PNNL

Abstract

We report the syntheses of two new series of methacrylate monomers with different backbones: ureidopyrimidinone (PU) and boron-substituted urea pyrimidine (U), which enhance both the mechanical and electrochemical properties of the solid-state electrolyte while improving the cycle life of lithium iron phosphate (LiFePO4, LFP) cathodes. The PU backbone is characterized by four hydrogen bonds, while the U backbone bears only two. Importantly, our research reveals that two hydrogen bonds (H bonds) in these monomers are optimal; in contrast, four are excessive. The exceptional mechanical properties and processability of the solid-state electrolyte with the U series additives, resulting from the optimal H bonds, were unexpectedly achieved. This leads to the establishment of a “Goldilocks rule” for additive design. The key strategies include: 1) reducing hydrogen-bonding (H-bonding) sites by changing pyrimidinone to pyrimidine, and 2) shifting from intermolecular to intramolecular H-bonding and p-p bonding. This reduction in H-bonding also offers significant advantages in processability. The advancement can be extended to electrode fabrication, making the manufacturing of all-solid-state batteries more practical and efficient.