Abstract
Background: LiNi1/3Mn1/3Co1/3O2 derived from the solid-state method suffers from the problem of significant irreversible charge-discharge behavior. To improve the electrochemical performance of LiNi1/3Mn1/3Co1/3O2, there are several important factors, such as starting raw materials, precursor, preparation method and conditions. In this work, the layered LiNi1/3Mn1/3 Co1/3O2 material was prepared by solid-state reaction. By varying the temperature and duration of synthesis thermal treatment, the greater crystallinity and well-ordered layered LiNi1/3Mn1/3Co1/3O2 cathode material has been successfully synthesized. The structural properties, morphology and electrochemical properties of LiNi1/3Mn1/3Co1/3O2 powders have been investigated in detail.
Methods: LiNi1/3Co1/3Mn1/3O2 cathode material was synthesized via a high-temperature solid-state method. Stoichiometric amounts of Ni(CH3COO)2•4H2O, Co(CH3COO)2•4H2O, Mn(CH3COO)2• 4H2O, and Li2CO3 as raw materials were homogenized mixed in a ball mill for 8 h at 240 rpm. By varying the temperature and duration of synthesis thermal treatment, LiNi1/3Co1/3Mn1/3O2 cathode materials with different electrochemistry performance were achieved. (a) The effect of the temperature of synthesis thermal treatment on electrochemistry performance of LiNi1/3Co1/3Mn1/3O2 was explored by calcining the above mixed powder at 800°C, 850°C, 900°C, 950°C, and 1000°C for 12 h in air at a rate of 5°C min-1. Then the target product was prepared at last. The obtained compound was named as N-800, N-850, N-900, N-950 and N-1000, respectively. (b) In order to explore the effect of the duration of synthesis thermal treatment on electrochemistry performance of LiNi1/3 Co1/3Mn1/3O2 cathode material, the above mixed raw materials were calcined at 900°C for 4 h, 8 h, 12 h, 16 h and 20 h in air at a rate of 5°C min-1. The obtained compound was named as N-4, N-8, N- 12, N-16 and N-20, respectively. The N-900 and N-12 are the same sample.
Results: The cathode material sintered at 900°C for 12 h revealed the best electrochemical performance, with high-capacity and recyclability compared with other materials. Its initial discharge capacity attains 182.4 mAh g-1 at 0.2 C in the voltage range of 2.5-4.6 V, which can be attributed to its greater crystallinity and well-ordered layered structure. Compared with other studies on lithium-ion batteries given in literature, this work provides a sample, optimal and mild synthetic conditions to synthesize the cathode materials with great electrochemistry performance.
Conclusion: A greater crystallinity and well-ordered layered LiNi1/3Mn1/3Co1/3O2 powders had been successfully synthesized by mixing raw materials under various temperatures and duration of synthesis thermal treatment. The XRD results indicated the I(003)/I(104) values of N-900 (N-12) is 1.591 larger than 1.2, which illustrates no undesirable cation mixing to be occurred. In this work, from the results of electrochemical property experiments, it can be indicated that the optimal synthesized conditions are 900°C for 12 h. When the calcination temperature is too low and the calcined time is too short, the material is poorly crystalline and has a poor layer structure. When the calcination temperature is too high and the calcined time is too long, lithium salt is evaporated completely during the calcination process resulting in a poor electrochemistry performance.
Keywords: Lithium ion battery, synthesized conditions, LiNi1/3Mn1/3Co1/3O2, cathode material, cation mixing, solid-state method.
Graphical Abstract
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