metal cations in the metal salt solution. The solubility of carbonate is low and it is easy to precipitate when the concentration is too high.

[0017] During the coprecipitation reaction, the temperature of the reaction system is 40-80°C. The bulk density of the precursor prepared at different reaction temperatures is different. As the temperature increases, the growth rate of the grains increases. However, if the temperature is too high, the kinetic energy of the reactant molecules increases too quickly, which is not conducive to the formation of stable crystal nuclei.

[0018] During the coprecipitation reaction, the stirring speed in the reaction container is 200-800r / min. When the metal salt solution is dripped into the reaction cover, the metal ions first complex with ammonia to form a metal complex, and then slowly release transition metal ions to react with carbonate to generate a large number of primary particle products. After that, these primary particles collide with each other during the stirring process, rotate along the inner wall of the container and slowly agglomerate to form secondary particles. Therefore, a reasonable stirring rate is a necessary condition for synthesizing spherical positive electrode materials with uniform size distribution.

[0019] During the coprecipitation reaction, the metal salt solution is added at a rate of 20 ml / min to 500 ml / min, and the precipitant solution is added at a rate of 20 ml / min to 500 ml / min. In order to make metal ions such as Co and Ni coprecipitate and crystallize uniformly at the same rate, we can control the pH value by controlling the injection speed of the metal salt solution and the precipitant, so that they can coprecipitate uniformly. At the same time, the injection time also has a great influence on the morphology of the precursor. The size of the secondary particles of the precursor will increase with the increase of the reaction time before reaching a stable value.

[0020] During the reaction, the base liquid is deionized water.

[0021] In summary, the present invention controls the particle growth by controlling the reaction speed, the addition time, and the concentration of ammonia water, so that most of the particles are relatively uniform spherical particles with a relatively smooth surface and a larger specific surface area. DETAILED DESCRIPTION

[0022] The general structural formula of the ternary sodium positive electrode material prepared in this embodiment is: NaMn x Fe y Ni zCO r O2, the specific preparation process is as follows: 1. Preparation of precursors.

[0023] 1. Prepare metal salt solution: The following nickel salt may be any one of nickel sulfate, nickel nitrate or nickel acetate.

[0024] The following manganese salt is any one of manganese sulfate, manganese nitrate or manganese acetate.

[0025] The following cobalt salt is any one of cobalt sulfate, cobalt nitrate or cobalt acetate.

[0026] In this embodiment, sulfate is used to prepare a mixed metal salt solution. Nickel sulfate hexahydrate, cobalt sulfate heptahydrate, ferrous sulfate, and manganese sulfate monohydrate are weighed separately, and deionized water is added to prepare a metal salt solution with a total concentration of 2 mol / L. The molar ratio of nickel salt, manganese salt, cobalt salt, and iron salt is based on the molecular formula NaMn x Fe y Ni z CO r O2 is determined, where x=0.35, y=0.2, z=0.35, r=0.1.

[0027] 2. Prepare precipitant solution: Weigh 106 g of sodium carbonate and add it to 1000 ml of deionized water to prepare a 1 mol / L (sodium carbonate concentration is 1 / 2 of the metal cation concentration in the metal salt solution) sodium carbonate aqueous solution; then add 20 ml of ammonia water to obtain a precipitant solution with a pH value of 7 to 9.

[0028] 3. Preparation process: Use 1500ml of deionized water as the base liquid, the base liquid temperature is 50 degrees, and add it into the reactor.

[0029] After the temperature in the reactor rises to 40-60°C, stirring is started at a speed of 260-500 r / min. The above metal salt solution and precipitant solution are slowly added dropwise to the bottom liquid to carry out carbonate co-precipitation reaction. During the reaction, heating is performed in a water bath at 40-60°C and nitrogen is continuously passed for half an hour.

[0030] The dropping speed of the metal salt solution and the precipitant solution can be kept consistent and set at 50 ml per minute.

[0031] After the above additions are completed, continue stirring in the reactor and age for 2 to 5 hours.

[0032] Discharge the material, let it stand and settle, and separate the supernatant and the lower sediment.

[0033] The lower precipitate is removed and washed with deionized water for 3 to 5 times, filtered, and the liquid phase is removed and placed in an electric heated air drying oven, dried at 70 to 80° C., and then ground to obtain a precursor.

[0034] 2. Preparation of quaternary and ternary sodium positive electrode materials.

[0035] 10 g of the precursor was uniformly mixed with 7.56 g (97%) of sodium carbonate, put into a crucible, and calcined in a muffle furnace.

[0036] Calcination temperature: first raise the temperature to 500°C, keep it warm for 3 hours, then raise the temperature to 900°C, keep it warm for 8 hours, and finally cool to room temperature with the furnace to obtain 8g of quaternary and ternary sodium positive electrode material.

[0037] 3. The comparative example adopts the same preparation method, but does not include cobalt doping.

[0038] 4. Performance test and results: 1. Assemble button batteries to test the charging and discharging performance of materials.

[0039] The prepared quaternary sodium positive electrode material, binder, and conductive carbon black were mixed evenly in a mass ratio of 8:1:1, and then an appropriate amount of 1-methyl-2-pyrrolidone was added dropwise to make a slurry, which was evenly coated on an aluminum foil with a thickness of about 5 mg / cm 3 , put it in the oven for drying, and then punch it out to make the positive electrode.

[0040] Using a sodium sheet as the negative electrode, the battery was assembled and tested in a glove box filled with argon.

[0041] The main properties of the embodiments and comparative examples are shown in Table 1. The discharge capacity of the cobalt-containing quaternary sodium positive electrode material of the present invention is about 140 mAh / g, and the initial charge and discharge efficiency is about 90%. Compared with the general ternary sodium positive electrode material, its capacity is increased by about 10 mAh / g. After 100 cycles, the capacity retention rate can reach about 95%, which is significantly improved.

[0042] Table 1

Claims

1. A quaternary sodium ion battery positive electrode material, characterized in that: The general structural formula of the material is: NaMn x Fe y Ni z CO r O2, where x+y+z+r=1.

2. The method for preparing the positive electrode material for a quaternary sodium ion battery according to claim 1, characterized in that: The following steps are involved: 1) Dissolve nickel salt, manganese salt, cobalt salt and iron salt in deionized water to obtain a mixed metal salt aqueous solution; dissolve sodium carbonate in deionized water, and then add a certain amount of ammonia water to obtain a precipitant solution with a pH value of 7.5-10.5; 2) first adding the base liquid into the reaction container, then adding the mixed metal salt aqueous solution and the precipitant solution into the reaction container to carry out a co-precipitation reaction under the protection of nitrogen; After the reaction is completed, the precipitate and the supernatant are separated, and the precipitate is washed, filtered, dried, and ground to obtain a precursor; 3) The precursor and the sodium salt are uniformly mixed and then calcined. During the calcination, the temperature is first raised to 400-500° C., kept warm for 3 hours, then raised to 700-900° C., kept warm for 8-24 hours, and finally cooled to room temperature to obtain a ternary sodium cathode material.

3. The preparation method according to claim 2, characterized in that The total concentration of the metal salts in the mixed metal salt aqueous solution is 0.5 to 2.2 mol / L.

4. The preparation method according to claim 2, characterized in that: The nickel salt is nickel sulfate, nickel nitrate or nickel acetate; the manganese salt is manganese sulfate, manganese nitrate or manganese acetate; the cobalt salt is cobalt sulfate, cobalt nitrate or cobalt acetate.

5. The preparation method according to claim 2, characterized in that: The concentration of sodium carbonate is 1 / 2 of the concentration of metal cations in the metal salt solution.

6. The preparation method according to claim 2, characterized in that: During the coprecipitation reaction, the temperature of the reaction system is 40-80°C.

7. The preparation method according to claim 2, characterized in that: During the coprecipitation reaction, the stirring speed in the reaction container is 200-800 r / min, the adding speed of the mixed metal salt aqueous solution is 20 ml / min-500 ml / min, and the adding speed of the precipitant solution is 20 ml / min-500 ml / min.

8. The preparation method according to claim 2, characterized in that: The base liquid is deionized water, and the base liquid temperature is 45-70°C.

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