Lithium-ion and sodium-ion batteries

Lithium-ion batteries enabled the success of portable electronics and find increasingly application in powering electric vehicles and in storage of electricity from intermittent renewable sources. Our research aims at increasing the energy and power density of lithium-ion batteries, improving the operational safety, and exploring alternative materials and processing routes.

 

As a member of the Swiss Competence for Energy Research “Heat and Electricity Storage”, our lab develops cathode materials for next-generation lithium-ion batteries with increased lithium storage capacity and reduced cobalt content. Cobalt is already classified as a critical raw material due to its high economic importance and high supply risk. We are investigating nickel-rich cathode materials, which offer higher capacity, in combination with novel electrolyte formulations to enable stable long-term cycling. We are also investigating cobalt-free cathode materials as an alternative (e.g. vanadium-based materials in a project with industry partner Belenos, a company of the Swatch group).

/documents/56087/4859795/Bild+Lithium-ion+and+sodium-ion+batteries+1/320e66b6-5081-4994-9c56-80b77daebe97?t=1533186875617
Fig. 1: a) Schematics of a lithium-ion battery with graphite anode and nickel-manganese-cobalt (NMC) oxide cathode. b) Scanning electron microscopy image of individual NMC cathode particles, c) Comparison of capacity of Co-rich (NMC111) and Ni-rich (NMC811) cathode at different discharge rates. A discharge rate of 1C corresponds to discharging the full capacity of the battery in 1 hour.

 

We are also exploring ways to replace the flammable liquid electrolyte in today’s lithium-ion batteries by a non-flammable liquid electrolyte to improve operational safety. We developed a non-flammable aqueous electrolyte for sodium-ion batteries extending the electrochemical stability window of water from 1.23 V to 2.6 V using highly concentrated aqueous salt solutions (water-in-salt). We successfully demonstrated a 2 V-class aqueous sodium-ion battery with an energy density comparable to lead-acid batteries.

/documents/56087/4859795/Bild+Lithium-ion+and+sodium-ion+batteries+2/1bc59bc7-cc7a-4739-b109-f7afc403f3dd?t=1533186884290
Fig. 2: a) Schematics of water-in-salt concept, at high salt concentration, almost all water molecules are part of the solvation shell of the cations. b) Linear sweep voltammetry scans of 35m NaFSI electrolyte with an electrochemical stability window of 2.6 V. Cyclic voltammograms of a NaTi2(PO4)3 anode and a Na3(VOPO4)2F cathode are also shown together with the thermodynamic onset of hydrogen and oxygen evolution (dashed lines). c) Cycling performance of aqueous sodium-ion battery developed at Empa.
Funding:
InnoSuisse, Competence Center for Energy and Mobility, Swiss Electric Research, Swiss State Secretariat for Education, Research, and Innovation.

Selected publications:

[1] R.-S. Kühnel, D. Reber, C. Battaglia. A high-voltage aqueous electrolyte for sodium-ion batteries, ACS Energy Lett., 2, 2017, 2005.

[2] D. Reber, R.-S. Kühnel, C. Battaglia, High-voltage aqueous supercapacitors based on NaTFSI, Sust. Energy & Fuels, 1, 2017, 2155.

[3] R.-S. Kühnel, D. Reber, A. Remhof, R. Figi, D. Bleiner, C. Battaglia, ‘‘Water-in-salt’’ electrolytes enable the use of cost-effective aluminum current collectors for aqueous high-voltage batteries, Chem. Comm., 52, 2016, 10435.

[4] CCEM Annual Activity Report 2015 (p.38)


Press releases:

The salt water battery, Empa press release , 8.1.2018 (deutschEnglish)