Materials and composites for
electrodes of lithium batteries
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Chemical and electrochemical reactivity of nano-objects
for energy storage applications 
version française |
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Coworkers at IMN
Dr. D. Guyomard, Dr. B. Lestriez, Dr. N. Dupré,
Dr. P. Moreau, Dr. A-C. Gaillot and Dr. P. Soudan
Coworkers
Pr. M. Quarton and Pr. G. Wallez (LCS, IMP, Paris),
Dr. S. Cassaignon, Dr. N. Steunou, Pr. J.P. Jolivet and
Pr. J. Livage (LCMCP, IMP, Paris), C.P. Grey (SUNY, Stony
Brook University, USA)
Post-doc: Dr. E. Mas
PhD: F. Tanguy and M. Dubarry (now Research Engineer
at the Electrochemical Power Systems Laboratory of the Hawaii
Natural Energy Institute)
Master students: B. Morel (now PhD student at CEA, France),
B. Chavillon (now PhD student at IMN)
Industrial contracts: BatScap (France), General
Motors (USA)…
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Overview of the research
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This work is concerned with the ability to understand and
tailor building steps as well as surface chemical and electrochemical
reactivity of nano-objects for energy storage applications.
Three main projects are developed:
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| 1-
From solute species to oxide nanograins |
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Lithium vanadium oxide, Li1+αV3O8
( α = 0.1-0.2), has been extensively studied over the past
20 years for its attractive electrochemical properties in
rechargeable lithium batteries. The material consists of
V3O83- hewettite layers
comprising octahedrally and pentacoordinated vanadium atoms,
present in a 2:1 ratio. Intercalation can occur between
the layers, the material providing fair energy density.
Two routes have been mainly used to synthesize these oxides,
solid-state reactions and sol-gel synthesis. The lithium
insertion behavior of Li1+αV3O8 strongly depends on the
firing temperature of the xerogel. Samples prepared upon
heating at 580°C exhibit a stable capacity of 180 mA·h/g
upon cycling, whereas those heated at 350°C, which can only
be prepared using a sol gel route, exhibit a larger initial
capacity (300 mA·h/g) that decreases rapidly on cycling.
Understanding the chemical nature of the gel-like precursor
and the chemical processes that lead from the gel-like precipitate
to anhydrous Li1+αV3O8 might suggest new approaches for
improving its electrochemical properties. Using X-ray diffraction
(XRD) and 51V magic-angle spinning (MAS) NMR spectroscopy,
this work demonstrates that the gel-like precipitate of
Li1+αV3O8 is actually a diphasic mixture, comprising a liquid
that contains protonated decavanadic acids and a solid with
the formula Li1.1V3O8·nH2O, consisting of Li+ ions
trapped in porous poorly crystallized hewettite layers (Figure
1).
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Figure 1: Formation mechanism of Li1.1V3O8
nanograins
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Upon drying at room temperature, the hewettite-like
layers of the solid component remain, while the liquid component
precipitates, presumably as a mixture of lithiated decavanadates.
The decavanadates transform to two hewettite-like compounds
upon drying at 90°C. Completion of dehydration leads to
a sample characterized by a bimodal grain size distribution,
the larger and smaller sized particles coming from the two
components of the xerogel (liquid and solid components),
respectively. The specific reactions undergone by these
two components have been identified: the solid component
gradually loses water by undergoing a series of phase transitions
involving layered phases with decreasing water concentrations,
the hewettite framework being maintained throughout the
reaction, whereas in the case of the dried liquid component
of the xerogel, the formation of anhydrous Li1+αV3O8 occurs
through the decomposition of lithium vanadates, which is
followed by the formation and then progressive dehydration
of a hydrated hewettite structure. The biphasic nature of
the pristine gel precursor has an impact on the electrochemical
behavior of anhydrous Li1+αV3O8.
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2-
Surface chemical reactivity : a main concern for
capacity retention on cycling nanograins
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Li1.1V3O8 nanograins synthesized via
the sol-gel route suffer from strong capacity fading on
cycling. The latter is characterized by the emergence of
polarized redox processes at the expense of initial ones.
From present investigations, bulk Li1.1V3O8 is not altered
during the fading process, although parts of the electrode
show a decreasing reactivity. Scanning electron microscopy
images show that on cycling, a layer forms at the positive
electrode-electrolyte interface and propagates toward the
current collector side. Concomitantly, X-ray photoelectron
spectroscopy and electrical impedance spectroscopy results
indicate that a layer stabilizes on cycling at the surface
of active material grains. Partial recovery of initial characteristics
both in terms of capacity and electrochemical behavior is
obtained once this layer is removed. Correlation of all
results suggests that fading mainly stems from the occurrence
of an original mechanism based on a partial to complete
insulation of initial active nanograins.
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| 3-
Chemical vs. electrochemical reactivity:
toward zero capacity fading and power applications |
The
formation of a vanadium oxide gel such as characterized
in part 1 but within a suspension of carbon black
leads to a homogeneous xerogel upon drying at 90°C.
Rapid heating of the latter at 350°C under argon
atmosphere allows preparation of nanocomposites
that contain β-Li1/3V2O5 and that are embedded in
a carbon matrix (Figure 2). The formation of β-Li1/3V2O5
is accompanied by the reduction of the initial Li1+αV3O8, along with insertion of Li+
ions to ensure the stoichiometry and presumably with Wadsley-type
defects. Carbon particles play three roles: they
act as a reducing agent (obtention of β-Li1/3V2O5,
a growth-limiting agent (nanosize objects of active
material), and a conductive agent to ensure an efficient
supply of electrons to the host material. All these
effects significantly improve capacity retention
and increase Li1+α+xV3O8 storage capacity (Figure
3).
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Figure 2 : TEM pictures of (a) standard material (b) most representative
part of the nanocomposite, (c) minor part (circled)
of the nanocomposite, and (d) image showing micrometric
needles of β-Li1/3V2O5. The inset provides the corresponding
close up along with the simulated image performed
in the [011] direction.
Figure 3 :Low chemical reactivity
nanocomposites with high electrochemical reactivity
that results in an improved capacity retention
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| Selected
publications |
- Uncommon potential hysteresis in the Li/Li2xVO(H2-xPO4)2
(0 < x < 2) system,
M. Dubarry, J. Gaubicher, G. Wallez, D. Guyomard and
M. Quarton, Electrochimica Acta (2008) in press
- Propagation of surface assisted side reactions, a
main cause for capacity fading of vanadium oxide nano-grains,
F. Tanguy, J. Gaubicher, P. Soudan, N. Bourgeon-Martin
, V. Mauchamp , D. Guyomard., Electrochem. Solid-State
Lett., Volume 10, Issue 8, pp. A184-A188 (2007)
- Synthesis of Li1+αV3O8 via a Gel Precursor:
Part II, from Xerogel to the Anhydrous Material,
Dubarry, M.; Gaubicher, J.; Guyomard, D.; Steunou, N.;
Livage, J.; Dupre, N.; Grey, C. P., Chem. Mater., 18
(2006) 629.
- Formation of Li1+nV3O8/β-Li1/3V2O5/C nanocomposites
by carboreduction and resulting improvements of the
Li capacity retention,
M. Dubarry, J. Gaubicher, P. Moreau, D. Guyomard, J.
Electrochem. Soc., 153 (2006) A295.
- Atypical Li1.1V3O8 Prepared by a Novel Synthesis Route,
A. Deptu a, M. Dubarry, A. Noret, J. Gaubicher, T. Olczak,
W. Ada, and D. Guyomard, Electrochem. Solid-State Lett.
9, A16 (2006)
- Sol Gel Synthesis of Li1+αV3O8. Part I, from Precursors
to Xerogel,
Dubarry, M.; Gaubicher, J.; Guyomard, D.; Durupthy,
O.; Steunou, N.; Livage, J.; Dupre, N.; Grey, C. P.,
Chem. Mater., 17 (2005) 2276.
- 7Li and 51V MAS NMR study of the electrochemical behavior
of LixV3O8
N. Dupré, J. Gaubicher, D. Guyomard, C.P. Grey,
Chem. Mater, 16 (2004) 2725.
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Selected patents
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- Matériau pour électrode composite, procédé
pour sa préparation,
D. GUYOMARD, D. GUY, B. LESTRIEZ, J. GAUBICHER et M. DESCHAMPS,
Demande de brevet français CNRS-BATSCAP n°0302891
du 07-03-2003, publiée sous le n° FR 2 852
148. Demande de brevet PCT/FR04/009529 pour extension internationale tous
pays, déposée le 5-03-04,
publiée le 23/09/2004 sous le n° WO 2004/082047.
- Procédé de préparation d'un oxyde de lithium et
de vanadium,
D. GUYOMARD, M. DUBARRY, J. GAUBICHER et M. DESCHAMPS,
Demande de brevet français CNRS-BATSCAP n°0401799
du 23-02-2004.
Demande de brevet PCT/FR05/00357 pour extension internationale
tous pays, déposée le 16-02-05, publiée
sous le n° WO 2005/09237 le 29-09-2005.
- Matériau nanostructuré, procédé pour sa
fabrication,
J. GAUBICHER, D. GUYOMARD, M. DUBARRY, P. MOREAU et M.
DESCHAMPS,
Demande de brevet français CNRS-BATSCAP n°0411243
du 22-10-2004.
Demande de brevet PCT/FR05/02581 pour extension internationale
tous pays, déposée le 18-10-2005, publiée
sous le n° WO 2006/045923 le 04-05-2006.
- Procédé de fabrication de gamma-LiV2O5,
J. GAUBICHER, B. MOREL, M. DUBARRY, D.GUYOMARD et M. DESCHAMPS,
Demande de brevet français CNRS-BATSCAP n°0411312
du 22-10-2004.
Demande de brevet PCT/FR05/02579 pour extension internationale
tous pays, déposée le 18-10-2005, publiée
sous le n° WO 2006/045921 le 04-05-2006.
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