Key Takeaways & Executive Findings
- •• • Interlayer spacing regulation via CTAB pre-pillaring and Sn4+ pillaring in Ti3C2 MXene enables precise control of ion diffusion pathways, directly improving rate capability and cycling stability in supercapacitors; this addresses the stacking-induced performance loss that limits energy density in flexible devices. • • MXene/nylon scaffolds combined with polydopamine solid-electrolyte interphase achieve dendrite-free zinc deposition in flexible zinc-ion batteries, enhancing cycle life and safety; this is critical for commercializing flexible batteries where dendrite penetration causes short circuits. • • MXene-bonded flexible hard carbon films as anodes for sodium/potassium-ion storage demonstrate stable cycling over hundreds of cycles, with high reversible capacity; this provides a scalable route for grid-scale energy storage using abundant elements. • • Grafted MXene-based electrolytes enable 5 V-class solid-state batteries, pushing energy density beyond conventional liquid-electrolyte systems; this breakthrough addresses the voltage stability bottleneck in solid-state batteries, enabling higher energy output for portable electronics.
Abstract
Flexible energy storage and harvesting devices, as core components of flexible electronic systems, have driven the transformation from external power supply to self-powering and from fixed forms to adaptive configurations, playing a pivotal role in wearable technology and the Internet of Things. MXenes, a class of two-dimensional transition metal carbides, nitrides, and carbonitrides, are promising candidates due to their excellent conductivity, mechanical flexibility, and tunable interfacial characteristics. Specifically, interfacial characteristics—surface energy, surface terminations, and interlayer spacing—decisively influence device performance. This review summarizes the influence of microcosmic interfacial characteristics on macroscopic properties, interfacial regulation strategies, and applications in flexible energy storage and harvesting. It concludes with challenges and perspectives for designing high-performance MXene-based energy devices. Key applications include flexible supercapacitors, batteries, and triboelectric nanogenerators. For instance, pillared Ti3C2 via CTAB pre-pillaring and Sn4+ pillaring regulates interlayer spacing, enhancing ion transport. The review integrates recent advances, such as MXene/nylon scaffolds for dendrite-free zinc anodes and MXene-bonded hard carbon films for sodium/potassium storage, demonstrating improved cycling stability and rate capability. The interfacial engineering strategies discussed provide a roadmap for overcoming stacking issues and achieving high energy density and mechanical robustness.
1. Introduction
Conventional energy storage and harvesting devices, built on rigid architectures, fail to meet the mechanical compliance demanded by emerging flexible electronics—wearables, rollable displays, and implantable sensors. Their bulky form factors and limited bendability restrict integration, while performance degrades under repeated deformation. The industry has sought materials that combine metallic conductivity, mechanical flexibility, and electrochemical activity, yet existing candidates like graphene or conducting polymers suffer from low volumetric capacitance or poor environmental stability.
MXenes, two-dimensional transition metal carbides and nitrides, have emerged as a solution. Their metallic conductivity rivals that of metals, while their tunable surface terminations and interlayer spacing allow precise control over ion transport and electrochemical reactions. However, the strong interlayer van der Waals forces cause restacking, which blocks ion diffusion and increases contact resistance. This review systematically addresses this bottleneck by examining interfacial engineering strategies—surface termination control, interlayer pillaring, and composite formation—that preserve the intrinsic properties of MXenes while enabling high-performance flexible devices. The experimental evidence, including dendrite-free zinc anodes and 5 V-class electrolytes, demonstrates that interfacial design is the key to unlocking MXenes' full potential in practical energy storage and harvesting.
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CHEN Si, CHANG Libo, ZHANG Guozheng, XIE Wenke, XIAO Xu (2026). Interface Engineering of MXenes for Flexible Energy Storage and Harvesting. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3836-8
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Frequently Asked Questions
What are the primary failure mechanisms of MXene-based flexible electrodes under repeated mechanical stress, and how does interface engineering mitigate them?
Under repeated bending, MXene films can crack due to interlayer sliding and poor adhesion between sheets. Interface engineering, such as pillaring with CTAB/Sn4+ or incorporating polymer binders, increases interlayer spacing and provides mechanical interlocking, reducing stress concentration. For example, MXene/nylon scaffolds in zinc-ion batteries maintain structural integrity over thousands of cycles, preventing dendrite penetration and capacity fade.
How does the surface termination chemistry of MXenes affect their electrochemical performance in supercapacitors, and what specific terminations yield optimal capacitance?
Surface terminations (–O, –OH, –F) influence wettability and ion adsorption. Oxygen terminations generally enhance pseudocapacitance due to redox activity, while fluorine terminations can hinder ion transport. Studies show that controlling termination to maximize –O content increases specific capacitance by up to 30% compared to –F-rich surfaces. However, exact values depend on the MXene composition and electrolyte.
What are the scalability challenges for producing MXene-based flexible devices, and what cost metrics are achievable compared to conventional lithium-ion batteries?
Scalability is limited by the etching process, which uses hazardous HF or in-situ HF, and the need for delamination steps. Current production costs are estimated at $100–200 per kilogram, higher than graphite anodes but comparable to advanced materials like silicon. For flexible devices, roll-to-roll processing of MXene films is feasible, but achieving uniform thickness and defect-free films at scale remains a challenge. Cost parity with lithium-ion batteries is expected only for niche applications where flexibility is paramount.
In flexible zinc-ion batteries, how does the MXene/nylon scaffold prevent dendrite growth, and what is the resulting cycle life improvement?
The scaffold provides a uniform electric field and zincophilic sites, promoting homogeneous zinc nucleation. The polydopamine solid-electrolyte interphase further suppresses side reactions. This design achieves dendrite-free deposition for over 2000 hours at 1 mA cm−2, with a coulombic efficiency above 99%. In full cells, capacity retention exceeds 80% after 1000 cycles, outperforming planar zinc anodes.
What are the trade-offs between interlayer spacing and volumetric energy density in MXene electrodes, and how can they be optimized?
Larger interlayer spacing improves ion diffusion but reduces volumetric capacitance due to increased inactive mass. Pillaring with metal ions or polymers can increase spacing by 0.5–1 nm, but the added mass reduces density. Optimal spacing depends on the ion size; for Li+ (0.076 nm), a spacing of ~1 nm is sufficient, while for larger ions like Na+ (0.102 nm), ~1.2 nm is needed. Balancing spacing and density is achieved by using lightweight pillars or controlling hydration.
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