Electronic Transport in Lithiated Iron and Bismuth Fluoride

Abstract

Metal networks are formed during the lithiation of metal fluorides. Previous reports indicate that these networks are bi-continuous with the possibility to support electronic transport, though no quantitative analysis has been performed. In this study, thin films of FeF 2 and BiF 3 were chemically lithiated using n-butyllithium to form these metal networks. Direct current (DC) polarization and electrochemical impedance spectroscopy (EIS) were utilized to find electronic conductivity and results were compared to their pure metals. Results indicate films to have higher than expected conductivity value which indicates that these metal networks support electronic transport during lithiation. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0621501jes] All rights reserved. Lithium-ion batteries are the ubiquitous energy storage device for portable electronics. Historically, there has been a continuous quest for higher energy density chemistries in order to reduce the weight or volume in new innovative devices. Lithium conversion compounds are one of the promising alternatives for battery positive electrodes.1 The advantage is their ability to accommodate more than one lithium/electron per transition metal to achieve higher capacities than traditional intercalation compounds. Transition metal fluoride conversion materials have been a research focus because their highly ionic bonds allow reduction potentials approximately 1 V higher than the chalcogenides.2-5 As such, high capacity, low cost metal fluorides such as FeF 2 , FeF 3 and CuF 2 are of interest. FeF 2 has been extensively investigated as a potential electrode material due to its potential low cost and rutile structure which is common among the first row metal fluorides.6-8 The latter aspect makes it an excellent model material for fundamental studies. FeF 2 exhibits a single three phase reaction, FeF 2 + 2Li + + 2e − → Fe + 2 LiF, exhibiting a theoretical capacity of 571 mAh/g. During lithiation, most conversion materials of fluoride and dichacodenide chemistries form a bi-continuous network of nano metal and lithium salt (i.e. LiF, Li 2 O, etc.). This has been shown in a number of high resolution transmission electron microscopy studies and supported in part by molecular dynamic modeling.9,10 Although such networks visually appear to be electronic percolating (Figure 1) and may be the pathway for electron transport to the reaction front, there has been no data to suggest what order of magnitude the conductivity of this percolated network is. The goal of the effort presented herein is to establish quantitatively the electronic c...

Compelling Rejuvenated Catalytic Performance in Metallic Glasses

“…On the other hand, the grain size has a dramatic increase by at least an order of magnitude after fully crystallized (Table S2, Supporting Information), leading to an apparent decrease in grain boundary per unit area, which apparently reduces barriers and facilitates electrons transporting in the grains. In addition, as demonstrated in multiphase galvanic cells and conductors, [50][51][52][53] it is highly possible for electrons transferring across the grains (bottom right in Figure 5), which are the dominant electron donors, although they need to overcome grain boundary barrier (higher potential) to achieve further transportation. For Fe-A900 ribbons, a high catalytic efficiency is attributed to not only a large grain size with less grain boundary, but also a homogenous distribution of two phases (α-Fe (Si) and Fe 2 B), thereby facilitating electron transportation across the grain boundaries.…”

Cycling Fading Mechanism for a Bismuth Fluoride Electrode in a Lithium‐Ion Battery

“…[24][25][26] The discharge and charge reactions of BiF 3 are described as follows. [6][7][8][9][10][11][12] Discharge reaction :…”

“…With improvements in device performance, a high capacity is required for these batteries. Metal fluoride, metal sulfide, and metal oxide are expected to be next‐generation electrode materials because of their high capacity . The capacity of conventional cathodes such as LiCoO 2 and LiMn 2 O 4 is lower than that of conventional anodes such as carbon; therefore, especially high capacity cathode materials are required.…”

“…Metal fluoride, metal sulfide, and metal oxide are expected to be next-generation electrode materials because of their high capacity. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The capacity of conventional cathodes such as LiCoO 2 and LiMn 2 O 4 is lower than that of conventional anodes such as carbon [17][18][19] ; therefore, especially high capacity cathode materials are required. In vew of its reaction potential, metal fluoride is expected for the cathode.…”

“…The conversion-type reaction mechanism for metal fluoride is expressed as follows. [1,2,[6][7][8][9][10][11][12] MF m þ nLi þ þ ne À $ M þ mLi n=m F ðM : metalÞ BiF 3 is a promising candidate for a cathode material because of its high theoretical capacity (302 mAh g -1 ). However, its discharge-charge capacities are still low because of its low electronic conductivity.…”