Nanostructured Film Electrodes for Efficient Li-ion Intercalations

To exploit LIBs to their maximum applications, innovative electrode materials should be developed and existing materials should be improved. As negative electrode materials are needed in excess in comparison with positive electrode materials (in terms of specific capacity) in a lithium-ion battery, it is important to reduce their amounts so as to reduce the cell size and production cost[1]. Moreover, innovative negative electrode material classes delivering high capacity and offering fast Li diffusion kinetics should be developed. Parallel to this, research in alternative low cost energy storage systems became more intensive. Due to the high abundance and cost effectiveness of the electrode materials used, Na-ion batteries have become one of the best alternative energy storage systems to LIBs. Many of the attractive Li-insertion electrode materials are also tested for Na-insertion as a part of developing this system further. As different from the wide variety of positive electrode materials, there are only few choices for negative electrode materials for Na-ion batteries[2]. Na does not insert into graphite. Binary alloys of Na with Sn, Pb or other metals and conversion metal oxides are expected to have very high gravimetric capacity[3]. However, the enormous volume changes are supposed to bring out poor cycling behavior of these materials. SnO2 is a promising negative electrode material for Li-ion batteries due to its high theoretical specific capacity of 1491 mAh g-1 [4]. The first step in the Li insertion of SnO2 is a conversion reaction involving 4 Li, where metallic Sn particles are formed in a matrix of Li2O. In the second step, metallic Sn alloys with Li and produce Li4.4Sn. Hence in total 8.4 Li ions can be inserted per formula unit of SnO2 [4]. Nevertheless, this material suffers from extreme volume changes which can lead to a drop in the electric contact and further to severe capacity fading during cycling. This can be overcome by preparing nanocrystalline materials, composite materials with carbon derivatives etc. In the present work, SnO2 nanoparticles are synthesized via a hydrothermal process. The obtained SnO2 material has a particle size of ~50 nm. The material was investigated as negative electrode candidate for both Li- and Na-ion batteries in corresponding half cells. The respective electrochemical mechanism was investigated by in situ and quasi in situ X-ray absorption spectroscopy. It was observed that at the end of discharge, SnO2 was converted to metallic Sn nanoparticles in a Li-ion cell (see Figure 1). Meanwhile, no complete reduction of the SnO2 was observed in the Na-ion cell at the end of discharge. The details of the electrochemical mechanism of SnO2 as negative electrode material for Li-ion and Na-ion batteries will be discussed. Acknowledgement: Financial support from DFG within the Research Priority Program SPP 1473, “Materials with new design for improved Li ion batteries-WeNDeLIB” under grant no EH183/16-2 is gratefully acknowledged. This work has benefitted from beam time allocation by the core-level absorption and emission spectroscopies (CLAESS) beamline, ALBA, Barcelona.

Effective harvest of electrochemical energy from insulating compounds serves as the key to unlocking the potential capacity from many materials that otherwise could not be exploited for energy storage. Herein, an effective strategy is proposed by employing LiCoO2, a widely commercialized positive electrode material in Li-ion batteries, as an efficient redox mediator to catalyze the decomposition of Na2CO3 via an intercalating mechanism. Differing from traditional redox mediation processes where reactions occur on the limited surface sites of catalysts, the electrochemically delithiated Li1-xCoO2 forms NayLi1-xCoO2 crystals, which act as a cation intercalating catalyzer that directs Na+ insertion-extraction and activates the reaction of Na2CO3 with carbon. Through altering the route of the mass transport process, such redox centers are delocalized throughout the bulk of LiCoO2, which ensures maximum active reaction sites. The decomposition of Na2CO3 thus accelerated significantly reduces the charging overpotential in Na-CO2 batteries; meanwhile, Na compensation can also be achieved for various Na-deficient cathode materials. Such a surface-induced catalyzing mechanism for conversion-type reactions, realized via cation intercalation chemistry, expands the boundary for material discovery and makes those conventionally unfeasible a rich source to explore for efficient utilization of chemical energy.

Ni-enriched layered materials are used as electrode materials of Li-ion batteries for electric vehicle applications. Stoichiometric LiNiO2 with cationic Ni3+/Ni4+ redox is the ideal electrode material, but the gradual loss of capacity at the high voltage region, associated with Ni ion migration, hinders its use for practical applications.1 Recently, the importance of non-stoichiometry and anti-site defects is discussed for LiNiO2, and highly reversible pure Ni-based layered materials without metal substitution is successfully developed through defects engineering.1 Another important target is the development of a practical and high-energy Co-/Ni-free Mn-based positive electrode material, which is necessary for the economical electric vehicles. Nanostructured Mn-based electrode materials are proposed as emerging materials for this purpose.2 However, these materials are generally synthesized by high-energy milling, which cannot be adopted for mass production. Recently, nanostructured LiMnO2 with high-energy density (~800 Wh kg–1) is successfully synthesized by using a conventional calcination reaction, which is potentially used for economical electric vehicle applications.3 To develop safe and high-energy Li-ion batteries, the use of solid electrolyte is an important strategy. Nevertheless, inevitable volume changes of electrode materials on cycling lead to the difficulty to maintain the stable interface between electrode materials and electrolyte. Recently, a nanostructured cation-disordered rocksalt oxide with a dimensionally invariable character is developed. Indeed, the excellent reversibility with solid electrolyte is achieved.5 From these results, the importance of nano-structured lithium insertion materials for practical Li-ion battery applications is discussed.References1) Konuma et al., and N. Yabuuchi, Energy Storage Materials, 66, 103200 (2024).2) Kanno et al., and N. Yabuuchi, ACS Energy Letters, 8, 2753 (2023).3) Miyaoka et al., and N. Yabuuchi, submitted4) R. Fukuma et al., and N. Yabuuchi, ACS Central Science, 8, 775 (2022).5) I. Konuma et al., and N. Yabuuchi, Nature Materials, 22, 225 (2023).

The capacity and stability of the constituent electrodes critically determine the performance of Li-ion batteries (LIBs). In this study, density functional theory is employed to explore the potential application of the recently synthesized two dimensional phosphorene as an electrode material in LIBs. Our results show that Li atoms can bind strongly with the phosphorene monolayer and double layer with significant electron transfer. Besides, the structure of phosphorene is not influenced much by lithiation and the volume change is only 0.2%. After lithiation, a semiconductor-to-conductor transition is observed. The diffusion barrier values of Li are calculated to be 0.76 and 0.72 eV on monolayer and double layer phosphorene, respectively. We further demonstrate that the theoretical specific capacity of the phosphorene monolayer is 432.79 mA h g−1, which is larger than those of other commercial anode materials. The influence of Si and S implantation is also examined and our results indicate that Si-doped phosphorene greatly improves the binding of Li atoms, while the diffusion barrier is not affected. Our findings show that the high capacity, low open circuit voltage, small volume change and electrical conductivity of lithiated phosphorene make it a good candidate for application as an electrode material in batteries.

Layered GeSe/thermally-reduced graphene oxide composites as efficient anodes for high-performance Li-ion batteries

In-operando nano-scale resolution X-ray computed tomography (nano-CT) imaging provides an excellent new possibility to investigate a wide variety of phenomena in the electrodes of Li-ion batteries. The 3D X-ray imaging provides direct observation of internal morphological changes in electrodes with up to 50 nm resolution regarding standard materials and electrolyte, which is difficult or impossible to achieve by electron microscopy. Such fine resolution enables the possibility to observe detailed structural changes like the deposition of electrolyte decomposition products within the electrode, transition from Li intercalation to electroplating on graphite, and lithium dendrite formation and growth. One task for applying in-situ nano-CT imaging on Li-ion battery imaging is to develop special lithium battery cells compatible with both the nano-CT instrument’s sample size constraint and X-ray attenuation length limits of higher atomic number materials. Herein, we have developed a planar cell design that allows us to use commercial electrode, separator, and electrolyte. Successful charging and discharging has been achieved with this planar cell design using commercial graphite, LiMn2O4, and lithium foil electrodes. In-operando nano-CT imaging is performed on planar cell lithium battery with focus on graphite anodes. The experimental methodology developed in this study has applicability to test wide ranges of electrolyte, separators and other electrode materials in Li-ion batteries.

The performance of LiNiN as electrode material in lithium batteries was successfully tested. Stable capacities of 142 mA·h/g, 237 mA·h/g, and 341 mA·h/g are obtained when the compound is cycled between 0 and 1.3 V, 1.45 V, and 1.65 V, respectively. These results confirm that it is a promising alternative as a negative electrode material in Li-ion batteries.

“Two-dimensional materials as electrodes” is believed to be one of the key solutions for the development of future battery technologies. Based on the first-principles calculations, we predict that a metallic carbon allotrope (net W), with high electrochemical performance, can be served as an anode material for Li-ion batteries (LIBs). The net W exhibits metallic conductivity, and the conductivity is excellently maintained after Li adsorption. Specifically, upon Li intercalation, only slight lattice variations (<1.5%) occur, which ensures a good cycling stability. The low diffusion barriers of 0.4 eV and the moderate average open circuit voltage of 0.42 V are in between those of the currently used anodes, graphite, and TiO2. Most remarkably, the storage capacity can be up to 1675 mA h g−1, which is about 4.5 times larger than that of the commercial graphite anode. The present findings identify that net W could be an excellent anode material for the application in LIBs.

Na-ion batteries (NIBs) are promising alternatives to Li-ion batteries (LIBs) due to the low cost, abundance, and high sustainability of sodium resources. However, the high performance of inorganic electrode materials in LIBs does not extend to NIBs because of larger ion size of Na+ than Li+ and more complicated electrochemistry. Therefore, it is vital to search for high-performance electrode materials for NIBs. To this end, organic electrode materials (OEMs) with the advantages of high structural tunability and abundant structural diversity show great promise in developing high-performance NIBs. To achieve advanced OEMs for NIBs, a fundamental understanding of the structure–performance correlation is desired for rational structure design and performance optimization. Tailoring molecular structures of OEMs can enhance their performance in Na-ion batteries, however, the substitution rules and the consequent effect on the specific capacity and working potential remain elusive. Herein, we explored the electrochemical performances and reaction mechanisms of various carboxylate-based anode materials, including halogenated sodium carboxylates, N-doped sodium carboxylates, etc. By examining sodium carboxylates with different functional groups, selective N substitution, and extended conjugation structure, we exploited the correlation between structure and performance to establish substitution rules for high-capacity OEMs. Our results show that substitution position and types of functional groups are essential to create active centers for uptake/removal of Na+ and thermodynamically stabilize organic structures. Furthermore, rational host design and electrolytes modulation were performed to extend the cycle life. In addition to sodium carboxylate-based anode materials, we also designed and synthesized novel organic cathode materials based on azo and carbonyl groups for NIBs. The electrochemical performance of the organic cathode materials with an extended conjugated structure such as a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the organic cathodes, nitrogen-doped or single layer graphene is employed to increase the conductivity and mitigate the dissolution of organic materials in the electrolytes. The resulting organic cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the organic cathode materials can undergo reversible redox reactions with Na+ for sustainable NIBs. Our work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Octahedral V2O5 derived Au-decorated disordered rock salt as high-rate and long-life anode materials for Lithium-ion storage

Prospect for Supramolecular Chemistry in High-Energy-Density Rechargeable Batteries

Intermetallic (Ni-Sn) nanoparticles are synthesized through a borohydride reduction with NaBH4 in a mixture of aqueous solutions of NiCl2.6H2O and SnCl2.2H2O at mass ratio and Ni:Sn = 45:55. The ratio is chosen in accordance with the Ni-Sn binary system phase diagram. A "template" technique which involves borohydride reduction of intermetallic nanoparticles on a support (carbon foam, graphite, carbon powder) is also used. The samples which are Ni-Sn alloys and carbon-based nanocomposites are studied by scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. The samples are electrochemically tested as electrode materials in Li-ion batteries.

When fuel cell electrodes are prepared by a conventional spraying or slot-die coating method, there is little or no control over the multi-scale organization of catalyst particles and polymer binder. Electrode structural features such as particle and binder interconnectivity, macro-porosity, and micro-porosity are difficult to control but are critically important when high-performance nanocatalysts are used. Nanofiber electrospinning is an electrode fabrication technique that can address fuel cell electrode morphology issues for next-generation MEAs. As a commercial fabrication method, electrospinning has been shown to be scalable, robust, and cost-effective, especially for the creation of non-woven mats of sub-micron-diameter polymer fibers. Electrospinning can also be used to prepare particle/polymer fiber networks with intra- and inter-fiber porosity. Such fiber mats have been used as the electrode material in Li-ion batteries, H2/Br2 redox flow batteries, and H2/air proton-exchange membrane fuel cells [1-4].Recent work on nanofiber electrodes at Vanderbilt has focused on inks containing pre-formed electrospun catalyst/binder fibers. With such inks, nanofiber electrode MEAs can be made using commercial roll-to-roll fabrication lines. For this poster presentation, experimental results will be presented on nanofiber mat electrode MEAs with Pt/C catalyst and Nafion™ binder. Procedures for preparing inks with nanofibers and then using the inks to create CCMs or GDEs will be shown. Fuel cell performance and durability results with the resulting MEAs will be contrasted with fuel cell data where the electrodes are made directly from electrospun mats, i.e., by the direct transfer of a mat from the electrospinner to a GDL or membrane, and made using a conventional catalyst powder + binder ink. The effects of catalyst loading and fuel cell operating conditions on fuel cell power output before and after a metal dissolution accelerated stress tests will also be presented. For example, an MEA with a Nafion 211 membrane and electrodes made using an ink with pre-formed fibers (TKK Pt/C catalyst at 0.13 mg/cm2 for the anode and 0.20 mg/cm2 for the cathode) generated 0.99 W/cm2 at 0.7 V, at 100% RH, 80oC, and 3 atmabs total pressure with gas feeds of H2 and air.AcknowledgmentThis work was funded by the U.S. Department of Energy’s Hydrogen and Fuel Cell Technologies Office, Fuel Cell Performance and Durability Project, under contract No. DE-EE0007653.References C. Self, M. Naguib, R. E. Ruther, E. C. McRen, R. Wycisk,G. Liu, J. Nanda, and P. N. Pintauro, “High Areal Capacity Si/LiCoO2 Batteries from Electrospun Composite Fiber Mats”, ChemSusChem, 10, 1823 – 1831 (2017).Saadi, X. Fan, S. S. Hardisty, P. Pintauro, and D. Zitoun, “Ultralow Platinum Loading for Redox-Flow Battery by Electrospinning the Electrocatalyst and the Ionomer in Core-Shell Fibers”, Journal of Energy Storage, 59, 106430-106435 (2023).Slack, M. Brodt, D. A. Cullen, K. S. Reeves, K. L. More, and P. N. Pintauro, “Impact of Polyvinylidene Fluoride on Nanofiber Cathode Structure and Durability in Proton Exchange Membrane Fuel Cells”, Journal of the Electrochemical Society, 167, 054517 (2020).Waldrop, J. J. Slack, C. Gumeci, J. Parrondo, N. Dale, K. Shawn Reeves, D. A. Cullen, K. L. More, and P. N. Pintauro, “Electrospun Nanofiber Electrodes for High and Low Humidity PEMFC Operation”, Journal of the Electrochemical Society, 170, 024507 (2023).

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In the present work, a simple solvothermal method is developed for the synthesis of hierarchical Co-based metal-organic framework (H-Co-MOF) microflowers. These microflowers are composed of nanosheets, consisting of small nanoflakes. Upon application as an electrode material in Li-ion batteries, H-Co-MOF shows ultrahigh specific capacity and long cycling performance. For instance, a remarkably superior capacity of 1345 mA h g-1 can be achieved after 100 cycles at a current density of 0.1 A g-1 . Even at 2 A g-1 , a large capacity of 828 mA h g-1 is maintained after 700 cycles. This excellent electrochemical performance might be ascribed to the intrinsic properties and unique hierarchical structure of the Co-based MOF.