【作者】 李娟娟；

【导师】 王朝阳； 赵大成；

【作者基本信息】 华南理工大学 ， 工程硕士（专业学位）， 2019， 硕士

【摘要】 硅的理论质量比容量为4200 mAh·g^-1,而且锂化/脱锂化电位低、在地壳中的储量丰富、安全性高,是下一代高能量密度锂离子电池最有应用前途的负极材料之一。粘结剂作为电池负极的重要组分之一,影响着电极的电化学性能。然而目前商业化的粘结剂还存在着粘结强度不够高、制备的电极能量密度低、循环稳定性和循环寿命不理想的问题,因此本文基于聚丙烯酸（PAA）设计了两种新型水性粘结剂,以改善锂离子电池的电化学性能,主要工作内容如下:（1）基于商业化的PAA与含双重酰胺键的甘氨酰胺的一步偶合反应合成了力学性能优异、具有自愈合性能的聚合物粘结剂（PAA-GA）,然后研究了PAA和PAA-GA两种粘结剂的理化性能和电化学性能。溶胀和流变测试表明PAA-GA在电解液中的溶胀率仅为4.52%,且PAA-GA具有自愈合性能。剥离和纳米压痕测试表明Si/PAA-GA电极的平均粘结力大小为1.3N,力学性能比Si/PAA电极更优异。电化学测试表明Si/PAA-GA电极具有显著提高的可逆比容量和循环稳定性,0.2C的电流密度下循环285圈后,可逆比容量为2597 mAh·g^-1,容量保持率为81.0%,甚至在5C的大电流密度下,仍有约991mAh·g^-1的质量比容量。Si/PAA-GA电极中引入了双重氢键,有利于维持电极结构的稳定性,缓解硅材料的体积膨胀,提高电极的可逆比容量,改善电池的长循环稳定性。（2）将商业化的无污染、成膜性和柔韧性好、粘结力强的水性聚氨酯（PU）与PAA-GA进行复配得到力学性能优异、韧性增强的复配粘结剂,然后研究了PAA,PAA-GA和复配粘结剂的理化性能和电化学性能。复合质量比为PU:PAA-GA=0.5:9.5(PU_0.5（PAA-GA）_9.5)。剥离测试表明Si/PU_0.5（PAA-GA）_9.5电极的平均粘结力大小约为0.35N·mm^-1,粘结强度最大。溶胀测试表明PU_0.5（PAA-GA）_9.5在电解液中的溶胀率为12.55%,略高于PAA-GA,显著低于PAA。纳米压痕测试表明Si/PU_0.5（PAA-GA）_9.5电极具有最大的硬度和弹性模量值,力学性能更优异。电化学测试表明,Si/PU_0.5（PAA-GA）_9.5电极的首次库伦效率为84.5%,高于Si/PAA和Si/PAA-GA电极,0.5C的电流密度下循环500圈后比容量仍有1699 mAh·g^-1,容量保持率为61.2%。PU具有高弹性和高拉伸性能,可以有效适应硅材料的体积膨胀,说明粘结剂具有适当的韧性可改善电池的电化学性能。更多还原

【Abstract】 As its high theoretical mass specific capacity of 4200 mAh·g^-1,low lithiation/delithiation potential,abundant in earth and safe,silicon is one of the most promising anode materials for next generation high energy density lithium-ion batteries.Binder,as one of the important components of the negative electrode of battery,affects the electrochemical performance of the electrode.There are still some problems in commercial binders,such as weak bonding strength,low energy density,and unsatisfactory cycle stability and cycle life.Therefore,we have designed two new water-soluble polyacrylic acid（PAA）based binders to improve the electrochemical performance of lithium-ion batteries.The main contents are as follows:（1）Polymer binder（PAA-GA）with excellent mechanical and self-healing properties was synthesized by a one-step coupling method of commercial PAA with glycinamide,which contains double amide bonds.The physical and chemical properties and electrochemical properties of PAA and PAA-GA binders were investigated.The swelling and rheological tests showed that the swelling ratio of PAA-GA in electrolyte was only 4.52%,and PAA-GA was self-healing.The 180^o peeling tests and nano-indentation tests illustrated that the average bonding strength of Si/PAA-GA electrode was 1.3N,and its mechanical properties were better than Si/PAA electrode.The electrochemical tests showed that the reversible specific capacity and cycle stability of Si/PAA-GA electrode were significantly improved.The reversible specific capacity of Si/PAA-GA electrode was 2597 mAh·g^-1 and the capacity retention was81.0%after 285 cycles at a current density of 0.2C.Notably,the mass specific capacity was around 991 mAh·g^-1 even at a high current density of 5C.It demonstrates that double hydrogen bonds in the PAA-GA are beneficial to maintain the stability of the electrode structure,alleviate the volume expansion of silicon particles,increase the reversible specific capacity of the electrode,and improve the long-term cycle stability of lithium-ion batteries.（2）The commercial waterborne polyurethane（PU）with non-pollution,good film-forming and toughness,and strong adhesion was blended with PAA-GA to obtain a binder with excellent mechanical properties and toughness.The physical and chemical properties and electrochemical properties of PAA,PAA-GA and complex binder were studied.The mass ratio of PU versus PAA-GA was 0.5:9.5(PU_0.5（PAA-GA）_9.5).The 180^o peeling tests showed that the average bonding force of Si/PU_0.5（PAA-GA）_9.5 electrode was about 0.35N·mm^-1,and the bonding strength was the highest.The swelling tests demonstrated that the swelling ratio of PU_0.5（PAA-GA）_9.5 in electrolyte was 12.55%,which slightly higher than PAA-GA and significantly lower than PAA.Nano-indentation tests showed that Si/PU_0.5（PAA-GA）_9.5 electrode had the highest hardness and elastic modulus values,indicting better mechanical properties.The electrochemical tests showed that the initial coulombic efficiency of Si/PU_0.5（PAA-GA）_9.5 electrode was 84.5%,which was higher than Si/PAA and Si/PAA-GA electrodes.The specific capacity was still 1699 mAh·g^-1 and the capacity retention was 61.2%at a current density of 0.5C after 500 cycles.PU has high elasticity and high tensile properties,which can effectively adapt to the volume expansion of silicon particles,illustrating that proper toughness of binder can promote the electrochemical performance of lithium-ion batteries.更多还原