![]() ![]() Such a similar situation has been observed in Na-rich and Na-deficient layered oxides 9, 10, 11, 12, 13, 14. Ceder and co-workers proposed the origin of anionic redox in Li-rich and cation-disordered oxides 5: the formation of Li–O–Li interactions function as the impetus to trigger oxygen redox due to the weak overlap between O 2 p and Li 2 s orbitals, thus favoring the O 2p band approximate to the Fermi level and facilitating the oxygen redox reaction. The sodium storage mechanism has been intensively proposed on the key points to motivate the anionic redox that reported in Li-rich compounds from the last two decades 3, 4, 5, 6, 7, 8. Anion redox reaction that occurs during high voltage desodiation of layered oxide cathodes offers an avenue to realizing high-energy-density NIBs as it provides an additional capacity by storing charges on both transition metal cations and oxygen anion. As for the cathode active material, it is required to be reversibly operated at a high voltage and with a large Na + extraction. To achieve the goal, a feasible strategy is to improve the specific energy and energy density at the cell level. Specifically, the Cost-Per-kWh of NIBs should be reduced to increase their market competitiveness against Li-ion batteries (LIBs). However, the practical implementation of NIBs faced the issue of lower specific energy due to the relatively heavier and less-reducing potential of Na compared with Li. The growing proliferation of robust layered cathode and carbon anode materials has been intensively reported in the last few years. Na-ion batteries (NIBs) have been recognized as sustainable solutions to alleviate the resource anxiety of Li-based electrochemical energy storage mainly from sufficient and low-cost sodium raw materials 1, 2. A 71.28 mAh single-coated lab-scale Na-ion pouch cell comprising a pre-sodiated hard carbon-based anode and B-doped cathode material is also reported as proof of concept. The B-doped cathode material promotes reversible transition metal redox reaction enabling a room-temperature capacity of 160.5 mAh g −1 at 25 mA g −1 and capacity retention of 82.8% after 200 cycles at 250 mA g −1. The presence of covalent B–O bonds and the negative charges of the oxygen atoms ensures a robust ligand framework for the NaLi 1/9Ni 2/9Fe 2/9Mn 4/9O 2 cathode material while mitigating the excessive oxidation of oxygen for charge compensation and avoiding irreversible structural changes during cell operation. Here, we report a doping strategy by incorporating light-weight boron into the cathode active material lattice to decrease the irreversible oxygen oxidation at high voltages (i.e., >4.0 V vs. However, the irreversible oxygen redox reaction at the high-voltage region in sodium layered cathode materials generates structural instability and poor capacity retention upon cycling. Na-ion cathode materials operating at high voltage with a stable cycling behavior are needed to develop future high-energy Na-ion cells. ![]()
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