1 research outputs found
Extended Solid Solutions and Coherent Transformations in Nanoscale Olivine Cathodes
Nanoparticle
LiFePO<sub>4</sub>, the basis for an entire class
of high power Li-ion batteries, has recently been shown to exist in
binary lithiated/delithiated states at intermediate states of charge.
The Mn-bearing version, LiMn<sub><i>y</i></sub>Fe<sub>1–<i>y</i></sub>PO<sub>4</sub>, exhibits even higher rate capability
as a lithium battery cathode than LiFePO<sub>4</sub> of comparable
particle size. To gain insight into the cause(s) of this desirable
performance, the electrochemically driven phase transformation during
battery charge and discharge of nanoscale LiMn<sub>0.4</sub>Fe<sub>0.6</sub>PO<sub>4</sub> of three different average particle sizes,
52, 106, and 152 nm, is investigated by operando synchrotron radiation
powder X-ray diffraction. In stark contrast to the binary lithiation
states of pure LiFePO<sub>4</sub> revealed in recent investigations,
the formations of metastable solid solutions covering a remarkable
wide compositional range, including while in two-phase coexistence,
are observed. Detailed analysis correlates this behavior with small
elastic misfits between phases compared to either pure LiFePO<sub>4</sub> or LiMnPO<sub>4</sub>. On the basis of time- and state-of-charge
dependence of the olivine structure parameters, we propose a coherent
transformation mechanism. These findings illustrate a second, completely
different phase transformation mode for pure well-ordered nanoscale
olivines compared to the well-studied case of LiFePO<sub>4</sub>