Cellulose nanocrystals (CNCs) are currently of great interest for many applications, such as energy storage and nanocomposites, because of their natural abundance. A number of carbonization studies have reported abnormal graphitization behavior of CNCs, although cellulose is generally known as a precursor for hard carbon (nongraphitizable carbon). Herein, we report a spray-freeze-drying (SFD) method for CNCs and a subsequent carbonization study to ascertain the difference in the structural development between the amorphous and crystalline phases. The morphological observation by high-resolution transmission electron microscopy of the carbonized SFD-CNC clearly shows that the amorphous and crystalline phases of CNC are attributed to the formation of hard and soft carbon, respectively. The results of a reactive molecular dynamics (RMD) study also show that the amorphous cellulose phase leads to the formation of fewer carbon ring structures, indicative of hard carbon. In contrast, the pristine crystalline cellulose phase has a higher density and thermal stability, resulting in limited molecular relaxation and the formation of a highly crystalline graphitic structure (soft carbon).

中文翻译：

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纤维素纳米晶体的异常高石墨结晶


纤维素纳米晶体（CNC）由于其天然丰富性，目前在能源存储和纳米复合材料等许多应用中引起了极大的兴趣。尽管纤维素通常被认为是硬碳（不可石墨化碳）的前体，但许多碳化研究报告了 CNC 的异常石墨化行为。在此，我们报告了一种用于 CNC 的喷雾冷冻干燥（SFD）方法以及随后的碳化研究，以确定非晶相和结晶相之间结构发展的差异。通过高分辨率透射电子显微镜对碳化SFD-CNC的形态观察清楚地表明，CNC的非晶相和结晶相分别归因于硬碳和软碳的形成。反应分子动力学（RMD）研究的结果还表明，无定形纤维素相导致形成较少的碳环结构，这表明硬碳。相比之下，原始结晶纤维素相具有较高的密度和热稳定性，导致有限的分子松弛并形成高度结晶的石墨结构（软碳）。