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Cui S.,Peking University | Wei Y.,Peking University | Liu T.,Peking University | Deng W.,Peking University | And 11 more authors.
Advanced Energy Materials | Year: 2016

Understanding and optimizing the temperature effects of Li-ion diffusion by analyzing crystal structures of layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) materials is important to develop advanced rechargeable Li-ion batteries (LIBs) for multi-temperature applications with high power density. Combined with experiments and ab initio calculations, the layer distances and kinetics of Li-ion diffusion of LiNixMnyCozO2 (NMC) materials in different states of Li-ion de-intercalation and temperatures are investigated systematically. An improved model is also developed to reduce the system error of the "Galvanostatic Intermittent Titration Technique" with a correction of NMC particle size distribution. The Li-ion diffusion coefficients of all the NMC materials are measured from -25 to 50 °C. It is found that the Li-ion diffusion coefficient of LiNi0.6Mn0.2Co0.2O2 is the largest with the minimum temperature effect. Ab initio calculations and XRD measurements indicate that the larger Li slab space benefits to Li-ion diffusion with minimum temperature effect in layered NMC materials. The temperature effect for kinetics of Li-ion diffusion in Li(NixMnyCoz)O2 materials is investigated systematically. The Li-ion diffusion coefficient of Li(Ni0.6Mn0.2Co0.2)O2 is the largest with the minimum temperature effect. Ab initio calculations and experimental measurements indicate that the larger Li slab space benefits to Li-ion diffusion with the minimum temperature effect in layered Li(NixMnyCoz)O2 materials. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Rao M.,South China Normal University | Rao M.,Shenzhen OptimumNano Energy Co. | Li X.,South China Normal University | Li X.,South China University of Technology | And 3 more authors.
Ionics | Year: 2015

A novel gel polymer electrolyte (GPE) based on an electrospun polymer membrane of polyimide (PI) activating with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and further coating with nano-Al2O3 was prepared, and its performance for lithium-sulfur (Li-S) cell was investigated. It is found that the Li-S cell using the new GPE enabled achieving a stable discharge capacity of 820 mAh g−1 after more than 100 cycles. This new GPE system with activating with PVDF-HFP and further coating with nano-Al2O3 was capable of upholding the electrolyte solution and can suppress the dissolution of the intermediate products generated during the discharge process and thus improves the performance of Li-S cell. © 2015, Springer-Verlag Berlin Heidelberg.

Wei Y.,Peking University | Zheng J.,Peking University | Cui S.,Peking University | Song X.,Peking University | And 10 more authors.
Journal of the American Chemical Society | Year: 2015

Using ab initio calculations combined with experiments, we clarified how the kinetics of Li-ion diffusion can be tuned in LiNixMnyCozO2 (NMC, x + y + z = 1) materials. It is found that Li-ions tend to choose oxygen dumbbell hopping (ODH) at the early stage of charging (delithiation), and tetrahedral site hopping (TSH) begins to dominate when more than 1/3 Li-ions are extracted. In both ODH and TSH, the Li-ions surrounded by nickel (especially with low valence state) are more likely to diffuse with low activation energy and form an advantageous path. The Li slab space, which also contributes to the effective diffusion barriers, is found to be closely associated with the delithiation process (Ni oxidation) and the contents of Ni, Co, and Mn. © 2015 American Chemical Society.

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