ON THE REVERSIBILITY AND FRAGILITY OF SODIUM METAL ELECTRODES
Metallic sodium is receiving renewed interest as a battery anode material because the metal is earth-abundant, inexpensive, and offers a high charge storage capacity (1166 mAh/g at -2.71 V vs the standard hydrogen potential). Unlike metallic lithium, the case for Na as the anode in rechargeable batteries has already been demonstrated on a commercial scale in high-temperature Na||S and Na||NiCl2-NaAlCl4 secondary batteries. This thesis describes an investigation of the reversibility of room temperature sodium anodes in galvanostatic plating/stripping reactions using in-situ optical visualization. The main result reported in the thesis is that orphaning of Na metal is the dominant source of irreversibility in liquid electrolytes. Additionally, it is found that orphaning is triggered by a root-breakage process during the stripping cycle, which is exacerbated by the fragility and low mass density of mossy Na electrodeposits formed during the plating cycle. As a first step towards electrode designs that are able to accommodate these fragile deposits, electrodeposition of Na in non-planar electrode architectures that provide continuous and morphology agnostic access to the metal at all stages of electrochemical cycling is studied. On this basis, non-planar Na electrodes is reported to exhibit high levels of reversibility (Coulombic Efficiency > 99% for 1mAh/cm2 Na throughput) in room-temperature, liquid electrolytes.
Supplemental file(s) description: supporting video for Figure 3.2.3a (40x speed up)
dendritic electrodeposition; energy storage; sodium metal batteries; Energy; Materials Science; hybrid anode
Archer, Lynden A.
Kourkoutis, Lena Fitting
Materials Science and Engineering
M.S., Materials Science and Engineering
Master of Science
dissertation or thesis