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Database development and evaluation for technoeconomic assessments of electrochemical energy storage systems Peter Stenzel1, Manuel Baumann2, Johannes Fleer1, Benedikt Zimmermann2, Marcel Weil2 1
Institute of Energy and Climate Research, Systems Analysis and Technology Evaluation, Forschungszentrum Jülich GmbH 52425 Jülich, Germany 1
[email protected] 2 Karlsruhe Institute of Technology (KIT), Institute for Technology Assessment and Systems Analysis (ITAS) KIT Campus-Nord 76133 Karlsruhe, Germany 2
[email protected]
Abstract—A battery storage technology database was developed to assess the state of the art of different battery types by a literature and manufacturer data review. The database contains key techno-economic parameters to provide a solid basis for common assessment, modeling and comparison of battery storage technologies. A new approach is the comparison of literature data with manufacturer data to identify possible inconsistencies between different data sources. Keywords: Batteries, Review, Techno-economic comparison.
I. INTRODUCTION Efficient and affordable energy storage systems are of high relevance for a future sustainable energy and transport system. Battery systems have to fulfill very specific and sometimes controversial requirements. There are still technical and scientific challenges which have to be overcome to solve potential trade-offs between energy and power density, lifetime or safety, etc. The presented work was realized within the Helmholtz Portfolio project “Electrochemical Storage in a systemic perspective – Reliability and Integration”. Aim of the project is to describe application requirements within the systematic research and development of battery systems including their integration in energy or transport systems. The development of new electrodes, cells, and batteries are main elements of the project. A supporting systems analysis is carried out at Karlsruhe Institute of Technology (KIT) and Research Center Jülich (FZJ) and has the aim to minimize innovation risks and to identify innovation potentials by developing techno-economic and -ecologic scenarios [1]. In focus of this work are state of the art battery technologies which are commercially available. Battery types which have not been commercialized yet and which are in an early R&D stage (e.g. metal-air batteries or next generation lithium batteries) are not considered. The paper presents a review of battery technologies and applications and includes the assessment and comparison of key performance technoeconomic battery parameters based on a database evaluation. II. BATTERY TECHNOLOGIES Electricity storage in rechargeable batteries is based on reversible electrochemical reactions in which electrical energy is converted into chemical energy and vice versa. Batteries are normally categorized by the active materials used in the cells which in turn influence the design and the characteristics of the battery system. In the following sections state of the art rechargeable battery technologies which are commercially
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available are introduced by giving an overview of the working principle and their main characteristics. A. Lead Acid Batteries Lead Acid batteries are composed of two lead-based electrodes in an electrolyte of dilute sulfuric acid (H2SO4). In the charged state, the anode consists of elementary lead (Pb), the cathode of lead dioxide (PbO2). There are different subtypes of Lead Acid systems depending on the battery containment and the condition of the electrolyte. Flooded Lead Acid batteries contain liquid sulfuric acid as electrolyte and can either have an open or a sealed containment. Valve-regulated Lead Acid (VRLA) batteries are sealed systems equipped with a valve to release possible overpressure. In VRLA systems the electrolyte is immobilized. Therefore it is either transformed into a gel (by adding silica) or an absorbent glass matrix (AGM) is soaked with electrolyte and filled into the space between the electrodes. Additional information on the working principle and the design of Lead Acid batteries is given in [2]. Lead Acid batteries offer low investment costs and acceptable energy and power densities for stationary applications. Furthermore, they are easy to handle since they come with inherent safety (non-flammable, controlled overload reaction) and do not require complex management systems. However, the sensitivity against high and low temperatures, the low tolerability of deep discharge and the low cycle life expectancy are major disadvantages. B. Nickel-Cadmium Batteries Nickel-cadmium (NiCd) batteries consist of metallic cadmium and nickel oxide hydroxide as electrodes. Potassium hydroxide solution is typically used as electrolyte. Different sizes and capacities are available from small, sealed standard round cells to very large vented cells. Advantages of NiCd batteries are the good performance at cold temperatures down to -50 °C, possibilities to use high Crates during charge and discharge together with a low impact on the available capacity, the high calendric lifetime and good cycle life even at high DoD. The robustness against overcharging and deep discharge is a major advantage to other battery types making NiCd batteries especially suitable for security relevant applications which require a high reliability (e.g. emergency power or medical applications). NiCd
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batteries are mechanically very robust and can withstand rough handling. Disadvantages are the relatively high discharge rate (especially for sealed standard cells), the higher costs compared to Lead Acid cells and the relatively low energy density. For some cell types the memory effect (reversible loss of capacity) has to be considered [2]. Until the 1990s NiCd batteries have been a widely used battery type in the end consumer sector. In the European Union a directive restricts the use of NiCd batteries in most applications due to the content of cadmium which is a heavy metal. Exceptions are emergency power supply, alarm systems, emergency lightning and medical equipment. The exception for power tools is limited to 31.01.2016 [3]. C. Nickel-Metal Hydride Batteries The characteristics of nickel-metal hydride (NiMH) batteries are somewhat comparable to NiCd batteries with the main difference that hydrogen absorbed in a metal alloy is used as negative electrode material instead of cadmium. Besides solving environmental problems by replacing cadmium, metal hydride electrodes have significantly higher energy densities. The general discharge behavior with low voltage drop depending on discharge current and temperature is also characteristic for NiMH batteries. Compared to NiCd batteries the high rate capability is slightly reduced and NiMH batteries are less tolerant against overcharge and deep discharge. NiMH batteries show a moderate memory effect and the operation temperature range is smaller [2]. Nevertheless NiMH batteries still show a good performance under fast charge and discharge. As a consequence NiMH batteries are a preferred solution for high power applications. The disadvantage of relatively high selfdischarge rates has been reduced by the development and market introduction of low self-discharge cells. Due to higher power densities and the limitation of cadmium use, NiMH batteries have widely replaced NiCd cells as small standard round cells (e.g. AA, AAA size) for consumer electronics, despite slightly higher battery costs. NiMH batteries are also available as prismatic or button cells for other applications (chapter III). D. Lithium-Ion Batteries The lithium-ion battery family includes different electrochemical systems which are all based on the exchange of lithium-ions (Li+) between anode and cathode. The anode is usually made of synthetic graphite applied on a current collector of copper. Other anode materials include e.g. titan oxide, lithium titanate (LTO) and lithiated silicon. Lithium manganese cobald oxide (NMC), lithium nickel cobalt aluminum oxide (NCA), lithium cobalt oxide (LCO), lithium manganese oxide (LMO) or lithium iron phosphate (LFP) are typical cathode materials. The electrode materials play a central role for numerous battery parameters, e.g. cell voltage, energy density, operational safety and stability. In most cases the electrolyte is a lithium salt (often LiPF6) dissolved in a liquid organic solvent. Lithium-ion polymer batteries contain gels or solid polymer electrolytes instead of liquid solvents. If the electrolyte is a liquid, an additional separator is required. This is mostly a thin (10-30 μm) microporous polyolefin film. Further information on lithium-ion batteries, especially on different cathode materials, can be found in [4, 5].
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The characteristics of lithium-ion batteries are highly dependent on the cell chemistry and can vary significantly for different types of the battery family. Nevertheless some general characteristics can be derived which do not necessarily apply for all lithium-ion battery types. The main advantages of lithium-ion batteries are their high cell voltages, high energy and power densities and low selfdischarge. Moreover, both cycle and calendric lifetime are expected to be longer compared to other battery technologies. Lithium-ion batteries are more tolerant against deep discharge than Lead Acid batteries, but are also sensitive against too high or too low temperatures. Further disadvantages include the absence of inherent safety (thermal runaway) and the requirement for an elaborate battery management system (including thermal management) to enable safe operation and sufficiently long lifetimes. The investment costs for lithiumion systems are still quite high, but there is a huge potential for cost reduction. Lithium-ion batteries can be designed for both high power and high energy applications. Different cell types are commercially available including standard round cells, prismatic cells and pouch bag cells. E. Sodium High Temperature Batteries The sodium sulfur (NaS) battery and the sodium nickel chloride (NaNiCl2) battery, also known as ZEBRA battery, form the group of sodium high temperature batteries. Their operating temperatures lie in the region of 270 to 350 °C which means that the electrodes are in the liquid state. Sodium high temperature batteries are similar in terms of design and working principle: Both battery types consist of a liquid sodium anode and a solid ceramic electrolyte (ȕ’’-aluminum, NaAl11O17) and are usually designed as cylindrical cells. The main difference is the cathode material. NaS cells have liquid sulfur cathodes, in ZEBRA batteries liquid nickel chloride is used as cathode material. High values for specific energy and long cycle and calendric lifetimes are advantages of the sodium high temperature batteries. Investment costs are lower than for comparable lithium-ion systems. However, operating safety is an issue. Due to the high temperatures and the high corrosiveness of the materials used, special containments made of highly corrosion-resistant steels are required. A rupture in the electrolyte can lead to a violent exothermic reaction between sodium and sulfur in the NaS cell and cause battery fires. Since this reaction cannot occur in NaNiCl2 cells, they are considered to be safer than NaS technology. More detailed information on sodium high temperature batteries can be found in [6]. If the battery is charged and discharged frequently (at least one cycle a day), the released reaction enthalpy is sufficient to keep the battery at operating temperature. However, if longer periods occur where the battery is not in operation, additional heating is required which leads to significant thermal losses. Both battery types are commercially available, but the number of manufacturers is limited (one for NaS, two for NaNiCl2). NaS batteries can be considered a mature technology and are available as large scale systems in MW/MWh scale with a typical energy to power ratio of 6:1. ZEBRA batteries have recently reached marketability and are available in kW/kWh scale. Larger systems can be realized by a modular approach.
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F. Redox Flow Compared to other battery types where electrode and electrolyte are spatially fixed to each other, the cell stack and the storage unit in redox-flow batteries (RFB) are separate units. The electrolyte can be an organic or inorganic solution. The storage of the electrolyte solutions is realized in two independent storage tanks. The cell stack is connected to two electrolyte circuits. Different types of RFB have been proposed. An overview of the working principle and the different RFB chemistries and electrolytes is given by [7, 8]. The different electrolytes have large impact on the system design, the battery characteristics and performance. Vanadium RFB and Zinc-Bromine RFB are commercially available as modular, container-based systems up to MW/MWh-scale. A major advantage of RFB is that storage capacity and rated power are independent from each other and can be varied according to the requirements of the desired application. This provides a high flexibility and makes RFB especially suitable for high energy applications with long operation times up to several hours. Furthermore, complete discharge cycles (100 % DoD) do not have a negative effect on the battery performance. Self-discharge in standby mode is marginal [9]. Power and energy densities of RFB are relatively small compared to other battery types. Without significant improvements, RFB are therefore limited to stationary applications. Also required are (mechanical) auxiliary systems for electrolyte circulation and temperature control. This results in higher reaction times, increased system complexity and reduced efficiency compared to other battery types. Special advantages of the Vanadium RFB are the superior calendric and cycle lifetime. There is also no aging of the electrolyte which allows a stack exchange without changing the electrolyte. Major disadvantage is the high cost of vanadium as electrolyte [10]. Zinc-Bromine RFB use low cost electrolytes resulting in a significant reduction of system costs. Major disadvantage of Zinc-Bromine RFB is that the cell reactions are only partly reversible including solid zinc formation on the electrode. The calendric and cycle lifetime are therefore significantly lower compared to Vanadium RFB. III. OVERVIEW OF BATTERY APPLICATIONS The demand for rechargeable batteries has seen a rapid growth during the last years [11]. In terms of value and battery capacity, the overall market is still dominated by Lead Acid batteries whereas lithium-ion batteries have the highest growth rates [11]. The following sections give an overview of the current situation and requirements for batteries in automotive, portable and stationary applications. A. Automotive applications The market for batteries in automotive applications can be further divided into starter batteries and traction batteries for different kind of vehicles.
Cars with extensive start-stop functionality and brake-energyregeneration (also called sub- or micro-hybrids) are based mainly on advanced Lead Acid batteries (e.g. AGM). In niche applications (e.g. military vehicles and aircrafts) also NiCd and NiMH batteries are deployed. 2) Electric road vehicles: The actual market for traction batteries of electric road vehicles is quite limited, but a fast market development in the following years is expected [11]. The segment of electric road vehicles can be further subdivided into hybrid electric vehicles (HEV), plug in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV). Range extender electric vehicles where a combustion engine is used to recharge the battery can be considered as a special type of BEVs. HEVs and PHEVs contain two drivetrains (electric and combustion), in contrast to BEVs, which have only an electric drivetrain. PHEVs and also some HEVs are able to drive a certain distance completely electric. Batteries in HEVs are typically high power batteries with a limited capacity. The requirement for larger battery capacities increases with higher electric range of the car. A detailed overview of electric vehicle concepts is given by [12]. The most important battery technology for HEVs is today NiMH which is mainly used by Toyota. Lithium-ion is also important and used by most of the other car manufacturers. In the future an increasing market share of lithium-ion batteries for HEVs can be expected [11, 13]. PHEVs and BEVs are exclusively based on lithium-ion batteries. Most of the battery pack manufacturers are using prismatic or pouch cells but also standard round cells are used e.g. by Tesla Motors. Further detailed technical specifications for batteries in electric road vehicles can be found in [14]. 3) Traction special vehicles: Traction batteries for special vehicles are used in a wide range of different vehicle types from wheelchairs, industrial machines, forklifts, robots, to electric scooters, trams, military equipment and golf carts. The battery requirements regarding peak loads and power density are in most cases lower compared to electric road vehicles which results in a significant market share of Lead Acid batteries. Lithium-ion batteries are also well established and it can be assumed that they will gain significant more importance in this segment in the future. 4) E-Bikes: The market for electric bikes is also considered to be a fast growing market [15]. The largest market is currently China where electric bikes are widely used for transportation purposes [16]. Most of the bikes in China are equipped with Lead Acid batteries due to the possibility to offer a low cost transportation solution. Nevertheless the worldwide market for high-end electric bikes is based nearly completely on lithium-ion batteries which are also considered to become the most important battery type in the future. At present typically standard round cells are used in the battery packs.
1) Starter Batteries: Starter batteries for vehicles are altogether still the biggest battery market in terms of value on a worldwide basis [11]. Starter batteries are required for all kinds of vehicles with combustion engines. This covers mainly road vehicles like cars, busses and trucks but also ships and railway locomotives. The market share of Lead Acid batteries in this segment is close to 100 %, although some lithium-ion based starter batteries are commercially available.
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TABLE I BATTERIES IN AUTOMOTIVE APPLICATIONS
Application Starter batteries
Battery type Lead Acid
Electric road vehicles – HEV Electric road vehicles – PHEV / EV Traction special
NiMH, Li-Ion Li-Ion Lead Acid, Li-
Characteristics High power, low DoD High power, low DoD High power and high energy High energy
ENERGYCON 2014 • May 13-16, 2014 • Dubrovnik, Croatia
vehicles E-Bikes
Ion (NiMH) Li-Ion (Lead Acid, NiMH)
High energy
B. Portable applications The use of rechargeable batteries in portable applications is common since the 1990s and this sector has seen a rapid growth during the last years. Portable applications cover a wide range of applications including power supply for mobile computers (tablets, laptops), mobile phones and smartphones, electric power tools and other small electronic devices (e.g. cameras, games, camcorders, household devices, toys). The market for batteries in portable applications in terms of volume and capacity is dominated by mobile computers and mobile phones. In the future the market will be driven mainly by the dynamic development and increasing market penetration of tablets, ultrabooks and smartphones [11]. A major trend which can be observed is the increase in battery capacity per device throughout all portable applications. A reason for that is the higher energy demand due to longer operation times and due to the utilization of high-performance components (e.g. displays for smartphones) [17]. In general the market for portable applications is dominated by lithium-ion cells. They reach market shares of 100 % in several segments like mobile phones and computers. Currently round and prismatic cells still have a considerable market share. Due to demand for slimmer electronic devices, pouch cell`s market share is rapidly increasing. Since pouch cells require less casing material their energy and power density is higher and they can be specially engineered to fit into the design of the device [11]. Other cell types (NiMH, NiCd) play only a minor role and their market share is decreasing. This is the case especially for power tools where lithium-ion batteries have nearly completely replaced other cell types. NiMH standard round cells are still used in low performance applications e.g. in household devices. The use of NiCd cells in portable medical applications is still common due to their excellent reliability. TABLE II BATTERIES IN PORTABLE APPLICATIONS
Application Mobile phones and computers Power tools Others
Battery type Li-Ion
Characteristics High energy
Li-Ion (NiMH, NiCd) Li-Ion (NiMH)
High power and high energy High energy
C. Stationary applications The market for batteries in stationary applications is the third largest battery market after automotive and portable applications [11]. There is a broad variety of stationary battery applications with the markets for uninterruptable power supply and telecommunications still being by far the most important segments [11]. The market for grid level storage systems has seen significant growth in the last years and is expected to develop further in the future. 1) Uninterruptable power supply (UPS): An uninterruptible power supply provides emergency power to a load in case of a failure of the standard power supply e.g. caused by a power outage of the electricity grid. UPS systems are widely used in applications where an unexpected power disruption could
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cause injuries, fatalities, serious business or industrial production disruption or data loss. An UPS system typically consists of a battery as an energy storage unit and an electric controller for power management. UPS systems are common in a broad range of applications from very small systems (e.g. UPS for a single desktop computer) to very large systems (e.g. UPS for data centers, power plants or industrial processes). In case of an online operation (battery under float-charging) a UPS is able to provide instantaneous power without interruption. The operation time of UPS systems typically varies between a few minutes and a maximum of one hour depending on the time which is required to either start an emergency power source (e.g. diesel generator or fuel cell) or for a controlled shut down of devices (e.g. computers). The standard technology for UPS systems today are VRLA batteries. Other batteries e.g. lithium-ion or NiCd or alternative technologies including flywheels or capacitors are also applied depending on the boundary conditions of the application. In some cases NaS (mostly in Japan) batteries are used, providing operation times up to 6 hours or more thus combining UPS functionality and emergency power. 2) Telecommunications: The telecommunications segment is still the largest market segment for stationary batteries [11]. Batteries are used as a backup power supply system mostly for transmission towers for mobile communication, so there is a strong relation to UPS applications. In general, there is a high demand for reliable power supply in the telecommunications sector as it belongs to critical infrastructure. The market for UPS applications is expected to increase due to rapidly increasing data volumes and service demands (e.g. mobile internet, cloud computing). The requirements for batteries for transmission towers are highly dependent on the stability of the power grid or the power supply for off-grid or standalone systems and the climatic conditions. Especially in developing countries with unstable or non-existing electric grids, batteries have to provide power for long operation times up to one day. These batteries need to have high cycling capabilities and good recharge abilities. In autonomous supply systems where the battery is combined with renewable energy sources, it plays a central role for balancing electricity supply and demand. Batteries in combination with on-grid transmission towers have UPS characteristics and are usually combined with an additional backup power system. The standard technology for telecommunications systems are also VRLA batteries. In case of high energy and high cycle requirements for off-grid solutions or extreme climatic conditions, lithium-ion and NiCd batteries are applied. These batteries are also favorable in case of high lifetime requirements or limited available space. 3) Grid level storage: The market for grid level storage systems is relatively small compared to the UPS and the telecommunications market, but a significant market development is expected especially in conjunction with the increasing share of fluctuating renewable energies [11, 17]. Grid level storage applications include bulk energy services, ancillary services, transmission and distribution network (T&D) investment deferral and services at end consumer sites. Multiple application services are also possible. An overview of the requirements and characteristics of the different applications is given in [18].
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Due to the very short response time of batteries, they are especially suited to provide ancillary services including frequency regulation, spinning reserve and voltage support. Furthermore battery systems for renewable energy grid integration are a growing segment. These projects are typically realized as scalable, container based systems. There are several multi-MW projects worldwide in operation with different battery technologies involved [19]. Lithium-ion batteries are used most frequently in high power applications with limited operation time (e.g. ancillary services) whereas NaS and Redox-flow batteries are chosen for high energy applications (e.g. arbitrage trade, renewable integration, peak load reduction, T&D investment deferral). Applications at end consumer sites include peak load reduction for industrial consumers as well as small scale storage systems in combination with photovoltaic (PV) installations in the residential sector. PV storage systems are used for renewable energy time-shift to achieve an increased self-consumption rate of locally produced electricity. Storage systems at end consumer site offer the possibility to reduce the overall costs of electricity in dependency of the electricity and the feed in tariff. For small scale PV storage solutions several systems based on Lead Acid and lithium-ion are commercially available. For larger systems, other battery types like NaS and Redox Flow are additionally available. The technology of choice is highly dependent on the required discharge durations and the energy-to-power ratio.
available technical data sheets and web pages. The primary goal of the database is to provide knowledge about the state of the art of storage technologies. Additionally, by including longer time series it will become possible to monitor developments and improvements due to learning curve effects. A new approach is the possibility to compare literature data with manufacturer data to identify possible inconsistencies between the data sources. The database is Excel-based and includes in total (status as of August 2013): • 446 different energy storage systems (128 consistent datasets from manufactures and 318 partially consistent datasets from literature) • 28 data categories (efficiency, gravimetric and volumetric energy density as well as power density, response time, investment costs, response time, calendric and cycle life time in dependence of depth of discharge, self-discharge, etc.) • 4.695 data points • Sources from the year 2011 to 2013 Only a selection of parameters and technologies available from the database is covered in this work. Technologies which are excluded due to the focus on commercially available battery technologies are SuperCaps, Iron-Chrome Redox-Flow and Polysulfide-Bromine Redox-Flow batteries and others. Furthermore only an excerpt of the database parameters is presented in the following techno-economic comparison and evaluation.
4) Others: In this segment a variety of applications is gathered ranging from systems for emergency lighting, emergency power supply for control, switch or measurement devices and security systems to off-grid solutions. These applications have a relatively low market share and different battery types are applied with Lead Acid and lithium-ion being the most common battery types.
A. Techno-economic comparison and evaluation Every energy storage technology has its specific characteristics and its optimal application area. The decision which technology should be chosen for a certain application depends on the amount of energy that has to be stored, the storage duration, charging and discharging power, number of cycles, specific costs and other factors. In the following plots technical parameters are analyzed. Only data from 2010 to 2013 was used to evaluate the state of the art. The shown data is based on manufacturer data. In Fig. 1 the specific power is plotted against the specific energy for different battery technologies (Ragone plot). The plotted data includes values for single cells, battery modules and complete battery systems. A precondition for the plotted data is that both parameters (power and energy density) are available in the database, otherwise the data is excluded.
TABLE III BATTERIES IN STATIONARY APPLICATIONS
Telecom Grid level storage
Others
Battery type Lead Acid (NiCd, others) Lead Acid (Li-Ion, NiCd) Li-Ion, NaS, Lead acid, Redox-flow (others) Lead Acid, LiIon (others)
Characteristics High power (floatcharging) High energy and high power High energy and high power High energy and high power
IV. ENERGY STORAGE DATABASE There are several energy storage technologies available or suitable for different application fields as explained before. All technologies are somehow in competition with each other within multiple stationary and automotive application areas. Therefore, an energy storage technology database was developed containing most important techno-economic parameters to provide a solid database for common assessment, modeling and comparison of energy storage technologies. The database is based on a comprehensive literature (conducted by KIT) and manufacturer data review (conducted by FZJ). Literature review is based on known sources for scientific papers as Scopus, Science direct and IEEE-Xplore. Manufacturer data is obtained from public
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Specific Power [W/kg]
Application UPS
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Specific Energy [Wh/kg] Lead Acid NaS Redox Flow V/V
Li-Ion NiCd Redox Flow Zn/Br
NaNiCl NiMH
Fig. 1: Specific power vs. specific energy of different batteries (Source: KIT/FZJ database)
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chemistry. However, a few conclusions can be drawn from the plot: Batteries with LiCO2 cathodes (LCO) show high values for specific power, while LiFePO4 batteries (LFP) tend to have lower specific energy and power. LiNiCoMnO2 batteries (NMC) have either high specific energy or high specific power. A problem of the available datasets is that not all of them are consistent, e.g. due to incomplete information about the cell chemistry and material structure. Plots similar to Fig. 2 and Fig. 3 are also possible for other battery types. In the following Ragone plot (Fig. 4) the data points are labeled with respect to their application field. The plot includes Li-ion and Lead Acid batteries. Specific Power [W/kg]
Specific Power [W/kg]
All recorded Lead Acid batteries have relatively low specific energy values, but vary across a large bandwidth of specific power which indicates different target applications. Vanadium RFB show both low specific energy and low specific power values, whereas Zinc-Bromine RFB reach a considerably higher specific energy and power rating. Sodium high temperature batteries are suitable especially for high energy applications with relatively low power ratings. Values for Li-ion batteries spread across a large bandwidth both in specific energy and in specific power. This is due to the fact that the family of Li-ion batteries includes numerous different cell chemistries and designs suitable for multiple applications. The Ragone plot in Fig. 2 contains only values for Li-ion batteries. The data points in the plot are labeled with respect to their system integration level. Single cells are marked in blue, modules in red and complete battery systems in green. 10,000 1,000 100
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Specific Energy [Wh/kg] Lead Acid Starter Li-Ion Stationary
1 0
50
100
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300
Li-Ion Module
Li-Ion System
Lead Acid Stationary Li-Ion Traction
Lead Acid Traction
Fig. 4: Specific power vs. specific energy in different application fields (Source: KIT/FZJ database)
Specific Energy [Wh/kg] Li-Ion Cell
Fig. 2: Specific power vs. specific energy of Li-Ion batteries distinguished by system integration level (Source: KIT/FZJ database)
The comparison shows that it is important to distinguish the system integration level for analyzes. As expected, single cells generally have the highest values for energy and power density, followed by battery modules and finally complete battery systems with the lowest values as they include packaging and system components (e.g. power electronics, battery management system). The data points in Fig. 3 belong also to the Li-ion family, but this time they are distinguished regarding their respective cell chemistry. Data is not divided into cells, modules and systems for a better abridgement. 10,000
Stationary Lead Acid and Li-ion batteries have relatively low specific energy and power values. One reason for that is that for stationary applications high energy and power ratings are subordinate to parameters like lifetime or investment costs. This is different for automotive applications where energy and power density considerably affects weight, range and acceleration and are therefore of key importance. Fig. 4 shows that the Lead Acid batteries reach sufficiently high power densities, but only energy densities lower than 50 Wh/kg. The Li-ion batteries tend to have significantly higher energy densities (up to 157 Wh/kg). The choice of the right battery system is dependent on the amount of cycles that are required for a certain application. The important correlation between cycle lifetime and DoD for different battery technologies is displayed in Fig. 5. 100,000
1,000 100
Cycles
Specific Power [W/kg]
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1,000 1 0
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Specific Energy [Wh/kg] Li4Ti5O12 Li-Ion Unspecific LiNiCoAlO2
LiCoO2 LiMn2O4 LiPoly
100
LiFePO4 LiNiCoMnO2
0
40
60
80
100
120
DoD [%] Lead Acid LiPoly Redox Flow Zn/Br
Fig. 3: Specific power vs. specific energy of Li-Ion batteries distinguished by cell chemistry (Source: KIT/FZJ database)
The data points are spread widely across the specific energy and power spectrum – even for batteries with the same cell
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LiFePO4 LiNiCoAlO2
LixTixOx Redox Flow V/V
Fig. 5: Cycle life time vs. depth of discharge of different batteries (Source: KIT/FZJ database)
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2 3 5 6 1 1 2 2 1 33
No. of Sources
Specific Costs [€/kW]
LTO, LFP and all-Vanadium RFB batteries tend to have high cycle lifetimes compared to other battery technologies. The Lead Acid batteries with a shorter cycle life are typically flooded Lead Acid systems, the ones lasting for more cycles are typically VRLA (Gel, AGM) batteries. The performance is also determined by the application field for which the battery was designed (e.g. UPS with low cycle numbers). Besides cycle-related aging, calendric aging is an additional effect which is based on chemical side reactions occurring over time when the battery is not being used. Fig. 6 shows bandwidths of calendric lifetimes for different technologies (if possible min. and max. median values).
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Specific Costs [€/kWh]
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Li-Ion batteries still are one of the most expensive technologies, but there is a high cost reduction potential in the future [21]. Lead Acid is one of the cheapest technologies regarding specific energy costs. Power specific costs can reach the same level as for Li-Ion batteries. Hardly any price data is available for other technologies such as Vanadium RFB and Zn/Br RFB. Specific costs according to the system integration level are 30 depicted in Fig. 9.
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Calendric lifetime [y]
Specific Costs [€/kW]
Fig. 6: Maximal and minimal calendric lifetime (median values) of different batteries and amount of comparable sources (Source: KIT/FZJ database)
Data for calendric lifetimes of batteries vary significantly – even within the same group of technology. This is probably due to missing long-term experience, different production processes as well as cell design and uncertainties in aging models making it difficult to estimate calendric lifetimes. The degree of efficiency is another important factor as it determines the amount of energy that can be stored and released. Fig. 7 shows DC-DC efficiency for different battery technologies.
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Lead Acid Module Li-Ion Module
LixTixOx Li Poly LiFePO4 Li-Ion unspec. Redox Flow V/V Redox Flow Zn/Br
1,000
1,500
2,000
2,500
3,000
Specific Costs [€/kWh] Lead Acid System Li-Ion System
Lead Acid Cell Li-Ion Cell
Fig. 9: Specific costs of different Lead Acid and Li-Ion cells, modules and systems (Source: KIT/FZJ database)
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100
DC-DC Efficiency [%] Fig. 7: Maximal and minimal DC-DC efficiency (median values) of different batteries and amount of comparable sources (Source: KIT/FZJ database)
Li-ion batteries have the highest DC-DC efficiencies compared to all other systems reaching up to 98 %. High temperature batteries and Redox Flow batteries have fair efficiency grades reaching from 65 % to almost 90 %. It has to be mentioned that efficiency is not a constant value, and varies in dependence of the C-rate, the ambient temperature and other factors [20]. The initial investment costs of an energy storage system determine its adequacy for a certain application field where electrochemical storage technologies may be in competition with other technologies (other storage technologies or alternatives, e.g. demand side management). The specific costs for different batteries are given in Fig. 8.
Most data was available for cell and module level and only a few for the system level. In general, systems have higher costs than cells and modules due to packaging and system components (e.g. power electronics, battery management system). Data showing specific costs regarding different application fields was only available for Lead Acid systems and is depicted in Fig. 10. Specific Costs [€/kW]
2 3 4 3 1 1
10,000
Lead Acid Li-Ion unspec. Redox Flow V/V Redox Flow Zn/Br Fig. 8: Specific costs of different batteries (Source: KIT/FZJ database)
Lead acid NaS LixTixOx LiFePO4 Li Poly LiNiCoAlO2 Li-Ion unspec. NiCd Redox Flow V/V Redox Flow Zn/Br 0
No. of Sources
100,000
4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 0
50
Lead Acid Starter
100
150
200
250
Specific Costs [€/kWh] Lead Acid Stationary
300
350
400
450
Lead Acid Traction
Fig. 10: Specific costs of Lead Acid batteries regarding different application fields (Source: KIT/FZJ data base)
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B. Combination and comparison of literature and manufacturer data The previous presented manufacturer data is compared with literature data to cope with uncertainties and to identify possible inconsistencies between the sources. A comparison of specific energy and power data is given in Fig. 11.
For NiCd, NaS and NaNiCl only literature data was found and plotted. In general it was easier to find cost data in literature. However, in some cases it is difficult to validate literature data due to missing manufacturer data. A comparison of literature and manufacturer data regarding calendric lifetime shows Fig. 13. The red bars indicate literature and the black bars manufacturer median values.
No. of Sources
1,000 100 10 1 0 0
50
100
150
200
Specific Energy [Wh/kg]
Lead Acid Manuf. Li-Ion Manuf. NaNiCl Manuf. NaS Manuf. Redox Flow V/V Manuf.
250
300
Lead Acid Lit. Li-Ion Lit. NaNiCl Lit. NaS Lit. Redox Flow V/V Lit.
0
Fig. 11: Specific energy and power of different battery technologies (manufacturer vs. literature data) (Source: KIT/FZJ data base)
In the case of Li-Ion and Lead Acid enough data was available to see that both sources show same tendencies. It was also observed that it is difficult to compare both source types for some technologies, as the number of available data points by source can vary largely. In the case of NaS seven sources from literature and only one from manufacturers was available. However, it can be seen that literature data has wide bandwidths which become even wider when compared with manufacturer data. Specific costs based on literature and manufacturer data for different technologies are given in Fig. 12. Additional cost data is available in the database in case of existing single data points (either power or energy costs).
No. of Sources
Specific Costs [€/kW]
1,000 100 10 1 1,000
1,500
2,000
Specific Costs [€/kWh]
Lead Acid Lit. Li-Ion Lit. NaS Lit. Redox Flow V/V Manuf. Redox Flow Zn/Br Manuf.
2,500
3,000
Lead Acid Manuf. Li-Ion Manuf. Redox Flow V/V Lit. NiCd Lit. Redox Flow Zn/Br Lit.
15
20
25
30
Lead acid Manuf. Lead acid Lit. NaS Manuf. NaS Lit. NaNiCl Manuf NaNiCl Lit. LixTixOx Manuf. LixTixOx Lit. Li Poly Manuf Li Poly Lit. LiFePO4 Manuf. LiFePO4 Lit. Li-Ion unspec. Manuf. Li-Ion unspec. Lit NiMH Manuf. NiMH Lit. NiCd Manuf. NiCd Lit. Redox Flow V/V Manuf. Redox Flow V/V Lit. Redox Flow Zn/Br Flow Manuf. Redox Flow Zn/Br Lit. 60
80
DC-DC Efficiency [%]
Fig. 12: Specific costs of different battery technologies (manufacturer vs. literature data) (Source: KIT/FZJ data base)
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Data availability varies a lot depending on the technology. In general the data given in literature was more unspecific e.g. in the case of Li-Ion batteries. In some cases high deviations occurred between the types of sources. Examples are V/V Redox Flow or Li-Ion undefined/unspecific batteries where literature indicates a significantly lower calendric lifetime than manufacturers. Most sources show high variations. Only a few manufacturer datasets on DC-DC efficiency grades were available in relation to literature. The comparison of both sources is given in Fig. 14.
10,000
500
5
Fig. 13: Maximal and minimal calendric life time (median values) of different batteries and amount of comparable sources (Source: KIT/FZJ data base)
100,000
0
Lead acid Manuf. Lead acid Lit. NaS Manuf. NaS Lit. NaNiCl Manuf NaNiCl Lit. LixTixOx Manuf. LixTixOx Lit. LiFePO4 Manuf. LiFePO4 Lit. Li Poly Manuf Li Poly Lit. Li-Ion unspec. Manuf. Li-Ion unspec. Lit NiMH Manuf. NiMH Lit. NiCd Manuf. NiCd Lit. Redox Flow V/V Manuf. Redox Flow V/V Lit. Redox Flow Zn/Br Manuf. Redox Flow Zn/Br Lit.
Calendric lifetime [y]
3 2 6 3 3 0 2 0 37 4 0 2 0 1 0 1 5 0 6 0 6 0
Specific Power [W/kg]
10,000
3 2 3 3 2 5 1 0 14 6 0 1 0 2 0 2 2 0 3 1 4 33
There are high differences between the costs of starter batteries, stationary and traction batteries. Lead Acid batteries for stationary application show very high deviations regarding their power specific costs, which indicates different target applications (high power vs. high energy).
100
Fig. 14: Maximal and minimal DC-DC efficiency (median values) of different batteries and amount of comparable sources (Source: KIT/FZJ data base)
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Reviewed literature bandwidths are wider and tend to be more pessimistic in relation to the collected manufacturer data. [1] However it is obvious that more data is required for a more robust comparison. C. Possible applications of the database The presented data is already used for probabilistic modeling of energy storage life cycle costs, optimization, benchmarking and dynamic simulation. The benchmarking of different battery technologies can be based on best performance systems and by calculating life cycle costs and to compare them with market requirements. The database allows it to choose different datasets e.g. manufacturer, literature or mixed values. This is useful if some parameters are missing within one type of source but information about one technology is required. Nevertheless data should be chosen carefully since data uncertainty can be very high (e.g. in the case of Li-Ion). V. CONCLUSION There are different battery storage technologies commercially available which to a certain extent compete with each other. There is a broad variety of automotive, portable and stationary battery applications which results in different requirements, battery characteristics and influences battery performance. It is important to validate available cost and performance data as they are dependent on several factors. The use of diametric data sources has both benefits and drawbacks. On the one hand literature data can be used to fill data gaps in the manufacturer data and vice versa. Such data gaps were observed in the case of efficiency grades, costs or calendric life times. On the other hand the mixture of sources can also result in higher uncertainty making it difficult to conduct a consistent assessment. The database can be used for different purposes e.g. modeling or benchmarking, but data has to be handled carefully. In most cases, manufacturer data can be considered as more detailed and up-to-date than literature data. An advantage of the use of literature data is that it enables to compare or evaluate new energy storage technologies which are still under development in a prospective way. Furthermore it could help to identify new technology or development trends. The review showed that it was easier to find complete data sets within manufacturer data sheets rather than in scientific literature due to the heterogenic and fragmentary provision of techno-economic data (e.g. missing information about cell, module, chemistry etc.). This is mainly observed for lithiumion batteries. However, several reviews, which can be found in literature and are still used in assessments, include obsolete data especially regarding specific power or capacity prices. In the future more data will be collected to further improve techno-economic comparisons and assessments.
[2] [3]
[4] [5] [6] [7] [8]
[9] [10]
[11] [12]
[13] [14] [15] [16]
[17] [18]
[19] [20]
[21]
VI. ACKNOWLEDGEMENT This work was realized within the Helmholtz Portfolio project “Electrochemical Storage in a systemic perspective – Reliability and Integration”.
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