Electrodes with a high areal capacity are critical for developing high-energy-density sodium-ion batteries (SIBs). The freestanding thick electrode is a promising candidate among the state-of-art electrodes, since it has the advantages of high areal mass, binder-free, current-collector-free, and no carbon additive; thus, the whole mass of the electrode is an active material that can contribute to capacity. However, enhancing areal density by introducing thick electrodes impinges on the transport of charge carriers including ions and electrons. Here we designed and synthesized an ultrathick (1500 μm) free-standing foam, which is a carbon framework with 1T-MoS 2 nanosheets embedded in the vertically aligned channel wall. To tune the areal mass and morphology of the as-obtained foam, a confined iterative self-assembly strategy was proposed. The Na + storage behavior was studied by using the as-obtained foam as a free-standing electrode against Na metal. Consequently, it displays good cycle stability even with a high areal mass of 20.74 mg cm −2 and delivers an astonishing reversible areal capacity of 19.75 mAh cm −2 at 0.01 A g −1 , which greatly exceeds that of most sodium storage materials. The proposed confined iterative self-assembly strategy for fabricating thick electrodes opens new avenues for high areal capacity batteries.
Lithium-ion batteries (LIBs) have become well-known electrochemical energy storage technology for portable electronic gadgets and electric vehicles in recent years. They are appealing for various grid applications due to their characteristics such as high energy density, high power, high efficiency, and minimal self-discharge. LIBs may now theoretically be tailored for a variety of operating circumstances and applications because of the ability to change the material properties of the electrodes and electrolytes. However, LIBs operating at low temperatures have significantly reduced capacity and power, or even do not work properly, which poses a technical barrier to market entry for hybrid electric vehicles, battery electric vehicles, and other portable devices. This review summarizes the state-of-art progress in electrode materials, separators, electrolytes, and charging/discharging performance for LIBs at low temperatures. Due to the sluggish kinetics, insufficient ionic conductivity at low temperatures, and sluggish desolvation, it became challenging to enhance the electrochemical performance of LIBs at reduced temperatures. This review recommends approaches to optimize the suitability of LIBs at low temperatures by employing solid polymer electrolytes (SPEs), using highly conductive anodes, focusing on improving commercial cathodes, and introducing lithiumrich materials into separators. Finally, we propose an integrated electrode design strategy to improve low-temperature LIB performance.
Lithium‐sulfur battery suffers from sluggish kinetics at low temperatures, resulting in serious polarization and reduced capacity. Here, this work introduces medium‐entropy‐alloy FeCoNi as catalysts and carbon nanofibers (CNFs) as hosts. FeCoNi nanoparticles are in suit synthesized in cotton‐derived CNFs. FeCoNi with atomic‐level mixing of each element can effectively modulate lithium polysulfides (LiPSs), multiple components making them promising to catalyze more LiPSs species. The higher configurational entropy endows FeCoNi@CNFs with extraordinary electrochemical activity, corrosion resistance, and mechanical properties. The fractal structure of CNFs provides a large specific surface area, leaving room for volume expansion and Li2S accumulation, facilitating electrolyte wetting. The unique 3D conductive network structure can suppress the shuttle effect by physicochemical adsorption of LiPSs. This work systematically evaluates the performance of the obtained Li2S6/FeCoNi@CNFs electrode. The initial discharge capacity of Li2S6/FeCoNi@CNFs reaches 1670.8 mAh g−1 at 0.1 C under ‐20 °C. After 100 cycles at 0.2 C, the capacity decreases from 1462.3 to 1250.1 mAh g−1. Notably, even under ‐40 °C at 0.1 C, the initial discharge capacity of Li2S6/FeCoNi@CNFs still reaches 1202.8 mAh g−1. After 100 cycles at 0.2 C, the capacity retention rate is 50%. This work has important implications for the development of low‐temperature Li‐S batteries.
Biomimetic porous materials have contributed to the enhancement of solar-driven evaporation rate in interfacial desalination and clean water production. However, due to the presence of numorous microbials in water environment,...
Freestanding electrodes are critical for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) with high energy density and long cycling stability. We fabricated freestanding MnO2 nanosheet-coated carbon nanofibers by synchronous in situ spraying of MnO2 nanosheets onto electrospinning polymer nanofibers, which might be a high-voltage electric field-induced assembly process. The designed film is used as anode material for LIBs and SIBs. It demonstrates good cycling stability without capacity loss after long cycling for LIBs, delivers a capacity of 256.4 mAh g–1 at 1.00 A g–1, and has an extremely stable cycle life for over 200 cycles at 0.05 A g–1. For SIBs, it delivers a capacity of 135.0 mAh g–1 at 1.00 A g–1 and has a stable cycle life for over 500 cycles at 0.50 A g–1. The capacitive contribution ratio increases from 44.4 to 76.2% (0.2–1.0 mV s–1), and the capacitive process plays a major role in the total capacity. The enhancement of the electrochemical performance is attributed to the good conductivity of the carbon nanofiber network and the one-dimensional (1D)/two-dimensional (2D) composite structure of the electrode, in which the high performance of carbon nanofibers and MnO2 nanosheets is fully exploited. Importantly, the combination of in situ spraying and electrospinning can be extended to two or more materials with different polarities, ζ-potential values, or solubilities, broadening the applications of composites.
Carbon-based materials are the most prospective anodes. Typically, a single carbon-based material is applied to different energy storage systems (EESs) without modification. However, the microcrystal structure of carbon plays a decisive role in the energy storage performance, and therefore, it should be adjusted when applied to different EESs. Here, a hierarchical porous carbon monomer monolith (HPCM) embedded with carbon nanotubes blooming on ZIF-67 was designed as a soft–hard carbon-based freestanding thick electrode for achieving high-energy lithium-ion and sodium-ion batteries. HPCM is resorcinol–formaldehyde (RF) resin-derived carbon, mainly composed of hard carbon, which has outstanding mechanical properties, a high surface area, and high porosity. Carbon nanotubes (CNTs) derived from ZIF-67 have extraordinary electronic conductivity, which provides soft carbon. High-temperature CO2 etching was performed to adjust the microcrystal structure, and the lithium/sodium storage performance of the electrode was evaluated. After CO2 etching, the materials lose almost half their weight (mainly hard carbon), and pseudocapacitive contribution decreases for both lithium-ion and sodium-ion batteries, whereas the specific capacity increases for lithium-ion batteries and decreases for sodium-ion batteries. Capacities of 5.96 mAh cm–2 (areal) and 132.48 mAh cm–3 (volumetric) were achieved for lithium storage, and those for sodium storage were 2.31 and 51.24 mAh cm–3, respectively. In summary, it is significant to adjust the microcrystal structure of carbon-based electrodes, and this study provides related experience for lithium and sodium storage.
Newly designed all-electrochem-active thick electrode (∼500 μm) with dual-continuous integrated skeletons of defective rutile-anatase TiO 2 (D-R-A-TiO 2 ) heterojunctions and carbon have been introduced to enhance efficient electron− ion transport for high-rate energy storage, which provides a new idea for low-temperature lithium storage. For the first time, we anneal anatase TiO 2 integrated carbon under CO 2 atmosphere for converting anatase to rutile and activating carbon simultaneously, to fabricate freestanding all-electrochem-active thick electrode. The D-R-A-TiO 2 heterojunctions contain a type II staggered band alignment, which significantly induce highly localized electrons and lower the migration barrier of ions. The continuous D-R-A-TiO 2 heterojunctions form synergistically advantageous electronic networks, and the thick electrode (up to 60.97 mg cm −2 ) delivers outstanding areal capacity (14.14 mAh cm −2 at 0.61 mA cm −2 ) under 30 °C. The areal capacity is 8.62 mAh cm −2 at 0.57 mA cm −2 under −10 °C. When the temperature drops to −20 °C, the areal capacity still delivers 4.92 mAh cm −2 at 0.57 mA cm −2 . And the D-R-A-TiO 2 electrode still delivers 3.2 mAh cm −2 capacity after 70 cycles at 0.57 mA cm −2 under −20 °C.
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