Sequencing Polymers for Room-Temperature Solid-State Batteries

For decades, liquid electrolytes have been adopted in lithium-ion batteries to bridge the interspace between electrodes and transport ions. In an era aspiring deep electrification and decarbonization in transportation and power sectors, polymers are expected to double energy density at the system level when combined with lithium anode, and enable all-solid-state battery (ASSB) that offers enhanced safety, processability and flexibility. Unfortunately, the long-standing crux to designing high-performance polymer electrolytes is their poor ion conductivity, which is limited by chain mobility and number of dissociated ions in polymer matrix. Previously, researchers have almost always focused on increasing segmental chain motion to improve ion transport, such as adding plasticizing additives or changing molecular compositions, which could lead to compromised mechanical integrity and polarization-related transport loss. In the meantime, though the importance of dissociated ions is empirically considered, the sequence strategy to modulate polymer transport and achieve delicate control of ion dissociation is almost universally overlooked.<br/><br/>Inspired by natural macromolecules that can achieve complex regulation by delicately controlling sequential arrangement of the backbone, we envision that manipulating polymer sequence could facilitate ion dissociation and strengthen control of transport in polymers. Herein, with a combination of experimental and computational methods, we prove the fundamental significance of polymer sequencing in ion transport and create homogeneous Li⁺distributions, non-aggregated Li⁺ solvation structures and enhanced Li⁺-anion dissociation in a designed solid-state fluorinated single-ion polymer electrolyte with alternating sequence (alter-SIPE). Perhaps most remarkably, in dry polymers, the alternately sequenced polymer leads to a concerted PEO-Li⁺-anion migration pathway, allowing conductivity tuned<i> </i>up by 1-3 orders of magnitude at 30 degC, which is comparable to that of liquid-state polyethylene oxide (PEO). In addition, we demonstrate that the exceptional ionic conduction capacity of our alter-SIPE could enable dendrite-free operation and reversible cycling in Li||LiFePO₄(LFP) ASSBs with a high coulombic efficiency.