Recently, there has been much discussion about Na-ion batteries (NIBs) emerging as one ideal technology for grid-level energy storage.  Large-scale usage of NIBs can be sustainable as the raw materials involved in making such batteries are cheap, plentiful and non-toxic.  Thus far, they have demonstrated very promising electrochemical performances in prototype experiments.

Despite the aforementioned benefits, there still remain technical issues associated with the electrode materials, which is currently hindering their development as a fully-functional commercial battery.  One of these pressing problems is the efficiency and cyclability of the anode material: an ideal material must possess both a high 1^st cycle coulombic efficiency and a stable long-term cycling life—as both of these are crucial to the performance of the battery.  However, most candidate materials currently proposed in the literature do not meet such criteria.

Herein, we study self-standing cellulose-derived carbon as a model carbon, where we attempt to understand factors affecting coulombic efficiency and long-term cycling.  This material displays one of the highest reported coulombic efficiencies for carbon-based anodes in the literature, with values averaging near 90% for the first cycle with a deep-sodiation in a half-cell.  On the other hand, the carbon material also displays extremely poor rate and long-term cycling performances, which leads us to an in-depth investigation of the fading mechanism of carbon materials used as NIB anodes.

Through the course of our investigation on the fading mechanism, we are able to uncover some structural-property relationships to understand the capacity loss during long-term cycling.  This was elucidated through the use of traditional characterization methods such as XRD, Raman spectroscopy and XPS measurements along with more advanced TEM characterization, using sample “lift-outs” to probe the structural effects of long-term cycling on the carbon material.  These claims are also further supported through electrochemical data including diffusivity tests, CV and EIS measurements.  Using the information learned on the efficiency/long-term decay mechanism, we were able to devise ‘proof-of-concept’ solutions to increase long-term cycling of carbon anode materials utilized in NIBs.