Yingying Ji

Intermittent renewable energy requires a powerful energy storage system to smoothen the relationship between power generation and power consumption. Due to the rapidly rising price of Li resources, the development of Li-ion batteries (LIBs) has been severely limited. Therefore, developing high-efficiency and low-cost Na-ion batteries has become an alternative to energy storage systems. The high potential plateau of most anode materials urges the exploration of the ultimate anode, the Na metal anode. However, three big dilemmas regarding Na metal anodes, including the formation of Na dendrites, the formation of dead Na, and the continuous appearance of bare Na lead to the degradation of the performance of Na metal batteries (NMBs). In this review, we mainly summarize the recent progress to address these dilemmas for NMBs by electrolyte optimization. We firstly discuss the liquid electrolyte progresses to improve the Na metal anode’s electrochemical performance by solvent chemistry, salt chemistry, and additive. In addition, considering the ultimate goal of NMBs is solid-state batteries, we also discuss the recent progress of polymer electrolytes and all-solid-state electrolytes for Na metal anodes and summarize the enhancement of Na-ion transport mechanisms and interface engineering mechanisms of different solid-state electrolytes. Furthermore, the critical challenges and new perspectives of NMBs using electrolyte optimization are also emphasized. We believe that our review will provide insight to conduct more comprehensive and effective electrolyte engineering for high-performance NMBs.

As a promising energy storage system, potassium (K) ion batteries (KIBs) have received extensive attention due to the abundance of potassium resource in the Earth’s crust and the similar properties of K to Li. However, the electrode always presents poor stability for K-ion storage due to the large radius of K-ions. In our work, we develop a nitrogen-doped carbon nanofiber (N-CNF) derived from bacterial cellulose by a simple pyrolysis process, which allows ultra-stable K-ion storage. Even at a large current density of 1 A g⁻¹, our electrode exhibits a reversible specific capacity of 81 mAh g⁻¹ after 3000 cycles for KIBs, with a capacity retention ratio of 71%. To investigate the electrochemical enhancement performance of our N-CNF, we provide the calculation results according to density functional theory, demonstrating that nitrogen doping in carbon is in favor of the K-ion adsorption during the potassiation process. This behavior will contribute to the enhancement of electrochemical performance for KIBs. In addition, our electrode exhibits a low voltage plateau during the potassiation–depotassiation process. To further evaluate this performance, we calculate the “relative energy density” for comparison. The results illustrate that our electrode presents a high “relative energy density”, indicating that our N-CNF is a promising anode material for KIBs.