Electrochemical energy storage devices, such as batteries and supercapacitors, allow us to store electrical energy as chemical energy. They are a vital component of the UK’s plans to achieve net-zero carbon emissions by 2050.¹ Nanomaterials offer properties such as short ion diffusion distances, high percolation to form conductive networks, and structural frameworks that can withstand mechanical stresses from successive volume expansion-contraction cycles on insertion-deinsertion of guest ions. Thanks to these properties, incorporation of nanomaterials into electrochemical energy storage devices could allow them to store more energy, last longer, and cope with the load cycles required for grid storage.² However, the use of nanomaterials in commercial devices is limited by their low density and tendency to agglomerate. In addition, established synthesis methods such as high energy sonication and Hummer’s method yield nanomaterials with properties that fall short of those predicted theoretically, by resulting in a distribution of few-layer materials, and introducing defects that might not benefit electrochemical performance.

This work uses highly reducing solutions, such as alkali metal-ammonia solutions or sodium naphthalide solutions, and subsequent spontaneous dissolution in polar aprotic solvents, to individualise nanomaterials and introduce negative charge to the surface in a single step (Figure 1).^3,4 This produces exclusively monolayer, pristine, negatively-charged, individualised nanomaterials (CINs). This synthesis route can be applied to a wide range of materials, such as layered materials like graphite and transition metal dichalcogenides, as well as carbon nanotubes and other carbonaceous materials. The negative charge introduced can be used in subsequent synthesis steps to add functionality, grow nanoparticles, and control assembly into 3D structure. Using starting materials such as graphite, carbon nanotubes, and phosphorus,⁵ this work presents the application of these methods to investigate what new materials can be made. Furthermore, their electrochemical performance in batteries and supercapacitors is discussed.

References

¹HM Government, Dep. Business, Energy Ind. Strateg., 2020, 1–38.

²E. Pomerantseva, F. Bonaccorso, X. Feng, Y. Cui, Y. Gogotsi, Science, 2019, 366, 969.

³P. L. Cullen, K. M. Cox, M. K. Bin Subhan, L. Picco, O. D. Payton, D. J. Buckley, T. S. Miller, S. A. Hodge, N. T. Skipper, V. Tileli, C. A. Howard, Nat. Chem., 2017, 9, 244–249.

⁴A. Clancy, J. Melbourne, M. S. P. Shaffer, J. Mater. Chem. A, 2015, 3, 16708–16715.

⁵M. C. Watts, L. Picco, F. S. Russell-Pavier, P. L. Cullen, T. S. Miller, S. P. Bartus, O. D. Payton, N. T. Skipper, V. Tileli, C. A. Howard, Nature, 2019, 568, 216–220.