Organic electrode materials, with low-cost synthesis and environmental friendliness, have gained significant research interest in lithium-ion batteries (LIBs). Polydopamine (PDA), as a bioderived organic electrode material, exhibits a low capacity of ∼100 mAh g–1, greatly limiting the practical application in LIBs. In this work, we find that a simple heat treatment at 300 °C can endow PDA-derived material (PDA300) with superior electrochemical performance. The obtained PDA300 electrode exhibits an ultrahigh capacity of 977 mAh g–1 at 50 mA g–1. Further combining the PDA300 with highly conductive Ti3C2T x MXene, the obtained PDA300/Ti3C2T x composite is demonstrated by high capacity (1190 mAh g–1, 50 mA g–1), excellent rate capability (remaining 552 mAh g–1 at 5 A g–1), and good cycling stability (82% retaining after 1000 cycles). The outstanding lithium storage performance is highly associated with the superlithiation process of the unsaturated carbon–carbon bonds in the PDA derivative and the introduction of the highly conductive Ti3C2T x substrate with a unique two-dimensional nanostructure. This work will provide new opportunities for the expansion of high-performance organic anodes for LIBs.

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The 2D carbon sheets have great potential for the construction of compact electrodes with high volumetric performance for electrical double‐layer capacitors (EDLCs), by virtue of their excellent electrical conductivity, high exposed surface area, free of interpores, and unimpeded ion‐diffusion channels. However, 2D nanosheets restack and aggregate during the preparation processes of electrodes, reducing available surface area, and limiting transport of ions. Herein, a facile and scalable method is presented to prepare highly porous crumple carbon balls (PCCBs) assembled by 2D carbon nanosheets. Such a unique nanostructure endows the PCCB electrode with large electrolyte‐accessible surface area and short ion‐diffusion pathways even when compressed at 40 MPa. Electrochemical evaluations in 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte indicate that the compressed PCCB electrodes still show superior gravimetric (103 F g−1) and volumetric capacitances (127 F cm−3) at 1 A g−1. The highest volumetric energy density of symmetrical EDLC based on compressed PCCB‐based electrode is 53.9 Wh L−1. This work provides a new direction for the development of high volumetric energy density carbon‐based EDLCs.

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