VACUUM CARBON TECHNOLOGIES

Next step in the development of new battery manufacturing technology.

Development of high performance lithium‐ion (Li‐ion) cells is a topic receiving significant attention in research today.

On the electrodes of the lithium-ion batteries flow two types of processes: reversible and irreversible.

Reversible – current-forming processes of the introduction and extraction of lithium – determine the useful work of the battery.

Irreversible lead to irreversible expenditure of electricity and can carry both positive and negative functions. Irreversible processes in lithium-ion batteries – electrolyte reduction on the negative electrode and electrolyte oxidation on the positive one.

As a result of these irreversible processes, a solid electrolyte film is formed on the surface of the electrodes, which is commonly known as SEI (Solid Electrolyte Interphase).

Irreversible capacity is mainly due to the formation of the surface layer on the carbon material of the negative electrode.

Irreversible capacity loss (ICL) is (20 – 80) % of the pledged power. 20% corresponds to traditional anodes, 80% – new anode materials (metallic lithium or silicon).

Eliminating ICL is crucial before the fabrication of practical Li‐ion cells with conventional cathodes.

There are numerous methods for eliminating ICL such as pre‐treating the electrode, usage of stabilized Li metal powder, chemical and electrochemical lithiation, sacrificial salts for both anode and cathode, etc.

A common disadvantage of the above methods is that they only partially reduce irreversible capacity and limit its formation to the first charge cycle.

On a negative electrode, such a layer, which has a conductivity of lithium ions, prevents further recovery, without complicating the processes of introduction and extraction of lithium.

Another problem is the formation and growth of lithium dendrite

Lithium dendrite growth is known since the 1960s, but despite all effort that was put into mitigating this problem, it still prevents the commercialization of lithium metal anodes and also haunts today’s lithium-ion systems. The attempts of suppressing the formation and growth have only shown little success as the understanding of the fundamentals of this problem is still very limited.

It was clearly shown by the experimental results that the current density has a major influence on dendrite formation and growth, but the exact predictions for different current densities are contradicting.

One of the models explaining the growth of dendrites makes it possible to calculate the formation time of dendrites for different metals.

The formation time of dendrites (τ) on the lithium anode (Li) is determined by the formula:

pic-2

where, J – is the density of the electric current, K – is a constant determined by the physical characteristics of the metal.

The formation of dendrites on tin (Sn): pic-3

The formation of dendrites on magnesium (Mg): pic-4

The formation of dendrites on copper (Cu): pic-5

The time of formation of dendrites for different metals relative to lithium is presented in the table below.

Li Cu Al Mg Zn Sn Na К
1,000 45,436 11,876 7,094 4,158 0,694 0,508 0,126

The highest rate of dendrite formation from these metals is in potassium (K).
The rate of dendrite formation in magnesium (Mg) is 7.1 times slower than in lithium.
Copper is the most stable anode in the list.
Our analysis of the reasons for the rapid degradation of batteries allowed us to develop a method for manufacturing a Current Collector and Active Electrodes, which allows us to highly reduce the irreversible capacity of negative electrodes, eliminate the growth of dendrites and increase the specific characteristics of lithium-ion batteries as a whole.
We offer the technology of manufacturing the Current Collector as the first step towards achieving a high level of specific energy of an electrochemical power source (battery, supercapacitor, fuel cell or flow cell).

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