钠电池为什么能量密度偏低？

Why is the energy density of Sodium-ion Battery low?    

钠电池能量密度偏低是物理特性和材料结构共同决定的天然短板，无法通过简单工艺优化彻底解决。第一，离子本身属性差异：钠离子的原子质量远大于锂离子，且离子半径是锂离子的1.8倍左右，单个钠离子占用的储钠空间更大、质量更高，单位质量的储电效率更低；第二，晶格储纳上限有限：正负极材料的晶格孔隙尺寸和数量有限，能够容纳的钠离子数量远少于锂离子，单位体积可存储的电荷总量更少；第三，电压平台偏低：钠电池单体标称电压低于锂电池，单位电荷的做功能力更弱。多重因素叠加，导致钠电池的能量密度天然低于锂电池。

The low energy density of Sodium-ion Battery is an inherent shortcoming determined by physical properties and material structure, which cannot be completely solved by simple process optimization. First, the difference in the properties of the ions themselves: the atomic mass of sodium ions is much larger than that of lithium ions, and the ionic radius is about 1.8 times that of lithium ions. A single sodium ion occupies a larger sodium storage space and has a higher mass, resulting in lower power storage efficiency per unit mass; second, the limited upper limit of lattice sodium storage: the lattice pore size and quantity of the cathode and anode materials are limited, and the number of sodium ions that can be accommodated is much less than that of lithium ions, resulting in less total charge that can be stored per unit volume; third, the low voltage platform: the nominal voltage of the sodium battery monomer is lower than that of the lithium battery, and the work capacity per unit charge is weaker. The superposition of multiple factors leads to the naturally lower energy density of sodium batteries than lithium batteries.