Technical Data
October 2012
3M™ Battery Electrolyte HQ-115
Introduction
3M™ Battery Electrolyte HQ-115 (lithium bis-trifluoromethanesulfonimide) is a high purity electrolyte salt ideal for use
in rechargeable lithium ion and lithium polymer batteries, as well as primary lithium batteries. Electrolyte HQ-115 is
widely used as an electrolyte additive at low concentrations in LiPF6-based electrolytes for enhancing the performance
and life of high capacity rechargeable lithium ion batteries. Because of its high conductivity, solubility and thermal
stability, electrolyte HQ-115 is also an ideal supporting electrolyte salt for rechargeable lithium polymer and primary
lithium battery systems.
3M Battery Electrolyte HQ-115 is manufactured to meet the strict purity requirements of the lithium battery industry.
Electrolyte HQ-115 is available in both dry and aqueous versions.
Advantages
Longer Battery Life
Battery performance can degrade rapidly when cells are exposed to high temperatures that are typical in consumer batteries
and even more common in large format transportation or grid storage batteries. The use of electrolyte HQ-115 as an
additive in high capacity lithium ion batteries has been shown to provide a 10% increase in capacity retention after only
300 cycles at 50°C. Used at a concentration of 2-5 wt%, electrolyte HQ-115 thus provides a cost effective method to
improve battery performance when cycled at high temperature. Studies have shown that there is a synergy between
electrolyte HQ-115 and VC (vinylene carbonate) and a combination of these two additives (utilizing 1-2 wt% VC)
generally works best for improving capacity retention and reducing the build-up of impedance in cells at elevated
temperatures.
Reduced Gas Generation
Generation of gases during high temperature cycling or storage can cause undesirable venting in lithium ion wound cells
and swelling in pouch or prismatic cells. The use of electrolyte HQ-115 in low concentrations can create a protective layer
at the electrode-electrolyte interface (SEI) and thereby suppress parasitic electrochemical reactions that can lead to the
generation of these gases. Consequently, gas generation and the resulting venting and swelling of cells can be reduced
through the use of electrolyte HQ-115.
Cell Impedance Control and Safety
The protective layers formed at the SEI when using electrolyte HQ-115 have been shown to provide a stabilizing effect on
cell impedance. As a result, the buildup of impedance (or resistance) within the cell during cycling or storage is reduced
and satisfactory rate capability can be maintained for longer periods through the use of low levels of electrolyte HQ-115,
thus extending the useful life of the battery. In certain types of lithium ion cells equipped with single layer polyethylene
separators, soft shorts can develop under high temperature storage (or float) conditions. This can limit the useful life of the
battery and is also a safety concern. Without electrolyte HQ-115, charged cells stored at 60°C have been seen to develop
soft shorts after approximately 20 days of storage. Adding electrolyte HQ-115 as an additive has been shown to eliminate
the incidents of shorting over at least a 35 day period, thus improving cell safety and extending the life of the cells. As a
result, electrolyte HQ-115 can enable improved cell designs that are more thermally stable and lower in cost.
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3M™ Battery Electrolyte HQ-115
Advantages (continued)
Solubility, Conductivity and Stability
Primary Li batteries have historically used LiClO4 or LiAsF6 as supporting electrolyte salts due to their good solubility,
oxidative stability and high ionic conductivity. However the explosive hazards associate with LiClO4 when combined with
organic solvents, especially at elevated temperature, and the toxicity concerns associated with arsenic have recently driven
the search for a suitable electrolyte replacement. 3M™ Battery Electrolyte HQ-115 has been identified as an excellent
replacement for these potentially hazardous salts, providing outstanding solubility in organic electrolyte solvents and a good
balance of ionic conductivity and long term stability, including thermal, hydrolytic and electrochemical stability.
Li polymer batteries typically employ dry polymer electrolytes based on polyethylene oxide and must operate at high
temperature (around 80°C) in order to provide adequate rate capability. This puts unique demands on the supporting
electrolyte salt in terms of solubility, thermal stability and ionic conductivity in relatively nonpolar media. It has been found
that electrolyte HQ-115 provides the ideal balance of properties for use in Li polymer batteries and is considered the
electrolyte of choice for this application.
Controlled Current Collector Passivation
When used alone as the primary supporting electrolyte in rechargeable Li batteries, electrolyte HQ-115 has been shown to
cause corrosion of bare aluminum current collectors, when used at the positive electrode (cathode). Cyclic voltammetry
experiments have shown that Al corrosion occurs in electrolyte HQ-115 supporting electrolyte above 3.7V vs. Li/Li+.
A number of solutions have been devised to remedy this problem, including use of a protective carbon coating on the Al
current collector or use of an all graphite current collector. Also, combining electrolyte HQ-115 with more passivating salts
like LiPF6 and LiBF4 eliminates the aluminum corrosion issue. In some cases, even small amounts (around 10 mole %) of
highly passivating salts, like Li-BOB (lithium bis-oxalatoborate), are sufficient to eliminate Al corrosion by electrolyte
HQ-115. LiPF6 based electrolytes containing 2-5 wt% electrolyte HQ-115 as additive are commonly used today in
commercial rechargeable Li ion cells equipped with bare aluminum current collectors and these display no problems
with aluminum corrosion. In such cells, the electrolyte HQ-115 provides significant performance benefits at elevated
temperature, including improved capacity retention, reduced gassing, reduced impedance build and reduced shorting.
Material Description
Properties
Electrolyte HQ-115
Chemical Name
Lithium bis-trifluoromethanesulfonimide
Chemical Formula
(CF3SO2)2N- Li+
CAS Number
90076-65-6
Formula Weight
287 amu
Melting Point
236°C
Thermal Decomposition Temperature (TGA)
375°C
Appearance
White Powder (hygroscopic, deliquescent)
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3M™ Battery Electrolyte HQ-115
Product Grades
The 3M™ Battery Electrolyte HQ-115 product family includes ultra-high purity, battery grade product in dry and aqueous
concentrate forms. Electrolyte HQ-115 is also available in non-battery grade (with reduced purity specifications) for ionic
liquid, antistatic and other industrial applications. Contact your 3M sales representative for detailed information.
3M™ Battery Electrolyte HQ-115 Physical Properties
•
Solubility (see Table 1)
°
The solubility of electrolyte HQ-115 in various aprotic organic solvents (at 25°C) is given in Table 1.
Solubilities in many of these solvents are excellent, thus making it possible to use solvent blends to improve
electrical conductivity and viscosity.
Table 1
Solubility Weight %
56
<25
50
63
63
63
50
63
46
56
Solvent
1,3-Dioxolane
1,4-Dioxane
γ -Butyrolactone
Diethyl Ether
Dimethoxyethane
Ethyl Acetate
Isopropyl Ether
Methyl t-Butyl Ether
Propylene Carbonate
Tetrahydrofuran
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3M™ Battery Electrolyte HQ-115
3M™ Battery Electrolyte HQ-115 Physical Properties (continued)
•
Conductivity (see Figures 1, 2 and 3)
°
In general, electrolyte HQ-115 (CF3SO2)2NLi, exhibits conductivity values which, in some solvents, can be up to
five times those typically found with Lithium Triflate, CF3SO3 Li. Figures 1, 2, and 3 illustrate the conductivity of
electrolyte HQ-115 in typical battery solvents. Electrolyte HQ-115 exhibits enhanced conductivity in high-ether,
low dielectric constant solvent blends of types commonly used in certain lithium batteries. Published literature
reports a value of 14.0 mS/cm at 25°C for a solution of DIOX:DME:PC in a 5:4:1 ratio.
Figure 2
Figure 1
Figure 3
8
7
8
6
4
2
0
0
.5
1
1.5
Conductivity (mS/cm) @ 25°C
7
10
Conductivity (mS/cm) @ 25°C
Conductivity (mS/cm) @ 25°C
12
6
5
4
3
2
1
6
5
HQ-115
4
3
2
Fluorad FC-122
1
2
Concentration of HQ-115 battery (mol/l)
0
0
.5
1
1.5
2
2.5
3
3.5
4
Concentration of HQ-115 battery (mol/l)
0
0
.5
1
1.5
Concentration (mol/l)
Figure 1 Conductivity of electrolyte
Figure 2 Conductivity of electrolyte
Figure 3 Conductivity of electrolyte
HQ-115 in Dimethoxyethane at
HQ-115 in Dioxolane at various
HQ-115 and Fluorad FC-122 in
various concentrations
concentrations.
propylene carbonate at various
concentrations.
Table 2*
Conductivities of LiN(CF3SO2)2-based non-aqueous electrolytes versus temperature
LiN(CF3SO2)2
(M)
Electrolyte
solvents
1.0
1.0
1.0
1
2-MeTHF
g-Butyrolactone
g-Butyrolactone
1.0
1.0
1.0
DME
DME
EC
1.0
1.0
EC
Ethylmonoglyme
Sulfolane
0.75
Vol. %
solvent
1
75
50
50
Conductivity (mS cm-1)
at Celsius temperature indicated
2
3
EC
PC
DME
Ethylmonoglyme
EC
PC
Ethylmonoglyme
PC
Sulfolane
2 3 -50 -40 -30 -20
12.5 12.5
2.07
3.40
50
4.30 5.72
50
2.50 3.58
-10 0
20
40
60
80
4.28 5.12 7.06 8.71 10.41 12.02
7.35 9.19 13.13 17.33 21.60 25.43
4.81 6.18 9.24 12.47 15.76 18.96
50 50
50 50
50 50
f 5.46 7.87 12.08 16.58 21.25 25.97
3.92 5.44 7.19 11.23 15.51 19.88 24.30
f 4.03 5.49 8.70 12.07 15.74 19.47
50 50
50 50
sppt 0.28 0.67 1.21 1.94 2.80 5.12 7.69 10.70 13.86
0.22 0.39 0.78 1.27 1.92 2.67 4.58 6.75 8.99 11.29
Triglyme
50 50
0.23 0.45 0.80 1.24 2.58 4.22
f = frozen
sppt = salt precipitation
* Journal of Power Sources 35, 59-82 (1991), “Conductivity for Rechargeable Lithium Batteries,” Moli Energy (1990) Ltd., 3958
Myrtle Street, Burnaby, BC V5C 4G2 (Canada)
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6.30
8.60
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3M™ Battery Electrolyte HQ-115
3M™ Battery Electrolyte HQ-115 Physical Properties (continued)
•
Thermal Stability (see Figure 4 )
°
The thermal stability of electrolyte HQ-115, as determined by thermo gravimetric analysis (TGA), indicates
good thermal stability to about 375°C. The TGA plots of typical battery electrolyte salts, including electrolyte
HQ-115, are shown in Figure 1 for comparison.
Figure 4
Figure 4 Thermogravimetric analysis of Li salts under
100
helium gas. The sample size was approximately 30 mg,
Weight (Percent)
80
the He flow rate was 50 cm3 min-1 and the temperature
was increased at 50°C.
60
40
20
LiBF4
LiPF6
LiAsF6
LiCF3SO3
LiN3(CF3SO2)2
0
0
100
200
300
400
500
600
Temperature (°C)
Electrolyte HQ-115 Performance in Rechargeable Graphite/LiCOO2 Cells
•
Improved High Temperature Cycle Life (see Figure 5)
°
°
°
Electrolyte HQ-115 improves high temperature cycle life performance.
Synergy is observed between electrolyte HQ-115 and VC additives - Combination works best.
The combination of 4% electrolyte HQ-115 and 2% VC provides 10% improvement in capacity retention vs.
control (with no additive).
Figure 5
Figure 5 Discharge Capacity vs. Cycle number. Test conditions: LiCoO2/Graphite 18650 cells; 4.2-2.8V; 50°C; C/2 charge
and 1C discharge rate; Control electrolyte is 1M LiPF6/EC:DMC:EMC (1:1:1 by weight).
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3M™ Battery Electrolyte HQ-115
3M™ Battery Electrolyte HQ-115 Performance in Rechargeable Graphite/LiC0O2 Cells (continued)
•
Reduced Gas Generation (see Figure 6)
Electrolyte HQ-115 reduces gas generation that can occur in cells at elevated temperature due to parasitic
°
electrochemical reactions of electrolyte. Electrolyte HQ-115 is particularly effective at reducing gas generation at
the negative electrode (i.e., gases formed by reduction of electrolyte components).
Figure 6
Figure 6 Gas Compositions and Volumes
Determined using GC-MS Techniques. Test
conditions: LiCoO2/ Graphite pouch cells; 4.252.8V; Float charge at 4.25V and 50°C for 120
hours and then at 4.25V and 60°C for 36 hours.
Reference electrolyte is 1M LiPF6/EC:DMC:EMC
(1:1:1 by weight) and electrolyte HQ-115 is :
0.93M LiPF6 + 0.07M electrolyte HQ-115 in
EC:EMC:DMC (1:1:1 by weight).
•
Reduced Impedance (see Figure7)
Electrolyte HQ-115 reduces the build-up of impedance at elevated temperature.
°
Figure 7
Figure 7 Nyquist Plots from Electrochemical Impedance
Spectroscopy. Test conditions: LiCoO2/Graphite pouch
cells; 4.25-2.8V; Float charge at 4.25V and 50°C for 20
Z" (Ohm)
days and then discharge to 100% Depth of Discharge.
Reference electrolyte is 1M LiPF6/EC:DMC:EMC (1:1:1
by weight) and electrolyte HQ-115 is 0.93M LiPF6 +
0.07M electrolyte HQ-115 in EC:EMC:DMC (1:1:1 by
weight).
Z' (Ohm)
Note: Similar performance benefits are observed with electrolyte HQ-115 when used in cells equipped with Graphite/MNC
electrodes.
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3M™ Battery Electrolyte HQ-115
3M™ Battery Electrolyte HQ-115 Performance in Rechargeable Graphite/LiC0O2 Cells (continued)
•
Reduced Shorting with Single Layer PE Separator (see Figure 8)
°
°
Shorting is observed under float charge conditions after ~20 days with no electrolyte additive present.
However no shorting is observed with 4% electrolyte HQ-115 present, even after > 35 days under float charge
conditions.
Figure 8
Figure 8 Current and Potential vs. Float Charge Time. Test conditions: LiCoO2/Graphite 18650 cells; Single layer PE separator
(23 micron); 4.2-2.8V; Float charge at 4.2V and 60°C for 900 hours; Reference electrolyte is 1M LiPF6/EC:DMC:EMC (1:1:1
by weight) and electrolyte HQ-115 is : 1M LiPF6 + 4 wt.% electrolyte HQ-115 in EC:EMC:DMC (1:1:1 by weight).
Note: Similar performance benefits are observed with electrolyte HQ-115 when used in cells equipped with Graphite/MNC
electrodes.
Product Handling and Shelf Life
Please refer to the material safety data sheet and product label for safety, health and environmental information before using
this product. MSDS sheets are available from your local 3M sales representative.
Limit moisture pick-up by storing electrolyte HQ-115 at or near room temperature in a tightly closed container. 3M will
warrant electrolyte HQ-115 specifications for one year from the date of manufacture, when stored in its original unopened
container.
Electrolyte HQ-115 is very hygroscopic (readily absorbs water to form hydrated Li+ cation), but it is also very stable, both
thermally and hydrolytically. It does not readily decompose at elevated temperatures in the presence or absence of water,
even at high or low pH. If it is inadvertently exposed to moisture, it can readily be re-dried at elevated temperature. Drying
at 140-160°C under full vacuum (< 0.1 Torr) overnight is usually sufficient to reduce moisture to acceptable levels for use
in lithium batteries (< 50 ppm). Because of its outstanding stability, electrolyte HQ-115 is also capable of being recycled
and reused, to limit battery waste and enable sustainable battery manufacturing.
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3M™ Battery Electrolyte HQ-115
For Additional Information
To request additional product information or to arrange for sales assistance, call toll free 1-800-810-8513. Address
correspondence to: 3M, Electronics Markets Materials Division, 3M Center, Building 224-3N-11, St. Paul, MN 55144-1000.
In Canada, phone: 1-800-364-3577.
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Electronics Markets Materials Division
3M Center, Building 224-3N-11
St. Paul, MN 55144-1000
1-800-810-8513 phone
www.3M.com/batterymaterials
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