Low Volume Change Research Articles

A metallic lithium anode for solid-state batteries with low volume change by utilizing a modified porous carbon host

Lithium metal is a promising negative electrode material for solid-state batteries (SSBs). However, uncontrolled lithium deposition and stripping cause several issues during cycling. Herein, the microporous carbon YP-50F and its modifications obtained by thermal ethene-based chemical vapor deposition (CVD) are investigated as 3D host to accommodate and control the deposition of metallic lithium. In half-cells vs. lithium, the CVD-YP composite electrode with Li6PS5Cl electrolyte shows significantly higher initial coulombic efficiency (79.5 %) than the pristine carbon (55.3 %) due to the reduction of side reactions. The metallic character of the deposited lithium is evidenced by 7Li Nuclear Magnetic Resonance spectroscopy. However, full cells with nickel-rich NCM (LiNi0.9Co0.05Mn0.05O2) positive electrode and CVD-YP composite negative electrode show reasonable performance over 50 cycles without occurrence of (micro-) short-circuits (in contrast to 2D reference electrodes). In addition, small prototype pouch cells are investigated and the thickness change during (dis)charging is less than one third compared to a bare lithium metal electrode. This demonstrates low breathing behavior of the CVD-YP electrode and confirms the reversible storage of metallic lithium within the 3D carbon-based composite electrode.

Composite Sand–Clay Infrastructural Soil Fills: Characteristic Consolidation and Hydraulic Properties

In the design construction of infrastructural projects comprised of geotechnical applications, including composite soil fill layers, compacted sand-clay soil fills are widely preferred as barrier layers, particularly in solid waste landfills, to minimize leakage, to prevent leachate from entering into groundwater. When bentonite clay with high water absorption capacity and low hydraulic conductivity is mixed with sand possessing relatively enhanced frictional properties, greater shear strength capacity, an effective fill material exhibiting low sensitivity to frost, and low volume change in case of wetting, drying can be obtained. On the other hand, when montmorillonite clay is loaded, due to highly critical volumetric contraction or dilation characteristics (high compressibility nature of clay), the soil fill composed of sand-clay will significantly consolidate. This situation may cause differential settlement problems of infrastructural fills employed in geotechnical applications. In this regard, the load conditions (mechanical effects) and the environmental conditions (physicochemical effects) in the field control compressibility characteristics and consolidation properties of sand-bentonite clay mixtures. This will ultimately impact the desired stability conditions of sand-clay soil layers built for constructed infrastructural fill, resulting in a deviation from anticipated performance conditions. To this end, in this study, the specimens of sand-bentonite clay mixtures prepared with different contents of sand-bentonite clay were subjected to one-dimensional consolidation tests to investigate the effect of bentonite content used in the mixture on consolidation behavior, hydraulic properties, and effect of sand amount on rate of consolidation and on resulting compressive strength behavior.

High-entropy Na4Fe2.65(NiCrMgCoMn)0.027(PO4)2P2O7 cathode for high-rate sodium-ion batteries

Na4Fe3(PO4)2P2O7 (NFPP) cathodes have received significant attention due to the promising theoretical capacity, high average working voltage, and low volume change, but usually suffer from poor rate performance and cycling stability due to their inferior electronic conductivity. Herein, we report a new high-entropy Na4Fe2.65(NiCrMgCoMn)0.027(PO4)2P2O7 (NFPPHE) as outstanding cathode materials for sodium-ion batteries, by which Fe-defects are generated and electronic & ionic transport kinetics are enhanced. The as assembled NFPPHE//Na half-cell demonstrates an excellent rate performance of 57 mAh/g at 100C and a high-capacity retention of 80 % after 4000 cycles at 20C. In addition, the full cell assembled with hard carbon anode displays an energy density of 165 Wh/kg with 76 % capacity retention after 300 cycles at 0.5C. These results demonstrate the feasibility of Fe-defect strategy to enhance the electrochemical performance of cathode material for sodium-ion batteries.

Evaluating the Influence of SiOx on the Calendar Lifetime of Li Ion Batteries across Varied Temperatures and State of Charge Conditions

Lithium-ion batteries (LIBs) have a wide range of application in various fields, such as automotive and stationary applications. The incorporation of silicon (Si) in the anode is an attractive strategy to increase energy density and enable fast charging. This is due to the excellent theoretical specific capacity of Si, which exceeds 3000 mAh/g. However, due to the alloying behavior of Si, a significant volume change can be observed by Si based anodes when cycled. In literature the rapid cyclic degradation is related to these volume changes. A practical approach is to use silicon oxide (SiOx) as anode material, which undergoes lower volume changes during cycling but still exhibits a specific capacity >2000 mAh/g. Studies on the cycle life of SiOx-containing cells are frequently published in literature, but calendar life studies are scarce.Here, the calendar life of two different 1 Ah pouch cell configurations, possessing different anode chemistries, were investigated. One cell contained artificial graphite and 10% SiOx (SiO-cell) while the other cell only used artificial graphite as anode material (G-cell). Both cell configurations were built with an NMC811 cathode. 1 M LiPF6 in EC: EMC (3:7 (wt.)) + 2%wt. VC was used as electrolyte. Temperatures of 20 °C, 40 °C and 60 °C and state of charge (SoC) levels of 20%, 40%, 60%, 80% and 100% were investigated in this study. It has been observed that for 20 °C and 40 °C, the degradation rate of both cell types intensifies when stored at 100% SoC. At 60 °C, however, the capacity fade already starts intensifying drastically at around 60% SoC. The capacity fading during storage experiments of the SiO- cells, depending on the parameters tested, is higher by a factor of around 1.1 to 4.1 than the capacity fading of the G- cells. Interestingly, the capacity fade ratio of the SiO-cell to G-cell is at maximum when cells were stored below 40% SoC at 20 °C. When stored at low SoC, SiOx is the anode active material being lithiated majorly. These findings indicate that SiOx indeed causes stronger calendaric degradation compared to graphite. Hence, in future studies on SiOx based anodes calendaric degradation is an interesting topic to address additionally to cyclic degradation.

Influence of Polypyrrole on Phosphorus- and TiO2-Based Anode Nanomaterials for Li-Ion Batteries.

Phosphorus (P) and TiO2 have been extensively studied as anode materials for lithium-ion batteries (LIBs) due to their high specific capacities. However, P is limited by low electrical conductivity and significant volume changes during charge and discharge cycles, while TiO2 is hindered by low electrical conductivity and slow Li-ion diffusion. To address these issues, we synthesized organic-inorganic hybrid anode materials of P-polypyrrole (PPy) and TiO2-PPy, through in situ polymerization of pyrrole monomer in the presence of the nanoscale inorganic materials. These hybrid anode materials showed higher cycling stability and capacity compared to pure P and TiO2. The enhancements are attributed to the electrical conductivity and flexibility of PPy polymers, which improve the conductivity of the anode materials and effectively buffer volume changes to sustain structural integrity during the charge and discharge processes. Additionally, PPy can undergo polymerization to form multi-component composites for anode materials. In this study, we successfully synthesized a ternary composite anode material, P-TiO2-PPy, achieving a capacity of up to 1763 mAh/g over 1000 cycles.

Evaluation of Different Fly Ash-Blast Furnace Slag Formulations for Design of Geopolymers in Radioactivity Disposal Applications

Geopolymers in radioactive waste management have in recent times gained dominance in disposal module acceptance. Here is a comparative study on formulations prepared from industrial wastes to be utilized as radionuclide disposal barriers in near surface disposal facilities (NSDFs). Different tools such as isocalorimetry, compressive strength, chemical durability were utilized for screening the formulations. Water leaching of the samples shows that the release of the ions to the leachant is minimal. Durability studies in acids (H2SO4, HCl and HNO3) show that the samples are mostly acid resistant. X-ray tomography suggests low pore volume change over a period of 2 years. The study concludes that the NSDF requirement of low permeability of water and better chemical durability criterion is met by the optimized geopolymerization formulation.

A novel bimetallic-polyanion Na4Fe2.82Ni0.18(PO4)2P2O7 cathode with superior rate performance and long cycle-life for sodium-ion batteries

Na4Fe3(PO4)2P2O7, with the advantages of strong structural stability, suitable voltage window, low cost and green pollution-free, is considered as a highly researchable cathode material for sodium-ion batteries. However, the low conductivity of Na4Fe3(PO4)2P2O7 and the inevitable electrochemical inertia from maricite-NaFePO4 impurity during the preparation process lead to the low reversible capacity and poor cycling stability. In this work, a new bimetallic-polyanion cathode material Na4Fe2.82Ni0.18(PO4)2P2O7 capped with an in-situ nitrogen-doped carbon layer is proposed. Ni-substituting inhibits the generation of electrochemical inert maricite-NaFePO4 impurity and enhances the Na+ ion conductivity. Meanwhile, a lower volume-change during the charging/discharging process can be achieved in Na4Fe2.82Ni0.18(PO4)2P2O7 electrode compared with conventional Na4Fe3(PO4)2P2O7 electrode. With the synergistic effect of in-situ N-doping and Ni-substituting, an ultra-high initial discharge capacity (128.4 mAh g−1 at 0.2C), superior rate performance (62.5 mAh g−1 at 50C) and significant long-term cycle life (capacity retention rate of about 83 % after 3000 cycles at 10C) can be achieved in the optimal Na4Fe2.82Ni0.18(PO4)2P2O7@C-N (Ni6-NFPP@C-N) cathode. This study suggests a practical strategy to produce Na4Fe3(PO4)2P2O7-based electrode material with no impurities and superior electrochemical properties for sodium-ion batteries.

Mo6+ bifunctional substitution of P2-type manganese oxide for high performance sodium-ion batteries

Due to its cost-effectiveness and high specific capacity, P2-type manganese (Mn) oxide is considered a highly promising cathode material for sodium ion batteries (SIBs). However, the practical application of this material is hindered by poor cyclic stability caused by the phase transition of P2-P’2 due to the Jahn-Teller effect of Mn3+ at low voltage and significant volume changes at high voltage. In this study, we utilized Mo6+ dual-function P2-Na0.67Mn0.99Mo0.01O1.997(PO4)0.0008 (NMMPO-1) to achieve exceptional magnification performance and cycle stability. Advanced electron microscopy and X-ray diffraction analysis revealed that Mo6+ acts as a pillar in replacing interlayer Na+ sites within the P2 phase, resulting in extended layer spacing and a stable crystal structure. Additionally, Mo6+ substitution for Mn3+ weakens the Jahn-Teller distortion effect of Mn3+. Ex-situ X-ray diffraction experiments demonstrated that NMMPO-1 effectively inhibits the P2-P’2 phase transition at low voltage while minimizing volume changes during charge–discharge cycles. Overall, our modified NMMPO-1 exhibits excellent cycle stability with 144.55 mA h g−1 after 100 cycles at 0.5C, retaining 83 % capacity retention rate, along with impressive rate performance achieving capacity of 100.57 mA h g−1 at 5C. Furthermore, NMMPO-1 demonstrates superior air stability compared to unmodified samples when exposed to air over multiple cycles. Moreover, through detailed analysis using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic intermittent titration technique (GITT) curves; it is observed that NMMPO-1 possesses enhanced Na+ diffusion capacity and kinetic properties compared to other materials. This research provides novel insights into the role of substituting high valence cations in layered Mn oxide materials which can contribute towards designing improved performance for future sodium ion battery applications.

Enhancing performance of silicon/graphene composites by transition lattice interfaces constructed using plasma

The silicon-based (Si) anodes have not widely used due to their low conductivity and severe irreversible volume changes until now. Graphene (G) is considered a promising material for inhibiting volume expansion and enhancing conductivity of Si, a large amount of work has been exploring effective composite of graphene and silicon. A new SiG composite structure (PB-SiG-1) with transition lattice interface is provided by N plasma assisted technique in this work. The phase interface undergoes lattice changes on the atomic scale with silicon, oxygen, and carbon bonding in new chemical bonds (Si-O-C). More importantly, the lattice spacing of Si (111) increases from 0.31 nm to 0.325 nm due to the insertion of carbon or oxygen atom into the Si body, which promotes the diffusion kinetics of lithium ions. This PB-SiG-1 exhibits better electrochemical performance with reversible specific capacity of 2013.9 mAh g−1 after 100 cycles at 0.2 A g−1, high capacity retention of 98.53% and coulombic efficiency of 99.4%. The multiple advanced in situ methods reveal that the PB-SiG-1 not only has the ability to quickly transfer ions, electrons, and form stable SEI, but also has a low irreversible volume expansion of 33.1 %. This proves that the transition lattice interface endows PB-SiG-1 with isotropy characteristic of lithium diffusion, leading to dynamically stable electrodes during cycles. This work proposes a Si-C composite structure with transition lattice interface, which opens a new insight for volume expansion and lithium transmission in Si-C composite.

Pressure-Induced Defects and Reduced Size Endow TiO2 with High Capacity over 20 000 Cycles and Excellent Fast-Charging Performance in Sodium Ion Batteries.

Anatase TiO2 as sodium-ion-battery anode has attracted increased attention because of its low volume change and good safety. However, low capacity and poor rate performance caused by low electrical conductivity and slow ion diffusion greatly impede its practical applications. Here, a bi-solvent enhanced pressure strategy that induces defects (oxygen vacancies) into TiO2 via N doping and reduces its size by using mutual-solvent ethanol and dopant dimethylformamide as pressure-increased reagent of tetrabutyl orthotitanate tetramer is proposed to fabricate N-doped TiO2/C nanocomposites. The induced defects can increase ion storage sites, improve electrical conductivity, and decrease bandgap and ion diffuse energy barrier of TiO2. The size reduction increases contact interfaces between TiO2 and C and shortens ion diffuse distance, thus increasing extra ion storage sites and boosting ion diffusion rate of TiO2. The N-doped TiO2 possesses highly stable crystal structure with a slightly increase of 0.86% in crystal lattice spacing and 3.2% in particle size after fully sodiation. Consequently, as a sodium-ion battery anode, the nanocomposite delivers high capacity and superior rate capability along with ultralong cycling life. This work proposes a novel pressure-induced synthesis strategy that provides unique guidance for designing TiO2-based anode materials with high capacity and excellent fast-charging capability.

Solar to thermal energy storage performance of composite phase change material supported by copper foam loaded with graphite and boron nitride

Phase Change Materials (PCM) have emerged as one of the potential candidates for solar Thermal Energy Storage (TES) because of their high energy density, low volume change, and easy availability in varying temperature ranges. However, PCM suffers from a few critical drawbacks such as leakage during phase transformation, low thermal conductivity, and poor photothermal energy conversion performance. In this study, shape-stable composite PCM loaded with varying percentages of Graphite (GR) and Boron Nitride (BN) were prepared. Copper foam of 96 PPI was used as 3-dimensional skeleton support to provide shape stability to the eutectic mixture of Lauric Acid (LA)-Myristic Acid (MA). Shape stable composite PCM CF/LA-MA/GR with 0 %, 5 %, 15 %, 25 %, and 35 % of GR and CF/LA-MA/BN with 0 %, 5 %, 15 %, 25 %, and 35 % of BN were prepared and characterized for thermal, physical, and photothermal energy conversion performance. A maximum loading percentage of 67 % of LA-MA in CF without leakage was obtained. The PCM composites show excellent thermal stability at elevated temperatures and suitable TES parameters for solar thermal storage applications. Among all the prepared samples, CF/LA-MA/GR35% shows a maximum rise of 76.1 % in heating rate and 81.2 % in photothermal energy conversion efficiency in comparison with CF/LA-MA/GR0%. In addition, CF/LA-MA/GR35% shows a maximum of 1.08 W/m-K of thermal conductivity at a melting enthalpy of 95.36 J/g. The shape-stable composite PCM shows a stable physical structure along with good surface morphology.

Inducing Na+ Site Rearrangement Through a Cosubstitution Strategy for Rapid Na Diffusion Kinetics of P2-Type Layered Metal Oxides.

The P2-layered metal oxide cathode materials are crucial for constructing high-rate sodium-ion batteries (SIBs); however, its practical application is hindered by the high Na+ diffusion barrier resulting from Na+/vacancy ordering. Herein, a Li/Zn cosubstitution P2-Na0.67Ni0.33Mn0.67O2 (NLNZM) cathode was synthesized via a sol-gel method assisted with citric acid, which can induce the rearrangement of Na+ sites to disrupt ordered structures. The XRD Rietveld refinement confirms a higher occupancy of Na+ at Nae sites with low diffusion barriers through the Li/Zn cosubstitution. In addition, the highly reversible phase evolution of the NLNZM is confirmed through in situ XRD results, thereby ensuring the stability of the structure with low volume change rate (0.78%). Furthermore, Li and Zn can reduce the surface energy and increase the interlayered distance to achieve rapid interfacial kinetics. As a result, the NLNZM has exhibited a high reversible capacity of 152.8 mAh g-1 and an outstanding rate performance of 103.4 mAh g-1 at 5C. After 200 cycles at 5C, the capacity retention rate is 81.1%. This work proposes a cosubstitution strategy to induce Na+/vacancy disorder for achieving rapid Na+ migration as a cathode material for SIBs.

A High-Voltage Cathode Material with Ultralong Cycle Performance for Sodium-Ion Batteries.

Vanadium-based polyanionic materials are promising electrode materials for sodium-ion batteries (SIBs) due to their outstanding advantages such as high voltage, acceptable specific capacity, excellent structural reversibility, good thermal stability, etc. Polyanionic compounds, moreover, can exhibit excellent multiplicity performance as well as good cycling stability after well-designed carbon covering and bulk-phase doping and thus have attracted the attention of multiple researchers in recent years. In this paper, after the modification of carbon capping and bulk-phase nitrogen doping, compared to pristine Na3V2(PO4)3, the well optimized Na3V(PO3)3N/C possesses improved electromagnetic induction strength and structural stability, therefore exhibits exceptional cycling capability of 96.11% after 500 cycles at 2C (1C=80mAg-1) with an elevated voltage platform of 4V (vs Na+/Na). Meanwhile, the designed Na3V(PO3)3N/C possesses an exceptionally low volume change of ≈0.12% during cycling, demonstrating its quasi-zero strain property, ensuring an impressive capacity retention of 70.26% after 10,000 cycles at 2C. This work provides a facial and cost-effective synthesis method to obtain stable vanadium-based phosphate materials and highlights the enhanced electrochemical properties through the strategy of carbon rapping and bulk-phase nitrogen doping.

Theoretical prediction of B5C8 monolayer as a high-performance anode material for lithium-ion batteries

The demand for high-performance energy storage systems has stimulated intensive research on high-performance electrode materials for lithium-ion batteries (LIBs). Two-dimensional (2D) materials have emerged as promising candidates for anode materials due to their unique structural and physicochemical properties. Based on first-principles calculations, we propose a 2D material, B5C8 monolayer, as an excellent anode material for LIBs. B5C8 monolayer exhibits inherent metallicity and outstanding dynamic, mechanical, and thermal stability. Furthermore, B5C8 monolayer shows not only remarkably high storage capacity (2856 mA h g−1) but also low barrier energy (0.25 eV) and small volume change (2.1%). More importantly, B5C8 possesses strong wettability toward commonly used electrolytes in LIBs, namely, solvent molecules and metal salts, indicating prime compatibility. Based on the above distinguished findings, we hope B5C8 monolayer can act as a well-balanced performance anode material for LIBs.

Entropy-Enhanced Multi-Doping Strategy to Promote the Electrochemical Performance of Na4Fe3(PO4)2P2O7.

Sodium-ion batteries (SIBs) have been regarded as promising candidates for large-scale energy storage system, and their electrochemical performance is determined by the cathode materials. Recently, the polyanion-type cathode Na4Fe3(PO4)2P2O7 (NFPP) demonstrates decent performance, while there exists promotion space with respect to its cycle stability and rate capability. Herein, an entropy-enhanced Na4Fe2.95(NiCoMnMgZn)0.01(PO4)2P2O7 (HE-NFPP) cathode is proposed with improved rate performance (67.1mAhg-1 at 50C) and cycle performance (retention of 92.0% after 1000 cycles at 1C). The enhancement of configuration entropy improves the structural stability of NFPP thermodynamically. In-situ XRD illustrates the sodium storage mechanism of HE-NFPP as an imperfect solid solution reaction driven by Fe2+/Fe3+ redox with a low volume change of 4.0% (90.9% of NFPP). Through doping, the structure distortion and abrupt rearrangement are inhibited. Additionally, HE-NFPP and hard carbon (HC) are utilized to fabricate pouch cell that demonstrates an average working voltage of 3.0V and a maximum energy density of 165Whkg-1 (based on the total mass of active materials). These results highlight the potential for enhancing the high-rate and long-cycle performance of NFPP as a promising cathode for SIBs through an entropy-enhanced multi-doping strategy.

KxVPO4F (x∼0): A New High‐Voltage and Low‐Stain Cathode Material for Ultrastable Calcium Rechargeable Batteries

AbstractThe utilization of high‐voltage intercalation cathodes in calcium‐ion batteries (CIBs) is impeded by the substantial size and divalent character of Ca2+ ions, which result in pronounced volume alterations and sluggish ion mobility, consequently causing inferior reversibility and low energy/power densities. To tackle these issues, polyanionic K‐vacant KxVPO4F (x∼0, designated as K0VPF) is proposed as high‐voltage and ultra‐stable cathode material in CIBs. The K0VPF demonstrates a decent calcium storage capacity of 75 mAh g−1 at 10 mA g−1 and remarkable capacity retention of 84.2% over 1000 cycles. The average working voltage of the K0VPF is 3.85 V versus Ca2+/Ca, representing the highest value reported for CIB cathodes to date. The combined experimental and theoretical investigations revealed that the low volume changes and hopping diffusion barriers contribute to the extraordinary stability and high‐power capabilities, respectively, of K0VPF. The distribution of Ca ions into polyanionic frameworks with pronounced spatial separation effectively attenuates the Ca2+–Ca2+ repulsive force and thus augmenting the Ca migration kinetics. The high voltage of K0VPF is attributed to the inductive effect from the largely electronegative fluorine. In conjunction with a calcium metal anode and a compatible electrolyte, Ca metal full cells featured a record‐high energy density of ≈300 Wh kg−1.

Spontaneous redox reaction-mediated interfacial charge transfer in titanium dioxide/graphene oxide nanoanodes for rapid and durable lithium storage.

Titanium dioxide (TiO2) anodes show significant advantages in ion storage owing to their low cost, abundant sources, and small volume change during cycling. However, their intrinsic low electronic conductivity and sluggish ion diffusion coefficient restrict the application of TiO2 anodes, especially at high current densities. The construction of a covalently-bonded interface in TiO2-based composite anodes is an effective approach to solve these issues. Covalent bonds are usually formed in situ during materials synthesis processes, such as high-energy ball milling, solvothermal reactions, plasma-assisted thermal treatment, and addition of a linking agent for covalent coupling. In this study, we demonstrate that a spontaneous redox reaction between defective TiO2 powder and an oxidative graphene oxide (GO) substate can be used to form interfacial covalent bonds in composites. Different structural characterization techniques confirmed the formation of interfacial covalent bonds. Electrochemical measurements on an optimized sample showed that a specific capacity of 281.3 mA h g-1 after 200 cycles can be achieved at a current density of 1 C (1 C = 168 mA g-1). Even at a high rate of 50 C, the electrode maintained a reversible capacity of 97.0 mA h g-1. The good lithium storage performance of the electrode is a result of the uniquely designed composite electrodes with strong interfacial chemical bonds.

Developing an abnormal high-Na-content P2-type layered oxide cathode with near-zero-strain for high-performance sodium-ion batteries.

Layered transition metal oxides (NaxTMO2) possess attractive features such as large specific capacity, high ionic conductivity, and a scalable synthesis process, making them a promising cathode candidate for sodium-ion batteries (SIBs). However, NaxTMO2 suffer from multiple phase transitions and Na+/vacancy ordering upon Na+ insertion/extraction, which is detrimental to their electrochemical performance. Herein, we developed a novel cathode material that exhibits an abnormal P2-type structure at a stoichiometric content of Na up to 1. The cathode material delivers a reversible capacity of 108 mA h g-1 at 0.2C and 97 mA h g-1 at 2C, retaining a capacity retention of 76.15% after 200 cycles within 2.0-4.3 V. In situ diffraction studies demonstrated that this material exhibits an absolute solid-solution reaction with a low volume change of 0.8% during cycling. This near-zero-strain characteristic enables a highly stabilized crystal structure for Na+ storage, contributing to a significant improvement in battery performance. Overall, this work presents a simple yet effective approach to realizing high Na content in P2-type layered oxides, offering new opportunities for high-performance SIB cathode materials.

On Synthesis and Electrochemical Performance of Na4Fe3(PO4)2(P2O7) Cathode for Sodium-Ion Batteries

Developing cost-effective and large-scale energy storage systems (ESSs) has been an important topic over the past years in order to implement efficient utilization of renewable electricity generated from sources like solar, wind, geothermal and tidal energy (1). Since the commercialization in 1991, lithium-ion batteries (LIBs) have been widely used in portable electronics, electric vehicles (EVs), and energy storage devices (2). However, there is an increase in demand for alternative energy sources based on abundant and low-cost materials due to the limited reserves and high costs of lithium compounds. In this context, sodium-ion batteries (SIBs) have received great attention because of their similarities to LIBs and the large abundance (2.3%) on earth, and low cost of sodium compounds (3). However, the energy density of most SIBs are lower that of LIBs, primarily due to the larger ionic radius and higher mass of Na+ ion compared to Li+ ions, as well as the lower electrochemical potential of sodium cells relative to lithium cells (4). Many efforts have been devoted to the development of high-performance cathode materials, including layered transition metal oxides, Prussian blue analogues (PBAs), sulfates, phosphates and pyrophosphates. Polyanionic compounds, in particular, are considered as promising cathode materials with regard to their high working voltage, structural stability, thermal stability and small volume change upon cycling (5). For example, iron phosphate-based materials have gained attention inspired by LiFePO4 for LIBs. However, the olivine NaFePO4 is predominantly produced through an ion exchange process (6). The maricite NaFePO4 is electrochemically inactive due to the lack of Na migration channels within its structure. On the other hand, Na2FeP2O7 shows long cycle life and structural stability with a low capacity because of its single electron diffusion process. Na4Fe3(PO4)2(P2O7) (NFPP) combines the benefits of both phosphate and pyrophosphate, offering potential advantages such as low-cost, environmental friendliness, high average working voltage (~ 3.1 V vs. Na+/Na), favorable theoretical capacity (129 mAh g-1), low volume change (< 4%) due to its open framework composed of [Fe3P2O13] layers connected by (P2O7)4- groups with 3D ion channels and low activation barriers for Na+ transport as well as structural and thermal stability. However, NFPP is susceptible to the formation of impurities such as NaFePO4 and Na2FeP2O7, which can arise from the synthesis temperature and adopted reaction materials, potentially restricting the electrochemical performance of NFPP. Additionally, the inherent insulating characteristics of the (PO4)3- group in NFPP may result in reduced electronic conductivity and slow ion diffusion, which hinders its practical application (7, 8). Therefore, various strategies have been developed to enhance conductivity such as nanosizing, carbon coating and metal ion doping.NFPP can be synthesized by various methods like solid-state, sol-gel, spray drying and combustion. In this study, we present our results on employing both sol–gel and combustion methods with distinct synthesis parameters. The structure, morphology and particle size of NFPP are characterized by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) techniques. The electrochemical performance of NFPP cathodes is investigated in both half- and full-cells via galvanostatic charge-discharge cycling tests. Keywords: sodium-ion batteries, cathode material, iron-based mixed phosphate, sol-gel synthesis, large scale M. Armand and J. M. Tarascon, Nature, 451, 652 (2008).J. B. Goodenough and K.-S. Park, Journal of the American Chemical Society, 135, 1167 (2013).B. Dunn, H. Kamath and J.-M. Tarascon, Science, 334, 928 (2011).M. H. Han, E. Gonzalo, G. Singh and T. Rojo, Energy & Environmental Science, 8, 81 (2015).P. Barpanda, L. Lander, S.-i. Nishimura and A. Yamada, Advanced Energy Materials, 8, 1703055 (2018).K. T. Lee, T. N. Ramesh, F. Nan, G. Botton and L. F. Nazar, Chemistry of Materials, 23, 3593 (2011).X. Wu, G. Zhong and Y. Yang, Journal of Power Sources, 327, 666 (2016).H. Kim, I. Park, S. Lee, H. Kim, K.-Y. Park, Y.-U. Park, H. Kim, J. Kim, H.-D. Lim, W.-S. Yoon and K. Kang, Chemistry of Materials, 25, 3614 (2013).

Unlocking the Potential of Dual-Ion Batteries: Identifying Polycyclic Aromatic Hydrocarbon Cathodes and Intercalating Salt Combinations through Machine Learning.

Dual-ion batteries (DIBs) represent a promising energy storage technology, offering a cost-effective safe solution with impressive electrochemical performance. The large combinatorial configuration space of the electrode-electrolyte leads to design challenges. We present a machine learning (ML) approach for accurately predicting the voltage and volume changes of polycyclic aromatic hydrocarbon (PAH) cathodes upon intercalation with a variety of DIB salts following different mechanisms. Gradient Boosting and XGBoost Regression models trained on the data set demonstrate exceptional performance in voltage and volume change prediction, respectively. The models are further cross-validated and utilized to predict the properties for ∼700 combinations of PAH and DIB salt intercalations, a subset of which is further validated by density functional theory. Using average voltage and volume change for all combinations of PAHs and salts, preferable combinations for high/low voltage requirements along with long-term stability are obtained. Overall, the study shows the applicability of PAHs in DIBs exhibiting good electrochemical performance with low volume change compared to graphite indicative of its potential to overcome the cycling stability issues of DIBs. This research establishes a reliable and broadly applicable ML-based workflow for efficient screening and accelerated design of advanced PAH cathodes and salts, thus driving progress in the field of DIBs.