The electric vehicle (EV) revolution is picking up the pace, with countries like the U.K. and France mandating deadlines to phase out petrol and diesel engine cars. Electric vehicles are the obvious replacement, but EV batteries have traditionally been expensive and relatively inefficient. Until recently, electric vehicles have struggled to travel further than 200 miles on a single charge, and the recharge time makes long journeys an ordeal.
That’s all about to change.
What is behind the change? A revolution in the materials used in rechargeable EV batteries that will increase their efficiency, making long distances achievable and creating shorter charging times.
The 5 main EV battery types
The five main battery types used for electric vehicles at the moment are all lithium-ion (Li-ion) based:
1. Lithium Cobalt Oxide (LCO)
LCO batteries are mainly used for portable electronic devices – smartphones, tablets, etc. but can also be used for smaller EVs. It is relatively non-volatile and safe. The main drawback is that they contain significant amounts of cobalt, which is an expensive material that comes with sourcing challenges. For this reason, it is rarely used in commercial EVs.
2. Lithium Nickel Manganese Cobalt Oxide (NMC)
NMC batteries are probably the most common type used to power EVs. They have a stable chemistry, and relatively low-cost materials containing only a small quantity of cobalt. They perform well, providing a high energy density and charge rapidly compared to other batteries.
3. Lithium Nickel Cobalt Aluminium (NCA)
NCA batteries were the first commercial attempt at replacing expensive cobalt with nickel in Li-ion batteries. They perform well, providing a good energy yield and are inexpensive to produce. They have been used extensively in both portable electronics and EVs, although NMC batteries have taken over as the preferred choice in recent years.
4. Lithium Iron Phosphate (LFP)
The safest of all the Li-ion batteries, with a very stable chemical makeup. It also has a very high energy density, making it ideal for larger electric vehicles such as vans, buses or trucks.
5. Lithium Manganese Oxide (LMO)
LMO batteries were among the first to be used in the early EVs due to its decent energy performance and low cost of materials. However, the drawback is that the cells aren’t as durable as other battery types, giving them a relatively short life cycle.
This article will take a look at some of the essential materials being used to create the different parts of the most efficient and cost-effective of these batteries, such as NMC, and why they have been chosen.
The electrolyte is a crucial part of any battery, acting as a catalyst to increase conductivity by helping to transfer ions from the cathode to the anode when charging, and vice versa when discharging. Electrolytes can be either liquid-state, i.e. acids such as sulphuric acid (H₂SO₄) or soluble salts, or solid-state using polymers such as polycarbonate.
At the moment, all EV batteries are liquid-state, but solid-state batteries offer many benefits such as being smaller and lighter, providing higher capacity and being cheaper to produce. Toyota announced that they plan to release an EV with a solid-state battery by 2020.
Most EV battery electrolytes are Li-ion based, meaning they use lithium to carry the charge between electrodes. Although the principle is the same as a mobile phone battery, a typical EV battery uses 10,000 times the amount of lithium. As a result, the price of lithium has soared as demand increases.
Cobalt was the first material used for cathodes in Li-ion batteries and has been used in vast amounts in recent years. Cobalt’s tight compound molecular structure makes it ideal to maintain a rapid flow of electrons through the battery.
However, cobalt is in increasingly short supply due to overuse in the Li-ion battery industry, taking a 55% share of the global cobalt supply. It is a by-product of copper and nickel mining and is expensive to extract. Another problem is that cobalt is not easily recycled, needing much refinement before becoming useable again which makes the cost prohibitive.
The cathode accounts for approximately 24% of a Li-ion battery’s overall cost, therefore less expensive alternatives to cobalt have become popular in recent years.
High purity nickel is needed to produce EV battery cathodes due to its extra durability. It is used in the cathode in nickel
Battery manufacturers are keen to use more nickel as it is so much cheaper than cobalt. It is often blended with small amounts of cobalt to produce more cost-effective cathodes. Therefore, the demand for class 1 nickel is expected to grow by 30% each year between 2018 and 2025, potentially reaching 570 kT, around ten times the current demand. These predictions mean that some recycling firms are showing an interest in nickel recycling from old batteries to help meet the demand.
High purity and high-grade manganese are often used to create the cathodes of NMC batteries. It is also sometimes used in Electrolytic Manganese Dioxide (EMD) form, produced by dissolving manganese dioxide (MnO2) in sulphuric acid and sending a current through two electrodes. The manganese dioxide dissolves into a
Graphite is the most commonly used material for EV battery anodes. 25kg of high purity graphite is needed for an average sized battery, and up to 54kg for large batteries such as those used in the Tesla Model S.
The process for manufacturing graphite anodes is a time-consuming and costly one. It involves creating synthetic graphite made from calcined or cleaned petroleum coke (an oil refinery by-product), a fine, gravelly material, which is bound together with coal tar pitch. For maximum absorption of lithium ions, the graphite used for the anode has to be high-quality, with a highly crystalline structure.
The mixture is then baked into pure carbon, which has virtually no conductive properties. Next, a process of ‘graphitisation’ or magnetic induction occurs, in which a low-voltage, high-current DC charge is applied through the furnace. Finally, wax or resin is applied as a moisture barrier, to prevent degradation of the anode in liquid-state batteries.
Silicon has a number of advantages over graphite as an anode material, including the lower cost of the material and manufacturing. Also, it can absorb and contain a much higher number of lithium ions upon charging than graphite. This increases the efficiency of the battery, meaning EVs can reach higher distances on a single charge. Silicon anodes are still in development, but it’s likely that they will be in commercial use by 2020.
The future of EV battery materials
Many of the main materials used in EV batteries are in short supply. Combined with the increasing numbers of electric vehicles being developed, there is rapid innovation in the batteries used to power them. Finding materials that can be cheaply produced as well as improving battery efficiency, durability and lowering weight are priorities for the industry.
For example, materials such as silicon and graphene are likely candidates to replace graphite as the materials of choice for the anode. Using these materials will increase the range that can be achieved by vehicles on a single charge.