Definitions and Conventions
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+).
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).
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).
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.
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.
|$a_i$||Thermodynamic activity of species $i$||dimensionless|
|$c_i$||Concentration of species $i$||mol dm-3|
|$D_i$||Diffusion coefficient of species $i$||cm2 s-1|
|$F$||Faraday’s constant||C||$F$ = 96485 C|
|$\mu_i$||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 sn||See Constant phase elements|
|$\sigma_i$||Partial conductivity of species $i$||S cm-1|
|$t_i$||Transport number of species $i$||dimensionless|
|$T_i$||Transference number of species $i$||mol Faraday-1|
|$T$||Temperature||K, or °C|
|$\theta$||Phase angle||°||See Principles of EIS|
|$\Delta V$||Potential difference||V or mV|
|$z_i$||Charge number of species $i$||dimensionless|
|$Z'$||Real part of the impedance||Ω|
|$Z’'$||Imaginary part of the impedance||Ω|