Remark:
Cross-corner between front and side sealing
Corrosion mode-II
Remark:
Cross-corner between front and degassing sealing
Corrosion mode-III
Remark:
Tip-effect due to mutual-folding
Corrosion mode-IV
Remark:
Weak spot after Hot-sealing/Folding/Activation/Aging
Corrosion mode-VRemark:
Front-sealing bar is too near from cell body
The relevant evidence for corrosion---DOE
Remark:
1.Positive electrode contacts with Al layer directly with different “R” value range;
2.Negative electrode contacts with Al layer directly with different “R” value range;
Ni tab点锡静置7天后腐蚀状况统计
Ni tab点锡静置40天后腐蚀状况统计
Ni tab点锡静置28天后腐蚀状况统计
Ni tab点锡静置40天后腐蚀状况统计
Corrosion Mechanism
Comments:
1.Weak points on sealing zone lead to Al layer exposure in electrolyte;
2.Measuring the resistance between Ni tab and Al foil can detect the weak point existence
Some potential failure causes-1
Remark:
导电柄间距变异，前封封头凹槽台阶压导电柄-------”R”值变小
Some potential failure causes-2
Remark:
电芯折边PP层折裂，Al层暴露-------”R”值变小
Some potential failure causes-3
Remark:
隔离膜参与前封-------”R”值变小
Some potential failure causes-4
Remark:
电芯折边PP胶粒压迫Al层，Al层断裂，外部水份侵入-------”R”值变小
Some potential failure causes-5
Remark:
封头凹槽台阶太锋利，热封后斩断Al层，外部水份侵入-------”R”值变小
Some potential failure causes-6无图
Remark:
极耳毛刺刺破PP层-------”R”值变小
Some potential failure causes-7无图
Remark:
Pack装配焊接PTC或Fuse过程中，折叠Ni tab两者直接发生短路：-------”R”值变小甚至为零
Some potential failure causes-8无图
Remark:
活性材料particle参与热封装：-------”R”值变小
Al tab点锡静置40天后腐蚀状况统计
Al tab和Ni tab都未点锡静置40天后腐蚀状况统计
Remark：
包装铝箔边缘与电芯的正极接通不会发生腐蚀，就像铝壳电池最外面
就是电池的正极，正极在充放电中得电子被还原保护--------不腐蚀
Remark：
软包装电芯的负极和包装铝袋的铝层之间要有足够大的电阻，将是
电芯不发生腐蚀的重要前提。
总结软包装电芯腐蚀现象杜绝须重视以下几个方面：
工序（热封装，弯边，折边）等需重视减少weak point的产生可能性；---PP胶粒形状、大小控制，未封区域宽度控制，减少弯边制具对封边剪切作用，折边减少铝袋尖角效应。“R”值检测是检验“weak point”，避免腐蚀的有效方法。很大一部分腐蚀的case是在客户端使用不当，或者是在装配Pack时没有充分考虑到负极和Al袋直接短接的潜在危害性。