Volume 2, Issue 1, Pages 125-140 (January 2018) Structure-Induced Reversible Anionic Redox Activity in Na Layered Oxide Cathode  Xiaohui Rong, Jue Liu, Enyuan Hu, Yijin Liu, Yi Wang, Jinpeng Wu, Xiqian Yu, Katharine Page, Yong-Sheng Hu, Wanli Yang, Hong Li, Xiao-Qing Yang, Liquan Chen, Xuejie Huang  Joule  Volume 2, Issue 1, Pages 125-140 (January 2018) DOI: 10.1016/j.joule.2017.10.008 Copyright © 2017 Elsevier Inc. Terms and Conditions

Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Crystal Structure of the Pristine Na0.6[Li0.2Mn0.8]O2 XRD pattern (λ = 0.24129 Å) of the as-prepared Na0.6[Li0.2Mn0.8]O2. The inset shows the structure of Na0.6[Li0.2Mn0.8]O2 material with the P3 stacking. The sodium, manganese, lithium, and oxygen atoms are shown in yellow, blue, green, and red, respectively. See also Figure S1 and Table S1. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Electrochemical Performance of Na0.6[Li0.2Mn0.8]O2 (A) Charge/discharge curves at different current rates of 0.1 C (10 mAg−1) and 2.0 C (200 mAg−1) within the voltage range of 3.5–4.5 V versus Na/Na+ for Na0.6[Li0.2Mn0.8]O2. (B) Comparison of discharge capacity and coulombic efficiency versus cycle number at 0.1 C and 2.0 C rate. See also Figure S2. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Crystal Structural Evolution of Na0.6[Li0.2Mn0.8]O2 The collected XRD patterns of Na0.6[Li0.2Mn0.8]O2/Na cell charged and discharged at a rate of C/20. See also Figure S12. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Detection of Local Structural Changes upon Desodiation Comparison of X-ray and neutron PDF of Na0.6[Li0.2Mn0.8]O2 collected at pristine and charged state (4.5 V). The representative peaks corresponding to such as the first coordinating O-O, Mn-O, and Mn-Mn bonding are labeled. Due to the relatively larger neutron scattering length of oxygen compared with that of manganese, the changes in the oxygen network associated with oxidation of oxygen anions are able to be detected by neutron PDF. See also Figures S4 and S5; Table S2. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 5 Structure of the Initial Charged (4.5 V) Sample Left: the refined 15-layer supercell model for the 4.5-V charged Na0.2[Li0.2Mn0.8]O2. Right: refinement results of the neutron diffraction data and PDF data using the structural model shown on the left. Local coordination environments of O and residual Na are shown as enlarged figure at the bottom. See also Tables S3 and S4. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 6 Spectroscopic Investigation of Charge Compensation Mechanism of Na0.6[Li0.2Mn0.8]O2 during Sodium Storage (A) The XPS O1s spectra collected for the pristine sample and samples charged to 4.5 V and discharged to 3.5 V. The peak at 530.5 eV appears/disappears at charged/discharged states, indicating the redox activity of lattice oxygen. (B and C) Mn K-edge (B) and Mn L-edge (C) spectra of Na0.6[Li0.2Mn0.8]O2 collected at different charge and discharge states. The Mn ions remain at Mn4+ in the voltage range between 3.5 and 4.5 V during Na+ deintercalation/intercalation. See also Figure S9. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 7 2D Nanoscale Mapping of Mn Oxidation States in Particles with Different Cycling History (A–H) The similarity in the overall color of the particles shown in the top row (pristine [A], charged at 4.5 V [B], discharged at 3.5 V [C], and discharged at 3.5 V after 30 cycles [D]) suggests the homogeneity of the Mn's oxidation states regardless of the SOC and the cycling history up to 30 cycles. The corresponding histograms of the Mn oxidation state over the highlighted particles are shown on the bottom row (E, F, G, and H). See also Figures S10 and S11. Joule 2018 2, 125-140DOI: (10.1016/j.joule.2017.10.008) Copyright © 2017 Elsevier Inc. Terms and Conditions