Enhanced electrochemical properties of Li(Ni0.4Co0.3Mn0.3)O2 cathode by surface modification using Li3PO4-based materials

The surface of a commercial Li[Ni0.4Co0.3Mn0.3]O2 cathode is modified using Li3PO4-based coating materials. The electrochemical properties of the coated materials are investigated as a function of the pH value of the coating solution and the composition of coating materials. The Li3PO4 coating solution with pH 2 is found to be favorable for the formation of stable coating layers having enhanced electrochemical properties. The Li3PO4, Li1.5PO4, and PO4 coating layers are formed as amorphous phases. However, the Li3−xNix/2PO4 coating layers are composed of small particles with a crystalline phase covered with an amorphous phase. Li3PO4 and Li1.5PO4 coatings considerably enhance the rate capability of the Li[Ni0.4Co0.3Mn0.3]O2 electrode. In contrast, the Li3−xNix/2PO4 coating material, which contained Ni, has an inferior rate capability compared to the LixPO4 series (x = 1.5 and 3), although the LiNiPO4-coated electrode shows a better rate capability than a pristine one. Li3PO4-based coating materials are effective at enhancing the cyclic performance of the electrode in the voltage range of 3.0–4.8 V. DSC analysis also confirms the improved thermal stability attained by coating the cathode with Li3PO4-based materials.