Abuse-Tolerant Electrolytes for Lithium-Ion Batteries

Abstract

Safety issues currently limit the development of advanced lithium-ion batteries (LIBs) and this is exacerbated when they are misused or abused. The addition of small amounts of fillers or additives into common liquid electrolytes can greatly improve resistance to abuse without impairing electrochemical performance. This review discusses the recent progress in such abuse-tolerant electrolytes. It covers electrolytes with shear thickening properties for tolerating mechanical abuse, electrolytes with redox shuttle additives for suppressing electrochemical abuse, and electrolytes with flame-retardant additives for resisting thermal abuse. It aims to provide insights into the functioning of such electrolytes and the understanding of electrolyte composition-property relationship. Future perspectives, challenges, and opportunities towards practical applications are also presented.

Keywords: electrolytes; flame retardants; lithium-ion batteries; redox shuttles; shear thickening.

Figure 1

Schematic illustration of the LIB failure and the correlated abuse conditions. Reproduced with permission.^{[ 11b ]} Copyright 2019, Elsevier Ltd.

Figure 2

a) Schematic illustration of the changes in microstructure of STFs for the transition from equilibrium to shear thickening and the hydrogen bonding interaction at surface between particles in a hydrocluster. b) Schematic demonstration of the protective mechanism of STEs under impact test. a) Reproduced with permission.^{[ 37 b]} Copyright 2016, The Royal Society of Chemistry. b) Reproduced with permission.^{[ 41 ]} Copyright 2013, Springer Nature.

Figure 3

Rheological and electrochemical properties of the electrolytes containing different amount of silica fillers. a) Rheological profile of the electrolytes (1 m LiPF₆ in EC/DMC) containing different amount of SiO₂: 0, 6.3, 9.1, and 10.7 wt%. b) Ionic conductivity as function of weight fraction (ω) of fumed silica for STEs. c) Discharge curves of LiFePO₄ electrodes in half‐cells with electrolytes containing SiO₂ of 0, 9.1, and 6.3 wt% under different energy impacts during the discharge. d) Rate performance comparison of LiFePO₄ electrodes in half cells with STE and standard electrolytes. e) Rate performance comparison of graphite electrodes in half cell with STE and standard electrolytes; Inset, cycling performance. f) Nyquist plots of graphite electrode in STEs before and after the impact. Reproduced with permission.^{[ 41 ]} Copyright 2013, Springer Nature.

Figure 4

a) Rheological diagram of viscosity as a function of shear stress for different shear thickening fluids. b) Discharge curves of a cell with the SAFIRE electrolyte; Inset, cycling performance. c) Voltage profiles of cells with PEEK scaffold separator and SAFIRE or standard electrolyte upon the impact. d) Discharge voltage stability of two pouch cells with the SAFIRE electrolyte under the impact energy of 5.65 J. Reproduced with permission.^{[ 42a ]} Copyright 2017, American Chemical Society.

Figure 5

a) TEM images of AR5 (top) and AR24 silica nanorods (bottom). b) Rheological results of AR5 silica nanorods in the standard electrolyte: I) viscosity (ƞ) versus shear stress (σ); II) viscosity (ƞ) versus shear rate ($\dot{\gamma }$). Yellow shaded area is the shear thickening region. c) Cycling profile of discharge capacity (I) and coulombic efficiency (II) for the NMC/graphite CR2032 full cell with the AR5 nanorods (Φ = 0.33) added EC/EMC/LiTFSI electrolyte at different current rates. d) Results of ballistic impact test for I) soft armor and II) hard armor under the conditions of without battery, with battery containing EC/EMC/LiTFSI electrolyte, and with battery containing AR5 nanorods (Φ = 0.358) in EC/EMC/LiTFSI electrolyte. Reproduced with permission.^{[ 43 ]} Copyright 2018, American Chemical Society.

Figure 6

a) Schematic fabrication of APTES modified glass fibers (GFs). b) Rheological results of viscosity versus shear rate for STEs with different filler volume fractions. c) Results of the high speed (79 m s−¹) impact test onto the conventional electrolytes (I) and STE (II) in a glass. Reproduced with permission.^{[ 46 ]} Copyright 2019, Elsevier B.V.

Figure 7

Schematic illustration of the redox shuttle effect during the overcharging in a battery system with graphite anode and carbon‐coated lithium iron phosphate cathode. The oxidized materials are diffused and reduced at the anode surface, and the reduced materials are oxidized to consume the overcharge current. Consequently, the charge potential can be maintained at the potential of redox shuttle molecules. Reproduced with permission.^{[ 50s ]} Copyright 2018, American Chemical Society.

Figure 8

Chemical structure of redox shuttle additives: a) TEMPO; b) 4‐cyano‐TEMPO; c) MPT; d) EPT; e) 3‐chloro‐EPT; and f) IPT. Reproduced with permission.^{[ 29 ]} Copyright 2016, Royal Society of Chemistry.

Figure 9

a) Synthesis of 2‐(pentafluorophenyl)‐tetrafluoro‐1,3,2‐benzodioxaborole (PFPTFBB). b) Cyclic voltammogramms of a Pt/Li/Li three‐electrode cell with PFPTFBB in 1.2 m LiPF₆ (3:7 EC/EMC). c) Charge and discharge capacities of a LiNi_0.8Co_0.15Al_0.05O₂/graphite cell with 5 wt% PFPTFBB during the whole overcharge test. a) Reproduced with permission.^{[ 56 ]} Copyright 2010, Elsevier B.V. b,c) Reproduced with permission.^{[ 50q ]} Copyright 2006, Elsevier B.V.

Figure 10

a) Cyclic voltammograms of 0.01 m Li₂B₁₂H₃F₉ (I) and 0.01 m Li₂B₁₂F₁₂ (II) in 1.0 m LiPF₆ in a Pt/Li/Li three‐electrode system. b) Voltage profiles as a function of time for mesocarbon microbeads/LiMn_1/3Ni_1/3Co_1/3O₂ cells in 0.4 m Li₂B₁₂H₃F₉ and 0.4 m Li₂B₁₂F₁₂ under overcharge at different currents. A solvent of 3:7 EC/EMC was used for all electrolytes. Reproduced with permission.^{[ 50r ]} Copyright 2010, ECS – The Electrochemical Society.

Figure 11

a) Schematic principle of the combustion and explosion of a LIB due to the flammable liquid electrolyte. b) Schematic illustration of the flame‐retardant effect during the thermal runway of LIBs. Reproduced with permission.^{[ 12d ]} Copyright 2018, American Association for the Advancement of Science.

Figure 12

Ethylene ethyl phosphate (EEP) as a FR additive in the electrolytes of 1 m LiPF₆ in 1:1 EC/DEC containing 0% (I) and 10% EEP (II). a) Chemical structure of EEP molecule. b) SET results of flammability testing for electrolytes (I) and (II); Inset images were scorched cotton ball (α) and intact cotton ball (β) after the flammability testing. c) The first charge–discharge voltage profiles of LiNi_1/3Co_1/3Mn_1/3O₂/Li half‐cells. d) Cycling performance of LiNi_1/3Co_1/3Mn_1/3O₂/Li half‐cells. e) The first charge–discharge voltage profiles of LiNi_1/3Co_1/3Mn_1/3O₂/graphite full‐cells. f) Cycling performance of LiNi_1/3Co_1/3Mn_1/3O₂/graphite full cells. Reproduced with permission.^{[ 68 ]} Copyright 2015, The Royal Society of Chemistry.

Figure 13

Bis(2,2,2‐trifluoroethyl) methylphosphonate (TFMP) as a FR additive in an electrolyte of 1 m LiPF₆ in EC/DMC. a) Chemical structure of TFMP molecule. b) Self‐extinguishing time as a function of the ignition time of the electrolyte with 5 wt% TFMP. The ignition time is the time in which the sample was exposed directly to a flame. c) The SET results and conductivity of electrolytes containing different concentration of TFMP and DMMP. d) Temperature results in dependency of time (I) and the expanded view (II) for the electrolyte with or without FR additives (standard electrolyte, black; TFP, pink; TTFPi, red; TFMP, yellow; PFPN, green; FPPN, blue) during the heat‐wait‐search experiments. (e,f), The electrochemical performance of LiFePO₄/Li half‐cells (e) and LiMn₂O₄/Li half‐cells (f) in the electrolyte with 20 vol% of TFMP. b,d) Reproduced with permission.^{[ 69f ]} Copyright 2018, Wiley‐VCH. c,e,f) Reproduced with permission.^{[ 71 ]} Copyright 2014, Elsevier Ltd.

Figure 14

a) Chemical structure of flame‐retardant additives of ethoxy (pentafluoro) cyclotriphosphazene (PFPN) and phenoxy (pentafluoro) cyclotriphosphazene (FPPN). b) Self‐extinguishing time as a function of the ignition time of the standard electrolyte containing 5 wt% PFPN (I) and 5 wt% FPPN (II). The ignition time is the time when the sample was exposed directly to a flame. c) The results of SET and COI for PFPN in 1.0 m LiPF₆ (1:1 EC/DMC) electrolyte. d) The cycling performance of LiCoO₂/Li half cells in 1.0 m LiPF₆ (1:1 EC/DMC) electrolyte containing I) 0% PFPN and II) 5 vol% PFPN. e) Self‐heating rate as a function of temperature for heat‐wait‐search measurement of a 5 Ah cell in the commercial electrolyte without or with 5 wt% FPPN. The red rectangle indicates the temperature range where FPPN decreases the self‐heating rate. The red dash rectangle marks the area of temperature range where the temperature rate of all cell samples increases. The black horizontal dash line indicates the thermal runaway threshold value of 10 K·min⁻¹. f) Electrochemical stability window for the commercial electrolyte (1.0 m LiPF₆ in 1:1 EC/DMC electrolyte) with 0 wt% FR [black], and 5 wt% FR including TFP [pink], TTFPi [red], TFMP [yellow], PFPN [green], and FPPN [blue]. b) Reproduced with permission.^{[ 69f ]} Copyright 2018, Wiley‐VCH. c,d,f) Reproduced with permission.^{[ 72 ]} Copyright 2018, Elsevier B.V. e) Reproduced with permission.^{[ 73 ]} Copyright 2018, Wiley‐VCH.