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

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.


Nitrogen adsorption-desorption isotherms of the MnO2 raw material and MnO2@Li(Ni,Mn)2O4 core@shell particles.
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Figure 3: Nitrogen adsorption-desorption isotherms of the MnO2 raw material and MnO2@Li(Ni,Mn)2O4 core@shell particles.

Mentions: The powder properties of the resultant MnO2@Li(Ni,Mn)2O4 core@shell particle were compared with those of the MnO2 raw material to discuss the formation of the core@shell particles. The particle size distribution after mechanical treatment shifted to a smaller size. The median size of the core@shell particles was 21 μm and decreased from 43 μm of the MnO2 raw particles. The nitrogen adsorption-desorption isotherms shown in figure 3 revealed microstructure of the particles. Both the MnO2 and core@shell powders showed a hysteresis loop at a relative pressure from 0.45 to 0.99. According to the pore size distributions calculated from the adsorption branches (figure 3, inset figure), the average pore diameter increased from 5.4 nm to 10.1 nm after mechanical treatment. On the other hand, the specific surface area and the pore volume decreased from 41.1 m2 g−1 and 0.056 cm3 g−1 of the MnO2 raw material to 19.3 m2 g−1 and 0.049 cm3 g−1 of the core@shell particles, respectively. These powder property changes are due to the formation of the Li(Ni,Mn)2O4 particles as the shell. The primary particle size of the MnO2 raw material, which was estimated from the specific surface area, was 29 nm. That is, the MnO2 raw material consists of the nanometer-sized primary particles. The formation of Li(Ni,Mn)2O4 particles arises at the nanometer-sized particle of the MnO2 surface through mechanical treatment. However, the shearing process of an attrition-type mill scrapes the synthesized Li(Ni,Mn)2O4 nanoparticles, and the fresh surfaces are created at the MnO2 particles. By repeating the formation and abrasion of Li(Ni,Mn)2O4 particles, the product particles are made more round in shape. Meanwhile, the synthesized Li(Ni,Mn)2O4 nanoparticles are progressively deposited on the particle surface of MnO2, and the core@shell structure is formed during mechanical treatment. This deposition process of the Li(Ni,Mn)2O4 nanoparticles onto MnO2 leads to the increase of the pore diameter and the decrease of the specific surface area. The mechanical treatment using an attrition-type mill allows surface coating of the larger species in the case of an obvious difference in particle size between reactants [30]. In this study, the synthesis of the shell particles and the formation of the core@shell structure were achieved by a one-step dry process.


Facile preparation of core@shell and concentration-gradient spinel particles for Li-ion battery cathode materials
Nitrogen adsorption-desorption isotherms of the MnO2 raw material and MnO2@Li(Ni,Mn)2O4 core@shell particles.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036501&req=5

Figure 3: Nitrogen adsorption-desorption isotherms of the MnO2 raw material and MnO2@Li(Ni,Mn)2O4 core@shell particles.
Mentions: The powder properties of the resultant MnO2@Li(Ni,Mn)2O4 core@shell particle were compared with those of the MnO2 raw material to discuss the formation of the core@shell particles. The particle size distribution after mechanical treatment shifted to a smaller size. The median size of the core@shell particles was 21 μm and decreased from 43 μm of the MnO2 raw particles. The nitrogen adsorption-desorption isotherms shown in figure 3 revealed microstructure of the particles. Both the MnO2 and core@shell powders showed a hysteresis loop at a relative pressure from 0.45 to 0.99. According to the pore size distributions calculated from the adsorption branches (figure 3, inset figure), the average pore diameter increased from 5.4 nm to 10.1 nm after mechanical treatment. On the other hand, the specific surface area and the pore volume decreased from 41.1 m2 g−1 and 0.056 cm3 g−1 of the MnO2 raw material to 19.3 m2 g−1 and 0.049 cm3 g−1 of the core@shell particles, respectively. These powder property changes are due to the formation of the Li(Ni,Mn)2O4 particles as the shell. The primary particle size of the MnO2 raw material, which was estimated from the specific surface area, was 29 nm. That is, the MnO2 raw material consists of the nanometer-sized primary particles. The formation of Li(Ni,Mn)2O4 particles arises at the nanometer-sized particle of the MnO2 surface through mechanical treatment. However, the shearing process of an attrition-type mill scrapes the synthesized Li(Ni,Mn)2O4 nanoparticles, and the fresh surfaces are created at the MnO2 particles. By repeating the formation and abrasion of Li(Ni,Mn)2O4 particles, the product particles are made more round in shape. Meanwhile, the synthesized Li(Ni,Mn)2O4 nanoparticles are progressively deposited on the particle surface of MnO2, and the core@shell structure is formed during mechanical treatment. This deposition process of the Li(Ni,Mn)2O4 nanoparticles onto MnO2 leads to the increase of the pore diameter and the decrease of the specific surface area. The mechanical treatment using an attrition-type mill allows surface coating of the larger species in the case of an obvious difference in particle size between reactants [30]. In this study, the synthesis of the shell particles and the formation of the core@shell structure were achieved by a one-step dry process.

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.