When fabricating battery electrodes, their properties are strongly determined by the adjusted drying parameters. This does not only affect their microstructure in terms of adhesion, but also influences cell performance. The reason is found to be the binder transported to the surface during drying. Herein, it is shown that when thicker electrodes are processed, new challenges arise. On the one hand, loss of adhesion associated with certain drying conditions becomes a more serious problem; on the other hand, cracking occurs at a certain drying rate and with increasing electrode thickness.
1/3 Mn 1/3 )O 2 (NCM111), morphologies such as preferentially oriented crystals in the particles, [2] nanobrick morphology, [3] one-dimensional hierarchical microrods, [4] and hierarchically structured particles [5][6][7][8][9] were investigated. The latter is achieved by forming secondary particles with open intraparticle pore structure from assembled primary particles. The advantages of such structures are higher rate capability and improved cycling stability, due to a larger interface between active material and electrolyte, smaller diffusion paths and lower mechanical stress during cycling. By modifying the particle morphology of commercial compact materials in a few additional process steps, a comparison can be made between the commercial starting material and the produced structured material. This approach was applied in the work of Wagner et al. [9] by grinding, spray drying and calcination commercial NCM111. The influences of the process parameters in the production of such structures on the electrochemical properties as a function of the particle morphology were investigated. The optimum sintering temperature was found to be between 850 and 900 C, resulting in primary particle diameters of 350 and 550 nm. It is the optimum between the demands of the ionic conductivity of the primary particles and the electrical conductivity of the secondary particles. During the sintering process, the primary particles grow, which aggravates ion diffusion but increases the electrical conductivity due to sinter necks. The specific capacity was improved from 20 to 100 mAh g À1 at 10C for the original and the structured particles, respectively. [9]
A nanostructured, porous NCM cathode material is investigated regarding its behavior during electrode processing and electrochemical performance. The results are related to the densely packed NCM original material from which the nanostructure has been derived. Chemical composition and structural parameters are not affected by the nanostructuring process; changes are limited to the particle morphology in terms of primary particle size, specific surface area, and porosity. Electrodes containing a porous NCM material deliver lower adhesion strength values when adding identical amounts of PVDF binder. Increasing the binder fraction from four to six parts increases also the adhesion strength to an acceptable level without deteriorating the cell capacity. Despite initially high electrode porosities of 65−70%, electrodes with nanostructured NCM are capable of withstanding calendering to 40% porosity without destroying the porous particles. Full-cell tests with 50 mAh pouch cells and graphite anodes reveal substantially improved C-rate capabilities for the nanostructured material in relation to the commercial original NCM. The advantage increases with increasing C-rate and corresponds to shorter diffusion pathways in nanostructured NCM. Remarkably, even at low C-rates (C/20) where diffusion effects are considered secondary, porous NCM lies ahead of the original material. This can be explained by the higher surface area and thereby enlarged interface to the electrolyte, which eases delithiation. Long-term cycling up to 1100 cycles displayed further benefits for the nanostructured active material as one of the most prominent degradation factors, that is, crack formation and particle fragmentation, does not occur throughout the complete cycling procedurein contrast to the bulk particles of original NCM.
LiNi0.5Mn1.5O4 (LNMO) based spinel cathode materials for lithium-ion batteries are promising alternatives to the widely used mixed transition-metal layered Li(Ni,Co,Mn)O2 (NCM) oxides. LNMO is cobalt free and thus cost efficient,...
Excessive moisture adsorbed in electrodes and separators of a Li‐ion battery hampers its performance and is, therefore, removed to a certain amount in a post‐drying process. An insufficient understanding of the process results thereby in high process costs. Cost reductions can only be achieved efficiently with an improved process understanding by modeling this post‐drying process. As process modeling requires knowledge of sorption equilibria of water in the components of the battery, the sorption equilibria of water in different anodes are determined by means of a magnetic suspension balance and compared with different experimental setups. The measured data of the adsorption isotherms are described mathematically and give an impression of the amount of moisture, which is going to adjust at an equilibrium starting from a dry anode. Moreover, the materials of the anode are evaluated for their moisture sorption behavior. It is shown that mass‐weighted sorption equilibria of water in the materials yield a good approximation of equivalent equilibria in the anode. In the investigated anodes, the binder and rheology additive carboxymethyl cellulose (CMC) accounts for the most water uptake.
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