# What causes rechargeable batteries to age? What can be done to extend life of these batteries?

These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices, over time these rechargeable batteries lose the ability to recharge, retain and discharge energy thus users have to replace the devices or rechargeable batteries.

It is my understanding that the rise in battery internal resistance is the primary cause the rechargeable battery aging. Is this accurate? If so what can be done to lower or eliminate the internal resistance in rechargeable batteries.

If my understanding is inaccurate what is the cause for rechargeable battery aging?

If the causes for battery aging are understood, how can electronic engineers design charging and discharging circuits to extend the rechargeable battery life?

References:

• Note: I deliberately kept both Internal Resistance/Battery Chemistry and electronic circuit design together – Mahendra Gunawardena Jan 24 '15 at 13:24
• This is a hot topic in research and development with a lot of money going into and still no satisfactorily solution. A very interesting question but I guess not easy to answer in detail, especially not the second part. – Trilarion Feb 4 '15 at 10:00
• I am hoping for an chemical engineer or chemistry professional or research to provide some insight. From an EE standpoint it is increase in impedance. Question would how can the increase in impedance be slowed down. – Mahendra Gunawardena Feb 4 '15 at 11:35
• Rise in internal resistance might be better understood as a symptom of ageing, not as the root cause of it. – Solomon Slow May 13 '16 at 18:32

One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the memory effect. The memory effect occurs when a rechargeable battery is not fully discharged. It then "forgets" that it has a greater capacity than it thinks it has, and so in the future it discharges less.

A good example is a water bottle. Initially, water bottles have a certain capacity for water. Let's say that I drink most of the water in a water bottle during one usage. If the memory effect affected water bottles, I would not be able to drink any water in the future occupying the space that had held the water that had not been drunken the last time. That extra space would be forever lost. Over time, this can wear down a rechargeable battery. Fortunately, this generally only affects $\text{NiCad}$ and $\text{NiMH}$ rechargeable batteries.

I haven't been able to find much about effects that influence only lithium ion batteries, but there are a lot of across-the-board factors. Here's a short list:

• Chemicals breaking down
• Passivation (which affects lithium ion batteries), which is when a layer of unwanted chemicals form on the battery cell. This discusses a related phenomenon on page 4258:

Unfortunately, on recharge, the lithium has a strong tendency to form mossy deposits and dendrites in the usual liquid organic solvents (cf. Figure 15B). This limits the cycle life to 100-150 cycles (considerably lower that the 300 cycles required for a commercial cell), as well as increasing the risk of a safety incident.

• Mechanical stresses and leaking. Batteries can be damaged in a variety of ways, causing internal components to break and causing chemicals to leak out. This can be very dangerous to humans.
There are other long-term factors that increase battery aging. The page I linked for the above list seems to be fond of the Arrhenius equation: $$k=Ae^{-E_a/RT}$$ which shows that the rate of chemical reations changes as temperature changes. High temperatures mean faster reactions but also possibly a shorter life; this can affect non-rechargeable batteries significantly.

Finally, there's the phenomenon of self-discharge, which is when unwanted reactions in the battery "eat away," so to speak, at the battery's capacity. The process can differ based on the type of battery. Battery University has a page on it, which you may have already seen. It reiterates that temperature can speed up this process. Scarily enough, lithium ion batteries may discharge as much as 5% within the first 24 hours, slowing down to 1-2% per month after that.

• What causes the memory effect? How are the dendrites detrimental? Does self discharge contribute to long term capacity loss or does it only use up capacity on that charge? – Rick Sep 17 '15 at 17:29
• @Rick Wikipedia gives one related temporary process and the mechanism behind it: Voltage depression is caused by repeated over-charging of a battery, which causes the formation of small crystals of electrolyte on the plates. These can clog the plates, increasing resistance and lowering the voltage of some individual cells in the battery. This causes the battery as a whole to seem to discharge rapidly as those individual cells discharge quickly and the voltage of the battery as a whole suddenly falls. – HDE 226868 Sep 17 '15 at 23:33
• Re, The "memory effect." Check out z80.info/nicd2.txt The short version is, Yes, there is such an effect, but most of the problems that have ever been blamed on it actually were due to other problems (most especially, poorly designed trickle chargers). This info ultimately comes from NASA engineers who were willing to spend a lot of money to understand the batteries that they planned to send on space missions. – Solomon Slow May 13 '16 at 18:44