NiO surface modification for NaNi1/3Fe1/3Mn1/3O2 cathode material
To improve the interface stability of O3-type layered oxide cathode material NaNi1/3Fe1/3Mn1/3O2(NFM)for enhancing its cycle stability and rate capability,NiO was used as a coating agent,surface modification of NFM was carried out by high-temperature solid-state reaction method.It is found that NiO coating has a melting aid effect,which is beneficial for particle growth and well crystallization.Compared with the uncoated sample,the specific surface area of the NiO-coated sample is reduces by about 50％,the NaOH content tested in the ethanol solvent is decreased by about 64％,and the pH value is also lowered significantly.Electrochemical performance tests show that the NiO-coated sample has a discharge specific capacity of 139.4 mA·h·g-1at 2.0-4.0V,with a 1 C capacity retention of 94.1％after 80 cycles.It also exhibits better rate performance and smaller polarization,significantly better than the uncoated sample.The performance improvement is attributed to the chemical reaction between NiO and residual sodium on the cathode surface during the heat treatment process,which generates a new sodium nickel oxide interfacial layer,preventing the electrolyte from corroding the cathode and suppressing the dissolution of the transition metals.The smooth and round surface of the cathode particles and the low specific surface area help to enhance the contact between particles and reduce side reactions with the electrolyte.Additionally,the newly generated NaFeO2 layer exhibits excellent electrochemical activity,promoting sodium ion diffusion and electron conduction between the cathode and electrolyte interface.
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