Unraveling the Structural Instability of Li(Ni0.80Co0.15Al0.05)O2 as a Cathode Material Due to Operating a Li‐ion Battery

The change of the crystal structure for Li(Ni0.80 Co0.15 Al0.05 )O2 as a cathode material in a Li-ion battery is traced. During charging and discharging, the crystallographic change of Lix (Ni0.80 Co0.15 Al0.05 )O2 (x ≈ 1.0-0.25) is confirmed with in situ X-ray diffraction, an electrochemical measurement, and the density functional theory calculation. Li atoms after cycling do not completely return to the initial state and defects in the Li-layer generate about 5%. The effect of defects in the Li-layer reveals the transformation of crystal structure and the change of lattice constants. Upon increasing the temperature, the instability of Li0.95 (Ni0.80 Co0.15 Al0.05 )O2 is clearly shown as the movement of transition metals using X-ray and neutron diffraction. The crystallographic values dramatically change upon increasing from 373 to 423 K, but linearly vary upon decreasing temperature. Furthermore, the result of the calculation demonstrates that the possible atom for mixing is Ni. The evolution of magnetic properties explicitly certifies the atomic movement that gives rise to a spin-glass state through the induction of ferromagnetism. In conclusion, defects are created in crystal structure during operation of the Li-ion battery and generate structural instability. The results provide the cause and mechanism of the degradation of cathode material in a Li-ion battery.