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Xu Z.,Wuhan University | Xu Z.,Zhejiang WELLY Energy Corporation | Xiao L.,Zhejiang WELLY Energy Corporation | Wang F.,Zhejiang WELLY Energy Corporation | And 7 more authors.
Journal of Power Sources | Year: 2014

The effects of the synthesis temperature, the synthesis time and the nature of the transition-metal hydroxide precursors on the physical and electrochemical properties of Li(Ni1-x-yCoxMn y)O2 synthesized using solid-state reactions are studied. Higher synthesis temperature results in larger primary and secondary particle sizes, a lower tap density and a broader secondary particle size distribution. Increase in reaction time improves the crystallinity and the cyclability. A smaller primary particle size of the precursor leads to a larger primary particle size of Li(Ni1-x-yCoxMny)O 2. Li(Ni1-x-yCoxMny)O2 with a better crystallinity, a well-defined layered structure and a better cation ordering exhibits a higher capacity, a better cycling performance and rate capability. The optimized synthesis conditions for precursors NCMOH111-α and NCMOH424-a is 950°C for 12 h and 950°C for 9 h, respectively. NCM111-α-950-12h delivers a discharge capacity of 165.5 mAh g-1 during the initial cycle at a rate of 0.1C with a columbic efficiency of 87%, a 3C rate capability of 91.25% and a 1C capacity retention rate of 98.25% after 40 cycles. © 2013 Elsevier B.V. All rights reserved. Source

Wu K.,Zhejiang WELLY Energy Corporation | Wang F.,Zhejiang WELLY Energy Corporation | Gao L.,Zhejiang WELLY Energy Corporation | Li M.-R.,Zhejiang WELLY Energy Corporation | And 8 more authors.
Electrochimica Acta | Year: 2012

Li(Ni 0.5Co 0.2Mn 0.3)O 2 layered materials were synthesized by solid-state reaction using Li 2CO 3 and three transition-metal hydroxide precursors of composition (Ni 0.5Co 0.2Mn 0.3)(OH) 2 (NMC Hydroxide) with different physical properties. Characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical testing, etc., the final Li(Ni 0.5Co 0.2Mn 0.3)O 2 products showed different physical and electrochemical properties depending on their synthesis temperatures and the properties of transition-metal hydroxide precursors were got. Higher reaction temperature results in bigger primary particle size (PPS) and broader size distribution. Precursor with smaller PPS results in larger PPS when synthesized at the same condition. The electrochemical performance is related to the physical properties of Li(Ni 0.5Co 0.2Mn 0.3) O 2. Better crystallized and cation ordered layered material has higher initial capacity while smaller and uniform PPS results in higher capacity retention rate. The Li(Ni 0.5Co 0.2Mn 0.3)O 2 synthesized at 880 °C for 10 h in atmosphere using (Ni 0.5Co 0.2Mn 0.3)(OH) 2 with smallest PPS size as the starting precursor showed the best overall electrochemical properties with a high discharge capacity over 171 mAh/g with a capacity retention >96% after 50 cycles at 1C rate in a half battery and tap density about 2.7 g/cm 3. © 2012 Elsevier Ltd. All rights reserved. Source

Xu Z.,Wuhan University | Xu Z.,Zhejiang WELLY Energy Corporation | Wang J.,Wuhan University | Quan X.,Zhejiang WELLY Energy Corporation | And 2 more authors.
Journal of Power Sources | Year: 2014

Lithium-rich oxygen non-stoichiometric Li1.07Mn 1.93O4-δ oxides with different oxygen vacancy values δ have been studied intensively using transmission electron microscope (TEM) at room temperature. The TEM observation shows that the dominant part of a given sample is the cubic spinel phase with secondary tetragonal phases, which have different lattice parameters. The detailed TEM study shows that the distortion level cp/ap ratio (ap and c p are the pseudo cubic unit cell parameters of the tetragonal phase) of the tetragonal phases ranges from 1.00 to 1.16. The diversity in values for the tetragonal phases is believed to be due to the differences in oxygen vacancy value among particles after annealing, which is related to the differences in their initial physical characteristics. The presence of twinning and defects in the tetragonal phases is common and the statistical results for the sample Li1.07Mn1.93O4-0.167 are given. The electrochemical test shows that the electrochemical performance of the annealed samples is dramatically deteriorated with increasing amount of oxygen vacancy. © 2013 Elsevier B.V. All rights reserved. Source

Zhang Z.,Ningbo Institute of Materials Technology and Engineering | Chen Z.,Ningbo Institute of Materials Technology and Engineering | Wang G.,Ningbo Institute of Materials Technology and Engineering | Wang G.,Wuhan University of Technology | And 12 more authors.
Physical Chemistry Chemical Physics | Year: 2016

Electrochemical cycling stabilities were compared for undoped and Al/Co dual-doped spinel LiMn2O4 synthesized by solid state reactions. We observed the suppression of particle fracture in Al/Co dual-doped LiMn2O4 during charge/discharge cycling and its distinguishable particle morphology with respect to the undoped material. Systematic first-principles calculations were performed on undoped, Al or Co single-doped, and Al/Co dual-doped LiMn2O4 to investigate their structural differences at the atomistic level. We reveal that while Jahn-Teller distortion associated with the Mn3+O6 octahedron is the origin of the lattice strain, the networking - i.e. the distribution of mixed valence Mn ions - is much more important to release the lattice strain, and thus to alleviating particle cracking. The calculations showed that the lattice mismatching between Li+ intercalation and deintercalation of LiMn2O4 can be significantly reduced by dual-doping, and therefore also the volumetric shrinkage during delithiation. This may account for the near disappearance of cracks on the surface of Al/Co-LiMn2O4 after 350 cycles, while some obvious cracks have developed in undoped LiMn2O4 at similar particle size even after 50 cycles. Correspondingly, Al/Co dual-doped LiMn2O4 showed a good cycling stability with a capacity retention of 84.1% after 350 cycles at a rate of 1C, 8% higher than the undoped phase. © the Owner Societies 2016. Source

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