The system is aimed at ‘mild hybrids’ with a small electric motor that can increase the engine’s power output, and allows a car to be driven in an electric-only mode at low speeds to cut exhaust emissions
Developed by Kia’s European R&D centre in Russelsheim, Germany, “the new hybrid system employs a 48V lead-carbon battery,” said Kia. “The development team selected lead-carbon batteries over lithium-ion equivalents as they require no active cooling, are more easily recyclable at the end of the vehicle’s life, and can function much more efficiently in sub-zero temperatures.”
Details include battery recharged under deceleration at all speeds, and automatic stop-start in heavy traffic and on urban roads.
The starter-generator is belt-driven – replacing the conventional alternator. “The engine is able to restart with almost no noise or vibration,” said Kia.
An electric supercharger is also part of the system, to increase torque and power at low engine speeds.
“Engineers behind the development of the power-train see the electric supercharger supporting a larger conventional turbocharger, which would seamlessly take over to provide greater power and torque as engine speeds rise.,” said Kia. “The new hybrid system could also be fitted without the electric supercharger for a simpler power-train layout in smaller models.”
In a production car, the firm claims “engineers are targeting reductions in CO2 emissions of up to 15%, while the electric supercharger is designed to deliver power increases of 15 to 20% depending on its application”. Compared to what, Kia did not specify.
One company making Pb-carbon batteries, although not necessarily the one Kia is using, is Axion Power of Pennsylvania.
Axion uses a conventional Pb02 positive plate combined with a supercapacitor negative electrode based on high-surface-area activated carbon.
This electrode has five-layers, with a central current collector sandwiched between two ‘corrosion barrier’ layers, and this assembly further sandwiched between activated carbon plates.
A deep cycle life far greater that conventional Pb-acid or Li-Ion is claimed, with none of the sulphation that gradually destroys Pb-acid batteries.
The chemical reaction at the positive plate is conventional Pb-acid.
At the negative electrode “the very high surface area activated carbon electrode stores the protons [H+] from the acid in a layer on the surface of the electrode”, said Axion. “The battery stores H+ in the negative electrode in the charged state which move to the positive electrode during discharge where they are neutralised to form water.”
Compared with conventional Pb-acid cells, said the firm: “The result is reduced acid concentration swing from the charged to discharged state which reduces grid corrosion on the positive electrode and leads to longer life of the positive electrode.”
Also compared with conventional Pb-acid, the firm is claiming >2,500 cycle life (to 100% discharge) compared with 400-600 cycle for “most Pb-acid batteries designed for deep discharge”.
However, according to charger company Cadex Electronics, which runs the ‘Battery University‘ website, the carbon electrode “lowers the specific energy to 15-25Wh/kg, instead of 30-50Wh/kg which a regular lead acid battery normally provides”.
Compared with Li-ion, Axion claims two to four times faster recharge rates when the battery is partially-charged, as well as “significantly better cold temperature performance.”
An often-overlooked feature of most Li-ion cells is that they cannot and must not be charged below 0°C, and have poor output current below 0°C.