A Preliminary Understanding of the "Platform Voltage" of lithium Batteries

Introduction

In modern electronic devices and energy storage systems, lithium batteries have become the preferred power solution due to their high energy density, long cycle life and relatively low self-discharge rate . The performance of lithium batteries can be evaluated in many ways, among which the plateau voltage is a key indicator.
This article will explore the concept of platform voltage, the main factors that affect its stability and height, and the characteristics of platform voltage. In addition, it will discuss the discharge rate, a parameter closely related to platform voltage, and delve into the essence of lithium battery discharge platform, explaining the scientific principles of voltage performance when electrochemical reactions reach dynamic equilibrium.

1. The concept of platform voltage

A plateau in a battery basically means that the charge/discharge curve of the battery is a plateau (flat). For example, the charge/discharge curve of a lithium-ion battery using lithium iron phosphate as the positive electrode material (positive electrode active material) and graphite as the negative electrode material has a plateau region.
The discharge process of a fully charged lithium battery usually includes three stages: the initial voltage drop, the subsequent stable period (plateau period), and the final voltage drop again. Among these three stages, the stable period is the longest. The longer it lasts, the higher the discharge platform of the battery, which is usually closely related to the manufacturing process of the battery .

2.Main influencing factors :

For ternary lithium batteries , under constant voltage conditions, stop charging when the voltage reaches 4.2V and the current is less than 0.01C, then leave it for 10 minutes. At any rate of discharge current, when the battery is discharged to 3.7V, the length of time it takes to discharge is an important indicator of battery quality. However, don't blindly pursue a high platform. Sometimes the platform voltage is high but the capacity is reduced, because the platform voltage is different under different rate conditions .

Battery manufacturing process: Different lithium battery manufacturers have different market positioning and technical process means, which leads to differences in the controlled discharge platform, thus affecting the quality of the battery .

Battery materials: The characteristics of the positive electrode material directly affect the discharge platform phenomenon. For example, the potential of solid solution materials such as lithium cobalt oxide changes little with the lithium ion concentration, while materials such as lithium iron phosphate that form a two-phase structure through phase change show a clear platform area during charge and discharge.

Charge and discharge rate: The discharge rate will affect the voltage change during battery discharge. The higher the discharge rate, the lower the battery discharge voltage platform may be.

3. Characteristics of platform voltage

Stability: The platform voltage is the most stable part of the battery voltage curve. When charging, the battery voltage remains stable in the platform stage; when discharging, the battery voltage is also relatively stable in the platform stage.

Typical value: Different types of lithium batteries (such as lithium cobalt oxide, lithium iron phosphate, nickel cobalt aluminum, etc.) have different typical platform voltages. For example, the charging platform voltage of lithium cobalt oxide batteries is usually around 4.2V, while that of lithium iron phosphate batteries is around 3.2V .

4. Discharge rate

The discharge rate (F) is a parameter that describes the speed of battery charge and discharge. It is defined as the "N-hour charge (discharge) rate" and is usually used to indicate how long it takes for a battery to be fully charged or fully discharged. For example, if the battery capacity is 2200mAh and it is charged at a current of 0.1C, then the charging current I = 2200mAh×0.1C=220mA

5. The nature of lithium battery discharge platform

The platform phenomenon of lithium battery discharge voltage is essentially the voltage performance when the electrochemical reaction reaches dynamic equilibrium. This equilibrium point is the difference between the standard potential and the polarization potential. The characteristics of the positive electrode material directly affect this phenomenon. For example, the potential of solid solution materials such as lithium cobalt oxide changes slightly with the lithium ion concentration. Although it looks like a platform, it is actually approximate. The real platform is a material like lithium iron phosphate, which forms a two-phase structure through phase change rather than solubility change. This characteristic makes it show a clear platform area during charging and discharging .

In Conclusion

As an important indicator of lithium battery discharge characteristics, the stability and height of platform voltage are directly related to the performance and manufacturing process of the battery. Understanding the characteristics of platform voltage and the concept of discharge rate is of great significance for the design, use and maintenance of lithium batteries. With the continuous advancement of battery technology, in-depth research on these basic characteristics will help promote the development of more efficient and safer battery systems.