• Energy Research

Abstract Ethyl-(2,2,2-trifluoroethyl) carbonate (ETFEC) is investigated as a solvent component in high-voltage electrolytes for LiNi0.5Mn1.5O4 (LNMO). Our results show that the self-discharge behavior and the high temperature cycle performance can be significantly improved by the addition of 10% ETFEC into the normal carbonate electrolytes, e.g., the capacity retention improved from 65.3% to 77.1% after 200 cycles at 60 °C. The main reason can be ascribed to the high stability of ETFEC which prevents large oxidation of the electrolyte on the cathode surface. In addition, we also explore the feasibility of electrolytes using single fluoriated-solvents with and without additives. Our results show that the cycle performance of LNMO material can be greatly improved in 1 M LiPF6 + pure ETFEC-solvent system with 2 wt% ethylene carbonate (EC) or ethylene sulfate (DTD). The capacity retention of the LNMO materials is 93% after 300 cycles, even better than that of carbonate-based electrolytes. It is shown that the additives are oxidized on the surface of LNMO particles and contribute to the formation of cathode/electrolyte interphase (CEI) films. This composite CEI film plays a crucial role in suppressing the serious decomposition of the electrolyte at high voltage.

AbstractMnOx‐surface‐modified Li1.2Ni0.4/3Co0.4/3Mn1.6/3O2 cathode materials have been prepared by solid‐state reaction with varying post‐annealing temperatures. The MnOx coating layers are homogeneous and crystalline with a thickness of 10 nm. Below a current rate of 0.1 C and in the voltage range of 2.0–4.8 V, the MnOx‐modified material, which has been post‐annealed at 300 °C, shows high discharge capacities of 308, 320, and 363 mAh g−1 at 20, 40, and 60 °C, respectively. Meanwhile, this sample shows good rate capability that can deliver discharge capacities of 278 and 178 mAh g−1, respectively, at 1 C and 10 C, both tested at 20 °C. However, the modified sample displays more serious capacity degradation compared to the pristine sample. The significantly higher extent of the transition metal dissolution from the modified sample is proved by compositional analysis. Cycling performance could be improved by replacing the conventional electrolyte with an ionic‐liquid‐based electrolyte.

This study unveils the intrinsic three-step thermodynamic and the two-step kinetics-limited pathways in all-solid-state sodium–sulfur batteries, providing crucial insights into sulfur reaction mechanisms for high-performance energy storage solutions.

AbstractSulfide‐based all‐solid‐state batteries (ASSBs) are one of the most promising energy storage devices due to their high energy density and good safety. However, due to the volume (stress) changes of the solid active materials during the charging and discharging process, the generation and evolution of electrochemomechanical stresses are becoming serious and unavoidable problems during the operation of all‐solid‐state batteries due to the lack of a liquid electrolyte to partially buffer the stress generated in the electrodes. To understand these electrochemo‐mechanical effects, including the origins and evolution of mechanical or internal stresses, it is necessary to develop some highly sensitive probing techniques to measure them precisely and bridge the relationship between the electrochemical reaction process and internal stress evolution. Herein, recent progress on uncovering the origins of the internal stresses, the working principle and experimental devices for stress measurement, and the application of those stress‐measuring techniques in the study of electrochemical reactions in sulfide‐based ASSBs are briefly summarized and overviewed. The investigation of precise and operando monitoring techniques and strategies for suppressing or relaxing these electrochemomechanical stresses will be an important direction in future solid‐state batteries.

Large-scale molecular dynamics simulations reveal the formation mechanism and structure of the solid electrolyte interphase between lithium metal and β-Li3PS4 in all-solid-state batteries.

Abstract Electrochemical voltage spectroscopy (EVS), which includes differential voltage analysis (DVA) and incremental capacity analysis (ICA), has been used extensively in revealing the aging mechanism and evaluating the operating state of Li-ion batteries. The EVS technique is conventionally limited to low-charging-rate scenarios such that the polarization effect has a negligible influence on the spectral characteristics. This makes EVS analysis both time-consuming and unfeasible in real-world scenarios. In this work, for the first time, we have expanded the EVS to realistic C-rate operating conditions by combining it with a programmed electromotive-force (EMF) extraction method to adapt the EVS-based SoH estimation model to any arbitrary charging scenarios. By tracking the features in the EVS curves, the model can properly estimate cell SoH even with partial (dis)charging data, with a maximum error of less than 3%. Furthermore, an electrochemical model is established to identify the thermodynamic attributes on capacity loss. The degradation performance of the NMC532/graphite battery system under different operating conditions was comprehensively studied based on the comparison analysis between the modeling and experimental results.

A fundamental electrochemical model is developed, describing the capacity fade of C6/LiFePO4 batteries as a function of calendar time and cycling conditions. At moderate temperatures the capacity losses are mainly attributed to Li immobilization in Solid-Electrolyte-Interface (SEI) layers at the anode surface. The SEI formation model presumes the availability of an outer and inner SEI layers. Electron tunneling through the inner SEI layer is regarded as the rate-determining step. The model also includes high temperature degradation. At elevated temperatures, iron dissolution from the positive electrode and the subsequent metal sedimentation on the negative electrode influence the capacity loss. The SEI formation on the metal-covered graphite surface is faster than the conventional SEI formation. The model predicts that capacity fade during storage is lower than during cycling due to the generation of SEI cracks induced by the volumetric changes during (dis)charging. The model has been validated by cycling and calendar aging experiments and shows that the capacity loss during storage depends on the storage time, the State-of-Charge (SoC), and temperature. The capacity losses during cycling depend on the cycling current, cycling time, temperature and cycle number. All these dependencies can be explained by the single model presented in this paper.

Highly reversible oxygen redox chemistry of Li2RuO3 enabled by a stabilizing electrode–electrolyte interphase with sulfide solid electrolyte.