Rechargeable sodium-ion batteries (SIBs) have been considered as promising energy storage devices owing to the similar "rocking chair" working mechanism as lithium-ion batteries and abundant and low-cost sodium resource. However, the large ionic radius of the Na-ion (1.07 Å) brings a key scientific challenge, restricting the development of electrode materials for SIBs, and the infeasibility of graphite and silicon in reversible Na-ion storage further promotes the investigation of advanced anode materials. Currently, the key issues facing anode materials include sluggish electrochemical kinetics and a large volume expansion. Despite these challenges, substantial conceptual and experimental progress has been made in the past. Herein, we present a brief review of the recent development of intercalation, conversion, alloying, conversion-alloying, and organic anode materials for SIBs. Starting from the historical research progress of anode electrodes, the detailed Na-ion storage mechanism is analyzed. Various optimization strategies to improve the electrochemical properties of anodes are summarized, including phase state adjustment, defect introduction, molecular engineering, nanostructure design, composite construction, heterostructure synthesis, and heteroatom doping. Furthermore, the associated merits and drawbacks of each class of material are outlined, and the challenges and possible future directions for high-performance anode materials are discussed.

Sodium‐ and potassium‐ion batteries have exhibited great application potential in grid‐scale energy storage due to the abundant natural resources of Na and K. Conversion‐alloying anodes with high theoretical capacity and low‐operating voltage are ideal option for SIBs and PIBs but suffer the tremendous volume variations. Herein, a hierarchically structural design and sp2 N‐doping assist a conversion‐alloying material, Sb2Se3, to achieve superior life span more than 1000 cycles. It is confirmed that the Sb2Se3 evolves into nano grains that absorb on the sp2 N sites and in situ form chemical bonding of C‐N‐Sb after initial discharge. Simulation results indicate that sp2 N has more robust interaction with Sb and stronger adsorption capacities to Na+ and K+ than that of sp3 N, which contributes to the durable cycling ability and high electrochemical activity, respectively. The ex situ transmission electron microscopy and X‐ray photoelectron spectroscopy results suggest that the Sb2Se3 electrode experiences conversion‐alloying dual mechanisms based on 12‐electron transfer per formula unit.

The large volume expansion and sluggish dynamic behavior are the key bottleneck to suppress the development of conversion-alloying dual mechanism anode for potassium-ion batteries (PIBs). Herein, Sb 2 S 3 nanorods encapsulated by reduced graphene oxide and nitrogen-doped carbon (Sb 2 S 3 @rGO@NC) are constructed as anodes for PIBs. The synergistic effect of dual physical protection and robust C-Sb chemical bonding boosts superior electrochemical kinetics and great electrode stability. Thus, Sb 2 S 3 @rGO@NC exhibits a high initial charge capacity of 505.6 mAh$g À1 at 50 mA$g À1 and a great cycle stability with the lifetime over 200 cycles at 200 mA$g À1 . Ex situ XRD, XPS, and TEM characterizations confirm that the electrode undergoes a multielectron transfer process (Sb 2 S 3 4 Sb + K 2 S 4 KSb + K 3 Sb), where K-ion insert into/extract from the material via dual mechanisms of conversion and alloying. This work sheds a light on the construction of high-performance anode materials and the understanding of K-ion storage mechanism.

Concern related to climate changes and environmental pollution caused by widespread using of fossil energy has prompted the research of novel and efficient energy storage systems. Among them, lithium-ion batteries (LIBs) have been widely used in portable electronic devices, hybrid electric vehicles, and electric vehicles owing to its high energy density, high power density and long cycling life. [1,2] Nevertheless, it is well known that the scarcity and high price of Li resources make LIBs difficult to meet the demand for large-scale energy electrical storage technologies in the future. [3,4] Hence, the emerging sodium ion batteries (SIBs) and potassium ion batteries (PIBs) have gained widespread attention and rapid development due to abundant and low-cost resources as well as the same "rocking chair" electrochemical reaction principle as LIBs. [5,6] What is the most surprising is PIBs with the condition of organic electrolyte is a more ideal energy storage device:1) The standard electrode potential of −2.93 V for K + /K (vs the standard hydrogen electrode) is closer to that of −3.04 V for Li + / Li and higher than that of 2.71 V for Na + /Na, which is beneficial to acquiring high operating voltage and energy density for K-ion full cell; 2) the propylene carbonate (PC) solvent will further lower the standard potential of K/K + compared with Li + / Li to obtain higher energy density; 3) The weaker Lewis acidity of K-ion leads to the smallest solvated ion of 3.6 Å for K compared with that of 4.8 Å for Li and 4.6 Å for Na to achieve better rate capability; 4) Potassium can react with graphite electrode to form an intercalation compound of KC 8 with the theoretical capacity of 279 mAh g −1 , displaying another advantage than SIBs. [7,8] The key bottleneck facing PIBs is to develop electrode materials with stable structure to store K-ion with large size of 1.38 Å. At present, the cathode materials can be roughly divided into Prussian blue (PB) analogues, [9,10] layered transition metal oxides, [11,12] polyanion compounds, [13,14] and organic crystals, [15,16] all which promote the development of cathodes with excellent electrochemical properties and illuminate in-depth the solid solution and phase transition mechanisms for K-ion The investigation of carbonaceous-based anode materials will promote the fast application of low-cost potassium-ion batteries (PIBs). Here a nitrogen and oxygen co-doped yolk-shell carbon sphere (NO-YS-CS) is constructed as anode material for K-ion storage. The novel architecture, featuring with developed porous structure and high surface specific area, is beneficial to achieving excellent electrochemical kinetics behavior and great electrode stability from buffering the large volume expansion. Furthermore, the N/O heteroatoms co-doping can not only boost the adsorption and intercalation ability of K-ion but also increase the electron transfer capability. It is also demonstrated by experimental results and DFT calculations that K-ion insertion/extraction proceeds through both intercalation and...