Everybody is talking about standards for EVs. I think, most likely eventually a series of industry standards will emerge. For a key element, a main cost driver and a new component unique to EV, let’s have a look at potential standards for EV battery systems.

Before we mention any potential EV battery standard, we need to be clear what exactly we are thinking about. Are we talking about a safety standard relating to flammability or are we talking about an overall standard allowing drop-in battery pack replacement, or anything in between?

For example, when we need to replace the 12V lead-acid starter battery in our car, we may purchase a battery with similar performance characteristics from a number of manufacturers, and all will fit the car’s battery bay and work fine. Thanks to industry-standard sizes and capacities, neither we as a consumer nor the OEM’s assembly plants are bound to a single source.

What might standardization look like in the Li-Ion EV car battery market?

There are several aspects of variability in batteries for EVs that all need to be considered if you are discussing EV battery standardization. First of al, not all EVs are alike: lightweight two wheelers like bicycles and scooters, whose battery can easily be detached and carried home for charging will obviously have completely different requirements than heavier motorcycles, tricycles and quadracycles (lightweight cars). Hybrid cars that only recharge during recuperation and Plug-in Hybrids or pure electric cars also have widely differing requirements.

For now, let’s assume we are talking about a plug-in battery electric car, possibly with range extender: so for the standardization of specific aspects of a battery that may benefit battery manufacturers, car designers, OEMs, customers and service personnel, we will still have to decide at which level we are talking:

Factors to be standardized at the cell level:

• physical cell properties like form factor, size, weight
• electrical cell properties depending on chemistry, cell layout and safety features
• thermal properties: thermal conductivity for cooling/heating as well as internal thermal distribution under load
• Charge/discharge properties depending on cell temperature
• Behavior of the cell in abnormal conditions (crushing, puncturing, overheating, external or internal short circuit, overcharging, deep discharge)

Standards at the battery pack level:

• Physical characteristics: Shape, Weight, stiffness if used as a structural element, crash protection of the battery cells, safety barrier between high voltage elements and passengers, service and rescue personnel etc.
• Electrical Interfaces: high-voltage connection to vehicle, high voltage connection to external DC charger, Battery Management System control interface
• Cooling/Heating Interfaces: passive, air, liquid or air conditioning system interfaces
• in case of field removable or switchable battery packs: physical retaining system, electrical connectors, cooling/heating system connectors

I can imagine battery systems consisting of a variable configuration of standardized modules – for example a packaged unit consisting of a number of cells and cell balancing circuitry – for example I can imagine each module could be a package providing 60Volts/50Ah = 3KWh, so a car designer could choose to make a 24 KWh pack by connecting 8 of those modules in series providing a total of 480V. Such a module could be standardized in terms of the following characteristics, and as long as the module meets or exceeds that specification, it should be replaceable regardless of the internal architecture, so the same standardized module could contain different internal architectures by different manufacturers, competing with each other on the best way to deliver the required features.

Battery module level characteristics to be standardized:

• package characteristics: shape, size
• electrical connectors
• passive or active cooling/heating interfaces
• performance characteristics: operating voltage range, peak power, steady state power, charging requirements, temperature operating and charging ranges
• Battery management system communication protocol
• Module failure management: internal short circuit, cell failure, cell balancing circuit failure
• Behavior under the influence of external factors like external short circuit, being outside of permissible ambient operating temperature range in case of passive cooling/heating or failure of cooling/heating system for active cooling/heating, physical compromise (crushing, shearing, excessive vibration)

Then there are further aspects like:

• service procedures, safety regulations and instructions for service personnel
• serviceability: for example, can single cells be replaced in the field? (keeping in mind that a battery pack’s capacity is always limited by the weakest element, the life of a pack may be conceivably extended indefinitely by regularly replacing the weakest cells)
• availability of spare parts over time

Each of the above points may be quantified or specified in a standard. Some of these standards may evolve into binding standards enforced by governments like some safety aspects, others affect engineering specifications, or consist of any other manufacturers choices evolving into de-facto industry standards by market choice.

At this stage this is a work in progress for all of us who are involved.