Behavior of Solid Electrolyte in Li-Polymer Battery with NMC Cathode via in-Situ Scanning Electron Microscopy.

We present the first results of in situ scanning electron microscopy (SEM) of an all-solid Li battery with a nickel-manganese-cobalt-oxide (NMC-622) cathode at 50 °C and an operating voltage of 2.7-4.3 V. Experiments were conducted under a constant current at several C rates (nC rate: cycling in 1/n h): C/12, C/6, and C/3. The microstructure evolution during cycling was monitored by continuous secondary electron imaging. We found that the chemical degradation of the solid polymer electrolyte (SPE) was the main mechanism for battery failure. This degradation was observed in the form of a gradual thinning of the SPE as a function of cycling time, resulting in gas generation from the cell. We also present various dynamic electrochemical and mechanical phenomena, as observed by SEM images, and compare the performance of this battery with that of an all-solid Li battery with a LiFePO4 cathode.

Porous Carbon Membrane-Supported Atomically Dispersed Pyrrole-Type FeN4 as Active Sites for Electrochemical Hydrazine Oxidation Reaction.

The rational design of catalytically active sites in porous materials is essential in electrocatalysis. Herein, atomically dispersed Fe-Nx sites supported by hierarchically porous carbon membranes are designed to electrocatalyze the hydrazine oxidation reaction (HzOR), one of the key techniques in electrochemical nitrogen transformation. The high intrinsic catalytic activity of the Fe-Nx single-atom catalyst together with the uniquely mixed micro-/macroporous membrane support positions such an electrode among the best-known heteroatom-based carbon anodes for hydrazine fuel cells. Combined with advanced characterization techniques, electrochemical probe experiments, and density functional theory calculation, the pyrrole-type FeN4 structure is identified as the real catalytic site in HzOR.

From Solid-Solution Electrodes and the Rocking-Chair Concept to Today's Batteries.

Lithium-ion batteries (LIBs) have become ubiquitous power sources for small electronic devices, electric vehicles, and stationary energy storage systems. Despite the success of LIBs which is acknowledged by their increasing commodity market, the historical evolution of the chemistry behind the LIB technologies is laden with obstacles and yet to be unambiguously documented. This Viewpoint outlines chronologically the most essential findings related to today's LIBs, including commercial electrode and electrolyte materials, but furthermore also depicts how the today popular and widely emerging solid-state batteries were instrumental at very early stages in the development of LIBs.

In-Situ Characterization of Lithium Native Passivation Layer in A High Vacuum Scanning Electron Microscope.

A technique to characterize the native passivation layer (NPL) on pure lithium metal foils in a scanning electron microscope (SEM) is described in this paper. Lithium is a very reactive metal, and consequently, observing and quantifying its properties in a SEM is often compromised by rapid oxidation. In this work, a pure lithium energy-dispersive x-ray spectrum is obtained for the first time in a high vacuum SEM using a cold stage/cold trap with liquid nitrogen reservoir outside the SEM chamber. A nanomanipulator (OmniProbe 400) inside the microscope combined with x-ray microanalysis and windowless energy dispersive spectrometer is used to fully characterize the NPL of lithium metal and some of its alloys by a mechanical removal procedure. The results show that the native films of pure lithium and its alloys are composed of a thin (25 nm) outer layer that is carbon-rich and an inner layer containing a significant amount of oxygen. Differences in thickness between laminated and extruded samples are observed and vary depending on the alloy composition.

In Situ Scanning Electron Microscopy Detection of Carbide Nature of Dendrites in Li-Polymer Batteries.

Li metal batteries suffer from dendrite formation which causes short circuit of the battery. Therefore, it is important to understand the chemical composition and growth mechanism of dendrites that limit battery efficiency and cycle life. In this study, in situ scanning electron microscopy was employed to monitor the cycling behavior of all-solid Li metal batteries with LiFePO4 cathodes. Chemical analyses of the dendrites were conducted using a windowless energy dispersive spectroscopy detector, which showed that the dendrites are not metallic lithium as universally recognized. Our results revealed the carbide nature of the dendrites with a hollow morphology and hardness greater than that of pure lithium. These carbide-based dendrites were able to perforate through the polymer, which was confirmed by milling the polymer using focused ion beam. It was also shown that applying pressure on the battery can suppress growth of the dendrites.

New Avenue for Limiting Degradation in NanoLi4Ti5O12 for Ultrafast-Charge Lithium-Ion Batteries: Hybrid Polymer-Inorganic Particles.

Lithium titanium oxide (Li4Ti5O12)-based cells are a very promising battery technology for ultrafast-charge-discharge and long-cycle-life batteries. However, the surface reactivity of lithium titanium oxide in the presence of organic electrolytes continues to be a problem that may cause expansion of pouch cells. In this study, we report on the development of a simple and economical grafting method for forming hybrid polymer-Li4Ti15O12 nanoparticles, which can be successfully applied in lithium-ion batteries. This method utilizes a low-cost and scalable hydrophobic polymer that is applicable in industrial processes. The hybrid materials demonstrated exceptional capability for preventing the degradation of cells in accelerated aging and operating over 150 cycles at 1C and 45 °C.

Measuring Spatially Resolved Collective Ionic Transport on Lithium Battery Cathodes Using Atomic Force Microscopy.

One of the main challenges in improving fast charging lithium-ion batteries is the development of suitable active materials for cathodes and anodes. Many materials suffer from unacceptable structural changes under high currents and/or low intrinsic conductivities. Experimental measurements are required to optimize these properties, but few techniques are able to spatially resolve ionic transport properties at small length scales. Here we demonstrate an atomic force microscope (AFM)-based technique to measure local ionic transport on LiFePO4 to correlate with the structural and compositional analysis of the same region. By comparing the measured values with density functional theory (DFT) calculations, we demonstrate that Coulomb interactions between ions give rise to a collective activation energy for ionic transport that is dominated by large phase boundary hopping barriers. We successfully measure both the collective activation energy and the smaller single-ion bulk hopping barrier and obtain excellent agreement with values obtained from our DFT calculations.

Ambient-Air Stable Lithiated Anode for Rechargeable Li-Ion Batteries with High Energy Density.

An important requirement of battery anodes is the processing step involving the formation of the solid electrolyte interphase (SEI) in the initial cycle, which consumes a significant portion of active lithium ions. This step is more critical in nanostructured anodes with high specific capacity, such as Si and Sn, due to their high surface area and large volume change. Prelithiation presents a viable approach to address such loss. However, the stability of prelithiation reagents is a big issue due to their low potential and high chemical reactivity toward O2 and moisture. Very limited amount of prelithiation agents survive in ambient air. In this research, we describe the development of a trilayer structure of active material/polymer/lithium anode, which is stable in ambient air (10-30% relative humidity) for a period that is sufficient to manufacture anode materials. The polymer layer protects lithium against O2 and moisture, and it is stable in coating active materials. The polymer layer is gradually dissolved in the battery electrolyte, and active materials contact with lithium to form lithiated anode. This trilayer-structure not only renders electrodes stable in ambient air but also leads to uniform lithiation. Moreover, the degree of prelithiation could vary from compensating SEI to fully lithiated anode. With this strategy, we have achieved high initial Coulombic efficiency of 99.7% in graphite anodes, and over 100% in silicon nanoparticles anodes. The cycling performance of lithiated anodes is comparable or better than those not lithiated. We also demonstrate a Li4Ti5O12/lithiated graphite cell with stable cycling performance. The trilayer structure represents a new prelithiation method to enhance performance of Li-ion batteries.

Accelerated Removal of Fe-Antisite Defects while Nanosizing Hydrothermal LiFePO4 with Ca(2).

Based on neutron powder diffraction (NPD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we show that calcium ions help eliminate the Fe-antisite defects by controlling the nucleation and evolution of the LiFePO4 particles during their hydrothermal synthesis. This Ca-regulated formation of LiFePO4 particles has an overwhelming impact on the removal of their iron antisite defects during the subsequent carbon-coating step since (i) almost all the Fe-antisite defects aggregate at the surface of the LiFePO4 crystal when the crystals are small enough and (ii) the concomitant increase of the surface area, which further exposes the Fe-antisite defects. Our results not only justify a low-cost, efficient and reliable hydrothermal synthesis method for LiFePO4 but also provide a promising alternative viewpoint on the mechanism controlling the nanosizing of LiFePO4, which leads to improved electrochemical performances.

Etched colloidal LiFePO4 nanoplatelets toward high-rate capable Li-ion battery electrodes.

LiFePO4 has been intensively investigated as a cathode material in Li-ion batteries, as it can in principle enable the development of high power electrodes. LiFePO4, on the other hand, is inherently "plagued" by poor electronic and ionic conductivity. While the problems with low electron conductivity are partially solved by carbon coating and further by doping or by downsizing the active particles to nanoscale dimensions, poor ionic conductivity is still an issue. To develop colloidally synthesized LiFePO4 nanocrystals (NCs) optimized for high rate applications, we propose here a surface treatment of the NCs. The particles as delivered from the synthesis have a surface passivated with long chain organic surfactants, and therefore can be dispersed only in aprotic solvents such as chloroform or toluene. Glucose that is commonly used as carbon source for carbon-coating procedure is not soluble in these solvents, but it can be dissolved in water. In order to make the NCs hydrophilic, we treated them with lithium hexafluorophosphate (LiPF6), which removes the surfactant ligand shell while preserving the structural and morphological properties of the NCs. Only a roughening of the edges of NCs was observed due to a partial etching of their surface. Electrodes prepared from these platelet NCs (after carbon coating) delivered a capacity of ∼ 155 mAh/g, ∼ 135 mAh/g, and ∼ 125 mAh/g, at 1 C, 5 C, and 10 C, respectively, with significant capacity retention and remarkable rate capability. For example, at 61 C (10.3 A/g), a capacity of ∼ 70 mAh/g was obtained, and at 122 C (20.7 A/g), the capacity was ∼ 30 mAh/g. The rate capability and the ease of scalability in the preparation of these surface-treated nanoplatelets make them highly suitable as electrodes in Li-ion batteries.

Toward practical application of functional conductive polymer binder for a high-energy lithium-ion battery design.

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries; however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxide (SiO) anode material, demonstrating stable and high gravimetric capacity (>1000 mAh/g) for ∼500 cycles and more than 90% capacity retention. Prelithiation of this anode using stabilized lithium metal powder (SLMP) improves the first cycle Coulombic efficiency of a SiO/NMC full cell from ∼48% to ∼90%. The combination enables good capacity retention of more than 80% after 100 cycles at C/3 in a lithium-ion full cell.

Structural Study of Sulfur-Added Carbon Nanohorns.

In the past few decades, nanostructured carbons (NCs) have been investigated for their interesting properties, which are attractive for a wide range of applications in electronic devices, energy systems, sensors, and support materials. One approach to improving the properties of NCs is to dope them with various heteroatoms. This work describes the synthesis and study of sulfur-added carbon nanohorns (S-CNH). Synthesis of S-CNH was carried out by modified chemical vapor deposition (m-CVD) using toluene and thiophene as carbon and sulfur sources, respectively. Some parameters such as the temperature of synthesis and carrier gas flow rates were modified to determine their effect on the properties of S-CNH. High-resolution scanning and transmission electron microscopy analysis showed the presence of hollow horn-type carbon nanostructures with lengths between 1 to 3 µm and, diameters that are in the range of 50 to 200 nm. Two types of carbon layers were observed, with rough outer layers and smooth inner layers. The surface textural properties are attributed to the defects induced by the sulfur intercalated into the lattice or bonded with the carbon. The XRD patterns and X-ray microanalysis studies show that iron serves as the seed for carbon nanohorn growth and iron sulfide is formed during synthesis.

Identification of the active triple-phase boundary of a non-Pt catalyst layer in fuel cells.

The rational design of non-Pt oxygen reduction reaction (ORR) catalysts and catalyst layers in fuel cells is largely impeded by insufficient knowledge of triple-phase boundaries (TPBs) in the micropore and mesopore ranges. Here, we developed a size-sensitive molecular probe method to resolve the TPB of Fe/N/C catalyst layers in these size ranges. More than 70% of the ORR activity was found to be contributed by the 0.8- to 2.0-nanometer micropores of Fe/N/C catalysts, even at a low micropore area fraction of 29%. Acid-alkaline interactions at the catalyst-polyelectrolyte interface deactivate the active sites in mesopores and macropores, resulting in inactive TPBs, leaving micropores without the interaction as the active TPBs. The concept of active and inactive TPBs provides a previously unidentified design principle for non-Pt catalyst and catalyst layers in fuel cells.

Highly Active and Durable Single-Atom Tungsten-Doped NiS0.5 Se0.5 Nanosheet @ NiS0.5 Se0.5 Nanorod Heterostructures for Water Splitting.

Developing robust and highly active non-precious electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) is crucial for the industrialization of hydrogen energy. In this study, a highly active and durable single-atom W-doped NiS0.5 Se0.5 nanosheet @ NiS0.5 Se0.5 nanorod heterostructure (W-NiS0.5 Se0.5 ) electrocatalyst is prepared. W-NiS0.5 Se0.5 exhibits excellent catalytic activity for the HER and OER with ultralow overpotentials (39 and 106 mV for the HER and 171 and 239 mV for the OER at 10 and 100 mA cm-2 , respectively) and excellent long-term durability (500 h), outperforming commercial precious-metal catalysts and many other previously reported transition-metal-based compounds (TMCs). The introduction of single-atom W delocalizes the spin state of Ni, which results in an increase in the Ni d-electron density. This causes the optimization of the adsorption/desorption process of H and a significant reduction in the adsorption free energy of the rate-determining step (O* → OOH*), thus accelerating the thermodynamics and kinetics of the HER and OER. This work provides a rational feasible strategy to design single-atom catalysts for water splitting and to develop advanced TMC electrocatalysts by regulating delocalized spin states.

Growth Mechanism of Micro/Nano Metal Dendrites and Cumulative Strategies for Countering Its Impacts in Metal Ion Batteries: A Review.

Metal-ion batteries are capable of delivering high energy density with a longer lifespan. However, they are subject to several issues limiting their utilization. One critical impediment is the budding and extension of solid protuberances on the anodic surface, which hinders the cell functionalities. These protuberances expand continuously during the cyclic processes, extending through the separator sheath and leading to electrical shorting. The progression of a protrusion relies on a number of in situ and ex situ factors that can be evaluated theoretically through modeling or via laboratory experimentation. However, it is essential to identify the dynamics and mechanism of protrusion outgrowth. This review article explores recent advances in alleviating metal dendrites in battery systems, specifically alkali metals. In detail, we address the challenges associated with battery breakdown, including the underlying mechanism of dendrite generation and swelling. We discuss the feasible solutions to mitigate the dendrites, as well as their pros and cons, highlighting future research directions. It is of great importance to analyze dendrite suppression within a pragmatic framework with synergy in order to discover a unique solution to ensure the viability of present (Li) and future-generation batteries (Na and K) for commercial use.

Cause and Mitigation of Lithium-Ion Battery Failure-A Review.

Lithium-ion batteries (LiBs) are seen as a viable option to meet the rising demand for energy storage. To meet this requirement, substantial research is being accomplished in battery materials as well as operational safety. LiBs are delicate and may fail if not handled properly. The failure modes and mechanisms for any system can be derived using different methodologies like failure mode effects analysis (FMEA) and failure mode methods effects analysis (FMMEA). FMMEA is used in this paper as it helps to identify the reliability of a system at the component level focusing on the physics causing the observed failures and should thus be superior to the more data-driven FMEA approach. Mitigation strategies in LiBs to overcome the failure modes can be categorized as intrinsic safety, additional protection devices, and fire inhibition and ventilation. Intrinsic safety involves modifications of materials in anode, cathode, and electrolyte. Additives added to the electrolyte enhance the properties assisting in the improvement of solid-electrolyte interphase and stability. Protection devices include vents, circuit breakers, fuses, current interrupt devices, and positive temperature coefficient devices. Battery thermal management is also a protection method to maintain the temperature below the threshold level, it includes air, liquid, and phase change material-based cooling. Fire identification at the preliminary stage and introducing fire suppressive additives is very critical. This review paper provides a brief overview of advancements in battery chemistries, relevant modes, methods, and mechanisms of potential failures, and finally the required mitigation strategies to overcome these failures.

Pillar-beam structures prevent layered cathode materials from destructive phase transitions.

Energy storage with high energy density and low cost has been the subject of a decades-long pursuit. Sodium-ion batteries are well expected because they utilize abundant resources. However, the lack of competent cathodes with both large capacities and long cycle lives prevents the commercialization of sodium-ion batteries. Conventional cathodes with hexagonal-P2-type structures suffer from structural degradations when the sodium content falls below 33%, or when the integral anions participate in gas evolution reactions. Here, we show a "pillar-beam" structure for sodium-ion battery cathodes where a few inert potassium ions uphold the layer-structured framework, while the working sodium ions could diffuse freely. The thus-created unorthodox orthogonal-P2 K0.4[Ni0.2Mn0.8]O2 cathode delivers a capacity of 194 mAh/g at 0.1 C, a rate capacity of 84% at 1 C, and an 86% capacity retention after 500 cycles at 1 C. The addition of the potassium ions boosts simultaneously the energy density and the cycle life.

Application of Magnetic Resonance Techniques to the In Situ Characterization of Li-Ion Batteries: A Review.

In situ magnetic resonance (MR) techniques, such as nuclear MR and MR imaging, have recently gained significant attention in the battery community because of their ability to provide real-time quantitative information regarding material chemistry, ion distribution, mass transport, and microstructure formation inside an operating electrochemical cell. MR techniques are non-invasive and non-destructive, and they can be applied to both liquid and solid (crystalline, disordered, or amorphous) samples. Additionally, MR equipment is available at most universities and research and development centers, making MR techniques easily accessible for scientists worldwide. In this review, we will discuss recent research results in the field of in situ MR for the characterization of Li-ion batteries with a particular focus on experimental setups, such as pulse sequence programming and cell design, for overcoming the complications associated with the heterogeneous nature of energy storage devices. A comprehensive approach combining proper hardware and software will allow researchers to collect reliable high-quality data meeting industrial standards.

Comprehensive Review of Polymer Architecture for All-Solid-State Lithium Rechargeable Batteries.

Solid-state batteries are an emerging option for next-generation traction batteries because they are safe and have a high energy density. Accordingly, in polymer research, one of the main goals is to achieve solid polymer electrolytes (SPEs) that could be facilely fabricated into any preferred size of thin films with high ionic conductivity as well as favorable mechanical properties. In particular, in the past two decades, many polymer materials of various structures have been applied to improve the performance of SPEs. In this review, the influences of polymer architecture on the physical and electrochemical properties of an SPE in lithium solid polymer batteries are systematically summarized. The discussion mainly focuses on four principal categories: linear, comb-like, hyper-branched, and crosslinked polymers, which have been widely reported in recent investigations as capable of optimizing the balance between mechanical resistance, ionic conductivity, and electrochemical stability. This paper presents new insights into the design and exploration of novel high-performance SPEs for lithium solid polymer batteries.

Improvement of the energy resolution of energy dispersive spectrometers (EDS) using Richardson-Lucy deconvolution.

A serious limitation in the use of energy dispersive spectrometers (EDS) for materials characterization arises from the fact that these x-ray detectors provide a poor energy resolution compared to other x-ray techniques. This is mainly due to the broadening function generated by the electronics of the detector. However, new windowless detectors are now capable of resolving low energy peaks like Li Kα with modified electronics and show a system peak full width at half maximum (FWHM) of around 30 eV. In this paper, we investigated how the Richardson-Lucy algorithm can be used to remove, or at least attenuate, the contribution of the broadening function to experimental spectra. This method proved to be efficient in improving the energy resolution at any energy in the EDS spectrum. The resulting system peak FWHM was reduced to as low as 7-8 eV and the separation of low energy x-ray peaks were demonstrated in the low energy range of the spectra. The method was also efficient in reducing the peak broadening at higher energies (Cu Kα) and the broadening function of the detector could be experimentally determined to provide higher accuracy in predicting peak broadening. Although some critical artefacts were noted on the restored spectra, like energy shifts and intensity variations, the method explored in this work is worth to be considered for further quantification tests.