Production hit 1 terawatt-hour in 2024. Half a billion EVs run on lithium cells. Consumer devices number in the billions. Since Sony shipped the first commercial unit in 1991, energy density tripled while costs dropped tenfold.
Forget the mental model of batteries as fuel tanks that "empty out." Lithium cells work through intercalation, a process where ions wedge themselves between atomic layers of electrode materials, then pull back out. No chemical bonds break permanently. Nothing dissolves or precipitates. The host structures remain intact across thousands of cycles.
Voltage per cell sits around 3.7V, versus 1.5V from alkalines. Whittingham figured out the intercalation electrode concept in the 1970s at Exxon. Goodenough developed lithium cobalt oxide cathodes at Oxford in 1980. Yoshino at Asahi Kasei added carbonaceous anodes. All three split the 2019 Nobel in Chemistry.
Four components. The anode, typically graphite, hosts lithium during the charged state. Carbon's layered crystal structure leaves gaps between graphene sheets where Li+ ions slot in without forcing permanent expansion. Silicon-carbon composites now appear in premium cells, pushing capacity gains around 30% over pure graphite. Adoption numbers vary by source, but IEA tracking suggests somewhere between 15-25% of new production uses silicon blends.
Cathodes determine most performance characteristics. The original lithium cobalt oxide still powers many phones and laptops. Lithium iron phosphate trades some energy density for thermal stability and longer cycle life. Chinese EVs and stationary storage favor it. NMC formulations (nickel-manganese-cobalt) dominate the high-end EV market. Manufacturers keep pushing nickel content higher; some 2025 production lines run NMC 9-0.5-0.5 compositions.
Between electrodes: electrolyte. Lithium hexafluorophosphate dissolved in carbonate solvents, usually. Conducts ions, blocks electrons. The stuff burns. Toyota, QuantumScape, and dozens of startups keep chasing solid-state alternatives for exactly that reason.
Separators get less attention but matter enormously. A 20-25 micron polymer membrane keeps electrodes from touching while letting ions through. Polyethylene, polypropylene, sometimes ceramic-coated. When separators fail, cells short internally. Fires start.
Copper foil backs the anode; aluminum backs the cathode. These current collectors feed electrons to external circuits.
Pull current from a lithium cell and oxidation kicks off at the anode. Lithiated graphite (written LiC6 in the literature) gives up lithium atoms. Each atom loses an electron, becoming Li+. Electrons can't cross the electrolyte. They route through whatever device draws power, then arrive at the cathode. Meanwhile, lithium ions drift through the electrolyte and insert themselves into the cathode structure.
Plug in a charger and voltage reversal forces the process backward. Cathode material releases ions; they migrate to the anode and recombine with electrons arriving through the external circuit.
Flat discharge curves distinguish lithium chemistry from older types. Lead-acid voltage sags continuously during use. Lithium cells hold 3.0-3.7V across most of their capacity range, dropping off sharply only near empty. Devices get consistent power until the battery dies.
Speed matters. Push too much current and ion migration can't keep pace. Lithium plates onto the anode surface as metal rather than intercalating properly. Dendrites form. They can puncture separators. Thermal runaway follows. Battery management systems exist largely to prevent such scenarios, tracking voltage, current, and temperature cell-by-cell.
Atomic number 3. Three protons, three electrons. Lowest density of any metal at 0.534 g/cm³. Standard electrode potential of -3.04V versus hydrogen reference, the most negative among practical options.
Small ionic radius (76 pm) lets Li+ slip between electrode layers without cracking host structures. Sodium ions measure 102 pm; they cause more mechanical stress during cycling. Magnesium carries double the charge, complicating insertion chemistry.
Lithium scarcity relative to sodium or iron raises supply chain concerns. But physics wins: nothing else matches the energy-to-weight ratio.
Two different metrics that get confused constantly.
Energy density (Wh/kg) measures total storage capacity per unit mass. Current commercial cells land in the 250-300 Wh/kg range. Lab prototypes with silicon anodes and high-nickel cathodes push toward 400 Wh/kg. Lead-acid manages 30-50 Wh/kg. Fine for car starters, hopeless for EVs.
Power density (W/kg) measures discharge rate capability. How fast can stored energy come out? Lithium delivers 200-400 W/kg sustained, with pulse capability exceeding 1,000 W/kg.
EV acceleration needs both. Grid storage prioritizes energy density; discharge happens over hours, not seconds. Power tools need burst capability. Phones mostly care about energy density within tight volume constraints.
Chemistry selection follows application requirements. LFP sacrifices energy density for longevity and safety. High-nickel NMC maximizes range. Lithium titanate anodes enable extreme cycle life and fast charging but cut energy density roughly in half.
Consumer electronics came first. Laptops and phones drove early adoption through the 1990s and 2000s. Modern smartphones pack 10-20 Wh; laptops run 50-100 Wh.
EVs now dominate demand growth. Tesla's 4680 cells use silicon-carbon anodes and tabless electrode designs. Pack-level energy density exceeds 300 Wh/kg in some configurations. NIO claims over 1,000 km range with semi-solid battery packs rated at 360 Wh/kg. Skepticism warranted on manufacturer range claims, but the trend line points upward.
Grid storage scaled rapidly after 2020. Tesla Megapacks store 3.9 MWh per unit. California runs over 3 GW of battery capacity for evening peak shaving when solar drops offline.
Power tools abandoned NiCd for lithium through the 2000s. Runtime improved 40%, weight dropped 30%. No memory effect to worry about.
Medical implants, satellites, Mars helicopters. Anywhere weight matters and reliability counts.
Solid-state remains the holy grail. Replace flammable liquid electrolyte with ceramic or polymer solids. Toyota targets pilot production around 2026, mass manufacturing by 2030. QuantumScape claims 80% charge in 15 minutes with their lithium-metal architecture. Promises have circulated for years; manufacturing at scale remains unproven.
Semi-solid designs ship now. NIO and BMW both have production vehicles running gel-type electrolytes. Safer than pure liquid, easier to manufacture than pure solid.
Cobalt reduction continues. Ethical sourcing concerns around DRC mining push manufacturers toward cobalt-free cathodes.
Sodium-ion entered commercial production. CATL and BYD both ship cells. Energy density around 160-200 Wh/kg, competitive with LFP, cheaper to manufacture, abundant raw materials. Volkswagen announced trials for entry-level models.
Recycling infrastructure finally exists at scale. Redwood Materials, Li-Cycle, and others recover 95%+ of lithium, nickel, and cobalt through hydrometallurgical processes.
Lithium cells store significant energy in compact volumes. Organic electrolytes burn. Multiple protection layers exist.
Battery management systems monitor every cell continuously. Voltage limits prevent overcharge (which plates lithium metal) and overdischarge (which dissolves copper current collectors). Temperature monitoring catches thermal excursions early.
Current interrupt devices physically disconnect cells if internal pressure spikes. Vents release gas rather than letting cells rupture explosively. PTC elements increase resistance as temperature rises, limiting current flow.
Separators incorporate shutdown mechanisms. At threshold temperatures around 130°C, pore structures collapse deliberately, halting ion transport. The cell dies but doesn't catch fire.
Active thermal management keeps cells in their comfort zone, roughly 20-35°C for best performance and longevity. Liquid cooling runs through EV packs; phase-change materials provide passive buffering.
When everything fails, module-level containment prevents propagation. Fireproof barriers between cell groups. Aerosol suppression systems. The goal: predictable failure modes rather than explosive disintegration.
LFP chemistry offers inherently better thermal stability than cobalt-based alternatives. Phosphate-oxygen bonds resist breakdown. Many manufacturers accept lower energy density in exchange for reduced fire risk.
