Many people in the construction industry understand the basics of how an internal combustion engine works, but what about the batteries used to power electrical construction equipment? Now is a good time to learn, as battery-powered electric machines are becoming more common in the workplace.
Most electric vehicles, such as Volvo cars and electric machines, use lithium-ion batteries, which are rechargeable batteries that are also used in electronic devices such as mobile phones, laptops and more. They are called “lithium ion” because lithium ions move between two electrodes during charge and discharge cycles to store and release energy.
THE ANATOMY OF AN ELECTRIC VEHICLE (EV).
First, electricity cannot be captured and stored. It must be converted into another form of energy (eg chemical energy) which can then be stored.
Batteries are like fuel tanks: they don’t produce energy, they store it. In an internal combustion engine, the bond energies of the gasoline or diesel molecules are broken and converted into heat, which in turn is transformed into the mechanical energy needed to drive the piston inside the engine. Similarly, batteries store electricity from the power grid in the form of chemical potential and then discharge energy to provide electricity when needed.
Lithium-ion batteries contain four main components:
- Anode (-)
- Cathode (+)
- Separator
- Electrolyte
A battery needs to be connected to an external circuit to absorb and release energy. Electrons move through the external circuit while lithium ions move through the electrolyte.
So what are anodes, cathodes, separators and electrolytes?
- anodes (the negative end) store and release lithium ions from the cathode during charging (conversely, they release lithium ions during discharge). They are usually made of graphite.
- cathodes (the positive end) serve as the source of lithium ions, playing a crucial role in determining the capacity and nominal voltage of the battery. They are usually made of active material [e.g., NMC (nickel, manganese and cobalt), NCA (nickel, cobalt and aluminum), or LFP (lithium, iron and phosphate)].
- The separator separates the anode and cathode and prevents direct contact between them.
- The electrolyte provides lithium ion conductivity. It is the chemical solution that transports lithium ions and prevents electrons from passing directly from the anode to the cathode inside the battery.
If you’re curious why lithium is used, according to the US Department of Energy it’s because of its “high energy per unit mass relative to other electrical energy storage systems.” It also has a high power-to-weight ratio, high energy efficiency, good high-temperature performance and low self-discharge.” This makes lithium an ideal element for making rechargeable batteries.
THIS IS HOW LITHIUM ION BATTERIES WORK
To explain what’s going on, let’s take the current state of the art and widespread adoption of lithium-ion chemistry as an example: NMC:
- During charging, electrons accumulate at the anode (electricity is converted to chemical potential).
- This causes an electrical difference between the anode and the cathode. You can think of this difference as an unstable accumulation of electrons.
- Lithium ions of opposite charge move inside the battery from the cathode through the electrolyte to balance the charge to produce a balanced system.
- As the battery discharges, the anode releases lithium ions to the cathode, generating a back-and-forth flow of electrons: it converts the stored chemical potential energy into electricity in the circuit and discharges the battery.
Over time, the irreversible nature of the process can change the chemistry and structure of the battery materials, which in turn can reduce battery life and performance.
It’s worth noting that different types of lithium-ion batteries have slightly different chemistry. Still, they all rely on the movement of lithium ions between electrodes to store and release energy.
The most common types of batteries are lead-acid, nickel and lithium-ion, and there are a few types of lithium-ion batteries based on the material they are made of. We are currently choosing NMC (Nickel, Manganese, Cobalt) from the perspective of 1) technological maturity, 2) manufacturing readiness, 3) energy density (gravimetric, kWh/kg and volumetric, kWh/ L), 4) the battery cycle. useful life, 5) safety and 6) recyclability rate.
Lithium-ion batteries are superior to lead-acid batteries in that they have three times the energy density, twice the battery life, consistently superior performance in high-temperature applications, no memory effect, fast charging and no maintenance. Among Li-ion batteries, NMC has better fast charging capabilities, better cold weather performance and higher energy density compared to LFP.
TIPS FOR CHARGING LITHIUM ION BATTERIES IN ELECTRICAL CONSTRUCTION EQUIPMENT
If you have heavy electrical equipment, here are a few tips to make sure you have plenty of power when you need it and limit battery degradation over time:
- Keep the electric machine at around 90% charge state and refrain from charging to 100% too often.
- Avoid letting the battery get too low. If you are not using the machine for an extended period, keep it around 40-50% (a fully charged battery has a higher self-discharge rate).
- Try using an AC slow charger at least once a week and let the battery management system (BMS) balance the battery packs.
- Pre-condition your machine, especially during the cold winter months. This may involve heating the battery or machine to a suitable temperature range to improve the efficiency of the charging process. By preconditioning, the internal temperature of the battery is brought to an ideal level, which allows for more efficient charging and potentially extends the life of the battery.
Note that for Volvo electrics, the SOC window is between 10% and 90%, compared to cars where the SOC window is wider. An electric machine showing 0% SOC is actually 10% for the battery, and showing 100% SOC is actually 90%.
We know this may still seem a bit complicated, but a large part of that is because it’s so new to our industry. Think how confusing it can be for someone new to learn how an internal combustion engine works. With time and experience, however, it all starts to make more sense, and this will too.
If you are interested in seeing how electric machines work, contact your local Volvo dealer. They can work with you or even operate a machine so you can better understand how it delivers the same power and performance as comparable diesel models.
