Fig. 1

Schematic of lithium ion conduction in polymer-based electrolytes. (a) Li-ion transport pathways in polymer electrolytes: In coordinating polymers Li-ion conduction occurs via intra-and interchain ion hopping, and segmental motion；(b) Li-ion pathways within LLZO (5%)-PEO (LiTFSI), LLZO (20%)-PEO (LiTFSI), LLZO (50%)-PEO (LiTFSI), and LLZO (50%)-PEO (LiTFSI) (50%)-TEGDME composite electrolytes[22]；(c) Schematic diagram of coupling/decoupling between Li+ and oxygen atoms in C＝O and C－O groups and transport path in PVEC-PE[23]；(d) single ion conduction in PEGDA and PTHFDA gel polymer electrolytes[24]"

Fig. 2

Schematic diagram of SEI and involved processes. (a) structure of the solid-electrolyte interface[25]; (b) Li+ diffusion in porous organic SEI layers and diffusion in dense inorganic SEI layers[26]; (c) Li+ transport map in Li2CO3 as a function of the voltage of nearby electrode materials referenced to Li metal (zero voltage)[27]; (d)pristine Li metal electrode and polymer-alloy-fluoride interphase-based Li metal electrode (PAF-Li) working at a low temperature of -40 ℃[28]"

Fig. 3

Structure and ionic conductivity of polymer-based composite electrolytes and electrochemical properties of solid-state batteries. (a) Discharge capacity and coulombic efficiency of a Li/CPE-10% LLZTO/LFP battery at -20 ℃ and -10 ℃ under different current rates[30]; (b) possible Li+ conduction pathways in LCPE-60 composite electrolytes[31]; (c) The charge-discharge voltage profiles of Li|LCPE60|LFP at 0.1C and (-10± 2) ℃[31]; (d) Schematic diagram of ionic conduction in composite polymer electrolytes[32]; (e) Cycling performance obtained from LiFePO4|CPE|Protected Li cell at 0.2C and -20 ℃[32]"

Fig. 4

Formation process of gel polymer electrolyte and electrochemical performances of solid-state lithium batteries at low temperatures. (a) Gel network formation via dynamic condensation of PEG-CHOs with CTH[39]; (b) Cycling performance (0.2C) of solid-state batteries at different temperatures[39]; (c) The ionic conductivity gradient of the developed electrolytes at 23 ℃ on the ternary phase diagram[40]; (d) Charge-discharge curves of the Li|QSPE|NMC811 cell between -30 and 20 ℃[40]; (e) Li/GPE/LFP battery operation at -35 ℃[41]"

Fig. 5

Molecular modification and ionic conduction in polymer-based electrolytes and electrochemical performances of solid-state lithium batteries. (a) Schematic illustration of the ion-dipole interactions in the SIPC[49]; (b) Illustration of Li+ transport patterns during battery charging[50]; (c) The charge-discharge curves of Li|CPCE|NCA full cells at -20 ℃ under 0.1C[51]; (d) Li+ transport model in the S-LHCE[52]; (e) Cycling performance of LFP cell at -10 ℃ and 0.1C/0.05C[52]"

Fig. 6

Conformal interfaces formed by in situ polymerization and electrochemical properties of corresponding solid-state lithium batteries. (a) The unwanted impacts of oligomers, residual monomers and free radicals on electrode/electrolyte interfaces[61]; (b) In-situ-formed QSPE/Li interface[63]; (c) Schematic diagrams of corrosion behaviors of the NCM811 cathode|electrolyte interface and Al current collector in 1 mol/L LiPF6-EC:DMC, 1 mol/L LiTFSI-DEE and NGPE[64]; (d) Cross-sectional SEM images of Li deposited on Cu foil at 0.2 mA/cm2 current density[65]"

Fig. 7

Design and formation of conductive SEI/CEIs. (a) Schematic diagram of the formation process of the solid electrolyte interface phase (SEI) formed on the Li metal electrode and the CEI on the positive electrode side in the Li||NCM811 cell[76]; (b), (c) Cryo-TEM images of deposited Li in the cell with the polymer electrolyte at different scales[76]; (d) TEM of NCM811 particles[76]; (e) SEM images of NCM811 particles[76]; (f) Top-view[77] and(g) cross-section SEM images of Li metal after 50 cycles in PDE[77]; Schematic diagrams of the charge and mass transport mediated by temperature-dependent SEI at (h) Low temperature, and [78] (i) ambient temperature[78]; morphology of (j), (k)recovered Li in Li||Li cell[79] and (l), (m) PTNB@Li electrode in PTNB@Li||PTNB@Li cell[79]"