A MOF-derived composite with multi-functional effects for high-performance Li–S batteries, especially its Co–N dual-catalyzing for S redox.

Dendrite growth of alkali metal anodes limited their lifetime for charge/discharge cycling. Here, we report near-perfect anodes of lithium, sodium, and potassium metals achieved by electrochemical polishing, which removes microscopic defects and creates ultra-smooth ultra-thin solid-electrolyte interphase layers at metal surfaces for providing a homogeneous environment. Precise characterizations by AFM force probing with corroborative in-depth XPS profile analysis reveal that the ultra-smooth ultra-thin solid-electrolyte interphase can be designed to have alternating inorganic-rich and organic-rich/mixed multi-layered structure, which offers mechanical property of coupled rigidity and elasticity. The polished metal anodes exhibit significantly enhanced cycling stability, specifically the lithium anodes can cycle for over 200 times at a real current density of 2 mA cm^–2 with 100% depth of discharge. Our work illustrates that an ultra-smooth ultra-thin solid-electrolyte interphase may be robust enough to suppress dendrite growth and thus serve as an initial layer for further improved protection of alkali metal anodes.

The redox reactions occurring in the Li-S battery positive electrode conceal various and critical electrocatalytic processes, which strongly influence the performances of this electrochemical energy storage system. Here, we report the development of a single-dispersed molecular cluster catalyst composite comprising of a polyoxometalate framework ([Co₄(PW₉O₃₄)₂]¹⁰⁻) and multilayer reduced graphene oxide. Due to the interfacial charge transfer and exposure of unsaturated cobalt sites, the composite demonstrates efficient polysulfides adsorption and reduced activation energy for polysulfides conversion, thus serving as a bifunctional electrocatalyst. When tested in full Li-S coin cell configuration, the composite allows for a long-term Li-S battery cycling with a capacity fading of 0.015% per cycle after 1000 cycles at 2 C (i.e., 3.36 A g⁻¹). An areal capacity of 4.55 mAh cm⁻² is also achieved with a sulfur loading of 5.6 mg cm⁻² and E/S ratio of 4.5 μL mg⁻¹. Moreover, Li-S single-electrode pouch cells tested with the bifunctional electrocatalyst demonstrate a specific capacity of about 800 mAh g⁻¹ at a sulfur loading of 3.6 mg cm⁻² for 100 cycles at 0.2 C (i.e., 336 mA g⁻¹) with E/S ratio of 5 μL mg⁻¹.

Through in situ nucleation and growth of α-MnO₂ nanorods on graphene nanosheets (GNs), a α-MnO₂ nanorod/GN hybrid was synthesized and employed as the catalyst for non-aqueous lithium oxygen (Li–O₂) batteries. The α-MnO₂/GN hybrid showed excellent catalytic property. It was demonstrated that the catalytic performance of α-MnO₂ for ORR and OER was not only associated with the morphology and size of the particles but also with their combination with graphene. The developed in situ synthetic strategy can also be applied to prepare analogous MO_x/GN hybrids used in Li–O₂ batteries and other energy storage systems.