Fully Conjugated Phthalocyanine Copper Metal-Organic Frameworks for Sodium-Iodine Batteries with Long-Time-Cycling Durability

Rechargeable sodium-iodine (Na-I-2) batteries are attracting growing attention for grid-scale energy storage due to their abundant resources, low cost, environmental friendliness, high theoretical capacity (211 mAh g(-1)), and excellent electrochemical reversibility. Nevertheless, the practical application of Na-I-2 batteries is severely hindered by their poor cycle stability owing to the serious dissolution of polyiodide in the electrolyte during charge/discharge processes. Herein, the atomic modulation of metal-bis(dihydroxy) species in a fully conjugated phthalocyanine copper metal-organic framework (MOF) for suppression of polyiodide dissolution toward long-time cycling Na-I-2 batteries is demonstrated. The Fe-2[(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Cu] MOF composited with I-2 (Fe-2-O-8-PcCu/I-2) serves as a cathode for a Na-I-2 battery exhibiting a stable specific capacity of 150 mAh g(-1) after 3200 cycles and outperforming the state-of-the-art cathodes for Na-I-2 batteries. Operando spectroelectrochemical and electrochemical kinetics analyses together with density functional theory calculations reveal that the square planar iron-bis(dihydroxy) (Fe-O-4) species in Fe-2-O-8-PcCu are responsible for the binding of polyiodide to restrain its dissolution into electrolyte. Besides the monovalent Na-I-2 batteries in organic electrolytes, the Fe-2-O-8-PcCu/I-2 cathode also operates stably in other metal-I-2 batteries like aqueous multivalent Zn-I-2 batteries. Thus, this work offers a new strategy for designing stable cathode materials toward high-performance metal-iodine batteries

Towards maximized volumetric capacity via pore-coordinated design for large-volume-change lithium-ion battery anodes

To achieve the urgent requirement for high volumetric energy density in lithium-ion batteries, alloy-based anodes have been spotlighted as next-generation alternatives. Nonetheless, for the veritable accomplishment with regards to high-energy demand, alloy-based anodes must be evaluated considering several crucial factors that determine volumetric capacity. In particular, the electrode swelling upon cycling must be contemplated if these anodes are to replace conventional graphite anodes in terms of volumetric capacity. Herein, we propose macropore-coordinated graphite-silicon composite by incorporating simulation and mathematical calculation of numerical values from experimental data. This unique structure exhibits minimized electrode swelling comparable to conventional graphite under industrial electrode fabrication conditions. Consequently, this hybrid anode, even with high specific capacity (527 mAh g(-1)) and initial coulombic efficiency (93%) in half-cell, achieves higher volumetric capacity (493.9 mAh cm(-3)) and energy density (1825.7 Wh L-1) than conventional graphite (361.4 mAh cm(-3) and 1376.3 Wh L-1) after 100 cycles in the full-cell configuration

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Department of Energy Engineering (Battery Science and Technology)As the era of Electric Vehicles (EVs) emerging, the needs for the electrochemical energy storage and conversion devices increasing. Due to its large energy density, Zn-air battery with a century old technology has been attracted recently. However, it is still under research and development stage so that its maximum application has been significantly limited to small portable device such as just hearing aid. Especially, sluggish rate of oxygen reduction reaction (ORR) which occurs in cathode site is the rate-determining step (RDS) of Zn-air battery. Therefore, how to facilitate ORR with proper catalysts has been a key technology to date. In this regard, many research reports have been reported to decrease overpotential of cathode site. However, owing to the lack of depth understanding of detailed mechanisms for ORR, still Pt-based electrocatalysts regarded as a proper electrocatalyst for Zn-air battery. On the strength of it, without the innovative electrocatalyst, it is hard to obtain high working potential of Zn-air battery. In addition, there have been tremendous efforts to increase bi-functional ability of Zn-air battery by adapting bi-functional electrocatalyst which covers both ORR and OER processes. Even there have been a number of issues to control for rechargeable Zn-air batteries such as degradation of Zn electrode owing to the formation of ZnO on the surface of the Zn electrode, evaporation of electrolyte, and the degradation of air electrode during electrocatalytic activities, among the addressed issues, the degradation of air electrode regarded as a severe problem for rechargeable Zn-air batteries. In this dissertation, I start with brief review of the overall Zn-air battery system in chapter 1 with the recent developed electrocatalyst for Zn-air battery with basic working principle. Then I introduced my research results related with electrocatalysts for oxygen redox reaction in alkaline solutions for Zn-air battery in chapter 2,3. Especially, non-precious metal based electrocatalyst receives huge attention due to not only high performance but also strong durability. In chapter 2, I synthesized nano-sized transition metal CuFe alloy encapsulated with a graphitic-carbon shell to earn highly efficient and durable electrocatalytic reaction in ORR so as to increase working potential for Zn-air battery in alkaline solution. Owing to the synergy effect of high oxygen binding affinity of Fe and high oxygen activity of Cu, the moderated binding affinity of oxygen could enhance ORR activity especially working potential for Zn-air battery. The increased performance also confirmed by density functional theory (DFT) calculation with proper electrochemical experiment results. In chapter 3, to facilitate the oxygen electrochemical ability of NiCo which is known as excellent bi-functional electrocatalyst, we combined Fe to increase oxygen absorptivity like iron in the hemoglobin thus red blood cell could carry oxygen molecules to mitochondrion. In addition, the carbon network increased electron conductivity and could work as protection layer against oxidation problem. The remarkable performances are mainly obtained at the both half-cell and the Zn-air battery and through the in situ XAS and DFT analysis, the plausible mechanism could be predicted. The reported NiCoFe electrocatalyst offers promising candidates in electrochemical energy storage and conversion devices. Through this dissertation, I expect that the non-precious metal based electrocatalysts with remarkable performance and excellent durability could be regarded as promising candidates for not only Zn-air batteries but also various energy conversion and storage devices.ope

Unveiling the Catalytic Origin of Nanocrystalline Yttrium Ruthenate Pyrochlore as a Bifunctional Electrocatalyst for Zn-Air Batteries

Zn-air batteries suffer from the slow kinetics of oxygen reduction reaction (ORR) and/or oxygen evolution reaction (OER). Thus, the bifunctional electrocatalysts are required for the practical application of rechargeable Zn-air batteries. In terms of the catalytic activity and structural stability, pyrochlore oxides (A2[B2-xAx]O7-y) have emerged as promising candidates. However, a limited use of A-site cations (e.g., lead or bismuth cations) of reported pyrochlore catalysts have hampered broad understanding of their catalytic effect and structure. More seriously, the catalytic origin of the pyrochlore structure was not clearly revealed yet. Here, we report the new nanocrystalline yttrium ruthenate (Y2[Ru2-xYx]O7-y) with pyrochlore structure. The prepared pyrochlore oxide demonstrates comparable catalytic activities in both ORR and OER, compared to that of previously reported metal oxide-based catalysts such as perovskite oxides. Notably, we first find that the catalytic activity of the Y2[Ru2-xYx]O7-y is associated with the oxidations and corresponding changes of geometric local structures of yttrium and ruthenium ions during electrocatalysis, which were investigated by in situ X-ray absorption spectroscopy (XAS) in real-time. Zn-air batteries using the prepared pyrochlore oxide achieve highly enhanced charge and discharge performance with a stable potential retention for 200 cycles

Fe-N-C combined with Fe 100-x-y-z P x O y N z porous hollow spheres on a phosphoric acid group-rich N-doped carbon as an electrocatalyst for zinc-air battery

Replacing the commercial Pt/C with non-precious metal-based electrocatalysts in the proton exchange membrane fuel cells and metal-air batteries is still challenging. Herein, an electrocatalyst (described as Fe-N-C/Fe 100-x-y-z P x O y N z /NPC, NPC is N, P co-doped carbon) composed of multiple active components, such as NPC, iron-based porous hollow spheres and Fe-N-C, is reported, which exhibits an excellent activity that is comparable to state-of-the-art Pt/C for half-cell and full zinc-air battery in alkaline media. This catalyst exhibits an excellent activity with a half-wave potential of 0.86 V for the ORR in alkaline media, which is 10 mV more positive than to that of Pt/C (0.85 V), and a gravimetric energy density for zinc-air battery is up to 675 Wh Kg zn ???1 . The excellent activity is attributed to the synergetic effect of active NPC, iron-based porous hollow spheres (Fe 100-x-y-z P x O y N z ) and Fe-N-C in its structure. In addition, phosphoric acid groups are partially remained in the structure for our catalyst that make the catalyst excellent hydrophilicity. This work adds a new member into family of non-precious metal-based ORR electrocatalysts

Recent Advances and Prospects of Atomic Substitution on Layered Positive Materials for Lithium-Ion Battery

This work not only summarizes the previous doping research that focused on the optimization of a bulk doping composition but also introduces a new doping strategy, namely, "electrochemical reaction mechanism control doping." The new electrochemical mechanism control technology enables the study of the precise deterioration mechanism of layered cathode materials for Li-ion batteries (LIBs). Accordingly, tremendous efforts have been devoted to the development of various types of layered cathode materials, such as lithium-rich, nickel-rich, and cobalt-rich materials, by using an electrochemical functioning doping method. This progress report also gives a perspective on potential future directions for this field. In this context, detailed methodological approaches are suggested for advanced doping studies, where the consideration of the doping method takes significance as great as designing doping configurations, e.g., chemical composition, doping depth, and doping site control, for the modification of battery material properties. As an instance of the methodological approaches for doping studies, a new "secondary doping" is shown with exemplary experimental results showing that functioning dopants (primary dopants) are homogeneously dispersed on the layered cathode materials by using supporting dopants (secondary dopants). This study will provide insights into the future direction of doping research of LIBs, as well as the history of the development of atomic substitution in layered cathode materials

Evaluation of the Volumetric Activity of the Air Electrode in a Zinc-Air Battery Using a Nitrogen and Sulfur Co-doped Metal-free Electrocatalyst

While numerous oxygen electrocatalysts have been reported to enhance zinc-air battery (ZAB) performance, highly efficient electrocatalysts for the oxygen electrocatalysis need to be developed for broader commercialization of ZABs. Furthermore, areal (instead of volumetric) power density has been used to benchmark the performance of ZABs, often causing ambiguities or confusions. Here, we propose a methodology for evaluating the performance of a ZAB using the volumetric (rather than the areal) power density by taking into consideration the air electrode thickness. A nitrogen and sulfur co-doped metal-free oxygen reduction electrocatalyst (N-S-PC) is used as a model catalyst for this new metric. The electrocatalyst exhibited a half-wave potential of 0.88 V, which is similar to that of the Pt/C electrocatalyst (0.89 V) due to the effects of co-doping and a highly mesoporous structure. In addition, the use of volumetric activity allows fair comparison among different types of air electrodes. The N-S-PC-loaded air electrode demonstrated a higher peak power density (5 W cm(-3)) than the carbon felt or paper electrode in the ZAB test under the same testing conditions

Gas phase synthesis of amorphous silicon nitride nanoparticles for high-energy LIBs

Various morphological nanoscale designs have come into the spotlight to address the failure in the mechanism of high-capacity Si anodes, i.e. severe volume expansion (similar to 300%). However, the nanostructured Si anodes designed still suffer mechanical degradation upon repeated cycling, and eventually become shredded and surrounded by accumulated solid electrolyte interphase (SEI) layers. Here, we introduce a highly homogenous phase design of Si with N by scalable gas phase synthesis, which tackles the intrinsic challenges of Si anodes, i.e. mechanical degradation and slow Li diffusion. Si-rich silicon nitride (SiN) nanoparticles are realized using a specially customized vertical furnace, where Si3N4 acts as not only a strong inactive matrix but also a Li ion conductor after lithiation. Owing to their stubborn and ionic conductive matrix, SiN nanoparticles exhibit superior rate performances and cycling stability while maintaining their dense structure. Accordingly, when combined with commercially viable graphite-blended system for the pouch-type 1 A h cell, SiN nanoparticles demonstrate high rate capability at 5C, as well as contributing much higher capacity than silicon nanoparticles by mitigating electrode swelling during cycling

A Highly Efficient and Robust Cation Ordered Perovskite Oxide as a Bifunctional Catalyst for Rechargeable Zinc-Air Batteries

Of the various catalysts that have been developed to date for high performance and low cost, perovskite oxides have attracted attention due to their inherent catalytic activity as well as structural flexibility. In particular, high amounts of Pr substitution of the cation ordered perovskite oxide originating from the state-of-the-art Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) electrode could be a good electrode or catalyst because of its high oxygen kinetics, electrical conductivity, oxygen capacity, and structural stability. However, even though it has many favorable intrinsic properties, the conventional high-temperature treatment for perovskite synthesis, such as solid-state reaction and combustion process, leads to the particle size increase which gives rise to the decrease in surface area and the mass activity. Therefore, we prepared mesoporous nanofibers of various cation-ordered PrBa0.5Sr0.5Co2-xFexO5+delta = 0, 0.5, 1, 1.5, and 2) perovskites via electrospinning. The well-controlled B-site metal ratio and large surface area (similar to 20 m(2) g(-1)) of mesoporous nanofiber result in high performance of the oxygen reduction reaction and oxygen evolution reaction and stability in zinc-air battery