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Friday, December 23, 2016

Sydney Airport Launch new Electric Bus Fleet for 2017

EV News was recently invited to preview the largest fleet of electric buses in Australia. Built by airport bus operator Carbridge in partnership with Gemiland coachworks and BYD, the new fleet of six battery powered buses are owned by Sydney Airport Corporation Limited as part of a $5 million investment in environmentally friendly ground transportation technology.

With a carrying capacity of 70 passengers, each bus has a range of 500 kilometres, making up to 100 transfer journeys on a single charge. The fleet will provide transportation for over two million travellers, visitors and airport workers who use the Blu Emu shuttle service every year.

The Electric Blu Toro buses, manufactured by a joint venture between BYD & Carbridge, feature custom Gemiland bus-bodies fabricated from aero-grade aluminium for significant weight reduction. The BYD chassis comprises a ZF front axle and a ZF clone rear axle featuring dual 90 kW / 350 Nm water cooled permanent magnet wheel-hub traction motors. A maximum motor shaft speed of 7,500 rpm coupled to the rear wheels via a two stage 17.7 to 1 planetary gear hub provides surprisingly rapid acceleration and a top speed of 70 km/h.

Energy storage is via a 324 kWh BYD iron phosphate battery with the pack split between the forward roof and rear engine compartment zones connected in parallel for a bus voltage of 400 vdc. Dual BYD 40 kW Mennekes AC chargers provide 80 kW fast charging via the dual traction inverters. Currently 6x grid connected charging stations top up the fleet overnight but solar power is the long term plan.

The new electric blu buses will replace the airport’s existing diesel bus fleet servicing the 7 km shuttle route between the T2/T3 terminal precinct and the Blu Emu Car Park.

Monday, December 12, 2016

The Chevy Bolt EV requires ZERO maintenance

Not only do electric vehicles cost literally cents per kilometre to drive, (or fractions of a cent per km with roof-top PV) but they also revolutionise car servicing. The maintenance schedule for Chevrolet's soon to be launched Bolt electric hatchback comprises tire rotation every 12,000 km (7,500 miles) and that's about it. If a wheel alignment is performed with every new set of tires then rotation can be skipped which means the Bolt requires practically zero maintenance.

Chevrolet does recommend a coolant system flush @ 240,000 km (150,000 miles) and replacing the brake fluid every five years but that's it. Typical consumable parts like brake pads and rotors can be expected to last in excess of half-a-million km (~300,000 miles)

And that's only the tip of the iceberg. What goes unsaid is that in EV applications electric motors practically last forever. The international standard for rating motor insulation is based on a half life of 20,000 hours. For every 10c increase in insulation rating life expectancy doubles. For example, the insulation systems of a class H (180c) motor that runs at 150c would lose half it's mechanical strength after 160,000 hours. Power electronic components such as those found in motor inverters are typically rated at up to 100,000 hours.

To put that into context, with average annual motoring of 15,000 km @ an average speed of 60 km/h, a typical EV motor will comfortably cover a minimum 1.2 million kilometres, or 80 years of maintenance free reliable motoring.

No wonder dealerships hate selling EVs!

Sunday, December 11, 2016

Driverless Car Hype Machine or Augmented Drive-by-wire?

"Look ma, no hands" 

While monitoring the 24/7 Internet news cycle it seems not an hour goes by without another 'news' story about driverless cars, usually showing someone behind the controls grinning from ear-to-ear with their hands off the steering wheel like they're riding a roller coaster. The fact that these systems are merely an advanced form of cruise control never seems to penetrate the reality distortion field generated by the hype machine pushing these stories.

History

Speed regulating cruise control (originally named “Auto-pilot”) was first put into a production car almost 60 years ago. Lane Keeping Assist features were first introduced almost 25 years ago. A Honda version of LKAS that provided 80% of steering torque to keep the car in the lane on highways has been on the market since 2003.

Similarly autonomous cruise control with auto brake features was also first introduced 25 years ago and there are now 15+ auto brands offering these systems. Even cars that park themselves have been on-sale for over a decade. (2003 Toyota Prius) Yet as we're about to hit 2017 these functions still have enough novelty value that some media types have branded them 'robot cars'??

Google

Self driving car (SDC) hype really leapt off the Richter scale when Google acquired a startup called 510 systems in 2008. A small team of UC Berkeley students with DARPA Challenge experience built a robotized Toyota Prius called “PriBot” for a TV show pizza delivery stunt.

It's clear that choosing a Toyota Prius to become the first road legal SDC was a strictly functional decision. The mass market adaption of hybrid and electric vehicle with brake regeneration has played a large role in enabling self driving cars. The two features that allow relatively easy implementation of robotic control in production cars are 1) electric power steering 2) brake-by-wire regenerative braking. In conjunction with by-wire throttle, these systems allow direct control of steering, acceleration & moderate braking via low-voltage electronic signals that can be generated in software. This is why all SDC's are either hybrid or electric cars.

What is less clear is how well self driving cars handle high speed emergency braking situations. Despite hybrids and EVs primarily using regen braking to the extent that brake pads now last the life of the vehicle, anti-lock and stability control functions are still part of the legacy friction brake system that requires human muscle input to be operated. The work-around has been to restrict Google prototype testing speeds to 25 mph (40 km/h) and requiring a safety drivers onboard at all times.

Despite the fact nine US states have passed legislation to allow public road testing of 'driverless' cars, by some estimates, Google cars are unable to use about 99% of US roads. Aside from their inability to drive in anything but perfect weather conditions, the cars do not carry the computing horsepower to process all the required data in real-time so the car’s exact route must be extensively mapped. Data from multiple passes by a special sensor vehicle must be pored over, meter by meter, by both computers and humans before any SDC can test a new route. It’s vastly more effort than what’s needed for Google Maps.

While there are half a dozen public 'trials' of self-driving cars/shuttles active around the world , they are either on private roads/campuses or if on public roads, they run in very geographically limited areas. None of them are strictly speaking 'driverless' as they all have human 'safety' drivers.

Safety

The original goal for Google's SDC program, as stated by the “godfather” of self-driving Sebastian Thrun, was to promote safety. A most laudable goal, but is a map localising, lane keeping, cruise control really the best solution to reduce 1 million road deaths and 50 million serious injuries every year?

Real world evidence is starting to suggest, maybe not! A long read by Tim Harford published by The Guardian makes the case that too much automation increases driver in-attention to the point that responding to emergency situations becomes more dangerous, a situation known as the automation paradox.

While governments around the world are cracking down on driver in-attention like texting while driving, to the point where the UK government is now suggesting that offenders could face a life prison sentence, self-driving/auto-pilot systems actively promote in-attention by lulling drivers into a false sense of security.

The fact is that while SDC systems are designed to replace the driver, they do nothing to improve functional vehicle safety. SDC's still have the same mechanical friction brakes with the same mandatory anti-lock and stability control systems as any other car on the road. A self-driving system has the same three basic controls to operate as a human driver, but an SDC system introduces new dangers to the driving environment by having to hand over to a human driver in emergency situations, who's situational awareness may not be up-to-speed, with very little notice. Yet with the introduction of electric vehicles the potential is there to develop an augmented digital drive-by-wire control system that can supervise not only human drivers but also algorithmic drivers, offering the opportunity to develop commercial aviation levels of safety for the automotive world.

Fly-by-wire was developed 50 years ago for aerospace during the Apollo program. Augmented fly-by-wire electronic control systems, standard equipment on fighter jets and commercial airliners for decades, aid and protect aircraft in flight via 'control laws' that provide flight envelope protection, a human machine interface (HMI) that prevents a pilot from making control commands that would force the aircraft to exceed its structural and aerodynamic operating limits. These augmented HMI systems are standard equipment on commercial aircraft and today’s impressive safety and reliability statistics are a testimony to the advanced technology represented in fly-by-wire digital flight control systems. Yet despite the ever increasing level of electronics in ICE powered vehicles, they are still primarily direct control mechanical systems with some limited power assistance.

Electric Vehicles

The introduction of electric powertrains opens the opportunity for augmented drive-by-wire control via primarily solid-state electric powertrains. Replacing mechanical friction brakes with electromagnetic braking by incorporating an electric motor for each individual wheel, either in-board or in-wheel, establishes a direct digital connection that allows precise control of vehicle dynamics and takes human muscle strength out of the loop. This enables the development of a rules based augmentation control system to compensate for a drivers lack of knowledge and/or skill while providing a 'guardian angel' to protect drivers from exceeding a vehicles dynamic limits, or in some cases can assist them in reaching those limits.

In 1992, Daimler-Benz performed a study that utilised its driving simulator in Berlin, which revealed some striking data about simulated panic stops and crashes. In the study, more than 90% of the drivers failed to apply enough pressure to the brakes when faced with emergency situations. This is co-incidentally the same figure the SDC industry often quotes, “some 90% of motor vehicle crashes are caused by human error.”

Based on the Daimler study it seems clear that despite the fact drivers do actively react to emergencies, their lack of training/familiarity with either the braking effort required and/or the capability of the vehicles braking system is the most probable cause of the majority of road accidents. In 1996 Mercedes-Benz introduced yet another extension to hydraulic brakes called Emergency Brake Assist which compensates for 1) human leg muscle strength still being required to operate a modern automobile 2) the "buzzing" feedback and sinking brake pedal during ABS operation.

So does a hybrid brake-by-wire system qualify as an advance that removes human leg muscles from the loop? For moderate brake applications yes, but because brake regeneration is limited by battery charge rates to 50-60 kw max, under emergency braking the car defaults back to the legacy hydraulic friction brake system with it's plethora of add-on systems like ABS, ESC, EBA, EBD etc that, while power assisted, still relies on leg muscle strength.

A drive-by-wire quad motor electric powertrain would provide a machine to machine (M2M) and/or human to machine interface (HMI) that would require only throttle pedal levels of leg effort to execute an emergency stop from any speed, while also incorporating all mandatory safety features in software to be executed via brake-mode torque vectoring all while keeping the vehicle within it's dynamic envelope. A drive-by-wire powertrain would provide a platform for map localising algorithms and various 3D sensor hardware to work together in a similar fashion to how augmented fly-by-wire provides a platform for auto-pilot in commercial aviation.

Drive-by-wire would provide a certifiable advanced computer control system to monitor and step-in to assist drivers in emergency situations. Augmented drive-by-wire could potentially make it possible to build an un-crashable car, dramatically improving road safety while we're all waiting the next 10-20-30 years for consumer ready, go-anywhere, self-driving cars.

Tuesday, November 29, 2016

German OEMs Plan 350 kW Fast Charging Network Across Europe

BMW, Daimler, Ford, Volkswagen, Audi and Porsche have signed a Memorandum of Understanding to create the highest-powered charging network in Europe. The goal is the quick build-up of a sizable number of stations in order to enable long-range travel for battery electric vehicle drivers. This will be an important step towards facilitating mass-market BEV adoption.

The projected ultra-fast high-powered charging network with power levels up to 350 kW will be significantly faster than the most powerful charging system deployed today. The build-up is planned to start in 2017. An initial target of about 400 sites in Europe is planned. By 2020 the customers should have access to thousands of high-powered charging points. The goal is to enable long-distance travel through open-network charging stations along highways and major thoroughfares, which has not been feasible for most BEV drivers to date. The charging experience is expected to evolve to be as convenient as refueling at conventional gas stations.

The network will be based on Combined Charging System (CCS) standard technology. The planned charging infrastructure expands the existing technical standard for AC- and DC charging of electric vehicles to the next level of capacity for DC fast charging with up to 350 kW. BEVs that are engineered to accept this full power of the charge stations can recharge brand-independently in a fraction of the time of today’s BEVs. The network is intended to serve all CCS equipped vehicles to facilitate the BEV adoption in Europe.

Saturday, November 26, 2016

Daimler ups-the-ante to €10 billion for electric vehicle R&D

Daimler is planning to invest up to €10 billion ($11 billion) in electric vehicles research and development, up from €7 billion announced only 6 months ago.

"By 2025 we want to develop 10 electric cars based on the same architecture," Thomas Weber told Stuttgarter Zeitung's Saturday edition.

"For this push we want to invest up to 10 billion euros," he said, adding three of the models will be Smart branded cars and that thanks to larger batteries they will be able to increase their cruising range up to 700 kilometers.

In September, a person familiar with Daimler's plans said that the car maker plans to roll out at least six electric car models as part of its push to compete with Tesla and Audi.

Separately, Daimler said on Friday that it will continue to sell diesel-powered vehicles in the United States, in contrast to German rival Volkswagen.

"There is currently no decision nor are there considerations to withdraw diesel from the U.S.", a company spokesman said, denying a report from weekly magazine Der Spiegel, which had said the carmaker was considering stopping its sales of such cars in the U.S. next year.

Diesel-powered cars account for less than one percent of the Mercedes brand's car sales in the U.S. this year, he added.

That compares to a diesel car share of about 5 percent several years ago, Der Spiegel said.

Daimler is conducting an internal investigation of its certification process for diesel exhaust emissions in the United States at the request of the Justice Department, after the U.S. Environmental Protection Agency said it would review all light-duty diesel vehicles.

According to Der Spiegel, the potential pullback of diesel cars from the U.S. market is not related to this probe.

Volkswagen said on Tuesday it would drop diesel vehicles in the United States and refocus on sport utility and electric vehicles, in the wake of a damaging diesel emissions cheating scandal.

Tesla to offer Zero Marginal Cost Mobility

We've all witnessed first-hand how in just two decades the internet has digitised industry after industry to deliver an increasingly zero marginal cost society (Marginal cost is the cost of producing an additional unit of a good or service after fixed costs have been absorbed.)

While I don't subscribe to the entire zero marginal cost society thesis, it is a good explanation for the effects that have transformed information industries like media, music & software. The same now applies increasingly to energy. While the fixed costs of the harvesting technologies to generate green electricity are decreasing exponentially, the marginal cost of producing renewable energy is near zero. The sun and the wind are free and only need to be captured and stored.

At a recent shareholder meeting, Elon Musk said Tesla's new solar shingles will cost less than a "normal roof" and the energy would essentially be free. Does this mark the dawn of mass market zero marginal cost mobility? Popular Mechanics recently ran the experiment, powering three electric vehicles with a conventional rooftop PV system. They concluded that buying a rooftop PV system to power your electric vehicle is comparable to prepaying three years worth of gasoline, based on $4/gallon, and never having to pay for it again.

We think the payback time for a retrofitted rooftop PV system can be even shorter! Based on average annual motoring of 15,000 km/year, a small 1.5 kW PV array (PM used 7.5 kw) could power a typical EV like a Nissan Leaf (114 Wh/km quoted energy consumption) on it's daily commute for 25+ years at an average cost of < $0.004/km.

Eliminating the $240/month a typical household spends on vehicle fuel, a modest rooftop PV system would pay for itself in just 6 months. Ticking the box to have Tesla tiles fitted to your new house eliminates the payback stage altogether. It is effectively a rooftop perpetual fuel pump where the per kilometre cost is zero from day 1.

Combine Tesla's solar shingles and EV powertrain which, irrespective of their "infinite Mile" 8 year warranty, is expected to last well in-excess of a million miles, (true for all EVs) with the ever growing installed base of rooftop PV systems (25% of households in some Australian states) and we could soon see zero marginal cost mobility becoming reality at internet speed, hammering another couple dozen nails in the coffin of ICE cars.

Monday, November 21, 2016

VW to Invest €3.5B in Battery Cell & Modular Electric Drive Plant

Volkswagen will invest €3.5-billion (US$3.7-billion) in e-mobility and digitalization for its German plants.

To bring Volkswagen up-to-date in the future-oriented areas of e-mobility and digitalization, the company will be making a massive investment in new technologies. The German plants are to enter the field of developing and producing electric vehicles and components. A pilot plant for battery cells and cell modules is to be developed. Volkswagen will be investing €3.5 billion in the transformation of the company.

New competences in future-oriented areas are to be developed at the various locations. About 9,000 additional jobs with a secure future are to be created. Volkswagen will mainly be filling these vacancies with existing employees and will also be recruiting specialists from outside the Group. Over the next few years, Volkswagen will be cutting up to 23,000 jobs via natural fluctuation and partial early retirement, taking the demographic curve into account. It is expressly stated that this reduction in the workforce will be accomplished without compulsory redundancies.

The pact for the future includes agreements on new future-oriented vehicle products. The plants at Wolfsburg and Zwickau are to assume responsibility for the production of electric vehicles based on the Modular Electric Drive Kit (MEB). In order to ensure efficient capacity deployment, a further model is to be produced at the Emden plant. At Wolfsburg, an additional Volkswagen Group vehicle will also be produced.

Future-oriented work is to be divided between the main German components plants. Brunswick will continue to produce the battery system for the Modular Transverse Toolkit and will also be developing and producing the battery system for the Modular Electric Drive Kit (MEB). Kassel is to develop the MEB drive system and to be responsible for the assembly of the entire system in addition to electric transmission production. Salzgitter will produce and supply MEB drive system components. In addition, the plant will be building a pilot facility for battery cells and cell modules.

By 2020, the Volkswagen brand intends to be completely repositioned.

Thursday, November 17, 2016

Axial Flux Induction Motor for Automotive Applications

Hybrid and electric vehicle technology has seen rapid development in recent years. The motor and generator are at the heart of the vehicle drive and energy system and often utilise expensive rare-earth permanent magnet material.

Existing hybrid and electric vehicles, such as Toyota Prius, Chevrolet Bolt, Nissan Leaf, and BMW i3 all use high-energy-density permanent magnet (PM) machines for electric propulsion. The magnetic material is usually sintered neodymium–iron–boron (NdFeB).

Squirrel cage induction motors (IM) have been successfully used in electric vehicles (GM and Tesla) and commercial vehicles (buses and trains). They are much cheaper and more robust although they can struggle to get the same torque density.

Figure 1

Currently, the interior permanent magnet synchronous motor (IPMSM) is the most common machine in use, but manufacturers are keen to develop drive motors with much lower magnet content. High torque density and efficiency are required, as well as a wide constant power range.

In an effort to improve the torque density of automotive induction motors Evans Electric have developed a double stator, copper rotor, axial flux induction motor. (AFIM) Like a typical squirrel cage induction motor, the AFIM eliminates the need for rare-earth permanent magnets entirely, yet matches the IPMSM for torque density and energy efficiency.

Axial Flux Torque Density (Nm/L)

The earliest electrical machines were axial flux motors with the first prototype built by Michael Faraday in 1831. Axial flux machines [Figure 2] (aka. Pancake motors) offer high torque and power density values. A double stator architecture offers the highest torque density coupled with balanced axial forces. Further, the short axial length and solid-core copper rotor construction (patented by Evans Electric) further enhance torque density values when compared to radial flux motors.

Figure 2

Conventional radial flux motor geometry [Figure 3] requires azimuthal travel of magnetic flux through the rotor. Azimuthal flux path volumes result in substantial parasitic eddy current losses unless laminates are used. A double stator, single rotor axial flux geometry [Figure 2] has a shorter flux return path that inherently avoids parasitic eddy current losses and results in a much smaller total rotor volume. Radial flux machines weigh an average of 40% more than axial flux machines at the same output.

For example, the Telsa Roadster AC induction motor outputs similar torque values but is dimensionally 3x the volume of the Evans Electric AFIM which was designed to achieve output torque density of 100 Nm/L.

AFIM torque density can be further increased by reducing the impedance of the machine and increasing the bar number. Typical pole numbers are 6 to 8 while the use of high rotor bar number increases torque and decreases torque vibration.

The use of copper in the disc rotor lowers rotor resistance which improves efficiency but can restrict starting torque.

To obtain high efficiency the machine should be running at low slip so that higher pole number is usually required along with low rotor resistance. However, this can restrict the starting torque. This means that the input impedance as a whole needs to be low which does lead to high input current. However, to get high power factor the input reactance should be low compared to the input resistance. This leads to the need for compromise.

Figure 3

In industrial motors deep bars or double cages can be used but these options are not available in an axial flux design. However, the solid steel rotor aids the starting torque since this appears as an effective high resistance rotor. The maximum torque can be increased by reducing the impedance of the machine and increasing the bar number.

Efficiency – Comparing IM and PM Machines

Efficiency is important for hybrid electric vehicle drive motors. With energetically ‘free’ excitation, low fundamental reactance and the ability to have a high pole count, permanent magnet machines can be extremely light in weight and highly efficient. This is particularly true for industrial applications that involve a restricted speed range, meaning a fixed terminal voltage.

In such applications the design strategy is to build in a high internal flux (which permanent magnets do admirably), so that torque is produced with minimal input current. Then efficiency is high, and the motor can be made light in weight and physically small.

Traction motors for applications such as automotive, are different in that they must operate over a wide speed range. Automotive traction motors require a certain torque (‘base torque’) at low speeds, up to what is called the ‘base speed’, and then a roughly constant power over a speed range from the base speed to a maximum speed that might be several times the base speed. In traction motor applications using wound field DC machines, this torque-speed characteristic is accomplished using what is called ‘field weakening’, or simply reducing field current at high speed.

Prius THS II

The requirement for performance over a relatively wide speed range can force some compromises in permanent magnet motor design. It is not possible to turn down the permanent magnet flux to control terminal voltage at high speed. It is possible, however, to counter the permanent magnet flux with armature current, and this can be done in permanent magnet fields if the permanent magnet flux is not too strong.

So permanent magnet machines built for wide speed range operation generally have relatively weak permanent magnet excitation. Then it is necessary to build a high degree of saliency into the machine so that torque can be produced by interaction of terminal current with that saliency. Thus the permanent magnet machines built for automotive traction operation do not have all of the attractive features one would expect of permanent magnet machines.

At low speed and high torque they do not really operate as permanent magnet machines: they are more akin to synchronous reluctance machines, using the interaction between saliency and (large) terminal currents to produce torque. At high speeds they employ much of their armature current capability to counter the permanent magnet flux, and this negatively affects efficiency at high speed. Such machines can be made to be quite efficient at relatively low torque level and intermediate speed.

The Evans Electric AFIM achieves maximum efficiency of 96%.

Evans Electric AFIM

Effective Efficiency of Traction Motors

To understand the impact of motor losses, including PM drag loss on actual machine operation, we now attempt to evaluate the effective efficiency of a machine with a realistic operating scenario.

Recognise that losses in machines come from two sources. First, acceleration force requires current in the windings, so resistive losses occur. Second, rotational speed produces loss from friction, windage and, most important, core loss.

In permanent magnet machines there is always flux present so that there will always be rotational losses. Induction motors can be de-excited so that core loss can be ‘turned off’ when the motor is not producing torque.

In actual operation as a traction motor the induction machine is more efficient and has a substantial advantage because it can be de-excited when it is not producing torque, eliminating electrical loss in that condition. Since those losses are present only when, and to the extent, the induction motor is producing torque, hybrid vehicles are expected to be more efficient when induction machines are used for the drive motor.

Cost Analysis

Rare-earth material costs can be up to several orders of magnitude more expensive than common steel and copper typically found in IM [Figure 1]. The reduced volume of an AFIM further lowers material costs compared to a conventional radial flux IM. A reduction in motor material costs not only improves Hybrid and electric vehicle profitability but also facilitates the long term trend towards multi-motor EV powertrain architectures ie. twin and quad motor AWD.

Source: Evans Electric

BorgWarner Launch Integrated Electric Drive Module for the EV Market

BorgWarner will launch its electric drive module (eDM) with integrated eGearDrive® transmission in two pure electric vehicles from a major Chinese automaker. Production is expected to begin in summer 2017.

"BorgWarner's new eDM combines our know-how in eGearDrive transmissions, first launched in 2009, with our newly acquired expertise in electric motor technology from the former REMY business," said Dr. Stefan Demmerle, President and General Manager, BorgWarner PowerDrive Systems. "Our first application of this integrated world-class propulsion solution will be produced locally in China."

BorgWarner's eDM provides primary or secondary propulsion for pure electric or P4-type hybrid vehicles. The integrated design of the electric motor and transmission enables weight, cost and space savings. Since both functions are combined into one housing, installation is also easier. Based on the vehicle manufacturer's desired propulsion characteristics, performance is optimized with various available gear ratios to provide a completely tailored solution. Featuring patented high voltage hairpin (HVH) technology and optional power electronics, BorgWarner's HVH 250 electric motor delivers superior performance with over 95 percent efficiency. Through its high-efficiency gear train and compact, low-weight design, the eGearDrive transmission contributes to extended battery-powered driving range, which in turn reduces the battery capacity required. An electronically actuated park lock system is also available.

BorgWarner's comprehensive product portfolio also includes numerous other leading technologies for hybrid and electric vehicles, such as the eBooster® electrically driven compressor, cabin heaters and auxiliary thermal coolant pumps. All of these technologies support automakers around the world in designing the clean and efficient vehicles of tomorrow.

Wednesday, November 16, 2016

Scientists develop new lithium-sulphur battery w/ 5x the energy density of Li-ion

Scientists have developed a new prototype battery inspired by human anatomy. The prototype – which offers up to 5x the energy density of the lithium-ion batteries – uses a lithium-sulphur cell with an intestine-mimicking design that could finally make these energy-dense batteries long-lasting enough for commercial use.

Headed by the University of Cambridge, this research has managed to overcome one of the major drawbacks to lithium-sulphur cells: the fact that they disintegrate very quickly, despite their superior energy density to lithium ions.

When a lithium-sulphur battery discharges, sulphur in the cathode absorbs lithium from the anode. This interaction causes the sulphur molecules to transform into chain-like structures called poly-sulphides.

After the battery goes through numerous charge-discharge cycles, the reaction starts to stress the cathode, leading to bits of the poly-sulphides breaking off and entering the battery's electrolyte, which joins the two electrodes.

When this happens, the battery starts to degrade, as it loses its active material.

Here is where bio-mimicry comes in. Our gut is lined with tiny protrusions called villi, which absorb nutrients during digestion. The villi increase the surface area of the intestines by 30x. Scientists have now developed a nano-structure made of zinc oxides which resembles and act like the villi. These prototype villi will absorb the polysulphides in the electrolyte, slowing down the degradation process of the lithium-sulphur cell.

In testing, after 200 cycles at 1C, the prototype nanostructure saw only 0.05% average capacity loss per cycle, making it almost as stable as lithium-ion – which ranges between 0.025 to 0.048 percent average capacity loss per cycle.

Source: Cambridge