Potassium-ion Batteries Research Articles

Electrolyte matching design for carboxylic acid-based organic K-storage anode

Carboxylic acid-based organic anodes are emerging as sustainable alternatives to traditional inorganic materials for potassium-ion batteries (PIBs), owing to their potential to improve both sustainability and K-storage performance. Herein, a readily available 4-fluorobenzoic acid (4FA) supported on ordered mesoporous carbon (4FA/CMK3) is proposed as a novel K-storage anode material. Importantly, we extensively investigated the compatibility of various electrolytes with the 4FA/CMK3 anode, focusing on electrolytes with tunable solvation structures to optimize electrode/electrolyte interfacial electrochemistry. A significantly decreased amount of free solvent in the optimized ether-based electrolytes compared to conventional ester-based electrolytes provides excellent compatibility with the modified 4FA/CMK3 anode, which promotes the formation of salt anion-derived interfacial phases, thereby improving K-storage performance. As a result, the optimized 4FA/CMK3||KFSI/DME storage system delivered a reversible capacity of 164 mAh/g with Coulombic efficiency above 99.8 % after 500 cycles at high current density of 200 mA/g. These excellent electrochemical properties are attributed to the synergistic effects of 4FA modification and electrolyte solvation structure modulation, which collectively mitigate the dissolution issues of organic actives and improve the cycling life of PIBs. This work presents a novel vision for designing PIBs with high energy density and long cycle life based on carboxylic acid-based organic electrodes.

Fast and robust potassium storage enabled by controllable hierarchical CoTe2/MoS2@C nanorods with semi-coherent heterogeneous interfaces

Constructing heterostructures in a controllable manner stands as a pivotal strategy for enhancing the potassium-ion storage capabilities of transition metal tellurides. However, the challenge lies in achieving a favorable morphology while simultaneously regulating the heterogeneous interface. This study employs a straightforward one-step hydrothermal method to grow few-layer MoS2 nanosheets on CoTe2 nanorods, thereby fabricating a controllable hierarchical structure with a dense three-dimensional (3D) network of MoS2 nanosheets and abundant semi-coherent heterojunction interfaces with CoTe2. The CoTe2/MoS2 heterostructure exhibits abundant semi-coherent interfaces, at which a built-in electric field is formed that facilitates the migration of electrons and ions. A hierarchical structure of CoTe2/MoS2@C was further formed by carbon coating, that applies a dual constraint on CoTe2 to effectively alleviate its volume expansion during charge and discharge processes. Employed as the anode of potassium-ion batteries, the hierarchical structure of CoTe2/MoS2@C demonstrates a significant improvement in high-rate capacity, achieving a high specific capacity of 144.0 mAh g−1 at 5.0 A g−1. The material also enables excellent long-term cycling stability with a capacity decay of only 0.016 % per cycle up to 1800 cycles at 1.0 A g−1.

Interlayer expansion and conductive networking of MoS2 nanoroses mediated by bio-derived carbon for enhanced potassium-ion storage

Potassium-ion batteries (PIBs) represent a promising battery technology for energy storage applications. Nevertheless, the progress of PIBs is still hindered by the lack of electrode materials that allow rapid and repeatable accommodation of the large K+ ions. Herein, a composite anode material containing interlayered-expanded MoS2 (55.6% larger) nanoroses in carbon nanonets (MoS2/C@CNs) is designed with the assistance of biomass bagasse, of which the dual carbon sources convert into interlayer and skeleton carbon, respectively. The unique structure facilitates electron/ion transport in the entire electrode and offers excellent structural stability, leading to much improved electrochemical performance compared to simple MoS2/C composite and pure MoS2. Furthermore, the role of electrolyte salts (potassium hexafluorophosphate and potassium bis(fluorosulfonyl)imide) and the electrolyte concentration on the interfacial properties in PIBs have been explored. The results indicate that the low-concentration potassium bis(fluorosulfonyl)imide electrolyte helps to produce optimized organic-inorganic solid electrolyte interface films, contributing to a capacity retention of 90% after 1,000 cycles at 2 A g-1.

Binder-Free Anodes for Potassium-ion Batteries Comprising Antimony Nanoparticles on Carbon Nanotubes Obtained Using Electrophoretic Deposition.

Antimony has a high theoretical capacity and suitable alloying/dealloying potentials to make it a future anode for potassium-ion batteries (PIBs); however, substantial volumetric changes, severe pulverization, and active mass delamination from the Cu foil during potassiation/depotassiation need to be overcome. Herein, we present the use of electrophoretic deposition (EPD) to fabricate binder-free electrodes consisting of Sb nanoparticles (NPs) embedded in interconnected multiwalled carbon nanotubes (MWCNTs). The anode architecture allows volume changes to be accommodated and prevents Sb delamination within the binder-free electrodes. The Sb mass ratio of the Sb/CNT nanocomposites was varied, with the optimized Sb/CNT nanocomposite delivering a high reversible capacity of 341.30 mA h g-1 (∼90% of the initial charge capacity) after 300 cycles at C/5 and 185.69 mA h g-1 after 300 cycles at 1C. Postcycling investigations reveal that the stable performance is due to the unique Sb/CNT nanocomposite structure, which can be retained over extended cycling, protecting Sb NPs from volume changes and retaining the integrity of the electrode. Our findings not only suggest a facile fabrication method for high-performance alloy-based anodes in PIBs but also encourage the development of alloying-based anodes for next-generation PIBs.

Construction of Bi/Bi2O3 particles embedded in carbon sheets for boosting the storage capacity of potassium-ion batteries

Bismuth-based materials have attracted interest in potassium-ion batteries (PIBs). However, the large volume expansion prevents further use of bismuth-based materials for potassium storage. This work employs a two-step synthesis method to innovatively synthesize of Bi/Bi2O3 nanoparticles assembled on N-doped porous carbon sheets (Bi/Bi2O3@CN). The layered structures with uniformly shaped and N-doped porous carbon skeleton buffer the expansion of Bi and the Bi/Bi2O3 particles increase the capacity of potassium storage. In brief, the Bi/Bi2O3@CN served as anode in half-cell of PIBs have a good rate capacity of more than 234.7 mAh/g at 20 A/g. The specific capacity retention was 73 % compared with 322.16 mAh/g at 1 A/g, demonstrating good holding capacity for diverse current densities. The cycle also displays 163 mAh/g after 1500 cycles at 2 A/g in the KPF6 metal salt solution, showing its potential as one of the anode materials in PIBs.

Construction of High-Performance Anode of Potassium-Ion Batteries by Stripping Covalent Triazine Frameworks with Molten Salt.

Covalent triazine frameworks (CTFs) are promising battery electrodes owing to their designable functional groups, tunable pore sizes, and exceptional stability. However, their practical use is limited because of the difficulty in establishing stable ion adsorption/desorption sites. In this study, a melt-salt-stripping process utilizing molten trichloro iron (FeCl3) is used to delaminate the layer-stacked structure of fluorinated covalent triazine framework (FCTF) and generate iron-based ion storage active sites. This process increases the interlayer spacing and uniformly deposits iron-containing materials, enhancing electron and ion transport. The resultant melt-FeCl3-stripped FCTF (Fe@FCTF) shows excellent performance as a potassium ion battery with a high capacity of 447 mAh g-1 at 0.1 A g-1 and 257 mAh g-1 at 1.6 A g-1 and good cycling stability. Notably, molten-salt stripping is also effective in improving the CTF's Na+ and Li+ storage properties. A stepwise reaction mechanism of K/Na/Li chelation with C═N functional groups is proposed and verified by in situ X-ray diffraction testing (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and theoretical calculations, illustrating that pyrazines and iron coordination groups play the main roles in reacting with K+/Na+/Li+ cations. These results conclude that the Fe@FCTF is a suitable anode material for potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and lithium-ion batteries (LIBs).

Recent advances in Sb-based anodes for Li/Na/K-ion batteries and all-solid-state Li-ion batteries

In recent decades, lithium-ion batteries (LIBs) have emerged as a primary focus in the energy-storage field owing to their superior energy and power densities. However, concerns regarding the depletion of non-abundant lithium resources have prompted the exploration and development of emerging energy-storage technologies, such as sodium- (SIBs) and potassium-ion batteries (PIBs). In addition, all-solid-state LIBs (ASSLIBs) have been developed to address the issues of flammability and explosiveness associated with liquid electrolytes. Among the various alloy-based anodes, antimony (Sb) anodes exhibit high energy densities owing to their high theoretical volumetric capacities that are attributable to their high densities. However, Sb anodes exhibit poor cyclabilities owing to excessive volume changes during cycling. To mitigate this issue, researchers have investigated the use of diverse solutions, including solid electrolyte interface control, structural control, and composite/alloy formation. Herein, we review and summarize Sb-based anode materials for LIBs, SIBs, PIBs, and ASSLIBs developed over the past five years (2018-present), focusing on their reaction mechanisms and multiple approaches used to achieve optimal electrochemical performance. We anticipate that this review will provide a comprehensive database of Sb-based anodes for LIBs, SIBs, PIBs, and ASSLIBs, thereby advancing relevant studies in the energy-storage-systems field.

Rational design of a setaria-like NiTe2/MoS2 semi-coherent heterogeneous interface for enhancing diffusion kinetics in potassium-ion batteries

Constructing unique heterostructures is a highly effective approach for enhancing the K+ storage capability of transition metal selenides. Such structures generate internal electric fields that significantly reduce the charge transfer activation energy. However, achieving a flawless interfacial region that maintains the optimal energy level gradient and degree of lattice matching remains a considerable challenge. In this study, we synthesised Setaria-like NiTe2/MoS2@C heterogeneous interfaces at which three-dimensional MoS2 nanosheets are evenly embedded in NiTe2 nanorods to form stabilised heterojunctions. The NiTe2/MoS2 heterojunctions display distinctive electronic configurations and several active sites owing to their low lattice misfits (δ = 13 %), strong electric fields, and uniform carbon shells. A NiTe2/MoS2@C anode in a potassium-ion battery (KIB) exhibited an impressive reversible capacity of 125.8 mAh/g after 1000 cycles at a rate of 500 mA g−1 and a stable reversible capacity of 111.7 mAh/g even after 3000 cycles at 1000 mA g−1. Even the NiTe2/MoS2@C//perylene tetracarboxylic dianhydride full battery configuration maintained a significant reversible capacity of 92.4 mAh/g after 100 cycles at 200 mA g−1, highlighting its considerable potential for application in KIBs. Calculations further revealed that the well-designed NiTe2/MoS2 heterojunction significantly promotes K+ ion diffusion.

Relationship between functionalization and structural defect density of graphite for application in potassium-ion batteries

Potassium-ion batteries (PIBs) have recently gained attention as an alternative to Li-ion batteries (LIBs) because Li and K belong to the same alkali metal group and are replaceable. However, the theoretical capacity of PIBs is hindered by the larger size of potassium ions compared to lithium ions. Generally, the surface treatment of graphite, an anode material in metal-ion batteries, enhances ion diffusivity and improves electrochemical performance. In this study, a straightforward approach is introduced in which graphite is treated with an acid to widen the interlayer spacing and an alkali to create pores. Acid and alkali treatments not only improve ion diffusivity but also control the surface charge of graphite in PIBs. Consequently, acid-treated graphite (AG) displays the highest specific capacity (206.2 mAh g−1 at 0.2 A g−1 after 100 cycles) with good durability. In addition, the trade-off between the physical ion pathway derived from structural defect density and functionalization-induced surface charge improves ion diffusivity.

Encapsulating Antimony metal nanoparticles in hierarchical porous carbon skeleton as high-performance potassium- and lithium-ion batteries anodes

Metallic antimony (Sb) as alkaline metal battery anode material, being thoroughly researched for its high theoretical specific capacity, but there is still a huge expansion problem with repeated insertion/de-insertion., We reported a unique composite material that encapsulates Sb nanoparticles in hierarchical porous carbon skeletons (Sb@HPCs) in this work, to explore the effect of the hierarchical porous carbon structure on the electrochemical performance of the Sb@HPCs as potassium-ion batteries (KIBs) and lithium-ion batteries (LIBs) anode materials. The macropores could promote the penetration of electrolyte, thus reducing the internal impedance of the battery. The mesopores provide a short ion diffusion path and a large diffusion region, which plays a crucial role in facilitating rapid ionic migration in both KIBs and LIBs. The micropores in the electrode material contribute to a larger specific surface area, which provides more surface area for charge storage, thus enhancing the energy density of the material. Importantly, when the Sb@HPCs composite material is applied as anode material of KIBs, it exhibits an outstanding specific capacity of 360 mAh g−1 after 100 cycles at 100 mA g−1. In the LIBs, the specific capacity of the composite material is 595.2mAh g−1 after 100 cycles at a current density of 0.1 A g−1; even at a high current density of 1.0 A g−1, the specific capacity still maintains at 320.4 mAh g−1 after 800 cycles, indicating an excellent cycling stability. The development of hierarchical porous three-dimensional structure offers a practical solution to the capacity degradation issues of metal anode in KIBs/LIBs.

Amorphous and crystalline Sb2S3 nanoparticles embedded in N/S co-doped carbon as anodes for potassium-ion batteries

Antimony trisulfide (Sb2S3) has emerged as a promising anode candidate for potassium-ion batteries (PIBs) owing to its low cost and high theoretical specific capacity. However, its large volume expansion upon K+ storage and sluggish kinetics result in poor cycling performance and rate capability. To address these challenges, rational structural design is highly desirable. Herein, we report the synthesis of amorphous and crystalline Sb2S3 nanoparticles embedded in N/S co-doped carbon composites (a-Sb2S3@NSC and c-Sb2S3@NSC) via a facile organic coating combined with subsequent carbonization and sulfidation processes. When used as a PIBs anode material, a-Sb2S3@NSC exhibits a high discharge specific capacity of 415.6 mAh g−1 after 50 cycles at 200 mA g−1 and a stable rate capability (224.8 mAh g−1 at 2 A g−1), which remarkably outperforms that of the c-Sb2S3@NSC with inferior specific capacity (311.5 mAh g−1) and poor rate capability (67.7 mAh g−1). The amorphous structure of Sb2S3 nanoparticles in a-Sb2S3@NSC provides abundant defects and structural disorder, which reduces the entropy energy and activation barrier associated with K+ incorporation, effectively facilitating the transport and storage of K+. Moreover, the synergistic interactions between amorphous Sb2S3 nanoparticles and N/S co-doped carbon can effectively improve the electron/ion reaction kinetics and buffer volume variations, thus leading to superior potassium storage performances.

Calcium-Pillar Boosting Smooth Phase Transition in Potassium Vanadate Nanobelts toward Superior Cycling Performance in Potassium-Ion Batteries.

The depletion of lithium resources has prompted exploration into alternative rechargeable energy storage systems, and potassium-ion batteries (PIBs) have emerged as promising candidates. As an active cathode material for PIBs, potassium vanadate (KxV2O5) usually suffers from structural damage during electrochemical K-ion insertion/extraction and hence leading to unsatisfactory cycling performance. Here, we introduce Ca2+ ions as pillars into the potassium vanadate to enhance its structural stability and smooth its phase transition behavior. The additional Ca2+ not only stabilizes the layered structure but also promotes the rearrangement of interlayer ions and leads to a smooth solid-solution phase transition. The optimal composition K0.36Ca0.05V2O5 (KCVO) exhibits outstanding cyclic stability, delivering a capacity of ∼90 mA h g-1 at 20 mA g-1 with negligible capacity decay even after 700 cycles at 500 mA g-1. Theoretical calculations indicate lower energy barriers for K+ diffusion, promoting rapid reaction kinetics. The excellent performances and detailed investigations offer insights into the structural regulation of layered vanadium cathodes.

KF-Containing Interphase Formation Enables Better Potassium Ion Storage Capability.

Rechargeable potassium ion batteries have long been regarded as one alternative to conventional lithium ion batteries because of their resource sustainability and cost advantages. However, the compatibility between anodes and electrolytes remains to be resolved, impeding their commercial adoption. In this work, the K-ion storage properties of Bi nanoparticles encapsulated in N-doped carbon nanocomposites have been examined in two typical electrolyte solutions, which show a significant effect on potassium insertion/removal processes. In a KFSI-based electrolyte, the N-C@Bi nanocomposites exhibit a high specific capacity of 255.2 mAh g-1 at 0.5 A g-1, which remains at 245.6 mAh g-1 after 50 cycles, corresponding to a high capacity retention rate of 96.24%. In a KPF6-based electrolyte, the N-C@Bi nanocomposites show a specific capacity of 209.0 mAh g-1, which remains at 71.5 mAh g-1 after 50 cycles, corresponding to an inferior capacity retention rate of only 34.21%. Post-investigations reveal the formation of a KF interphase derived from salt decomposition and an intact rod-like morphology after cycling in K2 electrolytes, which are responsible for better K-ion storage properties.

Scaly MoS2/rGO Composite as an Anode Material for High-Performance Potassium-Ion Battery.

Potassium-ion batteries (PIBs) have been widely studied owing to the abundant reserves, widespread distribution, and easy extraction of potassium (K) resources. Molybdenum disulfide (MoS2) has received a great deal of attention as a key anode material for PIBs owing to its two-dimensional diffusion channels for K+ ions. However, due to its poor electronic conductivity and the huge influence of embedded K+ ions (with a large ionic radius of 3.6 Å) on MoS2 layer, MoS2 anodes exhibit a poor rate performance and easily collapsed structure. To address these issues, the common strategies are enlarging the interlayer spacing to reduce the mechanical strain and increasing the electronic conductivity by adding conductive agents. However, simultaneous implementation of the above strategies by simple methods is currently still a challenge. Herein, MoS2 anodes on reduced graphene oxide (MoS2/rGO) composite were prepared using one-step hydrothermal methods. Owing to the presence of rGO in the synthesis process, MoS2 possesses a unique scaled structure with large layer spacing, and the intrinsic conductivity of MoS2 is proved. As a result, MoS2/rGO composite anodes exhibit a larger rate performance and better cycle stability than that of anodes based on pure MoS2, and the direct mixtures of MoS2 and graphene oxide (MoS2-GO). This work suggests that the composite material of MoS2/rGO has infinite possibilities as a high-quality anode material for PIBs.

A N–CoSe/CoSe2–C@Cu hierarchical architecture as a current collector-integrated anode for potassium-ion batteries

The highly reversible insertion/extraction of large-radius K+ into electrode materials remains a tough goal, especially for conversion-type materials. Herein, we design a current collector-integrated electrode (N–CoSe/CoSe2–C@Cu) as an advanced anode for potassium-ion battery (PIBs). The conductive CoSe/CoSe2 heterojunction with rich Se vacancy defects, conductive sp2 N-doped carbon layer, and the elastic copper foil matrix can greatly accelerate the electron transfer and enhance the structural stability. Consequently, the well-designed N–CoSe/CoSe2–C@Cu current collector-integrated electrode displays enhanced potassium storage performance with regard to a high capacity (325.1 mAh·g−1 at 0.1 A·g−1 after 200 cycles), an exceptional rate capability (223.5 mAh·g−1 at 2000 mA·g−1), and an extraordinary long-term cycle stability (a capacity fading of only 0.019% per cycle over 1200 cycles at 2000 mA·g−1). Impressively, ex situ scanning electron microscopy (SEM) characterizations prove that the elastic structure of copper foil is merged into the cleverly designed N–CoSe/CoSe2–C@Cu heterostructure, which buffers the deformation of structure and volume and greatly promotes the cycle life during the potassium/depotassium process.Graphical abstract

Unveiling the bifunctional roles of Cetyltrimethylammonium bromide in construction of Nb2CTx@MoSe2 heterojunction for fast potassium storage

Exploring robust electrode materials which could permit fast and reversible insertion/extraction of large K+ is a crucial challenge for potassium-ion batteries (PIBs). Smart interfacial design could facilitate electron/ion transport as well as assure the integrity of electrode. Herein, Cetyltrimethylammonium bromide (CTAB) was found to play bifunctional roles in construction of Nb2CTx@MoSe2 heterostructure. Firstly, functionalization of CTAB on the surface of Nb2CTx could influence the subsequent growth of MoSe2 by electrostatic effect, stereochemical effect and the synergetic Lewis acid-base interaction, leading to the formation of Nb2CTx@MoSe2 with tiled heterostructure. Secondly, the interlayer spacing of Nb2CTx was expanded from 0.77 to 1.21 nm owing to the pillar effect of CTAB. As excepted, the capacity retention was 80 % from 100 mA g−1 (406 mA h g−1) to 1000 mA g−1 concerning rate capability and the specific capacity maintained at 240 mA h g−1 (at 2000 mA g−1) over 300 cycles. The calculated DK values from Galvanostatic intermittent titration technique (GITT) measurement of the titled C-T-Nb2CTx@MoSe2@C electrode is two orders of magnitude larger than the traditional T-Nb2CTx@MoSe2@C electrode, further confirming intimate interface between MoSe2 and Nb2CTx could provide convenient potassium-ion transport channels and fast diffusion kinetics. Finally, ex-situ characterizations at different charging and discharging voltage stages, including ex-situ XRD/Raman/HRTEM/XPS have been carried out to reveal the potassium storage mechanism. This work provides a facile strategy for the regulation of interface engineering by the assist of CTAB which could extend to other MXenes-TMDs (Transition metal dichalcogenides) hybrid electrodes.

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.

Tailoring Stress-Relieved Structure for SnSe Toward High Performance Potassium Ion Batteries.

Metal chalcogenides as an ideal family of anode materials demonstrate a high theoretical specific capacity for potassium ion batteries (PIBs), but the huge volume variance and poor cyclic stability hinder their practical applications. In this study, a design of a stress self-adaptive structure with ultrafine SnSe nanoparticles embedded in carbon nanofiber (SnSe@CNF) via the electrospinning technology is presented. Such an architecture delivers a record high specific capacity (272 mAh g-1 at 50mA g-1) and high-rate performance (125 mAh g-1 at 1 A g-1) as a PIB anode. It is decoded that the fundamental understanding for this great performance is that the ultrafine SnSe particles enhance the full utilization of the active material and achieve stress relief as the stored strain energy from cycling is insufficient to drive crack propagation and thus alleviates the intrinsic chemo-mechanical degradation of metal chalcogenides.

Alleviated mechanical structure decay and accelerated transport kinetics via KNCHCF@NiHCF core–shell structure for aqueous potassium-ion batteries

The sluggish ion transport and mechanical decay caused by K+ intercalation can hinder the K+ storage ability of Prussian blue analogs (PBAs), potential cathode materials for potassium-ion batteries (PIBs). The construction of composite materials using adjustable chemical components of PB is an effective method to improve cycling stability. In this study, a core–shell structure of KNiCoFe(CN)6@NiFe(CN)6 (KNCHCF@NiHCF) was prepared to utilize the inertness of Ni2+ and the stability of Fe–CN–Ni bonds and enhance the performance of PBAs. Different concentrations of NiHCF coating (Ni-0, Ni-2, Ni-5, and Ni-60) were introduced into the outer layer of KNCHCF using a simple solution precipitation method. The aforementioned core–shell structure and the corresponding built-in electric field enhanced the structural stability and K+/e− transport kinetics of the fabricated materials. And Ni-5 exhibited the best electrochemical performance with excellent durable cycling stability and rate performance. Furthermore, the reversible single-phase insertion and extraction reaction of K+ storage mechanism within the Ni-5 cathode was revealed using ex-/in-situ characterization techniques. This strategy may facilitate the development of other cathode materials for rechargeable metal ion batteries.

Effects of cation substitution effects of dicarboxylic acid for energy storage applications

Organic materials (OMs) can accept alkali ions and function as energy storage systems, displaying several advantages such as low cost, ease of synthesis, and utilization of recyclable materials. Owing to their higher theoretical capacity, OMs exhibit a higher energy density, cheaper price, and easy recover than those of inorganic materials such as graphite, silicon, and metal oxides, respectively. This study reports the use of potassium 4-oxo-4H-pyran-2,6-dicarboxylic acid (K2CDA) and potassium 4-oxo-4H-pyran-2,6-dicarboxylic acid (K2CDO) as anode materials for potassium-ion batteries (KIBs) and lithium-ion batteries (LIBs). Although they share similar lightweight, carbonyl, and carboxylate functional groups, both materials display distinct reaction behaviors owing to differences in electronegative heteroatoms N and O. In this study, two alkaline salts (KFSI and LiFSI) have been discussed on the substitution effect of doping/ de-doping processes. K2CDA and K2CDO. Consequently, after 200 cycles, the K2CDA anodes deliver capacities of 310 (KFSI) and 485 (LiFSI) mAh g−1, respectively, at 0.1 C. The larger size of K+ compared with Li+ negatively impacts the performance of K2CDA. A similar trend is observed in the case of K2CDO in capacities of 220 (KFSI) and 405 mAh g‒1 (LiFSI), with 1.5 and 2.86 K+ ions participated in the corresponding redox reactions on the Fourier-transfer infrared spectroscopy analysis. The presence of N‒H in the K2CDA structure contributes to its superior performance and rate capability compared with K2CDO. In addition to the cation effect, the structural differences between K2CDA and K2CDO also influence their electrochemical activity.