Study On The Modification And Activation Of Cobalt Sulfide Used As Cathode For Rechargeable Aluminum-ion Batteries

Aluminum is the most abundant metal element in the earth's crust,accounting for8%of its total mass.The aluminum-based redox reaction can transfer three electrons during the electrochemical charge and discharge reactions,which provides an opportunity for batteries with higher storage capacity.In addition,aluminum's self-healing characteristics makes it safer than other metals,and aluminum is easier to mine and extract.Therefore,aluminum ion batteries are ideal candidates for large-scale energy storage systems.The purpose of this article is to explore cobalt sulfide as cathode for aluminum ion batteries,including the preparation of CoS₂@GO materials by compounding graphene with CoS₂ materials through a one-step hydrothermal,and detection of products after reaction.Moreover,the activation phenomenon of the Al-cobalt sulfide system batteries was studied by synthesizing vacant cobalt sulfide materials(CoS_1.097@C)as the cathode for the aluminum ion batteries,which have been evidenced by electrochemical measurements and the first-principles calculations.Firstly,CoS₂@GO composite materials with good crystallinity were synthesized by a one-step hydrothermal,which have small particles of different shapes and were uniformly distributed.After graphene combining,CoS₂ particles were significantly refined and the specific surface area of CoS₂@GO was increased.When this material is used as cathode of the aluminum ion batteries,exhibiting battery behavior with obvious activation phenomena.It is speculated that new substances are generated during the redox reaction process.The batteries have a peak specific capacity of¹30mAh g^-1,and the capacity retention rate exceeds 90%after 200 cycles.This composite electrode material has undergone a reduction process of aluminum ion insertion and an oxidation process of aluminum ion deintercalation with good reversibility.Secondly,using pure CoS₂ materials as cathode to explore the new material produced after the reaction of the batteries.After being charged,a part of the Al element remains in the cathode material evidenced by SEM,which is consistent with the XPS results.Therefore,aluminum ion batteries using cobalt sulfide as the electrode materials confirmed the formation of a stable new aluminum-containing materials during the charge and discharge process.Finally,CoS_1.097@C,a vacant cobalt sulfide material,was synthesized using a metal-organic framework to optimize the activation phenomenon in Al-cobalt sulfide system.SEM and TEM showed that the nano-sized CoS_1.097.097 particles are uniformly dispersed on the carbon matrix.The batteries with CoS_1.097@C electrode showed an initial specific discharge capacity of 70 mAh g^-1,and reached a peak of 160 mAh g^-1after 40 cycles.Furthermore,the retention capacity was 85 mAh g^-11 after 500 cycles and the coulomb efficiency remained at about 90%.Therefore,CoS_1.097@C cathode has excellent comprehensive electrochemical performance.At the same time,from the first-principles calculations,the crystal structure of the product is a cobalt vacancy-type defect.Compared with the perfect supercells of CoS,it is evidenced that aluminum ions are more likely to enter the cobalt vacancy-type supercells than the perfect supercells.Therefore,the cobalt vacancy-type defect cobalt sulfide material is helpful in improving the activation process and the electrochemical performance.In short,cobalt sulfide materials as cathode material for aluminum ion secondary batteries have great potential for development and application.The composite materials of CoS₂@GO and CoS_1.097@C can improve the electrochemical performance of pure cobalt sulfide,which exhibit a good application prospect in the practical application of aluminum ion secondary batteries.