Rational Electrolyte Solvent Screening for Practical Lithium–Sulfur Batteries

Practical lithium-sulfur (Li-S) batteries are severely plagued by the instability of solid electrolyte interphase (SEI) formed in routine ether electrolytes. Herein, an electrolyte with 1,3,5-trioxane (TO) and 1,2-dimethoxyethane (DME) as co-solvents is proposed to construct a high-mechanical-stability SEI by enriching organic components in Li-S batteries. The high-mechanical-stability SEI works compatibly in Li-S batteries. TO with high polymerization capability can preferentially decompose and form organic-rich SEI, strengthening mechanical stability of SEI, which mitigates crack and regeneration of SEI and reduces the consumption rate of active Li, Li polysulfides, and electrolytes. Meanwhile, DME ensures high specific capacity of S cathodes. Accordingly, the lifespan of Li-S batteries increases from 75 cycles in routine ether electrolyte to 216 cycles in TO-based electrolyte. Furthermore, a 417 Wh kg-1 Li-S pouch cell undergoes 20 cycles. This work provides an emerging electrolyte design for practical Li-S batteries.

Diluted High Concentration Electrolyte with Dual Effects for Practical Lithium-Sulfur Batteries

An ultrathick lithium metal anode (LMA) is a prerequisite for developing practical lithium-sulfur (Li-S) batteries that simultaneously meet the requirements of high areal capacity, lean electrolyte, and limited excess Li. Inspired by the electrochemical process for an organosulfur cathode, herein, we reconfigure such a sulfur cathode by using an overlithiation strategy to enable the formation of a high performance LMA. Specifically, an applicable ultrathick LMA is successfully constructed by overlithiating a well-known organosulfur cathode material, sulfurized polyacrylonitrile (SPAN). SPAN contains a polymeric pyridine structure with an outstanding lithium-ion affinity, so that it can act as a lithiophilic matrix. More importantly, a Li2S-rich solid electrolyte interphase (SEI) can be generated on the surface of SPAN during the overlithiation process. The synergistic effect of the lithiophilic matrix and a robust SEI leads to a dense deposition of lithium, which enables one to form an ultrathick LMA (159 μm, 30 mAh cm-2) with high Coulombic efficiency (99.7%). Such an LMA paired with a sulfur cathode of high areal capacity (up to 16 mAh cm-2) shows stable cycling under practical conditions of a lean electrolyte (2.2 μL mgS-1) and a negative-to-positive capacity (N/P) ratio as low as 1.3. The applicability of the ultrathick LMA was further verified with Li-S pouch cells, indicating a highly prospective route toward realization of practical Li-S batteries.

Lithium metal anodes are a key component of high-energy-density lithium-sulfur (Li-S) batteries. However, the issues associated with lithium anodes remain unsolved owing to the immature lithium anode construction and protection technology, which leads to internal short circuits, poor capacity retention, and low coulombic efficiency for high-sulfur-loading Li-S batteries. Herein, a highly stable 3D lithium carbon fiber composite (3D LiCF) anode for high-sulfur-loading Li-S batteries was demonstrated, in which a self-formed hybrid solid-electrolyte protection layer was constructed on a lithium metal surface through codeposition of thiophenolate ions and inorganic lithium salts by using diphenyl disulfide as a co-additive in the electrolyte. The aromatic components from thiophenolate could improve the stability of the protection layer, and the 3D structure of the carbon fiber could effectively buffer the volume effect during lithium cycling. A Li-S battery based on a 3D LiCF anode exhibited excellent cycling stability with an energy efficiency of 89.2 % for 100 cycles in terms of a high energy density of 22.3 mWh cm-2 (10 mAh cm-2 area capacity of lithium cycling). This contribution demonstrates versatile and ingenious strategies for the construction of a 3D lithium anode structure and protection layer, providing an effective solution for practical stable Li-S batteries.

Mott-Schottky electrocatalyst selectively mediates the sulfur species conversion in lithium-sulfur batteries

The recent research progress and prospect of gel polymer electrolytes in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries face critical challenges including sluggish polysulfide redox kinetics and the shuttle effect. This study presents a novel self-supporting carbon nanofibers decorated with Ti_xCr_1-xN solid-solution nanoparticles (CNFs@TCN) as Li₂S₆ host for lithium-sulfur (Li-S) batteries. By leveraging electrospinning and high-temperature nitridation reaction, we engineered a flexible electrode with tunable Ti/Cr ratios. Density functional theory (DFT) calculations and experimental analysis reveal that the TCN solid-solution phase optimizes electronic structure via Cr substitution, enhancing polysulfide adsorption and catalytic conversion kinetics. The CNFs@TCN-1/2 cathode (Ti:Cr = 1:2) exhibits exceptional performance of high initial capacity (1359 mAh g^-1), ultralow capacity decay (0.012% per cycle at 2 C), and remarkable rate capability (803 mAh g^-1 at 3 C). Under high sulfur loading (6.12 mg cm^-2) and lean electrolyte (E/S ratio=9.3 μL mg^-1), it delivers an areal capacity of 4.87 mAh cm^-2. This work demonstrates atomic-level d-band engineering of bimetallic nitrides as a powerful strategy to suppress shuttle effects and boost sulfur redox kinetics in practical Li-S batteries.

Lithium-sulfur (Li-S) batteries have great potential as high-energy-density energy storage devices. Electrocatalysts are widely adopted to accelerate the cathodic sulfur redox kinetics. The interactions among the electrocatalysts, solvents, and lithium salts significantly determine the actual performance of working Li-S batteries. Herein, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a commonly used lithium salt, is identified to aggravate surface gelation on the MoS2 electrocatalyst. In detail, the trifluoromethanesulfonyl group in LiTFSI interacts with the Lewis acidic sites on the MoS2 electrocatalyst to generate an electron-deficient center. The electron-deficient center with high Lewis acidity triggers cationic polymerization of the 1,3-dioxolane solvent and generates a surface gel layer that reduces the electrocatalytic activity. To address the above issue, Lewis basic salt lithium iodide (LiI) is introduced to block the interaction between LiTFSI and MoS2 and inhibit the surface gelation. Consequently, the Li-S batteries with the MoS2 electrocatalyst and the LiI additive realize an ultrahigh actual energy density of 416 W h kg-1 at the pouch cell level. This work affords an effective lithium salt to boost the electrocatalytic activity in practical working Li-S batteries and deepens the fundamental understanding of the interactions among electrocatalysts, solvents, and salts in energy storage systems.

Conductive RuO2 stacking microspheres as an effective sulfur immobilizer for lithium–sulfur battery

Construction of high-rate performance sulfurized Poly(acrylonitrile) nanofibers cathodes for practical lithium–sulfur batteries via tellurium catalytic regulation

Lithium-sulfur (Li-S) batteries constitute promising next-generation energy storage devices due to the ultrahigh theoretical energy density of 2600 Wh kg-1. However, the multiphase sulfur redox reactions with sophisticated homogeneous and heterogeneous electrochemical processes are sluggish in kinetics, thus requiring targeted and high-efficient electrocatalysts. Herein, a semi-immobilized molecular electrocatalyst is designed to tailor the characters of the sulfur redox reactions in working Li-S batteries. Specifically, porphyrin active sites are covalently grafted onto conductive and flexible polypyrrole linkers on graphene current collectors. The electrocatalyst with the semi-immobilized active sites exhibits homogeneous and heterogeneous functions simultaneously, performing enhanced redox kinetics and a regulated phase transition mode. The efficiency of the semi-immobilizing strategy is further verified in practical Li-S batteries that realize superior rate performances and long lifespan as well as a 343 Wh kg-1 high-energy-density Li-S pouch cell. This contribution not only proposes an efficient semi-immobilizing electrocatalyst design strategy to promote the Li-S battery performances but also inspires electrocatalyst development facing analogous multiphase electrochemical energy processes.

B/N co-doping rGO/BNNSs heterostructure with synergistic adsorption-electrocatalysis function enabling enhanced electrochemical performance of lithium-sulfur batteries

The lithium-sulfur (Li-S) battery is regarded as a promising high-energy-density battery system, in which the dissolution-precipitation redox reactions of the S cathode are critical. However, soluble Li polysulfides (LiPSs), as the indispensable intermediates, easily diffuse to the Li anode and react with the Li metal severely, thus depleting the active materials and inducing the rapid failure of the battery, especially under practical conditions. Herein, an organosulfur-containing solid electrolyte interphase (SEI) is tailored for the stabilizaiton of the Li anode in Li-S batteries by employing 3,5-bis(trifluoromethyl)thiophenol as an electrolyte additive. The organosulfur-containing SEI protects the Li anode from the detrimental reactions with LiPSs and decreases its corrosion. Under practical conditions with a high-loading S cathode (4.5 mgS cm-2 ), a low electrolyte/S ratio (5.0µL mgS -1 ), and an ultrathin Li anode (50µm), a Li-S battery delivers 82 cycles with an organosulfur-containing SEI in comparison to 42 cycles with a routine SEI. This work provokes the vital insights into the role of the organic components of SEI in the protection of the Li anode in practical Li-S batteries.

The sulfur conversion in lithium-sulfur (Li-S) batteries is largely hindered by sluggish conversion kinetics. Although highly active metal catalysts can promote this process, the intrinsic imbalance between electron transfer and ion transfer at the catalyst surface often leads to rapid passivation. Here, we address this critical challenge, particularly for highly active platinum (Pt) catalysts, by optimizing the electric double layer (EDL) at the catalyst-electrolyte interface, thereby enabling efficient and durable sulfur catalysis for high-energy Li-S batteries. The EDL structure is tuned by controlling the Pt surface charge density, achieved by grafting functional groups with varying electronegativities onto the carbon support to drive interfacial electron transfer from carbon to Pt. Using amine-functionalized carbon nanotube support to moderately increase charge density on Pt surface, we establish a well-balanced EDL that synchronizes coupled electron- and ion-transfer processes. This equilibrium facilitates efficient sulfur conversion while suppressing Pt sulfuration, maintaining a low activation energy (∼0.33eV) throughout the sulfur reduction reaction. Consequently, the corresponding batteries achieve 70% capacity retention under practical conditions after 300 cycles. A 2.0 Ah pouch cell delivers a high energy density of 516Wh kg-1. This work provides an effective strategy to design sulfuration-tolerant catalysts toward practical Li-S batteries.

Toward a practical Li-S battery enabled by synergistic confinement of a nitrogen-enriched porous carbon as a multifunctional interlayer and sulfur-host material