Organosulfur Compounds Enable Uniform Lithium Plating and Long-Term Battery Cycling Stability.

Lithium metal represents an ultimate anode material of lithium batteries for its high energy density. However, its large negative redox potential and reactive nature can trigger electrolyte decomposition and dendrite formation, causing unstable cycling and short circuit of batteries. Herein, we engineer a resilient solid electrolyte interphase on the Li anode by compositing the battery separator with organosulfur compounds and inorganic salts from garlic. These compounds take part in battery reactions to suppress dendrite growth through reversible electrochemistry and attenuate ionic concentration gradient. When the Li anode and the separator are paired with the LiFePO4 cathode, one obtains a battery delivering long-term cycling stability of 3000 cycles, a rate capacity of 100 mAh g-1 at 10 C (2.5 mA cm-2), a Coulombic efficiency of 99.9%, and a low battery polarization. Additionally, with high-loading 20 mg cm-2 LiFePO4 cathodes, an areal capacity of 3.4 mAh cm-2 is achieved at 0.3 C (1 mA cm-2).

A Highly Stable Separator from an Instantly Reformed Gel with Direct Post-Solidation for Long-Cycle High-Rate Lithium-Ion Batteries.

An efficient, scalable, and cost-effective approach was developed to synthesize a hierarchically constructed polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) separator from an instantly reformed solution. With partially dissolved PVDF-HFP as separator skeleton, the incorporation of warm PVDF-HFP solution in acetone led to a cross-linked structure before N-methyl-2-pyrrolidone (NMP) was added to solidify the hierarchical inner-bound structure of fresh PVDF-HFP. Owing to its hierarchical microporous structure, the separator exhibited remarkable wettability with a small contact angle of 18° and an electrolyte uptake of 114.81 %, leading to a high room-temperature ionic conductivity of 3.27×10-3  S cm-1 . The hierarchical structure provided short pathways for efficient ion transfer with more electrolyte trapped inside and small intervals between adjacent nanopores. The separator outperformed commercial separators, showing high rate capacities of 104.8 mAh g-1 at 5 C and 95 mAh g-1 at 10 C as well as unparalleled perfect capacity retention at 10 C after 1000 cycles.

Flame-Retardant Bilayer Separator with Multifaceted van der Waals Interaction for Lithium-Ion Batteries.

Safety issues induced by a flammable organic electrolyte challenge the practical applications of high-specific energy lithium-ion batteries (LIBs). Here, we develop a robust bilayer separator by incorporating MoO3 and Al-doped Li6.75La3Zr1.75Ta0.25O12 (LLZTO). The bilayer separator is highly flame-resistive and manages to endure intense fire. Density functional calculations reveal that abundant hydrogen bonds and van der Waals forces within the bilayer separator greatly suppress the combustion with interfacial adhesion of MoO3 and LLZTO to poly(vinylidene fluoride-hexafluoropropylene). With MoO3 and LLZTO, the graphitized carbon content of the carbon residues is increased, and the formation of molybdenum fluoride (MoFx) and lanthanum fluoride (LaFx) is induced during combustion, thus suppressing heat accumulation. The bilayer separator owns a large ductility (227%) and low thermal shrinkage (5%) after annealing at 160 °C for 4 h. Based on the bilayer separator, Li/LiFePO4 cells deliver a remarkable discharge capacity of 162 mA h/g at 0.5 C with a high capacity retention of 95% after 100 cycles. This work provides a new strategy for achieving safe LIBs.