Charged EVs | Battery cell qualification for EVs: Lucid’s cell specialist discusses the complicated process

Q&A with Lucid’s Battery Cell Technical Specialist Maithri Venkat.

In relation to battery cells for EVs, one dimension undoubtedly doesn’t match all. The properties of a selected cell act as constraining components for each side of a automobile’s design—and never just for automobile efficiency parameters equivalent to vary and energy, however for the event of producing processes as nicely. 

Lucid Motors has a staff of battery specialists that collaborates carefully with cell suppliers to guage and check battery cells at each step from automobile design by means of mass manufacturing. Charged spoke with Lucid Battery Cell Technical Specialist Maithri Venkat about how cell analysis works, and the way OEMs and cell suppliers can work collectively to enhance the method.

Charged: Might you inform us about your self and your journey to your current position at Lucid Motors?

Maithri Venkat: I’ve been working in lithium-ion cell growth for automotive functions for the previous eight years. In my present position as a Technical Specialist at Lucid, I lead next-generation cell choice, qualification and key provider partnerships for the Gravity SUV. I’ve labored on a number of facets of battery growth, from cell materials analysis to design tradeoff assessments to efficiency optimization and new product introduction.

Beforehand, I labored at XALT Energy, the place I benchmarked cell designs and sub-components for high-energy cells for transportation and marine necessities. I’ve additionally collaborated with top-tier OEMs and nationwide labs for 12 V Li-ion begin/cease battery growth. 

For efficiency functions, an organization must know tips on how to push the restrict. For financial system choices, the cells are the most important price driver within the automobile.

Charged: Are you able to elaborate on why battery cell growth is so essential for electrical autos?

Maithri Venkat: As automakers decide to electrification, the market necessities have gotten extra various for several types of EV merchandise—longer vary, sooner charging, sports activities car-level efficiency numbers and lengthy life. The battery cell impacts all of those. 

How one designs, tunes and manufactures the battery cells additionally impacts their effectiveness, efficiency and price. For efficiency functions, an organization must know tips on how to push the restrict. For financial system choices, the cells are the most important price driver within the automobile. 

Battery cell growth is vital at each step of the event of a automobile, however particularly in the beginning conceptual design section, the place the vehicle-level product definitions are translated into cell-level technical specs. Technical assessments and industrial necessities are evaluated by EV producers throughout cell choice and qualification. As soon as the cell design is finalized, it’s fine-tuned additional for power effectivity, quick cost functionality, energy functionality and lifelong necessities, previous to deployment in packs and autos. This early stage of cell growth paves the best way for best-in-class technological developments.

As soon as the cell design is finalized, it’s fine-tuned additional for power effectivity, quick cost functionality, energy functionality and lifelong necessities, previous to deployment in packs and autos.

Charged: Are you able to stroll us by means of the preliminary phases of the cell qualification course of? What do we have to think about even earlier than going into cell choice?

Maithri Venkat: Cell growth for automotive functions must occur years upfront. This ensures that we’ve got sufficient time to iterate by means of cell design modifications. Basically, cell growth begins with the creation of vehicle-level efficiency targets. 

For instance, a automobile’s meant usable vary is a key metric within the qualification course of. Goal vary necessities are outlined primarily based on an array of analysis, together with advertising surveys and shopper suggestions. With these established, we are able to apply technical constraints equivalent to automobile and powertrain effectivity, pack sizing and automobile weight class, to remodel vary into usable power per cell. 

Previous to defining battery pack constraints, we have to analyze and steadiness efficiency, sturdiness and price. This requires in-depth collaboration amongst cell engineering, techniques, automobile integration, effectivity, software program and advertising groups. 

Following automobile definitions and alignment on cell efficiency aims, specification sheets are despatched over to cell suppliers. This creates an iterative suggestions loop between OEM and cell provider, and triggers hole evaluation between necessities and expertise readiness. 

Figuring out these efficiency gaps and quantitatively understanding the restrictions of particular cell chemistries helps with future cell growth. For example, for high-energy cell design, material-level modifications equivalent to silicon for anodes, high-nickel cathodes, or solid-state chemistries could possibly be thought of. This may allow technological developments and outline clear actionable aims to bridge the variations between current-generation and next-generation applied sciences.

Charged: You talked about the necessity to translate vehicle-level necessities into cell-level targets. How will we accomplish that? 

Maithri Venkat: As soon as the automobile conceptual design has been finalized, necessities trickle right down to pack and module ranges earlier than getting right down to cell-level definitions. 

Each high-level goal may be tied to a person parameter of the battery cell. For instance, pack dimension, effectivity and vary may be outlined as power necessities for the cell. 20-80% SoC (state of cost) charging occasions may be translated to quick cost functionality of the cell. Product guarantee necessities [can be translated to] lifetime efficiency of the cell, and so forth. Type issue choice may be depending on pack sizing methods, thermal administration techniques for cooling, ease of manufacturability, and even ease of restore. 

Cell peak or steady energy targets are associated to the 0-60 mph automobile efficiency necessities and towing capability. Detailed energy functionality evaluation is useful to offer the required efficiency while you need to—for instance—tow your jet ski to Lake Tahoe. Or, on the best way residence, roll down a hill and regeneratively brake at freezing ambient temperatures for over an hour.

Charged: What are the steps an organization takes to qualify a brand new cell provider?

Maithri Venkat: We consider cell suppliers for a number of high priorities, together with security, high quality, price, efficiency, volumes, expertise roadmap and expertise capabilities. 

For instance, in terms of cell high quality inspection, manufacturing batch lot-to-lot variation should be throughout the outlined engineering specs, and course of variations must be inside Six Sigma management limits. Within the preliminary phases, routine beauty and electrochemical inspections must be performed on obtainable samples. Cell dimensional properties and look of dents, rust or scratches must be totally assessed to grasp manufacturing course of functionality. For electrochemical inspection, it might even be advantageous to conduct common testing for efficiency traits like power and resistance. If cell-to-cell power variations exceed sure threshold values, there are dangers when it comes to battery pack imbalances. 

One other side to think about is the provider timeline. Auto producers want to make sure that their growth timeline aligns with the cell producer’s milestones for idea, design and course of validation phases. Cell mass manufacturing must be nicely upfront of the product introduction timeline. 

Charged: As soon as a cell design is finalized, what are the following steps to be thought of? What kinds of exams are acceptable for every developmental section?

Maithri Venkat: Following cell design finalization, a number of workstreams occur in parallel as a part of the product growth cycle. I’m presently main and facilitating these efforts for Lucid’s Gravity SUV platform. These embrace quick cost, sturdiness, course of functionality, cell parameterization for software program controls, and testing for state of well being/thermal modeling. Listed below are some examples of that course of circulation at Lucid:

Parameter measurements: As soon as consultant cells can be found from the producer, an intensive suite of cell testing and information processing is kicked off for Equal Circuit Modeling (ECM) growth. The cell parameter datasets obtained from testing are important for correct state of cost (SoC) and state of well being (SoH) estimation. 

Utilizing precise cell testing information, we are able to get insights into establishing management limits, and hint how the gaussian power distributions would scale up at pack degree when cells are distributed in sequence and parallel connections.

Variability research: From the method functionality aspect, it’s important to trace cell-to-cell variability by means of design validation, course of validation and last mass manufacturing phases. This helps automobile techniques modeling, integration and product groups gauge the estimated vary and efficiency for the ultimate product. It’s additionally essential to characterize nominal capability and power distributions after analyzing consultant drive profiles with discharge/regeneration pulses integrated inside testing intervals. Utilizing precise cell testing information, we are able to get insights into establishing management limits, and hint how the gaussian power distributions would scale up at pack degree when cells are distributed in sequence and parallel connections. 

Optimization: Miles charged per minute defines quick cost capabilities. Complete testing is finished at cell, module and pack ranges to grasp the failure modes and lithium plating thresholds over the cell lifetime. This facilitates the choice of quick cost profiles and helps push the efficiency boundaries. 

Modeling: State of well being (SoH) for lithium-ion batteries must be predicted precisely for software program controls and for prolonging cell usable lifetime. Physics-based cyclic and calendar growing older capability decay fashions are developed to seize lack of optimistic/damaging electrode materials and lithium stock over battery utilization.

Charged: What are some widespread misconceptions about defining cell specs for automotive utilization eventualities? 

Maithri Venkat: Cell engineering specification sheets are extraordinarily conservative in sure instances. For instance, laboratory cell biking with 1C cost and 1C discharge may set off surprising degradation modes like lithium plating and gasoline technology. Within the case of the Lucid Air Dream Vary version, the automobile’s vary is 520 miles at high of cost, and 1C discharge would imply depleting 520 miles in a single hour. That is an unimaginable situation in the actual world, even when we assume the bottom efficiencies throughout discharge. Cells are much more succesful after we conduct experiments below the vary of circumstances accessible to a buyer. It’s due to this fact essential to think about that testing below the best circumstances may help entry extra consultant limits of efficiency boundaries. As an analogy, Olympic groups don’t decide their marathon runners primarily based on their efficiency in a 100-meter sprint!

Moreover, sure provider specification sheets are primarily based on shopper electronics, for which power estimations are calculated with extraordinarily low constant-voltage cutoffs on the finish of charging periods, or cells are cycled repeatedly between zero and 100% state of cost. Customers of EVs hardly ever cost to 100% after which drive right down to zero. Consequently, it doesn’t at all times make sense to carry out testing and specification setting with such utilization patterns.

Charged: How can automotive corporations assist cell suppliers develop specs?

Maithri Venkat: We must always be sure that provider specification sheets match automotive use instances. I acknowledge that it’s difficult to specify an actual automotive use case. Nonetheless, it might nonetheless be worthwhile to rewrite the specs to adapt extra carefully to what clients may expertise. 

At Lucid, battery information scientists use fleet telemetry information to grasp real looking utilization profiles. Quick cost efficiency boundaries are evaluated primarily based on the popular charger sort, temperature regimes and state of cost (SoC) for session starting and finish. Automotive corporations can train cell suppliers so much that will return into their growth processes and assist them make a greater product.

Subsequently, it might be useful to have steady communication between cell producers and OEMs for incorporating shopper utilization profiles in engineering specs. 

Lastly, it might be useful for automotive corporations to drive specs growth. Ultimately, this serves the most effective pursuits of each cell suppliers and OEMs.

Charged: You talked about real looking profiles earlier. How will we incorporate real-world growing older into laboratory testing? Is there a solution to strike a steadiness between utilizing aggressive growing older vs real looking growing older profiles for cell evaluations? 

Maithri Venkat: It’s of paramount significance to grasp the tradeoffs related to utilizing aggressive vs real looking growing older profiles previous to figuring out the design of experiments for laboratory cell assessments. Testing strategies involving slower cost/discharge, diminished depth of discharge and common temperatures may be supreme for replicating typical EV utilization. Underneath these circumstances, lithium-ion batteries would expertise the degradation mechanisms equivalent to strong electrolyte interphase (SEI) progress which can be noticed in real-world driving. Nonetheless, this might additionally indicate for much longer check timelines to acquire capability loss and resistance progress information. 

However, utilizing accelerated growing older may end in lithium plating on the anode resulting from diffusion limitations or gasoline technology from electrolyte solvent discount reactions. Whereas the testing time is diminished, the failure modes will not be consultant and even achievable for these nook instances. 

Ideally, one wants to decide on intermediate cost/discharge charges with relaxation steps integrated between cycles for efficient efficiency scale-up. 

Charged: What are the cell pattern portions mandatory for every developmental section?

Maithri Venkat: Cell pattern dimension required will enhance by means of the developmental phases. For provider analysis and cell design screening, it could possibly be ample to start out with tons of of early R&D pattern cells. Nonetheless, as soon as the design is confirmed, efficiency optimization and sturdiness testing would require hundreds of cell samples. After this, we get into module and pack testing. The cell amount required for that is 10 occasions extra in comparison with the earlier section. Subsequently, the ultimate automobile testing section would require over 100 occasions extra from the mass manufacturing line in comparison with preliminary R&D evaluations. You will need to do not forget that bigger portions for cell allocations must be obtainable far upfront of the beginning of auto manufacturing.

Charged: Why are consultant battery packs required for automobile testing months upfront of the beginning of manufacturing?

Maithri Venkat: That is associated to the kind of automobile validation and regulatory exams being performed. Having an early begin to validation helps offset longer lead occasions related to testing and information procurement. Examples embrace automobile fleet deployment, scorching/chilly climate local weather testing, homologation and SoC/SoH software program algorithm validation. Electrical autos must undergo mileage accumulation and standardized sturdiness testing to make sure constant long-term efficiency, reliability and guarantee assurance. 

Charged: Ultimately, the objective is to get cells into automobiles. What could be a number of the key duties that we have to observe whereas transferring in direction of manufacturing scale-up throughout EV manufacturing?

Maithri Venkat: Even after finishing efficiency optimization and reliability assessments, we nonetheless must be conscious of recent product introduction within the manufacturing facility. As we transfer in direction of manufacturing ramp-up, we have to think about cell integration into modules and packs on the manufacturing stage. Every cell sort must have a definite manufacturing half quantity, tools settings, and even information dealing with. Even mundane modifications like barcode placement on a cell field can dramatically affect yield if course of controls will not be totally optimized. 

One other instance is the implementation of totally automated in-line inspection strategies for checking key cell traits. These high-speed measurements, together with mid-process and end-of-line measurements, assist us be sure that the processes concerned in constructing modules and packs haven’t impacted the integrity or efficiency of our cells. 

Charged: What in regards to the general timing? How a lot time will we usually must qualify a cell for automotive utilization? 

Maithri Venkat: Cell growth for automotive functions occurs years upfront. Since each cell has distinctive traits, it’s important to conduct detailed testing all through the qualification phases to probe into cell degradation mechanisms and consider efficiency thresholds. 

We would want to guage the event timeline on a person foundation. The time required could be depending on necessities, expertise readiness, cell chemistry, manufacturing feasibility, and the meant EV utility and market. Talking usually, it’s a few years. 

It is usually potential that even a secular course of change from a cell producer may have unintended but extreme impacts downstream for an automotive maker. Subsequently, each single change to a cell must be scrutinized.

Let’s additionally think about a situation during which the cell chemistry is frozen, and there’s a change with respect to a minor course of throughout manufacturing. Whereas this may create a big enchancment in yield, the staff nonetheless wants to guage if it has an affect on efficiency or security. For this instance, it’s potential that a whole re-qualification of the cell shouldn’t be required, and the change may be rapidly authorised. Nonetheless, additionally it is potential that even a secular course of change from a cell producer may have unintended but extreme impacts downstream for an automotive maker. Subsequently, each single change to a cell must be scrutinized. I need to spotlight that each cell is exclusive. Qualification methods and developmental timelines must be evaluated on a case-by-case foundation. Battery cells may be some of the vital path gadgets in your EV growth. 

This text first appeared in Issue 66: October-December 2023 – Subscribe now.