In silico Design, Virtual Screening and Synthesis of Novel Electrolytic Solvents
Résumé
We report the building, validation and release of QSPR (Quantitative Structure Property Relationship) models aiming to guide the design of new solvents for the next generation of Li-ion batteries. The dataset compiled from the literature included oxidation potentials (E ox), specific ionic conductivities (k), melting points (T m) and boiling points (T b) for 103 electrolytes. Each of the resulting consensus models assembled 9-19 individual Support Vector Machine models built on different sets of ISIDA fragment descriptors. [1] They were implemented in the ISIDA/Predictor software. Developed models were used to screen a virtual library of 9965 esters and sulfones. The most promising compounds prioritized according to theoretically estimated properties were synthesized and experimentally tested. Despite the tremendous success in the development of new materials for positive electrodes of Lithium-ion batteries, so far little attention was paid to the design of suitable electrolytes. In principle, new electrodes support high voltage, but their application is limited by the poor electrolyte stability to oxidation in high-voltage lithium-ion batteries. Besides, security issues have to be managed due to possible exothermic reactions between the positive electrode and electrolytes, especially at high-voltage. In particular, classical electrolytes such as ethylene carbonate (EC)-dimethyl carbonate (DMC) + lithium hexafluorophos-phate (LiPF 6) can hardly be used at voltage greater than 4.2 V. Higher voltage may lead to dramatic decrease of the cycle ability of the battery and may increase the risk of explosion, fire and release of toxic substances. [2] Thus, increase of flash point, thermal stability and anodic stability of the solvent while minimizing electrolyte viscosity and maximizing ionic conductivity are important goals of electrolyte optimization. In this work, a QSPR approach has been used to guide the design of a new generation of electrolytic solvents. Particular attention was paid to molecules belonging to two different chemotypes: sulfones and esters/ethers. Although, esters and ethers were largely investigated in the literature, their physicochemical and electrochemical properties still need to be optimized for their use in electrolyte for Lithium-ion batteries. Sulfones remain liquid within a large range of temperature, their thermal behavior is very interesting as they are generally non-flammable and have very high flash points (for instance, the flash point of dimethylsulfone is 145°C whereas dimethyl carbonate and a mixture of ethylene carbonate:dimethylcarbonate (1 : 1) exhibit flash points equal to 16 and 25°C, respectively [3]). In this work, 4 key properties [3-4] were considered: ionic conductivities (k) and oxidation potentials (E ox) of lithium-based electrolytes as well as melting points (T m) and boiling points (T b) of dipolar aprotic organic solvents usually considered for Lithium-ion batteries. The electrolyte should have advantageous transport properties in order to reduce the ohmic-drop caused by the internal resistance of the battery cell (high ionic conductivity). The electrolyte must be in liquid state for a large range of temperatures (ideally between À 40°C and 120°C, considering an operating range between À 30°C and 60°C). Simultaneously, the electro-chemical window should be as wide as possible. Currently, oxidation potential of electrolytes reaches about 4-4.2 V at active cathode materials. At high voltage a massive electro-lyte oxidation may occur, leading to a steep increase of the current density with rapid loss of battery cycling performance. Thus, it is highly desirable to design new solvents exhibiting high oxidation potential in the presence of lithium salts. At a first stage, a dataset of 103 dipolar aprotic organic solvents was collected from the literature. This included 155 oxidation potential values measured at 5 mV/s in sulfone or ester solvents in the presence of 1 M LiPF 6 or Lithium bis [a] G.
Domaines
| Licence |
|---|