Different types of Lithium-Ion batteries are used for a range of applications. Operating environment for these applications is not always controllable and, sometimes, a battery has to experience quickly changing environmental conditions.
Performance of Lithium-Ion battery depends upon environment specially temperature. While high temperature causes performance degradation, shortens life, and poses dangers of thermal runaway; low temperature can reduce capacity, and slow down chemical reactions. Chemical reactions slow down as electrolyte thickens (freezing affect) and internal resistance increases.
Wide spread use of lithium-ion batteries urges researchers, and manufacturers to find ways to prevent Lithium-Ion battery from freezing in cold. Similarly, users want to know techniques to prolong their battery life without being impacted by cold weather. In this article, we will explore relevant concepts, cover various techniques in detail to improve battery performance by preventing battery freezing, and answer relevant questions.
What is Meant by Lithium-Ion Battery Freezing?
When lithium battery freezing or lithium-ion battery freezing is discussed, it is not referred to actual freezing of the battery or electrolyte within it. Actually, in extreme cold weathers (below 0°C), chemical reactions slow down because mobility of charged particles depends upon temperature. Electrolyte also becomes thicker or more viscous as temperature drops below a certain range. Moreover, electrolyte becomes less conductive. All these factors contribute towards increased internal resistance, causing capacity drop and reduction in power output. As mobility of ions decreases, lithium ions start depositing onto the anode as metallic lithium. This slows down reactions further, and poses safety hazards.
Conclusively, we can say that “battery freezing” usually refers to severe performance degradation caused by reduced ion mobility and lithium plating, rather than literal solidification of the electrolyte.
Lithium-Ion Battery Freezing Point:
Normal operating temperature range for lithium batteries falls between 15 to 35°C. Regardless of other factors, prolonged battery life and peak performance is ensured in this temperature window. Most of the batteries are safe for discharge operations typically between -20°C and 60°C temperature range. This range can vary slightly depending upon manufacturer and can be found on product catalogue. As this safe operating window varies so does freezing point of the battery.
Different manufacturers mention different freezing point for lithium-ion battery. It is worth highlighting that during lithium-ion battery freezing process, electrolyte becomes viscous and less conductive. This indicates that composition and concentration of electrolyte is deciding factor regarding battery freezing point. Generically, we can say for most of the batteries that performance is reduced below 0°C, but electrolyte still remains liquid. Below -20°C, battery struggles and experiences power loss. And below −40°C some electrolyte formulations may partially solidify, leading to permanent damage.
Factors Impacting Li-Ion Battery Performance in Cold Weather
While it is known scientifically and practically that lithium ion battery, like any other battery, is impacted negatively by temperature, question rises if all batteries (with a same chemistry) will be affected equally or is there any way to control this effect if totally inevitable. So, here are controlling factors which can reduce freezing impact on a lithium-ion battery when it is used at subzero temperatures.
- Quality and type of battery material
- Structure of battery and its design
- State of Charge (SoC) of the battery
- Time duration for which battery was used in the cold
- Degree of insulation and other in-built protective measures of the battery
- Concentration and composition of electrolyte
Lithium-Ion Battery Temperature Impact Table
| Temperature Range | Effect |
| 15–35°C | Optimal performance |
| 0–15°C | Reduced capacity |
| -20–0°C | Charging unsafe |
| Below -40°C | Risk of electrolyte solidification |
What can You Expect if Lithium Battery Freezes?
A non-technical user might need to know common observations associated with lithium-ion battery freezing. During lithium battery freezing, lithium deposits onto anode or causes dendrite growth. Resultantly, one can notice that
- Battery capacity is reduced so it would stop furnishing energy before its normal/expected time duration
- Battery would shut down even if BMS will show that battery is charged
- An attempt to charge the battery will take longer than normal routine
Consequences of Charging Lithium Batteries in Freezing Temperatures
If lithium-ion battery is charged below permissible optimal temperature range in long-term (as discussed above), it will have many negative consequences. Some of these are already mentioned above. Here, we will be discussing details of few.
Irreversible Damage to Li-Ion Battery Pack
Charging lithium-ion battery in cold or freezing weather can harm its structural integrity. As temperature drops, chemical reactions slow down, and lithium ions start depositing on anode in an uneven manner. Moreover, local current density increases at separator-cathode interface. These changes impact structural integrity of battery and increase internal resistance. As the layer of lithium metal keeps thickening on the anode, battery life keeps shortening, and chances of absolute failure are increased.
Reduction in Li-ion Battery Capacity
As it is discussed that cold weather thickens liquid electrolyte present in lithium-ion batteries. This spoiled electrolyte hinders movement of charges within it. Moreover, chemical reactions slow down. Both these factors contribute towards increased internal resistance. Resultantly, above nominal cut-off voltage/potential, terminals can’t push ions between them. Remaining energy which could have been delivered if ions could move, is lost energy. How much capacity would be lost in long -run depends upon number of cycles repeated in cold weather. For example, lithium-ion battery which underwent 132 charging cycles at subzero temperature , might lose 35% of its nominal capacity.
Dendrite Growth and Short Circuits
If a lithium battery is used in cold environment for long, deposition of lithium ions on electrode would keep increasing. Deposited layer will take the shape of dendrites which will cross anode compartment, pass through separator, and enter cathode compartment. As two compartments with opposite potentials will no longer be separated and movement of ions will not be controlled, So short circuit is the expected outcome. Short circuiting in Lithium-ion battery is not just financial loss but also safety hazard.
Thermal Runaway
Cold temperatures indirectly increase the risk of thermal runaway by promoting lithium plating and internal short circuits, particularly during charging or rapid re-warming. Both increased internal resistance and short circuiting can cause thermal runaways in their own ways.
To explain intricate relationship between internal resistance and thermal runaway, let’s consider a simple example. A wire with higher internal resistance heats up more than the other wire with lower internal resistance carrying same amount of current. Likewise, ions moving through viscous electrolyte cause more potential loss in form of waste energy and heat up battery to greater extent.
Similarly, short circuiting heats up battery very quickly as ions with varying potential come together and cause localized spark or fire. It must be noted that both reasons of thermal runaway are associated with each other for the case we are discussing. Though, there might be situations when one factor might not be leading the second factor in batteries.
Thermal runaway in lithium-ion battery, happening specifically in cold weather, might end up in explosions and fires which is a major safety hazard.
Preventing Lithium-Ion Battery Freezing in Cold Weather
Affects and hazards associated with using li-ion batteries in cold weather suggest that users shall avoid charging these batteries below 0°C unless specifically designed for low-temperature charging. Moreover, if use is non-omittable, then some special measures shall be taken to prevent lithium-ion battery freezing in cold environments. Here, some basic measures are discussed briefly.
- Warming-up Li-ion Battery Before Charging
As charging a lithium-ion battery could lead to gradual increase in internal resistance, dendrite growth, and electrolyte changes; So it is suggested that lithium-ion battery be warmed up to reach a safe temperature limit before charging cycle. Because pre-heating a lithium-ion battery before charging is the most effective way to prevent lithium plating in cold weather. There are different ways to warm-up the battery effectively and safely. E.g.
- If battery is small, you can keep them in your pocket or put it under your clothes or place it near some heat source for few minutes.
- You can also try to protect them from cold air by using insulated covers or casings
- For large batteries, you can bring them indoor to improve their thermal activity. For example, lithium-ion battery of an EV parked in freezing temperature shall be brought inside house to increase its temperature naturally.
- For small as well as large batteries, heating pads or battery blankets can be used to increase battery temperature.
- Heated compartments are available for battery testing and storage purposes so those compartments can be used to warm-up the batteries.
- Using specialized Chargers for Charging Batteries at Sub-zero Temperatures
While it is ascertained that charging a Lithium-Ion Battery in freezing temperatures is harmful for battery, research also confirms that damaged caused to li-ion battery upon charging it at sub-zero temperatures is proportional to charging rate. Indirectly, slow charging can reduce the damage. Slow charging is not always a suitable option, so specialized chargers are recommended for charging lithium batteries in cold weather.
Chargers designed to charge li-ion batteries in cold environment have capability to increase and decrease C-rate depending upon environmental temperature. This temperature is sensed by BMS and communicated through CAN or some other communication protocol. So chargers must also have appropriate communication circuitry.
- Appropriate Storage
Example of an EV battery is discussed above which was recommended to bring indoors before charging cycle. This example can serve as preface to suggest appropriate storage of li-ion battery. During storage, it must also be considered that battery is not left in cold weather, specially, if it is not under use. If there is no way to get battery out of vehicle or other cold space, then insulation covers shall be used to keep it warm. Finally, li-ion battery shall be kept at dry place.
- Avoiding Over-Discharging Li-Ion battery
If you are using li-ion battery in cold environments, then try maintaining its charge to 50% minimum. Lower the Stato-of-Charge (SoC), higher will be the chances of degradation. Charged battery has energy to resist the cold but uncharged battery doesn’t.
- Employing Advanced Battery Management Systems (BMS) to Maintain Temperature
Smart Battery Management Systems can monitor and control various factors that can limit the damage caused to battery when being charged in cold weather. BMS can employ heating techniques to heat up battery cells before starting the charging. It can control charging rate so damage is reduced. It will also be equipped with appropriate communication method and temperature monitoring techniques to monitor temperature continuously, direct charger to change charging level, and employ other suitable measures. A suitable BMS can also prevent battery from discharging below a specified level depending upon temperature.
Conclusion
Lithium-ion batteries which have liquid electrolytes, are prone to structural changes and damage when used in cold weather. Electrolyte thickens when battery is charged in cold, internal resistance of battery increases, dendrite growth takes place, chances of thermal runaway, fires, and explosions increase, and structural integrity of battery gets at stake.
Some temporary solutions are devised to limit this damage to lithium-ion batteries because of cold weather. These solutions include using heating pads, heated compartments, insulation jackets, advanced chargers, and improved Battery Management Systems (BMS). Apart from these technical solutions, some small tips and tricks can be used to prevent your li-ion battery from freezing in cold. These tips include storing your battery in warm indoor places, bringing them indoor before charging phase, place them near to heat source for few minutes, and avoiding over-discharging the li-ion battery.
FAQs:
Is it safe to leave a lithium-ion battery in cold weather for a long time?
A:No, it is not safe to leave a lithium-ion battery in very cold environment for long especially unattended. It is because of potential affects, a battery might undergo during this inappropriate storage phase leading to explosion, fire, or short circuiting. User must also consider that Long-term exposure to extreme cold accelerates degradation even if the battery is not in use.
Are there any symptoms of li-ion battery freezing?
A:If you are looking for any symptoms of damage after charging your li-ion battery in freezing environment, you shall observe it closely to find any cracks, or swelling parts. Moreover, performance of battery can also indicate upcoming danger. Sudden shutdowns, reduced capacity, voltage sag under load, charging refusal by BMS, and low power output are some of the factors, you can look for.
Can I prevent my li-ion battery from freezing in cold?
A:Yes, you can prevent your battery from absolute freezing and irreversible damage by employing some appropriate technology and following some suitable tips and tricks.
- Using smart chargers, appropriate BMS, heated compartments, and insulated casings are among basic technological techniques.
- Bringing li-ion battery indoor, placing it near some heat source, and using heating pads are some tips to improve thermal activity of battery and preventing it from freezing in the cold.
Author Introduction
Dr. Kevin Yang
Lead Electrical Engineer
Dr. Kevin Yang has 16 years of R&D experience in lithium battery power management systems (BMS) and 10 years in lithium ion battery engineer. Experienced in various lithium ion battery applications,he is capable of offering customized lithium battery solutions beyond cutomer expectation .
