| Spinel-structured CoNiO2 has the advantages of high specific capacity(717m Ah·g-1),good safety and high energy density,which is a highly competitive conversion-type anode material for lithium-ion battery.However,Co Ni O2 has poor conductivity and volume effect,which results in poor rate performance and cycle ability during charge/discharge process.This phenomenon is more obvious at high current density,thus limiting its large-scale application.In view of these shortcomings,modification methods,include the surface coating and composite,were applied to modify Co Ni O2 nanosheets to prepare composite electrode materials with outstanding electrochemical properties.CoNi O2 nanosheets were prepared by one-step hydrothermal method with a subsequent calcination in nitrogen.The effect of C coating on the microstructure and lithium storage performance of Co Ni O2 was studied where sucrose act as carbon sources.The SEM tests showed that Co Ni O2was completely encapsulated by carbon,and the morphology changed from nanosheet to microsphere when the C coating amount was the largest(15 wt.%).The electrochemical performance of Co Ni O2 was improved as the amount of C coating increased.The best electrochemical performance is obtained when the coating amount of C is 15 wt.%,and the discharge capacity at a current density of 500 m A·g-1 can maintain at 1241.8 m Ah·g-1 after 200cycles.This sample also exhibits the best rate performance and the smallest redox potential difference.The EIS results show that C coating can significantly reduce the inherent resistance and charge transfer resistance of the material.LiAlO2 was synthesized by solid phase method,and Li Al O2@Co Ni O2composites with Li Al O2 as matrix were prepared by a hydrothermal method with a subsequent calcination.As the amount(wt.%in the order of 0,3,5,10)of Li Al O2increases,the morphology of the material gradually shifts from nanosheet to nanorod.When the amount of composite Li Al O2 is 5 wt.%,this sample(LAO@CNO3)exhibited a sea urchin shape which is composed of nanorods.Compared with the pristine electrode,LAO@CNO3 exhibited excellent electrochemical performance:at the current densities of 500 and 1000 m A·g-1,it can provide high capacity of 1309.0and 933.6 m Ah·g-1,respectively after 400 cycles.After 500 cycles at the current density of 2000 m A·g-1,the capacity of LAO@CNO3 can reaches 358.1 m Ah·g-1 and the average attenuation rate per cycle is 0.052%.The EIS fitting results show that the charge transfer resistances of LAO@CNO1,LAO@CNO2,LAO@CNO3 and LAO@CNO4 are 595.1,429.4,331.7 and 380.4?,respectively.CoNiO2@CeO2 nanosheets were prepared by one-step hydrothermal method with a subsequent calcination.The effects of different composite amounts of Ce O2 on the microstructure and lithium storage performance were investigated.the SEM results show that all samples are composed of nanosheets.As the amount of Ce O2 coating increases,the particles on the surface of the material also increase gradually.The charge and discharge test showed that proper amount of Ce O2 can significantly improve the specific capacity and rate performance of Co Ni O2,while the performance of composite electrode would decrease if the amount of coating is excessive.The electrochemical performance of the sample with a coating amount of 5 wt.%(CNO@CO3)is optimal:the capacity is 1210.4 m Ah·g-1 after 400 cycles at a current density of 500 m A·g-1 and 820.7 m Ah·g-1 at a current density of 1000 m A·g-1 after500 cycle.CV and EIS tests show that Ce O2 can significantly reduce the inherent resistance,charge transfer resistance and polarization of the electrode material. |
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