Interphase Design by Localized Super-Concentrated Electrolyte for High-Voltage and High-Power Lithium Metal Batteries

Abstract

Batteries used in electric aircraft must deliver high-power on take-off and landing, providing in stride the ability to recharge at high voltage to make full use of the cathode capacity. Impedance rise associated with electrode–electrolyte interphases remains problematic with conventional electrolytes, resulting in unacceptable power fade. This is exacerbated when recharging cells at high voltage, which is where interphase generation remains poorly controlled. To address these issues, electrolyte design for high-voltage and high-power batteries should emphasize control over the interphase growth contributing to the impedance rise during charge. To this end, we will describe our recent efforts to alter the activity of various electrolyte components at electrode–electrolyte interfaces, granting access to exquisite control over interphase chemistry. Key to our success is the exploitation of ion clustering in locally super-concentrated electrolytes (LSCEs), which produces aggregates with intrinsically different reactivity than solvated species and from which new interphasial chemistries may be produced in-situ. We find in top-performing compositions that interphase stability is most affected by the activity of ethereal solvents in the formulations, particularly at high voltage, and that it is possible to design additives that suppress solvent activity even up to 4.5 V vs. Li/Li+. Li/NMC811 cells cycled with de-novo designed LSCEs maintain 70% of their initial discharge capacity after 1000 cycles with 4 C discharge rate at charge cut-off voltage of 4.35 V, outperforming most reported electrolytes for Li metal batteries. Furthermore, by taking an informatics approach to interphase characterization, we reveal fundamental patterns of reactivity that inform future selection criteria for advanced battery electrolytes.