Page 72 - Energize July 2022

TECHNICAL

resistance within a 5,9 Ah rated lithium short circuit, impact, overcharge and forced discharge.
soft-pack battery as the state of charge is However, all these tests are required for standard commercial transportation. What is
lowered down to 10% SOC. unforeseen is the transport of damaged cells with electrolyte leakage. In Europe, universal
An alternative solution is to actively standards have not yet been instituted, and so the transport of damaged cells is carried out
derate the cells. However, this reduces by individual solutions. Some examples are [1] storage of the battery for a minimum of 14
the universal applicability of the systems. days, [2] covering by vermiculite and cooling of batteries with dry ice which is very costly
A thermal management system is also and requires a lot of time-consuming labour effort.
required for most industrial/commercial
applications which adds to cost and Recycling
reduces system efficiency. Currently, Li-ion batteries are generally recycled like consumer and cellular phone batteries.
The major focus during the recycling process is the conductive electrode material (copper)
Safety and cell container (steel), as well as the active material (nickel and cobalt). Cobalt, like
The safety considerations for Li-ion nickel and lead are mainly driven by the material prices for those metals when it comes to
batteries is mainly defined by the recycling. Lithium, however, drops mostly as a slag and is added at best case as a concrete
electrolyte (organic electrolyte with a additive hardener for cement or is processed in the glass industry. Realistically, a traditional
burn behaviour like alcohol) and the recycling for the Li-ion battery industry does not exist. Therefore, in the case of lithium
cathode material. There are two main recycling, it can’t be spoken about as a closed raw-material recirculation. The recycling
problems to discuss with regard to the process itself (metallurgical or electro-chemical) is not cost neutral and the cost cannot be
safety of Li-ion cells: fully covered by the recovered materials from the Li-ion cells.
• Production quality and created short Due to the ambitious plans of the automobile industry for electric mobility (BEV, PHEV),
circuits in case of production failure, we should not lose sight of the fact that lithium is the most important raw material for
and future demand. In view of the chronicled uncertainty of lithium supply and the lack of
• Operation of the batteries at different optimized recycling procedures, energy storage cases above 1 kWh may remain a challenge
ambient temperatures outside the for the future. What is needed is to develop new recycling procedures (e.g., wet-chemical
permissible voltage ranges.

Both of these critical points may lead to
an ignition of the electrolyte. 5
The electrolyte transfers the energy
content/heat to the cathode material.
Therefore, the main question becomes
which of the cathode materials is installed
in the cell. In the case of lithium-iron-
phosphate (LFP), the limit of uncontrolled
energy output is really set by the
thermal behaviour of the LFP material.
The complete opposite is the case with
lithium cobalt oxide (LiCoO 2) which offers
the best energy content but remains Figure 9: Cathode material thermal behaviour (Source: ZSW)
very challenging with regard to the
thermal aspects with a high tendency for
overheating. Figure 9 shows the resultant
thermal behaviour of various cathode
materials at various temperature levels.
Therefore, a sufficient control of the
battery’s operational conditions as well
as an operation strategy is essential and
must be realized by on-board electronics.
Additionally, the transport of Li-ion
cells can be challenging. Before the cells/
system are approved, a safety test must
be performed at both an individual cell
and system level. UN transport testing
requirements include altitude simulation,
thermal test, vibration, shock, external Figure 10: Recycling process for Li-ion batteries

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