Scalable Dry-Pressed Electrodes Based on Holey Graphene

Binderless Dry Cathode Using a Nanoparticle Deposition System for Lithium-Ion Battery Applications

Binder-free dry cathodes are in high demand because they can significantly reduce production costs by eliminating solvent removal and recovery processes and increase energy density by eliminating the need for binders, which are electrochemically inactive materials. To address these critical challenges, to the best of our knowledge, this study is the first to propose and introduce a nanoparticle deposition system (NPDS) for producing binder-free dry cathodes for lithium-ion batteries. The NPDS process produces films via supersonic acceleration of the powder, followed by collision with the substrate, using a simple pressure difference between the spraying nozzle and deposition chamber. This method facilitates the fabrication of dry films using commercial powders without the need for binders as the particles are directly deposited onto the substrate. By optimizing the process parameters, binder-free dry cathodes using LiNi0.9Co0.05Mn0.05O2 were successfully developed, and their properties were compared with those of wet slurry-coated cathodes. Tape tests confirmed that the dry cathode exhibited better adhesion between the cathode materials and Al foil than the wet cathode. Further, the dry cathode exhibited better discharge capacity, rate capability up to 20 C, and cyclability exceeding 200 charge/discharge cycles compared to the wet cathode. Specifically, the dry cathode experienced only a 38% reduction in its initial capacity following 200 cycles owing to strong adhesion, whereas the wet cathode degraded by 56%, with significant material peeling from the Al foil. Consequently, due to this enhanced adhesion, the dry cathode exhibited greater discharge capacity, rate capability, and cyclability than the wet cathode. Therefore, this study successfully demonstrated the potential of NPDS for producing binder-free dry cathodes, thereby laying the groundwork for the development of advanced binder-free dry cathodes.

Analysis of Carbon Materials with Infrared Photoacoustic Spectroscopy

Measurement of infrared spectroscopy has emerged as a significant challenge for carbon materials due to the sampling problem. To overcome this issue, in this work, we performed measurements of IR spectra for carbon materials including C60, C70, diamond powders, graphene, and carbon nanotubes (CNTs) using the photoacoustic spectroscopy (PAS) technique; for comparison, the vibrational patterns of these materials were also studied with a conventional transmission method, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, or Raman spectroscopy. We found that the IR photoacoustic spectroscopy (IR-PAS) scheme worked successfully for these carbon materials, offering advantages in sampling. Interestingly, the profiles of IR-PAS spectra for graphene and CNTs exhibit negative bands using carbon black as the reference; the negative spectral information may provide valuable knowledge about the storage energy, production, structure, defect, or impurity of graphene and CNTs. Thus, this approach may open a new avenue for analyzing carbon materials.

Flat bands without twists: periodic holey graphene

Holey Graphene(HG) is a widely used graphene material for the synthesis of high-purity and highly crystalline materials. The electronic properties of a periodic distribution of lattice holes are explored here, demonstrating the emergence of flat bands. It is established that such flat bands arise as a consequence of an induced sublattice site imbalance, i.e. by having more sites in one of the graphene's bipartite sublattice than in the other. This is equivalent to the breaking of a path-exchange symmetry. By further breaking the inversion symmetry, gaps and a nonzero Berry curvature are induced, leading to topological bands. In particular, the folding of the Dirac cones from the hexagonal Brillouin zone (BZ) to the holey superlattice rectangular BZ of HG, with sizes proportional to an integerntimes the graphene's lattice parameter, leads to a periodicity in the gap formation such thatn≡0(mod 3). A low-energy hamiltonian for the three central bands is also obtained revealing that the system behaves as an effectiveα-T3graphene material. Therefore, a simple protocol is presented here that allows for obtaining flat bands at will. Such bands are known to increase electron-electron correlation effects. Therefore, the present work provides an alternative system that is much easier to build than twisted systems, allowing for the production of flat bands and potentially highly correlated quantum phases.

Holey penta-hexagonal graphene: a promising anode material for Li-ion batteries

Carbon allotropes are widely used as anode materials in Li batteries, with graphite being commercially successful. However, the limited capacity and cycling stability of graphite impede further advancement and hinder the development of electric vehicles. Herein, through density functional theory (DFT) computations and ab initio molecular dynamics (AIMD) simulations, we proposed holey penta-hexagonal graphene (HPhG) as a potential anode material, achieved through active site designing. Due to the internal electron accumulation from the π-bond, HPhG follows a single-layer adsorption mechanism on each side of the nanosheet, enabling a high theoretical capacity of 1094 mA h g-1 without the risk of vertical dendrite growth. HPhG also exhibits a low open circuit voltage of 0.29 V and a low ion migration barrier of 0.32 eV. Notably, during the charge/discharge process, the lattice only expands slightly by 1.1%, indicating excellent structural stability. This work provides valuable insights into anode material design and presents HPhG as a promising two-dimensional material for energy storage applications.

Holey Graphene/Ferroelectric/Sulfur Composite Cathodes for High-Capacity Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have attracted considerable interest as next-generation high-density energy storage devices. However, their practical applications are limited by rapid capacity fading when cycling cells with high mass loading levels. This could be largely attributed to the inferior electron/ion conduction and the severe shuttling effect of soluble polysulfide species. To address these issues, composites of sulfur/ferroelectric nanoparticles/ho ley graphene (S/FNPs/hG) cathodes were fabricated for high-mass-loading S cathodes. The solvent-free and binder-free procedure is enabled using holey graphene as a unique dry-pressable electrode for Li-S batteries. The unique structure of the holey graphene framework ensures fast electron and ion transport within the electrode and affords enough space to mitigate the electrode's volume expansion. Moreover, ferroelectric polarization due to FNPs within S/hG composites induces an internal electric field, which effectively reduces the undesired shuttling effect. With these advantages, the S/FNPs/hG composite cathodes exhibit sustainable and ultrahigh specific capacity up to 1409 mAh/g_s for the S/BTO/hG cathode. A capacity retention value of 90% was obtained for the S/BNTFN/hG battery up to cycle 18. The high mass loading of sulfur ranging from 5.72 to 7.01 mg_s/cm² allows maximum high areal capacity up to ∼10 mAh/cm² for the S/BTO/hG battery and superior rate capability at 0.2 and 0.5 mA/cm². These results suggest sustainable and high-yielding Li-S batteries can be obtained for potential commercial applications.