A Radical Pathway and Stabilized Li Anode Enabled by Halide Quaternary Ammonium Electrolyte Additives for Lithium-Sulfur Batteries

Highly Reversible Tin Film Anode Guided via Interfacial Coordination Effect for High Energy Aqueous Acidic Batteries

Sn metal is a preferable choice as anode material for aqueous acidic batteries due to its acid-tolerance, non-toxicity, and ease of recycling. However, the large size and irregular deposition morphology of polyhedral Sn particles are bad for constructing stable and high-capacity Sn metal anode because of severe hydrogen evolution and metal shedding. To tackle this critical issue, 4-tert-octylphenol pentaethoxylate (POPE) is used as an electrolyte additive to generate a thin-film Sn anode with reversible stripping/plating behavior. POPE can not only induce homogeneous surface chemistry by adsorbing on the Sn surface via coordination bonds but also inhibit hydrogen evolution by modulating the solvation shell of Sn2+. The Sn film anode delivers improved electrochemical stability over 480 h with satisfactory rate performance and low polarization. Moreover, the as-assembled PbO2//Sn battery can also provide outstanding durability at 10 mAh cm-2. This work offers new inspiration for developing a reversible Sn metal film anode.

Development of Electrolytes under Lean Condition in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries stand out as one of the promising candidates for next-generation electrochemical energy storage technologies. A key requirement to realize high-specific-energy Li-S batteries is to implement low amount of electrolyte, often characterized by the electrolyte/sulfur (E/S) ratio. Low E/S ratio aggravates the known challenges for Li-S batteries and introduces new ones originated from the high concentration of polysulfides in limited electrolyte reservoir. In this review, the connections between the fundamental properties of electrolytes and the electrochemical/chemical reactions in Li-S batteries under lean electrolyte condition are elucidated. The emphasis is on how the solvating properties of the electrolyte affect the fate of polysulfides. Built upon the mechanistic analysis, different strategies to design lean electrolytes to improve the overall process of Li-S reactions and Li anode protection are discussed.

Organic Electrolyte Additive: Dual Functions Toward Fast Sulfur Conversion and Stable Li Deposition for Advanced Li-S Batteries

Lithium-sulfur (Li-S) battery is of great potential for the next generation energy storage device due to the high specific capacity energy density. However, the sluggish kinetics of S redox and the dendrite Li growth are the main challenges to hinder its commercial application. Herein, an organic electrolyte additive, i.e., benzyl chloride (BzCl), is applied as the remedy to address the two issues. In detail, BzCl can split into Bz· radical to react with the polysulfides, forming a Bz-S-Bz intermediate, which changes the conversion path of S and improves the kinetics by accelerating the S splitting. Meanwhile, a tight and robust solid electrolyte interphase (SEI) rich in inorganic ingredients namely LiCl, LiF, and Li2 O, is formed on the surface of Li metal, accelerating the ion conductivity and blocking the decomposition of the solvent and lithium polysulfides. Therefore, the Li-S battery with BzCl as the additive remains high capacity of 693.2 mAh g-1 after 220 cycles at 0.5 C with a low decay rate of 0.11%. This work provides a novel strategy to boost the electrochemical performances in both cathode and anode and gives a guide on the electrolyte design toward high-performance Li-S batteries.

Facile preparation of a lightweight multifunctional interlayer for high-performance Li-S batteries

The construction of functional interlayers for separator modification in Li-S batteries has been proven to be a feasible and effective strategy to alleviate the shuttle effect. However, several challenging issues in interlayer design and fabrication, including the tedious material preparation process and high weight loading of the interlayer on the pristine separator, jeopardize the battery energy density. In this work, a nitrogen-abundant nanoporous carbon/graphene (NC/G) composite was synthesized by a facile method and fabricated into a lightweight membrane, which was investigated as a multifunctional interlayer in a Li-S battery. The abundant nitrogen sites and nanoporous structure of NC/G can effectively anchor and trap polysulfides; graphene (G) can create an excellent conductive network in NC/G. These attributes of NC/G are able to efficiently boost the sulfur redox reaction kinetics and significantly suppress the shuttle effect, leading to superb battery performance. More importantly, the low density of NC/G was conducive to reducing the load on the separator, thus reducing the decline in battery energy density, which is promising for practical applications. Even at an ultra-low loading of NC/G on the pristine separator (0.08 mg cm-2), the battery showed a competitive electrochemical performance compared with many reported materials. We believe this work provides a strategic guidance for the future fabrication of promising functional interlayers for practical Li-S battery applications.

Quantum Spin Exchange Interactions to Accelerate the Redox Kinetics in Li-S Batteries

Spin-engineering with electrocatalysts have been exploited to suppress the "shuttle effect" in Li-S batteries. Spin selection, spin-dependent electron mobility and spin potentials in activation barriers can be optimized as quantum spin exchange interactions leading to a significant reduction of the electronic repulsions in the orbitals of catalysts. Herein, we anchor the MgPc molecules on fluorinated carbon nanotubes (MgPc@FCNT), which exhibits the single active Mg sites with axial displacement. According to the density functional theory calculations, the electronic spin polarization in MgPc@FCNT not only increases the adsorption energy toward LiPSs intermediates but also facilitates the tunneling process of electron in Li-S batteries. As a result, the MgPc@FCNT provides an initial capacity of 6.1 mAh cm-2 even when the high sulfur loading is 4.5 mg cm-2, and still maintains 5.1 mAh cm-2 after 100 cycles. This work provides a new perspective to extend the main group single-atom catalysts enabling high-performance Li-S batteries.

Engineering Strategies for Suppressing the Shuttle Effect in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are supposed to be one of the most potential next-generation batteries owing to their high theoretical capacity and low cost. Nevertheless, the shuttle effect of firm multi-step two-electron reaction between sulfur and lithium in liquid electrolyte makes the capacity much smaller than the theoretical value. Many methods were proposed for inhibiting the shuttle effect of polysulfide, improving corresponding redox kinetics and enhancing the integral performance of Li-S batteries. Here, we will comprehensively and systematically summarize the strategies for inhibiting the shuttle effect from all components of Li-S batteries. First, the electrochemical principles/mechanism and origin of the shuttle effect are described in detail. Moreover, the efficient strategies, including boosting the sulfur conversion rate of sulfur, confining sulfur or lithium polysulfides (LPS) within cathode host, confining LPS in the shield layer, and preventing LPS from contacting the anode, will be discussed to suppress the shuttle effect. Then, recent advances in inhibition of shuttle effect in cathode, electrolyte, separator, and anode with the aforementioned strategies have been summarized to direct the further design of efficient materials for Li-S batteries. Finally, we present prospects for inhibition of the LPS shuttle and potential development directions in Li-S batteries.