Rechargeable lithium ion batteries are considered as one of the most attractive technologies to be applied on a large scale in electric vehicles and hybrid electric vehicles because of its high energy density and long service life. However, there still exist some problems to be solved on this particular aspect. For instance, graphite can react with electrolytes (∼1 V vs. Li/Li+) to form a solid electrolyte interphase film (SEI) on its surface, which causes electrolyte loss and low initial coulombic efficiency. It is therefore of great significance to find an anode material which can be used to achieve a high rate capability, long cycle life, and high safety.
Spinel Li4Ti5O12 (LTO) is considered to be a promising alternative to graphite as anode material in lithium ion batteries for electric vehicles. The spinel structure of LTO leads to the reversible lithium intercalation?deintercalation mechanism (zero-strain) and shows an excellent cycling performance. Titanium oxide with Ti4+/Ti3+ redox couple works at approximately 1.5V (vs. Li), which is far above the reduction potential of most organic electrolytes. The formation of solid-electrolyte interface (SEI) on the electrode can be mitigated and the lithium dendrites can also be avoided.
In the meantime, the chemical diffusion coefficient of Li+ in LTO is higher than that of graphite and so LTO anode can charge and discharge faster. However, the low electronic conductivity of LTO limits its high rate performance and so hinders its practical application in lithium ion batteries.
In this work, LTO is improved by adding a conductive additive, graphene plate and carbon nano-tubes(CNTs), because it shows high electrochemical performance. It is possible to achieve a uniform surface coating around the entire LTO particle. CNTs acts as a conductor to provide a conductive network through LTO particles. Graphene/CNTs added LTO anode material shows higher charge capacity at high C-rate, and it is due to the conductivity increase of anode.
LTO/graphene/CNTs compounds were prepared by conventional high temperature solid state reaction in a Li : Ti molar ratio of 4.2 : 5. Excess Li was provided to compensate for lithia volatilization during the high temperature of synthesis. The mixed reactant mixture was heated in a muffle furnace at 800℃ for 6h in Ar, followed by natural cooling to room temperature. The synthesized samples were ground before powder characterization and electrode preparation.
The New LTO/graphene/CNT presents the best discharge capacity among all the samples( at 1C-rate, 2C-rate, 5C-rate ; 138mAh/g, 127mAh/g, 100mAh/g ) and shows better reversibility and higher cyclic stability compared with pristine Li4Ti5O12.