I made some coin cells that metal oxide -coated MNMC622 was used as working electrode and Li chips as counter electrode. These coin cells charged and discharged for first time and their voltage was about 3.5 V. After EIS and CV tests, voltage lost to 2.9 V. After setting on battery tester, their voltage increase gradually and after 50 cycle, capacity had a serious decrease what cases can be reasons for this?
Dear Nasrin Azad ,
the reason(s) for 'this' has many different origins and explanations, but the main cause/origin starts from[1-4] the specs[3] of the (WE) cathode material (MNMC622).
So, what are
1) the original specifications (show a link/ref) of your WE (MNMC622), and
2) how did you prepare the (composite) WE in your NMC622 Li-half cell[5] ?
1. Lithium nickel manganese cobalt oxide https://www.sigmaaldrich.com/catalog/product/aldrich/761001?lang=en®ion=GR
2. Nmc622 Powder for Lithium Battery Cathode Materials https://gelonlib.en.made-in-china.com/product/obAJQURwOdpr/China-Nmc622-Powder-for-Lithium-Battery-Cathode-Materials.html
3. (Good specs, but with a high price, $239) Lithium Nickel Manganese Cobalt Oxide, LiNi0.6Mn0.2Co0.2O2 NMC 622 Cathode Powder, 500g https://www.msesupplies.com/products/lithium-nickel-manganese-cobalt-oxide-nmc622-cathode-powder?variant=7141237060
4. Lithium Nickel Manganese Cobalt Oxide (NMC) Tapes [Cathode Electrode Sheets] https://www.neicorporation.com/products/batteries/cathode-anode-tapes/lithium-nickel-manganese-cobalt-oxide-nmc-electrode-tapes/
5. ... The last voltage after first cycle that battery tester showed, was about 3.5V. But ...
https://www.researchgate.net/post/What_can_be_the_reason_between_two_successive_Nyquist_plot_after_the_first_charge-discharge_cycle_at_a_Li_ion_cell#view=5f2a84a64429eb6b9064b97c
I used industrial NMC622 from TOB. I made some coin cells from this material and everything was ok. But when I coated this by metal oxide, there was such these prombles? Is it possible for the separator to break down if it is in the globbox for a long time?
Dear Nasrin Azad ,
a) what is this metal oxide material, apart the cathode material (MNMC622) ?
b) Why did you coated the (WE) cathode material (MNMC622) by an (add-on) metal oxide ?
c) What is your separator[1] ?
1. Separators for Lithium-ion Batteries https://www.teijin.com/rd/technology/separator/
Dear Ioannis Samaras
Chromium oxide used for coating of NMC622 to decrease contact area of electrolyte and working electrode and improve cyclic performance.
Dear Nasrin Azad ,
the reason(s) for this[1] kind of voltage issues (and 'voltage loss'), is more than obvious, for such an R&D testing risk(s) of a very complicated, 'multi'-(double-) cathode, two-cathode-materials 'overloaded'-WE.
Also, a(ny) possible separator's[2] ageing[3] is, commonly, a minor issue, for your case.
1. Your initial question: 'What are the reasons for voltage loss in Li ion coin cells after EIS and CV tests? '
2. ' ... c) What is your separator[1] ? '
3. Characterisation and Topology-Based Design of Lithium Ion Battery Separators
https://www.research-collection.ethz.ch/bitstream/handle/20.500.11850/269609/Dissertation_noCV.pdf?sequence=3&isAllowed=y
Dear Ioannis Samaras
I used celgard 2300 as separator. I had fabricated my cells with different cathode material by using this separator without any problem and I obtained good results. But now, I don,t know what the problem is.
Dear Nasrin Azad ,
remake a new set of simple (NMC622, only) Li-half cells.
Also, make a new metallic "Li - Li" (symmetric) cell, and measure:
a) some[1] CV(s) in the V-range: -0.5V, +0.5V., and an
b) EIS in the f-range: 1mHz, 100kHz.
1. A proposal set of V-rates, for CV(s): 0.1mV/s, 1mV/s, 10mV/s.
Dear Ioannis Samaras
Thanks for your suggestion. Another question, charge and discharge tests were taken between 4.3-2.5V. Is it possible that the voltage of 2.5 V for the discharge process is the reason of capacity loss?
Dear Nasrin Azad,
increase the voltage of 2.5 V, towards 2.7 V, mostly for slow (Crates
Dear Ioannis Samaras
My method for coating and mass ratio were similar to the article of Article Improved electrochemical and thermal properties of nickel ri...
Dear Nasrin Azad ,
the old (wet) methods towards a thinner coating (of NMC622) have been improved[1-3].
1. Improved Capacity Retention of SiO2-Coated LiNi0.6 Mn0.2 Co0.2 O2 Cathode Material for Lithium-Ion Batteries https://www.researchgate.net/publication/335636687_Improved_Capacity_Retention_of_SiO2-Coated_LiNi06Mn02Co02O2_Cathode_Material_for_Lithium-Ion_Batteries
increase the voltage of 2.5 V, towards 2.7 V, mostly for slow (Crates