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--- en:av:technology [2020/06/11 09:00] – kristaps.vitols
+++ en:av:technology [2020/07/20 09:00] (current) – external edit 127.0.0.1
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 <figure label>
-{{:en:av:bfig_4_pba_dch.png?300|title}}
+{{:en:av:bfig_4_pba_dch_2.png?500|title}}
 <caption>Discharging process of a lead-acid cell.</caption>
 </figure>
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 <figure label>
-{{:en:av:bfig_5_pba_chg.png?300|title}}
+{{:en:av:bfig_5_pba_chg_2.png?500|title}}
 <caption>Charging process of a lead-acid cell.</caption>
 </figure>
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 <figure label>
-{{:en:av:bfig_8.png?400|title}}
+{{:en:av:bfig_8_2.png?700|title}}
 <caption>Generic chemical reactions of a Li-ion cell.</caption>
 </figure>
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 As previously noted, there are six common Li-ion chemistries. They differ according to the materials used in both electrodes. The widest variety is for the positive electrode (cathode) which can have five compositions: LCO, LMO, NMC, NCA and LFP. These three letters are abbreviations of the main chemical components of the active material. LCO and LMO are among the first commercially available Li-ion chemistries. Their composition is straightforward: L stands for lithium, C stands for cobalt, M stands for manganese and O stands for oxide/oxigen. Therefore, LCO Li ion cell has lithium cobalt oxide (LiCoO<sub>2</sub>) cathode (positive electrode) and LMO cell has lithium manganese oxide (LiMn<sub>2</sub>O<sub>4</sub> or Li<sub>2</sub>MnO<sub>3</sub>).  cathode. It gets a little bit complicated with NMC and NCA where N is nickel, C is cobalt, M is manganese and A is aluminum. In the names of these two materials lithium (L) and oxide (O) parts are omitted to maintain three-letter format. Therefore, NMC is lithium nickel manganese cobalt oxide (LiNiMnCo<sub>2</sub>) and NCA is lithium nickel cobalt aluminum oxide (LiNiCoAlO<sub>2</sub>). Finally, in LFP L stands for lithium, F for iron (from Latin: ferrum) and P for phosphate. Therefore, the cathode of LFP chemistry is made of lithium iron phosphate (LiFePO4). In all these five chemistries only the cathode (positive electrode) was the variable. The anode material in all five types remained the same: graphite. The remaining type is LTO where L is for lithium, T is for titanium and O is for oxide/oxygen. Due to some chemical nomenclature rules this material is called lithium titanate (Li<sub>2</sub>TiO<sub>3</sub>). LTO is used to replace the graphite anode. For some confusion, the cathode of an LTO cell can be made of LMO or NMC material. Additionally, the performance of these types is changing as battery technology is advancing. For example, NMC is a popular type for EVs. It used to have 1:1:1 ratio between nickel, manganese and cobalt hence an extended name was NMC111. Then chemistry was improved to reduce cobalt content (an expensive conflict mineral) and new NMC622 type modification was introduced. It is expected that NMC811 material will be available and become mainstream in near future. The key difference between these variations is the increase in gravimetric energy density.
-To summarize, each of six basic types have their specific characteristics: cost, energy density, specific power, safety, life span, temperature range even the voltage. From this, one significant conclusion can be drawn: the name “Li-ion battery” is quite generic – the true performance is revealed when the exact type of chemistry is known. To continue the confusion, a term lithium polymer (Li-poly, LiPo) battery exists. Despite the rumors that Li-poly is some special battery type, it is a type of Li-ion battery which has a sort-of solid electrolyte. In a Li-poly battery, the common liquid electrolyte of a traditional Li-ion battery is replaced with a gel-like electrolyte. In practice, majority of Li-ion cells have some additives and improved separator structure to confine liquid electrolyte thus essentially making Li-poly cells. These cells are mainly made in pouch format. A different variation is the solid-state Li-ion – as the name implies, the electrolyte is made fully solid thus making it possible to produce cells thinner than 1mm. Fully solid-state Li-ion technology is still in research and development stage, however it promises higher charge/discharge rates, longer lifecycles, higher energy density while being safer and less expensive. Most likely all promises will not be carried out but announcements from developer companies indicate that solid-state batteries will become commercially available during this decade. Progress in solid-state technology is intertwined with development of lithium-sulfur (Li-S) battery. Li-S battery could be the next breakthrough in energy density however it heavily relies on functional solid-state technology. A closer future is improved anode materials for existing chemistries. The common graphite anode can be replaced by silicon material which can store significantly more Li ions resulting higher energy density. However, silicon anode cannot provide required cycle life. Both materials are being combined to achieve both features. Advances in carbon materials promise improvements in battery chemistry. One novel carbon allotrope is graphene which excels in high electrical and thermal conductivity – both features can be used to improve performance of traditional graphite-based anodes.
+To summarize, each of six basic types have their specific characteristics: cost, energy density, specific power, safety, life span, temperature range even the voltage. A graphical representation of some different features is given in figure 9. From this, one significant conclusion can be drawn: the name “Li-ion battery” is quite generic – the true performance is revealed when the exact type of chemistry is known. To continue the confusion, a term lithium polymer (Li-poly, LiPo) battery exists. Despite the rumors that Li-poly is some special battery type, it is a type of Li-ion battery which has a sort-of solid electrolyte. In a Li-poly battery, the common liquid electrolyte of a traditional Li-ion battery is replaced with a gel-like electrolyte. In practice, majority of Li-ion cells have some additives and improved separator structure to confine liquid electrolyte thus essentially making Li-poly cells. These cells are mainly made in pouch format. A different variation is the solid-state Li-ion – as the name implies, the electrolyte is made fully solid thus making it possible to produce cells thinner than 1mm. Fully solid-state Li-ion technology is still in research and development stage, however it promises higher charge/discharge rates, longer lifecycles, higher energy density while being safer and less expensive. Most likely all promises will not be carried out but announcements from developer companies indicate that solid-state batteries will become commercially available during this decade. Progress in solid-state technology is intertwined with development of lithium-sulfur (Li-S) battery. Li-S battery could be the next breakthrough in energy density however it heavily relies on functional solid-state technology. A closer future is improved anode materials for existing chemistries. The common graphite anode can be replaced by silicon material which can store significantly more Li ions resulting higher energy density. However, silicon anode cannot provide required cycle life. Both materials are being combined to achieve both features. Advances in carbon materials promise improvements in battery chemistry. One novel carbon allotrope is graphene which excels in high electrical and thermal conductivity – both features can be used to improve performance of traditional graphite-based anodes.
+<figure label>
+{{:en:av:bfig_9_lion_types.png?500|title}}
+<caption>Characteristics of common Li-ion types.</caption>
+</figure>
 == Discharging ==
-All LIBs are characterized by relatively low self-discharge and no memory effect as opposed to the NiMH chemistry which requires occasional full discharge. In case of LIBs, full discharge is to be avoided to maximize battery lifespan. As for most batteries, the discharge rate affects the voltage of the cell – at high rates the voltage will drop more, in some cases it is beneficial to decrease the cut-off voltage to achieve desired end DoD. In most LIBs the discharge curve (vertical axis represents battery voltage while horizontal axis represents SoC or DoD) is linear with a drop at the final stage of discharge (90-100% DoD) when discharged at low rate. However, as the rate is increased, the drop at high DoD becomes flatter while the voltage drops faster at the opposite end of the curve, at low DoD (Fig. 9). The discharge performance is heavily affected by the temperature of the cell - in figure 9, the 6.6C rate curve does not reach 2.0V cut-off voltage because temperature of the cell has risen to the max limit. The nominal curve is given at 20, 23 or 25°C. At 45°C ambient temperature, the voltage curve of the cell is increased by less than 100mV, hence increased temperature minimally affect voltage under discharge. The situation is different if ambient temperature is decreased. At 0°C the voltage of a cell can a couple hundred mV lower (fig. 10). At negative temperatures the voltage decreases further limiting the discharge rate – if rate is too high the voltage drops below cut-off voltage and discharge should be terminated. This effect is somewhat mitigated if cell is operated at moderate discharge rate – due to internal losses the cell can self-heat and thus improve its performance. For most Li-ion types the available capacity rapidly decreases at low temperature (below -15°C). However, there exists a wide variety of different types and special purpose battery models which are designed to operate at high rates or low temperatures.
+All LIBs are characterized by relatively low self-discharge and no memory effect as opposed to the NiMH chemistry which requires occasional full discharge. In case of LIBs, full discharge is to be avoided to maximize battery lifespan. As for most batteries, the discharge rate affects the voltage of the cell – at high rates the voltage will drop more, in some cases it is beneficial to decrease the cut-off voltage to achieve desired end DoD. In most LIBs the discharge curve (vertical axis represents battery voltage while horizontal axis represents SoC or DoD) is linear with a drop at the final stage of discharge (90-100% DoD) when discharged at low rate. However, as the rate is increased, the drop at high DoD becomes flatter while the voltage drops faster at the opposite end of the curve, at low DoD (Fig. 10). The discharge performance is heavily affected by the temperature of the cell - in figure 9, the 6.6C rate curve does not reach 2.0V cut-off voltage because temperature of the cell has risen to the max limit. The nominal curve is given at 20, 23 or 25°C. At 45°C ambient temperature, the voltage curve of the cell is increased by less than 100mV, hence increased temperature minimally affect voltage under discharge. The situation is different if ambient temperature is decreased. At 0°C the voltage of a cell can a couple hundred mV lower (fig. 11). At negative temperatures the voltage decreases further limiting the discharge rate – if rate is too high the voltage drops below cut-off voltage and discharge should be terminated. This effect is somewhat mitigated if cell is operated at moderate discharge rate – due to internal losses the cell can self-heat and thus improve its performance. For most Li-ion types the available capacity rapidly decreases at low temperature (below -15°C). However, there exists a wide variety of different types and special purpose battery models which are designed to operate at high rates or low temperatures.
-It can be said that the type of chemistry plays a critical role in the discharge performance. The most obvious initial difference is the nominal voltage. It is commonly assumed that a single Li-ion cell has 3.6V nominal voltage although 3.7V are prevalent as well – these values are for the dominant group of LCO, LMO, NMC and NCA. On top of these two numbers, values around them can exist as well, for example, //LG Chem// produces 18650-size INR18650MJ1 cell (NMC type) whose datasheet’s nominal voltage is 3.635V. However, 3.6 and 3.7 values are close together and difference is not critically important in most cases.
+It can be said that the type of chemistry plays a critical role in the discharge performance. The most obvious initial difference is the nominal voltage (figure 12). It is commonly assumed that a single Li-ion cell has 3.6V nominal voltage although 3.7V are prevalent as well – these values are for the dominant group of LCO, LMO, NMC and NCA. On top of these two numbers, values around them can exist as well, for example, //LG Chem// produces 18650-size INR18650MJ1 cell (NMC type) whose datasheet’s nominal voltage is 3.635V. However, 3.6 and 3.7 values are close together and difference is not critically important in most cases.
 <figure label>
-{{:en:av:bfig_9_lion_rate.png?500|title}}
+{{:en:av:bfig_10_lion_rate.png?500|title}}
 <caption>Voltage curves of a single NMC Li-ion cell at different discharge rates.</caption>
 </figure>
 <figure label>
-{{:en:av:bfig_10_lion_temp.png?500|title}}
+{{:en:av:bfig_11_lion_temp.png?500|title}}
 <caption>Voltage curves of a single NMC Li-ion cell at different ambient temperatures.</caption>
 </figure>
@@ Line 303: / Line 308: @@
 LTO is characterized by even lower nominal voltage ranging from 2.2 to 2.4V. The minimum discharge cut-off is at 1.5V while in some models it is recommended to stop discharging when voltage decreases to 1.85V. The relatively low nominal voltage is the greatest disadvantage of this chemistry. As previously described, energy of a cell can be calculated by multiplying capacity (Ah) with nominal voltage (V). At same capacity and significantly lower voltage the resulting energy and volumetric/gravimetric energy density will be low. This further translates to high initial cost per kWh of the battery pack – the highest among all LIBs. Otherwise, LTO has some significant advantages. Both charging and discharging rates are high: typically quoted discharge rates are up to 10C with 30C pulses. Pulse (10 seconds) current capability of actual high-power optimized models can be as high as 75C. The cycle life is measured in several thousands and if reduced DoD range is used then cycle life can extend to tens of thousands of cycles. Additionally, the operational temperature range is wide and thermal stability is high making LTO the safest Li-ion chemistry. For a practical example, Leclanche manufactures LT34 LTO cell with 34Ah capacity at 2.2V weighting 1080g. Simple calculation yields that gravimetric energy density is just 70Wh/kg – less than high performance NiMH chemistry can provide. However, this cell can be discharged at 6C and 10C in pulses at temperature range from -20 to +55°C. Additionally, at 100% DoD cycling it is rated for 15000 cycles while 80% DoD cycling will extend cycle life to 20000 cycles. Given parameters make LTO suitable for large EVs (bus, tram, train) and stationary energy storage which requires high charge and discharge rates.
-Fig. Voltage curves of all types.
+<figure label>
+{{:en:av:bfig_12_lion_voltages.png?500|title}}
+<caption>Generalized voltage curves of single Li-ion cells of various chemistries.</caption>
+</figure>
 == Charging ==
-In general, the CCCV charging method is used to charge LIBs similarly to lead-acid chemistry. Hence, there are two main charging phases: the faster constant-current phase and the slower constant-voltage phase. If a battery is deeply discharged (below minimum voltage) then a pre-charge phase should be introduced before full current CC phase. The pre-charge current should be 10% or less than the nominal charging current (given in the datasheet) of the battery. Once the voltage of the battery is higher than minimal discharge voltage, charger can switch to full current charging in CC phase. In normal operation, pre-charge phase should be omitted as BMS (battery management system) has to prevent deep discharge and associated damage to the LIB. However, if the battery voltage is indicating deep discharge then pre-charge should be carried out to pre-condition both electrodes for effective lithium ion transport. Immediately applying full current (or even worse fast-charge current) to a deeply discharged LIB can result in additional heating (risk of thermal runaway and associated danger) and permanent damage to the electrodes.
+In general, the CCCV charging method is used to charge LIBs similarly to lead-acid chemistry. Hence, there are two main charging phases: the faster constant-current phase and the slower constant-voltage phase as shown in figure 13. If a battery is deeply discharged (below minimum voltage) then a pre-charge phase should be introduced before full current CC phase. The pre-charge current should be 10% or less than the nominal charging current (given in the datasheet) of the battery. Once the voltage of the battery is higher than minimal discharge voltage, charger can switch to full current charging in CC phase. In normal operation, pre-charge phase should be omitted as BMS (battery management system) has to prevent deep discharge and associated damage to the LIB. However, if the battery voltage is indicating deep discharge then pre-charge should be carried out to pre-condition both electrodes for effective lithium ion transport. Immediately applying full current (or even worse fast-charge current) to a deeply discharged LIB can result in additional heating (risk of thermal runaway and associated danger) and permanent damage to the electrodes.
 Most of the charge to the battery is delivered during the CC charging phase. The controllable parameter is current. The standard charging rate commonly is 0.5C which results in approximately 2-hour 0-100% battery charging (including CV phase). Older Li-ion chemistries were quite sensitive to charging current – higher rates would result in metallic lithium plating on electrodes, electrode expansion (package deformation) and overall performance deterioration. In worst case it would result in thermal runaway and venting with flame. Progress of technology and development of new types (NMC, NCA) have resulted in more robust cells with higher allowable charging rates. Now, faster charging can be achieved by using 1C or even 2C rates. However, fast charging has its limits. In standard charging, most time of charging is spent in CC phase, when battery is charged to 80-90% SoC. CC phase is terminated when charging voltage level is reached and charging transitions to CV phase during which the remaining charge is delivered to the battery. Charging during CV phase happens much slower due to ever decreasing current. When high rate is used in CC phase, the charging voltage limit is reached much faster due to cell heating and resistive drop (seen as voltage increase) similar to that of discharge curve (at high discharge current battery voltage drops, at high charge current voltage steps up). As a result, less charge is transferred to the cell, for example just 60 – 80% or even less. The remaining charge must be delivered in the slower CV phase. The other issue with fast charging is temperature rise. Both resistive losses and ionic conductivity losses produce heat which increase temperature of the battery. When max temperature threshold has been reached, charging current must be decreased hence fast charging transitions to standard charging. This problem can be alleviated if proper thermal management is used for the battery pack. A quality cooling system can keep temperature low (well below max limit, preferably not more that around 30°C) to allow fast charging while avoiding performance degradation. For some battery models, active cooling can allow to increase charging current even higher to achieve faster charging time. In general, it is commonly assumed that EV fast charging (CC phase) can charge battery only to 80% SoC level.
@@ Line 313: / Line 321: @@
 Both LFP and LTO chemistries have some charging advantages. As LFP is thermally more stable it can be charged with 3C rate if proper temperature monitoring is used. The charging performance of some LTO cell models is dramatically different. While typical charging rates can be as high as 6C, cells with 10C and 60C pulse charging capability are available on the market. Some of such cells can be charged to 80% SoC in just 6 minutes.
-The CC phase ends and transition to CV phase happens once the voltage of the cell reaches charging voltage limit. For LTO, LMO, NMC and NCA chemistries, the charging voltage is 4.2V. Charging to a higher voltage will result in small addition to the capacity however the cell will degrade faster and the safety risks increase dramatically. Some high-energy optimized cells can be charged to 4.3V however in automotive applications the charging voltage is lowered to improve battery lifespan. Lower charging voltage naturally results in lower max SoC hence it is an easy method to decrease used capacity range. As previously noted, decreased used capacity (never fully charged, never fully discharged) increases cycle life. Additionally, keeping a Li-ion cell at its maximum voltage (same as charging voltage) stresses the internal structure which leads to overall degradation. Lowering max voltage reduces this internal chemical stress and promotes longer calendar life. Again, LFP and LTO max charging voltage is significantly different, same as nominal voltage. Depending on the exact chemistry LFP max charging voltage can be in 3.65 - 4V range. 3.65V is the dominating voltage level while 4V in some datasheets will be given as the absolute maximum level after which damage is imminent. LTO cells can be charged to 2.8 – 3V level – significantly less than other graphite anode-based LIBs.
+The CC phase ends and transition to CV phase happens once the voltage of the cell reaches charging voltage limit. For LCO, LMO, NMC and NCA chemistries, the charging voltage is 4.2V. Charging to a higher voltage will result in small addition to the capacity however the cell will degrade faster and the safety risks increase dramatically. Some high-energy optimized cells can be charged to 4.3V however in automotive applications the charging voltage is lowered to improve battery lifespan. Lower charging voltage naturally results in lower max SoC hence it is an easy method to decrease used capacity range. As previously noted, decreased used capacity (never fully charged, never fully discharged) increases cycle life. Additionally, keeping a Li-ion cell at its maximum voltage (same as charging voltage) stresses the internal structure which leads to overall degradation. Lowering max voltage reduces this internal chemical stress and promotes longer calendar life. Again, LFP and LTO max charging voltage is significantly different, same as nominal voltage. Depending on the exact chemistry LFP max charging voltage can be in 3.65 - 4V range. 3.65V is the dominating voltage level while 4V in some datasheets will be given as the absolute maximum level after which damage is imminent. LTO cells can be charged to 2.8 – 3V level – significantly less than other graphite anode-based LIBs.
-Fig x. Charging profiles
+<figure label>
+{{:en:av:bfig_13_lion_charging.png?500|title}}
+<caption>Charging curves of an NMC Li-ion cell. Current is expressed in percent where 100% represents 1C rate.</caption>
+</figure>
-The charging (SoC increase) speed gradually decreases during CV phase as the current rate declines. In standard charging, CC phase lasts less than 1 hour while CV phase can be in the range of 1 to 2 hours. As previously noted, majority of charge is delivered to the battery during the short CC phase while the long CV phase delivers remaining fraction. If it is required to fully charge a battery the additional step of cell balancing can increase charging time. The charging is terminated when charging current decreases below cut-off limit. This limit traditionally is 10-3% of the 1C rate. Charging cut-off conditions are not always provided by the battery manufacturer, hence there is some engineering freedom. Additionally, charging timeout can be introduced as well. For example, the datasheet of US18650VTC6 cell (manufactured by Sony) states CCCV charging to 4.2V at 2.5A (0.5C) with 2.5h cut-off - a current cut-off limit is not specified. The timeout criterion can be helpful when the battery reaches its end of life. In some cases, the self-discharge/leakage current increases as the battery ages. If the leakage current is higher than current cut-off level, then battery charging current will never decrease below set cut-off and charger will indefinitely continue charging the battery. A timeout can prevent this situation.
+The charging (SoC increase) speed gradually decreases during CV phase as the current rate declines. In standard charging, CC phase lasts less than 1 hour while CV phase can be in the range of 1 to 2 hours. As previously noted, majority of charge is delivered to the battery during the short CC phase while the long CV phase delivers remaining fraction. If it is required to fully charge a battery the additional step of cell balancing can increase charging time. The charging is terminated when charging current decreases below cut-off limit. This limit traditionally is 10-3% of the 1C rate. Charging cut-off conditions are not always provided by the battery manufacturer, hence there is some engineering freedom. Additionally, charging timeout can be introduced as well. For example, the datasheet of //US18650VTC6// cell (manufactured by //Sony//) states CCCV charging to 4.2V at 2.5A (0.5C) with 2.5h cut-off - a current cut-off limit is not specified. The timeout criterion can be helpful when the battery reaches its end of life. In some cases, the self-discharge/leakage current increases as the battery ages. If the leakage current is higher than current cut-off level, then battery charging current will never decrease below set cut-off and charger will indefinitely continue charging the battery. A timeout can prevent this situation.
-Charging is affected by temperature. Cell/battery datasheets provide information about ambient temperature for three situations: discharge, charge and storage. Traditionally one would expect that storage temperature range is the broadest. It is not so in case of LIBs. For short term storage (less than a month) it is the same as discharge operating temperature whose range can be -20°C to +60°C. As the storage time increases, ambient temperature should be kept within -20°C to 25°C range to maintain calendar life. Temperature during charging must be in 0 to 45°C range, preferably below 30°C. Already under 10°C standard charging rate should be decreased to 0.25C. It is generally assumed that LIBs should not be charged if temperature is below 0°C – if temperature is lower, ion mobility is restricted and charging will cause deformation of electrodes, which in turn will degrade performance and safety due to plating of metallic lithium. Both the LIB and the charger should be equipped with temperature monitoring to perform charging only if temperature is within safe operation range. If a battery will be required to be charged at freezing temperatures (an EV in northern countries where the winter temperatures are well below 0°C), then battery pack has to be equipped with thermal management which can provide heating. Of course, the temperature of the LIB will rise on its own during charging due to internal losses – BMS has to prevent temperature rise above operating point. Temperature can be controlled by controlling current or by using active thermal management. It can be noted that charging temperature can vary from model to model and from chemistry to chemistry. Again, LTO excels in operation at low temperatures. An LTO LT34 pouch cell made by Leclanche can be both discharged and charged at temperatures ranging from -20°C to +55°C. Research laboratories are working on improvements for all Li-ion chemistries to allow charging at temperatures below freezing point. There are reports that some LIBs (non-LTO) can be charged at freezing temperatures albeit at very low rates.
+Charging is affected by temperature. Cell/battery datasheets provide information about ambient temperature for three situations: discharge, charge and storage. Traditionally one would expect that storage temperature range is the broadest. It is not so in case of LIBs. For short term storage (less than a month) it is the same as discharge operating temperature whose range can be -20°C to +60°C. As the storage time increases, ambient temperature should be kept within -20°C to 25°C range to maintain calendar life. Temperature during charging must be in 0 to 45°C range, preferably below 30°C. Already under 10°C standard charging rate should be decreased to 0.25C. It is generally assumed that LIBs should not be charged if temperature is below 0°C – if temperature is lower, ion mobility is restricted and charging will cause deformation of electrodes, which in turn will degrade performance and safety due to plating of metallic lithium. Both the LIB and the charger should be equipped with temperature monitoring to perform charging only if temperature is within safe operation range. If a battery will be required to be charged at freezing temperatures (an EV in northern countries where the winter temperatures are well below 0°C), then battery pack has to be equipped with thermal management which can provide heating. Of course, the temperature of the LIB will rise on its own during charging due to internal losses – BMS has to prevent temperature rise above operating point. Temperature can be controlled by controlling current or by using active thermal management. It can be noted that charging temperature can vary from model to model and from chemistry to chemistry. Again, LTO excels in operation at low temperatures. An LTO //LT34// pouch cell made by //Leclanche// can be both discharged and charged at temperatures ranging from -20°C to +55°C. Research laboratories are working on improvements for all Li-ion chemistries to allow charging at temperatures below freezing point. There are reports that some LIBs (non-LTO) can be charged at freezing temperatures albeit at very low rates.
 == Battery management system ==
@@ Line 345: / Line 356: @@
 === Supercapacitors ===
-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, pseudocapacitors and electrostatic double-layer capacitors (EDLC). One must not confuse SCs with common high capacity aluminum electrolytic capacitors which are made with rated voltages from few to hundreds of volts. The rated voltage of a single SC cell is in the range of 2.1 to 3V. While majority of SCs are available as single cells, commercial SC batteries (series/parallel) with voltages higher than 100V are available on the market. The capacity of single SCs ranges from hundreds of millifarads to a few kilofarads – they extend capacitor capacity range as the largest electrolytic capacitors are just around 1F in capacity. If compared to LIBs, SC main advantage is the high specific power density (up to 14kW/kg) and vast cycle life (1000000 cycles). However, they have not replaced LIBs or other batteries due to relatively miniscule specific energy (7.4Wh/kg for 3400F capacitor) which makes them inappropriate for bulk energy storage. SCs can be used to improve the power capability of battery systems, especially in applications where the bulk energy storage is a relatively low capacity battery (with low power) as in hybrid vehicles and fuel cell vehicles. SCs can be successfully implemented in applications requiring regenerative braking: the power handling capability of SCs is perfect for absorbing high power pulses of braking while the stored energy can be used for the following acceleration also requiring high power.
+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, pseudocapacitors and electrostatic double-layer capacitors (EDLC). One must not confuse SCs with common high capacity aluminum electrolytic capacitors which are made with rated voltages from few to hundreds of volts. The rated voltage of a single SC cell is in the range of 2.1 to 3V. While majority of SCs are available as single cells, commercial SC batteries (series/parallel) with voltages higher than 100V are available on the market. The capacity of single SCs ranges from hundreds of millifarads to a few kilofarads – they extend capacitor capacity range as the largest electrolytic capacitors are just around 1F in capacity. If compared to LIBs, SC main advantage is the high specific power density (up to 14kW/kg) and vast cycle life (1000000 cycles). However, they have not replaced LIBs or other batteries due to relatively minuscule specific energy (7.4Wh/kg for 3400F capacitor) which makes them inappropriate for bulk energy storage. SCs can be used to improve the power capability of battery systems, especially in applications where the bulk energy storage is a relatively low capacity battery (with low power) as in hybrid vehicles and fuel cell vehicles. SCs can be successfully implemented in applications requiring regenerative braking: the power handling capability of SCs is perfect for absorbing high power pulses of braking while the stored energy can be used for the following acceleration also requiring high power.
 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 so called lithium ion capacitor – as name suggests, it is more like a capacitor with some features of the Li-ion battery. The main advantage is elevated voltage: 3.8V rated voltage increases the specific energy narrowing the gap between SCs and LIBs. Future improvements using graphene materials could increase performance of SC, the same is true for LIBs.
+To conclude this chapter see figure 14 - a Ragone plot which is an effective tool to graphically compare gravimetric energy density (specific energy) and gravimetric power density (specific power) of various energy storage elements. The lowest performance is at the bottom left corner while the highest performance is at the top right corner - a spot to be taken by future technologies. Given figure represents generalized performance - higher performing application specific technologies exist and are under continuous development. As can be seen fuel cell technology can provide the highest specific energy while capacitors can provide the highest specific power. However, Li-ion technology with its high specific energy and good specific power is the right choice for most mobile/portable applications.
+<figure label>
+{{:en:av:bfig_14_ragone.png?500|title}}
+<caption>General Ragone plot of energy storage elements.</caption>
+</figure>

en/av/technology.1591866031.txt.gz · Last modified: 2020/07/20 09:00 (external edit)