Temperature, Chemical Reactions, and Battery Performance

Your food lasts longer in the freezer, but your industrial batteries do not. Is there a single reason for both? Simply put, the answer is yes.

Chemical reactions are, on a molecular level, only possible when particles collide; and specifically, collide with enough force to cause a reaction. If a substance is heated, its particles are moving faster and there are more chances for reactions to occur, but those particles need at least a minimum amount of force to cause a chemical reaction to begin with, even if they are colliding more frequently. This minimum amount of force is called activation energy.

Suppose we take two gasses that are reacting at 5C(41F, 278K) and raise the temperature to 20C (68F, 293K). Raising the temperature from 5C to 20C increases the frequency of collusion by the following:

Sqrt (293/278) = 1.027; or an increase of 2.7% in collision rate.

The key factor to reaction rate, however, is not the rate of collisions – but rather it’s the number of collisions above the above-mentioned activation energy limit.

In liquids and solids, and liquid-solid interfaces, the increase in particles colliding with energy above the activation energy limit typically doubles with every 10C (18F) rise in temperature.

Take our two examples, food and batteries:

In cold storage, food has fewer particles moving with enough activation energy and tends to react (or spoil) more slowly when cold, and the number of particles colliding above the activation energy limit when food is frozen is nearly zero.

This also means the same for cold batteries. When a battery is cold, the reaction rate drops dramatically and this is directly visible to a forklift operator as a reduction in performance. When a battery is cold, its internal resistance rises because it can facilitate fewer chemical reactions. This causes a higher voltage drop under load and, to the operator, looks like a weaker-running battery.

The battery also prematurely drops to the voltage at which it is considered dead, as it can’t supply the energy it needs to, quickly enough. Also, note that this voltage drop can be as damaging to a battery as hitting the same voltage drop in a warm battery is, as the voltage drop yields a similar amount of internal strain in the battery, whether it is cold or warm. A cold battery wears out more quickly than a warm one when put under the same operational stresses.

There are a few ways to solve this problem:

  1. Using a chemistry that has a higher reaction rate, such as lithium-ion

Lithium-ion batteries have significantly lower internal resistance than lead acid. In comparing lead-acid to lithium-ion, a cold lithium-ion battery still performs as well as a warm lead acid battery. Lithium-ion typically retains approximatly 90% to 95% efficiency even in cold applications, compared to lead-acid which loses close to 40% efficieny when operating in cold.

  1. Using battery pack heaters

Batteries with integrated heaters installed can keep themselves warm. The reaction rates are better and performance stays higher but at a cost of the energy that is used to warm the battery, and at a cost of additional space and battery capacity. Keeping lithium-ion evenly heated in cold applications can also extend cycle life.

  1. Insulating battery packs

Batteries can be insulated so that the heat they produce in operation keeps the battery warm.

This is not necessarily advisable, as batteries can still get cold over break times and during light operation. When a cold battery is put under a heavy electrical load, it exhibits significantly more wear and tear than a warm battery. Insulation can also cost much additional space, reducing available space for batteries.

  1. Better chemistry + battery pack heater + insulation

The best option is to use a combination of all three options to have a solution that is most able to put out the required power, keep itself warm to retain optimal performance, and is insulated so less energy is spent to keep the battery warm. The combination of all three of these solutions will yield the longest lifespan and the best performance.

Lithium-ion industrial systems such as Blue Line’s can have the pack heater and insulation integrated into the battery’s case. This keeps both performance and lifespan optimal in a variety of temperatures.

 

Published by: Dustin Herte, CEO