| 1. |
- Fan, Jianming, et al.
(author)
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Hydrothermal-assisted synthesis of Li-rich layered oxide microspheres with high capacity and superior rate-capability as a cathode for lithium-ion batteries
- 2015
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In: Electrochimica Acta. - 0013-4686. ; 173, s. 7-16
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Journal article (peer-reviewed)abstract
- Li-rich layered oxide materials possess high voltage and high specific capacity, which makes them attractive cathode candidates for lithium-ion batteries. However, they still suffer from a poor rate capability, which seriously blocks their widespread practical applications. In this work, Li(Li0.167Mn0.5Co0.167Ni0.167)O2 microspheres were synthesized by a hydrothermal-assisted method, in which Ni-Co-Mn-based microspherical precursors obtained by a hydrothermal process with polyethylene glycol-600 (PEG-600) as a surfactant were mixed with lithium sources and then sintered to yield the final products. It is found that the as-prepared Li-rich layered oxide microspheres exhibit high discharge capacity and superior rate performance: delivering an initial discharge capacity of 292 mAh g−1 at a current density of 20 mA g−1, 189 mAh g−1 at a current density of 600 mA g−1 and 142 mAh g−1 at a current density of 2000 mA g−1 (10C), which are better than that of the sample as-prepared by co-precipitation method. The high discharge capacity and improved rate-capability were beneficial from the microspheres assembled by uniform primary particles around 250 nm, more reversible redox and better electrode kinetics comparing to that of the co-precipitation sample. The preparation strategy reported here may offer hints for achieving various advanced Li-rich layered composite materials that would be used in high-performance energy storage.
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| 2. |
- Fu, Chaochao, et al.
(author)
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Nickel-Rich Layered Microspheres Cathodes: Lithium/Nickel Disordering and Electrochemical Performance
- 2014
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In: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 6:18, s. 15822-15831
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Journal article (peer-reviewed)abstract
- Nickel-rich layered metal oxide materials are prospective cathode materials for lithium ion batteries due to the relatively higher capacity and lower cost than LiCoO2. Nevertheless, the disordered arrangement of Li+/Ni2+ in local regions of these materials and its impact on electrochemistry performance are not well understood, especially for LiNi1–x–yCoxMnyO2 (1–x–y > 0.5) cathodes, which challenge one’s ability in finding more superior cathode materials for advanced lithium-ion batteries. In this work, Ni–Co–Mn-based spherical precursors were first obtained by a solvothermal method through handily utilizing the redox reaction of nitrate and ethanol. Subsequent sintering of the precursors with given amount of lithium source (Li-excess of 5, 10, and 15 mol %) yields LiNi0.7Co0.15Mn0.15O2 microspheres with different extents of Li+/Ni2+ disordering. With the determination of the amounts of Li+ ions in transition metal layer and Ni2+ ions in Li layer using structural refinement, the impact of Li+/Ni2+ ions disordering on the crystal structure, valence state of nickel ions, and electrochemical performance were investigated in detailed. It is clearly demonstrated that with increasing the amount of lithium source, lattice parameters (a and c) and interslab space thickness of unit cell decrease, and more Li+ ions incorporated into the 3a site of transition metal layer which leads to an increase of Ni3+ content in LiNi0.7Co0.15Mn0.15O2 as confirmed by X-ray photoelectron spectroscopy and a redox titration. Moreover, the electrochemical performance for as-prepared LiNi0.7Co0.15Mn0.15O2 microspheres exhibited a trend of deterioration due to the changes of crystal structure from Li+/Ni2+ mixing. The preparation method and the impacts of Li+/Ni2+ ions disordering reported herein for the nickel-rich layered LiNi0.7Co0.15Mn0.15O2 microspheres may provide hints for obtaining a broad class of nickel-rich layered metal oxide microspheres with superior electrochemical performance.
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| 3. |
- Li, Qi, 1990, et al.
(author)
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A Study on Storage Characteristics of Pristine Li-rich Layered Oxide Li1.20Mn0.54Co0.13Ni0.13O2: Effect of Storage Temperature and Duration
- 2015
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In: Electrochimica Acta. - 0013-4686. ; 154, s. 249-158
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Journal article (peer-reviewed)abstract
- Lithium-ion batteries always suffer from serious capability decay, especially when stored at high temperature and/or for prolonged duration. In this work, electrochemical performance for Li-rich layered oxides Li1.20Mn0.54Co0.13Ni0.13O2 was systematically investigated as a function of temperature and duration. Plenty of techniques like SEM, EDS, EIS, ARC, Raman, XRD, and XPS were utilized to characterize the structures, valence states, compositions, particle sizes, and morphologies of the layered oxides with varying temperature and duration. The results reveal that room temperature storage may alter surface kinetics, but hardly influence the electrochemical performance. While in the case of high temperature storage in pristine state, cycling stability is highly dependent on the storage duration. The degradation mechanism at high temperature storage with prolonged duration is demonstrated to be the accumulation of surface species like LiF/LixPFyOz initiated by the strong reactions between LiPF6 electrolyte and electrode. The results reported here may shed light on predicting electrochemical performance by surface analysis and also provide vital hints on enhancing the high-temperature storage stability of Li-rich layered oxides.
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| 4. |
- Li, Qi, 1990, et al.
(author)
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Balancing stability and specific energy in Li-rich cathodes for lithium ion batteries: a case study of a novel Li–Mn–Ni–Co oxide
- 2015
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In: Journal of Materials Chemistry. - 1364-5501 .- 0959-9428. ; 3:19, s. 10592-10602
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Journal article (peer-reviewed)abstract
- Lithium batteries for UPS, portable electronics and electrical vehicles rely on high-energy cathodes. Li-rich manganese-rich oxide (xLi2MnO3·(1 − x)LiMO2, M = transition metals) is one of the few materials that might meet such a requirement, but it suffers from poor energy retention due to serious voltage and/or capacity fade, which challenges its applications. Here we show that this challenge can be addressed by optimizing the interactions between the components Li2MnO3 and LiMO2 in the Li-rich oxide (i.e. stabilizing the layered structure through Li2MnO3 and controlling Li2MnO3 activation through LiMO2). To realize this synergistic effect, a novel Li2MnO3-stabilized Li1.080Mn0.503Ni0.387Co0.030O2 was designed and prepared using a hierarchical carbonate precursor obtained by a solvo/hydro-thermal method. This layered oxide is demonstrated to have a high working voltage of 3.9 V and large specific energy of 805 W h kg−1 at 29 °C as well as impressive energy retention of 92% over 100 cycles. Even when exposed to 55 °C, energy retention is still as high as 85% at 200 mA g−1. The attractive performance is most likely the consequence of the balanced stability and specific energy in the present material, which is promisingly applicable to other Li-rich oxide systems. This work sheds light on harnessing Li2MnO3 activation and furthermore efficient battery design simply through compositional tuning and temperature regulation.
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| 5. |
- Li, Qi, 1990, et al.
(author)
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K+-Doped Li1.2Mn0.54Co0.13Ni0.13O2: A Novel Cathode Material with an Enhanced Cycling Stability for Lithium-Ion Batteries
- 2014
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In: ACS Applied Materials & Interfaces. - 1944-8252 .- 1944-8244. ; 6:13, s. 10330-10341
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Journal article (peer-reviewed)abstract
- Li-rich layered oxides have attracted much attention for their potential application as cathode materials in lithium ion batteries, but still suffer from inferior cycling stability and fast voltage decay during cycling. How to eliminate the detrimental spinel growth is highly challenging in this regard. Herein, in situ K+-doped Li1.20Mn0.54Co0.13Ni0.13O2 was successfully prepared using a potassium containing α-MnO2 as the starting material. A systematic investigation demonstrates for the first time, that the in situ potassium doping stabilizes the host layered structure by prohibiting the formation of spinel structure during cycling. This is likely due to the fact that potassium ions in the lithium layer could weaken the formation of trivacancies in lithium layer and Mn migration to form spinel structure, and that the large ionic radius of potassium could possibly aggravate steric hindrance for spinel growth. Consequently, the obtained oxides exhibited a superior cycling stability with 85% of initial capacity (315 mA h g–1) even after 110 cycles. The results reported in this work are fundamentally important, which could provide a vital hint for inhibiting the undesired layered-spinel intergrowth with alkali ion doping and might be extended to other classes of layered oxides for excellent cycling performance.
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| 6. |
- Luo, Dong, et al.
(author)
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A New Spinel-Layered Li-Rich Microsphere as a High-Rate Cathode Material for Li-Ion Batteries
- 2014
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In: Advanced Energy Materials. - 1614-6840 .- 1614-6832. ; 4:11
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Journal article (peer-reviewed)abstract
- Li-rich layered materials are considered to be the promising low-cost cathodes for lithium-ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel-layered Li-rich Li-Mn-Co-O microspheres are reported as a new high-rate cathode material for Li-ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel-like component with a layered component by a heat treatment. When calcined at 700 °C, the amount of transition metal Mn and Co in the Li-Mn-Co-O microspheres maintained is similar to at 800 °C, while the structures of constituent particles partially transform from 2D to 3D channels. As a consequence, when tested as a cathode for lithium-ion batteries, the spinel-layered Li-rich Li-Mn-Co-O microspheres obtained at 700 °C show a maximum discharge capacity of 185.1 mA h g−1 at a very high current density of 1200 mA g−1 between 2.0 and 4.6 V. Such a capacity is among the highest reported to date at high charge-discharge rates. Therefore, the present spinel-layered Li-rich Li-Mn-Co-O microspheres represent an attractive alternative to high-rate electrode materials for lithium-ion batteries.
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| 7. |
- Luo, Dong, et al.
(author)
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LiMO2 (M = Mn, Co, Ni) hexagonal sheets with (101) facets for ultrafast charging–discharging lithium ion batteries
- 2015
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In: Journal of Power Sources. - 0378-7753. ; 276, s. 238-246
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Journal article (peer-reviewed)abstract
- Developing energy storage equipments that can work at very high charge–discharge rate is crucial, but highly challenging for more efficient use of energy. From the perspective of chemistry, high-rate property of Li-ion batteries can only be achieved by significantly improving the kinetics of lithium ions and electrons in electrode. Here, we for the first time report on a simple method to resolve kinetics problems of ultrafast charging–discharging Li-ion batteries by fabrication of layered LiMO2 (M = Mn, Co, Ni) hexagonal sheet exposing with facets {101}. The synthetic procedure of hexagonal sheets is proceeded via a simple PVP-assisted co-precipitation, which is followed by a heat treatment. All hexagonal sheets LiMnxCoyNizO2 were demonstrated to deliver a superior excellent rate capability and outstanding cycle stability at high current density of 3000 mA g−1 and under a high cutoff voltage of 4.4 V. The discharge capacity for the composition LiMn0.075Co0.775Ni0.15O2 at an ultrahigh charge–discharge rate of 10,000 mA g−1 is almost as large as that for LiMn2O4 and commercial LiFePO4 at low rate of 1C. The methodology reported here to resolve the kinetic problems of lithium ions and electrons in electrodes may have many implications that would help scientists to find more high-rate lithium-ion batteries for powering electric vehicles and other applications.
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| 8. |
- Xie, Dongjiu, et al.
(author)
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Improved Cycling Stability of Cobalt-free Li-rich Oxides with a Stable Interface by Dual Doping
- 2016
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In: Electrochimica Acta. - 0013-4686. ; 196, s. 505-516
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Journal article (peer-reviewed)abstract
- Li-rich cobalt-free oxides, popularly used as a cathode with high capacity in lithium ion battery, always suffer from poor cycling stability between 2.0 and 4.8 V vs Li+/Li, especially when cycled at high temperatures (>50 °C). To overcome this issue, Na+ and Al3+ dual-doped NaxLi1.2-xMn0.6-xAlxNi0.2O2 Li-rich cathode is prepared in this study. It is shown that the side reactions between cathode and electrolyte during cycling are suppressed. The improved cycling performance is observed for all of the doped samples, among which the sample with x = 0.03 exhibits the highest capacity retention of 86.1% after 200 cycles between 2.0 and 4.8 V at 2C (1C = 200 mA g−1) and shows a remarkable cycling stability, even at a high temperature of 55 °C (a capacity retention of 92.2% after 100 cycles). Moreover, the average voltage of the sample with x = 0.03 after 100 cycles at 0.5C remains at 3.11 V with a retention ratio of 86.6%. This work provides a new strategy to develop Li-rich cobalt-free cathodes with excellent cycling stability for lithium ion batteries at high temperatures.
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| 9. |
- Zhang, Yuelan, et al.
(author)
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Smart Solution Chemistry to Sn-Containing Intermetallic Compounds through a Self-Disproportionation Process
- 2016
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In: Chemistry - A European Journal. - 1521-3765 .- 0947-6539. ; 22:40, s. 14196-14204
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Journal article (peer-reviewed)abstract
- Developing new methods to synthesize intermetallics is one of the most critical issues for the discovery and application of multifunctional metal materials; however, the synthesis of Sn-containing intermetallics is challenging. In this work, we demonstrated for the first time that a self-disproportionation-induced in situ process produces cavernous Sn−Cu intermetallics (Cu3Sn and Cu6Sn5). The successful synthesis is realized by introducing inorganic metal salts (SnCl2⋅2 H2O) to NaOH aqueous solution to form an intermediate product of reductant (Na2SnO2) and by employing steam pressures that enhance the reduction ability. Distinct from the traditional in situ reduction, the current reduction process avoided the uncontrolled phase composition and excessive use of organic regents. An insight into the mechanism was revealed for the Sn−Cu case. Moreover, this method could be extended to other Sn-containing materials (Sn−Co, Sn−Ni). All these intermetallics were attempted in the catalytic effect on thermal decompositions of ammonium perchlorate. It is demonstrated that Cu3Sn showed an outstanding catalytic performance. The superior property might be primarily originated from the intrinsic chemical compositions and cavernous morphology as well. We supposed that this smart solution reduction methodology reported here would provide a new recognition for the reduction reaction, and its modified strategy may be applied to the synthesis of other metals, intermetallics as well as some unknown materials.
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