Miscellaneous impurities in electrolyte additives: 1. Impurities are unavoidable, and what impurities matter. 2. Some compatible impurities. 3. Little influence on impurities sulfate fluorion phosphate carbonate dimer or trimer residual solvent 4. Very large impurities chloride ions: water alcohols, aldehydes, acids, substances containing active hydrogen impurities Metal ions: environmental pollutants: 5. The impact is not clear. First of all, whether it is a benign influence or a small influence, it is not "do not control". All impurities need to be regulated, at least to know how much their content is, at least how much is allowed to depend on their nature.

In recent years, based on cobalt-free LiNi0.5Mn1.5O4 (LNMO) positive electrode (5 V class, vs. Li+/Li) and lithium metal anode (3.04 V vs. Ultrahigh pressure lithium metal batteries with standard hydrogen electrodes have attracted a lot of attention as promising candidates for the next generation of high energy density and sustainable batteries due to their theoretical energy density of up to ~650 Wh/kg. In contrast to the unstable layered oxide LiNixCoyMnzO2, the toxic Co element caused by the LNMO spinel structure is eliminated and the inherent safety is eliminated. However, their development is severely limited by the incompatibility between the state-of-the-art carbonate electrolyte and the two aggressive electrodes. Here, we have synthesized a new electrolyte additive,2, 2-difluoroethylmethyl sulfone (FS), which enables stable cycling of ultra-high pressure lithium metal batteries in conventional carbonate electrolytes. On the cathode side, unlike conventional electrolyte additives, FS can be selectively adsorbed on the LNMO surface to form a special assembled FS "buffer" layer that can effectively remove free carbonate molecules from the cathode surface. Therefore, during charging, the -CF2H group of FS is well decomposed by the anode to form an inorganic rich CEI, which effectively inhibits the micro-fracture and transition metal dissolution of LNMO. On the anode side, FS can also perform cathode decomposition well, resulting in an inorganic rich SEI for stable cycling of Li metal anodes. As a result, the carbonate electrolyte containing FS additives gives cobalt-free 5V-class lithium metal batteries unprecedented high performance, i.e. a 40um-Li /LNMO (load = 7 mg·cm2) full battery with a high capacity retention rate of 84% for 600 cycles at 1C using a commercial carbon-based low-concentration electrolyte. A complete battery consisting of a highly loaded cathode (20 mg·cm2) and an ultra-thin lithium anode (40 mm) has a capacity retention rate of 99% after 100 cycles at 0.25C. In addition, to our knowledge, previously unreported Li/LNMO bag-like batteries have been assembled and can run stably for more than 150 cycles. This paper is based on Rational molecular design of electrolyte additive endows stable cycling performance of cobalt-free 5 V-class lithium metal batteries, published in Energy & Environmental Science.