The interactions between electrolyte and electrodes and the impact on the cycle life in lithium ion cells
Honghe Zheng/郑洪河 苏州大学能源学院
时间： 2013.11.15----19
0.0005
0.0004 0.1 1 10 100
H. Zheng, J. Power Sources, 207-134-140, 2012
C rate
Capacity retention (%)
Fe precipitation at the anode
0.0008
80
summary
• Fe dissolution was determined at different conditions. • Dynamic dissolution is several times higher than the static dissolution. • The effects of dissolve Fe cations is not so significant as we generally believed.
DEC 56 38
DEC+10%FEC 33 -
The dissolution of LFP in electrolyte of different Li salts
LFP in EC+DMC based electrolyte of different Li salt under 60 ℃ for 2 weekS
Our main focus in this work This is closely related to the interaction between electrolyte and electrodes
Part 1 Transition metal dissolution and the resultant impedance rise • Dissolution of transition metal cations into electrolytes and the resultant impedance rise
Dissolution of LFP material in organic electrolyte at different charge states
After the electrode was charged to different charge states, it was stored in the electrolyte for 2 weeks at 60 ℃.
(b)
100% SOC
(a)
1.2 0.9 0.6 0.3 0.0 800 1000 1200 1400 1600
-1
Fresh LFP
1800 2000
Depth of discharge (%)
Wavenumber (cm )
Fe dissolution is severe at higher charge states
100
80
Iron content (ppm)
1mol/L LiBOB
60
1mol/L LiODFB 1mol/L LiClO4
0.2mol/L LiBOB + 1mol/L LiPF6
0.2mol/L LiODFB + 1mol/L LiPF6
40
2olvent and Li salt category on the dissolution of Fe from LFP material is almost negligible.
Capacity retention (%)
90
80
Q = Q1η(n-n1)
Stage 3：
70
60
Q = Q2(-2)-
Cycle No.
50
H zheng, J. Phys. Chem. C, 116：4875-4882， 2012
The main factors associated with capacity fade Capacity fade
EMC DEC
PC
EC
EC+DMC
EC+DEC +10%FEC 40
30 20 10 0
50
EC+DEC
EC
DMC EC+DMC+EMC PC
PC+DMC FECEC+DEC
EC PC
EC+DMC+EMC
1
2
3
4
5
6
电解液组合 EC PC
EC 28 -
PC 35
DMC 29 38
DMC+EMC 42 53
P-F bond(800-900cm-1，C=O bond (1600-1700cm-1), and C-H bond(13501450cm-1) can be observed.
Dissolution of other different cathode materials at different charge states
60 C 50 C
o
o
Iron content ( ppm )
36 30 24 18 12 6 0
30 C
o
40 C
o
30℃
40℃
45℃
50℃
60℃
70℃
80℃
Dissolution of Fe in LFP in 1M LiPF6 EC+DMC electrolyte at different temperatures
60 55 50 45
800 0.8 0.6 0.4 0.2 0.0 1000 1200 1400 1600 1800 2000
(c)
100% DOD
Iron content (ppm)
40 35 30 25 20 15 10 0 20 40 60 80 100
Absorbance units
0.4 0.3 0.2 0.1 0.0 1.5 1237
3.2
100 80 60 40 20 0
60C
2.0 1.6 1.2 0.8 0.4 0.0 40 50 Temperature (C) 60 0.20 0.16 0.12 0.08 0.04 0.00
50C
40C
25C
Capacity fade ratial (%/cycle)
Frist discharge Last discharge
Comparison between static and dynamic dissolution of Fe into electrolyte
80 70 60
p（原始）（未化成和循环） l（2.5V）（化成三周后放电至 2.5V） h（4.2V）（化成三周后充电至4.2V c（循环）（化成三周后约0.3C循环
200
Iron Content (ppm)
100
The color is getting darker with increasing storage time
0 1 2 3 4 5 6
Time (week)
Dissolution of Fe in LFP in 1M LiPF6 EC+DMC electrolyte
2.8
2.8
2.6 0 20 40 60 80 100
2.6 0 20 40 60 80
Depth of discharge (%)
Depth of discharge (%)
H Zheng, Electrochim. Acta, 62: 256–262, 2012
100
0.001
100 90
Capacity (Ah/cm2)
Dissolution (ppm)
50 40 30 20 10 0 Different conditions
120
Capacity retention (%)
Capacity fade rate (mAh/cycle)
Impact of Fe dissolution on the Internal resistance
70 0.0006 60 50 0.0004 40 30 0.0002 20 10 0 0 200 400 600 800 0 1000
Cycle No
0.001
0.0009
Capacity (Ah/cm2)
0.0008
0.0007
0.0006 Fresh electrode after cycling 3.6V after cycling 4.2V
25
25 C
o
3.2
o 40 C
0
100
200
300
400
500
600
Cycle number
3.0 3.0
Voltage (V)
2.8
2.8
2.6 0 20 40 60 80 100
2.6 0 20 40 60 80 100
3.2
o 50 C
3.2
o 60 C
Voltage (V)
3.0
3.0
Internal resistance rise at higher temperature is not so significant as it is generally accepted
The dissolution of LFP in electrolyte of different solvents