Method for improving stability of manganese-based positive electrode material

Abstract

The invention discloses a method for improving the stability of a manganese-based positive electrode material, and relates to the technical field of zinc ion batteries. The method comprises the step of adding 2M WS2 crystals into raw materials for preparing the manganese-based positive electrode material to obtain the stable manganese-based positive electrode material. The 2M WS2 crystal has nucleophilic and adsorption effects on electrochemical deposition of MnO2, so that the reaction kinetics of deposition is improved. On the basis, the cycling stability of the manganese-based positive electrode material is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of zinc ion batteries, and particularly to a method for improving the stability of manganese-based cathode materials. Background Art

[0002] In recent years, with the rapid growth of the demand for renewable energy, the development of alternative battery systems with high safety and environmental friendliness to replace lithium-ion batteries has attracted increasing attention. Aqueous zinc ion batteries have the advantages of low cost, high theoretical specific capacity, low redox potential, and good safety of aqueous electrolytes, and have become alternatives with broad application prospects. Many researchers have greatly expanded the development of zinc ion batteries, and the research interest mainly focuses on the exploration of cathode materials. Manganese dioxide materials have the advantages of environmental friendliness, easy preparation, high working voltage, high theoretical capacity, etc., and are considered to be one of the most promising cathode materials for the industrialization of zinc ion batteries. However, the cathode of zinc-manganese batteries faces challenges such as low ionic conductivity, the formation of inactive substances during electrochemical reactions, the dissolution of active substances, and the rapid degradation of battery capacity caused by the collapse of the structure.

[0003] People have been researching rechargeable aqueous zinc-manganese batteries for decades. According to relevant research reports, the cathode reaction may include the insertion / extraction of Zn ions, the conversion reaction between MnO 2 and protons, and the dissolution / deposition reaction. In a weakly acidic electrolyte, manganese dioxide will be electrochemically reduced to form intermediate MnOOH during battery discharge. MnOOH is extremely unstable, and a part of it will undergo a disproportionation reaction to generate Mn 2+ dissolved in the electrolyte, resulting in irreversible dissolution of active substances. In addition, in these cathode reactions, the conversion reaction and the dissolution reaction will cause obvious pH changes during cycling. By-products Zn 4 (OH) 6 SO 4 •xH 2 O (or ZHS) are generated on the cathode surface during battery discharge. Subsequently, during battery charging, ZHS that is not dissolved in time reacts with Mn 2+ to form low-crystalline (Zn,Mn) 2 Mn 5 O 12 •4H 2 O or ZMO). By-product ZMO is difficult to be reduced to Mn 2+ during further discharge, making the formation of ZMO irreversible. The ZMO layer increases the charge transfer resistance and seriously hinders the electrochemical behavior of the MnO 2 cathode. After long-term cycling, the entire MnO 2 cathode gradually turns into low-crystalline ZMO, resulting in capacity loss. Summary of the Invention

[0004] In view of the deficiencies in the above-mentioned background art, the present invention mainly solves the problems of poor stability and short cycle life of manganese-based cathode materials in the aqueous battery system in the prior art. The present invention provides a method for improving the stability of manganese-based cathode materials. This method refers to physically mixing 2M WS in the cathode slurry 2 A method for improving the cycle stability of the battery cathode by crystal form. Different proportions of 2M WS are added to the MnO cathode slurry by physical mixing 2 crystals, and during the discharge and charge processes of the battery, OH is consumed by its own oxidation 2 to maintain a weakly acidic environment in the battery, thereby reducing the generation of ZHS during discharge and promoting the dissolution of ZHS during charge to reduce the generation of irreversible product ZMO; secondly, during the battery charge process, through 2M WS - crystals have a nucleophilic and adsorption effect on the electrochemical deposition of MnO, improving the reaction kinetics of the deposition. Based on this, the cycle stability of the manganese-based cathode material is greatly improved. 2 crystals have a nucleophilic and adsorption effect on the electrochemical deposition of MnO 2 Thereby improving the reaction kinetics of the deposition. Based on this, the cycle stability of the manganese-based cathode material is greatly improved.

[0005] The first object of the present invention is to provide a method for improving the stability of manganese-based cathode materials, including: Adding 2M WS crystals to the raw materials for preparing manganese-based cathode materials to obtain stable manganese-based cathode materials. 2 crystals to obtain a stable manganese-based cathode material.

[0006] Preferably, the addition amount of the 2M WS crystals accounts for 8-15% of the mass percentage of the raw materials. 2 crystals accounts for 8-15% of the mass percentage of the raw materials.

[0007] Preferably, the 2M WS crystals are prepared according to the following steps: 2 crystals are prepared according to the following steps: Prepare K x WS 2 crystals; Place the K x WS 2 crystals in an acidic potassium dichromate aqueous solution and stir, then filter, wash, and freeze-dry to obtain 2M WS 2 crystals.

[0008] Preferably, the acidic potassium dichromate aqueous solution is prepared from a potassium dichromate aqueous solution and sulfuric acid; Among them, the potassium dichromate aqueous solution is prepared by dissolving potassium dichromate in a water solvent, and the molar concentration of the potassium dichromate aqueous solution is 0.08 mol / L to 0.1 mol / L; The molar concentration ratio of potassium dichromate to sulfuric acid is 1:14-15; The K xWS 2 The mass ratio of the crystal to the potassium dichromate is 3 to 5:1.

[0009] Preferably, the K x WS 2 crystal is prepared by grinding K 2 S 2 , sulfur powder and tungsten powder in a certain proportion, and then holding at 800 - 900 °C for 1000 - 1200 min in an argon atmosphere.

[0010] Preferably, the raw materials for preparing the manganese-based cathode material include the following components in mass percentages: 60% - 65% of the electrode active material, 17 - 19% of the electronic conductor, and 8 - 10% of the binder; The electronic conductor includes one or more of conductive carbon black, conductive acetylene black, and Ketjen black; The binder includes 28 - 33 wt.% of polyvinylidene fluoride and 67 - 72 wt.% of N-methylpyrrolidone; The electrode active material is α-MnO 2 powder.

[0011] Preferably, the stable manganese-based cathode material is prepared according to the following steps: Adding α-MnO 2 powder and 2M WS 2 crystal into the binder for stirring and mixing, and then adding the electronic conductor and continuing to stir to obtain a mixed slurry; Coating the mixed slurry evenly on the conductive current collector, and then performing a drying treatment to obtain the stable manganese-based cathode material.

[0012] Preferably, the conductive current collector is titanium foil or carbon cloth.

[0013] The second object of the present invention is to provide a stable manganese-based cathode material.

[0014] The third object of the present invention is to provide an application of a stable manganese-based cathode material in a zinc-manganese battery.

[0015] Compared with the prior art, the beneficial effects of the present invention are: The present invention provides a method for improving the stability of the manganese-based cathode material. The present invention proposes that 2M WS 2 has good electrical conductivity, and has nucleophilicity and adsorption to MnO 2 . During the charging process of the battery, the 2M WS 2 single crystal distributed on the electrode surface enables efficient reuse of Mn 2+ in the electrolyte, accelerating MnO 2The rate of electrodeposition supplements the content of the electrode active material, thus solving the gradual loss of battery capacity caused by the dissolution of the active material due to the dissolution of part of MnO during the battery discharge process. 2 Dissolved in the electrolyte in the form of Mn 2+ The step-by-step loss of battery capacity caused by the dissolution of the active material.

[0016] The present invention proposes that 2M WS 2 Will be oxidized at a certain potential in the electrolyte, and the stronger the acidic solution will inhibit the oxidation of 2M WS 2 At the same time, it is concluded from another aspect that 2M WS 2 Will react with OH in the solution - And to a large extent maintain the weak acidic environment of the solution.

[0017] The present invention proposes that 2M WS 2 Because part of OH is consumed during the charge and discharge process of the battery - Therefore, the large generation of ZHS is inhibited during the battery discharge process, and the dissolution of ZHS is promoted during the battery charging process. This also indirectly inhibits the generation of the by-product ZMO caused by the reaction of the ZHS that is not dissolved in time during the charging process with Mn in the solution 2+ And thus greatly alleviates the irreversible transformation of the active material, thereby improving the cycle stability of the positive electrode.

[0018] The present invention proposes a method for improving the stability of the manganese-based positive electrode material. When an auxiliary material with a mass ratio of 1:8 to the active material is added to the battery positive electrode, at a current density of 0.4 A / g, the capacity retention rate of the battery after 200 charge and discharge cycles is 82.06%. The positive electrode capacity retention rate of the unmodified MnO 2 Is increased by 45%.

[0019] The material proposed by the present invention to assist the electrode stability is added to the battery positive electrode in a physically mixed manner, saving preparation time, reducing raw material waste, reducing preparation costs, and the preparation process is energy-saving and environmentally friendly and can achieve large-scale batch production. Brief Description of the Drawings

[0020] Figure 1 Taking the samples prepared in Examples 1-3 as an example, it shows the X-ray diffraction patterns of the materials K x WS 2 And 2M WS used to assist the positive electrode cycle stability prepared according to the present invention 2 And the X-ray diffraction pattern of 2M WS.

[0021] Figure 2 Taking the samples prepared in Examples 1-3 as an example, it shows the Raman spectrum of the material 2M WS used to assist the positive electrode cycle stability prepared according to the present invention 2 And the Raman spectrum of 2M WS.

[0022] Figure 3 One of the mechanisms of action of the material 2M WS used in Examples 1-3 to assist in the stability of the battery positive electrode 2 In-situ light microscope images during the electrochemical deposition of MnO on different substrates 2 during the process.

[0023] Figure 4 One of the mechanisms of action of the material 2M WS used in Examples 1-3 to assist in the stability of the battery positive electrode 2 Two, 2MWS 2 Cyclic voltammograms in solutions with different pH values.

[0024] Figure 5 Taking the samples prepared in Examples 1-3 as an example, the composite positive electrode 2M WS prepared according to the present invention is shown 2 / α-MnO 2 Scanning electron microscope (SEM) characterization images. Figure 6 Taking the sample prepared in Example 1 as an example, a graph showing the relationship between the discharge voltage and discharge specific capacity of the button battery prepared according to the present invention.

[0025] Figure 7 Taking the sample prepared in Example 1 as an example, the composite positive electrode 2M WS prepared according to the present invention is shown 2 / α-MnO 2 and the charge-discharge cycle test results of a zinc-ion battery assembled with a zinc metal negative electrode.

[0026] Figure 8 Taking the sample prepared in Example 1 as an example, SEM characterization images of the battery after 200 charge-discharge cycles prepared according to the present invention are shown.

[0027] Figure 9 Taking the sample prepared in Comparative Example 1 as an example, the charge-discharge cycle test results of a zinc-ion battery assembled with the positive electrode α-MnO prepared according to Comparative Example 1 are shown 2 and a zinc metal negative electrode. Detailed implementation manners

[0028] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and the accompanying drawings, but the specific embodiments cited are not intended to limit the present invention.

[0029] Based on an aqueous electrolyte, Mn in the solution in the present invention 2+ participates in the reconstruction of MnO during the battery charging process x Adding MnSO 4 additives have been proven to avoid MnO2 One strategy for excessive dissolution; ZHS is a precursor of the irreversible product ZMO. Adjusting the proton distribution in the electrolyte has been proven to be one of the strategies to inhibit the growth of ZHS. In addition, if the full utilization of Mn in the solution can be achieved, the deposition kinetics of Mn during the charging process can be improved; and by adjusting the changes in the concentrations of OH and H during the charge and discharge processes of the battery, they will all be strategies to inhibit the generation of ZHS. Improving the positive electrode cycle stability of the Zn-MnO battery through the above two points has great application value. 2+ in the solution, and improving the deposition kinetics of Mn 2+ during the charging process; and by adjusting the OH - and H + concentrations during the charge and discharge processes of the battery will also be strategies to inhibit the generation of ZHS. 2 Improving the positive electrode cycle stability of the Zn-MnO battery through the above two points has great application value.

[0030] The purpose of the present invention is to solve the problems of poor stability and short cycle life of manganese-based positive electrode materials in the aqueous battery system in the prior art, and to provide a method for improving the positive electrode cycle stability of the battery by physically mixing 2M WS 2 in the positive electrode slurry.

[0031] It should be noted that "2M WS 2 crystal" refers to tungsten disulfide crystal with a 2M polytype structure. Polytype refers to the phenomenon that the same compound exists in two or more different layered crystal structures. Here, "2M" represents a specific layered stacking mode and crystal structure feature of the WS 2 crystal. "2" indicates that there are two atomic layers in one repeating period, and "M" represents the monoclinic crystal system.

[0032] To achieve the above purpose, the first aspect of the present invention provides a method for improving the stability of manganese-based positive electrode materials, including: Adding 2M WS 2 crystal to the raw materials for preparing manganese-based positive electrode materials to obtain a stable manganese-based positive electrode material.

[0033] The addition amount of the 2M WS 2 crystal accounts for 8-15% of the mass percentage of the raw materials.

[0034] The 2M WS 2 crystal is prepared according to the following steps: Prepare K x WS 2 crystal; Place the K x WS 2 crystal in an acidic potassium dichromate aqueous solution and stir, then filter, wash, and freeze-dry to obtain the 2M WS 2 crystal.

[0035] The acidic potassium dichromate aqueous solution is prepared from a potassium dichromate aqueous solution and sulfuric acid; Among them, the potassium dichromate aqueous solution is prepared by dissolving potassium dichromate in a water solvent, and the molar concentration of the potassium dichromate aqueous solution is 0.08 mol / L to 0.1 mol / L; The molar concentration ratio of the potassium dichromate to the sulfuric acid is 1:14 to 15; The x WS 2 The mass ratio of the crystal to the potassium dichromate is 3 to 5:1.

[0036] The x WS 2 The crystal is prepared by grinding K 2 S 2 , sulfur powder and tungsten powder in a certain proportion, and then keeping the temperature at 800 - 900 °C for 1000 - 1200 min in an argon atmosphere.

[0037] The raw materials for preparing the manganese-based cathode material include the following components in mass percentages: 60% - 65% of the electrode active material, 17 - 19% of the electronic conductive agent, and 8 - 10% of the binder; The electronic conductive agent includes one or more of conductive carbon black, conductive acetylene black, and Ketjen black; The binder includes 28 - 33 wt.% of polyvinylidene fluoride and 67 - 72 wt.% of N-methylpyrrolidone; The electrode active material is α-MnO 2 powder.

[0038] According to the present invention, the stable manganese-based cathode material is prepared according to the following steps: Adding the α-MnO 2 powder and 2M WS 2 crystal into the binder and stirring and mixing, then adding the electronic conductive agent and continuing to stir to obtain a mixed slurry; Coating the mixed slurry evenly on the conductive current collector, and then performing a drying treatment to obtain the stable manganese-based cathode material.

[0039] Among them, the conductive current collector is a titanium foil or a carbon cloth.

[0040] The present invention mainly uses a physical mixing method to add 2M WS 2 with different proportions to the MnO 2 positive electrode slurry, and consumes OH -Thus, it maintains a weakly acidic environment in the battery, thereby reducing the generation of ZHS during discharge and promoting the dissolution of ZHS during charging to reduce the generation of the irreversible product ZMO. Secondly, during the battery charging process, through 2M WS 2 has a nucleophilic and adsorption effect on the electrochemical deposition of MnO 2 , improving the reaction kinetics of the deposition. Based on this, the cycle stability of the manganese-based cathode material is greatly improved.

[0041] Exemplarily, a method for improving the stability of a manganese-based cathode material, including the synthesis and preparation of the cathode active material and the auxiliary material. Among them, the cathode active material α-MnO 2 The required chemicals include: MnSO 4 ·H 2 O, KMnO 4 ; The auxiliary material metal phase 2M WS 2 The required chemicals include: K 2 S 2 , sulfur powder, tungsten powder, potassium dichromate, dilute sulfuric acid. The specific steps include: Step 1. Preparation of α-MnO 2 : Drop a certain amount of MnSO 4 ·H 2 O aqueous solution into the KMnO 4 aqueous solution, stir at room temperature and then put the mixture into a high-pressure reaction kettle lined with polytetrafluoroethylene for heating. After the reaction is completed, collect the precipitate and wash it with deionized water and dry it overnight to prepare α-MnO 2 ; The molar ratio of the solutes of the MnSO 4 · H 2 O solution and the KMnO 4 solution is 1~1.5:1, the stirring time of the mixed solution at room temperature is 30min~60min, the heating temperature of the reaction kettle is 140~160°C, and the heating time is 12h.

[0042] Step 2. Preparation of K x WS 2 crystals: Grind K 2 S 2 , sulfur powder and tungsten powder in a ratio of 1:2:2, put them into a sealed test tube in an argon atmosphere, and put the sealed test tube into a muffle furnace to prepare single crystals of K x WS 2 through a method of heating up, holding and natural cooling; The heating rate of the muffle furnace is 3°C / min~3.5°C / min, and it is heated to 850°C, and the holding time is 1000min~1200min.

[0043] Step 3. 2M WS 2 Preparation of crystal: Put the K synthesized in Step 2 x WS 2 in a certain amount into an acidic potassium dichromate aqueous solution for stirring, then perform suction filtration and washing on the mixed solution, and finally freeze-dry the obtained powder to obtain 2M WS 2 ; The molar concentration of the potassium dichromate aqueous solution is 0.08 mol / L to 0.1 mol / L, and the mass ratio of K x WS 2 to potassium dichromate is 3:1 to 5:1, and the molar concentration ratio of potassium dichromate to sulfuric acid is 1:14 to 1:15.

[0044] The positive electrode slurry used in the method for improving the stability of the manganese-based positive electrode material provided by the present invention, calculated by mass fraction, the raw materials of the positive electrode slurry include 60% to 65% of electrode active material, 8% to 15% of auxiliary material (2M WS 2 ) and 17 to 19% of electronic conductive agent and 8 to 10% of binder.

[0045] The mass fraction of the electrode active material can be 60%, 61%, 62%, 63%, 64%, 65%, etc., the mass fraction of the auxiliary material can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., the mass fraction of the electronic conductive agent can be 17%, 18%, 19%, etc., and the mass fraction of the binder can be 8%, 9%, 10%, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0046] The electronic conductive agent includes one or more of conductive carbon black, conductive acetylene black, and Ketjen black.

[0047] Calculated by mass fraction, the binder includes 28 to 33 wt% of polyvinylidene fluoride and 67 to 72 wt% of N-methylpyrrolidone. The mass fraction of the polyvinylidene fluoride can be 28%, 29%, 30%, 31%, 32% or 33%, etc., and the mass fraction of the N-methylpyrrolidone can be 67%, 68%, 69%, 70%, 71% or 72%, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0048] The present invention provides a method for preparing a manganese-based positive electrode material, including: S1. Add a certain proportion of desulphidene fluoride to N-methylpyrrolidone and heat and stir to prepare a binder; the heating temperature in step S1 is 30-50° C., the stirring speed is 500 rpm-600 rpm, and the stirring time is 10 min-15 min.

[0049] S2, a certain proportion of α-MnO 2 and 2M WS 2 After sufficient grinding, the evenly ground 2M WS2 / α-MnO 2 Add a certain amount of the binder described in S1 and stir to mix, and finally add a certain amount of conductive agent to the above mixed slurry and continue to stir; the stirring speed of the mixed slurry in step S2 is 1500rpm~2000rpm, and the stirring time is 24h~48h.

[0050] S3, evenly apply the slurry described in S2 to the conductive current collector, and then dry it. In step S3, the conductive current collector is titanium foil or carbon cloth, and the drying temperature is 50°C to 60°C, and the drying time is 12h to 24h.

[0051] It should be noted that the prepared manganese-based positive electrode material is used as a composite positive electrode.

[0052] The second aspect of the present invention provides a stable manganese-based positive electrode material. The third aspect of the present invention provides an application of a stable manganese-based positive electrode material in a zinc-manganese battery.

[0053] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0054] Example 1 This embodiment provides a method for improving the stability of a manganese-based positive electrode material, comprising the following steps: (1) α-MnO 2 Preparation: Measure 15 ml of deionized water in two beakers and add 380 mg of MnSO 4 ·H 2 O and 237 mg KMnO 4 Put it into two beakers and stir thoroughly until the powder is completely dissolved, then add the prepared MnSO 4 The solution was added dropwise to KMnO 4 The mixture was stirred at room temperature for 60 min, and then heated in a Teflon-lined autoclave at 160 °C for 12 h. After the reaction, the precipitate was collected, washed with deionized water, dried at 80 °C overnight, and finally the bulk sample was ground to obtain α-MnO 2 powder.

[0055] (2) K x WS 2 Preparation of crystals: 284 mg, 128 mg and 735.36 mg of K 2 S 2 , S powder and W powder were put into a mortar, and after being fully ground, they were put into a quartz tube in an argon atmosphere, and the quartz tube was sintered and sealed. During the whole process, it must be ensured that the atmosphere in the quartz tube does not contain oxygen. The sealed quartz tube was placed in a muffle furnace and heated at a heating rate of 3°C / min. When the temperature reached 850°C, it was kept warm for 1000min, and then naturally cooled to prepare K x WS 2 of single crystal.

[0056] (3) 2M WS 2 Preparation of crystals: Measure 200 ml of deionized water in a 250 ml beaker, add 2 ml (1 mol / L) sulfuric acid and 1.36 ml (0.1 mol / L) potassium dichromate solution, stir the mixture thoroughly, and weigh 200 mg of K prepared in step 2. x WS 2 After stirring for 4 hours, the waste liquid was filtered out with a vacuum filtration device, and the 2M WS on the filter paper was washed with deionized water. 2 Rinse repeatedly and then dry.

[0057] (4) 2M WS 2 / α-MnO 2 Preparation of mixed positive electrode slurry: 1.2 ml of NMP solution was measured in a 10 ml glass bottle, 40 mg of PVDF was added, and the mixture was placed on a heating table at 30 °C for heating and stirring for 15 min to prepare a binder. 280 mg of a-MnO prepared in step 1 was weighed. 2 powder and 35 mg of 2MWS prepared in step 3 2 Put it into a mortar and grind it thoroughly. Add the mixed powder and 80 mg of conductive carbon black into a glass bottle containing a binder in sequence and stir it for 24 hours. Set the speed to 1500 r / min.

[0058] (5) 2M WS 2 / MnO 2 Preparation of hybrid electrode: The slurry prepared in step 4 was evenly spread on a 20 um titanium foil using a 100 um thick scraper, and then placed in an oven at 50°C for 12 hours for heating.

[0059] The intermediate samples and final samples prepared in Example 1 are actually tested below.

[0060] Figure 1 For the synthesized K x WS 2 and 2M WS 2 X-ray diffraction pattern, it can be clearly seen that for K x WS 2 and 2M WS 2 diffraction peaks. We prepared 2M WS x WS 2 single crystal by removing potassium ions from K 2 WS crystal, which is in good agreement with the previously reported results. Figure 2 For the Raman spectrum corresponding to the synthesis of 2M WS 2 at 133.72 cm -1 , 275.58 cm -1 , 409.42 cm -1 the peaks are similar to the Raman peak results of 2M-phase WS 2 nanosheets reported in the literature, which are the vibration peaks of J 1 , J 2 , J 3 respectively, further proving the successful preparation of high-purity 2M-phase WS 2 nanosheets. Figure 1 and Figure 2 are used to illustrate the successful preparation of the auxiliary material for improving the cycling stability of the manganese-based cathode. Figure 3 is the in-situ optical microscopy image of electrochemically deposited MnO 2 on different conductive substrates, graphite (Graphite), graphene (Graphene) and Au. It can be seen that the single crystal of 2M WS 2 is placed on the conductive substrates of graphite and graphene or Au, and MnO 2 will preferentially deposit on the surface of 2M WS 2 . It can be concluded that the nucleophilic and adsorption properties of 2M WS 2 towards MnO 2 accelerate the deposition kinetics of MnO 2 .

[0061] Figure 4 In (a), the cyclic voltammograms of 2M WS 2 in 0.01 / 0.1 / 0.2 mol / L H 2 SO 4 and 2 mol / L ZnSO 4 solutions are shown. It can be seen that 2M WS 2 will be oxidized at a certain potential, and the lower the pH, the more it will inhibit the oxidation of 2M WS 2 ; Figure 4 In (b), it is 2M WS2 In 1 mol / L H 2 SO 4 and 0.01 mol / L NaOH solution cyclic voltammograms, from the left shift of the oxidation potential of 2M WS in the alkaline solution 2 it can be seen that the oxidation of 2M WS 2 will consume OH in the solution - , thus it can be proved that 2M WS 2 has a beneficial effect on improving the cycling stability of the manganese-based cathode, and the consumption of OH - will inhibit the generation of ZHS during battery discharge, and at the same time promote the dissolution of ZHS during battery charging, while avoiding the generation of the by-product ZMO that cannot be consumed, thus reducing the active material of the cathode.

[0062] Figure 5 is the scanning electron micrograph of the composite cathode of 2M WS 2 / α-MnO 2 . It can be seen from the figure that 2M WS 2 single crystal inlays are distributed in the active material of linear α-MnO 2 .

[0063] Figure 6 is the relationship between the discharge voltage and discharge specific capacity of the battery at the 10th, 50th, 100th, and 200th cycles. The discharge specific capacity at the 10th cycle is 169.52 mAh g -1 , and it has been rising to 184.57 mAh g until the 50th cycle -1 , and then it has been cycling until the 100th cycle when the capacity reaches 175.13 mAh g -1 , and it drops to 131.63 mAh g at the 200th cycle -1 . Overall, the discharge curve maintains a stable trend, showing good cycling stability.

[0064] Figure 7 For the composite cathode 2M WS 2 / α-MnO 2 provided in Example 1, the charge-discharge test results of the zinc-ion battery at a current density of 0.4 A / g and a voltage range of 0.8 - 1.8 V (vs. Zn 2+ / Zn) show that, as can be seen from Figure 7 , the capacity of the battery can still remain at 82.06% after 200 cycles, and 2M WS 2 has reached a relatively high state for the cycling stability of the α-MnO 2 cathode.

[0065] Figure 8 is the composite cathode 2M WS 2 / α-MnO 2 The zinc ion battery has a current density of 0.4A / g and a voltage range of 0.8-1.8V (vs.Zn 2+ / Zn), the SEM image of the electrode surface after 200 charge and discharge tests shows that the 2M WS 2 It still maintains a relatively good state, and the surface is covered with electrochemically deposited MnO 2 In addition, the electrode also maintains the initial morphology before charge and discharge to a large extent, which is 2M WS 2 The result of indirectly inhibiting the production of a large amount of ZMO is also proved by 2M WS 2 The mixing of manganese-based positive electrode has a significant effect on improving the stability of the positive electrode material.

[0066] The above data prove that the battery made by the method for improving the stability of manganese-based positive electrode materials provided by the present invention has excellent electrochemical performance.

[0067] Example 2 This embodiment provides a method for improving the stability of a manganese-based positive electrode material, comprising the following steps: (1) α-MnO 2 Preparation: Measure 15 ml of deionized water in two beakers and add 330 mg of MnSO 4 ·H 2 O and 237 mg KMnO 4 Put it into two beakers and stir it thoroughly until the powder is completely dissolved. Then add the prepared MnSO 4 The solution was added dropwise to KMnO 4 The mixture was stirred at room temperature for 45 min, and then heated at 150 °C for 12 h in a Teflon-lined autoclave. After the reaction, the precipitate was collected, washed with deionized water, dried at 80 °C overnight, and finally the large block sample was ground to obtain α-MnO 2 powder.

[0068] (2) K x WS 2 Preparation of crystals: 284 mg, 128 mg and 735.36 mg of K 2 S 2 , S powder and W powder were put into a mortar, and after being fully ground, they were put into a quartz tube in an argon atmosphere, and the quartz tube was sintered and sealed. During the whole process, it must be ensured that the atmosphere in the quartz tube does not contain oxygen. The sealed quartz tube was placed in a muffle furnace and heated at a heating rate of 3.3℃ / min. When the temperature reached 850℃, it was kept warm for 1100min, and then naturally cooled to prepare K x WS 2single crystal

[0069] (3)2M WS 2 Preparation of crystal: Measure 200 ml of deionized water in a 250 ml beaker, then add 2 ml (1 mol / L) of sulfuric acid and 1.51 ml (0.09 mol / L) of potassium dichromate solution. Stir the mixture thoroughly, and then weigh 150 mg of K x WS 2 crystal prepared in step two. After stirring for 4 hours, filter out the waste liquid with a vacuum filtration device, and then repeatedly rinse the 2M WS on the filter paper with deionized water. Finally, perform drying treatment. 2

[0070] (4)2M WS 2 / α-MnO 2 Preparation of mixed positive electrode paste: Measure 1.3 ml of NMP solution in a glass bottle with a capacity of 10 ml. Add 40 mg of PVDF to it and place it on a heating table at 40 °C for heating and stirring. The stirring time is 13 min to prepare a binder. Weigh 280 mg of α-MnO 2 powder prepared in step one and 46.66 mg of 2M WS 2 prepared in step three, put them into a mortar for thorough grinding, and then add the mixed powder and 80 mg of conductive carbon black to the glass bottle containing the binder in sequence for 36 h of stirring, and set the rotation speed at 1700 r / min.

[0071] (5)2M WS 2 / α-MnO 2 Preparation of mixed electrode: Apply the paste prepared in step 4 evenly on a 20-μm thick titanium foil with a 100-μm thick scraper, and then place it in an oven at 50 °C for 13 h of heat treatment.

[0072] Example 3 This example provides a method for improving the stability of manganese-based positive electrode materials, including the following steps: (1)α-MnO 2 Preparation: Measure 15 ml of deionized water in two beakers, and then add 278 mg of MnSO 4 ·H2O and 237 mg of KMnO 4 into the two beakers respectively. Stir thoroughly until the powder is completely dissolved, and then add the prepared MnSO 4 solution dropwise to KMnO 4 ​The mixture was stirred at room temperature for 30 min, and then heated at 140 °C for 12 h in a Teflon-lined autoclave. After the reaction, the precipitate was collected, washed with deionized water, dried at 80 °C overnight, and finally the bulk sample was ground to obtain α-MnO 2 powder.

[0073] (2) K x WS 2 Preparation of crystals: 284 mg, 128 mg and 735.36 mg of K 2 S 2 , S powder and W powder were put into a mortar, and after being fully ground, they were put into a quartz tube in an argon atmosphere, and the quartz tube was sintered and sealed. During the whole process, it must be ensured that the atmosphere in the quartz tube does not contain oxygen. The sealed quartz tube was placed in a muffle furnace and heated at a heating rate of 3.5℃ / min. When the temperature reached 850℃, it was kept warm for 1200min, and then naturally cooled to prepare K x WS 2 of single crystal.

[0074] (3) 2M WS 2 Preparation of crystals: Measure 200 ml of deionized water in a 250 ml beaker, add 2 ml (1 mol / L) sulfuric acid and 1.7 ml (0.08 mol / L) potassium dichromate solution, stir the mixture thoroughly, and weigh 120 mg of K prepared in step 2. x WS 2 After stirring for 4 hours, the waste liquid was filtered out with a vacuum filtration device, and the 2M WS on the filter paper was washed with deionized water. 2 Rinse repeatedly and then dry.

[0075] (4) 2M WS 2 / α-MnO 2 Preparation of mixed positive electrode slurry: 1.4 ml of NMP solution was measured in a 10 ml glass bottle, 40 mg of PVDF was added, and the mixture was placed on a heating table at 50 °C for heating and stirring for 10 min to prepare a binder. 280 mg of α-MnO prepared in step 1 was weighed. 2 powder and 70 mg of 2MWS prepared in step 3 2 Put it into a mortar and grind it thoroughly. Add the mixed powder and 80 mg of conductive carbon black into a glass bottle containing a binder in sequence and stir it for 72 hours. Set the speed to 2000 r / min.

[0076] 2M WS 2 / α-MnO 2Preparation of hybrid electrode: The slurry prepared in step 4 was evenly spread on the carbon cloth with a scraper of 100 um thickness, and then placed in an oven at 50°C for 16 hours for heating treatment.

[0077] Comparative Example 1 (1) α-MnO 2 Preparation: Measure 15 ml of deionized water in two beakers and add 278 mg of MnSO 4 H2O and 237 mg KMnO 4 Put it into two beakers and stir it thoroughly until the powder is completely dissolved. Then add the prepared MnSO 4 The solution was added dropwise to KMnO 4 The mixture was stirred at room temperature for 30 min, and then heated at 140 °C for 12 h in a Teflon-lined autoclave. After the reaction, the precipitate was collected, washed with deionized water, dried at 80 °C overnight, and finally the bulk sample was ground to obtain α-MnO 2 powder.

[0078] (2) α-MnO 2 Preparation of positive electrode slurry: 1.4 ml of NMP solution was measured in a 10 ml glass bottle, 40 mg of PVDF was added, and the mixture was placed on a heating table at 50 °C for heating and stirring for 10 min to prepare a binder. 280 mg of α-MnO prepared in step 1 was weighed. 2 The powder was put into a mortar and ground thoroughly. The powder and 80 mg of conductive carbon black were added into a glass bottle containing a binder in sequence and stirred for 72 hours. The rotation speed was set at 2000 r / min.

[0079] α-MnO 2 Preparation of electrode: The slurry prepared in step 2 was evenly spread on the carbon cloth with a scraper of 100 um thickness, and then placed in an oven at 50°C for 16 hours for heating treatment.

[0080] Figure 9 The α-MnO provided in Comparative Example 1 2 The charge and discharge cycle test results of the zinc ion battery assembled with the electrode and zinc metal negative electrode. Figure 9 It can be seen that through the positive electrode α-MnO 2 The zinc ion battery has a current density of 0.4A / g and a voltage range of 0.8-1.8V (vs.Zn 2+ / Zn) charge and discharge test results, from Figure 9 It can be seen that the capacity of the battery decays to 37.08% of the original capacity after 200 cycles; Figure 7As can be seen, the capacity of the battery provided in Example 1 can still be maintained at 82.06% after 200 cycles, indicating that 2M WS 2 for α-MnO 2 plays a crucial role in improving the cycling stability of the positive electrode.

[0081] This invention describes the preferred embodiments and their effects. However, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications that fall within the scope of this invention.

[0082] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the stability of a manganese-based positive electrode material, characterized in that: include: 2M WS2 crystals were added to the raw materials for preparing manganese-based positive electrode materials to obtain stable manganese-based positive electrode materials.

2. The method for improving the stability of manganese-based positive electrode materials according to claim 1, characterized in that: The added amount of the 2M WS2 crystal accounts for 8-15% of the mass percentage of the raw materials.

3. The method for improving the stability of manganese-based positive electrode materials according to claim 2, characterized in that: The 2M WS2 crystals were prepared according to the following steps: Preparation of K x WS2 crystal; K x WS2 crystals are placed in an acidic potassium dichromate aqueous solution and stirred, and then filtered, washed, and freeze-dried to obtain 2M WS2 crystals.

4. The method for improving the stability of manganese-based positive electrode materials according to claim 3, characterized in that: The acidic potassium dichromate aqueous solution is prepared by mixing potassium dichromate aqueous solution and sulfuric acid; Wherein, the potassium dichromate aqueous solution is prepared by dissolving potassium dichromate in a water solvent, and the molar concentration of the potassium dichromate aqueous solution is 0.08 mol / L to 0.1 mol / L; The molar concentration ratio of potassium dichromate to sulfuric acid is 1:14-15; The K x The mass ratio of WS2 crystal to the potassium dichromate is 3-5:

1.

5. The method for improving the stability of manganese-based positive electrode materials according to claim 3, characterized in that: The K x WS2 crystal is obtained by grinding K2S2, S powder and W powder in a certain proportion, and then keeping the mixture at 800~900℃ for 1000~1200min in an argon atmosphere.

6. The method for improving the stability of manganese-based positive electrode materials according to claim 2, characterized in that: The raw materials for preparing the manganese-based positive electrode material include the following components in percentage by mass: 60% to 65% of electrode active material, 17% to 19% of electronic conductive agent, and 8% to 10% of binder; The electronic conductive agent includes one or more of conductive carbon black, conductive acetylene black, and Ketjen black; The binder comprises 28-33 wt.% polyvinylidene fluoride and 67-72 wt.% N-methylpyrrolidone; The electrode active material is α-MnO2 powder.

7. The method for improving the stability of manganese-based positive electrode materials according to claim 6, characterized in that: The stable manganese-based positive electrode material is prepared according to the following steps: Add α-MnO2 powder and 2M WS2 crystal into a binder and stir and mix, then add an electronic conductive agent and continue stirring to obtain a mixed slurry; The mixed slurry is evenly applied to the conductive current collector and then dried to obtain a stable manganese-based positive electrode material.

8. The method for improving the stability of manganese-based positive electrode materials according to claim 7, characterized in that: The conductive current collector is titanium foil or carbon cloth.

9. A stable manganese-based positive electrode material obtained by the method according to any one of claims 1 to 8.

10. Use of the stable manganese-based positive electrode material according to claim 9 in a zinc-manganese battery.

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