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).