THESIS
2015
xiv, 90 pages : illustrations ; 30 cm
Abstract
Lithium-ion battery is one kind of electrochemical energy storage system that has great potential in wide applications. However, lithium-ion battery has its own challenges, such as high cost, limited capacity, etc. One way to meet the challenges is to get high voltage and
also high specific capacity cathode material. The research objectives of the present study are
to investigate the mechanism of the lithium ion activation in Li
2CoP
2O
7, a kind of high voltage and capacity cathode material, and evaluate methods that can improve the specific
capacity of Li
2CoP
2O
7 by advanced simulation algorithm is used in this study.
The algorithm employed in all calculation in this study is called density functional
theory (DFT), which is based on physical laws and requires no experimental inputs....[
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Lithium-ion battery is one kind of electrochemical energy storage system that has great potential in wide applications. However, lithium-ion battery has its own challenges, such as high cost, limited capacity, etc. One way to meet the challenges is to get high voltage and
also high specific capacity cathode material. The research objectives of the present study are
to investigate the mechanism of the lithium ion activation in Li
2CoP
2O
7, a kind of high voltage and capacity cathode material, and evaluate methods that can improve the specific
capacity of Li
2CoP
2O
7 by advanced simulation algorithm is used in this study.
The algorithm employed in all calculation in this study is called density functional
theory (DFT), which is based on physical laws and requires no experimental inputs. The
average voltages of different redox reactions, the volume change, and the density of states of
Li
xCoP
2O
7 (x= 2, 1.5, 1, 0.5, 0) were calculated and discussed. The main reason why the second lithium ion cannot be activated in Li
2CoP
2O
7 was that the redox reaction potential of
O
2-/O
γ- is much higher than the upper limit of the electrolytes' working windows.
With the understanding of the lithium ion activation mechanism, a way to activate the
second lithium ion in Li
2CoP
2O
7 is proposed throughTi
2+ substitution. The properties and the lithium ion activation mechanism of the Ti
2+ substitution material Li
2Ti
0.5Co
0.5P
2O
7 were also
investigated by the density functional theory. Compared with Li
2CoP
2O
7, Li
2Ti
0.5Co
0.5P
2O
7 has smaller volume change (~2.5%) during the lithium ion activation and may have a better cycling performance. Meanwhile, 75% theoretical specific capacity of Li
2Ti
0.5Co
0.5P
2O
7 can be activated in the commercial electrolytes' working windows (from 1.5 to 4.9V) during charging and discharging processes.
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