Understanding sodium-ion diffusion in layered P2 and P3 oxides via experiments and first-principles calculations: a bridge between crystal structure and electrochemical performance

268

192

perspective, K-ion cells would be a more reasonable choice as a low-cost alternative to Li-ion since K has high natural abundance and a lower standard redox potential than Na (K/K + : −2.9 V and Na/ Na + : −2.7 V vs saturated hydrogen electrode in aqueous media). [1] Indeed, the potential of K/K + was theoretically calculated to be even more negative than that of Li/Li + in propylene carbonate, a well-known battery electrolyte solvent. [2] Experimental demonstration that the standard redox potential of K/K + is lower than that of Li/Li + by ≈0.15 V in ethylene carbonate/diethyl carbonate (EC/DEC) electrolyte is consistent with this prediction. [3] This interesting feature suggests that KIBs might potentially deliver a higher cell voltage than Na-ion batteries (NIBs) and even LIBs. In addition, K-ion technology would benefit from the fact that graphite can be used on the anode side [3,4] (as in Li ion), which is not the case for Na ion and has seriously limited application of Na-ion technology.Only a few cathode compounds have been reported to date for KIBs, [5][6][7][8][9] with most studies focusing on the development of anodes. [3,4,[10][11][12][13][14][15][16][17][18][19][20] For example, Eftekhari demonstrated that Prussian blue can reversibly store K ions in a nonaqueous electrolyte system. [5] Later, the amorphous phase of FePO 4 as well as organic materials were also suggested as cathodes for KIBs. [6][7][8][9] Recently, K-ion insertion was shown to be possible in K 0.3 MnO 2 , [21] but the low K content of that material requires the use of K metal or pre-potassiated anodes.In this paper, we demonstrate highly reversible cycling of a P2-type K 0.6 CoO 2 cathode, and show implementation of a full cell KIB using a graphite anode. Alkali transition metal oxides with an ordered rock salt structure have been widely studied as promising cathodes for LIBs and NIBs because their layered framework allows topotactic de/intercalation of alkali ions, leading to excellent energy storage properties. [22][23][24][25][26][27][28] Cyclability and rate capability of K x CoO 2 are shown to be very good, indicating that with further improvements K ion may be an effective technology for large-scale energy storage. To the best of our knowledge, this is the first demonstration of reversible K de/intercalation in P2-type layered K x CoO 2 in the range 0.33 < x < 0.68. This work creates new research opportunities for the development of KIBs as a particularly exciting and promising technology for large-scale energy storage applications. K-ion batteries are a potentially exciting and new energy storage technology that can combine high specific energy, cycle life, and good power capability, all while using abundant potassium resources. The discovery of novel cathodes is a critical step toward realizing K-ion batteries (KIBs). In this work, a layered P2-type K 0.6 CoO 2 cathode is developed and highly reversible K ion intercalation is demonstrated. In situ X-ray diffraction combined with electrochemical titration reveals that P2-type ...

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

K‐Ion Batteries Based on a P2‐Type K_0.6CoO₂ Cathode

Kim

et al. 2017

268

192

“…It can be found that the peak current I p is linearly related to the square root of scanning rate ν 1/2 (Figure 4b), indicating that the kinetics exhibit a behavior similar to diffusion process. The D app calculated from the slope of dI p /dν 1/2 is competitive among many layered metal oxides reported for NIBs [21,24] (Table S2, Supporting Information). The high Na-ion diffusion coefficient is responsible for the competitive rate property of this O3-type cathode material.…”

Section: Excellent Comprehensive Performance Of Na-based Layered Oxidmentioning

confidence: 99%

Excellent Comprehensive Performance of Na‐Based Layered Oxide Benefiting from the Synergetic Contributions of Multimetal Ions

Yao

Wang

et al. 2017

Na‐ion batteries are promising for large‐scale energy storage applications, but few cathode materials can be practically used because of the significant difficulty in synthesizing an electrode material with superior comprehensive performance. Herein, an effective strategy based on synergetic contributions of rationally selected metal ions is applied to design layered oxides with excellent electrochemical performances. The power of this strategy is demonstrated by the superior properties of as‐obtained NaFe0.45Co0.5Mg0.05O2 with 139.9 mA h g−1 of reversible capacity, 3.1 V of average voltage, 96.6% of initial Coulombic efficiency, and 73.9 mA h g−1 of capacity at 10 C rate, which benefit from the synergetic effect of Fe3+ (high redox potential), Co3+ (good kinetics), and inactive Mg2+ with compatible radii (stabilizing structure). Moreover, it is clarified that the superior property is not the simple superposition of performance for layered oxides with single metal ions. With the assistance of density functional theory calculations, it is evidenced that the wide capacity range (>70%) of prismatic Na+‐occupied sites during sodiation/desodiation is responsible for its high rate performance. This rational strategy of designing high‐performance cathodes based on the synergetic effect of various metal ions might be a powerful step forward in the development of new Na‐ion‐insertion cathodes.

“…[221] Similarly, Zhou and co-workers also proposed a P2-O3 composite (Figure 12b) with the composition Na 0. 66 Li 0.18 Mn 0. 71 Ni 0.21 Co 0.08 O 2+d .…”

Section: Multiple Metal-based Oxidesmentioning

confidence: 99%

“…Interestingly, layered Ti-substituted Na x Cr x Ti 1−x O 2 was explored as bifunctional electrode materials for SIBs based on Cr 3+ /Cr 4+ and Ti 3+ /Ti 4+ redox couples. [65,66] Yabuuchi and co-workers pointed out that the suppressing the formation of low-crystallinity phases upon Na removal, which might induce irreversible Cr migration into Na layers, is key to improving the reversible capacity of P2-type Na 2/3 Cr 1−x Ti x O 2 cathode material for Na batteries. [67] www.advenergymat.…”

Section: Single-metal-based Oxides Peculiar To Sibsmentioning

confidence: 99%

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

Wang

You

Yin

et al. 2017

619

464

sources into large-scale grids, inexpensive, efficient, and fast-responding electrical energy storage (EES) systems are essential to store the off-peak energy and releasing the stored energy during the onpeak period. Among various EES systems, rechargeable batteries represent one of the most competitive technologies because of their high conversion efficiency and environmental friendliness. [1][2][3][4] For stationary EES systems, batteries with low cost, high safety, high rate capability, and long cycle stability are highly desired.Lithium (Li)-ion batteries (LIBs) have achieved great success in the market of portable electronics and electric vehicles since their commercialization by Sony Company in 1991. However, the shortage of Li resources in nature gives rise to a concern about its sustainable development in grid scale. Compared with Li, sodium resource has rich natural abundance in the earth crust and a worldwide distribution, consequently leading to a low price of sodium-based raw materials (e.g., the cost of Na 2 CO 3 is about 25-30 times lower than that of Li 2 CO 3 ). Besides, sodium has a suitable redox potential (E 0 (Na + /Na) = −2.71 V versus standard hydrogen electrode (SHE), 0.3 V above that of Li + /Li) and similar physical and chemical properties with lithium. [5,6] Therefore, rechargeable sodium-ion batteries (SIBs), which have a similar "rockingchair" working principle of LIBs, are emerging as an appealing choice as alternatives for LIBs. Note that it is difficult for SIBs to bypass LIBs in terms of energy densities because of the much higher weight of Na and lower standard electrochemical potential. [7][8][9][10] Nevertheless, the use of low-cost materials, including inexpensive Na-based raw materials and Al current collectors for both cathodes and anodes in SIBs, could significantly reduce the cost. In this case, SIBs could be applied where cost-effectiveness rather than energy density is the most critical issue, e.g., in the field of large-scale EES. As a result, sodiumbased electroactive materials are enjoying renewed interest especially for very low cost systems for grid storage. [11,12] Given that cathode materials are the key component that determines energy density and cost, tremendous efforts have been devoted to exploring suitable positive electrode materials with high reversible capacity, rapid Na ions insertion/extraction, and good cycling stability in the past few years. [13,14] A broad range of compounds, including layered oxides, polyanionic frameworks, hexacyanoferrates, and organics, haveThe increasing demand for replacing conventional fossil fuels with clean energy or economical and sustainable energy storage drives better battery research today. Sodium-ion batteries (SIBs) are considered as a promising alternative for grid-scale storage applications due to their similar "rockingchair" sodium storage mechanism to lithium-ion batteries, the natural abundance, and the low cost of Na resources. Searching for appropriate electrode materials with acceptable electrochemical perfor...