Radiolysis as a solution for accelerated ageing studies of electrolytes in Lithium-ion batteries

Abstract

Diethyl carbonate and dimethyl carbonate are prototype examples of eco-friendly solvents used in lithium-ion batteries. Nevertheless, their degradation products affect both the battery performance and its safety. Therefore, it is of paramount importance to understand the reaction mechanisms involved in the ageing processes. Among those, redox processes are likely to play a critical role. Here we show that radiolysis is an ideal tool to generate the electrolytes degradation products. The major gases detected after irradiation (H2, CH4, C2H6, CO and CO2) are identified and quantified. Moreover, the chemical compounds formed in the liquid phase are characterized by different mass spectrometry techniques. Reaction mechanisms are then proposed. The detected products are consistent with those of the cycling of Li-based cells. This demonstrates that radiolysis is a versatile and very helpful tool to better understand the phenomena occurring in lithium-ion batteries.

Degradation of an Ethylene Carbonate/Diethyl Carbonate Mixture by Using Ionizing Radiation

“…[9][10][11] Indeed, we have shown that the highly reactive speciesc reated in the irradiated solution are the same as those obtained during the charging of aL IB with similars olvents. Following our studies on pure carbonate solvents (diethyl carbonate and propylene carbonate, with/ withoutL iPF 6 ), [9][10][11] the purpose of this work is to use radiolysis to investigate the properties of am ixture of al inear (nonpolar) and cyclical( polar) carbonate. Indeed, am ixture of ethylene carbonate and diethylc arbonate is more complex, realistic, and representative of the solvents used in LIBs.…”

“…Irradiation of the mixture shows the formation of molecules found in irradiated DEC (alkanes, e.g.,C 3 H 8 and C 4 H 10 ;e thers, e.g., C 2 H 5 OC 2 H 5 ). [9] Moreover, similar molecules werei dentified in aG C-MS study of the EC-DMC/LiPF 6 electrolyte recovered from ac ycled stainless-steel/Li cell at 55 8C, [34] for example, CH 3 OCH 3 (here C 2 H 5 OC 2 H 5 with DEC insteado fD MC) andC H 3 OCHO (here C 2 H 5 OCHO with DEC instead of DMC).A lthough H 2 ,C H 4 , and CO molecules were not detectedb yu sing GC-MS (Figure 4), they are indeed the main molecules produced upon irradiation, as revealed by mass spectrometry with electron ionization (EI/MS).T hey wered etected and quantified by using m-GC. The quantification by mass spectrometry (EI/MS) of all compounds formed under irradiation is difficult because many speciesa re formed and lead to the same fragmentation ions.…”

“…This is obviously not the case for H 2 and CH 4 (Figure 6a,b). Indeed, in this case, these two gases are mainlyp roduced from the excited state of DEC. [9] In DEC, which is as olvent with av ery low dielectric constant (2.82, see Figure 5. Evolution of the maindecomposition products formed in the gas phase and measured by using m-GC after g-irradiation of a) EC and b) EC/DEC as af unction of the dose.…”

“…Radiolytic yieldso ft he main decomposition gases,d etermined by using mGC [a] .The results for DEC are from Ref. [9]. Ta ble 1), the recombination of DECC + with the electron is highly favored and leads to the formation of DEC*.…”

Electrolytes Ageing in Lithium‐ion Batteries: A Mechanistic Study from Picosecond to Long Timescales

“…Inspired by other works, [9d,e] we recently developed an ew approacht os imulate the degradationo ft he solvent/ electrolyte of LIBs into decomposition products. [4] We used pulse radiolysis as at ool to study the early electron transfer processes in neat DEC, [12] and gamma radiolysis to generate, in am atter of hours at room temperature, stable degradation products similart ot he ones obtained in the charge/discharge cycles of batteries. [4] Overall, our resultsh ave shown that the decomposition products of neat linear carbonates (DEC, DMC) can be easily compared to those obtained by electrolysis, except that they are formed at av ery accelerated rate.…”