A sodium supplement having high electrical conductivity and a method of making the same

Abstract

The application provides a preparation method of a sodium supplement agent with high conductivity, comprising the following steps: S1) soaking bacterial cellulose in a sodium carbonate solution, and then freeze-drying to obtain product A; S2) calcining the product A in a protective atmosphere to obtain product B; and S3) mixing an aqueous oxalic acid solution with the product B, and then standing to obtain the sodium supplement agent. Compared with the prior art, the sodium supplement agent prepared by the method can supplement the consumption of sodium ions in the positive electrode material in the circulation process, and the sodium supplement agent has excellent controllability as the porous carbon carrier can effectively improve the conductivity of the sodium supplement agent as a skeleton, the high conductivity improves the DCR of the sodium ion battery, improves the kinetic performance, and thus improves the electrochemical performance of the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of ion battery technology, and particularly relates to a sodium supplement agent with high conductivity and its preparation method. Background Technology

[0002] Currently, lithium-ion batteries are widely used in consumer electronics, new energy electric vehicles, and renewable energy storage. However, limited lithium resources, uneven distribution, and high costs hinder their large-scale application in energy storage. Furthermore, the structural characteristics of commercially available graphite anodes in lithium-ion batteries impede further improvements in cycle performance and rate capability. Sodium-ion batteries, with their similar energy storage mechanism to lithium-ion batteries, are expected to replace lithium-ion batteries due to their abundant resources and low cost.

[0003] With the continuous advancement of fundamental research on key positive and negative electrode materials, electrolytes, and binders for sodium-ion batteries, the development of high-performance sodium-ion batteries is becoming increasingly important for promoting their industrial application. Currently, the hard carbon anodes used in sodium-ion batteries generally suffer from low coulombic efficiency in the first cycle. During battery cycling, the carbon anode consumes the limited sodium in the positive electrode material to form a solid electrolyte interphase (SEI) film. This irreversible consumption of sodium in the positive electrode material significantly reduces the energy density and cycle stability of sodium-ion batteries, and this problem has become one of the bottlenecks restricting the development of sodium-ion batteries.

[0004] Studies have found that sodium compensation at the cathode can effectively solve the problem of irreversible sodium loss in sodium-ion batteries. However, most current sodium compensation agents suffer from low conductivity. Improving the conductivity of sodium compensation agents can effectively reduce the battery's internal resistance (DCR), improve kinetics, and enhance rate performance. Therefore, developing sodium compensation agents with high conductivity is one of the key factors driving the development of sodium-ion batteries. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a sodium supplement with high conductivity and a method for preparing the same.

[0006] This invention provides a method for preparing a sodium supplement, comprising the following steps:

[0007] S1) Bacterial cellulose was soaked in sodium carbonate solution and then freeze-dried to obtain product A;

[0008] S2) The product A is calcined in a protective atmosphere to obtain product B;

[0009] S3) Mix the oxalic acid aqueous solution with product B and let it stand to obtain the sodium supplement.

[0010] Preferably, the concentration of the sodium carbonate solution is 0.5–5 mol / L.

[0011] Preferably, the soaking temperature is 30℃~60℃; the soaking time is 5~24h.

[0012] Preferably, the calcination in step S2) is a two-stage calcination;

[0013] In the two-stage calcination, the temperature of the first stage is 250℃~450℃; the calcination time of the first stage is 1~10h; and the heating rate of the first stage is 0.5~5℃ / min.

[0014] The two-stage calcination process involves a calcination temperature of 600℃ to 800℃, a calcination time of 1 to 10 hours, and a heating rate of 0.5 to 5℃ / min.

[0015] Preferably, the flow rate of the protective atmosphere in step S2) is 40-80 mL / min.

[0016] Preferably, the concentration of the oxalic acid aqueous solution is 0.5–1.2 mol / L;

[0017] In step S3), the oxalic acid aqueous solution is added dropwise to product B for mixing.

[0018] Preferably, the settling time is 6 to 12 hours; the settling temperature is 25°C to 50°C.

[0019] The present invention also provides a sodium supplement prepared by the above preparation method, comprising a carrier and sodium oxalate loaded on the carrier; wherein the carrier is porous carbon with a three-dimensional network structure.

[0020] Preferably, the resistivity of the sodium supplement powder is less than 5 Ω / cm.

[0021] The present invention also provides a sodium-ion battery comprising the sodium replenishing agent described above.

[0022] This invention provides a method for preparing a sodium replenishing agent with high conductivity, comprising the following steps: S1) soaking bacterial cellulose in a sodium carbonate solution and then freeze-drying it to obtain product A; S2) calcining product A under a protective atmosphere to obtain product B; S3) mixing product B with an oxalic acid aqueous solution and allowing it to stand to obtain the sodium replenishing agent. Compared with the prior art, the sodium replenishing agent prepared by this invention can replenish the sodium ion consumption in the positive electrode material during cycling. Furthermore, this sodium replenishing agent, using porous carbon as a carrier, has excellent controllability. As a framework for the sodium replenishing agent, it can effectively improve its conductivity. High conductivity improves the DCR of sodium-ion batteries, enhances their kinetic performance, and thus improves the electrochemical performance of sodium-ion batteries. Attached Figure Description

[0023] Figure 1This is a scanning electron microscope image of the sodium oxalate supplement obtained in Example 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for preparing a sodium supplement with high conductivity, comprising the following steps: S1) soaking bacterial cellulose in sodium carbonate solution and then freeze-drying it to obtain product A; S2) calcining product A in a protective atmosphere to obtain product B; S3) mixing product B with an oxalic acid aqueous solution and allowing it to stand to obtain a sodium supplement.

[0026] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0027] Bacterial cellulose is soaked in a sodium carbonate solution and then freeze-dried to obtain product A. Preferably, the bacterial cellulose is first soaked in water and then squeezed dry before being soaked in a sodium carbonate solution. The concentration of the sodium carbonate solution is preferably 0.5–5 mol / L, more preferably 1–3 mol / L, and even more preferably 1–2 mol / L. The soaking temperature is preferably 30°C–60°C, more preferably 40°C–50°C, and even more preferably 45°C. The soaking time is preferably 5–24 h, more preferably 5–20 h, even more preferably 8–16 h, and most preferably 10–12 h. After soaking, it is preferable to remove the cellulose, wipe off excess solvent with filter paper, and then freeze-dry it. The freeze-drying method can be any method known to those skilled in the art and is not particularly limited; preferably, freezing under negative pressure is sufficient. The freeze-drying temperature is preferably -20°C to -60°C, more preferably -30°C to -50°C, and even more preferably -40°C.

[0028] Product A is calcined in a protective atmosphere to obtain product B. The protective atmosphere can be any atmosphere well-known to those skilled in the art and is not particularly limited. In this invention, it is preferably one or more of nitrogen, argon, and helium. The flow rate of the protective atmosphere is preferably 40–80 mL / min, more preferably 60–80 mL / min. The calcination is preferably a two-stage calcination. The temperature of the first stage of the two-stage calcination is preferably 250°C–450°C, more preferably 300°C–450°C. In some embodiments provided by this invention, the temperature of the first stage of calcination is specifically 300°C, 400°C, or 450°C. The calcination time of the first stage is preferably 1–10 hours, more preferably... The calcination time is preferably 2-8 hours, more preferably 2-6 hours; in some embodiments provided by the present invention, the first-stage calcination time is specifically 2 hours, 3 hours, or 6 hours; the heating rate of the first-stage calcination is preferably 0.5-5℃ / min, more preferably 1-5℃ / min; the temperature of the second-stage calcination in the two-stage calcination is preferably 600℃-800℃; in some embodiments provided by the present invention, the temperature of the second-stage calcination is specifically 700℃, 800℃, or 600℃; the second-stage calcination time is preferably 1-10 hours, more preferably 1-8 hours, more preferably 1-6 hours, more preferably 2-4 hours, and most preferably 2-3 hours; the heating rate of the second-stage calcination is preferably 0.5-5℃ / min, more preferably 1-5℃ / min. In the present invention, unless otherwise specified, the calcination time refers to the time held after heating to the calcination temperature.

[0029] The oxalic acid aqueous solution is mixed with product B and then allowed to stand. The concentration of the oxalic acid aqueous solution is preferably 0.5-1.2 mol / L, more preferably 0.5-1 mol / L. In this invention, it is preferred to mix the oxalic acid aqueous solution by adding it dropwise to product B. The oxalic acid aqueous solution reacts with sodium carbonate supported on cellulose. In this invention, the amount of oxalic acid aqueous solution is preferably in excess. Specifically, the amount of oxalic acid aqueous solution is preferably enough to cover product B. The standing temperature is preferably 25℃-50℃, more preferably 30℃-50℃, and even more preferably 30℃-45℃. The standing time is preferably 6-12 hours.

[0030] After standing, the sodium supplement is preferably obtained by filtration, washing, and drying; the washing is preferably done with an alcohol solvent, and more preferably with ethanol or methanol.

[0031] The sodium replenisher prepared by this invention can replenish the sodium ions consumed in the cathode material during cycling. Furthermore, the sodium replenisher, with porous carbon as a carrier, has excellent controllability. As the skeleton of the sodium replenisher, it can effectively improve its conductivity. High conductivity improves the DCR of sodium-ion batteries, enhances their kinetic performance, and thus improves the electrochemical performance of sodium-ion batteries.

[0032] The present invention also provides a sodium supplement with high conductivity prepared by the above preparation method, comprising a carrier and sodium oxalate loaded on the carrier; wherein the carrier is porous carbon with a three-dimensional network structure.

[0033] More specifically, the resistivity of the sodium supplement powder is less than 5 Ω / cm.

[0034] The present invention also provides a sodium-ion battery comprising the sodium replenishing agent described above.

[0035] More specifically, the sodium-ion battery includes a positive electrode; the positive electrode includes the aforementioned sodium replenishing agent.

[0036] More specifically, the mass of the sodium supplement is 1% to 10% of the mass of the positive electrode active material, more preferably 3% to 8%, even more preferably 4% to 6%, and most preferably 5%.

[0037] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a sodium supplement with high conductivity and its preparation method.

[0038] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0039] The raw materials used in this invention, which involve specific brands, are not particularly limited in terms of their source. They can be products sold by conventional manufacturers of that brand that are well known to those skilled in the art.

[0040] There are no particular restrictions on the purity of any raw materials used in this invention. However, it is preferable to use analytical grade or conventional purity materials in the field.

[0041] The reagents and bacterial cellulose used in the following examples are all commercially available.

[0042] Example 1

[0043] 1.1 Take 10g of bacterial cellulose soaked in water until it is saturated, squeeze out the water by hand, and then place it in 40mL of 1M sodium carbonate solution. Soak overnight at 45℃, then remove. Wipe off excess solvent with filter paper, and freeze-dry under negative pressure at -40℃ to obtain product A.

[0044] 1.2 Product A was placed in a tube furnace and calcined in two stages to obtain product B. The temperature of the first stage of the two-stage calcination was 300℃, the holding time was 2h, the heating rate was 1℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min; the temperature of the second stage was 700℃, the holding time was 3h, the heating rate was 2℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min.

[0045] 1.3 Place 5g of product B into a crystallizing dish and add 0.5M oxalic acid aqueous solution dropwise until the oxalic acid solution covers product B. After standing at 30℃ for 12h, filter, wash with ethanol, and vacuum dry at 60℃ for 12h to obtain sodium oxalate supplement with high conductivity.

[0046] The sodium oxalate supplement obtained in Example 1 was analyzed using scanning electron microscopy, and its scanning electron micrograph is shown below. Figure 1 As shown.

[0047] Example 2

[0048] The only modification is to step 1.2 of Example 1, which involves placing product A in a tube furnace and calcining it in two stages to obtain product B. The first stage of calcination can be at a temperature of 400°C, with a holding time of 3 hours and a heating rate of 1°C / min. The gas used in the calcination process is nitrogen, with a flow rate of 80 mL / min. The second stage can be at a temperature of 800°C, with a holding time of 2 hours and a heating rate of 1°C / min. The gas used in the calcination process is nitrogen at a flow rate of 80 mL / min. The remaining steps are the same as in Example 1.

[0049] Example 3

[0050] The only difference is that step 1.3 of Example 1 is modified as follows: 5g of product B is placed in a crystallizing dish, and 1M oxalic acid aqueous solution is added dropwise until the oxalic acid solution completely covers product B. After standing at 45°C for 6 hours, the mixture is filtered, washed with ethanol, and dried under vacuum at 60°C for 12 hours to obtain a sodium oxalate supplement with high conductivity. The remaining steps are the same as in Example 1.

[0051] Example 4

[0052] The only difference is that step 1.2 of Example 1 is modified as follows: Product A is placed in a tube furnace and calcined in two stages to obtain product B. The first stage of calcination is at a temperature of 450°C, held for 6 hours, with a heating rate of 5°C / min, and nitrogen is used as the gas during calcination at a flow rate of 80 mL / min. The second stage is at a temperature of 600°C, held for 2 hours, with a heating rate of 5°C / min, and nitrogen is used as the gas during calcination at a flow rate of 80 mL / min. The remaining steps are the same as in Example 1.

[0053] Comparative Example 1

[0054] 1.1 50g of sodium carbonate was placed in a tube furnace and calcined in two stages to obtain product B. The temperature of the first stage of the two-stage calcination was 300℃, the holding time was 2h, the heating rate was 1℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min. The temperature of the second stage was 700℃, the holding time was 3h, the heating rate was 2℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min.

[0055] 1.2 Place 5g of product B into a crystallizing dish and add 0.5M oxalic acid aqueous solution dropwise until the oxalic acid solution completely covers product B. After standing at 30℃ for 12h, filter, wash with ethanol, filter and dry to obtain sodium oxalate supplement.

[0056] Comparative Example 2

[0057] 2.1 Take 10g of bacterial cellulose soaked in water until it is saturated, squeeze out the water by hand, and then place it in 40mL of 1M sodium carbonate solution. Soak overnight at 45℃, then remove. Wipe away excess solvent with filter paper. After freeze-drying, obtain product A.

[0058] 2.2 Product A was placed in a tube furnace and calcined to obtain product B. The calcination temperature was 700℃, the holding time was 3h, the heating rate was 2℃ / min, and the gas used in the calcination process was nitrogen at a flow rate of 80mL / min.

[0059] 2.3 Place 5g of product B into a crystallizing dish and add 0.5M oxalic acid aqueous solution dropwise until the oxalic acid solution completely covers product B. After standing at 30℃ for 12h, filter, wash with ethanol, filter and dry to obtain sodium oxalate supplement.

[0060] Comparative Example 3

[0061] 3.1 Take 10g of bacterial cellulose soaked in water until it is saturated, squeeze out the water by hand, and then place it in 40mL of 1M sodium carbonate solution. Soak overnight at 45℃, then remove. Wipe off excess solvent with filter paper, and freeze-dry under negative pressure at -40℃ to obtain product A.

[0062] 3.2 Product A was placed in a tube furnace and calcined in two stages to obtain product B. The temperature of the first stage of the two-stage calcination was 200℃, the holding time was 2h, the heating rate was 1℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min; the temperature of the second stage was 500℃, the holding time was 3h, the heating rate was 2℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min.

[0063] 3.3 Place 5g of product B into a crystallizing dish and add 0.5M oxalic acid aqueous solution dropwise until the oxalic acid solution completely covers product B. After standing at 30℃ for 12h, filter, wash with ethanol, filter and dry to obtain sodium oxalate supplement with high conductivity.

[0064] Comparative Example 4

[0065] 4.1 Take 10g of bacterial cellulose soaked in water until it is fully saturated with water, wipe off the excess solvent with filter paper, freeze-dry, and obtain product A.

[0066] 4.2 Product A was placed in a tube furnace and calcined in two stages to obtain product B. The temperature of the first stage of the two-stage calcination was 300℃, the holding time was 2h, the heating rate was 1℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min; the temperature of the second stage was 700℃, the holding time was 3h, the heating rate was 2℃ / min, and the gas used in the calcination process was nitrogen with a flow rate of 80mL / min.

[0067] 4.3 Place 5g of product B into a crystallizing dish, and add 0.5M sodium oxalate aqueous solution dropwise until the oxalic acid solution completely covers product B. After standing at 30℃ for 12h, filter, wash with ethanol, filter and dry to obtain sodium oxalate supplement.

[0068] The powder resistance of the sodium oxalate supplements obtained in Examples 1-4 and Comparative Examples 1-3 was tested using a PR510 powder resistance tester from Chuanyuan Technology. The test results are shown in Table 1.

[0069] Table 1 Powder resistance of sodium supplement materials

[0070] Powder resistance (Ω / cm) Example 1 3.6 Example 2 4.2 Example 3 3.9 Example 4 4.1 Comparative Example 1 2345 Comparative Example 2 5.2 Comparative Example 3 10.6 Comparative Example 4 9.6

[0071] As shown in Table 1, the sodium supplement powders prepared in Examples 1 to 4 have lower resistance than those in Comparative Example 1 and have better conductivity. Comparative Example 3 has a low calcination temperature, which results in a large specific surface area of ​​the product and poor conductivity such as dcr.

[0072] Positive electrode sheets were prepared using commercially available layered oxide sodium electrode material (Jiangsu Xiangying New Energy Technology Co., Ltd.) as the positive electrode active material (90%), with the addition of sodium supplementer (5% of the positive electrode active material mass) prepared in Examples 1-4 and Comparative Examples 1-3, conductive agent Super P (5%), and binder PVDF (5%). Negative electrode sheets were prepared using commercially available hard carbon as the negative electrode active material (92%), conductive agent Super P (2%), and binder CMC+SBR (5%). The electrolyte consisted of 1.0 mol / L NaPF6 as the sodium salt, PC (propylene carbonate) and EMC (ethyl methyl carbonate) as solvents (volume ratio 1:1), 5% FEC (fluoroethylene carbonate), and 1% DTD (ethylene sulfate) as additives. CR2032 button cells were assembled in an argon glove box. GCD was tested using a Land battery testing system within a voltage window of 1.5–3.95 V.

[0073] Test conditions: The assembled button cells were subjected to constant current charge and discharge tests at a rate of 0.02C, with a voltage range of 1.5 to 3.95V. The results are shown in Table 2.

[0074] The assembled button cells were tested using the HPPC method at different SOCs (50%, 20%) at room temperature (2C discharge for 30s). The test results are shown in Table 3.

[0075] The assembled button batteries were subjected to constant current charge-discharge tests at 0.5C / 1C rates, with a voltage range of 1.5 to 3.95V. After 500 cycles, the cycle performance results are shown in Table 4.

[0076] Table 2 Results of Constant Current Charge-Discharge Test

[0077] Capacity (mAh / g) First-time coulomb efficiency (%) Example 1 120.2 86.7 Example 2 119.7 85.7 Example 3 119.5 85.6 Example 4 120.4 86.0 Comparative Example 1 117.6 80.6 Comparative Example 2 118.7 83.1 Comparative Example 3 114.0 81.4 Comparative Example 4 115.4 80.2

[0078] Table 3 DCR Test Results at Room Temperature

[0079] 50% SOC DCR mΩ 20% SOC DCR mΩ Example 1 68.2 124.4 Example 2 67.4 125.1 Example 3 66.9 123.6 Example 4 67.5 126.7 Comparative Example 1 79.2 134.8 Comparative Example 2 70.9 128.6 Comparative Example 3 74.4 144.7 Comparative Example 4 77.5 145.3

[0080] Table 4 Cyclic performance test results

[0081] Current density 500 mA / g Capacity retention rate (%) Example 1 92.8 Example 2 91.5 Example 3 92.1 Example 4 93.0 Comparative Example 1 88.4 Comparative Example 2 90.8 Comparative Example 3 88.3 Comparative Example 4 88.9

[0082] As shown in Table 2, all button cells have high specific capacity (over 117 mAh / g) and initial stock efficiency exceeding 85%.

[0083] As shown in Tables 1 and 3, biomass carbon materials, as the framework for sodium supplementation, can effectively improve conductivity and reduce the DCR of sodium-ion batteries. Compared with the comparative examples, the DCR of button batteries prepared using Examples 1-4 as sodium supplementation agents was reduced by more than 15%.

[0084] As shown in Table 4, the capacity retention of button batteries prepared using Examples 1-4 as sodium supplements was significantly improved compared to the comparative examples.

Claims

1. A method for preparing a sodium supplement, characterized in that, Includes the following steps: S1) Bacterial cellulose was soaked in sodium carbonate solution and then freeze-dried to obtain product A; S2) The product A is calcined in a protective atmosphere to obtain product B; S3) Mix the oxalic acid aqueous solution with product B and let it stand to obtain the sodium supplement; The calcination in step S2) is a two-stage calcination; In the two-stage calcination, the temperature of the first stage is 250℃~450℃; the calcination time of the first stage is 1~10 h; and the heating rate of the first stage is 0.5~5℃ / min. The two-stage calcination process involves a calcination temperature of 600℃~800℃, a calcination time of 1~10 h, and a heating rate of 0.5~5℃ / min. In step S2), the flow rate of the protective atmosphere is 40~80 mL / min.

2. The preparation method according to claim 1, characterized in that, The concentration of the sodium carbonate solution is 0.5~5 mol / L.

3. The preparation method according to claim 1, characterized in that, The soaking temperature is 30℃~60℃; the soaking time is 5~24 h.

4. The preparation method according to claim 1, characterized in that, The concentration of the oxalic acid aqueous solution is 0.5~1.2 mol / L; In step S3), the oxalic acid aqueous solution is added dropwise to product B for mixing.

5. The preparation method according to claim 1, characterized in that, The settling time is 6-12 hours; the settling temperature is 25℃-50℃.

6. The sodium supplement prepared by the method according to any one of claims 1 to 5.

7. The sodium supplement according to claim 6, characterized in that, The resistivity of the sodium supplement powder is less than 5 Ω / cm.

8. A sodium-ion battery, characterized in that, The sodium supplement includes the sodium supplement prepared by the preparation method according to any one of claims 1 to 5 or the sodium supplement according to claim 6 or 7.

Images