【作者】 周昊；

【导师】 张治安； 汤依伟；

【作者基本信息】 中南大学 ， 工程（专业学位）， 2022， 硕士

【摘要】 在商业锂离子电池的实际生产制造的过程当中,电池的水分含量是我们应该十分注意并且严格管控的一个关键因素。但是,目前关于水分含量对电池性能的影响规律以及作用机制尚不清晰,有效筛分不同水分含量电池仍是一个难点,特别是针对小微电池这种现如今应用极其广泛的锂离子电池类型。为了解决以上这些问题,本论文以广东微电新能源有限公司所提供的M1254型号小微电池为研究对象,围绕着电池的水分含量开展一系列的研究工作,系统地建立关键工艺参数-电池水分含量-成品电池性能三者之间的关系,并且全面探索电池水分含量对电池性能的影响机制,在此基础之上,加速表征电池水分含量给电池性能带来的影响,本论文的主要结论如下:(1)电池中的水分主要都集中在负极片上,正极片上的水分含量只占到电池整体水分含量的5%-10%左右。烘烤这一工序是能够较为经济且有效地对电芯的水分含量进行调控的,随着烘烤时间的延长,电芯的水分含量逐渐降低,烘烤效率逐渐降低,并且目前产线上烘烤这一工序所采用的温度85℃、真空度-95 kpa、烘烤时间24 h这一组工艺参数,是可以极其有效地将电芯负极片上的水分含量降低到200ppm以下的。电池水分含量对电池性能的影响可以分成两个部分来看,以负极片上水分含量250 ppm左右为分界点,当电池的水分含量较高的时候,电池水分含量的升高所造成的电池各种性能的劣化十分的剧烈以及明显,容量衰减到60 m Ah以下,内阻增加到300 mΩ以上,常温下随着存储时间延长容量以及内阻不断恶化,但是当电池的水分含量较低的时候,电池的各种性能随着电池的水分含量的变化并不显著,容量稳定在60 m Ah以上,内阻稳定在300 mΩ以下,常温下60 d内存储性能表现良好。(2)当电池的水分含量较高的时候,在电池的负极表面上所形成的SEI膜会更加的厚实,水分含量升高之后,首次库伦效率由91.84%下降到89.31%。并且这一层更加厚实的SEI膜相对来说不够稳定,在循环的过程中会经历一个更为严重的腐蚀-再生成-再腐蚀的过程,水分含量升高之后,以2 C的倍率循环350圈之后的容量保持率由89.89%下降至81.81%。以上两个方面均会消耗更多的活性Li~+,造成容量方面的损失变得更大更快。(3)利用化成曲线在其走势上的不同之处,能够实现对水分含量差异在100 ppm以上的电池进行后端筛分的目的,但是,在水分含量较低的区间之内,对于水分含量比较接近的电池,化成曲线的筛分效果将会大打折扣甚至会出现无法进行有效筛分的情况。通过调整倍率这一因子能够对电池进行更为精细的后端筛分工作,倍率越高,筛分效果越好,越容易将水分含量比较接近的电池筛分开来,一般来说,将倍率提高到3 C左右便能够将水分含量差异在100 ppm以下的电池筛分开来,此外,提高温度会使得利用倍率来进行后端筛分的效果受到一定程度上的抑制。但是单纯提高温度可以加速电池的水分含量对SEI膜的影响,最终达到加速水分含量对电池性能的影响的目的。在容量方面,可以通过提高循环时的电压下限来缩短循环耗时,从而达到快速测试的目的,节约时间成本,在条件允许的情况之下,还可以通过温度的提高对电压区间的加速作用进行一个积极正向的修正。图38幅,表8个,参考文献87篇。更多还原

【Abstract】 In the actual manufacturing process of commercial lithium-ion batteries,the water content of batteries is a key factor that we should pay much attention to and strictly control.However,at present,the research on the relationship between the water content and the performance of batteries is no systematic,the research on the influence mechanism of the water content on the performance of batteries is not comprehensive,and it is still difficult to screen batteries with different water content effectively,especially about micro lithium-ion batteries which are now widely used.In order to solve the problems above,the paper takes the M1254 micro battery provided by Guangdong Micro-power New Energy Co.,Ltd as the research project,and carries out a series of experiments about the water content of batteries.On the one hand,we systematically establish the relationship about the key process parameters-the water content of batteries-the performance of finished batteries.On the other hand,we comprehensively explored the influence mechanism of the water content of batteries on the performance of batteries.On this basis,the influence of the water content of batteries on the performance of batteries is accelerated.The main conclusions of the paper are as follows:(1)The water content of batteries is mainly concentrated on anodes,and the water content of cathodes only accounts for 5%-10%of the overall water content of batteries.Baking is a key process which can regulate the water content of cells economically and effectively.With the extension of the baking time,the water content of cells is gradually reduced,and the baking efficiency is also gradually reduced.When baked at 85℃and-95 kpa for 24 h,the water content in anodes of batteries can be reduced to below 200 ppm effectively.It is worth mentioning that the influence of the water content of batteries on the performance of batteries can be divided into two parts,taking the water content of the anode at about 250 ppm as a cut-off point.When the water content of batteries is high,the degradation of the performance of batteries caused by the increase of the water content of batteries is very sharp and clear.The capacity is less than 60 m Ah,the impedance is more than 300 mΩ,and both the capacity and the impedance will become worse with the storage time extension at 25℃.But when the water content of batteries is low,the change of the performance of batteries is less significant with the variation of the water content of batteries.The capacity is more than 60m Ah,the impedance is less than 300 mΩ,and the storage performance is well within 60 days at 25℃.(2)When the water content of batteries is high,the SEI film,which forms on the surface of the anode of batteries,is more compact and thick.When the water content increases,the initial coulombic efficiencies is reduced from 91.84%to 89.31%.It is also not stable enough at the same time,and will go through a more serious process of decomposition-generation-decomposition during cycling.When the water content increases,the capacity retention is reduced from 89.89%to81.81%after 350 cycles at 2 C.Both of the two aspects above will consume more active Li~+,and make the loss of the capacity larger and faster.(3)The difference of the activation curves can be used to filtrate batteries whose water content difference is more than 100 ppm in the back-end.However,in the range of low water content,the filtration effect will greatly reduced or it is even impossible to carry out the filtration for batteries with similar water content.It can filtrate batteries more accurately in the back-end by adjusting the rate.The larger the rate is,the better the filtration effect is.And it is easier to filtrate batteries with similar water content.In general,batteries whose water content difference is less than 100 ppm can be screened when the rate is rised to about 3 C.In addition,the filtration effect of the rate in the back-end will be inhibited in a certain degree when the temperature increases.But the simple increase of the temperature can accelerate the influence of the water content of batteries on the SEI film,and finally accelerate the influence of the water content on the performance of batteries.In term of the capacity,the cycling time can be shortened by increasing the lower limit of the voltage.It can achieve the purpose of the rapid test,and save the time cost at the same time.Under certain circumstances,the acceleration effect of the voltage range can be corrected by increasing the temperature.There are 38 figures,8 tables and 87 references.更多还原