Deformation mechanism and prevention strategies of aluminum shell of Lithium-ion Batteries

Lithium-ion Batteries, with their advantages of regular structure and high energy density, are widely used in fields such as new energy vehicles. However, their anisotropic structural characteristics make them prone to deformation problems such as concave and convex cells due to uneven forces in the length and width directions during production, which in turn affects the safety and service life of the battery. The occurrence of deformation problems is closely related to multiple aspects such as material properties, manufacturing processes, and internal environmental control of Power Battery Cell. It is necessary to analyze the causes from multiple dimensions and implement targeted policies. This article provides an in-depth analysis of the core causes of deformation in Lifepo4 Power Cells and system prevention and control measures, providing technical reference for industry production practice.

In the lithium ion Batteries production system, the stability of the Lithium-ion Batteries shell structure is directly related to product reliability, and the occurrence of deformation problems is often the result of the synergistic effect of multiple factors, such as material properties, process control, and internal thermodynamic state. From the perspective of material and structural dimensions, the selection of aluminum shell material and strength design are the fundamental factors. If materials with insufficient tensile strength, such as 3003 aluminum alloy are used, or if the shell thickness is less than 0.6mm, they are prone to yield deformation under internal pressure and thermal stress. At the same time, the structural characteristics of the welding area cannot be ignored. The heat-affected zone formed during the welding process will experience a 20-30% decrease in local strength due to lattice reorganization, becoming a stress concentration area that is prone to deformation when subjected to subsequent stress.

The rationality of the welding process has a decisive impact on the structural stability of the shell of the Lithium Ion Battery for Solar System, and process defects are an important link in inducing deformation. Laser welding, as a mainstream process, if the heat input control is out of control, such as power exceeding 300W or welding speed below 30mm/s, it will cause local temperatures far exceeding the melting point of aluminum at 660 ℃, and the molten pool will be too deep, leading to a sharp increase in cooling shrinkage stress; Improper weld bead design, such as the absence of stress relief notches in continuous ring welding and weld bead width less than 0.8mm, can reduce the load-bearing capacity of the weld and further exacerbate the risk of deformation.

The abnormal internal pressure of the battery is the core thermodynamic cause of deformation, which also exists in mainstream systems such as LiFePO4 Lithium Ion Battery. Side reactions such as electrolyte decomposition and abnormal damage to SEI film inside the battery cell will accelerate gas production when the temperature exceeds 45 ℃, and when the internal pressure exceeds 10kPa, it will push the shell to deform; At the same time, the negative electrode expansion rate can reach 20-30% in a fully charged state. If the gap between the core and the inner wall of the shell exceeds 1.0mm (the industry standard gap is 0.3-0.8mm), the expansion force cannot be effectively constrained by the shell and will turn towards a higher degree of freedom in the vertical direction, causing deformation of the cover plate or side wall. In addition, in the production of Solar Energy Storage Systems Lithium Battery Pack, if the gap between the core and the inner wall of the shell exceeds the standard, the negative electrode will first fill the surrounding gaps when expanding, further amplifying the vertical deformation effect.

Process control deviations during the production process can also induce or exacerbate deformation problems. If the gap between the cover plate and the shell exceeds 0.2mm during the assembly process, the thermal stress during welding will superimpose with the gap displacement effect, directly leading to deformation; If the vacuum degree is set too low (below -90kPa) during the sealing stage, the external atmospheric pressure will directly act on the weak parts of the shell, causing passive compression deformation.

Based on the above deformation mechanism and industry technical practice, a prevention and control system can be constructed from dimensions such as material optimization, process improvement, internal pressure control, and process strengthening. In terms of material and structural optimization, the core idea is to improve the load-bearing capacity of the shell, which can be achieved by using 5052 aluminum alloy with a 30% increase in tensile strength, adding 0.5-1.0mm high reinforcement ribs in the top cover area, and increasing the thickness of the shell of Solar Home System Lithium Ion Batteries to 0.8-1.0mm. At the same time, a composite welding structure combining laser welding and ultrasonic welding is adopted to reduce single-point heat input and improve the stability of the welding area.

The improvement of welding process needs to focus on fine control, using gradient power welding strategy, that is, a combination of parameters of 200W/30mm/s for the starting section, 250W/25mm/s for the middle section, and 180W for the ending section, to control the depth of the heat affected zone within 0.5mm; At the same time, optimize the weld bead design by changing the continuous weld bead to a segmented welding mode, with each segment being 5-8mm and a 2mm stress release zone reserved. At the same time, increase the weld bead width to 1.2mm to enhance the weld bearing capacity.

Internal pressure control needs to start from two aspects: expansion compensation and gas production suppression. In terms of structural design, an elastic buffer layer with a compression rate exceeding 50% can be installed on the inside of the cover plate of Lithium Solar Batteries, leaving 0.5-1.0mm of expansion space to alleviate the pressure impact caused by negative electrode expansion; In terms of chemical system optimization, adding 1-2% FEC film-forming additives in the injection process can effectively suppress abnormal damage to the SEI film, control the gas production under full charge within 0.5ml/Ah (monitored in real-time through gas chromatography testing), and reduce internal pressure accumulation from the source.

The strengthening of process control requires the use of intelligent technology, introducing a visual positioning system in the assembly process to control the positioning accuracy within ± 0.05mm. At the same time, upgrading the welding fixture to a constant force clamping mode ensures a clamping force of 20-30N with fluctuations not exceeding 5%, reducing the deformation risk caused by assembly deviation. Add a pressure testing station in the chemical separation stage, which will automatically alarm when the detected pressure exceeds 5kPa. At the same time, combined with X-ray detection of shell deformation rate, the threshold will be controlled within 0.3% to achieve early identification and control of deformation problems in the Battery for Lithium-Ion Energy Storage System.

It should be noted that the deformation prevention and control of the shell of Lithium ion for BESS is a systematic engineering process. The technical parameters involved in the article need to be combined with specific production equipment, product models, and application scenarios, and optimized and verified through DOE experiments before implementation. For products with special application scenarios, such as Lithium-ion Batteries, it is necessary to further adjust the prevention and control parameters based on the temperature and pressure characteristics of the application environment to ensure the structural stability of the product throughout its entire lifecycle. In addition, the deformation prevention and control of Rechargeable Lithium Ion Battery Cell also needs to take into account the thermodynamic changes during the charging and discharging cycles, and achieve quality control throughout the entire process.