Toward Low-Cost All-Organic and Biodegradable Li-Ion Batteries

Organic electrodes based on redox-active covalent organic frameworks for lithium batteries

Electroactive organic materials have received much attention as alternative electrodes for metal-ion batteries due to their high theoretical capacity, resource availability, and environmental friendliness. In particular, redox-active covalent organic frameworks (COFs) have recently emerged as promising electrodes due to their tunable electrochemical properties, insolubility in electrolytes, and structural versatility. In this Highlight, we review some recent strategies to improve the energy density and power density of COF electrodes for lithium batteries from the perspective of molecular design and electrode optimisation. Some other aspects such as stability and scalability are also discussed. Finally, the main challenges to improve their performance and future prospects for COF-based organic batteries are highlighted.

Stabilization of lithium anode with ceramic-rich interlayer for all solid-state batteries

The deposition of thin layers of polymer/ceramic on a lithium surface to produce a strong barrier against dendrites was demonstrated. Different forms (needle, sphere, rod) and types of ceramic (Al₂O₃, Mg₂B₂O₅) were tested and polymer/ceramic interlayers of a few micrometers (4 μm minimum) between the lithium and the PEO-based solid polymer electrolyte (SPE) were deposited. Interlayers with high amounts of ceramic up to 85 wt% were successfully coated on the surface of lithium foil. Compact “polymer in ceramic” layers were observed when Al₂O₃ spheres were used for instance, providing a strong barrier against the progression of dendrites as well as a buffer layer to alleviate the lithium deformation during stripping/plating cycles. The electrochemical performance of the lithium anodes was assessed in symmetrical Li/SPE/Li cells and in full all-solid-state LiFePO₄ (LFP)/SPE/Li batteries. It was observed for all the cells that the charge transfer resistance was significantly reduced after the deposition of the polymer/ceramic layers on the lithium surface. In addition, the symmetrical cells were able to cycle at higher C-rates and the durability at C/4 was even improved by a factor of 8. Microscopic observations of Li/SPE/Li stacks after cycling revealed that the polymer/ceramic interlayer reduces the deformation of lithium upon cycling and avoids the formation of dendrites. Finally, LFP/SPE/Li batteries were cycled and better coulombic efficiencies as well as capacity retentions were obtained with the modified lithium electrodes. This work is patent-pending (WO2021/159209A1).

Significant electrochemical performance improvement of symmetric Li/Li polymer cells at C/4 by using ceramic-rich coated lithium anodes.

Unraveling the multivalent aluminium-ion redox mechanism in 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA)

Rechargeable Aluminium-organic batteries are an exciting emerging energy storage technology owing to their low cost and promising high performance, thanks to the ability to allow multiple-electron redox chemistry and multivalent Al-ion intercalation. In this work, we use a combination of Density Functional Theory (DFT) calculations and experimental methods to examine the mechanism behind the charge-discharge reaction of the organic dye 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) in the 1,3-ethylmethylimidazolium (EMIm⁺) chloroaluminate electrolyte. We conclude that, contrary to previous reports claiming the intercalation of trivalent Al³⁺, the actual ionic species involved in the redox reaction is the divalent AlCl²⁺. While a less-than-ideal scenario, this mechanism still allows a theoretical transfer of four electrons per formula unit, corresponding to a remarkable specific capacity of 273 mA h g^-1. However, the poor reversibility of the reaction and low cycle life of the PTCDA-based cathode, due to its solubility in the electrolyte, make it an unlikely candidate for a commercial application.

Octaphyrin(1.0.1.0.1.0.1.0) as an Organic Electrode for Li and Na Rechargeable Batteries

Organic electrode materials for rechargeable batteries have come into the spotlight due to their structural tunability and diversity. In this study, it is found that bisnickel(II) meso-mesityloctaphyrin(1.0.1.0.1.0.1.0) (Oct) is exhibiting multiple oxidation states with extended π-conjugation pathways to afford an active electrode material in Li and Na-organic batteries and secure interactions with Li⁺ (or Na⁺ ) and anions enabling efficient dual ionic charge/discharge behaviors. Cyclic voltammograms of the Oct electrode elucidate constantly reversible redox processes in both Li and Na organic batteries and pseudocapacitive behaviors at high currents. Subsequent absorption transformations in CV-UV/VIS/NIR spectroscopic analysis and TD-DFT calculations upon the different redox states of Oct conclusively indicate that six electrons are involved in redox-interconversions per unit cycle with corresponding absorption transformations, which also assessed with charge-and-discharge cell capacities. Significant contributions of the pseudocapacitive processes over the diffusion-controlled processes proceeding in Li- and Na-Oct cells induced fast charge/discharge performance and long-term cyclability.

Combined DFT and Molecular Mechanics Modeling of the Adsorption of Semiconducting Molecules on an Ionic Substrate: PTCDA and CuPc on NaCl

Experimental results suggest that molecular geometry and energies can be influenced by the presence of thin film substrates as well as surrounding molecules. It is imperative that computational models take this influence into account. The accurate computational modeling of these molecules is an efficient way of carrying out chemistry calculations and reinforcing experimental findings. In our study, density functional theory (DFT) and molecular mechanics (MM) are used to model the configurations of the organic semiconducting materials, 3,4,9,10-perylene tetracarboxylic dianhydride, C₂₄H₈O₆ (PTCDA), and copper(II) phthalocyanine, C₃₂H₁₆CuN₈ (CuPc), as adsorbed on single- and double-layer NaCl substrates of various dimensions and charge settings. After a geometry and charge optimization of the molecules using DFT, the molecular geometries are optimized under different environments using computational calculations with specific force-field settings in HyperChem Professional 8.0(TM) software using MM. Energies and geometries of the molecules are then recorded, and our data are compared to experimental results of similar systems. We find that, with the appropriate choice of substrate properties, the calculated molecular configurations directly reflect those found experimentally. Our results support the idea that this method of simulation can produce reliable models in the field of physical chemistry.

Thermoconformational Behavior of Cellulose Nanofiber Films as a Device Substrate and Their Superior Flexibility and Durability to Glass

The design and high-throughput manufacturing of thin renewable energy devices with high structural and atomic configurational stability are crucial for the fabrication of green electronics. Yet, this concept is still in its infancy. In this work, we report the extraordinary durability of thin molecular interlayered organic flexible energy devices based on chemically tuned cellulose nanofiber transparent films that outperform glass by decreasing the substrate weight by 50%. The nanofabricated flexible thin film has an exceptionally low thermal coefficient of expansion of 1.8 ppm/K and a stable atomic configuration under a harsh fabrication condition (over 190 °C for an extended period of 5 h). A flexible optoelectronic device using the same renewable cellulose nanofiber film substrate was found to be functionally operational over a life span of 5 years under an intermittent operating condition. The success of this device's stability opens up an entirely new frontier of applications of flexible electronics.

Becoming Sustainable, The New Frontier in Soft Robotics

The advancement of technology has a profound and far-reaching impact on the society, now penetrating all areas of life. From cradle to grave, one is supported by and depends on a wide range of electronic and robotic appliances, with an ever more intimate integration of the digital and biological spheres. These advances, however, often come at the price of negatively impacting our ecosystem, with growing demands on energy, contributions to greenhouse gas emissions and environmental pollution-from production to improper disposal. Mitigating these adverse effects is among the grand challenges of the society and at the forefront of materials research. The currently emerging forms of soft, biologically inspired electronics and robotics have the unique potential of becoming not only like their natural antitypes in performance and capabilities, but also in terms of their ecological footprint. This review outlines the rise of sustainable materials in soft and bioinspired robotics, targeting all robotic components from actuators to energy storage and electronics. The state-of-the-art in biobased robotics spans flourishing fields and applications ranging from microbots operating in vivo to biohybrid machines and fully biodegradable yet resilient actuators. These first steps initiate the evolution of robotics and guide them into a sustainable future.

Progress on V2O5 Cathodes for Multivalent Aqueous Batteries

Research efforts have been focused on developing multivalent ion batteries because they hold great promise and could be a major advancement in energy storage, since two or three times more charge per ion can be transferred as compared with lithium. However, their application is limited because of the lack of suitable cathode materials to reversibly intercalate multivalent ions. From that perspective, vanadium pentoxide is a promising cathode material because of its low toxicity, ease of synthesis, and layered structure, which provides huge possibilities for the development of energy storage devices. In this mini review, the general strategies required for the improvement of reversibility, capacity value, and stability of the cathodes is presented. The role of nanostructural morphologies, structure, and composites on the performance of vanadium pentoxide in the last five years is addressed. Finally, perspectives on future directions of the cathodes are proposed.

Multifunctional Batteries: Flexible, Transient, and Transparent

The primary task of a battery is to store energy and to power electronic devices. This has hardly changed over the years despite all the progress made in improving their electrochemical performance. In comparison to batteries, electronic devices are continuously equipped with new functions, and they also change their physical appearance, becoming flexible, rollable, stretchable, or maybe transparent or even transient or degradable. Mechanical flexibility makes them attractive for wearable electronics or for electronic paper; transparency is desired for transparent screens or smart windows, and degradability or transient properties have the potential to reduce electronic waste. For fully integrated and self-sufficient systems, these devices have to be powered by batteries with similar physical characteristics. To make the currently used rigid and heavy batteries flexible, transparent, and degradable, the whole battery architecture including active materials, current collectors, electrolyte/separator, and packaging has to be redesigned. This requires a fundamental paradigm change in battery research, moving away from exclusively addressing the electrochemical aspects toward an interdisciplinary approach involving chemists, materials scientists, and engineers. This Outlook provides an overview of the different activities in the field of flexible, transient, and transparent batteries with a focus on the challenges that have to be faced toward the development of such multifunctional energy storage devices.

Facile formulation and fabrication of the cathode using a self-lithiated carbon for all-solid-state batteries

We propose a innovative concept to boost the electrochemical performance of cathode composite electrodes using surface-modified carbons with hydrophilic moieties to increase their dispersion in a Lithium Nickel Manganese Cobalt Oxide (NMC) cathode and in-situ generate Li-rich carbon surfaces. Using a rapid aqueous process, the hydrophilic carbon is effectively dispersed in NMC particles followed by the conversion of its acid surface groups (e.g. –COOH), which interact with the NMC particles due to their basicity, into grafted Li salt (–COO⁻Li⁺). The solid-state batteries prepared using the cathode composites with surface-modified carbon exhibit better electrochemical performance. Such modified carbons led to a better electronic conduction path as well as facilitating Li⁺ ions transfer at the carbon/NMC interface due to the presence of lithiated carboxylate groups on their surface.