Sungho Lee

Silicon anodes for lithium-ion batteries offer high capacity but expand by more than 300% during cycling, which cracks the electrode and delaminates it from the current collector. Mitigating it is as much a processing question as a compositional one: the non-expanding phase has to remain finely dispersed and connected around the silicon, and the processing route is what sets that. Here Li₄Ti₅O₁₂ (LTO) nanoflakes are fragmented by high-energy ultrasonication and fixed in a carbon matrix by carbonizing polyacrylonitrile, giving a Si/LTO@C composite in which nanoscale LTO domains and silicon particles are interconnected through carbon. The optimized Si/LTO@C (1:3) electrode delivers an initial reversible capacity of ~600 mAh g⁻¹ at an initial Coulombic efficiency of ~77%, and retains 75% of its capacity after 100 cycles and 55% after 300 cycles. Its charge-transfer resistance falls from 46 to 3.7 Ω during cycling and post-mortem imaging shows no cracking or delamination. A Si/LTO@C (2:2) control, processed identically but with half the LTO, keeps an intact and adherent electrode yet fails by continuous solid-electrolyte interphase growth on fracturing silicon. Processing and composition therefore act at different scales: the processing route decides whether the electrode stays adherent, while the secondary-phase fraction decides whether the silicon within it is stabilized. Matching that fraction to the volume change of the active phase, and choosing a processing route that disperses it at the right length scale, are therefore the two controlling design variables for durable silicon composite electrodes.

Silicon anodes for lithium-ion batteries offer high capacity but expand by more than 300% during cycling, which cracks the electrode and delaminates it from the current collector. This is a composite design problem: the reinforcing phase has to stay continuous around the silicon at the length scale and volume fraction where load is actually transferred. Here Li₄Ti₅O₁₂ (LTO) nanoflakes are fragmented by high-energy ultrasonication and fixed in a carbon matrix by carbonizing polyacrylonitrile, giving a Si/LTO@C composite in which nanoscale LTO domains and silicon particles are interconnected through carbon. The optimized Si/LTO@C (1:3) electrode delivers an initial reversible capacity of ~600 mAh g⁻¹ at an initial Coulombic efficiency of ~77%, and retains 75% of its capacity after 100 cycles and 55% after 300 cycles. Its charge-transfer resistance falls from 46 to 3.7 Ω during cycling and post-mortem imaging shows no cracking or delamination. A Si/LTO@C (2:2) control, processed identically but with half the LTO, instead fails by continuous solid-electrolyte interphase growth inside a network that stays intact, showing that the reinforcement fraction rather than the processing sets the failure mode. Matching the reinforcement content to the volume change of the active phase, and choosing a processing route that places it at the right length scale, is therefore the controlling design variable for mechanically stable silicon composite electrodes.

Synthetic graphites have been widely used in industrial applications, including as anodes in lithium-ion batteries. Because they are produced at temperatur