Thermal Management of Lithium-ion Batteries

Transcription

1 Thermal Management of Lithium-ion Batteries APEC 2018 Greg Albright 1

2 What Are We Talking About? Maximize Vehicle Range (battery kwh; regen; charge time) Maximize Performance (power) Minimize Cost ($/mile) For as many years as possible 2

3 How a Battery Stores Energy Two electrodes separated by an electrolyte During discharge, lithium moves from the negative to positive electrode During charge, it reverses Positive electrode Electrolyte Separator e- Li+ Negative electrode 3

4 Main Battery Components Negative electrode (anode): graphite, silicon, titanate Positive electrode: metal oxide (NMC, NCA, LCO, LFP) Electrolyte: liquid salt solution (flammable!) Separator porous plastic Positive Electrode (cathode) Electrolyte Separator Negative Electrode (anode) Handbook of Batteries, 3 rd Ed., Linden, Reddy 4

5 Why Does My Battery Die? Every battery has a lifetime Calendar life: storage Cycle life: number of cycles Unwanted chemical reactions consume lithium and block its movement Try to avoid: Storing at high temperature and fully charged Always cycling the full range (0-100%) Power and Energy both fade Storage 23 C, 50% SOC 32 C, 50% SOC 23 C, 100% SOC 32 C, 100% SOC 5

6 vs

7 The Most Important Slide C = C 0 αt n βq m Calendar fade Cycle fade α = k 1 exp E a R 1 1 T T ref exp a 1F R 1+a 2 SOC+a 3 SOC 2 T 1+a 2SOC ref +a 3 SOC ref 2 T ref β = k 2 DOD DOD ref b 1 C Capacity today C 0 Initial capacity t time k1, k2, a1, a2, a3, b1, n, m experimentally fit exponent unique to each cell model Q Ah throughput for the cell E a Activation Energy R, F Gas constant and Faraday Constant T, T ref Cell temperature and reference temperature SOC State of Charge 7

8 Calendar Capacity Loss vs. Temperature 90% SOC; NMC

9 Calendar Capacity Loss vs. SOC 45 C; NMC

10 The Other Most Important Slide (Manage a) Cell Heat Gen: Q = I 2 R+I*T*dOCV/dT R = f(soc, T, SOH) docv/dt = f(ocv) I = Current from vehicle drive profile Other pack components have I 2 R heating Current collectors/bus bars Electronics 10

11 Example Resistance Graph Q = I 2 R+I*T*dOCV/dT docv/dt is the change of open circuit voltage as a function of temperature Temperature Increase 11

12 Example docv/dt (Absorb or Release Heat) Q = I 2 R+I*T*dOCV/dT 12

13 Temperature ( C) Thermal Runaway Heat Generation 800 Temperature vs Time ( 2.9 Ah cell) Cell goes into thermal runaway Total Test Time (min) 13

14 Goals of Thermal Management Keep Target Temperature Everywhere Prevent Spread of Thermal Runaway Keep neighboring cells below ~120 C Don t Ruin Cost Efficiency Robustness Scale Weight/Volume Complexity Supply chain Safety 14

15 Comparison of Thermal Management Methods Liquid Cooling Thermal Runaway Thermal Management Ambient Heat Weight Efficiency Cost Ease of Use Continuous Air Cooling Potting compounds or no cooling PCM Phase change materials 1 = Good; 10 = Bad *Source: AllCell analysis Air + PCM No Cooling Liquid 15

16 Basic Battery Module Current Collectors Cell Holders Cells Space for thermal management 16

17 How to Execute Design Modeling 0D tells you what you need here 2D, 3D tells you how to achieve it for all cells Testing tells you how wrong your models are Component System 17

18 2D/3D Model Input Geometry and Mesh Define Material Properties Define Boundary and Initial Conditions Output Temperature Input Heat Generation 18

19 Test Module/Pack 19

20 Tesla Model S Battery Source: Elektrek 20

21 Tesla Serpentine Liquid Cooling Cooling Channel - Water or coolant mixture 21

22 Liquid Cold Plate Becoming More Popular 22

23 Chevy Volt Cooling System Liquid cooling plate goes between alternating cells Cold liquid in Hot liquid out 23

24 Chevy Volt Coolant Loop C. Temp Regulating Flow Valve Positions A. Max Heat Loop B. Max Cold Loop C. Temp Regulating B. Max Cold Loop A. Max Heat Loop Source: 24

25 Thank You Questions? Further Reference What goes wrong? 25