Conversion of Lignin into Porous Carbons for High-Performance Supercapacitors via Spray Drying and KOH Activation: Structure-Properties Relationship and Reaction Mechanism

Lignin-derived porous carbons have emerged as promising electrode materials for supercapacitors.However,the challenge remains in designing and controlling their structure to achieve ideal electrochemical performance due to the complex molecular structure of lignin and its intricate chemical reactions during the activation process.In this study,three porous carbons were synthesized from lignin by spray drying and chemical activation with vary-ing KOH ratios.The specific surface area and structural order of the prepared porous carbon continued to increase with the increase of the KOH ratio.Thermogravimetric-mass spectrometry(TG-MS)was employed to track the molecular fragments generated during the pyrolysis of KOH-activated lignin,and the mechanism of the thermochemical conversion was investigated.During the thermochemical conversion of lignin,KOH facili-tated the removal of H2 and CO,leading to the formation of not only more micropores and mesopores,but also more ordered carbon structures.The pore structure exhibited a greater impact than the carbon structure on the electrochemical performance of porous carbon.The optimized porous carbon exhibited a capacitance of 256 F g-1 at a current density of 0.2 A g-1,making it an ideal electrode material for high-performance supercapacitors.

Advanced Li-SexSy battery system:Electrodes and electrolytes

The worldwide energy shortage has led to numerous researches for the exploration of new-type battery materials to deal with the energy crisis.To achieve a great leap in energy density,the study of high capacity electrode materials plays a major role.As a replacement to the energy accumulation system of lithium-sulfur(Li-S) and lithium-selenium(Li-Se) batteries,great concern is generated over lithium/selenium-sulfur(Li-SexSy) batteries as they combine the advantages of S(high capacity) and Se(improved electrical conductivity),consequently stands for extensive new cathode materials.In recent years,widespread researches have been conducted and great achievements have been published.This review sums up the research status on Li-SexSy batteries and concentrates on the outstanding work of SexSy cathode materials.The reaction mechanism and capacity fading mechanism are discussed.The performance-structure relationship is stated in regard of different cathode structures,including a variety of carbon hosts,conducting polymer hosts,transition metal-doped carbon electrodes and various Se/S ratio.The compatibilities of frequently-used carbonate-based and ether-based electrolyte and other new-type electrolytes for Li-SexSy battery are demonstrated.Prospects for the future developments of Li-SexSy batteries are finally proposed.

Phenylenediamine-formaldehyde chemistry derived N-doped hollow carbon spheres for high-energy-density supercapacitors

Porous carbon spheres represent an ideal family of electrode materials forsupercapacitors because of the high surface area,ideal conductivity,negligible aggregation,and ability to achieve space efficient packing.However,the development of new synthetic methods towards porous carbon spheres still remains a great challenge.Herein,N-doped hollow carbon spheres with an ultrahigh surface area of2044 m^(2)/g have been designed based on the phenylenediamine-formaldehyde chemistry.When applied in symmetric supercapacitors with ionic electrolyte(EMIBF_4),the obtained N-doped hollow carbon spheres demonstrate a high capacitance of 234 F/g,affording an ultrahigh energy density of 114.8 Wh/kg.Excellent cycling stability has also been achieved.The impressive capacitive performances make the phenylenediamine-formaldehyde resin derived N-doped carbon a promising candidate electrode material for supercapacitors.