Mechanism Research And Molecular Design Of Small Molecules Amine-Stabilizer In Electrolyte Of Lithium Batteries

Due to their good performance, high operation voltage, high energy density, long cyclic life and small self-discharge rate, lithium ion batteries have become the focus of new power sources. The electrolytes used in commercial lithium ion batteries are prepared by dissolving LiPF₆ into binary or ternary solvents, which are of the mixtures of non-cyclic carbonates, including dimethyl carbonate (DMC), ethyl (methyl) carbonate (EMC) and diethyl carbonate (DEC), with ethylene carbonate (EC). Nevertheless, even trace amounts of water can have negative influence on the cycling and storage stability of battery. Amines as a kind of stabilizer can stabilize small molecules with a nice performance in lithium ion batteries. Seldom theoretical research was reported about the mechanism. Therefore, research the mechanism of amines stabilizer and design new stabilizers were very important to improve performance of lithium ion batteries.ZZ @In this paper, Intermolecular interactions between ethylamine. ethylenediamine or ethanolamine and H₂O or HF were studied theoretically using density function theory (DFT) at the PBE0/6-31+G(d, p) level in gas-phase and solvent (SCI-PCM). The mechanism of amines stabilized small molecules was analysed. The conclusions were draw as follow: (1) In gas-phase, both HF and H₂O can be stabilized by amines through N…H-F(O),F(O)…H-N hydrogen bonds, electron localized effect n_N→σ_HF^*,n_N→σ_OH^*,n_F→σ_HN^* were happened, the stability of amine-HF complexes were stronger than amine-H₂O complexes. When solvent effect was calculated, the combination between amines with HF or H₂O became stronger, week hydrogen bond F(O)…H-C which existed in gas-phase was disappeared when it come to solvent. (2) In gas-phase, the stability sequence of amine-tabilizers was "ethylenediamine＞ethylamine＞ethanolamine"; in solvent, it turned to"ethanolamine＞ethylenediamine＞ethylamine". This result was agreed with experimental result.Afterwards, hydrogen ofethanolamine were replaced by-F,-Cl,-CH₃ and-C₆H₅, 18 kinds of amine ramifications combine with HF in gas-phase, which were studied theoretically at the PBE0/6-31+G(d, p) level. From this study, we can find that attract electron functions were replaced at 2 or 3 position in ethanolamine, stability of amines-associated complexes was obvious increased. The sequence of increase stability was Ph＞Cl＞F; repulse electron functions were replaced at 10 or 11 position in ethanolamine, stability of amines-associated complexes was obvious increased. Thereby, hydrogens of ethanolamine were replcace at 2 or 3 position by Ph and 10 or 11 position by Me, in those amine ramifications, 3-Ph, 10-Me replace was most stabile complex combine with HF, which was expected as new amine-stabilizer in electrolyte of Li⁺ battery.