A hybrid battery pack is one that uses more than one type of battery cell or supercapacitor. The aim being to provide a broader set of capabilities, such as:
- Energy and power
- Hot and cold performance
Examples of this approach:
NIO Standard-Range Hybrid-Cell Battery
A 75kWh pack that has LFP and NMC cells with the intention of improving the cold weather performance.
The pack has thermal insulation, improved BMS and a high power DC-DC.
It’s not just a case of mixing different cell chemistries in series and parallel, this won’t just work and could be extremely dangerous. It is more likely that you will need separate series and parallel strings for each chemistry and a DC-DC between the two so that you can align voltages over the state of charge, temperature and lifetime.
Concerns
There are a number of concerns with this approach and any design should be compared to the option of using just one chemistry:
- Overall cost
- multiple cell management systems in terms of hardware and software
- increased power electronics
- more complex manufacture and servicing
- Design complexity
- managing requirements from 2 different cells
- testing of 2 cells
- Diagnostics and service
- more parts => more cost
- more complexity => more difficult to diagnose failures and increased service
Optimisation
The work Tzermias et al [2] looks at a methodology for optimising a hybrid energy storage system. Focussing on mixing different types of Li-ion batteries with a range of power-dense and energy-dense battery chemistries.
The approach is based on a Ragone plot and does not require the use of a detailed electrochemical model and thus allows for an effective evaluation of different energy storage technologies at an early stage of the design process.
Ragone plot analysis method for evaluating the actual Pareto-front-based mass saving when using a hybrid energy storage system compared to a single energy storage system for different application PE ratios based on the currently available battery technology performances.
There are some offering tools to optimise battery and supercapacitor hybrid systems [3].
References
- NIO Launches the Standard-Range Hybrid-Cell Battery, NIO
- Tzermias, G.; Akehurst, S.; Burke, R.; Brace, C.; George, S.; Bernards, J.; Smith, C. Methodology for the Optimisation of Battery Hybrid Energy Storage Systems for Mass and Volume Using a Power-To-Energy Ratio Analysis. Batteries 2021
- Battery Builder, Kurt.energy