文档介绍：INTERFACE ISSUES OF
POSITIVE ELECTRODES FOR LITHIUM BATTERIES
D. Guyomard,
N. Dupré, . Martin,
Institut des Matériaux Jean Rouxel, Univ. Nantes, France
A. Yamada, R. Kanno
Tokyo Institute of Technology, Yokohama, Japan
Contact : -
1
2009 International Forum on Li-ion Battery Technology& Industrial Development, Beijing, Oct. 2009
Introduction
Principle of a Li-ion battery
SEI
Well mastered
Æ ics
Li0,5CoO2
Æ Long term
LiCoO2 Graphite
Positive Negative
Extensive research for 15 years:
Solid Electrolyte Interface (SEI) on negative electrodes
Recently (< 5 years) :
Interface on positive electrode Performance
but few studies, and contradictory results 2
Our strategy to study interface issues on positives
Comparison of LiMn1/2Ni1/2O2 (2-D) and LiFePO4 (3-D)
Æ Powders of various surface areas and morphologies
Æ Characterization: XPS, TEM, EIS,…
NEW : surface MAS NMR
TODAY :
- 7Li MAS NMR to detect surface layers
- Evolution of LiMn1/2Ni1/2O2 / electrolyte interface upon cycling
- Evolution of LiFePO4 / electrolyte interface upon cycling
(surface NMR, XPS, EIS) (Electrolyte = EC + DMC + LiPF6)
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1. 7Li MAS NMR Æ surface analysis.    Issue
NMR GENERALLY USED FOR BULK MATERIAL
Li in pounds 
(Li2CO3, LiOH, Li2O, LiF, 
LixPOyFz, anic)
Li in pound
HOW TO SEPARATE THE SIGNALS?
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USE  T2 RELAXATION TIMES
1. 7Li MAS NMR Æ surface analysis.    Technique
NMR specialist : N. Dupré
dipolar interaction dipolar interaction with surface Li2CO3
M t
2g Li 2s Less strong 7Li, 500MHz, 14kHz
r Long T2 Surface
No dead time a
Bulk
r ÒÆT Ò Strong
2 Dipolar
Short T2
interaction b
Free Induction Decay Dead time Surface
Li2CO3
Bulk Surface
pulse
  Li CO powder
2 3 c
/2
π
Time
3000 2000 1000 0 -1000 -2000
Measurement δ(ppm)
after a dead time 4-5µs
T2para
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Literature on MAS NMR / surface layers
Tucker, M. C.; Braun, A.; Bergmann, U.;