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

Celgard 2325 membranes were used. A CHI660C electrochemical workstation (Shanghai, Chenhua)
measured electrochemical impedance spectra (EIS) in a frequency range of 0.1 Hz to 1 MHz.

Full cells were assembled using LFP cathodes, a Celgard 2325 separator, and a Li composite anode (Li-C,
Li-Ba or LBAC anodes). As for LFP electrodes, a slurry of LFP powders, a super P conducting additive, and
a binder made of polyvinylidene fluoride (PVDF) was fabricated by mixing them together in N-methyl-2-
pyrrolidone (NMP) with a weight ratio of 8:1:1. The areal capacity of LFP electrodes was about
2.45 mA h cm . The voltage range for measuring the full cells based on LFP was set between 2.2 and 3.85 V.
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RESULTS AND DISCUSSION
The LBAC electrode is obtained by contacting CC disk with molten Li-Ba alloy. As shown in Figure 1A,
when the CC touches the liquid Li-Ba alloy, the silver-white molten Li-Ba alloy can fill up the entire CC in
less than 10 s, indicating that doping of metallic Ba can significantly lower the surface tension of liquid Li
and improve the wettability toward CC. Based on the phase diagram of Li-Ba [Supplementary Figure 1], we
can observe that phase segregated Li-Ba dual-phase alloy is composed of BaLi intermetallic compounds and
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Li metal when the Li atomic percentage is larger than 80% and the temperature is lower than 143 °C. Thus,
phase separation occurs when the temperature cools rapidly below 143 °C. On the contrary, the CC itself
exhibits poor wettability towards liquid Li, so the Li metal does not diffuse into the CC in more than 60 s
under the same conditions [Supplementary Figure 2A]. Notably, molten Li-Ba alloy exhibits more favorable
wettability than other Li alloys (such as Li-Ca and Li-Ag) , which is one of the important merits
[57]
considering the practical application. The top surface of LBAC is dark gray with the distinct textile pattern
of the carbon fibers. As depicted in the top-view scanning electron microscopy (SEM) images
[Figure 1B-D], the Li-Ba alloy fills the gaps between each bundle of carbon fibers. The phase segregation
behavior in the cooling process forces the BaLi phase to condense into a porous architecture with a
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relatively small diameter of about 20 μm. Apparently, the BaLi sub-skeleton in LBAC can further increase
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the specific surface area of CC, providing a lower local current density and abundant sites of Li nucleation
significantly. Meanwhile, the pores of the BaLi alloy scaffold were filled with metallic Li, suggesting that the
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porous framework of the BaLi network can host Li [Figure 1E-G]. Moreover, the pores of the BaLi alloy
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scaffold are filled with metallic Li completely, indicating no voids in the as-prepared LBAC anodes. By deep
contrast, as for the Li-C composite shown in Supplementary Figure 2B and C, the metallic Li almost covers
the skeleton surface of the CC, and the void spaces among carbon fibers have been occupied by Li metal.
From the side-view morphology of Li-C anodes [Supplementary Figure 2D and E], the metallic Li is not
tightly bonded to the carbon fibers. The ex-situ XRD test was performed for confirming the composition of
LBAC. As depicted in Supplementary Figure 3, the primary diffraction peaks of LBAC originate from the
metallic Li phase, BaLi and carbon. In Supplementary Table 1, the mass of Li in the LBAC anode is 16.2 mg
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with a weight percentage of ~42.1%. Additionally, LBAC exhibits a remarkable specific capacity of
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~1,519 mAh g after stripping Li to 2 V [Supplementary Figure 4], which closely approaches the theoretical
specific capacity (1,621 mA h g ).
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The Li stripping/plating behaviors of LBAC were conducted by SEM so as to analyze the function of BaLi
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alloy sub-scaffold. After 10 mA h cm Li was stripped, the internal porous array was further exposed, and
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the BaLi microchannels array was evidenced as a secondary scaffold in the CC framework [Figure 2A]. As
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the Li stripping capacity reaches 20 mA h cm , the ordered array of BaLi alloy microchannels is uniformly
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dispersed on the carbon fibers, providing a large number of Li nucleation sites and facilitating Li ion
diffusion [Supplementary Figure 5]. Furthermore, the lithiophilic Li-Ba alloy can reduce Li nucleation
overpotential and inhibit Li dendrite generation during the subsequent process of Li plating. Therefore,
when the Li is replated at 5 mA h cm [Figure 2B], the plated Li preferentially fills the microchannels in
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