Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||王志, 刘三平|
太阳能级电池板生产过程中会产生约40%晶硅切割废料，目前还未实现将废硅料提纯至6N级循环用于太阳能电池板原料。由于对原料硅的纯度要求较光伏电池等相对低，将处理后的切割废硅料用于锂离子电池负极材料引起了学者广泛的关注。硅在循环过程中，面临着体积膨胀巨大和导电性差的问题。为了缓解硅的体积膨胀，人们通常采用构筑“蛋黄-壳”结构、“石榴状”结构等硅碳负极材料，获得了较好的电化学性能。切割废硅料尺寸较大、形貌不规则，体积膨胀、导电性差的问题更加严重，但很难对切割废硅料实现这些复杂结构的构筑，同时也是不经济的。因此应使用简便、有效的方法对废硅进行改性使其用于硅碳负极材料。在现有的报道中，废硅碳负极是在较小的电流密度下完成的充放电循环，实现废硅碳负极在大电流密度下长而稳定的充放电循环仍然是巨大的挑战。本文通过材料结构设计（多维度碳包覆）与材料组分设计（杂原子掺杂与界面反应调控）合成了wSi@NC/Zn-2与wSi@C/CNTs复合结构，分别实现了硅碳的均匀复合与紧密结合，构建了缓冲结构和离子传输轨道，从而实现了材料在大电流密度下的较长的稳定循环，助力电极反应动力学。具体研究结果如下：1. 针对切割废硅料在脱嵌锂过程中体积膨胀大、导电性差的问题以及尺寸较大、形貌不规则的特点，设计了“一步法构造Zn/N双掺杂碳全包覆硅材料”的策略。实验过程中，PDDA的使用解决了负电性的无定型碳无法在尺寸较大、表面同为负电位的硅表面异相成核生长的问题。Zn/N双掺杂进一步提高材料的导电性，抑制硅与电解液发生副反应。制得的wSi@NC/Zn-2材料在0.5 A g-1的大电流密度下循环300圈后仍能维持1084.7 mAh g-1的可逆比容量，同时表现出优异的倍率性能。2. 针对上部分工作孤立零维颗粒间导电性差的问题，提出了“固相法生长碳纳米管构造颗粒间柔性的导电连接”的设计策略，创新性的使用自催化固相生长法构建了三维wSi@C/CNTs结构。wSi@C颗粒间通过交联碳纳米管实现的导电连接与Co/N掺杂共同助力了脱嵌锂动力学，柔性碳纳米管改善了wSi@C的结构稳定性。相比于零维wSi@C前驱体，本章所制三维wSi@C/CNTs材料具有优异的循环稳定性和倍率性能：0.5 A g-1的电流密度下循环500圈后，容量平稳在1000.7 mAh g-1左右，且容量保持率高达80.7%；高倍率循环60圈后回到初始电流密度，仍能恢复初始容量的99.2%。;More than 40% of the Si used in photovoltatic (PV) industries is directly being discarded as wafer-slicing waste. Considering the fact that there is still a long way to go before kerf-loss silicon can be reused for solar grade feedstock, which requires that the purity of silicon reaches at least 6N, it is meaningful and feasible to apply the kerf-loss silicon to the raw material for anode material used in lithium-ion batteries. Reusing of kerf-loss silicon as anode material for lithium-ion batteries (LIBs) is economically feasible.Unfortunately, the huge volume changes during the lithiation and delithiation process and Silicon material has poor conductivity. Si combined with carbonaceous material composite, such as “yolk-shell” structure and “pomegranate-like” structure, have demonstrated good electrochemistry performance. In view of the larger size and irregular shape of kerf-loss silicon, the volume expansion and poor conductivity problem is even more severe. However, it is impossible to mold kerf-loss silicon into either of these specific structures. Therefore, it is necessary to employ efficient and common methods to mold kerf-loss silicon into anode material for LIBs. In the current report, the Si/C composite material often completes the charge-discharge cycle at a small current density, and there is still a certain gap in achieving a fast charge-discharge cycle.By the way of architecture design (coated with different dimensional carbon materials) and introduction of different component, wSi@NC/Zn-2 and wSi@C/CNTs composite are designed and synthesized. Thanks to the uniform coating of carbon onto silicon and strong interaction between Si and C respectively, the construction of buffer matrix and introduction of transmission channel of lithium-ion, the cyclic stability and kinetics of lithium-ion transportation are greatly enhanced. Detail works are as follows:1. Aiming at the large-volume-change problem and poor conductivity of kerf-loss silicon, “kerf-loss silicon encapsulated with Zn/N co-doped carbon mesoporous core-shell structure” design is proposed. It is believed that the introduction of PDDA that solve the problem that the heterogeneous nucleation of phenolic resin cannot be realized on the surface of kerf-loss silicon, which may be caused by the larger scale and irregular morphology of kerf-loss silicon. PDDA serves as “glue” to bind phenolic resin and Si, insuring a robust ion transportation pathway. Furthermore, the co-doping of Zn and N helps to improve the conductivity of the obtained electrode and inhibit the occurrence of side-reaction. The obtained electrode delivers a reversible capacity of 1084.7 mAh g-1 after 300 cycles at a current density of 0.5 A g-1 with good rate performance.2. Aiming to improve poor conductivity between individual wSi@C particle, “CNTs cross-linked design” realized by thermal pyrolysis process is proposed. In this construction, zero-dimensional wSi@C is entangled into in-situ synthesis carbon-nanotubes based network to from flexible and conductive three-dimensional connection. The interwoven carbon-nanotubes with tight linkage with wSi@C contribute to ensure charge transfer highway and accommodate to the volume expansion during cycling. Additionally, Co/N co-doping leads to enhancement of electrochemistry performance. As expected, the wSi@C/CNTs electrode shows good rate performance and long term cyclic stability with capacity retention ratio as high as 80.7% after 500 cycles at 0.5 A g-1 with a reversible specific capacity of 1000.7 mAh g-1. After 60 cycles at higher current density, the reversible specific capacity recovers to 99.2% of the initial capacity.
|周琪琪. 切割废硅料基锂离子电池负极材料制备及储锂性能研究[D]. 中国科学院大学,2020.|
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