Core–shell structured Li[(Ni0.8Co0.1Mn0.1)0.7(Ni0.45Co0.1Mn0.45)0.3]O2 cathode material for high-energy lithium ion batteries

Highlights: • A core-shell cathode material is redesigned without composition change. • Core-shell material displayed a superior cyclability and thermal stability. -- Abstract: The comparative investigations between core–shell and non-core–shell structured layered materials with a same composition are seldom reported and extremely necessary. Li[Ni0.7Co0.1Mn0.2]O2 is firstly redesigned into core–shell structured Li[(Ni0.8Co0.1Mn0.1)0.7(Ni0.45Co0.1Mn0.45)0.3]O2 and the detailed comparative investigations between them are performed in this work. In this core–shell structure, Li[Ni0.8Co0.1Mn0.1]O2 with high capacity is encapsulated completely with Li[Ni0.45Co0.1Mn0.45]O2 as a stable layer. Transition metal hydroxide precursors were synthesized by coprecipitation method. The core–shell structure of hydroxide precursor as designed was identified by particle size analysis, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and derivative thermogravimetric analysis (DTG). The obtained core–shell precursor was calcined with stoichiometric Li2CO3 (nLi:nM = 1.05:1) at 850 °C for 16 h to get lithiated oxide. XRD results showed that lithiated oxide can be indexed to a typical layered structure with a R-3m space group. EDS analysis from the cross-section of core–shell material particles revealed somewhat diffusion of cations in core–shell structure resulting in a concentration gradient layer, however, the core–shell structure of lithiated oxide was still remained. The electrochemical and differential scanning calorimetry (DSC) tests showed that core–shell structured Li[Ni0.7Co0.1Mn0.2]O2 displayed remarkably improved cyclability and thermal stability compared with the non-core–shell structured one. These results can clarify the function of core–shell structure in core–shell structured layered materials by excluding the effects of composition variation