Energy Science and Technology III Winter Term 2015/16. Battery System Engineering I

Transcription

1 Energy Science and Technology III Winter Term 2015/16 Battery System Engineering I Michael A. Danzer Zentrum für Sonnenenergie- und Wasserstoff-Forschung (ZSW) Baden-Württemberg Contents Battery System Engineering Battery System Engineering I Applications and requirements Fundamentals of battery operation Characteristics, selection, and testing of cell types Charging methods Battery System Engineering II Battery modeling Battery modules and systems Battery management system Cell balancing State estimation -2-

2 Introduction Battery system engineering from cell to application materials components mechanical design production technology capacity power energy efficiency life Introduction Application and requirements Application? Power? Energy? Capacity? Voltage? Charge/discharge time? Weight? Size? Form factor? Specific energy / power? Energy / power density? Configuration serial/parallel? Efficiency? Life time expectation? Temperature range? -3- electrochemistry -4-

3 Introduction Applications portable mobile power tool stationary Black&Decker Drill/Drive with Lithium-Ion battery 2011 Voltwerk Sol-Ion inverter with Lithium-Ion battery 2011 Dr. Martin Cooper Motorola DynaTAC 1973 Lohner-Porsche Semper Vivus 1900 Screw driver, drill, hammer, saw Applications Power tool handheld

4 Vacuum cleaner Applications Power tool robots Military Lawn mower Applications Power tool requirements Energy Wh Energy density intermediate-high Power kw Power density high Power to energy ratio h -1 Life time expectation 2-5 years Temperature range C Charge current 1-5 C

5 PV self consumption, Backup, UPS 3-10 kwh electrical energy 3-5 kw power Bosch/Voltwerk Solion Applications Stationary PV-Battery-System Applications Stationary grid stabilization Transmission or distribution grid A123 Systems Electric Grid Energy Storage Solutions 2 MW, 2MWh

6 Applications Stationary requirements Energy 3 kwh 2 MWh Energy density low-intermediate Power 3 kw 2 MW Power density low Power to energy ratio <2 h -1 Life time expectation years Temperature range C Charge current C Applications mobile HEV: Mercedes Benz S400H First series-production vehicle with lithium-ion battery HP cylindrical cell from Saft Market launch June 2009 Mild-Hybrid

7 Applications mobile EV: Smart ED (Electric Drive) 2008 Sodium-Nickel-Chloride high temperature battery (Zebra-Batterie) (~250 C) 2011 Lithium-ion HE pouch cell from Li-Tech, Car2Go 2012 general market launch Applications Mobile: Requirements power energy self discharge energy efficiency temperature cold-crank charge capability cycle life calendar life cost safety recycability toxicity drive (discharge) kw (EV), kw (PHEV), recuperation (charge) driving range km (EV), km (PHEV) acceptable SOC loss per time especially for stand periods specific driving costs, environmental impact driving possible at temperatures -25 C to 50 C, recuperation? for HEV cranking internal combustion engine for temperatures as low as -25 C 3.5 kw or higher for fast charging charge/discharge cycles worst case > 8 years wish: not significantly higher than conventional vehicles Hazard level needs to be low: no explosion, no fire in abuse situations. every (?) battery needs to be recycled at its end of life Government regulations restricts the usage of toxic materials as Cadmium only for specified application

8 Characteristics, selection, and testing of cell types Ragone plot of electro-chemical storage systems Source: IEA Technology Roadmap Electric and plug-in hybrid electric vehicles 2011, Johnson Control - Saft 2005 and 2007 Characteristics, selection, and testing of cell types Specific power and energy Volumetric energy (Wh/L) EiG Gaia Kokam Saft AESC Alees LiTec E one Moli SK Saft GP Gaia GP EiG A123 Valence PSI GS Yuasa Hitachi K2 Alees Specific energy (Wh/kg) LFP NMC NCA LMO LMO/NCA LMO/NMC

9 Characteristics, selection, and testing of cell types Comparison of (electro-)chemical energy storage Source: Toyota, 2010 Characteristics, selection, and testing of cell types Theoretical and practical specific energy Quelle: Linden D., Reddy T.B., Handbook of Batteries Third Edition, McGraw-Hill,

10 Characteristics, selection, and testing of cell types Contributions to the specific energy of a cell Along with active materials other components are needed to receive an operational cell: current collectors, tabs, electrolyte, binder, separator, housing. Besides, the level of utilization of the active materials is below 100%. Percentage by weight of each component 5% 7% 18% 14% 6% 4% 2% 17% Anode active material (graphite) Anode inactive materials (binder, additives) Cu current collector Cathode active material (LiFePO4) Cathode inactive materials (binder, additives) Al current collector Electrolyte Separator Cell housing Source: ZSW 27% Here: Active material = 45 wt% of a cell Typically Active material = wt% of a cell Typically wt% overhead for system Hence: Active material = wt% of a system Characteristics, selection, and testing of cell types Power to energy ratio of applications r PE = power/energy in [W/Wh] = h -1 Typical values for r PE application r PE [h -1 ] laptop / cell phone 2 EV 3 PHEV 5-10 power tool HEV > 20 How to optimize cells towards power (HP) and towards energy (HE)?

11 Optimized battery design energy vs. power electrode and current collector high energy (HE) Thick active material layer Thin, space-saving current collector High mass ratio of active to passive materials high internal resistance low power density high power (HP) Thin active material layer Thick current collector low mass ratio of active to passive materials low internal resistance high power density low energy density tabs Few tabs long current paths high internal resistance low power density Many tabs short current paths low internal resistance high power density Characteristics, selection, and testing of cell types Quelle: J. Miller, Ford, Automotive Battery & Ultracapacitor Conference,

12 Glossary, definitions, and fundamentals I capacity rated capacity C C-rate state of charge (SOC) depth of discharge (DOD) The available quantity of electric charge Q of a battery or cell measured in Ampere hours (Ah). The capacity is dependant on the cutoff voltages, the temperature, and the discharging current. It is therefore important to state not just the capacity, but also the corresponding conditions. The capacity that is typically delivered when used under normal conditions (e.g. temperature) under a specified protocol (rest times, currents, cutoff voltages). The charging and discharging current of a cell is often expressed as a multiple of C. (Example: The 0.5 C current for a cell with a rated capacity of 14 Ah is 7 A). C-rate = I / C. [C-rate] = A/Ah. SOC is the equivalent of a fuel gauge for a cell or a battery pack. It is calculated as the ratio of the withdrawable electric charge (Q in Ah) and the rated capacity C under normal conditions, at a specified discharge current till a chemistry dependant discharge cutoff voltage is reached. SOC = Q / C = 0 1. DOD is the ratio of the withdrawn electric charge (Q in Ah) at a discharge and the rated capacity C under normal conditions. DOD = Q dc / C = 0 1. SOC = 75% Glossary, definitions, and fundamentals I State of charge (SOC). Q in charging SOC Q C fill level capacity Q 0 Qin ( t) Qout ( t) Q SOC( t) C ( t t loss ). Q loss self discharge. Q out discharging

13 Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A 3D Illustration and dimensions safety devices Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A Specifications and dimensions Specific energy and energy density Volume Energy Specific Energy Energy density V = r 2 π h = (½ 26 mm) 2 π 65 mm = 0,0345 l E = V N C = 3.6 V 2650 mah = 9,54 Wh E W = E/W = 106 Wh/kg E V = E/V = 277 Wh/l

14 Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A Charge characteristics start switch terminate 4.2 CC CV 250 Charging scheme Charge method CCCV CC charge current 1 C = 2.5 A switch criterion V = 4.2 V CV constant voltage V = 4.2 V termination criterion I < 250 ma temperature 25 C Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A Discharge characteristics current dependency temperature dependency Standard discharge initial condition fully charged CC discharge current 1 C = 2.5 A termination criterion V = 2.5 V temperature 25 C

15 Glossary, definitions, and fundamentals II self discharge self discharge rate capacity loss resistance rise begin of life (BOL) end of life (EOL) state of health (SOH) state of function (SOF) Self discharge is a temperature-dependant permanent chemical reaction process at battery electrodes, without connection to an external consumer. Self discharge rate corresponds to reaction kinetics and is quantified by the amount of electric charge lost over time (e.g. Ah/day). Over time and use the capacity of a battery decreases irreversibly. Over time and use the internal resistance of a battery increases irreversibly. The time of manufacture of a battery where it has its maximum utility for a specified application. The end of a battery s life is reached when it has lost the utility for a specified application. SOH is a figure of merit of the condition of a battery, compared to its ideal conditions. It determines its relative utility for the specified application. Typically, a battery's SOH will be 100% at begin of life (BOL), will decrease over time and use, and will be 0% at end of life (EOL). 0 SOH 1. SOF is a figure of merit of the condition of a battery and describes its capability to perform specified functions as cranking, recuperation, power capability. SOF = f(soc,soh) Battery aging Glossary, definitions, and fundamentals II State of health (SOH) battery aging State of health SOH does not correspond to a particular physical quality. It is defined by one or a combination of the following parameters: - internal resistance - capacity - self-discharge rate - power capability - available energy - number of cycles

16 Glossary, definitions, and fundamentals II State of health (SOH) examples SOH-definition based on capacity Capacity at BOL: C 0 =C(t=0) SOH = 1 Capacity at EOL: 80% C0 SOH = 0 (20% irreversible capacity loss) SOH C( t ) C( t) 1 C( t ) % SOH-definition based on resistance Resistance at BOL: R 0 =R(t=0) SOH = 1 Resistance at EOL: 200% R 0 SOH = 0 (100% irreversible resistance rise) SOH R( t) R( t ) 1 R( t ) % Alternative SOH-definitions Additionally to the examples above any combination of capacity loss and resistance rise can be used to define the state of health. Other variables used: self discharge rate, power capability, available energy, cycle count. Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A Cycle life characteristics 3 100% DOD cycling Capacity at begin of life C BOL = 2700 mah I [A] t [min] End of life criterion: e.g. 20% capacity loss C EOL = 0.8 C BOL = 2160 mah Cycles till EOL: How many cycles can be expected? How many cycles are needed for a BEV? Assumptions: 80 kwh battery, 20 kwh/100 km consumption, km traveled over life

17 Characteristics, selection, and testing of cell types Cell data sheet Panasonic CGR-26650A Which information is missing in the data sheet? Internal resistance Power Chemistry Safety Operation ranges Additional documents: - Safety data - Precautions Characteristics, selection, and testing of cell types Test protocols overview Freedom Car Battery Test Manual For Plug-In Hybrid Electric Vehicles Hybrid Pulse Power Characterization Test, Self-Discharge Test, Cold Cranking Test, Thermal Performance Test, Energy Efficiency Test, Charge-Sustaining Cycle Life Tests, Charge-Depleting Cycle Life Tests, Calendar Life Test, Reference Performance Tests EUCAR Specification of Test Procedures for High Voltage Hybrid Electric Vehicle Traction Batteries IEC Secondary batteries for the propulsion of electric road vehicles. Part1: Performance testing for lithium cells. March

18 Characteristics, selection, and testing of cell types Internal resistance and power Frequency dependant internal resistance = impedance Z cell I cell V cell OCV V cell Two characteristic resistance values: R AC resistance at 1 khz, R AC = real{z cell (f=1 khz)} R DC resistance according to voltage drop after current pulse, e.g. after 10 s (15, 18, 20)s R DC = real{z cell (f=0.1 Hz)} P cell power P cell = U cell I cell Characteristics, selection, and testing of cell types Resistance and Pulse Power Capability 15 I10 dc 5 I [A] 0-5 I ch I V 2,6 V -10 2,4 min t [s] resistance Vmin Vmax power capability t 0 t 1 t 2 t 3 R P P DCdc max,dc max,ch V V1 V0 I I V V min max I I dc max,dc max,ch V V min max V R DCdc V R DCch R DCch V V V V3 V2 I I min max V0 V R DCdc min Vmax V R DCch 2 ch 4,4 4,2 V max 4 3,8 3,6 V [V] 3,4 3,2 3 2,8 Source: FreedomCAR Battery Test Manual For Power-Assist Hybrid Electric Vehicles

19 Characteristics, selection, and testing of cell types Resistance and Pulse Power Capability Resistance and therewith power depend on SOC and temperature Sony US26650VT NMC 2.5Ah: Specific Power Capability vs. Vmin=2.5V, Vmax=4.15V temperature 750 spec Pdc [W/kg] discharge charge spec Pch [W] % 20% 30% 40% 50% 60% 70% 80% 90% SOC [ ] Characteristics, selection, and testing of cell types Useable energy SOC dependency of pulse power and comparison of cell types Source: A123 Systems White paper Usable Energy

20 Characteristics, selection, and testing of cell types Examples of cells cell type weight volume V N C E spec C C density spec E E density [g] [l] [V] [Ah] [Wh] [Ah/kg] [Ah/l] [Wh/kg] [Wh/l] A123 ANR ,90 0,0345 3,3 2,45 7,75 33,5 70,9 106,2 224 Sony US26650VT 90,52 0,0345 3,7 2,67 9,57 29,5 77,4 105,7 277 Panasonic CGR-26650B 93,35 0,0345 3,6 3,36 11,9 36,0 97,4 127,8 346 cell type P dc P ch spec P dc P dc density spec P ch P ch density r PE [W] [W] [W/kg] [W/l] [W/kg] [W/l] [ ] A123 ANR , ,4 Sony US26650VT 72,5 41, ,6 Panasonic CGR-26650B , ,8 Remarks - power capability caclulated using 10s 2C charge pulses at 50% SOC and room temperature - energy was measured at a full discharge of a fully charged cell Characteristics, selection, and testing of cell types Ragone plot of electro-chemical storage systems Source: IEA Technology Roadmap Electric and plug-in hybrid electric vehicles 2011, Johnson Control - Saft 2005 and

21 Characteristics, selection, and testing of cell types Selection criteria I Source: D. Linden, T.B. Reddy, Handbook of Batteries, 3rd ed., 2002 Characteristics, selection, and testing of cell types Selection criteria I Source: D. Linden, T.B. Reddy, Handbook of Batteries, 3rd ed.,

22 Characteristics, selection, and testing of cell types Life-cycle assessment (LCA) LCA is also known as life-cycle analysis, ecobalance, and cradle-to-grave analysis. LCA can help avoid a narrow outlook on environmental concerns by - Compiling an inventory of relevant energy and material inputs and environmental releases; - Evaluating the potential impacts associated with identified inputs and releases; - Interpreting the results and making more informed decisions. For battery production LCA can help to - identify bottlenecks of raw materials (e.g. availability of Lithium) - compare different battery technologies by their environmental impact and their overall energy balance (both from cradle to grave). Literature: Sources: Feb. 2012, ZSW Charging methods Introduction More batteries are damaged by bad charging techniques than all other causes combined. LCA is a technique to assess environmental impacts associated with all the stages of a product's life from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling (i.e. from-cradle-tograve). -44-

23 Charging methods Limitations of charging for Lithium-ion cells Equivalent circuit of a cell Potentials and voltages cell voltage at charge open circuit voltage cell voltage at discharge open circuit potential of the negative electrode open circuit potential of metallic Lithium potential decomposition potential of the electrolyte open circuit potential of the positive electrode Limitations High potentials at the positive electrode lead to decomposition of the electrolyte. Low potentials at the negative electrode lead to deposition of metallic lithium, planar and as dendrites. Consequences In general, charging currents need to be limited to prevent ageing and safety issues. Charging methods Fragmentation of charge current side reactions Example SOC = 20% clamp current current for side reaction H 2 O H 2 +1/2O 2 main reaction current for main reaction (charge process) 2Ni(OH) 2 + Cd(OH) 2 Cd + 2NiOOH + 2H 2 O In principle side reactions are undesired. Side reactions can be used for - limited overcharging - equalizing of states of charge (balancing) of cells through limited overcharging - mixing of the electrolyte in Lead-acid batteries through gas bubbles Side reactions lead to - gassing (loss of water, production of H 2, venting needed) - temperature increase (limitation of charge current, cooling SOC = SOC = 99%

24 Charging methods Charging rates Charging time 1h 10h 0.1h Normal charging Fast charge Super fast charge Pb Li-Ion NiMH NiCd Generally: The higher the SOC, the more difficult it becomes to charge: side reactions increase (lead acid, NiCd, NiMH) side reactions must be avoided (Li systems) The maximum charge current (power) becomes lower with increased SOC State of the art In future Charging methods Charger and charging schemes The charger has three key functions - getting the electric charge into the battery (charging) - optimizing the charging rate (stabilizing) - knowing when to stop (terminating) Charging methods are defined by the controlled variables and the control scheme - current or voltage - constant, pulsed, floated, Charging needs to be terminated using a switch or cutoff criterion defined by - absolute values for voltage, current, temperature, or time - or by calculated values (difference, derivative) A charging scheme is a combination of the charging and termination methods

25 Charging methods Basic charging schemes charging method charger charge termination comment used for constant voltage (CV or U) acts as DC power supply either by time or current level Lead-acid constant current (CC or I) varies the voltage applied to the battery to maintain constant current flow either by voltage or temperature current needs to be terminated precisely to prevent damage and ageing NiCd, NiMH constant current constant voltage (CCCV or IU) switches between constant current control and constant voltage source switch by voltage, terminate by current or time CC for bulk charge phase CV for finalizing full charge Lead-acid Lithium-ion Charging methods Constant current charging for NiCd and NiMH Cutoff criteria using cell temperature Voltage [V] Slope dt/dt (e.g. 1K/min) inflection point Absolute value (e.g. 45 C) temperature Temperature [ C] 1.30 voltage Temperature change T (NiMH e.g. 15 K) Time [h]

26 Charging methods Constant current charging for NiCd and NiMH Cutoff criterion using voltage difference Depending on cell design, temperature, charging parameters, and aging criterion could be too small. Voltage [V] expected voltage curve unexpected voltage curve: - V criterion too small - U 5mV Charging with 2A, - U = 5mV, 25 C Time [h] Charging methods Impact of charging methods for the aging of NiMH cells capacity in Ah charge factor = Q ch /Q dc charge factor 1.12 charging with - U criterion (5mV) charge factor 1.3 NiMH cell with C=1.5Ah, T = 43 C, 1C full cycles cycle

27 Charging methods CCCV charging of Lithium-ion cells switch criterion: cutoff criteria: - voltage reaches V max - current falls below I cutoff (e.g. I < C/30 C/10) - time at CV exceeds t cutoff (typical 1 3h) switch criterion: V=V max voltage SOC Voltage [V], current [A] CC - CV phase Time [h] cutoff criteria: t>t cutoff and/or I<I cutoff current SOC [%] Charging methods Parameters for CCCV charging of Lithium-ion cells CC charge current: CV charge voltage: typically 1C for HE standard cells depends on chemistry positive electrode negative electrode voltage LiCO 2 graphite 4.2 V NMC graphite 4.2 V 4.3 V NCA graphite 4.0 V 4.2 V LiFePO 4 graphite 3.6 V ( V) 4V cathode lithium titanate ca. 2.8 V LiFePO 4 lithium titanate ca. 2.3 V CV cutoff current: typically C/10 CV cutoff time: typically 1 3 h Charge temperature : typically: 0 40 C

28 Charging methods CCCV charging of Lithium-ion cells charge time CC current dependency Charging methods CCCV charging of Lithium-ion cells charge time Temperature dependency charge time [minutes] battery: capacity: CC Ich: CV Uch: cutoff: Li-ion polymer 1300 mah 750 ma 4.2 V I < 50 ma temperature [ C]

29 Charging methods CCCV charging of Li-ion useable capacity Comparison of switch and cutoff criteria: switch voltage / cutoff current or time useable capacity in %C N Charging methods CCCV charging of Li-ion Impact on aging Comparison of switch and cutoff criteria: switch voltage / cutoff current discharging: 1C for 15 min (25% DOD) charging: 1C, varying CC cutoff voltage and CV cutoff time and current overall time: always 1h temperature: 35 C relative capacity no CV C/ C/ C/ C/ no CV C/5 25% DOD cycles

30 Charging methods Conservation charging To keep the SOC constant and to compensate for the self discharge of the battery the following charging methods are used. Trickle charge Long term constant current charging for standby use. The charge rate varies according to the frequency of discharge. Not suitable for NiMH and Lithium, which are susceptible to damage from overcharging. Float charge Long term constant voltage below the battery's upper voltage limit. The battery and the load are permanently connected in parallel across the DC charging source Used for emergency power back up systems. Mainly used with lead acid batteries. Charging methods Pulsed charging Pulsed charging interrupted charge current: pulse width about 1s, rest periods of ms charging rate (average current) can be controlled by varying the width of the pulses short rest periods allow chemical processes in the battery to stabilize by equalizing the reaction throughout the bulk of the electrode before recommencing the charge claim: method can reduce unwanted chemical reactions at the electrode surface such as gas formation, crystal growth, and passivation. Reflex or burp charging used in conjunction with pulse charging to depolarize the cell short discharge pulse, typically 2-3 times the charging current for 5 ms during the rest period pulses dislodge any gas bubbles which have built up on the electrodes during charging ("burping ) pulses speed up the stabilization / equalization processes claim: grown dendrites might be removed current [A] charge pulse discharge pulse time [s]

31 Charging methods Alternative protocols Z. Li et al. / Journal of Power Sources 254 (2014) Charging methods Charging phases time charging phase pre-charging * main charging post charging * conservation charging description as a safety precaution and to test if charging is possible Charging is initiated with a low current. If there is no corresponding rise in the battery voltage it indicates that there is possibly a short circuit in the battery. fast charging side reactions do not matter bulk charge phase for combined charging schemes slow charging side reactions do matter utilizing maximum of cell capacity keep the cell fully charged through trickle or float charge * not applicable for all charging methods

32 Charging methods Charging phases example current [A], voltage [V] switch criterion 1 (voltage) switch criterion 2 (voltage difference) voltage NiMH battery 0.4 current pre-charging time [h] main charging conservation charging Further Reading A. Jossen, W. Weydanz: Moderne Akkumulatoren richtig einsetzen; Leipheim and Munich (Germany), (Book in German language). J. Garche (ed. in chief): Encyclopedia of electrochemical power sources; Elsevier, New York (USA), Pop et al.: Battery Management Systems; Springer, 2008 Weiker: A Systems Approach to Lithium-Ion Battery Management, Artech House Power Engineering, 2013 Linden D., Reddy T.B., Handbook of Batteries Third Edition, McGraw-Hill,

33 Links FreedomCAR Battery Test Manual For Power-Assist Hybrid Electric Vehicles IEA Technology Roadmap Electric and plug-in hybrid electric vehicles Varta: Battery know-how / battery glossary / e-learning Maxim application notes and tutorials Thank you for your attention! michael.danzer@zsw-bw.de Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg Lise-Meitner-Str. 24, Ulm -65- Stuttgart Widderstall Photovoltaics -66- & Solab Solar test-field Energy Policy & Energy Ulm Carriers University EST III 2015/16 BSE M.A.Danzer Ulm Electrochemical Energy Technologies Ulm elab