|Nissan’s new parallel hybrid system. Click to enlarge.|
At its Advanced Technology briefing in Tokyo, Nissan Motor unveiled prototypes of its original hybrid electric and new all-electric vehicles, both powered by lithium-ion batteries from the Nissan-NEC joint-venture, AESC (Automotive Energy Supply Corporation) (earlier post). Nissan plans to introduce production versions of the hybrid and the EV in 2010.
Hybrid Electric Vehicle (HEV). The hybrid system employs two new Nissan technologies: a parallel-powertrain hybrid system and a high-performance rear-wheel drive hybrid system. The parallel-powertrain system uses two clutches in which one motor is directly connected to the V-6 engine and transmission via two separate clutches.
The parallel-powertrain hybrid system eliminates the need for conventional torque converters, contributing to higher responsiveness and linear acceleration for improved driving feel, Nissan said.
|The four modes of hybrid system operation. Click to enlarge.|
AESC produces laminated lithium-ion cells using a manganese spinel cathode material (LiMn2O4). For its next generation cathode material, it is working with nickel-mixed Mn spinel. The battery pack for the new hybrid delivers twice the power density of the lithium-ion pack Nissan introduced in Japan in the Tino hybrid in 1999.
|The new Li-ion battery enables higher power density. Click to enlarge.|
To realize higher power, the electrodes are thinner to reduce internal resistance, and the lithium in the electrode material is closer to the electrode plate. A new passage inside the electrode material facilitates electron transfer, reducing electrical resistance within the material, and increasing power output.
The laminated structure enables a larger surface area to improve cooling efficiency.
Nissan is currently testing prototypes of the hybrid system on the road in Japan and the US.
|Mule with new Nissan EV system. The production version will have a unique bodystyle. Click to enlarge.|
Electric Vehicle (EV). The latest generation electric vehicle prototype features a front-wheel drive layout and uses a newly developed 80 kW motor and inverter. The advanced laminated compact lithium-ion batteries are installed under the floor, preserving cabin and cargo space.
The production vehicle to be introduced in 2010 will have a unique bodystyle and is not based on any existing Nissan model.
|The new pack for the EV features a new anode material and offers higher energy density. Click to enlarge.|
The Li-ion pack for the new EV has twice the energy density and 1.5 times the power of the battery pack introduced in the Hypermini in Japan in 2000. This enables a longer cruising range, and better acceleration. The pack also supports quicker regeneration to conserve energy consumption.
To increase the energy capacity, AESC is using a new graphite carbon anode material that is coated more thickly on the electrode to increase capacity.
Fuel Cell Stack. Nissan’s new fuel cell stack doubles the power density of the previous generation stack. The new fuel cell stack also achieves a 35% cost reduction mainly due to half the use of platinum.
|The new fuel cell stack. Click to enlarge.|
Test fleets incorporating the improved fuel cell stacks will be operational by the end of this year, and Nissan is targeting commercial production in the 2010s.
The doubling of the power density is achieved through improved conductivity of the electrolyte layer within the MEA, where the main chemical reaction occurs, coupled with a more densely-packed cell structure.
To create a more densely-packed cell structure, Nissan replaced the older carbon separator with a new thin metal separator. A specific coating applied to the separator helps improve conductivity and prevents chemical corrosion, leading to increased efficiency and durability throughout the fuel cell stack’s life-cycle.
|The new thin metal separator (bottom). Click to enlarge.|
Higher durability electrode material results in a 50% reduction of the platinum required compared to the previous generation. This in turn, provides a significant breakthrough in the cost of these components.
The combined improvements in the cell result in double the power density, which enables a downsizing of the fuel cell stack size by one-third along with a significant reduction in cost, without sacrificing performance. Compared to the previous generation, the new generation stack’s power output is increased 1.4 times from 90 kW to 130 kW. Stack size is reduced by 75% to 68 liters from 90 liters, which allows for improved packaging flexibility.