Influence of carbon additive on the properties of spherical Li4Ti5O_(12) and LiFePO4 materials for lithium-ion batteries

摘要

Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance and tap density of Li4Ti5O_(12) and LiFePO4 materials. Spherical Li4Ti5O_(12)/C and LiFePCVC composites are prepared by spray-drying-solid-state reaction method and controlled crystallization-carbothermal reduction method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer-Emmett-Teller, alternating current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical properties are obviously improved. The Li4Ti5O_(12)/C and LiFePCVC composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 gcm~(-3) and 8.26 m~2g~(-1) for spherical Li4Ti5O_(12)/C, which are 1.35 g cm~(-3) and 18.86 m~2g~(-1) for spherical LiFePCVC powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li4Ti5O_(12)/C is more than 150 mAh g~(-1) at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO4/C is close to 140 mAh g~(-1) at 1.0-C rate.