Understanding Lithium-Ion Technology Jim McDowall (updated from Battcon 2008) PE/SB Winter Meeting 2015, New Orleans
Background History Started with primary batteries with metallic lithium negatives True lithium ion Sony paper in 1990 Large-scale shipments in 1993 First mass-produced auto (Mercedes S400 mild hybrid) in 2008 Widespread deployments for grid-connected energy storage since ~2010 Issues Safety Safety Safety 2
Reaction mechanism e Charge Discharge e Oxygen Lithium Ion Charge Metal Ion Carbon Discharge Separator SEI POSITIVE NEGATIVE 3
Volts/Li VOLTAGE (V) Current chemistries Positive (cathode) LiCoO 2 (LCO) LiNiCoAlO 2 (NCA) LiNiMnCoO 2 (NMC) LiMn 2 O 4 (LMO) LiFePO 4 (LFP) Negative (anode) Graphite (C) Lithium titanate (LTO) 4,40 125 Ah/kg 145 Ah/kg 195 Ah/kg 4,20 4,00 3,80 162 Ah/kg 3,60 LiNiO2 3,40 LiCoO2 LiMn2O4 LiFePO4 3,20 3,00 0,00 50,00 100,00 150,00 200,00 250,00 CAPACITY (Ah/kg) 2 39 ESLS30 AD003 (6.5 m 2 /g) 60 C EC/DMC/EA (15/25/60) Graphite LiPF6 1,5M + 4.75% VC 20 ma/g at 60 C 1.5 1 0.5 353 mah/g 0 4 0 50 100 150 200 250 300 350 400 Capacity (mah/g)
Voltage vs. Li metal Technologies 4.5 4.0 3.5 3.0 2.5 2.0 LCO / C 3.8 V NCA / C 3.6 V LMO / C 3.7 V LFP / C 3.2 V LCO / LTO 2.5 V LFP / LTO 1.9 V 1.5 1.0 0.5 0.0 Voltage indicates approximate mid-point value 5
Future developments Avicenne Energy - 30 th INTERNATIONNAL BATTERY SEMINAR & EXHIBIT, March 11, 2013 6
Construction Lithium-ion cells Cylindrical Prismatic Lithium-ion polymer Pouch cells Lithium metal polymer Metallic lithium negative No liquid electrolyte 7
Safety discussion Will be covered in next presentation 8
Calendar aging Fundamental difference between systems Aging in aqueous systems driven by reaction kinetics Aging in Li-ion driven by thermodynamic stability Rate of aging influenced strongly by both temperature and operating voltage Typically linear capacity fading to 60% or 70% SOH Aging factor? 9
Calendar aging negative electrode Gradual leakage of lithium ions through SEI Metallic ions dissolved from positive provide conduit Emerging lithium ions react with solvents in electrolyte Increase in SEI thickness and impedance Some metals are more soluble than others LMO has relatively high solubility = more rapid capacity fading Some LFP products have solubility issues above 40 C to 45 C Loss of lithium ions ( fuel ) Temperature-dependent 10
Calendar aging positive electrode Primary aging process is oxidation reactions with electrolyte Affects intercalation ability Impedance increase NCA has slowest rate of aging Dependent on temperature AND voltage 11
Cycling aging Frequency and depth of discharge Influence of charge rate High temperature can reduce cycling aging 12
Voltage (V) Pros and cons of slope Lithium batteries must use electronics for balancing Systems with sloping SOC vs. voltage curve are easy to balance BUT non-ideal charging can impact SOC in service Charge voltage 14-cell NCA battery requires 56.0 V for 100% SOC Charging at 54.5 V gives ~90% SOC Temperature compensation can be a problem! 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 LCO NCA 0 10 20 30 40 50 60 70 80 90 100 State of charge (%) 13
Pros and cons of slope (cont.) Technologies with no slope are good for constant-power discharges Lack of slope poses problems in balancing Potential problems for long-term operation at intermediate SOC Steep rise at end of charge requires aggressive balancing or alternative approach Charging - LiFePO 4 14
Summary Broad family of lithium-ion electrochemistries Different cell formats and system architectures Should not be promoted or accepted in the same way as traditional batteries 15
Further reading Battcon 2010: Sophistication Versus Simplicity System Design Considerations for Li-Ion Batteries 16