Ni-rich cathode materials have been
increasingly studied due to
their satisfactory capacity. However, the rapid attenuation in capacity
and poor rate capability of Ni-rich cathodes, especially at a high
voltage, limit their practical use. We propose a new strategy for
codoping LiNi0.8Co0.1Mn0.1O2 with Na and Br. Various morphological and structural characterizations
show that Na doped at Li sites act as pillar ions that expand the
lithium-layer spacing, and Br doped at O sites form stronger covalent
bonds. Codoping inhibits Li+/Ni2+ mixing, decreases
residual lithium on the surface, and stabilizes the crystal structure.
Electrochemical tests show that codoping 0.02 mol of Na and Br provides
the best cycling performance and rate capability. The capacity retention
rate after 100 cycles reaches 87.68% at 0.2C and 94.41% at 1C at high
voltages of 3.0–4.5 V; in contrast, pristine LiNi0.8Co0.1Mn0.1O2 provides a capacity
retention rate of only 69.02% at 0.2C. Cyclic voltammetry and electrochemical
impedance show that the Li+ diffusion coefficient increases
and the charge-transfer resistance decreases, while the capacity versus
voltage curves demonstrate the inhibition of phase transitions. These
results indicate that codoping Na and Br is a simple and effective
strategy for developing high-performance Ni-rich cathode materials.
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