【作者】 王辉；

【导师】 王烨；

【作者基本信息】 郑州大学 ， 凝聚态物理， 2022， 硕士

【摘要】 对可再生能源存储日益增长的需求和电动汽车指数级增长需要传统锂离子电池（LIBs）之外的新电池技术。由于丰富的天然钠资源,钠离子电池（SIBs）被视为最有潜力替代锂离子电池的新一代储能器件。然而,当前钠离子电池的能量密度通常小于150 Wh kg^-1,可以使用高性能材料来提高其性能。钠金属负极具有高理论容量(1166 mAh g^-1)和低氧化还原电位（-2.71 V vs.SHE）,被视为极具潜力的钠离子电池负极材料。然而,钠金属具有非常高的反应活性以及无限的体积膨胀,从而在钠金属重复沉积/剥离过程中生成不稳定的固体-电解液界面（SEI）膜和不可控的钠枝晶。研究表明,钠成核初始阶段对后续钠沉积形态起至关重要影响,并决定最终电化学性能。因此控制钠金属成核是解决钠金属枝晶问题的关键手段之一。相对于二维平面铜箔集流体来说,三维结构能够有效降低电流密度,并提供更多成核位点,并且三维结构能提供一定的空间容纳供钠金属膨胀。深入研究表明Au可以与钠形成合金,有效降低成金属钠成核势垒,引导钠均匀沉积。石墨烯是一种经典的二维材料,还原氧化石墨烯（rGO）复合结构是理想的钠金属负极宿主。但是在rGO基础上复合Au纳米颗粒作为钠金属负极宿主的工作还未见系统报道。钠金属在Au/rGO上沉积的电化学行为还没有深入研究。基于上述分析,本论文通过简单的化学反应方法,设计合成了Au/rGO纳米复合材料。Au/rGO电极在电流密度为2 mA cm^-2,容量为2 mAh cm^-2时表现出3.5 m V的小过电位。同时,它可以在高电流密度为5 mA cm^-2,容量为1 mAh cm^-2下稳定循环400小时。原位光学显微成像和非原位SEM研究表明,优良的电化学性能主要是由于金纳米颗粒的亲钠表面,引导钠金属均匀沉积抑制枝晶的形成,从而有效地提高电化学性能。最后由Na@Au/rGO作为负极和Na₃V₂（PO₄）₃@C（NVP@C）作为正极组成的全电池,在100 mA g^-1电流密度下循环180圈后依然可以输出93.9 mAh g^-1的容量。利用3D打印可以快速构建人工可调分级多孔结构,这种结构可以作为理想的钠金属负极宿主。我们采用3D打印Au/rGO微网格气凝胶,构建了亚毫米-微米-纳米多孔结构。此电极结构能够增大比表面积并且提高钠离子迁移和电子传输速率。利用原位光学显微测试证明了3D打印Au/rGO电极可以有效的引导钠金属沉积,形成无枝晶光滑沉积表面。此外,利用原位XRD测试表明,Au的亲钠性源于Na₂Au合金。因此,3D打印Au/rGO电极表现出优异的电化学性能。例如:3D打印Au/rGO电极在8 mA cm^-2,8 mAh cm^-2测试条件下稳定循环100圈。3D打印Na@Au/rGO负极与Na₃V₂（PO₄）₃@C-rGO（NVP@C-rGO）正极匹配的全电池的容量在200次循环后依然可以达到83 mAh g^-1。更多还原

【Abstract】 The fast demand for renewable energy storage and the exponential growth of electric vehicles require new battery technologies beyond traditional lithium-ion batteries（LIBs）.Due to the abundant natural sodium resources,sodium-ion batteries（SIBs）have been regarded as a new energy storage technology to instead of LIBs with low-cost.However,the energy density of current SIBs is lower than 150 Wh kg^-1,which can be further improved by using new high capacity materials.Due to high theoretical capacity(1166 mAh g^-1)and low redox potential（-2.71 V vs.SHE）,Na metal is the most promising anode material of SIBs.However,Na metal has the intrinsic properties of high electrochemical reactivity and infinite volume expansion,leading to unstable solid-electrolyte-interface（SEI）film formation and uncontrollable Na dendrite growth during repeated deposition/stripping processes.Pioneer research work prove that the initial stage of Na nucleation play a critical role on the subsequent sodium deposition morphology,which determine the final electrochemical performance.Therefore,it is necessary to investigate the Na metal nucleation behavior and guide the Na metal growth.Compared with the tranditional two-dimensional（2D）Cu foil current collector,three-dimensional（3D）structure can effectively reduce the current density and provide the abundant nucleation center,as well as provide enough space to accommodate the Na metal expansion.Further investigation indicate that Au can guide the Na metal deposition due to the formation of Na Au alloy,which can reduce the nucleation barriers with high binding energy and guide the Na uniform deposition.In addition,graphene is a traditional 2D material,3D structure made of reduced-graphene oxide（rGO）is an ideal host for Na metal anode.However,there is rarely reports of using Au hybrided with rGO（Au/rGO）as the host of Na metal anode.Furthermore,the Na metal deposition behavior onto Au/rGO has not been systematically investigated.Based on the above analysis,Au/rGO composed of Au nanoparticles supported by rGO was designed and synthesized by a simple chemical reaction method.The Au/rGO electrode exhibits a small overpotential of 3.5 m V at a current density of 2mA cm^-2 with a specific capacity of 2 mAh cm^-2.Meanwhile,it can be stably cycled for 400 h at a high current density of 5 mA cm^-2 and a specific capacity of 1 mAh cm^-2.The excellent electrochemical performance is mainly due to the unform Na metal deposition formed dendrite-free morphology owing to the sodiophilic surface provided by Au nanopraticles demonstrated by the in-situ optical microscopy and ex-situ SEM characterization.Finally,a full-cell composed of Na@Au/rGO as the negative electrode and Na₃V₂（PO₄）₃@carbon（NVP@C）as the positive electrode shows a capacity of 93.9 mAh g^-1 after 180 cycles at 100 mA g^-1.Futher study was carried out based on 3D printed Au/rGO microlattice aerogel,since the 3D printing technology can easily fabricate artificial hierarchical porous structure,which is an ideal Na meal anode host.Therefore,subsequently,a sub-millimeter/micrometer/nanometer porous Au/rGO hierarchical structure was designed and fabricated by 3D printing technology.The fabricated hierarchical porous structure can increase the specific surface area and accelerate the Na ion migration rate and charge transfer speed.In-situ optical microscopy investigate the 3D printed Au/rGO can guide the Na deposition and effectively inhibit the Na dendrite formation with a dendrite free deposition morphology.Furthermore,in-situ XRD prove that the sodiophicity of Au is originated form the formed Na Au₂ and Na₂Au alloy during the initial Na deposition process.Therefore,the 3D printed Au/rGO electrode exhibits excellent electrochemical performance.It can stabily cycle over 100 cycles at a high current density of 8 mA cm^-2 with 8 mAh cm^-2.When the 3D printed Na@Au/rGO anode paired with the Na₃V₂（PO₄）₃@C-rGO（NVP@C-rGO）cathode,the full cell can deliver a high capacity of 83 mAh g^-1 after 200 cycles.更多还原