【作者】 姜霞；

【导师】 杨秀康；

【作者基本信息】 湘潭大学 ， 化学， 2020， 硕士

【摘要】 富锂锰基正极材料是下一代锂离子电池最有前景的正极材料之一,由于其独特的阴/阳离子氧化还原电荷补偿机制,使材料具有超高容量(>250 m Ah g^-1),同时其具有工作电压窗口宽、环境友好和成本低廉等优点,引起了国内外研究者的高度关注。但是,要想加快富锂锰基正极材料的商业化进程,不得不克服材料本身固有的缺陷,例如:大的首次不可逆容量损失、衰减过快的电压平台、较差的循环性能和倍率性能等缺陷。本论文主要以改善富锂锰基正极材料的电化学性能为目标,通过对材料的元素组分调节、表面结构设计和表面处理等方法来展开一系列研究,主要研究内容如下:（1）基于过渡金属元素组分调节,通过水热法合成不同过渡金属元素比例的球形碳酸盐前驱体(Mn_0.60Ni_xCo_0.40-xCO₃),再进行高温锂化煅烧后形成相应的富锂锰基正极材料。采用多种测试手段来表征目标产物,分析不同过渡金属元素比例对材料的电化学性能的影响,为后续的改性研究打下了实验基础。（2）基于表面结构设计,通过水热-高温固相法合成了富锂锰基正极材料Li_1.40Mn_0.60Ni_0.20Co_0.20O_2.4,开发了一种能同时结合尖晶石相的形成、表面包覆和表面处理优点的方法对其进行改性,最后材料表面形成一种独特的异质结构（具有尖晶石@NPPy（萘磺酸掺杂的聚吡咯）壳层）。所有处理过后的材料的首次库伦效率都超过了90%。其中包覆量为3%时得到的材料电化学能最佳,在2.0～4.6 V,0.5 C电流密度下循环200次,容量保持率为89%,而原材料仅为69%,同时其电压衰退也明显得到抑制。此外,在10 C的大倍率下,该材料的放电比容量仍有165 m Ah g^-1,而原材料的放电比容量仅为141 m Ah g^-1。（3）基于表面处理调控材料表面的晶相结构,首先通过共沉淀-高温固相法制备粒径更大的富锂锰基正极材料(Li_1.40Mn_0.60Ni_0.35Co_0.05O_2+δ),再用0.1 mol L^-1的HNO₃溶液对其进行表面预处理,然后在不同温度下退火得到不同晶相结构的材料。该过程导致材料表面形成了不同类型的尖晶石结构且激活了Li₂Mn O₃组分,由于尖晶石相独有的三维Li⁺扩散通道可以提高Li⁺扩散速率,因此可以改善材料的倍率性能和减少首次不可逆容量损失。研究结果表明,在400℃下退火的材料,材料表面形成了Li₄Mn₅O₁₂尖晶石结构,具有最高的首次放电比容量和最好的倍率性能。更多还原

【Abstract】 The lithium-rich manganese-based cathode material is one of the most promising cathode materials for the next generation of lithium-ion batteries,because of its unique anion/cation redox charge compensation mechanism and an ultra-high capacity(>250 m Ah g^-1).At the same time,it has the advantages of wide operating voltage window,friendly environment and low cost,which have attracted the attention of the world.However,in order to accelerate the commercialization of lithium-rich manganese-based cathode materials,it is necessary to overcome the inherent defects of the materials.The main disadvantages include large first irreversible capacity loss,excessive voltage decay,poor cycle stability and poor rate performance.This dissertation mainly aims at improving the electrochemical performance of lithium-rich manganese-based cathode materials,and conducts a series of researches on the adjustment of element composition,surface structure design and surface treatment of materials.The main research contents are as follows:（1）Firstly,spherical carbonate precursor with different proportions of transition metal elements(Mn_0.60Ni_xCo_0.40-xCO₃)was synthesized by solvothermal method,and then the corresponding lithium-rich manganese-based cathode material is formed after calcining at high temperature.The target materials were characterized by various test methods and the influence of different transition metal elements ratios on the electrochemical performances of the materials was analyzed,laying an experimental basis for subsequent modification research.（2）A lithium-rich cathode material Li_1.40Mn_0.60Ni_0.20Co_0.20O_2.4 was prepared by the solvothermal method and subsequent high-temperature solid phase method.We put forward a significant strategy to combine the advantages of the formation of spinel phase,surface coating and surface treatment via a one-step route to enhance the electrochemical properties of materials.The results show that a unique heterostructure（with spinel@NPPy（naphthalene sulfonic acid-doped polypyrrole）shell）is formed on the surface of the material.The initial coulombic efficiency of all processed materials exceeded 90%.Among them,the material with NPPy coating content of 3%has the best performance,with 200 cycles at 2.0～4.6 V and 0.5 C current density,and the capacity retention rate is 89%,while the raw material is only 69%,and its voltage decay is also significantly suppressed.At the same time,at a large rate of 10 C,the discharge specific capacity of the material is still 165 m Ah g^-1,while the discharge specific capacity of the raw material is only 141 m Ah g^-1.（3）Based on the crystalline phase structure of the material surface,a lithium-rich manganese-based cathode material with a larger particle size(Li_1.40Mn_0.60Ni_0.35Co_0.05O₂₊δ)was first prepared by co-precipitation process and high temperature solid state method.Then,the surface of the material was pretreated with0.1 mol L^-1 HNO₃ solutions,and then the material structure was stabilized by annealing at different temperatures.This process results in the formation of different types of spinel structures on the surface of the material and the activation of Li₂Mn O₃component.Since the spinel structure has a unique 3D Li⁺diffusion channel,it can accelerate the Li⁺diffusion rate,thus increasing the rate performance and reducing the first irreversible capacity loss of the materials.The results show that Li₄Mn₅O₁₂spinel structure is formed on the surface of the annealed material at 400℃,which has the best rate performance and the highest first discharge specific capacity.更多还原