Qualitative and Quantitative Proton Content Analysis of Chemically Delithiated Ni-Rich NCM Materials
Authors: Groen Corbinian , Qian Simon , Szentmiklósi László , Maróti Boglárka , Harsányi Ildikó , Gasteiger Hubert Andreas 
Published: December 2024

The development of long-lasting, high-energy-density batteries is crucial for the electrification of multiple sectors. The current scope for cathode active materials (CAM) to meet this demand are the next-generation Ni-rich layered oxides Li(NixCoyMnz)O2 (x+y+z=1, x>0.8). However, understanding their aging and degradation mechanisms is essential for improving their long-term stability. Chemical delithiation can be used to obtain pure CAM powders (rather than electrodes) at various degrees of delithiation to better understand these mechanisms and to develop countermeasures to improve cycling stability.[1] However, during chemical delithiation, protons can intercalate into the structure of CAMs by ion exchange of Li+ with H+.[2,3] This potentially compromises the use of chemically delithiated CAM powders for mechanistic studies.

Therefore, we investigated the amount of protons in the chemically delithiated materials and devised approaches to minimize the proton content. Quantifying the proton content presents unique challenges, for which we employed prompt gamma activation analysis (PGAA) for precise quantification. Based on this benchmark technique, we developed a more accessible method to quantify the proton content by correlating the gas release during heat treatment of the chemically delithiated materials to their weight loss. Furthermore, we analyzed the bulk and surface properties of a Ni-rich chemically delithiated NCM as well as its thermal decomposition in order to gain insights into the effects of chemical delithiation and its comparability to electrochemical delithiation. While the bulk remained intact and followed the expected lattice development upon delithiation,[4] chemically delithiated materials exhibited higher overpotentials during galvanostatic cycling, indicating a surface reconstruction which in electrochemical delithiation only occurs after a large number of charge/discharge cycles. Therefore, while chemical delithiation is a powerful tool to access characteristics not possible with electrochemical delithiation, it must be employed with the utmost care and consideration.

Acknowledgment

This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy (EXC 2089/1 –390776260, e-conversion). The authors would like to thank BASF SE for providing the active materials used for this study. S Q. further acknowledges funding by the German Federal Ministry of Education and Research (BMBF) within the project Aqua-Pop (grant number 03XP0329B).

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