Alternating Current Impedance Behavior and Overcharge Tolerance of Lithium-Ion Batteries Using Positive Temperature Coefficient Cathodes

Abstract

To improve the safety of lithium-ion battery, a new conceptual cathode, which contains a positive temperature coefficient ͑PTC͒ compound consisting of a carbon black/polyethylene composite as the conductive material, was fabricated. Cells that incorporated PTC cathodes not had only good discharge characteristics but also high safety performance. To investigate the safety mechanism of PTC cathodes, alternating current ͑ac͒ impedance spectra were measured and analyzed. Based on the results of fitting, the resistance of a PTC cell which corresponds to ohmic resistance increased several fold and the resistance which corresponds to charge transfer resistance increased more than one order of magnitude at 140°C, because the electrical resistance of PTC cathodes increased at high temperature. Moreover, an overcharge test was performed for laminated prismatic PTC cells under a charge rate of 1.5 C to 10 V. The cell temperature did not increase after the short circuit, because the cell voltage reached the set voltage early and the short-circuit current barely flowed due to an increase in the cell impedance. These results indicate that cells which incorporate PTC cathodes are safer than conventional cells.

Building Safe Lithium-Ion Batteries for Electric Vehicles: A Review

“…Figure 13b illustrates the directly mixed electrode. Kise et al [236,237] put forward a carbon black/ polyethylene composite as a PTC material to blend with active materials. Zhong et al [238] prepared the cathode by mixing the EVA-based PTC material with other reagents such as binders, conductive carbon and LiFePO 4 -active materials.…”

Smart Materials and Design toward Safe and Durable Lithium Ion Batteries

“…When the LIB's inner temperature rises to the critical point (i.e., the Curie temperature), the PTC material will rapidly convert from an electrical conductor to an insulator, due to the volume expansion of polyethylene at this temperature. This nonlinear and sharp increase in electrical resistance will cut off the conductive network amongst the materials and significantly lower the peak current inside the battery, which effectively switches off the chain of chemical reactions involved in thermal runaway …”

“…To improve the high‐rate performance, a quantity of acetylene black was used in a high density PE resin composite for LCO cathode . This acetylene black modified PTC cathode showed not only better rate performance and cycle life, but also a sharp increase in impedance of several dozen times when the battery's temperature rose to over 130 °C in the case of an internal short‐circuit . During the external short‐circuit test at about 145 °C, the current was almost completely shut off, showing the high safety of such PTC embedded LCO batteries.…”

“…While self‐healing binders can repeatedly heal the microcracks of silicon anode materials during cycling, so, self‐healing design may obviously improve the cycle performance of LIBs . For PTC‐mixed or coating layer design, batteries that used PTC‐mixed cathodes containing carbon black showed better discharge characteristics and a longer cycle life than those with a PTC cathode without carbon black . This is mainly caused by the more effective conductive network created when enough conductive carbon black is used.…”

Safe positive temperature coefficient composite cathode for lithium ion battery

“…Reducing the distance between the PTC device and the electrode can be an effective strategy to make PTC device function better, and basing on this, Kise and his coworker proposed a new cathode [5] containing the PTC component, it showed an sharp and nonlinear increase in the electrode resistivity at 130e140 C due to the expansion of polyethylene at its melting point. Yang reported a new PTC contained cathode [6], in which the PTC layer is sandwiched between the common electrode and the current collector.…”