| 摘要: | 可充電的鋰電池在近十多年來因為廣泛地應用在電動汽車工業、智慧型電網與行動裝置上而受到相當的關注。在現今的運輸產業中，鋰電池因為電池容量、工作穩定性以及壽命的需求不斷的增加，因此，新的陽極取代材料，例如二硫化錫(SnS2)與鋅銅錫硫化物(Cu2ZnSnS4，簡稱CZTS)，因為其極高的理論電容量逐漸受到關注。然而，這些料在導電能力上的不足以及低溫下不佳的性能表現，加上充放電循環時體積膨脹的問題使得電池中電化學可逆性(electrochemical reversibility)和循環穩定性(cycling stability)仍無法滿足應用上的需求。
為了提升SnS2 與 CZTS在鋰離子電池中不足的導電能力、低溫下性能的表現以及抑制電容的劣化，我們改善其材料的表面型態(例如: 奈米結構)、分層配置(hierarchical configurations)和表面性質。本研究的結果顯示了材料的合成方式以及導體電極支架(conductive electrode support)作為儲存鋰離子負極材料的積體電極(integrated electrode)極為關鍵。我們在各種支撐層(conductive support)，例如：無孔鉬箔(nonporous planar molybdenum foil)、多孔碳布(microporous carbon clothe)以及三維層狀碳管與碳布的複合材料(SnS2-CNT-CC)上直接沉積了片狀SnS2奈米結構。結果顯示，以SnS2生長於SnS2-CNT-CC表現出極佳的電容量保持能力(capacity retention)與循環充放電穩定性，優於片狀鉬與碳布的複合結構。SnS2-CNT-CC電極在循環充放電的表現以及速率比起其他電極架構好上許多，是因為在三維層狀CNT-CC的補助下具有較多的電子傳導途徑以及較大的表面積。
同樣地，我們也製備了CZTS薄膜，以探討在-10°C下、循環充放電時電解液與溫度效應。而結果顯示，透過水熱法(hydrothermal method)合成的四元鋅銅錫硫化物，在-10°C下，以EC/DEC/DMC作為電解液、在200次充放電循環後仍具有475 mAh g?1的可逆電容(reversible capacity); 相較之下，石墨電極在?10 °C、100次循環下為110 mAh g?1。CZTS的XPS陽極縱深分析(depth profile)結果也顯示在EC/DEC/DMC電解質中產生的固體電解質膜（solid electrolyte interphase，SEI）有較低的碳含量，其可能提供了低溫下界面的穩定性。CZTS循環充放電性質表現的提升可歸因於其改善後較佳的界面穩定性和鋰離子的動力學擴散機制，以及在低溫下形成活性材料架構。
;Rechargeable lithium-ion batteries have attracted considerable attention over the previous two decades for a wide variety of applications such as electric vehicles, smart electricity grids, and portable energy devices. However, today′s lithium-ion batteries lack the higher capacity, stable operation capabilities, and longer lifetime required in transportation applications. In this regard, alternative anode materials, including, SnS2 and Cu2ZnSnS4 have received intensive attention because they deliver ultrahigh theoretical capacity. However, insufficient conductivity, poor low-temperature performance, and as well as volume expansion during cycling lead to poor electrochemical reversibility and cycling stability.
To address the insufficient conductivity, poor low-temperature performance, and mitigate the capacity degradation of SnS2 and Cu2ZnSnS4 materials in lithium–ion storage, morphology (e.g., nanosheet and nanowalls structures), hierarchical configuration, and surface properties of materials need to be developed.
In this regard, we demonstrated a synthesis and the importance of conductive electrode supports as integrated electrodes for anode materials in lithium-ion storage. We directly synthesize SnS2 nanosheet anode materials on various conductive supports, including nonporous planar molybdenum foils, macroporous carbon cloth as well as 3D hierarchical carbon nanotube-carbon cloth composites. Our findings reveal that the SnS2 nanosheet grown on 3D hierarchical carbon nanotube-carbon cloth composites (SnS2-CNT-CC) shows superior capacity retention and cycle stability, compared to that on planar molybdenum (Mo) sheets and carbon cloth. The SnS2-CNT-CC electrode outperforms the other electrode configurations in the cyclic performance and rate capability due to the multi-electron pathway and high surface area derived from 3D hierarchical CNT-CC electrode support.
Similarly, copper zinc tin sulfide (Cu2ZnSnS4, CZTS) thin-film were prepared to study the electrochemical activities under low-temperature (?10 °C ) and the effects of electrolyte on the electrochemical performance. Our results reveal that the quaternary CZTS synthesized by a simple hydrothermal method shows a higher reversible capacity of 475 mAh g?1 after 200 cycles at ?10 °C with the EC/DEC/DMC-based electrolyte in the comparison with the graphite electrode (110 mAh g?1 after 100 cycles at ?10 °C). The depth-profiling XPS results of the CZTS anode reveal that a solid electrolyte interphase (SEI) layer with less carbon content is formed in the EC/DEC/DMC-based electrolyte likely associated with the interfacial stability at low temperature. The enhanced cycling performance of CZTS could be attributed to its improved interfacial stability and Li+ diffusion kinetics, along with the formation of interconnected active material architecture at low temperatures. |
