When a lithium-ion battery cell fails, it enters thermal runaway — a self-reinforcing reaction that generates extreme heat, toxic and flammable gases, and electrical fault propagation simultaneously. Existing inter-cell protection products address only one of these three hazards: ceramic spacers and mica sheets slow heat conduction, and aerogel pads provide thermal insulation. None of them neutralize the toxic and flammable gases released during venting, and none provide electrical isolation between a failed cell and its neighbors. The result is that a single failing cell can propagate fire and chemical hazard across an entire battery pack within seconds.

BTSB (Battery Thermal Safety Buffer) is a five-layer passive pad installed between battery cells in prismatic EV packs, grid storage systems, and other high-energy battery configurations. Each layer addresses one specific failure mode in a defined sequence. Layer 1, a pyrolytic graphite sheet, spreads the initial heat spike laterally across the pad surface before it concentrates on adjacent cells. Layer 2, a phase-change material based on RT64HC paraffin, absorbs the thermal energy through its latent heat of fusion, delaying temperature rise in neighboring cells during the runaway event. Layer 3, an expandable graphite intumescent layer, activates under direct flame exposure and physically blocks flame propagation and hot gas flow between cells. Layer 4, a zeolite and activated carbon gas absorption layer, captures and neutralizes the toxic and flammable gases — including CO, HF, HCN, and hydrocarbons — that vent from a failing lithium-ion cell during thermal runaway. Layer 5, a PVDF dielectric film, electrically isolates the failed cell from adjacent cells and modules, preventing conductive fault propagation through the inter-cell interface.

The novelty of this architecture is its simultaneous, multi-hazard response in a single passive layer requiring no power, no pumps, no moving parts, and no control system. Each of the five layers is independently functional, and the stack is designed so that the layers activate in sequence as the thermal event progresses — thermal buffering first, then flame blocking, then gas neutralization, then electrical isolation — matching the physical timeline of a real thermal runaway event rather than responding to a single worst-case condition.

The pad is designed to fit standard inter-cell gaps in prismatic battery formats, with a total compressed thickness of approximately 1.94mm in the primary variant. All five materials are commercially available from established suppliers, and the manufacturing process uses standard lamination techniques compatible with existing battery pack assembly lines. The product requires no battery pack redesign and no changes to cell chemistry or battery management system architecture.

Three product variants are in development: a passive prismatic pad for standard EV and grid storage applications, a cylindrical wrap for 18650, 21700, and 4680 cell formats, and a smart module with embedded fiber-optic sensing for real-time thermal health monitoring and fleet reporting. A patent application covering the five-layer architecture has been filed in India (application number IN 202641015643, not yet granted). Physical prototype fabrication and independent laboratory validation testing are the next development stage, following completion of the full engineering design and analytical thermal model.