多孔碳纤维基柔性锂负极的可控构筑和储锂性能研究

CONTROLLABLE CONSTRUCTION AND LITHIUM STORAGE PERFORMANCE OF FLEXIBLE LITHIUM ANODE BASED ON POROUS CARBON FIBERS

赵尚纯

11849238

硕士

材料物理与化学

邓永红

2020-05-30

2020-07-01

哈尔滨工业大学

深圳

随着人们对多功能电子设备的需求变高，柔性可穿戴电子设备被认为是具有广阔前景的下一代便携智能设备。这对其能源储存部件的能量密度、柔韧性和循环稳定性提出了更高的挑战。金属锂因为具有极高的理论比容量（3860 mAh/g）、较低的电化学电势（-3.04 V vs. SHE)、较低的质量密度（0.534 g/cm 3 ）等优势，成为当前高能量密度柔性锂电池体系理想的负极材料。但没有载体依托的金属锂在电化学循环和机械形变过程中易形成锂枝晶和疲劳断裂。由此引发的电池性能衰减与安全性问题严重限制着高能量密度柔性锂电池体系的发展与实际应用。选择三维柔性集流体与金属锂复合是目前抑制锂枝晶生长和增强机械柔韧性的有效策略。商用碳织物虽然具有三维网络编织孔结构、较高的弹性极限、较低的质量密度、优异的电化学与热力学稳定性，但是作为金属锂三维柔性集流体仍受制于其较差的亲锂性、单一的微米级孔隙以及较低的比表面积，无法实现高负载循环稳定性与优异的机械柔韧性。本文通过独特的含氮聚合物分子刷生长、无电金属沉积、热处理和酸刻蚀等有序过程制备出不同刻蚀时间的多孔碳纤维（PCF）；采用 TEM、SEM、XRD、XPS、BET、拉曼光谱和柔性弯折平台测试等表征手段对 PCF 的结构形貌、掺杂元素价态、掺杂元素比例和动态面电阻等物化性质进行了系统表征。实验结果证实 5 分钟镍沉积、4 小时热处理以及 9 小时酸刻蚀可获得最优化的 PCF。该 PCF 具有高比表面积（2.61m 2 /g），均匀的孔径大小（平均宽度 10.48 nm），丰富的氮、镍元素含量（N：2.09%，Ni：5.26%）和较稳定的动态面电阻（0.125±0.010 Ω）。该优化条件下获得 PCF 对电沉积锂表现出较低的成核过电位（36.5 mV），对熔融锂可实现快速、均匀的浸润和吸附（8 秒浸润和吸附 8 mg 熔融锂）。用浸润和吸附热熔锂金属的方法得到的锂负极PCF@Li 组装的对称电池在 2 mA/cm 2 @2 mAh/cm 2 条件下可稳定运行 250 小时，在 4mA/cm 2 @4 mAh/cm 2 条件下也可运行 75 小时以上。PCF@Li 与高负载、高电压NCM622 柔性正极匹配组装的全电池经过百余次循环后其容量仍可保持 53.4%。本文这种科学有效的改性方法实现了碳布多级微纳孔隙结构的构筑、比表面积的调控以及表面异质元素的掺杂，促使PCF对熔融锂和电沉积锂均具有良好的亲和性。因此，PCF 作为三维柔性集流体能够为金属锂和锂电池提供优异的机械柔韧性和电化学稳定性。文中制备的高亲锂性、高比表面积的 PCF 对未来柔性锂电池的研究具有一定的借鉴意义；PCF@Li 柔性锂负极的制备方法简单易实现，有潜在的产业化价值。

As the demand for multifunctional electronic devices becomes higher, flexible wearable electronic devices are considered to be the next generation portable smart devices with broad prospects. This poses a higher challenge to the energy density, flexibility and cyclic stability of the energy storage components. Metallic lithium has become the ideal material for flexible high-energy-density lithium-metal batteries because of its high theoretical specific capacity (3860 mAh/g), low electrochemical potential (-3.04 V vs. SHE), and low mass density (0.534 g/cm 3 ). However, if there is no carrier for the metallic lithium, there will be the growth of lithium dendrites and fatigue fracture during electrochemical cycling and mechanical deformation. The application of bare lithium-metal anode results in the attenuation of the performance of batteries and severe safety issues, which limits the development and practical application of flexible high-energy-density lithium-metal batteries. In order to suppress the growth of lithium dendrites and enhance mechanical flexibility, it is an effective strategy to choose a three-dimensional flexible current collector to combine with metallic lithium. Commercial carbon fabric cannot achieve good cycling stability with high loading and good mechanical flexibility due to its poor lithiophilicity, monotonous micrometer pores and low specific surface area, while it has a three-dimensional network with many pore structures, higher elastic limits, lower mass density, and excellent electrochemical and thermodynamic stability. This means commercial carbon fabric is still not a good choice for the carrier of metallic lithium. Herein, porous carbon fibers (PCF) with different etching times were prepared through an orderly process which involved the growth of nitrogen-containing polymer molecular brushes, electroless metal deposition, heat treatment and acid etching. The physical and chemical properties of carbon fiber (such as morphology, the valence and proportion of elements and dynamic surface resistance) were systematically characterized by methods of transmission electron microscope, scanning electron microscope, X-ray diffraction, energy- dispersive X-ray spectroscopy, BET, Raman spectra and bending test, etc. The experimental results confirmed that the optimized PCF could be obtained by 5 minutes nickel deposition, 4 hours heat treatment and 9 hours acid etching. The optimized PCF had high specific surface area （2.61 m 2 /g）, uniform pore size (average width 10.48 nm), rich nitrogen and nickel content (N: 2.09%, Ni: 5.26%) and relatively stable dynamic surface resistance (0.125±0.010 Ω). This PCF showed a low nucleation overpotential (36.5 mV) for electrodeposited lithium. Meanwhile, it could achieve rapid and uniform infiltration and adsorption of molten lithium (adsorbing 8 mg molten lithium within 8 seconds). The symmetrical batteries assembled by the as-obtained anode (PCF@Li) could be stably operated for 250 hours at 2 mA/cm 2 @2 mAh/cm 2 and for more than 75 hours at 4 mA/cm 2 @4 mAh/cm 2 . When PCF@Li was matched with the high-loading and high-voltage cathode NCM622, the capacity retention rate of the full battery remained 53.4% after more than 100 cycles. This scientific and effective modification method achieves the construction of multi- level micro-nano pore structure on commercial carbon cloth, the adjustment of specific surface area and the doping of heterogeneous elements on the surface, and thus promotes the lithiophilicity for both molten lithium and electrodeposited lithium. Therefore, as a three- dimensional flexible current collector, PCF is able to provide excellent mechanical flexibility and electrochemical stability for lithium metal and lithium-metal batteries. The as-obtained PCF with high lithiophilicity and high specific surface area has certain reference significance for the research of future flexible lithium-metal batteries. The orderly preparation process of flexible lithium anode (PCF@Li) is easy to be operated, which shows industrial potential.

锂金属电池 柔性 多孔碳纤维 掺杂 功能化

lithium metal battery flexible porous carbon fibers doping functionalization

中文

联合培养

南方科技大学

赵尚纯. 多孔碳纤维基柔性锂负极的可控构筑和储锂性能研究[D]. 深圳. 哈尔滨工业大学,2020.