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When Li-ion battery is discharged or being used, the positive lithium (Li+) ions move from anode to cathode through the electrolyte. Meanwhile the electrons move in the same direction through the external circuit. Why does this happen? I mean, why does a Li+ ion get attracted to the positive electrode (cathode)?

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Why does Li+ ion attract to the positive electrode (cathode)?

Let's first see how we define the Cathode and Anode based on electron movement.

A cathode is the electrode from which a conventional current leaves a polarised electrical device.

Now, importantly, Cathode polarity with respect to the anode can be positive or negative; it depends on how the device operates. Although positively charged cations always move towards the cathode (hence their name) and negatively charged anions move away from it, cathode polarity depends on the device type, and can even vary according to the operating mode. In a device which provides power, the cathode is positive.

Does it happens because of Redox Reactions?

Yes, you're correct. Another way to understand, the positive nature of Cathode, or build up of positive ions is, by considering the redox reactions occurring.

The anode is the electrode where the oxidation reaction

$Red \rightarrow Ox + e^{-}$ takes place while the cathode is the electrode where the reduction reaction

$Ox+e^- \rightarrow Red$ takes place.

That's how cathode and anode are defined.

Now at the cathode you have the reduction reaction which consumes electrons (leaving behind positive (metal) ions at the electrode) and thus leads to a build-up of positive charge in the course of the reaction until electrochemical equilibrium is reached. Thus this explains why positive ions move toward the cathode in a Lithium ion battery or more generally a galvanic cell.

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    $\begingroup$ > "The anode is the electrode where the oxidation reaction." No. "The anode is an electrode through which conventional current flows into a polarized electrical device." (en.wikipedia.org/wiki/Anode) It has nothing to do with reactions. As a matter of fact, there is NO chemical reaction inside a Li-ion cell during charging or discharging (unlike other chemistries). $\endgroup$ May 4, 2017 at 21:30
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In electrolytic cells the negative electrode are called cathode while positive electrode are called anode , in which +ve ions move towards cathode as cathode is negative electrode, and -ve ions move towards anode , while in electrochemical cells cathode is positive electrode while anode is considered to be negative electrode due to high density of electron. As these cells are electrochemical cells, So in li ion batteries, when external load is connected in full charging state electron starts moving from anode towards cathode and electronic density starts decreasing on anode , and increase on cathode, At the same time Li ions starts moving toward cathod due to high density of electron on cathode.

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