In the process of upgrading energy storage structures, sodium‐ion batteries (SIBs) are regarded as the most promising candidates for large‐scale grid storage systems. However, the difficulty in further improving their specific capacity and lifespan has become a major obstacle to promoting extensive application. Herein, by optimizing synthesis conditions, a biphasic‐Na2/3Ni1/3Mn2/3O2 cathode that exhibits an ultrahigh capacity of ≈200 mAh g‐1 without the involvement of anion redox reactions is successfully synthesized. Nevertheless, there is significant electrochemical performance degradation because of failure at the cathode‐electrolyte interface as revealed by comprehensive analyses. Further in‐depth research proves that the surface side reactions that occur at high operating voltages and the transition metal dissolution that occurs in low voltage are the root causes of electrode surface failure. Therefore, the metal oxide atomic layer deposition (ALD) protective layer is deliberately chosen to suppress such failures. The coating effectively blocks corrosion of the cathode material by the electrolyte and successfully anchors the transition metal ions on the particle surface. As a result, the cycle stability and rate performance of the electrode are improved considerably. This surface engineering strategy could provide concepts with broad applicability for suppressing the failure of sodium layered cathodes.

Ni-rich layered cathode materials are considered as promising electrode materials for lithium ion batteries due to their high energy density and low cost. However, the low rate performance and poor electrochemical stability hinder the large-scale application of Ni-rich layered cathodes. In this work, both the rate performance and the structural stability of the Ni-rich layered cathode LiNi0.8Co0.1Mn0.1O2 are significantly improved via the dual-site doping of Nb on both lithium and transition-metal sites, as revealed by neutron diffraction results. The dual-site Nb-doped LiNi0.8Co0.1Mn0.1O2 delivers 202.8 mAh·g–1 with a capacity retention of 81% after 200 electrochemical cycles, which is much higher than that of pristine LiNi0.8Co0.1Mn0.1O2. Moreover, a discharge capacity of 176 mAh·g–1 at 10C rate illustrates its remarkable rate capability. Through in situ X-ray diffraction and electronic transport property measurements, it was demonstrated that the achievement of dual-site doping in the Ni-rich layered cathode can not only suppress the Li/Ni disordering and facilitate the lithium ion transport process but also stabilize the layered structure against local collapse and structural distortion. This work adopts a dual-site-doping approach to enhance the electrochemical performance and structural stability of Ni-rich cathode materials, which could be extended as a universal modification strategy to improve the electrochemical performance of other cathode materials.

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