Effect of sodium additive on electrochemical properties of LiNi sub(0.5) Mn sub(1.5)O sub(4) for high-power lithium-ion batteries

Li sub(1-x)Na sub(x)Ni sub(0.5)Mn sub(1.5)O sub(4) (X = 0, 0.02, 0.04, 0.06 and 0.08) cathode materials have been synthesized via hydroxide co-precipitation method followed by a solid state reaction. The elementary composition, crystal structure features and electrochemical properties of the powder are studied in detail using inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), galvanostatic charge-discharge test and electrochemical impedance spectra (EIS). The results showed Na addition played an important role in the good cycling performance of LiNi sub(0.5)Mn sub(1.5)O sub(4). Charge/discharge tests revealed that the 6% Na-added sample showed a capacity retention of 94.1% at 1 C after 50 cycles in a high cutoff voltage range (3.5-4.8 V), while discharge capacity of LiNi sub(0.5)Mn sub(1.5)O sub(4) remains only 80.2% of that at 1 C. Ex-situ XRD analysis and EIS analysis indicated that the improved electrochemical properties of Na-added sample result from the more stable structure and lower resistance during the electrochemical cycling.