Enhancing the Cycling Stability by Tuning the Chemical Bonding between Phosphorus and Carbon Nanotubes for Potassium-Ion Battery Anodes

Rapid identification of P-C bonds in phosphorus-carbon anode materials

Phosphorus-carbon composites in alkali metal-ion batteries benefit from P-C bonds, enhancing stability and performance. Rapid P-C bond detection is crucial. X-ray photoelectron spectroscopy (XPS), balancing convenience and accuracy, was chosen in this study for its efficiency in analyzing P-C bond energies, aiding in the quick identification of these bonds in phosphorus-carbon anodes.

Electrochemical Atomic Force Microscopy of Black Phosphorus Composite Anodes: Electrode Destabilization and Degradation Mechanisms in Alkali-Ion Batteries

Despite their higher capacity compared to common intercalation- and conversion-type anodes, black phosphorus (BP) based anodes suffer from significant capacity fading attributed to the large volume expansion (∼300%) during lithiation. Downsizing BP into nanosheets has been proposed to mitigate this issue, and various methods, particularly mechanical mixing with graphitic materials (BP-C), have been explored to enhance electrochemical performance. However, the understanding of BP-C hybridization is hindered by the lack of studies focusing on fundamental degradation mechanisms within operational battery environments. Here we address this challenge by employing electrochemical atomic force microscopy (EC-AFM) to study the morphological and mechanical evolution of BP-C composite anodes during lithiation. The results reveal that BP-C binding interactions alone are insufficient to withstand the structural reorganization of BP during its alloying reaction with lithium. Furthermore, the study emphasizes the critical role of the solid electrolyte interphase (SEI) and BP-C interface evolution in determining the long-term performance of these composites, shedding light on the disparity in final electrode morphologies between binder-inclusive and binder-free BP-C composites. These findings provide crucial insights into the challenges associated with BP-based anodes and underscore the need for a deeper understanding of the dynamic behavior within operating cells for the development of stable and high-performance battery materials.

Homogeneous Adsorption of Multiple Potassiation Products of Red Phosphorus Anode toward Stable Potassium Storage

Potassium ion batteries (PIBs) are a viable alternative to lithium-ion batteries for energy storage. Red phosphorus (RP) has attracted a great deal of interest as an anode for PIBs owing to its cheapness, ideal electrode potential, and high theoretical specific capacity. However, the direct preparation of phosphorus-carbon composites usually results in exposure of the RP to the exterior of the carbon layer, which can lead to the deactivation of the active material and the production of "dead phosphorus". Here, the advantage of the π-π bond conjugated structure and high catalytic activity of metal phthalocyanine (MPc) is used to prepare MPc@RP/C composites as a highly stable anode for PIBs. It is shown that the introduction of MPc greatly improves the uneven distribution of the carbon layer on RP, and thus improves the initial Coulombic efficiency (ICE) of PIBs (the ICE of FePc@RP/C is 75.5% relative to 62.9% of RP/C). The addition of MPc promotes the growth of solid electrolyte interphase with high mechanical strength, improving the cycle stability of PIBs (the discharge-specific capacity of FePc@RP/C is 411.9 mAh g-1 after 100 cycles at 0.05 A g-1). Besides, density functional theory theoretical calculations show that MPc exhibits homogeneous adsorption energies for multiple potassiation products, thereby improving the electrochemical reactivity of RP. The use of organic molecules with high electrocatalytic activity provides a universal approach for designing superior high-capacity, large-volume expansion anodes for PIBs.

Strategies for developing layered oxide cathodes, carbon-based anodes, and electrolytes for potassium ion batteries

Lithium-ion batteries (LIBs) have become the most popular portable secondary energy storage facilities. However, the limited lithium resource results in possible unsustainable development. Potassium-ion batteries (PIBs) are considered promising alternatives to LIBs because of their high resource availability, low cost, and environmentally friendly features. In this field, high energy density layered cathodes and carbon-based anodes are also the main research objectives. However, compared to the most appealing alternative sodium-ion batteries (SIBs), despite having various theoretical advantages, PIBs exhibit poorer electrochemical performance in practice. Their poor capacity retention and narrow working voltage range seriously limit their applications. The performance of the electrodes is usually considered an important factor for battery performance, life, and safety. To solve these problems, many significant research studies have been carried out in the last decade, achieving numerous breakthroughs. Nevertheless, there are still many drawbacks and unclear mechanisms. In this comprehensive review, we examine the current state of high-performance layered oxide cathodes, electrolytes, and carbon-based anodes, to identify potential candidates for PIBs. Our focus lies on their structural characteristics, interface properties, underlying mechanisms, and modification techniques. The viewpoints of these advanced strategies are integrated, and concise development suggestions and strategies are subsequently proposed.

Unlocking Deep and Fast Potassium-Ion Storage through Phosphorus Heterostructure

Potassium-ion battery represents a promising alternative of conventional lithium-ion batteries in sustainable and grid-scale energy storage. Among various anode materials, elemental phosphorus (P) has been actively pursued owing to the ideal natural abundance, theoretical capacity, and electrode potential. However, the sluggish redox kinetics of elemental P has hindered fast and deep potassiation process toward the formation of final potassiation product (K3 P), which leads to inferior reversible capacity and rate performance. Here, it is shown that rational design on black/red P heterostructure can significantly improve K-ion adsorption, injection and immigration, thus for the first time unlocking K3 P as the reversible potassiation product for elemental P anodes. Density functional theory calculations reveal the fast adsorption and diffusion kinetics of K-ion at the heterostructure interface, which delivers a highly reversible specific capacity of 923 mAh g-1 at 0.05 A g-1 , excellent rate capability (335 mAh g-1 at 1 A g-1 ), and cycling performance (83.3% capacity retention at 0.8 A g-1 after 300 cycles). These results can unlock other sluggish and irreversible battery chemistries toward sustainable and high-performing energy storage.

Phosphorus/Phosphide-Based Materials for Alkali Metal-Ion Batteries

Phosphorus- and phosphide-based materials with remarkable physicochemical properties and low costs have attracted significant attention as the anodes of alkali metal (e.g., Li, Na, K, Mg, Ca)-ion batteries (AIBs). However, the low electrical conductivity and large volume expansion of these materials during electrochemical reactions inhibit their practical applications. To solve these problems, various promising solutions have been explored and utilized. In this review, the recent progress in AIBs using phosphorus- and phosphide-based materials is summarized. Thereafter, the in-depth working principles of diverse AIBs are discussed and predicted. Representative works with design concepts, construction approaches, engineering strategies, special functions, and electrochemical results are listed and discussed in detail. Finally, the existing challenges and issues are concluded and analyzed, and future perspectives and research directions are given. This review can provide new guidance for the future design and practical applications of phosphorus- and phosphide-based materials used in AIBs.

Chemically Binding Vanadium Sulfide in Carbon Carriers to Boost Reaction Kinetics for Potassium Storage

Potassium-ion batteries (PIBs) have received widespread interest on account of low redox potential, low price, and high abundance of potassium. However, attributing to the large radius of K⁺ ions, the structure of electrode material is easily damaged during the potassiation/depotassiation process. Herein, the unique chemical bonding of encapsulating V_5.45S₈ nanoparticles in N,S codoped multichannel carbon nanofibers (CB-VS@NSCNFs) is designed through electrospinning and in situ vulcanization techniques. The anchoring effect (V-C chemical bonding) of the V_5.45S₈ nanoparticles with carbon carriers assists in shortening the K⁺/e^- transport path and alleviating the structural changes, which is highlighted to acquire a stable cycle lifespan. Also, codoped multichannel carbon nanofibers provide abundant active sites for pseudocapacitive behavior to achieve fast kinetics. As a synergistic result, when CB-VS@NSCNFs are evaluated as anode material for PIBs, they exhibit a high reversible capacity of 411 mA h g^-1 at 0.1 A g^-1, decent rate property with a capacity of up to 123 mA h g^-1 at 6 A g^-1, and good cycling stability of 500 cycles at 1 A g^-1.

Improved photocatalytic activity and stability of black phosphorus/multi-walled carbon nanotube hybrid for RhB degradation

Black phosphorus (BP) is a two-dimensional (2D) semiconductor that has recently attracted much interest due to its unique characteristics. However, BP is susceptible to oxidization under ambient conditions. In this work, a facile one-step route is presented, in which stable P-C bonds were formed by ball milling bulk BP and multi-walled carbon nanotubes (MWCNTs) mixture without any additives. The BP-MWCNTs hybrid and the milled BP (m-BP) were both dispersed in water under ambient conditions, and their optical absorbances were monitored. The resulting data showed that the absorbance value of the BP-MWCNTs hybrid decreased by 10.87% after 5 d, whereas the m-BP decreased by 59.21%. Surprisingly, the BP-MWCNTs hybrid also exhibited ultrahigh photocatalytic activity in the visible light range. Within 60 min of irradiation, the removal efficiency of rhodamine B (RhB) by the BP-MWCNTs hybrid reached 88.42%, which is four times higher than that of the bare m-BP. This improvement can be attributed to the formation of the P-C bond and the enhanced surface adsorption capacity resulting from the introduction of the MWCNTs, indicating that the utilization of the charges on the surface of the photocatalyst is further improved. In short, this study not only provides an easy method to synthesize the stable BP-based material for practical applications but also represents a new approach to enhance the photocatalytic activity of BP.

Prospects of Electrode Materials and Electrolytes for Practical Potassium-Based Batteries

Potassium-ion batteries (PIBs) have attracted tremendous attention because of their high energy density and low-cost. As such, much effort has focused on developing electrode materials and electrolytes for PIBs at the material levels. This review begins with an overview of the high-performance electrode materials and electrolytes, and then evaluates their prospects and challenges for practical PIBs to penetrate the market. The current status of PIBs for safe operation, energy density, power density, cyclability, and sustainability is discussed and future studies for electrode materials, electrolytes, and electrode-electrolyte interfaces are identified. It is anticipated that this review will motivate research and development to fill existing gaps for practical potassium-based full batteries so that they may be commercialized in the near future.

Recent progress in electrochemical performance of binder-free anodes for potassium-ion batteries

Potassium ion batteries (PIBs) are regarded as one of the most promising candidates for large-scale stationary energy storage beyond lithium-ion batteries (LIBs), owing to the abundance of potassium resources and low cost. Unfortunately, the practical application of PIBs is severely restricted by their poor rate capacity and unsatisfactory cycle performance. In traditional electrodes, a binder usually plays an important role in integrating individual active materials with conductive additives. Nevertheless, binders are not only generally electrochemically inactive but also insulating, which is unfavorable for improving overall energy density and cycling stability. To this end, in terms of both improved electronic conductivity and electrochemical reaction reversibility, binder-free electrodes offer great potential for high-performance PIBs. Moreover, the anode is a crucial configuration to determine full cell electrochemical performance. Therefore, this review analyzes in detail the electrochemical properties of the different type binder-free anodes, including carbon-based substrates (graphene, carbon nanotubes, carbon nanofibers, and so on), MXene-based substrates and metal-based substrates (Cu and Ni). More importantly, the recent progress, critical issues, challenges, and perspectives in binder-free electrodes for PIBs are further discussed. This review will provide theoretical guidance for the synthesis of high-performance anode materials and promote the further development of PIBs.

Encapsulating V2O3 Nanoparticles in Hierarchical Porous Carbon Nanosheets via C-O-V Bonds for Fast and Durable Potassium-Ion Storage

Vanadium oxide (V₂O₃) has been considered as a promising anode material for potassium-ion batteries (PIBs), but challenging as well for the low electron/ion conductivity and poor structural stability. To tackle these issues, herein, a novel sheetlike hybrid nanoarchitecture constructed by uniformly encapsulating V₂O₃ nanoparticles in amorphous carbon nanosheets (V₂O₃@C) with the generation of C-O-V bonding is presented. Such a subtle architecture effectively facilitates the infiltration of electrolyte, relieves the mechanical strain, and reduces the potassium-ion diffusion distance during the repetitive charging/discharging processes. The generated C-O-V bonding not only accelerated charge transfer across the carbon-V₂O₃ interface but also strengthened the structural stability. Benefiting from the synergistic effects, the as-prepared V₂O₃@C nanosheets display fast and durable potassium storage behaviors with a reversible capacity of 116.6 mAh g^-1 delivered at 5 A g^-1, and a specific capacity of 147.9 mAh g^-1 retained after 1800 cycles at a high current density of 2 A g^-1. Moreover, the insertion/extraction mechanism of V₂O₃@C nanosheets in potassium-ion storage is systematically demonstrated by electrochemical analysis and ex situ technologies. This study will shed light on the fabricating of other metal oxides anodes for high-performance PIBs and beyond.