Research Development on Sodium-Ion Batteries

Room-temperature rechargeable sodium-ion batteries are considered as a promising alternative technology for grid and other storage applications due to their competitive cost benefit and sustainable resource supply, triumphing other battery systems on the market. To facilitate the practical realization of the sodium-ion technology, the energy density of sodium-ion batteries needs to be boosted to the level of current commercial Li-ion batteries. An effective approach would be to elevate the operating voltage of the battery, which requires the use of electrochemically stable cathode materials with high voltage versus Na+/Na. This review summarizes the recent progress with the emerging high-voltage cathode materials for room-temperature sodium-ion batteries, which include layered transitional-metal oxides, Na-rich materials, and polyanion compounds. The key challenges and corresponding strategies for these materials are also discussed, with an emphasis placed on the intrinsic structural properties, Na storage electrochemistry, and the voltage variation tendency with respect to the redox reactions. The insights presented in this article can serve as a guide for improving the energy densities of room-temperature Na-ion batteries.

Progress in High-Voltage Cathode Materials for Rechargeable Sodium-Ion Batteries

Sodium-ion batteries, representative members of the post-lithium-battery club, are very attractive and promising for large-scale energy storage applications. The increasing technological improvements in sodium-ion batteries (Na-ion batteries) are being driven by the demand for Na-based electrode materials that are resource-abundant, cost-effective, and long lasting. Polyanion-type compounds are among the most promising electrode materials for Na-ion batteries due to their stability, safety, and suitable operating voltages. The most representative polyanion-type electrode materials are Na3V2(PO4)3 and NaTi2(PO4)3 for Na-based cathode and anode materials, respectively. Both show superior electrochemical properties and attractive prospects in terms of their development and application in Na-ion batteries. Carbonophosphate Na3MnCO3PO4 and amorphous FePO4 have also recently emerged and are contributing to further developing the research scope of polyanion-type Na-ion batteries. However, the typical low conductivity and relatively low capacity performance of such materials still restrict their development. This paper presents a brief review of the research progress of polyanion-type electrode materials for Na-ion batteries, summarizing recent accomplishments, highlighting emerging strategies, and discussing the remaining challenges of such systems.

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Polyanion-Type Electrode Materials for Sodium-Ion Batteries.

The development of efficient and stable water oxidation catalysts is necessary for the realization of practically viable water-splitting systems. Although extensive studies have focused on the metal-oxide catalysts, the effect of metal coordination on the catalytic ability remains still elusive. Here we select four cobalt-based phosphate catalysts with various cobalt- and phosphate-group coordination as a platform to better understand the catalytic activity of cobalt-based materials. Although they exhibit various catalytic activities and stabilities during water oxidation, Na2CoP2O7 with distorted cobalt tetrahedral geometry shows high activity comparable to that of amorphous cobalt phosphate under neutral conditions, along with high structural stability. First-principles calculations suggest that the surface reorganization by the pyrophosphate ligand induces a highly distorted tetrahedral geometry, where water molecules can favourably bind, resulting in a low overpotential (∼0.42 eV). Our findings emphasize the importance of local cobalt coordination in the catalysis and suggest the possible effect of polyanions on the water oxidation chemistry.

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Coordination tuning of cobalt phosphates towards efficient water oxidation catalyst

Room-temperature sodium-ion batteries (SIBs) are regarded as promising candidates for smart grids and large-scale energy storage systems (EESs) due to their significant benefits of abundant and low-cost sodium resource. Among the previously reported cathode materials for SIBs, layered transition-metal oxides and polyanion-type materials are considered to be the most attractive options. Although many layered transition-metal oxides can provide high capacity due to their small molecular weight, their further application is hindered by low output voltage (mostly lower than 3.5 V), irreversible phase transition as well as storage instability. Comparatively, polyanion-type materials exhibit higher operating potentials due to the inductive effect of polyanion groups. Their robust 3D framework significantly decreases the structural variations during sodium ion de/intercalation. Moreover, the effect of strong X-O (X = S, P, Si, etc.) covalent bonds can effectively inhibit oxygen evolution. These advantages contribute to the superior cycle stability and high safety of polyanion-type materials. However, low electronic conductivity and limited capacity still restrict their further application. This review summarizes the recent progress of polyanion-type materials for SIBs, which include phosphates, fluorophosphates, pyrophosphates, mixed phosphates, sulfates, and silicates. We also discuss the remaining challenges and corresponding strategies for polyanion-type materials. We hope this review can provide some insights into the development of polyanionic materials.

Polyanion-type cathode materials for sodium-ion batteries

Study of Sr2−xPbxP2O7 (0⩽x⩽2) solid solutions and single-crystal structure of Sr1.34Pb0.66P2O7

The structure of the title mixed trimetallic diphosphate, K2Sr3Mn2(P2O7)3, is constructed of a three-dimensional matrix composed of SrO8–10, MnO5 and PO4 polyhedra. The sharing of O atoms between these polyhedra creates tunnels of large dimensions parallel to (010), in which are found columns of K+ ions. Thus, the presence of several cations differing in size in the solid matrix leads to the formation of large tunnels and potential conductivity.

Dipotassium tristrontium dimanganese tris­(diphosphate)

A new europium(III) silicophosphate, whose formula may be considered to be Eu2Si(PO4)2(P2O7), has been found to consist of phospho­silicate chains with Si—O—P—O—P—O—Si backbones extending in the a direction. The P2O7 group and the Si atom both lie on crystallographic twofold axes. Tetrahedral silicon is further bound to two monophosphate groups. This is a silicophosphate of previously unseen type.

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Dieuropium(III) silicodimonophosphatediphosphate

Rheology, calorimetry and electrical conductivity related-properties for monitoring the dissolution and precipitation process of cement-fly ash mixtures

Ali Boukhari

Papers

Study of Sr2−xPbxP2O7 (0⩽x⩽2) solid solutions and single-crystal structure of Sr1.34Pb0.66P2O7

Dipotassium tristrontium dimanganese tris(diphosphate)

Dieuropium(III) silicodimonophosphatediphosphate

Rheology, calorimetry and electrical conductivity related-properties for monitoring the dissolution and precipitation process of cement-fly ash mixtures

Synthesis and Characterization of (Zn,M)2P2O7 (M: Mn, Cu).

Ali Boukhari

Papers

Study of Sr2−xPbxP2O7 (0⩽x⩽2) solid solutions and single-crystal structure of Sr1.34Pb0.66P2O7

Dipotassium tristrontium dimanganese tris­(diphosphate)

Dieuropium(III) silicodimonophosphatediphosphate

Rheology, calorimetry and electrical conductivity related-properties for monitoring the dissolution and precipitation process of cement-fly ash mixtures

Synthesis and Characterization of (Zn,M)2P2O7 (M: Mn, Cu).

Dipotassium tristrontium dimanganese tris(diphosphate)