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How battery thermal management systems impact EV battery performance

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How battery thermal management systems impact EV battery performance

The US Advanced Battery Consortium (USABC) states that the battery used by a plug-in hybrid (PHEV) is expected to last for over 15 years and 300,000 charging cycles.

However, its lifetime hinges on different stress factors that strongly affect degradation rate, with temperature being a huge factor. Further, by being the most expensive element in an electric vehicle, the automotive industry is focused on developing better battery thermal management systems to avoid premature and costly battery replacement.

What are the latest developments in battery thermal management systems?

The relationship between degradation and temperature can be formulated by an Arrhenius-type behavior where degradation rate increases exponentially with temperature:

“The exact relation depends on the specific electrochemistry and design of the battery. Therefore, there is no single life model that models all different chemistries.”

Although the capacity increases as the operating temperature is raised, the degree of capacity fade also increases. On the other hand, poor performance is observed at low operating temperatures. In addition, excessive or uneven temperature rises in a system or pack reduces its lifecycle significantly.

As an industry reference, EV batteries reach their last days once they reach a 20 percent capacity loss or 30 percent internal resistance growth, and both active and passive battery thermal management systems (BTMS) are the main cards that engineers play to tackle battery overheating and poor performance.

Further, there are various types of BTMS techniques depending on the purpose, source and cooling medium. By purpose, there are systems based on cooling only rather than both heating and cooling. Source includes passive, if cabin air is used without extra pre-conditioning, or active, if a specific heating or cooling component is installed in the system to change the air before entering into the pack. Lastly, by cooling medium could mean air versus liquid.

“Efficient temperature management systems contribute significantly to battery health and extend the overall lifespan,” says Lyu et al in their 2019 paper Electric vehicle battery thermal management system with thermoelectric cooling. “Moreover, as the capacity and charge and discharge rate increase, battery security issues need more attention. Subsequently, various BTMS have been developed to meet the demand for higher power, faster charge rates, and improved driving performance.”

Regarding passive BTMS, phase change materials, heat pipes and hydrogels are utilized, with the benefit of no additional power consumption. On the downside, the cooling process is difficult to manage. In opposition, the paper continues, traditional active methods generally lead to forced circulation and circulation of specific cooling materials and substances such as water and air: “The main issue is that the cooling effect can be very limited under certain circumstances.”

TEC combined with other BTMS techniques

The first method for effective heat mitigation in Li-ion batteries is the choice of the electrode materials, which is inherent to the battery cell technology. One BTMS that is drawing attention in the EV industry is thermoelectric cooling, or TEC.
This is due to some benefits relating to their solid cooling capabilities and dependable working potential, besides being quiet, stable, and allowing an easier control of temperature by just adjusting the voltage supply.

Thermoelectric coolers are based on the conversion of voltage to the temperature difference. This Peltier–Seebeck effect, together with the Thompson effect, belongs to the thermoelectric effect. “The thermoelectric effect refers to all of the transformation processes from heat to electricity, and vice versa.” Several noted studies have been carried out in recent years.

In one, the cold sides of the thermoelectric coolers were connected to the heat sink in these designs and maximum temperature was kept below 55°C. “The cold air was blown into the battery pack and cabin for cooling. Later, a heatsink-fan set for both the cold side cooling and the hot side heat dissipation was incorporated.”

Besides, thermoelectric cooling can be combined with other battery thermal management systems, such as forced air cooling and liquid cooling.

In the air cooling system, the battery is cooled by an airflow sweeping the battery pack. The air typically comes from outside, but also from the cabin and additional AC units in systems that are more complex. The advantage of this method is its simple nature, where no insulation between the air and the battery is needed or which allows less maintenance and lighter components.

There are also drawbacks to this approach. The limited specific heat capacity of air requires larger space to be used for components constituting the BTMS. Moreover, special geometry for the coolant channel needs to be used and only a few cells can be cooled at once. Due to the above considerations, the airflow velocity needs to be increased, which leads to lower energy efficiency.

As for liquid cooled systems, components which contain a coolant are located in between cells or modules. The heat is then transported to a heat sink, placed away from the battery pack. The heat sink can be a simple radiator or a more complex system dissipating the heat into a refrigerant circuit. Usually, both are used in combination, where switching is done depending on various parameters.

The disadvantages of such a system are a higher weight resulting from the extra components and the proximity of the liquid coolant to the high voltage components. Hence, during operation and maintenance, various safety measures need to be in place.

Both of the above approaches are called active, because they use external components such as pumps and fans which use additional battery power. An additional disadvantage is the creation of noise and vibration in a generally silent setting, the need for extra maintenance, and a higher cost of components over time.

A combination of TEC and these BTMS is possible

Here, the liquid coolant acts as the medium to remove the heat generated from the battery during operation. Such BTMS design is a combination of TEC with forced air cooling and liquid cooling in which the liquid coolant works as the medium to remove heat from batteries:

“Forced air assisted heat removal is performed from the condenser side of the thermoelectric liquid casing. Detailed experiments are carried out on a simulated electric vehicle battery system.”

The battery is placed vertically in the center of the coolant container. Flowing liquid takes away a considerable amount of heat generated by the battery during operation. A water pump is used to drive liquid circulation. The TEC is used to manage the temperature of the coolant afterward. Lastly, the hot end of the TEC will be cooled by the heat sink and fan attached to it.

From the same paper, experimental results reveal a promising cooling effect with a reasonable amount of power dissipation: “Moreover, the experimental test shows that the battery surface temperature drops around 43ºC – from 55ºC to 12ºC – using a TEC-based water cooling system for a single cell with copper holder when 40V is supplied to the heater and 12V to the TEC module.”

However, the system performance is to be constantly enhanced to meet the demand of progressively higher heat generation. In another study, it was reported that COP of the BTMS decreases gradually with increasing power supply to the TEC and the maximum temperature of the battery was less than 36.2°C.

The EV revolution is nothing if the cars themselves can’t deliver. And that means not just after 15 days, or 15 months, but 15 years. As a result, it’s no surprise that so much time and effort has gone into refining battery thermal management systems, and will continue to do so to ensure EVs function time and again.

Published at Mon, 09 Dec 2019 15:38:31 +0000

Automotive

Tesla’s Heavy Trucking executive sells $6M+ in stocks

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Tesla’s President of Heavy Trucking Jerome M. Guillen sold over $6 million worth of TSLA stock earlier this week, according to a SEC Form 4 filing. Based on Guillen’s recent Form 4 submission, transactions occurred under transaction code M and code S.

Code M means to exercise or the conversion of derivative security receives from the company, like an option. Transaction code S means the sale of securities on an exchange or to another person. 

Based on the Form 4 filing, the Tesla executive acquired 10,000 stock for the price of $55.32, exercising his options under transaction code M. Under transaction code S, Tesla’s President of Heavy Trucking also disposed of 10,000 stocks at market value, ranging from $628.46 to $664.77. Guillen recently sold TSLA shares totaling $6,440,627.

Looking at Guillen’s activity throughout 2021 thus far, a trend emerges over the past few months. In April, he also sold 10,000 TSLA shares for an average price of $697.87 for a total amount of $6,978,659. Guillen executed similar transactions between January and March.

Compared to Guillen’s transactions, Tesla’s Chief Financial Officer (CFO) Zachary Kirkhorn sold less shares this year. In April 2021, Kirkhorn sold 1,250 shares for an average price of $718, totaling $897,500. While in March, the CFO sold 4,068 TSLA shares for an average of $655.81-$595.08 with a total amount of over $2 million. 

Jerome Guillen’s role in Tesla changed from president of Automotive to president of Heavy Trucking, according to a regulatory filing dated March 11, 2021. The shift in his role suggests that Guillen will have fewer overall responsibilities at Tesla in terms of overseeing the company’s entire automotive business. Instead, his new role suggests that Guillen will be concentrating more on the production of the Tesla Semi, the company’s much-anticipated all-electric Class-8 truck. 

The Teslarati team would appreciate hearing from you. If you have any tips, email us at [email protected] or reach out to me at [email protected].

Tesla’s Heavy Trucking executive sells $6M+ in stocks

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Source: https://www.teslarati.com/tesla-jerome-guillen-sells-tsla-stocks/

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SpaceX’s sootiest Falcon 9 booster yet returns to port after record reuse

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Three days after acing record-breaking tenth launch and landing, SpaceX’s sootiest Falcon 9 rocket booster yet has returned to Port Canaveral to begin the processing of preparing for its eleventh flight.

Almost exactly three years ago, speaking in a conference call focused on the debut of SpaceX’s ultimate “Block 5” Falcon booster upgrade, CEO Elon Musk revealed that Block 5 boosters were “designed to do 10 or more flights with no [scheduled] refurbishment” and “at least 100 flights [with moderate scheduled maintenance.]” Relative to the Space Shuttle, the only other operational orbital-class reusable rocket in history, 10 flights with little to no refurbishment would be an extraordinary achievement

Around 36 months later, albeit a year and a half after Musk anticipated SpaceX might reach that milestones, a Falcon 9 booster has successfully completed ten orbital-class launches and lived to tell the tale.

Falcon 9 B1051 is the first liquid rocket booster ever to complete ten launches and the rocket certainly looks the part. (Richard Angle)

26 months after the booster first took flight in support of Crew Dragon’s March 2019 uncrewed orbital launch debut, Falcon 9 B1051 has narrowly beaten several of flight-proven siblings to become the first liquid rocket booster of any kind to complete ten launches. Just four days prior to that historic tenth flight, Falcon 9 booster B1049 became the second SpaceX rocket (after B1051) to ace nine launches and landings.

SpaceX quickly processed booster B1049 after its own port return and Falcon 9 B1051 narrowly missed greeting its still-vertical sibling by just a few days. Together, over the course of the 19 orbital launches those two Falcon 9 boosters have supported in ~30 months, B1049 and B1051 have collectively delivered more than 260 metric tons (~570,000 lb) of satellites and spacecraft to low Earth orbit (LEO), geostationary transfer orbit (GTO), and the International Space Station (ISS).

Falcon 9 B1051 is pictured in January 2019 before its first launch. (SpaceX)
Two and half years and ten launches later, the booster looks decidedly “flight-proven.” (Richard Angle)

That performance is roughly equivalent to two expendable Saturn V Moon rocket launches for a total launch cost to SpaceX likely less than $500 million, while five of those 19 launches also brought in revenue on the order of $400M to $500M. In effect, even the small handful of commercial launches B1049 and B1051 have completed likely generated enough revenue to wholly amortize the cost of a dozen or more additional launches. SpaceX has still had to pay for propellant, maritime recovery assets, any necessary refurbishment, and the hundreds of satellites both boosters have launched, but Falcon booster reusability still offers an extraordinary return on investment even with that multitude of caveats.

Falcon 9 B1051’s safe return also means that SpaceX should have no trouble turning the booster around as it prepares to push past the ten-flight target behind Block 5’s upgrade. In recent months, multiple SpaceX executives have stated that SpaceX intends to push well beyond that ten-flight goal as boosters with more and more flight experience continue to come back in excellent condition. CEO Elon Musk even indicated that SpaceX may intentionally fly Falcon 9’s fleet-leader (B1051, in this case) until something on the booster fails during a launch or landing. SpaceX’s own Starlink launches offer the perfect opportunity for that kind of pragmatic risk-taking.

Falcon 9 booster B1051’s titanium grid fins have developed a rainbow patina over ten hypersonic reentries. (Richard Angle)
(Richard Angle)
B1051’s aft engine and landing legs section certainly looks like it’s been through 10 launches and hypersonic reentries. (Richard Angle)

SpaceX’s sootiest Falcon 9 booster yet returns to port after record reuse

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Source: https://www.teslarati.com/spacex-sootiest-falcon-9-booster-port-return/

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SpaceX’s sootiest Falcon 9 booster yet returns to port after record reuse

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Three days after acing record-breaking tenth launch and landing, SpaceX’s sootiest Falcon 9 rocket booster yet has returned to Port Canaveral to begin the processing of preparing for its eleventh flight.

Almost exactly three years ago, speaking in a conference call focused on the debut of SpaceX’s ultimate “Block 5” Falcon booster upgrade, CEO Elon Musk revealed that Block 5 boosters were “designed to do 10 or more flights with no [scheduled] refurbishment” and “at least 100 flights [with moderate scheduled maintenance.]” Relative to the Space Shuttle, the only other operational orbital-class reusable rocket in history, 10 flights with little to no refurbishment would be an extraordinary achievement

Around 36 months later, albeit a year and a half after Musk anticipated SpaceX might reach that milestones, a Falcon 9 booster has successfully completed ten orbital-class launches and lived to tell the tale.

Falcon 9 B1051 is the first liquid rocket booster ever to complete ten launches and the rocket certainly looks the part. (Richard Angle)

26 months after the booster first took flight in support of Crew Dragon’s March 2019 uncrewed orbital launch debut, Falcon 9 B1051 has narrowly beaten several of flight-proven siblings to become the first liquid rocket booster of any kind to complete ten launches. Just four days prior to that historic tenth flight, Falcon 9 booster B1049 became the second SpaceX rocket (after B1051) to ace nine launches and landings.

SpaceX quickly processed booster B1049 after its own port return and Falcon 9 B1051 narrowly missed greeting its still-vertical sibling by just a few days. Together, over the course of the 19 orbital launches those two Falcon 9 boosters have supported in ~30 months, B1049 and B1051 have collectively delivered more than 260 metric tons (~570,000 lb) of satellites and spacecraft to low Earth orbit (LEO), geostationary transfer orbit (GTO), and the International Space Station (ISS).

Falcon 9 B1051 is pictured in January 2019 before its first launch. (SpaceX)
Two and half years and ten launches later, the booster looks decidedly “flight-proven.” (Richard Angle)

That performance is roughly equivalent to two expendable Saturn V Moon rocket launches for a total launch cost to SpaceX likely less than $500 million, while five of those 19 launches also brought in revenue on the order of $400M to $500M. In effect, even the small handful of commercial launches B1049 and B1051 have completed likely generated enough revenue to wholly amortize the cost of a dozen or more additional launches. SpaceX has still had to pay for propellant, maritime recovery assets, any necessary refurbishment, and the hundreds of satellites both boosters have launched, but Falcon booster reusability still offers an extraordinary return on investment even with that multitude of caveats.

Falcon 9 B1051’s safe return also means that SpaceX should have no trouble turning the booster around as it prepares to push past the ten-flight target behind Block 5’s upgrade. In recent months, multiple SpaceX executives have stated that SpaceX intends to push well beyond that ten-flight goal as boosters with more and more flight experience continue to come back in excellent condition. CEO Elon Musk even indicated that SpaceX may intentionally fly Falcon 9’s fleet-leader (B1051, in this case) until something on the booster fails during a launch or landing. SpaceX’s own Starlink launches offer the perfect opportunity for that kind of pragmatic risk-taking.

Falcon 9 booster B1051’s titanium grid fins have developed a rainbow patina over ten hypersonic reentries. (Richard Angle)
(Richard Angle)
B1051’s aft engine and landing legs section certainly looks like it’s been through 10 launches and hypersonic reentries. (Richard Angle)

SpaceX’s sootiest Falcon 9 booster yet returns to port after record reuse

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Source: https://www.teslarati.com/spacex-sootiest-falcon-9-booster-port-return/

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Tesla sends brief update for Model S Plaid’s customer deliveries

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The excitement is palpable for the new Tesla Model S. Since it was formally announced, Tesla has mentioned that the demand for the flagship sedan has been particularly strong. But while orders for the new Model S may be notable, Tesla has found it a bit more challenging to actually get the vehicle to customers. 

During Tesla’s Q4 and FY 2020 earnings call, Elon Musk estimated that the new Model S would start customer deliveries sometime in February. Subsequent drone flyovers of the Fremont factory later showed that the flagship sedan was indeed getting produced. However, February came and went, and customer deliveries of the new Model S were still yet begin. 

Credit: Teslarati via @BlakeM in San Francisco

Elon Musk explained this delay in the first quarter earnings call last month. According to the CEO, Tesla met more challenges than expected in bringing the new Model S to market. This was partly due to the supply chain shortages that have been adversely affecting the auto industry. 

“With respect to the Model S and X, there were more challenges than expected in developing the Model S or what we call the Palladium program, which is the new version of Model S and X, which has revised interior and new battery pack and new drive units and new internal electronics,” Musk said

Just recently, however, some customers waiting for their new Model S orders received a message from the electric car maker. The message was short, though it provided a brief update on Tesla’s upcoming deliveries of the flagship sedan. 

Following is the message that a Tesla representative sent to a Model S reservation holder. It should be noted that the Tesla customer who received the message ordered his Model S late last year, not after the official announcement of the vehicle earlier this year. 

“Good afternoon, and hope you are having an awesome start to your week thus far!

“First off, thank you for your patience and professionalism towards myself and Tesla during this waiting period since you began the Model S order process with us. 

“Today, Tesla has begun to provide more information internally on when deliveries will potentially take place for Model S orders based upon when they began the order process with us, and I wanted to share your anticipated delivery timeframe with you. 

“Due to high volume of Model S orders Tesla has at this time, we currently don’t have an estimated delivery date for you but that should change within the next week, as soon as there is an estimated delivery date provided internally for you order, I will reach out ASAP.”

Granted, the message is a minor update than an actual timeframe for Model S refresh and Plaid deliveries. It does, however, hint that the EV maker is doing all it can to start customer deliveries of its best sedan to date. For a vehicle like the new Model S, after all, the long wait would likely be worth it.  

Don’t hesitate to contact us for news tips. Just send a message to [email protected] to give us a heads up.

Tesla sends brief update for Model S Plaid’s customer deliveries

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Source: https://www.teslarati.com/tesla-model-s-plaid-customer-delivery-update/

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