人造石墨改質作為動力鋰離子電池負極材料

Abstract

本研究目的主要在探討人造石墨的改質，作為鋰離子負極材料的應用，論文主要分成兩個主題進行：(1)利用工業廢棄物—燃油飛灰中的未燃碳，分別經由熱處理和酸處理對電化學性質的影響；(2)利用球形人造石墨與奈米矽，藉由煤焦瀝青於高溫中裂解成低結晶碳，在球形石墨及奈米矽上形成低結晶碳被覆，使奈米矽包覆在球形石墨上形成複合材料，再將高分子聚烯丙胺包覆於複合材料上，形成穩定石墨的層狀結構，同時對奈米矽體積的膨脹有緩衝效應。 第一部分：將研磨過的未燃碳經由2700℃熱處理，在0.1C的充放電下，其第一次庫倫效率為93.6%，而在經過50次充放電循環之後其放電電容量為325.5 mAhg-1，電容量保持率為97.5%。另一方面，研磨過的未燃碳經過2500℃熱處理之後酸處理（7M HNO3），其第一次庫倫效率由89.8%升至91.1%；經由50次充放電循環後，其可逆電容量為由293.7升至318.6 mAhg-1，電容量保持率由94.7升至98.5%。 第二部分：利用聚烯丙胺高分子聚合物包覆人造球形石墨/碳/奈米矽的複合材料，在0.1C的充放電下，第一次庫倫效率為89.1%，其第一次不可逆電容量由95.1降至55.0 mAhg-1，經過50次充放電循環後其放電電容量為410.1 mAhg-1，電容量保持率增加到91.5%。所以利用高分子聚烯丙胺包覆人造球形石墨/碳/奈米矽的複合材料，可以防止材料直接與電解液接觸，以及奈米矽體積膨脹所造成的破壞。

The purpose of this study focused on the modification of artificial graphite as anode material for lithium-ion battery. The work covers two areas: (1) Unburned carbon is an industrial waste product of oil-fired fly ash. From the viewpoint of waste recycling, using ground unburned carbon and applying either acid treatment or heat treatment, this study examines the electrochemical properties of unburned carbon used as anode materials in lithium-ion batteries. (2) A homopolymer of 2-propen-1-amine layer was coated on the surface of spherical artificial graphite /carbon/ Nano-Si composite materials. The homopolymer of 2-propen-1-amine provided surface modification and an elastic network, it prevented direct material contact with the electrolyte and the silicon volume expansion caused by structure destruction. First part：ground unburned carbon heat treatment at 2700℃, and both charge and discharge at 0.1 C, yields the first columbic efficiency of about 93.6%. Moreover, after 50 cycles, the discharge capacity is 325.5 mAhg-1, and the capacity retention is about 97.5%. On the other hand, ground unburned carbon after heat treatment at 2500ºC displayed an initial coulombic efficiency of approximately 89.8% at a charge and discharge rate of 0.1 C. The discharging capacity of this type of carbon was initially 293.7 mAhg-1, and its capacity retention was approximately 94.7% after 50 cycles. However, the initial coulombic efficiency of ground unburned carbon receiving nitric acid treatment after heat treatment increased to 91.1%, its discharging capacity increased to 318.6 mAhg-1, and its capacity retention increased to 98.5% after 50 cycles. Second part：This study reports the coating of spherical artificial graphite/disordered carbon/silicon (AG/C/Si) with a homopolymer of 2-propen-1-amine (PAA) layer. The resulting PAA-coated AG/C/Si electrode structure did not destroy locally for large volume change. For both charge and discharge at 0.1 C, the PAA-coated AG/C/Si yielded the first columbic efficiency of about 89.1% and the first irreversible capacity decreased from 95.1 to 55.0 mAhg-1. Moreover, the discharge capacity was 410.1 mAhg-1 after 50 cycles, and its capacity retention increased to 91.5%. The addition of PAA decreased the specific surface area (BET) of AG/C/Si composites and reduced the direct contact between the anode electrode surface and the electrolyte. These results indicate that PAA-coated AG/C/Si composites have relatively lower electrochemical resistance and good cycling stability.