How do lithium ion batteries fail

Using the incorrect charger for the lithium battery pack can also cause a range of problems. Most battery pack chargers for lithium-ion batteries are designed to prevent overcharging. However, using the wrong charger can cause overcharging or over voltage of the lithium battery pack as well as swelling.

Charging at this temperature can cause lithium plating this is when the lithium-ion collects along the anode's surface as metallic lithium becomes deposited there. This plating cannot be removed; it becomes permanent. Once this occurs, the battery becomes more susceptible to damage such as high rate charging that can lead to short circuits. It can also become more easily damaged from crushing or impacts. People using lithium battery packs have to be careful of over-discharge as much as overcharging of the battery.

Lithium-ion battery chemistries should never have the voltage fall below 2 volts. This issue can happen when the battery is placed into storage for long periods of time or when discharged too much. With the voltage below 2 volts, both the cathode and the anode begin to break down. The anode current collector will start to dissolve, as the copper dissolves into the electrolyte. The copper ions begin to precipitate into metallic copper that can cause a short circuit when the battery is charged above 2 volts.

Meanwhile, the cathode begins to release oxygen; the battery will start to experience permanent capacity loss after a few cycles.

One of the most common failures is the result of the battery pack overheating. Overcharging the battery is one cause to heating issues. The excess charge combines with higher temperatures such as direct sunlight. The battery pack experiences an increased level of stress. Thermal runaway is another factor that can impact lithium ion batteries. This occurs when the internal temperature in the battery pack becomes excessive along with the rise of pressure.

The rate of heat and pressure that begins to increase causes the electrolyte and the metal oxide cathode to break down. Gases begin to build in the battery pack; the safety vents cannot dissipate the gases from the battery pack fast enough.

Once one battery in the pack experiences thermal runaway, the next battery will start to experience thermal runaway as nothing can stop this effect until the battery ignites or explodes. Thermal runaway is usually prevented with the use of battery management systems BMS located in the battery pack. The BMS has safety features that will prevent overcharging, overvoltage, over-discharge, and other problems.

The system ensures that the battery continues to run at safe operating levels. It can also monitor and regulate the temperatures and bleed off excess energy during charging. It will store diagnostic information if there are problems with the battery pack as technicians can troubleshoot failures. Most of the problems with battery packs will be prevented by the BMS. Other problems such as small shorts or aging will simply cause the battery to stop working.

Yet, consumers should be aware of the dangers that can occur. Issues such as leakage and thermal runaway are the most dangerous. If that is indeed the case, then why did major global companies experience thermal events even after having passed compliance tests? And that brings up a bigger question — are standards-based tests such as UL safety tests sufficient to guarantee lithium-ion battery safety?

Sherlock What is Sherlock? Sherlock Services. DfR Solutions Team Events. Media Library. Why do Lithium Ion Batteries Fail? Futhermore, at low temperatures, the reduced reaction rate and perhaps contraction of the electrode materials slows down, and makes makes more difficult, the insertion of the Lithium ions into the intercallation spaces. As with over-voltage operation, when the electrodes can not accomodate the current flow, the result is reduced power and Lithium plating of the anode with irreversible capacity loss.

Operating at high temperatures brings on a different set of problems which can result in the destruction of the cell. In this case, the Arrhenius effect helps to get higher power out of the cell by increasing the reaction rate, but higher currents give rise to higher I 2 R heat dissipation and thus even higher temperatures.

This can be the start of positive temperature feedback and unless heat is removed faster than it is generated the result will be thermal runaway.

Several stages are involved in the build up to thermal runaway and each one results in progressively more permanenet damage to the cell.

The cells are normally fitted with a safety vent which allows the controlled release of the gases to relieve the internal pressure in the cell avoiding the possibility of an uncontrolled rupture of the cell - otherwise known as an explosion, or more euphemistically, "rapid disassembly" of the cell. Once the hot gases are released to the atmosphere they can of course burn in the air. The breakdown of the cathode is also highly exothermic sending the temperature and pressure even higher.

See methods used to avoid these problems in the section on Cell Protection. Lithium Cobalt Oxide was the first material used for the cathodes in Lithium secondary cells but safety concerns were raised for two reasons. The onset of chemical breakdown is at a relatively low temperature and when the cathode breaks down, prodigious amounts of energy are released. For that reason alternative cathode materials have been developed. The diagram below shows the breakdown characteristics of several alternative cathode materials.

The graph above shows that Lithium Iron Phosphate cathodes do not break down with the release of oxygen until much higher temperatures and when they do, much less energy is released. The reason is that the Oxygen molecules in the Phosphate material have a much stronger valence bond to the Phosphorus and this is more difficult to break. The other cathode chemistries are based on Lithium metal oxides which have much weaker valence bonds binding the Oxygen to the metal and these are more easily broken to release the Oxygen.

Note that consumer concern about the safety of Lithium batteries tends to be focussed on the Lithium cathode materials, whereas in reality, thermal runaway is initiated at the anode, NOT the cathode. Non-Uniformities Non-uniform current flow due to localised defects in the region of the interface between the separator and the anode surface can also give rise to Lithium plating. Examples of such defects are:. The corresponding high concentrations of Lithium ions give rise to Lithium plating.

Because of their flexible casing, pouch cells are more vulnerable to several of these defects than rigid cased cylindrical and prismatic cells. The electrodes of Lithium cells expand and contract during charging and discharging due to the effect of the intercalation of the Lithium ions into and out of the crystal structure of the electrodes. The cyclic stresses on the electrodes can eventually lead to cracking of the particles making up the electrode resulting in increased internal impedance as the cell ages, or in the worst case, a breakdown of the anode SEI layer which could lead to overheating and immediate cell failure.

A similar process, possibly augmented by the accumulated release of small amounts of gas due to the slow deterioration of the electrolyte each time it is heat cycled, could result in swelling of the cell and ultimately rupture of the cell casing. The effects of voltage and temperature on cell failures tend to be immdiately apparent, but their effect on cycle life is less obvious. We have seen above that excursions outside of the recommended operating window can cause irreversible capacity loss in the cells.

The cumulative effect of these digressions is like having a progessively debilitating disease which affects the life time of the cell or in the worst case causes sudden death if you overstep the mark..

The battery thermal management system must be designed keep the cell operating within its sweet spot at all times to avoid premature wear out of the cells. Beware: the cycle life quoted in manufacturers' specification sheets normally assumes operating at room temperature. This would be totally unrealistic for automotive applications.

Graphs showing how cycle life varies with tempeature like the one above are seldom provided by cell manufacturers. One of the main functions of the BMS is to keep the cells operating within their designed operating window the green box above. This is not too difficult to achieve using safety devices and thermal management systems.