Hard Carbon Materials for High-Capacity Li-ion Battery … · Outline • Background – Why hard...
Transcript of Hard Carbon Materials for High-Capacity Li-ion Battery … · Outline • Background – Why hard...
Managed by UT-Battellefor the Department of Energy
Sheng Dai, Xiao-Guang Sun,
Bingkun Guo
Oak Ridge National Laboratory
One Bethel Valley Road,
Oak Ridge, TN
May 12, 2011
Hard Carbon Materials for High-Capacity Li-ion Battery Anodes
Project ID: ES104This presentation does not contain any proprietary,
confidential, or otherwise restricted information
Overview
• Start date: - June, 2010
• Budget:-Funding received in FY 10: $120K
-Funding for FY 11: $300K
Barriers
• Barriers addressed • Low energy density• Poor cycle
performance• Cost
Outline
• Background– Why hard Carbon?– Why is hard carbon more suitable
for vehicle application? – Why mesoporous carbon?
• Progress report– Objective– Challenges and Approaches– Milestones– Progress towards milestones
• Future work
• Summary
Li, Dai*, et. al, J. Am. Chem. Soc. 2004, 126, 12782; Li, Dai*, et. al, Chem. Mater. 2005, 17, 1717 Liang, Dai*, J. Am. Chem. Soc. 2006, 128, 5316; Wang, Dai*, et. al., Langmuir 2008, 24, 7500 Wang, Dai*, et. al., Chem. Mater. 2008, 20, 4800; Lee, Dai*, et. al., J. Am. Chem. Soc. 2009, 131, 4596Wang, Dai*, Angew. Chem. Int. Ed. 2010, 49, 6664; Wang, Dai*, et. al., Chem. Mater. 2010, 22, 2178
Why hard carbon?
Disadvantages of Graphite• Limited Capacity: 372 mAh/g• Susceptibility to exfoliation by
electrolytes• Poor rate performance• Difficulty to form composites
and molecularly doped anodes
0 5 10 15 20 25 30 35 40 450
200
400
600
800
1000
1200
10C
MC-550 Graphite
2CC/10
Capa
city (
mAh/g
)
Cycle number
C/10
1C
5C
Advantages of Hard Carbon• High Capacity• No intercalation-induced
exfoliation• Fast rate capability• Easy to form composites and
molecularly doped anodes
Why is hard carbon more suitable for Vehicle applications?
• The I/V curve of hard carbon based battery can be used as a gaugefor power management
• The I/V curve of graphite based battery can’t be used as a gaugefor power management unless sophisticated power management system is in place!
Endo et al, SCIENCE, 264, 6556 (1994). Endo et al, Carbon, 38, 183 (2000).
0 20 40 60 80 100 1200
300
600
900
1200
1500
1800
0.2C
0.1C
50C30C10C20C
5C2C
1C0.5C
0.2C
MC-550 C-550
Ca
paci
ty (m
Ah/g
)
Cycle number
0.1C
0.0 0.2 0.4 0.6 0.8 1.00
100
200
300
400
500 MC550 C550
Amou
nt A
dsor
bed
(cm
3 g-
1 )
Relative Pressure (P/P0)
Why mesoporous hard carbon?
MC-550: 576 (m2/g) 10.1 nmC-550: 569 (m2/g) <1.2 nm
1. Li can be stored in the nanopores of the carbon via interfacial andsurface charging!
2. The mesoporous structure provides fast Li transport channel and alsoreduces the solid-state diffusion length for Li and thus render high ratecapability.
3. The mesoporous structure can buffer well against the local volumechange during the Li insertion/extraction reactions and thus enhancethe structural stability.
Objectives
To develop low-cost hard carbon materials with capacity higher than 372 mAh g-1 and offering good cycle performance for uses in lithium ion batteries targeted on EV applications.
Challenges and Approaches
1. Improve cycle performance by surface coating or doping
2. Improve initial coulombic efficiency (CE) by surface coatingwith single ion conductors
3. Improve volumetric capacityby forming carbon compositewith metal oxide
• Capacity fade with cycling
• Low initial coulombicefficiency
• Low density (low volumetric capacity)
Challenges Approaches
Milestones
• Finish investigation on the effect of carbonization temperature on physical and electrochemical properties of carbon materials. (03/30/2010)
• Improve long cycle performance of the carbon half cells. (9/30/2011)
• Optimize carbon || Li half cells and reduce the initial irreversible capacity. (09/30/2011)
• Identify the structural and surface changes of the carbon electrode after cycling. (09/30/2011)
Effect of Carbonization Temperature on cell performance
• Increasing temp. results in H, O reduction
• Surface area remains almost same
• Li stores in defects (Nanopores, Cavities)• Unstable defects result in the reduction
of the capacity with cycling.• Low initial capacity and coulombic efficiency are partially related to the lowcut off voltage of 2.0V; use 3.0V insteadwill increase capacity 200-300mAh g-1
and coulombic efficiency 15%-20%. 0 5 10 15 20 25 30 35 40
200
400
600
800
1000
1200
1400
1600
1800
550 oC 650 oC 750 oC 850 oC
Capa
city (
mAh
/g)
Cycle number
0.05 mA
0.10 mA
0.15 mA
0.20 mA
15wt% PVdF0.05 - 2.0V
T / oC C % H % N % O % BET (m2/g)
Pore Size(nm)
1st intercalation capacity (mAh g-1)
1st de-intercalation capacity (mAh g-1)
Coulombicefficiency (%)
550 82.90 2.55 0.98 10.08 517.6 9.0 1674.5 685.3 40.9
650 88.05 2.13 0.53 5.86 517.4 5.9 1212.5 526.2 43.4
750 88.17 1.38 0.52 3.09 505.1 7.5 1164.1 481.5 41.3
850 91.30 1.29 <0.5 3.64 530.1 6.2 1072.6 418.1 39.0
Approach 1: Improve Cycle Performanceby surface coating
0 20 40 60 800
200400600800
100012001400160018002000
MC-550-ppy-1 MC-550-ppy-2 MC-550
10C5C
2C1C
C/2C/5
Capa
city
(mAh
/g)
Cycle number
C/10
BET (m2/g)
Pore Size (nm)
MC-550 497 10.1MC-550-PPy-1 292.2 8.2MC-550-Ppy-2 232.5 7.5
• The surface coating of Polypyrrole (ppy) reduces unstable defects of mesoporous carbon and improves its cycle performance.
• The less contribution from surface charging due to the reduced surfacearea after Ppy coating is the cause of capacity reduction.
•Enhance electronic conductivity
0 10 20 30 40 50 600
100
200
300
400
500
MC-550 MC-550-0.1CNT MC-550-0.2CNT
50C30C
20C
10C
2C
Capa
city
(mAh
/g)
Cycle number
5C
• The distribution of CNT in the carbon matrix enhances the electronicconductivity of mesoporous carbon.
• The mesoporous structure of the composite provides fast Li+ transportchannels.
MC-550: 497 m2/g; 10.1 nm
MC-550-0.1CNT;499 m2/g;10.9 nm
MC-550-0.2CNT;484 m2/g;11.4 nm
Approach 1: Improve Cycle Performance by surface coating (con’t)
•Enhance electronic conductivity
0 50 100 150 200 250 300 350 400 450 500 5500
50
100
150
200
250
300
350
10% CNT 20% CNT
Cap
acity
/ m
Ah
g-1
Cycle number
5C
• Under the current rate of 5C, the cell with 20wt%CNT reaches stable cycling quickly! • Cell with 20wt% CNT has a lower charge transfer resistance that facilitates faster charge/discharge.
0 10 20 30 40 500
10
20
30
40
50
C-550-0.1CNT After cycle
-Z'
(Ω)
Z(Ω)
0 10 20 30 40 500
10
20
30
40
50
C-550-0.2CNT After cycle
Z (Ω)- Z
' (Ω)
Approach 1: Improve Cycle Performance by surface coating (con’t)
Approach 2: Improve coulombic efficiency by surface coating with single ion conductors
• The improvement in the initial coulombic efficiency by surface coating with single ion conductors is very limited.• Surface coating with single ion conductors indeed improved the cycling
stability.
0 200 400 600 800 1000 1200 1400 1600 18000.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
E / V
Capacity / mAh g-1
C550; CE = 0.574 C550-PALi; CE = 0.597 C550-PSSALi-MALi; CE = 0.604
C-550: 497 m2/g; 10.1 nmC550-PALi: 210 m2/g; 9.3 nmC550-PSSA-co-MALi: 224 m2/g; 8.9 nm
0 5 10 15 20 25 30 35 40 45 500
200
400
600
800
1000
1200
1400
1600
1800
C/20
CC/2
C/5
C/10
C550 C550-PALi C550-PSSA-co-MALi
Cap
acity
(mA
h g-1
)
Cycle number
C/20
• Use Single ion conductors as artificial SEI layer on carbon surface toimprove initial coulombic effciency
• Surface coating with single ion conductors reduces both SEI andcharge transfer resistance, either before cycling and after cycling.• PSSA-MALi is more effective than PALi in reducing the charge transfer resistance.
Approach 2: Improve coulombicefficiency by surface coating with single
ion conductors (con’t)
0 20 40 60 80 100 1200
20
40
60
80
100
120
C550 C550-PALi C550-PSSALi-MALi
-Z"
/ Ω
Z' / Ω
Before Cycling
0 10 20 30 40 50 60 700
10
20
30
40
50
60
70
After Cycling
C550 C550-PALi C550-PSSALi-MALi
-Z"
/ ΩZ' / Ω
0 5 10 15 200
200400600800
100012001400160018002000
MC-550-0.2LT; CE = 0.527 MC-550-0.1LT; CE = 0.496 MC-550; CE = 0.504
Capa
city (
mAh
/g)
Cycle number
C/10
BET (m2/g)
Pore Size (nm)
MC-550 497 10.1MC-550-0.1LT 344 9.4MC-550-0.2LT 329 8.9
• Coating is a suitable method to reduce unstable defects of mesoporous carbons and improve their cycle performance.
• Needs new approaches, new coating technique or combination of both to improve initial coulombic efficiency.
Approach 2: Improve coulombicefficiency by surface coating with single
ion conductors (con’t)
Approach 3: Improve volumetric capacity by forming carbon composite with metal oxide
10 20 30 40 50 60 70 800
50
100
150
200
250
300
350
400
Inte
nsity
(a.u
.)
2θ (degree)
Cr2O3: JCPDS #06-0504
0 100 200 300 400 500 60040
50
60
70
80
90
100
Wei
ght (
%)
Temperature (0C)
Carbon: 43 wt% Cr2O3: 57 wt%
• Form composite with metal oxide that have comparable capacity within the same discharge voltage range as mesoporous carbon but having poorreversibility.• Mesoporus carbon matrix provide electron conductivity and confinement effect to improve the overall performance.
Densities:Cr2O3 : 5.22 g/cm3; C550: 1.90 g/cm3; Composite: 3.0g/cm3
The density is increased by 58%!
0 5 10 15 20 25 30 35 400
200
400
600
800
1000
1200
1400
1600
1800
100mA/g
MC550-Cr2O3
Commercial Cr2O3
Capa
city
(mAh
/g)
Cycle number
50mA/g
200mA/g500mA/g
0 200 400 600 800 1000 1200
0.0
0.5
1.0
1.5
2.0
2.5
3.0 1st cycle 2nd cycle 3rd cycle
Volta
ge (V
)
Capacity (mAh/g)
3-0.01V
The cycling stability was greatly improved as a result of composite.
MC550: 497 m2/g; 10.1 nmMC550-Cr2O3: 505 m2/g; 4.5nm
Conversion (displacement)6Li + Cr2O3 ↔ 3Li2O + 2Cr Cr Li2O
CrCr
Li2OLi2O
Li2O
Approach 3: Improve volumetric capacity by forming carbon composite with metal
oxide (con’t)
Fulvio, Dai*, et. al., Adv. Funct. Mater., 2011, in press
Future Work
• Continue to seek suitable candidates and new methods in modifying the surface of mesoporous carbons to increase the initial coulombic efficiency and improve the cycle performance.
• Seek other high density or high capacity active materials to increase the volumetric capacity density of mesoporous carbons.
• Focus on characterization and diagnostic studies using XPS, XRD, EIS, SEM/TEM, Neutron etc.
Summary
• Hard carbons with high capacity (1000mAh g-1) have been made and their cycle stability has been improved by surface coating with polypyrrole and doping with carbon nanotube.
• Different single ion conductors have been used to improve the initial coulombic efficiency, however, only limited success is achieved.
-- Further improvement in initial coulombic efficiency is pendingupon characterization of the modified electrodes after first cycle to understand morphology, composition and their effectson coulombic efficiency.
-- Needs new approaches, new coating technique or combination of both to improve initial coulombic efficiency.
• The volumetric density of mesoporous carbon has been increased by forming composite with Cr2O3.