Naval Research Laboratory

Washington, DC 20375-5320

NRL/MR/6110--16-9695

A Survey of Low-Temperature Operational

Boundaries of Navy and Marine Corps
Lithium and Lithium-Ion Batteries

Joseph F. Parker
Jeffrey W. Long
Surface Chemistry Branch
Chemistry Division

Olga A. Baturina
Corey T. Love
Chemical Dynamics and Diagnostics Branch
Chemistry Division

September 29, 2016

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A Survey of Low-Temperature Operational Boundaries of Navy and 5b. GRANT NUMBER

Marine Corps Lithium and Lithium-Ion Batteries
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Joseph F. Parker, Jeffrey W. Long, Olga A. Baturina, and Corey T. Love 5e. TASK NUMBER

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

The U.S. Navy and U.S. Marine Corps have identified a strategic interest to operate lithium-ion batteries in cold climate regions as well as
undersea and in high altitude environments. The environmental operating envelope is expanded towards low temperatures, pushing the boundaries
of safe operation of lithium and lithium-ion batteries. While low-temperature discharge data is widely reported by battery manufacturers for
lithium and lithium-ion chemistries, there is a lack of data regarding the low-temperature recharging capability of lithium-ion batteries. This
report presents the need to understand and identify the lower threshold temperatures for safe, reliable recharging of lithium-ion batteries to
provide repeatable discharge capacities, a critical need for the Navy and Marine Corps to execute their missions. There is also a need to develop
robust low temperature recharging characterization tools, including in situ techniques, diagnostics, and postmortem studies. The development
of advanced materials and improved pulse recharging protocols could further support the warfighter with high-performance, safe lithium and
lithium-ion batteries.

15. SUBJECT TERMS

Lithium-ion batteries
Lithium batteries

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON
OF ABSTRACT OF PAGES Corey T. Love
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 CONTENTS

EXECUTIVE SUMMARY …………………………………………………………………………….. E-1

INTRODUCTION ………………………………………………………………………………………… 1

LITHIUM PRIMARY BATTERIES ………………………………………………..…………………….. 2

BB-5592 Li-SO2 Battery ………………………………………………………………….………. 2

BA-5390 Li-MnO2 Battery ……………………………………………………………………….. 4

LITHIUM-ION BATTERIES ................ ……………………………………………………………..…… 6

BB-2590 LiC6|CoO2 Battery ……………………………………………………………………… 6

28 V LBB for ITAS LiC6|NixCoyAlzO2 Battery ……………………………………………….…. 10

HEDB for GREENS LiC6|FePO4 Battery ……………………………………………………...… 11

SUMMARY AND FUTURE OPPORTUNITIES …………………………………………………….......13

APPENDIX …………………………………………………………………………………………...…. 15

REFERENCES ……………………………………………………………………………………...…… 16

iii
 EXECUTIVE SUMMARY

The U.S. Navy and Marine Corps have identified a strategic interest to operate lithium-ion batteries in
cold climate regions as well as undersea and high altitude environments. The environmental operating
envelope is expanded towards low temperatures pushing the boundaries of safe operation of lithium and
lithium-ion batteries. While low-temperature discharge data is widely reported by battery manufactures for
lithium and lithium-ion chemistries, there is a lack of data regarding the low-temperature recharging
capability of lithium-ion batteries. This report presents the need to understand and identify the lower
threshold temperatures for safe, reliable recharging of lithium-ion batteries to provide repeatable discharge
capacities, a critical need for the U.S. Navy and Marine Corps to execute their mission. There is also a
need to develop robust low temperature recharging characterization tools, including in-situ techniques,
diagnostics and post-mortem studies. The development of advanced materials and improved pulse
recharging protocols could further support the Warfighter with high performance, safe lithium and lithium-
ion batteries.

E-1
 Parker, Long, Baturina and Love

INTRODUCTION

The U.S. Navy and Marine Corps depend on lithium (Li) and lithium-ion (Li-ion) batteries as mission-
enabling power sources for the modern warfighter. With superior weight-normalized energy and power
compared to its nickel-metal hydride and lead-acid predecessors, in conjunction with low self-discharge
rates and no memory effects, Li-based batteries are currently the U.S. Navy and Marine Corps top choice
for telecommunications and personal portable power devices, and are being pursued aggressively for larger
systems such as vehicle propulsion and advanced high energy directed weaponry. Despite such advantages,
the poor low-temperature performance of Li-batteries is a concern, especially considering the U.S. strategic
interests in regions of cold climate, as covered by USNORTHCOM, USEUCOM, and USPACOM.1

The operation of Li-based batteries at low temperatures commonly leads to three problems:2,3,4
discharge capacity fade (i.e., less energy available), decreased power, and increased risk of thermal runaway
and fires upon charging (for secondary battery systems). In general, the discharge capacity fade at low
temperatures results from: (i) low electrolyte conductivity (~ 350% decrease when cooling standard
electrolytes from +25°C → –20°C); (ii) slower mass transport of lithium ions (cooling from 0°C → –20°C
decreases the Li+ diffusivity); and (iii) sluggish charge-transfer kinetics at the active electrodes. These low-
temperature limitations are exacerbated during the recharge cycle where Li-ion cells that typically use
graphite anodes undergo Li-ion insertion at potentials close to that of the Li/Li+ redox potential. As the
temperature is lowered and lithium transport and reaction kinetics at the graphite anode become slower,
lithium metal plating becomes more dominant than lithium-ion insertion, and metallic lithium dendrites
(needle-like whiskers) begin to form (Figure 1). Subsequent cycling can lead to internal short circuits where
dendrites pierce the separator of the cell leading to thermal runaway and the risk of a catastrophic event.

lithium
dendrites

lithiated
graphite
anode
Figure 1. Micrograph of lithium dendrites formed on the edge of a commercial Li-ion battery
graphite anode.

_______________
Manuscript approved July 13, 2016.

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 Parker, Long, Baturina and Love

The low temperature performance of Li-based batteries will vary based on the individual cell
chemistries as well as the identities of the electrolyte: solvent, salt, and chemical additives. Table 1 shows
several Li and Li-ion chemistries. The half-cell electrochemical reactions are provided in the Appendix for
reference.

Primary batteries utilize metallic lithium as the anode material and are non-rechargeable. Attempts to
recharge non-rechargeable chemistries such as Li–SO2 and Li–MnO2 can form dendrites after only a few
cycles, leading to a rapid temperature increase and eventual short-circuiting of the cell which could lead to
catastrophic thermal runaway. This behavior is exacerbated at lower temperatures as the lithium-ion
diffusivity decreases and lithium plating begins to occur at points of high current density. In comparison,
secondary or rechargeable classes of batteries use two complementary electrode materials that undergo Li-
ion insertion/intercalation reactions at different electrochemical potentials. When charged at near-ambient
temperatures (> 15°C), the potential of Li-ion intercalation into the anode (typically graphite) is above that
for lithium plating. The ability of Li-ion batteries to reversibly intercalate ions is the characteristic that
makes them rechargeable (secondary).

The present report summarizes the key properties and performance metrics, particularly at low-
temperature conditions, for the following military battery systems: the non-rechargeable BA-5590 and BA-
5390, the rechargeable BB-2590, 28 V LBB for ITAS (improved target acquisition system) and GREENS
(Ground Renewable Expeditionary Energy System) HEDBS (high energy density battery system) batteries.
The chemistry of each battery system is shown in Table 1.

Table 1. Overview of batteries surveyed for this report

Model Number Manufacturer Chemistry Operation Performance Specification
BA-5590 Saft Li–SO2 Primary MIL PRF 49471
BA-5390 Saft; Ultralife Li–MnO2 Primary MIL-PRF 32383
Saft; Ultralife; Patco;
BB-2590 Li6–CoO2 Secondary MIL-PRF 32052
BrenTronics
28 V LBB Saft LiC6- NiCoAlO2 Secondary Saft standard specification
HEDB UEC Electronics LiC6-LiFePO4 Secondary UEC Electronics specification

LITHIUM PRIMARY BATTERIES

BA-5590 — Li|SO2 Battery

The non-rechargeable BA-5590 battery manufactured by Saft is designed to meet military performance
specification MIL-PRF-49471 (Current Rev. 30 Nov 2000). Lithium-sulfur dioxide batteries are known for
their high specific energy (up to 250 Wh·kg–1), nominal cell voltage of ~2.8 V, very low self-discharge rate,
and wide operating temperature range. The BA-5590 batteries produced by Saft are available in two models;
(i) the standard capacity “BA-5590 B/U” and (ii) its high-capacity counterpart, the aptly named “BA-5590
High Capacity.” The BA-5590 B/U uses ten Saft LO 26 SX Li-SO2 D-cells, with two groups of five cells
in series, each cell with a nominal capacity of 7.75 Ah at 21°C and a 2 A discharge current. The high
capacity model uses ten LO 26 SXC D-cells, each with a nominal capacity of 9.2 Ah in the same
configuration. The general specifications for both cells are given in Table 2.

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 Parker, Long, Baturina and Love

Table 2. Operating specifications for Saft BA-5590 batteries

Nominal Voltage Capacity
Operating Storage
Model Series Parallel Series Parallel temperature temperature
Mode Mode Mode Mode
BA-5590 B/U
27 V 13.5 V 7.5 Ah 15 Ah –40°C t o +71°C
–40°C t o +71°C
(rec. max: +35°C)
BA-5590 –40°C t o +71°C
High Capacity 27 V 13.5 V 9.1 Ah 18.2 Ah –40°C t o +71°C
(rec. max: +35°C)

The nominal voltage and the capacity can be used to calculate the specific energy of the two Saft BA-
5590 batteries as 203 and 246 Wh·kg–1 for the standard and high-capacity versions, respectively. A hallmark
of the BA-5590 is the wide operating temperatures, from +71°C down to –40 °C. An overlay of typical
discharge curves for temperatures spanning this window is given in Figure 2 below.

Figure 2. Typical discharge curves of the Saft BA-5590 at various temperatures, operating at 2
A in 24 V series mode (high capacity version shown) (Ref: http://www.saftbatteries.com)

From the curves in Figure 2, it is apparent that the capacity of the BA-5590 battery declines dramatically
when discharged at temperatures less than 0 °C. At –40 °C, the capacity falls to < 60% of the nominal
capacity at the optimal operating temperature of +21°C and the discharge voltage falls from 27 V to ~24.25
V. The D-size Li–SO2 cells that comprise the BA-5590 batteries use acetonitrile as the solvent and lithium
bromide as the electrolyte salt. Electrolyte conductivity decreases when approaching these temperatures,
leading to the lowered discharge voltage observed.

As of September 2012, the BA-5590 was the main battery supply for telecommunications equipment
for the U.S. Marine Corps, with more than 350,000 batteries up to that time. During Operation Desert Storm
in 2003, the energy requirements of the U.S. military were so demanding that the Marines alone were
3
 Parker, Long, Baturina and Love

discharging > 3,000 Saft BA-5590 batteries per day, prompting Navy Capt. Clark Driscoll to declare that
“We literally [came] within days of running out of these batteries.” Ultimately, the unexpectedly high
demand of the BA-5590 prompted the U.S. Navy and Marine Corps to seek out longer lifetime primary
batteries and rechargeable Li-ion batteries to avoid this problem in the future. In the Marine Corps’ “Guide
to Employing Renewable Energy and Efficient Technologies” briefing,5 it was highlighted that “[i]ncreased
operational tempo and unexpected production shortfalls have severely reduced the availability of high
demand, high-use batteries.”

BA-5390 — Li|MnO2 Battery

The non-rechargeable BA-5390 battery was a first step in alleviating some of the operational lifetime
and energy density concerns of the BA-5590. The limitations of the BA-5590 described above led many
manufacturers, including Ultralife, to discontinue that technology and transition to the BA-5390. The
current BA-5390 available from Saft and Ultralife is designed based on the individual manufacturers’
specification, but were originally derived from the military performance specification MIL-PRF 32383
(Current Rev. 16 Jun 2011) for non-rechargeable Li–MnO2 batteries. Lithium-manganese oxide batteries
are known for their high specific energy (up to 280 Wh·kg–1; higher than Li–SO2), nominal cell voltage of
~2.8 V, very low self-discharge rate, and wide operating temperature.

The BA-5390 batteries produced by Saft come in two models: (i) the “BA-5390/U” and (ii) the “BA-
5390/U” with an onboard state-of-charge indicator—the performance specifications of the two are identical.
The Ultralife version has the standard model number BA-5390A/U. The BA-5390 for both manufacturers
use ten Li–MnO2 D-cells (Saft LM 33550 and Ultralife UHR-CR34610), with two groups of five cells in
series, each cell with a nominal capacity of 13 Ah and 11.1 Ah, respectively. The general specifications for
the available cells are given in Table 3.

Table 3. Operating specifications for Saft and Ultralife BA-5390 batteries

Nominal Voltage Capacity Operating Storage
Model
Series Mode Parallel Mode Series Mode Parallel Mode temperature temperature

Saft –40°C t o +71°C

27 V 13.5 V 12.4 Ah 24.8 Ah –40°C t o +71°C
BA-5390/U (rec. max: +35°C)

Ultralife
27 V 13.5 V 11.1 Ah 22.2 Ah –30°C t o +72°C –40°C t o +90°C
BA-5390A/U

The nominal voltage and the capacity can be used to calculate specific energy of the Saft BA-5390/U
and Ultralife BA-5390A/U as 237 and 225 Wh kg–1, respectively, representing >15% increase in specific
energy compared to their BA-5590 analogs. A hallmark of the BA-5390 system is not only its wide
operating temperatures, from +71°C down to –30 / –40 °C, but its ability to maintain a high depth-of-
discharge, even when discharging at those temperatures. An overlay of typical discharge curves for
temperatures spanning this window is given in Figure 3.

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 Parker, Long, Baturina and Love

Figure 3. Typical discharge curves of the Ultralife BA-5390 at various temperatures, operating
at 2 A in 24 V series mode (Ref: http://www.ultralifecorporation.com)

From the curves in Figure 3, it is apparent that the capacity of the BA-5390 is sustained, even when
discharging throughout the temperature range of –30°C to +55°C. At –30 °C, the capacity only falls ~ 5%
from its initial value at room temperature. Contrast these specifications with that of the BA-5590, for which
the capacity drops > 25% when discharging at –30°C . However, as observed in the BA-5590, average
voltage is lower when discharging at these low temperatures

The Li–MnO2 D-size cells use tetrahydrofuran (THF), propylene carbonate (PC), and 1,2-
dimethoxyethane (DME) as the solvent mixture and lithium perchlorate as the electrolyte salt. As with other
electrolytes, the conductivity of this specific electrolyte composition decreases at lower temperatures,
although less so than for the electrolyte composition in the BA-5590. In the absence of THF, mixtures of
PC and DME become more viscous and conductivity falls dramatically at lower temperatures. As the
volume-percent of THF is optimized, the viscosity and conductivity of LiClO4-containing solutions can
decrease (less THF) and increase (more THF), respectively.6

The enhanced capacity of the BA-5390 relative to the BA-5590, spanning the entire temperature range
of –40°C to +70°C, is the driving force behind the replacement in the field by the former and Ultralife’s
discontinuation of the latter. The impact of temperature on the discharge of the two primary batteries are
given in Figure 4.

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 Parker, Long, Baturina and Love

Figure 4. Relative capacities of the BA-5590 vs BA-5390 at elevated and reduced temperatures
(compared to their rating at room temperature; 21°C for BA-5590 and 23°C for BA-5390).

For mission-specific telecommunications and personal power applications, both of these primary
batteries may still have some utility, but as energy demands have continued to increase, it is apparent that
non-rechargeable batteries are not suitable as the sole go-to power source for the U.S. Navy and Marine
Corps. Specifically, in the Marine Corps’ “Guide to Employing Renewable Energy and Efficient
Technologies” briefing, it was further established that “[u]nits cannot continue to rely on primary batteries
as the sole source of power for their communications equipment.”

LITHIUM-ION BATTERIES

BB-2590 — LiC6|CoO2 Battery

While the BA-5390 extended mission lifetime beyond that achievable using the BA-5590, both suffer
from the same problem—they are non-rechargeable batteries and any attempts to recharge them would
likely cause rapid dendritic growth, thermal runaway, and pose the risk for catastrophic failure. Lithium-
ion batteries, replace the lithium metal anode with a graphite (C6) anode that intercalates/de-intercalates Li-
ions supplied from the cathode and electrolyte as the battery cycles. Over the past two decades, the
commercial success of Li-ion batteries has continued to grow and eventually led several manufacturers to
introduce the BB-2590 Li-ion for U.S. Navy and Marine Corps applications according to military
performance specification MIL-PRF 32052 (Current Rev. 6 Oct 2000) for rechargeable Li-ion batteries.

The benefits of Li-ion batteries beyond their cyclability include the possibility for high specific energy
(up to 250 Wh·kg–1), high cell voltage (around 3.7 V), and low self-discharge rate. The BB-2590 batteries
are produced by several manufacturers, including Saft, Ultralife, Patco, and BrenTronics, each with subtle
variations in their specifications. In general, the BB-2590 contains ICR-18650-sized cells; a principal
manufacturer for these individual cells is E-One Moli Energy Corp. Each manufacturer’s battery is
comprised of 24 18650-size cell, with three sets of eight cells in series (8S3P). Performance specifications
for the available batteries are given in Tables 4 & 5 for the discharge and charge operations, respectively.

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 Parker, Long, Baturina and Love

Table 4. Discharge specifications for commercial BB-2590 LiC6|CoO2 batteries

Nominal Voltage Capacity
Discharge Storage
Model Parallel Parallel
Series Mode Series Mode temperature temperature
Mode Mode
Saft
28.8 V 14.4 V 7.8 Ah 15.6 Ah –30°C t o +60°C –30°C t o +50°C
BB-2590/U SMBus

Saft
29.2 V 14.6 V 9.6 Ah 19.2 Ah –30°C t o +60°C –30°C t o +50°C
BB-2590HC/U SMBus

Ultralife
29.6 V 14.8 V 7.8 Ah 15.6 Ah –32°C t o +60°C –32°C t o +60°C
BB-2590/U SMBus

Patco
29.6 V 14.8 V 7.2 Ah 14.4 Ah –20°C t o +70°C –20°C t o +50°C
BB-2590/U SMB 7.2

Patco
28.8 V 14.4 V 8.7 Ah 17.4 Ah –30°C t o +70°C –20°C t o +50°C
BB-2590/U SMB 8.7

BrenTronics 7.5 Ah – 15.0 –

28.8 V 14.4 V –20°C † t o +60°C –40°C t o +40°C
BT-70791CX 9.9 Ah 19.8 Ah

BrenTronics
28.8 V 14.4 V 6.0 Ah 12.0 Ah –40°C t o +60°C –40°C t o +40°C
BT-70791JM
†
The BrenTronics BT-70791CE operates between –30°C to +60°C

Table 5. Charge specifications for commercial BB-2590 LiC6|CoO2 batteries

maximum
charging
Model charging method charging rate
temperature
(A)
Saft 8 A (parallel)
CC/CV† 0°C t o +45°C
BB-2590/U SMBus 4 A (series)

Saft 8 A (parallel)
CC/CV 0°C t o +45°C
BB-2590HC/U SMBus 4 A (series)
CC/CV
Ultralife 3.0 A to 16.8 V; Hold
4.8 A 0°C t o +45°C
BB-2590/U SMBus at 16.8 V until i < 300
mA
CV
Patco
constant 16.8 V until 3.0 A 0°C t o +45°C
BB-2590/U SMB 7.2
i < 100 mA
CV
Patco
constant 16.8 V until 3.0 A 0°C t o +45°C
BB-2590/U SMB 8.7
i < 100 mA
BrenTronics
proprietary chargers††
BT-70791XX
†
CC = constant current; CV = constant voltage
††
The BrenTronics BT-70791XX batteries use proprietary chargers and charging specifications are not
listed. However, the nuances of the charging profile are not expected to differ greatly from the requirements
of MIL-PRF-32052 and the charging temperature is not expected to differ from the previous manufacturers.

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 Parker, Long, Baturina and Love

The nominal voltage and the capacity can be used to calculate the average specific energy of
commercial BB-2590s as 165 ± 26 Wh·kg–1 with the highest specific energy achieved in the BrenTronics
BT-70791CG at 210 Wh·kg–1. The low-temperature discharge performance varies slightly among the
manufacturers, with the best performing example being the BrenTronics BT-70791JM, the only one capable
of discharge at –40°C. The Materials Safety Data Sheet for the BrenTronics 2590/U BT-70791XX batteries
list the electrolyte for all models as a combination of linear and cyclic carbonic solvents, the ratios of which
will ultimately determine the low-temperature performance. The MSDS for 18650-sized cells from E-One
Moli Energy Corp highlights the organic electrolyte combination to be LiPF6 in dimethyl
carbonate/ethylene carbonate/propylene carbonate. The ratio of these three solvents is variable among
models and can impart better low-temperature performance.6 An overlay of typical discharge curves for
temperatures spanning the –32°C to +60°C window is given in Figure 5.

Figure 5. Battery voltage as a function of discharge capacities for the Saft BB-2590/U at elevated
and reduced temperatures. (Ref: http://www.saftbatteries.com)

From the curves in Figure 5, it is apparent that the capacity of the BB-2590 is reasonably consistent
when discharging across a broad temperature range (–30°C t o +55°C), albeit with a modest decreased
discharge voltage and corresponding specific energy. At –30 °C, the capacity only falls ~ 13% of its initial
amount at room temperature. As stated above, the Li6|CoO2 18650-size cells that comprise the BB-2590
batteries use a combination of organic carbonates and lithium perchlorate as the electrolyte, which
maintains a reasonable conductivity, even to –30 °C.7

The temperatures discussed thus far for the BB-2590 solely apply to the discharge process. Because
this is a rechargeable battery, low-temperature charging must also be addressed. It is a well-established
problem that low-temperature charging results in Li metal plating onto, rather than Li+ insertion into, the
graphite anode, leading to the following problems: a) the battery does not recover all of the prior discharge
capacity upon subsequent charging, and b) dendrites begin to form and grow, posing the risk for shorting
and catastrophic failure. In Table 5, the charging specifications generally employ a constant-voltage (CV)
or a constant-current/constant-voltage (CC/CV) charging profile to avoid overcharging at the high voltages
incurred during recharge. Biphenyl and propane sulfone are additives included in some formulations; these
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 Parker, Long, Baturina and Love

are present to protect the cell against overcharge and high-temperature cycling, but they are
electrochemically unstable and their effect decreases with increasing cycle number.8 The various BB-2590
battery manufactures are also in agreement that charging should not be attempted under 0°C. While the
individual manufacturers do not portend to include charging curves for a BB-2590 battery below 0°C,
studies of individual LiCoO2 cells similar to those in this report have been reported previously (Figure 6).9

10°C 0°C

-10°C -20°C

Figure 6. Correlation of the cell voltage (red curve – right y-axis), cathode potential (black curve
– right y-axis), and anode potential (blue curve – left y-axis) with charging time for a 32 mAh
MCMB|LiCoO2 cell charging at a) 10°C b) 0°C c) –10°C and d) –20°C (reprinted from reference
9).

As the temperature of the cell decreases, the cell voltage falls, both as a consequence of the increased
cell resistance and Li+ diffusivity. However, the thermodynamic potential for lithium plating is unchanged.
The authors of this study conclude that for low-temperature charging, the potential of the graphite anode
must stay sufficiently positive of 0 V versus Li+/Li, but because of the high overpotential of graphite and a
decreased ionic conductivity, lithium plating is kinetically preferred, even at temperatures as high as 10°C,
with a complete absence of Li+ insertion at –20°C.

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 Parker, Long, Baturina and Love

The storage temperature of rechargeable Li-ion batteries is also a consideration because of the
increased prevalence of self-discharge at higher temperatures. The military specification MIF-PRF-32052/1
requires that 87% of nominal capacity of the BB-2590 be maintained when storing them at 50°C for 7 days.
Manufacturer specifications suggest that storing these batteries at extreme cold temperatures poses no
problems and, in accordance with the military requirements, they can be stored up to about 50°C.
Independent testing of BrenTronics’ BB-2590 has revealed that storing them at temperatures over 50°C
leads to a permanent loss in capacity, as detrimental as 65% when stored at 80°C for only seven days.10

28 V LBB for ITAS — LiC6|NixCoyAlzO2 Battery

The BB-2590 is the gold standard for rechargeable Li-ion batteries for routine field use in the U.S.
Navy and Marine Corps. However, some applications have more challenging operating specifications, as
in Raytheon’s Improved Target Acquisition System (ITAS), where the demand for high-power output
demands, structural robustness, longer-term storage, and low-maintenance operation, necessitate
development of other specialized batteries. In 2009, The Raytheon Company awarded a $13.5 million dollar
contract to Saft to provide the 28 V Li-ion battery box (LBB) that the ITAS requires.

The Saft 28 V LBB that powers the ITAS is comprised of individual VL 52E cells with LiC6–NiCoAlO2
chemistry. The ITAS is comprised of 16 of these large-type Li-ion cells, with two sets of eight cells in series
(8S2P). The general specifications for the ITAS LBB are given in Table 6.

Table 6. Specifications for the (left) Saft VL 52E cell and (right) 28 V LBB for the ITAS
28 V LBB Cell Battery
Specification Specification
Characteristics Characteristics
Nominal
Nominal voltage 3.6 V 28.8 V
voltage
Capacity @
+54 °C >80 Ah
Capacity at +25 °C 52 Ah
+21 °C >80 Ah
–32 °C >70 Ah
Maximum
Maximum discharge rate 52 A 30 A
discharge rate
Maximum
Maximum charge rate C/7 10 A
charge rate
charge temperature 5°C to +35°C
mass 29 kg
discharge temperature –25°C to +55°C
number of cells 16

The nominal voltage and the capacity can be used to calculate the average specific energy of the Saft
28 V LBB batteries, ~ 80 Wh·kg–1, a marked decrease in the specific energy when compared to the BB-
2590 above. However, this shortfall is a small price to pay for higher current output, higher power, structural
integrity, and longer lifetime for the applications that the ITAS requires, namely to power the tube-
launched, optically tracked, wire-guided (TOW) missile.

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 Parker, Long, Baturina and Love

Low-temperature discharge performance of the LBB is similar to that observed in the BB–2590,
maintaining > 85% of its nominal capacity when discharging as low as –32°C. A sample set of experiments
on the individual component cells (Saft VL 52E) is given in Figure 7, which are a demonstration of
exhaustive discharges at these temperatures. It is noteworthy that the explanation for a long, stable lifetime
of the Saft 28 V LBB is the limit of the depth-of-discharge when packaged in the 28 V LBB ITAS system.11
The Materials Safety Data Sheet for all Saft Li-ion batteries is the same: lithiated metal compounds (in this
case nickel cobalt aluminum oxide), organic electrolyte, graphite, copper, aluminum, and remainder
packaging materials. The Saft VLE cells (VL XXE) contain carbonate electrolytes with LiPF 6, which will
run into the same low-temperature limits as the BB–2590/U. Likewise, whenever graphite is the active
anode material, low-temperature recharge is not expected to be successful at temperatures < 10°C.

Figure 7. Battery voltage as a function of discharge capacities for the Saft VL 52E, an example
of an individual cell that makes up the 28 V LBB ITAS battery. (Ref:
http://www.saftbatteries.com)

Manufacturer’s experiments on individual VL 52E cells has also provided information on their self-
discharge and preferred storage conditions. A benefit of the Li-ion with NCA cathodes is their ability to be
stored at 100% state of charge, therefore not requiring an initial charge step prior to use. Storage for 10
years at 10°C and 30°C has led to a capacity loss of 0.5% and 1.2% per year, respectively. However, storage
at 60°C leads to a capacity loss >13% per year, still a marked improvement over the BB-2590, which drops
by 65% after storage at 50°C for only seven days. Storage at the lower bounds of the operating temperature
range is therefore preferred, so long as the operator brings the temperature of the cell back up > 10°C before
attempting any recharge processes.

HEDB for GREENS — LiC6–FePO4 Battery

The final technology surveyed in this report is the High Energy Density Battery system for the Ground
Renewable Expeditionary Energy Network System (GREENS). The GREENS project was initiated in 2009
as a means to harness solar energy using photovoltaic cells, store the energy in Li-ion batteries, and then

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use that power for in-field demand. The primary manufacturer of the HEDB system for GREENS is UEC
Electronics.

The Li-ion batteries on board the GREENS use the lithium-iron-phosphate (LiFePO4) cathode
chemistry paired with graphite anodes. The individual cells used are model number LFP26650EV
manufactured by K2 Electronics. The HEDB is comprised of 32 of these LiFePO4 cells, with four sets of
eight cells in series (8S4P). The general specifications for the HEDB and its components cells are given in
Table 7.

Table 7. Specifications for the (left) K2 LFP 26650EV cell and (right) HEDBS for the GREENS
LFP26650EV Cell Battery
Specification Specification
Characteristic Characteristic

Nominal voltage 3.2 V Nominal voltage 25.6 V

Capacity at +25 °C 3.2 Ah Capacity 51 Ah

Maximum discharge rate 20 A (6C)† Maximum discharge rate 40 A

Maximum charge rate C/7 discharge temperature –20°C t o +65°C

discharge temperature –20°C t o +65°C mass 18 kg

number of cells 32
†
While 6C is achievable, the manufacturers recommend continuous discharge to stay below 3.2 A for long-
term stability.

From the table above, the nominal voltage and the capacity can be used to calculate the average specific
energy of the UEC HEDB system as ~72 Wh·kg–1, a marked decrease in specific energy relative to other
batteries in this report. However, the application-specific benefit of providing silent and renewable energy
harvested from the sun justifies the lower specific energy.

The low-temperature discharge performance of the cells that comprise the HEDB maintains > 80% of
its nominal capacity when discharging as low as –20°C, but with the caveat that maintenance is only
achieved when discharging at much lower rates (Figure 8). For the KFP26650EV cells, a discharge current
of ~ 0.16 A is required to achieve the nominal capacity of the C/5 rate of ~ 3 A.12

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Figure 8. Battery voltage as a function of discharge capacities of the KFP26650EV at (top)

+23°C and (bottom) –20°C. (Ref: http://www.k2battery.com & personal correspondence)

The Materials Safety Data Sheet for the K2 KFP26650EV shows lithium iron phosphate, a graphite
anode, and an electrolyte mixture of lithium hexafluorophosphate in ethylene carbonate, dimethyl
carbonate, and ethyl methyl carbonate as components of the cell. As noted above, cells that use graphite
anodes are not expected to show successful recharging at temperatures < 10°C.

A benefit of LiFePO4 cathodes is their ability to be stored at 100% state of charge, and therefore not
requiring an initial charge step prior to use; they also maintain higher specific capacity at higher
temperatures. Solid-state lithium ionic conductivity is higher in the FePO4 case, compared to other battery
technologies in this report. However, storage at reasonable temperatures, <30°C is expected to optimize
battery lifetime and minimize self-discharge.

SUMMARY AND FUTURE OPPORTUNITIES

The low-temperature performance of the most common Li-based batteries for the U.S. Navy and Marine
Corps depends mainly on whether or not the batteries are intended to be recharged. Non-rechargeable
(primary) batteries use a sacrificial lithium metal as the anode material, and thus the limits of low-
temperature discharge depend on the limits of Li+ diffusivity and electrolyte conductivity at those
temperatures. The subtle variation of these properties in the components of the non-rechargeable batteries
surveyed in this report reveal that the BA-5390 exceeds the BA-5590 in terms of retention of capacity at
low-temperatures (ca. –30°C).

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The U.S. Military, aside from some niche applications, is moving beyond non-rechargeable lithium
metal batteries in favor of Li-ion batteries, so not only is low-temperature discharge a concern, but so is the
subsequent low-temperature recharge (perhaps more so). The common denominator in all of the
rechargeable (secondary) batteries highlighted in this report is that they all use graphite as the anode
insertion material. During low-temperature (< 10°C) recharge, the voltage required for Li-ion insertion falls
below that required for lithium plating at the graphite. This leads to metallic regions on the anode, dendrite
growth and ultimately the loss of discharge capacity. These drawbacks not only dramatically hinder long-
term stability of rechargeable batteries, but also are a primary cause for catastrophic damage; when the
dendrites grow long enough to short-circuit the battery, thermal runaway and fires are difficult to avoid.
Low-temperature recharging data are difficult to obtain. More data is required with repeated charges at low
temperatures to more accurately mimic anticipated field conditions. Additionally, the ability to gain
fundamental insights into battery operation and safety by observing electrode operation through advanced
characterization techniques will inform U.S. Navy and Marine Corps energy stakeholders of actual low-
temperature recharge limitations and identify more accurate low end temperature boundaries for safe and
reliable lithium battery operation.

The ranking of the capacity retention at low-temperature discharge can be summarized as BB-2590 >
LBB for ITAS > HEDB for GREENS, but this fails to take into account the many benefits of the LBB and
HEDB in their specific applications. Ranking these three batteries in terms of low-temperature recharge
would not be prudent, because they all suffer from the same limitations when using graphite anodes.

There are options for other technologies to meet the demand for low-temperature cyclability (both
discharge and recharge). For example, with a planned launch date of 2015, Saft began manufacturing the
XcelionTM battery, which is a 60 Ah, 26.4 V LiFePO4 system that incorporates on-board heaters that are
automatically engaged to achieve optimal charging, allowing recharge down to –40°C (see
www.saftbatteries.com). Achieving this comes at the expense of a balance of plant that drives the specific
energy down to 79 Wh kg–1, but allows an application space previously unrealized. Another recent
breakthrough is the use of lithium titanate as the anode material in lieu of graphite.13 The voltage of lithium
insertion into titanate is considerably less than that in graphite, so dendrite formation is effectively
eliminated, although high current recharging rates could nucleate lithium dendrites; however, that also
comes with the drawback of an overall lower cell voltage, perhaps a small price to pay for low-temperature
recharge without the safety hazards of modern lithium-ion. Also, cell heating and warming strategies have
been explored to maintain a safe cell temperature to ensure dendrite-free recharging. Perhaps most
promising is the development of informed pulse charging schemes unique to a cell’s chemistry and form
factor. These tailorable protocols provide optimal lithium-ion transport to the surface of the anode during a
charge pulse while allowing for ionic diffusion through the anode during the short rest, no current portion
of the pulse.

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APPENDIX

Half-cell electrochemical reactions are provided for the various cell chemistries listed in the present
report.
1. Li–SO2 cell:
Anode: Li  Li+ + e– 1a
Cathode: SO2 + e–  S2O4– 1b
2. Li–MnO2 cell:
Anode: Li  Li+ + e– 2a
Cathode: MnO2 + Li+ + e–  LiMnO2 2b
3. Li–CoO2 cell:
Anode: LiC6  Li+ + e– + C6 3a
Cathode: Li1-xCoO2 + xLi+ + xe–  LiCoO2 3b
4. Li–NiCoAlO2 cell:
Anode: LiC6  Li+ + e– + C6 4a
Cathode: Li1-x NiCoAlO2 + xLi+ + xe–  Li NiCoAlO2 4b
5. LiFePO4 cell:
Anode: LiC6  Li+ + e– + C6 5a
Cathode: FePO4 + Li+ + e–  LiFePO4 5b

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REFERENCES

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[12] K2 Energy, personal communication

[13] T. Yuan, X. Yu, R. Cai, Y. Zhao, and Z. Shao. “Synthesis of pristine and carbon-coated
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