Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries

Abstract

Lithium metal has gravimetric capacity ∼10× that of graphite which incentivizes rechargeable Li metal batteries (RLMB) development. A key factor that limits practical use of RLMB is morphological instability of Li metal anode upon electrodeposition, reflected by the uncontrolled area growth of solid-electrolyte interphase that traps cyclable Li, quantified by the Coulombic inefficiency (CI). Here we show that CI decreases approximately exponentially with increasing donatable fluorine concentration of the electrolyte. By using up to 7 m of Li bis(fluorosulfonyl)imide in fluoroethylene carbonate, where both the solvent and the salt donate F, we can significantly suppress anode porosity and improve the Coulombic efficiency to 99.64%. The electrolyte demonstrates excellent compatibility with 5-V LiNiMnO cathode and Al current collector beyond 5 V. As a result, an RLMB full cell with only 1.4× excess lithium as the anode was demonstrated to cycle above 130 times, at industrially significant loading of 1.83 mAh/cm and 0.36 C. This is attributed to the formation of a protective LiF nanolayer, which has a wide bandgap, high surface energy, and small Burgers vector, making it ductile at room temperature and less likely to rupture in electrodeposition.

A Highly Reversible, Dendrite‐Free Lithium Metal Anode Enabled by a Lithium‐Fluoride‐Enriched Interphase

“…Among them, LiF exhibits the highest interfacial energy against Li metal (73.28 meV Å −2 )18 and shows potential alteration of Li vertical growth patterns. Unfortunately, many efforts to enhance this strategy of LiF‐enriched SEI have to rely on the reduction of fluorinated electrolyte components,19 leading to the consumption of superfluous amounts of electrolyte before forming enough LiF passivation in a long cycle time. Another route involves an artificial LiF‐based SEI,20 by coating LiF layer on anode surface using precision instrument at a high cost.…”

A Sustainable Solid Electrolyte Interphase for High‐Energy‐Density Lithium Metal Batteries Under Practical Conditions

“…Among various approaches, LiF‐rich SEI (F‐SEI) and LiN x O y ‐contained SEI (N‐SEI) have arisen as exemplary methods to stabilize Li metal under mild conditions recently. F‐SEI is generated by fluorinated solvents or Li salts and N‐SEI is constructed by LiNO 3 additives in carbonate or ether electrolyte, respectively. Generally, F‐SEI and N‐SEI formed by additives as SEI precursors (<5 %, by weight or volume) cannot maintain sustainable due to irreversible exhaustion of limited additives under practical conditions .…”

“…[25][26][27][28][29] Tr emendous efforts have been devoted to constructing intrinsically uniform SEI by regulating the electrolyte solvation, i.e., the components and structure of electrolyte,such as concentrated electrolyte, [30][31][32][33][34] fluorinated electrolyte, [35][36][37] and sacrificial additives. [38][39][40] Among various approaches,LiF-rich SEI (F-SEI) and LiN x O y -contained SEI (N-SEI) have arisen as exemplary methods to stabilize Li metal under mild conditions recently.F -SEI is generated by fluorinated solvents or Li salts [37,[41][42][43][44][45] and N-SEI is constructed by LiNO 3 additives in carbonate or ether electrolyte, [40,[46][47][48][49][50][51] respectively. Generally,F -SEI and N-SEI formed by additives as SEI precursors (< 5%,b yw eight or volume) cannot maintain sustainable due to irreversible exhaustion of limited additives under practical conditions.…”

Achieving High Energy Density through Increasing the Output Voltage: A Highly Reversible 5.3 V Battery

“…However, the average operation potentials of these cathodes are still lower than 4.5 V. Even for the so-called ''5.0 V cathode materials,'' such as LiNi 0.5 Mn 1. 5 13 Current electrolytes suffer severe decomposition on these cathode surfaces when the cathodes are fully charged to a potential above 4.5 V. 14,15 Therefore, there has been no report of a highly reversible >5.0 V Li battery up to now.…”