CN108039443B - 一种锂电池用复合隔膜及其制备方法 - Google Patents
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Abstract
本发明提供了一种锂电池用复合隔膜,其为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000‑1000000、分子量分布指数Mw/Mn为4‑8、等规度>96%、熔体流动速率为1.3‑3.3;低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000‑300000、分子量分布指数Mw/Mn为4—8、熔体流动速率为0.2‑0.8。本发明的锂电池用复合隔膜具有较低的闭孔温度和较高的破膜温度,自关断安全窗口较宽,机械性能好,抗穿刺强度高,在锂离子电池的生产和使用过程中安全性能好,微孔孔径尺寸合适,分布均匀,贯通性好,电池的内阻小,有利于提高电池的工作效率。
Description
技术领域
本发明涉及一种锂电池用复合隔膜及其制备方法,属于锂电池技术领域。
背景技术
锂离子电池隔膜是锂离子电池中的一个重要组件,它是一种具有纳米级微孔的薄膜材料,在电池中起到阻隔正负电极、防止电池内部短路的作用;同时,它必须允许离子流快速通过,保证在电池充放电过程中锂离子在正负电极之间的快速传输。隔膜的微孔结构、物理性能、化学特性、热性能等决定了电池的界面结构、内阻等,直接影响电池的容量、循环性能以及安全性能等特性,性能优异的隔膜对提高电池的综合性能具有重要的作用。因此,电池隔膜在制造电池的材料中占有非常重要的地位,被称为电池的“第三电极”。正是由于电池隔膜的这种重要作用,高性能锂离子电池隔膜的开发成为电池生产企业技术研究的重点。
聚烯烃材料具有强度高、耐酸碱腐蚀性好、防水、耐化学试剂、生物相容性好、无毒性等优点,在众多领域得到了广泛的应用。当前,商品化的液态锂离子电池大多使用微孔聚烯烃隔膜,隔膜使用的聚烯烃材料目前主要是聚丙烯(PP)和聚乙烯(PE)两类。目前商品化锂电池隔膜的生产方法主要包括熔融拉伸法(干法)和热致相分离法(湿法)。熔融拉伸法通过流延成型得到具有硬弹性的基膜,该基膜具有低结晶度和高取向性,然后对基膜进行热处理(高温退火)以提高晶片厚度和结晶度,最后再将薄膜分别在低温和高温下进行单向拉伸,低温拉伸主要是产生微孔和银纹缺陷,高温拉伸是将微孔扩大,并将银纹缺陷拉伸形成微孔结构。热致相分离法利用高分子材料和特定的溶剂在高温条件下完全相容,冷却后产生相分离的特性,使富溶剂相连续贯穿于富聚合物相形成的连续固态相中,将溶剂萃取后在富聚合物相中形成微孔。湿法生产微孔膜时,孔径大小和孔隙率较易控制,孔的曲折度相对高,但是需要使用大量溶剂,工艺复杂,对环境污染较大;干法生产过程中工艺简单,孔曲折度较低,不仅可以生产单层隔膜,还可生产多层复合隔膜,提高生产效率,但是孔径大小较难控制。
隔膜在电池中直接接触具有硬表面的正极和负极,电极表面是由活性物质和炭黑混合物的微小颗粒所构成的凸凹面,尤其当电池内部形成枝晶时,被夹在极片间的隔膜易被穿破,从而引起正负极板接触发生短路,因此要求隔膜具有一定的抗穿刺强度。隔膜在电池中卷绕,在纵向承受一定的张力,因此隔膜还要具有一定的抗张强度,尤其是纵向抗张强度。
电池在充放电过程中会释放热量,尤其在短路或过充电的时候,会有大量热量放出,锂电池中隔膜的自关闭性质是锂离子电池限制温度升高及防止短路的有效方法。当温度接近聚合物熔点时,微孔闭合而产生自关闭,这时阻抗明显上升,通过电池的电流也受到限制,因而可防止由于过热而引起的***等现象。当电池内部温度继续升高的时候,闭孔后的隔膜应当保持原来的完整性和一定的机械强度,继续起到隔离正负电极的作用,防止短路发生。因此隔膜的闭孔温度和熔融破裂温度相差越大,电池的安全性就越好。材料的熔点决定了隔膜的闭孔温度,PE隔膜的闭孔温度在130℃左右,破膜温度在145℃左右;PP隔膜的闭孔温度在150℃左右,破膜温度在170℃左右。
由于PP隔膜机械强度高,耐高温性能好,而PE隔膜的闭孔温度低,因此PP、PE复合隔膜则综合了以上优点,具有较低的闭孔温度和较高的破膜温度,安全窗口温度可达到40℃,且机械性能优,抗张强度和抗穿刺强度高,保证了电池在生产和使用过程中更加安全。PP、PE复合隔膜成为目前锂电池隔膜领域研究开发的热点。
发明内容
鉴于上述现有技术存在的缺陷,本发明的目的是提供一种锂电池用复合隔膜及其制备方法;能够提高聚烯烃隔膜的安全性能,扩大隔膜使用的安全窗口温度,提高聚烯烃隔膜的机械强度。
本发明的目的通过以下技术方案得以实现:
一种锂电池用复合隔膜,其为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;
所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000-1000000、分子量分布指数Mw/Mn为4-8、等规度>96%、熔体流动速率为1.3-3.3;
低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000-300000、分子量分布指数Mw/Mn为4—8、熔体流动速率为0.2-0.8。
上述的锂电池用复合隔膜中,优选的,所述锂电池用复合隔膜的厚度为30-60μm;总孔隙率为40%-60%;微孔尺寸为0.01μm-0.15μm。
本发明还提供上述的锂电池用复合隔膜的制备方法,包括如下步骤:
将聚丙烯树脂熔融塑化,得到的熔体通过计量泵从三层模头的两个表层挤出,得到两层聚丙烯树脂挤出物料;
将聚乙烯树脂熔融塑化,得到的熔体通过计量泵从三层模头的芯层挤出,得到芯层聚乙烯树脂挤出物料;
两层聚丙烯树脂挤出物料和芯层聚乙烯树脂挤出物料在模头出口处汇合,牵引并不断冷却,得到PP/PE/PP复合厚片;
将PP/PE/PP复合厚片进行热处理,然后在常温和高温下分别进行单向拉伸,最后回缩定型,即得到锂电池用复合隔膜。
上述的制备方法中,优选的,所述模头的加热温度控制为200℃。
上述的制备方法中,优选的,将聚丙烯树脂熔融塑化的塑化温度为190℃-250℃。
上述的制备方法中,优选的,将聚乙烯树脂熔融塑化的塑化温度为190℃-230℃。
上述的制备方法中,优选的,所述热处理的温度为105℃-130℃。
上述的制备方法中,优选的,常温下单向拉伸的拉伸倍率为10%-50%。
上述的制备方法中,优选的,高温下单向拉伸的拉伸倍率为80%-140%。
上述的制备方法中,优选的,所述高温是指拉伸温度110℃-140℃。
上述的制备方法中,优选的,所述回缩定型的回缩比为-30%—-50%,回缩定型的温度为110℃-140℃。
本发明的锂电池用复合隔膜具有如下特性:
(1)厚度范围:30—60μm;
(2)总孔隙率:40%—60%,微孔尺寸:0.01μm—0.15μm;
(3)Gueley透气度值:<600s;
(4)纵向强度:>170MPa,抗穿刺强度:>190g;
(5)闭孔温度:105℃—115℃,破膜温度:165℃—175℃,安全窗口温度可达60℃。
本发明的突出效果为:
本发明的锂电池用复合隔膜具有较低的闭孔温度和较高的破膜温度,自关断安全窗口较宽,机械性能好,抗穿刺强度高,在锂离子电池的生产和使用过程中安全性能好。微孔孔径尺寸合适,分布均匀,贯通性好,电池的内阻小,有利于提高电池的工作效率。本发明的锂电池用复合隔膜的制备方法采用三层共挤的方法铸片,再进行热处理和单向拉伸,大大提高了复合微孔膜的生产效率,在隔膜的工业化生产中具有极其重要的意义。
具体实施方式
为了对本发明的技术特征、目的和有益效果有更加清楚的理解,现对本发明的技术方案进行以下详细说明,但不能理解为对本发明的可实施范围的限定。下述实施例中所述实验方法,如无特殊说明,均为常规方法;所述试剂和材料,如无特殊说明,均可从商业途径获得。
实施例1
本实施例提供一种锂电池用复合隔膜,其为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;
所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000-1000000、分子量分布指数Mw/Mn为4-8、等规度>96%、熔体流动速率为1.3-3.3;
低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000-300000、分子量分布指数Mw/Mn为4—8、熔体流动速率为0.2-0.8。
本实施例还提供上述的锂电池用复合隔膜的制备方法,包括如下步骤:
将聚丙烯树脂送入一台单螺杆挤出机内熔融塑化,塑化温度为210℃-220℃,得到的熔体通过计量泵从三层模头的两个表层挤出,得到两层聚丙烯树脂挤出物料;
将聚乙烯树脂送入另一台单螺杆挤出机内熔融塑化,塑化温度为210℃-220℃,得到的熔体通过计量泵从三层模头的芯层挤出,得到芯层聚乙烯树脂挤出物料;
两层聚丙烯树脂挤出物料和芯层聚乙烯树脂挤出物料在模头出口处汇合,牵引并不断冷却,得到PP/PE/PP复合厚片,厚片厚度36μm;整个过程中,模头的加热温度控制为200℃。
将PP/PE/PP复合厚片进行热处理,热处理的温度为115℃-125℃;然后在常温和高温下分别进行单向拉伸,常温下单向拉伸的拉伸倍率为10%,然后在拉伸温度120℃-130℃的高温下进行拉伸,拉伸倍率为100%;最后回缩定型,回缩定型的回缩比为-35%,回缩定型的温度为125℃-135℃,即得到锂电池用复合隔膜。
对得到的锂电池用复合隔膜进行测定,其中隔膜透气率和孔隙率的测试方法如下:
透气率:采用Gurley值表征隔膜的透气率。使用Gurley公司生产的4110型透气率测定仪,压力为20盎司,测试面积1.0平方英寸。记录100ml气体透过该测试面积所需的时间,即为Gurley透气度值。
总孔隙率:采用美国康塔公司的PoreMaster33型压汞仪测定隔膜的总孔隙率。
测定结果如下:。
锂电池用复合隔膜的厚度30μm,孔隙率为42%,微孔的孔径范围0.01μm-0.15μm,Gurley透气度值400s,纵向强度为196MPa,抗穿刺强度为209g,闭孔温度105℃-115℃,破膜温度165℃-175℃,安全窗口温度可达60℃。
实施例2
本实施例提供一种锂电池用复合隔膜,其为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;
所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000-1000000、分子量分布指数Mw/Mn为4-8、等规度>96%、熔体流动速率为1.3-3.3;
低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000-300000、分子量分布指数Mw/Mn为4—8、熔体流动速率为0.2-0.8。
本实施例还提供上述的锂电池用复合隔膜的制备方法,包括如下步骤:
将聚丙烯树脂送入一台单螺杆挤出机内熔融塑化,塑化温度为190℃-220℃,得到的熔体通过计量泵从三层模头的两个表层挤出,得到两层聚丙烯树脂挤出物料;
将聚乙烯树脂送入另一台单螺杆挤出机内熔融塑化,塑化温度为190℃-220℃,得到的熔体通过计量泵从三层模头的芯层挤出,得到芯层聚乙烯树脂挤出物料;
两层聚丙烯树脂挤出物料和芯层聚乙烯树脂挤出物料在模头出口处汇合,牵引并不断冷却,得到PP/PE/PP复合厚片,厚片厚度50μm;整个过程中,模头的加热温度控制为200℃。
将PP/PE/PP复合厚片进行热处理,热处理的温度为105℃-115℃;然后在常温和高温下分别进行单向拉伸,常温下单向拉伸的拉伸倍率为15%,然后在拉伸温度120℃-130℃的高温下进行拉伸,拉伸倍率为125%;最后回缩定型,回缩定型的回缩比为-30%,回缩定型的温度为125℃-135℃,即得到锂电池用复合隔膜。
对得到的锂电池用复合隔膜进行测定,其中隔膜透气率和孔隙率的测试方法如下:
透气率:采用Gurley值表征隔膜的透气率。使用Gurley公司生产的4110型透气率测定仪,压力为20盎司,测试面积1.0平方英寸。记录100ml气体透过该测试面积所需的时间,即为Gurley透气度值。
总孔隙率:采用美国康塔公司的PoreMaster33型压汞仪测定隔膜的总孔隙率。
测定结果如下:。
锂电池用复合隔膜的厚度40μm,孔隙率为56%,微孔的孔径范围0.01μm-0.15μm,Gurley透气度值490s,纵向强度为185MPa,抗穿刺强度为312g,闭孔温度105℃-115℃,破膜温度165℃-175℃,安全窗口温度可达60℃。
实施例3
本实施例提供一种锂电池用复合隔膜,其为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;
所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000-1000000、分子量分布指数Mw/Mn为4-8、等规度>96%、熔体流动速率为1.3-3.3;
低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000-300000、分子量分布指数Mw/Mn为4—8、熔体流动速率为0.2-0.8。
本实施例还提供上述的锂电池用复合隔膜的制备方法,包括如下步骤:
将聚丙烯树脂送入一台单螺杆挤出机内熔融塑化,塑化温度为220℃-250℃,得到的熔体通过计量泵从三层模头的两个表层挤出,得到两层聚丙烯树脂挤出物料;
将聚乙烯树脂送入另一台单螺杆挤出机内熔融塑化,塑化温度为220℃-230℃,得到的熔体通过计量泵从三层模头的芯层挤出,得到芯层聚乙烯树脂挤出物料;
两层聚丙烯树脂挤出物料和芯层聚乙烯树脂挤出物料在模头出口处汇合,牵引并不断冷却,得到PP/PE/PP复合厚片,厚片厚度70μm;整个过程中,模头的加热温度控制为200℃。
将PP/PE/PP复合厚片进行热处理,热处理的温度为125℃-130℃;然后在常温和高温下分别进行单向拉伸,常温下单向拉伸的拉伸倍率为15%,然后在拉伸温度120℃-130℃的高温下进行拉伸,拉伸倍率为115%;最后回缩定型,回缩定型的回缩比为-35%,回缩定型的温度为125℃-135℃,即得到锂电池用复合隔膜。
对得到的锂电池用复合隔膜进行测定,其中隔膜透气率和孔隙率的测试方法如下:
透气率:采用Gurley值表征隔膜的透气率。使用Gurley公司生产的4110型透气率测定仪,压力为20盎司,测试面积1.0平方英寸。记录100ml气体透过该测试面积所需的时间,即为Gurley透气度值。
总孔隙率:采用美国康塔公司的PoreMaster33型压汞仪测定隔膜的总孔隙率。
测定结果如下:。
锂电池用复合隔膜的厚度60μm,孔隙率为42%,微孔的孔径范围0.01μm-0.15μm,Gurley透气度值580s,纵向强度为205MPa,抗穿刺强度为424g,闭孔温度105℃-115℃,破膜温度165℃-175℃,安全窗口温度可达60℃。
有上可见,本发明实施例的锂电池用复合隔膜具有较低的闭孔温度和较高的破膜温度,自关断安全窗口较宽,机械性能好,抗穿刺强度高,在锂离子电池的生产和使用过程中安全性能好。微孔孔径尺寸合适,分布均匀,贯通性好,电池的内阻小,有利于提高电池的工作效率。本发明实施例的锂电池用复合隔膜的制备方法采用三层共挤的方法铸片,再进行热处理和单向拉伸,大大提高了复合微孔膜的生产效率,在隔膜的工业化生产中具有极其重要的意义。
Claims (8)
1.一种锂电池用复合隔膜的制备方法,其特征在于,由所述制备方法制备而成的复合隔膜为三层结构,两侧表层为高强度聚丙烯微孔膜、芯层为低熔点自关断聚乙烯微孔膜;
所述高强度聚丙烯微孔膜的原料为聚丙烯树脂,其分子量为300000-1000000、分子量分布指数Mw/Mn为4—8、等规度>96%;
所述低熔点自关断聚乙烯微孔膜的原料为高密度聚乙烯,其分子量为100000—300000、分子量分布指数Mw/Mn为4—8;
所述制备方法采用三层共挤的方法铸片,并具体包括如下步骤:
将聚丙烯树脂熔融塑化,得到的熔体通过计量泵从三层模头的两个表层挤出,设置熔体流动速率为1.3—3.3,得到两层聚丙烯树脂挤出物料;
将聚乙烯树脂熔融塑化,得到的熔体通过计量泵从三层模头的芯层挤出,设置熔体流动速率为0.2—0.8,得到芯层聚乙烯树脂挤出物料;
两层聚丙烯树脂挤出物料和芯层聚乙烯树脂挤出物料在模头出口处汇合,牵引并不断冷却,得到PP/PE/PP复合厚片;
将PP/PE/PP复合厚片进行热处理,然后在常温和高温下分别进行单向拉伸,最后回缩定型,即得到厚度为30—60μm、总孔隙率为40%—60%、微孔尺寸为0.01μm—0.15μm的锂电池用复合隔膜。
2.根据权利要求1所述的制备方法,其特征在于,所述模头的加热温度控制为200℃。
3.根据权利要求1所述的制备方法,其特征在于,将聚丙烯树脂熔融塑化的塑化温度为190℃—250℃,将聚乙烯树脂熔融塑化的塑化温度为190℃—230℃。
4.根据权利要求1所述的制备方法,其特征在于,所述热处理的温度为105℃—130℃。
5.根据权利要求1所述的制备方法,其特征在于,常温下单向拉伸的拉伸倍率为10%—50%。
6.根据权利要求1所述的制备方法,其特征在于,高温下单向拉伸的拉伸倍率为80%—140%。
7.根据权利要求1所述的制备方法,其特征在于,所述高温是指拉伸温度为110℃—140℃。
8.根据权利要求1所述的制备方法,其特征在于,所述回缩定型的回缩比为-30%—-50%,回缩定型的温度为110℃—140℃。
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