层叠式锂电池制造中金属极片的伺服超声波微焊接机理研究

It's generally known that, in the assembling process of lithium battery, the joining quality of metal foil has a remarkable impact on the consistency of the battery performance. However, how to realize the robust joining of more than 50-layer micron-grade aluminum/copper/nickel foil is still a major problem. The micro mechanical behavior (i.e. friction, yield, deformation flow) in the ultrasonic micro-welding process, along with the distinct cumulative effect of the energy transfer and the micro plastic deformation at contact area during the bonding process of multilayer pole pieces are the primary reasons. .Firstly, a control method oriented to macro-micro coupling for servo ultrasonic micro-welding will be developed to understand the thermal effect of ultrasound and the mechanism of frictional heat generation during ultrasonic micro-welding process. .Furthermore, a multiple scale model based on molecular dynamics and finite element coupling method will be proposed to reveal the deformation behavior and the mechanism of material softening at mesoscopic level. .Thirdly, a servo-driven ultrasonic micro-welding system will be built to achieve the precise control of bonding pressure and micro displacement. This project aims to address the key issues such as thermal effect, size effect of friction, plastic deformation and Casimir effect during ultrasonic micro-welding process. .New technology and equipment for ultrasonic micro-welding mesoscale metal foil will also be developed. Consequently, the manufacturing technology of lithium battery will be significantly promoted.

层叠式锂电池装配过程中金属极片连接接头的质量将显著影响电池性能的一致性。实现50层以上微米级铝/铜/镍金属极片的稳健连接是目前的瓶颈问题，原因在于超声波微焊接过程的摩擦生热、微观屈服、变形流动、加工硬化等耦合作用，介观尺度金属极片键合过程中多层接触界面间的能量累积和衰减效应显著。为此，本项目建立面向宏微耦合的伺服超声波微焊接控制方法，解决超声波微焊接过程的摩擦热效应、塑性变形尺度效应和接触界面间的Casimir力效应等关键问题。内容包括：1）建立基于塑性细观力学-流变力学的摩擦尺寸效应模型，揭示微焊接过程的超声热效应及摩擦生热机理；2）建立基于分子动力学与有限元耦合的多尺度模型，揭示介观尺度下接触区域的微塑性变形行为与材料软化机制；3）建立伺服驱动的超声波微焊接系统，实现键合压力/位移的精确控制。形成适合于50-80层异质超薄金属极片的超声波微焊接新工艺与新装备，推动锂电池制造技术的进步。

铝/铜/镍等异质多层超薄金属极片的超声波微焊接工艺方法，在锂电池封装、太阳能翼板中电池片组装以及层叠箔片超声増材制造中获得广泛应用，受焊接过程摩擦生热、微观屈服、变形流动、加工硬化等耦合作用，超声能场作用下的材料变形行为、接合区界面接触和热力耦合机制复杂，是制约介观尺度金属极片超声稳健连接的瓶颈问题。本项目综合应用弹塑性力学、接触力学和摩擦学等理论及数值模拟和实验研究方法，研究焊接过程中接合区塑性变形行为和界面摩擦生热特性，揭示热力耦合场作用下金属极片超声连接接头形成机理。主要研究内容和结论有：.1)建立材料变形、温升与超声能量的映射模型，基于超声能量传递规律推导温度解耦的超声软化材料本构模型，精确描述金属极片超声焊接过程的应力-应变演变规律，与传统的本构模型相比，精度提高了16%左右。.2)修正超声周期振动条件下的接触界面粘结-滑移判定准则，建立界面摩擦动力学模型，分析接合区塑性变形和相对滑移的变化规律，获得了焊接过程接合区的粘结-滑移转变时刻，为超声焊接过程温度场演变与声致变形预测提供理论判据。.3)建立超声能场作用下温度场/结构场耦合的有限元模型，获得了焊接过程中界面摩擦和声致变形的耦合变化规律，揭示了金属极片超声键合机理。建立超薄金属极片超声焊接工艺稳健优化模型，提出面向不同金属极片稳健连接的焊头形貌优化方法，实现超声连接接头几何特征和力学性能的综合调控。 . 本项目建立了面向多层金属极片超声稳健连接的相关理论和制造工艺方法，在介观尺度金属极片的超声波微焊接理论、多层超薄金属极片焊接工艺稳健优化方法和装备开发等方面取得了一系列研究成果，为锂电池制造一致性提升提供了理论和技术支撑。相关研究成果已在Welding Journal，ASME Transactions，Science and Technology of Welding and Joining等期刊上发表/录用SCI论文12篇，在焊接领域国际会议宣读论文6次，其中邀请报告1次。获得中国发明专利授权2项，公开美国发明专利1项。