Confined Solvation Electrolyte for 4.3-V-Class High-Voltage Sodium-Ion Pouch Cells.

P2-type layered transition metal oxides (NaxTMO2 TM are transition metal elements) are air-stability and low-cost but intrinsically limited in capacity, necessitating elevated charging voltages to unlock deeper Na+ extraction and higher energy density. However, practical high-voltage operation over wide temperature ranges is impeded by sluggish Na+ desolvation, aggravated parasitic reactions, and rapid cycling degradation. Here, we identify 1,1,1-trifluoro-N,N-dimethylmethanesulfonamide (Me2TFMSA) as a polar inducer that restructures Na+ solvation by confining carbonate molecules predominantly within the first solvation sheath, suppressing free-carbonate preferential accumulation at the cathode interface and enabling rapid ligand exchange during desolvation, while FSI- coordination forms an aggregate-rich solvation structure with weakened Na+-solvent interaction. This confining solvation electrolyte (CSE) allows a 4.3 V cutoff (vs 4.1 V conventionally) and delivers a 25.8% capacity gain for P2-type Na0.6[Mg0.04Ca0.02Ti0.1Mn0.55Ni0.29]O2 (NaNMO) cathodes, effectively suppressing parasitic reactions, transition-metal dissolution, surface phase reconstruction, and impedance growth. In 4.3-V-class Ah-level hard carbon||NaNMO pouch cells with the CSE deliver 74.8% capacity retention after 800 cycles at 0.5 C, whereas conventional carbonate electrolytes fail within 200 cycles. Stable performance is achieved from -30 to 45 °C, with good cycling performance at -20 °C. These results correlate solvation confinement with interfacial stability and 4.3-V-class pouch-cell performance in P2-type sodium-ion batteries.