ZnS coating of cathode facilitates lean‐electrolyte Li‐S batteries

Tremendous effort has been devoted to lithium‐sulfur batteries,where flooded electrolytes have been employed ubiquitously.The use of lean electrolytes albeit indispensable for practical applications often causes low capacity and fast capacity fading of the sulfur cathode;thus,the electrolyte/sulfur active mass ratios below 5μL/mg have been rarely reported.Herein,we demonstrate that ZnS coating transforms sulfur cathode materials electrolyte‐philic,which tremendously promotes the performance in lean electrolytes.The ZnS‐coated Li2S@graphene cathode delivers an initial discharge capacity of 944mAh/g at an E/S ratio of 2μL/mg at the active mass loading of 5.0 mg Li2S/cm^2,corresponding to an impressive specific energy of 500Wh/kg based on the mass of cathode,electrolyte,and the assumed minimal mass of lithium metal anode.Density functional theory calculations reveal strong binding between ZnS crystals and electrolyte solvent molecules,explaining the better wetting properties.We also demonstrate the reversible cycling of a hybrid cathode of ZnS‐coated Li2S@graphene mixed with VS2 as an additive at an E/AM(active mass)ratio of 1.1μL/mg,equivalent to the specific energy of 432 Wh/kg on the basis of the mass of electrodes and electrolyte.

Recent progress in Li and Mn rich layered oxide cathodes for Li-ion batteries

Li and Mn rich(LMR)layered oxides,written as xLi_(2) MnO_(3)·(1-x)LiMO_(2)(M=Mn,Ni,Co,Fe,etc.),have been widely reported in recent years due to their high capacity and high energy density.The stable structure and superior performance of LMR oxides make them one of the most promising candidates for the next-generation cathode materials.However,the commercialization of these materials is hindered by several drawbacks,such as low initial Coulombic efficiency,the degradation of voltage and capacity during cycling,and poor rate performance.This review summarizes research progress in solving these concerns of LMR cathodes over the past decade by following three classes of strategies:morphology design,bulk design,and surface modification.We elaborate on the processing procedures,electrochemical performance,mechanisms,and limitations of each approach,and finally put forward the concerns left and the possible solutions for the commercialization of LMR cathodes.

Recent advances in cathode materials for Li-S battery:structure and performance

Li–S battery is one of the most promising candidates for next-generation energy storage technology.However, the rapid capacity fading and low-energy-density limit its large-scale applications. Scholars invest a lot of effort to introduce new materials. A neglected problem is that reasonable structure is as important as new material. In this review, four kinds of cathode structures were analyzed through morphology and electrochemical properties. The relationship between structures and properties was elaborated through reaction mechanism. The advantages and disadvantages of each structure were discussed. We hope the summary and discussion provide inspiration for structure design in Li–S battery cathode materials.

Improved performance of Li-Se battery based on a novel dual functional CNTs@graphene/CNTs cathode construction

A dual functional CNTs@graphene/CNTs cathode for Li–Se battery was constructed by a CNTs@graphene network and a CNTs interlayer. CNTs were first integrated with graphene to form a three-dimensional（3D） framework and work together as a conductive matrix for Se confinement. The optimized composite cathode delivers a high initial capacity of 575 mAh·g^-1 at 0.5 A·g^-1 and good rate capacity with a retained capacity of 479 mAh·g^-1 at 2.0 A·g^-1（73% of the capacity at 0.2 A·g^-1）. CNTs were further served as an interlayer to confine the diffusion of polyselenides by constructing a thin CNTs layer outside the CNTs@graphene network. An improved initial capacity of 616 mAh·g^-1 at 0.5 A·g^-1 is achieved with a retained capacity of 538 mAh·g^-1 after 80 cycles, indicating the effective dual function of CNTs in this novel cathode construction and great application potential for Li–Se battery.

Reorganizing electronic structure of Li3V2(PO4)3 using polyanion(BO3)^3-:towards better electrochemical performances

Doping modification of electrode materials is a sought-after strategy to improve their electrochemical performance in the secondary batteries field. Herein,polyanion（BO3）^3-doped Li3V2（PO4）3 cathode materials were successfully synthesized via a wet coordination method. The effects of（BO3）^3- doping content on crystal structure, morphology and electrochemical performance were explored by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. All the asprepared samples have the same monoclinic structure;among them, Li3V2（PO4）（2.75）（BO3）（0.15） sample has relatively uniform and optimized particle size. In addition, this sample has the highest discharge capacity and the best cycling stability, with an initial discharge capacity of 120.4mAh·g^-1, and after 30 cycles at a rate of 0.1C, the discharge capacity still remains 119.3 mAh·g^-1. It is confirmed that moderate polyanion（BO3）^3- doping can rearrange the electronic structure of the bulk Li3V2（PO4）3,lower the charge transfer resistance and further improve the electrochemical behaviors.