Amorphous matrix-integrated Si nanocomposites were developed as high-performance anodes for Li-ion batteries (LIBs) and all-solid-state Li-ion batteries (ASSLIBs). Amorphous Ni<sub>3</sub>ZnSi<sub>2</sub> was employed as the elastic and conductive matrix because its unique crystal structure readily undergoes amorphization during high-energy milling, yielding a Si/a-Ni<sub>3</sub>ZnSi<sub>2</sub> nanocomposite in which Si nanocrystallites are uniformly encapsulated within the amorphous Ni<sub>3</sub>ZnSi<sub>2</sub> matrix. The amorphous Ni<sub>3</sub>ZnSi<sub>2</sub> matrix provides elastic recovery, high ionic/electronic conductivity, and effective buffering against large volume changes, thereby preserving electrode integrity during cycling. Incorporating a conductive graphite framework further produced dual-matrix Si/a-Ni<sub>3</sub>ZnSi<sub>2</sub>/G nanocomposites, where the amorphous Ni<sub>3</sub>ZnSi<sub>2</sub> and graphite frameworks synergistically enhance charge transport and mitigate mechanical stress. The Si/a-Ni<sub>3</sub>ZnSi<sub>2</sub>/G anode exhibited high initial Coulombic efficiency, high-rate capability, and long-term cycling stability in both LIBs and ASSLIBs. In LIB full cells comprising a Si/a-Ni<sub>3</sub>ZnSi<sub>2</sub>/G anode and a LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub> (NCM811) cathode, an energy density of 377.7 Wh kg<sup>-1</sup> was achieved with stable cycling performance and high-rate capability. In ASSLIB configurations with Li<sub>6</sub>PS<sub>5</sub>Cl solid electrolytes, the full cell delivered energy densities exceeding 300 Wh kg<sup>-1</sup> while maintaining electrochemical stability across wide ranges of temperature and current density. These findings highlight the scalability and potential applicability of Si/a-Ni<sub>3</sub>ZnSi<sub>2</sub>/G nanocomposites as next-generation anode materials for both LIBs and ASSLIBs.