Fig. 4

Electrochemical characterization of nSi/MXene anodes. a Rate performance comparison for nSi/MX-C electrodes with various MX-C mass fractions. Note that the capacity values are normalized to the mass of silicon (C/M_si). b Asymmetric charge-discharge curves of the typical nSi/MX-C electrode. Inset is the as-obtained C/M_Si at various delithiation rates. c Left: first cycle charge-discharge curves at a 0.15 A g⁻¹ (~1/20 C-rate) of the nSi/MX-C electrodes (MX-C M_f = 30 wt%) with the M_Si/A ranging from 0.9 to 3.8 mg cm⁻². Insets are the optical images of these electrodes. Right: first Coulombic efficiency (top) and areal capacity (bottom) of nSi/MX-C (MX-C M_f = 30 wt%) with various M_Si/A. The line slope indicates the average C/M_Si (~3200 mAh g⁻¹) achieved in various electrodes. d Cycling performance comparison among the electrodes with various M_Si/A. Also included are the control samples made with PAA/carbon black (CB), CMC/CB, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) as the aqueous binder and conductive agent, respectively. e Cross-sectional (left, scale bar = 10 µm) and top-view (right, scale bar = 1 µm) scanning electron microscopy images of nSi/MX-C (MX-C M_f = 30 wt%, M_Si/A = 2.4 mg cm⁻²) after cycling; also included is the energy-dispersive X-ray mapping, showing a uniform distribution of nSi and MX-C in the cycled electrode (scale bar = 50 µm). f Lifetime of nSi/MX-C and nSi/MX-N (MXene M_f = 30 wt%) electrodes at a low M_Si/A (0.9–1 mg cm⁻²) and a high rate (1.5 A g⁻¹). Also included is the Coulombic efficiency of nSi/MX-C (top)