Key Takeaways & Executive Findings
- •• High-sulfur loading and lean electrolyte conditions are critical for achieving high energy density in lithium–sulfur batteries, but they introduce significant challenges such as polysulfide shuttling and slow kinetics. • MXenes-based electrocatalysts, with metallic conductivity and abundant active sites, effectively enhance sulfur redox reactions and lithium plating/stripping behavior. • Optimization strategies for MXenes include d-band center tuning, internal electric field construction, single-atom seeding, and cocktail effects, which improve catalytic activity and battery performance. • The review establishes structure–activity relationships between MXenes-based electrocatalysts and LSB performance, guiding future design for practical applications.
Abstract
Lithium–sulfur batteries (LSBs) hold significant promise as advanced energy storage systems due to their high energy density, low cost, and environmental advantages. However, despite recent advancements, their practical energy density still falls short of the levels required for commercial viability. The energy density is critically dependent on both sulfur loading and the amount of electrolyte used. High-sulfur loading coupled with lean electrolyte conditions presents several challenges, including the insulating nature of sulfur and Li2S, insufficient electrolyte absorption, degradation of the cathode structure, severe lithium polysulfide shuttling, slow redox reaction kinetics, and instability of the Li metal anode. MXenes-based materials, with their metallic conductivity, large polar surfaces, and abundant active sites, have been identified as promising electrocatalysts to improve the redox reactions in LSBs. This review focuses on the significance and challenges associated with high-sulfur loading and lean electrolytes in LSBs, highlighting recent advancements in MXenes-based electrocatalysts aimed at optimizing sulfur cathodes and lithium anodes. It provides a comprehensive discussion on MXenes as both active materials and substrates in LSBs, with the goal of enhancing understanding of the regulatory mechanisms that govern sulfur conversion reactions and lithium plating/stripping behavior. Finally, the review explores future opportunities for MXenes-based electrocatalysts, paving the way for the practical application of LSBs.
1. Introduction
The increasing dependence on fossil fuels causes large-scale emissions of greenhouse gases and harmful pollutants and thus exacerbates the global energy crisis and intensifies environmental issues [1, 2]. Under this background, renewable energy sources like solar, wind, and biomass have garnered significant attention for their inexhaustibility and environmental sustainability in the past decades [3, 4]. However, the inherent intermittency and instability of these energy sources limit their practical applications, creating an urgent need for advanced energy storage systems capable of converting and storing renewable energy for stable and continuous power supply [5].
Among the available systems, rechargeable batteries have been widely applied in powering mobile devices, smart grids, and electric vehicles [6]. Lithium-ion batteries (LIBs) dominate the market for portable electronics, yet their energy density is approaching its theoretical maximum, making them inadequate for the growing demands of next-generation power applications [7]. Moreover, commercially available LIBs, with a relatively low energy density of no more than 300 Wh kg−1, cannot meet the demand for longer endurance, such as more than 300 miles for electric vehicles [8], which require an energy density of 500 Wh kg−1.
Compared to LIBs, lithium–sulfur batteries (LSBs), involving the multi-electron redox conversion mechanism, have emerged as a promising alternative, which can offer superior energy storage capabilities [9–12]. By utilizing elemental sulfur as cathode and Li metal as anode, LSBs can theoretically deliver an energy density as high as 2600 Wh kg−1, approximately six times higher than that of conventional LIBs [13–15]. Energy density relying on sulfur loading is a key metric for assessing the practical performance of batteries. In general, low-sulfur loading and excessive electrolyte usage in LSBs enable significantly improved specific capacity (>1000 mAh g−1), rate performance (>40C), and cycling stability (>1500 cycles) [16–18]. However, low-sulfur loading and high electrolyte-to-sulfur (E/S) ratios will greatly reduce energy density and increase electrolyte costs, limiting commercial viability [19]. LSBs usually operate at an average voltage of 2.15 V (lower than 3.60 V of typical LIBs), so an areal capacity of 4.0–8.0 mAh cm−2 seems to be required to compete effectively [19]. Research has shown that a sulfur loading less than 2.0 mg cm−2 cannot achieve the energy density of 500 Wh kg−1 under any E/S ratio (F
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Xintao Zuo, Yanhui Qiu, Mengmeng Zhen, Dapeng Liu, Yu Zhang (2025). Review on MXenes-Based Electrocatalysts for High-Energy-Density Lithium–Sulfur Batteries. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01726-z
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Frequently Asked Questions
What are the main challenges for high-energy-density lithium-sulfur batteries?
High-sulfur loading and lean electrolyte conditions are essential for high energy density but introduce challenges such as insulating sulfur and Li2S, insufficient electrolyte absorption, cathode degradation, severe polysulfide shuttling, slow redox kinetics, and lithium anode instability.
How do MXenes-based electrocatalysts improve lithium-sulfur battery performance?
MXenes offer metallic conductivity, large polar surfaces, and abundant active sites, which enhance sulfur redox reactions and lithium plating/stripping behavior, thereby improving capacity, rate capability, and cycling stability.
What strategies are used to optimize MXenes-based electrocatalysts?
Strategies include d-band center tuning, internal electric field construction, single-atom seeding, and cocktail effects, which modulate electronic structure and catalytic activity.
What is the significance of the structure-activity relationship in MXenes for LSBs?
Understanding the structure-activity relationship helps in designing MXenes with tailored properties to effectively regulate sulfur conversion reactions and lithium plating/stripping, leading to enhanced battery performance.
What are the future opportunities for MXenes-based electrocatalysts in LSBs?
Future opportunities include developing novel MXene composites, optimizing electrode architectures, and scaling up synthesis methods to achieve practical high-energy-density LSBs.
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