Characterization of an electroactive polymer for overcharge protection in secondary lithium batteries

Abstract

The optical, electronic, and electrochemical properties of thin films of the electroactive polymer, poly(3-butylthiophene) (P3BT), were studied in a lithium hexafluorophosphate electrolyte. Upon extraction of n electrons per polymer formula unit, anions are taken up to balance the charge, forming a polymer cation salt, (P3BT) mn+ (PF 6 -) mn (m is the number of formula units in the polymer chain), whose state of charge (SOC) varies with n. An in situ AC impedance method was developed to determine the electronic conductivity of the polymer at different states of charge. On oxidation of the insulating neutral P3BT polymer, the conductivity increased by eight orders of magnitude. The electrochemical potential, electronic conductivity, and optical spectrum at each state of charge were correlated, producing a color index of these primary characteristics. This allowed determination of the potential and state of charge as a function of location in transparent polymer films during propagation of an oxidation front across the film and during passage of steady-state currents through the polymer film.

Overcharge Protection for 4 V Lithium Batteries at High Rates and Low Temperatures

“…The steady state potential increased with the charging rate, resulting in increased oxidation (and electronic conductivity) of the polymers. 7 At a current density of 1.0 mA/cm 2 (2.7 C), the separator was able to maintain a voltage of 4.6 V. In this configuration, however, a steady state potential could not be maintained above…”

“…7 The current carrying properties of composite membranes coated with electroactive polymers are influenced by other factors, such as the loading of the polymer, the morphology of the deposited polymer, the porosity of the composite, and the availability of doping anions from the electrolyte. (Fig.…”

Polytriphenylamine used as an electroactive separator material for overcharge protection of rechargeable lithium battery

“…Various types of electrolyte additives, such as redox shuttles [4][5][6][7][8][9][10][11][12] and polymerizable monomers [13,14], have been proposed to protect the batteries from overcharging, but these additives can not provide sufficient shunting current at high rate charge or cause irreversible damages to batteries. In comparison, the use of electroactive polymer separator to control the charging voltage seems to be a more attractive method for overcharge protection because the polymer can be selected to switch between conductive and insulating states reversibly at required overcharging potentials and sustain sufficient high charging current [15][16][17][18][19][20].…”

“…The first electroactive polymer membrane was made of poly (3-butylthiophene) with an oxidation potential about 3.2 V (versus Li + /Li), which is quite low than the charging voltage required for controlling most of the currently used Li-ion batteries [15][16][17][18]. Subsequently, Chen et al [20] and Xiao et al [19] reported different types of bilayer electroactive polymer separators with extended high oxidation potential limits, but the bilayer configuration seems to be much more complicate for preparation and battery applications.…”

Electroactive Polymer Fiber Separators for Stable and Reversible Overcharge Protection in Rechargeable Lithium Batteries

“…[5][6][7] When incorporated into a microporous separator membrane, the elecroactive polymer remains insulating during normal cell charge and discharge, but it creates a reversible, resistive internal short upon overcharging. 8 The polymer limits the cell potential and protects the cell components from damage without restricting ion transport in the electrolyte or any significant leakage current. A bilayer configuration, in which a polymer with a higher oxidation potential is placed in contact with the cathode to set the protection voltage and a lower voltage polymer is placed next to the anode to protect the high voltage polymer from degradation at the anode potential, was later introduced to expand the operating voltage window in high-energy cells.…”