Electric vehicles

12Aug 2020

Three factors contribute to the mass penetration of electric vehicles:

  • Driving range that eliminates range anxiety;
  • Lower cost batteries for affordable vehicles;
  • Availability of fast charging.

A common denominator is the battery’s energy density: it is the amount of electrical energy per unit volume (or per unit weight) that a rechargeable battery can store. Energy is measured in units of kWh. Hence energy density is in units of Wh per liter (Wh/l), or Wh per kg (Wh/kg). State-of-the-art energy density figures for lithium-ion batteries stand today near 700 Wh/l and 300 Wh/kg.

Driving range is a direct function of the total energy capacity of the battery. The battery in a Tesla Model S with a driving range of 400 miles can hold 100 kWh. Whereas the battery in a Model 3 with a driving range of 322 miles can hold only 75 kWh. 

Energy density determines the size and weight of the battery. Both Model S and Model 3 vehicles use similar energy density, hence one would expect the battery in the Model S to be 25% bigger. And they are, approximately!

The second consequence of energy density is cost. The price of lithium-ion batteries is measured in units of dollars per kWh. This benchmark price stood in 2019 near $150 per kWh for the entire pack, i.e., a fully assembled battery including cells, wiring, electronics…etc. The cost implications are complex and depend on the scale of manufacturing but history over the past decade has shown that, in the long term, cost does trend down as energy density rises.

The third consequence of energy density impacts the wide availability of fast charging. An important note here: this means that the charging infrastructure needs to be upgraded to fast charging stations, and that EV batteries must be designed to safely accept the fast charging rate from these new stations. It is the latter part that is the subject relating to energy density.

Generally, there is a natural design tension between increasing energy density and fast charging. Increasing energy density means more tightly packed electrode layers inside the battery. But this packing makes it more challenging for the lithium ions to move “faster” during fast charging. This challenge can be mitigated with balancing the battery structural design and with intelligent algorithms to manage the battery charging.

So how do battery manufacturers raise the energy density? And what challenges do they face? Let’s explore a little.

Basic physics tell us that the stored energy in the battery takes the form of electrical charge; here it is strictly the positively charged lithium ion (Li+). Therefore, increasing energy density means holding more lithium ions in the space occupied by the battery. This space consists of the following materials: 

  • The positive electrode (cathode);
  • The negative electrode (anode);
  • And everything else, which includes connectors and insulators.

The two electrodes are the materials that can hold lithium ions – the ions intercalate physically within the fabric of the electrodes, like raisins embedded within a raisin bread. The rest are there to support the function of the battery but they do not hold electrical charge. So in some sense, everything other than the two electrodes is “overhead.”

For years, battery manufacturers increased energy density by minimizing this overhead. They reduced the thickness of its layers and made designs that minimized the amount of overhead material. By the middle of the past decade, these benefits were pretty much exhausted. So battery designs began to raise the electrical voltage across the battery. Since energy is the amount of charge multiplied by voltage, it was easier for manufacturers to play with the voltage knob. This method is also reaching its limit.

Now, battery manufacturers are facing the only remaining option: how to increase the number of ions that can be held within the two electrodes. This is precisely what large battery makers in Asia and the multitude of global startups are trying to accomplish. 

Let’s start with the first electrode. The cathode in your smartphone’s battery is made of a material called lithium-cobalt-oxide (LCO). Its capacity to hold ions has already maxed out. Another material commonly used in China, lithium-iron-phosphate (LFP), is safer than the fire-prone cobalt-laden LCO, but at the expense of much lower energy density. 

Modern EV batteries use two new types of composite cathode materials. Tesla batteries, made by Panasonic, use a cathode material called nickel-cobalt-aluminum-oxide (NCA). Batteries in EVs made for GM, VW, Daimler, BMW and several other car makers use a composite material made of nickel-cobalt-manganese-oxide (NCM). Both NCM and NCA are capable of holding more ions within their fabric – about 15% to 25% more, respectively. Some forms of NCM reduce the cobalt content by replacing it with nickel. Cobalt is a very expensive metal with primary mines in Africa.

The second electrode, the anode, is typically made of carbon, specifically, graphite…it is similar to the graphite in a pencil lead. It was Akira Yoshino’s discovery of graphite as an anode material in the 1980s that paved the way to mass manufacturing of lithium-ion batteries. For his work, he earned the 2019 Nobel Prize in Chemistry.

Graphite anodes are quite porous allowing the lithium ions to intercalate between the carbon atoms. This is how the electrical charge is held within the battery during charging. For each lithium ion, it takes six carbon atoms to store one unit of electrical charge. 

As an anode material, graphite has reached its limits. Enter silicon with a far higher capacity to store lithium ions in its fabric. One silicon atom can hold almost 4 lithium ions — or four units of charge (to be exact, 4 silicon atoms to 15 lithium ions). That’s a significant jump over graphite. But — there is always a but — the extra lithium ions cause the silicon to physically expand and swell, placing enormous mechanical stresses on its crystalline structure and ultimately causing its fracture. So much of the on-going material development is on methods to manufacture silicon-graphite composites that can hold more charge but be more resilient to mechanical failure. 

The combination of new cathode materials with silicon-graphite composite anodes promise to deliver energy densities around 900 ~ 1,000 Wh/l. Yet, the vast majority of lithium ion batteries continue to ship today with graphite anodes highlighting the difficulties and the long durations needed for bringing new materials to market. 

02Jul 2020

Tesla’s market valuation hit today $225 Billion, more than the valuation of any other auto manufacturer, highlighting the importance of the lithium-ion battery to our economies.

The battery is the product differentiator for electric vehicles, stationary energy storage and many consumer devices. Each category is pushing the specifications of the battery — and they all share similar themes: more charge capacity, faster charging, battery longevity, less weight, less cost, and absolute safety!

Many manufacturers shy away from sharing lessons learned from deploying batteries in large volume. In some respect, it is understandable — the battery is a competitive advantage. But by keeping opaque, the end user suffers. At Qnovo, our customers have deployed our battery management solutions on well over 100 million smartphones. Along the way, we learned a few important things. I will share here two relevant observations:

1. Optimizing between performance, cost and safety needs smart software: 

Innovation in materials is important but increasingly insufficient to give end users the experience they deserve. The battery has grown from nearly 1,500 mAh in early smartphone models (the original iPhone’s battery capacity was 1,400 mAh) to a whopping 5,000 mAh in 2020 models to accommodate 5G networks. With the increase in capacity and energy density comes a slew of design headaches leaving little margin for error: maintain the battery’s longevity; provide fast charging; minimize battery swelling, all at once. Optimizing between strict performance specifications, pressure to source from lower cost battery manufacturers in China, and absolute safety is no longer exclusively in the realm of materials. Instead it demands battery intelligence and smart software.

Similarly, electric vehicles are under similar if not tighter constraints. Longer driving range, faster charging, exposure to extreme temperatures, presence of minute manufacturing defects, and immense cost pressures make battery design a difficult task. It is no surprise that auto OEMs now rank battery intelligence software as critical to their systems. OEMs are also becoming more involved in the design and manufacturing of batteries. For instance, Apple designs its own batteries in Cupertino, and BMW invested €200 million in a battery cell competence center in Munich.

So what can intelligent battery management software do? Here’s one representative data point from our results. Our average longevity over 100 million smartphones shipping with our solutions is 1,900 cycles at 25 °C, and an incredible 1,300 cycles at the punishing temperature of 45 °C. Otherwise, an average smartphone will last between 500 and 1,000 cycles. Increasing longevity raises the available capacity and use time, improves the battery’s health and safety, reduces its swelling to make thin smartphones, and gives the end user a far better overall battery experience. 

2. Improvement in safety requires more predictive smart software:

The cell voltage rose from a safe 4.2V in early smartphone models to 4.47V in the newest 5G models — needed to add more energy to the battery. At these high voltages, the margin of safety is razor thin: battery swelling, extreme temperatures, user abuse, minute manufacturing defects, fast charging all contribute to an elevated risk of battery failure or fire!

Data from the field indicate that unsafe battery failures account for 10 to 20 incidents per million devices (measured as parts per million, or ppm) — these incidents lead to property damage or personal injury to the user. Any industry with failure rates in ppm can laud its accomplishments; but ppm levels are grossly inadequate for batteries. There are approximately 1.5 billion new smartphones sold worldwide every year. At ten ppm, there are 15,000 unsafe smartphone incidents annually! This is not acceptable. 

It is incorrect to assume that the industry can improve battery failure rates solely by tightening battery manufacturing processes. It is true that battery manufacturing defects contribute to failure — but defects are not the only reason why a battery may catch fire. Improper operation, poor smartphone design and specifications, and user abuse can all lead to premature unsafe failure. Battery manufacturers, especially in China, are also reluctant to add more controls and cost to their manufacturing processes — battery manufacturing remains an industry with thin financial profits at best, or more often endemic losses.

Let’s step back for a moment and briefly examine a different industry: lens making. Historically, making high quality lenses for photography was a specialty left to a few companies in Germany and Japan, e.g., Leica, Nikon or Canon. They excelled at their manufacturing prowess and accuracy. Then innovation struck in the form of cameras embedded in smartphones. These used cheap plastic lenses but corrected for their optical deficiencies using software. Images from modern smartphone cameras can surpass the quality of those from expensive DSLR cameras. The camera  industry showed that it can substitute manufacturing accuracy with computation, the latter being enormously less costly.

We use a similar philosophy to improve the safety of batteries. We recognize that manufacturing defects are part of building batteries. We use predictive algorithms to identify these defects long before they become a safety hazard, then manage the operation of the battery to reduce the risk of a failure. The result is that there were zero unsafe failures over 100 million smartphones in the field. 

09Mar 2020

Is it true that electric vehicles (EV) need 800-V battery packs for ultrafast charging? Is it true that the Porsche Taycan uses 800-V packs to enable ultrafast charging? Why did GM announce that its new battery platform will support 800 V? Let’s find out.

Let’s start with two essential ingredients required for ultrafast charging:

1. A charging station that is capable of providing a lot of electric power;

2. The ability for the battery to accept the extra charging power without being damaged or degraded.

Charging stations are like AC adapters we use to charge our smartphones. Of course, they provide a lot more power. Standard fast-charging stations in the Tesla network are rated to provide 72 kW; upgraded stations are capable of providing up to 150 kW. Electrify America’s network is adding stations that can charge at up to 350 kW — that’s sufficient to run about 50 average residential homes. 

When the vehicle is charging, its on-board computer communicates with the charging station. In essence, the vehicle tells the station, among other things, how much power it needs to charge the battery. It is the vehicle, not the charging station, that sets the charging power, and consequently the charging time — as long as the charging power is lower than the maximum power available at the charging station. The reason is that the vehicle must balance the charging power vs. the likelihood of battery degradation during charging.

When we speak of battery in an EV, we usually refer to a “pack.” A battery pack is made of hundreds or even thousands of individual smaller battery cells that are assembled together to increase the amount of stored electrical energy. A single battery cell may store anywhere from 17 W.h (e.g., Panasonic 21700 cell used in a Tesla) up to 300 W.h (e.g., cells used in some of the German-made EVs). 

The standard 50-kWh pack in the base Tesla Model 3 includes a total of 2,976 cells, organized into 96 modules, each module consisting of 31 individual cells.  A BMW i3 pack, by contrast, has a total capacity of 43 kWh and uses 96 modules, each module consisting of two cells. The cells in the BMW packs are substantially larger than the ones used by Tesla.

So we notice that the number “96” appears regularly in the pack design. That’s because there are 96 modules electrically connected “in series”: in other words, the electrical wiring of the pack is such that the voltage of the entire pack is the sum of the voltages of each individual cell or module. For the vast majority of lithium-ion cells used in automotive, the module voltage is on average 3.7 V, but can range from 3.1 V when the cell is depleted to  4.2 V when the cell is fully charged. 

We can now calculate the maximum voltage of the pack: 96 multiplied by 4.2 V equals 403 V. This is nominally the pack voltage for the vast majority of EVs on the market including all Tesla models, Chevy Bolt, Nissan Leaf, BMW i3, and many others.

Let’s now calculate the maximum charging current that a 400-V battery pack will request at an ultrafast-charging station. Porsche says that its Taycan can accept up to 270 kW at its dedicated Turbo Charging stations, so we will use this figure.

You may recall from basic physics that power equals voltage multiplied by current. Therefore, the charging current is power (270 kW) divided by voltage (403 V) equals 670 A !!! By any standard, this is a very large current that will require a thick copper cable harness, adding significant weight and cost. Porsche says the extra harness weight amounts to 66 pounds (30 kg) — quite a bit when compared to the pack’s overall weight of 1,389 pounds.

So what if we raise the voltage to 800 V, up from 400 V? You guessed correctly: the charging current drops by half…thus saving significant weight and cost.

That is exactly what the Porsche Taycan’s battery design does. Its packs contains a total of 396 individual cells made by LG Chem, mechanically arranged into 33 modules of 12 cells each. Electrically, the 396 cells are divided into two sets connected in parallel. In each set, there are 198 cells connected in series. The maximum voltage of the pack is 835 V (that’s 198 multiplied by 4.2 V).  Each LG Chem cell is rated at 64.6 A.h, equivalent to an energy capacity of 236 W.h. When the energy from all 396 cells is added, we calculate a total pack maximum energy capacity of 93.4 kWh — just a little less than the maximum pack energy capacity of the Tesla Model S (100 kWh).

So will it be 400-V or 800-V for future EV packs? You decide!

30Dec 2019

Whether related to the stock market, presidential elections or climate, December is the month to make predictions for the coming year and decade. So what battery trends should we expect for the upcoming 2020-2030 decade?

1.Lithium-ion batteries will power more applications — electrification of everything:  The 2019 Nobel Prize in Chemistry highlights the progress lithium-ion batteries achieved in the past four decades. From a laboratory experiment in the 1970s, they are now ubiquitous in consumer devices. Increasingly, they are making inroads in transportation and grid storage applications. 

There is no question that the 2020s are the decade of electrification of transportation, from electric vehicles to buses and trucks. The number of available electric-vehicle (EV) models jumped from about ten in 2015 to over 75 in 2020, including categories of sports cars, sedans, SUVs and light trucks. Automotive companies and their supply chain are inexorably transforming. This will not be an easy transformation — there will be winners and losers. Car manufacturers and Tier-1 suppliers that will not adapt in the next couple of years risk becoming irrelevant. The nature of skilled labor in transportation is also transforming. Labor unions are taking notice but much training is needed for this new labor force.

Electric utilities will implement more energy storage projects on their grids — partly driven by regulations as well as the proliferation of clean-energy grids with distributed wind and solar generation. 

Industrial applications with historically smaller unit volumes will benefit from the increased proliferation of lithium-ion batteries. As communities seek cleaner air, we will see local regulations banning just about anything powered by fossil fuel, from forklifts to lawnmowers.

2. Batteries will deliver better performance but with optimized compromises:

Bill Gates’ famous quote in 1981 “640KB ought to be enough [memory] for everybody” stands as a stark reminder that there is not enough of a good thing. Just like computers flourished with more computational power and memory, mobility will continue to thrive with more available battery capacity. Next-generation 5G wireless smartphones require more battery capacity. Electric vehicle drivers require longer driving ranges (300+ miles). More battery capacity means a continued drive to look for newer materials with higher energy density. 

The public will become more discerning and expecting better battery warranties. Longer cycle life (lifespan) while fast charging will become a standard of performance especially in transportation.

But at what cost? Manufacturers will learn to optimize the battery’s capacity, size, cycle life and charging time to the target application or user case. Electric vehicles in fleets will have  vastly different battery designs than those for, say, residential commuters. Backup batteries used in conjunction with solar power will be even more different. Buyers of electric vehicles will learn how to make informed choices based on the battery. Much like buyers historically learned to understand the difference between 4- and 8-cylinder engines, they will become more literate in understanding the differences between kWh-ratings.

3. Battery prices will continue to decline, but at a slower pace:

The cost of lithium-ion batteries declined in the past decade from over $1,100 per kWh to $150 per kWh in 2019. Forecasters expect this figure to drop below $100 in 2023. At such levels, electric vehicles will reach cost parity with traditional vehicles using internal combustion engines (ICE) — without government buyer incentives. Driven by scale, increased volumes, and a dominant battery manufacturing based in China, standard batteries are increasingly become commoditized. Supply chains are becoming more specialized in addressing the commoditization of batteries. In an effort to improve the profitability of EV models, auto manufacturers will increasingly apply traditional cost disciplines to their battery supply chain, spanning improved manufacturing efficiencies to hedging. A few select applications in need of higher performance will benefit from new developments in advanced materials, e.g., providing higher energy density, albeit at a higher cost, but probably with limited penetration.

The risk of trade tensions with China will continue to loom over the battery supply chain. Even as lithium-ion battery manufacturing facilities come online in other parts of Asia and Europe, China will continue to dominate the lithium-ion battery supply chain, from sourcing raw materials to final assembly. The United States federal and state governments will need to formulate clear policies to address the rapid transition to a battery-centric transportation system — or risk escalating trade tensions with China around battery technologies and manufacturing.

4. Batteries will become safer in the field:

Smartphones routinely catch fire in many parts of Asia — and it’s not even headline news. That will change. That must change. The expected standard of battery safety must improve substantially, especially as larger battery capacities become available (in electric vehicles or electric grids). Efficient inspection methods at the manufacturing site and intelligent battery management systems in the field can improve battery safety by orders of magnitude. 

Yet, it is sadly inevitable that battery fires will become headline news in the future before the industry invests heavily in improving battery safety, possibly even with intervention of some governments.

5. Governments will step in to regulate the recycling of lithium-ion batteries:

The industry will recognize that the recycling of lithium-ion batteries is existential to its future growth. The impact of lithium-ion batteries on the environment, from mining raw materials to disposal of depleted batteries, will be devastating if economic recycling methods are not put in place. For example, lead acid batteries are the no. 1 recycled consumer item in the United States with a recycling rate in excess of 99%. Unfortunately, history shows that governments will need to step in and regulate certain recycling targets for lithium-ion batteries. 

09Oct 2019

I was beaming with delight when I read that John Goodenough, Stanley Wittingham and Akira Yoshino received the 2019 Nobel Prize in Chemistry for the “development of lithium-ion batteries.”

Wittingham’s initial work on batteries dates back to the 1970s while at Exxon. Goodenough’s seminal work on LCO cathodes at Oxford was published in 1980. Yoshino’s contributions on the graphite anode came in 1980s at Asahi Kasei in Japan. Sony converted their ideas into the first commercial lithium-ion battery product in 1991.

courtesy: The Royal Swedish Academy of Sciences

So it is about time that these scientists are recognized for their contributions and for initiating a revolution in energy storage. The award shines the light on the contributions of thousands of scientists and engineers who have diligently worked in the past decades to make lithium-ion batteries ubiquitous in our lives. Just imagine your modern digital life, your iPhone, or your Tesla vehicle, without a lithium-ion battery. You simply can’t!

With today’s Nobel award, lithium-ion batteries join the ranks of great inventions such as the transistor or polymerase chain reaction (PCR). The invention of the silicon transistor in 1951 became the catalyst that led to modern-day Silicon Valley. Kari Mullis’ discovery of PCR technique in 1983 set in motion a vast industry in biochemistry and drug discovery.

Nearly 30 years have passed since Sony manufactured the first lithium-ion battery. Over these three decades, the lithium-ion battery went from powering early models of consumer camcorders to transforming transportation. Nonetheless, the industry remains in its early days with many more challenges to overcome and discoveries to be made. 

As the adoption of electric vehicles accelerates in the coming years, the lithium-ion battery takes a fundamental role in our economy no less than that assumed by the combustion engine in the early part of the 20th century. Challenges in battery performance, safety, manufacturing, cost, integration with complex electronic systems, all must be resolved….challenges also mean opportunities for innovation, and opportunities for scientists and engineers to make lasting contributions.

In an era where the meaning of “tech,” especially here in the San Francisco Bay Area, has become synonymous with the creation of new gadgets or new business models, we should not lose sight that science remains the engine that powers technology.