Project description:Thick electrodes can substantially enhance the overall energy density of batteries. However, insufficient wettability of aqueous electrolytes toward electrodes with conventional hydrophobic binders severely limits utilization of active materials with increasing the thickness of electrodes for aqueous batteries, resulting in battery performance deterioration with a reduced capacity. Here, we demonstrate that controlling the hydrophilicity of the thicker electrodes is critical to enhancing the overall energy density of batteries. Hydrophilic binders are synthesized via a simple sulfonation process of conventional polyvinylidene fluoride binders, considering physicochemical properties such as mechanical properties and adhesion. The introduction of abundant sulfonate groups of binders (i) allows fast and sufficient electrolyte wetting, and (ii) improves ionic conduction in thick electrodes, enabling a significant increase in reversible capacities under various current densities. Further, the sulfonated binder effectively inhibits the dissolution of cathode materials in reactive aqueous electrolytes. Overall, our findings significantly enhance the energy density and contribute to the development of practical zinc-ion batteries.
Project description:Lithium-ion batteries have received significant research interest due to their advantages in energy and power density, which are important to enabling many devices. One route to further increase energy density is to fabricate thicker electrodes in the battery cell; however, careful consideration must be taken when designing electrodes as to how increasing the thickness impacts the multiscale and multiphase molecular transport processes, which can limit the overall battery operating power. Design of these electrodes necessitates probing the molecular processes when the battery cell undergoes electrochemical charge/discharge. One tool for in situ insights into the cell is neutron imaging, because neutron imaging can provide information of where electrochemical processes occur within the electrodes. In this manuscript, neutron imaging is applied to track the lithiation/delithiation processes within electrodes at different current densities for a full cell with a thick sintered Li4Ti5O12 anode and LiCoO2 cathode. The neutron imaging reveals that the molecular distribution of Li+ during discharge within the electrode is sensitive to the current density, or equivalently discharge rate. An electrochemical model provides additional insights into the limiting processes occurring within the electrodes. In particular, the impact of tortuosity and molecular transport in the liquid phase within the interstitial regions in the electrodes are considered, and the influence of tortuosity was shown to be highly sensitive to the current density. Qualitatively, the experimental results suggest that the electrodes behave consistent with the packed hard sphere approximation of Bruggeman tortuosity scaling, which indicates that the electrodes are largely mechanically intact but also that a design that incorporates tunable tortuosity could improve the performance of these types of electrodes.
Project description:Unlike the interface between two immiscible electrolyte solutions (ITIES) formed between water and polar solvents, molecular understanding of the liquid-liquid interface formed for aqueous biphasic systems (ABSs) is relatively limited and mostly relies on surface tension measurements and thermodynamic models. Here, high-resolution Raman imaging is used to provide spatial and chemical resolution of the interface of lithium chloride - lithium bis(trifluoromethanesulfonyl)imide - water (LiCl-LiTFSI-water) and HCl-LiTFSI-water, prototypical salt-salt ABSs found in a range of electrochemical applications. The concentration profiles of both TFSI anions and water are found to be sigmoidal thus not showing any signs of a positive adsorption for both salts and solvent. More striking, however, is the length at which the concentration profiles extend, ranging from 11 to 2 µm with increasing concentrations, compared to a few nanometers for ITIES. We thus reveal that unlike ITIES, salt-salt ABSs do not have a molecularly sharp interface but rather form an interphase with a gradual change of environment from one phase to the other. This knowledge represents a major stepping-stone in the understanding of aqueous interfaces, key for mastering ion or electron transfer dynamics in a wide range of biological and technological settings including novel battery technologies such as membraneless redox flow and dual-ion batteries.
Project description:Quinones, which are ubiquitous in nature, can act as sustainable and green electrode materials but face dissolution in organic electrolytes, resulting in fast fading of capacity and short cycle life. We report that quinone electrodes, especially calix[4]quinone (C4Q) in rechargeable metal zinc batteries coupled with a cation-selective membrane using an aqueous electrolyte, exhibit a high capacity of 335 mA h g-1 with an energy efficiency of 93% at 20 mA g-1 and a long life of 1000 cycles with a capacity retention of 87% at 500 mA g-1. The pouch zinc batteries with a respective depth of discharge of 89% (C4Q) and 49% (zinc anode) can deliver an energy density of 220 Wh kg-1 by mass of both a C4Q cathode and a theoretical Zn anode. We also develop an electrostatic potential computing method to demonstrate that carbonyl groups are active centers of electrochemistry. Moreover, the structural evolution and dissolution behavior of active materials during discharge and charge processes are investigated by operando spectral techniques such as IR, Raman, and ultraviolet-visible spectroscopies. Our results show that batteries using quinone cathodes and metal anodes in aqueous electrolyte are reliable approaches for mass energy storage.
Project description:Driven by expanding interest in battery storage solutions and the success story of lithium-ion batteries, the research for the discovery and optimization of new battery materials and concepts is at peak. The generation of experimental (dis)charge data using coin cells is fast and feasible and proves to be a favorite practice in the battery research labs. The quantitative interpretation of the data, however, is not trivial and decelerates the process of screening and optimization of electrode materials and recipes. Here, we introduce the concept of polarographic map and demonstrate how it can be leveraged to quantify the contribution of different non-equilibrium phenomena to the performance limitation and total polarization of a lithium-ion cell. We showcase the accuracy and diagnostic power of this approach by preparing and analyzing the electrochemical performance of 54 sets of LiNixMnyCo1-x-yO2 electrodes with different formulations and designs discharged in a range of 0.2C-5C.
Project description:Water-in-salt (WIS) electrolytes provide a promising path toward aqueous battery systems with enlarged operating voltage windows for better safety and environmental sustainability. In this work, a new electrode couple, LiV3O8-LiMn2O4, for aqueous Li-ion batteries is investigated to understand the mechanism by which the WIS electrolyte improves the cycling stability at an extended voltage window. Operando synchrotron transmission x-ray microscopy on the LiMn2O4 cathode reveals that the WIS electrolyte suppresses the mechanical damage to the electrode network and dissolution of the electrode particles, in addition to delaying the water decomposition process. Because the viscosity of WIS is notably higher, the reaction heterogeneity of the electrodes is quantified with x-ray absorption spectroscopic imaging, visualizing the kinetic limitations of the WIS electrolyte. This work furthers the mechanistic understanding of electrode-WIS electrolyte interactions and paves the way to explore the strategy to mitigate their possible kinetic limitations in three-dimensional architectures.
Project description:The development of aqueous ammonium-ion batteries (AAIBs) is currently attracting great attention because of the interesting electrochemical features induced by the charge carrier NH4+. One possible way to improve the performance of AAIBs is increasing the salt concentration in the electrolyte. Yet, few studies focus on the complex electrode-electrolyte interface behaviors in highly concentrated electrolytes, which affect the electrochemical performance of AAIBs significantly. Herein, we aim to understand the impact of CH3COONH4 electrolyte concentration on the NH4+ storage performance of a bimetallic hydroxide material. Experimental and theoretical simulation results indicate that the acetate anion will participate in the construction of the solvated NH4+ in a highly concentrated electrolyte, facilitating the adsorption of the solvated NH4+ cluster on the electrode surface. Besides, a new partial de-solvation model is also proposed, demonstrating an energy favorable de-solvation process. Finally, an ammonium-ion hybrid battery is designed, which provides a high average discharge voltage of 1.7 V and good energy density of 368 W h kg(cathode)-1, outperforming most of the state-of-the-art aqueous batteries. This work provides new understanding about the electrode's interfacial chemistry in different concentrated CH3COONH4 electrolytes, establishes a correlation between the electrolyte concentration and the electrode's performances, and demonstrates the superiority of the hybrid ammonium-ion battery design.
Project description:The rapid development of electric vehicles has generated a recent demand for high energy density lithium-ion batteries (LIBs). One simple, effective way to enhance energy density of LIBs is to increase the thickness of electrodes. However, the conventional wet process used to fabricate thick electrodes involves the evaporation of large amounts of organic solvents, which causes an inhomogeneous distribution of conductive additives and binders. This weakens the mechanical and electrochemical network between active materials, resulting in poor electrochemical performance and structural degradation. Herein, we introduce a new strategy to produce homogeneous thick electrodes by using a dry, solvent-free process. Instead of using a conventional PVDF (polyvinylidene fluoride) binder, we employed a phenoxy resin as the binder in dry process for the first time. This thermoplastic binder exhibits better ductile properties than PVDF in the way that it generates a uniform network structure that connects the active materials during the hot press process. This enables the production electrochemically stable electrodes without using organic solvents, which record capacity retention rates of 73.5% over 50 cycles at a 40 mg/cm2 of thick electrodes. By contrast, thick electrodes produced with a PVDF binder via wet processing only have a capacity retention rate of 21.8% due to rapid structural degradation.
Project description:Formation of thick, high energy density, flexible solid supercapacitors is challenging because of difficulties infilling gel electrolytes into porous electrodes. Incomplete infilling results in a low capacitance and poor mechanical properties. Here we report a bottom-up infilling method to overcome these challenges. Electrodes up to 500??m thick, formed from multi-walled carbon nanotubes and a composite of poly(3,4-ethylenedioxythiophene), polystyrene sulfonate and multi-walled carbon nanotubes are successfully infilled with a polyvinyl alcohol/phosphoric acid gel electrolyte. The exceptional mechanical properties of the multi-walled carbon nanotube-based electrode enable it to be rolled into a radius of curvature as small as 0.5?mm without cracking and retain 95% of its initial capacitance after 5000 bending cycles. The areal capacitance of our 500??m thick poly(3,4-ethylenedioxythiophene), polystyrene sulfonate, multi-walled carbon nanotube-based flexible solid supercapacitor is 2662?mF?cm-2 at 2?mV?s-1, at least five times greater than current flexible supercapacitors.
Project description:Extensive efforts have recently been devoted to the construction of aqueous rechargeable sodium-ion batteries (ARSIBs) for large-scale energy-storage applications due to their desired properties of abundant sodium resources and inherently safer aqueous electrolytes. However, it is still a significant challenge to develop highly flexible ARSIBs ascribing to the lack of flexible electrode materials. In this work, nanocube-like KNiFe(CN)6 (KNHCF) and rugby ball-like NaTi2(PO4)3 (NTP) are grown on carbon nanotube fibers via simple and mild methods as the flexible binder-free cathode (KNHCF@CNTF) and anode (NTP@CNTF), respectively. Taking advantage of their high conductivity, fast charge transport paths, and large accessible surface area, the as-fabricated binder-free electrodes display admirable electrochemical performance. Inspired by the remarkable flexibility of the binder-free electrodes and the synergy of KNHCF@CNTF and NTP@CNTF, a high-performance quasi-solid-state fiber-shaped ARSIB (FARSIB) is successfully assembled for the first time. Significantly, the as-assembled FARSIB possesses a high capacity of 34.21 mAh cm-3 and impressive energy density of 39.32 mWh cm-3. More encouragingly, our FARSIB delivers superior mechanical flexibility with only 5.7% of initial capacity loss after bending at 90° for over 3000 cycles. Thus, this work opens up an avenue to design ultraflexible ARSIBs based on all binder-free electrodes for powering wearable and portable electronics.