New lithium ion battery chemistry should be able to power vehicles for over a million miles, while losing less than 10 per cent of its energy capacity, state Canadian electrochemical researchers
The researchers, from Dalhousie University in Halifax, Nova Scotia, are led by Jeffrey Dahn, who has an exclusive agreement with Tesla and is listed as the inventor on a recent patent the company has filed on new lithium battery technology. In a paper published in the Journal of the Electrochemical Society, Dahn and his team report a range of testing results on new batteries which, they state, can be used as benchmarks for other researchers looking into similar technologies.
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The innovative part of the Dahn team’s battery is the cathode. Different types of battery have used various lithium compounds to achieve good characteristics, and Dahn has been investigating a material known as NMC – this is lithium nickel manganese cobalt oxide, a material that has been used by many electric vehicle manufacturers including Nissan and Chevrolet, but not Tesla in the past. For the anode, Dahn uses synthetic graphite, and the electrolyte was a blend of lithium salts with other ionic compounds.
None of these components differ much from the compositions other battery makers are using, but Dahn took a different approach to the structure of the NMC cathode. Rather than using many small crystals, the Dalhousie team used larger single crystals which seem to be less likely to develop cracks as the battery cycles through charged and discharged states.
While other battery research has focused on improving the energy density of batteries – that is, increasing the range they can power on a single charge – Dahn’s team is instead looking at improving the overall lifetime of the battery, which would make it more suitable for applications such as long-haul electric trucks and robotic taxis, which will be expected to charge up and run down many times. Currently, a Tesla battery pack will last for 300,000 to 500,000 miles, which is not enough for these more arduous applications. The batteries described in the JEC paper are good for some 4000 charges – four times as many as current commercial batteries.
The categorisation of the paper as a “benchmarking” exercise suggests that the batteries it describes are not those that Tesla plans to use in its vehicles, although Dahn states that batteries of this type “should be able to power an electric vehicle for over a million miles and last at least two decades in grid energy storage.” However, days after its publication, Tesla and Dahn were awarded a patent for a single-crystal NMC lithium-ion battery very similar to those in the paper, using an additive called ODTO (1,2,6-oxadithiane 2,2,6,6-tetraoxide) which Dahn and team described in another JEC paper last year.
According to JEC batteries and storage technical editor Doron Aurbach, further improvements on the batteries in the current paper are likely to be possible. “Since the goal of the study was to provide a reliable benchmark and reference for Li-ion battery technology, the specific energy density of the batteries described is not the highest compared to what can be really reached by advanced Li-ion batteries. Based on the study, Li-ion batteries will soon be developed that make driving over 500km (over 300 miles) from charge to charge possible,” he said.