Multi-functional Single-Source Molecular Precursors for Carbon-Coated Mixed-Metal Phosphates

We introduce a new synthetic concept that can be broadly adopted for the low-temperature preparation of mixed-metal energy storage materials, such as phosphates, silicates, fluorides, fluorophosphates, and fluorosulfates that exhibit intrinsic low electronic conductivity and thus require a carbon modulation. The development of novel low-temperature approaches for assembling energy-related materials with a complex core-shell microstructure is of great importance for expanding their application scope. The traditional definition of single-source precursors refers to their ability to yield a phase-pure material upon thermal decomposition. We have developed a new way for the utilization of heterometallic molecular precursors in synthesis that goes beyond its common delineation as a single-phase maker. The utility of this approach has been demonstrated upon the low-temperature synthesis of lithium-iron phosphate@C, which represents a celebrated cathode material for Li-ion batteries. The first atomically precise carbonaceous molecular precursors featuring a desired Li:Fe:P ratio of 1:1:1, divalent iron, and sufficient oxygen content for the target LiFeIIPO4 phosphate were shown to enable a spontaneous formation of both the olivine core and conductive carbon shell, yielding a carbon-coated mixed-metal phosphate.

One-Pot Synthesis of a Copolymer Micelle Crosslinked Binder with Multiple Lithium-Ion Diffusion Pathways for Lithium-Sulfur Batteries

Fast lithium-ion diffusion is very important to obtain high capacity and excellent cycling stability of lithium-sulfur batteries. In this study, a copolymer micelle crosslinked binder (FNA) for lithium-sulfur batteries was successfully synthesized through a one-pot environmentally friendly approach. The micelles were used as crosslinkers and carriers for the electrolyte. The FNA binder provided multiple lithium-ion diffusion pathways to increase the lithium-ion diffusion, which reduced the polarization of the sulfur cathode during the cycling process. The lithium-ion diffusion pathways of the FNA were provided by the electrolyte hosted in the micelles, the polyethylene oxide and polypropylene oxide segments, and the carboxylate and sulfonate groups in the FNA. In addition, FNA possesses strong lithium polysulfides adsorption and high adhesion properties. Therefore, the electrode with the FNA binder presented a reversible capacity of 571 mAh g^-1 with a capacity fade of 0.032 % after 1000 cycles at a cycling rate of 0.5 C, which is much higher than those of the polyvinylidene fluoride (PVDF) sulfur cathode.

Inhibiting VOPO4 ⋅x H2 O Decomposition and Dissolution in Rechargeable Aqueous Zinc Batteries to Promote Voltage and Capacity Stabilities

VOPO₄ ⋅x H₂ O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf)₂ electrolyte. Investigations show the decomposition of VOPO₄ ⋅x H₂ O into VO_x in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO₄ ^3- was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl₂ salt in the electrolyte further prevents VOPO₄ ⋅x H₂ O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl₂ /0.8 m H₃ PO₄ aqueous electrolyte, in direct contrast to that in Zn(OTf)₂ where the decomposition product VO_x provides most electrochemical activity over cycling. Sequential H⁺ and Zn²⁺ intercalations into the structure are revealed, delivering a high capacity (170 mAh g^-1 ). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles.