Energy crises and environmental pollution have spurred the development of green energy harvesting technologies, among which triboelectric nanogenerators (TENGs) demonstrate significant potential. However, the scarcity of high-performance biodegradable negative triboelectric materials, coupled with inherent flaws in existing degradable TENG structures, such as fragile triboelectric layers and poor environmental adaptability, has constrained their practical application. This study successfully prepares a fully degradable negative triboelectric layer material (SCG-PCL) through co-extrusion of spent coffee grounds with polycaprolactone. When paired with degradable triboelectric materials conductive polylactic acid (PLA-C), cellulose, zein and chitosan respectively, SCG-PCL achieve triboelectric charge densities ranging from 67% to 127% of the corresponding PTFE combinations. This breakthrough offers a feasible strategy for replacing polytetrafluoroethylene (PTFE) and realizing fully biodegradable TENGs. Subsequently, SCG-PCL pellets are integrated with a conductive PLA 3D-printed housing to design a fully biodegradable, fully enclosed TENG (SP-TENG). At equivalent cost, the SP-TENG achieves an output voltage 1.7 times that of PTFE pellets-based TENGs, a volumetric power density of 12.28 mW·m−3, along with outstanding durability, scalability, and degradability. Furthermore, SP-TENG can be applied to wind energy harvesting in islands and complex road condition early warning systems. This work provides an innovative pathway for fabricating biodegradable negative triboelectric layer materials and green TENGs devices.