Preparation And Lithium Storage Properties Of Cobalt-Based Modified Porous Carbon Anode Materials

Lithium-ion batteries have been widely used in energy storage fields,due to its high energy density,non-memory effect and environmental friendness.The development and application of high-performance electrode materials is one of the keys to improving the performance of lithium-ion batteries.Commercial anode materials are mostly graphite,but it has been unable to meet the pursuits of high-performance batteries due to its low capacity.Porous carbon materials have become research hotspots due to large specific surface area,fast ion transmission,and exhibit a higher specific capacity.ZIF-67 can be used as a template or precursor to synthesize porous carbon materials due to its advantages,such as uniform pores,large specific surface area and adjustable composition and structure.However,ZIF-67 materials are easy to agglomerate and expand in volume.Therefore,how to effectively overcome volume expansion,improve the structural stability and increase the specific capacity of the materials is an urgent problem to obtain excellent anode materials.This paper aims to improve the electrochemical performance of ZIF-67 derived carbon materials,the design of stable nanostructures,and the introduce of components that can increase the specific capacity of the materials to obtain carbon-based lithium ion anode materials with excellent electrochemical performance.ZIF-67was prepared under mild conditions and used as a precursor or template,then carbon coating,heteroatom doping and bimetallic compositing were carried out,and Co@NC hollow nanospheres,Co@NSC hollow nanospheres and Zn-Co-S@NC nanocore-shell structure were successfully synthesized.The influence of carbon coating,heteroatom doping and bimetallic sulfide compositing on the lithium storage performance of these three carbon-based materials were investigated.The main contents were as follows.1.Cobalt nitrate and dimethylimidazole were used as raw materials to synthesize ZIF-67 that was used as a template,then coated with dopamine.After polymerization and subsequent pyrolysis,the Co@NC material was obtained.The Co@NC consisted of cobalt nanoparticles that evenly wrapped in nitrogen-doped hollow carbon nanospheres to form a nano-scale hollow structure.The outer layer electrons of the metal cobalt nanoparticles in the hollow structure were transferred to the nitrogen-doped carbon nanospheres,which improved the ability to adsorb lithium ions,and at the same time improved the conductivity of the carbon material.The introduction of nitrogen increased the defects and accelerated the transmission rate of lithium ion.The formation of this hollow porous structure relieved the volume expansion of the structure and enhanced the structural stability of the material.The Co@NC hollow porous sphere showed a higher specific capacity(At 0.5 A g^-1,the reversible specific capacity reached 627.5 m Ah g^-1after 300 cycles;the reversible specific capacity can still remain 358.6 m Ah g^-1 after 650cycles even at 1 A g^-1),but the rate performance needed to be improved(The reversible specific capacity reached 233.6 m Ah g^-1 at 5 A g^-1).2.Using ZIF-67 as the precursor,polydopamine as the second carbon source,and L-cysteine hydrochloride as the sulfur source,Co@NSC hollow nanospheres were prepared via thermal cracking.The cracking temperature and double atom doping on the lithium storage performance were investigated.In the hollow Co@NSC nanospheres,the increase of cobalt content further improved the conductivity of the carbon material.Meanwhile,the co-doping of nitrogen and sulfur caused abundant defects in the carbon material,which provided more active sites for lithium ion adsorption,thereby improving lithium storage performance of the materials(At 0.5 A g^-1,the reversible specific capacity reached790.0 m Ah g^-1 after 350 cycles;the specific capacity can still maintain 429.0 m Ah g^-1after 500 cycles even at 1 A g^-1),and the rate performance was significantly improved(Reversible specific capacity reached 424.8 m Ah g^-1 at 5 A g^-1).3.The Zn/Co-ZIF-67 precursor was prepared using cobalt nitrate,zinc nitrate and dimethylimidazole as raw materials,and then coated and vulcanized with dopamine to successfully prepared Zn-Co-S@NC nanospheres with a core-shell structure.The effects of cracking temperature,sulfur source types and bimetallic species on the lithium storage performance of carbon-based material was explored.In the Zn-Co-S@NC core-shell structure,the bimetallic sulfide exerted the high electrochemical reaction activity and the synergistic effect of the bimetallic species to further enhance the capacity.In addition,the core-shell structure further alleviated the volume expansion of the active material,and significantly improved the structural stability and reversible specific capacity(At 0.5 A g^-1,the reversible specific capacity reached 859.2 m Ah g^-1after 300 cycles;the capacity can still maintain 677.6 m Ah g^-1 after 800 cycles even at 1 A g^-1),and showed excellent rate performance(Reversible specific capacity reached 495.8 m Ah g^-1 at 5 A g^-1).