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Calciumion batteries (CIBs) are an appealing energy storage technology owing to the low redox potential of Ca2+/Ca and the abundant Ca reserves in the earth's crust. However, suitable cathode materials with high capacity and long lifespan are scarce. Herein, VO2(B)/reduced graphene oxide (rGO) heterojunction formed by interfacial V─O─C bonds is constructed and first reported as a cathode material for CIBs, which exhibits an ultrahigh discharge capacity of 319.2 mAh g−1 and exceptional long lifespan (3000 cycles at 500 mA g−1 with capacity retention of 85%). In addition, VO2(B)/rGO heterojunction also shows an outstanding rate capability at 50 °C (127.1 mAh g−1 at 1000 mA g−1). The remarkable electrochemical performance is attributed to the big tunnel structures of VO2(B) and the role of rGO in enhancing electronic conductivity. Density functional theory calculations reveal a feasible Ca2+ diffusion path at the interface. Furthermore, a reversible single‐phase insertion/extraction reaction is revealed by in situ X‐ray diffraction, ex situ Raman, and ex situ X‐ray photoelectron spectroscopy. This work demonstrates that VO2(B)/rGO holds great potential for building high‐capacity and long‐lifespan CIBs. [ABSTRACT FROM AUTHOR]

Calcium ion batteries (CIBs) are considered as an important candidate for post‐lithium energy storage devices due to their abundance of resources and low cost. However, CIBs still suffer from slow kinetics due to the large solvation structure and high desolvation energy of Ca2+ ions. Here, a solvation regulation strategy based on donor number (DN) is reported to achieve easy‐desolvation and rapid storage of Ca2+ in sodium vanadate (Na2V6O16·2H2O, NVO). Specially, the solvent with a low DN, represented by propylene carbonate (PC), forms the first solvation shell of calcium ions with weak binding energy and small shell structure, which facilitates the migration of Ca2+ in the electrolyte. More importantly, the low DN solvent is preferentially desolvated at the cathode/electrolyte interface, promoting the insertion of Ca2+ into the NVO electrode. Mechanism studies further confirm the highly reversible uptake/release of Ca2+ in the NVO cathode, along with the VO distance change in the coordination structure. Therefore, the NVO cathode achieves high capacity (376 mAh g−1 at 0.3 A g−1) and high‐rate performance (151 mAh g−1 at 5 A g−1). The weak solvation effect strategy further improves the electrochemical performance and provides great importance for the design of the long‐term development of CIBs. [ABSTRACT FROM AUTHOR]

Context: Two-dimensional borophene can be used in rechargeable batteries due to its high specific surface area. In this paper, the performance of borophene as an anode material for calcium ion batteries is predicted based on density functional theory calculations. The calculation results show that P doping enhances the calcium storage properties of borophene. The maximum adsorption number of calcium atoms in the P-doped system is 7, with a theoretical capacity of 964 mAh/g. DOS analysis showed that borophene exhibited metallic properties after adsorbing calcium atoms, which improved the electrical conductivity of the electrode material. Calculation of the diffusion energy barrier shows that strain has an effect on calcium diffusion in monolayer borophene, and compressive strain promotes calcium diffusion through borophene. The findings suggest that borophene may be a promising electrode material for calcium-ion batteries. Methods: In this paper, the intrinsic model and doping model of borophene are constructed by Material Studio 8.0, and the first-principles calculation is carried out by CASTEP module. [ABSTRACT FROM AUTHOR]

Calcium ion batteries (CIBs) are pursued as potentially low‐cost and safe alternatives to current Li‐ion batteries due to the high abundance of calcium element. However, the large and divalent nature of Ca2+ leads to strong interaction with intercalation hosts, sluggish ion diffusion kinetics and low power output. Herein, a small molecular organic anode is reported, tetracarboxylic diimide (PTCDI), involving carbonyl enolization (CO↔CO−) in aqueous electrolytes, which bypasses the diffusion difficulties in intercalation‐type electrodes and avoid capacity sacrifice for polymer organic electrodes, thus manifesting rapid and high Ca storage capacities. In an aqueous Ca‐ion cell, the PTCDI presents a reversible capacity of 112 mAh g−1, a high‐capacity retention of 80% after 1000 cycles and a high‐power capability at 5 A g−1, which rival the state‐of‐the‐art anode materials in CIBs. Experiments and simulations reveal that Ca ions are diffusing along the a axis tunnel to enolize carbonyl groups without being entrapped in the aromatic carbon layers. The feasibility of PTCDI anodes in practical CIBs is demonstrated by coupling with cost‐effective Prussian blue analogous cathodes and CaCl2 aqueous electrolyte. The appreciable Ca storage performance of small molecular crystals will spur the development of green organic CIBs. [ABSTRACT FROM AUTHOR]

The electrochemical activity of solvated Ca2+ in glyme‐based electrolytes is investigated using grand canonical density functional theory approach and Fukui functions. The obtained results reveal that the length of glyme molecules has little effect on the reduction potentials, but has significant impacts on the effective electron transfer process. In short chain glymes, the transferred electron is located on a Ca2+ center and the organic part of the solvation sphere, leading to a direct Ca2+ reduction and a partial degradation of the glyme molecules. As the glyme's length increases, the reduction process turns into the formation of solvated electrons rather than Ca2+ reduction, unless a partial desolvation occurs. Consequently, an effective Ca2+ reduction in long chain glyme‐based electrolytes is controlled by a (partial) desolvation of the solvation sphere. These results can be used as guiding information to design new electrolytes having the Ca2+ reduction potential in an accessible voltage range together with an effective Ca2+ reduction process. The methodology developed in this study can be universally applied to investigate the thermodynamic and kinetic properties of other battery systems using metal anodes, which might lead to a paradigm shift in the design of prospective electrolytes for future battery technologies. [ABSTRACT FROM AUTHOR]

A theoretical research study was conducted into the possibility of using a two-dimensional graphene-like material silicon carbide nano-sheet (2D-SiCNS) as an anode in rechargeable Ca-ion batteries by performing DFT computations. For this purpose, the electrochemical properties during the charging process, the diffusion of Ca ion, the electronic structures, and the changes in the geometrical structures were investigated. The adsorption energy (Ead) of Ca on top of the Si atom was more than Ead of other sites. The maximum theoretical capacity of the 2D-SiCNS reached 507 mAh/g, which was accompanied by a slight change in the spacing of the Si–C band. Also, open circuit voltage (OCV) changes with changes in the concentration of adsorbed Ca atoms on the 2D-SiCNS surface were investigated. Moreover, the appropriate OCV range of Ca atoms adsorbed on the 2D-SiCNS demonstrated that this nano-sheet was suitable as a anodic material. In addition, considerable charges were transferred from Ca to the 2D-SiCNS, making it electrically conductive as a suitable anode material. [ABSTRACT FROM AUTHOR]

Destiny functional theory (DFT) calculations are undertaken in order to scrutinize the electrochemical and calcium (Ca) storage characteristics of a graphyne-like aluminum nitride monolayer (G-AlNyen) as an electrode material for Ca-ion batteries (CIBs). The results show that the change in internal energy as well as the cell voltage values for the CIB with the G-AlNyen anode are comparable to others with two-dimensional 2D nano-materials. It is shown that Ca is adsorbed primarily onto the center of a hexagonal and triangular ring of G-AlNyen with absorption energies of −2.06 and −0.42 eV. After increasing the concentration of Ca atoms on G-AlNyen, the adsorption energy as well as the cell voltage decreases. Lower values of 0.15–0.32 eV related to the diffusion barrier confirm that the diffusion of Ca in the 2D nano-sheets is rapid. G-AlNyen shows a maximum theoretical capacity of approximately 869.23 mAh h g−1. The results are evaluated in terms of charge transfer, structure, energy as well as electronic characteristics and provide insight into the construction of better anode materials with higher capacity for the CIB. • G-AlNyen@Ca has changed his semiconductor character to metallic character. • Investigation of the adsorption and charge transfer of Ca on the G-AlNyen. • The diffusion energy of Ca, suggesting fast charging/discharging processes. [ABSTRACT FROM AUTHOR]

Calcium ion batteries (CIBs) are a promising energy storage device due to the low redox potential of the Ca metal and the abundant reserves of the Ca element. However, the large radius and divalent nature of Ca 2+ lead to its slow ion diffusion kinetics and the lack of suitable electrode materials for Ca storage. Here, a layered structure of Na 2 Ti 3 O 7 (NTO) is presented as an anode material for nonaqueous CIBs. This NTO anode demonstrates a high discharge capacity of 165 mA h g -1 at 100 mA g -1 and a remarkable capacity retention rate of 80%, even after 2000 cycles at 500 mA g -1 , surpassing the performance of all reported intercalation-type anode materials for CIBs. The NTO transfers to layered Ca VII Na IX Ti 3 O 7 (CNTO) with intercalation of Ca 2+ and extraction of Na + during the first discharge process. Then, the CNTO undergoes the reversible insertion/extraction of Ca 2+ during subsequent cycling. Additionally, density functional theory calculations reveal that NTO possesses a rapid two-dimensional diffusion pathway for Ca 2+ . Moreover, the full CIBs based on NTO as the anode further underscore its potential for CIBs. This work presents promising anode materials for CIBs, offering opportunities to promote the development of high-performance CIBs.

Calcium-ion batteries (CIBs) have emerged as a promising alternative for electrochemical energy storage. The lack of high-performance cathode materials severely limits the development of CIBs. Vanadium oxides are particularly attractive as cathode materials for CIBs, and preinsertion chemistry is often used to improve their calcium storage performance. However, the room temperature cycling lifespan of vanadium oxides in organic electrolytes still falls short of 1000 cycles. Here, based on preinsertion chemistry, the cycling life of vanadium oxides is further improved by integrated electrode and electrolyte engineering. Utilizing a tailored Ca electrolyte, the constructed freestanding (NH 4 ) 2 V 6 O 16 ·1.35H 2 O@graphene oxide@carbon nanotube (NHVO-H@GO@CNT) composite cathode achieves a 305 mAh g -1 high capacity and 10 000 cycles record-long life. Additionally, for the first time, a Ca-ion hybrid capacitor full cell is assembled and delivers a capacity of 62.8 mAh g -1 . The calcium storage mechanism of NHVO-H@GO@CNT based on a two-phase reaction and the exchange of NH 4 + and Ca 2+ during cycling are revealed. The lattice self-regulation of V─O layers is observed and the layered vanadium oxides with Ca 2+ pillars formed by ion exchange exhibit higher capacity. This work provides novel strategies to enhance the calcium storage performance of vanadium oxides via integrated structural design of electrodes and electrolyte modification., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Due to the low cost and low redox potential of calcium, calcium ion batteries (CIBs) are considered a competitive candidate for large‐scale energy storage systems and have attracted increasing attention in recent years. However, the development of CIBs is still in its infancy and hindered by the lack of high‐performance cathode materials. Herein, the metahewettite layered vanadium oxide with the Ca2+ pillar and water lubrication is reported as a cathode material for CIBs. Benefiting from the large interlayer spacing, pillar, and water lubrication effect, the as‐prepared CaV6O16·2.8H2O (CVO) delivers a high discharge capacity of 175.2 mAh g−1 at 50 °C and 131.7 mAh g−1 at room temperature, a long cycle life of 1000 cycles and the highest rate performance (up to 1000 mA g−1) in organic electrolyte. Furthermore, a single‐phase Ca2+ insertion and extraction reaction is revealed by in situ X‐ray diffraction and in‐situ Fourier transform infrared spectroscopy. Density functional theory computations indicate that Ca2+ tends to diffuse along the b direction with a low energy barrier of 0.36 eV in CVO. This work is bringing the performance of cathode materials for CIBs to a higher level and of great significance for accelerating the development of CIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigating Ca storage mechanism and properties of BeP 2 was calculated. • Ca has low diffusion barrier and high capacity on BeP 2 surface. • The interface electronic behavior of BeP 2 enhance the adsorption of Ca. One of the efficient methods for boosting the energy density of modern metal-ion batteries is finding electrode materials with high performance. Before and following the adhesion of metal ions, a BeP 2 monolayer (BeP 2 ML) has intrinsic metallicity and high conductance. The first-principles DFT computations demonstrate that BeP 2 ML is one of the encouraging electrode materials for Ca-ion batteries (CIBs). Furthermore, the theoretical capacity of a fully Ca phase Ca 2 BeP 2 for BeP 2 ML was high (629 mA h g−1) having an additional calcium ion layer, which outperformed other two-dimensional ones reported in the literature. Additionally, after the full adhesion of metal ions, BeP 2 ML exhibited a surprisingly low open circuit voltage and diffusion barrier (0.24 V). The present piece of research can provide insights into exploring new BeP 2 ML-type electrode materials for CIBs. [ABSTRACT FROM AUTHOR]

Abstract Herein, graphite is proposed as a reliable Ca2+‐intercalation anode in tetraglyme (G4). When charged (reduced), graphite accommodates solvated Ca2+‐ions (Ca‐G4) and delivers a reversible capacity of 62 mAh g−1 that signifies the formation of a ternary intercalation compound, Ca‐G4·C72. Mass/volume changes during Ca‐G4 intercalation and the evolution of in operando X‐ray diffraction studies both suggest that Ca‐G4 intercalation results in the formation of an intermediate phase between stage‐III and stage‐II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca‐G4 has a planar structure with Ca2+ surrounded by G4, which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g−1 at 1.0 A g−1 s vs 62 mAh g−1 at 0.05 A g−1) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca2+‐shuttling calcium‐ion batteries with a graphite anode, a full‐cell is constructed by coupling with an organic cathode and its electrochemical performance is presented.

[Display omitted] Presently, great attention is being paid to the search for promising anode materials for metal-ion batteries (MIBs) due to the rapid evolution of numerous modern electronic gadgets. In this investigation, we have predicted for the first time that the buckled-hexagonal Nb 2 S 2 monolayer which may be an efficient anode material for calcium-ion batteries (CIBs). To that objective, we have explored the pristine monolayer system's energetical, dynamical, and thermal stability. The inherent metallicity of the pristine monolayer facilitates its electrical conductivity as an electrode material. Our study also reveals the structural and electrical properties of the Ca-adsorbed Nb 2 S 2 monolayer. It is observed that Ca-atoms prefer to get intercalated on top of the buckled hexagon of the pristine monolayer, and the metallicity of the 2D nanosheet remains preserved. In the adsorption process, Bader charge analysis is used to determine the amount of charge transfer from the Ca atom to the Nb 2 S 2 monolayer. Furthermore, this system exhibits a high storage capacity of 1288.86 mAh/g and a moderately low diffusion energy barrier of 0.76 eV. The calculated open-circuit voltage of 0.49 V and the other results suggest that the Nb 2 S 2 monolayer may be a potential candidate for anode material for rechargeable Ca-ion batteries. [ABSTRACT FROM AUTHOR]

Because of cost-effective production and abundant resources of calcium, Ca-ion batteries (CIBs) are an appropriate option to alternate Li-ion batteries (LIBs). A new category of anode materials for CIBs has emerged since the successful synthesis of carbon nanotubes, which are B and N doped derivatives of it. For high-performance CIBs, BC 2 N nanotube (BC 2 NNT) has been studied as promising anode materials. In order to comprehend electrochemical attributes, cycling stability, and adsorption behavior of BC 2 NNT, first-principles computations have been executed. Based on nuclear magnetic resonance computations, two types of hexagonal rings (B 2 C 2 N 2 (I) and BC 4 N (II)) were specified that are non-aromatic. Ca has adsorption on B 2 C 2 N 2 and BC 4 N with adsorption energy (E ad) values of −47.44 and −28.50 kcal/mol, respectively. Specific capacity value has been determined to be as high as 840 mAh/g. The predicted average open-circuit voltage (OCV) for BC 2 NNT is 1.56 V, which has a larger value than that of other 2D materials. All mentioned reasons provide BC 2 NNT as an acceptable anode material for use in CIBs. In present research, results may create new ways of designing favorable boron-carbon-nitrogen based anode materials for CIBs. • DFT calculations have been performed for understanding the anodic properties of BC 2 NNTs for CIBs. • Mg preferably adsorbs on nearly B atom with E ad −47.44 kcal/mol. • The diffusion barriers have low values (0.11 eV), indicating that the MIBs in the BC 2 NNTs. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations are used to investigate the basic electrochemical characteristics of Si-based anodes in calcium ion batteries (CIBs). The calculated average voltage of Ca alloying with fcc-Si to form the intermetallic Ca x Si phases (0.5 < x ≤ 2) is of 0.4 V, with a volume variation of 306%. Decalciation of the lower Ca content phase, CaSi 2 , is predicted at an average voltage between 0.57 V (formation of Si-fcc, 65% volume variation) and 1.2 V (formation of metastable deinserted-Si phase, 29% volume variation). Experiments carried out in conventional alkyl carbonate electrolytes show evidence that electrochemical “decalciation” of CaSi 2 is possible at moderate temperatures. The decalciation of CaSi 2 is confirmed by different characterization techniques. [ABSTRACT FROM AUTHOR]

Herein, graphite is proposed as a reliable Ca2+‐intercalation anode in tetraglyme (G4). When charged (reduced), graphite accommodates solvated Ca2+‐ions (Ca‐G4) and delivers a reversible capacity of 62 mAh g−1 that signifies the formation of a ternary intercalation compound, Ca‐G4·C72. Mass/volume changes during Ca‐G4 intercalation and the evolution of in operando X‐ray diffraction studies both suggest that Ca‐G4 intercalation results in the formation of an intermediate phase between stage‐III and stage‐II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca‐G4 has a planar structure with Ca2+ surrounded by G4, which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g−1 at 1.0 A g−1 s vs 62 mAh g−1 at 0.05 A g−1) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca2+‐shuttling calcium‐ion batteries with a graphite anode, a full‐cell is constructed by coupling with an organic cathode and its electrochemical performance is presented. [ABSTRACT FROM AUTHOR]

Reversible intercalation of guest ions in graphite is the key feature utilized in modern battery technology. In particular, the capability of Li-ion insertion into graphite enabled the successful launch of commercial Li-ion batteries 30 years ago. On the road to explore graphite as a universal anode for post Li-ion batteries, the conventional intercalation chemistry is being revisited, and recent findings indicate that an alternative intercalation chemistry involving the insertion of solvated ions, designated as co-intercalation, could overcome some of the obstacles presented by the conventional intercalation of graphite. As an example, the intercalation of Na ions into graphite for Na-ion batteries has been perceived as being thermodynamically impossible; however, recent work has revealed that a large amount of Na ions can be reversibly inserted in graphite through solvated-Na-ion co-intercalation reactions. More recently, it has been extensively demonstrated that with appropriate electrolyte selection, not only Na ions but also other ions such as Li, K, Mg, and Ca ions can be co-intercalated into a graphite electrode, resulting in high capacities and power capabilities. The co-intercalation reaction shares a lot in common with the conventional intercalation chemistry but also differs in many respects, which has attracted tremendous research efforts in terms of both fundamentals and practical applications. Herein, we aim to review the progress made in understanding the solvated-ion intercalation mechanisms in graphite and to comprehensively summarize the state-of-the-art achievements by surveying the correlations among the guest ions, co-intercalation conditions, and electrochemical performance of batteries. In addition, the advantages and challenges related to the practical application of graphite undergoing co-intercalation reactions are presented., (Copyright © 2020 Park, Xu and Kang.)

Herein, graphite is proposed as a reliable Ca 2+ -intercalation anode in tetraglyme (G 4 ). When charged (reduced), graphite accommodates solvated Ca 2+ -ions (Ca-G 4 ) and delivers a reversible capacity of 62 mAh g -1 that signifies the formation of a ternary intercalation compound, Ca-G 4 ·C 72 . Mass/volume changes during Ca-G 4 intercalation and the evolution of in operando X-ray diffraction studies both suggest that Ca-G 4 intercalation results in the formation of an intermediate phase between stage-III and stage-II with a gallery height of 11.41 Å. Density functional theory calculations also reveal that the most stable conformation of Ca-G 4 has a planar structure with Ca 2+ surrounded by G 4 , which eventually forms a double stack that aligns with graphene layers after intercalation. Despite large dimensional changes during charge/discharge (C/D), both rate performance and cyclic stability are excellent. Graphite retains a substantial capacity at high C/D rates (e.g., 47 mAh g -1 at 1.0 A g -1 s vs 62 mAh g -1 at 0.05 A g -1 ) and shows no capacity decay during as many as 2000 C/D cycles. As the first Ca 2+ -shuttling calcium-ion batteries with a graphite anode, a full-cell is constructed by coupling with an organic cathode and its electrochemical performance is presented., Competing Interests: The authors declare no conflict of interest., (© 2019 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.)

Multivalent intercalation batteries have the potential to circumvent several fundamental limitations of reigning Li-ion technologies. Such batteries will potentially deliver high volumetric energy densities, be safer to operate, and rely on materials that are much more abundant than Li in the Earth's crust. The design of intercalation cathodes for such batteries requires consideration of thermodynamic aspects such as structural distortions and energetics as well as kinetic aspects such as barriers to the diffusion of cations. The layered α-V 2 O 5 system is a canonical intercalation host for Li-ions but does not perform nearly as well for multivalent cation insertion. However, the rich V-O phase diagram provides access to numerous metastable polymorphs that hold much greater promise for multivalent cation intercalation. In this article, we explore multivalent cation insertion in three metastable polymorphs, γ', δ', and ρ' phases of V 2 O 5 , using density functional theory calculations. The calculations allow for evaluation of the influence of distinctive structural motifs in mediating multivalent cation insertion. In particular, we contrast the influence of single versus condensed double layers, planar versus puckered single layers, and the specific stacking sequence of the double layers. We demonstrate that metastable phases offer some specific advantages with respect to thermodynamically stable polymorphs in terms of a higher chemical potential difference (giving rise to a larger open-circuit voltage) and in providing access to diffusion pathways that are highly dependent on the specific structural motif. The three polymorphs are found to be especially promising for Ca-ion intercalation, which is particularly significant given the exceedingly sparse number of viable cathode materials for this chemistry. The findings here demonstrate the ability to define cation diffusion pathways within layered metastable polymorphs by alteration of the stacking sequence or the thickness of the layers.