Project description:A cathode substrate with strong adsorption of lithium polysulfides (LiPSs) has been preferred for lithium-sulfur (Li-S) batteries. However, the recent finding that controlled growth of lithium sulfides (Li2 S) during discharge is crucial for S utilization stimulates improvement of this preference. Here, the Li2 S growth and cell capacity in the LiPS binding energy landscape of cathode substrates are investigated. Specifically, Co-based ternary oxides are employed to obtain binding energies in the range of 4.0-7.4 eV. Of these substrates, only the MnCo2 O4 substrate with moderate LiPS affinity exhibits 3D Li2 S growth. The MnCo2 O4 cells achieve high sulfur utilization up to 84% at 0.2 C and excellent performance even under high sulfur loading/lean electrolyte conditions. In contrast, weak affinity substrates such as ZnCo2 O4 and strong affinity substrates such as NiCo2 O4 and CuCo2 O4 exhibit low discharge capacity with 2D Li2 S growth. For optimal LiPS affinity driving 3D growth, a balance between promoting LiPS adsorption and diffusion limitation in the LiPS adsorption layer is suggested.
Project description:Lightweight and flexible energy storage devices are urgently needed to persistently power wearable devices, and lithium-sulfur batteries are promising technologies due to their low mass densities and high theoretical capacities. Here we report a flexible and high-energy lithium-sulfur full battery device with only 100% oversized lithium, enabled by rationally designed copper-coated and nickel-coated carbon fabrics as excellent hosts for lithium and sulfur, respectively. These metallic carbon fabrics endow mechanical flexibility, reduce local current density of the electrodes, and, more importantly, significantly stabilize the electrode materials to reach remarkable Coulombic efficiency of >99.89% for a lithium anode and >99.82% for a sulfur cathode over 400 half-cell charge-discharge cycles. Consequently, the assembled lithium-sulfur full battery provides high areal capacity (3 mA h cm-2), high cell energy density (288 W h kg-1 and 360 W h L-1), excellent cycling stability (260 cycles), and remarkable bending stability at a small radius of curvature (<1 mm).
Project description:Owing to the overwhelming advantage in energy density, lithium-sulfur (Li-S) battery is a promising next-generation electrochemical energy storage system. Despite many efforts in pursuing long cycle life, relatively little emphasis has been placed on increasing the areal energy density. Herein, we have designed and developed a 'pie' structured electrode, which provides an excellent balance between gravimetric and areal energy densities. Combining lotus root-like multichannel carbon nanofibers 'filling' and amino-functionalized graphene 'crust', the free-standing paper electrode (S mass loading: 3.6 mg cm(-2)) delivers high specific capacity of 1,314 mAh g(-1) (4.7 mAh cm(-2)) at 0.1 C (0.6 mA cm(-2)) accompanied with good cycling stability. Moreover, the areal capacity can be further boosted to more than 8 mAh cm(-2) by stacking three layers of paper electrodes with S mass loading of 10.8 mg cm(-2).
Project description:Lithium-sulfur (Li-S) batteries with high energy density and low cost are promising for next-generation energy storage. However, their cycling stability is plagued by the high solubility of lithium polysulfide (LiPS) intermediates, causing fast capacity decay and severe self-discharge. Exploring electrolytes with low LiPS solubility has shown promising results toward addressing these challenges. However, here, we report that electrolytes with moderate LiPS solubility are more effective for simultaneously limiting the shuttling effect and achieving good Li-S reaction kinetics. We explored a range of solubility from 37 to 1,100 mM (based on S atom, [S]) and found that a moderate solubility from 50 to 200 mM [S] performed the best. Using a series of electrolyte solvents with various degrees of fluorination, we formulated the Single-Solvent, Single-Salt, Standard Salt concentration with Moderate LiPSs solubility Electrolytes (termed S6MILE) for Li-S batteries. Among the designed electrolytes, Li-S cells using fluorinated-1,2-diethoxyethane S6MILE (F4DEE-S6MILE) showed the highest capacity of 1,160 mAh g-1 at 0.05 C at room temperature. At 60 °C, fluorinated-1,4-dimethoxybutane S6MILE (F4DMB-S6MILE) gave the highest capacity of 1,526 mAh g-1 at 0.05 C and an average CE of 99.89% for 150 cycles at 0.2 C under lean electrolyte conditions. This is a fivefold increase in cycle life compared with other conventional ether-based electrolytes. Moreover, we observed a long calendar aging life, with a capacity increase/recovery of 4.3% after resting for 30 d using F4DMB-S6MILE. Furthermore, the correlation between LiPS solubility, degree of fluorination of the electrolyte solvent, and battery performance was systematically investigated.
Project description:Coupling high-capacity cathode and Li-anode with solid-state electrolyte has been demonstrated as an effective strategy for increasing the energy densities and safety of rechargeable batteries. However, the limited ion conductivity, the large interfacial resistance, and unconstrained Li-dendrite growth hinder the application of solid-state Li-metal batteries. Here, a poly(ether-urethane)-based solid-state polymer electrolyte with self-healing capability is designed to reduce the interfacial resistance and provides a high-performance solid-state Li-metal battery. With its dynamic covalent disulfide bonds and hydrogen bonds, the proposed solid-state polymer electrolyte exhibits excellent interfacial self-healing ability and maintains good interfacial contact. Full cells are assembled with the two integrated electrodes/electrolytes. As a result, the Li||Li symmetric cells exhibit stable long-term cycling for more than 6000 h, and the solid-state Li-S battery shows a prolonged cycling life of 700 cycles at 0.3 C. The use of ultrasound imaging technology shows that the interfacial contact of the integrated structure is much better than those of traditional laminated structure. This work provides an interesting interfacial dual-integrated strategy for designing high-performance solid-state Li-metal batteries.
Project description:Organic compounds with active sites for lithiation can be used as electrode materials for lithium batteries. Their tunable structures allow a variety of materials to be made and investigated. Herein, a spectrum of dipyridyl polysulfides (Py2S x , 3 ≤ x ≤ 8) is prepared in electrolyte by a one-pot synthesis method from dipyridyl disulfide (Py2S2) and elemental sulfur. It renders up to seven dipyridyl polysulfides (i.e., Py2S3, Py2S4, Py2S5, Py2S6, Py2S7, and Py2S8) which show fully reversible electrochemical behavior in lithium batteries. In the discharge, the initial lithiation occurs at 2.45 V leading to the breakage of Sα-Sβ bonds in Py2S x and formation of lithium 2-pyridinethiolate, in which lithium is coordinated in between N and S atoms. The left sulfur species act as elemental sulfur, showing two voltage plateaus at 2.3 and 2.1 V. The molecular dynamics simulations show the attraction between pyridyl groups and lithium polysulfides/sulfide via N···Li···S bonds, which enable good retention of soluble discharge products within electrodes and stable cycling performance. In the recharge, low-order Py2S x (e.g., Py2S3, Py2S4, and Py2S5) remain as the charged products. The mixture catholyte exhibits superlong cycle life at 1C rate with 1200 cycles and 70.5% capacity retention.
Project description:Lithium-sulfur batteries are promising technology in electrical vehicles and large-scale energy storage systems. However, their market penetration is seriously impeded by great challenges such as the low electrical conduction of sulfur and lithium sulfides, and lithium polysulfides' shuttling effect. This work shows that such challenges can be partly resolved by encapsulating sulfur in crumpled reduced graphene oxide (S@crGO), which was synthesized by a facile and scalable one-step in situ method. The strong interaction between sulfur and the graphene host, micro- and meso-pore structures, and rich surface functional groups contribute to the high performance of the S@crGO cathode for lithium-sulfur batteries.
Project description:Storing pulsed energy harvested by triboelectric nanogenerators (TENGs) from ambient mechanical motion is an important technology for obtaining sustainable, low-cost, and green power. Here, we introduce high-energy-density Li-S batteries with excellent performance for storing pulsed output from TENGs. The sandwich-structured sulfur composites with multi-walled carbon nanotubes and polypyrrole serve as cathode materials that suppress the shuttle effect of polysulfides and thus preserve the structural stability of the cathode during Li-ion insertion and extraction. The charging time and energy storage efficiency of the Li-S batteries are directly affected by the rotation rates of the TENGs. The average storage efficiency of the batteries for pulsed output from TENGs can exceed 80% and even reach 93% at low discharge currents. The Li-S batteries also show excellent rate performance for storing pulsed energy at a high discharge current rate of 5 C. The high storage efficiency and excellent rate capability and cyclability demonstrate the feasibility of storing and exploiting pulsed energy provided by TENGs and the potential of Li-S batteries with high energy storage efficiency for storing pulsed energy harvested by TENGs.
Project description:The increasing demand for electrical energy storage makes it essential to explore alternative battery chemistries that overcome the energy-density limitations of the current state-of-the-art lithium-ion batteries. In this scenario, lithium-sulfur batteries (LSBs) stand out due to the low cost, high theoretical capacity, and sustainability of sulfur. However, this battery technology presents several intrinsic limitations that need to be addressed in order to definitively achieve its commercialization. Herein, we report the fruitfulness of three different formulations using well-selected functional carbonaceous additives for sulfur cathode development, an in-house synthesized graphene-based porous carbon (ResFArGO), and a mixture of commercially available conductive carbons (CAs), as a facile and scalable strategy for the development of high-performing LSBs. The additives clearly improve the electrochemical properties of the sulfur electrodes due to an electronic conductivity enhancement, leading to an outstanding C-rate response with a remarkable capacity of 2 mA h cm-2 at 1C and superb capacities of 4.3, 4.0, and 3.6 mA h cm-2 at C/10 for ResFArGO10, ResFArGO5, and CAs, respectively. Moreover, in the case of ResFArGO, the presence of oxygen functional groups enables the development of compact high sulfur loading cathodes (>4 mgS cm-2) with a great ability to trap the soluble lithium polysulfides. Notably, the scalability of our system was further demonstrated by the assembly of prototype pouch cells delivering excellent capacities of 90 mA h (ResFArGO10 cell) and 70 mA h (ResFArGO5 and CAs cell) at C/10.
Project description:Lithium metal is a promising anode candidate for the next-generation rechargeable battery due to its highest specific capacity (3860 mA h g-1) and lowest potential, but low Coulombic efficiency and formation of lithium dendrites hinder its practical application. Here, we report a self-formed flexible hybrid solid-electrolyte interphase layer through co-deposition of organosulfides/organopolysulfides and inorganic lithium salts using sulfur-containing polymers as an additive in the electrolyte. The organosulfides/organopolysulfides serve as "plasticizer" in the solid-electrolyte interphase layer to improve its mechanical flexibility and toughness. The as-formed robust solid-electrolyte interphase layers enable dendrite-free lithium deposition and significantly improve Coulombic efficiency (99% over 400 cycles at a current density of 2 mA cm-2). A lithium-sulfur battery based on this strategy exhibits long cycling life (1000 cycles) and good capacity retention. This study reveals an avenue to effectively fabricate stable solid-electrolyte interphase layer for solving the issues associated with lithium metal anodes.The practical application of lithium metal anodes suffers from the poor Coulombic efficiency and growth of lithium dendrites. Here, the authors report an approach to enable the self-formation of stable and flexible solid-electrolyte interphase layers which serve to address both issues.