Overcharge Investigations of LiCoO₂/Graphite Lithium Ion Batteries with Different Electrolytes

Abstract

Although overcharging has been under extensive investigation for lithium ion batteries, the mechanism underneath still remains a “dark art” with little rational understanding. In this work, the degradation behaviors of LiCoO2/artificial graphite full cells using 1 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) electrolyte or 1 M LiPF6 in EC/dimethyl carbonate (DMC) electrolyte (both with a 3/7 weight ratio) after overcharge are investigated in detail for the first time. By the means of combining liquid chromatography–quadruple time-of-flight mass spectrometry, gas chromatography–mass spectrometry, X-ray diffraction, and scanning electron microscopy, the fundamental chemistry and degradation mechanism underneath are explored thoroughly. It is found that as the cutoff voltage increases, the reactions between electrolyte and electrode become more complex. Furthermore, the EC/DEC electrolyte system is more advantageous against overcharging. The EC/DMC system goes through more severe side reactions, generating more gaseous and degradation products. Thus, the use of electrolyte with relatively large steric hindrance can slow down the reaction rate during the overcharge process and should be more advantageous. The overcharge performance and degradation mechanisms revealed in this study should be of serious consideration before implementing the cell chemistry in high-power commercial batteries.

Operando Monitoring of Electrode Temperatures During Overcharge‐Caused Thermal Runaway

“…The high terminal voltage at rupture possibly came from increase in cell internal resistance, which could originate from decomposition of electrode and electrolyte and separator shutdown. [ 18,30 ] It has been observed that LIBs overcharged at a 3 C rate had higher voltage at rupture compared with LIBs overcharged at 1 C rate. [ 39 ] The high overcharging rate can be the reason for the observed high voltage at rupture in this study.…”

“…To analyze the effect of charging rate on heat generation within the pouch cell, cell #1 was CC charged at 1 C rate up to 5.4 V. After reaching around 5.4 V, gas generation and electrode degradation in LIB became obvious. [ 11,30 ] Cell #1 was then CC charged at 5 C rate until explosion. Cell #2 was CC charged at 5 C rate constantly until cell explosion.…”

Multifunctional Fluoroethylene Carbonate for Improving High-Temperature Performance of LiNi0.8Mn0.1Co0.1O2||SiOx@Graphite Lithium-Ion Batteries

“…XPS measurements were conducted on a Thermo Fisher K -alpha (USA) XPS system to study CEI and SEI films . GC-MS measurements were adopted to analyze the electrolyte decomposition on a Thermo Scientific ISQ device . LC-QTOF-MS was performed on Xevo G2-XS QTOF (Waters Corporation, USA) to have a deeper investigation of the decomposition of the electrolyte qualitatively and quantitatively …”

“…The commercial electrolyte system usually comprises carbonate solvent and lithium salt, which undergoes reduction during the first charge–discharge cycle. As a result, SEI and CEI layers consisting of inorganic and organic decomposition compounds are formed. , In an ideal condition, the SEI and the CEI act as protective layers to prevent further electrolyte decomposition by the prohibition of the electron transport in the successive charge–discharge cycling . Through the surface films, lithium ions could intercalate into the electrode material without the structural changes of the host.…”

Stabilizing Hybrid Electrochromic Devices through Pairing Electrochromic Polymers with Minimally Color-Changing Ion-Storage Materials Having Closely Matched Electroactive Voltage Windows

“…The higher device voltage increases the probability of over-oxidation on the fast-switching ECP component before the reaction of the ion-storage materials reaches equilibrium (MO x + y Li + + y e – = Li y MO x ). Additionally, high device voltage leads to problems including interfacial electrolyte decomposition . Therefore, to stabilize ECP-based hybrid electrochromic devices, a low device voltage is beneficial. , This requires the MCC transition-metal oxide material to exhibit excellent charge-balancing capability in an electroactive window that is closely matched with that of the ECPs.…”