Research On New System Of Secondary Batteries Based On Zinc Anode

The zinc electrode has the advantages of abundant resources, low price, environmental friendliness, good reversibility, and so on. It is widely used as the negative electrode material of primary batteries. However, its application is limited in secondary batteries. In this paper, Zn was used as the negative electrode, Zn-PbO2 single flow battery system and Zn-LiMn2O4 battery system were proposed. The electrochemical properties of deposited zinc in acidic and nearly neutral (pH 4) aqueous media were studied. In order to improve the performance of Zn-LiMn2O4 system, firstly, we studied the fading mechanism of LiMn2O4 in aqueous solution. And then, the electrochemical performance of spinel LiMn2O4 was improved by being coated in situ with polyaniline and making the gel electrolyte. Finally, we proposed the design of double positive electrode and clarified the interaction mechanism of Zn2+, Mn2+ ions in aqueous solutions. The main research works are as follows:1, The electrochemical performance of deposited zinc with acidic and near neutral (pH 4) electrolyte shows that the zinc deposition is controlled by the mass transfer process. The increase of the concentration of sulfuric acid in the electrolyte is beneficial to improve the kinetic process of zinc deposition and dissolution, leading to higher energy efficiency. However, the high concentration of sulfuric acid leads to the increase of hydrogen evolution and accelerant of the corrosion rate, resulting in the decrease of coulomb efficiency. The most suitable electrolyte is composed of 1.25 mol·L-1 ZnSO4 and (1～1.5) mol·L-1 H2SO4 and the suitable current density is at 20～30 mA cm-2.2,The evaluation of substrate for the zinc deposition and dissolution was performed. The results show that the graphite composite electrode has higher overpotential of hydrogen evolution than the lead and lead alloy electrodes, which indicates that the corrosion current of composite graphite electrode is smaller than that of the lead and lead alloy electrodes through the calculation of the corrosion current. The electrochemical test results show that the cycle stability of zinc electrode on composite graphite substrate is significantly better than other substrates. Therefore, the appropriate substrate is proposed to be composite graphite substrate for zinc deposition and dissolution in acidic medium.3, Though the Zn-PbO2 single flow battery system exists the problems of high hydrogen evolution and self-dissolution of zinc corrosion, it still provides the high coulomb efficiency of 90% and the capacity retention rate of 80% after cycling for 150 times. Based on Zn-PbO2 system, we used the low-cost, environment-friendly and reversibility better LiMn2O4 as the cathode to structure the novel aqueous rechargeable battery of Zn-LiMn2O4 and mainly study the mechanism of capacity fading and effective method of enhancing stability in water medium in order to further improve the performance of the battery. The obtained conclusions are described as follows:4,The effect of electrolyte on spinel LiMn2O4 was investigated. The results show that the dissolution of Mn and the process of oxygen evolution are affected by anions in the electrolyte, which has great influence on the electrochemical performance. The amount of Mn dissolution in LiNO3 solutions is the least and the oxygen evolution over-potential is the highest. Therefore, the LiNO3 solution exhibits the most stable cycling performance. The capacity retention rate is 75% after 1000 cycles. After adding 2 mol·L-1 ZnSO4 electrolyte in 1 mol·L-1 Li2SO4, despite the discharge capacity of LiMn2O4 reduces a bit, the capacity retention rate is improved from 35% to 58% after 1000 cycles.5, The fade mechanism of LiMn2O4 in the mixed electrolyte of 1 mol·L-1Li2SO4 and 2 mol·L-1 ZnSO4 is similar to that of the organic electrolyte, but the manganese dissolution becomes more serious.6, The performance of the Zn-LiMn2O4 system is limited by the positive cycle stability. Based on this, the electrochemical performance of spinel LiMn2O4 is improved by in situ coating with polyaniline. The electrochemical tests show that the LiMn2O4 composite coated 10% polyaniline exhibits better rate capability and cycle stability than the composite without polyaniline. The LiMn2O4 composite coated 10% polyaniline has the capacity retention rate of 80% after the 320 cycles, while the uncoated material only charge-discharge cycles for 120 cycles. Compared with the aqueous solution, gel electrolyte can reduce the self-discharge of electrode and effectively improve the cycling stability of LiMn2O4. The amount of Mn dissolution is also reduced by half during cycling.7, Mn2+ in electrolyte can form a composite electrode with LiMn2O4. The energy storage mechanism is as follows: ε-MnO2 can be deposited on the surface of the electrode above 1.75v (vs.Zn2+/Zn) in the MnSO4 solution. The resultant deposited ε-MnO2 can be the main skeleton of the intercalation and deintercalation for Zn2+, conversion of Mn4+ to Mn3+ providing the discharge capacity. The intercalation and deintercalation of Li+ ions from LiMn2O4 occur above 1.5V, while Zn2+ can intercalate and deintercalate from ε-MnO2 in the voltage range of 1.4 V-1.0V.