作为一种绿色清洁能源，锂离子电池已经成为人们日常工作生活中必不可少的组成部分。电动汽车、智能电网等新的应用领域亟需具有更高能量密度、功率密度以及安全性的下一代锂离子电池。锂离子电池的电化学性能很大程度上取决于电极材料，因此对电极材料的设计与改性尤为重要。商用锂离子电池最常用的负极材料是石墨，具有资源丰富、价格低廉等优点，但倍率性能难以提升。另外，石墨低的电压窗口会引起锂枝晶的生长，从而造成很大的安全隐患。寻找更好的替代材料成为当今锂离子电池研究的一个热点。TiO₂具有更高的氧化还原电位，因此可以有效防止锂沉积，有望成为更安全的负极材料；TiO₂在充放电过程中体积膨胀小(4％)，具有优异的结构稳定性，这使得TiO₂能够与合金化型或者转换反应型负极材料功能复合进而提高比容量。作为负极材料使用时，TiO₂的主要缺点是其电子导电率差(10⁻⁹s ㎝⁻¹)、锂离子扩散系数低(10⁻¹¹-10⁻¹³ ㎝² s⁻¹)，造成可逆比容量和倍率性能的衰减。这些问题阻碍了其在锂离子电池中的实际应用。TiO₂的理论比容量(340 mAh g⁻¹)较低，也不利于锂离子电池能量密度的进一步提升。 针对上述TiO₂负极材料应用存在的问题，本文首先通过(还原、预锂化)表面改性获得黑色氧化钛材料，提高本征电子导电率和锂离子扩散系数；进一步地，通过功能复合改性(SnO₂，NiO)提高比容量。主要研究内容和结果如下： (1)提出可控镁还原法制备黑色氧化钛，通过还原提高黑色氧化钛的本征电子导电率，改善其用于锂离子电池负极材料的循环稳定性。首先，系统研究了不同金属对TiO₂的还原特性，优选金属Mg作为可控还原制备黑色氧化钛的还原剂。其次，选取金红石和锐钛矿相TiO₂探究初始TiO₂材料的物相对制备黑色氧化钛的影响，对比发现在相同还原条件下，纳米金红石相比锐钛矿相更容易发生表面还原。研究表明。通过镁还原能够调控样品的颜色、光吸收、Ti³浓度和导电率，其中锐钛矿相样品(A-3)具有最高的导电率(236.3 μS ㎝⁻¹)。用作锂离子电池负极材料，A-3表现出较好循环稳定性，1 C经过100个循环后，保持180 mA h g⁻¹的比容量； (2)合理设计并制备表面具有快速离子传导层的介孔黑色氧化钛，改善电极材料-电解液界面处离子传导，实现优异的倍率性能。通过熔盐辅助预锂化处理，获得具有富锂表面层的介孔结构黑色氧化钛。具有开放结构的富锂表面层具有较高的锂离子迁移率，锂离子扩散活化能较低。通过调控反应温度平衡样品的电子传导和离子传导。优化后的Li-TiO₂-300样品具有高电子导电率(198.2μS㎝⁻¹)和高比表面积(259 ㎝² g⁻¹)，用于锂离子电池负极材料，实现了高的锂离子扩散系数和优异的倍率性能(50 C，114 mAh g⁻¹；100 C，93 mA h g⁻¹)。进一步的动力学分析发现，电化学反应过程中赝电容对比容量的贡献随电流密度的增大而增大。 (3)基于功能复合的材料成分与结构调控思路制备黑色金红石型(Sn，Ti)O₂，其中SnO₂贡献高比容量，TiO₂提供结构支撑，结合还原工艺提高样品的电子导电率，实现较高的比容量和较好的倍率性能。通过共沉淀法结合氢-等离子体还原制备具有核壳结构的黑色(Sn，Ti)O₂，其导电率为35.7μS ㎝⁻¹。表面导电非晶层作为电子快速传输通道促进各向同性的电化学反应。固溶体结构使得Sn和Ti实现原子级的分散，锂化后Li〓TiO₂不仅作为离子传输通道还对Sn产生空间限域作用，保持结构稳定。对循环测试后样品的微观结构研究发现，即使在100个循环后，黑色(Sn，Ti)O₂固溶体的纳米结构仍然可以稳定保持。最终，黑色(Sn，Ti)O₂负极可以实现显著提升的可逆比容量(0.2 A g⁻¹，100个循环后保持583 mA h g⁻¹)、高倍率性能(2 Ag⁻¹为419 mA h g⁻¹和5 A g⁻¹为335 mA h g⁻¹)和优异的循环稳定性。 (4)基于功能复合的材料成分与结构调控思路，选取NiTiO₂(NiO+TiO₂)材料，并通过等离子体辅助气相沉积(PECVD)在其表面原位生长包覆石墨烯，提高电子导电率和结构稳定性，从而实现优异的循环稳定性和倍率性能。利用籽晶法生长制备微米尺寸的前驱体NiTi(OCH₂CH₂OH)₆单晶并解析确定其晶体结构。采用PECVD法部分还原NiTiO₂生成金属Ni，作为原位石墨烯生长的自催化剂，在NiTiO₃纳米棒表面完美包覆少层石墨烯。研究发现，NiTiO₂@Graphene的导电率为5.7 mS ㎝⁻¹，远高于NiTiO₂样品的0.2 μS ㎝⁻¹。同时表面包覆的石墨烯还起着稳定结构从而保持电接触的作用，能有效抑制电化学充放电过程中体积变化引起的粉化。在0.2Ag⁻¹的电流下，NiTiO₂@Graphene电极500个循环后仍然能保持83％的可逆比容量(556 mAhg⁻¹)。在此基础上发展了一种通用的材料设计策略，原位生长导电石墨烯作为MTiO₃(M=Ni，Co，Fe)材料的理想包覆材料以获得稳定的锂离子电池性能。 关键词：黑色氧化钛、表面改性、还原、功能复合、锂离子电池、电化学

 Lithium-ion batteries, as a green energy source, have become an indispensable part of nowadays daily life. However, to meet the needs of new markets such as electric vehicles and smart grids, new generations of lithium batteries are required with increased energy and power density, improved safety. The electrochemical performance of lithium-ion batteries is highly dependent on the electrode material, so the design and modification of the electrode material are particularly important. The most commonly used anode material for commercial lithium-ion batteries is graphite, which has the merits of abundant resources and low price, but the rate performance is difficult to improve. In addition, due to its low voltage window, it can cause the growth of lithium dendrites, which leads to safety issues. TiO₂ is effective in preventing lithium deposition due to its higher oxidation-reduction potential and is expected to be a safer anode material. Additionally, TiO₂ exhibits excellent structural stability during lithium ion intercalation-deintercalation reaction with low volume expansion (4%), which enables TiO₂ to be functionally combined with alloying type or conversion reaction type anode materials to increase specific capacity. However, the poor electronic conductivity (10⁻⁹ S ㎝⁻¹) and Li⁻⁹ diffusion coefficient (10⁻¹¹-10⁻¹² ㎝² s⁻¹) of titania restrict the rate performance and hinder its practical application in lithium-ion batteries. The relatively low theoretical specific capacity of TiO₂ (340 mA h g⁻¹) is still unsatisfying to fulfill the increasing requirement of the energy density of lithium-ion batteries. To address aforementioned challenges, in this dissertation, surface modification (reduction, pre-lithiation) was introduced to improve the intrinsic electron conductivity and lithium ion diffusion coefficient of black titania, and further increased its specific capacity through functional composite modification (SnO₂, NiO). The main research contents and results are as follows: (1)The controllable magnesium reduction method was first proposed to prepare black titania, and the intrinsic electronic conductivity of black titania was improved via reduction, resulting in enhanced cycling stability of lithium-ion batteries. A systematic study of black titania prepared by metal-reduction methods was provided and found out the best controllable magnesium reduction method. In addition, two commonly used TiO₂ phases, i.e. anatase and rutile, were prepared to explore the effect of crystal phase during the reduction process. It was found that nano rutile phase is preferentially reduced over anatase under the same reduction conditions. The color, absorption properties, concentrations of Ti³⁺, and electrical conductivities of the reduced samples can be easily tuned by the dosage of Mg metals, wherein the anatase phase sample (A-3) showed the highest conductivity (236.3 μS ㎝⁻¹). When used as anode material, A-3 delivered a high reversible capacity of 180 mA h g⁻¹ at 1C even after 100 cycles. (2)Rationally designed and created a fast ion-conducting surface layer of mesoporous titania, addressing the limited lithium diffusion across the interface between the electrolyte and the active electrode materials, and thus achieved superior high-rate performance. Via a facile molten-salt-assisted lithiation process, an amorphous lithiated surface layer was created and a mesoporous structure was formed simultaneously. The obtained lithiated surface layer with open structure resulted in higher Li⁺ ion migration with lower activation energy. Optimization between the electron conductivity and ion conduction was achieved by tuning the reaction temperature. The optimized Li-TiO〓-300 sample showed high electrical conductivity (198.2 μS ㎝⁻¹), high surface area (259 m² g⁻¹) with mesoporous structure, and high lithium diffusion coefficient. When used as anode material, Li-TiO〓-300 delivered remarkable reversible capacities as high as 114 mA h g⁻¹, 93 mA h g⁻¹ at high rates of 50 C and 100 C even after 1000 cycles. Further kinetic analysis found that the contribution of pseudocapacitance to the specific capacity of the electrochemical reaction increased with increasing current density. (3)Based on the concept of functional composite modification, black rutile (Sn,Ti)O₂ was prepared, in which SnO₂ contributes high specific capacity, TiO₂ provides structural support, and the electronic conductivity was further enhanced via reduction, thereby achieving high specific capacity and excellent rate performance. Black (Sn,Ti)O₂ with a core-shell structure was prepared through a facile co-precipitation followed by hydrogen plasma reduction, and its electrical conductivity was as high as 35.7 μS ㎝⁻¹. The conductive surface layer acted as highways for electron transfer to promote an isotropic electrochemical reaction. The rutile solid solution with a homogenous mixing of Sn and Ti helps to form a uniform distribution of Sn nanodots in an amorphous lithiated titania matrix after lithiation, and subsequently maintains a sub 10 nm scale nanostructure even after long-term cycling. The lithiated titania matrix can prevent the aggregation of tin nanodots, accommodate the volume change, and provide a stable conductive network for ion kinetics, which consequently results in excellent lithium-ion battery performance. Ultimately, the black (Sn,Ti)O₂ anode harvested significantly enhanced reversible capacity (583 mA h g⁻¹ after 100 cycles at 0.2 A g⁻¹), high rate performance (419 mA h g⁻¹ at 2 A g⁻¹ and 335 mA h g⁻¹ at 5 A g⁻¹) and superior cycling stability. (4) Based on the concept of functional composite modification, NiTiO₃ (NiO + TiO₂) nanorods were prepared, and in-situ grown graphene was further introduced by plasma-enhanced chemical vapor deposition (PECVD) to improve the electronic conductivity and structural stability, resulting in excellent cycling stability and rate performance. A two-step seeded growth procedure was developed to grow micrometer-sized single crystals of nickel titanium glycolate complex, leading to an unambiguous solution of crystal structure and precise refinement, i.e. NiTi(OCH₂CH₂OH)₄. Under the reductive plasma enhanced CVD atmosphere, partially reduced Ni served as self-catalysis substrates for in-situ graphene growth, enabling the perfect encapsulation of NiTiO₃ nanorods with few-layer graphene. The electrical conductivity of NiTiO₃@Graphene sample was 5.7 mS ㎝⁻¹, over four orders of magnitude improved over 0.2 μS ㎝⁻¹ of the bare NiTiO₃ sample. The graphene coating also helps to retain the electrical connectivity and suppress the pulverization caused by volume expansion during cycling. The NiTiO₃@Graphene anode ultimately harvested significantly enhanced reversible capacity (556 mA h g⁻¹ after 500 cycles at 0.2 A g⁻¹) and superior cycling stability. As a result, a general strategy for in-situ growth of a conductive graphene shell on MTiO₃ (M= Ni, Co, Fe) materials through a facile PECVD route to obtain stable lithium-ion batteries performance was proposed. Keywords: black titania, surface modification, reduction, functional composite, lithium-ion batteries, electrochemical