posted on 2022-01-05, 15:05authored byAlois Kuhn, Juan Carlos Pérez-Flores, Jesús Prado-Gonjal, Emilio Morán, Markus Hoelzel, Virginia Díez-Gómez, Isabel Sobrados, Jesús Sanz, Flaviano García-Alvarado
H2V3O8 (HVO) is a promising high-capacity cathode material for lithium-ion
batteries (LIBs). It allows reversible two-electron transfer during
electrochemical lithium cycling processes, yielding a very attractive
theoretical capacity of 378 mAh g–1. While an abundant
number of research works exclusively proved the outstanding electrochemical
lithium storage properties of H2V3O8, structural changes during the intercalation process have not been
scrutinized, and the crystallographic positions occupied by the guest
species have not been revealed yet. However, an in-depth understanding
of structural changes of cathode materials is essential for developing
new materials and improving current materials. Aimed at providing
insights into the storage behavior of HVO, in this work, we employed
a combination of high-resolution synchrotron X-ray and neutron diffraction
to accurately describe the crystal structures of both pristine and
lithiated H2V3O8. In HVO, hydrogen
is located on one single-crystallographic site in a waterlike arrangement,
through which bent asymmetric hydrogen bonds across adjacent V3O82– chains are established.
The role played by water in network stabilization was further examined
by density functional theory (DFT) calculations. Easy hydrogen-bonding
switch of structural water upon lithium intercalation not only allows
better accommodation of intercalated lithium ions but also enhances
Li-ion mobility in the crystal host, as evidenced by magic-angle spinning
(MAS) NMR spectroscopy. Facile conduction pathways for Li ions in
the structure are deduced from bond valence sum difference mapping.
The hydrogen bonds mitigate the volume expansion/contraction of vanadium
layers during Li intercalation/deintercalation, resulting in improved
long-term structural stability, explaining the excellent performance
in rate capability and cycle life reported for this high-energy cathode
in LIBs. This study suggests that many hydrated materials can be good
candidates for electrode materials in not only implemented Li technology
but also emerging rechargeable batteries.