Compliant Solid Polymer Electrolytes (SPEs) for Enhanced Anode-Electrolyte Interfacial Stability in All-Solid-State Lithium–Metal Batteries (LMBs)

Practical application of high energy density lithium–metal batteries (LMBs) has remained elusive over the last several decades due to their unstable and dendritic electrodeposition behavior. Solid polymer electrolytes (SPEs) with sufficient elastic modulus have been shown to attenuate dendrite growth and extend cycle life. Among different polymer architectures, network SPEs have demonstrated promising overall performance in cells using lithium metal anodes. However, fine-tuning network structures to attain adequate lithium electrode interfacial contact and stable electrodeposition behavior at extended cycling remains a challenge. In this work, we designed a series of comb-chain cross-linker-based network SPEs with tunable compliance by introducing free dangling chains into the SPE network. These dangling chains were used to tune the SPE ionic conductivity, ductility, and compliance. Our results demonstrate that increasing network compliance and ductility improves anode-electrolyte interfacial adhesion and reduces voltage hysteresis. SPEs with 56.3 wt % free dangling chain content showed a high Coulombic efficiency of 93.4% and a symmetric cell cycle life 1.9× that of SPEs without free chains. Additionally, the improved anode compliance of these SPEs led to reduced anode-electrolyte interfacial resistance growth and greater capacity retention at 92.8% when cycled at 1C in Li|SPE|LiFePO4 half cells for 275 cycles.


Figure S2 .
Figure S2.Photograph of ConSPEs used to determine sol fraction after soaking in THF and drying.

Figure S5 .
Figure S5.Representative chronoamperometry profiles and the impedance spectra before and after chronoamperometry test used to measure transference number for the symmetrical lithium cell 4PGMA-PEG2k(NH2)2 at 90 °C.

Figure S7 .
Figure S7.Plot of the short circuit time of ConSPEs vs. the percentage of PEG3k-NH2 out of total PEG in the network for Li/Li symmetric cells at a current density of 0.5 mA cm -2 and areal capacity of 1.5 mAh cm -2 .

Figure S8 . 12 Figure S9 .
Figure S8.Electrical impedance spectroscopy (EIS) scans for ConSPE Li/Li symmetric cells (a) before; (b) after 120 hours; (c) after 480 hours and (c) after 720 hours of cycling at a current density of 0.5 mA cm -2 and areal capacity of 1.5 mAh cm -2 .

Figure S13 .
Figure S13.XPS spectra of cycled lithium metal surface in Li|SPE|Cu cells after 38 cycles at a current density of 0.5 mA cm -2 and areal capacity of 0.25 mAh cm -2 .(a) F1s (b) O1s and (c) C1s spectra for 4PGMA-PEG2k(NH2)2 and 46PEG3k-NH2 prior to and after 1 min of etching with 2 kV Ar ion gun.

Figure S17 .
Figure S17.Equivalent circuit model used to fit EIS data of for Li|SPE|LiFePO4 prior to cycling.Ri , Qi, and Wi represent resistive, constant phase and semi-infinite Warburg elements, respectively.R1, R2 and R3 were taken to represent the bulk electrolyte, cathode-SPE and anode-SPE resistances, respectively.

Figure S18 .
Figure S18.Equivalent circuit model used to fit EIS data of for Li|SPE|LiFePO4 after cycling at 1C. Ri , Qi, and Wi represent resistive, constant phase and semi-infinite Warburg elements, respectively.R1 & R2 were taken to represent the bulk electrolyte and anode-SPE interfacial resistances, respectively.The W4 semi-infinite Warburg element was introduced to improve the fit in the lower frequency region.

Table S1 .
Electrolyte composition by weight percentage.

Table S3 .
Interfacial and bulk resistances obtained through fitting EIS data taken throughout the symmetric cell cycling experiments.

Table S4 .
Comparison of 46PEG3k-NH2 electrochemical performance to previously reported SPEs in literature (work published after 2019).
a Contains liquid electrolyte.bComposite solid electrolyte.* Values calculated using ImageJ analysis software.

Table S5 .
Interfacial and bulk resistances obtained through fitting EIS data for Li|SPE|LiFePO4

Table S6 .
Interfacial and bulk resistances obtained through fitting EIS data for Li|SPE|LiFePO4 cells after cycling.