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Research Article  |  Open Access  |  10 Mar 2025

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Views: 437 |  Downloads: 281 |  Cited:  1
Yawen Li1
, 
Natalia A. Kabanova2
, ... 
Junjie Wang1,*
J. Mater. Inf. 2025, 5, 21.
10.20517/jmi.2024.87 |  © The Author(s) 2025.
Author Information
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Cite This Article

Abstract

Cathode materials are crucial in potassium (K) batteries, directly impacting their performance and lifespan. In this study, we used a combination of geometrical-topological (GT) analysis, bond valence site energy (BVSE), Kinetic Monte Carlo (KMC), and first-principles calculations to screen potential cathode materials for K-ion batteries among inorganic phosphides. Through GT analysis, we screened 143 K- and P-containing compounds and identified 30 with two- or three-dimensional K-ion migration pathways. BVSE further narrowed down 13 compounds with K-ion migration energies below 1 eV. KMC simulations of ionic conductivity led to the selection of K3Cu3P2 for detailed first-principles calculations. It was demonstrated that K3Cu3P2 possesses a reversible capacity of 72.47 mAh·g-1, minimal volume change (1.47%), and a charge compensation mechanism involving Cu and P. Its low migration energy barrier contributes to a high ionic diffusion coefficient and conductivity of 1.87 × 10-3 S·cm-1 at 25 °C, making K3Cu3P2 a promising candidate for stable and efficient K-ion diffusion in cathode applications.

Graphical Abstract

Keywords

High-throughput calculation screening, potassium batteries, cathode material, geometrical-topological approach, bond valence site energy, density functional theory
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INTRODUCTION

Fossil fuels, including oil, gas, and coal, remain the dominant global energy source. However, their overuse has raised significant environmental and energy security concerns. To promote sustainable development, there is increasing momentum toward transitioning to clean energy sources such as solar, wind, and nuclear power, which can reduce greenhouse gas emissions and improve energy efficiency[1-5]. The development of electric vehicles and renewable energy technologies has garnered significant societal interest, with high-performance energy storage systems playing a key role in optimizing the use of clean energy[6-8]. Among these technologies, rechargeable batteries, particularly lithium (Li)-ion batteries, are seen as a critical solution for meeting diverse energy needs[9]. However, the limited lithium reserves pose a significant challenge[10-17]. As the demand for rechargeable batteries grows, there is an urgent need to develop sustainable alternatives that offer comparable performance to Li-ion batteries.

Compared to Li-ion batteries, sodium-ion batteries offer advantages such as greater abundance and lower cost[18]. However, their higher electrode potential [-2.71 V vs. standard hydrogen electrode (SHE)] leads to lower energy density and reduced energy storage performance[19-21]. Potassium (K), which shares similar physicochemical properties with lithium, is also abundant (2.09 wt%) and has a standard electrode potential (-2.93 V vs. SHE) close to that of lithium (-3.04 V vs. SHE). This similarity enables K-ion batteries to achieve high operating voltages and energy densities[22]. Replacing expensive materials such as lithium, cobalt, and copper, commonly used in Li-ion batteries, with more affordable and abundant alternatives such as potassium, iron, and aluminum can significantly lower costs while improving safety[23]. However, the larger ionic radius of potassium results in slower ion kinetics during the charging and discharging process, negatively impacting the electrochemical cycle performance and rate capability of K-ion batteries. Therefore, developing electrode materials that facilitate efficient and reversible K-ion transport is crucial[24-31]. High-throughput screening methods have emerged powerfully for accelerating the discovery and design of new materials[32,33]. K2CdO2, as a potential solid electrolyte, was selected from potassium oxides[34]. A topological quantum material, K2MnS2[35], was identified to be the most promising cathode for K-ion batteries.

Recently, several silicon phosphides have emerged as promising candidates for solid electrolytes. For example, Li8SiP4 and Li2SiP2, which are based on SiP4 tetrahedral building blocks, have shown potential applicability[36]. The ionic conductivity of Li8SiP4 ranges from 1.15 × 10-6 S·cm-1 at 0 °C to 1.2 × 10-4 S·cm-1 at 75 °C, with an activation energy of 0.49 eV. Li2SiP2[36] exhibits a conductivity of 6.6 × 10-6 S·cm-1 at 75 °C. Meanwhile, LiSi2P3, which adopts a diorite structure, demonstrates favorable ion transport properties with a low activation energy of 0.07 eV[37]. Additionally, HT-NaSi2P3 exhibits a high total conductivity of up to 4 × 10-4 S·cm-1 at 25 °C, featuring the largest supertetrahedral entities (T5)[38]. For K-ion conductors, KSi2P3 displays an ionic conductivity of 1.6 × 10-4 S·cm-1 at 25 °C with an average activation energy of 0.20 eV[39,40]. These findings suggest that phosphides, particularly silicon-based phosphides, are promising candidates for K-ion conductors and warrant further exploration for future applications.

In this study, we performed a high-throughput screening of all phosphide compounds in the Inorganic Crystal Structure Database (ICSD; version 2022/2) for the first time (Schemed in Figure 1)[41]. Initially, we used the geometrical-topological (GT) approach to screen K- and P-containing compounds. Next, we applied the bond valence site energy (BVSE) method to analyze the locations of mobile ions and roughly estimate the migration barriers. This process identified 13 promising K-ion conductors with low migration barriers, which were then selected for further evaluation through Kinetic Monte Carlo (KMC) simulations. Finally, we used density functional theory (DFT) to model charge-discharge products and simulate half-cells, focusing on the most promising compound, K3Cu3P2.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 1. Workflow for screening promising potassium-ion conductors.

MATERIALS AND METHODS

GT approach

The cationic conductivity of inorganic compounds is largely governed by the presence of a continuous network of channels and voids within the crystal structure, which facilitate cation migration. In the Voronoi partition approach, the crystal space is divided into two dual subspaces: atoms and voids. To analyze cation migration pathways, the vertices and edges of Voronoi polyhedra are treated as elementary voids and channels, based on key criteria derived from known solid electrolytes. The construction of the graph and polyhedral representations of the void space, as well as the subsequent analysis of their GT characteristics, is implemented in the ToposPro software package[42]. This GT approach has been successfully applied to predict suitable cathode and electrolyte materials for various cations, including Li+[43], Na+[44], and Zn2+[45].

To assess the geometric criteria for cation migration, we computed the radii of the elementary channels (rchan) and compared them with the minimum threshold value, rchan(min) = γ(r(K) + r(P)), where r(K) and r(P) represent the Slater radii of K and P, respectively[46]. The deformation coefficient γ is a function of the characteristics of the mobile cations and framework anions. For this study, we used γ = 0.8, reflecting the large radius and high charge of the P3- anion, and adopted rchan(min) = 2.5 Å as the minimal channel radius sufficient for potassium migration[47]. Additionally, we excluded channels that were solely surrounded by cations, regardless of their size, to investigate their impact on the overall conductivity pattern.

BVSE calculations

The BVSE approach[48], implemented in the GUI version of the softBV program[49,50], has become a widely adopted tool in crystal chemistry for investigating ionic migration pathways. This method is based on the principle of maintaining local bond strength equilibrium, which is essential for understanding ion movement within a crystal lattice. By considering the Coulombic repulsion between the migrating ion and the ions in the crystal framework, the migration energy barriers for the ions are calculated[51]. The migration energy landscape for K+ was computed using a Cube.file with a resolution of 0.1 and an automatically determined screening factor (f)[52].

To evaluate the dimensionality of the migration map, we determined the migration barrier energy (Em). The most promising candidates for KMC simulations and DFT calculations were selected based on the criterion that Em < 1 eV and the material should exhibit 2D or 3D ionic conductivity. This criterion is important because, although 1D ionic conductors can exhibit high conductivity under certain conditions, their sensitivity to defects and interfaces limits their practical applications.

KMC simulations

Ionic conductivities and diffusion coefficients were calculated using KMC simulations. For this purpose, supercells with volumes exceeding 10,000 Å3 were simulated for 1 to 10 million KMC steps at 300 K. The KMC algorithm, implemented in the command-line version of softBV, utilizes approximate site and migration energies derived from BVSE analysis. The results were averaged over five different configurations to ensure statistical reliability. The unit cells were relaxed using the softBV force field. The ionic diffusion coefficient is a key performance indicator for cathode materials. Compounds with high ionic diffusion coefficients are characterized by continuous ion transport channels and low migration barriers[53,54].

DFT calculations

All DFT calculations[55] were performed using the projected augmented wave (PAW) method[56], implemented in the Vienna Ab initio Simulation Package (VASP)[57,58]. The Perdew-Burke-Ernzerhof (PBE) functional in the generalized gradient approximation (GGA)[59] was used to describe the exchange-correlation interactions. Structural optimization was carried out using the conjugate gradient method, with convergence thresholds of 10-5 eV for energy and 0.03 eV/Å for interatomic forces. A plane-wave energy cutoff of 520 eV was employed. To correct the self-interaction error and account for strong correlation effects in localized electrons, Hubbard U corrections were applied, with a U value of 5.2 eV for Cu[60]. The Ewald summation method[61] was used to screen the system during the K-ion charging process, leading to the generation of various configurations.

The formation energy diagram was constructed to identify the configuration with the lowest energy at different optimized concentrations. Stable intermediate phases were identified as those on the convex hull, while other compounds were classified as metastable or unstable. The energy above the hull (Ehull) for stable intermediate phases was calculated, and the maximum potassium removal capacity was determined for those phases with Ehull < 0.1 eV/atom, providing the reversible capacity of the candidate cathode materials. Ionic migration barriers for K+ ions were calculated using the nudged elastic band (NEB) method[62], with input files generated via the PATHFINDER script (https://pathfinder.batterymaterials.info).

Compounds containing electrochemically active transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, W) were considered as promising cathode materials. The theoretical capacity (in mAh·g-1) was calculated using[63]:

C=nF3.6M

where n is the number of electrons transferred per formula unit, M is the molar mass of the compound, and F is the Faraday constant. The electronic band gap Eg was taken from the Materials Project (https://materialsproject.org). The average voltage profile for each cathode reaction was determined using[64]:

V≈EKx1−EKx2+(x2−x1)EK(x2−x1)e

where EKx1 and EKx2 are the DFT energies of the cathode at K concentrations x1 and x2, respectively. EK is the total energy of a K atom in metallic potassium (Im3¯m).

Ab initio molecular dynamics (AIMD) simulations were performed in the NVT ensemble for 50 ps with a time step of 1.0 fs[65]. A Nosé-Hoover thermostat was employed to control the system temperature. All AIMD simulations were carried out using a (2 × 2 × 1) supercell derived from the relaxed primitive unit cell, containing 96 atoms. The diffusion coefficient of K ions was modeled using the Arrhenius equation:

D=D0e−EakBT

where D is the diffusion coefficient, D0 is the prefactor of diffusion, kB is the Boltzmann constant, Ea is the activation energy, and T is the temperature. The ionic conductivity was calculated from the extrapolated diffusion coefficient[66] using:

σ=cK(qKe)2kBTD

where cK is the concentration of K ions, qK denotes the charge state of K ions, and e refers to the elementary charge.

RESULTS AND DISCUSSION

GT and BVSE analysis

For 143 compounds, the migration map was constructed using the criterion rchan(min). Of these, the diffusion of K ions was predicted to be two-dimensional (2D) for nine compounds and three-dimensional (3D) for 21 compounds [Supplementary Table 1]. The compounds were classified based on their framework types, with frameworks grouped according to the same space group and similar chemical compositions. Previous studies[67] have shown that when the energy barrier Em exceeds 1 eV, the diffusion of K ions is significantly hindered, although it may be overcome at elevated temperatures. In contrast, when the migration barrier Em is less than 1 eV, the ion migration process becomes relatively facile.

In general, the results obtained from the GT analysis and the BVSE method are consistent, and the migration map of the same dimensionality is obtained [Figure 2]. When considering all channels with rchan > rchan (min) for the construction of the migration map, an exception is found in K4CdP2[68], where the BVSE method predicts 2D migration, while the GT analysis indicates 3D migration. This compound exemplifies how geometrically accessible migration channels can still exhibit high energy barriers for diffusion. For instance, the channels responsible for migration along the [001] direction are sufficiently wide (with rchan = 3.49 Å) but are surrounded by Cd2+ cations [Figure 3]. The migration of K+ ions through these channels is hindered by repulsion between K+ and Cd2+ ions, a finding corroborated by the BVSE analysis. Another channel, which is also deemed inaccessible for migration according to BVSE, has two Cd2+ cations in its environment and a smaller radius (rchan = 3.08 Å), but it does not significantly affect the overall 2D conductivity [Figure 3]. In the cases of K4ZnP2[69] and K5AuP2[70], the channels surrounded by pure cation environments - Zn and Au, respectively - have high migration energies (1.50 eV), which limits the diffusion to 2D conductivity [Supplementary Table 1]. However, in K4BeP2[71] and K3Cu3P2[72], the channels surrounded by Be and Cu, respectively, exhibit much lower migration barriers (0.57-0.73 eV) and play a crucial role in facilitating conductivity, as indicated by the BVSE analysis [Supplementary Table 1].

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 2. The crystal structures of K3InP2, showing the 3D potassium ionic migration map from GT approach (left) and BVSE calculation (right). Hereafter ZA designates centers of elementary voids in the GT analysis. 3D: Three-dimensional; GT: geometrical-topological; BVSE: bond valence site energy.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 3. Crystal structures of K4CdP2, illustrating the 3D potassium ionic migration map (left) from the GT approach and the 2D migration map (right) derived from BVSE calculations. The relevant regions of the migration maps are highlighted in green. The elementary channels that are inaccessible to K+ migration due to surrounding Cd2+ cations are highlighted in red. 3D: Three-dimensional; GT: geometrical-topological; 2D: two-dimensional; BVSE: bond valence site energy.

Thirteen compounds with migration energy barriers lower than 1 eV were selected for KMC simulations at room temperature [Supplementary Table 2]. Compounds containing electrochemically active elements were considered as potential cathode materials [Table 1]. The KMC results indicate that K2AuP[73], K2CuP[68] and K3Cu3P2 exhibit moderate diffusion coefficients of approximately 1 × 10-14 cm2·s-1, similar to the well-known lithium cathode material LiFePO4[74] (10-14-10-15 cm2·s-1). Based on these results, K2AuP, K2CuP and K3Cu3P2 were identified as the most promising candidates for cathode materials.

Table 1

13 most promising K-/P-containing compounds after GT and BVSE analysis

FormulaICSD codeSpace groupMigration map (GT/BVSE)Emσ (S·cm-1)D (cm2·s-1)Cg (mAh/g)Eg (eV)
K2AuP300201Cmcm3/30.457.01 × 10-96.29 × 10-14175.120.95
K2CuP61082Cmcm3/30.681.38 × 10-91.18 × 10-14310.411.14
K3Cu3P212163R3¯m3/30.732.47 × 10-91.89 × 10-14217.421.29
KMnP89593P4/nmm2/20.452.34 × 10-115.25 × 10-16214.430
K4CdP261084C2/m3/20.322.77 × 10-162.81 × 10-21324.180.82
K3InP2300141Ibam3/30.481.06 × 10-31.08 × 10-8SE*0.79
K3AlP2300130P1¯3/30.581.01 × 10-56.61 × 10-11SE0.70
K6InP3300147P1¯3/30.404.50 × 10-63.41 × 10-11SE0.75
K3P25550P63/mmc3/30.211.24 × 10-69.67 × 10-12SE0.21
K4P364625Cmcm3/30.777.33 × 10-76.18 × 10-12SE0
KP14010P2121213/30.393.01 × 10-82.72 × 10-13SE1.03
K4BeP2300110R3¯m3/30.577.63 × 10-86.04 × 10-13SE1.14
K3BP2300104C2/c3/30.873.89 × 10-83.67 × 10-13SE1.67

*Potential base for solid electrolytes. GT: Geometrical-topological; BVSE: bond valence site energy.

Among all the phosphides considered, K3InP2[75] exhibits the highest ionic conductivity, approaching 1 × 10-3 S·cm-1. However, the narrow band gap of K3InP2 (approximately 0.75 eV) facilitates electronic conductivity, which can trigger redox reactions, potentially leading to material decomposition and affecting the long-term performance and lifespan of the battery. Note that the PBE functional exhibits a systematic underestimation in band gap predictions. According to statistical data[76], the band gaps calculated using PBE are typically 30%-50% lower than experimental values, which is attributed to the limitations of the PBE functional in describing electronic exchange and correlation energies. To mitigate this issue, the band gap of K3InP2 could be widened through doping, specifically by replacing In with elements of higher electronegativity or different valency. Such doping could enhance its performance as a solid electrolyte material. Substituting In with elements such as Ga or Al may be particularly effective, as these elements typically lead to a wider band gap due to their smaller atomic radii and higher electronegativities, which influence orbital overlap and the overall electronic structure. K3InP2 belongs to the topological type 43,8T23, where 4-coordinated cations (K+ and In3+) are connected to 8-coordinated P3- anions. According to the TopCryst system[77], five other compounds - Na3AlP2[78], Na3AlAs2[78], Ln2NCl3 (Ln = La, Ce, Pr)[79] - share the same topological type and space group (Ibam). Notably, Na3AlP2 demonstrates the potential for incorporating Al3+ atoms into the phosphide framework of this structural motif. Na3AlP2 shares the same structural framework and symmetry as K3InP2; it possesses a wider band gap (approximately 1.35 eV), which is a key factor in its potential use for incorporating Al into the In sites of K3InP2, forming K3In1-xAlxP2 with an expanded band gap. This approach aligns with our goal of improving the material’s performance while avoiding the redox issues observed in K3InP2.

DFT results

We calculated the reversible capacities of K2AuP, K2CuP and K3Cu3P2. The formation energies and convex hull phase diagrams were constructed to elucidate the structural evolution during K-ion insertion and extraction. Compounds with an energy above the convex hull (Ehull) exceeding 0.1 eV/atom are considered thermodynamically unstable[35,80]. As shown in Figure 4, K3Cu3P2 exhibits a reversible capacity of 72.47 mAh·g-1, significantly higher than that of K2AuP and K2CuP.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 4. Formation energies during charge and discharge, along with the energy above the convex hull (Ehull) for different compositions of (A) K2AuP, (B) K2CuP and (C) K3Cu3P2.

Supplementary Figure 1 reveals that K3Cu3P2 possesses a layered structure with the space group R3¯m, and we constructed a 3D migration map for K ions. During the charging process, two stable intermediate compounds, KxCu3P2 (x = 8/3, 2), were selected for analysis [Supplementary Figure 2]. We estimated the voltage for each reaction by evaluating the slope of the formation energy, revealing two primary voltage plateaus at 1.37 and 2.76 V, as shown in Figure 5A. Notably, one-third of the K ions are easily deintercalated, while the remaining ions are more challenging to extract, which influences the overall battery capacity. For comparison, the previously reported cathode material K2FeP2O7[81] has a reversible capacity of 60 mAh·g-1 and a voltage plateau of around 2.7 V. In contrast, K3Cu3P2 not only exhibits a higher reversible capacity but also a more favorable voltage profile, offering superior energy density.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 5. (A) Calculated voltages and (B) calculated changes in the unit cell volume. The dotted line indicates that this voltage plateau is difficult to achieve with conventional electrolytes.

During the charge/discharge cycles, K-ion insertion and extraction induce structural and volumetric changes in the cathode material. These volume changes can significantly affect the stability of the crystal structure. Large expansions or contractions can cause stress concentration within the lattice, leading to potential cracks or structural failure. As shown in Figure 5B, we analyzed the structural evolution of KxCu3P2 (x = 3, 8/3, 2). After the extraction of one-third of the K ions, the material experienced only a slight volume reduction of 1.47%, with minimal changes in lattice constants and angles, indicating exceptional structural stability [Supplementary Figure 3]. This suggests that K3Cu3P2 can maintain excellent reversibility and high capacity even after multiple charge-discharge cycles.

We performed a comprehensive analysis of the electronic structure of KxCu3P2 (x = 3, 8/3, 2) by examining the density of states (DOS). K3Cu3P2 is identified as a semiconductor, with a significant overlap between the 3d orbitals of Cu and the 3p orbitals of P, indicating a strong covalent interaction between Cu and P atoms. Upon the release of potassium atoms, some Cu+ ions in KxCu3P2 further undergo oxidation to Cu2+, resulting in a rightward shift in the DOS and a filling of the conduction band. This shift enhances the metallic characteristics of KxCu3P2 [Figure 6]. As an intermediate compound, K7/3Cu3P2 exhibits improved electronic conductivity compared to K3Cu3P2 [Supplementary Figure 4]. Furthermore, the increasing DOS near the Fermi level suggests that the release of potassium atoms further enhances the electronic conductivity of KxCu3P2, which in turn improves the high-rate charging performance of the material.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 6. Calculated partial DOS for KxCu3P2 (x = 3, 8/3, 2) with decreasing potassium content. DOS: density of states.

To further investigate the electronic behavior, we conducted Bader charge analysis[82] to calculate the charge distribution of each atom in KxCu3P2. As summarized in Supplementary Table 3, upon the release of 2/3 potassium atoms, the Cu and P atoms lose 0.089 and 0.064 electrons, respectively, which provides additional evidence for the contribution of Cu and P to charge compensation during ion migration.

Next, we examined the migration behavior of K ions, since migration energy barriers are critical in determining the charge and discharge rates of batteries, especially at high discharge currents, which can lead to rapid capacity fading. We identified two distinct diffusion pathways using the PATHFINDER script, and calculated the migration barriers through the CI-NEB method[83]. Path 1 involves K ion migration within the (001) plane, suggesting a 2D migration mechanism, while Path 2 follows the [001] direction, indicating a 3D migration pathway in Figure 7A. The calculated migration barriers for these two paths are 0.108 and 0.112 eV [Figure 7B], respectively, both of which are significantly lower than the results obtained from the BVSE analysis [Supplementary Table 1]. This discrepancy arises because the BVSE method does not account for lattice effects or structural transformations during cation migration[32]. For instance, previous studies on Li+ ions have shown that BVSE tends to overestimate the migration barrier compared to DFT by a significant margin (more than twice)[84]. In contrast, the migration barriers computed by both methods for Mg2+ exhibit close agreement[85]. Additionally, the correlation may be influenced by computational factors such as the choice of BVSE screening factor, the DFT functional, and the basis set employed in the calculations. However, the relative values of migration barriers computed for a series of compounds by BVSE and DFT are consistent, which allows one to use BVSE for the preliminary screening of prospective ionic conductors[41]. The low migration energy barriers of K3Cu3P2 indicate a high ionic diffusion coefficient, which is beneficial for fast ion transport.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 7. Illustration of (A) the migration pathways and (B) the calculated migration energy barriers for Path 1 and Path 2 in K3Cu3P2.

To estimate the overall K-ion migration activation energy and diffusion coefficient of the material at room temperature, we conducted AIMD simulations at temperatures ranging from 600 to 1,000 K. As shown in Figure 8A, the migration channel diagram obtained by AIMD is similar to that computed by CI-NEB. The activation energy barrier for K+ migration was found to be 0.11 ± 0.01 eV in Figure 8B, which is in good agreement with the value obtained from the CI-NEB calculations, confirming that the material undergoes minimal structural reorganization or phase transition during ionic migration. Based on the AIMD results, we can analyze the ion diffusion behavior during the charging process. The potassium atoms in K3Cu3P2 are located at K1 and K2 sites, respectively. The diffusion coefficients of both ions were calculated at 600 K [Supplementary Figure 5]. According to the reversible capacity calculation [Supplementary Figure 2], the ion configuration obtained by extracting potassium from the K2 site is the most stable. The ion diffusion coefficient at the K2 site (1.43 × 10-7 cm2·s-1) is larger than that at the K1 site (4.45 × 10-8 cm2·s-1). Therefore, during the charging process, K ions at the K2 site are more likely to diffuse, contributing to the capacity.

High-throughput screening of phosphide compounds for potassium-ion conductive cathode application

Figure 8. Illustration of (A) migration channel and (B) Arrhenius plot of the logarithm of the diffusivity, log (D), vs. 1000/T for K3Cu3P2.

The corresponding K-ion diffusion coefficient (D) at 300 K is calculated to be approximately 2.17 × 10-8 cm2·s-1, which is significantly higher than that of LiFePO4 (10-14-10-15 cm2·s-1). The potassium ionic conductivity, calculated using Equation (4), is about 1.87 × 10-3 S·cm-1 at 25 °C, which is also greater than that of KSi2P3 (1.6 × 10-4 S·cm-1 at 25 °C)[39].

CONCLUSIONS

In this study, we present a novel approach for screening phosphide compounds as potential cathode materials for K-ion batteries. Using a combination of GT analysis, BVSE calculations, KMC simulations, and DFT calculations, we have identified several promising candidates. The GT analysis revealed 30 previously unreported ionic conductors, while BVSE and KMC simulations highlighted 13 potential K-ion conductors. Among these, K3Cu3P2 emerged as the most promising cathode material, with a diffusion coefficient exceeding 1 × 10-14 cm2·s-1 and a theoretical capacity of 217.42 mAh·g-1. DFT calculations further assessed the thermodynamic stability of K3Cu3P2 by evaluating its formation energy and energy above the convex hull and predicting its reaction voltage platform. It is confirmed by DFT calculations that K3Cu3P2 exhibits a reversible capacity of 72.47 mAh·g-1 and a voltage platform of 2.76 V, outperforming the previously reported K2FeP2O7. Notably, this K3Cu3P2 compound demonstrates excellent structural stability, with a minimal volume change of only 1.47% during charge-discharge cycling. Additionally, K3Cu3P2 benefits from enhanced electronic conductivity, which facilitates high-speed charging. Its low activation energy of 0.11 eV, high diffusion coefficient of 2.17 × 10-8 cm2·s-1, and high conductivity of 1.87 × 10-3 S·cm-1 at 25 °C collectively contribute to improving the battery’s power density. Overall, this study highlights K3Cu3P2, discovered through our screening process, as a highly promising cathode material for K-ion batteries. It also represents an innovative step in exploring phosphides for advanced cathode applications in energy storage technologies.

DECLARATIONS

Authors’ contributions

Methodology, validation, formal analysis and data curation: Li, Y.; Kabanova, N. A.

Investigation, write-review and editing and visualization: Wang, J.; Blatov, V. A.

Availability of data and materials

The data supporting the findings of this study are included in the Supplementary Materials.

Financial support and sponsorship

This work is supported by the National Natural Science Foundation of China (Grant No. 52272307), the National Key Research and Development Program of Intergovernmental Cooperation in Science and Technology (Grant No.2022YFE0141100), and the Fundamental Research Funds for the Central Universities.

Conflicts of interest

All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Copyright

© The Author(s) 2025.

Supplementary Materials

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Cite This Article

Research Article
Open Access
High-throughput screening of phosphide compounds for potassium-ion conductive cathode application
Yawen Li, ... Junjie Wang

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Li, Y.; Kabanova, N. A.; Blatov, V. A.; Wang, J. High-throughput screening of phosphide compounds for potassium-ion conductive cathode application. J. Mater. Inf. 2025, 5, 21. http://dx.doi.org/10.20517/jmi.2024.87

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