Embedded Nanoparticle Composites as Li-Ion Battery Anode Materials

Graphite is used as an anode material in nearly all commercial Li-ion Batteries (LIBs). To increase energy density, Si and Sn-based materials (including SiO x ) are intensively being investigated as anode materials. If used to their full theoretical extent, they could increase LIB energy density by as much as 20%. 1 However, the widespread application of these elements is impeded due to their large volume change and unstable solid electrolyte interphase (SEI) formation that leads to capacity fade. A variety of design approaches have been taken to make alloy anodes compatible with commercial cells. 2-4 However, in most cases, the preparation procedures are complex, give low yields, and require expensive chemicals, making their large-scale production prohibitively expensive. Recently, we have shown that mechanofusion can be used to embed natural graphite (NG) with Si-nanoparticles (Si-NP). 5 In this process, the Si-NPs filled voids in the NG that had connections to the NG particle surface. The resulting Si-NP/NG composite particles had increased capacity and capacity retention even when no electrolyte additives were used. These results were highly promising. However, many unknowns remain, including: how the composite morphology and microstructure depend on the mechanofusion conditions, how many NPs can be inserted into NG, and how this process depends on the NP size. In this study, TiO 2 -NPs (rutile phase) were used as model guest particles to make TiO 2 -NP/NG composites and study the embedding process of NP into graphite. TiO 2 was selected for this study, since it is available in NPs of many different sizes and it has low electrochemical activity, allowing the electrochemistry of the NG to be studied after the embedding process. Fig. 1(a) and 1(b) show cross-section SEM images of NG embedded with 100 nm and 300 nm TiO 2 -NPs, respectively. It was found that mechanofusion conditions and NP size have a profound effect on the final composite morphology and microstructure. Importantly, the host graphite was found to retain high crystallinity under mechanofusion conditions that induce TiO 2 guest particle embedding, resulting also in good electrochemical performance of the host graphite. Moreover, the NP size was found to determine the porosity in the loading of the composites, with smaller NP size leading to increased NP loading and reduced internal porosity. These results demonstrate design strategies to NP/NG composite particles that can lead to new high energy density anode materials. Moreover, the dry processing method is cheap, scalable, and does not produce waste. Acknowledgements The authors acknowledge funding from NSERC and NOVONIX Battery Technology Solutions under the auspices of the NSERC Alliance grants program. References: N. Obrovac and V. Chevrier, Chemical Reviews , 114 , 11444-11502 (2014). Liu, Z. Lu, J. Zhao, M. T. McDowell, H. Lee, W. Zhao and Y. Cui, Nature Nanotechnology , 9 , 187-192 (2014). Wang, J.H. Ahn, J. Yao, S. Bewlay and H. Liu, Electrochemistry Communications , 6 , 689-692 (2004). Liu, H. Wu, M. T. McDowell, Y. Yao, C. Wang and Y. Cui, Nano Letters , 12 , 3315-3321 (2012). He, M. Salehabadi, S. Yasmin and M. N. Obrovac, Journal of the Electrochemical Society , 170 , 120511 (2023). Figure 1

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