# Mining Contract: Using Advanced Large-Format Energy Storage Technology in Underground Mines

Keywords:BatteriesChemistryElectrical safetyElectrical safety equipment

| Contract #                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | 200-2014-59035 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|
| 9/1/2014                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| 5/31/2015                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Large-format energy storage systems are already being used in underground mining vehicles. These vehicles utilize lead-acid technology which is packaged in open-frame (non-airtight) enclosures due to gas venting needs within the lead-acid system. This venting of gasses from open packaging—in conjunction with other lead acid battery failure modes—can lead to dangerous events that put miners at risk. Therefore, additional safety equipment is mandated in the lead-acid battery charging and maintenance areas of mines. Before mines can adopt advanced large-format energy storage, a comprehensive survey of the leading technologies and their likely failure modes is required.     |
| - Electrical Safety                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |

## Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

Mining equipment powered by energy storage systems has been a popular choice for underground mines because of the freedom from being tethered to a power center through a trailing cable or a trolley wire through a pole. In addition, battery-powered equipment when compared to diesel-powered equipment can offset certain health and safety concerns, requires less ventilation, and has excellent noise characteristics. Traditional battery systems use lead-acid technology, which presents hazards such as evolution of hydrogen gas and acid spills. Advanced battery technologies such as sodium-ion and lithium-ion can provide improved productivity and efficiencies from their higher power and energy densities. Despite this advancement, these technologies have not been evaluated widely for safety-critical applications such as underground mines, where explosive environments can exist. General Electric was contracted to identify the potential risks of these advanced chemistries, and determine if they could be packaged and tested to abate those risks.

The enabling technologies in this research are sodium metal halide and certain lithium-ion (Li-ion) energy storage technologies for use in large-format battery banks. Li-ion refers to a family of chemistries used in a variety of batteries. Some li-ion chemistries are more susceptible to thermal runaway than others. Certain newer, safer li-ion chemistries were the focus of this research.

The contractor identified one sodium-ion (sodium metal halide) and two lithium-ion (lithium iron phosphate and lithium titanate) chemistries that would most likely be considered for use in underground mining equipment. The construction and operation of a typical commercial product for each of the three chemistries was studied and documented. The study of the sodium metal halide battery identified 12 discrete failure modes, and the study of the lithium iron phosphate and lithium titanate identified 10 discrete failure modes.

The contractor’s final report recommends a battery management system (BMS) that monitors the charging and discharging of the cells within the battery assembly to ensure that parameters such as cell voltage, current, and temperature are within acceptable limits. The BMS protective features may electrically disconnect the problem cells if it detects over-stressed conditions. While a BMS may add many safety features to the lithium-ion battery assembly, it does not eliminate the possibility of cell failure. Therefore, additional safety devices such as cell vents, electrical fuses, and shut-down separators should also be incorporated in these batteries.

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National Institute for Occupational Safety and HealthMining Program

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