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The high price of lithium salts hinders the sustainable development of high concentration electrolytes, while the poor electrochemical performance limits the large-scale application of low concentration electrolytes. Herein, the electrochemical performance of a low concentration electrolyte is improved via dual interfacial modification of the fluoroethylene carbonate (FEC) solvent and the lithium difluoro(oxalato)borate (LiODFB) additive. LiODFB is preferentially oxidized via a ring-opening path to generate a lithium fluoride (LiF)-rich inner layer on the surface of a ferrous lithium phosphate cathode, and then a large amount of C–F polycarbonate oligomers is generated in the outer layer via a reaction between LiODFB and FEC. LiF has a large bandgap and a low lithium ion (Li+) diffusion barrier, and the electronegative C–F groups provide the lithiophilic sites to reduce the interaction between Li+ and solvents, resulting in a repulsive force towards the C＝O dipole of the carbonate ester solvent to improve the oxidation stability of the electrolyte. The clever design of the multi-layer cathode electrolyte interphase suppresses the excessive decomposition of the electrolyte, improves the diffusion of Li+, and enables much-improved cycling stability of the cathodes. This work gives a fruitful insight into the key role of cathode electrolyte interphase components in Li+ diffusion and improves the performance of low-concentration electrolytes. [ABSTRACT FROM AUTHOR]

The impurity of water, which should be controlled strictly during industrial production and storage processes, has a fatal influence on the performance of lithium ion batteries. Here, lithium bis(oxalato)borate is taken as an example to investigate the changes in properties of chelate-borate complexes when stored in a humid environment, using techniques of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetric (TG) analysis and density functional theory (DFT) calculations. Besides, the effect of heating on remediation is studied with acidity test and electrochemical performance measurement. Results show that high relative humidity can accelerate the rate of increase in weight, though the same constant weight will be achieved in the end. The increase in weight is caused by a comprehensive action including the occurrence of hydrolytic reactions, and the formation of adsorbed water and crystal water. Further studies indicate that hydrolytic decomposition is spontaneous at room temperature, but the backward reaction cannot proceed with a heating method, namely, the remediation will be limited due to the formation of harmful hydrolysis products, though both the adsorbed water and the crystal water can be removed thoroughly. Moreover, we believe that the existence of hydrolysis products will lead to a sharp impedance increase of the so-called solid electrolyte interphase film, which will give rise to the deterioration of electrochemical performance sequentially. [ABSTRACT FROM AUTHOR]

To satisfy the need of 5 V high-voltage cathode materials, lithium difluoro(oxalato)borate (LiDFOB) with excellent film-forming property has been chosen as lithium salt, and adiponitrile (ADN) with stable electrochemical performance has been evaluated as functional additive. An electrochemical investigation of this novel electrolyte solution shows a wide electrochemical oxidation window of nearly 6.0 V vs Li + /Li. Due to the positive effect of ADN on the cathode/electrolyte interface, LiNi 0.5 Mn 1.5 O 4 /Li half-cell with ADN-adding electrolyte exhibits prominent rate capability and cyclability. It is believed that the improvement of electrochemical performances has benefitted greatly from interfacial impedance reducing. Two modeling hypotheses have been used to explain interfacial interaction between ADN and LiNi 0.5 Mn 1.5 O 4 , by the means of analysis of X-ray photoelectron spectroscopy and theoretical calculation. Results show that ADN can enrich the surface of cathode material to hinder the further decomposition of the electrolyte, and contribute to the formation of a cathode-electrolyte interface passivation film with protective and conductive properties. [ABSTRACT FROM AUTHOR]

High nickel LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) cathode material has become one of the most promising cathode materials in the field of power batteries, but the side reaction between the conventional LiPF 6 -based electrolyte and the surface of the NCA material results in poor material interface stability. In this work, a compatible lithium difluoro(oxalate)borate (LiDFOB)-based electrolyte by the employment of sulfolane (SL) as a representative sulfur-containing solvent has been built to enhance the interfacial stability of NCA electrode. The composition, morphology and electrochemical properties are studied by X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy et al. Results show that the decomposition of LiDFOB on the surface of the positive electrode material contributes to forming a uniform cathode electrolyte interface (CEI) film, which subsequently reduces the dissolution of metal ions and hinders the structure transition of the material from the layered structure to spinel or rock-salt phases. Besides, the sulfur-containing products resulted from the decomposition of SL promote the conductivity of Li+ ions for CEI film, which makes up for shortcomings of LiDFOB. Moreover, more LiF has been formed due to the synergistic action between LiDFOB salt and SL solvent, improving the stability and density of CEI film, reducing the thickness of CEI film, and further improving the cycle performance of the battery. [ABSTRACT FROM AUTHOR]