Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20 M dimethoxyethane-solution of the phosphoric acid derivative (CF 3 CH 2 O) 2 P(O)OH (HBFEP), an artificial solid electrolyte interphase (SEI) is generated on the Li-metal surface. Hence, HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li-ion conducting inorganic coordination polymer. This film exhibits -due to the reversibly breaking ionic bonds -self-healing ability upon cycling-induced volume expansion of Li. The presence of LiBFEP as the major component in the artificial SEI is proven by ATR-IR and XPS measurements. SEM characterization of HBFEP-treated Li samples reveals porous layers on top of the Li surface with at least 3 μm thickness. LiÀ Li symmetrical cells with HBFEP-modified Li electrodes show a three-to almost fourfold cycle-lifetime increase at 0.1 mA cm À 2 in a demanding model electrolyte that facilitates fast battery failure (1 M LiOTf in TEGDME). Hence, the LiBFEP-enriched layer apparently acts as a Li-ion conducting protection barrier between Li and the electrolyte, enhancing the rechargeability of Li electrodes.

Ni-rich cathode active material Li 1+x [Ni 0.85 Co 0.10 Mn 0.05 ] 1−x O 2 (NCM851005) was exposed to BF 3 gas at room temperature with pressures between 25 mbar and 2478 mbar. It mainly gave an LiBF 4 coating by reaction with the basic surface lithium impurities. The electrochemical investigations up to full-cell level displayed a significantly improved long-term cycling behavior at 45 °C for only 0.08 wt% BF 3 coated NCM851005 material, compared to pristine NCM851005 material. The internal resistance of full-cells was reduced for all tested amounts of BF 3 coating (after 300 cycles: pristine NCM851005 +293% and 0.08 wt% BF 3 coated NCM851005 +133% resistance built-up). Moreover, online electrochemical mass spectrometry studies showed a reduced CO 2 release in the first cycle of half-cells built with the coated NCM851005 material compared to those with pristine NCM851005 material. The thermal annealing of the coated NCM851005 material at 200 °C or 400 °C led to a decrease of LiBF 4 , but to an increase of LiF content on the surface. However, coated NCM851005 material with thermal annealing exhibits lower discharge capacities after 250 cycles compared to NCM851005 material with equal coating amount, which were not thermally annealed.