Enhanced regional electric potential difference of graphdiyne through asymmetric substitution strategy boosts Li+ migration in composite polymer solid‑state electrolyte

A transformative study released in Nano-Micro Letters unveils an “enhanced regional electric potential difference” (EREPD) design that propels composite polymer solid electrolytes (CPSEs) to record-high performance. Led by Chao Jiang, Kaihang Wang and Ning Wang from Shandong University, the work introduces methoxy-substituted graphdiyne (OGDY) as a 2D nanofiller that simultaneously boosts ionic conductivity to 1.1 × 10^-3 S cm^-1, raises the Li⁺ transference number to 0.71 and suppresses dendrites in flexible, quasi-solid-state lithium cells.

Why This Research Matters

• Overcoming Low Ionic Conductivity: Conventional PEO-based solid electrolytes suffer from sluggish Li⁺ transport (≈10^-4 S cm^-1) and limited transference numbers (<0.3), hindering room-temperature operation of solid-state batteries. The EREPD strategy creates continuous potential gradients that slash activation energy to 0.42 eV—0.06 eV lower than pristine PEO—enabling safe, high-rate, long-life power sources.

• Enabling Flexible, High-Energy Devices: From wearable sensors to EV battery packs, applications demand thin, bendable electrolytes that withstand mechanical abuse. OGDY/PEO films retain 1280 % elongation, sustain 850 h of Li||Li cycling and power 42-LED arrays even after cutting, folding and bending, demonstrating real-world viability.

Innovative Design and Mechanisms

• Asymmetric Substitution & Periodic EREPD: Bottom-up Glaser–Hay coupling installs methoxy groups at three meta positions of the GDY benzene ring, generating alternating electron-rich (ERR) and electron-deficient (EDR) regions. NPA charge analysis reveals localized differences up to 0.94 e; the resulting 0.44 eV EREPD between ERR and EDR sites steers Li⁺ along low-barrier pathways.

• Dual Lewis Acid–Base Function: ERRs act as Lewis bases, weakening Li⁺–PEO binding (−1.29 to −2.52 eV vs −4.16 eV in PEO) and accelerating segmental motion. EDRs function as Lewis acids, anchoring TFSI^- (BE > 4.7 eV) to liberate free Li⁺ and suppress ion clusters. Raman shows 82.5 % free TFSI^- versus 76.2 % in PEO.

• Crystallinity Suppression & Mechanical Robustness: The 2D lamellar OGDY imposes steric hindrance and electrostatic attraction (−1.61 kcal mol^-1) that cut PEO crystallinity, lower Tg to −54.9 °C and triple ionic mobility while maintaining film flexibility.

Applications and Future Outlook

• Record Symmetric-Cell Lifespan: Li||OGDY/PEO||Li cells cycle 850 h at 0.1 mA cm^-2/0.1 mAh cm^-2, nine times longer than PEO (90 h). SEM reveals flat Li deposits and a 7.5 µm SEI versus 10.3 µm dendritic layers in PEO. Critical current density rises from 0.75 to 1.0 mA cm^-2.

• Full-Cell & Pouch-Cell Performance: LFP||OGDY/PEO||Li delivers 158.7 mAh g^-1 at 0.5 C, 91.4 % capacity retention after 205 cycles and retains 118 mAh g⁻¹ at 2 C. A 2 cm × 2 cm pouch survives bending, folding and cutting while continuously lighting LEDs, proving mechanical integrity and safety.

• Scalable Synthesis & Universal Design: Solution-processable OGDY is compatible with roll-to-roll coating and can be extended to Na⁺, K⁺ and Zn²⁺ systems. Future work will tailor substituent patterns and integrate OGDY with high-voltage cathodes for >400 Wh kg^-1 solid-state packs.

Conclusions
By orchestrating asymmetric methoxy substitution to create periodic EREPDs, this study transforms graphdiyne from a passive filler into an active Li⁺ highway. The resulting OGDY/PEO electrolyte simultaneously achieves high conductivity, high transference and dendrite suppression, charting a practical route toward flexible, safe and energy-dense all-solid-state lithium batteries.