Polarity of Electrodes for Rechargeable Battery

Let's take a look at the following diagram for a sodium-sulfur rechargeable battery.

Given that during discharge, sodium is oxidised and sulfur is reduced.

In this video created by Chemistry Guru, Singapore's leading JC Chemistry tuition centre, we are interested to deduce the charges of electrode J and K during charging and discharging of the battery.

Would the charges stay the same or be reversed?

1. Discharging

During discharging, a redox reaction takes place in the cell which gives rise to flow of electrons.

Hence the energy conversion is chemical energy to electrical energy.

The battery functions as an electrochemical cell during discharging.

During discharging,

Na is oxidised to Na⁺, electrode J that is in direct contact with sodium will be the anode.

Anode for electrochemical cell is negatively charged.

S is reduced to polysulfide S_x^2-, electrode K that is in direct contact with sulfur will be the cathode.

Cathode for electrochemical cell is positively charged.

Hence during discharging, electrode J is negative and electrode K is positive.

2. Charging

During charging, electricity flows through the cell and forces a chemical reaction to convert the products Na⁺ and S_x^2- back to sodium and sulfur.

Hence the energy conversion is electrical energy to chemical energy.

The battery functions as an electrolytic cell during charging.

During charging,

Na⁺ is reduced to Na, electrode J that is in direct contact with sodium will be the cathode.

Cathode for electrolytic cell is negatively charged.

S_x^2- is oxidised to S, electrode K that is in direct contact with sulfur will be the anode.

Anode for electrolytic cell is positively charged.

Hence during charging, electrode J remains negative and electrode K remains positive.

This means that the polarity of electrodes remains unchanged during charging and discharging of a rechargeable battery.

Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore

Back to other previous Physical Chemistry Video Lessons.

Found this A Level Chemistry video useful?

This free chemistry video lesson is brought to you by Chemistry Guru, Singapore's esteemed H2 Chemistry tuition centre since 2010.

Please like this video and share it with your friends!

Join my 18,000 subscribers on my YouTube Channel for new A Level Chemistry video lessons every week.

Check out other A Level Chemistry Video Lessons here!

Need an experienced tutor to make Chemistry simpler for you?

Do consider signing up for my JC Chemistry Tuition classes at Bishan or on-demand video lessons!