Batteries 101

Jordi Cabana Assistant Professor in Chemistry

jcabana@uic.edu Office: 4146SES, Tel: 312-355-4309

LAS493, 11/11/14

What is a battery? The Daniell cell

All  ba&eries  are  made  of: -­‐‑   Two  electrodes:  compounds  or  elements  at  different  potentials  (e.g.,  standard  reduction  potentials   in   solution).   They   must   uptake/release  ions  and  electrons. -­‐‑    An   electrolyte:   can   only   conduct   ions,  electronic  insulator. Electrons  flow  through  the  external  circuit.

Rechargeable batteries are based on redox reactions

Palacin, Chem. Soc. Rev. 38 (2009), 2565.

1) Anode  –  Oxidation 2) Cathode  –  Reduction Semantic   challenge:   strictly   speaking,   in   a   rechargeable   ba&ery,   the   anode/cathode   change   on  discharge/charge.  In  reality,  you  will  often  see  cathode  being  used  for  the  “positive  electrode”.

Batteries come in various flavors (I)

“Classical”: Two  solid  electrodes Liquid  electrolyte

Br2/HBr

H2

HBr

Charge

Discharge

H2↔ 2H+ +  2eH2↔ 2H+ +  2eBr2 +  2H+ +  2e  ↔ 2HBrBr2 +  2H+ +  2e  ↔ 2HBr

Air-­‐‑based: One  solid  electrode One  solid/gas  electrode   Liquid  electrolyte

Flow  cell: Two   solid   electrodes:   only  provide  electrons. Liquid   electrolyte:   also  carries   active   compounds.  ⇒  catholyte/anolyte.

Can   also   be   made   with   solid   electrolytes  (polymers,   ceramics):  may   require  operating  at  high  T,  molten  electrodes.

Combinations are possible (e.g. solid electrode vs. catholyte)

Girishkumar et al., J. Phys. Chem. Lett. 1 (2010), 2193.

Source:  A.  Weber

Q=nF

What metrics matter? 1)  Rechargeable   (secondary)   vs.   non-­‐‑rechargeable   (primary):   defined   by   the   extent   of  

undesired  and   irreversible  electrochemical   reactions  occur  during  discharge   (spontaneous  process).  E.g.:  Zn/MnO2  (primary)  vs.  Li-­‐‑ion  (secondary).

2)  Energy  storage:  Back  to  the  Daniell  cell… 1)  Anode  (oxidation):  Zn(s)  →  Zn2+

(aq)+  2e-­‐‑   E0  =  −0.76  V   2)  Cathode  (reduction):  Cu2+

(aq)  +  2e-­‐‑  →    Cu(s)     E0  =  +0.34  V ΔE=  1.1  V

•  Power  storage:  ability  of  the  cell  to  deliver  its  energy  fast  (days  to…  milliseconds?).

•  Life  can  be  defined  many  ways: •  Calendar  life:  time  before  a  ba&ery  dies,  whether  it  is  used  or  not. •  Shelf   life:   time   before   a   ba&ery   dies   if   it   is   being   stored   unused   (related   to   self-­‐‑

discharge). •  Cycle  life:  number  of  times  a  ba&ery  can  be  recharged  before  it  dies.

ΔG=QE

P=IE

5)  Anyone  said  Safety  and  Cost?  Simple:  no  explosions,  cheaper  than  gasoline!

Free Energy (Work)

How about those units?

E=QV=  Wh/kg  or  Wh/l In  SI:  1  Wh  =  1  VAh 1  mAh  =  3.6  C

P=IV=  W/kg  or  W/l

You  will  hear   a   lot   about   a   certain   electrode  material  delivering  x  mAh/g   (=Specific  capacity)

How do these units translate? The case of grid storage

Yang et al., Chem. Rev. 111 (2011), 3577.

How do these units translate? The case of electric vehicles

Source:  V.  Srinivasan

In plain numbers…

http://www.electricdrive.org/index.php?ht=d/sp/i/20952/pid/20952

Cash is king…

Costco  was  here on  11/10/14

Battery technology charges ahead, McKinsey&Co, July 2012 http://www.mckinsey.com/insights/energy_resources_materials/battery_technology_charges_ahead#

…and we still have ways to go! Battery technology charges ahead, McKinsey&Co, July 2012 http://www.mckinsey.com/insights/energy_resources_materials/battery_technology_charges_ahead#

“Developments  in  ba&ery  manufacturing  and  component  pricing  will  drive  the  majority  of  the  savings  from  2011  to  2015,  while  advances  in  capacity-­‐‑boosting  ba=ery  technologies  will  drive  the  majority  of  reductions  from  2016  to  2020  and  beyond”

How do we bend that curve downwards?

Goodenough and Kim, Chem. Mater. 22 (2010), 593. Possibility   1:   Engineer   the   device   to   minimize  “packaging”.  “Packaging”  needed  because: •   Ba&eries  need  intensive  management. •   Ba&eries  need  safety  features. •   We  cannot  cycle  electrodes  that  are  more  than  1 0 0   µ m   t h i c k   ⇒   l o w e r   a c t i v e  material/”packaging”  ratio.

Possibility   2:   Find   electrodes   and   electrolytes  that  enable  higher  Q  or  E  (higher  ΔG): •   We  have  a  lot  of  possibilities…  because  none  is  good  enough!

Let’s start with the Periodic Table

Remember

ΔG=QE

To  maximize  Q,  you  pick  the  lightest  (and  cheapest!)  elements  you  can

Noble  gases  are  out  because  they  are  essentially  not  redox  active

To  maximize  E,  pick  elements  that  have  redox  activity  a  very  different  potentials

1) Anode  (oxidation):  Li(s)  →  Li+  +  e-­‐‑   E0  =  −3.04  V   2) Cathode  (reduction):  F2(g)  +  2e-­‐‑  →    2F-­‐‑     E0  =  +2.87  V The  Li/F2  ba&ery:  at  5.91  V,  highest  energy  density  of  all,  but…

Li: F2:

Other less dangerous options… L i q u i d  Electrodes

S o l i d  Electrodes

Water Electrolytes

Solid Electrolytes

Organic Electrolytes

Note  the  progression  in  cell  voltage  from  water  to  organic…

Palacin, Chem. Soc. Rev. 38 (2009), 2565.

Looping back…

…we  conclude  that  electrolyte  choice  is  associated  with  energy  density.  Why?

Electrolyte determines achievable cell voltage

Compare the potential window of these organic solvents

•  We  need  the  electrolyte  to  be  stable  to  reduction  at  the  anode  and  oxidation  at  the  cathode,  i.e.,  inert  in  the  potential  window  defined  by  electrode  reactions.

•  To  maximize  E,  H2O  is  really  not  the  best  choice. •  Note   that   we   do   not   have   an   electrolyte   that   will   be   stable   on   both   sides   of   the   Li/F2  

ba&ery,  even  if  we  were  so  crazy  as  to  try…

Etacheri et al., Energy Environ. Sci. 4 (2011), 3243.

But, ultimately, electrodes define

both Q and E Let’s focus on them, using Li-ion batteries as

example

Raising Q is the most popular way to increase electrical energy

Q depends on the ability of a compound to accept-release ions (crystal chemistry) and electrons (redox chemistry). Do you know the stable oxidation states for transition metals? •  LiCoIIIO2 → CoIVO2 280 mAh/g (but we can only go halfway because CoO2 is very unstable)

•  Li + 6C → LiC6 372 mAh/g (these two are in your cellphones)

•  4Li + Si → Li4Si 3200 mAh/g

But putting a lot of Li comes at a price

+xLi Before After

4Li + Sn → Li4Sn 980 mAh/g (Compare with commercial graphite, at 370 mAh/g)

Xu et al., Nano Lett. 13 (2013), 1800.

This is how a battery looks like

Liu et al., Energy Environ. Sci. 4 (2011), 885.

Source:  Q.  Horn  (Exponent)

Source:  K.  A.  Persson

Batteries are a problem of multiple length scales

The atomic scale

Ni

Li O

Mn

0 5 10 15 20 2520

30

40

50

60

70

80

90

100

900C (air/1hr) 900C (air/1hr) + 500C (air/12hr) 900C (air/1hr) + 500C (O2/12hr) 900C (air/1hr) + 900C (air/12hr) 900C (O2/1hr) 900C (O2/1hr) + 500C (O2/12hr) 900C (O2/1hr) + 670C (O2/12hr)

900C (air/1hr) + 700C (O2/12hr) 900C (O2/1hr) + 700C (O2/12hr) 900C (air/1hr) + 700C (air/12hr) 900C (O2/1hr) + 730C (O2/12hr)

Nor

mal

ized

Dis

char

ge C

apac

ity (%

)

Cycle (#)

C/10

C/5

C/2

C

2C

5C

C/10

Disordered

Ordered

LiNi0.5Mn1.5O4

Atomic  scale  arrangement  of  ions  in  a  la&ice  can  affect  performance  in  an  electrode.

We have gazillions of tiny grains in a real electrode!

Contact with current collector (Ti3+-rich)

Cross section (Ti4+-rich)

Pristine 10%  DOD

25%  DOD

50%  DOD

Mechanism: Surface

+ Bottom-up

Kim et al., Adv. Funct. Mater. 23 (2013), 1214.

Li4Ti5O12

Electrode construction makes a huge difference

An   electrode   is   a   complex   structure   of:   1)   active   material,   2)   conductive   additive,   3)   polymer  binder,  4)  SPACE. Process  of  assembly  of  the  same  components  leads  to  dramatic  performance  differences.

Source:  G.  Liu  (LBNL)

Electrode-electrolyte interfaces

The  electrode   surface  may  become   to  oxidizing  or   reducing   for   the   electrolyte  ⇒   side   reactions  that  passivate  electrode  and/or  consume  electrolyte.

LNMO=LiNi0.5Mn1.5O4

Norberg et al., Electrochem. Commun. 34 (2013), 29.

Changing one electrode dramatically affects performance

LNMO=LiNi0.5Mn1.5O4

Pairing   a   given   positive   electrode  with   two   different   negative   electrodes   can   lead   to   cells  with  completely  different  behavior.

Source:  V.  S.  Ba=aglia  (LBNL)

So we work hard at visualizing how chemical reactions happen at multiple scales

Picture

Picture

C1

C/20

Ni-Metal Oxide NiOScalebar 0.2mmPicture

Halfway reduced:

Oxidized to 2V:

operando  XAS/XRD

3D  Chemical  tomography

TXM-­‐‑XANES

µ-­‐‑XAS

Atomic Particle Electrode Meirer et al., J. Synch. Rad. 18 (2011), 773.

Boesenberg et al., Sci. Rep. In press.

Conclusions •  Conceptually, batteries are simple. •  In reality, batteries are extremely complicated. Processes

that happen at very length scales can act as limiting. Need a large team to look at all of them! JCESR!

•  Bending the cost curve is challenging in both vehicle and grid applications.

•  In grid applications, the figure of merit requirements are not clear because specific applications vary (UPS-like to GW scale).

•  There are solutions from engineering, chemistry, physics… but it all boils down to two electrodes and an electrolyte!