Key Takeaways & Executive Findings
- •• • Li/Li symmetric cells with DN-FRQSPE achieve stable cycling beyond 2000 h without dendrite formation, directly addressing the short-circuit failure mode that limits conventional liquid electrolytes to <80 cycles in full-cell configurations. • • Li|DN-FRQSPE|LiFePO4 full cells retain 93% capacity after 200 cycles at 0.2C, corresponding to a 0.035% decay per cycle, which translates to a projected 10-year operational lifespan for stationary storage applications. • • The charge–discharge plateau gap remains only 0.13 V after 100 cycles, indicating low interfacial resistance and excellent compatibility between the DN-FRQSPE and both Li-metal anode and LFP cathode, a critical metric for high round-trip efficiency. • • XPS analysis shows suppressed Fe2+ to Fe3+ conversion in the LFP cathode with DN-FRQSPE, whereas liquid electrolytes cause continuous Fe3+ accumulation and capacity fade, demonstrating the electrolyte's role in stabilizing cathode–electrolyte interfaces.
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Abstract
Rechargeable lithium-metal batteries (LMBs) offer high energy density but suffer from dendrite formation and parasitic reactions with liquid electrolytes, leading to safety hazards and poor cycling stability. Quasi-solid-state polymer electrolytes (QSPEs) mitigate these issues but often exhibit inadequate thermal stability and Li-metal compatibility. This work presents a double-network structural hybrid polyester-based flame-retardant quasi-solid-state polymer electrolyte (DN-FRQSPE) synthesized via one-step in situ UV curing polymerization. The first network is a loosely cross-linked flame-retardant P-N containing polyacrylate from N,N-bis(2-hydroxyethyl acrylate) aminomethyl phosphonic acid diethylester (BHAAPE); the second network is highly cross-linked PMMA. The DN-FRQSPE exhibits excellent electrochemical performance, flexibility, and flame retardancy. Li/Li symmetric cells demonstrate stable cycling exceeding 2000 h with dendrite-free morphology. Li|DN-FRQSPE|LiFePO4 full batteries deliver a capacity retention of 93% after 200 cycles at 0.2C (0.035% decay per cycle) and a charge–discharge plateau gap of only 0.13 V after 100 cycles. The solid-state system outperforms liquid counterparts, which short-circuit within 80 cycles. Post-mortem SEM and XPS analyses reveal suppressed Fe2+ to Fe3+ conversion and reduced electrode corrosion. This DN-FRQSPE design provides a viable pathway for safe, long-life lithium-metal batteries.
1. Introduction
Rechargeable lithium-metal batteries (LMBs) promise energy densities far exceeding conventional graphite-anode Li-ion systems, but their commercial viability is stalled by two persistent failure modes: dendritic lithium deposition during plating and parasitic reactions between the highly reducing Li metal and liquid organic electrolytes. These reactions generate flammable gases (e.g., CH4, CO) and corrode the anode, leading to hazardous short circuits and rapid capacity fade. Quasi-solid-state polymer electrolytes (QSPEs) were proposed to mitigate these issues by combining the ionic conductivity of liquid electrolytes with the mechanical integrity of polymers. However, most QSPEs still suffer from poor thermal stability and inadequate compatibility with Li metal, resulting in inferior cycling stability and safety compared to liquid counterparts.
This work introduces a double-network structural hybrid polyester-based flame-retardant quasi-solid-state polymer electrolyte (DN-FRQSPE) synthesized via one-step in situ UV curing polymerization. The first network is a loosely cross-linked flame-retardant P-N containing polyacrylate derived from BHAAPE, while the second network is a highly cross-linked PMMA. This dual-network architecture simultaneously enhances mechanical strength, thermal stability, and flame retardancy. The in situ solidification process ensures intimate electrode–electrolyte contact, enabling dendrite-free Li plating/stripping for over 2000 h in symmetric cells and 93% capacity retention after 200 cycles in full cells. By suppressing Fe2+ to Fe3+ conversion and electrode corrosion, the DN-FRQSPE addresses the interfacial degradation that plagues liquid electrolytes, offering a scalable route to safe, long-life LMBs.
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XIA Wei, ZHANG Yu, ZHENG Ranran, CHEN Rufen, YAN Yang, WU Na, XIN Sen (2025). Building a safe and stable rechargeable lithium-metal battery by applying a flame-retardant, double-network structural hybrid polyester-based quasi-solid-state polymer electrolyte. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3350-4
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Frequently Asked Questions
What is the primary failure mechanism of conventional liquid electrolytes in lithium-metal batteries, and how does DN-FRQSPE specifically mitigate it?
Conventional liquid electrolytes react with the highly reducing Li metal anode, causing continuous electrolyte decomposition, gas evolution (CH4, CO), and dendrite growth that leads to short circuits. In full cells, liquid electrolytes also corrode the LFP cathode, accelerating Fe2+ to Fe3+ conversion and capacity fade. DN-FRQSPE mitigates these by forming a stable, flexible interface that suppresses dendrite formation (stable cycling >2000 h in Li/Li symmetric cells) and reduces Fe3+ accumulation, as confirmed by XPS. The solid-state full battery retains 93% capacity after 200 cycles, whereas the liquid counterpart short-circuits within 80 cycles.
What are the quantified electrochemical performance metrics of the DN-FRQSPE in full cells, and how do they compare to liquid electrolyte benchmarks?
Li|DN-FRQSPE|LiFePO4 full cells exhibit a capacity retention of 93% after 200 cycles at 0.2C (0.035% decay per cycle) and a charge–discharge plateau gap of 0.13 V after 100 cycles. In contrast, liquid electrolyte cells short-circuit within 80 cycles under identical conditions. The solid-state system also demonstrates rate performance comparable to liquid cells, attributed to a high lithium-ion transference number. These metrics indicate superior cycling stability and interfacial compatibility.
What is the role of the double-network structure in the DN-FRQSPE, and how does each network contribute to performance?
The first network, a loosely cross-linked flame-retardant P-N containing polyacrylate from BHAAPE, provides flame retardancy and ionic conduction pathways. The second network, highly cross-linked PMMA, enhances mechanical strength and thermal stability. Together, they form a hybrid structure that combines flexibility, flame retardancy, and electrochemical stability. FT-IR confirms that ester units in PMMA do not participate in polymerization, preserving its structural integrity. This dual-network design enables dendrite-free Li cycling and suppresses electrode corrosion.
What are the scalability and manufacturing implications of the in situ UV curing polymerization process for DN-FRQSPE?
The one-step in situ UV curing polymerization is compatible with roll-to-roll manufacturing, as it eliminates the need for separate electrolyte infiltration and cell assembly steps. The process uses commercially available photoinitiators and monomers (BHAAPE and PMMA precursors), and the liquid precursor wets electrodes intimately before solidification, ensuring good interfacial contact. However, UV penetration depth may limit thickness to <100 µm, and the cost of BHAAPE synthesis could be a barrier. Scale-up would require optimization of curing speed and monomer purity to maintain consistent ionic conductivity (>10^-4 S/cm) and mechanical properties.
How does the DN-FRQSPE address thermal runaway risks compared to conventional liquid electrolytes?
DN-FRQSPE incorporates a flame-retardant P-N containing polyacrylate network that intrinsically resists ignition, unlike flammable liquid carbonate electrolytes. The highly cross-linked PMMA network further enhances thermal stability, delaying decomposition. While specific limiting oxygen index (LOI) or self-extinguishing time (SET) values are not provided in the excerpt, the flame-retardant nature is a key design feature. This reduces the risk of thermal runaway in lithium-metal batteries, which is a critical safety concern for electric vehicles and grid storage.
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