K-ion Batteries Research Articles

Strategic approaches to observing 39K NMR signals from potassium–graphite intercalation compounds

Abstract Solid-state nuclear magnetic resonance (NMR) is an invaluable tool for potassium–graphite intercalation compounds (K-GICs), promising anode materials of K-ion batteries, but it has not yet been applied because of several issues. We attempted 39K NMR measurements of K-GICs sealed in glass using an 18.8 T NMR spectrometer with an NMR probe adjusted to the samples. The first observed 39K NMR signal of K-GICs showed the possibility of evaluating intralayer density, which cannot be ascertained from Raman measurements.

Electrochemical properties of two-dimensional zirconium nitrogen anode materials for K-ion battery by first-principles insights

Electrochemical properties of two-dimensional zirconium nitrogen anode materials for K-ion battery by first-principles insights

Correction: Application of B3S Monolayer as a Promising Anode in K-Ion Batteries

Correction: Application of B3S Monolayer as a Promising Anode in K-Ion Batteries

Mn-Based Transition Metal Oxide Positive Electrode for K-Ion Battery Using an FSA-based Ionic Liquid Electrolyte

Layered Mn-based transition metal oxides have gained interest as positive electrode materials for K-ion batteries due to their high capacity, excellent structural stability, and abundant resources. However, their practical utility is significantly hindered by insufficient electrochemical performances during operations. This study reports the successful synthesis of P3-K0.46MnO2 via the solid-state method and investigates its charge–discharge behavior as a positive electrode working in an FSA-based (FSA= bis(fluorosulfonyl)amide) ionic liquid electrolyte at 298 K. The K0.46MnO2 electrode demonstrates superior performance compared to previously reported K x MnO2 counterparts, delivering a reversible discharge capacity of about 100 mAh g−1 at a current density of 20 mA g−1 and a capacity retention of 68.3% over 400 cycles at 100 mA g−1. Ex situ X-ray diffraction analyses confirm the occurrence of reversible structural changes during the charge–discharge process. Further, we explore potassium storage mechanisms through ex situ synchrotron soft X-ray absorption spectroscopy. Spectra obtained in Mn L-edge region suggest that Mn is reversibly oxidized and reduced during K+ deintercalation and intercalation processes. Remarkably, discharging the electrode below 2.3 V induces reversible formation of Mn2+ from Mn3+/4+ on the electrode surface. The study demonstrates superior electrochemical performance of K0.46MnO2 positive electrode for K-ion battery using ionic liquid electrolyte.

Enhanced electrochemical performance of K0.67[Ni0.3Mn0.6Co0.1] O2 as a cathode material for secondary K-Ion batteries: Improved K-Ion insertion and reduced charge transfer barrier

Potassium-ion batteries, with their high operating voltage and cost-efficiency, emerged as promising contenders for large-scale energy storage system. Nevertheless, the practical application is hindered by the significant challenges of achieving high capacity and good rate capability in cathodes. Herein, a novel layered oxide cathode, K0.67[Ni0.3Mn0.6Co0.1] O2 (KNMCO), has been synthesized via solid-state (S-KNMCO) and co-precipitation (C-KNMCO) routes. The X-Ray diffraction (XRD) peaks of KNMCO are identified in R3 m space group and well-indexed to hexagonal unit cell. The FE-SEM shows non-spherical morphologies for both samples. Additionally, high-resolution transmission electron microscopy (HR-TEM) images of the synthesized cathode materials shows the interlayer spacing of S-KNMCO is higher than that of C-KNMCO. Furthermore, the electrochemical performance of S-KNMCO and C-KNMCO is characterized using K-metal as anode and electrolyte KPF6 in EC/DEC (1:1, v/v). The S-KNMCO and C-KNMCO exhibit the maximum specific discharge capacity of ∼101 mAhg-1 and ∼66 mAhg-1 at the current rate of C/20 respectively. Additionally, these cells show the good rate capability and coulombic efficiency (∼94%). This research offers novel perspectives on the development of cathode substances for KIBs.

Electrochemical behavior and reaction mechanism of nano-BiOBr/rGO composite micro flower with strong interface coupling as potassium-ion battery anodes

To explore the potential of bismuth oxybromide (BiOBr) as anodes for high-performance potassium (K)-ion batteries and understand its potassium storage mechanism, a novel nano-BiOBr/reduced graphene oxide (rGO) composite micro flower (labelled as SI-coupled nano-BiOBr/rGO micro flower), where nano-BiOBr slices are firmly anchored on rGO by strong interface coupling, is constructed. Unique microstructure accompanied by C-Bi bonds at the interface between BiOBr and rGO endows it with abundant high-speed charge transfer channels and excellent structural stability. As a result, it exhibits an excellent rate performance (a high reversible capacity of 278 mAh/g at 5 A/g) and a remarkable long-term cycling stability maintaining 95.4 % after 1000 cycles at 2.5 A/g. Furthermore, it is also found that SI-coupled nano-BiOBr/rGO micro flower anode undergoes intercalation, conversion, and alloying (BiOBr → KzBiOBr → Bi → KBi2 → K3Bi2 → K3Bi) at the initial discharge process, and the subsequent charge process is only reversible dealloying and conversion reaction (K3Bi → K3Bi2 → KBi2 → Bi → BiOxBry). This work not only demonstrates the large potential of BiOBr as high-performance K-ion battery anodes, but also elucidates for the first time its K storage mechanism.

Extremely Durable K-Ion Batteries Enabled by Heteroatom Co-Doped Highly-Ordered Porous Carbon Spheres with Nearly 100% Capacity Retention up to 11,000 Cycles.

Currently, one major target for exploring K-ion batteries (KIBs) is enhancing their cycle stability due to the intrinsically sluggish kinetics of large-radius K+ ions. Herein, we report a rationally designed electrode, the S/O co-doped hard carbon spheres with highly ordered porous characteristics (SPC), for extremely durable KIBs. Experimental results and theory calculations confirm that this structure offers exceptional advantages for high-performance KIBs, facilitating rapid K+ diffusion and (de)-intercalation, efficient electrolyte penetration and transport, improved K+ storage sites, and enhanced redox reaction kinetics, thus ensuring the long-term cycle stability. As a result, the as-constructed SPC anode delivers a high reversible capacity of ca. 200 mAh g-1 at a high current density of 2.0 A g-1 and robust stability with ∼100% capacity retention up to 11,000 cycles, outperforming most carbon-based KIB anodes. This work offers insight into developing advanced KIBs with durable stability toward practical applications.

Ultrahigh Pyridinic/Pyrrolic N Enabling N/S Co-Doped Holey Graphene with Accelerated Kinetics for Alkali-Ion Batteries.

Carbonaceous materials hold great promise for K-ion batteries due to their low cost, adjustable interlayer spacing, and high electronic conductivity. Nevertheless, the narrow interlayer spacing significantly restricts their potassium storage ability. Herein, hierarchical N, S co-doped exfoliated holey graphene (NSEHG) with ultrahigh pyridinic/pyrrolic N (90.6at.%) and large interlayer spacing (0.423nm) is prepared through micro-explosion assisted thermal exfoliation of graphene oxide (GO). The underlying mechanism of the micro-explosive exfoliation of GO is revealed. The NSEHG electrode delivers a remarkable reversible capacity (621 mAhg-1 at 0.05 Ag-1), outstanding rate capability (155 mAhg-1 at 10 Ag-1), and robust cyclic stability (0.005% decay per cycle after 4400 cycles at 5 Ag-1), exceeding most of the previously reported graphene anodes in K-ion batteries. In addition, the NSEHG electrode exhibits encouraging performances as anodes for Li-/Na-ion batteries. Furthermore, the assembled activated carbon||NSEHG potassium-ion hybrid capacitor can deliver an impressive energy density of 141 Whkg-1 and stable cycling performance with 96.1% capacitance retention after 4000 cycles at 1 Ag-1. This work can offer helpful fundamental insights into design and scalable fabrication of high-performance graphene anodes for alkali metal ion batteries.

Dual-active sites and reversible-structural covalent organic framework for highly stable alkali metal-ion batteries

Organic materials are promising candidates for energy storage due to their sustainability, environmental friendliness, and structural designability. However, their application is severely limited due to short lifespan and sluggish kinetics caused by low redox stability, solubility, and low electronic conductivity. Here, we designed a polyimide-conjugated covalent organic framework (NAA-COF). Its highly covalent framework cannot only endow the organic material with strong π–π interactions and robust network ensuring its structure stability, but also offer open channels for rapid ions/electrons transfer inside. Additionally, the introduction of multiple redox-active sites can significantly enhance ion-storage capacity. Consequently, when evaluated as a cathode for Li-ion batteries, NAA-COF exhibits large capacity of 220mAh/g, superb initial coulombic efficiency (90 %), good voltage platform, long lifespan (10000 cycles), and high-rate performance (110 mAh/g at 10 A/g). More importantly, even for Na-/K-ion batteries, the exceptional electrochemical performances can still be maintained. In situ transmission electron microscopy (TEM) and in/ex situ spectroscopy further elucidate the low volume expansion (12.2 %) during the lithiation process and 8-electron reaction mechanism for the NAA-COF cathode. This work provides a high-performance universal COF cathode material that can simultaneously satisfy the requirements of alkali metal-ion batteries.

Advanced 3D-Printed Potassium Ammonium Vanadate/rGO Aerogel Cathodes for Durable and High-Capacity Potassium-Ion Batteries.

A 3D-printed oxygen-vacancy-rich potassium ammonium vanadate/reduced graphene oxide (KNVOv/rGO) microlattice aerogel is designed for the cathode in high-performance K-ion batteries (KIBs). The 3D-printed KNVOv/rGO electrode with periodic submillimeter microchannels and interconnected printed filaments is composed of highly dispersed KNVOv nanobelts, wrinkled graphene nanoflakes, and abundant micropores. The well-defined 3D porous microlattice structure of the rGO backbone not only provides the interconnected conductive 3D network and the required mechanical robustness but also facilitates the penetration of the liquid electrolyte into inner active sites, consequently ensuring a stable electrochemical environment for K-ion intercalation/deintercalation within the KNVOv nanobelts. The 3D-printed KNVOv/rGO microlattice aerogel electrode has a high discharge capacity of 109.3 mAh g-1 with a capacity retention rate of 92.6% after 200 cycles at 50mA g-1 and maintains a discharge capacity of 75.8 mAh g-1 after 2000 cycles at 500mA g-1. The flexible pouch-type KIB battery consisting of the 3D-printed KNVOv/rGO has good mechanical durability and retains a high specific capacity under different forms of deformation such as bending and folding. The results provide valuable insights into the integration of advanced 3D-printed electrode materials into K-ion batteries and the design of flexible and wearable energy storage devices.

From Natural Fibers to High-Performance Anodes: Sisal Hemp Derived Hard Carbon for Na-/K-Ion Batteries and Mechanism Exploration.

Hard carbon (HC) is a promising anode material in alkali metal ion batteries owing to its cost-effectiveness, abundant sources, and low working voltage. However, challenges persist in achiving prolonged cycling stability and consistent capacity, and the sodium storage mechanism in HC is still debated. Herein, an unreported biomass precursor, "sisal," for deriving hard carbon is developed. A series of sisal hemp-derived hard carbon with natural 3D porous channels are prepared. Through phase characterization and electrochemical testing, the relationship between microstructure and sodium storage capacity is elucidated, further confirming the suitability of the "adsorption-insertion-filling" mechanism for sodium storage properties in hard carbon materials. Without the need for any additional modification strategies, this biomass-derived hard carbon demonstrates excellent electrochemical performance in both sodium-ion and potassium-ion batteries (SIBs and PIBs). The as-prepared HC-1300 demonstrates excellent ion storage capability, delivering a high reversible capacity of 345.2mAhg-1 in SIBs and 310mAhg-1 in PIBs at 0.1C. Moreover, it maintains a specific capacity of 237.3mAhg-1 over 1200 cycles at 1C when used in SIBs. The excellent cycling stability and superior rate performance are also presented in full cells, highlighting its potential for practical applications.

Van der Waals Electrides.

ConspectusElectrides make up a fascinating group of materials with unique physical and chemical properties. In these materials, excess electrons do not behave like normal electrons in metals or form any chemical bonds with atoms. Instead, they "float" freely in the gaps within the material's structure, acting like negatively charged particles called anions (see the graph). Recently, there has been a surge of interest in van der Waals (vdW) electrides or electrenes in two dimensions. A typical example is layered lanthanum bromide (LaBr2), which can be taken as [La3+(Br1-)2]+•(e-). Each excess free electron is trapped within a hexagonal pore, forming dense dots of electron density. These anionic electrons are loosely bound, giving vdW electrides some unique properties such as ferromagnetism, superconductivity, topological features, and Dirac plasmons. The high density of the free electron makes electrides very promising for applications in thermionic emission, organic light-emitting diodes, and high-performance catalysts.In this Account, we first discuss the discovery of numerous vdW electrides through high-throughput computational screening of over 67,000 known inorganic crystals in Materials Project. A dozen of them have been newly discovered and have not been reported before. Importantly, they possess completely different structural prototypes and properties of anionic electrons compared to widely studied electrides such as Ca2N. Finding these new vdW electrides expands the variety of electrides that can be made in the experiment and opens up new possibilities for studying their unique properties and applications.Then, based on the screened vdW electrides, we delve into their various emerging properties. For example, we developed a new magnetic mechanism specific to atomic-orbital-free ferromagnetism in electrides. We uncover the dual localized and extended nature of the anionic electrons in such electrides and demonstrate the formation of the local moment by the localized feature and the ferromagnetic interaction by the direct overlapping of their extended states. We further show the effective tuning of the magnetic properties of vdW electrides by engineering their structural, electronic, and compositional properties. Besides, we show that the complex interaction between the multiple quantum orderings in vdW electrides leads to many interesting properties including valley polarization, charge density waves, a topological property, a superconducting property, and a thermoelectrical property.Moreover, we discuss strategies to leverage the unique intrinsic properties of vdW electrides for practical applications. We show that these properties make vdW electrides potential candidates for advanced applications such as spin-orbit torque memory devices, valleytronic devices, K-ion batteries, and thermoelectricity. Finally, we discuss the current challenges and future perspectives for research using these emerging materials.

Surface-Dominated Potassium Storage Enabled by Single-Atomic Sulfur for High-Performance K-Ion Battery Anodes

Due to the large size and heavy mass of the K-ion, the pursuit of reliable anodes with outstanding comprehensive performance for K-ion batteries (KIBs) remains a formidable challenge. Typically, high-capacity potassium storage will lead to the electrodes’ serious volumetric expansion and elevated instability. Herein, it is identified that a single-atomic sulfur composite can act as a high-performance KIB anode with an excellent combination of capacity, cyclability, and rate. A high content (∼32 wt%) single-atomic sulfur can be covalently bonded into the carbon lattice of multi-shelled hollow nanospheres via a simple low-temperature pyrolyzation of the selected precursor. The superb redox reactivity of the single-atomic sulfur together with the porous architectures for the resultant S/C composite can not only enable a fast surface-dominated potassium storage but also ensure its structural resilience, thereby achieving high specific capacity together with outstanding rate and impressive cyclability. This study envisions new perspectives on designing high-performance sulfur-based electrodes.

Out-of-Plane Electron Transport in Graphite Intercalation Compounds with Applications in Battery Anodes

Graphite intercalation compounds (GICs) are commonly used as anode materials for alkali metal-ion batteries, such as Li-ion and K-ion batteries. Although typically prepared as a low-stage intercalation compound (with a high concentration of the intercalating metal), over several electrochemical cycles, the distribution of intercalate within the graphite sample is expected to be non-uniform with domains of high-stage regions where the intercalant fraction is low [1]. The mechanism of interlayer electron transport in GICs strongly depends on the intercalation staging and temperature, and is expected to vary over the lifetime of a battery.High-stage GICs and highly oriented pyrolytic graphite (HOPG), which is the upper limit of infinite-stage GIC, have an out-of-plane electrical conductivity that exponentially increases with temperature, whereas low-stage GICs have a conductivity that decreases as a function of temperature [2, 3, 4]. Although out-of-plane electron transport in low-stage GICs can be described by a metallic conduction model, the mechanism of out-of-plane electron transport in HOPG and high-stage GICs is a hitherto unresolved problem [5]. Out-of-plane electrical conductivity for HOPG and high-stage GICs increases exponentially with temperature, which cannot be described by metallic conduction, nor by conventional impurity or defect hopping mechanisms [6].We propose a new mechanism of electron transport that takes place in HOPG and high-stage GICs at temperatures relevant to battery operation. Electrons are transferred between graphite and intercalant layers through tunneling that is enhanced by large amplitude out-of-plane phonon modes in graphite layers. Due to weak interlayer interactions in adjacent graphite layers, GICs can accommodate large amplitude phonon modes in the out-of-plane direction that locally enhance the interlayer electron tunneling probability. The tunneling enhancement is temperature dependent, and exponentially depends on the population of out-of-plane phonon modes excited at a given temperature. The expression for the conductivity 𝜎 for the phonon amplitude-driven tunneling mechanism as a function of temperature T is shown in Eq. 1; the exponential dependence of conductivity with temperature qualitatively agrees with experimental observations in HOPG and high-stage GICs. On a quantitative level, we also observe from Fig.1 that the theory agrees with experimental values for out-of-plane conductivity in HOPG.The phonon amplitude-driven tunneling mechanism of electron transport is relevant in describing the kinetic over-potential in batteries that employ layered materials as anodes in ambient temperature operating conditions, and optimally sizing the anode accounting for both electron transport and ion diffusion rates.

Text Mining Analysis of Beyond Lithium-Ion Batteries

Li-ion batteries (LIBs) are the most commonly used energy storage technology in various consumer goods, including electric vehicles. However, several alternatives, so-called beyond-LIBs, are greatly investigated to decrease battery costs using abundant and globally distributed materials with high theoretical capacities. Among the diverse beyond LIB systems, this paper includes the top 6 researched chemistries: univalent (Na- and K-) and multivalent (Zn-) metal-ion, metal-air (Li-air and Zn-air), and Li-S batteries. Naturally, all these six battery chemistries have problems that must be addressed before mass commercialization. Although there are 24,523 publications on these batteries, a parallel examination of these technologies to transfer knowledge must be included in the literature. This study used text mining analysis to study the most common keywords and word connections for beyond-LIBs to learn from the general trends in the literature [1].First, the dataset was built using the Web of Science database in June 2023 by applying all the possible alternative names of beyond LIBs in the search with the Title option. Hence, the abstracts, author keywords, and keywords plus for each battery chemistry were obtained together with the article information. Afterward, data cleaning and text mining analysis were performed using the R Studio environment, specifically stringr, tm, pluralize, and tidytext libraries. The research interests in the primary battery parts and the single material-related words and two-word bigrams were investigated.The bibliometric analysis has shown that Li-S and Na-ion batteries are the most popular research areas in the beyond LIB literature. On the other hand, interestingly, Li-air batteries lost their popularity to Zn-air in around 2015. Publications on Zn-ion batteries have a sharp increasing trend, and K-ion batteries have started to share this research interest. When the single-word results are analyzed, it has been seen that anode, cathode, and electrolyte are the most commonly studied battery sections for Na- and K-ion, Zn-ion and Li-S, and finally, Zn- and Li-air batteries, respectively. Apart from the battery parts, regardless of the chemistry, the high frequency of carbon and graphene keywords are detected; hence, bigram analysis is further performed on these keywords to see the most associated words with these materials. It has been seen that carbon nanotubes are the first and nanofibers are the second preferred form of carbons, whereas the graphene oxides are found to be promising for all beyond LIBs, given only good results are reported in the literature.

Disentangling the Ligand and Electronic Structure in KVPO4F1-XOx Positive Electrode Materials by Valence-to-Core X-Ray Emission Spectroscopy

Among all positive electrode materials for K-ion batteries (KIBs), KVPO4F offers a high theoretical capacity of 131 mAh·g-1 and an average working potential reaching above 4.3 V vs K+/K, resulting in a theoretical energy density of up to 520 Wh·kg-1. [1] The anionic substitution of fluorine by oxygen in KVPO4F1-xOx (x = 0, 0.25, 0.5, 0.75, 1) induces an increasing working potential by activating the V3+/4+ and V4+/5+ redox couples and replacing the VO4F2 “ionic” entity by {V=O}O5 unit with a highly “covalent” vanadyl-type bond. [2] The accurate prediction of the electrode potential as well as the understanding of the mechanisms involved upon cycling requires the determination of how the coordination environment of the transition metal ion influences the ionicity/covalency of the metal-ligand bonds and thus the electronic structure. Nevertheless, discriminating these ligands remains a challenge due to the limited sensitivity to light elements of common characterization techniques such as X-ray diffraction and extended X-ray absorption fine structure. Despite the valuable information from these techniques, fundamental concerns still need to be addressed which include: i) the implication of the covalent V=O vanadyl bond in the electronic structure; ii) the difference of Vcis and Vtrans, the two different sites for V, in the electronic configuration of the material; and finally, (iii) the impact of F/O ligands on the electrochemical mechanism upon battery cycling.To address this issue, we employed valence-to-core Kβ X-ray emission spectroscopy (VtC XES) combined with ab initio modelling and conducted a systematic investigation of KVPO4F1-xOx: two distinct regions were identified in the spectra, Kβ" and Kβ2,5, which are critical to probe the electronic structure close to the Fermi level and to discriminate different ligands coordinated with the vanadium atoms. [3] Our approach allows distinguishing in KVPO4F1-xOx the contributions of V-F, V-O, and V=O bonds, with intensities at the Kβ" region highly correlated to the F- and O2- anionic composition. Additionally, the evolution of the features at the Kβ2,5 region is highly associated to the presence of short V=O bonds, strongly influencing the electrode potential of the material.Overall, we present a detailed and reliable approach for understanding the occupied electronic states of the electrode material, proving valuable for a thorough comprehension of the structural and redox mechanisms involved in batteries.AcknowledgementThis work was supported by the DESTINY Marie Skłodowska-Curie Actions COFUND PhD Programme (Grant Agreement #945357) co-funded by the European Union's Horizon2020 research and innovation program and the Synchrotron SOLEIL. ANR is also acknowledged for funding the RS2E network through the STORE-EX Labex Project ANR-10-LABX-76-01, and the ANR TROPIC project ANR-CE05-0026. Alistore-ERI network is also acknowledged.

Ecofriendly K-Ion Batteries Relying on Abundant Chemical Elements and Water-Based Processes

Current Li-ion batteries are mainly composed of a graphite anode and a cathode based on either NMC (LiNixMnyCozO2) or LFP (LiFePO4) materials. However, the rapid growth of the electric car market will generate significant stress on key chemical elements (nickel, cobalt, copper, lithium). Moreover, the production of NMC and LFP materials turns out to be very energy intensive (multiple calcinations) and uses toxic solvents (NMP, ammonia). Because of that, Li-ion batteries are quite expensive and their ecological footprint is relatively high.The scope of our work is to develop a potassium-ion battery which does not require any critical element and whose production significantly reduces the ecological footprint of the system. Such a battery technology could find its place either in low-cost electric cars or in large-scale-energy-storage devices.We focused our efforts on the development of a Prussian White cathode material based on potassium, manganese and iron (K2Mn[Fe(CN)6) showing a theoretical capacity of 155 mAh/g with a potential close to 4 V vs K+/K. The synthesis of this material takes place in water at ambient temperature and it does not involve any calcination. First we optimized the synthesis via a chelating route: tuning the morphology of the Prussian White particles allowed us to come closer to the theoretical capacity of the material. Then we developed water-based coating slurries for our material. We were able to obtain electrodes containing 90 wt% of active material by optimizing both carbon additive and binder. These electrodes showed similar performances compared to electrodes obtained with literature-standard conditions (70 wt% active material, NMP-based slurries). Finally, we tested our Prussian White in full cells versus graphite in coin cells and pouch cells. Figure 1

KxFeO2 As Electrode Material for K-Ion Batteries

To meet future energy demands, developing beyond-lithium energy storage technologies have become a major part of global research activities. Potassium-ion batteries (KIBs) represent a promising technology thanks to their chemical and economic advantages1–3. The majority of the work on layered transition oxide was done on the KxMnO2 family4,5 due to their safety and price advantage.Interestingly, KFeO2 structure is not a layered structure as for LiFeO2 or NaFeO2; this structure is defined as FeO4 tetrahedral linked by their corners. In electrochemistry, a reversible capacity of 60 mAh/g (for 0.3K+) was delivers6.In our presentation, we will detail the electrochemical behaviour of KFeO2 and discuss the structure/properties relationship of this family of materials, showing the interest in the exploration of such a system. Xu, Y. et al. 2023 roadmap for potassium-ion batteries. J. Phys. Energy 5, 021502 (2023).Tian, Y. et al. Promises and Challenges of Next-Generation “Beyond Li-ion” Batteries for Electric Vehicles and Grid Decarbonization. Chem. Rev. 121, 1623–1669 (2021).Zhang, W., Liu, Y. & Guo, Z. Approaching high-performance potassium-ion batteries via advanced design strategies and engineering. Sci. Adv. 5, eaav7412 (2019).Kim, H. et al. Investigation of Potassium Storage in Layered P3-Type K0.5MnO2 Cathode. Adv. Mater. 29, 1702480 (2017).Liu, C., Luo, S., Huang, H., Zhai, Y. & Wang, Z. Layered potassium-deficient P2- and P3-type cathode materials KxMnO2 for K-ion batteries. Chem. Eng. J. 356, 53–59 (2019).Han, S. C., Park, W. B., Sohn, K.-S. & Pyo, M. KFeO2 with corner-shared FeO4 frameworks as a new type of cathode material in potassium-ion batteries. J. Solid State Electrochem. 23, 3135–3143 (2019).

K3MnO4 a New Cathode Material for K-Ion Batteries

To meet future energy demands, developing beyond-lithium energy storage technologies have become a major part of global research activities. Potassium-ion batteries (KIBs) represent a promising technology thanks to their chemical and economic advantages1–3. To succeed in developing commercial KIBs, it is necessary to develop new cathode materials4 which must be non-toxic, inexpensive, easy to prepare and have a reasonable K+ diffusion pathway to improve their electrochemical performance. Here we have chosen to explore the inexpensive and non-toxic K-Mn-O system, where only two-dimensional materials of the KxMnO2 type have been studied so far for their electrochemical properties5,6.In this system, a composition attracted our attention: K3MnO4. In principle, up to two potassium ions can be removed from the structure, leading to KMnO4 with a theoretical capacity of 227 mAh/g.Hagenmuller and co-workers succeeded in preparing two polymorphs of K3MnO4 as single crystals7. The high temperature polymorph γ-K3MnO4 has a cubic symmetry (P213) with a disordered distribution of K and Mn in similar tetrahedral sites. The low temperature polymorph β-K3MnO4, can be prepared by annealing γ-K3MnO4 under argon. This polymorph has a tetragonal symmetry (I-42m) with ordered MnO4 tetrahedra. Mn is reported at the edge and at the center of the tetragonal unit cell, surrounded by four oxygens. These phases could be described as a 0D-type structure built of isolated MnO4 tetrahedra surround by potassium ions.We recently succeed in the synthesis of a new polymorph of K3MnO4, labelled α-K3MnO4,8 prepared by a conventional solid-state route by annealing a mixture of KO2 and MnO under vacuum at 500°C in a Al2O3 boat. The structure of this polymorph could be described with a “zig-zag” distribution of the MnO4 tetrahedra (Fig. 1a) and is isostructural to the iron-based K3FeO4 9,10 with an orthorhombic symmetry (Pnma). The blue colour of the powder is classically associated to the Mn+V oxidation state, as confirmed by magnetic and EDS analyses. K3MnO4 exhibits a reversible capacity of 70 mAh/g in the 1.6-3.5 V vs. K+/K potential window at C/20 (Fig. 1b).In our presentation, we will detail the electrochemical behaviour of K3MnO4 and discuss the structure/properties relationship of this family of materials, showing the interest in the exploration of such a system. Xu, Y. et al. 2023 roadmap for potassium-ion batteries. J. Phys. Energy 5, 021502 (2023).Tian, Y. et al. Promises and Challenges of Next-Generation “Beyond Li-ion” Batteries for Electric Vehicles and Grid Decarbonization. Chem. Rev. 121, 1623–1669 (2021).Zhang, W., Liu, Y. & Guo, Z. Approaching high-performance potassium-ion batteries via advanced design strategies and engineering. Sci. Adv. 5, eaav7412 (2019).Nathan, M. G. T. et al. Recent Advances in Layered Metal-Oxide Cathodes for Application in Potassium-Ion Batteries. Adv. Sci. n/a, 2105882.Liu, T. et al. Insight of K-deficient layered KxMnO2 cathode for potassium-ions batteries. J. Energy Chem. 64, 335–343 (2022).Liu, C., Luo, S., Huang, H., Zhai, Y. & Wang, Z. Layered potassium-deficient P2- and P3-type cathode materials KxMnO2 for K-ion batteries. Chem. Eng. J. 356, 53–59 (2019).Olazcuaga, R., Reau, J.-M., Leflem, G. & Hagenmuller, P. Préparation, Proprietés Cristallographiques et Magnétiques des Phases K3XO4 (X=V, Cr, Mn). Z. Für Anorg. Allg. Chem. 412, 271–280 (1975).Sagot, A., Stievano, L. & Pralong, V. K3MnO4: A New Cathode Material for K-Ion Batteries. ACS Appl. Energy Mater. 6, 7785–7789 (2023).Kokarovtseva, I. G., Belyaev, I. N. & Semenyakova, L. V. Oxygen Compounds of Iron(VI, V, IV). Russ. Chem. Rev. 41, 929–937 (1972).Hoppe, R. & Mader, K. Zur Konstitution von K3[FeO4]. Z. F ür Anorg. Allg. Chem. 586, 115–124 (1990). Figure 1

Confined graphitization induced pore generation for designing novel potassium-ion battery carbon anode with large capacity and ultra-long cycle life

Carbon is one of the most superior anode materials for K-ion batteries but faces the challenges of low capacity and poor cycle stability. In general, the K+ storage capacity depends on the graphitized carbon layers and defective structure, while the cycle stability can be enhanced by constructing sufficient nanospace to alleviate the volume expansion during the potassiation/depotassiation process. However, the above structures are difficult to integrate into a single carbon material because graphitization often eliminates defects and pore structures. In this work, we find that ultrathin carbon sheets have a confined graphitization effect, which allows the carbon layer to orientationally arrange at a low heating-treatment temperature. More importantly, this orientational arrangement causes size shrinkage, inducing structural splitting on the faces of the carbon sheets and producing abundant defects and a large number of pores. Based on this, we obtain a novel carbon with highly graphitized, large-surface-area and defect-rich frameworks, which gives a K+ storage capacity of 358 mAh g−1, and after 4000 cycles, this carbon shows no obvious capacity degradation, with a capacity retention rate of nearly 100 %. Carbon anodes of K-ion batteries with such large capacity and long cycling life have rarely been achieved before.