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Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials

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ABSTRACT

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO2 core and the Li(Ni,Mn)2O4 spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi0.32Mn1.68O4 are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi0.32Mn1.68O4 spinel cathode exhibits the high discharge capacity of 135.3 mA h g−1, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.

No MeSH data available.


Initial electrochemical performances of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode prepared by calcination at 700 °C: (a) charge-discharge curves and (b) cycle performances at a constant current of 0.1 C, (c) CV curves at a scan rate of 0.2 mV s−1 and (d) initial discharge capacities at different current rates.
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Figure 7: Initial electrochemical performances of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode prepared by calcination at 700 °C: (a) charge-discharge curves and (b) cycle performances at a constant current of 0.1 C, (c) CV curves at a scan rate of 0.2 mV s−1 and (d) initial discharge capacities at different current rates.

Mentions: From the results of the first charge-discharge curves, the concentration-gradient LiNi0.32Mn1.68O4 spinel prepared by calcination at 700 °C was selected to evaluate the further electrochemical performances. Although the obvious difference between the spinel cathodes prepared at 700 °C and 800 °C were not found in the first charge-discharge curves, calcination at a high temperature may lead to the formation of a Li1−xNixO phase [15]. The cycle behavior and cyclic voltammograms (CVs) during the initial 20 cycles and rate properties are summarized in figure 7. There was no change in the charge-discharge curves during 20 cycles at a constant current density of 14.6 mA g−1 (figure 7(a)). Accordingly, the discharge capacities during the cycles were recorded at around 135 mA h g−1 (figure 7(b)). The capacity retention after 20 cycles was 99.4%. If the discharge capacity decreases with increasing a cycle number, the capacity retention after 100 cycles extrapolated from the 20 cycles data shows 91.0%. However, the degradation by oxidation of an electrolyte at a high-voltage region is not negligible [31, 32], so it is necessary to further increase the cycle number. The CV curves recorded at a scan rate of 0.2 mV s−1 indicated the three redox peaks (figure 7(c)). A small hump centered at about 4.1 V corresponds to the redox couple of Mn3+/Mn4+, which is referred from the Mn3+ constituent in the concentration-gradient LiNi0.32Mn1.68O4 spinel. The partially overlapped peaks at about 4.7 and 4.8 V correspond to the redox couples of Ni2+/Ni3+ and Ni3+/Ni4+, respectively. These redox couples showed the reversibility and the cyclability. The rate properties of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode were tested up to 1.46 A g−1 (10 C rate) (figure 7(d)). The charge rate was equal to the discharge rate, and the constant-voltage charge for 5 h was conducted after achieving maximum voltage of 5 V. The first discharge capacities over 125 mA h g−1 were recorded until reaching a 1 C rate. Although the discharge capacity gradually decreased with increasing the applied current densities, 68.4 mA h g−1 was yielded at a 10 C rate. The discharge capacities at each rate were almost the same after 3 cycles. The concentration-gradient LiNi0.32Mn1.68O4 spinel showed favorable cathode properties in the initial electrochemical performances.


Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials
Initial electrochemical performances of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode prepared by calcination at 700 °C: (a) charge-discharge curves and (b) cycle performances at a constant current of 0.1 C, (c) CV curves at a scan rate of 0.2 mV s−1 and (d) initial discharge capacities at different current rates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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Figure 7: Initial electrochemical performances of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode prepared by calcination at 700 °C: (a) charge-discharge curves and (b) cycle performances at a constant current of 0.1 C, (c) CV curves at a scan rate of 0.2 mV s−1 and (d) initial discharge capacities at different current rates.
Mentions: From the results of the first charge-discharge curves, the concentration-gradient LiNi0.32Mn1.68O4 spinel prepared by calcination at 700 °C was selected to evaluate the further electrochemical performances. Although the obvious difference between the spinel cathodes prepared at 700 °C and 800 °C were not found in the first charge-discharge curves, calcination at a high temperature may lead to the formation of a Li1−xNixO phase [15]. The cycle behavior and cyclic voltammograms (CVs) during the initial 20 cycles and rate properties are summarized in figure 7. There was no change in the charge-discharge curves during 20 cycles at a constant current density of 14.6 mA g−1 (figure 7(a)). Accordingly, the discharge capacities during the cycles were recorded at around 135 mA h g−1 (figure 7(b)). The capacity retention after 20 cycles was 99.4%. If the discharge capacity decreases with increasing a cycle number, the capacity retention after 100 cycles extrapolated from the 20 cycles data shows 91.0%. However, the degradation by oxidation of an electrolyte at a high-voltage region is not negligible [31, 32], so it is necessary to further increase the cycle number. The CV curves recorded at a scan rate of 0.2 mV s−1 indicated the three redox peaks (figure 7(c)). A small hump centered at about 4.1 V corresponds to the redox couple of Mn3+/Mn4+, which is referred from the Mn3+ constituent in the concentration-gradient LiNi0.32Mn1.68O4 spinel. The partially overlapped peaks at about 4.7 and 4.8 V correspond to the redox couples of Ni2+/Ni3+ and Ni3+/Ni4+, respectively. These redox couples showed the reversibility and the cyclability. The rate properties of the concentration-gradient LiNi0.32Mn1.68O4 spinel cathode were tested up to 1.46 A g−1 (10 C rate) (figure 7(d)). The charge rate was equal to the discharge rate, and the constant-voltage charge for 5 h was conducted after achieving maximum voltage of 5 V. The first discharge capacities over 125 mA h g−1 were recorded until reaching a 1 C rate. Although the discharge capacity gradually decreased with increasing the applied current densities, 68.4 mA h g−1 was yielded at a 10 C rate. The discharge capacities at each rate were almost the same after 3 cycles. The concentration-gradient LiNi0.32Mn1.68O4 spinel showed favorable cathode properties in the initial electrochemical performances.

View Article: PubMed Central - PubMed

ABSTRACT

Core@shell and concentration-gradient particles have attracted much attention as improved cathodes for Li-ion batteries (LIBs). However, most of their preparation routes have employed a precisely-controlled co-precipitation method. Here, we report a facile preparation route of core@shell and concentration-gradient spinel particles by dry powder processing. The core@shell particles composed of the MnO2 core and the Li(Ni,Mn)2O4 spinel shell are prepared by mechanical treatment using an attrition-type mill, whereas the concentration-gradient spinel particles with an average composition of LiNi0.32Mn1.68O4 are produced by calcination of their core@shell particles as a precursor. The concentration-gradient LiNi0.32Mn1.68O4 spinel cathode exhibits the high discharge capacity of 135.3 mA h g−1, the wide-range plateau at a high voltage of 4.7 V and the cyclability with a capacity retention of 99.4% after 20 cycles. Thus, the facile preparation route of the core@shell and concentration-gradient particles may provide a new opportunity for the discovery and investigation of functional materials as well as for the cathode materials for LIBs.

No MeSH data available.