High-Performance Li(Li_0.18Ni_0.15Co_0.15Mn_0.52)O₂@Li₄M₅O₁₂ Heterostructured Cathode Material Coated with a Lithium Borate Oxide Glass Layer

The continuous phase transformation to spinel LiMn 2 O 4 seriously hinders the electrochemical properties of Li-excess layered oxides in lithium ion batteries. Herein, we prepared a heterostructured Li-excess layered cathode material consisting of a Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 active material in conjunction with a surface Li 4 M 5 O 12 spinel and a Li 2 O-LiBO 2 –Li 3 BO 3 glass coating layer. The material showed improved electrochemical kinetic properties with respect to its pristine counterpart because the Li 2 O–LiBO 2 –Li 3 BO 3 glass layer not only improved the ionic conductivity of the material but also depressed the side reactions of the electrode with the electrolyte. In addition, the surface Li 4 M 5 O 12 spinel constantly grew inward the bulk of the material during long-term charge–discharge cycling instead of the conventional LiMn 2 O 4 transformation for the pristine Li(Li 0.18 Ni 0.15 Co 0.15 Mn 0.52 )O 2 . As a result, the heterostructured cathode material showed overall improved electrochemical performance. An initial discharge capacity of 258.8 mAh g –1 was obtained at the 0.2 C rate with remarkable capacity retention of 92.2% after 100 cycles. Moreover, the material showed excellent rate capacity delivering a high discharge capacity of 130.4 mAh g –1 and 100.4 mAh g –1 at the 10 and 20 C rates, respectively. Differential scanning calorimetry showed that the exothermic temperature of the fully charged electrode was elevated to 324.2 °C with little thermal release of 232.5 J g –1, demonstrating good thermal safety of the material.