The Impact of Different Substituents in Fluorinated Cyclic Carbonates in the Performance of High Voltage Lithium-Ion Battery Electrolyte

Abstract

Ethylene carbonate (EC) has been used as the Solid-Electrolyte Interphase (SEI) former in the conventional electrolyte for decades. However, its low anodic stability leads to severe capacity decay during cycling under high voltage operation. Therefore, finding a viable electrolyte with high anodic stability and the ability to form robust SEI for high voltage lithium-ion batteries is of primary importance. In this study, a series of electrolytes containing various fluorinated cyclic carbonates as the SEI former have been designed, synthesized and evaluated. Linear sweep voltammetry study suggested that fluorinated cyclic carbonates generally possess higher anodic stability than EC. Based on the cycling performance of LiNi0.5Co0.2Mn0.3O2 (NMC532)/ graphite full cells, the electrolyte with DFEC/FEMC (1.0 M LiPF6) inhibited the oxidation side reaction on the cathode and forms a vigorous SEI on the anode. The high voltage NMC532/Graphite cell utilizing the novel electrolyte exhibits excellent cycling durability under both room and elevated temperature. The superior performance of the DFEC based electrolyte was further unveiled by SEM, EDAX and XRD. Both the anode and cathode of the full cell employing DFEC based electrolyte retained their intrinsic structures after cycling while the electrodes cycled in conventional electrolyte showed severe degradation.

An Active‐Oxygen‐Scavenging Oriented Cathode‐Electrolyte‐Interphase for Long‐Life Lithium‐Rich Cathode Materials

“…As shown in Figure S17, Supporting Information, the Nyquist plots of batteries charged to 4 V at different cycles are composed of a semicircle in the high frequency, a semicircle at medium frequency and a straight line at low frequency, corresponding to the interface impedance of CEI layer, the charge transfer resistance and the Warburg impedance, respectively. [16,23,24] After the first cycle, the CEI layer impedance and charge transfer resistance are basically similar in reference electrolyte system (R s : 22.83 Ω; R ct :53.87 Ω) and β-carotene-containing electrolyte system (R s : 31.36 Ω; R ct :49.26 Ω), indicating that the introduction of additives has little influence on the viscosity and conductivity of the electrolyte. However, with the increase of cycles, the impedance values of the two systems have changed dramatically.…”

“…Higher Mn content in the reference electrolyte system is due to the dissolution of transition metals on the cathode side at high voltage, which may be reduced to products such as MnF 2 , Mn, or MnO at the anode side. [23] But in the β-carotene-containing electrolyte system, no significant amount of Mn was observed on the anode side because of the protective layer formed by the additives. It can be observed from TEM images that the protective layer with uneven surface distribution in the reference electrolyte cannot play a protective role (Figure S15, Supporting Information).…”

High‐Voltage Electrolyte Chemistry for Lithium Batteries

“…He et al compared the oxidation potentials of different fluorinated solvents with linear sweep voltammetry, and the results showed that most of the systems replaced by fluorinated solvents had better antioxidant capacity than the common EC/EMC systems. [62] The HOMO level of sulfoxide solvents is also lower than that of conventional carbonate solvents. Moreover, it has higher electrochemical stability, which is attributed to the more electronegativity of sulfonyl group than carbonyl group, resulting in an electrochemical window of more than 5 V. Sulfone solvents have strong interactions with lithium salts to achieve high conductivity, and have lower combustibility than carbonate solvents, so they are a promising high-voltage solvent.…”

“…He et al compared the oxidation potentials of different fluorinated solvents with linear sweep voltammetry, and the results showed that most of the systems replaced by fluorinated solvents had better antioxidant capacity than the common EC/EMC systems. [ 62 ]…”

First-Principles-Based Optimized Design of Fluoride Electrolytes for Sodium-Ion Batteries

“…As discussed above, the effect of fluorination, including the aforementioned units on cyclic carbonate molecules [ 26 , 27 ], linear ethers [ 28 ], and other molecules on the LIB electrolytes, were investigated at the same time; the first-principles calculation was performed to study fluoride electrolytes for sodium-ion batteries [ 29 , 30 , 31 , 32 ]. However, limited studies have focused on the systematic design of fluoride electrolytes for SIBs based on the -CF 1 , -CF 2 , and -CF 3 units for the two types of solvent molecules.…”