The negative electrode materials currently adopted in the rechargeable battery include are graphite, non-graphitic carbonaceous material, and lithium titanate.
The carbon system is classified into soft carbon (easy graphitizable carbon) and hard carbon (hard graphitizable carbon) shown in the figure below. If graphite or soft carbon is used for the negative electrode material of the battery, the discharge curve becomes flat, and if hard carbon is used, the discharge curve tends to incline.
As a result, it reaches the discharge cutoff voltage earlier than graphite type batteries.
However, in the case of charging and discharging a large current in a short time such as a hybrid vehicle (HEV) or a plug-in hybrid vehicle (PHEV), since the hard carbon negative electrode material is suitable,battery manufacturers such as Panasonic are also currently producing hard carbon for high current and lithium-ion batteries using graphite composite negative electrode for high capacity.
As for the lithium titanate negative electrode material, the charge and discharge potential is as low as about 1.5 V and it is disadvantageous in terms of energy density, but since the cycle life is long and safety during short circuit is high, it may increase adoptions in products in the future.