Soteria Battery Innovation Group Single Layer Film Welding Page 1 Confidential Rev. 2, 3/2020

Soteria Battery Innovation Group Document Number: AN0007

Application Note Rev. 2, 3/2020

Ultrasonic Welding of Single Films to Tabs 1.0 Introduction Soteria Metallized film current collectors are designed for use in existing cells and are compatible with a wide selection of battery chemistries. Attaching tabs to the film current collectors can be accomplished with ultrasonic welding. This application note focuses on attaching a single sheet of Soteria metallized film current collector to a tab; a configuration especially suited for cylindrical and jelly roll style cells.

2.0 Background Metallized film current collectors respond to ultrasonic welding in most configurations of tabbing in use today. These fall into 2 main categories:

- Rolled cells. Long current collector electrode with 1 or more tabs attached. Each tab is therefore attached to a single sheet of current collector with the other end welded to internal parts of the cell packaging.

- Stacked cells. Many layers of electrode tabs attached to a single tab that exits the packaging of the cell

Soteria Battery Innovation Group Single Layer Film Welding Page 2 Confidential Rev. 2, 3/2020

Both configurations can be welded with ultrasonic welding. The principle of this weld is fundamentally that the welder can squeeze the substrate material out from the weld area while preserving the metallic coating on each side of the film current collector. The layers of thin metal are then free to be welded to each other and the tab. While these welds can use the same ultrasonic weld process that is very common in the Li-ion industry, the specifics are quite different and require development time on any particular setup to achieve good consistent results. The general theory of this weld is to squeeze the substrate (typically PET) out from between the metallization layers under the weld area via ultrasonic action and then collapse the layers of metal to each other and the tab as shown in the diagram:

Figure 1 – Metallized Film Weld in Theory with Flattened Pyramid Horn (FPH)

The moving part of the ultrasonic welder (horn) comes down from above and while under pressure is moved horizontally back and forth at ultrasonic frequencies (parallel to the surface of the film). Between the movement and the pressure, the substrate is heated and moved out of the way as the upper metal layer is stretched down to touch the lower layer and tab. The scrubbing motion of the horn cleans all the impurities from between the layers of metal and an ultrasonic weld is formed. The weld depicted above results from the use of a weld horn that has a Flattened Pyramid Horn (FPH) shape. A more commonly installed horn, a pointed pyramid, can also produce welds with good electrical conductivity, but with lower mechanical strength.

Soteria Battery Innovation Group Single Layer Film Welding Page 3 Confidential Rev. 2, 3/2020

Figure 2 – Horn Shapes

The weld produced by using a Pyramid Horn (PH) punches through the film, squeezes the substrate out from between the displaced layers with ultrasonic action, and then welds the thin metallization to the rim of the indent in the tab:

Figure 3 - Alternative Weld with Pointed Pyramid Horn Profile

This weld produces good electrical characteristics, but is mechanically weak and must be reinforced with tape (note that the weld is from the film side, the tape is on the tab side holding the tab to the film).

Soteria Battery Innovation Group Single Layer Film Welding Page 4 Confidential Rev. 2, 3/2020

Figure 4 – Tape Reinforcement

Tape on the tab side is commonly seen on rolled cylindrical cells where it is used to provide

insulation and cushioning of the tab. The same tape used for this purpose, typically

polypropylene tape, can be used for securing the PH weld. The weld side does not require any

tape, although adding tape does not hurt the weld.

Alternatively, super glue applied to the film side has shown good reinforcing capability. The

super glue fills the divots of the weld and forms a backfill for the entire structure. A potential

issue with using super glue is that it tends to stiffen the tab area which may lead to stress risers

in a tightly rolled cell, such as an 18650. For jelly roll cells where the tabs remain flat, this may

be an attractive reinforcement method.

Figure 5 - Glue Reinforcement

Soteria Battery Innovation Group Single Layer Film Welding Page 5 Confidential Rev. 2, 3/2020

3.0 Weld Setup (PH) This section provides some specific instructions and recommendations for welders and the specific components used to generate the documented results. There are manufacturer specific part numbers provided for reference, but the user should feel free to substitute machines/parts as the principles are similar across differing machines. Photos and drawings are provided to aid in setting up a welder. Helpful related lab techniques are in a later section.

Figure 6 - Pyramid Horn (PH) closeup

3.1 Welder Alignment (PH) Existing ultrasonic welders are designed for larger tolerances and dimensions than are typically employed in the welding of metalized film current collectors. One of the results of this is that the welds of metallized film battery materials produced from many existing welders may quickly achieve viable welds but may have a difficult time being repeatable across large numbers of samples or from day to day. As will be seen the power and amplitude and alignment are more critical than typically necessary for metal on metal welds. This typically results in operating the welder close to its limits in these areas. Alignment of the weld anvil to the horn is critical for the welding of such thin films. Typical welder setups that may otherwise operate very well may not have the necessary alignment to produce successful consistent results. The overall process for setting up an ultrasonic welder to successfully weld metallized film current collectors begins with a thorough alignment of the parallelism between the anvil and horn.

Soteria Battery Innovation Group Single Layer Film Welding Page 6 Confidential Rev. 2, 3/2020

Anvil to horn parallelism:

Figure 7 – Horn to Anvil Parallelism

The horn should be adjusted to be as parallel as possible for best results. Please consult your welders specific instructions on how best to achieve this. A helpful tool is an electronic level box. This tool displays the angle at which it is sitting on. The procedure is to place the level on the anvil and zero the reading for reference. Then the level is placed on the horn and the horn adjusted until it indicates zero degrees. A level box of at least 2 digits precision is recommended:

Figure 8 – Level box on horn

Horn

Anvil

Surfaces must

be Parallel

Horn

Anvil

Level box

showing 0.00

degrees to

referenced

anvil

Soteria Battery Innovation Group Single Layer Film Welding Page 7 Confidential Rev. 2, 3/2020

3.2 Welder Settings (PH) Weld setup:

- Tab on Anvil - Film on top - Horn coming down from above to perform the weld

Figure 9 – Weld setup

Specific tooling for an Emerson L20 welder (configuration #1): Horn: L1A91121 Horn, Half-Wave(Solid), Tabbed .0075 X .015 X 45 degrees

Anvil: L1A91122 Anvil, Bolt-On, 2-Lobe .0075 X .015 X 45 degrees

Figure 10 - Weld Horn PH closeup

Tab

Film

Horn

Anvil

Soteria Battery Innovation Group Single Layer Film Welding Page 8 Confidential Rev. 2, 3/2020

Figure 11 – Post weld

PH Configuration #1:

- Horn: Half-Wave(Solid) .0075 X .015 X 45 degrees: L1A91121

- Anvil: Half wave 28mm X 4.5mm area, .0075” x .015” x 45 knurl: L1A91122 - Pressure (pressure down on Horn during weld): 60 PSI - Amplitude of Horn for weld: 2um - Energy of weld: 18J - After burst: optional, but may help separate weld from horn - Weld clamp time before weld: 0.5s - Welder recorded performance: 0.75s duration, ~50W peak power

This weld is characterized by relatively high clamping pressure, low energy and very low amplitude.

PH Configuration #2:

- Welder setup with replaceable tip horn - Horn tip: 2 lobe 20kHz tip 0.015”x 0.030” x 45 knurl - Anvil Half wave 28mm X 4.5mm area, .0075” x .015” x 45 knurl: L1A91122 - Pressure of 60 PSI - Amplitude of 2 um - Energy of weld: 10 J - Weld clamp time before weld: 0.5s - After burst: optional as before - Welder recorded performance: 2.2s duration, 7W peak power

This weld is similar to configuration #1 using a PH with a coarser pitch. The weld uses less energy than with the finer pitch horn to achieve good electrical results. This weld also needs reinforcing to increase the mechanical strength.

Weld

Soteria Battery Innovation Group Single Layer Film Welding Page 9 Confidential Rev. 2, 3/2020

3.3 Weld Outcomes (PH) This section provides photos of successful welds as a guide for tuning in a specific welder setup. Microscope photos (~100x magnification, easily achieved via inexpensive USB microscopes) of film side post weld (PH configuration #1):

Figure 12 – PH weld film (horn) side post weld

Note how just the tips of the pyramids are indented on the film – the size of film between the indents is large and provides good conduction. The pitch of the indents is ~.26 mm, and the indents are ~ .10 mm across.

Soteria Battery Innovation Group Single Layer Film Welding Page 10 Confidential Rev. 2, 3/2020

Figure 13 – PH weld film (horn) side closeup

Note how the film is pierced in the center as depicted in the earlier drawing of the PH weld.

Tab (anvil) side Post weld:

Figure 14 – Tab side PH weld closeup

These are the witness marks left by the knurl on the anvil side. These do not penetrate the tab enough to influence the weld interface on the other side. The indents measure .39 mm in pitch. The anvil holds the tab steady for the weld and does not otherwise contribute to the welded structure. The specification of the anvil is not critical; it just has to hold the material steady during the weld. Test results

Test method: Current Capacity

Weld materials: 10um Aluminized film (500nm Al on each side), 4mm wide 100um thick Al tab

Current Capacity to failure: 6A

Film

pierced

Soteria Battery Innovation Group Single Layer Film Welding Page 11 Confidential Rev. 2, 3/2020

IR photo at fail (6A):

Note that at failure, the tab is 5C above ambient. Also note that the heating on the strip is due

to the reflective nature of the conductor showing the testers body heat.

This represents the current from one side of the film to a tab, in a cell both sides of the film

would carry current.

tab

Weld heating

Lowest temp on picture 23C

Soteria Battery Innovation Group Single Layer Film Welding Page 12 Confidential Rev. 2, 3/2020

4.0 Weld Setup (FPH) Flattened Pyramid Horn (FPH) weld setup is similar to PH weld setup. The main difference is, of course, the horn weld surface is flattened and polished resulting in a flattened pyramid structure. Using this type of horn, welds have been successfully made with flat to void ratios (the ratio of the flattened area of each pyramid vs. the whole weld area) of between 5% and 20%. Weld pressure and amplitude remain similar, but energy for the weld is different.

Figure 15 – Flattened and polished horn (FPH)

4.1 Welder Alignment (FPH) Welder alignment is similar to the PH setup, with parallelism between the horn and the anvil of paramount importance. The FPH requires a slight change in that the surface of the flattened horn is the critical surface to be made parallel with the anvil. This is typical for a flattened pyramid horn, but is worth noting as the true critical surface. Additionally, all the flattened areas must be in a single plane.

Soteria Battery Innovation Group Single Layer Film Welding Page 13 Confidential Rev. 2, 3/2020

4.2 Welder Settings (FPH)

Welder setup is similar to the PH weld:

- Parallel flattened pyramid surface to anvil plane.

- Tab is placed on anvil, with film on top, and the horn coming down from above.

FPH configuration 1:

- Branson L20 welder - Anvil Half wave 28mm X 4.5mm area, .0075” x .015” x 45 knurl: L1A91122 - Half wave replaceable tip horn (W5 20Khz) - Horn tip: 2 lobe 20kHz tip 0.015”x 0.030” x 45 knurl

Horn tips flattened and polished – flattened areas ~17% of total area.

Figure 16 – Flattened Pyramid Horn, Polished Configuration 1

Welder Parameters:

- Pressure (pressure down on Horn during weld): 60 PSI - Energy of weld: 10J - Amplitude of Horn for weld: 5um - Weld clamp time before weld: 0.5s - After burst: optional, but may help separate weld from horn

Weld outcome:

- Weld time

- Peak power

Flattened

and

polished

Horn

Anvil

Soteria Battery Innovation Group Single Layer Film Welding Page 14 Confidential Rev. 2, 3/2020

FPH configuration 2:

- Branson L20 welder - Anvil Half wave 28mm X 4.5mm area, .0075” x .015” x 45 knurl: L1A91122 - Horn Half wave 38mm x 3mm area, .0075” x .015” x 45 knurl: L1A91121

Horn tips flattened and polished – flattened areas ~15% of total area.

Figure 17 FPH Horn, Configuration 2

Welder parameters:

- Weld clamp pressure: 60 PSI - Energy of weld: 100 J - Amplitude of weld: 15 um - Weld clamp time before weld: 0.5s - Afterburst: optional

Outcome:

- 1.96 s weld time - 60 W peak weld power

Horn

Anvil

Flattened

and

polished

Soteria Battery Innovation Group Single Layer Film Welding Page 15 Confidential Rev. 2, 3/2020

4.3 Weld Outcomes (FPH) This section contains photos of successful weld outcomes.

Figure 18 – film side of FPH weld closeup (configuration 1)

Note that the flattened bottom areas of the weld display intact metallization from the film. The goal is to minimize any breakup of this film maximizing the electrical and mechanical strength of the weld. The tab side of this weld is similar to the PH weld in that witness marks are left by the anvil in the tab. Test results

Test method: Current Capacity

Weld materials: 10um Aluminized film (500nm Al on each side), 4mm wide 100um thick Al tab

Current Capacity to failure: 7A

Soteria Battery Innovation Group Single Layer Film Welding Page 16 Confidential Rev. 2, 3/2020

Weld Parameter Tuning Microscope photos are very helpful in tuning in weld settings to achieve good welds. The key is to look for unbroken areas of aluminum at the bottom of the weld. Side by side photos of good and poor welds: Good Weld Poor weld

Figure 19 – Good and Poor weld floor examples

Unbroken

Floor

Broken

Floor

Soteria Battery Innovation Group Single Layer Film Welding Page 17 Confidential Rev. 2, 3/2020

5.0 Lab Techniques Current Capacity measurement A good method of evaluating weld electrical quality is passing current through the weld and either testing to failure or observing the heating in the weld with an IR camera. Test setup:

Figure 0 – Current capacity IR test setup

- Negative electrode on the film side only - Positive electrode clipped to the tab (tab side down) - Current passed from positive electrode to negative - IR camera used to determine heat rise in weld, or note failure current

The negative electrode needs to have high surface area contact with the film to prevent high current densities in the film. High current densities in the film can lead to the film failing open, as is its design intent. A sheet of aluminum foil held down on the surface (in the above example, a glass slide is clamped down over an aluminum foil electrode that sits on top of the metallized film sample) is an easy way to achieve this. The opposite power supply lead can be simply clipped to the tab. Current is then increased through the weld. If using the failure current method, increase current in small steps pausing at each step for the setup to stabilize, until failure. Alternatively, a target current can be chosen, and an IR camera can be used to view any heating of the weld. Generally, the test current should be maintained through the weld for 30 seconds minimum to allow any heat blooms to be clearly visible on the IR camera.

Tab on

bottom

Aluminum

electrode

clamped under

glass slide

Power

supply

leads

Soteria Battery Innovation Group Single Layer Film Welding Page 18 Confidential Rev. 2, 3/2020

Either technique provides a simple way to evaluate the electrical performance of the weld. Example test results (IR camera technique):

Test 1 Test 2

Current through circuit (A) 2.00 5.00

Temp rise from ambient C <1.00 <1.00

IR Photo:

Figure 21 – IR photo of welded tab showing <1C rise in weld @ 5A

This measurement technique relies on passing relatively high currents through the weld and looking for IR generated heat rise in the weld as a sign of higher impedances. It also can yield good information on the consistency of the weld – if one side of the weld is heating more than the other, welder horn/anvil mis-alignment may be indicated.

Soteria Battery Innovation Group Single Layer Film Welding Page 19 Confidential Rev. 2, 3/2020

Direct Impedance measurement Direct impedance measurement of the weld is difficult due to 2 factors:

- The impedance of the weld is very low (if successful) and typically is at the limit of commonly available DMMs.

- The impedance of Soteria films varies with distance and is of a magnitude greater than the weld impedance

On single layer film welds it is of paramount importance when using a DMM to minimize the amount of film between the probe point and the weld (without actually putting the probe into the weld area as this might modify the weld connection).

Recall that Soteria metallized films have a surface impedance of around 50m/□ and the

expected impedance of a weld is around 1m. Measuring the weld impedance while minimizing the serial component of the film and, to a lesser extent, the tab surface impedances is key to evaluating weld quality. Hence the measurement needs to be taken in as repeatable a fashion as possible. A typical setup is shown below:

Figure 20 – 2-point impedance measurement setup

In figure 19, the black probe is on the film side and must be kept as close to the weld area as

possible. The red probe is on the very low impedance tab, so it’s position from the weld is not

as critical. Best practice is to keep both distances as consistent as possible with respect to the

weld.

A second area of concern is that the direct measurement technique provides a measure of

impedance using the very low currents the DMM generates. The Current Capacity method

above addresses this by putting a useful amount of current through the weld. It is possible to

Weld

area Tab (on bottom

side)

DMM

probes

Soteria Battery Innovation Group Single Layer Film Welding Page 20 Confidential Rev. 2, 3/2020

get welds that have low impedance as measured with a DMM but cannot pass significant

current when subjected to the Current Capacity method.

The direct impedance measurement approach has its drawbacks, but in concert with the

current capacity method can be helpful.

Soteria Battery Innovation Group Single Layer Film Welding Page 21 Confidential Rev. 2, 3/2020

To contact us: USA Soteria Battery Innovation Group, Inc.- USA 18B Brozzini Ct. Greenville, SC 29615 864-609-4165 Amy.Brinson@SoteriaBIG.com Europe Soteria Battery Innovation Group, Inc- Europe Juergen.Kellner@SoteriaBIG.com Asia Soteria Battery Innovation Group - China Jianli.Wang@SoteriaBIG.com Revision log: Rev. 0 12/30/19 Draft review release Rev. 1 2/6/20 Add config 2 to PH Rev. 3 3/20/20 Add FPH section, rewrite

Information in this document is provided solely to enable implementers to use Soteria Battery Innovation Group Inc. products. There are no express or implied copyright licenses granted hereunder to design or fabricate any separator products based on the information in this document. Soteria Battery Innovation Group, Inc. reserves the right to make changes without further notice to any products herein. Soteria Battery Innovation Group, Inc. makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Soteria Battery Innovation Group, Inc. assume any liability arising out of the application or use of any product and specifically disclaims any and all liability, including without limitation consequential or incidental damages. “Typical” parameters that may be provided in Soteria Battery Innovation Group, Inc. data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals", must be validated for each customer application by customer’s technical experts. Soteria Battery Innovation Group, Inc. does not convey any license under its patent rights nor the rights of others. Should Buyer purchase or use Soteria Battery Innovation Group, Inc. products for any unintended or unauthorized application, Buyer shall indemnify and hold Soteria Battery Innovation Group, Inc. and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Soteria Battery Innovation Group, Inc. was negligent regarding the design or manufacture of the product. Soteria™ and the Soteria logo are trademarks of Soteria Battery Innovation Group, Inc. All other product or service names are the property of their respective owners. © Soteria Battery Innovation Group, Inc., 2020. All rights reserved.