Pressure-Induced Polymerization and Disproportionation of Li₂C₂ Accompanied with Irreversible Conductivity...

Li₂C₂ has the highest theoretical capacity (1400 mA·h·g^-1) as the electrode material for Li-ion battery, but suffers from low conductivity. Here we found that under external pressure its conductivity was irreversibly enhanced by 10⁹-fold. To explain that, we performed X-ray diffraction, Raman, IR, gas chromatography-mass spectrometry, and theoretical investigations under external pressure. We found that the C₂^2- anions approached to each other and polymerized upon compression, which is responsible for the irreversible enhancement of conductivity. The polymer has a ribbon structure and disproportionates into Li₃C₄ (Li_2-0.5C₂) ribbon structure, Li₆C₃ (Li propenide) and Li₄C₃ (Li allenide) upon decompression, implying that the carbon skeletal is highly electrochemically active. Our work reported polymerized Li₂C₂ for the first time, demonstrated that applying pressure is an effective method to prepare novel Li-C frameworks, and hence shed light on the search for novel carbon-based electrode materials.