Nanomanufacturing—Key control characteristics—Nano-enabled electrical energy storage—Part 3: Contact and coating resistivity measurements for nanomaterials
GB/T 41232.3-2023 Nanomanufacturing - Key control characteristics - Nano-enabled electrical energy storage - Part 3: Contact and coating resistivity measurements for nanomaterials
1 Scope
This document provides a standardized test method for the measurement of contact and coating resistivity of nano-enabled electrode materials.
This document is applicable for evaluating the practicality of coated composite materials and selecting the appropriate combination of coated composite materials and preparation techniques for their application.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/TS 80004-1, Nanotechnologies - Vocabulary - Part 1: Core terms
3 Terms, definitions, acronyms and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/TS 80004-1 and the following apply.
3.1.1
electrode nanomaterial
material used in nano-enabled energy storage devices such as lithium-ion batteries or super-capacitors which contains a fraction of nanomaterial and exhibits function or performance made possible only with the application of nanotechnology
Note: Electrodes used in lithium-ion batteries or supercapacitors consist of mixed raw material powders (e.g. electrochemical active and carbon based nanomaterial powders) in a solvent with binder which forms a casting slurry. These slurries are coated by doctor blade process on thin metal collector foils, dried and subsequently calendar compressed to the final electrode. The electrode shows a multilayered layout, built up of an aluminium or copper current collector and the electrode material layer. This material layer consists of the active phase (cathode - lithium containing mixed oxides or phosphate, e.g. LCO, NCA, NCM, and LFP; anode, e.g. graphite and supercap - activated carbon), a conducting phase (e.g. carbon nanomaterials like CB, carbon nanotubes or fibres) and an organic binder (e.g. PVDF or SBR).
3.1.2
coating resistivity
resistance to the passage of an electric current through the electrode material layer
Note 1: It is expressed as electrical resistivity.
Note 2: The electric resistivity of the electrode material layer depends on several factors such as raw materials, the slurry processing step and the final electrode fabrication technology. Differences in the nanomaterial carbon content, the fabrication technology and the density or porosity of the layer can significantly influence its resistivity. It is possible to evaluate the resistivity by preparing a thin coating of electrode material on an isolator substrate. In the attached case study a sample design based on 5 cm2 ceramic substrates is shown.
3.1.3
contact resistivity
electrical contact resistance between the metal current collector and the electrode material layer for a contact area of 1 cm2
Note: During the life time of a battery the contact resistance influences the degradation stability (e.g. rise in internal resistance due to delamination), capacity loss during cycling or heating and rise of the internal temperature of the cell. The contact resistivity depends on the microstructure of the interface between metal collector and electrode material layer. The material and the electrode processing steps such as choice and pre-treatment of the metal collector or the calendaring process have an important influence on the contact resistivity. It is possible to evaluate the contact resistivity by preparation of a thin coating of electrode material on an isolator substrate. The method is derived from a “transmission line method” (TLM) used for characterization of contact resistivity of metal-semiconductor interfaces in the field of photovoltaics. In the attached case study a sample design based on 5 cm 2 ceramic substrates is shown. The measurement of coating resistivity is carried out using a 4-point probe method.
3.1.4
calendaring
process where the electrode foils pass under rollers at a high pressure
Note: Calendaring is an important step during the electrode manufacturing process, because by this method the final electrode microstructure and thickness is formed. Methods like rolling or lamination are used to densify the electrode material layer to a desired degree of thickness and porosity.
3.2 Acronyms and abbreviations
CB: carbon black
EDLC: electrical double-layer capacitor
LCO: lithium cobalt oxide, LiCoO2
LFP: lithium iron phosphate, LiFePO4
PVDF: polyvinylidene difluorite
SBR: styrene-butadiene rubber
TLM: transmission line method
4 Sample preparation methods
4.1 General
The preparation of electrode nanomaterial samples consists of the following steps:
a) mixing a casting slurry;
b) assembly of metal collector strips on isolator carrier substrates;
c) casting of the slurry on these carrier substrates; and
d) drying and densification of the samples.
4.2 Reagents
4.2.1 Casting slurry
An electrode casting slurry is prepared in steps by dispensing and mixing different powders with solvent and binder. The choice of material recipe and the procedure of slurry preparation depend on the user and can be carried out similar to the industrial processes. The viscosity of the casting slurry should be in the range 0.5 Pa·s to 6 Pa·s (at low shearing rate 1 /20 s). In this way, the slurry can be cast by doctor blade.
4.2.2 Isolator substrates
An isolator substrate serves as a carrier of the electrode coating. The substrate should be non-conductive, show a high accuracy in thickness homogeneity and flatness, a low roughness and a proper wettability with the casting slurry. Ceramic based thick film substrates like alumina with a thickness of (650 ± 5) µm, a flatness of < 10 mm per sample (50 mm × 50 mm substrate area) and a roughness Ra < 1 µm are recommended.
4.2.3 Metal collector strips and sample layout
Metal strips are cut out from the original current collector foil in the geometry of 2 mm width by 70 mm length. For the measurement of the coating resistivity four of these strips are bonded with glue based on cyanoacrylate in four-probe geometry (inner distance between metal strips contacts is 30 mm) on the isolator substrate. For the measurement of the contact resistivity 10 strips are bonded an equal distance (3 mm) from each other. Figure 1 shows the sample layouts. The choice of current collector material depends on the user and can be similar to industrial processes. Typical collector thicknesses are in the range 9 mm to 40 mm for aluminium and 10 mm to 20 mm for copper current collectors.
