Definitions and Conventions
Glossary
Electrode potential
Formally defined as the electromotive force (emf) of a galvanic cell comprising the electrode to be characterised and a reference electrode. Consequently, all electrode potentials must be stated versus the appropriate reference. By convention, standard electrode potentials are given relative to the standard hydrogen electrode (SHE). In lithium battery research, it is common to consider electrode potentials relative to a reference electrode comprising a lithium metal electrode immersed in a solution containing a lithium salt (Li/Li^{+}).
Negative electrode
In a rechargeable electrochemical cell, the negative electrode is the electrode with the lower electrode potential during normal operation, and functions as the anode (i.e., is oxidised) during discharge. The use of the term “negative electrode” avoids ambiguity when distinguishing electrodes as formally it is the anode only on discharge (and hence, when charging, becomes the cathode).
Positive electrode
In a rechargeable electrochemical cell, the positive electrode is the electrode with the higher electrode potential during normal operation, and functions as the cathode (i.e., is reduced) during discharge. The use of the term “positive electrode” avoids ambiguity when distinguishing electrodes as formally it is the cathode only on discharge (and hence, when charging, becomes the anode).
Transference number
In electrolytes, the transference number, $T_i$, is defined as the number of moles of species $i$ transferred by migration, per Faraday of charge (1 F = 96485 C). The sum of the transport numbers of all ionic species in an electrolyte is 1, but $T_i$ does not have any upper or lower bounds.
Transport number
In electrolytes, the transport number, $t_i$, is defined as the fraction of the ionic current carried by species $i$. The transport number must be between 0 and 1, and the sum of the transport numbers of all ionic species in an electrolyte is 1.
Terms
Symbol  Definition  Units  Notes 

$a_i$  Thermodynamic activity of species $i$  dimensionless  
$A$  Surface area  cm^{2}  
$c_i$  Concentration of species $i$  mol dm^{3}  
$C$  Capacitance  F  
$D_i$  Diffusion coefficient of species $i$  cm^{2} s^{1}  
$E$ 

V  
$\varepsilon$  Dielectric constant  dimensionless  
$f$  Frequency  Hz  
$F$  Faraday’s constant  C  $F$ = 96485 C 
$I$  Current  A  
$j$ 



$k$ 



$\mu_i$  Chemical potential of species $i$  kJ mol^{1}  
$Ne$  Newman number  dimensionless  See Transference number measurement 
$N_M$  MacMullin number  dimensionless  See MacMullin number measurement 
$\omega$  Angular frequency  rad s^{1}  
$Q$  Charge  C or Ah  1 Ah = 3600 C 
$Q_0$  Constant phase element parameter  S s^{n}  See Constant phase elements 
$R$ 



$\sigma_i$  Partial conductivity of species $i$  S cm^{1}  
$\sigma$ 



$t_i$  Transport number of species $i$  dimensionless  
$t$  time  s  
$T_i$  Transference number of species $i$  mol Faraday^{1}  
$T$  Temperature  K, or °C  
$\tau$  Time constant  s  
$\theta$  Phase angle  °  See Principles of EIS 
$\Delta V$  Potential difference  V or mV  
$z_i$  Charge number of species $i$  dimensionless  
$\pmb{Z}$  Electrical impedance  Ω  
$Z'$  Real part of the impedance  Ω  
$Z’'$  Imaginary part of the impedance  Ω 