Preparation And Performance Research Of Pitch-based Carbon Nanosheets As Anodes For Potassium Ion Batteries

In recent years,the excessive use of non-renewable energy sources such as coal and petroleum has affected the sustainable development of human society,and the energy structure of human society needs to be changed urgently.Strategies currently adopted include the development of renewable energy such as wind,water,and tidal energy.However,the renewable energy make higher requirements for energy storage equipment.Electrochemical energy storage has been widely used because of its advantages such as high efficiency and convenience.The traditional lithium-ion battery has the advantages of high energy efficiency and long life,so it is widely used in various fields.However,with the development of lithium-ion battery technology and the increase in demand,the limited reserves of metal lithium cannot meet the needs of social development.As an ideal substitute for lithium ion batteries,potassium ion batteries?KIBs?have been extensively investigated in recent years.However,KIBs face poor rate cycle performance,low reversible capacity,and safety issues that have restricted their further development.It is very important to develop high-performance potassium ion battery anodes.In this paper,mesophase pitch is used as raw material,based on capillary force induce nano-printing strategy,a carbon nanosheet with special morphology and heteroatom doping was successfully prepared and applied to KIBs anodes.The relationship between the structure and the electrochemical performance of the carbon-based anode was explored,and explored the effect of doping on the electrochemical performance at the same time.The main research work is as follows:?1?Using mesophase pitch as raw materials and NaCl/KCl as salt template,stacked tile-like carbon sheets?STCSs?with highly orientated carbon clusters was synthesized through capillary force-induced nano-rubbing method.The carbon clusters of STCSs are long-range orderly arranged,which makes the STCSs have a high K⁺diffusion coefficient and electrical conductivity.STCSs have excellent potassium ion storage performance when used as anode for KIBs.The reversible capacities of STCSs at 1 A g^-1 and 5 A g^-1 are 192 mAh g^-1 and 150 mAh g^-1.It also has a high reversible capacity of 314 mAh g^-1 at a current density of 0.05 A g^-1.After cycling 500 and 1000 cycles at a current density of 0.5 A g^-1,the capacity of STCSs can maintain 158 and 139 mAh g^-1,with the cycle retention is 83.1%and 73.2%,respectively.?2?Using mesophase pitch as raw material,NaCl/KCl as salt template,SnCl₂ as Sn source,sodium tripolyphosphate,phytic acid and red phosphorus as P source,combined with capillary force-induced nano-rubbing method,two different carbon-based KIBs anode,Sn-doped and P-doped materials were prepared.The experimental results show that the reasonable design of the nanostructure and composition of the material has a significant effect on the electrochemical performance of the potassium ion battery anode material.Electrochemical test results show that Sn doping will reduce the electrochemical performance of pitch carbon nanosheets,but proper Sn doping could improve the performance of carbon nanosheets.P-doping can significantly improve the electrochemical performance of anodes.The sample prepared by using sodium tripolyphosphate as P source has a reversible capacity of 367 mAh g^-1 at 0.05 A g^-1,54%of the initial coulomb efficiency?ICE?and high cycle retention of 84.9%after 1000 cycles.Red phosphorus-based pitch-based carbon nanosheets also has an excellent electrochemical performance,with a reversible capacity of 468 mAh g^-1 at a 0.05 A g^-1,a high ICE of 64%,and cycle retention of 83.8%after 1000 cycles at 0.5 A g^-1.