The prelithiation of SiO-based negative electrodes is essential for stable and high-energy-density Li secondary batteries. In this study, a new partial prelithiation method by two-stack electrodes was developed using lightweight and high-capacity carbon-coated silicon monoxide (SiO/C) films held in a sponge-like matrix of carbon nanotubes (CNTs). The charge-discharge cycles of a full cell with the partially prelithiated SiO/C-CNT negative electrode (p-LixSiO/C-CNT with SiO/C content of 85 mass%) and LiNi0.8Mn0.1Co0.1O2 (NCM811)-CNT positive electrode (NCM content of 97 mass%) reduced the irreversible capacity, achieving high energy densities per the total mass of the negative and positive electrodes of 542 and 420 W h kgelectrode−1 at the 1st and 300th cycle, respectively, with high areal capacities of 4.6 and 3.1 mA h cm−2 for the negative and positive electrodes. The flexible CNT sponge matrix expanded/shrunk reversibly during lithiation/delithiation and retained its structure, whereas the thin Li metal formed Li dendrites and dead Li after cycling, as demonstrated by scanning electron microscopy. The partial prelithiation method of simply stacking the pristine SiO/C-CNT film with a fully prelithiated film enables the careful control of the degree of prelithiation, contributing to full cells of various chemistries.

A lightweight, high-capacity negative electrode was developed by suspending carbon-coated silicon monoxide (SiO/C) particles in a sponge-like matrix of carbon nanotubes (CNTs) without using metal foils or polymeric binders. High initial delithiation capacities per electrode (SiO/C + CNT) of >1200 mA h gelectrode−1 and >1100 mA h cmelectrode−3 were achieved with an optimum SiO/C content of 85 mass%. The lithiation/delithiation cycle with capacity control at a 45% SiO utilization ratio achieved a high delithiation capacity of 584 mA h gelectrode−1 for 236 cycles. In addition, the flexible and electrically conductive CNT sponge matrix enabled reversible expansion/shrinkage of the entire electrode during lithiation/delithiation, as evidenced by scanning electron microscopy.

Lithium-sulfur battery suffers from the low utilization of sulfur and the high electrolyte/sulfur (E/S) ratio that decrease the cell-based performance. Lithium polysulfides (Li2Sx)-dissolved electrolyte, so called catholyte, enables high utilization of sulfur, but the cell inherently has high E/S ratio due to the limited solubility of Li2Sx. Herein, a composite electrode of Li2Sx (x = 4, 6, 8) and sub-millimeter-long few-wall carbon nanotube (CNT) is proposed. The CNT forms self-supporting sponge-like paper and works as a three-dimensional current collector, in which the Li2Sx is deposited by solution casting and drying. The Li2S6-CNT electrode realizes high specific capacity (1249 mAh gsulfur−1) under a lean electrolyte condition of E/S = 4 μL mgsulfur−1, which is much better than the S8-CNT electrode (233 mAh gsulfur−1). After full charge and conversion of Li2Sx to S, the Li2Sx-CNT electrode maintains its high capacity of 1100 mAh gsulfur−1. The full cell with the Li2S6-CNT and the Li thin foil electrodes realizes 400–500 Wh kgcell−1 for E/S = 4.0 at the 2nd and 3rd discharge and 300 Wh kgcell−1 for E/S = 5.8 at the 97th discharge, based on the total mass of the interior of a cell (electrodes, separator, and electrolyte). Holding solvated Li2Sx by the CNT sponge is the key for the high energy density.