Polyanionic Cathode Materials for Practical Na-Ion Batteries toward High Energy Density and Long Cycle Life

Abstract

Na-ion batteries (NIBs) as a supplement to Li-ion batteries deliver huge application potential in the field of grid-scale energy storage. At present, it is a particularly imperative to advance commercialization of the NIBs after ten years of intensive research. Among the exploited cathodes for NIBs, polyanionic compounds have great commercial prospects due to their favorable ion diffusion channels, high safety, and superior structure stability determined by their unique structure framework; however, there is still a long way to go before large-scale industrialization can be realized. This outlook summarizes the recent progress of polyanion-type cathodes for NIBs and includes V-based, Fe-based, and Mn-based polyanionic compounds toward high energy density and long cycle lifespan. The remaining challenges and guidelines/suggestions for the design of the practically available polyanionic cathode materials with desirable energy density and cycling performance are presented. We hope that this outlook can provide some insights into the development of polyanionic cathodes for practical NIBs toward commercialization.

Towards High-Performance Sodium-Ion Batteries via the Phase Regulation Strategy

“…The overuse of fossil fuels has caused severe energy shortages and environmental contamination problems. Nowadays, building a sustainable development human society via large-scale renewable energy storage technology has become a key to solving these problems. − Sodium-ion batteries (SIBs) had attracted wide attention because they work based on similar principles as lithium-ion batteries but replace lithium with sodium element to eliminate lithium dependence. − In the commercialization process of SIBs, cathode materials played a decisive role. − Up to now, these cathode materials with commercialized prospects were mainly divided into the following three categories: transition-metal oxides, − polyanion compounds, − and prussian blue analogues. − Polyanion-type Fe-based phosphate cathode materials have received extensive interest due to their nontoxic nature, high structural stability, and lower cost. − The widely utilized olivine lithium iron phosphate (LiFePO 4 ), known as LFP, has served as a representative polyanionic iron-based phosphate cathode for lithium-ion batteries (LIBs). However, its counterpart, olivine NaFePO 4 , is not suitable for SIBs due to its complex synthesis route.…”

Development of High-Performance Iron-Based Phosphate Cathodes toward Practical Na-Ion Batteries

“…Na-ion batteries (NIBs) have received great attention in large-scale energy storage systems and smart grids because of huge abundance and low cost of sodium sources. − Substantial efforts have been devoted to developing cost-effective and high-performance cathodes these years toward commercially available NIBs. − Particularly, the benign and cheap iron-based phosphates were regarded as one of the best choices for NIBs as parallel LiFePO 4 cathodes have gained huge commercial success in lithium-ion batteries. However, the olivine-NaFePO 4 candidates could not be directly obtained by the conventional ceramic method due to the unfavorable thermodynamics feature and trend to transform into the more stable maricite phase. , Unfortunately, the maricite-type NaFePO 4 is usually believed to be of electrochemical inertness due to absence of effective Na + ion diffusion channels .…”

Boosting Sodium Compensation Efficiency via a CNT/MnO2 Catalyst toward High-Performance Na-Ion Batteries

“…The air-stable additives tend to decompose at a high voltage above 4.0 V, even to 4.4 V, which is beyond the cutoff voltage of common layer oxide 21 or phosphate cathode. 22 To achieve controllable sodium compensation at a much-reduced decomposition voltage, researchers have focused on the relationship between the decomposition voltage and the electron structures of various sodium salts. According to the Kolbe electrolysis theory, 23,24 the decomposition potential is closely tied to the electron-donating effect of functional groups.…”

“…The sodium compensation strategy can effectively address the irreversible sodium loss during the formation process of SEI, thus promoting the electrochemical properties of SIBs. − To date, different self-sacrificial additives have been reported, including Na 2 S, Na 2 O 2 , NaN 3 , , Na 3 P, Na 2 NiO 2 , Na 2 C 2 O 4 , and Na 2 C 4 O 4 . , It is worth noting that the lower decomposition voltage additives like Na 2 S, NaN 3 , and Na 3 P are quite air-sensitive and not suitable for industrial use. The air-stable additives tend to decompose at a high voltage above 4.0 V, even to 4.4 V, which is beyond the cutoff voltage of common layer oxide or phosphate cathode . To achieve controllable sodium compensation at a much-reduced decomposition voltage, researchers have focused on the relationship between the decomposition voltage and the electron structures of various sodium salts.…”