Force and Pressure Sensors Could Give EV Batteries an Early Warning Voice

Electric vehicle batteries already report their voltage, current and surface temperature to the battery management system, yet these familiar signals can miss what is happening mechanically inside a pack as it ages or heads toward failure. A mini review published in Frontiers in Mechanical Engineering argues that expansion force and pressure sensing deserve a place alongside the conventional measurements, treating the mechanical response of a cell as a complementary observable rather than an afterthought. The authors, a team from Shandong Huayu University of Technology in China, link reversible swelling, irreversible deformation, gas generation and casing response to the electrochemical and thermal processes that drive them, and then assemble published results into a review-level framework for mechanics-aware battery management.

The physical logic is straightforward. As lithium ions move in and out of electrode materials during charging and discharging, the active particles swell and contract, so a free-standing cell expands and shrinks with state of charge. When that cell is constrained inside a module, the same motion registers as a measurable force against the surrounding structure. The review integrates established effective-stiffness approximations to connect free cell expansion to constrained force, and it separates the contributions that overlap in a single force trace: reversible, state-of-charge-dependent behavior, state-of-health-related baseline drift and hysteresis, gas-related anomalies, thermal effects, and slow viscoelastic relaxation of cell materials.

That separation matters because each mechanism unfolds on a different timescale. Reversible swelling tracks charge and discharge within seconds to minutes, aging shifts the force baseline over weeks and months, gas generation during abnormal reactions produces sharp deviations, and viscoelastic relaxation creeps along over hours. The authors outline a conceptual timescale-separated mechanics-residual framework that coordinates independent normal-force prediction, force-assisted state-of-charge estimation, slow aging-related updates, and rapid anomaly detection, so that each process is attributed to the signal component it actually causes. The framework is explicitly conceptual: the review states that it requires further experimental validation across cell formats, operating conditions and mechanical constraints before it can be considered proven.

The quantitative case for adding mechanical sensing rests on published studies that the review surveys. Electrical-mechanical sensor fusion, in which force or expansion data are combined with the usual voltage and current measurements, has reported state-of-charge estimation errors of approximately 3 percent or lower. For state of health, the review cites SOH errors below 1.5 percent in representative datasets. These figures come from the studies the authors examined, not from a single new experiment, and the review frames them as evidence that mechanical observables add information that electrical measurements alone do not fully capture.

Safety is where the mechanical channel may prove most distinctive. Under specific abuse conditions, swelling and strain-rate measurements have provided thermal-runaway warning lead times ranging from hundreds of seconds to more than 1,000 seconds, according to the published work the review compiles. A warning window measured in hundreds of seconds or more is a meaningful margin for a battery management system to intervene, derate the pack or alert the vehicle, compared with signals that may only register once a failure is already underway. The review is careful to scope this claim: the lead times apply under the specific abuse conditions tested in those studies, not to every failure mode in every cell format.

To position force sensing fairly, the authors examine strain sensing, optical-fiber sensing and ultrasonic sensing as benchmark technologies. Each offers complementary capabilities and limitations. Strain gauges measure deformation at specific points, optical fibers can distribute measurement along their length, and ultrasonic methods probe internal structure through the cell. The comparison is not a ranking but a map of what each technique observes, so that a mechanics-aware battery management system could combine mechanical observables according to the geometry, cost and failure modes relevant to a given pack design.

The review’s starting premise is that conventional battery management systems rely primarily on voltage, current and surface temperature, potentially overlooking mechanical signatures of degradation and incipient failure. Surface temperature, in particular, lags the internal thermal state of a large cell, and electrical signals can be confounded by aging, temperature and load simultaneously. Expansion force, by contrast, responds directly to the physical processes inside the cell, which is why the authors treat it as a complementary observable rather than a replacement for the existing measurement set.

Because this is a mini review, its contribution is synthesis rather than new measurement. The authors relate the mechanical phenomena to electrochemical and thermal processes, integrate the effective-stiffness approximations that connect expansion to force, and organize the published error figures and warning lead times into a coherent framework. They also state plainly what remains unproven: the proposed timescale-separated framework needs experimental validation across cell formats, operating conditions and mechanical constraints, and the reported error figures come from representative datasets rather than a universal benchmark.

The practical implication for next-generation electric vehicles is that a pack instrumented with force or pressure sensors could estimate state of charge more accurately, track aging drift explicitly, and detect gas-generating anomalies earlier than a purely electrical system can. The review concludes that force and pressure sensing offer promising complementary information for improving battery-state observability and early safety warning, while leaving the engineering validation, sensor integration and cost questions to future experimental work across the full range of cell formats and operating conditions that real vehicle packs encounter.

Subject of Research: Expansion force and pressure sensing as complementary observables for mechanics-aware battery management and early safety warning in electric vehicles

Article Title: Expansion force and pressure sensing for mechanics-aware battery management in electric vehicles: from state estimation to early safety warning

Article References: Li, F., Qiao, H., Jiang, L., Liu, X., Li, Y., & Li, J. (2026). Expansion force and pressure sensing for mechanics-aware battery management in electric vehicles: from state estimation to early safety warning. Frontiers in Mechanical Engineering, 12, Article 1979049. https://doi.org/10.3389/fmech.2026.1979049

Image Credits: AI Generated

DOI: 10.3389/fmech.2026.1979049

Keywords: battery management system, expansion force, pressure sensing, lithium-ion battery, state of charge, state of health, thermal runaway, sensor fusion, electric vehicles, strain sensing, optical-fiber sensing, ultrasonic sensing