Regulating the exposed crystal facets of electrode materials for Na-ion batteries: A review of recent advancements and future perspectives

Low-cost Na-ion batteries (NIBs) have manifested enormous potential for stationary energy storage and low speed vehicles. Despite their potential advantages, the use of large and heavy Na+ ions as charge carriers in NIBs results in relatively slow kinetics and an inferior rate capacity. Moreover, Na+ de-intercalation is commonly accompanied by irreversible phase transition and sizeable volume changes, leading to structural degradation and capacity decay. Recent advancements have shown that tailoring the crystal growth direction and employing specific exposed crystal facets can bring about significant improvement in the electrochemical performance of electrode materials for NIBs. This review presents an overview of the key techniques for optimizing crystal growth direction, including surfactant addition, template-assisted synthesis, and foreign ion doping, followed by a detailed discussion pertaining to the corresponding regulatory mechanisms. Subsequently, the structure-activity relationship between crystal orientation design and Na storage performance is thoroughly examined with regards to the crystal anisotropy of cathode and anode materials. The prevalent challenges and new developments in regulating crystal orientation have been discussed given the development of high-performance NIB electrodes.