Feixiang Ding

Surface Heterostructure Induced by PrPO4 Modification in Li1.2[Mn0.54Ni0.13Co0.13]O2 Cathode Material for High-Performance Lithium-Ion Batteries with Mitigating Voltage Decay

Lithium-rich layered oxides (LLOs) have been attractive cathode materials for lithium-ion batteries because of their high reversible capacity. However, they suffer from low initial Coulombic efficiency and capacity/voltage decay upon cycling. Herein, facile surface modification of Li1.2Mn0.54Ni0.13Co0.13O2 cathode material is designed to overcome these defects by the protective effect of a surface heterostructure composed of an induced spinel layer and a PrPO4 modification layer. As anticipated, a sample modified with 3 wt % PrPO4 (PrP3) shows an enhanced initial Coulombic efficiency of 90% compared to 81.8% for the pristine one, more excellent cycling stability with a capacity retention of 89.3% after 100 cycles compared to only 71.7% for the pristine one, and less average discharge voltage fading from 0.6353 to 0.2881 V. These results can be attributed to the fact that the modification nanolayers have moved amounts of oxygen and lithium from the lattice in the bulk crystal structure, leading to a chemical activation of the Li2MnO3 component previously and forming a spinel interphase with a 3D fast Li+ diffusion channel and stable structure. Moreover, the elaborate surface heterostructure on a lithium-rich cathode material can effectively curb the undesired side reactions with the electrolyte and may also extend to other layered oxides to improve their cycling stability at high voltage.

Effect of Nb 5+ charge neutralization substitution on the electrochemical performance of lithium-rich layered oxides

The effect of the Nb5+ substitution with a charge-compensated strategy in lithium-rich layered oxides (LLOs) Li1.2Ni0.13+xCo0.13-xMn0.54-xNbxO2 (x = 0, 0.01, 0.02, and 0.03) has been investigated systematically. A hydroxide co-precipitation method followed by a high-temperature solid-state reaction is adopted in the synthesis process. Structural characterization confirms that the low dose substituting of Nb5+ in the layered structures forms a solid solution, and the samples show low cation mixing and enlarged Li+-diffusing channels, which imply favorable high-rate capability. The initial charge/discharge measurements suggest that the oxygen loss from the network during the delithiation process has been suppressed by the substitution of Nb5+ due to the formation of robust Nb–O bonds and a decrease in TM-O (TMs are transition metals) covalence. Moreover, these Nb–O bonds contribute to the stabilization of the crystalline framework, resulting in an excellent cycle stability with a mitigated voltage decay.