Insight into the structure-capacity relationship in biomass derived carbon for high-performance sodium-ion batteries

Carbonaceous materials are the most promising candidates as the anode for sodium-ion batteries (SIBs), however, they still suffer from low electric conductivity and sluggish sodium ion (Na+) reaction kinetics. Appropriate composition modulation using heteroatoms doping and structure optimization is highly desired. A basic empirical understanding of the structure-capacity relationship is also urgent in tackling the above problems. Herein, multi-functional nitrogen (N) doped carbon micro-rods with enlarged interlayer spacing are synthesized and investigated as the anode in SIBs, showing an ultra-stable capacity of 161.5 mAh g^(−1) at 2 A g^(−1) for over 5000 cycles. Experimental investigations and first-principle calculations indicate that the enlarged interlayer spacing can facilitate Na+ intercalation and N doping can guarantee the high electric conductivity and favorable electrochemical active sites. Additionally, pyridinic N is theoretically proved to be more effective to enhance Na+ adsorption than pyrrolic N due to the lower adsorption energy and stronger binding energy with Na+. Full SIBs show a high capacity and cyclability, making the biomass-derived carbon micro-rods to be a promising anode for practical SIBs applications.

Alleviating mechanical degradation of hexacyanoferrate via strain locking during Na^(+) insertion/extraction for full sodium ion battery

Generation of large strains upon Na^(+) intercalation is one of the prime concerns of the mechanical degradation of Prussian blue(PB)and its analogs.Structural construction from the atomic level is imperative to maintain structural stability and ameliorate the long-term stability of PB.Herein,an inter nickel hexacyanoferrate(NNiFCN)is successfully introduced at the out layer of iron hexacyanoferrate(NFFCN)through ion exchange to improve structural stability through compressive stress locking by forming NNiFCN shell.Furthermore,the kinetics of sodium ion diffusion is enhanced through the built-in electric pathway.The electrochemical performance is therefore significantly improved with a remarkable long-term cycling stability over 3,000 cycles at 500 mA·g^(–1) in the full sodium-ion batteries(SIBs)with a maximum energy density of 91.94 Wh·g^(–1),indicating that the core-shell structured NNiFCN/NFFCN could be the low-cost and high-performance cathode for full SIBs in large-scale EES applications.

Local phenomena at grain boundaries:An alternative approach to grasp the role of oxygen vacancies in metallization of VO_(2)

Vanadium dioxide(VO_(2))undergoes an insulator to metal transition(MIT)and an accompanied phase transition from a monoclinic(M)structure to rutile(R)structure near room temperature,forming the basis for many VO_(2)-based functional devices.The MIT transition of VO_(2)and the functionality of VO_(2)-based devices can be controlled by a variety of chemical and physical stimuli.With these external stimuli,defects,such as oxygen vacancies,are often inevitably introduced.However,due to the VeO systeminduced challenge to synthesize stable VO_(2)with different oxygen vacancy concentrations,the impact of oxygen vacancies on the resistance and transition of the VO_(2)is not fully understood.Oxygen vacancy,as one of the typical defects in VO_(2),is expected to concentrate at grain boundaries,and hence a concentration gradient of oxygen vacancies may exist between the grains interior and the boundaries,and this suggests a possibility to study the effects of oxygen vacancies on the transition of VO_(2)by probing local phenomena at the grain boundaries.For investigating local phenomena at the grain boundaries,Scanning Probe Microscopy(SPM)techniques are effective,which allows probing the structure and various properties at the nanoscale.In this work,a series of SPM techniques,including Atomic Force Microscopy(AFM),conductive-AFM(c-AFM),Electrochemical Strain Microscopy(ESM),and Kelvin Probe Force Microscopy(KPFM),are employed to measure variations of the surface structure,the resistance,the oxygen vacancy concentration,and the work function between the grain interior and the grain boundary.It has been demonstrated that,for most cases,both the resistance and the work function are lower at the grain boundaries as a result of the accumulation of oxygen vacancies at those positions.In addition,the resistance change induced by the electric field has been observed in the deposited VO_(2)thin films,which may be associated with the generation/annihilation of the oxygen vacancies,rather than charge injection.This work has demonstrated the effects of oxygen vacancies in the transition of VO_(2)by probing the local phenomena at grain boundaries,also provided a new insight into the resistance change of VO_(2)under an electric field.

Effects of oxygen and moisture on the I-V characteristics of TiO_(2) thin films

Current-voltage(I-V)characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory(ReRAM).It has been observed that the atmospheric environment can affect the resistive switching performance,but the origin of this effect is still under debate.Conductive Atomic Force Microscopy(c-AFM)is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices.This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO_(2)thin film by performing c-AFM measurements in ambient air,synthetic air,and argon gas.It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching,and it can also reduce the resistance at the low resistance state(LRS).Where the moisture in the environment can increase the set and reset voltages,and increase the resistance at LRS.These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes,which have been further confirmed by Kelvin Probe Force Microscopy(KPFM)measurements.In addition,it is found that the local ionic dynamics of TiO_(2)during the resistive switching are strongly dependent of the environments by performing the FORC-IV(First Order Reversal Curve-Current-Voltage)measurements in the three gas environments.Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials,that is,the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip.

Piezo-/ferroelectric phenomena in biomaterials: A brief review of recent progress and perspectives

There have been overwhelming observations of piezo-/ferroelectric phenomena in many biological tissues and macromolecules,boosting the development of bio-based smart devices and the applications using electromechanical coupling phenomena in biological systems.The electromechanical coupling is believed to be responsible for various biophysical behaviors and remarkable biomaterial properties.Despite the abundant phenomenal observations,the fundamental understanding of the piezo-/ferroelectric effect in biomaterials/systems and the rational design of biobased macroscopic materials with desired piezoelectric responses are still scarce.In this review,we firstly present remarkable historical events on the development of piezo-/ferroelectricity in biomaterials,followed by a brief overview of the fundamental physics of piezo-/ferroelectricity.The developments of biopiezo-/bioferroelectricity in protein-based biomaterials and their implications are highlighted subsequently.In experimental studies,to identify the intrinsic piezo-/ferroelectric properties from other effects or artifacts is usually elusive.This issue is also addressed and discussed in detail,especially using piezoelectric force microscopy(PFM)and spectroscopy techniques to investigate the local piezo-/ferroelectric phenomena in nanostructured materials are highlighted emphatically.

Enhanced energy storage properties and temperature stability of fatigue-free La-modified PbZrO3 films under low electric fields

Electrostatic energy^-storage capacitors,with their ultrahigh storage density and high temperature stability,have been receiving increasing attention of late for their ability to meet the critical requirements of pulsed power devices in low^-consumption systems.In such a context,this work reports on the successful production of anti^-ferroelectric(AFE)thin films with excellent energy storage performance under a relatively low electric field.In particular,La^-doped Pb Zr O3 thin films were fabricated using a sol^-gel method,yielding a recoverable energy storage density of 34.87 J cm^-3 with an efficiency of 59.23%at room temperature under the electric field of^800 k V cm^-1.The temperature dependence of the energy storage property was demonstrated from room temperature to 210°C,indicating a stable density variation between 34.87 and 27.98 J cm^-3.The films also exhibited excellent anti^-fatigue property(endurance of up to 3×10^9cycles and the recoverable energy storage density varied from 39.78 to 29.32 J cm^-3 combined with an efficiency of 61.03%–44.95%under the test frequencies from 10 to 5000 Hz).All results were obtained using compact films with a high polarization(Pmax)of approximately 103.7μC cm^-2 and low remnant polarization(Pr^7μC cm^-2),which was owing to the combination of La Ni O3 buffer layers and vacancies at Pb sites.These results illustrate the great potential of pulsed power devices in low^-consumption systems operating in a wide range of temperatures and long^-term operations.

Variation of contact resonance frequency during domain switching in PFM measurements for ferroelectric materials

Piezoresponse Force Spectroscopy(PFS)is a powerful technique widely used for measuring the nanoscale electromechanical coupling of the ferro-/piezo-electric materials.However,it is found that certain nonferroelectric materials can also generate the“hysteresis-loop-like”responses from the PFS measurements due to many other factors such as electrostatic effects.This work therefore studies the signal of the contact resonance frequency during the PFS measurements.By comparing the results from ferroelectric and non-ferroelectric materials,it is found there are distinct differences between these two types of materials in the variation of the contact resonance frequency during the PFS measurements.A momentary and sharp increase of the contact resonance frequency occurs when the domain is switched by applying the DC bias,which can be regarded as a unique characteristic for the ferroelectric materials.After analyzing the reliability and mechanism of this method,it is proposed that the contact resonance frequency variation at the coercive bias is capable to differentiate the electromechanical responses of the ferroelectric and non-ferroelectric materials during the PFS measurements.

Correlation of resistance switching and polarization rotation in copper doped zinc oxide(ZnO:Cu)thin films studied by Scanning Probe Microscopy

This paper presents multiple-modes Scanning Probe Microscopy(SPM)studies on characterize the correlation of resistance switching(RS)and polarization rotation(PR)in copper doped ZnO(ZnO:Cu)thin films.Firstly,the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy(c-AFM).The PR with almost 180
phase angle is confirmed by using the Piezoresponse Force Microscopy(PFM)on the same location.In addition,it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy(KPFM).Furthermore,it is found that the region with downward polarization has low resistance state(LRS),whereas the region with upward polarization has high resistance state(HRS).Moreover,the Piezoresponse Force Spectroscopy(PFS)and Switching Spectroscopy PFM(SS-PFM)measurements further confirm that the existence of the built-in voltage,V_(built-in) is largest in the ZnO:Cu(8 at.%)film deposited at the oxygen partial pressure of 2×10^(-4) Torr.The schematic diagrams of energy band diagram with varied built-in field,Ebuilt-in,polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior.