Nontraditional, Safe, High Voltage Rechargeable Cells of Long Cycle Life.

A room-temperature all-solid-state rechargeable battery cell containing a tandem electrolyte consisting of a Li-glass electrolyte in contact with a lithium anode and a plasticizer in contact with a conventional, low cost oxide host cathode was charged to 5 V versus lithium with a charge/discharge cycle life of over 23,000 cycles at a rate of 153 mA·g of active material. A larger positive electrode cell with 329 cycles had a capacity of 585 mAh·g at a cutoff of 2.5 V and a current of 23 mA·g of the active material; the capacity rose with cycle number over the 329 cycles tested during 13 consecutive months. Another cell had a discharge voltage from 4.5 to 3.7 V over 316 cycles at a rate of 46 mA·g of active material. Both the Li-glass electrolyte and the plasticizer contain electric dipoles that respond to the internal electric fields generated during charge by a redistribution of mobile cations in the glass and by extraction of Li from the active cathode host particles. The electric dipoles remain oriented during discharge to retain an internal electric field after a discharge. The plasticizer accommodates to the volume changes in the active cathode particles during charge/discharge cycling and retains during charge the Li extracted from the cathode particles at the plasticizer/cathode-particle interface; return of these Li to the active cathode particles during discharge only involves a displacement back across the plasticizer/cathode interface and transport within the cathode particle. A slow motion at room temperature of the electric dipoles in the Li-glass electrolyte increases with time the electric field across the EDLC of the anode/Li-glass interface to where Li from the glass electrolyte is plated on the anode without being replenished from the cathode, which charges the Li-glass electrolyte negative and consequently the glass side of the Li-glass/plasticizer EDLC. Stripping back the Li to the Li-glass during discharge is enhanced by the negative charge in the Li-glass. Since the Li-glass is not reduced on contact with metallic lithium, no passivating interface layer contributes to a capacity fade; instead, the discharge capacity increases with cycle number as a result of dipole polarization in the Li-glass electrolyte leading to a capacity increase of the Li-glass/plasticizer EDLC. The storage of electric power by both faradaic electrochemical extraction/insertion of Li in the cathode and electrostatic stored energy in the EDLCs provides a safe and fast charge and discharge with a long cycle life and a greater capacity than can be provided by the cathode host extraction/insertion reaction. The cell can be charged to a high voltage versus a lithium anode because of the added charge of the EDLCs.