Lignin‐derived carbon with pyridine N‐B doping and a nanosandwich structure for high and stable lithium storage

Biomass‐derived carbon is a promising electrode material in energy storage devices.However,how to improve its low capacity and stability,and slow diffusion kinetics during lithium storage remains a challenge.In this research,we propose a“self‐assembly‐template”method to prepare B,N codoped porous carbon(BN‐C)with a nanosandwich structure and abundant pyridinic N‐B species.The nanosandwich structure can increase powder density and cycle stability by constructing a stable solid electrolyte interphase film,shortening the Li^(+) diffusion pathway,and accommodating volume expansion during repeated charging/discharging.The abundant pyridinic N‐B species can simultaneously promote the adsorption/desorption of Li^(+)/PF_(6)^(−) and reduce the diffusion barrier.The BN‐C electrode showed a high lithium‐ion storage capacity of above 1140 mAh g^(−1) at 0.05 A g^(−1) and superior stability(96.5% retained after 2000 cycles).Moreover,owing to the synergistic effect of the nanosandwich structure and pyridinic N‐B species,the assembled symmetrical BN‐C//BN‐C full cell shows a high energy density of 234.7Wh kg^(−1),high power density of 39.38 kW kg−1,and excellent cycling stability,superior to most of the other cells reported in the literature.As the density functional theory simulation demonstrated,pyridinic N‐B shows enhanced adsorption activity for Li^(+) and PF_(6)^(−),which promotes an increase in the capacity of the anode and cathode,respectively.Meanwhile,the relatively lower diffusion barrier of pyridinic N‐B promotes Li^(+) migration,resulting in good rate performance.Therefore,this study provides a new approach for the synergistic modulation of a nanostructure and an active site simultaneously to fabricate the carbon electrode material in energy storage devices.

In situ growth of NiS_(2) nanosheet array on Ni foil as cathode to improve the performance of lithium/sodium-sulfur batteries

The NiS;nanosheet array on Ni foil(NiS2/NF)was prepared using an in situ growth strategy and sulfidation method and was used as the cathode of lithium sulfur battery.The unique nanostructure of the NiS;nanosheet array can provide abundant active sites for the adsorption and chemical action of polysulfides.Compared with the sulfur powder coated pure NF(pure NF-S)for lithium sulfur battery,the sulfur powder coated NiS_(2)/NF(NiS_(2)/NF-S)electrode exhibits superior electrochemical performance.Specifically,the NiS_(2)/NF-S delivered a high reversible capacity of 1007.5 m Ah g^(-1) at a current density of 0.1 C(1 C=1675 mA g^(-1))and kept 74.5% of the initial capacity at 1.0 C after 200 cycles,indicating the great promise of NiS_(2)/NF-S as the cathode of lithium sulfur battery.In addition,the NiS_(2)/NF-S electrode also showed satisfactory electrochemical performance when used as the cathode for sodium sulfur battery.

Amorphous nickel borate nanosheets as cathode material with high capacity and better cycling performance for zinc ion battery

Zinc-ion batteries are under current research focus because of their uniqueness in low cost and high safety.However,the pursuing of high-performance cathode materials of aqueous Zinc ion batteries(AZBs)with low cost,high energy density and long cycle life has become the key problem to be solved.Herein we synthesized a series of amorphous nickel borate(AM-NiBO)nanosheets by varying corrosion time with in-situ electrochemical corrosion method.The AM-NiBO-T13 as electrode material possesses a high areal capacity of 0.65 m Ah/cm^(2) with the capacity retention of 95.1%after 2000 cycles.In addition,the assembled AM-NiBO-T13//Zn provides high energy density(0.77 m Wh/cm^(2) at 1.76 m W/cm^(2)).The high areal capacity and better cycling performance can be owing to the amorphous nanosheets structure and the stable coordination characteristics of boron and oxygen in borate materials.It shows that amorphous nickel borate nanosheets have great prospects in the field of energy storage.

Self-templating construction of hollow microspheres assembled by nanosheets with exposed active planes for sodium ion storage

P2-type layered metal oxides have been considered as one of the promising cathode candidates for high-performance Na-ion batteries(SIBs).However,it is still challenging to balance the contradiction of high energy density and long cycle life due to the structural degradation and sluggish ion diffusion dynamics.Here,the hierarchical P2-Na2/3Ni1/3Mn2/3O2 hollow microspheres assembled by nanosheets are constructed via a self-template approach.The obtained nanosheets with more exposed electrochemical active planes serving as desodiation/sodiation reactors can provide substantial Na+channels,shorten the diffusion pathways,and accommodate the volume changes during charge/discharge process.Benefiting from the facile Na+diffusion paths and optimal architecture modulation,the cathode delivers a high initial Coulombic efficiency of 96.0%with a high energy density of 299.7 Wh·kg^(−1).The highly reversible structural evolutions processes are verified by galvanostatic intermittent titration technique(GITT)and operando electrochemical impedance spectroscopy(EIS)measurement,which would significantly improve the cycle stability(83.3%capacity retention at 1.0 C over 500 loops).Furthermore,the full cell assembled by hard carbon presents a high reversible capacity of 71 mAh·g^(−1)at 0.2 C and promising capacity retention(91.5%after 50 cycles).The designing concept of morphological configuration in this work paves an accessible route for building high-performance electrode materials.

Flexible asymmetric supercapacitor based on MnO_2 honeycomb structure

A flexible asymmetric supercapacitor with high energy density was constructed by using a flexible substrate of carbonized silk-fabrics decorated with carbon nanotube, electroplating MnO2 nanosheets and dip-coating activated carbon powders as the positive and the negative electrodes, respectively. By controlling the electroplating time, the MnO2 nanosheets can be self-assembled to honeycomb structure and showed excellent electrochemical performance in 1 mol/L Na2SO4 electrolyte with SC950-EP30 performing the best. It exhibited a high specific capacitance（1110.85 F/g at a current density of 1 A/g based on the mass of MnO2） and superior rate capability（77.44% capacity retention from 1 A/g to 10 A/g）.Thus, the optimal asymmetric device assembled with this material as positive electrode can deliver a maximum energy density of 43.84 Wh/kg and a maximum power density of 6.62 kW/kg.

Simple chemical synthesis and isotropic negative thermal expansion in MHfF_(6)(M=Ca,Mn,Fe,and Co)

The rapid progress of modern technologies has accelerated the prominence of thermal expansion mismatch between materials,and tunable thermal expansion materials will be a powerful safeguard against this challenge.Here,isotropic MHfF_(6)(M=Ca,Mn,Fe,and Co)compounds with tunable thermal expansion have been produced via a low-cost synthetic method and investigated.By utilizing temperature dependent X-ray diffraction(XRD)and Raman spectroscopy,combined with first principles calculations,it was revealed that the transverse thermal vibrations of the F atoms are dominated by low-frequency phonons with negative Grüneisen parameters and are therefore the origin of the negative thermal expansion(NTE).Very interestingly,with the increase of the M atomic number,the metal…F atomic linkages become stiffer,reducing the number of vibrational modes with negative Grüneisen parameters,so that the strong NTE can be gradually adjusted to moderate NTE and to near zero thermal expansion.The present study achieves the tunable thermal expansion in a new compound family and shed light on the internal mechanism from the perspective of lattice vibrational dynamics.

Avoiding heating interference and guided thermal conduction in stretchable devices using thermal conductive composite islands

The miniaturization and high integration of devices demand significant thermal management materials.Current technologies for the thermal management of electronics show some limitations in the case of multiple chip arrays.A device in multiple chip array is affected by heat from adjacent devices,along with thermal conductive composite.To address this problem,we present a nano composite of aligned boron nitride(BN)nanosheet islands with porous polydimethylsiloxane(PDMS)foam to have mechanical stability and non-thermal interference.The islands of tetrahedrally-structured BN in the composite have a high thermal conductivity of 1.219 W·m^(-1)·K^(-1) in the through-plane direction(11.234W·m^(-1)·K^(-1)in the in-plane direction)with 16 wt.%loading of BN.On the other hand,porous PDMS foam has a low thermal conductivity of 0.0328W·m^(-1)·K^(-1) in the through-plane direction at 70%porosity.Heat pathways are then formed only in the structured BN islands of the composite.The porous PDMS foam can be applied as a thermal barrier between structured BN islands to inhibit thermal interference in multiple device arrays.Furthermore,this composite can maintain selective thermal dissipation performance with 70%tensile strain.Another beauty of the work is that it could have guided heat dissipation by assembling of multiple layers which have high vertical thermal conductive islands,while inhibiting thermal interference.The selective heat dissipating composite can be applied as a heatsink for multiple chip arrays electronics.