Silicon is a promising alternative to the conventional graphite anodes due to its high theoretical capacity and favorable lithiation potential for lithium-ion batteries (LIBs) with liquid as well as solid-state electrolytes. However, lithiation-induced extreme volume change causes severe mechanochemical deformation and continuous formation of solid-electrolyte interphase leads to cell failure. One of the strategies to mitigate this problem is alloying silicon with a suitable element that can alter the surface electrochemistry and/or lithiation pathways, and acts as mechanical buffer. Nonetheless, these benefits come with a compromise on the specific capacity, which strongly influences the mass loading of the electrodes, highlighting the need to deconvolute the intertwined influence of composition and mass loading when designing high performance electrodes. In this work, we systematically studied the influence of composition and mass loading in monolithic amorphous silicon and non-stoichiometric silicon nitride (SiN_x) electrodes on their electrochemical performance as LIB anodes. The incorporation of nitrogen in the electrode matrix clearly improves the electrochemical stability at the expense of reduced specific capacity, while higher mass loading accelerates capacity fading, most critically in amorphous silicon electrodes. Postmortem analysis reveals that such capacity fading in the electrodes with higher mass loading can be related to delamination due to evolved tensile stress during the charge–discharge cycle. Yet, nitrogen-rich SiN_x monolithic electrodes accommodate strain more effectively. These findings demonstrate that while pristine Si delivers high specific capacity and long-term stability in thin films, thicker (>1 µm) monolithic electrodes benefit from higher nitrogen content in SiN_x, which provides more stable cycling and sustained capacity.

Silicon (Si) anodes promise high energy density for all-solid-state batteries (ASSBs), while avoiding Li-metal dendrites. However, one of the key limitations is the initial loss of active Li, reflected in a low initial Coulombic efficiency (ICE), arising from solid electrolyte (SE) decomposition, lithium trapping, and native oxide conversion. Here, we report an (electro)chemically guided interfacial-engineering strategy leveraging an irreducible SE to construct a dynamic nanoscale Si|SE interface that enhances ICE. The intrinsic stability of the SE down to the working potentials of Si anodes eliminates decomposition, whereas mechanochemical mixing activates interfacial reactions that realize in situ prelithiation. The engineered interface manifests efficient ion transport and replenishes Li inventory through redox reactions, while stabilizing electrochemical performance. Our approach delivers a record-high ICE approaching 100% in Si half-cells, together with >95% in high-loading LiCoO₂ full cells, demonstrating that precise interface control can unlock the full potential of Si anodes for high-energy ASSBs.

Thin, fast-conducting and mechanically robust separators are expected to be advantageous in enabling all-solid-state batteries with high energy densities and good electrochemical performance. In this study, a potentially new scalable fabrication route for flexible thiophosphate-polymer separator membranes is demonstrated. By infiltrating a commercially available polymer mesh with the highly conductive inorganic solid ion conductor Li_5.5PS_4.5Cl_1.5, a hybrid separator membrane with a high ionic conductivity is realized. The electrochemical evaluation via rate capability tests reveals superior performance at low stack pressures and high C-rates, when comparing cells employing the hybrid membrane separator, to cells utilizing conventional solid electrolyte separators. As a proof of concept, a full cell implementing the hybrid membrane between a Si-based anode and a LiNi_0.83Co_0.11Mn_0.06O₂-Li_5.5PS_4.5Cl_1.5 composite cathode is evaluated. The experimental work is complemented by resistor network modelling of the hybrid membrane sheets, shedding light on potential challenges in cell operation.