Celine Cluzel, Shane Slater, Element Energy
George Paterson, Rebecca Trengove, Axeon
Recognizing the threat of rising temperature brought by climate change and what, as a developed country, the UK’s fair contribution to the global effort should be, the UK Government has set a legally binding target of 80 percent CO2 reduction by 2050 compared to 1990. The Committee on Climate Change (CCC) is an independent body that advises the UK Government on setting and meeting carbon reduction targets and on preparing for the impacts of climate change.
Given that around 22 percent of UK CO2 emissions are from surface transport, deep cuts in emissions from this sector are required. Decarbonization of road transport will rely on the electrification of vehicles combined with increased renewable electricity generation. Although electric vehicles (EVs) have been available to consumers for a number of years, uptake to date has been low, largely due to the higher capital cost of EVs relative to traditional vehicles. The battery is a key component in EVs, with a significant impact on overall cost and vehicle performance.
The CCC therefore commissioned Element Energy (a UK energy consultancy), Axeon (Europe’s leading independent designer and manufacturer of lithium-ion EV battery systems) and Professor Peter Bruce of St Andrews University, Scotland (an expert on lithium batteries) to investigate the future trajectory of EV batteries’ cost and performance.
The team developed a detailed cost model capable of analyzing costs of current and future cell chemistries, made robust by collecting the latest empirical data and interviewing industry experts, including cell suppliers, cell component manufacturers and battery pack manufacturers.
Overview of Current Lithium-Ion Batteries
1. Current Performance Characteristics
A range of battery chemistries has been deployed in EVs, most notably nickel metal hydride used in the Toyota Prius. However, lithium family chemistries have become the dominant chemistry for pure EV and Plug in Hybrid EV (PHEV) applications, implying that energy density is the most important metric in battery design.
Currently, cells suitable for transport applications typically have an energy density of 100 to 180 Wh/kg and are available at a capacity of 40 Ah/cell. Based on laboratory testing the expected life of cells is 1,000+ cycles and five to 10 years, depending on cell chemistries and how the battery is managed. It should be noted that due to the development time-lag in the automotive market between the mule (proof of concept vehicle) and the final production vehicle, which can take three to four years, pack life is yet to be tested in real world conditions. Because high temperatures diminish the life of the cells, thermal control is critical, and the associated costs must be included in pricing models.
Achieving a 10 year battery life in automotive applications requires careful thermal and operational management, a task fulfilled by the Battery Management System (BMS). The BMS is an essential component within a multiple cell battery pack, monitoring the state of a battery, measuring and controlling key operational parameters, and thus ensuring safety and life.
The BMS, housing and other components add weight and reduce the energy density of the battery, typically to 100 Wh/kg. For comparison, gasoline has an energy density of 13,000 Wh/kg.
2. Current Price Characteristics
Cell prices have been relatively stable in recent years, with prices partly reflecting the strategy of different cell suppliers (e.g. to secure market share) as well as quality differences. Today’s average EV cell price can be approximated at $400 to $450/kWh. However, high power cells, i.e. for hybrid applications, are typically 30 percent more expensive, though it is harder to generalize on price here as it is very sensitive to the power performance and total pack size.
The cells however represent only 60 percent of the total pack price; non-cell components bring the price to approximately $730/kWh for a midsize car. These components include the BMS, power electronics, wiring harnesses, pack housing and thermal management. Therefore for a midsized car with ~100 mile range, a typical battery system might cost around $22,000 (weight ~300 kg, 30 kWh, 80 percent usable energy).
Cell materials (electrodes, separator and electrolyte) account for around 30 percent of the overall pack price, with the electrodes being the most expensive components. Their cost is expected to decrease by reducing the amount of high-priced materials such as nickel and cobalt or developing cell materials that deliver more vehicle range per mass, i.e. with higher energy density.
Non-cell pack components account for another 30 percent of the overall pack price, with the BMS, housing and power electronics particularly significant. Standardization of these components, currently customized for each vehicle model in the case of the BMS and housing, is expected to lead to significant cost reductions. In addition, wireless monitoring could in future reduce the amount of wiring between the BMS and the cells and thus reduce both cost and weight.
Comparing the electric vehicle with a conventional internal combustion engine vehicle reveals the scale of the challenge: batteries would need to be at least 5 times cheaper for EVs to reach cost parity with a conventional vehicle. EVs’ operating costs are lower and therefore a capital cost premium may be accepted by consumers.
In summary, the technology durability needs to be proven in the field, usage patterns need to be better understood, and at the same time, significant cost and performance challenges remain.
Future Lithium-Ion Battery Technologies
Much of the current R&D activity is focused on improving the energy density of cells via new chemistries, which may increase vehicle range and offer potential cost savings as a result of less material per kWh and fewer cells to monitor. Two routes are being pursued to improve energy density: developing electrode materials with higher capacity (mAh/g); and developing cells using higher voltage chemistry.
The consumer cell market for electronics, such as cell phones and laptops, has been leading innovation so far and is an indicator of technologies to come in the automotive market. Small consumer cells cost under $250/kWh, but these figures do not translate directly to automotive cells because of the latter’s more stringent requirements in terms of safety, life (requirement for 1,000 cycles and 10 year life compared to 100 to 300 cycles and around three year life for consumer cells) and power, as well as the engineering challenge of manufacturing large cells. Thus there is a time lag of several years between battery chemistry innovations first appearing in the consumer electronic market and them becoming suitable for the more demanding automotive market.
Next-generation technologies delivering higher specific energy expected to come from the consumer market include nickel cobalt manganese cathodes and high capacity anodes (silicon), estimated to be available in a series vehicle by 2020. Composite and higher voltage cathode chemistries are expected to follow. These developments could double the energy density of lithium-ion cells from today’s values to around 300 Wh/kg. As the automotive market grows, new cells will be increasingly developed for that market as well as trickling down from the consumer cell market.
Future Lithium-Ion Battery Cost
As noted previously, current battery pack costs for a pure EV (a midsize car with 30 kWh pack) are around $730/kWh. The model developed by the team suggests that these will reduce to $320/kWh in 2020 and $215/kWh in 2030. In 2030, the pack cost is predicted to drop to $6,400 for an EV with a range of 150 miles, from more than $20,000 today for a 100 mile-range EV.
Batteries for PHEVs are more constrained by power density, as the smaller packs have higher discharge rates during acceleration. This in turn requires higher rated power electronics, more advanced thermal management and a more complex BMS, i.e. more expensive pack components. The result is a higher cost per kWh for a PHEV compared to a pure electric vehicle. Furthermore, some components (e.g. housing and components like the BMS with a cost proportionate to the number of cells) have a fixed cost element regardless of the pack size in kWh. The result is a PHEV pack cost curve that favors bigger packs, i.e. there is a strong decrease in $/kWh with increasing total capacity (kWh).
When car manufacturers choose the total kWh of a PHEV pack, they must compromise between the total vehicle cost, design constraints (such as weight and volume) and the electric range consumers expect. The future PHEV pack size modeled corresponds to a 50 mile electric range; this represents an increase compared to the ranges observed on the market today (15 to 35 miles). In future, new design strategies such as the combination of high energy and power packs (cells or capacitors) might bring further cost reduction for PHEV packs.
The research conducted by the authors identified and quantified two main cost reduction drivers: improvements in material properties delivering higher energy densities and production scale-up.
1. Improvement in Material Properties Delivering Higher Energy Densities
It is clear from a review of current R&D efforts and progress that there are considerable opportunities for improvements in material properties (the full report gives a detailed technology roadmap of lithium-ion cathode and anode characteristics up to 2030).
Increasing the material capacity (Wh/kg) reduces the amount of active material used to generate the same cell capacity. Alternatively, given the same cell footprint, increasing the active material capacity increases the total capacity of a single cell.
Cost reduction can therefore be achieved by using fewer cells per kWh, leading to a concomitant reduction in pack components (fewer connections, a smaller BMS, and a smaller housing) and lower production costs (fewer components to handle and test).
However, although some recent cell chemistry developments look promising, it is important to take into account the long development time necessary to translate a coin cell/laboratory performance into a large cell that can perform to the safety, calendar life and cycle life requirements of automotive batteries.
That said, it is likely that improvements in material properties, particularly in lithium-ion cathode and anode materials, will bring a gradual performance improvement of two to three times by 2030. The weight of a 30 kWh pack could decrease from 300 kg today to 200 kg by 2020 and 160 kg by 2030. With an expected improvement in vehicle energy consumption, range could increase to 160 miles.
2. Production Scale-Up
Cost improvements are likely to occur through increased volumes and cell size standardization. Pack assembly, a large contributor to the total pack cost, is also expected to benefit from increased volume and the standardization of components. The effect of production scale-up was modeled by applying learning rates to manufactured components under different scenarios of global uptake of EVs. Assuming the current policy support for EVs continues the global EV market share could follow the same trends as hybrid vehicles; this would bring the cumulative production of EVs to 30 million by 2030.
Barriers and Key Challenges
The technology roadmap assumes that lithium-ion chemistries will reach their highest practicable energy density through the development of high voltage cathodes. There are significant and fundamental technical challenges to be overcome before these technologies can be deployed, such as the development of an electrolyte stable at a high voltage.
The cost benefits offered by high production volume of battery packs are highly dependent on the uptake of EVs. Looking at the announced new production capacity, there is a significant risk of over-capacity in the next five years if consumers do not widely adopt the technology, which could stall further investment.
Long-Term Battery Performance
Several technologies currently in laboratory/prototype stage have the potential to offer superior battery performance. The most notable are lithium-sulfur batteries and lithium air batteries, which have the highest theoretical energy density (greater than 2,500 Wh/kg). However, significant technical challenges must be overcome before practical batteries with acceptable life and safety characteristics are available to the automotive market.
Based on the observed development times for battery technologies and the current challenges lithium-air cells face, practical lithium-air batteries for automotive applications are not expected before 2030.
The report sets out a reasonable basis for predicting future lithium-air performance between 500 and 1,000 Wh/kg. This is at pack level, a factor 3 to 4 improvement over expectations for lithium-ion in 2030, meaning that a range of 300+ miles would become practical. This forecast is based on historical data on the ratio between theoretical and practical energy of other chemistries and is in accordance with expert opinion.
Lithium-air batteries (if successfully deployed) could bring cost savings at the cell level. However, the benefit may be partially offset by the increased cost of packing arising from the lower cell voltage and the requirement for more air management. The cost modeling suggests that in the long term, the deployment of lithium-air would not be expected to bring a significant cost reduction on the pack level compared to the advanced lithium-ion batteries expected to be developed by 2030. However the approximately 50 percent weight saving which may be expected with lithium-air would have other benefits such as reduced chassis weight and enhanced performance.
Conclusions
The battery cost and performance modeling formed a central aspect of the CCC’s analysis of the transport sector, and the role of EVs as a carbon abatement option. Based on this study’s projections, the CCC’s wider analysis of total cost of ownership of a range of future vehicles suggests that EVs will be a cost effective CO2 abatement technology to decarbonise surface transport.
However, these cost forecasts indicate that a price premium for electric drivetrains will remain for around 20 years. It is highly debatable whether the mass market and late adopters will accept a price premium for such a period. To sustain the uptake required, it may be necessary to have either regulation focusing on car manufacturers (i.e. fleet average emissions targets favoring some EV production) or incentives (such as grants to reduce the cost difference to consumers).
Without a combination of regulation/incentives over the period to 2030, the predictions given in this paper may be optimistic. While material improvements are likely (due to other, larger markets for these high performance cells such as portable electronics), the production of large format cells, and the learning rate improvement in packing costs will not emerge if EV uptake stalls.
The full report of this article is available online at www.element-energy.co.uk/home/publications/.
For more information please visit www.element-energy.co.uk or www.axeon.com.
This article was printed in the 2012 Resource Guide of Battery Power magazine.
