An In-Depth Analysis On Batteries
Batteries to the world are like the heart of the human body. Just like batteries supply power, the heart supplies blood which supplies oxygen. With something as important as that, it’s no wonder that we see the progression of batteries advancing at such a rapid pace.
Some of their primary uses:
- Electric Vehicles(cars, planes, and even 🚀)
- Storing solar energy off-grid with batteries
- Basic Electronics(phones, computers, etc)
- Powering systems(i.e: security) in buildings
- Medical Equipment
- Oil Drilling
Batteries are solving some of the biggest problems in the world, including climate change. Based on a study in china, the average EV is 18% better than fossil-fueled cars
And in a place like New Zealand wherein 2017, 82% of energy for electricity generation came from renewable sources, their EV’s are around 62% better compared to the average fossil fuel-based vehicle.
Throughout this article, I’m going to be covering all the important topics in regards to the progression of batteries over the past couple of decades.
Going over the basics
There are a couple of main components to highlight for the average battery/cell(batteries can have 1 or more cells):
- An anode
- A cathode
- An electrolyte
- A separator
- Two current collectors(one being positive and the other being negative).
The basis of all batteries is converting chemical energy into electrical energy. It operates on the principles of reduction and oxidization.
When the anode and the electrolyte come into contact with each other, it triggers a chemical reaction that produces electrons(oxidation). Simultaneously, the cathode and anode come into contact and that triggers a chemical reaction that receives the electrons from the oxidation process(reduction).
There are two types of batteries, rechargeable, and non-rechargeable. They are also referred to as secondary and primary, respectively. Rechargeable batteries were invented to solve the biggest problem with primary batteries, an irreversible chemical reaction.
For any primary battery, the chemicals used to generate electrons will eventually reach a state of equilibrium, meaning they won’t react with each other anymore. Since they don’t react with each other, no electrons can flow which means the battery is dead and can’t be recharged.
The difference between secondary and primary is that secondary has the ability to receive a reverse charge. If we look at the lithium-ion battery when a charger is plugged in, electrons enter the anode from the charger.
These electrons attract lithium ions that are in the cathode. These ions start to travel to the anode from the cathode. When the device is unplugged the opposite happens. The electrons are sent through an external circuit that powers the device while the lithium ions travel to the cathode through the electrolyte.
The device will die when all the lithium ions have reached the cathode and will require charging to repeat that process all over again.
In all non-rechargeable batteries, the electrons start off at the max amount. The electrons go from the anode to the cathode until there isn’t any more left and that is the time you throw it out. Rechargeable batteries receive electrons from a charger which allows them to have a back and forth process.
Due to these very clear benefits that rechargeable batteries have, I will be talking about them for the rest of this article.
Important note: The materials that are used to build the batteries(i.e: lithium, cobalt, graphite, copper, aluminium, etc) are intentionally used because of the properties they have. For example, copper is the most commonly used anode current collector because of good stability and low electric potential.
The collectors are used to conduct the incoming electrons. The electrolyte is a liquid gel-like substance that is used to transfer the lithium ions from electrode to electrode.
While the battery field is going really well, there are some things that still need to be improved to achieve specific objectives.
Examples of these objectives include:
- Standardizing EVs to go 1000km on one charge.
- Making batteries much cheaper(ideally $80 kWh) to increase the production rate.
- Reducing the carbon footprint caused by mining lithium(1 Tesla Battery = 8 tonnes of CO2 which is the equivalent of two houses electricity consumption).
Again, these are objectives that should be fully implemented in almost all of their respective uses. Not only that but we need all these milestones achieved in one single battery. For example, lithium-air batteries have an extremely high energy density but lack in the other departments.
A battery pack alone makes up roughly 1/3 of an EV’s cost. There are several reasons for this, the biggest one being the use of materials that are used in the battery(refer to the chart below). To be more specific, the cathode materials cost the most money. So what’s used in the cathode?
Most of the materials used in the cathode are transition metal oxides. Depending on the type of battery and manufacturer, there are different oxides that are used for the cathode. For example, Tesla uses a nickel cobalt aluminum oxide(NMO) while a nickel manganese cobalt(NMC) oxide is used in most other electric vehicles.
Going even deeper we find the main material that makes batteries so expensive, Cobalt(which also happens to be used in the two most common metal oxides). This material is very scarce, toxic, and lustrous. It’s used for the cathode in combination with either nickel and manganese or nickel and aluminum.
It’s expensive because Cobalt itself isn’t mined. It’s a byproduct of mining other materials. This added on to the fact that The Democratic Republic Of Congo controls 60% of the global cobalt production makes the material very expensive.
Batteries can overheat for one of four main reasons.
- The battery is incorrectly inserted into the battery container(manual error)
- It is put in a hot environment originally
- The internal resistance of the battery is very high which will cause an increase in heat.
- Lithium Dendrites form in the anode.
Eventually, after increasing temperature due to resistance or being placed in a hot environment, the temperature is at a point where it can increase on its own and becomes self-sustaining. This process is known as thermal runaway. Thermal runaway means that at a critical temperature, the materials inside these batteries start to break down. And when heat cannot escape as fast as it’s being generated, this is a “runaway” reaction that cannot be stopped.
It can lead to the battery exploding or short-circuiting.
Something important to note is that the thermal runaway process is significantly expedited if there are hot environments around it. The reason this reaction can’t be stopped is due to ohms law. It says that voltage and resistance are directly proportional. In other words, as the resistance increases the voltage also increases proportionately.
The last major reason is the formation of needle-like structures known as lithium dendrites. Lithium dendrites are formed when extra lithium ions accumulate on the anode surface and cannot be absorbed into the anode in time.
These dendrites have the ability to cause short circuits or explosions. This was actually one of the reasons(not the main one) for the Samsung Galaxy Note 7’s catching on fire.
Another uncommon reason is from the shock of impact. If something with a battery is subjected to large amounts of impact, it will significantly increase the electrical discharge of the battery(and as I’ll talk about in the charging section, that leads to explosions). However, that’s much less common than the other 3 reasons in terms of how the problem plays into the grand scheme of things.
An alternative perspective behind energy density is instead of making it go longer on one charge we can also decrease charging times. This just adds to the most ideal experience when using anything that is primarily based on batteries.
The charging speed is determined by dividing the charging points kW by the total kWh of the battery(i.e: A 60kWh battery takes just under 8 hours to charge from empty-to-full with a 7kW charging point.)
In order to increase charging speed, we have to increase power density. This describes how quickly the device can deliver energy relative to the size of that device. In other words, the best chargers have high power densities, whether it’s the size or the total outputted power.
However, it’s much better to optimize for outputted power than it is for size in this instance. Power is the product of current(measured in amperes) and voltage(measured in volts). Current is the flow of charge per unit of time, whereas voltage represents electrical potential energy. Factoring in the resistance(measured in ohms)
The biggest flaw with the whole concept of increasing the power density of charging is there are limits that batteries have when it comes to accepting power from a source. If you add too much energy, because of Ohms Law, the battery could explode.
Something that demonstrates this is if you have a MacBook charging brick that has a USB-C input, plug in a USB-C to iPhone charger.
You will almost immediately notice that your phone becomes unusually hot. This is because you are using an 87W charger compared to the usual 20W. This adds much more power(4.35 times more) at once compared to what the Li-Ion battery is made to handle.
When you apply this to maybe 9 times more power than what it’s used to, there could be serious effects. All this is because batteries have limits to the amount of power they can accept.
Loss of battery life(battery degradation)
If you’ve ever felt like the battery life of your device was going down, it’s because it actually was. In fact, this problem could pose more threats to batteries than expected at first glance. This section talks about a decrease in total capacity, not the speed at which the battery goes down(because the decrease in capacity is the reason for that).
Despite our efforts in improving the overall battery capacity(talked about in the next section), it will be significantly less of an improvement than it could be if this problem is not solved.
At a high level, batteries lose charging capacity and lifespan which leads to the loss of total battery life. Going a bit deeper, the reason that there’s a loss of capacity is that the cathode wears out.
As I talked about, lithium ions flow in opposite directions during discharge vs charge. It goes from anode -> cathode during discharge and cathode -> anode during charge.
This process after a while wears out the cathode because of the switch of direction with li-ions. This is what leads to the overall reduced capacity of the battery. Just for some numbers, a high-end lithium-polymer battery can lose about 20 percent of its capacity after 1000 charge cycles(1 charge cycle is one cycle of charging and discharging).
It’s also important to remember that things like high temperatures also add to lower battery capacity. To give you a comparison a fully charged lithium-ion battery will lose about 20 percent of its capacity after a year of typical storage. Increase the external temperature to just above 100 Degrees Fahrenheit and that number is 35 percent.
^ As I mentioned, external temperature affects capacity.
Energy Density talks about how much energy is available to be discharged in a certain amount of space. It’s measured in watt-hours/per kilogram. In other words, how many lithium ions can you fit in one place. The more lithium ions, the more energy generated to make the vehicle go for longer.
To increase energy density you either decrease the size of the battery or increase the energy capacity in the battery. Both are important in the development of batteries.
The primary way we can increase the energy density is through nickel. It is one of the most energy-dense materials. The reason we don’t use it by itself is that it is unstable and reactive. It’s for this reason that cobalt is so heavily used in modern lithium-ion batteries.
It’s a material that is also energy-dense but helps balance the problems that nickel presents by itself. Any sort of alternative to this material would also have to be energy-dense.
Now that we know what batteries are and some of the problems associated with them, let’s talk about solutions that have been made to solve them.
Improves: Safety, Overheating, Electrical Stability, and Energy Density.
One of the most talked-about alternatives for the standard Lithium-Ion battery is the Solid-State Battery. Compared to most other secondary batteries, Solid State uses solid electrolytes(hence the name) instead of the normal liquid ones.
The problem with liquid electrolytes is the electrochemical instabilities and potential risks with safety, plus a low ion selectivity(i.e: lithium ions, etc). Unlike lithium-ion or any other rechargeable battery, they perform well in high temperature or impact environments. The electrolytes of the solid-state battery can come in the form of ceramics, glass, sulfites, or solid polymers.
Another benefit of solid-electrolytes is the prevention of lithium dendrites. As I talked about in the overheating/thermal runaway section, these could have catastrophic effects on lithium-ion batteries. The worst part is that this is naturally occurring, similar to how seaweed grows in the ocean.
Solid-State Batteries are very compact. Because of basic particle theory, there is a very small amount of space for the lithium dendrites to grow compared to the traditional gel-based(liquid) electrolyte.
Limitations with Solid-State Batteries:
- However, the biggest problem with Solid State Batteries is the cost. It costs around 2.5 times more money to make a Solid State Battery compared to Lithium-Ion Batteries(in $/kWh).
- Another problem with solid-state batteries is their low ionic conductivity relative to liquid electrolytes. Ionic conductivity talks about the tendency for ionic conduction. This involves the movement of an ion from the two electrodes through an electrolyte.
Reducing Cobalt or Removing It Entirely
Improves: Environmental Footprint and Cost.
Cobalt is a very useful material but also has several sustainability issues that I talked about before.
The main opportunities lie in either increasing the amount of nickel or removing cobalt entirely. The problems with both of these approaches are the same, just amplified for the second.
Without cobalt, the reactivity + unsustainability of nickel will become a very serious safety concern because there isn’t something to help reduce it. Think about if you put more of an already strong flavor into some sort of mixture. There has to be something to dilute it otherwise it will taste too strong.
It’s this plus the factor that cobalt-free cathodes are very limited in terms of testing with practical cells that make removing cobalt or reducing it very difficult to do.
Improves: Energy Density
Lithium-Air Batteries are one of the most promising alternatives to lithium-ion batteries. It uses the oxidation of lithium in the anode and reduction of oxygen at the cathode to induce a current flow that acts like wind for the existing current.
Current tests have shown that the energy density could potentially be increased by 10 times more compared to regular lithium-ion batteries which is a huge opportunity in terms of improving the range that EVs have.
There are 3 main types of lithium-air batteries that have been developed: aprotic, aqueous, and solid (they all operate on the principles of a lithium-air battery but use different electrolytes and electrodes).
Aprotic consists of a lithium metal anode, an air cathode, and an aprotic electrolyte and has a high energy density of 3,505 Wh/kg.
Problems such as a low practical areal capacity, low round-trip energy efficiency, and lack of air purification still restrict them from being used in Electric Vehicles. They also have the highest amounts of gum that form in the cathode.
When incoming lithium ions combine with carbon dioxide and water vapor in the air, it usually makes a sort of gum in the cathode. This gum, similar to the reverse of ions, significantly reduces battery capacity and drastically affects the overall performance of the battery.
Aqueous lithium-air batteries consist of a lithium metal anode, a porous cathode, and an aqueous electrolyte that is separated from the lithium anode by a water-stable(that’s where the aqueous comes from).
The energy density is 1,910 Wh/kg. While the energy density is around two times lower than the aprotic, it is still superior to a traditional internal combustion engine. Additionally, unlike the aprotic lithium-air battery, problems like the decomposition of the electrolyte or the clogging of the porous cathode from discharge are not appreciable in the system.
One of the problems with the aqueous system is that for a low specific area capacity, the weight and volume of the solid electrolyte separator can reduce the energy density significantly.
The solid electrolyte lithium-air battery consists of a lithium anode, a lithium-ion conducting solid electrolyte, and a carbon air electrode. This cell was designed with the intention of mitigating fires and explosion problems due to the fact that there was an aprotic electrolyte.
Both solid and aqueous lithium-air batteries don’t have the problems that aprotic batteries do. Most of this is because of the type of electrolyte that is used.
The problems these both suffer from are a lack of high power density and extended deep cycling. This with their exclusive problems that I talked about is why these two lithium-air batteries are still in development.
As a general note, lithium-air batteries all have very short lifespans(regardless of what type of electrolyte they use).
Batteries have the potential to be the future of things like plane travel provided the problems I talked about are solved. While some are more about sustainability and others are essential in the creation of the battery, they all play a part in irradicating fossil fuels for almost every industry.
I thought I would highlight some of the best opportunities I’ve seen in terms of improving current battery technology.
- Finding a way to make Solid-State Batteries cheaper without a loss on performance.
- Enforcing a more compact infrastructure on lithium-ion batteries to prevent the growth of lithium dendrites
- Reducing the amount of cobalt/increasing the amount of nickel while still maintaining stability and mitigating the potential for reactions.
- Reducing lost capacity by mitigating the force in which lithium ions exert upon switching between charge and discharge.