Porous hard carbons are synthesized via carbonizing lotus stems with naturally hierarchical structures. The hard carbon carbonized at 1400 °C (LS1400) delivers a total capacity 350 mAh g⁻¹ in the current density of 100 mA g⁻¹ and a plateau capacity of 250 mAh g⁻¹. Even cycled at 100 mA g⁻¹ after 450 cycles, the capacity still retains 94%. Further investigation shows that the sodium storage of LS carbons involves Na⁺ adsorption in the defect sites, Na⁺ insertion and Na metal deposition in the closed pores. However, the Na metal deposition in closed pores mainly contribute to the plateau capacity, leading to the excellent sodium storage performance of LS1400 with a large closed pore ratio of 66%. The results show that the intrinsic structure of natural biomass can inspire us to design hard carbon with large closed pore ratio as excellent anode for sodium ion batteries.

多孔硬碳是通过碳化具有自然层次结构的莲花茎而合成的。在1400°C碳化的硬碳（LS1400）在100 mA g ^-1的电流密度下提供350 mAh g ^-1的总容量，在250 mAh g ^-1的平稳容量下提供总容量。即使在450次循环后以100 mA g ^-1循环，容量仍保持94％。进一步的研究表明，LS碳的钠存储涉及缺陷部位的Na ⁺吸附，Na ⁺插入并在封闭的孔中沉积金属钠。但是，闭孔中的Na金属沉积主要是对平台容量的贡献，导致LS1400具有66％的大闭孔率，从而具有出色的钠储存性能。结果表明，天然生物质的内在结构可以启发我们设计具有大封闭孔率的硬碳作为钠离子电池的优良阳极。