Cells can be opened in the glove box and the electrodes can be washed using the electrolyte solvent to remove the salts. It must be then dried inside the glove box, mounted on the instrument sample holder and can be transferred to the instrument using air tight sample transfer vessels that are available. 

The partially de-lithiated cathode materials are emphatically sensitive to the oxygen and/or water of the atmosphere. Try to study 1st (as Amruth Bhargav, above[1]) an entirely de-lithiated cathode material, considering they are less sensitive.

1.  The electrodes can be washed using the electrolyte solvent, however this step (remove the salts, etc.) is very challenging, and responsive for some modifications.

Thanks for your advice, Amruth Bhargav and Ioannis Samaras.

I want to know why the partially delithiated cathodes are sensitive to the oxygen/water in the atmosphere.

Is it because of the partially reduced TM (such as Ni in NCM) ions or any other reason?

Yes, it is, because of :

1) the partially reduced TM ions (sustain, implicitly, the intercalated electronic factor) AND another, more visible, and distinct, reason,

2) the intercalated (alkali) ions (as a 2nd, noticeable, factor).

Both factors confirm the mobility model of the two cars driving (off) in sync, together[1], from a common parking garage design. If one of the two cars is interrupted, then the other is blocked, also.  So, the mobility of (both the electronic and the alkali-ions, as two parallel) concerted cars, is very different in a

Full vs "Free"

parking garage (mobility model). In other words, the mobilities are very different, when, two cars are driving off, together, from their parallel parking structures, e.g. under the driving (off) force of the oxygen/water (in the atmosphere).

1.  LFP (LiFePO4) is a prototype as a (stable) cathode material model (for LIBs) of a full parking garage model, invariable in the atmosphere. Both, the electronic and the alkali-ions, (as two parallel) concerted cars, are interrupted, so the stoichiometric LFP is stable in the atmosphere. Off-stoichiometry LFP is NOT stable in the atmosphere.

There is a mistake in my last expression. The delithiated cathode corresponds to the oxidized TM ions, not reduced TM ions.

Maybe the reason is like this, the highly-oxidized Ni(4+) is easy to be reduced in the atmosphere, I supposed.

But I have not found references mentioned that yet.

Both "end" cases (the stoichiometric cathode materials) have very low e- (and Li+) conductivities. The "full"[1] parking garage model is valid in both "end" cases.

1.  The cases of the "Free" parking garage model is valid for the OFF-stoichiometry cathode materials, they are NOT stable in the atmosphere and they have high e- (and Li+) conductivities.

Dear Ioannis Samaras, you confused me.

the "parking garage model", you mentioned several times, has compact relation to the instability of delithiated cathode in the air?

And I want to know WHY they are unstable in the air?

You'd better give some references.

Thanks a lot.

The phase-separating electrode ( LiFePO4; LFP) vary widely[1], ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation).

1. A ref (search for more): Current-induced transition from particle-by-particle to concurrent intercalation in phase-separating battery electrodes     http://www.nature.com/nmat/journal/v13/n12/full/nmat4084.html?foxtrotcallback=true

WHY they are unstable in the air? Because electrochemical window for H2O is 1.23 V vs H+/H2 and 2.09-3.32 V vs Li+/Li.

Dear Ioannis Samaras, thanks for the Ref you provided.

The phase-separation occurs in LFP is induced by charge-discharge, whether the LFP particles are exposed in the air, because it still happens even when the electrode materials are in the sealed coin-cells.

So, I supposed that Ref can not explain the reasons of this instability.

Thanks for your reply, Sergii Kuksenko.

You mean that the delithiated materials (eg. NMC) can catalyse the decomposition of H2O in the air, producing H2 or O2?

NMC (especially delithiated) is strong oxidizer for water in air atmosphere.

Dear Xu Mingquan,

instability is, almost, the "same" old story (intercalation), from another angle of view. The "same" instability (process), that is used for work (in "intercalation batteries", LIBs), is an issue for your work.