DOI: 10.1002/adma. 201404611 appropriate structures. Here, we fulfill this purpose by concentrating on intrinsic materials scope and fabricating a novel composite with MnCO 3 submicrometer-particles uniformly grafted on large-area graphene (LG, tens of micrometers in length and width). We have demonstrated that LG induces faceto-face self-assembly during ordinary electrode preparation and forms alternating layers with a continuous and close-packed configuration at the electrode level. Large-area composites were achieved by means of a reactantconversion route starting from LG and MnOOH precursor. Generally, this delicately designed architecture with selfassembly into orderly packed electrodes offers several advantages as LIB anodes (Figure S1 in the Supporting Information, shows a schematic illustration). First, LG offers perfect largearea support for MnCO 3 particles with uniform dispersion, allowing structural re-organization to be accommodated by the space between particles during cycling.[21, 22] Second, the continuous graphene networks existing in an ordered macroscopic electrode guarantee outstanding ion diffusion and electronic conduction, readily yielding high power delivery.[11, 23] Third, the inter-plane compact configuration of graphene domains provides sustained structural stability and high-packing-density energy storage.[13, 24, 25] Profiting from the combination of uninterrupted ion transport and effective structural stabilization, the MnCO 3-LG electrode delivered excellent electrochemical performance, and represents state-of-the-art design of high-power, high-efficiency, and low-cost anodes for next-generation LIBs. The LG was prepared by means of chemical exfoliation of natural graphite followed by thermal reduction. For intuitive comparison, graphite flakes with different sizes were utilized to achieve size-controlled fabrication of graphene. As shown in Figure S2 (Supporting Information), LG exhibits a two-dimensional (2D) transparent appearance with typically wrinkled texture, the characteristic size of which is several times that of small-area graphene (SG). We chose MnCO 3 as the target not only on account of traditional merits, such as high capacity, ecofriendliness, and abundant resources, but also for cost-effectiveness and low Li-storage plateau.[26, 27] The MnCO 3-LG composites were synthesized through a facile hydrothermal route, with self-assembly of MnOOH and in situ conversion to MnCO 3 on LG nanosheets (Figure S1, Supporting Information). The original 2D structure and large-area features (30–100 µm) of LG were perfectly preserved (as shown by the optical microscopy image in Figure S3 in the Supporting Information), differing from the commonly obtained aerogel consisting of 3D graphene networks. A representative freestanding MnCO 3-LG reveals a homogeneous dispersion of particles on expansive

The burgeoning development of various domains—from portable electronic devices to, especially, electrical vehicles and smart grids—is stimulating the growing appetite for next-generation electrical energy storage (EES) systems with higher power and energy density.[1–3] An effective strategy is to integrate complementary features of uprated EES systems such as supercapacitors into high-performance rechargeable batteries (such as lithium-ion batteries (LIBs)).[4, 5] Particularly, since the graphite anodes in commercial LIBs cannot meet such demanding criteria, myriad materials have been explored as promising candidates, such as Si, metal oxides and other conversion-based materials.[6–8] Nevertheless, it remains a crucial challenge to prepare electrode materials that simultaneously offer high …