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

Stabilizing metal battery anodes through the design of solid electrolyte interphases

Fast Rate and Long Life Potassium-Ion Based Dual-Ion Battery through 3D Porous Organic Negative Electrode

Sulfide electrolyte (SE)-based all-solid-state lithium batteries (ASSLBs) have gained worldwide attention because of their instrinsic safety and higher energy density over conventional lithium-ion batteries (LIBs). However, poor air stability of SEs, detrimental interfacial reactions, insufficient solid–solid ionic contact, and the large gap between fundamental study and practical engineering have impeded the commercialization of SE-based ASSLBs. This review aims to combine fundamental and engineering perspectives to rationally design practical SE-based ASSLBs with high energy density, covering SEs, interface, and practical all-solid-state pouch cells. First, the latest progress of typical pseudo-binary, pseudo-ternary, and pseudo-quaternary SEs is summarized, and effective strategies to improve ionic conductivity and chemical and electrochemical stability are highlighted. Moreover, challenges and strategies at the cathode and anode interfaces are reviewed separately. Furthermore, advanced in situ characterization techniques are examined to better understand the interface of ASSLBs. Encouraging demonstrations of SE-based all-solid-state lithium-ion and all-solid-state lithium–sulfur batteries are exemplified. Most importantly, energy-density-oriented all-solid-state pouch cells are designed using practical engineering parameters. The proposed design can serve as a quantitative framework to predict the practical energy density of SE-based all-solid-state pouch cells in future. Finally, future directions and our perspectives in SE-based ASSLBs are presented.

All-solid-state lithium batteries enabled by sulfide electrolytes: from fundamental research to practical engineering design

Sodium-ion batteries (SIBs) have attracted incremental attention as a promising candidate for grid-scale energy-storage applications. To meet practical requirements, searching for new cathode materials with high energy density is of great importance. Herein, a novel Na superionic conductor (NASICON)-type Na4 MnCr(PO4 )3 is developed as a high-energy cathode for SIBs. The Na4 MnCr(PO4 )3 nanoparticles homogeneously embedded in a carbon matrix can present an extraordinary reversible capacity of 160.5 mA h g-1 with three-electron reaction at ≈3.53 V during the Na+ extraction/insertion process, realizing an unprecedentedly high energy density of 566.5 Wh kg-1 in the phosphate cathodes for SIBs. It is intriguing to reveal the underlying mechanism of the unique Mn2+ /Mn3+ , Mn3+ /Mn4+ , and Cr3+ /Cr4+ redox couples via X-ray absorption near-edge structure spectroscopy. The whole electrochemical reaction undergoes highly reversible single-phase and biphasic transitions with a moderate volume change of 7.7% through in situ X-ray diffraction and ex situ high-energy synchrotron X-ray diffraction. Combining density functional theory (DFT) calculations with the galvanostatic intermittent titration technique, the superior performance is ascribed to the low ionic-migration energy barrier and desirable Na-ion diffusion kinetics. The present work can offer a new insight into the design of multielectron-reaction cathode materials for SIBs.

A Novel NASICON-Type Na4 MnCr(PO4 )3 Demonstrating the Energy Density Record of Phosphate Cathodes for Sodium-Ion Batteries.

Electrochemo‐Mechanical Effects on Structural Integrity of Ni‐Rich Cathodes with Different Microstructures in All Solid‐State Batteries

The growth of sodium dendrites and the associated solid electrolyte interface (SEI) layer is a critical and fundamental issue influencing the safety and cycling lifespan of sodium batteries. In this work, we use in-situ 23Na magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) techniques, along with an innovative analytical approach, to provide space-resolved and quantitative insights into the formation and evolution of sodium metal microstructures (SMSs; that is, dendritic and mossy Na metal) during the deposition and stripping processes. Our results reveal that the growing SMSs give rise to a linear increase in the overpotential until a transition voltage of 0.15 V is reached, at which point violent electrochemical decomposition of the electrolyte is triggered, leading to the formation of mossy-type SMSs and rapid battery failure. In addition, we determined the existence of NaH in the SEI on sodium metal with ex-situ NMR results. The poor electronic conductivity of NaH is beneficial for the growth of a stable SEI on sodium metal. Magnetic resonance imaging and spectroscopy provide quantitative insights into the growth of sodium microstructures in batteries.

Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy.

Research Progress in Multielectron Reactions in Polyanionic Materials for Sodium‐Ion Batteries

Practical use of lithium (Li) metal for high–energy density lithium metal batteries has been prevented by the continuous formation of Li dendrites, electrochemically isolated Li metal, and the irre...

Ziteng Liang

Papers

Electrochemo‐Mechanical Effects on Structural Integrity of Ni‐Rich Cathodes with Different Microstructures in All Solid‐State Batteries

Visualizing the growth process of sodium microstructures in sodium batteries by in-situ 23Na MRI and NMR spectroscopy.

Research Progress in Multielectron Reactions in Polyanionic Materials for Sodium‐Ion Batteries

Quantitatively analyzing the failure processes of rechargeable Li metal batteries.

Al and Fe-containing Mn-based layered cathode with controlled vacancies for high-rate sodium ion batteries