The application of solid-state batteries (SSBs) is challenged by the inherently poor interfacial contact between the solid-state electrolyte (SSE) and the electrodes, typically a metallic lithium anode. Building artificial intermediate nanofilms is effective in tackling this roadblock, but their implementation largely relies on vapor-based techniques such as atomic layer deposition, which are expensive, energy-intensive, and time-consuming due to the monolayer deposited per cycle. Herein, an easy and low-cost wet-chemistry fabrication process is used to engineer the anode/solid electrolyte interface in SSBs with nanoscale precision. This coordination-assisted deposition is initiated with polyacrylate acid as a functional polymer to control the surface reaction, which modulates the distribution and decomposition of metal precursors to reliably form a uniform crack-free and flexible nanofilm of a large variety of metal oxides. For demonstration, artificial Al2O3 interfacial nanofilms were deposited on a ceramic SSE, typically garnet-structured Li6.5La3Zr1.5Ta0.5O12 (LLZT), that led to a significant decrease in the Li/LLZT interfacial resistance (from 2079.5 to 8.4 Ω cm2) as well as extraordinarily long cycle life of the assembled SSBs. This strategy enables the use of a nickel-rich LiNi0.83Co0.07Mn0.1O2 cathode to deliver a reversible capacity of 201.5 mAh g-1 at a considerable loading of 4.8 mg cm-2, featuring performance metrics for an SSB that is competitive with those of traditional Li-ion systems. Our study demonstrates the potential of solution-based routes as an affordable and scalable manufacturing alternative to vapor-based deposition techniques that can accelerate the development of SSBs for practical applications.