IEST Lithium Battery Electrode Sheet Resistance Tester(BER2500)

1. The Importance of Electrode Resistance(conductivity) 

Electrode resistance (conductivity) influences the basic performance of batteries, not only on the power capability (internal resistance), but also on he reliabilitly or safety performance. Through the measurement of electrode resistance, the property of electric conductive,micro-structural unifommity of electrodes can be evaluated during the electrode manulaclure process in advance thus help us to research andimprove the formulation of composite elecrodes but also to control parameters of mixing, coating and calendering processes. In the composite electrodes, the electric conducliviy is determimned by several primary factors,such as the interiacial resistance between the coating layer and the conductive foil, the distributions of conductive agents, the intrinsic resistance of acive material and the contact areas between particles.

Our Unique Testing Process:

• Comprehensively assessment of tle mixing and coating stability of slurry, which helps to recognize the anomaly aggregation of conductive
  agents in advance;
• Recognition of uneven mixing on mixture silicon-carbon anodes;
• Assessment of electric conductivityof active materials with different formulas;
• Assessment of electric conductivity of different conductive agents;
• Assessment of electric conductivity of the fimctional pre-coating layers of current collector;
• Failure analysis for the electric conductive network of electrodes;
• Analysis of contact resistance of the positive or negative electrode after formation.

2. The limitations of traditional test methods

Currently, there are several methods have been used to test the electrode resistance, such as four point probe method or multi point probe method and single point probe method. Though these traditional methods may have been maturely used in di&rent types of film industry areas, for the evaluation of the composite electrode films in lithium ion batteries, there are still several deficiencies that can not be ignored.

The four point probe film resistance test method has been wildly used in thin films industries, which use four or even more probes array to test the film resistance form film sur&ce. Its test procedure is easy and simple, and it can reveal the anisotropic resistance components of thin film by a simple equivalent circuit model fitting. However, considering its test principle and model fitting process, this mediod can only be suitable for a uniform thin film with smooth sur&ce, and the test sample should be loaded on an insulating substrate for ideal resistance fitting. Unfortunately, the electrodes ofliduum ion batteries are composite electrode with complex compositions, rough sur&ce and loadit^ on a low resistance current collector, so their four point probe test data, are often inconsistent and difficult to analyze the result by theoretical models. Increasing die probe number and using more complicate models can improve the test reliability to a certain extent, but that need more complex structures, and again the result analysis is still difficult.

The single point test method was another wildly used method in the lithium ion batteries industry, which use a fixed probe on the end of the curtent collector and a mobile probe on the surface of the electrode to directly measure the electrode resistance. This is a very simple way of electrode resistance test often carry out by a homebuilt system for difierent users, but it is still a rough empirical test method without considering the influence of press pressure, conductive path length, substrate materul and so on. As a result, the single point probe method can not provide a reliable and consistent electrode resistance data as well.

3. The IEST’s Creative Solution

The balery electrode resistance analyzer(BER series)uses two pressure-controllable plane probes to directy measure the electrode resistance, which can obtain the overal resislance and resistivity in the thickness directon of the electrode, includimng the contact the collector and the current.

The dual-plane, pressure-controllable, high-conductivity probe specially designed for composite electrode and micron-level flat surface treatment ensure the measurement accuracy, the high-precision resistance resolution and the attached calibration module ensure the stability and reliability of the results. 

4. Software

5. Measurement System Analyze

6. Applictions

7. Material Evaluation

7.1 Correlation between powder conductivity and electrode conductivity

Results Analyze:

• Adjust the Ni content in the NCM material, and test the powder conductivity. It can be found that as the Ni content increases, the powder conductivity increases;
• Comparing three NCM pieces with different Ni content, it can also be obtained that as the Ni content increases, the conductivity of the electrode piece increases;

Powder resistivity and electrode have the same trend!

7.2 Evaluate the resistivity of uncalendered electrode pieces under different compaction densities

Results Analyze:

• For graphite electrode, with the increase of compaction density, the resistivity continues to decrease. The reason is that the contact between active materials increases, and the overall conductivity of the electrode becomes better;
• For NCM electrode, with the compaction density increases, the resistivity of the pole piece continues to decrease. The main reason is that as the pressure increases, the contact between terminals and the active material becomes better;

8. Process Evaluation

8.1 Evaluation of electrode primer technology

• The thicker the primer, the greater the resistance of the current collector;
• The thicker the primer, the greater the cathode resistance;
• After determining the best primer coating process based on the correlation between the two, the electrode resistance test can be used as a method for long-term monitoring of process stability.

8.2 Conductive agent distribution uniformity evaluation

• By monitoring the change use the resistance of the battery electrode, an abnormal battery electrode can be quickly identified, to prevent the bad battery electrode from flowing into the next process, and to save production costs.

9. Cell Evaluation

9.1 Analysis of electrode resistance during high temperature cycle & storage

• The resistance of the cathode continues to increase with the increase in the number of cycles, indicating that a large change has taken place on the cathode side after the high temperature cycle, which may be related to the byproducts on the surface of the cathode particles or the contact between the particles;
• The resistance of the anode membrane increases with the storage time, which indicates that the anode side has changed a lot during the storage process, which may be related to the increase of side reactions on the anode material surface.