Transition metal carbonate anodes for Li-ion battery: fundamentals,synthesis and modification

Even though transition metal carbonates(TMCs, TM = Fe, Mn, Co, Ni etc.), show high theoretical capacities, rich reserves and environmental friendliness as anodes for lithium-ion batteries(LIBs), they suffer from sluggish electronic/ionic conductivities and huge volume variation, which severely deteriorate the rate capacities and cycling performances. Understanding the intrinsic reaction mechanism and further developing ideal TMC-based anode with high specific capacity, excellent rate capabilities, and longterm cycling stability are critical for the practical application of TMCs. In this review, we firstly focus on the fundamental electrochemical energy-storage mechanisms of TMCs, in terms of conversionreaction process, pseudocapacitance-type charge storage, valence change for charge storage and catalytic conversion mechanisms. Based on the reaction mechanisms, various modification strategies to improve the electrochemical performance of TMCs are summarized, covering:(i) micro-nano structural engineering, in which the influence factors on the morphology are discussed, and multiple architectures are listed;(ii) elemental doping, in which the intrinsic mechanisms of metal/nonmetal elements doping on the electrochemical performance are deeply explored;(iii) multifunctional compositing strategies, in which the specific affections on structure, electronic conductivity and chemo-mechanical stability are summarized.Finally, the key challenges and opportunities to develop high-performance TMCs are discussed and some solutions are also proposed. This timely review sheds light on the path towards achieving cost-effective and safe LIBs with high energy density and long cycling life using TMCs-based anode materials.

Dual-salt assisted synergistic synthesis of Prussian white cathode towards high-capacity and long cycle potassium ion battery

Prussian blue analogues(PBAs) are considered as superior cathode materials for potassium-ion batteries(PIBs) because of their three-dimensional open framework structure,high stability,and low cost.However,the intrinsic lattice defects and low potassium content typically results in poor rate and cycling performance,thus limited their practical applications.In this work,high-quality K1.64FeFe(CN)6(PW-HQ)material with less crystalline water(6.21%) and high potassium content(1.64 mol^(-1)) was successfully synthesized by a novel coprecipitation method with potassium citrate(K-CA) and potassium chloride(KCl) addition.Specifically,the electrode delivers a reversible capacity of 113.1 mA h g^(-1)at the current rate of 50 mA g^(-1)with~100% coulombic efficiency.Besides,the electrode retained 90% reversible capacity at 500 mA g^(-1)current density after 1000 cycles,indicating only 0.01% capacity decay per cycle.Moreover,we have revealed that the introduction of K-CA controlled the chelating rate of Fe(Ⅱ) and the addition of KCl increased the K+content,hence improving the capacity and stability of the asprepared electrodes.Structural evolution and potassium storage mechanism were further investigated by detailed ex-situ X-ray diffraction and in-situ Raman measurements,which demonstrated reversible potassiation/depotassiation behavior and negligible volume change during the electrochemical process.In general,this work provides an efficient strategy to eliminate water contents in Prussian blue cathode and improve its electrochemical performance,which plays a key role in promoting the industrialization of potassium ion batteries.

Mo_(3)Nb_(14)O_(44): A New Li^(+) Container for High-Performance Electrochemical Energy Storage

Intercalating Nb-based oxides are promising anode compounds for lithiumion batteries since they have both good safety and large capacities.However,the research in this field is still limited.Here,Mo_(3)Nb_(14)O_(44)with a large theoretical capacity of 398 mAh g^(–1)(Mo^(64)←→Mo^(4+)and Nb^(5+)←→Nb^(3+))is exploited as a new Nb-based oxide anode compound,and Mo_(3)Nb_(14)O_(44)micron-sized particles(Mo_(3)Nb_(14)O_(44)-M)and Mo3Nb14O44 nanowires(Mo_(3)Nb_(14)O_(44)-N)are demonstrated.Mo3Nb14O44 owns a tetragonal shear ReO_(3)crystal structure(high-symmetric 14 space group)constructed by 4×4×∞(Mo,Nb)O_(6)octahedron blocks linked by Mo O4 tetrahedra,forming an A–B–A layered structure with a large interlayer spacing.This interesting structure allows fast Li+storage within the interlayers and significant intercalation-pseudocapacitive behavior,leading to the high rate performance of Mo_(3)Nb_(14)O_(44)-M/Mo_(3)Nb_(14)O_(44)-N with a large 10 C versus 0.1 C capacity retention percentage of 38.1/54.2%.Mo_(3)Nb_(14)O_(44)-M/Mo_(3)Nb_(14)O_(44)-N further exhibits a safe operating potential of 1.72/1.68 V,large reversible capacity of 323/321 m Ah g^(–1)at 0.1 C,high initial coulombic efficiency of 92.2/90.0%,and good cycling stability with 71.8/75.8%capacity retention after 1000 cycles at10 C.Additionally,a Li Mn_(2)O_(4)/Mo_(3)Nb_(14)O_(44)-N full cell also performs well.Therefore,Mo_(3)Nb_(14)O_(44)holds great promise as a fast-charging,safe,largecapacity,high-efficient,and long-life Li^(+)anode container.

Accurate quantification of TiO_(2)(B)'s phase purity via Raman spectroscopy

Bronze phase titanium dioxide(TiO_(2)(B))could be a promising high-power anode for lithium ion battery.However,TiO_(2)(B)is a metastable material,so the as-synthesized samples are inevitably accompanied by the existence of anatase phases.It has been found that the TiO_(2)(B)'s purity is positively correlated with its electrochemical performance.Herein,we have established an accurate quantification of the TiO_(2)(B)/anatase ratio,by figuring out the function between the purity of TiO_(2)(B)phase in the high purity range and its Raman spectra features in combination of the calibration by the synchrotron radiation X-ray diffraction(XRD).Compared with the time-consuming electrochemical method,the rapid,sensitive and non-destructive features of Raman spectroscopy have made it a promising candidate for determining the purity of TiO_(2)(B).Further,the correlations developed in this work should be instructive in synthesizing pure TiO_(2)(B)and furthermore optimizing its electrochemical charge storage properties.

圆台-线栅型水平极化电磁脉冲模拟器的仿真分析

以双锥–线栅型水平极化天线为原型,使用不同大小的圆柱体替换双锥的锥尖,设计出圆台–线栅型水平极化天线,并利用CST MWS电磁仿真软件计算了当激励源为双指数波时的两种天线结构的输出波形。将两种天线模型的输出波形分别与高空核电磁脉冲标准波形进行对比,结果显示:圆台–线栅型水平极化天线模型的仿真结果在主要参数上更贴近高空核电磁脉冲标准波形,其中,输出波形的场强峰值提升了2.47%,上升沿(脉冲从峰值的10%到峰值的90%的时间宽度)误差由20.40%减小为0.04%,半高宽误差由8.26%减小为1.46%。