Being the first to adopt lithium into LEV’s back in 2008 and bringing Lithium(LFP) to aviation in Jan. 2011, , Aerolithium still dominates the market in custom designed batteries. We started with Lithium and now have transitioned to the latest tech innovation in battery material: Sodium. Sodium-ion chemistry is gaining attention and implementation and we are pleased to be the first again to bring the latest battery chemistry; Sodium, to the aviation/aerospace market.
Aerolithium’s proprietary Sodium cells provide the most stable molecular structure for safety , fast charging and high efficiency leading to greater life cycles, dependability and MUCH lower acquisition and ownership costs compared to lithium or lead.
Lithium had a good run, but, there are lingering issues that not everyone is comfortable with.
There are several sodium chemistry’s and the one Aerolithium will be using is Na3V2(PO4)3. This polyanion compound has the highest energy density, very stable lattice structure, making it safer than both LiFepo4 AND AGM’s, and has the greatest discharge capability. This is the latest and greatest battery breakthrough since Lifepo4 was years ago. Sodium has all the benefits of both lithium and AGM without the downsides of either. Wider operating voltage and temperature ranges, lightweight and most importantly, safer than either LiFEpo4(LFP) or AGM (lead acid) !
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Energy density comparison between AGM and sodium-ion batteries:
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AGM batteries typically have an energy density range of 50-70 Wh/kg
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They represent a mature lead-acid technology with relatively low energy density, requiring more weight and volume to store the same amount of energy compared to modern chemistries.
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Sodium-ion batteries have a significantly higher energy density, generally between 110 to 160 Wh/kg, with some sources citing up to 150-160 Wh/kg in advanced cells
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This is double the energy density of AGM batteries. Sodium-ion batteries are thus lighter and more compact for the same energy storage compared to AGM batteries.
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This considerable difference means sodium-ion batteries can deliver the same energy storage capacity at a much lower weight and volume than AGM batteries, improving efficiency especially in space- and weight-sensitive applications similar to lithium.
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Other advantages of sodium-ion batteries include:
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Better low-temperature performance
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Faster charging capabilities (up to 90% in ~15-20 minutes)
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Longer cycle life of 3,000+ cycles versus 1,000–1,200 cycles for AGM batteries
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Batteries that have a higher internal resistance, will heat up
quicker and suffer from voltage sag under heavy loads.
The prize for high internal resistance of course goes to
lead acid batteries. The disadvantage with PbA chemistry
is the changing internal resistance of each cell that increases
as more current is discharged, while the acid electrolyte and
anode and cathode components undergo a chemical
transformation that has to be reconstituted during charging.
This non linear chemical change is called the Peukart effect
of lead acid batteries, where cell voltage drops off
exponentially as more current is drawn and internal resistance continues to
increase. This voltage drop plagues lead acid batteries to supply the rated power
consistently to a load. As the voltage drops, the current must increase to
maintain power. This is especially troubling for starting turbine engines.
Sodium Vanadium Phosphate is a type of layered oxide chemistry used in sodium-ion batteries, known for its stable electrochemical performance and higher energy density compared to other sodium chemistries. It offers advantages such as better performance at low temperatures and a more sustainable and cost-effective alternative to both Lead and Lithium-ion batteries.
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Why is Sodium better ?
First and foremost: SAFETY
Sodium chemistry has been tested and proven to be absolutely safer than either lead or lithium LiFepo4/LFP,
Sodium does not need a BMS to “keep it safe” nor constant maintenance. charging that an AGM lead-acid needs.
Sodium cells are encased in a steel shell making them more durable and safer than Lifepo4 pouch cells.
An Aerolithium Sodium battery is bar-none THE safest aircraft battery in existence today.
Adoption of a new battery technology is intrinsically linked to its safety and public confidence in that safety. Yet for all it’s developments, LiFepo4 are still considered hazardous material, thus the total dependence on an intricate BMS to keep the battery safe. Unfortunately, this leaves zero tolerance for any BMS or cell malfunction. For all its attributes, Lithium still has not taken over the battery market from lead acid as many assumed it would. Lithium was not the holy grail to replace lead as two companies have bet the farm on.
Sodium is the answer, not lithium.
https://analyticalscience.wiley.com/content/article-do/sodium-ion-batteries-future-energy-storage
Sodium has all the benefits of both lithium and lead without the downsides.
Sodium has zero reactivity compared to LiFePo4
LiFePo4, which by its very nature needs protection from a BMS and can never be as safe as a battery that has no such need.
Other factors:
Cost: Better value, more eco-friendly, zero maintenance, charge retention higher than lead or lithium.
Resources; Sodium is more abundant and sustainable
We will go into detail why and let you decide.
There are several factors relating to the airworthiness of a battery used in aircraft ;
1. OVERCHARGING
As it relates to LFP batteries; First we have to acknowledge the fact that BMS’s sometimes DO fail.
One LFP battery mfgr strongly advises using a separate additional over voltage protection module ( crowbar) to supplement the BMS for their battery’s protection. BMS’s are designed to prevent overcharging / thermal runaway to protect the battery ( not the airplane ). Electronically dependent aircraft need a battery that WILL sacrifice itself to save the airplane, meaning, to accept an abnormally high voltage event for a few minutes without going into thermal runaway.
If a BMS detects an over voltage event it will cut off further charging from the alternator. When this happens, it takes away the batteries capacitive ability to absorb a voltage/current surge, cuts off any input, which then exposes the main bus to see the full unregulated output. A BMS protected battery would not absorb an over voltage event like a lead acid battery would. Remember, the first priority of a BMS is to protect the battery.
A Sodium battery does not need BMS over voltage protection to make it safe, thus the Sodium battery protects the aircraft.
Sodium cells can accept up to 4.8V maximum / 19.2V giving the pilot much more time to react.
2. OVER DISCHARGE
In a LFP type battery, below 2.5V starts the formation of copper dendrites leading to higher internal resistance, diminished capacity, shorter lifespan and irreversible damage. Mfgr’s of lithium aviation battery’s continually stress the liability of an undercharged battery. Similar to an undercharged lead acid battery. Starting in 2026, the IATA will mandate a 30% SOC for any transportation of lithium batteries, thus requiring LFP batteries to be shipped undercharged.
Testing on a Sodium battery shows no negative effects at a lower SOC, in fact, a Sodium cell has been discharged to zero volts and able to recover. https://nadionenergy.com/the-safety-advantages-of-transporting-over-discharged-sodium-ion-batteries/
This is why a Sodium aircraft battery can never die from any low voltage /over discharged event.. ex; leaving the master switch on accidentally.
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3. OVERTEMP
Continuous discharging (engine cranking) LFP batteries if at or above 45c/113F can accelerate the chemical reactions within the cells, degrading them, possibly leading to thermal runaway (similar to an AGM ). (thus the requirement for heat shields/cooling tubes firewall forward). This can lead to cell venting and a total loss of electrical power from the battery in flight. Operating LFP batteries at elevated temperatures is not recommended and reduces the efficiency of the ion movement leading to degradation of the cathode material in particular which becomes more unstable over time. Heightened environmental working temps also increase the Lithium self discharge rate and leaving your plane sitting out in the hot summer sun is slowly shortening its lifespan. Thus, the claimed 6 – 8 year life span by some suppliers which is based on ideal conditions is unrealistic in actual practice.(again, similar to AGM batteries ). Note that all BMS protected batteries will disconnect in an over temp situation to save the battery.
Sodium on the other hand can handle up to 80c/176F max
and will not disconnect.
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4. UNDERTEMP​
LFP mfgr’s often state an operational range down to – 30c/-22F. This is for Discharging only. Charging a LFP battery below 0c / 32F must be avoided as permanent lithium plating damage will occur over time and reduce it’s lifespan. Lithium plating occurs when charge current forces the lithium ions to move at a faster reaction rate and thus accumulate on the anode surface vs being absorbed.
If you start your aircraft with a lithium battery in subzero temps, the internal resistance increases inside the battery and reduces the chemical exchange rate. This causes a permanent reduction in the batteries capacity and discharge ability. Engine cranking will not raise the internal temperature of the battery enough to prevent this. The BMS in your typical aviation battery is not sophisticated enough to limit the charge current after engine start. ( especially in turbine applications ) So then, most of the Lithium ions fail to intercalate - https://www.youtube.com/watch?v=SnguPqdx4FA -- https://www.valipod.com/post/intercalation-process-in-lithium-ion-batteries - into the graphite anode. Instead they plate the surface with metallic lithium, thus the engine alternator / generator charging the battery electroplates the battery instead of charging it. This leads to increased internal resistance and thus the danger; plating creates dendrites, those sharp tiny spears that pierce the separator film and will ultimately lead to failure in a spectacular fashion.
AGM’s can handle lower temps than LFP, down to -40c/f before they freeze up. Of course a drastic reduction in performance occurs before this point. Prolonged exposure to subzero temps causes the electrolyte and internal components to expand which may affect the internal structure leading to tiny cracks , pressure buildup and rupture expelling harmful gases and fumes. Some things to watch out for in cold temps – cracks in the casing, noticing an unusual smell, like rotten eggs, battery struggles to hold a charge.
Many use AGM aircraft batteries because of their cold temp advantages over lithium. However, and AGM batteries efficiency is highly temperature dependent. High temps have a detrimental effect on AGM (VRLA) by reducing performance and reduction in overall lifespan. Sometimes quite suddenly.
Cycle life is greatly impacted and higher temps accelerate internal chemical reactions leading to increased corrosion on the cathode grid. This is known as grid corrosion and cannot be reversed. It is the primary reason AGM batteries fail. Second, heat leads to decreased efficiency; the internal resistance decreases, leading to a higher self discharge rate and a reduced charge acceptance causing the battery to struggle to accept a full charge. In a few cases, sustained high temps can lead to thermal runaway causing leakage and fire. Electrolyte will evaporate, even in ‘sealed’ AGM batteries under sustained heating causing permanent loss of capacity making it unusable. This is one reason AGM battery mfgrs strongly suggest using a battery maintainer.
Low Temp Impact on AGM – Reduced capacity and slower chemical reactions leads to a greater voltage drop and increased current to compensate on engine starting. Below 0c/32F AGM’s provide only 50-60% of rated capacity. Freezing temps increase internal resistance which results in slower and incomplete charging which causes sulfation, a common cause of AGM failures in cold environments and infrequent use of the battery https://www.power-sonic.com/blog/what-is-a-sulfated-battery-and-how-do-you-prevent-it/
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5. BMS’s;
Required on all LiFEpo4 batteries. Will eventually drain a battery as they consume power when not in use. Is considered a point of failure . Protects the battery to make it safe.
Quote of the day:
“ If lifepo4 batteries are so safe, a BMS would not be needed “to make them safe” !
Since Lithium batteries need a BMS to make them safe, if the BMS ever indicates a 'fault' then, by default that would make them unsafe.
Sodium batteries do not require a BMS as they do not need overvoltage/overcharging protection or undervoltage/overdischarge protection or thermal protection like a lifepo4 battery.
This is one of the main advantages to a Sodium battery.
All that is needed is cell balancing similar to a lithium battery but, unlike a lithium BMS, a Sodium balancer uses the more efficient active type that has a higher energy transfer capability of 2A vs 200 -300milliamps for your typical aircraft lithium battery.
6. Weight: In general, a Sodium battery will weigh 1/3rd that of a AGM battery
ex. 16.0ah Sodium will weigh 5.3 lbs, lithium 15.6ah 4.9 lbs, lead pc680 15.4 lbs
7. Cost: about 1/3rd less than lithium and little more than AGM
8. Monitoring: Bluetooth available
9. Safety; Compared to Lithium, Sodium possesses better safety features with lower probability of dendrite growth, higher internal resistance, and higher thermal runaway temperature. range (−40 °C to 80 °C, with a capacity retention rate of nearly 90% at −20 °C)
​Sodium has a wider temp and voltage range, maintaining reliability in extreme temperature swings common in flight operations, so no vent tube required making sodium ideal for inside the cabin. Higher thermal activation threshold and slower heat generation rate. Can take more electrical/environmental abuse giving consistent performance w/o the risk of sudden power loss as in lithium or lead.
Sodium is best suited for 'safety-critical' applications.
10. Na-Ion Batteries
Common electrode materials used for SIBs are hard carbon as the anode and transition metal layered oxides (Na1−xMO2) as the cathode. Analogous to LIBs, SIBs work based on the intercalation of Na-ions into the guest species of the cathode. Layered oxide materials present the advantage of low molecular weight and, therefore, higher specific capacity. Using a suitable cathode presents minimal structural change during intercalation to ensure a longer cycle life.
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11. Self-discharge per month: Sodium - about 1% , LiFEpo4 - about 2 to 3% per month , AGM - about 5 to 6% per month
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12. CAPACITY ANALYSIS
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presents the results for the LFP cells. Here, the 10% SOC cell presented the best capacity retention, and the 70% SOC cell presented the biggest capacity loss. This might come from the transition from stage II to I of graphite, where more SEI growth can take place. Another interesting fact that can be observed in Fig. 8b is the thermal instability of LFP cells. 56,57 After the voltage hold at 55 °C, the capacity drop is much steeper (between check-ups 3 and 4), indicating elevated degradation. This may be one of the reasons why LFP cells lose so much capacity compared to the other cell types.
Figure 8c shows the NFM Na-Ion results. The 10% SOC condition presents the best capacity retention, including a 0.2% recovery after the first voltage hold at 25 °C, which could be caused by the anode overhang equalization effects. A recovery effect at 10% SOC was expected for all cell types investigated. Interestingly, it only happened for the Na-Ion cell, which could be due to the low capacity fade of the Na-Ion cells, which are more sensitive to the recovery effect. The 40% and 50% SOC conditions present the highest capacity drop. Here again, the high SOCs do not present an elevated capacity loss similar to the behavior of the NMC811 cells. This means that for the investigated Na-Ion NFM cells, the maximum capacity degradation observed is at about 40% to 50% SOC.
When analyzing, a better comparison between the different cell types can be done. Here, it becomes clear that all cell types have better capacity retention at 90% and 100% SOCs, compared to 70% or 50% SOCs, where the highest capacity loss occurs. In addition, the big capacity loss of the LFP cells becomes clear, reaching almost a 6% loss for 70% SOC. In comparison, the NFM Na-Ion cells all lose less than 2% capacity.
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SOC CHART FOR SODIUM;
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Notes;
A Na battery can use 100% of its Ah capacity
A Na battery voltage has a noticeable sloping gradient discharge curve (vs a flatter lithium curve )
A Na battery engine cranking amps are maintained longer than lead acid because of Sodium's higher energy density.
A Na battery follows the same charging and discharging protocols of a LFP battery
*An interesting fact about lithium(LFP) cells inside a battery pack is their divergence in levels of charge, thus capacity, with each discharge/charge cycle. Even perfectly matched cells can not prevent this over time. This condition degrades the battery performance and will eventually lead to overcharging or overdischarging of cells.
A cell will be permanently damaged if overdischarged or overcharged just one time *
When overcharged, a LiFepo4 cell can rupture releasing toxic fumes and smoke.
*( taken from a popular LFP battery sellers website )
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REFERENCES:
https://www.youtube.com/watch?v=yRAJSH_raW8
https://www.youtube.com/watch?v=c0EFZl2IShs
https://www.youtube.com/watch?v=u4hcpYYD2lc
https://www.youtube.com/watch?v=7yhcyn_4cUc
https://faradion.co.uk/technology-benefits/superior-safety/
https://www.grepow.com/blog/lifepo4-battery-explosion-causes-and-consequences.html
https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2023-04/DOT-SIB-Testing-Report-Web-Version.pdf.
LOW Self-Discharge HIGH
What method of cell balancing does your lithium battery use ??
The basic method of balancing lithium cells hasn't changed in years.
The two types can be divided into Passive cell balancing and and the newer Active balancing type.
Passive balancing drains charge from cells with excess charge and dissipates the drained energy as heat. Active balancing on the other hand transfers charge from higher charged cells to lesser charged cells.
Cell balancing is not only important for improving the performance and life cycles of a lithium battery, it also improves safety of the lithium battery.
Both Active and Passive cell balancing are ways to improve system health by monitoring and matching each cells SOC. But, unlike passive cell balancing which simply dissipates the charge during the charge cycle, Active balancing redistributes the charge during charge and discharge cycles.
Therefore, Active cell balancing increases system run time and improves charging efficiency without generating the internal heat of a Passive resistor system.
Passive balancing is the method most used today to keep costs down at the expense of battery efficiency. A cheaper type of 'integrated' BMS is used in all lithium batteries seen in the market today using the Passive method where battery performance is not critical or safety dependent.
These cheaper BMS's may try to add other features like alleged redundancy or fault indicators to compensate for the inevitable early demise of the battery due to the imbalanced state of the cell pack.
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VS
The faster the charging, the greater the imbalance that is occurring.
It is a common weakness with all lithium batteries that cell imbalance is a liability in every battery system. If lithium batteries are overheated or overcharged, those conditions will accelerate battery degradation and quickly shorten the batteries lifespan. Just as there are no two identical snowflakes, so too are there no two identical cells. There are always subtle differences in SOC, self-discharge rate, capacity, impedance and temperature characteristics. This is the case even if the cells are the same model, same manufacturer or same production batch.
Without a robust balancing ability the results are a large difference in SOC over time decreasing capacity.
In Passive balancing, the practical goal is to achieve capacity balance at the end of charge. However, due to the typical low balancing current, if the cells begin to diverge in SOC, it is virtually impossible to correct the charge imbalance at the end of charging. In other words, Passive balancing, while avoiding overcharging of the strongest cells does not allow a full charge of the weaker cells because extra energy is wasted in shunt resisters as heat... a LOT of heat!
With Active type balancing, 2 goals - achieving voltage parity at the end of charge and minimizing V differences among cells can be achieved at the same time. Energy is conserved and transferred to the less charged cells which results in increased safety, discharge capacity and life of the battery.
Unless the cells are well balanced, a ' weaker ' cell in the pack will limit the overall performance of the battery and eventually render the battery unusable. To avoid this, the cells should be balancing at all times not just while being charged so that the differences between cells are as small as possible.
Operational wise; the Passive method is simple and straightforward - the BMS uses resisters to dissipate energy. It is cost effective and this method is used in all older tech lithium aircraft batteries still being sold today. However, since 100% of the excess energy is turned into heat inside the battery, and it is incapable of keeping up with the incoming charging current, imbalance is assured and cycle life is diminished.
A typical BMS with Passive balancing comes with 50 - 200milliamps capability. When the charging current is high - such as from an alternator/generator - the resisters are overwhelmed and the heat generated by them degrades the cell pack over time.
Active balancing on the other hand utilizes capacitive or inductive charge shuttling to deliver energy where it is most needed with minimal loss and heat generation.