Key Takeaways & Executive Findings
- •• • RM-enhanced LACB achieved over 250 cycles at 2 mA cm−2 with a limited capacity of 0.5 mAh cm−2, demonstrating a 1.28-fold improvement over PP-RM-LACB (218 cycles) and addressing cyclability bottlenecks for practical high-power applications. • • Charging voltage reduced by 0.54 V at 0.1 mA cm−2 compared to RM-free system, directly improving energy efficiency and reducing parasitic reactions, critical for lowering operational costs in grid-scale storage. • • Aluminum foil sealing technique enabled a power density of 13.8 mW cm−2 at 6 mA cm−2, overcoming mass transport limitations in open-cell configurations, essential for high-rate applications such as electric vehicle regenerative braking. • • PET oxygen barrier film (superior barrier) yielded 279 cycles at 1 mA cm−2 with 0.5 mAh cm−2 limit, 1.28 times higher than PP-RM-LACB (218 cycles), and maintained 0.5 mAh cm−2 at 4 mA cm−2 vs. 0.13 mAh cm−2 for PP, proving that effective oxygen isolation preserves capacitor electrode porosity and RM-mediated electron transfer, enhancing rate capability and longevity.
Abstract
Lithium-air capacitor batteries (LACBs) integrate the rapid charge-discharge capability of supercapacitors into conventional lithium-oxygen batteries, significantly enhancing power density. However, their cycling stability remains unsatisfactory. In this study, we incorporated redox mediators (RMs) into an LACB featuring a dual-cathode configuration. This design facilitates sustained electron transfer between the electrode and Li2O2/Oxygen, thereby delaying RM deactivation caused by electrode passivation and improving overall electrochemical performance. The RM-enhanced battery achieved over 250 cycles at 2 mA cm−2 with a limited capacity of 0.5 mAh cm−2, while exhibiting a 0.54 V reduction in charging voltage at 0.1 mA cm−2 compared to the RM-free system. Furthermore, application of an aluminum foil sealing technique enabled a power density of 13.8 mW cm−2 at 6 mA cm−2, overcoming mass transport limitations inherent in open-cell configurations. We also investigated the influence of oxygen barrier films with varying barrier capabilities on LACB performance. Results indicate that films with superior oxygen resistance better maintain a clean capacitor electrode surface, thereby providing more stable electron supply to the RMs and enhancing rate capability and cycling performance. These findings underscore the potential of redox mediators in improving the performance and longevity of LACBs, offering a promising strategy for their future development.
1. Introduction
Conventional lithium-air batteries (LABs) offer ultrahigh theoretical energy density but suffer from sluggish oxygen reduction/evolution kinetics and high charging overpotentials, limiting power output and cycle life. Supercapacitors (SCs) deliver high power density and long cycle life but lack energy density. The lithium-air capacitor battery (LACB) concept, integrating a dual-cathode configuration (air electrode and capacitor electrode) sharing a single electrolyte, aims to combine high energy and high power. However, early LACB prototypes exhibited poor cyclability and high charging voltage, hindering practical deployment. The primary bottleneck lies in the passivation of the air electrode by insoluble discharge products (Li2O2) and the deactivation of soluble redox mediators (RMs) that are essential for facilitating charge transfer. Additionally, oxygen crossover to the capacitor electrode degrades its porous structure, impairing rapid ion adsorption/desorption.
This study addresses these challenges by incorporating redox mediators into a dual-cathode LACB and systematically evaluating oxygen barrier films with different permeabilities. The RM-enhanced system demonstrates sustained electron transfer between the electrode and Li2O2/O2, delaying RM deactivation and reducing charging voltage by 0.54 V. The use of a high-barrier PET film effectively isolates the capacitor electrode from oxygen, preserving its porosity and enabling superior rate capability (0.5 mAh cm−2 at 4 mA cm−2) and cycling stability (279 cycles at 1 mA cm−2). These innovations directly tackle the commercial friction of poor cycle life and low power density, offering a viable pathway for high-energy, high-power storage systems.
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Chuyi Zhong, Jingke Yang, Jiewen Yang, Pengwei Jing, Shuaiqi Li, Pei Tang, Jian Zhu, Cuiying Lu, Bingjun Yang, Qingyun Dou, Xingbin Yan (2026). Advancing lithium-air capacitor batteries through redox pair-enabled dual-cathode configurations. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3774-3
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Frequently Asked Questions
What is the failure mechanism of redox mediators in LACBs and how does the dual-cathode configuration mitigate it?
Redox mediators (RMs) deactivate due to electrode passivation by insoluble discharge products (Li2O2) that block electron transfer. The dual-cathode configuration separates the air electrode (AE) and capacitor electrode (CE), allowing the CE to maintain a clean surface and provide sustained electron supply to RMs, delaying deactivation. This is evidenced by improved cycling: RM-enhanced LACB achieved over 250 cycles at 2 mA cm−2 with 0.5 mAh cm−2 limit, compared to 218 cycles for PP-RM-LACB.
How does the oxygen barrier film affect the performance of the capacitor electrode and overall battery?
The oxygen barrier film prevents oxygen from reaching the capacitor electrode (CE), preserving its porous structure and preventing deposition of discharge products. PET film, with superior oxygen resistance, maintained a cleaner CE surface, leading to higher rate capability (0.5 mAh cm−2 at 4 mA cm−2 vs. 0.13 mAh cm−2 for PP) and improved cycling (279 cycles at 1 mA cm−2 vs. 218 cycles for PP). However, excessive barrier can limit oxygen supply to the air electrode, slightly reducing maximum discharge capacity at low current densities.
What is the practical significance of the 0.54 V reduction in charging voltage?
A 0.54 V reduction in charging voltage at 0.1 mA cm−2 directly improves round-trip energy efficiency by reducing overpotential. This translates to lower energy consumption during charging and reduced parasitic reactions, which is critical for commercial viability. For example, in grid-scale storage, a 0.54 V reduction can lead to significant operational cost savings over the battery's lifetime.
How does the aluminum foil sealing technique achieve high power density and what are its limitations?
Aluminum foil sealing minimizes oxygen and moisture ingress, reducing electrolyte degradation and mass transport limitations. This enabled a power density of 13.8 mW cm−2 at 6 mA cm−2, which is higher than typical open-cell configurations. However, the sealing may limit oxygen availability for the air electrode, potentially reducing discharge capacity at low current densities. The trade-off between power density and capacity must be optimized for specific applications.
What are the scalability challenges for the dual-cathode LACB with redox mediators?
Scalability challenges include ensuring uniform distribution of redox mediators in large-format cells, managing oxygen barrier film integrity over large areas, and maintaining low internal resistance. The study demonstrates laboratory-scale performance, but industrial scale-up would require cost-effective manufacturing of dual-cathode structures and high-barrier films. Additionally, the long-term stability of RMs and electrolyte under repeated cycling must be validated. The reported cycling data (up to 279 cycles) suggests potential, but further optimization is needed for commercial lifespans exceeding 1000 cycles.
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