Succinic Anhydride as an Enabler in Ethylene Carbonate-Free Linear Alkyl Carbonate Electrolytes for High Voltage Li-Ion Cells

Abstract

Ethylene carbonate-free electrolytes containing 1 M LiPF 6 in ethyl methyl carbonate with succinic anhydride as an enabler exhibited promising cycling and storage performance in Li(Ni 0.4 Mn 0.4 Co 0.2 )O 2 /graphite pouch type Li-ion cells tested to 4.5 V. Although cells using 1 M LiPF 6 in EMC can barely function due to the poor passivation of the graphite electrode, the addition of 1% succinic anhydride allows cells to operate well. Compared to other enablers such as vinylene carbonate, succinic anhydride provides similar cycling and storage performance at 40 • C and improved storage or cycling performance at 60 • C. Succinic anhydride also limits gas evolution, especially at high temperatures where cells with vinylene carbonate normally produces large amounts of gas. Symmetric cell studies showed that adding succinic anhydride to cells greatly increased the impedance of the graphite electrode after formation. However, the impedance of the graphite electrode decreased substantially during cycling, leading to a significant decrease of impedance in the full pouch cells. With succinic anhydride as an enabler, ethylene carbonate-free linear alkyl carbonate electrolytes may be suitable for high temperature applications in some Li-ion cells. Long life and energy dense Li-ion cells are attractive to battery manufacturers and electric vehicle (EV) makers. Cycling a Li-ion cell to higher voltage increases its energy density but normally decreases cell lifetime. This is because electrolyte solvents are unstable at high voltages and the positive electrode/electrolyte interface becomes more reactive as the potential increases.1,2 Recent results have shown that ethylene carbonate (EC) itself is responsible for many issues associated with the operation of NMC/graphite cells to high potentials. 3,4 Reactions involving EC at the positive electrode cause gas evolution and impedance growth, leading to cell failure. Such reactions become very problematic above 4.5 V vs. Li/Li + regardless of the electrolyte additives used. 5The removal of EC has been shown to enhance high voltage performance of NMC(442)/graphite cells at both room temperature and high temperature.4 When used at small loadings, several cyclic carbonates including vinylene carbonate (VC), fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DiFEC), can enable the use of linear alkyl carbonate-based electrolytes without ethylene carbonate.3 The cycling performance of these EC-free electrolytes was determined to be dependent upon the initial loading of passivating agent added, which must be high enough to passivate the graphite electrode, yet low enough to ensure low impedance (for VC and DiFEC) and low gassing during cell use. The addition of co-additives helps lower polarization growth during high voltage cycling. 4 Problems with EC-free ethyl methyl carbonate (EMC)-based electrolytes include gas evolution during both cycling and storage at high temperatures. Figure S1 (supporting information) shows open circuit voltage (OCV) versus time as well as gas ...

Highly Fluorinated Interphases Enable High-Voltage Li-Metal Batteries

“…At a high potential of 5.0 V, the anodic current density in 10 M LiFSI-EC/DMC electrolyte is only 1/100 that of 4 M LiFSI-DME or 1/7 that of 1 M LiFSI-EC/DMC electrolyte. As indicated by Dahn et al, 48 the oxidation of carbonate solvents (especially EC) at a high voltage is usually responsible for impedance growth and cell failure. The excellent oxidation stability of concentrated LiFSI-EC/ DMC electrolyte can be ascribed to the following two reasons: (1) the less stable organic component in possible cathode interphase is largely reduced because of the much lower presence of solvent in the concentrated electrolytes (Figure S15); and (2) a fluorine-rich interphase, which is mainly from anion oxidation, passivates the cathode surface and stabilizes the electrolyte solvents ( Figure S16).…”

All-Climate High-Voltage Commercial Lithium-Ion Batteries Based on Propylene Carbonate Electrolytes

“…Lithium-ion batteries (LIBs) have developed rapidly in the past few decades, have occupied the market of portable devices and electric vehicles, and now are moving toward a large-scale energy storage market. − Recently, LIBs are required to have higher energy density, longer lifespan, and wider operating temperature to meet the application requirements. Nevertheless, the currently used ethylene carbonate (EC)-based electrolytes become the bottleneck for next-generation LIBs because EC has a high melting point of 36.4 °C, which hinders the low-temperature performance of LIBs. − More critically, EC has the limited electrochemical window of 4.3 V; thus, it is easily oxidized on the surface of the high-nickel cathodes with strong catalytic activity, leading to the decomposition of electrolytes, gas evolution, and the performance degradation of batteries. − So, it is crucial to develop EC-free electrolytes with modified properties for the purpose of next-generation LIBs. − …”

Lessons Learned from Long-Term Cycling Experiments with Pouch Cells with Li-Rich and Mn-Rich Positive Electrode Materials

“…Upper cut-off was limited to 4.6 V because very little capacity can be gained when increasing UCV from 4.6 V to 4.7 V while the extent of parasitic reactions increases considerably. 38,54 Panels e-h in Fig. 5 show that LNMA-2 cells have the same amount of graphite (300 mAh) as LNMA-1, but the positive electrode loading has been reduced which translates to lower cell capacities at full SOC.…”