Lithium-rich antiperovskites (APs) have attracted significant research attention due to their ionic conductivity above 1 mS cm −1 at room temperature. However, recent experimental reports suggest that proton-free lithium-rich APs, such as Li 3 OCl, may not be synthesized using conventional methods. While Li 2 OHCl has a lower conductivity of about 0.1 mS cm −1 at 100 °C, its partially fluorinated counterpart, Li 2 (OH) 0.9 F 0.1 Cl, is a significantly better ionic conductor. In this article, using density functional theory simulations, we show that it is easier to synthesize Li 2 OHCl and two of its fluorinated variants, i.e., Li 2 (OH) 0.9 F 0.1 Cl and Li 2 OHF 0.1 Cl 0.9 , than Li 3 OCl. The transport properties and electrochemical windows of Li 2 OHCl and the fluorinated variants are also studied. The ab initio molecular dynamics simulations suggest that the greater conductivity of Li 2 (OH) 0.9 F 0.1 Cl is due to structural distortion of the lattice and correspondingly faster OH reorientation dynamics. Partially fluorinating the Cl site to obtain Li 2 OHF 0.1 Cl 0.9 leads to an even greater ionic conductivity without impacting the electrochemical window and synthesizability of the materials. This study motivates further research on the correlation between local structure distortion, OH dynamics, and increased Li mobility. Furthermore, it introduces Li 2 OHF 0.1 Cl 0.9 as a novel Li conductor.
self-discharge rates. [1-3] LIBs permeate nearly every aspect of human life. They are widely used in portable electronics (e.g., smartphones, smart-watches, and laptops), transportation (e.g., electric and hybrid vehicles), and biomedical applications (e.g., cardiac pacemakers and cochlear implants). In light of these achievements, J.B. Goodenough, M.S. Whittingham, and A. Yoshino won the 2019 Nobel prize in chemistry. [4] Despite the considerable success of conventional LIBs, their operational regime is typically around room temperature (RT). Operating at low (<0 °C) or high (>60 °C) temperatures usually deteriorate the performance and leads to safety risks. [5] We should also note that commercial LIBs are highly hazardous as they can ignite and explode in case of an accident, overheating, and overcharging, requiring more stringent safety standards, e.g., wide temperature operability and nonflammability. For example, electric vehicles require battery systems that can deliver a stable performance while maintaining a high energy density even in extreme climates, such as cold mountainous areas, where the temperatures can be as low as −40 °C, and hot deserts, where equipment exposed to sunlight can reach temperatures exceeding 70 °C. [6] Moreover, task-specific applications call for reliable energy storage solutions at extreme temperatures, including subsurface exploration (such as for mineral, oil, and gas), aerospace engineering, safety and rescue, and sterilizable medical devices. [2] Conventional LIBs are composed of a positive electrode or cathode (e.g., LiFePO 4 (LFP), LiNi x Mn y Co z O 2 (x + y + z = 1, NMC) and LiCoO 2 (LCO)), an electrolyte (including solvents, Li salts, and additives), a separator (typically a polyolefin membrane), and a negative electrode or anode (e.g., graphite and Li 4 Ti 5 O 12 (LTO)). Generally, the electrode materials are nonflammable and thermal stable (>300 °C). While the polyolefin membrane will melt/shrink over 120 °C, the commercial separators composited with ceramic nanoparticle (e.g., SiO 2 and Al 2 O 3) have been developed to reduce thermal shrinkage when exposed to overheating. [7,8] Therefore, the major challenge of commercial LIBs at extreme operating temperatures comes to the electrolyte. Carbonates are commonly used as solvents for conventional LIB electrolytes. However, these compounds are Li-ion batteries (LIBs) are the energy storage systems of choice for portable electronics and electric vehicles. Due to the growing deployment of energy storage solutions, LIBs are increasingly required to function safely and steadily over a broad range of operational conditions. However, the conventional electrolytes used in LIBs will malfunction when the temperatures fall below zero or elevate above 60 °C. Further, conventional electrolytes are toxic and flammable, leading to severe safety risks, especially in the case of an accident or overheating. Therefore, an ever-growing body of research has been dedicated to the development of electrolytes characterized by high ionic conduct...
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