I think it is not a dissolution phenomenon, during the charge and discharge process, the structure change is very terrible, then the material will shell from your substrate. Of course, this problem can be solved if your paste of your material, carbon black and PVDF is good. So, this is also a technical challenge.

Thank You sir for your reply, but it happened after charging and discharging cycles. this phenomenon does not happen without charge discharge cycles. 

Dear Hari Raj,

say, please, after how many charging-discharging[1]  Number No of cycles did you notice the (cathode ! ) material "passing"  through(?) the separator[2] ?

How did you verify(?), please, that it is about the cathode material  "stored on Li metal anode side(reference electrode)" ?

1.   How fast.did you charging-discharging (C ?)   ? 

2.   What is the separator.?

Dear Ioannis Samaras Sir,

I opened many cells inside the glove box to check what is the problem, some of them after the first cycle and some of them after 5-10 cycles at C-rate 0.1C (1C=170 mA/g).

I saw some black material stored on and on the side of the Li metal foil by passing through the separator. my cathode material is carbon coated so I am assuming that it probably cathode material.  

Separator material is polyethylene. We are using cylindrical Teflon cell assembly with stainless steel connector for charge-discharge. 

For more information, I am attaching the pic of the opened cell after 5 cycles, this image showing black material deposited around the Li-metal foil (reference electrode). how can be materials deposited on Li-foil through the separator?

Please give me a solution for this.  

Thank You 

Dear Hari Raj[1],

an image showing the (other) side[2] of the Li-metal foil will be more useful.

Also, could you, please, make a new test with a unique cell[3], using, now, a double sheet of your separator (2 layers) ?

1.   Your note is a relevant safety issue (for such batteries) in power applications (EVs etc.) that appears, principally, after a big, deep charging-discharging, Number of cycles (No>>500).       a)http://batteryuniversity.com/index.php/learn/article/safety_concerns_with_li_ion      b)https://www.usatoday.com/story/tech/news/2016/09/02/samsung-battery-lithium-ion-fire-burning-explosion/89782856/

2.   The side view from the  "Li // separator".         BU-306: What is the Function of the Separator?   http://batteryuniversity.com/learn/article/bu_306_battery_separators

3.   Open it after 5-10 cycles,  under the same (charging-discharging testing) conditions.

Dear Ioannis Samaras Sir,

Thank You, sir for your kind help. I will try according to your suggestion and let you know what happened. 

Dear Hari Raj,

I agree with the suggestion from Dr. Ioannis Samaras.

I have additional suggestions for you. You should check the composition of the black part by XPS or EDS. If you can find the Fe of POx on Li surface, you can say that is dissolution species from the cathode. From my experience, sometimes the contamination (ex: water) from the electrolyte and/or electrode also cause the color change on Li metal. 

In the case of cathode dissolution, it is due to dissolution of Fe2+ from the cathode and deposit onto Li metal anode, [1-2] especially in the solution containing acidic species (ex. HF) and high-temperature operation. To suppress the dissolution of Fe2+, I suggest you add LiBOB as electrolyte additive for forming stable SEI, that could reduced metal dissolution.

Good luck.

N.D.Thien

[1] http://www.sciencedirect.com/science/article/pii/S1388248105001177

[2] "6.7 On the Surface Chemistry of LiMPO4 -Type Cathodes" from T.R. Jow, K. Xu, O. Borodin, M. Ue, “Electrolytes for Lithium Ion Batteries,” 2014. doi:10.1007/978-1-4939-0302-3. 

Dear Nguyen sir,

Thank You for your ans. I have one more quarry... We have purchased this electrolyte 7-8 years back, can the problem be inside the electrolyte?? for how many years electrolyte remains in good condition?

Dear Hari Raj [Q: ... can the problem be inside the electrolyte?? ...],

this is a very complex task. 

However, you might be interested for a simple (initial) test, convenient for your case. After cutting a Li metal, in your GB, dive it (the fresh cut Li metal), inside your electrolyte. You have to supervise it; also, you might be interested to note (or take some photos[1]) the time[3], when the metallic shine is about to be roughly pale, or the metallic shine is to be "lost".

1.  If you take photos, then choose a reflection[2] angle, in reference to a spot light source, e.g. try to use the (fresh cut Li) metal as a quasi mirror(-like) surface. Take one photo per 5 minutes, as a useful (invariable) rate.

2.  Reflection      https://en.wikipedia.org/wiki/Reflection_(physics).

3.  As total supervision time extent-sweep it, for at least 30 minutes. Take a photo, after a day, also.

Dear Hari Raj,

Definitely, you should buy new electrolyte. The electrolyte changes with storage time. Electrolyte components (ex LiPF6) are decomposed, especially, in the presence of contamination (ex.H2O). The stability of electrolyte depends on electrolyte composition and how you store it. In our case, we usually replace the new electrolyte every 6-12 months from the day that electrolyte bottles were opened.