combining li-excess and reversible oxygen charge transfer...

Combining Li-Excess and Reversible Oxygen Charge Transfer to Achieve High Capacity Cathodes

Alexander Urban, Jinhyuk Lee, Dong-Hwa Seo,

Xin Li, Aziz Abdellahi, and Gerbrand Ceder

Department of Materials Science and Engineering,

University of California, Berkeley.

[email protected]

Phoenix, AZ, April 20, 2017

Download these slides at http://ceder.berkeley.edu

Towards cathode materials with greater energy density

Apr. 20, 2017 Alex Urban - MRS Spring Meeting 2

Amount of electrons (= Li) per mass or volume that can utilized

Voltage

Potential difference between electrodes.

Capacity

Cathode material (positive electrode) is the bottleneck for capacity & voltage in LIBs.

Capacity × Voltage = Energy Density

Highest energy density cathodes are layered, but further improvement hard with layered structure


O3-type layered LiCoO2-structure

O TM

Li

LCO (Co) NCA (Ni, Co, Al) NCM (Ni, Co, Mn)

Limited chemistry: Co, Ni, Mn, Al (no TM migration)

Cannot utilize entire Li content

Limited capacity: 140-200 mAh/g

Need greater capacity for higher energy density


Data from: Nitta et al., Materials Today 18 (2015) 252-264.

Greater specific capacities

needed

Energy Density (Wh/kg)

Cation-Disordered Cathode Materials for Li-Ion Batteries



layered O3

disordered rocksalt

J. Lee, A. Urban, X. Li, D. Su, G. Hautier, G. Ceder, Science 343 (2014) 519-522.

Li1.211Mo0.467Cr0.3O2 (LMCO) forms in layered structure but becomes cation disordered when cycled

well-separated Li and TM layers

intense cation mixing

Cation-disordered LMCO has a remarkable capacity


1 Li per LiMO2


~1 Li atom per LiMO2 formula unit can be reversibly cycled

LiCoO2

Fast (low-barrier) 0-TM channel

Cation-disorder creates fast 0-TM diffusion channels that do not exist in stoichiometric layered materials


0-TM

1+

1+

2-TM

3+

3+

1-TM

1+

3+

? ?

Cation disordered

Layered

Excess Li needed to increase 0-TM channel concentration


The 0-TM channel concentration is just 6% in the stoichiometric LiMO2

Small concentration of 0-TM channels

0-TM channels =

Locally Li-rich environment


Layered

Disordered

Percolation threshold

A. Urban, J. Lee, and G. Ceder, Adv. Energy Mater. 4 (2014) 1400478.

One Li 0-TM cyclable at

~25 % Li excess

Li1.211Mo0.467Cr0.3O2

Around 10% Li excess enables 0-TM percolation in cation disordered structures

0-TM

Impact on Li-ion battery cathode research 1991: Li3V2O5 = Li1.2V0.8O2

C. Delmas, S. Brèthes and M. Ménétrier ω-LixV2O5, J. Power Sources 34 (1991) 113-118.

1998: LiMO2 (M=Ti, Mn, Fe, Co, Ni) by mechanochemical synthesis (ball-milling)

M. Obrovac, O. Mao, and J. Dahn, Solid State Ionics 112 (1998) 9-19.

2014: Li1.211Mo0.467Cr0.3O2

J. Lee, A. Urban, X. Li, D. Su, G. Hautier, and G. Ceder, Science 343 (2014) 519-522.


2015: Li2VO2F = Li1.333V0.666O1.333F0.666

R. Chen, S. Ren, M. Knapp, D. Wang, R. Witter, M. Fichtner, and H. Hahn, Adv. Energy Mater. 5 (2015) 1401814.

2015: Li1.3NbxM0.7-xO2 (M = Mn, Fe, Co, Ni)

N. Yabuuchi, M. Takeuchi, M. Nakayama, H. Shiiba, M. Ogawa, K. Nakayama, T. Ohta, D. Endo, T. Ozaki, T. Inamasu, K.

Sato, and S. Komaba, Proc. Natl. Acad. Sci. USA 112 (2015) 7650–7655.

2015: Li1.25Nb0.25Mn0.5O2

R. Wang, X. Li, L. Liu, J. Lee, D.-H. Seo, S.-H. Bo, A. Urban, G. Ceder, Electrochem. Commun. 60 (2015) 70–73.

2015: Li1.2Ni0.333Ti0.333Mo0.133O2

J. Lee, D.-H. Seo, M. Balasubramanian, N. Twu, X. Li and G. Ceder, Energy Environ. Sci. 8 (2015) 3255–3265.

2015: Li1+xTi2xFe1-3xO2

S. L. Glazier, J. Li, J. Zhou, T. Bond and J. R. Dahn, Chem. Mater. 27 (2015) 7751–7756.

2016: Li1.333Ni0.333Mo0.333O2

N. Yabuuchi, Y. Tahara, S. Komaba, S. Kitada and Y. Kajiya, Chem. Mater. 28 (2016) 416-419.

2016: Li1.3Nb0.3V0.4O2

N. Yabuuchi, M. Takeuchi, S. Komaba, S. Ichikawa, T. Ozaki, and T. Inamasu, Chem. Commun. 52 (2016) 2051-2054.

The new materials have high energy densities


LCO, NMC, NCA data from: Nitta et al., Materials Today 18 (2015) 252-264.


The chemical space for disordered cathodes is much larger than for layered materials


Abundance data from: www.webelements.com (3/2017)

A new opportunity space for Co-free cathodes

Cation disorder is beneficial

Cation mixing does not affect practical capacity for compositions with more than 15% Li excess

Increased structural stability when delithiated enables very high capacities

Much larger chemical space


A. Urban, J. Lee, and G. Ceder, Adv. Energy Mater. 4 (2014) 1400478.


Capacity

Understanding the effect of cation disorder


Understood conditions for high reversible capacities in DO-LiTMO2

Voltage

How does cation disorder affect the voltage?

Can disordered materials achieve high voltages?


LCO, NMC, NCA data from: Nitta et al., Materials Today 18 (2015) 252-264.

Higher voltage desirable


Cation disorder can raise or reduce the voltage


A. Abdellahi†, A. Urban†, S. Dacek, and G. Ceder, Chem. Mater. 28 (2016) 5659-3665.

Cation disorder does not necessarily lead to low voltages

Slope of voltage profiles depends on TM species


Vo

ltag

e (

V)

A. Abdellahi, A. Urban, S. Dacek, and G. Ceder, Chem. Mater. 28 (2016) 5373-5383.

Small slope for High-V TMs

Extra capacity beyond TM redox: oxygen redox enables very high capacity Li-excess cathodes


J. Lee, G. Ceder et al., Energy Environ. Sci. 8 (2015) 3255–3265.

N. Yabuuchi et al., PNAS 112 (2015) 7650.

R. Wang, G. Ceder et al., Electrochem. Commun. 60 (2015) 70–73.

First observed in layered Li-excess materials

Very common in cation disordered cathodes

Li1.2Ni1/3Ti1/3Mo2/15O2

O redox Mn redox

Clear change of oxygen K edge from oxygen redox


R. Wang, G. Ceder et al., Electrochem. Commun. 60 (2015) 70–73.

Relationship of cation disorder and oxygen redox


• What is the origin of oxygen redox?

• When does oxygen redox provide extra capacity beyond TM redox?

• Are cation-disordered materials more likely to exhibit O redox?

Origin of Oxygen Redox Activity


Conventional view: TM redox originates from antibonding M-O state


M orbital

O orbital

bonding “O ” state

antibonding “M ” state

e- Energy

regular redox state

M orbital

O orbital

bonding “O ” state

Contribution from oxygen 2p

regular redox state

e-

TM redox also exhibits some O contribution but that does not affect the capacity


Energy

Ceder et al., Nature 392 (1998) 694.

Extra capacity = utilize electrons from bonding states

Strong M-O covalency impedes oxygen redox


Energy

M orbital

O orbital

M orbital

O orbital

More Covalent Less Covalent

Bonding state lowered Electron is stabilized

Stoichiometric layered materials possess only hybridized (covalent) oxygen states


three Li-O-M e.g., stoichiometric layered Li-M oxides

M b

and

s O

ban

ds

LiMO2

Li-O-M

t1u*

a1g*

eg*

t2g

t1ub

E

egb

a1gb

DH. Seo†, J. Lee†, A. Urban, R. Malik, SY. Kang, and G. Ceder, Nat. Chem. 8 (2016) 692-697.

Lithium excess/cation disorder creates Li-O-Li configurations with unhybridized O states


one Li-O-Li, two Li-O-M e.g., Li-excess layered/cation-disordered

Li-M oxides

M b

and

s O

ban

ds

e.g., Li(Li1/3M2/3)O2

Li-O-Li

Li-O-Li

t1u*

a1g*

eg*

t2g

t1ub

E

egb

a1gb


Lithium excess/cation disorder creates Li-O-Li configurations with unhybridized O states



M b

and

s O

ban

ds

e.g., Li(Li1/3M2/3)O2

Li-O-Li

t1u*

a1g*

eg*

t2g

t1ub

E

egb

a1gb

M orbital

O orbital

bonding O state

anti-bonding M state

unhybridized state (Li-O-Li)

Accurate first-principles electron densities confirm the Li-O-Li mechanism



4 Li and 2 Ni 3 Li and 3 Ni 2 Li and 4 Ni

Electron localized along Li-O-Li configuration

1 e- per LiNiO2

Yellow iso-surface: electron density

The labile electron along the Li-O-Li configuration becomes redox accessible. Same mechanism for: Li(Ni,Mn)O2, Li(Ru,Sn)O2, Li(Ni,Ti,Mo)O2, Li(Mn,Nb)O2

Cation disorder & Li excess promote oxygen redox participation by creating Li-O-Li


Li

M M M

Li Li

O

Stoichiometric layered Li-M oxides (LiMO2)

Li Li Li

M M M

O

Li

Li

Li Li

M M

O

Li-excess layered Li-M oxides (Li1.2M0.8O2)

Li Li

Li Li

Li

Li

Li Li M

M M

O O

Li

Li

Li Li

M M

O

Li Li

Li

M

M M

O

Li Li Li

Li Li M

M M M M M M

O O

Li-excess cation-disordered Li-M oxides (Li1.2M0.8O2)

Li

Statistically, at 15% Li excess every O atom in a cation disordered structure is part of an Li-O-Li bond


Probability of any O to be part of Li-O-Li

x in Li1+xM1-xO2

Explains high O redox activity in cation disordered cathodes

Summary


High capacity through cation disorder

• Cation disorder creates new type of fast 0-TM Li diffusion channel

• 15% Li excess enables 0-TM Li percolation

• Affects average voltage, voltage slope, and redox mechanism

Extra capacity from oxygen redox

• Oxygen redox originates from labile non-bonding oxygen states created by Li-O-Li configurations

• Increased O-M covalency does not result in extra capacity

• Li excess and cation disorder promote oxygen redox

Lee, Urban, Ceder et al., Science 343 (2014) 519-522.

Urban, Lee, Ceder, Adv. Energy Mater. 4 (2014) 1400478.

Abdellahi†, Urban†, Dacek, Ceder, Chem. Mater. 28 (2016) 5659-3665.

Abdellahi, Urban, Dacek, Ceder, Chem. Mater. 28 (2016) 5373-5383.

Seo†, Lee†, Urban, Ceder et al., Nat. Chem. 8 (2016) 692-697. Seo, Urban, Ceder, Phys. Rev. B 92 (2015) 115118.

Acknowledgments


Jinhyuk Lee Xin Li (now Harvard U)

Aziz Abdellahi (now at A123)

Gerd Ceder Dong-Hwa Seo

Ceder Group 2016

combining li-excess and reversible oxygen charge transfer...

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