【作者】 韩建华；

【导师】 龚俊波； 汤伟伟；

【作者基本信息】 天津大学 ， 化学工程与技术， 2022， 硕士

【摘要】 氢氧化锂作为锂离子电池的基础锂盐材料,具有熔点低、反应活性强等优点,正逐渐取代传统碳酸锂成为正极材料的锂源,近年来其需求和价格逐步提升。然而,单水氢氧化锂产品存在着晶体表面粗糙、细晶偏多、晶习差等问题,导致产品的吸湿性和结块性强,不利于长时间储存。为解决以上问题,本文利用结晶过程与晶体工程学手段,开展了单水氢氧化锂介稳区与成核动力学、蒸发-冷却结晶工艺优化以及晶习调控过程中的添加剂作用机理研究,成功制备出了粒度均一、晶习完整、表面光滑的氢氧化锂单水合物块状晶体,改善了产品的吸湿性和结块性。首先,针对单水氢氧化锂产品粒度分布不均、细晶占比较多的问题,本文测定了蒸发-冷却结晶过程的介稳区,为结晶工艺优化提供数据基础。利用Nyvlt模型和修正Sangwal模型推导获得了氢氧化锂单水合物晶体的成核动力学参数。结果表明,随着饱和温度的升高,单水氢氧化锂的成核级数m、固液界面能?_sl均随之下降,这与随着温度升高而快速升高的溶解度有关。其次,针对单水氢氧化锂的晶体表面粗糙、晶习差导致产品易结块的问题,本文对蒸发-冷却结晶的工艺条件进行了优化,探究了晶种种类、母液组成、蒸发温度和蒸发速率等条件对晶体形貌的影响。结果表明,提高蒸发温度至90℃,增大蒸发速率为0.75 m L/min,可以在重结晶母液中得到纯度较高的块状晶体;此外,吸湿性实验表明,最优工艺条件下的产品质量增加值变为原来的1/4,结块问题得到了有效控制。最后,为了探究添加剂对单水氢氧化锂主要晶面的作用机理,本文筛选富羟基聚合物、富氧基聚合物和阴离子表面活性剂三类添加剂。结果表明,富氧基聚合物会抑制晶体生长,但因主要晶面暴露基团均为水和氢氧根离子,其对主要晶面的吸附未呈现出取向抑制效果;阴离子表面活性剂由于受不同晶面电负性差异的影响,对（0 1 1）和（0 1 1）晶面表现出选择性吸附,由于静电作用促进剂在晶面上局部富集了锂离子,呈现出生长促进效果。总之,针对单水氢氧化锂粒度分布不均、晶体形貌差的问题,本文利用结晶过程与晶体工程策略,改善了产品的粉体性质,并对添加剂的形貌调控机理进行了探究。更多还原

【Abstract】 As the basic lithium salt material of lithium-ion battery,lithium hydroxide has the advantages of low melting point and strong reaction activity.It is replacing the traditional lithium carbonate as the lithium source of cathode material step by step.In recent years,its demand and price have gradually increased.However,lithium hydroxide monohydrate products have some problems,such as rough crystal surface,more fine crystals,poor crystal habit and so on.Therefore,the product has strong moisture absorption and caking,which is not conducive to long-term storage.In order to solve the above problems,by means of crystallization process and crystal engineering,this paper carried out the research on the metastable zone and nucleation kinetics of lithium hydroxide monohydrate,the optimization of evaporative cooling crystallization process and the mechanism of additives in the process of crystal habit regulation.The lithium hydroxide monohydrate block crystals with uniform particle size,complete crystal habit and smooth surface were successfully prepared,which improved the moisture absorption and caking of the products.Firstly,aiming at the problems of uneven particle size distribution and large proportion of fine crystals of lithium hydroxide monohydrate,the metastable zone of evaporative cooling crystallization process is determined in this paper,which provides a data basis for the optimization of crystallization process.The nucleation kinetic parameters of lithium hydroxide monohydrate crystals were derived from Nyvlt model and modified Sangwal’s model.It is found that with the increase of saturation temperature,the nucleation order m and solid-liquid interface energy?_sldecrease,probably resulting from the rapidly increasing solubility with temperature.Secondly,aiming at the problem that the product is easy to agglomerate due to the rough crystal surface and poor crystal habit of lithium hydroxide monohydrate,the process conditions of evaporative cooling crystallization are optimized,and the effects of crystal seed type,mother liquor composition,evaporation temperature and evaporation rate on the crystal morphology are explored.It is found that by raising the evaporation temperature to 90℃and increasing the evaporation rate to 0.75 m L/min,high purity bulk crystals can be obtained in the recrystallization mother liquor;In addition,the moisture absorption experiment shows that the added value of product quality under the optimal process conditions becomes 1/4 of the original,and the caking problem is effectively controlled.Finally,aiming at exploring the mechanism of the additives on the main crystal faces of lithium hydroxide monohydrate,three kinds of additives including hydroxy-rich polymers,oxygen-rich polymers and anionic surfactants were screened in this paper.It is found that the oxygen-rich polymer can inhibit the crystal growth,but the adsorption effect on the main crystal faces does not show orientation inhibition because all the main exposed groups are water and hydroxide ions.Influenced by the electronegativity of different crystal faces,anionic surfactants show selective adsorption on（0 1 1）and（0 1 1）crystal faces.The accelerators locally accumulate lithium ions on crystal faces due to electrostatic action,showing growth promotion effect.In a word,aiming at the problems of uneven particle size distribution and poor crystal morphology of lithium hydroxide monohydrate,this paper uses the crystallization process and crystal engineering strategy to improve the powder properties of the product,and explores the morphology regulation mechanism of additives.更多还原