Technical note | Review of Battery Technologies for Military Land Vehicles
This report provides an overview of battery technologies and related issues relevant to their use in military land vehicles. It explains the advantages and disadvantages of specific battery technologies along with integration considerations for military land vehicles and the future direction of each technology. It concludes that lead-acid batteries will remain relevant for military land vehicles in the immediate future, but variants of lithium ion batteries have the potential to improve operational performance and should be investigated further for implementation in current and future military land vehicles.
The functions of military land vehicles are becoming increasingly dependent on electrical energy. As these vehicles are fitted with more electronic equipment, their electrical energy demands will continue to increase and it is anticipated that their limited electrical energy storage capabilities (i.e. their batteries) will present issues during the vehicles’ life of type. Insufficient electrical energy storage can inhibit operational performance, particularly when conducting silent watch (i.e. engine-off operation of electrical equipment) where batteries with low energy capabilities will last short periods of time when providing power and will have to be regularly recharged.
Military operations present unique requirements, which differ from those of most cars and commercial vehicles. Batteries on military land vehicles require high energy (for silent watch) and must also be capable of delivering high power (for engine starting and load levelling). Furthermore, they must withstand harsh military environmental conditions and should provide sufficient overhead to accommodate future growth in vehicle electrical power requirements.
Lead-acid batteries are currently used on the majority of military land vehicles and they are expected to remain in use in the immediate future since they are reliable and low cost. However, the low energy capabilities of lead-acid batteries combined with their long charging times have significantly restricted silent watch performance of military land vehicles.
The purpose of this report is to explore current and emerging secondary (i.e. rechargeable) battery technologies and to assess their suitability for improving the operational capability of military land vehicles. Key aspects considered are the ability to improve silent watch endurance, the ability to be fast charged (to minimise engine-on time during silent watch operations), cycle life, cost, safety, and the effect of temperature. In addition, this report aims to introduce batteries and how they function, and highlight key considerations pertaining to the integration of batteries on future military land vehicles. It is intended that the findings of this report will inform Defence stakeholders involved in the acquisition and sustainment of military land vehicle capabilities as to the benefits, potential drawbacks and integration requirements for various battery technologies.
Information presented in this report has been sourced through discussions with experts in this field, attendance at relevant conferences and through being conversant with open source literature. Furthermore, an understanding of the electrical energy storage needs of Australian military land vehicles has been established through ongoing research and analysis in this space by the authors of this report. The combination of information from these activities has allowed identification of the battery technologies that are relevant for military land vehicles and those that warrant attention into the future. In conducting this review, it was identified that the most suitable battery technologies for military land vehicles are those that can be used as drop-in replacements for lead-acid batteries (e.g. compatible voltage window and similar form factor). In this case, the vehicle’s electrical system requires no or minimal modification to accommodate the alternative battery. This reduces the integration overhead and cost required for new battery technologies. Two of the most promising battery technologies that meet this requirement are variants of lithium ion batteries, namely lithium iron phosphate batteries and lithium titanate batteries.
Lithium ion batteries in general offer improved power and energy performance and improved cycle life compared to lead-acid batteries. It is expected that silent watch endurance on military land vehicles could improve if utilising lithium iron phosphate batteries or lithium titanate batteries owing to their greater energy capabilities. However, the distinguishing aspects of these batteries (compared to other lithium ion batteries) is their compatible voltage window, which permits them being used as drop-in replacements for lead-acid batteries, and their improved safety properties, which reduces their risk of catching fire when damaged. These batteries have the added benefit of being able to be fast charged. The high cost of lithium ion batteries may be an inhibiting factor in replacing lead-acid batteries, but this will be partially offset by their higher cycle lives, which will reduce frequency of replacement and lifetime costs. Further investigation of lithium iron phosphate batteries and lithium titanate batteries for military land vehicles is warranted, but is outside the scope of this report.
A number of other battery technologies are considered in this report that may offer performance improvements over lead-acid batteries in military land vehicles, including the UltraBattery, lithium ion batteries using ionic liquid electrolytes, and lithium-sulphur batteries. The UltraBattery, an advanced lead-acid battery, has improved performance at high discharge rates and very high cycle life, but it is unlikely to significantly improve silent watch performance. Furthermore, it is primarily being developed for hybrid electric vehicle applications therefore its characteristics are not being developed to suit conventionally-powered vehicles (i.e. powered by an internal combustion engine only). Lithium ion batteries using ionic liquid electrolytes are of interest due to their potential for improved safety and lithium-sulphur batteries (a subset of lithium-metal batteries) are of interest due to their low cost and high energy capabilities. However, both of these batteries are immature technologies and are not expected to be immediately relevant for military land vehicles, but their development should be monitored.