Fast and Durable Potassium Storage Enabled by Stress Management

Energy storage systems are useful assets for utilities involved in generating, supplying and usage of energy. Besides the most widely used lithium-ion batteries, potassium-ion batteries (PIBs) have been extensively researched as a potential alternative for energy storage due to their low-cost and high natural abundance. Generally, the reaction mechanism involving anode materials used in PIBs can be divided into three categories: insertion, alloying and conversion reactions. Due to the limitations associated with insertion and alloying materials, conversion materials are generally more promising for designing high-performance PIBs.

Among conversion materials, transition metal dichalcogenides (TMDCs) are promising anode materials for PIBs owing to their relatively higher theoretical capacities and two-dimensional (2D) layered structures. Unfortunately, TMDCs have several drawbacks such as huge changes in the volume during reaction, low electronic conductivity that results in poor kinetics reactions, severe electrode polarization and accelerated capacity fading. Consequently, the excess volume expansion causes severe structural damage than in their lithium counterparts since potassium ions have a larger radius. Despite developing several strategies to address these issues, the results are far from satisfactory. Notably, previous findings revealed that the larger tensile stress on the outer surface of nanoparticles during metal ion intercalation causes contact stress, which reduces the structural integrity of the electrodes. Thus, reducing contact stress is vital in constructing stable electrodes for PIBs and has formed the basis of subsequent research studies.

Herein, PhD candidate Hehe Zhang, Dr. Yong Cheng, Professor Qiaobao Zhang, Dr. Weibin Ye and led by Professor Ming-Sheng Wang from Xiamen University, together with Dr. Xiaohua Yu from Kunming University of Science and Technology, designed stress-dispersed Co₃Se₄ nanocrystallites structures anchored on graphene sheets for durable and fast potassium storage. The authors utilized a two-step hydrothermal treatment to reduce the possible structural deterioration during the process. The ability of the well-dispersed Co₃Se₄ nanocrystallites to reduce contact stress during potassium ion intercalation was investigated. Furthermore, density functional theory calculations and in-situ and ex-situ characterizations via TEM and XRD were carried out to elucidate the storage mechanism of the Co_3­Se₄. The authors hoped to improve the potassium storage performance of conversion materials. The work is published in the journal, ACS Nano.

The research team showed that the stress-dispersed Co₃Se₄/GO composite provided a robust, efficient and reliable anode architecture than its two counterparts with more agminated structures. This was mainly attributed to the highly conductive network provided by the graphene matrix and the ability to reduce the contact stress during volume expansion due to the large specific surface area and uniform crystallite dispersion. Due to these advantages, when used as anode for PIB, the optimized electrode delivered an outstanding rate capacity, high reversible capacity, and excellent stable cycling performance. Through in-situ and ex-situ characterization, potassium storage mechanism of Co₃Se₄ was elucidated, and the fast-electrochemical kinetics as well as the durability of the resulting electrode, was also revealed.

In a nutshell, a stress-dispersed strategy for anchoring Co₃Se₄ nanocrystallites on graphene sheets via two-step hydrothermal treatment was presented as an efficient, reliable and robust anode for PIBs. Due to the benefits associated with the dispersed Co₃Se₄ nanocrystallites, the optimized electrode exhibited significantly improved electrochemical properties. Based on the electrochemical kinetics analysis, the improved nanocrystallites dispersion would improve the control of capacitive processes. The study insights provided deep insights for effective contact stress management for optimized cycling stability, which is crucial in improving the potassium storage performance of conversion materials. In a statement to Advances in Engineering, Professor Ming-Sheng Wang, the corresponding author said their research work offers a reliable and efficient approach for designing high-performance conversion-type electrodes for PIBs.