Browsing by Author "Kan, WH"
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- ItemConsolidating the grain boundary of garnet electrolyte LLZTO with Li3BO3 for high performance LiNi0. 8Co0. 1Mn0. 1O2/LiFePO4 hybrid solid batteries(Royal Society of Chemistry, 2019-07-10) Xie, H; Li, C; Kan, WH; Avdeev, M; Zhu, C; Zhao, Z; Chu, X; Mu, D; Wu, FAll solid-state batteries have received significant attention due to their excellent safety performance. As a key component, the garnet-type electrolyte is one of the best known electrolytes due to its air stability and good compatibility with metallic lithium. However, the total Li+ conductivity of this kind of electrolyte is usually lower than that of the bulk electrolyte primarily due to the grain boundary resistance. In this study, we focused on engineering the electrolyte Li6.4La3Zr1.4Ta0.6O12 (LLZTO) by introducing Li3BO3 (LBO) into it to form the electrolyte LLZTO/LBO with the aim to consolidate the grain boundary. Via characterization by both neutron and X-ray diffraction, the as-prepared LLZTO was indexed as a pure cubic phase, where Ta certainly substituted the Zr sites. LLZTO/LBO still maintained the cubic structure, and the B atoms did not occupy any cation sites in the unit cell. It was demonstrated that an amorphous phase of a boracic substance was trapped inside the cubic LLZTO phase. The amorphous boracic phase sutured the gaps among the LLZTO grains and then lowered the grain boundary resistance without introducing impurities, ultimately consolidating the solid-state electrolyte. Electrochemical impedance spectroscopy revealed that the total Li+ conductivity of LLZTO/LBO reached 5.47 × 10−4 S cm−1, much higher than those of the as-prepared Li7La3Zr2O12 (LLZO) and LLZTO. Using LLZTO/LBO as an electrolyte, the LiNi0.8Co0.1Mn0.1O2/LiFePO4 hybrid solid battery showed an excellent cycling performance with the reversible capacity of 147.8 mA h g−1 at 0.2C for 100 cycles and the capacity retention of 93.8%. These results suggest that the consolidation of the grain boundary with LBO is a promising way to achieve an improved electrolyte, LLZO, with higher total Li+ conductivity. © Royal Society of Chemistry 2019
- ItemCorrection: Consolidating the grain boundary of the garnet electrolyte LLZTO with Li3BO3 for high-performance LiNi0.8Co0.1Mn0.1O2/LiFePO4 hybrid solid batteries(Royal Society of Chemistry, 2019-08-19) Xie, H; Li, C; Kan, WH; Avdeev, M; Zhu, C; Zhao, Z; Chu, X; Mu, D; Wu, FCorrection for ‘Consolidating the grain boundary of the garnet electrolyte LLZTO with Li3BO3 for high-performance LiNi0.8Co0.1Mn0.1O2/LiFePO4 hybrid solid batteries’ by Huilin Xie et al., J. Mater. Chem. A, 2019, DOI: 10.1039/c9ta03263k. © The Royal Society of Chemistry 2019
- ItemDopant distribution in co-free high-energy layered cathode materials(American Chemical Society, 2019-11-21) Mu, L; Zhang, R; Kan, WH; Zhang, Y; Li, LX; Kuai, C; Zydlewski, B; Rahman, MM; Sun, CJ; Sainio, S; Avdeev, M; Nordlund, D; Xin, HL; Lin, FThe practical implementation of Co-free, LiNiO2-derived cathodes has been prohibited by their poor cycle life and thermal stability, resulting from the structural instability, phase transformations, reactive surfaces, and chemomechanical breakdown. With the hierarchical distribution of Mg/Ti dual dopants in LiNiO2, we report a Co-free layered oxide that exhibits enhanced bulk and surface stability. Ti shows a gradient distribution and is enriched at the surface, whereas Mg distributes homogeneously throughout the primary particles. The resulting Mg/Ti codoped LiNiO2 delivers a material-level specific energy of ∼780 W h/kg at C/10 with 96% retention after 50 cycles. The specific energy reaches ∼680 W h/kg at 1C with 77% retention after 300 cycles. Furthermore, the Mg/Ti dual dopants improve the rate capability, thermal stability, and self-discharge resistance of LiNiO2. Our synchrotron X-ray, electron, and electrochemical diagnostics reveal that the Mg/Ti dual dopants mitigate phase transformations, reduce nickel dissolution, and stabilize the cathode–electrolyte interface, thus leading to the favorable battery performance in lithium metal and graphite cells. The present study suggests that engineering the dopant distribution in cathodes may provide an effective path toward lower cost, safer, and higher energy density Co-free lithium batteries. © 2019 American Chemical Society
- ItemDual-ion intercalation to enable high-capacity VOPO4 cathodes for Na-ion batteries(Elsevier, 2021-01-01) Zhang, Z; Ni, Y; Avdeev, M; Kan, WH; He, GVOPO4 is a potential cathode candidate in sodium-ion batteries for multi-electron reactions to attain high capacity up to 330 mAh g−1. However, most current efforts are focused on the V5+/V4+ redox reaction with a moderate capacity of <150 mAh g−1. Here, we report for the first time the Na intercalation behaviors for both αI- and β-VOPO4 polymorph cathodes through the V5+/V4+/V3+ redox reactions. Electrochemical evaluations suggest further reduction of V4+ ions can be attained for both cathodes, as indicated by the high discharge capacities derived from a large plateau below 1.5 V vs Na/Na+ as well as various structural analyses of electrodes at different discharge states. However, only the layered αI- cathode is preferable for deep sodiation to maintain stable structure over cycling. Theoretical studies by bond-valence sum (BVS) mismatch map calculations reveal similar Na-ion migration pathways in VOPO4•2H2O and αI-NaVOPO4, but H2O molecules in the hydrate cathode have negative effect on the diffusion of Na-ions in betweenVOPO4 layers. © 2020 Elsevier Ltd. All rights reserved.
- ItemElectrical properties of hollandite-type Ba1.33Ga2.67Ti5.33O16, K1.33Ga1.33Ti6.67O16, and K1.54Mg0.77Ti7.23O16(American Chemical Society, 2019-03-28) Cao, C; Singh, K; Kan, WH; Avdeev, M; Thangadurai, VElectrical conductivity and electrochemical catalytic activity for H2 oxidation of Ti-based hollandite-type Ba1.33Ga2.67Ti5.33O16 (BGT), K1.33Ga1.33Ti6.67O16 (KGT), and K1.54Mg0.77Ti7.23O16 (KMT) were investigated, along with the chemical stability of KMT under H2 at elevated temperature. BGT, KGT, and KMT crystallized in a tetragonal structure with the space-group I4/m. The electrical conductivity in H2 increases with increasing Ti content, and the highest total electrical conductivity of 2 S/cm at 800 °C in H2 was observed for KMT. KGT:Fe (1:1) + 20% LSGM + 30% porosity composite electrode showed the lowest area specific resistance of ca. 1.6 Ω cm2 at 800 °C for hydrogen oxidation reaction (HOR) under the open circuit condition. Moderate catalytic activity for HOR could be attributed to poor oxide ion conductivity and exclusion of potassium and hydrogen uptake in H2 at elevated temperature. Bond valence sum mismatch map calculation showed that the ionic transport happens along the 1D channel of c-axis in the hollandite oxides. © 2019 American Chemical Society
- ItemEvaluation of polymorphism and charge transport in a BaO–CaO–Ta2O5 perovskite phase diagram using TOF-neutron and synchrotron X-ray diffraction, the bond-valence method and impedance spectroscopy(Royal Society of Chemistry (RSC), 2022-10-26) Singh, K; Yang, H; Zhang, Z; Avdeev, M; Huq, Ashfia; Wu, DY; Lee, JJ; Kan, WH; Thangadurai, VAmong the alkaline earth-based perovskite oxides, the Ba-based perovskites have superior chemical stability and tunable electrical/catalytic property via chemical substitution/doping. One of the best-known examples is Ba3Ca1.18Nb1.82O8.73 as a ceramic proton conductor for all-solid-state steam electrolysis and solid oxide fuel cells (SOFCs). Structural ordering variation is often driven by chemical composition, which directly correlates with their chemical/physical properties. In the present work, we develop a comprehensive functional perovskite-type phase diagram for the Ba–Ca–Ta–O quaternary system Ba3Ca1+xTa2−xO9−3x/2 (0 ≤ x ≤ 0.36) with a wide chemical composition between 1000 and 1550 °C, coupled with theoretical calculations to investigate the cation ordering in supercells. Furthermore, the impact of cation clustering on the diffusion pathways of O2− ions was evaluated as a case study. Experimentally, precise cation ordering and other structural features are quantitively determined by TOF-neutron and synchrotron X-ray diffraction analyses. This work provides a comprehensive evaluation of some potential applications of the Ba–Ca–Ta–O quaternary system. The electrochemical impedance data were also systematically studied by impedance spectroscopy genetic programming (ISGP). The electrical conductivity was found to increase from x = 0 to x = 0.27 and then decrease for the end member when x = 0.36 due to a decrease in mobile charge carrier concentration. Interestingly, in dry air, the electrical conductivity was found to increase from x = 0 to x = 0.36. However, only Ba3Ca1.18Ta1.82O8.73 (BCT18) and Ba3Ca1.27Ta1.73O8.595 (BCT27) were found to show an increasing trend in conductivity in humid atmospheres, and this indicates that the clustering effect was pO2 dependent. © Royal Society of Chemistry 2024
- ItemLayered-rocksalt intergrown cathode for high-capacity zero-strain battery operation(IOP Publishing, 2021-10-10) Tong, W; Li, N; Sun, ML; Kan, WH; Zhuo, ZQ; Hwang, SY; Renfrew, SE; Avdeev, M; Huq, A; McCloskey, BD; Su, D; Yang, WLThe continuous dependence on high-performance lithium-ion batteries leads to a pressing demand for advanced cathode materials of high energy density along with excellent cycling stability. Here we demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each individual phase, including the high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt phase. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (R-3m) with intergrown rocksalt (Fm-3m) is developed, which delivers a high capacity with good rate performance. More importantly, the interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for the layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a general design principle is successfully extrapolated and experimentally verified in a series of compositions. The success of such layered-rocksalt intergrown structure exemplifies a new concept of battery electrode design and opens up a vast space of compositions to develop high-performance intergrown cathodes for advanced energy storage devices. © 2021 ECS - The Electrochemical Society
- ItemLayered-rocksalt intergrown cathode for high-capacity zero-strain battery operation(Springer Nature, 2021-04-20) Li, N; Sun, ML; Kan, WH; Zhuo, ZQ; Hwang, SY; Renfrew, SE; Avdeev, M; Huq, A; McCloskey, BD; Su, D; Yang, WL; Tong, WThe dependence on lithium-ion batteries leads to a pressing demand for advanced cathode materials. We demonstrate a new concept of layered-rocksalt intergrown structure that harnesses the combined figures of merit from each phase, including high capacity of layered and rocksalt phases, good kinetics of layered oxide and structural advantage of rocksalt. Based on this concept, lithium nickel ruthenium oxide of a main layered structure (R3¯m) with intergrown rocksalt (Fm3¯m) is developed, which delivers a high capacity with good rate performance. The interwoven rocksalt structure successfully prevents the anisotropic structural change that is typical for layered oxide, enabling a nearly zero-strain operation upon high-capacity cycling. Furthermore, a design principle is successfully extrapolated and experimentally verified in a series of compositions. Here, we show the success of such layered-rocksalt intergrown structure exemplifies a new battery electrode design concept and opens up a vast space of compositions to develop high-performance intergrown cathode materials. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License
- ItemLithiated Prussian blue analogues as positive electrode active materials for stable non-aqueous lithium-ion batteries(Springer Nature, 2022-12-16) Zhang, Z; Avdeev, M; Chen, H; Yin, W; Kan, WH; He, GPrussian blue analogues (PBAs) are appealing active materials for post-lithium electrochemical energy storage. However, PBAs are not generally suitable for non-aqueous Li-ion storage due to their instability upon prolonged cycling. Herein, we assess the feasibility of PBAs with various lithium content for non-aqueous Li-ion storage. We determine the crystal structure of the lithiated PBAs via neutron powder diffraction measurements and investigate the influence of water on structural stability and Li-ion migration through operando X-ray diffraction measurements and bond valence simulations. Furthermore, we demonstrate that a positive electrode containing Li2-xFeFe(CN)6⋅nH2O (0 ≤ x ≤ 2) active material coupled with a Li metal electrode and a LiPF6-containing organic-based electrolyte in coin cell configuration delivers an initial discharge capacity of 142 mAh g−1 at 19 mA g−1 and a discharge capacity retention of 80.7% after 1000 cycles at 1.9 A g−1. By replacing the lithium metal with a graphite-based negative electrode, we also report a coin cell capable of cycling for more than 370 cycles at 190 mA g−1 with a stable discharge capacity of about 105 mAh g−1 and a discharge capacity retention of 98% at 25 °C. © The Authors CC 4.0
- ItemMechanochemically enabled metastable niobium tungsten oxides(American Chemical Society, 2024-04-08) Raji-Adefila, B; Wang, Y; Ding, Y; Avdeev, M; Outka, A; Gonzales, H; Engelstad, K; Sainio, S; Nordlund, D; Kan, WH; Zhou, S; Chen, DCMetastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed-close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Finally, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field. © 2024 American Chemical Society.
- ItemNovel low-strain layered/rocksalt intergrown cathode for high-energy Li-ion batteries(American Chemical Society (ACS), 2023-11-16) Xu, L; Chen, S; Su, Y; Shen, X; He, J; Avdeev, M; Kan, WH; Zhang, B; Fan, W; Chen, L; Cao, D; Lu, Y; Wang, L; Wang, M; Bao, L; Zhang, L; Li, N; Wu, FBoth layered- and rocksalt-type Li-rich cathode materials are drawing great attention due to their enormous capacity, while the individual phases have their own drawbacks, such as great volume change for the layered phase and low electronic and ionic conductivities for the rocksalt phase. Previously, we have reported the layered/rocksalt intergrown cathodes with nearly zero-strain operation, while the use of precious elements hinders their industrial applications. Herein, low-cost 3d Mn4+ ions are utilized to partially replace the expensive Ru5+ ions, to develop novel ternary Li-rich cathode material Li1+x[RuMnNi]1-xO2. The as-designed Li1.15Ru0.25Mn0.2Ni0.4O2 is revealed to have a layered/rock salt intergrown structure by neutron diffraction and transmission electron microscopy. The as-designed cathode exhibits ultrahigh lithium-ion reversibility, with 0.86 (231.1 mAh g-1) out of a total Li+ inventory of 1.15 (309.1 mAh g-1). The X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectra further demonstrate that the high Li+ storage of the intergrown cathode is enabled by leveraging cationic and anionic redox activities in charge compensation. Surprisingly, in situ X-ray diffraction shows that the intergrown cathode undergoes extremely low-strain structural evolution during the charge-discharge process. Finally, the Mn content in the intergrown cathodes is found to be tunable, providing new insights into the design of advanced cathode materials for high-energy Li-ion batteries. © 2024 American Chemical Society.
- ItemOptimizing the structure of layered cathode material for higher electrochemical performance by elucidating structural evolution during heat processing(Elsevier, 2020-12-01) Huang, ZY; Chu, MH; Wang, R; Zhu, WM; Zhao, WG; Wang, CQ; Zhang, YJ; He, LH; Chen, J; Deng, SH; Mei, LW; Kan, WH; Avdeev, M; Pan, F; Xiao, YGImproving electrochemical performance of cathode materials for lithium-ion batteries requires comprehensive understanding of their structural properties which could facilitate or impede the diffusion of lithium during charge-discharge. In order to optimize the structure and improve the electrochemical performance of layered cathode material, the detailed structural evolution as a function of heat treatment temperature in LiNi0.8Co0.1Mn0.1O2 was investigated by in-situ and ex-situ neutron powder diffraction methods. We show that both cycling stability and rate performance of LiNi0.8Co0.1Mn0.1O2 can be improved by performing heat treatment at 400 °C, which is attributed to the optimization of surface structure and the enlargement of c/a ratio. Heat treatment of LiNi0.8Co0.1Mn0.1O2 at higher temperature induces a layered-to-rock-salt structure phase transition accompanied with the precipitation of lithium oxide. A 3D phase diagram, which correlates the high temperature phases and room temperature phases, is constructed. The presentation of comprehensive phase diagrams up to 1000 °C could provide the basis for further research on not only synthesis strategy but also thermal stability in Ni-rich layered cathode materials. © 2020 Elsevier Ltd.
- ItemAn ordered P2/P3 composite layered oxide cathode with long cycle life in sodium-ion batteries(American Chemical Society, 2019-10-16) Rahman, MM; Mao, J; Kan, WH; Sun, CJ; Li, LX; Zhang, Y; Avdeev, M; Du, XW; Lin, FDeveloping stable cathode materials represents a crucial step toward long-life sodium-ion batteries. P2-type layered oxides are important as cathodes for their reversibility, but their long-term performance in full cells remains a key challenge. Herein, we report Na0.75Co0.125Cu0.125Fe0.125Ni0.125Mn0.5O2 with an intergrowth of ordered P2 and P3 phases, studied by neutron diffraction and Rietveld refinement. A stable electrochemical performance is achieved in Na half cells with 100% capacity retention at a rate of C/10 after 100 cycles (initial capacity of 90 mAh/g), 96% capacity retention at a rate of 1 C after 500 cycles (initial capacity of 70 mAh/g), and 85% capacity retention at a rate of 5 C after 1000 cycles (initial capacity of 55 mAh/g). Stable full cell performance is achieved with 84.2% capacity retention after 1000 cycles at a rate of 1 C. Synchrotron X-ray diffraction, spectroscopy, and imaging are applied to elucidate the relationship between chemical/structural evolution and battery performance. A reversible local and global structural evolution is observed during initial cycles. Meanwhile, the challenges with enabling prolonged cycling (beyond 1000 cycles) may be associated with Fe dissolution and formation of a copper oxide phase. This study implies that cathodes with complex chemical and structural formations may stabilize electrochemical performance and highlights the importance of decoupling the contribution of each transition metal to performance degradation. © 2019 American Chemical Society
- ItemOver‐stoichiometric metastabilization of cation‐disordered rock salts(Wiley, 2023-12-21) Wang, Y; Outka, A; Takele, WM; Avdeev, M; Sainio, S; Liu, R; Kee, V; Choe, W; Raji‐Adefila, B; Nordlund, D; Zhou, S; Kan, WH; Habteyes, TG; Chen, DCCation‐disordered rock salts (DRXs) are well known for their potential to realize the goal of achieving scalable Ni‐ and Co‐free high‐energy‐density Li‐ion batteries. Unlike in most cathode materials, the disordered cation distribution may lead to more factors that control the electrochemistry of DRXs. An important variable that is not emphasized by research community is regarding whether a DRX exists in a more thermodynamically stable form or a more metastable form. Moreover, within the scope of metastable DRXs, over‐stoichiometric DRXs, which allow relaxation of the site balance constraint of a rock salt structure, are particularly underexplored. In this work, these findings are reported in locating a generally applicable approach to “metastabilize” thermodynamically stable Mn‐based DRXs to metastable ones by introducing Li over‐stoichiometry. The over‐stoichiometric metastabilization greatly stimulates more redox activities, enables better reversibility of Li deintercalation/intercalation, and changes the energy storage mechanism. The metastabilized DRXs can be transformed back to the thermodynamically stable form, which also reverts the electrochemical properties, further contrasting the two categories of DRXs. This work enriches the structural and compositional space of DRX families and adds new pathways for rationally tuning the properties of DRX cathodes. © 1999-2024 John Wiley & Sons, Inc or related companies.
- ItemSimple synchronous dual-modification strategy with Zr4+ doping and CeO2 nanowelding to stabilize layered Ni-rich cathode materials(American Chemical Society, 2023-05-22) Liu, JK; Yin, ZW; Zheng, WC; Zhang, J; Deng, SS; Wang, Z; Deng, Li; Xie, SJ; Liu, ZK; Avdeev, M; Qu, F; Kan, WH; Zhou, Y; Li, JTA Ni-rich layered oxide, one promising cathode for lithium-ion batteries (LIBs), exhibits the advantages of low cost and high capacity but suffers from rapid capacity loss due to bulk structural instability and surface side reactions. Herein, a simple synchronous dual-modification strategy with Zr4+doping and CeO2nanowelding is proposed to address such issues. Utilizing the migration energy difference of Zr and Ce ions in layered structures, one-step high-temperature sintering of LiNi0.8Co0.1Mn0.1O2particles with Zr and Ce nitrate distributions enables simultaneous doping of Zr ions in the bulk and CeO2surface modification. Therein, Zr ions in the bulk occupying the Li sites can improve the Li+diffusion rate and stabilize the crystal structure, while CeO2on the surface provides nanowelding between the grain boundaries and resistance to electrolyte erosion. Theoretical calculations and a series of structure/composition characterizations (i.e., neutron scattering, in situ X-ray diffraction, etc.) validated the proposed strategy and its role in stabilizing the Ni-rich cathodes. The synergistic effect of Zr4+doping and CeO2nanowelding enables an impressive initial capacity of 187.2 mAh g-1(2.7-4.3 V vs Li/Li+) with 86.1% retention after 200 cycles at 1 C and rate capabilities of 146.6 and 127.3 mAh g-1at 5 and 10 C, respectively. Upon increasing the testing temperature to 60 °C, the dual-modified Ni-rich cathode exhibits an initial discharge capacity of 203.5 mAh g-1with a good retention of 80.8% after 100 cycles at 0.5 C. The present strategy utilizing the migration energy difference of metal ions to achieve synchronous bulk doping and surface modification will offer fresh insights to stabilize layered cathode materials for LIBs, which can be widely used in other kinds of batteries with various cathode materials. © American Chemical Society
- ItemStructural and electrochemical impacts of Mg/Mn dual dopants on the LiNiO2 cathode in Li-metal batteries(American Chemical Society, 2020-03-04) Mu, L; Kan, WH; Kuai, C; Yang, Z; Li, LX; Sun, CJ; Sainio, S; Avdeev, M; Nordlund, D; Lin, FDoping chemistry has been regarded as an efficient strategy to overcome some fundamental challenges facing the “no-cobalt” LiNiO2 cathode materials. By utilizing the doping chemistry, we evaluate the battery performance and structural/chemical reversibility of a new no-cobalt cathode material (Mg/Mn-LiNiO2). The unique dual dopants drive Mg and Mn to occupy the Li site and Ni site, respectively. The Mg/Mn-LiNiO2 cathode delivers smooth voltage profiles, enhanced structural stability, elevated self-discharge resistance, and inhibited nickel dissolution. As a result, the Mg/Mn-LiNiO2 cathode enables improved cycling stability in lithium metal batteries with the conventional carbonate electrolyte: 80% capacity retention after 350 cycles at C/3, and 67% capacity retention after 500 cycles at 2C (22 °C). We then take the Mg/Mn-LiNiO2 as the platform to investigate the local structural and chemical reversibility, where we identify that the irreversibility takes place starting from the very first cycle. The highly reactive surface induces the surface oxygen loss, metal reduction reaching the subsurface, and metal dissolution. Our data demonstrate that the dual dopants can, to some degree, mitigate the irreversibility and improve the cycling stability of LiNiO2, but more efforts are needed to eliminate the key challenges of these materials for battery operation in the conventional carbonate electrolyte. © 2020 American Chemical Society
- ItemSurface characterization of Li-substituted compositionally heterogeneous NaLi0.045Cu0.185Fe0.265Mn0.505O2 sodium-ion cathode material(American Chemical Society, 2019-04-11) Rahman, MM; Zhang, Y; Xia, S; Kan, WH; Avdeev, M; Mu, L; Sokaras, D; Kroll, T; Du, XW; Nordlund, D; Liu, Y; Lin, FThe understanding of surface chemical and structural processes can provide some insights into designing stable sodium cathode materials. Herein, Li-substituted and compositionally heterogeneous NaLi0.045Cu0.185Fe0.265Mn0.505O2 is used as a platform to investigate the interplay between Li substitution, surface chemistry, and battery performance. Li substitution improves the initial discharge capacity and energy density. However, there is no noticeable benefit in the long-term cycling stability of this material. The Li substitution in the transition-metal (TM) layer also seems to influence the transition-metal (TM) 3d–oxygen (O) 2p hybridization. Upon desodiation, the surface of active particles undergoes significant transition-metal reduction, especially Mn. Furthermore, the presence of electrolyte drastically accelerates such surface degradation. In general, the Li-substituted material experiences severe surface degradation, which is partially responsible for the performance degradation upon long-term cycling. While some studies have reported the benefits of Li substitution, the present study suggests that the effectiveness of the Li substitution strategy depends on the TM compositional distribution. More efforts are needed to improve the surface chemistry of Li-substituted sodium cathode materials. © 2019 American Chemical Society
- ItemUnlocking fast and reversible sodium intercalation in NASICON Na4MnV(PO4)3 by fluorine substitution(Elsevier, 2021-11) Hou, J; Hadouchi, M; Sui, L; Liu, J; Tang, M; Kan, WH; Avdeev, M; Zhong, G; Liao, YK; Lai, YH; Chu, YH; Lin, HJ; Chen, CT; Hu, ZW; Huang, YH; Ma, JThe exploitation of high energy and high power densities cathode materials for sodium ion batteries is a challenge. Na-super-ionic-conductor (NASICON) Na4MnV(PO4)3 is one of promising high-performance and low-cost cathode materials, however, still suffers from not reaching the theoretical capacity, low rate capability, and poor cycling stability. In this work, we deploy a novel sodium-deficient NASICON fluorinated phosphate cathode material for sodium ion batteries which demonstrates, notably, high energy and high power densities concomitant with high sodium diffusion kinetics. The enhanced performance of this novel Na3.85⬜0.15MnV(PO3.95F0.05)3 cathode was evidenced by demonstrating a relatively high energy density of ∼380 Wh kg−1 at low rate with much improved rate capability compared to non-doped Na4MnV(PO4)3, and long cycling life over 2000 cycles at high current rates. The structural investigation during battery operation using in situ x-ray diffraction (XRD) reveals bi-phase mechanism with high structural reversibility. The combined XRD and 23Na nuclear magnetic resonance (NMR) analyses demonstrate that the sodium extraction/insertion from Na2 is faster than Na1 site. These findings open promising prospects for unlocking of high energy and high power densities of NASICON phosphate materials by fluorine substitution towards high-performance sodium ion batteries. © 2021 Elsevier B.V.