Preparation And Electrochemical Properties Of Oxide Cathode And Metal Anode For Sodium Ion Batteries

The shortage of fossil energy and the serious environmental pollution caused by it force people to develop and use clean energy on a large scale.However,at present,most of clean energy(such as solar energy,wind energy,tidal energy,geothermal energy,etc.)is still limited by time,place,season and other conditions,and there will be unstable supply,as well as obvious "peak"and "peak valley".Therefore,people have to develop large-scale energy storage system for energy storage to meet the stable demand.At present,lithium-ion secondary battery has been widely favored because of its high energy density,good cycle performance and small self-discharges.However,for large-scale energy storage system,the first thing to consider is cost-effectiveness,and energy density is second.The lower abundance of lithium resources in the earth's crust and the uneven distribution of lithium resources in the world lead to the high price of lithium-ion batteries,which leads to the inability of lithium-ion batteries to be used in large-scale energy storage systems;Sodium becomes the most promising battery system to replace lithium-ion batteries because of its high abundance in the earth's crust,wide distribution of resources and similar properties with lithium in the same main group.Therefore,P2 type Na0.8Zn0.06Ni0.22Mn0.66 cathode material and sodium metal anode material is selected as the research object in this paper,The electrochemical performance of the material is significantly improved by in-situ coating of dopamine and reasonable design of sodium metal anode structure,and the reason and mechanism of electrochemical performance improvement are systematically analyzed and explained in detail.The specific research contents are as follows:(1)In this work,we adopt in-situ coating method to prepare PDA-coated Na0.80Ni0.22Zn0.06Mn0.66O2(P2@PDA)sample through the polymerization route,which dopamine(DA)is served as carbon sources.The P2@PDA sample is carbonized at 550? to obtain P2@C-PDA nanoparticles.The resulting P2@C-PDA materials are employed as the anode material for sodium ion batteries.Benefiting from the continuous and uniform carbonized PDA(C-PDA)layers with a thickness of?5 nm,the C-PDA-coated Na0.80Ni0.22Zn0.06Mn0.66O2 exhibits a higher discharge capacity(123.5 mAh g-1 at 12 mA g-1),better rate capability(61.5 mAh g-1 at 1536 mA g-1)and better cycling stability(90.7%capacity retention over 100 cycles)than the uncoated sample.XRD,SEM,TEM,XPS analysis and electrochemical measurement technology are used to discuss the effects of carbon coating for the electrochemical properties of P2 sample.The results show that the polydopamine-derived carbon coating is an effective strategy to enhance the interfacial stability of P2-type Na0.80Ni0.22Zn0.06Mn0.66O2,which can not only prevent the sodium extraction from the surface of P2-type Na0.80Ni0.22Zn0.06Mn0.66O2 particles during electrode fabrication process,but also avoid the formation of electrochemically harmful Na2C03/NaOH species.Thus,the cycle stability and rate capability of P2-type Na0.80Ni0.22Zn0.06Mn0.66o2 was improved significantly.(2)In this thesis,a facile and controllable oxidation treatment strategy is used to in-situ construct a fluffy CuO surface layer on the skeleton of commercial Cu foam(SF-Cu).The oxidation degree and interphase structure of Cu foam can be rationally designed by adjusting the concentration of(NH4)2SoO8 oxidant,which is directly related to the driving force of Na infusion.Then,SF-Cu is employed as a 3D current collector to accommodate Na metal for stable sodium metal batteries(SMBs).With an optimized interface,Na metal can be rapidly infused into SF-Cu within five seconds and a structurally complete Na/SF-Cu composite electrode with a flat surface and no visible void can be obtained.The SF-Cu with a large surface area can be used as a 3D host for Na metal to lower the local current density during cycling,resulting in uniform Na deposition without dendrite formation and growth.In virtue of the structural advantages,the symmetric Na/SF-Cu cell exhibits flat charge/discharge plateaus with a low overpotential of 12 mV and stable cycling up to 1000 h at 0.5 mA cm-1.Moreover,the symmetric Na/SF-Cu cell can maintain a stable cyclability at a high current density of 5 mA cm-1.When paired with NaTi2(PO4)3,the rate performance of the full cell using the Na/SF-Cu composite anode is significantly better than that of the full cell using a bare Na anode.This work sheds new light on the role that interphase structure plays in accommodating sodium metal into a 3D current collector for high-energy and high-rate SMBs.