Rechargeable batteries are the mainstay of portable devices, such as mobile phones and laptops, to electric vehicles. A major challenge for the development of these technologies has always been battery density, that is, how much electricity storage, watt-hours [Wh] per kilogram of weight.
We all remember those brick phones that charged for 10 hours and had a whopping 30 minute talk time. Those phones were mostly battery. Mobile phone technology has greatly benefited from the advancements in rechargeable battery technology, and electric vehicles [EV] can also benefit. One of the main marketing problems for EVs is their limited range, because more range would make the batteries simply too heavy to be economical.
By changing materials, NEC Corp was able to develop a higher voltage, longer lasting, rechargeable Lithium-ion [Li-ion] battery. The new battery can also withstand higher temperatures without breaking down, maintaining 80% capacity after 500 cycles at 20°C [60°F], and 60% capacity after 500 cycles at 45°C [113°F].
The positive electrode was modified from spinel-type lithium-manganese oxide [LiMn2o4] by substituting nickel [Ni]. The new electrode, Li(Ni0.5Mn1.5)O4, when combined with graphite, enabled them to realize a higher 4.5V, about 0.7V higher than the LiMn2O4 compound. The problem with the higher voltage though, was that it led to oxidation of the polycarbonate-based electrolyte. To combat this issue, NEC developed a flourinated solvent.
By increasing the voltage of the positive electrode and minimizing the oxidation of the electrolyte, NEC Corp has increased the energy-density of the new rechargeable battery by about 30%, from about 150Wh/kg to over 200Wh/kg. The full details of the battery will be revealed this week at PriME 2012, an electrochemistry conference taking place through October 12th.
It is interesting to note that Nissan and NEC have been working on a longer range battery pack for their EVs. Nissan’s CEO Carlon Ghosn said, “There is a second generation of battery coming which is less costly than the previous one.”
In 2009, Nissan was working on a long range lithium-ion battery using a lithium nickel manganese cobalt oxide (LiNiMnCo) cathode. By 2015, the new battery pack was expected to give an EV like the Nissan Leaf a range of over 180 miles. Could this new NEC development be the culmination of that partnership?
