Preparation method for constructing metal electrode with stable deposition structure through thermal driving

Abstract

The invention discloses a preparation method of a metal electrode for constructing a stable deposition structure through thermal driving. The preparation method comprises the following steps: cutting an active metal sheet / foil into a size required by the metal electrode; the metal electrode is subjected to oxide removal treatment; and the metal electrode treated in the second step is subjected to heat treatment in the protective atmosphere, natural cooling is conducted after heat treatment is finished, and the metal electrode with the stable deposition structure constructed through thermal driving is obtained. According to the method, the optimal structure of the metal electrode can be obtained in one step through simple heating, compared with an untreated metal electrode, the obtained metal electrode material has the advantages that polishing marks disappear, machining stripes become finer, and the electrochemical performance is obviously improved. The method is simple to operate and high in repetition rate, and can be used for large-scale production.

Description

Technical Field

[0001] The present invention relates to the field of secondary battery metal electrodes, and in particular to material selection, structural design and preparation methods of metal electrodes. Background Art

[0002] Metal batteries have attracted extensive attention due to their ultra-high theoretical capacity and low electrochemical potential. However, there is inevitable dendrite growth during battery operation, which not only penetrates the separator and causes battery short circuit, but also accelerates the side reaction between the electrolyte and the metal electrode at the interface, leading to electrolyte depletion and battery damage. This limits the application of metal batteries in the next generation of secondary batteries. Therefore, solving the dendrite growth problem is the key to improving the comprehensive performance of metal battery systems.

[0003] From the perspective of the cause, dendrites are mainly caused by the uneven ion flow during metal ion transfer and the oriented growth of the deposition reaction. The growth site and growth rate are affected by multiple factors such as the surface state of the metal electrode, the surface ion distribution, and the exposed crystal planes of the crystal. Studies have shown that crystal stress in metal electrodes can lead to rapid growth of dendrites, which in turn leads to a decrease in battery performance and an increase in the risk of short circuits. The stress in metal electrodes is mainly caused by changes in lattice size, changes in crystal structure, and phase transitions between crystals and amorphous phases accompanied by insertion / removal reactions. This change causes the electrode material to deform to resist the constraints of inactive areas of the electrode or other parts of the battery. Therefore, increased stress in the electrode material is one of the main reasons for the capacity decay and eventual failure of metal batteries.

[0004] During the machining process, metal electrodes have problems such as rough electrode surface and increased stress, which hinders the further development of metal batteries. At present, there is little research on metal electrode processing technology at home and abroad. Therefore, it is of great significance to improve the crystal structure of metal electrodes by using low-cost and easy-to-control methods to improve the stability of deposition reactions on the surface of metal electrodes and promote the large-scale application of metal batteries. Summary of the invention

[0005] In response to the problems raised in the background technology, the present invention aims to provide a method for preparing a metal electrode with a thermally driven stable deposition structure, by heating the metal electrode at a certain temperature to obtain the optimal exposed crystal surface of the metal, thereby promoting uniform ion distribution on the surface of the metal electrode and reducing stress.

[0006] The present invention is specifically implemented by the following method.

[0007] A method for preparing a metal electrode with a thermally driven stable deposition structure comprises the following steps:

[0008] 1) Cut the active metal sheet / foil to the required size of the metal electrode;

[0009] 2) removing oxide from the metal electrode;

[0010] 3) The metal electrode treated in step 2) is subjected to heat treatment under a protective atmosphere, and is naturally cooled after the heat treatment to obtain a metal electrode with a thermally driven stable deposition structure.

[0011] Preferably, the protective atmosphere is one or more of nitrogen, helium, neon, krypton, and xenon, and more preferably, argon.

[0012] Preferably, the active metal sheet / foil is selected from one of metals such as lithium, sodium, potassium, magnesium, zinc, etc. or an alloy thereof.

[0013] Preferably, the thickness of the metal sheet / foil is 0.01-0.5 mm, more preferably 0.08-0.21 mm.

[0014] Preferably, the oxide removal treatment can be performed by sandpaper polishing, electrolysis, ultrasonic cleaning, etc., wherein the sandpaper size can be 500-3000 mesh, more preferably 900-1800 mesh.

[0015] Preferably, the heat treatment is carried out under a protective atmosphere. When the metal electrode is zinc metal, the heating temperature is 200-400°C, when the metal electrode is lithium metal, the heating temperature is 50-100°C, and when the metal electrode is sodium metal, the heating temperature is 100-200°C; the heating time is 20-180 min, more preferably 100-140 min.

[0016] Preferably, a constant temperature heating table is used for heat treatment. During the heat treatment, the metal electrode is turned over at a turning speed of 30 to 140 rpm, more preferably 60 to 110 rpm.

[0017] Compared with the prior art, the present invention has the following advantages and outstanding effects:

[0018] In the process of preparing metal electrodes, it is inevitable to mechanically process metal blocks or sheets, resulting in irregular metal crystal structures on the metal electrode surfaces. The present invention can obtain the optimal structure of the metal electrode in one step by simply heating. Compared with the untreated metal electrode, the obtained metal electrode material has no polishing marks, thinner processing stripes, and significantly improved electrochemical performance. The method is simple to operate, has a high repetition rate, and can be mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the voltage distribution diagram in the corresponding symmetrical battery of the zinc electrode before heat treatment and the 60min-zinc electrode in Example 1.

[0020] Figure 2This is the corresponding SEM image of the 20min-zinc electrode prepared in Example 1.

[0021] Figure 3 This is the corresponding SEM image of the 60min-zinc electrode prepared in Example 1.

[0022] Figure 4 Graph showing performance parameters of lithium, sodium and zinc metal batteries prepared in Examples 1-3. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited thereto.

[0024] Example 1

[0025] (1) A 0.08 mm thick zinc foil was polished with 1500 mesh sandpaper and then cut into 12 mm*12 mm zinc electrode sheets (before heat treatment).

[0026] (2) Under nitrogen gas protection, a constant temperature heating plate was used to stabilize the temperature at 350°C, and the zinc electrode sheet was placed on it for heat treatment for 20 min and 60 min respectively. During the heat treatment process, it was flipped at a flipping speed of 60 rpm to expose the (001) crystal plane of the zinc electrode.

[0027] (3) Under nitrogen protection, the zinc sheets heat-treated for 20 min and 60 min were removed from the constant temperature heating plate and allowed to cool naturally, thereby obtaining two heat-treated zinc electrodes, which were named 20 min-zinc electrode and 60 min-zinc electrode, respectively.

[0028] (4) The proportion I 2 I mixed with activated carbon 2 Add the powder to deionized water, mix well, and freeze-dry. 2 @C), conductive carbon black and binder polyvinylidene fluoride were uniformly ground in a ratio of 8:1:1, and added to n-methylpyridone solvent and mixed. The mixed solution was coated on aluminum foil. After drying, I 2 @C electrode.

[0029] (5) Weigh an appropriate amount of ZnSO 4 Mix with a certain proportion of deionized water. Stir to obtain ZnSO 4 Transparent liquid.

[0030] (6) Under the protection of protective gas, the 60min-zinc electrode obtained in step (3) was used as the working electrode to assemble a button cell. The separator was a Whatman glass microfiber separator, and the electrolyte was the prepared ZnSO 4 Solution. According to the positive electrode shell-I 2 @C electrode-80ml ZnSO4 The electrolyte-Whatman glass microfiber separator-zinc metal negative electrode-negative electrode shell was assembled, and the obtained zinc full battery was allowed to stand at 25°C for 12 hours.

[0031] The corresponding SEM images of the 20min-zinc electrode and the 60min-zinc electrode are shown in Figure 2. Figure 2 , as shown in Figure 3, we can see the changing trend of zinc structure at different temperatures.

[0032] Example 2

[0033] (1) A 0.06 mm thick lithium metal was polished with 1600-grit sandpaper and then cut into a 16 mm diameter circular lithium electrode sheet.

[0034] (2) Under nitrogen gas protection, a constant temperature heating plate was used to stabilize the temperature at 80°C, and a lithium electrode sheet was placed thereon for heat treatment for 60 min. During the heat treatment, the sheet was flipped at a speed of 60 rpm to expose the (110) crystal plane of the lithium metal electrode.

[0035] (3) Under the protection of nitrogen gas, the lithium sheet is then removed from the constant temperature heating plate and allowed to cool naturally to obtain a heat-treated lithium electrode sheet.

[0036] (4) LiFePO 4 , conductive carbon black, and binder polyvinylidene fluoride were evenly ground in a ratio of 8:1:1 and mixed in n-methylpyridone solvent. 4 The solution was coated on aluminum foil and dried to obtain LiFePO 4 electrode.

[0037] (5) Under the protection of protective gas, the heat-treated lithium electrode sheet is used as the working electrode to assemble a button cell. The diaphragm is a polyethylene diaphragm, and the positive electrode is LiFePO 4 Electrode. The electrolyte is 1 mol / L LiPF 6 Dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) electrolyte with a volume ratio of 1:1. 4 Electrode - 80ml LiPF 6 The electrolyte-polyethylene separator-lithium metal negative electrode-negative electrode shell was assembled, and the obtained lithium full battery was allowed to stand at 25°C for 12 hours.

[0038] Example 3

[0039] (1) A 0.01 mm thick sodium metal was polished with 1400 grit sandpaper and then cut into a 16 mm diameter circular sodium electrode sheet.

[0040] (2) Under nitrogen gas protection, a constant temperature heating plate was used to stabilize the temperature at 150° C., and a sodium electrode sheet was placed thereon for heat treatment for 60 min. During the heat treatment, the sheet was flipped at a speed of 60 rpm to expose the (110) crystal plane of the sodium metal electrode.

[0041] (3) Under the protection of nitrogen gas, the sodium sheet is then removed from the constant temperature heating plate and allowed to cool naturally to obtain a heat-treated sodium electrode sheet.

[0042] (4) NVP, conductive carbon black, and binder polyvinylidene fluoride are uniformly ground in a ratio of 8:1:1 and mixed in an n-methylpyridone solvent. The NVP solution is coated on an aluminum foil and dried to obtain an NVP electrode.

[0043] (5) Under the protection of protective gas, the heat-treated sodium electrode sheet was used as the working electrode to assemble a button cell. The diaphragm was Whatman glass microfiber diaphragm, the positive electrode was NVP electrode, and the electrolyte was 1 mol / L NaPF 6 Dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC) electrolyte with a volume ratio of 1:1. According to the positive electrode shell-NVP positive electrode-80ml NaPF 6 The electrolyte-Whatman glass microfiber separator-sodium metal negative electrode-negative electrode shell was assembled, and the obtained sodium full battery was allowed to stand at 25°C for 12 hours.

[0044] Performance Testing

[0045] The heat-treated metal electrodes prepared in Examples 1 to 3 were used as the counter electrode and working electrode of button cells respectively. The Zn symmetric cell used 1M ZnSO 4 electrolyte, current density 10mAcm -2 The Li symmetric battery and the Na symmetric battery use 1M LiPF 6 Electrolyte and 1M NaPF 6 The electrolyte was tested at a current density of 5 mAh cm -2 . Zn full battery, Li full battery and Na full battery use 1M ZnSO 4 Electrolyte, 1M LiPF 6 Electrolyte and 1MNaPF 6 The electrolyte and cathode materials are selected as I 2 @C electrode, LiFePO 4 Electrode and NVP electrode. The full cell test current density is 1C. The electrochemical performance of the symmetrical electrode and full cell is measured in an environment of 25±1℃.

[0046] The performance test results are as follows:

[0047] The zinc metal electrode of Example 1 was -2 After 1000 cycles at the current density, the voltage stabilized at 51 mV. The lithium metal electrode of Example 2 and the sodium metal electrode of Example 3 were stable at 0.5 mA cm -2 After 1600 cycles at the current density, the voltage can be stabilized within 28mV and 49mV respectively, and the voltage platform is stable without obvious fluctuations. This is because after the metal electrode is heated to a certain temperature, the metal ions can pass through the activation energy barrier and diffuse to the most stable exposed surface, forming the best metal structure. The voltage distribution diagram of the zinc electrode before heat treatment and the 60min-zinc electrode symmetric battery is shown in Figure 2. Figure 1 As shown, the performance parameters of batteries prepared with zinc, lithium and sodium electrodes are as follows Figure 4 shown.

Claims

1. A method for preparing a metal electrode with a thermally driven stable deposition structure, characterized in that: The steps include: 1) Cut the active metal sheet / foil to the required size of the metal electrode; 2) removing oxide from the metal electrode; 3) The metal electrode treated in step 2) is subjected to heat treatment under a protective atmosphere, and is naturally cooled after the heat treatment to obtain a metal electrode with a thermally driven stable deposition structure.

2. The method according to claim 1, characterized in that The protective atmosphere is one or more of nitrogen, helium, neon, krypton and xenon, preferably argon.

3. The method according to claim 1, characterized in that The active metal sheet / foil is selected from one of lithium, sodium, potassium, magnesium, zinc metals or alloys thereof.

4. The method according to claim 1, characterized in that The thickness of the metal sheet / foil is 0.01-0.5 mm, more preferably 0.08-0.21 mm.

5. The method according to claim 1, characterized in that The oxide removal treatment may be performed by sandpaper polishing, electrolysis, ultrasonic cleaning, etc., wherein the sandpaper size may be 500-3000 mesh, more preferably 900-1800 mesh.

6. The method according to claim 1, characterized in that The heat treatment is carried out under a protective atmosphere. When the metal electrode is zinc metal, the heating temperature is 200-400 °C, when the metal electrode is lithium metal, the heating temperature is 50-100 °C, and when the metal electrode is sodium metal, the heating temperature is 100-200 °C; the heating time is 20-180 min, more preferably 100-140 min.

7. The method according to claim 1, characterized in that A constant temperature heating table is used for heat treatment. During the heat treatment, the metal electrode is turned over at a turning speed of 30 to 140 rpm, more preferably 60 to 110 rpm.

Images