【作者】 陶鑫；

【导师】 谢松； 何涪；

【作者基本信息】 中国民用航空飞行学院 ， 交通运输， 2024， 硕士

【摘要】 在双碳战略背景和国际民航组织推动下,搭载锂离子电池的全电/多电飞机发展迅速。锂离子电池在低气压环境下的循环性能和安全性问题备受关注,循环老化后电池的安全状态评估问题更是亟需解决。本文围绕低气压环境下钛酸锂电池循环性能和热安全特性演变规律,建立基于机器学习算法的安全状态评估模型。主要结论如下:（1）低气压循环导致电池循环性能和热安全性降低。通过开展不同气压环境工况下钛酸锂电池电化学测试实验、绝热环境和开放空间热失控实验,基于实验数据分析了电池容量衰减规律、放电直流内阻变化和热安全特性演变规律,结果表明:在低气压环境下循环性能衰减明显,20 k Pa下电池容量衰减达到9.5%,放电直流内阻增加30.5%。通过容量增量分析发现电池正极材料损伤和活性物质损失主导电池循环性能衰减。通过X射线扫描发现低气压环境循环电芯间存在膨胀和断裂,SEM、XRD和XPS测试表明低气压环境工况加剧了电池正负极沉积物生成,并且负极中Ti⁴⁺转化Ti³⁺导致负极结构变化,加剧电池产气。低气压环境循环后电池热失控触发温度降低,热失控触发时间缩短,电池热安全性降低。此外,不同气压环境循环后钛酸锂电池热失控现象不同,低压环境循环电池更容易发生起火现象,而常压环境循环电池爆炸程度更剧烈。（2）低气压环境加剧了不同倍率循环电池间循环性能和热安全性的衰退。通过开展了不同气压环境下不同循环倍率电池电化学测试和绝热环境热失控实验,基于实验数据分析了电池循环性能和热安全特性的演变规律,结果表明:高倍率循环会导致电池循环性能衰减和热安全特性降低,并且不同循环倍率电池的循环性能和热安全特性的差异性在低气压环境下更加明显,2 C、5 C和8 C倍率循环电池容量保持率在低压循环后分别比常压循环工况减少1.4%、7.6%和7.9%。此外,在低气压环境下,高倍率循环电池样品表面温度在单位时间内提升更高,热滥用下更具有危害性。（3）搭建基于机器学习算法模型的电池安全状态评估模型。通过定量评估手段分析各项电化学特征与电池自放热速率联系。研究结果表明:随着电池在低气压环境下循环老化,电池安全状态呈非线性下降趋势。并且低气压环境钛酸锂电池安全状态等级划分为Ⅰ（安全）、Ⅱ（警告）和Ⅲ（不安全）三个等级,分别对应取值为[0.858-1]、[0.507-0.858]和[0-0.507]更多还原

【Abstract】 The development of all-electric aircraft/multipower aircraft equipped with lithium-ion batteries has been rapidly progressing,driven by the dual-carbon strategy and the efforts of the International Civil Aviation Organization.However,concerns have been raised regarding the cycling performance and safety of lithium-ion batteries in low-pressure environments.Additionally,there is an urgent need to address the issue of safety state assessment for batteries after cycle aging.This thesis focuses on the evolution patterns of cycling performance and thermal safety characteristics of lithium-ion batteries under low-pressure environments and proposes a safety state assessment model based on machine learning algorithms.The main conclusions are as follows:（1）The cycling performance and thermal safety of the battery are reduced due to cycling under low-pressure conditions.By conducting electrochemical testing experiments on lithium titanium batteries under different pressure environments,as well as adiabatic environments and open-space thermal runaway experiments,the capacity decay patterns,changes in discharge DC internal resistance,and evolution of thermal safety characteristics of the battery were analyzed based on experimental data.The results indicate that:Under low-pressure environments,the decay in cycle performance is evident,with a battery capacity decay of 9.5%observed at 20 k Pa,and a corresponding increase of 30.5%in discharge DC internal resistance.Through capacity increment analysis,it is identified that the deterioration of battery cycle performance is primarily governed by damage to the positive electrode material and the loss of active substances.Significant expansion and fracture between battery cells were observed through X-ray scanning in low-pressure environments.SEM,XRD,and XPS testing demonstrated that the low-pressure operational conditions exacerbated the formation of deposits on both the positive and negative electrodes.Additionally,the conversion of Ti⁴⁺to Ti³⁺in the negative electrode resulted in structural changes,intensifying gas production in the battery.The triggering temperature for thermal runaway in the battery decreased,and the duration of thermal runaway events shortened after cycling in low-pressure environments,leading to a decrease in battery thermal safety.Furthermore,there were differences in the thermal runaway phenomena of lithium titanate batteries after cycling in different pressure environments.Low-pressure batteries were more prone to ignition,while atmospheric-pressure batteries exhibited a more severe explosion.（2）The degradation of cycling performance and thermal safety between different rate cycles is exacerbated in low-pressure environments.By conducting electrochemical testing on batteries with different cycling rates under various pressure conditions,as well as adiabatic environment thermal runaway experiments,the evolution patterns of battery cycling performance and thermal safety characteristics were analyzed based on experimental data.The results indicate that:High-rate cycling results in a degradation of battery cycling performance and a reduction in thermal safety characteristics.The differences in cycling performance and thermal safety characteristics among batteries with different cycle rates are even more pronounced in low-pressure environments.After low-pressure cycling,the capacity retention rates of batteries cycled at 2 C,5 C,and 8 C decrease by 1.4%,7.6%,and 7.9%,respectively,compared to the normal-pressure cycling conditions.Additionally,under low-pressure environments,the surface temperature of high-rate cycling battery samples increases more rapidly within a given time period,making them more hazardous under thermal abuse.（3）A battery safety state assessment model based on machine learning algorithms is constructed.The relationship between various electrochemical features and the self-heating rate of the battery is analyzed through quantitative evaluation methods.The research results indicate that:As the battery undergoes cycle aging in low-pressure environments,the safety state of the battery exhibits a nonlinear declining trend.Furthermore,for lithium titanate batteries in low-pressure environments,the safety state is divided into three levels:Level I（safe）,Level II（warning）,and Level III（unsafe）,corresponding to values within the ranges of[0.858-1],[0.507-0.858],and[0-0.507].更多还原