锂硫电池（LSBs）拥有环境友好、能量密度高、成本低等优点，有望替代锂离子电池成为下一代新型电池，然而循环过程中多硫化锂（LiPSs）严重的“穿梭效应”、硫的体积膨胀（~80%）、硫与Li₂S₂/Li₂S较差的导电性等问题制约了其进一步发展。为解决锂硫电池中正极材料存在的问题，本文设计合成了几种金属化合物与导电基底材料形成具有特殊结构的复合材料负载硫，以提高硫正极的电化学性能。一方面，具有极性的金属化合物对LiPSs有较强的吸附能力，可以有效抑制LiPSs的“穿梭效应”。此外，有研究表明部分金属化合物可以促进多硫化锂的转化，提高硫的储锂能力。另一方面，多维导电基底可以提高硫复合物的导电性，同时设计的空间结构可以解决硫体积膨胀的问题。基于以上材料制备的经验进行了应用的延伸，制备了石墨烯基多孔碳负载氧化锌纳米颗粒，作为锂离子电池的负极材料展现出良好的电化学性能。主要的研究内容如下：

（1）基于锂硫电池中S₈还原过程（SRR）的吸附-扩散-转化理论模型，设计合成CeO₂纳米颗粒修饰的有序介孔碳（CMK-3）作为主体材料负载硫（CMK-3@CeO₂@S），并研究其电化学性能。通过向CMK-3孔道内注入硝酸铈，并在氮气保护下高温热解，可以得到3-6 nm的CeO₂颗粒修饰的CMK-3。CMK-3作为硫主体材料可以提高硫复合物的导电性，规则的空岛结构可以容纳硫的体积形变，但其非极性表面对多硫化锂的捕获能力较弱。通过CeO₂纳米颗粒的修饰可以改善CMK-3骨架的表面极性，有效的捕获多硫化锂，抑制其穿梭效应。此外，XPS分析表明，CeO₂纳米颗粒中Ce³⁺的存在可以在其表面形成氧空位，有助于吸附多硫化锂并促进其转化。因此，相比纯CMK-3负载的硫（CMK-3@S），CMK-3@CeO₂@S具有更好的电化学性能。在0.5 C的倍率下，200次循环后其比容量为1032 mA h/g，在1.0 C的倍率下，循环800次后容量保持在736 mA h/g。本工作还探究了CeO₂颗粒尺寸对CMK-3@CeO₂@S电化学性能的影响。研究发现，小尺寸CeO₂纳米颗粒具有更多的表面活性位点，有利于多硫化锂的吸附和转化，因此含有小尺寸CeO₂的CMK-3@CeO₂@S具有更好的电化学性能。

（2）在上一个工作的基础上，设计合成了FeF₃修饰的CMK-3复合物作为主体材料负载硫，并对其电化学性能进行研究。采用硝酸铁与1-丁基-3-甲基咪唑四氟硼酸盐（[Bmim][BF₄]）作为前驱体，通过水热合成方法，在CMK-3表面原位生长FeF₃纳米颗粒（FeF₃-CMK-3@S）。FeF₃纳米颗粒修饰后的CMK-3具备极性表面，可以有效的吸附LiPSs，同时促进其快速转化。因此，相比CMK-3@S，FeF₃-CMK-3@S展现出更好的电化学性能，在0.5 C 倍率下，200次循环后，仍可以保持852 mA h/g的放电比容量。但是，对比CeO₂修饰的CMK-3复合物，FeF₃纳米颗粒无法均匀的生长在CMK-3骨架上，导致FeF₃-CMK-3@S的电化学性能低于CMK-3@CeO₂@S。

（3）基于FeF₃晶体在导电载体上的生长和分散，设计合成Ti₃C₂ MXene基FeF₃作为主体材料负载硫（FeF₃-Ti₃C₂@S）。先将Ti₃AlC₂颗粒在LiF和HCl混液中刻蚀并超声得到Ti₃C₂纳米片，再用表面活性剂CTAB对其层间进行支撑，并对表面修饰阳离子，随后以硝酸铁和[Bmim][BF₄]为前驱体，在水热条件下得到Ti₃C₂基FeF₃主体材料（FeF₃-Ti₃C₂）。Ti₃C₂纳米片作为二维导电载体可以提高硫正极的导电性，同时其表面活性位点Ti与FeF₃中的Fe可以双重捕获多硫化锂，抑制LiPSs穿梭效应，同时FeF₃纳米颗粒还可以催化多硫化锂的转化。因此，对比Ti₃C₂纳米片负载硫（Ti₃C₂@S），FeF₃-Ti₃C₂@S展现出更好的电化学性能，在0.5 C的倍率下，FeF₃-Ti₃C₂@S的首圈放电比容量高达到1260 mA h/g，经过200次循环后稳定在918 mA h/g。但仍需指出，二维Ti₃C₂纳米片容易发生堆叠，尽管FeF₃纳米颗粒的表面修饰一定程度上可以抑制Ti₃C₂纳米片的聚集，但仍不如CMK-3的多孔结构对硫的容纳能力，因此其作为硫的主体材料电池比容量略低于CMK-3@CeO₂。

（4）基于硫主体材料的结构和性能的优化，设计合成了NiFe-LDHs纳米颗粒修饰的碳纳米管作为主体材料负载硫（NiFe-CNT@S），并研究其电化学性能。首先通过共沉淀法分别制备CoZn-LDHs，CoFe-LDHs和NiFe-LDHs三种主体材料来负载硫，研究发现NiFe-LDHs负载硫具有最好的电化学性能。随后，在水热条件下制备NiFe-LDHs纳米颗粒修饰的碳纳米管（NiFe-CNT）。由于CNT具有交联网络状结构，不但可以提供一个导电网络基底，同时有利于锂离子的迁移。NiFe-LDHs纳米颗粒存在双金属吸附位点，对多硫化锂有较强的吸附作用，高活性反应界面同时可以促进多硫化锂的转化。负载硫后得到NiFe-CNT@S （标为NiFe-CNT-1@S），在0.5 C的倍率下循环150圈后仍保持1077 mA h/g的比容量，其电化学性能要优于NiFe-LDHs纳米片负载的硫（NiFe-LDHs@S），在2.0 C的倍率下循环，电池的初始容量为1010 mA h/g，500次循环后容量仍能保持在876 mA h/g。此外，本工作还研究了NiFe-LDHs的颗粒尺寸对NiFe-CNT@S电化学性能的影响。在更高的前驱体浓度下生成的NiFe-CNT中含有较大的NiFe-LDHs纳米片，导致对多硫化锂的吸附和催化转化能力下降，因此负载硫后（标为NiFe-CNT-2@S）展现出略低的电化学性能。综上，设计高分散、小尺寸的NiFe-LDHs颗粒修饰CNT作为硫主体材料具有更好的电化学性能。

5）通过对导电载体的形貌结构调控以优化电极的性能，同样适应于锂离子电池的电极材料，本工作设计合成了电化学剥离石墨烯（EEG）基多孔碳负载ZnO纳米颗粒（EEG-PC-ZnO），作为锂离子电池负极材料。首先以EEG为载体，在其表面原位生长ZIF-8纳米颗粒，再在氮气保护下高温碳化得到EEG-PC-ZnO。该方法得到的石墨烯基多孔碳载体具有二维多孔结构，且被氮掺杂，具有优异的导电性，并有利于锂离子的迁移。3~5 nm的ZnO纳米颗粒均匀的分散在孔道中，有效抑制充放电过程中ZnO颗粒的团聚和脱落。相比由ZIF-8高温碳化制备的氮掺杂多孔碳负载的ZnO纳米颗粒（PC-ZnO），EEG-PC-ZnO展现出更好的电化学性能。在0.1 C倍率下，100次循环后，EEG-PC-ZnO的放电比容量为736 mA h/g，远高于PC-ZnO的放电比容量（316 mA h/g）。此外，本工作还研究了ZIF-8颗粒在EEG表面的生长过程，并探讨了ZIF-8颗粒尺寸对EEG-PC-ZnO电化学性能的影响。研究发现由小颗粒的ZIF-8生成的EEG-PC-ZnO具有更好的电化学性能。

Lithium-sulfur batteries (LSBs) as the next generation battery have drawn much attention for their high energy density, environmental friendliness, and low cost. However, the commercialization of LSBs batteries is hindered by some technical obstacles, such as poor electrical conductivity of sulfur and its discharge products (Li₂S₂/Li₂S), the migration/shuttle of soluble polysulfide intermediates of tcathode and the huge volume fluctuation (~80%) of sulfur during the lithiation/delithiation process. In this paper, we envision constructing different hybrid architectures, consisting of metal compounds decorated conductive substrates as sulfur host materials to partially solve issues of LSBs. On the one hand, polar metal compounds can adsorb LiPSs by chemical interaction and promote the conversion of LiPSs during cycling process. On the other hand, multi-dimensional conductive substrates can improve the conductivity of sulfur cathode. While the unique structure of composites can buffer the volume expansion of sulfur. In addition, graphene-based porous carbon-supported ZnO nanoparticles were also prepared in this paper, which exhibited superior electrochemical performance as anode materials for lithium-ion batteries. The research contents are as follows:

(1) Based on the theoretical model of S₈ reduction process (SRR) in lithium-sulfur batteries, CeO₂ nanoparticles decorated mesoporous carbon (CMK-3) was synthesized as sulfur host material (CMK-3@CeO₂@S). CeO₂ nanoparticles (3-6 nm) can be homogeneously embedded in the nanorods of CMK-3 by injecting cerium nitrate into the pores of CMK-3 and pyrolyzing at high temperature under nitrogen protection, which change the non-polar surface of CMK-3 into the polar CeO₂ surface. Therefore, compared to CMK-3@S, CMK-3@CeO₂@S exhibits superior electrochemical performance. CMK-3 can provide the required conductivity and space for sulfur. CeO₂ can adsorb and even accelerate the redox reaction of LiPSs, thereby restraining the shuttle effect. Besides, this work also explores the effect of CeO₂ particle size on the electrochemical performance of CMK-3@CeO₂@S. It is found that the small-sized CeO₂ nanoparticles have more active sites on the surface, which are beneficial to the adsorption and conversion of lithium polysulfides, so the CMK-3@CeO₂@S containing small-sized CeO₂ has better electrochemical performance.

(2) Based on the first work, FeF₃ nanoparticles modified CMK-3 composite was synthesized as the sulfur host material. Using ferric nitrate and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF₄]) as precursors, FeF₃ nanoparticles were grown in situ on the surface of CMK-3 by a hydrothermal method (FeF₃-CMK-3@S). The CMK-3 modified with FeF₃ nanoparticles can enhance the sulfur cathode conductivity and exhibit adsorption capability towards soluble LiPSs. Besides, FeF₃ not only shows strong chemisorption for anchoring LiPSs, but also displays excellent electrocatalytic effect to accelerate the redox conversion kinetics of LiPSs intermediates. Therefore, FeF₃-CMK-3@S exhibits better electrochemical performance than CMK-3@S, and can maintain a specific discharge capacity of 852 mA h/g after 200 cycles at 0.5 C. However, compared with the CMK-3@CeO₂, FeF₃ nanoparticles cannot grow uniformly on the CMK-3 framework, resulting in lower electrochemical performance of FeF₃-CMK-3@S than CMK-3@CeO₂@S.

(3) Ti₃C₂ MXene-based FeF₃ was fabricated as the sulfure host material (FeF₃-Ti₃C₂@S). First, Ti₃AlC₂ particles were etched in LiF and HCl mixed solution and sonicated to obtain Ti₃C₂ nanosheets. Then CTAB was added to support the interlayer of Ti₃C₂ and modify the surface with cations to grow FeF₃. As a two-dimensional conductive carrier, Ti₃C₂ nanosheets can improve the conductivity of sulfur cathode. Meanwhile, FeF₃ nanoparticles have a strong adsorption with LiPSs and can catalyze the conversion of LiPSs. Therefore, FeF₃-Ti₃C₂@S exhibits better electrochemical performance than Ti₃C₂ nanosheets supported sulfur (Ti₃C₂@S). FeF₃-Ti₃C₂@S has a higher discharge specific capacity in the first cycle of 1260 mA h/g, and stabilized at 918 mA h/g after 200 cycles at 0.5 C. However, it should be pointed out that two-dimensional Ti₃C₂ nanosheets are prone to stacking. Although the surface modification of FeF₃ nanoparticles can inhibit the aggregation of Ti₃C₂ nanosheets, it is still not as good as CMK-3 in electromchemical performance.

(4) Synthesised of NiFe-LDHs nanoparticle decorated carbon nanotubes as the sulfur host material (NiFe-CNT@S). Firstly, three host materials, CoZn-LDHs, CoFe-LDHs and NiFe-LDHs, were prepared by the co-precipitation method and used as the sulfur hosts. NiFe-LDHs supported sulfur cathode shows the best electrochemical performance among samples. Subsequently, NiFe-LDHs nanoparticles decorated carbon nanotubes (NiFe-CNT) were prepared by adding the modified carbon nanotubes into a solution containing nickel nitrate, iron nitrate, urea, and sodium citrate, and treating under hydrothermal conditions. The NiFe-CNT host material has a cross-linked network structure, which can not only provide a conductive network substrate, but also facilitates the migration of lithium ions. Furthermore, NiFe-LDHs nanoparticles have a strong adsorption with LiPSs as well as promote the conversion of lithium polysulfides. Therefore, NiFe-CNT@S exhibits good electrochemical activity with a specific discharge capacity of 1077 mA h/g after 150 cycles at 0.5 C. At 2.0 C, the initial capacity of the battery is 1010 mA h/g, and the capacity can still be kept at 876 mA h/g after 500 cycles. In addition, the size effect of NiFe-LDHs nanoparticles on the electrochemical performance of NiFe-CNT@S is also investigated. It is suggested that CNTs decorated with highly dispersed small-sized NiFe-LDHs have optimal electrochemical performance as the sulfur host material.

(5) ZIF-8 particles were in-situ grown on the surface of EEG, and carbonized at high temperature under nitrogen protection to obtain EEG-PC-ZnO. The EEG-based porous carbon substrate (EEG-PC) has a two-dimensional porous structure and is doped with nitrogen, while 3~5 nm ZnO nanoparticles are uniformLy dispersed in its mesopores. As a control sample, nitrogen-doped porous carbon supported ZnO (PC-ZnO) was prepared by carbonization of ZIF-8 particles. The discharge specific capacity of EEG-PC-ZnO is 736 mA h/g at 0.1 C after 100 cycles, which is much higher than that of PC-ZnO (316 mA h/g). The EEG substrate has better electrical conductivity than amorphous porous carbon, and the two-dimensional porous structure of EEG-PC can expose more pore channels for the lithium ions diffusion. Therefore, EEG-PC-ZnO has better electrochemical performance than PC-ZnO. In addition, the growth process of ZIF-8 particles on EEG and the size effect of ZIF-8 particle on the electrochemical performance of EEG-PC-ZnO were also studied. It is found that EEG-PC-ZnO generated from small ZIF-8 particles has optimal electrochemical performance.