International Battery Association meeting 2013 Functional Electrolytes
Recent Advances in Development of Additives
for Impedance Reduction
14 March, 2013 K. Abe, M. Colera, K. Shimamoto, M. Kondo, K. Miyoshi (Joint Venture of The Dow Chemical Company and UBE Industries, Ltd)
History of Our Electrolyte Development
'92 Started High Purity DMC Production '94 Started Commercial‐Production of MEC and DEC
'96 Started Lithium Battery Electrolyte Research
'97 Commercial‐Production of “Functional Electrolytes” “Functional Electrolytes” : High Purity + High Performance Electrolytes
→ Functions are introduced with a small amount of additives.
UBE Industries, Ltd., Battery and Power Supply in Techno‐Frontier Symposium, Makuhari, Japan, 14 Apr. (1999) '11 Established Spain Development Branch (Castellón)
'11 UBE‐Dow Joint Venture Launched 2
Typical DMC Commercial Process
① Phosgene Process（Classic）
UBE DMC Plant
High Chlorine Contents
② Gas Phase Process (UBE)
Ultra‐pure DMC
③ Trans Esterification Process
Containing Many Impurities
3
Technical Features of Electrolytes ‐ Point 1
(1) Base Electrolyte Should be Highly Pure Highly Stable for a Long Time, Remains Colorless
(Keep HF Concentration Low)
HF concentration (ppm)
60
Brown Color 50
∼
40
Regular
commercial electrolyte
Regular Commercial Electrolyte
30
Highly Purified Electrolyte
UBE
electrolyte
20
Colorless
10
0
0
20
40
60
Time (day)
80
100
4
Technical Features of Electrolytes ‐ Point 2
(2) Utilization of Additives ( = Functional Electrolytes）
(i) Anode Additives
(ii) Cathode Additives
(iii) Additives for Safety Issues etc.
Examples of Commercialized Additives 5
＊
CTL Concept : Anode Additives
During initial charge, additive is first reductively decomposed prior to the main solvents (PC, EC) to form SEI intentionally.
⇒ Solvent decomposition is prevented and Li+ is intercalated smoothly.
Functional Electrolytes Pure Electrolyte + Pure Additives
PC is Incompatible with Graphite
Separator
Cathode
Li+
Graphite Anode
Additives Control Interface
Al collector
Controlled Thin Layer
Cu collector
Li+
Intentional Additive Decomposition
Anode
Li+
Li+
+
+ Li
Li
Li+
Li+
ＰＣ O
O
O
Exfoliation
＊ CTL: Controlled Thin layer
PC系solvent
PC系
PC
No Additive
添加剤なし
30μm
6
Presented IBA 2004 (Graz) Cathode Additives
＊
ECM Concept During charging, additives are decomposed at local high potential sites (active sites) to form surface film, which prevents electrolyte decomposition.
⇒ Important in the case of higher charging voltage and longer electrode
Image for Voltage Distribution of Cathode Surface in Charge
We investigated
Targeted Additives：
Oxidatively Decomposed Prior to Main Solvents
Film Formed on the Surface:
Extremely Thin Conducting Membrane
＊Electro‐Conducting Membrane = ECM
K.Abe et al., J. Power Sources, 153, 328 (2006).
Active Sites
7
Gear Change Concept : Overcharge Protection
Shifting Oxidation Potential Higher by Combination of Multiple Additives Gear Change Concept：Stepwise Shifting Down to Low Gear (= Higher Potential) Like the Image of Engine Breaking of Car Driving
◆Solo Use ◆Combination Use Additive A
Oxidation Potential (V)
: Theoretical Line : Actual Line Current
Current
: Theoretical Line : Actual Line Additive C
Additive A
Shift
Potential
Higher
Additive B
Oxidation Potential (V)
8
Presented at IBA 2007 (Shenzhen, China)
◆ Esters with Triple‐bond + VC (Ester with Double‐bond) Anode: Very Thin SEI
Cathode: Thin Surface Film ◆ Keys for the Synergetic Effect VC
PMS
1. Greater difference in the reduction potential is preferred.
2. Structural difference in the unsaturated moiety is necessary.
⇒ PMS + VC
◆ Assumed Surface Film Formation Mechanism
reduction
X
O
decomposition
X
O
+
X
O
Co‐polymerization ?
O
O
O
K.Abe et al., J. Power Sources, 184, 449 (2008).
9
New Additives Derived from PMS
Anode Side
PMS
・High Reduction Potential
・Anode Protection Capability
⇒ Surface Protection by Triple bond
Cathode Side
Decomposed Product at Anode Works for Cathode Surface Film Formation B
◆ Experimental A
Sulfonate Plays a Key Role for Cathode Surface
⇒Effective for Impedance Reduction
Coin Cell（LiCoO2/Artificial Graphite）
Base Electrolyte: 1.2M LiPF6 EC/MEC/DMC(30/30/40) DC‐IR: SOC 50%, ‐20oC （Summarized Relative DC‐IR Values in Comparison with the Electrolyte with No Additive）
10
A: Chain‐Type (Monomesylate)
A
DC-IR (Relative Value, %)
◆Initial DC‐IR
99%
100
99%
91%
90
86%
81%
80
70
60
No Additive
Highly Branched Structure Shows Superior Impedance Reduction
11
A: Chain‐Type (Dimesylate)
A
DC-IR (Relative Value, %)
◆Initial DC‐IR
98%
100
88%
90
81%
80
70
60
No Additive
Highly Branched Structure is Also Effective for Dimesylate 12
A: Cyclic‐Type (Dimesylate)
A
DC-IR (Relative Value, %)
◆Initial DC‐IR
100
96%
90
86%
80
70
60
No Additive
Strained Structure is Also Effective as Highly Branched Structure
13
B: Chain‐Type (Disulfonate)
B
B
DC-IR (Relative Value, %)
◆Initial DC‐IR
100%
100
90
81%
81%
81%
81%
80
70
60
No Additive
Substituent on Sulfonate Shows No Effect
14
Confirmation of Cathode Side Effect
◆Impedance at ‐20oC (SOC 100%)
100
95
90
85
80
75
70
65
60
No Additive
With Additive
Cathode Resistance
No Additive
With Additive
Anode Resistance
Sulfonate Works on Cathode for Impedance Reduction
15
Cathode Surface Film Analysis
◆TOF‐SIMS No Additive
With Additive
P Atom
63PO
2
79PO
3
85POF 101PO F
2 2
2
No Additive
S Atom
48SO
145PF
6
In the Presence of Additive
 LiPF6 Incorporation is Decreased
 Sulfonate Incorporation is Observed
With Additive
64SO
2
80SO
3
95SO CH
4
3
16
Chemical Reactivity Test by Electrolyte Replacement Chemical
(Cell Formation & Storage)
Cell A
Electrochemical
(Aging Process)
No Additive（Ref.)
Cell B
With Additive
Cell C
No Additive
Replace
Electrolyte
No Additive
With Additive
◆Impedance at ‐20oC (SOC 100%)
Cathode Resistance
Anode Resistance
100
100
95
95
90
90
85
85
80
80
75
75
70
70
65
65
60
60
Cell A
Cell B
Cell C
Cell A
Cell B
Cell C
Cathode Impedance Reduction is NOT via Simple Chemical Reaction 17
Electrochemical Property of Disulfonate
A
Structure of A Oxidation Potential
(V vs Li/Li+)
5.00
5.00
5.00
5.00
Reduction Potential
(V vs Li/Li+)
0.83
0.84
0.87
0.82
The Order of Reductive Decomposition on Anode during Charging
<
<
18
Expansion of SO3 Concept to Propane Sultone Derivatives
We found cyclic SO3 compounds (Propane sultone derivatives)
also have similar impedance reducing effect. ◆Initial DC‐IR
100
95%
90
81%
79%
80
72%
70
60
No Additive
Highly Branched Structure is Also Effective 19
Fact of 1,3‐Propanesultone
O
O
S
Compound
O
1,3‐Propane Sultone (PS)
N‐Methyl pyrrolidone (NMP)
REACH/CLP Regulation
(CMR : Carcinogenic, Mutagenic or toxic for Reproduction ) Registered
Appearance
Solid（mp: 31oC, bp: 220oC) Liquid (mp: ‐24 oC, bp: 204 oC )
Utilized Amount for 18650
0.005g (1% in electrolyte)
15g (50% active material slurry) 3000 times
PS is Solid and Low Risk for Vapor Exposure
◆ Mutagenicity (Ames Test)
H2O
PS
48,000
In Air
Rapidly Transformed
HPSA
Negative
PS is Quickly Transformed to “Ames Negative HPSA” by Atmospheric Moisture
Once PS is Transformed, Handling Risk is Equivalent to Normal Electrolyte
20
Expansion of SO3 Concept to Li‐Salt Compounds
We found SO3 containing Li‐salts compounds have similar impedance reducing effect like organic SO3 compounds. B
DC-IR (Relative Value, %)
◆Initial DC‐IR
100%
100
90
80
72%
72%
72%
72%
70
60
No Additive
MFn = BF3
MFn = PF5
SO3 Structure is a Key for Impedance Reduction
21
Conclusion
Highly branched sulfonate compounds are effective for reducing impedance.
→ Sulfonate compounds are effective by modifying cathode surface.
Cathode impedance reduction is NOT via simple chemical reaction.
Reduction potentials of sulfonate compounds are important in a
standpoint of reductive decomposition (trigger) timing during charging.
→ Cathode protection in earlier stage of charging is effective.
Sulfonate structure (SO3) plays a key role for impedance reduction regardless of whether organic compounds or Li‐salt compounds. Overview of Our Castellón Site
Thank you for your kind attention!!
22