A Quantum Chemical Study on Cathode Active Materials of Organic Radical Molecules in Secondary Battery.pdf

1、Recently，lithium-ion (Li-ion) batteries have been used as the power supply of smartphones and electric cars owing to the high energy density and high power density as well as long life and environmental friendliness. How

2、ever，Li-ion batteries with lithium cobalt oxide (LiCoO2) as the cathode-active material have faced serious resource problems because of the high cost of cobalt (Co) atoms in cathode active materials. For the resolution o

3、f these problems，in 2011，Y. Morita et al. proposed organic radical-molecules as cathode active materials such as a 6-oxophenalenoxyl (6OPO)，a tri-tert-butylated trioxotriangulene ((t-Bu)3TOT) and a tribrominated trioxotr

4、iangulene (Br3TOT). These organic radical-molecules do not contain expensive and heavy Co atoms in these organic radical-molecules，successfully achieving Co-free lithium-ion batteries. Additionally，these small organic mo

5、lecules have received broad attention due to their innovative physical properties such as multi-stage redox activities (6OPO+2e-?6OPO2-，and R3TOT+4e-?R3TOT4-with R being t-Bu or Br) resulting in a higher capacity and str

6、ong one-dimensionalπ―πstacking in crystals leading to a low solubility. However，the mechanism of the multi-stage redox behaviors still remains to be accounted for. To solve this problem，theoretical investigations can gre

7、atly aid in explaining the experimentally observed multi-stage redox behaviors.
　　Firstly，the electron state changes were investigated in the process of adding electrons to elucidate the mechanism of the multi-stage r

8、edox reactions. As a result，the energy levels of singly occupied molecular orbital (SOMO) and lowest unoccupied molecular orbital (LUMO) were elevated by adding electrons gradually. Secondly，Li adsorption patterns were i

9、nvestigated by using quantum chemical calculation. We elucidated the lowest energy conformation for the Li adsorption patterns by replacing the Li atoms in all possible initial positions and by relaxing the only Li atoms

10、 from geometry optimization calculation at the monomer and dimer level. Additionally，Li adsorption patterns were analyzed in the stacked Br3TOT hexamer by using Elongation (ELG) method. It was found that Br3TOT hexamer a

11、dsorbing 6 Li atoms by three-times rotated alternative between the oxygen atoms was the most stable at the 1st stage reaction. Thirdly，the interaction energy between organic radical molecules and Li atoms was investigate

12、d at each stage reaction. The results show the difficulty of the 5th stage reaction at both dimer and hexamer level，which agrees with the experimental results. Finally，the method to estimate the spin state varied with ch

13、anges in temperature was developed by considering the medium spin states between the high and low spin states. It is inferred from this method that one-dimensional crystal of Br3TOT maintains the radicals at room tempera