Biphase-to-monophase structure evolution of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) toward ultradurable Na-ion batteries

Layered composite oxide materials with O3/P2 biphasic crystallographic structure typically demonstrate a combination of high capacities of the O3 phase and high operation voltages of the P2 phase.However,their practical applications are seriously obstructed by difficulties in thermodynamic phase regulation,complicated electrochemical phase transition,and unsatisfactory cycling life.Herein,we propose an efficient structural evolution strategy from biphase to monophase of Na_(0.766+x)Li_(x)Ni_(0.33-x)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) through Li+substitution.The role of Li+substitution not only simplifies the unfavorable phase transition by altering the local coordination of transition metal(TM)cations but also stabilizes the cathode–electrolyte interphase to prevent the degradation of TM cations during battery cycling.As a result,the thermodynamically robust O_(3)-Na_(0.826)Li_(0.06)Ni_(0.27)Mn_(0.5)Fe_(0.1)Ti_(0.07)O_(2) cathode delivers a high capacity of 139.4 mAh g^(-1) at 0.1 C and shows prolonged cycling life at high rates,with capacity retention of 81.6%at 5 C over 500 cycles.This work establishes a solid relationship between the thermodynamic structure evolution and electrochemistry of layered cathode materials,contributing to the development of long-life sodium-ion batteries.

Insights into layered-tunnel dynamic structural evolution based on local coordination chemistry regulation for high-energy-density and long-cycle-life sodium-ion oxide cathodes

The pursuit of high energy density while achieving long cycle life remains a challenge in developing transition metal(TM)oxide cathode materials for sodium-ion batteries(SIBs).Here,we present a concept of precisely manipulating structural evolution via local coordination chemistry regulation to design high-performance composite cathode materials.The controllable structural evolution process is realized by tuning magnesium content in Na0.6Mn1-xMgxO2,which is elucidated by a combination of experimental analysis and theoretical calculations.The substitution of Mg into Mn sites not only induces a unique structural evolu-tion from layered–tunnel structure to layered structure but also mitigates the Jahn–Teller distortion of Mn3+.Meanwhile,benefiting from the strong ionic inter-action between Mg2+and O2-,local environments around O2-coordinated with electrochemically inactive Mg2+are anchored in the TM layer,providing a pinning effect to stabilize crystal structure and smooth electrochemical profile.The layered–tunnel Na0.6Mn0.95Mg0.05O2 cathode material delivers 188.9 mAh g-1 of specific capacity,equivalent to 508.0 Wh kg-1 of energy density at 0.5C,and exhibits 71.3%of capacity retention after 1000 cycles at 5C as well as excellent compatibility with hard carbon anode.This work may provide new insights of manipulating structural evolution in composite cathode materials via local coordi-nation chemistry regulation and inspire more novel design of high-performance SIB cathode materials.

Engineering upconverting core–shell nano-probe for spectral responsive fluid velocimetry

Particle velocimetry based on the temporal feature of upconversion luminescent nanocrystals is a newly-raising fluid velocimetry.Exploiting the availability to low flow rate fluid and exempting redundance external calibration(achieving once calibration for all)are highly expected and challenging.Herein,an engineered core–shell nano-probe,NaYF4:Yb/Ho/Ce@NaGdF4,was proposed,in which the Ce3+ions were utilized to manipulate the upconversion dynamic of Ho3+.Through optimization,a superior sensitive against low-speed flow is achieved,and the external calibrations before each operation can be avoided.Application demonstrations were conducted on a fluid circulation system with controllable flow rate.The fluid velocity was monitored successfully,no matter it is permanent,or cyclically variating(imitating the in vivo arterial blood).Moreover,this velocimetric route is competent in spatial scanning for handling the spatially inhomogeneous velocity field.Such sensing nanomaterial and fluid velocimetric method exhibit promising application potential in human blood velocimetry,industrial control,or environmental monitoring.

Self-supported hard carbon anode from fungus-treated basswood towards sodium-ion batteries

Hard carbon derived from biomass is regarded as a promising anode material for sodium-ion batteries(SIBs)because of its low operating potential,high capacity,resource availability,and low cost.However,scientific and technological challenges still exist to prepare hard carbon with a high initial Coulombic efficiency(ICE),an excellent rate capability,and good cycling stability.In this work,we report a self-supported hard carbon electrode from fungus-pretreated basswood with an improved graphitization degree and a low tortuosity.Compared with the hard carbon derived from basswood,the hard carbon electrode from fungus-pretreated basswood has an improved rate capability of 242.3 mAh·g^(−1)at 200 mA·g^(−1)and cycling stability with 93.9%of its capacity retention after 200 cycles at 40 mA·g^(−1),as well as the increased ICE from 84.3%to 88.2%.Additionally,ex-situ X-ray diffraction indicates that Na+adsorption caused the sloping capacity,whereas Na+intercalation between interlayer spacing corresponded to the low potential plateau capacity.This work provides a new perspective for the preparation of high-performance hard carbon and gains the in-depth understanding of Na storage mechanism.

Air-stability of sodium-based layered-oxide cathode materials

Sodium-ion batteries have the potential to be an alternative to lithium-ion batteries especially for applications such as large-scale grid energy storage. The development of suitable cathode materials is crucial to the commercialization of sodium-ion batteries.Sodium-based layered-type transition metal oxides are promising candidates as cathode materials as they offer decent energy density and are easy to be synthesized. Unfortunately, most layered oxides suffer from poor air-stability, which greatly increases the cost of manufacturing and handling. The air-sensitivity severely limits the development and commercial application of sodium-ion batteries. A review that summarizes the latest understanding and solutions of air-sensitivity is desired. In this review,the background and fundamentals of sodium-based layered-type cathode materials are presented, followed by a discussion on the latest research on air-sensitivity of these materials. The mechanism is complex and involves multiple chemical and physical reactions. Various strategies are shown to alleviate some of the corresponding problems and promote the feasible application of sodium-ion batteries, followed by an outlook on current and future research directions of air-stable cathode materials. It is believed that this review will provide insights for researchers to develop practically relevant materials for sodium-ion batteries.

Understanding the structural evolution and Na^＋ kinetics in honeycomb-ordered O＇3-Na3Ni2SbO6 cathodes

The development of new sodium ion battery （SIB） cathodes with satisfactory performance requires an in-depth understanding of their structure-function relationships, to rationally design better electrode materials. In this work highly ordered, honeycomb-layered Na3Ni2SbO6 was prepared to elucidate the structural evolution and Na~ kinetics during electrochemical desodiation/sodiation processes. Structural analysis involving in situ synchrotron X-ray diffraction （XRD） experiments, electrochemical performance measurements, and electrochemical characterization （galvanostatic intermittent titration technique, GITT） methods were used to obtain new insights into the reaction mechanism controlling the （de）intercalation of sodium into the host NaB-xNi2SbO6 structure. Two phase transitions occur （initial O＇3 phase → intermediate P＇3 phase→final O1 phase） upon Na^＋ extraction; the partial irreversible O＇3-P＇3 phase transition is responsible for the insufficient cycling stability. The fast Na^＋ mobility （average 10^-12 cm^2·s^-1） in the interlayer, high equilibrium voltage （3.27 V）, and low voltage polarization （50 mV） establish the linkage between kinetic advantage and a good rate performance of the cathode. These new findings provide deep insight into the reaction mechanism operating in the honeycomb cathode; the present approach could be also extended to investigate other materials for SIBs.

新型有机硅基离子塑晶材料作为固态电解质用于锂离子电池（英文）

目的:合成新型的有机硅基离子塑晶材料[DTMA][TFSI],测试材料的物理和电化学性能,研究其掺杂改性并作为固态电解质用于锂离子电池。创新点:1.合成新型的有机硅基离子型塑晶材料;2.将三元复合塑晶材料作为固态电解质在室温下用于锂离子电池。方法:1.通过热性能分析,得到材料的塑晶温度区间和融化熵值(图1和表1);2.通过电导率测试,确定塑晶掺杂对导电性能的影响(图2);3.通过对扣式电池的充放电性能、倍率性能、循环性能以及阻抗的测试(图4~7),得到塑晶复合物作为固态电解质的电化学性能以及电池循环的稳定性和可逆性。结论:1.合成新型有机硅基离子塑晶材料[DTMA][TFSI],塑晶温度区间为–26°C到54°C;2.在纯塑晶IPC中添加10% LiODFB和10%PC,得到复合物的电导率为1×10^(-4) S/cm,提高塑晶作为固态电解质在室温下应用的可行性;3.将复合物用于LiFePO_4/Li半电池测试,在C/20倍率下,电池的放电比容量为144 mA·h/g,库伦效率为99%。在50次循环后,容量保持率为94%;4.测试结果表明,新型有机硅基离子塑晶的复合物可作为固态电解质材料应用于锂离子电池,以及更高能量密度的锂-硫和锂-空电池。