(Invited) Evaluation of Tailored Organic Molecules for Cathode Passivation in High Voltage Lithium-Ion Batteries

Redox-active organic compounds have been explored as electrolyte additives for lithium-ion batteries, for purposes ranging from mitigation of excess current in overcharging cells to passivation of electrode surfaces to stabilize surfaces that would otherwise lead to electrolyte decomposition. Especially when expanding the voltage range in charging of lithium-ion cells, passivation becomes more critical to cell longevity during operation. Electrolyte additives containing purposefully weak covalent bonds have been employed in high-voltage (e.g. NMC cathodes) lithium-ion cells, which are tailored to react with hydrofluoric acid – a product of decomposition of fluorine-containing anions present in the electrolyte. Here we report results from the investigation of organic molecules as electrolyte additives with functionality aimed to react with/at cathode surfaces to form passivating films. These organic molecules with varying oxidation potentials (3.4 V vs. Li+/0 and above) house main group ad-atoms unique from those contained in the electrode, binder, conductive fillers, and electrolyte solutions. This allows for surface imaging and electrolyte analysis to determine the location and reaction of such additives following formation cycling.