Multifunctional Additives for High-Energy-Density Lithium-Ion Batteries: Improved Conductive Additive/Binder Networks and Enhanced Electrochemical Properties

Crystallization behavior of polyvinylidene fluoride (PVDF) in NMP/DMF solvents: a molecular dynamics study

In this study, the crystallization behavior of polyvinylidene fluoride (PVDF) in NMP/DMF solvent at 9 to 67 weight percent (wt%) was analyzed by molecular dynamics (MD) simulation. The PVDF phase did not gradually change with the incremental increase in PVDF wt%, but displayed rapid shifts at 34 and 50 wt% in both solvents. The solvation behavior between the two solvents was quite identical from the similar radial distribution functions. However, PVDFs in DMF solvent showed a higher ratio of β phase crystalline structures than those in NMP solvent. It was found that DMF solvents were more tightly packed near trans state PVDF fluorine compared to NMP solvents. Also, NMP oxygen atoms interacted more favorably with gauche state PVDF hydrogen atoms over DMF oxygen atoms. The evaluation of properties observed in atomic scale interactions, such as trans state inhibition and gauche state preference, can be used as indicators in future solvent research.

Synthesis of Highly Dispersible Functionalized Carbon Nanotubes as Conductive Material through a Facile Drying Process for High-Power Lithium-ion Batteries

Herein, surface-functionalized carbon nanotubes (CNTs) were successfully synthesized by dry ball milling that facilitates industrial application. The optimal conditions were determined by analyzing the physicochemical characteristics of CNTs, including the content of the carboxyl group (-COOH) induced on the surface of CNTs by co-existing dry ice based on the ball milling time. Among them, 30 s ball milling (CNTs-30s) showed a high dispersibility in N-methyl-2-pyrrolidone (NMP) while retaining most carboxyl groups and maintaining the intrinsic high conductivity. In the evaluation of rate capability and 5 C/5 C cyclability applied to the Li_1+x (Ni_1-y-z Co_y Mn_z )_1-x O₂ with 60 % Ni (NCM622) cathode, CNTs-30s showed excellent performance based on a well-formed conductive network. Regarding improved dispersion properties and electrochemical performance, the optimal surface functionalization conditions, dispersibility, and electrode properties according to the processing time were analyzed; based on these, the correlation with electrochemical performance was confirmed.

Ultrahigh loading dry-process for solvent-free lithium-ion battery electrode fabrication

The current lithium-ion battery (LIB) electrode fabrication process relies heavily on the wet coating process, which uses the environmentally harmful and toxic N-methyl-2-pyrrolidone (NMP) solvent. In addition to being unsustainable, the use of this expensive organic solvent substantially increases the cost of battery production, as it needs to be dried and recycled throughout the manufacturing process. Herein, we report an industrially viable and sustainable dry press-coating process that uses the combination of multiwalled carbon nanotubes (MWNTs) and polyvinylidene fluoride (PVDF) as a dry powder composite and etched Al foil as a current collector. Notably, the mechanical strength and performance of the fabricated LiNi_0.7Co_0.1Mn_0.2O₂ (NCM712) dry press-coated electrodes (DPCEs) far exceed those of conventional slurry-coated electrodes (SCEs) and give rise to high loading (100 mg cm^-2, 17.6 mAh cm^-2) with impressive specific energy and volumetric energy density of 360 Wh kg^-1 and 701 Wh L^-1, respectively.