리튬이차전지용 양극활물질 LiNi0.5Mn1.5O4의 표면개질에 의한 전기화학적 특성에 관한 연구

Abstract

This study examines the effect on the electrochemical cycling performance of LiNi0.5Mn1.5O4 by surface modification. The effect of the Li2O–2B2O3 (LBO) glass coating on the charge–discharge cycling performance of LiNi0.5Mn1.5O4 was investigated in the range of 3.5–4.9 V at high temperature (60 oC). LBO amorphous film with the thickness in the range of 3-5 nm are observed on the surface of LiNi0.5Mn1.5O4 particles. The discharge capacity of pristine LiNi0.5Mn1.5O4 decreases from 131.69 to 86.45 mAh g−1 after 50 cycles, the reduced capacity being 69.03 % of the initial capacity. However, the discharge capacity of the LiNi0.5Mn1.5O4 powders with 0.3 wt% glass material decreases from 123.43 to 106.94 mAh g−1 after 100 cycles. The capacity retention is 86.64% of the initial capacity. The lithium boron oxide (LBO) glass material improves the cycle performance of the LiNi0.5Mn1.5O4 powders at high voltage. LiNi0.5Mn1.5O4 spinel cathode materials were coated with vanadium pentoxide by solution process, followed by calcination at 400 oC for 3 h in air. XRD patterns of V2O5-coated LiNi0.5Mn1.5O4 revealed that the coating did not affect the main crystal structure or the [Fdm] space group of the cathode materials compared to uncoated LiNi0.5Mn1.5O4. However the peaks of LixNi1-xO gradually decreased by V2O5 coating. TEM image showed Nanoparticle of V2O5 was observed on the surface of cathode material. The XPS data illustrated that the V2O5 completely coated the surface of the cathode materials. V2O5 coated material demonstrated higher rate capability and cycle performance than pristine material. CV curve estimated the presence of LiNiVO4 in the range of 0.1 – 3.0 V. Discharge capacity of the coated electrode was 132 and 37 mAh g-1 at 0.1 and 20C rates, respectively, while uncoated electrode was 137 and 11 mAh g-1, respectively. The enhanced electrochemical properties were due to both decreasing the impurity and forming the lithium nickel vanadate.