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The prevailing account attributes the positive effects of boron-based additives on solid electrolyte interface (SEI) layers to its solid products by prior decomposition. However, this study proves the BOF2− anion, a soluble product of film formation additive of lithium difluoro(oxalato)borate, plays a crucial role in improving the SEI layer. Specifically, BOF2− suppresses the excessive decomposition of salt anions by aggregating on the electrode surface. Meanwhile, it catalyzes the reduction of ethylene carbonate, leading to improving the stability of the interface. In the end, ultrasound shaking is used to generate more BOF2− anion and increase the cycle performance of cells at a high rate as excepted. This work helps to understand the effects of soluble products on the SEI forming process and provides new insights for improving the stability of electrode electrolyte interfaces. [Display omitted] • An effect mechanism of SEI formation is proved from the view of soluble product. • The soluble product of LiDFOB prevents its excessive decomposition. • The soluble product catalyzes the reduction of EC. [ABSTRACT FROM AUTHOR]

• Formation of lif-rich cathode-electrolyte interphase via potentiostatic reduction. • The lif-rich CEI inhibits the corrosion of FSI− anion on aluminum collector. • The electrochemical performances of l -std-F reach the level of 1.0 m LiPF6-DEC/EC. The low concentration electrolyte shows the advantages of low viscosity and low cost, but the formation of porous and soluble organic cathode-electrolyte interphase (CEI) limits its performance. Herein, the electrochemical performance of the low concentration electrolyte of 0.45 M LiPF 6 ‑diethyl carbonate (DEC)/ ethylene carbonate (EC) (1:1, in volume ratio) is improved by 0.05 M bis(fluorosulfonyl)imide (LiFSI) additive, aided by the antecedent process of potentiostatic reduction at a low potential of 1.5 V. Results show that LiFSI is preferentially reduced via breaking the structure of FSI− anion to form a robust LiF-rich CEI on the surface of LiFePO 4 (LFP) cathode, solving the problem that it is difficult to form inorganic LiF on the cathode surface. In the subsequent cycling of LFP/Li half-battery, the as-formed CEI inhibits the corrosion of aluminum collector, suppresses the excessive decomposition of the electrolyte and improves the diffusion of Li+, resulting in a much-enhanced cycle stability of the cathode. Therefore, the cyclic performance of the LFP/Li half-battery using the modified low concentration electrolyte with the antecedent process of potentiostatic reduction is on a par with that using the standard electrolyte (1.0 M LiPF 6 -DEC/EC). Compared with the traditional electrolyte engineering of constructing a LiF-rich CEI by the direct oxidation defluorination of fluorinated anions, this strategy needs a lower reaction energy and can play a positive role at a lower reaction potential. This work provides an effective way to construct LiF-rich CEI which helps to improve the performance of low concentration electrolytes. [Display omitted] [ABSTRACT FROM AUTHOR]

Water has a fatal influence on the performance of lithium ion batteries. In this work, Lithium hexafluoro phosphate(LiPF 6 )-ethylene carbonate (EC)/diethyl carbonate (DEC) and lithium bis(oxalato)borate (LiBOB)-tetramethylene sulfone (SL)/DEC are taken as examples to investigate the influences of water concentration for electrochemical window, acidity, impedance and cycling performance for lithium ion batteries by adjusting water concentrations in the electrolytes. Results show that LiBOB-based electrolyte has better water tolerance compared with LiPF 6 -based system, due to the formation of LiBOB·xH 2 O compounds by consuming the additive trace water. Besides, inductively coupled plasma test result shows that Mn ion dissolution in LiPF 6 systems is extremely severe, which is mainly caused by the corrosive reaction between LiMn 2 O 4 and by-product HF acid. And we believe that Mn ion dissolution and the following deposition should be responsible for failure work of LiPF 6 -based cells. But for LiBOB-based cells, stable SEI layers and good electrochemical performances have been obtained, benefitting from the synergistic effect between LiBOB salt and SL solvent. And the presence of high-resistance B(C 2 O 4 ) (OH) and LiB(C 2 O 4 ) (OH) 2 products on surface of graphite electrode is the main reason for a small number of capacity fading. [ABSTRACT FROM AUTHOR]

Complexes of lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB) and lithium difluorobis(oxalato) phosphate (LiDFBOP) are the promising additives for advanced lithium ion batteries because of their high reactivity and easy synthesis, in which the changeable central atom and ligand bring diverse properties for salts. In this study, their structure-function relationship has been surveyed by exploring the reduction pathways. According to the analysis of experiments and quantum chemistry calculations, we have established that the steric-hindrance effect of ligands is the key effect on the bond-broken of these lithium salts. Specifically, more oxalate ligands are beneficial to the breaking of C–O and the bond of the central atom (M) with O atom, resulting in CO and CO 2 release as well as the generation of MO 2 -type soluble products. The as-generated MO 2 -type soluble products undergo a further self-aggregate process to form macromolecular complexes. In contrast, fewer oxalate ligands just encourage the bond breaking of the M − O bond, leading to CO 2 release and the generation of MF 2 -type soluble products. In addition, the universal promoting effect of soluble products on ethylene carbonate decomposition is verified. These results offer theoretic support for the molecular design of advanced functional chelae lithium salts. • Steric-hindrance effects of ligands affect complex salts decomposition mechanism. • More ligands always lead to the prior C–O bond break in oxalic acid rings. • Fewer ligands always lead to the prior break of the bond between central atoms and O. [ABSTRACT FROM AUTHOR]