THERMAL MANAGEMENT OF LITHIUM ION BATTERY USING PHASE CHANGE MATERIAL

FINAL 8^TH SEMESTER PRESENTATION (FINAL YEAR PROJECT) BY:

JITHIN REGI MATHEW-160934009

SANYAM JUNEJA -160934148

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B.TECH AUTOMOBILE ENGINEERING

MANIPAL INSTITUTE OF TECHNOLOGY

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INTRODUCTION:

About lithium ion batteries:

• Lithium-Ion Batteries offer power source solution across the spectrum from energy storage solutions to portable electronic devices like laptops, mobile phones etc.
• Li-ion batteries are also a safer alternative compared to other batteries such as lead-acid batteries
• With high energy density, high power density and long life-span these batteries are widely adopted as the traction batteries in electric vehicles either pure or hybrid type vehicle

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ADVANTAGES OF LI-ION BATTERIES IN VEHICLES:�

• Li-ion batteries are chosen as they are the most suitable power source for EVs/HEVs due to their high specific energy density, low weight, low discharging rate, and good stability
• Electric vehicles will greatly contribute in reducing green house gas emissions that cause air pollution
• It also helps reduce noise Pollution

• Number of moving parts in a vehicle are reduced and hence, it becomes easier to maintain the vehicle

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DISADVANTAGES OF LI-ION BATTERIES:

• A serious downside of the application of Li-ion batteries is the amount of heat it generates.
• This, in time, leads to the shorter life span and thermal runaway of the battery due to overheating
• Safe applications of batteries under high temperatures is also a concern as it may lead to disasters such as fire and explosion
• Studies have shown that the maximum battery operation temperature should not exceed 60 degree Celsius

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NECESSITY OF BTMS FOR A BATTERY:

• The development of BTMS is vital for Li-ion batteries as it helps to maintain the operational temperature of the battery within a suitable range.
• The technologies adopted ranged from air-cooled to liquid-cooled to the use heat pipes and PCMs.

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Thermal Map of a BTMS using PCM

USE OF PCM IN BTMS:

• The use of PCM in the BTMS have become popular due to its many advantages which include temperature stability, large latent heat, simple structure and low power consumption etc.
• To further improve its thermal conductivity, other substances such as expanded graphite, carbon fiber, carbon nanotubes, carbon foam etc. are often added to pure PCM

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Pure Paraffin Wax PCM

OBJECTIVES:

• To develop an efficient cooling system to control peak temperature in Li-ion battery packs using phase change materials.
• Prevent thermal runaway in battery and improve safety with the application of PCM
• Control the working temperature range to 25-40 and reducing the occurrence of peak temperatures (60 degrees and above).

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• The goal is to optimize thermal performance for a BTMS with PCM
• Expended graphite (EG) will be an addition to the PCM to further enhance its performance and the thermo-physical properties of PCM are used in the experimental- optimization of the BTMS

• When the temperature of the PCM unit reaches the phase change temperature, the solid PCM will gradually melt. As the phase change is taking place, the rising trend of heater’s temperature will slow down because of the isothermal characteristic of the PCM.
• Besides, the large latent heat of the PCM further helps to improve the cooling effect of the BTMS. Hence, we will be able to prove that the working life and the safety of Li-ion batteries can be greatly improved when BTMS with PCM is used.

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METHODOLOGY

PROCESS

Experimental

Simulation to prevent thermal runway and control temperature range

3S2P Battery configuration is developed using mock lithium ion batteries

Cylindrical cells liberate radially, so PCM+EG is filled near cell and to evaluate process with 12 thermocouples.

PCM-In-organic Fatty Acid-Based

MOCK LITHIUM ION CELL

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• 14mm* 65mm Heater Cartridge
• 100 Watt,230 Volt
• Material-Stainless Steel
• Six cells of this
• dimensions would make up a
• 3S2P Battery Module
• VC
• Hollow Aluminium Cylindrical Shell
• 18mm*72mm
• Material-Al 6061
• Sliding Fit between Heater and
• Aluminium Casing

BATTERY MODEL SPECIFICATIONS

Systematic configurations like cell to cell distance, spacing and layout play a major role in controlling temperature rise

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As support from various research theories we have kept our cell to cell spacing as 40mm and wall to cell distance is 22mm. The cells held in rectangular configuration as thermal analysis can be done optimally and PCM is filled in the empty spaces.

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Draft of the 3S2P battery model 180mm*120mm*100mm (l*b*h),

Six 18mm cell and 40mm of cell to cell distance.

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CAD VIEW OF BATTERY MODEL WITH SIX CELLS AND SENSOR LOCATIONS:

• All the experiments would be simulated by keeping the cells in an acrylic container box of 6mm thickness. It has melting point above 100°C and the battery experimental range we are validating is in range from 40-60°C.

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• PCM of required quantity is filled in the box as coolant.

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SIMULATING CIRCUIT SET-UP

• The experimental test-rig has been set-up to carry out the iterations to validate the thermal performance of the designed battery module. Various electronic and electrical components have been applied in the setup. A precise power supply to the mock batteries using 15 ampere analog thermostat with 0-100 temperature scale. The mock heater cells are made to heat up-to required 45-55C temperature and PCM is filled in the model to control the heat and support cooling. The PCM and cell temperature is monitored using 12 K-type thermocouples giving twelve indication a digital channel.
• Four surface thermocouple bonded by High Temperature tape to cell surface and 8 space thermocouples to monitor the PCM condition in cooling the battery. The first four temperature sensors are at height of 70mm evaluating the first pair, second four space sensors to evaluate mid-profile and third pack to evaluate the lower end cell pairs.

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Experimental Battery Setup for thermal monitoring of the cells using sensors and electronic units.

NUMERICAL SIMULATION-CELL MODEL WITH PCM

• The simulation is investigated in fluent tab with designing the 3D model with same specifications as mentioned earlier. Using design modeler tools the sketch is generated and boolean operations are been applied to make the six cells confined inside the pcm structure.

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3D PCM Structure

3D-Cells

3S2P battery model 180mm*120mm*100mm (l*b*h), six cells of 18mm diameter and a distance of 40mm between each cell wall is maintained.

PCM

• According to research data and simulation processes the experimental pcm has limitations instead a paraffin based pcm is applied. As the paraffin pcm data is been extracted from research paper in which modulated temperature differential scanning calorimetry experiment is conducted on paraffin and its properties like specific heat variation with temperature is evaluated.

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SPECIFIC HEAT VARIATIONS WITH TEMPERATURE OF PCM

• The specific heat of pcm varies with temperature,the variation is accounted in three temperature intervals. In simulation the pcm material properties are added according to variation as linear and piecewise-polynomial.

�����������������������THE GRAPH DEPICTS THE SPECIFIC HEAT VARIATION VS TEMPERATURE.

ASSUMPTIONS

• The initial cell temp. is kept close to the ambient temp. of 27⁰C and all initial conditions have been set to ambient conditions.
• The heat flux density of 24560W/m² is kept constant for all the cells.
• Radiation factor is neglected and all heat transfer between cells and fluids (air and pcm) are to take place in an adiabatic condition.
• Heat generation of all the wall interfaces is considered zero.
• PCM is analysed as per simulation condition for temperature control at high peak cell temperatures and liquid phase analysis of pcm is not considered.
• No liquid flow of pcm in the module is considered.
• The pcm thermal conductivity issues of low values is not evaluated and direct pcm volume is considered for analysis with no change in composition.

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SIMULATION PROCESS

• The simulation includes analysis conditions, processes, cell wall temperature variations at peak temperatures as well as at high temperatures ranging from 48 -55⁰C. The results have been accessed through CFD post process in the result tab by plotting temperature contours at various time steps after specific iterations to get the required condition.
• Meshed Model

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• Fluent Analysis-Pressure based transient analysis, Solidification/melting-On, Energy-On

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• Cell-Zone Conditions-Cells(heater)-5457988W/m^3 PCM-0 W/m^3.

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• Boundary Conditions-Interfaces-Cell Wall(CW) with Heat Flux-24560W/m^2,PCMWALL(PW) and boundary walls with adiabatic condition i.e Heat Flux=0

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• Intialisation and Calculation with time step calculations.

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• Result-CFD post processors.

RESULT AND DISCUSSION

• The simulation is done considering all the ranges and cell wall temperature is reduced due to pcm cooling action. The simulation is done in temperature time steps, keeping the heat flux and heat output of cells constant. The solution is solved using pressure based solver, unsteady time and 1^st Order Explicit, viscous conditions to be laminar, heat transfer and solidification/melting is turned “on”. The battery module is analysed from 27⁰C-30⁰C to the peak battery temperature (47⁰C-55⁰C). The results are plotted in the CFD post-processor, inserting plane in XY plane.
• The following are the temperature contours of PW (coolant wall adjacent to battery cells) when the cells heat up with heat flux of 24560W/m², heat generation rate of 5457988W/m³ and heating up with time steps to get to required temperature conditions.

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TEMPERATURE CONTOURS OF PW(PCM WALL)�300K-327K

300K

307K

310K-313k

313K-317K

317K

313K-320K

319-320K

322K

THE PCM TEMPERATURE CONTOURS SHOW THE TREND OF INCREASING TEMPERATURE AT UNIFORM RATE DUE TO HEAT TRANSFER BETWEEN THE CELL WALL AND PCM WALL. INTERFACES HAVE BEEN CREATED TO EVALUATE THESE TEMPERATURES.THE CELL HEAT IS BEING DISSIPATED TO THE PCM WALL AND CONTROL THE CELL TEMP. AT PEAK LOADS.�

321-323K

324K-327K

PCM EFFECT

• The heat generation by the cells has directly activated the pcm walls. So in the contours, it is visible that with increasing cell wall temperature, the pcm temperature also increases rapidly to start cooling action and there is nearly 2-3K rise in every time step.
• The battery cell temperature is brought to normal by controling the peak value due to the action of pcm as its melting point is 53⁰C. The cell wall temperature is reduced simuntaneously as the heat flux is kept constant with limiting temperature to peak numbers.
• The pcm is considered to be in solid state and solid-liquid interference is neglected. The cell wall temperature contours have been plotted at regular time steps, ambient conditions like high temperature range during heavy load on the batteries, high discharging rate, high temperature condition, environmental condition where the battery temperature rises rapidly. The high temperature conditions of the battery cells depicts the reduction of cell wall temperature from 327K to 314K due to the presence of pcm during 15-20 minutes of action as the temperature range is near to the melting point of pcm, hence maximum heat transfer takes place between the two interfaces.

CELL WALL TEMPERATURE

327K

323K-324K

324K

317K

314K

• There is a drop in maximum cell wall temperture from 327K to 314K in the simulation in a few time steps. The major temperature drop is in the third all of the six cells drop temperature by 4k from 327K to 323K each cell has little bit temperature variotion due to pcm cooling and its thermal conductivity.Then cell wall temperature drop to 321K with minmum as 318K and in the last step to bring battery cell wall temperature in the range of 317K with least 314K

CELL WALL VS PCM WALL COMPARISON

The graphical data depicts the maximum PW and CW temperatures between 300K and 327K with respest to time in seconds.The graph is plotted using output values from the simulation with maximum cw temperature 327K in 600 seconds due to pcm action the cw temperature drops to 314K and the pcm temperature rise first linearly and after break at melting point becomes straight at 330K.

CELL WALL TEMPERATURE WITH N WITHOUT PCM

The graph is plotted using simulation data and literature data of cell wall temperature in two conditions one without pcm and other with pcm.It is visble from the graph pcm is able to control peak cell wall temperatures.

CONCLUSION

The potential of a battery can be severely affected by its ambient conditions. When it comes to thermal characteristics of a battery, it is largely reliant on its rate of discharge and ambient temperature.

The use of a pcm can impact the heat generation in an effective manner, considerably lowering the temperature of heat given off by the cells and regulating the overall temp. of the battery pack. Paraffin wax pcm was adopted for this study to check its efficiency at various temperatures.

Tests were done with pcm and without pcm. Without the application of pcm, when the cells were heated up with a heat flux density of 24560W/m², the cell temperature reached a maximum temperature of 330K and air wall temperature was recorded as 329k at the warmest point and 323K at coolest point.

When the pcm was incorporated, maintaining the same heat flux and heat generation values, the ambient temperatures of the battery were able to be brought down by 2-3K. The peak temperature of the cell wall was recorded at 327K compared to 330K recorded without the application of pcm. The peak pcm temperature was recorded at 327K. The cell heat is dissipated into the pcm and controls the cell temperature at peak loads. This brings down the general temp. of the battery.

From the results, the efficiency of a pcm as a TMS for a battery can be observed. It will greatly improve and preserve the performance of the battery over time and help minimize the dangers of an overheated battery