We have already told you how an electric car works and how it differs from an ordinary car with an internal combustion engine (ICE). Now let us take a closer look at an electric car battery – the main source of energy that, so to say, sets the wheels in motion. At the same time, it is the most expensive and complex component of an electric car.
EV Battery: Why is it the Most Expensive Component of the Electric Car?
It was estimated that in 2010, when electric cars began to make their way to the market, battery price was $1,183 per kWh, which was 100,000 times more expensive than the energy it could store. Over ten years of development of EV battery technologies, this parameter has fallen to $150, and the price of electricity storage will keep falling — according to calculations, by about 10-15 percent per year. Nevertheless, the price of the electric car still mostly consists of the battery price: the "fuel tanks" of the electric cars will be expensive for a long time to come.
Firstly, it is due to the size of the battery that should be able to store enough electricity. Currently, the battery pack for the passenger BEV that can travel at least 350 km on a single charge weighs approximately 500 kg. Secondly, 80-90% of the electric vehicle battery is made up of powerful busbars and expensive battery cells. Their manufacture requires rare chemical elements, non-ferrous, and even precious metals.
Finally, EV batteries consist of numerous units and sensors, several protection circuits, and a thermal management circuit. Such complex design is vital because the high-voltage EV battery operates under high-cycling conditions (charge during each acceleration and discharge during regenerative braking) and under very high currents. Let us take a look at each of its components.
Why Electric Car Needs the High-Voltage Battery
Operating voltage proves to be the most prominent difference between the EV traction battery and the ordinary car battery. Instead of 12 V (or 24 V for trucks) known to every motorist, the operating voltage of the mass-produced electric cars - even the first ones - has reached up to hundreds of volts. Nowadays, the voltage is usually 350-450 V. But this is not the limit either. The e-platform of Porsche Taycan relies on the 800-volt system. What's more, the electric cargo vehicles of the future are predicted to have 1200-1600-volt batteries!
Such high figures can be explained by the laws of physics. In a high-voltage system, much more electrical energy can be stored per unit mass of the battery. If one tries to use ordinary car lead batteries to assemble a Tesla battery, one will need a truck to transport them. Additionally, in the high-voltage system, at the same electric motor power, the currents will be lower. Therefore, thinner wires can be used to reduce the general weight.
Surely, 400-800 V sound frightening, as far as even significantly less voltage is deadly for a human. However, there is no real threat of getting electrocuted provided that all necessary protection measures are taken.
Classic 12 V battery in electric cars, by the way, are used solely for starting the car or providing for the work.
What Types of Cells are Used in Electric Car Batteries?
Unlike most car batteries, the battery cells of the electric car have no electrolyte or gel inside. They are "dry" and their filling brings them closer to household batteries for gadgets.
The first electric cars used nickel-metal hydride batteries (Ni-MH). They were promised to have very high energy storage capacity: theoretically, one kilogram of such a battery could have stored up to 300 Wh. However, in fact, only a fifth of their potential capabilities was used. A few years later, lithium-ion cells became the standard for electric vehicles (and a lot of other equipment). Due to the higher price, they have long been considered unprofitable. But only such cells could provide real storage density of 100-250 Wh/kg.
Tesla has started using cylindrical 18650 Li-Ion cells (slightly larger and thicker than AA batteries), which were originally intended for laptop batteries. In Tesla Model S 7104, such cells are assembled in sixteen 25-Volt modules.
Japanese EV manufacturers preferred battery cells designed specifically for electric cars: they are flat and they are convenient to be placed in pouches of the desired capacity. European manufacturers tend to work with even more technologically advanced cells that look like rather heavy bars. The technology of manufacturing Li-Ion cells has already been well developed by several large companies, mainly from Southeast Asia: Panasonic, Toshiba, LG Chem, Samsung SDI, Automotive Energy Supply Corp, CATL, BYD, etc. Each format has its own advantages and disadvantages. For instance, cylindrical cells are larger, but, simultaneously, easier to cool.
In general, Li-Ion is an umbrella term for a group of completely different batteries. For example, there are lithium-ion cobalt oxide batteries that provide the highest storage density, but, at the same time, they are the most difficult to handle, have a limited resource, are explosive and toxic. Lithium-ion manganese oxide batteries are less unpredictable and not so expensive, but they store less energy and do not work at -10 degrees. The lithium-iron-phosphate batteries prove to be the most stable and highly resourceful. Their storage density is equal to other types of Li-Ion batteries, but their self-discharge capacity and the operating temperature threshold are lower (up to -30°С). There are batteries based on mix of various metals, among them - special lithium-titanate batteries. They are currently the most expensive ones, but due to their extremely low internal resistance, they can be charged with high currents extremely quickly.
Even despite such a wide choice, one cannot definitely state that Li-Ion technology has taken the ultimate lead. There are some interesting alternatives to this product: scientists look for a cheap option to replace lithium by offering aluminum-ion and metal-air cells. Polymer graphene and lithium sulfur batteries are developed to achieve faster charging and more higher energy storage capacity.
How Electronics Control the Battery
The traction battery is a matrix of low-voltage cells connected in a certain way. Their charge-discharge cycle is controlled by a network of microprocessors at the different levels of this matrix.
For example, each battery cell has one or two temperature sensors and its own controller. It ensures safe current modes, protects against overvoltage, overcharge, overheating etc. It is responsible for a safe work of one cell.
Charging of the units consisting of dozens or hundreds of cells is controlled by the BMU controller. Its function is to balance the currents between series or parallel cells.
Overall control and distribution of energy, depending on the type of charging (full, conventional, accelerated or ultra-fast), is the responsibility of the central BMS controller. It is also usually responsible for the resource parameters of the entire battery, making sure that the load is distributed optimally on all modules.
By the way, the values 0 and 100% shown on the electric car dashboard or charging console, are just conventionality. The manufacturer does not fully charge the battery leaving a certain margin from the nominal value. It is gradually used as the battery is inevitably aging and its energy storage capacity is declining. A full discharge of the batteries is not possible as well: even when the electric car stops being unable to move, there is little energy still left in the battery. It is necessary to prevent undesirable and irreversible chemical processes in the cells.
What do Electronics Protect the Battery and People from?
The above-mentioned control units control both battery cells and the entire network interconnecting those cells. If any cell deviates from its rated operation conditions for any reason, the control system will reduce the load on it or even "retire" it and stop charging to eliminate the slightest risk of internal damage to the battery.
The electric car's power supply circuits are also electronically controlled. There are powerful relays that are able to break the circuits in case of abnormal deviations in the drive or any charge leakage. There are classic fuses that protect against short circuits. The physical condition of all critical connections is monitored by the end-to-end supervisory bus. Shock sensors are used to protect against electric shock in the event of an accident – when they are triggered, voltage is removed from high-voltage circuits. Finally, the latter are covered with bright orange insulation that warns of the danger of improper handling. In the service centers of authorized dealers, only qualified employees are allowed to work with power plants of electric cars.
Both passive temperature monitoring and active thermal management are used in modern batteries. The processes are carried out through the system of delivery pipes filled with antifreeze. Under high loads or during ultra-fast charging, such system remove excess heat, and at low temperatures, conversely, heats up the cells.
How the Battery Case is Built
When electric cars were built on the basis of the ordinary cars, their batteries were of very unusual shape, as far as they replaced fuel tanks, spare wheels and unnecessary shafts. Nowadays, in most electric cars, the battery is placed under the floor area and, therefore, it looks like a flat slab. Such shape is very convenient for modular batteries — "slabs" that are different in weight, size, capacity and price, but can be substituted within a single e-platform.
However, such layout demands stronger battery case. Its power cell is designed in such a way that it could withstand the impact from all sides (which is much more powerful than the impact deadly to a human). The bottom of the battery must ensure its integrity and resist isolated damage – for example, from stones or off-road impacts. Therefore, the battery is the most durable and virtually unbreakable EV component.
Its characteristics also include hydraulic protection, a tube system for cooling and ventilation, a set of special protected high-voltage connectors and other components necessary for the diagnostics. In addition, it is bolted to the body, which in some electric cars makes the battery a part of its power facilities. Therefore, a simple "battery box" turns into a technical masterpiece that is not automatically stamped out, but made using a complex technology with the use of high-strength aluminum alloys and stainless steel.
Why the Battery Ages and How Quickly it Happens
The battery of a modern electric car is a self-regulating system equipped with artificial intelligence that will not enable any harmful modes. The battery does not require maintenance, except for reading possible electronics errors and, if necessary, updating its firmware.
The experience confirms that even when intensively used and frequently recharged, the battery can easily handle 100-160 000 kilometer within the warranty period. Theoretically, the first year of operation is the most critical period, when some individual cells may break down. But it is like "dead pixels" in monitors: the remaining ones will keep working reliably, and the total battery capacity will only subtly decrease.
The first signs of battery aging will be evident only after three years of operation when the battery capacity will be 10-15% lower than initial capacity. But then the degradation process slows down. Even after eight years of work, the battery capacity is significantly higher than guaranteed 70%.
How Long an Electric Car Battery Last and How to Use it Correctly
Remember the operation rules for mobile phones in the early years of their use? The mobile phone was to be fully discharged and than charged up to 100%. Otherwise, the memory effect took place and the battery quickly lost its capacity.
Nowadays, the EV owner doesn't need to worry about this problem – the battery for electric car can be charged at any time. For Li-Ion cells, the optimal discharge levels in the entire cell matrix are controlled by an entire processor system. However, there are certain aspects that can reduce the battery life or, conversely, slightly extend it.
On the one hand, the battery life can suffer from the frequent use of high-speed charging at DC charging stations with a capacity of more than 100 kW. For long distance trips, this is a real salvation: 30-40 of such charging can replenish the electric car power reserve by 150-200 km. As a bonus, you can also relax and have a snack while waiting. However, charging with ultra-high currents is stressful for battery cells. For regular charging, it would be better to use stations with a capacity of 25-50 kW. By the way, our GO TO-U app shows you the power of the charger when booking the latter, so you can take into account this information as well.
The second potentially stressful event is working at extremely low temperatures. For sure, a modern battery controller will do its best to limit the current on cold cells and quickly warm them up with the help of a built-in inverter air conditioner (that will help warm up the interior as well). Yet, in winter, it will be much better both for you and your EV battery to charge it until the departure and turn on the heating timer in advance.
The third potentially stressful event is regular charging up to 100%, when the cell undergoes almost irreversible changes in the chemical balance. Thus, a tiny "comfortable" undercharge proves to be useful for Li-Ion cells of your electric car.
How to Dispose the Battery
This issue was of concern for a long time since initially there were no technologies for cheap, deep, and eco-friendly ways of recycling Li-Ion cells. Though they have already been created by now: cases and copper busbars are recycled as ordinary non-ferrous metal; cells are diluted with the help of specific agents - as a result, obtained lithium and other elements can be reused.
Such enterprises are still few in number, so an effective, albeit temporary, solution is to reuse cells or batteries for electric cars for various stationary sources for energy storage. For example, they can be useful for solar stations or wind farms. They can also be used in private households or for the needs of the city power network. For example, in Japan, disused electric car batteries produce energy for street lighting; in Paris, they are used for driving elevators; in Amsterdam, they provide energy supply for an entire stadium.
So, We Can Draw the Following Conclusions
– EV batteries are still expensive, though they have become almost three times cheaper over the last 10 years. Their capacity has increased by almost three times as well.
– All traction batteries for electric cars work on high voltage (from 350 to 800 V), but the multi-circuit protection system virtually eliminates the risk of electrocution.
– Li-Ion is just an umbrella term for a group of absolutely different batteries. It includes lithium-ion cobalt oxide, lithium-ion manganese oxide, lithium iron phosphate, lithium-titanate batteries etc. All of them have their advantages and disadvantages.
– A complex multi-level system with a large number of temperature sensors manages the distribution of power flows inside the battery. Every cell, module, circuit segment and battery as a whole is under control.
– Most of the battery price is not only due to cells but also a case. It is an extremely durable component that is tricky to make.
- In case of regular operation, the electric car battery wears out in a rather peculiar way. The storage capacity can quickly degrade by a few percent due to faulty cells. Then it gradually decreases by 15-20 percent over several years. Finally, the process slows down making it possible to reuse the battery, for instance, in stationary systems.
- Technologies for comprehensive utilization of batteries have already been developed, but so far such services are provided by an extremely limited number of companies and not in all countries.
