Full-cell Configuration Research Articles

Advanced Electrochemical Impedance Analysis Using Distribution of Relaxation Times for in Operando Mechanistic Insights of Fuel Cell and Water Electrolyzer Designs

The development of sustainable and carbon-neutral alternative energy frameworks and chemical feedstocks requires rapid production of scalable water electrolyzer designs for hydrogen production.[1] Coupling electrolyzers to renewable energy supplies can provide a ‘green’ hydrogen production pathway, enabling clean production of chemical feedstocks as well as an energy storage framework. Current acid-based electrolyzer designs, however, integrate precious metals for stable operation, where drastic reductions in iridium use and increased cell durability are required for scalable deployment.[2] This requires the ability to monitor changes to the cell in operando for rapid diagnostics during initial and long-term operation under sustained or intermittent profiles. One technique proposed is electrochemical impedance spectroscopy (EIS), which can provide a breakdown of the cell resistances based on the timescale of the process.[3] Further analysis by circuit modeling, however, requires significant insight into the system for accurate interpretations. By coupling conventional EIS methods with distribution of relaxation times (DRT) analysis, the number of processes impacting cell operation can be determined without a priori knowledge of the system.[4] This has improved circuit modeling analysis of Li-ion batteries and solid oxide fuel cells.[5] Here, we demonstrate the power of EIS-coupled DRT analysis by analyzing the operation porous cathode and anode films of Nafion-based electrolyzer cells in half-cell and full cell configuration. Analysis of the electrodes in half-cell configurations provides estimates of kinetic parameters, active area, ionic conductivity, and diffusion coefficients associated with the electrode from a single EIS spectrum that are comparable to values obtained from in situ values.[6] Further analysis of the full cell operation with variable cathode gas composition provides insight as to the effect of the cathode gas composition on both the cathode and anode operation and stability. The work presented here will show the versatility and limitations of DRT-coupled EIS analysis of novel fuel cell and electrolyzer designs as well as present key findings for improving electrolyzer performance and stability.[1]Ayers, K. et al. Annu. Rev. Chem. Biomolec. Eng. 2019, 10, 219-239.[2]Pham, C. et al Adv. Energy Mater. 2021, 11, 2101998.[3]Liu, H. et al. J. Phys. Chem. Lett. 2022, 13, 6520-6531.[4]Wan, T. et al. Electrochimica Acta 2015, 184, 483-499.[5]Dierickx, S., Ivers-Tiffee, E. Electrochimica Acta 2020, 355, 136764.[6]Giesbrecht, P.K., Freund, M.S. J. Phys. Chem. C 2022, 126, 132-150.

(Invited) Degradation Processes at the Potassium Hexacyanoferrate Electrode in Potassium-Ion Batteries

Prussian blue analogues (PBAs)[1] with the general composition A2M[Fe(CN)6] (A: alkali metal; M: Fe, Mn, etc) are an attractive positive electrode for potassium-ion batteries, owing to their chemical composition based on widely abundant materials, ease of synthesis, high electrochemical reversibility and higher average potential compared to its sodium congener [1]. The combination of a PBA electrode with a graphite negative electrode in a full cell configuration showed great promise as post-Li battery system. However, the upper cut-off potentials of K2Fe[Fe(CN)6] and K2Mn[Fe(CN)6] pose serious stability issues with respect to irreversible electrolyte degradation reactions. In addition, the electrolyte components have to be compatible with the potassium intercalation reaction at the graphite electrode[2], thus limiting the number of suitable electrolyte constituents.In this presentation, we discuss aspects of the material synthesis and electrolyte degradation processes at high potentials in liquid carbonate-based electrolytes. As we will be shown the choice of the precursors is paramount to arrive at suitable particle sizes and has a great impact on the electrochemical behavior of the material. Likewise, the density of Fe-vacancies strongly depends on the chosen synthesis and may lead to significant losses in the achievable discharge capacity.The electrode-electrolyte interface in half and full cell configurations was studied by in-house and synchrotron-based photoelectron spectroscopy (PES) for a detailed characterization of the surface layer and the oxidation states of iron in K2Fe[Fe(CN)6] electrodes. This combined analysis of electrochemical and surface-sensitive analytical studies provides a general picture of the electrode degradation at high potentials and fosters the development of better electrolyte mixtures. Our results further show, how a deliberate choice of electrolyte components can help to reduce irreversible reactions and improve cycling stability and cycle life of potassium-ion batteries. For this we have recently expanded our activities also to solid polymer electrolytes, showing superior capacity retention to liquid electrolyte systems[3].Figure 1. left: K2Fe[Fe(CN)6] obtained using different Fe-precursors; right: capacity retention of PBA-K cells cycled in either a liquid (black) or solid polymer (red/purple) electrolyte. Reference s : [1] Kim et al., Trends Chem. 1 (2019) 682–692. [2] Allgayer et al., ACS Appl. Energy Mater. 5 (2022) 1136–1148.[3] Khudyshkina et al., ACS Appl. Polym. Mater. 4 (2022) 2734–2746. Figure 1

Negating Crosstalk in High Voltage Spinel (LiNi0.5Mn1.5O4)/ Graphite Full Cellsby Electrode Modifications

Since its discovery, the high-voltage spinel oxide LiNi0.5Mn1.5O4 (LNMO, sg: Fd-3m) has been widely pursued as a promising cathode for next generation Li-ion batteries due to advantages that include the following: high operating voltage, excellent rate capability and low manufacturing cost (1, 2). However, the LNMO cathode when paired with graphite shows poor capacity retention and increased cell impedance due to oxidation of the organic liquid electrolyte and Mn2+ migration onto the anode (2, 3). Herein, we aim to understand the causes of poor capacity retention in LNMO/graphite full cells and systematically address those issues with various electrode modification strategies. Cycling performance of cells with carbon-nanotube (CNTs) in the LNMO electrode (LNMO-CNT), and with a thin layer of Al2O3 on the graphite electrode (Gr-Al2O3), is examined in half, full and three-electrode cell configurations. The cells with LNMO-CNT electrode show significantly lower cell impedance than cells with LNMO electrodes (without the CNT). Additionally, cells with the Al2O3-coated graphite electrode show improved capacity retention compared to cells with the uncoated graphite. Furthermore, cells containing Li4Ti5O12 anodes display the best capacity retention. We investigate and compare the physiochemical changes in electrodes and electrolyte using various diagnostic techniques; data from these experiments will be reported during the presentation. References : M. M. Thackeray, W. I. F. David, P. G. Bruce and J. B. Goodenough, Materials Research Bulletin, 18, 461 (1983).S. Patoux, L. Daniel, C. Bourbon, H. Lignier, C. Pagano, F. Le Cras, S. Jouanneau and S. Martinet, J Power Sources, 189, 344 (2009).F. Zou, H. C. Nallan, A. Dolocan, Q. Xie, J. Y. Li, B. M. Coffey, J. G. Ekerdt and A. Manthiram, Energy Storage Materials, 43, 499 (2021). Acknowledgements: This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.

Steady State Performance Evaluation of Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency. This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst that is cost effective and can show a comparable HER (Hydrogen Evolution Reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen Evolution Reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance. In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering. This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear Sweep Voltammetry)/CV (Cyclic Voltammetry). This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.

Engineering Transition Metals As Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency.[1] This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst which can show a comparable HER (Hydrogen evolution reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen evolution reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance.[2] In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering.[3] This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear sweep voltammetry)/CV (Cyclic Voltammetry).[4] This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.[1] J. Zhang et al., “Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics,” Nat. Commun., vol. 8, no. May, pp. 1–8, 2017, doi: 10.1038/ncomms15437.[2] L. A. Santillán-Vallejo et al., “Supported (NiMo,CoMo)-carbide, -nitride phases: Effect of atomic ratios and phosphorus concentration on the HDS of thiophene and dibenzothiophene,” Catal. Today, vol. 109, no. 1–4, pp. 33–41, 2005, doi: 10.1016/j.cattod.2005.08.022.[3] B. Wei et al., “Bimetallic vanadium-molybdenum nitrides using magnetron co-sputtering as alkaline hydrogen evolution catalyst,” Electrochemistry Communications, vol. 93. pp. 166–170, 2018, doi: 10.1016/j.elecom.2018.07.012.[4] S. Anantharaj and S. Kundu, “Do the Evaluation Parameters Reflect Intrinsic Activity of Electrocatalysts in Electrochemical Water Splitting?,” ACS Energy Lett., vol. 4, no. 6, pp. 1260–1264, 2019, doi: 10.1021/acsenergylett.9b00686. Figure 1

Aqueous Manufacturing of Ni-Rich Cathodes Using Polyacrylic Acid As Binder for Lithium-Ion Batteries

In the field of secondary batteries, the lithium-ion battery (LIB) is one of the most promising candidates for future electric vehicle (EV) applications, due to its high specific energy and good specific power [1]. However, to meet the demands in large scale storage, not only higher energy and power density and lower cost are needed, but environmentally friendly processing of LiBs is getting more in the focus of research.To meet the desirable requirements, one necessity is to tune the cathode in terms of sustainable production and materials. Ni-rich layered LiNi x Mn y Co1−x−y O2 (NMCs, x ≥ 0.8) cathodes are poised to be the dominating cathode materials for lithium-ion batteries for the foreseeable future due to its high energy density [2]. The state-of-the-art NMC based cathode production in both industrial and lab scale is with polyvinylidene fluoride (PVDF) in organic solvent N-methyl-2-pyrrolidone (NMP). NMP is a toxic, expensive, and highly flammable organic solvent [3]. Replacing NMP with water in the production of LiB cathodes is critical in terms of process cost savings and environmental concerns. Aqueous processes of NMC based cathodes are highly favorable as well as challenging due to the high reactivity of NMC particles. During the slurry preparation, the surface of Ni-rich particles undergoes Li leaching via exchange between H+ from water and Li+ from the active material which leads to increase in pH of the slurry. Li leaching leads to capacity fade and reduces the specific capacity of the cathode. The high pH of the slurry causes corrosion on the aluminum current collector. Surface treatment of NMC particles is a way to prevent Li leaching as well as using carbon coated Al current collector to resist the corrosion, but in terms of production cost these methods are not favorable.In this study, our fundamental aim is to demonstrate the manufacturing of large scale water based NMC811-PAA cathodes. We therefore employ a well-known binder material, polyacrylic acid (PAA), which is water soluble and an anionic polymer. During the mixing processes of the slurry, H+ from PAA can drive Li+ leaching, the leached Li+ reacts with carboxylic groups of PAA and binds to the PAA backbone. Thus, the reaction of H+ and OH- neutralizes the pH of the slurry. Bonded Li+ on PAA creates an active binder in which these Li ions can participate as an additional Li source to aid to prevent capacity decrease. This method has been successfully implemented in the lab scale [4]. Our main target is to investigate the slurry behavior and scalability of the cathodes with a PAA binder. Herein, we report high solid content of slurry behavior of NMC with PAA and the comparison to the conventionally produced slurry for the first time. Also, we show how the slurry behavior is affected by the mixing techniques from lab scale to pilot scale, which is an important parameter for later transfer to industrial production. The electrodes and successfully formed LiPAA as binder are shown by Fourier transformed infrared (FTIR) and Raman spectroscopy. The electrochemical tests are performed both in half and full cell configuration for NMC811-PAA and NMC811-PVDF cathodes.

(Invited) 3D Printed Carbon Microlattices As Electrodes in Electrochemical Cells

With unprecedented freedom in materials design, additive manufacturing (AM) technologies provide us with the capabilities to leverage from geometric complexity. If properly exploited, this allows us to design performance instead of geometry, where the latter is not user defined but a result of a computer optimization. Entirely new mathematically defined, dimensionally stable carbon materials are presented that shrink isotopically under a pyrolysis process generating complex CAD defined 3D shapes with theoretically two to three orders of magnitude increases in permeability and ohmic conductance over conventional Gas Diffusion Layers. The shown lattices can be structured with resolution in the 10 µm regime having total dimensions over several cm. Initial performance tests in full cell configurations inside a PEMFC are presented. The area of mathematically defined, ordered materials with predictable and optimized performances might shape an entirely research field relevant for low cost and high-performance energy converters. Figure 1

Modeling Cathode/Separator/Lithium Metal Sandwich Including Porous Electrode Effects and Plating/Stripping - Proper Formulation, Transformation, and Efficient Numerical Simulation

The high theoretical capacity (3860 mAh g-1) and electrochemical potential of lithium (-3.040V v/s standard hydrogen electrode) makes it a promising candidate as a negative electrode for next-generation batteries.1 However, lithium electrodeposition on the metal anode surface creates dendrites that can lead to short-circuiting of the cell and loss of cyclability.There have been several approaches to modeling lithium electrodeposition in literature. Our past work entailed modeling the deposition as a moving interface, where the equations undergo coordinate transformation to track the changes in concentration and potential as deposition occurs.2 We have also shown that inducing convection in the boundary conditions at the moving interface that properly conserves the mass of lithium in the domain.3 The electrodeposition of lithium on the metal anode produces signatures in the voltage response of the cell. In the past, we have shown that these signatures can be simulated with models that capture the transport phenomena during electrodeposition.This work extends our previous approaches to model the electrodeposition on the surface of the metal anode for a full-cell configuration, which includes a porous cathode. The influences of lithium electrodeposition on the voltage response for different cathode materials are analyzed. References D. Lin, Y. Liu, and Y. Cui, Nat. Nanotechnol., 12, 194 (2017).M. Uppaluri, A. Subramaniam, L. Mishra, V. Viswanathan, and V. R. Subramanian, J. Electrochem. Soc., 167, 160547 (2020).L. Mishra et al., J. Electrochem. Soc., 168, 092502 (2021).

Electrochemical performance of LiNi1/3Co1/3Mn1/3O2 cathode recovered from pyrolysis residue of waste Li-ion batteries

Cycling performances of lithium-ion batteries using the cathodes of LiNi 1/3 Co 1/3 Mn 1/3 O 2 recovered from pyrolysis residue of a waste automotive lithium-ion battery stack (Recovered NCM111 including impurities), and commercial LiNi 0.5 Co 0.2 Mn 0.3 O 2 (Commercial NCM523). • A bare waste Li-ion battery stack was pyrolyzed at 800 °C under air-free conditions. • LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode was hydrometallurgically recovered from pyrolyzed stack. • The cathode included Al, Cu, and Fe impurities at a total of 4 mass% and residual F. • Cathode exhibited a specific capacity of 120 mAh g −1 and very high cycling stability. • High-level coexistence of Al, Cu, and Fe was not harmful to the recovered cathodes. A methodology for time-effective, automatic, and safe extraction of cathode active materials from waste lithium-ion battery (LIB) stacks without complex mechanical disassembly and using electrically and chemically harmless processes can be beneficial for the sustainable fabrication of LIB. Herein, we present a feasibility study on the recovery of ternary Li transition metal oxide (LTMO) cathode active materials from the residue of a waste automotive LIB stack using pyrolysis at 800 °C without exposure to air. Sequential processes from pyrolysis, residue grinding, classification (sieving), wet magnetic separation, acid leaching, hydroxide precipitation, and desalination to drying were used to prepare the precursor of the cathode active material. The precursor was mixed with Li 2 CO 3 and sintered in air at 800 °C, which yielded LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) with metallic impurities of Al, Cu, and Fe at a total of 4 mass% as well as excess Li and residual F. The electrochemical performance of waste LIB-derived LiNi 1/3 Co 1/3 Mn 1/3 O 2 (W-NCM) cathode active materials was evaluated in half-cell and full-cell configurations and compared with that of a commercial LIB cathode active material of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM) used in automobile applications. The Li-ion extraction/insertion specific capacity of W-NCM in the half-cell was 120 mAh/g at 15 mA g −1 , which was 70.4 % that of NCM. The specific capacity of W-NCM in a full-cell using a graphite anode at 0.1 C was 85 mAh/g, which was 69.1 % that of NCM. However, W-NCM in the full-cell exhibited much higher capacity retention (91.2 %) after 1000 charge–discharge cycles at 2 C, while the capacity retention of NCM was 34.0 %. The excellent cycling performance of W-NCM was attributed to the co-existence of metallic impurities. The proposed cathode recovery method may be further explored for applications in large-scale and automatic recycling of waste LIBs.

Electrochemical Performance of Li2TiO3//LiCoO2 Li-Ion Aqueous Cell with Nanocrystalline Electrodes

A challenge in developing high-performance lithium batteries requires a safe technology without flammable liquid electrolytes. Nowadays, two options can satisfy this claim: all-solid-state batteries and aqueous-electrolyte batteries. Commercially available Li-ion batteries utilize non-aqueous electrolytes (NAE) owing to a wide potential window (>3 V) that achieves high energy density but pose serious safety issues due to the high volatility, flammability, and toxicity of NAE. On the contrary, aqueous electrolytes are non-flammable, low-toxic, and have a low installation cost for humidity control in the production line. In this scenario, we develop a new aqueous rechargeable Li-ion full-cell composed of high-voltage cathode material as LiCoO2 (LCO) and a safe nanostructured anode material as Li2TiO3 (LTO). Both pure-phase LTO and LCO nanopowders are prepared by hydrothermal route and their structural and electrochemical properties are studied in detail. Simultaneously, the electrochemical performances of these electrodes are tested in both half- and full-cell configurations in presence of saturated 1 mole L−1 Li2SO4 aqueous electrolyte medium. Pt//LCO and Pt//LTO half-cells deliver high discharge capacities of 142 and 133 mAh g−1 at 0.5 C rate with capacity retention of ~95% and 94% after 50 cycles with a Coulombic efficiency of 98.25% and 99.89%, respectively. The electrochemical performance of a LTO//LCO full cell is investigated for the first time. It reveals a discharge capacity of 135 mAh g−1 at 0.5 C rate (50th cycle) with a capacity retention of 94% and a Coulombic efficiency of 99.7%.

A homogeneous and mechanically stable artificial diffusion layer using rigid-flexible hybrid polymer for high-performance lithium metal batteries

Artificial solid electrolyte interphase (SEI) is promising to inhibit uncontrollable lithium dendrites and enable long cycling stability for lithium metal batteries. However, the essential mechanical stability is limited since organic layers generally have low modulus whereas intrinsic brittleness for inorganic ones remains a great concern. Polymer-based SEIs with rigid and flexible chains in adequate mechanical properties are supposed to address this issue. Herein, a homogeneous and mechanically stable diffusion layer is achieved by blending rigid chains of polyphenylene sulfone (PPSU) with flexible chains of poly (vinylidene fluoride) (PVDF) in a hybrid membrane, enabling uniform diffusion and stabilizing the lithium metal anode. The Li||Cu cell with the protected electrode exhibits a long lifetime more than 450 cycles (0.5 mA cm−2, 1.0 mA h cm−2) (fourfold longer than the control group) with higher average Coulombic efficiency of 98.7%. Enhanced performances are also observed at Li||Li and full cell configurations. The improved performances are attributed to the controlled morphology and stable interphase, according to scanning electron microscopy (SEM) and electrochemical impedance. This research advances the idea of uniform lithium plating and provides a new insight on how to create a homogeneous and mechanically stable diffusion layer using rigid-flexible polymers.

The Poor Academic’s DC-Offset for Reversing Polarity in Electrochemical Cells: Application to Redox Flow Cells

We provide a simple and inexpensive manual DC-offset method for extending the accepted voltage range of a battery cycler to negative voltages, without interfering with the actual operation of the electrochemical cell under the test or exceeding the voltage specs of the battery cycler instrument. We describe the working principles of the method and validate the proposed setup by operating short-term and long-term redox flow battery cycling using compositionally symmetric cell, with open-circuit voltage of zero, and full cell configurations. The method can be used to extend the capability of battery cycler instrumentation to operate any electrochemical cell that requires the polarity to be reversed during operation. Applications include cycling of other symmetric cells (e.g., Li-ion cells), implementation of polarity reversal steps for rejuvenation of electroactive species or rebalancing electrochemical cells, and alternating polarity for electrochemical synthesis.

Engineering honeycomb-like carbon nanosheets encapsulated iron chalcogenides: Superior cyclability and rate capability for sodium ion half/full batteries

Metal chalcogenide-based anodes have attracted extraordinary attention for rechargeable sodium-ion batteries (SIBs) due to their cost-effectiveness and relatively high theoretical capacities. However, they usually exhibit poor electrochemical performance due to large volume change and low ionic/electronic conductivity. Herein, an effective strategy is developed to fabricate nitrogen doping 3D honeycomb-like carbon nanosheets-wrapped FeS nanoparticles for SIB anodes with outstanding sodium storage performance. As a result, FeS@NC anode exhibits high sodium ion storage capacity of 666.0 mAh g−1 at a current density of 0.1 A g−1, excellent rate capability of 617.3 mAh g−1 at 2 A g−1 and superior cycling stability. Moreover, the FeS@NC anode in a full-cell configuration shows high cyclic stability (no capacity attenuation over 200 cycles with 99.9% coulombic efficiency). Accordingly, this work provides a new avenue to construct high-performance anode materials for SIBs.

Anisotropic Self-Assembly of Asymmetric Mesoporous Hemispheres with Tunable Pore Structures at Liquid-Liquid Interfaces.

Asymmetric materials have attracted tremendous interest because of their intriguing physicochemical properties and promising applications, but endowing them with precisely controlled morphologies and porous structures remains a formidable challenge. Herein, a facile micelle anisotropic self-assembly approach on a droplet surface is demonstrated to fabricate asymmetric carbon hemispheres with a jellyfish-like shape and radial multilocular mesostructure. This facile synthesis follows an interface-energy-mediated nucleation and growth mechanism, which allows easy control of the micellar self-assembly behaviors from isotropic to anisotropic modes. Furthermore, the micelle structure can also be systematically manipulated by selecting different amphiphilic triblock copolymers as a template, resulting in diverse novel asymmetric nanostructures, including eggshell, lotus, jellyfish, and mushroom-shaped architectures. The unique jellyfish-like hemispheres possess large open mesopores (∼14 nm), a high surface area (∼684 m2 g-1), abundant nitrogen dopants (∼6.3 wt %), a core-shell mesostructure and, as a result, manifest excellent sodium-storage performance in both half and full-cell configurations. Overall, our approach provides new insights and inspirations for exploring sophisticated asymmetric nanostructures for many potential applications.

Practical Implementation of Magnetite-Based Conversion-Type Negative Electrodes via Electrochemical Prelithiation.

We report the performance of a conversion-type magnetite-decorated partially reduced graphene oxide (Fe3O4@PrGO) negative electrode material in full-cell configuration with LiNi0.8Co0.15Al0.05O2 (NCA) positive electrodes. To enable practical implementation of the conversion-type negative electrodes in full cells, the beneficial impact of electrochemical prelithiation on mitigating active lithium losses and improving cycle life is shown here for the first time in the literature. The initial Coulombic efficiency (ICE) of the full cells is improved from 70.8 to 91.2% by prelithiation of the negative electrode to 35% of its specific delithiation capacity. The prelithiation is shown to improve the surface passivation of the Fe3O4@PrGO electrodes, leading to less electrolyte reduction on their surface which is prominent from the significantly lowered accumulated Coulombic inefficiency values, lower polarization growth, and doubled capacity retention by the 100th cycle. The reduced surface reactions of the negative electrode by prelithiation also aids in reducing the extent of aging of the NCA positive electrode. Overall, the prelithiation leads to a longer cycle life, where a retained capacity of 60.4% was achieved for the prelithiated cells by the end of long-term cycling, which is 3 times higher than the capacity retention of the non-prelithiated cells. Results reported herein indicate for the first time that the electrochemical prelithiation of the Fe3O4@PrGO electrode is a promising approach for making conversion negative electrode materials more applicable in lithium-ion batteries.

Revealing the rate-limiting electrode of lithium batteries at high rates and mass loadings

Lithium-ion batteries with superior capacities and rate performance are needed due to the soaring demands for higher energy and power device requirements. However, the main hurdle on achieving this predominately results from the poor rate performance of electrode, which is related to thermodynamic limitations and slow kinetics. To determine the rate-limiting electrode in NMC622 vs graphite cells, a methodology based upon the galvanic intermittent titration technique, for investigating the diffusion and reaction kinetics from the observed overpotential at each electrode has been developed. Variable current densities have been used to simultaneously extract the thermodynamic and kinetic properties of each electrode with increasing mass loading. Graphite is observed to reach its thermodynamic limits quicker than NMC, due to the flat plateaus and overpotentials observed from the charge transfer kinetics and mass transport. At high rates and high mass loadings, the graphite electrode is responsible for limiting both Li+ diffusion and reaction rates in full cells. Slow diffusion kinetics are caused by the transport of the electrolyte in the porous electrode, which limits the availability of Li+ for reaction at the surface of graphite. This methodology is proposed as a fast single technique for comprehensively parameterizing the rate limitations observed in a full cell configuration.

Char of Tagetes erecta (African marigold) flower as a potential electrode material for supercapacitors

A char of Tagetes erecta flowers (TFC) was derived through simple thermal decompo­sition of Tagetes erecta flowers (TF). Physico-chemical properties of as-prepared TFC were evaluated using XRD, FESEM, FTIR, TGA, N2 adsorption-desorption isotherm analysis and water contact angle measurements. The practicality and applicability of TFC as promising electrode material in supercapacitors (SCs) were evaluated in full-cell configuration by performing electrochemical characterizations like CV, GCD and EIS on a lab-scale TFC-based symmetric SC. TFC exhibited a remarkable specific capacitance of 118.4 F g-1 at a constant current density of 0.2 A g-1 and a specific energy of 4.1 Wh kg-1 at specific power of 0.1 kW kg-1. TFC showed excellent cyclic stability by retaining 92 % of its initial capacitance even after 6000 GCD cycles at 2 A g-1. The superior capacitive behaviour and cyclic stability of TFC could be attributed to its good wettability towards water. This excellent supercapacitive performance of TFC estab­lishes it as a potential floral waste-derived carbon-based electrode material for SCs.

Offsetting Initial Lithium Loss By Pre-Forming SEI Layer on Graphite Surface

The irreversible lithium loss due to the formation of solid electrolyte interphase (SEI) in the initial cycle greatly reduced the overall cell energy density of lithium ion batteries. Cathode prelithiation methods have been widely explored to compensate this lithium loss. However, these cathode additives with high lithium contents inevitable lower the active cathode materials loading. Here we report a facile graphite prelithiation method by pre-forming SEI layers on graphite surface (Pre-SEI graphite) in a flow cell. The Li accommodation in graphite anode could be controlled by the operation of the time and current density in flow cell for the electrochemical SEI formation. As a result, we demonstrate a 10% initial Columbic efficiency increase of the LiFePO4 electrode in a full cell configuration with our Pre-SEI graphite. The electrochemical pre-formation of SEI on graphite offers a novel route to offset initial lithium loss without a sacrifice of active cathode loading.

Regulating Lithium Metal Deposition for Safe Cell Operation and to Extend Cyclic Performance of an Anode-Free Lithium Metal Battery

Using the ideal Lithium metal (Li) as an anode material for Lithium metal batteries (LMBs) displays considerable potential in enlightening energy density and power density than conventional lithium-ion batteries (LIBs). Nevertheless, the low Coulombic efficiency, significant volume changes during operation, which reduces electrode mechanical stability, and Lithium (Li) dendrites formed and growth from nonuniform Li deposition during cell operation causes safety issues and limits potential uses of Li as an anode material for LMBs. Recently, anode free (Lithium free) lithium metal batteries (AFLMBs) protocol have got great attention due to their higher energy density, reduces cell weight, costs effectiveness, easy fabrication, and safety during the process of cell manufacture. Nevertheless, in AFLMBs, the uncontrolled plating of lithium on bare copper foil imposes a more severe lithium dendrite growth. Hence, planning proper design on an anode current collector which is appropriate for AFLMBs is essential. Herein, we handle the growth of lithium dendrite by guiding lithium metal deposition site to the backside of the gold-sputtered perforated polyimide film (PI@Au), which used as an anode current collector. Hence, metallic lithium (Li) starts to plate on the modified PI@Au surface, and sequentially, growth of Li takes place in the direction away from the separator face (ASF). This backside deposition and growth approach allow the battery to operate safely, even when lithium dendrite exists. . Surprisingly, the dendrite-free surface on the separator-facing side (SF) of PI@Au anode reveals significantly improved cycling stability. As a result PI@Au//Li cell (2 mAh/cm2 and 0.5 mA/cm2) offers stable cycling performance for 1400 h without significant voltage polarization. Conversely, Cu//Li cell cycling with results higher voltage hysteresis and face short-circuit below 600 h at same working conditions. Besides, PI@Au//LFP anode-free full cell configuration maintained 20 % capacity retention (CR) with average Coulombic efficiency of 98.7 % after 340 cycles (0.5 mA/cm2). On the contrary, the Cu//LFP full cell runs only for 165 cycles under the same value of CR. Guiding the plating of Li to the backside of perforated polyimide film insights into an innovative technique for developing ultra-safe AFLMBs and also proves the viability of the electrical insulator substrates as anode current collectors by improving their conductivity and lithiophilicity.

Improvement in cycling stability of Prussian blue analog-based aqueous sodium-ion batteries by ligand substitution and electrolyte optimization

In this study, we investigated the effects of ligand substitution in Prussian blue analog (PBA) cathode materials on the performance of aqueous sodium-ion batteries. NaCu[Fe(CN)6] (NaCuHCF) and ligand-modified PBAs, NaxCu[Fe(CN)5(C6H4N2)] (NaxCuCNPFe), and NaxCu[Fe(CN)5(CH3C6H4NH2)] (NaxCuTolFe) were tested in different electrolytes. The NaxCuCNPFe and NaxCuTolFe cathodes exhibited the best capacity retention of ∼50% after 2000 cycles in 1 M Na2SO4, which is much higher than that of the NaCuHCF cathode (0% capacity remained after 2000 cycles). To understand the charge–discharge mechanism of PBA cathodes, in situ synchrotron X-ray absorption spectroscopy and X-ray diffraction were performed. To demonstrate practical energy storage applications, PBAs were tested in full-cell configurations with an anode made of sodium titanium phosphate (NTP) coated with reduced graphene oxide and carbon (NTP@C@RGO). The NaxCuCNPFe//NTP@C@RGO and NaxCuTolFe//NTP@C@RGO full cells in 17 m NaClO4 aqueous electrolyte exhibited high power densities of up to 4338 W kg−1 (with an energy density of 18.11 Wh kg−1) and 4742 W kg−1 (with an energy density of 11.87 Wh kg−1), respectively. Our study demonstrates the potential of optimizing organic ligands in PBAs and electrolytes for the improvement of the cycling stability of high-power aqueous sodium-ion batteries.