Picture: Jörg Exner

Research project: Sig­nif­i­cant­ly increas­ing the ener­gy den­si­ty of sol­id-state batteries

In the umbrel­la con­cept “Research Fac­to­ry Bat­tery” of the Fed­er­al Min­istry of Edu­ca­tion and Research (BMBF), the Uni­ver­si­ty of Bayreuth is now also involved in the com­pe­tence clus­ter for sol­id-state bat­ter­ies “Fes­t­Batt”. A new research project coor­di­nat­ed from Bayreuth is pur­su­ing the goal of sig­nif­i­cant­ly increas­ing the ener­gy den­si­ty of recharge­able sol­id-state bat­ter­ies and mak­ing the pro­duc­tion of these bat­ter­ies more sus­tain­able. For this pur­pose, the pow­der aerosol depo­si­tion (PAD) method is a promis­ing tech­nique that will be used in the future for the coat­ing of cath­odes and sol­id elec­trolytes. Research part­ners are Saar­land Uni­ver­si­ty and the Karl­sruhe Insti­tute of Technology.

Recharge­able bat­ter­ies with a sol­id elec­trolyte promise increased safe­ty com­pared to cells with liq­uid elec­trolytes. At the same time, it appears pos­si­ble to sig­nif­i­cant­ly increase their ener­gy den­si­ty. The great­est chal­lenge for indus­tri­al pro­duc­tion of sol­id-state bat­ter­ies with high ener­gy den­si­ty lies in pro­duc­ing cath­odes and elec­trolytes that are made up of fine ceram­ic layers.

In recent years, the pow­der aerosol depo­si­tion (PAD) method has estab­lished itself as an effi­cient method for pro­duc­ing such coat­ings. This spray­ing process can be used to apply dense ceram­ic lay­ers to very dif­fer­ent types of mate­ri­als, such as steel, glass, sil­i­con or plas­tic. How high the result­ing lay­ers are in detail can be deter­mined exact­ly in advance. As a rule, they are between 0.5 and 50 microm­e­ters thin. By com­par­i­son, a human hair mea­sures about 60 microns. The coat­ing can be car­ried out at room tem­per­a­ture, is inex­pen­sive and con­sumes lit­tle ener­gy. There­fore, the PAD is a sus­tain­able method and in this respect also a con­tri­bu­tion on the way to the “green battery”.

“Fes­t­Batt” is already the fifth com­pe­tence clus­ter of the umbrel­la con­cept “Research Fac­to­ry Bat­tery”, in which the Uni­ver­si­ty of Bayreuth is involved with its own project. The over­all man­age­ment of this project with the acronym “AdBatt” (“Aerosol Depo­si­tion for the Pro­duc­tion of Bat­ter­ies with Grad­ed Cath­ode”) lies with Prof. Dr.-Ing. Ralf Moos, hold­er of the Chair of Func­tion­al Mate­ri­als at the Uni­ver­si­ty of Bayreuth. Togeth­er with his research team, he has dri­ven the fur­ther devel­op­ment and opti­miza­tion of the PAD in recent years.
“The pow­der aerosol depo­si­tion method is a pow­er­ful yet envi­ron­men­tal­ly friend­ly process. We now want to use it togeth­er with our part­ners in Karl­sruhe and Saar­brück­en to real­ize a vol­u­met­ric ener­gy den­si­ty of 1,150 Wh/l in the field of sol­id-state bat­ter­ies,” says the Bayreuth engi­neer­ing sci­en­tist. An impor­tant aspect of the research work is the devel­op­ment of a process that makes it pos­si­ble to pro­duce cath­odes with vari­able pro­por­tions of dif­fer­ent mate­r­i­al types. These include the cath­ode active mate­r­i­al, the sol­id elec­trolyte pow­der and elec­tron­i­cal­ly con­duc­tive additives.

At the same time, the Chair of Elec­tri­cal Ener­gy Sys­tems at the Uni­ver­si­ty of Bayreuth, head­ed by Prof. Dr.-Ing. Michael Danz­er, is also par­tic­i­pat­ing in the new project. The research work focus­es on the elec­tro­chem­i­cal behav­ior of grad­ed elec­trodes with sol­id elec­trolyte, but also on the gen­er­al con­di­tions for safe bat­tery oper­a­tion. For this pur­pose, suit­able oper­at­ing val­ues and lim­its must be defined for the para­me­ters tem­per­a­ture, pres­sure and cur­rent density.
“Of cen­tral impor­tance to our research is pre­cise mod­el­ing and effi­cient sim­u­la­tion of elec­tro­chem­i­cal process­es, espe­cial­ly with regard to the inter­ac­tions between elec­trolyte, elec­trode and full cell. On this basis, we will be able to grad­u­al­ly opti­mize the design of the grad­ed sol­id-state bat­ter­ies we are aim­ing for,” says Danz­er, who is also head of the Bavar­i­an Cen­ter for Bat­tery Tech­nol­o­gy (Bay­Batt) at the Uni­ver­si­ty of Bayreuth.