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.

energy density, low cost, and good thermal stability, which is a promising highperformance cathode material for lithiumion batteries. [2] Unlike ternary cathode materials, lithium cobalt oxide and other cathode materials, lithium-rich cathode materials (LR) can simultaneously invoke the redox of transition metal cations and oxygen anion. [3] The redox activity of oxygen in lithium-rich cathode materials provides innovative insights for high specific energy cathode materials, but it also brings a series of problems such as the change of crystal structure on the electrode surface, the release of oxygen and the decomposition of electrolyte. These severe problems often lead to continuous capacity fading and voltage decay on the cathode. [4] The electrochemical activation of Li 2 MnO 3 with superlattice component inevitably releases oxygen-active species, including oxygen (O 2 ), superoxide radicals (O 2• ¯), and singlet oxygen ( 1 O 2 ) during the first charge process. These oxygen-active species will decompose electrolyte solvents, accompanied by the generation of CO 2 , CO, and other gases. This reaction greatly destroys the structural stability of cathode materials and threatens the safety performance of batteries. [4b,5] Furthermore, unfavorable decomposition will be produced by carbonate electrolyte under severe conditions of high voltage, which is not conducive to the construction of a stable and robust cathode-electrolyte interface (CEI) layer and leads to the continuous consumption of active lithium ions. [6] Introducing electrolyte additives is one of the direct and effective methods to optimize the interface between cathode and electrolyte. A series of additives were developed to improve the cycling stability of lithium-ion batteries under high voltage, such as cathode film-forming additives (TPFPB, [7] TTFP, [8] FEC [9] ) flame-retardant additives (TFP, [10] TMP [11] ) and overcharge protection additives (BP, [12] 2,5-di-tert-butyl-1,4-dimethoxybenzene [13] ). In order to solve the problem of active oxygen in high-voltage LR mentioned above, superoxide radicals scavenger was proposed to eliminate oxygen free radicals that induced adverse reactions, thereby significantly improving the electrochemical stability of LR. [6b] In this work, β-carotene (C 40 H 56 ) was selected as a scavenging molecule, by adding it in electrolyte, to capture the active-oxygen Lithium-rich layered oxides with high energy density are promising cathode materials, thus having attracted a large number of researchers. However, the materials cannot be commercialized for application so far. The crucial problem is the releasing of lattice oxygen at high voltage and resulting consequence, such as decomposition of electrolyte, irreversible phase transition of crystal structure, capacity degradation, and voltage decay. Therefore, capturing active-oxygen and further constructing a cathode-electrolyte-interface (CEI) protective layer via the scavenging effects should be a fundamental step to solve these issues. Herein, β-carotene with...

The sodium plating/stripping with high reversibility is very challenging for sodium-based batteries. To build a robust solid-electrolyte interphase (SEI) film on the surface of sodium electrode is a pragmatic and...