Structure and interfaces of compositionally graded Li(Ni, Mn)_xO_y cathodes on (111) Nb-doped SrTiO₃

ABSTRACT

Core–shell Li(Ni, Mn)_xO_y thin film has been deposited onto a (111) single-crystal Nb-doped SrTiO₃ substrate by pulsed laser deposition. The thin film is ∼350–400 nm thick with a ∼60 nm-thick Ni-rich interface. The orientation relationship between the cubic Li(Ni, Mn)₂ O₄ spinel and distorted rhombohedral-layered Li(Ni, Mn)O₂ phases and the substrates are [112] _STO ||[112]_Spinel and ($\overline{1}\overline{1}$1) _STO ||($\overline{1}\overline{1}$1) _Spinel; [112] _STO ||[210] _LiNiO2 and ($\overline{1}\overline{1}$1) _STO ||(00$\overline{3}$) _LiNiO2; and [112] _Spinel ||[210] _LiNiO2 and ($\overline{1}\overline{1}$1) _Spinel ||(00$\overline{3}$) _LiNiO2. The film–substrate interface is sharp, non-reactive and free of planar defects. The interfaces between spinel, rhombohedral-layered Li(Ni, Mn)O₂ and the order–disorder domains are coherent and diffused. As the spacing between octahedral cations in the spinel phase and in the Li(Ni, Mn)O₂ phase is different; these two phases could be distinguished by quantifying the spacings between two octahedrally located cations. The electro-chemical behaviour of the film is not likely to be optimum even with the intended phase composition and chemistry due to disordering in Li (Ni, Mn)O₂ and unsuitable orientation of the phases. Understanding such structural details is a precursor to tailor the electro-chemical activity in Li(Ni, Mn)_xO_y.

KEYWORDS:

• Li(Ni,Mn)₂O₄ spinel
• rhombohedral-layered Li(Ni,Mn)O₂
• pulse laser deposition
• electron microscopy
• order–disorder domain

Acknowledgements

This work was initiated while JB was working as a Guest Researcher at the National Institute for Standard and Technologies, Gaithersburg, MD, USA. JB thanks the NIST and the US Department of Commerce for hosting his visit. JB also thanks the Department of Atomic Energy, Govt. of India for the grant of EOL for this visit. Authors take the opportunity to thank the reviewers for their constructive criticism and useful suggestions, which has helped improving the paper.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that supports the findings of this study are available within the article.

Additional information

Funding

This work was funded by the Department of Science & Technology (DST), Government of India through the FIST grant.