Weather conditions and battery performance

Hot weather can reduce power output and increase charging times, affecting both immediate and long-term battery health. We’ve addressed heat related issues in this article, but cold weather influences battery performance as well.

An overheated EV battery struggles to cool down because heat accelerates its chemical processes. This decreases range and may lead to longer charging times, among other issues. What happens when the opposite applies and batteries become too cold? 

Thermal management of batteries is a very complex subject. While thermal management generally applies to handling heat and less to avoiding cold, temperature changes do impact the kinetic energy of batteries and therefore their performance and endurance, as chemical reactions in the cells of batteries are temperature dependent. When it gets cold, these processes slow down and batteries start to struggle to deliver the power needed. This has always been an issue with the lead-acid starter batteries in combustion engine cars, but modern Li-ion batteries in electric vehicles are also affected.

Ideal temperatures

First of all, Li-ion batteries should ideally be stored in cool, dry conditions at a temperature above 15° Celsius. Generally speaking, acceptable temperatures for EV batteries are between minus 20° C and plus 60° C, but the temperature range for optimal performance of Li-ion cells lies between 5° C and 25 C – although some say up to 35° C (which can depend on the exact chemistry and cell design). On either side of that region, batteries will degrade fast and show an increased risk of safety problems. 

If temperatures are too cold, say for instance 0°C, it can result in a loss of capacity due to the chemical reactions inside the battery slowing down. Low temperatures are said to increase the internal resistance of the cell, dropping the voltage. Moreover, the ability to charge will be restricted – research suggests up to 23 percent less than the usual 100 percent state of charge. Quick-charge is affecting, while fast charging of very cold cells will damage them. The range of the vehicle can be affected tremendously, with a loss of up to 20 percent as well. 

Lithium plating

A specific issue with Li-ion batteries that are exposed to cold temperatures, is that the electrolytes inside the battery can become more viscous and less mobile, adversely affecting the movement between electrodes while charging. When the battery is charged at low temperatures, lithium ions may have difficulty inserting themselves back into the host material on the anode and instead deposit on the surface, forming metallic lithium.

This process is called lithium plating. Extreme weather conditions notwithstanding – lithium plating is more likely to occur under extreme low temperature (below -32° C) or high current conditions –, it can also occur at normal charging rates at temperatures between 5-10° C as the specific range varies depending on the chemistry and design of the battery. 

The metallic lithium on the anode can create very small needles or hairs called dendrites, which can grow over the next charge and discharge cycles. The risk there is that in extreme cases, dendrites might penetrate the space between the anode and the cathode, potentially leading to short circuits. Moreover, it can result in permanent loss of capacity as the lithium that has been plated is no longer available for the electrochemical reactions during charging. 

What role do PSA tapes have in addressing these challenges?

PSA tape solutions are a great way to fix heating films to battery packs, providing great assistance in making sure that the cells can operate within the ideal temperature range. Tapes can compensate for different thermal expansions, bond over the full surface thus removing stress concentrations. They take up very little space and are heat resistant.

Thermal insulation materials added to the pack can keep the warmth in and protect cells from cold, and PSAs are one way to attach them. They are already used to attach all sorts of components to cars, including heat shields in combustion engine vehicles. 

Moreover, where cooling plates and ribbons are used that can also introduce warmth, self-adhesive films provide electrical insulation. Lastly, an interesting new approach is immersion cooling by having the battery cells directly immersed in a dielectric fluid. The fluid passes through the battery between and around the cells. PSAs can help with sealing to resist fluid penetration. 

How can drivers address EV battery problems in cold weather? 

Here are some simple tips to help you mitigate issues with your EV in cold weather:

• park the car where it is protected from the cold;

• reduce short journeys where cells cannot warm up during use;

• reduce the load on the battery by reducing the heating, relying instead on local heating (for instance from the seats and the steering wheel). Often the HVAC system is powered by the (high voltage) traction battery, but the other ancillaries like seat heating are powered by the simple low voltage – usually 12V – battery (which is why EVs still have the old-fashioned lead acid battery);

• follow the manufacturer's recommendations on charging in cold weather conditions.