Effect of Calcination Temperature on the Structural and Electrochemical Properties of NMC Cathodes for Lithium-Ion Batteries

Abstract

The electrochemical and thermal properties of Li[NixMnyCoz]O2 are strongly dependent on its composition and structural characteristics [1]. Among many options available there is no observed middle ground since each of the component cations has a different, specific function in the cathode material [2]. Developing an ideal cathode material with both high capacity and safety is a challenging task that requires precise control of microstructure and physicochemical properties of the electrode [3]. Firstly, the most promising amendment is the increase of nickel content as it enhances the specific discharge capacity, although the gradual safety characteristics decrease over cycling [4]. The optimum composition of NMC has not yet been found, thus, research aiming at improving its properties is still ongoing. The aim of this study is to analyze the impact of calcination temperature on the structural, morphological, and electrochemical properties of lithium nickel-manganese-cobalt oxides. The research focuses on optimization of the last step of the synthesis process. The results will be further used for the gradient structure material design based on nickel-rich core, since in that case the calcination step seems to be crucial for final material properties.Materials were prepared by coprecipitation method of the complex metal hydroxide precursor NixMnyCoz(OH)2, subsequently mixed with lithium hydroxide and annealed at different temperatures in air to obtain the lithiated powders. Constant monitoring of the conditions, such as synthesis temperature, solution pH, stirring frequency and calcination temperature, enable to control the particle morphology, which has a significant impact on lithium cations migration capability, and performance characteristics of the assembled Li-ion cells. To control the optimization process and furtherly investigate the material structure we used various methods. All NMC samples were analyzed using in-situ temperature dependent XRD, followed by the SEM and chronopotentiometry investigation. As the thermal and electrochemical stabilities are related to the structural stability, the various synthesized NMC materials were subjected to variable temperature measurements of X-ray diffraction (VT-XRD). The nickel-rich NMC are supposed to be calcinated in lower temperatures than its nickel-poor NMC analogs. The VT-XRD makes it possible to presume one optimal calcination temperature for both: nickel-poor and nickel-rich phases within the gradient NMC structure. X-ray powder diffraction was used to characterize the crystal structure of the prepared materials, giving general information about the phases present and their crystallographic parameters. Furthermore, scanning electron microscopy (SEM) was used to explore the morphologies of the prepared powders, both before, and after calcination at different temperatures. Understanding the influence of grain and particle as well as grain boundaries characteristics on overall material properties is also crucial, as small primary particle sizes with high surface areas contribute essentially to discharge capacities. To validate the formed hypothesis electrochemical tests have been conducted. Chronopotentiometry allowed for determination of battery cycling parameters, such as specific discharge capacity and cyclability. The combination of these three methods helps to identify the material characteristics and shows a direction for further material development.A detailed analysis will be presented during the conference. This work was funded by the National Science Center in Poland through the Sonata 17 programme (No. UMO-2021/43/D/ST5/03094).Reference: Amalia Christina Wagner et al. Hierarchical Structuring of NMC111-Cathode Materials in Lithium-Ion Batteries. ACS Applied Energy Materials 2020 3 (12), 12565-12574.Thomas Entwistle et al. Co-precipitation synthesis of nickel-rich cathodes for Li-ion batteries, Energy Reports, Volume 8, Supplement 11, 2022, Pages 67-73, 2352-4847.Dong Ren, et al. Systematic Optimization of Battery Materials. ACS Applied Materials & Interfaces 2017 9 (41), 35811-35819. Hyung-Joo Noh et al. , Comparison of the structural and electrochemical properties of layered Li[NixCoyMnz]O2 cathode material for lithium-ion batteries, Journal of Power Sources, Volume 233, 2013, Pages 121-130, 0378-7753.