Porous Organic Polymers for Polysulfide Trapping in Lithium–Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries have attracted considerable attentions in electronic energy storage and conversion because of their high theoretical energy density and cost effectiveness. The rapid capacity degradation, mainly caused by the notorious shuttle effect of polysulfides (PSs), remains a great challenge preventing practical application. Porous organic polymers (POPs) are one type of promising carbon materials to confine PSs within the cathode region. Here, the research progress on POPs and POPs-derived carbon materials in Li-S batteries is summarized, and the importance of pore surface chemistry in uniform distribution of sulfur and effective trapping of PSs is highlighted. POPs serve as promising sulfur host materials, interlayers, and separators in Li-S batteries. Their significance and innovation, especially new synthetic methods for promoting sulfur content, reversible capacity, Coulombic efficiency and cycling stability, have been demonstrated. The perspectives and critical challenges that need to be addressed for POPsbased Li-S batteries are also discussed. Some attractive electrode materials and concepts based on POPs have been proposed to improve energy density and electrochemical performance, which are anticipated to shed some light on future development of POPs in advanced Li-S batteries. a theoretical capacity of 3840 mA h g −1 , the conventional Li-S batteries could provide an average battery voltage of 2.2 V and a high theoretical energy density of 2570 W h kg −1 , which is 2-3 times higher than practical energy density of the commercial lithium ion batteries (LIBs). [4][5][6] Moreover, low cost, natural abundance, and environmental friendliness of sulfur endow Li-S batteries with great development potential and space compared with LIBs. Despite the overwhelming advantages, the practical application of Li-S batteries suffers from several technological obstacles, such as (i) poor electrical conductivities of sulfur and solid-state discharging products (Li 2 S 2 and Li 2 S); (ii) the dissolution of soluble lithium polysulfides (PSs) intermediates in the electrolytes and their free migration between cathode and anode, which results in notorious shuttle effect of PSs; (iii) huge volume fluctuation (≈80%) of the active materials during discharge and charge owing to large density difference between element sulfur and solid-state products. The major disadvantage is the shuttle effect of PSs among the above problems. During discharge and charge cycle, the dissolved high-order PSs generated in the cathode move toward the anode and react with lithium metal to form low-order PSs or a passive layer on the anode surface, low-order PSs diffuse back to the cathode and produce high-order PSs again. This process usually causes irreversible loss of active materials and low Coulombic efficiency, which are associated with fast capacity fading, low energy efficiency, severe self-discharge, and poor cycling stability. [1,[7][8][9][10] To address these problems, considerable efforts have been devoted to the devel...

Selenium as Extra Binding Site for Sulfur Species in Sulfurized Polyacrylonitrile Cathodes for High Capacity Lithium‐Sulfur Batteries

“…The coulombic efficiencies of SeSPAN and SPAN are both close to 100 %, indicating that the shuttle effect is prohibited during charge/discharge process. [45][46][47] Se also contributes to the capacity as it is a cathode material with a theoretical capacity of 675 mA h g À 1 . The initial discharge process shows a different discharge curve due to the activation process and side reactions ( Figure S2).…”

Trapping of Polysulfides with Sulfur‐Rich Poly Ionic Liquid Cathode Materials for Ultralong‐Life Lithium–Sulfur Batteries

“…However, the insulating nature of sulfur and the dissolution of lithium polysulfides in organic electrolytes limit the practical application of Li–S batteries . Therefore, to solve the above problems, previous studies of Li–S batteries focused on developing advanced host materials for sulfur, including carbon nanotubes, graphene, porous carbon, metal oxides, covalent organic framework (COFs), metal–organic frameworks (MOFs), polymers, and others . Although significant improvements in discharge capacity and long‐cycling performance of Li–S batteries have been achieved, the complex preparation and the high cost of these host materials remain a challenge…”

Multiple Covalent Triazine Frameworks with Strong Polysulfide Chemisorption for Enhanced Lithium‐Sulfur Batteries

“…Among them, porous organic polymers (POPs) with rich functional groups such as conjugated microporous polymers (CMPs), and covalent organic frameworks (COFs) show great advantages in this aspect. In particular, they provide high flexibilities for molecular design of frameworks and nanopores, and it is possible to design POPs with high affinity toward sulfur ,. However, elimination of polysulfide dissolution to an ideal level remain challenging.…”

“…Lithium-sulfur batteries (LSBs) have gained great interest due to their high theoretic energy density (up to 2567 Wh kg À 1 ), low cost and environmental friendliness, [1][2][3][4][5] which are superior to the traditional lithium-ion batteries. [6][7][8] But how to make practical LSBs in large scale remains big challenge.…”