High Performance Low‐Temperature Lithium Metal Batteries Enabled by Tailored Electrolyte Solvation Structure

Abstract

conductivity and even fails; [1][2][3][4] (3) limited charge transfer rate across the interface between the electrode and electrolyte at low temperature, which also depends on the de-solvation kinetics of the solvated Li + at the interface; (4) severe Li plating due to the large polarization of the anode at low temperature. [9][10][11] Since some recent studies demonstrated that the poor low-temperature performance of LIBs is manly limited by the low ionic diffusion in the graphite anode other than the cathode and the electrolyte, [12] graphite is not an ideal anode for the low temperature LIBs. Logically, Li metal anode has become a better alternative, which has higher energy density (3860 mAh g −1 ) and better performances in the low-temperature environments. [4,[13][14][15][16][17] However, harsh lithium dendrite growth and instability interface at low temperature are still huge challenges. According to previous reports, the electrolyte components have significant effects on the Li plating. Rational electrolyte formulation can not only inhibit the vigorous lithium dendrite growth, regulate the interfacial composition, but also increase the ionic conductivity of the electrolyte at low temperature, which greatly improves the low-temperature performances of lithium batteries. [10,15,[18][19][20][21][22] Traditional low-temperature electrolytes for lithium metal batteries are mainly ether electrolytes. Although ethers have low melting points, their electrochemical windows are narrow and often do not match with cathodes such as LFP and NCM. [4] In addition, ether electrolytes without tailoring solvation structure are prone to produce a large amount of organic components at the interface, which is not stable during the charging and discharging process. [23] Therefore, designing a novel electrolyte with tailored solvation structure, low melting point is an effective route to obtain a high performance low-temperature lithium metal battery. [11,24] Fluorinated solvents can provide more inorganic SEI components (mainly LiF) prior to solvent decomposition, which is due to the lower LUMO energies originated from the strong electronwithdrawing ability of F. [11,[25][26][27] Carboxylic esters generally have lower melting points than carbonates and higher oxidation limit than ethers. [2] Herein, diethyl fluoromalonate (DEFM) and fluoroethylene carbonate (FEC) are combined as the co-solvent of the electrolyte. And lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is selected as the lithium salt in this fluorinated carboxylic ester electrolyte due to its high ion conductivity and thermal stability. [14,[28][29][30] Furthermore, high concentrated 2 m LiTFSI The electrochemical performances of lithium metal batteries are determined by the kinetics of interfacial de-solvation and ion transport, especially at low-temperature environments. Here, a novel electrolyte that easily de-solvated and conducive to interfacial film formation is designed for low-temperature lithium metal batteries. A fluorinated carboxylic ester, diethyl fl...

Weakly Solvating Few-Layer-Carbon Interface toward High Initial Coulombic Efficiency and Cyclability Hard Carbon Anodes

“…The NaF in the SEI is determined by the F 1 s profile. Compared with CHC, PCHC displays higher content of F. The higher distribution of NaF is maintained against cycling, which may facilitate the rigidity and stability of the SEI with a thinner and smoother morphology …”

High Chaos Induced Multiple-Anion-Rich Solvation Structure Enabling Ultrahigh Voltage and Wide Temperature Lithium-Metal Batteries

“…The effect of increased chaos of the electrolyte on the solvation structure was verified by molecular dynamics (MD) simulations and Raman spectra (Figure a–b, Figures S3–S4). For the HC-E system, the high g­(r) peak of anions and Li + indicates anions can participate in the formation of the Li + -EMC-DMC-DFOB – -PO 2 F 2 – -PF 6 – solvation structure, which is conducive to the formation of an inorganic-rich interphase. In Figure c–d, the binding energy of Li + and each linear carbonate solvent is significantly lower than that of Li + -EC, indicating a much weaker solvating interaction between Li + and EMC/DMC, which promotes low temperature kinetics.…”

Synergy of Weakly Solvated Electrolyte and LiF-Reinforced Interphase Enables Long-Term Operation of Li-Metal Batteries at Low Temperatures

“…In the former case, Li + diffuses through solid electrodes and liquid electrolytes, and in the latter case, Li + is stripped from solvation sheath and subsequently diffused in SEI. When it comes to mass transfer, the common optimization strategy is to use cosolvents with low viscosity and melting point, like ethers, − esters, − and nitriles. , Owing to the similar functional groups to carboxylates, the low melting point, and the good salt dissociation degree, carboxylic esters have been extensively studied. As compared to other linear carboxylic esters, methyl acetate (MA) has the shortest chain length, the lowest melting point (−98 °C), and the lowest viscosity (0.37 cP), which made it a highly competitive low-temperature cosolvent.…”