Identification of Li Battery Electrolyte Degradation Products Through Direct Synthesis and Characterization of Alkyl Carbonate Salts

Abstract

Aiming toward the identification of carbonate-based electrolyte degradation species formed during high-temperature cycling of Li/M-O cells, we have embarked in the synthesis and characterization of lithium-based alkyl carbonates. Through the reaction of commercial or synthesized lithium alkoxides with carbon dioxide, we succeeded in preparing lithium methyl, ethyl, propyl mono carbonates, and therefore we have extended our work to the synthesis of lithium ethandiol-bis carbonate. Their analytical characterization ͑ 1 H and 13 C nuclear magnetic resonance, electrospray ionization-mass spectroscopy, Fourier transform: infrared/ attenuated total reflection͒ is described. Furthermore, to our surprise, we managed to demonstrate that these well-known alkyl carbonates show some electrochemical reactivity toward Li.Organic carbonates, because of their numerous attractive chemical properties, are used among others in pharmaceutical and energy storage applications as chemical synthesis precursors or as nonaqueous battery electrolyte, respectively. Mixtures of both cyclic carbonates ͓ethylene carbonate ͑EC͒ and/or propylene carbonate ͑PC͔͒ together with noncyclic ones ͓dimethyl carbonate ͑DMC͒ and/or ethyl methyl carbonate ͑EMC͔͒ are among the most employed solvent combinations in the preparation of today's electrolytes for Li-based batteries. Their attractiveness is nested in their high electrochemical stability toward lithium combined with a high dielectric constant provided by cyclic carbonates, which favors ion separation, and a decent viscosity provided by the suitable addition of noncyclic carbonates. Due to their key role in the proper functioning of Li-based cells, many studies have already been carried out on Li-based carbonate electrolytes, and numerous reports describing their properties and their Li-driven reduction mechanisms leading to the growth of the well-known solid electrolyte interphase ͑SEI͒ at the Li surface are available. 1-6 Usually, besides Li 2 CO 3 , alkyl carbonates are reported as the most common species resulting from electrolyte reduction with occasionally the possibility of forming poly͑ethylene oxide͒ ͑PEO͒ oligomers. However, some uncertainties still remain not only on the exact nature of the alkyl-carbonate formed, which can be mono or bis-carbonates, but also on the exact composition of this SEI layer. Attempts to answer such questions are quite a tedious task due to ͑i͒ the usually limited growth ͑e.g., small amount of materials͒ of the SEI so that we must rely on passive analytical techniques ͓Fourier transform infrared ͑FTIR͒, AC-impedance spectroscopy͔, and ͑ii͒ the highly air/moisture sensitivity of the Li-based materials so that results of surface characterization analyses, such as atomic force microscopy ͑AFM͒ or X-ray photoelectron spectroscopy ͑XPS͒, could largely differ among research groups. 7 Recently, in studying the electrochemical reactivity of 3d-metal oxides ͑CoO, Co 3 O 4 , CuO. . .͒ toward Li, we unraveled a novel reactivity mechanism. Such materials were shown to rever...

Reduction Reactions of Electrolyte Salts for Lithium Ion Batteries: LiPF6, LiBF4, LiDFOB, LiBOB, and LiTFSI

“…Electrolyte salts dissolved in either THF or Et 2 6 could not be measured reliably by NMR spectroscopy. However, in all cases low concentrations of residual salt are observed after the reduction reactions and some of the reduction products may precipitate prior to complete reduction, so the number of electrons required for reduction of the different salts should be viewed as approximate.…”

“…The SEI has been proposed to contain lithium alkyl carbonates, lithium carbonate, lithium oxalate, lithium alkoxides, and lithium oxide from the carbonate solvents and LiF, lithium fluorophosphates, lithium fluoroborates, and lithium oxalate from the reduction of electrolyte salts, depending upon the salt utilitzed. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Electrolyte additives have also been used to tailor the properties of the SEI through preferential reduction on anode. 1 Despite significant effort over the last two decades, the formation mechanism of the SEI is not well understood.…”

Hydrolysis of Ethylene Carbonate with Water and Hydroxide under Battery Operating Conditions

“…9 For simplicity, Reaction 2.3 in Scheme 1 only depicts the CO 2 generating reaction via the attack at the alkylene carbon, which eventually leads to the formation of poly-EG − . Gireaud et al 13,14 observed the formation of poly-EG oligomers already at 55…”

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

“…13 Actually, significant evolution of gaseous products such as CO 2 , CO, O 2 , H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 and C 3 H 8 from the decomposition of carbonate solvents and lithium during battery operation has been detected by various characterization techniques. [14][15][16][17][18][19][20][21] In addition, utilizing isotope analysis, Onuk et al have unambiguously identified the origin of gases evolving in LIBs. 22 Furthermore, by adopting in situ transmission electron microscopy (TEM) 23 and neutron radiography (NR), 9,11 the generation of gaseous bubbles channels formed by the gas have recently been visualized.…”