Large-Scale Nanofiber Manufacturing| High-Performance Alginate-Poly(ethylene oxide)-Based SolidPolymer Electrolyte

Liu Shuai (Ocean University of China) & Liu Jie (Qingdao University): High-Performance Alginate-Poly(ethylene oxide) Based Solid Polymer Electrolyte

Traditional lithium secondary batteries face challenges like low energy density and safety concerns, severely limiting their application in electric vehicles and large-scale energy storage systems. Developing high-performance, safer lithium batteries is urgently needed. Replacing liquid electrolytes with safer solid electrolytes is widely regarded as an effective strategy to improve energy density and safety.Among options, solid polymer electrolytes (SPEs) are considered one of the most promising alternatives due to high elasticity, low electrode/electrolyte interface impedance, easy processing, and low cost. However, limitations like low ion conductivity, insufficient mechanical strength, and unsatisfactory flame retardancy hinder further development.

Recently, Liu Shuai's team (Ocean University of China) and Liu Jie's team (Qingdao University) published their latest research "High-Performance Alginate-poly(ethylene oxide) Based Solid Polymer Electrolyte" in ACS Applied Materials & Interfaces. They designed a PEO-based SPE using electrospun calcium alginate (CA) nanofiber membranes as frameworks.The abundant C=O and -OH groups in CA macromolecules effectively weaken Li+ coordination environments and promote LiTFSI dissociation, facilitating Li+ migration along PEO chains. Meanwhile, introduced Ca2+ during crosslinking significantly improves flame retardancy (Fig.1).

Fig.1: Preparation process and ion transport mechanism of CA-PEO SPE

The 40 CA-PEO SPE exhibits high ionic conductivity (3.86×10-4 S cm-1 at 30°C), excellent mechanical strength (2.01 MPa), and wide electrochemical window (5.32 V). Assembled Li-metal symmetric cells stably cycled over 3000 hours at 30°C. LiFePO4 (LFP)||Li all-solid-state batteries showed excellent cycling stability at 0.3C (141.2 mAh g-1 discharge capacity, 92.5% retention after 300 cycles).

Fig.2: Morphology/structure characterization and mechanical/flame-retardant tests

CA nanofiber membranes prepared by electrospinning were successfully incorporated into PEO-based SPEs (Fig.2). Results show CA nanofibers significantly reduce polymer crystallinity and modify Li+ coordination environments. The membranes also provide excellent mechanical strength (2.01 MPa) to suppress Li dendrite growth while improving flame retardancy for safer batteries.

Fig.3: Electrochemical performance and DFT calculations

As shown in Fig.3, the 40 CA-PEO SPE demonstrates the highest ionic conductivity (3.86×10-4 S cm-1 at 30°C), lowest activation energy (0.38 eV), widest electrochemical window (5.32 V), and highest transference number (0.62). When paired with LFP cathodes, it shows the highest Li+ diffusion coefficient (5.56×10-11 cm2 s-1) and fastest redox kinetics. DFT calculations further elucidate ion transport mechanisms.

Fig.4: Interface stability in Li symmetric cells

Interface stability was investigated using Li-metal symmetric cells (Fig.4). The 40 CA-PEO SPE exhibited lowest interface impedance, polarization voltage, and highest critical current density with optimal cycling stability at 30°C. Post-cycling morphology characterization confirmed effective dendrite suppression.

Fig.5: Rate capability and cycling stability of LFP||Li batteries

LFP||Li full cell tests validated 40 CA-PEO SPE compatibility (Fig.5). The cells demonstrated excellent rate capability, low polarization, and outstanding cycling stability (141.2 mAh g-1 capacity with 92.5% retention after 300 cycles at 0.3C).This work maximizes synergistic effects between alginate's unique macromolecular structure and electrospun nanofiber architectures, providing insights for developing high-performance all-solid-state lithium metal batteries.