In order to meet the critical energy-storage challenges of the future, a next-generation lithium-ion battery will need to achieve a higher energy density and longer cycle life. While increasing the nickel content in layered LiMO 2 (M = Ni, Mn, Co) significantly improves the capacity of the material, nickel-rich cathodes cycled in conventional organic electrolytes commonly suffer from crystallographic phase transformation and the growth of a resistive interfacial layer, both of which result in voltage fade and capacity degradation during cycling. However, pairing a nickel-rich cathode with an appropriate ionic liquid (IL) electrolyte enables exceptional cycling stability and energy retention. This work demonstrates how a pyrrolidinium-based IL electrolyte not only allows for cycling to higher voltages but shows a 95% energy retention and average discharge capacity of 189 mAh g −1 over 150 cycles between 3 and 4.5 V vs. Li/Li + with a nickel-rich layered cathode. Based on electrochemical and crystallographic analyses, the exceptional performance of the cells cycled in IL is attributed to the stability of the electrode-electrolyte interfacial layer formed by the IL which protects the active material and suppresses the structural degradation commonly observed in nickel-rich cathodes.

Ionic liquid (IL) electrolytes offer a number of advantages over conventional carbonate-based electrolytes but commonly suffer from poor performance at high charge and discharge rates due to their relatively low ionic conductivity and high viscosity. While increasing the lithium salt content of an IL electrolyte beyond optimal levels exacerbates both of those characteristics, this work demonstrates the surprising kinetic capabilities of highly concentrated IL electrolytes. Results presented herein show that NMC-811 half-cells cycled in PYR13FSI with a high-concentration of LiFSI exhibit superior rate performance as compared to lower-concentration IL solutions. Furthermore, extended cycling shows that higher LiFSI concentrations promote enhanced stability during long-term cycling, significantly outperforming the capabilities of a conventional organic electrolyte. Transference number calculations, differential capacity analyses, and electrochemical impedance spectroscopy were used to illuminate the underlying mechanisms contributing to the performance improvements at high concentrations, ultimately revealing the significance of LiFSI molarity in the formation of a robust and conductive solid-electrolyte interphase layer capable of promoting rapid lithium-ion transport as well as stable long-term cycling. The results of this study highlight the unique capability of IL electrolytes to enable successful implementation of a challenging high-energy electrode material.

The full electrochemical utilization of a crude micron-silicon anode is enabled by a simple and scalable cyclized-polyacrylonitrile (cPAN) electrode architecture paired with an innovative room temperature ionic liquid (RTIL) electrolyte. Field emission scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy show that the resilient cPAN coating mechanically contains the cycling-induced expansion, contraction, and fragmentation of the oversized silicon particles while an electrochemically robust solid-electrolyte interphase (SEI) layer prevents the perpetuation of irreversible side reactions. Prolonged electrochemical cycling data demonstrates unprecedented performance in both half-cell and full-cell configurations. Implementation of the micron-silicon anode constitutes a significant development in the evolution of safe and commercially-viable high-performance lithium-ion batteries.

As an alternative to conventional carbonate-based electrolytes, ionic liquid (IL) electrolytes exhibit several advantageous characteristics including non-flammability, negligible volatility, high electrochemical and thermal stability, and the ability to form robust yet conductive passivation layers on a number of high-energy electrode materials. However, IL electrolytes traditionally suffer from poor rate performance owing to their high viscosity and low ionic conductivity as compared to traditional electrolyte solutions. The following study will assess the kinetic capabilities of an IL electrolyte paired with a high-energy, nickel-rich layered cathode. The effects of temperature, electrode mass loading, and electrode composition are investigated in order to form an understanding of the kinetically limiting factors. Cycling tests performed at elevated temperatures not only show that IL electrolytes enable stable high-temperature operation but that elevated temperatures facilitate substantial improvements in rate capabilities. Analysis by electrochemical impedance spectroscopy ultimately illuminates a critical correlation between electrode wettability and rate performance. The trends established by this study will to help inform the optimal performance of IL electrolytes in high-rate applications.