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Iron oxides are considered as potential anode materials for lithium‐ion batteries thanks to their high theoretical capacity, rich resources, and environmental friendliness. However, the rapid capacity decay and sluggish kinetics greatly limit their practical application. Herein, a simple surface fluorination strategy is developed to greatly improve the electrochemical properties of Fe3O4. The fluorinated layer can act as a protective film to stabilize the electrode/electrolyte interface, enhance the wettability of the electrode to shorten the Li+ diffusion pathway, and provide more active centers to facilitate charge storage. Consequently, the fabricated fluorinated Fe3O4 electrode demonstrates high specific capacity (1379 mAh g−1 at 0.5 A g−1 after 300 cycles) and impressive high‐rate performance (876, 802, and 456 mAh g−1 at 5, 10, and 20 A g−1, respectively, after 1000 cycles), which outperforms most of the Fe3O4‐based electrodes recorded so far. This material design strategy may open up a new way for the development of high‐performance anode materials for energy storage based on earth‐rich materials, and advance the understanding of the core role of electrode surfaces/interfaces in battery systems. [ABSTRACT FROM AUTHOR]

By now, as the promising high‐energy cathode materials of lithium‐ion batteries (LIBs), the high‐nickel LiNi0.8Co0.1Mn0.1O2 (NCM811) still have technical problems such as poor electrode‐electrolyte interface stability and sensitivity to H2O and HF in the electrolyte to be solved. In this work, isocyanoethyl methacrylate (IMA) containing −N=C=O group is developed as a bifunctional electrolyte additive through the film‐forming, H2O removal, and HF reduction to modify the electrode‐electrolyte interfaces and improve the performance of NCM811/graphite LIBs. After 450 cycles under the normal voltage range of 2.75 to 4.20 V, the capacity retention of the battery with 0.5 wt.% IMA additive increases from 50.7 % to 78.0 % compared to the battery without the additive. And under the high voltage range of 2.75 to 4.40 V, the capacity retention of the battery with IMA increases from 62.8 % to 81.9 % after 150 cycles. It is demonstrated that the IMA additive as the H2O and HF scavenger of electrolyte also facilitate the electrochemical oxidation‐reduction reactions on two electrodes to form high‐quality interfacial films, which stabilizes the anode and cathode interfaces and subsequently improves the cycling performance of the batteries. These results show that the electrolyte with IMA additive has promising prospects in the application of high‐nickel NCM‐based LIBs and provide the idea to evaluate the organic molecules containing −N=C=O group as the functional electrolyte additives as well. [ABSTRACT FROM AUTHOR]

The energy density of lithium cobalt oxide (LiCoO2)‐based cells can be increased by charging at voltages above 4.2 V. However, the poor interface stability of the cathode/electrolyte deriving from the continuous severe decomposition of the electrolyte on the cathode/electrolyte surface and the instability of the structure of the cathode at high‐voltage operation limits their wider commercial application. Herein, a new fluoro‐functionalized electrolyte additive, tetrafluoroethane beta‐sultone (TFBS), is used for promoting the electrochemical performance of LiCoO2‐based cells. Upon cycling between 3.0 and 4.5 V (vs. Li/Li+) with 0.5 C (1 C=274.4 mAh/g), it is shown that the capacity retention of the LiCoO2/graphite pouch‐cell with TFBS‐controlled electrolyte reaches 96.8 % (183.9 mAh g−1), yet it is 66.5 % (126.3 mAh g−1) for the pouch‐cell without TFBS in baseline electrolyte at the 100th cycle. All the results indicate that TFBS can be decomposed prior to the solvents in the electrolyte and can then form low‐resistance, high‐conductivity interface layers on the surfaces of the cathode‐electrolyte and the anode‐electrolyte, respectively, thus improving the cycling stability of the cells at a high charging cutoff voltage (4.5 V). [ABSTRACT FROM AUTHOR]

A functional electrolyte containing 3,3‐diethylene di‐sulfite (DES) additive is developed to improve the performances of LiNi0.8Co0.1Mn0.1O2 (NCM811)/graphite batteries, especially at high charging cut‐off voltage of 4.50 V. It is indicated that under the conventional conditions of 25 °C and 1 C after 300 cycles in the voltage range of 2.75–4.30 V, the batteries with 0.25 % DES can increase the maximum capacity retention from 66.61 % to 77.25 % initial discharge capacity compared with the batteries without DES. Especially, when the charge cut‐off voltage is increased to 4.50 V, the batteries with 1 % DES exhibit higher capacity retention (82.53 %) after 150 cycles than the batteries without DES (51.19 %). The electrochemical tests and spectroscopic characterization show that this functional DES electrolyte additive well regulates the anode and cathode interfaces with more stabilized films and smaller impedance, which promotes the interfacial extraction and insertion of Li+. In addition, the interfacial film can inhibit the dissolution of the transition metal element Ni from the cathode and protect the structure stability of NCM811 material. The electrolyte containing DES additive reveals promising prospects in the application of NCM811/graphite batteries. [ABSTRACT FROM AUTHOR]

The behaviors and mechanism for the different performance degradation trends of 18650 cylindrical lithium‐ion batteries (LIBs) with LiNi0.33Co0.33Mn0.33O2 cathodes under long‐term storage at a high temperature (HT) of 80 °C are investigated to gain insight on the safe use of LIBs. It is indicated that the direct current resistance (DCR) increases sharply within 240 h and then slows down gradually, whereas the open‐circuit voltage (OCV) and the recoverable capacity (RC) fading are relatively stable in the initial 240 h, but then speeds up from 240 h to 720 h. With the aid of analyses of the anode, cathode, and separator materials in batteries stored at 80 °C for 0 h, 240 h, 480 h, and 720 h, the mechanism of the performance degradation of batteries is elucidated. It is pointed out that the DCR rise is mainly caused by the anode materials peeling off from the copper foil, as is the subsequent interface resistance increase. The RC fading is attributed to the partial break of the cathode structure, owing to the dissolution of transition metal ions (Ni2+, Co3+, and Mn4+), and the dissolution becomes more severe as the time extends. In addition, the separator suffers a combination of stretching (machine direction), squeezing (anode side), oxidation (cathode side), and destruction, resulting in internal short circuit and sharp OCV drop, as well as the other potential safety risks of LIBs. These results are valuable to establish an accelerated testing method to evaluate batteries in a short time range to advance the safe use of LIBs under high‐temperature storage. [ABSTRACT FROM AUTHOR]

A positive‐temperature‐coefficient graphite anode as a thermal runaway firewall of LiCoO2/graphite lithium‐ion batteries (LIBs) is prepared by introducing thermally sensitive polymer microspheres (TSPMs) into the anode to improve battery safety under abusive conditions. The TSPMs are composed of an acrylonitrile and acrylate copolymer shell and a cyclopentane hydrocarbon core. Due to the thermally sensitive properties of TSPMs, the graphite anode swells under abusive conditions, and the electric connection of active materials and current collector can be cut off. Thus, the resistance of LIBs is increased to solve the thermal runaway and safety problems before the temperature of LIBs approaches explosion limit. The TSPMs with a size distribution of 4–20 μm and an initial foaming temperature of 95–110 °C exhibit excellent stability and foaming properties. Compared with the batteries without TSPMs, under abusive conditions including overcharge at 1 C/10 V, thermal shock from 20 to 130 °C, and external short circuit with a resistance of ≈80 mΩ, the batteries with TSPMs effectively mitigate thermal runaway. In addition, TSPMs do not show obvious influences on the conventional performances of LIBs, indicating that adding TSPMs into graphite anodes is a promising method to improve the safety of LIBs under abusive conditions. [ABSTRACT FROM AUTHOR]