Journal of Power Sources 170 (2007) 160–172
Ageing of V
2
O
5
thin films induced by Li intercalation multi-cycling
Jolanta
´
Swiatowska-Mrowiecka
a,∗
, Vincent Maurice
a
, Sandrine Zanna
a
,
Lorena Klein
a
, Emrick Briand
b
, Ian Vickridge
b
, Philippe Marcus
a
a
Laboratoire de Physico-Chimie des Surfaces, CNRS (UMR 7045), Ecole Nationale Sup´ erieure de Chimie de Paris,
Universit´ e Pierre et Marie Curie, 11 rue Pierre et Marie Curie, 75005 Paris, France
b
Institut des Nanosciences de Paris, CNRS (UMR 7588), Universit´ es Pierre et Marie Curie et Denis Diderot,
Campus Boucicaut, 140 rue de Lourmel, 75015 Paris, France
Received 15 December 2006; received in revised form 27 March 2007; accepted 5 April 2007
Available online 12 April 2007
Abstract
Cyclic voltammetry, XPS, RBS and AFM have been combined to study the ageing mechanism of Li intercalation in V
2
O
5
thin films prepared
by thermal oxidation of vanadium metal. Multi-cycling tests were performed in 1 M LiClO
4
-PC in the potential range E ∈ [3.8, 2.8 V] versus
Li/Li
+
, corresponding to the -to- phase transition. XPS and AFM were performed using direct anaerobic and anhydrous transfer. Capacity fading
remains inferior to 20% during ∼2500 cycles. XPS shows slight modifications of the oxide composition with a V
4+
concentration increasing from
∼5% prior to cycling to ∼16–27% after cycling, due to Li trapped in the oxide film and to the loss of V
2
O
5
active material. The presence of lithium
carbonate and lithium-alkyl carbonate species evidences the formation of the so-called SEI layer. AFM evidences the loss of crystalline material
by grain exfoliation from the outer V
2
O
5
layer of the oxide film. By further exfoliation, the inner VO
2
layer of the oxide film is reached and pits are
formed, occupying ∼9–13% of the surface. This de-cohesion at grain boundaries is attributed to the strain generated by repeated lattice distortions.
After 3300 cycles, the disappearance of lithium carbonates, whereas Li-alkyl carbonates and/or Li-alkoxides remain on the surface, indicates the
dissolution and/or conversion of the SEI layer. After 4500 cycles, the oxide film became very labile and could be stripped away by rinsing to reveal
the vanadium metal substrate.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Vanadium pentoxide; Lithium intercalation; Ageing; XPS; AFM; RBS
1. Introduction
Vanadium pentoxide can be used as cathode material in bat-
tery applications owing to its Li intercalation properties. The
orthorhombic layered crystal structure of the -V
2
O
5
phase is
characterized by weak vanadium–oxygen bonds between the
layers, that allow small alkaline metal ions (M
+
), like Li
+
and
Na
+
[1,2] to be inserted. In the potential range between 2.5 and
3.5 V versus Li/Li
+
(the so-called “safe” potential range), the
process of intercalation leads to a partial reduction of vanadium
from V
5+
to V
4+
accompanying the insertion of 1 mol Li mol
-1
of V
2
O
5
to form the -LiV
2
O
5
phase. At lower potentials, irre-
versible phase transformations occur. The structural changes of
∗
Corresponding author. Tel.: +33 144276736; fax: +33 146340753.
E-mail addresses: jolanta-swiatowska@enscp.fr,
jeesm@agh.edu.pl (J.
´
Swiatowska-Mrowiecka).
V
2
O
5
were widely studied for the first time by Murphy et al. [3]
and Cocciantelli et al. [4].
Cycle life is a critical parameter for the properties of Li
intercalation for battery applications. Cycling the insertion and
extraction of Li in the potential range indicated above induces
repeated phase transitions that can cause fatigue damage to the
microstructure [5,6]. However, the capacity fading observed
upon ageing by multi-cycling may not originate from struc-
tural/microstructural changes only, but also from modifications
of the composition of the oxide and breakdown, and/or con-
version of the so-called solid electrolyte interface (SEI) layer
formed at the surface [7].
The aim of the present work was to investigate the ageing
of V
2
O
5
thin films formed by thermal oxidation of vanadium
metal. V
2
O
5
thin films are interesting materials for rechargeable
lithium microbatteries due to their high specific energy densities
and capacities [8–13]. Many investigations concern the electro-
chemical properties of vanadium oxide thin films prepared by
0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jpowsour.2007.04.014