A paper currently in the pre-proof stage of publication in the journal Energy Storage Materials has explored the relationship between the electrochemical and mechanical properties of metallic lithium, providing new insights into this key material.
Study: Li plating on alloy with superior electromechanical stability for high energy density anode-free batteries. Image Credit: tunasalmon/Shutterstock.com
Metallic Lithium Batteries
Lithium is a key metal in the 21st century, as it is vital for the construction of lithium metal batteries, which have been proposed as key rechargeable energy storage devices for a vast range of electronic applications. The high energy density and low working potential of metallic lithium anodes are key to the performance of these devices.
Incorporating ultrathin lithium metal anodes or initial-lithium-free anodes can improve the energy density of these devices, but ultrathin lithium metal is hindered by poor mechanical processability, poor electrochemical reversibility, and reactivity with ambient moisture and oxygen. Anode-free batteries with initial Li-free anodes can overcome these issues and maximize the energy density of devices. Lithium is provided by cathodes and metallic lithium is deposited on current collectors during charging and dissolved during discharge.
During lithium plating, dendritic and porous lithium deposits can form. These dendrites possess inferior electrochemical reversibility and mechanical durability, which severely limits the performance of batteries. A solid electrolyte interphase is formed by the reaction between dendritic lithium and the electrolyte. Accumulation of inactive metallic lithium has severe consequences for devices, including deteriorated Coulombic efficiency and failure.
Suppressing the formation of inactive metallic lithium in these devices and improving their electrochemical reversibility and mechanical stability is key to designing efficient and reliable metallic lithium batteries.
Substrate Regulation of Metallic Lithium Performance
Several studies have demonstrated that substrate metals can regulate the mechanical and electrochemical properties and performance of metallic lithium. Lithium can form stable alloys with other metals such as tin, zin, and antimony. Metallic lithium plating can display huge discrepancies on different substrates. For instance, gold and silver substrates and materials deliver low Li over-nucleation potential. Using these elements improves the Li electrochemical plating behaviors, but these materials are expensive and can precipitate during lithium dissolution.
Using metals that have low or no solubility in lithium (like zinc, tin, and antimony) overcomes the challenges with novel metals like silver and gold, which can potentially cause long-term instability over several cycles. How substrates regulate metallic lithium’s electromechanical behavior and electrochemical reversibility performance is still a poorly understood phenomenon.
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The Study
The research has investigated the relationship between mechanical and electrochemical properties in metallic lithium to help improve the electrochemical performance of metallic lithium batteries.
In-plane metallic lithium growth on lithophilic Li-metal alloys could help to realize better electromechanical stability. Using current collectors with these metallic species provides advantages, as lithophilic metal alloys are deposited in situ before lithium plating occurs.
The authors have stated that current collectors with plane geometries are advantageous in comparison to other forms, such as 3D structured porous materials, as they produce a dense lithium metal deposition layer without presenting a large surface area to liquid electrolytes. Moreover, these materials can achieve good mechanical stability and high packing density.
In the research, the authors have reported a design that employs a lithium-tin alloy interphase on commercial copper foil. The method developed in the paper improves the electromechanical stability of the initial lithium-free anode. This was due to the low lithium nucleation energy barrier and high binding energy in the material.
Results of the Study
The modified electrode demonstrated superior CE compared to bare copper electrodes. Failure occurred after seventy cycles without the modification, and with the modification, reliable performance was achieved over 400 cycles. The electrode was tested in a carbonate electrolyte, and the lithium layer remained intact, and contact was kept with the copper foil during cycling.
Both cycling capacity and capacity retention were increased in anode-free batteries using the method developed by the authors. On the bare copper electrode, lithium peeling occurred after 50 cycles.
These results demonstrated the improvements in mechanical behavior and electromechanical performance using the proposed lithium-tin alloy in metallic lithium batteries. To demonstrate the generality of using lithium alloys for these devices, the authors conducted studies on aluminum, antimony, and zinc interphases on copper foils, which also demonstrated improvements in electrochemical reversibility. Overall, this research provides a route toward realizing metallic lithium batteries with vastly improved mechanical and electromechanical performance.
Further Reading
Wang, X et al. (2022) Li plating on alloy with superior electromechanical stability for high energy density anode-free batteries [online, pre-proof] Energy Storage Materials | sciencedirect.com. Available at: https://www.sciencedirect.com/science/article/abs/pii/S2405829722001982
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