Functional Polymer Materials by ATRP: Preparation and Applications in Lithium Metal Batteries

Lithium metal batteries have been regarded as the “holy grail” for next-generation highenergy-density batteries in the past few decades, due to its high theoretical capacity (3860 mAh/g) and low electrochemical potential (-3.4 V versus the standard hydrogen electrode). As one of the most crucial components in lithium metal batteries, the role of functional polymers cannot be understated. Therefore, it becomes important to employ defined and well-controlled approaches through molecular engineering to synthesize and prepare functional polymers with specific structures, architectures, and properties for applications in Li metal batteries. 

In this thesis, preparation of functional polymer materials for lithium metal batteries via atom transfer radical polymerization (ATRP) is discussed. Chapter 1 introduces the history and development of Li metal batteries, the state-of-the-art of research on various polymer materials applied in Li metal batteries and the creation of functional polymer materials with tailored properties by ATRP.

Chapters 2-5 cover research projects that I have worked on during my Ph.D. study. Chapter 2 discusses a new category of artificial SEI based on oxygen vacancy-rich hybrid nanoparticles prepared by covalently grafting polymers from yttria–stabilized zirconia (YSZ) nanoparticles via surface-initiated atom transfer radical polymerization (SI-ATRP). The hairy nanoparticles exhibited high ionic conductivity (>1 x 10^-4 S/cm at r.t.), and good mechanical properties (Young’s modulus 7.56 GPa). No dendrite formation on a lithium metal protected by such artificial SEI was observed by in-situ optical microscopy. Protected anodes were stably cycled at 3 mA/cm² and 3 mAh/cm² with low overpotentials (20 mV) for >2500 hours. 

Chapter 3 focuses on polymer-stabilized liquid metal nanoparticles (LM-P NPs) of eutectic gallium indium (EGaIn) to create uniform Li nucleation sites enabling homogeneous lithium electrodeposition. Block copolymers of poly(ethylene oxide) and poly(acrylic acid) (PEO-b-PAA) were grafted onto the EGaIn surface, forming stabilized, well-dispersed NPs. The lithiophilic PEO sites and interactive carboxyl groups guided Li deposition and the Li-EGaIn alloying process greatly reduced the Li⁺ diffusion barrier, therefore enabled fast Li transport through the coating layer and decreased nucleation overpotential. The stabilization of Li metal by LM-P NPs under practical loading conditions (N/P ratio <1) was achieved. 

Chapter 4 summarizes polymer electrolytes based on a crosslinked system of using an “inverted” structure of OEOMA monomer and crosslinker, which showed higher ionic conductivities than regular OEOMA based polymer electrolytes; exploration of various polymer architectures as binder materials are presented using NCM811 as a model electrode. 

Chapter 5 focuses on a new synthetic route developed to engineer PVDF binders by covalently grafting copolymers from poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) with multiple functionalities using atom transfer radical polymerization (ATRP). The grafted random copolymer binder provided excellent flexibility (319% elongation), adhesion strength (50 times higher than PVDF), transition metal chelation capability, and efficient ionic conductivity pathways, which significantly enhanced the performance of NCM811 cathodes. 

Finally, chapter 6 provides a summary with outlook on future directions of employing functional polymer materials by ATRP in next-generation Li metal batteries. 

Appendices demonstrates another two projects/papers I published on the synthesis of gradient copolymer-grafted nanoparticles and a review study of the performance of artificial SEIs in Li metal batteries.