Effect of Sodium Content on the Reversible Lithium Intercalation into Sodium-Deficient Cobalt–Nickel–Manganese Oxides NaxCo1/3Ni1/3Mn1/3O2 (0.38 ≿x ≿0.75) with a P3 Type of Structure

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• 作者：Svetlana Ivanova ; Ekaterina Zhecheva ; Rositsa Kukeva ; Georgi Tyuliev ; Diana Nihtianova ; Lyuben Mihailov ; Radostina Stoyanova
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：February 25, 2016
• 年：2016
• 卷：120
• 期：7
• 页码：3654-3668
• 全文大小：1031K
• ISSN：1932-7455

文摘

Layered lithium transition metal oxides with optimized nickel–manganese content are nowadays of primary interest as electrode materials for lithium ion batteries, since they are able to deliver a high capacity at a low cost. Herein we report a new class of less expensive cathode materials, which comprise sodium-deficient cobalt–nickel–manganese oxides Na_xCo_1/3Ni_1/3Mn_1/3O₂ characterized with a layered structure and broad concentration range of sodium solubility. Na_xCo_1/3Ni_1/3Mn_1/3O₂ oxides are obtained by thermal decomposition of mixed acetate–oxalate precursors, followed by thermal annealing between 700 and 800 °C. In the concentration range of 0.33 < x ≤ 0.75, Na_xCo_1/3Ni_1/3Mn_1/3O₂ oxides assume a layered structure with a three-layer stacking (i.e., P3 type of structure). Based on electron paramagnetic resonance spectroscopy operating in the X-band (9.4 GHz), it is found that the charge compensation of Na deficiency is achieved by preferential oxidation of Ni²⁺ to Ni³⁺ and Ni⁴⁺, while Co and Mn ions retain their oxidation state of 3+ and 4+ within the whole concentration range. The electrochemical performance of Na_xCo_1/3Ni_1/3Mn_1/3O₂ in model lithium cells is simply controlled by the amount of sodium content in the pristine compositions: a higher reversible capacity is achieved for sodium-rich oxides (i.e., 0.75 ≥ x ≥ 0.67), while sodium-poor oxides (i.e., 0.38 ≤ x ≤ 0.50) display a lower reversible capacity and improved cycling stability. The mechanism of the lithium intercalation into Na_xCo_1/3Ni_1/3Mn_1/3O₂ is discussed on the basis of ex situ XRD, HRTEM, and X-ray photoelectron spectroscopy analyses.