Study On Synthesis And Properties Of LiNi_0.8Co_0.15Al_0.05O₂ Ternary Lithium Ion Battery Cathode Materials

Due to the lack of resources and environmental pollution,lithium ion batteries,as efficient energy storage devices for clean energy,have received unprecedented attention.LiNi0.5Co0.15AI0.05O2(NCA),as a high-nickel ternary material,is considered to be a new generation of lithium ion battery cathode materials due to its high capacity(up to 200 mAh g-1),low price and good cycle stability.However,the poor rate performance of NCA limits its practical application.We found that the electrode materials of different micro-nanostructures have different electrochemical properties,which is expected to improve its rate performance.In this paper,NCAs with different micro-nanostructures synthesized by three different methods were explored.The optimal synthesis process of NCAs with different micro-nanostructures was discussed,whose characterization and testing were carried out to obtain NCA lithium ion battery cathode material with excellent electrochemical performance.The research results of this paper are as follows:(1)NCA microparticles were synthesized by high-temperature solid phase one-step method,the nickel,cobalt and aluminum oxide as raw materials,which were sufficiently ball-milled with a lithium source.Scanning electron microscopy(SEM),transmission electron microscopy(TEM)and X-ray diffractometry(XRD)were used to characterize the microstructure and crystal structure of NCA microparticles synthesized by solid phase method,whose electrochemical performance was further tested.The effects of different milling time,calcination temperature and calcination time on the morphology,crystal structure and electrochemical properties of NCA microparticles were investigated to obtain optimal electrochemical properties of NCA microparticles,whose synthesis conditions were recorded.The results show that the NCA microparticles having best electrochemical performance are solid particles with particle size of about 1.5 ?m.At a low current density of 0.1 C,the specific capacity is 183.6 mAh g-1.At the highest current density(5 C),the specific capacity maintains at 90.7 mAh g-1.The specific capacity is143.9 mAh g-1 at 1 C current density,and maintained 78.7%after 80 cycles.(2)Related studies have shown that the microscopic size of lithium ion battery electrode material has a great impact on its electrochemical performance.Hydrothermal method is an important method for synthesizing inorganic crystals.The substances synthesized by hydrothermal method have the advantages of small particle size and uniform distribution.In order to reduce the microscopic scale of NCA,the nickel,cobalt and aluminum salt as raw materials,NCA precursors were synthesized by hydrothermal method.The ball-milled mixed powder of NCA precursors and lithium source were calcined at a high temperature to obtain NCA nanoparticles.SEM,TEM and X-ray photoelectron spectroscopy(XPS)were used to characterize the microstructure and crystal structure of NCA nanoparticles synthesized by hydrothermal method.The electrochemical performance of NCA nanoparticles was further tested.The effects of different hydrothermal reaction concentration of the NCA precursors,calcination temperature and calcination time on the morphology,crystal structure and electrochemical properties of NCA nanoparticles were investigated to obtain optimal electrochemical properties of NCA nanoparticles and their synthesis conditions.Researches show that the NCA nanoparticles with best electrochemical performance are solid particles with particle size of about 400 nm.At a low current density of 0.1 C,the specific capacity is 198.8 mAh g-1.The specific capacity is 102.3 mAh g-1 at the highest current density(5 C).The specific capacity is 153.6 mAh g' at 1 C current density,and maintained 81.7%after 80 cycles.(3)Based on hydrothermal synthesis of NCA nanoparticles,hollow silica hard template was added to synthesize NCA with hollow structure.First silica hollow spheres(SiO2 HSs)were synthesized,and were used as precursors growth site,and the nickel,cobalt and aluminum salt were used as raw materials to synthesize the hollow structure NCA precursors[SiO2 HSs@(Ni0.8Co0.15Al0.05)CO3]by hydrothermal method.Finally,the above precursors and the lithium source were calcined at high temperature to synthesize hollow structure NCAs.SEM,TEM,XRD,XPS and inductively coupled plasma ray(ICP)were used to characterize the microstructure and crystal structure of hollow structure NCA,whose electrochemical performance was further tested.The results display that the hollow structure NCAs are hollow spheres of about 1.8 ?m in diameter,which are composed of nanoparticles and have wall thickness of about 300 nm.Comparing with the electrochemical performance of NCA microparticles and NCA nanoparticles,we found that hollow structure NCAs exhibit excellent capacity performance and rate performance as cathode materials for lithium ion batteries.At a low current density of 0.1 C,the specific capacity is 202.4 mAh g-1,and as the current density increases,the specific capacity decreases little.Hollow structure NCAs still have a specific capacity close to 170 mAh g-1 until 2 C.But at 5 C high current density,the specific capacity of hollow structure NCAs suddenly drops below 140 mAh g-1,which may be related to partial fragmentation and collapse of the spherical structure at high current density.The specific capacity is 179.1 mAh g-1 at 1 C current density,maintained 82.1%after 80 cycles.The electrochemical performance of the hollow structure LiFePO4 was further explored.The result shows that the hollow structure can improve the performance of the lithium ion battery cathode materials.