Shape Matters: The Effect of Particle Morphology on the Fast-Charging Performance of LiFePO4/C Nanoparticle Composite Electrodes

For the successful use of lithium-ion batteries in automotive applications, reliable availability of high storage capacity and very short recharging times are essential. In order to develop the perfect battery for a certain application, structure-property relationships of each active material must be fully understood. LiFePO4 is of great interest due to its fast-charging capability and high stability regarding its thermal resistance and chemical reactivity. The anisotropic lithium-ion diffusion through the LiFePO4 crystal structure indicates a strong dependence of the electrochemical performance of a nanostructured active material on particle morphology. In this paper, the relationship of the particle morphology and fast-charging capability of LiFePO4/C core/shell nanoparticles in half-cells was studied. For this purpose, a new multistep synthesis strategy was developed. It involves the combination of a solvothermal synthesis followed by an in situ polymer coating and thermal calcination step. Monodisperse rodlike LiFePO4 nanoparticles with comparable elongation along the b-axis (30-50 nm) and a varying aspect ratio c/a (2.4-6.9) were obtained. A strong correlation of the fast-charging capability with the aspect ratio c/a was observed. When using LiFePO4 nanoparticles with the smallest aspect ratio c/a, the best electrochemical performance was received regarding the specific capacity at high C-rates and the cycling stability. A reduction of the aspect ratio c/a by 30% (3.6 to 2.4) was found to enhance the charge capacity at 10 C up to an order of magnitude (7.4-73 mA h.g(-1)).

Automated summary

This paper studied the relationship between the fast-charging capability of LiFePO4 batteries and the particle morphology, finding a strong correlation with the aspect ratio c/a of the nanoparticles. LiFePO4 nanoparticles with the smallest aspect ratio c/a exhibited the best electrochemical performance at high C-rates, and reducing the aspect ratio c/a by 30% significantly increased the charge capacity.