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Oxygen‐containing functional groups (OFGs) grafted by carbon materials surface can serve as active sites to reversibly store potassium and simultaneously contribute to forming a stable solid‐electrolyte interphase layer, leading to increased capacity and cycling stability. However, the excessive OFGs will damage conductivity and hence causes the increase in electron transfer resistance, easily resulting in a poor rate. Herein, it is theoretically demonstrated that the embedded metallic Co particles can synergize with C‐O‐C moieties in OFGs to accelerate K‐ion adsorption (△E = −1.62 eV) and regulate electronic structure, ensuring high capacity and rate. In view of this, O‐doped carbon with implanted Co is well established, and it is found that pyrolysis temperature can effectively regulate Co content and C‐O‐C proportion. Various characterizations unveil that the introduced Co species not only evidently promote the adsorption capability of C‐O‐C to K‐ion, but catalyze the generation of graphitic carbon. Benefiting from these merits (e.g., enhanced adsorption ability and electronic conductivity), the sample with the optimal Co content and C‐O‐C proportion presents a high capacity of 254.7 mAh g−1 and an excellent rate capability (202.9 mAh g−1 at 2 A g−1). The unique design route makes fast and stable K‐storage of carbon anode possible. [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 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]

[Display omitted] • Polyaniline coated hollow mesopore hard carbon spheres are precisely tailored. • Polyaniline coating greatly boosts conductivity, while keeping considerable mesopores. • Polyaniline coating helps to form a stable and inorganic-rich SEI layer. • An excellent rate capacity (233.9 mAh g−1 at 5 A g−1) and a high ICE (70.7%) are realized. Hard carbon with rich mesopores is considered as one of the most promising anodes for potassium-ion batteries, resulting from its shortened ions diffusion distance, good electrolyte penetration ability, and highly released stress. However, the well-developed pore channels tend to separate graphite-domains and enlarge direct contact area between electrode/electrolyte, which easily cause discontinuous electrons transfer paths and extra electrolyte depletion, thus leading to poor rate performance and initial Coulombic efficiency (ICE). Hence, we propose polyaniline conductive layer coated hollow mesoporous carbon spheres (HMCS@PAN) tailored based on local protonation reaction strategy, which can enhance conductivity and simultaneously maintain considerable pore structure, accounting for an ultrahigh-rate performance (233.9 mAh/g at 5 A/g) and long cycling life (216.8 mAh/g at 5 A/g over 2000 cycles). Besides, PAN coating can inhibit the direct contact between inner pore channels and electrolyte and reduce the excessive depletion of active ions in the filling of pores with larger pore size, which is conducive to building an even, stable, and inorganic-rich solid electrolyte interphase (SEI) layer, resulting in an excellent ICE (70.7%). This work provides a guidance for the structure design of mesopore hard carbon to improve its rate and ICE. [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]

A series of N-doped graphitic carbons with different carbonization temperatures (denoted as ENGC-T) are controllably synthesized. The correlation between different N-doping species and interlayer spacing is explored, and thus demonstrating that pyrrolic-N (N-5) content has a substantial effect of the expanded interplanar spacing. The resulting ENGC-850 with the optimal N-5 configuration achieves excellent electrochemical performance in terms of capacity, rate capability, and cycling stability. [Display omitted] • A series of N-doped graphitic carbons are controllably synthesized. • High edge-N doping ratio is conducive to promote capacitive-controlled K-storage. • Pyrrolic-N configuration has a substantial effect on the interlayer spacing. • The resultant product delivers excellent rate capability and exceptional cyclability. Nitrogen (N) doped graphitic-carbon materials as anode have been intensively studied for potassium-ion batteries (PIBs). However, insufficient N-doping content, especially the low edge-N ratio composed of pyridinic-N (N-6) and pyrrolic-N (N-5) cannot provide excellent rate capability and ultra-long cycle lifespan. Meanwhile, the intercorrelation between N-doping species and enlarged interlayer spacing remains unclear and needs to be further explored. Based on this, a series of N-doped graphitic carbons with different carbonization temperatures (denoted as ENGC-T) are controllably synthesized. It is found that a high edge-N doping ratio is conducive to increase active sites to promote capacitive-controlled K-storage. And the correlation between N-doping species and interlayer spacing reveals that N-5 configuration has a substantial effect on the interlayer spacing, due to its stronger electrostatic repulsion. Accordingly, the resultant ENGC-850 with both an ultra-high edge-N ratio (76.6%) and N-5 content (42%) achieves the most abundant defects and the largest interspacing, ensuring high capacity and cycling stability. Besides, good crystallization characteristics guarantees fast electron transfer, favoring conductivity. As expected, ENGC-850 electrode delivers high capacity, excellent rate (228.9 mAh g−1 at 2 A g−1), and prolonged cycle lifespan (188.9 mAh g−1 over 2200 cycles). [ABSTRACT FROM AUTHOR]