Study On The PTC Safe Electrode Of Lithium-ion Batteries

Lithium-ion batteries are now widely used in various portable electronic devices because of their intrinsic advantages of high energy density and long cycle life. However, safety is a major obstacle to limit lithium-ion batteries for commercial EV applications, and when suffered to abuse lithium-ion batteries could potentially cause catastrophic accidents. In this paper, we study on three safe electrodes-positive temperature coefficient electrodes, which can suppress thermal runaway and improve safety of the electrode.By analysis on the mechanism and compared with physical and chemical properties of PTC material, we choose high impact polystyrene(HIPS) and poly(vinylidene fluoride)(PVDF) as PTC matrix, and mainly research effect of HIPS/Ni-PTC layer, PVDF/Ni-PTC layer and PVDF/Ni-PTC film on performance of electrode. The primary methods are charge-discharge performance at constant rate, electrochemical impedancespectra (EIS), Cyclic voltammetry (CV), analysis of heat expansion and so on. The brief results are presented as follows:1. HIPS/Ni-PTC layer:PTC material containing75wt%Ni has suitable transition temperature and PTC intensity. This layer can limit mostly electrochemical reactions at90℃, and improve the ability of electrode to resist thermal runaway. However, this layer electrode suffers higher polarization and lower reversibility compared with the electrode without PTC layer at room temperature.2. PVDF/Ni-PTC layer:PTC material containing65wt%Ni is inserted to electrode.When temperature exceeds90℃, electric resistance and charge transfer resistance of elertrode increase rapidly, electrochemical reactions are all inhibited, so the ability of cut-off overheat can be improved. PVDF/Ni layer can advance interface between Al foil and active material layer, reduce the polarization and improve the power performance.3. PVDF/Ni-PTC film:The PTC film is chose to replace the current collector-Al. This PTC film electrode can absolutely prevent electrochemical reactions at90℃and the electrochemical performance of this electrode is similar to that of the electrode used Al foil as current collector. There are30figures,2tables and89references in the paper.