Lithium batteries, especially lithium-ion batteries, have been widely used in various fields. Although lithium-ion batteries have developed rapidly and are widely used, if safety issues arise, the consequences will be very serious. Early lithium batteries used metallic lithium in the negative electrode, which was prone to lithium dendrites and even corrosion during charging. This significantly shortened the battery cycle time and service life, and in severe cases, could even lead to short circuits or explosions.

By searching for lithium battery patent literature online , and analyzing the relevant technical indicators of lithium batteries from metrological perspective, the analysis results show that the application volume in the field of lithium batteries has shown a rapid growth trend in recent years.

This article obtained the basic characteristic parameters of lithium-ion batteries through basic experimental testing, and established an electrochemical model of lithium-ion batteries using numerical simulation software Comsol, verifying the accuracy of the model. On this basis, combined with some electrochemical equations, the voltage changes of lithium batteries in different environments were analyzed through simulation.

The main research purpose and content of this article is to analyze the influence of temperature and negative electrode particle radius on the charging and discharging performance of lithium batteries. Using the modeling software Comsol, the influence of temperature and negative electrode particle radius on the charging and discharging performance of lithium batteries was studied using the control variable method, while keeping other variables constant.

1 Working principle of lithium batteries

When the battery is charged, lithium-ion is generated on the positive electrode and moves through the electrolyte to the negative electrode. The structure formed by carbon in the negative electrode has many pores, and lithium ions that reach the negative electrode will be embedded in the micropores of the carbon layer. Charging capacity is positively correlated with the number of embedded lithium ions.

When the battery is discharged, the lithium ions embedded in the cathode carbon layer leave, enter the electrolyte, penetrate the polymer film, and finally embed into the positive electrode active material. Finally, the more lithium ions returned to the positive electrode, the higher the discharge capacity. In fact, the discharge process is achieved through the deinking and embedding behavior of lithium ions in bipolar active materials. So battery capacity is usually referred to as “discharge capacity”.

2 The influence of temperature

Due to the influence of external temperature on the charging and discharging characteristics of lithium batteries, it is used as a variable to observe the discharge voltage of the same battery at different temperatures to determine its performance and measure its working ability.This model studied the curve images of battery voltage at 300 K and 500 K.

For two curves, it was found that the temperature changed from 300 K to 500 K, and the voltage at the highest point increased by nearly 0.1 V, while the voltage at the lowest point decreased by nearly 0.1 V. Further observation and comparison of the curves revealed that during the initial discharge stage, the voltage of the lithium battery decreased rapidly, and the slope of the voltage curve decreased; At the end of discharge, the voltage curve drops sharply and eventually drops to the cut-off voltage.

Through analysis, it was found that the voltage curve of battery discharge undergoes significant changes at different temperatures. Under the same other conditions, as the temperature decreases, the initial discharge voltage decreases and the discharge time shortens. Therefore, the voltage drops sharply in the initial stage of discharge, then slowly decreases, and due to the increase in internal resistance, the internal temperature increases with the discharge, resulting in an increase in the ion conductivity of the electrolyte.

At the end of discharge, the voltage drops sharply because the concentration of negative reactants decreases and the amount of lithium ions embedded in the positive electrode structure increases, leading to the end of the reaction. As the ambient temperature decreases, the rate of voltage decrease increases. When a lithium battery is discharged, lithium ions are embedded in the cathode.

The more lithium ions are embedded, the more charges are released, and the voltage will correspondingly decrease. Similarly, during the charging process, the more lithium ions are removed from the anode, the more charge is charged, and the voltage will correspondingly increase. However, as the temperature continues to decrease and the electrolyte viscosity continues to increase, lithium ion migration will become very difficult, leading to a gradual decrease in migration amount.

3 The influence of negative electrode particle radius size

At a certain temperature, it can be seen from the changes in battery voltage and applied battery current density that under the condition of 300 K temperature, the commonality of lithium-ion batteries is as follows: the slope of the voltage curve is high in the initial discharge stage, and the change in slope is slow. Finally, it drops to the cutoff voltage at a fixed rate and then suddenly changes.

At the end of discharge, the slope of voltage drop first increases and then decreases. During the discharge process, lithium ions are embedded in the negative electrode, releasing more charge and causing a decrease in voltage. On the contrary, when charging, positive lithium ions are embedded, causing more charges to surge in, resulting in an increase in voltage.

By analyzing data on different negative electrode particle radii, it can be concluded that as the negative electrode particle radius decreases, when the current density of the battery unit used is the same and close to zero, the smaller the negative electrode particle radius, the lower the battery voltage, and the smaller the internal stress of the battery. Therefore, the battery life is longer compared to batteries with larger negative electrode particles.

4 Conclusion

By using appropriate modeling software, the performance of lithium-ion battery charging and discharging can be studied in detail and accurately from macro to micro, from experiments to models. This article starts with the electrochemical reaction of lithium-ion batteries and draws the following conclusions:

(1) Temperature can affect the internal active substances and electrolyte viscosity of lithium-ion batteries, thereby altering the efficiency of charging and discharging.

(2) The size of the negative electrode particle radius will affect the debonding between particles and the negative electrode, further affecting the conductivity efficiency and ultimately affecting the efficiency of charging and discharging.