Modification of artificial graphite as anode material for high power lithium-ion battery
Date Issued
2011
Date
2011
Author(s)
Yeh, Tzoo-Shing
Abstract
The purpose of this study focused on the modification of artificial graphite as anode material for lithium-ion battery. The work covers two areas: (1) Unburned carbon is an industrial waste product of oil-fired fly ash. From the viewpoint of waste recycling, using ground unburned carbon and applying either acid treatment or heat treatment, this study examines the electrochemical properties of unburned carbon used as anode materials in lithium-ion batteries. (2) A homopolymer of 2-propen-1-amine layer was coated on the surface of spherical artificial graphite /carbon/ Nano-Si composite materials. The homopolymer of 2-propen-1-amine provided surface modification and an elastic network, it prevented direct material contact with the electrolyte and the silicon volume expansion caused by structure destruction.
First part：ground unburned carbon heat treatment at 2700℃, and both charge and discharge at 0.1 C, yields the first columbic efficiency of about 93.6%. Moreover, after 50 cycles, the discharge capacity is 325.5 mAhg-1, and the capacity retention is about 97.5%. On the other hand, ground unburned carbon after heat treatment at 2500ºC displayed an initial coulombic efficiency of approximately 89.8% at a charge and discharge rate of 0.1 C. The discharging capacity of this type of carbon was initially 293.7 mAhg-1, and its capacity retention was approximately 94.7% after 50 cycles. However, the initial coulombic efficiency of ground unburned carbon receiving nitric acid treatment after heat treatment increased to 91.1%, its discharging capacity increased to 318.6 mAhg-1, and its capacity retention increased to 98.5% after 50 cycles.
Second part：This study reports the coating of spherical artificial graphite/disordered carbon/silicon (AG/C/Si) with a homopolymer of 2-propen-1-amine (PAA) layer. The resulting PAA-coated AG/C/Si electrode structure did not destroy locally for large volume change. For both charge and discharge at 0.1 C, the PAA-coated AG/C/Si yielded the first columbic efficiency of about 89.1% and the first irreversible capacity decreased from 95.1 to 55.0 mAhg-1. Moreover, the discharge capacity was 410.1 mAhg-1 after 50 cycles, and its capacity retention increased to 91.5%. The addition of PAA decreased the specific surface area (BET) of AG/C/Si composites and reduced the direct contact between the anode electrode surface and the electrolyte. These results indicate that PAA-coated AG/C/Si composites have relatively lower electrochemical resistance and good cycling stability.
Subjects
lithium-ion batteries
anode materials
unburned carbon
electrochemical
high power
Type
thesis
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