Accelerating the Development of New Silicon-Based Anode Materials
Authors: Skare Marte , Nemaga Abirdu Woreka , Koposov Alexey , Ulvestad Asbjørn 
Published: February 2024

In this work we have demonstrated the feasibility of using thin film systems as a steppingstone to accelerate the development of commercially relevant silicon-based anode materials for Li-ion batteries. Understanding new materials in conventional particle-based electrode systems is often complex. Lithium and electrolyte interact not only with the active material particles, but also with the different supporting components of the electrode, leaving it difficult to directly assess the electrochemical contribution of the active material. This is further complicated by the electrochemical behavior of such electrodes also being strongly dependent on processing conditions, like casting and drying procedures. Additionally, it is often also a challenge to synthesize such materials in particle form with the required chemical composition and monodispersity in the first place. Therefore, it would be highly beneficial to study and screen new anode materials without having to assume and assess these different factors. That is of particular importance during the optimization stage of the chemical composition for the active material, for which a significant number of samples is typically needed. Thus, evaluating the material in a thin film system is a simple and reproducible method of determining a material’s potential as a future anode material.
Such thin films of active materials can reliably be made with a large range of thicknesses, compositions, element combinations and coatings, using multiple flexible and reproducible thin film deposition techniques available. In the present work, we have investigated silicon-based materials made by PECVD and sputtering: pure silicon and sub-stoichiometric versions of silicon nitride, silicon carbide, and silicon phosphide (SiNx, SiCx, SiPx). For evaluation of the applicability of the thin film model system, in several cases we have also compared the results to particles of the same material with similar chemical composition synthesized via a free space CVD process [1].
Preliminary evaluation shows good agreement between results for thin film systems compared to what is known for particles of the same material. SiNx particles show good agreement with thin film results where a high nitrogen content decreases the capacity, while increasing the stability due to the formation of a stabilizing matrix around the active silicon [2]. Differences in the differential capacity analysis of similar materials in particle and thin film forms demonstrates the greater complexity in interpreting the data from the more intricate particle-based systems. SiCx is known to react in a similar fashion as SiNx where its coulombic efficiency and capacity decreases with increasing carbon-content, while its stability has been seen to increase due to a similar stabilizing matrix [3].

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[1] H. F. Andersen et al., ECS Trans., vol. 62, no. 1, pp. 97–105, 2014.
[2] A. Ulvestad et al., ACS Nano, vol. 15, no. 10, pp. 16777–16787, 2021.
[3] X. D. Huang et al., RSC Adv., vol. 8, no. 10, pp. 5189–5196, 2018.