Review of Separator Modification Strategies: Targeting Undesired Anion Transport in Room Temperature Sodium–Sulfur/Selenium/Iodine Batteries

Abstract

Rechargeable sodium–sulfur/selenium/iodine (Na–S/Se/I2) batteries are regarded as promising candidates for large‐scale energy storage systems, with the advantages of high energy density, low cost, and environmental friendliness. However, the electrochemical performances of Na–S/Se/I2 batteries are still restricted by several inherent issues, including the “shuttle effect” of polysulfides/polyselenides/polyiodides (PSs/PSes/PIs), sluggish kinetics of the conversion reactions at the cathodes, and Na dendrite growth at the anodes. Among these challenges, uncontrolled “shuttle effect” of PSs/PSes/PIs is a major contributing factor for the irreversible loss of active cathode materials and severe side reactions on Na metal anodes, leading to rapid failure of the batteries. Separator modification has been demonstrated to be an effective strategy to suppress the shuttling of PSs/PSes/PIs. Herein, the latest achievement in modifying separators for high‐performance Na–S/Se/I2 batteries is comprehensively reviewed. The reaction mechanisms of each battery system are first discussed. Then, strategies of separator modification based on the different functions for regulating the transportation of PSs/PSes/PIs are summarized, including applying electrostatic repulsive interaction, introducing conductive layers, improving sieving effects, enhancing chemisorption capability, and adding efficient electrocatalysts. Finally, future perspectives on the practical application of modified separators in high‐energy rechargeable batteries are provided.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

“…To date, surface modification of the separator or the introduction of an interlayer has proven to be an effective strategy to address the above challenges simultaneously. In terms of function, these strategies can be divided into three categories: 1) regulating the transport of NaPS on the separator through electrostatic repulsive interaction, sieving effect and chemisorption; 2) By introducing conductive layer to activate NaPS, promote the interfacial charge and mass transfer of redox reaction; 3) The redox kinetics of NaPS on the separator is accelerated by electrochemical catalysis …”

“…It significantly shortens the transport path of Na-ion diffusion in the thin coating layer. Developing a promising strategy to effectively inhibit the “shuttle effect” of NaPS and improve the reoxidation kinetics of NaPS that accumulates near the surface of the separator is critical to increasing the utilization of sulfur by Na-S cells over the long cycle . Therefore, in recent years, catalytic materials have been used to modify it to improve the redox kinetics of NaPS.…”

Binary Atomic Sites Enable a Confined Bidirectional Tandem Electrocatalytic Sulfur Conversion for Low‐Temperature All‐Solid‐State Na−S Batteries

“…Besides the obvious advantages of strong chemisorption toward polysulfides, catalyzing their fast liquid-solid multiphase transformation conversion to discharge/charge products (e.g., Na 2 S and S 8 ) is also necessary to realize highly efficient sulfur redox. [25] Accordingly, the catalytic activities and the underlying kinetics of matrix-dependent polysulfide redox were systemically investigated via cyclic voltammetry (CV) in a symmetric cell with Na 2 S 4 electrolyte filled between two identical electrodes. The CV test was performed within a voltage range of À 0.6 to 0.6 V. As exhibited in Figure 3f, the symmetric cell with MnCo-NC electrodes exhibits higher peak current response and maximum peak area than Mn-NC and NC electrodes, indicating faster redox kinetics and higher charge storage capability.…”

Janus Binder Chemistry for Synchronous Enhancement of Iodine Species Adsorption and Redox Kinetics toward Sustainable Aqueous Zn–I2 Batteries

“…This is primarily attributed to their exceptional properties, including a high theoretical specific capacity (211 mAh g –1 ), satisfying energy density, excellent rate performance, availability of abundant and cost-effective raw materials (iodine storage: 55 μg L –1 ), and excellent safety features. − Nevertheless, the ZIBs face certain limitations that hinder their potential for large-scale application, such as low conductivity and sluggish kinetics of the iodine cathode, the large volume expansion of the host, and the severe shuttle effect caused by polyiodide ions. − These factors contribute to a high self-discharge rate, low Coulombic efficiency, and a short cycle life of the ZIB devices. To address the multiple challenges mentioned above, a majority of the existing research endeavors have prioritized the following aspects: (i) rational design on cathodic iodine host, aiming at enhancing conductivity and catalytic kinetic process of iodine species conversion (from I 3 – to I – ), further boosting the redox activity during battery service, , (ii) a routine on metallic zinc anode protection and electrolyte alteration, involving optimization on specific composition of electrolytes to facilitate uniform deposition of Zn as well as stabilize reversible stripping by increasing the anode modification layer, adjusting the composition of electrolyte to promote uniform deposition of zinc, and protecting the anode from polyiodide attack, ,, and (iii) functional modification on the separator, in general, grafting appropriate functional terminations to regulate the flux of Zn 2+ which can impede the shuttling of polyiodide …”

“…To address the multiple challenges mentioned above, a majority of the existing research endeavors have prioritized the following aspects: (i) rational design on cathodic iodine host, aiming at enhancing conductivity and catalytic kinetic process of iodine species conversion (from I 3 − to I − ), further boosting the redox activity during battery service, 18,19 specific composition of electrolytes to facilitate uniform deposition of Zn as well as stabilize reversible stripping by increasing the anode modification layer, adjusting the composition of electrolyte to promote uniform deposition of zinc, and protecting the anode from polyiodide attack, 16,20,21 and (iii) functional modification on the separator, in general, grafting appropriate functional terminations to regulate the flux of Zn 2+ which can impede the shuttling of polyiodide. 22 While these solutions have proven to be effective in enhancing the performance of ZIBs, they often concentrate on addressing specific difficulties and fail to provide comprehensive advantages in other aspects. Moreover, there is a significant concern that arises from the implementation of certain existing tactics, as they may use materials with high costs, toxicity, and limited reserves in ZIBs systems.…”