硬碳负极材料的热稳定性及其钠离子电池安全性能评测

钠离子电池作为一种有应用前景的能量储存系统，技术发展日趋完善。钠离子电池由于钠资源丰富，在大规模储能及低速电动车应用等领域具有成本优势，引起学术及产业界的广泛关注。随着钠离子电池产业的推进，电池安全性是亟待研究及数据积累的重点问题之一。近年来，随着电动汽车数量的增加和动力电池能量密度的提高，汽车安全事故时有发生，究其原因多为电池单体热量耗散造成。本工作从负极硬碳材料热稳定性、电芯过放电、极端破坏(挤压针刺等)和热失控等方面对钠离子电池进行安全性评测。结果表明，电解液的存在会降低嵌钠态硬碳的稳定性，且随负极嵌钠量增加，放热峰的位置也随之前移且更明显；与无过放电芯比较，软包电芯过放电至0 V对电芯的长循环稳定性基本无影响，循环500周后的容量保持率基本一致，且电流密度大小(0.1和1 C)对电芯容量恢复和循环性能亦无明显影响；挤压针刺测试结果表明钠离子电池安全性能良好，绝热加速量热仪(ARC)测试发现电芯安全性能并未随着荷电状态(SOC)增加趋于不稳定，实验结果表明30% SOC状态下电芯安全性最好。

Evaluation of safety performance and thermal stability of hard carbon anode for sodium-ion battery

As a promising energy storage system, the sodium-ion battery has attracted wide attention due to its rich sodium resources and cost advantages in energy storage and low-speed electronic vehicle application. With the development of the sodium-ion battery industry, battery safety is one of the key issues which is often caused by the heat loss of battery cells. In this work, the safety factors of sodium-ion batteries were studied, including thermal stability of hard carbon materials, over-discharge test, safety test (extrusion and acupuncture, etc.), and thermal runaway test. According to the first cycle discharge curve of a hard carbon coin cell, the solid electrolyte interphase (SEI) of hard carbon in different discharge potentials with differential scanning calorimetry (DSC) at 0.9, 0.5, 0.15 and 0.01 V, respectively were studied. The results showed that with the increase of sodium embedded in the hard carbon, the position of the exothermic peak appeared earlier and became more obvious and the presence of electrolytes reduces the stability of hard carbon embedded with sodium. The safety performance of full sodium-ion batteries can be evaluated by calorimetric analysis of the thermal runaway process of batteries. 1 Ah soft package batteries were prepared to study the over-discharge test and safety test. Compared with the non-over-discharge cells, cells over-discharge to 0 V had little difference in cycle performance after 500 cycles. The current density (0.1 or 1 C) had no significant influence on capacity recovery and cycle performance of the battery. The extrusion and acupuncture tests showed that the sodium-ion battery had good safety performance as the batteries were no fire and no explode. In addition, the thermal runaway test as calorimetric analysis was generally carried out by an accelerating rate calorimeter (ARC). The ARC test showed that the onset temperature of detectable self-heating were 136.6, 131.6, 136.3, 128.2, 166.6 and 138.6℃ at 80% state of charge (SOC), 60% SOC, 50% SOC, 40% SOC, 30% SOC and 0% SOC, respectively. Moreover, the thermal runaway occurred at 240.9℃ only at 80% SOC. It proved that the safety performance of the sodium-ion battery was good and the sodium-ion battery had the best safety performance at 30% SOC.