Electrochemical Properties of Si‐Ge Heterostructures as an Anode Material for Lithium Ion Batteries

Si‐Ge composites have recently been explored as an anode material for lithium‐ion batteries due to their stable cycle performance and excellent rate capability. Although previous reports show the benefits of Si‐Ge composites on electrochemical performance, the specific mechanism and structural effects have been overlooked. Here, the structural effect of Si‐Ge heterogeneous nanostructures on both mechanics and kinetics is systematically studied through theoretical analysis and detailed experimental results. Si‐Ge and Ge‐Si core–shell nanowires are employed for this study. The Si‐Ge core–shell nanowires show a much improved electrochemical performance, especially cycle performance and rate capability, when compared to those of the Ge‐Si core–shell nanowires electrode. On the basis of the detailed experimental results and associated theoretical analysis, its is demonstrated that the strain distribution and Li diffusivity and/or diffusion path are significantly affected by the Si‐Ge heterostructure, which induce different mechanics and kinetics associated with lithium.     

磷酸铁锂电池在通信行业的应用研究

随着新技术、新材料的应用,生产工艺的日趋成熟,新型磷酸铁锂蓄电池在通信行业的应用也越来越受到人们的关注。文中在研究新型磷酸铁锂电池工作原理及产品性能的基础上,分析了磷酸铁锂电池在通信行业应用的可行性及系统工作方式,阐述了当前磷酸铁锂电池在应用中存在的问题,并介绍了其适用的场景,为今后通信行业后备式蓄电池的应用提供了新思路。     

Polyanion Sodium Vanadium Phosphate for Next Generation of Sodium‐Ion Batteries—A Review

Polyanion‐type sodium (Na) vanadium phosphate in the form of Na₃V₂(PO₄)₃ has demonstrated reasonably high capacity, good rate capability, and excellent cyclability. Two of three Na ions per formula can be deintercalated at a potential 3.4 V versus Na⁺/Na with oxidation of V^3+/4+. In the reversible process, two Na ions intercalate back resulting in a discharge capacity of 117.6 mAh g^?1. Further intercalation is possible but at a low potential of 1.4 V versus Na⁺/Na accompanied by vanadium reduction V^3+/2+, leading to a capacity of 60 mAh g^?1. Due to its marvelous electrochemical performance, it has attracted a lot of attention since its discovery in the 1990s. To develop truly useable polyanion‐type vanadium phosphate, better understanding of its crystal configuration, sodium ions' transportation, and electronic structure is essential. Therefore, this review only focuses on the inside of crystal configuration and electronic structure of polyanion‐type vanadium phosphate, Na₃V₂(PO₄)₃, since there are a few good reviews on various processing technologies.     

N‐Doped Graphene‐SnO2 Sandwich Paper for High‐Performance Lithium‐Ion Batteries

A new facile route to fabricate N‐doped graphene‐SnO₂ sandwich papers is developed. The 7,7,8,8‐tetracyanoquinodimethane anion (TCNQ^?) plays a key role for the formation of such structures as it acts as both the nitrogen source and complexing agent. If used in lithium‐ion batteries (LIBs), the material exhibits a large capacity, high rate capability, and excellent cycling stability. The superior electrochemical performance of this novel material is the result from its unique features: excellent electronic conductivity related to the sandwich structure, short transportation length for both lithium ions and electrons, and elastomeric space to accommodate volume changes upon Li insertion/extraction.     

高锂含量碱金属铌酸盐的结构与性能研究

采用传统固相法陶瓷制备工艺制得高锂铌酸基无铅压电陶瓷体系xLiNbO3-(1-x)(Na0.5K0.5)NbO3(简写为xLN-(1-x)NKN,其中x=0.146,0.236,0.292,0.348,0.361,0.382,0.438,0.472,0.500,0.528,0.618),研究了该体系的晶相结构,断面形貌及电学性能随x的变化。研究表明,随x的增加,样品主晶相有一个四方钙钛矿到四方钨青铜结构再到LiNbO3三方结构的过程;压电常数d33随着x的增加而减小,但在x=0.236~0.438时保持相对稳定,约为75~80 pC/N;当x=0.5时,居里温度TC为537℃,此系列陶瓷适用于高温环境的压电陶瓷。     

Reversible Sodium and Lithium Insertion in Iron Fluoride Perovskites

Li‐ion batteries are omnipresent in consumer electronics and are seen as the most promising technology for electric vehicles. Na‐ion batteries have emerged as viable and cheaper alternatives for stationary applications where Li‐ion batteries are too expensive. However, the larger size of sodium ion compared to lithium makes traditional positive materials for Li‐ion batteries not always suitable for the reversible insertion of sodium ions. Herein, a microwave‐assisted solution synthesis of NaFeF₃ perovskite nanoparticles from presynthesized rutile FeF₂ colloidal particles, sodium ethoxide, and ammonium fluoride is presented. This NaFeF₃ material shows a reversible electrochemical activity of 1Na or 1Li per iron with low polarization and excellent capacity retention after 100 cycles. The unexpected reversible insertion of both sodium and lithium ions, herein studied through ex situ and operando X‐ray diffraction measurements, is attributed to a kinetic stabilization of corner‐shared cubic A_xFeF₃ (A = Li, Na) frameworks along the cycles involving low volume change without high thermodynamic cost as supported by a polymorphism theoretical analysis.     

磷酸铁锂电池及其在通信行业中的应用

通过对锂电池和传统阀控式密封铅酸蓄电池的分析,分别指出了2种电池的优缺点,并给出了锂电池在通信行业中的应用案例和应用前景。     

Evaluation of Half‐Heusler Compounds as Thermoelectric Materials Based on the Calculated Electrical Transport Properties

A theoretical evaluation of the thermoelectric‐related electrical transport properties of 36 half‐Heusler (HH) compounds, selected from more than 100 HHs, is carried out in this paper. The electronic structures and electrical transport properties are studied using ab initio calculations and the Boltzmann transport equation under the constant relaxation time approximation for charge carriers. The electronic structure results predict the band gaps of these HH compounds, and show that many HHs are narrow‐band‐gap semiconductors and, therefore, are potentially good thermoelectric materials. The dependence of Seebeck coefficient, electrical conductivity, and power factor on the Fermi level is investigated. Maximum power factors and the corresponding optimal p‐ or n‐type doping levels, related to the thermoelectric performance of materials, are calculated for all HH compounds investigated, which certainly provide guidance to experimental work. The estimated optimal doping levels and Seebeck coefficients show reasonable agreement with the measured results for some HH systems. A few HHs are recommended to be potentially good thermoelectric materials based on our calculations.     

铌锑酸镁陶瓷的烧结和微波介电性能

用固相反应法制备了一系列铌锑酸镁(Sb含量x≤2)陶瓷,研究了该陶瓷的烧结性能、物相结构和微波介电性能。结果表明,当x≤1.6时,铌锑酸镁形成了连续固溶体,少量Sb5+对Nb5+的取代(0.4≤x≤0.8),使得陶瓷最佳烧结温度从1400℃降到1300℃,而材料εr和Q·f值没有降低。1300℃,5h烧结的铌锑酸镁陶瓷具有优异的微波介电性能:εr为11.61,Q·f为169820GHz,τf为–54.4×10–6℃–1。     

The Effects of Crystallinity on Charge Transport and the Structure of Sequentially Processed F4TCNQ‐Doped Conjugated Polymer Films

The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F₄TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F₄TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm² V^?1 s^?1 in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.     

Impact of Fluorine-Based Lithium Salts on SEI for All-Solid-State PEO-Based Lithium Metal Batteries

LiF-rich solid-electrolyte-interphase (SEI) can suppress the formation of lithium dendrites and promote the reversible operation of lithium metal batteries. Regulating the composition of naturally formed SEI is an effective strategy, while understanding the impact and role of fluorine (F)-based Li-salts on the SEI characteristics is unavailable. Herein, LiFSI, LiTFSI, and LiPFSI are selected to prepare solid polymer electrolytes (SPEs) with poly(ethylene oxide) and polyimide, investigating the effects of molecular size, F contents and chemical structures (F-connecting bonds) of Li-salts and revealing the formation of LiF in the SEI. It is shown that the F-connecting bond is more significant than the molecular size and F element contents, and thus the performances of cells using LiPFSI are slightly better than LiTFSI and much better than LiFSI. The SPE containing LiPFSI can generate a high amount of LiF, and SPEs containing LiPFSI and LiTFSI can generate Li₃N, while there is no Li₃N production in the SEI for the SPE containing LiFSI. The preferential breakage bonds in LiPFSI are related to its position to Li anode, where Li-metal as the anode is important in forming LiF, and consequently the LiPFSI reduction mechanism is proposed. This study will boost other energy storage systems beyond Li-ion chemistries.     

Design Strategies of 3D Carbon-Based Electrodes for Charge/Ion Transport in Lithium Ion Battery and Sodium Ion Battery

Advanced 3D carbon-based electrodes have the potential to significantly enhance the energy-power density of lithium ion batteries and sodium ion batteries, due to their continuous conductive networks, proper porosity distribution, and integrated stable structure. However, it still remains a fundamental scientific challenge to accurately understand the charge/ion transport in 3D carbon-based electrodes. In this review, the operating mechanism of charge/ion transport in 3D carbon-based electrodes are comprehended by introducing a useful architectural analogy to provide a physical insight. In order to better understand the relationship between 3D carbon-based electrode structure and electrode process characteristics, the main design strategies of 3D carbonbased electrodes according to the specific characteristic of pore tortuosity is proposed. Through analysis of 3D carbon electrode architectural models, several key scientific issues and related characterization technologies that are beneficial to improving the charge/ion transport efficiency are also raised. The kinetics difference of ionic transport between Li⁺ and Na⁺ ions is also taken into account. Furthermore, the critical parameters of porous structure including porosity and tortuosity to investigate the parameter-structure-performance relationships of 3D carbon-based architecture electrodes are highlighted, which in turn would guide more rational battery design in tradeoff between the high capacity and fast transport.     

磷酸铁锂电池在宽带大提速中的应用

宽带大提速是中国电信实现企业转型和"三网合一"战略的重要举措,随着宽带大提速业务的不断推进,近几年来以FTTN为接入方式的室外机柜大规模建设。文章主要介绍了磷酸铁锂电池在室外机柜中使用的优良特性及其应用前景,并通过实验证明了磷酸铁锂电池能够满足通信后备电源保障需求,作为新型节能环保电池,将逐步代替传统的铅酸蓄电池。     

Cu掺杂对ZnO氧化物电子结构与电输运性能的影响

采用平面波超软赝势密度泛函理论计算的方法研究了p型Cu掺杂的纤锌矿结构氧化物ZnO的电子结构,在此基础上分析了其电输运性能。计算结果表明,Cu掺杂ZnO氧化物具有0.6eV的直接带隙,且为p型半导体,在导带和价带中都出现了由Cu电子能级形成的能带,体系费米能级附近的能带主要由Cup态、Cud态和Op态电子构成,且他们之间存在着强相互作用。电输运性能分析结果表明,Cu掺杂的ZnO氧化物价带中的载流子有效质量较大,导带中的载流子有效质量较小;其载流子输运主要由Cup态、Cud态、Op态电子完成,且需要载流子（空穴和电子）跃迁的能隙宽度较未掺杂的ZnO氧化物减小。     

Kinetic Monte Carlo Simulations of Anisotropic Lithium Intercalation into LixFePO4 Electrode Nanocrystals

The kinetic anisotropy of lithium ion adsorption and lithium absorption for Li_xFePO₄ olivine nanocrystals is simulated and reported. The kinetics depend on the orientation of the electrolyte/Li_xFePO₄ interface with respect to the far‐field ionic flux. As a consequence of these kinetics and a Li miscibility gap in Li_xFePO₄, the particle geometry and orientation also have an effect on the morphology of the two‐phase evolution. These processes accompany the charge and discharge behavior in battery microstructures and a direct influence on battery behavior is suggested. A kinetic Monte Carlo (KMC) algorithm based on a cathode particle rigid lattice is used to simulate the kinetics in this system. In these simulations the adsorption kinetics of the electrolyte/electrode interface are treated by coupling the normal flux outside the particle from a continuum numerical simulation of Li‐ion diffusion in the electrolyte to the atomistic KMC model within the particle. The interfacial reaction depends on local concentration and the potential drop at the interface via the Butler–Volmer (B–V) relation. The atomic potentials for the KMC simulation are derived from empirical solubility limits (as determined by OCV measurements). The main results show that the galvanostatic lithium‐uptake/cell‐voltage has three regimes: 1) a decreasing cell potential for Li‐insertion into a Li‐poor phase; 2) a nearly constant potential after the nucleation of a Li‐rich phase Li_(1‐β)FePO₄; 3) a decreasing cell potential after the Li‐poor phase has been evolved into a Li‐rich phase. The behavior in the second regime is sensitive to crystallographic orientation.