Ab Initio Calculations of the Redox Potentials of Additives for Lithium-Ion Batteries and Their Prediction through Machine Learning

Ab initio molecular orbital calculations were carried out to examine the redox potentials of 149 electrolyte additives for lithium-ion batteries. These potentials were employed to construct regression models using a machine learning approach. We chose simple descriptors based on the chemical structure of the additive molecules. The descriptors predicted the redox potentials well, in particular, the oxidation potentials. We found that the redox potentials can be explained by a small number of features, which improve the interpretability of the results and seem to be related to the amplitude of the eigenstate of the frontier orbitals

Ab Initio Calculations for Decomposition Mechanism of CH₃O(CH₂CH₂O)_<i>N</i>CH₃ (<i>N</i> = 1–4) by the Attack of O₂^– Anion

Ab initio molecular orbital calculations were done to examine C–O bond-breaking reactions in glyme series CH₃O­(CH₂CH₂O)_<i>N</i>CH₃ (<i>N</i> = 1–4) by the attack of superoxide anion. We focused our study on <i>N</i> = 4 case where the reaction barrier for the bond break becomes the highest among four glymes. Intrinsic reaction coordinate calculations showed that the barrier height measured from the reaction precursor is 1.087 eV. The value is much higher than that of the analogous bond-breaking reaction in propylene carbonate

Highly Efficient Br^–/NO₃^– Dual-Anion Electrolyte for Suppressing Charging Instabilities of Li–O₂ Batteries

The main issues with Li–O₂ batteries are the high overpotential at the cathode and the dendrite formation at the anode during charging. Various types of redox mediators (RMs) have been proposed to reduce the charging voltage. However, the RMs tend to lose their activity during cycling owing to not only decomposition reactions but also undesirable discharge (shuttle effect) at the Li metal anode. Moreover, the dendrite growth of the Li metal anode is not resolved by merely adding RMs to the electrolytes. Here we report a simple yet highly effective method to reduce the charge overpotential while protecting the Li metal anode by incorporating LiBr and LiNO₃ in a tetraglyme solvent as the electrolyte for Li–O₂ cells. The Br^–/Br₃^– couple acts as an RM to oxidize the discharge product Li₂O₂ at the cathode, whereas the NO₃^– anion oxidizes the Li metal surface to prevent the shuttle reaction. In this work, we found that both anions work synergistically in the mixed Br^–/NO₃^– electrolyte to dramatically suppress both parasitic reactions and dendrite formation by generating a solid Li₂O thin film on the Li metal anode. As a result, the charge voltage was reduced to below 3.6 V over 40 cycles. The O₂ evolution during charging was more than 80% of the theoretical value, and CO₂ emission during charging was negligible. After cycling, the Li metal anode showed smooth surfaces with no indication of dendrite formation. These observations clearly demonstrate that the Br^–/NO₃^– dual-anion electrolyte can solve the problems associated with both the overpotential at the cathode and the dendrite formation at the anode

Potassium Ions Promote Solution-Route Li₂O₂ Formation in the Positive Electrode Reaction of Li–O₂ Batteries

Lithium–oxygen system has attracted much attention as a battery with high energy density that could satisfy the demands for electric vehicles. However, because lithium peroxide (Li₂O₂) is formed as an insoluble and insulative discharge product at the positive electrode, Li–O₂ batteries have poor energy capacities. Although Li₂O₂ deposition on the positive electrode can be avoided by inducing solution-route pathway using electrolytes composed of high donor number (DN) solvents, such systems generally have poor stability. Herein we report that potassium ions promote the solution-route formation of Li₂O₂. The present findings suggest that potassium or other monovalent ions have the potential to increase the volumetric energy density and life cycles of Li–O₂ batteries

Improved Energy Capacity of Aprotic Li–O₂ Batteries by Forming Cl-Incorporated Li₂O₂ as the Discharge Product

Aprotic lithium–oxygen (Li–O₂) batteries are promising devices for use in sustainable energy management systems as they have the potential to achieve significantly higher energy densities than current state-of-the-art Li-ion batteries. However, the low electrical conductivity of the main discharge product, lithium peroxide (Li₂O₂), which forms on the positive electrode, gradually suppresses the electrochemical reactions involved in the discharge process, thereby lowering the energy capacity of these systems. Herein, we demonstrate that the energy capacity of Li–O₂ batteries can be significantly improved by simply adding chloride ions to the electrolyte. Scanning electron microscopy analysis revealed that thick chloride (Cl)-incorporated Li₂O₂ films formed on the positive electrode as the discharge product. Using conductive atomic force microscopy, the Cl-incorporated Li₂O₂ films were shown to exhibit much higher electric conductivity than pristine Li₂O₂. Taken together, the present findings suggest that modulation of the electrical conductivity of the discharge product by the incorporation of heteroatoms is an effective approach for constructing Li–O₂ batteries with high volumetric energy density