Organic solid-electrolyte interface layers for Zn metal anodes.

Zinc ion batteries (ZIBs) have emerged as promising candidates for renewable energy storage owing to their affordability, safety, and sustainability. However, issues with Zn metal anodes, such as dendrite growth, hydrogen evolution reaction (HER), and corrosion, significantly hinder the practical application of ZIBs. To address these issues, organic solid electrolyte interface (SEI) layers have gained traction in the ZIB community as they can, for instance, help achieve uniform Zn plating/stripping and suppress side reactions. This article summarizes recent advances in organic artificial SEI layers for ZIB anodes, including their fabrication methods, electrochemical performance, and degradation suppression mechanisms.

Enhancing Proton Co-Intercalation in Iron Ion Batteries Cathodes for Increased Capacity.

Recently, aqueous iron ion batteries (AIIBs) using iron metal anodes have gained traction in the battery community as low-cost and sustainable solutions for green energy storage. However, the development of AIIBs is significantly hindered by the limited capacity of existing cathode materials and the poor intercalation kinetic of Fe2+. Herein, we propose a H+ and Fe2+ co-intercalation electrochemistry in AIIBs to boost the capacity and rate capability of cathode materials such as iron hexacyanoferrate (FeHCF) and Na4Fe3(PO4)2(P2O7) (NFPP). This is achieved through an electrochemical activation step during which a FeOOH nanowire layer is formed in situ on the cathode. This layer facilitates H+ co-intercalation in AIIBs, resulting in a high specific capacity of 151 mAh g-1 and 93% capacity retention over 500 cycles for activated FeHCF cathodes. We found that this activation process can also be applied to other cathode chemistries, such as NFPP, where we found that the cathode capacity is doubled as a result of this process. Overall, the proposed H+/Fe2+ co-insertion electrochemistry expands the range of applications for AIBBs, in particular as a sustainable solution for storing renewable energy.

Synthesis Pathway of Layered-Oxide Cathode Materials for Lithium-Ion Batteries by Spray Pyrolysis.

We report the synthesis of LiCoO2 (LCO) cathode materials for lithium-ion batteries via aerosol spray pyrolysis, focusing on the effect of synthesis temperatures from 600 to 1000 °C on the materials' structural and morphological features. Utilizing both nitrate and acetate metal precursors, we conducted a comprehensive analysis of material properties through X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Our findings reveal enhanced crystallinity and significant oxide decomposition within the examined temperature range. Morphologically, nitrate-derived particles exhibited hollow, spherical shapes, whereas acetate-derived particles were irregular. Guided by high-temperature X-ray diffraction (HT-XRD) data, the formation of a layered LCO oxide structure, with distinct spinel Li2Co2O4 and layered oxide LCO phases was shown to emerge at different annealing temperatures. Optimally annealed particles showcased well-defined layered structures, translating to high electrochemical performance. Specifically, nitrate-based particles annealed at 775 °C for 1 h demonstrated initial discharge capacities close to 179 mAh/g, while acetate-based particles, annealed at 750 °C for 3 h, achieved 136 mAh/g at a 0.1C discharge rate. This study elucidates the influence of synthesis conditions on LCO cathode material properties, offering insights that advance high throughput processes for lithium-ion battery materials synthesis.

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes.

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact.

Identifying Current Collectors that Enable Light-Battery Interactions.

In recent years, there has been an increased focus on studying light-battery interactions in the context of operando optical studies and integrated photoelectrochemical energy harvesting. However, there has been little insight into identifying suitable "light-accepting" current collectors for this class of batteries. In this study, fluorine-doped tin oxide, indium-tin oxide, and silver nanowire-graphene films are analyzed along with carbon paper, carbon nanotube paper, and stainless-steel mesh as current collectors for optical batteries. They are categorized into two classes - transmissive and non-transmissive, based on the orientation of the light-electrode interaction. Various methods to prepare the electrode are highlighted, including drop casting and the fabrication of free-standing electrodes. The optical and electrical properties of these current collectors as well as their electrochemical stability are measured using linear sweep voltammetry against zinc and lithium anodes. Finally, the rate performance and long-term cycling stability of lithium manganese oxide (LiMn2O4) cathodes are measured against lithium anodes with these current collectors and their performance is compared. These results show which current collector to choose depends on the application and cell chemistry. These guidelines will assist in the design of future optical cells for in-situ measurements and photoelectrochemical energy storage.

Hydrogenated V2O5 with Improved Optical and Electrochemical Activities for Photo-Accelerated Lithium-Ion Batteries.

Solar power represents an abundant and readily available source of renewable energy. However, its intermittent nature necessitates external energy storage solutions, which can often be expensive, bulky, and associated with energy conversion losses. This study introduces the concept of a photo-accelerated battery that seamlessly integrates energy harvesting and storage functions within a single device. In this research, a novel approach for crafting photocathodes is presented using hydrogenated vanadium pentoxide (H:V2O5) nanofibers. This method enhances optical activity, electronic conductivity, and ion diffusion rates within photo-accelerated Li-ion batteries. This study findings reveal that H:V2O5 exhibits notable improvements in specific capacity under both dark and illuminated conditions. Furthermore, it demonstrates enhanced diffusion kinetics and charge storage performance when exposed to light, as compared to pristine counterparts. This strategy of defect engineering holds great promise for the development of high-performance photocathodes in future energy storage applications.

Electrochemically Responsive 3D Nanoarchitectures.

Responsive nanomaterials are being developed to create new unique functionalities such as switchable colors and adhesive properties or other programmable features in response to external stimuli. While many existing examples rely on changes in temperature, humidity, or pH, this study aims to explore an alternative approach relying on simple electric input signals. More specifically, 3D electrochromic architected microstructures are developed using carbon nanotube-Tin (Sn) composites that can be reconfigured by lithiating Sn with low power electric input (≈50 nanowatts). These microstructures have a continuous, regulated, and non-volatile actuation determined by the extent of the electrochemical lithiation process. In addition, this proposed fabrication process relies only on batch lithographic techniques, enabling the parallel production of thousands of 3D microstructures. Structures with a 30-97% change in open-end area upon actuation are demonstrated and the importance of geometric factors in the response and structural integrity of 3D architected microstructures during electrochemical actuation is highlighted.

Kinetics of Light-Responsive CNT / PNIPAM Hydrogel Microactuators.

Light-responsive microactuators composed of vertically aligned carbon nanotube (CNT) forests mixed with poly(N-isopropylacrylamide) (PNIPAM) hydrogel composites are studied. The benefit of this composite is that CNTs act as a black absorber to efficiently capture radiative heating and trigger PNIPAM contraction. In addition, CNT forests can be patterned accurately using lithography to span structures ranging from a few micrometers to several millimeters in size, and these CNT-PNIPAM composites can achieve response times as fast as 15 ms. The kinetics of these microactuators are investigated through detailed analysis of high-speed videos. These are compared to a theoretical model for the deswelling dynamics, which combines thermal convection and polymer diffusion, and shows that polymer diffusion is the rate-limiting factor in this system. Applications of such CNT/hydrogel actuators as microswimmers are discussed, with light-actuating micro-jellyfish designs exemplified, and >1500 cycles demonstrated.

Re-imagining the daniell cell: ampere-hour-level rechargeable Zn-Cu batteries.

The Daniell cell (Cu vs. Zn), was invented almost two centuries ago, but has been set aside due to its non-rechargeable nature and limited energy density. However, these cells are exceptionally sustainable because they do not require rare earth elements, are aqueous and easy to recycle. This work addresses key challenges in making Daniell cells relevant to our current energy crisis. First, we propose new approaches to stabilise Zn and Cu plating and stripping processes and create a rechargeable cell. Second, we replace salt bridges with an anion exchange membrane, or a bipolar membrane for alkaline-acid hybrid Zn-Cu batteries operating at 1.56 V. Finally, we apply these changes in pouch cells in order to increase energy and power density. These combined developments result in a rechargeable Daniell cell, which can achieve high areal capacities of 5 mA h cm-2 and can easily be implemented in 1 A h pouch cells.

Does Heat Play a Role in the Observed Behavior of Aqueous Photobatteries?

Light-rechargeable photobatteries have emerged as an elegant solution to address the intermittency of solar irradiation by harvesting and storing solar energy directly through a battery electrode. Recently, a number of compact two-electrode photobatteries have been proposed, showing increases in capacity and open-circuit voltage upon illumination. Here, we analyze the thermal contributions to this increase in capacity under galvanostatic and photocharging conditions in two promising photoactive cathode materials, V2O5 and LiMn2O4. We propose an improved cell and experimental design and perform temperature-controlled photoelectrochemical measurements using these materials as photocathodes. We show that the photoenhanced capacities of these materials under 1 sun irradiation can be attributed mostly to thermal effects. Using operando reflection spectroscopy, we show that the spectral behavior of the photocathode changes as a function of the state of charge, resulting in changing optical absorption properties. Through this technique, we show that the band gap of V2O5 vanishes after continued zinc ion intercalation, making it unsuitable as a photocathode beyond a certain discharge voltage. These results and experimental techniques will enable the rational selection and testing of materials for next-generation photo-rechargeable systems.

Permselective Ionic-Shield for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LiSBs) are promising next-generation batteries because of their low cost and high theoretical energy densities. Despite remarkable advances over the decades, polysulfide (PS) shuttling during battery cycling remains a challenge in the development of commercial LiSBs and is accelerated under practical conditions. Herein, we report a permselective ionic shield between the electrodes that blocks PS shuttles and passes Li ions to high-performance LiSBs. This shield is easily built onto the separator by ionic complexation and intermolecular bonding of functional polymers, thereby improving the battery performance and safety. The LiSB with the developed shield delivers a remarkable discharge capacity of 917 mAh g-1 after 1000 cycles at 2 C. In addition, the behavior of LiSBs under practical conditions that can realize a high energy density is investigated to achieve the optimal balance in this system. This study provides new insights into the imminent development of separators for practical LiSBs.

Three-dimensional operando optical imaging of particle and electrolyte heterogeneities inside Li-ion batteries.

Understanding (de)lithiation heterogeneities in battery materials is key to ensure optimal electrochemical performance. However, this remains challenging due to the three-dimensional morphology of electrode particles, the involvement of both solid- and liquid-phase reactants and a range of relevant timescales (seconds to hours). Here we overcome this problem and demonstrate the use of confocal microscopy for the simultaneous three-dimensional operando measurement of lithium-ion dynamics in individual agglomerate particles, and the electrolyte in batteries. We examine two technologically important cathode materials: LixCoO2 and LixNi0.8Mn0.1Co0.1O2. The surface-to-core transport velocity of Li-phase fronts and volume changes are captured as a function of cycling rate. Additionally, we visualize heterogeneities in the bulk and at agglomerate surfaces during cycling, and image microscopic liquid electrolyte concentration gradients. We discover that surface-limited reactions and intra-agglomerate competing rates control (de)lithiation and structural heterogeneities in agglomerate-based electrodes. Importantly, the conditions under which optical imaging can be performed inside the complex environments of battery electrodes are outlined.

Interrogating the Light-Induced Charging Mechanism in Li-Ion Batteries Using Operando Optical Microscopy.

Photobatteries, batteries with a light-sensitive electrode, have recently been proposed as a way of simultaneously capturing and storing solar energy in a single device. Despite reports of photocharging with multiple different electrode materials, the overall mechanism of operation remains poorly understood. Here, we use operando optical reflection microscopy to investigate light-induced charging in LixV2O5 electrodes. We image the electrode, at the single-particle level, under three conditions: (a) with a closed circuit and light but no electronic power source (photocharging), (b) during galvanostatic cycling with light (photoenhanced), and (c) with heat but no light (thermal). We demonstrate that light can indeed drive lithiation changes in LixV2O5 while maintaining charge neutrality, possibly via a combination of faradaic and nonfaradaic effects taking place in individual particles. Our results provide an addition to the photobattery mechanistic model highlighting that both intercalation-based charging and lithium concentration polarization effects contribute to the increased photocharging capacity.

3D Porous Cu-Composites for Stable Li-Metal Battery Anodes.

Lithium (Li) metal is a promising anode material for lithium-ion batteries (LIBs) because of its high theoretical specific capacity of 3860 mAh g-1 and the low potential of -3.04 V versus the standard hydrogen electrode (SHE). However, these anodes rely on repeated plating and stripping of Li, which leads to consumption of Li inventory and the growth of dendrites that can lead to self-discharge and safety issues. To address these issues, as well as problems related to the volume change of these anodes, a number of different porous conductive scaffolds have been reported to create high surface area electrode on which Li can be plated reliably. While impressive results have been reported in literature, current processes typically rely on either expensive or poorly scalable techniques. Herein, we report a scalable fabrication method to create robust 3D Cu anodes using a one-step electrodeposition process. The areal loading, pore structure, and electrode thickness can be tuned by changing the electrodeposition parameters, and we show how standard mechanical calendering provides a way to further optimize electrode volume, capacity, and cycling stability. Optimized electrodes achieve high Coulombic efficiencies (CEs) of 99% during 800 cycles in half cells at a current density of 0.5 mA cm-2 with a total capacity of 0.5 mAh cm-2. To the best of our knowledge, this is the highest value ever reported for a host for Li-metal anodes using lithium bis(trifluoromethanesulfonyl)imide LITFSI based electrolyte.

Nonlinear Inflatable Actuators for Distributed Control in Soft Robots.

As soft robotic systems grow in complexity and functionality, the size and stiffness of the needed control hardware severely limits their application potential. Alternatively, functionality can be embodied within actuator characteristics, drastically reducing the amount of peripherals. Functions such as memory, computation, and energy storage then result from the intrinsic mechanical behavior of precisely designed structures. Here, actuators are introduced with tunable characteristics to generate complex actuation sequences from a single input. Intricate sequences are made possible by harnessing hysteron characteristics encoded in the buckling of a cone-shaped shell incorporated in the actuator design. A large variety of such characteristics are generated by varying the actuator geometry. This dependency is mapped and used for creating a tool to determine the actuator geometry that yields a desired characteristic. Using this tool, a system with six actuators is created that plays the final movement of Beethoven's Ninth Symphony with a single pressure supply.

Spinodal Decomposition Method for Structuring Germanium-Carbon Li-Ion Battery Anodes.

To increase the energy density of lithium-ion batteries (LIBs), high-capacity anodes which alloy with Li ions at a low voltage against Li/Li+ have been actively pursued. So far, Si has been studied the most extensively because of its high specific capacity and cost efficiency; however, Ge is an interesting alternative. While the theoretical specific capacity of Ge (1600 mAh g-1) is only half that of Si, its density is more than twice as high (Ge, 5.3 g cm-3; Si, 2.33 g cm-3), and therefore the charge stored per volume is better than that of Si. In addition, Ge has a 400 times higher ionic diffusivity and 4 orders of magnitude higher electronic conductivity compared to Si. However, similarly to Si, Ge needs to be structured in order to manage stresses induced during lithiation and many reports have achieved sufficient areal loadings to be commercially viable. In this work, spinodal decomposition is used to make secondary particles of about 2 µm in diameter that consist of a mixture of ∼30 nm Ge nanoparticles embedded in a carbon matrix. The secondary structure of these germanium-carbon particles allows for specific capacities of over 1100 mAh g-1 and a capacity retention of 91.8% after 100 cycles. Finally, high packing densities of ∼1.67 g cm-3 are achieved in blended electrodes by creating a bimodal size distribution with natural graphite.

Photo-enhanced lithium-ion batteries using metal-organic frameworks.

The development of photo-enhanced lithium-ion batteries, where exposing the electrodes to light results in higher capacities, higher rate performance or self-charging, has recently gained substantial traction. The challenge in these devices lies in the realisation of photo-electrodes with good optical and electrochemical properties. Herein, we propose copper-hexahydroxybenzene as the active photo-electrode material which both harvests light and stores energy. This material was mixed with reduced graphene oxide as a conductive additive and charge transfer medium to create photo-active electrodes. Under illumination, these electrodes show improved charge storage kinetics resulting in the photo-accelerated charging and discharging performance (i.e. specific capacities improvement from 107 mA h g-1 to 126 mA h g-1 at 200 mA g-1 and 79 mA h g-1 to 97 mA h g-1 at 2000 mA g-1 under 1 sun illumination as compared to dark).

Porous Carbon Coated on Cadmium Sulfide-Decorated Zinc Oxide Nanorod Photocathodes for Photo-accelerated Zinc Ion Capacitors.

The development of devices with dual solar energy-harvesting and storage functionalities has recently gained significant traction for off-grid power supply. In their most compact embodiment, these devices rely on the same electrode to harvest and store energy; however, in this approach, the development of energy-efficient photoelectrodes with intrinsic characteristics of good optical and electrochemical activities remains challenging. Here, we propose photoelectrodes with a porous carbon coated on a zinc oxide-cadmium sulfide heterostructure as an energy-efficient photocathode for photo-accelerated zinc ion capacitors (Photo-ZICs). The Photo-ZICs harvest light energy and store charge simultaneously, resulting in efficient charge storage performance under illumination compared to dark conditions (∼99% capacity enhancement at 500 mA g-1 under illumination compared to dark conditions). The light absorption ability and charge separation efficiency achieved by the photocathodes meet the requirements for photo-ZIC applications. Moreover, Photo-ZICs display stable charge storage capacities over long-term cycling, that is, ∼1% capacity loss after 10,000 cycles.

Out-of-Plane Soft Lithography for Soft Pneumatic Microactuator Arrays.

Elastic pneumatic actuators are fueling new devices and applications in soft robotics. Actuator miniaturization is critical to enable soft microsystems for applications in microfluidics and micromanipulation. This work proposes a fabrication technique to make out-of-plane bending microactuators entirely by soft lithography. The only bonding step required is to seal the embedded fluidic channels, assuring the structural integrity of the microactuators. The process consists of fabricating two SU8 mold halves using different lithographic layers. Polydimethilsiloxane is poured on the bottom mold, which is subsequently aligned and assembled with the top mold. The process allows for out-of-plane actuators with a diameter of 300 µm and for fabricating arrays of up to 36 actuators that are row addressable. These active micropillars have an aspect ratio of 1:1.5 and, when pressurized at 1 bar, show a bending angle of ∼30°.

Simultaneously enhanced tenacity, rupture work, and thermal conductivity of carbon nanotube fibers by raising effective tube portion.

Although individual carbon nanotubes (CNTs) are superior to polymer chains, the mechanical and thermal properties of CNT fibers (CNTFs) remain inferior to synthetic fibers because of the failure of embedding CNTs effectively in superstructures. Conventional techniques resulted in a mild improvement of target properties while degrading others. Here, a double-drawing technique is developed to rearrange the constituent CNTs. Consequently, the mechanical and thermal properties of the resulting CNTFs can simultaneously reach their highest performances with specific strength ~3.30 N tex-1 (4.60 GPa), work of rupture ~70 J g-1, and thermal conductivity ~354 W m-1 K-1 despite starting from low-crystallinity materials (IG:ID ~ 5). The processed CNTFs are more versatile than comparable carbon fiber, Zylon and Dyneema. On the basis of evidence of load transfer efficiency on individual CNTs measured with in situ stretching Raman, we find that the main contributors to property enhancements are the increasing of the effective tube contribution.