Impact of precursor characteristics on the structural and electrochemical performance of spinel LiNi0.5Mn1.5O4 cathode materials

The spinel lithium nickel manganese oxide (LiNi_0.5Mn_1.5O₄, LNMO) has been paid wide attraction due to the features such as cobalt-free, environmental friendliness, high operating voltage and high energy density in material level. The precursor plays the key role in pursuing such goal. In this paper, LNMO was synthesized by co-precipitation method using two types of precursors (main differences were particle size and surface morphology). The discharge specific capacity of S-LNMO (prepared using smaller-size precursor) can reach high up to 139 mAh g⁻¹ (1 C = 150 mA g⁻¹), with a retention of 92.2 % after 100 cycles. After carefully characterized employing XRD, SEM, BET, in situ XRD and XPS, the origins of better electrochemical performance for S-LNMO could be summarized as follows: firstly, the precursor does not change the crystal structure of the LNMO material. Secondly, a ‘fusion phenomenon’ is observed during charging/discharging cycles in both LNMO materials, but the surface morphological evolutions are various with each other. Thirdly, S-LNMO sample with higher crystallinity and fewer structural defects suffer less from the respiratory effect during long-term lithiation/de-lithiation process. Fourthly, less amount of Mn³⁺ diminished the consequence of structural distortion during electrochemical reaction. In addition, the full battery further demonstrates that the structure of the S-LNMO material is more stable. These results provide insights for the design of advanced high-performance cathode materials for lithium-ion batteries.