New Composite Electrolyte Containing Poly(vinylidene fluoride) for Lithium Batteries

Poly (vinylidene fluoride) (PVDF)-based fluoropolymers have been widely used as electrode binders, separators and electrolyte materials for batteries and supercapacitors due to their good mechanical properties, electrical properties and chemical stability. With the rapid development of energy storage devices, functional compounding of PVDF-based fluoropolymers to meet the needs of batteries and supercapacitors has become the focus of the development of poly(vinylidene fluoride-based polymer composites. As the matrix material of polymer composite materials, PVDF has good chemical stability, mechanical strength, easy processing, piezoelectric and pyroelectric properties.

In the experiment, the researchers added another biodegradable polymer, polydopamine, to PCL to stimulate bone growth. Then they added human bone cells to the polymer. After a few days, the bone cells not only multiplied, but also produced very important bone-forming proteins.

If this technology can be used, it will give doctors a new way to treat facial deformities caused by injury, surgery, and birth defects. The most common method currently is to use bone harvested from somewhere like the hip and reshaped. However, this method is risky, as the bones are difficult to reshape and fit perfectly. Surgeons may also choose to use tin oxide or adhesive to close the gap, but this method results in brittle bones and no pores for the bone to regenerate itself.

PVDF-HFP-LLZO composite electrolyte has the advantages of good flexibility, non-burning, simple preparation process, wide electrochemical stability window and large lithium ion migration number. However, commercial liquid electrolyte has problems such as easy combustion, small lithium ion migration number, and narrow electrochemical stability window. Moreover, the PVDF-HFP-LLZO composite electrolyte added with commercial liquid electrolyte is still difficult to form a stable interface layer with the lithium metal anode. . Therefore, LiFePO₄||Li batteries assembled using PVDF-HFP-LLZO composite electrolyte added with commercial liquid electrolyte have poor cycle stability and safety performance. In view of this, replacing the commercial liquid electrolyte with a flame-retardant electrolyte that has high ionic conductivity and lithium ion migration number, a wide electrochemical stability window, and can stabilize the metallic lithium anode is a feasible method to improve battery cycle life and safety performance.

Some researchers started from the polymer solution and adjusted the interaction between the polymer molecular chain, the flame-retardant solvent molecules and the lithium salt, that is, by controlling the number of hydrogen bonds formed between each component, a flame-retardant gel electrolyte layer was successfully prepared. By laminating the flame-retardant gel electrolyte layer with the PVDF-HFP-LLZO composite electrolyte, a multilayer composite electrolyte with good performance was prepared.

The researchers conducted electrochemical performance tests on multilayer composite electrolytes (MHE) and PVDF-HFP-LLZO composite electrolytes (LCPE) adding commercial liquid electrolytes. In the gel layer of the multi-layer composite electrolyte, due to the hydrogen bonding between the anions in the lithium salt and the polymer molecular chains and flame-retardant solvent molecules, the movement of the anions in the lithium salt is restricted and the lithium ion migration number is increased. At the same time, the application of flame-retardant gel electrolyte also ensures that the multi-layer composite electrolyte has a wide electrochemical stability window.

The researchers also conducted research on the interfacial stability of MHE and LCPE on lithium metal. In the cycle test of lithium metal batteries, MHE can form a Li₃PO₄-rich solid electrolyte interface (SEI) layer with the lithium metal surface. This SEI layer can stabilize the lithium metal surface and inhibit the growth of lithium dendrites.