Controlling Gas Generation of Li-Ion Battery through Divinyl Sulfone Electrolyte Additive.

The focus of mainstream lithium-ion battery (LIB) research is on increasing the battery's capacity and performance; however, more effort should be invested in LIB safety for widespread use. One aspect of major concern for LIB cells is the gas generation phenomenon. Following conventional battery engineering practices with electrolyte additives, we examined the potential usage of electrolyte additives to address this specific issue and found a feasible candidate in divinyl sulfone (DVSF). We manufactured four identical battery cells and employed an electrolyte mixture with four different DVSF concentrations (0%, 0.5%, 1.0%, and 2.0%). By measuring the generated gas volume from each battery cell, we demonstrated the potential of DVSF additives as an effective approach for reducing the gas generation in LIB cells. We found that a DVSF concentration of only 1% was necessary to reduce the gas generation by approximately 50% while simultaneously experiencing a negligible impact on the cycle life. To better understand this effect on a molecular level, we examined possible electrochemical reactions through ab initio molecular dynamics (AIMD) based on the density functional theory (DFT). From the electrolyte mixture's exposure to either an electrochemically reductive or an oxidative environment, we determined the reaction pathways for the generation of CO2 gas and the mechanism by which DVSF additives effectively blocked the gas's generation. The key reaction was merging DVSF with cyclic carbonates, such as FEC. Therefore, we concluded that DVSF additives could offer a relatively simplistic and effective approach for controlling the gas generation in lithium-ion batteries.

l-Tryptophan: Antioxidant as a Film-Forming Additive for a High-Voltage Cathode.

l-tryptophan (TrP) was investigated as a functional film-forming additive on a lithium-rich layered oxide cathode because it has a much lower oxidation potential than other common carbonate-based electrolytes. Owing to its prior oxidation to a base electrolyte, an artificial cathode-electrolyte interphase (CEI) was formed on the cathode surface, which could be confirmed via X-ray photoelectron spectroscopy and scanning electron microscopy and verified through density functional theory calculations. The functional film formed on the cathode surface suppressed the side reactions between the cathode and electrolyte during cell cycling. As a result, the film prevented CEI thickening and performance deterioration. The optimum weight of TrP was determined to be 0.4 wt % for obtaining the best performance.

Reductive reactions via excess Li in mixture electrolytes of Li ion batteries: an ab initio molecular dynamics study.

The electro-reduction of battery electrolytes plays a critical role in the formation of solid-electrolyte interphase (SEI) layers on the surfaces of negative electrodes. These layers have a significant influence on the performance of rechargeable battery cells. Using ab initio molecular dynamics, we demonstrate the electro-reduction of mixture electrolytes computationally by adding a certain number of excess Li+ first to form the solvation structure and the same number of electrons later for reductive reactions. Our method enables direct observations of the ring opening of one cyclic carbonate followed by merging with another solvent molecule as well as gas generation. When we examined FEC- and EC-based electrolytes, we were able to observe the differences in terms of reaction products. In particular, the two gaseous products that are generated the most are in accordance with recent in situ gas measurements in the literature. The different reaction products of each electrolyte also match well with the SEI constituents reported experimentally. By tracing reaction pathways, we found that Li+ ions facilitate many otherwise difficult electrochemical reactions, presumably by lowering energy barriers. We also found that the excess Li+ forms cationic clusters of Li2PF6+, which enable the reductive decomposition of salt anions and which do not occur easily simply by increasing the electronic occupation. Based on the reaction products of FEC-based electrolytes, here we propose a possible mechanism of polymerization through aldehyde intermediates that are known to bond with surrounding radical anions.

Tetrathiafulvalene as a Conductive Film-Making Additive on High-Voltage Cathode.

Tetrathiafulvalene (TTF) is investigated as a conductive film-making additive on an overlithiated layered oxide (OLO) cathode. When the OLO/graphite cell is cycled at high voltage, carbonate-based electrolyte without the additive decomposes continuously to form a thick and highly resistant surface film on the cathode. In contrast, TTF added into the electrolyte becomes oxidized before the electrolyte solvents, creating a thinner film on the cathode surface. This film inhibits further electrolyte decomposition through cycling and stabilizes the interface between the cathode and the electrolyte. The cells containing the OLO cathode with TTF-added electrolyte afforded enhanced capacity retention and rate capability, making TTF a prospective electrolyte additive for higher energy density lithium-ion cells.

Inclusion and dielectric properties of a vinylidene fluoride oligomer in coordination nanochannels.

The dynamics of oligo(vinylidene fluoride) (OVDF) confined in regular nanochannels of a porous coordination polymer (PCP) was studied by means of dielectric spectroscopy. The OVDF chains in the PCP nanopores showed two Arrhenius-type relaxation processes at lower temperatures than the relaxation temperature observed for the neat OVDF, showing the enhanced mobility of the confined OVDF.