Preparation and application of zinc negative electrode modified by organic-inorganic interface layer

Abstract

The invention discloses preparation and application of an organic-inorganic interface layer modified zinc negative electrode. The preparation method comprises the following steps: firstly, dispersing organic polymer polylactic acid and zinc sulfide powder into tetrahydrofuran, then coating the surface of zinc foil with the dispersed solution, and drying a solvent at 70 DEG C, so as to prepare the zinc negative electrode modified by an organic-inorganic interface layer. According to the interface layer, zinc ion deposition is regulated and controlled, and the problem of zinc dendrite growth is solved. In addition, the polylactic acid-zinc sulfide composite coating can effectively improve the redox kinetics of zinc ions and improve the coulombic efficiency of the zinc negative electrode. Due to the good ionic conductivity, the interface modification layer can improve diffusion of zinc ions, and the polarization influence caused by the concentration gradient of the zinc ions is relieved. Therefore, the prepared polylactic acid-zinc sulfide composite interface layer modified zinc negative electrode symmetric battery has more excellent cycling stability, the half battery has more stable coulombic efficiency, and the assembled total battery has more prominent capacity retention rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode material preparation, and specifically relates to the preparation and application of a zinc negative electrode modified with an organic-inorganic interface layer. Background Art

[0002] With the continuous development of society, people's demand for renewable resources is increasing day by day, which promotes the development of safe, stable and low-cost chemical energy storage systems. With the continuous exposure of problems such as the safety, high cost and low ionic conductivity of lithium-ion batteries, many researchers are driven to develop a more reliable energy storage system. Among them, aqueous zinc-ion batteries are considered to be one of the most promising energy storage systems because of their high safety, low cost and high ionic conductivity. However, problems such as dendrite growth, hydrogen evolution side reaction, corrosion / passivation of the zinc negative electrode result in poor stability and Coulombic efficiency of the zinc negative electrode, which seriously hinders the commercialization of zinc-ion batteries. To solve the current problems of the zinc negative electrode, researchers have mainly proposed the following improvement methods, including the structural design of the zinc negative electrode, electrolyte modification, separator modification, and interface modification layer of the zinc negative electrode. Among them, the simplest and most effective method is the interface modification layer of the zinc negative electrode. The interface modification layer materials reported in the past include metals, inorganic salts, organic substances, and oxide coatings, and they show different effects due to different materials.

[0003] Chinese Patent CN114613933A discloses a porous CeO2 interface modification layer synthesized by a one-step solvothermal method. Since CeO2 has good corrosion resistance and stability, when it is used on the surface of the zinc negative electrode, it can significantly inhibit the hydrogen evolution side reaction and corrosion. The zincophilic oxygen atoms in CeO2 can induce the deposition of zinc ions by adsorption, and improve the deposition mode of zinc ions to achieve the effect of inhibiting dendrite growth. Therefore, the CeO2@Zn / / CeO2@Zn symmetric battery can stably cycle for 1000 hours under the conditions of 0.5 mA·cm -2 、0.5 mAh·cm -2 , and the CeO2@Zn / / Ti half-cell can stably cycle 400 times at 2 mA·cm -2 、1 mAh·cm -2 , and the cycle stability of the zinc negative electrode is also improved.

[0004] Chinese Patent CN117293261A discloses a method of pulverizing sphalerite, mixing it with an adhesive and an organic solvent to prepare a slurry, and coating the slurry on the surface of a zinc negative electrode. This can effectively isolate the direct contact between the electrolyte and the zinc negative electrode during the cycling process, so as to slow down the occurrence of the hydrogen evolution side reaction and corrosion. In addition, natural sphalerite has excellent zincophilicity, which can provide nucleation sites for the deposition process of zinc ions, so as to improve the zinc ion deposition and inhibit the growth of dendrites. Therefore, the cycling stability of the sphalerite-coated zinc negative electrode is improved.

[0005] Chinese Patent CN118522884A discloses an interface modification layer obtained by thermally decomposing phosphate into metaphosphate through a gas-phase method, and an interface modification layer is in-situ synthesized on the surface of the zinc negative electrode. Since the synthesized metaphosphate has good ionic conductivity, it can accelerate the transport of zinc ions, so as to reduce the influence brought by concentration polarization. On the other hand, this metaphosphate can act as a physical barrier to isolate the electrolyte from the zinc negative electrode, so as to weaken the occurrence of the hydrogen evolution side reaction and corrosion of the zinc negative electrode. The heat-treated metaphosphate can induce the rearrangement of zinc crystal planes during the deposition process and form a zinc negative electrode with a highly oriented (002) crystal plane. Therefore, the modified zinc negative electrode can stably cycle under more severe conditions.

[0006] Although these materials can significantly overcome the shortcomings of the zinc negative electrode such as dendrite growth and side reactions, in the previous studies on the interface modification of the zinc negative electrode, the issue of the discharge depth of the modified zinc negative electrode is often lacking. This is because many modified negative electrodes can rarely stably cycle at a high discharge depth, which will inevitably lead to the problem of low utilization rate of the zinc negative electrode material. In addition, many studies on the interface modification of the zinc negative electrode rarely conduct tests on cycling at a larger current density. Research shows that when the current density increases, the degree of dendrite growth and hydrogen evolution side reaction of the zinc negative electrode will intensify, so it is difficult to stably cycle. Moreover, under high-intensity discharge conditions, the interface modification layers of many zinc negative electrodes will face the situation that it is difficult to stably maintain the modification layer due to the destruction of the zinc structure. Therefore, in order to enable the zinc negative electrode to be used at a higher discharge depth, it is very necessary to study an interface modification layer that can support the stable cycling of the zinc negative electrode under harsh conditions. Summary of the Invention

[0007] Aiming at the above technical problems, the present invention provides a preparation method and application of an organic-inorganic interface-modified zinc negative electrode. The poly(lactic acid) (PLA) and zinc sulfide (ZnS) are prepared on the zinc surface by a coating method, which inhibits dendrite growth and improves the redox kinetics. The interface modification layer with good ionic conductivity can significantly improve the transport of zinc ions. Therefore, the modified composite-coated zinc negative electrode can stably cycle at a higher current density.

[0008] To achieve the above object, the present invention provides a zinc negative electrode modified with an organic-inorganic interface layer, comprising a zinc substrate and a polylactic acid-zinc sulfide interface modification layer coated on its surface.

[0009] A method for preparing a zinc negative electrode modified with an organic-inorganic interface layer, comprising the following steps: (1) Mix and disperse polylactic acid, zinc sulfide and tetrahydrofuran to obtain a dispersion; (2) Uniformly coat the dispersion on the surface of zinc foil and dry it to obtain a zinc negative electrode modified with a polylactic acid-zinc sulfide interface modification layer, PZS@Zn.

[0010] The mass ratio of the polylactic acid to the zinc sulfide is 1:(0.25 - 1), preferably 1:0.5.

[0011] The mass ratio of the polylactic acid to the tetrahydrofuran is 1:(400 - 500), and the purity of the tetrahydrofuran is ≥99.5%.

[0012] The dispersion time in step (1) is 10 - 12 h, and the obtained dispersion is milky white.

[0013] The coating method in step (2) is at least one of drop coating, spraying or spin coating; the drying condition is drying with hot air at 70 - 100 °C for 8 - 12 h.

[0014] The zinc foil in step (2) is a pretreated zinc foil, and the zinc foil pretreatment steps are: placing the zinc foil in an organic solvent for ultrasonic cleaning, and then cutting and flattening the zinc foil; The organic solvent is ethanol or acetone, and the mass percentage is ≥95%; the zinc foil is cut into small round pieces with an area of 1.13 cm 2 area.

[0015] The zinc negative electrode modified with the organic-inorganic interface layer is used as a negative electrode material in an aqueous zinc ion battery.

[0016] An aqueous zinc ion battery uses the zinc negative electrode modified with the organic-inorganic interface layer as the negative electrode.

[0017] For the aqueous zinc ion battery, the positive electrode material is at least one of CNT@MnO2 or MnO2, preferably CNT@MnO2; the electrolyte is an aqueous zinc salt solution; the separator is a glass fiber.

[0018] The beneficial effects of the present invention are as follows: 1. A zinc negative electrode with a PLA-ZnS coating is prepared by a coating technique. Due to its excellent zincophilicity, this coating can significantly improve the redox kinetic performance of zinc ions.

[0019] 2. The prepared interfacial modified zinc anode can significantly improve the dendrite growth problem of the zinc anode and can stably cycle at a larger current density.

[0020] 3. The PLA-ZnS coated modified zinc anode has excellent deposition and stripping capabilities, can stabilize the cycling process of the zinc anode, and thus has a more stable Coulombic efficiency.

[0021] 4. PLA-ZnS can be assembled with the cathode material of CNT@MnO2 into a full battery, which can improve the capacity retention rate of the full battery.

[0022] 5. The present invention prepares a PLA-ZnS interfacial modification layer by a coating method, which has the advantages of simple process, short time consumption, low material price, and significant effect, is applicable to aqueous zinc batteries, and can be widely promoted and applied. Description of the Drawings

[0023] Figure 1 The zinc anodes prepared in Examples 1-4 and the zinc anodes prepared in Comparative Examples 1-3 were tested under the conditions of 5 mA·cm -2 and 2.5 mAh·cm -2 .

[0024] Figure 2 The zinc anodes prepared in Example 2 and Comparative Example 3 were tested under the conditions of 10 mA·cm -2 and 20 mAh·cm -2 .

[0025] Figure 3 Fourier transform infrared spectroscopy test diagrams of the electrodes prepared in Example 2 and Comparative Example 1.

[0026] Figure 4 High-resolution S 2p spectrograms of X-ray photoelectron spectroscopy tests of Example 2, Comparative Example 3, and ZnS powder.

[0027] Figure 5 The electrodes prepared in Example 2 and Comparative Examples 1-3 were assembled with a Cu electrode into a half-cell and tested under the conditions of 2 mA·cm -2 , 1 mAh·cm -2 .

[0028] Figure 6 (a) SEM test diagram of the electrode prepared in Comparative Example 3; (b) SEM test diagram of the electrode prepared in Example 2.

[0029] Figure 7 (a) SEM test diagram of the electrode prepared in Comparative Example 3 after cycling for a period of time; (b) SEM test diagram of the electrode prepared in Example 2 after cycling for a period of time.

[0030] Figure 8 The electrodes prepared in Example 2 and Comparative Example 3 and the cathode material prepared in Example 4 were assembled into a full cell for charge-discharge cycling at 2 A·g -1 The charge-discharge cycling diagram is shown below. Detailed implementation manners

[0031] The embodiments of the present invention will be described in detail below in conjunction with the examples. The following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0032] Example 1 (1) Cleaning of the anode material: Place the zinc foil in an ethanol solution and ultrasonically clean it for 2 min to obtain a clean and tidy zinc foil. Then cut it into a zinc disc with an area of 1.13 cm 2 and flatten the cut disc.

[0033] (2) Weigh 2 mg of PLA and 0.5 mg of ZnS (the mass ratio of PLA to ZnS is 1:0.25) with an electronic balance and add them to a 5-ml glass bottle. Add a stir bar of appropriate size and pipette 1 ml of tetrahydrofuran (purity 99.5%) into the bottle.

[0034] (3) Place the glass bottle on a magnetic stirrer at a stirring speed of 400 r / min for 12 hours to ensure that PLA and ZnS are evenly dispersed in tetrahydrofuran.

[0035] (4) Pipette 40 μl of the dispersed solution and evenly drop it onto the flattened zinc foil to ensure full coverage. Place the drop-coated zinc foil in a forced-air drying oven to dry the solvent at 70°C for 12 hours to obtain PZS (1:0.25) @Zn.

[0036] Example 2 The method and steps are the same as those in Example 1, except that the mass of ZnS in step (2) is changed to 1 mg (the mass ratio of PLA to ZnS is 1:0.5), and a PZS (1:0.5) @Zn-coated zinc anode is prepared.

[0037] Example 3 The method and steps are the same as those in Example 1, except that the mass of ZnS in step (2) is changed to 2 mg (the mass ratio of PLA to ZnS is 1:1), and a PZS (1:1) @Zn-coated zinc anode is prepared.

[0038] Example 4 The method and steps are the same as those in Example 2, except that the drying condition in step (4) is changed to: drying the solvent in a vacuum drying oven.

[0039] Comparative Example 1 The method and steps are the same as those in Example 1, except that the mass of ZnS in step (2) is changed to 0 mg, and a PLA@Zn-coated zinc negative electrode is prepared.

[0040] Comparative Example 2 The method and steps are the same as those in Example 1, except that the mass of PLA in step (2) is changed to 0 mg, and a ZnS@Zn-coated zinc negative electrode is prepared.

[0041] Comparative Example 3 The pure zinc negative electrode was washed with ethanol and sonicated for 2 minutes to obtain a clean zinc foil, which was then cut into a circular foil with a size of 1.13 cm 2 to obtain a Bare Zn electrode.

[0042] Example 5 The synthesis of the CNT@MnO2 cathode material was carried out using the method reported in previous literature. First, 0.25 g of CNT was ultrasonically dispersed in 50 mL of aqueous solution containing 1.69 g of Mn(CH3COO)2·4H2O for 30 minutes. Then, it was added to 60 mL of KMnO4 aqueous solution (the content of KMnO4 was 0.727 g / 60 mL), and then continuously stirred and heated at 85 °C for 5 hours. The obtained solid product (CNT@MnO2) was filtered, washed with deionized water multiple times, and dried at 60 °C for 8 hours. Then, the dried CNT@MnO2, conductive carbon black, and PVDF were uniformly mixed in a mass ratio of 7:2:1, and a slurry was prepared using NMP as a solvent and uniformly coated on the surface of a 0.1-mm-thick graphite paper. The coated cathode material was dried at 80 °C for 12 hours for use. Each cathode material was cut into a circular piece with an area of 1.13 square centimeters, and the active material content on each circular piece was between 0.6 and 1.0 mg per square centimeter.

[0043] Analysis and testing: (1) Two zinc negative electrodes prepared in Examples 1 to 4 and two zinc negative electrodes prepared in Comparative Examples 1 to 3 were each assembled with a 2M ZnSO4 electrolyte, a glass fiber separator, a positive electrode case, a negative electrode case, gaskets, and shrapnel into a symmetric cell. Tests were carried out under the conditions of 5 mA·cm -2 and 2.5 mAh·cm -2 , and the test software used was the LAND battery test system. The test process included first performing constant current discharge and then charging until the battery short-circuited or exceeded the protection voltage. The results are as Figure 1 shown, where the BareZn symmetric cell short-circuited after cycling for 49 hours under these conditions; while PZS (1:0.25)The Zn symmetric battery was cycled for 530 hours. At this time, due to the small amount used, the improvement in cycling performance was not significant. PZS (1:0.5) The Zn symmetric battery short-circuited after being cycled for more than 1280 hours. PZS (1:1) The Zn symmetric battery was cycled for more than 690 hours, the PLA@Zn symmetric battery was cycled for more than 770 hours, and the cycling duration of the ZnS@Zn symmetric battery was 320 hours. However, when the amount of ZnS was too low, due to the poor conductivity of the PLA material, the improvement effect on the zinc anode was not significant. When the amount of PLA was small, the ZnS material was prone to be damaged at high discharge depths because of its certain rigidity and was difficult to play a protective role. Only when the amounts of PLA and ZnS were appropriate, the improvement effect on the zinc anode was better. When the sample was prepared in a vacuum drying oven, the obtained sample was PZS (1:0.5) The cycling performance of the @Zn withoutoxided was far inferior to that of the sample prepared in a forced-air drying oven, which was related to the oxidation of zinc sulfide when it contacted with air during the drying process in Examples 1-3. In this patent, the one with the most excellent cycling performance was PZS (1:0.5) For the @Zn electrode, if not specified otherwise later, the PZS@Zn mentioned all refers to PZS (1:0.5) @Zn electrode.

[0044] (2) Take two zinc anodes prepared in Example 2 and Comparative Example 3 respectively, and assemble them into symmetric batteries together with 2 M ZnSO4 electrolyte, glass fiber separator, positive electrode case, negative electrode case, gasket and shrapnel. At 10 mA·cm -2 and 20 mAh·cm -2 conditions for testing, and the testing software used was the LAND battery testing system. The testing process included first performing constant current discharge and then charging until the battery short-circuited or exceeded the protection voltage. The results are as Figure 2 shown. Among them, Bare Zn short-circuited after being cycled for 40 hours under this condition, while the PZS@Zn electrode short-circuited after being cycled for 650 hours. The stability was improved by more than 15 times compared with the pure zinc electrode. At this time, the discharge depth reached more than 36%, which required a very high ability of the modified electrode to inhibit dendrite growth and side reactions, indicating that the PZS coating could significantly inhibit dendrite growth and the occurrence of side reactions.

[0045] (3) Fourier transform infrared spectroscopy tests were carried out on the electrodes prepared in Example 2 and Comparative Example 1, and the test wavenumber range was 500~4000 cm -1 , and the results are as Figure 3 shown. In the infrared spectroscopy results of the PLA@Zn electrode and PZS@Zn, the characteristic peaks of polylactic acid could correspond to each other. Among them, the sources of the peaks were as follows. At 2996 cm -1 and 2948 cm-1 At -1 , stretching vibration absorption peaks of C-H bonds on methyl and secondary carbon were respectively observed; at 1757 cm -1 there appeared a stretching vibration absorption peak of carbonyl group; at 1582 cm -1 it might be the absorption peak of carbon-oxygen double bond in cyclic lactone; at 1457 cm -1 and 1369 cm -1 corresponded to the bending vibration absorption peak and asymmetric stretching vibration absorption peak of antisymmetric methyl respectively; at 1184 cm -1 and 1092 cm -1 were the antisymmetric and symmetric stretching vibration absorption peaks of C-O-C bond respectively; at 1044 cm -1 was the carbon-methyl vibration of lactic acid unit; at 872 cm -1 was the asymmetric stretching vibration absorption peak of C-O bond; while at 713 cm -1 corresponded to the asymmetric stretching vibration absorption peak of C-C single bond. It indicated the existence of polylactic acid material on the electrode.

[0046] (4)X-ray photoelectron spectroscopy tests were carried out on the samples of Example 2 and Comparative Example 3 with ZnS powder. The results are as Figure 4 shown. In the high-resolution spectrum of S 2p, the Bare Zn surface contained no sulfur, while the peaks of PZS@Zn and ZnS powder were at 161.6 eV and 162.6 eV respectively, which were attributed to S 2p 1 / 2 and S 2p 3 / 2 of Zn-S bond respectively; the existence state of PZS@Zn electrode was different from that of ZnS powder. Since ZnS in the PZS@Zn electrode would undergo slow oxidation in air, a peak of sulfite appeared at 168.9 eV. These sulfides in different states and PLA formed a solid electrolyte film on the surface of zinc anode. Combining Figure 1 the data, it can be known that the oxidation of part of ZnS into sulfite can promote the improvement of cycling performance.

[0047] (5)The electrodes prepared in Example 2 and Comparative Examples 1 - 3 were assembled with Cu electrodes into half-cells, and half-cell cycling was carried out under the conditions of 2 mA·cm -2 , 1 mAh·cm -2 . The test software was LAND battery test system, and the test process was constant current first discharge and then charge until the battery short-circuited or exceeded the protection voltage. The results are as Figure 5As shown, Bare Zn / / Cu shorted after 100 cycles, and the Coulombic efficiency was unstable; while the PLA@Zn / / Cu and ZnS@Zn / / Cu half-cells shorted after 240 and 590 cycles respectively, and the PZS@Zn / / Cu cell shorted after 860 cycles and had a more stable Coulombic efficiency, indicating that the PZS coating can significantly improve the zinc deposition and stripping ability and the stability of the zinc anode.

[0048] (6)The electrodes prepared in Example 2 and Comparative Example 3 were subjected to SEM testing, and the results are as Figure 6 shown. By observing the SEM of pure zinc (6a), it was found that there were obvious unevenness on its surface, which easily led to uneven deposition of zinc ions and thus triggered the growth of dendrites. On the surface of PZS@Zn (6b), it can be seen that the PZS coating uniformly covered the zinc surface in small spherical shapes. This uniform PZS coating can effectively isolate the electrolyte from the zinc anode, thereby reducing the probability of the hydrogen evolution side reaction, and this small spherical distribution can provide more nucleation sites for the deposition of zinc ions.

[0049] (7)The electrodes prepared in Example 2 and Comparative Example 3 were cycled for 6 hours at a current density of 1 mA·cm -2 and 0.5 mAh·cm -2 , and then the surface morphology was tested. The results are as Figure 7 shown. It can be clearly observed that there were obvious dendrite growths on the surface of pure zinc after cycling (7a), while the zinc deposition on the surface of PZS@Zn was uniform and there was no obvious dendrite growth (7b), which means that the PZS coating can promote the uniform deposition of zinc ions and inhibit the growth of dendrites.

[0050] (8)The electrodes prepared in Example 2 and Comparative Example 3 were respectively assembled with the cathode material prepared in Example 5 into full cells and charged and discharged at 2 A·g -1 . The test software was the LAND battery test system, and the test process was constant current first discharge and then charge until the battery shorted or exceeded the protection voltage. The results are as Figure 8 shown. The initial specific capacity of the unmodified full cell was 138 mAh·g -1 . After 800 cycles, the specific capacity dropped to 71.8 mAh·g -1 , and the capacity retention rate was 52.0%. While the initial capacity of the full cell with the modified electrode was 171.2 mAh·g -1 . After 800 cycles, the specific capacity almost remained at 169.7 mAh·g -1 , and the capacity retention rate was as high as 99.1%. This further indicates that the PZS coating significantly improves the cycling performance of the full cell.

Claims

1. A zinc negative electrode modified with an organic-inorganic interface layer, characterized in that, It includes a zinc substrate and a polylactic acid-zinc sulfide interfacial modification layer coated on its surface.

2. A preparation method of a zinc negative electrode modified by an organic-inorganic interface layer, characterized in that, It includes the following steps: (1) Mix and disperse polylactic acid, zinc sulfide, and tetrahydrofuran to obtain a dispersion; (2) Uniformly coat the dispersion on the surface of zinc foil and dry it to obtain a zinc negative electrode PZS@Zn modified with a polylactic acid-zinc sulfide interfacial modification layer.

3. The preparation method according to claim 2, characterized in that, The mass ratio of the polylactic acid to the zinc sulfide is 1:(0.25 - 1), preferably 1:0.

5.

4. The preparation method according to claim 2, characterized in that, The mass ratio of the polylactic acid to the tetrahydrofuran is 1:(400 - 500), and the purity of the tetrahydrofuran is ≥99.5%.

5. The preparation method according to claim 2, characterized in that, The dispersion time in step (1) is 10 - 12 h, and the obtained dispersion is milky white.

6. The preparation method according to claim 2, characterized in that, The coating method in step (2) is at least one of drop coating, spraying, or spin coating; the drying condition is blowing drying at 70 - 100 °C for 8 - 12 h.

7. The preparation method according to claim 2, characterized in that, The zinc foil in step (2) is a pretreated zinc foil. The zinc foil pretreatment steps are: placing the zinc foil in an organic solvent for ultrasonic cleaning, and then cutting and flattening the zinc foil; The organic solvent is ethanol or acetone with a mass percentage ≥ 95%; the zinc foil is cut into small round pieces with an area of 1.13 cm 2 2.

8. Use of a zinc negative electrode modified with an organic-inorganic interface layer as described in claim 1 or a zinc negative electrode modified with an organic-inorganic interface layer obtained by the preparation method described in any one of claims 2 to 8, characterized in that, It is used as a negative electrode material in an aqueous zinc ion battery.

9. An aqueous zinc-ion battery, characterized in that, Using the zinc negative electrode described in claim 1 or the zinc negative electrode obtained by the preparation method described in any one of claims 2 - 8 as the negative electrode.

10. The aqueous zinc-ion battery according to claim 9, characterized in that, The positive electrode material is at least one of CNT@MnO2 or MnO2, preferably CNT@MnO2; the electrolyte is an aqueous zinc salt solution; The separator is glass fiber.

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