What is the power bank?

It is a portable power charger that can store their own electrical energy and be carried around, mainly is used for charging mobile phone, tablet and other consumer electronics products. Its main components include: Case, battery cells used for energy storage, circuit board with power control, input and output, converters and so on.

About lithium-ion battery

Lithium-ion batteries: The electrolyte of lithium-ion batteries is liquid, usually using a liquid electrolyte. The positive electrode material can be lithium cobalt oxide, lithium manganese oxide, ternary material, or lithium iron phosphate. The negative electrode material is graphite. Easy to explode in high temperature and pressure environments.

About polymer lithium battery

Polymer lithium battery is a type of lithium-ion battery that uses polymer electrolytes. The raw materials include polymer electrolytes (solid or colloidal) and organic electrolytes.

Polymer lithium batteries use aluminum-plastic film as the outer shell, and when organic electrolytes are used internally, even if the liquid is very hot, it will not explode, but it will swell.

Polymer lithium batteries cycle time is usually around 500 times, but the actual achievable frequency is influenced by various factors, including usage environment, charging method, and battery quality.

Polymer lithium batteries have various obvious advantages, such as high energy density, miniaturization, ultra-thinness, lightweight, high safety, and low cost. Due to its excellent performance, which are widely used in mobile devices including mobile phone, tablet, power bank, smartwatches, and other electronic products.

Due to the safety issue of power bank, nowadays, polymer lithium batteries are the first option to be chosen as components of power bank.

Lithium battery chemical properties

All rechargeable batteries are consumables, and as the battery chemical age increasing, its performance will decrease. As the chemical age of lithium batteries increases, the amount of electricity they can store will decrease, leading to a shortened time for devices to be used before they need to be recharged. 

One factor that affects battery power output is impedance, which may increase when the chemical age of the battery is too high. In low battery conditions and low-temperature environments, the impedance of the battery will temporarily increase, and coupled with a higher chemical age, the increase in impedance will be more pronounced. These are the chemical characteristics of batteries, which are applicable to all lithium-ion batteries in the industry.

Self-discharging of polymer lithium batteries

The self-discharge phenomenon of a battery refers to the spontaneous loss of its capacity when the battery is placed in an open circuit, also known as the charge holding capacity. Self-discharge reaction is inevitable, which not only leads to a decrease in the capacity of the battery itself, but also seriously affects the grouping and cycle life of the battery. Long term self-discharge can cause over discharge and result in battery failure. The self-discharge rate of polymer lithium batteries is generally 2% to 5% per month.

Self-discharge can generally be divided into two types: reversible Self-discharge and irreversible Self-discharge. The reversible Self-discharge can compensate for the loss of capacity reversibly, and its principle is similar to the normal discharge reaction of a battery. The Self-discharge that cannot be compensated for due to loss of capacity is called irreversible Self-discharge, which is mainly caused by irreversible reactions occurring inside the battery, including reactions between the positive electrode and electrolyte, reactions between the negative electrode and electrolyte, reactions caused by impurities in the electrolyte, and irreversible reactions caused by micro short circuits caused by impurities carried during production.

Transportation of power banks in international trading

Power bank is a very popular product as rise of consumer electronics products, are widely demanded in all over the world. Due to the characteristics of lithium batteries, The power bank normally is classified into Class 9 DG cargo according to IATA regulation and IOM regulation who have very strict requirement in Sea, Air and road transportation.

The SOC< 30% is strictly required in air shipment as now become factory default, which is normally in 20-25% of the total capacity. Even the Sea shipment also will remain < 50% to be ensured the safety during transportation, which is normally in 40-50%.

The timeline from the moment of power banks is shipped from factory to buyer, and then to end user takes very long. However, its’ self-discharge already starts from the moment it is off from the production line, which have to be concerned and take consideration about its remaining power inside during transportation and local storage time. And take action to prevent the power bank over-discharge cause lowing its battery life or even totally failure.

What factors affect the self-discharge of polymer lithium batteries

1. Temperature: High temperature environments will accelerate the rate of self-discharge.
2. Storage time: The longer the storage time, the faster the self-discharge speed.
3. Storage environment: Excessive humidity or the presence of acidic gases in the air can accelerate the self-discharge rate.

In summary, although the self-discharge rate of polymer lithium batteries is relatively low, it is still necessary to pay attention to the storage environment to avoid accelerating the self-discharge rate and affecting the battery life.

How to reduce self-discharge phenomenon?

1. Storage of batteries: When storing lithium polymer batteries, attention should be paid to the storage environment. Do not let the battery overheat or become too cold. Generally, it needs to be stored in a dry and cool place.
2. Regular charging: Regular charging can reduce the rate of battery self-discharge. It is recommended to charge the battery every 3-6 months to maintain its healthy condition.

Suitable operating and storage temperatures for lithium polymer batteries

The storage temperature of batteries is generally 25 ± 5℃ at room temperature, which can affect the activity of lithium ions. The higher the temperature, the higher the activity. However, if the temperature exceeds 60℃, it may cause irreversible damage to the isolation film inside the battery, leading to battery scrapping. If the temperature is too low, the lithium-ion activity will be too low, resulting in the battery capacity not being discharged, which means it will run out of power.

Maintenance of power banks

1. Waterproof and moisture-proof:

As an electronic product, accidental water ingress or prolonged exposure to humid air can cause varying degrees of corrosion or oxidation to its internal electronic components, short circuit of battery as well.

2. Anti drop and shock:

The internal components of the power bank cannot withstand impact, so it is necessary to prevent accidental landing during use. Do not throw, strike, or vibrate the mobile power supply. Rough handling of mobile power sources can damage internal circuit boards and internal short circuit of battery.

3. Cold and heat protection:

High temperatures can shorten the lifespan of electronic devices and cause some plastic components to deform or melt. Working in a cold environment can cause moisture damage to the circuit board within a mobile power supply.

4. Correct charging and discharging:

It is best to discharge and charge once a month to ensure that the internal battery cells remain in optimal condition and effectively extend their service life. Avoid over charging or over discharging. When the battery level is too low, it should be charged in a timely manner; When the battery level is too high, charging or use should be stopped. Long time charging may cause the power bank overheat, and may even damage the power bank or cause safety hazards.

5. Storage:

Power banks should be stored in a moderately warm and dry place to prevent exposure to sunlight. The power bank must not be stored in a non-charged state for a long time to prevent damage to the battery due to over self-discharging. The power bank must be recharged at least once for every 3-6months. It is best to maintain the battery level between 60% and 70% before not using it. Please do not transport or store with metal items such as necklaces, hair clips, etc.

6. Safety usage:

Do not use the power bank too frequently, and do not charge too frequently. If used too frequently, it will shorten the service life of the power bank and increase the risk of danger. Stop using the power bank if it occurs expansion, swell or break down, May cause on fire.

Alarm or remind for charging of power bank

Due to the lithium battery special character, especially for air shipment, the IATA regulation requirements of SOC cause remaining battery power from Ex-factory is already very low. 2-5% self-discharge rate will consume its remaining power quickly, can’t last for a long-term storage.

A good charging and discharging maintenance can extend the power bank shelf time for many years.  

So, it is necessary to establish an alarm or reminding system to help reminding to charge the power bank regularly in warehouse before dispatched or sold.

Contact UUTEK for a “Storage Remind Table” to maintain your power bank stock in a proper and easy process.