Conversion-type cathodes for lithium metal batteries are considered long-term targets due to their low cost and high energy density. However, they suffer from poor cycling life. In this study, we present an interface engineering strategy that involves constructing a three-dimensional (3D) ionic-electronic network to overcome this challenge. In detail, we fabricate a cathode-electrolyte interphase (CEI) as an ionic conductor using a specially designed localized high-concentration electrolyte (LHCE). Additionally, we construct a durable electronic network by applying a functional binder and carbon nanotubes (CNTs) onto the surface of the active material. We demonstrate that micro-sized FeS₂ cathode achieves a capacity retention of 72.6% after 700 cycles at a current rate of 0.5 C and 4 mAh/cm². This work addresses the construction of a stable ionic-electronic network that is key to achieving stable performance. Moreover, it reveals the potential of conversion cathodes, even in micro-size, for practical applications.