Surface Reinforcing Balloon Trick-Inspired Separator/Li Metal Integrated Assembly To Improve the Electrochemical Performance of Li Metal Batteries

Li metal experiences significant morphological changes during operation, resulting in rapid electrochemical performance degradation. In this study, a traditional balloon trick is applied to the Li metal surface to release mechanical stress and hinder morphological changes during operation. Polymer separators directly attach to the Li metal surface using a polymeric adhesive to fabricate a separator/Li metal integrated assembly. The separator/Li metal assembly improves not only the electrochemical performance but also safety issues related to Li metal anodes. This approach has three main advantages: (i) Li metal surface stabilization. The separator/Li metal assembly mechanically stabilize the Li metal surface, resulting in improved rate capability and cycle performance [85.0% of initial discharge capacity (90.2 mAh g–1) at a 7C condition for rate capability and 87.6% of discharge capacity (95.5 mAh g–1) at the 220th cycle] compared with the bare Li metal without separator integration [82.6% of initial discharge capacity (84.5 mAh g–1) at a 3C condition for rate capability and 58.0% of discharge capacity (62.6 mAh g–1) at the 120th cycle]. (ii) Suitability for high energy density battery implementation. The thickness of the polymeric adhesive is less than 1 μm, which is one-tenth of the coating layer of conventional thermally stable separators, but exhibits similar thermal shrinkage characteristics (0% shrinkage at 140 °C for 30 min). By reducing the thickness of inactive components, a larger volume of active material can be loaded into the battery system to increase the energy density of the battery. (iii) Simple process for mass production. The separator/Li metal integration process (“stick” and “dry”) is very simple and can be easily applicable across industries

Preplanting Nanosilica into Binderless Battery Electrodes for High-Performance Li-Ion Batteries

The energy density of Li-ion batteries (LIBs) can be effectively enhanced by increasing the thickness of a LiNixMnyCo1–x–yO2 (NMC) electrode and limiting the use of inactive components. However, the deficiency of a binder in thick NMC cathodes causes mechanical failure, such as crack formation and delamination, resulting in performance deterioration. To address the detrimental issues associated with thick electrodes, this study proposes the preplanting of nanosilica (SiO2) into a NMC composite electrode. SiO2 preplanted in the PVDF polymer solution can alter the viscoelastic properties of the NMC slurry and regulate the binder distribution within the NMC cathode. A lower binder concentration at the interface assisted by SiO2 preplanting enhances the charge transfer without compromising adhesion. The hydrophilic nature of fumed SiO2 can facilitate the penetration of the electrolyte through a thick NMC cathode, enhancing its high-power capability up to 4 C-rate. Owing to the HF scavenging role of fumed SiO2, the SiO2 preplanted cathode exhibited stable cycling at an elevated temperature (60 °C) by alleviating the side reactions triggered by salt decomposition

DataSheet1_Simulation Study on Internal Short Circuits in a Li-Ion Battery Depending on the Sizes, Quantities, and Locations of Li Dendrites.docx

The internal short circuit caused by the Li dendrite is well known to be a major cause for fire or explosion accidents involving state-of-the-art lithium-ion batteries (LIBs). However, post-mortem analysis cannot identify the most probable cause, which is initially embedded in the cell, because the original structure of the cell totally collapses after the accident. Thus, multiphysics modeling and simulation must be an effective solution to investigate the effect of a specific cause in a variety of conditions. Herein, we reported an electrochemical-thermal model to simulate the internal short circuit depending on Li dendrite’s sizes (1, 3, 5, 7, and 9 μm), quantities (1–9), relative locations (0, 25, 50, 100, and 150 μm), and external temperature (−10, 10, 30, and 50°C). Through monitoring the temperature change affected by the joule and reaction heats for each case, we suggested critical conditions that led to unavoidable thermal runaway. Thus, this model can be a steppingstone in understanding the correlation between internal short circuits and Li dendrites.</p

Three-Dimensional Adhesion Map Based on Surface and Interfacial Cutting Analysis System for Predicting Adhesion Properties of Composite Electrodes

Using a surface and interfacial cutting analysis system (SAICAS) that can measure the adhesion strength of a composite electrode at a specific depth from the surface, we can subdivide the adhesion strength of a composite electrode into two classes: (1) the adhesion strength between the Al current collector and the cathode composite electrode (<i>F</i>_Al–Ca) and (2) the adhesion strength measured at the mid-depth of the cathode composite electrode (<i>F</i>_mid). Both adhesion strengths, <i>F</i>_Al–Ca and <i>F</i>_mid, increase with increasing electrode density and loading level. From the SAICAS measurement, we obtain a mathematical equation that governs the adhesion strength of the composite electrodes. This equation revealed a maximum accuracy of 97.2% and 96.1% for <i>F</i>_Al–Ca and <i>F</i>_mid, respectively, for four randomly chosen composite electrodes varying in electrode density and loading level

Journal of Korean nature

A highly adhesive and thermally stable copolyimide (P84) that is soluble in organic solvents is newly applied to silicon (Si) anodes for high energy density lithium-ion batteries. The Si anodes with the P84 binder deliver not only a little higher initial discharge capacity (2392 mAh g^–1), but also fairly improved Coulombic efficiency (71.2%) compared with the Si anode using conventional polyvinylidene fluoride binder (2148 mAh g^–1 and 61.2%, respectively), even though P84 is reduced irreversibly during the first charging process. This reduction behavior of P84 was systematically confirmed by cyclic voltammetry and Fourier-transform infrared analysis in attenuated total reflection mode of the Si anodes at differently charged voltages. The Si anode with P84 also shows ultrastable long-term cycle performance of 1313 mAh g^–1 after 300 cycles at 1.2 A g^–1 and 25 °C. From the morphological analysis on the basis of scanning electron microscopy and optical images and of the electrode adhesion properties determined by surface and interfacial cutting analysis system and peel tests, it was found that the P84 binder functions well and maintains the mechanical integrity of Si anodes during hundreds of cycles. As a result, when the loading level of the Si anode is increased from 0.2 to 0.6 mg cm^–2, which is a commercially acceptable level, the Si anode could deliver 647 mAh g^–1 until the 300th cycle, which is still two times higher than the theoretical capacity of graphite at 372 mAh g^–1

DataSheet1_A Thermo-Electrochemical Model of 18.5 V/50 Ah Battery Module for Railway Vehicles.PDF

We developed a thermo-electrochemical model of a 50 Ah pouch-type lithium-ion cell and utilized a cell model to build an 18.5 V/50 Ah module to analyze the thermal behavior under various operating conditions and design cooling systems for optimal operating temperature ranges. Specifically, the heat generated by electrochemical reactions was simulated through an electrochemical cell model, and then the calculated heat was coupled with a heat transfer model reflecting the actual 3D structure of the cell. By fitting two temperature-dependent parameters, i.e., the chemical diffusion coefficient and exchange current density, the model accurately estimated the electrochemical and thermal properties with errors less than 3%, even under wide temperature (25°C, 35°C, and 45°C) and C-rate (0.5, 1, 2, and 5C) conditions. Based on this reliable cell model, we built an 18.5 V/50 Ah module model with five cells in series to simulate both the amount of heat generated and the required heat sink. Finally, both the cell and module models were used to predict the electrochemical and thermal behaviors under actual wireless tram operations in Turkey. The model results were compared with experimental results to confirm their reliability.</p

Enhancing the Cycling Stability of Sodium Metal Electrodes by Building an Inorganic–Organic Composite Protective Layer

Owing to the natural abundance of sodium resources and their low price, next-generation batteries employing an Na metal anode, such as Na–O₂ and Na–S systems, have attracted a great deal of interest. However, the poor reversibility of an Na metal electrode during repeated electrochemical plating and stripping is a major obstacle to realizing rechargeable sodium metal batteries. It mainly originates from Na dendrite formation and exhaustive electrolyte decomposition due to the high reactivity of Na metal. Herein, we report a free-standing composite protective layer (FCPL) for enhancing the reversibility of an Na metal electrode by mechanically suppressing Na dendritic growth and mitigating the electrolyte decomposition. A systematic variation of the liquid electrolyte uptake of FCPL verifies the existence of a critical shear modulus for suppressing Na dendrite growth, being in good agreement with a linear elastic theory, and emphasizes the importance of the ionic conductivity of FCPL for attaining uniform Na plating and stripping. The Na–Na symmetric cell with an optimized FCPL exhibits a cycle life two times longer than that of a bare Na electrode

Electrospun Core–Shell Fibers for Robust Silicon Nanoparticle-Based Lithium Ion Battery Anodes

Because of its unprecedented theoretical capacity near 4000 mAh/g, which is approximately 10-fold larger compared to those of the current commercial graphite anodes, silicon has been the most promising anode for lithium ion batteries, particularly targeting large-scale energy storage applications including electrical vehicles and utility grids. Nevertheless, Si suffers from its short cycle life as well as the limitation for scalable electrode fabrication. Herein, we develop an electrospinning process to produce core–shell fiber electrodes using a dual nozzle in a scalable manner. In the core–shell fibers, commercially available nanoparticles in the core are wrapped by the carbon shell. The unique core–shell structure resolves various issues of Si anode operations, such as pulverization, vulnerable contacts between Si and carbon conductors, and an unstable sold-electrolyte interphase, thereby exhibiting outstanding cell performance: a gravimetric capacity as high as 1384 mAh/g, a 5 min discharging rate capability while retaining 721 mAh/g, and cycle life of 300 cycles with almost no capacity loss. The electrospun core–shell one-dimensional fibers suggest a new design principle for robust and scalable lithium battery electrodes suffering from volume expansion

Self-Healing Wide and Thin Li Metal Anodes Prepared Using Calendared Li Metal Powder for Improving Cycle Life and Rate Capability

The commercialization of Li metal electrodes is a long-standing objective in the battery community. To accomplish this goal, the formation of Li dendrites and mossy Li deposition, which cause poor cycle performance and safety issues, must be resolved. In addition, it is necessary to develop wide and thin Li metal anodes to increase not only the energy density, but also the design freedom of large-scale Li-metal-based batteries. We solved both issues by developing a novel approach involving the application of calendared stabilized Li metal powder (LiMP) electrodes as anodes. In this study, we fabricated a 21.5 cm wide and 40 μm thick compressed LiMP electrode and investigated the correlation between the compression level and electrochemical performance. A high level of compression (40% compression) physically activated the LiMP surface to suppress the dendritic and mossy Li metal formation at high current densities. Furthermore, as a result of the LiMP self-healing because of electrochemical activation, the 40% compressed LiMP electrode exhibited an excellent cycle performance (reaching 90% of the initial discharge capacity after the 360th cycle), which was improved by more than a factor of 2 compared to that of a flat Li metal foil with the same thickness (90% of the initial discharge capacity after the 150th cycle)

Defect-Free, Size-Tunable Graphene for High-Performance Lithium Ion Battery

The scalable preparation of graphene in control of its structure would significantly improve its commercial viability. Despite intense research in this area, the size control of defect-free graphene (df-G) without any trace of oxidation or structural damage remains a key challenge. Here, we propose a new scalable route for generating df-G with a controllable size of submicron to micron through sequential insertion of potassium and pyridine at low temperature. Structural and chemical analyses confirm that the df-G perfectly preserves the intrinsic properties of graphene. The Co₃O₄ (<50 nm) wrapped by ∼10.5 μm² df-G has unprecedented capacity, rate capability, and cycling stability with capacities as high as 1050 mAh g^–1 at 500 mA g^–1 and 900 mAh g^–1 at 1000 mA g^–1 even after 200 cycles, which suggests enticing potential for the use in high performance lithium ion batteries