What are the core differences between sodium-ion batteries and Ni-Cd batteries?

性能、环保、寿命、成本四大维度差距显著。一环保毒性：镍镉含剧毒镉金属，废弃造成土壤水体重金属污染，多国限制生产；钠无有毒重金属，回收绿色合规。二循环寿命：钠 3000 次以上，镍镉仅 300~800 次，更换频率极高。三记忆效应：镍镉存在严重记忆，浅充浅放大幅衰减容量；钠无记忆效应，任意充放电区间稳定运行。四低温性能：-20℃钠保留 85% 容量，镍镉低温容量折半。五自放电：钠月 2%~4%，镍镉月 10% 左右，闲置快速亏电。六能量密度：钠 120~160Wh/kg，镍镉仅 40~60Wh，同等容量重量大两倍。七使用成本：钠可循环复用，全周期支出远低于镍镉；镍镉一次性购置加频繁替换长期成本高。八政策约束：镍镉逐步淘汰，钠为政策扶持新型储能技术。九场景：钠户储、叉车、光伏；镍镉仅剩老旧工业备用电源，市场持续萎缩。

Obvious gaps exist in performance, environmental toxicity, service life and cost. 1. Environmental hazard: Ni-Cd contains toxic cadmium causing soil & water heavy metal pollution with production restricted worldwide; sodium is heavy-metal-free with eco-compliant recycling. 2. Cycle life: Sodium exceeds 3,000 cycles vs merely 300~800 for Ni-Cd with frequent replacement. 3. Memory effect: Severe memory loss for Ni-Cd under shallow cycling; sodium operates stably at any charge-discharge window without memory effect. 4. Low temperature: Sodium retains 85% capacity at -20℃ while Ni-Cd capacity halves. 5. Self-discharge: Monthly sodium loss 2%~4%, ~10% for Ni-Cd with rapid standby power depletion. 6. Energy density: Sodium 120~160 Wh/kg vs only 40~60 Wh for Ni-Cd, twice heavier at equal capacity. 7. Life-cycle cost: Reusable sodium delivers far lower total expenditure; Ni-Cd accumulates high expense from frequent replacement. 8. Policy: Ni-Cd is phased out while sodium receives industrial support. 9. Scenarios: Sodium for household storage, forklifts and PV; Ni-Cd limited to outdated industrial backups with shrinking demand.