Electrochemical study of durability aspects in large vehicle batteries

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1 KTH ROYAL INSTITUTE OF TECHNOLOGY Electrochemical study of durability aspects in large vehicle batteries Abdilbari Shifa Mussa, Matilda Klett, Göran Lindbergh, Rakel Wreland Lindström Energirelaterad fordonsforskning 5 oktober 2017, Göteborg

2 Project Title: Electrochemical study of durability aspects in large vehicle batteries Period: (3 months extention 2018) PL: Rakel Wreland Lindström, Applied Electrochemistry, KTH Program: Energy effective vehicles Budget: SEK Associated to: Swedish Electromobility Centre Fast charging of large energy optimized Li-ion cells for electrical drivelines (Batterifonden project) 2

3 Project goals Batteries age with time and use. It is a performance, cost, and safety issue! The goal is to increase the lifetime of batteries by optimizing the usage conditions for better performance and minimized ageing. Improving battery lifetime decrease safety risks! Our objectives: Understand how fast-charging affects battery lifetime Identify and quantify internal battery state-of-health using nondestructive electrochemical techniques Understand non-uniform ageing in large format cells Identify the conditions that cause the non-uniform ageing 3

4 Li-ion battery Positive Negative Matal oxides (NMC, LCO...) Metal phosphates (LFP) Graphite Adapted from: 4

5 Li-ion battery Positive Negative Matal oxides (NMC, LCO...) Metal phosphates (LFP) Graphite Adapted from: 5

6 Li-ion battery ageing mechanisms 6

7 Fast charging effects Capacity loss with cycling Why lower ageing during fast charging? Temperature? - No 0.5 C => 26.5 o C 1.5 C => 30 o C Charing current? - No State-of-Charge range? - Yes! Full charging aged the battery more than the fast charging! A.S. Mussa, M. Klett, M. Behm, G. Lindbergh, R.W. Lindström, Journal of Energy Storage, 13 (2017)

8 What happens inside? A voltage fitting non-destructive analysis Graphite mass loss Capacity loss Li + loss Cell capacity loss completely dominated by loss of cyclable lithium! Negligible graphite active mass loss Significant NMC/LMO active mass loss that doesn t affect cell capacity loss A.S. Mussa, M. Klett, M. Behm, G. Lindbergh, R.W. Lindström, Journal of Energy Storage, 13 (2017)

9 NMC/LMO capacity What happens inside? Post-mortem analysis Non-uniform ageing in graphite electrode Edge Middle Graphite capacity Edge Post-mortem analysis confirmed the non-destructive analysis The electrode jelly-roll aged nonuniformly A.S. Mussa, M. Klett, M. Behm, G. Lindbergh, R.W. Lindström, Journal of Energy Storage, 13 (2017)

10 What cause non-uniform ageing - Pressure distribution - Temperature distribution - Current distribution? 10

11 Pressure cell Battery tabs Thermocouple hole Heating element Pressure spring 11

12 Effect of pressure on performance Impedance in a fresh cell Parallel cells Higher pressure higher impedance Differences lead to current distribution 12

13 Effect of pressure on single cell ageing Capacity with cycling (3C/3C) Ageing mechanism (dv/dq) Capacity fade with pressure There is optimal pressure that extend the battery life The optimal pressure reduces cyclable lithium loss 13

14 Group 1 Effect of pressure distribution on ageing Cell capacity after cycle-ageing (3C/3C) 1.32 MPa 0.66 MPa Group MPa 0.66 MPa No significant increase in ageing is found at the low pressure (0.66 Mpa) cell coupled to the cell with the optimal pressure (1.32 MPa). Pressure distribution causes current distribution but does not affect ageing rate. 14

15 Effect of temperature on ageing Impedance with temperature Current distribution in parallel connected cells c Capacity fade with cycle ageing Cell impedance decreases with temperature Ageing increases with temperature Temperature distribution lead to current distribution No non-uniform ageing due to temperature distribution in parallel connected cells (32-40 C) 15

16 Thank you for your attention! Mussa KTH, Applied electrochemistry 16

Understanding Lithium-Ion Technology Jim McDowall (updated from Battcon 2008)

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