Why Do Good Batteries Go Bad?

Batteries have become an integral part of our lives. They are found everywhere, from small electronic equipment to high-power energy storage plants, to electric vehicles (EVs).

A battery generates electricity from electrochemical processes. If the process is controlled within nominal parameters, the battery will operate properly and have a long life. However, many factors can influence battery stability, and a damaged battery represents a serious safety risk.

One form of battery damage is battery swelling, which we recently discussed in our article The Microsoft Surface Swollen Battery Problem. However, this problem is not specific to certain devices and can affect batteries in all types of systems. Swollen batteries should not be kept inside a device; however, their removal and disposal can also be dangerous and cause serious harm.

This article will elaborate on how batteries suffer damage and the risks such batteries present. We’ll look at what causes batteries to swell, and how to avoid and predict battery swelling. This information is useful for those who use batteries in their own lives (read: everybody) but will also help engineers understand how to properly design battery systems to prevent eventual consequences.

Most electronic devices today use lithium-ion (Li-ion) batteries. This is because Li-ion batteries have a high specific capacity and energy, as well as a long service life. They are also lightweight, have a good energy/size ratio, recharge quickly, and have low self-discharge rates. These batteries have widespread use in both low and high-power applications, including cell phones, laptops, power tools, EVs, and even airplanes.

Li-ion batteries also have drawbacks. Lithium is a much more reactive element than most of the substances found in other batteries, which can cause the generation of gasses under increased temperatures. Released gases increase the pressure within the battery and cause it to swell.

Li-ion batteries are very sensitive to high temperatures. In most applications, devices include an electrical circuit that shuts the battery down if temperature issues are detected. If the battery is poorly designed, it can be dangerous and difficult to transport.  

High battery energy density requires a high voltage of the cathode material. A promising cathode material is lithium nickel manganese cobalt oxide (NMC batteries) which increases the battery capacity and energy density. The high voltage increases the lithium efficiency rate, but also leads to considerable gas generation. For this reason, these batteries currently limit their voltage to around 4.3 V. Still, gases are generated on both cathode and anode.

Battery degradation can be accelerated by irregular conditions, but it naturally occurs over time and over charge-discharge cycles. Both calendar aging and cycle aging influence battery degradation, which results in reduced battery capacity and output power. The capacity refers to the energy that can be stored in the battery, and is commonly expressed in ampere hours or watt hours. In EV applications, a reduced battery capacity means a reduced driving range before recharging. Battery power fade is caused by increasing the internal battery resistance, which results in a reduced rate at which the battery can absorb or release energy. In the case of EVs, this impacts charging times as well as driving performance such as acceleration or grade ability.

Batteries degrade in part due to loss of lithium inventory (LLI), where the lithium ions do not attach to the electrodes and leave the battery circulation process. This can be caused when the electrodes degrade and damage the sites where the lithium ions normally attach. There is an acceptable rate of lithium inventory losses. The first charge of a new battery reduces the available lithium as ions normally plate onto the anode. This is known as a protective solid electrolyte interphase (SEI) layer. After many battery cycles, repeated electrode lithiation and delithiation can change the electrode’s size by ±10 percent. This process can damage the SEI layer and cause lithium replating which means more lithium out of circulation.

If a battery is exposed to high temperature, it generally generates gas. High temperature can be caused by several factors:

• frequent battery charging and over-using
• overcharging or deep discharging
• manufacturer defects or battery damage
• using an inappropriate charger (unsuitable charger specification or damaged charger)
• too much current flowing inside a battery cell

The paper Mechanism of Gases Generation during Lithium-Ion Batteries Cycling details a study of the gases released in NMC111 batteries in the voltage ranges of 2.6 to 4.2 V and 2.6 to 4.8 V and temperatures of 25°C and 60°C. The gases were analyzed using on-line electrochemical mass spectrometry (OEMS). The study reveals that in Li-ion battery operation carbon dioxide (CO₂) and carbon monoxide (CO) are released from the cathodes and ethylene (C₂H₄), hydrogen (H₂), and CO from the anodes.

CO₂, CO, and H₂ gases are released due to electrolyte decomposition. CO and H₂ are directly generated from the electrochemical reaction of this decomposition, while CO₂ is the result of an additional chemical reaction where the previously released CO gas interacts with oxygen (O₂) from the cathode. Cycling conditions including temperature and cutoff voltage mostly define the gas ratio of CO₂/CO, which was found to vary from 0.82 to 2.42.

H₂ gas is released because of its adsorption (surface assimilation) in pores of powdered graphite on the anode. The researchers believe that the reduction of residual moisture on the anode contributes to hydrogen releasing. The residual moisture can appear because of electrolyte contamination by water or incorrect drying of electrodes and other battery components. Therefore, batteries should be tested and verified in different humidity conditions.

Excessive gas generation causes batteries to swell, which represents a significant safety risk. Devices with swollen batteries should not be used and their batteries should be properly replaced and discarded. Swollen batteries left in the device can be extremely dangerous. The battery housing could become punctured, which would allow hazardous gases to escape. The battery could also catch fire and explode, causing serious injury.

Swollen batteries should be replaced by experienced personnel in a proper workshop. It is useful if the battery is discharged before having it removed from the device. The battery is discharged when the device cannot run anymore (the device is not connected to the charger). Due to the heat, the battery could be stuck in the device. Forceful battery extraction (crushing, dropping, bending, breaking, or puncturing) should be avoided. The battery must not be disassembled or exposed to high temperature. Swollen batteries are hazardous waste and must be disposed of at a proper facility.

Devices supplied by Li-ion batteries usually employ built-in heat sensors and overcharging protection circuits. In addition, these batteries have a strong casing to prevent gas leaks.

Generally, batteries despise heat, which causes many issues and shortens their lifespan. Even when the device is turned off it can still draw a small current from the battery, called leakage current. If a device will not be in use for a long period, it is advisable to store the battery in a cool and dry place. Hot and humid places have a negative impact on the battery.

Likewise, devices supplied by Li-ion batteries should not be plugged in all the time. It is useful for Li-ion batteries to discharge and recharge to renew their capacity. Users usually make a mistake with the laptops at home or in the office and keep them constantly connected to the charger.  

The battery charger condition and its specifications are very important for a healthy battery. The charger should always be used as recommended by the manufacturer. Improper chargers can cause high current and heat the battery or overcharge it.

Weak batteries should be replaced on time. This should be done before the battery is completely dead—i.e., when the battery capacity is low and it discharges very fast.

Some applications can get away with simple, low-cost battery solutions, while others—such as EVs—require more expensive and complex solutions. In the first case, it is not costly to replace old batteries, but it can be very costly in the second case. However, in both cases, there are significant safety risks created by old or damaged batteries. It is useful to explore the manufacturer guidelines to extend battery life and prevent the problems caused by damaged batteries.

In general, the following factors contribute to battery health:

Temperature: Temperature has a significant impact on battery performance and condition. Batteries should not be exposed to high temperatures, regardless of whether they’re in active use, standby or long-term storage. It is also important to minimize exposure to low temperatures and high moisture environments. Expensive and complex battery systems often have a battery management system including thermal control that ensures proper battery conditions.

Mechanical Damage: Batteries must be hermetically sealed. If the housing cracks, external moisture can short circuit cells. Any damage that can cause the battery to short circuit will render it inoperable and present safety risks.

Fully Charging: A 100 percent state of charge has a negative impact on a battery. Batteries operate better when they are not at full charge. To this end, smart chargers can be integrated with a personal calendar to predict how much energy is required for each day, and charge to the proper amount below 100 percent.

Over-discharging: A very low state of charge has a significant negative impact on batteries. Usually, one can protect against over-discharge by shutting down the device. However, other secret enemies could over-discharge the battery, and it is the self-discharge effect that could discharge the battery to zero. Self-discharge is a battery process that causes the battery to discharge because of its internal chemical reactions, even though no load is connected to the battery. Every battery has a self-discharge process, but the rate is different for different battery types and conditions. The self-discharge process cannot be completely avoided, but can be minimized when the battery is stored in cool (10 to 25°C) and dry areas. High-temperatures accelerate self-discharge.

Fast Charging: Although it seems like a better option for end-users, fast charging is not good for a battery. However, for applications such as EVs, fast charging is one of the key requirements. Manufacturers of EVs, batteries, and chargers are constantly working to improve fast charging features to balance efficiency with battery health.

Fast Discharging: Just like fast charging, fast discharging also has a negative impact on batteries. Since aggressive battery discharging means high currents and increased temperature, it should be avoided whenever possible.

Advanced battery systems such as those found in EVs, electric boats, and heavy machines usually incorporate a battery management system (BMS) to ensure safe operation of the battery. Battery systems can also have built-in protection circuits that measure the battery voltage and switch off the load to protect the battery from deep discharge. There are also battery overheating protection circuits which measure the battery temperature. If the temperature is too high, the charging process is stopped or the load is disconnected or decreased.

More details can be found in our series on battery management systems: Part 1: Battery Modeling, Part 2: Battery State Estimation, and Part 3: Battery Charging Methods.