The Effect of the Fluoroethylene Carbonate Additive in LiNi_0.5Mn_1.5O₄- Li₄Ti₅O₁₂Lithium-Ion Cells

Abstract

The effect of the electrolyte additive fluoroethylene carbonate (FEC) for Li-ion batteries has been widely discussed in literature in recent years. Here, the additive is studied for the high-voltage cathode LiNi 0.5 Mn 1.5 O 4 (LNMO) coupled to Li 4 Ti 5 O 12 (LTO) to specifically study its effect on the cathode side. Electrochemical performance of full cells prepared by using a standard electrolyte (LP40) with different concentrations of FEC (0, 1 and 5 wt%) were compared and the surface of cycled positive electrodes were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results show that addition of FEC is generally of limited use for this battery system. Addition of 5 wt% FEC results in relatively poor cycling performance, while the cells with 1 wt% FEC showed similar behavior compared to reference cells prepared without FEC. SEM and XPS analysis did not indicate the formation of thick surface layers on the LNMO cathode, however, an increase in layer thickness with increased FEC content in the electrolyte could be observed. XPS analysis on LTO electrodes showed that the electrode interactions between positive and negative electrodes occurred as Mn and Ni were detected on the surface of LTO already after 1 cycle. 1 In addition to the high voltage plateau, the intrinsic structure of the spinel phase allows fast lithiation and de-lithiation kinetics 2,3 which is attributed to the 3-D lithium transport among the available tunnels in the crystal. 4 The advantage of higher voltage (thus higher energy density) and good power capability are two main reasons behind the growing interest for this material, especially for electric vehicle applications. However, the electrode material is prone to side reactions with conventional electrolytes, not least electrolyte decomposition at high voltages and transition metal dissolution from the spinel structure, particularly observed at elevated temperatures. These obstacles need to be resolved before wide-scale commercial application of LNMO electrodes. 5,6 One possible approach to overcome these problems is to use electrolyte additives that could ideally form an in-situ passivating layer on the positive electrode surface, similarly to the solid electrolyte interphase (SEI) observed on negative LiB electrodes. 7,8 A number of electrolyte additives have been reported in recent years for the purpose of passivating the cathode/electrolyte interface at high operating voltages.7 Some of these additives include LiBOB, 9 succinic anhydride, 10 HFiP 11 and DMMP. 12 It is important to note that the use of such cathode interface additives should also be compatible with the anode interface in full cells, or vice versa for additives intended for the anode side. Therefore, it is essential to study the effect of anode additives on the cathode side as well, if new fullcell chemistries are to be realized. Fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are common examples of such additives where the former has been used mostly to improve an...

Tuning Two Interfaces with Fluoroethylene Carbonate Electrolytes for High-Performance Li/LCO Batteries

“…Although the electrolytes showed high cycling stability of the Li-metal electrode, side reaction of FEC at the LCO cathode may cause the lower initial discharge capacities. 41 To verify the FEC decomposition and consequent LCO passivation for the electrolytes with high FEC contents, we also conducted a three-electrode impedance analysis for the Li/LCO cells with the control and 70FEC/30DEC electrolytes. As shown in Figure S6a, the cathode impedances for the control and 70FEC/30DEC electrolytes in the fully charged state after the first cycle exhibited two semicircles; the high frequency (500 Hz) and low frequency (5 Hz) semicircles are associated with Li + ion migration through a CEI film and with the charge-transfer process, respectively.…”

Degradation of high-voltage cathodes for advanced lithium-ion batteries – differential capacity study on differently balanced cells

“…The measurements shown here were carried out with ordered LNMO and Whatman® separators. Aktekin et al and Xiang et al showed longer cycle stability with disordered LTO/LNMO full cells with Celgard® separators [28,29]. However, the performance of the cells is not priority in this article but the mechanism of the degradation.…”

Artificial Interface Derived from Diphenyl Ether Additive for High‐Voltage LiNi0.5Mn1.5O4 Cathode

“…Different families of additives had proven their ability to improve the electrochemical performances of LNMO based cells. [18][19][20][21][22][23][24] Tu et al [19] found that trimethylsilyl cyclopentadiene as a novel electrolyte additive afforded a protection layer on LiNi 0.5 Mn 1.5 O 4 electrode surface, inhibiting additional electrolyte decomposition and transition metal dissolution for high temperature application of LiNi 0.5 Mn 1.5 O 4 . Xu et al [23] reported that addition of 0.5 wt% tri (pentafluorophenyl) phosphine (TPFPP) to the baseline electrolyte increased the capacity retention from 70.3 % to 85.0 % of its initial capacity for LiNi 0.5 Mn 1.5 O 4 after 55 cycles (0.2C).…”

“…In the past few years, scientists were dedicated to searching for film‐forming additives that can be oxidized prior to the carbonate‐based electrolyte and formed a protective film to suppress further oxidative decomposition of the electrolyte and protect the active cathode from destruction at room and elevated temperature. Different families of additives had proven their ability to improve the electrochemical performances of LNMO based cells . Tu et al .…”