Sodium-ion battery oxide single-crystal positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a sodium ion battery oxide single crystal positive electrode material and a preparation method and application thereof, and belongs to the technical field of battery materials. The chemical formula of the prepared positive electrode material is Na Fe < x > Mn < y > M < z > NO2, a < = 1.1, 0.4 < = x < = 1, 0 < = y < = 1, M is a doping element, 0.005 < = z < = 0.11, and N is a coating element. The positive electrode material provided by the invention is prepared by adopting an efficient microwave sintering mode without using expensive noble metals such as nickel, cobalt and copper as raw materials, so that the price of the positive electrode material of the sodium-ion battery can be reduced by more than 50% compared with the existing price, and the preparation efficiency is improved by more than 6 times; meanwhile, the prepared sodium-ion battery positive electrode material has good single crystal morphology and relatively high discharge capacity and cycle index, so that the cost of the sodium-ion battery can be greatly reduced, the performance of the sodium-ion battery can be improved, and large-scale popularization and application of the sodium-ion battery are facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a sodium ion battery oxide single crystal positive electrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy vehicles, new energy batteries are also in constant research and development and innovation. From the perspective of classification, new energy batteries include lithium-ion batteries, sodium-ion batteries, lead-acid batteries, hydrogen fuel cells, etc. Among them, lithium-ion batteries have gradually become the main part of modern new energy batteries due to their huge advantages in battery capacity, service life, safety performance, charging and discharging speed, and green environmental protection, but other new energy batteries still have certain market prospects.

[0003] Sodium-ion batteries mainly rely on the movement of sodium ions between the positive and negative electrodes to work. They work in a similar way to lithium-ion batteries, but they have the advantages of excellent low-temperature performance, high safety, fast charging and low cost. Therefore, the development of sodium-ion batteries is a favorable supplement and replacement for lithium iron phosphate lithium-ion batteries and ternary lithium-ion batteries. Due to the inherent advantages of sodium-ion batteries, they can be widely used in power tools, small energy storage, large energy storage and passenger cars. In the future, as the cost of sodium-ion batteries continues to decrease, it is an inevitable trend to replace lead-acid batteries used in two-wheeled vehicles and low-speed vehicles.

[0004] At present, the two main factors that lead to the slow application of sodium-ion batteries in the market are the high cost and poor performance of positive electrode materials. The main performance of sodium-ion batteries, such as poor processing performance, low discharge capacity, high gas production and short cycle life, is mainly due to the low active Na content inside the lattice of the positive electrode material. The residual alkali and pH of the positive electrode material are too high, resulting in less active Na inside the lattice, and causing the positive electrode material to have a large impedance and a small diffusion coefficient of Na ions. On the other hand, the main chemical components of the positive electrode materials of layered oxide sodium-ion batteries contain main elements such as Ni, Cu, Mn, and Fe. Since the prices of Ni and Cu are relatively expensive, the prices of metal Ni and Cu are 126,000 yuan / ton and 77,000 yuan / ton respectively (SMM data on February 7, 2025), while the sulfate prices of Mn and Fe are 5,000 yuan / ton and 6,000 yuan / ton respectively. Therefore, the sales price of layered oxide sodium-ion battery positive electrode materials containing precious metals Ni and Cu is very high, resulting in high cost and difficulty in promoting sodium-ion batteries. In addition, compared with polycrystalline materials, single crystal materials have the characteristics of high compaction, high safety, low gas production and long cycle, but the preparation technology threshold is relatively high. Therefore, preparing a highly active and low-cost single crystal oxide positive electrode material for sodium ion batteries is a key technical challenge. Summary of the invention

[0005] In view of the above-mentioned prior art, the present invention discloses a sodium-ion battery oxide single-crystal cathode material, a preparation method thereof and an application thereof, so as to solve the problems in the prior art that the electrochemical performance of the sodium-ion battery oxide single-crystal cathode material decreases due to low activity, the cost is high, resulting in an expensive battery price, and it is difficult to synthesize a single-crystal cathode material.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: to provide a sodium-ion battery oxide single-crystal cathode material, the chemical formula of which is Na a Fe x Mn y M z NO 2 , where 0.7 < a ≤ 1.1, 0.4 ≤ x ≤ 1, 0 ≤ y ≤ 1; M is a doping element, 0.005 ≤ z ≤ 0.11, and M is at least one of Ni, Cu, Zr, Cs, Mo, Sn, Zn, Ca, Li, Ru, K, In, Se, Si, S, B, Te, Cr, Sb, Sn, La and Gd; N is a coating element, and N is at least one of Cu, Zr, Cs, Mo, Sn, Zn, Ca, Ti, W, Ru, In, Se, Si, B, Te, Cr, Sb, La, Gd and Al, and the coating element accounts for 0.1 - 0.8% of the total mass of the cathode material.

[0007] The beneficial effect of the above technical solution is: This cathode material does not use expensive Ni and Cu as the main raw materials, but uses inexpensive Fe and Mn as the main raw materials, reducing the raw material cost by more than 70%.

[0008] The present invention also discloses a preparation method of this sodium-ion battery oxide single-crystal cathode material, which includes the following steps: S1: After uniformly mixing an iron-manganese composite, a sodium salt and a dopant containing a doping element M, perform the first microwave sintering, pulverization and screening to obtain an intermediate; the iron-manganese composite is Fe x Mn 1-x (OH) 2 or Fe x Mn 1-x CO 3 , 0 < x ≤ 1; M is at least one of Ni, Cu, Zr, Cs, Mo, Sn, Zn, Ca, Li, Ru, K, In, Se, Si, S, B, Te, Cr, Sb, Sn, La and Gd; S2: Coating the intermediate with a coating agent containing a coating element N, and then performing the second microwave sintering, pulverization and screening to obtain the product; N is at least one of Cu, Zr, Cs, Mo, Sn, Zn, Ca, Ti, W, Ru, In, Se, Si, B, Te, Cr, Sb, La, Gd and Al.

[0009] The beneficial effect of the above technical solution is that the sintering temperature and sintering time are greatly reduced by adopting efficient microwave sintering technology, so the processing cost can be reduced by more than 50%, and finally, the price of the existing sodium ion battery oxide single crystal positive electrode material is reduced by more than 50%. The traditional heating method is to use the radiation and conduction generated by the high temperature heat source to heat the surface of the object first, and then gradually heat it in depth inside the object by conduction and convection. This method is inefficient and takes a long time to heat. However, the microwave heating method generates microwaves inside the heated object, and the heat source comes from the inside of the object, so it can be heated evenly without temperature difference, so it can heat up quickly, improve heating efficiency, realize continuous production, and reduce the comprehensive energy consumption by about 70%. Therefore, microwave heating can make sodium ions diffuse and migrate evenly on the surface and inside of the layered oxide single crystal positive electrode material particles, thereby reducing residual alkali and increasing the active k value, k=(1-δ) / a, where a is the molar amount of sodium and δ is the total free sodium of the sodium positive material. At the same time, due to the uniformity of microwave heating temperature and heating from the inside of the particles, it helps to form a uniform single crystal particle morphology.

[0010] Based on the above technical solution, the present invention can also be improved as follows.

[0011] Furthermore, in step S1, the sodium salt is at least one of sodium carbonate, sodium bicarbonate and sodium hydroxide; and the ratio of the total molar amount of iron and manganese elements in the iron-manganese complex to the molar amount of sodium element in the sodium salt is 1:0.7-1.1.

[0012] Furthermore, the particle size D of the dopant 50 <1μm; the dopant is a compound including M; or the dopant is at least one of nickel oxide, nickel hydroxide, copper oxide, copper hydroxide, zirconium oxide, zirconium hydroxide, cesium oxide, molybdenum oxide, ammonium molybdate, tin oxide, zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, lithium carbonate, lithium hydroxide, ruthenium oxide, potassium oxide, potassium hydroxide, indium oxide, selenium oxide, silicon oxide, sulfur oxide, boric acid, boron oxide, chromium oxide, tellurium oxide, lanthanum oxide and gadolinium oxide.

[0013] Furthermore, in step S1, the microwave sintering temperature is 650-800° C., and the microwave sintering time is 1-3 h.

[0014] Furthermore, the particle size D of the coating agent 50<50nm; the coating agent is a compound including N, or the coating agent is at least one of copper oxide, copper hydroxide, zirconium oxide, zirconium hydroxide, cesium oxide, molybdenum oxide, ammonium molybdate, tin oxide, zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, titanium oxide, tungsten oxide, ammonium tungstate, ruthenium oxide, indium oxide, selenium oxide, silicon oxide, boric acid, boron oxide, tellurium oxide, chromium oxide, antimony oxide, lanthanum oxide, gadolinium oxide, aluminum oxide and aluminum hydroxide; Furthermore, in step S2, the microwave sintering temperature is 200-500° C., and the microwave sintering time is 1-3 hours.

[0015] Furthermore, in the primary microwave sintering and / or the secondary microwave sintering, the sintering atmosphere is air, oxygen or a mixed gas with an oxygen concentration of ≥10%.

[0016] The invention also discloses application of the sodium ion battery oxide single crystal positive electrode material in preparing the sodium ion battery.

[0017] The beneficial effects of the present invention are: 1. The present invention uses low-cost Fe and Mn elements as main raw materials and prepares high-activity iron-manganese binary sodium ion battery oxide single crystal sodium ion battery positive electrode material through low-cost microwave sintering technology. In the preparation process, on the one hand, the use of doping technology helps to form a single crystal morphology and can form a superlattice structure, which can inhibit the Na in the sodium metal layer. + H in water molecules in the air + Na + / H + exchange, thus, it can reduce the residual alkali on the surface of the sodium ion material and improve the stability of the sodium ion material; at the same time, the doping element can expand the distance between the sodium metal layers and reduce the distance between the transition metal layers, thereby increasing the Na + The diffusion coefficient of sodium ion battery oxide single crystal positive electrode material can be reduced, thereby reducing the residual alkali on the surface of the sodium ion battery oxide single crystal positive electrode material. On the other hand, a nano-coating material that can neutralize excessive free sodium is added during the secondary sintering process to form a conductor coating layer with ions and electrons. The coating layer reduces the surface residual alkali on the one hand, and enhances the interface stability and cycle performance of the sodium ion battery oxide single crystal positive electrode material and reduces the generation of gas on the other hand. In addition, the microwave sintering technology is used to accelerate the diffusion of sodium ions inside the positive electrode material to reduce the surface residual alkali. Therefore, by combining bulk phase doping, surface nano-coating and microwave sintering processes, the activity value k of sodium ions in the sodium ion battery oxide single crystal positive electrode material can be increased, k≥99%, k=(1-δ) / a, the larger the k value, the higher the capacity, first efficiency and rate of the sodium ion battery positive electrode material. At the same time, coating and doping can also improve the processing performance, capacity, cycle and gas production of sodium ion batteries.

[0018] 2. The present invention adds a variety of effective combinations of dopants that improve the sodium ion diffusion rate during the preparation of the sodium ion battery oxide single crystal positive electrode material, thereby reducing the residual alkali content at the source. At the same time, by coating a variety of combinations of nano-residual alkali-reducing coating agents. The doping and coating technologies are used to synergistically reduce the residual alkali, so that the pH of the sodium ion battery oxide single crystal positive electrode material can be reduced to below 12, and the free sodium is controlled within 5000ppm. The beneficial result is that the active k value is greater than 99%, so the discharge capacity and cycle number of the sodium ion battery positive electrode material can be increased. On the other hand, the prepared sodium ion battery positive electrode material has a single crystal morphology, so it can increase the compaction density of the pole piece, improve gas production and improve the battery cycle performance, which is conducive to the large-scale promotion and use of sodium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a SEM image of the high-activity, low-cost iron-manganese binary sodium ion battery oxide single crystal positive electrode material in Example 1; Figure 2 This is a SEM image of the low-activity iron-manganese binary sodium ion battery oxide single crystal positive electrode material sintered conventionally in Comparative Example 1; Figure 3 Capacity curves of single crystal oxide cathode materials for sodium ion batteries of Example 1 and Comparative Example 1; Figure 4 The cycle curves of the sodium ion battery oxide single crystal positive electrode material of Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0021] Example 1 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.90 Cu 0.06 Zr 0.015 Cs 0.005 Mo 0.015 Sn 0.005 (Zr+Ti+W+P)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, FeCO 3 With NaHCO 3 Weigh according to the molar ratio of total metal atoms to sodium atoms of 1: (0.7-1.1), and add Cu(OH) in the above molecular formula at the same time.2 、ZrO 2 , Cs 2 O、(NH 4 ) 2 MoO 4 and SnO 2 Five dopants, particle size D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 2h under an oxygen atmosphere and 700℃, and then crushed and sieved to obtain an intermediate, the mesh number of the sieve is 325 mesh; S2: Use coating agent (ZrO 2 、TiO 2 NH 4 ) 6 W 7 O 24 6H 2 O and NH 4 H 2 PO 4 ) The intermediate is coated, the amount of the coating agent is based on (Zr+Ti+W+P) accounting for 0.6% of the total mass of the positive electrode material, wherein the molar ratio of Zr, Ti, W and P is 1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, secondary sintered at 330°C for 1h, and then crushed and sieved to obtain the intermediate, the mesh number of the sieve is 325 mesh.

[0022] Example 2 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.40 Mn 0.50 Cu 0.02 Mo 0.05 5 Zn 0.015 Se 0.005 B 0.005 (Sn+Zn+Ca+Se)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, Fe 0.45 Mn 0.55 (OH) 2 Weigh the total metal atoms and sodium atoms in a molar ratio of 1: (0.7-1.1) with NaOH, and add the molar ratio of Cu(OH) in the above molecular formula. 2 NH 4 ) 2 MoO 4 , ZnO, SeO 2 and H 3 BO3 Five dopants, particle size D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 3h in a 10% oxygen atmosphere and 650℃, and then crushed and sieved to obtain an intermediate, the mesh number of the sieve is 325 mesh; S2: Coating agent (SnO, ZnO, CaO and SeO) is used in the coating machine. 2 ) The intermediate is coated, the amount of the coating agent is based on (Sn+Zn+Ca+Se) accounting for 0.1% of the total mass of the positive electrode material, wherein the molar ratio of Sn, Zn, Ca and Se is 1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, secondary sintered at 200°C for 3h, and then crushed and sieved to obtain the intermediate, the mesh number of the sieve is 325 mesh.

[0023] Example 3 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.45 Mn 0.45 Ni 0.06 Zr 0.01 5 Zn 0.005 Si 0.015 Sn 0.005 (Cu+Zr+Ca+B)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, Fe 0.5 Mn 0.5 CO 3 with Na 2 CO 3 Weigh according to the molar ratio of total metal atoms to sodium atoms of 1: (0.7-1.1), and add Ni(OH) in the above molecular formula at the same time. 2 、ZrO 2 、ZnO、SiO 2 and SnO 2 Five dopants, particle size D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 1h in an air atmosphere at 800℃, and then crushed and sieved to obtain an intermediate, the mesh number of the sieve is 325 mesh; S2: Use coating agent (CuO, Zr(OH) 4 , Ca(OH) 2 and H 3 BO 3) is used to coat the intermediate, the amount of the coating agent is based on (Cu+Zr+Ca+B) accounting for 0.6% of the total mass of the positive electrode material, wherein the molar ratio of Cu, Zr, Ca and B is 1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, sintered for a second time at 500℃ for 1h, and then crushed and sieved to obtain the intermediate, and the mesh number of the sieve is 325 meshes.

[0024] Example 4 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.40 Mn 0.49 Ca 0.07 Li 0.01 5 Ru 0.005 Te 0.005 La 0.005 (Cs+Mo+Ca+Ru+Se)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, Fe 0.45 Mn 0.55 (OH) 2 with Na 2 CO 3 and NaOH in a molar ratio of 1:(0.7-1.1) between total metal atoms and sodium atoms, and at the same time add CaO, Li 2 CO 3 、RuO 2 、TeO 2 and La 2 O 3 Five dopants, particle size D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 1h under 80% oxygen atmosphere and 780℃, and then crushed and sieved to obtain an intermediate, the mesh number of the sieve is 325 mesh; S2: Use coating agent (Cs 2 O、MoO 2 、CaO、RuO 2 and SeO 3 ) is coated on the intermediate, the amount of the coating agent is based on (Cs+Mo+Ca+Ru+Se) accounting for 0.3% of the total mass of the positive electrode material, wherein the molar ratio of Cs, Mo, Ca, Ru and Se is 1:1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, sintered for a second time at 450°C for 2h, and then crushed and sieved to obtain the intermediate, with a mesh size of 325.

[0025] Example 5 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.75 Mn 0.24 K 0.16 In 0.0 2 B 0.015 Sb 0.005 (In+Si+B+Te+Cr)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, Fe 0.75 Mn 0.25 (OH) 2 with Na 2 CO 3 and NaOH in a molar ratio of 1:(0.7-1.1) between total metal atoms and sodium atoms, and at the same time add K 2 O、In 2 O 3 , B 2 O 3 and Sb 2 O 3 Four dopants, particle size of dopants D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 1.5h in an air atmosphere at 680℃, and then crushed and sieved to obtain an intermediate; the mesh number of the sieve is 325 mesh; S2: Use coating agent in coating machine (In 2 O 3 、SiO 2 , B 2 O 3 、TeO 2 and CrO 3 ) is coated on the intermediate, the amount of coating agent is based on (In+Si+B+Te+Cr) accounting for 0.8% of the total mass of the positive electrode material, wherein the molar ratio of In, Si, B, Te and Cr is 1:1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, sintered for a second time at 350°C for 3h, and then crushed and sieved to obtain the intermediate, with a mesh size of 325.

[0026] Example 6 A sodium ion battery oxide single crystal positive electrode material, whose chemical formula is Na 0.7-1.1 Fe 0.65 Mn 0.25 Se 0.06 S0.02 Cr 0.015 G 0.005 (Ti+Sb+La+Gd)O 2 , and its preparation method comprises the following steps: S1: According to the molecular formula, Fe 0.75 Mn 0.25 (OH) 2 with Na 2 CO 3 Weigh according to the molar ratio of total metal atoms to sodium atoms 1: (0.7-1.1), and add SeO 2 、SO 2 CrO 3 and Gd 2 O 3 Four dopants, particle size of dopants D 50 <1μm, then the raw materials are placed in a high-speed mixer and mixed evenly; then the mixture is placed in a microwave sintering furnace, sintered for 1h under an oxygen atmosphere and 800℃, and then crushed and sieved to obtain an intermediate, the mesh number of the sieve is 325 mesh; S2: In the coating machine, a coating agent (TiO 2 , Sb 2 O 3 ,La 2 O 3 and Gd 2 O 3 ) The intermediate is coated, the amount of the coating agent is based on (Ti+Sb+La+Gd) accounting for 0.5% of the total mass of the positive electrode material, wherein the molar ratio of Ti, Sb, La and Gd is 1:1:1:1, and the particle size of the coating agent is less than 50nm; then the coated intermediate is placed in a microwave sintering furnace, secondary sintered at 500°C for 3h, and then crushed and sieved to obtain the intermediate, the mesh number of the sieve is 325 mesh.

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that microwave sintering is not performed during the preparation process, but traditional box furnace sintering is adopted, with a primary sintering temperature of 980° C. and a holding time of 16 h, and a secondary sintering temperature of 680° C. and a holding time of 8 h.

[0028] Comparative Example 2 The difference between this comparative example and Example 1 is that no residual alkali reducing dopant and residual alkali reducing coating agent are added during the preparation process.

[0029] Test example The performance of the sodium ion battery oxide single crystal positive electrode material prepared in the embodiments of the present invention is similar. Taking Embodiment 1 as an example, the performance of the related products is described.

[0030] 1. Structural characterization The samples prepared in Example 1 and Comparative Example 1 were subjected to electron microscope scanning, and the SEM images are as follows: Figure 1~2 As shown in the figure, the sodium ion battery positive electrode material particles in Example 1 are relatively dispersed and in a single crystal morphology, while the conventional sintering method in Comparative Example 1 causes the sodium ion battery positive electrode material particles to agglomerate and fail to form a dispersed single crystal morphology. The traditional sintering method is externally heated, which will cause a temperature gradient difference, resulting in uneven heating of the sodium ion battery positive electrode material and consistent sodium ion diffusion rate, and sodium ions can reduce the single crystal growth temperature, so different concentrations of sodium ions will cause partial unevenness in the single crystal morphology. Microwave heating is heated from the inside, resulting in the absence of a temperature gradient difference inside the sodium ion battery positive electrode material, so the sodium ion diffusion rate is consistent and the sodium ions are evenly distributed, so a single crystal morphology with a complete morphology and uniform dispersion can be formed, while the heating temperature and heating time are shortened.

[0031] 2. Discharge capacity and cycle performance test The positive electrode material, conductive carbon black and binder PVDF (polyvinylidene fluoride) prepared in the embodiment and comparative example are mixed in a mass ratio of 80:10:10, and NMP is added to form a uniform slurry, which is coated on aluminum foil. After drying and rolling, it is cut into positive electrode sheets with a diameter of 14 mm. Sodium ion batteries are assembled using CR2032 button batteries. The diaphragm is glass fiber, the electrolyte is a 1 mol / L NaPF6 solution with EC / PC / DEC as the solvent, and the negative electrode is a sodium sheet. Sodium ion battery test conditions: temperature is 25℃±1℃, charge and discharge cycle voltage range is 2.0~4.0V, current is 0.1C (120mAh / g), and the cycle test is carried out at 0.5C charge and 1C discharge. The results are shown in Table 1 and Figure 3~4 shown.

[0032] Table 1

[0033] As shown in Table 1, the discharge capacity, cycle and activity value k of the sodium ion battery positive electrode materials prepared in Examples 1 to 6 are extremely excellent. For example, the 50-week cycle retention rate is above 95%, and the activity value k is above 99%. Figure 3~4 It can also be seen that the Na in Example 1 0.7-1.1 Fe 0.9 Cu 0.06 Zr 0.015 Cs 0.005 Mo 0.015 Sn 0.005 (Zr+Ti+W+P)O 2The first discharge capacity is 159mAh / g, the cycle retention rate of 50 weeks is 95.64%, and the activity value is 99.67%; while the first capacity in comparative example 1 is only 151mAh / g, the cycle retention rate of 50 weeks is 88.71%, and the activity value is 95.41%. The high activity value and high discharge capacity indicate that the electrochemically active sodium content in the unit cell of the high-activity and low-cost sodium ion battery oxide single crystal positive electrode material is high, while the non-electrochemically active free sodium on the surface is low, so the number of sodium ions deintercalated in the electrochemical reaction is large; at the same time, the cycle performance is also relatively good, which also shows that the interface electrochemical resistance of the high-activity and low-cost sodium ion battery oxide single crystal positive electrode material is small, the single crystal degree is high, and the single crystal structure is more stable. Therefore, microwave sintering and the addition of residual alkali reduction dopants and coating agents can effectively reduce the content of non-electrochemically active free sodium in the positive electrode material of the sodium ion battery, improve the single crystal morphology and interface stability of the positive electrode material of the sodium ion battery, and improve the discharge capacity and cycle performance of the sodium ion battery.

[0034] Although the specific implementation of the present invention is described in detail in conjunction with the embodiments, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A sodium ion battery oxide single crystal positive electrode material, characterized in that: The chemical formula is Na a Fe x Mn y M z NO2, where 0.7 < a ≤ 1.1, 0.4 ≤ x ≤ 1, 0 ≤ y ≤ 1; M is a doping element, 0.005 ≤ z ≤ 0.11, and M is at least one of Ni, Cu, Zr, Cs, Mo, Sn, Zn, Ca, Li, Ru, K, In, Se, Si, S, B, Te, Cr, Sb, Sn, La, and Gd; N is a coating element, N is at least one of Cu, Zr, Cs, Mo, Sn, Zn, Ca, Ti, W, Ru, In, Se, Si, B, Te, Cr, Sb, La, Gd, and Al, and the coating element accounts for 0.1 - 0.8% of the total mass of the cathode material.

2. The method for preparing the sodium ion battery oxide single crystal positive electrode material according to claim 1, characterized in that: The following steps are involved: S1: After the iron-manganese complex, sodium salt and dopant containing doping element M are uniformly mixed, the first microwave sintering is performed, and the intermediate is obtained after crushing and screening; the iron-manganese complex is Fe x Mn 1-x (OH)2 or Fe x Mn 1-x CO3, 0<x≤1; M is at least one of Ni, Cu, Zr, Cs, Mo, Sn, Zn, Ca, Li, Ru, K, In, Se, Si, S, B, Te, Cr, Sb, Sn, La and Gd; S2: The intermediate is coated with a coating agent containing a coating element N, and then subjected to a second microwave sintering, and then crushed and sieved to obtain the intermediate; N is at least one of Cu, Zr, Cs, Mo, Sn, Zn, Ca, Ti, W, Ru, In, Se, Si, B, Te, Cr, Sb, La, Gd and Al.

3. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: In step S1, the sodium salt is at least one of sodium carbonate, sodium bicarbonate and sodium hydroxide; the ratio of the total molar amount of iron and manganese in the iron-manganese complex to the molar amount of sodium in the sodium salt is 1:0.7-1.

1.

4. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: The particle size D of the dopant 50 <1μm; the dopant is a compound including M, or the dopant is at least one of nickel oxide, nickel hydroxide, copper oxide, copper hydroxide, zirconium oxide, zirconium hydroxide, cesium oxide, molybdenum oxide, ammonium molybdate, tin oxide, zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, lithium carbonate, lithium hydroxide, ruthenium oxide, potassium oxide, potassium hydroxide, indium oxide, selenium oxide, silicon oxide, sulfur oxide, boric acid, boron oxide, chromium oxide, tellurium oxide, lanthanum oxide and gadolinium oxide.

5. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: In step S1, the microwave sintering temperature is 650-800° C., and the microwave sintering time is 1-3 hours.

6. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: The particle size D of the coating agent 50 <50nm; the coating agent is a compound including N; or the coating agent is at least one of copper oxide, copper hydroxide, zirconium oxide, zirconium hydroxide, cesium oxide, molybdenum oxide, ammonium molybdate, tin oxide, zinc oxide, zinc hydroxide, calcium oxide, calcium hydroxide, titanium oxide, tungsten oxide, ammonium tungstate, ruthenium oxide, indium oxide, selenium oxide, silicon oxide, boric acid, boron oxide, tellurium oxide, chromium oxide, antimony oxide, lanthanum oxide, gadolinium oxide, aluminum oxide and aluminum hydroxide.

7. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: In step S2, the microwave sintering temperature is 200-500° C., and the microwave sintering time is 1-3 hours.

8. The method for preparing a sodium ion battery oxide single crystal positive electrode material according to claim 2, characterized in that: In the primary microwave sintering and / or the secondary microwave sintering, the sintering atmosphere is air, oxygen or a mixed gas with an oxygen concentration of ≥10%.

9. An application of a sodium ion battery oxide single crystal positive electrode material, characterized in that: The sodium ion battery oxide single crystal positive electrode material according to claim 1 is used to prepare a sodium ion battery.

Images