Basics of Battery Technology Tampere 2016-04-13 Kai Vuorilehto - - PowerPoint PPT Presentation

Basics of Battery Technology

Tampere 2016-04-13 Kai Vuorilehto

Adjunct professor, kai.vuorilehto@helsinki.fi Director R&D, kai.vuorilehto@eas-germany.de

Secondary batteries - chemistries

• Pb-PbO2
• NiOOH-Cd mostly forbidden
• NiOOH-MH
• Li-ion (C-CoO2)

Secondary batteries - energy

• Pb-PbO2

35 Wh/kg

• NiOOH-Cd

35 Wh/kg

• NiOOH-MH

75 Wh/kg

• Li-ion (C-CoO2)

150 Wh/kg

Wh/kg and W/kg

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

Principle of the lithium-ion battery

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"

Properties of lithium-ion batteries

• High energy density
• Rather high power density
• Long cycle life
• Good charge retention
• High energy efficiency

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%, Li0.5CoO2

• for 7g of Li the electrode has 189g of extra Li0.5CoO2
• collapses without lithium

– thermal runaway – positive potential at the upper end of the electrolyte stability window

Negative electrode (anode)

• Graphite LiC6

– 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 CoO2 – negative potential can cause lithium plating

• Li+ +e- -> Li(metal)

– negative potential is outside the electrolyte stability window

Electrolytes

• Ethylene carbonate & its derivatives as solvent
• Lithium hexafluorophosphate LiPF6 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

What should be better?

• Safety

– Lithium plating – CoO2 collapse – Thermal runaway – SEI layer destruction

• Price

– Cobalt – Electrolyte

• Calendar life

– SEI layer destruction

• Environmental impact

– Cobalt

Positive electrodes (cathodes)

• Mixed oxides LiNi1-x-yCoxMyO2

– Cobalt oxide like materials, about 3.7V – NMC (LiNi1/3Mn1/3Co1/3O2) less expensive & less dangerous – NCA (LiNi0.8Co0.15Al0.05O2) higher capacity, dangerous

• Mn and Al do not react, but prevent overcharge
• LMO = Manganese oxide = LiMn2O4

– three-dimensional spinel structure, 3.8V – cheap, environmentally friendly – less dangerous – Mn(IV) -> (III) at discharge – 2Mn(III) -> Mn(II) + Mn(IV)

• soluble Mn2+ destroys SEI layer on graphite

Positive electrodes (cathodes)

• LFP = Iron phosphate = LiFePO4

– three-dimensional olivine structure, 3.2V – can be fully charged to almost Li0.0FePO4 – extremely stable, negligible lattice changes – fast charge and discharge, Fe(III) -> Fe(II) at discharge – natural product – lower energy density – low conductivity

Wrong positive electrode?

Boeing dreamliner 2013

Negative electrodes (anodes)

• LTO = Titanate Li4Ti5O12

– extremely stable – fast charge and discharge – inside the electrolyte stability window, no SEI needed – cheap when combined with Mn2O4 – low voltage, about 2V with CoO2

» (promising for hybrid use?)

• Tin Li4.4Sn

– alloy, not intercalating material – for 7g of Li the electrode theoretically needs 27g of Sn – extremely unstable due to volume change

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

Materials for electric cars

• NMC(+LMO) /graphite

– Most electric vehicles

• NCA/graphite

– Tesla, small cells

• LFP/graphite

– Fisker Karma

• NMC/titanate?

– Mitsubishi MiEV

Future materials

• Lithium-sulfur

– Lithium metal – Sulfur is cheap – After my retirement

• Lithium-air

– Oxygen is in the air – Low mass – Pure science fiction