Rechargeable magnesium metal batteries need an electrolyte that forms a stable and ionically conductive solid electrolyte interphase (SEI) on the anodes. Here, we used molecular dynamic simulation, density functional theory calculation, and X-ray photoelectron spectroscopy analysis to investigate the solvation structures and SEI compositions in electrolytes consisting of dual-salts, magnesium bis(trifluoromethanesulfonyl)imide (MgTFSI₂), and MgCl₂, with different additives in 1,2-dimethoxyethane (DME) solvent. We found that the formed [Mg₃(μ-Cl)₄(DME)_mTFSI₂] (m = 3, 5) inner-shell solvation clusters in MgTFSI₂-MgCl₂/DME electrolyte could easily decompose and form a MgO- and MgF₂-rich SEI. Such electron-rich inorganic species in the SEI, especially MgF₂, turned out to be detrimental for Mg plating/stripping. To reduce the MgF₂ and MgO contents in SEI, we introduce an electron-deficient tri(2,2,2-trifluoroethyl) borate (TFEB) additive in the electrolyte. Mg//Mg cells using the MgTFSI₂-MgCl₂/DME-TFEB electrolyte could cycle stably for over 400 h with a small polarization voltage of ~150 mV. Even with the presence of 800 ppm H₂O, the electrolyte with TFEB additive could still preserve its good electrochemical performance. The optimized electrolyte also enabled stable cycling and high-rate capability for Mg//Mo₆S₈ and Mg//CuS full cells, showing great potential for future applications.

The polysulfides shuttle effect represents a great challenge in achieving high capacity and long lifespan of lithium/sulfur (Li/S) cells. A comprehensive understanding of the shuttle-related sulfur speciation and diffusion process is vital for addressing this issue. Herein, we employed in situ/operando X-ray absorption spectroscopy (XAS) to trace the migration of polysulfides across the Li/S cells by precisely monitoring the sulfur chemical speciation at the cathodic electrolyte-separator and electrolyte-anode interfaces, respectively, in a real-time condition. After we adopted a shuttle-suppressing strategy by introducing an electrocatalytic layer of twinborn bismuth sulfide/bismuth oxide nanoclusters in a carbon matrix (BSOC), we found the Li/S cell showed greatly improved sulfur utilization and longer life span. The operando S K-edge XAS results revealed that the BSOC modification was bi-functional: trapping polysulfides and catalyzing conversion of sulfur species simultaneously. We elucidated that the polysulfide trapping-and-catalyzing effect of the BSOC electrocatalytic layer resulted in an effective lithium anode protection. Our results could offer potential stratagem for designing more advanced Li/S cells.

Magnesium/sulfur battery (Mg/S) has recently received wide attention due to its high theoretical energy density (3,260 Wh/L) and low cost. To further improve its safety and flexibility, developing a polymer electrolyte that can be compatible with both electrophilic S and Mg is critical. Here, we report a magnesium chloride-(fluorinated tetraethylene glycolic)borate (MgCl-FTGB) based non-nucleophilic, gel-type polymer electrolyte for Mg/S battery via a facile synthetic method through commercially available reagents. This electrolyte coupled with glass fiber allows reversible Mg deposition/dissolution (100% coulombic efficiency) with low polarization (500 μA/cm², 300/300 mV), and shows a wide electrochemical window of 4.8 V (vs. Mg/Mg²⁺). Mg/S battery assembled with this electrolyte can cycle over 50 times with a high specific discharge capacity retention of over 1,100 mAh/g.

Fiber-shaped supercapacitors (FSCs), owing to their high-power density and feasibility to be integrated into woven clothes, have drawn tremendous attentions as a key device for flexible energy storage. However, how to store more energy while withstanding various types of mechanical deformation is still a challenge for FSCs. Here, based on a magnetron sputtering method, different pseudocapacitive materials are conformally coated on self-supported carbon nanotube aligned films. This fabrication approach enables a stretchable, asymmetric, coaxial fiber-shaped supercapacitors with high performance. The asymmetric electrode configuration that consists of CNT@NiO@MnO_x cathode and CNT@Fe₂O₃ anode successfully extends the FSC’s electrochemical window to 1.8 V in an aqueous electrolyte. As a result, a high specific capacitance of 10.4 F·cm^-3 is achieved at a current density of 30 mA·cm^-3 corresponding to a high energy density of 4.7 mWh·cm^-3. The mechanical stability of the stretchable FSC is demonstrated with a sustainable performance under strains up to 75% and a capacitance retention of 95% after 2,000 cycles under 75% strain.

Rational design of a robust carbon matrix has a profound impact on the performance of flexible/wearable lithium/sulfur batteries. Herein, we demonstrate a freestanding three-dimensional super-aligned carbon nanotube (SACNT) matrix reinforced with a multi-functionalized carbon coating for flexible, high-areal sulfur loading cathode. By employing the sulfur/nitrogen co-doped carbon (SNC) "glue", the joints in the SACNT scaffold are tightly welded together so that the overall mechanical strength of the electrode is significantly enhanced to withstand the repeated bending as well as the volume change during operation. The SNC also shows intriguing catalytic effect that lowers the energy barrier of Li ion transport, propelling a superior redox conversion efficiency. The resulting binder-free and current collector-free sulfur cathode exhibits a high reversible capacity of 1, 079 mAh·g^-1 at 1 C, a high-rate capacity of ~ 800 mAh·g^-1 at 5 C, and an average capacity decay rate of 0.037% per cycle at 2 C for 1, 500 cycles. Impressively, a large-areal flexible Li/S pouch cell based on such mechanically robust cathode exhibits excellent capacity retention under arbitrary bending conditions. With a high areal sulfur loading of 7 mg·cm^-2, the large-areal flexible cathode delivers an outstanding areal capacity of 6.3 mAh·cm^-2 at 0.5 C (5.86 mA·cm^-2), showing its promise for realizing practical high energy density flexible Li/S batteries.

Lithium metal anode for batteries has attracted extensive attentions, but its application is restricted by the hazardous dendritic Li growth and dead Li formation. To address these issues, a novel Li anode is developed by infiltrating molten Li metal into conductive carbon cloth decorated with zinc oxide arrays. In carbonate-based electrolyte, the symmetric cell shows no short circuit over 1, 500 h at 1 mAdcm^-2, and stable voltage profiles at 3 mAdcm^-2 for ~ 300 h cycling. A low overpotential of ~ 243 mV over 350 cycles at a high current density of 10 mAdcm^-2 is achieved, compared to the seriously fluctuated voltage and fast short circuit in the cell using bare Li metal. Meanwhile, the asymmetric cell withstands 1, 000 cycles at 10 C (1 C = 167 mAhdg^-1) compared to the 210 cycles for the cell using bare Li anode. The excellent performance is attributed to the well-regulated Li plating/stripping driven from the formation of LiZn alloy on the wavy carbon fibers, resulting in the suppression of dendrite growth and pulverization of the Li electrode during cycling.