Surface Analysis of Electrodes from Cells Containing Electrolytes with Stabilizing Additives Exposed to High Temperature

Abstract

We have conducted a detailed investigation of the effect of thermal stabilizing additives, including dimethyl acetamide ͑DMAc͒, N-methyl pyrrolidone, vinylene carbonate ͑VC͒, and vinylethylene carbonate ͑VEC͒, on the reactions of the electrolyte with the surface of the electrodes in lithium-ion cells. Cells were constructed with mesocarbon microbead anodes, LiNi 0.8 Co 0.2 O 2 cathodes, and 1.0 M LiPF 6 in 1:1:1 ethylene carbonate/diethyl carbonate/dimethyl carbonate electrolyte with and without electrolyte additives. The cells were stored sequentially at 55, 60, and 65°C for 10 days at each temperature. The cells were then dismantled, and the surfaces of the electrodes were analyzed via a combination of infrared spectroscopy with attenuated total reflection, X-ray photoelectron spectroscopy, and scanning electron microscope-energy dispersive spectroscopy. The surface of the electrodes extracted from cells containing the baseline electrolyte contained thick surface films composed of electrolyte decomposition products. The addition of 1% DMAc inhibits the reaction of the electrolyte with surface of the electrodes, especially on the anode. The addition of 1.5% VC results in the formation of poly͑vinylene carbonate͒ on both electrodes and inhibits the reaction of electrolyte with the electrodes, especially the cathode. The addition of 1.5% VEC or 10% DMAc did not significantly impede the reaction of the electrolyte with the electrodes.Lithium-ion batteries have found wide application in small electronic devices due to their high energy densities. However, calendar life, performance after exposure to elevated temperatures, and safety concerns have limited application for many large power supplies, such as hybrid electric vehicles. Postmortem analyses of electrodes from lithium-ion cells that have undergone accelerated aging experiments suggest that electrolyte decomposition reactions result in the formation of surface films on both the anode and cathode. 1-4 Although degradation of the anode solid electrolyte interface ͑SEI͒ is reported to be the leading cause of capacity loss, 3 the impedance increase at the cathode side is proposed to be the main contributor to the cell impedance rise during cell aging. 4 Introducing low concentrations of additives into the electrolyte is a convenient and efficient way to impede the reactions of the electrolyte with the surface of the electrodes and improve the stability, performance, and safety of lithium-ion batteries.Various electrolyte additives have been probed to improve the performance of lithium-ion batteries. Ethylene sulfite, carbon dioxide, and 1,3-propane sulfone have been used to assist the formation of a stable SEI on the graphite anode. 5-7 Addition of sodium or potassium ions, Li 2 CO 3 , cyclohexane, and 1-methyl-2-pyrrolidinone ͑NMP͒ in the electrolyte were reported to reduce the initial irreversible capacity loss during the first formation cycle. 8-12 A family of vinyl-containing additives, including acrylic acid nitrile, vinylpyridine, vinylethylene carbonate ͑V...

Tris(trimethylsilyl)phosphite as electrolyte additive for high voltage layered lithium nickel cobalt manganese oxide cathode of lithium ion battery

“…The O 1 s spectra at 529.7 eV, 531.5 eV and 533 eV correspond to metal oxide, Li 2 CO 3 and lithium alkyl carbonates, respectively [28,29]. The peak of metal oxide appears for the cycled electrode in the standard electrolyte but cannot be observed for that TMSPicontaining electrolyte, confirming the thinner film formed on the LiNi 1/3 Co 1/3 Mn 1/3 O 2 particles.…”

Effect of propane sultone on elevated temperature performance of anode and cathode materials in lithium-ion batteries

“…New peaks are observed in the 287.5-290 eV range suggesting the presence of Li 2 CO 3 (290 eV), lithium alkyl carbonates (R-CH 2 OCO 2 Li, 287.5 eV and R-CH 2 OCO 2 Li, 288.5 eV), alkanes (285 eV) and ethers (286 eV) [6,18]. The major peaks in O 1s spectra at 531.6 eV and 532.5-533.5 eV correspond to Li 2 CO 3 and lithium alkyl carbonates (R-CH 2 O(C O)OLi (532.5 eV) and R-CH 2 O(C O)OLi (533.5 eV), respectively [6]. Analysis of the F 1s spectrum suggests three main peaks consistent with the presence of LiF (684.5 eV), and PVDF (687.6 eV).…”

“…However, commercial cells with LiPF 6 -based electrolyte have several problems, including loss of power and capacity upon storage or prolonged use, especially at elevated temperature [2,3], which complicates the use of LiPF 6 -based electrolytes in lithium-ion batteries for many large power applications, such as hybrid electric vehicles and satellites. Analyses of electrodes from lithium-ion cells that have undergone accelerated aging experiments suggest that electrolyte decomposition reactions result in the formation of surface films on both the anode and cathode [2,[4][5][6][7]. The surface layers on both anode and cathode protect the electrodes from further reaction with the electrolyte, but they also create a barrier for lithium-ion intercalation/de-intercalation which increases cell impedance and decreases cycling efficiency.…”

Inhibition of Electrolyte Oxidation in Lithium Ion Batteries with Electrolyte Additives

“…Recent investigations on the effect of the incorporation of VC into lithium ion batteries uncovered that VC reacts on the surface of the cathode. [8][9][10] There have also been several other recent reports where electrolyte additives have been reported to react on the surface of the cathode. 11,12 These results along with a recent interest in the development of higher voltage cathode materials prompted our investigation of additives designed to form passivating cathode surface films.…”