A three-dimensional functional layer of zinc negative electrode, in-situ preparation method thereof and battery

Abstract

The invention discloses a three-dimensional functional layer of a zinc negative electrode, an in-situ preparation method thereof and a battery. The functional layer of the zinc negative electrode is a three-dimensional topological zinc layer prepared in-situ at a microscopic scale by an electrochemical method. The zinc negative electrode of the structure makes zinc particles regularly distributed at a microscopic scale. The three-dimensional functional layer of the zinc negative electrode provided by the invention can effectively buffer the volume shrinkage and expansion problems of the zinc negative electrode during the cycle, ensure the continuity of the electronic connection network, avoid the pulverization of the zinc negative electrode and the generation of zinc dendrites, and maintain the integrity of the zinc negative electrode after long-term circulation, thereby effectively improving the coulomb efficiency of the aqueous zinc ion battery and extending the cycle life. The preparation method is simple to operate, has low energy consumption, and can be operated on a large scale. Using the three-dimensional functional layer of the zinc negative electrode prepared by the invention, an aqueous zinc ion battery with excellent cycle stability and safety performance can be prepared, and the practical progress of high specific energy aqueous zinc ion batteries can be promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of aqueous zinc ion batteries, and in particular relates to a three-dimensional functional layer of a zinc negative electrode, an in-situ preparation method thereof, and a battery. Background Art

[0002] Aqueous zinc-ion batteries have a broad prospect in large-scale energy storage applications due to their high theoretical weight volume capacity, relatively low redox potential, environmental friendliness, low cost, and ease of mass production. However, as the negative electrode, the volume of metallic zinc will undergo repeated contraction and expansion during long-term cycles. Frequent volume changes may cause electronic contact inactivation and electrode pulverization. At the same time, during the battery charge and discharge cycle, due to the uneven deposition and dissolution of metallic zinc, dendrites are easy to grow on the surface of the negative electrode. The dendrites have poor adhesion to the metal matrix and are easy to detach from the negative electrode to form "dead zinc", and the pole piece is eventually pulverized. These have adverse effects on the battery, such as capacity attenuation, coulomb efficiency decline, and cycle life attenuation, which greatly limits the practical application of aqueous zinc-ion batteries. In recent years, a series of strategies have been proposed for the optimization of zinc negative electrodes, including macroscopic three-dimensional structure design of zinc metal negative electrodes, coating protection, and electrolyte modification. Although these strategies can effectively alleviate the dendrite problem, the preparation process is cumbersome, or the cost is high, or the battery energy density is reduced, which greatly hinders the practical application of aqueous zinc-ion batteries. Summary of the invention

[0003] Aiming at the problem that zinc negative electrode in aqueous zinc ion battery is easy to grow dendrites and the electrode volume expansion leads to electrode pulverization, the present invention provides an in-situ preparation method of a three-dimensional functional layer of zinc negative electrode. The zinc negative electrode functional layer has a three-dimensional topological network structure, and the three-dimensional functional layer has the characteristics of reversible dissolution-deposition of zinc. Compared with the traditional three-dimensional coating technology, the weight of inactive substances in the zinc negative electrode will not be increased. This structure can effectively buffer the problem of volume shrinkage and expansion, ensure good electronic contact, and effectively avoid the generation of zinc dendrites and dead zinc, greatly improving the coulomb efficiency and cycle life of the battery. At the same time, the preparation method is simple and low-cost, which is conducive to the practical application of aqueous zinc ion batteries.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] An in-situ preparation method of a zinc negative electrode three-dimensional functional layer, the method comprising the following steps:

[0006] 1) Mix triethyl phosphate and water in a certain proportion to form a transparent solution.

[0007] 2) Weigh a certain molar amount of zinc bistrifluoromethanesulfonate, dissolve it in the mixed solution in step 1), stir until completely dissolved, and let stand.

[0008] 3) Assembling a battery using metallic zinc as the negative electrode, then adding the electrolyte prepared in step 2), leaving it in an environment for a period of time to allow the electrolyte to fully contact the negative electrode, and then taking it out and packaging it.

[0009] 4) The battery is first discharged at a constant current and then charged at a constant current, and a modified zinc negative electrode is formed in situ after several cycles.

[0010] 5) The battery is disassembled, the zinc negative electrode is taken out, and it is washed with water to obtain the three-dimensional functional layer of the zinc negative electrode.

[0011] Preferably, the metallic zinc used is one or more of zinc flakes, foamed zinc, porous zinc and the like.

[0012] Preferably, the thickness of the metallic zinc used is 0.01 mm to 1 mm.

[0013] Preferably, triethyl phosphate and water are miscible in a certain proportion, wherein the mass fraction of triethyl phosphate is 10 wt % to 90 wt %.

[0014] Preferably, the solute in the specific electrolyte is zinc bistrifluoromethanesulfonate, and its concentration is 0.5 to 3.5 mol L -1 .

[0015] Preferably, the metal zinc is used as the negative electrode, and the zinc negative electrode is charged and discharged at a constant current to repeatedly deposit and peel, and the charge and discharge current density is 0.1 to 20 mA cm -2 , the deposition and stripping surface capacity is 0.1~20mA*h / cm 2 , the number of cycles is more than 5.

[0016] The modified zinc negative electrode comprising the three-dimensional functional layer described above can be used as a zinc negative electrode of an aqueous zinc ion battery or a zinc-based liquid flow battery.

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

[0018] 1. The present invention proposes a simple method for preparing a three-dimensional topological zinc functional layer with a stable microstructure. The three-dimensional functional layer of the zinc negative electrode is prepared in situ by an electrochemical method, which is conducive to the high stability and reversibility of the metal zinc negative electrode structure during the cycle. Compared with commercial metal zinc sheets, the coulombic efficiency of the zinc negative electrode is effectively improved and the cycle life is improved.

[0019] 2. The microscopic topological structure of the three-dimensional functional layer of the zinc negative electrode enables uniform three-dimensional spatial distribution of zinc, effectively avoiding the growth of dendrites and improving the safety and cycle stability of aqueous zinc-ion batteries.

[0020] 3. The three-dimensional functional layer of the zinc negative electrode has the characteristics of reversible dissolution-deposition of zinc. Compared with the traditional three-dimensional functional layer preparation technology, it will not increase the weight of inactive substances in the zinc negative electrode.

[0021] 4. The microscopic topological structure of the three-dimensional functional layer of the zinc negative electrode makes the zinc negative electrode self-supporting, which can effectively buffer the volume expansion problem and help maintain the continuity of the electronic conduction network in the zinc negative electrode. This feature can significantly improve the collapse and pulverization problems of the zinc negative electrode in the late cycle, effectively maintain the integrity of the negative electrode, and make the zinc negative electrode have good cycle stability.

[0022] 5. The preparation method is simple to operate, has low energy consumption, and is easy to further scale up. The obtained three-dimensional functional layer of metallic zinc can be used in different electrolytes and obtains good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 (a) is a high-resolution transmission electron micrograph of the zinc negative electrode in comparative example 1 and (b) is a high-resolution transmission electron micrograph of the three-dimensional functional layer of the zinc negative electrode in example 1 of the present invention.

[0024] Figure 2 (a) is a scanning electron microscope (SEM) image of the zinc negative electrode in comparative example 1 and (b) is a scanning electron microscope image of the zinc negative electrode including a three-dimensional functional layer in example 1 of the present invention after 30 cycles.

[0025] Figure 3 The zinc negative electrode prepared in Examples 1, 2 and Comparative Examples 1, 2, 3, and 4 was heated to 3 mol L -1 Comparison of medium and long cycle performance in Zn(TfO)2 electrolyte.

[0026] Figure 4 This is a full battery performance diagram of a zinc negative electrode including a three-dimensional functional layer in Example 4 of the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the drawings and embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0028] Example 1

[0029] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 2.18g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1mA*h / cm 2After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and it was washed with deionized water to obtain the zinc negative electrode containing the three-dimensional functional layer.

[0030] Example 2

[0031] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 0.73g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and it was washed with deionized water to obtain the zinc negative electrode containing the three-dimensional functional layer.

[0032] Example 3

[0033] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 0.73g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1mA*h / cm 2 After 10 cycles, the battery was disassembled, the zinc negative electrode was taken out, and it was washed with deionized water to obtain the zinc negative electrode containing the three-dimensional functional layer.

[0034] Example 4

[0035] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 0.73g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 5mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and it was washed with deionized water to obtain the zinc negative electrode containing the three-dimensional functional layer.

[0036] Example 5

[0037] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 0.73g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 5mA / cm 2 , surface capacity is 1mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and washed with water three times to obtain a zinc negative electrode containing a three-dimensional functional layer.

[0038] Comparative Example 1

[0039] Weigh 2.00g of water, weigh 2.18g of zinc bistrifluoromethanesulfonate and add them to the water, stir until completely dissolved, and let the electrolyte stand for 12h. Use the metal zinc sheet as the negative electrode and the copper sheet as the positive electrode, then add the electrolyte prepared above to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and then encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and the zinc negative electrode after the cycle was cleaned with deionized water.

[0040] The difference between Comparative Example 1 and Example 1 is that there is no triethyl phosphate in the solvent of the comparative example.

[0041] Comparative Example 2

[0042] Weigh 0.01g of triethyl phosphate and 1.99g of water, mix them evenly to form a transparent mixed solution. Weigh 2.18g of zinc bistrifluoromethanesulfonate into the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1 mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and the zinc negative electrode after the cycle was cleaned with deionized water.

[0043] The difference between Comparative Example 2 and Example 1 is that the amount of triethyl phosphate in the solvent of the comparative example is 1 wt %.

[0044] Comparative Example 3

[0045] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 3.75g of zinc bis(trifluoromethanesulfonyl)imide and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use the metal zinc sheet as the negative electrode and the copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. The half-cell is first discharged at a constant current and then charged at a constant current with a current density of 1 mA / cm 2 , surface capacity is 1mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and the zinc negative electrode was obtained by washing with deionized water.

[0046] The difference between Comparative Example 3 and Example 1 is that the solute in Comparative Example 3 is not zinc bistrifluoromethanesulfonate, but zinc bistrifluoromethanesulfonimide with the same concentration.

[0047] Comparative Example 4

[0048] Weigh 0.50g of triethyl phosphate and 1.50g of H2O, mix them evenly to form a transparent mixed solution. Weigh 0.15g of zinc bistrifluoromethanesulfonate and dissolve it in the above mixed solution, stir until completely dissolved, and let the electrolyte stand for 12h. Use a metal zinc sheet as the negative electrode and a copper sheet as the positive electrode, then add the above-prepared electrolyte to assemble a half-cell. Let the half-cell stand in the environment for a period of time to allow the electrolyte to fully contact the negative electrode, and encapsulate the battery. First, discharge the half-cell at a constant current and then charge it at a constant current, with a current density of 1mA / cm 2 , surface capacity is 1mA*h / cm 2 After 30 cycles, the battery was disassembled, the zinc negative electrode was taken out, and the zinc negative electrode was obtained by washing with deionized water.

[0049] The difference between Comparative Example 4 and Example 1 is that the concentration of zinc trifluoromethanesulfonate in Comparative Example 4 is lower than 0.5 mol L -1 .

[0050] The long cycle performance test results of the assembled half-cells were respectively obtained by using the zinc negative electrode obtained in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 as the negative electrode. The copper sheet was used as the positive electrode and 3 mol L -1 Zn(TfO)2 was used as the electrolyte and the test current density was 1 mA / cm 2 , surface capacity is 1mA*h / cm 2 . Testing the cycling stability and reversibility of the zinc anode.

[0051] Figure 1 is the HRTEM image of the three-dimensional zinc negative electrode obtained in Example 1 and the zinc negative electrode obtained in Comparative Example 1. Figure 1 (a) shows that the microstructure of the three-dimensional functional layer of the zinc negative electrode presents a regular similar topological structure. Figure 1 (b) shows that the zinc negative electrode obtained in Comparative Example 1 has a disorderly distributed granular structure in its inner layer.

[0052] Figure 2 1 is a cross-sectional SEM image of the zinc negative electrode including the three-dimensional functional layer obtained in Example 1 and the zinc negative electrode obtained in Comparative Example 1. Figure 2 In (a), it can be seen that the cross section of the zinc negative electrode containing the three-dimensional functional layer is flat after cycling, the thickness remains basically unchanged, and there is still a lot of fresh metal zinc remaining. Figure 2 (b) shows that the cross section of the zinc negative electrode obtained in Comparative Example 1 has moss-like dead zinc, structural collapse, and volume expansion.

[0053] Figure 3 The long cycle performance test results of the assembled half-cells using the zinc negative electrodes obtained in Examples 1 and 2 and Comparative Examples 1, 2, 3, and 4 as negative electrodes. As can be seen from the figure, the zinc negative electrodes containing the three-dimensional functional layer obtained in Examples 1 and 2 have a long cycle performance of 3 mol L -1 The Zn(TfO)2 electrolyte can still be stably cycled for more than 100 cycles while maintaining a relatively high coulombic efficiency (>90%). However, the zinc negative electrodes obtained in Comparative Examples 1, 2, 3, and 4 fail prematurely, or the coulombic efficiency quickly drops below 70%.

[0054] Figure 4 The electrochemical performance of the full battery assembled with the zinc negative electrode containing the three-dimensional functional layer and the vanadium pentoxide positive electrode in Example 1 was tested at a rate of 5C. The zinc negative electrode containing the three-dimensional functional layer can stably cycle the full battery for more than 500 cycles, and the specific capacity is maintained at 250 mA*hg -1 , which further illustrates the practicality of the zinc negative electrode containing a three-dimensional functional layer described in the present invention.

Claims

1. A three-dimensional functional layer of a zinc negative electrode, characterized in that: The three-dimensional functional layer is obtained in situ by electrochemical method of metal zinc in a specific electrolyte; the specific electrolyte is a solution obtained by using zinc bistrifluoromethanesulfonate as solute and a mixed solution of triethyl phosphate and water as solvent, and the concentration of zinc bistrifluoromethanesulfonate is 0.5-3.5 mol L -1 The mass fraction of triethyl phosphate in the solvent is 10 wt% to 90 wt%, and the pores distributed inside the three-dimensional functional layer form a three-dimensional interconnected topological network structure.

2. The three-dimensional functional layer of the zinc negative electrode according to claim 1, characterized in that: The pore size is less than 10 nm.

3. The three-dimensional functional layer of the zinc negative electrode according to claim 1, characterized in that: The metal zinc is one or more of zinc flakes, foamed zinc and porous zinc.

4. The three-dimensional functional layer of the zinc negative electrode according to claim 3, characterized in that: The thickness of the metal zinc is 0.01 mm to 1 mm.

5. The three-dimensional functional layer of the zinc negative electrode according to claim 1, characterized in that: The electrochemical method is as follows: using metal zinc as the negative electrode, the zinc negative electrode is charged and discharged at a constant current to repeatedly deposit and peel, and the charge and discharge current density is 0.1~20 mAcm -2 , the deposition and stripping surface capacity is 0.1~20 mAh cm -2 , the number of cycles is more than 5.

6. A method for preparing a three-dimensional functional layer of a zinc negative electrode as claimed in any one of claims 1 to 5, characterized in that: The steps include: 1) Mix triethyl phosphate and water evenly to form a transparent solution; 2) Weigh zinc bistrifluoromethanesulfonate, dissolve it in the solution in step 1), stir until completely dissolved, and let the electrolyte stand; 3) Assembling a symmetrical cell or half-cell with zinc metal as the negative electrode, then adding the electrolyte prepared in step 2) and leaving it in an environment for a period of time to allow the electrolyte to fully contact the negative electrode; 4) The battery is first discharged at a constant current and then charged at a constant current, and a modified zinc negative electrode can be formed in situ after several cycles; 5) Disassemble the battery in step 4), take out the zinc negative electrode, and wash it with water to obtain the three-dimensional functional layer of the zinc negative electrode.

7. An aqueous zinc ion battery, characterized in that: A modified zinc negative electrode is used, wherein the modified zinc negative electrode comprises the three-dimensional functional layer as described in any one of claims 1 to 5.

8. A zinc-based flow battery, characterized in that: A modified zinc negative electrode is used, wherein the modified zinc negative electrode comprises the three-dimensional functional layer as described in any one of claims 1 to 5.

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