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

Abstract

The present invention belongs to the technical field of sodium ion battery positive electrode materials, and relates to sodium silicate-coated sodium ion layered oxide positive electrode materials and a preparation method thereof. The chemical formula of the positive electrode material is Na a Si b O c @Na x TMO2, the coating layer is evenly coated on the surface of the sodium ion layered oxide, Na x The TM in TMO2 includes at least two of the transition metals Ni, Co, Mn, Cu, Fe, and Ti. In the preparation method, the coating is first performed by a slightly soluble acid ultrasonic in-situ reaction method, and the generated weak acid sodium salt directly occupies the residual alkaline site of the material and forms a layer of rock salt phase material on the surface. Then, during calcination, medium-low temperature pre-sintering is performed first and then medium-high temperature sintering is performed. The present invention effectively blocks 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 and the structural stability of the positive electrode material are also improved. Therefore, the present invention can effectively improve the rate performance and cycle stability of sodium ion batteries.

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 commercially viable energy storage battery. Global demand for lithium resources continues to increase, but due to dwindling and unevenly distributed lithium reserves, 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 exceeding demand has begun to emerge. Compared with lithium resources, my country has abundant sodium resources, which can be mined and utilized on a large scale, thus breaking the bottleneck of lithium resource supply and demand. At the same time, sodium-ion batteries have greater industrial potential due to their similar operating principles and structure 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 TMO2, where TM stands for transition metal) is considered to be one of the most promising positive electrodes due to its low cost and high theoretical capacity. Among the positive electrode materials for sodium-ion batteries, layered transition metal oxides are a very promising class of positive electrode materials for sodium-ion batteries due to their simple synthesis and easy adjustment of components. However, the current layered transition metal oxide positive electrode materials also face problems such as cycle instability and poor rate performance; the reason is that the residual alkali content (Na2CO3, NaOH) on the surface of the layered transition metal oxides is relatively high, which increases the irreversible capacity loss and reduces the cycle performance, and also makes it difficult to coat 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 has plagued 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 Na a Si b O c @Na x TMO2, of which Na a Si b O c As coating layer, Na x TMO2 is a sodium ion layered oxide; the coating layer is evenly coated on the surface of the sodium ion layered oxide, Na xThe TM in TMO2 includes at least two of the transition metals Ni, Co, Mn, Cu, Fe, and Ti; Na a Si b O c @Na x In TMO2, 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, which is used to prepare the above-mentioned positive electrode material and comprises the following steps:

[0007] Step 1: Ultrasonic treatment is performed on an inorganic acid containing Si element and a solvent to fully disperse and mix the inorganic acid and the solvent to obtain a mixture I. Since ultrasound can generate strong vibration and local high pressure, thereby generating a cavitation effect in the liquid medium, ultrasound can disperse and mix the inorganic acid and the solvent. The purpose of the first ultrasonic treatment is to disperse the inorganic acid.

[0008] Step 2: Na x TMO2 was added to the mixture I obtained in step 1 and ultrasonically treated to fully disperse the inorganic acid and Na x At the same time as TMO2, the reaction of Si-containing inorganic acid with residual alkali on the surface of the material is promoted 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 the inorganic acid and the initial positive electrode material; and promote the chemical reaction between the inorganic acid and the initial positive electrode material, so ultrasonic treatment can promote the chemical reaction between the residual alkali in NaxTMO2, lattice sodium and Si-containing inorganic acid, thereby improving 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, and at the same time, the weak acid will also react 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 the chemical reaction.

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

[0010] Step 4: Pre-sintering the mixed powder obtained in step 3 at a medium to low temperature to promote the decomposition of the Si-containing inorganic acid while removing volatile components, promoting initial crystallization, and improving the microstructure; then, sintering at a medium to high temperature to promote material densification, optimize the 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, medium-low temperature pre-sintering is first carried out during calcination, and then medium-high temperature sintering is carried out; 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 carried out first, and then medium-high temperature sintering is carried out. This staged heating strategy is to control the microstructure and properties 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 the microstructure can be improved; and during medium-high temperature sintering, densification can be promoted, the 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 includes at least one of orthosilicic acid H4SiO4, metasilicic acid H2SiO3, and disilicate H2Si2O5.

[0018] Preferably, in step 2, the sodium ion layered oxide Na x The particle size of TMO2 particles is 2 to 10 μm.

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

[0020] The present invention coats the positive electrode active material of the sodium ion battery by a method of ultrasonic in-situ reaction of slightly soluble acid. During the reaction, the generated weak acid sodium salt directly occupies the residual alkaline 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 sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Graphs showing the cycling performance 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 before and after coating at 1C in Example 4 of the present invention. DETAILED DESCRIPTION

[0023] The following will provide a clear and complete description of the relevant technologies in the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall 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 can effectively block the side reaction between the positive electrode active material and the electrolyte and the dissolution of nickel and manganese. + Three-dimensional channels for ion diffusion, effectively increasing Na + Ion conduction also improves the structural stability of the positive electrode material.

[0025] Example

[0026] Example 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 0.15Mn 0.3 Ti 0.15 The O2 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 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.

[0029] Example 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 The O2 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] Example 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 Fe0.15Mn 0.3 Ti 0.15 The O2 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] Example 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 0.07The O2 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] Example 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 The O2 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 was 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] Example 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 The O2 layered oxide positive electrode material was ultrasonically treated for 30 minutes, and then the solvent was evaporated at 60°C and 500rpm to obtain a composite material.

[0043] 6.2 The composite material obtained in step 6.1 was 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 forced air 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 the button cell: Place the sodium sheet in the middle of the negative electrode shell, insert the separator (Whatman GF / D 1823-090 glass fiber filter), add 160uL of electrolyte, place the positive electrode material face down on the separator, then place the gasket, spring and positive electrode shell. Finally, use a battery sealing machine to press and assemble into a CR2032 battery. Let it stand for 6 hours before testing.

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

[0047] from Figure 1 It can be seen that the cycling performance of the layered transition metal oxide cathode has improved significantly after coating. When discharged at a current density of 5C, after 200 cycles, the capacity retention rate of the layered oxide cathode material before coating was only 78.6%. However, the cycling stability was greatly improved after coating, with the discharge capacity retention rates after 200 cycles being 85.5%, 83.5%, and 87.0%, respectively.

[0048] from Figure 2 It can be seen that the cycling performance of the layered transition metal oxide cathode has been significantly improved after coating. After 100 cycles at a current density of 1C, the capacity retention rate of the layered oxide cathode material before coating was only 86.7%. However, the cycling stability was greatly improved after coating, with the discharge capacity reaching 91.7% after 600 cycles.

[0049] In summary, the present invention is coated by a method of slightly soluble acid ultrasonic in-situ reaction. During the reaction process, the generated weak acid sodium salt directly occupies the residual alkaline 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 sodium ion batteries.

[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. A method for preparing a sodium silicate-coated sodium ion layered oxide positive electrode material, characterized in that: The preparation method comprises the following steps: Step 1: ultrasonically treating an inorganic acid containing Si element and a solvent to fully disperse and mix the inorganic acid and the solvent to obtain a mixture I; Step 2: Adding NaxTMO2, a layered cathode material for sodium ion batteries, to the mixture I obtained in step 1, and performing ultrasonic treatment to fully disperse the inorganic acid and NaxTMO2 while promoting the reaction between the Si-containing inorganic acid and the residual alkali on the surface of the material to obtain a mixture II; Step 3: heating and stirring the mixture II obtained in step 2 and evaporating the solvent to obtain a mixed powder; Step 4: Pre-sintering the mixed powder obtained in step 3 at a medium to low temperature to promote the decomposition of the Si-containing inorganic acid while removing volatile components, promoting initial crystallization, and improving the microstructure; then, sintering at a medium to high temperature to promote material densification, optimize the microstructure, and complete crystallization to obtain a sintered product; Step 5: Grinding the sintered product obtained in step 4 to obtain a sodium silicate-coated sodium ion layered positive electrode material; 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; The chemical formula of the positive electrode material is expressed as NaaSibOc@NaxTMO2, wherein the NaaSibOc is a coating layer and the NaxTMO2 is a sodium ion layered oxide; the coating layer is uniformly coated on the surface of the sodium ion layered oxide, and the TM in the NaxTMO2 includes at least two of the transition metals Ni, Co, Mn, Cu, Fe, and Ti; in the NaaSibOc@NaxTMO2, 0.6≤x≤1, 1≤a≤3, 1≤b≤4, and c satisfies the charge balance of NaaSibOc.

2. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, characterized in that: The thickness of the coating layer is 2 to 30 nm.

3. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, wherein: In the step 1, the solvent includes water and / or ethanol.

4. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, wherein: In the step 1, the ultrasonic treatment time is 10 to 30 minutes.

5. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, characterized in that: In step 2, the ultrasonic treatment time is 20 to 60 minutes.

6. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, characterized in that: In the step 3, the temperature of heating and stirring is 60-80° C., and the rotation speed is 150-500 rpm.

7. The method for preparing the sodium silicate-coated sodium ion layered oxide positive electrode material according to claim 1, characterized in that: In step 1, the inorganic acid containing Si element includes at least one of orthosilicic acid H4SiO4, metasilicic acid H2SiO3, and disilicate H2Si2O5.

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