Observation of reversible pore change in mesoporous tin phosphate anode material during Li alloying/dealloying

Abstract

We observed the pore expansion and contraction of mesoporous tin phosphate during Li alloying/dealloying using small-angle X-ray scattering and transmission electron microscopy. As-prepared mesoporous tin phosphate showed pore and porewall sizes of 3 and 2 nm, respectively. During lithium alloying (discharging), pore size was slightly contracted, but porewall size was slightly expanded within the range of 1 nm. However, during lithium dealloying (charging), pore and porewall sizes recovered to their original sizes before cycling. The charged sample had a nanoscale pore (∼3 nm) array with a more or less uniformly sized open-porewall structure of amorphous lithium phosphates with metallic α-Sn face-centered-cubic nanocrystals ∼2 nm in diameter.