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.

Enhancing Li cycling coulombic efficiency while mitigating “shuttle effect” of Li-S battery through sustained release of LiNO_(3)

In practical lithium-sulfur batteries(LSBs),the shuttle effect and Li cycling coulombic efficiency(CE) are strongly affected by the physicochemical properties of solid electrolyte interphase(SEI).LiNO_(3) is widely used as an additive in electrolytes to build a high-quality SEI,but its self-sacrificial nature limits the ability to mitigate the shuttle effect and stabilize Li anode during long-term cycling.To counteract LiNO_(3) consumption during long-term cycling without using a high initial concentration,inspired by sustainedrelease drugs,we encapsulated LiNO_(3) in lithiated Nafion polymer and added an electrolyte co-solvent(1,1,2,2-tetrafluoroethylene 2,2,2-trifluoromethyl ether) with poor LiNO_(3) solubility to construct highquality and durable F-and N-rich SEI.Theoretical calculations,experiments,multiphysics simulations,and in-situ observations confirmed that the F-and N-rich SEI can modulate lithium deposition behavior and allow persistent repair of SEI during prolonged cycling.Hence,the F-and N-rich SEI improves the Li anode cycling CE to 99.63% and alleviates the shuttle effect during long-term cycling.The lithium anode with sustainable F-and N-rich SEI shows a stable Li plating/stripping over 2000 h at 1 mA cm^(-2).As expected,Li‖S full cells with this SEI achieved a long lifespan of 250 cycles,far exceeding cells with a routine SEI.The Li‖S pouch cell based on F-and N-rich SEI also can achieve a high energy density of about300 Wh kg^(-1) at initial cycles.This strategy provides a novel design for high-quality and durable SEls in LSBs and may also be extendable to other alkali metal batteries.

A strategy to achieve high loading and high energy density Li-S batteries

Lithium-sulfur(Li-S) batteries are one of the most promising rechargeable storage devices due to the high theoretical energy density.However,the low areal sulfur loading impedes their commercial development.Herein,a 3 D free-standing sulfur cathode scaffold is rationally designed and fabricated by coaxially coating polar Ti_3 C_2 T_x flakes on sulfur-impregnated carbon cloth(Ti_3 C_2 T_x@S/CC) to achieve high loading and high energy density Li-S batteries,in which,the flexible CC substrate with highly porous structure can accommodate large amounts of sulfur and ensure fast electron transfer,while the outer-coated Ti_3 C_2 T_x can serve as a polar and conductive protective layer to further promote the conductivity of the whole electrode,achieve physical blocking and chemical anchoring of lithium-polysulfides as well as catalyze their conversion.Due to these advantages,at a sulfur loading of 4 mg cm^(-2),Li-S cells with Ti_3 C_2 T_x@S/CC cathodes can deliver outstanding cycling stability(746.1 mAh g^(-1) after 200 cycles at1 C),superb rate performance(866.8 mAh g^(-1) up to 2 C) and a high specific energy density(564.2 Wh kg^(-1) after 100 cycles at 0.5 C).More significantly,they also show the commercial potential that can compete with current lithium-ion batteries due to the high areal capacity of 6.7 mAh cm^(-2) at the increased loading of 8 mg cm^(-2).

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.

A Mixed Ether Electrolyte for Lithium Metal Anode Protection in Working Lithium-Sulfur Batteries

Lithium-sulfur(Li-S) battery is considered as a promising energy storage system to realize high energy density.Nevertheless,unstable lithium metal anode emerges as the bottleneck toward practical applications,especially with limited anode excess required in a working full cell.In this contribution,a mixed diisopropyl ether-based(mixed-DIPE) electrolyte was proposed to effectively protect lithium metal anode in Li-S batteries with sulfurized polyacrylonitrile(SPAN) cathodes.The mixed-DIPE electrolyte improves the compatibility to lithium metal and suppresses the dissolution of lithium polysulfides,rendering significantly improved cycling stability.Concretely,Li | Cu half-cells with the mixed-DIPE electrolyte cycled stably for 120 cycles,which is nearly five times longer than that with routine carbonate-based electrolyte.Moreover,the mixedDIPE electrolyte contributed to a doubled life span of 156 cycles at 0.5 C in Li | SPAN full cells with ultrathin 50 μm Li metal anodes compared with the routine electrolyte.This contribution affords an effective electrolyte formula for Li metal anode protection and is expected to propel the practical applications of high-energy-density Li-S 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.

Regulation of impedance matching feature and electronic structure of nitrogen-doped carbon nanotubes for high-performance electromagnetic wave absorption

In this study,we developed a facile method to fabricate three-dimensional(3D)structures composed of FeNi alloy nanoparticles encapsulated in N-doped carbon nanotubes that grafted on the SiO_(2) spheres(Fe_(x)Ni_(y)@NCNT@SiO_(2))for electromagnetic wave(EMW)absorption.The experimental results suggest that the impedance matching characteristic can be tuned by the introduction of SiO_(2) spheres in the 3D structure.Density functional theory(DFT)calculations showed that the introduction of Ni improved the polarization and conductive losses of the Fe_(x)Ni_(y)@NCNT@SiO_(2).As a result,the optimal 3D structure exhibits excellent EMW absorption property with a reflection loss and effective absorption bandwidth are-49.39 dB and 4.32 GHz,respectively,even though the matching thickness is only 1.6 mm,superior to most magnetic carbon-based composites.Thus,our current approach opens up an effective way to the development of low-cost,high-performance EMW absorbers.

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.

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.

Single-electron pumping in a ZnO single-nanobelt quantum dot transistor

Diluted magnetic semiconductors(DMSs)have traditionally been employed to implement spin-based quantum computing and quantum information processing.However,their low Curie temperature is a major hurdle in their use in this field,which creates the necessity for wide bandgap DMSs operating at room temperature.In view of this,a single-electron transistor(SET)with a global back-gate was built using a wide bandgap ZnO nanobelt(NB).Clear Coulomb oscillations were observed at 4.2 K.The periodicity of the Coulomb diamonds indicates that the Coulomb oscillations arise from single quantum dots of uniform size,whereas quasi-periodic Coulomb diamonds correspond to the contribution of multi-dots present in the ZnO NB.By applying an AC signal to the global back-gate across a Coulomb peak with varying frequencies,single-electron pumping was observed;the increase in current was equal to the production of electron charge and frequency.The current accuracy of about 1%for both single-and double-electron pumping was achieved at a high frequency of 25 MHz.This accurate single-electron pumping makes the ZnO NB SET suitable for single-spin injection and detection,which has great potential for applications in quantum information technology.