Safety Of Lithium-sulfur Batteries Research Articles

Metalloporphyrin conjugated porous polymer in-situ grown on a Celgard separator as multifunctional polysulfide barrier and catalyst for high-performance Li-S batteries

The severe shuttling of soluble polysulfides (LiPSs) (Li2Sx, 4 ≤ x ≤ 8) and sluggish kinetics of solid–solid conversion (Li2S2 → Li2S), lead to the premature end of discharge, resulting in fast capacity decay, limiting the practical performance and safety of lithium-sulfur batteries (LSBs). Functional modifiers on separators exhibit significant performances in migrating diffusion and promoting conversion for LiPSs; thus, endowing the separator with multiple high-performance parameters by multifactorial engineering to address the two issues mentioned above is an urgent need. Herein, for the first time, an ultra-light (≈0.14 mg cm−2) and multifunctional modifier consisting of metalloporphyrin conjugated porous polymer (Al-CPP) is interface-induced growth on the commercial separator to develop advanced LSBs. The electrocatalyst of metalloporphyrin is covalently constructed by an imidazolium-containing linker with bis(trifluoromethane)sulfonimide (TFSI−) anions within the porous skeleton, improving diffusion and conversion of LiPSs as well as facilitating electrolyte accessibility and Li+ transport, thereby performing enhanced full-range sulfur redox kinetics, and guiding uniform Li deposition. The in-situ growth of metalloporphyrin conjugated porous polymer is further verified in LSBs that realize superior rate performances and long lifespans. This contribution proposes an efficient in-situ growth of an ultra-light modifier design strategy to functionalize separators and inspires multi-function synergetic integration facing high-performance LSBs.

Boosting the cycle stability and safety of lithium-sulfur batteries via a bilayer, heat-treated electrospun separator

A multifunctional lithium–sulfur–battery separator, the heat-treated PAN/CB/VOOH-PAN/PVDF(HFP) (HPCVPP), was synthesized using a single-step electrospinning technique and heat treatment. The HPCVPP separator has two layers for its functions. (i) The PAN/CB/VOOH, close to the Li–S battery cathode, acts as the conductive blocking layer. The conductive blocking layer provides a site for the electrochemical reaction of LIPS species. In addition, the polar VOOH of this layer can adsorb and catalyze LIPS species, slowing down the ‘shuttle effect’. The batteries using the HPCVPP separator exhibited a close-to-theoretical-maximum capacity of 1391 mAh/g at 0.1C and maintained a high capacity (644 mAh/g) even after 500 cycles at 2C. (ii) The second layer is PAN/PVDF(HFP). In particular, the PAN/PVDF(HFP) helps achieve good thermal stability of the HPCVPP separator. The HPCVPP contour can still be maintained at 250 °C, which can ensure the high-temperature safety of the battery. Moreover, the PVDF(HFP) was heat-treated and generated a crosslinked structure between the nanofibers, enhancing the mechanical strength of the separator from 10.6 to 20.8 MPa, which can further improve battery safety. The HPCVPP separator exhibited outstanding performance, including high level of porosity (70.7%), high electrolyte uptake (510.4%), good ionic conductivity (2.81 mS/cm), and excellent electrochemical performance.

Lithium-Sulfur Batteries: Advances and Trends

A review with 132 references. Societal and regulatory pressures are pushing industry towards more sustainable energy sources, such as solar and wind power, while the growing popularity of portable cordless electronic devices continues. These trends necessitate the ability to store large amounts of power efficiently in rechargeable batteries that should also be affordable and long-lasting. Lithium-sulfur (Li-S) batteries have recently gained renewed interest for their potential low cost and high energy density, potentially over 2600 Wh kg−1. The current review will detail the most recent advances in early 2020. The focus will be on reports published since the last review on Li-S batteries. This review is meant to be helpful for beginners as well as useful for those doing research in the field, and will delineate some of the cutting-edge adaptations of many avenues that are being pursued to improve the performance and safety of Li-S batteries.

Research Progress of Sulfur/Carbon Composite Cathode Materials and the Corresponding Safe Electrolytes for Advanced Li-S Batteries

Lithium-sulfur (Li-S) battery is one of the most promising secondary batteries for its high energy density, high natural abundance and environment friendly nature of sulfur. However, the commercial application of Li-S battery faces some technical obstacles, such as low cycling stability resulted from the shuttle effect of polysulfides, low electrical conductivity of sulfur and volume expansion during charge/discharge process. Furthermore, due to the flammability of organic solvents in liquid electrolytes, the continuous formation of lithium dendrites and the low ignition temperature of carbon–sulfur mixtures, safety of Li-S batteries has become another critical issue to be solved. In recent years, many different strategies have been put forward to improve the electrochemical performance and safety of Li-S batteries, containing the development of carbon/sulfur composite cathodes, design of flame retardant electrolytes and protection of negative electrodes. In this review, the recent progress of sulfur/carbon composite cathode materials for Li-S battery is first introduced. Then the evaluation methods and latest development of high-safety electrolytes toward advanced Li-S batteries are summarized. Finally, the development trends of Li-S battery are forecasted.

A Novel Zwitterionic Ionic Liquid-Based Electrolyte for More Efficient and Safer Lithium-Sulfur Batteries.

The shuttle effect of polysulfide and the flammability of the conventional electrolyte are the two major obstacles restricting the development progress of lithium-sulfur batteries. Exploring highly efficient electrolyte components coupled with the conventional electrolyte is a reliable strategy to solve these issues. However, the current electrolyte components usually relieve these issues at the expense of the sacrificed electrochemical performance. Herein, a novel zwitterionic ionic liquid named as TLTFSI is reported, which exhibits a high ionic conductivity of 3.7 × 10-3 S cm-1, a wide electrochemical potential window from 1.51 to 4.82 V at 25 °C, and a high thermal decomposition temperature of 275 °C. The optimized TLTFSI-based electrolyte is nonflammable and performs superior electrochemical performance in terms of larger capacity, better rate capability, and longer cyclic life compared with the conventional organic electrolyte. The robust performance is attributed to the high intrinsic ionic conductivity, the suppressed polysulfide dissolution/diffusion, and the high interface compatibility toward the lithium anode of the TLTFSI-based electrolytes. This present work represents the first demonstration of the zwitterionic ionic liquid to efficiently improve the overall electrochemical performance and the safety of lithium-sulfur batteries.

Robust Lithium Metal Anodes Realized by Lithiophilic 3D Porous Current Collectors for Constructing High-Energy Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are attractive candidates for next-generation rechargeable batteries. With the steady development of sulfur cathodes, the recent revival of research on dendrite-free Li metal anodes offers opportunities to improve the stabilities and safety of Li-S batteries. However, the low capacities and low Li utilizations of current Li anodes hinder the improvement of the energy densities of Li-S batteries. Here, we present a facile approach to fabricate lithiophilic three-dimensional porous current collectors by modifying commercial metal foams with yolk-shell structured N-doped porous carbon nanosheets. Benefiting from the structure-based rational design, this current collector is able to generate dendrite-free Li anodes with improved Coulombic efficiencies and life spans, enabling carbon/sulfur cathodes to exhibit significantly enhanced stabilities (e.g., 78.1% of capacity retention after 1400 cycles). More importantly, we successfully constructed a high-areal-capacity Li-S full cell (9.84 mAh cm-2) with 82% Li utilization. This work provides a promising route toward high-energy-density Li-S batteries.

The Role of Electrolyte Additives on the Stability and Electrochemical Performance of Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are attractive owing to their high theoretical energy density (2600 Wh kg-1)1, low cost, and natural abundance. However, a major drawback of LSBs is an uncontrolled lithium dendrite formation during cycling leading to serious safety issue, low Coulombic efficiency and poor cycle performance. To overcome this drawback, electrolyte additives are typically used to control the lithium dendrite growth by chemically forming stable solid-electrolyte interphase (SEI) above the metallic Li anode. The SEI layers are formed via several steps with rather complex mechanisms2. To elucidate the mechanisms of SEI formation, in this work, many electrolyte additives with different anions (e.g., LiNO3, LiClO4, LiBr, LiI, LiBF4) have been investigated using computational chemistry calculations along with the experimental study to gain fundamental understanding. The different additives exhibit different reaction pathways with LiTFSI to form the decomposed products over lithium surface and directly correlate to the evolution of LiF. This affects the cell performance in terms of the coulombic efficiency and capacity retention. For example, the LiNO3 provides the highest efficiency while it gives poor capacity retention. LiClO4 can provide high capacity retention over cycling. We believe that this work will provide the understanding of the effect of the additives that can enhance overall performance and safety of lithium-sulfur batteries. REFERENCES Chen, L.; Shaw, L. L. J. Power Sources 2014, 267, 770-783.Lili, W.; Yusheng, Y.; Nan, C.; Yongxin, H.; Li, L.; Feng, W.; Renjie, C. Adv. Funct. Mater. 2018, 0 (0), 1800919. Figure 1

Two-dimensional vermiculite separator for lithium sulfur batteries

Lithium-sulfur batteries have been considered as one of the most promising battery system for their high theoretical energy density. However, the lithium-sulfur batteries suffer from the dissolution and diffusion of polysulfides, which induce parasitic reactions with lithium metal anodes. The safety of lithium-sulfur batteries is also concerned with the risk of dendrite growth on lithium metal anodes. To simultaneously address the challenges in the shuttle effect and safety problems, we demonstrate herein a two-dimensional vermiculite separator. With the assembly of the 2D exfoliated vermiculite sheets, the vermiculite separator can suppress the diffusion of polysulfides across the separator through electrostatic interaction and steric hindrance. Meanwhile, the inorganic sheets with high strength and Young’s modulus prevent the penetration of lithium metal dendrite and potentially improve the safety of the system. This work elucidates a promising strategy for safe and stable lithium sulfur batteries, and can also be extended to other electrochemical systems based on metal anodes.

A thin multifunctional coating on a separator improves the cyclability and safety of lithium sulfur batteries.

Lithium-sulfur batteries are one of the most promising next-generation batteries due to their high theoretical specific capacity, but are impeded by the low utilization of insulating sulfur, unstable morphology of the lithium metal anode, and transport of soluble polysulfides. Here, by coating a layer of nano titanium dioxide and carbon black onto a commercial polypropylene separator, we demonstrate a new composite separator that can confine the polysulfides on the cathode side, forming a catholyte chamber, and at the same time block the dendritic lithium on the anode side. Lithium-sulfur batteries using this separator show a high initial capacity of 1206 mA h g-1 and a low capacity decay rate of 0.1% per cycle at 0.5C. Analyses reveal the electrocatalytic effect and the excellent dendrite-blocking capability of the ∼7 µm thick coating.