Understanding of Thermal Stabilities of Components in Li- ion Batteries Luu Van Khue Department of Applied Chemistry Hanbat National University 2013, February, 19
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Understanding of Thermal Stabilities of Components in Li-ion Batteries
Luu Van Khue
Department of Applied ChemistryHanbat National University
2013, February, 19
Outline of cathode materials
Electrochemical performance
LiFePO4, LiMn2O4
LiCoO2, LiNi0.8Co0.15Al0.05O2, LiNi1/3Co1/3Mn1/3O2.
V. Etacheri, Ener. & Env. Scie., 4, 3243 (2011).
Material LiFePO4 LiMn2O4 LiCoO2 LiNiO2 NMCCrystal Struc-ture
Olivine Spinel Layered Layered Layered
Discharge Voltage
3.4 4.0 3.9 3.8 3.8
Capacity 155 (170) 110-148 140-274 180-274 140-277
Density (g/cm3) 3.6 4.29 5.05 4.76 4.75
Energy density (Wh/g)
530 440 550 680 570
Energy Density (Wh/L)
1900 1880 2770 3230 2700
Electronic Conductivity (S/cm)
10-8 10-5 10-3 10-2 10-3
Transition metal deposits
106< 430 7 62 -
Relative Cost 1 2.2 45 10 19
ARC Analysis
E. P. Roth et al., Journal of Power Sources, 101, 375 (2001).
EC:PC:DMC1.2M LiPF6
Decreased Cathode Reactions Associated with Decreasing Oxy-
gen Release
Charged State
dT/
dt
Introduction
LiCoO2 → Li1-xCoO2 + xLi+ + e- 6C + xLi+ + xe- → LixC6
Theoretical: 274mAhg-1x = 1 Practical: 140-160 mAhg-1
x ~ 0.5-0.6
Concept (1980) ⇔ Commercialization: Sony (1990)
J.-M. Tarascon and M. Armand, Nature, 414, 359–67 (2001).
Specific capacity = Number of e- or Li+
Molecular weight
LiCoO2LiM-n2O4LiFePO4
GraphiteLi4T5O12Silicon
Positive Materials
• LiCoO2
• NCA (LiNi0.8Co0.15Al0.05O2) and NCM (LiNi1/3Co1/3Mn1/3O2)
• LiMn2O4
• LiFePO4
- Good electrochemical perfor-mances- Relatively high working voltage (4.2V)
- High cost- Toxicity
- Good electrochemical performances- High working voltage (4.3V)
- Fast intercalation process- Electrochemically and thermally stable- Low cost- Environmental friendliness
- Low capacity (110-120mAh/g)- Mn ions dissolution
- Relatively high capacity (170mAh/g)- Most stable positive material- Low cost- Environmental friendliness
- Low ionic and electronic conductivity- Low working voltage (Fe2+/Fe3+ vs. Li/Li+ = ~3.5V)- Dissolution ??
First generation of cathode ma-terial for portable electronic de-vices: mobile phones, laptops,
digital cameras
First cathode genera-tion
for vehicular applica-tions
L. Lu, Journal of Power Sources, 226, 272–288 (2013).
LiFePO4
Comparison of LiFePO4 nanoplates with thick plates
Saravanan et al., J. Mater. Chem., 19 (2009) 605
LiO6 octahedra arranged following the b-axis → Li diffusion directionFeO6 octahedra is not continuous due to the corner shared with PO4 tetra-hedra→ Low electronic conductivity
⇒ Reduce to nanosize and coating with car-bon
Considered as second generation of positive material for vehicular applications
Thermal stability of Lithium ion batteries
Q. Wang et al., Jour. of Pow. Sour., 208, 210 (2012).
Possible Thermal Reactions of Cathode Materi-als
LixCoO2 xLiCoO2 + Co3O4 + O2
Thermal behavior of cathode itself
Co3O4 → 3CoO + O2
CoO → Co + O2
• During charging process– Li ion is removed from cathode left vacant sites inside the material– To stabilize the structure ⇒ partial structural change
Possible reactions with electrolyte
Li0.5CoO2 + 0.1C3H4O3 (EC) → 0.5LiCoO2 + 0.5CoO + 0.3CO2 + 0.2H2O
1. Thermal reactions of solvent with positive material
O2 + C3H4O3 (EC) →3CO2 + 2H2O2. Combustion reaction of solvents
J. R. Dahn, Solid State Ionics, 69, 265–270 (1994).
V. Etacheri, Ener. & Env. Scie., 4, 3243 (2011).
More exactly, is thermal degradation
DSC Measurements
Thermal Stability Battery’s Components
• SEI is thermally decomposed at around 100-140oCThe first exothermic reaction occurring in LIB
D. D. MacNeil, Jour. of The Electro. Soc., 150, A21 (2003).
Improved Cathode Stability Results in Increased Thermal Runaway Temperature
Solid Electrolyte Interface/interphase (SEI)
• Products of redox reactions of electrolyte, reactions of elec-trolyte-electrodes, etc.
– Inorganic species: Li2Co3, LiOH, LiF, Li2O etc.– Organic species: Alkyl carbonates, (CH2OCO2Li)2, ROCO2Li, etc.
– Polymer species: polycarbonates, PEO-like polymers, etc.• Anode
– Reduction reactions take place as low as 0.5-1.5 V vs. Li/Li+
– Surface activity such as graphite • Cathode
– Oxidation reactions at potential of as high as >3V vs. Li/Li+
The SEI on negative electrode is considered more resistive than the one on cathode
K. Xu, J. of Mat. Chem., 21, 9849 (2011).
P. Verma, Electrochimica Acta, 55, 6332 (2010).
Understanding of SEI
D. Aurbach et al., Journal of Materials Chemistry, 21, 9938 (2011).
Possible reactions of EC in electrolyte systems
Effect of LiPF6
Lithium salts
• LiPF6
LiPF6(s) → LiF(s) + PF5(g)PF5 + H2O → 2HF + PF3O
LiPF6
Melting
Decomposition
Thermally decomposed at 270oC
S. E. Sloop, Journal of Power Sources, 119-121, 330–337 (2003).
Formation of the PEO-like polymers upon cathodesas a oxidative products of EC⇒ Increase the thermal stability of cathode materials
(Exceptions for LiMn2O4 and LiFePO4)
-e-
LiBOB
Decomposition
LiBOB
• LiBOB
Thermally decomposed at 320oC
K. Xu, Electro. and Sol. Let., 6, A144 (2003).
Reduction mechanism and product of LiBOB
Additives
• Polymerizable additives: VC, VEC (vinyl ethylene carbonate), FEC, etc. – Containing double bonds that can be polymerized
• Retardant additives – To prevent capability of solvents combustion
Mechanism of additive polymerization
• Normally, the additives are added to make a more stable SEI layer on the anode material
S. S. Zhang, Jour. of Pow. Sour., 162, 1379 (2006).
– Containing functional groups: e.g. LiBOB
Conclusions
• Basically, most studies on the thermal stability of Li-ion bat-teries based on:
– The nature of materials– The thermal stability of the SEI layer: new additives, or electrolyte solu-
tions, which is how to improve the stability of the SEI.• Works on thermal stability
– LiFePO4 is considered as the best candidate for near future vehicular applications
– Dissolution of carbon coated-LiFePO4 (capacity fading) at high working temperature (60oC)
– Salts or Additives (LiBOB, VC, FEC)
Effect of LiPF6 based electrolyte to electrochemical performances of LiFePO4
• LiFePO4– Thickness: 40 – Density: 2.0 g/cm3
• Testing – Precycling
• Formation: 0.1C• Stabilization: 0.5C for 4 cycles
– Cycling• 100 cycles at room temperature• 100 cycles at 60oC
Top
Spring
Spacer
LiFePO4
Separa-tor
Li-metal
gasket
Bottom
LiFePO4 and 0.75 M LiPF6 in EC/DEC= ½ (v/v)
Thickness: 40mDensity: 2.0g/cm3
Cycle Form 2nd 3rd 4th 5th
Eff. 88.6598 36.8679 53.0879 76.3025 90.4
0 20 40 60 80 100 120 1402.5
3
3.5
4
4.5Precycling
Form. 0.1C2nd 0.5C3rd 0.5C4th 0.5C5th 0.5C
Capacity (mAh/g)
Volt
age
(V)
LiFePO4 and 1.0 M LiPF6 in EC/DEC= ½ (v/v)
0 20 40 60 80 100 120 140 1602.5
3
3.5
4
4.5Precycling
Form 0.1C2nd 0.5C3rd 0.5C4th 0.5C5th 0.5C
Capacity (mAh/g)
Volt
age
(V)
Thickness: 40mDensity: 2.0g/cm3
Cycle Form 2nd 3rd 4th 5th
Eff. 90.51383 94.26854 94.47853 94.4898 94.09369
LiFePO4 and 1.2 M LiPF6 in EC/DEC= ½ (v/v)
0 20 40 60 80 100 120 140 1602.5
3
3.5
4
4.5Precycling
Form.0.1C2nd 0.5C3rd 0.5C4rd 0.5C5th 0.5C
Capacity (mAh/g)
Pote
ntia
l (V)
Thickness: 40mDensity: 2.0g/cm3
Cycle Form 2nd 3rd 4th 5th
Eff. 90.51383 94.26854 94.47853 94.4898 94.09369
LiFePO4 and 1.0 M LiPF6 in EC/DEC= ½ (v/v)
0 20 40 60 80 100 120 140 1602.5
3
3.5
4
4.5Precycling
Form. 0.1C2nd 0.5C3rd 0.5C4th 0.5C5th 0.5C
Capacity (mAh/g)
Volt
age
(V)
Adding 2% VC Thickness: 40mDensity: 2.0g/cm3
Cycle Form 2nd 3rd 4th 5th
Eff. 54.47667 93.73737 96.70103 97.1134 96.3039
Vision
• Cycling at high temperature• Additives: FEC, LiBOB
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