Sodium-ion layered oxide positive electrode material coated with sodium silicate and preparation method of sodium-ion layered oxide positive electrode material

Abstract

The invention belongs to the technical field of sodium ion battery positive electrode materials, and relates to a sodium silicate coated sodium ion layered oxide positive electrode material and a preparation method thereof, the chemical formula expression of the positive electrode material is NaaSibOc at-NaxTMO2, the surface of a sodium ion layered oxide is uniformly coated with a coating layer, and TM in the NaxTMO2 comprises at least two of transition metals Ni, Co, Mn, Cu, Fe and Ti; according to the preparation method, firstly, coating is carried out through a slightly soluble acid ultrasonic in-situ reaction method, generated weak acid sodium salt directly occupies residual alkali sites of the material, a layer of rock salt phase material is generated on the surface of the material, and then medium-low temperature presintering and medium-high temperature sintering are carried out in the calcining process; according to the invention, side reaction between the positive electrode active material and electrolyte and dissolution of nickel and manganese are effectively blocked, Na < + > ion conduction is effectively increased by virtue of a three-dimensional channel for diffusion of Na < + > ions of sodium silicate, and the structural stability of the positive electrode material is also improved, so that the rate capability and the cycling stability of the sodium ion battery can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion layered oxide positive electrode materials, and relates to a sodium ion layered oxide positive electrode material coated with sodium silicate and a preparation method thereof. Background Art

[0002] In recent years, with the growth of electric vehicles and the development of electrochemical energy storage, lithium-ion batteries have become a mature and large-scale commercial energy storage battery. The global demand for lithium resources continues to increase. However, due to the decreasing reserves and uneven distribution of lithium resources, it is difficult to simultaneously meet the needs of future electric vehicles, large-scale power grids, and a large number of smart devices. The pressure of supply and demand has begun to emerge. Compared with lithium resources, my country has abundant reserves of sodium resources, which can be mined and utilized on a large scale, breaking through the bottleneck of lithium resource supply and demand. At the same time, sodium-ion batteries have greater industrial potential due to their similar working principles and structures to lithium-ion batteries, as well as their compatibility with many basic equipment.

[0003] As an important component of sodium-ion batteries, cathode materials are the key to the development of sodium-ion batteries. It can be said that the performance of cathode materials determines the upper limit of the electrochemical performance of sodium-ion batteries. x TMO 2 , where TM stands for transition metal) is considered to be one of the most promising cathodes due to its low cost and high theoretical capacity. Among the cathode materials for sodium-ion batteries, layered transition metal oxides are a very promising class of cathode materials for sodium-ion batteries due to their simple synthesis and easy adjustment of components. However, layered transition metal oxide cathode materials currently also face problems such as unstable cycles and poor rate performance; the reason is that the residual alkali content (Na 2 CO 3 , NaOH) is high, which increases the irreversible capacity loss and reduces the cycle performance, and also makes it difficult to apply the material slurry. Therefore, how to reduce the residual alkali content of sodium ion layered oxide positive electrode materials has always been a key issue that plagues the preparation of sodium ion positive electrode materials. Summary of the invention

[0004] The technical solution adopted by the present invention to solve the technical problem is: a sodium ion layered oxide positive electrode material coated with sodium silicate, the chemical formula of the positive electrode material is expressed as Na a Si b O c @Na x TMO 2 , where Na a Si b O c As coating layer, Na x TMO 2It is a sodium ion layered oxide; the coating layer is evenly coated on the surface of the sodium ion layered oxide, Na x TMO 2 The TM in the transition metal comprises at least two of Ni, Co, Mn, Cu, Fe, and Ti; Na a Si b O c @Na x TMO 2 , 0.6≤x≤1, 1≤a≤3, 1≤b≤4, c satisfies Na a Si b O c of charge balance.

[0005] Preferably, the coating layer has a thickness of 2 to 30 nm.

[0006] The present invention also discloses a method for preparing a sodium silicate-coated sodium ion layered oxide positive electrode material, the preparation method is used to prepare the positive electrode material, and the preparation method comprises the following steps:

[0007] Step 1, subjecting the inorganic acid containing Si element and the solvent to ultrasonic treatment, and fully dispersing and mixing the inorganic acid and the solvent to obtain a mixture I; since the ultrasonic wave can generate strong vibration and local high pressure, thereby generating a cavitation effect in the liquid medium, the ultrasonic wave can disperse and mix the inorganic acid and the solvent; the first ultrasonic treatment is used to disperse the inorganic acid;

[0008] Step 2: Layered positive electrode material Na x TMO 2 Add to the mixture I obtained in step 1, perform ultrasonic treatment, and fully disperse the inorganic acid and Na x TMO 2 At the same time, it promotes the reaction between Si-containing inorganic acid and residual alkali on the surface of the material to obtain mixture II; since ultrasound can generate strong vibration and local high pressure, thereby generating cavitation effect in the liquid medium, ultrasound can disperse and mix inorganic acid and initial positive electrode material; and promote the chemical reaction between inorganic acid and initial positive electrode material, so ultrasonic treatment can promote NaxTMO 2 The chemical reaction between the residual alkali, lattice sodium and Si-containing inorganic acid improves the reaction efficiency and the uniformity of the coating layer; during the reaction, the weak acid sodium salt generated directly occupies the residual alkali site of the material. At the same time, the weak acid also reacts with the sodium in the lattice of the positive electrode material to form a layer of rock salt phase material on the surface; it can effectively block the side reaction between the positive electrode active material and the electrolyte and the dissolution of nickel and manganese, while relying on the Na + Three-dimensional channels for ion diffusion, effectively increasing Na +Ion conduction also improves the structural stability of the positive electrode material; at the same time, silicate or silicic acid can introduce Si elements into the layered positive electrode material through chemical reaction, which can change the structure and performance of the material and improve its electronic conductivity, cycle stability and sodium storage capacity; the role of the second ultrasonic treatment is to promote chemical reactions;

[0009] Step 3, heating and stirring the mixture II obtained in step 2 to evaporate the solvent to obtain a mixed powder;

[0010] Step 4: pre-sinter the mixed powder obtained in step 3 at a medium-low temperature to promote the decomposition of Si-containing inorganic acid while removing volatile components, promoting initial crystallization, and improving microstructure; then, sinter at a medium-high temperature to promote material densification, optimize microstructure, and complete crystallization to obtain a sintered product;

[0011] Step 5: Grind the sintered product obtained in step 4 to obtain a sodium silicate-coated sodium ion layered positive electrode material.

[0012] Preferably, in step 1, the solvent includes water and / or ethanol.

[0013] Preferably, in step 1, the ultrasonic treatment time is 10 to 30 minutes.

[0014] Preferably, in step 2, the ultrasonic treatment time is 20 to 60 minutes.

[0015] Preferably, in step 3, the temperature of heating and stirring is 60-80° C., and the rotation speed is 150-500 rpm.

[0016] Preferably, in step 4, during calcination, medium-low temperature pre-sintering is first performed and then medium-high temperature sintering is performed; the medium-low temperature pre-sintering temperature is 150-200°C, and the medium-low temperature pre-sintering time is 2-6 hours; the medium-high temperature sintering temperature is 550-750°C, and the medium-high temperature sintering time is 2-10 hours; medium-low temperature pre-sintering is performed first, and then medium-high temperature sintering is performed. Such a staged heating strategy is to control the microstructure and performance of the material; during medium-low temperature pre-sintering, volatile components can be removed, silicon-containing inorganic acids can be decomposed, initial crystallization can be promoted, and microstructure can be improved; and during medium-high temperature sintering, densification can be promoted, microstructure can be optimized, and complete crystallization can be achieved; the staged calcination strategy can effectively avoid structural defects that may occur at high temperatures, while ensuring that the final performance of the material meets the requirements; and the specific temperature and time are adjusted according to the characteristics and target performance of the coating layer and the sodium ion layered oxide.

[0017] Preferably, in step 1, the inorganic acid containing Si element comprises: orthosilicic acid H 4 SiO 4 、Methosilicic acid H2 SiO 3 , disilicate H 2 Si 2 O 5 At least one of .

[0018] Preferably, in step 2, the sodium ion layered oxide Na x TMO 2 The particle size is 2 to 10 μm.

[0019] The beneficial effects of the present invention are:

[0020] The present invention uses a method of in-situ ultrasonic reaction of slightly soluble acid to coat. During the reaction process, the generated weak acid sodium salt directly occupies the residual alkali site of the material. At the same time, the weak acid also reacts with the sodium in the lattice of the positive electrode material to generate a layer of rock salt phase material on the surface. The present invention coats a layer of sodium silicate film on the surface of the positive electrode active material of the sodium ion battery, which can effectively block the side reaction between the positive electrode active material and the electrolyte and the dissolution of nickel and manganese. At the same time, relying on the Na + Three-dimensional channels for ion diffusion, effectively increasing Na + Ion conduction also improves the structural stability of the positive electrode material; therefore, the present invention can effectively improve the rate performance and cycle stability of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a cycle performance curve diagram at 5C before and after coating of the positive electrode material in Examples 1 to 3 of the sodium silicate-coated sodium ion layered oxide positive electrode material and the preparation method thereof of the present invention;

[0022] Figure 2 This is a cycle performance curve diagram of the positive electrode material at 1C before and after coating in Example 4 of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] refer to Figures 1-2 In this embodiment, a layer of sodium silicate film is coated on the surface of the positive electrode active material of the sodium ion battery, which can effectively block the side reaction between the positive electrode active material and the electrolyte and the dissolution of nickel and manganese. At the same time, the sodium silicate has a strong Na+ Three-dimensional channels for ion diffusion, effectively increasing Na + Ion conduction also improves the structural stability of the positive electrode material.

[0025] Example

[0026] Embodiment 1:

[0027] 1.1 Weigh 0.05g of silicic acid and add it to 15ml of ethanol. Ultrasonicate for 10min, then weigh 1g of Na 0.95 Ni 0.4 Fe 0.15 Mn 0.3 Ti 0.15 O 2 The layered oxide positive electrode material was ultrasonically treated for 20 min, and then the solvent was evaporated at 60°C and 150 rpm to obtain a composite material.

[0028] 1.2 The composite material obtained in step 1.1 is calcined, first at 150°C for 4 hours and then at 600°C for 4 hours to obtain a coated modified layered oxide positive electrode material.

[0029] Embodiment 2:

[0030] 2.1 Weigh 0.03g of silicic acid and add it to 15ml of ethanol, ultrasonicate for 10min, then weigh 1g of Na 0.95 Ni 0.4 Fe 0.15 Mn 0.3 Ti 0.15 O 2 The layered oxide positive electrode material was ultrasonically treated for 20 min, and then the solvent was evaporated at 60°C and 150 rpm to obtain a composite material.

[0031] 2.2 The composite material obtained in step 2.1 was calcined, first at 150°C for 4 hours and then at 600°C for 4 hours to obtain a coated modified layered oxide positive electrode material.

[0032] Embodiment 3:

[0033] 3.1 Weigh 0.01g of silicic acid and add it to 15ml of ethanol. Ultrasonicate for 10min. Then weigh 1g of Na 0.95 Ni 0.4 Fe 0 .15Mn 0.3 Ti 0.15 O 2 The layered oxide positive electrode material was ultrasonically treated for 20 min, and then the solvent was evaporated at 60°C and 150 rpm to obtain a composite material.

[0034] 3.2 The composite material obtained in step 3.1 was calcined, first at 150°C for 4 hours and then at 600°C for 4 hours to obtain a coated modified layered oxide positive electrode material.

[0035] Embodiment 4:

[0036] 4.1 Weigh 0.05g of silicic acid and add it to 25ml of ethanol. Ultrasonicate for 10min. Then weigh 1g of Na 0.7 Li 0.03 Mg 0.03 Ni 0.27 Mn 0.6 Ti 0.07 O 2 The layered oxide positive electrode material was ultrasonically treated for 30 min, and then the solvent was evaporated at 60°C and 150 rpm to obtain a composite material.

[0037] 4.2 The composite material obtained in step 4.1 was calcined, first at 150°C for 4 hours and then at 600°C for 4 hours to obtain a coated modified layered oxide positive electrode material.

[0038] Embodiment 5:

[0039] 5.1 Weigh 0.05g of silicic acid and add it to 25ml of water. Ultrasonicate for 30min. Then weigh 1g of Na 0.7 Li 0.03 Mg 0.03 Ni 0.27 Mn 0.6 Ti 0.07 O 2 The layered oxide positive electrode material was ultrasonically treated for 60 min, and then the solvent was evaporated at 80°C and 500 rpm to obtain a composite material.

[0040] 5.2 The composite material obtained in step 5.1 is calcined, first at 200°C for 2 hours and then at 550°C for 10 hours to obtain a coated modified layered oxide positive electrode material.

[0041] Embodiment 6:

[0042] 6.1 Weigh 0.02g of silicic acid and add it to 25ml of ethanol. Ultrasonicate for 10min. Then weigh 1g of Na 0.7 Li 0.03 Mg 0.03 Ni 0.27 Mn 0.6 Ti 0.07 O 2 The layered oxide positive electrode material was ultrasonically treated for 30 min, and then the solvent was evaporated at 60°C and 500 rpm to obtain a composite material.

[0043] 6.2 The composite material obtained in step 6.1 is calcined, first at 150°C for 6 hours and then at 750°C for 2 hours to obtain a coated modified layered oxide positive electrode material.

[0044] Preparation of the positive electrode: Mix layered oxide powder: conductive carbon black: polyvinylidene fluoride in a mass ratio of 7.5:1.5:1, add an appropriate amount of NMP, put it into a ball mill and stir it for 0.5h, then evenly apply it on aluminum foil; first dry it in a blast drying oven at 80℃ for 20min, then put it in a vacuum drying oven at 80℃ and vacuum dry it for 12h; after taking it out, use a slicer to cut it into 10mm circular electrode pieces, weigh it and put it into the glove box.

[0045] Assembly of button battery: Place the sodium sheet in the middle of the negative electrode shell, insert the diaphragm (Whatman GF / D 1823-090 glass fiber filter), add 160uL electrolyte, place the positive electrode material downward on the diaphragm, then place the gasket, shrapnel and positive electrode shell, and finally use a battery sealing machine to press and assemble into a CR2032 battery, and test it after standing for 6 hours.

[0046] Figure 1 The cycle performance curves of the coated modified layered oxide positive electrode material and the uncoated positive electrode material at 5C in Examples 1 to 3; Figure 2 The graph is a cycle performance curve of the coated layered positive electrode material and the uncoated layered positive electrode material at 1C in Example 4.

[0047] from Figure 1 It can be seen that the cycle performance of the layered transition metal oxide positive electrode has been improved to a certain extent after coating. When discharged at a current density of 5C, after 200 cycles, the capacity retention rate of the layered oxide positive electrode material before coating was only 78.6%; after coating, the cycle stability was greatly improved, and the discharge capacity retention rates after 200 cycles were 85.5%, 83.5%, and 87.0%, respectively.

[0048] from Figure 2 It can be seen that the cycle performance of the layered transition metal oxide positive electrode has been greatly improved after coating. Discharging at a current density of 1C, after 100 cycles, the capacity retention rate of the layered oxide positive electrode material before coating was only 86.7%; after coating, the cycle stability was greatly improved, and the discharge capacity was 91.7% after 600 cycles.

[0049] In summary, the present invention uses a method of in-situ ultrasonic reaction of slightly soluble acid to coat. During the reaction process, the generated weak acid sodium salt directly occupies the residual alkali site of the material. At the same time, the weak acid also reacts with the sodium in the lattice of the positive electrode material to generate a layer of rock salt phase material on the surface. The present invention coats a layer of sodium silicate film on the surface of the positive electrode active material of the sodium ion battery, which can effectively block the side reaction between the positive electrode active material and the electrolyte and the dissolution of nickel and manganese. At the same time, relying on the Na + Three-dimensional channels for ion diffusion, effectively increasing Na + Ion conduction also improves the structural stability of the positive electrode material; therefore, the present invention can effectively improve the rate performance and cycle stability of the sodium ion battery.

[0050] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. Sodium silicate coated sodium ion layered oxide positive electrode material, It is characterized in that The chemical formula of the positive electrode material is Na a Si b O c @Na x TMO 2 , wherein the Na a Si b O c As the coating layer, the Na x TMO 2 is a sodium ion layered oxide; the coating layer is uniformly coated on the surface of the sodium ion layered oxide, the Na x TMO 2 The TM in the transition metal comprises at least two of Ni, Co, Mn, Cu, Fe and Ti; the Na a Si b O c @Na x TMO 2 , 0.6≤x≤1, 1≤a≤3, 1≤b≤4, c satisfies Na a Si b O c of charge balance.

2. The sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, It is characterized in that The coating layer has a thickness of 2 to 30 nm.

3. Preparation method of sodium silicate-coated sodium ion layered oxide positive electrode material, It is characterized in that The preparation method is used to prepare the positive electrode material according to any one of claims 1 to 2, and the preparation method comprises the following steps: Step 1, subjecting the inorganic acid containing Si element and the solvent to ultrasonic treatment, and fully dispersing and mixing the inorganic acid and the solvent to obtain a mixture I; Step 2: Layered positive electrode material Na x TMO 2 Add to the mixture I obtained in step 1, perform ultrasonic treatment, and fully disperse the inorganic acid and Na x TMO 2 At the same time, the reaction between the Si-containing inorganic acid and the residual alkali on the surface of the material is promoted to obtain a mixture II; Step 3, heating and stirring the mixture II obtained in step 2 to evaporate the solvent to obtain a mixed powder; Step 4: pre-sinter the mixed powder obtained in step 3 at a medium-low temperature to promote the decomposition of Si-containing inorganic acid while removing volatile components, promoting initial crystallization, and improving microstructure; then, sinter at a medium-high temperature to promote material densification, optimize microstructure, and complete crystallization to obtain a sintered product; Step 5: Grind the sintered product obtained in step 4 to obtain a sodium ion layered positive electrode material coated with sodium silicate.

4. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In the step 1, the solvent includes water and / or ethanol.

5. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In the step 1, the ultrasonic treatment time is 10 to 30 minutes.

6. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In the step 2, the ultrasonic treatment time is 20 to 60 minutes.

7. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In step 3, the temperature of heating and stirring is 60-80° C., and the rotation speed is 150-500 rpm.

8. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In the step 4, during calcination, medium-low temperature pre-sintering is first performed and then medium-high temperature sintering is performed; the medium-low temperature pre-sintering temperature is 150-200° C., and the medium-low temperature pre-sintering time is 2-6 hours; the medium-high temperature sintering temperature is 550-750° C., and the medium-high temperature sintering time is 2-10 hours.

9. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 3, It is characterized in that In step 1, the inorganic acid containing Si element includes: orthosilicic acid H 4 SiO 4 、Methosilicic acid H 2 SiO 3 , disilicate H 2 Si 2 O 5 At least one of .

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