Fig. 1

Three stages for the thermal runaway process. Stage 1: The onset of overheating. The batteries change from a normal to an abnormal state, and the internal temperature starts to increase; Stage 2: Heat accumulation and gas release process. The internal temperature quickly rises, and the battery undergoes exothermal reactions; Stage 3: Combustion and explosion. The flammable electrolyte combusts, leading to firesand even explosions[6]"

Fig. 2

(a) Typical molecular structures of flame-retardant additives; (b) The mechanism for the flame retardation effects of phosphorus-containing compounds; (c) The self-extinguish time (SET) of the typical carbonate electrolyte can be signifificantly reduced with the addition of triphenyl phosphate[20]"

Fig. 3

(a) Illustration of the migration inhibition of the ionic or electron conduction between electrodes via reversibly thermal-responsive polymers for preventing the thermal runaway of electrochemical storage devices[22]; (b) Illustrative schematic of a thermally-controllable polymer electrolyte for electrochemical energy storage; (c) pH and ionic conductivity response to temperature of 2.2% (weight fraction) solution containing the PNcA at a heating rate of approximately 4.7 ℃/min[23]"

Fig. 4

(a) Photographs of the PEO/IL phase separation[25]; (b) Schematic of the LIB setup, the thermal-response machanism at high temperatures at the electrode surface and the structure of the responsive polymer, PBMA, and ionic liquid, [EMIM][TFSI]; (c) Electrochemical performance of a cell composed of LTO/LFP electrode, 5% PBMA and 0.2 mol/L/0.5 mol/L LiTFSI/[EMIM][TFSI] at 60 ℃ and 150 ℃[26]"

Fig. 5

(a) Schematic diagram of a membrane with thermal-triggered flame retardant consisting of a core-shell structure (flame retardant as core, polymer as shell); (b) After thermal triggering, the polymer shell melts and the encapsulated flame retardant is released into the electrolyte, effectively inhibiting the ignition and combustion of the electrolytePhotographs of the PEO/IL phase separation[21]; (c) Schematic illustration of a thermally responsive gel system used as an electrolyte in electrochemical storage devices. Upon heating, the sol–gel transition of the thermoplastic elastomer solution inhibits the motion of ions, thus actively shutting down the device at high temperature; (d) The temperature dependent rheological behavior of a 30% Pluronic solution; (e) Pictures of a Pluronic solution in the sol and gel states[27]"

Fig. 6

(a) The change of colloid microstructure explains the transition to shear thinning or shear thickening[31]; (b) Schematic diagram of STF electrolyte protection mechanism[32]"

Fig. 7

(a) The relationship between viscosity and shear rate at different volume fractions; (b) The relationship between shear rate and viscosity and normal force of 37% suspension[35]; (c) Silica nanorods of controllable aspect ratio are synthesized from tetraethyl orthosilicate (TEOS) using sodium citrate, polyvinylpyrrolidone (PVP), ammonium hydroxide, ethanol and pentanol in an emulsion approach[37]"

Fig. 8

(a) The distributions of fumed silica particles in the liquid electrolyte at different status; (b) Rheology graph of bare electrolyte and composite electrolytes with 6.3% SiO2, 9.1% SiO2 and 10.7% SiO2; (c) Room temperature variation of ionic conductivity of composite electrolytes (SiO2/LiPF6 in EC/DMC) versus weight fraction of fumed silica. Inset: Ionic conductivity of composite electrolyte with 9.1% SiO2 after impact tests;(d) Discharge curve of LiFePO4 electrode in the STF electrolyte of EC/DMC/LiPF6 with 9.1% SiO2[32]；(e) Voltage stability during impact with and without STE[41]"

Fig. 9

(a) A General view of aggregation of bare silica nanoparticles in solution, B Scheme depicting attachment of organosilane to silica colloid surfaces (top) and grafting of poly(methyl methacrylate) (PMMA) brushes from colloid surfaces via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) (bottom), C Schematic diagram of silica nanoparticles sterically stabilized via surface tethered PMMA brushes[43]; (b) Rheological diagram of electrolyte containing silicon nanorods with different aspect ratios and volume fractions; The discharge capacity (c) and Coulombic efficiency (d) for a full cell composed by NMC| EC/EMC/LiTFSI/33%, AR (5), SiO2 nanorods | graphite and cycled at rates of C/10, 1 C, 2 C, and 1 C[37]；(e) Scheme of APTES modifified GFs preparation process[44]"

Fig. 10

The results of overcharge induced TR for a commercial lithium-ion batteries[46]"

Fig. 11

Schematic illustration of the redox shuttles overcharge protection mechanism[48]"

Fig. 12

(a) Schematic illustration of the ferrocene-based redox shuttle mechanism[50]; (b) Charging voltage profile for graphite/C-LFP pouch cells without and with 0.4 mol/L DBBB additive[51]; (c) Three-step synthesis ofN-ethyl3,7-bis(trifluoromethyl)phenothiazine[53]; (d) schematic illustration of the TAC cationelectrostatic-shielding mechanism[54]"