A Detailed Investigation of the Thermal Reactions of LiPF[sub 6] Solution in Organic Carbonates Using ARC and DSC

Abstract

The thermal stability of 1 M LiPF 6 solutions in mixtures of ethylene carbonate, diethyl carbonate, and dimethyl carbonate in the temperature range of 40 to 350°C was studied by accelerating rate calorimeters ͑ARC͒ and differential scanning calorimeters ͑DSC͒. Nuclear magnetic resonance ͑NMR͒ was used to analyze the condensed reaction products at different reaction stages. Studies by DSC and pressure measurements during ARC experiments with LiPF 6 solutions detected a gas-releasing endothermic reaction starting at ϳ170°C, involving diethyl carbonate which occurs before a number of exothermic reactions, which follow as the temperature increases. Fluoride ions are released and react with the alkyl carbonate molecules both as bases and as nucleophiles. The bulk analysis by NMR shows that HO-CH 2 -CH 2 -OH, FCH 2 CH 2 -OH, F-CH 2 CH 2 -F, and polymer are major products. Gas analysis by NMR and Fourier transform infrared spectroscopy shows PF 5 , CO 2 , CH 3 F, CH 3 CH 2 F, and H 2 O as major gaseous products of the thermal reaction of these solutions.

Thermal instability of Olivine-type LiMnPO4 cathodes

“…The peak position, however, is about 30 • C higher in our DSC profile, which could be due to improved sealing of our DSC pans. The exotherm is attributed to redox reactions of LiPF 6 and its decomposition products, such as PF 5 , with the carbonate solvents [15].…”

Electrolyte and Solid-Electrolyte Interphase Layer in Lithium-Ion Batteries

“…Ping et al [Ping, 2010] confirmed that the addition of lithium salt reduces drastically the thermal stability of the solvent due to the strong Lewis acidity of PF 5 in the case of LiPF 6 and BF 3 in the case of LiBF 4 even if BF 3 is a weaker Lewis acid than PF 5 . The following mechanism of degradation was proposed according to different works reported in the literature [Ping, 2010;Sloop, 2003;Wang, 2005 ;Gnanaraj, 2003a ;Gnanaraj, 2003b The results of the thermal stability studies show that the thermal stabilities of lithium salt in inert atmosphere can be ranked as LiTFSI (lithium bis(trifluoromethylsulfonyl)imide) <LiPF 6 <LiBOB (lithium bis(oxalate)borate)<LiBF 4 and the thermal stabilities of EC electrolytes follows this order: 1 M LiPF 6 /EC + DEC<1 M LiBF 4 /EC + DEC<1 M LiTFSI/EC + DEC< 0.8 M LiBOB/EC + DEC. Nevertheless, it may be pointed out that electrocatalytic reactions onto the positive electrode associated with high reactivity of the electrolyte at high temperature can significantly reduce the thermal stability compared to the thermal stability of the electrolyte without any contact with a positive electrode.…”

Analysis of multi-wall carbon nanotube based porous Li battery electrodes’ using TOF-SIMS ion imaging

“…In addition, due to the usage of organic additives, formation of lithium formate, lithium acetate, lithium carbonate, LiO, LiOH, Li x PO y F z are also reported [18,19]. Presence of LiHCO 3 , LiOH, Li 2 O, LiOH, PF 5 , CH 3 F, C 2 H 5 F, C 2 H 6 0 2 , C 2 H 5 OF, C 2 H 4 F 2 are also reported from LiPF 6 salts' based battery electrolyte reactions along with traces of Mn and Co ions [20,21,22]. Based on the above multifaceted information, presence of all these ions if any, using our TOF-SIMS data were then checked.…”

“…There was a 2 order of magnitude increase in the Li 2 O+, F+ ion concentration after cycling, and a 3 order of increase in counts for LiOH+, and an order of magnitude increase in the peak intensity for C 2 A possible reason for such room temperature electrochemical cycling and related slow degradation observed is that the resultant heat generation from charging -discharging and associated chemical transition slowly but steadily thermally breaks up the Li salt and also induces chemical reactions with ambient oxygen and moisture [22]. Observed slow degradation suggests that statistically and microscopically, due to non-uniformity issues among others, local heating can lead to local temperature rise up to 200 o C. [20,23]. Perhaps if and where feasible, a possible way to reduce this could be to keep such Li battery ambient cooler and better air ventilated to dissipate heat or reduce ambient temperatures and also by increasing the battery external surface area for faster cooling.…”