聚合物电介质储能——让电容器不再只是罐头
什么是聚合物电介质？
聚合物电介质可以看成“高分子塑料+电偶极子”。一般是由长链碳骨架+极性基团（如C–F、C=O）构成；在外电场作用下，分子内部正负电荷瞬间分离，形成极化电荷，从而“锁住”能量。一句话：它像塑料一样柔韧，却又像陶瓷一样能够“储存”电场[1-4]。
为什么选它做电容器？
首先聚合物密度≈1 g cm⁻³，只有陶瓷的1/3；其次柔性好，可弯曲、可卷曲、可拉伸；而且易成膜，5 μm超薄薄膜连续卷绕，一张A4大小的薄膜可绕出100 m长带；除此之外介电常数可调，可通过分子设计，εr在2~100任君挑选；最后其具有自愈合能力，金属化薄膜在点击穿点瞬间“烧掉”缺陷，器件还可以继续工作。
PEI学名又名聚醚酰亚胺（Polyetherimide）具有透明琥珀色无定形颗粒外观；由芳香酰亚胺环+柔性醚键构成分子密码；Tg ≈ 217 °C，可在150 °C长期服役εr ≈ 3.15（1 MHz）几乎不随温度漂移；击穿强度可达16–20 kV mm⁻¹（薄膜级）[5-7]。根据电容公式C = ε₀εr A / d可知PEI的εr虽只有3.2左右，但d可以做得很薄（2 μm），且击穿强度高，因此单位体积能量密度Ue = ½ ε₀ εrE2可达0.5~1 J cm-3，远高于同厚度的聚丙烯。但PEI因本身苯环的π-π 共轭结构仍存在电导损耗大导致热失控的风险[8]。
蒙脱石具有天然的二维层状纳米片结构，且禁带宽度大及绝缘性能良好[9-11]。将蒙脱石纳米片引入聚合物基体中，能够提高载流子跃迁势垒就像是在电子跨栏中提高了栏杆高度，增大电子跳过去的难度，从而抑制传导电流[12-14]，提高聚合物的高温储能性能。
聚合物电介质现广泛应用于电动汽车、新能源并网以及先进激光武器等领域。“会储能的塑料”让电容器不再只是‘罐头’，而是可弯曲、可穿戴、可植入的未来元件。
参考文献
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