In this study, the use of biorefined wood materials in the fabrication of organic redox supercapacitors is proposed. Oak‐derived hard carbon (HC) is revealed to have a nanographite domain structure, showing conductivity as high as that of artificial graphite. The CO2‐activated hard carbon (A–HC) has a conductivity one order higher than that of commercial activated carbon, with a surface area of 1126 m2 g−1. The energy densities of supercapacitors composed of a tetrachlorohydroquinone cathode and anthraquinone (AQ) or 1,5‐dichloroanthraquinone (DCAQ) anode are 19.0 and 13.8 Wh kg−1, respectively. The utilization rate of AQ with A–HC is 97.6% (250.9 mAh g−1), which is much higher than those in previous reports (≈80%). After 1000 cycles, 91.0% of the discharge capacity is retained when the DCAQ anode is used. Biorefined wood materials lead to a remarkable improvement in the operation of organic supercapacitors. This is intriguing, because the functional carbon material herein is easily prepared from a natural resource, wood, whereas numerous studies have prepared such materials from artificial chemical sources. Therefore, the use of oak‐derived HC enhances the usability of organic active materials for energy storage devices and potentially has a far‐reaching impact on the environment.

Hard carbon (HC) is the most promising candidate for sodium‐ion battery anode materials. Several material properties such as intensity ratio of the Raman spectrum, lateral size of HC crystallite (La), and interlayer distance (d002) have been discussed as factors affecting anode performance. However, these factors do not reflect the bulk property of the Na+ intercalation reaction directly, since Raman analysis has high surface sensitivity and La and d002 provide only one‐dimensional crystalline information. Herein, it was proposed that the crystallite interlayer area (Ai) defined using La, d002, and stacking height (Lc) governs Na+ intercalation behavior of various HCs. It was revealed that various wood‐derived HCs exhibited the similar total capacity of approximately 250 mAh g−1, whereas the Na+ intercalation capacity (Ci) was proportional to Ai with the correlation coefficient of R2=0.94. The evaluation factor of Ai was also adaptable to previous reports and strongly correlated with their Ci, indicating that Ai is more widely adaptable than the conventional evaluation methods.

Supercapacitors, which can be charged/discharged rapidly, play important roles in a sustainable society. Thick electrodes can reduce the ratio of inactive components in the overall cell while simultaneously improving energy and power densities. However, thick electrodes induce longer ion diffusion pathways, and capacitance drops dramatically after a certain thickness. To overcome this, precisely designed macro-and nano-porous 3D-hierarchical carbon lattices, where ions can diffuse freely inside the electrode, are prepared by combining an inexpensive stereolithography-type 3D printer, whose resolution is 50 µm, with a simple CO 2 activation process. The activated 3D carbon lattice with a 66% burn-off ratio (3D-CL-A66%) has ordered macropores (≈150 µm) and uniform nanopores (2-3 nm), exhibiting a maximum areal capacitance of 5251 mF cm -2 at 3 mA cm -2 . Furthermore, manganese oxide is electrochemically deposited on 3D-CL-A16% for 8 min (3D-CL-A16%-MnO 2 -8 min), increasing the areal capacitance by 2.5-times. Finally, an all-3D-printed asymmetric 1.8 V supercapacitor is prepared by combining 3D-CL-A16%-MnO 2 -8 min and 3D-CL-A66% as the positive and negative electrodes, respectively, demonstrating a maximum energy density of 0.808 mWh cm -2 at a power density of 2.48 mW cm -2 . The achieved values are one of the highest areal energy and power densities reported so far.

ephemeral forms of energy. In order to use the stored energy when needed and as fast as desired, batteries must exhibit high capacity and high power at an affordable cost. Researchers have made tremendous efforts to develop such technologies including silicon anodes for lithium-ion batteries (LIBs) with a gravimetric capacity an order of magnitude higher than graphite, [1][2][3] solid state electrolytes to improve the safety of batteries, [4] replacement of inorganic compounds by organic materials which requires less energy for mass production, [5][6][7][8][9] and substitution of lithium by other more abundant metals such as sodium, [10][11][12][13][14] potassium, [11] calcium, [15] magnesium, [16] aluminum, [17] and zinc. [17] Nevertheless, it still remains a challenging goal to simultaneously achieve high performance and low cost as they generally conflict with each other.One possible way to achieve this goal is to increase the mass loading of active materials in a single cell (Figure 1). [18][19][20][21][22][23][24][25] A single cell with 5 times thicker electrodes, instead of a stack of 5 cells, can reduce the amount of inactive components (separator, current collector, tabs, etc.) to one fifth, downsizing the overall cell size while saving as much as 26.1% of the cost per battery as shown in Table 1. [18] Based on the conventional film electrode fabrication process that uses a slurry containing the active materials as powders, increasing the amount of slurry per electrode is a simple concept. However, two problems arise: First, the kinetics of ion diffusion limits the maximum Increasing mass loadings of battery electrodes critically enhances the energy density of an overall battery by eliminating much of the inactive components, while compacting the battery size and lowering the costs of the ingredients. A hard carbon microlattice, digitally designed and fabricated by stereolithography 3D-printing and pyrolysis, offers enormous potential for high-mass-loading electrodes. In this work, sodium-ion batteries using hard carbon microlattices produced by an inexpensive 3D printer are demonstrated. Controlled periodic carbon microlattices are created with enhanced ion transport through microchannels. Carbon microlattices with a beam width of 32.8 µm reach a record-high areal capacity of 21.3 mAh cm −2 at a loading of 98 mg cm −2 without degrading performance, which is much higher than the conventional monolithic electrodes (≈5.2 mAh cm −2 at 92 mg cm −2 ). Furthermore, binder-free, pure-carbon elements of microlattices enable the tracking of structural changes in hard carbon that support the hypothesized intercalation of ions at plateau regions by temporal ex situ X-ray diffraction measurements. These results will advance the development of high-performance and low-cost anodes for sodium-ion batteries as well as help with understanding the mechanisms of ion intercalations in hard carbon, expanding the utilities of 3D-printed carbon architectures in both applications and fundamental studies.

While organic batteries have attracted great attention due to their high theoretical capacities, high‐voltage organic active materials (> 4 V vs Li/Li + ) remain unexplored. Here, density functional theory calculations are combined with cyclic voltammetry measurements to investigate the electrochemistry of croconic acid (CA) for use as a lithium‐ion battery cathode material in both dimethyl sulfoxide and γ ‐butyrolactone (GBL) electrolytes. DFT calculations demonstrate that CA dilitium salt (CA–Li 2 ) has two enolate groups that undergo redox reactions above 4.0 V and a material‐level theoretical energy density of 1949 Wh kg –1 for storing four lithium ions in GBL—exceeding the value of both conventional inorganic and known organic cathode materials. Cyclic‐voltammetry measurements reveal a highly reversible redox reaction by the enolate group at ≈4 V in both electrolytes. Battery‐performance tests of CA as lithium‐ion battery cathode in GBL show two discharge voltage plateaus at 3.9 and 3.1 V, and a discharge capacity of 102.2 mAh g –1 with no capacity loss after five cycles. With the higher discharge voltages compared to the known, state‐of‐the‐art organic small molecules, CA promises to be a prime cathode‐material candidate for future high‐energy‐density lithium‐ion organic batteries.