Li-Ion Battery Performance with FSI-Based Ionic Liquid Electrolyte and Fluorinated Solvent-Based Electrolyte

Abstract

We evaluated the electrochemical behavior of a LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) electrode in a neat ionic liquid, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI), electrolyte. According to charge/discharge measurements, the discharge capacity of the NMC cathode in EMImFSI at 1 C in a voltage range of 3.0-4.5 (vs. Li/Li + ) shows 165 mAh g -1 , which is higher than that in a conventional electrolyte, EC+DMC. The rate capability of a cell with EMImFSI exceeds that with EC+DMC, especially at high rates, probably due to a low resistance at the electrode/electrolyte interface. These results suggest that EMImFSI is a suitable electrolyte for Li-ion batteries utilizing a NMC cathode. Also, we applied fluorine-containing solvents (FCSs) to an electrolyte for Li-ion batteries with a cobalt oxide (LiCoO 2 ) cathode to enhance the upper voltage limit and investigated its electrochemical properties in a proposed FCS-based electrolyte. A test cell containing a FCS-based electrolyte exhibits high and stable discharge capacity for 30 cycles even with a high upper cutoff voltage of 4.5 V when compared with a cell containing a conventional electrolyte. IntroductionAmbient temperature ionic liquids have attracted increasing attention in batteries because of their wide potential window, acceptable conductivity, high thermal stability and negligible vapor pressure. However, Li-ion batteries with ionic liquid electrolytes have some difficulties in their charge-discharge performance. Decomposition of ionic liquids on a negative electrode and intercalation of an organic cation, which lead to irreversible Li + insertion/extraction, are serious problems of losing their charge-discharge capacity.We successfully applied bis(fluorosulfonyl)imide anion (FSI)-based ionic liquids to electrolytes for Li-ion secondary batteries, which provide reversible Li-ion insertion/extraction and high charge-discharge efficiency for a graphitized negative electrode without any additives (1-5). We have also investigated electrochemical behavior of various electrodes in these ionic liquids, e.g., Ni-Si-C composite or La-Ni-Sn alloy (6). We found these electrodes exhibit reversibility in our various ionic liquid electrolytes. Furthermore, a LiNi 1/3 Mn 1/3 Co 1/3 O 2 positive electrode showed excellent reversibility even at 4.5V in an EMIFSI-based electrolyte with an initial capacity of 171 ECS Transactions, 33 (28) 29-36 (2011) 10.1149/1.3563087 © The Electrochemical Society 29 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 141.211.4.224 Downloaded on 2015-07-12 to IPmAh g -1 and 98% of this capacity at the 50th cycle. Elexcel Co. tested Li-ion batteries containing FSI ionic liquids. A Li-ion battery with LiMn 1/3 Ni 1/3 Co 1/3 O 2 as cathode material maintained over 80% of its initial capacity in 2000 cycles at 100% DOD. The power density of the cell reached to 2050W kg -1 at 50% SOC.On the other hand, recently, a nonflammable fluorine-containing solvent (FCS) has ...

Fluorinated Electrolytes for Li-S Battery: Suppressing the Self-Discharge with an Electrolyte Containing Fluoroether Solvent

“…[16][17][18] Recently, our group reported for the first time that the fluorinated electrolyte could significantly prevent the redox shuttling effect, thus greatly improve the coulombic efficiency and capacity retention of Li-S battery. 13,19 Fluoroether-containing electrolytes have been reported by other groups to enhance the performance of the Liion battery due to their unique physical and chemical properties; [20][21][22][23] however, it is our idea to use it as an electrolyte co-solvent/additive for the Li-S battery. In this paper, we report the self-discharge characteristics of Li-S battery with the fluorinated electrolyte containing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).…”

Long-term Cycling of High Energy Li-Ion Battery with NCM Electrode and High Voltage Electrolyte

“…During our investigation on high loading NCM cathode (NCM, LiNi 1/3 Co 1/3 Mn 1/3 O 2 ), we also realized that, as the lithium ion transportation medium, the electrolyte also played critical roles in maintaining the battery's long-term capacity, and power density at relatively high current rate. 2 Figure 1 shows the rate test results in a conventional electrolyte (1M LiPF 6 in 1:2 EC/DEC) and a high voltage (HV) electrolyte for an NCM electrode of 120µm thick with a loading around 5mAh/cm 2 . After the cell was charged at C/10 to 4.3V, corresponding to a current density about 0.51mA/cm 2 , the discharge capacities with the HV electrolyte were dramatically increased in the range from 1C to 5C relative to those with the conventional electrolyte.…”