Silicon (Si) is a leading candidate for next-generation lithium-ion battery anodes due to its exceptionally high theoretical specific capacity (3,579 mAh g⁻¹). However, its practical implementation is hindered by the ~300% volume expansion during lithiation, which induces mechanical fracture, loss of electrical connectivity, and unstable solid-electrolyte interphase (SEI) growth. Because these processes occur simultaneously and interact, they obscure the fundamental mechanisms governing long-term performance, highlighting the need for simplified, reproducible model systems that allow individual degradation pathways to be isolated.

In this work, we employ a 100% silicon nanowire (SiNW) anode as a controlled platform to investigate degradation and transport limitations in silicon electrodes. SiNWs are synthesized via a solvent free floating catalyst CVD process that assembles them into freestanding macroscopic textiles with tunable loading, thickness, and porosity [1]. The resulting electrodes exhibit high structural uniformity, enabling reproducible electrochemical measurements and minimizing variability from fabrication.

Electron microscopy and spectroscopy show that the electrodes consist of crystalline ~20 nm nanowires forming a mechanically robust, highly interconnected network that operates without conductive carbon or polymeric binders [2]. These electrodes deliver reproducible capacities of ~2700 mAh g⁻¹ at C/20 and maintain areal capacities above 6 mAh cm⁻² in thicker configurations. Long-term cycling demonstrates that mechanical degradation (dominant in particle-based Si anodes) is not the limiting factor here: the network remains intact after hundreds of cycles, ruling out pulverization and electrical disconnection as primary causes of capacity fading [3].

Instead, a progressive increase in electrochemical polarization emerges as the dominant degradation mode. Differential capacity analysis, impedance spectroscopy, and image-based quantification show that polarization growth correlates with continuous SEI thickening, which increases interfacial resistance and reduces accessible porosity, as well as with the stability of the interface with the current collector. Adhesion-controlled experiments confirm that poor interfacial bonding accelerates resistance growth and voltage hysteresis.

Interpreting these results also requires acknowledging the limitations of lithium metal counter electrodes in half-cell studies. Morphological instability, electrolyte depletion, and uneven current distribution in Li metal can artificially amplify the apparent polarization of high-capacity anodes, complicating the separation of intrinsic degradation from counter-electrode artefacts.

Finally, the talk will argue that Si anodes are a central material for the electrification of transport in coming decades, and strategically important for Europe given its lack of battery critical raw materials. Si anodes could enable EV ranges close to 1000 km and charge times below 15 minutes, while reducing pressure on natural graphite by hundreds of kilotonnes per annum. This transition could avoid megatonne-scale CO₂ emissions from battery-material production, according to estimates.