In order to meet the growing need for portable energy storage future batteries need to provide improved energy densities. One major problem lies in the current use of intercalation based electrode materials which are typically limited to storing one lithium ion per formula unit. Improved energy storage can be achieved through the use of conversion and alloying reactions where it is possible to store multiple lithium ions per formula unit. Even though impressive energy densities can be obtained through the use of conversion and alloying anode materials, only surpassed by the use of lithium metal itself, these systems are typically plagued by capacity fading during cycling. The origin is generally ascribed to irreversible reactions with the electrolyte amplified by major volume expansion, causing the growth of a solid electrolyte interphase (i.e. SEI). One promising strategy to address this issue is through the use of nanosized electrode materials (e.g. Si nanoparticles), as it has been shown that nanoparticles and nanowires show better cycling stability than their bulk counterparts [1, 2]. Large particles (i.e micrometer sized) form cracks during cycling as opposed to smaller particles (i.e. < 150 nm) [3]. Even though the use of nanoparticles can reduce crack formation and the accompanied SEI growth, capacity fading is still observed for these systems. Our work has focused on studying freestanding nanostructured conversion materials (e.g. Cu₂O nanowires), which offer in depth analyses of the conversion reactions without disturbance from binders or conducting additives. Contrary to previous understanding nanosized Cu₂O thin films and multi-layered nanostructures show an increase in capacity during cycling [4, 5]. This behaviour is caused by improved access to the entire material when using the nanomaterials. The system has also shown improved performance during cycling likely caused by electrochemical milling of the particles thereby consistently reducing the particle size and thus allowing more of the material to be accessible. With the successful use of nanosized conversion materials our research is now focused on addressing the stability problems of alloying materials by studying the effect of nanomaterials. 

References:

1.         A. Magasinski, et al.. Nat. Mater., 2010. 22: p. 353-358

2.         C.K. Chan, et al.. Nat. Nanotechnol., 2008. 3: p. 31-35

3.         X. H. Liu, et al.. Adv. En. Mater., 2012. 2: p. 722-741

4.         M Valvo, et al.. J. Mat. Chem. A., 2014. 2: p. 9574-9586

5.         D. Rehnlund, et al.. Nanoscale, 2015. 7: p. 13591-13604