This investigation explores the differentiated electrochemical behavior of silicon (Si) anodes in lithium-ion batteries (LIBs) under different operating protocols defined by specific voltage windows and capacity control strategies. Our investigation reveals distinctive responses of the Si anode to different state of charge (SoC) ranges, translating delivered capacity into significant variations in cycle life. While predominantly mostly lithiated Si anodes at 0.01-0.32 V subjected to voltage-controlled operation with an SoC between 75% and 100% exhibit poor cycle life, a similar situation with predominantly mostly delithiated anodes at 0.23-1.5 V and an SoC of 0%-25% also results in inferior cycle performance. Conversely, predominantly partially lithiated Si anodes at 0.01-0.5V under voltage-controlled conditions with an SoC range of 65%-100% show superior cycle life performance. However, predominantly partially delithiated Si anodes at 0.1-1.5 V, voltage controlled with an SoC of 0%-40%, lead to a cycle life with obvious degradation. Likewise, Si anodes subjected to full lithiation followed by delithiation at 1200 mA h g-1, controlled by delithiation capacity, demonstrate excellent cycle life within a SoC range of 65%-100%. On the contrary, full delithiation followed by lithiation at 1200 mA h g-1 results in less favorable cycle life within an SoC range of 0%-35%. In short, maintaining the lithiation state at a higher level, i.e. a high SoC, throughout the cycle allows Si anodes to maintain low impedance, resulting in outstanding cycle performance. These results provide important insights into tailoring operating parameters to optimize Si anode cycle performance in LIBs.
The limited reversibility and high reactivity of lithium metal with the liquid electrolyte in lithium batteries hinder its widespread adoption. The formation of an unstable solid electrolyte interphase layer and the sensitivity of lithium metal to moisture and air are major issues that need to be addressed. To overcome the practical challenges associated with the application of lithium anodes in lithium metal batteries, a well-thought-out design of a protective layer is proposed. Here, we have developed a composite coating comprising polyvinylidene fluoride, fumed colloidal silica, and paraffin wax as a protective layer for lithium metal anodes. The coating exhibits excellent electrochemical stability, high ionic conductivity, and mechanical stability, effectively suppressing dendrite growth and accommodating lithium volume changes during cycling. Moreover, the hydrophobic wax component can mitigate the atmospheric sensitivity of metallic lithium anodes. The coating process employed is facile and economically viable, significantly enhancing the scalability of lithium metal batteries. Experimental characterizations confirm the structure and composition of the coating, and electrochemical measurements demonstrate the improved electrochemical performance and cyclability of the coated lithium metal anodes. The results indicate that the developed composite coating has great potential for enhancing the electrochemical and processing stability of metallic lithium anodes for lithium metal batteries.
