Rapid Impedance Growth and Gas Production at the Li-Ion Cell Positive Electrode in the Absence of a Negative Electrode

Abstract

The effects of electrolyte additives on gas evolution, gas consumption and impedance growth at elevated temperature have been studied using Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells and pouch bags containing delithiated NMC442 or lithiated graphite electrodes plus electrolyte. It was found that there was much more gas, mostly CO 2 , generated in pouch bags containing charged positive electrodes than pouch cells. It was found that the impedance of the charged positive electrodes stored in pouch bags increased dramatically, while those stored in pouch cells did not. The two observations show that there are interactions between positive and negative electrodes that limit gas evolution and reduce impedance growth in Li-ion cells. To verify this, CO 2 intentionally added to pouch bags containing lithiated graphite and electrolyte was consumed. The use of several electrolyte additives, known to affect gassing and high voltage cycling did not substantially alter these conclusions. XPS studies were used to eliminate some possible mechanisms responsible for these phenomena. Lithium-ion battery packs for electrified vehicles and grid energy storage need longer lived cells, operating over a wide range of temperatures. A pouch-type lithium-ion cell, cycled at elevated temperature, may experience volume expansion due to gas production, leading to rapid capacity fade.1-6 When Li-ion cells are charged above 4.2 V, reactions between the electrolyte and the positive electrode can cause charge-transfer impedance (R ct , electron transfer and diffusion of lithium ions through the SEI) growth at the positive electrodeelectrolyte interface, depletion of liquid electrolyte, capacity loss and eventual cell failure.7-12 The use of electrolyte additives is an effective way to suppress gas evolution and impedance growth for cells cycled at high voltage and high temperature. [13][14][15][16][17][18][19] Xia et al. and Li et al. found that prop-1-ene-1,3-sultone (PES) suppressed gas evolution when cells were cycled to an upper cutoff voltage of 4.2 V at elevated temperature.13,14 Nie et al. found that pyridine boron trifluoride (PBF) also suppressed gassing at high temperature, when cells were cycled to 4.4. [16][17][18] Vinylene carbonate (VC) is a popular additive which is widely used in industry and has been extensively studied. [20][21][22][23][24] This additive can cause severe gas evolution at high temperature and high voltage if residual VC remains in the electrolyte after the formation cycle. 26-28 However, impedance growth for NMC442/graphite cells containing these additives or additive blends cannot yet be controlled as the cutoff voltage increases above 4.4 V.27 Figure 1 shows that the impedance of NMC442/graphite cells increases dramatically as the cycle number increases. Symmetric cells made from electrodes harvested from pouch cells tested above 4.4 V showed that the impedance growth originates from the positive electrode ( Figure 1b) rather than from the negative electrode (Figure 1c). Detailed informa...

Prospect and Reality of Ni‐Rich Cathode for Commercialization

“…[56,58,60] Furthermore, the gas consumption in the full cell was closely associated with the reduction of the carbon dioxide at the anode, forming the lithium carbonate, carbon monoxide, hydrocarbons, and polyethylene. [34,[61][62][63][64] The gassing behavior at ≈4.3 V was caused by the electrochemical decomposition of the residual lithium compounds and electrolyte at the cathode, resulting in the formation of the carbon dioxide (Figure 4e,f). [14,60] Moreover, the ethane gas could be oxidized to the carbon dioxide by the nucleophilic reaction.…”

Chromatographic Techniques in the Research Area of Lithium Ion Batteries: Current State-of-the-Art

“…FID [234] FTIR [198] MS [198,235] TCD [234,[236][237][238][239][240] VUV [217] n/a [241,242] Model Aging of LIB Components (Thermal; Radiolysis, etc.) FTIR [243,244] MS [151,207,208,211,[243][244][245][246][247][248][249][250] TCD [207,208,249,250] n/a [251][252][253] The analyses of permanent gases emerging during the formation procedure was investigated by a variety of different research groups. Yoshida et al [57] focused their work on open prismatic cells and their findings are already discussed in 3.3, while Ota et al [228] used an assembly-type cell (stainless steel).…”

Calendar Aging and Gas Generation in Commercial Graphite/NMC-LMO Lithium-Ion Pouch Cell

“…In a series of publications, Dahn and co-workers used gas chromatography (GC-MS and GC-TCD) and a lab-made apparatus based on Archimedes' principle to investigate gas generation during the formation cycles of batteries filled with various electrolyte formulations. [14][15][16][17][18][19][20] The gaseous species were shown to be mostly generated at the onset of the first charging step (i.e., low voltages) and then almost entirely consumed throughout the remainder of the formation period.…”