The Porous Carbon Matrix for High Rate Performance Lithium-Sulfur Battery

As the demand for sustainable, clean energy technologies increases, rechargeable lithium-ion batteries remain one of the most feasible alternatives for the future.¹ However, the ability to deliver safe and high-energy density components at low cost is a major obstacles for Li-ion batteries for use in electric vehicles (EVs) and energy storage systems (ESS).² Lithium-Sulfur batteries, one of the alternatives, has a large theoretical specific capacity of 1675 mAh g^-1 and an energy density of 2600 Wh kg^-1.³ Sulfur is also abundant in nature, inexpensive and eco-friendly. In spite of these benefits, Li-S cells have reached their limits due to their intrinsic characteristics. Firstly, sulfur has an insulating nature. Secondly, the resulting product, lithium polysulfide, is easily dissolved in the electrolyte, which causes active material loss. Lastly, slow kinetics occur at a lower plateau during charging-discharging processes. There are several approaches to overcome the slow kinetics and dissolution of lithium polysulfide, such as employing mesoporous carbon or a graphene oxide coating on sulfur. However, the utilization of sulfur is still a challenge due to the slow kinetics. One approach to address this issue is to limit the voltage range to reduce the formation of Li₂S₂ and Li₂S. The lower plateau region (Li₂S₄ ↔ Li₂S) has slow kinetics due to the phase transformation from a liquid to solid state by the Li₂S growth mechanism.⁴ Moreover, the Li₂S species that accumulate on the electrode surface may reduce the cycle life due to poor conductivity. We previously limited the voltage range of the upper plateau region (~2.1V vs Li⁺/Li); known as the fast kinetics region (S₈ ↔ Li₂S₄) with a theoretical capacity of 419 mAh g^-1,⁵ so as to hinder the formation of insoluble species (Li₂S₂, Li₂S). Herein, we simply upgrade the structure with a porous cathode material ( activated carbon, AC) with a gas diffusion layer (GDL); this porous carbon GDL (PCG) was compared with the conventional Al foil current collector (porous carbon Al foil, PCA) through an electrochemical performance test. This unique porous structure enhanced the facile transportation of the Li-ion in the liquid state Li-S cells so that the rate capability of the Li-S cells was increased.

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