A silver-zinc battery cathode, its preparation method and application

Abstract

This invention discloses a silver-zinc battery positive electrode, its preparation method, and its application. The positive electrode comprises silver oxalate with a particle size of 10–200 nm. It is obtained by charging silver to 1.8–2.2 V in a novel aqueous electrolyte at a current density of 0.1–10 A / g. The aqueous electrolyte for the silver-zinc battery consists of oxalic acid and sodium hydroxide, with an oxalic acid concentration of 0.1–10 mol / L and a sodium hydroxide concentration of 0.1–15 mol / L. The pH value of the aqueous electrolyte is 4–10. This invention utilizes the low solubility of silver oxalate formed by the silver positive electrode and the electrolyte during charging to suppress the loss of positive electrode material, increase battery capacity, and thus improve the cycle stability of the battery. Furthermore, the zinc negative electrode undergoes a redox reaction with the aqueous electrolyte, preventing the dissolution and redeposition of zinc metal, thereby solving the problem of zinc dendrite growth in silver-zinc batteries and improving the cycle stability of the battery. The positive electrode specific capacity of the present invention is more than 34% higher than that of the prior art, and after 2000 charge-discharge cycles, its specific capacity can still be maintained at close to 96.7% of its initial state.

Description

Technical Field

[0001] This invention relates to the field of silver-zinc battery technology, specifically a silver-zinc battery cathode, its preparation method, and its application. Background Technology

[0002] Alkaline silver-zinc (Ag-Zn) batteries possess advantages such as high energy density, stable output potential, and environmental friendliness, making them one of the most promising aqueous batteries. However, their specific capacity is low (reported in literature as 100 mAg). -1 The poor specific capacity and cycle stability of alkaline silver-zinc batteries (Energy Storage Materials, 2020, 31, 44) significantly limit their application in large-scale energy storage. The reasons for the low specific capacity and poor cycle stability of alkaline silver-zinc batteries are generally considered to be twofold: First, the silver anode dissolves during cycling. For example, the dissolution of silver oxides such as Ag₂O formed during charging can lead to the loss of cathode material, thus reducing battery capacity. Second, zinc dendrites can form during cycling, which may puncture the separator, causing internal short circuits and affecting the battery's cycle stability.

[0003] To address these two issues, researchers have conducted extensive studies. The research group of Professor Niu Zhiqiang at Nankai University (Carbon Energy 2021, 3, 167) used PVA-KOH as the electrolyte for silver-zinc batteries to slow down zinc dendrite growth and extend the cycle life. However, this method did not help address the poor battery cycle performance caused by the dissolution of silver oxide formed during charging at the silver cathode. Furthermore, this method did not improve the specific capacity of the silver-zinc battery. The research group of Professor Zhi Chunyi at City University of Hong Kong (Energy Storage Materials 2019, 25, 3) used mild zinc chloride as the electrolyte for silver-zinc batteries. Compared to alkaline electrolytes, zinc dendrites were significantly suppressed in the neutral electrolyte. Moreover, the reversibility of the redox reaction between chloride ions and silver was much greater than that between hydroxide ions and silver (the solubility of silver chloride is much lower than that of silver oxide). However, this method still did not solve the problem of zinc dendrite growth. Furthermore, it remains to be seen whether there are substances with lower solubility than silver chloride compounds formed during the charging process of the silver cathode to reduce the loss of cathode material and thus improve the cycle stability of the battery. Although the above studies have improved the cycle stability of silver-zinc batteries to some extent, these methods have not fundamentally solved the problem of zinc dendrite growth or minimized the solubility of compounds formed on the silver cathode during charging. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a silver-zinc battery positive electrode, an aqueous electrolyte, its preparation method, and its applications. The aim is to suppress the loss of positive electrode material and increase battery capacity by forming a new compound (silver oxalate) with the electrolyte during charging, whose solubility is lower than that of silver chloride and silver oxide. This improves the battery's cycle stability. Furthermore, the zinc negative electrode undergoes a redox reaction with the electrolyte, preventing the dissolution and redeposition of zinc metal, thus fundamentally solving the problem of zinc dendrite growth in silver-zinc batteries and further enhancing the battery's cycle stability.

[0005] To achieve the above objectives, according to one aspect of the present invention, a silver-zinc battery positive electrode is provided, comprising silver oxalate, which is obtained by charging silver in an aqueous electrolyte. The silver oxalate has a particle size of 10–200 nm, exhibiting a nanoparticle structure. The aqueous electrolyte comprises a mixed solution of oxalic acid and sodium hydroxide, wherein the concentration of oxalic acid is 0.1–10 mol / L, the concentration of sodium hydroxide is 0.1–15 mol / L, and the pH value of the mixed solution of oxalic acid and sodium hydroxide is 4–10.

[0006] Preferably, the silver oxalate has a particle size of 10–80 nm.

[0007] Preferably, the oxalic acid concentration is 0.3–5 mol / L.

[0008] Preferably, the concentration of sodium hydroxide is 0.3 to 10 mol / L.

[0009] Preferably, the pH value of the electrolyte is 6.5 to 7.5.

[0010] According to another aspect of the present invention, a method for preparing a silver oxalate positive electrode generated during the charging process of the above-mentioned electrolyte with silver is also provided, comprising the following steps:

[0011] S1: Using metallic silver as the positive electrode, metallic zinc as the negative electrode, and glass fiber as the separator, 0.05–0.5 ml of the above-mentioned aqueous electrolyte is added and encapsulated into a coin cell. The metallic zinc includes at least one of zinc foil, zinc nanoparticles, and zinc nanowires.

[0012] S2: Charge the coin cell to 1.8–2.2V at a current density of 0.1–10A / g.

[0013] Preferably, the electrolyte is 0.1–0.3 ml;

[0014] Preferably, the metallic silver is silver nanowires and / or silver nanoparticles;

[0015] Overall, compared with the prior art, the above-described technical solutions conceived in this invention, using silver oxalate as the positive electrode of a silver-zinc battery and a mixture of oxalic acid and sodium hydroxide as the electrolyte, can achieve at least the following beneficial effects.

[0016] 1. This invention addresses the problem of poor cycle stability in current alkaline silver-zinc batteries by using a mixed solution of oxalic acid and sodium hydroxide as the electrolyte. This alters the reactions occurring at the positive and negative electrodes of the silver-zinc battery, suppresses the loss of positive electrode material, and improves battery capacity. The specific capacity of the zinc oxalate positive electrode reaches 164 mA / g, which is 34% higher than that of existing neutral electrolyte silver-zinc batteries (Energy Storage Materials 2019, 25, 3).

[0017] 2. This invention addresses the problem of poor cycle stability in current alkaline silver-zinc batteries by using a novel electrolyte that reacts with zinc to suppress the loss of positive electrode material, thereby fundamentally improving the cycle stability of silver-zinc batteries. After 2000 charge-discharge cycles, the specific capacity still maintains 96.7% of the initial state, which is 100% higher than the cycle count of existing technologies.

[0018] 3. In the new electrolyte, the zinc anode undergoes a redox reaction with the electrolyte, avoiding the dissolution and redeposition of the zinc anode, fundamentally preventing the growth of zinc dendrites, thereby extending the cycle life of the silver-zinc battery.

[0019] 4. A mixed solution of oxalic acid and sodium hydroxide is preferred as the electrolyte for silver-zinc batteries, and the pH value is adjusted to be close to neutral. This method is low-cost, simple, green and environmentally friendly, and suitable for large-scale production. Attached Figure Description

[0020] Figure 1 The X-ray diffraction patterns of the silver nanowires prepared in Comparative Example 1 and Example 1 of this invention are shown below.

[0021] Figure 2 These are scanning electron microscope images of the silver nanowires prepared in Comparative Example 1 and Example 1 of this invention;

[0022] Figure 3 This is a scanning electron microscope image of the silver nanowires prepared in Example 1 of the present invention after 2000 charge-discharge cycles.

[0023] Figure 4 The X-ray diffraction pattern of the silver nanowires prepared in Example 1 of this invention after 2000 cycles of charge and discharge.

[0024] Figure 5 The image shows a scanning electron microscope image of the zinc sheet of the silver-zinc button battery (zinc chloride electrolyte) prepared in Comparative Example 1 of this invention after 2000 charge-discharge cycles.

[0025] Figure 6 Scanning electron microscope image of the zinc sheet of the silver-zinc button battery (novel electrolyte) prepared in Example 1 of the present invention after 2000 charge-discharge cycles;

[0026] Figure 7 The constant current charge-discharge diagram shows the silver-zinc button cell (zinc chloride electrolyte) prepared in Comparative Example 1 of this invention.

[0027] Figure 8 The constant current charge-discharge diagram is shown for the silver-zinc button cell (novel electrolyte) prepared in Example 1 of this invention.

[0028] Figure 9 The cycle life diagram shows the silver-zinc button cell (zinc chloride electrolyte) prepared in Comparative Example 1 of this invention.

[0029] Figure 10 This is a cycle life diagram of the silver-zinc button cell (novel electrolyte) prepared in Example 1 of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0031] This invention provides a silver-zinc battery cathode comprising silver oxalate, wherein the silver oxalate exhibits a nanoparticle structure with a particle size of 10–200 nm, preferably 10–80 nm. The novel electrolyte is composed of oxalic acid and sodium hydroxide, wherein the concentration of oxalic acid is 0.1–10 mol / L, preferably 0.3–5 mol / L, and the concentration of sodium hydroxide is 0.1–15 mol / L, preferably 0.3–10 mol / L. The pH value of the novel electrolyte is 4–10, preferably 6.5–7.5.

[0032] The silver oxalate positive electrode is generated during the charging process of the electrolyte and silver. The charging device is a coin cell battery. The electrolyte in the coin cell battery is 0.05–0.5 ml, preferably 0.1–0.3 ml. When the electrolyte is too low, it cannot completely wet the separator and positive and negative electrodes, reducing the zinc ion transport pathway and increasing the battery resistance, thus affecting the battery's capacity and cycle performance. Conversely, when the electrolyte is too high, leakage is likely to occur, corroding the coin cell battery casing and increasing self-discharge. The charging current density of the coin cell battery is 0.1–10 A / g, and the charging voltage is 1.8–2.2 V.

[0033] The pH value of the aqueous electrolyte determines the reaction of the negative electrode of the silver-zinc battery. If the pH value is too low, the metallic zinc negative electrode is prone to dissolution reaction with hydrogen ions in the solution, thus affecting the cycle life of the silver-zinc battery. If the pH value is too high, there is a serious hydrogen evolution reaction of metallic zinc during the charging and discharging process, which consumes electrolyte and affects the cycle life of the silver-zinc battery. Therefore, the preferred pH value of the new electrolyte is 6.5 to 7.5.

[0034] The above-mentioned method for preparing the positive electrode of the silver-zinc battery includes the following steps:

[0035] S1: In a beaker, oxalic acid and sodium hydroxide are mixed to form a solution, wherein the concentration of oxalic acid is 0.1-10 mol / L, the concentration of sodium hydroxide is 0.1-15 mol / L, and the pH value of the mixed solution is 4-10.

[0036] S2: Using metallic silver as the positive electrode, metallic zinc as the negative electrode, and glass fiber as the separator, 0.05–0.5 ml of the novel electrolyte prepared in S1 is used to assemble a coin cell. Smaller silver particle sizes shorten the ion transport distance between the aqueous electrolyte and metallic zinc, thus improving the battery's electrochemical performance. Therefore, small-sized silver nanowires or silver nanoparticles are preferred as the metallic silver positive electrode material; metallic zinc is preferably selected from at least one of zinc foil, zinc nanoparticles, and zinc nanowires.

[0037] S3: The button cell is charged to 1.8–2.2V at a current density of 0.1–10A / g. The higher the charging current density, the less fully the metallic silver reacts with the new electrolyte at the same charging potential; if the charging voltage exceeds 2.2V, a severe oxygen evolution reaction will occur at the positive electrode; if the voltage is below 1.8V, the reaction between silver and the new electrolyte will be incomplete.

[0038] Comparative Example 1

[0039] Two beakers, labeled A and B, were prepared. In beaker A, 0.1 g of polyvinylpyrrolidone, 0.5 mg of ferric chloride, and 10 ml of ethylene glycol were added and stirred until dissolved. In beaker B, 1 g of AgNO3 and 10 ml of ethylene glycol solution were added and stirred until dissolved. Then, the liquid in beaker B was added dropwise to beaker A. After the liquid was prepared, it was placed in an autoclave at 160 °C for 2.5 hours. After natural cooling, it was centrifuged to obtain silver nanowires.

[0040] Prepare 100 ml of 0.1 mol / L zinc chloride solution in a beaker. Use silver nanowires as the positive electrode, zinc foil as the negative electrode, and glass fiber as the separator. Add 0.1 ml of zinc chloride electrolyte and encapsulate to form a coin cell. Charge to 1.5 V at a current density of 1 A / g to obtain the silver chloride positive electrode.

[0041] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0042] Example 1

[0043] S1: Dissolve 0.1g polyvinylpyrrolidone and 0.5mg ferric chloride in 10ml of ethylene glycol solution, then add dropwise 1g AgNO3 dissolved in 10ml of ethylene glycol solution, stir for 10 minutes, place in an autoclave at 160℃ for 2.5 hours, and centrifuge after natural cooling to obtain silver nanowires;

[0044] S2: Take two beakers. Prepare 100 ml of 1 mol / L oxalic acid solution in beaker A and 200 ml of 1 mol / L sodium hydroxide solution in beaker B. Add the solution from beaker B dropwise into beaker A until the pH value of the beaker is 7, thus obtaining a new electrolyte.

[0045] S3: Using the silver nanowires obtained above as the positive electrode, zinc foil as the negative electrode, and glass fiber as the separator, 0.1 ml of a novel electrolyte was added, and the mixture was encapsulated into a coin cell. The coin cell was charged to 2.2V at a current density of 1 A / g to obtain the silver oxalate positive electrode.

[0046] The preparation conditions for Examples 2-8 are listed in Table 1, and the rest are the same as in Example 1.

[0047] Table 1 Preparation conditions of Examples 2-8

[0048]

[0049] Experimental Results and Analysis

[0050] Figure 1 and Figure 2 The X-ray diffraction patterns (JCPDS 04-0783) and scanning electron microscope images of the silver nanowires prepared in Comparative Example 1 and Example 1 are shown respectively. It can be seen that pure silver was obtained in Example 1 and Comparative Example 1 without any other impurities. The pure silver prepared is nanowire with a length of 1-8 μm and a diameter of 10-30 nm.

[0051] Figure 3 The image shown is a scanning electron microscope image of the silver nanowires prepared in Example 1 after 2000 charge-discharge cycles. It can be seen that after 2000 charge-discharge cycles, the morphology of the silver nanowires changed from nanowires to nanoparticles with a particle diameter of 10-80 nm. Figure 4 The X-ray diffraction pattern of the silver nanowires prepared in Example 1 after 2000 charge-discharge cycles shows that the silver nanowires also changed from pure silver to silver oxalate (JCPDS 22-1335) after 2000 charge-discharge cycles.

[0052] Figure 5The image shown is a scanning electron microscope image of the zinc sheet of the silver-zinc button battery (zinc chloride electrolyte) prepared in Comparative Example 1 of this invention after 2000 charge-discharge cycles. It can be seen that after 2000 charge-discharge cycles, a layer of nanosheets was uniformly grown on the surface of the zinc sheet, which is consistent with the zinc dendrites reported in the literature (ACS Appl. Mater. Interfaces 2018, 10, 26, 22059).

[0053] Figure 6 The image shown is a scanning electron microscope image of the zinc sheet of the silver-zinc button battery (novel electrolyte) prepared in Example 1 of this invention after 2000 charge-discharge cycles. It can be seen that after 2000 charge-discharge cycles, a uniform and dense layer of nanoparticles forms on the surface of the zinc sheet, and no nanoparticles are formed on the zinc sheet surface. Figure 5 The uniform presence of zinc dendrites indicates that the silver-zinc battery using the novel electrolyte can effectively prevent the growth of zinc dendrites, thereby extending the cycle life of the silver-zinc battery.

[0054] Figure 7 The image shows the constant current charge-discharge curve of the silver-zinc button cell (zinc chloride electrolyte) prepared in Comparative Example 1 of this invention. It can be seen that the charge-discharge curve has an ultra-flat discharge plateau, with a discharge plateau of 0.989 V and a discharge rate of 1 A / g. -1 At the discharge current density, the specific capacity is 122 mAh g. -1 . Figure 8 The constant current charge-discharge curve (1 A / g) of the silver-zinc button cell (novel electrolyte) prepared in Example 1 of this invention shows that the discharge plateau is 1.36 V, which is higher than the discharge plateau in Comparative Example 1 of this invention. This is beneficial to improving the output voltage of the silver-zinc battery. -1 At the discharge current density, the specific capacity is 164 mAh g. -1 Compared with Comparative Example 1 of the present invention, the specific capacity is increased by 34%, making it more suitable as a power supply device for hybrid electric vehicles and all electric vehicles with high output voltage and high energy density.

[0055] Figure 9 and Figure 10 The figures show the cycle life of the silver-zinc button cell (zinc chloride electrolyte) prepared in Comparative Example 1 and the silver-zinc button cell (novel electrolyte) prepared in Example 1, respectively. It can be seen that the silver-zinc battery using the novel electrolyte retains 96.7% of its initial capacity after 2000 charge-discharge cycles (1 A / g constant current charge-discharge), compared to... Figure 9 After 1000 charge-discharge cycles, it retains 84% ​​of its initial capacity, demonstrating a significant improvement in cycle stability.

[0056] The same tests were performed on Examples 2-8, yielding results similar to those of Example 1. It can also be seen that the silver oxalate cathodes obtained in Examples 1-8 exhibit a nanoparticle structure with a particle size of 10-200 nm. Examples 2-8 demonstrate good specific capacity and cycle stability.

[0057] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode for a silver-zinc battery, characterized in that, The invention includes silver oxalate, which is obtained by charging silver in an aqueous electrolyte, wherein the aqueous electrolyte comprises a mixed solution of oxalic acid and sodium hydroxide; the silver oxalate has a particle size of 10-80 nm; the silver oxalate cathode is specifically obtained by charging silver in an aqueous electrolyte to 1.8-2.2 V at a current density of 0.1-10 A / g; the oxalic acid concentration is 0.3-5 mol / L. The concentration of sodium hydroxide is 0.3~10 mol / L; the pH value of the aqueous electrolyte is 6.5~7.

5.

2. A method for preparing the positive electrode of a silver-zinc battery as described in claim 1, characterized in that, Includes the following steps: S1: An aqueous electrolyte is prepared using oxalic acid and sodium hydroxide; S2: Using metallic silver as the positive electrode, metallic zinc as the negative electrode, glass fiber as the separator, and aqueous electrolyte prepared in S1, a coin cell is assembled. S3: Charge the button cell to 1.8~2.2 V at a current density of 0.1~10 A / g.

3. The preparation method according to claim 2, characterized in that, The metallic silver is silver nanowires and / or silver nanoparticles.

4. The preparation method according to claim 2, characterized in that, The zinc metal is at least one of zinc foil, zinc nanoparticles, and zinc nanowires.

5. A silver-zinc battery, characterized in that, Includes the positive electrode as described in claim 1.

Images