Abstract
Concentrated electrolytes usually demonstrate good electrochemical performance and thermal stability, and are also supposed to be promising when it comes to improving the safety of lithium-ion batteries due to their low flammability. Here, we show that LiN(SO2F)2-based concentrated electrolytes are incapable of solving the safety issues of lithium-ion batteries. To illustrate, a mechanism based on battery material and characterizations reveals that the tremendous heat in lithium-ion batteries is released due to the reaction between the lithiated graphite and LiN(SO2F)2 triggered thermal runaway of batteries, even if the concentrated electrolyte is non-flammable or low-flammable. Generally, the flammability of an electrolyte represents its behaviors when oxidized by oxygen, while it is the electrolyte reduction that triggers the chain of exothermic reactions in a battery. Thus, this study lights the way to a deeper understanding of the thermal runaway mechanism in batteries as well as the design philosophy of electrolytes for safer lithium-ion batteries.
Highlights
Concentrated electrolytes usually demonstrate good electrochemical performance and thermal stability, and are supposed to be promising when it comes to improving the safety of lithium-ion batteries due to their low flammability
Flammable carbonate-based electrolytes have been widely used in commercial lithium-ion batteries (LIBs), and they are considered to be responsible for thermal runaway[2,3,20], which is reasonable, as they are among the main fuels that increase vigorous combustion
The LiFSI/trimethyl phosphate (TMP) concentrated electrolyte in the pouch cell was investigated for two cycles before safety evaluation, and it delivered a coulombic efficiency of 99.5% (Fig. 1a)
Summary
Concentrated electrolytes usually demonstrate good electrochemical performance and thermal stability, and are supposed to be promising when it comes to improving the safety of lithium-ion batteries due to their low flammability. A mechanism based on battery material and characterizations reveals that the tremendous heat in lithium-ion batteries is released due to the reaction between the lithiated graphite and LiN(SO2F)[2] triggered thermal runaway of batteries, even if the concentrated electrolyte is non-flammable or low-flammable. The lithiated anode consumes the highly oxidative gases released during the cathode phase transition, producing tremendous heat that brings the battery to the thermal runaway point[12]. The charged anode reacts with LiFSI and releases a considerable amount of heat that triggered thermal runaway
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