What is self-discharge of a battery?

What is self-discharge of a battery?

From the reaction equation, it can be seen that a sufficient and necessary condition for battery discharge is to have an electron transfer circuit or other means to “transfer” the electrons on the negative electrode from the negative electrode to the positive electrode. This “moving” can be continuous or intermittent; it can be external or internal; it can be solid or liquid. Eg;

① Connect the wires to the positive and negative poles to make the electrical appliance work;
②Between the positive and negative poles of the shell, such as the condensed acid on the top cover of the battery;
③Ions with valence that can be changed go back and forth between the positive and negative electrodes of the battery, such as iron ions.

In order to deepen the understanding, further analysis is now made.

In Figure 1, the battery is fully charged. If the two connecting wires are connected to the positive and negative poles respectively, the electrons on the negative plate in the battery will flow through the negative pole-wire-bulb-wire-positive pole-positive plate, which is the normal use of electricity. If there is a non-metallic conductor on the top cover of the battery, such as acid solution, alkaline water, rainwater, etc., as shown in Figure 2, if it is connected between the positive and negative poles, the battery will also self-discharge. At this time, electrons enter the polluted liquid from the negative plate-negative column, and an electrolytic reaction occurs at the interface between the polluted liquid and the negative column, and becomes ionic conductivity in the electrolyte; at the same time, an electrolytic reaction also occurs on the interface of the positive column—enters the positive column – Positive plate, which also causes the discharge of the battery.

What is self-discharge of a battery?
Figure 1 Working discharge of the battery
What is self-discharge of a battery?
Figure 2 External pollution discharge

If we inject acid into the battery shown in Figure 3, it is easy to understand that the positive and negative plates do not discharge when the acid is injected to the A level. When the acid is injected to the B height, the acid liquid has submerged the pole, and the battery does not have a discharge reaction at this time. Because there is no path for electron conduction between the positive and negative electrodes at this time, the part flooded by the electrolyte undergoes the same electrochemical reaction. In Figure 3, there is a section of electronic conductors-pole between the electrode plate and the conductive liquid of the top cover. The pole and the submerged plate constitute the battery, and the pole and the polluted liquid constitute the electrical appliance, so the results of the two are completely different.

What is self-discharge of a battery?
Figure 3 Reasonable height of internal electrolyte

The third case is shown in Figure 4. When the iron ion in the electrolyte moves to the negative electrode, it will take an electron from the negative electrode and become Fe2+, so due to the heat causes random Brownian motion, the Fe2+ on the negative plate also moves to the positive electrode randomly. When reaching the positive plate, Fe2+ emits another electron to become Fe3+, which “moves” an electron on the negative plate to the positive plate, which causes the self-discharge of the battery.

What is self-discharge of a battery?
Figure 4 Self-discharge of harmful ions