Synthesis And Modification Of LiNi

LiNio.8Coo.1sAlo.05O2, as the high nickel cathode materials of lithium battery cathode material, have the most widely prospect of application and highest commercial value due to its outstanding advantages on high specific capacity and low cost than LiNiO2. Besides, while doped with Co and Al, it has improved its difficulties on synthesis and serious cation mixing. To improve the performance further (better cycling stability, higher capacity, widely commercialization) scientists have done numerous research.In this paper, Firstly,we prepared spherical LiNio.8Coo.15Alo.05O2 precursor by the method of crystallization, then took thermodynamic analyzes of precursor, further discussed the effect of the sintering temperature and sintering atmosphere on the structure and properties of LiNio.8Co0.15Al0.05O2, at the same time, we studied effect of coating AlF3, AIPO4. At last, SEM, TEM, XRD, ICP-AES, XPS, laser particle size, AC Impedance of samples were taken.Thermodynamic analysis of Me2+-NH3-OH’-H2O co-precipitation reaction system shows: The most important factors which have a great influence on crystallization of are PH and solubility of ammonium. In this paper, we have obtained a most suitable PH and zone of ammonium for the formation of uniform initial grain, which have n moderate degree of super saturation in this zone. It can offers enough energy for the grain nucleating and growth in those areas, at the same time, moderate nucleation and grain growth rate is beneficial to obtain uniform initial grainThe mechanism of high-density spherical precursors are as follows:a large number of minuteness crystal nucleus rapidly reunite with each other to a secondary grain, the formation and reuniting of initial grains were happened in this period. With the grow of initial grains, surface energy will be greatly reduced, and cause the reducing of thermodynamic driving force, so the rapid of reuniting will become slower, in this period, the grow of grain depend on initial grains adsorbing at secondary grains, At last, the effect of filling the valleys and removing crest make the secondary grain into a dense spherical ball.With the study of different sintering temperature and atmosphere, we found that when sintering temperature is 720℃ and oxygen partial pressure is 0.1 MPa sintered samples have the lowest content of Ni2+, cationic mixing and the best degree of sphericity, at the same time, the particle size is moderate.The initial discharge capacity was 178.2mAh/g and the efficiency was 83.4%. After cycling 30 times, the capacity retention rate could reach 90.9%, per cycle capacity fade rate was just about 0.30%.Then, we coated AIF3 and AIPO4 on the surface of LiNio.8Coo.15Alo.05O2 with the ratio of 0wt%,1 wt%,2wt%,4wt%. ICP-AES, TEM, XPS tests confirmed that AlF3 was indeedly coated on sample surface, the thickness of cladding layer varied from several nanometers to twenty nanometers. The XRD results shows that coating does not change layered structure of LiNio.8Coo.15Alo.05O2. The value of c/a is bigger than 4.9,1(003)/Ⅰ(104) is bigger than 1.2, and value of R is less than 0.4, indicated that different coating ratio has no effect on tomic arrangement. With the increase of coating ratio, First discharge/charge capacity declines but first charge/discharge efficiency increases, and cycle stability become better. Capacity of LiNio.8Coo.15Alo.05O2 which coating 4wt% of AIPO4 only fades 4.8% after 30-cycle charge/discharge, each per cycle capacity fades 0.16%.Capacity retention rate of Samples which coating 4wt% of AIF3 can reach 92.6% (fading7.4%), per cycle capacity fading rate is 0.25%. Even though coating have tiny negative effect on first charge/discharge capacity loss, it remarkably improve cycling performance of LiNio.8Coo.15Alo.05O2...