Aerospace Battery Systems - Battery Design

Aerospace battery systems cover an unusually wide span of duty cycles: a lead-acid pack quietly holding charge for standby avionics on a piston aircraft, a lithium-ion pack in an eVTOL air taxi being asked for a 60C discharge pulse during vertical climb, and a primary lithium cell on a planetary lander that has to survive a decade of vacuum and radiation before it is ever used. Each application pushes a different part of the design envelope, and each sits under its own certification regime. This page covers the main engineering constraints, failure modes and standards that shape battery design across commercial and military aviation, electric vertical takeoff and landing (eVTOL) aircraft, and spacecraft.

Where Aerospace Batteries Are Used

In conventional commercial and general aviation, batteries power navigation displays, standby avionics, emergency cabin lighting, flight controls and engine starting. Piston-engine general aviation aircraft still lean heavily on sealed lead-acid batteries, while turbine-powered aircraft typically use nickel-cadmium or lithium-ion packs for starting and critical backup loads. Military and tactical UAV platforms operate under tighter mass and voltage-response constraints again: a custom pack for a military drone or handheld controller might need to deliver 120 Wh from a 32 V pack at a weight of just 2 kg, while still starting reliably at -30°C.

eVTOL air taxis and other urban air mobility (UAM) aircraft push discharge rates well outside normal EV territory. Where high-power EV testing is usually framed around 2C to 5C pulses, vertical lift forces eVTOL batteries into a dual-pulse profile: a very high discharge rate, commonly cited in the 10C to 60C range, during vertical takeoff and climb, a steady roughly 1C cruise phase, and a second high-power pulse during descent and landing when the pack is already down to 20-30% state of charge. That combination of high current at both full and low charge accelerates polarisation and capacity fade in a way conventional EV duty cycles don’t really test for.

Space is a different problem again: extreme temperature swings, hard vacuum and ionising radiation, over mission durations that can run from days to well over a decade. Early satellites such as Sputnik and Explorer relied on primary silver-zinc and zinc-mercury oxide cells built purely to survive launch and a short mission. Later orbital platforms, including the Hubble Space Telescope and the International Space Station, moved to rechargeable nickel-hydrogen and then lithium-ion (NCA) packs, chosen for cycle life running into the tens of thousands of charge and discharge cycles as the spacecraft passes in and out of eclipse. Planetary rovers such as Curiosity use rechargeable lithium-ion cylindrical cells that have to survive the Martian diurnal temperature swing and the vibration of entry, descent and landing, while landers and sample-return capsules more often use primary lithium cells chosen for a long dry shelf life and high pulse power rather than rechargeability.

Structural and Thermal Design Constraints

A large part of an aerospace battery pack’s weight comes from certification requirements rather than the cells themselves. RTCA DO-160G environmental testing and DO-311A both require the casing to survive rapid decompression, the sudden pressure differential created when an aircraft’s pressurised cabin fails, without structural rupture, and to physically contain any solid ejecta and flame if a cell goes into thermal runaway (gas and liquid venting is permitted, but the casing itself must not fail). NASA’s work scaling battery packs for the X-57 Maxwell electric aircraft used dedicated cell-to-pack scaling laws and optimisation tools, such as the eXtended Design Structure Matrix, specifically to try to claw back some of that structural mass penalty, since a heavier containment structure eats directly into aircraft range and payload.

Thermal management has to prevent local hot spots and stop a single cell’s failure propagating to its neighbours, and different applications solve this differently. Aircraft packs commonly use active liquid cooling channels or air-cooling blowers to handle the resistive heating generated at discharge rates up to around 10C. Some space applications, including high-temperature sodium-sulfur batteries, instead use passive variable conductance heat pipes: sealed titanium loops with a cesium working fluid and a grooved wick that can move several hundred watts of heat while holding the pack within a narrow temperature band, with no moving parts to fail. Between cells, lightweight silica aerogels, intumescent sheets or phase change materials are often used as a physical barrier to stop propagation, though the same low thermal conductivity that makes them good barriers can also trap heat during normal operation if the pack design doesn’t account for it.

Electrical Faults and Degradation Mechanisms

Lithium-ion battery management systems are far less forgiving of charging anomalies than the lead-acid or Ni-Cd systems they’re replacing, and a mismatch between a ground power unit’s charging profile and the pack’s programmed protection limits can trip a fault and strand an aircraft on the ground. A more subtle electrical failure mode shows up in the wiring itself: silver-plated copper conductors, common in aerospace harnesses, are vulnerable to a galvanic corrosion mechanism nicknamed “Red Plague,” where trace moisture reaching a break in the silver plating rapidly oxidises the copper underneath. SAE ARP6400 sets out handling and routing practices specifically to keep moisture away from that plating during manufacture and assembly.

At the cell level, overcharging to 100-120% state of charge forces extra lithium out of the cathode and can push its layered crystal structure toward a more disordered spinel phase, while driving the anode potential down toward metallic lithium plating on the graphite surface, which reacts with the electrolyte and builds an unstable SEI layer. Over-discharge is arguably the more interesting failure mode: as a cell is driven below about 2.0 V, the anode potential climbs, the SEI layer starts breaking down and releasing gas, and if the anode potential keeps rising the copper current collector itself starts to dissolve. Those copper ions migrate across the separator and re-plate as dendrites on recharge, which can pierce the separator and cause an internal short. It is often a survivable, self-limiting failure in that the cell simply dies, but it quietly damages thermal stability in a way that can resurface later under normal cycling. It is a specific enough problem that some aerospace research is now looking at copper-free anode designs, such as germanium-aluminium electrodes on aluminium current collectors, precisely to remove that dissolution pathway.

Thermal Runaway by Chemistry

Once a cell is pushed into thermal runaway by mechanical, electrical or thermal abuse, it tends to move through a fairly consistent sequence: exothermic SEI decomposition from around 60-80°C, separator melting and internal micro-shorting around 100-120°C, direct reaction between intercalated lithium and the electrolyte from about 130-150°C, and cathode structural collapse with active oxygen release above roughly 180-200°C, which is what drives the final ignition and gas-venting phase. How fast a cell moves through that sequence, and how violently it ends, depends heavily on chemistry and format. A 2024 comparative review of cylindrical cells in ACS Chemical Health & Safety found a wide spread between chemistries:

Chemistry and Format	Onset Temperature	Peak Temperature	Observed Failure Behaviour
LFP 18650	220°C	243°C	Benign venting of gas and smoke; no jet flames observed
NMC622 cylindrical/pouch	140°C	up to 870°C	High flammability; jet flames spanning over 0.3 m²
NMC 21700 cylindrical	88°C	over 950°C	Risk of casing explosion from rapid internal pressure buildup
NCA 21700 cylindrical	105°C	up to 1,258°C	Separator collapse triggers rapid internal shorting and explosive combustion

The pattern holds across most reviews of the topic: LFP’s onset temperature is far higher and its failures tend to be comparatively benign, while nickel-rich NMC and NCA chemistries, chosen for their higher energy density, fail earlier and more violently. That trade-off is a big part of why chemistry selection for aerospace applications is rarely just about specific energy.

Certification, Standards and Transport

Certifying a lithium battery for flight touches several overlapping standards bodies. RTCA’s Special Committee 225 wrote DO-311A, which sets the core performance baseline (overcharge, over-discharge, external short circuit and thermal runaway containment) that the FAA and EASA both build their Special Conditions around, since existing rules such as 14 CFR Part 25.1353 were written for lead-acid and Ni-Cd batteries and don’t directly cover lithium chemistries. SAE’s AE-7D subcommittee maintains a parallel set of design and BMS standards, including SAE AS6968 for light electric aircraft charging connectors, alongside broader material and process standards from ASTM International. We cover several of these certification documents individually, including FAA TSO-179b and FAA AC 20-184A.

Crewed spaceflight works to a separate standard again: NASA’s JSC-20793, which requires at least one-fault tolerance against catastrophic hazards, and mandates a single-cell thermal runaway test, proving non-propagation to neighbouring cells, for any battery over 80 Wh built from cells with a specific energy above 80 Wh/kg.

Getting a battery onto an aircraft or spacecraft at all also means clearing transport regulation first. Lithium batteries are classed as Class 9 Dangerous Goods, and shipping one legally means passing the eight tests set out in UN 38.3: altitude simulation, thermal cycling, vibration, mechanical shock, external short circuit, crush or impact (cylindrical cells over 20mm in diameter specifically face a 9.1 kg mass dropped onto them from 61cm), overcharge, and forced discharge. Passenger-carried devices face a separate, simpler rule: EASA’s May 2025 safety bulletin caps passenger-carried portable electronics at 100 Wh without airline approval, up to a hard limit of 160 Wh, and requires spare batteries to travel in the cabin rather than checked baggage.