Solubility of Lithium Salts Formed on the Lithium-Ion Battery Negative Electrode Surface in Organic Solvents

Abstract

The solubility of lithium salts in dimethyl carbonate ͑DMC͒ found in solid electrolyte interface ͑SEI͒ films was determined. The salt-DMC solutions evaporated, and the salts were transferred into water for ion conductivity measurements. The salts examined included lithium carbonate ͑Li 2 CO 3 ͒, lithium oxalate ͓͑LiCO 2 ͒ 2 ͔, lithium fluoride ͑LiF͒, lithium hydroxide ͑LiOH͒, lithium methyl carbonate ͑LiOCO 2 CH 3 ͒, and lithium ethyl carbonate ͑LiOCO 2 C 2 H 5 ͒. The salt molarity in DMC ranged from 9.6 ϫ 10 −4 mol L −1 ͑LiOCO 2 CH 3 ͒ to 9 ϫ 10 −5 mol L −1 ͑Li 2 CO 3 ͒ in the order of LiOCO 2 CH 3 Ͼ LiOCO 2 C 2 H 5 Ͼ LiOH Ͼ LiF Ͼ ͑LiCO 2 ͒ 2 Ͼ Li 2 CO 3. X-ray photoelectron spectroscopy measurements on SEI films on the surface of the negative electrode taken from a commercial battery after soaking in DMC for 1 h suggested that the films can dissolve. Separately, the heat of dissolution of the salts was calculated from computer simulations for the same salts, including lithium oxide ͑Li 2 O͒, lithium methoxide ͑LiOCH 3 ͒, and dilithium ethylene glycol dicarbonate ͓͑CH 2 OCO 2 Li͒ 2 :LiEDC͔ in both DMC and ethylene carbonate ͑EC͒. The results from the computer simulations suggested that the order in which the salt was likely to dissolve in both DMC and EC was LiEDC Ͼ LiOCO 2 CH 3 Ͼ LiOH Ͼ LiOCO 2 C 2 H 5 Ͼ LiOCH 3 Ͼ LiF Ͼ ͑LiCO 2 ͒ 2 Ͼ Li 2 CO 3 Ͼ Li 2 O. This order agreed with the experiment in DMC within the experimental error. Both experiment and computer simulations showed that the organic salts are more likely to dissolve in DMC than the inorganic salts. The calculations also predicted that the salts dissolve more likely in EC than in DMC in general. Moreover, the results from the study were used to discuss the capacity fading mechanism during the storage of lithium-ion batteries.

Online Electrochemical Mass Spectrometry of High Energy Lithium Nickel Cobalt Manganese Oxide/Graphite Half- and Full-Cells with Ethylene Carbonate and Fluoroethylene Carbonate Based Electrolytes

“…The reactions Li 2 CO 3 + LiPF 6 → 3LiF + POF 3 + CO 2 [1] and Li 2 CO 3 + PF 5 → 2LiF + POF 3 + CO 2 [2] have been proposed in the literature. 47 Based on these reactions, increased POF 3 (and CO 2 ) formation could be explained by higher amounts of Li 2 CO 3 inside the FEC:DEC electrolyte. This would obviously require either the availability or the solubility of Li 2 CO 3 to be enhanced in FEC:DEC compared to EC:DEC electrolyte.…”

Adsorbed Water on Nano-Silicon Powder and Its Effects on Charge and Discharge Characteristics as Anode in Lithium-Ion Batteries

“…It is widely known that a trace amount of water in a cell causes many problems in SEI formation and decomposition on graphite anodes. [12][13][14][15][16] The moisture generates H 2 and LiOH, and decomposes LiPF 6 into LiF, HF and POF 3 , which deteriorates SEI and accelerates the decomposition of electrolyte solution.…”

Studies of Lithium Diffusivity of Silicon-Based Film Electrodes for Rechargeable Lithium Batteries

“…Thus, lithium diffusivity finds its importance in obtaining a good cycling performance of rechargeable lithium batteries, in particular, rate capability and cycling stability. Various methods have been used to determine the lithium diffusivity in Si anode such as electrochemical impedance spectroscopy (EIS), [11][12][13] cyclic voltammetry (CV), 11,[14][15][16][17] galvanostatic intermittent titration technique (GITT) 16) and potentiostatic intermittent titration technique (PITT). However, the reported diffusivities are not consistent with each other, since the measurements were conducted while having the occurrence of volume change and particle cracking, and interfacial instability with electrolyte.…”