Application of composite electrolyte in lithium metal battery

Composite electrolytes with high ionic conductivity and stable seamless interfaces are considered as potential options for all-solid-state batteries (SSBs). Rechargeable lithium metal batteries (LMBs) have attracted much attention as candidates for high energy density energy storage systems, but the safety issues brought by traditional liquid organic electrolytes and problems such as lithium ion heterodeposition limit their application. All-solid-state batteries are regarded as the ultimate development direction of lithium metal batteries due to their excellent safety performance. However, the large-scale application of solid-state electrolytes (SSEs) in lithium metal batteries is still limited by problems such as low lithium ion transport efficiency and electrode/electrolyte interface incompatibility. Polyethylene oxide (PEO) is a commonly used polymer electrolyte matrix, but its ionic conductivity is extremely low at room temperature. Researchers often introduce functional inorganic materials to improve its ionic conductivity. In this paper, a flexible all-solid-state composite electrolyte composed of bronze-phase titanium dioxide (TiO 2O (B) nanotubes and polyethylene oxide was synthesized. The study found that the composite electrolyte can provide excellent interfacial conductivity and good electrode compatibility for all-solid-state batteries. The interface phase formed between TiO 2O (B) and the polymer constructs a new lithium ion transport path, and density functional theory (DFT) and molecular dynamics (MD) simulations show that TiO 2O (B) can promote the dissociation of lithium salts, resulting in more free lithium ions, thereby improving ionic conductivity. In addition, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Cryo-Transmission Electron Microscopy (Cryo-TEM), and COMSOL multiphysics simulations show that the introduction of TiO (B) can form an interfacial layer rich in lithium fluoride (LiF), enabling rapid lithium-ion transport and uniform lithium deposition. Ultimately, the symmetric lithium battery exhibited excellent electrochemical performance for more than 2350 hours and a high critical current density of 1.6 mA cm², and the prepared LiFePO/Li all-solid-state battery achieved an ultra-long cycle life of more than 3100 cycles at a 1 C rate.

central content

This article focuses on TiO 2O (B) nanotubes modifying PEO-based solid-state electrolytes to improve the performance of all-solid-state lithium metal batteries. The specific content includes:

• Preparation of TiO 2 (B) nanotubes and construction of composite electrolyte: TiO 2 (B) with nanotube structure was prepared by hydrothermal method, and it was combined with PEO and LiTFSI in a mass ratio of 10:4:1 to form a PEO-TiO 2 (B) composite electrolyte. Compared with PEO-TiO 2 (A) constructed by anatase phase titanium dioxide (TiO 2 (A)), PEO-TiO 2 (B) has a denser microstructure, no obvious grain boundaries, uniform element distribution, and good flexibility and mechanical properties. The Young's modulus is 18.9 MPa, which is higher than the 7.57 MPa of PEO-TiO 2 (A).
• Explore the performance improvement mechanism of the composite electrolyte: the interfacial interaction between TiO (B) and PEO forms a new lithium ion transport path, which can weaken the interaction between lithium ions and polymers and reduce the lithium ion transport energy barrier; at the same time, promote LiTFSI dissociation, increase the number of free lithium ions, so that the ionic conductivity of PEO-TiO (B) at 50 ° C reaches 0.262 mS cmS cmS, which is higher than the 0.128 mS cmS of PEO-TiO (A), and the lithium ion migration number is also increased from 0.31 to 0.40. In addition, the electrochemical stability window of PEO-TiO (B) is widened to 5.0 V (vs Li /Li), providing good thermal stability for high-voltage all-solid-state batteries.
• Analysis of interfacial layer characteristics and lithium deposition behavior: PEO-TiO (B) can induce the formation of a stable and seamless interfacial layer rich in LiF, which has a low lithium ion diffusion barrier, which can accelerate lithium ion transport and promote uniform deposition; At the same time, there are also electronic insulators such as Li N in the interfacial layer, which can inhibit electron transport and hinder lithium dendrite growth. COMSOL multiphysics simulation shows that the composite electrolyte can make the lithium ion flux distribution uniform and reduce concentration polarization. SEM observations confirm that lithium deposition is dense, smooth and dendrite-free.
• Verify the practical application performance of the battery: The symmetrical lithium battery with PEO-TiO (B) as the electrolyte can be stably cycled for more than 2350 hours at a current density of 0.1 mA cm², and the critical current density is 1.6 mA cm²; Li/PEO-TiO (B)/LiFePO + all-solid-state battery at 50 ° C and 1 C rate, the discharge capacity after 3100 cycles remains above 93 mAh g ², the capacity per cycle attenuates only 0.0077%, and it exhibits better discharge capacity and cycle stability than PEO-TiO (A) at different rates of 0.2 C-2.0 C.

Conclusion

The paper confirms that the introduction of TiO 2O (B) nanotubes into a PEO-based solid-state electrolyte facilitates the formation of a stable and seamless interface rich in LiF. This stable protective layer ensures stable plating/peeling cycles for more than 2350 hours in symmetric lithium batteries. In addition, density functional theory simulations show that TiO 2O (B) can weaken the interaction between lithium ions and polymers, reduce the lithium-ion transport energy barrier, and accelerate the dissolution kinetics of lithium salts. More notably, the Li/PEO-TiO 2O (B)/LiFePO~ all-solid-state battery exhibited excellent cycle stability at a 1 C rate, with more than 3100 cycles. The results confirm that TiO (B) is feasible as a functional inorganic material in solid electrolytes for lithium metal batteries. This simple and effective strategy can build a robust interface and improve ion conduction dynamics. This research opens up a new direction for the application of PEO-based materials in long-life all-solid-state lithium metal batteries, with great commercialization and large-scale potential.

References

Li, J., Cai, Y., Zhang, F., Cui, Y., Fang, W., Da, H., Zhang, H., & Zhang, S. (2023). Exceptional interfacial conduction and LiF interphase for ultralong life PEO-based all-solid-state batteries. Nano Energy, 118, 108985. https://doi.org/10.1016/j.nanoen.2023.108985