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 Li₂CoP₂O₇, a kind of high voltage and capacity cathode material, and evaluate methods that can improve the specific capacity of Li₂CoP₂O₇ 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....[ Read more ]

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 Li₂CoP₂O₇, a kind of high voltage and capacity cathode material, and evaluate methods that can improve the specific capacity of Li₂CoP₂O₇ 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_xCoP₂O₇ (x= 2, 1.5, 1, 0.5, 0) were calculated and discussed. The main reason why the second lithium ion cannot be activated in Li₂CoP₂O₇ 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 Li₂CoP₂O₇ is proposed throughTi²⁺ substitution. The properties and the lithium ion activation mechanism of the Ti²⁺ substitution material Li₂Ti_0.5Co_0.5P₂O₇ were also investigated by the density functional theory. Compared with Li₂CoP₂O₇, Li₂Ti_0.5Co_0.5P₂O₇ has smaller volume change (~2.5%) during the lithium ion activation and may have a better cycling performance. Meanwhile, 75% theoretical specific capacity of Li₂Ti_0.5Co_0.5P₂O₇ can be activated in the commercial electrolytes' working windows (from 1.5 to 4.9V) during charging and discharging processes.