Synthesis, characterization, and electrochemistry of cathode material Li[Li_0.2Co_0.13Ni_0.13Mn_0.54]O ₂ using organic chelating agents for lithium-ion batteries

Oxalic acid, tartaric acid (TA), and succinic acid (SA) are studied as chelating agents for sol-gel synthesis of Li[Li_0.2Co _0.13Ni_0.13Mn_0.54]O₂ as a cathode material for lithium-ion batteries. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy show that the materials are single-phase compounds with good crystallinities and layered α-NaFeO ₂ structures. The TA-material has the smallest particles (0.2-0.3 μm), with a smooth surface, and uniform distribution. Electrochemical studies indicate that the TA-material exhibits the highest initial discharge capacity (281.1 mAh g^-1 at 0.1 C, 192.8 mAh g^-1 at 2.0 C), the highest reversible capacity after 50 cycles (240.5 mAh g^-1 at 0.1 C, 167.4 mAh g^-1 at 0.5 C), and the best rate performance. The cycling stability of the SA-material is the best, with capacity retentions of 87.4% at 0.1 C and 80.1% at 0.5 C after 50 cycles. Mn^4+/3+ reduction peaks appear at the first discharge process and become more evident with increasing cycle number, resulting in a spinel structure, as proved by cyclic voltammetry and differential capacity curves. Electrical impedance spectroscopy confirms that the low charge-transfer resistance of the TA-material is responsible for its superior discharge capacity and rate performance.