As the automotive world is moving towards electrification, Electric vehicle charging is the talk of the town. Range anxiety is one of the biggest issues of electric vehicle adoption. Charging or Fast charging electric vehicle is key infrastructure requirement. The process of adding energy to a battery cell or cells in a pack and so moving the State of Charge from a low value towards 100%. This simple process is actually far from simple and covers the electrochemical, thermal, electrical, infrastructure, standardisation and all the way through to electricity generation.
Key Parameters in Fast Charging
When looking at the key parameters in fast charging a battery pack it is worth looking at the complete system. Also, it is good to look from the cell at atomic scale through the thermal system design to the charging algorithms and handshakes.
The drive for a 10 min fast charge to reach 80% state of charge is tough against the other pressures of reducing cost and shrinking the pack. In most cases this fast charge is the worst case in terms of power requirements for the battery pack.
Stepped Fast Charge Limits
We often see stepped fast charge limits as shown in this BMW iX3 graph.
Often the result of a limited test regime applied by the cell supplier (in this case CATL) to establish the maximum charge current for the cell.
These limits are them applied by the BMS team and without more data they have to drop back to safe charge current limits between these points.
Charge time is a key metric for a battery pack, especially packs in transport applications.
As technology evolves there is a push to reduce charge times.
Not surprisingly the peak fast charge power is increasing versus year.
Types of EV Charging Connectors
Alternating current (AC) Chargers – This type of Chargers are good for Home, work and Public use. They are mostly slow to mid speed charging. AC chargers are split into Type 1 and Type 2.
Direct Current (DC) Chargers – These type of chargers are mostly found in Public environment as they need special additional equipment, network connections etc. They are mostly used for Fast Charging. These are called CHAdemo or Combo Type 1 or 2 (CCS connector).
Current from the Grid (AC) goes through EVSE (Charging Station Either Level 1 or 2) through a connector to the On Board Charger. The Onboard Charger rectifies or converts the current into DC and sends it via the Battery Management System (BMS) to the Battery Pack. The Alternating Current AC can be either Phase 1 or 3 depending on the Chargers.
Bank Charging
Bank charging is where we split the pack in two to charge it. Thus an 800V drive pack becomes two 400V packs in series for charging.
V2G
Vehicle to Grid (V2G) allows the battery in an electric vehicle to put energy back into the electricity grid. Essentially the battery has a bi-directional connection. This allows:
- energy to be sold back to the grid
- support for local brown-outs
- ability to power your house off-grid
V2V
Vehicle to Vehicle (V2V) allows the battery pack on one vehicle to be used to charge another electric vehicle.
Hot Swap versus Fast Charge
There are pros and cons with both options. Nio has demonstrated that battery swapping is viable and well liked by customers, showing that it doesn’t need to be a design constraint with a 150kWh semi-solid-state pack that fits the existing vehicle envelope. That pack entered rental service in mid-2024, though Nio has since scaled back production after limited demand for it.[1]
However, the cost of fast charging is roughly equivalent to the cost of the battery swap. Plus you need to pay up-front for the battery swaps. Overall for me this makes the pay as you go fast charging a better option for the average user as a lot of the time you will charge at home, slower but much cheaper.
References
- Nio drops 150 kWh battery with semi-solid electrolyte again, electrive.com
See also: Charging Connectors