Study On Biomass Carbon Derived From Hemp Stalks As Anode For Lithium Ion Battery And Its Electrochemical Properties

In this age,energy and the environment are the two major concerns of world development.In recent years,due to the abundance of agricultural waste resources such as rice husks,stalks,and fibers and their renewable nature,the rational use of these agricultural wastes is of great significance.Among them,the use of biomass carbon to prepare anode materials for lithium-ion batteries is an important approach.The negative electrode of a lithium-ion battery has a large impact on its electrochemical performance,but so far,it has not yet been determined which materials and processes will have a large beneficial effect on battery performance.The reasonable application of agricultural waste,such as rice husks and stalks,can not only reduce environmental pollution and waste of resources caused by improper disposal of agricultural waste,but also increase the added value of the corresponding industry and increase agricultural income.It is the concern of domestic and foreign researchers hot issues.At present,China has abundant hemp stalks resources,and most of them have not been effectively used.The application prospect of hemp stalks is environmentally friendly and sustainable.The material itself has the advantages of natural porosity,and the process for preparing anode materials is simple,convenient,efficient and green.In this paper,hemp stalks,which are cheap and readily available,are used to prepare high-value porous carbon anode materials.Porous carbon materials and cryogenic porous carbon materials are prepared by different treatment methods and process flows,respectively.The microstructures of these materials were characterized and analyzed.They were used in anode of lithium-ion battery and tested for electrochemical performance.The main research contents and results are as follows:?1?Formulation of experimental scheme:Hemp stalks has a good natural porous structure,so chemical activation can be used to take advantage of its porosity.In order to reduce the impact of tar on the activation process and increase the yield of activated carbon,two-step activation method was adopted to prepare hemp stalks derived activated carbon material instead of one-step activation method.Since the cryogenic process has the effect of thermal expansion and contraction of the material,the activated carbon material can be further subjected to the cryogenic process by this principle to achieve the effect of widening the pore diameter.It can be known from the relevant literature that the activation temperature and the cryogenic temperature have a relatively important influence on the performance of activated carbon,so the best activator and activation ratio can be initially selected directly through single-factor experiments without orthogonal experimental design.Finally,the influence mechanism between the above factors,the structure of the porous carbon material and the electrochemical performance is reasonably obtained.?2?Hemp stalks is used as the raw material to prepare porous carbon material by two-step activation method,including remove the oil by low-temperature carbonization,activate pores structure at high temperature and removing impurities by pickling.Prepared porous carbon material is used as anode material for lithium ion battery,and its electrochemical performance is analyzed.The influence of activator and activation ratio on the electrochemical performance of lithium ion batteries was discussed,and the effect of activation temperature on the ZnCl₂ activation method of hemp stalks was investigated.At600?,hemp stalks and ZnCl₂ have the best activation effect when the mass ratio is 1:5.There are a lot of micropores and a few mesopores in the activated carbon,and the specific surface area is 589 m²/g.When it is used as the negative electrode of a lithium ion battery,the discharge specific capacity is the highest,and after cycling 100 times at 0.2 C rate,it reaches 495.4 mAh/g.Compared with the unactivated hemp stalks-based carbon material,the electrochemical performance has been greatly improved,which is mainly due to the good activation effect leading to a more reasonable distribution of the internal pore structure of the activated carbon material and a large number of active sites.?3?Hemp stalks is used as the raw material.The above-mentioned activated carbon derived from hemp stalks was subjected to high-temperature treatment to remove oxygen-containing functional groups,and placed in a deep-freezing box for deep-cooling treatment,then gradually cooled to-185?.Then returned to room temperature to obtain a cryogenic activated carbon material.This was used as a negative electrode material for lithium ion batteries,and its electrochemical performance was analyzed.The influence of activation ratio on the final structure and morphology of the material is discussed,and the mechanism affecting the electrochemical performance of lithium ion batteries is analyzed.The effects of activation temperature on cryogenic activated carbon materials derived from hemp stalks were investigated.When the activation temperature is 500?and the cryogenic treatment is performed at-180?,the material has a better pore structure,the material is more fragmented,and more mesopores and new pores are generated.The specific surface area of the material is 1728 m²/g.These features will provide more active sites for the cyclic insertion/extraction of lithium ions,and provide greater free movement space for the rapid transport of lithium ions in the material.After 100 cycles of charging and discharging at 0.2 C,the specific capacity It reached 756.8 mAh/g.