PL248953B1 - Potassium-ion cell with a shungite-based negative electrode - Google Patents

Abstract

The subject of the application is a potassium-ion cell with a shungite-based negative electrode operating in a liquid organic electrolyte, in which the active material of the negative electrode is natural shungite in the amount of 85% by weight of the negative electrode, and the electrolyte contains a potassium conducting salt, preferably potassium hexafluorophosphate.

Description

Description of the invention

The subject of the invention is a potassium-ion cell with a shungite-based negative electrode operating in a liquid organic electrolyte.

Lithium-ion cells currently dominate the global battery market in terms of capacity and energy delivery. However, a significant threat to the continued rapid development of this technology is the limited lithium resources in the Earth's crust and its difficult recovery from used batteries. To ensure the continued production of chemical power sources for electric vehicles, stationary renewable energy storage systems, and portable electronic devices, research has been underway for years on alternatives to lithium cells, with potassium-ion cells enjoying considerable popularity. Potassium is one of the most abundant elements in the Earth's crust. It ranks eighth on the list of elements by mass stored in the Earth's crust, placing it significantly above lithium. The abundant availability of this raw material translates into its lower price, prompting intensified work on implementing this element in commercial electrochemical devices. Before this can happen, difficulties related to potassium's incompatibility with some electrode materials used in lithium cells must be resolved.

Pressing problems particularly concern the instability of potassium cathode materials. However, anode materials for negative electrodes are also being developed. Negative electrodes are most often made from carbon materials, and in the case of lithium-ion cells, this is typically natural or synthetic graphite. Although potassium-ion cells can utilize this crystalline allotropic form of carbon, efforts should be made to diversify the origins of electrode materials. Currently, there is a shift away from relying solely on crude oil as a source of polymer and carbon materials. Hence, efforts are being made to find compatible materials from other sources. One such material could be shungite – a metamorphic form of carbon formed from organic Precambrian sediments. Until now, it has been associated primarily with drinking water filters, but it is increasingly finding applications in electrochemistry, particularly electrocatalysis. The specific structure of this material also suggests its use in batteries.

Potassium-ion cells are potential replacements for lithium batteries due to the greater abundance of potassium in the Earth's crust. The operating principle of these two types of cells is analogous and depends on the type of electrodes used (Y. Ma, Y. Ma, H. Euchner, X. Liu, H. Zhang, B. Qin, D. Geiger, J. Biskupek, A. Carlsson, U. Kaiser, A. GroB, S. Indris, S. Passerini, D. Bresser, ACS Energy Lett. 6, 2021: 915-924):

a) in the case of intercalation electrodes (e.g. graphite - negative electrode, lithiated cobalt oxide - positive electrode), ions of a given alkaline element undergo reversible intercalation in the electrode materials, this is a mechanism called the "rocking chair",

b) in the case of conversion electrodes, alkali metal ions undergo a chemical reaction, resulting in the formation of, for example, an alloy of lithium with another metal.

Conversion-type electrodes require further development before widespread commercial application due to the instability of the resulting products, rapid changes in electrode volume during charging and discharging, and limited cyclic efficiency. Hence, there is continued interest in and ongoing development of proven intercalation electrodes. The most commonly used intercalation electrode in lithium-ion cells is graphite. It is a crystalline form of carbon with a hexagonal structure, capable of intercalating with both lithium and potassium ions (Y. Wen, K. He, Y. Zhu, F. Han, Y. Xu, I. Matsuda, Y. Ishii, J. Cumings, C. Wang, 5, 2014: 4033).

An example of a naturally occurring, non-graphitizing carbonaceous material is shungite. There is some uncertainty about its geological origin, but geologists believe it is an ancient metamorphic rock formed in the Precambrian (more precisely, in the lower Proterozoic) by the transformation of sedimentary oil shales derived from algae (V.A. Melezhik, M.M. Filippov, A.E. Romashkin, Ore Geology Reviews, 24, 2004: 135-154). Some researchers consider it to be a highly altered bitumen (V.V. Kovalevski, RR. Buseck, J.M. Cowley, Carbon, 39, 2001: 243-256). Moreover, it was in this rock that naturally occurring fullerenes were discovered - one of the allotropic varieties of carbon (P.R. Buseck, S.J. Tsipursky, R. Hettich, Science, 257, 1992: 215-217). The largest deposits of shungite are found in Karelia, although other bitumens are widespread, among others, throughout Scandinavia, Canada and partly in the USA (V.V. Kovalevski, RR. Buseck, J.M. Cowley, Carbon, 39, 2001: 243-256). Shungite is classified according to carbon content into five classes: I (84-98%), II (42-84%),

III (30-37%), IV (15-20% and V (3-6%) (A.Z.Z. Peter, R. Buseck, P.L. Galdobina, V.V. Kovalevski, N.N. Rozhkova, W.J. Valley, Can. Mineral. 35, 1997: 1363-1378).

In the available literature, only two examples of the use of this material in negative electrodes for lithium-ion cells have been found. In both cells, the negative electrode made of unprocessed shungite reached a specific capacity in the range of 150-170 mAh g ^-1 (RM Humana, MG Ortiz, JE Thomas, SG Real, M. Sedlarikova, J. Vondrak, A. Visintin, J. Solid State Electrochem., 20, 2016: 1053-1058; NH Chou, N. Pierce, Y. Lei, N. Perea-Lopez, K. Fujisawa, S. Subramanian, JA Robinson, G. Chen, K. Omichi, SS Rozhkov, NN Rozhkova, M. Terrones, AR Harutyunyan, Carbon, 130, 2018: 105-111), and after grinding shungite at a reduced temperature, this value increased significantly, exceeding 200 mAh g ^-1 (N.H. Chou, N. Pierce, Y. Lei, N. Perea-Lopez, K. Fujisawa, S. Subramanian, J. A. Robinson, G. Chen, K. Omichi, S. S. Rozhkov, N. N. Rozhkova, M. Terrones, A. R. Harutyunyan, Carbon, 130, 2018: 105-111).

More common applications of shungite are in electrocatalysis and electroanalysis (N. Kazimova, K. Ping, M. Alam, M. Danilson, M. Merisalu, J. Aruvali, P. Paiste, M. Kaarik, V. Mikli, J. Leis, K. Tammeveski, P. Starkov, N. Kong, J. Catalysis, 395, 2021: 178-187; Z. Chen, W. Chen, B.J. Ni, Int. A.A. Kovalchuk, N.N. Rozhkova, A.V. Prikhodko, Current Nanosci. 19, 2023: 82-89).

To the best of the developers' knowledge, shungite has not been previously used as a negative electrode in potassium-based secondary battery technologies.

The essence of the invention is a potassium-ion cell with a shungite-based negative electrode operating in a liquid organic electrolyte, in which the active material of the negative electrode is natural shungite in an amount of at least 85% by weight of the negative electrode, and the electrolyte is a 0.8-molar solution of a potassium conducting salt in the form of potassium hexafluorophosphate in a mixture of ethylene carbonate and diethyl carbonate in equal volume fractions.

The shungite used is class I shungite with a high carbon content of 84-98%, crushed by high-energy grinding to an average particle diameter of 6 μm.

Thanks to the use of the presented solution, the following technical and operational effects were achieved:

• selecting a carbon electrode compatible with the main alkaline elements used in battery technologies (in this case: potassium); • stable cyclic operation of the negative electrode with high current efficiency; • operating parameters of potassium cells similar to those of a lithium cell with the same negative electrode. The presented solution offers a number of benefits, enabling the development of battery technologies based on elements found in the Earth's crust in greater abundance than lithium. In the presented invention, this element is potassium. The negative electrode made of shungite is compatible with both lithium and potassium thanks to the turbostatic structure of this material. This is a rare property, which means that the presented solution can facilitate the replacement of lithium with other alkali metals. The resulting technical and operational properties of potassium and sodium cells with a negative electrode made of shungite are similar to lithium cells with a similar electrode. This supports the use of this material in alternative battery technologies. Furthermore, the material is of natural origin, reducing the need for crude oil, which has previously been necessary for the production of carbon materials from petroleum-derived polymers via pyrolysis.

EXAMPLE 1

The potassium-ion cell which is the subject of the invention was made in a two-electrode electrochemical vessel using the following elements:

• potassium applied to a steel current collector with a diameter of 12 mm, • a liquid organic electrolyte being a 0.8-molar solution of potassium hexafluorophosphate in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with equal volume fractions (approx. 150 μl of electrolyte per cell), • a glass fiber separator with a diameter of 12 mm, • a negative electrode with a diameter of 12 mm made of natural shungite with a carbon content of 93.5%, crushed by high-energy grinding to an average particle diameter of 6 μm.

The negative electrode was prepared as follows: active material (shungite), polymer binder (poly(vinylidene fluoride) in the form of a 10% solution in N-methylpyrrolidone) and an additive increasing

PL 248953 Β1 conductivity (carbon black) was mixed in a mass ratio of 85:10:5. N-methylpyrrolidone was then added until a thin paste was obtained. Mixing was continued for 24 hours. The prepared paste was applied to degreased copper foil discs. The electrodes were dried for 12 hours at 55°C and then for 8 hours under vacuum at 105°C. The electrodes and electrolyte components were stored in an argon-filled glove box.

Potassium cells with a shungite-electrolyte potassium design were constructed in polypropylene electrochemical vessels in a glove box. Cyclic operation of the cells was tested by galvanostatic charge/discharge at a 20-hour C/20 current load. The theoretical capacity was assumed to be 372 mAh g- ¹ of graphite. Electrochemical stability of the cells was studied using electrochemical impedance spectroscopy in the frequency range of 100,000-0.01 Hz. The study was performed after the first formation cycle and after the 10th cell cycle. These data were used to determine the main components of the system resistance, i.e., the ohmic resistance of the cell R _s , the resistance of the SEI passive layer on the negative electrode surface R s , and the charge transfer resistance Ret . The results are summarized in Table 1.

Table 1

Summary of electrochemical technical and operational properties of potassium cells with an anode made of shungite and a liquid electrolyte of 0.8M KPFe in EC:DEC (50:50 by volume).

Discharge capacity Q _d [mAh g- ¹ ] Cycle current efficiency [%] Cell energy E [mWh g Formation 155.7 49.1 390.9 Cycles 158.6 87.6 Cycle 2 160.2 92.7 Cycle 3 160.1 93.6 Cycle 4 157.1 91.6 Cycle 5 158.3 96.1 Cycle 6 155.3 93.6 Cycle 7 156.1 95.9 Cycle 8 154.7 97.9 Cycle 9 151.9 95.7 Cycle 10 151.3 96.8 Main components of cell resistance after formation: Ohmic resistance R _s fRl Resistance SEI R$ _E1 |K| Charge transfer resistance Rc _t [R] 7.51 11.01 531.39 Main components of cell resistance after 10 cycles: Ohmic resistance R, fRl Resistance SEI Rs _E1 |R| Charge transfer resistance R^ [R] 10.33 45.34 470.14

Claims (1)

1. A potassium-ion cell with a negative electrode based on shungite operating in a liquid organic electrolyte, characterized in that the active material of the negative electrode is natural shungite in the amount of 85% by weight of the negative electrode, and the electrolyte is a 0.8 molar solution of potassium hexafluorophosphate in a mixture of ethylene carbonate and diethyl carbonate in equal volume fractions, wherein the natural shungite has a carbon content in the range of 84-98% and is used in a ground form with an average particle diameter of 6 µm.