Highlights

  • Li-S Energy's 10 Ah lithium-sulfur cells have successfully completed repeated pressure cycles simulating dives to 1,000 metres depth in testing conducted at the company's Battery Testing Centre in Geelong in collaboration with UK undersea systems specialist MSubs.
  • No mechanical damage, swelling, leakage, or mass loss was observed in the cells following testing, and cell voltage remained stable throughout the pressure cycles and for 24 hours after completion, demonstrating structural integrity under extreme pressure conditions.
  • MSubs, which has developed extra-large uncrewed underwater vehicle platforms for the UK Ministry of Defence and US Navy, expressed satisfaction with the results and confirmed its intention to continue the assessment process with Li-S Energy.
  • Agreed next steps include pressure testing at greater depths, charging as well as discharging at depth, and thermal operating profile testing, with the ultimate goal of trialling a Li-S Energy battery pack on an actual dive mission in open water.

Li-S Energy Limited (ASX:LIS) is an ASX-listed Australian battery technology company developing lithium-sulfur cells designed to offer materially higher energy density than conventional lithium-ion batteries. Its cells are targeted at applications where weight is critical, including aerospace, drones, and defence platforms. On 5 November 2026, the company announced a significant milestone in its collaboration with MSubs Limited, a UK-based designer and manufacturer of crewed and uncrewed underwater vehicles: its 10 Ah lithium-sulfur pouch cells had successfully completed repeated pressure testing simulating dives to 1,000 metres depth — equivalent to 100 bar of pressure — with no damage, mass loss, or voltage instability observed.

The Test Programme and Its Results

The testing was conducted in an MSubs pressure vessel commissioned at Li-S Energy's Battery Testing Centre in Geelong, with the programme designed to evaluate whether the cells could withstand the extreme pressure conditions encountered by uncrewed underwater vehicles operating at significant depths. The test protocol cycled cells from surface pressure to the pressure equivalent of 1,000 metres depth and back to the surface, simulating a repeated porpoising dive profile. Cells were tested at different states of charge, both under open-circuit conditions and while delivering the propulsion discharge current representative of an extra-large UUV's main drive.

The results were described as a complete success. All cells completed their assigned pressure profiles. Visual inspection confirmed no mechanical damage, swelling, or leakage following testing, and measurement confirmed no mass loss. Cell voltage remained stable throughout every pressure cycle under both open-circuit and discharge conditions, and the open-circuit voltage continued to remain stable for 24 hours and beyond after testing, confirming that no internal damage had occurred. The discharged cells recovered normally to their equilibrium voltage once discharge stopped. MSubs' engineering director confirmed the company was very pleased with the outcome and expressed confidence in continuing the qualification process.

Why This Matters for the UUV Market

The uncrewed underwater vehicle market is growing rapidly, driven by defence procurement programs in Australia, the United Kingdom, and the United States, alongside commercial applications in subsea inspection, offshore energy, and seabed survey. These platforms place demanding requirements on their battery systems — combining energy density, weight, and pressure tolerance in ways that conventional lithium-ion technology addresses imperfectly. Standard lithium-ion cells require heavy pressure containment vessels or extensive buoyancy compensation when used at depth, adding weight and complexity to UUV designs.

Li-S Energy's cells offer approximately twice the energy density of lithium-ion and are characterised by near-neutral buoyancy, meaning they do not require the same heavy containment systems. The successful pressure testing demonstrates that the cells can operate at ambient pressure in a water-filled vehicle at 1,000 metres depth — a key capability requirement for large UUV platforms. The company noted that Australia alone committed A$1.7 billion to its Ghost Shark extra-large UUV programme in 2025, and similar procurement programs are underway in the UK and US, with MSubs' XV Excalibur already delivered to the Royal Navy.

Key Takeaways

Li-S Energy's 1,000-metre pressure test success represents a technically significant milestone for the company's efforts to access the defence and commercial UUV market. By demonstrating that its cells can withstand the pressure of repeated simulated deep dives while maintaining voltage stability and structural integrity, the company has cleared a major qualification gate that opens the door to further testing and ultimately a trial battery pack on an actual dive mission. The MSubs relationship, given that company's direct customer relationships with the UK MoD and US Navy, positions Li-S Energy to compete for a share of a defence procurement market that is growing with each new national UUV programme. The progression through subsequent qualification steps — greater depths, charging at depth, thermal profiles, and open-water trials — will be the milestones investors follow over the coming quarters.