​Enhanced electrochemical performance of Ni-rich cathode for lithium ion batteries under elevated cut-off voltage (4.5 V): Elongated cycle stability of cathode by relaxed mechanical stress in the presence of internal porous layer
The improved cycling performance for Ni-rich cathode materials of LiNi0.8Co0.1Mn0.1AlxO2 with an inner porous layer (LNCMA@iPL) were obtained under a high cut-off potential of 4.5 V. The cathode materials (LNCMA@iPL) were prepared by the intermittent addition of Al salt during hydroxide precursor co-precipitation, exhibiting the spherical morphology with the structure of core (active material particle) and shell (inner porous layer). The as-formed cathode material (LNCMA@iPL) showed the elongated cycling performance under the cut-off potential of 4.5 V, attributable to the reduced mechanical stresses (or reduced inner particle crack propagation) from anisotropic phase transformation of the hexagonal (2) (H2) to the hexagonal (3) (H3). As a result, our LNCMA@iPL cathode exhibited high reversible discharge capacity of 222 mAh/g at 0.1C, indicating almost full utilization of charges in the cathode. More importantly, the as-constructed cathode of Ni-rich LNCMA with iPL (LNCMA@iPL) exhibited almost the record high Ni-rich cathode performance of 98.2 % capacity retention after 100 cycles under a high current density (1C = 190 mAh/g) and a cut-off voltage (4.5 V). Such an excellent performance of LNCMA@iPL cathode was further corroborated by the hardness measurements for material and AC-impedance, revealing a retained particle strength above 90 MPa and reduced total resistance (48 %) compared with that of LNCMA after 100 cycles.​