Figure 5. (a) Nyquist plots and (b) linear sweep voltammograms of PP, cellulose and cellulose/CaCO3 membrane. Ionic conductivities of (c) cellulose and (d) cellulose/CaCO3-1 membranes in variable temperatures.
The cycling performances of LiFePO4/Li batteries assembled with cellulose and cellulose/CaCO3-1 membranes were evaluated. As shown in Figure 6a , the initial discharge capacity of LiFePO4/Li batteries assembled with cellulose/CaCO3-1 membrane reaches 144.2 mAh g-1, which is higher than that of cellulose membrane based battery (138.7 mAh g-1). The reason may be attributed to the higher ionic conductivity of cellulose/CaCO3-1 membrane. With the formation of solid electrolyte interface (SEI), the interfacial resistance reduces. Consequently, the discharge capacity of batteries increases steadily. For the battery with cellulose/CaCO3-1 membrane, the stable capacity is 149.0 mAh g-1. Moreover, capacity retention is as high as 97.4% after 230 cycles. In contrast, the battery with cellulose membrane has a severe decay and only remains 121.3 mAh g-1 after 100 cycles. The excellent cycle performance is ascribed to the electrochemically interfacial stability.
The electrode morphology after the battery cycle can reveal the actual electrochemical reaction condition of the battery. In order to further analyze the difference in battery performance, the surface of Li anodes after cycling was observed (Figure 6b ). As for cellulose based battery, Li anode became black according to the digital photo, which is caused by the diffusion of active cathodes.[27] As regards the CaCO3-modified battery, Li anode can retain the original appearance even after 230 cycles. Besides, the morphologies were observed by SEM, and corresponding results are supplied inFigure 6b . Notably, the Li structure of cellulose based battery is broken, while the CaCO3 modified battery is complete. Furthermore, the electrolyte/electrode interface is damaged by HF generated by electrolyte decomposition. Conversely, the negative impact of HF on cellulose/CaCO3-1 based battery can be eliminated through the neutralization of nano-CaCO3. With higher thermal and dimensional stability, the battery equipped with cellulose/CaCO3-1 membrane exhibits high-performance and great potential application in new energy fields.