04-jpowsour-2016-multi-issue

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Abstract chars: 1182

Li-rich layered oxides have been regarded as valuable cathode materials for high energy density lithium-ion batteries. However, high initial irreversible capacity, bad rate capability, as well as serious capacity fading and voltage decay hinder their commercial application. In this paper, a nano CoF2 protective layer is coated on the surface of Li1.2Ni0.2Mn0.6O2 via a facial wet chemistry method. A high initial discharge capacity of 264.4 mAh g  1 is obtained for 0.5% CoF2-coated sample and 259.1 mAh g  1 for 1% CoF2-coated sample owing to the suppression of irreversible release of O2 and the contribution of electrochemical conversion of CoF2/LiF. Furthermore, 1% CoF2-coated sample exhibits the excellent rate capability of 167.5 mAh g  1 at 5 C rate, the superior cycling stability with the capacity retention of 241.0 mAh g  1 and the ameliorative voltage drop of 0.312 V at 0.1C after 100 cycles. The enhanced rate performance as well as stability of capacity and voltage can be attributed to the nano coatings which inhibit the electrolyte-electrode side reaction, enhance the electrochemical kinetics and mitigate structure transition from layered to spinel phase.

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• Body (419 chars)
• 1. Introduction (3551 chars)
• In order to investigate the capacity and voltage stability for the (68 chars)

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• p5 scientific_body coverage=0.0: exhibit two distinguished voltage regions during the first charge process. The sloping curve below 4.5 V is attributed to the lithium extraction from LiNi0.5Mn0.5O2 with hexagonal layered structure along with the oxidation of Ni2þ/Ni3þ/Ni4þ, and the plateau abo
• p6 scientific_body coverage=0.266: ion vacancy in TM layers during initial discharge procedure resulting in a large irreversible capacity loss [31,42,43], corresponding sche- matic view of extraction/insertion of Liþ during initial charge- discharge process in LNMO active materials shown in Fig
• p6 scientific_body coverage=0.184: As shown in Fig. 5(a), all the samples deliver similar initial charge capacity, while CF-0.1, CF-0.5 and CF-1.0 samples exhibit higher initial discharge capacities of 254.3 mAh g1, 264.4 mAh g1
• p7 scientific_body coverage=0.23: the one hand, the relatively thicker coating layer not only sup- presses excessively the release of O2 but also prevents the extrac- tion/insertion of Liþ in layered structure, resulting in low capacity. On the other hand, the low reduction potential of 2.854
• p7 scientific_body coverage=0.136: In order to investigate the capacity and voltage stability for the sample whose CoF2 coating content is higher than 1.0 wt%, Fig. S1 in supplementary materials presents the operation voltages versus specific capacities of 2.0 wt% CoF2-coated sample (CF-2.0) and
• p8 scientific_body coverage=0.03: 5 C, CF-1.0 exhibits the highest capacity of 167.5 mAh g1, yet that of LNMO is only 120.1 mAh g1. Moreover, when the current density is back to 0.1 C, the discharge capacity returns to 98.7% of its initial value for CF-1.0, implying good reversibility and st
• p8 scientific_body coverage=0.005: fitted with the equivalent circuits in the inset. Fig. 7(a) presents the EIS curves of the cells at open circuit potential before cycling. The intercept on the x-axis at the highest frequency is related to ohmic resistance of the electrolyte (Rs), the diameter
• p9 scientific_body coverage=0.02: growth of the unacceptable SEI film as well as the interfacial re- action have been mitigated by CoF2 coating layer. Thus, the improvement of electrochemical kinetics, the suppression of the formation of SEI film and side reaction between electrolyte and electro
• p9 scientific_body coverage=0.018: To disclose the reasons for improving the capacity fading and voltage decay upon cycling of CoF2-coated samples, LNMO and CF- 1.0 after several cycles were observed using TEM. Fig. 8 (b1 and b2) presents TEM image and corresponding SAED pattern of LNMO after 5
• p10 scientific_body coverage=0.011: particle in Fig. 8(c2), indicating complete structure transition after 100 cycles. However, the thin SEI film mixed with CoF2 coating layer can be observed in Fig. 8(d1) for CF-1.0 after 100 cycles owing to the inhibition of the release of oxygen during initial
• p10 scientific_body coverage=0.057: In this paper, a nano protective layer of CoF2, in situ synthesized by means of a common wet chemistry technology, was coated on LNMO. The results of SEM, TEM, EDS and XPS demonstrate that CoF2 coating, belong to cubic structure, distributes homogeneously on t
• p10 scientific_body coverage=0.04: vacancies proved by the CV measurements. In addition, the higher first discharge capacity of 259.1 mAh g1 compared to bare LNMO of 244.0 mAh g1, the excellent cycling stability with the capacity retention rate of 93.0% after 100 cycles at 0.1 C, the improved
• p10 back_matter coverage=0.0: This work was supported by National Natural Science Founda- tion of China (Grant no. E51504196), the China Postdoctoral Science Foundation (no. 2012M521760) and the Fundamental Research Funds for the Central Universities (no. xjj2014052).