Lithium Ion Battery (LIB)

Current generation PCs and mobile devices are powered by lithium ion batteries (LIB). In the near future, LIBs will be used extensively as a power source for Electric Vehicles (EV).

Rough outline for mechanism of LIB system

[Current]
Active material: Graphite
Theoretical capacity: 370 mAh/g

(Discharge)  (Charge)
C6 + Li+ + e- ⇔ C6Li

[Next generation]
Active material: Silicon (Si)
Theoretical capacity: 4300 mAh/g

LIB-img02.jpg

(Discharge )    (Charge)
Si + 4.4Li+ + 4.4e- ⇔ Li4.4Si

Si anode has potential more than decuple capability comparing with graphite anode.

Si anode technology is a highly anticipated development for LIB enhancement. Si anode technology will facilitate higher capacity and downsizing of the battery cell.


Difference between graphite and Silicon as anode

Graphite anode Silicon anode
Charge mode is intercalation system Charge mode is an alloy formation of Si-Li
LIB-img03.jpg LIB-img04.jpg
During charging, Li ions are inserted between layers of graphite. Currently, the graphite (anode) thickness does not change before/after a charging event.

WEA is good additive for SEI formation.
During charging, Li ions combine with Si to form an alloy of Si-Li, The Si-Li complex expands 4x under charge, while the Si anode shrinks to 1/4 its original size in the discharge state. Si anodes are damaged through the constant expansion and contraction.

The binder for Si is required a function to maintain the shape/size of Si anode.

FUJIFILM Wako develops CLPA in new binder for Si anode.


Additive for SEI formation

LIB-img05.jpg

Relatively low LUMO (WEA-series)

→ formation of SEI with low electricity consumption


Cyclic Voltamograms of Electrolytes with Novel Additives (WEA)

LIB-img06.jpg LIB-img07.jpg
LIB-img08.jpg Reduction potential
WEA-67 > WEA-14 > WEA-36
(1.6V)   (1.4V)   (1.2V)

LUMO energy
WEA-67 < WEA-14 < WEA-36
(1.44eV)  (2.40eV)  (2.50eV)

Performance of CLPA on Si and graphite composite electrode

LIB-img09.jpg

The detailed results are reported on following letter.

Reference

Komaba, S. et al.: Journal of The Electrochemical Society, 162 (12) A2245-A2249 (2015)

Author: H. Mizuta

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