Porous carbon prepared from polyacrylonitrile for lithium-sulfur battery cathodes using phase inversion technique

Diffusional Features of a Lithium-Sulfur Battery Exploiting Highly Microporous Activated Carbon

Diffusion processes at the electrode/electrolyte interphase drives the performance of lithium-sulfur batteries, and activated carbon (AC) can remarkably vehicle ions and polysulfide species throughout the two-side liquid/solid region of the interphase. We reveal original findings such as the values of the diffusion coefficient at various states of charge of a Li-S battery using a highly porous AC, its notable dependence on the adopted techniques, and the correlation of the diffusion trend with the reaction mechanism. X-ray photoelectron spectroscopy (XPS) and X-ray energy dispersive spectroscopy (EDS) are used to identify in the carbon derived from bioresidues heteroatoms such as N, S, O and P, which can increase the polarity of the C framework. The transport properties are measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The study reveals Li⁺ -diffusion coefficient (D_Li ⁺ ) depending on the technique, and values correlated with the cell state of charge. EIS, CV, and GITT yield a D_Li ⁺ within 10^-7 -10^-8  cm²  s^-1 , 10^-8 -10^-9  cm²  s^-1 , and 10^-6 -10^-12  cm²  s^-1 , respectively, dropping down at the fully discharged state and increasing upon charge. GITT allows the evaluation of D_Li ⁺ during the process and evidences the formation of low-conducting media upon discharge. The sulfur composite delivers in a Li-cell a specific capacity ranging from 1300 mAh g^-1 at 0.1 C to 700 mAh g^-1 at 2C with a S loading of 2 mg cm^-2 , and from 1000 to 800 mAh g^-1 at 0.2C when the S loading is raised to 6 mg cm^-2 .

All-Carbon Monolithic Composites from Carbon Foam and Hierarchical Porous Carbon for Energy Storage

We designed high-volumetric-energy-density supercapacitors from monolithic composites composed of self-standing carbon foam (CF) as the conducting matrix and embedded hierarchically organized porous carbon (PICK) as the active material. Using multiprobe scanning tunneling microscopy at selected areas, we were able to disentangle morphology-dependent contributions of the heterogeneous composite to the overall conductivity. Adding PICK is found to enhance the conductivity of the monoliths by providing additional links for the CF network, enabling high and stable performance. The resulting all-carbon CF-PICK composites were used as self-standing electrodes for symmetric supercapacitors without the need for a binder, additional conducting additive, metals as a current collector, or casting/drying steps. Supercapacitors achieved a capacitance of 181 F g^-1 based on the entire mass of the monolithic electrode as well as an outstanding rate capability. Our symmetrical supercapacitors also delivered a record volumetric energy density of 19.4 mW h cm^-3 when using aqueous electrolytes. Excellent cycling stability with almost quantitative retention of capacitance was found after 10,000 cycles in 6.0 M KOH as the electrolyte. Furthermore, charge-discharge testing at different currents demonstrated the fast charge-discharge capability of this material system that meets the requirements for practical applications.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO₂). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm^-2 (maximum: 23.6 mg·cm^-2) provide an ultrahigh areal capacitance of 1.13 F·cm^-2 (volumetric capacitance: 22.6 F·cm^-3), an outstanding energy of 627.8 μWh·cm^-2, and a maximum power density of 64 mW·cm^-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Oxygen-Functionalized Polyacrylonitrile Nanofibers with Enhanced Performance for Lithium-Ion Storage

Functionalization and morphological construction can promote lithium-ion storage performance of organic polymers. In this contribution, exceptional lithium ion storage performance is empowered to porous polyacrylonitrile (PAN) nanofibers via the integration of template-assisted electrospinning technology and thermal treatment. It is found that the atmosphere adopted during the annealing process controls the storage behaviors of Li⁺. Impressively, the samples annealed in air present competitive capacities, rate capabilities, and a stable lifetime, compared with other counterparts (PAN powders and PAN fibers treated in N₂). Such enhancement in performance is attributed to the enriched oxygen-based functionalities (mainly C=O group) which guarantee a high specific capacity and the porous structure which facilitates the transportation of Li⁺ and electrons to improve the rate capability. It is envisioned that such morphology control and surface functionalization open up new horizons in the development of organic electrode materials with enhanced lithium-ion storage performances.

Engineering Bifunctional Host Materials of Sulfur and Lithium-Metal Based on Nitrogen-Enriched Polyacrylonitrile for Li-S Batteries

Lithium-sulfur batteries (LSBs) still suffer from the shuttle effect on the cathode and the lithium dendrite on the anode. Herein, polyacrylonitrile (PAN) is developed into a bifunctional host material to simultaneously address the challenges faced on both the sulfur cathode and lithium anode in LSBs. For the sulfur cathode, PAN is bonded with sulfur to produce sulfurized PAN (SPAN) to avoid the shuttle effect. The SPAN is accommodated into a conductive 3D CNTs-wrapped carbon foam to prepare a self-supporting cathode, which improves the electronic and ionic conductivity, and buffers the volume expansion. Thereby, it delivers reversible capacity, superb rate capability, and outstanding cycling stability. For the Li-metal anode, PAN aerogel is carbonized to give macroporous N-doped cross-linked carbon nanofiber that behaves as a lithiophilic host to regulate Li plating and suppress the growth of Li dendrite. Combining the improvements for both the cathode and anode realizes a remarkable long-term cyclability (765 mAh g^-1 after 300 cycles) in a full cell. It provides new opportunity to propel the practical application of advanced LSBs.

Triple-Layered Carbon-SiO2 Composite Membrane for High Energy Density and Long Cycling Li-S Batteries

Here we report a highly scalable yet flexible triple-layer structured porous C/SiO₂ membrane via a facile phase inversion method for advancing Li-sulfur battery technology. As a multifunctional current-collector-free cathode, the conductive dense layer of the C/SiO₂ membrane offers hierarchical macropores as an ideal sulfur host to alleviate the volume expansion of sulfur species and facilitate ion/electrolyte transport for fast kinetics, as well as spongelike pores to enable high sulfur loading. The triple-layer structured membrane cathode enables the filling of most sulfur species in the macropores and additional loading of a thin sulfur slurry on the membrane surface, which facilitates ion/electrolyte transport with faster kinetics than the conventional S/C slurry-based cathode. Furthermore, density functional theory simulations and visual adsorption measurements confirm the critical role of the doped SiO₂ nanoparticles (∼10 nm) in the asymmetric C membrane in suppressing the shuttle effect of polysulfides via chemisorption and electrocatalysis. The rationally designed C/SiO₂ membrane cathodes demonstrate long-term cycling stability of 300 cycles at a high sulfur loading of 2.8 mg cm^-2 with a sulfur content of ∼75%. This scalable yet flexible self-supporting cathode design presents a useful strategy for realizing practical applications of high-performance Li-S batteries.