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1. Size-Dependent Reaction Mechanism of λ -MnO ₂ Particles as Cathodes in Aqueous Zinc-Ion Batteries

   https://doi.org/10.34133/2022/9765710  

   Tang, Zhichu ; Chen, Wenxiang ; Lyu, Zhiheng ; Chen, Qian ( February 2022 , Energy Material Advances)

   Manganese dioxide (MnO 2 ) with different crystal structures has been widely investigated as the cathode material for Zn-ion batteries, among which spinel λ -MnO 2 is yet rarely reported because Zn-ion intercalation in spinel lattice is speculated to be limited by the narrow three-dimensional tunnels. In this work, we demonstrate that Zn-ion insertion in spinel lattice can be enhanced by reducing particle size and elucidate an intriguing electrochemical reaction mechanism dependent on particle size. Specifically, λ -MnO 2 nanoparticles (NPs, ~80 nm) deliver a high capacity of 250 mAh/g at 20 mA/g due to large surface area and solid-solution type phase transitionmore »pathway. Meanwhile, severe water-induced Mn dissolution leads to the poor cycling stability of NPs. In contrast, micron-sized λ -MnO 2 particles (MPs, ~0.9  μ m) unexpectedly undergo an activation process with the capacity continuously increasing over the first 50 cycles, which can be attributed to the formation of amorphous MnO x nanosheets in the open interstitial space of the MP electrode. By adding MnSO 4 to the electrolyte, Mn dissolution can be suppressed, leading to significant improvement in the cycling performance of NPs, with a capacity of 115 mAh/g retained at 1 A/g for over 500 cycles. This work pinpoints the distinctive impacts of the particle size on the reaction mechanism and cathode performance in aqueous Zn-ion batteries.« less
2. Vertically Stacked 2H‐1T Dual‐Phase MoS ₂ Microstructures during Lithium Intercalation: A First Principles Study

   https://doi.org/10.1111/jace.17367  

   Parida, Shayani ; Mishra, Avanish ; Chen, Jie ; Wang, Jin ; Dobley, Arthur ; Carter, C. Barry ; Dongare, Avinash M. ( July 2020 , Journal of the American Ceramic Society)

   Layered transition-metal dichalcogenides (TMDs) have shown promise to replace carbon-based compounds as suitable anode materials for Lithium-ion batteries (LIBs) owing to facile intercalation and de-intercalation of lithium (Li) during charging and discharging, respectively. While the intercalation mechanism of Li in mono- and bi-layer TMDs have been thoroughly examined, mechanistic understanding of Li intercalation-induced phase transformation in bulk or films of TMDs is still largely unexplored. This study investigates possible scenarios during sequential Li intercalation and aims to gain a mechanistic understanding of the phase transformation in bulk MoS2 using density functional theory (DFT) calculations. The manuscript examines the role ofmore »concentration and distribution of Li-ions on the formation of dual-phase 2H-1T microstructures that have been observed experimentally. The study demonstrates that lithiation would proceed in a systematic layer-by-layer manner wherein Li-ions diffuse into successive interlayer spacings to render local phase transformation of the adjacent MoS2 layers from 2H-to-1T phase in the multilayered MoS2. This local phase transition is attributed to partial ionization of Li and charge redistribution around the metal atoms and is followed by subsequent lattice straining. In addition, the stability of single-phase vs. multiphase intercalated microstructures, and the origins of structural changes accompanying Li-ion insertion are investigated at atomic scales.« less
3. (Invited Talk): Designing smart materials for efficient energy conversion: The story of transition metal chalcogenides

   Nath, Manashi ; Masud, Jahangir ; Swesi, Abdurazag ; De Silva, Umanga ; Amin, Bahar ; Umapathi, Siddesh ; Liyanage, Wipula ( March 2018 , 255th ACS National Meeting & Exposition, New Orleans, LA, United States, March 18-22, 2018 (2018), ENFL-330)

   Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Among these, water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-​air batteries, fuel cells, to solar-​to-​fuel energy conversion systems. In fact, solar water splitting is one of the most promising method to produce Hydrogen without depleting fossil-​fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited bymore »the anodic oxygen evolution reaction (OER)​, which is a kinetically sluggish, electron-​intensive uphill reaction. A slow OER process also slows the other half- cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER process from earth-​abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient OER electrocatalysts. We have proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chem. potential around the transition metal center, [e.g. lowering the Ni 2+ -​-​> Ni 3+ oxidn. potential in Ni-​based catalysts where Ni 3+ is the actually catalytically active species]​. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-​Fe, Co, and Ni-​Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA​/cm 2 [Ni 3 Se 2 - 200 - 290 mV; Co 7 Se 8 - 260 mV; FeNi 2 Se 4 -​NrGO - 170 mV (NrGO - N-​doped reduced graphene oxide)​; NiFe 2 Se 4 - 210 mV; CoNi 2 Se 4 - 190 mV; Ni 3 Te 2 - 180 mV]​.« less
4. Interfacial processes in electrochemical energy systems

   https://doi.org/10.1039/d1cc01703a  

   Wang, Maoyu ; Feng, Zhenxing ( October 2021 , Chemical Communications)

   Electrochemical energy systems such as batteries, water electrolyzers, and fuel cells are considered as promising and sustainable energy storage and conversion devices due to their high energy densities and zero or negative carbon dioxide emission. However, their widespread applications are hindered by many technical challenges, such as the low efficiency and poor long-term cyclability, which are mostly affected by the changes at the reactant/electrode/electrolyte interfaces. These interfacial processes involve ion/electron transfer, molecular/ion adsorption/desorption, and complex interface restructuring, which lead to irreversible modifications to the electrodes and the electrolyte. The understanding of these interfacial processes is thus crucial to provide strategiesmore »for solving those problems. In this review, we will discuss different interfacial processes at three representative interfaces, namely, solid–gas, solid–liquid, and solid–solid, in various electrochemical energy systems, and how they could influence the performance of electrochemical systems.« less
5. Experimental Study of NCM-Si Batteries With Bi-Directional Actuation

   https://doi.org/10.1115/SMASIS2021-67596  

   Shan, Shuhua ; Gonzalez, Cody ; Rahn, Christopher ; Frecker, Mary ( September 2021 , 2021 ASME SMASIS)

   Silicon is regarded as one of the most promising anode materials for lithium-ion batteries. Its high theoretical capacity (4000 mAh/g) has the potential to meet the demands of high-energy density applications, such as electric air and ground vehicles. The volume expansion of Si during lithiation is over 300%, indicating its promise as a large strain electrochemical actuator. A Si-anode battery is multifunctional, storing electrical energy and actuating through volume change by lithium-ion insertion.

   To utilize the property of large volume expansion, we design, fabricate, and test two types of Si anode cantilevers with bi-directional actuation: (a) bimorph actuator andmore »(b) insulated double unimorph actuator. A transparent battery chamber is fabricated, provided with NCM cathodes, and filled with electrolyte. The relationship between state of charge and electrode deformation is measured using current integration and high-resolution photogrammetry, respectively. The electrochemical performance, including voltage versus capacity and Coulombic efficiency versus cycle number, is measured for several charge/discharge cycles. Both configurations exhibit deflections in two directions and can store energy. In case (a), the largest deflection is roughly 35% of the cantilever length. Twisting and unexpected bending deflections are observed in this case, possibly due to back-side lithiation, non-uniform coating thickness, and uneven lithium distribution. In case (b), the single silicon active coating layer can deflect 12 passive layers.

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