A high sodium content tunnel-type oxide positive electrode material, preparation method, sodium ion battery positive electrode and sodium ion battery

Abstract

The present invention belongs to the technical field of sodium-ion batteries, and provides a tunnel-type oxide cathode material with a high sodium content, a preparation method, a sodium-ion battery cathode, and a sodium-ion battery. The cathode material is prepared by a solid-phase secondary calcination method, and its chemical formula is Na 0.44+ x Mn 1‑y W y O2@Na2WO4, where 0 ≤ x ≤ 0.22 and 0.005 ≤ y ≤ 0.1. Based on the original tunnel phase, the present invention introduces a high-valence element tungsten during the secondary calcination process to expand the sodium-ion diffusion channels and improve the rate performance, and forms a sodium tungstate protective layer on the surface of the cathode material to improve the interface stability. At the same time, sodium carbonate is added to drive more sodium ions to embed into the tunnel phase at high temperature, forming a tunnel-type cathode material with a high sodium content, avoiding the transformation from the tunnel phase to the P2-phase material, and effectively improving the rate performance and the first-cycle Coulombic efficiency of the tunnel-type oxide cathode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a high sodium content tunnel-type oxide positive electrode material, a preparation method, a sodium ion battery positive electrode and a sodium ion battery. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and other fields due to their high energy density and excellent cycle performance. However, the further development of lithium-ion batteries is severely restricted by the scarcity, uneven distribution and high price of lithium resources. As a member of the same group in the periodic table, sodium has similar chemical properties to lithium, and its resources are abundant in nature and widely exist in different forms, which has prompted rechargeable sodium-ion batteries to be used as a beneficial supplementary technology in the field of large-scale energy storage. Among them, the positive electrode material is the main factor determining the energy density and cost of the battery. At present, the positive electrode materials of sodium-ion batteries mainly include layered transition metal oxides, tunnel-type transition metal oxides, Prussian blue analogs and polyanion materials. Although Prussian blue analogs have stable structures, they have problems such as difficult removal of crystal water and high toxicity. Polyanion materials have wide and conductive three-dimensional ion transport channels that are conducive to the rapid migration of sodium ions, but their electronic conductivity is low and additional conductive agents need to be introduced. Layered transition metal oxides dominate the market due to their high theoretical specific capacity and simple synthesis methods. However, their Ni-based redox reactions make it difficult for the price advantage of sodium-ion batteries to be reflected. At the same time, their unique layered structure leads to drastic phase changes during charging and discharging, and poor cycle stability.

[0003] Tunnel-type manganese-based oxides Na 0.44 MnO2 can promote Na + The transmission of Mn 3+ / Mn 4+ The redox center can significantly reduce the cost of raw materials, further reflecting the low-cost advantage of sodium-ion batteries. However, due to the Mn 3+ The Jan-Taylor effect and the easy reaction with the electrolyte lead to poor interface stability and rate performance. In addition, the sodium ion content of the tunnel-type manganese-based oxide itself is low, and its first-cycle coulomb efficiency is only 50%, requiring additional sodium replenishment when assembling a full battery. If the initial sodium content in the tunnel phase material is directly increased, it will lead to the transformation of the tunnel phase to the P2 phase, losing its structural advantage.

[0004] Therefore, how to improve rate performance, interface stability and first-cycle coulombic efficiency while maintaining the tunnel phase structure is a key technical problem that needs to be urgently solved in the commercial application of sodium-ion batteries. Summary of the invention

[0005] In order to solve the problem of low first cycle coulombic efficiency and poor rate performance of tunnel-type manganese-based oxide positive electrode materials in the prior art, the present invention proposes a high sodium content tunnel-type oxide positive electrode material, a preparation method, a sodium ion battery positive electrode and a sodium ion battery. The method of the present invention simultaneously improves the rate and first efficiency of the tunnel-type oxide positive electrode material.

[0006] The technical solution of the present invention is as follows:

[0007] The first aspect of the present invention provides a method for preparing a high sodium content tunnel oxide positive electrode material, using a solid phase secondary sintering method, comprising the following steps:

[0008] (1) high-energy ball milling, mixing the sodium source and the manganese source in proportion, and vacuum drying to obtain the first precursor powder;

[0009] (2) high temperature calcination, calcining the first precursor powder obtained in step (1) at 600-1000° C. for 10-15 hours directly or after tableting, and cooling naturally to obtain the original tunnel-type positive electrode material;

[0010] (3) high-energy ball milling, mixing the original tunnel-type cathode material obtained in step (2) with the sodium source and the tungsten source in proportion, and vacuum drying to obtain a second precursor powder;

[0011] (4) secondary calcination: calcining the second precursor powder obtained in step (3) at 500-900° C. for 10-15 hours directly or after tableting, and cooling naturally to obtain a high sodium content tunnel-type oxide positive electrode material.

[0012] The first calcination is for phase formation, and the second calcination is to achieve local ion diffusion based on the phase formation.

[0013] In order to further improve the contact between the sodium source and the manganese source and enhance the diffusion of the elements, the first precursor powder is pressed into tablets and then calcined for the first time.

[0014] Furthermore, in step (1), the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium hydroxide.

[0015] Furthermore, in step (1), the manganese source is one or more of dimanganese trioxide, manganese dioxide, and trimanganese tetroxide.

[0016] Furthermore, in step (1), the molar ratio of the sodium source to the manganese source is 0.44-0.6:0.9-1.

[0017] Preferably, in step (1), the sodium source is sodium carbonate, the manganese source is manganese trioxide, and the molar ratio of the sodium source to the manganese source is 0.44:1.

[0018] Preferably, in step (2), the first precursor powder is calcined at 700-900° C. for 13-15 hours.

[0019] Preferably, in step (4), the second precursor powder is calcined at 500-700° C. for 13-15 hours.

[0020] Furthermore, in step (3), the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium hydroxide, and the amount of the sodium source added is 3% to 20% of the amount of the original tunnel-type positive electrode material. If the amount of the sodium source added is lower than this range, the first efficiency is not significantly improved. If it is higher than this range, an impurity phase will be generated or directly converted to a P2 phase.

[0021] Preferably, the amount of the sodium source added is 5% to 15% of the amount of the original tunnel-type positive electrode material.

[0022] Furthermore, in step (3), the tungsten source is one or both of tungsten trioxide and tungsten dioxide. The amount of the tungsten source added is 0.5% to 10% of the amount of the original tunnel-type positive electrode material. Adding too much tungsten will affect the specific capacity and ion diffusion. If the amount added is too little, the rate enhancement effect is not obvious.

[0023] Preferably, the amount of the tungsten source added is 1% to 8% of the amount of the original tunnel-type positive electrode material.

[0024] Furthermore, in step (2) and step (4), the calcination heating rate is 1 to 5°C / min, and the calcination atmosphere is one of air, nitrogen or oxygen.

[0025] The second aspect of the present invention is to provide a high sodium content tunnel oxide positive electrode material prepared by the above preparation method, characterized in that the chemical formula is Na 0.44+x Mn 1-y W y O2@Na2WO4, 0≤x≤0.22, 0.005≤y≤0.1, @ indicates surface coating, and the morphology is a tunnel-type rod-like structure with a length of 8-12 μm and a width of 2-3 μm.

[0026] The third aspect of the present invention provides a sodium ion battery positive electrode, which uses the above-mentioned high sodium content tunnel-type oxide positive electrode material as an active material, and the mass ratio of the high sodium content tunnel-type oxide positive electrode material, conductive carbon black (Super P) and PVDF (polyvinylidene fluoride) adhesive is 8:1:1.

[0027] The fourth aspect of the present invention provides a sodium ion battery, which adopts the above-mentioned sodium ion battery positive electrode, uses a metal sodium sheet as a negative electrode material, uses a glass fiber membrane as a separator, and NaPF6 (1M) dissolved in diethylene glycol dimethyl ether as an electrolyte.

[0028] Advantages and beneficial effects of the present invention:

[0029] 1. The present invention uses simple solid phase ball milling to mix materials in the original tunnel phase (Na 0.44 MnO2), a high-valent element tungsten is introduced during the secondary calcination process to expand the sodium ion diffusion channel to improve the rate performance and form a sodium tungstate protective layer on the surface of the positive electrode material to improve the interface stability. At the same time, sodium carbonate is added at high temperature to drive more sodium ions to embed into the tunnel phase, effectively improving the rate performance, interface stability and first-week coulomb efficiency of the tunnel-type oxide positive electrode material.

[0030] 2. The method used in the present invention has low cost, simple and controllable process, high reproducibility, and can be used for large-scale production. The raw materials used are widely distributed in nature, easy to mine, environmentally friendly and cheap, which greatly reduces the production cost and environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the XRD spectrum of the materials shown in Example 1~Example 2 and Comparative Example 1~Comparative Example 3;

[0032] Figure 2 is a SEM image of the material structure shown in Example 2;

[0033] Figure 3 is a TEM image of the material structure shown in Example 2;

[0034] Figure 4 This is a SEM image of the material structure shown in Comparative Example 1;

[0035] Figure 5 This is a TEM image of the material structure shown in Comparative Example 1;

[0036] Figure 6 The charge and discharge curves of the materials shown in Comparative Examples 1 to 3 (active material loading: ~5 mg / cm 2 , current density: 50 mA / g);

[0037] Figure 7 The charge-discharge curves of the materials shown in Examples 1 to 2 and Comparative Example 1 (active material loading: ~5 mg / cm 2 , current density: 50 mA / g);

[0038] Figure 8The rate curves of the materials shown in Example 2 and Comparative Example 1 (active substance loading: ~5 mg / cm 2 );

[0039] Fig. 9 The capacity cycle comparison diagram of the materials shown in Example 1 to Example 2 and Comparative Example 1 to Comparative Example 3 (active material loading: ~5 mg / cm 2 , current density: 100 mA / g); DETAILED DESCRIPTION

[0040] The present invention is further illustrated by specific examples below. This section generally describes the experimental methods used in the present invention.

[0041] The purity of the sodium carbonate, manganese trioxide, tungsten trioxide and organic solvent used in the examples is not less than 99%.

[0042] Embodiment 1:

[0043] Tunnel-type manganese-based cathode material Na 0.6 The preparation method of MnO2, the specific steps are as follows:

[0044] (1) Sodium carbonate and manganese trioxide were weighed and mixed in a molar ratio of 0.44:1 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a first precursor powder.

[0045] (2) The first precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, calcined for the first time at 750 °C for 15 h in an air atmosphere, and cooled naturally to obtain the original tunnel-type manganese-based positive electrode material Na 0.44 MnO2.

[0046] (3) The positive electrode material and sodium carbonate obtained in step (2) were weighed and mixed in a molar ratio of 1:0.113 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a second precursor powder.

[0047] (4) The second precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, and calcined at 650 °C for 15 h in an air atmosphere. The sheet was cooled naturally to obtain a tunnel-type manganese-based positive electrode material Na 0.6 MnO2.

[0048] Its XRD pattern is shown in Figure 1 ,from Figure 1 It can be seen that Example 1 maintains a good tunnel structure and has high crystallinity.

[0049] Embodiment 2:

[0050] Tunnel-type manganese-based cathode material Na 0.6 Mn 0.98 W 0.02 The preparation method of O2@Na2WO4, the specific steps are as follows:

[0051] (1) Sodium carbonate and manganese trioxide were weighed and mixed in a molar ratio of 0.44:1 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a first precursor powder.

[0052] (2) The first precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, calcined for the first time at 750 °C for 15 h in an air atmosphere, and cooled naturally to obtain the original tunnel-type manganese-based positive electrode material Na 0.44 MnO2.

[0053] (3) The positive electrode material obtained in step (2) and sodium carbonate and tungsten trioxide were weighed and mixed in a molar ratio of 1:0.113:0.02 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a second precursor powder.

[0054] (4) The second precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, and calcined at 650 °C for 15 h in an air atmosphere. The sheet was cooled naturally to obtain a tunnel-type manganese-based positive electrode material Na 0.6 Mn 0.98 W 0.02 O2@Na2WO4.

[0055] Its XRD pattern is shown in Figure 1 ,from Figure 1 It can be seen that Example 2 maintains a good tunnel structure, and at the same time has a characteristic peak of sodium tungstate, and has high crystallinity. Figure 2 ,from Figure 2 It can be seen that the morphology is a tunnel-shaped rod-like structure, about 8-12 μm long and about 2-3 μm wide. Figure 3 ,from Figure 3 It can be seen that there is an obvious coating layer on the surface of the bulk phase with a thickness of 4-6 nm.

[0056] Comparative Example 1:

[0057] Original tunnel-type manganese-based cathode material Na 0.44 The preparation method of MnO2, the specific steps are as follows:

[0058] (1) Sodium carbonate and manganese trioxide were weighed and mixed in a molar ratio of 0.44:1 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a precursor powder.

[0059] (2) The precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, and calcined for the first time at 750 °C for 15 h in an air atmosphere, and then naturally cooled to obtain the original tunnel-type manganese-based positive electrode material Na 0.44 MnO2.

[0060] Its XRD pattern is shown in Figure 1 ,from Figure 1 It can be seen that Comparative Example 1 maintains a good tunnel structure and high crystallinity. Figure 4 ,from Figure 4 It can be seen that the morphology is a tunnel-shaped rod-like structure, about 10-14 μm long and about 2-3 μm wide. Its TEM image is shown in Figure 5 ,from Figure 5 It can be seen that there is no coating layer on the surface of the bulk phase and the lattice fringes are uniform.

[0061] Comparative Example 2:

[0062] The original tunnel phase was calcined with sodium carbonate to obtain the P2 phase cathode material Na 0.6 MnO2, the specific steps are as follows:

[0063] (1) Sodium carbonate and manganese trioxide were weighed and mixed in a molar ratio of 0.6:1 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a precursor powder.

[0064] (2) The precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, calcined at 750 °C for 15 h in an air atmosphere, and cooled naturally to obtain the P2 phase positive electrode material Na 0.6 MnO2.

[0065] Its XRD pattern is shown in Figure 1 ,from Figure 1 It can be seen that comparative example 2 changes from a tunnel-type structure to a layered structure, and a diffraction peak corresponding to P2 appears.

[0066] Comparative Example 3:

[0067] The original tunnel phase was calcined by adding tungsten trioxide to the P2 phase cathode material Na 0.44 Mn 0.98 W 0.02O2, the specific steps are as follows:

[0068] (1) Sodium carbonate, manganese trioxide and tungsten trioxide were weighed and mixed in a molar ratio of 0.44:0.98:0.02 and placed in a ball mill for wet ball milling for 4 h. Subsequently, the slurry was dried in a forced air oven at 80 °C for 30 min to obtain a precursor powder.

[0069] (2) The precursor powder was pressed into a 5 mm sheet at a pressure of 30 MPa for 10 min, placed in an Al2O3 crucible, calcined at 750 °C for 15 h in an air atmosphere, and cooled naturally to obtain the P2 phase positive electrode material Na 0.44 Mn 0.98 W 0.02 O2.

[0070] Its XRD pattern is shown in Figure 1 ,from Figure 1 It can be seen that comparative example 3 transforms from a tunnel-type structure to a layered structure, and a diffraction peak corresponding to P2 appears.

[0071] The electrochemical performance test results of the positive electrode materials prepared in all the embodiments and comparative examples are shown in Tables 1 to 2 and Figure 6~Figure 9 shown.

[0072] Test method:

[0073] Preparation of pole piece: The prepared tunnel-type manganese-based positive electrode material, conductive carbon black (Super P) and PVDF binder were weighed in a mass ratio of 8:1:1, mixed evenly, and an appropriate amount of NMP dispersant was added to make a slurry. The slurry was evenly coated on the aluminum foil current collector, dried at 80 °C in a vacuum environment for 10 h, and then cut into positive electrode discs with a diameter of 12 mm.

[0074] Battery preparation: The assembly of sodium-ion batteries was completed in an argon-protected glove box. Sodium metal sheets were used as negative electrode materials, glass fiber membranes were used as separators, and NaPF6 (1M) dissolved in diethylene glycol dimethyl ether was used as electrolyte to assemble CR2032 button batteries.

[0075] Test conditions:

[0076] The batteries prepared in the examples and comparative examples were tested at a temperature of 25°C and a charge and discharge voltage range of 2.0 V to 4.0 V. Constant current charge and discharge were performed at a current density of 50 mA / g to obtain the first cycle charge and discharge curve ( Figure 6~Figure 7 ), the rate curves were obtained by testing at current densities of 0.5 C, 1 C, 2 C, 5 C, 10 C, 20 C, and 30 C ( Figure 8). Tested at a current density of 100 mA / g, the capacity retention rate after 100 cycles was obtained ( Fig. 9 ).

[0077] In Comparative Example 1, the original tunnel phase has a low coulombic efficiency of only 53.2% in the first cycle due to its low sodium content, and the capacity retention rate is 100% after 100 cycles. In Comparative Example 2, the original tunnel phase is transformed from the tunnel phase to the P2 phase after adding sodium carbonate and calcining once. Due to the low sodium content and Mn 3+ The Jiang-Taylor effect leads to low first efficiency and poor cycle stability. The first coulomb efficiency is 31.3%, and the capacity retention rate is 92.2% after 100 cycles. Comparative Example 3 The original tunnel phase is transformed from the tunnel phase to the P2 phase after adding tungsten trioxide and calcining once. The first coulomb efficiency is 49.6%, and the capacity retention rate is 80.9% after 100 cycles. Example 1 adds an appropriate amount of sodium carbonate to the original tunnel phase, and after a second high-temperature calcination, more sodium ions are embedded in the tunnel phase, which increases the first cycle coulomb efficiency to 82.9%, and the capacity retention rate is 100% after 100 cycles. Example 2 adds an appropriate amount of sodium carbonate and tungsten trioxide to the original tunnel phase. After a second high-temperature calcination, the first cycle coulomb efficiency is increased to 79.7%, and the capacity retention rate is 100% after 100 cycles, as shown in Table 1.

[0078] Comparative Example 1: The capacity of the original tunnel phase at 0.5 C is 101.6 mAh g -1 , 30 C capacity is 64.7 mAh g -1 The capacity retention rate at 30 C / 0.5 C is 63.6%. Example 2: On the basis of the original tunnel phase, appropriate amounts of sodium carbonate and tungsten trioxide are added. After secondary high-temperature calcination, the capacity at 0.5 C is 100.3 mAh·g -1 , 30 C capacity is 87.6 mAh·g -1 , the capacity retention rate at 30 C / 0.5 C is 87.3%, as shown in Table 2.

[0079] Table 1 Electrochemical performance test results of examples and comparative examples

[0080]

[0081] Table 2 Test results of rate performance of examples and comparative examples

[0082]

[0083] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a high sodium content tunnel oxide positive electrode material, characterized in that: The solid phase secondary sintering method includes the following steps: (1) high-energy ball milling, mixing a sodium source and a manganese source in proportion by ball milling, and vacuum drying to obtain a first precursor powder, wherein the molar ratio of the sodium source to the manganese source is 0.44-0.6:0.9-1, the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium hydroxide, and the manganese source is one or more of manganese trioxide, manganese dioxide, and manganese tetraoxide; (2) high temperature calcination, calcining the first precursor powder obtained in step (1) at 600-1000° C. for 10-15 hours directly or after tableting, and cooling naturally to obtain the original tunnel-type positive electrode material; (3) high-energy ball milling, mixing the original tunnel-type cathode material obtained in step (2) with a sodium source and a tungsten source in proportion, and vacuum drying to obtain a second precursor powder, wherein the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium acetate, and sodium hydroxide, and the amount of the sodium source added is 3% to 20% of the amount of the original tunnel-type cathode material; the tungsten source is one or more of tungsten trioxide and tungsten dioxide, and the amount of the tungsten source added is 0.5% to 10% of the amount of the original tunnel-type cathode material; (4) secondary calcination: calcining the second precursor powder obtained in step (3) at 500-900° C. for 10-15 hours directly or after tableting, and cooling naturally to obtain a high sodium content tunnel-type oxide positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step (2), the first precursor powder is calcined at 700-900° C. for 13-15 hours.

3. The preparation method according to claim 1, characterized in that: In step (1), the sodium source is sodium carbonate, the manganese source is manganese trioxide, and the molar ratio of the sodium source to the manganese source is 0.44:

1.

4. The preparation method according to claim 1, characterized in that: In step (4), the second precursor powder is calcined at 500-700° C. for 13-15 hours.

5. The preparation method according to claim 1, characterized in that: In step (3), the amount of the sodium source added is 5% to 15% of the amount of the original tunnel-type positive electrode material.

6. The preparation method according to claim 1, characterized in that: In step (3), the amount of tungsten source added is 1% to 8% of the amount of the original tunnel-type positive electrode material.

7. The preparation method according to claim 1, characterized in that: In step (2) and step (4), the calcination heating rate is 1-5°C / min, and the calcination atmosphere is one of air, nitrogen or oxygen.

8. A high sodium content tunnel oxide positive electrode material prepared by the method according to any one of claims 1 to 7, characterized in that: The chemical formula is Na 0.44+x Mn 1-y W y O2@Na2WO4, 0≤x≤0.22, 0.005≤y≤0.1, @ indicates surface coating, and the morphology is a tunnel-type rod-like structure with a length of 8-12 μm and a width of 2-3 μm.

9. A sodium ion battery positive electrode, characterized in that: The high sodium content tunnel-type oxide positive electrode material according to claim 8 is used as the active material.

10. A sodium ion battery, characterized in that: The sodium ion battery positive electrode according to claim 9 is used.

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