Page 30 - European Energy Innovation - autumn 2017 publication
P. 30
30 Autumn 2017 European Energy Innovation
ELECTROMOBILITY
Modern battery engineering
By Prof. Dr.-Ing. Kai Peter Birke and Christoph Bolsinger, Electrical Energy Storage Systems, University of Stuttgart
B attery development for is also developing and there are the cell as a self-supporting part. One
electromobility is driven by standards such as 18650 and 21700 cylindrical cell may fail under static
continuous energy density for cylindrical cells, and for prismatic load tests. However, a multiple array
enhancement (Wh/kg, Wh/l). ones that standardization committees easily sustains the automotive standard
This applies for weight and volume as are at last accepting. deformation test conditions from
well as for the costs of batteries in €/ different directions (x, y, z) for traction
kWh. If more energy can be stored by However, the situation on battery batteries. This is an important result
using the same raw materials, batteries level (assembled cells) is surprisingly which has already been achieved
become more cost effective. lacking in focus. As a rule of thumb, in this project. Such a cell array is
only half of the energy density remains depicted in Figure 1. On module level
Lately the focus has been more and on battery level for most of the 180 Wh/kg can still be preserved and
more on volumetric energy density. batteries which are actually installed in this shows the power of the concept
Here Li-Ion cells show a unique electric vehicles. This means that, from of self-supporting cell arrays. The final
property since volumetric energy 200 Wh/kg on cell level only, 100 Wh/ battery housing has thus no tasks to
density is double that of gravimetric kg are available on battery level. For prevent against deformation and can
energy density. This is why Li-sulfur volumetric energy density it is often be constructed with very lightweight
cannot be a competitive technology less than one third. Additionally, those materials. The cooling board will be
any more for applications in electric batteries are not easily recyclable. made out of modern plastics. The final
vehicles. Even Li-air (on realistic cell target of the project is to reduce the
level, not by theoretical calculation) The reasons may be seen in battery loss of energy density from a factor 2
may not be able to compete any more constructions which satisfy firstly the (if gravimetric energy density from cell
in this field. safety and lifetime. First generation is divided through energy density of
Li-Ion batteries for hybrid vehicle the battery) to at least 1.5, preferably
Generally, the focus of energy density application show a very rigid housing 1.3. The level from cell to module (as
improvement is still extremely targeted which withstands harsh deformation shown in Figure 1) is actually in the
on cell level. The latest potential from outside, and thus satisfies safety regime of 1.2.
advancement can be seen in the demands. For the lifetime of the
renaissance of Li-metal solid state battery, usually welded connections of Additionally, a recycling concept on
cells. The level of standardization the cells are employed. All this makes cell level is successfully employed.
recycling very difficult. The modules can be completely
Figure 1 disassembled since the cells are
However, looking at the tremendous screwed on and clamped. Here,
potential of energy density experimental results show that this way
enhancement by avoiding senseless of cell connection is fully competitive
losses from cell to battery level, new with the conventional cell welding
construction methods are necessary. methods. However, these results still
It is important to consider that energy have to be verified over lifetime. The
density enhancement of Li-based cells recycling concept is supported by a pure
will be more and more exhausted optical based communication concept
within the next decade. to the Battery Management System.
Here the project “LIBELLE”, founded Generally, battery production
by the “VECTOR-Stiftung” shows concepts still show a huge lack of
new directions. The project has been industrialisation which, surprisingly,
undertaken by the Electrochemical lacks the focus applied to
Energy Storage Systems team at the standardisation efforts on cell level.
University of Stuttgart in Germany, A Giga-Factory usually means a cell
under the supervision of Professor Kai factory. Looking at the cost structure,
Peter Birke. The basic idea is to use the ratio between cell and battery
www.europeanenergyinnovation.eu
