Basics of Battery Technology

Transcription

1 Basics of Battery Technology Tampere Kai Vuorilehto Adjunct professor, Director R&D,

2 Secondary batteries - chemistries Pb-PbO 2 NiOOH-Cd NiOOH-MH Li-ion (C-CoO 2 ) mostly forbidden

3 Secondary batteries - energy Pb-PbO 2 35 Wh/kg NiOOH-Cd 35 Wh/kg NiOOH-MH 75 Wh/kg Li-ion (C-CoO 2 ) 150 Wh/kg

4 Wh/kg and W/kg

5 Secondary Batteries - characteristics Voltage Wh/kg Wh/L W/kg W/L Min. temp Max. temp Voltage profile Shelf life Cost Safety Environment Cycle life Calendar life Charge retention Charge acceptancy Energy efficiency

6 Principle of the lithium-ion battery

7 Principle of the lithium-ion battery NOT a lithium battery, as there is no metallic lithium Metallic lithium could form dendrites and cause short circuit Lithium ions are intercalated in host lattices (graphite etc.) Each ion has its "own home"

8 Properties of lithium-ion batteries High energy density Rather high power density Long cycle life Good charge retention High energy efficiency

9 Positive electrode (cathode) Cobalt oxide standard material, 3.7V (combined with graphite) expensive, toxic and dangerous layered structure Co(IV) -> Co(III) at discharge can be charged only 50%, Li 0.5 CoO 2 for 7g of Li the electrode has 189g of extra Li 0.5 CoO 2 collapses without lithium thermal runaway positive potential at the upper end of the electrolyte stability window

10 Negative electrode (anode) Graphite LiC 6 standard material (earlier coke) Litium is intercalated between graphene layers for 7g of Li the electrode has 72g of extra C high voltage, 3.7V with CoO 2 negative potential can cause lithium plating Li + +e - -> Li(metal) negative potential is outside the electrolyte stability window

11 Electrolytes Ethylene carbonate & its derivatives as solvent Lithium hexafluorophosphate LiPF 6 as salt reaction with water gives HF Hardly any alternatives a strong solid electrolyte interphase (SEI) is needed on the graphite surface to prevent electrolyte decomposition Lithium polymer batteries can use polymer electrolytes

12 What should be better? Safety Lithium plating CoO 2 collapse Thermal runaway SEI layer destruction Price Cobalt Electrolyte Calendar life SEI layer destruction Environmental impact Cobalt

13 Positive electrodes (cathodes) Mixed oxides LiNi 1-x-y Co x M y O 2 Cobalt oxide like materials, about 3.7V NMC (LiNi 1/3 Mn 1/3 Co 1/3 O 2 ) less expensive & less dangerous NCA (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) higher capacity, dangerous Mn and Al do not react, but prevent overcharge LMO = Manganese oxide = LiMn 2 O 4 three-dimensional spinel structure, 3.8V cheap, environmentally friendly less dangerous Mn(IV) -> (III) at discharge 2Mn(III) -> Mn(II) + Mn(IV) soluble Mn 2+ destroys SEI layer on graphite

14 Positive electrodes (cathodes) LFP = Iron phosphate = LiFePO 4 three-dimensional olivine structure, 3.2V can be fully charged to almost Li 0.0 FePO 4 extremely stable, negligible lattice changes fast charge and discharge, Fe(III) -> Fe(II) at discharge natural product lower energy density low conductivity

15 Wrong positive electrode? Boeing dreamliner 2013

16 Negative electrodes (anodes) LTO = Titanate Li 4 Ti 5 O 12 extremely stable fast charge and discharge inside the electrolyte stability window, no SEI needed cheap when combined with Mn 2 O 4 low voltage, about 2V with CoO 2» (promising for hybrid use?) Tin Li 4.4 Sn alloy, not intercalating material for 7g of Li the electrode theoretically needs 27g of Sn extremely unstable due to volume change

17 Electrode material summary Positive electrodes LCO traditional, expensive, unsafe NMC cheaper, safer NCA cheaper, highest energy LMO very cheap & safe, short lifetime LFP cheaper, very safe, lower energy Negative electrodes Graphite traditional, unsafe Titanate very safe, very low energy Tin & silicon high energy, very short lifetime

18 Materials for electric cars NMC(+LMO) /graphite Most electric vehicles NCA/graphite Tesla, small cells LFP/graphite Fisker Karma NMC/titanate? Mitsubishi MiEV

19 Future materials Lithium-sulfur Lithium metal Sulfur is cheap After my retirement Lithium-air Oxygen is in the air Low mass Pure science fiction