Gradual release fluorine from additive to construct a stable LiF-rich cathode electrolyte interphase for high-voltage all-solid-state lithium batteries

Constructing a stable cathode interface is essential for achieving prolonged cycle life for high-voltage all-solid-state lithium metal batteries (ASSLBs). To this end, utilizing functional additives to regulate the composition and/or structure of the cathode electrolyte interphase (CEI) is regarded as one of the most straightforward and effective strategies for polymer-based ASSLBs. Herein, we systematically explore the impacts of 2,3,4,5,6-pentafluorophenylacetic acid (PFPAA) as a novel electrolyte additive on the interfacial stability of high-voltage ASSLBs through comprehensive theoretical calculations and experimental investigations. The results indicate that PFPAA is incompatible with lithium metal anode. To avoid the detrimental effects of PFPAA on the anode interface, double-layer electrolytes are employed in ASSLBs to investigate the effect of different amounts of PFPAA on battery performance. It is observed that fluorine-rich PFPAA can act as a self-sacrificing CEI film-forming additive, enabling the gradual release of fluorine to promote the formation of a thin CEI film with uniformly dispersed LiF, and thereby effectively stabilizing the cathode/electrolyte interface and significantly improving the cycle stability of high-voltage ASSLBs. As a result, a high-voltage LiNi_0.88Co_0.09Al_0.03O₂-based ASSLB employing an ultrathin integrated double-layer electrolyte (∼ 30 μm) composed of optimal compositions exhibits a high discharge specific capacity of 155.5 mAh g⁻¹ along with a high capacity retention of 68.6 % after 500cycles at 1.0C. This work demonstrates that PFPAA is a promising CEI film-forming additive for high-voltage polymer-based ASSLBs. © 2024 Elsevier B.V.