How far exactly can an Electric Vehicle (EV) travel?
Since 2017, many countries have announced or begun setting timelines for banning sales of conventional vehicles. This is exciting yet unsettling news for automobile makers. On one hand the direction has been set, removing any lingering hesitation but on the other hand, purely from the perspective of recharge mileage, few commercially available EVs fulfill consumer expectations at this moment. To date, the 500km range achieved by Tesla’s Model S still holds the record in terms of EV development.
Diagram 1: Highest mileage range of various Tesla S models (Source: Tesla)
Moreover, market incentives have already declined before technical barriers can be overcome. This June, China's Ministry of Finance adjusted its EV subsidy policy by removing subsidies for new energy vehicles with ranges of less than 150 km. Only vehicles with mileage above 300 km are eligible for subsidies comparable to those offered in 2017. The mindset behind this change is clear: funding is targeted to support EV makers that possess more advanced technologies. The crowding out effect has already manifested, with data showing that sales in June are 22% lower than May.
Therefore, "how far can an EV travel" is no longer just a question of mileage range technology but also one of great concern to businesses within the field, or rather how much more the industry can achieve. Quite understandably, this has become a major issue of concern.
From the technical perspective, two problems must be resolved so EVs can "travel further": increasing energy density and conserving energy. "Increasing energy density" pertains to improvements in power battery technology so that vehicles are equipped with higher energy capacity while "conserving energy" refers to better battery control and management so as to improve operational safety efficiency and optimize potential. This is where BMS comes into play.
Let us temporarily put aside unrealized technologies not yet commercially viable and focus on lithium ion battery technologies that are already in use commercially or nearing market launch. Lithium ion batteries are typically categorized according to the electrode material used. Types that can be categorized by their use of cathode materials include the lithium manganese battery, lithium manganese iron phosphate battery, lithium iron phosphate battery, and ternary battery. Categorized by the use of anode materials, they can be differentiated into graphite and lithium titanate batteries. See Table 1 for the performance and properties of these batteries.
Among them, lithium manganese batteries melt easily under high temperatures and perform poorly in terms of stability and safety. Lithium manganese iron phosphate batteries are not yet technologically mature and have a short lifespan. Neither of the above are therefore suitable for powering EVs. Lithium iron phosphate batteries exhibit stable voltage and are economical, able to withstand temperatures up to 800℃, and highly safe. For these reasons, they are widely applied in electric passenger cars that require high battery energy levels, long run time, extended lifespan, and high safety performance. Meanwhile, ternary batteries have high energy density, long lifespans, and are able to withstand temperatures of up to 200℃, but cannot be manufactured into high capacity single cells due to safety constraints. They are however becoming increasingly prevalent in the passenger car market where demands on spatial constraints, mileage range and energy density are high. For example, Tesla uses ternary batteries supplied by Panasonic.
Innovation in anode materials is another key to improving battery performance. Lithium-metal dendrite precipitates on the surface of the carbon electrode during overcharge that can pierce the membrane separator in the middle of the battery, causing internal short-circuit and thermal runaway. This has always been one of the safety concerns of lithium ion batteries. If lithium titanate is utilized as the anode material, however, lithium-metal dendrite will not precipitate, thereby eliminating the risk of thermal runaway. Such batteries perform well in low temperatures, exhibit high power efficiency, and can be charged up to 10,000 cycles. Lithium titanate batteries nevertheless have several disadvantages such as high temperature flatulence, lower inherent voltage, and high cost. Therefore, they are currently used mainly in low range scenarios or hybrid vehicles, and do not contribute much to a longer traveling distance. It is worth noting, however, that lithium titanate batteries have the advantage of fast recharging, a feature that may change user conceptions of battery charging from " charge once for a longer distance" to "recharge along the way".
Developing new battery technologies and enhancing battery mileage range are now no longer the objectives of individual enterprises, but have escalated into national strategies. Countries all around the world are now formulating plans to develop power battery technologies. For example, the US Department of Energy has proposed a series of technological improvements to increase battery energy density from 100W.h/kg in 2012 to 250W.h/kg in 2017, while China plans, in its "13th Five-Year Plan", to phase in batteries with 300W.h/kh energy density for commercial use and begin development of batteries with 400-500W.h/kg energy density.
Even though we have yet to identify a clear winner from existing power battery technologies, and a perfect solution for EV application has yet to emerge, the sheer amount of resources that have been poured into relevant developments can perhaps serve as assurance that future prospects remain bright.