Solvation Structure-Tunable Phase Change Electrolyte for Stable Lithium Metal Batteries

Abstract

Li + solvation structure (LSS) is considered to be the decisive factor in determining the electrochemical performance of lithium metal batteries. Herein, we propose a phase change electrolyte (PCE) whose LSS can be in operando regulated by changing the physical state of the electrolyte. The primary solvent of a PCE is dimethyl dodecanedioate (DDCA), which stands out among a series of solvents, exhibiting excellent comprehensive performance. The PCE shows high ionic conductivity, lithium transference number, and a wide electrochemical stability window in the solid and liquid states. Moreover, the LSS of the obtained PCE can reversibly transform between the solventseparated ion pair (SSIP) and contact ion pair (CIP) structure according to its physical state. This characteristic enables PCE to outperform conventional liquid electrolytes in suppressing lithium dendrite growth and dissolution of active anodic materials, especially at varying temperatures. The assembled Li-LiMn 2 O 4 full cells display outstanding electrochemical performance, high Coulombic efficiency, and capacity retention.

Atomic Insights into Advances and Issues in Low‐Temperature Electrolytes

“…Before salting out, the strong anion-cation interaction driven by low temperature promotes the formation of more CIPs, which undoubtedly causes the preferential anion-decomposition to form inorganic-rich SEI. For example, Li et al [45] reported that the solvation structure of the electrolyte changed from solvent separated ion pair (SSIP) to CIP with the temperature decrease, which was proved by Raman spectrum (Figure 5a 1 ,a 2 ). Then, strong cation-anion interaction promoted the reduction potential of anions on anode surface, resulting in the SEI film containing LiF (Figure 5a 3 ).…”

“…However, high polarity (dielectric constant) also implies strong solventsolvent interactions, resulting in the high freezing point and the poor low temperature dissolution ability. For example, the EC has good solubility to common lithium and sodium salts [45] Copyright 2022, American Chemical Society. b) The organic components of SEI films at b 1 ) 20 °C, b 2 ) −20 °C, and b 3 ) −40 °C, respectively.…”

“…Third, even after solidification, the special solvent still has a good ion transport rate. For example, Li et al [45] constructed a phase change electrolyte by screening high melting point (>15 °C) solvent dimethyl dodecanedioate (DDCA), which could reversible change the physical state at 22 °C (Figure 11c 1 ). Near the phase change point, the ionic conductivity of the electrolyte changed, obviously (Figure 11c 2 ).…”

Thermally responsive polymers for overcoming thermal runaway in high-safety electrochemical storage devices

“…38 Similarly, thermal dedoping involves the removal of active ions at high temperatures so that the voltage cannot reach the cut-off voltage, thereby inhibiting thermal runaway. 39,40 Specifically, thermal dedoping of PF 6…”

“…38 Similarly, thermal dedoping involves the removal of active ions at high temperatures so that the voltage cannot reach the cut-off voltage, thereby inhibiting thermal runaway. 39,40 Specifically, thermal dedoping of PF 6 − has been extensively studied. The thermal expansion strategy utilized the thermal expansion of a polymer matrix with a high thermal expansion coefficient at high-temperature to separate the conductive particles and destroy the conductive pathway to shut down the battery, thus preventing thermal runaway caused by continued overheating in ESDs.…”