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 CO2 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%‐MnO2‐8 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%‐MnO2‐8 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.
A 3D‐hierarchical carbon lattice with ordered macropores (≈150 µm) and uniform nanopores (2–3 nm) for supercapacitor electrodes is successfully prepared using an inexpensive 3D printer and a simple gas activation process. The 3D‐ordered macropores facilitate ion transport inside the thick electrodes. The achieved areal energy and power densities are among the highest values reported to date.
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.
Interesting interlayer: Factors affecting hard carbon performances as Na‐ion battery anodes are still controversial. In this report, using hard carbons derived from six wood species, it was found for the first time that the total interlayer area of crystallite (Ai) is proportionally correlated with the intercalation capacity. Ai also shows strong correlations in previous reports, indicating that Ai is a more critical factor than conventional ones.
Inexpensive, high-performing, and environmentally friendly energy storage devices are required for smart grids that efficiently utilize renewable energy. Energy storage devices consisting of organic ...active materials are promising because organic materials, especially quinones, are ubiquitous and usually do not require harsh conditions for synthesis, releasing less CO
during mass production. Although fundamental research-scale aqueous quinone-based organic supercapacitors have shown excellent energy storage performance, no practical research has been conducted. In this study, we aimed to develop a practical-scale aqueous-quinone-based organic supercapacitor. By connecting 12 cells of size 10 cm × 10 cm × 0.5 cm each in series, we fabricated a high-voltage (> 6 V) aqueous organic supercapacitor that can charge a smartphone at a 1 C rate. This is the first step in commercializing aqueous organic supercapacitors that could solve environmental problems, such as high CO
emissions, air pollution by toxic metals, and limited electricity generation by renewable resources.
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–Li2) 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.
Croconic acid (CA) is investigated as a high‐energy‐density organic cathode material for lithium‐ion batteries. Its theoretical energy density is beyond those of most conventional materials thanks to its high‐voltage (>4 V) redox potentials of the two enolate groups. The electrochemical experiments confirm that CA undergoes reversible multi‐electron redox reactions around 4 V, which can be utilized for energy storage.
In this study, we investigated the synthesis of wood-sawdust-derived high-crystalline graphite-like carbon. The sawdust was first impregnated with Fe and semi-carbonized by a hydrothermal treatment ...(HT) at 250°C, followed by the second carbonization under N2 atmosphere and acid washing. For an iron-to-sawdust weight ratio of 4:10, graphite-like carbon was synthesized at a very low temperature of 850°C. This carbon has an average interlayer distance and crystallite size (d002: 0.337 nm, La: 35.8 nm, and Lc: 56.1 nm) comparable to those of commercial graphite. The large size of the Fe crystal particles facilitates the development of a stacked structure of carbon sheets. The HT with Fe-impregnated sawdust generates larger iron oxide particles than simple semi-carbonization with Fe-impregnated sawdust under N2 atmosphere at 250°C, facilitating the development of more crystalline graphite-like carbon. It was also found that the crystallinity of the graphitic carbon obtained after second carbonization may be controlled by the amount and particle size of the added Fe.
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 easily prepared by Japanese traditional carbonization of oak wood, showing a conductivity as high as that of artificial graphite. The use of oak‐derived hard carbon for quinone‐based organic supercapacitors dramatically improves the utilization rate of anode active material (97.6%) while that in conventional reports using petroleum‐derived activated carbon is 80% at most.
There is an urgent need to develop renewable sources of energy and use existing resources in an efficient manner. In this study, in order to improve the utilization of unused biomass and develop ...green processes and sustainable technologies for energy production and storage, unused Douglas fir sawdust (SD) was transformed into catalysts for the oxygen reduction reaction. Fe and N were doped into SD during hydrothermal carbonization, and the N- and Fe-doped wood-derived carbon (Fe/N/SD) was carbonized in a nitrogen atmosphere. After the catalyst had been calcined at 800°C, its showed the highest current density (−5.86 mAcm
−2
at 0.5 V versus reversible hydrogen electrode or RHE) and E
onset
value (0.913 V versus RHE). Furthermore, its current density was higher than that of Pt/C (20 wt% Pt) (−5.66 mA cm
−2
@0.5 V versus RHE). Finally, after 50 000 s, the current density of sample Fe/N/SD (2 : 10 : 10) remained at 79.3% of the initial value. Thus, the synthesized catalysts, which can be produced readily at a low cost, are suitable for use in various types of energy generation and storage devices, such as fuel cells and air batteries.
This article is part of the theme issue ‘Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)’.
Supercapacitors
In article number 2201544, Yuto Katsuyama, Richard B. Kaner, and co‐workers show that 3D‐printed thick supercapacitor electrodes having bimodal porosity (≈20 μm macropores and 2–3 nm ...nanopores) can significantly enhance the overall cell energy/power densities by eliminating the use of inactive components such as current collectors and separators.
Silicon microparticles (SiMPs) have gained significant attention as a lithium-ion battery anode material due to their 10 times higher theoretical capacity compared to conventional graphite anodes as ...well as their much lower production cost than silicon nanoparticles (SiNPs). However, SiMPs have suffered from poorer cycle life relative to SiNPs because their larger size makes them more susceptible to volume changes during charging and discharging. Creating a wrapping structure in which SiMPs are enveloped by carbon layers has proven to be an effective strategy to significantly improve the cycling performance of SiMPs. However, the synthesis processes are complex and time-/energy-consuming and therefore not scalable. In this study, a wrapping structure is created by using a simple, rapid, and scalable “modified reprecipitation method”. Graphene oxide (GO) and SiMP dispersion in tetrahydrofuran is injected into n-hexane, in which GO and SiMP by themselves cannot disperse. GO and SiMP therefore aggregate and precipitate immediately after injection to form a wrapping structure. The resulting SiMP/GO film is laser scribed to reduce GO to a laser-scribed graphene (LSG). Simultaneously, SiO x and SiC protection layers form on the SiMPs through the laser process, which alleviates severe volume change. Owing to these desirable characteristics, the modified reprecipitation method successfully doubles the cycle life of SiMP/graphene composites compared to the simple physically mixing method (50.2% vs. 24.0% retention at the 100th cycle). The modified reprecipitation method opens a new synthetic strategy for SiMP/carbon composites.
Silicon has gained significant attention as a lithium‐ion battery anode material due to its high theoretical capacity compared to conventional graphite. Unfortunately, silicon anodes suffer from poor ...cycling performance caused by their extreme volume change during lithiation and de‐lithiation. Compositing silicon particles with 2D carbon materials, such as graphene, can help mitigate this problem. However, an unaddressed challenge remains: a simple, inexpensive synthesis of Si/graphene composites. Here, a one‐step laser‐scribing method is proposed as a straightforward, rapid (≈3 min), scalable, and less‐energy‐consuming (≈5 W for a few minutes under air) process to prepare Si/laser‐scribed graphene (LSG) composites. In this research, two types of Si particles, Si nanoparticles (SiNPs) and Si microparticles (SiMPs), are used. The rate performance is improved after laser scribing: SiNP/LSG retains 827.6 mAh g−1 at 2.0 A gSi+C−1, while SiNP/GO (before laser scribing) retains only 463.8 mAh g−1. This can be attributed to the fast ion transport within the well‐exfoliated 3D graphene network formed by laser scribing. The cyclability is also improved: SiNP/LSG retains 88.3% capacity after 100 cycles at 2.0 A gSi+C−1, while SiNP/GO retains only 57.0%. The same trend is found for SiMPs: the SiMP/LSG shows better rate and cycling performance than SiMP/GO composites.
Silicon/graphene composites for lithium‐ion battery anodes are successfully prepared by a rapid and scalable laser‐scribing process. The well‐exfoliated 3D graphene network formed by laser irradiation facilitates fast ion transport within the electrode, enabling fast charging and discharging. The laser process also improves the cycling performance of the cell by better dispersion of silicon particles after laser treatment.
