Investigation of N-Ethyl-2-Pyrrolidone (NEP) as Electrolyte Additive in Regard to Overcharge Protecting Characteristics

Abstract

We report on overcharge protection characteristics of N-ethyl-2-pyrrolidone (NEP) as electrolyte additive. The electrochemical stability of this organic compound was investigated on a platinum working electrode using linear sweep voltammetry. We investigated the overcharge protection effect on a lithium iron phosphate (LFP), a lithium nickel manganese cobalt oxide (NMC) and on a LiMn 2 O 4 (LMO) cathode. Via electrochemical quartz crystal microbalance (EQCMB) measurements the effects of NEP during overcharge were studied and revealed that NEP acts not like a redox shuttle, but is forming a protecting polymeric film. The oxidation products on the cathode were studied by analyzing the surface of the lithium iron phosphate (LFP) and LiMn 2 O 4 (LMO) cathode using XPS spectroscopy.

The Role of Sub- and Supercritical CO2 as “Processing Solvent” for the Recycling and Sample Preparation of Lithium Ion Battery Electrolytes

“…Electrolyte additives are used up to 5%, either by weight or by volume [ 71 ]. Due to the application of additives, the electrolyte properties can be influenced: improvement of the flammability, enabling overcharge protection [ 71 , 72 , 73 ] or the SEI formation [ 25 , 74 , 75 , 76 , 77 , 78 ]. The SEI is formed during the first charge/discharge (formation cycles) of the LIB cell and is essential for safety and performance due to its protection of the electrolyte from further reductive decomposition at the anode surface [ 79 , 80 , 81 ].…”

The truth about the 1st cycle Coulombic efficiency of LiNi1/3Co1/3Mn1/3O2 (NCM) cathodes

“…[7][8][9] At the cathode side, organic carbonate solvent based electrolytes are considered to be relatively stable with the typical cathode materials that are charged to 4.2-4.3 V vs. Li/Li + . 10,11 However, with the search for high voltage battery cells based on cathodes operating at charging cut-off potentials higher than 4.3 V vs. Li/Li + , the electrolyte must withstand such electrochemical conditions as a fundamental requirement. There are two approaches to achieve a sufficient practical electrochemical stability of the electrolyte at high voltage: (i) to design new electrolytes which are intrinsically thermodynamically stable against electrochemical decomposition within the used voltage range, 12 or (ii) to achieve kinetic stability via a passivation layer at the electrode/electrolyte interface, e.g., by cathode material surface coatings or by the application of film forming electrolyte additives that form a cathode electrolyte interphase (CEI) similar to the well-known SEI on the anode.…”

Triphenylphosphine Oxide as Highly Effective Electrolyte Additive for Graphite/NMC811 Lithium Ion Cells

“…Various literature reports deal with the influence of these electrolyte additives, such as HF-scavengers, oxidative stability enhancers, flame retardants, or overcharge protection additives, on the overall cell performance, demonstrating the great relevance of this specific research field. − Furthermore, film forming additives are expected to be either oxidized or reduced prior to the electrolyte solvent in order to build a thin and homogeneous passivation film (SEI or CEI) on both the anode and cathode surface to prevent the electrolyte from ongoing (electro-) chemical decomposition. − In general, it has to be considered that the electrolyte can react with both, anode and cathode, and that these reactions mutually impact each other in the complete battery cell, depending on capacity and mass balancing. , …”