钠离子电池因资源丰富与成本优势被视为下一代储能技术的核心候选，但其循环过程中因钠离子半径较大引发的体积膨胀效应严重制约了电池的可靠性与寿命。现有研究多聚焦于单一因素（如温度或电压）对膨胀力的影响，对多因素耦合作用下的动态演变机制缺乏探讨。本文通过构建温度（35℃/45℃）与充电截止电压（3.95 V/4.0 V）的多变量协同实验模型，结合原位膨胀力监测分析，揭示了钠离子电池膨胀力的非线性演化规律及其与SEI膜增厚关联机制。研究发现，高温（45℃）与高截止电压（4.0 V）会加剧钠离子嵌入动力学失衡，导致硬碳结构畸变与微孔不可逆填充，并使界面副反应倍增，使电池膨胀力持续增长。此外，提出“膨胀力阈值释放”策略，通过应力释放可将容量保持率短期提升0.5%，为钠离子电池的多维度寿命优化提供理论依据。

Owing to its abundant resources and cost-effectiveness, the sodium-ion battery(SIB) is regarded as a core candidate for next-generation energy storage technologies. However, the relatively large ionic radius of sodium ions induces significant volume expansion during the cycling process, which severely constrains the reliability and lifespan of SIBs. Current research predominantly focuses on the influence of individual factors, such as temperature or voltage, on the expansion force, while the dynamic evolution mechanisms under the coupling of multiple factors remain under explored. In this study, a multi-variable synergistic experimental model incorporating temperature(35 ℃ and 45 ℃) and charging cut-off voltage(3.95 V and 4.0 V) was constructed. Combined with in situ monitoring and analysis of the expansion force, the nonlinear evolution law of the expansion force in SIBs and its correlation mechanism with SEI film thickening were elucidated. It was found that high temperature(45 ℃) and elevated cut-off voltage(4.0 V) exacerbate the kinetic imbalance of sodium ion intercalation, leading to structural distortion and irreversible micropore filling in the hard carbon, thereby triggering a proliferation of interfacial side reactions and a continuous increase in the battery's swelling force. Additionally, a "threshold release of expansion force" strategy was proposed. By releasing stress, the capacity retention rate can be temporarily enhanced by 0.5%, providing a theoretical basis for multidimensional lifespan optimization of sodium-ion batteries.