Encapsulating tin dioxide nanoparticles into COF to develop high capacity Lithium ion battery anodes

Abstract

Covalent Organic Frameworks (COFs) are porous crystalline polymers formed by organic linkers connected through covalent bonds. They have numerous advantages such as high porosity, controllable pore size, thermal stability, functional tunability and low solubility in electrolyte. COFs have attracted wide attention due to their robust network, enhanced stability and open pores that will aid the inclusion of electrolyte ions when used as electrodes in LIBs. In recent years, COFs have attracted a lot of attention as prospective anode materials for rechargeable batteries due to their structural diversity and atomic-level functional adaptability. We have already demonstrated that COF have the potential to deliver excellent rate-performance for LIBs, but their ion-storage capacity needs to be further improved to achieve practical energy densities. Incorporating metal nanoparticles into the COFs and employing this as an electrode will help to enhance ionic or electrical conductivity for LIBs. Owing to their high theoretical specific capacity, tin dioxide is considered as a potential LIB anode. However, due to the severe agglomeration and significant volume fluctuations of SnO2 particles during the Li intercalation de-intercalation, its use in real lithium-ion batteries is still constrained. Aggregation of particles result in poor electrochemical performance as it restricts the availability of active sites for Li+ ions and huge volume changes lead to electrode cracking which in turn restricts the cycling capability of electrodes. An effective approach to solve the above problems is either reduces the size of SnO2 particles and provides a support that can disperse these particles and mitigate the associated volume changes. The nano confinement of the SnO2 particles in the COF would prevent their coagulative growth into undesirable sizes, which can lead to electrode cracking. Here we have used COF namely, IISERP-COF6 as the porous support which was successful in dispersing tin dioxide as SnO2 nanoparticles. This SnO2 loaded IISERP-COF6 was employed as the anode material for LIB and this composite exhibited a specific capacity of 1100 mAh/g at 100 mA/g current density.