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electric conductivity) within a coin cell are shown place overall on charging and discharging are shown
alongside the corresponding charging and discharg- in Figs. 2(e) and 2(f), respectively.
ing curves in Fig. 1 (vs. Li /Li). The electrode material Energy Science
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was stable under this characterization with 8-keV In summary, operando neutron powder diffraction
X-rays, as expected from previous TXM tests on sim- and a transmission X-ray microscope were applied
ilar electrodes at these energies. The features of the to characterize the structural and morphological
charge-discharge curves of this coin cell are nearly evolution of the Li 2MnO 3·LiMO 2 (M = Li, Ni, Co, Mn)
identical to that of a pouch cell containing LTO used composite electrode, with the operando approach
ACTIVITY REPORT 2016
in the NPD work. The diameter of the approximately enabling this information to be directly correlated
spherical Li 2MnO 3·LiMO 2 particle at the open-cir- with electrochemical function. The unique combina-
cuit voltage (OCV) was ~10 μm (Fig. 1(b)). During tion of these operando methods revealed the under-
charging to 4.5 V, cracks appeared in the Li 2MnO 3·Li- lying phase transformations and mechanisms that are
MO 2 electrode particle (red dotted box in Fig. 1(c)), responsible for the initiation and intensification of
which developed further during charging to 4.7 V particle cracking, which likely leads to pulverization
(Figs. 1(d) and 1(e)). During discharging, the particle and capacity fading of this electrode. Overall, both
cracking faded (Fig. 1(f)), and the particle appeared the magnitude of the phase lattice change and the
almost to heal and to become slightly smaller than in phase separation lead to capacity fading of the
its initial state, by 2.0 V (Fig. 1(g)). Li 2MnO 3·LiMO 2 composite electrode; this work indi-
cates that the minimization of phase separation is key
The varied size of the Li 2MnO 3·LiMO 2 particle during to diminishing the capacity fading of this electrode.
charging and discharging was quantified; the change (Reported by Yan-Gu Lin)
in the particle appearance is shown in the differential
TXM images in Fig. 2. There is a strong correlation
between the change in the Li 2MnO 3·LiMO 2 electrode This report features the work of Ru-Shi Liu and his
particle cracking and the particle volume. The appear- co-workers published in J. Am. Chem. Soc. 138, 8824
ance of cracks in the Li 2MnO 3·LiMO 2 electrode particle (2016).
on charging to 4.5 V (vs. Li /Li, red circle in Fig. 2(a))
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was accompanied by a ~2% decrease of volume. The
significant development of the particle cracks on TLS 01B1 SWLS – X-ray Microscopy
charging to 4.7 V was accompanied by a more signif- • TXM
icant ~3%) decrease of particle volume (Fig. 2(b)). • Materials Science, Environmental and Earth Science,
Almost no change in the particle cracks or the particle Methodology and Instrumentation
volume occurred during discharging to 3.6 V (Fig.
1(c)), but further discharging to 2.0 V revealed partial
healing of the cracks in the Li 2MnO 3·LiMO 2 electrode, | Reference |
accompanied by a ~3% volume expansion (Fig. 1(d)). 1. C. J. Chen, W. K. Pang, T. Mori, V. K. Peterson, N.
The formation of particle cracks and healing taking Sharma, P. H. Lee, S. H. Wu, C. C. Wang, Y. F. Song,
and R. S. Liu, J. Am. Chem. Soc. 138, 8824 (2016).

(a) (b) (c)

(d) (e) (f)

Fig. 2: Differential TXM images recorded between (a) 4.5 V and
OCV, (b) 4.7 and 4.5 V, (c) 3.6 and 4.7 V, (d) 2.0 and 3.6 V,
(e) 4.7 V and OCV, and (f) 2.0 V and OCV. Voltage is vs.
Li /Li. [Reproduced from Ref. 1] TLS 01B1 SWLS – X-ray Microscopy
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