Supercritical Hydrothermal Synthesis of
Lithium Iron Phosphate (LiFePO4) Nanoparticles
Seung-Ah Hong, Jae Hoon Kim1*, Jae-Duck Kim1, Jeong Won Kang2
Energy & Environment Research Division, Korea Institute of Science and Technology (KIST)1
Dept. of Chemical & Biological Engineering, Korea University2
Introduction
™ LiFePO4
™ Supercritical Hydrothermal Synthesis (SHS)
z
Expensive due to Co
z
Unstable at high
temperature
z
z
LiCoO2
LiFePO4
Advantages
Supercritical Water
Stable at high
temperature
Safe under abusive
conditions
z
Good energy density
z
Low cost
•
•
•
•
Low dielectric constant
Clean solvent
- High Li diffusivity; smaller particles
- High conductivity; carbon or copper coating
Requirement for Cathode Active Materials
• High reaction rate
• High quality, single crystals
• No calcination required
High Diffusivity
z Requirements of LiFePO4 for high performance cathode active materials
™ Important factors for Synthesizing
Cathode Active Materials
High nucleation rate
Nanosize particles
High production rate (< 1 min)
Continuous process
High capacity
High
charge/discharge
capacity
Higher stability
Single crystal
Single phase
Small particle
Simultaneous
co-precipitation
High
nucleation rate
Short
residence time
Rapid heating
Low solubility
of Intermediates
• No chemical waste
Supercritical Hydrothermal Synthesis
High-quality, nanosize particles
Environmental-friendly, green technology
Fast and continuous process
High
diffusivity of
Intermediates
scH2O Hydrothermal Reaction
Experimental Apparatus & Experimental Method
Objectives of Research
™ Small, nanosize particles (~ 50 nm)
™ Single crystals, Single phase
™ Voltage 3.4-3.5 V, capacity 170mAh/g
™ Higher stability of electro-conductivity
™ Higher charge/discharge performance
™ Experimental Apparatus
™ Experimental Method
Purge precursor and distilled water by N2
Heat and pressurize until target condition
Circulate precursor and distilled water
into the reactor
Experimental Result (Ⅰ)
Collect the particle from filter
™ Effect of Concentration
Concentration [M]
Flow rate [g/min]
Name
P [bar]
T
[℃]
FeSO4
H3PO4
LiOH
FeSO4/H3PO4
LiOH
H2O
Surface area
[m2/g]
Size
[nm]
1
250
406
0.01
0.01
0.03
2.83
2.79
18.0
10.6
255
2
250
413
0.03
0.03
0.09
3.04
2.98
18.0
12.2
222
3
250
405
0.06
0.06
0.18
3.24
3.25
18.0
17.2
157
¾ Exp. 1
¾ Exp. 2
Analysis the particle by SEM, TEM, BET,
XRD and electro- conductivity
¾ Properties of Water with temperature at 250bar
¾ Continuous process system
Reactor Volume : 47 cm3
Temperature range : ~ 700℃
Pressure range : ~ 500 bar
Product rate : 0.5 g/h
¾ Exp. 3
Supercritical Water
¾ Reactant; precursor
LiOH·H2O : + 98 % Aldrich
FeSO4·7H2O : + 99 % Aldrich
H3PO4
: + 98 % Aldrich
Acetone
Hexane
MeOH
™ Effect of Temperature
Concentration [M]
Flow rate [g/min]
Name
P [bar]
T
[℃]
FeSO4
H3PO4
LiOH
FeSO4/H3PO4
LiOH
H2O
Surface area
[m2/g]
Size
[nm]
4
250
300
0.01
0.01
0.03
1.57
1.56
25.0
11.8
230
5
250
415
0.01
0.01
0.03
1.51
1.53
25.0
17.5
155
¾ Exp. 4
¾ Exp. 5
Experimental Result (Ⅱ)
™ Effect of Flow Rate
™ Charge / Discharge Test
Concentration [M]
Flow rate [g/min]
Name
P
[bar]
T
[℃]
FeSO4
H3PO4
LiOH
FeSO4/H3PO4
LiOH
H2O
2
250
413
0.03
0.03
0.09
3.04
2.98
18.0
6
250
403
0.03
0.03
0.09
1.74
1.73
9.0
8
250
412
0.03
0.03
0.09
1.77
1.75
36.0
¾ Exp. 2
charge / discharge
[mAh/g]
Surface area
[m2/g]
Size
T
[℃]
Concentration [M]
Flow rate [g/min]
LiOH
H2O
Surface area
[m2/g]
Size
[nm]
6
250
403
0.03
0.03
0.09
1.74
1.73
9.0
7.0
388
7
250
408
0.03
0.03
0.09
1.77
1.78
18.0
13.7
199
8
250
412
0.03
0.03
0.09
1.77
1.75
36.0
24.8
109
9
250
402
0.03
0.03
0.09
2.98
3.04
9.0
6.4
428
2
250
413
0.03
0.03
0.09
3.04
2.98
18.0
12.2
222
10
250
411
0.03
0.03
0.09
2.92
3.03
36.0
16.8
162
Name
P [bar]
FeSO4
H3PO4
LiOH
FeSO4/H3PO4
¾ Exp. 6
¾ Exp. 7
¾ Exp. 8
¾ Exp. 9
¾ Exp. 2
¾ Exp. 10
[nm]
Calcination
62-64
15.4
176
carbon coating
109-88
16.6
163
Calcination
86-73
carbon coating
Calcination
48
25.4
107
carbon coating
32-38
32.7
83
¾ Exp. 8
Conclusion
™ Produce continuously ~ 400 nm LiFePO4 particles with small amount of impurities at 250 bar, 400 ℃, < 1 min
™ Flow rate plays important role in particle morphology
™ Need to calcination for crystallization