UDT 2020 Lithium-Ion Batteries for Submarines: development and - - PDF document

UDT 2020 UDT Extended Abstract Presentation/Panel

UDT 2020 – Lithium-Ion Batteries for Submarines: development and

• perational benefits

Marie LEVEQUE1, Hervé FERAL2 and Anthony COVARRUBIAS3

1Lithium-Ion Batteries Project Director, NAVAL GROUP, Bouguenais, France, marie.leveque@naval-group.com 2Lithium-Ion Batteries Architect, NAVAL GROUP, Lorient, France, herve.feral@naval-group.com 3Business Development Senior Manager, NAVAL GROUP, Paris, France, anthony.covarrubiascastro@naval-group.com

Abstract — In 2014, we had the opportunity to present at UDT Liverpool edition the vision of what Lithium-Ion technology could bring to submarines, describing what steps and considerations should be adopted in their integration

• n board [1], with special emphasis on the safety aspects. For this edition of UDT, we will present the development

achieved by Naval Group in the integration of Lithium-Ion batteries onboard submarines, considering the high demands of safety, architecture and of course the operational advantages that respond to the demanding challenges of submarine warfare, describing the process that allowed us to move from a vision to a real and safe existing solution.

1 Introduction

In addition to advances in sensors, weapons and stealth, the evolution of conventional submarines, begin to break the paradigm of the small submarine restricted to a small patrol zone at low speed waiting for a surface force. Today conventional submarines are looking for long range deployments with an enhanced endurance, increasing in some cases their size and displacement. These advances must be accompanied by a coherent power system, i.e. the main battery, which must be a source of energy that facilitates the submarine missions and does not restrict them. With the need to increase the dived autonomy, improving the useful range of available capacity of the batteries, the lithium technology appears as a solution in which submarine designers have fixed their interest.

2 Main integration constraints of Li-Ion batteries on submarines

Even if Lithium-Ion battery (LIB) technology is strongly widespread in the civilian field, especially in transport applications, including maritime, as far as submarines are concerned, Li-Ion is a new technology. Indeed, if the potential of LIB is enormous, so is the technical challenge of its integration on board submarines. LIBs can certainly increase the operational performance of submarines, but how can several hundred strings be integrated into a coherent system that will provide a submarine with the energy it needs? The main constraints respond to two specificities:

• Large quantities of energy to be stored, compared to

current civilian applications,

• Safety aspects related to the specific environment of

submarines: confined atmosphere, co-localization of chemicals (batteries) and pyrotechnical components (weapons), human presence (crew). Since the beginning of our development, the main factors that were considered in the integration of this type of batteries were the chemical intrinsic stability, the use of industrial cells, parameter monitoring and battery management, the arrangement architecture, the potential evolution offered by this technology and the most important topic, safety analysis methodology and expertize regarding safety barriers like physical, electrical and thermal. To address these constraints, we managed several topics:

2.1. Architecture:

In order to obtain the best performances from the technology, it was important to consider an arrangement

• f the LIB fully adapted to the submarine architecture

from the first stages. This allowed taking advantage of mass gain provided by LIB, without excluding a possibility for retrofitting an existing submarine. This architecture must be adapted to evolve during the lifecycle of the submarine, according to expected evolution of Li-Ion technology. Thanks to LIB flexibility for arrangement on board, Naval Group opted for a horizontal configuration, which provides more energy than the vertical arrangement. Another challenge of LIB integration to a power plant was the short circuit current management, which becomes more relevant in a submarine network, where selectivity must be guaranteed to avoid blackouts. For this purpose, Naval Group developed a specific solution of DC/DC converters in

• rder to optimize the global battery efficiency.

Moreover, the LIB unlike lead-acid battery must be monitored by a BMS. In a submarine equipped with LIB

UDT 2020 UDT Extended Abstract Presentation/Panel the number of elementary cells imposes a huge number of BMS electronics devices. Another challenge has also been to have an easy access to the electronic, without removing the battery, which is particularly important for maintenance.

Fig.1. LIB architecture

2.2.

Safety Due to the high-energy concentration and confined environment on board the submarine, feared events were identified with the corresponding causes. Safety is based on the depth defense concept. This concept is applied by Naval Group for all submarine

• designs. Safety barriers are defined at each level of the

battery. To prevent these risks and consequences, a series of tests were carried out to qualify the cells in abusive conditions, according to Naval Group methodology and expertise in propulsion, energy and weapons integration on board submarines. 2.2.1. Chemistry Naval Group selected a chemistry considering its low level of reactivity under abusive conditions. This choice does not rule out access in the near future to other chemistries that may give a better overall advantage, with increased energy for the same level of safety. 2.2.2. Cell manufacturing With an experienced supplier in the development of LIB, capable of providing cells already developed for the civilian field with a good reliability and intrinsic safety. 2.2.3. String Cells are organized in modules, modules in packs and finally in strings (pack and control electronics). Modules and packs are placed on a specific casing with their own sensors and electrical connectors. String design include mechanical barrier to prevent the propagation of a possible thermal runaway and protect cells again high temperatures. 2.2.4. Battery Management System Naval Group has implemented a precise management of cells, through dedicated electronics, such as its charge/discharge, balance of voltage and a real surveillance of all individual cells parameters such as temperature, voltage, state of charge, remaining capacity. To control and monitor each string, a Battery Management Module (BMM) was integrated to each string in order to maintain this surveillance even in case

• f failure of the Master Battery Management Module

2.2.5. Safety validation conclusion Safety has been successfully validated through incremental tests:

• Cell abusive tests to validate the chemistry;
• Module non-propagation tests to validate module

barrier;

• Pack non-propagation to validate pack barrier ;
• Internal short circuit test to verify that there is

neither impact on the battery, nor the submarine;

• Water immersion ;
• Heat-exposure.

3 System validation process

Functional and environment tests have been performed:

• Short circuit management system test to validate the

concept of DC/DC converter and interactions between converts and between converters and circuit breaker.

• Vibration and choc test to validate mechanical

conception.

• Functional tests on the BMS functions to validate

balancing, safety functions.

• EMC test on electronics.

Finally, the performance of the system, with charge and discharge cycle tests on single and multiple strings, has been validated and the battery performance measured.

Fig.2. Validation test

4 Operational benefits

Higher available energy: for the same battery volume

• n board, this means a prolonged submerged period.

Reduced indiscretion rate: there is no charge rate reduction while charging even for a full charge at sea. With the appropriate diesel generator set, the charging time will be less and in addition, due to this efficiency,

UDT 2020 UDT Extended Abstract Presentation/Panel less energy dissipation is generated in comparison with lead-acid technology and therefore saving diesel oil. Operationally available energy: greater than lead-acid batteries, besides not suffer degradation during the patrol. A lead-acid battery will never reach its maximum capacity once the submarine is at sea. At the same time it will be recommended not to discharge it under 20%, for safety reasons (of course except under exceptional conditions and aware of the associated risks as a loss of capacity, sulphating and polarity reversal).

• Fig. 3. Charging graph

If we consider the typical battery charging graph here above, we can see that LIB will remain on the first charging step that means that there is no reduction in the charging power with a positive impact on the indiscretion rate and no gassing stage. High speed available no matter the state of charge: submarines today require medium and high speed ranges to deal with different tactical situations, including the evasion of datum, to intercept a force, higher speed of advance to reach their operational scenario, evade a torpedo or simply bearing rate generation for long range contact tracking. Those conditions, with lead acid batteries, will be conditioned to the residual capacity of the battery and therefore will limit the planning of the commanding officer during the fulfilment of his mission. With LIB this will not be a constraint anymore. Even with a low residual capacity, higher speed will be available and for a long period. Maintenance: lead-acid batteries require strict compliance with their maintenance charges, especially those requiring prolonged gassing periods in order to recover their active mass and therefore their capacity to the maximum. This generates the periodical immobilization of the submarine in port given the high production of hydrogen. To the above must be added the need to perform individual record of each cell and fill with electrolyte, which implies a physical activity that must be carried out by the crew with the associated risks. In the case of LIB, there are no such charges of gassing and no strict periodicity, which translates into greater availability of the submarine in operation. On the other hand, having a battery management system (BMS) associated with each string, allows a better monitoring of the operating parameters of the battery without the need for local intervention. LIB life cycle is completely in line with that of submarines and could have a positive impact

• n the prolongation of the maintenance cycle of

conventional submarines, which to a certain point is conditioned by the replacement of the battery. Safety: The fact of not generating hydrogen, as it is the case of lead-acid batteries, is undoubtedly one of the main advantages, especially for the crew, added to the fact of not having to carry out inspections, measurements, etc within the battery room, decreases the always existing risk of an accident. However, the main risk with a LIB battery is the fire owing to a thermal runaway of several cell parts of a pack : by its design and demonstrated by a series of tests, Naval Group proposes a solution for which it is no longer a risk. Ability to evolve: One of the great advantages over lead acid batteries is the ability to evolve over time of LIB, which is a tangible reality in existing applications in the civil field. This evolution is directly related to the stored energy density, which is expected to increase over time, allowing the submarine to offer a greater capacity in each change of battery (usually during an overhaul period). This increase in energy density anticipates drastic reduction of charging periods throughout a mission, which will mean a revolutionary operational advantage for conventional submarines. In the same way, we can expect an important evolution in the life cycle of these batteries, which, although already superior to lead batteries, should increase even more, which will allow rethinking the maintenance periods associated with those

• f the submarine.

5 Conclusions

After 14 years of research and development, we are able to present here that we have reached the level of maturity necessary to integrate LIB on board submarines, with the necessary safety considerations and convinced of the

• perational contribution that this technology will bring to

the submarines.

References

[1] N. Pierre, UDT Liverpool Conferences, DCNS, (2014)

Author/Speaker Biographies

Anthony Covarrubias: Former surface ship and submarine commanding officer in the Chilean Navy. Graduated in 1996 from the Polytechnic Naval Academy as Weapons Naval Engineer. Specialist in submarines, Master in naval and maritime sciences and graduated from the Chilean Naval War College. Actually at Naval Group as Submarine business development Senior Manager and part of Lithium-ion batteries team project as

• perational adviser.

Hervé Feral: Architect of the Naval Group Lithium-Ion

• battery. After a PhD in electrical engineering he spends

10 years in the energy and thermal engineering industries. He worked for several applications satellite, automotive, railway traction, nuclear industry. Three years ago he

UDT 2020 UDT Extended Abstract Presentation/Panel joined Naval Group in the Lithium-ion team to continue the development of the submarine lithium ion battery. Marie Leveque: General Engineer with demonstrative experience in purchasing, supply chain and project management in different companies. She joined Naval Group in 2011 and held different management roles, particularly for R&D projects.