Preparation method of zinc bromide / lithium bromide composite electrolyte for zinc ion battery

Abstract

The invention relates to a high-concentration aqueous zinc ion battery electrolyte, and aims to improve the electrochemical performance of a battery, especially the low-temperature ion transport capacity, the working temperature range and the cycle life of the battery. The electrolyte comprises zinc bromide, lithium bromide and deionized water, the concentration of the zinc bromide is 5-12 mol / L, the concentration of the lithium bromide is 10-24 mol / L, and the molar ratio of the zinc bromide to the lithium bromide is 1: (0.2-5). And lithium bromide is added as an additive, so that a long-range ordered local cluster network of zinc bromide is broken, the high-entropy electrolyte is formed, and the ionic conductivity and the electrochemical performance are remarkably improved. Experimental results show that the electrolyte shows excellent ionic conductivity and coulombic efficiency at different temperatures, and is suitable for a wide working temperature range.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary energy storage batteries, and particularly relates to an aqueous zinc-ion battery electrolyte and a preparation method thereof. Background Art

[0002] The sustainability of the environment and resources has become increasingly important for the development of next-generation battery technologies, which need to meet the growing market for renewable energy storage in smart grids and automotive electrification. Lithium-ion battery (LIBs) technology currently dominates this field due to its high energy density and long cycle life. However, as the demand for energy storage capacity continues to increase, price and resource fluctuations caused by the scarcity of lithium and transition metals are attracting more and more attention. In addition, LIBs require an energy-intensive manufacturing process, usually using toxic and environmentally unfriendly chemicals. The potential safety issues during the operation of LIBs and their tolerance to mechanical abuse have not been fully resolved.

[0003] Since zinc (Zn) is compatible with aqueous electrolytes, aqueous zinc batteries have become one of the promising battery types. Zinc is relatively abundant and the recycling infrastructure is mature. Recently, the application of "water-in-salt" electrolytes has expanded the electrochemical stability window of aqueous electrolytes and enabled new electrochemical properties, including zinc batteries that were previously limited to primary use. However, the advantages of salt-in-water electrolytes for aqueous zinc batteries are not sufficient to overcome the commercialization barriers because of the poor reversibility of zinc plating / stripping, insufficient energy efficiency, and weak low-temperature transport ability.

[0004] Different from simply increasing the salt concentration in a single-salt electrolyte, adding concentrated supporting salts has proven to be another promising strategy that can largely exclude the solvation of water for Zn in aqueous solutions. 2+ Therefore, the hydrolysis ability of this electrolyte is significantly reduced, while the reversibility of zinc plating / stripping is correspondingly improved. Moreover, since the "free water" in the electrolyte is bound by the concentrated salts, the freezing point of the electrolyte is greatly reduced, thereby enhancing its low-temperature ion transport ability. Summary of the Invention

[0005] The present invention aims to provide an aqueous zinc-ion battery electrolyte containing zinc bromide salt and lithium bromide salt, which reduces the length of zinc solvation structure aggregates and destroys the hydrogen bond network of free water through the synergistic action of anions and cations, thereby generating a unique high-entropy solvation structure, enhancing the low-temperature ion transport ability, inhibiting dendrite growth, and broadening the working temperature range.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A high-concentration aqueous zinc-ion battery electrolyte, characterized in that the aqueous zinc-ion battery electrolyte includes zinc bromide, lithium bromide and deionized water, and specifically includes the following steps:

[0007] (1) At 20 °C, use a pipette to transfer 5 mL of deionized water with a conductivity less than 18 μs / cm into a 10 mL glass vial;

[0008] (2) At 20 °C, weigh a certain amount of zinc bromide salt and add it to deionized water. In the temperature range of 10 - 60 °C, add a magnetic stirrer and stir for 1 h, where the concentration of zinc bromide is 5 - 12 mol / L;

[0009] (3) At 20 °C, weigh a certain amount of lithium bromide salt and add it to the zinc bromide solution. In the temperature range of 10 - 60 °C, add a magnetic stirrer and stir the mixed solution for 1 h. After stirring, an aqueous zinc-ion battery electrolyte is obtained; where the concentration of lithium bromide is 10 - 24 mol / L;

[0010] (4) The molar ratio of the added zinc bromide salt to the lithium bromide salt is 1:(0.2 - 5)

[0011] Further, in the step (2), the concentration of the zinc bromide salt is 6 - 10 mol / L.

[0012] Further, in the step (3), the concentration of the lithium bromide salt is 10 - 24 mol / L.

[0013] Further, in the step (4), the molar ratio of the added zinc bromide salt to the lithium bromide salt is 1:(0.5 - 4).

[0014] Further, in the steps (2) and (3), the temperature range is 20 - 40 °C.

[0015] In the above technical solution of the present invention, zinc bromide salt dissolved in pure water solvent is used as an electrolyte for the blank sample, and its electrochemical performance is improved by adding lithium bromide as an additive. The electrolyte of a single high-concentration zinc bromide salt dissolved in pure water has a long-range ordered local cluster network, the free solvent network is destroyed, and the free solvent is restricted in the cluster network, thus restricting the ion transport ability, resulting in a significant reduction in ionic conductivity, thereby affecting the electrochemical performance. After adding lithium bromide, additional bromide ions are given to zinc bromide to satisfy the preferred tetrahedral coordination structure of the tetrabromozincate anion, thereby breaking its long-range ordered local cluster network and becoming shorter aggregates, forming a so-called high-entropy electrolyte.

[0016] The aqueous zinc-ion battery electrolyte of the present invention includes zinc bromide, lithium bromide and deionized water; compared with the blank sample electrolyte, it has stronger low-temperature ion transport ability, a wider operating temperature range, and more excellent cycle life. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of the solvation structure of the high-entropy electrolyte

[0018] Figure 2 It is the Coulomb efficiency curve of the electrolyte of this aqueous zinc-ion battery compared with that of the blank sample electrolyte

[0019] Figure 3 It is the ionic conductivity curve of the electrolyte of this aqueous zinc-ion battery and the blank sample electrolyte at different temperatures Detailed Embodiments

[0020] The following will elaborate on the present invention in further detail in combination with specific embodiments. It should be understood that the embodiments described in the present invention are only preferred embodiments of the present invention and are not used to limit the embodiments of the present invention

[0021] Example 1

[0022] At room temperature, use a pipette to transfer 5 mL of deionized water into a 10 mL glass vial, and then weigh 6.76 g of zinc bromide salt and 2.61 g of lithium bromide and add them to the deionized water. Stir magnetically with a magnetic stirrer for 1 h. After the stirring is completed, an electrolyte for an aqueous zinc-ion battery is obtained. Using a zinc foil as the negative electrode, this aqueous electrolyte as the electrolyte, and a copper foil as the positive electrode, a CR2025 type button battery is assembled. Use a LAND battery test system to perform constant current charge and discharge tests. The test current density is 0.5 mAh / cm 2 , and the test procedure is to discharge for 1 h, charge to 0.5 V, and repeat the charge and discharge. At different temperatures, use a conductivity meter to test the blank sample electrolyte and this aqueous electrolyte, and compare the ionic conductivity of the two

[0023] Example 2

[0024] At room temperature, use a pipette to transfer 5 mL of deionized water into a 10 mL glass vial, and then weigh 7.88 g of zinc bromide salt and 3.03 g of lithium bromide and add them to the deionized water. Stir magnetically with a magnetic stirrer for 1 h. After the stirring is completed, an electrolyte for an aqueous zinc-ion battery is obtained. Using a zinc foil as the negative electrode, this aqueous electrolyte as the electrolyte, and a copper foil as the positive electrode, a CR2025 type button battery is assembled. Use a LAND battery test system to perform constant current charge and discharge tests. The test current density is 0.5 mAh / cm 2 , and the test procedure is to discharge for 1 h, charge to 0.5 V, and repeat the charge and discharge. At different temperatures, use a conductivity meter to test the blank sample electrolyte and this aqueous electrolyte, and compare the ionic conductivity of the two

[0025] Example 3

[0026] At room temperature, use a pipette to transfer 5 mL of deionized water into a 10 mL glass vial. Then, weigh 9 g of zinc bromide salt and 3.47 g of lithium bromide and add them to the deionized water. Stir with a magnetic stirrer for 1 h to obtain an aqueous zinc-ion battery electrolyte. Using a zinc foil as the negative electrode, this aqueous electrolyte as the electrolyte, and a copper foil as the positive electrode, assemble a CR2025 type button battery. Use a LAND battery test system to conduct a constant current charge-discharge test, with a test current density of 0.5 mAh / cm 2 , and the test procedure is to discharge for 1 h, charge to 0.5 V, and repeat the charge-discharge process. At different temperatures, use a conductivity meter to test the blank sample electrolyte and this aqueous electrolyte, and compare the ionic conductivity of the two.

[0027] Example 4

[0028] At room temperature, use a pipette to transfer 5 mL of deionized water into a 10 mL glass vial. Then, weigh 10.13 g of zinc bromide salt and 3.90 g of lithium bromide and add them to the deionized water. Stir with a magnetic stirrer for 1 h to obtain an aqueous zinc-ion battery electrolyte. Using a zinc foil as the negative electrode, this aqueous electrolyte as the electrolyte, and a copper foil as the positive electrode, assemble a CR2025 type button battery. Use a LAND battery test system to conduct a constant current charge-discharge test, with a test current density of 0.5 mAh / cm 2 , and the test procedure is to discharge for 1 h, charge to 0.5 V, and repeat the charge-discharge process. At different temperatures, use a conductivity meter to test the blank sample electrolyte and this aqueous electrolyte, and compare the ionic conductivity of the two.

[0029] Example 5

[0030] At room temperature, use a pipette to transfer 5 mL of deionized water into a 10 mL glass vial. Then, weigh 11.26 g of zinc bromide salt and 4.34 g of lithium bromide and add them to the deionized water. Stir with a magnetic stirrer for 1 h to obtain an aqueous zinc-ion battery electrolyte. Using a zinc foil as the negative electrode, this aqueous electrolyte as the electrolyte, and a copper foil as the positive electrode, assemble a CR2025 type button battery. Use a LAND battery test system to conduct a constant current charge-discharge test, with a test current density of 0.5 mAh / cm 2 , and the test procedure is to discharge for 1 h, charge to 0.5 V, and repeat the charge-discharge process. At different temperatures, use a conductivity meter to test the blank sample electrolyte and this aqueous electrolyte, and compare the ionic conductivity of the two.

[0031] Example Initial cycle Coulomb efficiency (%) Average Coulomb efficiency in cycles (%) 1 91.3 99.1 2 93.5 99.3 3 94.8 99.4 4 96.8 99.7 5 97.1 99.7

Claims

1. A high-concentration aqueous zinc ion battery electrolyte, characterized in that: The aqueous zinc ion battery electrolyte comprises zinc bromide, lithium bromide and deionized water, and specifically comprises the following steps: (1) At 20°C, use a pipette to transfer 5 mL of deionized water with a conductivity of less than 18 μs / cm into a 10 mL glass vial; (2) At 20°C, weigh a certain amount of zinc bromide salt and add it to deionized water. Stir with a magnetic stirrer for 1 hour at a temperature range of 10-60°C, wherein the zinc bromide concentration is 5-12 mol / L; (3) At 20° C., weigh a certain amount of lithium bromide salt and add it to zinc bromide solution. At a temperature range of 10-60° C., add a magnetic particle to stir the mixed solution for 1 hour. After the stirring is completed, an aqueous zinc ion battery electrolyte is obtained; wherein the lithium bromide concentration is 10-24 mol / L; (4) The molar ratio of the added zinc bromide salt to the lithium bromide salt is 1:(0.2-5).

2. The aqueous zinc ion battery electrolyte according to 1, characterized in that: The concentration of zinc bromide salt in step (2) is 6-10 mol / L.

3. The aqueous zinc ion battery electrolyte according to 1, characterized in that: The concentration of lithium bromide salt in step (3) is 10-24 mol / L.

4. The aqueous zinc ion battery electrolyte according to 1, characterized in that: The molar ratio of the zinc bromide salt to the lithium bromide salt added in step (4) is 1:(0.5-4).

5. The aqueous zinc ion battery electrolyte according to 1, characterized in that: The temperature range in step (2) and step (3) is 20-40°C.

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