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High energy density lithium-ion batteries using Ni-rich cathode (such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay. P-toluenesulfonyl fluoride (pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell. In comparison with the baseline electrolyte, a small dose of pTSF can significantly improve the cyclic stability of the cell. Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode, respectively. These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte, reduce the interphasial impedance, as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage. This finding is beneficial for the practical application of high energy density graphite/ LiNi0.6Co0.2Mn0.2O2 cells.

Owing to the high specific capacity and high voltage, Ni-rich (LiNi0.8Co0.1Mn0.1O2, LNCM811) cathode has been considered as one of the most promising candidate cathode materials for next generation lithium ion batteries, whereas severe capacity fading greatly hinders its practical application. Notably, the compatibility of Ni-rich materials with LiBF4-containing electrolyte has not yet been realized. Herein, 1 M LiPF6-based electrolyte with introducing 2 M LiBF4 is proposed to dramatically improve the cyclic stability of high voltage LNCM811/Li half-cell. Addition of high concentrated LiBF4 improves the moisture stability of electrolyte, which hinders the generation of harmful by-product HF, resulting in improved interfacial stability of LNCM811. Lithium plating/stripping reaction of Li/Li symmetric cell confirms that the enhanced cyclic stability is ascribed to the improved interfacial stability of LNCM811 instead of lithium electrode. Morphology and composition characterization results reveal that LiBF4 participates in the CEI film-forming reaction, resulting in suppressed oxidation of electrolyte and interfacial structural destruction of LNCM811.

Performances of lithium-ion batteries at subambient temperatures are extremely restricted by the resistive interphases originated from electrolyte decomposition, especially on the anode surface. This work reports a novel strategy that an anode interphase of low impedance is constructed by applying an electrolyte additive dimethyl sulfite (DMS). Electrochemical measurements indicate that the as-constructed interphase provides graphite/LiNi0.5Co0.2Mn0.3O2 pouch cells with excellent low-temperature performance, outperforming the interphase constructed by 1,3,2-dioxathiolane 2,2-dioxide (DTD), a common commercially used electrolyte additive. Spectral characterizations in combination with theoretical calculations demonstrate that the improved performance is attributed to the unique molecular structure of DMS, which presents appropriate reduction activity and constructs the more stable and ionically conductive anode interphase due to the weaker combination of its reduction product with lithium ions than DTD. This rational design of interphases via an additive structure has been proven to be a low cost but rather an effective approach to tailor the performances of lithium-ion batteries.

Energy density of lithium ion batteries based on transition metal oxide cathodes can be enhanced by increasing the end-off charge voltage to a great extent, because the cathodes can deliver a larger specific discharge capacity under an elevated charge voltage. However, this operation is always accompanied by the oxygen evolution from the cathode oxides, which might cause the crystal destruction of the cathode oxides and the severe electrolyte decomposition on the cathodes, leading to the fast failure of the batteries. In this work, we report a new finding that the oxygen evolution in graphite/LiNi0.6Mn0.2Co0.2O2 pouch cell can be efficiently suppressed and thus the cyclic stability of the cell is significantly improved by using tributyl borate (TBB) as electrolyte additive, even under 4.5 V. Electrochemical tests indicate that, with adding 1 wt% TBB to the electrolyte, the capacity retention of the cell is enhanced from in 35.1% to 94.9% after 120 cycles. The physical characterizations combining theoretical calculations demonstrate that the B-containing species in the cathode electrolyte interphase, originated from the oxidation of TBB, present a strong combination with oxygen and suppress efficiently the oxygen evolution.

Improving the interphasial stability of electrode/electrolyte is crucial to the large-scale applications of lithium-ion battery with high energy density. Herein, a novel electrolyte additive, phenyl trans-styryl sulfone (PTSS), is proposed to reconstruct the interphasial structure and composition of electrode/electrolyte and to improve the cyclic stability of high voltage LiNi0.8Co0.1Mn0.1O2 (NCM811)/graphite full-cell. Specifically, the cell with PTSS additive maintains 63% of its initial capacity after 100 cycles at 1C, which is about 15% higher than that of baseline electrolyte. Theoretical calculation and experimental characterization reveal that the high electrochemical reactivity PTSS decomposes prior to the baseline electrolyte, generating a protective film on NCM811 cathode and graphite anode surface. The uniform and thin CEI film effectively enhanced the interphasial stability of NCM811 cathode via suppressing electrolyte oxidation and electrode interphasial destruction during long term cycling. In addition, the PTSS induced-SEI film enhances the interphasial stability of graphite anode.