Understanding Lithium-Ion Technology

Jim McDowall (updated from Battcon 2008)

PE/SB Winter Meeting 2015, New Orleans

Background

2

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

PE/SB WM2015 - Understanding Lithium Ion Technology

Reaction mechanism

3

Lithium Ion

Metal Ion

Carbon

Oxygen

Separator

POSITIVE NEGATIVE

SEI

e–

Charge

Charge

Discharge

Discharge

e–

PE/SB WM2015 - Understanding Lithium Ion Technology

Current chemistries

PE/SB WM2015 - Understanding Lithium Ion Technology 4

Positive (cathode)

LiCoO2 (LCO)

LiNiCoAlO2 (NCA)

LiNiMnCoO2 (NMC)

LiMn2O4 (LMO)

LiFePO4 (LFP)

Negative (anode)

Graphite (C)

Lithium titanate (LTO)

195 Ah/kg145 Ah/kg

125 Ah/kg

162 Ah/kg

3,00

3,20

3,40

3,60

3,80

4,00

4,20

4,40

0,00 50,00 100,00 150,00 200,00 250,00

CAPACITY (Ah/kg)

VO

LT

AG

E (V

)

LiNiO2

LiCoO2

LiMn2O4

LiFePO4

0

0.5

1

1.5

2

0 50 100 150 200 250 300 350 400

ESLS30 AD003 (6.5 m2/g)

EC/DMC/EA (15/25/60)

LiPF6 1,5M + 4.75% VC

20 mA/g at 60°C

Vo

lts

/Li

Capacity (mAh/g)

60°C

353 mAh/g

39

Graphite

Technologies

5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Vo

ltag

e v

s.

Li

meta

l

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

Voltage indicates approximate mid-point value

LFP / LTO

1.9 V

PE/SB WM2015 - Understanding Lithium Ion Technology

Future developments

PE/SB WM2015 - Understanding Lithium Ion Technology 6

Avicenne Energy - 30th INTERNATIONNAL BATTERY SEMINAR & EXHIBIT, March 11, 2013

Construction

7

Lithium-ion cells

Cylindrical

Prismatic

Lithium-ion polymer

‘Pouch cells’

Lithium metal polymer

Metallic lithium negative

No liquid electrolyte

PE/SB WM2015 - Understanding Lithium Ion Technology

Safety discussion

8

Will be covered in next presentation…

PE/SB WM2015 - Understanding Lithium Ion Technology

Calendar aging

9

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?

PE/SB WM2015 - Understanding Lithium Ion Technology

Calendar aging – negative electrode

10

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

PE/SB WM2015 - Understanding Lithium Ion Technology

Calendar aging – positive electrode

11

Primary aging process is oxidation reactions with electrolyte

Affects intercalation ability

Impedance increase

NCA has slowest rate of aging

Dependent on temperature AND voltage

PE/SB WM2015 - Understanding Lithium Ion Technology

Cycling aging

12

Frequency and depth of discharge

Influence of charge rate

High temperature can reduce cycling aging

PE/SB WM2015 - Understanding Lithium Ion Technology

Pros and cons of ‘slope’

13

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!

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

0 10 20 30 40 50 60 70 80 90 100

Vo

ltag

e (V

)

State of charge (%)

LCO

NCA

PE/SB WM2015 - Understanding Lithium Ion Technology

Pros and cons of ‘slope’ (cont.)

14

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 - LiFePO4

PE/SB WM2015 - Understanding Lithium Ion Technology

Summary

15

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

PE/SB WM2015 - Understanding Lithium Ion Technology

Further reading

16

Battcon 2010: Sophistication Versus Simplicity – System Design Considerations for Li-Ion Batteries

PE/SB WM2015 - Understanding Lithium Ion Technology