VSe_(2)/V_(2)C heterocatalyst with built-in electric field for efficient lithium-sulfur batteries:Remedies polysulfide shuttle and conversion kinetics

Lithium sulfur(Li-S)battery is a kind of burgeoning energy storage system with high energy density.However,the electrolyte-soluble intermediate lithium polysulfides(Li PSs)undergo notorious shuttle effect,which seriously hinders the commercialization of Li-S batteries.Herein,a unique VSe_(2)/V_(2)C heterostructure with local built-in electric field was rationally engineered from V_(2)C parent via a facile thermal selenization process.It exquisitely synergizes the strong affinity of V_(2)C with the effective electrocatalytic activity of VSe_(2).More importantly,the local built-in electric field at the heterointerface can sufficiently promote the electron/ion transport ability and eventually boost the conversion kinetics of sulfur species.The Li-S battery equipped with VSe_(2)/V_(2)C-CNTs-PP separator achieved an outstanding initial specific capacity of 1439.1 m A h g^(-1)with a high capacity retention of 73%after 100 cycles at0.1 C.More impressively,a wonderful capacity of 571.6 mA h g^(-1)was effectively maintained after 600cycles at 2 C with a capacity decay rate of 0.07%.Even under a sulfur loading of 4.8 mg cm^(-2),areal capacity still can be up to 5.6 m A h cm^(-2).In-situ Raman tests explicitly illustrate the effectiveness of VSe_(2)/V_(2)C-CNTs modifier in restricting Li PSs shuttle.Combined with density functional theory calculations,the underlying mechanism of VSe_(2)/V_(2)C heterostructure for remedying Li PSs shuttling and conversion kinetics was deciphered.The strategy of constructing VSe_(2)/V_(2)C heterocatalyst in this work proposes a universal protocol to design metal selenide-based separator modifier for Li-S battery.Besides,it opens an efficient avenue for the separator engineering of Li-S batteries.

Nb_(2)CT_(x) MXene: High capacity and ultra-long cycle capability for lithium-ion battery by regulation of functional groups

MXenes are well known for their potential application in supercapacitors due to their high-rate intercalation pseudocapacitance and long cyclability.However,the reported low capacity of pristine MXenes hinders their practical application in lithium-ion batteries.In this work,a robust strategy is developed to control the functional groups of Nb_2 CT_x MXene.The capacity of pristine Nb_2 CT_x MXene can be significantly increased by Li~+ intercalation and surface modification.The specific capacity of the treated Nb_2 CT_x is up to 448 mAh g^(-1) at 0.05 A g^(-1),and at a large current density of 2 A g^(-1) remains a high reversible capacity retention rate of 75% after an ultra-long cycle of 2000 cycles.These values exceed most of the reported pristine MXenes(including the most studied Ti_3 C_2 T_x) and carbon-based materials.It demonstrates that this strategy has great help to improve the electrochemical performance of pristine MXene,and the results enhance the promise of MXenes in the application of lithium-ion batteries.

Tailoring the Spatial Distribution and Content of Inorganic Nitrides in Solid-Electrolyte Interphases for the Stable Li Anode in Li-S Batteries

Among the alternatives to lithium-ion batteries,lithium-sulfur(Li-S)batteries are considered as an attractive option because of their high theoretical energy density of 2570 Wh kg^(−1).However,the application of the Li-S battery has been plagued by the rapid failure of the Li anode due to the Li dendrite growth and severe parasitic reactions between Li and lithium polysulfides.The physicochemical properties of the solid-electrolyte interphase have a profound impact on the performance of the Li anode.Herein,a lithium polyacrylic acid/lithium nitrate(LPL)-protective layer is developed to inhibit the dendrite Li growth and parasitic reactions by tailoring the spatial distribution and content of LiN_(x)O_(y) and Li_(3)N at the SEI.The modified SEI is thoroughly investigated for compositions,ion transport properties,and Li plating/stripping kinetics.Consequently,the Li-S cell with a high S loading cathode(5.0 mg cm^(−2)),LPL layer-protected thin Li anode(50μm),and 40μL electrolyte shows a long life span of 120 cycles.This work evokes the avenue for regulating the spatial distribution of inorganic nitride at the SEI to suppress the formation of Li dendrites and parasitic reactions in Li-S batteries and perhaps guiding the design of analogous battery systems.

Composing atomic transition metal sites for high-performance bifunctional oxygen electrocatalysis in rechargeable zinc-air batteries

Rechargeable zinc-air batteries have attracted extensive attention as clean,safe,and high-efficient en-ergy storage devices.However,the oxygen redox reactions at cathode are highly sluggish in kinetics and severely limit the actual battery performance.Atomic transition metal sites demonstrate high electro-catalytic activity towards respective oxygen reduction and evolution,while high bifunctional electro-catalytic activity is seldomly achieved.Herein a strategy of composing atomic transition metal sites is proposed to fabricate high active bifunctional oxygen electrocatalysts and high-performance recharge-able zinc-air batteries.Concretely,atomic Fe and Ni sites are composed based on their respective high electrocatalytic activity on oxygen reduction and evolution.The composite electrocatalyst demonstrates high bifunctional electrocatalytic activity(ΔE=0.72 V)and exceeds noble-metal-based Pt/C+Ir/C(ΔE=0.79 V).Accordingly,rechargeable zinc-air batteries with the composite electrocatalyst realize over 100 stable cycles at 25 mA cm-2.This work affords an effective strategy to fabricate bifunctional oxygen electrocatalysts for high-performance rechargeable zinc-air batteries.

Additive-free porous assemblies of Ti3C2Tx by freeze-drying for high performance supercapacitors

Ti3C2Tx has shown great potential in energy storage filed,but the restacking between Ti3C2Tx nanosheets seriously hampers the maximization of its capacitance.In this study,we rationally designed and synthesized porous Ti3C2Tx assemblies without any additive by introducing ice as spacers using a facile freeze-drying method.The porous Ti3C2Tx assemblies have a three-dimensional network structure,which consists of ultra large Ti3C2Tx lamellar walls and lots of macro-and mesopores.It has been proven that there are more-O groups on the surface of the porous Ti3C2Tx assemblies than the Ti3C2Tx film.The porous Ti3C2Tx assemblies deliver a maximum areal capacitance of 1668 mF/cm^2 when the mass loading is 8.4 mg/cm^2,an optimized specific capacitance of 247.2 F/g when the mass loading is 5.3 mg/cm^2,and87%capacitance retention over 10000 cycles.The symmetric solid-state supercapacitors based on the porous Ti3C2Tx assemblies show an areal capacitance of 355.8 mF/cm^2,the maximum power density of50 mW/cm^2 and an outstanding flexibility under different deformation.

Low-Temperature Working Feasibility of Zinc–Air Batteries with Noble Metal-Free Electrocatalysts

Expanding the application scenario for rechargeable batteries is the key to the terminal utilization of renewable energy.Enabling zinc–air batteries at low temperatures is drawing increasing attention,yet the low-temperature working feasibility of zinc–air batteries with noble metalfree electrocatalysts remains indistinct.In this contribution,the low-temperature performances of zinc–air batteries with noble metal-free electrocatalysts are comprehensively investigated.Armed with a representative noble metal-free bifunctional oxygen electrocatalyst,the zinc–air batteries demonstrate satisfactory yet relatively depressed performance at low temperatures,compared with that at room temperatures.The reduced electrolyte conductivity is identified as one of the limiting factors for the reduced low-temperature performance.Furthermore,electrolyte engineering via solvation structure regulation is performed on the zinc–air batteries with noblemetal-free electrocatalysts,where an improved low-temperature performance is achieved.This work reveals the compatibility between noble metal-free electrocatalysts and low-temperature feasibility/low-temperature performance enhancement strategies for zinc–air batteries and affords new opportunities to satisfy low-cost and efficient energy storage at harsh working conditions.

Mitigating side reaction for high capacity retention in lithium-sulfur batteries

Li-S batteries have shown great potential as secondary energy batteries.However,the side reaction between Li anodes and polysulfides seriously limited their practical application.Herein,the artificial protective film,which is consisted of Li-Nafion and TiO_(2),was designed and successfully prepared to achieve a corrosion-resistant Li anode in Li-S battery.In the composite protective film,the Li-Nafion could efficiently prevent the contact between Li anodes and polysulfides,and the incorporation of TiO_(2)nanoparticles into the Nafion could significantly increase the ionic conductivity and mechanical strength of the protective film.Li-Li symmetric cells with an optimal artificial protective film exhibited an extended cycle-life of 750 h at a current density of 1 mA/cm^(2)in Li_(2)S_(8)electrolyte.Moreover,the Li-S full battery with an optimal protective Li anode exhibited higher capacity retention of 777.4 mAh/g after 100 cycles at 0.1 C as well as better rate performance than the cell with a pure Li anode.This work provides alternative insights to suppress the side reaction for Li-S batteries with high capacity retention.

Bimetallic Ni-Mo nitride@C_(3)N_(4) for highly active and stable water catalysis

Non-noble metal electrocatalysts for water cracking have excellent pro-spects for development of sustainable and clean energy.Highly efficient electrocatalysts for the oxygen evolution reaction(OER)are very important for various energy storage and conversion systems such as water splitting devices and metal-air batteries.This study prepared a NiMo4@C_(3)N_(4) catalyst for OER and hydrogen evolution reaction(HER)by simple methods.The catalyst exhibited an excellent OER activity based on the response at a suitable temperature.To drive a current density of 10 mA-cm^(-2) for OER and HER,the overpotentials required for NiMo4@C_(3)N_(4)-800(prepared at 800℃)were 259 and 118 mV,respectively.A two-electrode system using NiMo4@C_(3)N_(4)-800 needed a very low cell potential of 1.572 V to reach a current density of 10 mA-cm^(-2).In addition,this catalyst showed excellent durability after long-term tests.It was seen to have good catalytic activity and broad application prospects.