Lecture #8 Batteries and thermal energy storage

Size: px

Start display at page:

Download "Lecture #8 Batteries and thermal energy storage"

Amberlynn Summers
6 years ago
Views:

1 Lecture #8 Batteries and thermal energy storage PHYS-E0483_ Peter Lund

2 Contents Lecture # 8 Basic principles of batteries Li-ion battery Comparison of battery technologies Application Thermal storage principles Advanced thermal storage Large-scale applications

3 Main components of a battery Anode (negative electrode) Cathode (positive electrode) Electrolyte (ionic conductor) Anions (negative ions) Cations (positive ions) Slides 3-14 from D. Linden: Handbook of Batteries, 2 nd Edition, 1995

4 Operating principle of a battery Charging/discharging of a battery; reversed current flows Example Zn/Cl 2 cell negative electrode (oxidation): Znà Zn 2+ +2e - positive electrode (reduction): Cl 2 +2e - à 2Cl - overall reaction (discharge): Zn+Cl 2 à Zn 2+ +2Cl - (ZnCl 2) negative electrode (reduction): Zn 2+ +2e - à Zn positive electrode (oxidation): 2Cl - à Cl 2 +2e - overall reaction (charge): Zn 2+ +2Cl - à Zn+Cl 2

Important battery parameters (1) Theoretical voltage, capacity, energy density Free energy change in the reaction ΔG = n F E 0 n=electrons involved in the reaction F= Faradays constant (26.

5 Important battery parameters (1) Theoretical voltage, capacity, energy density Free energy change in the reaction ΔG = n F E 0 n=electrons involved in the reaction F= Faradays constant (26.8 Ah) E 0 = standard cell potential (V) Standard cell potential = anode (ox. potential) +cathode (red. potential) From table (à) Reaction Zn+Cl 2 à ZnCl 2 Znà Zn 2+ +2e - -(-0.76V) Cl 2 +2e - à 2Cl V = 2.12 V

6 Important battery parameters (2) Theoretical voltage, capacity, energy density Capacity = total amount of electricity involved in the electrochemical reactions Theoretical max. : 1gram of material = 26.8 Ah/g Energy density = Theoretical Wh x capacity/ weigth ZnCl 2 battery system: 1.22 g/ah g/ah = 2.54 g/ah= Ah/g 2.12 V x Ah/g = Wh/g = kwh/kg

7 Parameters for major battery systems

8 Performance characterization of major battery systems (primary and secondary batteries)

9 Electrochemical principles of a battery Theore&cal values drop because of inideali&es, e.g. charge transfer limita&ons, contact resistance, etc = Polariza(on effects

10 A battery at equilibrium (E 0 ) One electrode reac,on (forward=reduc,on) aa+ne cc One electrode reac,on (forward=oxida,on) bb-ne dd Total aa+bb cc+dd Free energy change for this reaction ΔG = - n F E 0 Nernst equation for non-standard conditions

11 A battery at non-equilbrium During opera,on current I> 0 à voltage losses (electrode reac,os, charge transport etc) à electrode polariza,on (so-called polariza,on) η ; E =E-η a,b are bakery specific parameters (see Fig) Tafel-equa&on

12 A battery in practice Characterzing bakery discharging/charging by the C-rate: amount of current a bakery delivers when discharged in one hour to the point of 100% depth of discharge I = M x C n ; I (A) = C n (Ah)/1 (h), C n = rated bakery capacity, n=,me based in hours for which the rated capacity is declared, M=mul,ple frac,on of C C/10 discharge rate, e.g. if 10 Ah bakery à I = 1 A for 10 hours C/5 discharge rate, e.g. if 10 Ah bakery à I = 2 A for 5 hours Resistance increases when discharging/charging due to accumula,on of reac,on products, ac,va,on, concentra,on etc. à effec,ve capacity drops

13 Li-ion battery Octavio Salazar: Li-Ion Battery Model

Improved Li-ion battery performance through nanocrystals Recent interest in Li 4 Ti 5 O 12 nanocrystals for anodes Accommodation of strain of Li+insertion/ extraction Higher

14 Improved Li-ion battery performance through nanocrystals Recent interest in Li 4 Ti 5 O 12 nanocrystals for anodes Accommodation of strain of Li+insertion/ extraction Higher electrode/electrolyte area allows higher charge/discharge rate Short path lengths for electronic transport Short path length for Li+transport Less reactive as bulkli 0.5 CoO 2 +

15 Battery comparison Octavio Salazar: Li-Ion Battery Model

16 Li-ion battery performance Battery performance is temperature dependent, in particular in at low temperatures (up to 50% of capacity lost at -20 C)

eletrocde: V 3+ +e - V 2+ 2 electrolytes in tanks separated by a

17 Flow battery Vanadium redox flow battery Vanadium in 4 different oxidation states Pos. eletrocde: VO 2+ +H 2 O-e - VO H + Neg. eletrocde: V 3+ +e - V 2+ 2 electrolytes in tanks separated by a membrane Wh/L 1 kwh-10 MWh Pilot stage Zinc Bromine flow battery

18 Aluminium-air-battery Al+ alkaline solution+air electrode Al Al 3+ +3e - hydrophobic layer (carbon+pt+ptfe): 2H O 2 + 4e - OH - e - air Anode : 4 (Al+4OH - Al(OH) e- ) Cathode: 3 (O 2 +2H 2 0+4e - 4OH - ) Al Electrolyte: 4 (Al(OH) - 4 Al(OH) 3 + OH- ) total: 4 Al(s) + 6H 2 0(l) + 3O 2 (g) 4Al(OH) 3 (s) Hydrophilic layer Hydrophobic layer 400 Wh/kg, 175 W/kg

19 Battery characteristics PHYS-E0483_ Peter Lund 2015

20 Batteries vs applications vs other storage types PHYS-E0483_ Peter Lund

21 Li-ion battery costs and targets PHYS-E0483_ Peter Lund 2015

22 PHYS-E0483_ Peter Lund 2015

23 Effect on LCOE Battery may increase LCOE with /MWh (past) à in future PHYS-E0483_ Peter Lund 2015

24 PV-EV [Tesla]

25 PV & Tesla battery Hours when PV NOT meeting supply (black) Case Finland: 3 kwp PV for a household (100%) PV not battery PV + 1 Tesla batt. PV + 2 Tesla batt Tammikuu Direct use of PV Heinäkuu 32% 74% 76%

26 Thermal energy storage

27 Sensible thermal storage Q= c p Δ T, where c p =thermal capacitance (kj/kgk) water, rock, ceramics; capacity kwh/m 3 (H 2 O 1.17 kwh/m 3 /K large scale storage 10, ,000 m 3 (steel tanks, subsurface) case OULU: 200,000 m 3 rock cavern water storage, 2-4 bar, o C, 100 MW/10 GWh load levelling, optimal operating strategy heat elec CHP storage Peak boiler

28 Micro-CHP thermal storage (e.g. CHP-DESS)

29 Large-scale water storage

30 Advanced thermal storage - introduction Phase change thermal energy storage phase change absorbs/releases heat (e.g. between solid and liquid) phase change enthalpy ΔH and phase change temperature inorganic salts Na 2 SO 4 x 10 H 2 O (251 kj/kg, 24 C), NaOH x 3.5H 2 0 (272 kj/kg, 64 C) fatty acids (paraffin, stearic acid, ca o C, kj/kg) small scale (up to a few m 3 ) Thermochemical heat storage sorption processes XY+heat X + Y Y=working medium (water, NH 3, ROH, SO 2, SO 3, CO 2, H 2, O 2 ) X=absorbent (e.g. Me, silica gel) storage capacity kwh/m 3 (th), kwh/m 3 (pr)

31 Phase change heat storage heat

33 Chemical thermal storage Principles: 1) chemical reactions without sorption, 2) sorption Heat of sorption/ desorption: Wh/kg

34 Classifiction

35 Energy storage densities for sorption storage Water as sorbate, Wh/kg

36 Solid adsorption (silica gel/water) <100 kwh/m3

37 Working principle of thermochemical storage

38 Thermodynamics of thermochemical storage Vapour pressure: sorbent/sorbate

39 Thermochemical heat distribution DH= water in pipe, heat loss & capacity limitiation Chemical DH = thermochemical routes, gas in pipes CH 3 OH +heat CO+H 2 minor losses, high energy density

40 Hydrogen energy storage

17.1 Redox Chemistry Revisited

Chapter Outline 17.1 Redox Chemistry Revisited 17.2 Electrochemical Cells 17.3 Standard Potentials 17.4 Chemical Energy and Electrical Work 17.5 A Reference Point: The Standard Hydrogen Electrode 17.6