For a next-generation sodium battery to replace lithium ion batteries, it is essential to develop an anode with a long cycle life and high rate. Sn is considered to be an ideal candidate for the anode of sodium ion batteries. Here, we report a Sn anode that exhibits ultra-long-term cycle stability with a high capacity of 554 mA h g⁻¹ at 10C-rate for 5000 cycles. The optimized cell configuration consists of 1,2-dimethoxyethane as the electrolyte, a double separator including a nanoporous membrane, and a Sn anode with MWCNT as a conductive additive. Its capacity retention reaches up to 99.8% and its coulombic efficiency is near 100% for 5000 cycles. Surprisingly, we have discovered that the Sn powder exhibits a self-healing phenomenon during cycling. Sn is initially pulverized into a nanometer-sized powder, and then forms a three-dimensional porous coral-like structure in which ligament-shaped micrometer-sized Sn particles are connected with a low coordination number by room temperature sintering. The coral-like structure is mechanically stable towards volume change and electrically connected. The self-healing structure and mechanism provide a direction for the design of other electrodes with alloying mechanisms.

During the development of sodium ion batteries (SIBs), a long cycle life, high capacity, and high rate are required for the anode materials. In this study, CuS is synthesized by heating S on a Cu current collector at 80 °C for 5 h, which is a simple and scalable process. The CuS exhibits excellent cycle stability of 517 mA h g⁻¹ at 5 A g⁻¹ after 2000 cycles, with 99.2% retention and a coulombic efficiency of almost 100%. CuS also exhibits an ultrahigh rate capability up to 100 A g⁻¹ with a 268 mA h g⁻¹. The CuS electrode is suitable for mass production and displays excellent electrochemical performance; therefore, it is a promising anode for SIBs. Moreover, ex situ scanning electron microscopes are applied to investigate their structural changes. During cycling, the shape of the electrode changes to multiundulating, and then to a flat plate covered with nanometer-sized particles, which can be induced by cracking, pulverization, and agglomeration. Through agglomeration, the CuS recovers from the electric isolation caused by pulverization. This self-healing characteristic could represent a new way of obtaining a long cycle life for anodes with volume changes.

Porous Na₃V₂(PO₄) cathode affords ultrafast kinetics (44 mA h g⁻¹ at 854C) and long cycle life (95 000 cycles at 50 A g⁻¹) using dimethyl ether (DME) electrolyte.