Studying a Phenomenon during Overcharge of a Lithium-Ion Battery with Methacrylate Additives for the Gel Electrolyte

Abstract

A lithium-ion battery containing methacrylate compounds as "additives" in the gel electrolyte has been developed such that an increase in its voltage greater than normal does not cause a thermal runaway. This phenomenon was studied by analysis of the positive active material, lithium cobaltate ͑LiCoO 2 ͒, by measurement of the species on the negative electrode and the composition of the generated gases, and by estimating the abundance of the species in the electrolyte after/during charging the battery. The potential of the positive electrode maintained a constant value, the crystals of the positive material did not change, metallic Li and oxides of Li were produced on the negative electrode, CO 2 and CO were generated, and the relative abundance of the species from the additives did not change during overcharging of the battery. We postulated that, in the lithium-ion battery sample with the additives, oxygen gas and/or carbon dioxide gas is generated at the positive electrode during overcharge, moves to the negative electrode, and oxidizes the Li deposited on the negative electrode. This reaction process has been suggested to be similar to that observed on overcharging of Ni-Cd or Ni-MH sealed batteries, and the battery with the additives remained safe during the overcharge. The lithium-ion battery has been developed for cellular phones and notebook PCs since it was put to practical use in 1991.1 At that time, the lithium-ion battery was manufactured using lithium cobaltate ͑LiCoO 2 ͒, lithium nickelate ͑LiNiO 2 ͒ or lithium manganate ͑LiMn 2 O 4 ͒ as the positive electrode material, carbon that could intercalate and release lithium ion as the negative electrode material, and an organic solvent that dissolves the lithium salt as the electrolyte. 2-4The lithium-ion battery with LiCoO 2 as the positive material was put into practical use earlier than LiNiO 2 and LiMn 2 O 4 because it has good characteristics which are a high discharge voltage and a long cycle life. [5][6][7] Recently, the lithium-ion battery has been expected to be used in electric vehicles and the HEV; 8 therefore, a less expensive and more long-lived battery has been requested. Because the cobalt reserves are extremely low at about eight million t/year and are expensive, 9 LiCoO 2 is expected to shift to LiNiO 2 and LiMn 2 O 4 in the future. However, the discharge voltage of the lithium-ion battery with LiNiO 2 as the positive material is low, about 3.8 V. The synthesis of LiNiO 2 is difficult and the cycle life of the lithium-ion battery with LiNiO 2 is shorter because LiNiO 2 , which has the unstable state of Ni 3+ at high temperature, easily becomes a nonstoichiometric compound.10-12 Although LIMn 2 O 4 is less expensive and thermally stable, the capacity of the lithium-ion battery with LiMn 2 O 4 during cycle life decreases remarkably because manganese elutes into electrolyte easily.5,13,14 Therefore, advanced developments are needed so that the lithium-ion battery with LiNiO 2 or LiMn 2 O 4 can be put into practical use, and the lithiumion ...

Approach of Development of Electric Double Layer Capacitor for High Power and Long Life

“…The positive and negative electrodes were selected by a predetermined weight. An element with the positive electrode and the negative electrode and the reference electrode which was made by welding Al ribbon to an etched Al foil [16] alternately stacked with the polyethylene film separators (NI040A, Nippon Sheet Glass Co., Ltd.) was constructed.…”