Transforming a Primary Li-SOCl2 Battery into a High-Power Rechargeable System via Molecular Catalysis

Ion-Docking Effect Enabling Rechargeable High-Voltage Magnesium-Iodine/Chlorine Battery

Rechargeable magnesium (Mg) batteries represent a promising energy storage system by offering low cost and dendrite-less propensity. However, the limited selection of cathode materials, and often with low voltage and capacity, constrain Mg batteries. Herein, by exploiting the ion-docking effect between two halogen species-iodine cations (I+) and chlorine anions (Cl-)-we activate the cathodic activity of halogens and develop a magnesium-iodine/chlorine (Mg-I/Cl) battery prototype with high energy and power density. The ion-docking effect enables I+ and Cl- to mutually balance and disperse their charges, and weakens the coordination strength between Cl- and Mg2+ while enhancing the stability of I+, thus facilitating the multi-electron (2 + 1/3) redox reactions of halogens. We also find the solvation state of iodine species determines the reaction process of the I0/I3 -/I- redox couples. The here-developed magnesium-iodine/chlorine battery features an impressively high discharge plateau of up to 3.0 V with a high capacity exceeding 400 mAh g-1, and demonstrates a stable lifespan for 500 cycles, with the ability of ultra-fast charging at 20C and low-temperature cycling under -30 °C. These findings may provide new insights for developing high-energy-density Mg battery systems.

Ultrafast Rechargeable Aluminum-Chlorine Batteries Enabled by a Confined Chlorine Conversion Chemistry in Molten Salts

Rechargeable metal chloride batteries, with their high discharge voltage and specific capacity, are promising for next-generation sustainable energy storage. However, sluggish solid-to-gas conversion kinetics between solid metal chlorides and gaseous Cl2 cause unsatisfactory rate capability and limited cycle life, hindering their further applications. Here we present a rechargeable aluminum-chlorine (Al-Cl2) battery that relies on a confined chlorine conversion chemistry in a molten salt electrolyte, exhibiting ultrahigh rate capability and excellent cycling stability. Both experimental analysis and theoretical calculations reveal a reversible solution-to-gas conversion reaction between AlCl4- and Cl2 in the cathode. The designed nitrogen-doped porous carbon cathode enhances Cl2 adsorption, thereby improving the cycling lifespan and coulombic efficiency of the battery. The resulting Al-Cl2 battery demonstrates a high discharge plateau of 1.95 V, remarkable rate capability without capacity decay at different rates from 5 to 50 A g-1, and good cycling stability with over 1200 cycles at a rate of 10 A g-1. Additionally, we implemented a carbon nanofiber membrane on the anode side to mitigate dendrite growth, which further extends the cycle life to 3000 cycles at an ultrahigh rate of 30 A g-1. This work provides a new perspective on the advancement of high-rate metal chloride batteries.

New Redox Chemistries of Halogens in Aqueous Batteries

Halogen-based redox-active materials represent an important class of materials in aqueous electrochemistry. The existence of versatile halogen species and their rich bonding coordination create great flexibility in designing new redox couples. Novel redox reaction mechanisms and electrochemical reversibility can be unlocked in specifically configurated electrolyte environments and electrodes. In this review, the halogen-based redox couples and their appealing redox chemistries in aqueous batteries, including redox flow batteries and traditional static batteries that have been studied in recent years, are discussed. New aqueous electrochemistry provides hope to outperform the state-of-the-art materials and systems that are facing resources and performance limitation, and to enrich the existing battery chemistries.

Tetraphenylethene-Containing Nanofilm via Interfacial Confinement Self-Assembly for Fluorescent Monitoring of SOCl2 Leakage in a Li-SOCl2 Battery Electrolyte

Lithium thionyl chloride (Li-SOCl2) batteries are widely used due to their high energy density and long shelf life. However, the corrosive nature of SOCl2 poses a safety hazard, necessitating effective leak detection methods. We report an approach for real-time fluorescent detection of SOCl2 leakage in Li-SOCl2 batteries using a tetraphenylethene-based nanofilm. The nanofilms were prepared through the interfacial confined self-assembly method and exhibit excellent flexibility, homogeneity, tunable size and thickness, and adaptability to various substrates, enabling easy integration into sensor devices. They possess high photochemical stability and a photoluminescence quantum yield exceeding 25%, demonstrating their potential as high-performance fluorescent sensing material. The nanofilms also exhibit high sensitivity, good reproducibility, and selectivity toward SOCl2 detection. Upon exposure to SOCl2 vapor, the nanofilm shows a red-shifted and fluorescence quenching response, attributed to the protonation of the acylhydrazone bond in the nanofilm by the hydrolysis product of SOCl2, which disrupts the electronic structure of the nanofilm and leads to a decrease in the fluorescence intensity and a shift in the emission wavelength. A detection limit of ∼1.31 ppt and excellent repeatability over 300 cycles are demonstrated, highlighting their high sensitivity and reliability. This work paves the way for a highly sensitive and reliable leak detection system for Li-SOCl2 batteries, enhancing their safety and reliability in various applications.

Iodine-induced self-depassivation strategy to improve reversible kinetics in Na-Cl2 battery

Rechargeable sodium-chlorine (Na-Cl2) batteries show high theoretical specific energy density and excellent adaptability for extreme environmental applications. However, the reported cycle life is mostly less than 500 cycles, and the understanding of battery failure mechanisms is quite limited. In this work, we demonstrate that the substantially increased voltage polarization plays a critical role in the battery failure. Typically, the passivation on the porous cathode caused by the deposition of insulated sodium chloride (NaCl) is a crucial factor, significantly influencing the three-phase chlorine (NaCl/Na+, Cl-/Cl2) conversion kinetics. Here, a self-depassivation strategy enabled by iodine anion (I-)-tuned NaCl deposition was implemented to enhance the chlorine reversibility. The nucleation and growth of NaCl crystals are well balanced through strong coordination of the NaI deposition-dissolution process, achieving depassivation on the cathode and improving the reoxidation efficiency of solid NaCl. Consequently, the resultant Na-Cl2 battery delivers a super-long cycle life up to 2000 cycles.

Rechargeable alkali metal-chlorine batteries: advances, challenges, and future perspectives

The emergence of Li-SOCl2 batteries in the 1970s as a high-energy-density battery system sparked considerable interest among researchers. However, limitations in the primary cell characteristics have restricted their potential for widespread adoption in today's sustainable society. Encouragingly, recent developments in alkali/alkaline-earth metal-Cl2 (AM-Cl2) batteries have shown impressive reversibility with high specific capacity and cycle performance, revitalizing the potential of SOCl2 batteries and becoming a promising technology surpassing current lithium-ion batteries. In this review, the emerging AM-Cl2 batteries are comprehensively summarized for the first time. The development history and advantages of Li-SOCl2 batteries are traced, followed by the critical working mechanisms for achieving high rechargeability. The design concepts of electrodes and electrolytes for AM-Cl2 batteries as well as key characterization techniques are also demonstrated. Furthermore, the current challenges and corresponding strategies, as well as future directions regarding the battery are systematically discussed. This review aims to deepen the understanding of the state-of-the-art AM-Cl2 battery technology and accelerate the development of practical AM-Cl2 batteries for next-generation high-energy storage systems.

Engineering Triple-Phase Interfaces around the Anode toward Practical Alkali Metal-Air Batteries

Alkali metal-air batteries (AMABs) promise ultrahigh gravimetric energy densities, while the inherent poor cycle stability hinders their practical application. To address this challenge, most previous efforts are devoted to advancing the air cathodes with high electrocatalytic activity. Recent studies have underlined the solid-liquid-gas triple-phase interface around the anode can play far more significant roles than previously acknowledged by the scientific community. Besides the bottlenecks of uncontrollable dendrite growth and gas evolution in conventional alkali metal batteries, the corrosive gases, intermediate oxygen species, and redox mediators in AMABs cause more severe anode corrosion and structural collapse, posing greater challenges to the stabilization of the anode triple-phase interface. This work aims to provide a timely perspective on the anode interface engineering for durable AMABs. Taking the Li-air battery as a typical example, this critical review shows the latest developed anode stabilization strategies, including formulating electrolytes to build protective interphases, fabricating advanced anodes to improve their anti-corrosion capability, and designing functional separator to shield the corrosive species. Finally, the remaining scientific and technical issues from the prospects of anode interface engineering are highlighted, particularly materials system engineering, for the practical use of AMABs.

Organocatalytic Lithium Chloride Oxidation by Covalent Organic Frameworks for Rechargeable Lithium-Chlorine Batteries

Rechargeable Li-Cl2 battery is a promising high energy density battery system. However, reasonable cycle life could only be achieved under low specific capacities due to the sluggish oxidation of LiCl to Cl2 . Herein, we propose an amine-functionalized covalent organic framework (COF) with catalytic activity, namely COF-NH2 , that significantly decreases the oxidation barrier of LiCl and accelerates the oxidation kinetics of LiCl in Li-Cl2 cell. The resulting Li-Cl2 cell using COF-NH2 (Li-Cl2 @COF-NH2 ) simultaneously exhibits low overpotential, ultrahigh discharge capacity up to 3500 mAh/g and a promoted utilization ratio of deposited LiCl at the first cycle (UR-LiCl) of 81.4 %, which is one of the highest reported values to date. Furthermore, the Li-Cl2 @COF-NH2 cell could be stably cycled for over 200 cycles when operating at a capacity of 2000 mAh/g at -20 °C with a Coulombic efficiency (CE) of ≈100 % and a discharge plateau of 3.5 V. Our superior Li-Cl2 batteries enabled by organocatalyst enlighten an arena towards high-energy storage applications.

Enrichment of Chlorine in Porous Organic Nanocages for High-Performance Rechargeable Lithium-Chlorine Batteries

Rechargeable Li-Cl2 batteries are recognized as promising candidates for energy storage due to their ultrahigh energy densities and superior safety features. However, Li-Cl2 batteries suffer from a short cycle life and low Coulombic efficiency (CE) at a high specific cycling capacity due to a sluggish and insufficient Cl2 supply during the redox reaction. To achieve Li-Cl2 batteries with high discharge capacity and CE, herein, we propose and design an imine-functionalized porous organic nanocage (POC) to enrich Cl2 molecules. Based on density functional theory (DFT) calculations, the imine group sites in host cages strongly interact with Cl2 molecules, facilitating the rapid capture of Cl2. As a result, the output capacity of the Li-Cl2 battery using POC (Li-Cl2@POC) is significantly boosted, achieving an ultrahigh discharge capacity of 4000 mAh/g at ∼100% CE. Benefiting from the designed POC, the highest utilization ratio of deposited LiCl at the first cycle in the Li-Cl2@POC battery reaches as high as 85%, superior to all reported values. The Li-Cl2@POC battery exhibits excellent electrochemical performance even at low temperatures, delivering stable cycling over 200 cycles under a capacity of 2000 mAh/g at -20 °C with a voltage plateau of 3.5 V and an average CE of 99.7%. We also demonstrate that the Li-Cl2@POC cells can be assembled and well-operated in a dry room, showing advantages for mass production. Our designed POC promotes the practical deployment of rechargeable Li-Cl2 batteries.