Developing Aqueous Processed Transition Metal Oxide Cathodes with Sustainable Binders for High Energy Density Lithium-Ion Batteries from Lab Scale to Manufacturing Scale
Authors: Boz Buket , Savur Hergul , Neidhart Lukas , Froehlich Katja , Fafilek Guenter , Jahn Marcus 
Published: December 2024

Transitioning toward more sustainable materials and manufacturing methods is critical to continue supporting the rapidly expanding market for lithium-ion batteries (LIBs). Meanwhile, energy storage applications are requiring higher power and energy densities with demanding performance targets like fast charging and a wide range of operating voltages. Alongside high-performance demands, environmental considerations such as organic solvent use, low abundance of Co and other mining related issues, urgently need to be addressed by the LIBs community [1]. High voltage spinel LiNi0.5Mn1.5O4 (LNMO) is considered a highly promising cathode candidate for the next generation high performance LIBs due to a high energy density (650 W H kg -1), high operating voltage (∼4.7 V vs Li), low environmental impact, and low-cost fabrication [2]. However, severe capacity degradation during cycling has impeded wide application and commercialization.

In this study, we investigated LNMO thoroughly as a cathode material using only aqueous processing, covering the processing range from small scale to the research pilot line level. Aqueous electrode processing is highly critical to eliminate organic solvent use in LIBs production. On the anode side, aqueous processing has already been established on the industrial level, whilst cathode aqueous processing still needs to be tuned to reach to the same level of feasibility. The main challenge in aqueous processing of transition metal oxides is the high surface sensitivity towards water, resulting in Li/proton exchange. Consequently, pronounced Li+ loss is observed on the electrode during cycling. In literature, acid treatment is one of the most common approaches to avoid this phenomenon during slurry preparation [3]. In this work, we investigate different crystal structure with combination of two binders. Understanding the impact of the different crystal structure of LNMO particles on lithium leaching during slurry processing is one the targets of the study. On the particle level, single, poly crystalline and mixed of single and poly crystal powders are characterized to select the most promising candidate in terms of processing and cycling performance. Two different binder systems were studied, including carboxymethyl cellulose (CMC) with acrylic based binder as baseline for water-borne cathodes, and Na-Alginate as a more sustainable binder option specifically for LNMO.

The formulation development started at the laboratory scale with slurries characterized with pH control and regarding their rheological behavior. Detailed electrochemical analysis with cycling and electrochemical impedance spectroscopy (EIS) was performed along with comprehensive surface characterization and scanning electron microscopy (SEM) before cycling and post-mortem. Subsequently, the most promising candidates were successfully upscaled to the research pilot line. By characterizing three crystal structures of LNMO with two binders, we demonstrate the capabilities of LNMO as an active material using the most sustainable processing conditions. Depending on the crystal structure, single crystal LNMO with Na-Alginate binder was found to be the most promising candidate (capacity retention ∼130 mAh g -1 after 150 cycles), especially for fast charging applications. This study is to serve as guideline for better understanding of LNMO and its aqueous processability.

References

[1] W. Yao et al., “A 5 V-class cobalt-free battery cathode with high loading enabled by dry coating,” Energy Environ Sci, vol. 16, no. 4, pp. 1620–1630, 2023, doi: 10.1039/D2EE03840D.

[2] G. Liang, V. K. Peterson, K. W. See, Z. Guo, and W. K. Pang, “Developing high-voltage spinel LiNi0.5Mn1.5O4cathodes for high-energy-density lithium-ion batteries: Current achievements and future prospects,” Journal of Materials Chemistry A, vol. 8, no. 31. Royal Society of Chemistry, pp. 15373–15398, Aug. 21, 2020. doi: 10.1039/d0ta02812f.

[3] J. He et al., “Surface Structure Evolution and its Impact on the Electrochemical Performances of Aqueous-Processed High-Voltage Spinel LiNi0.5Mn1.5O4 Cathodes in Lithium-Ion Batteries,” Adv Funct Mater, vol. 32, no. 46, Nov. 2022, doi: 10.1002/adfm.202207937.

Acknowledgment

This project has received funding from European Union’s Horizon EUROPE Research and Innovation Programme under Grant Agreement N° 101069612 (NoVOC).