Written by Dr Euan McTurk, Electrochemist at Dukosi.


Dukosi’s integrated Cell Management System (CMS) represents a significant leap forward in both cell and battery pack design, and makes life easier for everyone involved throughout the entire lifespan of the cell.  Here, we highlight the key advantages of the Dukosi CMS from an economic perspective and how cell and pack manufacturers, maintenance engineers, second life applications and recyclers can all expect to benefit through the use of this system.

Lithium-ion Battery Management Systems (BMS) perform a crucial role in maintaining the State of Health (SOH) of the individual cells in a battery pack.  Sensors relay cell voltages and temperatures to the BMS master chip, which attempts to optimise pack performance whilst ensuring that the cells are not exposed to conditions that can cause them to degrade or undergo thermal runaway.  However, the BMS and its surrounding infrastructure are expensive to implement, which leads to technical compromises in their design and added complexity for the manufacture, maintenance and disposal of the battery pack.  Dukosi have designed an integrated CMS which offers a raft of technical benefits over today’s solutions and allows considerable cost and time savings from pack assembly through to maintenance, Second Life applications and cell End of Life (EoL).

Tailored formation cycles, faster manufacturing process

The advantages of the Dukosi CMS begin even before the cells are ready to assemble into a pack.  The formation process of a cell, i.e. the period immediately after its manufacture when it is cycled to form a Solid Electrolyte Interphase (SEI) on the electrodes, usually involves cycling the cell on a standard program.  The Dukosi CMS embedded in or onto the cell can instruct a power supply to charge or discharge the cell as it sees fit, thus tailoring its formation process to ensure the best results in the least amount of time.

After the formation process, cell manufacturers regularly store their cells for several weeks prior to shipping and then test each cell individually to ensure that none display any signs of defects.  Conversely, the Dukosi CMS allows cells to be shipped directly to customers, who can wirelessly confirm the SOH of each cell upon arrival within a matter of seconds.  This frees up a significant amount of space on the factory floor, which can be dedicated to increasing the size of the production line and the throughput of the factory without requiring any physical expansion.

Less wiring, more data

A conventional BMS relies on complex wiring networks which are costly and time-consuming to implement and introduce multiple possibilities for error or failure.  To simplify the design, voltage and temperature sensing is typically only performed at a module or submodule level, with a resultant compromise in the amount of data available to the BMS.  As a result, the BMS may struggle to detect disparities in performance or aging at individual cell level.  This, in turn, results in premature pack aging and expensive maintenance, potentially within the warranty period.  The Dukosi CMS removes the need to compromise on design by simplifying the infrastructure of the battery pack, eliminating up to 95% of the wiring harness, whilst providing on-cell voltage and temperature sensors on every cell in the pack.

Fewer components, faster integration

The connections between the sensors and the wiring harness in a conventional BMS must meet automotive standards and be tested for their moisture ingress protection level, which adds expense in terms of testing and component costs.  Current and voltage sensing alone are estimated to cost $100 to integrate into each EV battery pack [1].  Such wiring harnesses are time consuming to implement, involving neat channelling of the delicate wires through crevasses in the battery pack, thus contributing an extra $54/kWh towards the cost of the pack [2].  Furthermore, sensor wires complicate the battery pack servicing process, requiring disconnection from the cells of interest and potentially from neighbouring cells if their cables are causing an obstruction, which adds time, complexity and, subsequently, expense.  When the battery pack is disassembled and the cells repurposed for Second Life applications, the wiring harness is discarded.

Dukosi’s CMS wirelessly communicates with the BMS to provide voltage and temperature readings for each cell in the pack.  The near-total elimination of the wiring harness reduces the cost of materials (connectors, copper, trunking and cables tidies) and associated testing, and increases the velocity of the battery pack assembly flow process, leading to increased throughput on existing production lines.  Costs associated with recycling or disposing of wiring harnesses at EoL are avoided.  Since the Dukosi CMS is embedded within the cell, the time, materials and disposal cost savings associated with the elimination of the wiring harness are shared throughout the lifespan of the cell, including Second Life applications and beyond.

On-demand cell history for simplified servicing, Second Life repurposing and recycling

For an OEM, the cost of responsibly disposing of battery packs can be considerable.  Uncertainty surrounding the SOH of cells can result in prohibitive disposal costs that must either be absorbed by the OEM or incorporated into the price of the pack.  Commonly, packs are repurposed for Second Life applications.  However, uncertainty regarding SOH affects the residual value of the cells and therefore requires each cell to undergo time-consuming and costly testing.  Dukosi’s CMS uniquely stores cell history within the cell, with a detailed account of voltages, temperatures and SOH.  This allows cells to be quickly classified by their SOH and reassembled into modules or packs of cells of similar condition.  As a result, testing time is significantly reduced and the residual value of each cell is maximised.  Any cells that are deemed to have reached End of Life will have a detailed account of their SOH and history obtainable via their cell-powered Dukosi CMS.  Cell information is available both wirelessly and on-demand, whether still connected within the battery pack or in isolation.  This benefits cell recyclers as they will be able to quickly assess the safety considerations for each cell during the recycling process, which translates into further potential savings for OEMs through reduced recycling costs.

Everyone benefits from the Dukosi CMS

The Dukosi CMS presents clear advantages throughout the product life cycle of the battery pack, from faster cell, module and pack assembly through to reduced SOH degradation and easier maintenance, repurposing and disposal.  Costs are also saved through the elimination of a plethora of components associated with a conventional wired BMS, and the associated expense of testing the weatherproofing and roadworthiness of these components.   These factors all combine to provide economic benefits for all parties involved during the lifespan of the cell, including cell and pack manufacturers, maintenance engineers, customers for Second Life applications and cell recyclers.


References:

[1]  P. A. Nelson, K. G. Gallagher, I. Bnetwork, and D. W. Dees, “Modeling the Performance and Cost of Lithium-Ion Batteries for Electric-Drive Vehicles,” pp. 1–102, 2011.
[2]  C. Cluzel and C. Douglas, “Cost and performance of EV batteries: Final report for The Committee on Climate Change,” p. 21, 2012.


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