Direct in situ measurements of electrical properties of solid-electrolyte interphase on lithium metal anodes

The solid-electrolyte interphase (SEI) critically governs the performance of rechargeable batteries. An ideal SEI is expected to be electrically insulative to prevent persistently parasitic reactions between the electrode and the electrolyte and ionically conductive to facilitate Faradaic reactions of the electrode. However, the true nature of the electrical properties of the SEI remains hitherto unclear due to the lack of a direct characterization method. Here we use in situ bias transmission electron microscopy to directly measure the electrical properties of SEIs formed on copper and lithium substrates. We reveal that SEIs show a voltage-dependent differential conductance. A higher rate of differential conductance induces a thicker SEI with an intricate topographic feature, leading to an inferior Coulombic efficiency and cycling stability in Li∣∣Cu and Li∣∣LiNi0.8Mn0.1Co0.1O2 cells. Our work provides insight into the targeted design of the SEI with desired characteristics towards better battery performance.

Sulfurized Polyacrylonitrile for High-Performance Lithium-Sulfur Batteries: In-Depth Computational Approach Revealing Multiple Sulfur's Reduction Pathways and Hidden Li+ Storage Mechanisms for Extra Discharge Capacity

Like no other sulfur host material, polyacrylonitrile-derived sulfurized carbon (SPAN) promises improved electrochemical performance for lithium-sulfur batteries, based on its compatibility with carbonate solvents and ability to prevent self-discharge and shuttle effect. However, a complete understanding of the SPAN's lithiation mechanism is still missing because its structural features vary widely with synthesis conditions, and its electrochemical performance deviates from elemental sulfur. This study continues our research on the elucidation of the SPAN's structural characteristics and lithiation mechanisms via computational approaches. Our models reproduce most experimental data regarding carbon's graphitization level and conjugated ordering, sulfur-carbon covalent bonding, sulfur loading, and elemental composition. Our simulations emulate the discharge voltage observed in experiments for the first discharge, which reveals that sulfur follows multiple reduction pathways based on its interaction with the carbon backbone. Sulfur reduction takes place above 1.0 V vs Li/Li⁺ mostly in the SPAN-like material, with no long-chain lithium polysulfide formation. Below 1.0 V vs Li/Li⁺, the backbone's electrochemical activity occurs via multiple C-Li and N-Li interactions, mostly with edge carbon atoms and pyridinic nitrogen. Moreover, we identify Li⁺ binding sites throughout the graphitized backbone that might lead to prohibited energy costs for Li⁺ deintercalation, which may explain the irreversible capacity loss between the first and second discharges. This work improves understanding of lithiation mechanisms in sulfurized carbon, which is useful for rationally designing SPAN synthesis pathways tailored to increase sulfur loading and enhanced electrochemical performance.

Mechanisms of alumina growth via atomic layer deposition on nickel oxide and metallic nickel surfaces

Decomposition of tri-methyl aluminum on catalyst surfaces leads to various products that are precursors of an alumina coating.

Formation of Multilayer Graphene Domains with Strong Sulfur-Carbon Interaction and Enhanced Sulfur Reduction Zones for Lithium-Sulfur Battery Cathodes

A newly designed sulfur/graphene computational model emulates the electrochemical behavior of a Li-S battery cathode, promoting the S-C interaction through the edges of graphene sheets. A random mixture of eight-membered sulfur rings mixed with small graphene sheets is simulated at 64 wt %sulfur loading. Structural stabilization and sulfur reduction calculations are performed with classical reactive molecular dynamics. This methodology allowed the collective behavior of the sulfur and graphene structures to be accounted for. The sulfur encapsulation induces ring opening and the sulfur phase evolves into a distribution of small chain-like structures interacting with C through the graphene edges. This new arrangement of the sulfur phase not only leads to a less pronounced volume expansion during sulfur reduction but also to a different discharge voltage profile, in qualitative agreement with earlier reports on sulfur encapsulation in microporous carbon structures. The Li₂ S phase grows around ensembles of parallel graphene nanosheets during sulfur reduction. No diffusion of sulfur or lithium between graphene nanosheets is observed, and extended Li₂ S domains bridging the space between carbon ensembles are suppressed. The results emphasize the importance of morphology on the electrochemical performance of the composite material. The sulfur/graphene model outlined here provides new understanding of the graphene effects on the sulfur reduction behavior and the role that van der Waals interactions may play in promoting formation of multilayer graphene ensembles and small Li₂ S domains during sulfur reduction.