The Synthesis Of NiO Based Composites As Anode Materials For Lithium-ion Batteries

Lithium ion batteries（LIBs）,as a kind of significant electrochemical power source,exhibited lots of excellent properties,including high capacities,high working voltages,no memories,no pollution,high rate charge/discharge properties and so on.The developing trends of LIBs are excellent performance,low costs,high Safety and long cycle life.According of LIBs history,the research on anode materials has limited its development.In consider of the lithium storage mechanism of anode materials and the disadvantages of NiO based materials,NiO-SnO₂/Graphene and Ni-NiO/G based composites with different contents of metal Ni were synthesized by hydrothermal method in this paper.All composites physical structure had been tested by XRD,TG,Raman,SEM and TEM;Electrochemical performances had been tested by galvanostatic,CV,EIS and GITT.The electrochemical measurements were used to analyze lithium storage properties of anode materials.Firstly,the induced graphene relieved the structure collapse progress of metal oxides in charge/discharge progresses and improved the conductivity.In addition,this research has confirmed the synergistic effect amon g of graphene and metallic nickel particles in promoting the reversible decomposition progress about Li ₂O and SEI films.The main research and results are as follows:（1）Graphene Oxide（GO）was synthesized by chemical oxidation method.There are many oxygen-containing functional groups,which are easy to escape when heated,grew up on the surface of GO,thus,it was reduced into graphene by rapid thermal expansion method.It’s worth noting that there are a small number of oxygen-containing groups remained on graphene sheets even after thermal reduction.These groups provided transition metal ions a lot of active sites for adsorbing on the surface of materials.The basement,which was used in the next experimental process,had been prepared after this reactio n.（2）The NiO-SnO₂ composite was synthesized by hydrothermal method.During the electrochemical progress,materials reunited into a large block due to its structural characteristics.The catalytic activity of metal nickel can not to exhibit after this progress.Thus,the discharge capacity was rapid fade from1022.2 mAh/g to 213.9 mAh/g under 100 mA/g after 50 cycles.The SEM showed that oxide particles were dispersed on laylers and formed to a homogeneous sheet like structure when graphene was induced.With a larger raise in the degree of dispersion,this kind of structure relieved volume effect and improved contact degree among oxide particles,therefore,the reversible degree of non-activated Li₂O had been promoted.The electrochemical tests indicated th at the oxidation peak current at 1.48V for Li₂O decomposition increased significantly compared with NiO electrodes.The discharge capacity can be still stable at 650 mAh/g after50 cycles.（3）In order to study the effect about graphene and metal Ni on cathode electrodes preformance,Ni-NiO/G based materials with different content of Ni had been synthesized.Besides the mitigation processes on volume effects of composites,graphene would generate amount of SEI films during the discharge progress which reduced the initial coulombic efficiency in quantity（from 75.4%to51.4%）.In this part,Ni-NiO/G-2 and Ni-NiO/G-4 were prepared by roasting at different temperature.Tests revealed the anodic peak at 1.44V strengthened.After systematic study on this side reaction,the catalytic effect about Ni particles on SEI films had been confirmed.Anything else,the reversible reaction of SEI films contributed greatly to capacitance stability,the reversible degree of capacitance about Ni-NiO/G-4 was 99.3%,which means there are more active particles,the reversible degree will be more intense.