Batteries for electric commercial vehicles and mobile machinery

Transcription

1 Batteries for electric commercial vehicles and mobile machinery Tekes EVE annual seminar, Dipoli Dr. Mikko Pihlatie VTT Technical Research Centre of Finland

2 2 Outline 1. Battery technology for electric vehicles and mobile machinery Current state-of-the-art Challenges and limitations Beyond state-of-the-art 2. From battery cells to applications Application-specific requirements Battery use and operation window Cost analysis factors

3 3 What is a battery? A battery contains one or more electrochemical cells for storage of electric energy; these may be connected in series or parallel to provide the desired voltage and power The anode is the negative electrode from which electrons are generated to do external work The cathode is the positive electrode to which positive ions migrate inside the cell and electrons migrate through the external electrical circuit The electrolyte allows the flow of positive ions from one electrode to another. The electrolyte is commonly a liquid solution containing a salt dissolved in a solvent. The electrolyte must be stable in the presence of both electrodes. Typically lithium salt (LiPF 6 ) + mixed organic solvent (ethylene carbonatedimethyl carbonate EC-DMC). The current collectors allow the transport of electrons to and from the electrodes. B. Scrosati, Journal of Power Sources 195 (2010)

4 4 Basic principle of Li-ion battery charging - discharging Source: auto.howstaffworks.com

5 5 Operation principle of SEI formation in a C/LiCoO 2 battery The C/LiMO 2 system with current electrolytes is thermodynamically unstable (low kinetics!) Reaction with the electrolyte creates a passive Solid Electrolyte Interface (SEI) on the anode side Normally the SEI stabilises the cell (normal operation limits) Abnormal conditions can lead to oxidative processes on the cathode cell failure risk B. Scrosati, Journal of Power Sources 195 (2010)

6 6 Li-ion batteries a large range of possible materials combinations Positive electrodes Electrode material Average potential difference Specific capacity Specific energy LiCoO V 140 ma h/g kw h/kg LiMn 2 O V 100 ma h/g kw h/kg LiNiO V 180 ma h/g kw h/kg LiFePO V 150 ma h/g kw h/kg Li 2 FePO 4 F 3.6 V 115 ma h/g kw h/kg LiCo 1/3 Ni 1/3 Mn 1/3 O V 160 ma h/g kw h/kg Li(Li a Ni x Mn y Co z )O V 220 ma h/g kw h/kg Negative electrodes Electrode material Average potential difference Specific capacity Specific energy Graphite (LiC 6 ) V 372 ma h/g kw h/kg Hard Carbon (LiC 6 )? V 450 ma h/g? kw h/kg Titanate (Li 4 Ti 5 O 12 ) 1-2 V 160 ma h/g kw h/kg Si (Li 4.4 Si) [38] V 4212 ma h/g kw h/kg Ge (Li 4.4 Ge) [39] V 1624 ma h/g kw h/kg

7 7 Li-ion battery materials roadmap expected innovations

8 8 Tradeoffs among state-of-the-art Li-ion battery technologies

9 9 The safe operability window for Lithium-ion battery The battery should be strictly kept in the proper operating window Safety concerns from improper use or conditions Durability and performance suffer greatly when misoperated Requirements for pack design and battery management FTA, US Department of Transportation, Report No. FTA-MA

10 10 Li-ion and beyond status and outlook Energy density insufficient for full EV operation New electrode materials for higher capacity / lower cost Lithium-metal alloys for anode, e.g. Li-Si (4000 mah/g) and Li-Sn (990 mah/g) anodes instead of graphite (370 mah/g) Higher voltage cathodes, such as LMO ( stability of electrolytes!) Challenges with safety of operation Replacement of the organic carbonate lquid electrolyte solutions with more reliable and safer electrolytes E.g., solid polymer or ionic liquid electrolytes Inherently safe electrode materials, such as LTO anodes ( improved cycle life) Power capability when quick charging becomes imprative, both electrodes have to be optimised for this Completely new systems will take several years to come to demonstrations, but clear performance improvements are expected Metal-air (Li-air) batteries bring potentially high electrode capacity (1200 mah/g) Li-S Lithium-suphur batteries offer potentially great capacity (2500 Wh/kg)

11 11 Battery pack engineering towards application case by case Nissan Leaf battery pack Exact designs highly dependent on vehicle / application Geometries and the available space vary drastically depending on vehicle / application Source: Wikipedia

12 12 Relative performance of electrochemical storage devices Different types of power sources have each their optimal application areas Li-ion batteries are struggling to fulfil requirements for all-electric vehicles Venkat Srinivasan, Almaden Conf. 2009: The Batteries for Advanced Transportation Technologies (BATT) Program. )

13 13 Battery management system vs. vehicle energy balance The tasks of the BMS Protect the cells or the battery from damage Prolong the life of the battery Maintain the battery in a state in which it can fulfil the functional requirements of the application for which it was specified Communication interfaces BMS vehicle control BMS charger Charger power/energy grid Source: Electropaedia,

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15 15 Comparison of different current Li-ion battery types (power/energy) Work cycle analysis and end-user view are central in designing the driveline and energy storages Right choice of battery type and battery design are the key to succesful EV design Source: Al-Hallaj, EV Li-ion Battery forum, Barcelona 2012

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17 17 Batteries cost OEM s about 1100 $/kwh at low volumes (2010)

18 18 Battery cost will decline drastically by 2020

19 19 Battery lifetime has a crucial impact on the total system cost Calendar life or cycle life may be limiting Different fading modes Capacity loss Impedance rise Increase in self discharge Strong effect from how the battery is used Load cycles (C-rate) Temperature Depth of discharge

20 20 Thank you!