Develop & evaluate materials &additives that enhance thermal & overcharge abuse

Khalil Amine (PI)Zonghai Chen, Y. Qin, L. Zhang, W. Weng and J. Zhang

Argonne National LaboratoryJune 10th, 2010

Project ID: ES035

This presentation does not contain any proprietary, confidential, or otherwise restricted information.

Overview

• Start: 10/01/2008• End: 09/30/2014• 30% completed

• Barriers addressed– Cell safety– Cell flammability

• Total project funding– DOE - $880K– Contractor - $ 0

• Funding received in FY09– $440K

• Funding for FY10 – DOE - $440K

Timeline

Budget

Barriers

• Sandia National Laboratory• EnerDel• Hitachi Chemicals• ECPRO

Partners

3

Identify the role of each cell components in the abuse characteristics of different cell chemistries.

Identify and develop more stable cell materials that will lead to more inherently abuse tolerant cell chemistries.

Secure sufficient quantities of these advanced materials (and electrodes) & supply them to SNL for validation of safety benefits in 18650 cells.

Objectives of the work

Approach

Secure materials

• Commercial source

• Partners• In-house

synthesis

Impact on safety at

component level

• Thermal analysis• Electrochemical

analysis

Validation at cell level

• SNL• Industrial

partners

Current targets: a) Safer electrode materials – cathode and anodeb) additives for stable SEI on anodec) surface modification for safer cathoded) safer electrolyte components – solvent and salte) redox shuttles for overcharge protection

5

Recent Accomplishments and Progress SEI formation on different carbon anodes

o Material investigated: MCMB-1028, 3 types of surface modified graphite from Hitachi, and Hard carbon

o 18650 cells using LiFePO4 and different carbons were secured and sent to SNL for ARC study.

o Both DSC(ANL) and ARC (SNL) data agreed that the type of carbon anode significantly impact the safety of lithiated carbon.

Electrolyte additive for stable SEI layero Three electrolyte additives were identified to provide stable SEI on graphite and

hence improve the safety of lithium ion cells.o Better capacity retention with the electrolyte additives.o SNL is quantifying the impact of LiDFOB at the 18650 cell level.

OB

O F

F

O

OLi

OP

O F

F

O

OLi

F

F

PO

O

O

O O

O

OO

O

O

O O

Li

LiDFOB

6

Recent Accomplishments and Progress (cont’d)

Role of LiPF6 for the thermal reactivity of cathodeso The reaction of delithiated NMC with electrolyte components studied with DSC.o LiPF6 was investigated against pure solvents, LiBF4, LiTFSI and Li2B12F12.o LiPF6 has negative impact on safety of cathode by reducing the onset temperature

from ~310oC to about ~230oC.

Surface coating of cathode materialso Al2O3 coating was shown to be beneficial to the electrochemical performance of

NCA.o 18650-cells using NCA and Al2O3 coated NCA were secured from industrial

partner to verify the impact of coating at the cell level.- Some cells were provided to INL/ANL for life test.- 10 cells were shipped to SNL for abuse tests.- 10 cells were shipped to EnerDel for overcharge and nail penetration

test.

Redox shuttles for overcharge protectiono Three new aromatic redox shuttles with a redox potential of 4.17, 4.2 and

4.85 V vs. Li+/Li were synthesized at ANL.o Their overcharge protection functionality was confirmed in coin cells.o The structures of redox shuttle are in the process of being patented, and

might be disclosed at the merit review.

Recent Accomplishments and Progress (cont’d)

Only 2 of 5 areas are selected for oral discussion today.

(1) SEI decomposition reaction on different carbons.

(2) Redox shuttles for overcharge protection.

Importance of SEI on graphite safety

50 100 150 200 250 300 350-1.5-1.0-0.50.0 (d) Separator

Temperature, oC

01020 (c) lithiated MCMB in Gen3E

0246

(b) delithiated NCM (Gen3P) in Gen3E

Hea

t flo

w, W

/g

-1012

(a) 1.2 M LiPF6 in EC/EMC (3:7) / Gen3E • Thermal runaway of LIB can be triggered at about 140-180oC.

• SEI decomposition is the only exothermal reaction below 200oC.

• The continuous SEI decomposition plays a critic role in triggering the major reaction of cathode with electrolyte at above 200oC.

• A good SEI is expected to decompose at high temperature and generate low exothermal heat flow.

MCMB-1028 SMG-N-7b SMG-N-20 SMG-Ns-15f HC

Description MCMB Surface modified

Nature graphite

Surface modified

Hard carbon

D50 (μm) 11.8 11.1 19.5 21.6 TBD

BET (m2/g) 2.01 5.0 5.1 0.7 TBD

Carbon anodes used for the safety study

MCMB-1028 SMG-N-7b SMG-N-20 SMG-Ns-15f

• Physical parameters investigated: bulk structure, particle size, surface area• Physical characterization of hard carbon is ongoing.

Reaction of lithiated carbons with electrolyte

1.2M LiPF6 in EC/EMC (3:7)•Major exothermal reaction was

observed above 220oC for all carbons.

•The focus is the SEI decomposition that trigger thermal runaway at low temperature.

At temperature below 200oC,MCMB generated more heat than surface modified graphite (SMG series). Hard carbon generate the least heat.

Heat flow of SMG-N-20 is lower than SMG-N-7b, and SMG-Ns-15f.

Kinetics of the SEI decomposition is another key parameter.

50 100 150 200 250 300 350

0

3

6

9

12

15

18

21

24

Hea

t flo

w, W

/g

Temperature, oC

MCMB SMG-N-7b SMG-N-20 SMG-Ns-15f Hard carbon

100 110 120 130 140 1500.0

0.5

1.0

1.5

2.0

2.5

3.0

SEI Decomposition kinetics on different carbons

100 150 200 250 300 350 4000

10

20

30

40

50

60

70

80

10 oC/min 20 oC/min 30 oC/min 40 oC/min

Heat

flow

, W/g

Temperature, oC

100 120 140 1600

2

4

6

1.6 1.8 2.0 2.2 2.4 2.6

-15

-14

-13

-12

Peak 3Peak 2

ln(φ/

Tp2 )

1000/(Tp/k)

Peak 1

Lithiated MCMB-1028 with 1.2M LiPF6 in EC/EMC(3:7)

SEI decomposition

Model free kinetics determination: RTE

kT ap −=)/ln( 2φ

MCMB-1028 SMG-N-7b SMG-N-20 SMG-Ns-15f HC

Ea (kJ/mol) 53.54 88.08 92.66 78.46 87.34

•Kinetics: SMG-N-20 > SNG-N-7b ~ Hard carbon > SMGNs-15f > MCMB-1028•How about the response at cell level?

DSC results confirmed by ARC study on 18650 cells

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

50 150 250 350 450 550Temperature (C)

Rat

e (C

/min

)

SMG-N-7b VC0 (29) SMG-N-7b VC2 (35) SMG-N-20 VC0 (19)SMG-Ns-15f VC2 (18) HQ Cell LiFePO4 18650 (0.9Ah)

Done by P. Roth (SNL)•LiFePO4 was used as cathode to minimize the exothermal reaction on cathode side.

•Three carbons were examined: SMG-N-7b, SMG-N-20, and SMG-Ns-15f.

•SMG-N-20 > SMG-N-7b > SMG-Ns-15f

•Cell safety data is similar to components level safety data

13

Overcharge abuse of lithium ion batteries

~V

Normal Normal NormalWeak

~V

Normal Normal NormalWeak

(a)

(b)

~V

Normal Normal NormalWeak

~V

Normal Normal NormalWeak

~V

Normal Normal NormalWeak

~V

Normal Normal NormalWeak

(a)

(b)

Possible consequences:- Accelerate capacity/power fade;

shortening life.- Decomposition of cathode electrode.- Lithium plating on anode.- Heat generation; possibly triggering

thermal runaway.- Electrolyte decomposition and gassing;

potential leakage.- Internal short.

RS RS+•

+++++++++

--------------

E

0 5 10 15 20 25 303.0

3.3

3.6

3.9

4.2

Volta

ge, V

Time, hrs

Charge

OverchargeRS activated.

Normaldischarge

MCMB/LiNi0.8Co0.15Al0.05O2 F

F

F

F

O

O

B

F F

F

FF

• The cell voltage can be properly capped with a stable redox shuttle.

• The redox potential of redox shuttle is required to be at least 0.2 V higher than the working potential of the cathode.

• Possible cell balancing with a shuttle

Unmatched long term overcharge protection

0 50 100 150 200 250 300 350 400 450 5000.0

0.5

1.0

1.5

2.0

2.5

Capa

city,

mAh

Cycle number

ANL-RS-1 mixed with propriatory redox shuttleMNC vs. MCMB-2528 25oC.

•Cathode: Li1.1[Mn1/3Ni1/3Co1/3]0.9O2•Anode: MCMB-1028•Current: C/3

New redox shuttles synthesized at ANL

3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2

E=4.85 V

E=4.20 V

(c) ANL-RS-3

Voltage vs. Li+/Li, V

(b) ANL-RS-2

Curr

ent

(a) ANL-RS-4

E=4.17 V

• Three new redox shuttles were synthesized at ANL (IP in the process of being generated)

• ANL-RS-2 and ANL-RS-4 are good candidates for 4 V class materials.

• ANL-RS-3 is promising for high voltage materials such us Composite electrode material.

Long term electrochemical performance of new redox shuttle (ANL-RS-4)

0 10 20 30 400

2

4 Chanrge Capacity Discharge capacity

Capa

city

(mAh

)

Cycle number

LiFePO4/LTO; 1.2 M LiPF6 in EC/EMC (3:7); 2.3 wt% of redox shuttle

•ANL-RS-4 showed excellent electrochemical performance in LiFePO4/LTO cell. More study is needed for other lithium ion chemistry like oxides cathode and carbon anodes.•Electrochemical study of ANL-RS-2 and ANL-RS-3 is ongoing, and will be reported later.

Collaborations

• Partners-Sandia National Laboratory: cell level verification of safety improvement using components identified at ANL.

-EnerDel: overcharge abuse and nail penetration test of 18650 cells.-Hitachi Chemical: collaboration on the safety characteristics of carbon anodes and 18650 cell fabrication.

-ECPRO: collaboration on 18650 cell fabrication using NCA based 18650 cells ( Coated & non–coated NCA)

• Technology transfer:Collaboration with EnerDel & JCI to validate ANL’s redox shuttles.

- overcharge protection- cell capacity balancing

18

Proposed Future work Continue exploring electrolyte additive to reduce heat flow from SEI decomposition at low

temperature.

Investigate the safety of anode that doesn’t require SEI

Quantify the impact of LiPF6 on the thermal stability of delithiated cathode and explore the possible safety mitigation techniques.

Investigate the role of none flammable electrolyte & ionic liquid on the safety of lithium battery

Investigate the effect of cathode composition, morphology and surface area on safety

Systemic characterization of ANL’s new redox shuttles, and continue exploring new shuttle structures.

Work with SNL and industrial partner to validate new shuttles in a full cell configuration ( focus on overcharge & cell balancing)

Work with industrial partner to make 18650 cell using ANL composite electrode & investigate the safety performance of this high energy material in collaboration with SNL

19

Summary•Several components were investigated for safety improvement:

(a) carbon anodes; Role of SEI(b) electrolyte additives for more stable SEI layer;(c) electrolyte components;(d) redox shuttles for overcharge protection;(e) oxide (LiNi0.8Co0.15Al0.05O2) coated with Al2O3

•SMG-N-20 and a hard carbon were identified as potentially safer anode than MCMB-1028.

•Three new stable redox shuttles discovered at ANL are promising for overcharge protection for 4 V class cathode materials.

20

Collaborations

P. Roth ( SNL) ( provide materials and cells for cell level safety studies)

Hitachi chemical ( make 18650 cells based on LiFePO4 and several carbon made from the same process but have different surface area)

ECPRO (make 18650 cells with Al2O3 coated and non coated NCA) EnerDel (Overcharge test, nail penetration of 18650 cells)

EnerDel and JCI ( shuttle validation and effect on cell monitoring) Daikin ( provide new non flammable solvent and flame retardant)

3M (provided new shuttle for ANL for screening purpose)

Many Japanese and Korean companies ( supplied material that impact the safety of lithium batteries)