Understanding of thermal stability of lithium ion batteries
Transcript of Understanding of thermal stability of lithium ion batteries
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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
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Outline of cathode materials
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Electrochemical performance
LiFePO4, LiMn2O4
LiCoO2, LiNi0.8Co0.15Al0.05O2, LiNi1/3Co1/3Mn1/3O2.
V. Etacheri, Ener. & Env. Scie., 4, 3243 (2011).
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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
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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
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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
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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).
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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
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Thermal stability of Lithium ion batteries
Q. Wang et al., Jour. of Pow. Sour., 208, 210 (2012).
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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
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DSC Measurements
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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
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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).
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Understanding of SEI
D. Aurbach et al., Journal of Materials Chemistry, 21, 9938 (2011).
Possible reactions of EC in electrolyte systems
Effect of LiPF6
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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-
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LiBOB
Decomposition
LiBOB
• LiBOB
Thermally decomposed at 320oC
K. Xu, Electro. and Sol. Let., 6, A144 (2003).
Reduction mechanism and product of LiBOB
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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
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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)
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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
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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)
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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
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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
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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
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Vision
• Cycling at high temperature• Additives: FEC, LiBOB