RU2488196C1 - Manufacturing method of cathode of lithium current source - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: result is achieved due to increase in homogeneity of electrode active mass and increase of lithium diffusion coefficient; for this purpose in the suggested method active mass is mixed with electroconductive additive, the received mass is saturated with solution of polymer electrolyte, cathode mass is dried and grinded in ball crusher and press-fitted to current tap; at that after drying cathode mass is treated additionally in plastic yield process at torsion under pressure of at least 1.7 GPa and relative strain of 22-24.

EFFECT: improvement of technological effectiveness in cathode manufacturing process with increase of its discharge capacity.

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Description

The invention relates to the electrical industry and can be used in the manufacture of lithium current sources. The cathodes of lithium current sources are composite materials: they are a mixture of active mass, conductive additives and a binder. As the active mass of the cathode, metal oxides (MnO ₂ ), fluorinated carbon (CF ₄ ), lithium metal phosphates (LiFePO ₄ , LiTi ₂ (PO ₄ ) ₃ ), lithium-vanadium bronzes (LiV ₃ O ₈ ), and the binder is fluoroplastic. These cathodes are porous materials, and their pores during operation of lithium current sources are filled with a solution of liquid electrolyte [1]. Its chemical aggressiveness and destruction during storage lead to a decrease in the energy parameters of lithium current sources. Therefore, it has recently been proposed to use a polymer electrolyte as a binder and, simultaneously, an electrolyte in the pores of the cathode.

A known method of manufacturing a cathode, which consists in mixing CF ₄ and soot with a solution of polymer electrolyte in a mortar, applying the cathode mixture to the collector and drying for 2 hours at 80 ° C [2]. The disadvantages of this method include poor manufacturability caused by the multi-stage process and the duration of each operation and the low discharge capacity of the cathodes.

The closest in technical essence and the achieved results is a method of manufacturing cathodes based on lithium vanadium bronze, which includes the following operations: mixing powdered LiV ₃ O ₈ in a mortar with an electrically conductive additive (type pyrographite grade PR-3), impregnating the resulting mass with a polymer solution electrolyte (lithium perchlorate and polysulfone at a mass ratio of components of 20: 100) in dimethylacetamide, drying the cathode mass, grinding in a ball mill and pressing on the collector. The disadvantages of this method are the poor reproducibility of the results and low capacitive parameters during intense discharges.

The technical problem solved by the invention is to increase the manufacturability of the cathode manufacturing process and increase its capacity. The technical result, which consists in increasing the homogeneity of the active mass of the electrode and increasing the diffusion coefficient of lithium is achieved by the fact that in the known method of manufacturing the cathode, which consists in mixing the active mass with a conductive additive, impregnating the resulting mass with a polymer electrolyte solution, drying the cathode mass, grinding in a ball mill and pressing on the collector, according to the invention, carry out additional processing of the cathode mass in the plastic flow during torsion according to leniem not less than 1.7 GPa, and the strain values of 22-24.

The figure schematically shows a device for implementing the method, including the active mass of the electrode 1, punch 2, Bridgman anvil.

The method is as follows. The active mass (MnO ₂ , CF ₄ , LiFePO ₄ , LiTi ₂ (PO ₄ ) ₃ , LiV ₃ O ₈ ) is poured into a ceramic cup where an electrically conductive additive (carbon black, pyrographite) is added, the mixture is impregnated with a polymer electrolyte solution, dried in a muffle furnace . The resulting mass 1 is poured onto the anvil 2, pressed from above by a punch 3 and placed under a press. Then the mass is subjected to relative deformation of 22-24 at a pressure of at least 1.7 GPa. Schematically, this is shown in the drawing. The result is a flat disk with a thickness of 1.0 to 1.5 mm, which is ground in a ball mill and the resulting mass is pressed onto a down conductor.

The apparatus, on which additional mixing was carried out, makes it possible to subject the test substances to the simultaneous action of uniaxial compression and shear stresses, the magnitude of which does not exceed the yield strength of the material at a given pressure. A feature of this type of apparatus is that as the pressure increases, the stress necessary to maintain a constant rate of plastic deformation increases. At constant pressure, the voltage required to maintain a constant rate of plastic deformation remains constant. Plastic flow on apparatus of this type is realized in the case when the surface friction force is greater than or equal to the yield strength of the material being processed. Such a relationship for the studied mixtures occurs at pressures of the order of 1.7 GPa, at lower pressures, the anvil and punch compressing substances slip over the surface of the substance, and the initial powdery materials remain in the form of a powder. At pressures above 1.7 GPa, powdered materials compact, i.e. constituent parts undergo plastic deformation. With this technique, it is possible to develop plastic materials in the materials under study at pressures above the threshold ones in a wide range without breaking the continuity of the samples. In our case, plastic deformation refers not to the single particles that make up the mixture, but to the entire sample, which is a cylinder. For this pattern of influence and the geometry of the samples, it is necessary to apply the concept of torsion deformations when torsional stresses act on the cylindrical body: These deformations can be characterized by the ratio of the length of the helical line into which the cylinder generatrix transforms during deformation to the initial cylinder height [4]. With a relative deformation of less than 17 units, insufficient uniform mixing of the components is obtained, which leads to a deterioration in the electrochemical characteristics of the cathode. With a relative deformation of less than 22 units, an insufficiently uniform distribution of the cathode components is obtained, which leads to a decrease in its electrochemical characteristics. With a relative deformation of more than 24 units, MnO ₂ , CF ₄ , LiFePO ₄ , LiTi ₂ (PO ₄ ) ₃ , LiV ₃ O ₈ go into the phase of high ordering, i.e. characterized by a small number of structural defects, which complicates the diffusion of lithium ion over the solid phase during the discharge of the current source and, accordingly, leads to a decrease in the discharge capacity of the cathode. It is characterized by low diffusion coefficients of lithium ion and, correspondingly, increased polarization losses. Thus, the excess of the above parameters beyond these limits leads to a decrease in the efficiency of the method.

The implementation of this method allows to increase the capacity of the cathodes and their resource by 20-25%, and also significantly increase the reproducibility of the results in mass production. For the implementation of the method requires a press, punch, anvil and a muffle furnace.

Example 1. 400 mg of MnO _{2 was} mixed with 50 mg of carbon black in a dry form, soaked in 10 ml of a 5% polymer electrolyte solution, dried for 1 hour at a temperature of 100 ° C, an additional treatment was performed under torsion at a pressure of 1.7 GPa and a relative deformation of 22, were ground and pressed onto the down conductor under a pressure of 10 MPa. After assembly, the Li-MnO ₂ elements in frame size CR-2025 gave a capacity of 140 mA * h.

Example 2. 200 mg CF _{4 was} mixed with 25 mg of carbon black. dry, soaked in 5 ml of a 5% solution of polymer electrolyte, dried for 1 hour at a temperature of 100 ° С, additional processing was performed under torsion at a pressure of 1.8 GPa and a relative strain of 23, milled and pressed onto a collector under a pressure of 10 MPa. After assembly, the Li-CF ₄ elements in frame size BR-2016 gave a capacity of 80 mA * h.

Example 3. 4100 mg of LiFePO _{4 was} mixed with 520 mg of carbon black in a dry form, soaked in 104 ml of a 5% polymer electrolyte solution, dried for 1 hour at a temperature of 100 ° C, an additional treatment was performed under torsion at a pressure of 1.7 GPa and a relative deformation of 23, were ground pressed onto the down conductor under a pressure of 10 MPa. After assembling the Li-LiFePO ₄ battery in size AA, its discharge capacity was 750 mA * h.

Example 4. 4100 mg of LiTi ₂ (PO ₄ ) _{3 was} mixed with 520 mg of carbon black in a dry form, soaked in 104 ml of a 5% polymer electrolyte solution, dried for 1 hour at a temperature of 100 ° C, an additional treatment was performed under torsion at a pressure of 1.8 GPa and relative deformations 24, were ground and pressed onto a down conductor under a pressure of 10 MPa. After assembling the Li-LiTi ₂ (PO ₄ ) ₃ battery in size AA, its discharge capacity was 720 mA * h.

Example 5. 4100 mg of LiV ₃ O _{8 was} mixed with 520 mg of PR-3 pyrographite in dry form, soaked in 104 ml of a 5% polymer electrolyte solution, dried for 1 hour at 100 ° C, and additional processing was performed under torsion at a pressure of 1.7 GPa and relative strain 22, grinded and pressed onto the collector under a pressure of 10 MPa. After assembling the Li-LiV ₃ O ₈ battery in size AA, its discharge capacity was 740 mA * h.

In all cases, the elements and batteries met the requirements of GOST in terms of capacity, discharge voltage and resource.

SOURCES OF INFORMATION TAKEN INTO ACCOUNT

1. Suzuki S., Miyayama M. // J. Power Sources. 2011. V.196. Number 4. R.2269-2273.

2. Tulibaeva G.Z., Yarmolenko O.V., Ishmukhametova K.G. // Materials of the 18th Mendeleev Congress on General and Applied Chemistry. 2007.M. S.225.

3. Smirnov S. S., Zhorin V. A., Kiselev M. R. // Journal of Applied Chemistry. 2010.V. 83. Number 7. S.1109-1113.

4. Zhorin V.A., Usichenko V.M., Epikolonyan N.S. // High molecular weight compounds. 1982.V.24. No. 9, S.1889-1893.

Claims (1)

A method of manufacturing a cathode of a lithium current source in which the active mass is mixed with an electrically conductive additive, the resulting mass is impregnated with a polymer electrolyte solution, the cathode mass is dried, milled and pressed onto a collector, characterized in that the cathode mass is further processed during plastic flow during torsion under pressure of at least 1.7 GPa and relative strain values of 22-24.