Ultrastable and High Energy Calcium Rechargeable Batteries Enabled by Calcium Intercalation in a NASICON Cathode

Ca-ion batteries (CIBs) have been considered a promising candidate for the next-generation energy storage technology owing to the abundant calcium element and the low reduction potential of Ca²⁺ /Ca. However, the large size and divalent nature of Ca²⁺ induce significant volume change and sluggish ion mobility in intercalation cathodes, leading to poor reversibly and low energy/power densities for CIBs. Herein, a polyanionic Na superionic conduction (NASICON)-typed Na-vacant Na₁ V₂ (PO₄ )₂ F₃ (N₁ PVF₃ ) with sufficient interstitial spaces is reported as ultra-stable and high-energy Ca ion cathodes. The N₁ PVF₃ delivers exceptionally high Ca storage capacities of 110 and 65 mAh g^-1 at 10 and 500 mA g^-1 , respectively, and a record-long cyclability of 2000 cycles. More interestingly, by tailoring the fluorine content in N₁ PVF_x (1 ≤ x ≤ 3), the high working potential of 3.5 V versus Ca²⁺ /Ca is achievable. In conjunction with Ca metal anode and a compatible electrolyte, Ca metal batteries with N₁ VPF₃ cathodes are constructed, which deliver an initial energy density of 342 W h kg^-1 , representing one of the highest values thus far reported for CIBs. Origins of the uncommonly stable and high-power capabilities for N₁ PVF₃ are elucidated as the small volume changes and low cation diffusion barriers among the cathodes.

Promises and Challenges of Next-Generation "Beyond Li-ion" Batteries for Electric Vehicles and Grid Decarbonization

The tremendous improvement in performance and cost of lithium-ion batteries (LIBs) have made them the technology of choice for electrical energy storage. While established battery chemistries and cell architectures for Li-ion batteries achieve good power and energy density, LIBs are unlikely to meet all the performance, cost, and scaling targets required for energy storage, in particular, in large-scale applications such as electrified transportation and grids. The demand to further reduce cost and/or increase energy density, as well as the growing concern related to natural resource needs for Li-ion have accelerated the investigation of so-called "beyond Li-ion" technologies. In this review, we will discuss the recent achievements, challenges, and opportunities of four important "beyond Li-ion" technologies: Na-ion batteries, K-ion batteries, all-solid-state batteries, and multivalent batteries. The fundamental science behind the challenges, and potential solutions toward the goals of a low-cost and/or high-energy-density future, are discussed in detail for each technology. While it is unlikely that any given new technology will fully replace Li-ion in the near future, "beyond Li-ion" technologies should be thought of as opportunities for energy storage to grow into mid/large-scale applications.

Decreasing the Ion Diffusion Pathways for the Intercalation of Multivalent Cations into One-Dimensional TiS2 Nanobelt Arrays

The sparse selection of available cathode materials that allow for reversible intercalation (deintercalation) of Al³⁺ species represents a major hurdle in the development of efficient Al-ion batteries. Herein, we developed cathodes based on TiS₂ nanobelts that are capable of withstanding the high charge density of Al-ion species with minimal host lattice/ion interactions. The fabricated TiS₂ nanobelts are highly anisotropic and are directly grown on a carbon current collector yielding a spatially controlled array. The sum of evidence presented in this work indicates that one-dimensional TiS₂ nanobelt arrays can reversibly accommodate an unprecedented amount of Al ion species within their layered structure with no significant volume expansion as well as full retention of the nanobelt morphology. Thus, the one-dimensional morphology, nanoscale dimensions, short ion diffusion paths, high electrical conductivity, and absence of additives that hinder ion migration lead to Al-based TiS₂ electrochemical devices exhibiting high specific capacity, less capacity fade, and resilience under higher cycling rates at both room temperature and elevated temperatures when compared to TiS₂ platelets. We also present the effects of sulfur vacancies on the electrochemical performance of Al-based TiS_2-x nanobelt array batteries. Although Al-ion batteries are still in their infancy, we believe our TiS₂ nanobelt array cathode insertion hosts may play an important role in addressing the poor kinetics of solid-state Al-ion diffusion to enable efficient alternatives beyond lithium energy storage devices.

Fe2CS2 MXene: a promising electrode for Al-ion batteries

Aluminum-ion batteries are one of the most promising candidates for next-generation rechargeable batteries. However, the strong electrostatic interactions between highly ionic Al³⁺ and the electrode hinder the reversible intercalation and fast transport of Al ions. This study suggests a design strategy for a MXene electrode for realizing high-performance Al-ion batteries. Instead of early transition metals and oxygen, the metal M and surface termination T of general MXene (M_n+1X_nT_x), the use of late transition metals and sulfur can dramatically improve the capacity and rate capability, respectively. The capacity increases 2.2-fold, from 288 mA h g^-1 (Ti₂CO₂) to 642 mA h g^-1 (Fe₂CS₂), and the Al-ion diffusivity increases 10⁴-fold, from 2.8 × 10^-16 cm² s^-1 (Ti₂CO₂) to 6.0 × 10^-12 cm² s^-1 (Fe₂CS₂). This remarkable performance enhancement is due to the charge redistribution in the M and T layers by the late transition metals and the shallowing of the potential energy surface for Al-ion intercalation by sulfur.

Computational investigation of chalcogenide spinel conductors for all-solid-state Mg batteries

Seven MgLn2X4 (Ln = lanthanoid, X = S, Se) spinels are calculated with density functional theory to have low barriers for Mg migration (<380 meV) and are stable or nearly stable (within 50 meV per atom of stability with respect to competing structures and compositions). As the size of the Ln increases, Mg mobility is found to increase, but stability in the spinel structure is found to decrease.

Challenges and benefits of post-lithium-ion batteries

Post-Li-ion batteries based on Na, Mg, and Al offer substantial electrochemical and economic advantages in comparison with Li-ion batteries.

Paving the Path toward Reliable Cathode Materials for Aluminum-Ion Batteries

Aluminum metal is a high-energy-density carrier with low cost, and thus endows rechargeable aluminum batteries (RABs) with the potential to act as an inexpensive and efficient electrochemical device, so as to supplement the increasing demand for energy storage and conversion. Despite the enticing aspects regarding cost and energy density, the poor reversibility of electrodes has limited the pursuit of RABs for a long time. Fortunately, ionic-liquid electrolytes enable reversible aluminum plating/stripping at room temperature, and they lay the very foundation of RABs. In order to integrate with the aluminum-metal anode, the selection of the cathode is pivotal, but is limited at present. The scant option of a reliable cathode can be accounted for by the intrinsic high charge density of Al³⁺ ions, which results in sluggish diffusion. Hence, reliable cathode materials are a key challenge of burgeoning RABs. Herein, the main focus is on the insertion cathodes for RABs also termed aluminum-ion batteries, and the recent progress and optimization methods are summarized. Finally, an outlook is presented to navigate the possible future work.

First-principles study of VPO4O as a cathode material for rechargeable Mg batteries

The electrochemical properties of VPO₄O as a cathode for Mg batteries were studied by performing first principles calculations.

Opportunities and Challenges in the Development of Cathode Materials for Rechargeable Mg Batteries

Recent years have seen an intense and renewed interest in the Mg battery research, naming Mg-S the ≫Holy Grail≪ battery, and expectations that Mg battery system will be able to compete and surpass Li-ion batteries in a matter of years. Considerable progress has been achieved in the field of Mg electrolytes, where several new electrolytes with improved electrochemical performance and favorable chemical properties (non-corrosive, non-nucleophilic) were synthesized. Development in the field of cathodes remains a bit more elusive, with inorganic, sulfur, and organic cathodes all showing their upsides and downsides. This review highlights the recent progress in the field of Mg battery cathodes, paying a special attention to the performance and comparison of the different types of the cathodes. It also aims to define advantages and key challenges in the development of each type of cathodes and finally specific questions that should be addressed in the future research.

A critical review of cathodes for rechargeable Mg batteries

Benefiting from a higher volumetric capacity (3833 mA h cm-3 for Mg vs. 2046 mA h cm-3 for Li) and dendrite-free Mg metal anode, reversible Mg batteries (RMBs) are a promising chemistry for applications beyond Li ion batteries. However, RMBs are still severely restricted by the absence of high performance cathodes for any practical application. In this review, we provide a critical and rigorous review of Mg battery cathode materials, mainly reported since 2013, focusing on the impact of structure and composition on magnesiation kinetics. We discuss cathode materials, including intercalation compounds, conversion materials (O2, S, organic compounds), water co-intercalation cathodes (V2O5, MnO2etc.), as well as hybrid systems using Mg metal anode. Among them, intercalation cathodes are further categorized by 3D (Chevrel phase, spinel structure etc.), 2D (layered structure), and 1D materials (polyanion: phosphate and silicate), according to the diffusion pathway of Mg2+ in the framework. Instead of discussing every published work in detail, this review selects the most representative works and highlights the merits and challenges of each class of cathodes. Advances in theoretical analysis are also reviewed and compared with experimental results. This critical review will provide comprehensive knowledge of Mg cathodes and guidelines for exploring new cathodes for rechargeable magnesium batteries.

Ab initio study of Li, Mg and Al insertion into rutile VO2: fast diffusion and enhanced voltages for multivalent batteries

Vanadium oxides are among the most promising materials that can be used as electrodes in rechargeable metal-ion batteries. In this work, we systematically investigate thermodynamic, electronic, and kinetic properties associated with the insertion of Li, Mg and Al atoms into rutile VO₂. Using first-principles calculations, we systematically study the structural evolution and voltage curves of Li_xVO₂, Mg_xVO₂ and Al_xVO₂ (0 < x < 1) compounds. The calculated lithium intercalation voltage starts at 3.50 V for single-atom insertion and decreases to 2.23 V for full lithiation, to the LiVO₂ compound, which agrees well with the experimental results. The Mg insertion features a plateau about 1.6 V up to Mg_0.5VO₂ and then another plateau-like region at around 0.5 V up to Mg₁VO₂. The predicted voltage curve for Al insertion starts at 1.98 V, followed by two plateaus at 1.48 V and 1.17 V. The diffusion barrier of Li, Mg and Al in the tunnel structure of VO₂ is 0.06, 0.33 and 0.50 eV, respectively. The demonstrated excellent Li, Mg and Al mobility, high structural stability and high specific capacity suggest promising potential of rutile VO₂ electrodes especially for multivalent batteries.

A rechargeable aluminum-ion battery based on a VS2 nanosheet cathode

Herein, we designed VS₂ modified with graphene for AIBs, which delivers better cycling performance. Electrochemical characterizations confirm that the layered framework of VS₂ is suitable for Al³⁺ ions intercalation.