we are trying to use different new families of material for Li ion battery cathode, I want to know the clear differences that determine a material to be used as cathode or anode for Li ion battery . please help me in this regard.
Redox potential and the mechanism associated with it.
There are three mechanisms that I know of: intercalation, conversion, and alloying. Typical cathodes with high redox potential utilize intercalation. Ions are exchanged in and out of the material, and the ionic crystal structure remains relatively the same. Intercalation requires enough room in the host crystal to accept guest species. Also need to take note of the valence state of your transition metal species. For example if your ionic material contains Fe3+, then it can be reduced to Fe2+ and accept a Li ion if there is space. If your material is synthesized as Fe2+, then there must be something like Li+ that starts inside your crystal that can come out during the initial charge cycle.
Conversion and alloying usually occur at lower potentials, so mostly anodes utilize this mechanism. An example would be Li + SnO to Sn metal and Li2O as conversion, then Li+Sn to LiSn as alloying. Cu2+ to Cu(0) could be a candidate for conversion reaction in cathodes due to its relatively higher redox, but mixing conversion with intercalation is not very stable because the crystal drastically changes during the conversion reaction, which decreases cyclability.
The electrochemical potential of these redox sites are influenced by their surrounding environment, for example what its coordination is and what is its nearest and next nearest neighbors (i.e. Fe-O-P vs Fe-O-S). The crystal field will affect electrochemical potential, the same reason why Cr3+ makes ruby red but also makes emerald green.
Redox potential and the mechanism associated with it.
There are three mechanisms that I know of: intercalation, conversion, and alloying. Typical cathodes with high redox potential utilize intercalation. Ions are exchanged in and out of the material, and the ionic crystal structure remains relatively the same. Intercalation requires enough room in the host crystal to accept guest species. Also need to take note of the valence state of your transition metal species. For example if your ionic material contains Fe3+, then it can be reduced to Fe2+ and accept a Li ion if there is space. If your material is synthesized as Fe2+, then there must be something like Li+ that starts inside your crystal that can come out during the initial charge cycle.
Conversion and alloying usually occur at lower potentials, so mostly anodes utilize this mechanism. An example would be Li + SnO to Sn metal and Li2O as conversion, then Li+Sn to LiSn as alloying. Cu2+ to Cu(0) could be a candidate for conversion reaction in cathodes due to its relatively higher redox, but mixing conversion with intercalation is not very stable because the crystal drastically changes during the conversion reaction, which decreases cyclability.
The electrochemical potential of these redox sites are influenced by their surrounding environment, for example what its coordination is and what is its nearest and next nearest neighbors (i.e. Fe-O-P vs Fe-O-S). The crystal field will affect electrochemical potential, the same reason why Cr3+ makes ruby red but also makes emerald green.
Generally, the principal characteristics of a material that determine its use as Cathode material of Li ion battery are :
1. Nominal Capacity
2. Electrical conductivity.
3. High electrochemical potential.
4. The voltage stability.
5. Self Discharge.
6. Recharge Time.
7. Cost.
Regards
Redox potential, Conductivity, Electrochemical potential, Stability, Discharge Time, Availability and cost
In addition. Not simply conductivity.
Cathode material should have good ionic conductivity of potential-forming ion!
So, ionic conductivity of electrode material should be about same order as electronic one!
Thermal conductivy also has important role.
And yet, the requirements at the macro level (particles) have matching on micro level (crystal lattice). Therefore the requirements system becomes more complicated.
Besides the comments, it depends upon your goal that what specific characters/properties of battery you would like.
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