On September 29, General Motors (GM) announced that Ultium Cells, its joint venture with LG Energy Solution, plans to produce lithium manganese-rich (LMR) prismatic battery cells at its Spring Hill, Tennessee, plant. Retooling of the plant will begin in 2026 and is expected to be completed in 2028.
GM's aim is to use more of the relatively inexpensive metal manganese to balance the driving range and battery cost of electric vehicles (EVs). The announcement gives a specific production site to the commercialization plan the company presented in 2025. However, the energy density figure GM cites, the durability confirmed in research cells, and the plant's mass-production schedule each refer to different subjects and conditions.
Spring Hill plant to be retooled for 2028 mass production
In May 2025, GM and LG Energy Solution announced they would commercialize LMR prismatic cells for future electric trucks and large SUVs. At the time, they set a goal of starting commercial production in the United States by 2028, with preliminary production at an LG Energy Solution facility from the second half of 2027.
The U.S. mass-production site has now been chosen: Spring Hill, near Nashville. The 2028 target has not been moved up; the existing commercialization plan has simply advanced to concrete plant retooling.
GM expects the site to become the world's first plant to commercially mass-produce LMR prismatic cells. The company plans to hire 500 new workers for the retooling, in addition to the roughly 1,200 people currently employed there. Completion of the retooling in 2028 does not mean that vehicles equipped with LMR batteries will go on sale that year. The announcement did not specify which models will use the batteries or when they will launch.
The investment plan also includes a separate battery business that is already under way. According to Ultium Cells' announcement, the Spring Hill plant has been producing lithium iron phosphate (LFP) cells for stationary energy storage systems since June 2026. These are supplied to LG Energy Solution Vertech customers and should be distinguished from LFP cells for EVs.
The combined investment in the two businesses, LMR and stationary LFP, plus facility improvements is planned to reach $1 billion by 2030. The State of Tennessee has also announced an additional $1 billion investment, but based on Ultium Cells' explanation, the full amount is not dedicated solely to LMR. A breakdown by business has not been disclosed.
Spring Hill will thus prepare to mass-produce new batteries for EVs while also producing stationary storage batteries. The aim is also to make it a plant that can serve multiple types of demand rather than being tied to a single battery chemistry or application.
The key to exploiting cheap manganese: controlling oxygen reactions
LMR is a battery chemistry that raises the proportion of manganese in the cathode material to reduce reliance on expensive nickel and cobalt. "Prismatic," on the other hand, refers to the cell's shape. The chemistry and the cell format are separate elements, and GM is trying to change not just the materials but also the structure of the cells and battery packs.
In its December 2024 announcement of the extended partnership between GM and LG Energy Solution, GM explained that prismatic cells can use space inside a battery pack efficiently and may reduce weight and cost by cutting the number of modules and mechanical parts. The idea is to combine LMR, which keeps material costs down, with prismatic cells, which make it easier to simplify pack structure.
However, adding more manganese does not automatically produce a high-performance battery.
In LMR, the cell draws out more energy by using not only transition metals such as nickel but also the oxygen in the cathode material for redox reactions. But if oxygen oxidized during charging does not return sufficiently to its original state during discharge, it can lead to structural degradation inside the material and gas generation.
In large cells in particular, the internal space available to hold gas is relatively small compared with the cell's capacity. The problem of rising internal pressure from generated gas damaging cell life and stability therefore becomes more serious.
To address this, a research team from LG Energy Solution and Seoul National University reexamined both charging and discharging conditions. Research introduced by LG on September 7 showed that, in addition to lowering the upper voltage limit during charging, setting a lower end-of-discharge voltage allows oxidized oxygen to be reduced more fully. What matters is not only how far oxygen is oxidized during charging but also how far it is returned to its original state after discharge.
In a peer-reviewed paper published in Nature Communications on August 4, Munsoo Song and colleagues also optimized the conditions for the initial charge-discharge process (formation), which activates large cells after manufacturing.
For 40Ah-class cells, they confirmed that adopting relatively mild formation conditions of 35°C and 2.00–4.55V suppressed gas generation compared with conventional conditions. The result shows that not only the material composition but also the formation process in the factory and the subsequent charge-discharge conditions affect LMR lifespan.
"33% higher density," "92.2% after 883 cycles," and "2028" are different numbers
The "33% higher energy density than LFP" that GM cites, the "92.2% retention after 883 cycles" confirmed in research cells, and the "commercial production in 2028" each mean something different. They cannot be treated as proven performance of the same mass-produced battery.
Separating who presented each figure, and for what subject, gives the following.
| Figure / timing | Source and subject | What it shows and under what conditions |
|---|---|---|
| 33% higher energy density than LFP | GM and LG Energy Solution, LMR prismatic cells under development | The May 2025 announcement said the cells would deliver 33% higher energy density than high-performance LFP-based cells at comparable cost. The model of the comparison cell and the absolute energy density have not been disclosed |
| 92.2% of initial energy retained after 883 cycles | Seoul National University and LG Energy Solution, 40Ah-class pouch cell | Long-term test at 25±1°C with 0.33C charge and discharge. Final charge-discharge voltage range of 4.25–2.00V |
| 2028 | GM and Ultium Cells, U.S. production plan | The commercial production start target announced in 2025, and the expected completion of Spring Hill retooling announced in 2026. Separate from the launch timing of vehicles with LMR |
Sources: GM's 2025 announcement, GM's 2026 announcement, Nature Communications paper. The table is not meant to compare which performs better, but to clarify what each figure means.
For GM's 33% comparison, the announcement does not specify whether it refers to gravimetric (per weight) or volumetric (per volume) energy density. The conditions used to calculate cost have not been disclosed either, so the figure cannot be used for a strict performance comparison with other companies' cells, or to convert it into a claim such as "real-world vehicle range increases by 33%."
The 92.2% durability figure, meanwhile, is the retention rate relative to the energy that could be extracted at the start of the test. The values given in the paper of 663Wh/kg initially and 612Wh/kg after 883 cycles are also specific energy calculated on the basis of the mass of the cathode active material, not the energy density of the entire cell including the casing and anode.
The LMR cathode material used in the test also contains 0.27 wt% cobalt, so it is not completely cobalt-free.
Scaling cells up to the 40Ah class and tackling the problems of gas generation and lifespan is significant for the practical use of automotive batteries. However, the cells tested were pouch cells with a flexible casing. Because this is not the same design as the prismatic cells GM plans to mass-produce, the test results alone cannot be used to judge lifespan in actual vehicles, including fast charging and cold-weather conditions.
Whether EV prices fall depends on mass-produced cells
GM names electric trucks and full-size SUVs as the first applications for LMR. For vehicles that need large-capacity batteries, being able to cut pack costs while securing sufficient energy leaves more room to hold down vehicle prices.
The 2025 announcement said the company aimed for a range of more than 400 miles (about 644 km) in electric trucks using LMR. This is a future development goal, not a certified range for a mass-produced vehicle equipped with LMR.
GM will also continue to use high-nickel batteries. The latest announcement again explains that high-nickel batteries will remain the option offering the longest range in its lineup.
LMR's role is not to replace high-nickel chemistry and aim for top performance in every EV. It is to pursue higher performance than LFP using relatively inexpensive materials, so that batteries with different balances of price and range can be chosen for each vehicle.
Judging whether that aim is achieved will require the absolute energy density of the mass-produced prismatic cells and the actual cost of battery packs built from them. Even if a single cell achieves high energy density, the effect changes at the level of the battery pack, including cooling systems and safety measures, and the vehicle as a whole.
Which models the retooled Spring Hill plant will supply with LMR cells, and what range and price those vehicles will actually achieve, remain to be seen. Only once that is known can LMR's real value to GM's EV strategy be assessed.
If the plant plans for 2028 move forward, the control of oxygen reactions and gas generation demonstrated at the research stage can be reproduced in mass-produced cells, and vehicle-level validation then leads to cost reductions, GM could offer lower-priced options even for large EVs that demand long range.