Synthesis And Electrochemical Performance Of Cobalt-based Oxides And Sulfides As Anode Materials For Potassium Ion Battery

Benefiting from low cost and high crustal abundance,potassium-ion batteries are regarded as a potential alternative to lithium-ion batteries.However,compared with Li⁺,K⁺not only has a slower diffusion rate,but also has a larger radius.The volume expansion caused by disembedding in the material is more intense and the damage to the structure is more serious,especially for the anode materials of potassium ion battery.Cobalt-based oxides and sulfides are considered as one of the best anode materials for potassium ion battery due to their high discharge specific capacity.However,due to the serious structural damage caused by the K⁺disintercalation process,their rate performance is poor and cycle life is short.Through reasonable structure design and carbon coating process,the volume expansion problem caused by disintercalation of cobalt oxide and sulfide can be significantly improved,and the rate performance and cycling stability of the materials can be greatly improved.In this paper,through ingenious experimental design,we successfully synthesized carbon-coated cobalt oxide（Co O@C）and cobalt sulfide loaded on hollow carbon spheres（Co S@HCS）respectively,and tested the performance of potassium storage.The main contents are as follows:（1）Carbon-coated cobalt oxide（Co O@C）composite anode material was synthesized by oleoamine pyrolysis and a simple coating process with dopamine hydrochloride.The results showed that the electrochemical properties of Co O were improved by the bonded carbon layer.The obtained Co O@C composite showed excellent electrochemical performance:at the current density of 100 m A g^-1,it retained a reversible capacity of 230 m Ah g^-1 after 100 cycles;At the current density of 1A g^-1,a capacity of 185.9 m Ah g^-1 was maintained after 500 cycles.（2）Using Co O nanoparticles and polymethyl acrylate as precursors,cobalt sulfide loaded on hollow carbon spheres（Co S@HCS）was prepared by electrostatic spray and sulfuration process.After various test characterizations,the following characteristics were found:Co S@HCS material had a spherical hollow structure,and each spherical particle size was about1μm.Among them,the cobalt sulfide particles were loaded on the hollow carbon spheres,the thickness of the carbon wall of the hollow carbon spheres was about 50 nm,and the dual-doping phenomenon of nitrogen and sulfur was found in the hollow carbon spheres.（3）We had carried out a deep study on the potassium-storage performance of Co S@HCS.The results showed that Co S@HCS composite had excellent cycle life:at the current density of 100 m A g^-1,it still retained the capacity of 332 m Ah g^-1 after 100 cycles;At a large current density of 1 A g^-1,the reversible capacity of 196 m Ah g^-1 was still retained after 1000 cycles.The assembled full battery still retained a capacity of 82.4 m Ah g^-1 after 50 cycles at a current density of 100 m A g^-1.The paper also revealed that the potassium storage mechanism of Co S@HCS material was the transformation reaction of Co S and the contribution of pseudocapacitance.It was found that Co S@HCS has excellent diffusion kinetics by GITT method and electrochemical impedance method（EIS）.