| dc.description.abstract | LiNi0.5Mn1.5O4 (LNMO) has the highest operating voltage (4.7 V vs. Li/Li+) and moderate capacity (140 mAh g-1), which lead to a favorable energy density. However, the high operating voltage (>4.5V) will cause the decomposition of commercial electrolyte (lithium hexafluorophosphate (LiPF6) dissolved in organic carbonates) easily. It would be accelerated by high-voltage cathode side, resulting in battery failure. On the other hand, the electrode composition will also cause some problem at high operating voltage. For example, the aluminum is used as a current collector for the positive electrode. It accelerates the dissolution of the current collector and even the shedding of active substances at high voltage. Besides, the polymer binder PVDF used in electrodes has the characteristic of insulation, hindering electron transfer from the active materials to the current collector and degrading the whole performance of the electrode.
To solve these problems, we provide two strategies in the study. First, we used carbon paper (CP) to replace the aluminium current collector. This is because the CP has the 3D structure to enhanced the diffusion of Li+ and also avoid the shedding of active substances. Second, we carbonized polyvinylpyrrolidone (PVP) and used it to replace the PVDF binder. This tactic not only increased the electrical conductivity of electrode, but also prevented insulating binder which may induce some side reactions with the electrolyte. Besides, when we carbonized the PVP, a carbon coating layer can be formed on LNMO. This coating layer may protect the activity material from the attack of corrosive products of electrolyte degradation and mitigate the electrolyte decomposition. In addition, the properties of the PVP binders changed drastically because of the interactions with the different solvents (water, ethanol), significantly affecting the capacity and electrochemical cycle stability of the electrodes.
Among all of the samples, water /ethanol (50 / 50 wt%) as a solvent and annealed for 2 hours have the highest discharge capacity (122.5mAh g-1) and excellent rate capability and cycle stability (93.4%). The modified electrode has better cycle stability than the traditional electrodes made of carbon paper and aluminum foil current collectors (rate capability: 79.2% and 65.6%). | en_US |