A method for improving the electrochemical performance of sodium-ion battery alloy anode materials

Abstract

This invention provides a method for improving the electrochemical performance of alloy anode materials in sodium-ion batteries. The method involves modifying the surface of Sn powder with a polyacrylamide layer to obtain a Sn@PAM anode material. Then, the Sn@PAM anode material, a conductive agent, and a binder are coated onto a current collector to form an anode sheet. The anode sheet, cathode sheet, separator, and electrolyte are then assembled into a sodium-ion half-cell or sodium-ion full-cell. This invention modifies the surface of micron-sized Sn with a PAM layer using a simple stirring and centrifugation method. Utilizing the hydrogen bonding between PAM and the binder CMC, a self-healing, soft-inner-hard-outer structure is constructed, which provides strong adhesion and mechanical properties during cycling, ensuring the stable electrochemical performance of micron-sized Sn.

Description

Technical Field

[0001] This invention relates to a method for improving the electrochemical performance of alloy anode materials for sodium-ion batteries, belonging to the field of sodium-ion battery technology. Background Technology

[0002] Compared to highly polluting fossil fuels like coal and oil, and renewable clean energy sources such as solar, wind, and tidal power, which are intermittent, rechargeable batteries have gained widespread application in the energy storage market due to their high environmental friendliness and reasonable price. Lithium-ion batteries (LIBs), with their advantages of lightweight design, long cycle life, and excellent energy density, have stood out in the competition for electrochemical energy storage systems and are widely used in portable electronic devices, electric vehicles, and many other applications. However, the low abundance of lithium in the Earth's crust makes it difficult for existing lithium resources to sustain the current high market demand. Compared to lithium, sodium has a relatively high abundance and wide distribution in the Earth's crust, and both elements belong to the same main group and have similar chemical properties. Therefore, many advanced and mature research results on LIBs are also applicable to SIBs. However, sodium's potential relative to the standard hydrogen electrode (-2.71V) is only 300mV higher than that of lithium, resulting in lower energy density in SIBs. Furthermore, sodium ions have a larger radius than lithium ions. This results in a greater volume effect caused by the insertion and extraction of sodium ions in the electrode material, affecting the cycle stability of the battery.

[0003] Currently, the main anode materials for sodium-ion batteries are based on conversion, intercalation / deintercalation, and alloying mechanisms. Compared to the former two, alloying mechanisms offer advantages such as high theoretical capacity, low voltage, and high conductivity. Among the many alloying mechanisms, Sn stands out due to its high theoretical specific capacity (847 mAh·g). -1 Sn is considered one of the most promising anode materials due to its high safety and high performance. However, similar to other alloy-mechanism anode materials, Sn undergoes a huge volume change (~420%) during sodium formation / desodium formation, causing material fragmentation, which reduces battery capacity and degrades cycle performance (ΔV Bi ~244%, ΔV Sb ~293%).

[0004] To address the aforementioned problems, methods such as reducing particle size, constructing porous structures, or carbon coating the material surface have been employed. While these methods reduce tin particle breakage and extend tin's cycle life to some extent, they are cumbersome, costly to produce, and introduce new problems such as reduced first-time efficiency and low tap density. Recently, attention has been focused on electrode material preparation, using different binders to improve the electrochemical performance of tin anodes. However, the electrochemical performance of tin anodes still needs further improvement; therefore, this invention is proposed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for improving the electrochemical performance of sodium-ion battery alloy anode materials. Invention Overview

[0007] This invention modifies the surface of micron-sized Sn with a PAM layer through simple stirring and centrifugation. Utilizing the hydrogen bonding between PAM and the binder CMC, a self-healing, soft-inner-hard-outer structure is constructed, providing strong adhesion and mechanical properties during cycling to ensure the stable electrochemical performance of micron-sized Sn. Compared to CMC, Sn@PAM-CMC exhibits superior cycle life at 2Ag... -1 At high current densities, it can achieve 4000 cycles, far exceeding Sn@CMC (only 100 cycles). Furthermore, a 5.7mAh cm⁻¹ current density can be achieved. -2 High surface area capacity and approximately 7.7 mg / cm³ -2 High-quality loading. This new method provides a simple and economical way to achieve excellent electrochemical performance with simple processing.

[0008] The technical solution of the present invention is as follows:

[0009] A method for improving the electrochemical performance of alloy anode materials for sodium-ion batteries involves modifying the surface of Sn powder with a polyacrylamide (PAM) layer to obtain Sn@PAM anode material, then coating the Sn@PAM anode material, conductive agent, and binder onto a current collector to form an anode sheet, and finally assembling the anode sheet, positive electrode sheet, separator, and electrolyte into a sodium-ion half-cell or sodium-ion full-cell.

[0010] According to a preferred embodiment of the present invention, the particle size of the Sn powder is 2-15 μm.

[0011] According to a preferred embodiment of the present invention, the step of modifying the Sn powder surface with a polyacrylamide (PAM) layer is as follows: Sn powder is added to an aqueous solution of polyacrylamide (PAM), stirred, and then centrifuged. The resulting solid is washed successively with water and anhydrous ethanol by centrifugation and then dried to obtain Sn@PAM anode material.

[0012] More preferably, the concentration of the polyacrylamide (PAM) aqueous solution is 0.1-0.15 g / L; and the weight-average molecular weight of the polyacrylamide is 8 million to 20 million.

[0013] More preferably, the mass ratio of the Sn powder to the volume of the polyacrylamide (PAM) aqueous solution is 1g:150-180mL;

[0014] More preferably, the stirring time is 10-15 hours; the drying is carried out at 25-30°C for 12-18 hours.

[0015] According to a preferred embodiment of the present invention, the conductive agent in the negative electrode sheet is acetylene black, Ketjen black, carbon nanotubes or conductive carbon black; the binder in the negative electrode sheet is sodium carboxymethyl cellulose (CMC); and the current collector in the negative electrode sheet is copper foil.

[0016] According to a preferred embodiment of the present invention, the negative electrode sheet is prepared by the following method:

[0017] Sn@PAM anode material, conductive agent, and binder are mixed, water is added, and ball milling is performed to obtain a slurry. The obtained slurry is coated on a current collector, dried, and cut to obtain anode sheet.

[0018] More preferably, the mass ratio of the Sn@PAM anode material, conductive agent, and binder is 7:2:1; the ratio of the total mass of the Sn@PAM anode material, conductive agent, and binder to the volume of water is 1g:5.5-6mL.

[0019] More preferably, the ball mill rotation speed is 300-400 r / min, and the ball milling time is 3-5 h;

[0020] More preferably, the drying is performed by vacuum drying at 55-65°C for 10-15 hours;

[0021] More preferably, the loading of Sn@PAM anode material on the anode sheet is 1.2-7.7 mg / cm³. -2 .

[0022] According to a preferred embodiment of the present invention, the preparation method of the positive electrode sheet is a prior art; preferably, the positive electrode sheet is prepared by the following method: active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1, N-methylpyrrolidone (NMP) is added, the mixture is ball-milled into a slurry, coated onto aluminum foil, dried at 100°C, rolled, and cut into positive electrode sheets, wherein the mass of positive active material per unit area of ​​the positive electrode sheet is 7-8 mg / cm². -2 ;

[0023] More preferably, the conductive agent in the positive electrode is acetylene black, and the binder in the positive electrode is sodium carboxymethyl cellulose;

[0024] More preferably, the ratio of the total mass of the active material, conductive agent, and binder to the volume of N-methylpyrrolidone (NMP) in the preparation of the positive electrode sheet is 1g:5-5.5mL;

[0025] More preferably, when forming a sodium-ion half-cell, the active material on the positive electrode is Na, and when forming a sodium-ion full-cell, the active material on the positive electrode is NaV2(PO4)3 / rGO.

[0026] According to a preferred embodiment of the present invention, the diaphragm is a Whatman GF / F glass fiber membrane.

[0027] According to a preferred embodiment of the present invention, the electrolyte is a NaPF6-DIGLYME solution, which is a mixture of NaPF6 dissolved in diethylene glycol dimethyl ether (DIGLYME), and the concentration of NaPF6 is 1 mol / L.

[0028] According to the present invention, the test voltage of the negative electrode during the half-cell electrochemical performance test is 0.01-1.0V vs Na / Na. + The test voltage of the negative electrode during the full-cell electrochemical performance test is 2.5-3.8V.

[0029] The technical features and beneficial effects of this invention are as follows:

[0030] 1. This invention uses micron-sized commercial Sn powder as the negative electrode material, which is cheaper than preparing nanoscale Sn.

[0031] 2. This invention modifies the surface of micron-sized Sn with a PAM layer by simple stirring and centrifugation. The hydrogen bonding between PAM and the binder CMC results in a self-healing structure that is soft inside and hard outside. It can provide strong adhesion and mechanical properties during cycling to ensure the stable electrochemical performance of micron-sized Sn.

[0032] 3. This invention only requires pre-modification of micron-sized tin, eliminating the need for complex morphology and structure control, thus significantly improving its cycle stability at 2Ag. -1 It achieved excellent rate capacity and stable cycling performance of 4000 cycles at a current density. Attached Figure Description

[0033] Figure 1 These are electrochemical charge-discharge curves of the sodium-ion half-cells obtained in Example 1 and Comparative Example 1, within the negative electrode charge-discharge test voltage range (0.01-1.0V); the current density in both cases is 0.1Ag. -1 a is the charge-discharge curve of Sn-CMC at the negative electrode of battery in Example 1; b is the charge-discharge curve of Sn@PAM-CMC at the negative electrode of battery in Example 1.

[0034] Figure 2These are scanning electron microscope (SEM) images of the negative electrode of the sodium-ion half-cells obtained in Example 1 and Comparative Example 1 before and after cycling within the voltage range of the charge-discharge test. Where a and b are SEM top views of the uncycled Sn-CMC electrode surface of Comparative Example 1 at low and high magnification, respectively; c is a SEM cross-sectional view of the uncycled Sn-CMC electrode surface of Comparative Example 1; d and e are SEM top views of the uncycled Sn@PAM-CMC electrode surface of Example 1 at low and high magnification, respectively; f is a SEM cross-sectional view of the uncycled Sn@PAM-CMC electrode surface of Example 1; and g and h are SEM images of the Sn-CMC electrode of Comparative Example 1 at 2A g. -1 SEM top views at low and high magnifications after 20 cycles, i is the Sn-CMC electrode of Comparative Example 1 at 2A g. -1 SEM cross-sectional image after 20 cycles, j and k are the Sn@PAM-CMC electrode of Example 1 at 2A g. -1 SEM top views at low and high magnifications after 20 cycles, l is the Sn@PAM-CMC electrode of Example 1 at 2A g. -1 SEM cross-sectional image after 20 cycles.

[0035] Figure 3 This is an investigation and schematic diagram to prove that PAM and CMC have self-healing ability. In the diagram, a is a picture of PAM and CMC prepared into a solid hydrogel state, with red representing CMC hydrogel and white representing PAM hydrogel. b is a schematic diagram of the distribution of PAM and CMC on the electrode surface.

[0036] Figure 4 This is a comparison graph (a) of the long-cycle performance of the sodium-ion half-cells obtained in Example 1 and Comparative Example 1, with a current density of 0.1 A g in the first three cycles. -1 The subsequent current density is 2Ag -1 Example 2 shows the linear relationship between the active material loading and volumetric capacity of the sodium-ion half-cell prepared at a current density of 0.1 Ag. -1 (b); First charge-discharge curves of sodium-ion half-cells obtained with different active material loadings in Example 2, with a current density of 0.1 Ag. -1 (c); The linear relationship curve between the active material loading and the areal capacity of the sodium-ion half-cell prepared in Example 2, and the mass capacity under different active material loadings (d); The active material loading in Example 2 was 5.1 mg / cm³. -2 Cycle performance (e) of sodium-ion half-cells; Active material loading in Example 2 was 5.1 mg cm⁻¹ -2 Rate performance (f) of sodium-ion half-cells.

[0037] Figure 5Cycle performance of batteries prepared by modifying tin with different concentrations of polyacrylamide aqueous solution.

[0038] Figure 6 This is a comparison chart of the long-cycle performance of the full cells obtained in Example 1 and Comparative Example 1. Detailed Implementation

[0039] The present invention will now be described in more detail with reference to the accompanying drawings and embodiments, but the present invention is not limited thereto.

[0040] All raw materials used in the examples were purchased from the market.

[0041] The weight-average molecular weight of polyacrylamide is 12 million.

[0042] Example 1

[0043] A method for improving the electrochemical performance of alloy anode materials for sodium-ion batteries includes the following steps:

[0044] (1) Preparation of Sn@PAM anode material

[0045] 0.3 g of tin powder (particle size 3-15 μm) was added to 50 mL of 0.1 g / L polyacrylamide (PAM) aqueous solution and stirred at room temperature for 12 h. After centrifugation, the solid obtained by centrifugation was washed successively with water and anhydrous ethanol and dried at 30 °C for 12 h to obtain Sn@PAM anode material.

[0046] (2) Preparation of negative electrode

[0047] Sn@PAM anode material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 7:2:1. Water was then added, and the total mass ratio of Sn@PAM anode material, conductive agent, and binder to water volume was 1 g: 5.5 mL. The mixture was ball-milled at 300 r / min for 4 hours to obtain a slurry. The slurry was coated onto copper foil and vacuum-dried at 60 °C for 12 h. After rolling, the slurry was cut into electrode sheets to obtain the anode sheet, denoted as Sn@PAM-CMC. The mass (loading) of the active material Sn@PAM anode material per unit area of ​​the anode sheet was 1.3 mg / cm². -2 .

[0048] (3) Preparation of positive electrode

[0049] The active material, conductive agent acetylene black, and binder sodium carboxymethyl cellulose were mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was then added. The total mass ratio of the positive electrode material, conductive agent, and binder to the volume of N-methylpyrrolidone (NMP) was 1 g:5 mL. The mixture was ball-milled into a slurry, coated onto aluminum foil, dried at 100°C, rolled, and cut into electrode sheets. The mass (loading) of active material per unit area was 7 mg / cm². -2 When forming a sodium-ion half-cell, the active material on the positive electrode is Na; when forming a sodium-ion full-cell, the active material on the positive electrode is NaV2(PO4)3 / rGO.

[0050] (4) Battery assembly

[0051] The battery is assembled into a sodium-ion half-cell or sodium-ion full-cell, including a positive electrode (Na electrode or NaV2(PO4)3 / rGO positive electrode), a negative electrode, a Whatman GF / F glass fiber separator, a NaPF6-DIGLYME electrolyte (NaPF6 concentration of 1 mol / L) and a casing (model 2025). The battery assembly is carried out in a glove box.

[0052] Half-cell electrochemical charge-discharge test voltage range: 0.01-1.0V vs Na / Na + The full-cell electrochemical charge-discharge test voltage range is 2.5-3.8V.

[0053] Example 2

[0054] A method for improving the electrochemical performance of sodium-ion battery alloy anode materials is described in Example 1, except that in step (2), the mass (loading) of the active material Sn@PAM anode material per unit area of ​​the anode sheet is 1.5, 2.6, 4.0, 5.1, 6.2, and 7.7 mg / cm², respectively. -2 .

[0055] Comparative Example 1

[0056] A method for applying a tin anode material in a sodium-ion battery is described in Example 1, except that: the Sn anode modification in step (1) is not performed, and tin powder is directly used to replace the Sn@PAM anode material in step (2), and the resulting anode sheet is denoted as Sn-CMC.

[0057] Comparative Example 2

[0058] A method for improving the electrochemical performance of sodium-ion battery alloy anode materials is described in Example 1, except that the concentrations of the polyacrylamide (PAM) aqueous solution in step (1) are 0 g / mL, 0.05 g / mL, 0.2 g / mL, and 0.4 g / mL, respectively.

[0059] Experimental Example 1

[0060] Electrochemical performance and morphology testing

[0061] Charge-discharge tests were performed on the half-cells obtained in Example 1 and Comparative Example 1, and the results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the first-cycle coulombic efficiency of the two is similar, and the modification of the electrode by polyacrylamide does not affect the charging and discharging process of μ-Sn (micrometer Sn).

[0062] Figure 2 These are scanning electron microscope (SEM) images of the negative electrode sheets of the sodium-ion half-cells obtained in Example 1 and Comparative Example 1 before and after cycling. A comparison of Figures a and d shows that in the Sn@PAM-CMC electrode sheet of Example 1, the active particles are uniformly dispersed on the electrode, the Sn particles are surrounded by conductive carbon, and the electrode has good contact with the copper current collector. However, in the Sn-CMC electrode of Comparative Example 1, the active particles are not uniformly distributed by conductive carbon, and cracks appear on the surface. After 20 cycles, the Sn-CMC electrode structure of Comparative Example 1 becomes less dense and fractures occur. Figure 2 h), the loose structure and cracks on the electrode indicate the electrode's instability. Worse still, the electrode containing active particles loses electrical contact with the copper current collector and exhibits reduced electrochemical activity. Figure 2 i). The Sn@PAM-CMC electrode sheet in Example 1 did not exhibit cracks or loose structures. Figure 2 k), and the electrode maintains good contact with the copper current collector ( Figure 2 l). SEM images directly confirmed the stability of the Sn@PAM-CMC binder during cycling. The stability of the binder ensures good electrical contact with the copper current collector and stable electrochemical performance.

[0063] Figure 3 PAM and CMC were prepared into a solid hydrogel state and brought into contact at room temperature. After ten minutes, the two spontaneously polymerized. When picked up with tweezers, the two did not break. Figure 3 a) It can be seen that PAM and CMC spontaneously polymerize during electrode cycling. As the Sn particles increase in volume due to cycling, the soft and hard protective shells formed by the two slow down their expansion rate, thereby increasing the electrochemical performance of Example 1.

[0064] Experiment Example 2

[0065] Half-cell performance testing was conducted on Example 1 and Comparative Example 1 using sodium-ion half-cell long-cycle testing. The results are as follows: Figure 4 As shown in (a), the Sn@PAA-CMC electrode of Example 1 has better cycle capacity compared to the Sn-CMC electrode of Comparative Example 1. Figure 4 a) Sn@PAA-CMC electrode in 2Ag-1 At a current density of [specific value], it can exhibit a fairly long cycle life of 4000 cycles. However, the Sn-CMC electrode, measured under the same conditions, only lasted 100 cycles.

[0066] Volumetric load capacity depends linearly on mass load ( Figure 4 b) The areal capacity of the Sn@PAA-CMC electrode in Example 2 increases linearly from 1.5 mAh / cm² to 5.7 mAh / cm² with increasing mass loading. -2 ( Figure 4 d). Due to the delay in charge transport in thick electrodes, the overpotential inevitably increases slightly, such as Figure 4 As shown in c. Even at 7.7 mg cm -2 Under high-quality load, the Sn@PAA-CMC electrode also achieved a capacity of 740 mAh g. -1 , with 1.5mg cm -2 The mass loading was retained at 93.67%, and this high capacity retention is attributed to the excellent sodium ion transport mechanism and self-healing ability. The thick electrode also exhibits outstanding cycling capacity at a mass loading of 5.1 mg / cm³. -2 And the current density is 0.54 mA cm -2 At that time, the area capacity can reach 6.12mAh cm⁻¹ -2 ( Figure 4 e). Similarly, @PAM-CMC can function in other alloying mechanisms (Bi, Sb), and from Figure 4 As can be seen from f, the obtained battery has good rate performance.

[0067] Figure 5 The results are from electrochemical cycling performance tests of tin modified with polyacrylamide aqueous solutions of different concentrations (0-0.4 g / L). It can be seen that the 0.1 g / L concentration of tin modified in Example 1 has the best electrochemical performance.

[0068] Experimental Example 3

[0069] Sodium-ion full-cell long-cycle tests were performed on Example 1 and Comparative Example 1. The full-cell assembly was pre-sodium-treated, and the results are as follows: Figure 6 As shown, after 500 cycles, the reversible capacity of the Sn@PAA-CMC / / NVP@C full cell reaches 369 mAh g. -1 In contrast, Sn-CMC / / NVP@C at 2A g -1 It can only cycle 150 times, which shows that the Sn@PAA-CMC / / NVP@C full battery can provide higher capacity.

Claims

1. A method for improving the electrochemical performance of sodium-ion battery alloy anode materials, characterized in that, This method involves modifying the surface of Sn powder with a polyacrylamide layer to obtain Sn@PAM anode material. Then, Sn@PAM anode material, conductive agent, and binder are coated onto a current collector to prepare a negative electrode sheet. The negative electrode sheet, positive electrode sheet, separator, and electrolyte are then assembled into a sodium-ion half-cell or sodium-ion full-cell.

2. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The Sn powder has a particle size of 2-15 μm.

3. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The step of modifying the surface of Sn powder with a polyacrylamide layer is as follows: Sn powder is added to a polyacrylamide aqueous solution and stirred. After centrifugation, the resulting solid is washed successively with water and anhydrous ethanol by centrifugation and then dried to obtain Sn@PAM anode material.

4. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 3, characterized in that, The concentration of the polyacrylamide aqueous solution is 0.1-0.15 g / L; the weight-average molecular weight of the polyacrylamide is 8 million-20 million. The mass ratio of Sn powder to the volume of polyacrylamide aqueous solution is 1g:150-180mL. The stirring time is 10-15 hours; the drying is carried out at 25-30°C for 12-18 hours.

5. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The conductive agent in the negative electrode sheet is acetylene black, Ketjen black, carbon nanotubes, or conductive carbon black; the binder in the negative electrode sheet is sodium carboxymethyl cellulose; and the current collector in the negative electrode sheet is copper foil.

6. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The negative electrode sheet is prepared according to the following method: Sn@PAM anode material, conductive agent, and binder are mixed, water is added, and the mixture is ball-milled to obtain a slurry. The slurry is then coated onto a current collector, dried, and cut to obtain the anode sheet.

7. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 6, characterized in that, The mass ratio of the Sn@PAM anode material, conductive agent, and binder is 7:2:1; the ratio of the total mass of the Sn@PAM anode material, conductive agent, and binder to the volume of water is 1g:5.5-6mL. The ball milling speed is 300-400 r / min, and the ball milling time is 3-5 h; the drying is vacuum drying at 55-65℃ for 10-15 h; The loading of Sn@PAM anode material on the anode sheet is 1.2-7.7 mg / cm³. -2 .

8. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The positive electrode sheet is prepared by the following method: Active material, conductive agent, and binder are mixed in a mass ratio of 8:1:1, N-methylpyrrolidone is added, the mixture is ball-milled into a slurry, coated onto aluminum foil, dried at 100°C, rolled, and cut into positive electrode sheets. The mass of positive active material per unit area of ​​the positive electrode sheet is 7-8 mg / cm². -2 .

9. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 8, characterized in that, The conductive agent in the positive electrode is acetylene black, and the binder in the positive electrode is sodium carboxymethyl cellulose. In the preparation of the positive electrode sheet, the ratio of the total mass of the active material, conductive agent, and binder to the volume of N-methylpyrrolidone is 1g:5-5.5mL; When forming a sodium-ion half-cell, the active material on the positive electrode is Na; when forming a sodium-ion full-cell, the active material on the positive electrode is NaV2(PO4)3 / rGO.

10. The method for improving the electrochemical performance of sodium-ion battery alloy anode materials according to claim 1, characterized in that, The diaphragm is a Whatman GF / F glass fiber membrane; the electrolyte is a NaPF6-DIGLYME solution, which is a mixture of NaPF6 dissolved in diethylene glycol dimethyl ether, and the concentration of NaPF6 is 1 mol / L.

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