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Lithium Operating Issues in a Stationary Environment

Lithium Operating Issues in a Stationary Environment. Jim McDowall IEEE ESSB WM2018. Resources. IEEE ESSB SM2017 Energy Storage Tutorial IEEE Std 1679.1-2017 (to be published in February) Battcon archive papers McDowall 2014 (safety) and 2016 (Li-ion technology selection)

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Lithium Operating Issues in a Stationary Environment

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  1. Lithium Operating Issues in a Stationary Environment Jim McDowallIEEE ESSB WM2018

  2. Resources • IEEE ESSB SM2017 Energy Storage Tutorial • IEEE Std 1679.1-2017 (to be published in February) • Battcon archive papers • McDowall 2014 (safety) and 2016 (Li-ion technology selection) • Tremeling 2015 (safety) • Ponchaut 2016 (fire safety and regulations) WM2018 - Lithium Operating Issues in a Stationary Environment

  3. Li-ion battery management systems • Main functions • Avoid unsafe operation where possible • Avoid conditions that cause excessive battery damage / aging • Main components • Hardware (sensors, switches, comms) • Software (operating algorithms, comms protocols) • Parameters (operating setpoints, alarm levels) WM2018 - Lithium Operating Issues in a Stationary Environment

  4. Charging issues • Charging can impact: • State of charge • Aging • Safety WM2018 - Lithium Operating Issues in a Stationary Environment

  5. Charging issues – SOC • The most energy-dense chemistries exhibit ‘slope’ • SOC depends on charge voltage • Most Li-ion cells are packaged in multicell modules • May be difficult to achieve high SOC at ‘traditional’ voltages WM2018 - Lithium Operating Issues in a Stationary Environment

  6. Charging issues – SOC (cont.) • The telecom dilemma • Normal VRLA charging at 54.0V • Telcordia GR-3150 overcharge test at 60.0V • 13 cells or 14 cells? • 13-cell battery gives 100% SOC on float but could experience a safety event on overcharge • 14-cell battery has good safety on overcharge but significantly impacted SOC on float WM2018 - Lithium Operating Issues in a Stationary Environment

  7. Charging issues – Aging • Charge rate has an impact on cycle life • Allowable charge rate is significantly impacted by temperature • Max temperature cutoff must be adapted to application(e.g. telecom) WM2018 - Lithium Operating Issues in a Stationary Environment

  8. Charging issues - safety • Extremely high charge current can form lithium dendrites • Short circuits • Safety events • Normally controlled by BMS • Extremely high voltage can lead to severe fires • Chemistry-dependent • Very low probability with today’s chargers WM2018 - Lithium Operating Issues in a Stationary Environment

  9. Charger interface • ‘Smart’ chargers • Full communication with BMS • Response to maximum-current signals from battery • ‘Bright’ chargers • No communication but advanced features • Battery current limit setting • High-temperature shutdown • ‘Dumb’ chargers • No communication • No response to battery condition • Relies entirely on BMS operability • Consider carefully before large-scale deployment! WM2018 - Lithium Operating Issues in a Stationary Environment

  10. Discharging issues • Thermal management • Max temperature cutoff must be adapted to application • End-of-discharge management • Copper dissolution below ~1.5V/cell • Causes shorts upon recharge • (Analogous to hydration shorts inlead-acid) WM2018 - Lithium Operating Issues in a Stationary Environment

  11. Operating philosophy • A lithium-ion string is normally limited by its weakest cell • ESS philosophy is to safeguard battery investment • String disconnection when first cell reaches critical low voltage • …or when minimum battery voltage reached • Standby philosophy is to safeguard protected load • Accept battery damage in order to power loads for maximum possible time • BMS operation should be adapted to the need WM2018 - Lithium Operating Issues in a Stationary Environment

  12. Reliability versus availability • In Li-ion, electrochemistry is overlaid by electronics • Electronic chip for each cell or group of parallel-connected cells • 14 chips for 48V; 35 chips for 125V; 10s of thousands for utility-scale ESS • Prudent safety practice is to disconnect string on chip failure • Standard MTBF calcs predict relatively frequent failures in large systems • Reliability issues mitigated by modular architecture • Multiple strings are a must for critical applications • At least n+1 redundancy • Availability can be very high WM2018 - Lithium Operating Issues in a Stationary Environment

  13. Summary • Li-ion deployment more complex than for traditional batteries • Particularly with uncontrolled environments • Integration with ‘smart’ chargers desirable • BMS operation should be compatible with operating philosophy • Parallel strings and redundancy are a must WM2018 - Lithium Operating Issues in a Stationary Environment

  14. Questions? jim.mcdowall@saftbatteries.com WM2018 - Lithium Operating Issues in a Stationary Environment

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