CdS additive modified AgO positive electrode material, preparation method and zinc-silver battery

Abstract

The invention relates to a CdS additive modified AgO positive electrode material, a preparation method and a zinc-silver battery, and belongs to the technical field of zinc-silver batteries. The mass of the CdS is 2-10% of the mass of the AgO positive electrode material, and the PbS and the AgO positive electrode material are used for inhibiting the decomposition of AgO and improving the conductivity after being ball-milled and mixed. By introducing CdS as an additive into the AgO positive electrode material, on one hand, the stability of AgO can be improved, and the decomposition of AgO in the storage period is slowed down, so that the zinc-silver battery has a longer storage life; on the other hand, the conductivity of the positive electrode material can be improved by introducing the additive, and electrode reaction kinetics can be improved.

Description

Technical Field

[0001] The invention relates to a CdS additive-modified AgO positive electrode material, a preparation method and a zinc-silver battery, belonging to the technical field of zinc-silver batteries. Background Art

[0002] Zinc-silver batteries play an important role in many fields due to their advantages such as short activation time, high specific energy, stable voltage output, large current discharge, and long working time. Zinc-silver reserve batteries can be stored in a dry state for 5 to 8 years. When used, the battery can be activated and discharged by injecting electrolyte.

[0003] However, with the continuous updating and iteration of instruments and equipment, the requirements for zinc-silver batteries, one of the main components, are gradually increasing, and a longer storage time is required to meet the service life of the equipment. The reasons for the performance degradation of zinc-silver batteries during storage are: (1) Decomposition of AgO in the positive plate. AgO, the main active material in the positive plate, is thermodynamically unstable and will decompose during storage to generate Ag2O and O2. The formation of Ag2O not only reduces the available capacity of the battery, but also increases the internal resistance of the battery due to its high resistivity, resulting in a decrease in discharge voltage; (2) Oxidation of Zn, the active material in the negative plate. Zn in the negative plate will gradually oxidize during storage, which not only reduces the active material of the negative electrode, but also may increase the internal resistance of the battery and affect the battery performance; (3) Deterioration of diaphragm performance. The diaphragm may oxidize during storage, hindering the ion transmission in the electrolyte, resulting in an increase in the internal resistance of the battery and a decrease in the output voltage of the battery.

[0004] In view of the many reasons for the above failures, the optimization of positive electrode materials, improvement of negative electrode design, enhancement of diaphragm performance, and strengthening of battery maintenance are usually adopted to extend the life of zinc-silver storage batteries and improve their performance. Considering that the decomposition reaction of AgO, the active material of the positive electrode of zinc-silver batteries, is the main reason for the attenuation of battery performance, modifying the AgO material and improving its stability is the key to solving this problem.

[0005] Introducing additives into AgO materials or performing surface coating is a common strategy, but the above modification methods usually improve the stability of the positive electrode material while inevitably reducing the conductivity of the material. Therefore, it is necessary to develop a method that can improve the stability of the positive electrode material without reducing its conductivity. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a CdS additive-modified AgO positive electrode material, a preparation method and a zinc-silver battery.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] A CdS additive-modified AgO positive electrode material, wherein the mass of CdS is 2% to 10% of the mass of the AgO positive electrode material, and PbS is ball-milled and mixed with the AgO positive electrode material to inhibit the decomposition of AgO and improve the conductivity.

[0009] Preferably, the mass of the CdS is 3% to 5% of the mass of the AgO positive electrode material.

[0010] Preferably, taking the total mass of the AgO positive electrode material as 100%, the raw material components and their mass percentages are AgO 90% to 95%, Ag2O 1% to 4%, and Ag 4% to 6%.

[0011] A method for preparing the CdS additive-modified AgO positive electrode material of the present invention, the method steps comprising:

[0012] The CdS and AgO positive electrode materials are mixed, and an organic solvent is added to wet ball mill at 200-400 r / min for 3-12 hours. After the ball milling is completed, the mixture is dried by forced air at 50-60° C. for 8-12 hours to obtain a CdS additive-modified AgO positive electrode material.

[0013] Preferably, during wet ball milling, the diameter of the ball milling beads is 6 to 10 mm.

[0014] Preferably, during wet ball milling, the organic solvent is isopropanol, cyclohexane, tetrahydrofuran or acetonitrile, more preferably isopropanol.

[0015] A zinc-silver battery, wherein the positive electrode material of the battery is the CdS additive-modified AgO positive electrode material described in the present invention.

[0016] Beneficial Effects

[0017] The present invention introduces CdS as an additive into the AgO positive electrode material, which can improve the stability of AgO and slow down its decomposition during storage, thereby making the zinc-silver battery have a longer storage life; on the other hand, the introduction of the additive can also improve the conductivity of the positive electrode material, which is beneficial to improving the electrode reaction kinetics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the SEM image of the positive electrode material of Comparative Example 1.

[0019] Figure 2 This is the SEM image of the positive electrode material of Comparative Example 2.

[0020] Figure 3 This is the SEM image of the positive electrode material of Example 1.

[0021] Figure 4 This is the XRD diagram of the positive electrode material in Comparative Examples 1-3.

[0022] Figure 5 It is the XRD diagram of the positive electrode material in comparative example 1 and examples 1-2.

[0023] Figure 6 TG diagrams of the positive electrode materials in Examples 1-2 and Comparative Examples 2-3.

[0024] Figure 7 2 are the DC polarization curves of the positive electrode materials in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with specific embodiments.

[0026] In order to verify the extended storage life of the modified AgO positive electrode, an AgO electrode stored for 14 years was obtained by a high-temperature accelerated storage experimental method. The high-temperature accelerated storage method of the present invention is to place the material in a vacuum oven at 70°C for 256 hours. The principle is:

[0027] The aging and accelerated aging processes of the main component AgO in the AgO positive electrode material at room temperature, and the decomposition kinetic equations are:

[0028] K1=A1exp(-E a1 / RT1) (1)

[0029] K2=A2exp(-E a2 / RT2) (2)

[0030] Where E a =116.56KJ mol -1 , A=17.20s -1 .

[0031] Due to the E corresponding to the decomposition reaction of AgO at different temperatures a It is not much different from A, so we have:

[0032]

[0033] Therefore, when T1 = 298K (25°C) and T2 = 343K (70°C), the corresponding value of the reaction rate constant K2 / K1 is 479.25.

[0034] For the solid phase reaction 2AgO+Ag→Ag2O, the relationship between the equilibrium constant and the storage time at a certain temperature is:

[0035]

[0036] Where n is the number of sample storage temperature sections, m i0 is the initial mass of the sample in the i-th section, mi is the mass after the end of storage in the i-th stage, t i is the storage time. Under constant temperature conditions, K = (m0-m) / t. Since the initial mass is the same, the value of (m0-m) corresponding to the same retention rate is the same when decomposed. From formula (4), we can get t1 / t2 = K2 / K1. For the positive electrode stored for 14 years, t1 is 5110 days, and t2 = 10.66 days.

[0037] Therefore, placing the positive electrode material in a vacuum oven at 70°C for 256 hours can achieve the result of storing it at room temperature for 14 years.

[0038] SEM characterization: Instrument: FEI-Quanta 250 from Thermo Fisher Scientific, Voltage: 25 kV.

[0039] XRD characterization: Instrument: Rigaku's Ultima IV, scanning angle range: 10-80°, scanning speed: 5° / min.

[0040] TG characterization: Instrument: WCT-D of Beijing Beiguang Century Instrument Co., Ltd., heating rate: 5°C / min, temperature range: 30°C~800°C.

[0041] Example 1

[0042] (1) Ball milling: Add 6 mm diameter ball milling beads to a ball mill jar, which accounts for 2 / 3 of the volume of the ball mill jar. According to the ratio of 90.21 wt % of AgO, 2.82 wt % of Ag2O, 3.97 wt % of Ag and 3.00 wt % of CdS, weigh 0.9021 g of AgO, 0.0282 g of Ag2O, 0.0397 g of Ag and 0.0300 g of CdS, put them into the ball mill jar, add 5 mL of isopropanol as solvent, and ball mill for 3 h at a speed of 200 r / min.

[0043] (2) Drying: The ball-milled material was placed in a forced air drying oven and dried at 50° C. for 12 h to obtain a CdS additive-modified AgO positive electrode material.

[0044] Example 2

[0045] The CdS additive-modified AgO positive electrode material obtained in Example 1 was placed in a vacuum oven at 70° C. for 256 hours.

[0046] Comparative Example 1

[0047] (1) Grinding: 0.9300 g of AgO, 0.0290 g of Ag2O and 0.0410 g of Ag were weighed according to the ratio of 93.00% by mass of AgO, 2.90% by mass of Ag2O and 4.10% by mass of Ag, put into a mortar and grind for 30 min, mix well, and obtain an AgO positive electrode material.

[0048] Comparative Example 2

[0049] (1) Ball milling: Add 6 mm diameter ball milling beads to a ball milling jar, which accounts for about 2 / 3 of the volume of the ball milling jar. Then, according to the mass fraction of AgO being 93.00%, the mass fraction of Ag2O being 2.90%, and the mass fraction of Ag being 4.10%, 0.9300 g of AgO, 0.0290 g of Ag2O, and 0.0410 g of Ag are weighed and placed in the ball milling jar. About 5 mL of isopropanol is added as a solvent, and the mixture is ball milled at a speed of 200 r / min for 3 h.

[0050] Step (2) is the same as in Example 1, to obtain an AgO positive electrode material.

[0051] Comparative Example 3

[0052] (1) The dried material in Comparative Example 2 was placed in a vacuum oven at 70° C. for 256 hours.

[0053] Comparative Example 1, Comparative Example 2, and Example 1 were characterized by SEM. Figure 1 , Figure 2 , Figure 3 It can be seen that the particles in Comparative Example 1 without ball milling are intact and uniform in size. The particles in Comparative Example 2 after ball milling are broken, rough in surface, and agglomerated in large quantities. Compared with Comparative Example 2, the particles in Example 1 with the addition of CdS additive have a smoother surface, uniform in size, and reduced agglomeration, indicating that the addition of CdS can reduce the degree of particle damage during ball milling.

[0054] The above Examples 1-2 and Comparative Examples 1-3 were characterized by XRD to determine their compositions. The XRD spectrum of AgO (PDF#43-1038) has diffraction peaks at 2θ of 32.01°, 32.28°, 34.17°, 37.18° and 39.38° corresponding to (200), (111), (002), (111) and (202) crystal planes, respectively. Figure 4It can be seen that compared with Comparative Example 1, the characteristic peaks corresponding to the AgO (002), (111) and (202) crystal planes at 4.17°, 37.18° and 39.38° in the XRD spectrum of Comparative Example 2 disappear, and only the characteristic peaks corresponding to the (200) and (111) crystal planes appear at 32.01° and 32.28°, indicating that AgO will decompose during the ball milling process. The characteristic peaks corresponding to AgO (PDF#43-1038) in the XRD spectrum of Comparative Example 3 after accelerated aging all disappear, indicating that AgO will decompose a lot during the aging process. Figure 5 It can be seen that the characteristic peak corresponding to AgO (PDF#43-1038) still exists in the XRD spectrum of Example 1 with the introduction of CdS additive, which shows that the introduction of CdS can effectively inhibit the decomposition of AgO during the ball milling process. Moreover, the characteristic peak of the (111) crystal plane of AgO in the XRD spectrum of Example 2 after accelerated aging is only slightly weakened, and other characteristic peaks still exist, indicating that only a small amount of AgO decomposes during the accelerated aging process, and the introduction of CdS also effectively inhibits the decomposition of AgO during the aging process.

[0055] In order to further explore the effect of CdS on the decomposition of AgO, the above Examples 1-2 and Comparative Examples 2-3 were characterized by TG. Figure 6 The results of TG characterization show that the thermogravimetric platform can be divided into three stages, and the weight loss in the first stage corresponds to the decomposition process of AgO:

[0056]

[0057] The second weightlessness stage (platform zone) corresponds to the decomposition process of the solid solution formed in the first stage:

[0058]

[0059] In the first and second stages, the total weight loss rates of the materials of Comparative Example 2, Comparative Example 3, Example 1 and Example 2 were 3.60%, 2.97%, 5.11% and 4.91% respectively.

[0060] The third stage weight loss corresponds to the decomposition of Ag2O:

[0061] 2Ag2O→4Ag+O2↑(7)

[0062] The total weight loss rates of the materials in Comparative Example 2, Comparative Example 3, Example 1 and Example 2 are 6.00%, 6.03%, 5.20% and 5.03% respectively.

[0063] Table 1 shows the calculated contents of AgO, Ag2O and Ag in the material. The content of AgO in the material before ball milling is 93.00%, while the content of AgO in Comparative Example 2 after ball milling is only 55.82%, indicating that AgO will decompose in large quantities during the ball milling process. The content of AgO in Example 1 with the addition of CdS is increased to 79.21%, indicating that the addition of CdS can effectively inhibit the decomposition of AgO during the ball milling process. The content of AgO in Comparative Example 3 is only 46.0%, and the decomposition rate of AgO during the aging process is 17.56%. The content of AgO in Example 2 with the addition of CdS is increased to 76.11%, and the decomposition rate of AgO during the aging process is only 3.91%, indicating that the addition of CdS can effectively inhibit the decomposition of AgO during the aging process.

[0064] Table 1

[0065]

[0066] In order to explore the effect of CdS addition on the conductivity of the positive electrode material, the above Example 1 and Comparative Example 2 were subjected to a double-blocking electrode DC polarization test. After the positive electrode material powder was cold pressed into shape using a mold, a constant voltage of 0.2V DC polarization was applied for 1000s using an electrochemical workstation CHI660e. The time-current curve was measured as follows: Figure 7 As shown, the average current of 800s to 1000s is taken as the steady-state current. The steady-state current of Example 1 is 29.58μA, and the steady-state current of Comparative Example 2 is 5.23μA. The resistance R of the material can be calculated according to Ohm's law, and the conductivity is calculated according to the following formula:

[0067]

[0068] Where:

[0069] σ——Conductivity of positive electrode material (S cm -1 );

[0070] l——thickness of positive electrode material (cm);

[0071] R——Resistance of positive electrode material (Ω);

[0072] S——Area of ​​positive electrode material (cm 2 ).

[0073] The calculated results are shown in Table 2. The conductivity of Comparative Example 2 is 1.63×10 -7 S cm -1 The conductivity of Example 1 with CdS added is 8.10×10 -7 S cm -1The conductivity of the AgO positive electrode material with added CdS has been greatly improved, which shows that the addition of CdS is beneficial to the transmission of electrons and increases the conductivity of the material.

[0074] Table 2

[0075]

[0076] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A CdS additive-modified AgO positive electrode material, characterized in that: The mass of CdS is 2% to 10% of the mass of the AgO positive electrode material, and PbS is mixed with the AgO positive electrode material by ball milling to inhibit the decomposition of AgO and improve the conductivity.

2. The CdS additive-modified AgO positive electrode material according to claim 1, characterized in that: The mass of the CdS is 3% to 5% of the mass of the AgO positive electrode material.

3. The CdS additive-modified AgO positive electrode material according to claim 1, characterized in that: Taking the total mass of the AgO positive electrode material as 100%, the raw material components and their mass percentages are AgO 90% to 95%, Ag2O 1% to 4%, and Ag 4% to 6%.

4. A method for preparing a CdS additive-modified AgO positive electrode material according to any one of claims 1 to 3, characterized in that: The method steps include: The CdS and AgO positive electrode materials are mixed, and an organic solvent is added to wet ball mill at 200-400 r / min for 3-12 hours. After the ball milling is completed, the mixture is dried by forced air at 50-60° C. for 8-12 hours to obtain a CdS additive-modified AgO positive electrode material.

5. The method for preparing a CdS additive-modified AgO positive electrode material according to claim 4, characterized in that: During wet ball milling, the diameter of the ball milling beads is 6 to 10 mm.

6. The method for preparing a CdS additive-modified AgO positive electrode material according to claim 4, characterized in that: During wet ball milling, the organic solvent is isopropanol, cyclohexane, tetrahydrofuran or acetonitrile.

7. The method for preparing a CdS additive-modified AgO positive electrode material according to claim 4, characterized in that: The organic solvent is isopropanol.

8. A zinc-silver battery, characterized in that: The positive electrode material of the battery is a CdS additive-modified AgO positive electrode material as claimed in any one of claims 1 to 3.

Images