4 research outputs found
Data_Sheet_1_Revealing Operando Transformation Dynamics in Individual Li-ion Electrode Crystallites Using X-Ray Microbeam Diffraction.pdf
<p>For the development of next-generation batteries it is important to understand the structural changes in electrodes under realistic non-equilibrium conditions. With microbeam X-ray diffraction it is possible to probe many individual electrode grains concurrently under non-equilibrium conditions in realistic battery systems. This makes it possible to capture phase transformation behavior that is difficult or even impossible with powder diffraction. By decreasing the X-ray beam size, the diffraction powder rings fall apart in the (hkl) reflections belonging to individual electrode crystallites. Monitoring these reflections during (dis)charging provides direct insight in the transformation mechanism and kinetics of individual crystallite grains. Here operando microbeam diffraction is applied on two different cathode materials, LiFePO<sub>4</sub> (LFP) displaying a first-order phase transformation and LiNi<sub>1/3</sub>Co<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub> (NCM) displaying a solid solution transformation. For LFP four different phase transformation mechanisms are distinguished within a single crystallite: (1) A first-order phase transformation without phase coexistence, (2) with phase coexistence, (3) a homogeneous solid solution phase transformation and (4) an inhomogeneous solid solution crystal transformation, whereas for NCM only type (3) is observed. From the phase transformation times of individual crystallites, the local current density is determined as well as the active particle fractions during (dis)charge. For LFP the active particle fraction increases with higher cycling rates. At low cycling rates the active particle fraction in NCM is much larger compared to LFP which appears to be related to the nature of the phase transition. In particular for LFP the grains are observed to rotate during (dis)charging, which can be quantified by microbeam diffraction. It brings forward the mechanical working of the electrodes due to the volumetric changes of the electrode material possibly affecting electronic contacts to the carbon black conducting matrix. These results demonstrate the structural information that can be obtained under realistic non-equilibrium conditions, combining local information on single electrode crystallites, as well as global information through the observation in many crystallites concurrently. This provides new and complementary possibilities in operando battery research, which can contribute to fundamental understanding as well as the development of electrodes and electrode materials.</p
Rate-Induced Solubility and Suppression of the First-Order Phase Transition in Olivine LiFePO<sub>4</sub>
The
impact of ultrahigh (dis)Âcharge rates on the phase transition
mechanism in LiFePO<sub>4</sub> Li-ion electrodes is revealed by in
situ synchrotron diffraction. At high rates the solubility limits
in both phases increase dramatically, causing a fraction of the electrode
to bypass the first-order phase transition. The small transforming
fraction demonstrates that nucleation rates are consequently not limiting
the transformation rate. In combination with the small fraction of
the electrode that transforms at high rates, this indicates that higher
performances may be achieved by further optimizing the ionic/electronic
transport in LiFePO<sub>4</sub> electrodes
Photostrictive/Piezomagnetic Core–Shell Particles Based on Prussian Blue Analogues: Evidence for Confinement Effects?
High-quality core–shell particles,
which associate a photostrictive core (Rb<sub>0.5</sub>CoÂ[FeÂ(CN)<sub>6</sub>]<sub>0.8</sub>·<i>z</i>H<sub>2</sub>O, <b>RbCoFe</b>) and a ferromagnetic shell (Rb<sub>0.2</sub>NiÂ[CrÂ(CN)<sub>6</sub>]<sub>0.7</sub>·<i>z</i>′H<sub>2</sub>O, <b>RbNiCr</b>), were successfully grown by a multistep protocol
based on coprecipitation in water. High-resolution transmission electron
microscopy shows that well-defined heterostructures are formed and
that the core–shell interface is abrupt with the epitaxial
relationship [001](001)<b>RbCoFe</b>//[001]Â(001)<b>RbNiCr</b>, confirmed by simulations of the X-ray diffraction line widths.
The core particles are monocrystalline, with 50 nm sides, and the
shell consists of large platelet-like crystallites, with a height
that corresponds to the shell thickness and lateral dimensions comparable
to the size of the core particles. Analysis of the diffracted intensities
as a function of shell thickness (9–26 nm) shows that the epitaxial
shell growth does not lead to a thick pseudomorphic layer at the interface.
In contrast, Williamson–Hall plots suggest that a structural
relaxation takes place to adapt the mismatched lattices, with the
formation of misfit dislocations distributed over the entire shell
thickness. This later finding is indicative of an effective mechanical
coupling within the heterostructures. However, a magnetization increase
by only a few percent was observed under light irradiation for these <b>RbCoFe</b>@<b>RbNiCr</b> particles. We showed from in situ
synchrotron X-ray diffraction measurements that these small changes
most likely reflect confinement effects as photoswitching of the core
phase is partly or completely blocked depending on the shell thickness
<i>Operando</i> Nanobeam Diffraction to Follow the Decomposition of Individual Li<sub>2</sub>O<sub>2</sub> Grains in a Nonaqueous Li–O<sub>2</sub> Battery
Intense interest in the Li–O<sub>2</sub> battery system
over the past 5 years has led to a much better understanding of the
various chemical processes involved in the functioning of this battery
system. However, detailed decomposition of the nanostructured Li<sub>2</sub>O<sub>2</sub> product, held at least partially responsible
for the limited reversibility and poor rate performance, is hard to
measure <i>operando</i> under realistic electrochemical
conditions. Here, we report <i>operando</i> nanobeam X-ray
diffraction experiments that enable monitoring of the decomposition
of individual Li<sub>2</sub>O<sub>2</sub> grains in a working Li–O<sub>2</sub> battery. Platelet-shaped crystallites with aspect ratios
between 2.2 and 5.5 decompose preferentially via the more reactive
(001) facets. The slow and concurrent decomposition of individual
Li<sub>2</sub>O<sub>2</sub> crystallites indicates that the Li<sub>2</sub>O<sub>2</sub> decomposition rate limits the charge time of
these Li–O<sub>2</sub> batteries, highlighting the importance
of using redox mediators in solution to charge Li–O<sub>2</sub> batteries