The electrochemical stability of the lithium ion battery electrolyte is typically represented by an electrochemical window refers to the difference in potential of the electrolyte oxidation reaction and the reduction reaction. The wider the electrochemical window, the stronger the electrochemical stability of the electrolyte. One of the primary conditions as an electrolyte application should ensure the qualitative of the positive and negative electrode material in the charge and discharge process, the electrochemical window of the electrolyte must be more than 4.5 V.
The electrochemical stability of the electrolyte is determined by a variety of factors such as the lithium salt, organic solvent, electrolyte and electrode material constituting the electrolyte. Although electrochemical stability of the electrolyte can be contained in a variety of methods such as circulating voltammetry, the electrochemical decomposition process is determined by a variety of 1AI, different researchers, and different conditions may be different. This section is from lithium salts and solvents
Also, the electrochemical stability of the electrolyte is made.
The lithium salt cation used by the lithium ion battery electrolyte is the same. Therefore, the electrochemical stability of the lithium salt is actually determined by the anion, and the electrolyte composed of these anions is used as the electrolyte, the glass carbon (GC) electrode as an inert electrode, and at 1.OMA / CN42 The current density conditions set out the electrochemical windows of a variety of anions. For inorganic anions, electrochemical stability is reduced in the order of SBFFI> ASFS> – PFFI> BF4> CIO, and for organic anions according to C4 F3SO3> N (SO22CF3) 2> L’F3SO3> B (C2 H3) 4> BPH3 The order of order. Obviously, the inorganic anion has higher oxidative stability than organic anions: the fluorine-containing organic anion is stronger than the anionic oxidation resistance of the unsteady. Quantum chemical calculations show that the anionic electrochemical stability is related to the size of the ionization.
In addition, the type of solvent has a significant effect on the stability of the anion, for example, the decomposition voltage of different lithium salts in EC-DEE solution at room temperature According to CLO2> N (SO2CF3) 2> CF3SO2> ASFS> PF6> BFA Sequential changes, but when replacing DEE with linear tataricate (DMC), the sequence of decomposing compulsion becomes (10PF6, BF4> A2F2> N (SO), CF3), (F3SO3, PF6, and BF6 stability significantly “mainly Because the DEE History is not as stable in the Solvent of DEE History. The main reason may be relatively small in the Decomposition voltage of the itself, resulting in the electrochemical chemistry of the decomposition voltage of the itself. Poor stability. Compare the oxidation potential of PFF and A, F6 under different conditions, clearly see (Table 2-5), electrode material, current density, test method, etc., various assays of the anionic oxidation resistance will be affected. Therefore, it is considered that the electrochemical stability of the lithium salt should be carried out under the same conditions.
The reduction process of different anions on the negative electrode interface is also significantly different. Due to the solution of LIPF6 and LiBF6 may contain trace HF, the LIF can be generated on the surface of the negative electrode, and the LIF can significantly increase the migration resistance of lithium ions, improve the internal resistance of the battery. LIAS, the electrolytic solutions constituted by LIAS, and the electrolyte composed does not exist. If the content of HF in LiPF6 is reduced during purification and storage, the performance of the electrolyte of LiPF6 can also be improved.
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