Latent Heat Storage Based Thermal Management Materials For Lithium-Ion Batteries

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1 Latent Heat Storage Based Thermal Management Materials For Lithium-Ion Batteries Battery Power 2015 Presenter: Joe Kelly Materials Scientist

2 Outline Introduction-Outlast Technologies, LLC Background for Passive Thermal Management of Lithium-Ion Batteries Introduction to Latent Heat Storage Materials (LHS) Formulation of LHS for Thermal Control Test Results and Thermal Modeling Using LHS Summary

3 What We Do Outlast Technologies, LLC is a division of Coorstek which focuses on engineering latent heat storage materials into a wide variety of products for thermal control. Originally designed for use in NASA s astronaut spacesuits, Outlast LHS technology has been used for: Thermal regulation of body temperatures in textiles, bedding and medical products to improve comfort and manage heat. Maintain optimal temperature environments for packaging, i.e. medical and food industries. Improve overall thermal management in electronic applications such as portable electronics and battery-powered devices.

4 Why Portable Devices? Mobile Electronic Devices Globally market trends show that mobile consumer electronics are steadily increasing. Grew to 7bn in 2014 from 6.5bn end of Rechargeable Lithium-ion batteries are the primary power source Revenue of over $6bn in Expected growth to $9.7bn in 2023 Portable Power Tools/Medical Devices Lithium-ion batteries have quickly replacing traditional Ni-Cd and Ni-MH chemistries in majority of consumer power tools. Over 50% of commercial power tools utilize lithium-ion packs. Portable medical devices such as defibrillators and monitoring sensors rely primarily on rechargeable lithium-ion technology. As portability/mobility demands increase, there is a proportional need for better power trends related to capacity, running time, weight, and volume.

5 Temperature Dependent Li-ion Battery Performance Temperature Sensitive Degradation can occurs at 50 C or higher Susceptible to cycle life degradation at higher operating temperatures through rapid loss of capacity. Capacity Loss translates to shorter run times. Reduction in power capabilities Safety Thermal runaway probability is greatly enhanced Pack electronics/packaging can become damaged before safety cutoffs are triggered. Thermal management for lithium-ion cells is critical in meeting high performance demands required for portable electronics.

6 Thermal Management Benefits Li-ion Thermal Management Reduce new product development cost Maintain battery performance/lifetime of current commercial batteries. Decrease thermal stress on other device components Reduce surface touch temperatures for user comfort For portable electronics thermal design requires: Effective thermal dissipation Simplicity in design to fit in compact form factors Relatively costeffective Passive Thermal Design

7 Phase Change Materials Phase Change Materials (PCMs) depend on changing states of matter or phase changes in order to absorb and release heat while maintaining a constant temperature. Outlast Latent Heat Storage (LHS) materials derived from PCMs can offer enhance passive thermal management performance through enhanced thermal energy storage properties.

Formulation Testing A variety of LHS formulations were evaluated for effective thermal control of 18650 cells at high current discharges.

8 Formulation Testing A variety of LHS formulations were evaluated for effective thermal control of cells at high current discharges. Temperature (C ) Cells at ~10A Continuous Discharge Uncoated Control PCM formulation 1 PCM formulation 2 PCM formulation Time (mins) Formulations and polymer controls were molded into sleeves to fit on cells Formulation 3 was able to keep surface temperatures below 50 C by the end of discharge compared to both uncoated and polymer controls.

Formulation Validation Determining the ability for the LHS system to handle multiple power profiles is important for device versatility: Average Temperature ( C) 65 60 55 50 45 40 35 30 25 20 18650

9 Formulation Validation Determining the ability for the LHS system to handle multiple power profiles is important for device versatility: Average Temperature ( C) Cells at 20A Continuous Discharge Average of First Five Cycles PCM Sleeve Control Time (mins) Simultaneously tested control and LHS sleeved cells at 20A discharges showed an averaged end of discharge cell surface temperatures of 63 C and 46 C respectively. 17 C difference compared to 26 C difference for the 10A discharge case. It is necessary to match LHS content (latent heat properties/applied mass) with maximum and minimum thermal flux outputs for device depending on desired thermal control.

Thermal History Comparison 70 Charging Dschg Rest Charging 65 Temperature ( C) 60 55 50 45 40 35 30 25 Total: 97 C/min Dschg: 62 C/min + Chg: 35 C/min) Curves intersect at 37 C 38 C/min Total Thermal

10 Thermal History Comparison 70 Charging Dschg Rest Charging 65 Temperature ( C) Total: 97 C/min Dschg: 62 C/min + Chg: 35 C/min) Curves intersect at 37 C 38 C/min Total Thermal History Reduction from LHS Sleeve: 59 C/min Time (s) Numerical integration of thermal curves show that control cells have an higher thermal history of 97 C/min during cycling until reaching 37ºC during the cool-down/charge phase. Below 37 C LHS sleeved cells had a higher thermal history than that of control batteries until ambient reached due to thermal dissipation of stored energy. Approx. 60% of total thermal history of control occurs above maximum cell surface temps (47 C) of LHS sleeved cells. This higher thermal history for the control cells is compounded upon each subsequent cycle

11 Discharge Capacity Retention Larger thermal stress on the non-lhs cells leads to loss in electrochemical capacity retention across operation lifetime of the cell or battery pack. LHS cells remained above 75% capacity retention for 40% overall increase in cycle life.

12 LHS Thermal Cycling Behavior ~ T= 3.8 C ~ T= 3.2 C Temperature deviation after 650 cycles (taking into account surrounding environment fluctuations/cell conditioning) was less than 3.5 C for the LHS sleeve. No significant temperature deviation between LHS Sleeve vs. Control cells for 650 cycles. LHS sleeve maintained its effective thermal absorption properties over the lifetime of the battery.

Thermal Modeling of Li-ion Battery Performance Behavior with LHS Finite differencing heat transfer analysis was conducted using SINDA/FLUINT thermal programming Advanced modeling

13 Thermal Modeling of Li-ion Battery Performance Behavior with LHS Finite differencing heat transfer analysis was conducted using SINDA/FLUINT thermal programming Advanced modeling used to determine effect of LHS material property variation in a number of different pack designs Thermal performance effect on battery packs by enhancement of LHS thermal conductivity.

Thermal Model Pack Design Simulations of Enhanced Thermal Conductivity LHS Materials Objective: Quantify the effect of enhancing the thermal conductivity of the LHS material on cell surface

14 Thermal Model Pack Design Simulations of Enhanced Thermal Conductivity LHS Materials Objective: Quantify the effect of enhancing the thermal conductivity of the LHS material on cell surface temperatures in a battery pack. Three cases: Plastic control material Standard LHS material LHS material with ~8x greater thermal conductivity than standard LHS. LHS Battery Housing cell dissipating 12W Testing Parameters: Ten minute discharge with battery pack dissipating a total of 144W (12W x 12 cells) Natural convection around top/sides of battery housing.

Interior Facing Surface Exterior Facing Surface Side Li-ion LHS Battery Housing 18650

15 Thermal Model Pack Design Simulations of Enhanced Thermal Conductivity LHS Materials Thermal Model Probe Locations: Top Right Top Left Top Center Center Li-ion Cell (#4) Interior Facing Surface Exterior Facing Surface Side Li-ion LHS Battery Housing Li-ion Cell 1mm spacing between cells and 2mm spacing between cells and battery housing walls.

Thermally Conductive Standard PCM Better thermal

16 Thermal Model Pack Design Simulations of Enhanced Thermal Conductivity LHS Materials Plastic Control Standard LHS PCM Thermally Conductive Standard PCM Better thermal conductivity gives more efficient utilization of the LHS material in pack.

17 Heat Spreading Effect on Battery Housing From Increased Thermal Conductivity Standard Enhance LHS PCM: thermal Heat conductivity Spreading moves Effect From Increased Thermal Conductivity heat (Battery away from Housing) center of pack. Center of Battery Housing Edges of Battery Housing Enhance thermal conductivity moves heat away from center, and out to edge. Temperature (K) Time (s) Standard LHS PCM Thermally Cond. Standard LHS PCM Plastic Control Temperature (K) Time (s) Standard LHS PCM Thermally Cond. Standard LHS PCM Plastic Control Temperature (K) Top Right Location of Battery Housing Enhance thermal conductivity allows for more effective utilization of PCM Time (s) Standard LHS PCM Thermally Cond. Standard LHS PCM Plastic Control

Heat Spreading Effect on Cell Surface From Increased Thermal Conductivity Maximum T Experienced by Battery Surfaces Interior Facing Cell Surface

5 K Lower cell surface temperatures were observed in LHS PCMs with improved thermal conductivity (8x higher conductivity). Therm. Cond. Stand.

18 Heat Spreading Effect on Cell Surface From Increased Thermal Conductivity Maximum T Experienced by Battery Surfaces Interior Facing Cell Surface Exterior Facing Cell Surface 6.3 K 6.5 K Lower cell surface temperatures were observed in LHS PCMs with improved thermal conductivity (8x higher conductivity). Therm. Cond. Stand. LHS PCM: Interior and exterior facing cell surface were 4-6K cooler by end of discharge. Balance of key LHS properties (latent heat, phase change temp, thermal conductivity, etc.) is necessary to achieve an efficient and cost-conscious design for optimal thermal performance.

19 Improved Thermal Management Concluding Remarks Outlast s latent heat storage materials offer a simple and low cost passive thermal management system that effectively reduced li-ion battery surface temps. With LHS sleeves surface temperatures remained below 50 C for the duration of discharge at 10-20A with format. Reduce thermal stress experienced by the battery leads to minimization of thermal degradation: Enhanced cycle life through better capacity retention. Longer run times by keeping battery within safety design limits throughout entire charge/discharge. Under certain applications, LHS materials also provide improved abuse tolerances for devices in a number of adverse environments. Enhanced impact resistance due to mechanical properties Corrosion resistance/waterproofing due to hydrophobic nature. Flame retardant packaging. UL94-V0 rating with high latent heat properties.

20 Corporate Headquarters Outlast Technologies LLC 831 Pine Ridge Road, Golden, CO outlast.com Facebook.com/OutlastTech Twitter.com/OutlastTech Youtube.com/OutlastTech Outlast Asia LLC Japan Phone: Fax: Outlast Europe GmbH Germany Phone: Fax:

PASSIVE THERMAL MANAGEMENT OF LITHIUM-ION BATTERIES USING LATENT HEAT STORAGE MATERIALS

PASSIVE THERMAL MANAGEMENT OF LITHIUM-ION BATTERIES USING LATENT HEAT STORAGE MATERIALS WHITE PAPER Joe Kelly - Materials Scientist, March 2015 Rev: 2 INTRODUCTION As demand steadily grows for more powerful