Electrochemical performance of 5 V LiNi0.5Mn1.5O4 cathode modified with lithium carbonate addition in electrolyte

• A novel lithium carbonate sand-like electrolyte is prepared.
• Capacity fading rate of the 5 V cathode is reduced by using the electrolyte.
• Li2CO3 can consume PF5 in the electrolyte.
• The oxidizability of Ni4+ on the cathode surface is weakened by adding Li2CO3.
• Intensive electrolyte oxidation is suppressed during cycling under high voltage.

LiNi0.5Mn1.5O4 electrode modification is achieved in this work through adding inorganic lithium carbonate (Li2CO3) into carbonate electrolyte. Superior cyclic stability of the cathode in the range of 5–2 V is attained, a capacity of 0.3698 mAh g−1 is lost per cycle, which is half of the value in the Li2CO3-free condition. The capacity loss above and below 3.5 V are both alleviated in the presence of Li2CO3. Its effect on both the electrolyte bulk and the cathode surface is analyzed with SEM, TEM and XPS measurements. The density functional theory (DFT) calculation is carried out to discuss the modification mechanism. It is speculated that Ni4+⋯CO32− coordination may be formed through the interaction between Ni and O, weakening the oxidizability of Ni4+ on the electrode surface. In addition, Li2CO3 can consume PF5 in the electrolyte. The interphase film can also maintain thin and steady during the cycling within 5–2 V.