Lithium Superionic Sulfide Cathode for All-Solid Lithium–Sulfur Batteries

This work presents a facile synthesis approach for core–shell structured Li₂S nanoparticles with Li₂S as the core and Li₃PS₄ as the shell. This material functions as lithium superionic sulfide (LSS) cathode for long-lasting, energy-efficient lithium–sulfur (Li–S) batteries. The LSS has an ionic conductivity of 10^–7 S cm^–1 at 25 °C, which is 6 orders of magnitude higher than that of bulk Li₂S (∼10^–13 S cm^–1). The high lithium-ion conductivity of LSS imparts an excellent cycling performance to all-solid Li–S batteries, which also promises safe cycling of high-energy batteries with metallic lithium anodes

Artificial Solid Electrolyte Interphase To Address the Electrochemical Degradation of Silicon Electrodes

Electrochemical degradation on silicon (Si) anodes prevents them from being successfully used in lithium (Li)-ion battery full cells. Unlike the case of graphite anodes, the natural solid electrolyte interphase (SEI) films generated from carbonate electrolytes do not self-passivate on Si, causing continuous electrolyte decomposition and loss of Li ions. In this work, we aim at solving the issue of electrochemical degradation by fabricating artificial SEI films using a solid electrolyte material, lithium phosphorus oxynitride (Lipon), which conducts Li ions and blocks electrons. For Si anodes coated with Lipon of 50 nm or thicker, a significant effect is observed in suppressing electrolyte decomposition, while Lipon of thinner than 40 nm has a limited effect. Ionic and electronic conductivity measurements reveal that the artificial SEI is effective when it is a pure ionic conductor, but electrolyte decomposition is only partially suppressed when the artificial SEI is a mixed electronic–ionic conductor. The critical thickness for this transition in conducting behavior is found to be 40–50 nm. This work provides guidance for designing artificial SEI films for high-capacity Li-ion battery electrodes using solid electrolyte materials

Influence of Lithium Salts on the Discharge Chemistry of Li–Air Cells

In this work, we show that the use of a high boiling point ether solvent (tetraglyme) promotes the formation of Li₂O₂ in a lithium–air cell. However, another major constituent in the discharge product of a Li–air cell contains halides from the lithium salts and C–O from the tetraglyme used as the solvent. This information is critical to the development of Li–air electrolytes, which are stable and promote the formation of the desired Li₂O₂ products

Gold Nanoparticles Supported on Carbon Nitride: Influence of Surface Hydroxyls on Low Temperature Carbon Monoxide Oxidation

This paper reports the synthesis of 2.5 nm gold clusters on the oxygen free and chemically labile support carbon nitride (C₃N₄). Despite having small particle sizes and high enough water partial pressure these Au/C₃N₄ catalysts are inactive for the gas phase and liquid phase oxidation of carbon monoxide. The reason for the lack of activity is attributed to the lack of surface −OH groups on the C₃N₄. These OH groups are argued to be responsible for the activation of CO in the oxidation of CO. The importance of basic −OH groups explains the well documented dependence of support isoelectric point versus catalytic activity

Unravelling the Impact of Reaction Paths on Mechanical Degradation of Intercalation Cathodes for Lithium-Ion Batteries

The intercalation compounds are generally considered as ideal electrode materials for lithium-ion batteries thanks to their minimum volume expansion and fast lithium ion diffusion. However, cracking still occurs in those compounds and has been identified as one of the critical issues responsible for their capacity decay and short cycle life, although the diffusion-induced stress and volume expansion are much smaller than those in alloying-type electrodes. Here, we designed a thin-film model system that enables us to tailor the cation ordering in LiNi_0.5Mn_1.5O₄ spinels and correlate the stress patterns, phase evolution, and cycle performances. Surprisingly, we found that distinct reaction paths cause negligible difference in the overall stress patterns but significantly different cracking behaviors and cycling performances: 95% capacity retention for disordered LiNi_0.5Mn_1.5O₄ and 48% capacity retention for ordered LiNi_0.5Mn_1.5O₄ after 2000 cycles. We were able to pinpoint that the extended solid-solution region with suppressed phase transformation attributed to the superior electrochemical performance of disordered spinel. This work envisions a strategy for rationally designing stable cathodes for lithium-ion batteries through engineering the atomic structure that extends the solid-solution region and suppresses phase transformation

Influence of Hydrocarbon and CO₂ on the Reversibility of Li–O₂ Chemistry Using <i>In Situ</i> Ambient Pressure X‑ray Photoelectron Spectroscopy

Identifying fundamental barriers that hinder reversible lithium–oxygen (Li–O₂) redox reaction is essential for developing efficient and long-lasting rechargeable Li–O₂ batteries. Addressing these challenges is being limited by parasitic reactions in the carbon-based O₂–electrode with aprotic electrolytes. Understanding the mechanisms of these parasitic reactions is hampered by the complexity that multiple and coupled parasitic reactions involving carbon, electrolytes, and Li–O₂ reaction intermediates/products can occur simultaneously. In this work, we employed solid-state cells free of carbon and aprotic electrolytes to probe the influence of surface adventitious hydrocarbons and carbon dioxide (CO₂) on the reversibility of the Li–O₂ redox chemistry using <i>in situ</i> synchrotron-based ambient pressure X-ray photoelectron spectroscopy. Direct evidence was provided, for the first time, that surface hydrocarbons and CO₂ irreversibly react with Li–O₂ reaction intermediates/products such as Li₂O₂ and Li₂O, forming carboxylate and carbonate-based species, which cannot be removed fully upon recharge. The slower Li₂O₂ oxidation kinetics was correlated with increasing coverage of surface carbonate/carboxylate species. Our work critically points out that materials design that mitigates the reactivity between Li–O₂ reaction products and common impurities in the atmosphere is needed to achieve long cycle-life Li–O₂ batteries

Anomalous High Ionic Conductivity of Nanoporous β‑Li₃PS₄

Lithium-ion-conducting solid electrolytes hold promise for enabling high-energy battery chemistries and circumventing safety issues of conventional lithium batteries. Achieving the combination of high ionic conductivity and a broad electrochemical window in solid electrolytes is a grand challenge for the synthesis of battery materials. Herein we show an enhancement of the room-temperature lithium-ion conductivity by 3 orders of magnitude through the creation of nanostructured Li₃PS₄. This material has a wide electrochemical window (5 V) and superior chemical stability against lithium metal. The nanoporous structure of Li₃PS₄ reconciles two vital effects that enhance the ionic conductivity: (1) the reduction of the dimensions to a nanometer-sized framework stabilizes the high-conduction β phase that occurs at elevated temperatures, and (2) the high surface-to-bulk ratio of nanoporous β-Li₃PS₄ promotes surface conduction. Manipulating the ionic conductivity of solid electrolytes has far-reaching implications for materials design and synthesis in a broad range of applications, including batteries, fuel cells, sensors, photovoltaic systems, and so forth

Structure of Spontaneously Formed Solid-Electrolyte Interphase on Lithiated Graphite Determined Using Small-Angle Neutron Scattering

We address the reactivity of lithiated graphite–anode material for Li-ion batteries with standard organic solvents used in batteries (ethylene carbonate and dimethyl carbonate) by following changes in neutron scattering signals. The reaction produces a nanosized layer, the solid-electrolyte interphase (SEI), on the graphite particles. We probe the structure and chemistry of the SEI using small-angle neutron scattering (SANS) and inelastic neutron scattering. The SANS results show that the SEI fills 20–30 nm sized pores, and inelastic scattering experiments with H/D substitution show that this “chemical” SEI is primarily organic in nature; that is, it contains a large amount of hydrogen. The graphite–SEI particles show surface fractal scattering characteristic of a rough particle–void interface and are interconnected. The observed changes in the SEI structure and composition provide new insight into SEI formation. The chemically formed SEI is complementary and simpler in composition to the electrochemically formed SEI, which involves a number of different reactions and products that are difficult to deconvolute