Electrochemical Cycling Research Articles

Synergistic Regulation of Hydrogen Bonds and Electrocrystallization for Enhanced Aqueous Zinc Batteries

AbstractAqueous zinc ion batteries are promising candidates for large scale energy‐storage due to their combination of inherent security and abundant reserves. The Zn metal undergoes continuous plating and stripping during electrochemical cycling, accompanied by parasitic side reactions and dendrite growth, which severely impedes the commercialization of batteries. Here, an innovative strategy is introduced in electrolyte engineering, dedicated to enhancing the stability at the Zn/electrolyte interface. Theoretical calculations and in situ experimental analyses collectively demonstrate that methyl sulfonyl methane (MSM) additives are beneficial in jointly modulating the hydrogen bonding network and the Zn2+ solvation structure, which in turn restricts H2O activity at the interface. Concurrently, the preferential adsorption of MSM on the Zn surface facilitates the controlled growth of compact zinc layers while suppressing dendritic and parasitic reactions. By modulating the electrolyte and managing the electrode interface, the Zn||Zn symmetric battery can be reversibly cycled over 150 days at a current density of 2 mA cm−2, and the assembled Zn||Cu half‐batteries show impressive cycling stability over 3100 cycles. This study provides an in‐depth comprehension of the Zn2+ plating/stripping behavior, and the development of sophisticated electrolyte systems offers practical guidance for constructing high‐performance zinc‐based batteries.

Modeling Metal Nitrides for Interface Design in Lithium-Sulfur Batteries with GPUs and CPUs

As current batteries reach their limits, finding new battery materials is crucial. Lithium-sulfur batteries are a promising next-generation technology but face three major issues: low active material utilization, cathode pulverization, and limited polysulfide conversion leading to anode corrosion. Nano-deposition of metal nitride (MNx, M = Ti, V, Zr, etc.) layers on the graphene sulfur cathodes could significantly improve conductivity and cycling performance. Nevertheless, the large number of potential metal candidates requires preliminary and efficient computational screening using density-functional theory (DFT). This modeling framework can be used to calculate many properties of the coatings and screen out poor candidates. Firstly, the surface-adsorption ability of metal nitride candidates for lithium polysulfide intermediates involved in the electrochemical cycle (Li2S, Li2S2, Li2S4, Li2S6, Li2S8, S8) must be greater than the adsorption by dioxolane and dimethyl ether electrolytes (>~0.99eV). Secondly, the electronic properties before and after adsorption must feature significant density of states near the Fermi level, as a possible indicator of good electrical conductivity. Lastly, the free-energy profiles for the sulfur reduction reaction (SRR) over the remaining candidates will be estimated to better understand the catalytic properties of the metals. Particular attention will be paid to the Li2S2 reduction to Li2S, the potential limiting step. The top catalyst candidates should allow for an exergonic reaction. Finally, this application serves as a case study for our modeling platform, and the relative merits of standard for CPUs and GPUs in terms of computation time and accuracy will be discussed. Careful analysis of binding energy results, densities of states, and energy profiles for the various metal candidates provides valuable insights into the design of experimentally viable lithium-sulfur batteries, as well as advanced interface design in the broader field of battery research.

Operando Tracking the Dissolution and Deposition Dynamics in Aqueous Zn-MnO2 Batteries

Aqueous Zn–MnO2 batteries have received extensive attention for next-generation large-scale energy storage because of their low cost and outstanding safety. Despite efforts to achieve better performances, the charge-storage chemistry of MnO2 cathodes remains controversial. Zn-ion insertion, Zn-ion/proton co-insertion, proton insertion, and electro-dissolution have been proposed as the mechanism of the MnO2 cathodes. More specifically, the pathway of Mn dissolution is debatable: while intercalation chemistry leads to dissolution caused by the Jahn–Teller effect of Mn(III), electro-dissolution relies on a conversion from Mn(IV) to Mn(II). Furthermore, it is recently considered that Mn dissolution/redeposition efficiency is crucial to the reversibility of MnO2 cathodes, depending on pre-added Mn in the electrolyte. The role of trace Mn additive is also confusing. Last but not least, Mn dissolution and deposition is conjectured to be linked to the dissolution/redeposition of Zn‐based species-that is, Zn4SO4·(OH)6·xH2O (ZSH). To understand these key scientific questions that enlighten the further design of materials and electrolytes, it is imperative to develop operando measurements of the MnO2 cathodes. In our study, we utilized synchrotron X-ray fluorescence microscopy with high spatial resolution to probe the evolution of Zn and Mn species during electrochemical cycling. We can quantify the relationship between Zn and Mn concentrations from the electrode level to the single-particle level. We conclude that during the first discharge, MnO2 delivers the capacity by electro-dissolution, accompanied by the rapid precipitation of ZSH due to change of pH. ZSH surrounds the MnO2, which has high reversibility with the pre-added Mn additive in electrolytes. Our work provides in-depth insights into the complex Zn/Mn deposition and deposition near the electrode surface which will guide the further development of aqueous Zn-MnO2 batteries.

3D Printed Symmetric Carbon Supercapacitors: A Study Comparing Electrochemical Performance and Cycle Life Depending on 3D Printing Technique and Materials

With the ongoing global energy crisis, producing reliable and efficient methods of energy storage remains an integral part of cutting-edge materials research. Within this topic, 3D-printing (also known as additive manufacturing) is evolving from a niche hobby to a reliable scientific tool for materials science research [1-3]. 3D-printing energy storage materials provides unparalleled levels of customisation [4-9] and freedom of design, while also eliminating waste material during the manufacturing process.3D-printing energy storage materials has been widely covered, but usually just focuses on one method of 3D-printing. Directly comparing more than one 3D-printing method within a single energy storage study is far more seldom researched. This work directly compares the electrochemical performances of symmetric carbon-based supercapacitor devices made using two 3D-printing techniques, SLA (stereolithography) and FDM (fused deposition modelling). Two cell types are made in this study, one with gold-sputtered SLA-printed current collectors, the other with conductive PLA (polylactic acid) FDM-printed current collectors. Carbon-based electrode (various combinations of SWCNT, GNP, Super-P, PVDF) slurries and aqueous 6M KOH electrolyte are implemented in these cells. The benefits and limitations of these 3D-printing methods are directly compared, with the electrochemical performance of the supercapacitor cells being analysed using cyclic voltammetry and galvanostatic charge-discharge tests.The sputtered conductive SLA current collector cells display better conductivity and more ideal rectangular cyclic voltammetry curves for electronic double-layer capacitors (EDLCs) but suffer from poor cycle life in initial experiments (~5,000 charge-discharge cycles before losing all specific capacitance). The FDM current collector cells have poorer conductivity, less ideal cyclic voltammetry curves, and are less structurally sound (causing some electrolyte leakage over long term cycling) but offer extremely stable cycle life for supercapacitor cells, retaining most of their specific capacitance after 100,000 charge-discharge cycles. The cycle lives of the gold-sputtered SLA current collector cells are greatly improved after several changes made during the study, such as reducing the voltage window from 0.0-1.0 V to 0.2-0.7 V, and exploring additives for the carbon-based slurry electrodes, such as Super-P and PVDF (polyvinylidene fluoride).

Syntheses of Ni-Based Layered-Double Hydroxide Materials Via Liquid Phase Deposition Method for Alkaline Water Electrolysis

For the sustainable society, hydrogen production has received much attention during decades. The alkaline water electrolysis process has been recognized as one of the important processes for hydrogen products. For the achievements of an effective water electrolysis system, the decrease of the overpotential on the oxygen evolution reaction (OER), which is the four-electron and proton transfer process. These complex 4-electron sluggish processes lead to the large energy losses in the whole water electrolysis. Although the noble catalysts such as IrO2 or RuO2 exhibit high OER activity, their large-scale applications are limited due to cost problem. From this point of view, the low-cost transition metal materials, especially Ni-based catalysts, have been extensively studied. And also, it has been reported that the well-defined layered double hydroxide (LDH) structures can promote water oxidation through the interlayer anion effects. Despite this fact, the specific procedures for the preparation of Ni-based LDH structures have not been well established. Therefore, in this study, we have investigated the preparation of Ni-based LDH structures in the aqueous solution at room temperature, the so-called liquid phased deposition (LPD) method.Through the LPD method, we have synthesized various types of Ni-based LDH structures. As an example, the Ni-Al LDH structures were synthesized on the conductive substrate. It was found that our synthesized Ni-Al LDH exhibited relatively high OER activity and durability against electrochemical potential cycling [1]. In addition, the dependencies of the OER activity on the interlayer anion species were clearly demonstrated. In addition, the other types of Ni alloy LDHs were also prepared and their OER activity was investigated. Through the electrochemical measurements, we have confirmed the advantages of our materials prepared by LPD methods as an anode for alkaline water electrolysis.

Pseudocapacitive Storage in Molybdenum Oxynitride Nanostructures Reactively Sputtered on Stainless-Steel Mesh Towards an All-Solid-State Flexible Supercapacitor

Exploiting pseudocapacitance in rationally engineered nanomaterials offers greater energy storage capacities at faster rates. The present research reports a high-performance Molybdenum Oxynitride (MoON) nanostructured material deposited directly over stainless-steel mesh (SSM) via reactive magnetron sputtering technique for flexible symmetric supercapacitor (FSSC) application. The MoON/SSM flexible electrode manifests remarkable Na+-ion pseudocapacitive kinetics, delivering exceptional ~881.83 F.g-1 capacitance, thanks to the synergistically coupled interfaces and junctions between nanostructures of Mo2N, MoO2, and MoO3 co-existing phases, resulting in enhanced specific surface area, increased electroactive sites, improved ionic and electronic conductivity. Employing 3D Bode plots, b-value, and Dunn’s analysis, a comprehensive insight into the charge-storage mechanism has been presented, revealing the superiority of surface-controlled capacitive and pseudocapacitive kinetics. Utilizing PVA-Na2SO4 gel electrolyte, the assembled all-solid-state FSSC (MoON/SSM||MoON/SSM) exhibits impressive cell capacitance of 30.7 mF.cm-2 (438.59 F.g-1) at 0.125 mA.cm-2. Moreover, the FSSC device outputs superior energy density of 4.26 μWh.cm-2 (60.92 Wh.kg-1) and high power density of 2.5 mW.cm-2 (35.71 kW.kg-1). The device manifests remarkable flexibility and excellent electrochemical cyclability of ~91.94% over 10,000 continuous charge-discharge cycles. These intriguing pseudocapacitive performances combined with lightweight, cost-effective, industry-feasible, and environmentally sustainable attributes make the present MoON-based FSSC a potential candidate for energy-storage applications in flexible electronics. Figure 1

Intergranular Shielding of Ultrafine-Grained Ni-Rich Layered Cathode for Advanced Lithium-Ion Batteries

To achieve carbon neutrality on a global scale, fuel-powered vehicles are being steadily phased out over environmentally recommended electrified vehicles (EVs) with low greenhouse gas emissions. In a battery, the cathode is among the foremost components, as it predominantly determines the LIB’s performance and price. However, since current fleet of layered oxide NCM and NCA cathodes have a relatively lower Ni content, they can extract only a limited amount of reversible capacity (210 mAh∙g-1), restricting the driving range of EVs. To achieve higher energy densities, many studies have focused on increasing the average fraction of Ni in NCM or NCA cathodes to more than 90%. However, the extraction of large amounts of lithium ions is seriously compromised by the rapid deterioration of both cycle life and thermal safety. Recent studies on X-doped cathodes (X = B, Nb, Ta, Sb, W, and Mo) have offered promising results by engineering their geometric microstructural configurations to suppress intergranular cracking.1,2 This approach has proven its potential to improve the electrochemical cycling performance of Ni-rich NCA, NCM(A), and NM cathodes. However, prolonged exposure of the Ni-enriched (Ni ≥ 95%) cathode to the electrolyte generally results in continuous oxidative decomposition of electrolytes and subsequent cathode structural transformation, rendering the cathode unsuitable for applications requiring long battery life.3 Herein, we propose a highly stabilized Ni-enriched (Ni ≥ 95%) layered cathode by adopting a multi-stage engineering strategy, i.e., the construction of an ultrafine-scaled microstructure and subsequent intergranular shielding of the refined grains. The formation of an F induced protective layer at the intergranular boundaries of the ultrafine grains in Li[Ni0.95Co0.04Mo0.01]O2 (denoted as Mo1-NC96) noticeably improved both the structural and chemical stability of the cathode, with a limited degree of structural degradation and gas evolution. Reference s : [1] U.-H. Kim, G.-T. Park, B.-K. Son, G.W. Nam, J. Liu, L.-Y. Kuo, P. Kaghazchi, C.S. Yoon, Y.-K. Sun, Nat. Energy, 5 (2020) 860-869.[2] G.-T. Park, B. Namkoong, S.-B. Kim, J. Liu, C.S. Yoon, Y.-K. Sun, Nat. Energy, 7 (2022) 946-954.[3] F. Kong, C. Liang, L. Wang, Y. Zheng, S. Perananthan, R.C. Longo, J.P. Ferraris, M. Kim, K. Cho, Adv. Energy Mater., 9 (2019) 1802586.

Characterization of Degradation Mechanisms of Alternative Electrolytes Solutions in Fast Charging Li-Ion Batteries

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

Direct Observation of Reversible Surface Potential in Pseudocapacitive Electrochromic Films by Kelvin Probe Force Microscopy

High-resolution topography and local potential images together are very powerful tools for understanding the local environment of nanomaterials. In electrochemistry, there are significant changes within the electrode materials upon charging and discharging. However, the surface changes for pseudocapacitive materials in repetitive electrochemical cycling are easily being overlooked. Thanks to the advances in Atomic Force Microscopy, it becomes feasible to visualize the electrical changes in surface upon charge transfer with Kelvin Probe Force Microscopy (KPFM) equipped with a conductive tip. We report the KPFM surface potential images and profiles of NiO electrochromic films upon bleaching (charging) and coloration (discharging). The measured surface potential is about 60 times higher in bleaching state upon charging at 20mC/cm2. What is interesting is that the potential profile shows identical topographic features with the height profile of surface morphology. The surface particles further demonstrate shape entanglement in one direction (from ~100nm to ~140nm) and shrinkage in the orthogonal direction, suggesting the charge-induced electrical stress. According to the pseudocapacitive features in the cyclic voltammetry and electrochemical impedance spectroscopy, the surface-dominant redox behavior is within expectation. Though, this dynamic surface potential change is not well studied but important, and associated with work function fluctuations and various kinds of nanoscale charge-sensitive properties, especially for efficient electrochromic supercapacitor energy storage.

Using Micrometer Scale X-Ray CT and Pore Network Modeling to Assess High-Energy Bi-Layer Li-Ion Battery Cathode Structures

The optimization of cathode pore space is pivotal for enhancing the rate capability of lithium-ion battery electrodes. Previous studies on simulated cathodes have highlighted the importance of achieving an optimal porosity gradient, with a gradual increase from the current collector side to the separator side to accommodate the growing demand for ion transport in that direction [1]–[3]. In this research, we address this requirement by introducing and investigating bi-layer NCM 811 cathodes. These cathodes consist of a slurry-coated dense bottom layer and a spray-coated highly porous top layer with varying relative thickness to approximate the desired porosity gradient. Employing Micrometer-scale X-ray CT characterization and pore network modeling, we evaluate the structural features, demonstrating the effectiveness of the design, and quantify essential parameters such as porosity and tortuosity. Furthermore, the cathodes are integrated into lithium anode half-cells and subjected to electrochemical cycling at different rates to assess ion transport and rate capability. Our findings reveal that to achieve the highest discharge spatial energy density above 1C for cathodes approximately 100μm thick, the compressed bottom layer with 30% porosity should have a thickness of 60μm, while the highly porous top layer with around 47% porosity should be 40μm thick.Reference:[1] A. Shodiev et al., “Deconvoluting the benefits of porosity distribution in layered electrodes on the electrochemical performance of Li-ion batteries,” Energy Storage Mater., vol. 47, pp. 462–471, May 2022, doi: 10.1016/j.ensm.2022.01.058.[2] X. Lu et al., “3D microstructure design of lithium-ion battery electrodes assisted by X-ray nano-computed tomography and modelling,” Nat. Commun., vol. 11, no. 1, p. 2079, Apr. 2020, doi: 10.1038/s41467-020-15811-x.[3] K. Song, C. Zhang, N. Hu, X. Wu, and L. Zhang, “High performance thick cathodes enabled by gradient porosity,” Electrochimica Acta, vol. 377, p. 138105, May 2021, doi: 10.1016/j.electacta.2021.138105.

Immobilization of PCET Materials for Electrochemical pH Swing Driven Carbon Capture

Proton-coupled electron transfer (PCET) is a promising method in the realm of carbon capture and release mechanisms. Its fundamental capacity lies in electrochemically inducing pH swings within an aqueous solution, leveraging the high solubility of carbonates in highly alkaline water to capture CO2 and subsequently release iton demand when the aqueous solution is acidified. PCET-based methods promise higher energy efficiency for carbon capture compared to other electrochemical carbon capture methods because they feature fast charge transfer kinetics and can decouple gas-liquid contact and electrochemical activation. In theory, they also allow the use of cheap, widely available small-molecule PCET agents. However, in practice, PCET agents have shown a key limitation that has, thus far, hindered their scalability: oxygen-induced chemical degradation with continued electrochemical cycling. In this work we mitigate the prevailing issue of oxygen sensitivity by immobilizing PCET agents onto a fabric substrate. Via reactive vapor deposition (RVD), porous and conductive films composed of PEDOT-Cl and poly-aminoanthroquinone (PAAQ) are deposited on the surface of a wool felt blend fabric. This approach resulted in the development of a cost-effective, metal-free, and efficient electrode for both capture and release of CO2. Through electrochemical evaluation, the performance of PCET-active quinone moieties present on PAAQ was measured. The overall efficiency of electrochemical capture from gaseous CO2 was found to be 197 kJ/molCO2, substantiating the efficacy of this novel electrode. This work highlights the potential of fabric-immobilized PCET agents and presents a promising avenue towards a sustainable, efficient, and economically viable approach to carbon capture and release technologies.

High-Valence Ion Doped Compositionally Partitioned Li[Ni0.78Co0.10Mn0.12]O2 Cathode for Advanced Lithium-Ion Batteries

Numerous approaches have been employed to reduce the intrinsic instability of Ni-rich cathodes. Among them, the introduction of concentration gradient (CG), i.e., a strategy to protect the labile Ni-enriched compartment with a chemically protective Mn-rich shell, has proven successful in commercial applications.1 However, because the segmentation of transition metal (TM) constituents and the formation of unique geometric configurations are characteristics inherited from the CG hydroxide precursor; it is crucial to select the optimal calcination temperature and precisely control it.2 Excessive thermal energy input can result in concentration planarization because the CG of the hydroxide precursor is intrinsically susceptible to the interdiffusion of TM elements during lithiation. Moreover, the immoderate coarsening of the primary particles can eliminate the advantageous features of the CG design by producing equiaxed primary particles.2 In this study, we propose a strategy that can effectively ameliorate the deterioration of Ni-rich CG cathodes resulting from excessive thermal energy input and remarkably improve their electrochemical cycling performance. It was revealed that a trace amount of tungsten incorporation during the cathode calcination can effectively mitigate the high-temperature-induced cathode degeneration and maintain outstanding product quality over a wide range of temperatures. Thus, the proposed strategy opens new avenues for the facile synthesis of long-life Ni-rich CG cathodes. Reference s : [1] Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak, K. Amine, Nat. Mater. 8 (2009) 320-324.[2] G.-T. Park, H.-H. Ryu, T.-C. Noh, G.-C. Kang, Y.-K. Sun, Mater. Today 52 (2022) 9-18.

Analytical design of electrode particle debonding for battery applications

A physics-based analytical methodology is presented to describe the debonding of a statistically representative electrochemically active particle from the surrounding binder-electrolyte matrix in a porous electrode. The proposed framework enables to determine the space of C-Rates and electrode particle radii that suppresses or enhances debonding. Results are graphically summarized into maps where four debonding descriptions are identified: (a) the spontaneous debonding description, which occurs when the electrode particle spontaneously detaches from the matrix; (b) the continuous debonding description, which occurs when the electrode particle gradually loses contact with the surrounding matrix; (c) the electrochemical cycling fatigue description, which causes gradual growth of the flaw due to electrochemical cycling; and (d) the microstructural debonding description, which is a result of the microstructural stochastics of the electrode and is embodied in terms of the debonding probability of particles. The particle-dependent critical C-Rates for debonding power-law relation enables the experimental identification of individual failure mechanisms, thereby providing a context to formulate design strategies to minimize debonding and provide robust, physics-based, phenomenological, and statistics-based estimates for electrochemically driven failure.

Retrieving lost Li in LIBs for co-regeneration of spent anode and cathode materials

Direct regeneration of spent Li-ion battery electrode materials has garnered considerable attention due to its streamlined procedure, low energy consumption, and high economic viability. Typically, an Li source is required to address the vacant Li defects in spent cathodes for regeneration, while the removal of residual Li is crucial for regenerating spent anodes. Here, given our discovery that approximately 65 % of the residual Li in spent graphite demonstrates reactivity with water, we propose a straightforward water extraction method for purifying and regenerating spent graphite anode. By carefully controlling the concentrations of OH- and Li+ ions in the obtained Li-rich solution, it can be directly used to relithiate spent NCM cathodes. In this method, Li+ ions lost from the cathode during electrochemical cycling were reintroduced back into the cathode via aqueous relithiation, eliminating the need for additional Li sources to repair the Li deficiencies in spent cathode, effectively reducing recycling costs and minimizing the environmental impact associated with raw materials. The regenerated NCM cathode and graphite anode demonstrated specific capacities of 163 mAh/g and 386 mAh/g at a rate of 0.1C, respectively, both reaching the performance levels of pristine materials. Importantly, compared to traditional direct recycling methods, the Li-retrieving regeneration method reduced greenhouse gas emissions by 16 %, energy consumption by 17 %, water consumption by 17 %, and overall recycling costs by 12 %.

Parametric optimization for enhancing the electrical performance of hybrid photovoltaic/thermal and thermally regenerative electrochemical cycle system

Globally, the efficient utilization of solar energy has garnered significant attention. A hybrid system of photovoltaic/thermal (PV/T) modules integrated with thermally regenerative electrochemical cycle (TREC), i.e., PV/T-TREC has emerged recently and shows higher efficiency for solar-to-electrical conversion than a standalone PV system. However, there is a trade-off between the electricity generation from PV/T and TREC because the thermal energy from PV/T degrades the efficiency of the PV/T but improves that of TREC. Previous studies have failed to investigate this problem. This study therefore focuses on the key parameters that significantly affect the thermal output of PV/T, i.e., different PV materials, air gaps, heat storage tank volumes, and working fluids to investigate the maximum electrical efficiency of the hybrid system. The mathematical and transient-state numerical models are developed with the validation/refinement from the experiments. The results show that the hybrid system with PV material of cadmium telluride presents the best overall electrical efficiency of 25.37 %. The case of the air gap fosters the solar-to-electrical conversion. The electrical efficiency versus heat storage tank volume shows a convex curve, peaking at 200 L. The nanofluid performs the best. This study may help guide the practical application of such a high-efficiency electricity generation system.

Si3N4 as an Alternative of Silicon for the Anode Application in All‐Solid‐State Li‐Ion Batteries

ABSTRACTThe intermittent nature of renewable energy generation can be tackled by integrating them with electrochemical energy storage, which can also close the gap between supply and demand effectively. It has recently been demonstrated that Si3N4‐based negative electrodes are a promising option for lithium‐ion batteries due to their large theoretical capacity and appropriate working potential with extremely low polarization. In the present work, Si3N4 was utilized as anode material in all‐solid‐state lithium‐ion battery with lithium borohydride as a solid electrolyte and Li foil placed as a counter electrode. The electrochemical properties were investigated using galvanostatic charge/discharge profiling whereas the mechanism of lithiation delithiation was investigated in detail using x‐ray diffraction (XRD). The highest capacity of the composite materials was obtained as 1700 mAhg−1 at 0.05 C current rate in the first cycle, which is reduced to 370 in 5 cycles. However, a stability in the capacity was observed in subsequent cycles and a retention of almost 88% could be achieved in 150 cycles. The interfacial resistance before and after the electrochemical cycling was observed as 326 Ω and 13 kΩ, respectively which is also supported by the microstructural investigations where the cracks are observed because of thermochemical reactions.

Diffusion of lithium in copper current collectors of lithium metal anodes in liquid cells

Conflicting views are found in the literature on the significance of lithium diffusion into copper current collectors of lithium metal anodes. Previously published in situ Neutron Depth Profiling (NDP) measurements in a liquid cell revealed reversible Li diffusion in the current collector during electrochemical cycling, resulting in concentrations of ∼ 1 at. %. Herein, a model for these experiments is presented, in which stress in the deposit is induced by Li diffusion accompanying plating and stripping. This in turn produces stress gradients in the current collector, which together with composition gradients drive reversible grain boundary diffusion in Cu during cycling. Quantitative agreement with the NDP results is obtained for a fit diffusivity comparable to previous in situ measurements, but much larger than values from ex situ measurements using Li–Cu bilayers. Creep due to grain boundary diffusion is found to relax stress in the copper foil, resulting in low levels of stress and deformation during cycling. The results clarify the significance of Li diffusion in Cu, and also help elucidate the origin of stress in the lithium anode during cycling, which may induce interfacial instability.

Separating Cationic and Anionic Redox Activity in the Lithium-Rich Antiperovskite (Li2Fe)SO.

Lithium-rich antiperovskites promise to be a compelling class of high-capacity cathode materials due to the existence of both cationic and anionic redox activity. Little is however known about the effect of separating the electrochemical cationic process from the anionic process and the associated implications on the electrochemical performance. In this context, we report the electrochemical properties of the illustrative example of three different (Li2Fe)SO materials with a focus on separating cationic from anionic effects. With the high-voltage anionic process, an astonishing electrochemical capacity of around 400 mAh g-1 can initially be reached. Our results however identify the anionic process as the cause of poor cycling stability and demonstrate that the fading reported in previous literature is avoided by restricting to only the cationic processes. Following this path, our (Li2Fe)SO-BM500 shows strongly improved performance as indicated by constant electrochemical cycling over 100 cycles at a capacity of around 175 mAh g-1 at 1 C. Our approach also allows us to investigate the electrochemical performance of the bare antiperovskite phase excluding extrinsic activity from initial or cycling-induced impurity phases. Our results underscore that synthesis conditions are a critical determinant of electrochemical performance in lithium-rich antiperovskites, especially with regard to the amount of electrochemical secondary phases, while the particle size has not been found to be a crucial parameter. Overall, separating and understanding the effects of the cationic from the anionic redox activity in lithium-rich antiperovskites provides the route to further improve their performance in electrochemical energy storage.

High-Capacity spatial confined deposition/stripping enabled by biphasic modulation strategy for highly reversible zinc anodes

The development of aqueous zinc ion batteries (AZIBs) faces two major challenges: dendrites Zn and parasitic reaction, which originates from the random zinc deposition at the anode interface and the abundant free H2O activity of the solvation structure. Here, we report a biphasic modulation strategy (anode interface construction and solvation structure regulation) to solve these two issues simultaneously. Through introducing trace dynamic molecular additives, the rampant alkaline zincate byproducts at the anode interface are in situ converted to three-dimensional (3D) interconnected zinc deposition/stripping templates, while the solvation structure is effectively tailored to inhibit the overactivity of electrolyte. In situ Raman and molecular dynamics simulations verify that the Zn2+ flux during the electrochemical cycles is regulated in an orderly manner, hydrogen evolution reactions (HER) and dendrites zinc growth are effectively prevented. Zinc metal deposition/stripping is effectively confined to the 3D host space by solvation structure modulation and templates guidance, thus optimizing the crystallographic and zinc metal utilization rate during electrochemistry cycling. Even under extreme conditions, such as a high (dis)charge capacity of 10 mAh cm−2, symmetrical cells assembled based on a biphasic modulation strategy maintain long-term stability of over 1000 h.

High-Performance All-Solid-State on-Chip Planar Micro-Supercapacitors Based on Aminated Graphene Quantum Dots by Photolithography

Rapid development of portable miniaturized electronic devices has put forward higher requirements for microenergy. Functionalized graphene quantum dots combine the properties of both functionalized graphene and quantum dots, and are expected to promote further development of high-performance energy storage devices. Here, all-solid-state on-chip planar micro-supercapacitors (PMSCs) were fabricated based on aminated graphene quantum dots by modified liquid-gas interface self-assembly and photolithography, with the electrode width/gap of 24 μm/8 μm. The electrochemical performance was analyzed by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectrometry and cycle stability in PVA/H2SO4 gel electrolyte. The results indicated that the fabricated PMSCs showed good capacitive response at the scan rates of 0.01 V s−1 to 10000 V s−1. The CV curves of the PMSCs displayed a typical pseudocapacitive feature at the scan rates of 0.01 V s−1 to 1 V s−1. The PMSCs had ultrahigh rate capability of up to 10000 V s−1, and the GCD curves were near triangle-shaped curves, demonstrating excellent electrochemical reversibility. The PMSCs showed ideal capacitive behavior at the low frequency region of the Nyquist plot. The Nyquist plot of the PMSCs showed a semicircle at the high frequency region. The relaxation time constant of the PMSCs were 3.59 μs, indicating that the PMSCs had fast frequency response. After 10000 charge-discharge cycles at the scan rate of 500 V s−1, the initial capacitance retention rate of the PMSCs were 99.17%, indicating that the PMSCs possessed good long-term electrochemical stability. This study provides an important reference for the application of functional graphene quantum dots in the field of the PMSCs.