Abstract
Lithium metal batteries are gaining increasing attention due to their potential for significantly higher theoretical energy density than conventional lithium ion batteries. Here, we present a novel mechanochemical modification method for lithium metal anodes, involving roll-pressing the lithium metal foil in contact with ionic liquid-based solutions, enabling the formation of an artificial solid electrolyte interphase with favorable properties such as an improved lithium ion transport and, most importantly, the suppression of dendrite growth, allowing homogeneous electrodeposition/-dissolution using conventional and highly conductive room temperature alkyl carbonate-based electrolytes. As a result, stable cycling in symmetrical Li∥Li cells is achieved even at a high current density of 10 mA cm–2. Furthermore, the rate capability and the capacity retention in NMC∥Li cells are significantly improved.
Highlights
Nowadays, established energy sources such as fossil fuels and nuclear power plants are getting replaced by more environmentally friendly and renewable energy sources, e.g., wind and solar power
To evaluate the chemical stability of the modified surface layer against the organic carbonate-based electrolyte and its ability to passivate the lithium metal while still enabling sufficient ionic conductivity, symmetric Li∥Li cells were assembled and kept at open-circuit voltage (OCV) while the evolution of the solid electrolyte interphase (SEI) resistance was monitored by electrochemical impedance spectroscopy (EIS) for 10 days
The ratio between the different fluorine species occurs to be of importance, a higher ratio of non-LiF fluorine species seems favorable. This is in contrast with several recent reports in the literature claiming that a LiF-rich SEI is the key to homogeneous electrodeposition/-dissolution and improved electrochemical performance.[45−47] LiF is known to be a major component of the inner SEI,[9] but here, due to the low detection depth of X-ray photoelectron spectroscopy (XPS), we mainly investigated the outer layer of the SEI
Summary
Nowadays, established energy sources such as fossil fuels and nuclear power plants are getting replaced by more environmentally friendly and renewable energy sources, e.g., wind and solar power. Many studies focus on new electrolyte formulations including SEI forming additives, solid polymer electrolytes, or highly concentrated electrolytes.[17,18] electrolyte additives usually get consumed during cycling and can only improve short-term cycling.[19−21] In highly concentrated electrolytes, the majority of solvent molecules coordinate to salt cations, which suppresses reactions between lithium metal and free solvent molecules They are expensive and viscous due to the high salt content.[22−24] Solid polymer electrolytes significantly enhance the safety of the cells and allow a good wetting and mechanical confinement of lithium metal, especially at higher temperatures where lithium metal is more ductile. The morphology change during cycling was monitored by operando solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy and the surface roughness of the lithium metal after applying different modification methods was compared by atomic force microscopy (AFM)
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