Investigation On Electrochemical Properties Of Metallic Nickel And Manganese Oxide Composites For Lithium-ion Battery Anodes

Since the Industrial Revolution,the sources of energy have become a significant material basis and driving force for the growth of modern science and technology,as well as an important support for social development.Among the many energy storage devices,lithium-ion batteries(LIBs)are currently the leader in various types of batteries and are widely used in portable electric driven equipment because of the profits of high specific energy,high operating voltage(3.7-3.8 V),good cycle performance and environmental protection.High-performance anode materials are crucial for the LIBs,and they have been the focus of development and research.Low-cost and environmentally friendly nickel has been extensively studied as electrode material for LIBs,while manganese oxides have become candidates for large-scale practical application of lithium-ion battery anodes due to their high theoretical capacity and low cost.Therefore,in this paper,composites of metallic nickel and manganese oxides with network structure,heterojunction structure and porous structure have been synthesized by simple methods such as hydrothermal,solvothermal and one-step annealing.Through the structural characterization and electrochemical performance tests,the effects of these unique structures on the electrochemical properties such as lithium storage ability and cycle stability are elucidated.It shows that through reasonable composition regulation and structural design to fabricate nanocomposites,better performance anodes of lithium ion batteries can be obtained.The following statements are the main research contents of this paper:(1)Firstly,a hybrid structure of carbon network adorned with nickel particles(Ni/CN)has been developed.The ultra-fine interconnected carbon nanonetworks not only provide a larger specific surface area,but also improve the overall conductivity of the composites.Nickel nanoparticles in carbon nanonetworks can also play an anchoring role to stabilize the overall structure.The carbon around nickel nanoparticles is graphitized at high temperature to become soft carbon with large interlayer spacing and good conductivity,which is conducive to the rapid intercalation and deintercalation of Li⁺ions.Ni/CN material possesses both large specific surface area and open internal space,which can optimize the diffusion path of lithium ions,contribute to the high-speed move and diffusion of lithium ions and negative charges,and make the overall structure adapt to the volume strain in the repeated lithium and de-lithium processes.With the above advantages,Ni/CN as the anode electrode of LIB shows super stable cycle performance.Even after 2000 times of charge and discharge at 1 A g^-1,its specific capacity is 544.7 m Ah g^-1 and has a capacity retention rate of 121.1%.With high capacity and long cycle life,Ni/CN electrode materials have expanded application prospects in the anode materials for LIBs.(2)The MnO/Mn₂O₃ nanowires coated by porous N-doped carbon(MnO/Mn₂O₃-NC)layers are fabricated via wrapping ZIF-8 on MnO₂ combined with annealing postprocessing.The staggered MnO/Mn₂O₃ nanowires form a three-dimensional hollow structure inside the material,which provides sufficient space for the rapid intercalation/deintercalation of lithium ions,avoids the structural collapse caused by stress concentration and improves the cycle stability.Meanwhile,the porous carbon in the outer layer can also provide lithium-ion transmission path,so as to improve the overall conductivity of the material.When used as anode electrode for LIB,the material shows excellent initial discharge specific capacity(up to1429.4 m Ah g^-1 at 0.1 A g^-1 current density)and improved rate performance retention of 65%(10-fold amplification from 0.5 to 5 A g^-1).Particularly,up to an ultrahigh current density of10 A g^-1,this anode material also possesses great cycling stability of 87%after 10 000 cycles(merely 0.0013%capacity decay per cycle),which is the best among the reported values for Mn-based compounds.On the basis of experiment data and density functional theory calculations,the finer stability for the MnO/Mn₂O₃-NC anode is mainly attributed to the mutual support characteristics of heterojunction synergy,thus avoiding damage and vice versa during the energy storage process.Herein,a special nanostructure with heterojunction synergy is proposed to improve the cycling stability and rate capability of manganese-based material anodes for Li-ion batteries.(3)The porous raspberry-shaped nickel-enhanced MnO-based carbon-containing composite(Ni/MnO-C)have been synthesized by one hydrothermal step and subsequent calcination.Through the addition of metallic nickel,the overall conductivity of MnO has been improved successfully,so that the specific capacity of LIBs can be increased.The porous nanostructure composed of many uniform nanoparticles with enough buffer space can effectively prevent the structural damage caused by volume variation.In addition,in the process of repeated insertion and extraction of lithium ions,raspberry like nanostructures will be destroyed into some smaller nanoparticles,which will expose more active sites and provide some additional capacity.Employed as anode materials for LIBs,the Ni/MnO-C electrodes have a high first discharge specific capacity of 1536.9 m Ah g^-1 at 0.2 A g^-1.Impressively,the reversible capacity of Ni/MnO-C can be retained after 3500 long-term cycles at a current density of 1 A g^-1.Furthermore,the practical application of Ni/MnO-C in LIBs is further demonstrated by powering smartphones and smart watches.