2 research outputs found
Lithium Migration in Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> Studied Using in Situ Neutron Powder Diffraction
We used in situ neutron powder diffraction
(NPD) to study the migration
of Li in Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> anodes with different
particle sizes during battery cycling. The motivation of this work
was to uncover the mechanism of the increased capacity of the battery
made with a smaller-particle-sized anode. In real time, we monitored
the anode lattice parameter, Li distribution, and oxidation state
of the Ti atom, and these suggested an increase in the rate of Li
incorporation into the anode rather than a change in the migration
pathway as a result of the particle size reduction. The lattice of
these anodes during continuous lithiation undergoes expansion followed
by a gradual contraction and then expansion again. The measured lattice
parameter changes were reconciled with Li occupation at specific sites
within the Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> crystal structure,
where Li migrates from the 8<i>a</i> to 16<i>c</i> sites. Despite these similar Li-diffusion pathways, in larger-particle-sized
Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> the population of Li at
the 16<i>c</i> site is accompanied by Li depopulation from
the 8<i>a</i> site, which is in contrast to the smaller-particle-sized
anode where our results suggest that Li at the 8<i>a</i> site is replenished faster than the rate of transfer of Li to the
16<i>c</i> site. Fourier-difference nuclear density maps
of both anodes suggest that 32<i>e</i> sites are involved
in the diffusion pathway of Li. NPD is again shown to be an excellent
tool for the study of electrode materials for Li-ion batteries, particularly
when it is used to probe real-time crystallographic changes of the
materials in an operating battery during charge鈥揹ischarge cycling
The Origin of Capacity Fade in the Li<sub>2</sub>MnO<sub>3</sub>路Li<i>M</i>O<sub>2</sub> (<i>M</i> = Li, Ni, Co, Mn) Microsphere Positive Electrode: An <i>Operando</i> Neutron Diffraction and Transmission X鈥憆ay Microscopy Study
The mechanism of
capacity fade of the Li<sub>2</sub>MnO<sub>3</sub>路Li<i>M</i>O<sub>2</sub> (<i>M</i> = Li,
Ni, Co, Mn) composite positive electrode within a full cell was investigated
using a combination of <i>operando</i> neutron powder diffraction
and transmission X-ray microscopy methods, enabling the phase, crystallographic,
and morphological evolution of the material during electrochemical
cycling to be understood. The electrode was shown to initially consist
of 73(1) wt % <i>R</i>3虆<i>m</i> Li<i>M</i>O<sub>2</sub> with the remaining 27(1) wt % <i>C</i>2/<i>m</i> Li<sub>2</sub>MnO<sub>3</sub> likely existing
as an intergrowth. Cracking in the Li<sub>2</sub>MnO<sub>3</sub>路Li<i>M</i>O<sub>2</sub> electrode particle under <i>operando</i> microscopy observation was revealed to be initiated by the solid-solution
reaction of the Li<i>M</i>O<sub>2</sub> phase on charge
to 4.55 V vs Li<sup>+</sup>/Li and intensified during further charge
to 4.7 V vs Li<sup>+</sup>/Li during the concurrent two-phase reaction
of the Li<i>M</i>O<sub>2</sub> phase, involving the largest
lattice change of any phase, and oxygen evolution from the Li<sub>2</sub>MnO<sub>3</sub> phase. Notably, significant healing of the
generated cracks in the Li<sub>2</sub>MnO<sub>3</sub>路Li<i>M</i>O<sub>2</sub> electrode particle occurred during subsequent
lithiation on discharge, with this rehealing being principally associated
with the solid-solution reaction of the Li<i>M</i>O<sub>2</sub> phase. This work reveals that while it is the reduction of
lattice size of electrode phases during charge that results in cracking
of the Li<sub>2</sub>MnO<sub>3</sub>路Li<i>M</i>O<sub>2</sub> electrode particle, with the extent of cracking correlated
to the magnitude of the size change, crack healing is possible in
the reverse solid-solution reaction occurring during discharge. Importantly,
it is the phase separation during the two-phase reaction of the Li<i>M</i>O<sub>2</sub> phase that prevents the complete healing
of the electrode particle, leading to pulverization over extended
cycling. This work points to the minimization of behavior leading
to phase separation, such as two-phase and oxygen evolution, as a
key strategy in preventing capacity fade of the electrode