Effects of Concentrated Salt and Resting Protocol on Solid Electrolyte Interface Formation for Improved Cycle Stability of Anode-Free Lithium Metal Batteries

Abstract

The combined effect of concentrated electrolyte and cycling protocol on the cyclic performance of the anode-free battery (AFB) is evaluated systematically. In situ deposition of Li in the AFB configuration in the presence of a concentrated electrolyte containing fluorine-donating salt and resting the deposit enables the formation of stable and uniform SEI. The SEI intercepts the undesirable side reaction between the deposit and solvent in the electrolyte and reduces electrolyte and Li consumption during cycling. The synergy between the laboratory-prepared concentrated 3 M LiFSI in the ester-based electrolyte and our resting protocol significantly enhanced cyclic performances of AFBs in comparison to the commercial carbonate-based dilute electrolyte, 1 M LiPF6. Benefitting from the combined effect, Cu∥LiFePO4 cells delivered excellent cyclic performance at 0.5 mA/cm2 with an average CE of up to 98.78%, retaining a reasonable discharge capacity after 100 cycles. Furthermore, the AFB can also be cycled at a high rate up to 1.0 mA/cm2 with a high average CE and retaining the encouraging discharge capacity after 100 cycles. The fast cycling and stable performance of these cells are attributed to the formation of robust, flexible, and tough F-rich conductive SEI on the surface of the in situ-deposited Li by benefiting from the combined effect of the resting protocol and the concentrated electrolyte. A condescending understanding of the mechanism of SEI formation and material choice could facilitate the development of AFBs as future advanced energy storage devices.

Anode‐Free Full Cells: A Pathway to High‐Energy Density Lithium‐Metal Batteries

“…Beyene et al introduced a resting and cycling protocol for anode‐free full cells, which when combined with a high‐concentration electrolyte, produced a considerably more robust SEI on the surface of the in situ deposited lithium metal. [ 67 ] They employed a twofold approach, where after cell assembly, the cell was charged and lithium was deposited at a low rate of 0.1 mA cm −2 . After the first charge, the cell was rested for 24 h in order to allow the formation of a robust SEI layer rich in fluorinated species, which originates from the LiFSI electrolyte salt.…”

“…al., favorable optimization of cycling parameters depends significantly on the electrolyte employed. [ 67 ] Genovese et al reported the effects of a “hot formation” procedure, where the initial two cycles were carried out at an elevated temperatures of 40 °C. [ 69 ] They found that the high‐temperature formation cycles enable the deposited lithium metal to form dense, columnar growths, when compared with formation cycles carried out at 20 °C.…”

“…Moreover, when the pressure was increased to 1200 kPa, anode‐free full cells employing the hot formation procedure exhibited 85% capacity retention at 100 cycles (LIRR = 99.8%). It is possible that this hot formation procedure stabilizes lithium deposition in a manner similar to the high‐rate conditioning steps employed by Hwang's group, [ 67 ] although the hot formation procedure also leads to considerable gas generation in the cell. This work utilized a highly optimized LiDFOB/LiBF 4 dual‐salt electrolyte in FEC:DEC (1:2, v/v) solvent, with varying concentrations of LiDFOB and LiBF 4 .…”

Driving high capacity anode-free lithium metal batteries under unpressurized and lean electrolyte condition by an electron-deficient current collector

“…Considerable efforts have recently been made to control Li plating/stripping on the current collector, including the use of various host materials [8][9][10][11][12] , a coherent lattice 13 , and an increase of temperature or pressure 2, [14][15][16][17][18] . While the efficacy of three dimensional (3D) porous current collectors in reducing the effective current density has been proven, their enlarged electroactive surface area can accompany a larger degree of electrolyte decomposition.…”

In Situ Growth of Lithiophilic MOF Layer Enabling Dendrite-free Lithium Deposition

“…To overcome these issues, colossal efforts have been made to achieve uniform deposition of Li metal (He et al, 2019;Assegie et al, 2019;Hou et al, 2017, Hou et al, 2019Nan et al, 2019a, Nan et al, 2019bKamphaus et al, 2019;Beyene et al, 2019;Wang et al, 2019a, Wang et al, 2019b. Among these, various additives have been introduced into the electrolytes to restrain the lithium dendrites by stabilizing the SEI (Zhou et al, 2019;Yang et al, 2017;Yu et al, 2019a, Yu et al, 2019b.…”