A CATHODE MATERIAL

Abstract

The cathode material contains the active component, the conductive component and the connecting component. Organic biomaterial is used as the active component, acetylene carbon black is used as the conductive component and polyvinylidene fluoride is used as the connecting component.

Description

The useful model claimed relates to the field of electrical engineering, namely cathode materials, which are a mixture of active, conductive and coupling components and can be used in the manufacture of current sources and/or energy storage devices, including high-power batteries capacitors, hybrid supercapacitors that can be used to store energy and power portable electronics, power tools, electric vehicles, and more.

From the prior art known are lithium-ion batteries with active cathode material based on complex oxides LiCoO2, LiMn2O4, LiCo1/3Ni1/3Mn1/3O2. There are several common ways to obtain such materials, such as the methods described in patents [U.S. Pat. No. 5,135,732] and [U.S. Pat. No. 4,246,253]. The main disadvantages of such cathode materials are the distortion of the structure and the course of adverse reactions during the cycling of the battery, which leads to irreversible loss of capacity.

There is also known the method of forming lithium current cathodes according to the patent of Ukraine No. 112896 for the invention, the date of publication, which includes the manufacture of a cathode composition by mixing mesoporous maghemite (iron oxide γ-Fe2O3), acetylene black, polyvinylidene fluoride, and solvent of the cathode by applying the cathode composition to the aluminum foil followed by drying, provided that the mass ratio of the components of the cathode composition, (wt. %):

mesoporous maghemite    60-80
acetylene black         10-30
polyvinylidene fluoride the rest.

Despite the certain advantages obtained by the above method of cathode material, the disadvantage is the low electronic conductivity of the material obtained, as well as power loss with increasing number of the discharge cycle.

In recent years, the attention of inventors is increasingly attracted to organic materials for use as active components of cathode materials for chemical current sources, in particular for high-energy chemical current sources. There is a method of obtaining a cathode material for lithium current sources based on hydrolysis of lignin according to RF patent No. 2482571, date of publication May 20, 2013. It is necessary to note the large number of stages and the length of the cathode material manufacturing process, as well as the relatively low practical energy intensity of lithium-based lithium current sources (up to 650 W·g/kg).

There is also known the method of obtaining a cathode material for chemical current sources according to RF patent No. 2597607, date of publication 10 Sep. 2016, which includes processing by fluorination of wood containing carbon, using pre-grinding, drying, sealing, creating pressure of not more than 0.1 kg/cm2, filling with a mixture of fluorine gas with nitrogen, and fluorination with continuous stirring until the reaction is complete. The resulting thermally stable product (up to 300° C.) has a theoretical energy content of 4.5 kW g/kg and a specific electronic conductivity of 1·10-11 cm/cm. The disadvantages are the low energy intensity, the low electronic conductivity and, as a consequence, the low discharge currents of the chemical current source.

The object of the claimed utility is to provide a cathode material for permanent and/or renewable current and/or energy storage units with high specific capacitance values, the ability to store high discharge and charge capacities with a large number of discharge/charge cycles.

The problem is solved by a cathode material containing the active component, the conductive component and the coupling component, where as the active component used organic biomaterial, as the conductive component used acetylene carbon black and as the coupling component used polyvinylidene fluoride, in the following component. (wt. %):

organic biomaterial     40-85
acetylene black         15-35
polyvinylidene fluoride the rest

provided that the organic biomaterial includes (wt. %):

peptides of plant or 0, 1-50
animal origin of     the rest
NaCI and K2HPO4 in
equal proportions of

It should be noted immediately that the claimed cathode material can be used not only with the lithium anode, but also with the anode of any suitable metal or alloys of any suitable metal. The prerequisites for use as an active component of biomaterials, in particular of peptides of plant or animal origin, are that peptides always carry a positive charge and are high conductivity material.

It has been unexpectedly found that the use of peptides with a molecular weight in the range from 1 to 150 kDa, and the primary structure contains from 2 to 200 amino acids, significantly increase the electrical conductivity of the material, which includes peptides. This fact is explained by that these small active peptides act at very small (nano- and pico-) concentrations, and small molecules more easily transport positively charged ions of suitable metal between the positive and negative electrodes in the discharge and charge process. Due to this, during the charge of the current source, a complex chemical compound is produced, rather than separate simple compounds and elements, such as pure carbon. This, in turn, prevents unwanted sediment from depositing on the surface of the cathode material. As a rule, the anode material does not participate in these processes, so there are no problems with electrode restoration, which provides stability and safety when using the battery.

Research has shown that the use of organic biomaterials as the basis of a cathode composition significantly increases the specific energy characteristics of current sources. The results of these studies have not only confirmed the effectiveness of the use of organic biomaterials as the active component of the cathode material, but also several times exceeded the performance of the known best samples of batteries and hybrid supercapacitors. In the course of the study of the new cathode material, unusual effects and regularities were discovered which, by their very nature, had never been encountered in similar current sources before.

Unexpectedly, a feature was invented, which the inventors called the “relaxation recovery effect” of the cathode material, the essence of which is the ability of a rechargeable battery or supercapacitor to recover a specific capacity without connecting to external sources of energy. That is, the process of the “relaxation recovery effect” is somewhat similar to the process of charging a current source, but proceeds more smoothly and is slower. This effect can be very interesting for building prototypes of self-renewing electrochemical power sources. From the viewpoint of the inventors, the nature of this effect may lie in the properties of the active peptide component of the organic biological material and may be associated with the restoration of the structure of the active component after removal of the load. In any case, the operating parameters of current sources based on the following principles of restorative work can significantly exceed the corresponding characteristics of traditional current sources. Therewith, additional studies have shown that using the relaxation recovery mode (effect) results in a significant increase in the final discharge capacity of current sources compared to a conventional galvanostatic discharge, with the final discharge capacity of current sources increasing without wasting energy.

Also, during the study of the cathode material were found periodic “relaxation” leaps potential when used as a cathode material composite material consisting of organic biomaterial and as the second component of the nanosized composite SiO2 and Al2O3, mixed mechanically in a ratio of 1:1. It should be noted the value of the specific discharge capacity, which reached the value of 4000 mA·g/g, which is a very high value of the capacity. According to the inventors, the effect of “relaxation” leaps of potential recorded in the galvanostatic mode is the result of the combined action of charge transfer between the composite particles with different conductivity. In particular, since SiO2 and Al2O3 are characterized by low conductivity and peptide material, according to literature, is a material with high conductivity, a local charge accumulation at discharge is possible at the contact points of different particles, which will be reflected as a “relaxation” jump of potential. That is, as a result of studies of the cathode material using organic biomaterials as the active component, a fixed effect is discovered, which opens a new non-classical mechanism for the operation of current sources.

The following drawings, as well as a description of examples of specific implementation of the cathode material, are given to explain the claimed utility model and do not limit the scope defined by the utility model formula:

FIG. 1—CVA curves of current sources (biomaterial) at different speeds of potential change;

FIG. 2—CVA curves of current sources (biomaterial) obtained at the rate of change of potential S=3 mV/s: a) 1st cycle, c) 100th cycle

FIG. 3—The discharge curve of the cathode based on biomaterial/SA20 composite (galvanostatic mode).

In the experimental studies used the cathode material in the following ratio of major components (wt. %): Organic biomaterials—40-85, acetylene black—15-35, polyvinylidene fluoride—the rest. The ranges of each of the components of the organic biomaterial were determined experimentally.

Example 1. The composition of the cathode material includes: biomaterial—77%, acetylene carbon black—18, polyvinylidene fluoride—the rest. All components were mechanically mixed at ambient room temperature under normal conditions. The resulting paste mixture was applied to the substrate and dried for 72 hours (at 55° C.).

At that, as a rule, three types of substrates were used: carbon tablet, aluminum foil and non-woven polypropylene. As a result, a sealed layout of the two-electrode cell was created. Lithium metal was used as the anode, as the electrolyte was a 1 M solution of LiBF4 in γ-butyrolactone. Testing of the operational parameters of the test models was carried out in galvanostatic and potentiodynamic modes (charge/discharge at the Tionit stand) at room temperature (25° C.). To determine the type (kinetics) of electrochemical reactions, cyclic voltammetry (CVA) was performed. Since the rates of electrochemical reactions for different materials differ, a certain range of velocity sweeps of potential S was tested, with corresponding curves being obtained and analyzed. The created layout of the current source (based on biological material) with a carbonic substrate was investigated in the voltage range 1-3.5 V using the velocity sweep potential S=1, 3, 5, 10, 15, 20, 30 mV/s. The study gave the appearance of a curve CVA close to rectangular shape (with no pronounced peaks on the charge and discharge branches) (FIG. 1), which indicates the capacitive accumulation of charge on the cathode as a result of the formation of a double electric layer, which clearly indicates a direct connection the process of charge accumulation with the formation of a double electric layer on the surface of the peptide component of the biological material. On the basis of the obtained CVA curves, the capacities of the charge and discharge processes of the current source (biological material) and the Coulomb efficiency are calculated, as shown in Table 1.

TABLE 1
		C (discharge),	C (charge),
No	S, mV/s	mA * h/g	mA * h/g	Q,%
1	1	932	1269	73.4
2	3	1035	1044	99.1
3	5	886	922	96.1
4	10	633	675	93.8
5	15	525	557	94.3
6	20	460	493	93.3
7	30	354	386	91.7

It is noted that the specific capacitances of the discharge and charge decrease exponentially as the scanning speed increases. The obtained values of the specific capacitance of the discharge and charge at low speeds are high enough for the operation of the current source in the potentiodynamic mode. The maximum Coulomb efficiency corresponds to a scan rate of 3 mV/s and is approximately 99% when charge is accumulated by forming a double electric layer.

Example 2. At the stage of determining the capacity of storage capacity during the charge/discharge cycles was used cathode material similar to Example 1. Will be performed 100 cycles of charge/discharge in the potential-dynamic mode at a rate of change of potential of 3 mV/s in a potential window of 1.0-4.0 V. the curves separately for the 1st and 100th charge/discharge cycles are shown in FIG. 2 (a, b). The calculated charge and discharge capacities for the 1st and 100th cycles are presented in Table 2. As a result, it is found that after 100 cycles of charge/discharge, the current source (biological material) does not lose its ability to operate in charge/discharge mode. The degree of degradation (capacitive attenuation) on the 100th cycle compared to the first cycle is about 12%.

TABLE 2
		C (discharge),	C (charge),
No	S, mV/s	mA * h/g	mA * h/g	Q,%
1-	3	1328	1347	98.6
100-	3	1152	1186	97.1

Example 3. To check the “relaxation recovery effect” of the cathode material was performed discharge cell current source with a cathode, made analogously to Example 1 in the mode of intermittent galvanostatic titration. The current source was discharged to a certain potential and then left unplugged for 5 hours. Then again discharged in the previous conditions. In the future, several more digit stages were carried out under the same scheme. In the first step, the load cut-off potential was 1.7 V, and after each relaxation step it decreased in 0.1 V increments on FIG. 3. As can be seen from the comparison of the discharge curves, the current source capacity at galvanostatic titration reaches 3900 mAh/h, while the ordinary discharge provides a capacity of only 2700 mAh/h. That is, due to the “relaxation recovery effect” of the cathode material, there is an increase in the capacity by 44% in the titration mode.

Example 4. The biological material was used as the active additive of the electrode composite of the supercapacitor. To perform the comparison and evaluation of the effectiveness of the biological material as a control (basic) working material for the electrode was taken highly porous carbon material C42. A close analog of the symmetrical supercapacitor was a two-electrode stainless steel capacitor type. The electrodes were prepared by crimping a mixture of C42/acetylene carbon black in a 3:1 ratio, respectively. An aqueous solution of 3.5 M KOH was used as the electrolyte. The layout of the symmetric supercapacitor was tested in galvanostatic mode in the voltage range 0-1 V at different values of the load current. The composite material, which included biological material and C42 in a 1:1 ratio, was obtained by ultrasonic treatment for 1 h. Water was used as the solvent. Salts of biological material were dissolved in water and, together with peptide centers, were adsorbed into the pores of carbon. The composite mixture was air-dried for 48 hours at 55° C. The finished composite was made of electrodes and received a model of a supercapacitor for testing in galvanostatic mode. Comparison of the calculated discharge capacity at different values of currents for the C42-based supercapacitor and the biological material/C42 composite showed a positive contribution of the biological material to the process of accumulation of the capacitor. The average discharge capacity increased by 10 F/h.

As a result of studies of current sources (DS) with a cathode based on biomaterials in different modes of operation at discharge up to 1V (mmax DS=4 g) at a relative load current Iroz./mcatode. =0.1 mA/g (mcatode=5 mg) maximum capacity is 3900 mAh/h and specific energy is 4400 W/h. The obtained results exceed the parameters of the available current sources and significantly exceed the parameters of the Li-ion sources of high energy current. That is, the possibility of using organic biological material as the active component of the cathode material of the original current sources has been confirmed. Additional information on the electrochemical properties of the biomaterial-based cathode material was obtained by comparing the integral specific energy

$\begin{array}{c}\int l\\ \left(W=·U\left(C\right)\mathrm{dC}\right)\\ m·t\end{array}$

characteristics, in particular the specific energy released during the discharge of the current source.

It is revealed that at a current of 0.1 mA the specific energy is about 1000 mWh/h, while at a current of 0.4 mA-3400 mWh/h. At a relatively lower discharge current (I=0.1 mA), the electrochemical processes at the cathode occur with the preservation of thermodynamic equilibrium without sudden changes in potential and have sufficient time for the intercalation of metal ions, in particular Li+, into the structure of the cathode material. This is accompanied by the equilibrium flow of redox processes without the accumulation of excess charge on the cathode. An increase in the discharge current will cause an increase in the charge density and its accumulation on the surface of the cathode material. In this case, the reduction of the cathode potential occurs without the intercalation of metal ions, in particular Li+ into the structure of the cathode material, and the redox processes occur only in the surface layers of the material. However, it should be noted that in the cathode material the proportion of biomaterial, as an electrochemically active substance, for which the peptides stand, is not more than 10%. In view of this, as well as the addition of acetylene carbon black and polyvinylidene fluoride to the cathode material, it is safe to say that, in terms of the active mass of the substance, the specific discharge capacity at given currents can increase by about an order of magnitude.

Utility cathode material claimed by biomaterial provides efficient operation of permanent and/or renewable current sources and/or energy storage units with high specific capacitance values, ability to store high discharge and charge capacities, with a large number of discharge cycles, has sufficient potential to significantly exceed all of the above indicators and has good prospects for use in many industries where current sources are used.

Claims

1. A cathode material containing an active component, a conductive component and a connecting component, which is characterized in that an organic biomaterial is used as an active component, acetylene carbon black is used as a conductive component, and the connecting component used polyvinylidene fluoride, in the following ratio of components (wt. %):

2. The cathode material according to claim 1, characterized in that for organic biomaterials are selected peptides with a molecular weight in the range from 1 to 150 kDa, the primary structure of which contains from 2 to 200 amino acids.