(Invited) Nanostructured Positive Electrode Materials for Li-Ion Battery Applications

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.

Rational construction of Na3V2(PO4)3 nanoparticles encapsulated in 3D honeycomb carbon network as a cathode for sodium-ion batteries

A furnace is described forin situX-ray diffraction studies, in transmission mode, of structural changes in electrode materials for Li-ion (polymer) batteries in the ambient to 300°C temperature range. The method exploits the thin flat-cell geometry of the lithium-polymer battery concept. The flat sample is able to oscillate about a horizontal axis in its own plane in the X-ray beam, to provide better averaging during the diffraction experiment. The use of the device is demonstrated in a study of lithium intercalation in graphite (a commonly used anode material in lithium-ion batteries) during electrochemical cycling and storage at 70°C.

The rapid growth of the electric vehicle (xEV) and energy storage system (ESS) industries has generated an urgent demand for high-performance Li-ion batteries (LIBs) that incorporate advanced electrode materials. Electrode materials play a crucial role in determining the energy density and overall performance of batteries. Therefore, the development of advanced electrode materials is imperative for the advancement of high-performance battery technologies.In this study, we developed a method for synthesizing or modifying electrode materials for LIBs through a straightforward gas-phase decomposition reaction of ammonium fluoride (NH4F). We begin by discussing the development of metal fluoride/porous carbon nanocomposites as high-capacity cathode materials based on conversion reactions, which serves as the foundation of this study. Based on the reaction mechanism for synthesizing metal fluoride nanocomposites, we investigated the enhancement of the purity and morphological properties of silicon anodes, as well as the surface fluorination of lithium titanate (LTO) anodes. Furthermore, by employing this gas-phase reaction on commercial lithium nickel oxide (LNO), we successfully synthesized Ni/LiF nanocomposites intended for use as sacrificial cathodes, which have the potential to compensate for the low initial coulombic efficiencies of advanced LIBs. The synthesis approach used in this study is simple and relatively safe compared to conventional methods that directly use HF solutions or F2 gases. Consequently, this research is expected to offer new strategies for the development of advanced electrode materials for LIBs.

“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.

High Rate Li-Ion Batteries with Cation-Disordered Cathodes

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.

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.

The choice of electrode materials in lithium ion batteries and supercapacitors is important for the stability, capacity, and cycle life of the device. Despite its low capacity, graphite has often been used as an electrode material due to its inherent stability. Due to an increasing demand for large-capacity energy storage systems, there is also a demand for the development of large-capacity Li ion batteries and supercapacitors. Therefore, carbonaceous materials like graphene and carbon nanotubes (CNTs), which have high stability as well as excellent electrical conductivity and mechanical strength, are receiving attention as new electrode materials. Recently, starting from simply applying graphene and CNTs as electrode materials and progressing to the development of hybrid materials, there have been increasing research efforts in enhancing the performance of Li ion batteries and supercapacitors through the use of carbonaceous materials. This paper will discuss new composite materials and electrode structures that use graphene and CNTs for applications in Li ion batteries and supercapacitors.

With the invention of the electric cars and the exponential growth in portable electronics over the last decade, energy storage systems that can supply and store more power are of utmost importance. Li-ion batteries (LIBs) entered the market less than a decade ago to keep up with market demands and have since become the most efficient way to store energy due to their reversible nature. Graphite is currently the most widely used material in (LIB) anodes due to its long cycle life and low manufacturing cost, its main drawback being its low theoretical capacity of 372 mAg-1. Metal oxides have been of interest as electrode materials for (LIBs) due to their inherently high theoretical capacities and low cost. However, the main drawback of metal oxide-based anodes includes high volume expansion, particle agglomeration, and dendrite formation. Developments in composites and novel micro/nano-structures that withstand large temperature ranges and maintain structural stability have attracted interest for their use as electrode materials in LIBs. Here, we explore the performance of Iron Oxide (Fe2O3), Tin Oxide (SnO2), Zinc Oxide (ZnO), and Cobalt Oxide (Co3O4), coated on carbon fibers as hosts for lithium ion insertion/de-insertion during charge/discharge process. The synthesis and design of Fe2O3/Carbon and SnO2/C composite fibers were reiliazed by the centrifugal spinning of metal-oxides precursors in polyacrylonitrile (PAN)/ dimethylformamide (DMF) solutions and followed by calcination at 600 °C in an inert gas. The characterization of Fe2O3/C, ZnO/C, Co3O4/C and SnO2/C composite fibers was conducted using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and energy dispersive X-ray analysis (EDAX). The pre-coated carbon fibers with metal-oxide nanoparticle precursors showed improved electrochemical performance compared to the pristine composite carbon-fibers anodes.

Thermodynamic analysis and perspective of aqueous metal-sulfur batteries

The electrochemical properties and thermal stabilities of a new positive electrode material for Li-ion batteries, , were investigated over a wide potential window. This electrode material was synthesized via a coprecipitation method. X-ray diffraction studies indicated that the synthesized material crystallized into an layered structure . The positive electrode has a discharge capacity of in the voltage range of . This high capacity was retained throughout cycling. The thermal stability of was measured by differential thermal calorimetry and found to be comparable to that of . This positive electrode material was also characterized in a full cell configuration (graphite negative electrode) by the hybrid pulse power characterization tests following the FreedomCAR battery test manual for plug-in hybrid electric vehicles (PHEVs). The pulse power capability and available energy met the goals for PHEVs.

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

Rechargeable Li batteries as electrochemical energy storage and conversion devices are continuously changing human life. In order to meet the increasing demand for energy and power density, it is essential and urgent to exploit the electrode materials with high capacity and fast charge transfer (for Li-ion and Li-S batteries) and electrocatalysts with high activity (for rechargeable Li-O2 batteries). The high capacity is attributed to high electron transfer number and low molecular weight of the electrode materials. Combined with proper nanostructure design, the electronic transfer and ionic conductivity will be improved. This review summarizes recent efforts to apply electrode materials for Li-ion batteries with multi-electron reaction, Li-S batteries, and efficient electrocatalysts for Li-O2 batteries. The methods to enhance the cycling and rate performance have been discussed in detail. Advanced rechargeable Li batteries with multi-electron reaction will become the research emphasis in the future.

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