|Proceedings of a Workshop—in Brief|
Electrification of the Army’s Light Combat Vehicle Fleet
Proceedings of a Workshop—in Brief
On November 3–4, 2022, the National Academies of Sciences, Engineering, and Medicine’s Board on Army Research and Development (BOARD) convened a workshop on the Electrification of the Army’s Light Combat Vehicle Fleet. The workshop explored the technology opportunities for the Army to electrify portions of its fleet and included experts from industry, academia, government, and the national laboratories. The information summarized in this Proceedings of a Workshop—in Brief reflects the knowledge and opinions of individual workshop participants and should not be viewed as a consensus of the workshop participants, the BOARD, or the National Academies.
Committee chair John Koszewnik, NAE, independent consultant, noted in his opening remarks that this workshop was conceived as a follow-on activity to the National Academies’ Powering the U.S. Army of the Future (PTA) consensus study.1 The PTA consensus study reached several overarching conclusions: (1) liquid hydrocarbons will continue to be the Army’s primary power source through 2035; (2) realistic options exist to significantly reduce fuel transport to the field; and (3) the electrification of ground vehicles is highly desirable but should take the form of hybrid-electric (rather than fully electric) through 2035. Informed by new information encountered in the lead-up to the workshop, Koszewnik stated that he now perceives opportunities for all-electric Army vehicles in certain applications, and greater opportunities more generally for battery-electric vehicles (BEVs), battery-hybrid-electric vehicles (BHEVs), and fuel-cell-electric vehicles (FCEVs). As battery energy densities increase, plug-in hybrids (PHEVs) and battery-electric vehicles with range extenders (BEVs with REs) may also prove to be viable, collecting electric power from the operating base grid during normal peacetime operations and using high-energy, dense liquid hydrocarbons while on the battlefield.
Koszewnik observed that the rationale for pursuing electrification of Army vehicles is clear. Electrification promises major performance benefits such as silent watch,2 silent mobility,3 and faster acceleration, and it provides a mobile power source on the battlefield. Keith Jadus, a
1 National Academies of Sciences, Engineering, and Medicine, 2021, Powering the U.S. Army of the Future, Washington, DC: The National Academies Press, https://doi.org/10.17226/26052.
2 The ability to maintain power to a vehicle’s onboard electronics and communications without continuously running an onboard internal combustion engine that generates a thermal or acoustic signature.
3 The ability to drive/move a vehicle without generating a substantial thermal or acoustic signature.
representative of the study sponsor from the Office of the Deputy Assistant Secretary of the Army for Research and Technology (DASA[RT]), stressed the need for anti-idle capabilities and increased onboard energy to power a burgeoning number of onboard electronics systems, including sensors and directed energy (DE) weapons. Furthermore, Jadus and Koszewnik observed that electrification efforts (to include BEVs, BHEVs, and FCEVs) are integral to achieving the goals of the recently articulated Army Climate Strategy.4 Jeff Singleton, the director of technology at DASA(RT), characterized this workshop as an opportunity for DASA(RT) to acquire an independent assessment of the path toward electrification of the Army’s light combat vehicle fleet. “We want to make sure that we are on the right path forward to achieve capability for the warfighter,” remarked Singleton.
ARMY REQUIREMENTS BASELINE
Dean McGrew, Army Ground Vehicle Systems Center (GVSC), and Mike Smith, Army Futures Command (AFC), informed the workshop participants of the Army’s current and future requirements for combat vehicles. Energy is a weapon on the battlefield, noted McGrew, which allows the Army to get in the fight, stay in the fight, and win. McGrew articulated three key advantages from the electrification of Army combat vehicles. First, it would enable the Army to achieve its goal of extending the operational duration5 from 3 to 5 days to outlast the adversary. Idling kills fuel consumption, and thus anti-idle is currently the most important capability in extending operational duration. Second, electrification enables silent mobility by reducing the acoustic and thermal signatures of the vehicle. Third, the Army requires electrification to generate the onboard energy needed to power advanced warfighting capabilities, such as DE. Onboard DE systems require power, as do the electronic warfare systems, such as high-power jammers, necessary to ensure ground vehicle survivability on the modern battlefield, noted McGrew. Smith assessed electrification to be achievable in the near term and noted that ongoing prototyping of the electric light reconnaissance vehicle (eLRV) will allow a more detailed assessment of required capabilities (see Figure 1). Vehicles such as the eLRV, Smith judged, will enable independent expeditionary deep maneuver that enhances combined arms maneuver.
Several workshop participants articulated additional requirements considerations, including off-roading, thermal issues, recharging time, and transportation. Workshop planning committee member Peter Schihl, GVSC, recognized that Army vehicles require substantial off-road capabilities. McGrew noted that combat vehicles require multipurpose tires that can operate on both hard and soft surfaces. On hard surfaces, the multipurpose tires are less efficient than tires designed specifically for hard surfaces—that is, on paved roads, combat vehicles will consume 5–10 percent more energy than vehicles with tires tailored to hard surfaces. GVSC currently collects data to understand exactly how much more energy vehicles will consume on secondary and soft soil.
Workshop planning committee member William Mustain, University of South Carolina, inquired about the thermal requirements for batteries in armored vehicles. McGrew stated that power electronics must be able to survive the 120°C air temperatures in the engine compartment. Currently, GVSC uses a chiller to reduce temperatures for increased battery life. While high-temperature tolerant batteries are the goal, McGrew asserted that the requisite technology does not yet exist. Workshop planning committee member Anna Stefanopoulou, University of Michigan,
4 Department of the Army, Office of the Assistant Secretary of the Army for Installations, Energy, and Environment, February 2022, “United States Army Climate Strategy,” Washington, DC, https://www.army.mil/e2/downloads/rv7/about/2022_army_climate_strategy.pdf.
5 The length of time that an army unit can continuously engage in operations without resupply.
wondered what considerations were in place to deal with a battery fire. McGrew stressed the value of modularity in battery design to ensure that damaged components can be isolated without compromising the entire system. It is also vital, McGrew noted, to ensure that the batteries do not outgas when the vehicle takes rounds.
Workshop planning committee member LTG Sean MacFarland, U.S. Army (ret.), emphasized the importance of rapid recharging requirements. While the Army is aiming for a 15-minute recharging time, he judged 5 minutes (comparable to liquid hydrocarbon refueling time) to be operationally desirable. Last, McGrew reminded the workshop planning committee that Army platforms will also need to satisfy the Navy’s safety requirements, because Navy ships will transport Army platforms to the battlespace.
CURRENT MILITARY ELECTRIFICATION PROJECTS
Rick Kewley, GM Defense, discussed pathways toward electrification. Since 2010, GM has undertaken three generations of battery development for its vehicles. GM has invested $9 billion in a joint venture with LG to mass produce GM’s Ultium battery cell using friendly nation vertical supply chains. Kewley noted that GM expects energy density to continue to improve rapidly and next-generation Ultium cell designs to nearly double in energy density at a lower cost compared to today’s Ultium cell. GM also invests in hydrogen FCEV technology, such as the HYDROTEC Power Cube, an efficient modular system with the ability to power vehicles and provide mobile power generation that is quieter than conventional generators. Electrification is an operational advantage, asserted Kewley. Electrification technologies provide capability for extended mission duration and powering mission equipment. They enable silent watch, low thermal and acoustic signature, and significant fuel demand reduction. For example, in an analysis of a light tactical vehicle mission profile that includes 140 miles driving and 80 hours of silent watch, a series hybrid BHEV or hydrogen FCEV can reduce liquid hydrocarbon demand by up to 50 percent. As such, GM Defense invests in a variety of military BEV, BHEV, and FCEV applications such as series-hybrid and hydrogen FCEV tracked/wheeled vehicles, light-hybrid combat vehicles, and anti-idle tactical wheeled vehicles.
Scott Davis, BAE, provided an overview of the Bradley Hybrid-Electric Vehicle program. The Bradley Hybrid, two of which (at the time of the workshop) were scheduled for delivery to Aberdeen Proving Ground in the coming months, features a 600 HP Duramax engine generator, a cooling system, EX drive transmission, and swappable components. It provides about 5 hours of silent watch and recharges its battery in 30 minutes.
Scott Hall, General Dynamics Land Systems (GDLS), noted that, going forward, GDLS will exclusively invest in hybrid platforms. Several factors motivated this decision, he stated. First, batteries are becoming lighter, with 2.5 percent reductions in weight per year in a straight-line projection. Second, batteries are becoming more diverse, and he expects a greater number of alternatives to lithium-ion (Li-ion). Third, Hall predicted a 3–5 percent improvement in energy storage over the next decade. GDLS, he noted, is taking steps to assess the requisite infrastructure, workforce, and facilities for its vehicles.
Michael Foster, Allison Transmission, posited that there is no “one-size-fits-all” solution for electrification: the Army will need flexibility, exportable power, and a full range of capabilities. That said, Foster assessed plug-in hybrids to be the most versatile electrification arrangement for defense applications. Allison’s research and development (R&D) mission for BEV technology entails several facets. It seeks to improve efficiency and power-torque density, de-risk its supply chain by reducing or eliminating rare-earth magnet materials from its products, and achieve full system integration and system-level energy management. Foster stated that onboard energy management should be a focus for military vehicle applications. He identified research funding opportunities for the Army to supplement industry’s collaborative and self-funded research in components and subsystems, in vehicles, and in the electrification ecosystem.
While it is obviously desirable to be ahead of competitive/adversarial nations in this space, Koszewnik argued that it is also important that the United States remains at the leading edge among allied nations. The United States should be a standard-setter, rather than a follower, he noted. Remaining at the leading edge requires collaboration
between the military and industry, stated Koszewnik. Davis observed that the Army can be an unpredictable partner for industry and often changes its mind about what it wants. Inconstancy, he noted, reduces the probability that firms recover their investments, and it delays and constricts the process of contracting with the Department of Defense (DoD), making it appear expensive and risky to engage in this area. As a counterpoint, Hall posited that industry views electrification as a persistent macro trend and will move into this area regardless of DoD support.
Workshop participants also queried speakers on specific voltage standards. The Army currently uses a 600-volt standard, but some of the automotive sector is moving to 800 volts. Davis argued that the Army should avoid diverging too much from industry, lest it find itself unable to leverage advances in the automotive sector. Additionally, Foster observed that the defense industry will want to leverage the scale and cost of higher-volume civilian applications. There is an economic incentive, he noted, for manufacturers to develop voltages that present the highest commonality and volumes. McGrew explained that the Army chose the 600-volt standard with the expectation that it might experience damage caused by the impact of enemy projectiles (e.g., high-explosive shells, armor-piercing rounds); taking a round at 800 volts can cause the voltage to rise high enough that it destroys the electronics. Any efforts to move to a higher voltage standard, he noted, would require appropriate mitigation mechanisms. Michael Gonzalez, Command, Control, Communications, Computers, Cyber, Intelligence, Surveillance, and Reconnaissance (C5ISR) Center, expressed skepticism that the Army would alter its AC voltage standard any time soon.
Maintenance considerations were a further topic of discussion. Jadus emphasized that reducing sustainment costs for platforms is a serious focus for the Army. Kewley observed that BEVs are, generally, more reliable and easier to maintain than internal combustion engine (ICE) vehicles—particularly in fleet environments. For example, Hall and Smith both noted that BEVs have significantly fewer parts than ICE vehicles. Nevertheless, workshop participants highlighted a few maintenance challenges particular to military applications. Mustain noted that military vehicles may sit in a warehouse for years prior to deployment. This will necessitate continuous monitoring of where batteries are in their life cycles—perhaps an appropriate application for artificial intelligence/machine learning, argued LTG MacFarland. It will be imperative, asserted Foster, to utilize data and analytics to assess where and when power is needed across the BEV fleet. McGrew added that BEVs can potentially participate in base maintenance prior to deployment: if they are Internet connected and microgrid compatible, they can help generate power for the base. Last, workshop planning committee member Chester Osborne, Massachusetts Department of Transportation, reminded the workshop participants about the existing demographics of Army maintenance personnel: while many enlisted personnel are familiar with ICE maintenance, the BEVs they use in combat may be the first they have encountered, and maintenance will require new training.
The workshop participants also discussed ways to reduce the overall weight of vehicles (e.g., increased reliance on active protection systems, reduced armor weight, lighter armor via materials substitution6). Koszewnik noted that cutting the weight of the vehicle is operationally equivalent to increasing the energy density of batteries. While Hall stated that vehicle weight reductions are a major industry focus, Davis observed that it can be difficult to sell the accompanying trade-offs for military vehicle applications. There is a cultural aversion to risk, he asserted, and it can be difficult to convince the military to give up any element of force protection. Nevertheless, he judged trade-offs to be inescapable in this space.
TECHNOLOGY DEVELOPMENTS IN THE COMMERCIAL SECTOR
Gary Parker, Cummins, noted that his company is pursuing several zero-emissions technologies, including electrolyzers, fuel cell systems, electrified components, and ePowertrain systems. While Cummins possesses real-world experience with BEVs, Parker stated that they are finding it difficult to meet battery energy demands for
6 For more information, see National Academies of Sciences, Engineering, and Medicine, 2018, Combat Vehicle Weight Reduction by Materials Substitution: Proceedings of a Workshop, Washington, DC: The National Academies Press, https://doi.org/10.17226/23562.
applications like buses and are increasingly turning to hydrogen fuel cells (HFCs) to fill the gaps.7 To create the hydrogen ecosystem, Cummins works across the value chain and focuses on infrastructure in addition to power-trains and vehicles. Cummins is in the early stages of creating a fuel cell roadmap that targets a 1,000-mile range by 2030 using hydrogen as a fuel source. Parker mentioned that infrastructure and combat acceptance present Army adoption challenges for hydrogen. Additionally, Stefanopoulou inquired about the water purity requirements for hydrogen refueling. Parker acknowledged that filtration is required to achieve the appropriate water quality level.
David Mielke, PACCAR, discussed battery and charger requirements for BEV trucks. PACCAR has multiple R&D programs for hybrid applications and fuel cells, and has also developed several battery layouts for different applications. By 2030, PACCAR expects BEV trucks to make up half of its product offerings. In terms of battery requirements, Mielke stated that iron-based battery chemistry will soon play a major role, owing to its life-cycle benefits and cleaner supply. He noted that nickel-based batteries also have a future in longer-range applications that need fast recharge. Further in the future, Mielke identified solid-state lithium metals as a promising solution (with at least 2× to 3× power density improvements) but predicted their adoption to be unlikely until the mid-2030s. Lithium-air batteries may come first, he noted. In terms of charger requirements, Mielke admitted that the current state of the art for fast charging takes several hours. PACCAR targets 1 megawatt (MW) of charging, which would offer a charge time on par with typical diesel fueling. Foster reminded the committee of the need to balance the limitations of the charging systems and battery life with the expectation of fueling times on par with diesel. Mielke noted, however, that there are physical limits to how much more voltage and amplitude they can achieve.
Chris Moore, Canoo, presented his company’s light-duty BEV platform and identified risks to the BEV supply chain. Canoo provided its first BEV to the Army in December 2022 for a demonstration.8 Canoo created a multipurpose platform that uses the same chassis—including motor, wheelbase, batteries, and all essential components—for all models. The top section of the vehicle is swappable and can be removed and replaced with a separate configuration within a day. Canoo targets future improvements in materials science to reduce weight, in vehicle technology to increase efficiency, and in remote driving design, battery life, and charging technologies. Moore also identified risks to BEV production. He observed that a select number of countries mine lithium, several of which are hostile to the United States. While there are significant deposits of lithium in the United States, permitting reform must occur before the domestic supply is accessible. Moore also pointed to cybersecurity as a serious risk: the United States lacks control over the software development of components that go into its products. As a result, Moore assessed a serious cyber risk for software in vehicles. He noted that Canoo develops all of the software for its vehicles in the United States.
Additionally, workshop participants discussed the merits of vehicle-to-grid compatibility and of tactical micro-grids. Moore advocated for vehicle-to-grid capabilities that provide greater resilience. Gonzalez noted that tactical microgrid standards may be critical to enabling systems to communicate with one another. Moore, however, warned the Army against overly constraining its partners with burdensome systems requirements that lock everyone into the same standards. He encouraged the Army to allow industry to “feel its way forward” by rewarding creativity and innovation. The current environment facilitates innovative solutions, he asserted.
EMERGING BATTERY TECHNOLOGIES
Jie Xiao, Pacific Northwest National Laboratory, provided an overview of the Battery500 Consortium, a research program to develop next-generation, high-energy lithium-metal (Li-metal) batteries. The effort involves four national laboratories, eight universities, and an industry advisory board. Battery500 seeks to design,
7 Some participants also noted that hydrogen can be created through sustainable sources, adding further impetus for industry to pursue the technology.
8 Electrive, 2022, “Canoo Delivers LTV to US Army,” December 5, https://www.electrive.com/2022/12/05/canoo-delivers-ltv-to-us-army/.
fabricate, and validate high-energy pouch cells up to 500 watt-hours per kilogram (Wh/kg)9 and 100 cycles. The program is working on several integrated innovations to extend the cycling of Li-metal batteries. Currently, it is prototyping a 350 Wh/kg lithium-nickel-manganese-cobalt oxides (Li-NMC) cell with record cycling. It features a localized concentrated electrolyte, a lower concentration gradient, less electrolyte for solid electrolyte interphase formation during each cycle, and an electrode architecture to accelerate fast ion diffusion. More broadly, Xiao emphasized that battery technology research is duty-cycle driven: researchers require accurate duty cycles and use cases to guide their research.
Ilias Belharouak, Oak Ridge National Laboratory, discussed advances in battery technologies. Like other presenters, he observed that China dominates the Li-ion battery world market. For the first time, however, the dynamic is changing as the U.S. government aggressively funds battery research and shores up its supply chains. Belharouak pointed to the $2 billion allocated for 21 companies working on battery materials processing in 2022. The United States, he asserted, is beginning to create its own battery manufacturing ecosystem that will drive advances in next-generation rechargeable batteries. Belharouak noted that significant basic research remains to be done before next-generation batteries—like Na-ion, solid state, and lithium-sulfur—are achievable.
Belharouak identified several critical technical battery R&D drivers. To increase energy density, technical approaches include high-capacity and high-voltage cathodes. To reduce costs, cobalt-free, next-generation cathodes; slurry formulations and processing; and electrode and cell engineering can all play a role. To enhance performance and safety, Belharouak identified materials surface modifications, electrolytes and additives, and cell balancing and formation as promising technical approaches.
Significant challenges remain, noted Belharouak, particularly in the battery supply chain. The United States, he argued, must rethink its battery supply chain by viewing the entire process—from mining of critical materials to recycling of batteries—holistically. It should produce battery cells with protected recipes within the United States, he stated. He advocated for greater government spending on lithium resources and electrolytes, as well as mining, refining, and processing of critical materials. As an example, he pointed out that the United States has lithium within its own borders but lacks the knowledge of how to properly extract it.
Belharouak also advocated for rethinking battery performance metrics. He asserted that new matrices—that go beyond energy density and cycle life—are required for different application spaces, such as consumer electronics, electric vehicles, defense, and grid. He suggested the inclusion of considerations such as safety, manufacturability, and recyclability. (The comprehensive list can be seen in Figure 2.) LTG MacFarland and Stefanopoulou identified the recycling of battery materials as critical. Concurring, Belharouak posited that recycling considerations should be a central metric of battery development. Jadus asserted that the reuse and recycling of batteries should be a sustainment consideration for the Army. Koszewnik endorsed the parameters of Belharouak’s battery performance metric chart and posited that the Army needs similar criteria to select its power sources based on mission profiles.
Judy Jeevarajan, Electrochemical Safety Research Institute (ESRI), explored the challenges of future energy technologies, including solid-state batteries (SSBs), battery swapping, and new battery chemistries. SSBs, she noted, promise several advantages: they are safer owing to the lack of a flammable liquid electrolyte, have no electrolyte leak effect, offer high energy and power density, and have low deadweight. Most types of solid electrolytes,
9 A unit of measure for the density of energy in batteries.
however, are problematic. Jeevarajan pointed to SSB issues with chemical, electrochemical, mechanical, and thermal stability. To overcome these challenges, ESRI is actively studying how chemical and structural properties affect mechanical deformation and how the mechanical and chemical properties of grain boundaries influence lithium dendrite suppression.
Jeevarajan identified several important considerations for battery swapping: the chemistry must be known, the state of health10 must be assessed, and the charger must be appropriately programmed to handle aging batteries. She noted that as a battery ages, it reaches the same voltage faster during charging. Jeevarajan observed that several factors affect the life of a battery. Its cycle life is influenced by the charge/discharge rate, environmental temperature, number of cycles, internal temperature gradient within the battery, usage voltage range, and cell uniformity within the battery. The battery’s calendar life is shaped by the storage state of charge,11 cell uniformity, storage conditions, use, and environmental temperature, and by the battery management system. Koszewnik suggested the use of digital twins to monitor battery health, an application that Jeevarajan judged to be uncommon but potentially useful for assessing aging in future battery-swapping applications.
Jeevarajan also provided her assessment of two other battery chemistries. She judged Li-sulfur batteries to possess poor cycle life, voltage range restrictions, cell shortening, and safety issues. Sodium-ion batteries, which are cheaper than Li-ion, she noted, suffer from slow transport kinetics, short cycle life, and low energy density. Bruno Millonig, BOARD director, observed that today, in terms of development, sodium-ion batteries are where Li-ion batteries were 10 years ago. He wondered if sodium-ion could achieve comparability if it experienced a similar level of investment to Li-ion. Jeevarajan agreed that the community should invest in researching its chemistry, noting that sodium-ion batteries hold the promise of mitigating supply chain vulnerabilities.
Chungsheng Wang, University of Maryland, presented ongoing work at the Center for Research on Extreme Batteries (CREB), a battery center focused on the development of batteries with extreme performance, extreme safety, and environmental capabilities for the defense industry. CREB partners with the Department of Energy (DOE) Vehicle Technologies Office on R&D for several types of batteries: enhanced Li-ion (graphite/NMC), next-generation Li-ion (silicon [Si]/NMC), and Li-metal/NMC or sulphur. Wang observed that many current state-of-the art battery chemistries cannot meet the operating temperatures required for defense applications. Army applications would benefit from a nonflammable liquid electrolyte, noted Wang, and DoD partners with CREB on several solid-state, Li-metal battery projects. He highlighted three types of next-generation Li-ion batteries for Army BEV applications: all-temperature NMC graphite cells; high-energy micro-Si/lithium-nickel-cobalt-aluminum oxide cells; and nonflammable and all-temperature electrolytes for Li/NMC811 cells. Like other speakers, Wang identified vulnerabilities in DoD’s supply chain, and he advocated for a transition to metal-free cathodes for all Army BEVs.
Ajay Goel, SUN Mobility, described the operations of his commercial BEV fleet, which relies on battery swapping. Battery swapping, he stated, achieves cost parity between electric and ICE vehicles. SUN Mobility uses an integrated BEV energy platform composed of a smart battery, advanced quick interchange stations for battery swaps, plug-and-play integration, and Internet of Things (IoT)-enabled assets. SUN Mobility employs the same proprietary smart battery (in two sizes) for its entire fleet of e-rickshaws, e-bikes, and e-buses. The IoT-enabled batteries allow the company to conduct constant monitoring, diagnostics, and software updates for its battery assets. The battery swapping stations—20-foot containers that mount on a truck—hold 15 battery swaps per unit, are temperature controlled, and conduct swaps in 2 minutes. For military applications, Mustain observed that any swapping stations would need to be similarly mobile. Like the batteries, they are IoT-enabled. All information from the company’s assets feeds back into SUN Mobility’s command center, which remotely monitors stations, batteries, and vehicles. Additionally, SUN Mobility maintains a digital twin for all of its assets. Koszewnik
suggested that battery swaps could play a role in the Army’s suite of BEV solutions. When operating on base, for example, an Army BEV might employ a swappable battery that has experienced many life cycles. For off-base missions, when greater reliability is required, the BEV might pivot to an extended-range nonswappable battery with low life cycles.
POTENTIAL APPLICATIONS FOR FUEL CELLS
Dimitrios Papageorgopoulos, DOE Hydrogen and Fuel Cell Technologies Office, presented details of DOE’s hydrogen program. DOE maintains a portfolio of hydrogen fuel cell activities, as part of its “Hydrogen Shot,” from the production to end-use phases, with the aim of reducing the cost and increasing the performance of fuel cells and hydrogen production, delivery, and storage. The Hydrogen Shot targets “$1 for 1 kg of clean hydrogen in 1 decade.” DOE’s National Hydrogen Strategy Roadmap sets targets for hydrogen production at 10 million metric tons (MMT)/year by 2030, 20 MMT/year by 2040, and 50 MMT/year by 2050.
Papageorgopoulos highlighted several program-enabled accomplishments. Thus far, the program has facilitated 10 MMT of hydrogen produced annually and laid 1,600 miles of hydrogen pipeline. From 2021 to 2022, the United States tripled its proton-exchange membrane (PEM) electrolysis, to >620 MW. The program also reduced light-duty vehicle hydrogen fuel cell costs by 70 percent from 2008 to 2020, cut catalyst loading, and increased cell power density. Recently, DOE awarded a $1 million prize to a team that built the first mobile hydrogen refueler capable of filling vehicles 95–100 percent full in 3 to 5 minutes.
Papageorgopoulos mentioned two challenges on which DOE continues to focus: thermal management and degradation-adjusted performance. Heavy-duty applications struggle to dissipate heat, he noted. DOE is studying better hybridization schemes to mitigate thermal management issues, such as combining a smaller fuel cell with a larger battery. Papageorgopoulos also noted that fuel cells are generally more efficient at lower-power densities. They can meet durability requirements, but at a higher cost. The DOE Million Mile Fuel Cell Truck Consortium seeks to address these challenges by advancing efficiency and durability and lowering the cost of PEM fuel cells for heavy-duty applications. Mustain reminded the workshop participants that, compared to DOE’s cycle profiles for civilian applications, the Army’s unique requirements demand simulation of a far more diverse set of mission cycles. He also noted the absence of real field data for Army applications of FCEVs, and queried Papageorgopoulos about DOE’s use of digital twins. Papageorgopoulos stated that DOE puts significant emphasis on digital twins but stressed that these are dependent on adequate requirements profiles. Stefanopoulou inquired about materials modeling at DOE, to which Papageorgopoulos responded that “modeling drives our effort, our strategy, and tells us what to do.”
DOE, Papageorgopoulos noted, also maintains a comprehensive program for hydrogen storage. Hydrogen, he observed, can be transported via compressed gas, via liquification, and—in the future—via pipelines. Refueling stations keep hydrogen in compressed form. He highlighted two types of pressure vessels for storage: a metal liner with a full fiber composite overwrap (Type III) and a nonmetallic liner with a full fiber composite overwrap (Type IV). Currently, a 5.6 kg H2 Type IV tank has 0.8 volumetric kWh/L and costs $16/kWh. DoD targets an eventual 1.7 volumetric kWh/L at $8/kWh. Carbon fiber is the biggest cost driver for hydrogen storage in light- and heavy-duty tanks, he observed. Initial analyses also indicate that liquid hydrogen and cryo-compressed hydrogen offer high onboard capacities at lower cost and weight than compressed hydrogen. For military applications, he recommended transport in ammonia form to portable electrolyzers in theater.
Karen Swider-Lyons, Plug Power, Inc., discussed the green hydrogen ecosystem and the use of HFCs for military applications. Her company, Plug Power, produces and delivers liquid hydrogen to warehouse sites where companies—to include Amazon and Walmart—use liquid-hydrogen-powered commercial forklifts. Plug Power is creating a domestic green hydrogen infrastructure to include renewable-powered hydrogen plants, hydrogen dispensers in warehouses, and hydrogen-powered forklifts and trucks. Plug Power’s green hydrogen production plant in Camden, Georgia, produces 51 tons per day12 of liquid hydrogen using Plug Power’s PEM stack technology.
12 One ton of hydrogen = 33 MWh; 51 tons of hydrogen = 1.7 GWh.
As of 2021, Plug Power maintains 3 active plants and aims for 6 plants by the end of 2023 and 10 plants by 2025.
Swider-Lyons assessed HFCs to be ready for military applications (technologically, although not in terms of cost, she specified) and outlined several benefits. HFCs enable fast fueling, are quiet, and have low thermal signatures. Echoing other speakers, she argued that different energy technologies are appropriate for different missions/applications. While HFCs possess longer endurance than batteries for larger vehicles (with the requisite space for hydrogen storage), batteries are preferable for smaller systems and shorter-duration missions (as can be seen in Figure 3). Swider-Lyons also noted that heavily used fuel cell stacks can take on a valuable second life, once their vehicle propulsion career is over, in on-base battery charging applications.
The Army can leverage commercial-sector fuel cell efforts for its light tactical vehicles, stated Swider-Lyons. The technology, she observed, has improved dramatically over the past 7 years and is already under testing by the services. The Marine Corps and Army have both tested hydrogen fuel tanks for light vehicles, for example, by striking them with rocket-propelled grenades to assess their robustness. She noted that the military has successfully demonstrated fuel cell versions of small uncrewed air vehicles (UAVs), tactical generators, and portable power. Additionally, feasible methods of field refueling exist, such as a Naval Research Laboratory–designed method for UAVs, which refuels from commercial bottles of 6,000 psi hydrogen in roughly 2 minutes. Although flammability is an often-repeated concern for HFC military applications, Swider-Lyons noted that all energy sources, including JP8, can catch fire under the right conditions, and that trade-offs will need to be assessed. HFCs, like other fuel sources, will require their own hazards analyses. Jadus stated that the Army is unlikely to adopt HFCs unless it can demonstrate their safety. He encouraged workshop participants to consider ways to package HFCs so that they do not present a flammable/explosive or noxious risk to the vehicle crew.
To facilitate military adoption of HFCs, Swider-Lyons made several recommendations for the Army. First, continue to monitor HFC programs conducted by DOE as well as by other nations. Second, study the specifics of hydrogen applications on the battlefield. Third, compile and assess information on all DoD fuel cell demonstrations over the past 20 years. Fourth, assess the merits of in-field hydrogen generation versus hydrogen supply convoys. Fifth, perform a hazards analysis to assess Army-specific safety risks for HFCs and research methods to manage/mitigate any that are identified. Adding to this point, Jeevarajan recommended that the Army specifically model hydrogen explosions—in addition to assessing the safety of hydrogen production, storage, and transportation.
Scott Mahar, General Atomics, explored ways to produce hydrogen in theater. No hydrogen infrastructure will exist where the Army expects to operate, leaving two options: ship hydrogen or generate it on-site. The former method relies on large, flammable convoys carrying hydrogen in a lower-density form. Stefanopoulou noted that the goal for the Army is to generate hydrogen as needed. Mahar stated that several techniques exist to make on-site generation of hydrogen feasible. In particular, he identified aluminum water and hydrocarbon pyrolysis as promising methods. Water reacts with unpassivated aluminum to produce both hydrogen (4.4 kWh/kg) and heat (4.2 kWh/kg). Although aluminum will naturally form an oxide to prevent the reaction, if alloyed with gallium, oxidation can be prevented. The Army is using the aluminum–water reaction as the basis for its Hydrogen On-Demand Platform, a towable trailer that
generates PEM-quality hydrogen on demand and would refuel PEM fuel cell vehicles on the battlefield. The platform is scheduled for a system demonstration in Spring 2023.
While Mahar advocated for aluminum–water reactions in refueling applications, he proposed hydrocarbon pyrolysis as the preferred technique to hybridize a vehicle. Hydrocarbon pyrolysis entails the thermal decomposition of a hydrocarbon (such as JP8 fuel) at a high temperature, resulting in high-purity hydrogen (sufficient for a PEM fuel cell). The system is small (approximately a 2 ft3 cube) and enables onboard pyrolysis for a vehicle. It requires no pretreating (desulfurization) of the hydrocarbon, requires no catalysts, has minimal maintenance needs, and produces no carbon dioxide. Thus, Mahar recommended that a vehicle have both an ICE (for sustained travel) and a fuel cell (for silent watch and silent mobility), with an onboard hydrocarbon-pyrolysis reformer to generate hydrogen for the fuel cell.
Mahar concluded that the Army needs hydrogen to enable new types of missions—like silent watch and silent mobility. The appropriate hydrogen-generation method depends on the application and mission profile (e.g., hydrocarbon pyrolysis for hybridized vehicles). Similar to other speakers, Mahar advocated for greater engagement between industry and government on hydrogen production methods.
Dennis Bushnell, NASA Langley Research Center, discussed horizon energy topics such as NASA’s nuclear battery (Nuclear Thermionic Avalanche Cell [NTAC]), low-energy nuclear reactions (LENR), and spaced-based solar power. Bushnell identified several drawbacks to state-of-the-art nuclear batteries: the optimal nuclear battery currently in use is only 6 percent efficient, generates 10 watts/kg of isotope, and cannot shut down. By contrast, he presented NASA’s experimentally demonstrated NTAC battery, which he stated eliminates nuclear waste and self-shields. NTAC is currently at Technology Readiness Level (TRL) 3, he noted.
Bushnell also touted LENR as a groundbreaking technology. Over the past 10 years, Japanese scientists devoted significant resources to addressing replication and scaling issues with LENR, discovering that nano-asperities are the key to concentrating area energy. At present, Clean Planet, a Japanese company, develops commercial 1 kW and 600 kW devices. LENR—currently at TRL 4—emits no radioactive emissions, which eliminates the need for a shield and subsequently reduces device weight, stated Bushnell. He judged LENR to possess significant potential as a petroleum replacement for power transportation and facilities energy.
By contrast with NTAC and LENR, Bushnell assessed space-based solar power to be unaffordable and incompatible with Army operations owing to its economics, safety, and vulnerabilities—among other concerns.
CROSSCUTTING WORKSHOP THEMES
Throughout the presentations and during discussions, workshop participants observed several recurring themes, such as mission profiles, charging, data, modeling and simulation, collaboration with industry, and supply-chain vulnerabilities. The following sections capture the highlights of participant commentary on these salient topics.
The Value of Mission Profiles in Developing Electrification Technologies
Several workshop participants reiterated that the appropriate power source for Army light combat vehicles is, in large part, dependent on the specific mission profile. The mission profile is critical in deciding what technology is appropriate, argued Kewley and Jadus. Koszewnik observed that fuel cells are optimal for certain applications (heavy duty, long range) and batteries or hybrids for others (lighter duty, short range, silent watch, etc.). Everything must be application-driven, stated Schihl, and program managers need to be cognizant of the mission profile when setting the parameters for their proposed solution. As Foster succinctly summarized earlier, there is no “one-size-fits-all” solution for the Army’s electrification needs.
Workshop participants identified several ways to better incorporate mission profiles into the development of electrification technologies. Koszewnik advocated for more roadmaps that are sensitive to different mission
profiles. He touted Belharouak’s proposed matrix for rethinking battery performance (see Figure 2 above) as a step in the direction of using new parameters to assess a power source’s relevancy to a given mission. Koszewnik observed that while electrification efforts have primarily focused on getting vehicles to the fight, consideration of battlefield uses of power, such as DE and onboard electronics, have their own separate mission profiles and metrics of success. Several workshop participants suggested that DoD collaborate with industry to articulate explicit mission profiles; Kewley noted that GM Defense is already doing this. Swider-Lyons also advocated for collaboration on detailed hazards analyses. Prompted by the recurrence of the mission profiles and mission requirements theme throughout the workshop, Koszewnik suggested that the topic was sufficiently important and complex as to warrant its own National Academies’ consensus study.
McGrew and Jadus advocated for accelerating the placement of electrification technologies in warfighter experiments. Warfighter experiments allow operators to interact with the technology and assess how best to use it, which in turn provides more detailed mission profiles to researchers. Such experiments, they emphasized, demonstrate that it is possible to accelerate deployment and learning capture prior to meeting full defense requirements.
Recharging/Refueling in Theater
BEV charging, at installations and when deployed, remains the “elephant in the room,” noted Jadus. Recharge is critical, as is assessing different ways to bring energy from home to the battlefield, observed another participant. Osborne reminded the workshop participants of the extensive casualties associated with energy supply lines in recent conflicts.
Data, Models, and Simulations
McGrew described the current state of operations as “information poor.” He noted that most fuel trucks return with full tanks owing to a lack of information about who needs fuel and where. A benefit of electrification, he argued, is that it is beginning to enable the Army to capture and monitor relevant information on the health and needs of its fleet in a way that was not previously possible. Stefanopoulou observed that the Army will need to find ways to process the large volume of data that attends the monitoring of batteries and fuel cells for the entire vehicle fleet.
Stefanopoulou stated that the Army needs more relevant data to power logistics models, complex simulations, and systems-level models to assess how different electrification technologies will influence its operations. Foster articulated a similar need for industry, stating that companies require data on the Army’s missions and how it expects to use its vehicles. Stefanopoulou recommended that the Army leverage some of DOE’s models to simulate the entire lifetimes of its vehicles.
Several workshop participants emphasized the role of modeling and simulation in guiding the Army’s electrification efforts. Parker stressed the importance of simulations for ecosystems and battery duty cycles. Stefanopoulou suggested greater materials modeling efforts. Koszewnik, Mustain, and Swider-Lyons, among others, stressed the value of digital twins. Mustain and Swider-Lyons stated that digital twins will play a critical role when data from field testing are not available.
Army Collaboration with Industry
Kewley averred that the Army cannot afford to wait for the perfect solution; it must collaborate with the government customer on adapting emerging technologies and move toward point solutions. Several workshop participants highlighted the need for closer collaboration on independent R&D in electrification technologies. Several participants also suggested that the Army closely monitor and remain responsive to developments in industry, such as the automotive sector’s move to 800-volt architectures. As Davis argued, the Army must remain cognizant that it is not constraining itself in a way that would render it incapable of leveraging commercial advancements in the automotive industry.
Throughout the workshop, participants repeatedly observed that the U.S. supply chains remain vulnerable for materials critical to electrification. Several speakers
noted that nonfriendly nations, particularly China, control a significant portion of the rare-earth mineral supply chain. To mitigate supply-chain vulnerabilities, Belharouak recommended that the U.S. government focus on mining and refining the lithium resources that exist within the United States. He also advocated for changes to existing permitting requirements that are necessary to mine lithium.
Several speakers suggested that the United States turn to alternative materials. Foster recommended that the Army pursue technologies that reduce or eliminate the need for rare-earth magnet materials. Belharouak and Jeevarajan proposed sodium-ion as a complementary technology to Li-ion, which would ease pressures on existing lithium supply chains. Several speakers, including Moore, suggested keeping supply-chain ownership of critical materials for electrification in the United States, or at least in friendly nations.
Millonig added a final high-level observation: the Army would benefit from more forums and dialogues that present opportunities to collaborate with industry, particularly for the purpose of directing and concentrating R&D for electrification. The more purposeful the approach, the faster the Army will arrive at its intended target. He concluded by expressing the BOARD’s deep gratitude for the efforts of the workshop planning committee, speakers, staff, and all participants who contributed to a fruitful 2-day discussion.
WORKSHOP PLANNING COMMITTEE John Koszewnik (NAE) (Chair), Independent Consultant; Vincent Freyermuth, Argonne National Laboratory; Sean MacFarland, U.S. Army (ret.); William Mustain, University of South Carolina; Omer Onar, Oak Ridge National Laboratory; Chester Osborne, Massachusetts Department of Transportation; Cindy Powell, Pacific Northwest National Laboratory; Peter Schihl, Ground Vehicle Systems Center; Anna Stefanopoulou, University of Michigan; Levi Thompson (NAE), University of Delaware.
STAFF William Millonig, Board Director; Steven Darbes, Program Officer; Sarah Juckett, Program Officer; Tina Latimer, Program Coordinator; Travon James, Senior Program Assistant; Clement Mulock, Program Assistant; Cameron Malcom, Research Associate; Nia Johnson, Program Officer.
DISCLAIMER This Proceedings of a Workshop—in Brief was prepared by Clement Mulock as a factual summary of what occurred at the workshop. The statements made are those of the rapporteur or individual workshop participants and do not necessarily represent the views of all workshop participants; the planning committee; or the National Academies of Sciences, Engineering, and Medicine.
REVIEWERS To ensure that it meets institutional standards for quality and objectivity, this Proceedings of a Workshop—in Brief was reviewed by Michael Foster, Allison Transmission; Rick Kewley, GM Defense; and Ryan Murphy, National Academies of Sciences, Engineering, and Medicine. Katiria Ortiz, National Academies of Sciences, Engineering, and Medicine, served as the review coordinator.
SPONSOR This workshop was supported by the Department of the Army.
SUGGESTED CITATION National Academies of Sciences, Engineering, and Medicine. 2023. Electrification of the Army’s Light Combat Vehicle Fleet: Proceedings of a Workshop—in Brief. Washington, DC: The National Academies Press: https://doi.org/10.17226/26886.
For additional information regarding the workshop, visit https://www.nationalacademies.org/event/11-03-2022/electrification-of-the-armys-light-combat-vehicle-fleet-a-workshop.
Division on Engineering and Physical Sciences
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