Modification Of Li Rich Cathode Material With Low Co Content For Lithium-ion Batteries

The lithium ion batteries?LIBs? have a rapid development since its coming out. Indeed,LIBs have been used in many fields. Yet, they suffer from problems such as short cycle life and poor safety. Furthermore, the cathode is a vital factor in restricting further scale application of LIBs. In recent years, the rich lithium materials denoted as x Li₂ Mn O₃·?1-x?Li MO₂?0< x< 1, M= Mn, Co, Ni? caused much attention due to the high specific capacity and low cost. This article synthesized Li rich materials with low cobalt considering the high cost and toxicity of Co. And doping modification was carried on to improve the cycling performance of these materials.The Mg doped Li_1.17Ni_0.25Mn_0.58O₂ materials were synthesized via co-precipitation method, and the effect of Mg doping on the material structure and electrochemical performance of the material was explored. The results show that the composites have well layer structure, and the average particle size is 200 nm. Moreover, the discharge capacity is improved with the doping. The first discharge capacities of Li_1.17Ni_0.25-x Mn_0.58 Mgx O₂?x= 0,0.01, 0.02, 0.05? are 116.6, 142, 155.9 and 155.9 m Ah·g^-1 at 2 C, respectively. These materials still obtain 107.8, 127.6, 148.3 and 54.5 m Ah·g^-1 after 100 cycles. It shows that the material has excellent cycling performance as the doping amount is 2%, and it achieves a first discharge specific capacity of 214.1 m Ah g^-1 at 55 °C.The Al doped Li_1.2Mn_0.56Ni_0.16Co_0.08O₂ cathodes were synthesized through sol-gel process. SEM images show that the average particle size is of 100-200 nm. The particle size and the structure of the materials have no apparent change after doping. The 0.05 Al doped Li_1.2Mn_0.56Ni_0.16Co_0.08O₂ shows the best rate performance. The first specific capacity of the pure and Li_1.2Mn_0.56Ni_0.16Co_0.03Al_0.05O₂ are 164.4 and 225.4 m Ah·g^-1 at 0.2 C.Capacity retention of the two materials are 78.7% and 99.3% under 2 C after 100 cycles.CV tests show that a certain amount of Al doping can reduce the the electrochemical polarization of the electrodes. Besides, electrode polarization is minimized as Al doping amount is 0.05. EIS spectra indicates that the charge transfer resistance becomes smaller after doping, and the lithium ion diffusion coefficient becomes larger.The Fe doped Li_1.2Mn_0.56Ni_0.16Co_0.08O₂ cathodes were prepared by sol-gel method. XRD pattern shows that the powders obtained have well layer structure, and the doping of Fe³⁺does not change the structure. The doping has no apparent change in the morphology, butthe surface of the materials agglomerates. The first discharge capacity of Li_1.2Mn_0.56Ni_0.16Co_0.08-x Fex O₂?x= 0, 0.01, 0.03, 0.05 and 0.08? are 70.8, 79.6, 85.8, 108.9,and 82.6 m Ah·g^-1 at 2 C, respectively. These materials still obtained 73.2, 75.2, 85.3, 104.7and 74.8 m Ah·g^-1 after 100 cycles. Cyclic voltammograms tests show that doping one Li_1.2Mn_0.56Ni_0.16Co_0.03Fe_0.05O₂ has lower potential difference, indicating better reversibility.EIS spectra shows that the charge transfer resistance Rct decreases with the doping. The composite displays smaller resistance in the insertion of lithium ion, which is more conducive for the lithium ion. The diffusion coefficient of the pure and Li_1.2Mn_0.56Ni_0.16Co_0.03Fe₍0.05_O2 are 3.67×10^-17 and 2.52×10^-16 cm²·s^-1 after calculation, which indicates that the diffusion coefficient increases with doping.