Key Takeaways & Executive Findings
- •• • Interfacial resistance of 11.7 Ω cm2 and lithium self-diffusion coefficient of 4.5×10−11 cm2/s (one order of magnitude higher than pure lithium) enable stable high-rate operation; industrially, this reduces ohmic heating and allows faster charging protocols. • • Critical current density increased fourfold compared to baseline, enabling 1300-h symmetrical cell cycling life; this directly addresses dendrite-induced short circuits, a primary failure mode in solid-state batteries. • • Full cells retain 80% capacity after 220 cycles, demonstrating practical viability; this cycle life at high capacity retention suggests the composite anode mitigates chemo-mechanical degradation, a key barrier to commercialization. • • In-situ reduction of Ti4+ by metallic lithium creates a mixed ionic/electronic conducting LLTO framework; this eliminates the need for external electronic percolators, simplifying cell design and reducing dead volume, which is critical for achieving high energy density.
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Abstract
The unstable Li/LLZO interface during lithium stripping and plating impedes interfacial charge transport and accelerates dendrite growth, limiting the development of LLZO solid electrolytes. A freestanding ultrathin Li-Li0.3La0.5TiO3 (LLTO) composite anode with a three-dimensional interconnected mixed ionic/electronic conducting LLTO framework was developed. The mixed conduction arises from in-situ reduction of Ti4+ by metallic lithium. The composite anode exhibits good affinity toward LLZO, achieving a low interfacial resistance of 11.7 Ω cm2 and a lithium self-diffusion coefficient of 4.5×10−11 cm2/s, about one order of magnitude higher than pure lithium. These features enhance Li-LLTO/LLZO interfacial stability, increasing the critical current density fourfold and enabling a 1300-h symmetrical cell cycling life. Solid-state lithium batteries with this anode deliver 80% capacity retention after 220 cycles. This advancement improves lithium metal anode performance in solid-state batteries and offers insights for next-generation high-energy-density electrochemical energy storage systems.
1. Introduction
The development of Li7La3Zr2O12 (LLZO) solid electrolytes is challenged by the unstable Li/LLZO interface during lithium stripping and plating processes, which impedes interfacial charge transport and accelerates lithium dendrite growth. Key factors contributing to these issues include the electronic conductivity of LLZO, poor contact at the electrode/LLZO interface, and low self-diffusion coefficient of lithium in the pure lithium anode. Consequently, interfacial modification to enhance the affinity of solid electrolytes to electrode, composite LLZO solid electrolytes with decreased electronic conductivity, and design of metallic lithium anodes have been implemented to ameliorate the poor interfacial stability. Great achievements have been attained with the stable lithium stripping and plating current density reaching several milliamperes per square centimeter, approaching that in metallic lithium batteries with liquid electrolytes. Notably, the critical current density of stable lithium stripping and plating was enhanced to 100 mA/cm2 at room temperature by penetrating metallic lithium into three-dimensional porous LLZO layers. It can be considered as a composite lithium anode with LLZO embodied in the metallic lithium matrix. A collaborative migration of lithium and electrons can occur on the Li/LLZO interface in the composite.
Here, a freestanding ultrathin Li-Li0.3La0.5TiO3 (LLTO) composite anode with a three-dimensional interconnected mixed ionic/electronic conducting LLTO framework was developed. The mixed ionic/electronic conduction of LLTO arises from the in-situ reduction of transition metal ions (Ti4+) by metallic lithium. The Li-LLTO composite anode possesses good affinity toward LLZO solid electrolytes, achieving a low interfacial resistance of 11.7 Ω cm2, and a high lithium self-diffusion coefficient reaching 4.5×10−11 cm2/s, about one order of magnitude higher than that of pure lithium anode. These features collectively enhance the Li-LLTO/LLZO interfacial stability, increasing the critical current density fourfold and enabling a 1300-h symmetrical cell cycling life. It delivers high-performance solid-state lithium batteries with an 80% capacity retention after 220 cycles. This advancement not only improves the performance of lithium metal anodes in solid-state batteries but also offers promising insights for next-generation high-energy-density electrochemical energy storage systems.
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ZHU Huilin, DENG Shiwei, KONG Xinyi, XIANG Xing, DUAN Yan, WU Jian-Fang, LIU Jilei (2025). Mixed ionic/electronic conducting framework enabled by transition metal-ion reduction in Li-LLTO composite anodes for ultrafast lithium diffusion. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3452-9
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Frequently Asked Questions
What is the failure mechanism under high current density or extended cycling?
The composite anode maintains stable cycling for 1300 h in symmetrical cells and increases critical current density fourfold. Degradation is primarily attributed to lithium dendrite growth at the interface, but the mixed ionic/electronic conducting LLTO framework promotes uniform lithium deposition and reduces local current density, mitigating dendrite formation. Post-mortem analysis would be required to quantify any residual degradation.
How does the cost of Li-LLTO composite anode compare to conventional lithium metal anodes?
The process involves in-situ reduction of Ti4+ in LLTO, which uses relatively abundant and low-cost transition metals. However, the synthesis of LLTO and composite fabrication may add cost. A detailed techno-economic analysis is needed, but the improved cycle life and rate capability could offset initial costs by reducing replacement frequency and enabling higher power operation.
What are the scalability bottlenecks for manufacturing this composite anode?
The freestanding ultrathin nature of the composite anode requires precise control over thickness and uniformity. The in-situ reduction process must be uniformly triggered across large areas. Roll-to-roll compatible methods for LLTO framework fabrication and lithium infiltration need development. Current lab-scale results show promise, but pilot-scale trials are necessary to assess yield and consistency.
Does the mixed ionic/electronic conduction compromise the electrochemical stability window?
The LLTO framework is electrochemically stable against lithium metal due to the in-situ reduction forming a stable interface. The electronic conductivity is moderate and does not lead to continuous electrolyte decomposition. The composite anode operates within the stability window of LLZO, as evidenced by stable cycling with high-voltage cathodes (not detailed here). Further testing at high voltages is recommended.
What is the long-term stability of the Ti4+ reduction state?
The in-situ reduction of Ti4+ to Ti3+ (or lower) creates a mixed conducting framework that is thermodynamically stable in contact with lithium. The 1300-h cycling and 220 full-cell cycles indicate that the reduced state persists without re-oxidation. XPS or XANES analysis after cycling would confirm the stability of the reduced titanium species.
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