Electric vehicles (EVs) have been commercially available for some time, but their popularity has been growing in recent years as greater emphasis has been placed on green alternatives to traditional fuels, and their average cost has come down. Rapid advances in technology to support EV efficiency and charging capabilities look set to make EVs even more attractive, as government targets and regulations also drive their adoption.
The first mass-produced EV was developed in the mid-1990s by General Motors leading to the release of its EV1 model. In 2008 Tesla, now perhaps the most well-known manufacturer of EVs, released its first model, the Roadster, which was the first EV to use a lithium ion battery as its power source. Lithium-ion batteries are now the most widely used technology in battery-powered EVs.
Over time the costs associated with lithium-ion technology have reduced, and innovations focusing on energy density have led to more efficient batteries, meaning that greater distances can now be travelled before needing to recharge. However, as lithium-ion technology matures, there has also been interest in other battery technologies. Investment in this area is likely to continue as part of the various government plans to decarbonise transport in line with its commitments to tackle climate change. For example, the UK's recent white paper on energy announced that the UK will end the sale of new petrol and diesel cars and vans by 2030 and £582 million of grants will be made to help consumers to buy zero or ultra-low emission vehicles.
The uptake of battery-powered EVs has also been inhibited by a lack of charging infrastructure to support them. This problem has been exacerbated by the limitations of the battery technology itself and the ranges possible as a result. The combination of rapid innovation in battery technology and charging infrastructure (including the smart grids that support it) mean EVs are finally becoming a realistic alternative to petrol and diesel-powered cars to the mass market.
According to the European Patent Office (EPO), more than 7,000 international patent families related to electricity storage were published in 2018, up from just over 1,000 in 2000. The acceleration of innovation in this area is also striking. The EPO reported an annual growth rate of 14% between 2005 and 2018, compared with just 3.5% on average for all technology areas, with 88% of these energy storage patents related to battery technology.
The dominant battery technology in EVs still uses lithium-ions cells, in which positively charged lithium ions are carried by a liquid electrolyte from the anode to the cathode through a separator. Indeed, lithium-ion batteries remain the most actively researched area of technology, with 8,300 patents reportedly filed outside of China in 2019 alone.
Initially, EVs were developed using lithium cobalt oxide and lithium manganese oxide cathodes as these were already in use in consumer-focused electronics, such as smartphones. In order to extend the battery life of EVs and increase their commercial viability, emphasis was placed on identifying alternative materials for cathodes. The most promising options found to improve energy density have predominantly been cobalt or nickel based. Specifically, these cathodes utilise nickel manganese cobalt oxide, also known as NMC; or nickel cobalt aluminium oxide, NCA. Panasonic introduced lithium-ion cells with NCA cathode chemistry for Tesla’s Model 3 in 2017, which reportedly offered the highest energy density battery technology in EVs to date.
However, cobalt is expensive and its use is increasingly controversial due to a problematic supply chain (60% of cobalt deposits are from the Democratic Republic of Congo). As a result there has been much research to find alternative compounds. In July 2020, Tesla announced its plans to eliminate the use of cobalt in the batteries used in its EVs, and instead focus on lithium-iron technologies such as lithium iron phosphate. If successful this could lead to significant cost savings which if passed on to consumers is likely to accelerate further growth in the EV market.
Another promising advance in battery technology is the potential use of lithium-based solid-state batteries. Rather than using liquid electrolytes such as those in the lithium-ion cells, these use solid-state electrolytes and are anticipated to enable the use of smaller batteries with higher energy density, a longer lifespan, and a more attractive safety profile. The costs currently associated with solid-state batteries limit the opportunities to commercialise this technology for the time being. However, these technologies have been the focus of significant innovation in recent years, with the EPO reporting an increase in patenting activity by an average of 25% per year since 2010.
Although lithium remains the predominant metal for use in EV battery technology, alternatives are also being explored. Sodium, for instance, is in the same group of elements as lithium and is a cheaper, more widely available material. Sodium has not traditionally been considered a promising option for batteries as it is significantly heavier than lithium, meaning that the energy density of any battery produced would be much lower. However, it has recently been reported that double layer graphene electrodes (a form of carbon only one atom thick) could increase storage capacity to such an extent to overcome these issues, making this another potentially attractive technology for future development.
In addition to battery technologies, hydrogen has been identified as a fuel to decarbonise transport. Hydrogen fuel-cell cars are powered by an electric motor and are often described as fuel cell electric vehicles (FCEVs). The crucial difference between battery powered EVs and FCEVs is that hydrogen cars produce their own power through a reaction of hydrogen and oxygen in the fuel cell rather than a battery.
FCEVs are locally emission free, their only waste product being water vapour, and so are often considered the greenest option for EVs. However, how the hydrogen is produced is an important consideration in the overall energy calculation. The most common method of hydrogen production involves separating it from natural gas via steam-methane reforming, which works by pressuring methane and steam in the presence of a precious metal catalyst. The energy to drive this process can come from sources with a variety of carbon intensities.
Currently, the biggest challenges faced by FCEV technology are twofold. Firstly, hydrogen-powered cars are expensive and, therefore, inaccessible to most consumers compared to traditional vehicles or even battery-powered EVs. Secondly, the infrastructure for hydrogen fuel is limited, with only a handful of stations currently available in the UK. BMW has announced plans to expand its hydrogen fuel charging network to 130 in Germany by 2022, which may lead to broader uptake throughout Europe. However, on current trends, it seems likely that battery technology will continue to dominate for the majority of EVs, with hydrogen's high energy density giving it the edge in certain forms of transport such as buses, which can be refuelled at a central depot, or scooters, which have limited room for storing fuel.
For the time being, lithium-ion batteries continue to dominate EVs. This is reflected in the sustained numbers of patents being filed for this technology. The pace of research is, however, accelerating along with increased interest in tackling climate change. This is leading to reduced costs and ever more alternatives to the "traditional" lithium-ion battery. As this market continues to mature, it will be interesting to see how new technologies continue to emerge and develop.