Synthesis And Electrochemical Properties Of Self-supporting NiO Composites

With the increasing demand for energy in emerging fields such as wearable electronic devices and electric vehicles,various efficient energy storage devices have received widespread attention in recent years.Among electrochemical energy storage devices,lithium-ion batteries(LIBs)are very popular electronic devices,which have the advantages of high energy density,wide use voltage range,no memory effect,safety and environmental protection.However,the theoretical capacity of commercial graphite anodes is only 372 m A h g^-1,which cannot meet the needs of higher energy density and power density of power batteries.In order to improve the energy density and power density of LIBs,there is an urgent need to find a new negative electrode material with low cost,high capacity and good durability.As a conversion reaction anode material,NiO is a promising candidate material for LIBs,which has a higher theoretical capacity(718 m A h g^-1)than graphite intercalated anode.However,NiO has many defects such as poor conductivity and severe volume expansion,which limits its practical application.In addition,the traditional electrode preparation method needs to mix active material with conductive agent and binder to adjust the slurry,and then coat it on an aluminum foil or a copper foil.This preparation process inevitably causes the problems of low active substance loading and low area specific capacity,thereby affecting the output power of batteries.In order to improve the conductivity and volume expansion of NiO anode materials,the necklace-liked NiO/Ni@Co/N-C self-supporting electrode was prepared by electrospinning and calcination.The effect of annealing temperature on the morphology,composition and electrochemical performance of NiO/Ni@Co/N-C self-supporting electrodes was investigated.When the annealing temperature is 500?,the ZIF-67derived Co/N co-doped carbon nanocage tightly wraps the NiO nanoparticles,effectively suppressing the volume expansion of NiO and improving the conductivity of the electrode.The conductive carbon fiber network connects carbon nanocages continuously,which improves the charge transfer rate and ensures the flexible self-supporting characteristics of the electrodes.The reduced metal Ni during carbonization also helps to improve the electrical contact between the carbon nanocage and NiO nanoparticles.The prepared necklace-shaped NiO/Ni@Co/N-C self-supporting electrode has good cycle stability and high areal capacity.After 400 cycles at a current density of 0.5 m A cm^-2,it still provides 0.6 m A h cm^-2 areal capacity.In order to further improve the loading and areal capacity of self-supporting NiO anode materials,bamboo mat-like NF@NiO nanoarray electrodes were prepared by two steps of hydrothermal method and calcination.The effects of the amount of nickel nitrate added and the hydrothermal reaction time on the morphology of the nanoarray were explored.When the addition amount of nickel nitrate is 0.008 mol and the hydrothermal time is 12 h,the self-assembled NiO nanoarray grows uniformly on the foamed nickel collector with a thickness of 1.35?m and a loading of up to 5.5 mg cm^-2.The nickel foam current collector can provide more growth points,and the self-assembled NiO nanoarray achieves a high loading of active material.Two-dimensional mesoporous NiO nanosheets shorten the diffusion path of Li⁺ions and improve the rate performance of the electrode.The prepared bamboo mat-like NF@NiO nanoarray electrode has a high areal capacity.At a low current density of 0.5 m A cm^-2,the areal capacity of the first cycle is 6.6 m A h cm^-2,and it can still provide 1.2 m A h cm^-2 areal capacity after 100 cycles.In order to improve the volume expansion of the self-supporting NiO electrode with high loading,the self-supporting NF@NiO@PPy(polypyrrole)nanoarray electrode was prepared by electrochemical oxidation polymerization.The effect of deposition time on the morphology and electrochemical performance of NF@NiO@PPy nanoarray electrode was investigated.When deposited at 10 m A for 3 min,PPy layer was deposited uniformly on the surface of the NP-3 electrode,and the thickness of the PPy coating was 12-15 nm.The PPy coating suppresses the volume expansion of the NiO nanoarray during charge and discharge process,and prevents the NiO nanoarray from powdering and falling off from the nickel foam collector.At the same time,PPy coating avoids the direct contact between the electrode and the electrolyte,prevents the electrode from dissolving in the electrolyte,and improves the conductivity of the electrode.The NF@NiO@PPy nanoarray electrode has good cycling stability.At a current density of 0.5 m A cm^-2,the NF@NiO@PPy nanoarray electrode can provide 4.9m A h cm^-2 areal capacity after 50 cycles.Even after 200 cycles at a high current density of 2.5 m A cm^-2,the NF@NiO@PPy nanoarray electrode can still provide 1.1 mA h cm^-2areal capacity.