10 most important things about charging lithium batteries for battery’s long life

Now-a-days we use lithium ion batteries in our day to day equipment and devices. The way it is charging and discharging became very important as it is one way by which we can increase its life. 

So before buying any device which works on lithium ion batteries we must be fully aware about the importance and facts on charging lithium batteries. This article is going to touch on all the relevant points that one must know about charging lithium batteries in detail. So let’s dive deeper into the topic.

What is the best way to charge a lithium battery

Devices and equipment like marine application, powerwall and golf carts use lithium ion batteries. So by charging lithium batteries properly we are making devices’ life spans longer. Make sure to look for a few things before plugging device for charging lithium batteries.

● Check whether your device has below or equal to 50% charge or not

In common sense, charging lithium batteries is different from charging conventional battery. For conventional batteries, you should only charge them when the charge is low enough because having a fully charged battery will not improve battery life but lead to more serious memory effects, which will affect the available capacity of the battery.

Many devices will tell you the percentage of battery left and how much a device can operate with that percentage of battery. This will help you to identify when device should be plugin for charging your device. For charging lithium batteries, it is advised to keep the charge between 20% to 80% and you can charge and discharge as you like. Because lithium battery has no memory effect.

● Switch of your device before charging

If you are sure that you need to charge device then switch off device fully and then plug that device in as it allows effectively charging lithium batteries. Don’t worry if you are not able to switch off device while charging lithium batteries as switching off device will be ideal.

● Connecting device to the power supply

Connect device to the device charger first before connecting charger to the power supply and disconnect device when battery reaches above 80%. Keep checking device and don’t allow it to charge 100% constantly when charging lithium batteries as it damages that battery health.

How does lithium battery charging work-chemical reaction during charging lithium batteries

Before we are able to use a lithium ion battery we need it to charge by a lithium ion battery charger first. Before charging lithium batteries the lithium ions are intercalated within the cathode and it doesn’t have the ability to produce electricity yet. As we start charging lithium batteries, an oxidation reaction occurs at the cathode end which causes it to lose some negatively charged electrons.

So to maintain the charge balance an equal number of positively charged ions dissolved in the electrolyte solution. Now these ions travel to the anode where they are intercalated within the graphite.

Chemical reaction involved in this process include:

● Reduction

It takes place at the cathode. Cobalt oxide combined with lithium ion to generate lithium cobalt oxide ( LiCoO2 ).

CoO2 + Li+ + e- → LiCoO2

● Oxidation

It takes place at the anode. The graphite compound LiC6 forms graphite and lithium ions.

LiC6 → C6 + Li+ e-

● Full chemical reaction for charging and discharging

LiC6 + CoO2 ⇄ C6 + LiCoO2

What’s the mode of lithium battery charging

There are four commonly used charging methods :
● CC mode of charging
● CV mode of charging
● CC-CV mode of charging
● MCC mode of charging

As our focus is Charging Lithium Batteries, we will directly jump to the CC-CV mode of charging. CC-CV mode is the hybrid mode of charging that basically utilises both CC and CV mode of charging. 

It uses CC ( Constant Current ) mode of charging in the first stage of charging and when voltage reaches a set threshold value then the charging process shifts to the CV ( constant Voltage ) mode of charging.

When charging lithium batteries , we need to have much longer CC mode than CV mode as shown in the graph.

Change of current and voltage during charging of lithium batteries

The change in current and voltage when charging lithium batteries is divided in four stages as shown in the figure.

1. Voltage rises at constant current
2. Voltage peaks, current decreases
3. Charge terminates
4. Occasional topping charge

Battery fully changed when the current level drops to the set value.

What voltage should a lithium battery be charged at

Charging lithium batteries commonly requires constant current and voltage supply as its charging method is CC-CV mode. At the beginning of charging, the voltage of the battery to be charged should be detected first. 

If the voltage is lower than 3V, pre-charging should be carried out first. The charging current is 1 / 10 of the set current, and generally, about 0.05C is selected.

After the voltage rises to 3V, you will enter the standard charging process. The standard charging process is: constant current charging with the set current. When the battery voltage rises to 4.20V, it is changed to constant voltage charging, and the charging voltage is kept at 4.20V. 

At this time, the charging current gradually drops, and when the current drops to 1 / 10 of the set charging current, the charging ends.

Should lithium-ion batteries be fully discharged before charging

No, avoid discharging your battery fully before charging as it will affect battery’s life adversely. Discharging a lithium-ion battery below 2.5 volt can cause short circuit due to internal metal plates making the battery unusable and unsafe. Many lithium batteries have a protection circuit named BMS that cut off the power if the battery voltage drops below 2 or 2.5 volt.

Do I need a special charger for lithium batteries and why

Yes, you do need a special charger for charging lithium batteries because it will fully follow the charging mode of lithium-ion batteries. 

If you are using a single cell lithium battery then it needs a specific voltage ( 4.2 volt mostly) and constant current to avoid damage to the battery. If you are using multiple cell lithium batteries then use a charger of the corresponding specification.

If you are using a lead-acid battery charger for charging lithium batteries then the battery may fail and catch fire. So try using proper lithium charging batteries as it will give more security and safety to you and your battery.

How do you tell if a battery is fully charged

By looking at the voltage of the battery you can tell how charged it is! This is known as OCV ( open circuit voltage ) which means measurement when not used in the circuit. Let’s understand it with an example. 

A lithium NMC cell has a maximum voltage range at 4.2 volt, so after letting it charge for a few hours, If it measures around 4.2 volt then you can assume that your battery is fully charged. So having proper documentation of your battery is important as the maximum voltage differs according to the specifications of the battery and its type.

Does fast charging reduce battery life

Yes, It does affect the battery life. As the rate of charging increases, instead of intercalation of lithium ions at the graphite, ions stick to the surface and form metallic lithium on the particles. They react with the surrounding of the electrolyte which cause them to become immobilised in chemical compounds, blocking the smooth movement of lithium ions.

The rapid movement of lithium ions causes the graphite to stress, warp and distort its atomic structure which affects its ability to accept lithium ions and hence degrading cell performance.

How many times can a lithium-ion battery be recharged and how often should I charge it

It basically depends on the chemistry of the battery and what you consider as the end of life cycle. Generally DOD 80% is considered as the end of life cycle.

● LCO – Around 700 cycles
● LMO ( Used in some older electric cars ) – Around 500 cycles
● NCA/NCM ( most electric cars ) – Around 1000 cycles
● LFP – 4000 + Cycles
● LTO – 4000 + Cycles
● NMC – 2000 cycles

Try charging your lithium battery as often as possible because lithium batteries have serious issues when discharged completely. Keeping the charge within a range of 20%-80% is better for the battery life. If the lithium battery is stored for a long time, it shall keep the power within the range of 30% to 50%, and conduct a complete charge and discharge cycle every three months.

FAQs

1. Can you leave a lithium battery charging overnight

Yes if you use a proper charger for your battery. Proper chargers have circuits that will disconnect the charger or move the device into the tickle mode when fully charged but it is advisable to avoid doing so.

2. How long can a lithium-ion battery last without charging

How long can a lithium-ion battery last without charging depends on the usage, brand type, and even the environment in which it is placed. 

The self discharge rate of lithium ion batteries is 3.5% per month, which is lower than other types of batteries. But if you are going to store a lithium ion battery for a long time, charging and discharging it one time every three months is helpful for the battery life.

3. How long does it take to charge a 12 volt lithium battery

The charging time depends on the charge rate. The charge rate of lithium-ion battery is 0.2C, so it takes five hours to charge a 12 volt lithium battery. It is recommended to purchase a special charger for charging to avoid affecting the normal use of the battery. At the same time, it is better to charge within a limited time because overcharging will affect the battery life.

4. Can you charge a lithium battery with a regular 12 volt charger

No, you can’t. As they both operate at different voltage and current values and the charge modes are also different.

5. What happens if you leave a device plugged in even after it is charged 100%

If you leave a battery even after 100% charge, It can overheat the battery which causes it to reduce its lifespan. Regular lithium-ion battery products will have a good battery management system which can prevent overcharge and overdischarge. So choosing a professional manufacturer is necessary.

The BMS of professional manufacturers adopts intelligent high-end imported chip BMS system, which can monitor the battery status in real time and provide multi-level warning. In contrast, small factories use domestic size or small factory protection boards, which have slightly poor safety and stability.