低扩展包的荷电状态(SOC)磷酸铁锂(LFP)/石墨方形电池电池存储后问题一直是众多电池制造商和用户持续关注的焦点。本研究采用商用LFP/石墨体系成功复现了这一现象电池。失效分析表明，HO应是产气主因，因为在搁置的10% SOC电池中检测到大量氢气。负极表面的Li %%2一氧化碳2阳极表面3在90%SOC电池中高于10%SOC电池，推测是由于电解液副反应产生的CO与90%SOC电池阳极中的锂发生反应，从而消耗CO使得高SOC电池表现出比低SOC电池更低的膨胀率。严格控制LFP/石墨电池制造过程中的水分可有效防止低SOC电池存储后出现较高膨胀的问题。2 generated by the side reaction of electrolyte with water and the lithium in the anode electrode of the 90 % SOC battery, thus consuming CO2 to make the high SOC battery showed a lower expansion rate than the low SOC battery. Strictly controlling moisture during the manufacturing process of LFP/graphite batteries can effectively prevent the issue of low-SOC batteries exhibiting higher expansion after storage.
锂离子电池因其卓越的能量密度、长循环寿命和环境友好特性而备受关注，广泛应用于便携式电子设备、电动汽车（EVs）和储能系统[[1], [2], [3]]。对于电动汽车而言，实际驾驶行为具有驾驶员特异性，不同的驾驶和充电方式会导致电池性能衰退轨迹的差异。除行驶与充电阶段外，电动汽车电池还长期处于搁置状态。储能电池在其整个生命周期中同样存在搁置阶段。此外，锂离子电池在生产完成至使用阶段前的期间也存在一定时长的搁置时间。因此需要详细研究电池在搁置期间的性能表现，该性能受温度、湿度和SOC等因素影响。电池的shelf life（货架寿命）是指其在不出现显著性能衰减条件下可存储的持续时间。 为理解电池在搁置温度与SOC条件下的shelf life，已有大量研究开展[4]。特别值得注意的是，搁置温度对电池性能具有显著影响[5]。低温会降低电池内部化学反应速率，长期循环测试和电极表征结果表明，低温存储后未发现负面影响[6]。存在一个普遍结论：高温储存通常会加速电解液与电极间的反应，导致活性锂离子消耗[7,8]和电池膨胀[[9], [10], [11]]，进而引发不可逆容量损失。Hou等人[12]揭示了锂电池中氧化还原反应在40°C以上时会在电极与电解液之间加剧。此外，荷电状态（SOC）对电池储存寿命也具有显著影响。石墨/LiNix锰（Mn）y钴（Co）1-x-y锂锰合金（LiMn）2高温高荷电状态（SOC）条件下，软包电池会显著加速燃料费（Gas）生成并导致电池容量衰减[13]。圆柱形锂离子电池中也观察到类似趋势[14]。然而，尽管磷酸铁锂/石墨电池的容量衰减程度随存储温度和SOC值升高而显著加剧[7]，且18650[15]或38123圆柱电池在老化研究中未表现出膨胀现象，但Lu等研究者发现————[16]采用方形磷酸铁锂/石墨电池的测试表明，0%SOC存储条件下的电池扩展包（Expansion）速率反而高于100%SOC状态。国内其他磷酸铁锂/石墨方形电池制造商也报告了难以解释的现象：高温存储时，电池SOC值越低，燃料费（Gas）析出行为越严重[17,18]。受石墨和磷酸铁锂（LFP）晶格体积变化影响，30% SOC与100% SOC状态下的电池体积显著高于其他荷电状态[19]，但该现象仍无法解释低SOC条件下LFP/石墨电池的高体积膨胀率。2O4 pouch batteries at the higher temperature and SOC were sufficient to dramatically accelerate the gas generation and the degradation of the battery capacity [13]. The similar trends were also found in the cylinder Li-ion batteries [14]. However, though the extent of capacity fade of LFP/graphite strongly increased with storage temperature and SOC [7], and the 18650 [15] or 38123 cylindrical batteries were used in the ageing studies without swelling performance, but Lu et al. [16] revealed that the LFP/graphite square batteries with 0 % SOC storage condition exhibited a higher expansion rate compared to that of 100 % SOC storage condition. Other LFP/graphite square battery manufacturers in China also showed the inexplicable phenomenon that the gas evolution of the battery became serious with the decrease of the SOC when the battery was stored at higher temperature [17,18]. Affected by changes in lattice volume of graphite and LFP, the battery volumes of 30 % SOC and 100 % SOC were much higher than others [19], which also cannot explain the high volume expansion rate of low SOC LFP/graphite battery. 本工作研究了不同温度与荷电状态(SOC)条件下存储对含LFP/石墨活性材料的商用21 Ah方形电池保质期的影响。实验通过周期性表征测试及简易的失效分析，以深入理解容量衰减与体积扩展包的机理。重点探讨了存储期间低SOC电池与高SOC电池在扩展包速率上的差异性表现。
