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Design of a Porous Cathode for Ultrahigh Performance of a Li-ion Battery: An Overlooked Pore Distribution

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ABSTRACT

Typical cathode materials of Li-ion battery suffer from a severe loss in specific capacity, and this problem is regarded as a major obstacle in the expansion of newer applications. To overcome this, porous cathodes are being extensively utilized. However, although it seems that the porosity in the cathode would be a panacea for high performance of LIBs, there is a blind point in the cathode consisting of porous structures, which makes the porous design to be a redundant. Here, we report the importance of designing the porosity of a cathode in obtaining ultrahigh performance with the porous design or a degraded performance even with increase of porosity. Numerical simulations show that the cathode with 40% porosity has 98% reduction in the loss of specific capacity when compared to the simple spherical cathode when the C-rate increases from 2.5 to 80 C. In addition, the loss over total cycles decreases from 30% to only about 1% for the cathode with 40% porosity under 40 C. Interestingly, however, the specific capacity could be decreased even with the increase in porosity unless the pores were evenly distributed in the cathode. The present analysis provides an important insight into the design of ultrahigh performance cathodes.

No MeSH data available.


Effect of pore distribution on the specific capacity of the cathode.Specific capacities of the porous cathode with evenly distributed pores (red) and unevenly distributed pores (blue) at (A) 5 C, (B) 10 C, (C) 40 C, and (D) 80 C. (E) Cross-sectional image of the Li-ion concentration in the cathode with 40% porosity with an even distribution (left) and an uneven distribution (right). (F) Specific capacities of the cathode with evenly distributed pores (red) and unevenly distributed pores (blue) according to the diameter of the pore. The porosity is 40% and the C-rate is 80 C. (G) Cross-sectional image of the Li-ion concentration in the 40% porosity cathode according to the pore diameter variation: with even distribution (top) and uneven distribution of pores (bottom).
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f4: Effect of pore distribution on the specific capacity of the cathode.Specific capacities of the porous cathode with evenly distributed pores (red) and unevenly distributed pores (blue) at (A) 5 C, (B) 10 C, (C) 40 C, and (D) 80 C. (E) Cross-sectional image of the Li-ion concentration in the cathode with 40% porosity with an even distribution (left) and an uneven distribution (right). (F) Specific capacities of the cathode with evenly distributed pores (red) and unevenly distributed pores (blue) according to the diameter of the pore. The porosity is 40% and the C-rate is 80 C. (G) Cross-sectional image of the Li-ion concentration in the 40% porosity cathode according to the pore diameter variation: with even distribution (top) and uneven distribution of pores (bottom).

Mentions: Next, the performance according to the distribution of pores in the cathode was investigated under 5, 10, 40, and 80 C-rate conditions. Porous cathodes that have an even and uneven distribution of pores were designed for each porosity. The specific capacities of each porous cathode with evenly distributed pores (i.e., red line) and unevenly distributed pores (i.e., blue line) are presented in Fig. 4A–D. Figure 4A to D presents the specific capacities at the 5, 10, 40, and 80 C-rates, respectively. The simulation reveals that the porous cathodes have up to 55% variation in the specific capacity according to the distribution of pores. Interestingly, the porosity of cathode could be a superfluous unless the pores are evenly distributed. Qualitatively, the cathode with well-distributed pores has a higher Li-ion concentration than the cathode with an uneven distribution of pores (Fig. 4E). This result can be explained by the pore-concentrated region that results in the restrictive use of cathode material. In other words, Li-ion is primarily intercalated at the pore-concentrated region due to the excessively shortened pathway of diffusion into the cathode and the much earlier onset of the ε phase than the other regions. Li-ions are increasingly accumulated in the region where the ε phase is generated due to the significantly lower diffusivity of Li-ion, and thus the discharging process is terminated without full utilization of the cathode. Additionally, the effect of the diameter of pores on the specific capacity was investigated (Fig. 4F and G). The porosity and C-rate were set at 40% and 80 C, respectively. Five different pore diameters, namely 60, 80, 100, 120, and 140 nm, were considered. As the diameter of the pore decreases, the specific capacity of the evenly designed porous cathode can be improved because the surface area increases with the decrease in pore diameter, while that of the unevenly designed porous cathode deteriorates (Fig. 4F). This deterioration originates from the pore-concentrated region and is due to the excessively shortened pathway of Li-ion diffusion as the pore diameter decreases, which results in early termination of the discharging process without full utilization of the cathode. The cathode with a pore diameter of 60 nm shows more restrictive utilization than that observed with a pore diameter of 120 or 140 nm (Fig. 4G), as the region where Li-ion cannot reach (i.e., the blue region) for the cathode with 60 nm pores increases in comparison to that with 120 nm or 140 nm pores.


Design of a Porous Cathode for Ultrahigh Performance of a Li-ion Battery: An Overlooked Pore Distribution
Effect of pore distribution on the specific capacity of the cathode.Specific capacities of the porous cathode with evenly distributed pores (red) and unevenly distributed pores (blue) at (A) 5 C, (B) 10 C, (C) 40 C, and (D) 80 C. (E) Cross-sectional image of the Li-ion concentration in the cathode with 40% porosity with an even distribution (left) and an uneven distribution (right). (F) Specific capacities of the cathode with evenly distributed pores (red) and unevenly distributed pores (blue) according to the diameter of the pore. The porosity is 40% and the C-rate is 80 C. (G) Cross-sectional image of the Li-ion concentration in the 40% porosity cathode according to the pore diameter variation: with even distribution (top) and uneven distribution of pores (bottom).
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f4: Effect of pore distribution on the specific capacity of the cathode.Specific capacities of the porous cathode with evenly distributed pores (red) and unevenly distributed pores (blue) at (A) 5 C, (B) 10 C, (C) 40 C, and (D) 80 C. (E) Cross-sectional image of the Li-ion concentration in the cathode with 40% porosity with an even distribution (left) and an uneven distribution (right). (F) Specific capacities of the cathode with evenly distributed pores (red) and unevenly distributed pores (blue) according to the diameter of the pore. The porosity is 40% and the C-rate is 80 C. (G) Cross-sectional image of the Li-ion concentration in the 40% porosity cathode according to the pore diameter variation: with even distribution (top) and uneven distribution of pores (bottom).
Mentions: Next, the performance according to the distribution of pores in the cathode was investigated under 5, 10, 40, and 80 C-rate conditions. Porous cathodes that have an even and uneven distribution of pores were designed for each porosity. The specific capacities of each porous cathode with evenly distributed pores (i.e., red line) and unevenly distributed pores (i.e., blue line) are presented in Fig. 4A–D. Figure 4A to D presents the specific capacities at the 5, 10, 40, and 80 C-rates, respectively. The simulation reveals that the porous cathodes have up to 55% variation in the specific capacity according to the distribution of pores. Interestingly, the porosity of cathode could be a superfluous unless the pores are evenly distributed. Qualitatively, the cathode with well-distributed pores has a higher Li-ion concentration than the cathode with an uneven distribution of pores (Fig. 4E). This result can be explained by the pore-concentrated region that results in the restrictive use of cathode material. In other words, Li-ion is primarily intercalated at the pore-concentrated region due to the excessively shortened pathway of diffusion into the cathode and the much earlier onset of the ε phase than the other regions. Li-ions are increasingly accumulated in the region where the ε phase is generated due to the significantly lower diffusivity of Li-ion, and thus the discharging process is terminated without full utilization of the cathode. Additionally, the effect of the diameter of pores on the specific capacity was investigated (Fig. 4F and G). The porosity and C-rate were set at 40% and 80 C, respectively. Five different pore diameters, namely 60, 80, 100, 120, and 140 nm, were considered. As the diameter of the pore decreases, the specific capacity of the evenly designed porous cathode can be improved because the surface area increases with the decrease in pore diameter, while that of the unevenly designed porous cathode deteriorates (Fig. 4F). This deterioration originates from the pore-concentrated region and is due to the excessively shortened pathway of Li-ion diffusion as the pore diameter decreases, which results in early termination of the discharging process without full utilization of the cathode. The cathode with a pore diameter of 60 nm shows more restrictive utilization than that observed with a pore diameter of 120 or 140 nm (Fig. 4G), as the region where Li-ion cannot reach (i.e., the blue region) for the cathode with 60 nm pores increases in comparison to that with 120 nm or 140 nm pores.

View Article: PubMed Central - PubMed

ABSTRACT

Typical cathode materials of Li-ion battery suffer from a severe loss in specific capacity, and this problem is regarded as a major obstacle in the expansion of newer applications. To overcome this, porous cathodes are being extensively utilized. However, although it seems that the porosity in the cathode would be a panacea for high performance of LIBs, there is a blind point in the cathode consisting of porous structures, which makes the porous design to be a redundant. Here, we report the importance of designing the porosity of a cathode in obtaining ultrahigh performance with the porous design or a degraded performance even with increase of porosity. Numerical simulations show that the cathode with 40% porosity has 98% reduction in the loss of specific capacity when compared to the simple spherical cathode when the C-rate increases from 2.5 to 80 C. In addition, the loss over total cycles decreases from 30% to only about 1% for the cathode with 40% porosity under 40 C. Interestingly, however, the specific capacity could be decreased even with the increase in porosity unless the pores were evenly distributed in the cathode. The present analysis provides an important insight into the design of ultrahigh performance cathodes.

No MeSH data available.