What are structural batteries, and could they replace battery packs?

What a structural battery is

A structural battery is a device that stores electrical energy and bears mechanical loads at the same time (Chaudhary et al., 2024). Whether a structure that also stores energy saves weight in a finished product is a separate question, covered below.

How it works

The papers cited here all come from Leif Asp's group at Chalmers University of Technology in Sweden and its collaborators. Their designs use carbon fibre in two roles: as part of the battery and as the reinforcement that carries load.

In the group's earlier laminated design, carbon fibres act as both the active material and the reinforcement in the negative electrode, while the positive electrode is lithium iron phosphate particles bonded to aluminium foil. A 2025 modelling study simulates this design (Larsson et al., 2025).

The 2024 design replaced the foil. It uses plain carbon fibre as the negative electrode, carbon fibre coated with lithium iron phosphate as the positive electrode, and a thin cellulose separator between them. All components are embedded in a structural battery electrolyte and cured into a rigid composite. The authors credit the thin separator with raising energy density (Chalmers research record for the 2024 paper). Chalmers says the electrolyte in this design is semi-solid rather than liquid (Chalmers news, September 2024).

What has been demonstrated

The first two items below are laboratory cells reported in peer-reviewed papers. The third is a peer-reviewed computer model, included for completeness; it is not a measurement.

• 2024 cell, lithium iron phosphate. The Advanced Materials paper on an all-carbon-fibre structural battery, published online on 10 September 2024 (Chaudhary et al., 2024), reports an energy density of 30 Wh/kg, an elastic modulus above 76 GPa when tested along the fibre direction, and cyclic stability for up to 1,000 cycles at about 100 percent Coulombic efficiency (Chalmers research record). The abstract gives no capacity retention figure or test conditions for the cycling result.
• 2025 cell with an NMC111 cathode. The Composites Part B paper reports a full cell with plain carbon fibre as the negative electrode and carbon fibre coated with lithium nickel manganese cobalt oxide (NMC111) as the positive electrode. It reports 187 Wh/kg with a liquid electrolyte and 84 Wh/kg with a structural battery electrolyte (Chalmers research record). The abstract does not state the mass basis for either figure, so the numbers cannot be compared with others without checking the full paper.
• 2025 model. The npj Computational Materials paper models the laminated design and reports that it captures the general trend of measured voltage profiles across a range of charge rates (Chalmers research record). It uses a simplified representation of the positive electrode, and parameters not available from experiments were calibrated against measured charge and discharge curves at two rates (Larsson et al., 2025).

What is only reported

In a news article dated 24 June 2025, Chalmers reported that an ongoing study had produced structural battery composites with an energy density of over 60 Wh/kg and an elastic modulus of over 100 GPa (Chalmers news, June 2025). The article does not link these figures to a paper or dataset. It lists two recent publications, but does not say either reports them. Treat them as reported, not demonstrated, until a paper with a stated mass basis is available.

What is speculative

In September 2024, Leif Asp said the group had made calculations showing that electric cars could drive up to 70 percent further than today if they had competitive structural batteries (Chalmers news, September 2024). The article does not describe the calculation method, assumptions or baseline, and it depends on structural batteries becoming competitive, so it is a projection, not an observed range increase.

The 2024 Advanced Materials paper says structural batteries could replace structural parts of electric vehicles and reduce the number of conventional batteries, offering mass savings (Chaudhary et al., 2024). In the same Chalmers article, Asp suggested that very thin phones or lighter laptops may be the nearest uses, and that electronics in cars or planes could one day be powered by structural batteries (Chalmers news, September 2024). These are expectations. The sources read for this article describe no built product, vehicle or aircraft that uses a structural battery.

Limits and open problems

Energy density. The 2025 figures show the trade-off plainly. Moving from a liquid electrolyte to a structural battery electrolyte in that cell lowered the reported energy density from 187 Wh/kg to 84 Wh/kg (Chalmers research record for the 2025 cell). The 2024 cell's 30 Wh/kg is lower still. The mass basis is not stated, and a cell-level figure does not show that a full product is lighter.

Power delivery. Chalmers states that getting high power through the semi-solid electrolyte used in its 2024 design is challenging, and that more research is needed (Chalmers news, September 2024).

Manufacturing. Chalmers also says a lot of engineering work remains before the cells move from small-scale lab manufacturing to large-scale production (Chalmers news, September 2024).

Durability and safety. The sources read for this article do not report results on ageing, fatigue or impact damage while a load-bearing cell is charged and discharged. In June 2025 a Chalmers researcher said the group is investigating how mechanical stress affects battery performance (Chalmers news, June 2025). The sources also do not cover how a damaged cell behaves in a crash or fire, how it can be isolated, or how fibres, resin and electrolyte can be recycled together. These are open questions.

What to watch next

• The full paper behind the over 60 Wh/kg and over 100 GPa figures, with its mass basis and test conditions stated. Chalmers described this study as ongoing in June 2025; it may have been published since.
• Cycling and damage tests on cells that carry mechanical load while charging and discharging.
• Power delivery with structural electrolytes, which Chalmers names as a weak point of the 2024 design.
• Whole-product mass comparisons that count protection, wiring and support, not just cell energy density.

Until those arrive, a structural battery is best read as a laboratory material with measured cell results, not a replacement for battery packs.