Revealing the Impact of Film-Forming Electrolyte Additives on Lithium Metal Batteries via Solid-State NMR/MRI Analysis

Abstract

Because of the high specific capacity and low redox potential, lithium metal constitutes a promising material and might be an option for high energy density next-generation battery technologies, though application of lithium metal batteries (LMBs) is currently limited by poor long-term performance and severe safety issues when liquid electrolytes are used. These challenges arise from formation of “dead” lithium or inhomogeneous lithium deposits as well as ineffective solid electrolyte interphase (SEI) layers on lithium metal electrodes. Notably, lithium consumed by SEI formation and fractions of “dead” lithium was derived from in situ 7Li nuclear magnetic resonance (NMR) of pouch-type cells, while 19F 1D magnetic resonance imaging (MRI) profiling along with operando optical microscopy analysis revealed the nature of lithium deposits, considering the impact of electrode kinetics on the occurrence of dendritic lithium microstructures, governed by processes of electrodeposition and electrodissolution. Various electrolyte formulations were compared in view of different cell configurations, including Li||Li symmetric cells as well Li||Cu cells, Cu||NMC cells, and finally NMC||Li full cell systems, establishing the origin and likely contributions to irreversible capacity losses while systematically evaluating different active materials (including electrolyte formulations, cathode material, and lithium metal anodes). Indeed, a mixture of film-forming additivesfluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2)was demonstrated to afford both “better” interfacial/interphasial properties and more homogeneous lithium deposition, thus exhibiting promising electrochemical performance.

In situcharacterization of lithium-metal anodes

“…Similarly, Hsieh et al analyzed the effect of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO 2 F 2 ) as electrolyte additives on LMBs. 152 Fig. 11d shows the 7 Li NMR spectra for different electrolyte formulations.…”

The Importance of Interphases in Energy Storage Devices: Methods and Strategies to Investigate and Control Interfacial Processes

“…Recently, nuclear magnetic resonance (NMR) was also exploited for the in-situ investigation of LIBs, thanks to the introduction of high-resolution solid-state techniques, sequences for the investigation of paramagnetic compounds, and (micro)imaging methods (magnetic resonance imaging or MRI) [38,39,[108][109][110][111]. NMR offers nuclear selectivity, and the different interactions (magnetic dipolar, electric quadrupolar, chemical shift anisotropy) can be exploited to better characterize the different components in the electrode and electrolyte.…”

Considerations in applying neutron depth profiling (NDP) to Li-ion battery research

“…However, quantication from NMR data is complex and may require the use of a secondary, conrmatory technique. 7 Li detection at relevant timescales (s, min, h) without the need for additional instrumentation for quantication can be achieved by neutron depth proling (NDP). NDP is a neutron absorption technique that can quantify 6 Li non-destructively.…”