Operation Lithium–air battery

1 operation

1.1 anode
1.2 cathode , electrolyte

1.2.1 acidic electrolyte
1.2.2 alkaline aqueous electrolyte

operation

schematic of lithium-air battery charge , discharge cycles

although details vary battery design, in general, lithium ions move between anode , cathode sides across electrolyte. under discharge, electrons follow external circuit electric work , lithium ions migrate across electrolyte. during charge (when external potential becomes greater standard potential discharge reaction), lithium metal plates onto anode, freeing o

2 @ cathode. both non-aqueous(mccloskey, burke et al. 2015) (with li2o2 or lio2 discharge products) , aqueous (lioh discharge product) li-o2 batteries have been considered (balaish, kraytsberg, et al. 2014, imanishi , yamamoto 2014). aqueous battery requires protective layer on negative electrode keep li metal reacting water.

schematic of artificial vs. spontaneous electrolyte interface


anode

lithium metal typical anode choice. @ anode, electrochemical potential forces lithium metal give off electrons via oxidation (without involving cathodic oxygen). half-reaction is:

li ↔ li + e

lithium has high specific capacity (3840 mah/g) compared other metal-air battery materials (820 mah/g zinc, 2965 mah/g aluminium). several issues affect such cells.

upon charging/discharging in aprotic cells, layers of lithium salts precipitate onto anode, covering , creating barrier between lithium , electrolyte. barrier prevents corrosion inhibits reaction kinetics between anode , electrolyte. chemical change of solid-electrolyte interface (sei) results in varying chemical composition across surface, causing current vary point point. uneven current distribution furthers branching dendrite growth , typically leads short circuit between anode , cathode.

in aqueous cells problems @ sei stem high reactivity of lithium metal water.

several approaches have been taken overcome problems @ sei:

formation of li-ion protective layer using di- , triblock copolymer electrolytes. according seeo, inc., such electrolytes (e.g., polystyrene high li-ion conductivity of soft polymer segment, such poly(ethylene oxide (peo) , li-salt mixture) ) combine mechanical stability of hard polymer segment high ionic conductivity of soft polymer–lithium- salt mixture. hardness inhibits dendrite shorts via mechanical blocking.
li-ion conducting glass or glass-ceramic materials (generally) readily reduced lithium metal, , therefore thin film of stable lithium conducting material, such li

3p or li

3n, can inserted between ceramic , metal. ceramic-based sei inhibits formation of dendrites , protects lithium metal atmospheric contamination.

cathode , electrolyte

at cathode during charge, oxygen donates electrons lithium via reduction. mesoporous carbon has been used cathode substrate metal catalysts enhance reduction kinetics , increase cathode s specific capacity. manganese, cobalt, ruthenium, platinum, silver, or mixture of cobalt , manganese being considered metal catalysts. under circumstances manganese-catalyzed cathodes performed best, specific capacity of 3137 ma·h/g carbon , cobalt-catalyzed cathodes performed second best, specific capacity of 2414 ma·h/g carbon. based on first pore-scale modeling of lithium-air batteries, micro-structure of cathode affects battery capacity in both non-pore-blocking , pore-blocking regimes.

li-air cell performance limited efficiency of reaction @ cathode because of voltage drop occurs there. multiple battery chemistries have been assessed, distinguished electrolytes. discussion focuses on aprotic , aqueous electrolytes solid-state electrochemistry poorly understood.

in cell aprotic electrolyte lithium oxides produced through reduction @ cathode:

li + e +o

2 + * → lio

2*
li + e +lio

2* →li

2o

2*

where * denotes surface site on li

2o

2 growth proceeds, neutral li vacancy in li

2o

2 surface.

lithium oxides insoluble in aprotic electrolytes, leads cathode clogging.

in cell aqueous electrolyte reduction @ cathode can produce lithium hydroxide:

acidic electrolyte

2li + ½ o

2 + 2h → 2li+ h

2o

a conjugate base involved in reaction. theoretical maximal li-air cell specific energy , li-air cell energy density 1400 w·h/kg , 1680 w·h/l, respectively.

alkaline aqueous electrolyte

2li + ½ o

2 + h

2o → 2lioh

water molecules involved in redox reactions @ air cathode. theoretical maximal li-air cell specific energy , li-air cell energy density 1300 w·h/kg , 1520 w·h/l, respectively.

the development of new cathode materials must account accommodation of substantial amounts of lio

2, li

2o

2 and/or lioh without causing cathode pores block , employ suitable catalysts make electrochemical reactions energetically practical.

dual pore system materials offer promising energy capacity.






the first pore system serves oxidation product store.
the second pore system serves oxygen transport.








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^ charles p. andersen, han hu, gang qiu, vibha kalra, , ying sun, pore-scale transport resolved model incorporating cathode microstructure , peroxide growth in lithium-air batteries , j. electrochem. soc., 162, (2015) a1135-a1145
^ cite error: named reference read2002 invoked never defined (see page).
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