Design And Research Of Sodium Ion Battery Anode Based On Co-Co Layered Double Hydroxide And Hollow Carbon Sphere

Decades have passed since John Goodenough invented the rechargeable lithium-ion batteries（LIBs）,and LIBs energy storage technology has matured.However,in recent years,the"cask effect"in this field has attracted people’s attention:lithium is a rare metal,and excessive mining and processing can easily cause environmental problems such as water pollution and land degradation,and the uneven distribution of lithium resources will also lead to create geopolitical tensions and trade imbalances.Therefore,it is becoming more and more urgent to explore alternative battery technologies for sustainable supply of resources.The abundant raw material sources,low manufacturing cost,and similar physical and chemical properties between lithium and sodium elements of sodium-ion batteries（SIBs）make SIBs gradually become a potential substitute for LIBs.However,sodium ions have a large diameter and a low diffusion coefficient,making it difficult to shuttle freely without causing structural damage.Therefore,finding anode materials that can efficiently intercalate and release Na ions is one of the major challenges in developing high-performance SIBs.Layered double hydroxides（LDHs）,a class of inorganic layered materials,have attracted extensive attention due to their unique structures and properties.One of the most striking features of LDHs is their ability to undergo anion exchange reactions,which allows intercalation of various anions into the interlayer space.This property has led to extensive research in the field of LDH-based nanocomposites.LDHs are often used as host materials to bind various organic molecules,inorganic ions,and biomolecules.Likewise,these excellent properties are also promising in the field of energy storage.Therefore,this paper takes cobalt-based materials as the main line of research and design,and first explores and tries combining MOF materials on LIBs.Then,the summarized improvement scheme was applied to SIBs,and the anode material with excellent electrochemical performance was prepared by using the carbon sphere frame structure and Co-Co LDH.The specific research contents are as follows:（1）Co₃O₄ and ZIF-8 were uniformly compounded by ball milling,and the prepared Co₃O₄@ZIF-8 was used as LIBs anode material and its electrochemical performance was tested.The discharge capacity of Co₃O₄@ZIF-8 at the current density of 0.1 A g^-1 was 1146.4 m Ah g^-1 in the first cycle,and it showed a slow upward trend before 149 cycles,until it reached the peak capacity of 1530.6 m Ah g^-1and then began to decline slowly.As of the 200th cycle,the capacity retention rate of Co₃O₄@ZIF-8 reached 93.8%compared with the peak capacity.And after experiencing the rate performance test with a current density gradient of 0.1-10.0 A g^-1,the capacity can still recover to 1530 m Ah g^-1.In addition,this paper also designed a Co₃O₄@ZIF-8 composite ratio experiment,and determined that Co₃O₄:ZIF-8=2:1 is the best performance ratio.The overall superiority of the LAND test curves of Co₃O₄and ZIF-8 compared with the control group（pure Co₃O₄ and pure ZIF-8）indicates that Co₃O₄ exhibits a certain synergistic effect after being fully milled with ZIF-8:On the one hand,Co₃O₄ makes the main contribution to the high cycle capacity;on the other hand,the high surface area and high porosity of ZIF-8 provide the composite with excellent activation effect.But it is worth noting that the capacity of Co₃O₄@ZIF-8 has a sudden drop under high current,this is attributed to the fact that Co₃O₄@ZIF-8 lacks a more robust base frame or shell structure as a protective layer,so that the dramatic volume expansion of metal oxides during charge and discharge is not resolved.（2）Based on the above experience summary,this paper improved the synthesis scheme and used a one-step hydrothermal method to compound Co-Co LDH on the nitrogen-doped carbon nanosphere framework.And the NHCNS@Co Se₂@C composite electrode material was finally synthesized by calcination selenization and carbon coating treatment.In this design concept,the cavity structure of carbon nanospheres not only provides structural strength,but also forms shorter electron diffusion paths and higher cycle stability.The introduction of nitrogen element increases the number of defect sites and the charge density of porous carbon materials,and together with Co Se₂ improves the conductivity of the target product.The prepared carbon-skeleton anode material NHCNS@Co Se₂@C can reach 59.7%in the first cycle Coulombic efficiency,it has an initial stable discharge capacity of 465.6m Ah g^-1 at a current density of 0.1 A g^-1,and still maintains a specific capacity of373.8 m Ah g^-1 after 100 cycles.Moreover,NHCNS@Co Se₂@C exhibits a high rate performance of 285.6 m Ah g^-1 at a current density of 5 A g^-1.