Triggering Li-ion Battery Cells with Laser Radiation

The Ram-Dent Thermal Runaway Triggering Device is capable of trig-gering mild short circuits that are similar to internal defects, and more extreme short circuits that are comparable to those initiated by an implanted internal short circuit device – all without having to modify the battery cell in any way. The device imparts a high velocity, low mass blunt impact onto a small surface area of a Li-ion battery cell can wall allowing a small hemispherical dent to form. This impact deforms and tears the internal separator of the battery cell, causing a short circuit, and induces thermal runaway. Several methods for initiating TR on demand currently exist, but they have characteristics and biases that make them more unfavorable for certain testing objectives. Heat-based insult in any form requires additional thermal energy to be applied to the battery cell, potentially distorting the signal-to-noise ratio in FTRC measurement, and increas-ing the severity of failure beyond what is intended. This methodology also requires time to heat the battery cell to critical temperature, and it potentially weakens the battery cell can wall causing abnormal kinetics and rupture. Mechanical insult methodologies, such as crush testing and nail penetration, have unique applications but rely on deformation of the battery cell itself which alters the flow characteristics of internal gases and the material integrity of the battery cell. This technology aims to solve these limitations by implementing a cost-effective method to create a natural short circuit failure in Li-ion batteries that does not alter nominal vent paths and energy yields, potentially yielding the most unbiased calorimeter tallies yet. The Ram-Dent Thermal Runaway Triggering Device is at a technology readiness level (TRL) 4 (component and/or breadboard validation in laboratory environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.

For years, NASA and the battery industry have been improving passive propagation resistant (PPR) Li-ion battery cell technology by enhancing their material and design choices. These efforts help ensure that a single cell’s TR event does not overheat adjacent cells or the entire battery pack ultimately causing fire or explosion. To improve cell integrity, single cells within battery packs are triggered into TR so that the battery pack can be analyzed for its TR resistance. ThermoArc operates by initiating a plasma arc, capable of delivering thermal energy up to 100W, to a very small (1mm diameter) section of the cell. The extremely localized high heat flux rapidly degrades a small section of the internal cell separator, resulting in a short circuit that leads to TR. This technology comprises several components: a high-turn-ratio step-up transformer capable of producing a minimum of 1,000 V upon the secondary winding, an H-bridge electronic circuit to drive the transformer on the primary side, two tungsten electrodes to deliver the plasma arc, and a power supply unit. ThermoArc applications may exist in any Li-ion battery cell/pack testing application where TR must be induced in an individual cell. Such applications could include testing of PPR battery packs to ensure single cell runaway does not cause catastrophic damage, more general battery destructive testing designed to better understand battery failure states, or other experimental testing. Companies interested in licensing this innovation may include those that manufacture internal short-circuit (ISC) cells or other devices used to induce TR at the individual cell level, battery testing firms, and Li-ion battery manufacturers with a focus on Li-ion battery packs for critical applications. ThermoArc is at a technology readiness level (TRL) 5 (component and/or breadboard validation in laboratory environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.

Li-ion batteries are an integral part of energy storage systems used in NASA's Exploration program, as well as many modern terrestrial industries. Innovators at the NASA Johnson Space Center wanted a better way to measure total and fractional heat response of specific types of Li-ion cells when driven into a thermal runaway condition. They developed a calorimeter with at least two chambers, one for the battery cell under test and at least one other chamber for receiving the thermal runaway ejecta debris. Both are designed to be structurally strong and thermally insulated. When the test cell is intentionally driven into thermal runaway, ejecta explodes into the ejecta chamber and is decelerated and collected. Thermal sensors are strategically placed throughout the chambers to collect thermal data during the test. Customized software analyzes the thermal data and determines key calorimeter parameters with a high degree of accuracy.

The Thermal Ejecta Shielding System comprises strategically layered materials that fasten to the top of a Li-ion cylindrical battery pack casing. It can protect individual battery cells in a battery pack by shielding them from a neighboring cell’s hot thermal ejecta during a TR event while providing primary functions of connecting, insulating, grounding, and distributing power. In laboratory testing, this technology improved the resistance to TR collateral damage of a PPR battery pack by overcoming two primary drawbacks of its design. Modern Li-ion cylindrical battery cell packs comprise a nickel bus plate that aligns with and connects the positive buttons along the battery tops to distribute power. Insulating G10 composite layers sandwich the bus plate atop the cells, however, these are rendered vulnerable to burn-through during a TR event due to their thinness, and they can allow escaping thermal ejecta to penetrate the button cavities of neighboring battery cells within the battery pack. Additionally, the nickel and composite bussing layering is prone to separation, or "tenting", when subjected to extreme heat, as it relies solely on an adhesive bond to prevent delamination. The hot ejecta spray stemming from a battery cell undergoing a TR event can weaken this adhesive bond. These issues can lead to adjacent battery cell damage resulting in their reduced performance, zero-voltage, or susceptibility to a larger TR event. The Thermal Ejecta Shielding System for Li-ion Battery Packs was developed from a multi-pronged strategy to improve upon the drawbacks by introducing these novel components and accompanying features: • Capture Plate Cell “Chimney” - Redirects ablative ejecta away from adjacent cells and creates a volume for liquid “sealer” protection; • Adhesively Backed Mica Cell Donut - Provides an insulative layer to protect the positive bus plate from creating a short circuit to the negative cell can during TR; • Adhesive Transfer Tape - Provides an adhesive layer for a more uniform/reproducible bond between the nickel bussing, mica, the G10/FR4 insulating layer, and the aluminum layers; • Continuous Mica Cell Cover Sheet - Replaces individually installed mica covers (upper layer of G10/FR4) with a single sheet of perforated mica; • Rupture Sheet Cover Plate - Introduces a thin aluminum fastener plate above the Continuous Mica Cell Cover Sheet to prevent delamination of bussing sandwich layers; • Narrowed Bus Plate Tab - Introduces a narrowed tab to allow for unrestricted header expansion and severing/separation during TR; • Steel Ring - Protects cell from spin groove ruptures and redirects ablative ejecta away from adjacent cells; and • Liquid Cell Covers - Introduces a high temperature liquid “sealer” to fill the void between cell button and mica cover to prevent ejecta burn-through from compromising the seal.

Astronauts' lives depend on the safe performance and reliability of lithium-ion (Li-ion) batteries when they are working and living on the International Space Station. These batteries are used to power everything such as communications systems, laptop computers, and breathing devices. Their reliance on safe use of Li-ion batteries led to the research and development of a new device that can more precisely trigger internal short circuits, predict reactions, and establish safeguards through the design of the battery cells and packs. Commercial applications for this device exist as well, as millions of cell phones, laptops, and electronic drive vehicles use Li-ion batteries every day. In helping manufacturers understand why and how Li-ion batteries overheat, this technology improves testing and quality control processes. The uniqueness of this device can be attributed to its simplicity. In a particular embodiment, it is comprised of a small copper and aluminum disc, a copper puck, polyethylene or polypropylene separator, and a layer of wax as thin as the diameter of one human hair. After implantation of the device in a cell, an internal short circuit is induced by exposing the cell to higher temperatures and melting the wax, which is then wicked away by the separator, cathode, and anode, leaving the remaining metal components to come into contact and induce an internal short. Sensors record the cell's reactions. Testing the battery response to the induced internal short provides a 100% reliable testing method to safely test battery containment designs for thermal runaway. This jointly developed and patented technology is available for your company to license and develop into a commercial product. NASA does not manufacture products for commercial sale.