Carbonization Behavior Of Straw Under High Pressure And Its Application As Anode Material Of Lithium Ion Battery

In recent years,low-cost biomass material as a renewable resource has been widely concerned in the preparation of carbon materials.Natural biomass materials usually have rich microstructure,which makes it possible to prepare carbon materials with different structures.In addition,when these bio derived carbon materials are used as the anode materials of LIBS,they show high capacity,good rate performance and cycle stability.Although various preparation technologies have been used to study the carbonization behavior of biomass materials under different temperatures and pressures,such as crystallinity,chemical composition and microstructure,and many innovative results have been obtained.However,at present,carbonation research under pressure,such as self boosting method and hydrothermal method,belongs to one-way thermodynamic behavior,that is,temperature controlled pressure,lacking of a study on carbonation behavior under pressure and temperature controlled state.Based on this,in this paper,the carbonization behavior,such as structure,morphology and electrochemical lithium storage performance of corn straw under different pressure and temperature were studied by static high pressure pyrolysis:?1?The carbonization behavior of corn stalks and leaves and the effect on the morphology and structure of pyrolyzed carbon under different temperature and pressure conditions were studied.It was found that the graphitization degree,crystallinity and order degree of the two pyrolytic carbon increased with the increase of temperature and pressure.Under the same conditions,the graphitization degree of pyrolysis carbon of straw stem is higher than that of straw leaf.In addition,under the action of temperature and pressure,the pyrolysis carbon of straw stems is easy to appear interconnected macroporous sheet structure,while the pyrolysis carbon of straw leaves is easy to appear petal like particle structure.Finally,based on van Krevelen diagram,we speculated on the mechanism of carbon nano sheet formation under pressure.?2?The above-mentioned carbon materials were used as the anode of lithium-ion batteries,and their electrochemical lithium storage performance was studied.We found that the increase of pressure and temperature reduced the specific discharge capacity of the first cycle of pyrolysis carbon of straw stem and leaf,improved the first cycle coulomb efficiency,and the rate performance became worse.At the same time,temperature has a great influence on the reversible capacity of the carbon.With the increase of temperature,the reversible capacity of the carbon decreases to some extent,while the pressure has a little influence on the reversible capacity of the carbon.In addition,the reversible capacity of pyrolysis carbon of straw leaves prepared under low pressure is higher,and the increase of pressure will lead to the decrease of reversible capacity of pyrolysis carbon of straw leaves.It was found that the increase of temperature and pressure enhanced the conductivity of the two carbon materials,but the ion transfer rate decreased.?3?In order to further improve the electrochemical performance of the pyrolytic carbon anode,we prepared a Co₃O₄?NiO?/C composite material under pressure using corn straw as a carbon source.The study found that with the increase of the metal oxide content,the disorder and the degree of defects of the composites increased.In addition,Co₃O₄/C composites are prone to produce spherical nano-flower-like structures,while NiO/C composites are prone to produce nano-flaky structures.Based on this,we have studied the electrochemical properties and lithium storage mechanism of Co₃O₄?NiO?/C composites.