Silicon monoxide (SiO) with its high capacity of about 1000 to 1500 mAh g^-1 with a relatively smaller volume change (<200%) than silicon during lithiation is a potential anode for next-generation lithium-ion batteries. However, because of the formation of inactive lithiated silicate during initial discharge, the first Coulombic efficiency (FCE) of SiO is only about 60-70%. So, larger amount of cathode material has to be added to compensate for the loss of lithium in the SiO anode in a full cell, and the overall energy density is hardly improved.

To harness the benefit of SiO, most researchers improve its FCE by pre-lithiating the SiO electrode with various chemical or electrochemical methods.[1-3] However, so far, the pre-lithiation processes have to be conducted in a glovebox or dry room due to the use of highly-reactivity lithium metal, or involve disassembling and reassembling of batteries which are hardly commercially-viable. In this work, we recognize that the irreversible capacity is due to the active oxygen within the SiO matrix, and develop a facile heat treatment method to deactivate the oxygen atoms. By annealing SiO with a few weight percent of Na₂CO₃ in Ar atmosphere, the initial discharge capacity is reduced and the corresponding FCE is increased from 61% to 86%. Figure 1 shows the initial discharge-charge curve of SiO and pre-treated SiO. XRD analysis suggests that the pre-treatment process with the addition of Na facilitates the disproportionation of SiO into Si and crystalline SiO₂. which deactivates the oxygen atoms and preventing them from reacting irreversibly with Li. We have further demonstrated a full cell with the pre-treated SiO anode and a LiFePO₄ cathode that gives a FCE of 85.8% with good cycle stability. When the pre-treated SiO is coupled with a high-capacity Ni-based metal-oxide cathode, the volumetric energy density of LIB is expected to exceed 900 Wh L^-1.

Another advantage of the treatment process is that it improves the thermal stability of SiO with smaller heat generation from differential scanning calorimetry test. In addition,

the pre-treated material is stable in air and can be used readily in common battery electrode manufacturing process. Our technology can bring SiO one step closer to commercial applications.

Reference

[1] Y. Li, Y. Qian, J. Zhou, N. Lin, Y. Zhou, Nano Research, (2021) 1-8.

[2] Q. Meng, G. Li, J. Yue, Q. Xu, Y.-X. Yin, Y.-G. Guo, ACS Applied Materials & Interfaces, 11 (2019) 32062-32068.

[3] C. Shen, R. Fu, Y. Xia, Z. Liu, RSC Advances, 8 (2018) 14473-14478.