• Energy Research

AbstractThe ionic liquid (IL)‐based electrolyte comprising 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) (ILE) has been evaluated as a suitable system for the high‐voltage cathode material LiNi0.5−xMn1.5+xO4 (LNMO) when cycled vs. graphite anodes. The oxidative stability of the ILE was evaluated by linear sweep voltammetry (LSV) and synthetic charge‐discharge profile voltammetry (SCPV) and was found to exceed that of state‐of‐the‐art 1 M LiPF6 in 1 : 1 ethylene carbonate (EC) : diethylcarbonate (DEC) (LP40). Improved cycling performance both at 20 °C and 45 °C was found for LNMO||graphite full cells with the IL electrolyte. X‐ray photoelectron spectroscopy (XPS) analysis showed that robust and predominantly inorganic surface layers were formed on the LNMO cathode using the ILE, which stabilized the electrode. Although the high viscosity of the ILE limits the rate performance at 20 °C, this ILE is a promising alternative electrolyte for use in lithium‐ion batteries (LiBs) with high‐voltage cathodes such as LNMO, especially for use at elevated temperatures.

AbstractThe ionic liquid (IL)‐based electrolyte comprising 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) (ILE) has been evaluated as a suitable system for the high‐voltage cathode material LiNi0.5−xMn1.5+xO4 (LNMO) when cycled vs. graphite anodes. The oxidative stability of the ILE was evaluated by linear sweep voltammetry (LSV) and synthetic charge‐discharge profile voltammetry (SCPV) and was found to exceed that of state‐of‐the‐art 1 M LiPF6 in 1 : 1 ethylene carbonate (EC) : diethylcarbonate (DEC) (LP40). Improved cycling performance both at 20 °C and 45 °C was found for LNMO||graphite full cells with the IL electrolyte. X‐ray photoelectron spectroscopy (XPS) analysis showed that robust and predominantly inorganic surface layers were formed on the LNMO cathode using the ILE, which stabilized the electrode. Although the high viscosity of the ILE limits the rate performance at 20 °C, this ILE is a promising alternative electrolyte for use in lithium‐ion batteries (LiBs) with high‐voltage cathodes such as LNMO, especially for use at elevated temperatures.

Spinel LiNi0.5Mn1.5O4 as one of the high-energy positive electrode materials for next generation Li-ion batteries has attracted significant interest due to its economic and environmental advantages. However, the sensitivity of this type of material upon short to long term ambient storage conditions and the impact on the electrochemical performances remains poorly explored. Nevertheless, this remains an important aspect for practical large-scale synthesis, storage and utilization. Herein, we study and compare the evolution of surface chemistry, bulk crystal structure and elemental content evolution and distribution of LiNi0.5Mn1.5O4 using a variety of characterization techniques including XPS and STEM-EDS-EELS, as well as electrochemical analysis. We show that Mn species dominate the outer surface (0–5 nm), while Ni and Li are preferentially located further away and in the bulk. The studied LiNi0.5Mn1.5O4 material is found to be stable, with minor changes in surface or bulk characteristics detected, even after 12 months of storage under ambient air conditions. The low surface reactivity to air also accounts for the minor changes to the electrochemical performance of the air-exposed LiNi0.5Mn1.5O4, compared to the pristine material. This study provides guidance for the appropriate storage, handling and processing of this high-performance cathode material.

Spinel LiNi0.5Mn1.5O4 as one of the high-energy positive electrode materials for next generation Li-ion batteries has attracted significant interest due to its economic and environmental advantages. However, the sensitivity of this type of material upon short to long term ambient storage conditions and the impact on the electrochemical performances remains poorly explored. Nevertheless, this remains an important aspect for practical large-scale synthesis, storage and utilization. Herein, we study and compare the evolution of surface chemistry, bulk crystal structure and elemental content evolution and distribution of LiNi0.5Mn1.5O4 using a variety of characterization techniques including XPS and STEM-EDS-EELS, as well as electrochemical analysis. We show that Mn species dominate the outer surface (0–5 nm), while Ni and Li are preferentially located further away and in the bulk. The studied LiNi0.5Mn1.5O4 material is found to be stable, with minor changes in surface or bulk characteristics detected, even after 12 months of storage under ambient air conditions. The low surface reactivity to air also accounts for the minor changes to the electrochemical performance of the air-exposed LiNi0.5Mn1.5O4, compared to the pristine material. This study provides guidance for the appropriate storage, handling and processing of this high-performance cathode material.