106 research outputs found
Essays in Macroeconomics
No full textThis dissertation consists of three papers focusing on the effects of firm and worker
strategies on economic aggregates. The first chapter estimates the effects of corporate
political connections with Congressional committee members on the rise of market
power of large firms in the United States. By exploiting the committee exile as a quasiexogenous
shock, it shows that on average 10% higher political connections increase
0.58% in markups. The effects can be mostly explained by lower production cost. The
second chapter study how search frictions affect job matching quality and spatial sorting.
I develop a spatial general equilibrium model with two-sided heterogeneity and
frictional labor markets. The model predicts less spatial sorting when search costs fall,
but more sorting with skill-biased technical change. I use this framework to quantify
the roles of SBTC, search frictions, and amenities in spatial trends. The third chapter
examines how the internal organization of firms shapes asymmetric wage risks over the
business cycle using matched employer-employee data in Germany. We document that
the internal organization of firms introduces a trade-off between wage premiums and
wage risks.Aquesta tesi doctoral consta de tres articles que se centren en els efectes de les estratègies
de les empreses i els treballadors sobre els agregats econòmics. El primer
capítol estima els efectes de les connexions polítiques corporatives amb membres dels
comitès del Congrés en l’augment del poder de mercat de les grans empreses als Estats
Units. Aprofitant l’exili del comitè com a xoc quasi-exògen, es demostra que, de mitjana,
un 10% més de connexions polítiques incrementen un 0.58% els marges. Aquests
efectes es poden explicar principalment per costos de producció més baixos. El segon
capítol estudia com les friccions en la cerca afecten la qualitat de l’emparellament laboral
i la classificació espacial. Desenvolupo un model d’equilibri general espacial amb
heterogeneïtat bilateral i mercats laborals amb friccions. El model prediu menys classificació
espacial quan cauen els costos de cerca, però més classificació amb un canvi
tècnic inclinat cap a habilitats. Utilitzo aquest marc per quantificar els rols del canvi
tècnic inclinat cap a habilitats, les friccions en la cerca i els serveis en les tendències
espacials. El tercer capítol examina com l’organització interna de les empreses modela
els riscos salarials asimètrics al llarg del cicle econòmic utilitzant dades emparellades
d’empleador-empleat a Alemanya. Documentem que l’organització interna de les empreses
introdueix un trade-off entre primes salarials i riscos salarials.Programa de Doctorat en Economia, Finances i Empres
Solvent control of water O−H bonds for highly reversible zinc ion batteries
No full textAqueous Zn-ion batteries have attracted increasing research interest; however, the development of these batteries has been hindered by several challenges, including dendrite growth, Zn corrosion, cathode material degradation, limited temperature adaptability and electrochemical stability window, which are associated with water activity and the solvation structure of electrolytes. Here we report that water activity is suppressed by increasing the electron density of the water protons through interactions with highly polar dimethylacetamide and trimethyl phosphate molecules. Meanwhile, the Zn corrosion in the hybrid electrolyte is mitigated, and the electrochemical stability window and the operating temperature of the electrolyte are extended. The dimethylacetamide alters the surface energy of Zn, guiding the (002) plane dominated deposition of Zn. Molecular dynamics simulation evidences Zn2+ ions are solvated with fewer water molecules, resulting in lower lattice strain in the NaV3O8·1.5H2O cathode during the insertion of hydrated Zn2+ ions, boosting the lifespan of Zn|| NaV3O8·1.5H2O cell to 3000 cycles.Yanyan Wang, Zhijie Wang, Wei Kong Pang, Wilford Lie, Jodie A. Yuwono, Gemeng Liang, Sailin Liu, Anita M. D, Angelo, Jiaojiao Deng, Yameng Fan, Kenneth Davey, Baohua Li, Zaiping Gu
Investigation of cobalt-free lithium-rich layered oxide cathodes for high-performance lithium-ion batteries
No full textLi-rich layered oxides (LLOs) are considered as one of the most promising cathode candidates for next-generation lithium-ion batteries. Unfortunately, their development is challenging, due to the detrimental structure changes and voltage decay that resulted from irreversible oxygen redox and transition metal (TM) migration. This thesis focuses on studying the structural evolution of Co-free LLO cathodes and improving their electrochemical performance. The mechanistic behaviour of Li1.2Ni0.2Mn0.6O2 (LNMO) was comprehensively studied using a series of synchrotron-based characterizations. An intrinsic mechanistic behaviour transition from the monoclinic (C2/c) to the hexagonal (R3̅m) was demonstrated for the first time. Based on this understanding, electrochemically active 4d metal Ruthenium (Ru) was introduced into both R3̅m and C2/c components in LNMO to improve the stability of LNMO. With 3 w.t. % Ru doping, the oxygen lattice is strengthened and the best voltage retention (</p
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Fate of Women Sent-Down Youths During the Up to the Mountains and Down to the Countryside Movement
No full textThis paper focus on the marriage and married life of sent-down youths from Shanghai to Jilin Province during the Down to the Countryside Movement. The main historical materials are the oral interviews conducted by the author. My analysis also incorporates regional records, memories and diaries
Enhanced High Voltage Stability of Spinel-Type Structured LiNi0.5Mn1.5O4 Electrodes: Targeted Octahedral Crystal Site Modification
No full textHigh-voltage spinel-type structured LiNi0.5Mn1.5O4 (LNMO) shows promise as a next-generation high-energy-density lithium-ion battery cathode material, however, capacity decay on extended cycling hinders its widespread adoption, underscoring an urgent need for further development. In this work, we introduce Zn at octahedral 16c crystal sites in LNMO with Fd3m space group to improve rate capability and reduce the rapid capacity decay otherwise experienced during extended cycling. The current work resolves the detailed influence of isolated modification at octahedral 16c crystal sites, unveiling the mechanism for these performance improvements. We show that occupation of Zn at previously empty 16c sites prevents the migration of Ni/Mn to adjacent 16c sites, eliminating transformation to a rock-salt type structured Ni0.25Mn0.75O2 phase above 4.8 V, preventing structure degradation and suppressing voltage polarization. This study provides insights into the fundamental structure-function relationship of the LNMO battery cathode, pointing to pathways for the crystal structure engineering of materials with superior performance.Jinshuo Zou, Gemeng Liang, Shilin Zhang, Lars Thomsen, Yameng Fan, Wei Kong Pang, Zaiping Guo, and Vanessa K. Peterso
Selective Extraction of Critical Metals from Spent Li-ion Battery Cathode: Cation-Anion Coordination and Anti-Solvent Crystallization
No full textOwing to continuing global use of lithium-ion batteries (LIBs), in particular in electric vehicles (EVs), there is a need for sustainable recycling of spent LIBs. Deep eutectic solvents (DESs) are reported as “green solvents” for low-cost and sustainable recycling. However, the lack of understanding of the coordination mechanisms between DESs and transition metals (Ni, Mn and Co) and Li makes selective separation of transition metals with similar physicochemical properties practically difficult. Here, it is found that the transition metals and Li have a different stable coordination structure with the different anions in DES during leaching. Further, based on the different solubility of these coordination structures in anti-solvent (acetone), a leaching and separation process system is designed, which enables high selective recovery of transition metals and Li from spent cathode LiNi(1/3)Co(1/3)Mn(1/3)O(2) (NCM111), with recovery of acetone. Recovery of spent LiCoO2 (LCO) cathode is also evidenced and a significant selective recovery for Co and Li is established, together with recovery and reuse of acetone and DES. It is concluded that the tuning of cation–anion coordination structure and anti-solvent crystallization are practical for selective recovery of critical metal resources in the spent LIBs recycling.Yanqiu Lyu, Jodie A. Yuwono, Yameng Fan, Jingxi Li, Jingxiu Wang, Rong Zeng, Kenneth Davey, Jianfeng Mao, Chaofeng Zhang, and Zaiping Gu
Catalytic role of in-situ formed C-N species for enhanced Li2CO3 decomposition
No full textSluggish kinetics of the CO2 reduction/evolution reactions lead to the accumulation of Li2CO3 residuals and thus possible catalyst deactivation, which hinders the long-term cycling stability of Li-CO2 batteries. Apart from catalyst design, constructing a fluorinated solid-electrolyte interphase is a conventional strategy to minimize parasitic reactions and prolong cycle life. However, the catalytic effects of solid-electrolyte interphase components have been overlooked and remain unclear. Herein, we systematically regulate the compositions of solid-electrolyte interphase via tuning electrolyte solvation structures, anion coordination, and binding free energy between Li ion and anion. The cells exhibit distinct improvement in cycling performance with increasing content of C-N species in solid-electrolyte interphase layers. The enhancement originates from a catalytic effect towards accelerating the Li2CO3 formation/decomposition kinetics. Theoretical analysis reveals that C-N species provide strong adsorption sites and promote charge transfer from interface to *CO2 2− during discharge, and from Li2CO3 to C-N species during charge, thereby building a bidirectional fast-reacting bridge for CO2 reduction/evolution reactions. This finding enables us to design a C-N rich solidelectrolyte interphase via dual-salt electrolytes, improving cycle life of Li-CO2 batteries to twice that using traditional electrolytes. Our work provides an insight into interfacial design by tuning of catalytic properties towards CO2 reduction/evolution reactions.Fangli Zhang, Wenchao Zhang, Jodie A. Yuwono, David Wexler, Yameng Fan, Jinshuo Zou, Gemeng Liang, Liang Sun, Zaiping Gu
Understanding H2 evolution electrochemistry to minimize solvated water impact on zinc anode performance
No full textPublished online: 20 September 2022H2 evolution is the reason for poor reversibility and limited cycle stability with Zn metal anodes, and impedes practical application in aqueous zinc ion batteries (AZIB). Here we demonstrate for the first time, using combined gas chromatography experiment and computation, that H2 evolution primarily originates from solvated water, rather than free water without interaction with Zn2+ . We evidence, using linear sweep voltammetry (LSV) in salt electrolytes that H2 evolution occurs at a more negative potential than zinc reduction because of high overpotential against H2 evolution on Zn metal. We test our hypothesis and confirm, using glycine additive to reduce solvated water, that H2 evolution and "parasitic" side reactions are suppressed on the Zn anode. We evidence that this electrolyte additive suppresses H2 evolution, reduces corrosion and gives a uniform Zn deposition in Zn|Zn and Zn|Cu cells when compared with bare ZnSO4 electrolyte. We demonstrate Zn|PANI (highly conductive polyaniline) full cells exhibit boosted electrochemical performance in 1 M ZnSO4 -3 M glycine electrolyte and, a high reversible capacity of 100 mAh g-1 in a practical Zn|PANI pouch cell. We conclude that this new understanding of electrochemistry of H2 evolution can be used for design of relatively low-cost and safe AZIB for practical large-scale energy storage. Findings will be of immediate benefit in electrolyte design for high performance rechargeable batteries and therefore of wide interest to researchers and manufacturers. This article is protected by copyright. All rights reserved.Fuhua Yang, Jodie A. Yuwono, Junnan Hao, Jun Long, Libei Yuan, Yanyan Wang, Sailin Liu, Yameng Fan, Shiyong Zhao, Kenneth Davey, and Zaiping Gu
Size-Dependent Effects of Ru Nanoparticles on Li-CO2 Batteries
No full textLetter.
Published: September 30, 2024Li-CO₂ batteries capture and convert CO₂ into a valuable energy storage medium, promoting both energy storage and environmental sustainability. While Ru-based catalysts exhibit exceptional catalytic activity and are widely deployed in Li-CO₂ batteries, the Ru nanoparticle size effects on electrolysis remains underexplored. Herein, we synthesized Ru nanoparticles ranging from ∼1.1 to ∼7.4 nm to unveil the size-dependent activity in Li-CO₂ batteries. As Ru size decreases, the d-band center of Ru is identified upshifted toward the Fermi level, and the Gibbs energy change for the rate-determining step during charge is lowered. The binding energy of C=O and Li−O is notably reduced, confirming that a strong interaction between small Ru and Li₂CO₃ can destabilize Li₂CO₃ and facilitate its decomposition. Furthermore, small Ru nanoparticles can alleviate Li₂CO₃ accumulation on cathodes. This work provides insight and guidance for catalyst design and optimization in Li-CO₂ batteries, which can be extended to other battery systems involving solid product formation and decomposition.Jinshuo Zou, Gemeng Liang, Jodie A. Yuwono, Fangli Zhang, Yameng Fan, Shilin Zhang, Bernt Johannessen, Liang Sun, and Zaiping Gu
Unlocking the potential of silicon anodes in lithium-ion batteries: A claw-inspired binder with synergistic interface bonding
No full textBinders play a crucial role in enhancing the cycling stability of silicon anodes in next-generation Li-ion batteries. However, traditional linear polymer binders have difficulty withstanding the volume expansion of silicon during cycling. Herein, inspired by the fact that animals’ claws can grasp objects firmly, a claw-like taurine-grafted-poly (acrylic acid) binder (Tau-g-PAA) is designed to improve the electrochemical performance of silicon anodes. The synergistic effects of different polar groups (sulfo and carboxyl) in Tau-g-PAA facilitate the formation of multidimensional interactions with silicon nanoparticles and the diffusion of Li ions, thereby greatly improving the stability and rate performance of silicon anodes, which aligns with results from density functional theory (DFT) simulations. As expected, a Tau-g-PAA/Si electrode exhibits excellent cycling performance with a high specific capacity of 1003 mA h g1 at 1 C (1 C ¼ 4200 mA h g1 ) after 300 cycles, and a high rate performance. The design strategy of using polar small molecule-grafted polymers to create claw-like structures could inspire the development of better binders for silicon-based anodes.Jun Shen, Shilin Zhang, Haoli Wang, Renxin Wang, Yingying Hu, Yiyang Mao, Ruilin Wang, Huihui Zhang, Yumeng Du, Yameng Fan, Yingtang Zhou, Zaiping Guo, Baofeng Wan
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