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| en:av:autonomy_and_autonomous_systems:technology:power_sources [2021/06/14 08:56] – agrisnik | en:av:autonomy_and_autonomous_systems:technology:power_sources [Unknown date] (current) – external edit (Unknown date) 127.0.0.1 | ||
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| There are two main battery types: single-use - **primary** and rechargeable - **secondary**. Electric vehicles (EV) and most of the other autonomous systems use secondary batteries (except for small toy vehicles and special applications) hence in this chapter the term battery mean secondary battery unless noted otherwise. From an economic perspective, | There are two main battery types: single-use - **primary** and rechargeable - **secondary**. Electric vehicles (EV) and most of the other autonomous systems use secondary batteries (except for small toy vehicles and special applications) hence in this chapter the term battery mean secondary battery unless noted otherwise. From an economic perspective, | ||
| - | From everyday knowledge, it is known that batteries have different voltages. A wall clock typically uses an AA or AAA size 1.5V battery while a car has a 12V lead-acid battery under the hood. There are two reasons for different battery voltages: chemistry and series connection. The chemical composition of battery materials determines the voltage in the range of 1.2V to 3.9V. How come a car lead-acid battery has 12V? It actually has multiple smaller batteries inside and they are series-connected (mind the polarity) to sum up their voltages. These individual internal batteries are called cells. Figure 1 shows some multi-cell batteries. It would be technically correct to say that a battery is in fact two or more series-connected cells of the same kind. Hence a battery composed of just a single cell would not be a battery but rather just a cell. However, to not cause confusion it is accustomed in everyday language to use the term battery for any number of cells while a cell means a single element. This notation will be used here as well. One of-the-shelf battery is the car lead-acid battery which has six 2.1V cells inside (the voltage is rounded to 12V for convenience), | + | From everyday knowledge, it is known that batteries have different voltages. A wall clock typically uses an AA or AAA size 1.5 V battery while a car has a 12 V lead-acid battery under the hood. There are two reasons for different battery voltages: chemistry and series connection. The chemical composition of battery materials determines the voltage in the range of 1.2 V to 3.9 V. How come a car lead-acid battery has 12 V? It actually has multiple smaller batteries inside and they are series-connected (mind the polarity) to sum up their voltages. These individual internal batteries are called cells. Figure 1 shows some multi-cell batteries. It would be technically correct to say that a battery is in fact two or more series-connected cells of the same kind. Hence a battery composed of just a single cell would not be a battery but rather just a cell. However, to not cause confusion it is accustomed in everyday language to use the term battery for any number of cells while a cell means a single element. This notation will be used here as well. One of-the-shelf battery is the car lead-acid battery which has six 2.1 V cells inside (the voltage is rounded to 12 V for convenience), |
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| **Voltage** | **Voltage** | ||
| - | The chemical composition of electrodes defines the voltage of a single cell. All types of battery cells have a certain nominal voltage Unom. As previously noted, the nominal voltage of different chemistries is in the range of 1.2 V to 3.9V. The nominal voltage is somewhere between maximal voltage Umax (charging voltage) and minimal voltage Umin (discharge cut-off voltage, end-of-discharge). The nominal voltage is used for calculations to determine the voltage of the battery pack if cells are series-connected. Discharge cut-off voltage is the voltage beyond which discharge should be terminated to prevent damage to the cell. A battery discharge voltage curve is given in the figure below. For primary batteries, it is desirable to have a flat curve which translates to a stable supply voltage. | + | The chemical composition of electrodes defines the voltage of a single cell. All types of battery cells have a certain nominal voltage Unom. As previously noted, the nominal voltage of different chemistries is in the range of 1.2 V to 3.9 V. The nominal voltage is somewhere between maximal voltage Umax (charging voltage) and minimal voltage Umin (discharge cut-off voltage, end-of-discharge). The nominal voltage is used for calculations to determine the voltage of the battery pack if cells are series-connected. Discharge cut-off voltage is the voltage beyond which discharge should be terminated to prevent damage to the cell. A battery discharge voltage curve is given in the figure below. For primary batteries, it is desirable to have a flat curve which translates to a stable supply voltage. |
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| The next electrical parameter is current. A good battery datasheet will provide at least a few current values at different conditions. Common parameters are standard charge current, rapid charge current, max. continuous discharge current and standard discharge current. Often the charging current ratings are significantly lower than discharge ratings. | The next electrical parameter is current. A good battery datasheet will provide at least a few current values at different conditions. Common parameters are standard charge current, rapid charge current, max. continuous discharge current and standard discharge current. Often the charging current ratings are significantly lower than discharge ratings. | ||
| - | In engineering and battery datasheets there is another battery-specific parameter that is directly related to Ah rating: the C-rate. The value of 1C is the number same as the nominal capacity of the battery. The C-rate itself has no unit of measurement but when it is converted to current it is expressed in amps A. C-rate is used to determine current for both charge and discharge. It comes in handy when comparing the current capabilities of different batteries and simply estimating how large the current is with respect to the capacity of the battery. For example, the 2C discharge rate of a 10Ah battery is 20A while the 0.5C charge rate of the same battery is 5A | + | In engineering and battery datasheets there is another battery-specific parameter that is directly related to Ah rating: the C-rate. The value of 1 C is the number same as the nominal capacity of the battery. The C-rate itself has no unit of measurement but when it is converted to current it is expressed in amps A. C-rate is used to determine current for both charge and discharge. It comes in handy when comparing the current capabilities of different batteries and simply estimating how large the current is with respect to the capacity of the battery. For example, the 2 C discharge rate of a 10Ah battery is 20A while the 0.5 C charge rate of the same battery is 5A |
| **Cycle life and ageing** | **Cycle life and ageing** | ||
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| The most notable fuel cell technology is the proton exchange membrane fuel cell (PEM FC). The basic elements of a fuel cell are anode, cathode and electrolyte. A PEM layer contains an electrolyte and separates the anode from the cathode. Fuel is delivered to the anode side while oxygen is delivered to the cathode side. Popular fuels are hydrogen and methanol. As an electrochemical reaction takes place, protons from fuel are transferred through the PEM to the cathode side where waste is produced: water in case of hydrogen fuel and CO2 if methanol FC is used. As usual, the electrical load is connected to anode and cathode to deliver electrical energy. | The most notable fuel cell technology is the proton exchange membrane fuel cell (PEM FC). The basic elements of a fuel cell are anode, cathode and electrolyte. A PEM layer contains an electrolyte and separates the anode from the cathode. Fuel is delivered to the anode side while oxygen is delivered to the cathode side. Popular fuels are hydrogen and methanol. As an electrochemical reaction takes place, protons from fuel are transferred through the PEM to the cathode side where waste is produced: water in case of hydrogen fuel and CO2 if methanol FC is used. As usual, the electrical load is connected to anode and cathode to deliver electrical energy. | ||
| - | Common efficiencies are in the 50 to 60% range which means that a significant amount of heat will be generated during power production – a cooling system like one of the common ICE vehicles is required as the temperature operating range of FCs is limited. | + | Common efficiencies are in the 50% to 60% range which means that a significant amount of heat will be generated during power production – a cooling system like one of the common ICE vehicles is required as the temperature operating range of FCs is limited. |
| A key issue for hydrogen FC adoption is the lack of refuelling infrastructure. Hydrogen gas is extremely flammable, it can diffuse in and through metals and it can cause metal embrittlement hence manufacturing, | A key issue for hydrogen FC adoption is the lack of refuelling infrastructure. Hydrogen gas is extremely flammable, it can diffuse in and through metals and it can cause metal embrittlement hence manufacturing, | ||
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| In simplistic terms, supercapacitors (SC) are capacitors with extremely high capacity. In fact, they use special physical effects (electrochemical pseudocapacitance and/or electrostatic double-layer capacitance) to provide capacity. Depending on brand names and physical effects, supercapacitors are also called boost capacitors, ultracapacitors, | In simplistic terms, supercapacitors (SC) are capacitors with extremely high capacity. In fact, they use special physical effects (electrochemical pseudocapacitance and/or electrostatic double-layer capacitance) to provide capacity. Depending on brand names and physical effects, supercapacitors are also called boost capacitors, ultracapacitors, | ||
| - | One must not confuse SCs with common high capacity aluminium electrolytic capacitors which are made with rated voltages from a few to hundreds of volts. The rated voltage of a single SC cell is in the range of 2.1 to 3V. | + | One must not confuse SCs with common high capacity aluminium electrolytic capacitors which are made with rated voltages from a few to hundreds of volts. The rated voltage of a single SC cell is in the range of 2.1 V to 3 V. |
| The capacity of single SCs ranges from hundreds of millifarads to a few kilofarads – they extend the capacitor capacity range as the largest electrolytic capacitors are just around 1F incapacity. However, they have not replaced batteries due to relatively minuscule specific energy (7.4Wh/kg for 3400F capacitor), which makes them inappropriate for bulk energy storage. | The capacity of single SCs ranges from hundreds of millifarads to a few kilofarads – they extend the capacitor capacity range as the largest electrolytic capacitors are just around 1F incapacity. However, they have not replaced batteries due to relatively minuscule specific energy (7.4Wh/kg for 3400F capacitor), which makes them inappropriate for bulk energy storage. | ||
| SC technology is evolving to improve the overall performance. Hybrid capacitors have been developed – they use both SC and Li-ion technology. The result is a so-called lithium-ion capacitor – as the name suggests, it is more like a capacitor with some features of the Li-ion battery. | SC technology is evolving to improve the overall performance. Hybrid capacitors have been developed – they use both SC and Li-ion technology. The result is a so-called lithium-ion capacitor – as the name suggests, it is more like a capacitor with some features of the Li-ion battery. | ||
