Work-function effect of Ti₃C₂/Fe-N-C inducing solid electrolyte interphase evolution for ultra-stable sodium storage

In the quest to enhance the efficiency of sodium-ion batteries, the dynamics of solid electrolyte interphase (SEI) formation are of paramount importance. The SEI layer’s integrity is integral to the charge–discharge efficiency and the overall longevity of the battery. Herein, a novel two-dimensional Ti₃C₂ fragments enmeshed on iron-nitrogen-carbon (Fe-N-C) nanosheets (Ti₃C₂/Fe-N-C) has been synthesized. This electrode features a matrix which has been shown to expedite SEI layer formation through the facilitation of selective anion adsorption, thus augmenting battery performance. Density functional theory calculation reveals that the SEI evolution energy of NaPF₆ at the Ti₃C₂/Fe-N-C interface is 0.81 eV, significantly lower than the Ti₃C₂ (1.23 eV). This process is driven by the electron transportation from Ti₃C₂ to Fe-N-C substrate, facilitated by their work-function difference, leading to the formation of ferromagnetic Fe species, which possesses Fe 3d \(\mathrm{d}_{xz}\mathrm{d}_{yz}\mathrm{d}_{z^{2}}\) $${\mathrm{d}}_{xz}{\mathrm{d}}_{yz}{\mathrm{d}}_{z^2}$$ orbitals and undergoes hybridization with the π and σ orbitals of NaF, creating a key intermediate during charging. This process diminishes the antibonding energy and attenuates the orbital interaction with NaF, thus reducing the activation energy and improving the SEI formation reaction kinetics. Consequently, it leads to the creation of multi-interface SEI characterized by high-throughput ion transport and an efficient reaction network.