Preparation And Application Of Battery Anode Material From Pulping Waste Liquid

With the expansion of the paper and paperboard demand,the size and the pulp and paper industry have been rapidly developed in the last decades.During the manufaction of paper,the generated pulping waste liquid（PWL）is usually sent to the alkali recovery section for direct combustion,where the recovery of inorganic sodium salts and the thermal energy could be achieved.However,this process caused a tremendous waste of plant resources.In PWL,the main inorganic substance are sodium salts,while lignin is the major organic component.In addition,lignin is also a wide-spreading renewable resource on the earth and is considered as a good biomass carbon precursor.The utilization of sodium ions and lignin in the PWL could not only contribute to the pollution control of the industry,but also improve the economic viability of the process.Therefore,it becomes one of the key problems to be solved by the pulp and paper industry.In this work,PWL was used as a biomass carbon precursor to synthesize lithium and sodium ion battery anode materials.Activation and doping treatment were used during the preparation to generate anode materials with high specific capacity.This work could provide a theoretical guidance for the preparation of PWL-based biomass carbon materials and their applications in energy storage materials.The main research results of the thesis are listed as follows.A sulfur-doped porous carbon material was synthesized through the self-activation and in-situ sulfur doping of eucalyptus sulfate PWL.Applications of this carbon material as the anode material in lithium ion battery was investigated,where the initial specific discharge capacity reached up to 688 m Ah·g^-1,and the first coulombic efficiency was 53.96%.A specific discharge capacity of 150 m Ah·g^-1,was viewed under a large charge-discharge current density(2 A·g^-1).In addition,after1000 cycles,68%capacity retention rate could be achieved at a current density of 1A·g^-1.The formation of porous structure could be attributed to the activation of residual alkali in the PWL,while the sulfur doping sourced from the unreacted cooking agent like Na₂S and other sulfates.Porous carbon precursors with stable skeleton structure and carbon quantum dots with ultraviolet fluorescence characteristics were obtained by applying air activation treatment on the eucalyptus sulfate PWL.These porous carbon precursors were further activated by phosphoric acid to generate graded porous carbon materials with a specific surface area upto 1653.6 m²·g^-1.The amount of phosphoric acid for the activation and calcination treatment temperature was optimized to prepare anode material of lithium ion battery.These anode materials presented outstanding electrochemical performance,where the first discharge specific capacity reached up to1498 m Ah·g^-1,the specific capacity was about 200 m Ah·g^-1 at a current density of 2A·g^-1,the reversible specific capacity maintained at about 242 m Ah·g^-1 at a current density of 1 A·g^-1,and the capacity retention rate was 82.8%after 700 cycles.Sulfur powder was added into air activated carbon precursor from eucalyptus sulfate PWL to perform sulfur doping.The sulfur doped porous carbon material was obtained with 1:3 doping at 600℃calcination temperature.The carbon material generated was of 27%sulfur doping rate,408 m²·g^-1specific surface area and rich in micropores.Remarkably,this carbon material showed an outstanding cycle and rate performance when applied as the anode material of sodium ion battery,where the first discharge specific capacity reached up to 594.8 m Ah·g^-1,the first coulomb efficiency reached upto 63.82%,the reversible specific capacity remained around 166 m Ah·g^-1under 2 A·g^-1 charge and discharge current density,and with the reversible specific capacity returned to 320 m Ah·g^-1 when the current density was 50 m Ah·g^-1.The reaction mechanism was invastigated through XRD,Raman,SEM,TEM,XPS,and BET characterization.It was proposed that sulfur doping helped electron conduction during charge and discharge,expanded the interlayer spacing of the carbon layer,and provided more active sites for Na⁺.Therefore,this work prepared high-capacity SIBs anode materials through a noval approach by combining inexpensive and abundant sulfur powder with papermaking waste liquid.