Realization of Enhanced Interfacial Lithium-Ion Transfer in Composite Polymer Electrolytes via Grafting Oligo-PEG Molecular Brushes on Silica-Coated Nanofibers for All-Solid-State Lithium Metal Batteries.

Polyether-based polymer electrolytes are attractive but still challenging for high-energy-density solid-state lithium metal batteries due to their limited Li-ion conductivity at room temperature. Herein, an oligomeric polyethylene glycol methyl ether methacrylate (PEGMEM)-modified silica-coated polyimide fibrous scaffold (PINF@PEGMEM-SiO2) was introduced in polyethylene glycol dimethyl ether (PEGDME) to enhance the Li-ion transportation at room temperature. PINF@PEGMEM-SiO2 was developed to build a continuous and interconnected interface for continuous Li-ion transportation in bulk. The carbonyl groups (C═O) of PEGMEM on SiO2 can promote the dissociation of lithium salts and enhance the migration of free Li ions at the interface. The same -C-C-O- unit contained in both PEGMEM and PEGDME ensures the compatibility of PEGMEM at the interface and PEGDME in the bulk. The prepared PEGDME-based polymer electrolyte exhibits a high ionic conductivity of 1.14 × 10-4 S cm-1 at 25 °C and an improved Li-ion transference number of 0.41. Furthermore, LiFePO4/Li and LiNi0.8Co0.1Mn0.1O2/Li cells with excellent cyclability and rate capability at ambient temperature are obtained.

Self-Assembled Macrocyclic Copper Complex Enables Homogeneous Catalysis for High-Loading Lithium-Sulfur Batteries.

The practical viability of high-energy-density lithium-sulfur (Li-S) batteries stipulates the use of a high-loading cathode and lean electrolyte. However, under such harsh conditions, the liquid-solid sulfur redox reaction is much retarded due to the poor sulfur and polysulfides utilization, leading to low capacity and fast fading. Herein, a self-assembled macrocyclic Cu(II) complex (CuL) is designed as an effective catalyst to homogenize and maximize the liquid-involving reaction. The Cu(II) ion coordinated with four N atoms features a planar d sp 2 ${\mathrm{d}}_{{\mathrm{sp}}^{2}}$ hybridization, showing a strong bonding affinity toward lithium polysulfides (LiPSs) along the d z 2 ${\mathrm{d}}_{{z}^{2}}$ orbital via steric effects. Such a structure not only lowers the energy barrier of the liquid-solid conversion (Li2 S4 to Li2 S2 ) but also guides a 3D deposition of Li2 S2 /Li2 S. As such, with a 1 wt% electrolyte additive of CuL, a high initial capacity of 925 mAh g-1 and areal capacity of 9.62 mAh cm-2 with a low decay of 0.3%/cycle can be achieved under a high sulfur loading of 10.4 mg cm-2 and low electrolyte/sulfur ratio of 6 µL mgs -1 . This work is expected to inspire the design of homogenous catalysts and accelerate the uptake of high-energy-density Li-S batteries.

Deeply Cyclable and Ultrahigh-Rate Lithium Metal Anodes Enabled by Coaxial Nanochamber Heterojunction on Carbon Nanofibers.

Lithium metal anodes (LMAs) are the most promising candidates for high-energy-density batteries due to the high theoretical specific capacity and lowest potential. However, the practical application of LMAs is hampered by the short lifespan and unsatisfactory lithium utilization (<50%). An oxide-oxide heterojunction enhanced with nanochamber structure design is proposed to improve lithium utilization and cycling performance of LMA under ultrahigh rates. Typically, a MnO2 -ZnO heterojunction provides high binding energy for strong absorption of Li-ions and intimately bonded interfaces for fast transfer of electrons. Under the guidance of the smooth Li-ion migration and rapid electron flow, the Li metal can be restricted as thin layers within submicro scale in nanochambers with constrain boundary and stress dissipation, inhibiting the local agglomeration and blocking. Thus, the lithiophilic active sites can be effectively exposed to the Li-ions within submicro scale, improving the reversible conversion for high lithium utilization during long-term cycling. As such, the Li@MnZnO/CNF electrode achieves a high lithium utilization of 70% at a record-high current density of 50 mA cm-2 with areal capacity of 10 mAh cm-2 . This work offers an avenue to improve lithium utilization for long-lifespan LMAs working under high current densities and capacities.

A (110) Facet-Dominated Vanadium Dioxide Enabling Bidirectional Electrocatalysis for Lithium-Sulfur Batteries.

Catalysis is an effective way to improve the performance of lithium-sulfur (Li-S) batteries by enhancing the reaction kinetics of polysulfides. However, the bidirectional catalysis for discharging and charging processes in Li-S battery is still challenging. Herein, a (110) facet-dominated VO2 is prepared through the thermal-induced partial decomposition of (NH4)2V4O9 (NVO), forming a (110)VO2@NVO hybrid with the bidirectional catalysis ability. This (110) facet-dominated VO2 shows the ability to break the S-S bond to guide the Li2S deposition in the reduction process and reduce the delithiation barrier of Li2S to promote the oxidation process. The above hybrid is loaded on carbon nanofiber (CNF) to build an interlayer, where the 3D CNF and the conductive NVO ensure the fast electron transfer. The assembled battery with the above interlayer exhibits a high capacity of 1038 mAh g-1 after 300 cycles at 0.1 C (capacity retention: 70%). At a high rate of 5 C, a high capacity of 521 mAh g-1 after 1000 cycles is reached. Even under an ultrahigh sulfur loading of 10.3 mg cm-2 and a low electrolyte/sulfur ratio of 4 µL mgS-1, stable cycling performance with a high capacity of >3 mAh cm-2 is also achieved.

A Fishing-Net-Like 3D Host for Robust and Ultrahigh-Rate Lithium Metal Anodes.

Constructing an architectural host is demonstrated to be an effective strategy for long-life lithium metal anodes (LMAs). Herein, an integrated 3D host for stable and ultrahigh-rate LMAs is developed by a binary highly conductive network of 2D reduced graphene oxide (rGO) and 1D carbon nanofibers (CNF) anchored with 0D ultrasmall MgZnO nanoparticles (MgZnO/CNF-rGO). A facile net-fishing strategy is proposed to combine the rGO nanosheets with free-standing CNF matrix as interconnected paths for fast electron transport. Notably, serving as Li nucleation sites, the superlithiophilic MgZnO nanoparticles are uniformly distributed and tightly contacted with the conductive matrix without agglomeration due to the rGO confinement. Such a delicate nanoscale combination guarantees the effective transportation and uniform deposition of Li-ions in the inner surface of the host. The symmetric cell of Li@MgZnO/CNF-rGO exhibits a long lifespan above 1450 cycles under an ultrahigh current density of 50 mA cm-2 with an areal capacity of 1.0 mAh cm-2 . Impressively, it also delivers a high reversible capacity of 10 mAh cm-2 at 50 mA cm-2 . This work offers an avenue to promise the prospect for practical LMAs working under high rates and capacities.