| 摘要: | 為了減少人們對化石燃料的依賴及減少溫室氣體的排放，許多國家積極的開發綠色能源，其中能夠順利的利用其能源，發展出大規模儲存電力的設備及技術是不可或缺的，而高能量密度的鋰離子電池被廣泛的應用，為了進一步提高鋰離子電池性能，開發新型負極材料是的一大關鍵。ZnMn2O4 (ZMO)作為一種典型的三元過渡金屬氧化物，因為其鋅與錳的資源豐富、價格低廉、無毒，且具有優異的理論電容量(~784 mAh/g)，但在實際應用仍面臨挑戰，因為其導電性差，充放電過程中體積變化大，很容易導致顆粒破碎，進而導致倍率性能差和電容量快速下降。
本實驗首先透過簡單操作的共沉澱法及鍛燒製程，以製備出我們的ZMO奈米顆粒，接著採用溶膠-凝膠法將二氧化鈦包覆在ZMO奈米顆粒上，形成核殼結構複合材料，實驗結果表明，在包覆適當厚度二氧化鈦殼層的ZMO顆粒，也就是最佳參數ZMO@TiO2-0.052下，成功改善了材料的體積膨脹效應，並提供了鋰離子快速擴散的通道，使其於充放電 100 圈後擁有985.46 mAh/g 之比電容量(在100 mA/g電流密度下)，以及因為Mn有更高氧化態出現提升了電容量，然而包覆二氧化鈦後比電容量增長更顯著，因其奈米級尺寸和短擴散路徑促進了鋰化，且二氧化鈦的價帶與導帶結構改善了電荷轉移和阻抗，加上其材料表層會有一層可逆形成、分解的有機聚合物/凝膠狀薄膜，產生贗電容現象及行為，使ZMO@TiO2-0.052在1000 mA/g電流密度下仍還有500.88 mAh/g的比電容量，電容保持率為74.0%，表現出比ZMO奈米顆粒更高的電容量及穩定性。
接著為了進一步提升材料的導電率，在本研究中我們將煉油廢棄物瀝青利用鍛燒製程來製備出軟碳負極材料，並且藉由球磨的方式將先前製備出來的核殼材料與軟碳進行複合，根據結果顯示，在最佳軟碳複合比參數ZMO@TiO2/SC 1：0.25在100 mA/g電流密度下，於100圈充放電循環後表現出1171.83 mAh/g的比電容量，表示少量的軟碳複合比可以有效地提供導電路徑，並再度增強了抑制體積膨脹效應的能力，也發現因為軟碳孔洞結構的關係，提供了更好的離子通道條件和額外的鋰儲存位點，加上界面氧原子在碳質材料和二氧化鈦之間的鍵結增強了鋰離子的穩定性，再度加強了贗電容行為的貢獻，導致最佳參數在1000 mA/g電流密度下，其比電容量仍達到620.97 mAh/g，並擁有79.4%的電容保持率，最後與其他利用ZMO負極材料進行研究的論文相比較，本研究所製備出的複合材料表現出出色的性能表現。;Many countries are actively developing green energy sources to reduce reliance on fossil fuels and decrease greenhouse gas emissions. Developing large-scale energy storage devices and technologies is essential to utilize these energy sources efficiently. High-energy-density lithium-ion batteries are widely used for this purpose. To further improve the performance of lithium-ion batteries, developing new anode materials is crucial. ZnMn2O4 (ZMO), as a typical ternary transition metal oxide, is known for its abundant and low-cost zinc and manganese resources, non-toxicity, and excellent theoretical capacity (~784 mAh/g). However, its practical application faces challenges due to poor conductivity and significant volume changes during charge-discharge cycles, which can easily lead to particle breakage, resulting in poor rate performance and rapid capacity decay.
In this experiment, we first prepared ZMO nanoparticles through a simple co-precipitation method followed by calcination. Next, we used the sol-gel method to coat titanium dioxide on the ZMO nanoparticles, forming a core-shell structured composite material. The experimental results showed that coating the ZMO particles with an appropriate thickness of titanium dioxide, specifically under the optimal parameter ZMO@TiO2-0.052, successfully mitigated the volumetric expansion effect and provided a rapid diffusion channel for lithium ions. This resulted in a specific capacity of 985.46 mAh/g after 100 charge-discharge cycles at a current density of 100 mA/g. Additionally, the increased oxidation state of Mn enhanced the capacity. The coated ZMO particles exhibited a more significant capacity increase due to the nanometer-sized titanium dioxide with short diffusion paths promoting lithiation, and the improved valence and conduction band structure of titanium dioxide facilitated charge transfer and reduced impedance. Furthermore, the material′s surface formed a reversible organic polymeric/gel-like layer, exhibiting pseudo-capacitance-type behavior. As a result, ZMO@TiO2-0.052 maintained a specific capacity of 500.88 mAh/g at a current density of 1000 mA/g, with a capacity retention rate of 74.0%, showing higher capacity and stability compared to ZMO nanoparticles.
To further enhance the material′s conductivity, we prepared soft carbon anode material from refinery waste pitch through calcination. The core-shell material was then composited with the soft carbon using ball milling. The results indicated that the optimal soft carbon composite ratio, ZMO@TiO2/SC 1:0.25, exhibited a specific capacity of 1171.83 mAh/g after 100 charge-discharge cycles at a current density of 100 mA/g. This suggests that a small amount of soft carbon can effectively provide conductive pathways and further suppress volumetric expansion effects. The porous structure of the soft carbon provided better ion channel conditions and additional lithium storage sites. Additionally, the bond between interfacial oxygen atoms in the carbon material and titanium dioxide enhanced lithium-ion stability, further contributing to pseudo-capacitance-type behavior. Consequently, the optimal parameter maintained a specific capacity of 620.97 mAh/g at a current density of 1000 mA/g, with a capacity retention rate of 79.4%. Compared with other studies using ZMO anode materials, the composite material prepared in this study demonstrated outstanding performance. |
