Lithium metal batteries (LMBs) hold the promise to pushing cell level energy densities beyond 300 Wh kg −1 while operating at ultra-low temperatures (< −30°C). Batteries capable of both charging and discharging at these temperature extremes are highly desirable due to their inherent reduction of external warming requirements. Here we demonstrate that the local solvation structure of the electrolyte defines the charge-transfer behavior at ultra-low temperature, which is crucial for achieving high Li metal coulombic efficiency (CE) and avoiding dendritic growth. These insights were applied to Li metal full cells, where a high-loading 3.5 mAh cm −2 sulfurized polyacrylonitrile (SPAN) cathode was paired with a one-fold excess Li metal anode. The cell retained 84 % and 76 % of its room temperature capacity when cycled at −40 and −60 °C, respectively, which presented stable performance over 50 cycles. This work provides design criteria for ultra-low temperature LMB electrolytes, and represents a defining step for the performance of low-temperature batteries.

A modified liquefied gas electrolyte with the addition of fully coordinated cosolvent enables unique Li solvation structures. Their favorable properties lead to dendrite-free high Coulombic efficiency Li-metal anode cycling and enable lowtemperature operation even down to À60 C with high Li-metal efficiency. The system shows potential for improved energy density and low-temperature operation of Li-metal batteries.

Improving the extremely low temperature operation of rechargeable batteries is vital to the operation of electronics in extreme environments, where systems capable of high‐rate discharge are in short supply. Herein, we demonstrate the holistic design of dual‐graphite batteries, which circumvent the sluggish ion‐desolvation process found in typical lithium‐ion batteries during discharge. These batteries were enabled by a novel electrolyte, which simultaneously provides high electrochemical stability and ionic conductivity at low temperature. The dual‐graphite cells, when compared to industry‐type graphite ∥ LiCoO2 full‐cells demonstrated an 11 times increased capacity retention at −60 °C for a 10 C discharge rate, indicative of the superior kinetics of the “dual‐ion” storage mechanism. These trends are further supported by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) measurements at reduced temperature. This work provides a new design strategy for extreme low‐temperature batteries.

Liquefied gas electrolytes with unique solvation structure enable high ionic conductivity in extended temperature ranges, supporting wide-temperature high-voltage lithium metal batteries.

Lithium metal batteries are capable of pushing cell energy densities beyond what is currently achievable with commercial Li-ion cells and are the ideal technology for supplying power to electronic devices...

temperatures (≤−20°C) is limited by reduced ionic transport properties of the electrolyte, as well as by severe charge-transfer polarization. Herein, we demonstrate that this low-temperature cycling limitation can be overcome in LiNi x Mn y Co z O 2 (x + y + z = 1) (NMC)||graphite type full cells with a methyl propionate (MP)-based ester electrolyte. This electrolyte, consisting of LiPF 6 dissolved in MP and fluoroethylene carbonate (FEC), delivers successful cycling at the high rate of 0.5C at −20°C. It also sustains stable charge and discharge cycling at −40°C with 60% capacity retention compared with room-temperature operation. This outstanding electrochemical performance is further supported by electrochemical impedance spectroscopy (EIS) in threeelectrode pouch cells to investigate the internal resistances between cathode and anode, as well as careful structure and composition characterizations at the electrode interfaces. This work offers a new avenue for high-performance LIBs capable of ultralow-temperature charging−discharging operation.

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