| The rapid development of electronic devices,electric vehicles(EVs),and energy storage puts higher requirements on the performance of the high energy density lithium-ion batteries(LIBs),including improved energy/power densities,cycle lives,and safety performance.However,the traditional graphite anode cannot meet the requirements of the high energy density LIBs due to its poor Lip intercalation kinetics and low theoretical capacity(372 mAh·g-1).Therefore,it is very important to develop new anode with excellent performance,low cost and good safety.Conversion-based anode materials have become promising anode materials because of their high reversible capacity and low cost.However,their practical applications are limited due to the low conductivity and the volume effect in charge/discharge process,which lead to poor cycle performance and rate performance.These problems can be solved by synthesizing nano materials or Compositing with carbon materials.Therefore,we investigated the synthesis,morphologies and electrochemical properties of MnC2O4/RGO and LDHs/RGO.Manganese oxalates with different structures and morphologies were prepared by precipitation method in the mixture of dimethyl sulfoxide(DMSO)and proton solvents.The proton solvents play a key role in determining their structures and morphologies of manganese oxalate.Monoclinic MnC2O4·2H2O microrod is prepared in H2O-DMSO,while MnC2O4·H2O nanorod and nanosheet with low crystallinity are synthesized in ethylene glycol-DMSO and ethanol-DMSO,respectively.The corresponding dehydrated products are mesoporous MnC2O4 microrod,nanorod,and nanosheet,respectively.When used as anode material for Li-ion batteries,mesoporous MnC2O4 microrod,nanorod,and nanosheet deliver a capacity of 800,838,and 548 mAh·g-1 after 120 cycles at 8 C,respectively.The electrochemical performance is greatly influenced by the synergistic effect of surface area,morphology,and size.Based on the synthesis of manganese oxalate nanorods,a mesoporous MnC2O4 nanorod/RGO composite is prepared via precipitation followed by a reflux reduction process,where MnC2O4 nanorods are attached to the surface of graphene through electrostatic adsorption.This composite delivers a discharge capacity of 1082,964,and 808 mAh·g-1 after 200 cycles at 3,5,and 8 C,respectively.The good electrochemical performance can be attributed to the synergistic effect between mesoporous nanorods and RGO,which not only offers high conductivity,nanoparticles,and abundant mesopores to accelerate electrode kinetics but also provides a more stable structure to reduce the volume effect during the charge/discharge process.Therefore,the mesoporous MnC2O4 nanorod/RGO composite could be used as an excellent candidate for its potential application in high-energy lithium-ion batteries.We synthesized C2O42-pillared CoFe-LDH/RGO composites(CF-2/RGO)by a hydrothermal ion exchang method.The pillared C2O42-broadens the interlayer spacing of CoFe-LDH.The lithium storage mechanism of CoFe-LDH/RGO is similar to that of hydroxycarbonate.The tetravalent carbon in oxalate is gradually converted to low valent carbon under the electrocatalysis of cobalt and iron.CoFe-LDH/RGO exhibits high specific capacity(1603 mAh g-1 after 120 cycles of 0.5 Ah g-1)and good cyclic-stability at high current density(1240 mAh g-1 after 500 cycles of 2 Ah g-1).The improved electrochemical performance can be ascribed to the synergistic effects of C2O42-and RGO that enhance the Li+and electron transport rate.At the same time,the heterogeneous interface formed by CoF e-LDH/AGO after discharge can accelerate Li+and electron transport,which can further improve the catalytic activity of cobalt and iron metal for lithium oxalate.Therefore,CoFe-LDH/RGO can find potential application in high energy density lithium-ion batteries. |
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