Deciphering the potassium storage phase conversion mechanism of phosphorus by combined solid-state NMR spectroscopy and density functional theory calculations

Phosphorus is the potential anode material for emerging potassium-ion batteries(PIBs)owing to the highest specific capacity and relatively low operation plateau.However,the reversible delivered capacities of phosphorus-based anodes,in reality,are far from the theoretical capacity corresponding to the formation of K3P alloy.And,their underlying potassium storage mechanisms remain poorly understood.To address this issue,for the first time,we perform high-resolution solid-state31P NMR combined with XRD measurements,and density functional theory calculations to yield a systemic quantitative understanding of(de)potassiation reaction mechanism of phosphorus anode.We explicitly reveal a previously unknown asymmetrical nanocrystalline-to-amorphous transition process via rP←→(K_(3)P_(11),K_(3)P_(7),beta-K_(4)P_(6))←→(alpha-K4P6)←→(K_(1-x)P,KP,K_(4-x)P3,K_(1+x)P)←→(amorphous K4P3,amorphous K3P)that are proceed along with the electrochemical potassiation/depotassiation processes.Additionally,the corresponding KP alloys intermediates,such as the amorphous phases of K_(4)P_(3),K_(3)P,and the nonstoichiometric phases of“K_(1-x)P”,“K_(1+x)P”,“K_(4-x)P_(3)”are experimentally detected,which indicating various complicated K-P alloy species are coexisted and evolved with the sluggish electrochemical reaction kinetics,resulting in lower capacity of phosphorus-based anodes.Our findings offer some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for PIBs.

High-capacity Bi_(2)O_(3) anode for 2.4 V neutral aqueous sodium-ion battery-supercapacitor hybrid device through phase conversion mechanism

Aqueous battery-supercapacitor hybrid devices(BSHs)are of great importance to enrich electrochemical energy storage systems with both high energy and power densities.However,further improvement of BSHs in aqueous electrolytes is greatly hampered by operating voltage and capacity limits.Different from the conventional intercalation/de-intercalation mechanism,Bi_(2)O_(3) implements charge storage by a reversible phase conversion mechanism.Herein,taking Bi_(2)O_(3) electrode with wide potential window(from-1.2 to 1 V vs.saturated calomel electrode)and high capacity as battery-type anode,we propose that the overall performance of aqueous BSHs can be greatly upgraded under neutral condition.By paring with stable layer-structuredδ-MnO_(2) cathode,a sodium-ion Bi_(2)O_(3)//MnO_(2) BSH with an ultrahigh voltage of 2.4 V in neutral sodium sulfate electrolyte is developed for the first time.This hybrid device exhibits high capacity(~215 C g^(-1) at 1 mA cm^(-2)),relatively long lifespan(~77.2%capacity retention after 1500 cycles),remarkable energy density(71.7 Wh kg^(-1)@400.5 W kg^(-1))and power density(3204.3 W kg^(-1)@18.8 Wh kg^(-1)).Electrochemical measurements combining a set of spectroscopic techniques reveal the reversible phase conversion between bismuth oxide and metallic bismuth(Bi_(2)O_(3)?Bi0)through Bi^(2+) transition phase in neutral sodium sulfate solution,which can deliver multielectron transfer up to 6,leading to the high-energy BSHs.Our work sheds light on the feasibility of using Bi_(2)O_(3) electrode under neutral condition to address the issue of narrow voltage and low capacity for aqueous BSHs.

Laser-induced phase conversion of n-type SnSe_(2)to p-type SnSe

We report a facile phase conversion method that can locally convert n-type SnSe_(2)into p-type SnSe by direct laser irradiation.Raman spectra of SnSe_(2)flakes before and after laser irradiation confirm the phase conversion of SnSe_(2)to SnSe.By performing the laser irradiation on SnSe_(2)flakes at different temperatures,it is found that laser heating effect induces the removal of Se atoms from SnSe_(2)and results in the phase conversion of SnSe_(2)to SnSe.Lattice-revolved transmission electron microscope images of SnSe_(2)flakes before and after laser irradiation further confirm such conversion.By selective laser irradiation on SnSe_(2)flakes,a pattern with SnSe_(2)/SnSe heteostructures is created.This indicates that the laser induced phase conversion technique has relatively high spatial resolution and enables the creation of micron-sized in-plane p-n junction at predefined region.

Mechanosynthesis of polymer-stabilized lead bromide perovskites:Insight into the formation and phase conversion of nanoparticles

The application of polymers to replace oleylamine(OLA)and oleic acid(OA)as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based processing.Herein,we report a mechanosynthesis of lead bromide perovskite nanoparticles(NPs)stabilized by partially hydrolyzed poly(methyl methacrylate)(h-PMMA)and highmolecular-weight highly-branched poly(ethylenimine)(PEI-25K).The as-synthesized NP solutions exhibited green emission centered at 516 nm,possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield(PL QY)as 85%,while showing excellent durability and resistance to polar solvents,e.g.,methanol.The colloids of polymer-stabilized NPs were directly processable toform stable and strongly-emitting thin films and solids,making them attractive as gain media.Furthermore,the roles of h-PMMA and PEI-25K in the grinding process were studied in depth.The h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of NPs.The PEI-25K with large amounts of amino groups induced significant enrichment of PbBr_(2)in the reaction mixture,which in turn caused the formation of CsPb_(2)Br_(5)-mPbBr_(2)and CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr NPs.The presence of CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr NPs was responsible for the high PL QY,as the Cs_(4)PbBr_(6)phase with a wide energy bandgap can passivate the surface defects of the CsPbBr_(3)phase.This work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.

Mechanism for suspension magnetization roasting of iron ore using straw-type biomass reductant

As an alternative reductant for fossil fuel in the future,straw-type biomass contributes to emission reduction and green utilization in the suspension roasting process.In this study,the influences of the roasting time,roasting temperature and dose of straw-type biomass after suspension magnetization roasting(SMR) and separation were investigated.The optimal conditions were determined to be a roasting time of 7.5 min with a straw-type biomass dose of 20 wt% and a roasting temperature of 800℃ in which an iron grade of 71.07% and recovery of 94.17% were obtained for the iron concentrate.The maximum saturation magnetization under optimal conditions was 35.05 A·m^(2)·g^(-1),and the gaseous regulation of the biomass revealed that cumulative reducing gas volume was 293.93 mL at the optimal roasting time of450 s.The transformation of hematite to magnetite was detected by X-ray diffraction(XRD).During microstructure evolution,the outer layer consisting of fissures and tiny holes continuously deepened toward the core.