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Design,Preparation And Lithium Storage Performance Of Three-dimensional Porous Carbon-based Composites

Posted on:2021-05-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:X H TianFull Text:PDF
GTID:1361330605453409Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
With the increasingly serious energy crisis and environmental pollution,the research and development of renewable clean energy to replace non-renewable fossil energy has become a major problem to be solved urgently.Secondary batteries are a kind of important energy storage devices,among which the lithium ion battery is widely used due to its advantages of high energy density and long cycle life.The cathode is the core component of lithium ion battery.Both Li FePO4 and Ni-Co-Mn ternary cathode materials are currently the most promising cathodes for lithium ion battery.However,their own shortcomings result in the poor high rate performance and cycle stability.Therefore,the development of cathodes with excellent performance and low cost is the research focus of lithium ion batteries.Lithium sulfur battery is recognized as the most promising next-generation lithium secondary batteries due to its high theoretical specific energy and theoretical specific capacity.However,lithium sulfur battery has shortcomings such as low conductivity of elemental sulfur and Li2S,high solubility of intermediate lithium polysulfides in the electrolyte,and large volume changes during charge and discharge processes,leading to low utilization of active materials,poor rate performance and short cycle life,and severely restricting their commercial development.Therefore,how to improve the utilization rate of active material,cycle life and rate performance has become a research focus of lithium sulfur battery.Constructing a three-dimensional porous carbon-based composite can significantly increase the electrical conductivity,increase the specific surface area,and ease the volume change,thereby promoting the rapid diffusion of electrons and Li+,reducing the polarization of electrode reactions,and improving the reaction kinetics and stability of the electrodes.Therefore,designing simple and controllable methods to construct three-dimensional porous carbon-based composites has important research significance.Based on this,the main research of this thesis is as follows:?1?The three-dimensional porous graphene aerogel framework was introduced into Li FePO4 submicron-rods and LiNi0.6Co0.2Mn0.2O2 nanoparticles using rapid freeze-drying technology and hydrothermal method respectively,to realize the synergistic effect of three-dimensional porous graphene aerogel and micro-nano structure.The results showed that when three-dimensional porous graphene aerogel was combined with the above-mentioned Li FePO4 submicron-rods or LiNi0.6Co0.2Mn0.2O2 nanoparticles,the electrochemical properties of the composites were significantly improved,which are expected to become excellent cathode materials for high-performance lithium ion battery.?2?The ideal sulfur host for lithium sulfur battery should possess the large hollow structure,strong lithium polysulfides affinity and good conductivity.The three-dimensional porous graphene aerogel-supported NiCo2O4 and Co9S8 nanoparticles were successfully prepared as the high performance sulfur hosts in this thesis.The three-dimensional porous graphene aerogel structure composed of the intertwined highly conductive graphene can significantly improve the utilization of active materials,physically inhibit the loss of lithium polysulfide and relieve volume change during charge and discharge processes,and accelerate electrons/Li+transfer,thus improving the rate performance and stability of composites.Meanwhile,metal oxides or metal sulfides can not only chemisorb lithium polysulfides generated during the charge and discharge processes,but also promote the catalytic conversion of lithium polysulfide,thus significantly inhibiting the"shuttle effect".The results showed that due to the synergistic effect of high conductivity,porosity,enhanced adsorption and catalytic conversion,the three-dimensional porous graphene aerogel-supported NiCo2O4 and Co9S8 nanoparticles are expected to be the sulfur hosts for high performance lithium sulfur battery.The design provides a new feasible way for the preparation of cathode material for high performance and long life lithium sulfur battery.?3?In order to achieve the high areal sulfur loading and low E/S value of lithium sulfur battery electrode materials,the hierarchical porous polar NiCo2O4 nanosheets or porous polar Co9S8 nanosheets were successfully grown in situ on a porous conductive carbon cloth substrate by solvothermal method.The obtained composites can accommodate a large amount of sulfur or lithium polysulfide,and which were subsequently used as electrode material directly for lithium sulfur batteries.Due to the synergy between the fast electron transfer framework originated from the porous conductive carbon cloth and the porous structure constructed by the interconnected nanosheets,the obtained three-dimensional porous composite electrodes can significantly accelerate the electron/Li+transfer and effectively alleviate the volume change during the charge and discharge processes when directly acted as the sulfur hosts.In addition,the porous structure formed by interlacing polar Ni Co2O4/Co9S8 nanosheets can not only provide a large space for the physical adsorption of lithium polysulfide,but also capture lithium polysulfide through the chemical interaction with lithium polysulfide,thus effectively inhibiting the"shuttle effect"in the continuous charging and discharging processes.More importantly,the chemical interaction between the polar NiCo2O4/Co9S8and lithium polysulfide also significantly enhanced the redox reaction kinetics of lithium polysulfide conversion.Due to the synergy between high electrical conductivity,strong physical/chemical adsorption of lithium polysulfide,large three dimensional void space and high catalytic activity,the three-dimensional porous composite electrodes used in lithium sulfur batteries exhibit the high specific capacity,excellent rate capability and good cycle stability even at high areal sulfur loading and low E/S value,which are expected to be used in high-performance commercial lithium sulfur battery.
Keywords/Search Tags:Three-dimensional porous structure, Graphene aerogel, Self-supporting composite electrode, Lithium ion battery, Lithium sulfur battery
PDF Full Text Request
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