Polysulfide binding and trapping to prevent dissolution into the electrolyte by a variety of materials has been well studied in Li−S batteries. Here we discover that some of those materials can play an important role as an activation catalyst to facilitate oxidation of the discharge product, Li 2 S, back to the charge product, sulfur. Combining theoretical calculations and experimental design, we select a series of metal sulfides as a model system to identify the key parameters in determining the energy barrier for Li 2 S oxidation and polysulfide adsorption. We demonstrate that the Li 2 S decomposition energy barrier is associated with the binding between isolated Li ions and the sulfur in sulfides; this is the main reason that sulfide materials can induce lower overpotential compared with commonly used carbon materials. Fundamental understanding of this reaction process is a crucial step toward rational design and screening of materials to achieve high reversible capacity and long cycle life in Li−S batteries. T he ever-increasing demand for energy storage devices with high energy density, low material cost, and long cycle life has driven the development of new battery systems beyond the currently dominant lithium ion batteries (LIBs) (1). Among alternative battery chemistries, lithium−sulfur (Li−S) batteries have attracted remarkable attention due to their high theoretical energy density of 2,600 watt hours per kilogram, 5 times higher than those of state-of-the-art LIBs (2-4). In addition, sulfur, as a byproduct of the petroleum refining process, is naturally abundant, inexpensive, and environmentally friendly (5). However, the practical application of Li−S batteries is still plagued with numerous challenges. For example, the insulating nature of sulfur and discharge products Li 2 S/Li 2 S 2 leads to low active material utilization. In addition, the easy dissolution of lithium polysulfides (LiPSs) into the electrolyte causes LiPSs shuttling between cathode and anode and uncontrollable deposition of sulfide species on the lithium metal anode, inducing fast capacity fading and low coulombic efficiency (2, 6).Tremendous efforts have been taken to circumvent these concerns, with the nanostructuring of electrodes as one of the most effective approaches to overcoming the issues facing highcapacity electrode materials (2, 7). For example, the integration of nanostructured carbon materials with sulfur is one of the primary strategies for improving the electrical conductivity of the composites and suppression of polysulfide shuttling through physical confinement (8-14). However, it was first recognized by Zheng et al. (11) that the weak interaction between nonpolar carbon-based materials and polar LiPSs/Li 2 S species leads to weak confinement and easy detachment of LiPSs from the carbon surface, with further diffusion into the electrolyte causing capacity decay and poor rate performance. Therefore, the introduction of heteroatoms into carbonaceous materials (such as nitrogen, oxygen, boron, phosphorous, sulfur, or ...

Prelithiation is an important strategy to compensate for lithium loss in lithium-ion batteries, particularly during the formation of the solid electrolyte interphase (SEI) from reduced electrolytes in the first charging cycle. We recently demonstrated that LixSi nanoparticles (NPs) synthesized by thermal alloying can serve as a high-capacity prelithiation reagent, although their chemical stability in the battery processing environment remained to be improved. Here we successfully developed a surface modification method to enhance the stability of LixSi NPs by exploiting the reduction of 1-fluorodecane on the LixSi surface to form a continuous and dense coating through a reaction process similar to SEI formation. The coating, consisting of LiF and lithium alkyl carbonate with long hydrophobic carbon chains, serves as an effective passivation layer in the ambient environment. Remarkably, artificial-SEI-protected LixSi NPs show a high prelithiation capacity of 2100 mA h g(-1) with negligible capacity decay in dry air after 5 days and maintain a high capacity of 1600 mA h g(-1) in humid air (∼10% relative humidity). Silicon, tin, and graphite were successfully prelithiated with these NPs to eliminate the irreversible first-cycle capacity loss. The use of prelithiation reagents offers a new approach to realize next-generation high-energy-density lithium-ion batteries.

Lithium-based rechargeable batteries have been widely used in portable electronics and show great promise for emerging applications in transportation and wind-solar-grid energy storage, although their safety remains a practical concern. Failures in the form of fire and explosion can be initiated by internal short circuits associated with lithium dendrite formation during cycling. Here we report a new strategy for improving safety by designing a smart battery that allows internal battery health to be monitored in situ. Specifically, we achieve early detection of lithium dendrites inside batteries through a bifunctional separator, which offers a third sensing terminal in addition to the cathode and anode. The sensing terminal provides unique signals in the form of a pronounced voltage change, indicating imminent penetration of dendrites through the separator. This detection mechanism is highly sensitive, accurate and activated well in advance of shorting and can be applied to many types of batteries for improved safety.

A novel “smart” separator with thermal-triggered flame-retardant properties for lithium-ion batteries to improve their safety.

A reaction-protective separator that slows the growth of lithium dendrites penetrating into the separator is produced by sandwiching silica nanoparticles between two polymer separators. The reaction between lithium dendrites and silica nanoparticles consumes the dendrites and can extend the life of the battery by approximately five times.

No abstract

Lithium–sulfur (Li–S) batteries are regarded as promising next-generation high energy density storage devices for both portable electronics and electric vehicles due to their high energy density, low cost, and environmental friendliness. However, there remain some issues yet to be fully addressed with the main challenges stemming from the ionically insulating nature of sulfur and the dissolution of polysulfides in electrolyte with subsequent parasitic reactions leading to low sulfur utilization and poor cycle life. The high flammability of sulfur is another serious safety concern which has hindered its further application. Herein, an aqueous inorganic polymer, ammonium polyphosphate (APP), has been developed as a novel multifunctional binder to address the above issues. The strong binding affinity of the main chain of APP with lithium polysulfides blocks diffusion of polysulfide anions and inhibits their shuttling effect. The coupling of APP with Li ion facilitates ion transfer and promotes the kinetics of the cathode reaction. Moreover, APP can serve as a flame retardant, thus significantly reducing the flammability of the sulfur cathode. In addition, the aqueous characteristic of the binder avoids the use of toxic organic solvents, thus significantly improving safety. As a result, a high rate capacity of 520 mAh g–1 at 4 C and excellent cycling stability of ∼0.038% capacity decay per cycle at 0.5 C for 400 cycles are achieved based on this binder. This work offers a feasible and effective strategy for employing APP as an efficient multifunctional binder toward building next-generation high energy density Li–S batteries.

Safe operation is crucial for lithium (Li) batteries, and therefore, developing separators with dendrite-detection function is of great scientific and technological interest. However, challenges have been encountered when integrating the function into commercial polyolefin separators. Among all polymer candidates, polyimides (PIs) are prominent due to their good thermal/mechanical stability and electrolyte wettability. Nevertheless, it is still a challenge to efficiently synthesize PI separators, let alone integrate additional functions. In this work, a novel yet facile solution synthesis was developed to fabricate a nanoporous PI separator. Specifically, recyclable LiBr was utilized as the template for nanopores creation while the polymer was processed at the intermediate stage. This method proves not only to be a facile synthesis with basic lab facility but also to have promising potential for low-cost industrial production. The as-synthesized PI separator exhibited excellent thermal/mechanical stability and electrolyte wettability, the latter of which further improves the ionic conductivity and thus battery rate capability. Notably, stable full-cell cycling for over 200 cycles with a PI separator was further achieved. Based on this method, the fabrication of an all-integrated PI/Cu/PI bifunctional separator for dendrite detection can be fulfilled. The as-fabricated all-integrated separators prove efficient as early alarms of Li penetration, opening up the opportunity for safer battery design by separator engineering.