Shenzhen OptimumNano Energy Co.

Shenzhen, China

Shenzhen OptimumNano Energy Co.

Shenzhen, China
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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.


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.


Zheng J.,Peking University | Liu T.,Peking University | Hu Z.,Peking University | Wei Y.,Peking University | And 10 more authors.
Journal of the American Chemical Society | Year: 2016

Understanding and further designing new layered Li(NixMnyCoz)O2 (NMC) (x + y + z = 1) materials with optimized thermal stability is important to rechargeable Li batteries (LIBs) for electrical vehicles (EV). Using ab initio calculations combined with experiments, we clarified how the thermal stability of NMC materials can be tuned by the most unstable oxygen, which is determined by the local coordination structure unit (LCSU) of oxygen (TM(Ni, Mn, Co)3-O-Li3-x′): each O atom bonds with three transition metals (TM) from the TM-layer and three to zero Li from fully discharged to charged states from the Li-layer. Under this model, how the lithium content, valence states of Ni, contents of Ni, Mn, and Co, and Ni/Li disorder to tune the thermal stability of NMC materials by affecting the sites, content, and the release temperature of the most unstable oxygen is proposed. The synergistic effect between Li vacancies and raised valence state of Ni during delithiation process can aggravate instability of oxygen, and oxygen coordinated with more nickel (especially with high valence state) in LSCU becomes more unstable at a fixed delithiation state. The Ni/Li mixing would decrease the thermal stability of the "Ni - Mn" group NMC materials but benefit the thermal stability of "Ni-rich" group, because the Ni in the Li layer would form 180° Ni-O-Ni super exchange chains in "Ni-rich" NMC materials. Mn and Co doping can tune the initial valence state of Ni, local coordination environment of oxygen, and the Ni/Li disorder, thus to tune the thermal stability directly. © 2016 American Chemical Society.


PubMed | Pacific Northwest National Laboratory, Argonne National Laboratory, Shenzhen Tianjiao Technology Development Co., Peking University and Shenzhen OptimumNano Energy Co.
Type: Journal Article | Journal: Journal of the American Chemical Society | Year: 2016

Understanding and further designing new layered Li(Ni


Mezaal M.A.,Nanjing Southeast University | Mezaal M.A.,University of Basrah | Qu L.,Nanjing Southeast University | Li G.,Nanjing Southeast University | And 6 more authors.
Journal of Solid State Electrochemistry | Year: 2016

Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g−1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M = Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M* = Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g−1 at 20 mA g−1, and retains 90 % of its discharge capacity at 100 mA g−1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density. [Figure not available: see fulltext.] © 2016 Springer-Verlag Berlin Heidelberg


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.

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