Nonflammable, robust and flexible electrolytes enabled by phosphate coupled polymer-polymer for Li-metal batteries

Manipulating the ionic conductivity and interfacial compatibility of polymer-in-dual-salt electrolytes enables extended-temperature quasi-solid metal batteries

Solid polymer electrolytes (SPEs) have shown great promise in the development of lithium-metal batteries (LMBs), but SPEs' interfacial instability and limited ionic conductivity still prevent their widespread applications. Herein, high-concentration hybrid dual-salt "polymer-in-salt" electrolytes (HDPEs) through formulation optimization were facilely prepared to simultaneously boost ionic conductivity, improve interfacial compatibility, and ensure a wide-temperature-range operation with high safety. An optimized electrolyte (HDPE-0.6) shows negligible corrosion to the aluminum current collector after manipulating the salt ratio of lithium bis(trifluoromethane)sulfonimide and lithium bis(oxalato)borate. In addition, HDPE-0.6 has excellent ionic conductivity (i.e., ∼0.536, ∼0.898, and ∼1.28 mS cm-1 at 0, 30, and 60 °C), approaching 1 mS cm-1 at room temperature. Furthermore, HDPE-0.6 exhibits a high lithium transference number of 0.6 and a high electrochemical oxidation stability potential of > 4.8 V vs. Li/Li+. Additionally, due to the formulation of high-concentration thermally stable lithium salts and the employment of flame-retardant trimethyl phosphate as the solvent, HDPE-0.6 has no safety issues. The resultant LiFePO4|HDPE-0.6|Li cell exhibits high discharge capacity, good rate capability, and excellent cycle stability at extended temperatures of 0, 30, and 60 °C. By coupling theoretical calculations and in-depth X-ray photoelectron spectroscopy, we attribute the excellent cycle stability to the formation of a stable interphase. Moreover, our formulation strategy is suitable for the Na3V2(PO4)3//Na battery when replacing the lithium salts with sodium salts (i.e., sodium bis(trifluoromethane)sulfonimide and sodium bis(oxalato)borate) to yield HDPE-0.6-Na, as demonstrated by excellent cycle stability (e.g., 98.6 % of capacity retention after 300 cycles). Our work demonstrates that the as-developed quasi-solid HDPEs are suitable for LMBs and sodium-metal batteries, and HDPEs can function normally in a wide temperature range.

Multiple Na+ transport pathways and interfacial compatibility enable high-capacity, room-temperature quasi-solid sodium batteries

Sodium-metal batteries (SMBs) are ideal for large-scale energy storage due to their stable operation and high capacity. However, they have safety issues caused by severe dendrite growth and side reactions, particularly when using liquid electrolytes. Therefore, it is critically important to develop electrolytes with high ionic conductivity and improved safety that are non-flammable and resistant to dendrites. Here, we developed polymerized polyethylene glycol diacrylate (PEGDA)-modified poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrolytes (PPEs) with highly conductive sodium bis(trifluoromethanesulfonyl)imide and corrosion-inhibitive sodium bis(oxalato)borate salts for SMBs. Well-complexed PEGDA not only increases the amorphicity of the PVDF matrix, but also offers numerous Lewis basic sites through the polar groups of carbonyl and ether groups (i.e., electron donors). The presence of the Lewis basic sites facilitates the dissociation of sodium salt and transportation of Na+ within the PVDF matrix. This results in the generation of additional Na+ transport pathways, which can enhance the performance of the battery. Among PPEs, the optimized PPE-50 exhibits a high ionic conductivity of 3.42 × 10-4 S cm-1 and a mechanical strength of 14.0 MPa. A Na||Na symmetric cell with PPE-50 displays high stability at 0.2 mA cm-2 for 800 h. PPE-50 further displays high capacity, e.g., a Na3V2(PO4)3|PPE-50|Na battery delivers a decent discharge capacity of 101.5 mAh g-1 at 1.0C after 650 cycles. Our work demonstrates the development of high-performance quasi-solid polymer electrolytes with multiple transport pathways suitable for room-temperature SMBs.

A Heat-Resistant Polymer Based on the Reversible Change in Polymer Skeleton Structure for Self-Anticounterfeiting

Heat-resistant polymer materials have been widely used in many fields, but their anticounterfeit is still a significant challenge. This work has successfully constructed a heat-resistant polymer material that can achieve self-anticounterfeit. In response to changes in the external environment, the color of polymer changes from yellow-green to red reversibly, which is due to the fact that polymer material's backbone undergoes isomerization. Therefore, this high-performance polymer material can not only be used in a high-temperature environment for a long time but also achieve its anticounterfeit and be used in advanced security applications.

Electrochemical properties and facile preparation of hollow porous V2O5 microspheres for lithium-ion batteries

Vanadium pentoxide (V₂O₅) has shown great potential to be used in lithium-ion batteries (LIBs), but it has limited applications because it has cycle instability and poor rate capability, and its lithiation mechanism is not well understood. In this work, hollow porous V₂O₅ microspheres (HPVOM) were obtained by a facile poly(vinylpyrrolidone) and ethylene glycol-assisted soft-template solvothermal method. Half cells with HPVOM exhibited good capacity, rate capability, and stability, delivering 407.9 mAh g^-1 at 1.0 A g^-1 after 700 cycles. Furthermore, a LiFePO₄/HPVOM full cell had a discharge capacity of 109.9 mAh g^-1 after 150 cycles at 0.1 A g^-1. Using an equivalent circuit model (ECM) and distribution of relaxation times (DRT), we found that the charge-transfer (including the solid-state interface resistance) and bulk resistances varied regularly with the charge/discharge state, while the electrolyte resistance was largely maintained. The bulk resistance finally vanished, indicative of dynamic activation. The method used to prepare the hollow microspheres, as well as the display of electrode kinetics via ECM and DRT, could be broadly applied in developing efficient electrodes for LIBs.