Multi-functional yolk-shell structured materials and their applications for high-performance lithium ion battery and lithium sulfur battery

Lithium-ion (Li-ion) and lithium-sulfur (Li-S) cells have aroused widespread concern regarding as prospective compositions for most commonly energy storage devices because of high specific capacity and excellent energy density. But some weaknesses still exist such as high cost and low theoretical specific capacity of Li-ion cell, which is difficult to meet people's increasing demand for high energy density. And unsatisfactory conductivity and notorious "shuttle effect" of lithium polysulfides (LiPSs) for Li-S cell, which will affect the commercialization. In various structures of battery materials, yolk-shell structured materials, possessing hollow shell and interior core, show outstanding applied potential for the cells because of having appropriate pore sizes, abundant active sites, prevented aggregation of active materials, accommodated volume expansions and more facilitated channels for electrons and Li+ transportation and functional groups to effectively adsorb LiPSs. Thus many novel yolk-shell structured materials are applied to cell materials to resolve the problems mentioned above. In this review, recent progresses on yolk-shell structured materials used in the cells including their preparation methods, geometric morphology design, action mechanisms in enhancing electrochemical performances and safety are generalized. Then we have a sufficient discussion for yolk-shell structured materials in the cells and build structure-function relationships between structured materials and cell performances. At last, some challenges and suggestions about their preparations, functional modifications and actual applications of yolk-shell structured materials in the cells are summarized. We hope the review can attract more people's attention and conduct more researches on yolk-shell structured materials for various secondary batteries.