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

2. Resources IEEE ESSB SM2017 Energy Storage Tutorial
IEEE Std (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)
WM 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)
WM Lithium Operating Issues in a Stationary Environment

4. Charging issues Charging can impact: State of charge Aging Safety
WM 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
WM 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
Voltage
13 cells
14 cells
54.0V
4.15V/cell
3.86V/cell
60.0V
4.61V/cell
4.29V/cell
WM 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)
WM 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
WM Lithium Operating Issues in a Stationary Environment

9. Charger interface ‘Smart’ chargers ‘Bright’ chargers ‘Dumb’ 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!
WM Lithium Operating Issues in a Stationary Environment

10. Discharging issues Thermal management End-of-discharge 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 in lead-acid)
WM 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
WM 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
WM 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
WM Lithium Operating Issues in a Stationary Environment

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