Lithium-sulfur batteries promise more than double the energy density of today's best lithium-ion cells, using sulfur, one of the most abundant elements on Earth, instead of the cobalt and nickel that make conventional batteries expensive and geopolitically fraught. The chemistry has been known for decades. What's changed in 2025 and 2026 is that commercial cells are finally shipping. Lyten , the San Jose-based company leading commercialization, has already delivered lithium-sulfur cells for drone and defense applications. The company acquired Northvolt's Swedish gigafactory assets in February 2026 and is planning the world's first lithium-sulfur gigafactory in Nevada. This article explains how lithium-sulfur batteries work, why the chemistry is compelling, what the engineering challenges are, and where the technology stands today. AI-generated image Lithium-sulfur pouch cell — the format Lyten ships for drone and defense applications. Credit: AI-generated How Lithium-Sulfur Batteries Work A lithium-sulfur (Li-S) cell uses a sulfur-based cathode and a lithium metal anode. During discharge, lithium ions travel from the anode through the electrolyte to the cathode, where they react with sulfur to form lithium polysulfides, then lithium sulfide (Li2S). The reaction runs in reverse during charging. 313 Wh/kg Lyten Cell Energy Density (C/3 rate) 600 Wh/kg Theoretical Potential at Maturity 50% Weight Reduction vs. NMC 0 Cobalt, Nickel, Manganese, Graphite 500+ Wh/kg Sion Power Licerion (Li-metal, drone) 2027 Lyten Nevada Gigafactory Target Compared to lithium-ion's theoretical maximum of around 200-300 Wh/kg at the cell level, lithium-sulfur's theoretical ceiling is roughly 2,600 Wh/kg (based on the mass of active materials alone). Practical cells won't approach that ceiling because the electrolyte, current collectors, separator, and packaging all add mass. But even at 30-40% of theoretical performance, Li-S cells would roughly double what lithium-ion can achieve. The cathode material is sulfur itself, either in elemental form or as a sulfur composite. Lyten uses 3D graphene , a proprietary carbon scaffold, to host the sulfur particles and improve conductivity and cycle stability. Sulfur is a byproduct of petroleum refining and natural gas processing, making it extremely cheap, roughly sh.10 per kilogram, compared to the cobalt at 0+ per kilogram or nickel at 0+ per kilogram used in NMC cathodes. Why the Anode Matters Lithium-sulfur cells use a lithium metal anode rather than the graphite anode in most lithium-ion cells. Lithium metal has roughly 10 times the theoretical capacity of graphite (3,860 mAh/g vs. 372 mAh/g). But lithium metal is reactive, prone to forming dendrites (needle-like structures that can pierce the separator and cause short circuits), and difficult to handle in manufacturing. Managing the lithium metal anode is the central engineering challenge that separates promising lab results from durable commercial cells. The Polysulfide Shuttle: The Chemistry's Biggest Problem Lithium-sulfur batteries have been known since the 1960s. The reason they have taken 60 years to reach commercialization comes down to one fundamental issue: the polysulfide shuttle. When sulfur reacts with lithium during discharge, it passes through a sequence of intermediate compounds called lithium polysulfides (Li2Sx, where x is 4 to 8). These polysulfides are soluble in the liquid electrolyte. That means they dissolve out of the cathode, drift across the cell, and react with the lithium anode. The process is self-defeating: sulfur slowly migrates out of the cathode and gets consumed at the anode, causing rapid capacity fade. A cell that performs well on the first few cycles can lose 50% of its capacity within 100 cycles. Several approaches exist to suppress the polysulfide shuttle: • Cathode architecture: Confining sulfur inside porous carbon structures (like Lyten's 3D graphene) that physically trap polysulfides near the cathode, limiting dissolution. • Electrolyte engineering: Using electrolyte compositions that reduce polysulfide solubility or promote protective surface films on the lithium anode. • Solid-state electrolytes: A solid electrolyte physically blocks polysulfide migration. Some solid-state Li-S designs show dramatically improved cycle life, though solid-state manufacturing adds its own complexity. • Separator modifications: Coating the separator with materials that chemically block polysulfide passage while allowing lithium ion transport. • Anode protection: Coating the lithium metal anode with artificial SEI (solid electrolyte interphase) layers that resist polysulfide attack and dendrite formation. Lyten's commercial cells achieve adequate cycle life for drones and defense applications, where missions are measured in dozens of cycles rather than thousands. The automotive and grid storage markets, which require 500-1,500 cycles minimum, remain the medium-term target as cycle life improves. Who Is Building Lithium-Sulfur Batteries AI-generated image Battery gigafactory-scale production is the next frontier for lithium-sulfur commercialization. Credit: AI-generated Company Technology Energy Density Status (2026) Lyten Li-S with 3D graphene cathode 313–362 Wh/kg Shipping (drones, defense) Sion Power Li-metal (Licerion platform) >500 Wh/kg Shipping Q3 2026 (mil. drones) OXIS Energy Li-S polymer electrolyte 350–450 Wh/kg Development (aviation focus) NexTech Li-S with ceramic separator 280–320 Wh/kg Pilot production Lyten's February 2026 acquisition of Northvolt's Swedish assets, including the Skellefteå Northvolt Ett facility with 16 GWh of manufacturing capacity, was a significant strategic move. The facility will initially produce lithium-ion NMC cells for commercial sale in the second half of 2026, while Northvolt Labs transitions to industrializing Lyten's Li-S chemistry at gigascale. The Nevada Li-S gigafactory, targeting a 2027 opening with more than billion in planned investment, would be the first facility in the world manufacturing lithium-sulfur cells at that scale. Sion Power operates from a different direction. Their Licerion platform uses a lithium metal anode (like Li-S, but with a conventional high-voltage cathode) and has demonstrated more than 800 cycles with energy densities above 500 Wh/kg. In April 2026, they launched the Licerion Strike (primary, non-rechargeable) and Echo (rechargeable) cells for military drone applications, with shipments beginning Q3 2026. These cells offer more than 50% higher energy density than advanced lithium-ion while reducing weight by about 30%. Where Lithium-Sulfur Fits: Applications by Readiness Not every application needs the same cycle life. The commercialization path for Li-S follows market segments in order of their cycle life requirements, starting with the most forgiving. Drones and UAVs (Now) Military and commercial drones typically fly fewer than 100 missions before maintenance or replacement. Li-S's 200-500 cycle life is adequate. The weight reduction (50% vs. NMC) directly extends range or payload capacity, which is mission-critical. Lyten is shipping here today. Defense and Space (Near-term) Satellites, missiles, and specialized military equipment use batteries in controlled environments with defined cycle counts. Weight is at a premium and cost tolerance is high. Both Lyten and Sion Power target this segment. Electric Aviation (Medium-term) Electric aircraft demand the highest possible energy density at cell level. Li-S at 400-600 Wh/kg could make regional electric aviation viable where lithium-ion at 250-300 Wh/kg falls short. Cycle life requirements for commercial aircraft (2,000+ cycles) are the limiting factor. Electric Vehicles (Longer-term) EV buyers expect 8-year/100,000-mile warranties requiring 1,000+ cycles. Li-S must close the cycle life gap significantly before competing with NMC or LFP in passenger vehicles. The economic case improves if sulfur's cost advantage flows through to pa