1 research outputs found
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<sup>+</sup>-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<sup>–1</sup> of active material. A
larger positive electrode cell with 329 cycles had a capacity of 585
mAh·g<sup>–1</sup> at a cutoff of 2.5 V and a current
of 23 mA·g<sup>–1</sup> 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<sup>–1</sup> of active
material. Both the Li<sup>+</sup>-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<sup>+</sup> 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<sup>+</sup> extracted from the cathode particles at the plasticizer/cathode-particle
interface; return of these Li<sup>+</sup> 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<sup>+</sup>-glass
electrolyte increases with time the electric field across the EDLC
of the anode/Li<sup>+</sup>-glass interface to where Li<sup>+</sup> from the glass electrolyte is plated on the anode without being
replenished from the cathode, which charges the Li<sup>+</sup>-glass
electrolyte negative and consequently the glass side of the Li<sup>+</sup>-glass/plasticizer EDLC. Stripping back the Li<sup>+</sup> to the Li<sup>+</sup>-glass during discharge is enhanced by the
negative charge in the Li<sup>+</sup>-glass. Since the Li<sup>+</sup>-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<sup>+</sup>-glass electrolyte leading to a capacity increase
of the Li<sup>+</sup>-glass/plasticizer EDLC. The storage of electric
power by both faradaic electrochemical extraction/insertion of Li<sup>+</sup> 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