A zinc-iodine battery electrolyte that utilizes the chain length of quaternary ammonium salts to regulate the negative electrode double layer and the iodine confinement at the positive electrode.

Abstract

This invention discloses a zinc-iodine battery electrolyte that utilizes quaternary ammonium salt chain length to regulate the negative electrode double layer and the positive electrode iodine confinement. The electrolyte comprises a soluble zinc salt and quaternary ammonium salt additives. At the negative electrode, the quaternary ammonium salt constructs double layers of varying thickness and hydrophobicity through different chain lengths, suppressing dendrite growth and hydrogen evolution side reactions. At the positive electrode, through hydrophobic confinement and dual coordination, it stabilizes high-valence iodine species and activates the four-electron reaction of iodine, significantly improving the battery's specific capacity and cycle stability. This provides a new approach for the synergistic optimization of positive and negative electrodes in zinc-iodine batteries and other multi-electron transfer energy storage systems.

Description

Technical Field

[0001] This invention belongs to the field of aqueous zinc-iodine battery technology, and particularly relates to a zinc-iodine battery electrolyte that utilizes the chain length of quaternary ammonium salt to regulate the negative electrode double layer and the iodine confinement of the positive electrode, and its application. Background Technology

[0002] Compared to non-aqueous lithium-ion batteries, which suffer from limited lithium resources, high prices, and environmental impact, zinc-iodine batteries exhibit significant advantages. Nature possesses abundant zinc resources, which are environmentally friendly, non-toxic, malleable, and easy to process. Furthermore, aqueous zinc-ion batteries offer a high volumetric capacity (5855 mAh·cm³). −3 ) and theoretical specific capacity (820 mAh·g −1 Iodine has attracted widespread attention due to its abundant resources and moderate redox potential (−0.76 vs SHE). Through a four-electron transfer mechanism, iodine cathodes can provide up to 422 mAh g⁻¹. −1 Its theoretical specific capacity is significantly higher than that of traditional two-electron reactions.

[0003] However, in practical applications, zinc-iodine batteries still face challenges such as dendrite growth and hydrogen evolution side reactions, low theoretical specific capacity due to two-electron transfer redox reactions, and the high valence of iodine ions being easily hydrolyzed, which limits energy density. Fundamentally, the uneven initial distribution of charge on the electrode surface causes zinc ions to preferentially deposit at more active sites at the interface, forming crystal nuclei. The protruding parts of the zinc sheet further exacerbate the uneven distribution of the interfacial electric field and ions, thus promoting dendrite formation. High current densities easily trigger hydrogen evolution reactions, resulting in low coulombic efficiency.

[0004] Therefore, developing a material that can achieve uniform deposition and synergistically optimize multi-electron transfer is one of the effective ways to realize high-performance zinc-iodine batteries. Currently, there are no reports on simultaneously achieving double-layer controlled deposition on the negative electrode and four-electron reactions driven by hydrophobic confinement / dual coordination on the positive electrode using quaternary ammonium salts of different chain lengths as the core. On the negative electrode side, quaternary ammonium salts construct double layers of varying thickness and hydrophobicity through different alkyl chain lengths, achieving precise control over zinc deposition behavior; on the positive electrode side, quaternary ammonium salts utilize the micro-region confinement effect of their hydrophobic alkyl chains and the interaction between quaternary ammonium cations and Br... − Its dual coordination function effectively stabilizes high-valent iodine species, driving the traditional I- − / I₂ double electron reaction transforms into I₂ − / I2 / I + Four-electron redox reactions. Therefore, this invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing zinc-iodine batteries, such as poor matching between the positive and negative electrodes and low iodine utilization efficiency, and to provide a zinc-iodine battery electrolyte control strategy that utilizes the chain length of quaternary ammonium salts to regulate the negative electrode double layer and the iodine confinement at the positive electrode. On the negative electrode side, double layers of varying thickness and hydrophobicity are constructed using quaternary ammonium salts with different chain lengths to suppress dendrite growth and hydrogen evolution side reactions. On the positive electrode side, the hydrophobic confinement and dual coordination effects of quaternary ammonium salts are utilized to stabilize high-valence iodine species and drive four-electron redox reactions, thereby achieving a synergistic improvement in battery specific capacity and cycle stability.

[0006] The objective of this invention is achieved through the following technical solution: a zinc-iodine battery electrolyte that utilizes the chain length of quaternary ammonium salts to regulate the negative electrode double layer and the iodine confinement at the positive electrode, characterized in that it comprises: an aqueous electrolyte matrix, a soluble zinc salt, and quaternary ammonium salt additives. The general structural formula of the quaternary ammonium salt additives is [N(R)4]. + Br − In this process, R can be methyl, ethyl, propyl, or butyl. By controlling the alkyl chain length of R, double layers of varying thickness and hydrophobicity are constructed at the negative electrode interface to regulate zinc deposition behavior and suppress dendrite growth and hydrogen evolution side reactions. At the positive electrode interface, the micro-region confinement effect of the hydrophobic alkyl chain of the quaternary ammonium salt and the dual coordination between the quaternary ammonium cation and Br⁻ are utilized to stabilize high-valent iodine species and drive the conventional I₂ ​​deposition. − / I₂ double electron reaction transforms into I₂ − / I2 / I + A four-electron redox reaction. Further, the quaternary ammonium salt compound is a tetraalkyl quaternary ammonium salt with the general structural formula [N(R)4]. + Br − , where R is methyl, ethyl, propyl and butyl.

[0007] According to claim 1, a zinc-iodine battery electrolyte for controlling the negative electrode double layer and the positive electrode iodine confinement using quaternary ammonium salt chain length is characterized in that the preparation of the electrolyte includes the following steps: S1. Weigh zinc sulfate (ZnSO4·7H2O) and dissolve it in deionized water. Stir until completely dissolved to prepare a 2 M zinc sulfate basic electrolyte. S2. Add quaternary ammonium salt compound additives to the basic electrolyte prepared in step S1, stir until completely dissolved, so that the concentration of quaternary ammonium salt compound is 0.1 M, and obtain the electrolyte.

[0008] According to claim 1, a zinc-iodine battery electrolyte for controlling the negative electrode double layer and the positive electrode iodine confinement using quaternary ammonium salt chain length is characterized in that the preparation of the positive electrode material includes the following steps: S1. The positive electrode material consists of conductive carbon black, elemental iodine, Super P, and sodium carboxymethyl cellulose in a ratio of 4:4:1:1. After grinding for 20 minutes, add 10 ml of ultrapure water and stir for three days.

[0009] S2. The positive electrode material obtained in step S1 is coated onto the current collector and dried in a vacuum drying oven at 40 °C for 6 hours to obtain the positive electrode sheet.

[0010] An aqueous zinc-iodine battery, characterized in that the aqueous zinc-iodine battery is assembled from an electrolyte of 0.1 M quaternary ammonium salt concentration as described in claims 1-2, a separator, a zinc negative electrode, and an iodine positive electrode as described in claim 3.

[0011] According to claims 4-5, an aqueous zinc-iodine battery is characterized in that the electrolyte is a 0.1 M quaternary ammonium salt solution, the positive electrode is an iodine positive electrode, the separator is glass fiber, and the negative electrode is a zinc sheet.

[0012] Compared with existing technologies, this invention has the following advantages: This invention is the first to propose using quaternary ammonium salts with different chain lengths as electrolyte additives, while simultaneously regulating the positive and negative electrode interfaces of zinc-iodine batteries. On the negative electrode side, the quaternary ammonium salts construct double layers of varying thickness and hydrophobicity through different chain lengths, thereby accelerating ion migration rates, reducing the desolvation energy barrier, and suppressing dendrite growth and hydrogen evolution side reactions.

[0013] Through systematic experimental research, on the positive electrode side, the hydrophobic alkyl chains of quaternary ammonium salts with different chain lengths provide micro-region confinement effects. Short chains have weak hydrophobic confinement and are easily hydrolyzed by iodide ions; long chains have large steric hindrance and poor dual coordination effect; tetraethylammonium bromide with a moderate chain length achieves a balance between hydrophobic confinement and dual coordination, stabilizes high-valence iodine species, activates four-electron reactions, and improves specific capacity.

[0014] The Zn||Zn symmetric cell assembled according to this invention, as tested, shows that the ion transference number of tetraethylammonium bromide is as high as 0.739, at 5 mA cm⁻¹. −2 and 5 mAh cm −2 The cycle life under certain conditions exceeds 500 hours; the zinc-iodine full cell using tetraethylammonium bromide has a cycle life of 1 A g. −1 Under these conditions, the initial capacity is 380 mAh g. −1 The capacity retention rate is 84.5%. Therefore, the electrolyte provided by this invention can significantly improve the cycle stability and energy density of aqueous zinc-iodine batteries, and provides a new approach for the synergistic regulation of positive and negative electrodes in multi-electron transfer energy storage systems, which has important academic significance and practical value. Attached Figure Description

[0015] Figure 1 These are the double-layer capacitors of different electrolyte systems in Example 1.

[0016] Figure 2 It is the zinc ion transference number in different electrolyte systems in Example 2.

[0017] Figure 3 The diagram shows the diffusion activation energy of zinc ions in different electrolyte systems of Example 3.

[0018] Figure 4 The different quaternary ammonium salt electrolytes in Example 4 were tested at 5 mA cm⁻¹. −2 and 5 mAh cm −2 Constant current charge-discharge cycle test of Zn||Zn symmetric cell under the condition.

[0019] Figure 5 The different quaternary ammonium salt electrolytes in Example 5 were used at 1 A g −1 Long-cycle performance of Zn-I2 full cells under certain conditions.

[0020] Figure 6 In Example 6, tetraethylammonium bromide was used at 1 A g. −1 Long-cycle performance of Zn-I2 full cells under certain conditions. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many other ways different from those described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.

[0022] Example 1: (1) Zinc sheets were ultrasonically cleaned with deionized water and anhydrous ethanol for 10 minutes each and then set aside. A 2 M ZnSO4 electrolyte was prepared, and tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide were added as modifying additives, with a uniform concentration of 0.1 M. A Zn||Zn symmetric cell was assembled using glass fiber as the separator and zinc sheets as the electrodes.

[0023] (2) Within a small voltage window of −15 mV to 15 mV, at voltages of 2, 4, 6, 8, and 10 mV s respectively. −1 Cyclic voltammetry tests were performed on Zn||Zn symmetric cells at different scan rates. The double-layer capacitance was calculated based on the linear relationship between the capacitance current and the scan rate at different scan rates.

[0024] (3) The double-layer capacitance of the zinc electrode under different electrolyte systems, such as Figure 1 As shown, the capacitance of the electric double layer is inversely proportional to its thickness; a smaller capacitance indicates a thicker electric double layer. The electric double layer gradually thickens as the chain length increases.

[0025] Example 2: (1) The preparation method and materials used for the modified additive in this example are the same as those in Example 1, in order to determine the Zn content in different electrolyte systems. 2+ The transference number was determined using a potentiostatic polarization method combined with electrochemical impedance spectroscopy to test the Zn||Zn symmetric cell. A potentiostatic polarization voltage of −150 mV was applied for a polarization time of 3000 s, and the initial and steady-state currents were recorded. Electrochemical impedance spectroscopy was performed in the frequency range of 100 kHz to 0.01 Hz with an AC amplitude of 10 mV, and the interfacial resistance before and after polarization was measured.

[0026] (2) Test results are as follows Figure 2 As shown, the Zn in the tetraethylammonium bromide (TEAB) system 2+ The migration number is significantly higher than other electrolyte systems. This system constructs an electrical double layer of moderate thickness, which effectively shields water molecules and suppresses side reactions without excessively hindering Zn. 2+ The migration of these molecules improves the selectivity of ion transport.

[0027] Example 3: (1) The preparation method and materials used for the modified additive in this example are the same as those in Example 1, in order to determine the Zn content in different electrolyte systems. 2+ The activation energy of the desolvation process was determined by electrochemical impedance spectroscopy (EIS) measurements of the symmetric cell at different temperatures. The test temperatures were set at 25 °C, 35 °C, 45 °C, 55 °C, 65 °C, and 75 °C, with a frequency range of 100 kHz to 0.01 Hz and an AC amplitude of 10 mV.

[0028] (2) The interfacial charge transfer resistance (Rct) at different temperatures was obtained by impedance spectroscopy fitting. A linear fit was performed between ln(1 / Rct) and 1 / T, and the Zn content in each electrolyte system was calculated from the slope. 2+ Activation energy (Ea) for the desolvation process. Activation energies for different electrolyte systems are as follows: Figure 3 As shown, tetraethylammonium bromide significantly reduced the zinc ion desolvation energy, accelerated the desolvation process, and promoted uniform zinc deposition.

[0029] Example 4: (1) The preparation method and materials used for the modified additives in this example are the same as those in Example 1. The CR2025 type aqueous button cell was assembled and subjected to constant current charge-discharge test in the Xinwei Battery Test System. The test conditions were 5 mA cm⁻¹. −2 and 5 mAh cm −2 .

[0030] (2) Test results are as follows Figure 5As shown, the ZS-TEAB system exhibits low polarization voltage and good cycling stability during cycling. The polarization voltage of the ZS-TEAB system is always maintained below 100 mV, and the stable cycling time exceeds 500 hours.

[0031] Example 5: (1) The preparation method and materials used for the modified additives in this example are basically the same as those in Example 1. The difference is that conductive carbon black, iodine, super P and sodium carboxymethyl cellulose are weighed in a ratio of 4:4:1:1, ground for 20 minutes, and then 10 ml of ultrapure water is added and stirred for three days. The stirred slurry is coated on the current collector and dried in a vacuum drying oven at 40°C for 6 hours. The resulting positive electrode sheet and zinc sheet form a Zn-I2 full cell. Cyclic charge-discharge tests are performed in the Xinwei Battery Test System. The current density is 1 A g. −1 .

[0032] (2) Test results are as follows Figure 5 As shown, tetraethylammonium bromide significantly improves the battery's capacity retention and cycle stability. The synergistic stabilization of the positive and negative electrodes jointly suppresses capacity decay, thereby significantly improving the capacity retention of the Zn-I2 full cell.

[0033] Example 6: (1) The steps in this example are basically the same as those in Example 5. The difference is that the concentration of tetraethylammonium bromide is increased to 0.3 M while the current density remains unchanged.

[0034] (2) Figure 6 This is a long-cycle test graph for tetraethylammonium bromide, showing an initial specific capacity of 380 mAh g. −1 It can be stably cycled for 8000 cycles with a capacity retention rate of 84.5% and a coulomb efficiency of over 99.47%, demonstrating excellent cycle stability.

[0035] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A zinc-iodine battery electrolyte that utilizes the chain length of quaternary ammonium salts to regulate the negative electrode double layer and the iodine confinement at the positive electrode, characterized in that, The quaternary ammonium salt compound is a tetraalkyl quaternary ammonium salt with the general structural formula [N(R)4]. + Br - Where R is methyl, ethyl, propyl, or butyl; the quaternary ammonium salt compound reconstructs Zn at the negative electrode interface. 2+ The solvation structure and the construction of an electric double layer are used to regulate zinc deposition behavior, and coordination with iodine species at the positive electrode interface are used to regulate the redox reaction pathway of iodine.

2. The zinc-iodine battery electrolyte according to claim 1, which utilizes the quaternary ammonium salt chain length to regulate the negative electrode double layer and the positive electrode iodine confinement, is characterized in that... The preparation of the electrolyte includes the following steps: S1. Weigh zinc sulfate (ZnSO4·7H2O) and dissolve it in deionized water. Stir until completely dissolved to prepare a 2 M zinc sulfate basic electrolyte. S2. Add quaternary ammonium salt compound additives to the basic electrolyte prepared in step S1, stir until completely dissolved, so that the concentration of quaternary ammonium salt compound is 0.1 M, and obtain the electrolyte.

3. The zinc-iodine battery electrolyte according to claim 1, which utilizes the quaternary ammonium salt chain length to regulate the negative electrode double layer and the positive electrode iodine confinement, is characterized in that... The preparation of the cathode material includes the following steps: S1. The positive electrode material consists of conductive carbon black, elemental iodine, super p, and CMC in a ratio of 4:4:1:

1. After grinding for 20 minutes, 10 ml of ultrapure water is added and stirred for three days. S2. The positive electrode material obtained in step S1 is coated onto the current collector and dried in a vacuum drying oven at 40 °C for 6 hours to obtain the positive electrode sheet.

4. An aqueous zinc-iodine battery, characterized in that, The aqueous zinc-iodine battery is assembled from the electrolyte of 0.1 M quaternary ammonium salt as described in claims 1-2, a separator, a zinc negative electrode, and an iodine positive electrode as described in claim 3.

5. The aqueous zinc-iodine battery according to claim 4, characterized in that, The electrolyte is a 0.1 M quaternary ammonium salt solution, the positive electrode is an iodine positive electrode, the diaphragm is glass fiber, and the negative electrode is a zinc sheet.

Images