DOE AND STATISTICAL MODELLING OF A LARGE SCALE AGEING EXPERIMENT FOR TWO POPULAR LITHIUM ION CELL CHEMISTRIES

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1 DI Wenzel Prochazka (TU Graz) Dr Martin Cifrain (ViF) DOE AND STATISTICAL MODELLING OF A LARGE SCALE AGEING EXPERIMENT FOR TWO POPULAR LITHIUM ION CELL CHEMISTRIES 1

2 Agenda Problem: Solution: Experiment: Result: Ageing of lithium ion cells Design-of-Experiment Large-Scale Experiment State-of-Health (SoH) 2

3 Lithium ion cell Graphit NEGATIV ELEKTROLYT POSITIV Sauerstoff Metall Kupfer Aluminium SEI Li + Discharge Charge Load SEI... Solid Electrolyte Interface Each chemical process induces side- and ageing processes running concurrently. M. Winter, Kraftwerk Batterie, Essen

Cell-Knowledge & Model Cell Ageing Measurements Model Parameterization Simulation Durability prediction Ageing process network 4 external influences (U,I,T,SoC) >40 internal state variables 6

4 Cell-Knowledge & Model Cell Ageing Measurements Model Parameterization Simulation Durability prediction Ageing process network 4 external influences (U,I,T,SoC) >40 internal state variables 6 measurable effects (dr, dc, 3x dz, dq) [dz in 3 frequency segments khz to mhz] External observation of the true processes is very limited. Professor Wien, Graz, Horst November Cerjak,

5 State-of-X State-of-Charge [SoC]: Percentage of the remaining charge within the cell. Defined by the total charge transferred, when slowly cycling between two cell voltage limits. State-of-Health [SoH]: Scalar of the remaining functional state of the cell between its new state (SoH = 1) and a defined broken state (SoH = 0). SoH = f(c aktuell / C initial, R aktuell / R initial, ) State-of-Function (or State-of-Power) [SoF]: Percentage of the remaining power to lower / upper limit 5

6 Experimental cell small capacity cheap in production simple to vary parameters close to series produced cell LFP and NCA cathodes versus graphite anodes 6

7 Design-of-Experiment Target: A model for the survival time of a cell in dependece of the controllable factors Uncontrollable factors Cell build variations Controllable design factors Electric current (I) contamination of cell materials ambient humidity measurement error change in cycling protocols time table measurement drift Temperature (T) State-of-charge (SoC) Delta state-of-charge (dsoc) Pressure Cell geometry Vibration Formation procedure Cell capacity decay, cell resistance increase Noisance (blocking ) factors Held constant design factors >170 cells (= largest published experiment [Feb 2013]) 7

8 Optimization of test space usage = LFP cells * = NCA cells Test space -15 C < T < 70 C 0 C < I < 5 C 10% < SoC < 90% 0% <dsoc < 80% Restrictions due to interactions SoC ~ dsoc I ~ T I ~ dsoc 8

9 current alternating Zellen & Alterung DoE Versuch Ergebnisse Experimental conduction Test sequence Measurement starts at cell activation repeated, standardized reference tests measure the SoH relevant values loads are simple, symmetric pulses electrolyte flooding formation procedure reference reference temperature reference design temperature cycling design temperature reference design temperature every 3 rd reference reference temperature Ø SoC dsoc time Most important is a reproducible reference test, incorporating all measures for parameterization. 9

10 Reference test Rate test C 100% dsoc GITT <0.5 C 5 x 20% dsoc + 3h Rest 0,2C 0,5C 1C 2C5C GITT (5 Pulse 0,5C) SoC 50% 10

11 The life of

Cycle counting for cell 10110314 Very good load point stability Fitting data tests for model

12 Cycle counting for cell Very good load point stability Fitting data tests for model parameterization Reference test at reference temperature Load point Reference test Cycles for SoC resetting 12

13 Coverage of test space Test results are spread over test space, also extrema are covered. 13

14 Capacity loss Diagram per load point Heading features factor levels: T / Crate / SoC / dsoc --- single cell mean -o-o- cell, which best represents load point Different ageing behaviours: 2 variations of staging 14

15 Results for LFP cells Damage staging type 1 Results were used to calibrate linear statistical model of the cell life depending on the influence factors of 2nd order: t(soh=0) = a 0 + a 1 *T + a 2 *I + Influences: temperature > dsoc > c-rate > SoC 15

16 Results for NCA cells Damage staging type 2 Results were used to calibrate linear statistical model of the cell life depending on the influence factors of 2nd order: t(soh=0) = a 0 + a 1 *T + a 2 *I + Influences: temperature > c-rate > dsoc > SoC 16

17 Overall result logarithmic survival time factors as isoconturs within test space I Test space upper LFP lower NCA SoC 2D plots, so the other factors are out of a sandard set: 30 / 0 / 50 / 0 dsoc Best compromise between pure calendar life and high energy throughput: ~ 15 / 0.5 / 60 / 70 T 17

18 Thank you. Ageing is the only evidence of life. after John Henry Newman 18

Performance analysis of Lithium-ion-batteries: status and prospects

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