LiO 2 (NCA) and LiO 2 (NCM) layered cathode materials were obtained from these efforts, and they are currently the two most widely used layered cathode materials in commercial batteries 13. Therefore, mixtures of LCO and LNO, supplemented with a wide variety of tertiary elements (LiO 2 (M = doping element)), have been explored to realise cathodes with adequate capacity and cycling performance 10, 11, 12. Metallic dopants (such as Al, Ga, Mn, Mg, and Ti) were added to LNO for stability however, they could not overcome the loss in capacity 5, 6, 7, 8, 9. Although LNO delivered much higher capacity at lower cost, it was unsuitable for commercial application owing to its inferior cycling and thermal stabilities, which were ascribed to the heightened surface chemical reactivity of Ni 3+/4+ and crystal structure destabilisation resulting from anisotropic internal strain caused by phase transitions in the deeply charged state 2, 3, 4. This material showed adequate electrochemical performance however, due to its high cost, toxicity, and mediocre capacity, LiNiO 2 (LNO) was suggested as an alternative. The first transition metal (TM) oxide to be applied as a LIB cathode was LiCoO 2 (LCO) 1. Among the various LIB components, the cathode is the most expensive and heaviest, and thus, it considerably influences the cost as well as the overall performance of a LIB hence, the development of cathodes is critical to the success of LIBs. Lithium-ion batteries (LIBs) have attracted significant attention as power sources for contemporary electric vehicles (EVs). Furthermore, physicochemical measurements and analyses suggest substantial differences in the grain geometries and crystal lattice structures of the various cathode materials, which contribute to their widely different battery performances and correlate with the oxidation states of their dopants. In particular, Li-ion pouch cells with Ta 5+- and Mo 6+-doped LiO 2 cathodes retain about 81.5% of their initial specific capacity after 3000 cycles at 200 mA g −1. Galvanostatic cycling measurements in pouch-type Li-ion full cells show that cathodes featuring dopants with high oxidation states significantly outperform their undoped counterparts and the dopants with low oxidation states. Here, we explore the impact of the oxidation states of various dopants (i.e., Mg 2+, Al 3+, Ti 4+, Ta 5+, and Mo 6+) on the electrochemical, morphological, and structural properties of a Ni-rich cathode material (i.e., LiO 2). Many studies on various dopants have been reported however, a general relationship between the dopants and their effect on the stability of the positive electrode upon prolonged cell cycling has yet to be established. Doping is a well-known strategy to enhance the electrochemical energy storage performance of layered cathode materials.
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