Bernd Fuchsbichler

Development of a 3d current collector for the positive electrode in lithium-ion batteries

So far, expanded metals or metal foils have been used as current collectors for the positive electrode in state of the art lithium-ion batteries (LIBs). In this work, a new 3D current collector for the positive electrode of LIBs was investigated. Non-woven polymer was metallized with Al by physical vapour deposition (PVD). To prove its feasible application as a current collector in LIBs, LiCoO2 (LCO) composite electrodes were fabricated and compared to common LCO composite electrodes coated on “state of the art” aluminium foil. All cathodes were characterised by scanning electron microscopy, as well as electrochemical methods, and the results were compared. In combination with the main advantages of 3D current collectors such as improved mechanical stability and possibility of higher mass loadings, the 3D structure of the non-woven polymer increases the contact surface by five times compared to conventional current collector foils, reducing the assignment of Al significantly.

Next-generation materials for electrochemical energy storage – Silicon and magnesium

The paper describes two ways for increasing the specific energy of Li-ion batteries in order to extend the EV driving range. The first way is the development of a Si/graphite anode. This anode consists of n-Si/graphite composite particles, a special cellulose based binder and a 3D-collector (POLYMET®). With this anode a specific capacity of ∼1,200 mAh/g is obtained. More than 500 cycles with this anode and prelithiation is reachable. As a second way, for higher specific energy, Mg-ion systems are addressed. The main problem of Mg-ion cells is the anode. Mg and also graphite are forming together with the electrolyte (except Grignard type electrolytes) surface layers, which have no Mg2+ conductivity. By changing the electrolyte, however, an intercalation/deintercalation into graphite can be shown for the first time. Based on this innovation Mg-ion cells with MgxV2O5 as cathode are possible having a cell voltage of ∼3.7 V.

Charge-Induced Defect Formation in LixCoO2 Battery Cathodes: XRD and PA Spectroscopy Study

Lithium-ion batteries have developed into most advanced battery systems, e.g. laptops and mobile phones. LiCoO2 is a typical intercalation battery cathode material. However, reversible charge-discharge cycling of LiCoO2 is only possible down to 50% of the available Li-ions since further removal of Li-ions drastically reduces the capacity and cycle stability. The formation of vacancy-type defects during the charging process in LixCoO2 battery cathodes was investigated by XRD and position life-time spectroscopy and Doppler broadening of positron-electron annihilation (PA) radiation as defect specific techniques [1]. Li+-extraction, which in a battery mode corresponds to charging, was performed at 293 K under electrochemical control in a 3-electrode test-cell with a Maccor Series 4000 battery tester. The composition of the lithium-ion electrode material used was: 88wt.% LiCoO2 particles, 7 wt.% carbon black as conducting agent, 5 wt.% binder material (polyvinylidene difluoride hexafluoropropylene copolymer). Structural analysis of the electrode samples was performed by means of X-Ray diffraction using a Bruker D8 Advance diffractometer in Bragg-Brentano geometry with Cu-K -Theta angle range from 15° to 130° and were analysed by Rietveld refinement with the programs FULLPROF [2] and X’PertHighScorePlus (Panalytical). For positron annihilation measurements a positron source (22NaCl) was sandwiched between two identical LiCoO2 electrode samples. Positron lifetime measurements were performed with a fast-fast spectrometer with a time resolution of 221 ps. The spectra were analysed by using the program pfposfit [3]. Doppler broadening (DB) measurements were performed in a coincidence setup with two high purity Ge detectors.with energy -line in the detector system corresponds to ca. 0.88keV (FWHM). Both the Doppler broadening S parameter as we extraction; the S-extraction causes a decrease of S and ollowed by a re-increase for x<0.55. Conclusions: The regime of reversible charging is dominated by vacancy-type defects on the Li+-sublattice the size of which increases with increasing Li+-extraction. Indication is found that Li+-reordering which occurs at the limit of reversible Li+-extraction (x = 0.55) causes a transition from the two-dimensional agglomerates into onedimensional vacancy chains. Degradation upon further Li+-extraction is accompanied by the formation of vacancy complexes on the Coand anion sublattice.