Cobalt-doped molybdenum tungsten sulfide, method for preparing the same, method for plasma processing, and use thereof

Abstract

The application discloses a cobalt-doped molybdenum tungsten sulfide as well as a preparation method, a plasma treatment method and application thereof, relates to the technical field of electrode materials, and comprises the following steps: dissolving a tungsten source, a molybdenum source, a cobalt source, a sulfur source and a complexing agent in deionized water, and then performing a hydrothermal reaction to obtain the cobalt-doped molybdenum tungsten sulfide; and performing plasma treatment on the cobalt-doped molybdenum tungsten sulfide. The cobalt-doped molybdenum tungsten sulfide can shorten the ion diffusion path, improve the conductivity, increase the active sites, and make the molybdenum tungsten sulfide have more superior conductivity. The plasma treatment can clean the surface impurities of the cobalt-doped molybdenum tungsten sulfide, expose the active sites, form defects, and thus improve the electrochemical performance of the cobalt-doped molybdenum tungsten sulfide.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrode materials, in particular to a cobalt-doped molybdenum tungsten sulfide as well as a preparation method, a plasma treatment method and application thereof. BACKGROUND

[0002] With the rapid development of renewable energy, its intermittency and instability problems need to be solved. Electrochemical energy storage technology has become an ideal solution due to its high energy density, high efficiency conversion and long cycle life. Supercapacitors and lithium batteries, as two main pillars in the field of electrochemical energy storage, have their own characteristics. Supercapacitors are known for their fast charging and discharging capabilities, making them suitable for scenarios requiring instant high-power output. Lithium batteries, on the other hand, have high energy density and good cycle stability. The selection and design of electrode materials are viable strategies to improve the energy storage and working efficiency of supercapacitors and lithium batteries. Molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are two typical two-dimensional materials with unique layered structures, and have been widely studied and applied in the field of electrochemistry. However, MoS2 and WS2 have become a key bottleneck for improving their electrochemical performance due to their material structure limitations.

[0003] Molybdenum tungsten sulfide compounds (Mo x W y S2) have shown significant advantages in the field of electrochemistry: they have high electrical conductivity, which can accelerate the transfer of electrons between the electrode and the electrolyte, improving the rate and efficiency of electrochemical reactions; they have high specific capacity, which is beneficial to improving the energy density of batteries; they have good electrochemical stability, with stable structure and performance during the cycle process, prolonging the service life of electrochemical equipment; the rich oxidation states of molybdenum and tungsten enable them to participate in various redox reactions, making them suitable for a variety of electrochemical devices; their energy band structure can be adjusted to meet different application requirements, making them have great potential in many electrochemical applications such as batteries and supercapacitors.

[0004] In the field of material structure and performance control, impurity atom doping as a cutting-edge and efficient strategy has become a core means to optimize material performance due to its precise control characteristics, highly controllable implementation path, and significant modification effect. Especially for MoS2 and WS2, the introduction of Fe, Co, Ni, Cu and other transition metal elements through doping technology has been proven to significantly improve their electrochemical performance. From the perspective of electronic structure, the doping process can effectively increase the electron state density at the Fermi level of MoS2 or WS2, greatly improving the intrinsic conductivity of the material. In terms of crystal structure, the introduction of doping atoms changes the coordination environment of atoms around MoS2 or WS2, causing lattice mismatch and generating a local stress field. This stress-induced effect can promote the transformation of MoS2 or WS2 from the thermodynamically stable 2H phase (hexagonal crystal) to the 1T phase (tetragonal crystal) with metallic characteristics, thereby exhibiting its unique electronic delocalization characteristics and abundant active sites, which can significantly enhance the electrocatalytic activity and energy storage performance of the material.

[0005] Plasma, as one of the ways to control the structure and phase of materials, is widely used due to its non-contact, high controllability, and multi-functionality. Plasma treatment is a technology that uses plasma to physically and chemically treat the surface of materials. Under the action of plasma, the surface of the material can undergo cleaning, oxidation modification, thin film deposition, and other processes. Plasma activates gas molecules, producing active species such as ions, radicals, and excited-state molecules, which can react with the material surface to achieve surface cleaning, organic matter removal, and enhanced surface adhesion, providing an important means to enhance material performance and functionality.

[0006] The present invention aims to improve the electrochemical performance of Mo x W y S2 by the synergistic effect of impurity atom doping and plasma treatment. SUMMARY

[0007] The technical problem to be solved by the present invention is to provide a method for preparing plasma cobalt-doped molybdenum tungsten sulfide. On the one hand, impurity atom doping can control the electronic structure and crystal defects of molybdenum tungsten sulfide, introduce more active sites, optimize its electrical conductivity and redox reaction activity, and thus improve the specific capacity. On the other hand, plasma treatment can modify the surface of molybdenum tungsten sulfide, improve the interface contact between molybdenum tungsten sulfide and electrolyte, enhance the wettability of molybdenum tungsten sulfide, and reduce the charge transfer resistance, thereby effectively improving the electrochemical performance and providing strong support for the development of high-performance electrochemical devices.

[0008] The technical problem to be solved by the present invention is solved by the following technical solution:

[0009] The first object of the present application is to provide a preparation method of cobalt-doped molybdenum tungsten sulfide, which comprises dissolving a tungsten source, a molybdenum source, a cobalt source, a sulfur source and a complexing agent in deionized water and then performing a hydrothermal reaction to obtain the cobalt-doped molybdenum tungsten sulfide.

[0010] The second object of the present application is to provide the cobalt-doped molybdenum tungsten sulfide obtained by the aforementioned preparation method.

[0011] The third object of the present application is to provide a plasma treatment method of the cobalt-doped molybdenum tungsten sulfide.

[0012] The fourth object of the present application is to provide the application of the cobalt-doped molybdenum tungsten sulfide and the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method in lithium ion batteries and supercapacitors.

[0013] The fifth object of the present application is to provide a lithium ion battery, which uses the cobalt-doped molybdenum tungsten sulfide or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method as a negative electrode material.

[0014] The sixth object of the present application is to provide a supercapacitor, which uses the cobalt-doped molybdenum tungsten sulfide or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method as a negative electrode material.

[0015] The beneficial effects of the present application are as follows:

[0016] (1) The preparation method of the cobalt-doped molybdenum tungsten sulfide provided by the present application has the characteristics of low cost, easy availability of raw materials, low energy consumption and simple process, and can realize the macro preparation of the cobalt-doped molybdenum tungsten sulfide, which is conducive to the realization of scientific research popularization and industrialization.

[0017] (2) The cobalt-doped molybdenum tungsten sulfide modified by the present application can shorten the ion diffusion path, improve the electrical conductivity, increase the active sites, and make the molybdenum tungsten sulfide have more superior electrical conductivity.

[0018] (3) The plasma treatment of the present application can clean the surface impurities of the cobalt-doped molybdenum tungsten sulfide, expose the active sites, form defects, and thus improve the electrochemical performance of the cobalt-doped molybdenum tungsten sulfide. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 X-ray diffraction (XRD) patterns of the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment in Examples 1-5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1;

[0020] Figure 2 Scanning electron microscope (SEM) images of the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment in Examples 1-5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1;

[0021] Figure 3 SEM images, TEM images and EDS images of the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Example 3 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1; wherein (a-c) are TEM images of the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1; (d) is a SEM image of the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1; (e-g) are TEM images of the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Example 3; (h) is a SEM image of the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Example 3; (i-m) are EDS images of (h);

[0022] Figure 4 Cyclic voltammograms (CV), galvanostatic charge-discharge (GCD) curves, rate performance curves and electrochemical impedance spectra (EIS) of the three-electrode lithium ion batteries assembled by using the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1-5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 as negative electrode materials, respectively; wherein (a) is a CV curve; (b) is a GCD curve; (c) is a rate performance curve; (d) is an EIS;

[0023] Figure 5 CV and GCD curves of the three-electrode lithium ion batteries assembled by using the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 and the molybdenum tungsten sulfide compound without cobalt doping and without plasma treatment in Comparative Example 2 as negative electrode materials, respectively; wherein (a) is a CV curve; (b) is a GCD curve;

[0024] Figure 6 Rate performance curves of the lithium ion batteries assembled by using the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1-5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 as negative electrode materials, respectively.

[0025] Figure 7 Cycle performance curves of the lithium ion batteries assembled by using the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1-5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 as negative electrode materials, respectively. DETAILED DESCRIPTION

[0026] In order to make the technical means, creative features, purposes and effects realized by the present application easy to understand, the present application is further described below in combination with specific embodiments and drawings.

[0027] The application provides a preparation method of cobalt-doped molybdenum tungsten sulfide.

[0028] Further, the tungsten source is ammonium paratungstate.

[0029] Further, the molybdenum source is ammonium molybdate, sodium molybdate and hydrates thereof.

[0030] Further, the cobalt source is cobalt nitrate and hydrates thereof.

[0031] Further, the sulfur source is at least one of thiourea, thioacetamide and cysteine.

[0032] Further, the complexing agent is oxalic acid.

[0033] Further, the mass ratios of the tungsten source, the molybdenum source, the cobalt source, the sulfur source and the complexing agent are 18-23%, 9-10%, 0.3-3%, 51-53% and 14-16% respectively, and the total mass ratio is 100%.

[0034] Further, the temperature of the hydrothermal reaction is 180-220 DEG C, and the time is 24-48 h.

[0035] The application provides the cobalt-doped molybdenum tungsten sulfide obtained by the preparation method.

[0036] Further, the molecular formula of the molybdenum tungsten sulfide in the cobalt-doped molybdenum tungsten sulfide is Mo 0.64 W 0.36 S2.

[0037] Further, the cobalt doping amount in the cobalt-doped molybdenum tungsten sulfide is 0.3-0.5%.

[0038] The application also provides a plasma treatment method of the cobalt-doped molybdenum tungsten sulfide.

[0039] Further, the plasma treatment is carried out at normal temperature and pressure, the power is 0-50 W, and the treatment time is 5-10 min.

[0040] Further, the gas of the plasma treatment is air. The advantage of using air is that the cost is extremely low, the air is convenient to obtain, the air is environmentally friendly, no secondary pollution is caused, and the air is suitable for large-scale industrial production.

[0041] The application also provides applications of the cobalt-doped molybdenum tungsten sulfide and the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method in lithium ion batteries and supercapacitors.

[0042] The application also provides a lithium ion battery, wherein the cobalt-doped molybdenum tungsten sulfide or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method is used as a negative electrode material.

[0043] The application also provides a supercapacitor, wherein the cobalt-doped molybdenum tungsten sulfide or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method is used as a negative electrode material.

[0044] Example 1

[0045] (1) Ammonium paratungstate (0.6240 g, 0.19 mmol), thiourea (1.4209 g, 18.67 mmol), ammonium molybdate tetrahydrate (0.2897 g, 0.23 mmol), oxalic acid (0.4256 g, 4.73 mmol) and cobalt nitrate hexahydrate (0.0114 g, 0.04 mmol) were stirred and dissolved in 20 mL of deionized water, and then transferred to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene, and then the autoclave was placed in a 220°C oven for hydrothermal reaction for 24 h. After the reaction was completed, the oven was naturally cooled to room temperature, the reaction solution was taken out, centrifuged with 25 mL of deionized water for three times, and centrifuged with 25 mL of 95% ethanol for two times, the centrifuge speed was 8000 rpm, and the centrifugation time was 3 min each time. The obtained solid was vacuum dried at 60°C for 24 h to obtain the cobalt-doped molybdenum tungsten sulfide.

[0046] (2) The cobalt-doped molybdenum tungsten sulfide prepared in step (1) was placed in a quartz transparent glass container with a hole left at the top, and then the container was placed in a plasma generator for plasma treatment at room temperature and normal pressure for 5 min, and the power was 10 W to obtain the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method.

[0047] Examples 2-5

[0048] According to the method of Example 1, except that the plasma treatment power was adjusted to 20, 30, 40 and 50 W, respectively.

[0049] Comparative Example 1

[0050] According to the method of Example 1, except that the cobalt-doped molybdenum tungsten sulfide was not subjected to plasma treatment.

[0051] The cobalt-doped molybdenum tungsten sulfide sample prepared in Comparative Example 1 was tested by inductively coupled plasma spectroscopy, the sample mass was 0.0546 g, and the constant volume was 25 mL. The test results are shown in Table 1.

[0052] Table 1

[0053]

[0054] From the elemental content in Table 1, the molecular formula of the molybdenum-tungsten sulfide compound can be determined as Mo 0.64 W 0.36 S2.

[0055] Comparative Example 2

[0056] The method of Example 1 was followed, except that the molybdenum-tungsten sulfide was not cobalt-doped and the molybdenum-tungsten sulfide was not subjected to plasma treatment.

[0057] Figure 1 The XRD patterns of the cobalt-doped molybdenum-tungsten sulfide after plasma treatment in Examples 1-5 and the cobalt-doped molybdenum-tungsten sulfide without plasma treatment in Comparative Example 1 are shown in Figure 1. Figure 1 As can be seen from the XRD patterns, the characteristic diffraction peaks at 14.0°, 32.7° and 57.0° correspond to the (002), (100) and (110) crystal planes, respectively. After plasma treatment, the (002) peak becomes stronger, indicating that the crystallinity of the sample becomes better, which will lead to an improvement in ion / electron transport efficiency, improve the interface stability of the sample and enhance the reaction reversibility.

[0058] Figure 2 The SEM images of the cobalt-doped molybdenum-tungsten sulfide after plasma treatment in Examples 1-5 and the cobalt-doped molybdenum-tungsten sulfide without plasma treatment in Comparative Example 1 are shown in Figure 2. Figure 2 As can be seen from the SEM images, the cobalt-doped molybdenum-tungsten sulfide after plasma treatment has a nanoflower spherical structure with a layered structure, which provides more active sites for electrochemical reactions.

[0059] Figure 3 The TEM image and EDS image of the cobalt-doped molybdenum-tungsten sulfide after plasma treatment in Example 1 are shown in Figure 3. Figure 3 As can be seen from the TEM image and EDS image, the cobalt-doped molybdenum-tungsten sulfide is successfully prepared and the cobalt element is uniformly distributed. At the same time, the micro-morphology of the cobalt-doped molybdenum-tungsten sulfide after plasma treatment is a nanoflower spherical structure formed by stacking nanosheets.

[0060] The assembly of the supercapacitor was carried out using the following steps:

[0061] (1) The foam nickel was cut into a size of 1 cm x 2 cm, weighed and recorded as m1.

[0062] (2) 80 mg of the cobalt-doped molybdenum-tungsten sulfide after plasma treatment in Examples 1-5 or the cobalt-doped molybdenum-tungsten sulfide without plasma treatment in Comparative Example 1, 10 mg of SuperP and 10 mg of PVDF powder were placed in a mortar, an appropriate amount of N-methyl pyrrolidone (NMP) was added, and the mixture was ground thoroughly to obtain a uniform slurry.

[0063] (3) The slurry was uniformly coated on the foamed nickel with a coating area of 1 cm x 1 cm, and dried in a 60°C vacuum drying oven for 12 h to obtain an electrode sheet, which was weighed and recorded as m 2。

[0064] (4) The electrode sheet with m2-m1=1~2mg was used as the working electrode, the platinum electrode was used as the counter electrode, the Ag / AgCl electrode was used as the reference electrode, and the electrolyte was a sodium sulfate solution (1 mol / L). The electrochemical performance of the assembled three-electrode system was tested.

[0065] Figure 4 The CV curves, GCD curves, rate performance curves and EIS of the three-electrode systems assembled with the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1~5 and the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 were compared. From Figure 4 It can be seen that the three-electrode system assembled with the cobalt-doped molybdenum tungsten sulfide after 30W plasma treatment as the negative electrode material has the longest discharge time. The specific capacitance can be calculated according to the formula C=It / mV, so the three-electrode system assembled with the cobalt-doped molybdenum tungsten sulfide after 30W plasma treatment as the negative electrode material has the highest specific capacitance, and its specific capacitance at each current density is significantly better than that of the cobalt-doped molybdenum tungsten sulfide under other plasma treatment powers, and the cobalt-doped molybdenum tungsten sulfide after plasma treatment is significantly better than the cobalt-doped molybdenum tungsten sulfide without plasma treatment, which proves that plasma treatment helps to improve the electrochemical performance of the cobalt-doped molybdenum tungsten sulfide.

[0066] Figure 5 The CV curves and GCD curves of the three-electrode systems assembled with the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 and the molybdenum tungsten sulfide compound without cobalt doping and without plasma treatment in Comparative Example 2 as the negative electrode material were compared. From Figure 5 It can be seen that the CV curve of the cobalt-doped molybdenum tungsten sulfide has a larger area, and the GCD curve also has a longer discharge time, i.e. a larger specific capacitance, indicating that cobalt doping improves the electrochemical performance of the molybdenum tungsten sulfide compound.

[0067] The following steps were used to assemble the lithium ion battery:

[0068] (1) 0.4g PVDF powder was dissolved in 20mL NMP to obtain a PVDF solution.

[0069] (2) 35mg of the cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1~5 or the cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1, 10mg SuperP and 250μL of the PVDF solution prepared in step (1) were added, and an appropriate amount of NMP was added. After stirring, a uniform slurry was obtained.

[0070] (3) The copper foil was wiped with alcohol to remove the surface oxide layer, and cut into a disc with a diameter of 1.2 cm, weighed, and recorded as m1.

[0071] (4) The slurry prepared in step (2) was uniformly coated on the rough surface of the copper foil with a coating thickness of 100 μm. After coating, it was dried in an oven at 60°C for 1 h. The copper foil loaded with active material was compacted using a tablet press to obtain an electrode sheet, which was weighed and recorded as m2.

[0072] (5) The battery assembly was carried out in an argon environment glove box (oxygen content ≤0.01 ppm, water content ≤0.01 ppm). The electrode sheet prepared in step (2) was placed in the center of the negative shell, 2-3 drops of electrolyte (LiPF6, EC: EMC: DMC = 1:1:1 v%) were added, a PP separator was covered, 1-2 drops of electrolyte were added, a lithium sheet was added, a gasket and a spring were pressed, and finally a positive shell was covered. The battery was packaged using a punch press with a punch pressure of 5 MPa and a punch time of 10 s. The obtained button cell was taken out of the glove box and the surface residual electrolyte was wiped off to obtain a lithium ion battery.

[0073] (6) The lithium ion battery obtained in step (5) was allowed to stand for 8 h, and the performance test was carried out using a blue battery test system. The rate performance and cycle performance of the lithium ion battery were tested under different currents set at different current densities.

[0074] The calculation formula of the current is as follows:

[0075] I = 0.7 · ρ 电流 · m · 1000

[0076] Wherein, m = m2-m1.

[0077] Figure 6 The rate performance curves of lithium ion batteries assembled with cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1-5 and cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 as negative electrode material. From Figure 6 It can be seen that the specific capacity of the lithium ion battery assembled with cobalt-doped molybdenum tungsten sulfide after 30 W plasma treatment as negative electrode material is the largest under a current density of 5C, which shows that plasma treatment can improve the electrochemical performance of cobalt-doped molybdenum tungsten sulfide.

[0078] Figure 7 The cycle performance curves of lithium ion batteries assembled with cobalt-doped molybdenum tungsten sulfide after plasma treatment in Examples 1-5 and cobalt-doped molybdenum tungsten sulfide without plasma treatment in Comparative Example 1 as negative electrode material. From Figure 7It can be seen that the lithium ion battery assembled with the cobalt-doped molybdenum tungsten sulfide treated by the 30 W plasma as the negative electrode material has the best cycle performance, and has the highest specific capacity after 600 cycles.

[0079] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-mentioned embodiments, and the above-mentioned embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. The application of cobalt-doped molybdenum tungsten sulfide in lithium-ion batteries and supercapacitors, the preparation method of the cobalt-doped molybdenum tungsten sulfide is: dissolving a tungsten source, a molybdenum source, a cobalt source, a sulfur source and a complexing agent in deionized water and then performing a hydrothermal reaction to obtain the cobalt-doped molybdenum tungsten sulfide; and the cobalt-doped molybdenum tungsten sulfide is subjected to plasma treatment. The tungsten source is ammonium paratungstate. The molybdenum source is ammonium molybdate, sodium molybdate and their hydrates. The cobalt source is cobalt nitrate and its hydrate. The sulfur source is at least one of thiourea, thioacetamide and cysteine. The complexing agent is oxalic acid. The mass ratio of the tungsten source, the molybdenum source, the cobalt source, the sulfur source and the complexing agent is 18-23%, 9-10%, 0.3-3%, 51-53% and 14-16%, respectively, with the total mass ratio being 100%. The temperature of the hydrothermal reaction is 180-220℃, and the time is 24-48 h. The molecular formula of the molybdenum tungsten sulfide in the cobalt-doped molybdenum tungsten sulfide is Mo 0.64 W 0.36 S2; The cobalt doping amount in the cobalt-doped molybdenum tungsten sulfide is 0.3-0.5%.

2. The cobalt-doped molybdenum tungsten sulfide prepared by the preparation method of the cobalt-doped molybdenum tungsten sulfide in the application of claim 1.

3. A plasma treatment method of the cobalt-doped molybdenum tungsten sulfide of claim 2.

4. The plasma processing method of claim 3, wherein: The plasma treatment is performed at normal temperature and pressure, with a power of 0-50 W and a treatment time of 5-10 min; and the gas of the plasma treatment is air.

5. A lithium-ion battery, characterized by: The cobalt-doped molybdenum tungsten sulfide of claim 2 or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method of any one of claims 3-4 is used as a negative electrode material.

6. An ultracapacitor characterized by: The cobalt-doped molybdenum tungsten sulfide of claim 2 or the cobalt-doped molybdenum tungsten sulfide treated by the plasma treatment method of any one of claims 3-4 is used as a negative electrode material.

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