Design and Performance Study of Highly Reliable Marine Battery Based on Solid Polymer Electrolyte

Currently, electric propulsion is playing an increasingly important role in marine propulsion systems.Lithium metal batteries are new-generation high-performance energy storage system with development prospect. Traditional flammable and volatile organic liquid electrolytes pose a risk of thermal runaway, while solid-state lithium metal batteries using solid electrolytes have significant advantages in energy density and safety, and are considered the most promising mobile power sources. Among numerous solid electrolyte systems, polymer solid electrolytes have excellent flexibility, good interface compatibility, and good processing characteristics, which have attracted the attention of researchers. Polyurethane (PU) is a common polymer with high mechanical strength and a flexible and adjustable molecular structure, making it one of the best choices for polymer electrolyte matrices. Based on the structural design of polyurethane polymers, this paper explores polycaprolactone type polyurethane electrolyte and the effect of high dielectric constant polycaprolactone on the dissolution and dissociation of lithium salts was studied. We found that polycaprolactone, as the soft segment, exhibits greater electronegativity and provides more oxygen atoms for coordination with lithium ions, which is crucial for enhancing lithium ion transport and improving ionic conductivity.The prepared PU-based solid polymer electrolyte has a conductivity of up to 2.4 × 10^-4S/cm, lithium ion migration number 0.78, electrochemical stability window 4.74V. The tensile strengths of PU-based solid polymer electrolyte can reach 2.36 MPa, that balance ionic conductivity and mechanical strength.Besides, it also possesses excellent thermal stability.The symmetrical battery assembled based on the prepared PU-based solid polymer electrolyte exhibits excellent cycling stability (400 hours). The assembled solid-state lithium metal battery based on LiFePO4 can stably cycle for 200 cycles at a current density of 1C, with a Coulombic efficiency of over 99% and a capacity retention rate of up to 99.4%, demonstrating exceptional reliability.