Advances in Nanomaterials for Lithium-Ion/Post-Lithium-Ion Batteries and Supercapacitors

Energy storage and conversion are key factors for enabling the transition from fossil fuels to intermittent renewables [...

A review of the degradation mechanisms of NCM cathodes and corresponding mitigation strategies

Li-ion batteries (LIBs) are the most widely used form of energy storage in mobile electronic devices and electric vehicles. Li-ion battery cathodes with the composition LiNixMnyCozO2 (NCMs) currently display some of the most promising electrochemical characteristics for high performance LIBs. NCM compositions with high nickel content (x > 0.8) exhibit the largest specific capacity while undergoing fast degradation and presenting safety issues. As the main degradation mechanisms of NCM materials and the mitigation of their degradation, are still subjects of many ongoing studies, this work summarizes the current knowledge on the subject. Here, the existing literature is reviewed to present the structural and electrochemical degradation of NCM with varying Ni stoichiometries (NCM111, NCM622, NCM811, and beyond). Routes for hindering the degradation of NCM are discussed as a function of Ni content in NCM and include doping, application of protective coatings, and engineering of the microstructure. A comprehensive understanding of the main degradation pathways of NCM is key to applying the most appropriate mitigation strategies and keep advancing towards higher energy NCM materials with longer cycle-life.Comment: Accepted manuscript, 94 pages, 12 figures, 1 tabl

Study of water-based lithium titanate electrode processing: the role of pH and binder molecular structure

This work elucidates the manufacturing of lithium titanate (Li$_{4}$Ti$_{5}$O$_{12}$, LTO) electrodes via the aqueous process using sodium carboxymethylcellulose (CMC), guar gum (GG) or pectin as binders. To avoid aluminum current collector dissolution due to the rising slurries’ pH, phosphoric acid (PA) is used as a pH-modifier. The electrodes are characterized in terms of morphology, adhesion strength and electrochemical performance. In the absence of phosphoric acid, hydrogen evolution occurs upon coating the slurry onto the aluminum substrate, resulting in the formation of cavities in the coated electrode, as well as poor cohesion on the current collector itself. Consequently, the electrochemical performance of the coated electrodes is also improved by the addition of PA in the slurries. At a 5C rate, CMC/PA-based electrodes delivered 144 mAh·g$^{-1}$, while PA-free electrodes reached only 124 mAh·g$^{-1}$. When GG and pectin are used as binders, the adhesion of the coated layers to the current collector is reduced; however, the electrodes show comparable, if not slightly better, electrochemical performance than those based on CMC. Full lithium-ion cells, utilizing CMC/PA-made Li[Ni$_{0.33}$Mn$_{0.33}$Co$_{0.33}$]O$_{2}$ (NMC) cathodes and LTO anodes offer a stable discharge capacity of ~120 mAh·g$^{ 1}$$_{(NMC)}$ with high coulombic efficiencies

Onset Shift of Li Plating on Si/Graphite Anodes with Increasing Si Content

Mixing graphite with Si particles in anodes of Li-ion batteries provides increased specific energy. In addition, higher Si contents lead to thinner anode coatings at constant areal capacity. In the present study, we systematically investigated the influence of the Si content on the susceptibility of Li plating on Si/graphite anodes. Si/graphite anodes with Si contents from 0 to 20.8 wt% combined with NMC622 cathodes were manufactured on pilot-scale. After initial characterization in coin half cells and by SEM, pouch full cells with fixed N/P ratios were built. Rate capability at different temperatures, and Post-Mortem analysis were carried out. Results from voltage relaxation, Li stripping, SEM measurements, glow discharge optical emission spectroscopy (GD-OES) depth profiling, and optical microscopy were validated against each other. A decreasing susceptibility to Li plating with increasing Si content in the anodes could be clearly observed. A critical C-rate was defined, at which Li plating was detected for the first time. It was also found that at 0 °C the critical C-rate increases with increasing Si contents. At 23 °C the SOC at which Li dendrites were first observed on the anode also increased with higher Si content

Layered P2-Nax_xMn3/4_{3/4}Ni1/4_{1/4}O2_2 Cathode Materials For Sodium-Ion Batteries: Synthesis, Electrochemistry and Influence of Ambient Storage

Sodium-ion batteries promise efficient, affordable and sustainable electrical energy storage that avoids critical raw materials such as lithium, cobalt and copper. In this work, a manganese-based, cobalt-free, layered Na$_x$Mn$_{3/4}$Ni$_{1/4}$O$_2$ cathode active material for sodium-ion batteries is developed. A synthesis phase diagram was developed by varying the sodium content x and the calcination temperature. The calcination process towards a phase pure P2-Na$_{2/3}$Mn$_{3/4}$Ni$_{1/4}$O$_2$ material was investigated in detail using in-situ XRD and TGA-DSC-MS. The resulting material was characterized with ICP-OES, XRD and SEM. A stacking fault model to account for anisotropic broadening of (10l) reflexes in XRD is presented and discussed with respect to the synthesis process. In electrochemical half-cells, P2-Na$_{2/3}$Mn$_{3/4}$Ni$_{1/4}$O$_2$ delivers an attractive initial specific discharge capacity beyond 200 mAh g−1, when cycled between 4.3 and 1.5 V. The structural transformation during cycling was studied using operando XRD to gain deeper insights into the reaction mechanism. The influence of storage under humid conditions on the crystal structure, particle surface and electrochemistry was investigated using model experiments. Due to the broad scope of this work, raw material questions, fundamental investigations and industrially relevant production processes are addressed

Sodium Cyclopentadienide as a New Type of Electrolyte for Sodium Batteries

Owing to the low cost and high abundance of sodium, sodium‐based batteries, especially those employing metallic sodium anodes, are considered for post‐lithium energy storage. In order to develop high‐performance and long‐lasting sodium‐metal batteries, however, the reversible Na‐metal stripping and plating challenge must be addressed. Most organic electrolytes suffer from non‐uniform and continuous formation of the solid electrolyte interphase as well as unfavorable dendritic growth. The use of sodium cyclopentadienide dissolved in tetrahydrofuran as the electrolyte reveals an improved reversibility of sodium dissolution and electrodeposition combined with an electrochemical stability window of around 2.2 V vs. Na/Na+ and an ionic conductivity of 1.36 mS cm−1 at 25 °C. Furthermore, the plated electrodes showed a remarkable morphology of the Na deposits, that is, no dendrite formation, whereby the above‐mentioned electrolyte could overcome the aforementioned cycling issues, thus suggesting suitability for further studies