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Page 6 of 11 Wang et al. Energy Mater 2024;4:400031 https://dx.doi.org/10.20517/energymater.2023.103

that the Li metal in the vicinity of carbon fibers can be dissolved in a higher selectivity and increase the
visibility of carbon fiber bundles, which may be attributed to the high electrical conductivity of the carbon
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fiber bundles. When replated with 5 mA h cm Li [Supplementary Figure 6B], the severe aggregation of
deposited Li metal on the upper surface of the CC is apparent clearly, indicating that the CC has a large Li
nucleation overpotential which easily causes irregular Li deposition . Notably, the deposited Li grows
[57]
unrestrictedly since the Li deposition occurs on the upper surface. While the Li deposition capacity
increases to 10 mA h cm , the subsequently deposited Li metal accumulates on the previously deposited Li,
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causing the generation of numerous Li dendrites on the Li-C electrode [Supplementary Figure 6C-I]. This
undesirable behavior poses a significant safety risk. These results clearly illustrate that the limited specific
surface area and poor lithiophilicity of CC can result in uneven nucleation and unrestricted growth of Li to
form Li dendrites.

To further evaluate the electrochemical performance for LBAC anodes, symmetrical cells were assembled
using LBAC electrodes for assessing electrochemical cycling performances under different current densities.
The Li-C/Li-C and Li-Ba/Li-Ba symmetric cells were also assembled separately for comparison to highlight
the synergistic effect of the BaLi alloy sub-framework and CC framework. As shown in Figure 3A, the time-
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voltage curve tells that the voltage hysteresis of LBAC cells can stabilize at 30 mV for 1,000 h under
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1 mA cm /1 mA h cm , which is ascribed to the distinct multiscale scaffold structure of LBAC. By deep
contrast, The Li-Ba symmetric cell has a much higher voltage hysteresis, especially after 200 h,
demonstrating the aggregation of “dead Li” on the anode surface, leading to the cell failure. Similarly, the
voltage polarization of Li-C cells increases abruptly at 350 h, which is much lower than that of the LBAC
composite electrode. The lifespan of the Li-C and Li-Ba cells only maintains a shorter period with a larger
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overpotential after the current density exceeds 3 mA cm (Li-Ba: ~120 mV for 140 h; Li-C: ~150 mV for
170 h). However, LBAC/LBAC cells exhibit longer cycling life without any voltage fluctuation (~40 mV for
420 h), which highlights the excellent Li affinity and structural stability of LBAC. The overpotential of
LBAC anodes is much lower than Li-C anodes, which can be attributed to excellent lithiophilicity of Li-Ba
alloy. Furthermore, the surface of LBAC anodes is not flat; in other words, the Li-rich Li-Ba alloy does not
completely cover the CC surface, and the carbon fibers and Li-Ba alloy coexist on the LBAC anode surface.
Therefore, LBAC anodes have larger specific area than Li-Ba anodes, exhibiting lower overpotential. The
cells assembled with LBAC electrodes can cycle continuously for 220 h even at 5 mA cm , while Li-Ba and
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Li-C-based cells can cycle for only 70 and 110 h with significant voltage fluctuations, separately. This can be
attributed to the fact that the extremely high current density can trigger Li dendrite formation, while the
interconnected microchannels in LBAC can confine the Li stripping/plating behavior in the alloy scaffold.
Additionally, the larger specific surface area of LBAC anodes eliminates the high current density, so the Li
dendrite growth can be effectively suppressed to ensure the cycling stability. As the typical areal capacity of
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commercially available Li-ion batteries is approximately 3 mA h cm , the testing parameters are set to
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3 mA/3 mA h cm . Supplementary Figure 7 illustrates that the LBAC composite can achieve a cycling life of
about 300 h. In contrast, the Li-Ba and Li-C cells display a short lifespan and the voltage hysteresis reaches
1,000 mV at 120 and 150 h due to the gradual thickening of the solid electrolyte interface (SEI) and the
accumulation of inactive Li.

EIS were measured to assess the internal stability of symmetric cells, as shown in Figure 3B. The R value of
ct
Li-Ba (~450 Ω) and Li-C symmetric cells (~550 Ω) is higher compared to LBAC symmetric cells before
cycling (~200 Ω). After 100 cycles, the R of the LBAC composite decreases to ~50 Ω, which remains smaller
ct
than that of the Li-Ba (75 Ω) and Li-C (125 Ω) cells, indicating that LBAC has faster charge transfer kinetics
and a SEI layer with enhanced stability that facilitates reversible process of Li stripping/plating [Figure 3C].
The superior electrochemical performance indicates that the microchannels of the Li deposition behavior