New Salts for Lithium-Ion Cells - Low Fluorine and Nonfluorine Electrolytes for Higher Safety

For the last 30 years, Li-ion cells have become the primary choice as power source for all electronic devices, mobile electronics and electric vehicles of all sorts. During this time huge advance took place in electrode active materials, separators and engineering of electrodes. However, lithium salt used in commercially available Li-ion cells (LiPF6) is still the same. It is known for its thermal instability, chemical incompatibility with silicon-based electrodes and reactions with even traces of water resulting in large costs of anhydrous solvents as well as need for desiccation systems of whole factories. Apart from known issues, it is also a reason for enormous fluorine content in Li-ion cells. Salt itself contains as high as 75% of fluorine in its mass. Thus, electrolytes contain ca. 10% of pure fluorine (typical 1 mol/kg concentration). As whole world makes an effort to drop toxic components, prevent formation of toxic wastes, it is also needed to drop use of fluorine in consumer products, including batteries. Previously, we presented LiTDI salt, which is now on the market, that contains only ca. 30% of fluorine in its mass and can be used at lower concentrations, decreasing fluorine content in the electrolyte to below 1.5-3% (depending on the application and electrolyte composition). Here we present first non-fluorine salts that successfully work in Li-ion cells environment. This way electrolyte fluorine content can reach 0% for the first time in Li-ion cell technology history. We show that getting rid of fluorine from the electrolyte does not necessarily means that good performance of both electrolyte and a cell is not possible. Ionic conductivity (over 8 mS/cm), and even more important, lithium cation conductivity values (σLi+ over 3 mS/cm) are comparable to those of LiPF6 and LiTDI, while not giving up on stability properties. Both thermal (up to at least 270°C) and electrochemical (at least up to 4.3 V vs Li) stabilities are still at the satisfactory level. It is still possible to use new salts with all active electrode materials available on the market as well as new ones that currently are not possible to use due to their incompatibility with fluorine-containing salts. In this presentation we will show newest results of development and investigation of novel anions including low-fluorine-content and nonfluorine ones as main electrolytes in Li-ion cells.