Carbonate Free Electrolyte for Lithium Ion Batteries Containing γ-Butyrolactone and Methyl Butyrate

Abstract

A novel carbonate free electrolyte, 1 M lithium difluoro(oxalato) borate (LiDFOB) in 1:1 gamma-butyrolactone (GBL)/methyl butyrate (MB), has been compared to a standard electrolyte, 1 M LiPF 6 in 1:1:1 EC/DMC/DEC, and a 1 M LiDFOB in 1:1:1 EC/DMC/DEC electrolyte. The conductivity of 1 M LiDFOB in GBL/MB is higher at low temperature, but slightly lower at higher temperature compared to the standard electrolyte. The 1 M LiDFOB in GBL/MB electrolyte has comparable cycling performance to the standard electrolyte, and better cycling performance than the 1 M LiDFOB in EC/DMC/DEC electrolyte. The reversible cycling performance suggests that the LiDFOB in GBL/MB electrolyte forms a stable anode solid electrolyte interface (SEI) in the presence of GBL. Ex-situ surface analysis of the extracted electrodes has been conducted via a combination of XPS, FTIR-ATR and SEM which suggests that the stable anode SEI results is primarily composed of reduction products of LiDFOB. The widespread implementation of electric vehicles (EVs) requires further improvements in lithium ion batteries.1-3 Some of the biggest challenges for lithium ion batteries in EVs are cost, low temperature performance and battery lifetime.2,3 Improvements in the electrolyte can assist in the resolution of each of these problems.1,4,5 Most commercial electrolytes are composed of LiPF 6 in a mixture of carbonate solvents.5 However, the high cost and poor thermal and hydrolytic stability of LiPF 6 is problematic for the electrolyte.6-8 In addition, ethylene carbonate (EC) is typically a required component of the electrolyte due to the role of EC in the formation of the solid electrolyte interphase (SEI) on the anode. 5,9-14 Since EC is a solid at room temperature, electrolytes containing EC frequently have poor performance at low temperature.15 Despite the shortcomings of LiPF 6 / EC based electrolytes, these formulations have proven very difficult to replace. While there have been significant efforts to develop novel electrolytes with superior performance to LiPF 6 in carbonates, there has been limited success. The development of novel solvent systems has been more limited and frequently targeted toward specific problems such as high voltage cathodes, salt solubility, or reactivity issues. [16][17][18][19][20][21] The development of novel salts has encountered problems related to salt solubility and corrosion of the aluminum current collector on the cathode. 21,22 One of the more interesting and promising alternative salts is lithium difluoro(oxalato) borate (LiDFOB). 1,4,23,24 LiDFOB is promising due to good solubility, thermal stability, passivation of the aluminum current collector, stable SEI formation, and potentially lower cost. While there have been a limited number of investigations of LiD-FOB as the conducting salt in the electrolyte, 4,16,25 there have been several reports of the use of LiDFOB and the related salts lithium bis(oxalato) borate (LiBOB) and lithium tetrafluoro(oxalato) phosphate (LiTFOP) as additives to LiPF 6 based electrolytes to form...

Recent advances toward high voltage, EC-free electrolytes for graphite-based Li-ion battery

“…Researchers have confirmed that, at 1.7 V and below, in carbonate-based electrolytes [98], the reduction products of LiDFOB (e.g. lithium oxalate, other oxalate containing species, and borates [98,101]) dominate the SEI composition [97]. The SEI is thicker (the impedance of the cell is higher as well) as compared with a LiPF6-containing EC-based electrolyte at low temperature [101] but helps reaching good cycling retention of graphite at room temperature in SL:DMC-electrolyte [92].…”

“…lithium oxalate, other oxalate containing species, and borates [98,101]) dominate the SEI composition [97]. The SEI is thicker (the impedance of the cell is higher as well) as compared with a LiPF6-containing EC-based electrolyte at low temperature [101] but helps reaching good cycling retention of graphite at room temperature in SL:DMC-electrolyte [92]. In alkyl dinitrile solvent mixtures such as ADN:DMC, 99.9% efficiency has been reached for graphite (in combination with FEC), whereas ADN and alkyl nitriles in general are usually detrimental for SEI formation [102].…”

Adiponitrile-based electrolytes for high voltage, graphite-based Li-ion battery

“…This is clearly due to more stable interfaces in LiDFOB cells. Indeed, it is known that LiDFOB allows, in some cases, graphite cycling in EC-free electrolyte [26], due to its own reduction, prior to other electrolyte components at ca. 1.8 V [21].…”

Investigation of Dimethyl Carbonate and Propylene Carbonate Mixtures for LiNi0.6Mn0.2Co0.2O2‐Li4Ti5O12 Cells

“…Attempts to solve these problems have been made by replacing EC with other carbonate‐based solvents such as ethyl methyl carbonate (EMC) . These electrolytes do, however, not form as stable SEI layers as EC does, and various SEI‐forming electrolytes and additives have therefore been investigated to develop EC‐free electrolytes …”

“…[2,3] These electrolytes do, however, not form as stable SEI layers as EC does, and various SEI-forming electrolytes and additives have therefore been investigated to develop EC-free electrolytes. [5][6][7][8] Propylene carbonate (PC) has a far higher dielectric constant than the common carbonate solvents used in LIB electrolytes, and is therefore ideal as a replacement for EC. [9] The melting point of PC is far lower as compared to EC, which is also why it previously has been a part of EC-containing electrolytes intended for low temperatures.…”