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Design and Fabrication of Microspheres with Hierarchical Internal Structure for Tuning Battery Performance

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The development of higher performance lithium ion batteries (LIBs) requires not only higher capacity materials but also their rational structuring for optimal function within the LIB... This is true for both existing intercalation compounds and next generation conversion compounds; in intercalating transition metal oxides, the particle internal structure can be used to tune the trade‐off between energy density and power. 1, 2 In conversion systems such as silicon and tin, such internal structure can be used to accommodate for their large volume expansion. 3, 4, 5 Structuring of intercalation compounds has already been the subject of extensive investigation... Materials with rather slow lithium ion diffusion, such as lithium titanate (LTO), exhibit enhanced performance with nanostructuring that does not significantly impact the electron transport in the material. 6, 7, 8, 9 Structuring generates a pore network that enables penetration of the liquid electrolyte into the particle, such that lithium ions are transported in the electrolyte and lithium ion have a shorter diffusion path in the solid... Assembling nanoparticles into micrometer‐sized spherical particles with a defined structure is a particularly attractive approach for fabricating active materials for LIBs both in terms of electrode manufacturing and electrochemical performance of the resulting cell. 10, 11, 12, 13 Such assembled nanostructured microparticles have a higher tap density than nanopowders, which results in a higher packing density of the particles in the electrodes and therefore higher volumetric energy density. 14, 15, 16 Furthermore, less polymeric binder and conductive agent is required to ensure an electrical path between the particles and the current collector compared to nanopowders... In addition, particle handling may be easier and safer in view of concerns associated with nanoparticles in industry. 17 Finally, spherically shaped microparticles are advantageous over platelets or ellipsoidal‐shaped particles in terms of decreased electrode tortuosity as shown by Ebner et al. 18 Every batch is characterized for frequency particle size distribution (PSD) using laser diffraction, specific surface area (SSA) using nitrogen adsorption, and morphology using scanning electron microscopy (SEM)... PSD and SSA results are given in Particles before calcination are shown in Figure S1 (Supporting Information)... The one hour calcination step at 750 °C does not alter the phase composition of the LTO, as shown by X‐ray diffraction (XRD) results in Figure S2 (Supporting Information)... To demonstrate the scalability of the template‐based spray drying approach, we also fabricate particles in a pilot‐scale spray dryer32, 33 capable of a production rate of 4 kg h... This is repeated until the axes do not intersect with neighboring ellipsoids or until the minimal axes size, defined beforehand by the user and corresponding to the smallest nanoparticles, is reached... Macropores or channels are also added by taking single ellipsoids away or moving them until they do not touch... Since template‐assisted spray drying is generalizable to a variety of starting nanoparticles or precursors, this approach could be applied to engineer a variety of battery materials ranging from intercalation compounds such as Li(Ni,Mn,Co)O2,25 Li(Ni,Co,Al)O2 to strongly expanding active materials such as silicon or sulfur.

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a) Volume‐based particle size frequency distributions (PSDs) of dense particles (no templates) and those fabricated with 3 and 5 wt% cellulose. b) PSDs of dense particles and those fabricated with PS and CF templates. c) Comparison of PSD of particles obtained with the laboratory and pilot‐scale spray dryers without templates.
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advs201500078-fig-0002: a) Volume‐based particle size frequency distributions (PSDs) of dense particles (no templates) and those fabricated with 3 and 5 wt% cellulose. b) PSDs of dense particles and those fabricated with PS and CF templates. c) Comparison of PSD of particles obtained with the laboratory and pilot‐scale spray dryers without templates.

Mentions: First, we tune the nanoscale porosity of the LTO microspheres by adding hydrophilic cellulose into the water‐based spray dry slurry and subsequently removing it via calcination of the resulting micrometer‐sized particles formed during the spray‐drying process. Particles before calcination are shown in Figure S1 (Supporting Information). The one hour calcination step at 750 °C does not alter the phase composition of the LTO, as shown by X‐ray diffraction (XRD) results in Figure S2 (Supporting Information). Analysis of the diffraction patterns by Rietveld refinement indicates an average crystal size of 121 nm before and 183 nm after calcination. This indicates slight sintering of the nanoparticles, which stabilizes the microspherical structure. When increasing the amount of cellulose in the slurry from 0 to 5 wt%, the PSD of the microspheres (Figure2a) remains comparable, while the nitrogen adsorption measurements (Table 1) show increasing SSA with increasing cellulose content, indicating a more extensive pore network through the microspheres.


Design and Fabrication of Microspheres with Hierarchical Internal Structure for Tuning Battery Performance
a) Volume‐based particle size frequency distributions (PSDs) of dense particles (no templates) and those fabricated with 3 and 5 wt% cellulose. b) PSDs of dense particles and those fabricated with PS and CF templates. c) Comparison of PSD of particles obtained with the laboratory and pilot‐scale spray dryers without templates.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016769&req=5

advs201500078-fig-0002: a) Volume‐based particle size frequency distributions (PSDs) of dense particles (no templates) and those fabricated with 3 and 5 wt% cellulose. b) PSDs of dense particles and those fabricated with PS and CF templates. c) Comparison of PSD of particles obtained with the laboratory and pilot‐scale spray dryers without templates.
Mentions: First, we tune the nanoscale porosity of the LTO microspheres by adding hydrophilic cellulose into the water‐based spray dry slurry and subsequently removing it via calcination of the resulting micrometer‐sized particles formed during the spray‐drying process. Particles before calcination are shown in Figure S1 (Supporting Information). The one hour calcination step at 750 °C does not alter the phase composition of the LTO, as shown by X‐ray diffraction (XRD) results in Figure S2 (Supporting Information). Analysis of the diffraction patterns by Rietveld refinement indicates an average crystal size of 121 nm before and 183 nm after calcination. This indicates slight sintering of the nanoparticles, which stabilizes the microspherical structure. When increasing the amount of cellulose in the slurry from 0 to 5 wt%, the PSD of the microspheres (Figure2a) remains comparable, while the nitrogen adsorption measurements (Table 1) show increasing SSA with increasing cellulose content, indicating a more extensive pore network through the microspheres.

View Article: PubMed Central - PubMed

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

The development of higher performance lithium ion batteries (LIBs) requires not only higher capacity materials but also their rational structuring for optimal function within the LIB... This is true for both existing intercalation compounds and next generation conversion compounds; in intercalating transition metal oxides, the particle internal structure can be used to tune the trade‐off between energy density and power. 1, 2 In conversion systems such as silicon and tin, such internal structure can be used to accommodate for their large volume expansion. 3, 4, 5 Structuring of intercalation compounds has already been the subject of extensive investigation... Materials with rather slow lithium ion diffusion, such as lithium titanate (LTO), exhibit enhanced performance with nanostructuring that does not significantly impact the electron transport in the material. 6, 7, 8, 9 Structuring generates a pore network that enables penetration of the liquid electrolyte into the particle, such that lithium ions are transported in the electrolyte and lithium ion have a shorter diffusion path in the solid... Assembling nanoparticles into micrometer‐sized spherical particles with a defined structure is a particularly attractive approach for fabricating active materials for LIBs both in terms of electrode manufacturing and electrochemical performance of the resulting cell. 10, 11, 12, 13 Such assembled nanostructured microparticles have a higher tap density than nanopowders, which results in a higher packing density of the particles in the electrodes and therefore higher volumetric energy density. 14, 15, 16 Furthermore, less polymeric binder and conductive agent is required to ensure an electrical path between the particles and the current collector compared to nanopowders... In addition, particle handling may be easier and safer in view of concerns associated with nanoparticles in industry. 17 Finally, spherically shaped microparticles are advantageous over platelets or ellipsoidal‐shaped particles in terms of decreased electrode tortuosity as shown by Ebner et al. 18 Every batch is characterized for frequency particle size distribution (PSD) using laser diffraction, specific surface area (SSA) using nitrogen adsorption, and morphology using scanning electron microscopy (SEM)... PSD and SSA results are given in Particles before calcination are shown in Figure S1 (Supporting Information)... The one hour calcination step at 750 °C does not alter the phase composition of the LTO, as shown by X‐ray diffraction (XRD) results in Figure S2 (Supporting Information)... To demonstrate the scalability of the template‐based spray drying approach, we also fabricate particles in a pilot‐scale spray dryer32, 33 capable of a production rate of 4 kg h... This is repeated until the axes do not intersect with neighboring ellipsoids or until the minimal axes size, defined beforehand by the user and corresponding to the smallest nanoparticles, is reached... Macropores or channels are also added by taking single ellipsoids away or moving them until they do not touch... Since template‐assisted spray drying is generalizable to a variety of starting nanoparticles or precursors, this approach could be applied to engineer a variety of battery materials ranging from intercalation compounds such as Li(Ni,Mn,Co)O2,25 Li(Ni,Co,Al)O2 to strongly expanding active materials such as silicon or sulfur.

No MeSH data available.


Related in: MedlinePlus