CO[sub 2] Gas Evolution on Cathode Materials for Lithium-Ion Batteries

Abstract

The gas evolution related to the film formation on cathode materials for lithium-ion batteries was studied using differential electrochemical mass spectrometry and subtractively normalized interfacial Fourier transform infrared spectroscopy. With both methods the oxidative formation of CO 2 was observed in standard battery electrolytes. We show the strong influence of the type of the electrolyte and especially of the additive, vinylene carbonate ͑VC͒, as well as the effect of the temperature on the CO 2 gas formation rate. The VC additive significantly reduces the gas formation rate in the commonly used voltage window between 3.0 and 4.3 V. Long cycling experiments show that test cells containing VC have a higher cycling stability compared to cells cycled without this additive. Cycling at elevated temperatures ͑60°C͒ results in a high, enduring CO 2 gas evolution, already starting at a lower cell voltage of about 3.5 V.In the current generation of commercially available lithium-ion batteries, graphitic carbon is used as the anode material and insertion oxides as the cathode material. The electrochemical potential of both electrode materials is far beyond the thermodynamic stability window of the commonly used organic electrolytes. Hence, reductive and oxidative electrolyte decomposition occurs, leading to gas evolution in the electrochemical cell. This process increases the internal cell pressure, which may raise the safety risk due to possible cell leakage. The calendar life of the cell would be shorter, too. Fortunately the solid electrolyte interphase ͑SEI͒ formed at the surface of the negative electrode material prevents further reductive electrolyte decomposition. A similar protective film is also reported for positive electroactive materials such as LiMn 2 O 4 and LiCoO 2 , but the two-decades-old discussion about the SEI on positive electrodes is still controversial and the influence of this film formation process on the behavior of the cells is still a matter of intense investigations. [1][2][3] Different in situ methods like Fourier transform infrared ͑FTIR͒ and Raman spectroscopy as well as scanning electron microscopy ͑SEM͒ have been successfully introduced for the examination of film formation on the electrode surface. 4-9 Recently we were able to show that it is possible to observe the film formation on cathode materials with post mortem SEM. 10 The results of this work proved that various parameters like type of cathode material, electrolyte composition ͑in particular the application of certain additives͒, and the temperature affect the extent of the formation of the cathodic SEI. From investigations on graphite anode material it is known that the film formation is often accompanied by gas evolution. 11-13 The same has also been reported for different cathode materials. 14 It has been shown that primarily CO 2 is formed by oxidative decomposition processes on the oxide surface. 15 Obviously, in an extreme case the CO 2 evolution could lead, over a longer period of time, to a reduced life time of the...

Direct evidence of oxygen evolution from Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 at high potentials

“…4). The CO 2 evolution is due to the electrolyte oxidation, as demonstrated by us for a number of electroactive oxides elsewhere [14,15]). In contrast, for the overlithiated NMC oxide, both CO 2 and O 2 evolution is observed in the high voltage region but only during the first cycle.…”

“…Experimental details on both the DEMS method and the used cell are given in [13,14]. The DEMS experiments were performed at 25°C in a separator-free cell accommodating metallic lithium counter and oxide working electrode, respectively, on titanium current collectors.…”

“…Figure 2 shows that, for the stoichiometric sample, neither the peak shape nor the peak potential change significantly during both HV and LV experiments indicating that the course of the repeated lithium de-intercalation and re-intercalation process remains basically unchanged. The peak in the high voltage region ([4.5 V) is assigned to the electrolyte oxidation [14].…”

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

“…6 Especially gas evolution is a formidable technological and fundamental challenge 7 since gas generated in hermetically sealed batteries can lead to detrimental effects: on the one hand, gas generation during storage results in a diminished shelf life and eventually a markedly reduced cycle lifetime. 8 On the other hand, gas evolution during cycling leads to electrolyte displacement, 9 which causes a decrease of Li-ion diffusion and/or Li-ion conduction in the electrolyte and ultimately contributes to a tremendous increase of battery resistance. 10 In both cases, the internal pressure build-up may also induce battery bulging, mechanical stress inside the electrodes and even severe gas leakage, 11 all of which are detrimental to longevity and reliability of energy storage battery systems.…”

Investigating Li2NiO2–Li2CuO2 Solid Solutions as High-Capacity Cathode Materials for Li-Ion Batteries

“…The CO 2 detected could originate from side reactions with the electrolyte, surface contaminants, or from excited O release from the oxide electrode. 42,43 Beginning at ∼4.0 V, there was a burst of O 2 evolution not explained by electrolyte oxidation, suggesting that lattice oxygen ions were directly involved in the redox reaction. 9,21 The gas evolution measurement provides useful insights into the understanding of anionic oxygen redox during charge, especially in the high voltage region.…”