Lithium Ion Batteries


​​
Battery 101​​

Fossil-fuel energies create environmental concern due to emission of carbon dioxide and other greenhouse gases in the atmosphere. ​ If electric vehicles (EVs) replace the majority of gasoline powered transportation, batteries can significantly reduce detrimental gas emissions.

Li-ion batteries consists of lithium ions as charge carriers, anode (negative) and cathode (positive) electrodes, electrolyte, separator between anode and cathode and current collectors.  During charging / discharging the batteries, lithium ions shuffles between anode and cathode electrode.  

Significant improvement in the charge rate and discharge power of lithium-ion batteries is required for widespread adoption in demanding applications such as electric vehicles.   Key challenges are:

  • The volumetric expansion of the electrodes upon Li+ ion intercalation
  • The formation of solid electrolyte interface (SEI) due to interaction of electrodes with electrolyte species
  • The dissolution of active material into the electrolyte.   
Electrochemical Stiffness Change in Lithium Manganese Oxide

In situ strain and stress measurements were performed on composite electrodes to monitor potential-dependent stiffness changes in lithium manganese oxide (LMO). Lithium insertion and removal results in asynchronous strain and stress generation in the electrode.

Electrochemical stiffness changes were calculated by combining coordinated stress and strain measurements.  Changes in the electrochemical stiffness reveal that the underlying mechanisms governing stress and strain are intrinsically different.
   
The state of charge and phase transitions of the electrode govern strain generation in LMO during delithiation and lithiation.

Stress is governed by surface resistance against lithium removal from the electrode into the electrolyte during delithiation and repulsive interactions between already occupied Li+ ions and new inserted Li+ ions during lithiation.

Electrochemical stiffness provides a powerful tool for characterizing chemo-mechanical processes in different electrodes.
   
Ö. Ö.  Çapraz, K. L. Bassett, A. A. Gewirth and N. R. Sottos, Adv. Energy Mater. , 1601778, 2016, doi: 10.1002/aenm.201601778, link
   
Irreversible Deformations in Composite Graphite Electrodes

      
Reversible expansion/contraction of the composite electrodes was correlated with localized changes in graphite layer spacing associated with different graphite-lithium intercalation compounds.
    
Irreversible electrode deformation is correlated with deposition of electrolyte decomposition products on graphite particles during the formation and growth of the solid electrolyte interphase (SEI).
   
PVDF-based electrode experienced much larger irreversible volumetric expansions due to electrolyte decomposition, compared to CMC-based electrode. 

E. M.C. Jones, Ö. Ö.  Çapraz, S.R. White and N.R. Sottos, J. Electrochem. Soc., 163, 9, A1965-A1974,2016, doi: 10.1149/2.0751609jes, link
Strain Evolution in Li-Ion Cathode Electrode 
   
Irreversible strain evolution and surface resistance were highly sensitive to the electrochemical changes occurring during the first cycle and correlate with the removal of the native surface layer and the formation of cathode electrolyte interface layer on the electrode surface.

Chemo-mechanical degredation lead to simultanous reduction in capacity and strain evolution in the electrode. 

The in situ strain measurements provided new insight into the electrochemical-induced volumetric changes in LMO electrodes with progressing cycling and may provide guidance for materials-based strategies to reduce strain and capacity fade.

Ö. Ö.  Çapraz, S. Rajput, S. White, and N. Sottos, Experimental Mechanics, 2018, link
 
   
     
   
Controlling the Volumetric Expansions in the Cathode Electrodes via Surface Modification

A surface of the cathode electrode was modified with coating conductive thin layer.  
    
Volumetric expansion in the coated electrode was found to be significantly smaller than electrode without coating at faster scan rates.

High damage tolerance electrode materials can be fabricated by applying material based strategies to improve lifetime and performance of the batteries.

Ö. Ö.  Çapraz, S. Rajput, K.L. Bassett, A. Gewirth, S. White, and N. Sottos, The Society of Engineering Science, 54th Annual Technical  Meeting in Boston, 2017. Link  
(Manuscript is available upon request)
   
Direct Detection of Manganese Ions in Organic Electrolyte by UV-vis Spectroscopy
      
Dissolution of active material into electrolytes significantly contribute to performance degredation in Li-ion batteries.  However, dissolution mechanism is not well understood due to lack of highly-sensitive in situ experimental detections. 

New technique for directly measurement of the manganese ion (Mn2+) concentration in a typical Li-ion carbonate electrolyte was developed using 4-(2- pyridylazo) resorcinol (PAR) as a UV-vis probe.
   
Chelation between PAR and Mn2+ ion induces a characteristic absorption peak where the peak intensity corresponds to Mn2+ ion concentration in the electrolyte.

      
The in situ characterization of Mn dissolution in a customized battery cell is performed during cyclic voltammetry.
   
   
L. Zhao, E. Chenard, Ö. Ö.  Çapraz, N. Sottos and S. White , J. Electrochem. Soc. , 165 (2), A345-A348, 2018, Link doi: 10.1149/2.1111802jes