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Li- and Mn-rich materials have high capacities but serious voltage attenuation, whereas Ni-rich materials LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM) have good rate characteristics but poor stabilities, and they readily to oxidize organic electrolytes. The core–shell strategy with Ni-rich materials as the core and Li- and Mn-rich materials as the shell was expected to balance these merits and drawbacks. In this work, simple and concentration-gradient Li- and Mn-rich shell were successfully synthesized on NCM and critically compared. As expected, a distinct core–shell interface was observed for the simple core–shell cathode, which causes the shell to crack during cycling and exhibits worse electrochemical performance than the single Li- and Mn-rich cathodes and Ni-rich cathodes. In contrast, the fabricated concentration-gradient core–shell cathode shows the uniform fusion of the core and shell at the atomic level, and the overall electrochemical performance is far superior to that of the simple core–shell and pristine cathodes. In addition, it delivers an initial reversible capacity of 226.6 mAh g−1 at a C-rate of 0.1C and 120.2 mAh g−1 at 10.0C, and it retains 86.9% of its capacity after 100 cycles to 4.6 V at 1.0C. Differential capacity versus potential (d Q /d V versus V) and EIS analyses show that the concentration-gradient core–shell cathode has a stable impedance and very stable average voltage. Obviously, the concentration-gradient coating of the Li- and Mn-rich shell can maximize the merits of the core and shell. • Both simple and concentration gradient Li- and Mn-rich shell coated samples increase the capacity of LiNi 0.8 Mn 0.1 Co 0.1 O 2. • A distinct core-shell interface was observed in simple core-shell cathode. • Simple core-shell structure exhibits a negative effect on cycling stability, rate capability and Li-ion diffusivity. • The concentration gradient Li- and Mn-rich shell is able to relieve side reactions and largely improved cycling stability. [ABSTRACT FROM AUTHOR]

The direct preparation of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (LNCM811) cathode materials from the hydrochloric acid leaching of laterite are promising; however, there are Cl− ions and other impurities in the hydrochloric acid leaching solution, thereby limiting the commercial application of LNCM811. In this study, we compared the LNCM811 prepared from Cl−- and SO 4 2−- ion precursor solutions, and observed that the existence of Cl− ions could result in agglomerate disjointed and the primary particles grew separately during the sintering process, further deteriorating the electrochemical performance. Therefore, the initial raw Ni/Co solid residues were washed with deionised water and leached with 25 wt% H 2 SO 4 solution to obtain an enriched Ni/Co solution with SO 4 2− anions. Furthermore, considerable impurities in the enriched Ni/Co solution caused primary particle separation during the sintering process and led to the LNCM811 having poor electrochemical properties. Therefore, it was further purified by extraction with Cyanex272 to obtain a pure NiSO 4 solution. The impurities in the NCM811 precursor prepared from this pure NiSO 4 solution were below standard limits, the corresponding lithiated cathode delivers an initial reversible capacity of 192.1 mAh g−1 at 0.1C with an initial Coulombic efficiency of 86.5%; it retains 85.1% of its capacity after 100 cycles at 1.0C in 2.8–4.3 V, thereby achieving the standard of commercial LNCM811. On this basis, combined with the previous research of our group, high-value utilisation of laterite for preparing cathode materials includes the following processes: hydrochloric acid leaching, preliminary purification, alkaline oxidation precipitation, conversion of the Cl− solution system to the SO 4 2− ion solution system, extraction, solution-phase synthesis, and calcination. Moreover, compared with the conventional process of preparing NCM811 from metal sulfates, the cost saving through the proposed process was found to be approximately 265.8 $/ton. • Cl− ions result in disjointed agglomeration of LiNi 0.8 Co 0.1 Mn 0.1 O 2. • Mg could lead to poor particle morphology and layered structure. • Extracting impurities via Cyanex272 shortened the production of pure NiSO 4 solution. • LiNi 0.8 Co 0.1 Mn 0.1 O 2 was synthesised from hydrochloric acid leaching of laterite. [ABSTRACT FROM AUTHOR]