Rechargeable Zn-air batteries initiated by nickel–cobalt bimetallic selenide

A Zn-air battery is a potential next-generation energy storage device owing to its extremely high theoretical energy density. Currently, it is important to explore non-precious metal electrocatalysts with high electroactivity and stability in the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for the development of Zn-air batteries. In this work, porous(Ni,Co)Se2 nanosheets were synthesized by selenizing Ni Co2O4 nanosheets. By regulating the conductivity and morphology of the sample, the prepared porous(Ni,Co)Se2 nanosheets show enhanced electrocatalytic activity for OER and ORR compared to Ni Co2O4 nanosheets. The aqueous Zn-air battery using porous(Ni,Co)Se2 nanosheets as the air cathode exhibits superior charge and discharge performance(1.98 V for charging and 1.17 V for discharging), high specific capacity(770 m Ah/g), and excellent cycle stability(140 h). These results indicate that the porous(Ni,Co)Se2 nanosheets are suitable as a bifunctional electrocatalyst for future Zn-air batteries.

In-situ construction of conducting alloy interphase towards modulating Li-ion storage kinetics

Interface engineering strategy shows great promise in promoting the reaction kinetic and cycling performance in the field of electrochemical energy storage application.In this work,an in-situ interface growth strategy is proposed to introduce a robust and conducting MoGe_(2) alloy interphase between the electrochemical active Ge nanoparticle and flexible MoS_(2) nanosheets to modulate their Li-ion storage kinetics.The structural evolution processes of the Ge@MoGe_(2)@MoS_(2) composite are unraveled,during which the initially-generated Ge metals serve as a crucial reduction mediator in the formation of MoGe_(2) species bridging the Ge and MoS_(2).The as-generated MoGe_(2) interface,chemically bonding with both Ge and MoS_(2),possesses multi-fold merits,including the maintaining stable framework of electrochemically inactive Mo matrix to buffer the strain-stress effect and the"welding spot"effects to facilitate the efficient Li^(+)/e^(-)conduction.As well,the introduction of MoGe_(2) interface leads to a unique sequential lithiation/de^(-)lithiation process,namely in the order of the electrochemically active MoS_(2)-MoGe_(2)-Ge during lithiation and vice versa,during which the electrode strain could be more effectively released.Benefited from the robust and rigid MoGe_(2) interface,the delicately designed Ge@MoGe_(2)@MoS_(2) composite exhibits an improved charge/discharge performances(866.7 mAh g^(-1) at 5.0 A g^(-1) and 838.5 mAh g^(-1) after 400 cycles)while showing a high tap density of 1.23 g cm^(-3).The as-proposed in-situ interface growth strategy paves a new avenue for designing novel high-performance electrochemical energy storage materials.

Carbon confinement synthesis of interlayer-expanded and sulfur-enriched MoS2+x nanocoating on hollow carbon spheres for advanced Li-S batteries

High energy density and low-cost lithium-sulfur batteries have been considered as one of the most promising candidates for next-generation energy storage systems.However,the intrinsic problems of the sulfur cathode severely restrict their further practical application.Here,a unique double-shell architecture composed of hollow carbon spheres@interlayer-expanded and sulfur-enriched MoS2+x nanocoating composite has been developed as an efficient sulfur host.A uniform precursor coating derived from heteropolyanions-induced polymerization of pyrrole leads to space confinement effect during the in-situ sulfurization process,which generates the interlayer-expanded and sulfur-enriched MoS2+x nanosheets on amorphous carbon hollow spheres.This new sulfur host possesses multifarious merits including sufficient voids for loading sulfur active materials,high electronic conductivity,and fast lithium-ion diffusive pathways.In addition,additional active edge sites of MoS2+x accompanied by the nitrogen-doped carbon species endow the sulfur host with immobilizing and catalyzing effects on the soluble polysulfide species,dramatically accelerating their conversion kinetics and re-utilization.The detailed defect-induced interface catalytic reaction mechanism is firstly proposed.As expected,the delicately-designed sulfur host exhibits an outstanding initial discharge capacity of 1,249 mAh·g^−1 at 0.2 C and a desirable rate performance(593 mAh·g^−1 at 5.0 C),implying its great prospects in achieving superior electrochemical performances for advanced lithium sulfur batteries.

Terminal sulfur atoms formation via defect engineering strategy to promote the conversion of lithium polysulfides

The defect engineering shows great potential in boosting the conversion of lithium polysulfides intermediates for high energy density lithium-sulfur batteries(LSBs),yet the catalytic mechanisms remain unclear.Herein,the oxygen-defective Li_(4)Ti_(5)O_(12)-xhollow microspheres uniformly encapsulated by N-doped carbon layer(OD-LTO@NC)is delicately designed as an intrinsically polar inorganic sulfur host for the research on the catalytic mechanism.Theoretical simulations have demonstrated that the existence of oxygen deficiencies enhances the adsorption capability of spinel Li_(4)Ti_(5)O_(12)towards soluble lithium polysulfides.Some-S-S-bonds of the Li2S6on the defective Li_(4)Ti_(5)O_(12)surface are fractured by the strong adsorption force,which allows the inert bridging sulfur atoms to be converted into the susceptible terminal sulfur atoms,and reduces the activation energy of the polysulfide conversion in some degree.In addition,with the N-doped carbon layer,secondary hollow microspheres architecture built with primary ultrathin nanosheets provide a large amount of void space and active sites for sulfur storage,adsorption and conversion.The as-designed sulfur host exhibits a remarkable rate capability of 547 m Ah g^(-1)at 4C(1 C=1675 m A g^(-1))and an outstanding long-term cyclability(519 m Ah g^(-1)after 1000 cycles at 3 C).Besides,a high specific capacity of 832 m Ah g^(-1)is delivered even after 100 cycles under a high sulfur mass loading of 3.2 mg cm^(-2),indicating its superior electrochemical performances.This work not only provides a strong proof for the application of oxygen defect in the adsorption and catalytic conversion of lithium polysulfides,but offers a promising avenue to achieve high performance LSBs with the material design concept of incorporating oxygen-deficient spinel structure with hierarchical hollow frameworks.

Selenium vacancies enable efficient immobilization and bidirectional conversion acceleration of lithium polysulfides for advanced Li-S batteries

Heterostructures composed of oxides and sulfides(nitrides or carbides)show great potential as sulfur host additives because of the strong adoptability of oxides and catalytic capability of sulfides towards the notorious lithium polysulfides(LiPSs).However,the migration and conversion pathway of LiPSs is seriously confined at a localized interface with inadequate active sites.In this work,the introduction of selenium vacancies into VSe_(2−x)has been demonstrated to successfully synergize the adsorbability and catalytic reactions of LiPSs at an integrated functional surface.The N-doped carbon nanosheets-assembled flower architectures embedded with selenium vacancy-rich VSe_(2−x)and partial vanadium oxides have been controllably synthesized and employed as the cathode additives for lithium-sulfur(Li-S)batteries.Both the experiments and first-principle calculations reveal their strong adsorption to LiPSs and their bidirectional catalytic functionality towards the conversion between S8 and Li_(2)S.As expected,the charge and discharge kinetics of VSe_(2−x)containing sulfur cathodes is fundamentally improved(an outstanding rate capabilitiy with 693.7 mAh·g^(−1)at 2 C,a remarkable long-term cyclability within 1,000 cycles at 2 C with S loading 2.27 mg·cm^(−2),and an excellent areal capacity with 3.44 mAh·cm^(−2)within 100 cycles at 0.5 C).This work presents an effective resolution to couple the adsorbability and catalytic reactions of LiPSs at the material design perspective,and the insights on bidirectional catalytic functionality are of vital to develop functional materials for advanced Li-S batteries.