Nitrogen-rich three-dimensional porous carbon mosaicked Na₄Ge₉O₂₀ as anode material for high-performance lithium-ion batteries

Germanium-based material has attracted numerous attentions and been regarded as a promising anode material for lithium-ion batteries due to its high theoretical capacity. However, drastic pulverization and rapid capacity fading caused by large volume variation during cycling limit its practical application. In this work, three-dimensional N-doped carbon framework-wrapped Na₄Ge₉O₂₀ nanoparticles (3D Na₄Ge₉O₂₀@N-C) have been synthesized via freeze-drying approach with NaCl as both template and sodium source for ion-exchanging. The employment of NaCl has two special roles: on the one hand, the NaCl crystals act as template and facilitate the formation of 3D porous structure, while on the other hand, the NaCl crystals serving as sodium source and support the ion exchange between NaCl and GeO₂ promote the formation of Na₄Ge₉O₂₀. Benefiting from the unique method, the prepared 3D Na₄Ge₉O₂₀@N-C not only suppresses the volume change by using carbon as buffer layers but also demonstrates an improved electronic conductivity and a shortened ionic diffusion. When utilized as an anode material for LIBs, the 3D Na₄Ge₉O₂₀@N-C composites deliver high reversible capacity (896.2 mAh·g⁻¹ at 0.1 A·g⁻¹ after 100 cycles), good cycling stability (520.8 mAh·g⁻¹ at 2.0 A·g⁻¹after 400 cycles) and excellent rate performance (636.0 mAh·g⁻¹ at 2.0 A·g⁻¹). This work provides a strategy to improve the electrochemical performance of germanium-based anode materials for lithium-ion batteries.