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.

Among the key materials of lithium-ion batteries, the electrolyte is often underestimated as a simple "ion transport medium," but its true role is that of a "system control hub"​ that integrates battery performance. By regulating the solvation structure​ and interface reaction pathways, it governs the formation of the SEI/CEI protective films, thereby determining the battery's fast-charging capability, cycle life, and safety. The essence of electrolyte design lies in skillfully balancing multiple inherent contradictions: achieving high ionic conductivity​ requires overcoming the limitations of solvent high viscosity; constructing a stable electrode interface​ necessitates utilizing the property of "selective decomposition" of electrolyte components; meanwhile, enhancing flame retardancy​ often comes at the cost of conductivity. More importantly, it is the critical bottleneck​ for the industrialization of next-generation high-energy-density batteries (such as high-nickel cathodes, silicon-based anodes, and lithium metal anodes), requiring specialized formulations to address specific pain points like high-voltage oxidation, significant volume expansion, and lithium dendrite growth. Ultimately, there is no "perfect" electrolyte, only the engineering-optimal solution​ found for a specific battery system and performance requirements, balancing conductivity, stability, safety, and compatibility.

As lithium-ion battery energy density rises, the flammability of the carbonate-based electrolyte remains a critical safety bottleneck. This article provides a deep dive into electrolyte flame-retardant technology, positioning it as the key to an intrinsic safety revolution beyond external protection. It analyzes the limitations of traditional approaches and highlights the paradigm shift towards high-performance, multifunctional flame-retardant additives. Using the star additive PFPN (Ethoxy(pentafluoro)cyclotriphosphazene)​ as a prime example, the article details how its unique phosphazene structure enables a synergistic gas-phase and condensed-phase flame-retardant mechanismwith just 5% addition. Crucially, PFPN goes beyond safety: it enhances electrochemical performanceby forming stable SEI/CEI films, improving cycle life and compatibility with high-voltage cathodes. The analysis concludes that such additives, which integrate safety with performance enhancement, are evolving from optional to essential components for next-generation high-energy, high-safety batteries in EVs and energy storage.