elf-adaptive strain-relaxation opti

elf-adaptive strain-relaxation optimization for high-energy lithium storage material through crumpling of graphene
High-energy lithium battery materials based on conversion/alloying reactions have tremendous potential applications in new generation energy storage devices. However, these applications are limited by inherent large volume variations and sluggish kinetics. Here we report a self-adaptive strain-relaxed electrode through crumpling of graphene to serve as high-stretchy protective shells on metal framework, to overcome these limitations. The graphene sheets are self-assembled and deeply crumpled into pinecone-like structure through a contraction-strain-driven crumpling method. The as-prepared electrode exhibits high specific capacity (2,165mAhg1), fast charge-discharge rate (20Ag1) with no capacity fading in 1,000 cycles. This kind of crumpled graphene has self-adaptive behaviour of spontaneous unfolding–folding synchronized with cyclic expansion–contraction volumetric variation of core materials, which can release strain and maintain good electric contact simultaneously. It is expected that such findings will facilitate the applications of crumpled graphene and the self-adaptive materials.
High energy- and power-density rechargeable batteries are in high demand for energy storage systems1–4. Commercialized materials of lithium ion batteries, such as graphite, LiCoO2 and LiFePO4, have limited capacity due to their intercalation mechanism. Beyond mechanism limitations, conversion and alloying reaction-based electrode materials usually have higher capacity over 1,000mAhg1, owing to their multiple electrons transfer per redox centre (two to six electron transfer for conversion and alloying reaction versus no more than one electron transfer for intercalation reaction)1,5–8. However, particle pulverization that results from the inherent large volume variations (Fig. 1a and Supplementary Fig. 1), combined with intrinsically sluggish charge and mass transfer kinetics, can seriously limit the cycling, rate performance and further applications5,9–11. To buffer the large volume expansion and enhance their kinetics, much research has focused on conductive encapsulation, mostly through carbon or conductive polymer coating12,13. However, collapse of the shell and increasing of core-shell interspaces during long cycles will induce structure damage, conductivity deteriorating and further lead to the electrochemical performance fading (Fig. 1b). To construct robust protection for large-volume-change materials, our group designed and synthesized semihollow bicontinuous graphene scrolls to protect the nanowire structure and show an enhanced capacity retention14. Cui’s group created yolk-shell nanoarchitecture15,16, pomegranate-inspired structure17 to provide free-space for large volumetric expansion and impede solid-electrolyte interphase formation. Distinction of our work and previous reports14–19 is that we propose a further-optimized and novel electrode with more stretchy protective shell and sustainable core-shell contact rather than void space, yielding rapid strain-relaxation and sustainable electric contact simultaneously. To realize the sustainable contact of optimized electrode, one of the optimal approaches is the utilization of ‘self-adaptive
materials’. To our knowledge, the concept of ‘self-adaptive materials’ was first proposed in 1994: if a two-dimensional elastic continuum for minimum compliance subject to a constraint on the total volume of material, which is termed self-adaptive behaviour, the material can obtain the optimal strain relaxation20. However, due to the lack of the ideal materials and/or appropriate synthetic methods, this kind of material or behaviour was seldom reported. On the other side, to realize the stretchy protective shell, crumpled graphene (cG) has been recently demonstrated to possess high stretch ability, more active sites and ultrafast mass transfer21–26. These advantages indicate that cG could offer unprecedented opportunities to serve as stretchy shell for conversion or alloying-based electrode materials. To maximize the potential and utilization of cG as protective shell in electrochemical devices, it is crucial to establish an effective synthetic strategy to deeply crumple the graphene shell. Moreover, comprehensive characterization and incisive theoretical analysis, such as in situ and ex situ electron microscopic characterization, theoretical simulation, should be applied to study the new strain-relaxation behaviours in folding–unfolding process. In this work, we describe the design of cG encapsulated threedimensional (3D) electrode (Fig. 1c) through a contractionstrain-driven crumpling method during liquid–solid transition of encapsulated particles. The crumpled construction combined with 3D framework yields significant improvements in the cycling stability and rate performance for Li batteries. Further structural analysis and mechanism studies followed by ex situ scann

結果 (中文) 1:

高能锂存储材料通过揉的石墨烯的精灵自适应的应变弛豫优化基于转换/合金反应的高能锂电池材料在新的一代能源存储设备有巨大的应用潜力。然而，这些应用程序受到固有的大体积变化和缓慢的动力学。在这里，我们报告通过揉的石墨烯作为高弹性防护壳的金属框架，以克服这些限制的自适应应变放宽电极。石墨烯是自组装和深深皱到松果状结构通过收缩应变驱动皱方法。作为编写电极展品高具体能力 (165mAhg1，2)，快速充放电率 (20Ag1) 与 1000 次没有能力衰落。皱巴巴的石墨烯这种具有自适应行为的自发性展开 — — 折叠与循环膨胀-收缩体积变化的核心材料，可以释放应变，同时保持良好的电气接触同步。预计这种单疱助皱巴巴的石墨烯和自适应材料的应用。高的能量和功率密度可充电电池在能量存储制度 1 — — 4 的高需求。商业化的锂离子电池材料的石墨、 LiCoO2 和 LiFePO4，由于他们插层机理的能力有限。超越机制的局限性，转换和合金化的基于反应的电极材料，通常有更高的容量超过 1，000mAhg1，由于其多个电子传递每个氧化还原中心 （转换和合金化与插层反应不多于一个电子转移反应的二至六电子转移） 1，5-8。然而，从固有的大体积变化 （图 1a 和补充的图 1），结果结合本质上缓慢充电和传质动力学的粒子粉碎可以严重限制的循环，率性能和进一步 applications5，9-11。缓冲大体积膨胀，并提高其反应动力学，多研究集中在导电的封装，主要是通过碳或导电聚合物 coating12 13。然而，崩溃的壳，并在长周期过程中的核-壳空隙增加会导致结构损伤，电导率恶化及电化学性能衰落 (图 1b) 进一步导致。要构建强健的保护，为大体积变化材料，我们组设计并合成了 semihollow 双连续相石墨烯羊皮卷保护纳米线结构和显示增强的能力 retention14。崔的创建组蛋黄壳 nanoarchitecture15，16，石榴启发 structure17 为大体积膨胀提供免费空间，阻碍固体电解质界面形成。我们的工作和以前 reports14-19 的分别是我们提出更多弹性保护壳和可持续核-壳接触而不是空的空间，进一步优化和新型电极同时产生快速的应变弛豫和可持续的电接触。为了实现可持续的优化电极接触的最佳方法之一是利用 ' 自适应materials’. To our knowledge, the concept of ‘self-adaptive materials’ was first proposed in 1994: if a two-dimensional elastic continuum for minimum compliance subject to a constraint on the total volume of material, which is termed self-adaptive behaviour, the material can obtain the optimal strain relaxation20. However, due to the lack of the ideal materials and/or appropriate synthetic methods, this kind of material or behaviour was seldom reported. On the other side, to realize the stretchy protective shell, crumpled graphene (cG) has been recently demonstrated to possess high stretch ability, more active sites and ultrafast mass transfer21–26. These advantages indicate that cG could offer unprecedented opportunities to serve as stretchy shell for conversion or alloying-based electrode materials. To maximize the potential and utilization of cG as protective shell in electrochemical devices, it is crucial to establish an effective synthetic strategy to deeply crumple the graphene shell. Moreover, comprehensive characterization and incisive theoretical analysis, such as in situ and ex situ electron microscopic characterization, theoretical simulation, should be applied to study the new strain-relaxation behaviours in folding–unfolding process. In this work, we describe the design of cG encapsulated threedimensional (3D) electrode (Fig. 1c) through a contractionstrain-driven crumpling method during liquid–solid transition of encapsulated particles. The crumpled construction combined with 3D framework yields significant improvements in the cycling stability and rate performance for Li batteries. Further structural analysis and mechanism studies followed by ex situ scann