Unraveling the Charge Storage Mechanism of MXenes in Aqueous Zinc Electrolytes
Authors:   , Matthews Kyle , Gogotsi Yury 
Published: January 2025

The last decade has seen an ever-increasing demand in the energy storage space, and such a demand has prompted the revolution in lithium-ion batteries. While lithium-ion battery technologies continue to improve while simultaneously reducing their cost, the demand for diverse energy storage solutions is growing. There is a need for higher power and energy density devices, more energy storage platforms, and versatility in the face of grid storage, electric vehicles, and the internet of things (IoT). In the case of flexible/wearables and in stationary grid storage, the flammability and dangers of lithium-ion battery technology poses a large hurdle against mass implementation and adoption. One of the alternative chemistry solutions that shows particular promise is zinc-based energy storage systems. Zinc batteries are wide in variety, with varying cost as well as energy and power density. One thing that becomes abundantly clear very quickly is that the versatility of the zinc battery chemistries can fill different niches in the energy storage market. Nickel-Zinc and Zn-MnO₂ chemistries are comparable between lead acid and li-ion batteries at a much lower cost than either system. It is an industrially mature technology thanks to the primary battery industry, which make scalability essentially a non-issue. However, its use in rechargeable batteries has been limited so far due to rechargeability issues at both the anode and cathode. Many efforts to improve the reversibility on one electrode decreases it on the other. New electrolyte configurations offering anode stability need to be explored and new materials that are compatible in aqueous zinc chemistries are required to make zinc batteries emerge as a prevalent technology in the energy storage landscape. MXenes are a new and emerging class of 2D nanomaterials discovered in 2011. They have quickly grown into the largest family of 2D material and are widely researched due to their desirable properties, which are as follows: High electronic conductivity, electrochemical stability in a wide range of electrolytes (acidic, basic, halogens, etc.), water dispersible/processable, redox active/capable of ion intercalation. These properties make it a standout material for use in an aqueous zinc-based system. This dissertation focuses on uncovering and understanding the material-ion interactions, and the charge storage mechanism of MXenes in aqueous zinc electrolytes. Numerous studies have been published on MXene-ion interactions, and likewise on MXenes being used in zinc-based energy storage systems. However, little work has been done to address fundamental zinc ion interactions with MXenes and even more so have MXenes beyond Ti₃C₂T_x been ignored on this front. To address this, complementary in-situ and ex-situ characterization techniques were used to study MXene electrodes under multiple conditions in aqueous zinc-based systems. In order to expand the work beyond Ti₃C₂T_x MXenes, new etching and processing protocols were developed and formulated into a guideline for synthesizing V₂CT_x MXene. With these needs met, this work focused on uncovering the difference in charge storage between Ti₃C₂T_x and V₂CT_x MXenes in aqueous zinc electrolytes.