Calcium-ion Batteries Research Articles

(Invited) Calcium-Ion Cathode Materials

Calcium-ion batteries (CIBs) could be an alternative to lithium-ion batteries (LIBs) for certain niche applications due to their theoretically high operating potentials and the high natural abundance of calcium. However, the development of CIBs has been limited by the lack of proper electrolytes and electrode materials due to the difficulties identifying Ca-ion insertion host materials. Previous efforts to develop CIB cathodes have been made mainly based on intercalation materials such as Prussian blue-based materials (1) , layered oxide materials (MoO3 (2), V2O5 (3), CaCo2O4 (4-5), and layered phosphates (VOPO4·2H2O) (6). In this discussion we will be reviewing the state of Ca-ion battery materials and delve into an analysis of several functional polyanionic materials that show promising properties and characteristics as CIB cathodes. The NASICON-type NaV2(PO4)3, derived from de-sodiation of Na3V2(PO4)3, has been shown to reversibly intercalate Ca2+ -ions (capacity 81 mA h g-1) above 3V (vs. Ca2+/Ca) with stable cycling performance. DFT calculations, XAS, XRD, and TEM studies were used to support the insertion of Ca-ions and give insights into the diffusion mechanism of the materials involved (7,8). The presentation will also provide insights into materials design aspects of CIB materials and note areas of need that would benefit the MV battery community.

(Invited) Intercalation-Type Cathode Materials for Nonaqueous Calcium-Ion Batteries

Calcium-ion batteries (CIBs) represent a promising alternative to the current lithium-ion batteries (LIBs). Calcium ions can transfer two electrons per ion. Thus, in principle, the capacity of a host material can double due to the divalency of calcium, provided the host material can release and accept the transferred electrons. The final battery product is expected to be cost-effective, owing to the earth-abundance of calcium reserves. The redox potential of calcium is close to that of lithium, enabling a high cell voltage. The larger ionic radius of calcium (1.0 Å) compared to those of other divalent ions (0.60–0.74 Å) could be a disadvantage because a narrow diffusion pathway sufficient for smaller ions will not allow the passage of larger Ca ions. However, the larger ionic radius ensures a lower effective intercalant-ion charge density, which can be rather advantageous for the diffusion in the host materials as well as in the electrolytes.Recent discoveries of reversible plating or alloying of calcium provoked considerable interest in calcium-based rechargeable batteries. Theoretical calculations also predict that the energy barriers for Ca diffusion are lower than other multivalent ions in some structures, and the development of positive materials are anticipated. However, only a few cathode materials have been reported so far, only to exhibit low energy-storage capability and poor cyclability. In this talk, the synthesis, structural and electrochemical properties of new cathode materials for nonaqueous CIBs will be presented, which were recently developed in our group. Some examples include NASICON-type NaV2(PO4)3, FeV3O9∙1.2H2O, Ca0.13MoO3·(H2O)0.41. These stimulating discoveries will lead to the development of new strategies for obtaining high energy density CIBs.

Electrochemical Behavior in Calcium Aqueous Electrolyte of Spinach, Malabar Spinach and Komatsuna

Multivalent-ion rechargeable batteries using calcium ions have an attracted attention as one of next generation batteries. Calcium-ion batteries using a metal negative electrode that does not form dendrites can contribute the twice number of electrons per cation compared with lithium ion, which increase the charge capacity for the specific insertion host. In recent years, the electrochemical stripping and plating of calcium metal has been a report for anode. [1] On the other hand, the calcium insertion hast for cathode active materials such as NiFe(CN)6 [2] and MnFe(CN)6 [3] have been reported. However, their capacity and potential are far from those of lithium-ion battery cathode materials, and there are not so many candidates for cathode active materials. This is because the diffusion of multivalent ions in the inorganic compound is disturbed by a large interaction with cations and anions in the host structure. It is still challenge to improve ionic conduction drastically by the conventional concept and novel material concept is needed. We focused on the fact that, among the calcium compounds using natural products, calcium is contained relatively in green vegetables. Since green vegetables such as Spinach, Malabar spinach, and Komatsuna contain a relatively large amount of calcium and a metal cation, electrochemical insertion / deinsertion of calcium would be realized. Then, new material guideline can be established by analyze the chemical structure for calcium insertion / deinsertion. In this study, we report the electrochemical behavior of Spinach, Malabar spinach, and Komatsuna as active materials. Spinach, Malabar spinach, and Komatsuna were vacuum dried at 75 ℃ and grind in a mortar. The vegetable powder was mixed with acetylene black and PTFE at weight ratio of 75:15:10. The pelletized electrode was pressed between two Ti meshes. The three-electrode cell using Ag / AgCl reference electrode and an activated carbon counter electrode was assembled with 2.5 M Ca(NO3) aqueous electrolyte.CV measurement was performed at the scan rate of 10 mV s-1 with the potential range of -0.8 V to 0.9 V. Figure 1 shows the CV of Spinach, Malabar spinach, and Komatsuna in aqueous Ca(NO3) electrolyte. All samples are swept to cathodic first and then anodic. No distinct reduction peaks were observed, whereas the anodic sweep confirmed the distinct peaks. The anodic peaks were observed around 0.3 V for spinach and malabar spinach, and around 0.5 V for komatsuna. Higher anodic current is observed, particularly in komatsuna which has different chemical species of calcium, and the peak position is shifted towards positive direction. Among the three vegetables, the calcium content is in the order of komatsuna, malabar spinach, spinach, which consists with the order in the peak currents. When this anodic current is assumed to be derived from electrochemical deinsertion of calcium ions, it is estimated that the approximately 30 to 50% of the calcium content is extracted in this reaction.Reference.[1] A. Ponrouch, C. Frontera, F. Bardé and M. R. Palacín, Nature. Mater., 15, 169-172 (2016).[2] T. Tojo et al, Electrochem. Acta., 207, 22-27, (2016)[3] A. L. Lipson et al., Chem. Mater., 27, 8442-47, (2015) Figure 1

Fluorinated Alkoxyaluminates As Electrolytes for Calcium-Ion Batteries

In the field of multivalent Batteries, the reversibility of stripping and plating of the metal in question will dictate the overall performance of a battery. With recent advances in non-aqueous calcium electrolytes, it is now possible to reversibly strip and plate calcium at room temperature. Several new electrolytes were found since then, which all suffer from short cycle lives, due to the strong tendency of calcium metal surfaces to passivate. An alternative route to achieve longer cycle life is to alloy the Calcium anode. It was shown that Ca-Sn alloy anodes can help, extend the cycle life by preventing the formation of impenetrable passivisation layers. However, this comes with the cost of decreased energy density, since the alloying material is not involved in the Energy storage process. In this work we focused on a new electrolyte that can extend the cycle life of a calcium-ion battery (CIB) and still work with a pure calcium metal anode. Electrolytes based on alkoxy-aluminates in glycol ethers have shown high conductivity and electrochemical stability when used in Mg-Ion batteries. But more importantly, the metal deposits obtained are remarkably pure, even after hundreds of cycles. In this work, we present the Calcium homologue,calcium-tetra-1,1,1,3,3,3-hexaflouroisopropylo-aluminate Ca[Al(HFIP)4]2, in Dimethoxyethane (DME) as a promising candidate for calcium-ion batteries. Besides its high conductivity (8.99 mS/cm2 at 25°C ) and high anodic stability (>3V vs. Ca0/Ca2+), reversible stripping and plating could be sustained for up to 550 cycles.

High-Voltage Phosphate Cathodes for Rechargeable Ca-Ion Batteries

Calcium-ion batteries (CIBs) are under investigation as next-generation energy storage devices due to their theoretically high operating potentials and lower costs tied to the high natural abundanc...

Layered potassium vanadate K2V6O16 nanowires: A stable and high capacity cathode material for calcium-ion batteries

Calcium-ion batteries are promising candidate as alternative to lithium-ion batteries with appealing features of abundant resource and high theoretical specific capacity up to 1337 mAh g−1. However, the development of calcium-ion batteries is primarily hindered by the lack of satisfactory electrode materials due to the large radius and charge density of calcium ion. Herein, we report the reversible calcium ion intercalation in layered potassium vanadate K2V6O16·2.7H2O as stable cathode with impressive electrochemical performance for Ca ion battery. The potassium vanadate nanowires obtained by facile hydrothermal process (typical lengths of 0.5–1.5 μm, widths of 70–100 nm) deliver a high initial capacity of 113.9 mAh g−1 at current density of 20 mA g−1 and high capacity retention of 78.30% at 50 mA g−1 after 100 cycles. In addition, the reversible intercalation of calcium ion in this layered potassium vanadate material with stable crystal structure is verified by ex-situ XPS and XRD techniques, demonstrating that layered K2V6O16·2.7H2O could be a potential cathode material for calcium-ion batteries.

Defect, transport, and dopant properties of andradite garnet Ca3Fe2Si3O12

There is growing interest to discover suitable calcium containing oxides that can be used as electrode materials in calcium ion batteries. A comprehensive computational investigation of ionic defects and Ca-ion diffusion in Ca-bearing oxide materials at the atomic level is important so as to predict their suitability for use in Ca-ion batteries. In this study, we apply atomistic simulation techniques to examine the energetics of defects, dopants, and Ca-ion diffusion in Ca3Fe2Si3O12. The calculations suggest that the Ca/Fe anti-site defect is the most favorable intrinsic defect causing such significant disorder, which would be sensitive to synthesis conditions. Diffusion of Ca2+ ions within Ca3Fe2Si3O12 is three-dimensional, with the activation energy of migration of 2.63 eV inferring slow ionic conductivity. The most favorable isovalent defects are Mn2+, Sc3+, and Ge4+ on Ca, Fe, and Si, respectively, for this process. The formation of extra calcium was considered to increase the capacity and diffusion of Ca in this material. It is found that Al3+ and Mn2+ are the candidate dopants on the Si and Fe sites, respectively, for this process and there is a reduction observed in the activation energies. The electronic structures of favorable dopant configurations are discussed using density functional theory simulations.

Aqueous Calcium-Ion Battery Based on a Mesoporous Organic Anode and a Manganite Cathode with Long Cycling Performance.

Aqueous batteries have attracted increasing and extensive attention, owing to their high safety, low cost, and low toxicity. These factors have become increasingly important, given the current focus on the rapid development of green energy technologies. In particular, multivalent-ion batteries are emerging as alternatives to lithium-ion batteries. Unfortunately, magnesium and aluminum ions have high polarization strengths that are unfavorable for electrode materials. In contrast, calcium-ion batteries successfully avoid the problem of high polarization. Herein, an aqueous calcium-ion battery (CIBs) based on mesoporous silica SBA-15 with a two-dimensional hexagonal through-hole structure is reported. The poly(3,4,9,10-perylentetracarboxylic diimide) (PPTCDI) organic material supported on SBA-15 is used as the anode and displays a capacity of 201 mAh g-1 , with a stable cycling performance of 95 % capacity retention after 1500 cycles. SBA-15@PPTCDI‖Ca2 MnO4 aqueous CIBs demonstrate a high energy density of 130.6 Wh kg-1 in the cell voltage range from 0.0 to 1.8 V, with a high capacity and excellent cycling stability. As the anode material, SBA-15@PPTCDI shows special bonding of redox electrons that leads to its highly stable performance, which paves the way for addressing the shortcomings of traditional organic electrode materials. The localization and delocalization of the redox electron offers additional voltage stability, which is another important advantage for practical applications. This study highlights the potential of organic electrode materials for applications in aqueous multivalent-metal-ion batteries.

Calcium Molybdenum Bronze as a Stable High-Capacity Cathode Material for Calcium-Ion Batteries

Calcium-ion batteries (CIBs) are gaining increasing attention due to their theoretically high capacity, owing to the divalency of calcium, and low cost. However, only a few calcium insertion electrode materials are reported, and most of them exhibit low capacity or poor cyclability in nonaqueous electrolytes. Herein, we demonstrated high-performance calcium molybdenum bronze Ca0.13MoO3·(H2O)0.41 as a potential CIB cathode material at room temperature, with a reversible discharge capacity of 192 mAh g–1 at 86 mA g–1, an average voltage of 2.4 V (vs Ca/Ca2+), and excellent cyclability. This work provides the feasibility of developing high-capacity CIB cathode materials.

(Invited) Nasicon-Type NaV2(PO4)3 As a Cathode Material for Calcium-Ion Batteries

Li-ion batteries (LIBs) have been the most prevailing rechargeable batteries for the last three decades. However, the present LIBs have energy densities close to the theoretical limits, and the Li resources are scarce. Calcium-ion batteries (CIBs) are one of the promising candidates to overcome such limitations of LIBs. The divalency of calcium as the carrier ion can increase the capacity of a host material because two electrons are transferred per carrier ion. The earth-abundance of calcium resources provides potential cost-effectiveness to the products. Calcium has the redox potential (Ca/Ca2+ = −2.87 V vs. SHE) close to Li, potentially leading to a higher cell operating voltage. Calcium ion also has a relatively low effective intercalant-ion charge density (0.49 e/Å3), compared to other multivalent cations such as Mg2+ (1.28 e/Å3), Zn2+ (1.18 e/Å3), and Al3+ (4.55 e/Å3), enabling fast diffusion kinetics for Ca ions in solids as well as in electrolytes. Recent discoveries of reversible plating or alloying of calcium provoked considerable interest in calcium-based rechargeable batteries. Theoretical calculations also predict that the energy barriers for Ca diffusion are lower than other multivalent ions in some structures, and the development of positive materials are anticipated. However, only a few positive materials have been reported so far, only to exhibit low energy-storage capability and poor cyclability. In this work, we report NASICON-type NaV2(PO4)3 as a cathode material for nonaqueous CIBs, with high capacity and voltage with a good cyclability. This work demonstrates experimentally that an oxide material can be a good host structure for Ca diffusion at room temperature with high energy-storage capability.

A Highly Conductive and Thermally Stable Ionic Liquid Gel Electrolyte for Calcium-Ion Batteries

Calcium-ion batteries are promising alternatives for post-lithium-ion batteries. However, their progress remains limited by challenges associated with the development of stable and effective electr...

Enabling High Performance Calcium-Ion Batteries from Prussian Blue and Metal–Organic Compound Materials

Full cell calcium-ion batteries (CIBs) were fabricated from Prussian blue and metal–organic compound (MOC) materials and characterized. The anode materials were prepared via the simple precipitatio...

Stable and High-Power Calcium-Ion Batteries Enabled by Calcium Intercalation into Graphite.

Calcium-ion batteries (CIBs) are considered to be promising next-generation energy storage systems because of the natural abundance of calcium and the multivalent calcium ions with low redox potential close to that of lithium. However, the practical realization of high-energy and high-power CIBs is elusive owing to the lack of suitable electrodes and the sluggish diffusion of calcium ions in most intercalation hosts. Herein, it is demonstrated that calcium-ion intercalation can be remarkably fast and reversible in natural graphite, constituting the first step toward the realization of high-power calcium electrodes. It is shown that a graphite electrode exhibits an exceptionally high rate capability up to 2 A g-1 , delivering ≈75% of the specific capacity at 50 mA g-1 with full calcium intercalation in graphite corresponding to ≈97 mAh g-1 . Moreover, the capacity stably maintains over 200 cycles without notable cycle degradation. It is found that the calcium ions are intercalated into graphite galleries with a staging process. The intercalation mechanisms of the "calciated" graphite are elucidated using a suite of techniques including synchrotron in situ X-ray diffraction, nuclear magnetic resonance, and first-principles calculations. The versatile intercalation chemistry of graphite observed here is expected to spur the development of high-power CIBs.

Graphite as a Long-Life Ca2+-Intercalation Anode and its Implementation for Rocking-Chair Type Calcium-Ion Batteries.

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.

Electrolyte Dependency on Ca2+ Insertion/Extraction Properties of V2O5

Recently, calcium ion batteries (CIBs) have been attracting attention as next-generation batteries because of their higher energy density, higher safety, lower costs and more abundant elements than lithium ion batteries (LIBs). On the other hand, CIBs have several problems impeding their progress. One critical issue is the development of a suitable organic electrolyte without a negative impact on the electrochemical properties of the electrode material. In our past study, we reported that the overvoltage decreased when water was added to the electrolyte1. One reason for the decrease of overvoltage is a change in the electrolyte structure such as the solvation structure and the degree of salt dissociation. In this study, we investigated the electrolyte structure with varied organic solvent species and salt concentration, and examined the electrolyte dependency on Ca2+ insertion and extraction properties of V2O5. We used Ca(TFSI)2 as the electrolyte salt, which was vacuum dried at 150℃ for 12h before use. For the organic solvents, EC: DMC (1:1 in vol.), EC: PC (1:1 in vol.), triglyme (G3) and acetonitrile (AN) were used. The concentration of electrolyte was adjusted to 0.2-0.5 molL-1.V2O5 nano-sheet synthesized by hydrothermal-assisted method2 was used as the working electrode. The electrode was prepared by mixing the synthesized V2O5, acetylene black and polyvinylidene difluoride dissolved in N-methyl-2pyrrolidinone with a weight ratio of 70:20:10, then coated onto a carbon coated titanium foil and vacuum dried at 120℃ overnight. A constant current discharge-charge experiment was performed at 0.05C-1C. The results of electrolyte structure analysis showed that the contact ion pair (CIP) decreased as the dipole moment of the organic solvent decreased except for G3. When G3 was used, it is considered that the solvent-separated ion pair (SSIP) was formed because of the small dipole moment of G3. Interestingly, a decrease in the amount of CIP due to the decrease of concentration was observed when using EC: DMC or EC: PC, but not when using G3 or AN. The results of the constant current discharge-charge experiment were strongly related to the amount of CIP. The coulombic efficiency tended to improve as the amount of CIP decreased except for using G3, in particular, a high coulombic efficiency of 95% was shown when using 0.3M Ca(TFSI)2/EC: DMC. As a factor of the instability of electrolyte when G3 was used, Ca2+(G3)TFSI- SSIP may also be reductively unstable as Ca2+TFSI- CIP. On the other hand, G3-based electrolyte showed the lowest overvoltage and the best rate performance. According to the surface analysis of the electrode after the test, the concentration of calcium in the surface film was less than that for other solvents. It suggests that the nature of the surface film may be related to a decrease in the overvoltage. When a solvent other than G3 was used, the overvoltage decreased as the amount of CIP decreased, and a relatively high rate performance was obtained for 0.3 molL-1 Ca(TFSI)2/EC: DMC, similar to the tendency of coulombic efficiency. Reference s : [1] Y. Murata et al., Electrochim. Acta 294 (2019) 210-216. [2] H. Song et al., J. Power Sources 294 (2015) 1-7.

Layered Iron Vanadate As a High-Energy Cathode Material for Nonaqueous Calcium-Ion Batteries

Calcium-ion batteries (CIBs) are one of the promising candidates for post-lithium-ion batteries. However, only a few types of host materials are known to intercalate calcium ions reversibly in a nonaqueous electrolyte. Here, we demonstrate the electrochemical performances and evidence of calcium-ion intercalation into iron vanadate, FeV3O9∙xH2O, as a cathode material for CIBs at ambient temperature. FeV3O9∙xH2O was prepared via a facile water-bath method. It shows reversible calcium intercalation with a first discharge capacity of 334.4 mAh g−1 at 20 mA g−1 rate with an average voltage of ~2.26 V (vs. Ca/Ca2+) and excellent capacity retention in an electrolyte of 0.5 M Ca(ClO4)2 in acetonitrile. The high performance of the material with a layered structure and a wide range of vanadium oxidation states provides insights into the search for new oxide-based high-energy cathode materials for CIBs.

Calcium-Ion Batteries: Identifying Ideal Electrolytes for Next-Generation Energy Storage Using Computational Analysis

Calcium-ion batteries show promise as high-density, next-generation replacements for current lithium-ion batteries. The precise chemical structure of the carbonate electrolyte solvent has a large i...

Bilayered Mg0.25V2O5·H2O as a Stable Cathode for Rechargeable Ca-Ion Batteries

The calcium-ion battery is an emerging energy storage system that has attracted considerable attention recently. However, the absence of high-performance cathode materials is one of the main challe...

Effect of Ball Milling Process on Electrochemical Properties of Copper Hexacyanoferrate Active Material for Calcium-Ion Batteries

This study investigates the electrochemical properties of ball-milled copper hexacyanoferrate (CuHCF), a Prussian blue analogue, as a cathode material in aqueous calcium-ion batteries (CIBs). X-ray diffraction analysis confirmed that the ball milling process did not destroy the crystal structure of the CuHCF active material. The general grain size and crystal surface of the synthesized CuHCF active materials were confirmed from the scanning electron microscopy (SEM) images. The electrochemical test results revealed that prolonged ball milling improved the charge/discharge capacity in the initial cycle. After 200 cycles, structural collapse of the CuHCF electrode occurred, as observed by SEM.

Electrochemical Properties of Ball-Milled Zinc Hexacyanoferrate Cathode Material for Calcium Ion Batteries

In this study, ball-milled zinc hexacyanoferrate (ZnHCF) active materials, a Prussian blue analogues (PBAs), were applied in the aqueous rechargeable calcium-ion battery (ARCIB) system. X-ray diffraction (XRD) analysis confirmed that there was no structural destruction of the ZnHCF active materials upon ball milling. A comparison of the pristine and ball-milled ZnHCF active materials by scanning electron microscopy (SEM) confirmed that the ball-milled ZnHCF active material particles were smaller than those of the pristine material. The highest initial charge/discharge capacity was observed on the electrode based on the ZnHCF active material that was ball-milled for 9 h. As the time of the ball mill process was reduced, the initial charge/discharge capacity of the electrodes gradually decreased. XRD and SEM confirmed the eventual collapse of the electrode structure, which explained why the increased capacity of the ARCIB system was not sustained.