Aqueous battery and electrolyte thereof

Abstract

The present invention relates to aqueous battery systems, specifically to an aqueous battery electrolyte comprising a homogeneous aqueous solution containing an electrolyte salt and a compound (#imgabs0#) of Formula 1. In Formula 1, n is an integer from 1 to 4. The concentration of the compound (#imgabs0#) in the aqueous battery electrolyte is 3 to 18 M. The present invention also provides applications of the aqueous electrolyte, which exhibits excellent low-temperature performance.

Description

Technical Field

[0001] The invention belongs to the technical field of aqueous battery energy storage and relates to an aqueous battery electrolyte. Technical Background

[0002] The vigorous development of the new energy industry cannot be separated from the construction of energy storage systems, because it can meet the convenient use of energy by storing and releasing energy in a timely manner. Secondary batteries, as efficient carriers of energy storage and conversion, have therefore been favored by energy storage system applications. Compared with the currently commercialized lithium-ion batteries, aqueous batteries have an irreplaceable advantage in using water as a solvent. On the one hand, water, as a flame retardant, can protect batteries from the risk of fire and explosion; in addition, water and water-soluble electrolytes are relatively inexpensive, which helps to reduce the cost of batteries, and the components of aqueous batteries are not sensitive to air and can be assembled in an atmospheric atmosphere with simple manufacturing conditions; the ionic conductivity of aqueous electrolytes (about 0.1S cm -1 ), much higher than that of organic electrolytes (1-10mS cm -1 ), so it has excellent rate performance and power density. Aqueous solvents also have the advantages of being non-toxic and environmentally friendly, and they also have huge advantages in the recycling of discarded batteries. The above advantages make aqueous batteries extremely promising for application in energy storage systems. The aqueous batteries that are currently being studied more are aqueous lithium-ion batteries and aqueous zinc-ion batteries. However, because they are aqueous solution systems, the freezing point of the electrolyte is generally low (around -10°C). When the operating temperature is around zero degrees, the performance of the aqueous battery will drop significantly. When it reaches around minus ten degrees, the battery is basically unusable, especially in areas north of the Yangtze River in China. Aqueous batteries cannot be used normally throughout the year. Therefore, designing a high-performance aqueous electrolyte that is resistant to low temperatures is crucial for the practical application of aqueous batteries.

[0003] On the other hand, aqueous lithium-ion batteries often suffer from short cycle life due to corrosion by hydrogen protons in water and unstable electrode material structures, which seriously restricts their development. Furthermore, aqueous zinc-based ion batteries face problems such as dendrites, corrosion, and hydrogen evolution at the zinc anode, which also hinder their development. Therefore, designing a high-performance aqueous electrolyte that can operate over a wide temperature range is of great significance to the development of aqueous batteries. Summary of the Invention

[0004] The first object of the present invention is to provide an electrolyte for an aqueous battery, aiming to improve its low-temperature electrochemical performance.

[0005] The second object of the present invention is to provide an application of the electrolyte in assembling an aqueous battery.

[0006] A third object of the present invention is to provide an aqueous battery containing the aqueous electrolyte.

[0007] The electrolyte of aqueous batteries is prone to solidification at low temperatures, which will greatly affect the electrochemical performance. In response to the problem of unsatisfactory low-temperature performance of aqueous batteries, the main idea in the industry is to add low-freezing-point components to lower the overall freezing point of the electrolyte. However, in existing methods, while lowering the freezing point, it is easy to bring new problems, such as reducing the solubility of the electrolyte in the aqueous system, reducing the conductivity, increasing polarization, etc., making it difficult for the aqueous electrolyte to have both good antifreeze properties and low-temperature electrochemical performance. In response to this problem, the present invention has proposed the following solutions after extensive research:

[0008] An aqueous battery electrolyte, which is a homogeneous aqueous solution in which an electrolyte salt and a compound of formula 1 are dissolved;

[0009]

[0010] In formula 1, n is an integer of 1 to 4;

[0011] In the aqueous battery electrolyte, the concentration of the compound of formula 1 is 3 to 18M.

[0012] The present invention has found that the innovative use of Formula 1 as an antifreeze additive for aqueous electrolytes, combined with further concentration control, can achieve synergy and significantly improve the antifreeze properties of aqueous electrolytes. In addition, it can avoid the problems of decreased solubility and conductivity of electrolyte salts, and help reduce polarization and electrode corrosion. In this way, it is possible to achieve antifreeze while also taking into account excellent low-temperature electrochemical performance.

[0013] In the present invention, the control of the annular -CONH- structure in Formula 1 and its concentration is the key to synergistically improving the antifreeze property of the aqueous electrolyte, improving the electrical conductivity, reducing polarization, and thus improving the low-temperature electrochemical performance.

[0014] Preferably, in the compound of formula 1, n is 2 or 3, preferably 3.

[0015] Preferably, the concentration of the compound of formula 1 in the aqueous battery electrolyte is 4 to 12 M, preferably 6 to 8 M. Studies have found that at the preferred concentration, the aqueous electrolyte can achieve excellent frost resistance, low conductivity loss, and less polarization increase, thereby achieving both frost resistance and improved low-temperature electrochemical performance.

[0016] Preferably, the electrolyte salt is at least one of a water-soluble zinc salt and a water-soluble lithium salt;

[0017] Preferably, the water-soluble zinc salt is at least one of zinc sulfate, zinc acetate, zinc chloride, zinc trifluoromethanesulfonate, and zinc nitrate.

[0018] Preferably, the water-soluble lithium salt is at least one of lithium sulfate, lithium acetate, lithium chloride, lithium trifluoromethanesulfonate, and lithium nitrate.

[0019] Preferably, the electrolyte salt is zinc sulfate and / or lithium sulfate. The present invention has found that sulfate-type electrolyte salts are more susceptible to the effects of antifreeze additives, more likely to cause a decrease in solubility and crystallization after addition. However, in the present invention, thanks to the use of Formula 1, the effect of Formula 1 on the solubility of sulfate-type electrolyte salts can be avoided. Thus, while achieving good antifreeze properties, high low-temperature electrochemical performance can also be achieved.

[0020] Preferably, the concentration of the electrolyte salt is 0.2 to 3M, more preferably 1 to 2M.

[0021] Preferably, the aqueous battery electrolyte further comprises a water-soluble compound of formula 2:

[0022]

[0023] In formula 2, R is H, a C1-C2 alkyl group or a hydroxyalkyl group.

[0024] The present invention also discovered that, based on Formula 1, further combining Formula 2 can unexpectedly achieve synergy, which can further improve the low-temperature antifreeze properties of aqueous electrolytes. Not only that, it can also solve the problems of decreased electrolyte salt solubility, affected conductivity, and increased polarization caused by the addition of antifreeze additives, and can significantly improve the low-temperature electrochemical properties of aqueous electrolytes.

[0025] Preferably, in the aqueous battery electrolyte, the molar ratio of Formula 1 to Formula 2 is 6-8:0.1-2, more preferably 7-7.8:0.2-1.

[0026] Preferably, in the aqueous battery electrolyte, the concentration of the compound of formula 2 is less than or equal to 2M, preferably 0.5 to 1M.

[0027] The present invention also provides an application of the aqueous battery electrolyte, which is used as an electrolyte to assemble an aqueous battery;

[0028] Preferably, the electrolyte salt is a water-soluble zinc salt, and the electrolyte is assembled to form an aqueous zinc ion battery; or, the electrolyte salt is a water-soluble lithium salt, and the electrolyte is assembled to form an aqueous lithium ion battery; or, the electrolyte salt contains a water-soluble zinc salt and a water-soluble lithium salt, and the electrolyte is assembled to form an aqueous zinc-lithium dual ion battery.

[0029] The present invention also provides an aqueous battery, which comprises the aqueous battery electrolyte of the present invention.

[0030] The aqueous battery of the present invention may have known components, structures and materials except for the electrolyte of the present invention.

[0031] For example, preferably, the aqueous battery is an aqueous zinc ion battery, and in the electrolyte, the electrolyte salt is a water-soluble zinc salt;

[0032] Alternatively, the aqueous battery is an aqueous lithium-ion battery, and in the electrolyte, the electrolyte salt is a water-soluble lithium salt;

[0033] Alternatively, the aqueous battery is an aqueous zinc-lithium dual-ion battery, and in the electrolyte, the electrolyte salt is a water-soluble zinc salt and a water-soluble lithium salt;

[0034] Preferably, in the aqueous zinc ion battery, the active material of the positive electrode is at least one of activated carbon, polyaniline, manganese dioxide, vanadium pentoxide, polypyrrole, and vanadium disulfide;

[0035] Preferably, in the aqueous lithium-ion battery, the active material of the positive electrode is at least one of lithium iron phosphate, lithium manganese oxide, and lithium cobalt oxide, and the active material of the negative electrode is at least one of vanadium dioxide and LiV3O8.

[0036] Beneficial effects

[0037] In the electrolyte described in the present invention, thanks to the use of the solid component with a high freezing point of Formula 1, further combined with the joint control of the addition concentration of Formula 1, the freezing point of the aqueous electrolyte can be unexpectedly significantly lowered. Not only that, it can also unexpectedly avoid the decrease in the solubility and conductivity of the water-soluble electrolyte salt, which helps to reduce electrode corrosion and polarization, and helps to significantly improve the low-temperature electrochemical performance of the aqueous electrolyte.

[0038] With the innovative use of Formula 1, further combined with Formula 2, unexpected synergy can be achieved, which can further synergistically improve the low-temperature performance of aqueous electrolytes and further improve the low-temperature electrochemical performance.

[0039] The aqueous electrolyte of the present invention has strong universality and can also obtain good low-temperature electrochemical performance in an aqueous lithium-ion battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The freezing point test data of aqueous electrolyte and the freezing conditions of electrolytes containing 0, 1, 6, 12, and 18 M of formula 1 (n=3) at -22°C.

[0041] Figure 2 Molecular dynamics simulation diagram of aqueous zinc electrolyte system and the corresponding radial distribution function.

[0042] Figure 3 Comparison of the cycle life of aqueous Zn||Zn symmetric batteries at room temperature.

[0043] Figure 4 Comparison of the cycle life of aqueous Zn||Zn batteries at -20°C.

[0044] Figure 5 Comparison of linear polarization curves of aqueous Zn||Zn.

[0045] Figure 6 This is a test of the hydrogen evolution potential of lithium sulfate electrolyte.

[0046] Figure 7 The cycling data of an aqueous lithium-ion battery containing the lithium sulfate electrolyte of Formula 1 (n=3).

[0047] Figure 8 The cycling data of an aqueous zinc ion battery containing the zinc sulfate electrolyte of formula 1 (n=3) are shown.

[0048] Figure 9 The full cell cycle data of the aqueous zinc / lithium dual-ion battery containing Formula 1 (n=3) and Formula 2 at a low temperature of -50°C. DETAILED DESCRIPTION

[0049] Example 1

[0050] Prepare a 1M aqueous solution of zinc sulfate; a mixed aqueous solution of 1M zinc sulfate and Formula 1 (n=3), wherein the concentration of Formula 1 (n=3) is 1, 3, 6, 8, 12, and 18 M. The freezing point curve of the 12M Formula 1 (n=3) solution obtained by thermogravimetric testing is as follows Figure 1 As shown, the freezing point of a solution containing Formula 1 (n=3) can reach -58°C, while ordinary zinc sulfate solutions freeze at only -22°C (the freezing point of zinc sulfate reported in the literature is -9°C). However, solutions containing Formula 1 (n=3) at concentrations of 6, 12, and 18 M remain clear and transparent, demonstrating that the addition of Formula 1 (n=3) can significantly lower the freezing point of aqueous electrolytes. The relationship between different concentrations of Formula 1 and conductivity, polarization, freezing point, and solubility of zinc sulfate was also determined, as shown in Table 1. This indicates that the optimal concentration of Formula 1 (n=3) is 6-12 M.

[0051] Table 1. Properties of different concentrations of Formula 1 (n=3)

[0052]

[0053] Example 2

[0054] A molecular dynamics simulation system of a 1M zinc sulfate electrolyte system was constructed, in which there were 20 zinc ions, 20 sulfate ions, and 1100 water molecules. Molecular dynamics simulation was performed to calculate the solvation structure of the zinc ions and determine the water molecules and anions around the zinc ions. A molecular dynamics simulation system of a 1M zinc sulfate electrolyte containing 6M and 12M of formula 1 (n=3) was then constructed. The interaction between zinc ions and the molecules of formula 1 (n=3) was simulated using Material Studio software. Figure 2 It can be found that Formula 1 (n=3) occupies the original coordination position of water molecules and participates in the solvation of zinc ions. It is also found that the coordination number of zinc ions and sulfate ions in the electrolyte with the addition of Formula 1 (n=3) increases significantly, which can explain the reason for the decrease in the freezing point of the electrolyte: the molecules of Formula 1 (n=3) have a strong coordination effect with cations, reduce the charge density of cations, promote the coordination and coupling between cations and anions, weaken the hydrogen bonds in the electrolyte, and lower the freezing point of the electrolyte.

[0055] Example 3

[0056] Prepare 1M zinc sulfate aqueous solution (electrolyte A); 1M zinc sulfate aqueous solution-Formula 1 (n=3) mixed solution, where the concentration of Formula 1 (n=3) is 6M (electrolyte B); Electrolyte A and B are used as electrolytes, respectively, and zinc foil and glass fiber are assembled into 2025 symmetrical cells, and the reaction temperature is 1mA cm -2 -1mAh cm -2 The constant current charge and discharge were carried out under the conditions of , in order to evaluate the polarization and cycle life of the electrolyte. Figure 3 It can be seen that at room temperature, the aqueous zinc-ion battery containing the additive of formula 1 (n=3) can cycle for more than 900 hours, while the pure zinc sulfate electrolyte shows obvious instability in less than 100 hours. In addition, the electrolyte containing formula 1 (n=3) has a lower polarization voltage, which is beneficial to improving the overall performance of the zinc-ion battery.

[0057] Example 4

[0058] Using the two electrolytes in Example 3 (electrolyte A or electrolyte B), a zinc-zinc symmetrical battery was assembled and a constant current charge-discharge test was performed at -20°C with a test current density of 0.5 mA cm -2 -0.5mAh cm -2 ,from Figure 4It can be seen that the electrolyte containing formula 1 (n=3) can operate stably for more than 1000 h at low temperature, while the electrolyte not containing formula 1 (n=3) cannot operate at low temperature. This can be attributed to the increase in ion transfer resistance caused by the solidification of ordinary zinc sulfate electrolyte at low temperature, while the electrolyte containing formula 1 (n=3) still has low viscosity and high ionic conductivity at low temperature.

[0059] Example 5

[0060] The two electrolytes (electrolyte A or electrolyte B) in Example 3 were used to test the linear polarization curves of the zinc-zinc symmetric battery to characterize the corrosion current and corrosion potential of zinc in the electrolyte. Figure 5 It can be seen that the zinc battery using the electrolyte containing Formula 1 (n = 3) has a lower corrosion current and negative corrosion potential, indicating that the electrolyte containing Formula 1 (n = 3) can significantly inhibit the corrosion of the zinc negative electrode. Similarly, the electrochemical hydrogen evolution potential of 1M lithium sulfate aqueous solution and 1M lithium sulfate-water-Formula 1 (n = 3) solution was tested. Figure 6 It can be seen that the hydrogen evolution potential of the electrolyte containing Formula 1 (n=3) is significantly negative than that of the ordinary electrolyte, which shows that the addition of Formula 1 (n=3) can significantly inhibit the decomposition of water and improve the energy density of aqueous lithium / zinc ion batteries.

[0061] Example 6

[0062] A 1M lithium sulfate aqueous solution (electrolyte a) and a 1M lithium sulfate-water-8M solution of Formula 1 (n=3) (electrolyte b) were tested. Aqueous lithium-ion batteries were assembled, using lithium manganese oxide as the positive electrode and vanadium pentoxide as the negative electrode. The preparation of the positive and negative electrodes followed the following process: lithium manganese oxide (vanadium dioxide), conductive carbon black, and (PVDF) were mixed in an NMP solvent in a weight ratio of 7:2:1. The resulting slurry was coated on a stainless steel mesh, dried at 80°C for 12 hours, and cut into discs with a diameter of 11 mm to obtain the relevant positive electrode, in which the active material loading was approximately 1.8 mg cm -2 From the cycling data of aqueous lithium-ion batteries Figure 7 It can be seen that adding the electrolyte of formula 1 (n=3) can make the battery have a higher discharge specific capacity and cycle life. At the same time, the modified electrolyte can still circulate normally and stably at -20°C, while the electrolyte without formula 1 (n=3) has frozen and cannot operate at low temperatures.

[0063] Example 7

[0064] A 1M zinc sulfate aqueous solution and a 1M zinc sulfate-water-8M solution of formula 1 (n=3) were tested. Aqueous zinc ion batteries were assembled, using manganese dioxide as the positive electrode and zinc as the negative electrode. The positive electrode sheet was prepared by rolling a mixture of manganese dioxide, conductive carbon black, and PTFE in a ratio of 7:2:1 on a steel mesh. The active material loading was approximately 2 mg cm -2 At room temperature, 1Ag -1 The cycling performance of aqueous zinc batteries was tested at a current density of Figure 8 It can be found that the electrolyte containing Formula 1 (n=3) can provide a long cycle life and a high specific capacity.

[0065] Example 8

[0066] To demonstrate the synergistic effect of Formula 1 and Formula 2, the relationship between conductivity, freezing point, and polarization at different mixture concentrations was experimentally determined, as shown in Table 2. This demonstrates that Formula 1 (n=3) and Formula 2 (m=1, R is methyl) have a significant synergistic effect.

[0067] Table 2. Properties of solutions of formula 1 (n=3) and formula 2 (m=1, R is methyl) at different concentrations

[0068]

[0069] As described in Table 2, by combining Formula 1 and Formula 2, especially when the molar ratio of the two is controlled at 6-8:0.1-2, and more preferably at a ratio of 7-7.8:0.2-1, an excellent synergistic effect can be unexpectedly obtained, which can synergistically improve the antifreeze performance. In addition, it can also reduce the conductivity loss and polarization, which helps to further improve its electrochemical performance at ultra-low temperatures.

[0070] Example 9

[0071] like Figure 9 As shown, further testing of the effect of the mixed electrolytes in Group e in Table 2 on the lifespan of zinc symmetric batteries at -50°C revealed that the Zn||Zn symmetric battery containing the synergistic electrolytes of Formulas 1 and 2 could cycle for over 700 hours, while the electrolyte containing only Formula 1 (n=3) (Experimental Group 5 in Table 2) could no longer cycle at -50°C. This shows that the combination of Formulas 1 and 2 enables ultra-low temperature operation. Furthermore, it also achieves both excellent conductivity and low polarization at ultra-low temperatures, resulting in superior ultra-low temperature electrochemical cycling stability.

Claims

1. An aqueous zinc ion battery electrolyte, characterized in that A homogeneous aqueous solution consisting of an electrolyte salt, a compound of formula 1, and water; wherein the electrolyte salt is zinc sulfate; The aqueous zinc ion battery electrolyte further comprises a water-soluble compound of formula 2; Formula 1 In formula 1, n is 3; Formula 2 In formula 2, R is a methyl group, and m is 1; The molar ratio of Formula 1 to Formula 2 is 6-8:0.1-2; In the aqueous zinc ion battery electrolyte, the concentration of the compound of formula 1 is 3-18 M; the concentration of the electrolyte salt is 1-2 M.

2. The aqueous zinc ion battery electrolyte according to claim 1, wherein The concentration of the compound of formula 1 is 4-12 M.

3. The aqueous zinc ion battery electrolyte according to claim 1, wherein The concentration of the compound of formula 1 is 6-8 M.

4. The aqueous zinc ion battery electrolyte according to claim 1, wherein The molar ratio of formula 1 to formula 2 is 7-7.8:0.2-1.

5. The aqueous zinc ion battery electrolyte according to claim 1, wherein The concentration of the compound of formula 2 is 0.2~1 M.

6. Use of the aqueous zinc ion battery electrolyte according to any one of claims 1 to 5, characterized in that: It is used as an electrolyte to assemble aqueous zinc-ion batteries.

7. An aqueous zinc ion battery, characterized in that An aqueous zinc ion battery electrolyte comprising the aqueous zinc ion battery electrolyte according to any one of claims 1 to 5; In the aqueous zinc ion battery, the active material of the positive electrode is at least one of activated carbon, polyaniline, manganese dioxide, vanadium pentoxide, polypyrrole, and vanadium disulfide.

Images