© A. Latour, CEA for SPARTACUS.

SPARTACUS makes bat­ter­ies strong

Bat­ter­ies for e‑cars and mobile devices are easy to use, but fre­quent charg­ing and dis­charg­ing and the asso­ci­at­ed aging process­es impair the per­for­mance of bat­tery cells and short­en their ser­vice life. In the SPARTACUS research project, Fraun­hofer ISC researchers are using a range of dif­fer­ent sen­sors to mon­i­tor the inter­nal sta­tus of bat­tery cells. The data enables the bat­tery man­age­ment sys­tem to opti­mize charg­ing and dis­charg­ing process­es and the load on indi­vid­ual cells in the bat­tery mod­ule. This can sig­nif­i­cant­ly speed up charg­ing — and even extend the life of the batteries.

In the high-tech age, bat­ter­ies are regard­ed as uncom­pli­cat­ed helpers. They let the alarm clock ring in the morn­ing, sup­ply smart­phones with ener­gy and help the mobile Blue­tooth speak­er to make music. They also pow­er e‑cars and e‑scooters and thus play a cru­cial role in the mobil­i­ty rev­o­lu­tion. Once the bat­tery is emp­ty, it is recharged. But the sim­ple usage con­cept con­trasts with the amaz­ing­ly com­plex inner work­ings of the bat­ter­ies. This offers a lot of poten­tial for improv­ing per­for­mance and extend­ing lifespan.

Researchers at Fraun­hofer ISC in Würzburg want to make bet­ter use of this poten­tial. Togeth­er with project part­ners, Fraun­hofer experts are work­ing on a tech­nol­o­gy in which sen­sors reg­is­ter the sta­tus of the bat­tery cell as part of a Europe-wide research ini­tia­tive in the SPARTACUS project. With the help of this data, the inte­grat­ed bat­tery man­age­ment sys­tem can opti­mal­ly con­trol the charg­ing and dis­charg­ing cur­rents. “A major advan­tage here is that the charg­ing time is reduced by up to 20 per­cent with­out sac­ri­fic­ing bat­tery per­for­mance and ser­vice life,” explains Ger­hard Domann, project coor­di­na­tor at Fraun­hofer ISC, Würzburg.

Ultra­son­ic sen­sors gen­er­ate a sonogram

The con­cept of SPARTACUS (Spa­tial­ly resolved acoustic, mechan­i­cal and ultra­son­ic sens­ing for smart bat­ter­ies) exploits the phe­nom­e­non that a num­ber of com­plex elec­tro­chem­i­cal and phys­i­cal process­es take place in the bat­tery cell. The acoustic, mechan­i­cal and ther­mal sen­sors used at Fraun­hofer ISC mon­i­tor and mea­sure the process­es. Ultra­son­ic sen­sors, for exam­ple, emit sound puls­es that pass through var­i­ous lay­ers of the bat­tery cells and are detect­ed again by sen­sors. If, for exam­ple, a cell expands dur­ing charg­ing or a defect occurs at an elec­trode, this will affect the prop­a­ga­tion time of the sound sig­nal. In this way, a kind of sono­gram of the bat­tery cell is cre­at­ed. Equal­ly impor­tant: the pres­sure-sen­si­tive mechan­i­cal sen­sors. They reg­is­ter how cer­tain com­po­nents change their vol­ume dur­ing charg­ing or dis­charg­ing. Ther­mal sen­sors, in turn, mea­sure the tem­per­a­ture changes.

“All sen­sor data is trans­mit­ted to the bat­tery man­age­ment sys­tem, where it is eval­u­at­ed. It is thus able to con­trol the elec­tri­cal cur­rents when dis­charg­ing and charg­ing the bat­tery in such a way that, on the one hand, the max­i­mum pos­si­ble pow­er is avail­able but, on the oth­er hand, this is done so gen­tly that the rel­e­vant func­tion­al lay­ers (anodes, cath­odes, etc.) of the bat­tery are not exces­sive­ly stressed. This is how we extend the ser­vice life of the bat­tery cell,” says Domann. The seem­ing­ly sim­ple ener­gy stor­age device becomes an intel­li­gent bat­tery that mon­i­tors its cells and active­ly con­trols the elec­tri­cal cur­rents dur­ing oper­a­tion and charging.

The result­ing exten­sion of ser­vice life is worth­while not only for bat­ter­ies in e‑cars, in which sev­er­al 100, some­times even more than 1000 indi­vid­ual cells are installed, but also for sta­tion­ary systems.

Analy­sis of the aging processes

But there are more effects observed by the sen­sors. The mechan­i­cal stress of use and the nat­ur­al aging process­es leave traces in the sen­si­tive inner life of the cells. In the case of the bat­tery cell elec­trodes, this may lead to cracks and detach­ment of the graphite lay­er, or tree-like met­al struc­tures may form on the out­side of the elec­trodes, known as den­drites. All these phe­nom­e­na weak­en the per­for­mance and in extreme cas­es can cre­ate a short cir­cuit in the cell, which can lead to a bat­tery fire. “The mul­ti­func­tion­al sen­sor array helps us bet­ter under­stand the com­plex elec­tro­chem­i­cal process­es in the bat­tery and adjust bat­tery man­age­ment accord­ing­ly,” Domann says. Fraun­hofer ISC has many years of expe­ri­ence in elec­tro­chem­istry, as well as in the devel­op­ment of sen­sors and bat­tery tech­nol­o­gy. This exper­tise flowed into the devel­op­ment of the mul­ti­func­tion­al sen­sor arrays.

The sec­ond life of the battery

The sen­sor tech­nol­o­gy devel­oped in SPARTACUS can be used for the entire life cycle of a bat­tery prod­uct. It already helps to opti­mize qual­i­ty dur­ing design and devel­op­ment. In pro­duc­tion, ultra­son­ic sen­sors ensure that the fin­ished prod­uct comes off the line in opti­mum con­di­tion. “When the bat­tery’s per­for­mance inevitably degrades after a few years and less than 80 per­cent of the orig­i­nal pow­er is avail­able, the sen­sors from the SPARTACUS project could also be used to qual­i­fy the bat­tery for a sec­ond life, or sec­ondary use for a less demand­ing appli­ca­tion,” Domann says.

In the future, the tech­nol­o­gy will not only be applic­a­ble to lithi­um-ion bat­ter­ies, but can also be applied to sol­id-state bat­ter­ies or lithi­um-sul­fur bat­ter­ies, for exam­ple. Fraun­hofer ISC and its project part­ners have already test­ed the func­tion­al­i­ty and prac­ti­cal­i­ty of the tech­nol­o­gy. In the next step, the research team will work on the con­crete imple­men­ta­tion and cor­re­spond­ing prototypes.

SPARTACUS is not an iso­lat­ed project. It is part of the large-scale EU research ini­tia­tive BATTERY 2030+, which aims to sig­nif­i­cant­ly improve the sus­tain­abil­i­ty and per­for­mance of bat­ter­ies in Europe for var­i­ous appli­ca­tion scenarios.