The analysis discharge curve of lithium battery

A,The feature of battery capacity

Battery testing under different ratio of discharge voltage and capacity curve is shown in figure 3.

Figure 3 different magnification relation curve of the discharge voltage and capacity

Can be seen from the diagram, in the whole course of the discharge lithium ion batteries voltage curve can be divided into three stages:

1) battery terminal voltage falling fast in the initial stage, the discharge rate, the greater the voltage drop in the faster;

2) battery voltage into a slow change of phase, this paragraph of time is called a battery of platform area, the smaller the discharge rate, the platform area, the longer the duration of platform and the higher the voltage, voltage drop, the more slowly.In the process of actual use of lithium ion battery, hope the battery work as much as possible in the platform area;

3) on the battery close to put out, the battery load voltage start fell sharply until discharge cut-off voltage is reached.In the aftermath of the capacity test, at the same time also can get the curve of the discharge current and the capacity of the relationship, as shown in figure 4.

Figure 4 different relation curve of the discharge current and capacity

Can be seen from the graph, the size of the battery discharge current, will directly affect the actual capacity of the battery.Discharge current, the greater the battery capacity decreases, this suggests that the larger the discharge current, the shorter the time of arrival in termination voltage experience.So when it comes to battery capacity, shall indicate the discharge current, discharge ratio).

Second, the battery open circuit voltage characteristic

Open circuit voltage test [6] for lithium ion battery open circuit voltage and the curve of the battery SOC is shown in figure 5.

Figure 5 battery charging and discharging OCV - SOC curve

Can be seen from the diagram, battery OCV - SOC curve and the battery discharge voltage curve trend is basically the same.In the middle of the SOC interval (20% < SOC < 80%), battery OCV change is very small, the battery to the courts;In the SOC at both ends of the interval (SOC < 10% and SOC > 10%), OCV the rate of change is bigger, the whole lithium iron phosphate batteries flat OCV - SOC curve of the middle area, the appearance of the steep on both ends of the head to tail, open circuit voltage method is the use of this stable corresponding relation between SOC estimation.

Lithium ion battery OCV - SOC relation curve affected by temperature, discharge ratio, aging degree of smaller [7], but in the condition of charging and discharging two, there are certain differences between the two characteristic curve.

Determination of battery discharge curve, is one of the basic method of the battery performance, according to the discharge curve, can be judged whether the battery performance is stable, and the battery in the allowed maximum current stable work.This paper comprehensively introduces the basic knowledge of lithium ion battery discharge curve.Due to the limited level of the author, the wrong place, welcome to comment.In this paper, longer, more than 10000 words, the main content includes:

1 battery voltage

1.1 lithium ion battery materials of electrode potential

1.2 open circuit voltage of the battery

1.3 the battery polarization

1.4 working voltage of the battery

The basic principle of 2 discharge test

2.1 discharge test mode

The information contained in 2.2 discharge curve

2.3 the basic form of discharge curve

3 discharge curve of the differential treatment

The working voltage of lithium ion battery discharge, it is always constantly changing, with a continuation of the time made ordinate, the working voltage of the battery discharge time, or capacity, or charged state of (SOC), or the depth of discharge (DOD) do abscissa, drawn curve is called the discharge curve.To know the discharge characteristic curve of the battery, first need to understand from the principle of voltage of the battery.

1 battery voltage

Electrode reaction to form the cell must meet the following conditions: losing electrons in chemical reaction process (oxidation) and get the electronic process (i.e. the reduction reaction process) must be separated in two different areas, this differs from the general REDOX reaction;Two electrode active material to meet the need of the REDOX reaction of electronic must by external transfer, this difference in micro cell reaction of metal corrosion process.Battery voltage is a potential difference between the positive and negative, specific key parameters including open circuit voltage and working voltage, charge and discharge cut-off voltage, etc.

1.1 lithium ion battery materials of electrode potential

Electrode potential refers to solid material immersed in electrolyte solution, shows the effect of electricity, i.e. the potential difference between the surface of the metal and solution, this potential difference is called the metal in the solution of the potential or electrode potential.Simple said electrode potential is said by reduction of certain ions or atoms for electronic trend.

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