Kinetic‐Coordinated Mechano‐Electrochemical Steady‐State in All‐Solid‐State Si–Se Batteries

Mechanical degradation induced by electrode volume fluctuations remains a fundamental barrier for all‐solid‐state lithium‐ion batteries (ASSLBs). Here, a kinetic‐coordinated mechano‐electrochemical steady‐state architecture is proposed for Li x Si–Se ASSLBs. It dynamically counterbalances the Se cathode volumetric expansion with the continuous contraction of the Li x Si anode during cycling. The conversion kinetics of Se promote temporal coordination with the anode, thereby mitigating transient mechanical imbalance. This volumetric and kinetic dual‐matching results in a pressure change of −0.137 MPa at the discharge–charge transition in the 20th cycle. Its absolute magnitude is more than one order of magnitude lower than that of the Li–Se cell (−2.721 MPa). The mechanically stabilized interfaces suppress long‐range cracking and help maintain continuous solid–solid contact. Consequently, the Li x Si–Se system delivers excellent specific capacities of 579.1, 510.4, 369.4, 260.1, and 170.5 mAh g −1 at 0.1, 0.2, 0.5, 1, and 2C, respectively. More importantly, scaled‐up 10 × 10 cm 2 pouch cells achieve a high reversible capacity of 1.13 Ah. Their peak capacity of 1.16 Ah corresponds to a calculated gravimetric energy density of 274.15 Wh kg −1 based on the combined masses of the cathode, solid‐state electrolyte, and anode. This work establishes this dual‐matching paradigm as a general design principle for overcoming interfacial mechanical failures in high‐energy ASSLBs.