The Automation Core

LMR Battery Explained: GM's Gen 4 EV Platform vs LFP, Voltage Fade and the 33% Density Claim

· EV battery chemistry, GM Gen 4 EV platform, lithium manganese rich, LMR battery, LMR vs LFP, NMC, prismatic cells, The Engineering Core, Ultium Cells, voltage fade,

 


Bottom line: EV batteries have long forced a choice: LFP for cost, NMC/NCA for range. On Oct 21 at GM Forward, GM put a third option on its roadmap: the fourth-generation EV platform will run on lithium manganese rich (LMR) cells, which GM calls the world’s first production LMR battery. Below are four engineering takeaways: what changes in the cathode, why voltage fade is the real hurdle, what “20% more range per kWh” means for pack size, and what the prismatic format buys at the pack level. Vehicle consumption, pack size and mass conversions are my own assumptions and illustrative arithmetic, not GM data.

What happened: GM’s Gen 4 platform and LMR cells

  • Oct 21, GM Forward (New York): the Gen 4 platform combines LMR prismatic cells, new drive units and a central compute architecture, for roughly 20% more range per kWh. Cells come from Ultium Cells, GM’s joint venture with LG Energy Solution, in Spring Hill, Tennessee.
  • GM’s numbers: 33% more energy density than LFP at comparable cost; 40% fewer parts per drive unit; 30% less wiring; more than 300,000 battery designs simulated before the first physical prototype, and one month from first LMR pack concept to program approval.
  • Car and Driver adds: GM’s Zach Walker cited about 15% lower vehicle mass, 25% lower drag coefficient and 20% more efficient drive units, adding up to roughly 20% less battery capacity. GM gave no pack kWh, cost per kWh, launch models or dates.

LMR in one sentence: a layered-oxide cathode (same family as NMC) with extra lithium packed into the lattice and manganese replacing most of the nickel and cobalt. The extra lithium raises capacity and the manganese cuts cost; the price is a structural rearrangement on the first high-voltage charge and a slow downward drift in voltage afterwards.

Engineering point 1: the LMR recipe trades nickel and cobalt for manganese

GM’s own comparison is blunt: a typical high-nickel cell is roughly 85% nickel, 10% manganese, 5% cobalt; its LMR cell is about 35% nickel, 65% manganese, virtually no cobalt (TechCrunch and WIRED quote ranges of 60–70% Mn, 30–40% Ni, 0–2% Co). Manganese is cheaper and more plentiful than nickel or cobalt, which is how GM can claim LFP-like cost. On energy, GM says 33% above LFP, and Car and Driver describes it as close to today’s NMCA. In other words, LMR aims to sit between LFP and high-nickel and take the best of both. GM has not said whether the 33% is gravimetric or volumetric, which matters for the math below.

Engineering point 2: voltage fade, the decade-old blocker

LMR’s extra capacity comes from the Li₂MnO₃ component of the lattice. The US DOE “Deep Dive” review describes the first charge in stages: lithium leaves the conventional layered regions around 4 V, and above about 4.45 V the Li₂MnO₃ domains activate, with oxygen taking part in the redox. Argonne’s synchrotron work saw lattice strain and oxygen release at about 4.46 V. After activation, manganese migrates into the lithium layer, local ordering shifts to lower-energy sites, and the discharge voltage sags a little every cycle. A 2017 modelling paper argued fade must get down to around 0.1 mV per cycle for transportation use and suggested capping the upper cutoff below about 4.6 V. GM says proprietary dopants, surface coatings, particle engineering and process changes solved it, with life matching current high-nickel cells, but no public cycling curves exist yet to check that.

Engineering point 3: what 20% more range per kWh does to pack size

“20% more range per kWh” and “20% less battery” are not quite the same. For the same range you need 1 ÷ 1.2 ≈ 0.83 of the energy, about 17% less; the “roughly 20%” figure is rounded. An example with my own assumptions: a midsize crossover targeting 300 miles at 3.3 mi/kWh needs about 91 kWh; with a 20% efficiency gain it needs about 76 kWh. Stack LMR’s 33% density advantage over LFP on top (assuming it is gravimetric) and cell mass for the same energy is 1 ÷ 1.33 ≈ 0.75. Multiply the two and you get about 0.63: cell mass could be more than a third lower than a same-range LFP design at today’s efficiency. That ignores pack structure, cooling and safety margins.

Engineering point 4: prismatic cells strip out modules and parts

Today’s Ultium packs use pouch cells; LMR moves to prismatic hard-case cells. GM said in 2025 that prismatic cells cut module components by 75% and total pack components by 50%, lowering the share of inactive material. The rigid can carries some of the structural and swelling loads, so the pack needs fewer brackets and compression pads. The BMS gets new homework too: layered-oxide discharge curves already slope more than LFP’s, which makes voltage-based state-of-charge estimation easier, but if the curve drifts down with age, the SOC-OCV lookup has to be corrected over life or the range estimate will degrade (my engineering inference).

Open questions

  • No pack kWh, cost per kWh, cycle-life curves or independent voltage-fade tests have been published.
  • First application is reported differently: Car and Driver says full-size electric trucks first, InsideEVs quotes a spokesperson pointing to crossovers, and Bloomberg mentions a mainstream EV SUV in about three years.
  • Whether the 33% is gravimetric or volumetric is unstated; my 3.3 mi/kWh, 300-mile and 0.63× mass figures are assumptions.

Related videos: NMC, LFP and EV battery cost

NMC vs LFP explained video thumbnail, the baseline for comparing LMR battery chemistry

Your call: if a 2028 EV used LMR, cost about the same as an LFP car and went 20–30% farther, would you buy it, or wait for 100,000 km of voltage-fade data and stick with proven LFP? Tell me in the comments.

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