Study On Crystallization Process Of Battery Grade Nickel Sulfate

Lithium ion battery(LIB)is the most promising candidate power supply for electric vehicles,and the most commonly used cathode material is nickel cobalt manganese ternary material.As an important nickel source for ternary cathode materials,battery grade nickel sulfate has very strict requirements such as : purity and crystal size distribution(CSD)have an important impact on the performance of cathode materials.Cooling crystallization is a common preparation method of battery grade nickel sulfate,whose solubility is closely related to temperature.The effects of stirring speed,seed dosage,cooling rate,terminal temperature,seed size and p H value on CSD properties during cooling crystallization were studied.Furthermore,the crystallization process of battery grade nickel sulfate was studied.(1)The effect of cooling crystallization process on the crystal size distribution of battery grade nickel sulfate was studied.The extremely high and low stirring speeds make the crystal size distribution wider,and the bimodal mode appears.Too high or too low seeding dosage will reduce the mean crystal size and broaden the size distribution range.The cooling rate will affect the supersaturation of the solution,a slower cooling rate is conducive to obtaining a larger mean crystal size.A larger seed crystal size can improve the uniformity of the crystal size product.A higher p H value is conducive to the formation of more coarse particles and the reduction of the number of fine particle.The optimum condition of the batch cooling crystallization was 200 rpm of stirring speed,75 g/L of seeding dosage,3°C/h of cooling rate,34°C of terminal temperature,550 μm of seed crystal size,and p H 3.5 of initial solution.(2)The cooling crystallization process of nickel sulphate under optimized conditions was studied.In the first 60 min,the crystals are mostly irregular and basal plate,and the particle size distribution is unimodal.From 100 min to 180 min,the crystals grew gradually,and the crystal size distribution appeared double peaks,and the secondary peak became higher.Until 240 min,the secondary peak is almost the same as the main peak,and the crystals are mainly basal crystals and short prism crystals.At300 min,the crystal size further increased,and the crystal shape was mainly long prism.After 420 min of crystallization time,the crystal size showed a unimodal distribution,and the size was larger,and the long prismatic crystal was dominant.