Storage conditions and self-discharge characteristics of lithium-ion batteries

I. Main Factors Affecting the Self-discharge Rate of Lithium-ion Batteries:

Self-discharge rate of battery cells and battery storage temperature

The consumption current generated by the battery management circuit within the battery pack

The consumption current generated by the static current of the device when the battery is installed inside the main unit

The consumption current generated by the static current of the charging circuit when the battery is connected to the charger

The capacity of the battery, including the number of parallel cells in the battery pack

Ii. What is self-discharge of lithium-ion batteries?

Due to the spontaneous physical and chemical discharges within lithium-ion batteries, self-discharge occurs slowly within the battery cells, causing them to lose charge and resulting in the loss of chemical energy. Under normal circumstances, the self-discharge rate of lithium-ion batteries is 0.5% to 3% per month. The storage temperature of the battery has the greatest impact on the self-discharge rate. Higher temperatures will intensify the internal chemical reactions of the battery, leading to more self-discharge. Therefore, the storage environment of the battery has a significant influence on its lifespan.

Iii. Self-consumption of Battery Management System (BMS)

In addition to the battery cells, a smart battery also requires a battery management circuit (BMS) to monitor the battery current, voltage and temperature in real time, providing safety protection and power calculation for the battery. Besides the self-discharge of the battery cells, these electronic components will also consume additional current for the battery product.

The battery management system is meticulously designed to minimize current consumption and features various working modes with different current consumption in each mode.

The size of the battery capacity has a direct relationship with the storage shelf life of the battery. Batteries with smaller capacity can be stored for a shorter time, while larger capacity or more parallel battery packs can be safely stored for a longer period.

The battery's power status is directly related to its storage shelf life. Before long-term storage, the battery should be recharged to more than 30%.

The battery should be inspected every six months. If its capacity drops below 30%, it should be recharged to over 30%.

Four. Shutdown Mode

The Battery management system (BMS) is equipped with a shutdown mode to minimize current consumption. When the cell voltage drops below 2.2V, the BMS will enter the shutdown mode and turn off the battery output. At this point, the self-consumption of the BMS will be reduced to approximately 1uA, preventing severe battery undervoltage and permanent battery failure. This mode requires charging to be activated.

If the customer requires long-term storage or long-distance sea transportation, the main unit can actively send instructions to make the battery enter the shutdown mode. This can minimize the self-consumption of the battery and extend the battery storage time to the greatest extent. Shutdown command: Send the 0x0010 command to the battery address 0X16 twice consecutively within 2 seconds.

V. Transportation Safety

Since 2016, IATA/UN/DOT has limited the battery charging state to less than 30%. We must comply with these requirements, so all of our batteries are shipped with a battery level below 30%. It is recommended that you charge the battery as soon as you receive it. If you do not use it for a long time after receiving it, the battery power may drop to zero. If you do not charge it six months after the production date, there is a risk of permanent failure of the battery.

Six. Fully charged storage

Considering the battery's self-discharge, some customers may store the battery fully charged for the maximum storage time. However, lithium-ion batteries should not be stored at 100% charge. If they are continuously stored in a 100% charged state, lithium-ion batteries will lose a certain amount of capacity. This is very common in UPS applications and laptops. When kept fully charged continuously, lithium batteries will lose 5% to 10% of their original capacity. We recommend that the battery store about 50% of its capacity for a long time.

Vii. Calendar Life

Even if the battery is not charged or discharged, due to the aging of the chemical substances inside the battery cells, there will still be certain wear and tear during long-term storage. Our empirical value is 5% per year.

If used normally, the empirical value is that the battery capacity is reduced by about 5% for every 100 cycles.

Viii. Summary

There are still many factors that affect the actual shelf life of lithium-ion batteries. For the general maintenance methods of lithium-ion batteries, we suggest:

• Check the inventory batteries every four months; Especially for those that have been installed inside the device and have not been used for a long time, the battery cannot be charged.

Under low SOC conditions, the storage time of lithium-ion batteries must not exceed six months.

Storage temperature has a significant impact on batteries. Store batteries at room temperature or slightly below room temperature (ideally 10-20°C).

When batteries need to be transported, keep their power level below 30% to comply with regulatory requirements.

Our product stipulates that capacity checks should be conducted every six months. If necessary, charge it in a timely manner.