| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 105 === Lithium-rich cathode materials are drawing high attention recently as next generation cathode materials for Li-ion battery due to its high operating voltage and high capacity ~270 mAhg-1. However, its poor electronic conductivity, rapid voltage fading during cycles and interphase instability still hinder its practical applications.
This study consists of two parts: first, to deposit carbon on Li rich powders by chemical vapor deposition (CVD) with dilute ethylene and argon for enhancing electronic conductivity of powder. Second, to form a carbonaceous layer (Artificial SEI layer) covering Li-rich particles by CVD with a mixture of gases of dilute hydrogen, carbon dioxide and argon with the aim of enriching high stability and interface stability.
The effects of the combination and applied sequence of two aforementioned approaches on the properties and electrochemical performance of cathode powders are also studied and compared against the individually treated and pristine materials.
In the results and discussion part, the modified powders are examined by bulk/surface structure and surface composition separately. Finally, it is summarized by enhanced electrochemical properties without impairing bulk structure.
The most potential modified sample, C1S4, was coated by CVD carbon deposition first, followed by the coverage of 3 nm carbonaceous layer and Li2CO3 growth on the Li-rich powder surface. It is also to note that a spinel-like structure was also formed in the depth of 5 nm. Overall, the C1S4 modified sample delivered a discharging capacity as high as 80 mAhg-1 at 3C and high retention of 85.7% after 110 cycling test, which surpassed the pristine powder, 5.4% higher.
This research sheds light on carbon coating and carbonaceous layer covering as an artificial SEI layer onto Li-rich cathode material with novel combination of reducing gases via CVD. The improved material performance and the process features make this proposed surface modification method suitable for production in near future.
Keywords: Lithium-rich, cathode material, surface modification, carbon coating, solid electrolyte interphase, interphase stability, electronic conductivity.
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