Ni-rich cathode material with isolated porous layer hindering crack propagation under 4.5 V high cut-off voltage cycling

This study reports on a preparation of novel Ni-rich cathode material with isolated porous layer and its application into cathode in lithium ion batteries extending cut-off potential into 4.5 V. Using intermittent addition of Al salt during co-precipitation of Ni_xCo_1-x(OH)₂ (0 < x < 1), the isolated porous layer is easily formed inside the final active material particles maintaining overall mechanical integrity and their spherical shape without the change of external particle morphology. Even under severe cut-off potential of 4.5 V, volume expansion/contraction by anisotropic mechanical stress from hexagonal 2 to 3 (H2 → H3) phase transition is greatly reduced by hindering inner particle crack propagation into the external area at particle surface. Due to this phenomena, 227 mAh/g initial capacity at 0.1C was obtained upon 86 mol% of Ni content, with 75 % cathode capacity retention after 100 cycles under 1C, which is highest available capacity value among ever reported. Under full cell configuration, capacity retention at 100 cycles was 77 % and total available energy was increased into 15 % when compared with normal cycling condition of 4.3 V cut-off. From microtomic transmission electron microscope analysis, the porosity of inner particle was maintained as low as 6.67 % under 12 % increase of average primary particle size even after 100 cycles under 4.5 V cut-off voltage. From our advanced utilization of capacity and cut-off voltage, available energy in full cell application of our Ni-rich cathode material exhibited 20 % increase when compared with 4.3 V cut-off voltage.