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Potassium‐ion batteries (PIBs) exhibit a considerable application prospect for energy storage systems due to their low cost, high operating voltage, and superior ionic conductivity. As a vital configuration in PIBs, the two‐phase interface, which refers to K‐ion diffusion from the electrolyte to the electrode surface (solid–liquid interface) and K‐ion migration between different particles (solid–solid interface), deeply determines the diffusion/reaction kinetics and structural stability, thus significantly affecting the rate performance and cyclability. However, researches on two‐phase interface are still in its infancy and need further attentions. This review first starts from the fundamental understanding of solid–liquid and solid–solid interfaces to in‐depth analyzing the effect mechanism of different improvement strategies on them, such as optimization of electrolyte and binders, heterostructure design, modulation of interlayer spacing, etc. Afterward, the research progress of these improvement strategies is summarized comprehensively. Finally, the major challenges are proposed, and the corresponding solving strategies are presented. This review is expected to give an insight into the importance of two‐phase interface on diffusion/reaction kinetics, and provides a guidance for developing other advanced anodes in PIBs. [ABSTRACT FROM AUTHOR]

A P/N co-doped three dimensional (3D) interconnected carbon nanocage was synthesized and highly stable electrochemical performance for potassium-ion batteries was realized. [Display omitted] Heteroatoms doping strategies are often considered to be an effective approach to provide rich active sites for capacitive-controlled potassium storage, and enlarged interspacing for intercalation process. However, the excess doping level will form a large number of sp3 defects and thus severely damage π-conjugated system, which is unfavorable for electron transfer. Herein, a P/N co-doped three-dimensional (3D) interconnected carbon nanocage (denoted as PN-CNC) is prepared with the help of a template-assisted method. The use of template and P heteroatom can contribute to forming a 3D interconnected carbon nanocage to prevent conductive carbon matrix from being excessively damaged, favoring a high electronic conductivity. The co-existence of P/N doping configurations with suitable content not only generate abundant defects, edge-voids, and micropores for significant capacitive behaviors, but also supply adequate interlayer space for intercalation process, and all these together ensure enhanced ion storage. As a result, the optimized PN-CNC electrode exhibits an exceptional reversible capacity (262 mAh g−1) and a superior rate capability (214.2 mAh g−1). Besides, long-term cycling stability is easily fulfilled by delivering a high capacity of 188.7 mAh g−1 at 2 A g−1 after 3000 cycles. [ABSTRACT FROM AUTHOR]

Carbonaceous materials with various morphologies and structures have been widely investigated as anode for potassium-ion batteries (PIBs), due to their low cost, nontoxicity, and high conductivity. However, there is still sluggish bulk diffusion in most carbon electrodes, which cannot well meet ever-increasing requirements for high power density. Herein, hierarchical porous one-dimensional carbon nanofibers (HPCNF-5) are successfully fabricated, in which one-dimensional (1D) conductivity nanostructure can facilitate electrons transfer. While the in-situ N-doping and suitable micro/mesopores configurations are beneficial for promoting surface-induced capacitive behaviors. Also, the resulting HPCNF-5 has excellent mechanical flexibility, indicating it can be directly used as a self-supporting electrode, thus endowing decreased overall battery weight and promoting reaction reversibility. These prominent structure advantages give HPCNF-5 electrode a fast ions/electrons diffusion capability, thus realizing superior rate property at a high current density of 2 A g−1 (204.6 mAh g−1) and excellent cyclability (with a capacity retention of 88% after 2000 cycles). Therefore, the findings demonstrate the comprehensive merits by combining 1D conductivity nanostructure, N-doping, hierarchical porous, and flexible self-supporting in one material, contributing to offering reference for constructing other advanced carbon materials. • Hierarchical porous one-dimensional carbon nanofibers were successfully fabricated. • The obtained product had high conductivity and improved capacitive behaviors. • Excellent rate capability especially at a high current density was achieved. [ABSTRACT FROM AUTHOR]

Carbonaceous materials with various structures and morphologies have been widely investigated as anode for potassium-ion batteries (PIBs), owing to their low cost, non-toxicity, environmental-benignity, etc. Among them, carbon nanofibers (CNFs) synthesized by electrospinning technique usually exhibit higher flexibility, thus they can be directly used as a self-supporting electrode. Accordingly, the overall electrochemical performance is obviously improved, and the batteries assembly procedure is also greatly simplified. However, intrinsic electronic conductivity of CNFs cannot sufficiently meet fast charging/discharging requirements at high current densities. Herein, iron phosphide nanoparticles-doped CNFs (Fe 2 P-CNFs) are well fabricated by electrospinning, phosphorylation, and carbonization route. The resulting Fe 2 P-CNFs, their internal Fe 2 P nanoparticles with high electronic conductivity (3.3 × 10−1 S cm−1, Fe 2 P single crystal) can accelerate electrons transfer, and simultaneously create numerous defects for K-ions storage. Besides, amorphous features of CNFs can provide adequate sites/voids to accommodate more K-ions. Based on this, when Fe 2 P-CNFs are used as a self-supporting anode for PIBs, they deliver excellent reversible capacity (379.2 mAh g −1), high-rate capability, and ultra-long cycle lifespan (179.6 mAh g −1 over 2000 cycles at 2000 mA g −1). Therefore, this work demonstrates the unique merits of Fe 2 P doping for improving conductivity, which may help exploit other carbon materials with high performance. [ABSTRACT FROM AUTHOR]

Transition-metal selenides, especially cobalt selenides (CoSe), are widely regarded as a promising anode for potassium-ion batteries (KIBs) due to their high theoretical capacity and good electrical conductivity. However, CoSe easily suffers from a substantial volume change upon repeated cycling, leading to a fast capacity decay and poor cycling stability. Herein, a dual-carbon confined CoSe is successfully designed by using metal-organic frameworks as raw materials. Various characterizations disclose that the introduction of the extra carbon phase is conducive to the growth of (101) plane of CoSe, and based on this, rationally regulating carbonization temperature can further promote the exposure of (101) plane. Such fully exposed (101) plane not only provides sufficient active surface to uptake K-ions, but also favors the accommodation of electrode structure fluctuation, accounting for a high capacity and prolonged cycle lifespan. As a result, the optimized sample (denoted as 750 °C NC@CoSe/NC) delivers 392.5 mAh g−1 at 0.5 A g−1, accompanied by an excellent cycling stability over 400 cycles with 196.7 mAh g−1 at a high current density of 1 A g−1. This work is expected to offer effective guidance for constructing advanced CoSe anode toward KIBs. [ABSTRACT FROM AUTHOR]

Boron (B) and nitrogen (N) co-doped hard carbons usually tend to deliver an excellent rate and ultra-long cycle lifespan, because of the formed B-N moieties can accelerate both ion/electron transfer. However, the rational regulation of B-N moieties content is rarely mentioned, and correlating rate and reversible capacity with B-N moieties content is still lacking yet. Hence, a series of B/N co-doped hard carbons are designed based on varied carbonization temperatures. Systematic characterizations prove that the introduced B-heteroatoms can create more defects and form well-developed pore channels. Besides, with increasing carbonization temperatures, B-N moieties content first increases and then decreases, which is in accordance with the evolution of defect degree of carbon matrix. Therefore, rich B-N moieties can induce more defect sites to greatly improve capacitive contribution, and as a result both rate and reversible capacity are strongly correlated with B-N moieties content. Based on this, the electrode with the highest B-N moieties content (79.6 %) realizes an excellent rate (220.9 mAh g−1 at 2 A g−1) and cycling stability (over 2000 cycles). Note that the storage of B-N moieties on K + only occurs in a high potential region (>0.5 V), and this process is highly reversible. [ABSTRACT FROM AUTHOR]

• Particles size decreases while defects increase with increasing carbonization time. • Suitable size can reduce ion diffusion distance while defect favors ion storage. • The optimized sample delivers an excellent rate and cycling stability. A series of defect-rich carbon particles with different sizes are successfully synthesized via a facile synthesis process. Various characterizations demonstrate that the particle size increases with the carbonization time increases, while the defect level presents an opposite trend, and as a result the defect-enriched carbon annealing at 800 ℃ for 2 h (DEC-800-2) achieves the optimum balance between them, which is favorable for increasing potassium storage sites and improving conductivity. Thus, the DEC-800-2 electrode delivers 220.9 mAh g−1 at 0.5 A g−1 after 100 cycles, accompanied by a good rate capability (156.9 mAh g−1 at 2 A g−1 after 2000 cycles). [ABSTRACT FROM AUTHOR]

Implanting nano-scaled CoP particles into hollow carbon is usually regarded as an effective strategy to improve structural stability for potassium ion batteries (PIBs). Hence, we employ tannic acid (TA) as the chemical-etching agent to elaborately synthesize a novel hollow hybrid composite composed of highly dispersed CoP nanoparticles (10-20 nm) embedded in well-developed carbon shell (CoP/C-2). The nano-sized CoP significantly shortens the diffusion distance of K-ions within electrode, while the highly dispersed features can expose more active surface to electrolyte by avoiding self-agglomeration, endowing improved reaction kinetics. Besides, the presence of carbon shell provides sufficient buffer space for volume variation, all of which are conducive to maintaining structural integrity against pulverization upon repeated cycling. When used as an anode for PIBs, the optimized CoP/C-2 exhibits an extraordinary cycling stability by keeping a high reversible capacity of 103.4 mAh g−1 after 1000 cycles at 2 A g−1, outperforming most previously reported literatures. The strategy presented in this work may provide a reference for constructing other advanced CoP-based abodes for PIBs. [ABSTRACT FROM AUTHOR]

Carbon materials with three-dimensional (3D) superstructure are a promising anode for potassium-ion batteries (PIBs) because of its rich micropores and defects. However, plenty of micropores often need more time to make electrolyte fully infiltrate, and their irreversible trapping effect will inevitably cause the loss of active K-ions upon cycling. Besides, excessive defects easily arouse poor conductivity because the absence of continuous graphite domains. Hence, dual-carbon coupled 3D superstructure is constructed by pyrolyzing the mixture of zeolitic imidazolate framework and polyvinylpyrrolidone (ZIF8@PVP). Since the preferential decomposition of external PVP, the micropores in ZIF8-derived carbon are effectively inhibited while keeping considerable mesopores, thus substantially shortening ions diffusion distance. Moreover, the decomposition and shrinkage of ZIF8 particles in return prompt the PVP-derived carbon to create more defects, which favors the adsorption storage of K-ions. Not only that, the metallic Zn can catalyze the formation of continuous graphite domains, endowing fast electron migration rate. Accordingly, the optimized product not only delivers an excellent rate (188.2 mAh g−1 at 2 A g−1) and cyclability (over 1800 cycles) in K-half cells, but presents a high energy density (181.5 Wh kg−1) in potassium-ion hybrid capacitors. [ABSTRACT FROM AUTHOR]

Graphitic carbon with high electronic conductivity has been widespreadly reported as an anode material for potassium-ion batteries (PIBs). However, it cannot accommodate more K ions and alleviate huge volume variations during cycling due to a narrow interlayer spacing of 0.335 nm, resulting in poor electrochemical behavior. Herein, by rational design, N-doping multi-forks amorphous carbon with hierarchical pores (NCTS) was successfully fabricated. The obtained NCTS exhibited enlarged interlayer spacing (0.376 nm), high specific surface area (396.6 m2 g−1), and well developed unique porous structure. These features can reduce the diffusion distance for both ions and electrons, and maintain the stability of the electrode structure. Hence, the NCTS electrode exhibits remarkable electrochemical performance with high specific capacity of 350.3 mA h g−1 at 500 mA g−1, ultra-long lifespan (over 2000 cycles at 2000 mA g−1), and outstanding rate capability (292.3 mA h g−1 at 1000 mA g−1). This work provides efficient guidance for constructing high-performance carbon anode materials to storage potassium. [ABSTRACT FROM AUTHOR]