High-voltage liquid electrolytes for Li batteries: progress and perspectives

Abstract

Recent advances, fundamental mechanisms and design strategies of high-voltage liquid electrolytes are comprehensively summarized in this review.

High-voltage dilute ether electrolytes enabled by regulating interfacial structure

“…Since ether solvent typically decomposes as voltage exceeds 4.0 V (refs. 8,14,19,21 ), it is intriguing to unveil how such a small amount of NO3could boost the oxidation stability of the conventional dilute ether electrolyte at the cathode. Considering that the current common views of electrolyte design, especially with regard to the well-understood salt-concentrated electrolytes, mostly focus on passivating CEI 14,21,23 or changing electrolyte ion solvation 16 , similar mechanisms are worthy of being checked here.…”

“…17,18 Therefore, research on the design of dilute ether electrolytes with extraordinary oxidation stability has drawn much attention and become one of the frontiers in the battery community. 19 The early entry of ether electrolytes for high-voltage LMBs adopted the high-concentration formulations (e.g., triglyme and tetraglyme solvents with equimolar Li salt). 20 Although the oxidation stability can be improved to ~5 V on the platinum electrode, only limited cycling stability (200 cycles) was achieved on the LiCoO2 cathode with a cutoff voltage of 4.2 V. Until now, the high-concentration ether electrolytes 14,21,22 and localized high-concentration ether electrolytes 23,24 effectively developed for 4.3/4.4 V NMC cathodes have all followed the same design concept, namely, high salt/solvent molar ratio.…”

“…25 Hence, compared with these salt-concentrated solutions, dilute ether electrolytes are thus long required to have high-voltage tolerance; however, limited by their intrinsic poor oxidation stability, 8 such achievements are rarely reported. 19 Recently, a molecular design strategy was proposed by introducing fluorinated segment into the ether backbone to improve the oxidation stability of ether. 26,27 These delicately designed ether electrolytes share the common feature of high-voltage tolerance with the hydrofluoroethers.…”

A High‐Voltage Lithium‐Metal Batteries Electrolyte Based on Fully‐Methylated Pivalonitrile

“…[11] More importantly, the metallic Li can react with lots of organic solvents and lithium salts for the sack of its spontaneous brisk reactivity, thus it is easy to form a heterogeneity solid-electrolyte interphase (SEI) layer with low mechanical/chemical stability and ionic conductivity, [12][13][14] which leads to inhomogeneous Li-ion flux and growth of dendrites, [15,16] Additionally, When applying Ni-rich Li-[Ni x Co y Mn z ]O 2 (NCM) as cathode materials in lithium metal batteries, undesirable HF resulting from the reaction of lithium with trace water will attack the alkaline cathode material and lead to the dissolution of transition metal elements (such as Ni, Co, Mn). [17,18] To overcome the above limitations, much efforts have been devoted to develop electrolytes with high interfacial stability of high-voltage cathodes in lithium metal batteries, [19][20][21][22][23][24][25] including fluorinated electrolytes, [26,27] deep eutectic solvent electrolytes, [28] sulfone-type electrolytes, [29,30] amide-type electrolytes, [31] and nitrile-type electrolytes. [32][33][34][35] Among them, nitrile-type electrolyte (such as succinonitrile, adiponitrile) with high chemical stability and oxidation resistance has been widely employed to improve the cycling performance and stability of cathodes at high voltage.…”

Starch as the Flame Retardant for Electrolytes in Lithium-Ion Cells

“…Many requirements are imposed on them, including electrochemical inertness, physical and chemical stability, appropriate viscosity, conductivity, solubility, non-toxicity and cheapness, in addition to having an appropriate boiling point. The disadvantage is the deterioration of electrochemical properties caused by the increasing of the resistance in the circuit [4].…”