Batteries for Electric Vehicles a Survey and Recommendation

Transcription

1 PRELIMINARY REPORT FOR THE UNIVERSITYCITY PROJECT Batteries for Electric Vehicles a Survey and Recommendation Volkan Y. Senyurek and Cheng-Xian (Charlie) Lin Department of Mechanical and Materials Engineering College of Engineering and Computing Florida International University Miami, Florida Mach 17,

2 Table of Contents Batteries for Electric Vehicles a Survey and Recommendation... 1 Summary... 3 Introduction... 4 Technical Parameters... 4 Battery Types... 6 Lead Acid Batteries... 6 Nickel-based Batteries... 7 Lithium Batteries... 8 Comparison of Energy Storage Devices for Vehicle Solutions... 9 Conclusions References

3 Summary The performance of an electric car, which uses electricity stored in a battery pack to power an electric motor, largely depends on the batteries it installs and uses. Although numerous battery technologies exist, selection of the batteries for a specific application requires a detailed comparative study. In this report, a survey of the existing battery technologies is performed, and recent development trend is identified. Through the analysis of the technical data, we have proposed the most suitable batteries technology for the UniversityCity bus project. 3

4 Introduction It is well recognized that electric vehicles have many advantages over fuel-combustion based classic vehicles, particularly due to its low or zero emission of CO2 and other pollutants. Energy storage systems, usually batteries, are essential parts for electric vehicles. The performance of the batteries will dictate the performance of the electric vehicles. Therefore, it is very important to select the right batteries for the electric vehicles for specific applications. A number of different battery technologies exist. The lead acid battery has been used to supply vehicle electricity for a number of decades. With the introduction of the first modern EVs, Nickelcadmium batteries were originally used, then later replaced in hybrid vehicles by nickel-metal hydride batteries. Other batteries types are in the intensive growth and expansion, including Lithium-ion battery (Li-ion), Li-ion polymer battery, Sodium Nickel Chloride battery (NaNiCl), Lithium iron phosphate battery (LiFePO4), and Zinc Air battery. In the following, we will first define some important technical parameters that are usually used to indicate the performance of the batteries. We will then provide a comparison of the different batteries available, with the goal to identify a battery type that is most suitable for the UniversityCity bus project. Technical Parameters There are many importance parameters used to measure the performance of a battery. These parameters includes specific energy, energy density, specific power, typical voltages, commercial availability, cost, operating temperatures, self-discharge rates, number of life cycles and recharge rates. Figure 1 shows the typical battery equivalent circuit for an energy cell, where Rm is the resistance of the metallic path including terminals, electrodes and inter-connections. Ra is the electrochemical path Figure 1 Battery equivalent circuits 4

5 resistance. Cb is the capacitance of the parallel plates. Ri is the non-linear contact resistance between the plate and electrolyte. Cell voltages All electric cells have nominal voltages which gives the approximate voltage when the cell is delivering electrical power. The cells can be connected in series to give the overall voltage required. Charge (or Amp-hour) capacity The total Amp-hours (Amp-hr) available when the battery is discharged at a specific current. Specific Energy Specific energy is the amount of electrical energy stored for every kilogram of battery mass. It has units of Wh/kg Specific power Maximum power (Watts) that the battery can provide per unit mass, function of internal resistance of battery. The normal units are W/kg. Self-discharge rates Most batteries discharge when left unused, and this is known as self-discharge. The rate varies with battery type, and with other factors such as temperature; higher temperatures greatly increase self-discharge. Depth of Discharge (DOD) The percentage of battery capacity that has been discharged. Battery life and number of deep cycles This is one of the key cell performance parameters and gives an indication of the expected working lifetime of the cell. The cycle life is defined as the number of cycles a cell can perform before its capacity drops to 80% of its initial specified capacity. 5

6 Battery Types Lead Acid Batteries The traditional 12 V vehicle electrical system battery has plates made from lead and lead/lead oxide and are used as electrodes. Sulfuric acid is the electrolyte. Lead acid batteries are well established commercially with good backup from industry. They are the cheapest rechargeable batteries per kilowatt-hour of charge. However, they have low specific energy for a long-range vehicle design. Lead Figure 2 Lead acid battery acid batteries require a very long recharge period, as long as 6 to 8 hours. Lead acid batteries, because of their chemical makeup, cannot sustain high current or voltage continuously during charge [1]. Table 1 provides some nominal battery parameters (specific energy, energy density, specific power, nominal cell voltage, self-discharge rate, number of life cycles, and recharge time) for lead acid batteries. Table 1 Nominal battery parameters for lead acid batteries [1] Specific energy Energy density Specific power Nominal cell voltage Self-discharge, Number of life cycles Recharge time Wh/kg Wh/L 250 W/kg 2 V 2% per day Up to 800 to 80% capacity 8 h (but 90% recharge in 1 h possible) 6

7 Nickel-based Batteries Figure 3 Nickel Metal Hydride battery group These batteries include nickel iron, nickel zinc, nickel cadmium and nickel metal hydride batteries. Among of them the nickel metal hydride batteries have the most promise. In terms of energy density and power density the metal hydride cell is better than the NiCad battery. Ni/MH batteries have a nominal specific energy of about 65 Wh/kg and a nominal energy density of 150 Wh/L and a maximum specific power of about 200 W/kg. The nominal cell voltage is 1.2 V. NiMH are not as susceptible to heat and can be recharged very quickly, allowing for high current or high voltage charges which can bring the battery from a 20% state of charge to an 80% state of charge in as quick as 20 minutes. Initial cost of the NiMH high than Lead acid battery [1-3]. Table 2 provide the nominal batter parameters for the nickel metal hydride batteries. Table 2 Nominal battery parameters for nickel metal hydride batteries [1] Specific energy Energy density Specific power Nominal cell voltage Self-discharge, Number of life cycles Recharge time 65 Wh/kg 150 Wh/L 200 W/kg 1.2 V 5% per day 1000 to 80% discharge 1 h, rapid charge to 60% capacity 20 mins 7

8 Lithium Batteries Lithium batteries offer increased energy density in comparison with other rechargeable batteries, though at greatly increased cost. Cells that Li+ cations low within the cell are referred to as Li-ion. Figure 4 Typical Lithium-ion cell battery parameters for lithium ion batteries. There are many variations consisting of different electrode materials. Positive electrode materials include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMnO4) and lithium iron phosphate (LiFePO4). The nominal cell voltage is dependent on the materials. Generally Lithium batteries have better specific power, specific energy and cell voltage characteristics. But initial cost and lower cycle life are the disadvantages of them. They needs control and protection circuit since if lithium-ion batteries are exposed to high temperatures, decomposition processes can result in the battery. This can lead to fire or the emission of dangerous gases [4-6]. Table 3 provide the nominal Table 3 Nominal battery parameters for lithium ion batteries. [1] Specific energy 90 Wh/kg Energy density 153 Wh/L Specific power 300 W/kg Nominal cell voltage 3.5 V Self-discharge, 10% per month Number of life cycles >1000 Recharge time 2-3 h 8

9 Each specific type of battery has characteristics which make it either more or less desirable to use in a specific application. Table 4 shows the comparison of some commercially available batteries. Table 4 comparison of some commercially available batteries [7]. Battery Type Energy Density Power Density W/kg Life Cycles Per Battery Cost on scale of 1 to 10 Whr/kg Current Lead Acid Advanced Lead Acid GM Ovonic NiMH >600 8 SAFT NiMH ,500 8 SAFT lithium ion Lithium polymer < Zebra sodiumnickel < chloride Impact on Vehicle performance Range Acceleration Life Cycle Cost, Replacement Cost Initial Cost, Replacement Cost Comparison of Energy Storage Devices for Vehicle Solutions Summary of main characteristics of energy storage devices for some vehicles is given in Table 5. The vehicles covered in the Table include bus, truck, and car. The energy capacity for each battery type is also indicated in the Table. 9

10 Table 5 Several vehicle solutions with different energy storage types BUS TRUCK CAR VEHICLE ENERGY STORAGE TYPE ENERGY CAPACITY Optare Solo EV Battery Electric Bus LiFePO4 Battery 80 kwh Solaris Urbino Electric Bus Li-ion Battery 120kWh BYD ebus-12 LiFePO4 Battery 324 kwh Battery Electric Bus Tindo ZEBRA (NaCl+Ni) 261,8 kwh Solar Electric Bus MotoEV Electro Transit Buddy 28 Lead Acid battery 36kWh Passenger 2x 12 x T-145 Phoenix Motorcars Ford E350/E450 lithium ion phosphate 105kWh Proterra Catalyst 35-Foot Lead Acid battery kwh GreenPower Motor EV250 LiFePO4 Battery 210kWh US Hybrid ecargo Li-ion Battery 36kWh US Hybrid Drayage Truck Li-ion Battery 240kWh E-Force 18t Electric Truck LiFePO4 Battery 240kWh Iveco ZEBRA (NaCl+Ni) 21.2kWh Tesla Roadster Li-ion Battery 53kWh Nissan LEAF LiNiMnCoO2 (NMC) 24kWh Ford Focus E Li-ion Battery 33.5kWh Mitsubishi i-miev Lithium Titanate 16kWh When we examine table 4 and 5, lithium batteries better options for electric vehicles nowadays because of their power and energy density. But there are many lithium based batteries and they have different characteristics and usage field. Lithium Cobalt Oxide (LiCoO2) the popular choice for mobile phones, laptops and digital cameras since its high specific energy. The drawback of Li-cobalt is a relatively short life span, low thermal 10

11 stability and limited specific power. Li-cobalt should not be charged and discharged at a current higher than its C-rating. Forcing a fast charge or discharging causes overheating and undue stress. Lithium Manganese Oxide (LiMn2O4) has low internal cell resistance and this future enables fast charging and high-current discharging. A further advantage of spinel is high thermal stability and enhanced safety. Li-manganese is used for power tools, as well as hybrid and electric vehicles. But energy capacity, the cycle and calendar life are limited. Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC) is maybe one of successful Li-ion battery. NMC has good overall performance and excels on specific energy. This battery is the preferred candidate for the electric vehicle and has the lowest self-heating rate. Lithium Iron Phosphate (LiFePO4) is one of the most popular battery type for electrical vehicles. Main advantages are high current rating and long cycle life, besides good thermal stability, enhanced safety and tolerance if abused. But Li-phosphate has a higher self-discharge than other Li-ion batteries. Lithium Nickel Cobalt Aluminum Oxide (LiNiCoAlO2) shares similarities with NMC by offering high specific energy, reasonably good specific power and a long life span. High cost and marginal safety are disadvantages of its. Lithium Titanate (Li4Ti5O12) can be fast charged and delivers a high discharge current. The cycle life is higher than that of a regular Li-ion. Li-titanate is safe, has excellent low-temperature discharge. However, the battery is expensive and at the specific energy is lower than other Li-ion batteries. Conclusions Among all the Li-ion batteries, NMC and LiFePO4 are more suitable for heavy applications like as our SW-1 bus. Both of them have good power and energy density performance. LiFePO4 has more specific power and cost advantages. It s one of safest Li-ion battery also. LiFePO4 looks best options battery for SW-1 vehicle. 11

12 References [1] Larminie, James, and John Lowry. Electric vehicle technology explained. John Wiley & Sons, [2] Živanović, Zlatomir, and Zoran Nikolic. The application of electric drive technologies in city buses. INTECH Open Access Publisher, [3] Eudy, Leslie, et al. "Foothill Transit battery electric bus demonstration results." National Renewable Energy Laboratory. (2016). [4] Onori, Simona, Lorenzo Serrao, and Giorgio Rizzoni. "Hybrid Electric Vehicles Energy Management Strategies." SpringerBriefs in electrical and computer engineering, Control, automation and robotics (2016). [5] Volkswagen Self Study Program Basics of Electric Vehicles Design and Function (2013) [6] Yoshio, Masaki, Ralph J. Brodd, and Akiya Kozawa. Lithium-ion batteries. Vol. 1. New York: Springer, [7] Center for Energy. Transportation and Environment/ (accessed: march 2017) [8] (accessed: march 2017) [9] Optare Electric Vehicles Solo Brochure (accessed: march 2017) [10] Solaris Electric Buses experience and further development. (accessed: march 2017 ) [11] 2014 BYD 12m Electric Bus Specifications. (accessed: march 2017) [12] Tindo the World s First Solar Electric Bus. df (accessed: march 2017) [13] Phoenix Motorcars Ford E350/E450 specs. (accessed: march 2017) [14] The Proterra Catalyst 35-Foot Transit Vehicle. foot-catalyst/ (accessed: march 2017) 12

13 [15] GreenPower Motor EV250 specs. (accessed: march 2017) 13