Triggering anionic redox activity in Fe/Mn-based layered oxide for high-performance sodium-ion batteries

High-Voltage Layered Manganese-Based Oxide Cathode with Excellent Rate Capability Enabled by K/F Co-doping

“…The lattice fringes presented in the HR-TEM images of all samples are clear, and the crystal lattice fringe spacings d = 0.249 and d = 0.260 nm correspond to the P2 (1 0 0) and P′2 (0 2 0) crystal planes of the un-doped sample, respectively. When substituted by K + and F – , the d-spacing of the lattice fringe of P2 (1 0 0) and P′2 (0 2 0) crystal planes is increased to 0.254 and 0.263 nm, respectively, which is consistent with the XRD refinement results and further evidences K and F elements have been successfully incorporated into the lattice of the material . The lattice stripes of the two phases crossed together without obvious demarcation, indicating that the material belonged to the P2/P′2 hybrid structure.…”

“…As a result, the TM–O bond length increased, while the Na layer spacing decreased. Many studies have confirmed that the expansion of the Na layer reduces the Na + diffusion energy barrier and effectively promotes the migration of Na + ions in the bulk phase. − At the same time, the strengthened Na layer spacing mitigates the increased O–O layer repulsion as the sodium is removed and suppresses oxygen layer slipping, and the enhancement of TM-O layer binding has a positive effect on stabilizing the octahedral structure of TMO 6 and inhibiting the slip of the O layer during the cycling process.…”

“…With the increase of the KF doping ratio, the ratio of Mn 3+ /Mn 4+ changed from 2.314 to 2.489, 2.505, and 2.846, respectively, indicating that the content of electrochemically active element Mn 3+ continued to increase due to the charge compensation mechanism. Recent reports have pointed out that an appropriate increase in the content of Jahn–Teller active element Mn 3+ is conducive to providing structural flexibility to promote Na + diffusion and increase sodium storage capacity. , Turning to the high-resolution spectrum of O 1s, as shown in Figure b, the peaks near 529.5, 531.2, and 532.8 eV correspond to lattice oxygen, oxygen vacancies, and surface deposited oxygen species, respectively. , The calculated lattice oxygen proportion of NMO0, NMO25, NMO50, and NMO75 samples are 57.98, 63.47, 67.29, and 69.91%, respectively. It is generally believed that the larger the lattice oxygen ratio, the more stable the crystal structure .…”

“…When substituted by K + and F − , the d-spacing of the lattice fringe of P2 (1 0 0) and P′2 (0 2 0) crystal planes is increased to 0.254 and 0.263 nm, respectively, which is consistent with the XRD refinement results and further evidences K and F elements have been successfully incorporated into the lattice of the material. 35 The lattice stripes of the two phases crossed together without obvious demarcation, indicating that the material belonged to the P2/P′2 hybrid structure. At the same time, in the selected electron diffraction pattern of the NMO50 sample, the diffraction spots are bright and orderly arranged, corresponding to the P2 and P′2 single crystal diffraction patterns along the axis [0 0 1] and [1−1 1] directions, respectively, indicating that the material has good crystallinity.…”

Completely suppressed high-voltage phase transition of P2/O3-Na0.7Li0.1Ni0.1Fe0.2Mn0.6O2viaLi/Ni co-doping for sodium storage

“…[8][9][10][11] Among various cathode materials, P2-type Fe, Mn-based layered oxides for SIBs have been attractive owing to the huge abundance, eco-friendliness, and low price of Fe and Mn. [12][13][14][15] In particular, P2-Na 2/3 Fe 1/2 Mn 1/2 O 2 possesses a high capacity of 190 mA h g −1 within the potential range from 1.5 to 4.3 V, benefitting from those two redox couples of Fe 3+ /Fe 4+ and Mn 3+ /Mn 4+ . 16 However, P2-type cathode materials suffer from the adverse phase transformation of P2 to Z phase during the sodiation and desodiation processes.…”