Influence of Electrode Design and Lithium Source Format on the Performance Metrics of Pre-Lithiation of Anodes in an Energy Storage Device

Abstract

Energy storage devices like batteries and supercapacitors, have become the crucial part of electrification of transportation. Better and more efficient energy storage devices are the need of the hour, critical to achieving this goal. In our earlier work [1,2], we have shown that several fabrication and design measures, like an advanced dry method of electrode fabrication, an optimized design of anode to cathode capacity ratio, an array of pre-lithiation methods, a composite cathode, etc., can be ingeniously combined to enhance the performance characteristics of energy storage devices in terms of specific energy (Wh.kg-1), specific power (W.kg-1), cycle life and cost. Among these performance enhancing measures, the process of pre-lithation is a necessary measure on multiple fronts, namely, to compensate for the initial cycle loss from solid electrolyte interface formation on anodes, to improve first cycle coulombic efficiency, to prevent the loss of active Li content in electrolyte and to achieve an improved cell working voltage range by initially driving the anode potential to lower permissible limits. We have also shown in our previous work [3] that an array of Li metal sources can be employed for achieving pre-lithiation through the internal short method in carbon electrodes. Over a time limited condition, we demonstrated the importance of different lithium source structures and their effect on the rate of pre-lithiation and pre-lithiation capacities that can be achieved. In our present work, we have eliminated the time limiting condition, allowing for the complete ionization of the Li-sources employed, hence enabling a complete pre-lithiation process in all Li-source formats that were employed. We have also performed a comparative study between the internal short circuit method of pre-lithiation and the external short circuit method. Different Li-source formats, based on their surface area and structure, exhibit different ionization and pre-lithiation speeds, capacities and efficiencies. Fig. 1 presents an illustration of different pre-lithiation methods organized based on their speed of pre-lithiation, with the fastest process being stabilized Li-metal powder (SLMP - leftmost) and slowest of the pre-lithiation processes occouring in lithium strip in electrode gap method and in an external short circuit method using an appropriate current limiting resistor (rightmost). On account of spherical micro nature of SLMP particles, they possess a larger active surface area for the ionization process to continue more vigorously and hence faster speed of pre-lithiation. Our analysis of reversible capacities after pre-lithiation, electrode cycle life, DC life, safety and cost aspects, etc., will also be presented. Figure 1