Anode For KIBs Research Articles

Less energy-intensive synthesis of mesoporous multi-oriented graphite microspheres with low defect concentration for advanced potassium-ion battery anodes

Potassium-ion batteries (KIBs) have emerged as prospective alternatives to lithium-ion batteries (LIBs) given the wide availability of K resources and the similar operating voltage. As in the case of LIBs, graphite is regarded as the most promising anode material for KIBs due to high energy density attributed to its low potential plateau and resource abundance. However, the practical use of graphite in KIBs is hindered by poor stability due to huge volume changes during K+ ion insertion-deinsertion. Here, a facile and scalable synthesis method of mesoporous multi-oriented graphite microspheres via pilot-scale spray drying process and less energy-intensive graphitization step is introduced. A high degree of graphitization is achieved even at 1100 °C by virtue of in situ formed Fe nanocrystals within the microsphere that serve as graphitization catalyst. The degree of graphitization can be further improved by selective removal of amorphous carbon by oxidation at 450 °C, which greatly increases the initial Coulombic efficiency and reversible capacity of the graphite microspheres. The synthesized microspheres with the multi-oriented graphite grains and the mesoporous network enable rapid K+ ion insertion-deinsertion, and alleviate stress from volume changes during cycling, thereby exhibiting markedly improved cyclability (247 mA h g−1 after 400 cycles at 0.5C) and rate performance (58 mA h g−1 at 3C) that outperform those of commercial artificial graphite. This study provides a new perspective for designing reliable nanostructured graphite materials for advanced KIB anodes.

3D freestanding CuO@Copper foam as an anode for potassium ion batteries

The use of nanoelectrode materials is an efficient way to improve electrochemical performance of potassium ion batteries (KIBs), due to the large ionic radius and poor reaction kinetics of potassium ions. However, nanoelectrode materials with high specific surface areas and tendency to agglomerate generate unstable solid electrolyte interphase (SEI) films or severe side reactions, resulting in poor performance. Herein, a three-dimensional (3D), freestanding and binder-free electrode of CuO@copper foam (CuO@CF) is synthesized by anchoring nanostructured CuO on copper foam as anode for KIBs. CuO@CF electrode delivers a better initial coulombic efficiency, cycling stability and rate performance than that of nanostructured CuO electrode. Meanwhile, the K+ storage mechanism of CuO anode is further elucidated by in-situ X-ray diffraction (XRD), ex-situ XRD, X-ray photoelectron spectroscopy (XPS), and High-resolution transmission electron Microscope (HR-TEM). The as-prepared 3D freestanding CuO@CF electrode mitigates the degradation of nanostructured CuO electrode and provides a promising anode material for KIBs.

Stabilizing SEI by cyclic ethers toward enhanced K+ storage in graphite

The poor cycling stability of graphite in traditional ester electrolyte limits its applications as anodes for potassium ion batteries (KIBs). Herein, we demonstrate that the introduction of cyclic ether co-solvents into ester electrolytes can remarkably enhance the cycling stability of graphite anodes. The graphite anode in ester electrolyte with cyclic ether could achieve a reversible capacity of 196.1 mAh g−1 after 100 cycles at 0.3 C (1 C = 280 mA g−1), about three times higher than those in ester electrolytes with or without linear ether. Compared with the SEI formed in ester electrolytes, the addition of tetrahydrofuran promotes the generation of K2CO3 and ethylene oxide oligomers (PEO), of which the K2CO3 is expected to be more conductive and PEO is mechanically robust. The more uniform, conductive and stable solid electrolyte interphases (SEIs) on graphite in electrolytes with cyclic ethers contribute to the enhancement of the electrochemical performances of graphite. This work provides a novel design of commercialized electrolytes to achieve high-performance anodes for KIBs, which potentially accelerates the development of KIBs.

N, P Codoped Hollow Carbon Nanospheres Decorated with MoSe2 Ultrathin Nanosheets for Efficient Potassium-Ion Storage.

Potassium-ion batteries (KIBs) are gradually being considered as an alternative for lithium-ion batteries because of their non-negligible advantages such as abundance and low expenditure of K, as well as higher electrochemical potential than another alternative─sodium-ion batteries. Nevertheless, when the electrode materials are inserted and extracted with large-sized K+ ions, the tremendous volume change will cause the collapse of the microstructures of electrodes and make the charging/discharging process irreversible, thus disapproving their extended application. In response to this, we put forward a feasible strategy to realize the in situ assembly of layered MoSe2 nanosheets onto N, P codoped hollow carbon nanospheres (MoSe2/NP-HCNSs) through thermal annealing and heteroatom doping strategies, and the resulting nanoengineered material can function well as an anode for KIBs. This cleverly designed nanostructure of MoSe2/NP-HCNS can broaden the interlayer spacing of MoSe2 to boost the efficiency of the insertion/extraction of K ions and also can accommodate large volume change-caused mechanical strain, facilitate electrolyte penetration, and prevent the aggregation of MoSe2 nanosheets. This synthetic method generates abundant defects to increase the amounts of active sites, as well as conductivity. The hierarchical nanostructure can effectively increase the proportion of pseudo-capacitance and promote interfacial electronic transfer and K+ diffusion, thus imparting great electrochemical performance. The MoSe2/NP-HCNS anode exhibits a high reversible capacity of 239.9 mA h g-1 at 0.1 A g-1 after 200 cycles and an ultralong cycling life of 161.1 mA h g-1 at 1 A g-1 for a long period of 1000 cycles. This nanoengineering method opens up new insights into the development of promising anode materials for KIBs.

Three-Dimensional Porous h-BC2N Based on BN Chains and Prismane C8 Units for Alkali Metal Ion Battery Anodes.

Here, a new three-dimensional (3D) porous h-BC2N was designed via the assembly of prismane C8 and boron nitride chains as the candidates for alkali metal ion battery anodes. By systematic calculations, it is found that h-BC2N is both thermally and mechanically stable, even at a temperature as high as 1000 K. Li ions can migrate with multiple diffusion directions in h-BC2N, and the minimum diffusion barrier is only 0.10 eV lower than that of graphite. The theoretical specific capacity of the h-BC2N anode for Li is 549 mAh/g, which is higher than that reported for graphite. h-BC2N is also a promising anode for sodium (NIBs) and potassium ion batteries (KIBs) whose specific capacities are also large (549 mAh/g), and the energy barriers are 0.35 and 0.19 eV, respectively. Additionally, LIBs, NIBs, and KIBs exhibit voltage stability upon charging/discharging and good cycling stability. This theoretical exploration may open a new frontier in the search for more practical 3D porous structures as LIBs, NIBs, and KIBs anodes.

Mechanistic Elucidation of Electronically Conductive PEDOT:PSS Tailored Binder for a Potassium‐Ion Battery Graphite Anode: Electrochemical, Mechanical, and Thermal Safety Aspects

AbstractPotassium‐ion batteries (KIBs) are considered more appropriate for grid‐scale storage than lithium‐ion batteries (LIBs) due to similar operating chemistry, abundant precursors, and compatibility with low‐cost graphite anodes. However, a larger ion reduces rate capabilities and exacerbates capacity fading from volumetric expansion. Herein, conductive polymer, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is substituted for standard insulating polyvinylidene fluoride (PVDF). Half‐cells using carbon black (CB) in continuously conductive PEDOT:PSS/CB binder outperforms PVDF/CB by mitigating electrically isolated “dead” graphite, improving 100 cycle capacity retention at C/10 from 63 to 80%. Enhanced electrical contact with PEDOT:PSS/CB also reduces ion impedance and improves rate capabilities. Without CB however, PEDOT:PSS binder performs poorly in electrochemical studies despite promising ex situ electronic conductivity. This discrepancy is mechanistically elucidated through identification of redox activity between PEDOT:PSS and K+ which results in high impedances in the anode operating voltage window. Additionally, the impact of conducting binder on mechanical properties and thermal safety of the anode is investigated. Brittleness and poor wettability of PEDOT:PSS are identified as issues, but greater stability against reactive KC8 reduces overall heat generation. Binder substitution offers a promising means of mitigating issues with current KIB anodes regardless of active material, and the work herein addresses issues towards further improvement.

Carbon nanotubes-based anode materials for potassium ion batteries: A review

Potassium ion batteries (KIBs) are appealing candidates for new rechargeable batteries for large-grid electrochemical energy storage systems due to their substantial reserves and low cost. However, due to the large ionic size of K+, anode materials for KIBs have slow K+ ion reaction kinetics, substantial volume expansions, and an unstable solid electrolyte interface film, all of which can have a significant impact on the electrochemical properties of KIBs anodes. To create feasible KIBs anodes it is important to optimize both structural and electrochemical performance, which requires pragmatic structural design based on relevant materials. Carbon nanotubes (CNTs) has been attractive materials in the investigation as anode materials for KIBs due to their unique structural, mechanical, and electrical capabilities. This work reports the applications of CNTs in KIBs with their future development as electrically conductive framework materials in KIBs anodes. Various synthesis methods for the preparation of CNTs-based anodes for KIBs are addressed, which has shown remarkable morphological and electrochemical performance. Recent studies have focused on developing unique nanoarchitectures for KIB anodes to boost their capacity and lifetime. Moreover, to determine the differences, the electrochemical performances of CNTs-based anodes for LIBs and NIBs are compared to that of CNTs-based anodes for KIBs.

A Strain‐Relaxation Red Phosphorus Freestanding Anode for Non‐Aqueous Potassium Ion Batteries

AbstractRed phosphorus (RP), as a promising anode for potassium‐ion batteries (KIBs), and has attracted extensive attention due to its high theoretical capacity, low redox potential, and abundant natural sources. However, RP shows dramatic capacity decay and rapid structure degradation caused by huge volume expansion and poor electronic conductivity. Here, a volume strain‐relaxation electrode structure is reported, by encapsulating well‐confined amorphous RP in 3D interconnected sulfur, nitrogen co‐doped carbon nanofibers (denoted as RP@S‐N‐CNFs). In situ transmission electron microscopy and the corresponding chemo‐mechanical simulation reveal the excellent structural integrity and robustness of the N, S carbon matrix. As a freestanding anode for KIBs, the RP@S‐N‐CNFs electrode exhibits high reversible capacities (566.7 mAh g−1 after 100 cycles at 0.1 A g−1) and extraordinary durability (282 mAh g−1 after 2000 cycles at 2 A g−1). The highly reversible one‐electron transfer mechanism with a final discharge product of KP and faster kinetics are demonstrated through in situ characterizations and density functional theory calculations. This work sheds light on the rational design of large‐volume‐vibration type anodes for next‐generation high‐performance KIBs.

Surface modification and in situ carbon intercalation of two-dimensional niobium carbide as promising electrode materials for potassium-ion batteries

Potassium ion batteries (KIBs) have a great potential in large scale energy storage because of their cost advantages and similar working mechanism to lithium ion batteries (LIBs). However, the larger ionic radius of K+ presents great challenges to find suitable electrode materials for K+ insertion/extraction. Herein, the surface-modified and in-situ carbon-intercalated Nb2CTx MXene is rationally designed and synthesized as electrode for KIBs. The as-prepared Nb2C/C has larger effective interlayer distance (i.e. gallery height), higher specific surface area and electrical conductivity, and lower concentration of surface functional groups. As a result, Nb2C/C exhibits a significantly increased coulombic efficiency (67.6% for Nb2C/C, 28.5% for Nb2CTx) and its specific capacity is two times higher than that of Nb2CTx at 0.02 A·g−1, three times at 0.1 A·g−1. The Nb2C/C delivers an initial specific capacity of 397.9 mAh·g−1 at 0.02 A·g−1 and 338.1 mAh·g−1 at 0.1 A·g−1, and maintains 80.0% after 100 cycles at 0.02 A·g−1 and 76.2% after 200 cycles at 0.1 A·g−1, respectively. Notably, Nb2C/C possesses outstanding cyclic stability and rate performance at various current densities, outperforming most of reported MXene-based anodes for KIBs. The excellent potassium storage performance of Nb2C/C can be ascribed to the abundant active sites exposed to electrolyte, rapid diffusion kinetics of K+ and few side reactions at the electrode/electrolyte interface. This work proposes an effective strategy for the MXene-based materials to maximize their potential applications in various fields such as batteries, supercapacitors and catalysts.

Investigating the Electrical and Electrochemical Performance of a Conducting Binder for a Fast-Charging Potassium-Ion Battery Anode

Energy from intermittent sources such as wind and solar requires large-scale storage to match production with consumption. Rechargeable batteries, and in particular lithium-ion batteries (LIBs), have been a strong contender for their long cycle life, high energy density, and high efficiency. However, the scarcity and uneven distribution of lithium deposits has brought forth concerns whether future supply will meet rapidly increasing demand. Sustainable potassium-ion batteries (KIBs) use earth-abundant resources and operate on a similar principle as LIBs, providing a promising complementary field of research. However, the shorter cycle life and limited rate capabilities have precluded commercial success. A larger cation impedes insertion into layered graphite, reducing kinetic capabilities. Capacity fading is also exacerbated due to significant volumetric expansion (60%). These factors have critical implications for quickly storing negatively priced surplus electricity as well as annualized costs.We therefore aim to improve the charging speed and mitigate the capacity fading mechanism through enhanced electronic properties. While the literature has largely attempted to address these issues with unscalable nanostructured carbons and expensive salt-concentrated or ionic liquid electrolytes, few studies have addressed the binder, despite being a critical component of the composite electrode. To our knowledge, no studies currently exist on conductive polymer binders for KIB anodes. To this end we substitute the standard insulating polymer binder poly(vinylidene fluoride) (PVDF) for an electronically conductive polymer mixture, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).Substitution of PVDF for PEDOT:PSS in graphite electrodes with conductive carbon black (CB) additive shows significantly improved performance in half-cell cycling studies, with the 100 cycle capacity retention increasing from 63 to 72%. The higher initial capacity (240 vs 311 mAh g-1) at C/10 also indicates enhanced electrical contact and reduction of electronically isolated material. This capacity even exceeds the theoretical capacity of KC8 (279 mAh g-1) due to the additional capacitive charge storage. Further, through electrochemical impedance spectroscopy (EIS) we show a reduced charge transfer impedance (RCT) from 2310 to 1020 Ω, which enables faster kinetics. At a rate of C/3, the capacities are 160 and 40 mAh g-1, respectively. Removal of the carbon black (CB) for graphite with PEDOT:PSS binder however results in a high RCT, poor rate capabilities, and shortened cycle lifetime despite ex-situ results showing comparable or better electrical conductivity of the PEDOT:PSS to a PVDF/CB composite. This discrepancy is a subject of interest, as removing CB has the potential to increase the fraction of active material. In efforts to identify the underlying cause, we find poor electrolyte uptake of the PEDOT:PSS, and through EIS and half-cell cycling we show that electrical and electrolyte contact are competing factors for this system. Additionally, through cyclic voltammetry (CV) we identify reversible redox activity at 2.5 V vs. K/K+ of the PEDOT:PSS during the reductive scan as K+ coordinates with the negatively charged PSS, diminishing the concentration of charge carrying holes on the PEDOT polymer. EIS highlights a significant reversible change in electrochemical behavior when crossing this voltage threshold, supporting this claim. These factors likely contribute to the increased charge-transfer resistance. Results overall, however, showcase a promising avenue towards improving KIBs independent of the electrode active material, and identify issues to address in further improving lifetime and charging rates using this material. Figure 1

Constructing hollow CoSe2/SnSe2 heterostructures covered with N-doped carbon shell for high-efficiency potassium-ion storage

Potassium ion batteries (KIBs) are competitive energy storage systems for large-scale applications. However, developing suitable electrode materials to allow KIBs to achieve high electrochemical performances remains a significant challenge owing to the large radius of K+. In this study, hollow nanostructures composed of tin–cobalt bimetallic selenides and an N-doped carbon sheath (CS-Se@NC) were successfully fabricated from CoSn(OH)6 precursors via simple polydopamine coating and subsequent selenization. The synergy of the two active species and the structural features promoted electrochemical redox reactions and alleviated volume expansion during cycling. Moreover, the N-doped carbon coating reinforced the nanocomposite against particle pulverization while improving the electrode conductivity. Consequently, when tested as an anode for KIBs, the CS-Se@NC electrode exhibited a high potassium storage performance, remarkable cycling performance of 370 mA h g−1 at 0.5 A g−1 after 200 cycles, and excellent rate capability of 184 mA h g−1 at 2.0 A g−1. Thus, this electrode shows potential for practical use in the energy storage field.

Woven microsphere architected by carbon nanotubes as high-performance potassium ion batteries anodes

Owing to the abundance of potassium resources and compared performance to Lithium-ion batteries (LIBs), Potassium ion batteries (KIBs) are becoming an important supplement to the energy market dominated by LIBs now. Graphitic carbon is a mainstream anode material for LIBs, and also has great potential as anode of KIBs. But due to the limited layer spacing of graphitic carbon, the intercalation of large K+ results in poor rate and low temperature performance and limited life of battery. Here, microspheres knitted by robust carbon nanotubes (CNTs) are constructed through one step injected pyrosis using thiophene as both carbon and co-catalyst source, ferrocene as both catalyst precursor and part carbon source and followed by graphitization, finally giving graphitic carbon with both toughness and rapid ionic conductivity. When used as the anode of KIBs, it presents a stable and slight increased capacity of 155.5 mAh g−1 after 1000 cycles at 1C due to stability of unique structure. It is proven that local amorphization of carbon in the pore increases more K+ storage active sites, resulting an increased capacity with cycle. Moreover, the anode can achieve high power density with depotassiated capacity of 164.3 mAh g−1 as current density high as 70C (less than 1 min) and outstanding low temperature performance with 167.8 mAh g−1 at −40℃, proving its super dynamic and potential in low temperature scenarios. All in all, the unique structurally engineered graphitic carbon provides an insightful idea to promote the further application of graphite anode for KIBs.

Electrospun MOF-based ZnSe nanocrystals confined in N-doped mesoporous carbon fibers as anode materials for potassium ion batteries with long-term cycling stability

Potassium ion batteries (KIBs) are promising energy storage systems for large-scale applications. However, owing to the large diameter of K+, these batteries show limited electrochemical performance, particularly in terms of cycling stability. Thus, it is essential to design novel electrode materials for practical applications of KIBs. In this study, novel N-doped porous carbon nanofibers embedded with ultrafine ZnSe nanocrystals were successfully prepared as an advanced anode material for KIBs via electrospinning of a Zn-based zeolitic imidazolate framework (ZIF-8) and subsequent thermal treatment. Numerous mesopores were generated within the nanofibers by the transformation of ZIF-8 nanoparticles into a hollow carbon frame during thermal treatment. The unique 1D structure provided sufficient active sites for K+ storage, shortened the diffusion path for ions, and enhanced the structural robustness of the electrode. The N-doped carbon matrix also effectively alleviated the mechanical stress in the ZnSe nanocrystals and improved the electrical conductivity. Consequently, the 1D porous nanostructured electrodes exhibited excellent long-term cycling stability for 1000 cycles when tested as anodes for KIBs, with a reversible capacity of 270 mA h g−1 at 0.5 A g−1 and a high-rate capacity of 139 mA h g−1 at 2.0 A g−1.

Mo2C quantum dots inlaid in nitrogen-doped carbon nanofibers as free-standing anodes with long-term stability K-ion storage

Potassium ion batteries (KIBs) have attracted worldwide attention on account of low cost and abundance of resources, and potentially high energy density. However, the development of KIBs is blocked by the sluggish reaction kinetics and the instability electrode materials caused by repetitive intercalation/deintercalation of large ions size of K+. Herein, the novel flexible and free-standing Mo2C/NCNFs anode for KIBs, in which the Mo2C quantum dots are inlaid in N-doped carbon nanofibers, is synthesized via a simple electrospinning route. The rationally designed structure with Mo2C quantum dots uniformly embedded in NCNFs can not only facilitate to accelerate the K+ reaction kinetics but also potentially alleviated the expansion and pulverization of Mo2C during the long-term cycling process. Furthermore, the N doping carbon nanofibers can provide a highway for K+ ions and electrons transport, while the whole electrode also offers a free-standing electrode without the addition of conductive agents and adhesives, facilitating to promote energy density of batteries. As a result, the Mo2C/NCNFs as anode for KIBs demonstrate impressive long-term stability with the capacity fading ratio of only 0.026% per cycle until 1000 cycles at 1.0 A g−1. More importantly, Mo2C/NCNFs as anode for hybrid potassium-ion capacitors (KICs) deliver a high energy/power density of 88.2 W h kg−1/629.9 W kg−1, as well as excellent capacity retention of about 80.4% after 1000 cycles. The versatile strategy, excellent cycling stability and ultra-robust flexibility make the Mo2C/NCNFs a great prospect for application in the field of alkali metal ion batteries, electrocatalyst and flexible wearable devices.

Adsorption of K Ions on Single-Layer GeC for Potential Anode of K Ion Batteries.

Potassium ion batteries (KIBs) are considered as promising alternatives to lithium ion batteries (LIBs), following the rapid increase of demand for portable devices, and the development of electric vehicles and smart grids. Though there has been a promising breakthrough in KIB tech niques, exploring the promising anode materials for KIBs is still a challenge. Rational design with first-principle methods can help to speed up the discovery of potential anodes for KIBs. With density functional calculations, GeC with graphene-like 2D structure (g-GeC) is shown to be a desired anode material for applications in KIBs. The results show that the 2D g-GeC with a high concentration of K ions is thermodynamically stable, due to the strong interaction between C and Ge in GeC layer with the proper interaction between K and GeC. The storage capacity can be about 320 mAh/g, higher than that (279 mAh/g) in graphite. The low energy barrier (0.13 eV) of K ions diffusion on the honeycomb structure with proper voltage profile indicates the fast charge transfer. These theoretical finds are expected to stimulate the future experimental works in KIBs.

Metal sulfoselenide solid solution embedded in porous hollow carbon nanospheres as effective anode material for potassium-ion batteries with long cycle life and enhanced rate performance

Recently, potassium-ion batteries (KIBs) have been investigated as promising alternative to lithium-ion batteries, and significant advances in terms of new compositions and nanostructures are being made. In this regard, the strategy of introducing hetero-anions into metal compounds has been considered as an innovative method. After the initial electrochemical reaction, hetero-anion metal compounds are divided into individual metal compounds to form heterointerfaces, thus enhancing the electrochemical kinetics. Herein, a new strategy for the synthesis of metal sulfoselenide solid solution embedded in the porous shells of hollow carbon nanospheres is introduced; here, porous hollow carbon nanospheres are utilized as a co-infiltrating matrix to create electrode material with robust stability and high conductivity. The conversion reaction mechanism of metal sulfoselenide with potassium ions was investigated through systematic structural and electrochemical analyses, where metal sulfide/metal selenide hetero-interface was formed after the initial cycle. As anode for KIBs, CoSSe–C exhibited impressive electrochemical properties including particularly long cycle life (286 mA h g−1 for 3000 cycles at 1.5 A g−1) and excellent rate capability (185 mA h g−1 at 5.0 A g−1).

Bi-continuous ion/electron transfer avenues enhancing the rate capability of SnS2 anode for potassium-ion batteries

Potassium-ion batteries (KIBs) are considered to be promising energy-storage-systems in the post-Li-ion batteries. Conversion and alloy reaction anode materials draw much attention owing to high theoretical capacities. However, their inherent volume expansions always block the K-ion diffusion or interrupt electron transfer to a degree, resulting in degraded performances at high rates. It is supposed that the rate capability of the anode would be improved when the avenues for ion/electron are kept expedite simultaneously. Herein, SnS2 and carbon hybrid submicro-fibers with optimized channels were prepared as integrated KIBs electrodes to clarify the effect of the bi-continuous avenues on the rate capability. In this configuration, SnS2 nanosheets are confined by carbon and further crosslinked into 3D network. The 3D carbon submicro-fibers are adopted as a network for electron transfer, while the channels play the role of ion diffusion avenues. Owing to the stable and expedite bi-continuous electron/ion avenues, the rate capability of the SnS2@C–1V1 SMF electrode (137.5 mAh g−1 at 2.0 A g−1) is improved when compared to the counterparts (3.6 mAh g−1 and 94.5 mAh g−1 at the same condition). This work will offer an important reference for the optimization design and construction of KIBs anode materials with high rate capability.

Metallic two-dimensional P2C3: A promising flexible anode for high-performance potassium-ion batteries

Due to the earth-abundant potassium resource and intrinsic safety, potassium ion batteries (KIBs) are widely regarded as a promising alternative to lithium ion batteries. Nonetheless, the development of KIBs is very slow and severely impeded by the lack of a suitable anode material. Herein, based on the comprehensive first principles computations, we systematically explored the recently developed phosphorus carbide (P2C3) monolayer as an anode of KIBs. Our results demonstrate that P2C3 exhibits a metallic characteristic, providing good electrical conductivity for the rapid electronic transport. Meanwhile, P2C3 monolayer possesses excellent mechanical flexibility and large adsorption energy (−3.25 to −2.41 eV), which could avoid the anode pulverization during cycling. Furthermore, the theoretical capacity of P2C3 is 729.28 mA h/g, higher than most of the reported KIBs anode materials. The lowest diffusion barrier of K ion is only 0.0053 eV. All these appealing results demonstrate that P2C3 monolayer is an outstanding flexible anode of KIBs.

Amorphous carbon/graphite coupled polyhedral microframe with fast electronic channel and enhanced ion storage for potassium ion batteries

Carbonaceous materials are well suitable for potassium-ion batteries (KIBs) anode due to the advantages of low cost and excellent K+ intercalation/deintercalation reversibility. Nevertheless, it is attractive but challenging to achieve satisfactory electrochemical performance in terms of rate, capacity and stability. Herein, N-doped amorphous carbon/graphite coupled polyhedral microframe (NCM) is successfully synthesized as an advanced anode for KIBs. The graphite acts as fast electronic channel while the amorphous carbon can host more K+ and accommodate the volume change, thus boosting its rate, capacity and stability. The von Mises stress distribution after K+ intercalation is also studied to demonstrate the optimization process of strain caused by the volume change through the finite element method. Along with the large interlayer spacing (0.368 nm), rich active sites and highly accessible surface, the NCM electrode exhibits high reversible capacity of 358.4 mAh g−1 at 500 mA g−1, outstanding rate property (272.2 mAh g−1 at 1000 mA g−1) and superb cycling performance (189.5 mAh g−1 after 1800 cycles at 2000 mA g−1). Moreover, a K-ion full cell is successfully assembled on the basis of potassium Prussian blue (KPB)/NCM, exhibiting large energy density (177.6 Wh kg−1) and good cycling stability.

First-principle study of Ti2XS2 (X = C/N) MXenes as high capacity anodes for rechargeable potassium-ion batteries

Potassium-ion batteries (KIBs) are potential substitutions of lithium-ion batteries, considering the superiority of K in abundance and safety compared with lithium. Recently, the MXenes emerged as a significant class of two-dimensional materials in energy storage applications. Herein we investigated the performances of two S-functionalized MXenes (S-MXenes), Ti2CS2 and Ti2NS2, as anodes for KIBs through first-principle calculations. The results show that both S-MXenes possess metallic nature and structural integrity. Besides, the two functionalized structures exhibit strong adsorptions and low diffusion energy barriers, suggesting fast charge–discharge rates. By reaching the ultimate structural configurations, the theoretical capacities are as high as 312 mAh/g with low but positive open circuit voltage. All the performances reveal that the S-MXenes are promising anode materials for KIBs and expand their application as electrode materials.