Unsymmetrical fluorinated malonatoborate as an amphoteric additive for high-energy-density lithium-ion batteries

Abstract

To cater for drastically growing demands for batteries with high energy density and long-term cycle life in transportation sector and large-scale energy storage systems, advancement of energy storage technologies is urgently required. Because ultimate energy density of batteries can be realized through developing high-capacity electrode materials, structural optimization of electrode materials that are capable of storing high energy has been intensively addressed. In this study, we demonstrate the significant roles of artificially constructed surface on high-capacity Li-rich cathodes preventing mechanical fracture of the cathode particles, mitigating the exposure of inner surface of the cathode toward electrolytes by intergranular cracking, and alleviating voltage decay of the cathode by phase transformation and vulnerable interface. Newly synthesized asymmetric boron-centered ionic additive with partially fluorinated malonate bonded to a central boron core is employed as a functional additive ensuring interfacial stability of high-capacity SGC anodes and Li-rich cathodes. The action of the protective surface layer created by asymmetric boron-centered ionic additive on intergranular cracking of Li-rich cathode particles synthesized via co-precipitation is explored using field emission scanning electron microscopy (FE-SEM). The unique feature of asymmetric boron-centered ionic additive -induced interfacial structure scavenging the oxygen species derived by Li2MnO3 and mitigating undesirable phase transformation of Li-rich cathodes are elucidated through in situ differential electrochemical mass spectrometry (DEMS) and high-resolution transmission electron microscopy (HR-TEM) analyses, respectively. Furthermore, we examine the chemistry of the surface of both electrodes evolved by asymmetric boron-centered ionic additive using ex situ X-ray photoelectron spectroscopy (XPS) and demonstrate the possible mechanisms of asymmetric boron-centered ionic additive constructing stable electrolyte-electrode interface.