Sustained-release salt reservoir enables durable solid electrolyte interphases for practical micron-sized silicon composite anodes

An anode-preloaded NaBF 4 reservoir enables long-lasting SEI regulation. • Solubility contrast allows NaBF 4 incorporation via aqueous slurry processing. • BF 4 − -derived species promote a B/F-rich, low-impedance SEI. • Ah-level Si-graphite pouch cells retain 89.2% capacity after 160 cycles. • The SRE strategy is extendable to graphite and SiO x /C anodes. Persistent active lithium (Li) loss caused by repeated rupture and reconstruction of the solid electrolyte interphase (SEI) remains a major barrier to long-life Li-ion batteries, especially for silicon (Si)-containing anodes with pronounced interfacial instability. Here, we report a sustained-release-enhanced (SRE) interphase strategy that enables long-lasting SEI regulation through an anode-preloaded NaBF 4 reservoir. By exploiting the high solubility of NaBF 4 in the aqueous slurry and its limited solubility in the carbonate electrolyte, NaBF 4 can be uniformly implanted during electrode fabrication and maintain the prolonged availability of BF 4 − -derived species near the anode/electrolyte interface during cycling. This solubility-governed process enhances anion participation in interfacial solvation and promotes the formation of a B/F-rich SEI with improved mechanical robustness and Li + transport kinetics. Importantly, the strategy is successfully demonstrated in a practically relevant micron-sized Si-graphite composite anode, where long-term interfacial stabilization is particularly challenging, delivering reduced polarization, improved rate capability, and markedly enhanced cycling stability. The strategy is further applicable to graphite and SiO x /C anodes. In practical full cells paired with a LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode, the SRE anode increases the initial Coulombic efficiency from 73.86% to 81.58%, and an Ah-level pouch cell retains 89.2% of its capacity after 160 cycles. This work provides a scalable route to regulate long-term SEI evolution in practical micron-sized Si-containing anodes and extend the lifetime of high-energy Li-ion batteries. A low-cost NaBF 4 salt is preloaded into the anode coating via aqueous slurry processing to construct a local reservoir. The prolonged availability of BF 4 − -derived species promotes a B/F-rich, low-impedance SEI, reducing lithium loss and interfacial resistance. As a result, silicon-graphite cells and Ah-level pouch cells achieve improved cycling stability, retaining 89.2% capacity after 160 cycles. Download: Download high-res image (169KB) Download: Download full-size image