| The development and utilization of new energy has taken seriously due to environmental crisis.Lithium ion batteries are considered as one of the most promising energy storage systems.Transition metal oxides are worthy of exploring,not only because of its cheap and environmental friendly,but also its better properties of high specific capacity.Mn3O4 has a high theoretical specific capacity(937 mAh g-1),but a poor cycle stability cased by poor electrical conductivity.To tackle with these issues,graphene with high electrical conductivity and buffer matrix have been widely employed as matrixes for Mn3O4-based materials to improve their conductivity and stability.In addition,sodium ion batteries are now actively pursued as the most attractive alternative to lithium ion batteries.As a cathode material for sodium battery,Co3O4 has a change of volume that leads to larger capacity loss in the process of charging and discharging.Graphene has more edges and togological defects to generate a more disordered structure,and it has strong adsorption of Na+.Therefore,development of composite material based on Co3O4 and rGO should be a promising method to enhance the electrochemical performance of Co3O4.In this paper,we prepared Mn3O4/rGO and Co3O4/rGO hybrid materials via a facile homogeneous co-precipitation method,and used them as athode materials for lithium/sodium ion batteries respectively,investigated their electrochemical performance.The main research work is as follows:(1)Graphite oxide(GO)was prepared by the modified Hummers method,and the Mn3O4/rGO hybrid materials with different rGO content were synthesized by homogeneous co-precipitation method.MnCl2·4H2O as source of manganese,CO(NH2)2 as the mineralizer,GO as the carrier,hydrazine hydrate as the reductant to reduce GO.In the process of heating,CO(NH2)2 could gradually decompose and form a weak alkaline environment,which makes manganese ion deposition on graphene.Then the precursor anneals in the Ar to form Mn3O4/rGO.The XRD,SEM,Raman and galvanostatic charge and discharge measurements,cyclic voltammetry and so on were applied to characterize materials.The SEM results show that:Mn3O4 particle stacked on the lamellar structure of rGO,with the size between 10 and 100 nm.Galvanostatic charge and discharge measurements show that:with the increase of the content of rGO,hybrid materials'charge and discharge specific capacity increasing,but the coulomb efficiency appears a trend of reducing.In brief,the hybrid materials that the content of rGO was 18.3%has obvious advantages.In the voltage range of 0.05-3 V and the current density of 100 mA g-1,the hybrid materials can deliver an initial discharge specific capacity of 1481.6 mAh g-1 and an initial charge specific capacity of 999.7 mAh g-1,the Coulomb efficiency is 67.47%.Then,we test the cycle performance and rate performance,after 45 cycles,the hybrid materials can hold a specific capacity of 1296.8 mAh g-1.When the current density is as high as 2000 mA g-1,the specific capacity of Mn3O4/rGO remains 610 mAh g-1.The Mn3O4/rGO hybrid materials show the good cycle performance and rate performance,and it is a good choice as anode material for lithium ion battery.(2)The Ci3O4/rGO hybrid materials were synthesized via co-precipitation method,CoCl2·6H2O as source of cobalt,CO(NH2)2 as the mineralizer,GO as the carrier,hydrazine hydrate as the reducing agent to reduce GO.The precursor anneals in the Ar to form Co3O4/rGO.The composites were characterized by SEM,XRD,Raman and galvanostatic charge and discharge measurements,cyclic voltammetry.The SEM results show that:Co3O4 nanorods with the size of 30-50 nm and the Co3O4 nanorods stacked on the lamellar structure of rGO.Galvanostatic charge and discharge measurements shows that:in the voltage range of 0.05-3V and the current density of 50 mA g-1,the Co3O4/rGO hybrid materials can deliver an initial specific discharge capacity of 1017 mAh g-1,and an initial specific charge capacity of 451.7 mAh g-1,the Coulomb efficiency is 44.4%.After 50 cycles,Co3O4/rGO hybrid materials with the reversible specific capacity of 135 mAh g-1.When the current density of 800 mA g-1,the specific reversible capacity of 75 mAh g-1.When the current density returns back to 50 mA g-1,the specific capacity recovers to 288.4 mAh g-1.It can be seen that Co3O4/rGO hybrid materials can be used as anode materials for sodium ion batteries. |
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