Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeugen

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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von tesla-andi » 6. Mär 2018, 11:39

Na aber dann macht es ja eigentlich keinen Sinn den Wagen mit einem Batteriestand von 65% Zuhause einzustecken selbst wenn man weis, dass das Auto einige Tage steht aber in der Zeit nicht unter 50% Batteriestand fallen wird. Warum rät dann Tesla dazu, den Wagen IMMER einzustecken?
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von sustain » 6. Mär 2018, 11:44

tesla-andi hat geschrieben:Na aber dann macht es ja eigentlich keinen Sinn den Wagen mit einem Batteriestand von 65% Zuhause einzustecken selbst wenn man weis, dass das Auto einige Tage steht aber in der Zeit nicht unter 50% Batteriestand fallen wird. Warum rät dann Tesla dazu, den Wagen IMMER einzustecken?


Nun ja wenn sie zum Gegenteil raten würden könnte das in bösen Akkuschäden enden, deswegen raten sie zum IMMER anstecken, kann ja nix schlimmes passieren dadurch! Reine Absicherung.
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von VOLTtaner » 6. Mär 2018, 12:29

Wie ist es eigentlich wenn das Auto länger steht ohne Lademöglichkeit, welcher Wert sollte nicht unterschritten werden? 20%??
 
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von tornado7 » 6. Mär 2018, 12:35

tesla-andi hat geschrieben:Das bedeutet, das Einstecken bei Ladezustand 65% und Ladelimit 60% oder gar 50% hat solange keine Auswirkung, bis das Ladelimit erreicht ist, ...

Sogar noch weiter: Das Fahrzeug lädt erst nach, wenn der Ladestand 5% unter das von dir gesetzte Limit fällt. Also einstecken mit 53%, Limit auf 50% setzen, einen Monat wegfahren, nachgeladen wird erst bei 45.49% (= Anzeige 45%). Wenn du nach Hause kommt, hat das Auto irgendetwas zwischen 45.50% und 50.49% im Akku.
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von sustain » 6. Mär 2018, 13:07

VOLTtaner hat geschrieben:Wie ist es eigentlich wenn das Auto länger steht ohne Lademöglichkeit, welcher Wert sollte nicht unterschritten werden? 20%??


In der Bedienungsanleitung steht das er mit SoC 0% noch 2 Monate stehen kann. Dann fährt er aber alle Systeme runter und schützt nur noch den Akku(sogenannte Brickwall Reserve). Das ist aber eine reine Notmassnahme und niemals wissentlich zu empfehlen. Erst recht nicht im Winter. Ich persönlich würde immer drauf achten das er auf mittleren Ladeniveau bleibt wenn er länger steht alles um die 50% sind ideal, oder wenn kein Lademöglichkeit da ist und er lange steht stell ihn lieber mit 80% ab dann ist das sicher besser und du hast Reserven nach unten, ja nachdem wie lange du planst weg zu sein.
SoC 20% und etwas darunter sind für ein paar Tage aber auch kein Problem, das hängt immer von den Randbedingungen ab wie Außentemperatur, wie oft man mobil zugreift und das Auto weckt(kostet immer Energie) und wie lang man ihn stehen lassen will usw.
Stellst du ihn im Winter bei minus 10 Grad den Wagen nach langer Fahrt mit SoC 20% und warmen Akku ab kann es sein das er am nächsten Tag nur noch 10% anzeigt, das kommt durch das abkühlen des Akkus und ist normal. Im Sommer wirst du so einen Verlust gar nicht oder nur sehr gering sehen.
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von tornado7 » 6. Mär 2018, 16:07

sustain hat geschrieben:
VOLTtaner hat geschrieben:Stellst du ihn im Winter bei minus 10 Grad den Wagen nach langer Fahrt mit SoC 20% und warmen Akku ab kann es sein das er am nächsten Tag nur noch 10% anzeigt, das kommt durch das abkühlen des Akkus und ist normal.

... und kommt durch die Erwärmung beim Fahren auch wieder zurück, ist also nicht verbraucht sondern nur (wortwörtlich) eingefroren. Das merkt aber kaum jemand, ganz im Gegensatz zum parkierten Auto ;)
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von sustain » 7. Mär 2018, 01:23

tornado7 hat geschrieben:
sustain hat geschrieben:
VOLTtaner hat geschrieben:Stellst du ihn im Winter bei minus 10 Grad den Wagen nach langer Fahrt mit SoC 20% und warmen Akku ab kann es sein das er am nächsten Tag nur noch 10% anzeigt, das kommt durch das abkühlen des Akkus und ist normal.

... und kommt durch die Erwärmung beim Fahren auch wieder zurück, ist also nicht verbraucht sondern nur (wortwörtlich) eingefroren. Das merkt aber kaum jemand, ganz im Gegensatz zum parkierten Auto ;)


Yepp so siehts aus ;).
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von egn » 18. Nov 2018, 20:36

Jetzt kann man die Dissertation von Peter Keil lesen. Sie enthält noch mehr interessante Informationen zu NCA Zellen.

Wer nicht alles lesen möchte dem reichen vielleicht die Hinweise zur Ladestrategie.

Strategies for Maximizing the Battery Life in Electric Vehicles
To maximize battery life, calendar aging as well as cycle aging has to be minimized. The results of
the experimental studies presented in the three preceding chapters have revealed valuable insights
into the predominant mechanisms of battery aging under different operating conditions. Based on
the findings of the three aging studies, ideal operating strategies are deduced in this chapter.
Moreover, battery life estimations are made that demonstrate under which operating conditions,
the USABC development goals of 15 years battery life and 1000 cycles for 2020 EV batteries [7] can
already be reached with today’s battery technology.

Reducing Calendar Aging
The calendar aging studies have shown that the capacity fade results predominantly from a loss of
cyclable lithium owing to side reactions at the anode. Keeping the SoC at a low or medium level and
lowering the battery temperature minimizes calendar aging.

Avoiding the SoC Regime Corresponding to the Lowest Anode Potential
The side reactions at the anode have shown a strong dependency on the anode potential and
aggravate with lower potentials. As the anode potential exhibits certain plateaus, a reduction of the
storage SoC does not automatically reduce these side reactions. Instead, SoC regions covering more
than 20–30% of the cell’s nominal capacity, exhibit a rather constant degradation. As the LiC6/LiC12
two-phase regime represents the lowest voltage plateau, an SoC in this regime leads to the fastest
capacity fade. As a consequence, the degree of lithiation of the graphite anode should be kept below
50% when the cells are kept at the same SoC for a longer time, e.g., during parking.
The low-voltage plateau of the anode typically starts at 55–80% SoC, depending on the electrode
balancing of the cell. To identify the beginning of the low-voltage plateau of the graphite anode in
the full-cell, a DVA measurement should be performed. The characteristic central graphite peak
indicates directly the beginning of the LiC6/LiC12 two-phase regime which is associated with a higher
rate of side reactions. DVA measurements should be repeated from time to time because the
balancing of the electrodes often changes with the aging of the cells.
For a battery at 25°C, a capacity fade after 15 years of 8–9% has been projected for low and medium
SoCs. By contrast, a capacity fade of 16% has been estimated for 15 years of calendar aging at a high
SoC within the LiC6/LiC12 two-phase regime.


Keeping the Battery Temperature Low during Nonoperating Periods
As the side reactions at the anode aggravate with higher temperature, the EV battery should be
kept cool when the battery is not operated. For the cell type examined in this thesis, lowering the
battery temperature from 25°C to 10°C has decreased the capacity fade in the 15-years projections
by ca. 40%.

Avoiding Very High States of Charge
For SoCs above 80%, an increasing cathode degradation has been observed. This has led to coupled side reactions and a marked increase of the charge transfer resistance of the NCA cathode. If the
SoC cannot be kept in the low or medium SoC regime during long-lasting nonoperating periods to
avoid accelerated side reactions at the anode, at least the very high SoCs of 80% and above should
be avoided to reduce cathode degradation.
However, the beneficial effects of this mean remain
limited as the anodic side reactions remain the dominant driver for capacity fade.

Timing of Battery Charging
As a low SoC reduces calendar aging, the battery life can be improved be an intelligent timing of
battery charging. When the battery is always recharged directly after driving, it spends the
subsequent nonoperating periods at higher SoCs. Thus, a delayed charging, which keeps the battery
at a low SoC as long as possible and completes the charging procedure shortly before the next
driving period, also helps to reduce calendar aging.


Reducing Cycle Aging
The aging owing to charging and discharging the EV battery is substantially more complex than pure
calendar aging. In addition to SoC and temperature, charge throughput, cycle depth, and current
rates have a considerable impact on cycle aging.
Less Cycle Aging at Higher Temperatures
Cycling cells at different temperatures with a highway driving load profile has revealed that the
capacity fade in addition to that owing to calendar aging decreases with higher temperature. This is
in contrast to calendar aging, where a higher temperature generally accelerates degradation. As a
consequence, the battery should be kept warm during cycling. This means that a battery does not
have to be cooled down to 25°C during driving or charging. Instead, a heating of the battery to 40°C
can reduce the stress and degradation caused by the intercalation and deintercalation processes.

When the EV is parked after a driving sequence, the battery should cool down again to minimize
calendar aging during the nonoperating periods. As the operating periods are rather short compared
to the nonoperating periods for a typical passenger car, a higher battery temperature during
charging or discharging does not have a considerable impact on calendar aging.

Applying Reasonable Charging Currents
High-energy lithium-ion cells are typically more susceptible to lithium plating due to their thick
anodes with low porosity. High charging currents should be avoided, particularly at low
temperatures and high SoCs, which correspond to the lowest anode potential. But even when higher
charging currents are applied only at low SoC, this usually leads to considerably higher stress for the
battery cells. Charging with high currents leads to a degradation of the anode active material and
lithium plating. Thus, fast-charging protocols should only be applied occasionally and not be used
for every-day charging, unless the cell is explicitly designed for high charging currents.
In the latter
case, however, the required electrode design is generally associated with a lower energy density.
Standard CCCV charging protocols typically provide a reasonable compromise between charging
duration and cycle life. The study on charging protocols has shown that below a certain current
value, lower charging currents do not further improve battery life.

Lowering Cycle Depth Reduces Resistance Increase
The resistance increase of the lithium-ion cells examined in this thesis has originated largely from
rising charge transfer resistances of the NCA cathode. Particularly for large cycle depths and deep
discharging, the resistances have increased markedly. When reducing the typical cycle depth to 20–
40%, the resistance rise of an EV battery can be minimized.
This maintains a higher power capability
of the battery also for an aged battery.
Hence, a frequent recharging of the battery can be beneficial as it reduces the average cycle depth.
However, this keeps the average SoC at a higher level, which might provoke a faster calendar aging.
The combination of a low cycle depth and a low average SoC leads to the longest battery life.
However, performing only partial charging is only applicable when not the entire driving range of
the EV is needed.
Deep discharging is typically not such a critical issue for EVs as the drivers typically do not drive until
the battery is completely discharged, but recharge the vehicle much earlier under most operating
conditions. Moreover, the vehicle manufacturers usually program their battery management
systems in such a way that a certain capacity reserve remains which is not accessible during the
driving operation to prevent a deep discharging and an overdischarging of the battery.

Maximum Utilization of Regenerative Braking Beneficial for Battery Life
The extensive investigations on the impact of regenerative braking on battery aging have shown
that regenerative braking always had a beneficial effect on battery life. As a consequence, high
recharging peak currents during braking periods should be tolerated, also at low temperatures of
10°C or even 0°C, as they did not harm the battery but reduced the overall cycle depth. The
improvements in battery life owing to regenerative braking have been observed particularly at low
temperatures and high SoCs. It has been concluded that the shorter recharging sequences at the
charging station helped to minimize lithium plating.


Optimizing Capacity Utilization
The aging study comparing different charging protocols has demonstrated that a lower charging
voltage reduces the relative capacity fade at the cost of a lower absolute available capacity, which
represents the driving range of the EV. After 1000 EFC, the cell with the maximum charging voltage
specified in the datasheet still provided a higher remaining driving range than the cells with a lower
charging voltage.
From the viewpoint of mathematical optimization, there is no advantage of reducing the charging
voltage when it does not retain a higher driving range for aged batteries. However, when taking also
effects from psychology and behavioral economics into account, a reduced charging voltage can yet
have its benefits. According to the endowment effect, there is the tendency for people who own a
good to value it more than people who do not [268⁠,269]. Transferred to battery degradation, this
means that losing part of the driving range possessed at the beginning of the vehicle life can be
perceived as a more severe loss than a reduced driving range from the very beginning. Such a
reduced driving range can result from a restricted utilization of the available battery capacity by a lower charging voltage; this represents an unused driving range the customer has never possessed.
This demonstrates that defining the charging protocol for an EV is not only a mathematical
optimization problem but also has to take the psychological perception of the customers into
account.


Battery Life Estimations
For EVs in 2020, the USABC development goals demand a cycle life of 1000 cycles and a battery life
of 15 years. For a battery operation at 25°C, different battery life projections can be made based on
the results from the aging studies on calendar aging and driving operation. Moreover, the impact of
higher and lower temperatures on battery life is discussed.

Cycle Depth of 60% in Combination with Storage at Medium SoC
According to the results of the aging study on driving operation for a cycle depth of 61% CN at 25°C,
1000 EFC have been achieved with ca. 13% capacity fade (see Figure 88a, p.127). Together with ca.
10% capacity fade from calendar aging after 15 years, when the battery is kept at medium SoCs
during nonoperating periods (see Figure 44b, p.69), a total capacity fade of about 23% is obtained.

Cycle Depth of 40% in Combination with Storage at High SoC
When the battery is operated with smaller cycles of only up to 40% CN but is kept at high SoC during
nonoperating periods, Figure 88a has shown that cycle aging decreases by ca. 2 percentage points
whereas calendar aging over 15 years increases by ca. 5 percentage points in Figure 44. Thus, the
long times at high SoC decrease battery life more than the smaller cycles can prolong it. This
demonstrates that always recharging to a high SoC after every short drive does not maximize battery
life, although it is beneficial for keeping the resistance increase low.

Cycle Depth of 40% in Combination with a Medium/Low SoC
Only when a reduced cycle depth is combined with an operation predominantly at medium and low
SoCs, battery life improves notably.
A cycle depth of ca. 40% CN at medium and low SoCs leads to
10% capacity fade from cycling, as illustrated in Figure 88a, plus ca. 10% of capacity fade owing to
calendar aging, as shown in Figure 44b. With this way of operation, a battery life of 15 years and
1000 EFC can already be reached with the cell type examined in this thesis. Moreover, the resistance
increase can be kept low

Impact of High Battery Temperatures
High battery temperatures increase calendar aging by accelerating parasitic side-reactions. Thus,
the battery temperature should be kept low during the long nonoperating periods. During charging
and discharging, a warm battery reduces cycle aging. As long as the battery is only at higher
temperatures during operation and cools down again for the nonoperating periods, no
disadvantagesfor the battery life have to be expected. Instead, the battery life prolongs by reducing
the cycling-induced degradation. As a consequence, the USABC development goals can also be
reached without a strict cooling of the EV battery during operation.

Low-Temperature Operation Remains Critical
While the USABC development goals for future EV batteries can already be reached today for
operating temperatures of 25°C and above, low-temperature operation still remains a critical issue. Operating at temperatures of 10°C or lower does not only reduce the available capacity but also
accelerates aging when the cells are cycled. This thesis has demonstrated that not only charging at
low temperature, but also discharging at low temperature can cause severe degradation of the
lithium-ion battery of an EV.
Although the contributions to capacity fade from calendar aging
decrease when lowering the battery temperature to 10°C, the contributions from cycling operation
increase substantially more. Considering the cycle depths of 60% CN and 40% CN in combination with
a high charging voltage, only 500 EFC and less have been achieved before a failure of the cells
occurred owing to internal overpressure caused by side-reactions releasing gaseous reaction
products. Only for low cycle depths of about 20% CN or a medium cycle depth of 40% CN at a low or
medium SoC, no failures have occurred and more than 1000 EFC have been achieved.
To improve the battery life, the lithium-ion batteries should be heated in winter when there are
subzero temperatures. Furthermore, high discharging currents should only be drawn from the
battery after a certain warming of the cells.

Zuletzt geändert von egn am 19. Nov 2018, 20:39, insgesamt 1-mal geändert.
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von McCoy-Tyner » 18. Nov 2018, 21:38

Hallo Egn,
na, wenn ich das so lese, so verstehe ich nicht, warum bei Tesla die Regenration im Winter heruntergefahren wird ..... gerade jetzt bei Temperaturen unter 10°C merkt man das mehr als deutlich - und das ist vom Fahren her auch bescheuert, weil das Auto plötzlich ein anderes Verhalten an den Tag legt. Würde mich ja interessieren, warum Tesla hier eine andere Strategie fährt als Hr. Keil das vorschlägt bzw. bewertet.
Gruß

Dieter
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Re: Neue Studie zur Lebensdauer von NCA Akkus in E-Fahrzeuge

von T-Drive » 18. Nov 2018, 23:56

Hallo egn,

danke für den Link zu der interessanten Arbeit! Ich hab sie mal diagonal durchgelesen, insbesondere auch die von Dir oben zitierten Schlusspassagen. Mein persönliches Fazit:
  • Es werden zwei Gründe für Alterung der Fahrbatterie unterschieden: kalendarische Alterung und Alterung durch Lade-/Entladezyklen.
  • Kalendarische Alterung ist am geringsten bei niedrigen Temperaturen und niedrigem SoC. Sie beschleunigt sich insbesondere oberhalb 80% SoC, niedriger als 55% SoC ist besser.
  • Daher: Laden direkt vor der Abfahrt ist günstiger als nach der Ankunft
  • Die Alterung durch Lade-/Entladezyklen verhält sich umgekehr zur kalendarischen Alterung: sie wird durch niedrige Temperaturen der Batterie beschleunigt. Das bedeutet, Laden und Entladen bei möglichst warmer Batterie, <10°C ist ungünstig
  • flache, häufige Zyklen bei eher niedrigem SoC sind besser
  • Rekuperation unterstützt dies, also auf max. stellen
  • Supercharging/hohe Ladeströme verstärken die Alterung, daher nicht täglich
  • Eine Nutzungsdauer der Batterie von 15 Jahren und 1000 vollen Zyklen mit weniger als 10% Kapazitätsverlust ist mit den heutigen Batterietechnologien möglich
Tesla's BMS macht eigentlich alles richtig. Ich werde mein Ladelimit im Alltag von 70 auf 60% reduzieren und lasse den Rangemode auch auf Kurzstrecken weiter aus. Ansonsten fahre ich viel Langstrecke und werde daher meine 40-50% SuC-Nutzung beibehalten :D
Viele Grüße, T-Drive

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