Nanoscale morphological and chemical changes of high voltage lithium-manganese rich NMC composite cathodes with cycling.

Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium-manganese rich cathode material of composition Li(1 + x)M(1 - x)O2 (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (∼ 30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface.

Transforming Residual Lithium Compounds on the LiNi0.8Mn0.1Co0.1O2 Surface into a Li-Mn-P-O-Based Composite Coating for Multifaceted Improvements.

LiNi0.8Mn0.1Co0.1O2 (NMC811) is the most promising cathode material for next-generation lithium-ion batteries (LIBs). However, the chemical instability of the material during air exposure leads to the formation of residual lithium compounds (RLCs: LiOH and Li2CO3) on the surface and inhibits its practical application. Here, we propose a chemical conversion process to remove RLCs by utilizing them and forming a hybrid coating layer on the surface of NMC811 that contains Li3PO4, LiMn2O4, and LiMnPO4 phases, yielding multifaceted benefits. The hybrid layer on the surface protects the material from undesirable side reactions. It improves the cycle life of NMC811 by retaining 80% of its initial capacity after 300 cycles and 66% after 500 cycles at a 0.5C rate in the operating voltage of 3.0-4.3 V. The process enables high-voltage (4.7 V vs Li+/Li) operation by stabilizing the electrode-electrolyte interface, reduces the degree of cationic disorder and the voltage polarization for phase transitions, improves Coulombic efficiency and ion diffusion kinetics, and minimizes the secondary particle crack formation over long-term cycling. In fact, the coating reduces the detrimental effects of RLCs, leaves the surface for better Li+ transport, and hence significantly improves the electrochemical performance of NMC811.

A Novel and Sustainable Approach to Enhance the Li-Ion Storage Capability of Recycled Graphite Anode from Spent Lithium-Ion Batteries.

The ubiquitous manufacturing of lithium-ion batteries (LIBs) due to high consumer demand produces inevitable e-waste that imposes severe environmental and resource sustainability challenges. In this work, the charge storage capability and Li-ion kinetics of the recovered water-leached graphite (WG) anode from spent LIBs are enhanced by using an optimized amount of recycled graphene nanoflakes (GNFs) as an additive. The WG@GNF anode exhibits an initial discharge capacity of 400 mAh g-1 at 0.5C with 88.5% capacity retention over 300 cycles. Besides, it delivers an average discharge capacity of 320 mAh g-1 at 500 mA g-1 over 1000 cycles, which is 1.5-2 times higher than that of WG. The sharp increase in electrochemical performance is due to the synergistic effects of Li-ion intercalation into the graphite layers and Li-ion adsorption into the surface functionalities of GNF. Density functional theory calculations reveal the role of functionalization behind the superior voltage profile of WG@GNF. Besides, the unique morphology of spherical graphite particles trapping into graphene nanoflakes provides mechanical stability over long-term cycling. This work explains an efficient strategy to upgrade the electrochemical compatibility of recovered graphite anode from spent LIBs toward next-generation high-energy-density LIBs.

Ultrafast, dry microwave superheating for the synthesis of an SbOx-GNP hybrid anode to investigate the Na-ion storage compatibility in ester and ether electrolytes.

The impact of ester and ether-based electrolytes on sodium-ion reversible storage in an SbOx-GNP hybrid anode synthesised by ultrafast dry microwave superheating is investigated. Kinetic and diffusion studies further support the higher capacity, good C-rate performance, and superior cycling stability of the hybrid anode in the ester-based electrolyte.

Nanostructured Silicon-Carbon 3D Electrode Architectures for High-Performance Lithium-Ion Batteries.

Silicon is an attractive anode material for lithium-ion batteries. However, silicon anodes have the issue of volume change, which causes pulverization and subsequently rapid capacity fade. Herein, we report organic binder and conducting diluent-free silicon-carbon 3D electrodes as anodes for lithium-ion batteries, where we replace the conventional copper (Cu) foil current collector with highly conductive carbon fibers (CFs) of 5-10 µm in diameter. We demonstrate here the petroleum pitch (P-pitch) which adequately coat between the CFs and Si-nanoparticles (NPs) between 700 and 1000 °C under argon atmosphere and forms uniform continuous layer of 6-14 nm thick coating along the exterior surfaces of Si-NPs and 3D CFs. The electrodes fabricate at 1000 °C deliver capacities in excess of 2000 mA h g-1 at C/10 and about 1000 mA h g-1 at 5 C rate for 250 cycles in half-cell configuration. Synergistic effect of carbon coating and 3D CF electrode architecture at 1000 °C improve the efficiency of the Si-C composite during long cycling. Full cells using Si-carbon composite electrode and Li1.2Ni0.15Mn0.55Co0.1O2-based cathode show high open-circuit voltage of >4 V and energy density of >500 W h kg-1. Replacement of organic binder and copper current collector by high-temperature binder P-pitch and CFs further enhances energy density per unit area of the electrode. It is believed that the study will open a new realm of possibility for the development of Li-ion cell having almost double the energy density of currently available Li-ion batteries that is suitable for electric vehicles.

Role of surface functionality in the electrochemical performance of silicon nanowire anodes for rechargeable lithium batteries.

We report the synthesis of silicon nanowires using the supercritical-fluid-liquid-solid growth method from two silicon precursors, monophenylsilane and trisilane. The nanowires were synthesized at least on a gram scale at a pilot scale facility, and various surface modification methods were developed to optimize the electrochemical performance. The observed electrochemical performance of the silicon nanowires was clearly dependent on the origination of the surface functional group, either from the residual precursor or from surface modifications. On the basis of detailed electron microscopy, X-ray photoelectron spectroscopy, and confocal Raman spectroscopy studies, we analyzed the surface chemical reactivity of the silicon nanowires with respect to their electrochemical performance in terms of their capacity retention over continuous charge-discharge cycles.