發(fā)布時(shí)間：2019-02-13 05:54

【摘要】：硅作為鋰離子電池負(fù)極材料的理論比能量高達(dá)4200mAh/g，但是在嵌鋰過(guò)程中其體積會(huì)發(fā)生急劇膨脹，造成循環(huán)性能差、SEI膜不斷破裂修復(fù)等諸多問(wèn)題，從而限制商業(yè)化。為真正克服硅膨脹的難題，必須通過(guò)巧妙的結(jié)構(gòu)設(shè)計(jì)，形成微納混合結(jié)構(gòu)，同時(shí)顆粒內(nèi)部預(yù)留一定空體積以容納硅的體積膨脹。本文先從刻蝕制備多孔硅著手，為后期材料制備打基礎(chǔ)；然后設(shè)計(jì)并制備了類石榴結(jié)構(gòu)和中空多孔核殼結(jié)構(gòu)硅基材料。通過(guò)XRD、SEM、BET等手段表征了材料的結(jié)構(gòu)特征，同時(shí)采用恒流充放電和交流阻抗評(píng)價(jià)其電化學(xué)性能。 采用Ag/HF-H2O2體系刻蝕硅能成功制備出多孔硅，然而其循環(huán)性能依然很差；采用Ag/HF-H2O2體系刻蝕SiO，，溶劑為水/乙醇(1:1)且HF濃度為5mol/L時(shí)刻蝕效果較好；采用Cu/HF-H2O2體系和Cu/HF-Fe3+體系刻蝕硅均只能在硅表面刻蝕出淺孔。NaOH刻蝕歧化SiO制備出的多孔材料，首次可逆容量為793mAh/g，30次循環(huán)容量保持率為72.9%。 通過(guò)歧化、刻蝕、碳包覆的技術(shù)路線制備類石榴結(jié)構(gòu)硅基材料，并研究了各步驟的工藝條件及對(duì)性能的影響。研究發(fā)現(xiàn)，為確保SiO發(fā)生歧化，溫度至少得升至900℃；HF刻蝕歧化SiO可以制備出相互交聯(lián)的多孔結(jié)構(gòu)。同時(shí)，詳盡研究了物料裝載量、乙炔氣體流速、包覆溫度與時(shí)間對(duì)乙炔氣相碳包覆的的影響。 以聚苯胺為碳源制備中空多孔核殼結(jié)構(gòu)硅基材料，并進(jìn)一步優(yōu)化了結(jié)構(gòu)參數(shù)。研究發(fā)現(xiàn)，碳?xì)ぴ龊窈涂阵w積增大均利于循環(huán)性能提高。將20%石墨與HF-mSiO@C材料混合后可將100次容量保持率提升至95.2%。通過(guò)選用蔗糖為碳源，可將制備步驟簡(jiǎn)化為球磨、歧化+碳化、刻蝕。制備出的HF-mSiO@C材料首次可逆容量為1067mAh/g，首次庫(kù)倫效率為60.1%，140次循環(huán)容量保持率為86.4%，平均庫(kù)倫效率為99.5%。預(yù)嵌鋰30min的HF-mSiO@C材料，首次庫(kù)倫效率達(dá)到80.0%，150次循環(huán)容量保持率達(dá)到88.8%。通過(guò)更長(zhǎng)時(shí)間的預(yù)嵌鋰，可使首次庫(kù)倫效率超過(guò)100%。 通過(guò)測(cè)試循環(huán)前后極片的橫截面，證實(shí)了中空多孔核殼結(jié)構(gòu)可有效緩解硅的體積膨脹。研究了電極最終失效的主要原因，研究發(fā)現(xiàn)，空體積無(wú)法完全容納硅的體積膨脹，致使碳?xì)け粨纹疲罱K造成硅核與碳?xì)ね耆蛛x，硅核失去電接觸而失效。
[Abstract]:The theoretical specific energy of silicon as a cathode material for lithium ion batteries is as high as 4200mAh/ g, but its volume will expand rapidly in the process of lithium intercalation, resulting in poor cycling performance, continuous rupture and repair of SEI films, and so on, thus limiting commercialization. In order to overcome the problem of silicon expansion, the micro-nano mixed structure must be formed by ingenious structural design, and a certain void volume is reserved in the grain to accommodate the volume expansion of silicon. In this paper, we first prepare porous silicon by etching, and then design and prepare pomegranate like structure and hollow porous core shell structure silicon based materials. The structure of the material was characterized by XRD,SEM,BET, and its electrochemical performance was evaluated by constant current charge-discharge and AC impedance. Porous silicon can be prepared successfully by etching silicon with Ag/HF-H2O2 system, but its cycling performance is still very poor, and the etching effect of SiO, solvent is water / ethanol (1:1) and HF concentration is 5mol/L when using Ag/HF-H2O2 system. Both Cu/HF-H2O2 system and Cu/HF-Fe3 system can only etch shallow pores on the surface of silicon. The first reversible capacity of porous material prepared by NaOH etching of SiO is 793mAh/ g ~ (-1) and the retention rate of 30 cycles is 72.9%. The silicon-based pomegranate structure materials were prepared by the technological route of disproportionation, etching and carbon coating, and the technological conditions of each step and their effects on the properties were studied. It is found that the temperature must rise to 900 鈩

本文編號(hào)：2421244