Stable Li–Metal Batteries Enabled by in Situ Gelation of an Electrolyte and In-Built Fluorinated Solid Electrolyte Interface

Abstract

Lithium–metal batteries (LMBs) are the focus of upcoming energy storage systems with extremely high-energy density. However, the leakage of liquid electrolyte and the uncontrollable dendritic Li growth on the surface of the Li anode lead to their low reversibility and safety risks. Herein, we propose a stable quasi-solid LMB with in situ gelation of liquid electrolyte and an in-built fluorinated solid electrolyte interface (SEI) on the Li anode. The gel polymer electrolyte (GPE) is readily constructed via cationic polymerization between lithium hexafluorophosphate and ether electrolyte. The fluorine-containing additive, fluoroethylene carbonate (FEC), plays a crucial role in the building of a dense SEI with fast interfacial charge transport. The ex situ spectroscopic characterizations suggest that the enhanced LiF species in the SEI with the addition of FEC and the in situ optical microscopy reveal the inhibited dendritic Li growth. Moreover, GPE@FEC exhibits a high oxidative stability beyond 5.0 V (vs Li/Li+). The significantly improved Li plating/stripping efficiency (400 cycles, 98.7%) is presented for the Li∥Cu cells equipped with GPE@FEC. Decent cycling stability is also available for the cells with the LiFePO4 cathode, reflecting the feasibility of GPE@FEC for practical LMBs with enhanced stability and safety.

Synergy of an In Situ-Polymerized Electrolyte and a Li3N–LiF-Reinforced Interface Enables Long-Term Operation of Li-Metal Batteries

“…The weak LiF and Li 3 N peak should be generated from the decomposition of LiTFSI, and the lithium carbonates are induced by the reduction of organic solvents. The peak of Li 3 N appears stronger on the Li surface with LiNO 3 –GPE because of the reduced LiNO 3 , which readily participates in the formation of the SEI. , The enhanced signal of LiF indicates that LiNO 3 may accelerate the decomposition of LiTFSI, as has been confirmed by Zhang et al The peak intensity of LiF becomes stronger for Li with FEC/LiNO 3 –GPE, suggesting that the reduction of FEC plays a role to produce LiF. − In terms of the N 1s spectra (Figure d), the weak signals of Li 3 N (398.8 eV) and −NSO 2 CF 3 (398.8 eV) from the reduction of LiTFSI can still be seen with base liquid electrolyte. For the GPEs consisting of LiNO 3 , besides the strong signals of −NSO 2 CF 3 and Li 3 N, the two peaks at 403.2 and 408.1 eV are attributed to LiN x O y .…”

[tert-Butyl(diphenyl)silyl] trifluoromethanesulfonate acts as an effective additive for high-voltage lithium metal batteries

“…To address these issues, researchers have established stable SEI films to promote uniform deposition of lithium ions, which ultimately inhibits the growth of lithium dendrites. 12,13 At present, the specific measures mainly include using electrolyte additives, 14,15 building an artificial SEI layer, 16,17 applying the polymer electrolytes, [18][19][20] etc. Among them, the use of electrolyte additives has received attention because of their simplicity, greenness, and excellent effects.…”

Gentle Haulers of Lithium-Ion–Nanomolybdenum Carbide Fillers in Solid Polymer Electrolyte

“…The stable and compact SEI film is an excellent lithium-ion conductor and electronic insulator. 39 Solid F−Mo 2 C−LCPP electrolytes react with the anodes to produce lithium compounds, so the generated SEI film can exist more stably and weaken the dissolution and destruction of the SEI film in the electrochemical cycling. Compared with those of liquid batteries, dendrites and nuggets decrease after 100 cycles.…”

“…Transition metal carbide/oxide heterojunction nanofillers can reduce the energy barrier for lithium-ion transference. They also increase the effective carrier concentration between the electrode and electrolyte interfaces. − …”

“…In contrast, the intensity of the component characteristic peak on the polymer electrolyte without Mo 2 C at the anode–electrolyte interface after cycling is weak (Figure S29). The stable and compact SEI film is an excellent lithium-ion conductor and electronic insulator …”