What‘s the self-discharge of a lithium battery? What‘s the self-discharge rate of various kinds of lithium batteries?

The basic self-discharge phenomenon is primarily talked about in secondary batteries like LiPo battery, Li-ion battery, NiMH battery, and others. Self-discharge is also referred to as the charge holding ability. This means the battery‘s ability to store the power under particular environmental circumstances in an open circuit state. Normally, storage conditions, materials, and manufacturing processes mainly affect the self-discharge. Self-discharge is a principal parameter for determining the battery‘s performance. Generally, a lower battery storage temperature means a lower self-discharge rate. Nonetheless, it must be noted that very high or very low temperature might cause the battery to be corrupted and then it can‘t be used. BYD traditional batteries need a temperature range of -20 to 45 for storage.

After the battery is completely charged and left open for some duration of time, a particular degree of self-discharge is expected. According to the IEC standard, after NiMH and Ni-Cd batteries are totally charged, they are left open for 28 days at a temperature level of 20 ° C and a humidity of 65 %. Compared to other rechargeable battery units, the self-discharge rate of solar batteries having liquid electrolytes is considerably lower, at about 10 % per month at 25 ° C.

What Is Overcharging and How It Affects a Battery‘s Performance?

Overcharging is the process of continuing to charge your battery after it has actually been completely charged after a specific charging procedure. Given that the capacity of the -Ve (negative) electrode is greater than that of the +Ve (positive) electrode throughout the design, the gas produced by the +Ve electrode moves through the separator paper and is combined again with cadmium produced by the -Ve electrode. Under regular situations, the internal pressure of the battery won‘t increase substantially, however, if the charging current is quite big, or the charging takes too much time, the oxygen that is produced is too late to be taken in and it might cause the internal pressure to increase and the battery to deform and leak. Also, its performance will be reduced by a considerable amount.

What Is Over-Discharging and How It Affects the Battery‘s Performance?

Over-discharge means the behavior of a battery to continue to discharge after it has been discharged from the internal charge. The extreme discharge of the battery might result in irreparable repercussions to the battery. In case the extreme discharge increases the battery‘s internal pressure, the battery‘s capacity will be substantially attenuated. The discharge current determines the discharge cutoff voltage.

Over-discharge of the battery might bring disastrous repercussions to the battery, particularly high current over-discharge, or repetitive over-discharge has a higher effect on the battery.

What Are the Control Approaches for Overcharging?

In order to avoid the battery from becoming overcharged, it is essential to manage the charging endpoint. When the battery is completely charged, there is some unique info available to figure out whether the charging has actually reached the completion point. There are 6 methods to avoid the battery from being overcharged:

ü  V control: When a battery is completely charged and reaches the peak voltage, the voltage will reduce by a specific value.

ü  Timing control: Set a specific charging time to manage the charging endpoint. Normally set the time needed to charge 130 % of the nominal capacity to manage.

ü  TCO control: Thinking about the security and qualities of the battery, charging at elevated temperatures need to be prevented, so charging needs to be suspended when the battery temperature level increases by 60 ℃.

ü  T control: When a battery is completely charged, the distinction between the temperature level and the ambient temperature level will reach the maximum.

ü  dT/ dt control: Determining the rate of change in the battery‘s peak temperature by judging the charging‘s endpoint.

ü  Peak voltage control: Identify completion of charging by identifying the battery‘s peak voltage.