Exfoliator Interlayer And Composite Modification Of Nickel-cobalt Hydroxide By Strengthening

Electrochemical energy storage technology plays a key role in the development of new energy industries.Supercapacitors are a popular class of energy storage devices due to their high power density,fast charging and discharging,and environmental friendliness.However,supercapacitors still have the problem of low energy density,and electrode material is one of the key factors affecting their performance.Nickel-cobalt layered double hydroxide(Ni-Co LDH)electrode materials have attracted much attention due to its high theoretical specific capacity and rich chemically active sites.However,Ni-Co LDH has problems such as poor rate capability and cycling stability.In this paper,based on the problems of low rate capability and cycling stability of Ni-Co LDH,two methods of exfoliation intercalation and composite are proposed to modify it,and the modification process is strengthened by high gravity technology to improve the electrochemical performance of Ni-Co LDH.On this basis,the high gravity intercalation and composite integrated process is established,which can provide ideas for the synthesis of efficient electrochemical energy storage materials.The main research contents of this paper are as follows:(1)The anionic surfactant aqueous solution was used to treat lamellar Ni-Co LDH by liquid-phase intercalation in a cyclonic field.The influence of different process conditions on the electrochemical performance of Ni-Co LDH are investigated,and the suitable process parameters are obtained: the intercalators is sodium dodecyl benzene sulfonate,the intercalators concentration is 2.75 g/L,and the intercalators time is 3 h.The Ni-Co LDH after intercalation is characterized,it is revealed that the SDBS intercalation can expand the interlayer spacing of Ni-Co LDH,accelerate the diffusion of electrolyte ions,which facilitates the redox reaction process and makes it easier for the electrolyte to contact with materials,and thus improve its specific capacity and rate capability.Using high gravity device enhance the liquid-phase intercalation process,further suitable operating parameters are obtained: the cycle time is 30 min,and the high gravity factor is 41.74.The specific capacity of the Ni-Co LDH after highgravity liquid-phase intercalation is 984 C/g(2 A/g),and its rate capability is improved from72% to 80%(1～30 A/g).It is shown that high-gravity enhances the diffusion and intercalation process of the exfoliator,which is beneficial to improve the electrochemical performance of the electrode material.Finally,the Ni-Co LDH after high-gravity liquid-phase intercalation is used as the positive electrode material and AC as the negative electrode material to assemble the NiCo LDH //AC supercapacitor has a high energy density of 50 Wh/kg at a power density of 363W/kg.(2)Ni-Co LDH/PPy wss prepared by chemical reaction deposition of needle-shaped NiCo LDH and polypyrrole(PPy).The influence of different process conditions on the electrochemical performance of Ni-Co LDH/ PPy were investigated,and the suitable process parameters were obtained: the pyrrole concentration was 0.4 g/L,the molar ratio of pyrrole to ammonium persulfate was 1:3,and the pyrrole impregnation time was 3 h.The PPy distribution in the composite Ni-Co LDH/PPy prepared under these conditions was not uniform.Using high gravity technique strengthen the PPy reaction and composite process,the Ni-Co LDH/PPy prepared under suitable operating parameters had a specific capacity of 1309 C/g(2 A/g);After10,000 charge/discharge tests at 10 A/g current density,its specific capacity retention rate is61%,which is 22% higher than that of Ni-Co LDH before composite modification.It is shown that the compounding of PPy with Ni-Co LDH can improve the specific capacity and cycling stability of the electrode material.Finally,the Ni-Co LDH/PPy after high-gravity composite modification as the positive electrode material and AC as the negative electrode material to assemble the Ni-Co LDH/PPy//AC supercapacitor has a high energy density of 51 Wh/kg at a power density of 363 W/kg.(3)Based on the research basis of high-gravity intercalation and high-gravity composite of Ni-Co LDH,the high-gravity intercalation and composite integration process experiments were carried out.The effect law of pyrrole concentration on the electrochemical performance of Ni-Co LDH/PPy was investigated,and the optimal pyrrole concentration was obtained to be0.04 g/L.Under this condition,the Ni-Co LDH/PPy specific capacity was 1206 C/g(2 A/g);compared with lamellar Ni-Co LDH,its rate capability is improved 24%(1～30 A/g);after 5,000charge/discharge tests at 10 A/g current density,its specific capacity retention rate is improved7%.The above results show that the integration of the two processes can combine the advantages of both modification methods,and thus effectively improve the electrochemical performance of electrode materials.The final assembled Ni-Co LDH/PPy//AC supercapacitor has a high energy density of 52 Wh/kg(363 W/kg).