【作者】 张强；

【导师】 程新群；

【作者基本信息】 哈尔滨工业大学 ， 材料与化工（专业学位）， 2022， 硕士

【摘要】 新能源汽车具有低污染和低排放乃至零排放等优点,近年来得到迅速发展。而电池作为新能源汽车的动力关键,其续航能力和安全性能至关重要。现阶段市场主流纯电动汽车以及混合动力汽车均使用锂离子电池。TiNb₂O₇材料（TNO）作为一种高倍率型锂离子电池负极材料,十分契合动力电池的充放电需求,同时其五个氧化还原电对提供了优异的理论比容量,高的对锂电位提高了电池的安全性。但是其自身电子和离子导电性较差的问题限制了其进一步商业化的应用,因此本论文分别采用了氧化石墨复合和镨掺杂对多孔球形TNO材料进行了性能改善研究。首先利用多种工艺制备了不同形貌的纯相TNO,其中通过水热法制备的TNO前驱体在750℃下煅烧的材料具有优异的多孔球形结构,数十纳米的一次微粒组装而成的微米结构提供了更高的比表面面积,有利于电解液的均匀分散。之后探究了煅烧温度以及GO复合量对材料形貌以及电化学性能的影响,其中2%-GO-TNO-750由于复合后导电性的增强以及比表面积的进一步增大而展现了最佳的电化学性能。将其和锂金属组成扣式电池,容量相对纯相材料有一定提升,500周循环后容量保存率高达91.70%,并且在高倍率下也展现了优越性能。和镍钴锰811材料构成扣式全电池测试1-3 V性能,2%GO复合后的TNO材料在800周1-3 V循环后仍有70.2%的容量保存率,远优于纯相材料全电池。最后利用半电池和全电池研究了宽电压区间充放电行为,改性后的材料展现了远优于纯相材料的循环性能,同时根据全电池充放电曲线进一步验证了氧化石墨参与反应生成稳固的SEI膜。利用第一性原理的密度泛函理论计算了镨掺杂铌酸钛材料的能带结构和态密度等信息,得出了镨掺杂理论上会提高材料的本征导电性和晶面间距的结论,提供了镨掺杂改性的理论可行性。后续通过XRD精修,透射电子显微镜以及紫外等表征方式测定了晶面间距和带隙的变化,验证了理论计算的正确性。通过XPS以及电化学性能测试推测,以任意化学计量比值进行材料制备,镨离子总会进入铌位点,这和实际材料中钛铌混排以及两种离子半径相近有关。实验结果表明4%镨掺杂的两种材料性能最为优越,相对于纯相TNO-750材料容量有不同程度的提升,循环性能和倍率性能也得到改善,这是由于材料掺杂后本征导电性改善,半径较大的镨离子增大了晶胞体积,并有氧空位的产生,拓宽了锂离子传输通道,有利于嵌脱锂的快速进行。恒电流间歇滴定技术以及赝电容半定量分析进一步研究了材料的嵌脱锂特性,镨离子的掺杂使得材料的锂离子扩散系数提高了5～10倍,同时使材料的电容容量占比提高,这也说明了材料优异的高倍率性能的来源。通过和NCM811材料组装全电池测试实际循环性能,600周循环后4%镨掺杂材料比能量和保存率均有较大改善,说明了镨掺杂是一种实用的改性方法。更多还原

【Abstract】 New energy vehicles have the advantages of low pollution and low emissions or even zero emissions,and have developed rapidly in recent years.Battery is the key power for new energy vehicle,its life and safety performance are very important.At this stage,the mainstream battery of pure electric vehicles and hybrid vehicles in the market are lithium-ion batteries.As a high-rate lithium-ion battery anode material,Ti Nb₂O₇ material（TNO）is very suitable for the charging and discharging needs of power batteries.At the same time,its five redox pairs provide excellent theoretical specific capacity,and its high potential to lithium Improves battery safety.However,its existing poor electronic and ionic conductivity limit its further commercial application.Therefore,in this paper,graphite oxide composite and praseodymium doping are used to improve the performance of porous spherical TNO materials,respectively.First,a variety of morphological pure-phase TNO were synthesized in a variety of synthesis methods,and the TNO precursor prepared by the hydrothermal method was calcined at 750°C.Microstructures assembled from primary particles of tens of nanometers provide higher specific surface area,which is beneficial to the uniform dispersion of the electrolyte.The effects of calcination temperature and GO recombination amount on the morphology and electrochemical properties of the material were explored.Among them,2%-GO-TNO-750 exhibited the best electrochemical performance due to the enhanced conductivity and further increase of the specific surface area after recombination.Compared with pure-phase materials,the capacity of the button battery composed of lithium metal has a certain improvement.After 500 cycles,the capacity retention rate is as high as 91.70%,and it also shows superior performance at high rates.In addition,the coin-type full battery is formed with Ni-Co-Mn-811material to test the performance of 1-3 V.The TNO material after 2%GO composite still has a capacity retention rate of 70.2%after 800cycles of 1-3 V,which is much better than that of pure phase Material full battery.Finally,the half-cell and full-cell charge-discharge behaviors were studied in a wide voltage range.The modified material showed much better cycle performance than the pure-phase material.At the same time,according to the full-cell charge-discharge curve,it was further verified that graphite oxide participated in the reaction to generate stable SEI film.The energy band structure and density of states of praseodymium-doped titanium niobate materials were calculated by first-principles density functional theory.In conclusion,the theoretical feasibility of praseodymium doping is provided.Subsequently,the changes of interplanar spacing and band gap were measured by XRD refinement,transmission electron microscopy and ultraviolet characterization methods,which verified the correctness of the theoretical calculation.It is speculated through XPS and electrochemical performance tests that praseodymium ions will always enter the niobium site when the material is prepared at any stoichiometric ratio,which is related to the mixing of titanium and niobium in the actual material and the close radii of the two ions.The experiments show that the performance of the two materials doped with 4%praseodymium is the most superior.Compared with the pure phase TNO-750 material,the capacity is improved to varying degrees,and the cycle performance and rate performance are also improved.This is due to the intrinsic conductivity after the material is doped.The praseodymium ion with a larger radius increases the unit cell volume and generates oxygen vacancies,which widens the lithium ion transport channel and is beneficial to the intercalation and delithiation.Constant current intermittent titration technology and pseudocapacitance semi-quantitative analysis further study the intercalation and delithiation characteristics of the material.The doping of praseodymium ions increases the lithium ion diffusion coefficient of the material by 5-10 times,and at the same time increases the capacitance ratio of the material.The source of the material’s excellent high-rate performance is also illustrated.The actual cycle performance was tested by assembling a full battery with NCM811 material.After 600 cycles,the specific energy and retention rate of the 4%praseodymium doped material were greatly improved,indicating that praseodymium doping is a practical modification method.更多还原