Recent Advances Towards Practical LiNiO2 Cathode Materials: Optimised Calcination and Modification with W Via a Single Step Synthesis Route
Authors: Bianchini Matteo , Goonetilleke Damian , Weber Daniel , Fauth Francois , Ma Yuan , Mazilkin Andrey , Riewald Felix , Kurzhals Philipp , Sommer Heino , Gasteiger Hubert Andreas , Brezesinski Torsten , Janek Juergen 
Published: November 2022

LiNiO2 has been long considered as a promising cathode material owing to its high practical energy density [1,2]. However, structural and surface instabilities, coupled with complexities in the synthesis, have thus far prevented its commercialisation [3]. In this talk I will review our recent work towards the use of LiNiO2 as an actual cathode solution, via carefully controlled calcination conditions [4,5] and stabilization especially in terms of elemental substitution (doping) [6,7], but also of protective surface coating.

To address issues with the material’s stability during synthesis and cycling, the use of an ammonium tungstate flux to modify both the LiNiO2 crystal structure and primary particle morphology without introducing additional steps into the synthesis will be discussed here in particular detail. The successful preparation of LiNiO2 modified with an industrially relevant amount of W (< 5 mol %) was confirmed using a combination of electron microscopy and synchrotron-based X-ray diffraction (XRD). Refinement of structural models against the data suggests tungsten dopant ions occupy the Ni site and concurrently induce migration of Ni2+ to the Li sites. Moreover, W enrichment at grain boundaries has been observed under some of the synthesis conditions. Variable temperature XRD was used to highlight the improved stability of the W-doped materials during the calcination at high temperatures. Electrochemical characterisation shows that W-doped LiNiO2 offers improved cycle life at the expense of little specific capacity. The structural consequences of tungsten doping on the behaviour of the material during electrochemical cycling was also investigated using operando XRD, showing reduced mechanical stress upon cycling. In conclusion, we will show that LiNiO2 modified by W with a simple route and no additional processing steps exhibits structural stability at high temperatures, offering a path towards the reliable synthesis of LiNiO2 with controlled morphology, improved chemomechanics and longer cycling life.

Reference
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[1] Dahn et al., Structure and Electrochemistry of Li1+-yNiO2 and a New Li2NiO2 Phase with the Ni(OH)2 Structure, Solid State Ionics 1990, 44 (1-2), 87-97.

[2] Rougier et al., Optimization of the composition of the Li1-zNi1+zO2 electrode materials: Structural, magnetic, and electrochemical studies, Journal of the Electrochemical Society 1996, 143 (4), 1168-1175

[3] Bianchini et al., There and Back Again-The Journey of LiNiO2 as a Cathode Active Material. Angew. Chem., Int. Ed. 2019, 58, 10434−10458.

[4] Kurzhals et al., The LiNiO2 Cathode Active Material: A Comprehensive Study of Calcination Conditions and their Correlation with Physicochemical Properties. Part I. Structural Chemistry, Journal of the electrochemical society, 2021, 168 (11) 110518.

[5] Riewald et al., The LiNiO2 Cathode Active Material: A Comprehensive Study of Calcination Conditions and their Correlation with Physicochemical Properties. Part II. Morphology, Journal of the electrochemical society, 2022, 10.1149/1945-7111/ac4bf3

[6] Goonetilleke et al., Single step synthesis of W-modified LiNiO2 using an ammonium tungstate flux, Journal of Materials Chemistry A 2022, 10.1039.D1TA10568J.

[7] Weber et al., Tracing Low Amounts of Mg in the Doped Cathode Active Material LiNiO2, Journal of the electrochemical society, 2022, 10.1149/1945-7111/ac5b38.