Amorphous 2D‐Nanoplatelets of Red Phosphorus Obtained by Liquid‐Phase Exfoliation Yield High Areal Capacity Na‐Ion Battery Anodes

Abstract

The development of sodium ion batteries will require high‐performance electrodes with very large areal capacity and reasonable rate performance. Although red phosphorus is a very promising electrode material, it has not yet fulfilled these requirements. Here, liquid phase exfoliation is used to convert solid red phosphorus into amorphous, quasi‐2D nanoplatelets. These nanoplatelets have lateral sizes of hundreds of nanometers, thickness of 10s of nanometers and are quite stable in ambient conditions, displaying only low levels of oxidation on the nanosheet surface. By solution mixing with carbon nanotubes, these nanoplatelets can be fabricated into nanocomposite battery anodes. After employing an extended activation process, good cycling stability over 1000 cycles and low‐rate capacitances >2000 mAh gP−1 is achieved. Because of the high conductivity and mechanical robustness provided by the nanotube network, it is possible to fabricate very thick electrodes. These electrodes display extremely high areal capacities approaching 10 mAh cm−2 at currents of ≈1 mA cm−2. Detailed analysis shows these electrodes to be limited by solid‐state diffusion such that the thickest electrodes have state‐of‐the‐art rate performance and a near‐optimized combination of capacity and rate performance.

Cobalt Oxide 2D Nanosheets Formed at a Polarized Liquid|Liquid Interface toward High-Performance Li-Ion and Na-Ion Battery Anodes

“…This indicates that the combination of 2D nanoplatelets of Co 3 O 4 with the use of SWCNTs as both binder and conductive additive allows full utilization of the active material for the storage of both ion types. This is consistent with a number of previous studies on various 2D material-based electrodes. ,,,, In both cases, the n -values are very close to 0.5, indicating that both electrode types are diffusion-limited, at least for this electrode thickness (∼10 μm).…”

“…This is consistent with a number of previous studies on various 2D material-based electrodes. 26,32,37,38,67 In both cases, the nvalues are very close to 0.5, indicating that both electrode types are diffusion-limited, at least for this electrode thickness (∼10 μm).…”

“…This is particularly evident when single-walled carbon nanotubes (SWCNTs) are used in place of both the conductive additive and polymeric binder . Such an electrode architecture yields high out-of-plane electrode conductivity, facilitating charge delivery and allowing the capacity and rate capability to be maximized. ,, In addition, the mechanically tough SWCNT network allows the electrode to cope with both volumetric and morphological changes. , …”

“…Methods that yield nanostructured active materials, such as using an ITIES, are useful in battery research as small active particles give porous electrodes with high capacity and excellent rate performance. − In particular, using active particles in the form of 2D platelets has an advantage over spherical particles because they possess three times less surface area per volume for a given solid-state diffusion length. , This gives short diffusion lengths, and so reduced solid-state diffusion times and enhanced rate performance, without extremely large active surface areas. In this manner, unwanted parasitic reactions are reduced between the active electrode materials and the nonaqueous electrolyte at different potentials …”

“…One advantage of using carbon nanotubes is that in addition to enhancing the conductivity, they mechanically strengthen the electrode. This reinforcement allows the electrode to accommodate the expansion and contraction that occurs during lithiation/delithiation and sodiation/desodiation. , In recent years, we have studied composites of a range of active materials mixed with carbon nanotubes using no additional binder/conductive additive. ,,− This type of electrode architecture allows us to produce LIB and SIB electrodes that almost always display near-theoretical capacities. In addition, this architecture enhances conductivity to deliver charge throughout the electrode by accommodating the expansion and contraction associated with lithiation/sodiation and delithiation/desodiation.…”