High Temperature And High-pressure Preparation Of Anode Materials For Carbon-based Lithium Ion Batteries

In recent years,along with the process of economic globalization and the rising demand for energy,various energy-saving devices such as rechargeable batteries and supercapacitors have become research hotspots in the energy field.Among them,lithium-ion batteries are favored by people because of their high voltage,high energy density,long cycle life and light weight.However,the commercial lithium-ion batteries at this stage cannot fully meet the energy requirements such as hybrid electric vehicles（HEVs）,pure electric vehicles（EVs）,and large equipment in terms of energy density.The reason is that in addition to the influencing factors such as the cathode and the electrolyte,the graphite carbon anode has a low theoretical capacity and cannot meet the requirements of a high-performance lithium ion battery.Therefore,under the premise of ensuring the safety of the battery,how to improve the specific capacity of the carbon anode by changing the structure of carbon is an urgent task for researchers.The morphology and structure of carbonaceous anode materials have an important influence on the energy storage performance of lithium.The pores and surface structures can enhance the surface-to-volume ratio of the electrode-electrolyte interface,shorten the ion transport length,reduce the charge transport resistance and enhance the electrode material.The ionic conductivity can thus improve the performance of LIBs.Therefore,it is important to design and develop appropriate methods to modify the morphological structure of carbonaceous anode materials or to explore carbonaceous anode materials with higher energy/power density,lower cost,and safety.In fact,the changes in microstructure,morphology and graphitization of carbon materials depend mainly on their preparation process and precursor materials.Among them,since the pressure can change the solubility,viscosity,density,phase separation and carbon graphitization behavior of the precursor carbonization process,the carbonization technology under pressure provides a wider range of control of material composition and microstructure,and then optimizes A new approach to material performance.Based on this,in the past few decades,researchers have conducted a lot of research in order to obtain high-performance carbon anode materials by self-boosting method,hydrothermal carbonization method and reduction of CO₂ under pressure,and have achieved many gratifying results.However,we have found that in the past,due to the limitations of synthetic equipment,carbonization studies under many pressures have this one-way thermodynamic behavior of temperature control pressure,that is,carbonization studies under many pressures only consider one of two parameters.Such as high-pressure carbonization rather than high temperature,or at high temperatures rather than high pressure.However,there is still a lack of research on the use of pressure and temperature synergistic pyrolysis carbonization under static pressure.In this paper,the filter paper rich in wood fiber was used as the starting material,and the thermodynamic behaviors such as temperature,pressure and heating rate of carbonization were studied by means of static pressure sintering technology.Moreover,the pyrolytic carbon materials with different morphology and structure were tested as the negative electrode of the lithium ion battery.The results are as follows:（1）The effects of temperature,pressure and heating rate on the carbonization behavior of filter paper and the morphology and structure of carbon materials were studied.On the basis of this,these pyrolytic carbons were used as the anode materials of lithium ion batteries for electrochemical research.（2）The preparation of porous carbon by template method under high temperature and high-pressure conditions was carried out to increase its capacity.Different molar masses of transition metal（Fe,Co）ions were used as catalysts for increasing the degree of graphitization and were carbonized after isostatic pressing.（Fe,Co）ions to prepare a porous carbon material having a high degree of graphitization.On this basis,its electrochemical performance and lithium storage mechanism were analyzed.（3）Previous studies have shown that the defects of carbon materials are beneficial to the storage of lithium ions.Therefore,we investigated the process of preparing carbon anode by static pressure sintering with metal ion as template.The electrochemical tests show that the anode prepared by this method has good performance.