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Browsing by Author "Wang, D"

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Ab initio thermodynamic optimization of Ni-rich Ni–Co–Mn oxide cathode coatings
(Elsevier, 2020-02-29) Liu, B; Liu, JH; Yang, J; Wang, D; Ye, CC; Wang, DY; Avdeev, M; Shi, S; Yang, JH; Zhang, WQ
The effectiveness of surface coatings in improving the stability and cycling performance of cathodes has been demonstrated since they are first proposed in the 1990's. However, the progress since then is made mostly using the trial-and-error method. Herein, an automated electrochemical-chemical stability design scheme based on first-principles thermodynamics calculations of reaction models is presented to optimize coatings for Ni-rich nickel–cobalt–manganese oxide (NCM) cathodes. Given that the coating must possess a wider electrochemical window than the cathode without the occurrence of Li-ion redistribution at the cathode/coating interface, the reaction energies of both lithium insertion/extraction and decomposition process associated with the coating are used as one of the two screening criteria. As the coating is also required to be chemically stable in Li residues and hydrofluoric-acid containing liquid environment, the positive reaction energy achieved by adjusting molar ratio of the components is used as another criterion. Using these two screening criteria, we demonstrate that lithium-containing metal phosphates, rather than previously suggested Li-containing metal oxides, are the optimal coatings for Ni-rich NCM cathodes, which is confirmed experimentally. The proposed approach is general and can be used to find optimal coating materials for any other cathodes. © 2020 Elsevier B.V.
CAVD, towards better characterization of void space for ionic transport analysis
(Springer Nature, 2020-05-22) He, B; Ye, AJ; Chi, ST; Mi, PH; Ran, YB; Zhang, LW; Zou, XX; Pu, BW; Zhao, Q; Zou, Z; Wang, D; Zhang, WQ; Zhao, JT; Avdeev, M; Shi, S
Geometric crystal structure analysis using three-dimensional Voronoi tessellation provides intuitive insights into the ionic transport behavior of metal-ion electrode materials or solid electrolytes by mapping the void space in a framework onto a network. The existing tools typically consider only the local voids by mapping them with Voronoi polyhedra vertices and then define the mobile ions pathways using the Voronoi edges connecting these vertices. We show that in some structures mobile ions are located on Voronoi polyhedra faces and thus cannot be located by a standard approach. To address this deficiency, we extend the method to include Voronoi faces in the constructed network. This method has been implemented in the CAVD python package. Its effectiveness is demonstrated by 99% recovery rate for the lattice sites of mobile ions in 6,955 Li-, Na-, Mg- and Al-containing ionic compounds extracted from the Inorganic Crystal Structure Database. In addition, various quantitative descriptors of the network can be used to identify and rank the materials and further used in materials databases for machine learning. © 2020, The Author(s)
Correlated migration invokes higher Na+‐ion conductivity in NaSICON‐type solid electrolytes
(Wiley, 2019-10-01) Zhang, ZZ; Zou, Z; Kaup, K; Xiao, RJ; Shi, S; Avdeev, M; Hu, YS; Wang, D; He, B; Li, H; Huang, XY; Nazar, LF; Chen, LQ
Na super ion conductor (NaSICON), Na1+nZr2SinP3–nO12 is considered one of the most promising solid electrolytes; however, the underlying mechanism governing ion transport is still not fully understood. Here, the existence of a previously unreported Na5 site in monoclinic Na3Zr2Si2PO12 is unveiled. It is revealed that Na+‐ions tend to migrate in a correlated mechanism, as suggested by a much lower energy barrier compared to the single‐ion migration barrier. Furthermore, computational work uncovers the origin of the improved conductivity in the NaSICON structure, that is, the enhanced correlated migration induced by increasing the Na+‐ion concentration. Systematic impedance studies on doped NaSICON materials bolster this finding. Significant improvements in both the bulk and total ion conductivity (e.g., σbulk = 4.0 mS cm−1, σtotal = 2.4 mS cm−1 at 25 °C) are achieved by increasing the Na content from 3.0 to 3.30–3.55 mol formula unit−1. These improvements stem from the enhanced correlated migration invoked by the increased Coulombic repulsions when more Na+‐ions populate the structure rather than solely from the increased mobile ion carrier concentration. The studies also verify a strategy to enhance ion conductivity, namely, pushing the cations into high energy sites to therefore lower the energy barrier for cation migration. © 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
Crafting the magnonic and spintronic response of BiFeO3 films by epitaxial strain
(Nature Publishing Group, 2013-04-28) Sando, D; Agbelele, A; Rahmedov, D; Liu, J; Rovillain, P; Toulouse, C; Infante, IC; Pyatakov, AP; Fusil, S; Jacquet, E; Carrétéro, C; Deranlot, C; Lisenkov, S; Wang, D; Le Breton, JM; Cazayous, M; Sacuto, A; Juraszek, J; Zvezdin, AK; Bellaiche, L; Dkhil, B; Barthélémy, A; Bibes, M
Multiferroics are compounds that show ferroelectricity and magnetism. BiFeO3, by far the most studied, has outstanding ferroelectric properties, a cycloidal magnetic order in the bulk, and many unexpected virtues such as conductive domain walls or a low bandgap of interest for photovoltaics. Although this flurry of properties makes BiFeO3 a paradigmatic multifunctional material, most are related to its ferroelectric character, and its other ferroic property—antiferromagnetism—has not been investigated extensively, especially in thin films. Here we bring insight into the rich spin physics of BiFeO3 in a detailed study of the static and dynamic magnetic response of strain-engineered films. Using Mössbauer and Raman spectroscopies combined with Landau–Ginzburg theory and effective Hamiltonian calculations, we show that the bulk-like cycloidal spin modulation that exists at low compressive strain is driven towards pseudo-collinear antiferromagnetism at high strain, both tensile and compressive. For moderate tensile strain we also predict and observe indications of a new cycloid. Accordingly, we find that the magnonic response is entirely modified, with low-energy magnon modes being suppressed as strain increases. Finally, we reveal that strain progressively drives the average spin angle from in-plane to out-of-plane, a property we use to tune the exchange bias and giant-magnetoresistive response of spin valves. © 2013, Nature Publishing Group.
A customized strategy to design intercalation-type Li-free cathodes for all-solid-state batteries
(Oxford University Press, 2023-01-10) Wang, D; Yu, J; Yin, X; Shao, S; Li, Q; Wang, YC; Avdeev, M; Chen, LQ; Shi, SQ
Pairing Li-free transition-metal-based cathodes (MX) with Li-metal anodes is an emerging trend to overcome the energy-density limitation of current rechargeable Li-ion technology. However, the development of practical Li-free MX cathodes is plagued by the existing notion of low voltage due to the long-term overlooked voltage-tuning/phase-stability competition. Here, we propose a p-type alloying strategy involving three voltage/phase-evolution stages, of which each of the varying trends are quantitated by two improved ligand-field descriptors to balance the above contradiction. Following this, an intercalation-type 2H-V1.75Cr0.25S4 cathode tuned from layered MX2 family is successfully designed, which possesses an energy density of 554.3 Wh kg−1 at the electrode level accompanied by interfacial compatibility with sulfide solid-state electrolyte. The proposal of this class of materials is expected to break free from scarce or high-cost transition-metal (e.g. Co and Ni) reliance in current commercial cathodes. Our experiments further confirm the voltage and energy-density gains of 2H-V1.75Cr0.25S4. This strategy is not limited to specific Li-free cathodes and offers a solution to achieve high voltage and phase stability simultaneously. TheAuthor(s) 2023. Published byOxfordUniversity Press on behalf of China Science Publishing&Media Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License
A database of ionic transport characteristics for over 29 000 inorganic compounds
(Wiley, 2020-06-25) Zhang, LW; He, B; Zhao, Q; Zou, ZY; Chi, ST; Mi, PH; Ye, AJ; Li, YJ; Wang, D; Avdeev, M; Adams, S; Shi, S
Transport characteristics of ionic conductors play a key role in the performance of electrochemical devices such as solid-state batteries, solid-oxide fuel cells, and sensors. Despite the significance of the transport characteristics, they have been experimentally measured only for a very small fraction of all inorganic compounds, which limits the technological progress. To address this deficiency, a database containing crystal structure information, ion migration channel connectivity information, and 3D channel maps for over 29 000 inorganic compounds is presented. The database currently contains ionic transport characteristics for all potential cation and anion conductors, including Li+, Na+, K+, Ag+, Cu(2)+, Mg2+, Zn2+, Ca2+, Al3+, F−, and O2−, and this number is growing steadily. The methods used to characterize materials in the database are a combination of structure geometric analysis based on Voronoi decomposition and bond valence site energy (BVSE) calculations, which yield interstitial sites, transport channels, and BVSE activation energy. The computational details are illustrated on several typical compounds. This database is created to accelerate the screening of fast ionic conductors and to accumulate descriptors for machine learning, providing a foundation for large-scale research on ion migration in inorganic materials.© 1999-2021 John Wiley & Sons, Inc.
Efficient potential-tuning strategy through p-type doping for designing cathodes with ultrahigh energy density
(Oxford Academic, 2020-07-27) Wang, ZQ; Wang, D; Zou, Z; Song, T; Ni, DX; Li, ZZ; Shao, XC; Yin, WJ; Wang, YC; Luo, WW; Wu, MS; Avdeev, M; Xu, B; Shi, S; Ouyang, CY; Chen, LQ
Designing new cathodes with high capacity and moderate potential is the key to breaking the energy density ceiling imposed by current intercalation chemistry on rechargeable batteries. The carbonaceous materials provide high capacities but their low potentials limit their application to anodes. Here, we show that Fermi level tuning by p-type doping can be an effective way of dramatically raising electrode potential. We demonstrate that Li(Na)BCF2/Li(Na)B2C2F2 exhibit such change in Fermi level, enabling them to accommodate Li+(Na+) with capacities of 290–400 (250–320) mAh g−1 at potentials of 3.4–3.7 (2.7–2.9) V, delivering ultrahigh energy densities of 1000–1500 Wh kg−1. This work presents a new strategy in tuning electrode potential through electronic band structure engineering. © The Author(s) 2020. Creative Commons CC BY Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.
A high-temperature performing and near-zero energy loss lead-free ceramic capacitor
(Royal Society of Chemistry, 2023-08-21) Li, D; Xu, D; Zhao, W; Avdeev, M; Jing, H; Guo, Y; Zhou, T; Liu, W; Wang, D; Zhou, D
A pivotal obstacle of obtaining dielectric ceramics with large recoverable energy density (Wrec) and ultrahigh energy efficiency (η) desperately needs to be overcome for the development of advanced energy storage devices for high pulsed power systems, especially via an environment-friendly lead-free method. Here we report a series of lead-free dielectric bulk ceramics for high-temperature energy storage capacitors with near-zero energy loss. Confirmed by aberration-corrected scanning transmission electron microscopy and phase-field simulation, a judiciously designed heterostructure in which rhombohedral and tetragonal polar nanoregions are embedded in a cubic paraelectric matrix was constructed. The combination of the increased breakdown strength and the minimized polarization hysteresis, respectively, based on the heterostructure design and repeated rolling process, contributes to a large Wrec of 10.28 J cm−3 and a record-high η of 97.11%, superior to the reported lead-free bulk ceramics. Based on such structure-induced advantages, the wide-temperature stability (25–200 °C) and high performance (Wrec ∼ 6.35 ± 9.1% J cm−3, η ∼ 94.82% ± 3.4%) of the dielectric ceramics broaden their application in high temperature energy storage systems. This work conspicuously contributes to the development of the next generation high-temperature capacitors and suggests a new paradigm that may stimulate the development of higher-performance energy storage dielectrics. Facebook Twitter LinkedIn YouTube© Royal Society of Chemistry 2024
High-throughput computational screening of Li-containing fluorides for battery cathode coatings
(American Chemical Society, 2020-12-16) Liu, B; Wang, D; Avdeev, M; Shi, S; Yang, J; Zhang, WQ
Cathode degradation is a key factor that limits the cycling stability and rate capability of Li-ion batteries. Coating the surface of cathode particles with metal oxides or fluorides has been reported to suppress this degradation. However, poor Li-ion conductivity of metal oxide and fluoride coatings typically decreases the overall ionic conductivity. In addition, side (electro)chemical reactions at the coating/cathode interface and coating/hydrofluoric acid liquid environment also limit the performance of Li-ion batteries. Identification of stable coating materials with high Li-ion conductivity, which is typically done via a trial-and-error approach, remains a challenge. In this work, we perform high-throughput computational screening of ternary Li-containing fluorides for application as cathode coatings for Li-ion batteries, focusing on their phase stability, electrochemical stability, chemical stability, and Li-ion conductivity. Using the tiered screening approach, we identify 10 promising coating candidates from all the 920 Li-containing fluorides listed in the Materials Project database, including the two experimentally studied Li2ZrF6 and Li2TiF6 compounds. The identified cathode coatings are expected to exhibit optimal battery cycling and rate performance. In particular, Li2MF6 (M = Si, Ge, Zr, Ti) compounds offer the best combination of electrochemical and chemical stability and ionic conductivity, surpassing the performance of common coatings such as oxides and binary fluorides. © 2019 American Chemical Society
High-throughput screening platform for solid electrolytes combining hierarchical ion-transport prediction algorithms
(Springer Nature, 2020-05-21) He, B; Chi, ST; Ye, AJ; Mi, PH; Zhang, LW; Pu, B; Zou, Z; Ran, YB; Zhao, Q; Wang, D; Zhang, WQ; Zhao, JT; Adams, S; Avdeev, M; Shi, S
The combination of a materials database with high-throughput ion-transport calculations is an effective approach to screen for promising solid electrolytes. However, automating the complicated preprocessing involved in currently widely used ion-transport characterization algorithms, such as the first-principles nudged elastic band (FP-NEB) method, remains challenging. Here, we report on high-throughput screening platform for solid electrolytes (SPSE) that integrates a materials database with hierarchical ion-transport calculations realized by implementing empirical algorithms to assist in FP-NEB completing automatic calculation. We first preliminarily screen candidates and determine the approximate ion-transport paths using empirical both geometric analysis and the bond valence site energy method. A chain of images are then automatically generated along these paths for accurate FP-NEB calculation. In addition, an open web interface is actualized to enable access to the SPSE database, thereby facilitating machine learning. This interactive platform provides a workflow toward high-throughput screening for future discovery and design of promising solid electrolytes and the SPSE database is based on the FAIR principles for the benefit of the broad research community. © 2020, The Author(s)
Identifying chemical factors affecting reaction kinetics in Li-air battery via ab initio calculations and machine learning
(Elsevier, 2021-03-01) Wang, AP; Zou, ZY; Wang, D; Liu, Y; Li, YJ; Wu, JM; Avdeev, M; Shi, S
Redox mediators are promised to thermodynamically resolve the cathode irreversibility of Li-air battery. However, the sluggish chemical reaction between mediators and discharge products severely restrains fast charging. Here, we combine ab initio calculations and machine learning method to investigate the reaction kinetics between LiOH and I2, and demonstrate the critical role of the disorder degree of LiOH and the solvent effect. The Li+ desorption is identified as the rate determining step (rds) of the reaction. While LiOH turns from the crystalline to disordered/amorphous structure, the rds energy barrier will be reduced by ∼500 meV. The functional group of the solvent is detected as the key to regulating the solvation effect and phosphate-based solvent is predicted to accelerate the decomposition kinetics most with the strongest solvation capability. These findings indicate that the faster reaction kinetics between mediators and the discharge products can be achieved by rational discharge product structure regulation and appropriate solvent selection. © 2020 Elsevier B.V.
Identifying migration channels and bottlenecks in monoclinic NASICON-type solid electrolytes with hierarchical ion-transport algorithms
(Wiley, 2021-09-07) Zou, Z; Ma, N; Wang, AP; Ran, YB; Song, T; He, B; Ye, AJ; Mi, PH; Zhang, LW; Zhou, H; Jiao, Y; Liu, JP; Wang, D; Li, YJ; Avdeev, M; Shi, S
Monoclinic natrium superionic conductors (NASICON; Na3Zr2Si2PO12) are well-known Na-ion solid electrolytes which have been studied for 40 years. However, due to the low symmetry of the crystal structure, identifying the migration channels of monoclinic NASICON accurately still remains unsolved. Here, a cross-verified study of Na+ diffusion pathways in monoclinic NASICON by integrating geometric analysis of channels and bottlenecks, bond-valence energy landscapes analysis, and ab initio molecular dynamics simulations is presented. The diffusion limiting bottlenecks, the anisotropy of conductivity, and the time and temperature dependence of Na+ distribution over the channels are characterized and strategies for improving both bulk and total conductivity of monoclinic NASICON-type solid electrolytes are proposed. This set of hierarchical ion-transport algorithms not only shows the efficiency and practicality in revealing the ion transport behavior in monoclinic NASICON-type materials but also provides guidelines for optimizing their conductive properties that can be readily extended to other solid electrolytes. © 2021 Wiley-VCH GmbH
Investigation of phonon dynamic in single crystal lead-halide perovskites by inelastic neutron scattering
(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Dubajic, M; Wang, D; Mahmud, A; Upama, M; Jia, X; Rule, KC; Srestha, S; Bremner, S; Conibeer, G
The lead halide perovskite materials have recently risen to prominence for remarkably high photovoltaic efficiencies in polycrystalline materials that are highly defected [1] Some of the reasons for this good defect tolerance are the very low exciton binding energy and consequent highly de localized electrons and holes leading to high mobilities in these materials, coupled to low thermal conductance. Other recent work by our group has shown long lifetimes for hot carriers in a range of perovskites with organic lead iodide perovskites having the longest lifetimes [2]. In order to explain those rather promising physical properties, a closer investigation of phonon dynamics is needed. Al though ab initio simulations (DFT) can predict phonon dispersions to a reasonably accurate extent (comparison between different phonon modes) [2, 3], scaling their energies to actual phonon energies (particularly at high momenta near the zone edge) can be rather inaccurate. In order to obtain a detailed phonon dispersion to overcome the limits of the ab initio methods, scattering techniques can be used (as they offer full Brillouin zone mapping and are suitable for large single crystal samples). The thermal triple axis spectrometer (TAS) on TAIPAN at OPAL reactor at ANSTO was used with the aim to map phonon dispersion of single crystal Methyl Ammonium Lead Halide Perovskites, CH3NH3PbBr3 and CH3NH3PbI3 [4]. The alignment was performed so that we could scan through [h k l] and [ 0 k l] planes in reciprocal space for MAPbBr3 and MAPbI3 samples, respectively. Assuming the cubic space group, ABX3, for the MAPbBr3 sample, we were able to perform transverse and longitudinal scans along each high symmetry direction in the Brillouin zone (Г-X and Г-M) which would ensure the mapping of all phonon modes in the h k plane of the Brillouin zone. The full phonon dispersions that will be obtained with this method can be of great significance as by adding up to the already simulated data we will be able to have a deeper insight into the undergoing physics that is responsible for the previously observed properties (such as significantly extended hot carrier lifetimes) where phonon dynamics will play a significant role. © 2018 The Authors.
The origin of solvent deprotonation in LiI‐added aprotic electrolytes for Li‐O2 batteries
(Wiley, 2023-03-27) Wang, AP; Wu, XH; Zou, Z; Qiao, Y; Wang, D; Xing, L; Chen, Y; Lin, Y; Avdeev, M; Shi, SQ
LiI and LiBr have been employed as soluble redox mediators (RMs) in electrolytes to address the sluggish oxygen evolution reaction kinetics during charging in aprotic Li‐O2 batteries. Compared to LiBr, LiI exhibits a redox potential closer to the theoretical one of discharge products, indicating a higher energy efficiency. However, the reason for the occurrence of solvent deprotonation in LiI‐added electrolytes remains unclear. Here, by combining ab initio calculations and experimental validation, we find that it is the nucleophile that triggers the solvent deprotonation and LiOH formation via nucleophilic attack, rather than the increased solvent acidity or the elongated C−H bond as previously suggested. As a comparison, the formation of in LiBr‐added electrolytes is found to be thermodynamically unfavorable, explaining the absence of LiOH formation. These findings provide important insight into the solvent deprotonation and pave the way for the practical application of LiI RM in aprotic Li‐O2 batteries. © 1999-2024 John Wiley & Sons, Inc
Relationships between Na+ distribution, concerted migration, and diffusion properties in rhombohedral NASICON
(Wiley, 2020-06-24) Zou, ZY; Ma, N; Wang, AP; Ran, YB; Song, T; Jiao, Y; Zhou, H; Shi, W; He, B; Wang, D; Li, YJ; Avdeev, M; Shi, S
Rhombohedral NaZr2(PO4)3 is the prototype of all the NASICON-type materials. The ionic diffusion in these rhombohedral NASICON materials is highly influenced by the ionic migration channels and the bottlenecks in the channels which have been extensively studied. However, no consensus is reached as to which one is the preferential ionic migration channel. Moreover, the relationships between the Na+ distribution over the multiple available sites, concerted migration, and diffusion properties remain elusive. Using ab initio molecular dynamics simulations, here it is shown that the Na+ ions tend to migrate through the Na1–Na3–Na2–Na3–Na1 channels rather than through the Na2–Na3–Na3–Na2 channels. There are two types of concerted migration mechanisms: two Na+ ions located at the adjacent Na1 and Na2 sites can migrate either in the same direction or at an angle. Both mechanisms exhibit relatively low migration barriers owing to the potential energy conversion during the Na+ ions migration process. Redistribution of Na+ ions from the most stable Na1 sites to Na2 on increasing Na+ total content further facilitates the concerted migration and promotes the Na+ ion mobility. The work establishes a connection between the Na+ concentration in rhombohedral NASICON materials and their diffusion properties. © 1999-2021 John Wiley & Sons, Inc.
Software for evaluating ionic conductivity of inorganic–polymer composite solid electrolytes
(American Association for the Advancement of Science, 2023-01) Ding, Y; He, B; Wang, D; Avdeev, M; Li, YJ; Shi, S
Inorganic–polymer composite solid electrolytes (IPCSEs) obtained by filling the polymer matrix with inorganic materials usually have higher ionic conductivity compared with individual phases. This important increase in ionic conductivity is explained in terms of the new percolation paths formed by the highly conductive interface between inorganic filler and polymer. The conduction in such systems can be investigated using the effective medium theory (EMT) and random resistance model (RRM). EMT can be used to analyze the effect of filler size on the ionic conductivity of disordered IPCSEs, while RRM can describe the composites with inorganic fillers of various shapes (nano-particles, nano-wires, nano-sheets, and nano-networks) in ordered or disordered arrangement. Herein, we present software evaluating the ionic conductivity in IPCSEs by combining EMT and RRM. The approach is illustrated by considering the size, shapes, and arrangements of inorganic fillers. The ionic conductivities of different types of IPCSEs are predicted theoretically and found in good agreement with the experimental values. The software can be used as an auxiliary tool to design composite electrolytes. © 2023 Yuqing Ding et al. Exclusive licensee Beijing Institute of Technology Press. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY 4.0)
Ultralow loss and high tunability in a non‐perovskite relaxor ferroelectric
(Wiley, 2022-11-10) Li, R; Xu, D; Avdeev, M; Zhang, L; Chen, XF; Gou, GY; Wang, D; Liu, WF; Zhou, D
Dielectric ceramics are fundamental for electronic systems, including energy storages, microwave applications, ultrasonics, and sensors. Relaxor ferroelectrics show superb performance among dielectrics due to their high efficiency and energy density by the nature of nanodomains. Here, a novel non‐perovskite relaxor ferroelectric, Bi6Ti5WO22, with ultralow loss, ≈10−3, highly tunable permittivity, ≈2200 at room temperature with 40% tunability and the superparaelectric region at room temperature is presented. The actual crystal structure and the nanodomains of Bi6Ti5WO22 are demonstrat Various‐temperature neutron powder diffraction and in situ high‐resolution transmission‐electron‐microscopy illustrate the twinning effect, subtle structure change and micro‐strain in the material influenced by temperature, manifesting the actual crystal structure of Bi6Ti5WO22. Compared with dielectric loss of BaTiO3‐based dielectric tunable materials, the loss of Bi6Ti5WO22 is more than an order of magnitude lower, which makes it exhibit a figure of merit (≈240), much higher than that of conventional dielectric tunable materials (< 100), endorse the material great potential for direct applications. The present research offers a strategy for discovering novel relaxor ferroelectrics and a highly desirable material for fabricating energy storage capacitors, microwave dielectrics, and ultrasonics. © 1999-2024 John Wiley & Sons, Inc
Uncovering the potential of M1‐site‐activated NASICON cathodes for Zn‐Ion batteries
(Wiley, 2020-02-20) Hu, P; Zou, Z; Sun, XW; Wang, D; Ma, J; Kong, QY; Xiao, DD; Gu, L; Zhou, XH; Zhao, JW; Dong, SM; He, B; Avdeev, M; Shi, S; Cui, GL; Chen, LQ
There is a long‐standing consciousness that the rhombohedral NASICON‐type compounds as promising cathodes for Li+/Na+ batteries should have inactive M1(6b) sites with ion (de)intercalation occurring only in the M2 (18e) sites. Of particular significance is that M1 sites active for charge/discharge are commonly considered undesirable because the ion diffusion tends to be disrupted by the irregular occupation of channels, which accelerates the deterioration of battery. However, it is found that the structural stability can be substantially improved by the mixed occupation of Na+/Zn2+ at both M1 and M2 when using NaV2(PO4)3 (NVP) as a cathode for Zn‐ion batteries. The results of atomic‐scale scanning transmission electron microscopy, analysis of ab initio molecular dynamics simulations, and an accurate bond‐valence‐based structural model reveal that the improvement is due to the facile migration of Zn2+ in NVP, which is enabled by a concerted Na+/Zn2+ transfer mechanism. In addition, significant improvement of the electronic conductivity and mechanical properties is achieved in Zn2+‐intercalated ZnNaV2(PO4)3 in comparison with those of Na3V2(PO4)3. This work not only provides in‐depth insight into Zn2+ intercalation and dynamics in NVP unlocked by activating the M1 sites, but also opens a new route toward design of improved NASICON cathodes. © 1999-2021 John Wiley & Sons, Inc.
Understanding the Li diffusion mechanism and positive effect of current collector volume expansion in anode free batteries
(IOP Publishing, 2020-03-09) Zhuang, Y; Zou, ZY; Lu, B; Li, YJ; Wang, D; Avdeev, M; Shi, S
In anode free batteries (AFBs), the current collector acts as anode simultaneously and has large volume expansion which is generally considered as a negative effect decreasing the structural stability of a battery. Moreover, despite many studies on the fast lithium diffusion in the current collector materials of AFB such as copper and aluminum, the involved Li diffusion mechanism in these materials remains poorly understood. Through first-principles calculation and stress-assisted diffusion equations, here we study the Li diffusion mechanism in several current collectors and related alloys and clarify the effect of volume expansion on Li diffusion respectively. It is suggested that due to the lower Li migration barriers in aluminum and tin, they should be more suitable to be used as AFB anodes, compared to copper, silver, and lead. The Li diffusion facilitation in copper with a certain number of vacancies is proposed to explain why the use of copper with a thickness ≤ 100 nm as the protective coating on the anode improves the lifetime of the batteries. We show that the volume expansion has a positive effect on Li diffusion via mechanical–electrochemical coupling. Namely, the volume expansion caused by Li diffusion will further induce stress which in turn affects the diffusion. These findings not only provide in-depth insight into the operating principle of AFBs, but also open a new route toward design of improved anode through utilizing the positive effect of mechanical–electrochemical coupling. © 2020 Chinese Physical Society and IOP Publishing Ltd

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