Lithium-sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core-shell γ-MnO -coated sulfur nanocomposite through the redox reaction between KMnO and MnSO . The multifunctional MnO shell facilitates electron and Li transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ-MnO crystallographic form also provides one-dimensional (1D) tunnels for the Li incorporation to alleviate insoluble Li S /Li S deposition at high discharge rate. More importantly, the MnO phase transformation to Mn O occurs during the redox reaction between polysulfides and γ-MnO is first thoroughly investigated. The S@γ-MnO composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn O phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li-S cells.

Metal−organic frameworks (MOFs) and covalent−organic frameworks (COFs) are promising precursors for preparing high-performance carbonaceous materials for capacitive deionization (CDI). However, the simple pyrolysis of single MOFs or COFs usually leads to carbonaceous materials with disadvantages in salt adsorption capacity (SAC) and cycling stability, which are unfavorable to the further development of CDI. To address this issue, herein, we report the directed core−shell motif hybridization of COFs on MOFs to obtain selectively functionalized carbonaceous precursors, NH 2 -MIL-125(Ti) @TP-DQ COF, which then produce titanium dioxide nanoparticle-embedded nitrogenrich carbon architectures, called TiO 2 @COF, via pyrolysis. It is evidently expected that the resulting TiO 2 @COF possesses several advantageous features: (1) the inner core, which contains titanium dioxide nanoparticles, provides abundant faradic active sites for ion accommodation contributing additionally to the high SAC; (2) the outer capacitive shell, which is fibrous nitrogen-rich carbon, not only protects the inner core from the harsh environment of the solution and stabilizes the cycling performance but also affords plentiful nitrogen dopants for enhanced pseudocapacitive capacity and abundant pores for ion adsorption and electrolyte permeation; and (3) the outer COF-derived fibers interconnect with each other, giving rise to increasing electrical conductivity. As a result, TiO 2 @COF delivers a high SAC of 33.66 mg g −1 and favorable cycling stability over 40 cycles, significantly exceeding those of CDI electrodes derived from single MOFs or COFs. This work is expected to enrich the construction of selectively functionalized carbonaceous particles from MOFs and COFs and may also endow multiple promising applications of core−shell motif hybrids.

The shuttle effect of lithium polysulfides (LiPS) and potential safety hazard caused by the burning of flammable organic electrolytes, sulfur cathode, and lithium anode seriously limit the practical application of lithium–sulfur (Li–S) batteries. Here, a flame‐retardant polyphosphazene (PPZ) covalently modified holey graphene/carbonized cellulose paper is reported as a multifunctional interlayer in Li–S batteries. During the discharge/charge process, once the LiPS are generated, the as‐obtained flame‐retardant interlayer traps them immediately through the nucleophilic substitution reaction between PPZ and LiPS, effectively inhibiting the shuttling effect of LiPS to enhance the cycle stability of Li–S batteries. Meanwhile, this strong chemical interaction increases the diffusion coefficient for lithium ions, accelerating the lithiation reaction with complete inversion. Moreover, the as‐obtained interlayer can be used as a fresh 3D current collector to establish a flame‐retardant “vice‐electrode,” which can trap dissolved sulfur and absorb a large amount of electrolyte, prominently bringing down the flammability of the sulfur cathode and electrolyte to improve the safety of Li–S batteries. This work provides a viable strategy for using PPZ‐based materials as strong chemical scavengers for LiPS and a flame‐retardant interlayer toward next‐generation Li–S batteries with enhanced safety and electrochemical performance.

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium−sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their "dissolved" status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g −1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.

Lithium‐sulfur batteries have recently attracted academic/industrial attention due to the high theoretical energy density. However, the capacity decay mainly caused by the polysulfides shuttle effect and poor conductivity of sulfur. Herein, in situ growth of ZnCo2O4 quantum dots (ZCO‐QDs) embedded into the hollow carbon‐carrier sphere (HCS) to form the ZnCo2O4 quantum dots nanocapsule (ZCO‐QDs@HCS) as the multifunctional sulfur host is rationally demonstrated. Based on density‐functional theory calculations, in situ spectroscopic techniques, and electrochemical studies, the synergistic effects on anchoring/catalyzing polysulfide of the ZCO‐QDs@HCS composite in Li‐S batteries is investigated. Interestingly, the ZCO‐QDs@HCS also allows for the controlled release of ZCO‐QDs into the Li‐S electrolyte. Subsequently, it is first discovered that these diffused ZCO‐QDs can act as self‐repairing initiators to stabilize Li metal anodes via rebuilding the damaged solid electrolyte interphase and suppressing Li dendrites growth. With this concept, quantum dots‐based catalyst delivery systems is first constructed in a Li‐S battery, which is similar to the use of nanocarrier‐based drug delivery systems in cancer therapy. The Li‐S cells with the S@ZCO‐QDs@HCS cathode display significantly superior electrochemical performances with a high specific capacity (1350.5 mAh·g−1 at 0.1 C) and excellent cycling stability (capacity decay rate of 0.057% per cycle after 1000 cycles at 3.0 C).