What is the charging principle of 18650 lithium battery charger?

What is the charging principle of 18650 lithium battery charger?

Positive electrode: A copper rod is inserted into a copper sulfate solution (forming a Cu2+/Cu redox pair),

Negative electrode: A zinc rod is inserted into a zinc sulfate solution, forming a Zn2+/Zn redox pair
The two solutions are connected by a salt bridge (potassium chloride saturated solution), and the copper rod and zinc rod are connected by wires, thus forming the primary battery  

So electrons will flow from the negative electrode to the positive electrode, and what you need to ask is why electrons need to flow in a directional manner I don't know if you have learned the concept of standard electrode potential, but this value can be measured through experiments. The standard electrode potential of the oxidation-reduction pair composed of elemental zinc and zinc ions is negative compared to the standard electrode potential of the oxidation-reduction pair composed of elemental copper and copper ions (the electrode potential of the standard hydrogen electrode is set to 0), while the copper electrode is positive. Therefore, when connecting two electrodes with a wire, due to the potential difference between the two electrodes, electrons will flow from the negative electrode to the negative electrode, and the direction of the current is from the positive electrode to the negative electrode, opposite to the direction of electron flow. As we often say, water flows to a lower place because there is a height difference (terrain difference) between high potential and low terrain. It's a spontaneous process  

By using the standard electrode potential, the reactivity of metals can also be known. The lower the electrode potential, the stronger the reactivity of the metal element. We have learned in chemistry class that metals have an activity sequence table: potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin, lead, hydrogen, copper, mercury, silver, platinum, gold; This table is arranged based on the values of the standard electrode potential. We can see from this table that the metal element before hydrogen can displace hydrogen from the solution. As mentioned earlier, the electrode potential of the standard hydrogen electrode is set to 0. Therefore, the standard electrode potential of the redox pair formed by the metal before hydrogen and its cation is less than 0, while the standard electrode potential of the metal after hydrogen is greater than 0.