VW’s new e-Golf may lead the way to lithium-air power

  • 15-Apr-2014 03:05 EDT
VW04-14 e-GOLF_grey_22.jpg

VW's new pure electric e-Golf uses lithium-ion batteries, but lithium-air technology is being researched by the company in a bid to avoid "range anxiety."

Herbert Ruholl, Volkswagen’s Head of Technical Projects Management, e-Vehicles, has an answer for critics of the hitherto slow progress of battery development: “We expect the next generation of lithium-ion batteries in 2016 to show an improvement in energy density of 30-40%. At present we have a capacity of 24.2 kW·h; we anticipate this will rise to 33-36 kW·h, which means the range of the e-Golf can be expected to reach at least 250 km.”

It sounds like a promising move towards greatly reducing car buyers’ “battery resistance” and “range anxiety” but, said Ruholl, there is more. He has high hopes for very significant development of lithium-air batteries by the start of the next decade: “Then we can talk of doubling or even tripling the capacity we have at present. That is our expectation—and it is possible.”

Where does this place fuel-cell development, which continues to struggle to become established as a practical, affordable, credible, high-volume alternative energy source, but continues to be blighted by the need for a hydrogen supply infrastructure? “The near future, 5 to 10 years, will be very interesting because we are having a competition between the two technologies, and if lithium-air is proven—let’s say next decade—then yes, the fuel cell is not really necessary,” stated Ruholl.

He stressed that the fuel cell, which forms a significant part of VW's R&D programs, remains “very complex on the chemistry side” and added: “There are a lot of problems still to solve to make a good product for regular customers. For example, tank systems at 800 bar and made of carbon fiber would be necessary to save weight, but that adds cost. Perhaps we will overcome all the problems, but that still leaves the infrastructure issue; a lot of people will not buy fuel-cell cars because of the missing filling stations.”

Ruholl was speaking at the launch of the pure electric e-Golf, which is based on the system previously described by Automotive Engineering for the small VW e-Up (see http://articles.sae.org/12810/). It is an elegantly engineered solution to city travel requirements, but has a maximum range limited—depending on ambient weather and traffic conditions and based on an average energy consumption of 12.7 kW·h/100 km—to 190 km (118 mi). That was fine in Berlin, where VW chose to launch the car (in good weather and moderately heavy traffic flows) and caused no range anxiety as the e-Golf’s sat-nav system guided this editor along a convoluted route that took in the Brandenburg Gate, Reichstag, and the former Checkpoint Charlie East-West crossing point.

Its 85-kW motor, manufactured by VW, produces 270 N·m (199 lb·ft) of torque, gave it very brisk performance despite an unladen EU weight of 1585 kg (3494 lb) or 1510 kg DIN. Compared to an equivalent version with 1.6-L diesel engine, the e-Golf is 245 kg (540 lb) heavier.

Acceleration from 0 to 100 km/h (0 to 62 mph) takes 10.2 s and top speed is 140 km/h (87 mph). Battery nominal capacity is 24.2 kW·h. Using the effects of regenerative braking, which has four modes, it was possible to decelerate safely with seldom use of the brake pedal. However, if it had been necessary to make a detour outside the city or to a town in the area, and if grey clouds turned to black with the necessity to use headlights and windshield wipers, that muted anxiety about range would have set in at once.

In terms of design, packaging, and power controls’ experience, the e-Golf is seen as a significant step towards a far more acceptable and less costly alternative energy solution. It will be joined later this year by a plug-in hybrid version designated GTE, with 1.4-L turbocharged TSI 110-kW (148-hp) gasoline power unit and a 75-kW electric motor positioned between engine and gearbox. The GTE is expected to achieve a 950-km (590-mi) range, some 50 km (31 mi) of which will be in pure electric mode. Official CO2 emissions are expected to be 35 g/km.

Build cost will be “a little higher” than the pure electric version, and weight will add a further 20 kg (44 lb). Significantly reducing the size of current lithium-ion batteries would result in reduced capacity, so, at present, big, heavy batteries will continue.

Will they become cheaper in both lithium-ion and lithium-air forms? “Maybe, maybe not,” said Ruholl cautiously. “But in the near future, we do see recycling of batteries provided we are selling cars in hundreds of thousands of units. That would see a reduction in costs.” The e-Golf sells in Germany for €34,900, €3000 more than an equivalent diesel-engine version.

It is battery size and weight plus the weight of associated systems that might have been expected to create major design challenges, but the latest Mk. VII Golf was conceived at the outset for alternative drivetrains. In packaging terms, the e-Golf version loses 40 L (1.4 ft³) of trunk capacity; VDA volume ranges from 343 to 1233 L (12.1 to 43.5 ft³). Otherwise, it offers the cabin space of a regular example.

The e-Golf is significantly more aerodynamic than the conventional examples, achieving 0.28 Cd versus 0.31 Cd. Special ultra-low rolling resistance (co-efficient is 0.0065, 10% better than a conventional Golf Blue Motion's 0.0072) Continental tires are fitted to the electric version.

Beneath the car, between the axles, the sheet metal for the e-Golf is a bespoke design to accommodate the battery. It is the use of the VW Group’s MQB modular, flexible architecture that makes this possible. The new VW Passat, due late this year, also uses the MQB and has the same alternative powertrain capability.

VW underlines the importance of the car’s power electronics module, a crucial link that controls the high energy flow between the motor and battery and that varies from 250 to 430 V. Power electronics convert DC current stored in the battery to AC. The primary interfaces of the power electronics module are its traction network connection to the battery, three-phase connection to the motor, connector from the DC/AC converter to the 12-V electrical system, and a connection for the high-voltage power distributor.

Driven extensively in Berlin, the e-Golf impressed both via its projection of quality, with very little noise from its motor or ancillary systems, and its quick step-off. Ruholl made the point that an electric car must not only be efficient: “Being fun to drive is a very important part of its development.” The e-Golf is, and if lithium-air technology delivers on time, on cost, and on performance, it could become even more so.

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