Lithium Battery Over Discharge

18650 lithium battery cell

With the technology change, everything is getting more advance and upfront. Now people love to adopt more reliable and cost-worthy technology for their use. The trend is also touched the regular use of batteries by bringing more advancement regarding their material and charging and discharging approach. Lithium-ion batteries have been the choice of interest for every commercial and local electric automotive need. Gone are the days when industries do not focus much on the little details of their products. Now, the age is on the edge of a significant technological revolution; with a prime focus on AI, batteries have also changed.

Lithium batteries have been in substantial commercial demand for a long time because of their various essential features. Every year the global market size of lithium batteries has been heightened. The high energy density of lithium battery technology makes this kind of battery more popular and prominent. Now people want to know more about lithium battery features, including charge and discharge cycle, to understand the potential hazard level if there is any. In this article, we summarize all the possible causes and effects of lithium battery over-discharge.

What is Lithium Battery Technology?

Lithium-ion batteries have become the ultimate battery choice compared to other regular and local batteries. The concept of rechargeable lithium batteries is not very new or even of this century. Infect was introduced for the very first time in the early 1970s. After some more advancement on the idea and evolution, it becomes commercially available sometime in the 1980s. Obviously, the concept holds power but required more modification, so the initial attempt somehow get failed. Over time with the gradual advancement in technology, lithium batteries earned a top position among the other batteries for their better function and cost-friendly approach. Now lithium-ion batteries hold prime importance in Electric Vehicle and automotive industries.

The integration of lithium batteries into portable devices has become popular due to many reliable facts, including low power density, lightweight, enhanced safety, good charge/discharge cycle, and reduced material cost. The prime feature of any battery technology is its charge and discharge cycle. Over-discharge and overcharge are the fundamental safety concerns that are tagged with each battery. But the impactful battery management system of the lithium-ion batteries gave its technology an upper hand compared to the lead-acid and nickel batteries.

What is Lithium Battery Discharge?

Battery discharge is a common technique that people mainly adopt to estimate a rechargeable battery life cycle. Basically, the process involves using all the battery power stored in a regular rechargeable battery. The discharge cycle is completed once the battery does not hold any power to operate thoroughly. Lithium-ion batteries also offer a significant discharge to charge cycle. In most cases, a new lithium battery from the factory has about 30% of the charging. This is the standard battery power.

Sometimes people suggest that why could not factories charge it fully? The reason is the safety issues. The lithium-ion batteries only hold as low as 5% of the battery power during the discharging process. This process is also known as protected discharge. During the protected discharging process, the voltage becomes lower to a certain point. But in case of over-discharge or deep discharge, the voltage could be lower than a critical value which could cause potential damage to the battery life, efficiency, and functioning. Lithium batteries are subjected to protected discharging but deep discharging, or over-discharging could cause difficulty in charging the battery again. In that way, sometimes, the battery may lose all the functioning capacity.

Lithium Battery Over Discharge

Although lithium-ion batteries offer a great range of reliabilities still it is harmful to deeply discharge your battery. If your lithium-ion battery is deeply discharged and you let it unused in that state for a long time, then there are high chances of potential harm and damage to the battery’s progress or function. There are various factors for these harmful impacts, most of which are linked to the lithium-ion battery’s internal chemistry. When discharge the lithium battery below to a standard safe voltage, the copper from the anode copper current collector can dissolve into the electrolyte.

The abundance of copper ions can stick to the anode during charging by chemical reduction. This reaction might cause dendrites. The dendrites are the least favorable and essential in any battery as they might cause a potential short circuit inside the battery. During the overcharging, these dendrites could be formed by lithium instead of copper. Under normal circumstances, the lithium battery pack holds a supervisory circuit that loads or disconnects the cells from the charger when the cells have above or below voltage compared to the recommended numbers.

Self-Discharge Of Lithium-Ion Batteries

Lithium batteries hold great importance because of their excellent charge-to-discharge cycle. The critical feature of lithium-ion batteries is their protected discharging. The average self-discharge value of the batteries is high, especially of those which hold the high deep discharge. Lithium batteries came with a protection circuit that protects the battery from damage and potential abuse. During the over-discharge, this safeguard automatically turns off the battery. By this step, the battery could be unusable while being slipped into a sleeping mode. This mode is customarily activated when you need to store a lithium-ion battery pack in a discharged state for some time.

The self-discharging could deplete the remaining charge if not slipped battery in the sleeping mode. The lithium-ion battery pack’s protection or supervisory circuit can cut off between 2.2V and 2.9V per cell. But the actual values might depend on the manufacturer. The battery chargers hold the specific wake-up feature, which is known as a boost. This feature reactivates the discharged batteries from their sleep mode. The random charging would not help at all to reactivate them.  Boost applies a small current and activates the protection circuit. The correct cell voltage once reached, the standard charging of the battery starts gradually. The one crucial aspect to note here is that you could not boost the lithium batteries that have dwelled voltage below 1.5V per cell for longer than a week. Because the chances are that the copper shunts might have been formed inside the cell, leading to a partial or a total electric short.

Effect of Over-discharge on Lithium-ion Battery

Lithium-ion batteries hold great importance in various big industries, and their sheer market size depicted their great values. Multiple researchers have performed many experiments on lithium-ion batteries to evaluate, evolve or understand their efficiency in various ways. According to the experimental finding of different Chinese researchers on the over-discharge of lithium-ion batteries, the high internal temperature act as a great tool in the discharging process. According to their results, when the over-discharged cells of the lithium battery pack were cooled down, the ac impedance and internal temperature suffered an abnormal increase when the current was applied. The cell could be lost most of its working capacity.

Under the designed situations, the lithium-ion batteries could reach the cut-off voltage in a short span of 10 minutes. This process indicates the failure of the cell. According to various published reports, the average self-discharge rate of lithium-ion battery cells is 1-5% per year. Under the adverse temperature, this figure could go from 3-10% per year. The overall battery could reach its complete and discharge within a year if stored in a high-temperature environment.  The dissolved copper from the anode collector will move from the separator. This might lead to the internal short. The separator is semi-permeable that located between the cathode and anode. The lithium ions move from this separator to activate the working efficiency and lithium battery’s chemistry.

Storing of Lithium-ion Batteries

Manufacturers make sure to store them in the right place for the proper functioning and working efficacy of lithium-ion batteries. Storing lithium batteries always linked with appropriate uncertainties. Sometimes manufacturers ask to keep the lithium batteries at a charge state of 40 to 50%, but this could cause losing them to over-discharge. But the best process of storing lithium-ion batteries is to keep them in a cold place with a high charge. There is still potential ambiguity present in the storing process. Storing lithium-ion batteries at a low charge might work at room temperature.

Various manufactures suggest storing lithium batteries in a refrigerator to maintain their working efficacy while protecting them from a different kind of battery abuse. New lithium batteries are generally delivered with a charging of 30% depending on the assembly and its mAh. But this is the standard value. Having them with a full charge can bring potential hazards, including internal short and deep discharge risk, etc. Recharging is also essential to maintain the proper functioning of your lithium-ion battery. Make sure to not leave your unused battery be discharged for longer than a week.


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