New anode of potassium ion battery: hollow carbon material grafted with sulfur

As the most successful commercial ion battery at present, the lithium-ion battery with high energy storage density, convenient carrying and long service life has penetrated into all aspects of human life, but at present, the energy density level of lithium-ion battery has gradually failed to meet the growing demand of electric vehicles and smart grid, plus the abundance of lithium resources in the earth's crust (0.0017 wt%) ）And the pollution that accompanied the mining process, these restrictions forced people to seek better ion batteries As a homologous element of lithium, ion batteries based on sodium and potassium are superior to lithium in both resource content and mining difficulty Compared with sodium ion batteries, potassium ion batteries have higher working voltage and theoretical capacity In addition, compared with Li +, Na +, K + has weaker Lewis acid and smaller solvation radius, so the transfer in the electrolyte is easier However, higher quality and larger ion radius will cause serious volume expansion in the process of charge and discharge of potassium ion battery, which will cause damage to the structure of the material Therefore, it is of great significance to develop more suitable electrode materials for potassium ion battery for its commercialization Recently, Professor Zhong Cheng of the Key Laboratory of advanced ceramics and processing technology of the Ministry of education of Tianjin University and Professor David mitlin of Clarkson University in the United States reported a kind of anode material (SHCS) for potassium ion batteries The material will contain a large amount of sulfur (38 wt%) by in-situ vulcanization ）The hybrid material prepared by grafting onto the spherical carbon material with hollow structure not only has a diffusion distance of about 40 nm, but also the C-S bond in the structure can effectively reduce the attenuation of cycle capacity and coulomb efficiency This achievement was published in advanced materials (DOI: 10.1002 / ADMA 201900429) under the title of "sulfur graftedhollow carbon spheres for potassium ion battery anodes" Figure 1 Preparation process of sulfur grafted hollow carbon based materials (photo source: adv mater.) the author first prepared the surface containing resorcinol (R) and formaldehyde (formaldehyde) by hydrothermal method, F) Silicon ball SiO2 @ RF can be obtained by fully mixing the silicon ball and sulfur powder through grinding, and then the silicon ball SiO2 @ RF @ s containing sulfur can be obtained at 450 At high temperature of ℃, resorcinol and formaldehyde on the surface of silicon spheres are carbonized as carbon sources At the same time, sulfur mixed with carbon materials is vulcanized with carbon Finally, after the reaction of sulfurization and carbonization, silicon spheres react with hydrofluoric acid to remove the silicon core to obtain carbon based materials with hollow structure (Figure 1) By means of SEM, TEM and HRTEM, it can be found that the morphology of the carbon layer in the material is well preserved after silicon removal The size of the whole hollow carbon sphere is about 400 nm, and the thickness of the carbon layer is about 40 nm In addition, based on hadf images and eels, the oxygen and sulfur elements in the carbon layer are uniformly dispersed in the whole material (Fig 2) Fig 2 SEM, TEM, HRTEM, HAADF, eels of sulfur grafted hollow carbon based materials (source: adv mater.) next, the author focused on some battery related properties of SHCs as electrode materials through electrochemical experiments (Fig 3) The results show that the SHCs based battery has a reversible capacity of 581 MAH / G under the condition of 0.025 A / g charge and discharge, which is the highest among the reported potassium ion batteries based on carbon anode materials, and the electrode materials can still retain 93% capacity after multiple charge and discharge In addition, SHCs based batteries also have ideal rate performance (202, 160, and 110 MAH / g at 1.5, 3, and 5 A / g) In order to better reflect the energy density of the new materials, the author compared the data of some carbon based electrode materials reported in the literature and calculated theoretically The results showed that SHCs as anode materials showed the highest relative energy density Figure 3 Electrochemical performance of SHCs based batteries (photo source: adv mater.) full text author: Jia Ding, Hanli Zhang, Hui Zhou, Jun Feng, Xuerong Zheng, Chengzhong, eunsu Paek, Wenbin Hu and David mitlin.