P2‐NaCo_0.5Mn_0.5O₂ as a Positive Electrode Material for Sodium‐Ion Batteries

Abstract

As a promising positive electrode material for sodium-ion batteries (SIBs), layered sodium oxides have attracted considerable attention in recent years. In this work, stoichiometric P2-phase NaCo(0.5)Mn(0.5)O2 was prepared through the conventional solid-state reaction, and its structural and physical properties were studied in terms of XRD, XPS, and magnetic susceptibility. Furthermore, the P2-NaCo(0.5)Mn(0.5)O2 electrode delivered a discharge capacity of 124.3 mA h g(-1) and almost 100% initial coulombic efficiency over the potential window of 1.5-4.15 V. It also showed good cycle stability, with a reversible capacity and capacity retention reaching approximately 85 mA h g(-1) and 99%, respectively, at the 5 C rate after 100 cycles. Additionally, cyclic voltammetry and ex situ XRD were employed to explain the electrochemical behavior at the different electrochemical stages. Owing to the applicable performances, P2-NaCo(0.5)Mn(0.5)O2 can be considered as a potential positive electrode material for SIBs.

Layered Oxide Cathodes for Sodium‐Ion Batteries: Phase Transition, Air Stability, and Performance

“…Cycling in an expanded voltage window, P2-Na 0.67 Co 0.5 Mn 0.5 O 2 , delivered 0.56 Na + (147 mA h g −1 ) reversibly extracted in the voltage range of 1.5-4.3 V versus Na + /Na at 0.1 C rate, and nearly capacity retention of 100% demonstrating excellent cyclic stability over at least 100 cycles at 1 C. Moreover, no phase transition occurred with a single-phase solid solution reaction during cycling as shown in Figure 8c, which is consistent with the smooth charge/discharge curves without obvious plateau. [185,186] Due to the absence of long-range ordering of Co and Mn ions in the slab or Na + /vacancy in the interslab space, P2-Na 2/3 Co 2/3 Mn 1/3 O 2 was able to deliver the first discharge capacity of ≈119 mA h g −1 between 1.25 and 4 V versus Na + /Na at C/100, corresponding to intercalate ≈0.5 Na ions per formula unit. Interestingly, the charge compensation was achieved by the stabilization of low-spin Co 3+ and Mn 4+ ions.…”

Electrochemistry and Solid‐State Chemistry of NaMeO2 (Me = 3d Transition Metals)

“…P2‐Na 2/3 Mn 1/3 Co 2/3 O 2 can accommodate more Na in the structure and HS Mn IV and LS Co III were reported to reduce into HS Mn III and HS Co II , respectively, with major modification of hybridization between Me 3d and O 2p orbitals by Na insertion on discharge below 2.5 V. The electronic structures significantly change with formation of Jahn–Teller active Mn III and from LS‐Co III to HS‐Co II on the discharge, resulting in much lower voltage than P2‐Na 2/3 CoO 2 below 2.5 V in the Na cells . 0.16 Na can be reversibly inserted into Na 2/3 Mn 1/3 Co 2/3 O 2 on discharge from 2.5 to 1.25 V and large reversible capacity is obtained in P2‐Na x Mn 1/2 Co 1/2 O 2 but Na compensation is necessary for the practical use. Although P2‐Na 2/3 [Mn, Co, Ni]O 2 has been also extensively studied in Na batteries, the low working voltage and indispensableness of external Na compensation are drawbacks for P2‐Na 2/3 [Mn, Co]O 2 and the related materials.…”

A Safer Sodium‐Ion Battery Based on Nonflammable Organic Phosphate Electrolyte

“…Similar to their Li counterparts,1 though sodium‐based system has similar electrochemical reaction characteristics compared to lithium‐based one, the larger ionic radius for sodium ion cause sluggish kinetics and volume change during Na storage, leading to lower capacity, poor cycling and rate properties of the Na storage materials. Recently, major efforts have been devoted to promote the electrochemical performance of Na storage materials, for example, Na x MO 2 ,2, 3, 4, 5, 6, 7, 8, 9, 10 polyanionic framework compounds,11, 12, 13, 14, 15, 16, 17, 18, 19 hexacyanoferrate,20, 21, 22, 23, 24, 25, 26, 27 for the cathode materials, and hard carbons,28, 29, 30, 31, 32, 33 alloys,34, 35, 36, 37, 38, 39, 40, 41 oxides,42, 43 sulfides37, 44, 45, 46 for the anode materials.…”