Cycle life tests of High Energy density cylindrical cells | Page 7

Some information about the upcoming Lishen format 5.8Ah cell (LRSK):

- Rated at 20.88Wh or 5.8Ah at 3.6V, with given minimum capacity of 5.65Ah @ -0.2C
- Efficiency at -1C is >93% efficiency, making the cell probably closer to 5.2Ah-5.3Ah under use.
- Cycle life given is >80% capacity after 500 cycles at -1C (down to 2.75V and +0.5C up to 4.20V) with 30mins intervals between cycles (both at end of charge and start of discharge).

The technical datasheet was found here.
Cells are available for retail purchase there from a company in the USA based in Las Vegas, Nevada.

I am taking this opportunity to include a roadmap for by Lishen which shows, amongst others, two cells (energy and power variants, 33Ah and 30Ah respectively) and two tabless power cells (4.0Ah and 5.0Ah):


I'd also like to include a roadmap schedule for the 46mm cylindrical series by Lishen that I found for the and formats:

Attachments

• Lishen LRSK (5.8Ah).pdf

Yeah, which is why it's weird.

Some HE cells despise being charged at 1C at ambient temps (20/25C depending on testing criteria), but it shouldn't be that bad even then.

yea, looking at the chart above, some of the Lishen cells say 60% after 300 cycles, that also seems horrendous. Assuming contractors buy power tools that use them, and assuming they use them for 2 cycles a day, they will have lost almost half of their capacity after 5 months? wow

yea, looking at the chart above, some of the Lishen cells say 60% after 300 cycles, that also seems horrendous. Assuming contractors buy power tools that use them, and assuming they use them for 2 cycles a day, they will have lost almost half of their capacity after 5 months? wow

Yes. If you're using plain CC-CV and don't even have proper passive cooling at the end of the discharge, your cell will die rather quickly.

There's a reason makers and EV makers are hell bent on maximizing charging efficiency through the usage of better charging algos and active thermal management.

Heck, even CP-CV (Constant Power Constant Voltage) charging will help cycle life decently, so it should be the basis to all modern chargers, but it currently isn't. @Pajda I have a special request.

Can your set your charger to turn on and off at X interval?

You could test mild pulse charging like I've seen in 2 scientific articles recently discussing of adding low complexity charging algorithms to existing devices:

Analysis on pulse charging–discharging strategies for improving capacity retention rates of lithium-ion batteries - Ionics

The capacity fade of lithium-ion batteries (LIBs) are intimately dependent upon charging–discharging strategies. In this work, a pseudo-two-dimensional model coupled with thermal effects was developed to investigate the effects of pulse current charging–discharging strategies on the capacity...
To make it short, mild pulse charging uses low frequency charging/relaxation steps.

Opposite to high frequency pulse charging switching at 1Hz-10kHz, we go sub 1Hz with intervals of up to 25s charging-25s relaxation.

This increases battery efficiency a bit, increasing cycle life and being very easy to implement. It doesn't have the larger gains fully optimized frequency (fzmin) charging has, but it doesn't have the downsides of a complex implementation or the possibility of not being better at all than mild CC-CV charging.

In summary, I would like for you to (if you can of course):

- Do a normal 4.2V cycle life test with 0.5C CCCV charging.
- Do a tweaked 4.2V cycle life test with 25s 1C charging/25s relaxation mild pulse charging.
You could also try 20s 1C charging/20s relaxation mild pulse charging to exactly mirror other litterature (0.05Hz).

Both would use a run of the mill >=5Ah cell to test an average cell.
This would be a hard test for such a cell, but doable and would allow us to see if there are benefits with the types of cells that we like to use.

Thank you again for everything you do. On the topic of scientific articles:

This article is inherently super interesting for high energy density lithium-ion cells that utilize silicon in their anodes without any special design or encapsulation considerations because of possible rate-independent lithium plating that happens if negative and positive electrode capacities aren't matched:

Generally, the
latter can be avoided in fresh cells by simply using a negative
electrode to positive electrode capacity ratio (n ratio) greater than 1
(Fig. 7a). However, if active material from the negative electrode is
lost during aging, rate-independent lithium plating will occur even in
cells with excess negative electrode capacity (Fig. 7b).

Since uncontained silicon tends to behave weidrly when utilized vs graphite, any loss of usable silicon will more unevenly reduce anode capacity, creating a situation where rate independent lithium plating can happen.

Umm, this is interesting.

Cell internal resistance
often increases during aging, in part due to the growth of side
reaction products on the surface of the electrode particles. This effect
is most pronounced for oxide-based positive electrode materials like
NMC, nickel cobalt aluminum oxide (NCA), lithium cobalt oxide
(LCO), and lithium manganese oxide (LMO), as they operate well
above the stability window of the electrolyte

Huh, that would explain a lot of things.

@Pajda I have a special request.

Can your set your charger to turn on and off at X interval?

Sorry for later reply, we were a little flooded in central Europe. Yes this topic is very interesting and my BTS can do this.

I guess we need to figure out the specific test settings. Typically what type of cell to choose (HE/HP), DoD range and then whether to stay with 0.5C CCCV base charging or move to 1C CCCV base compared to 2C mild pulse charging., where I expect more visible practical benefits?

Sorry for later reply, we were a little flooded in central Europe. Yes this topic is very interesting and my BTS can do this.

I guess we need to figure out the specific test settings. Typically what type of cell to choose (HE/HP), DoD range and then whether to stay with 0.5C CCCV base charging or move to 1C CCCV base compared to 2C mild pulse charging., where I expect more visible practical benefits?

The cell you should use first are HE cells of the "generic" 5Ah variety. I vote for the Samsung 50E since it's a widely available "last gen" cell, not a leading edge cell like current tabless ones like the P50B that eats up high current charging due to its thin high Si-C anode.

The DOD should be 2.5-4.2V so it stresses both the anode SEI and the cathode interfacial resistance related degradation to the max for both charging protocols. It's mostly to see the difference in IR growth compared to CCCV because even if capacity loss is higher, a lower IR growth progression rate is very interesting to see.

Good idea on the current protocol part. We'll test with 2C 0.05Hz 50% duty cycle pulse charging vs 1C CCCV to make the initial testing much faster and see any interesting patterns popping up; if it both improves cycle life and lowers IR growth, we won't need additional testing. If it lowers IR growth but increases capacity loss, you could do a 1C 0.05Hz 50% pulse vs 0.5C CCCV to check if the cycling loss is a general tendency or if the cell truly can't handle 2C currents without active thermal management.

In summary:
Samsung 50E cell.

Cell 1 is with 2C 50% duty cycle 0.05Hz pulse charging with a last step CV once the cell reaches 4.2V to avoid an overvoltage situation.

Cell 2 is with 1C CCCV.

As batteries were beginning to be mass-produced, the jar design changed to the cylindrical format. The large F cell for lanterns was introduced in and the D cell followed in . With the need for smaller cells, the C cell followed in , and the popular AA was introduced in . See BU-301: Standardizing Batteries into Norms.

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Cylindrical Cell

The cylindrical cell continues to be one of the most widely used packaging styles for primary and secondary batteries. The advantages are ease of manufacture and good mechanical stability. The tubular cylinder can withstand high internal pressures without deforming.

Many lithium and nickel-based cylindrical cells include a positive thermal coefficient (PTC) switch. When exposed to excessive current, the normally conductive polymer heats up and becomes resistive, stopping current flow and acting as short circuit protection. Once the short is removed, the PTC cools down and returns to the conductive state.

Most cylindrical cells also feature a pressure relief mechanism, and the simplest design utilizes a membrane seal that ruptures under high pressure. Leakage and dry-out may occur after the membrane breaks. Re-sealable vents with a spring-loaded valve are the preferred design. Some consumer Li-ion cells include the Charge Interrupt Device (CID) that physically and irreversibly disconnect the cell when activated to an unsafe pressure builds up. Figure 1 shows a cross section of a cylindrical cell.

Typical applications for the cylindrical cell are power tools, medical instruments, laptops and e-bikes. To allow variations within a given size, manufacturers use partial cell lengths, such as half and three-quarter formats, and nickel-cadmium provides the largest variety of cell choices. Some spilled over to nickel-metal-hydride, but not to lithium-ion as this chemistry established its own formats. The illustrated in Figure 2 remains one of the most popular cell packages. Typical applications for the Li-ion are power tools, medical devices, laptops and e-bikes.

In , 2.55 billion cells were produced. Early Energy Cells had 2.2Ah; this was replaced with the 2.8Ah cell. The new cells are now 3.1Ah with an increase to 3.4Ah by . Cell manufacturers are preparing for the 3.9Ah .

The could well be the most optimized cell; it offers one of the lowest costs per Wh and has good reliability records. As consumers move to the flat designs in smart phones and tablets, the demand for the is fading and Figure 3 shows the over-supply that is being corrected thanks to the demand of the Tesla electric vehicles that also uses this cell format for now. As of end of , the battery industry fears battery shortages to meet the growing demand for electric vehicles.

The demand for the would have peaked in had it not been for new demands in military, medical and drones, including the Tesla electric car. The switch to a flat-design in consumer products and larger format for the electric powertrain will eventually saturate the . A new entry is the .

There are other cylindrical Li-ion formats with dimensions of , and . Meanwhile, Tesla, Panasonic and Samsung have decided on the for easy of manufacturing, optimal capacity and other benefits. While the has a volume of approximately 16cm3 (16ml) with a capacity of around mAh, the cell has approximately 24cm3 (24ml) with a said capacity of up to mAh, essentially doubling the capacity with a 50% increase in volume. Tesla Motor refers to their company’s new as the “highest energy density cell that is also the cheapest.” (The nomenclature Tesla advocates is not totally correct; the last zero of the model describes a cylindrical cell harmonizing with the IEC standard.)

The larger cell with a diameter of 26mm does not enjoy the same popularity as the . The is commonly used in load-leveling systems. A thicker cell is said to be harder to build than a thinner one. Making the cell longer is preferred. There is also a made by E-One Moli Energy.

Some lead acid systems also borrow the cylindrical design. Known as the Hawker Cyclone, this cell offers improved cell stability, higher discharge currents and better temperature stability compared to the conventional prismatic design. The Hawker Cyclone has its own format.

Even though the cylindrical cell does not fully utilize the space by creating air cavities on side-by-side placement, the has a higher energy density than a prismatic/pouch Li-ion cell. The 3Ah delivers 248Ah/kg, whereas a modern pouch cell has about 140Ah/kg. The higher energy density of the cylindrical cell compensates for its less ideal stacking abilities and the empty space can always be used for cooling to improve thermal management.

Cell disintegration cannot always be prevented but propagation can. Cylindrical cells are often spaced apart to stop propagation should one cell take off. Spacing also helps in the thermal management. In addition, a cylindrical design does not change size. In comparison, a 5mm prismatic cell can expand to 8mm with use and allowances must be made.

Button Cell

The button cell, also known as coin cell, enabled compact design in portable devices of the s. Higher voltages were achieved by stacking the cells into a tube. Cordless telephones, medical devices and security wands at airports used these batteries.

Although small and inexpensive to build, the stacked button cell fell out of favor and gave way to more conventional battery formats. A drawback of the button cell is swelling if charged too rapidly. Button cells have no safety vent and can only be charged at a 10- to 16-hour charge; however, newer designs claim rapid charge capability.

Most button cells in use today are non-rechargeable and are found in medical implants, watches, hearing aids, car keys and memory backup. Figure 4 illustrates the button cells with a cross section.

CAUTIONKeep button cells to out of reach of children. Swallowing a cell can cause serious health problems. See BU-703 Health Concerns with Batteries.

Prismatic Cell

Introduced in the early s, the modern prismatic cell satisfies the demand for thinner sizes. Wrapped in elegant packages resembling a box of chewing gum or a small chocolate bar, prismatic cells make optimal use of space by using the layered approach. Other designs are wound and flattened into a pseudo-prismatic jelly roll. These cells are predominantly found in mobile phones, tablets and low-profile laptops ranging from 800mAh to 4,000mAh. No universal format exists and each manufacturer designs its own.

The company is the world’s best cylindrical cells supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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Prismatic cells are also available in large formats. Packaged in welded aluminum housings, the cells deliver capacities of 20–50Ah and are primarily used for electric powertrains in hybrid and electric vehicles. Figure 5 shows the prismatic cell.

The prismatic cell improves space utilization and allows flexible design but it can be more expensive to manufacture, less efficient in thermal management and have a shorter cycle life than the cylindrical design. Allow for some swelling.

The prismatic cell requires a firm enclosure to achieve compression. Some swelling due to gas buildup is normal, and growth allowance must be made; a 5mm (0.2”) cell can grow to 8mm (0.3”) after 500 cycles. Discontinue using the battery if the distortion presses against the battery compartment. Bulging batteries can damage equipment and compromise safety.

Pouch Cell

In , the pouch cell surprised the battery world with a radical new design. Rather than using a metallic cylinder and glass-to-metal electrical feed-through, conductive foil-tabs were welded to the electrodes and brought to the outside in a fully sealed way. Figure 6 illustrates a pouch cell.

The pouch cell offers a simple, flexible and lightweight solution to battery design. Some stack pressure is recommended but allowance for swelling must be made. The pouch cells can deliver high load currents but it performs best under light loading conditions and with moderate charging.

The pouch cell makes most efficient use of space and achieves 90–95 percent packaging efficiency, the highest among battery packs. Eliminating the metal enclosure reduces weight, but the cell needs support and allowance to expand in the battery compartment. The pouch packs are used in consumer, military and automotive applications. No standardized pouch cells exist; each manufacturer designs its own.

Pouch packs are commonly Li-polymer. Small cells are popular for portable applications requiring high load currents, such as drones and hobby gadgets. The larger cells in the 40Ah range serve in energy storage systems (ESS) because fewer cells simplify the battery design.

Although easily stackable, provision must be made for swelling. While smaller pouch packs can grow 8–10 percent over 500 cycles, large cells may expand to that size in 5,000 cycles. It is best not to stack pouch cells on top of each other but to lay them flat, side by side or allow extra space in between them. Avoid sharp edges that can stress the pouch cells as they expand.

Extreme swelling is a concern. Users of pouch packs have reported up to 3 percent swelling incidents on a poor batch run. The pressure created can crack the battery cover, and in some cases, break the display and electronic circuit boards. Discontinue using an inflated battery and do not puncture the bloating cell in close proximity to heat or fire. The escaping gases can ignite. Figure 7 shows a swollen pouch cell.

Swelling can occur due to gassing. Improvements are being made with newer designs. Large pouch cells designs experience less swelling. The gases contain mainly CO2 (carbon dioxide) and CO (carbon monoxide).

Pouch cells are manufactured by adding a temporary “gasbag” on the side. Gases escape into the gasbag while forming the solid electrolyte interface (SEI) during the first charge. The gasbag is cut off and the pack is resealed as part of the finishing process. Forming a solid SEI is key to good formatting practices. Subsequent charges should produce minimal gases, however, gas generation, also known as gassing, cannot be fully avoided. It is caused by electrolyte decomposition as part of usage and aging. Stresses, such as overcharging and overheating promote gassing. Ballooning with normal use often hints to a flawed batch.

The technology has matured and prismatic and pouch cells have the potential for greater capacity than the cylindrical format. Large flat packs serve electric powertrains and Energy Storage System (ESS) with good results. The cost per kWh in the prismatic/pouch cell is still higher than with the cell but this is changing. Figure 8 compares the price of the cylindrical, prismatic and pouch cells, also known as laminated. Flat-cell designs are getting price competitive and battery experts predict a shift towards these cell formats, especially if the same performance criteria of the cylindrical cell can be met.

Historically, manufacturing costs of prismatic and pouch formats (laminate) were higher, but they are converging with cellular design. Pricing involves the manufacturing of the bare cells only.

Asian cell manufacturers anticipate cost reductions of the four most common Li-ion cells, which are the , , prismatic and pouch cells. The promises the largest cost decrease over the years and economical production, reaching price equilibrium with the pouch by (Figure 9).

Automation enables price equilibrium of the with the pouch cell in . This does not include packaging where the prismatic and pouch cells have a cost advantages.

Fraunhofer predicts the fastest growth with the and the pouch cell while the popular will hold its own. Costs per kWh do not include BMS and packaging. The type cell chosen varies packaging costs as prismatic can easily be stacked; pouch cells may require some compression and cylindrical cells need support systems that create voids. Large packs for electric vehicle also include climate control that adds to cost.

Summary

With the pouch cell, the manufacturer is attempting to simplify cell manufacturing by replicating the packaging of food. Each format has pros and cons as summarized below.

Want more information on Cylindrical Lithium-ion Cell? Feel free to contact us.

• Cylindrical cell has high specific energy, good mechanical stability and lends itself to automated manufacturing. Cell design allows added safety features that are not possible with other formats (see BU-304b: Making Lithium-ion Safe); it cycles well, offers a long calendar life and is low cost, but it has less than ideal packaging density. The cylindrical cell is commonly used for portable applications.
• Prismatic cell are encased in aluminum or steel for stability. Jelly-rolled or stacked, the cell is space-efficient but can be costlier to manufacture than the cylindrical cell. Modern prismatic cells are used in the electric powertrain and energy storage systems.
• Pouch cell uses laminated architecture in a bag. It is light and cost-effective but exposure to humidity and high temperature can shorten life. Adding a light stack pressure prolongs longevity by preventing delamination. Swelling of 8–10 percent over 500 cycles must be considered with some cell designs. Large cells work best with light loading and moderate charge times. The pouch cell is growing in popularity and serves similar applications to the prismatic cell.

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