Next Generation Li-Ion Calorimeter

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 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.

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.

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.

This technology is based upon a 120-watt IR laser is coupled to a fiber optic cable that is routed from the output of the laser into a series of focusing optics which directs energy onto a battery cell mounted to a test stand. When activated, heat from the laser penetrates the metal housing, heating the internals of the cell. At a specific temperature, the separator in the first few layers of the cell melts allowing the anode and cathode to make contact and initiates an internal short circuit. The internal short circuit then propagates throughout the battery eventually causing thermal runaway. The lower the wavelength of the laser used to produce the thermal runaway, the more heat-energy will be absorbed into the cell producing a faster result. The fiber optic cable can be terminated into a series of optics to focus the laser at a specific target, or the fiber optic cable can be stripped bare and placed next to the target to heat an isolated location. This method can also be used on a wide variety of cells, including Li-ion pouch cells, Li-ion cylindrical cells and Li-ion Large format cells. The innovation Triggering Li-ion Cells with Laser Radiation is at TRL 6 (which means a system/subsystem prototype has been demonstrated in a relevant environment) and the related patent application is now available to license and develop into a commercial product. Please note that NASA does not manufacture products itself for commercial sale.