Studies Of The Capacity Fading Mechanism Of Lini_1/3Co_1/3Mn_1/3O₂and Suface Modification With Metal Oxides By Atomic Layer Despition

as the lithium insertion positive electrode material has the advantage of high capacity, long circle life, safety and low cost and thus becomes the main composite of commercial lithium-ion batteries. However, it also has shortcomings such as poor charge-discharge performance at high rate, low conductivity and so on. Apart from those disadvantages resulting from its own property, breaking down of layered crystal structures in the cycling process, lost of conductive carbon are also the factors which restrict the application of LiNi1/3Co1/3Mn1/3O2. In this paper, these disadvantages are systematically analyzed and the atomic layer deposition is used to coat the LiNi1/3Co1/3Mn1/3O2cathode with metal oxides to improve its property.First, The α-NaFeO2layered structure LiNi1/3Co1/3Mn1/3O2cathode materials were successfully synthesized in air by carbonate co-precipitation method. XRE、 SEM、charge-discharge test and so on were employed to examine the structure, morphology, electrochemical performance of the products.18650lithium-ion battery was tested at rate of0.5C and1C by constant current-constant voltage protocol. The result of0.5C rate testing shows that our specimen possesses a good cyclic performance, i.e. the first Coulomb efficiency reaches83%and the capacities remains74%after300cycles. But the capacity decreases fast when it is under1C rate. To investigate the mechanism of capacity decrease under cycling to provide guidance to the coating experiment, we have conducted experiments to find out how the cathode damages in each cycles. Measurement methods including SEM、XRD、EDS、EIS demonstrate that the reasons leading to the decrease of capacities are listed below: destruction of the LiNi1/3Co1/3Mn1/3O2aggregates, breaking down of layered crystal structures in the cycling process, lost of conductive carbon,and Co dissolution from the structure by HF attack, and so on.We applied the atomic layer deposition techniques to coat LiNi1/3Co1/3Mn1/3O2 cathode with metal oxides to improve the electrochemical performance. Results show that property of the battery with the ZnO film doesn’t have a large enhancement since the ZnO film reacts with the li-ion and consumes some of it. As a result, an irreversible loss of capacity is caused. Furthermore, the ZnO film will dissolve in the electrolyte. However, measurements show good capacities of113mAh.g-1,91mAh.g-1and72mAh.g-1and capacity retention of80.7%,84.9%and85.7%when the material is coated with the Al2O3film after5,10or20ALD cycles, respectively, after90cycles are conducted. This capacity is far more than56.6%for the uncoated material. With the increase of ALD cycles, the capacity goes downward which indicates that the5-ALD-cycle has the best effect. The fact that more ALD cycles will decrease the battery capacities may be attributed to the semiconductor property of Al2O3, and a thicker Al2O3film will affect the cathode’s surface conductivity and suppress the lithium ion diffused.Electrochemical impedance spectroscopy (EIS) was applied to study the effects of the battery structure on the charge transfer and lithium ion diffusion rate, the result shows that18650winding cell’s charge transfer and lithium ion diffusion rate are obviously better than the2032cell. Thus,18650winding cells has batter cycle performances.