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Aim• Investigation of the system CuO/GeO2/P2O5 with respect to existing
phases and phase relations
• Investigation of the discharge behavior of copper oxide germanate
phoshate Cu3GeP2O10
Motivation• Copper oxide phosphates like Cu4O(PO4)2 and Cu3Ag2O(PO4)2 show
advantages in comparison with MnO2 as active material in lithium
batteries [1]. Especially the capacity of the oxide phosphates increases
remarkably (Tab. 1).
• The influence of germanium on the electrochemical properties of oxide
phosphates is of great interest. First, due to the standard potential for
the transition Ge4+/Ge0 with +0,12 V, the open circuit voltage of the
oxide phosphate should not be decreased significantly. Second, the
capacity is to be enhanced by an increasing number of exchangeable
electrons. Third, in the opposite to the facts before, the higher ionic
charge of Ge4+ could be the reason for a reduced diffusion ability of Li+
with the effect of a decreasing of the voltage and the capacity.
• A comparison of theoretical specific capacity and open circuit voltage
from selected materials is presented in Tab. 1.
Experimental• Preparation of powder samples by homogenising of a stochiometric ratio
of CuO, GeO2 and (NH4)2HPO4
• Heating of the powder samples stepwise beginning at 160 °C for 24 h,
followed at 250 °C for 24 h and finished at 950 °C for 72 h.
• Characterization of the products by XRPD, UV-VIS-, IR-Spectroscopy
and thermal analysis.
• Construction of cells for electrochemical characterization:
anode: Li foil,
cathode: 70 % active material, 25 % graphite, 5 % PTFE,
electrolyte: Selectilyte (BASF)
Potentiostat/Galvanostat/ZRA Reference 3000 (Fig. 1) (Gamry Inst.)
Investigations at the Quasi-ternary System CuO/GeO2/P2O5
for the Development of Battery Materials
Iren Weimann, Christian Hanzelmann, Jörg Feller; Hochschule für Technik und Wirtschaft (HTW) Dresden
Zdirad Zak; Masaryk University, Brno/Czech Republic
17. Vortragstagung der Fachgruppe Festkörperchemie und Materialforschung 15.-17. September 2014 in Dresden
References
[1] T. Traulsen, G. Fehrmann, Th. Hucke, A. Deckert, J. Feller,
T. Schuffenhauer, DE Patent 2011, Patent Number 1020110793798.
[2] EL-CELL GmbH: User Manual for Electrochemical Test Cell - ECC-REF
Release 2.0, 2012
Single Crystals of Cu3GeP2O10
A new compound with the formula Cu3GeP2O10 was identified. It was
possible to obtain single crystals by a melting procedure. The single crystal
structure analysis have been carried out and the crystallographic data
Cu3GeP2O10 (ICSD 426627) are presented in Fig. 3.
Materialtheoretical spec. capacity
[mAh/g]Voltage
[V]
MnO2 309 3.0
Cu4O(PO4)2466 2.2
Cu3Ag2O(PO4)2350 2.5
Cu3GeP2O10553 ?
Ge5O(P2O8)3565 ?
Crystal system monoklin
Space group P1 21/m 1 (Nr. 11)
Lattice constants a = 4,6355(4) Å
b = 8,2943(7) Å
c = 9,5074(8) Åβ = 103,22(1) °
Z 2
Volume 355,86(7) Å3
Density (calc.) 4,528 g/cm3
Fig. 1 Work Station and Test Cell (right) [2]
Fig. 5 Discharge Characteristic at 500 µA
Fig. 6 Phase Diagram CuO/GeO2/P2O5 at 950 °C
Cu4O(PO4)2 Ge5O(P2O8)3 CuGeO3Cu3GeP2O10
Fig. 2 Selected Powder Products from the Quasi-ternary System CuO/GeO2/P2O5
Fig. 4 Structure Presentation of Cu3GeP2O10
Fig. 3 Cu3GeP2O10 Crystals (left), Crystallographic Data (right)
• In contrary to the expectation,
the examined parameters like
voltage and capacity of the new
oxide phosphate are reduced in
comparison with Cu4O(PO4)2.
• The phase Cu3GeP2O10 with a
useable specific capacity of 220
mAh/g and a voltage of 1,9 V
may be interesting for secondary
cells, if the reaction with lithium
would be reversible. But cyclo-
voltammetric tests could not
confirm this theory.
• Pure germanium phosphate
does not show advantageous
properties for electrochemical
applications.
mm
The structure contains layers of edge-connected [CuO6] octahedra parallel
to the (b, c) plane (dark green, Fig. 4). This layers are linked via triples
[GeP2O10] formed by [GeO4] (blue) and [PO4] tetrahedra (red) along the a
axis.
Tab. 1 Electrochemical Properties
Products of the Heating Procedure• Powdered products are presented in Fig. 2.
Galvanostatic Discharge
Phase Diagram
• The phase diagram of the
quasi-ternary system
CuO/GeO2/P2O5 at 950 °C
was obtained by XRPD from
heated powder samples (Fig.
6).
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