© Fraunhofer ISIT

Ener­gy-effi­cient, envi­ron­men­tal­ly friend­ly man­u­fac­tur­ing process for elec­trodes in lithi­um-poly­mer batteries

Lithi­um-ion bat­ter­ies have become an indis­pens­able part of our every­day lives. Con­ven­tion­al sol­vent-based elec­trode pro­duc­tion deliv­ers very good results, but is char­ac­ter­ized by high resource and ener­gy con­sump­tion. Sci­en­tists at Fraun­hofer ISIT are work­ing on how pro­duc­tion can be car­ried out more cost-effec­tive­ly and in a more envi­ron­men­tal­ly friend­ly man­ner, focus­ing on sol­vent-free pro­duc­tion of the electrodes.

 

This is because cost-effec­tive and at the same time envi­ron­men­tal­ly friend­ly pro­duc­tion meth­ods are a must for future bat­tery cell pro­duc­tion in order to serve the numer­ous fields of application.

As a rule, elec­trode foils are man­u­fac­tured in larg­er quan­ti­ties in a roll-to-roll process. In coat­ing plants, the sub­strate mate­r­i­al, which is on large rolls, is con­tin­u­ous­ly unwound over a num­ber of rollers and coat­ed with the elec­trode mate­r­i­al. In this process, a sus­pen­sion of sol­vent, active mate­r­i­al and a binder, which ensures the adhe­sion of the mate­r­i­al, is applied to a met­al foil. The coat­ed elec­trode foil then pass­es through a dry­ing oven and is final­ly rewound onto anoth­er roll. These plants are very large; they can be up to a hun­dred meters long, depend­ing on the dura­tion of the dry­ing process.

This pro­duc­tion process has sev­er­al dis­ad­van­tages: the prepa­ra­tion of the sus­pen­sion takes a very long time, the sol­vent is harm­ful to the envi­ron­ment, and due to the long dry­ing time in the oven, the process itself is very energy-intensive.

For this rea­son, the ISIT sci­en­tists rely on a sol­vent-free dry coat­ing process. They pro­duced a pow­der mix­ture of active mate­r­i­al, con­duc­tive addi­tives and a suit­able binder. In order to pro­duce as uni­form an appli­ca­tion as pos­si­ble and pre­cise­ly defined lay­er thick­ness­es, this pow­der mix­ture is applied to the sub­strate using a spe­cial spread­ing process.

The pow­der appli­ca­tion quan­ti­ty can be pre­cise­ly adjust­ed by the spread­ing para­me­ters, as well as via the through­put speed of the car­ri­er film in the machine. In prin­ci­ple, the sci­en­tists faced the same chal­lenge as a con­fec­tion­er who wants to spread pow­dered sug­ar on his cake as even­ly as pos­si­ble, with­out lumps. The mate­r­i­al is then fixed to the sub­strate in a short tem­per­a­ture process.

The new sol­vent-free dry coat­ing process patent­ed by ISIT for the pro­duc­tion of Li-ion bat­tery elec­trodes shows great promise. With com­pa­ra­ble elec­tro­chem­i­cal prop­er­ties to elec­trodes from estab­lished pro­duc­tion, this new process will not only enable sig­nif­i­cant­ly more com­pact pro­duc­tion lines in the future, but also pri­ma­ry ener­gy sav­ings of up to 50 %, since the long and ener­gy-inten­sive dry­ing sec­tions dur­ing pro­duc­tion are elim­i­nat­ed. Both the time sav­ings in the pro­duc­tion of the pow­der mix­ture and the sig­nif­i­cant­ly reduced ener­gy require­ments dur­ing coat­ing, due to the elim­i­na­tion of dry­ing, offer opti­mum con­di­tions for reduc­ing the use of resources and costs.

“The dry coat­ing tech­nol­o­gy has the poten­tial to sig­nif­i­cant­ly reduce the costs and emis­sions of elec­trode pro­duc­tion com­pared to the process­es com­mon­ly used today. The process devel­oped at ISIT thus makes a direct con­tri­bu­tion to the devel­op­ment of eco­nom­i­cal and envi­ron­men­tal­ly friend­ly stor­age tech­nolo­gies for mobile and sta­tion­ary appli­ca­tions,” sum­ma­rizes the head of the project at Fraun­hofer ISIT, Jannes Ophey.