A Guide to the Application and Customization of Three-Electrode Systems In Battery Testing

In the development and production of batteries, the three-electrode test system is an important analytical tool for accurately measuring and analyzing the electrochemical properties of battery electrodes. Compared with the traditional two-electrode system, the three-electrode system can better dissect the electrode behavior and reaction kinetics in batteries, and is therefore widely used in material testing and pole-and-ear cell testing. In this paper, we will introduce in detail the principle, working mechanism, application scenarios, equipment and fixture selection of three-electrode testing, as well as the influence of pole-ear design in three-electrode testing, safety considerations, and the need for equipment features.

1. Three-electrode material testing

1.1 Principle of three-electrode testing

A three-electrode system consists of a working electrode, a reference electrode, and a counter electrode. The working electrode is the centerpiece of the study and is usually one of the electrodes of the cell to be tested, such as the positive or negative electrode. The working electrode can be a solid or a liquid. When solid electrodes are used, care must be taken to establish a suitable electrode pretreatment step in order to ensure the reproducibility of the experiment. Mercury or amalgam electrodes are commonly used in liquid electrodes, both of which have reproducible homogeneous surfaces.

The reference electrode is used to provide a stable potential reference whose potential does not vary as a result of current flow. The working electrode is measured against the reference electrode by means of a potential difference meter with high input impedance, similar to the potentiometric device, which is the line used to monitor the potential of the working electrode. The reference electrode should have the following properties: good reversibility, the electrode potential in line with Nernst equation ; exchange current density is high, the electrode potential can be quickly restored to its original state when a small current flows; have good potential stability and reproducibility, etc..

Commonly used reference electrodes for aqueous systems are saturated calomel electrode (SCE), Ag/AgCl electrode, standard hydrogen electrode (SHE or NHE), mercuric oxide electrode and so on. For non-aqueous solutions, non-aqueous reference electrodes, such as Ag/Ag+ (acetonitrile) electrodes, are generally used. In the measurement of the potential of the working electrode, the solution within the reference electrode and the composition of the solution of the system under study is often different, in order to reduce or eliminate the potential of the liquid connection, commonly used salt bridge will be connected to the reference electrode and the solution under test; in order to reduce the uncompensated resistance of the solution, often use Luggin capillary.

The counter electrode is an auxiliary electrode, usually made of an inert material such as platinum or graphite, which is responsible for conducting the current to complete the current loop. Compared with the working electrode, the auxiliary electrode should have a larger surface area so that the polarization applied externally mainly acts on the working electrode, and the auxiliary electrode itself should have a smaller resistance. Voltmeter can be used directly to determine the potential between the auxiliary electrode and the working electrode, i.e., the tank pressure, without the need for dual reference electrodes to determine the potential of the two electrodes.

In a three-electrode system, current flows between the working electrode and the counter electrode, while the potential is controlled by the reference electrode. The principle of this test system is based on the control and measurement of the electrochemical behavior of the electrodes, and the behavioral properties of the material in an electrochemical reaction are understood by accurately monitoring the changes in the potential of the working electrode.

1.2 Working Mechanisms

The working mechanism of a three-electrode test system can be controlled by electrochemical test instruments, typical types of tests include:

-Cyclic voltammetry (CV): the kinetics of the electrode reaction is assessed by observing the relationship between current and potential by controlling the scanning of the electrode potential.

-Potentiometric intermittent titration (PITT) and constant current intermittent titration (GITT): the diffusive behavior and reaction kinetics of the electrode are analyzed by monitoring the change in current or voltage at a constant potential or constant current, respectively.

-AC Impedance Spectroscopy (EIS): Measurement of the impedance characteristics of a cell by applying an AC electrical signal to analyze the nature of the electrode-electrolyte interface.

These test methods can help researchers gain insight into the electrochemical properties of electrode materials, such as diffusion coefficient, redox reaction rate, cycling stability, etc.

1.3 Application scenarios

The three-electrode test system is mainly used in the following application scenarios:

-Development of new electrode materials: By accurately measuring the electrochemical properties of different materials, it helps researchers to screen out materials with superior performance.

-Electrode aging analysis: Through long-term testing, the decline mechanism of electrode materials can be evaluated to optimize battery life.

-Electrolyte-electrode interface study: analyze the interaction between electrolyte and electrode surface, especially the formation and stability of the solid electrolyte interface layer (SEI layer).

1.4 Major equipment

The equipment used for three-electrode testing is mainly recommended for Neware's equipment and corresponding fixtures. Comprehensive content, meet the requirements of the equipment for the R2 sector 4/8 series of milliamp devices (10mA/20mA/50mA/100mA), due to the existence of multiple voltage sampling, the need for auxiliary channel equipment (due to the requirements of the high input impedance, so can only choose the auxiliary channel of the high anodic program equipment).

-CT-4008Q-5V100mA-10Hz

-CT-8002Q-5V100mA-100HZ

-CT-8008Q-5V100mA-100HZ

-CA-4008n-1U-10VT-TC-HiZ

1.5 Clamp selection

Depending on the electrode material and test requirements, the design of the fixture can vary greatly to ensure stable contact between the electrode and the electrolyte.

When selecting a fixture for three-electrode testing, the following are the main considerations, and the use of small alligator clips is recommended:

-Size and shape of the electrode material: Select the appropriate fixture according to the size of the working electrode to ensure its full contact with the electrolyte.

-Position of reference electrode and counter electrode: The fixture design should be able to stably fix the three electrodes, so that the distance between the reference electrode and the working electrode is kept in the optimal state to avoid potential drift.

-Corrosion resistance and stability: The fixture material should have good chemical resistance to cope with a wide range of electrolytes and electrode materials.

1.6 Operational guidance

To perform the three-electrode test, the following steps need to be followed:

1. Preparation of electrodes: Prepare suitable working electrodes, reference electrodes and counter electrodes according to the test requirements.

2. Assemble the fixture: Fix the electrodes in the appropriate fixture, make sure the distance between each electrode is moderate to avoid short circuit.

3. Connecting the test equipment: Use the cable to connect each electrode to the test equipment and set the required test parameters (e.g. potential range, current range, scanning speed, etc.).

4. Conducting tests: according to the preset test program, run the test and monitor the current and potential changes of the electrodes in real time.

5. Data analysis: After the test is completed, the data are analyzed through software to draw current-potential curves, etc. to evaluate the performance of the electrode material.

1.7 Frequently Asked Questions

Q: What is the difference between a three electrode test and a two electrode test?

Three-electrode testing allows for more precise control and monitoring of electrode potentials and is particularly suitable for studying electrode reaction kinetics, whereas two-electrode systems are more suitable for overall cell performance testing.

Q: How do I choose the right reference electrode?

When selecting a reference electrode, it is necessary to consider its potential stability to match the experimental conditions, such as pH, electrolyte type, and so on. Common reference electrodes include Ag/AgCl and SCE.

2. Three-electrode lug cell test

2.1 Influence of polar ear design

Electrode lugs are an important part of the conductive connection inside the battery, and their design directly affects the performance, stability and safety of the battery. In three-electrode lug battery testing, the geometry, material and position of the lugs will have a significant impact on the test results:

-Conductivity: The conductivity of the lug material affects the internal resistance of the battery, which in turn affects the current distribution of the test.

-Heat dissipation: The design of the pole lugs also determines the efficiency of the battery's heat dissipation, and excessive temperatures may cause safety hazards.

-Electrode spacing: The arrangement of the lugs may affect the uniformity of the electrodes, which in turn affects the overall performance of the battery.

2.2 Security considerations

Safety is an important consideration in the testing of three-electrode lug batteries. The safety of the lug design and test equipment is especially critical because of the potential for heat, gas and even short circuits during the charging and discharging process.

-Thermal management system: Ensure that the test equipment has a good thermal management system to prevent excessive battery temperature.

-Pressure control: The pressure change of the gas inside the battery also needs to be closely monitored to avoid excessive pressure near the lugs.

2.3 Equipment and fixture customization

To ensure the stability and accuracy of the lug cells during testing, the equipment and fixtures are customized to meet the following requirements:

-Flexibility: The device needs to be able to accommodate different sizes and shapes of lug cells.

-High accuracy: The accuracy of the test equipment must be high enough to capture the minute voltage and current variations in the pole ear cells.

-Fixture design: The fixture must ensure good contact of the electrode to prevent the electrode position from shifting during the test.

2.4 Equipment Characterization Requirements

In three-electrode testing of polar ear cells, the equipment should have the following characteristics:

-Multi-channel support: able to test multiple batteries at the same time to improve testing efficiency.

-Precise potential control: Ensures potential stability, especially in cases where the design of the pole lugs may result in potential variations.

-Real-time monitoring and protection mechanism: with real-time monitoring system of temperature, pressure and voltage to ensure test safety.

2.5 Clamp customization points

The design of the fixture for the pole lug cells is particularly critical, and the following are the key points to consider when customizing them:

-Material selection: Select corrosion-resistant and conductive materials to ensure good electrical contact between the lugs and the equipment.

-Adjustability: Fixture design needs to have flexible adjustment function to adapt to different specifications of the battery.

-Insulation protection: Insulation needs to be considered in the fixture to prevent short-circuiting of current through undesired paths.

2.6 Frequently Asked Questions

Q: What are the main effects of pole ear design on battery performance?

The design of the lugs affects the internal resistance, heat dissipation performance, and current distribution of the battery, which in turn affects the efficiency and safety of the battery.

Q: How do I ensure that the fixture makes proper contact with the lugs during the testing of lug cells?

Make sure the fixture can firmly and stably fix the pole ear part of the battery to avoid poor contact during testing. Meanwhile, the design of the insulating part is also very important to prevent short circuit and error.

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