CN116632244A - 负极浆料及制备方法、负极片和锂离子电池 - Google Patents
负极浆料及制备方法、负极片和锂离子电池 Download PDFInfo
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Classifications
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Abstract
本发明属于锂电池领域,具体涉及一种负极浆料及制备方法、负极片和锂离子电池。所述负极浆料包括负极浆料添加剂,其结构如式(I)示出;其中,M为氢、锂、钠或钾中的至少一种;4≤n≤14,且为整数。本发明提供的负极浆料制备的原位高浸润负极片,制备工艺简单,既不影响电解液电导率,也无需进行前期预处理,同时避免负极片的高度溶胀带来的电池鼓包风险,还可一定程度防止涂布过程中负极片开裂,并且具有高粘结力和高电导率特性,能够提升电池的倍率性能,具有良好的应用前景。
Description
技术领域
本发明属于锂电池领域,具体涉及一种负极浆料及制备方法、负极片和锂离子电池。
背景技术
近年来,在政策的大力支持下,锂离子电池进入了新的战略发展关键期。随着涂覆量和压实的进一步提升,电解液对极片的快速浸润成为重要挑战。负极界面的浸润性是否良好影响着SEI膜的形成好坏,负极片浸润不良导致界面处传质阻抗增加,去溶剂化过程缓慢,锂离子嵌入负极的动力学行为受限,由此在界面诱发锂盐沉积,劣化负极界面状态。久而久之,随着充放电进行,浸润性不良导致负极界面电解液副反应加剧,SEI膜持续增厚,阻碍锂离子传输,最终恶化倍率性能,影响容量发挥,导致循环跳水。
此外,涂布烘干过程中由于负极片的高表面张力导致极片开裂,造成极片电阻增大,同样会恶化倍率和循环性能。此外,改善极片开裂及粘结力差的传统方法是增加极片中的粘结剂用量,但是这种方法不可避免地会造成极片电阻增加,最终导致电池的倍率性能下降,电性能变差。
因此,寻找一种能够原位改善负极界面浸润性,保证极片粘结力,防止极片开裂,同时能够不影响极片电阻及电池倍率性能的方法,对于提升锂离子电池综合电性能至关重要。
现阶段,改善负极片对电解液浸润性的手段主要有在电解液配方中引入浸润剂和在负极匀浆过程中加入添加剂。CN114583276A公开了一种高浸润电解液配方,所选浸润剂为乙烯基三(2,2,2-三氟)乙氧基硅烷,改善了电解液对极片的浸润性,但此种浸润剂的加入量稍多就会影响电解液的电导率,加入量过少则对浸润性改善无效。CN112500542A公开了一种用于负极片的苯丙共聚物-b-PEO-b-苯丙共聚物嵌段共聚物的水溶***联物添加剂,依靠聚合物中的网络结构和亲水基团改善了负极片与电解液的亲和性,提升了负极片的保液性,但此种聚合物制备工艺复杂,且交联物吸液后溶胀,增加了负极片在循环后期膨胀以及电池鼓包风险。CN114388792A公开了一种用于负极片的丙烯酸类树脂及其衍生物添加剂,在制备负极浆料时可形成阴离子高分子乳液,利用粒子胶膜在电解液中发生高度溶胀,从而增加负极片的浸润性,此种树脂类添加剂虽免去制备工艺,但吸液后的高度溶胀仍会加剧电池鼓包风险,劣化后期循环性能。
发明内容
本发明的目的在于克服现有技术中的缺点,提供一种负极浆料及制备方法、负极片和锂离子电池。
为实现上述目的,本发明采用的技术方案为:
一种负极浆料添加剂,结构如式(I)示出;
其中,M为氢、锂、钠或钾中的至少一种;4≤n≤14,且为整数。
优选的,结构如式(I I)示出;
本发明还包括一种负极浆料,包括所述的负极浆料添加剂;所述负极浆料添加剂为负极浆料制备材料的总干重的0.05%-0.2%,优选为0.1%-0.15%,更优选为0.15%。
负极浆料制备材料包括负极活性主料、导电剂、粘结剂以及负极浆料添加剂;以负极浆料制备材料的总干重为100%计,负极活性主料的干重占93%-98%,所述导电剂的干重占0.5%-5%,所述粘结剂的干重占0.5%-3%。
所述负极活性主料为碳材料,包括天然石墨、人造石墨、中间相碳微球、硬碳和软碳等中的至少一种。
所述导电剂为Super-P、ECP、CNT、石墨烯和乙炔黑等中的至少一种。
所述粘结剂包括丁苯橡胶、羧甲基纤维素钠、海藻酸钠和聚丙烯酸中的至少一种。
本发明还包括一种所述的负极浆料的制备方法,包括下述步骤:
(1)将负极活性主料与导电剂按照组分量进行混合;
(2)在(1)得到的混合浆料中加入粘结剂,加溶剂后充分搅拌,进行第一次固含量调试;
(3)在(2)得到的混合浆料中再次加入粘结剂,加溶剂后充分搅拌,进行第二次固含量调试;
(4)在(3)得到的混合浆料中再次加入粘结剂,加溶剂后充分搅拌,进行第三次固含量调试;
之后,调控溶剂的加入量,直至浆料粘度达到要求;
所述负极浆料添加剂在(2)、(3)、(4)中任意一步或多步分别加入。
优选的,最终浆料固含量在40%-60%,粘度在3000±200cp。
本发明还包括一种锂离子电池,包括负极片;所述的负极片采用所述的负极浆料涂覆到负极集流体表面得到。
与现有技术相比,本发明的有益效果是:
本发明所述阴离子型聚合物添加剂,具有以下优点:1)C-F键的键能较大,具有较强的电化学稳定性,电池充放电过程中不会发生额外副反应;2)依靠全氟碳链的疏水作用和羧基基团的亲水性,协同改善匀浆时浆料状态,有助于获得原位高浸润负极片;3)羧基基团可与CMC分子之间产生氢键相互作用力,同时氟碳链可与SBR分子的丁二烯共轭链相互缠绕,因此匀浆时可稳定悬浮于混合浆料中,在不增加整体粘结剂用量的情况下,提升负极片的粘结力,避免由于SBR和CMC的增加对电池倍率性能的损害;4)羰基氧原子的孤对电子云,可以促进锂离子迁移,提升极片电导率,进而改善倍率性能;5)在极低添加量下,即可显著减少相间界面张力,缓解涂布时负极片开裂现象。
本发明提供的原位高浸润负极片,制备工艺简单,既不影响电解液电导率,也无需进行前期预处理,同时避免负极片的高度溶胀带来的电池鼓包风险,还可一定程度防止涂布过程中负极片开裂,并且具有高粘结力和高电导率特性,进而提升电池的倍率性能,具有良好的应用前景。
附图说明
图1为本发明实施例以及对比例的恒流充入比图;
图2为本发明实施例以及对比例的循环性能测试图。
具体实施方式
为了使本技术领域的技术人员更好地理解本发明的技术方案,下面结合实施例对本发明作进一步的详细说明,需要说明的是,本申请中的百分含量,如无特殊说明均为质量百分含量。
本申请中所用负极浆料添加剂为阴离子型聚合物添加剂,如无特殊说明,均为式(II)示出,分子式为C7HF13O2;
实施例1
负极片及锂离子电池的制作,步骤如下:
(1)准备负极片制备材料,人造石墨、导电炭黑Super P、羧甲基纤维素CMC和丁苯橡胶SBR的干重比(wt%)为96.3:1.0:1.2:1.5。
(2)制备CMC胶液,其中,CMC固含量为1.5%,溶剂为去离子水。
(3)将人造石墨和Super P按照设定比例进行投料混合,低速搅拌后加入60%(占CMC胶液总投料量的质量分数)CMC胶液和去离子水,充分混合后,进行第一次固含量调试。
(4)向上述混合浆料中再次加入20%CMC胶液和去离子水,加入负极片制备材料总干重0.05%的阴离子型聚合物添加剂充分搅拌后,进行第二次固含量调试。
(5)向(4)得到的混合浆料中再次加入20%CMC胶液和去离子水,混合充分后,进行第三次固含量调试;之后,通过调控去离子水的加入量,调节浆料粘度至3000cp;再次向得到的混合浆料中加入SBR,最终浆料固含量在50%(可以根据需要在40%-60%之间);低速搅拌后,抽真空,过100目筛出料。
(6)将所得负极浆料涂布在负极集流体表面,经碾压制片后,与磷酸铁锂正极片和隔膜一起装配,注液化成后得到锂离子电池。
本申请同样对于不同的负极浆料添加剂(结构如式(I)示出,结构式为CF3(CF2)nCOOM)进行测试;
M为氢、锂、钠或钾;4≤n≤14的化合物,例如,n为4、8、10、12进行了测试,由于其均含有阴离子羧基改善电解液的亲和性,且含有不同聚合度的氟化物的疏水作用,因此,均能在不同程度上改善浆料状态,从而获得原位高浸润负极片,而其中尤以式(II)化合物效果为佳,因此,以其作为优选实施例进行示例性说明。
实施例2
与实施例1的区别仅在于步骤(4)中加入0.1%阴离子型聚合物添加剂。
实施例3
与实施例1的区别仅在于步骤(4)中加入0.15%阴离子型聚合物添加剂。
实施例4
与实施例1的区别仅在于步骤(4)中加入0.2%阴离子型聚合物添加剂。
对比例1
与实施例1的区别仅在于步骤(4)中未加入阴离子型聚合物添加剂。
对比例2
与对比例1的区别仅在于步骤(4)中加入式(III)所示全氟碳链化合物。
观察对比例1-2和实施例1-4的浆料和所制备负极片表面状态,测试浆料表面张力和负极片的浸润性、粘结力,对所制备的锂离子电池进行电性能测试。
(1)吸液率测试
将制备的负极片用取样器制备成直径3cm的小圆片,称重,记为m0。然后,将圆片置于电解液中4h,取出后再次称重,记为m1,吸液率(%)表示为(m1-m0)/m0。
(2)电性能测试
倍率充电性能:分别以0.2C,0.5C,1.0C和2.0C恒流充电至3.65V后,恒压充电至0.05C,均1C放电至2.5V。
45℃循环性能:采用1C/1C的充放电循环制式,电压范围为2.5V-3.65V。
对比例1-2和实施例1-4中浆料状态、极片表面状态和浆料表面张力测试结果如表1所示,极片粘结力、接触角和吸液率测试结果如表2所示,电性能测试结果如表3所示。
表1
从表1看出,对比例2的浆料出现团聚现象,极片表面有大颗粒,其余对比例和各实施例的浆料流动性均较好,极片表面较为平整,说明式(III)化合物由于C-F键的疏水作用,导致匀浆时分散性较差,浆料发生团聚,涂布后极片呈现大颗粒。然而阴离子型聚合物添加剂由于亲水性羧基基团的存在,可以完美匹配负极浆料体系。同时,对比例1和2的极片表面微裂,浆料表面张力较大,而各实施例极片表面均未开裂,浆料表面张力较小,说明阴离子型聚合物添加剂引入负极浆料可以显著降低相间界面张力,减少涂布时极片开裂现象。
表2
从表2看出,各实施例的极片粘结力均较大,而对比例均较小,其中对比例2的粘结力最小,说明阴离子型聚合物添加剂凭借羧基基团与CMC之间的氢键相互作用力,以及氟碳链与SBR丁二烯共轭链的相互缠绕,可以保证负极片的强粘结力。而式(III)化合物由于缺少羧基间的氢键相互作用力以及匀浆时与负极浆料体系的排斥,导致对比例(2)的粘结力没有优势。此外,采用商业化电解液测试不同方案负极片的接触角,结果表明,各对比例的接触角较大,吸液率较小,各实施例的接触角较小,吸液率较大,说明阴离子型聚合物添加剂由于亲水性羧基基团的存在,可以明显改善极片对电解液的亲和性,其中实施例3的接触角最小,仅有11.32°,吸液率最大,达到了28.87%,表明阴离子型聚合物添加剂的最佳添加量为0.15%,在此最佳添加量下,极片的浸润程度改善最好,最有利于电解液润湿极片。
表3
图1为本发明实施例以及对比例的恒流充入比图;图2为本发明实施例以及对比例的循环性能测试图。从表3、图1和图2看出,相比于各个实施例,对比例在不同充电倍率下的恒流充入比均较小,且45℃循环1000圈的容量保持率均较低。然而,实施例3在不同充电倍率下的恒流充入比均最大,特别是在2C充电倍率下的恒流充入比已达到98.23%,高出对比例1已有0.48%。此外,实施例3在45℃下循环的容量保持率达到88.5%,高出对比例1已有1.1%。综上,说明阴离子型聚合物添加剂由于羰基氧原子孤对电子云的存在,提升了极片电导率,促进了锂离子迁移,同时得益于全氟碳链的疏水作用和羧基基团的亲水性,改善了极片对电解液的亲和性,因此表现出最佳的倍率性能和高温循环性能。
同样的,对于不同的负极浆料制备材料例如,负极活性主料为碳材料,包括天然石墨、人造石墨、中间相碳微球、硬碳和软碳;导电剂为Super-P、ECP、CNT、石墨烯和乙炔黑等,粘结剂为丁苯橡胶、羧甲基纤维素钠、海藻酸钠、聚丙烯酸等,并调配了不同比例的各物质,即在以负极浆料制备材料的总干重为100%计,负极活性主料的干重占93%、95.8%或98%,所述导电剂的干重占0.5%、2.7%、3%或5%,所述粘结剂的干重占0.5%、1.5%、2.6%或3%进行调整后发现,与相对应的对比例1、2即分别不添加阴离子型聚合物添加剂、以及添加式(III)的化合物相比,其均能不同程度的改善与电解液的浸润程度,从而最终改善电池的性能,在此,不在一一赘述。
本发明提供的原位高浸润负极片,制备工艺简单,既不影响电解液电导率,也无需进行前期预处理,同时避免负极片的高度溶胀带来的电池鼓包风险,还可一定程度防止涂布过程中负极片开裂,并且具有高粘结力和高电导率特性,进而提升电池的倍率性能,具有良好的应用前景。
以上所述仅是本发明的优选实施方式,应当指出,对于本技术领域的普通技术人员来说,在不脱离本发明原理的前提下,还可以做出若干改进和润饰,这些改进和润饰也应视为本发明的保护范围。
Claims (10)
1.一种负极浆料,其特征在于,所述负极浆料包括负极浆料添加剂,负极浆料添加剂的结构式如式(I)示出;
其中,M为氢、锂、钠或钾中的至少一种;4≤n≤14,且为整数。
2.根据权利要求1所述的负极浆料,其特征在于,所述负极浆料添加剂的结构式如式(II)示出;
3.根据权利要求1或2所述的负极浆料,其特征在于,所述负极浆料添加剂为负极浆料制备材料的总干重的0.05%-0.2%,优选为0.1%-0.15%,更优选为0.15%。
4.根据权利要求1-3之一所述的负极浆料,其特征在于,负极浆料制备材料包括负极活性主料、导电剂、粘结剂以及负极浆料添加剂;以负极浆料制备材料的总干重为100%计,负极活性主料的干重占93%-98%,所述导电剂的干重占0.5%-5%,所述粘结剂的干重占0.5%-3%。
5.根据权利要求1-4之一所述的负极浆料,其特征在于,所述负极活性主料为碳材料,包括天然石墨、人造石墨、中间相碳微球、硬碳和软碳中的至少一种。
6.根据权利要求1-5之一所述的负极浆料,其特征在于,所述导电剂为Super-P、ECP、CNT、石墨烯和乙炔黑中的至少一种。
优选的,所述粘结剂包括丁苯橡胶、羧甲基纤维素钠、海藻酸钠和聚丙烯酸中的至少一种。
7.一种权利要求1-6之一所述的负极浆料的制备方法,其特征在于,包括下述步骤:
(1)将负极活性主料与导电剂按照组分量进行混合;
(2)在(1)得到的混合浆料中加入部分粘结剂,加溶剂后充分搅拌,进行第一次固含量调试;
(3)在(2)得到的混合浆料中加入部分粘结剂,加溶剂后充分搅拌,进行第二次固含量调试;
(4)在(3)得到的混合浆料中加入剩余粘结剂,加溶剂后充分搅拌,进行第三次固含量调试;
之后,调控溶剂的加入量,直至浆料粘度达到要求;
所述负极浆料添加剂在(2)、(3)、(4)中任意一步或多步分别加入。
8.一种权利要求7所述的负极浆料的制备方法,其特征在于,最终浆料固含量在40%-60%,粘度在3000±200cp。
9.一种负极片,其特征在于,所述负极片包括负极集流体和负极活性材料层,所述负极活性材料层采用权利要求1-6之一所述的负极浆料制备得到。
10.一种锂离子电池,其特征在于,包括权利要求9所述的负极片。
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