Electrochemical intercalation of Ca2+ ions into TiS2 in organic electrolytes at room temperature

Freestanding Ammonium Vanadate Composite Cathodes with Lattice Self-Regulation and Ion Exchange for Long-Lasting Ca-Ion Batteries

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 (NH4)2V6O16·1.35H2O@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 NH4 + and Ca2+ during cycling are revealed. The lattice self-regulation of V─O layers is observed and the layered vanadium oxides with Ca2+ 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.

First-principles calculations of bulk XTe2 (X = Mo, W) as anode materials for Ca ion battery

CONTEXT

Transition metal chalcogenides are excellent anode materials for calcium ion batteries (CIBs). In this study, the structural stability, electronic structure, and diffusion barrier of bulk XTe2 (X = Mo, W) were studied by first-principles calculations within the framework of density functional theory. The density of states analysis shows the metal behavior of XTe2 (X = Mo, W) during calcification. The voltage ranges of CayMoTe2 and CayWTe2 are 1.53-0.45 V and 1.48-0.41 V (y = 0-5), respectively. The diffusion barrier of Ca+ through XTe2 indicates that the compressive strain promotes the diffusion of calcium through XTe2. XTe2 is considered to be a promising electrode material for CIBs.

METHODS

In this paper, the transition metal chalcogenides model is constructed by Material Studio 8.0, and the first-principles calculation is carried out by CASTEP module.

Towards a Stable Layered Vanadium Oxide Cathode for High-Capacity Calcium Batteries

Calcium-based batteries have promising advantages over multivalent ion batteries. However, the fabrication of highly efficient calcium batteries is limited by the quality of available cathode materials, which motivates the exploration of electrodes that can enable reversible, stable Ca²⁺ intercalation. Herein, layered vanadium oxide Mg_x V₂ O₅ ·nH₂ O is used as a calcium battery cathode, and it exhibits a high capacity of 195.5 mA h g^-1 at 20 mA g^-1 and an outstanding cycling life (93.6% capacity retention after 2500 cycles at 1 A g^-1 ). Combining theoretical analysis and experimental design, a series of layered oxides (M_x V₂ O₅ ·nH₂ O, M = Mg, Ca, Sr) is selected as a model system to identify the Ca storage mechanism. It is found that the hydrated alkaline earth metal ions in the vanadium-based layered oxide interlayers play a critical role as pillared stabilizers to facilitate Ca²⁺ insertion/extraction. Compared with Ca²⁺ and Sr²⁺ , the presence of Mg²⁺ provides vanadium oxides with a rigid framework that allows for minimized volume fluctuation (a tiny variation of ≈0.15 Å of the interlayer spacing). Such an understanding of the Ca storage mechanism is a key step in the rational design and selection of materials for calcium batteries to achieve a high capacity and long cycle life.

A new high-voltage calcium intercalation host for ultra-stable and high-power calcium rechargeable batteries

Rechargeable calcium batteries have attracted increasing attention as promising multivalent ion battery systems due to the high abundance of calcium. However, the development has been hampered by the lack of suitable cathodes to accommodate the large and divalent Ca2+ ions at a high redox potential with sufficiently fast ionic conduction. Herein, we report a new intercalation host which presents 500 cycles with a capacity retention of 90% and a remarkable power capability at ~3.2 V (vs. Ca/Ca2+) in a calcium battery. The cathode material derived from Na0.5VPO4.8F0.7 is demonstrated to reversibly accommodate a large amount of Ca2+ ions, forming a series of CaxNa0.5VPO4.8F0.7 (0 < x < 0.5) phases without any noticeable structural degradation. The robust framework enables one of the smallest volume changes (1.4%) and the lowest diffusion barriers for Ca2+ among the cathodes reported to date, offering the basis for the outstanding cycle life and power capability.

Recent Advances and Perspectives on Calcium-Ion Storage: Key Materials and Devices

The urgent demand for cost-effective energy storage devices for large-scale applications has led to the development of several beyond-lithium energy storage systems (EESs). Among them, calcium-ion batteries (CIBs) are attractive due to abundant calcium resources, excellent volumetric and gravimetric capacities of Ca metal anode, and potential high energy density coming from the multivalent feature of Ca-ion. Therefore, the exploration of CIBs electrode materials and the construction of CIBs devices are gaining increasing research interest. Relevant publications cover a wide range of materials by both theoretical and experimental investigations, whereas the performances of rocking-chair CIBs have been unsatisfactory. Meanwhile, multi-ion strategies using more than one ion as the charge carrier have been demonstrated to be feasible and promising options in realizing room temperature CIBs. The summary and reflection of previous studies would provide useful information for future exploration and optimization. In this circumstance, this paper overviews the reported CIBs electrode materials, including both anode and cathode, and presents the latest progress of multi-ion strategies in CIBs. Fundamental challenges, potential solutions, and opportunities are accordingly proposed, mimicking other more mature EESs. This review may promote the development of electrode materials and accelerate the construction of low-cost and high-performance CIBs.

VOPO4·2H2O as a new cathode material for rechargeable Ca-ion batteries

VOPO₄·2H₂O, as a new cathode material for Ca-ion batteries, exhibits a discharge capacity of 100.6 mA h g^-1, excellent cycling stability (200 cycles) and good rate performance (42.7 mA h g^-1 at 200 mA g^-1). In situ X-ray diffraction and in situ Raman results demonstrate the calcium-ion-storage mechanism of VOPO₄·2H₂O is a single-phase reaction based on asymmetric Ca²⁺ insertion and deinsertion.

Achievements, Challenges, and Prospects of Calcium Batteries

This Review flows from past attempts to develop a (rechargeable) battery technology based on Ca via crucial breakthroughs to arrive at a comprehensive discussion of the current challenges at hand. The realization of a rechargeable Ca battery technology primarily requires identification and development of suitable electrodes and electrolytes, which is why we here cover the progress starting from the fundamental electrode/electrolyte requirements, concepts, materials, and compositions employed and finally a critical analysis of the state-of-the-art, allowing us to conclude with the particular roadblocks still existing. As for crucial breakthroughs, reversible plating and stripping of calcium at the metal-anode interface was achieved only recently and for very specific electrolyte formulations. Therefore, while much of the current research aims at finding suitable cathodes to achieve proof-of-concept for a full Ca battery, the spectrum of electrolytes researched is also expanded. Compatibility of cell components is essential, and to ensure this, proper characterization is needed, which requires design of a multitude of reliable experimental setups and sometimes methodology development beyond that of other next generation battery technologies. Finally, we conclude with recommendations for future strategies to make best use of the current advances in materials science combined with computational design, electrochemistry, and battery engineering, all to propel the Ca battery technology to reality and ultimately reach its full potential for energy storage.