Research On Preparation Of Cathode Materials By Double-membrane Three-chamber Electrolysis Of Sodium Sulfate Solution

Aiming at the gaps of high value-added utilization of sodium sulfate wastewater in metallurgical chemical industry,this essay proposes the efficient utilization of sodium sulfate wastewater and produce of multiple hydroxide precursors by double-membrane three-chamber electrolysis.By designing and constructing a double-membrane three-chamber electrolysis device,the rules of electrolysis conditions on the properties of precursors were studied,and then the effect of sintering regime on the properties of Li Ni_1/3Co_1/3Mn_1/3O₂ materials was studied.Based on the high sulfur content and poor electrochemical performance of the obtained material,the effect of the sulfur removal method on the final sulfur content and electrochemical performance of the material was discussed.Firstly,the nickel-cobalt-manganese ternary precursor was simultaneously prepared by double-membrane three-chamber electrolysis of sodium sulfate solution.The effects of electrolysis conditions on the morphology and element composition of the precursor were studied.The results show that this method can prepare hydroxide precursors with uniform distribution of transition metals and good proportions in a wide range of conditions.The sulfur content of the precursor has a significant effect on the electrochemical performance of the cathode material.The optimized conditions are:the current density is 25 m A/cm²,the electrolysis temperature is constant temperature of 60℃,the electrolyte concentration in the cathodic compartment is 0.3 mol/L,no aging after electrolysis.Secondly,Li Ni_1/3Co_1/3Mn_1/3O₂ cathode materials synthesised by high temperature solid phase method,and the effects of sintering parameters on the morphology and electrochemical performance of cathode materials were studied.The results show that with the increase of sintering temperature and time,the grain size of the material gradually becomes larger.Under the optimized synthetic conditions（930℃,10 h）,the cathode material has a good layered structure and low cation mixing,and exhibits good cycle performance.Finally,the effects of three different methods for reducing sulfur content on the final sulfur content and electrochemical performance of the material were investigated.Sulfur content was significantly reduced after precursor washing.The sulfur content of the cathode material is further reduced after washing.After washing and post-sintering for cathode material at 400℃for 5 h,the specific discharge capacity and electrochemical reversibility of the cathode material were significantly improved,the cathode material has a specific capacity of 185.88 m Ah/g in the voltage range of 2.5-4.5 V at 0.5 C with a capacity retention of 86.98%after 100 cycles.The high-temperature oxidative pre-sintering of the precursor can also reduce the sulfur content of the material,and the higher temperature of pre-sintering,the lower the sulfur content of the material.The sulfur content of the precursor was reduced to 0.10%after pre-sintering at 800℃for 4 h.Correspondingly,the cathode material has a specific capacity of 180.13 m Ah/g in the voltage range of 2.5-4.5 V at 0.5C with a capacity retention of 88.77%after 100 cycles.