Inverse Fabrication of Li₂S‐Nanocrystals@Doped‐Carbon Loaded on Woven Carbon Fibers to Spatial Structure Cathodes for High‐Stable Lithium–Sulfur Batteries

Abstract

development. First, the low electronic conductivity of elemental sulfur results in a low active material utilization and large polarization. Second, the high solubility and shuttle effect of lithium polysulfide intermediates cause an irreversible loss of the active material and low Coulombic efficiency. Third, the significant volume expansion of sulfur (80%) in the lithiation process destroys the structural integrity of electrodes and induces the rapid capacity decay. [3] Furthermore, conventional lithium-sulfur batteries are generally composed of a sulfur cathode and a lithium metal anode. The uncontrollable lithium dendrites on the lithium metal anode during the charging-discharging process will result in short-circuit and safety problems. [4] In recent years, considerable efforts have been made to overcome these shortcomings. Although significant progress has been noticed in the improvement of electrochemical performance, safety issues arising from the lithium metal anode have already hampered the industrial commercialization of lithium-sulfur batteries. Li 2 S, fully lithiated sulfur, with an outstanding theoretical specific capacity of 1166 mA h g −1 , is a promising cathode material for high-performance lithium-sulfur batteries. In comparison with sulfur, the Li 2 S-based cathode could be paired with an anode made of graphite, silicon, or tin, which avoids the internal short-circuit and safety hazards caused by lithium metal. Moreover, no volume expansion issue occurs during the lithiation-delithiation process because Li 2 S is at the maximum volume state. [5] In addition, Li 2 S can be modified at high temperatures due to its high thermal stability. Unfortunately, similar to sulfur, Li 2 S also endures low electronic conductivity and high dissolution of polysulfide intermediates, resulting in high overpotential in the initial charging state, low capacity, low Coulombic efficiency, and drastic capacity decay. Moreover, high cost and preparation and processing difficulties severely hinder Li 2 S from widespread application in lithium-sulfur batteries. [6] The introduction of the electrically conductive additives, such as carbonaceous materials, into Li 2 S cathodes is a simple and effective method to enhance the conductivity and the active material utilization. [7] The encapsulation of Li 2 S into Lithium sulfide (Li 2 S) is an attractive cathode material for lithium-sulfur batteries due to its matching with the lithium-metal-free anode, but limited by its preparation and processing difficulty, low electronic conductivity, and high dissolution of polysulfide intermediates. Herein, a novel, low-cost, and scalable method (termed as inverse fabrication route) is proposed to directly prepare Li 2 S-based electrodes. This methodology uniformly anchors in situ generated Li 2 S nanocrystals with a controllable size of 5-10 nm on the woven carbon fibers (WCF) substrate to fabricate a spatial conductive network structure, which provides continuous high-speed pathways for electron/ion transport. Furthermore, Li 2 S na...

Lithium Sulfide: Magnesothermal Synthesis and Battery Applications

“…Among these methods, the carbothermal reduction method is the industrial process, with its corresponding reaction equation as follows: which uses cheap carbon and Li 2 SO 4 as feedstocks. Because the fabrication of Li 2 S cathodes for Li–S batteries needs conductive additives, this carbothermal method is often adapted in research laboratories to prepare Li 2 S–C composites by using organic chemicals to provide the carbon reductant. ,− As reaction is not thermodynamically favorable under standard conditions (Δ G m θ ≫ 0), it has to operate at high temperatures. According to the Gibbs free energy equation, the reaction might proceed spontaneously at temperatures around 400 °C .…”

Simultaneous Prelithiation and Compatible Modification toward Ultrafast and Ultrastable Lithium-Ion Capacitors

“…Figure 3a,b shows the initial 10 cycles of CV curves at a scan rate of 0.1 mV s −1 in the voltage range of 2−4.5 V vs Li/ Li + . A broad peak at 3.8 V vs Li/Li + with a small peak at 4.2 V vs Li/Li + can be observed in the first anodic scan for the electrolyte with the LiDFOB additive, corresponding to the two-step decomposition of Li 2 S to form polysulfide and S. 26 As expected, these two obvious anodic peaks are replaced by two inconspicuous characteristic peaks at 2.3 and 2.7 V vs Li/Li + related to the mutual conversion of Li 2 S and S in the subsequent cycles, respectively. In sharp contrast, the CV curves measured in the electrolyte without the LiDFOB additive exhibit serious distortion with one anodic peak positively shifted to 4.3 V in the first cycle and a broad but much less intense anodic peak at 4.1 V vs Li/Li + in the subsequent cycles, suggesting the severe polarization and incomplete conversion of Li 2 S to S. 33 The initial galvanostatic charge−discharge (GCD) profiles of the Li 2 S@NPCNF cathode at a current density of 0.1 A g −1 with respect to the mass of the NPCNF are presented in Figure 3c.…”

Li2S In Situ Grown on Three-Dimensional Porous Carbon Architecture with Electron/Ion Channels and Dual Active Sites as Cathodes of Li–S Batteries

“…After 100 cycles, it retains a high capacity of 727 mAh g –1 and a retention rate of 82.3%. Obviously, the Li 2 S/NSPC electrode shows a remarkable increase in capacity and cycling stability that can be attributed to the N/S codoped carbon skeleton, which enhanced the ionic/electronic conductivity and electrochemical reactivity of Li 2 S and prevented the dissolution of LiPSs and shuttle effects effectively …”

“…Obviously, the Li 2 S/NSPC electrode shows a remarkable increase in capacity and cycling stability that can be attributed to the N/S codoped carbon skeleton, which enhanced the ionic/electronic conductivity and electrochemical reactivity of Li 2 S and prevented the dissolution of LiPSs and shuttle effects effectively. 31 To understand the cycling performance of Li 2 S/NSPC and Li 2 S/PC electrodes at 1C, and the Coulombic efficiency and cyclic life curves are exhibited in Figure 6e. The results indicate that the Li 2 S/NSPC and Li 2 S/PC composites all show a high Coulombic efficiency.…”