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.

A search map for organic additives and solvents applicable in high-voltage rechargeable batteries.

Chemical databases store information such as molecular formulas, chemical structures, and the physical and chemical properties of compounds. Although the massive databases of organic compounds exist, the search of target materials is constrained by a lack of physical and chemical properties necessary for specific applications. With increasing interest in the development of energy storage systems such as high-voltage rechargeable batteries, it is critical to find new electrolytes efficiently. Here we build a search map to screen organic additives and solvents with novel core and functional groups, and thus establish a database of electrolytes to identify the most promising electrolyte for high-voltage rechargeable batteries. This search map is generated from MAssive Molecular Map BUilder (MAMMBU) by combining a high-throughput quantum chemical simulation with an artificial neural network algorithm. MAMMBU is designed for predicting the oxidation and reduction potentials of organic compounds existing in the massive organic compound database, PubChem. We develop a search map composed of ∼1 000 000 redox potentials and elucidate the quantitative relationship between the redox potentials and functional groups. Finally, we screen a quinoxaline compound for an anode additive and apply it to electrolytes and improve the capacity retention from 64.3% to 80.8% near 200 cycles for a lithium ion battery in experiments.

Silicon/Carbon Nanotube/BaTiO3 Nanocomposite Anode: Evidence for Enhanced Lithium-Ion Mobility Induced by the Local Piezoelectric Potential.

We report on the synergetic effects of silicon (Si) and BaTiO3 (BTO) for applications as the anode of Li-ion batteries. The large expansion of Si during lithiation was exploited as an energy source via piezoelectric BTO nanoparticles. Si and BTO nanoparticles were dispersed in a matrix consisting of multiwalled carbon nanotubes (CNTs) using a high-energy ball-milling process. The mechanical stress resulting from the expansion of Si was transferred via the CNT matrix to the BTO, which can be poled, so that a piezoelectric potential is generated. We found that this local piezoelectric potential can improve the electrochemical performance of the Si/CNT/BTO nanocomposite anodes. Experimental measurements and simulation results support the increased mobility of Li-ions due to the local piezoelectric potential.

Design of novel additives and nonaqueous solvents for lithium-ion batteries through screening of cyclic organic molecules: an ab initio study of redox potentials.

We have screened 142 cyclic organic compounds in search of novel functional additives and nonaqueous solvents for use in lithium-ion batteries through the use of ab initio calculations, and have determined redox potentials for all molecules. We have estimated the range of variation in oxidation potentials through heteroatom replacement and structure modification. By analyzing the oxidative properties of these compounds, we have shown that substituted heteroatoms and isomers in cyclic organic molecules can induce large variations of oxidation potentials more than 2.3 V. Calculations of reduction potentials show that the substituted heteroatoms, isomers, and the number of double bonds in cyclic organic molecules can change reduction potentials more than 1.7 V. Additionally, we have identified seventeen and twelve compounds that could serve as additives in eliciting film formation on cathodes and anodes, respectively. We have also identified five compounds that could function in the overcharge protection of over-lithiated layered oxide cathodes. Finally, we have identified five compounds that could serve as electrochemically stable solvents for high-voltage (>6 V vs. Li/Li(+)) applications. These inductive screenings and their analyses and findings extend our empirical knowledge into quantitative estimation in the design of materials.

Direct synthesis of ordered mesoporous materials constructed with polymer-silica hybrid frameworks.

Highly ordered mesoporous materials constructed with integrated polymer-silica hybrid frameworks can be obtained via a one-step synthetic strategy using a mixture of polymer and silicate as the framework sources in the presence of a structure-directing agent.