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]O-2 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]O-2 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. (C) 2010 Elsevier B.V. All rights reserved.