The lithium-sulfur battery holds a high theoretical energy density, 4-5 times that of today's lithium-ion batteries, yet its applications have been hindered by poor electronic conductivity of the sulfur cathode and, most importantly, the rapid fading of its capacity due to the formation of soluble polysulfide intermediates (Li(2)S(n), n = 4-8). Despite numerous efforts concerning this issue, combatting sulfur loss remains one of the greatest challenges. Here we show that this problem can be effectively diminished by controlling the sulfur as smaller allotropes. Metastable small sulfur molecules of S(2-4) were synthesized in the confined space of a conductive microporous carbon matrix. The confined S(2-4) as a new cathode material can totally avoid the unfavorable transition between the commonly used large S(8) and S(4)(2-). Li-S batteries based on this concept exhibit unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior rate capability, which promise a practicable battery with high energy density for applications in portable electronics, electric vehicles, and large-scale energy storage systems.

Hybrid anode materials for Li-ion batteries are fabricated by binding SnO2 nanocrystals (NCs) in nitrogen-doped reduced graphene oxide (N-RGO) sheets by means of an in situ hydrazine monohydrate vapor reduction method. The SnO2NCs in the obtained SnO2NC@N-RGO hybrid material exhibit exceptionally high specific capacity and high rate capability. Bonds formed between graphene and SnO2 nanocrystals limit the aggregation of in situ formed Sn nanoparticles, leading to a stable hybrid anode material with long cycle life.

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co-Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized CoMnCH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm for HER can be also achieved on CoMnCH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional CoMnCH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

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Substantial efforts have been devoted in the past decade to developing rechargeable lithium-ion batteries with high energy density and long cycle life for portable electronics, electric vehicles (EVs), and renewable energy storage. [1][2][3][4][5][6][7][8][9][10][11] The low theoretical capacity (372 mA h g − 1 ) of currently commercialized graphite cannot satisfy the demand of high energy density. Various anode materials with higher specifi c capacities have been proposed for lithium-ion batteries. Among these, silicon has attracted enormous attention owing to its low lithium-uptake potential and the highest theoretical capacity (4200 mA h g − 1 ). [12][13][14][15][16] However, the practical application of Si as an anode material is seriously hampered by the low intrinsic electric conductivity and large volume changes (greater than 300%) during lithium insertion and extraction from Si, resulting in dramatic pulverization of Si particles and electrical disconnection from the current collector, [ 17 ] and leading to rapid capacity fade upon cycling. To overcome these obstacles, fabrication of Si nano structures including nanowires, nanotubes, and hollow nanospheres and preparation of highconductivity carbon-coated Si nanocomposites have been well developed. [18][19][20][21][22][23][24][25][26][27] However, there is still a need for well-designed Si-based nanomaterials and their facile synthetic methods towards high-performance anode materials.Recently, the utilization of graphene in coating Si nanoparticles as anode materials for lithium-ion batteries is becoming more and more appealing due to its unique properties, such as high two-dimensional electrical conductivity, superior mechanical fl exibility, high chemical and thermal stability, and large surface area. [28][29][30][31][32][33][34] These coating techniques are primarily basing on graphene and can not only provide enough fl exibility to accommodate huge volume changes of Si nanoparticles, but also can enhance the conductivity of Si nanoparticles. For example, Si nanoparticle-graphene composites and paper composites have been prepared by a simple mixing method, [ 34 ] or a fi ltration-directed assembly approach. [31][32] Though both attempts have obtained improvements on lithium storage, they do not provide good dispersion of Si nanoparticles between graphene sheets, leading to a limited electrochemical performance enhancement. Therefore, the uniform dispersion of Si nanoparticles in the desired Si nanoparticle-graphene composite remains a great challenge.Electrostatic self-assembly is a well-established strategy to create well-mixed nanocomposites. It is based on the electrostatic attraction between consecutively adsorbed, oppositely charged species. [35][36][37] Silicon is easy to oxidize to form a layer of silicon oxide on its surface and endow with a negative charge. Graphene oxide (GO) shows a negative charge owing to ionization of the carboxylic acid and phenolic hydroxyl groups existing on the GO. [ 38 ] Here, in view of the negatively charged Si nan...