2 research outputs found
Li<sub>3</sub>Mo<sub>4</sub>P<sub>5</sub>O<sub>24</sub>: A Two-Electron Cathode for Lithium-Ion Batteries with Three-Dimensional Diffusion Pathways
The structure of the novel compound
Li<sub>3</sub>Mo<sub>4</sub>P<sub>5</sub>O<sub>24</sub> has been solved
from single crystal X-ray
diffraction data. The Mo cations in Li<sub>3</sub>Mo<sub>4</sub>P<sub>5</sub>O<sub>24</sub> are present in four distinct types of MoO<sub>6</sub> octahedra, each of which has one open vertex at the corner
participating in a Moî—»O double bond and whose other five corners
are shared with PO<sub>4</sub> tetrahedra. On the basis of a bond
valence sum difference map (BVS-DM) analysis, this framework is predicted
to support the facile diffusion of Li<sup>+</sup> ions, a hypothesis
that is confirmed by electrochemical testing data, which show that
Li<sub>3</sub>Mo<sub>4</sub>P<sub>5</sub>O<sub>24</sub> can be utilized
as a rechargeable battery cathode material. It is found that Li can
both be removed from and inserted into Li<sub>3</sub>Mo<sub>4</sub>P<sub>5</sub>O<sub>24</sub>. The involvement of multiple redox processes
occurring at the same Mo site is reflected in electrochemical plateaus
around 3.8 V associated with the Mo<sup>6+</sup>/Mo<sup>5+</sup> redox
couple and 2.2 V associated with the Mo<sup>5+</sup>/Mo<sup>4+</sup> redox couple. The two-electron redox properties of Mo cations in
this structure lead to a theoretical capacity of 198 mAh/g. When cycled
between 2.0 and 4.3 V versus Li<sup>+</sup>/Li, an initial capacity
of 113 mAh/g is observed with 80% of this capacity retained over the
first 20 cycles. This compound therefore represents a rare example
of a solid state cathode able to support two-electron redox capacity
and provides important general insights about pathways for designing
next-generation cathodes with enhanced specific capacities
Single-Phase Lithiation and Delithiation of Simferite Compounds Li(Mg,Mn,Fe)PO<sub>4</sub>
Understanding
the phase transformation behavior of electrode materials
for lithium ion batteries is critical in determining the electrode
kinetics and battery performance. Here, we demonstrate the lithiation/delithiation
mechanism and electrochemical behavior of the simferite compound,
LiMg<sub>0.5</sub>Fe<sub>0.3</sub>Mn<sub>0.2</sub>PO<sub>4</sub>.
In contrast to the equilibrium two-phase nature of LiFePO<sub>4</sub>, LiMg<sub>0.5</sub>Fe<sub>0.3</sub>Mn<sub>0.2</sub>PO<sub>4</sub> undergoes a one-phase reaction mechanism as confirmed by ex situ
X-ray diffraction at different states of delithiation and electrochemical
measurements. The equilibrium voltage measurement by galvanostatic
intermittent titration technique shows a continuous change in voltage
at Mn<sup>3+</sup>/Mn<sup>2+</sup> redox couple with addition of Mg<sup>2+</sup> in LiMn<sub>0.4</sub>Fe<sub>0.6</sub>PO<sub>4</sub> olivine
structure. There is, however, no significant change in the Fe<sup>3+</sup>/Fe<sup>2+</sup> redox potential