Positive electrode material for aqueous Zn-I2 battery, electrode plate, preparation method of positive electrode material and preparation method of electrode plate, and battery

Abstract

The invention discloses a positive electrode material for a water-based Zn-I2 battery, an electrode plate, a preparation method of the electrode plate and the battery, and belongs to the field of batteries, the positive electrode material for the water-based Zn-I2 battery comprises copper acetylacetonate Cu (acac) 2 and activated carbon; the problem of multi-iodide shuttling is solved, and meanwhile, the problems of poor conductivity of iodine and slow reaction kinetics are solved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode material for an aqueous Zn-I2 battery, an electrode sheet, a preparation method thereof, and a battery. Background Art

[0002] Aqueous zinc-ion batteries have great potential in the field of high-performance, low-cost electrochemical energy storage. Among the zinc-based battery family, Zn-I2 batteries have a high theoretical specific capacity (211 mAh g) due to their abundant raw material reserves, low cost, environmental friendliness, and high specific capacity (211 mAh g). -1 ) and a higher discharge platform voltage (relative to Zn / Zn 2+ However, Zn-I2 batteries currently face several key challenges. In aqueous electrolytes, iodide ions (I - ) and iodine (I2) readily form soluble polyiodides. These polyiodides trigger a shuttle effect, which, due to their high solubility, leads to severe zinc anode corrosion and irreversible capacity loss. Furthermore, iodine's poor conductivity results in sluggish reaction kinetics. These issues collectively reduce battery life and performance. Therefore, inhibiting polyiodide shuttles and enhancing iodine redox kinetics are key to developing high-performance aqueous Zn-I2 batteries with long-term cycling stability and excellent capacity retention.

[0003] To address these challenges, various strategies have been proposed, including the development of carbon-based host materials, separator modification, and electrolyte engineering. Among these, the design of carbon-based host materials has garnered significant attention. For example, porous carbon derived from zinc citrate is calcined at high temperatures to confine iodine within its pore structure rather than on its surface. Its high surface area and capillary adsorption effect immobilize iodine species and inhibit polyiodide dissolution. Similarly, mesoporous carbon has been synthesized in situ. Its ordered structure shortens the diffusion paths for ions and electrons, promoting rapid charge transfer while spatially confining the conversion between polyiodides and iodide ions within the mesopores. Although these studies primarily rely on physical adsorption between the porous structure and iodine species to mitigate shuttling, weak interfacial interactions often lead to insufficient long-term cycling performance. Furthermore, these approaches fail to address the sluggish redox kinetics of iodine itself. Consequently, research has shifted towards heteroatom-doped porous carbon materials. For example, nitrogen-doped porous carbon, in which different nitrogen configurations (pyridinic, pyrrolic, and graphitic nitrogen) synergistically enhance the adsorption and catalytic effects of iodide ions / polyiodide species. The high conductivity of the material improves electron transport, compensating for the poor conductivity of iodine. In addition, graphitic nitrogen induces electron redistribution of adjacent carbon atoms, weakens the II bond, and accelerates the iodine conversion process (I2→I -). Strong chemical adsorption further suppresses the generation of intermediate iodide species. To further improve the catalytic efficiency of polyiodide conversion, the application of metal single-atom catalysts has become an efficient strategy. For example, nickel single-atom catalysts embedded in hierarchical porous carbon frameworks provide a high specific surface area for physical confinement of polyiodides. The uniformly distributed Ni-N4 coordination sites act as dual-functional centers of chemical adsorption and catalytic activity, accelerating the conversion kinetics of polyiodides. Although these methods have made significant progress in inhibiting polyiodide shuttling and catalyzing their conversion, their practical application is hindered by complex synthesis processes. For example, the former requires precise high-temperature control to regulate the graphitic carbon content, while the latter involves complex preparation steps, high cost and scalability limitations, which poses a major obstacle to commercialization. Therefore, there is an urgent need to develop host materials with simple preparation processes, excellent performance and scalability to effectively inhibit polyiodide shuttling while solving the problems of poor electrical conductivity and sluggish reaction kinetics of iodine. Summary of the Invention

[0004] In order to alleviate or partially alleviate the above technical problems, the solutions of the present invention are as follows:

[0005] A positive electrode material for aqueous Zn-I2 batteries includes copper acetylacetonate Cu(acac)2 and activated carbon.

[0006] Preferably, the mass ratio of copper acetylacetonate Cu(acac)2 to activated carbon is 1:4.

[0007] This solution also provides an electrode sheet, which includes the above-mentioned positive electrode material for aqueous Zn-I2 batteries.

[0008] Preferably, the electrode sheet further comprises a conductive agent, an adhesive and a solvent; the conductive agent is acetylene black, the adhesive is PVDF; and the solvent is N-methylpyrrolidone;

[0009] Preferably, the mass ratio of the active material, the conductive agent and the binder is 8:1:1.

[0010] The method for preparing the electrode sheet comprises the following steps:

[0011] Cu(acac)2 and activated carbon are mixed and ground according to a mass ratio, and then the resulting mixture is mixed with a conductive agent, a binder, and a solvent to obtain a slurry;

[0012] The uniform slurry was evenly coated on carbon paper and dried to prepare a Cu (acac)2 electrode;

[0013] Subsequently, the cathode liquid was dropwise coated on the Cu (acac) 2 electrode and dried; the cathode liquid included an aqueous solution of 0.1 M KI and 0.01 M I2.

[0014] This solution also provides an aqueous Zn-I2 battery, comprising: a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the above-mentioned electrode sheet or the electrode sheet prepared by the above-mentioned preparation method.

[0015] Preferably, the negative electrode comprises zinc foil.

[0016] Preferably, the electrolyte comprises a ZnSO4 solution.

[0017] Preferably, the concentration of the ZnSO4 solution is 2M.

[0018] The technical solution of the present invention has one or more of the following beneficial technical effects:

[0019] This proposal proposes a novel cathode material composed of the metallo-organic catalyst copper acetylacetonate (Cu(acac)2) mixed with activated carbon. This design synergistically combines the physical adsorption capacity of activated carbon for iodine with the chemisorption and catalytic activity of Cu(acac)2 to enhance electron transport, resulting in an iodine cathode with high conductivity and catalytic efficiency. Material characterization and density functional theory (DFT) calculations reveal bidirectional charge accumulation / depletion between Cu(acac)2 and iodine species, indicating a strong chemical interaction. Furthermore, upon binding to iodine, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels shift, and the energy gap decreases significantly, indicating a more favorable redox process: I2 is more readily reduced, while I⁻ is more readily oxidized, thereby promoting the interconversion of iodine species. In situ Raman spectroscopy confirms that the Cu(acac)2-iodine battery maintains a low polyiodide concentration during operation and exhibits accelerated polyiodide conversion kinetics. The assembled Cu(acac)2-iodine battery exhibited excellent electrochemical performance and rate capability, achieving ultra-long cycle stability at various current densities, including at 2Ag -1 More than 17,000 cycles and 4Ag -1 This study proposes a high-performance iodine cathode material with mature raw materials, simple preparation and excellent performance, which provides a promising approach to promote the development of high-performance aqueous Zn-I2 batteries.

[0020] In addition, other beneficial effects of the present invention will be mentioned in the specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 a is the cyclic voltammetry curve of Cu (acac)2 battery and AC battery;

[0022] Figure 1 b is the electrochemical impedance spectra of Cu (acac)2 battery and AC battery;

[0023] Figure 1 c is the Cu(acac)2 cell at 0.2–2 mV s -1 CV curves at scan rates;

[0024] Figure 1 d is the fitting curve of peak current and scan rate;

[0025] Figure 1 e is the scan rate of 0.4 mV s -1 When Cu (acac) 2 battery capacitance contribution ratio;

[0026] Figure 1 f is the capacitance contribution ratio at different scan rates;

[0027] Figure 2 a is the Cu (acac)2 battery and AC battery at 0.2 A g -1 Cycling performance at different current densities;

[0028] Figure 2 b is the Cu (acac)2 battery and AC battery at 0.2 A g -1 Initial specific capacity-voltage curve under current density;

[0029] Figure 2 c is the Cu (acac)2 battery at 0.2 A g -1 Specific capacity-voltage curves at different cycle numbers under current density;

[0030] Figure 2 d is the rate performance test curve of Cu (acac)2 battery and AC battery;

[0031] Figure 2 e is the specific capacity-voltage curve of Cu (acac)2 battery during different rate performance tests;

[0032] Figure 2 f is Cu (acac)2 battery and AC battery 2 A g -1 Comparison of cycling performance under different current densities;

[0033] Figure 2 g for Cu (acac)2 battery and AC battery 4 A g -1 Comparison of cycling performance under different current densities;

[0034] Figure 2 h is a demonstration diagram of Cu (acac)2 battery lighting up LED panel;

[0035] Figure 3 a is the charge density distribution diagram of Cu (acac)2 molecules;

[0036] Figure 3 b is the electrostatic potential distribution diagram;

[0037] Figure 3 c is the visualization experiment of Cu (acac)2 and KI / I2 solution;

[0038] Figure 3 d is the ultraviolet-visible spectrum (UV-vis) of KI+I2 solution and after adsorption of Cu (acac)2;

[0039] Figure 3 e is the scanning electron microscope (SEM) image of the original Cu (acac)2;

[0040] Figure 3 f is the scanning electron microscopy (SEM) image of Cu (acac)2-I complex;

[0041] Figure 3 g is the Cu 2p X-ray photoelectron spectra (XPS) of pristine Cu (acac)2 and Cu (acac)2-I complex;

[0042] Figure 3 h is the I 3d XPS spectrum of the Cu (acac)2-I complex;

[0043] Figure 3 i is the X-ray diffraction (XRD) patterns of the original Cu (acac)2 and Cu (acac)2-I complex;

[0044] Figure 4 a is the adsorption energy of graphene, Cu (acac)2 and iodine species;

[0045] Figure 4 b is the differential charge density diagram of the interaction between Cu (acac)2 and iodine species;

[0046] Figure 4 c is the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy level of iodine species and the iodine species after binding to Cu (acac)2;

[0047] Figure 4 d is the HOMO-LUMO energy gap of the corresponding system;

[0048] Figure 4 e is the rotating ring disk electrode (RRDE) test results of AC cathode and Cu (acac)2 cathode;

[0049] Figure 4 f is the electron transfer number fitting curve;

[0050] Figure 4 g is the free energy change step diagram of the iodine catalysis process;

[0051] Figure 5 a is the in-situ Raman test result of the AC battery during the charge and discharge process;

[0052] Figure 5 b is the in-situ Raman test result of Cu (acac)2 battery during the charge and discharge process;

[0053] Figure 5 c is the ex situ I 3d spectrum of the Cu (acac)2 battery cathode during the charge and discharge process;

[0054] Figure 5 d is a schematic diagram of the working mechanism of AC battery and Cu (acac)2 battery. DETAILED DESCRIPTION

[0055] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0056] Example 1

[0057] Cu(acac)2 and activated carbon AC were mixed in a mass ratio of 1:4 and ground. The resulting mixture was then mixed with acetylene black and PVDF in a mass ratio of 8:1:1 using N-methylpyrrolidone (NMP) as the solvent. The homogeneous slurry was evenly coated on carbon paper, dried at 80°C for 6 hours, and punched into sheets with a loading of 1 mg / cm. -2 carbon paper to prepare Cu(acac)2 positive electrode;

[0058] The cathode solution was prepared by dissolving 0.1 M KI and 0.01 M I2 in deionized water. Subsequently, a 100 μL droplet of the cathode solution was applied to the Cu(acac)2 electrode and then dried at 40°C for 6 h. The negative electrode consisted of a zinc foil (area 1.54 cm 2 , thickness 50μm), the electrolyte is an aqueous solution containing 2M ZnSO4; the diaphragm is a glass fiber diaphragm.

[0059] Comparative Example 1

[0060] The AC positive electrode was prepared using the following protocol, where AC, acetylene black, and PVDF were mixed in the same 8:1:1 mass ratio. The cathode solution was prepared by dissolving 0.1 MKI and 0.01 Ml2 in deionized water. Subsequently, a 100 μL droplet of the cathode solution was applied to the AC electrode and then dried at 40°C for 6 hours. The negative electrode consisted of zinc foil (area 1.54 cm 2 , thickness 50μm), the electrolyte is an aqueous solution containing 2MZnSO4; the diaphragm is a glass fiber diaphragm.

[0061] Example 2

[0062] The electrochemical performance of the Zn-I2 batteries assembled in Example 1 and Comparative Example 1 was evaluated using CR2032 button cells. In all tests, the specific capacity and current density were normalized to the mass of iodine in the positive electrode, with an active material loading of approximately 1 mg cm -2 The calculation of specific capacity and energy density is based on the mass of I2. Constant current charge and discharge (GCD) tests were performed using a Xinwei BTS-51 battery test system. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on an Autolab M204 electrochemical workstation. Cyclic voltammetry (CV) measured the CV curves of the two batteries in the voltage range of 0.6 V to 1.6 V at different scan rates; EIS measurements were performed at 10 -2 –10 5 All electrochemical tests were performed at room temperature (25 ± 2 °C).

[0063] The rotating ring disk electrode (RRDE) test was performed by an electrochemical workstation (Donghua, 7003, China). The rotating disk electrode, Ag / AgCl electrode and carbon rod were used as the working electrode, reference electrode and counter electrode, respectively. 0.004 g of Cu(acac)2 and AC material mixed in a mass ratio of 1:4 was dispersed in a solution consisting of 375 μL deionized water, 125 μL isopropanol and 20 μL Nafion (5 wt%). After ultrasonic treatment for 0.5 h, 8 μL of ink was drop-coated on the surface of a rotating ring disk electrode with a diameter of 5 mm and allowed to dry for testing. The electrolyte was 0.5 M ZnSO4 + 0.01 M KI. The linear sweep voltammogram (LSV) was obtained at 10 mVs -1 The scanning was performed at a scanning rate of 400 rpm, 900 rpm, 1600 rpm, and 2500 rpm. The electron transfer number (n) of the reaction can be calculated according to the Koutecký-Levich (KL) equation (as shown in the following formulas (1) and (2)):

[0064] (1)

[0065] (2);

[0066] Among them, J d 、J k and J f are the experimentally measured disk current density, kinetic control current density, and diffusion-limited current density, respectively. ω is the rotation speed of the disk electrode, n is the number of electron transfers, and F is the Faraday constant (96485 Cmol -1 ), C0 is the concentration of I⁻ in the solution (0.01M), D0 is the diffusion coefficient of the reactant, ν is the kinematic viscosity of the solution (0.01cm 2 s -1 ).

[0067] Powder X-ray diffraction (XRD) analysis was performed on a Bruker AXS GmbH diffractometer (Germany) with a 2θ scanning range of 10–80° and a scanning rate of 10° min -1 . Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were performed using a Hitachi SU8100 system (Japan) to examine the surface morphology and elemental distribution. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Thermo Fisher K-Alpha spectrometer, and the binding energy was calibrated with the CC reference peak (284.8 eV) using Avantage software. In situ Raman spectroscopy was achieved using a 532 nm laser through a custom-designed anode chamber with a quartz observation window. UV-visible spectroscopy was used to analyze the changes in KI+I2 solution before and after the reaction with Cu(acac)2. In order to monitor the dissolution of polyiodides in real time, an in situ optical testing device was developed. The battery was operated at 0.4 Ag -1 The Zn-I2 battery was charged to 1.6 V and then discharged to 0.6 V, during which the absorption spectrum was collected. The constant current charge and discharge curves of the Zn-I2 battery were recorded using a Blue Power battery test system.

[0068] All DFT calculations were performed using the DMol3 module in Materials Studio 2020 software. For exchange-correlation interactions, the Perdew-Burke-Ernzerhof (PBE) functional was used within the generalized gradient approximation (GGA) framework. The core electrons were characterized using the DNP4.4 basis set combined with the DFT semi-core pseudopotential (DSPP), while the van der Waals correction was implemented using Grimme's DFT-D2 method. The key calculation parameters were configured as follows: a global orbital cutoff radius of 5.2 Å, an orbital occupation broadening of 0.005 Ha, and convergence criteria including an energy tolerance of 1 × 10 -5 Ha, maximum force less than 0.002HaÅ -1, the maximum atomic displacement is limited to 0.005Å. To suppress periodic image interactions, a 20Å vacuum layer is introduced during system construction, and the k-space sampling is limited to only Gamma point configurations. The self-consistent field (SCF) iteration process uses 1×10 -6 Energy convergence threshold of Ha. Adsorption energy (E ads ) is determined using the following formula (3):

[0069] (3)

[0070] Among them, E AB is the total energy of the adsorption system, E A / E B represents the energy of the adsorbate (iodine species) and the original surface. Negative E ads represents exothermic adsorption, with more negative values ​​reflecting stronger interactions.

[0071] The differential charge density (Δρ) is given by the following equation (4):

[0072] (4)

[0073] Among them, ρ AB , ρ A and ρ B The charge density of the iodine adsorption system, isolated iodine species, and the bare surface are shown, respectively. Charge accumulation and depletion are visualized in yellow and light blue, respectively.

[0074] The free energy change (ΔG) of the iodine reduction step was calculated by the following formula (5):

[0075] (5)

[0076] Here, ΔE ZPE and TΔS are the zero-point energy correction and the entropy change at 298.15 K, respectively.

[0077] The results of the effect of Cu(acac)2 on the electrochemical performance of Zn-I2 batteries are as follows: The electrochemical performance of the batteries assembled with the Cu(acac)2 positive electrode of Example 1 and the AC positive electrode of Comparative Example 1 were tested, which are called Cu(acac)2 batteries and AC batteries respectively. First, in the voltage range of 0.6V to 1.6V, the Zn-I2 battery was charged at 1mVs -1 The CV curves of the two batteries were measured at a scan rate of Figure 1 As shown in a, both batteries exhibit a pair of redox peaks between 1.10 V and 1.25 V, corresponding to the I - Oxidized to I 0 And then restore back to I -process. It is worth noting that the peak oxidation current (3.69 mA) of the Cu(acac)2 battery is higher than that of the AC battery (2.50 mA), and its peak reduction current (-4.40 mA) is also greater than that of the AC battery (-3.14 mA), indicating that the Cu(acac)2 battery has higher electrochemical activity and excellent reaction kinetics. In addition, the redox potential difference (127 mV) of the Cu(acac)2 battery is smaller than that of the AC battery (141 mV), indicating that the use of Cu(acac)2 reduces the voltage polarization of the battery, which will help enhance the battery reaction kinetics and improve the cycle reversibility. These enhancements may be attributed to the role of the Cu(acac)2 material, which improves I - / I 0 The conversion reactivity was enhanced and the shuttling of polyiodide ions was suppressed, thereby improving the energy efficiency of the battery. Figure 1 b depicts the electrochemical impedance of the two batteries. It can be seen that the impedance of the Cu(acac)2 battery (R ct =6.15Ω) is lower than the AC battery (R ct =13.9Ω), which is consistent with the smaller redox potential difference observed in the CV results. In addition, the ohmic impedance of the Cu(acac)2 battery (Rs=1.95Ω) is smaller than that of the AC battery (Rs=2.35Ω). These findings suggest that the application of Cu(acac)2 material promotes charge transfer in the electrode material, which may be related to its ability to regulate the pores of the electrode material to shorten the ion transport path.

[0078] In order to verify the conversion kinetics of iodine cathode in Zn-I2 battery, the -1 The CV curves were measured at a scan rate of . Figure 1 As shown in c, the oxidation peak potential of the Cu(acac)2 battery gradually increases, while the reduction peak potential decreases, indicating an increase in overpotential. However, at different scan rates, the redox potential difference of the Cu(acac)2 battery is always smaller than that of the AC battery, further demonstrating the enhanced reaction kinetics in the Cu(acac)2 battery. These results indicate that the Cu(acac)2 positive electrode significantly reduces the polarization of the battery and improves its reaction performance.

[0079] The relationship between peak current (i) and scan rate (v) in Equation (6) can be used to analyze the main reaction control mechanism in the battery:

[0080] (6)

[0081] Where a and b are adjustable parameters. The value of b can be determined from the slope of log(i) vs. log(v). A b value of 1 indicates capacitive-dominated battery behavior, while a b value of 0.5 corresponds to diffusion-dominated battery behavior. Figure 1d shows that the calculated b values ​​for the oxidation and reduction processes are 0.82 and 0.83, respectively, indicating the joint contribution of capacitance and diffusion behavior. The capacitance and diffusion contributions can be determined using the following equation (7):

[0082] (7)

[0083] Among them, k1 represents the capacitance contribution coefficient, and k2 represents the diffusion control contribution coefficient. Figure 1 e and Figure 1 f shows that the Cu(acac)2 battery exhibits a high capacitance contribution percentage, which gradually increases with the increase of scan rate (84.22%, 88.55%, 89.73%, 90.23% and 93.93%). This enhanced capacitance contribution is believed to support high-rate performance, indicating that the addition of Cu(acac)2 will effectively improve the rate capability of the battery. In summary, the electrochemical performance tests show that the CV curve of the Cu(acac)2 battery has a small peak potential difference, a large peak current and a reduced charge transfer impedance, indicating an enhanced specific capacity and accelerated reaction kinetics in the Cu(acac)2 battery. The fitted b value reveals the synergistic effect of capacitance and diffusion mechanisms in the Cu(acac)2 battery, with capacitance behavior being dominant. High capacitance contribution indicates an enhancement in the battery rate capability.

[0084] The cycling performance of Cu(acac)2 batteries and AC batteries was systematically compared, and all specific capacities and current densities were normalized to the active iodine mass. Figure 2 As shown in a, at 0.2Ag -1 At a current density of 1.5 GHz, the stable initial specific capacity comparison shows that the specific capacity of the Cu(acac)2 battery is 181 mAh g -1 , higher than the 155mAhg of AC battery -1 As the number of cycles increases, the capacity of both batteries gradually decays. After 2500 cycles, the Cu(acac)2 battery retains 133 mAhg -1 The specific capacity of the battery is 99.65%, with an average Coulombic efficiency (CE) of 73%. In contrast, the AC battery only retains 92 mAhg -1 , the capacity retention rate is 59%. This shows that under long-term cycling conditions, the Cu(acac)2 battery effectively suppresses the multi-iodide shuttle effect, thereby improving the capacity retention rate. In contrast, the physical adsorption of iodine species by activated carbon in AC batteries is weak and cannot provide satisfactory performance in long-term cycling. Further analysis of its specific capacity-voltage curve shows that two voltage platforms appear between 1.1V and 1.3V, indicating the presence of iodine redox activity in this voltage range ( Figure 2 b) This is consistent with Figure 1The CV curve results in a are consistent. At the same time, tracking the specific capacity-voltage curve of the Cu(acac)2 battery at different cycle times found that as the cycle number increases, the voltage platform remains stable, indicating that the battery has good cycle reversibility. In addition, the specific capacity difference gradually decreases, indicating that the specific capacity of the battery gradually stabilizes ( Figure 2 c). In sharp contrast, the voltage plateau of the AC battery gradually shortens with increasing cycle number, indicating that the multi-iodide shuttle effect leads to the loss of active materials and causes the rapid decay of specific capacity.

[0085] Further rate performance comparisons are as follows Figure 2 d. At 0.2Ag -1 to 4Ag -1 At a current density of 202 mAh g, the Cu(acac)2 battery provided 202 mAh g -1 , 189mAhg -1 、183mAhg -1 , 179mAhg -1 , 175mAhg -1 , 166mAhg -1 , 161mAhg -1 and 137mAhg -1 Under the same conditions, the specific capacity of AC battery is lower, which is 161mAhg -1 , 154mAhg -1 , 149mAhg -1 , 146mAhg -1 , 144mAhg -1 , 136mAhg -1 , 133mAhg -1 and 112mAhg -1 . The specific capacity of both batteries decreases with increasing current density. This is because higher current density results in shorter charge and discharge times, which prevents the complete reaction of the active material. The lower specific capacity observed in the AC battery indicates that the generation of intermediate polyiodide species leads to irreversible loss of active material. At the same time, Figure 2 e more intuitively demonstrates the high specific capacity and stable voltage platform of Cu(acac)2 battery at different current densities, highlighting its excellent rate capability, which is consistent with its high capacitance contribution. This further confirms the effective suppression of the multi-iodide shuttle effect by Cu(acac)2 at different current densities. Subsequently, the cycle stability test at higher current density was carried out. Figure 2 f, in 2Ag -1 At a current density of 1.5 GHz, the initial specific capacity of the Cu(acac)2 battery is 161 mAh g -1 , higher than the 130mAhg of AC battery-1 After 17,000 cycles, the Cu(acac)2 battery retained 101 mAhg -1 The specific capacity of the AC battery is 78 mAh g / cm2, with an average CE of 99.92%. In contrast, the capacity curve of the AC battery shows convexity near 6000 cycles, 9000 cycles, 12000 cycles and 15000 cycles, indicating that it is susceptible to external interference, which destroys the cycle stability. Finally, the specific capacity of the AC battery drops to 78 mAh g / cm2. -1 It is worth noting that, if Figure 2 g, in 4Ag -1 At a current density of 1.5 GHz, the Cu(acac)2 battery achieved a cycle life of more than 55,000 times, with an extremely low capacity decay rate of 0.00086% per cycle. In contrast, the AC battery not only has a lower initial specific capacity (114 mAh g -1 ), and the capacity decays rapidly after 7000 cycles, and finally drops to 13 mAh g at about 16000 cycles. -1 This accelerated degradation may be due to insufficient reaction of active materials at high current density, which further promotes the formation of polyiodides. The highly soluble polyiodides shuttle to the surface of the zinc anode, causing zinc corrosion, which seriously damages the battery cycle life. To study this phenomenon, the 0.2Ag -1 The Zn anodes of the Cu(acac)2 battery and AC battery were subjected to post-cycling SEM characterization. The results show that the surface defects of the cycled Zn foil (left) of the AC battery are present, including pits, pores, and protrusions (10-20μm in size). These morphological changes confirm the damage of the Zn surface corrosion caused by polyiodide shuttle and Zn ion stripping / electroplating process. This observation confirms the AC battery under 4Ag -1 The reason for the shorter cycle life under these conditions is that the zinc foil surface of the cycling Cu(acac)2 battery is smoother and has fine granular zinc deposits, indicating that Cu(acac)2 effectively inhibits the multi-iodide shuttle effect. This inhibition mechanism significantly improves the cycle life of the battery. The electrochemical performance of this battery exceeds that of similar batteries reported recently. Finally, three Cu(acac)2 batteries were used to light up the LED indicator panel ( Figure 2 h), demonstrating the practical feasibility of Cu(acac)2 batteries and providing strong support for the future application of aqueous zinc-iodine batteries in the field of new energy storage.

[0086] Cu(acac)2 is a dark blue crystalline powder in which Cu(II) serves as the central coordinating ion, forming a tetracoordinate planar structure with two acetylacetonate ligands. It has very low solubility in aqueous solution. In Example 1 above, Cu(acac)2 was used as a carrier for the positive electrode material of an aqueous Zn-I2 battery. The following test results further explore the interaction between Cu(acac)2 and iodine species and the mechanism of Cu(acac)2 action.

[0087] The charge distribution of Cu(acac)2 molecular structure is as follows Figure 3 As shown in (a), the central Cu atom has the highest positive charge (+0.537). The surrounding oxygen atoms exhibit a negative charge (-0.439). The carbon atoms bonded to the oxygen atoms exhibit a positive charge (+0.364) due to electron transfer to the oxygen atoms through covalent interactions. Conversely, the carbon atoms bonded to hydrogen atoms exhibit a negative charge (-0.379) due to electron transfer from the hydrogen atoms, while the hydrogen atoms have a positive charge. Figure 3 The electrostatic potential map in b further confirms the strong positive potential at the central Cu atom. This obvious positive charge center provides the possibility for the electrostatic adsorption of negatively charged iodide ions / polyiodide ions.

[0088] Visualization of the interaction between Cu(acac)2 material and negatively charged iodide ions / polyiodide ions is shown in Figure 2. Figure 3 First, prepare solutions A and B, which contain the same amount of 10mM KI and 1mM I2. Since I2 and I⁻ easily combine to form polyiodide ions that are easily soluble in aqueous solution, such as I3 - 、I5 - Etc., the solution is yellow. This color makes it possible to quickly and easily determine whether the solution contains a large amount of polyiodide ions. Then, the Cu(acac)2 material is added to solution A. Since these materials float on the surface of the liquid, the contact and reaction of Cu(acac)2 with the solution are enhanced by vigorous shaking. This immediately causes the solution to change from brown to colorless. After standing for 10 minutes, most of the Cu(acac)2 material settled at the bottom of the container, a small part of the material floated on the surface of the solution, and the solution became completely clear and transparent. Subsequently, the precipitate was centrifuged and dried at room temperature to obtain a dark purple material, labeled as Cu(acac)2-I complex. The centrifuged solution (KI+I2 after reaction) was subjected to UV-visible spectroscopy and compared with the original solution (KI+I2). In Figure 3 d, belongs to I3 - The peak intensities of the characteristic peaks of the ion at 288 nm and 350 nm decreased, which means that due to the interaction between Cu(acac)2 and I2⁻, I3 -SEM examination was then immediately performed to investigate the morphology of Cu(acac)2 and Cu(acac)2-I complexes. Figure 3 e shows that the original Cu(acac)2 material presents needle-shaped crystals with smooth surfaces and a length of 10~30μm. Figure 3 f shows that the Cu(acac)2-I complex maintains the basic needle-like morphology, but the crystal surface becomes rough. EDS elemental mapping also shows a uniform distribution of C, O, Cu, and I. These findings suggest the interaction between Cu(acac)2 and iodine species, which may be suitable for the development of Zn-I2 batteries.

[0089] XPS was used to analyze the surface chemical state of Cu(acac)2 and Cu(acac)2-I complexes and explore the chemical environment of the elements. The full XPS spectrum showed the presence of C, O, Cu, and I elements in the Cu(acac)2-I complex, which was consistent with the EDS results. In the Cu2p spectrum of the Cu(acac)2 material ( Figure 3 g), the characteristic peaks at 934.0 eV and 953.8 eV are respectively attributed to the typical Cu2p 3 / 2 and Cu2p 1 / 2 , indicating the presence of Cu(II). In the Cu2p spectrum of the Cu(acac)2-I complex, these peaks shift to lower binding energies (Cu2p2p 3 / 2 :933.6eV,Cu2p 1 / 2 : 953.4eV). At the same time, two new obvious peaks appear at 932.0eV and 952.2eV, indicating the presence of Cu(I). This may be related to the interaction between the Cu(acac)2 material and the electron-rich iodine, which causes some electrons to transfer from iodine to copper, changing the chemical state of copper. Figure 3 In the I3d spectrum of h, characteristic peaks at 618.2 eV and 629.9 eV are attributed to I3d5 / 2 and I3d3 / 2, respectively, indicating the presence of I⁻. Meanwhile, peaks at 619.4 eV and 631.2 eV correspond to II. In the C1s spectrum, peaks at 284.8 eV and 287.0 eV correspond to CC / C=C and CO / C=O, respectively. In the O1s spectrum, peaks at 530.9 eV and 530.4 eV arise from C=O bonds and metal oxides (Cu-O). Comparison of the C1s and O1s spectra of Cu(acac)2 reveals no significant differences from the spectrum of the Cu(acac)2-I complex. Combined with the changes observed in the Cu2p spectrum, this suggests that the iodine species primarily interact with the Cu atoms, with minimal effects on the C and O atoms.

[0090] XRD analysis was used to investigate the structural phase differences between Cu(acac)2 and Cu(acac)2-I complexes. Figure 3 As shown in Figure 1, the diffraction peaks at 11.3°, 11.8°, 15.6°, 17.2°, and 26.2° correspond to typical peaks of Cu(acac)2. New diffraction peaks were observed for the Cu(acac)2-I complex. Weak peaks at 21.77°, 25.21°, 35.92°, 42.38°, 44.39°, 58.36°, and 64.58° are likely due to trace amounts of CuI (PDF#06-0246) and KI (PDF#04-0471). Based on these experimental observations and analysis, it can be hypothesized that the high positive charge of copper in the Cu(acac)2 material facilitates interaction with electron-rich iodine species (I⁻, I₂, I⁻, etc.), which can limit the presence of multiple iodide ions in solution. This opens the possibility of developing high-performance Zn-I⁻ batteries.

[0091] Based on the above material characterization and experimental results, DFT calculations were further used to investigate the interaction mechanism between Cu(acac)2 and iodine species in aqueous Zn-I2 batteries. Calculations of the charge distribution and electrostatic potential in Cu(acac)2 indicate that the central Cu atom exhibits a significant positive charge, effectively capturing negatively charged iodide / polyiodide ions. Figure 4 The adsorption energy model results of a show that the adsorption energy of Cu(acac)2 with I⁻, I2, I3⁻ and I5⁻ is lower than the adsorption energy of AC with iodine species, which means that AC exhibits stronger adsorption to iodine species. However, Figure 4 The calculation of the differential charge density in (b) reveals a "push-pull" electron transfer mechanism between Cu(acac)2 and iodine species. Specifically, due to the coordination of negatively charged iodine ions with Cu, some electrons are transferred to the positively charged Cu atoms, and then further transferred to the electronegative O atoms due to the pulling effect caused by their high electronegativity, changing the charge distribution of the entire molecule. All atoms of the Cu(acac)2-iodine species exhibit localized electron accumulation regions (yellow) and depletion regions (light blue), indicating electron redistribution in the Cu(acac)2-iodine species. In sharp contrast, the graphene surface exhibits yellow regions of electron accumulation, indicating that only a unidirectional electron transfer process from iodine species to graphene exists. This indicates that the interaction between Cu(acac)2 and iodine species involves chemical adsorption, while the interaction between graphene and iodine species corresponds to physical adsorption.

[0092] Subsequently, the HOMO-LUMO energy levels of iodine and iodine species bound to Cu(acac)2 were calculated to study their electrochemical properties. According to molecular orbital theory, the LUMO energy level is related to electron affinity, while the HOMO energy level is related to electron donation ability. Compared with pure iodine species, the HOMO and LUMO energy levels of the Cu(acac)2-iodine complex have changed, indicating that there is electron transfer between iodine and Cu(acac)2 ( Figure 4 c). The HOMO and LUMO energy levels of the Cu(acac)2-iodine complex are reduced, indicating that oxidation and reduction are more readily possible at the electrode. Furthermore, the lower HOMO-LUMO energy gap contributes to higher electronic conductivity and enhanced reactivity. Figure 4 d shows that the energy gap of the Cu(acac)2-iodine complex is reduced compared with that of the pure iodine species, indicating that the binding with Cu(acac)2 significantly enhances the conductivity and reactivity of the iodine species, which is the same as the catalytic process.

[0093] The catalytic oxidation of I⁻ by Cu(acac)2 and AC cathodes was evaluated by RRDE in 0.05M ZnSO4+0.1M KI electrolyte. Figure 4 e shows the LSV curve recorded at a rotation speed of 1600 rpm. The Cu(acac)2 cathode shows a higher oxidation current (7.05 mA) at 0.8 V (vs. Ag / AgCl) than the AC cathode (6.64 mA). In addition, its reduction current is also lower than that of the AC cathode. In addition, at a potential of 0.8 V, the LSV curve shows a two-step oxidation wave at a rotation rate of 400-2500 rpm, corresponding to the conversion of I⁻ to I3⁻ at a lower potential and the conversion of I3⁻ to I2 at a higher potential. According to the Koutecký-Levich equation, the Cu(acac)2 cathode can almost achieve two electron transfers, while the electron transfer of the AC electrode is lower (close to 1.8) ( Figure 4 f). These findings suggest that they all follow the I⁻-I3⁻-I2 transformation mechanism. However, the oxidation reaction kinetics are accelerated due to the catalytic effect of Cu(acac)2, which can effectively suppress the shuttling of polyiodide ions.

[0094] In order to verify the catalytic activity of iodine species on Cu(acac)2 and AC, Figure 4The free energies are given in Figure g. Comparisons show that the free energy changes (ΔG) for each conversion step are negative, indicating that the conversion of iodine species on both surfaces is spontaneous and exothermic. This confirms the thermodynamic feasibility of these conversions in battery systems. A detailed comparison of their free energy changes provides deeper insights into the catalytic processes. In the I₂ adsorption step (3I₂+6*→3I₂+3), the free energy changes for Cu(acac)₂ and AC are -1.93 eV and -2.14 eV, respectively, indicating comparable adsorption propensities for both materials at this step. In the second step involving the conversion of I₂ to I⁻ (3I₂+3 +2e⁻→2I⁻+4), the free energy change for the AC surface (-12.36 eV) is greater than that for Cu(acac)₂ (-9.47 eV), indicating a stronger propensity for polyiodide ion conversion on the AC surface, which could lead to an increased polyiodide ion concentration in AC batteries. In the final step involving the conversion of polyiodide ions to iodide ions (2I3⁻+4 +4e⁻→6*I⁻), the free energy change on the Cu(acac)2 surface (-12.46 eV) is greater than that on AC (-10.72 eV). This indicates that the conversion of polyiodide ions on the Cu(acac)2 surface has a greater thermodynamic advantage, enabling rapid completion of the conversion process and reducing the polyiodide ion concentration, thereby effectively suppressing the shuttling effect.

[0095] In situ Raman spectroscopy was used to monitor the evolution of polyiodide ions during charge and discharge of Zn-I2 batteries. Figure 5 a, AC battery ~110cm -1 and ~160cm -1 The high-intensity peaks at are attributed to I3⁻ and I5⁻. During the charging process, the intensities of these two peaks gradually increase, indicating the oxidation reaction of I⁻ ions at the positive electrode. The broadening of the peak shape of polyiodide ions further indicates that the iodine conversion kinetics is slow. In the subsequent discharge process, the peak intensity corresponding to I5⁻ gradually weakened with the passage of discharge time, and finally disappeared completely when discharged to ~0.8V, indicating that the polyiodide ions were completely converted. In sharp contrast, during the charging process, the intensities of I3⁻ and I5⁻ in the Cu(acac)2 battery decreased significantly, indicating that Cu(acac)2 catalyzes the rapid conversion of polyiodide ions ( Figure 5 b). This effectively reduces the concentration of polyiodide ions on the cathode surface, thereby suppressing the shuttle effect. During discharge, the two peaks disappear rapidly, indicating that I2 is rapidly converted to I⁻, further highlighting the catalytic role of Cu(acac)2 in the conversion of polyiodide ions.

[0096] Ex situ XPS was further used to study the chemical state of elemental iodine in Cu(acac)2 batteries at different charge and discharge stages. Figure 5In Figure c, four peaks corresponding to the characteristic peaks of I⁻ and I₂ appear in the pristine cathode. After charging to 1.2 V, the ratio of the characteristic peak of I⁻ to the characteristic peak of I₂ increases, suggesting the oxidation reaction of I⁻ to I₂. When charged to 1.6 V, this ratio further decreases, indicating a more complete oxidation reaction. Conversely, when discharged to 1.2 V, the ratio increases again, indicating the reduction reaction of I₂ to I⁻. When discharged to 0.6 V, the value rises further due to more iodine reduction reactions. These observations reveal a highly reversible iodine redox reaction during battery charge and discharge, consistent with the above results. In summary, adsorption energy calculations and differential charge density analysis indicate that Cu(acac)₂ enables electron transfer with iodine species through chemical adsorption. The reduced HOMO-LUMO energy gap of the Cu(acac)₂-iodine species complex indicates enhanced conductivity and reactivity, contributing to a higher effective capacity. Simultaneously, the improved catalytic effect effectively suppresses the shuttle effect, which is verified by free energy calculations. Therefore, the schematic diagram of AC and Cu(acac)2 battery is as follows Figure 5 Due to the improved reaction kinetics and the suppression of the multi-iodide ion shuttle effect, Cu(acac)2 batteries will achieve excellent cycling reversibility and extended life.

[0097] In summary, this scheme proposes a cathode material designed with a metal organic catalyst to fix polyiodides and catalyze their reaction kinetics through synergistic adsorption and catalysis. Experimental and theoretical studies have shown that the positively charged central Cu atom in Cu(acac)2 promotes coordination with the negatively charged polyiodides. This chemical adsorption promotes electron transfer from polyiodides to Cu atoms, which has been confirmed by XPS spectroscopy. In addition, HOMO-LUMO energy level analysis shows that the redox activity of iodine species is enhanced after binding to Cu(acac)2, and the reduced energy gap accelerates the mutual conversion between polyiodides, thereby inhibiting their accumulation - this mechanism has been verified by in situ Raman spectroscopy. Cu(acac)2 batteries exhibit excellent rate capability and ultra-long cycle stability at 4Ag -1 The proposed simple yet high-performance iodine-based cathode design provides key insights for advancing aqueous zinc-iodine battery technology.

[0098] To better illustrate the present invention, numerous specific details are provided in the detailed description above. Those skilled in the art will appreciate that the present invention can be practiced without certain specific details. In some instances, methods, means, components, and circuits well known to those skilled in the art have not been described in detail in order to highlight the main purpose of the present invention.

[0099] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A positive electrode material for aqueous Zn-I2 batteries, characterized in that: Including copper acetylacetonate Cu(acac)2 and activated carbon.

2. The positive electrode material for aqueous Zn-I2 batteries according to claim 1, characterized in that The mass ratio of the copper acetylacetonate Cu(acac)2 to the activated carbon is 1:

4.

3. An electrode sheet, characterized in that: The electrode sheet comprises the positive electrode material for an aqueous Zn-I2 battery as described in any one of claims 1-2.

4. The electrode sheet according to claim 3, characterized in that: The invention also includes a conductive agent, an adhesive and a solvent; the conductive agent is acetylene black, the adhesive is PVDF; and the solvent is N-methylpyrrolidone.

5. The electrode sheet according to claim 4, characterized in that: The mass ratio of the active material, the conductive agent and the binder is 8:1:

1.

6. The method for preparing an electrode sheet according to any one of claims 3 to 5, characterized in that: The steps include: Cu(acac)2 and activated carbon are mixed and ground according to a mass ratio, and then the resulting mixture is mixed with a conductive agent, a binder, and a solvent to obtain a slurry; The uniform slurry was evenly coated on carbon paper and dried to prepare a Cu (acac)2 electrode; Subsequently, the cathode liquid was dropwise coated on the Cu (acac) 2 electrode and dried to obtain the cathode liquid; the cathode liquid included an aqueous solution of 0.1 M KI and 0.01 M I2.

7. Aqueous Zn-I2 battery, characterized in that include: A positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the electrode sheet according to any one of claims 3 to 5 or the electrode sheet prepared by the preparation method according to claim 6.

8. The aqueous Zn-I2 battery according to claim 7, characterized in that: The negative electrode includes zinc foil.

9. The aqueous Zn-I2 battery according to claim 6, characterized in that: The electrolyte includes a ZnSO4 solution.

10. The aqueous Zn-I2 battery according to claim 9, characterized in that: The concentration of the ZnSO4 solution is 2M.

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