Effect of Surface Modification with Spinel NiFe₂O₄ on Enhanced Cyclic Stability of LiMn₂O₄ Cathode Material in Lithium Ion Batteries

The spinel NiFe 2 O 4 widely used as anode active material for lithium ion batteries (LIBs) was prepared as a coating layer on LiMn 2 O 4 particles via a sol–gel route followed by heat treatment. The effect of the surface modification on the electrochemical performances of the cathode material was investigated both in LiMn 2 O 4 ∥Li and LiMn 2 O 4 ∥graphite batteries. The well-crystallized NiFe 2 O 4 coating layer shows a continuous and uniform film with a thickness of 10–11 nm on the surface of the LiMn 2 O 4 material. The as-prepared LiMn 2 O 4 /NiFe 2 O 4 composite with a coating amount of 1% shows an improved rate performance due to the high activity of the coating material. At an elevated temperatures of 55 °C, the initial discharge capacity at 0.1 C is 130.8 mAh/g, and the capacity retention is 84.5% after 400 cycles at 1 C when it is tested in a LiMn 2 O 4 ∥Li cell, while a full battery with the modified LiMn 2 O 4 ∥graphite as cathode material shows a capacity retention of 89.1% after 500 cycles. The enhanced cyclic performance can be attributed to the good physical properties of mechanical strength and thermal stability from NiFe 2 O 4 material. The rate performance is also improved due to the higher Li cyclability of the coating layer, which has been proven by the CV and EIS tests. The inherent advantages of natural abundance, ecofriendliness, and low cost make it practical for large-scale modification of the relevant electrode materials which are attacked by electrolyte when charged to high potentials and similarly could benefit from surface stabilization.