First-Principles
Study on the Thermal Stability of
LiNiO<sub>2</sub> Materials Coated by Amorphous Al<sub>2</sub>O<sub>3</sub> with Atomic Layer Thickness
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Abstract
Using first-principles calculations,
we study how to enhance thermal
stability of high Ni compositional cathodes in Li-ion battery application.
Using the archetype material LiNiO<sub>2</sub> (LNO), we identify
that ultrathin coating of Al<sub>2</sub>O<sub>3</sub> (0001) on LNO(012)
surface, which is the Li de-/intercalation
channel, substantially improves the instability problem. Density functional
theory calculations indicate that the Al<sub>2</sub>O<sub>3</sub> deposits
show phase transition from the corundum-type crystalline (c-Al<sub>2</sub>O<sub>3</sub>) to amorphous (a-Al<sub>2</sub>O<sub>3</sub>) structures as the number of coating layers reaches three. Ab initio
molecular dynamic simulations on the LNO(012) surface coated by a-Al<sub>2</sub>O<sub>3</sub> (about 0.88 nm) with three atomic layers oxygen
gas evolution is strongly suppressed at <i>T</i> = 400 K.
We find that the underlying mechanism is the strong contacting force
at the interface between LNO(012) and Al<sub>2</sub>O<sub>3</sub> deposits,
which, in turn, originated from highly ionic chemical bonding of Al
and O at the interface. Furthermore, we identify that thermodynamic
stability of the a-Al<sub>2</sub>O<sub>3</sub> is even more enhanced
with Li in the layer, implying that the protection for the LNO(012)
surface by the coating layer is meaningful over the charging process.
Our approach contributes to the design of innovative cathode materials
with not only high-energy capacity but also long-term thermal and
electrochemical stability applicable for a variety of electrochemical
energy devices including Li-ion batteries