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10 Interesting Knowledge of Lithium-ion Battery You Should Know

2020-05-28

Batteries are widely used for power supply currently. Did you really learn about these batteries which bring power for your torches, cellphones, laptops, vehicles and even your home solar storage system. Generally, batteries can be classified into different types and categories, from chemical composition, size, application, and so on. But batteries can be divided into two major battery types:

1. Primary Batteries

2. Secondary Batteries

What kind of battery does lithium-ion battery belong to? Is it rechargeable? Can it be fully charged? What is discharge rate? In this article, we will explain 10 interesting general knowledge of lithium-ion battery. 

Q1: What kind of battery does lithium-ion battery belong to? What is primary battery and secondary battery?

Primary Batteries are non-rechargeable batteries that once depleted. Primary batteries exist in different forms ranging from coin cells to AA batteries. One of the most popular type of primary batteries is Alkaline batteries.

Secondary batteries is rechargeable after the energy on the battery has been depleted. Because lithium-ion battery can be recharged after using up through the movement of lithium ions between the anode and cathode, it belongs to rechargeable batteries which also referred to as secondary batteries. Based on different chemistry which affects the cycle life, lifespan, specific energy of batteries, secondary batteries can be classified into several types, including Nickel Cadmium(Ni-Cd), Nickel-Metal Hydride( Ni-MH), Lead-acid and lithium-ion.


Q2: What is lithium-ion battery composed of?

Lithium-ion battery is made of one or more power-generating compartments called cells.

The components of each cell is as shown below:

1) the anode and the cathode;

2) a separator between the two electrodes;

3) an electrolyte that fills the remaining space of the battery.

The anode and cathode are capable of storing lithium ions. By lithium ions moving between the negative (anode) and positive (cathode) electrodes through the electrolyte, the batteries can be charged and discharged. The positive electrode is typically made from a chemical compound called lithium-cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4) and other chemicals. The negative electrode is generally made from carbon (graphite) and the electrolyte varies from one type of battery to another. 

Q3: What is fully charged of lithium ion batteries?

How do you know whether the battery is fully charged? Here are two ways to learn.

1. While charging: Measure the current flowing into the battery. If the current is very low, (the charging current is reduced to C/10 the battery is nearly charged.

2. While Idle: Measure the terminal voltage, if it is equal to to around the max charging voltage,  which the difference is less than 100mV, it should be fully charged.

However, a fully charged Li-ion is more likely to failure than one that is partially charged. (See: How to prolong lithium-ion batteries life?)

Q4: What is state of charge (SoC) of lithium-ion batteries?

Essentially, the SoC acts like a fuel gauge of a car. The users are able to learn about the information of how much longer they can use the batteries before the batteries run out of power and be recharged. The state- of-charge (SoC) shows the rest energy available in the battery, usually expressed as a percentage. Understanding the SoC of a battery is better to help look after it. Sometimes the SoC is divided into: ASoC and RSoC.

ASoC is the absolute state-of-charge. It means the total amount of specified energy the battery contains when the battery is a new one. The ASoC of a new battery which is fully charged is 100% while an aging battery is hard to reach 100% when it is fully charged. RSoC is the relative state -of-charge, which means the current energy capacity that is available after taking capacity fade into account. 

Q5: What is depth of discharge (DoD) of lithium-ion batteries?

Depth of discharge (DoD) is the opposite of state of charge. It refers to the amount of battery energy that has been discharged in relation to its overall capacity. UFO lithium ion batteries is good enough to hold at a partial state of charge, or discharged to a 80% DoD.

 

Q6: What is the maximum charging voltage of lithium-ion batteries?

The maximum charging voltage is related to the chemical composition and characteristics of the battery. The nominal voltage of lithium-ion is 3.60V/cell. Most lithium ion batteries can be charged to a voltage of 4.2V per cell and there is a tolerance of around ± 50 mV per cell. If the lithium ion battery is charging over voltage, it could result in a shorten battery life and reduce the battery capacity.

 

Q7: What is the minimum discharging voltage of lithium-ion batteries?

Lithium-ion batteries is not suggested to be discharged to below their minimum voltage. It can be defined by the cut-off discharge voltage. The empirical voltage value is 2.7V-3.0V. The voltage value may change which is relative to temperature, load, aging degree or other factors.

 

Q8: What is charge and discharge rate of lithium-ion batteries?

The charge and discharge rate is also refer to C-rates, which specifies the charging or discharging ratio of a lithium-ion battery. If the lithium-ion battery is discharged at 1C, it means that the discharge current will deplete the entire rated capacity of battery in 1 hour.


Eg. 1C rate for a battery with a capacity of 100Amp-hrs  = A discharge current of 100 Amps

       2C rate for a battery with a capacity of 100Amps-hrs = A discharge current of 200 Amps

       0.2C rate for a battery with a capacity of 100Amps-hrs= A discharge current of 20 Amps

 

Q9: What is self-discharge of lithium-ion batteries?

Self-discharge, which is a typical characteristic of battery, refers to the electrical capacity that the battery lost when it is not used. All batteries are affected by self-discharge. But the amount of electrical self-discharge are different depending on battery type and chemistry. Lithium-ion batteries have a lower self-discharge among various batteries. According to Battery University, the self-discharge of Li-ion is about 5 percent in the first 24 hours and then loses 1-2% per month, the protection circuit adds another 3 percent per month. Figure 1 sums up the amount of self-discharge of different batteries. 


Figure 1: Self-discharge rate of different Batteries,Source: Battery University


In addition, self-discharge can be affected by age, cycling and elevated temperature and finally cause an increase of self-discharge. Normally, the self-discharge of Li-ion is fairly stable. However, if the lithium-ion batteries is fully charged in storage or store at high temperature, it could result in a higher self-discharge and also shorten the batteries’ life. In order to reduce self-discharge of lithium-ion batteries, it is suggested to store batteries at 40% charge at moderate room temperature. Figure 2 demonstrates the self-discharge of Lithium-ion batteries per month at diverse temperatures and state-of-charge (SoC). 


Figure 2: Self-discharge of Lithium-ion batteries per month at diverse temperatures and state-of-charge (SoC). 

Source: Battery University

Figure 3: Performance of lithium battery self-discharge rate at different temperatures (20℃, 40℃, 60℃)


Q10: What is cycle life of lithium-ion batteries?

Cycle life is the number of charge and discharge cycles that a battery can complete before it reaching its maximum cycle life and its performance deteriorated. Each round of full discharge and then full recharge is a cycle life. A full cycle is when you discharge the battery all of the way down, and then all of the way back up. But if you discharge a battery half way and then charge it back up, this is only half of a cycle. You had to do this twice before it would equal a full cycle. The cycle life of Li-ion batteries can be affected by the depth of discharge (DoD). Figure 4 shows the cycle life of lithium-ion batteries at different depth of discharge. 

Figure 4: Different Cycle Life at Different Depth of Discharge, Source: Battery University





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