In Situ Solid-State DETFPi-PDOL Electrolyte and Its Impact on the Interfaces and Performance of NCM811||Li Batteries

Abstract

Solid electrolytes are generated through in situ polymerization within batteries, which is one of the most promising methods for achieving solid-state lithium metal batteries with good interfacial contact, high safety, and high performance. Poly-1,3-dioxolane (PDOL), although a good in situ solidified electrolyte for lithium stability, has poor applicability in high-voltage battery systems. In order to improve the interfacial compatibility between PDOL and both the cathode and anode of high-voltage batteries. we herein design a sacrificial additive, diethyl (2,2,2-trifluoroethyl) phosphite (DETFPi), with a lower lowest unoccupied molecular orbital (LUMO) and higher highest occupied molecular orbital (HOMO) energy, through methods of calculation. After being loaded into the battery, DETFPi-DOL is in situ polymerized to form DETFPi-PDOL electrolyte. The Li||DETFPi-PDOL||Li symmetric battery operates stably for 2000 h at 0.5 mA cm^–2, with an overpotential of only 16 mV. XPS analysis shows that an SEI layer with high LiF content is formed on the surface of the lithium anode after cycling, which promotes the uniform deposition of lithium ions and inhibits the growth of lithium dendrites. After 300 cycles, the NCM811||DETFPi-PDOL||Li battery exhibits a remaining capacity of 154.8 mAh g^–1 (81%) within the 3.0–4.35 V range, meanwhile demonstrating excellent rate performance. Moreover, a uniform CEI layer containing pentavalent phosphorus and low LiF content is formed on the surface of the cathode after battery cycling. Finally, due to the improvement of the cathode interface, the increase of interfacial impedance of the battery after 300 cycles is reduced to half that of the PDOL battery.