Improvement of Activation Processes for Lithium-Ion Secondary Battery through Electrochemical Characteristics

Abstract

A lithium-ion secondary battery that has not undergone the activation process may experience compromised cycleability and safety. Therefore, the activation process following the manufacturing of lithium-ion secondary batteries plays a crucial role in enhancing safety and extending cycleability. Through the pre-charging process of the activation procedure, additives within the electrolyte undergo chemical reactions at the anode interface, forming a thin solid layer on the anode surface. The solid layer formed on the anode surface through this process is referred to as the Solid Electrolyte Interphase (SEI) layer. The SEI (Solid Electrolyte Interphase) layer serves to inhibit direct decomposition reactions between the electrolyte and the anode interface, similar to the role of a separator. It can contribute to long-term lifespan and safety. However, if formed beyond a certain thickness, the SEI (Solid Electrolyte Interphase) layer may go beyond the function of a separator and instead develop into a single, thick solid layer. Furthermore, if formed below a certain thickness, the SEI (Solid Electrolyte Interphase) may easily collapse, failing to fulfill the role of the solid layer and leading to issues of capacity loss and safety concerns. Therefore, the process of creating a robust SEI (Solid Electrolyte Interphase) layer with a consistent thickness, without deviation, is of utmost importance.In this study, to enhance the activation process, a Double Layer Cell (DLC) with a capacity of 80 mAh was manufactured, and the State of Charge (SOC, %) during the pre-charging process was adjusted. To create a robust SEI (Solid Electrolyte Interphase) layer, the State of Charge (SOC, %) was maintained at 20%, 50%, and 80% after pre-charging at temperatures of 25°C, 45°C, and 60°C for a specified duration in each formation process. During these formation processes, impedance analysis (EIS) was employed to evaluate the resistance of the cell itself and the interface resistance in relation to changes in SOC (%) and temperature. Additionally, the crystal structure of the SEI was elucidated through XRD. Furthermore, chemical characteristics and bonding states of the cathode surface were analyzed using XPS. The morphology and composition of the SEI were observed through SEM and EDS, providing an analysis of the components of the SEI. Subsequently, the DLC was subjected to output verification through C-rate at room temperature based on SOC (%). The electrochemical characteristics were evaluated by measuring the cycleability of 1000 cycles at both room temperature and high temperature, assessing the impact of the pre-charging process.