Challenges and Strategies toward Manganese Hexacyanoferrate for High-Performance Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are considered as a beneficial complement to lithium-ion batteries for large-scale energy storage systems because of the abundant sodium resources. However, the relatively large ionic radius of Na⁺ inevitably results in a huge volume change and sluggish electrochemical reaction kinetics, which put forward higher requirements for electrode materials. Among the reported cathode materials for SIBs, the manganese hexacyanoferrate (MnHCF) with the merits of large channels for fast sodium ion transport, high theoretical capacity and low cost has attracted extensive attention. In this review, the recent achievements of MnHCF for SIBs are focused. The key challenges of MnHCF limiting the practical application include the interstitial water, vacancies, low electronic conductivity, and the Jahn-Teller effect. Subsequently, the mainstream strategies to boost the sodium storage performance of MnHCF are summarized (such as structure regulation, surface coating, hybridization with carbon materials, and element substitution). Finally, the potential research directions are also proposed to promote the practical application of MnHCF for SIBs. This review is expected to provide a whole insight into exploring MnHCF cathode materials for SIBs.