Mixed Chemistry Battery Pack

The mixed chemistry battery pack consists of two types of battery cell with different chemistry in one battery pack. The aim being to offer the best of both chemistries:

  • energy and power
  • wide temperature range

A look at the power density versus energy density graph. This shows that high power tends to be at the expense of energy.

Hence, the question: “what if we could combine two technologies?”.

This post has been built based on the support and sponsorship from: MAHLE Powertrain LtdThermo Fisher ScientificEatron TechnologiesAbout:Energy and Quarto Technical Services.

There are a number of options for connecting the cells together electrically:

  • match the discharge curves
  • throttle the electrical output with power electronics
  • use a DC-DC to align the outputs of each chemistry

The CATL designed mixed chemistry pack for NIO used LFP and NMC, the NMC improving the energy density and cold temperature performance of a 100% LFP pack.

The hybrid layout of ternary lithium cells and LFP cells makes full use of the low-temp performance advantage of ternary lithium cells to improve the overall battery performance in low temperature. And the dual chemistry control algorithm precisely controls the performance of ternary lithium and LFP cells in cold temperature to improve low-temp energy efficiency of the whole battery system.

NIO’s self-developed hybrid-cell battery SoC estimation system integrates the innovation of software algorithm and hardware application, which reduces the estimation error to less than 3%, reaching the level of ternary lithium battery SoC estimation. The dual chemistry SoC algorithm fully takes advantage of ternary lithium and LFP battery systems to realize constant battery SoC estimation and guarantee the accuracy. A high-power DCDC within the battery ensures fast, real-time and balanced SoC calibration

The prototype battery developed by ONE appears to have a similar arrangement as the NIO CATL pack.

ONE’s early packs will consist of lithium-iron-phosphate (LFP) cells, along with cells using an experimental high-energy-density chemistry based on a proprietary material rich in manganese with a bare copper current collector known as an “anode-free” design. ONE says its LFP cells will provide 99% of the pack’s everyday usage, while the high-energy lithium-manganese cells will handle the extreme conditions that make up the last 1%—reducing the edge-case stress on the LFP cells to allow them to operate within their ideal range of conditions. 

ONE says that this particular dual-chemistry configuration will reduce lithium use by 20%, reduce graphite use by 60%, and minimize the use of nickel and cobalt.

ONE’s hybrid battery pack combines the best aspects of two chemistries to deliver 600 miles of EV range, ChargedEVs

The downside of a mixed chemistry battery pack is complexity and hence cost:

  • two BMS, one for each chemistry
  • two cells to validate in isolation and together
  • extra power electronics
  • complex characterisation and modelling

Hence, for all the benefits it is often simpler to use just one chemistry [1].

References

  1. NIO Switches Its Standard 75-kWh Battery From Hybrid-Cell LFP/NCM To All-LFP, InsideEVs
  2. ONE’s hybrid battery pack combines the best aspects of two chemistries to deliver 600 miles of EV range, ChargedEVs

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