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A supercritical carbon dioxide (SCCO2) fluid, characterized by gas‐like diffusivity, near‐zero surface tension, and excellent mass transfer properties, is used as a precursor to produce silicon oxycarbide (SiOC) coating. SCCO2 disperses and reacts with Si particles to form an interfacial layer consisting of Si, O, and C. After an 850 °C annealing process, a conformal SiOC coating layer forms, resulting in core‐shell Si@SiOC particles. High‐resolution transmission electron microscopy and its X‐ray line‐scan spectroscopy, X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, and Raman spectroscopy, are used to examine the SiOC formation mechanism. Effects of SCCO2 interaction time on the SiOC properties are investigated. The SiOC layer connects the Si@SiOC particles, improving electron and Li+ transport. Cyclic voltammetry, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy are employed to examine the role of SiOC during charging/discharging. Operando X‐ray diffraction data reveal that the SiOC coating reduces crystal size of the formed Li15Si4 and increases its formation/elimination reversibility during cycling. The Si@SiOC electrode shows a capacitiy of 2250 mAh g−1 at 0.2 A g−1. After 500 cycles, the capacity retention is 72% with Coulombic efficiency above 99.8%. A full cell consisting of Si@SiOC anode and LiNi0.8Co0.1Mn0.1O2 cathode is constructed, and its performance is evaluated. [ABSTRACT FROM AUTHOR]

A cost‐effective chemical prelithiation solution, which consists of Li+, polyaromatic hydrocarbon (PAH), and solvent, is developed for a model hard carbon (HC) electrode. Naphthalene and methyl‐substituted naphthalene PAHs, namely 2‐methylnaphthalene and 1‐methylnaphthalene, are first compared. Grafting an electron‐donating methyl group onto the benzene ring can decrease electron affinity and thus reduce the redox potential, which is validated by density functional theory calculations. Ethylene glycol dimethyl ether (G1), diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether solvents are then compared. The G1 solution has the highest conductivity and least steric hindrance, and thus the 1‐methylnaphthalene/G1 solution shows superior prelithiation capability. In addition, the effects of the interaction time between Li+ and 1‐methylnaphthalene in G1 solvent on the electrochemical properties of a prelithiated HC electrode are investigated. Nuclear magnetic resonance data confirm that 10‐h aging is needed to achieve a stable solution coordination state and thus optimal prelithiation efficacy. It is also found that appropriate prelithiation creates a more Li+‐conducing and robust solid‐electrolyte interphase, improving the rate capability and cycling stability of the HC electrode. [ABSTRACT FROM AUTHOR]

To enhance Li storage properties, nitrogenation methods are developed for Si anodes. First, melamine, urea, and nitric oxide (NO) precursors are used to nitrogenize carbon‐coated Si particles. The properties of the obtained particles are compared. It is found that the NO process can maximize the graphitic nitrogen (N) content and electronic conductivity of a sample. In addition, optimized N functional groups and O─C species on the electrode surface increase electrolyte wettability. However, with a carbon barrier layer, NO hardly nitrogenizes the Si cores. Therefore, bare Si particles are reacted with NO. Core‐shell Si@amorphous SiNx particles are produced using a facile and scalable NO treatment route. The effects of the NO reaction time on the physicochemical properties and charge–discharge performance of the obtained materials are systematically examined. Finally, the Si@SiNx particles are coated with N‐doped carbon. Superior capacities of 2435 and 1280 mAh g−1 are achieved at 0.2 and 5 A g−1, respectively. After 300 cycles, 90% of the initial capacity is retained. In addition, differential scanning calorimetry data indicate that the multiple nitrogenation layers formed by NO significantly suppress electrode exothermic reactions during thermal runaway. [ABSTRACT FROM AUTHOR]

This study reports five types of metal-doped (Co, Cu, Sn, V, and Zr) NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP)/polymer composite solid electrolytes (CSEs) enabling Li4Ti5O12 (LTO) anodes to have high rate capability and excellent cycling performance. The high Li+-conductivity LATP samples are successfully synthesized through a modified sol–gel method followed by thermal calcination. We find that the cation dopants clearly influence the substitution of Al for Ti, with the type of dopant serving as a crucial factor in determining the ionic conductivity and interfacial resistance of the solid electrolyte. The CSE containing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Sn-LATP shows an ionic conductivity of 1.88 × 10−4 S cm−1 at ambient temperature. The optimum conductivity can be attributed to alterations in the lattice parameters and Li+ transport pathways owing to Sn doping. The solid-state cell equipped with the LTO-supported CSE containing Sn-LATP fillers demonstrates both excellent high rate capability at 5 C (with a capacity retention of 86% compared to the value measured at 0.2 C) and superior cycling stability, maintaining high Coulombic efficiency (>99.0%) over 510 cycles. These findings indicate that the proposed CSE is highly promising for use in solid-state lithium batteries with desirable charge–discharge properties and high durability. [ABSTRACT FROM AUTHOR]

Transition metal high‐entropy oxides (HEOs) are an attractive class of anode materials for high‐performance lithium‐ion batteries (LIBs). However, owing to the multiple electroactive centers of HEOs, the Li+ storage mechanism is complex and debated in the literature. In this work, operando quick‐scanning X‐ray absorption spectroscopy (XAS) is used to study the lithiation/delithiation mechanism of the Cobalt‐free spinel (CrMnFeNiCu)3O4 HEO. A monochromator oscillation frequency of 2 Hz is used and 240 spectra are integrated to achieve a 2 min time resolution. High‐photon‐flux synchrotron radiation is employed to increase the XAS sensitivity. The results indicate that the Cu2+ and Ni2+ cations are reduced to their metallic states during lithiation but their oxidation reactions are less favorable compared to the other elements upon delithiation. The Mn2+/3+ and Fe2+/3+ cations undergo two‐step conversion reactions to form metallic phases, with MnO and FeO as the intermediate species, respectively. During delithiation, the oxidation of Mn occurs prior to that of Fe. The Cr3+ cations are reduced to CrO and then Cr0 during lithiation. A relatively large overpotential is required to activate the Cr reoxidation reaction. The Cr3+ cations are found after delithiation. These results can guide the material design of HEOs for improving LIB performance. [ABSTRACT FROM AUTHOR]