The mechanism of in-homogeneous mass transfer process of separators in lithium-ion batteries.

The liquid-phase mass transport is the key factor affecting battery stability. The influencing mechanism of liquid-phase mass transport in the separators is still not clear, the internal environment being a complex multi-field during the service life of lithium-ion batteries. The liquid-phase mass transport in the separators is related to the microstructure of the separator and the physicochemical properties of electrolytes. Here, in-situ local electrochemical impedance spectra were developed to investigate local inhomogeneities in the mass transfer process of lithium-ion batteries. The geometric microstructure of the separator affects the mass transfer process, with a reduction in porosity leading to increased overpotentials. There is a competitive relationship among porosity, tortuosity, and membrane thickness in the geometric parameters of the separator, resulting in a peak of polarization. The resistance of the liquid-phase mass transfer process is positively correlated with the viscosity of the electrolyte, making ion migration difficult due to high viscosity. Polarization is closely related to the electrochemical performance, so a phase diagram of battery performance and inhomogeneous mass transfer was developed to guide the design of the battery. This study provides a guiding basis for the development of high stability lithium-ion batteries.

Stable Photo-Rechargeable Al Battery for Enhancing Energy Utilization.

Photovoltaic cells (PVs) are able to convert solar energy to electric energy, while energy storage devices are required to be equipped due to the fluctuations of sunlight. However, the electrical connection of PVs and energy storage devices leads to increased energy consumption, and thus energy storage ability and utilization efficiency are decreased. One of the solutions is to explore an integrated photoelectrochemical energy conversion-storage device. Up to date, the integrated photo-rechargeable Li-ion batteries often suffer from unstable photo-active materials and flammable electrolytes under illumination, with concerns in safety risks and limited lifetime. To address the critical issues, here a novel photo-rechargeable aluminum battery (PRAB) is designed with safe ionic liquid electrolytes and stable polyaniline photo-electrodes. The integrated PRAB presents stable operation with an enhanced reversible specific capacity ≈191% under illumination. Meanwhile, a simplified continuum model is established to provide rational guidance for designing electrode structures along with a charging/discharging strategy to meet the practical operation conditions. The as-designed PRAB presents an energy-saving efficiency ≈61.92% upon charging and an energy output increment ≈31.25% during discharging under illumination. The strategy of designing and fabricating stable and safe photo-rechargeable non-aqueous Al batteries highlights the pathway for substantially promoting the utilization efficiency of solar energy.

Surface Engineering Based on Conductive Agent Dispersion Uniformity: Strategies toward Performance Consistency of Lithium-Ion Batteries.

The consistency of lithium-ion battery performance is the key factor affecting the safety and cycle life of battery packs. Surface engineering of electrodes in production processes plays an important role in improving the consistency of battery performance. In this study, the drying process in the electrode manufacturing process is studied as the effect on surface engineering of the electrode materials, with consideration on impacting the battery performance. Specifically, the solid content of the slurry and drying temperature are considered to be the two factors that affect conductive agent dispersion uniformity in the porous electrodes. To achieve surface engineering on the dispersion uniformity of the conductive agent, the optimal processing parameters can be obtained by adjusting the temperature and solid content of the slurry. The mechanism of dispersion uniformity of the conductive agent is mainly related to the polyvinylidene fluoride grid structure. In the manufacturing of lithium-ion batteries, the electrode coated with 66% solid slurry and dried at 90-100 °C presents stable energy storage performance, which is beneficial to maintain the stable performance of the battery pack in the application.

Single-Particle Measurements: A Powerful Method for Investigating Electrochemical Reactions.

The relationship between interface structure (e. g., the facet of the solid phase and the configuration of solvation) and the reactivity of the corresponding electrode is a critical issue in electrochemistry. Compared to macroscopic electrode measurements, electrochemical methods established on the single-particle scale have advantages in establishing the structure-property relationship. In recent years, great achievements have been made in electrochemical energy storage and electrocatalysis that allow the evolution and kinetics of electrodes to be understood by employing single-particle measurements. This concept aims to provide an overview of the update of single-particle measurements in related electrochemical processes. Furthermore, the challenges and prospects for the development and application of single-particle measurements are also discussed.

Toward Stable Al Negative Electrodes of Aluminum-Ion Batteries: Kinetic Parameters and Electrode Structure.

Rechargeable aluminum-ion batteries have attracted significant attention as candidates for next-generation energy storage devices owing to their high theoretical capacity, safe performance, and abundance of raw materials. Al metal is the best option as the negative electrode, while its issues such as dendrite growth and corrosion accompanying hydrogen evolution in ionic liquid electrolyte have been seriously overlooked. Understanding the electrochemical mechanism of the surface evolution behavior of Al metal is a vital pathway for solving these issues. Kinetic parameters and electrode structure are the two key parameters that affect the surface evolution behavior of Al negative electrodes. Herein, the qualitative relationship between the kinetic parameters and surface evolution behavior of the Al negative electrode was established through a combination of in-situ optical technology and multi-physical field numerical simulation method. The key kinetic parameters, including ion concentration and transfer coefficient, exhibited different laws of influence on the surface evolution behavior, such as dendrite growth and corrosion. The electrochemical mechanism on the surface evolution was explored to guide the optimization design of Al-ion batteries. Based on the coupling design of the electrode structure and kinetic parameters, a highly stable porous aluminum structure composed of Al powder with a particle size of 100 µm was constructed to obtain highly stable and high-performance aluminum-ion batteries. This method provides new sight into the design of high-performance aluminum-ion batteries.

Correlating Electrochemical Kinetic Parameters of Single LiNi1/3 Mn1/3 Co1/3 O2 Particles with the Performance of Corresponding Porous Electrodes.

Characterizing microscale single particles directly is requested for dissecting the performance-limiting factors at the electrode scale. In this work, we build a single-particle electrochemical setup and develop a physics-based model for extracting the solid-phase diffusion coefficient (Ds ) and exchange current density (i0 ) from electrochemical impedance measurements. We find that the carbon coating on the LiNi1/3 Mn1/3 Co1/3 O2 surface enhances i0 . In addition, Ds and i0 decay irreversibly by ≈25 % and ≈10 %, respectively, when the cutoff charge voltage increases from 4.3 V to 4.4 V. Moreover, we correlate intrinsic parameters of single particles with the performance of porous electrodes. Porous electrodes assembled with active particles with higher i0 values deliver a greater capacity and faster capacity fade. The methods developed in this combined experimental and theoretical work can be useful in correlating the single-particle scale and porous-electrode scale for other similar systems.

Rechargeable Metasurfaces for Dynamic Color Display Based on a Compositional and Mechanical Dual-Altered Mechanism.

Dynamic color display can be realized by tunable optical metasurfaces based on the compositional or structural control. However, it is still a challenge to realize the efficient modulation by a single-field method. Here, we report a novel compositional and mechanical dual-altered rechargeable metasurface for reversible and broadband optical reconfiguration in both visible and near-infrared wavelength regions. By employing a simple fabrication and integration strategy, the continuous optical reconfiguration is manipulated through an electro-chemo-mechanical coupled process in a lithium ion battery, where lithiation and delithiation processes occur dynamically under a low electric voltage (≤1.5 V). By controlling the phase transformation from Si to Li xSi, both structural morphology and optical scattering could be rapidly and dramatically tailored within 30 s, exhibiting high-contrast colorization and decolorization in a large-area nanofilm and showing long cyclic stability. Significant wide-angle reconfiguration of high-resolution structural colors in bowtie metasurfaces is demonstrated from anomalous reflection. The results provide a multifield mechanism for reconfigurable photonic devices, and the new platform can be introduced to the multidimensional information encryption and storage.

Metal-organic framework derived hollow porous CuO-CuCo2O4 dodecahedrons as a cathode catalyst for Li-O2 batteries.

Herein, hollow porous CuO-CuCo2O4 dodecahedrons are synthesized by using a simple self-sacrificial metal-organic framework (MOF) template, which resulted in dodecahedron morphology with hierarchically porous architecture. When evaluated as a cathodic electrocatalyst in lithium-oxygen batteries, the CuO-CuCo2O4 composite exhibits a significantly enhanced electrochemical performance, delivering an initial capacity of 6844 mA h g-1 with a remarkably decreased discharge/charge overpotential to 1.15 V (vs. Li/Li+) at a current density of 100 mA g-1 and showing excellent cyclic stability up to 111 charge/discharge cycles under a cut-off capacity of 1000 mA h g-1 at 400 mA g-1. The outstanding electrochemical performance of CuO-CuCo2O4 composite can be owing to the intrinsic catalytic activity, unique porous structure and the presence of substantial electrocatalytic sites. The ex situ XRD and SEM are also carried out to reveal the charge/discharge behavior and demonstrate the excellent reversibility of the CuO-CuCo2O4 based electrode.

Effect of Defects on Diffusion Behaviors of Lithium-Ion Battery Electrodes: In Situ Optical Observation and Simulation.

Lithium-ion batteries (LIBs) with high energy efficiency are urgently needed in various fields. For the LIBs electrodes, defects would be generated during the manufacturing processes and mechanical degradation and significantly impact the stability and performance of the LIBs. However, the effects of electrode defects on the electrochemical processes are still not clear. Herein, an in situ optical observation system is developed for monitoring the Li diffusion around the preintroduced defects in the commercial graphite electrodes. The experiments show that the gas-filled defects vertical to the direction of the Li diffusion would obviously decelerate the Li diffusion, whereas the electrolyte-filled defects parallel to the direction of the Li diffusion would accelerate the Li diffusion. In addition, finite element analysis (FEA) suggests, consistent with the experiments, a nonuniform distribution of local Li concentration around the defect. The equivalent diffusivity obtained by the FEA is also dependent on the configuration of the defects. The diffusivities of the electrolyte-filled parallel defect and gas-filled vertical defect are 12.6 and 11.0%, respectively. For the gas-filled defects, the size-effect calculation manifests that the equivalent diffusivity would decrease with the enlarged defect size, and the shape of the defects would substantially impact the decrease rate. The results directly reveal the mechanisms of the defect-induced diffusion behavior change in the electrodes by the new equivalent two-dimensional experiments, and the equivalent diffusivity would be useful for optimizing the electrode designs in LIBs.

Failure mechanisms of 2D silicon film anodes: in situ observations and simulations on crack evolution.

An in situ optical system was used to observe the failure processes of two-dimensional silicon film anodes, suggesting a new debonding mode based on crack crushing. The stress evolution upon lithiation was quantitatively analyzed via fully coupled finite element simulations, confirming the crack crushing induced failure mechanisms in 2D silicon anodes.

A Novel Ultrafast Rechargeable Multi-Ions Battery.

An ultrafast rechargeable multi-ions battery is presented, in which multi-ions can electrochemically intercalate into graphite layers, exhibiting a high reversible discharge capacity of ≈100 mAh g-1 and a Coulombic efficiency of ≈99% over hundreds of cycles at a high current density. The results may open up a new paradigm for multi-ions-based electrochemical battery technologies and applications.

High-Performance Aluminum-Ion Battery with CuS@C Microsphere Composite Cathode.

On the basis of low-cost, rich resources, and safety performance, aluminum-ion batteries have been regarded as a promising candidate for next-generation energy storage batteries in large-scale energy applications. A rechargeable aluminum-ion battery has been fabricated based on a 3D hierarchical copper sulfide (CuS) microsphere composed of nanoflakes as cathode material and room-temperature ionic liquid containing AlCl3 and 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) as electrolyte. The aluminum-ion battery with a microsphere electrode exhibits a high average discharge voltage of ∼1.0 V vs Al/AlCl4-, reversible specific capacity of about 90 mA h g-1 at 20 mA g-1, and good cyclability of nearly 100% Coulombic efficiency after 100 cycles. Such remarkable electrochemical performance is attributed to the well-defined nanostructure of the cathode material facilitating the electron and ion transfer, especially for chloroaluminate ions with large size, which is desirable for aluminum-ion battery applications.