The Role of Cation Vacancies in Electrode Materials for Enhanced Electrochemical Energy Storage: Synthesis, Advanced Characterization, and Fundamentals

Abstract

The incorporation of atomic scale defects, such as cation vacancies, in electrode materials is considered an effective strategy to improve their electrochemical energy storage performance. In fact, cation vacancies can effectively modulate the electronic properties of host materials, thus promoting charge transfer and redox reaction kinetics. Such defects can also serve as extra host sites for inserted proton or alkali cations, facilitating the ion diffusion upon electrochemical cycling. Altogether, these features may contribute to improved electrochemical performance. In this review, the latest progress in cation vacancies‐based electrochemical energy storage materials, covering the synthetic approaches to incorporate cation vacancies and the advanced techniques to characterize such vacancies and identify their fundamental role, are provided from the chemical and materials point of view. The key challenges and future opportunities for cation vacancies‐based electrochemical energy storage materials are also discussed, particularly focusing on cation‐deficient transition metal oxides (TMOs), but also including newly emerging materials such as transition metal carbides (MXenes).

Recent Progress of Vacancy Engineering for Electrochemical Energy Conversion Related Applications

“…[ 22 ] As a special type of defect, research of vacancy engineering to tune physical properties has become a focus of efforts to promote electrochemical performance. Liu and co‐workers [ 23 ] recently reviewed applications of cationic vacancy to enhance electrochemical energy storage application. In 2008, Ho and co‐workers [ 24 ] reviewed the use of vacancies in water splitting applications for noble metal‐free nanocatalysts.…”

Intrinsic Structure Modification of Electrode Materials for Aqueous Metal‐Ion and Metal‐Air Batteries

“…Recently, vacancy was used to be incorporated into the lattice structure of host materials to enhance the electrochemical activity of the electrode materials in the electrochemical energy storage. [ 52,53 ] Owing to controllably regulating the local atomic structures/coordination environments of electrode materials, the introduction of vacancy can effectively optimize the electronic and structural properties in intrinsic structure modification manner, and then bring about superior electrochemical performance of reduced diffusion energy barriers, enhanced extra intercalation sites, rapid electrode kinetics and excellent electrocatalytic activity. [ 54 ] In addition, vacancy regulation, consisting of cation vacancy and anion vacancy, could also easily combine with other methods without complex process, which has a synergistic effect on enhanced electrochemical property of electrode materials.…”

“…Via optimization of the electronic and crystal structures, cation vacancy cannot only generate more storage sites for inserted proton or alkali cations, but also elevate charge transfer, ion diffusion, and redox reaction kinetics, which ultimately contribute to superior discharge capacity and rate performance in ARBs. [ 53 ] Lately, Li vacancy has been used to improve electrochemical excellent performance of electrode. And Li vacancy imperceptibly alters the crystal structure and apparent morphology of the electrode materials due to small Li atomic sizes, which ensure intrinsic ionic conductivity and cycling stability.…”

Recent progress of defect chemistry on 2D materials for advanced battery anodes

“…Indeed, 2D materials as well as the defect chemistry constitutes for some years now a relevant approach allowing in particular the modification and improvement of surface properties and electronic structure of 2D materials and was largely applied in anode materials for rechargeable batteries. [4][5][6][7][8] In recent decade, 2D materials namely graphene, [9,10] black phosphorene (BP), [11,12] hexagonal boron phosphide/nitride/ arsenic (h-BP, h-BN, and h-BAs), [13,14] transition-metal dichalcogenide (TMDs) including MS 2 with M = Mo, W, Ta, Fe, Co, Ni, and Sn, [15] etc. have been widely studied and constitute one of the most interesting category of materials.…”

“…In addition, given the fact that both the electronic properties with the nature of anode materials have the potential to characterize the charge transfer process as well as the charge/discharge kinetics, a modification and improvement of the electrochemical features can be achieved through the adjustment of the anode material structure. Indeed, 2D materials as well as the defect chemistry constitutes for some years now a relevant approach allowing in particular the modification and improvement of surface properties and electronic structure of 2D materials and was largely applied in anode materials for rechargeable batteries [4–8] …”