【作者】 刘璐；

【导师】 欧阳婷；

【作者基本信息】 湖南大学 ， 材料科学与工程， 2023， 硕士

【摘要】 目前,便携式电子产品和电动汽车等新能源市场呈爆发性增长,这在很大程度上促进了锂电池（LIBs）的技术创新。为了提高LIBs的面积容量和功率密度,电极结构设计需要进一步优化。厚电极设计可以通过最小化非活性组分占比来显著提高电极活性材料负载,从而提高LIBs的整体能量密度。然而,电极厚度增加也会导致电极电荷动力学缓慢和电极机械不稳定性问题。在本论文中,使用商业化活性材料降低成本,微米级碳纤维作为骨架,酚醛树脂作为粘结剂,通过浆料制备、真空抽滤、固化和炭化的过程制备高负载量自支撑厚电极,并在其中复合导电性能优异的CNT来改善整体电极材料电荷传输。研究工作从以下三个方面开展:（1）通过浆料制备、真空抽滤、固化和炭化制得的复合不同含量CNT的3D自支撑Ti O₂基厚电极为多孔结构,可以促进电解液的在电极内部渗透以及锂离子的快速传输。复合20%CNT的厚电极CTC-20表现出最优异的倍率性能,分别在电流密度为0.0125、0.025、0.05、0.1和0.25 A g^-1时,其可逆容量有6.1、5.5、4,9、4.2和1.8 m Ah cm^-2。同时,CTC-20具有良好的循环稳定性,在0.1 A g^-1的电流密度下,循环200圈,仍然能保持3.4 m Ah cm^-2的面积比容量,这可得益于CNT的添加提高厚电极的导电性,从而提高了活性材料的利用率。（2）通过浆料制备、真空抽滤、固化和炭化成功制备复合0和20%含量CNT的3D自支撑商业化Nb₂O₅和Li Fe PO₄（LFP）基高负载量自支撑厚电极,在厚电极优良的机械稳定性基础上分析20%CNT添加量的厚电极制备策略对Nb₂O₅和Li Fe PO₄（LFP）基厚电极电化学性能和锂离子传输动力学的影响。复合20%CNT的CNC-20和CLC-20均表现出最优异的倍率性能,CNC-20在不同的倍率0.1、0.3、0.5、0.8、2、3 C测试条件下可逆容量有5.2、4.4、4.0、3.5、1.8、0.7 m Ah cm^-2。CLC-20在不同的倍率0.05、0.1、0.2、0.5、1、2 C测试条件下,其可逆容量分别为5.3、4.9、4.6、4.2、3.6、2.3 m Ah cm^-2。同时,CNC-20和CLC-20具有良好的循环稳定性,在1 C电流密度下循环200圈后仍然能表现出较好面积比容量。添加CNT之后的厚电极表现出更好的储锂容量和循环稳定性可归因于厚电极导电性能的提升。（3）对于不同的商业化活性材料,复合20%CNT的自支撑厚电极均表现出最优的电化学性能,通过原位拉曼分析CNT对不同活性材料厚电极在充放电过程中的原位光谱的以及拉曼特征峰D峰G峰强度变化的影响。不同电压下拉曼光谱的I_D/I_G变化均说明复合CNT之后其变化差异减小,可以说明加入CNT之后其结构稳定性得到提升;同时与不加入CNT的厚电极相比其I_D/I_G值相对较小,这归因于CNT的加入提高整体电极的导电性能。更多还原

【Abstract】 The current explosive growth of new energy markets such as portable electronics and electric vehicles has largely contributed to the technological innovation of lithium batteries（LIBs）.In order to improve the area capacity and power density of LIBs,the electrode structure design needs to be further optimized.Thick electrode designs can significantly increase the electrode active material loading by minimizing the percentage of inactive components,thus improving the overall energy density of LIBs.However,increased electrode thickness can also lead to slow electrode charge kinetics and electrode mechanical instability problems.In this thesis,high loading self-supporting thick electrodes are prepared using commercially available active materials at reduced cost,micron-scale carbon fibers as the backbone,and phenolic resin as the binder,and the overall electrode material charge transport is improved by compounding CNTs with excellent electrical conductivity into them through the process of slurry preparation,vacuum filtration,curing,and carbonization.The research work was carried out in three aspects as follows:（1）The 3D self-supported Ti O₂-based high loading thick electrodes doped with different contents of CNT were fabricated as porous structures to promote electrolyte penetration and rapid lithium ion transport.The thick electrode CTC-20 doped with 20%CNT exhibited the most excellent multiplicative performance with reversible capacities of 6.1,5.5,4,9,4.2 and 1.8 m Ah cm^-2 at current densities of 0.0125,0.025,0.05,0.1and 0.25 A g^-1,respectively.meanwhile,CLC-20 had good mechanical properties and cycling Meanwhile,CLC-20 shows good mechanical properties and cycling stability,maintaining an area specific capacity of 3.4 m Ah cm^-2 at a current density of 0.1 A g^-1for 200 cycles,which can be attributed to the addition of CNT to improve the conductivity of the thick electrode,thus increasing the utilization of the active material.（2）3D self-supported commercial Nb₂O₅（CNC-0 and CNC-20）and Li Fe PO₄（LFP）（CLC-0 and CLC-20）based high loading self-supported thick electrodes doped with 0and 20%content of CNT were successfully prepared,and the thick electrode preparation strategy with 20%CNT addition was analyzed on the basis of the excellent mechanical stability of the thick electrodes on the Nb₂O₅ and Li Fe PO₄（LFP）-based thick electrodes on the electrochemical performance and lithium ion transport kinetics based on the excellent mechanical stability of the thick electrodes.Both CNC-20 and CLC-20 exhibited the most excellent multiplicative performance,with CNC-20 having reversible capacities of 5.2,4.4,4.0,3.5,1.8,and 0.7 m Ah cm^-2 at different multiplicative rates of 0.1,0.3,0.5,0.8,2 C.The reversible capacities of CLC-20 are5.3,4.9,4.6,4.2,3.6 m Ah cm^-2 at different multipliers of 0.05,0.1,0.2,0.5,1,and 2C.At the same time,CNC-20 and CLC-20 have good mechanical properties and cycling stability,and still exhibit good areal specific capacity after 200 cycles at 1 C.The thick electrode after the addition of CNT exhibits better lithium storage capacity and cycling stability can be attributed to the improved conductivity of the thick electrode.（3）For different commercially available active materials,the self-supported thick electrodes doped with 20%CNT exhibited the optimal electrochemical performance,and the effect of CNT on the in situ spectra of thick electrodes with different active materials during charging and discharging as well as the Raman characteristic peak D peak G peak was analyzed by in situ Raman.The variation of I_D/I_G in Raman spectra at different voltages indicated that the variation was reduced after CNT doping,which could indicate that the structural stability was improved after CNT addition;meanwhile,the I_D/I_G values were relatively small compared with those of thick electrodes without CNT addition,which was attributed to the addition of CNT to improve the overall electrode conductivity.更多还原