The conducting salt in lithium-ion batteries, LiPF6, can react with water contaminations in the battery electrolyte, releasing HF and further potentially harmful species, which decrease the battery performance and can become a health hazard in the case of a leakage. In order to quantify the hydrolysis products of LiPF6 in a water-contaminated battery electrolyte (1 mol L–1 LiPF6 in EC/DEC) and in aqueous solution, ion chromatography (IC), coulometric Karl Fischer titration (cKFT), and acid–base titration were used on a time scale of several weeks. The results show that the nature of the hydrolysis products and the kinetics of the LiPF6 hydrolysis strongly depend on the solvent, with the main reaction products in the battery electrolyte being HF and HPO2F2. From the concentration development of reactants and products, we could gain valuable insight into the mechanism of hydrolysis and its kinetics. Since the observed kinetics do not follow simple rate laws, we develop a kinetic model based on a simplified hydrolysis process, which is able to explain the experimentally observed kinetics.

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Most electrolytes in today's lithium-ion batteries contain a large proportion of ethylene carbonate (EC) mixed with other alkyl carbonate-based solvents. EC has, however, been shown to be unstable at the high potentials at which several novel cathode materials are electrochemically active. Here, different mixtures of sulfolane and DMC are investigated in this context. The electrochemical stability is explored in addition to galvanostatic cycling of LiNi 0.6 Mn 0.2 Co 0.2 O 2 -Li 4 Ti 5 O 12 (NMC-LTO) cells. The measurement of the ionic conductivity showed that mixing 25 % sulfolane into DMC improved the electrolyte properties as compared to pure DMC, making the conductivity similar to EC: DEC electrolytes and therefore fully functional. Moreover, the addition of sulfolane slightly enhanced the capacity retention, likely caused by formation of thinner and more stable surface layers on the LTO electrodes as determined by X-ray photoelectron spectroscopy (XPS). The cycling performance is especially improved for sulfolane-based electrolytes during cycling at sub-zero temperatures.[a] Dr.

Lithium metal is considered as the 'holy-grail' among anode materials for lithium-ion batteries, but it also has some serious drawbacks such as the formation of dendritic and dead lithium. In this study, the interplay of external pressure and different carbonate-and ether-based electrolytes on the (ir)reversible expansion of lithium metal during cycling against lithium titanate and lithium iron phosphate is studied. In carbonatebased electrolytes without any additives, lithium metal shows tremendous irreversible expansion and significant capacity reduction at elevated current densities due to the formation of mossy and dead lithium. The addition of fluoroethylene carbonate can reduce irreversible expansion and capacity reduction, especially when a high external pressure is applied. When an ether-based electrolyte is used, the irreversible dilation of the lithium metal is suppressed when applying increased external pressures. Overall, increased external pressure appears to reduce the formation of mossy and dead lithium and improve the performance.

It has recently been shown that ethylene carbonate (EC) experience poor stability at high potentials in lithium‐ion batteries, and development of electrolytes without EC, not least using ethyl methyl carbonate (EMC), has therefore been suggested in order to improve the capacity retention. In this context, we here explore another alternative electrolyte system consisting of propylene carbonate (PC) and dimethyl carbonate (DMC) mixtures in NMC‐LTO (LiNi0.6Mn0.2Co0.2O2, Li4Ti5O12) cells cycled up to 2.95 V. While PC experience wettability problems and DMC has difficulties dissolving LiPF6 salt, blends between these could possess complementary properties. The electrolyte blend showed superior cycling performance at sub‐zero temperatures compared to EC‐containing counterparts. At 30 °C, however, the PC‐DMC electrolyte did not show any major improvement in electrochemical properties for the NMC‐LTO cell chemistry. Photoelectron spectroscopy measurements showed that thin surface layers were detected on both NMC (622) and LTO electrodes in all investigated electrolytes. The results suggest that both PC and EC will react on the electrodes, but with EC forming thinner layers comprising more carbonates. Moreover, the electrochemical stability at high electrochemical potentials is similar for the studied electrolytes, which is surprising considering that most are free from the reactive EC component.