Synergistic interface and structural engineering for high initial coulombic efficiency and stable sodium storage in metal sulfides.

Transition metal sulfides (TMS) have gained significant attention as potential anode materials for sodium ion batteries (SIBs) due to their high theoretical capacity and abundance in nature. Nevertheless, their practical use has been impeded by challenges such as large volume changes, unstable solid electrolyte interphase (SEI), and low initial coulombic efficiency (ICE). To address these issues and achieve both long-term cycling stability and high ICE simultaneously, we present a novel approach involving surface engineering, termed as the "dual-polar confinement" strategy, combined with interface engineering to enhance the electrochemical performance of TMS. In this approach, CoS crystals are meticulously coated with polar TiO2 and embedded within a polar S-doped carbon matrix, forming a composite electrode denoted as CoS/TiO2-SC. Significantly, an ether-based electrolyte with chemical stability and optimized solvation properties synergistically interacts with the Co-S-C bonds to create a stable, ultra-thin SEI. This concerted effect results in a notably high ICE, reaching approximately 96%. Advanced characterization and theoretical simulations confirm that the uniform surface modification effectively facilitates sodium ion transport kinetics, restrains electrode pulverization, and concurrently enhances interaction with the ether-based electrolyte to establish a robust SEI. Consequently, the CoS/TiO2-SC electrode exhibits high reversible capacity, superior rate capability, and outstanding cycling stability.

Investigating the critical characteristics of thermal runaway process for LiFePO4/graphite batteries by a ceased segmented method.

Lithium-ion batteries (LIBs) are widely used as the energy carrier in our daily life. However, the higher energy density of LIBs results in poor safety performance. Thermal runaway (TR) is the critical problem which hinders the further application of LIBs. Clarifying the mechanism of TR evolution is beneficial to safer cell design and safety management. In this paper, liquid nitrogen spray is proved to be an effective way to stop the violent reaction of LIBs during the TR process. Based on extended-volume accelerating rate calorimetry, the liquid nitrogen ceasing combined with non-atmospheric exposure analysis is used to investigate the TR evolution about LiFePO4/graphite batteries at critical temperature. Specifically, the geometrical shape, voltage, and impedance change are monitored during the TR process on the cell level. The morphologies/constitution of electrodes and separators are presented on the component level. Utilizing the gas analysis, the failure mechanism of the prismatic LiFePO4/graphite battery is studied comprehensively.

Comprehensive Investigation of a Slight Overcharge on Degradation and Thermal Runaway Behavior of Lithium-Ion Batteries.

Overcharge is a hazardous abuse condition that has dominant influences on cell performance and safety. This work, for the first time, comprehensively investigates the impact of different overcharge degrees on degradation and thermal runaway behavior of lithium-ion batteries. The results indicate that single overcharge has little influence on cell capacity, while it severely degrades thermal stability. Degradation mechanisms are investigated by utilizing the incremental capacity-differential voltage and relaxation voltage analyses. During the slight overcharge process, the conductivity loss and the loss of lithium inventory always occur; the loss of active material starts happening only when the cell is overcharged to a certain degree. Lithium plating is the major cause for the loss of lithium inventory, and an interesting phenomenon that the arrival time of the dV/dt peak decreases linearly with the increase of the overcharge degree is found. The cells with different degrees of overcharge exhibit a similar behavior during adiabatic thermal runaway. Meanwhile, the relationship between sudden voltage drop and thermal runaway is further established. More importantly, the characteristic temperature of thermal runaway, especially the self-heating temperature (T1), decreases severely along with overcharging, which means that a slight overcharge severely decreases the cell thermal stability. Further, post-mortem analysis is conducted to investigate the degradation mechanisms. The mechanism of the side reactions caused by a slight overcharge on the degradation performance and thermal runaway characteristics is revealed.