On our website recently, we started to ask and answer a fundamental question that is critical for the global energy storage industry to address – If cobalt is so bad, why are some companies still using it in lithium-ion batteries?

You can see Part One here.

As a quick recap regarding cobalt:

• Cobalt is a choice in lithium ion – there are alternatives that are safe, non-hazardous and cost-effective
• It is the primary culprit in battery fires and explosions
• Cobalt is toxic, inhalation causes lung disease and heart failure, and those unfortunate enough can develop cancer from exposure
• Cobalt extraction spoils land and waterways, rendering them unusable for farming, irrigation, and drinking water
• Most cobalt (60%+) comes from parts of the Democratic Republic of Congo where abuses and forced labor is common, including children as young as seven sent into claustrophobic ‘artisanal’ mines to extract the ore by hand

The destructive consequences of cobalt mining and usage are both well documented and heartbreaking.

Proponents typically point to rapidly declining costs and increased energy density as justification for using the conflict metal in their batteries, but even those reasons just don’t hold up under basic scrutiny. And surgent demand for electric vehicles and stationary energy storage systems will only exacerbate these problems.

#NotAllLithium

An important reminder is that not all lithium batteries are created equally, and lithium-ion batteries do not have to use cobalt. The chart below highlights some of the main types of lithium-ion (Li-Ion) battery chemistries.

When comparing differing types of batteries, there are three key technical considerations to keep in mind – chemistry, form factor, and manufacturer. All three are important to understanding the performance, cost, and safety of the final product.

In this blog series, we are focusing on the underlying chemistry of different Li-Ion batteries used in stationary energy storage applications, and the significant differences between those that use cobalt and those that do not.

The Cost of Cobalt

In our last post, we addressed the first point, that the costs of cobalt-based Li-Ion batteries are not falling as rapidly as frequent media statistics would imply. In fact, cost declines slowed considerably around 2017, as the price of raw materials became a much larger portion of a battery and the impact of economies of scale began to diminish.

But cost alone (measured in dollars per kilowatt-hour or $/kWh) tells you very little about a battery, and this normalized dollar figure ignores the operational realities of different chemistries, form factors and manufacturers. Depending on which specific chemistry is used, a battery may not be suitable for stationary applications, it may require energy-draining cooling and costly fire-safety equipment, as well as pose other technical performance limitations that may prevent a customer from even being able to access its full rated capabilities.

In this post, we are going to examine different Li-Ion chemistries side-by-side and discuss some of these limiting factors, how customers may not receive what is advertised, and the true cost of cobalt in certain lithium-ion batteries.

Inherent Differences Add Up

We are going to delve into some technical aspects of batteries here, and at SimpliPhi Power we like to, well, simplify things wherever possible. Even though there are no moving parts, there is a lot going on inside of a battery when it is in standby, charging and discharging.

To keep it simple, we will discuss just three technical aspects of battery chemistry to demonstrate how these differences impact the basic $/kWh metric.

Round-Trip Efficiency:

Each time you move energy or change it from one state to another you will lose a percentage to different forces. When electricity is sent to your house from a powerplant, for example, all the electric wires and substations between you and the plant will keep wasting small fractions. In total, the electric grid wastes 5-15% of all electricity generated before it is delivered. Keep in mind these transmission and distribution losses occur after significant losses at the power plant, estimated to be as high as 65% in the US.

If you have ever stood near high voltage lines and heard a crackling or buzzing sound, that is electricity escaping – both as electric energy and as waste heat as it courses down the line.

When it comes to batteries, what we are interested in is how much energy is lost in the round trip – including both charging and discharging the energy. Basically, we want to know how much energy will get back if we store it inside our battery. This is called ‘round-trip efficiency.’

If you have ever felt the back of your phone or computer after using it for a while, you have probably felt the significant heat that builds up. All that heat you feel is energy wasted as the electricity moves into and out of the battery and related components.

This is because almost all cell phones and laptops use cobalt-based Li-Ion batteries, which have an unimpressive roundtrip efficiency rate of about 90%. Meaning every time you put energy into those batteries, 10% of it is wasted. This is not only lost energy (which is also lost money), but it increases the danger of cobalt-based batteries, because if too much heat is generated, fires and explosions are likely to happen.

Lithium ferro phosphate (LFP) batteries on the other hand do not generate waste heat, which is part of why they have a high round-trip efficiency of 98% and do not catch fire. Only 2% of the energy stored in an LFP battery is lost, mostly to electrical resistance inherent in the internal battery components.

So, if your cobalt-based battery says 10kWh on the label, you can only use 9kWh, as 10% will just turn into waste and heat. With an LFP, you will get 9.8kWh of usable capacity. Of course, the rate at which a battery is charged and discharged impacts the efficiency rate and usable energy capacity (versus the rated or nameplate capacity) as well.

In this comparison, we have assumed a 2-hour charge and discharge rate to determine the round-trip efficiency. When a cobalt-based lithium battery is charged and discharged in 2 hours or less, it generates much more heat, has a much lower round-trip efficiency for total available (or usable capacity) with each cycle, and increases the likelihood of overheating, fire, and explosion.

Cycle Life:

Another important factor in understanding battery chemistry is how many times a battery can be charged and discharged before its overall capacity becomes limited. Typically, this is calculated as how many times you can cycle the battery before it is limited to 80% its ‘nameplate’ (or labeled) capacity. All chemical-based batteries lose some of their capacity as they are used over time.

For cobalt-based Li-Ion, again, things do not look so good. The typical NMC or NCA battery can handle about 3,500 cycles before it reaches the 80% limit. This means over the course of charging and discharging 3,500 times, at least 20% of its capacity will be gone for good. Again, the rate of charge and discharge can significantly impact the number of total cycles. If a cobalt-based Li-Ion NMC or NCA battery is discharged or charged at a rate that is 2 hours or less, the cycle life is shortened, the round-trip efficiency rate is lower, and the heat build-up is higher – leading to possible overheating and fires.

LFP batteries can sustain for more than 10,000 cycles before reaching that same point, declining at a much slower rate. So, after 2,000 full cycles, an NMC/NCA (cobalt-based) battery has lost 12% or more of its available capacity, but an LFP battery has only lost 4% (and has another 8,000 cycles left!)

Steady Voltage:

Another significant difference in Li-Ion battery chemistries is how consistent voltage stays at different states of charge.

Have you have ever noticed when your cell phone battery is getting low that the percent remaining seems to drop much faster? That is not just your imagination.

This is a bit of a simplification, but voltage is the ‘pressure’ from an electrical circuit’s power source that pushes charged electrons. Like a garden hose, if the pressure drops then only a trickle comes out the end.

In electronics, to meet the demanding needs of a cell phone or laptop – or in bigger batteries to power a house or business – if the voltage drops, then more energy is needed to get the same amount of power out of the battery. A battery’s available energy can be expressed as the voltage x charge.

For cobalt-based Li-Ion batteries, as the available energy drops, the voltage also ‘sags’, and more energy is needed to achieve the same rate of output. This is due to internal resistance building up as it discharges

For LFP batteries, internal resistance does not build up and voltage is able to stay constant across its discharge curve. So, it takes the same amount of ‘pressure’ to push the electrons across its usable kWh, meaning less energy wasted just to move it through the battery itself.

The exact amount of difference depends on several factors including how intensive the application is, the depth of discharge, and even the surrounding air temperature. But, taken in total, an LFP battery will provide much more consistent performance and more consistent rate of output.

Cumulative Impact

There are many other advantages when comparing lithium ferro phosphates to its cobalt-based chemistry cousins, but these variances alone paint a stark competitive difference. LFP batteries are safer, more reliable, last much longer, and you can use much more of the energy that is stored.

It is also important to note that these inherent differences are cumulative! Even just looking at round trip efficiency and cycle life, the true $/kWh cost of cobalt-based Li-Ion is greatly increased compared to the price quoted.

If your cobalt battery is limited to 80% depth of discharge under warranty, has a round trip efficiency of only 90%, and after 2,000 cycles you have lost 12% of capacity to degradation, you can now only use 63% of the energy claimed on the label! That is almost half your capacity gone! And factor into this the rate at which you can discharge the battery. If the discharge rate cannot be less than 3 or 4 hours to preserve the cycle life and round-trip-efficiency, you have much less available energy hour over hour that you can use.

So, the next time someone is sharing their lithium-ion battery pricing, ask them first if their battery contains cobalt. If it does, for economic, fire-safety, and moral reasons (supply chain w/ child labor), you should scrutinize their cost, performance, and safety claims thoroughly.

If you want to simplify your decision making, avoid toxic and fire-prone cobalt batteries, and get the most out of the battery you paid for, then lithium ferro phosphate is the solution for you.

You can see more about our different product offerings and system sizing on our products page. And if you are ready for safe, reliable, cost-effective energy storage, contact us today!