Fluoride engineering in zinc-ion batteries: principles, strategies, and perspectives.

Introduction

Increasing energy demand and escalating environmental concerns are driving the long-term pursuit of renewable energy sources. However, due to the instability of energy supply and output, the rational and efficient storage and utilization of renewable energy remain significant challenges. Among the currently widely researched and applied energy storage technologies, rechargeable batteries are regarded as one of the most promising and efficient solutions because of their relatively low cost, high power and energy density, and long cycle life [1,2]. Rechargeable lithium-ion batteries (LIBs) have gained prominence among various battery types and are extensively utilized in electronic devices and transportation vehicles. Nevertheless, limited lithium resources and safety concerns pose significant challenges for LIBs [3,4]. Fortunately, zinc-ion batteries (ZIBs) exhibit several advantages, including high safety, abundant resources, non-toxicity, low cost, and a low redox potential (-0.76 V vs. SHE) [5]. Additionally, ZIBs possess a high theoretical specific capacity (820 mA h g^-1) and a straightforward battery assembly process, making them a promising candidate for next-generation energy storage systems [[6], [7], [8]]. The structure of ZIBs primarily comprises four components: the cathode, electrolyte, separator, and anode (Fig. 1a) [9].

At present, the research on ZIBs primarily concentrates on the design of anode and cathode electrodes as well as the optimization of electrolytes [10,11]. During the charge-discharge cycle, zinc deposition on the anode surface remains a critical issue [12]. The nonuniform distribution of current density on the surface of Zn leads to localized current concentration, resulting in uneven deposition of Zn²⁺ and irregular zinc dendrites [13], accompanied by unavoidable corrosion and hydrogen evolution reactions (HER) at the interface, leading to irreversible degradation of battery life (Fig. 1b) [14,15]. Traditional approaches to address the challenges of the zinc anode electrode involve electrolyte modulation [16,17] and interface engineering [[18], [19], [20], [21]]. Research on cathode materials mainly focuses on manganese-based, vanadium-based, Prussian blue analogues, and organic materials [[22], [23], [24]], which encounter three fundamental challenges: sluggish kinetics from hydrated Zn²⁺ insertion, structural dissolution/collapse, and irreversible by-product formation (Fig. 1c). Modification strategies for these materials typically include doping, interlayer intercalation, defect engineering, and the development of composite materials [[25], [26], [27], [28]]. In the present research, the modification strategy involving fluoride has exhibited remarkable advantages in the cathode, anode, and electrolyte, showcasing substantial potential for compensating inherent electrode defects in ZIBs and has experienced rapid development in recent years [29]. Fig. 2 depicts recent applications of fluorides in ZIBs. The fluorinated interface engineering markedly enhances the uniformity and interfacial stability of zinc deposition by regulating the orientation of Zn²⁺ deposition, constructing a hydrophobic barrier to inhibit water-induced side reactions, and forming a solid-electrolyte interphase (SEI) film with high ionic conductivity. The incorporation of fluorine into cathode materials leverages its strong electronegativity to optimize the electronic structure, thereby enhancing lattice stability and reducing the energy barrier for Zn²⁺ desolvation. Furthermore, the introduction of high-electronegativity fluorine to form fluoride-based materials not only elevates the operating voltage but also demonstrates exceptional energy storage potential [30,31].

In this review, the multifunctional role of fluorides in ZIBs is systematically analyzed from the perspective of the “anode-interface-electrolyte-cathode” chain system, encompassing material design and interface regulation. Fig. 3 outlines fluorination engineering enabling high-performance ZIBs in this review. We provided a comprehensive analysis of the mechanisms of zinc dendrite formation, HER, and corrosion passivation, as well as their detrimental impacts on battery performance. Subsequently, various fluoride-related zinc anode protection approaches to address these issues are elaborated, including the artificial and in-situ formation of fluorine-rich SEI films and the optimization of fluoride-containing electrolytes. Furthermore, the application of fluoride in cathode materials is comprehensively discussed, covering fluorine doping modification strategies, fluoride-based active materials, and fluorinated binders. Finally, the core advantages and current challenges of fluorination technology are summarized, and future perspectives for the development of high-performance ZIBs are provided.

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