Toward High Performance Anodes for Sodium-Ion Batteries: From Hard Carbons to Anode-Free Systems

Abstract

Sodium-ion batteries (SIBs) have been deemed to be a promising energy storage technology in terms of costeffectiveness and sustainability. However, the electrodes often operate at potentials beyond their thermodynamic equilibrium, thus requiring the formation of interphases for kinetic stabilization. The interfaces of the anode such as typical hard carbons and sodium metals are particularly unstable because of its much lower chemical potential than the electrolyte. This creates more severe challenges for both anode and cathode interfaces when building anode-free cells to achieve higher energy densities. Manipulating the desolvation process through the nanoconfining strategy has been emphasized as an effective strategy to stabilize the interface and has attracted widespread attention. This Outlook provides a comprehensive understanding about the nanopore-based solvation structure regulation strategy and its role in building practical SIBs and anode-free batteries. Finally, guidelines for the design of better electrolytes and suggestions for constructing stable interphases are proposed from the perspective of desolvation or predesolvation.

Competitive Coordination of Sodium Ions for High-Voltage Sodium Metal Batteries with Fast Reaction Speed

“…3,4 To achieve higher energy density, there is no doubt that metallic sodium is the ultimate anode for sodiumbased batteries due to its high theoretical specific capacity (1166 mAh g −1 ) and low redox potential (−2.714 V vs SHE). 5,6 However, the sodium metal anode faces similar or even more severe problems than those in the lithium metal anode. 7 The higher reactivity of sodium metal undergoes more rampant parasitic reactions with the electrolytes, forming a fragile solid electrolyte interface (SEI) with poor chemical/electrochemical stability.…”

“…Along with the increasing demand for electric vehicles and large-scale energy storage, the anxiety for limited lithium resources is increasing and driving the exploration of alternative energy storage systems with low cost and high energy density beyond lithium-based batteries. , Sodium-based batteries are considered a promising complementary technology due to their similar energy storage mechanism as lithium-based batteries and the wide geographic distribution and low cost of sodium resources. , To achieve higher energy density, there is no doubt that metallic sodium is the ultimate anode for sodium-based batteries due to its high theoretical specific capacity (1166 mAh g –1 ) and low redox potential (−2.714 V vs SHE). , However, the sodium metal anode faces similar or even more severe problems than those in the lithium metal anode . The higher reactivity of sodium metal undergoes more rampant parasitic reactions with the electrolytes, forming a fragile solid electrolyte interface (SEI) with poor chemical/electrochemical stability.…”

Improved Interface Construction on Anode and Cathode for Na‐Ion Batteries Using Ultralow‐Concentration Electrolyte Containing Dual‐Additives

“…[9,10] The solvation structure can be divided into solvent-separated ion pairs (SSIPs) in the low-concentration electrolyte solution, contact ion pairs (CIPs) and cation-anion aggregates (AGGs) in the high-concentration electrolyte. [11,12] In low-concentration electrolyte, the solvent decomposes first to form the organic-rich and inconsecutive CEI/SEI (such as sodium alkyl carbonates), which may even result in enhanced gas evolution. [13][14][15] To enhance the proportion of CIPs and AGGs and form an anion-driven, inorganic-rich interface (such as NaF), high-cost strategies like high concentration electrolyte (HCE), [16] local high-concentration electrolyte (LHCE), [17] and solvent modification [18] have been used.…”

Biomimetic-Mineralization-Assisted Self-Activation Creates a Delicate Porous Structure in Carbon Material for High-Rate Sodium Storage

“…Because of the similar energy storage mechanisms with lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) can not only meet the requirements of low cost, long cycle-life, and high stability/safety in the market of electrochemical energy storage, but also alleviate the limited development of LIBs to some extent, which is caused by the shortage of lithium resources. − Therefore, SIBs gradually serve as an important supplement to LIBs while replacing lead-acid batteries. , However, commonly used anode materials lose their advantage in SIBs due to the larger radius of Na + (0.102 nm) than Li + (0.076 nm); , especially, commercial graphite fails to insert Na + in carbonate ester-based electrolytes. ,, As a substitute of graphite, hard carbons suit Na + storage due to their distorted graphene layers, large interlayer spacing, and open/closed pores. , Yet, hard carbons usually deliver an inferior reversible capacity (∼300 mAh g –1 ) with poor high-rate capability (≤2 A g –1 ), because of the low diffusion coefficient of Na + (8.88 × 10 –7 cm 2 s –1 ) in carbonate ester-based electrolytes. ,,, Porous carbons have merits of high specific surface area (SSA), expanded interlayer distance, hierarchical pores, heteroatoms doping, and plentiful defects, which pave the way for obtaining high-rate-capability SIBs through increases in the physisorption/chemisorption for high capacitive capacity (fast Na + storage kinetics). − Nevertheless, porous carbons suffer from the conventional preparation strategies: physical/chemical activation creates rich pores but with irregular structure; artificial templates can obtain regular structure but with difficult post-purification. , As a result, there is an urgent need to develop novel synthetic methods of carbon-based anodes with delicate structural regulation and demonstrate their feasibility for high-performance practical SIBs.…”