A NaZr 2 (PO 4 ) 3 Preparation of negative electrode materials and their application in sodium ion batteries

Abstract

Preparation of a NaZr2(PO4)3 Anode Material and Its Application in Sodium-Ion Batteries. The present invention provides a sodium-ion battery anode material, and the composition of the anode material is NaZr2(PO4)3@C. Among them, the component NaZr2(PO4)3 has a NASICON structure, and the mass content of C is 5-50%. The anode material can be prepared by a high-temperature solid-phase method or a sol-gel method. The anode material obtained in the present invention has a low working voltage, a high specific capacity, a rate capacity, and excellent cycle stability. The NaZr2(PO4)3@C sodium-ion battery anode material has a specific capacity of 215.5 mAh g ‑1 at 50 mA g ‑1 ; a specific capacity of 166.5 mAh g ‑1 at 8000 mA g ‑1 , and the capacity retention rate after 700 charge-discharge cycles at a rate of 100 mA g ‑1 is 84%.

Description

Technical Field

[0001] The present invention belongs to the field of sodium ion batteries and specifically relates to the preparation of a high-performance NASICON type NaZr2(PO4)3 negative electrode material and its application in sodium ion batteries. Background Art

[0002] In recent years, the efficient use of renewable energy urgently requires new and cheap energy storage technologies. Among the many energy storage technologies, secondary batteries have attracted much attention due to their portability and flexibility. At present, lithium-ion batteries have occupied the main market in portable electronic equipment products with their advantages such as high energy density and long cycle life; at the same time, lithium-ion batteries, as the best choice for electric vehicle power batteries, are developing increasingly strongly. With the widespread use of lithium-ion batteries in electric vehicles, the cost and reserves of related raw materials are facing severe problems. Although the energy density and development maturity of sodium-ion batteries are not as good as those of lithium-ion batteries, the advantages of abundant sodium resources and low cost are of great benefit to the development of large-scale energy storage, and are expected to become a beneficial supplement to lithium-ion batteries in related fields.

[0003] The research and development of electrode materials, especially negative electrode materials, is one of the keys to the development and application of sodium ion battery technology. Carbon-based negative electrode materials have the advantages of abundant raw materials and low cost, and have attracted much attention from experts and scholars at home and abroad. Carbon material negative electrodes include graphite and non-graphite. Due to the mismatch between the radius of sodium ions and the lattice parameters of graphite, graphite cannot be used as a negative electrode material for sodium ion batteries. As one of the carbon material negative electrodes, hard carbon has a larger interlayer spacing than graphite and can be used as a negative electrode material for sodium ion batteries. However, the ion diffusion rate is slow during the charging process, which makes it have poor rate performance. In addition, the conversion type and alloy type negative electrodes have a higher theoretical capacity, but they are accompanied by severe volume expansion / contraction during the charging and discharging process, and the cycle performance is poor. In contrast, NaTi2(PO4)3 with NASICON structure has a stable 3D open skeleton structure, which can ensure rapid ion diffusion inside the crystal, and thus has excellent rate performance. However, its low theoretical specific capacity and high working voltage limit its practical application. Summary of the invention

[0004] In view of the above technical problems, the purpose of the present invention is to provide a method for preparing a new type of NaZr2(PO4)3 negative electrode material with a NASICON structure and its application in sodium ion batteries, so as to improve the specific capacity, rate capacity and cycle stability of sodium ion batteries.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] On the one hand, the present invention provides a negative electrode material for a sodium ion battery, wherein the negative electrode material is composed of NaZr2(PO4)3@C, wherein the component NaZr2(PO4)3 has a NASICON structure, and the mass of C accounts for 5-50% of the total mass of the negative electrode material.

[0007] Based on the above solution, preferably, the mass of C accounts for 10-20% of the total mass of the negative electrode material.

[0008] On the other hand, the present invention provides two methods for preparing the above-mentioned negative electrode materials, wherein the methods are high-temperature solid phase method or sol-gel method; the high-temperature solid phase method comprises the following steps:

[0009] (1) Ingredients: Grind and mix the sodium-containing compound, the zirconium-containing compound, the phosphorus-containing compound and the carbon source uniformly, wherein the molar ratio of sodium, zirconium and phosphorus in the added raw materials is 1:2:3;

[0010] (2) Material synthesis by high temperature solid phase reaction: The raw materials mixed in step (1) are kept at 700-1100°C for 5-10 hours under an inert atmosphere at a heating rate of 1-5°C / min, and then naturally cooled to room temperature to obtain NaZr2(PO4)3@C material.

[0011] The sol-gel method comprises the following steps:

[0012] (1) Ingredients: dissolving a sodium-containing compound, a zirconium-containing compound, a phosphorus-containing compound and a carbon source in water, heating in a water bath at 80-100° C. to evaporate the solvent until a sol is formed; drying the formed wet sol at 100-150° C. for 4-10 hours, taking it out and grinding it for later use; wherein the molar ratio of sodium, zirconium and phosphorus is 1:2:3;

[0013] (2) High-temperature sintering for material synthesis: The raw material ground in step (1) is kept at 700-1100°C for 5-10 hours under an inert atmosphere at a heating rate of 1-5°C / min, and then naturally cooled to room temperature to obtain NaZr2(PO4)3@C material.

[0014] The following is a typical chemical reaction for preparing NaZr2(PO4)3 compounds:

[0015] Na2CO3+4ZrO2+6NH4H2PO4→2NaZr2(PO4)3+CO2+6NH3+9H2O

[0016] Based on the above scheme, preferably, the sodium-containing compound is one or more of sodium hydroxide, sodium carbonate, sodium acetate, sodium oxalate or sodium nitrate.

[0017] Based on the above scheme, preferably, the zirconium-containing compound is one or more of zirconium dichloride octahydrate, zirconium acetylacetonate, and zirconium oxide.

[0018] Based on the above scheme, preferably, the phosphorus-containing compound is one or more of diammonium phosphate, diammonium hydrogen phosphate, ammonium phosphate, and phosphoric acid.

[0019] Based on the above scheme, preferably, the molar ratio of carbon source: zirconium is 1:5-2:1; the carbon source is one or more of sucrose, glucose and citric acid.

[0020] Beneficial Effects

[0021] The negative electrode material obtained by the present invention has a lower operating voltage, a higher specific capacity and rate capacity and excellent cycle stability. 2 5s 2 ), with multiple electron transfer, the negative electrode material NaZr2(PO4)3@C has a lower operating voltage, higher specific capacity, higher rate capacity and excellent cycle stability in non-aqueous sodium ion batteries compared to NaTi2(PO4)3@C. NaZr2(PO4)3@C sodium ion battery negative electrode material has a voltage range of 0-3V, 50mA g -1 The specific capacity is 215.5 mAh g -1 (The discharge medium voltage at this time is about 0.25V); 8000mA g -1 The specific capacity is 166.5 mAh g -1 (The discharge medium voltage at this time is about 0.33V); 100mA g -1 The capacity retention rate after 700 charge and discharge cycles at high rate is 84%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the XRD pattern of NaTi2(PO4)3@C prepared in Comparative Example 2.

[0023] Figure 2 This is the XRD pattern of NaZr2(PO4)3@C prepared in Example 1.

[0024] Figure 3 This is the XRD pattern of NaZr2(PO4)3@C prepared in Example 4.

[0025] Figure 4 NaTi2(PO4)3@C and NaZr2(PO4)3@C prepared in Comparative Example 2 and Example 1 were subjected to 50 mA g -1 Comparison of charge and discharge curves.

[0026] Figure 5 It is a comparison chart of the rate performance of the button cells of Comparative Example 1-2 and Example 1-4.

[0027] Figure 6 It is a comparison chart of the cycle performance of the button batteries of comparative examples 1-2 and embodiments 1 and 4. DETAILED DESCRIPTION

[0028] The following examples are provided to further illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] Comparative Example 1

[0030] The purchased Kuraray hard carbon (5 microns) was used as the electrode active material, super P was used as the conductive agent, and polyvinylidene fluoride (PVDF) was used as the binder to prepare the slurry, and the composition ratio was 8:1:1. The copper foil was used as the current collector, and the electrode was coated with a thickness of 100 microns and dried at 60°C. At this time, the electrode load was about 1 mg cm -2 A sodium|hard carbon half-cell was assembled using a sodium sheet with a diameter of 1.6 mm, a glass fiber membrane as a separator, 1 M NaPF6 as a supporting electrolyte, a mixed solution of EC / DEC (volume ratio of 1:1) as a solvent, and a mixed solution of 5% FEC additive as an electrolyte. -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0031] Comparative Example 2

[0032] Dissolve 0.015mol of citric acid and 0.01mol of tetrabutyl titanate in 20mL of anhydrous ethanol and stir at 40°C. Dissolve 0.005mol of lithium acetate and 0.015mol of phosphoric acid in 10mL of anhydrous ethanol respectively and slowly add them to the solution containing the titanium source and the carbon source in turn. Stir in a water bath for 2h to obtain a clear mixed solution. Add 3mL of deionized water to form a gel precursor. After drying in an 80°C water bath, grind, heat to 350°C at a heating rate of 3°C / min under an argon atmosphere and keep warm for 4h. Take out and grind after cooling, continue to heat to 750°C at a heating rate of 3°C / min and keep warm for 10h, and cool naturally to room temperature to obtain NaTi2(PO4)3@C active material (carbon content 11.7%). The obtained active material, conductive carbon black (Super P), and binder (PVDF) were dissolved in an appropriate amount of N-methylpyrrolidone solvent at a mass ratio of 8:1:1, and then evenly mixed and coated with a wet film preparation device to form an electrode with a thickness of 100 microns. After drying at 60°C, they were cut into electrode sheets with a diameter of 14 mm using a slicer. Sodium sheets were used as negative electrodes, glass fiber membranes as separators, 1M NaPF6 as supporting electrolytes, and solvents were EC / DEC mixed solutions (volume ratio of 1:1), and a mixed solution with 5% FEC additives was added as electrolytes to assemble sodium|NaTi2(PO4)3@C half-cells. At 50mA g -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0033] Example 1

[0034] Dissolve 0.005mol sodium hydroxide, 0.01mol zirconium dichloride octahydrate, 0.015mol ammonium dihydrogen phosphate and 0.01mol citric acid in 200mL deionized water, heat in a water bath at 80℃ to evaporate the solvent until a sol is formed; transfer the formed wet sol to a 120℃ oven and dry for 5 hours. Grind it for later use after taking it out. Place the crucible containing the above ingredients in a tube furnace protected by an inert gas (argon or nitrogen), heat it from room temperature to 800℃ at a heating rate of 3℃ / min, keep it warm for 8 hours and then naturally cool it to room temperature to obtain NaZr2(PO4)3@C material (carbon content 13.5%). Dissolve the obtained active material, conductive carbon black (SuperP) and binder (PVDF) in an appropriate amount of N-methylpyrrolidone solvent in a mass ratio of 8:1:1, mix them evenly and apply them to an electrode with a thickness of 100 microns using a wet film preparation device, dry them at 60℃ and cut them into electrode sheets with a diameter of 14mm using a slicer. The sodium sheet was used as the negative electrode, the glass fiber membrane was used as the separator, 1M NaPF6 was used as the supporting electrolyte, the solvent was a mixture of EC / DEC (volume ratio of 1:1), and a mixed solution of 5% FEC additive was added as the electrolyte to assemble the sodium|NaTi2(PO4)3@C half-cell. -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0035] Example 2

[0036] Dissolve 0.005mol sodium hydroxide, 0.01mol zirconium dichloride octahydrate, 0.015mol ammonium dihydrogen phosphate and 0.005mol citric acid in 200mL deionized water, heat in a water bath at 80℃ to evaporate the solvent until a sol is formed; transfer the formed wet sol to a 120℃ oven and dry for 5 hours. Grind it for later use after taking it out. Place the crucible containing the above ingredients in a tube furnace protected by an inert gas (argon or nitrogen), heat it from room temperature to 800℃ at a heating rate of 3℃ / min, keep it warm for 8 hours and then naturally cool it to room temperature to obtain NaZr2(PO4)3@C material (carbon content 7.2%). Dissolve the obtained active material, conductive carbon black (SuperP) and binder (PVDF) in an appropriate amount of N-methylpyrrolidone solvent in a mass ratio of 8:1:1, mix them evenly and apply them to an electrode with a thickness of 100 microns using a wet film preparation device, dry them at 60℃ and cut them into electrode sheets with a diameter of 14mm using a slicer. The sodium sheet was used as the negative electrode, the glass fiber membrane was used as the separator, 1M NaPF6 was used as the supporting electrolyte, the solvent was a mixture of EC / DEC (volume ratio of 1:1), and a mixed solution of 5% FEC additive was added as the electrolyte to assemble the sodium|NaTi2(PO4)3@C half-cell. -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0037] Example 3

[0038] Dissolve 0.005 mol sodium hydroxide, 0.01 mol zirconium dichloride octahydrate, 0.015 mol ammonium dihydrogen phosphate and 0.015 mol citric acid in 200 mL deionized water, heat in a water bath at 80°C to evaporate the solvent until a sol is formed; transfer the formed wet sol to an oven at 120°C and dry for 5 hours. Grind it for later use after taking it out. Place the crucible containing the above ingredients in a tubular furnace protected by an inert gas (argon or nitrogen), heat it from room temperature to 800°C at a heating rate of 3°C / min, keep it warm for 8 hours, and then cool it naturally to room temperature to obtain NaZr2(PO4)3@C material (carbon content 22.6%). The obtained active material, conductive carbon black (SuperP), and binder (PVDF) were dissolved in an appropriate amount of N-methylpyrrolidone solvent at a mass ratio of 8:1:1, and then evenly mixed and coated with a wet film preparation device to form an electrode with a thickness of 100 microns. After drying at 60°C, they were cut into electrode sheets with a diameter of 14 mm using a slicer. Sodium sheets were used as negative electrodes, glass fiber membranes as separators, 1M NaPF6 as supporting electrolytes, and solvents were EC / DEC mixed solutions (volume ratio of 1:1), and a mixed solution with 5% FEC additives was added as electrolytes to assemble sodium|NaTi2(PO4)3@C half-cells. At 50mA g -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0039] Example 4

[0040] 0.0025mol sodium carbonate, 0.01mol zirconium oxide and 0.015mol ammonium dihydrogen phosphate were ground and mixed evenly, and 10% of the mass of sucrose of NaZr2(PO4)3 was added and mixed evenly; the crucible containing the above ingredients was placed in a tube furnace protected by inert gas (argon or nitrogen), and the temperature was raised from room temperature to 800℃ at a heating rate of 3℃ / min, and then naturally cooled to room temperature after 8 hours of heat preservation to obtain NaZr2(PO4)3@C material (carbon content 12.8%). The obtained active material, conductive carbon black (SuperP) and binder (PVDF) were dissolved in an appropriate amount of N-methylpyrrolidone solvent at a mass ratio of 8:1:1, and after uniform mixing, they were coated into electrodes with a thickness of 100 microns using a wet film preparation device, and cut into electrode sheets with a diameter of 14mm using a slicer after drying at 60℃. The sodium sheet was used as the negative electrode, the glass fiber membrane was used as the separator, 1M NaPF6 was used as the supporting electrolyte, the solvent was a mixture of EC / DEC (volume ratio of 1:1), and a mixed solution of 5% FEC additive was added as the electrolyte to assemble the sodium|NaTi2(PO4)3@C half-cell. -1 , 100mA g -1 , 250mA g -1 , 500mA g -1 , 1000mA g -1 , 2000mA g -1 , 4000mA g -1 and 8000mA g -1 Carry out charge and discharge test.

[0041] like Figure 1 As shown, the method described in Comparative Example 2 can prepare pure phase NaTi2(PO4)3@C material.

[0042] like Figure 2-3 As shown, pure phase NaZr2(PO4)3@C material can be prepared by sol-gel method and high temperature solid phase method.

[0043] like Figure 4 As shown, due to the unique valence electron structure of zirconium, the NaZr2(PO4)3@C material prepared in Example 1 has a higher specific capacity and a lower operating voltage than the NaTi2(PO4)3@C material. For negative electrode materials, a lower operating voltage is conducive to the assembly of high-voltage sodium ion full batteries. Therefore, compared with NaTi2(PO4)3@C material, NaZr2(PO4)3@C material has more significant practical value.

[0044] like Figure 5 As shown in Figure 2, although the hard carbon anode has a higher specific capacity (at 50 mA g -1The reversible specific capacity is close to 300 mAh g -1 ), but its poor rate capacity limits its practical application (at 8000mA g -1 The reversible specific capacity is only 18 mAh g -1 Compared with NaTi2(PO4)3@C material, the prepared NaZr2(PO4)3@C material has higher specific capacity and rate performance (taking Example 1 as an example, at 50 mA g -1 The reversible specific capacity is 215.5 mAh g -1 ; at 8000mA g -1 The reversible specific capacity is as high as 166 mAh g -1 ). Moreover, the carbon content has a significant effect on the rate performance of NaZr2(PO4)3@C materials, and a suitable carbon content helps to maximize its rate capacity.

[0045] like Figure 6 As shown in Figure 2, compared with the hard carbon anode and NaTi2(PO4)3@C anode, the NaZr2(PO4)3@C anode has a better cycling performance, 100mA g -1 The capacity retention rate after 700 charge and discharge cycles at high rate is 84%.

Claims

1. A method for preparing a negative electrode material, characterized in that: The negative electrode material is synthesized by a high temperature solid phase method, and the high temperature solid phase method comprises the following steps: (1) Ingredients: Grind and mix the sodium-containing compound, the zirconium-containing compound, the phosphorus-containing compound and the carbon source uniformly, wherein the molar ratio of sodium, zirconium and phosphorus in the added raw materials is 1:2:3; (2) Synthesizing the material by high-temperature solid-phase reaction: The raw materials mixed in step (1) are kept at 700-1100° C. for 5-10 hours under an inert atmosphere, and then naturally cooled to room temperature to obtain NaZr2(PO4)3@C material; The component NaZr2(PO4)3 has a NASICON structure, and the mass of C accounts for 5-50% of the total mass of the negative electrode material.

2. A method for preparing a negative electrode material, characterized in that: The negative electrode material is synthesized by a sol-gel method, and the sol-gel method comprises the following steps: (1) Ingredients: dissolve a sodium-containing compound, a zirconium-containing compound, a phosphorus-containing compound and a carbon source in water, and heat in a water bath at 80-100° C. to evaporate the solvent until a sol is formed; dry the formed wet sol at 100-150° C. for 4-10 hours, take it out and grind it for later use; wherein the molar ratio of sodium, zirconium and phosphorus is 1:2:3; (2) High-temperature sintering for material synthesis: the raw material ground in step (1) is kept at 700-1100°C for 5-10 hours under an inert atmosphere, and then naturally cooled to room temperature to obtain NaZr2(PO4)3@C material; The component NaZr2(PO4)3 has a NASICON structure, and the mass of C accounts for 5-50% of the total mass of the negative electrode material.

3. The preparation method according to claim 1 or 2, characterized in that: The sodium-containing compound is one or more of sodium hydroxide, sodium carbonate, sodium acetate, sodium oxalate or sodium nitrate; The mass of C accounts for 10-20% of the total mass of the negative electrode material.

4. The preparation method according to claim 1 or 2, characterized in that: The zirconium-containing compound is one or more of zirconium dichloride octahydrate and zirconium acetylacetonate.

5. The preparation method according to claim 1 or 2, characterized in that: The phosphorus-containing compound is one or more of diammonium phosphate, diammonium hydrogen phosphate, ammonium phosphate and phosphoric acid.

6. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of carbon source: zirconium is 1:5-2:1; the carbon source is one or more of sucrose, glucose and citric acid.

7. Use of a negative electrode material prepared by the preparation method according to claim 1 or 2 in a sodium ion battery.

8. The use according to claim 7, characterized in that: The sodium ion battery is a non-aqueous sodium ion battery.

Images