“Lithiation and delithiation in LiFePO4 is highly anisotropic with lithium ions diffusing along the channels perpendicular to the {010} facets,” explains team leader Guihua Yu. “Although researchers have previously tried to control the orientation of nanosheets in this battery material, we are the first to have succeeded in synthesizing {010}-oriented LiFePO4 nanosheets with probably the highest surface-to-thickness ratio.”

The team prepared the {010}-oriented plate-like LiFePO4 using diethylene glycol as a solvent, which binds strongly to the {010} facets, so preventing them from growing further. This naturally leads to a larger percentage of oriented {010} facets during nanosheet growth.

Higher reversible capacity

The oriented LiFePO4 nanosheets boast a much higher reversible capacity – that is how much energy they can store – compared with commercially available LiFePO4 particles containing random shapes. What is more, battery electrodes made from these nanosheets also last longer and their capacity remains the same over 1000 cycles, said team member Yu Zhao. “And, most importantly the LiFePO4 can rapidly charge/discharge, maintaining 70% of its theoretical capacity (of around 170 mAh/g) at a current rate of 10C (six minute battery charge or discharge time),” he told nanotechweb.org.

“Our work shows that controlling the crystal orientation of battery electrode materials is an effective way to improve their performance,” added Yu.

The Texas researchers say that they are now trying to more precisely control the thickness of the nanosheets and to investigate the relationship between the thickness and the electrochemical characteristics of LiFePO4. “We also hope to study shape and structure-controlled synthesis of different battery electrode materials, such as the other phospholivines, with a view to ultimately building better energy storage devices with significantly improved performance,” revealed Yu.

The current work is detailed in Nano Lett. DOI: 10.1021/nl5008568.