Advances in Battery Technology

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FROM MOTOR MAGAZINE, JANUARY 2015 ISSUE:


Eye on Electronics

By Mike Dale | January 2015

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One might argue that innovative thinking shouldn't be wasted on developing fancier cupholders. But when it's applied to higher goals, like improved fuel economy, new battery designs are one result.

Developing new automotive technology is a tough business. It just doesn't happen that a light suddenly pops on with a great idea that will   increase  fuel mileage. What usually happens is that new technology is developed over a period of several years, one step at a time. Over those years, there are salaries to pay and buildings to maintain. All of that time and money has to be invested, with no guarantees that success will come.

Where it really gets tricky is when the underlying numbers suddenly change. All kinds of decisions are made based on the expected price of fuel and what the government regulations say you have to do. At the moment, the issue is the falling price of oil and gasoline. Already down a dollar a gallon from last year, there are predictions that the price of gasoline might not stabilize until it touches the $2 per gallon mark. What technology development made sense at $4 a gallon totally goes out the window at the lower prices we're seeing now.

The stabilizing factor in this is government regulation. It's unlikely that federal standards will be relaxed any time soon regardless of what happens with the price of fuel. As it stands, we'll still have to meet federal regulations that call eventually for real-world mileage of more than 40 mpg average. In addition, there are regulations on the books that will limit the amount of carbon dioxide that can be emitted. CO2 is especially a concern in Europe, where global warming is a hot button political issue. These requirements are already phasing in and will continue to do so out to 2020 and beyond, regardless of fuel pricing.

Meeting these mileage requirements is almost certainly going to require that every vehicle be a hybrid of some sort. Right now there's lost energy in the heat from the radiator, the exhaust and the brakes. Mild hybrid technology can recapture some of those losses.

The term hybrid covers a lot of ground. Micro hybrids may not do much more than have some sort of regenerative braking that saves energy by reducing the load on the alternator. Full hybrids have typically large, heavy batteries of either lithium-ion (Li-ion) or nickel-metal hydride (NiMH) technology. This gives them electric motor drive capability. It's the ability to move under gasoline power or electric drive that defines a true hybrid.

What's of great interest at the moment is in the mild hybrid arena. What defines a mild hybrid is the presence of a small electric motor that can add its torque to the output of a conventional gasoline engine. A key to this is the planetary gear system first used in bicycles and the Model T Ford. This gear set can be used to add the outputs of the two power sources. The gasoline engine selected for the application is chosen to be only large enough to meet the average power demand. For extra-demand situations, like acceleration and passing, the electric motor adds its contribution to the total output.

A good example of this are some vehicles currently being demonstrated to the big car companies. A group called the Advanced Lead Acid Battery Consortium (ALABC) has put together some mild hybrid demonstrator vehicles—VW Passats. These test vehicles use different electrical systems based on either 12, 24 or 48V. ALABC claims they can match the performance of a 2.0L vehicle with a 1.4L power plant that gets occasional help from an electric boost motor and the battery that powers it. The savings comes in the smaller carbon footprint of the 30% smaller displacement engine. So far, on the European test cycle, the Passats are said to produce 42-mpg fuel economy   results.

Yes, we have already seen some mild hybrids in the marketplace. GM's E-Assist does exactly this sort of thing. The problem so far with mild hybrids has been the poor performance of the batteries used to power the electric motor. A vehicle traveling at 70 mph has a stored kinetic energy based on its speed and mass. Conventional brakes create friction to slow the vehicle. This turns the kinetic energy expended, and just paid for in the cost of fuel, into waste heat and brake dust. Regenerative brakes try to capture this energy. The problem has been that the braking pulses are often too short and too fast for the batteries now in use to accept and store much of the output from the brakes.

All of the battery chemistries out there have disadvantages. Standard lead-acid batteries have a chemistry that's too slow to accept the charge pulses from the brakes. Lithium-ion batteries are expensive and heavy and need to be kept in a temperature-controlled environment for best performance. In fact, Li-ion batteries cannot accept a charge when they're below 32*F. You actually have to expend energy to warm the Li-ion battery to operate in low temperatures. What's needed is a battery that's faster, better and cheaper.

What's different in the ALABC mild hybrid test vehicles is the battery that supplies the power for the electric motor. ALABC is using a lead-carbon battery, which was invented by an Australian group called CSIRO. East Penn and Furukawa are two battery companies that have licensed the technology and are setting up to make the batteries. According to CSIRO, "the Ultra battery is about 70% cheaper to make than batteries with comparable performance."

The lead-carbon battery is a three-electrode device with a single positive electrode and two negative electrodes—one negative electrode is carbon and the other lead. All three electrodes use the normal sulfuric acid-water electrolyte. What happens here is that the negative carbon electrode forms one side of an Ultra capacitor, or supercapacitor. The other side is the battery's normal positive electrode. The positive electrode then forms a regular lead-acid battery with the other negative electrode made of lead. In effect, you have both a supercapacitor and a regular vehicle battery in the same box with the same electrolyte.

To understand why this is special, you need to know a little bit about capacitors. One thing is that capacitors store electricity in the form of electrons. Inside a typical capacitor are layers of metal foil separated by insulation, usually plastic film. How many electrons can be stored depends on the area of the plates and the separation gap between the plates. For most capacitors used in electronics, the storage is on the order of a tenth or two of a microfarad (1 microfarad = 1 millionth of a farad).

In a super or Ultra cap, the carbon electrode is three-dimensional. Electrons can be stored not only on the surface of the plate, but in the thickness of the plate as well. This raises the storage capability by a factor of a million or more. Values in the range of 10 to 40 farads are possible. With some help from the lead-acid side, this can be enough power to run a 3-hp booster motor for short periods of time.

Another advantage of the super capacitor can be seen on the discharge side. A typical lead-acid battery is comparatively slow to release its power. A capacitor is not like that; you can get a flow of electrons without first having to work through the chemical conversion process. This actually works both ways; compared to a lead-acid battery, you can quickly charge the battery and discharge the capacitor just as quickly.

The more fully charged a lead-acid battery is, the less efficient it is at capturing new energy and storing it. A lead-acid battery at 90% state-of-charge (SOC) is only 50% efficient in storing new energy. The supercap in a lead-carbon battery is said to be 93% to 95% efficient in terms of energy in vs. energy out on discharge.

Another big advantage to lead-carbon is that from the outside, a lead-carbon battery looks about the same as a conventional lead-acid battery. Existing factories can make these batteries. Yes, there will be some new equipment required, but it's not as though a whole new factory is needed. Lead-carbon batteries also mount into the usual locations on a vehicle. Yet another plus is that they can be recycled at the end of their life right along with regular lead-acid batteries.

There's more to this than just the combination of a supercap and a lead-acid battery. In discharging, a conventional lead-acid battery forms a white crystalline lead sulfate powder on the negative plates. If it's left there during a longperiod of partial battery discharge, the sulfate can harden. When this happens, it becomes very difficult to remove. More importantly, it blocks the active battery materials from interacting with the electrolyte. That's why it's desirable to keep a conventional lead-acid battery at 90% or more fully charged. A lead-carbon battery is different. These batteries can run happily along in the range of 30% to 60% SOC without becoming hopelessly sulfated.

Another company, Axion, says it uses a conventional lead-oxide (PbO2) positive plate in conjunction with a supercapacitor negative electrode based on high surface area activated carbon. The carbon electrode has five layers. In the middle is a current collector layer while on the outside there are two corrosion barrier layers and then further outside are two activated carbon layers. The very high surface area stores hydrogen ions that then move to the positive electrode during discharge. At that location they return to water. The company says the result is reduced acid concentration swing between charged and discharged states. This reduces grid corrosion and leads to a much longer battery life.

Better, faster, cheaper. Technology doesn't happen overnight. Lead-carbon battery technology has taken more than 10 years to develop. But lead-carbon batteries are here, and they'll empower the mild hybrids that are on the way to local dealerships...and eventually, your shop.

[Airbornemaikai]

I don't see any mention of how long they actually last though, are they safe for off road usage, and what are their cold crank capabilities as well as warranty. It's inevitable that new battery technology be more widely available, but it sounds like it still has a long way to go or I would suspect that info would of been available in the article. Thanks for sharing


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[SHOdded]

A bit more info on PbC batteries:
http://www.altenergymag.com/emagazine.php?issue_number=09.02.01&article=leadcarbon
Link to the DOE presentation referred to in the article:
http://www.sandia.gov/ess/docs/pr_conferences/2008/hund_snl.pdf