Impact of composite structure and morphology on electronic and ionic conductivity of carbon contained LiCoO2 cathode

Abstract

Cathodes in lithium ion batteries consist of an ionic conductor, an electronic conductor and a binder in order to make a composite that is both electronically and ionically conductive. The carbon coating on the cathode material plays a critical role for the electrochemical properties of lithium ion batteries due to the increased electronic conductivity. We explain the relationship between the electrochemical properties and the characteristics of composites prepared using the ball-milling process in this report. We investigated two types of carbonaceous materials (graphite and carbon black) in LiCoO 2 electrodes. These selected carbon materials have different characteristics and structure upon ball-milling with LiCoO 2 . The composite prepared by ball-milling for 5 min leads to better mixing of carbon and LiCoO 2 , an intimate contact of carbon on LiCoO 2 , a higher lithium ion diffusion (D Li ) than non ball-milled and longer ball-milled composites. On the other hand, a longer time of ball-milling (30 and 60 min) decreases the electronic and ionic conductivity due to an increase of disordered structure of carbon and a thick and dense carbon coating layer on LiCoO 2 particles, preventing the diffusion of lithium ions, respectively.

Extrusion‐Based Processing of Cathodes: Influence of Solid Content on Suspension and Electrode Properties

“…Furthermore, CB is located mostly near or on the surface of the NMC particles. The coating of the active material with CB particles has already been observed in high intensive dry‐mixing and wet ball milling processes by other authors . The benefits of that preprocessing can be achieved also in a high intensive extrusion process at high solid contents.…”

“…With increasing solid contents, the dispersion of the CB particles is enhanced, thus leading to more favorable electrical contacts and a higher number of transit percolation pathways in vertical direction. The increase in the resistance at 80% solid contents is explainable by the attachment of CB onto the NCM surface due to high stress in the mixing process and a lack of free available conductive additives within the structure to form transit percolation pathways for electrons . In the literature, anisotropic conductive pathways were discussed.…”

“…At a given component formulation, the changes in electrochemical performance are the result of the discussed structural variations arisen in the dispersion, coating, drying, and calendering processes . The structure influences the two important conductive mechanisms in a LiB electrode: electronic and ionic conductivities …”

“…An increase in the solid content of battery suspensions causes more time and energy‐efficient CB dispersion due to a higher efficiency of the dispersion process since higher shear stress can be transferred . A CB coating on the active material can be proven at high solid contents in the dispersing process . Although CB plays a crucial role in the electrode, the determination of CB aggregate and agglomerate size in battery suspensions is quite difficult.…”

Nitrogen-doped carbon nanofiber decorated LiFePO4 composites with superior performance for lithium-ion batteries

“…LiFePO 4 (LFP) with an olivine structure is a popular subject of intensive investigations because it has been reported to be an attractive electrode material for next-generation high-power LIBs [5][6][7][8]. Compared with LiCoO 2 cathode materials [9][10][11], LFP presents inherent advantages of non-toxicity, low cost, long cycle ability, high thermal and chemical stability, and acceptable operating voltage [12]. However, poor electronic conductivity and slow diffusion of lithium ions across the LFP/FePO 4 (FP) phase prevent its wider practical application [13].…”